US20140053979A1 - Reduced number of masks for ic device with stacked contact levels - Google Patents
Reduced number of masks for ic device with stacked contact levels Download PDFInfo
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- US20140053979A1 US20140053979A1 US14/070,333 US201314070333A US2014053979A1 US 20140053979 A1 US20140053979 A1 US 20140053979A1 US 201314070333 A US201314070333 A US 201314070333A US 2014053979 A1 US2014053979 A1 US 2014053979A1
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- H01L21/71—Manufacture of specific parts of devices defined in group H01L21/70
- H01L21/768—Applying interconnections to be used for carrying current between separate components within a device comprising conductors and dielectrics
- H01L21/76801—Applying interconnections to be used for carrying current between separate components within a device comprising conductors and dielectrics characterised by the formation and the after-treatment of the dielectrics, e.g. smoothing
- H01L21/76802—Applying interconnections to be used for carrying current between separate components within a device comprising conductors and dielectrics characterised by the formation and the after-treatment of the dielectrics, e.g. smoothing by forming openings in dielectrics
- H01L21/76805—Applying interconnections to be used for carrying current between separate components within a device comprising conductors and dielectrics characterised by the formation and the after-treatment of the dielectrics, e.g. smoothing by forming openings in dielectrics the opening being a via or contact hole penetrating the underlying conductor
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- H01L21/71—Manufacture of specific parts of devices defined in group H01L21/70
- H01L21/768—Applying interconnections to be used for carrying current between separate components within a device comprising conductors and dielectrics
- H01L21/76801—Applying interconnections to be used for carrying current between separate components within a device comprising conductors and dielectrics characterised by the formation and the after-treatment of the dielectrics, e.g. smoothing
- H01L21/76802—Applying interconnections to be used for carrying current between separate components within a device comprising conductors and dielectrics characterised by the formation and the after-treatment of the dielectrics, e.g. smoothing by forming openings in dielectrics
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- H01L21/71—Manufacture of specific parts of devices defined in group H01L21/70
- H01L21/768—Applying interconnections to be used for carrying current between separate components within a device comprising conductors and dielectrics
- H01L21/76838—Applying interconnections to be used for carrying current between separate components within a device comprising conductors and dielectrics characterised by the formation and the after-treatment of the conductors
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- H01L23/522—Arrangements for conducting electric current within the device in operation from one component to another, i.e. interconnections, e.g. wires, lead frames including external interconnections consisting of a multilayer structure of conductive and insulating layers inseparably formed on the semiconductor body
- H01L23/5226—Via connections in a multilevel interconnection structure
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- H01L27/04—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components specially adapted for rectifying, oscillating, amplifying or switching and having at least one potential-jump barrier or surface barrier; including integrated passive circuit elements with at least one potential-jump barrier or surface barrier the substrate being a semiconductor body
- H01L27/06—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components specially adapted for rectifying, oscillating, amplifying or switching and having at least one potential-jump barrier or surface barrier; including integrated passive circuit elements with at least one potential-jump barrier or surface barrier the substrate being a semiconductor body including a plurality of individual components in a non-repetitive configuration
- H01L27/0688—Integrated circuits having a three-dimensional layout
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Definitions
- the present invention relates generally to high density integrated circuit devices, and more particularly to interconnect structures for multi-level three-dimensional stacked devices.
- thin film transistor techniques are applied to charge trapping memory in Lai, et al., “A Multi-Layer Stackable Thin-Film Transistor (TFT) NAND-Type Flash Memory,” IEEE Int'l Electron Devices Meeting, 11-13 Dec. 2006; and in Jung et al., “Three Dimensionally Stacked NAND Flash Memory Technology Using Stacking Single Crystal Si Layers on ILD and TANOS Structure for Beyond 30 nm Node,” IEEE Int'l Electron Devices Meeting, 11-13 Dec. 2006.
- TFT Thin-Film Transistor
- conductive interconnects used to couple the lower levels of memory cells to decoding circuitry and the like pass through the upper levels.
- the cost to implement the interconnections increases with the number of lithographic steps needed.
- One approach to reduce the number of lithographic steps is described in Tanaka et al., “Bit Cost Scalable Technology with Punch and Plug Process for Ultra High Density Flash Memory,” 2007 Symposium on VLSI Technology Digest of Technical Papers; 12-14 Jun. 2007; pages 14-15.
- one of the drawbacks with conventional 3-D stacked memory devices is that a separate mask is typically used for each contact level. Therefore, if there are, for example, 20 contact levels, 20 different masks are commonly required, each contact level requiring the creation of a mask for that level and an etching step for that level.
- the present invention only requires N masks to provide access to a landing area at 2 N contact levels.
- 2 x-1 contact levels are etched for each mask sequence number x.
- a first example of a method, for use with a three-dimensional stacked IC device having a stack of contact levels at an interconnect region, is used to create interconnect contact regions aligned with and exposing landing areas at the contact levels.
- a set of N etch masks is used to create up to and including 2 N levels of interconnect contact regions at the stack of contact levels.
- Each mask comprises mask and etch regions.
- N is an integer equal to at least 2.
- At least a portion of any upper layer overlying the stack of contact levels at the interconnect region is removed.
- the interconnect region is etched N times using said masks in a chosen order.
- contact openings extending from a surface layer to each contact level.
- the contact openings are aligned with and provide access to landing areas at each of the 2 N contact levels.
- 2 x-1 contact levels are etched during the etching step for each mask of sequence number x. Electrical conductors can then be formed through the contact openings to contact the landing areas at the contact levels.
- Some examples include the following steps: a fill material is applied over the openings to define a via pattern surface; vias are opened through the fill material to expose the landing areas in each contact level; and a conductive material is deposited within the vias.
- the accessing step is carried out with N equal to at least 4.
- the removing step is carried out using an additional mask exposing the interconnect region while in other examples, the removing step is carried out using a blanket etching step at the interconnect region.
- sidewall material acts as one of the N etch masks.
- the IC device is of a type comprising an interconnect region, the interconnect region including an upper layer with a stack of at least first, second, third and fourth contact levels beneath the upper layer.
- At least first and second openings are formed in the upper layer, each opening exposing a surface portion of a first contact level, the first and second openings partially bounded by upper layer sidewalls.
- a sidewall material is deposited on the sidewalls of each of the first and second openings and on a first part of each of the surface portions while leaving a second part of the surface portions without sidewall material thereon.
- the first and second openings are extended through the second parts of the surface portions to expose a surface of the second contact level for each of the first and second openings. At least some of the sidewall material at each opening is removed to expose at least some of the first part of the surface portion at each opening, thereby forming interconnect contact regions at the second openings. The interconnect contact regions at the second opening are aligned with landing areas at the first and second contact levels.
- the first opening is further extended from (1) the exposed first part of the surface portion, through the first and second contact levels to expose a surface of a third contact level, and (2) an exposed surface of the second contact level through the second and third contact levels to expose a surface of the fourth contact level.
- the electrical conductors forming step comprises: applying a fill material over the openings to define a via pattern surface; opening vias through the fill material to expose the landing areas in each contact level; and depositing a conductive material within the vias.
- An example of a set of masks is used to create interconnect contact regions aligned with landing areas at a stack of contact levels of an interconnect region for a three-dimensional stacked IC device, the stack of contact levels covered by an upper layer.
- Each mask of a set of N etch masks comprises mask and etch regions, the etch regions used to create interconnect contact regions alignable with landing areas at up to and including 2 N-1 contact levels of an interconnect region for a three-dimensional stacked IC device.
- N is an integer equal to at least 3.
- sidewall material acts as one of the N etch masks.
- the etch masks comprise a dummy mask region on at least one of said etch masks. In some examples, the etch masks comprise dummy mask regions at corresponding locations on at least some of said etch masks. In some examples, the etch masks comprise at least one dummy mask region at corresponding locations on each of said etch masks. In some examples, N is greater than or equal to 4.
- Each mask of a set of N masks comprises mask and etch regions, the etch regions used to create interconnect contact regions alignable with landing areas at up to and including 2 N contact levels of an interconnect region for a three-dimensional stacked IC device.
- N is an integer equal to at least 2.
- FIGS. 1-16 and the associated description are taken from U.S. patent application Ser. No. 12/579,192 filed 14 Oct. 2009 and entitled 3D Integrated Circuit Layer Interconnect having the same assignee as this application, the disclosure of which is incorporated by reference.
- FIG. 1 illustrates a cross-sectional view of a device including a three-dimensional structure having an interconnect structure 190 with a small footprint where conductors 180 extend to various levels 160 - 1 to 160 - 4 in the device.
- FIG. 2A illustrates a plan view of level 160 - 1 showing the landing areas.
- FIG. 2B illustrates a plan view of level 160 - 2 showing openings adjacent the landing areas.
- FIG. 2C illustrates a plan view of level 160 - 3 showing openings adjacent the landing areas.
- FIG. 2D illustrates a plan view of level 160 - 4 showing openings adjacent the landing area.
- FIGS. 3A and 3B illustrate respective orthogonal views of a portion of a three-dimensional stacked integrated circuit device including a 3D interconnect structure with a small footprint.
- FIG. 4 illustrates a top view layout of an embodiment of the device which includes interconnect structures in the periphery on two sides of a memory array.
- FIG. 5 illustrates a top view layout of an embodiment of the device which includes interconnect structures in the periphery on four sides of a memory array.
- FIG. 6 is a schematic diagram of a portion of the memory device including an interconnect structure as described herein.
- FIG. 7 is a simplified block diagram of an integrated circuit device including a 3D memory array having an interconnect structure as described herein.
- FIGS. 8A-8C to 15 illustrate steps in a fabrication sequence for manufacturing an interconnect structure as described herein.
- FIG. 16 illustrates a plan view of an opening in a mask having a width varying in the longitudinal direction in a step-like manner, to accommodate varying widths of landing areas on the levels.
- the present invention is described primarily with reference to FIGS. 17-47 .
- FIG. 17 is a simplified flowchart for a method for creating interconnect contact regions according to the present invention.
- FIGS. 18-27 illustrate a first example of a method for creating interconnect contact regions at a number of contact levels at an interconnect region of a three-dimensional stacked IC device.
- FIG. 18 is a simplified cross-sectional view of a stack of contact levels with an additional mask formed above an upper layer.
- FIG. 19 shows the result of etching through an open region in the additional mask of FIG. 18 through the upper layer.
- FIG. 20 shows a first mask applied to the stack of contact levels of FIG. 19 .
- FIG. 21 shows the result of etching a single contact level using the first mask.
- FIG. 22 shows a second mask applied to the stack of contact levels of FIG. 21 .
- FIG. 23 shows the results of etching through two contact levels of FIG. 22 .
- FIG. 24 shows the structure of FIG. 23 with the second mask removed thereby exposing interconnect contact regions at four different contact levels.
- FIG. 25 shows the structure of FIG. 24 with an etch stop layer applied over the exposed surfaces of the structure of FIG. 24 .
- FIG. 26 shows the structure of FIG. 25 covered by interlayer dielectric.
- FIG. 27 shows the structure of FIG. 26 after electrical conductors have been formed through the interlayer dielectric and the etch stop layer to make contact with landing areas at the interconnect contact regions of each of the four contact levels.
- FIGS. 28-34 illustrate a second example of a method for creating interconnect contact regions at a number of contact levels at an interconnect region of a three-dimensional stacked IC device.
- FIGS. 35-44 illustrate a third example of a method for creating interconnect contact regions at a number of contact levels at an interconnect region of a three-dimensional stacked IC device.
- FIGS. 45 and 46 illustrate a process example for a stack of 16 contact levels with FIG. 46 illustrating the etching results.
- FIG. 47 illustrates the etching results when the masks have dummy contact regions so to create dummy stacks between the interconnect contact regions.
- FIG. 1 illustrates a cross-sectional view of a device including three-dimensional structure having an interconnect structure 190 with a small footprint where conductors 180 extend to various levels 160 - 1 to 160 - 4 in the device.
- four levels 160 - 1 to 160 - 4 are shown.
- the small interconnect structure 190 described herein can be implemented in a structure having levels 0 to N, where N is at least 2.
- the conductors 180 are arranged within the interconnect structure 190 to contact landing areas on the various levels 160 - 1 to 160 - 4 . As described in more detail below, the conductors 180 for each particular level extend through openings in the overlying levels to contact the landing areas 161 - 1 a , 161 - 1 b , 161 - 2 a , 161 - 2 b , 161 - 3 a , 161 - 3 b , 161 - 4 .
- the conductors 180 are used in this example for coupling the contact levels 160 - 1 to 160 - 4 to interconnect lines 185 in a wiring layer overlying the levels 160 - 1 to 160 - 4 .
- the landing areas are the portions of contact levels 160 - 1 to 160 - 4 used for contact with conductors 180 .
- the sizes of the landing areas are large enough to provide room for the conductors 180 to adequately couple the electrically conductive landing areas within the landing areas of the various contact levels 160 - 1 to 160 - 4 to the overlying interconnect lines 185 , as well as to address issues such as misalignment between the conductors 180 and the overlying openings in one level for landing areas in different levels.
- the size of a landing area thus depends on a number of factors, including the size and number of conductors used, and will vary from embodiment to embodiment. In addition, the number of the conductors 180 can be different for each of the landing areas.
- the levels 160 - 1 to 160 - 4 consist of respective planar conductive layers of material such as doped polysilicon, with layers of insulating material 165 separating the levels 160 - 1 to 160 - 4 .
- the levels 160 - 1 to 160 - 4 need not be planar stacked material layers, and instead the layers of material can vary in the vertical dimension.
- the conductors 180 contacting the different levels 160 - 1 to 160 - 4 are arranged in a direction extending along the cross-section illustrated in FIG. 1 .
- This direction defined by the arrangement of the conductors 180 contacting different levels 160 - 1 to 160 - 4 is referred to herein as the “longitudinal” direction.
- the “transverse” direction is perpendicular to the longitudinal direction, and is into and out of the cross-section illustrated in FIG. 1 . Both the longitudinal and transverse directions are considered to be “lateral dimensions”, meaning a direction that is in a two-dimensional area of a plan view of the levels 160 - 1 to 160 - 4 .
- the “length” of structures or features is its length in the longitudinal direction, and its “width” is its width in the transverse direction.
- Level 160 - 1 is the lowest level in the plurality of levels 160 - 1 to 160 - 4 .
- the level 160 - 1 is on insulating layer 164 .
- the level 160 - 1 includes first and second landing areas 161 - 1 a , 161 - 1 b for contact with conductors 180 .
- the level 160 - 1 includes two landing areas 161 - 1 a , 161 - 1 b on opposite ends of the interconnect structure 190 .
- one of the landing areas 161 - 1 a , 161 - 1 b is omitted.
- FIG. 2A is a plan view of a portion of level 160 - 1 , including the landing areas 161 - 1 a , 161 - 1 b within the footprint of the interconnect structure 190 .
- the footprint of the interconnect structure 190 can be close to the width of the via size for the conductors, and have a length that can be much longer than the width.
- landing area 161 - 1 a has a width 200 in the transverse direction and a length 201 in the longitudinal direction.
- Landing area 161 - 1 b has a width 202 in the transverse direction and a length 203 in the longitudinal direction.
- FIG. 1 is a plan view of a portion of level 160 - 1 , including the landing areas 161 - 1 a , 161 - 1 b within the footprint of the interconnect structure 190 .
- the footprint of the interconnect structure 190 can be close to the width of the via size for the conductors, and have a length that can be much longer than the width
- the landing areas 161 - 1 a , 161 - 1 b each have a rectangular cross-section.
- the landing areas 161 - 1 a , 161 - 1 b may each have a cross-section that is circular, elliptical, square, rectangular, or somewhat irregularly shaped.
- level 160 - 1 is the lowest level, the conductors 180 need not pass through the level 160 - 1 to underlying levels. Thus, in this example, level 160 - 1 does not have openings within the interconnect structure 190 .
- level 160 - 2 overlies level 160 - 1 .
- Level 160 - 2 includes an opening 250 overlying the landing area 161 - 1 a on level 160 - 1 .
- the opening 250 has a distal longitudinal sidewall 251 a and a proximal longitudinal sidewall 251 b defining the length 252 of the opening 250 .
- the length 252 of the opening 250 is at least as large as the length 201 of the underlying landing area 161 - 1 a , so that the conductors 180 for the landing area 161 - 1 a can pass through the level 160 - 2 .
- the level 160 - 2 also includes opening 255 overlying the landing area 161 - 1 b .
- the opening 255 has distal and proximal longitudinal sidewalls 256 a , 256 b defining the length 257 of the opening 255 .
- the length 257 of the opening 255 is at least as large as the length 203 of the underlying landing area 161 - 1 b , so that the conductors 180 for the landing area 161 - 1 b can pass through the level 160 - 2 .
- the level 160 - 2 also includes first and second landing areas 161 - 2 a , 161 - 2 b adjacent the openings 250 , 255 respectively.
- the first and second landing areas 161 - 2 a , 161 - 2 b are the portions of level 160 - 2 used for contact with the conductors 180 .
- FIG. 2B is a plan view of a portion of level 160 - 2 , including the first and second landing areas 161 - 2 a , 161 - 2 b and the openings 250 , 255 within the interconnect structure 190 .
- opening 250 has longitudinal sidewalls 251 a , 251 b defining the length 252 , and has transverse sidewalls 253 a , 253 b defining the width 254 of the opening 250 .
- the width 254 is at least as large as the width 200 of the underlying landing area 161 - 1 a , so that the conductors 180 can pass through the opening 250 .
- Opening 255 has longitudinal sidewalls 256 a , 256 b defining the length 257 , and has transverse sidewalls 258 a , 258 b defining the width 259 .
- the width 259 is at least as large as the width 202 of the underlying landing area 161 - 1 b , so that the conductors 180 can pass through the opening 255 .
- the openings 250 , 255 each have a rectangular cross-section.
- the openings 250 , 255 may each have a cross-section that is circular, elliptical, square, rectangular, or somewhat irregularly shaped, depending on the shape of the mask used to form them.
- landing area 161 - 2 a is adjacent the opening 250 and has a width 204 in the transverse direction and a length 205 in the longitudinal direction.
- Landing area 161 - 2 b is adjacent the opening 255 and has a width 206 in the transverse direction and a length 207 in the longitudinal direction.
- level 160 - 3 overlies level 160 - 2 .
- Level 160 - 3 includes an opening 260 overlying landing area 161 - 1 a on level 160 - 1 and landing area 161 - 2 a on level 160 - 2 .
- the opening 260 has distal and proximal longitudinal sidewalls 261 a , 261 b defining the length 262 of the opening 260 .
- the length 262 of the opening 260 is at least as large as the sum of the lengths 201 and 205 of the underlying landing areas 161 - 1 a and 161 - 2 a , so that the conductors 180 for the landing areas 161 - 1 a and 161 - 2 a can pass through the level 160 - 3 .
- the distal longitudinal sidewall 261 a of opening 260 is vertically aligned with the distal longitudinal sidewall 251 a of the underlying opening 250 .
- the openings can be formed using the opening in a single etch mask and one additional mask formed over the opening in the single etch mask, as well as processes for etching the addition mask without a critical alignment step, resulting in the formation of openings having distal longitudinal sidewalls ( 261 a , 251 a , . . . ) along the perimeter of the single etch mask that are vertically aligned.
- the level 160 - 3 also includes opening 265 overlying the landing area 161 - 1 b on level 160 - 1 and landing area 161 - 2 b on level 160 - 2 .
- the opening 265 has outside and inside longitudinal sidewalls 266 a , 266 b defining the length 267 of the opening 265 .
- the outside longitudinal sidewall 266 a of opening 265 is vertically aligned with the outside longitudinal sidewall 256 a of the underlying opening 255 .
- the length 267 of the opening 265 is at least as large as sum of the lengths 203 and 207 of the underlying landing areas 161 - 1 b and 161 - 2 b , so that the conductors 180 for the landing areas 161 - 1 b and 161 - 2 b can pass through the level 160 - 3 .
- the level 160 - 3 also includes first and second landing areas 161 - 3 a , 161 - 3 b adjacent the openings 260 , 265 respectively.
- the first and second landing areas 161 - 3 a , 161 - 3 b are the portions of level 160 - 3 used for contact with the conductors 180 .
- FIG. 2C is a plan view of a portion of level 160 - 3 , including the first and second landing areas 161 - 3 a , 161 - 3 b and the openings 260 , 265 within the interconnect structure 190 .
- opening 260 has outside and inside longitudinal sidewalls 261 a , 261 b defining the length 262 , and has transverse sidewalls 263 a , 263 b defining the width 264 a , 264 b of the opening 260 .
- the width 264 a is at least as large as the width 200 of the underlying landing area 161 - 1 a
- width 264 b is at least as large as the width 204 of the underlying landing area 161 - 2 a , so that the conductors 180 can pass through the opening 260 .
- widths 264 a and 264 b are substantially the same.
- the widths 264 a and 264 b can be different, in order to accommodate landing areas having different widths.
- Opening 265 has longitudinal sidewalls 266 a , 266 b defining the length 267 , and has transverse sidewalls 268 a , 268 b defining the width 269 a , 269 b .
- the width 269 a is at least as large as the width 202 of the underlying landing area 161 - 1 b
- the width 269 b is at least as large as the width 206 of the underling landing area 161 - 2 b , so that the conductors 180 can pass through the opening 265 .
- landing area 161 - 3 a is adjacent the opening 260 and has a width 214 in the transverse direction and a length 215 in the longitudinal direction.
- Landing area 161 - 3 b is adjacent the opening 265 has a width 216 in the transverse direction and a length 217 in the longitudinal direction.
- level 160 - 4 overlies level 160 - 3 .
- Level 160 - 4 includes an opening 270 overlying the landing area 161 - 1 a on level 160 - 1 , the landing area 161 - 2 a on level 160 - 2 , and the landing area 161 - 3 a on level 160 - 3 .
- the opening 270 has longitudinal sidewalls 271 a , 271 b defining the length 272 of the opening 270 .
- the length 272 of the opening 270 is at least as large as the sum of the lengths 201 , 205 , and 215 of the underlying landing areas 161 - 1 a , 161 - 2 a , 161 - 3 a so that the conductors 180 for the landing areas 161 - 1 a , 161 - 2 a , 161 - 3 a can pass through the level 160 - 4 .
- the longitudinal sidewall 271 a of opening 270 is vertically aligned with the longitudinal sidewall 261 a of the underlying opening 260 .
- the level 160 - 4 also includes opening 275 overlying the landing area 161 - 1 b on level 160 - 1 , the landing area 161 - 2 b on level 160 - 2 , and the landing area 161 - 3 b on level 160 - 3 .
- the opening 275 has longitudinal sidewalls 276 a , 276 b defining the length 277 of the opening 275 .
- the longitudinal sidewall 276 a of opening 275 is vertically aligned with the longitudinal sidewall 266 a of the underlying opening 265 .
- the length 277 of the opening 275 is at least as large as sum of the lengths 203 , 207 , and 217 of the underlying landing areas 161 - 1 b , 161 - 2 b and 161 - 3 b , so that the conductors 180 for the landing areas 161 - 1 b , 161 - 2 b , and 161 - 3 b can pass through the level 160 - 4 .
- the level 160 - 4 also includes a landing area 161 - 4 between the openings 270 , 275 .
- the landing area 161 - 4 is the portion of level 160 - 4 used for contact with the conductors 180 .
- the level 160 - 4 has one landing area 161 - 4 .
- the level 160 - 4 may include more than one landing area.
- FIG. 2D is a plan view of a portion of level 160 - 4 , including landing area 161 - 4 and the openings 270 , 275 within the interconnect structure 190 .
- opening 270 has longitudinal sidewalls 271 a , 271 b defining the length 272 , and has transverse sidewalls 273 a , 273 b defining the width 274 a , 274 b , 274 c of the opening 270 .
- the widths 274 a , 274 b , 274 c are at least as large as the widths 200 , 204 , and 214 of the underlying landing areas 161 - 1 a , 161 - 2 a and 161 - 3 a , so that the conductors 180 can pass through the opening 270 .
- Opening 275 has longitudinal sidewalls 276 a , 276 b defining the length 277 , and has transverse sidewalls 278 a , 278 b defining the width 279 a , 279 b , 279 c .
- the widths 279 a , 279 b , 279 c are at least as large as the widths 202 , 206 , and 216 of the underlying landing areas 161 - 1 b , 161 - 2 b and 161 - 3 b , so that the conductors 180 can pass through the opening 275 .
- landing area 161 - 4 is between the openings 270 , 275 and has a width 224 in the transverse direction and a length 225 in the longitudinal direction.
- the distal longitudinal sidewalls 271 a , 261 a , and 251 a of openings 270 , 260 , and 250 are vertically aligned, so that the difference in the length of the openings 270 , 260 , and 250 is due to the horizontal offset of the sidewalls 271 b , 261 b , and 251 b .
- elements or features “vertically aligned” are substantially flush with an imaginary plane perpendicular to both the transverse and longitudinal directions.
- the term “substantially flush” is intended to accommodate manufacturing tolerances in the formation of the openings using the opening in a single etch mask and multiple etch processes which may cause variations in the planarity of the sidewalls.
- the longitudinal sidewalls 276 a , 266 a , and 256 a of openings 275 , 265 , and 255 also are vertically aligned.
- the transverse sidewalls of the openings in the levels are also vertically aligned.
- the transverse sidewalls 273 a , 263 a , and 253 a of openings 270 , 260 , and 250 are vertically aligned.
- the transverse sidewalls 273 b , 263 b , and 253 b are vertically aligned.
- the longitudinal sidewalls 276 a , 266 a , and 256 a are vertically aligned
- the transverse sidewalls 278 b , 268 b , and 258 b are vertically aligned.
- the openings in the various levels 160 - 1 to 160 - 4 have substantially the same width in the transverse direction.
- the width of the openings can vary along the longitudinal direction, for example, in a step-like manner, in order to accommodate landing areas having different widths.
- This technique for implementing the interconnect structure 190 as described herein significantly reduces the area or footprint needed for making contact to the plurality of levels 160 - 1 to 160 - 4 , compared to prior art techniques. As a result, more space is available for implementing memory circuits in the various levels 160 - 1 to 160 - 4 . This allows for higher memory density and a smaller cost per bit in the upper levels compared to prior art techniques.
- the openings within the interconnect structure 190 result in the levels having a staircase-like pattern on both sides of the landing area 161 - 4 on level 160 - 4 . That is, the two openings in each level are symmetrical about an axis perpendicular to both the longitudinal and transverse directions, and the two landing areas of each level are also symmetrical about that axis.
- the term “symmetrical” is intended to accommodate manufacturing tolerances in the formation of the openings using the opening in a single etch mask and multiple etch processes which may cause variations in the dimensions of the openings.
- each level includes a single opening and a single landing area
- the levels have a staircase-like pattern on only one side.
- level (i) for (i) equal to 1 through N, overlies level (i ⁇ 1), and has an opening (i) adjacent the landing area (i) on level (i).
- the opening (i) extends over the landing area (i ⁇ 1) on level (i ⁇ 1), and for (i) greater than 1, over the adjacent opening (i ⁇ 1) in level (i ⁇ 1).
- the opening (i) has a distal longitudinal sidewall aligned with the distal longitudinal sidewall of opening (i ⁇ 1) in level (i), and a proximal longitudinal sidewall defining a length of the opening (i).
- the length of the opening (i) is at least as large as the length of the landing area (i ⁇ 1) plus the length of the opening (i ⁇ 1), if any.
- the opening (i) has transverse sidewalls aligned with the transverse sidewalls of opening (i ⁇ 1) in level (i ⁇ 1) and defines a width of the opening (i) at least as large as the width of the landing area (i ⁇ 1).
- memory cells and configurations can be used in alternative embodiments.
- Examples of the other types of memory cells which may be used include dielectric charge trapping and floating gate memory cells.
- the levels of the device may be implemented as planar memory cell arrays separated by insulating material, with the access devices and access lines formed within the levels using thin film transistors or related technologies.
- the interconnect structure described herein can be implemented in other types of three-dimensional stacked integrated circuit devices, where having conductors extending to various levels in the device within a small footprint is useful.
- FIG. 3A is a cross-section of a portion of a three-dimensional stacked integrated circuit device 100 including a memory array region 110 and a periphery region 120 with an interconnect structure 190 as described herein.
- the memory array region 110 is implemented as one-time programmable multi-level memory cells as described in U.S. patent application Ser. No. 12/430,290 by Lung, which is commonly owned by the assignee of the present application and incorporated by reference herein. It is described here as a representative integrated circuit structure in which the 3D interconnect structure described herein can be implemented.
- the memory array region 110 includes a memory access layer 112 including horizontal field effect transistor access devices 131 a , 131 b having source regions 132 a , 132 b and drain regions 134 a , 134 b in a semiconductor substrate 130 .
- the substrate 130 can comprise bulk silicon or a layer of silicon on an insulating layer or other structures known in the art for supporting integrated circuits.
- Trench isolation structures 135 a , 135 b isolate regions in the substrate 130 .
- Word lines 140 a , 140 b act as gates for the access devices 131 a , 131 b .
- Contact plugs 142 a , 142 b extend through inter-layer dielectric 144 to couple the drain regions 134 a , 134 b to bit lines 150 a , 150 b.
- Contact pads 152 a , 152 b are coupled to underlying contacts 146 a , 146 b , providing connection to the source regions 132 a , 132 b of the access transistors.
- the contact pads 152 a , 152 b and bit lines 150 a , 150 b are within an inter-layer dielectric 154 .
- the levels consist of respective planar conductive layers of material such as doped polysilicon.
- the levels need not be planar stacked material layers, and instead the layers of material can vary in the vertical dimension.
- Insulating layers 165 - 1 to 165 - 3 separate the levels 160 - 1 to 160 - 4 from one another.
- An insulating layer 166 overlies the levels 160 - 1 to 160 - 4 and insulating layers 165 - 1 to 165 - 3 .
- a plurality of electrode pillars 171 a , 171 b are arranged on top of the memory cell access layer 112 and extend through the levels.
- a first electrode pillar 171 a includes a central conductive core 170 a made, for example, of tungsten or other suitable electrode material, surrounded by a polysilicon sheath 172 a .
- the levels 160 - 1 through 160 - 4 comprise a relatively highly doped, n-type polysilicon in this example, while the polysilicon sheath 172 a comprises a relatively lightly doped, p-type polysilicon.
- the thickness of the polysilicon sheath 172 a is greater than the depth of the depletion region formed by the p-n junction. The depth of the depletion region is determined in part by the relative doping concentrations of the n-type and p-type polysilicon used to form it.
- the levels 160 - 1 through 160 - 4 and the sheath 172 a can be implemented using amorphous silicon as well. Also, other semiconductor materials could be utilized.
- the first electrode pillar 171 a is coupled to the pad 152 a .
- a second electrode pillar 171 b including conductive core 170 b , polysilicon sheath 172 b , and anti-fuse material layer 174 b is coupled to the pad 152 b.
- Interface regions between the plurality of levels 160 - 1 through 160 - 4 and the pillars 171 a , 171 b include memory elements comprising a programmable element in series with a rectifier, as explained in more detail below.
- the layer 174 a of anti-fuse material of pillar 171 a which can be a silicon dioxide, silicon oxynitride, or other silicon oxide, has a high resistance.
- Other anti-fuse materials may be used, such as silicon nitride.
- the plurality of conductive layers of levels 160 - 1 to 160 - 4 extend into the periphery region 120 where supporting circuitry and conductors 180 are made to the plurality levels 160 - 1 to 160 - 4 .
- a wide variety of devices are implemented in the periphery 120 to support decoding logic and other circuits on the integrated circuit 100 .
- the conductors 180 are arranged within the interconnect structure 190 to contact landing areas on the various levels 160 - 1 to 160 - 4 . As discussed in more detail below, the conductors 180 for each particular level 160 - 1 to 160 - 4 extend through openings in the overlying levels to a wiring layer including conductive interconnect lines 185 .
- the conductive interconnect lines 185 provide for interconnection between the levels 160 - 1 to 160 - 4 and decoding circuitry in the periphery 120 .
- the conductors 180 contacting the different levels 160 - 1 to 160 - 4 are arranged in the longitudinal direction extending into and out of the cross-section illustrated in FIG. 3A .
- FIG. 3B is a cross-sectional view in the longitudinal direction taken along line FIG. 3B-FIG . 3 B through the interconnect structure 190 of FIG. 3A , showing a view of the interconnect structure 190 like that shown in FIG. 1 .
- the conductors 180 for each particular level extend through openings in the overlying levels to contact the landing areas.
- levels 160 - 1 through 160 - 4 are shown. More generally, the small interconnect structure described herein can be implemented in levels 0 to N, where N is at least 2.
- levels of the device may be implemented as planar memory cell arrays separated by insulating material, with the access devices and access lines formed within the levels using thin film transistors or related technologies.
- the interconnect structure described herein can be implemented in other types of three-dimensional stacked integrated circuit devices, where having conductors extending to various levels in the device within a small footprint is useful.
- FIGS. 3A-3B a single interconnect structure 190 is shown.
- a plurality of interconnect structures can be arranged at various locations in the device, such as surrounding the memory array region 110 , so as to provide more even power distribution.
- FIG. 4 illustrates a top view layout of an embodiment of the device 100 which includes a two series of interconnect structures, including series in the regions 190 - 1 and 190 - 2 in the periphery 120 on respective sides of an array.
- FIG. 5 illustrates a top view layout of an embodiment which includes four series of interconnect structures, including series 190 - 1 , 190 - 2 , 190 - 3 , and 190 - 4 , in the periphery 120 on all four sides of an array.
- the length of the area occupied by one interconnect structure is about 2F times the number of levels or 20F, while the pitch per word line is about 2F or more making the width of the array about 2000F.
- about 100 interconnect structures could be formed in a series such as series 190 - 3 along the array width, and a similar number could be formed in a series such as series 190 - 1 along the array length.
- one or more interconnect structures can be implemented within the memory array region 110 in addition to, or as a replacement of, having an interconnect structure in the periphery 120 .
- the interconnect structures can extend diagonally or in any other direction, rather than being parallel to an edge of the memory array region 110 .
- FIG. 6 is a schematic illustration of a portion of the memory device including an interconnect structure as described herein.
- First electrode pillar 171 a is coupled to the access transistor 131 a which is selected using the bit line 150 a and word line 140 a .
- a plurality of memory elements 544 - 1 through 544 - 4 are connected to the pillar 171 a .
- Each of the memory elements includes a programmable element 548 in series with a rectifier 549 . This series arrangement represents the structure shown in FIGS. 3A-3B , even though the layer of anti-fuse material is placed at the p-n junction.
- the programmable element 548 is represented by a symbol often used to indicate anti-fuses. However, it will be understood that other types of programmable resistance materials and structures can be utilized.
- the rectifier 549 implemented by the p-n junction between the conductive plane and the polysilicon in the electrode pillar can be replaced by other rectifiers.
- a rectifier based on a solid electrolyte like germanium silicide, or other suitable material could be used to provide a rectifier. See U.S. Pat. No. 7,382,647 for other representative solid electrolyte materials.
- Each of the memory elements 544 - 1 through 544 - 4 is coupled to corresponding conductive levels 160 - 1 through 160 - 4 .
- the levels 160 - 1 to 160 - 4 are coupled via conductors 180 and interconnect lines 185 to a plane decoder 546 .
- the plane decoder 546 is responsive to addresses to apply a voltage, such as ground 547 , to a selected level so that the rectifier in the memory element is forward biased and conducting, and to apply a voltage to or float unselected levels so that the rectifier in the memory element is reversed biased or non-conducting.
- FIG. 7 is a simplified block diagram of an integrated circuit device 300 including a 3D memory array 360 having an interconnect structure as described herein.
- a row decoder 361 is coupled to a plurality of word lines 140 arranged along rows in the memory array 360 .
- a column decoder 363 is coupled to a plurality of bit lines 150 arranged along columns in the memory array 360 for reading and programming data from the memory cells in the array 360 .
- the plane decoder 546 is coupled to a plurality of levels 160 - 1 to 160 - 4 in the memory array 360 via conductors 180 and interconnect lines 185 . Addresses are supplied on bus 365 to column decoder 363 , row decoder 361 , and plane decoder 546 .
- Sense amplifiers and data-in structures in block 366 are coupled to the column decoder 363 in this example via data bus 367 .
- Data is supplied via the data-in line 371 from input/output ports on the integrated circuit 300 , to the data-in structures in block 366 .
- other circuitry 374 is included on the integrated circuit 300 , such as a general purpose processor or special purpose application circuitry, or a combination of modules providing system-on-a-chip functionality.
- Data is supplied via data-out line 372 from the sense amplifiers in block 366 to input/output ports on the integrated circuit 300 , or to other data destinations internal or external to the integrated circuit 300 .
- a controller implemented in this example using bias arrangement state machine 369 controls the application of bias arrangement supply voltages generated or provided through the voltage supply or supplies in block 368 , such as read and program voltages.
- the controller can be implemented using special-purpose logic circuitry as known in the art.
- the controller comprises a general-purpose processor, which may be implemented on the same integrated circuit, which executes a computer program to control the operations of the device.
- a combination of special-purpose logic circuitry and a general-purpose processor may be utilized for implementation of the controller.
- FIGS. 8A-8C to 15 illustrate steps in an embodiment of a fabrication sequence for manufacturing an interconnect structure having a very small footprint as described herein.
- FIGS. 8A and 8C illustrate cross-sectional views, and FIG. 8B illustrates a top view, of a first step of the fabrication sequence.
- the first step involves forming a plurality of levels 160 - 1 to 160 - 4 overlying the provided memory cell access layer 112 .
- the structure illustrated in FIGS. 8A-8C is formed using processes described in commonly owned U.S. patent application Ser. No. 12/430,290 by Lung, which was incorporated by reference above.
- the levels can be formed by standard processes as known in the art and may include access devices such as transistors and diodes, word lines, bit lines and source lines, conductive plugs, and doped regions within a substrate, depending upon the device in which the interconnect structure described herein is to be implemented.
- access devices such as transistors and diodes, word lines, bit lines and source lines, conductive plugs, and doped regions within a substrate, depending upon the device in which the interconnect structure described herein is to be implemented.
- a first mask 800 having an opening 810 is formed on the structure illustrated in FIGS. 8A-8C , resulting in the structure illustrated in the top and cross-sectional views of FIGS. 9A and 9B respectively.
- the first mask 800 can be formed by depositing the layer for the first mask 800 , and patterning the layer using lithographic techniques to form the opening 810 .
- the first mask 800 may comprise, for example, a hard mask material such as silicon nitride, silicon oxide, or silicon oxynitride.
- the opening 810 in the first mask 800 surrounds the perimeter of the combination of landing areas on the levels 160 - 1 to 160 - 4 .
- the width 192 of the opening 810 is at least as large as the widths of the landing areas on the levels 160 - 1 to 160 - 4 , so that the subsequently formed conductors 180 can pass through the openings in the levels.
- the length 194 of the opening 810 is at least as large as the sum of the lengths of the landing areas on the levels 160 - 1 to 160 - 4 , so that the subsequently formed conductors 180 can pass through the openings in the levels.
- a second etch mask 900 is formed on the structure illustrated in FIGS. 9A-9B , including within the opening 810 , resulting in the structure illustrated in the top and cross-sectional views of FIGS. 10A and 10B respectively.
- the second etch mask 900 has a length 910 less than the length 194 of the opening 810 , and has a width at least as large as the width 192 of the opening 810 .
- the second etch mask 900 comprises a material that can be selectively etched relative to the material of the first mask 800 , so that the length of the second mask 900 within the opening 810 can be selectively reduced in subsequent process steps described below.
- the material of the second mask 900 has an etching rate greater than an etching rate of the material of the first mask 800 for the process used to reduce the length of the second mask 900 .
- the second mask can comprise photoresist.
- an etching process is performed on the structure illustrated in FIGS. 10A-10B using the first and second masks 800 , 900 as etch masks, resulting in the structure illustrated in the top and cross-sectional views of FIGS. 11A and 11B respectively.
- the etching process can be carried out using a single etch chemistry using, for example, timing mode etching. Alternatively, the etching process can be carried out using different etch chemistries to individually etch through insulating layer 166 , level 160 - 4 , insulating material 165 - 3 , and level 160 - 3 .
- the etching forms an opening 1000 through the level 160 - 4 to expose a portion of level 160 - 3 .
- the opening 1000 overlies the landing area 161 - 1 a on level 160 - 1 .
- the opening 1000 has a length 1002 at least as large as the length of the landing area 161 - 1 a , and has a width 1004 at least as large as the width of the landing area 161 - 1 a.
- the etching also forms opening 1010 through the level 160 - 4 to expose a portion of level 160 - 3 .
- the opening 1010 overlies the landing area 161 - 1 b on level 160 - 1 .
- the opening 1010 has a length 1012 at least as large as the length of the landing area 161 - 1 b , and has a width 1004 at least as large as the width of the landing area 161 - 1 b
- the length 910 of the mask 900 is reduced to form reduced length mask 1100 with length 1110 , resulting in the structure illustrated in the top and cross-sectional views of FIGS. 12A and 12B respectively.
- the mask 900 comprises photoresist, and can be trimmed, for example, using reactive ion etching with CL2 or HBr based chemistries.
- an etching process is performed on the structure illustrated in FIGS. 12A-12B using the first mask 800 and the reduced length mask 1100 as etch masks, resulting in the structure illustrated in the top and cross-sectional views of FIGS. 13A and 13B .
- the etching process extends the openings 1000 , 1010 through level 160 - 3 to expose underlying portions of the level 160 - 2 .
- the etching also forms openings 1200 , 1210 through the portions of the level 160 - 4 no longer covered by the mask 1100 due to the reduction in the length of mask 1100 , thereby exposing portions of level 160 - 3 .
- the opening 1200 is formed adjacent opening 1000 , and overlies the landing area 161 - 2 a on level 160 - 2 .
- the opening 1200 has a length 1202 at least as large as the length of the landing area 161 - 2 a , and has a width 1204 at least as large as the width of the landing area 161 - 2 a.
- the opening 1210 is formed adjacent opening 1010 , and overlies the landing area 161 - 2 b on level 160 - 2 .
- the opening 1210 has a length 1212 at least as large as the length of the landing area 161 - 2 b , and has a width 1204 at least as large as the width of the landing area 161 - 2 b.
- the length 1110 of the mask 1100 is reduced to form reduced length mask 1300 with length 1305 .
- the etching process extends the openings 1000 , 1010 through level 160 - 2 to expose the landing areas 161 - 1 a , 161 - 1 b on level 160 - 1 .
- the etching process also extends the openings 1200 , 1210 through level 160 - 3 to expose the landing areas 161 - 2 a , 161 - 2 b on level 160 - 2 .
- the etching also forms openings 1310 , 1320 through the portions of the level 160 - 4 no longer covered due to the reduction in the length of mask 1300 , thereby exposing the landing areas 161 - 3 a , 161 - 3 b on level 160 - 3 .
- the opening 1310 is formed adjacent opening 1200 .
- the opening 1310 has a length 1312 at least as large as the length of the landing area 161 - 3 a , and has a width 1314 at least as large as the width of the landing area 161 - 3 a.
- the opening 1320 is formed adjacent opening 1210 .
- the opening 1320 has a length 1322 at least as large as the length of the landing area 161 - 3 b , and has a width 1324 at least as large as the width of the landing area 161 - 3 b.
- insulating fill material 1400 is deposited on the structure illustrated in FIGS. 14A-14B and a planarization process such as Chemical Mechanical Polishing (CMP) is performed to remove the masks 800 , 1300 , resulting in the structure illustrated in the cross-sectional view of FIG. 15 .
- CMP Chemical Mechanical Polishing
- a lithographic pattern is formed to define vias to the landing areas for the conductors 180 .
- Reactive ion etching can be applied to form deep, high aspect ratio vias through the insulating fill material 1400 to provide vias for the conductors 180 .
- the vias are filled with tungsten or other conductive material to form the conductors 180 .
- Metallization processes are then applied to form interconnect lines 185 to provide interconnection between the conductors 180 and plane decoding circuitry on the device.
- back end of line BEOL processes are applied to complete the integrated circuit, resulting in the structure illustrated in FIGS. 3A-3B .
- the openings in the various levels used for passing conductors to the landing areas on underlying levels are formed by patterning the levels using the opening 810 in the single etch mask 800 , as well as processes for etching the additional mask without a critical alignment step. As a result the openings in the various levels having vertically aligned sidewalls are formed in a self-aligned manner.
- the opening 810 in the mask 800 has a rectangular cross-section in plan view.
- the openings in the various levels have substantially the same width along the transverse direction.
- the opening in the mask 800 can have a cross-section that is circular, elliptical, square, rectangular, or somewhat irregularly shaped, depending on the shape of the landings areas of the various levels.
- the width of the opening in the mask 800 can vary along the longitudinal direction, in order to accommodate landing areas having different widths.
- FIG. 16 illustrates a plan view of an opening 1510 in the mask 800 having a width varying in the longitudinal direction in a step-like manner, which results in the widths of the openings in the levels varying accordingly.
- FIG. 17 is a simplified flowchart for a method 10 for creating interconnect contact regions 14 according to the present invention.
- the interconnect contact region creating method 10 of FIG. 17 includes obtaining a set of N masks at obtaining step 12 . Further steps in the method 10 shown in FIG. 17 will be discussed below in conjunction with FIGS. 18-27 , which illustrate a first example of a method for carrying out the present invention.
- the set of N masks are used to create up to 2N levels of interconnect contact regions 14 , see FIG. 27 , at the stack 16 of contact levels 18 . 1 , 18 . 2 , 18 . 3 , 18 . 4 , the stack 16 being at the interconnect region 17 of a three-dimensional stacked IC device.
- the interconnect region 17 will typically be a peripheral interconnect region, such as shown in FIGS. 4 and 5 , but may be located elsewhere.
- four contact levels are shown on a substrate 19 for simplicity of illustration; three-dimensional stacked IC devices will commonly have many more contact levels.
- each mask comprises mask and etch regions
- N is an integer equal to at least 2
- a portion removing step 20 is carried out to remove a portion 22 , see FIG. 19 , of an upper layer 24 overlying the stack 16 of contact levels 18 .
- upper layer 24 includes first and second silicon oxide layers 26 , 28 with a charge trapping layer 27 , typically of silicon nitride, therebetween.
- this removal is accomplished using an additional mask 30 having an open region 32 , see FIG. 18 , to permit the etching of a portion 22 of upper layer 24 as shown in FIG. 19 .
- contact levels 18 each include an upper conductive layer 34 , typically a polysilicon layer patterned to form conductors such as word lines, and a lower insulating layer 36 , typically a silicon oxide or silicon nitride compound.
- layer 34 will typically be referred to as polysilicon layer 34 .
- layer 34 may be made of other appropriate materials, such as metals, metal silicides and multilayer combinations of more than one of polysilicon, metal silicides and metals.
- the etching through dielectric layer 28 of upper layer 24 is typically controlled by the use of material-selective etching processes.
- any additional layer 24 is removed from the interconnect contact region using a blanket etch without the need for an additional mask.
- FIG. 20 illustrates the formation of a first mask 38 . 1 on the stack 16 of contact levels 18 of FIG. 19 .
- first mask 38 . 1 comprises photoresist mask elements 40 . 1 , 40 . 2 and 40 . 3 with mask element 40 . 2 covering a central portion 42 . 1 of the first polysilicon layer 34 . 1 and mask element 40 . 3 covering an edge portion 42 . 2 of the first polysilicon layer 34 . 1 .
- FIG. 21 illustrates the result of an etching step in which the portions of contact level 18 . 1 not covered by photoresist mask elements 40 are etched down to contact level 18 . 2 . That is, one contact level 18 is etched in this first etching step.
- FIG. 22 illustrates the formation of a second photoresist mask 38 . 2 on the stack 16 of contact levels 18 of FIG. 21 .
- Mask 38 . 2 covers otherwise exposed portions of polysilicon layers 34 . 1 and 34 . 2 that are subsequently to be used as interconnect contact regions 14 . 1 and 14 . 2 as suggested by the dashed lead lines in FIG. 22 .
- FIG. 23 shows the result of a second etching step in which two contact levels are etched.
- exposed surface portion 44 of polysilicon layer 34 . 2 is etched down two layers to expose a portion 46 of polysilicon layer 34 . 4 .
- the exposed portion 42 . 3 of polysilicon layer 34 is etched down two layers to expose a portion 46 of polysilicon layer 34 .
- FIG. 24 shows the result of removing second mask 38 . 2 leaving portions of the polysilicon layers 34 . 1 , 34 . 2 , 34 . 3 and 34 . 4 to act as interconnect contact regions 14 . 1 , 14 . 2 , 14 . 3 and 14 . 4 .
- the thin column portion 48 of contact level 18 . 1 sometimes called a dummy stack or a partial height dummy stack, may be formed on purpose or as the result of manufacturing tolerances.
- the interconnect region 17 is etched N times using N masks to create an interconnect contact region 14 at each of 2N contact levels 18 .
- the interconnect contact regions 14 are aligned with and provide access to landing areas 56 , discussed below with reference to FIG. 27 , at each of the 2N contact levels.
- Each etching step comprises etching through 2x ⁇ 1 contact levels for each mask of sequence number x. See interconnect region etch step 49 of FIG. 17 .
- FIG. 25 illustrates the result of the optional step of applying etch stop layer 50 , such as a silicon nitride layer when the interlayer insulator is silicon oxide, over the exposed surfaces of the etched stack 16 of contact levels 18 .
- etch stop layer 50 such as a silicon nitride layer when the interlayer insulator is silicon oxide
- an interlayer dielectric 52 is deposited on the structure of FIG. 25 as illustrated in FIG. 26 and by the etch regions fill step 53 of FIG. 17 .
- electrical conductors 54 through the interlayer dielectric 52 and etch stop layer 50 to make electrical contact with the electrically conductive landing areas 56 at the interconnect contact regions 14 .
- Conductors 54 may be formed using a tungsten plug process, that includes forming vias through the dielectric fill which provide openings to the landing areas on the selected layers, then using a CVD or PVD process, an adhesive liner may be formed in the via followed by deposition of tungsten to fill the vias, forming vertical conductors 54 . This is illustrated in FIG. 27 and is shown as the electrical conductors forming step 60 of FIG. 17 .
- FIGS. 28-34 A second example will be discussed with reference to FIGS. 28-34 with like reference numerals referring to like elements of the first example of FIGS. 17-27 .
- the stack 16 of contact levels 18 at interconnect region 17 of FIG. 28 has the same basic structure as in FIG. 18 .
- dielectric layer 26 and charge trapping layer 27 of upper layer 24 are removed with a blanket etch process thereby eliminating the need for additional mask 30 .
- First mask 38 . 1 is formed on dielectric layer 28 , mask 38 . 1 with open regions 41 . 1 , 41 . 2 between mask elements 40 . 1 and 40 . 2 and between mask elements 40 . 2 and 40 . 3 . This is followed by the first etching step shown in FIG.
- a second mask 38 . 2 is then formed on the etched stack 16 of contact levels 18 .
- Second mask 38 . 2 includes mask elements 40 . 4 and 40 . 5 with mask element 40 . 5 covering opening 63 while leaving opening 62 and a portion 64 dielectric layer 28 between openings 62 , 63 uncovered.
- FIG. 33 illustrates result of the second etching step in which two contact levels are etched. Specifically, opening 62 is etched down to oxide layer 36 . 3 while portion 64 of dielectric layer 28 is etched two contact levels down to oxide layer 36 . 2 . Thereafter, second mask 38 . 2 is removed and interlayer dielectric 52 is deposited on the etched structure as shown in FIG. 34 . This is then followed by the formation of electrical conductors 54 . 1 - 54 . 4 through the interlayer dielectric 52 and the oxide layers 28 , 36 . 1 , 36 . 2 , 36 . 3 covering polysilicon layers 34 . 1 - 34 . 4 so to make contact with the landing areas 56 . 1 - 56 . 4 at the interconnect contact regions 14 . 1 - 14 . 4 .
- the interconnect region 17 is etched N times using N masks to create an interconnect contact region 14 at each contact level 18 .
- the interconnect contact regions 14 are aligned with and provide access to landing areas 56 at each of the 2N contact levels.
- the etching step comprising etching through 2x ⁇ 1 contact levels for each mask of sequence number x.
- FIGS. 35-44 illustrate a third example of a method for carrying out the present invention again with like reference numerals referring to like elements.
- First mask 38 . 1 is formed over upper layer 24 and stack 16 of contact levels 18 at interconnect region 17 .
- Photoresist mask elements 40 . 1 , 40 . 2 and 40 . 3 form open regions 66 . 1 and 66 . 2 between mask elements 40 . 1 and 40 . 2 and between mask elements 40 . 2 and 40 . 3 as shown in FIG. 35 .
- the portions of upper layer 24 underlying open regions 66 . 1 and 66 . 2 are etched down to polysilicon layer 34 . 1 of first contact level 18 creating first and second openings 68 . 1 , 68 . 2 in upper layer 24 . Openings 68 . 1 and 68 . 2 expose surface portions 70 . 1 , 70 . 2 of first polysilicon layer 34 . 1 .
- FIG. 38 shows result of depositing sidewall material 72 . 1 and 72 . 2 on the sidewalls of the first and second openings 68 . 1 , 68 . 2 .
- This can be accomplished in different ways, such as by depositing blanket layer of insulating material such as silicon nitride by CVD or sputtering over the wafer, followed by anisotropic etching until the material is removed from horizontal surfaces of the wafer, except regions adjacent vertical sidewalls, at which sidewall spacers are left.
- Sidewall material 72 . 1 and 72 . 2 covers a first part 74 . 1 , 74 . 2 of each of the surface portions 70 . 1 , 70 . 2 while leaving a second part 76 . 1 , 76 . 2 of each of the surface portions 70 . 1 , 70 . 2 uncovered.
- FIG. 38 is then etched, such as by an anisotropic reactive ion etch that does not attack the side wall material, but only reduces the size of sidewall material 72 . 1 , 72 . 2 and extends the first and second openings 68 . 1 , 68 . 2 through one contact level to expose polysilicon layer 34 . 2 . See FIG. 39 .
- sidewall material 72 . 1 , 72 . 2 is removed, see FIG. 40 , to expose first parts 74 . 1 , 74 . 2 of surface portions 70 . 1 , 70 . 2 .
- FIG. 41 shows second mask 38 . 2 on the structure of FIG. 40 filling second opening 68 . 2 .
- First opening 68 . 1 is then etched through two contact levels 18 to expose portions 78 of third polysilicon layer 34 . 3 beneath first part 74 . 1 and portion 80 of forth polysilicon layer 34 . 4 beneath the second part 76 . 1 .
- FIG. 44 illustrates result of the formation of conductors 54 . 1 - 54 . 4 contacting the landing areas 56 . 1 - 56 . 4 at the interconnect contact regions 14 . 1 - 14 . 4 .
- FIGS. 35-44 The method illustrated in FIGS. 35-44 is especially suited when a relatively thick upper layer 24 is used above a stack 16 of contact levels 18 .
- a SiN layer 50 used with the FIGS. 18-27 example, may be used with the second and third examples.
- FIG. 45 illustrates a process example for a stack of 16 contact levels 18 .
- interconnect contact regions 14 for each of the 16 contact levels 18 can be accessed using only 4 masks 38 .
- first mask 38 . 1 has 8 photoresist mask elements 40 , labeled 1 , 3 , 5 , etc., followed by open etch regions 41 , labeled 2 , 4 , 6 , etc.
- each mask element 40 and each edge of region 41 has a 1 unit longitudinal dimension.
- One layer is etched for the first mask 38 . 1 .
- Second mask 38 is etched for the first mask 38 .
- Second mask 38 . 2 has 4 photoresist mask elements, labeled 1 / 2 , 5 / 6 , etc., followed by open etch regions labeled 3 / 4 , 7 / 8 , etc., each having a 2 unit longitudinal dimension.
- Two layers are etched with second mask 38 . 2 .
- Third mask 38 . 3 has 2 photoresist mask elements, labeled 1 - 4 , 9 - 12 , followed by open etch regions, labeled 5 - 8 , 13 , 16 , each having a 4 unit longitudinal dimension.
- Four layers are etched with third mask 38 . 3 .
- Fourth mask 38 . 4 has 1 photoresist mask element, labeled 1 - 8 , followed by an open etch region, labeled 9 - 16 , each having an 8 unit longitudinal dimension.
- Eight layers are etched with fourth mask 38 . 4 .
- any contact level 18 between 1 and 16 can be accessed by using some combination of etching 1 level, etching 2 levels, etching 4 levels and etching 8 levels.
- the 4 masks represent a four digit binary number, that is 0000, 0001, 0010, . .
- FIG. 47 shows an example in which 4 masks 38 are configured to create a stack 16 of 16 contact levels 18 having full height dummy stacks 82 between each interconnect contact region 14 and a full height boundary stack 84 adjacent to contact region 14 . This is achieved by providing dummy mask regions 86 for each mask 38 wherever a dummy stack 82 is to be created. In this example, there is a dummy stack 82 between each interconnect contact region 14 . However, in some examples, one or more of the dummy stacks 82 could be eliminated. Also, the longitudinal dimension of dummy stacks 82 need not be the same.
- the masks 38 be used in the order of the number of contact levels 18 etched with each mask. That is, mask 38 . 2 could be used before mask 38 . 1 . However, it is preferred that the masks be used in an ascending order of the number of contact levels etched, that is with the mask used with etching of one contact level first, the mask used with etching of two contact levels second, etc. for larger process window.
- dummy mask regions 86 are provided at corresponding positions at each mask 38 so that the resulting dummy stack 82 is a full height dummy stack. Partial height dummy stacks, such as thin column portion 48 of FIG. 24 , can be made by providing dummy mask regions 86 at corresponding positions for one or more but not all of masks 38 .
- N 2N levels of interconnect contact regions
- N up to and including 2N levels of interconnect contact regions
- the 4 masks can be used to create fewer than 16 levels of interconnect contact regions, such as 13, 14 or 15 levels of interconnect contact regions.
Abstract
A three-dimensional stacked IC device has a stack of contact levels at an interconnect region. According to some examples of the present invention, it only requires a set of N etch masks to create up to and including 2N levels of interconnect contact regions at the stack of contact levels. According to some examples, 2x-1 contact levels are etched for each mask sequence number x, x being a sequence number for the masks so that for one mask x=1, for another mask x=2, and so forth through x=N. Methods create the interconnect contact regions aligned with landing areas at the contact levels.
Description
- This application is a divisional of U.S. patent application Ser. No. 13/049,303 filed 16 Mar. 2013, attorney docket MXIC 1965-2; which claims the benefit of U.S. provisional patent application No. 61/434,086 filed 19 Jan. 2011, attorney docket MXIC 1965-1.
- This application is related to the following: U.S. provisional patent application No. 61/434,423 filed 19 Jan. 2011, attorney docket MXIC 1971-1; U.S. patent application Ser. No. 12/579,192 filed 14 Oct. 2009, now U.S. Pat. No. 8,154,128, attorney docket MXIC 1901-1.
- 1. Field of the Invention
- The present invention relates generally to high density integrated circuit devices, and more particularly to interconnect structures for multi-level three-dimensional stacked devices.
- 2. Description of Related Art
- In the manufacturing of high density memory devices, the amount of data per unit area on an integrated circuit can be a critical factor. Thus, as the critical dimensions of the memory devices approach lithographic technology limits, techniques for stacking multiple levels of memory cells have been proposed in order to achieve greater storage density and lower costs per bit.
- For example, thin film transistor techniques are applied to charge trapping memory in Lai, et al., “A Multi-Layer Stackable Thin-Film Transistor (TFT) NAND-Type Flash Memory,” IEEE Int'l Electron Devices Meeting, 11-13 Dec. 2006; and in Jung et al., “Three Dimensionally Stacked NAND Flash Memory Technology Using Stacking Single Crystal Si Layers on ILD and TANOS Structure for Beyond 30 nm Node,” IEEE Int'l Electron Devices Meeting, 11-13 Dec. 2006.
- Also, cross-point array techniques have been applied for anti-fuse memory in Johnson et al., “512-Mb PROM With a Three-Dimensional Array of Diode/Anti-fuse Memory Cells,” IEEE J. of Solid-State Circuits, Vol. 38, No. 11, November 2003. See, also U.S. Pat. No. 7,081,377 to Cleeves entitled “Three-Dimensional Memory.”
- Another structure that provides vertical NAND cells in a charge trapping memory technology is described in “Novel 3-D Structure for Ultra-High Density Flash Memory with VRAT and PIPE,” by Kim et al., 2008 Symposium on VLSI Technology Digest of Technical Papers;” 17-19 Jun. 2008; pages 122-123.
- In three-dimensional stacked memory devices, conductive interconnects used to couple the lower levels of memory cells to decoding circuitry and the like pass through the upper levels. The cost to implement the interconnections increases with the number of lithographic steps needed. One approach to reduce the number of lithographic steps is described in Tanaka et al., “Bit Cost Scalable Technology with Punch and Plug Process for Ultra High Density Flash Memory,” 2007 Symposium on VLSI Technology Digest of Technical Papers; 12-14 Jun. 2007; pages 14-15.
- However, one of the drawbacks with conventional 3-D stacked memory devices is that a separate mask is typically used for each contact level. Therefore, if there are, for example, 20 contact levels, 20 different masks are commonly required, each contact level requiring the creation of a mask for that level and an etching step for that level.
- According to some examples of the present invention, it only requires N masks to provide access to a landing area at 2N contact levels. According to some examples, 2x-1 contact levels are etched for each mask sequence number x.
- A first example of a method, for use with a three-dimensional stacked IC device having a stack of contact levels at an interconnect region, is used to create interconnect contact regions aligned with and exposing landing areas at the contact levels. A set of N etch masks is used to create up to and including 2N levels of interconnect contact regions at the stack of contact levels. Each mask comprises mask and etch regions. N is an integer equal to at least 2. x is a sequence number for the masks so that for one mask x=1, for another mask x=2, and so forth through x=N. At least a portion of any upper layer overlying the stack of contact levels at the interconnect region is removed. The interconnect region is etched N times using said masks in a chosen order. Doing so creates contact openings extending from a surface layer to each contact level. The contact openings are aligned with and provide access to landing areas at each of the 2N contact levels. 2x-1 contact levels are etched during the etching step for each mask of sequence number x. Electrical conductors can then be formed through the contact openings to contact the landing areas at the contact levels. Some examples include the following steps: a fill material is applied over the openings to define a via pattern surface; vias are opened through the fill material to expose the landing areas in each contact level; and a conductive material is deposited within the vias. In some examples, the accessing step is carried out with N equal to at least 4. In some examples, the removing step is carried out using an additional mask exposing the interconnect region while in other examples, the removing step is carried out using a blanket etching step at the interconnect region. In some examples, sidewall material acts as one of the N etch masks.
- Another example of a method provides electrical connections to landing areas at a stack of contact levels of an interconnect region for a three-dimensional stacked IC device. The IC device is of a type comprising an interconnect region, the interconnect region including an upper layer with a stack of at least first, second, third and fourth contact levels beneath the upper layer. At least first and second openings are formed in the upper layer, each opening exposing a surface portion of a first contact level, the first and second openings partially bounded by upper layer sidewalls. A sidewall material is deposited on the sidewalls of each of the first and second openings and on a first part of each of the surface portions while leaving a second part of the surface portions without sidewall material thereon. The first and second openings are extended through the second parts of the surface portions to expose a surface of the second contact level for each of the first and second openings. At least some of the sidewall material at each opening is removed to expose at least some of the first part of the surface portion at each opening, thereby forming interconnect contact regions at the second openings. The interconnect contact regions at the second opening are aligned with landing areas at the first and second contact levels. The first opening is further extended from (1) the exposed first part of the surface portion, through the first and second contact levels to expose a surface of a third contact level, and (2) an exposed surface of the second contact level through the second and third contact levels to expose a surface of the fourth contact level. Doing so forms interconnect contact regions at the first opening aligned with landing areas at the third and fourth contact levels. Electrical conductors are formed to the landing areas at the first, second, third and fourth contact levels. In some examples, the electrical conductors forming step comprises: applying a fill material over the openings to define a via pattern surface; opening vias through the fill material to expose the landing areas in each contact level; and depositing a conductive material within the vias.
- An example of a set of masks is used to create interconnect contact regions aligned with landing areas at a stack of contact levels of an interconnect region for a three-dimensional stacked IC device, the stack of contact levels covered by an upper layer. Each mask of a set of N etch masks comprises mask and etch regions, the etch regions used to create interconnect contact regions alignable with landing areas at up to and including 2N-1 contact levels of an interconnect region for a three-dimensional stacked IC device. N is an integer equal to at least 3. x is the sequence number for the masks so that for one mask x=1, for another mask x=2, and so forth through x=N. In some examples, sidewall material acts as one of the N etch masks. In some examples, the etch masks comprise a dummy mask region on at least one of said etch masks. In some examples, the etch masks comprise dummy mask regions at corresponding locations on at least some of said etch masks. In some examples, the etch masks comprise at least one dummy mask region at corresponding locations on each of said etch masks. In some examples, N is greater than or equal to 4.
- Another example of a set of masks is used to create interconnect contact regions aligned with landing areas at a stack of contact levels of an interconnect region for a three-dimensional stacked IC device. Each mask of a set of N masks comprises mask and etch regions, the etch regions used to create interconnect contact regions alignable with landing areas at up to and including 2N contact levels of an interconnect region for a three-dimensional stacked IC device. N is an integer equal to at least 2. x is the sequence number for the masks so that for one mask x=1, for another mask x=2, and so forth through x=N.
- Other aspects and advantages of the present invention can be seen on review of the drawings, the detailed description, and the claims which follow.
-
FIGS. 1-16 and the associated description are taken from U.S. patent application Ser. No. 12/579,192 filed 14 Oct. 2009 and entitled 3D Integrated Circuit Layer Interconnect having the same assignee as this application, the disclosure of which is incorporated by reference. -
FIG. 1 illustrates a cross-sectional view of a device including a three-dimensional structure having aninterconnect structure 190 with a small footprint whereconductors 180 extend to various levels 160-1 to 160-4 in the device. -
FIG. 2A illustrates a plan view of level 160-1 showing the landing areas. -
FIG. 2B illustrates a plan view of level 160-2 showing openings adjacent the landing areas. -
FIG. 2C illustrates a plan view of level 160-3 showing openings adjacent the landing areas. -
FIG. 2D illustrates a plan view of level 160-4 showing openings adjacent the landing area. -
FIGS. 3A and 3B illustrate respective orthogonal views of a portion of a three-dimensional stacked integrated circuit device including a 3D interconnect structure with a small footprint. -
FIG. 4 illustrates a top view layout of an embodiment of the device which includes interconnect structures in the periphery on two sides of a memory array. -
FIG. 5 illustrates a top view layout of an embodiment of the device which includes interconnect structures in the periphery on four sides of a memory array. -
FIG. 6 is a schematic diagram of a portion of the memory device including an interconnect structure as described herein. -
FIG. 7 is a simplified block diagram of an integrated circuit device including a 3D memory array having an interconnect structure as described herein. -
FIGS. 8A-8C to 15 illustrate steps in a fabrication sequence for manufacturing an interconnect structure as described herein. -
FIG. 16 illustrates a plan view of an opening in a mask having a width varying in the longitudinal direction in a step-like manner, to accommodate varying widths of landing areas on the levels. - The present invention is described primarily with reference to
FIGS. 17-47 . -
FIG. 17 is a simplified flowchart for a method for creating interconnect contact regions according to the present invention. -
FIGS. 18-27 illustrate a first example of a method for creating interconnect contact regions at a number of contact levels at an interconnect region of a three-dimensional stacked IC device. -
FIG. 18 is a simplified cross-sectional view of a stack of contact levels with an additional mask formed above an upper layer. -
FIG. 19 shows the result of etching through an open region in the additional mask ofFIG. 18 through the upper layer. -
FIG. 20 shows a first mask applied to the stack of contact levels ofFIG. 19 . -
FIG. 21 shows the result of etching a single contact level using the first mask. -
FIG. 22 shows a second mask applied to the stack of contact levels ofFIG. 21 . -
FIG. 23 shows the results of etching through two contact levels ofFIG. 22 . -
FIG. 24 shows the structure ofFIG. 23 with the second mask removed thereby exposing interconnect contact regions at four different contact levels. -
FIG. 25 shows the structure ofFIG. 24 with an etch stop layer applied over the exposed surfaces of the structure ofFIG. 24 . -
FIG. 26 shows the structure ofFIG. 25 covered by interlayer dielectric. -
FIG. 27 shows the structure ofFIG. 26 after electrical conductors have been formed through the interlayer dielectric and the etch stop layer to make contact with landing areas at the interconnect contact regions of each of the four contact levels. -
FIGS. 28-34 illustrate a second example of a method for creating interconnect contact regions at a number of contact levels at an interconnect region of a three-dimensional stacked IC device. -
FIGS. 35-44 illustrate a third example of a method for creating interconnect contact regions at a number of contact levels at an interconnect region of a three-dimensional stacked IC device. -
FIGS. 45 and 46 illustrate a process example for a stack of 16 contact levels withFIG. 46 illustrating the etching results. -
FIG. 47 illustrates the etching results when the masks have dummy contact regions so to create dummy stacks between the interconnect contact regions. -
FIG. 1 illustrates a cross-sectional view of a device including three-dimensional structure having aninterconnect structure 190 with a small footprint whereconductors 180 extend to various levels 160-1 to 160-4 in the device. In the illustrated example, four levels 160-1 to 160-4 are shown. More generally, thesmall interconnect structure 190 described herein can be implemented in astructure having levels 0 to N, where N is at least 2. - The
conductors 180 are arranged within theinterconnect structure 190 to contact landing areas on the various levels 160-1 to 160-4. As described in more detail below, theconductors 180 for each particular level extend through openings in the overlying levels to contact the landing areas 161-1 a, 161-1 b, 161-2 a, 161-2 b, 161-3 a, 161-3 b, 161-4. Theconductors 180 are used in this example for coupling the contact levels 160-1 to 160-4 to interconnectlines 185 in a wiring layer overlying the levels 160-1 to 160-4. - The landing areas are the portions of contact levels 160-1 to 160-4 used for contact with
conductors 180. The sizes of the landing areas are large enough to provide room for theconductors 180 to adequately couple the electrically conductive landing areas within the landing areas of the various contact levels 160-1 to 160-4 to theoverlying interconnect lines 185, as well as to address issues such as misalignment between theconductors 180 and the overlying openings in one level for landing areas in different levels. - The size of a landing area thus depends on a number of factors, including the size and number of conductors used, and will vary from embodiment to embodiment. In addition, the number of the
conductors 180 can be different for each of the landing areas. - In the illustrated example, the levels 160-1 to 160-4 consist of respective planar conductive layers of material such as doped polysilicon, with layers of insulating
material 165 separating the levels 160-1 to 160-4. Alternatively, the levels 160-1 to 160-4 need not be planar stacked material layers, and instead the layers of material can vary in the vertical dimension. - The
conductors 180 contacting the different levels 160-1 to 160-4 are arranged in a direction extending along the cross-section illustrated inFIG. 1 . This direction defined by the arrangement of theconductors 180 contacting different levels 160-1 to 160-4 is referred to herein as the “longitudinal” direction. The “transverse” direction is perpendicular to the longitudinal direction, and is into and out of the cross-section illustrated inFIG. 1 . Both the longitudinal and transverse directions are considered to be “lateral dimensions”, meaning a direction that is in a two-dimensional area of a plan view of the levels 160-1 to 160-4. The “length” of structures or features is its length in the longitudinal direction, and its “width” is its width in the transverse direction. - Level 160-1 is the lowest level in the plurality of levels 160-1 to 160-4. The level 160-1 is on insulating
layer 164. - The level 160-1 includes first and second landing areas 161-1 a, 161-1 b for contact with
conductors 180. - In
FIG. 1 the level 160-1 includes two landing areas 161-1 a, 161-1 b on opposite ends of theinterconnect structure 190. In some alternative embodiments one of the landing areas 161-1 a, 161-1 b is omitted. -
FIG. 2A is a plan view of a portion of level 160-1, including the landing areas 161-1 a, 161-1 b within the footprint of theinterconnect structure 190. The footprint of theinterconnect structure 190 can be close to the width of the via size for the conductors, and have a length that can be much longer than the width. As shown inFIG. 2A , landing area 161-1 a has awidth 200 in the transverse direction and alength 201 in the longitudinal direction. Landing area 161-1 b has awidth 202 in the transverse direction and alength 203 in the longitudinal direction. In the embodiment ofFIG. 2A the landing areas 161-1 a, 161-1 b each have a rectangular cross-section. In embodiments, the landing areas 161-1 a, 161-1 b may each have a cross-section that is circular, elliptical, square, rectangular, or somewhat irregularly shaped. - Because level 160-1 is the lowest level, the
conductors 180 need not pass through the level 160-1 to underlying levels. Thus, in this example, level 160-1 does not have openings within theinterconnect structure 190. - Referring back to
FIG. 1 , level 160-2 overlies level 160-1. Level 160-2 includes anopening 250 overlying the landing area 161-1 a on level 160-1. Theopening 250 has a distallongitudinal sidewall 251 a and a proximallongitudinal sidewall 251 b defining thelength 252 of theopening 250. Thelength 252 of theopening 250 is at least as large as thelength 201 of the underlying landing area 161-1 a, so that theconductors 180 for the landing area 161-1 a can pass through the level 160-2. - The level 160-2 also includes
opening 255 overlying the landing area 161-1 b. Theopening 255 has distal and proximallongitudinal sidewalls length 257 of theopening 255. Thelength 257 of theopening 255 is at least as large as thelength 203 of the underlying landing area 161-1 b, so that theconductors 180 for the landing area 161-1 b can pass through the level 160-2. - The level 160-2 also includes first and second landing areas 161-2 a, 161-2 b adjacent the
openings conductors 180. -
FIG. 2B is a plan view of a portion of level 160-2, including the first and second landing areas 161-2 a, 161-2 b and theopenings interconnect structure 190. - As shown in
FIG. 2B , opening 250 haslongitudinal sidewalls length 252, and hastransverse sidewalls width 254 of theopening 250. Thewidth 254 is at least as large as thewidth 200 of the underlying landing area 161-1 a, so that theconductors 180 can pass through theopening 250. -
Opening 255 haslongitudinal sidewalls length 257, and hastransverse sidewalls width 259. Thewidth 259 is at least as large as thewidth 202 of the underlying landing area 161-1 b, so that theconductors 180 can pass through theopening 255. - In the plan view of
FIG. 2B theopenings openings - As shown in
FIG. 2B , landing area 161-2 a is adjacent theopening 250 and has awidth 204 in the transverse direction and alength 205 in the longitudinal direction. Landing area 161-2 b is adjacent theopening 255 and has awidth 206 in the transverse direction and alength 207 in the longitudinal direction. - Referring back to
FIG. 1 , level 160-3 overlies level 160-2. Level 160-3 includes anopening 260 overlying landing area 161-1 a on level 160-1 and landing area 161-2 a on level 160-2. Theopening 260 has distal and proximallongitudinal sidewalls length 262 of theopening 260. Thelength 262 of theopening 260 is at least as large as the sum of thelengths conductors 180 for the landing areas 161-1 a and 161-2 a can pass through the level 160-3. - As can be seen in
FIG. 1 , the distallongitudinal sidewall 261 a ofopening 260 is vertically aligned with the distallongitudinal sidewall 251 a of theunderlying opening 250. In the manufacturing embodiment described in more detail below, the openings can be formed using the opening in a single etch mask and one additional mask formed over the opening in the single etch mask, as well as processes for etching the addition mask without a critical alignment step, resulting in the formation of openings having distal longitudinal sidewalls (261 a, 251 a, . . . ) along the perimeter of the single etch mask that are vertically aligned. - The level 160-3 also includes
opening 265 overlying the landing area 161-1 b on level 160-1 and landing area 161-2 b on level 160-2. Theopening 265 has outside and insidelongitudinal sidewalls length 267 of theopening 265. The outsidelongitudinal sidewall 266 a ofopening 265 is vertically aligned with the outsidelongitudinal sidewall 256 a of theunderlying opening 255. - The
length 267 of theopening 265 is at least as large as sum of thelengths conductors 180 for the landing areas 161-1 b and 161-2 b can pass through the level 160-3. - The level 160-3 also includes first and second landing areas 161-3 a, 161-3 b adjacent the
openings conductors 180. -
FIG. 2C is a plan view of a portion of level 160-3, including the first and second landing areas 161-3 a, 161-3 b and theopenings interconnect structure 190. - As shown in
FIG. 2C , opening 260 has outside and insidelongitudinal sidewalls length 262, and hastransverse sidewalls width opening 260. Thewidth 264 a is at least as large as thewidth 200 of the underlying landing area 161-1 a, andwidth 264 b is at least as large as thewidth 204 of the underlying landing area 161-2 a, so that theconductors 180 can pass through theopening 260. - In the illustrated embodiments,
widths widths -
Opening 265 haslongitudinal sidewalls length 267, and hastransverse sidewalls width width 269 a is at least as large as thewidth 202 of the underlying landing area 161-1 b, and thewidth 269 b is at least as large as thewidth 206 of the underling landing area 161-2 b, so that theconductors 180 can pass through theopening 265. - As shown in
FIG. 2C , landing area 161-3 a is adjacent theopening 260 and has awidth 214 in the transverse direction and alength 215 in the longitudinal direction. Landing area 161-3 b is adjacent theopening 265 has awidth 216 in the transverse direction and alength 217 in the longitudinal direction. - Referring back to
FIG. 1 , level 160-4 overlies level 160-3. Level 160-4 includes anopening 270 overlying the landing area 161-1 a on level 160-1, the landing area 161-2 a on level 160-2, and the landing area 161-3 a on level 160-3. Theopening 270 haslongitudinal sidewalls length 272 of theopening 270. Thelength 272 of theopening 270 is at least as large as the sum of thelengths conductors 180 for the landing areas 161-1 a, 161-2 a, 161-3 a can pass through the level 160-4. As shown inFIG. 1 , thelongitudinal sidewall 271 a ofopening 270 is vertically aligned with thelongitudinal sidewall 261 a of theunderlying opening 260. - The level 160-4 also includes
opening 275 overlying the landing area 161-1 b on level 160-1, the landing area 161-2 b on level 160-2, and the landing area 161-3 b on level 160-3. Theopening 275 haslongitudinal sidewalls length 277 of theopening 275. Thelongitudinal sidewall 276 a ofopening 275 is vertically aligned with thelongitudinal sidewall 266 a of theunderlying opening 265. - The
length 277 of theopening 275 is at least as large as sum of thelengths conductors 180 for the landing areas 161-1 b, 161-2 b, and 161-3 b can pass through the level 160-4. - The level 160-4 also includes a landing area 161-4 between the
openings conductors 180. InFIG. 1 , the level 160-4 has one landing area 161-4. Alternatively, the level 160-4 may include more than one landing area. -
FIG. 2D is a plan view of a portion of level 160-4, including landing area 161-4 and theopenings interconnect structure 190. - As shown in
FIG. 2D , opening 270 haslongitudinal sidewalls length 272, and hastransverse sidewalls width opening 270. Thewidths widths conductors 180 can pass through theopening 270. -
Opening 275 haslongitudinal sidewalls length 277, and hastransverse sidewalls width widths widths conductors 180 can pass through theopening 275. - As shown in
FIG. 2D , landing area 161-4 is between theopenings width 224 in the transverse direction and alength 225 in the longitudinal direction. - Referring back to
FIG. 1 , the distallongitudinal sidewalls openings openings sidewalls - As shown in
FIG. 1 , thelongitudinal sidewalls openings - Similarly, the transverse sidewalls of the openings in the levels are also vertically aligned. Referring to
FIGS. 2A-2D , thetransverse sidewalls openings transverse sidewalls openings longitudinal sidewalls transverse sidewalls - In the illustrated embodiment, the openings in the various levels 160-1 to 160-4 have substantially the same width in the transverse direction. Alternatively, the width of the openings can vary along the longitudinal direction, for example, in a step-like manner, in order to accommodate landing areas having different widths.
- This technique for implementing the
interconnect structure 190 as described herein significantly reduces the area or footprint needed for making contact to the plurality of levels 160-1 to 160-4, compared to prior art techniques. As a result, more space is available for implementing memory circuits in the various levels 160-1 to 160-4. This allows for higher memory density and a smaller cost per bit in the upper levels compared to prior art techniques. - In the cross-section of
FIG. 1 , the openings within theinterconnect structure 190 result in the levels having a staircase-like pattern on both sides of the landing area 161-4 on level 160-4. That is, the two openings in each level are symmetrical about an axis perpendicular to both the longitudinal and transverse directions, and the two landing areas of each level are also symmetrical about that axis. As used herein, the term “symmetrical” is intended to accommodate manufacturing tolerances in the formation of the openings using the opening in a single etch mask and multiple etch processes which may cause variations in the dimensions of the openings. - In alternative embodiments in which each level includes a single opening and a single landing area, the levels have a staircase-like pattern on only one side.
- In the illustrated example, four levels 160-1 through 160-4 are shown. More generally, the small interconnect structure described herein can be implemented in
levels 0 to N, where N is at least 2. Generally, level (i), for (i) equal to 1 through N, overlies level (i−1), and has an opening (i) adjacent the landing area (i) on level (i). The opening (i) extends over the landing area (i−1) on level (i−1), and for (i) greater than 1, over the adjacent opening (i−1) in level (i−1). The opening (i) has a distal longitudinal sidewall aligned with the distal longitudinal sidewall of opening (i−1) in level (i), and a proximal longitudinal sidewall defining a length of the opening (i). The length of the opening (i) is at least as large as the length of the landing area (i−1) plus the length of the opening (i−1), if any. For (i) greater than 1, the opening (i) has transverse sidewalls aligned with the transverse sidewalls of opening (i−1) in level (i−1) and defines a width of the opening (i) at least as large as the width of the landing area (i−1). - Other types of memory cells and configurations can be used in alternative embodiments. Examples of the other types of memory cells which may be used include dielectric charge trapping and floating gate memory cells. For example, in an alternative the levels of the device may be implemented as planar memory cell arrays separated by insulating material, with the access devices and access lines formed within the levels using thin film transistors or related technologies. In addition, the interconnect structure described herein can be implemented in other types of three-dimensional stacked integrated circuit devices, where having conductors extending to various levels in the device within a small footprint is useful.
-
FIG. 3A is a cross-section of a portion of a three-dimensional stackedintegrated circuit device 100 including amemory array region 110 and aperiphery region 120 with aninterconnect structure 190 as described herein. - In
FIG. 3A , thememory array region 110 is implemented as one-time programmable multi-level memory cells as described in U.S. patent application Ser. No. 12/430,290 by Lung, which is commonly owned by the assignee of the present application and incorporated by reference herein. It is described here as a representative integrated circuit structure in which the 3D interconnect structure described herein can be implemented. - The
memory array region 110 includes amemory access layer 112 including horizontal field effecttransistor access devices source regions drain regions Trench isolation structures Word lines access devices inter-layer dielectric 144 to couple thedrain regions lines - Contact
pads 152 a, 152 b are coupled to underlying contacts 146 a, 146 b, providing connection to thesource regions contact pads 152 a, 152 b and bitlines inter-layer dielectric 154. - In the illustrated example, the levels consist of respective planar conductive layers of material such as doped polysilicon. Alternatively, the levels need not be planar stacked material layers, and instead the layers of material can vary in the vertical dimension.
- Insulating layers 165-1 to 165-3 separate the levels 160-1 to 160-4 from one another. An insulating
layer 166 overlies the levels 160-1 to 160-4 and insulating layers 165-1 to 165-3. - A plurality of
electrode pillars cell access layer 112 and extend through the levels. In this drawing, afirst electrode pillar 171 a includes a centralconductive core 170 a made, for example, of tungsten or other suitable electrode material, surrounded by apolysilicon sheath 172 a. Alayer 174 a of anti-fuse material, or other programmable memory material, is formed between thepolysilicon sheath 172 a and the plurality of levels 160-1 through 160-4. The levels 160-1 through 160-4 comprise a relatively highly doped, n-type polysilicon in this example, while thepolysilicon sheath 172 a comprises a relatively lightly doped, p-type polysilicon. Preferably, the thickness of thepolysilicon sheath 172 a is greater than the depth of the depletion region formed by the p-n junction. The depth of the depletion region is determined in part by the relative doping concentrations of the n-type and p-type polysilicon used to form it. The levels 160-1 through 160-4 and thesheath 172 a can be implemented using amorphous silicon as well. Also, other semiconductor materials could be utilized. - The
first electrode pillar 171 a is coupled to thepad 152 a. Asecond electrode pillar 171 b includingconductive core 170 b,polysilicon sheath 172 b, andanti-fuse material layer 174 b is coupled to the pad 152 b. - Interface regions between the plurality of levels 160-1 through 160-4 and the
pillars - In the native state, the
layer 174 a of anti-fuse material ofpillar 171 a, which can be a silicon dioxide, silicon oxynitride, or other silicon oxide, has a high resistance. Other anti-fuse materials may be used, such as silicon nitride. After programming by applying appropriate voltages to the word lines 140,bit lines 150, and the plurality of levels 160-1 to 160-4, thelayer 174 a of anti-fuse material breaks down and an active area within the anti-fuse material adjacent a corresponding level assumes a low resistance state. - As shown in
FIG. 3A , the plurality of conductive layers of levels 160-1 to 160-4 extend into theperiphery region 120 where supporting circuitry andconductors 180 are made to the plurality levels 160-1 to 160-4. A wide variety of devices are implemented in theperiphery 120 to support decoding logic and other circuits on theintegrated circuit 100. - The
conductors 180 are arranged within theinterconnect structure 190 to contact landing areas on the various levels 160-1 to 160-4. As discussed in more detail below, theconductors 180 for each particular level 160-1 to 160-4 extend through openings in the overlying levels to a wiring layer including conductive interconnect lines 185. Theconductive interconnect lines 185 provide for interconnection between the levels 160-1 to 160-4 and decoding circuitry in theperiphery 120. - As represented by the dashed line in
FIG. 3A , theconductors 180 contacting the different levels 160-1 to 160-4 are arranged in the longitudinal direction extending into and out of the cross-section illustrated inFIG. 3A . -
FIG. 3B is a cross-sectional view in the longitudinal direction taken along lineFIG. 3B-FIG . 3B through theinterconnect structure 190 ofFIG. 3A , showing a view of theinterconnect structure 190 like that shown inFIG. 1 . As can be seen inFIG. 3B , theconductors 180 for each particular level extend through openings in the overlying levels to contact the landing areas. - In the illustrated example, four levels 160-1 through 160-4 are shown. More generally, the small interconnect structure described herein can be implemented in
levels 0 to N, where N is at least 2. - Other types of memory cells and configurations can be used in alternative embodiments. For example, in an alternative the levels of the device may be implemented as planar memory cell arrays separated by insulating material, with the access devices and access lines formed within the levels using thin film transistors or related technologies. In addition, the interconnect structure described herein can be implemented in other types of three-dimensional stacked integrated circuit devices, where having conductors extending to various levels in the device within a small footprint is useful.
- In
FIGS. 3A-3B , asingle interconnect structure 190 is shown. A plurality of interconnect structures can be arranged at various locations in the device, such as surrounding thememory array region 110, so as to provide more even power distribution.FIG. 4 illustrates a top view layout of an embodiment of thedevice 100 which includes a two series of interconnect structures, including series in the regions 190-1 and 190-2 in theperiphery 120 on respective sides of an array.FIG. 5 illustrates a top view layout of an embodiment which includes four series of interconnect structures, including series 190-1, 190-2, 190-3, and 190-4, in theperiphery 120 on all four sides of an array. For an example array size including 1000 columns and 1000 rows of cells, and having 10 levels, with a feature size F defining the word line width and the bit line width, and in which the size of the landing areas on the levels is about F, then one can see that the length of the area occupied by one interconnect structure is about 2F times the number of levels or 20F, while the pitch per word line is about 2F or more making the width of the array about 2000F. Thus, following this example, about 100 interconnect structures could be formed in a series such as series 190-3 along the array width, and a similar number could be formed in a series such as series 190-1 along the array length. - In yet other alternative embodiments, one or more interconnect structures can be implemented within the
memory array region 110 in addition to, or as a replacement of, having an interconnect structure in theperiphery 120. In addition, the interconnect structures can extend diagonally or in any other direction, rather than being parallel to an edge of thememory array region 110. -
FIG. 6 is a schematic illustration of a portion of the memory device including an interconnect structure as described herein.First electrode pillar 171 a is coupled to theaccess transistor 131 a which is selected using thebit line 150 a andword line 140 a. A plurality of memory elements 544-1 through 544-4 are connected to thepillar 171 a. Each of the memory elements includes aprogrammable element 548 in series with arectifier 549. This series arrangement represents the structure shown inFIGS. 3A-3B , even though the layer of anti-fuse material is placed at the p-n junction. Theprogrammable element 548 is represented by a symbol often used to indicate anti-fuses. However, it will be understood that other types of programmable resistance materials and structures can be utilized. - Also, the
rectifier 549 implemented by the p-n junction between the conductive plane and the polysilicon in the electrode pillar can be replaced by other rectifiers. For example, a rectifier based on a solid electrolyte like germanium silicide, or other suitable material, could be used to provide a rectifier. See U.S. Pat. No. 7,382,647 for other representative solid electrolyte materials. - Each of the memory elements 544-1 through 544-4 is coupled to corresponding conductive levels 160-1 through 160-4. The levels 160-1 to 160-4 are coupled via
conductors 180 andinterconnect lines 185 to aplane decoder 546. Theplane decoder 546 is responsive to addresses to apply a voltage, such asground 547, to a selected level so that the rectifier in the memory element is forward biased and conducting, and to apply a voltage to or float unselected levels so that the rectifier in the memory element is reversed biased or non-conducting. -
FIG. 7 is a simplified block diagram of anintegrated circuit device 300 including a3D memory array 360 having an interconnect structure as described herein. Arow decoder 361 is coupled to a plurality ofword lines 140 arranged along rows in thememory array 360. Acolumn decoder 363 is coupled to a plurality ofbit lines 150 arranged along columns in thememory array 360 for reading and programming data from the memory cells in thearray 360. Theplane decoder 546 is coupled to a plurality of levels 160-1 to 160-4 in thememory array 360 viaconductors 180 andinterconnect lines 185. Addresses are supplied onbus 365 tocolumn decoder 363,row decoder 361, andplane decoder 546. Sense amplifiers and data-in structures inblock 366 are coupled to thecolumn decoder 363 in this example viadata bus 367. Data is supplied via the data-inline 371 from input/output ports on theintegrated circuit 300, to the data-in structures inblock 366. In the illustrated embodiment,other circuitry 374 is included on theintegrated circuit 300, such as a general purpose processor or special purpose application circuitry, or a combination of modules providing system-on-a-chip functionality. Data is supplied via data-outline 372 from the sense amplifiers inblock 366 to input/output ports on theintegrated circuit 300, or to other data destinations internal or external to theintegrated circuit 300. - A controller implemented in this example using bias
arrangement state machine 369 controls the application of bias arrangement supply voltages generated or provided through the voltage supply or supplies inblock 368, such as read and program voltages. The controller can be implemented using special-purpose logic circuitry as known in the art. In alternative embodiments, the controller comprises a general-purpose processor, which may be implemented on the same integrated circuit, which executes a computer program to control the operations of the device. In yet other embodiments, a combination of special-purpose logic circuitry and a general-purpose processor may be utilized for implementation of the controller. -
FIGS. 8A-8C to 15 illustrate steps in an embodiment of a fabrication sequence for manufacturing an interconnect structure having a very small footprint as described herein. -
FIGS. 8A and 8C illustrate cross-sectional views, andFIG. 8B illustrates a top view, of a first step of the fabrication sequence. For the purposes of this application, the first step involves forming a plurality of levels 160-1 to 160-4 overlying the provided memorycell access layer 112. In the illustrated embodiment the structure illustrated inFIGS. 8A-8C is formed using processes described in commonly owned U.S. patent application Ser. No. 12/430,290 by Lung, which was incorporated by reference above. - In alternative embodiments, the levels can be formed by standard processes as known in the art and may include access devices such as transistors and diodes, word lines, bit lines and source lines, conductive plugs, and doped regions within a substrate, depending upon the device in which the interconnect structure described herein is to be implemented.
- As noted above, other types of memory cells and configurations for the
memory array region 110 can also be used in alternative embodiments. - Next, a
first mask 800 having anopening 810 is formed on the structure illustrated inFIGS. 8A-8C , resulting in the structure illustrated in the top and cross-sectional views ofFIGS. 9A and 9B respectively. Thefirst mask 800 can be formed by depositing the layer for thefirst mask 800, and patterning the layer using lithographic techniques to form theopening 810. Thefirst mask 800 may comprise, for example, a hard mask material such as silicon nitride, silicon oxide, or silicon oxynitride. - The
opening 810 in thefirst mask 800 surrounds the perimeter of the combination of landing areas on the levels 160-1 to 160-4. Thus, thewidth 192 of theopening 810 is at least as large as the widths of the landing areas on the levels 160-1 to 160-4, so that the subsequently formedconductors 180 can pass through the openings in the levels. Thelength 194 of theopening 810 is at least as large as the sum of the lengths of the landing areas on the levels 160-1 to 160-4, so that the subsequently formedconductors 180 can pass through the openings in the levels. - Next, a
second etch mask 900 is formed on the structure illustrated inFIGS. 9A-9B , including within theopening 810, resulting in the structure illustrated in the top and cross-sectional views ofFIGS. 10A and 10B respectively. As shown in the figures, thesecond etch mask 900 has alength 910 less than thelength 194 of theopening 810, and has a width at least as large as thewidth 192 of theopening 810. - In the illustrated embodiment, the
second etch mask 900 comprises a material that can be selectively etched relative to the material of thefirst mask 800, so that the length of thesecond mask 900 within theopening 810 can be selectively reduced in subsequent process steps described below. In other words, the material of thesecond mask 900 has an etching rate greater than an etching rate of the material of thefirst mask 800 for the process used to reduce the length of thesecond mask 900. For example, in embodiments in which thefirst mask 800 comprises a hard mask material, the second mask can comprise photoresist. - Next, an etching process is performed on the structure illustrated in
FIGS. 10A-10B using the first andsecond masks FIGS. 11A and 11B respectively. The etching process can be carried out using a single etch chemistry using, for example, timing mode etching. Alternatively, the etching process can be carried out using different etch chemistries to individually etch through insulatinglayer 166, level 160-4, insulating material 165-3, and level 160-3. - The etching forms an
opening 1000 through the level 160-4 to expose a portion of level 160-3. Theopening 1000 overlies the landing area 161-1 a on level 160-1. Theopening 1000 has alength 1002 at least as large as the length of the landing area 161-1 a, and has awidth 1004 at least as large as the width of the landing area 161-1 a. - The etching also forms opening 1010 through the level 160-4 to expose a portion of level 160-3. The
opening 1010 overlies the landing area 161-1 b on level 160-1. Theopening 1010 has alength 1012 at least as large as the length of the landing area 161-1 b, and has awidth 1004 at least as large as the width of the landing area 161-1 b - Next, the
length 910 of themask 900 is reduced to form reducedlength mask 1100 withlength 1110, resulting in the structure illustrated in the top and cross-sectional views ofFIGS. 12A and 12B respectively. In the illustrated embodiment themask 900 comprises photoresist, and can be trimmed, for example, using reactive ion etching with CL2 or HBr based chemistries. - Next, an etching process is performed on the structure illustrated in
FIGS. 12A-12B using thefirst mask 800 and the reducedlength mask 1100 as etch masks, resulting in the structure illustrated in the top and cross-sectional views ofFIGS. 13A and 13B . - The etching process extends the
openings - The etching also forms
openings mask 1100 due to the reduction in the length ofmask 1100, thereby exposing portions of level 160-3. Theopening 1200 is formedadjacent opening 1000, and overlies the landing area 161-2 a on level 160-2. Theopening 1200 has alength 1202 at least as large as the length of the landing area 161-2 a, and has awidth 1204 at least as large as the width of the landing area 161-2 a. - The
opening 1210 is formedadjacent opening 1010, and overlies the landing area 161-2 b on level 160-2. Theopening 1210 has alength 1212 at least as large as the length of the landing area 161-2 b, and has awidth 1204 at least as large as the width of the landing area 161-2 b. - Next, the
length 1110 of themask 1100 is reduced to form reducedlength mask 1300 withlength 1305. An etching process performed using thefirst mask 800 and themask 1300 as etch masks, resulting in the structure illustrated in the top and cross-sectional views ofFIGS. 14A and 14B . - The etching process extends the
openings openings - The etching also forms
openings mask 1300, thereby exposing the landing areas 161-3 a, 161-3 b on level 160-3. - The
opening 1310 is formedadjacent opening 1200. Theopening 1310 has alength 1312 at least as large as the length of the landing area 161-3 a, and has awidth 1314 at least as large as the width of the landing area 161-3 a. - The
opening 1320 is formedadjacent opening 1210. Theopening 1320 has alength 1322 at least as large as the length of the landing area 161-3 b, and has awidth 1324 at least as large as the width of the landing area 161-3 b. - Next, insulating
fill material 1400 is deposited on the structure illustrated inFIGS. 14A-14B and a planarization process such as Chemical Mechanical Polishing (CMP) is performed to remove themasks FIG. 15 . - Next, a lithographic pattern is formed to define vias to the landing areas for the
conductors 180. Reactive ion etching can be applied to form deep, high aspect ratio vias through the insulatingfill material 1400 to provide vias for theconductors 180. After opening the vias, the vias are filled with tungsten or other conductive material to form theconductors 180. Metallization processes are then applied to forminterconnect lines 185 to provide interconnection between theconductors 180 and plane decoding circuitry on the device. Finally, back end of line BEOL processes are applied to complete the integrated circuit, resulting in the structure illustrated inFIGS. 3A-3B . - The openings in the various levels used for passing conductors to the landing areas on underlying levels are formed by patterning the levels using the
opening 810 in thesingle etch mask 800, as well as processes for etching the additional mask without a critical alignment step. As a result the openings in the various levels having vertically aligned sidewalls are formed in a self-aligned manner. - In the illustrated examples described above, the
opening 810 in themask 800 has a rectangular cross-section in plan view. As a result, the openings in the various levels have substantially the same width along the transverse direction. Alternatively, the opening in themask 800 can have a cross-section that is circular, elliptical, square, rectangular, or somewhat irregularly shaped, depending on the shape of the landings areas of the various levels. - For example, the width of the opening in the
mask 800 can vary along the longitudinal direction, in order to accommodate landing areas having different widths.FIG. 16 illustrates a plan view of anopening 1510 in themask 800 having a width varying in the longitudinal direction in a step-like manner, which results in the widths of the openings in the levels varying accordingly. - The present invention will now be described primarily with reference to
FIGS. 17-47 . - The following description will typically be with reference to specific structural embodiments and methods. It is to be understood that there is no intention to limit the invention to the specifically disclosed embodiments and methods but that the invention may be practiced using other features, elements, methods and embodiments. Preferred embodiments are described to illustrate the present invention, not to limit its scope, which is defined by the claims. Those of ordinary skill in the art will recognize a variety of equivalent variations on the description that follows. Like elements in various embodiments are commonly referred to with like reference numerals.
-
FIG. 17 is a simplified flowchart for amethod 10 for creatinginterconnect contact regions 14 according to the present invention. The interconnect contactregion creating method 10 ofFIG. 17 includes obtaining a set of N masks at obtainingstep 12. Further steps in themethod 10 shown inFIG. 17 will be discussed below in conjunction withFIGS. 18-27 , which illustrate a first example of a method for carrying out the present invention. - The set of N masks are used to create up to 2N levels of
interconnect contact regions 14, seeFIG. 27 , at thestack 16 of contact levels 18.1, 18.2, 18.3, 18.4, thestack 16 being at theinterconnect region 17 of a three-dimensional stacked IC device. Theinterconnect region 17 will typically be a peripheral interconnect region, such as shown inFIGS. 4 and 5 , but may be located elsewhere. In the three examples ofFIGS. 18-44 , four contact levels are shown on asubstrate 19 for simplicity of illustration; three-dimensional stacked IC devices will commonly have many more contact levels. As will be discussed below, each mask comprises mask and etch regions, N is an integer equal to at least 2, and x is a sequence number for the masks so that for one mask x=1, for another mask x=2, and so forth through x=N. When x=1, the etching step for the associated mask will etch one contact level 18, when x=2, the etching step for the associated mask will etch two contact levels, etc. - Next, a
portion removing step 20, seeFIG. 17 , is carried out to remove aportion 22, seeFIG. 19 , of anupper layer 24 overlying thestack 16 of contact levels 18. In this example,upper layer 24 includes first and second silicon oxide layers 26, 28 with acharge trapping layer 27, typically of silicon nitride, therebetween. In this example, this removal is accomplished using anadditional mask 30 having anopen region 32, seeFIG. 18 , to permit the etching of aportion 22 ofupper layer 24 as shown inFIG. 19 . In this example, contact levels 18 each include an upper conductive layer 34, typically a polysilicon layer patterned to form conductors such as word lines, and a lower insulating layer 36, typically a silicon oxide or silicon nitride compound. For ease of reference layer 34 will typically be referred to as polysilicon layer 34. However, layer 34 may be made of other appropriate materials, such as metals, metal silicides and multilayer combinations of more than one of polysilicon, metal silicides and metals. The etching throughdielectric layer 28 ofupper layer 24 is typically controlled by the use of material-selective etching processes. For example, whendielectric layer 28 is silicon oxide and layer 34 is polysilicon, using reactive ion etching to etch throughdielectric layer 28, the etching is effectively stopped upon reaching layer 34. Similar techniques can be used to control the depth of etching in other situations. Other techniques for controlling the depth of etching may also be used.Additional mask 30 may not be considered a part of the set of N masks because it is used to simply open a space for etching of thestack 16 of contact levels 18. In the example discussed below with regard toFIGS. 28-34 , anyadditional layer 24 is removed from the interconnect contact region using a blanket etch without the need for an additional mask. -
FIG. 20 illustrates the formation of a first mask 38.1 on thestack 16 of contact levels 18 ofFIG. 19 . In this example, first mask 38.1 comprises photoresist mask elements 40.1, 40.2 and 40.3 with mask element 40.2 covering a central portion 42.1 of the first polysilicon layer 34.1 and mask element 40.3 covering an edge portion 42.2 of the first polysilicon layer 34.1.FIG. 21 illustrates the result of an etching step in which the portions of contact level 18.1 not covered byphotoresist mask elements 40 are etched down to contact level 18.2. That is, one contact level 18 is etched in this first etching step. -
FIG. 22 illustrates the formation of a second photoresist mask 38.2 on thestack 16 of contact levels 18 ofFIG. 21 . Mask 38.2 covers otherwise exposed portions of polysilicon layers 34.1 and 34.2 that are subsequently to be used as interconnect contact regions 14.1 and 14.2 as suggested by the dashed lead lines inFIG. 22 .FIG. 23 shows the result of a second etching step in which two contact levels are etched. In particular, exposedsurface portion 44 of polysilicon layer 34.2 is etched down two layers to expose aportion 46 of polysilicon layer 34.4. In addition, the exposed portion 42.3 of polysilicon layer 34.1 is also etched down two contact levels to expose aportion 47 polysilicon layer 34.3.FIG. 24 shows the result of removing second mask 38.2 leaving portions of the polysilicon layers 34.1, 34.2, 34.3 and 34.4 to act as interconnect contact regions 14.1, 14.2, 14.3 and 14.4. Thethin column portion 48 of contact level 18.1, sometimes called a dummy stack or a partial height dummy stack, may be formed on purpose or as the result of manufacturing tolerances. - In the example of
FIGS. 18-24 , two masks 38.1, 38.2 were used to provide access to landing areas at four interconnect contact regions 14.1-14.4 at four different contact levels 18.1-18.4. According to the present invention, theinterconnect region 17 is etched N times using N masks to create aninterconnect contact region 14 at each of 2N contact levels 18. Theinterconnect contact regions 14 are aligned with and provide access to landing areas 56, discussed below with reference toFIG. 27 , at each of the 2N contact levels. Each etching step comprises etching through 2x−1 contact levels for each mask of sequence number x. See interconnectregion etch step 49 ofFIG. 17 . -
FIG. 25 illustrates the result of the optional step of applyingetch stop layer 50, such as a silicon nitride layer when the interlayer insulator is silicon oxide, over the exposed surfaces of the etchedstack 16 of contact levels 18. Thereafter, aninterlayer dielectric 52 is deposited on the structure ofFIG. 25 as illustrated inFIG. 26 and by the etch regions fillstep 53 ofFIG. 17 . This is followed by formation of electrical conductors 54 through theinterlayer dielectric 52 andetch stop layer 50 to make electrical contact with the electrically conductive landing areas 56 at theinterconnect contact regions 14. Conductors 54 may be formed using a tungsten plug process, that includes forming vias through the dielectric fill which provide openings to the landing areas on the selected layers, then using a CVD or PVD process, an adhesive liner may be formed in the via followed by deposition of tungsten to fill the vias, forming vertical conductors 54. This is illustrated inFIG. 27 and is shown as the electricalconductors forming step 60 ofFIG. 17 . - A second example will be discussed with reference to
FIGS. 28-34 with like reference numerals referring to like elements of the first example ofFIGS. 17-27 . Thestack 16 of contact levels 18 atinterconnect region 17 ofFIG. 28 has the same basic structure as inFIG. 18 . In this example,dielectric layer 26 andcharge trapping layer 27 ofupper layer 24 are removed with a blanket etch process thereby eliminating the need foradditional mask 30. First mask 38.1 is formed ondielectric layer 28, mask 38.1 with open regions 41.1, 41.2 between mask elements 40.1 and 40.2 and between mask elements 40.2 and 40.3. This is followed by the first etching step shown inFIG. 31 wherebyopenings dielectric layer 28 and polysilicon layer 34.1 at the openings 41.1 and 41.2 between the mask elements 40.1/40.2 and between the mask elements 40.2/40.3. Although such etching step could be continued down to polysilicon layer 34.2, it is not necessary for reasons that will be evident when discussingFIGS. 33 and 34 . A second mask 38.2 is then formed on the etchedstack 16 of contact levels 18. Second mask 38.2 includes mask elements 40.4 and 40.5 with mask element 40.5 coveringopening 63 while leavingopening 62 and aportion 64dielectric layer 28 betweenopenings -
FIG. 33 illustrates result of the second etching step in which two contact levels are etched. Specifically, opening 62 is etched down to oxide layer 36.3 whileportion 64 ofdielectric layer 28 is etched two contact levels down to oxide layer 36.2. Thereafter, second mask 38.2 is removed andinterlayer dielectric 52 is deposited on the etched structure as shown inFIG. 34 . This is then followed by the formation of electrical conductors 54.1-54.4 through theinterlayer dielectric 52 and the oxide layers 28, 36.1, 36.2, 36.3 covering polysilicon layers 34.1-34.4 so to make contact with the landing areas 56.1-56.4 at the interconnect contact regions 14.1-14.4. - As with the example of
FIGS. 18-24 , two masks 38.1, 38.2 were used in the example ofFIGS. 28-34 to provide access to landing areas 56.1-56.4 at four interconnect contact regions 14.1-14.4 at four different contact levels 18.1-18.4. According to the present invention theinterconnect region 17 is etched N times using N masks to create aninterconnect contact region 14 at each contact level 18. Theinterconnect contact regions 14 are aligned with and provide access to landing areas 56 at each of the 2N contact levels. Again, the etching step comprising etching through 2x−1 contact levels for each mask of sequence number x. -
FIGS. 35-44 illustrate a third example of a method for carrying out the present invention again with like reference numerals referring to like elements. First mask 38.1 is formed overupper layer 24 and stack 16 of contact levels 18 atinterconnect region 17. Photoresist mask elements 40.1, 40.2 and 40.3 form open regions 66.1 and 66.2 between mask elements 40.1 and 40.2 and between mask elements 40.2 and 40.3 as shown inFIG. 35 . The portions ofupper layer 24 underlying open regions 66.1 and 66.2 are etched down to polysilicon layer 34.1 of first contact level 18 creating first and second openings 68.1, 68.2 inupper layer 24. Openings 68.1 and 68.2 expose surface portions 70.1, 70.2 of first polysilicon layer 34.1. -
FIG. 38 shows result of depositing sidewall material 72.1 and 72.2 on the sidewalls of the first and second openings 68.1, 68.2. This can be accomplished in different ways, such as by depositing blanket layer of insulating material such as silicon nitride by CVD or sputtering over the wafer, followed by anisotropic etching until the material is removed from horizontal surfaces of the wafer, except regions adjacent vertical sidewalls, at which sidewall spacers are left. Sidewall material 72.1 and 72.2 covers a first part 74.1, 74.2 of each of the surface portions 70.1, 70.2 while leaving a second part 76.1, 76.2 of each of the surface portions 70.1, 70.2 uncovered. - The structure of
FIG. 38 is then etched, such as by an anisotropic reactive ion etch that does not attack the side wall material, but only reduces the size of sidewall material 72.1, 72.2 and extends the first and second openings 68.1, 68.2 through one contact level to expose polysilicon layer 34.2. SeeFIG. 39 . Next, sidewall material 72.1, 72.2 is removed, seeFIG. 40 , to expose first parts 74.1, 74.2 of surface portions 70.1, 70.2.FIG. 41 shows second mask 38.2 on the structure ofFIG. 40 filling second opening 68.2. First opening 68.1 is then etched through two contact levels 18 to exposeportions 78 of third polysilicon layer 34.3 beneath first part 74.1 andportion 80 of forth polysilicon layer 34.4 beneath the second part 76.1. - Second mask 38.2 is then removed and the structure of
FIG. 42 is covered byinterlayer dielectric 52 as shown inFIG. 43 .FIG. 44 illustrates result of the formation of conductors 54.1-54.4 contacting the landing areas 56.1-56.4 at the interconnect contact regions 14.1-14.4. - The method illustrated in
FIGS. 35-44 is especially suited when a relatively thickupper layer 24 is used above astack 16 of contact levels 18. ASiN layer 50, used with theFIGS. 18-27 example, may be used with the second and third examples. -
FIG. 45 illustrates a process example for a stack of 16 contact levels 18. According to the present invention,interconnect contact regions 14 for each of the 16 contact levels 18 can be accessed using only 4 masks 38. In this example, first mask 38.1 has 8photoresist mask elements 40, labeled 1, 3, 5, etc., followed byopen etch regions 41, labeled 2, 4, 6, etc. In this example, eachmask element 40 and each edge ofregion 41 has a 1 unit longitudinal dimension. One layer is etched for the first mask 38.1. Second mask 38.2 has 4 photoresist mask elements, labeled 1/2, 5/6, etc., followed by open etch regions labeled 3/4, 7/8, etc., each having a 2 unit longitudinal dimension. Two layers are etched with second mask 38.2. Third mask 38.3 has 2 photoresist mask elements, labeled 1-4, 9-12, followed by open etch regions, labeled 5-8, 13, 16, each having a 4 unit longitudinal dimension. Four layers are etched with third mask 38.3. Fourth mask 38.4 has 1 photoresist mask element, labeled 1-8, followed by an open etch region, labeled 9-16, each having an 8 unit longitudinal dimension. Eight layers are etched with fourth mask 38.4. - As discussed above, when using first mask 38.1, with x=1, a single layer 18 is etched (2x−1=20=1); when using second mask 38.2, 2 layers 18 are etched (2x−1=21=2); when using third mask 38.3, 4 layers 18 are etched (2x−1=22=4); when using fourth mask 38.4, 8 layers 38 are etched (2x−1=23=8). In this way any contact level 18 between 1 and 16 can be accessed by using some combination of
etching 1 level,etching 2 levels,etching 4 levels andetching 8 levels. Another way to think about this is that the 4 masks represent a four digit binary number, that is 0000, 0001, 0010, . . . 1111 corresponding to the decimal numbers 1-16. For example, to access theinterconnect contact regions 14 at contact level 18 requires etching through 12 contact levels which can be accomplished usingopen regions 41 for third mask 38.3 (etching through 4 contact levels) and fourth mask 38.4 (etching through 8 contact levels). The result of use of masks 38.1-38.4 ofFIG. 45 withstack 16 of contact levels 18 is shown inFIG. 46 . Conventional methods would typically require 16 different masks resulting in a much higher processing expense and increased chance of failure due to tolerance buildup. - The example of
FIGS. 45 and 46 results in a continuous, open step region forinterconnect contact regions 14 aligned with landing areas 56.FIG. 47 shows an example in which 4 masks 38 are configured to create astack 16 of 16 contact levels 18 having full height dummy stacks 82 between eachinterconnect contact region 14 and a full height boundary stack 84 adjacent to contactregion 14. This is achieved by providingdummy mask regions 86 for each mask 38 wherever a dummy stack 82 is to be created. In this example, there is a dummy stack 82 between eachinterconnect contact region 14. However, in some examples, one or more of the dummy stacks 82 could be eliminated. Also, the longitudinal dimension of dummy stacks 82 need not be the same. - It is not necessary that the masks 38 be used in the order of the number of contact levels 18 etched with each mask. That is, mask 38.2 could be used before mask 38.1. However, it is preferred that the masks be used in an ascending order of the number of contact levels etched, that is with the mask used with etching of one contact level first, the mask used with etching of two contact levels second, etc. for larger process window.
- In the example of
FIG. 47 ,dummy mask regions 86 are provided at corresponding positions at each mask 38 so that the resulting dummy stack 82 is a full height dummy stack. Partial height dummy stacks, such asthin column portion 48 ofFIG. 24 , can be made by providingdummy mask regions 86 at corresponding positions for one or more but not all of masks 38. - While the invention has been discussed with reference to N=2 with regard to
FIGS. 17-44 and with N=4 with regard toFIGS. 45-47 , the number of masks could be other than 3 or N could be greater than 4. While a set of N masks can be used to create 2N levels of interconnect contact regions, it can also be used to create up to and including 2N levels of interconnect contact regions. For example, with N equal to 4, the 4 masks can be used to create fewer than 16 levels of interconnect contact regions, such as 13, 14 or 15 levels of interconnect contact regions. - While the present invention is disclosed by reference to the preferred embodiments and examples detailed above, it is to be understood that these examples are intended in an illustrative rather than in a limiting sense. It is contemplated that modifications and combinations will readily occur to those skilled in the art, which modifications and combinations will be within the spirit of the invention and the scope of the following claims.
- Disclosures of any and all patents, patent applications and printed publications referred to above are incorporated by reference.
Claims (10)
1. A set of masks, used to create interconnect contact regions aligned with landing areas at a stack of contact levels of an interconnect region for a three-dimensional stacked IC device, the stack of the contact levels covered by an upper layer, comprising:
a set of N etch masks, each mask comprising mask and etch regions, the etch regions used to create the interconnect contact regions alignable with the landing areas at up to and including 2N-1 contact levels of an interconnect region for a three-dimensional stacked IC device, N being an integer equal to at least 3, x being the sequence number for the masks so that for one mask x=1, for another mask x=2, and so forth through x=N.
2. The set of masks according to claim 1 , wherein sidewall material acts as one of the N etch masks.
3. The set of masks according to claim 1 , wherein the etch masks comprise a dummy mask region on at least one of said etch masks.
4. The set of masks according to claim 1 , wherein the etch masks comprise dummy mask regions at corresponding locations on at least some of said etch masks.
5. The set of masks according to claim 1 , wherein the etch masks comprise at least one dummy mask region at corresponding locations on each of said etch masks.
6. The set of masks according to claim 1 , wherein longitudinal dimensions for the etch regions for a chosen etch mask are about equal.
7. The set of masks according to claim 1 , wherein:
the mask and etch regions have longitudinal dimensions; and
the longitudinal dimensions for the mask and etch regions for a chosen mask are about equal to one another.
8. The set of masks according to claim 1 , wherein:
the mask and etch regions have longitudinal dimensions; and
the longitudinal dimensions for the mask and etch regions for all of the masks are about equal to one another.
9. The set of masks according to claim 1 , wherein N is greater than or equal to 4.
10. A set of masks, used to create interconnect contact regions aligned with landing areas at a stack of contact levels of an interconnect region for a three-dimensional stacked IC device, comprising:
a set of N masks, each mask comprising mask and etch regions, the etch regions used to create the interconnect contact regions alignable with the landing areas at up to and including 2N contact levels of an interconnect region for a three-dimensional stacked IC device, N being an integer equal to at least 2, x being the sequence number for the masks so that for one mask x=1, for another mask x=2, and so forth through x=N.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
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US14/070,333 US20140053979A1 (en) | 2011-01-19 | 2013-11-01 | Reduced number of masks for ic device with stacked contact levels |
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US14/070,333 US20140053979A1 (en) | 2011-01-19 | 2013-11-01 | Reduced number of masks for ic device with stacked contact levels |
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Also Published As
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KR20120084241A (en) | 2012-07-27 |
US20120184097A1 (en) | 2012-07-19 |
KR101812987B1 (en) | 2017-12-28 |
US8598032B2 (en) | 2013-12-03 |
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