US20060268607A1 - Operation method of non-volatile memory structure - Google Patents
Operation method of non-volatile memory structure Download PDFInfo
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- US20060268607A1 US20060268607A1 US11/491,157 US49115706A US2006268607A1 US 20060268607 A1 US20060268607 A1 US 20060268607A1 US 49115706 A US49115706 A US 49115706A US 2006268607 A1 US2006268607 A1 US 2006268607A1
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Classifications
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C16/00—Erasable programmable read-only memories
- G11C16/02—Erasable programmable read-only memories electrically programmable
- G11C16/04—Erasable programmable read-only memories electrically programmable using variable threshold transistors, e.g. FAMOS
- G11C16/0491—Virtual ground arrays
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/40—Electrodes ; Multistep manufacturing processes therefor
- H01L29/41—Electrodes ; Multistep manufacturing processes therefor characterised by their shape, relative sizes or dispositions
- H01L29/423—Electrodes ; Multistep manufacturing processes therefor characterised by their shape, relative sizes or dispositions not carrying the current to be rectified, amplified or switched
- H01L29/42312—Gate electrodes for field effect devices
- H01L29/42316—Gate electrodes for field effect devices for field-effect transistors
- H01L29/4232—Gate electrodes for field effect devices for field-effect transistors with insulated gate
- H01L29/42324—Gate electrodes for transistors with a floating gate
- H01L29/42328—Gate electrodes for transistors with a floating gate with at least one additional gate other than the floating gate and the control gate, e.g. program gate, erase gate or select gate
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
- H01L29/68—Types of semiconductor device ; Multistep manufacturing processes therefor controllable by only the electric current supplied, or only the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched
- H01L29/76—Unipolar devices, e.g. field effect transistors
- H01L29/772—Field effect transistors
- H01L29/78—Field effect transistors with field effect produced by an insulated gate
- H01L29/788—Field effect transistors with field effect produced by an insulated gate with floating gate
- H01L29/7887—Programmable transistors with more than two possible different levels of programmation
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10B—ELECTRONIC MEMORY DEVICES
- H10B41/00—Electrically erasable-and-programmable ROM [EEPROM] devices comprising floating gates
- H10B41/30—Electrically erasable-and-programmable ROM [EEPROM] devices comprising floating gates characterised by the memory core region
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10B—ELECTRONIC MEMORY DEVICES
- H10B69/00—Erasable-and-programmable ROM [EPROM] devices not provided for in groups H10B41/00 - H10B63/00, e.g. ultraviolet erasable-and-programmable ROM [UVEPROM] devices
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C16/00—Erasable programmable read-only memories
- G11C16/02—Erasable programmable read-only memories electrically programmable
- G11C16/04—Erasable programmable read-only memories electrically programmable using variable threshold transistors, e.g. FAMOS
- G11C16/0408—Erasable programmable read-only memories electrically programmable using variable threshold transistors, e.g. FAMOS comprising cells containing floating gate transistors
- G11C16/0441—Erasable programmable read-only memories electrically programmable using variable threshold transistors, e.g. FAMOS comprising cells containing floating gate transistors comprising cells containing multiple floating gate devices, e.g. separate read-and-write FAMOS transistors with connected floating gates
- G11C16/0458—Erasable programmable read-only memories electrically programmable using variable threshold transistors, e.g. FAMOS comprising cells containing floating gate transistors comprising cells containing multiple floating gate devices, e.g. separate read-and-write FAMOS transistors with connected floating gates comprising two or more independent floating gates which store independent data
Definitions
- the present invention is related to an operation method of a non-volatile memory structure and, more particularly, to an operation method of a symmetrical and self-aligned non-volatile memory structure with high cell density.
- EPROMs Erasable programmable read only memories
- EEPROMs electrically erasable programmable read only memories
- the conventional non-volatile memory cells normally need high currents to operate, e.g., 200 microamperes ( ⁇ A), for hot electron programming, so it is not suitable for low-power devices that are in the trend of chip development. Therefore, one form of an EEPROM device includes a so-called “split-gate” electrode has been developed to obtain high efficiency and low current programming, where the programming current can be diminished to, for example, 1 ⁇ A.
- EEPROM devices use two polysilicon layers (one for the formation of the floating gate and another for the formation of the control gate and possibly electrical interconnects) whereas other EEPROM devices use three polysilicon layers.
- U.S. Pat. No. 4,302,766 provides a first polysilicon layer serving as the floating gate, a second polysilicon layer serving as the control gate, and a third polysilicon layer coupled through an erase window to a portion of the first polysilicon layer for use during erasure of the cell.
- U.S. Pat. No. 4,331,968 also uses a third layer of polysilicon to form an erase gate
- U.S. Pat. Nos. 4,561,004 and 4,803,529 use three polysilicon layers in their own specific configurations.
- U.S. Pat. No. 4,622,656 describes an EEPROM device in which a reduced programming voltage is provided by having a highly doped channel region under the select gate, and having the channel region under the floating gate being either lightly doped or doped to the opposite conductivity type, thereby providing a significant surface potential gap at the transition location of the channel.
- U.S. Pat. No. 5,712,180 discloses a flash EEPROM cell layout as shown in FIG. 1 ( a ), and the cross-sectional diagram of line A-A in FIG. 1 ( a ) is shown in FIG. 1 ( b ).
- EEPROM cell 101 includes a buried source region 102 and a buried drain region 103 , each being buried by a relatively thick layer of dielectric 104 and 105 , respectively.
- Channel region 106 is divided into a first portion 106 - 1 and a second portion 106 - 2 .
- the first portion 106 - 1 is influenced by the polysilicon layer 109 and serves as a select gate
- the second portion 106 - 2 is influenced by a floating gate 107 formed of a polysilicon layer and which, in turn, is influenced by control gate 108 formed of a polysilicon layer.
- suitable dielectric layers such as thermally grown oxide are located between channel 106 , polysilicon layer 109 , and polysilicon layer 107 for insulation.
- suitable dielectric layers such as oxide or composite oxide/nitride are formed between the three layers of polysilicon.
- Metal silicide can be used in place of one or more of the polysilicon layers 108 and 109 .
- a highly-doped P + region 120 is used within channel 106 - 2 adjacent to buried drain region 103 , so as to provide a stable threshold voltage of the memory transistor including channel 106 - 2 .
- the floating gate 107 has to be larger than the polysilicon layer 109 in width direction, i.e., the longitudinal direction shown in FIG. 1 ( a ) for alignment tolerance consideration. Therefore, it is hard to decrease the scale of this type of structure.
- U.S. Pat. No. 5,414,693 also disclosed a flash EEPROM memory structure as shown in FIG. 2 , and the cross-sectional diagram of line B-B in FIG. 2 is shown in FIG. 3 .
- the cell structure is formed in a P-doped substrate 206 with a drain 204 of a transistor 201 and a drain 205 of a transistor 202 .
- the drains 204 and 205 serve as bit lines.
- the transistor 201 includes a floating gate 207 a and an overlying control gate 208 a.
- the transistor 202 includes a floating gate 207 b and a control gate 208 b located thereon.
- a word line 209 extends over the two transistors 201 and 202 and forms the control gate 209 a of the select gate between the floating gate transistors 201 and 202 .
- the word line 209 serially connects the select gates in one row of a memory array and runs perpendicular to the bit lines in columns, i.e., the drains 204 and 205 .
- floating gates 207 a and 207 b need to be larger than the select gate 209 a in width direction, i.e., the longitudinal direction as shown in FIG. 2 . Therefore, the memory cell size is difficult to be decreased significantly more.
- the objective of the present invention is to provide an operation method of a memory structure for low power device applications, and this memory structure comprises competitive small memory cells so that the cell density can be increased effectively.
- the memory structure essentially comprises a first conductive line, two conductive blocks, two first dielectric spacers, a first dielectric layer, and a second conductive line.
- the first conductive line e.g., a polysilicon line
- the two conductive blocks for example, composed of polysilicon are formed at the two sides of the first conductive line and insulated from the first conductive line with the two first dielectric spacers.
- the first dielectric layer such as an oxide/nitride/oxide (ONO) layer is formed on the two second conductive blocks and above the first conductive line, and the second conductive line is formed on the first dielectric layer and is substantially perpendicular to the two doping regions.
- ONO oxide/nitride/oxide
- the stack of the conductive block, the first dielectric layer, and the second conductive line form a typical floating gate structure, i.e., the conductive block can store charges.
- the first conductive line and conductive blocks function as a select gate and floating gates, respectively, whereas the doping regions and the second conductive line function as bit lines and a word line, respectively.
- the first conductive line may also serve as an erase gate for data erasure.
- a bias voltage is applied to the doping region next to the other conductive block so that the depletion region is created across the other conductive block whereby ignoring the effect of the other conductive block if being programmed, and the unselected second conductive lines, i.e., unselected word lines, are applied by negative voltages.
- the above split gate memory structure can be manufactured by the following steps. First of all, two fourth conductive lines are formed above a semiconductor substrate, and two first dielectric spacers are formed on both sides of each fourth conductive line. Then, dopants are implanted into the semiconductor substrate to form two doping regions next to the two fourth conductive lines, and a first conductive line is formed between the two fourth conductive lines.
- the first conductive line can be formed by depositing conductive material and planarizing it afterwards.
- the two fourth conductive lines are etched to form two conductive blocks next to the first conductive line. Then, the first dielectric layer is formed on the two conductive blocks and above the first conductive line, and a second conductive line perpendicular to the doping regions is formed on the first dielectric layer.
- a dielectric layer is deposited and etched so as to form two second dielectric spacers beside the second conductive line.
- the second dielectric spacers can be formed by oxidation also.
- a third conductive line substantially parallel to the second conductive line is formed, where the third conductive line serves as another word line and the second dielectric spacer function as an insulator between them, and a dielectric, e.g., oxide or ONO, is located between the third conductive line and the semiconductor substrate.
- a dielectric e.g., oxide or ONO
- FIGS. 1 ( a ) and 1 ( b ) illustrate a known memory structure
- FIGS. 2 and 3 illustrate another known memory structure
- FIGS. 4 ( a ) through 4 ( i ) illustrate the processes of manufacturing the memory structure in accordance with the present invention
- FIG. 5 illustrates the circuit schematic with reference to the memory structure in accordance with the present invention
- FIG. 6 illustrates the top view of the memory structure in accordance with the present invention.
- a process for making a memory cell of the NMOS type is exemplified as follows with a view to illustrating the features of the present invention.
- a gate dielectric layer 402 ranging from 70 to 110 angstroms is thermally grown on the surface of a semiconductor substrate 401 , and followed by sequentially depositing a conductive layer 403 and a mask layer 404 thereon.
- the conductive layer 403 may be composed of polysilicon and have a thickness between 500-1000 angstroms
- the mask layer 404 may be a silicon nitride layer of a thickness between 200-1000 angstroms.
- the gate dielectric layer 402 , the conductive layer 403 , and the mask layer 404 are patterned by lithography and etching so as to form a plurality of conductive lines 403 .
- dielectric spacers 405 ranging from 100 to 300 angstroms are formed beside each conductive line 403 , and then photoresist blocks 406 are formed and N + dopants, e.g., arsenic ions with 1 ⁇ 10 14 -5 ⁇ 10 15 atoms/cm 2 are implanted into the semiconductor substrate 401 that are uncovered by the photoresist blocks 406 , so as to form N + regions 407 .
- the dielectric spacers 405 can be formed by either oxidation or deposition of low pressure chemical vapor deposition (LPCVD) oxide, or high temperature oxide (HTO), and followed by etching back. Then, the photoresist blocks 406 are stripped away.
- LPCVD low pressure chemical vapor deposition
- HTO high temperature oxide
- dielectric layers 408 and 409 are formed on the semiconductor substrate 401 , in which the dielectric layers 408 and 409 are disposed alternately.
- the dielectric layers 409 are formed on the doped regions 407 , so that the thicknesses thereof are thicker than those of the dielectric layers 408 under oxidation.
- the dielectric layers 408 and 409 can be either oxide or ONO layers.
- a conductive layer such as a polysilicon or polysilicon/tungsten silicide (poly/WSi) layer 410 , is deposited thereon.
- the conductive layer 410 is planarized by either chemical mechanical polishing (CMP) or etching back to be a plurality of conductive lines 410 . Then, dielectric layers 411 are formed on the top of the conductive lines 410 .
- the dielectric layers 411 can be formed by either CVD oxide deposition followed by etching back or by thermal growth, i.e., oxidation.
- the mask layer 404 is removed by, for example, phosphoric acid, and then a dielectric layer such as an ONO layer 412 is formed along the contour of the device. Afterwards, another conductive layer 413 is deposited thereon.
- FIG. 4 ( f ) illustrates the top view of the device shown in FIG. 4 ( e ).
- the conductive layer 413 is etched to form separated conductive lines 413 serving as word lines, and at the same time the conductive lines 403 are separated into a plurality of conductive blocks.
- the stack of the conductive block 403 , the ONO layer 412 and the conductive line 413 serve as a floating gate structure, i.e., the conductive block 403 is used for storage.
- CVD oxide is deposited and planarized to form isolating lines 414 between the conductive blocks 403 and between the conductive lines 413 .
- FIG. 4 ( g ) illustrates the cross-sectional view of line 1 - 1 in FIG. 4 ( f ), where the nitride layer 416 is used as a mask on the conductive lines 413 for the planarization to the CVD oxide while the isolating lines 414 are being formed.
- FIG. 4 ( i ) is the cross-sectional view of line 2 - 2 in FIG. 4 ( h ).
- dielectric spacers 417 can be formed beside the conductive lines 413 , and then conductive lines 418 , also serving as word lines, are formed between the dielectric spacers 417 so that, ideally, the density of the word lines can be doubled.
- FIG. 5 illustrates a schematic diagram with reference to the split gate memory structure put forth in the present invention, in which the memory cell architecture is the same as that shown in FIG. 4 ( e ). Yet some components are renamed by their functionality: a data line (bit line) is denoted by DL x , a select gate is denoted by SG x , and a word line is denoted by WL x . Floating gate cells are denoted by FG x , where the floating gate cells at two sides of a select gate SG 2 are denoted by T L and T R , respectively. Examples for the reading, programming, and erasing of memory cells T L and T R are shown in Table 1.
- T L , DL 2 and DL 3 are 5V and 0V respectively
- WL 2 is 12V
- SG 2 is 1V.
- T L and T R are turned on by the voltage of WL 2 coupling to T L and T R
- SG 2 is turned on as well. Consequently, 5V bias is generated underneath floating gate FG 1 . Therefore, electrons will jump into the storage cell of T L for programming.
- T L For reading T L , in addition to that of WL 2 and SG 2 are 5V and 3V respectively, and the DL 3 of 1.5V is intended to deplete the doping region of DL 3 so as to ignore the effect of T R , i.e., regardless of whether T R is programmed or not. Accordingly, no current occurs if T L is programmed, and, in contrast, current occurs if T L is not programmed.
- This read operation uses so-called “reverse read” approach, i.e., to read the right hand side cell programmed or not, bias voltage is put on the left hand side bit line rather than the right hand side.
- a highly negative voltage such as ⁇ 18V is applied to WL 2 to expel electrons out of floating gate FG 1 and into the semiconductor substrate through the dielectric layer underneath.
- a manner by partitioning voltage can be employed as shown in Erase (II).
- DL 1 , DL 2 , and DL 3 are 5V, and WL 2 is ⁇ 10V. Therefore approximately ⁇ 5V will be coupled to the FG 1 in the case of a 50% coupling ratio. Therefore, 10V bias is generated across the FG 1 .
- the dielectric spacer 405 may function also as a tunnel oxide
- the conductive line 410 such as SG 2 , may function as an erase gate. Such erase conditions are listed in Erase (III).
- TABLE 1 SG 1 SG 2 SG 3 WL 1 WL 2 WL 3 DL 1 DL 2 DL 3 T L Program 0 V 1 V 0 V 0 V 12 V 0 V 0 V 5 V 0 V Read 0 V 3 V 0 V 0 V 5 V 0 V 0 V 0 V 1.5 V Erase (I) 0 V 0 V 0 V 0 V 0 V ⁇ 18 V 0 V 0 V 0 V 0 V 0 V Erase (II) 0 V 0 V 0 V 0 V ⁇ 10 V 0 V 5 V 5 V 5 V Erase (III) 0 V 12 V 0 V 0 V 0 V 0 V 0 V 0 V 0 V T R Program 0 V 1 V 0 V 0 V 12 V 0 V 0 V 0 V 5 V Read 0 V 3 V 0 V 0 V 5 V 0 V 0 V 0 V 0 V 1.5 V Erase (I) 0 V 0 V 0 V 0
- unselected wordlines e.g., WL 1 and WL 3
- they can be applied by negative voltages, e.g., ⁇ 2V as shown in Table 2.
- the unselected word lines can be applied by negative voltages, e.g. ⁇ 2V as shown in Table 2.
- FIG. 6 is a plan view of the memory layout with reference to FIG. 5 specifying the relationship of the floating gates FG 1 , FG 2 , and FG 3 , select gates SG 2 and SG 3 , data lines DL 2 and DL 3 , and word line WL.
- the floating gates are totally self-aligned to the select gates and word line so that there is no need for alignment tolerance at all. Consequently, a very competitive small size can be achieved, thereby significantly increasing the cell density of the memory structure.
- the PMOS type transistor can also be implemented by doping boron ions without departing from the spirit of the present invention.
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Abstract
An operation method for a memory structure formed between two doping regions serving as bit lines in a semiconductor substrate, the memory structure comprising a first conductive line serving as a select gate and being formed above the semiconductor substrate, two conductive blocks serving as floating gates and being formed at the two sides of the first conductive line and insulated from the first conductive line with two first dielectric spacers therebetween, a first dielectric layer formed on the two second conductive blocks, a selected second conductive line serving as a word line and being formed on the first dielectric layer and substantially perpendicular to the two doping regions, and a plurality of unselected second conductive lines parallel to the selected second conductive line; wherein reading the programmed status of one of the conductive blocks comprising the step of putting a bias voltage on the doping region next to the other conductive block so that the depletion region is created across the other conductive block whereby ignoring the effect of the other conductive block if being programmed, and the unselected second conductive lines are applied by negative voltages.
Description
- (A) Field of the Invention
- The present invention is related to an operation method of a non-volatile memory structure and, more particularly, to an operation method of a symmetrical and self-aligned non-volatile memory structure with high cell density.
- (B) Description of the Related Art
- Erasable programmable read only memories (EPROMs) and electrically erasable programmable read only memories (EEPROMs) are well known non-volatile memory devices capable of being stored data, as well as erased and rewritten data, as desired.
- The conventional non-volatile memory cells normally need high currents to operate, e.g., 200 microamperes (μA), for hot electron programming, so it is not suitable for low-power devices that are in the trend of chip development. Therefore, one form of an EEPROM device includes a so-called “split-gate” electrode has been developed to obtain high efficiency and low current programming, where the programming current can be diminished to, for example, 1 μA.
- Many EEPROM devices use two polysilicon layers (one for the formation of the floating gate and another for the formation of the control gate and possibly electrical interconnects) whereas other EEPROM devices use three polysilicon layers. For example, U.S. Pat. No. 4,302,766 provides a first polysilicon layer serving as the floating gate, a second polysilicon layer serving as the control gate, and a third polysilicon layer coupled through an erase window to a portion of the first polysilicon layer for use during erasure of the cell. U.S. Pat. No. 4,331,968 also uses a third layer of polysilicon to form an erase gate, and U.S. Pat. Nos. 4,561,004 and 4,803,529 use three polysilicon layers in their own specific configurations.
- U.S. Pat. No. 4,622,656 describes an EEPROM device in which a reduced programming voltage is provided by having a highly doped channel region under the select gate, and having the channel region under the floating gate being either lightly doped or doped to the opposite conductivity type, thereby providing a significant surface potential gap at the transition location of the channel.
- Moreover, some recently developed innovative memory structures with accompanying figures are introduced in detail as follows.
- U.S. Pat. No. 5,712,180 discloses a flash EEPROM cell layout as shown in
FIG. 1 (a), and the cross-sectional diagram of line A-A inFIG. 1 (a) is shown inFIG. 1 (b). EEPROMcell 101 includes a buriedsource region 102 and a burieddrain region 103, each being buried by a relatively thick layer of dielectric 104 and 105, respectively.Channel region 106 is divided into a first portion 106-1 and a second portion 106-2. The first portion 106-1 is influenced by thepolysilicon layer 109 and serves as a select gate, whereas the second portion 106-2 is influenced by afloating gate 107 formed of a polysilicon layer and which, in turn, is influenced bycontrol gate 108 formed of a polysilicon layer. As is well known in the art, suitable dielectric layers such as thermally grown oxide are located betweenchannel 106,polysilicon layer 109, andpolysilicon layer 107 for insulation. Similarly, suitable dielectric layers such as oxide or composite oxide/nitride are formed between the three layers of polysilicon. Metal silicide can be used in place of one or more of thepolysilicon layers drain region 103, so as to provide a stable threshold voltage of the memory transistor including channel 106-2. Accordingly, thefloating gate 107 has to be larger than thepolysilicon layer 109 in width direction, i.e., the longitudinal direction shown inFIG. 1 (a) for alignment tolerance consideration. Therefore, it is hard to decrease the scale of this type of structure. - U.S. Pat. No. 5,414,693 also disclosed a flash EEPROM memory structure as shown in
FIG. 2 , and the cross-sectional diagram of line B-B inFIG. 2 is shown inFIG. 3 . The cell structure is formed in a P-dopedsubstrate 206 with adrain 204 of atransistor 201 and adrain 205 of atransistor 202. Thedrains transistor 201 includes afloating gate 207 a and anoverlying control gate 208 a. Likewise, thetransistor 202 includes afloating gate 207 b and acontrol gate 208 b located thereon. Aword line 209 extends over the twotransistors control gate 209 a of the select gate between thefloating gate transistors word line 209 serially connects the select gates in one row of a memory array and runs perpendicular to the bit lines in columns, i.e., thedrains gates select gate 209 a in width direction, i.e., the longitudinal direction as shown inFIG. 2 . Therefore, the memory cell size is difficult to be decreased significantly more. - To sum up, the floating gates in U.S. Pat. No. 5,712,180 and U.S. Pat. No. 5,414,693 are completely defined by the control gates during control gate patterning, so the floating gates have to be larger than the select gate in width direction to allow alignment tolerance. Under such circumstances, the memory cell size could not be reduced significantly.
- The objective of the present invention is to provide an operation method of a memory structure for low power device applications, and this memory structure comprises competitive small memory cells so that the cell density can be increased effectively.
- In order to achieve the above objective, an operation method of a memory structure, for example, including two cells formed between two doping regions, in a semiconductor substrate is disclosed. The memory structure essentially comprises a first conductive line, two conductive blocks, two first dielectric spacers, a first dielectric layer, and a second conductive line. The first conductive line, e.g., a polysilicon line, is formed above the semiconductor substrate, and the two conductive blocks, for example, composed of polysilicon are formed at the two sides of the first conductive line and insulated from the first conductive line with the two first dielectric spacers. The first dielectric layer such as an oxide/nitride/oxide (ONO) layer is formed on the two second conductive blocks and above the first conductive line, and the second conductive line is formed on the first dielectric layer and is substantially perpendicular to the two doping regions.
- Accordingly, the stack of the conductive block, the first dielectric layer, and the second conductive line form a typical floating gate structure, i.e., the conductive block can store charges. The first conductive line and conductive blocks function as a select gate and floating gates, respectively, whereas the doping regions and the second conductive line function as bit lines and a word line, respectively. In addition, the first conductive line may also serve as an erase gate for data erasure.
- While reading the programmed status of one of the conductive blocks, a bias voltage is applied to the doping region next to the other conductive block so that the depletion region is created across the other conductive block whereby ignoring the effect of the other conductive block if being programmed, and the unselected second conductive lines, i.e., unselected word lines, are applied by negative voltages.
- The above split gate memory structure can be manufactured by the following steps. First of all, two fourth conductive lines are formed above a semiconductor substrate, and two first dielectric spacers are formed on both sides of each fourth conductive line. Then, dopants are implanted into the semiconductor substrate to form two doping regions next to the two fourth conductive lines, and a first conductive line is formed between the two fourth conductive lines. The first conductive line can be formed by depositing conductive material and planarizing it afterwards. The two fourth conductive lines are etched to form two conductive blocks next to the first conductive line. Then, the first dielectric layer is formed on the two conductive blocks and above the first conductive line, and a second conductive line perpendicular to the doping regions is formed on the first dielectric layer.
- Further, with a view to increasing the word line integrity, the following process may be added. A dielectric layer is deposited and etched so as to form two second dielectric spacers beside the second conductive line. The second dielectric spacers can be formed by oxidation also. Then, a third conductive line substantially parallel to the second conductive line is formed, where the third conductive line serves as another word line and the second dielectric spacer function as an insulator between them, and a dielectric, e.g., oxide or ONO, is located between the third conductive line and the semiconductor substrate. As a result, the word line density will be almost doubled.
- FIGS. 1(a) and 1(b) illustrate a known memory structure;
-
FIGS. 2 and 3 illustrate another known memory structure; - FIGS. 4(a) through 4(i) illustrate the processes of manufacturing the memory structure in accordance with the present invention;
-
FIG. 5 illustrates the circuit schematic with reference to the memory structure in accordance with the present invention; -
FIG. 6 illustrates the top view of the memory structure in accordance with the present invention. - Embodiments of the present invention will now be described with reference to the accompanying drawings.
- A process for making a memory cell of the NMOS type is exemplified as follows with a view to illustrating the features of the present invention.
- As shown in
FIG. 4 (a), agate dielectric layer 402 ranging from 70 to 110 angstroms is thermally grown on the surface of asemiconductor substrate 401, and followed by sequentially depositing aconductive layer 403 and amask layer 404 thereon. Theconductive layer 403 may be composed of polysilicon and have a thickness between 500-1000 angstroms, and themask layer 404 may be a silicon nitride layer of a thickness between 200-1000 angstroms. - Sequentially, the
gate dielectric layer 402, theconductive layer 403, and themask layer 404 are patterned by lithography and etching so as to form a plurality ofconductive lines 403. - In
FIG. 4 (b), twodielectric spacers 405 ranging from 100 to 300 angstroms are formed beside eachconductive line 403, and then photoresist blocks 406 are formed and N+ dopants, e.g., arsenic ions with 1×1014-5×1015 atoms/cm2 are implanted into thesemiconductor substrate 401 that are uncovered by the photoresist blocks 406, so as to form N+ regions 407. Thedielectric spacers 405 can be formed by either oxidation or deposition of low pressure chemical vapor deposition (LPCVD) oxide, or high temperature oxide (HTO), and followed by etching back. Then, the photoresist blocks 406 are stripped away. - In
FIG. 4 (c),dielectric layers semiconductor substrate 401, in which thedielectric layers dielectric layers 409 are formed on the dopedregions 407, so that the thicknesses thereof are thicker than those of thedielectric layers 408 under oxidation. Alternatively, thedielectric layers layer 410, is deposited thereon. - In
FIG. 4 (d), theconductive layer 410 is planarized by either chemical mechanical polishing (CMP) or etching back to be a plurality ofconductive lines 410. Then,dielectric layers 411 are formed on the top of theconductive lines 410. Thedielectric layers 411 can be formed by either CVD oxide deposition followed by etching back or by thermal growth, i.e., oxidation. - In
FIG. 4 (e), themask layer 404 is removed by, for example, phosphoric acid, and then a dielectric layer such as anONO layer 412 is formed along the contour of the device. Afterwards, anotherconductive layer 413 is deposited thereon. -
FIG. 4 (f) illustrates the top view of the device shown inFIG. 4 (e). Theconductive layer 413 is etched to form separatedconductive lines 413 serving as word lines, and at the same time theconductive lines 403 are separated into a plurality of conductive blocks. As a result, the stack of theconductive block 403, theONO layer 412 and theconductive line 413 serve as a floating gate structure, i.e., theconductive block 403 is used for storage. Then, CVD oxide is deposited and planarized to form isolatinglines 414 between theconductive blocks 403 and between theconductive lines 413. -
FIG. 4 (g) illustrates the cross-sectional view of line 1-1 inFIG. 4 (f), where thenitride layer 416 is used as a mask on theconductive lines 413 for the planarization to the CVD oxide while the isolatinglines 414 are being formed. - As shown in FIGS. 4(h) and 4(i),
FIG. 4 (i) is the cross-sectional view of line 2-2 inFIG. 4 (h). Alternatively,dielectric spacers 417 can be formed beside theconductive lines 413, and thenconductive lines 418, also serving as word lines, are formed between thedielectric spacers 417 so that, ideally, the density of the word lines can be doubled. -
FIG. 5 illustrates a schematic diagram with reference to the split gate memory structure put forth in the present invention, in which the memory cell architecture is the same as that shown inFIG. 4 (e). Yet some components are renamed by their functionality: a data line (bit line) is denoted by DLx, a select gate is denoted by SGx, and a word line is denoted by WLx. Floating gate cells are denoted by FGx, where the floating gate cells at two sides of a select gate SG2 are denoted by TL and TR, respectively. Examples for the reading, programming, and erasing of memory cells TL and TR are shown in Table 1. For instance, when programming TL, DL2 and DL3 are 5V and 0V respectively, WL2 is 12V, and SG2 is 1V. Accordingly, TL and TR are turned on by the voltage of WL2 coupling to TL and TR, and SG2 is turned on as well. Consequently, 5V bias is generated underneath floating gate FG1. Therefore, electrons will jump into the storage cell of TL for programming. - For reading TL, in addition to that of WL2 and SG2 are 5V and 3V respectively, and the DL3 of 1.5V is intended to deplete the doping region of DL3 so as to ignore the effect of TR, i.e., regardless of whether TR is programmed or not. Accordingly, no current occurs if TL is programmed, and, in contrast, current occurs if TL is not programmed. This read operation uses so-called “reverse read” approach, i.e., to read the right hand side cell programmed or not, bias voltage is put on the left hand side bit line rather than the right hand side.
- For erasing TL, as shown in Erase (I) of Table 1, a highly negative voltage such as −18V is applied to WL2 to expel electrons out of floating gate FG1 and into the semiconductor substrate through the dielectric layer underneath. To avoid a very high negative voltage which causes complex circuit design, a manner by partitioning voltage can be employed as shown in Erase (II). For instance, DL1, DL2, and DL3 are 5V, and WL2 is −10V. Therefore approximately −5V will be coupled to the FG1 in the case of a 50% coupling ratio. Therefore, 10V bias is generated across the FG1. Furthermore, the
dielectric spacer 405 may function also as a tunnel oxide, and theconductive line 410, such as SG2, may function as an erase gate. Such erase conditions are listed in Erase (III). - The programming, reading and erasing of TR is substantially the same as that of TL, so that the detailed description is omitted herein.
TABLE 1 SG1 SG2 SG3 WL1 WL2 WL3 DL1 DL2 DL3 TL Program 0 V 1 V 0 V 0 V 12 V 0 V 0 V 5 V 0 V Read 0 V 3 V 0 V 0 V 5 V 0 V 0 V 0 V 1.5 V Erase (I) 0 V 0 V 0 V 0 V −18 V 0 V 0 V 0 V 0 V Erase (II) 0 V 0 V 0 V 0 V −10 V 0 V 5 V 5 V 5 V Erase (III) 0 V 12 V 0 V 0 V 0 V 0 V 0 V 0 V 0 V TR Program 0 V 1 V 0 V 0 V 12 V 0 V 0 V 0 V 5 V Read 0 V 3 V 0 V 0 V 5 V 0 V 0 V 1.5 V 0 V Erase (I) 0 V 0 V 0 V 0 V −18 V 0 V 0 V 0 V 0 V Erase (II) 0 V 0 V 0 V 0 V −10 V 0 V 5 V 5 V 5 V Erase (III) 0 V 12 V 0 V 0 V 0 V 0 V 0 V 0 V 0 V - Moreover, to avoid the interference of unselected wordlines, e.g., WL1 and WL3, they can be applied by negative voltages, e.g., −2V as shown in Table 2.
- Moreover, to avoid the leakage current from unselected memory cells, e.g., WL1, DL2, SG2, DL3, and WL3, DL2, SG2, DL3 indicated as dashed-circles, to interfere the read status of TR or TL, the unselected word lines can be applied by negative voltages, e.g. −2V as shown in Table 2.
TABLE 2 SG1 SG2 SG3 WL1 WL2 WL3 DL1 DL2 DL3 TL Program 0 V 1 V 0 V 0 V 12 V 0 V 0 V 5 V 0 V Read 0 V 3 V 0 V −2 V 5 V −2 V 0 V 0 V 1.5 V Erase (I) 0 V 0 V 0 V 0 V −18 V 0 V 0 V 0 V 0 V Erase (II) 0 V 0 V 0 V 0 V −10 V 0 V 5 V 5 V 5 V Erase (III) 0 V 12 V 0 V 0 V 0 V 0 V 0 V 0 V 0 V TR Program 0 V 1 V 0 V 0 V 12 V 0 V 0 V 0 V 5 V Read 0 V 3 V 0 V −2 V 5 V −2 V 0 V 1.5 V 0 V Erase (I) 0 V 0 V 0 V 0 V −18 V 0 V 0 V 0 V 0 V Erase (II) 0 V 0 V 0 V 0 V −10 V 0 V 5 V 5 V 5 V Erase (III) 0 V 12 V 0 V 0 V 0 V 0 V 0 V 0 V 0 V -
FIG. 6 is a plan view of the memory layout with reference toFIG. 5 specifying the relationship of the floating gates FG1, FG2, and FG3, select gates SG2 and SG3, data lines DL2 and DL3, and word line WL. The floating gates are totally self-aligned to the select gates and word line so that there is no need for alignment tolerance at all. Consequently, a very competitive small size can be achieved, thereby significantly increasing the cell density of the memory structure. - Besides the manufacturing method regarding the NMOS type transistor mentioned above, the PMOS type transistor can also be implemented by doping boron ions without departing from the spirit of the present invention.
- The above-described embodiments of the present invention are intended to be illustrative only. Numerous alternative embodiments may be devised by those skilled in the art without departing from the scope of the following claims.
Claims (2)
1. An operation method for a non-volatile memory structure formed between two doping regions serving as bit lines in a semiconductor substrate, the non-volatile memory structure comprising a first conductive line serving as a select gate and being formed above the semiconductor substrate, two conductive blocks serving as floating gates and being formed at the two sides of the first conductive line and insulated from the first conductive line with two first dielectric spacers therebetween, a first dielectric layer formed on the two second conductive blocks, a selected second conductive line serving as a word line and being formed on the first dielectric layer and substantially perpendicular to the two doping regions, and a plurality of unselected second conductive lines parallel to the selected second conductive line;
wherein reading the programmed status of one of the conductive blocks comprising the step of putting a bias voltage on the doping region next to the other conductive block so that the depletion region is created across the other conductive block whereby ignoring the effect of the other conductive block if being programmed, and the unselected second conductive lines are applied by negative voltages.
2. The operation method of claim 1 , wherein the conductive block is programmed by generating a bias voltage underneath the conductive block, and the bias voltage is generated by turning on the first conductive line and the two conductive blocks and applying different voltages to the two doping regions.
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US7554840B2 (en) * | 2006-05-22 | 2009-06-30 | Taiwan Semiconductor Manufacturing Co., Ltd. | Semiconductor device and fabrication thereof |
KR20080111963A (en) * | 2007-06-20 | 2008-12-24 | 삼성전자주식회사 | Nonvolatile memory device and method of forming the same |
US8320191B2 (en) | 2007-08-30 | 2012-11-27 | Infineon Technologies Ag | Memory cell arrangement, method for controlling a memory cell, memory array and electronic device |
KR101572482B1 (en) * | 2008-12-30 | 2015-11-27 | 주식회사 동부하이텍 | Method Manufactruing of Flash Memory Device |
US20140181621A1 (en) * | 2012-12-26 | 2014-06-26 | Skymedi Corporation | Method of arranging data in a non-volatile memory and a memory control system thereof |
US10720444B2 (en) | 2018-08-20 | 2020-07-21 | Sandisk Technologies Llc | Three-dimensional flat memory device including a dual dipole blocking dielectric layer and methods of making the same |
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US7541638B2 (en) | 2009-06-02 |
CN100568508C (en) | 2009-12-09 |
US20070004142A1 (en) | 2007-01-04 |
CN1828907A (en) | 2006-09-06 |
US20060192244A1 (en) | 2006-08-31 |
US7745872B2 (en) | 2010-06-29 |
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