MICRO-ELECTRO-MECHANICAL-SYSTEM (MEMS) MIRROR DEVICE AND METHODS FOR FABRICATING THE SAME FIELD OF THE INVENTION
The present invention pertains to the field of micro-electro-mechanical-system (MEMS) devices More particularly, the present invention relates to a MEMS mirror devices and methods for fabncating the same. BACKGROUND OF THE INVENTION
A MEMS device is a micro-sized mechanical structure having electπcal circuitry fabπcated using conventional integrated circuit (IC) fabrication methods. A well-known MEMS device is a microscopic gimbaled mirror mounted on a substrate A gimbaled mirror is a device that may pivot on a hinge about an axis. By pivoting about an axis, a gimbaled mirror can redirect light beams to varying positions. Typically, MEMS gimbaled mirrors are arranged in an array on single silicon wafer substrate.
A pπor process for fabncating MEMS gimbaled minors on a substrate is a surface micro-machining process. A surface micro-machining process utilizes thm layers to mount the MEMS minors off the substrate. A disadvantage with using the micro-machin g process is that the gimbaled minors are mounted by only at a few μm ("micro-meters") off the substrate At such a small height, the gimbaled minor is inhibited from pivoting at large angles with respect to an axis thereby limiting the number of positions for redirecting light.
One kind of micro-machining process to make gimbaled minors is the stress curling method. The stress curling method applies a stress gradient on a thm cantilever layer. The stress gradient causes the end of the cantilever layer to curl that is used to lift a gimbaled minor off the substrate. A disadvantage with using the stress curling method is that it is process dependent and it is difficult to control the stress gradient Another disadvantage with the stress curling method is that cantilever layer requires a large area on the substrate that reduces the number of gimbaled minors that can be ananged on the substrate.
Another kind of micro-machining process to make gimbaled mirrors utilizes hmges and scratch motors. A scratch motor uses electrostatic force to move a mass that raises a gimbaled minor off the substrate by rotating the mass around a hinge. A disadvantage with using scratch motors and hinges is that it requires a large area of space on the substrate to make the scratch motors and hinges thereby limiting the number of gimbaled mirrors to be arranged on the substrate. Furthermore, scratch motors are difficult to make at a microscopic level.
SUMMARY OF THE INVENTION
A micro-electro-mechanical-system (MEMS) minor device is disclosed. The MEMS minor device includes a substrate. Electrodes are formed supported by the substrate. A support structure is formed adjacent to the electrodes. A hinge pattern and a minor pattern having a center mirror component are formed such that support structure supports the hinge pattern and minor pattern. The support structure also supports the hinge pattern and minor pattern such that a bottom surface of the center mirror component in a stationary non-rotating position is capable of exceeding a height of 50μm above the electrodes.
A MEMS minor device fabrication method is disclosed. A substrate is exposed selectively to form exposed regions and unexposed regions in the substrate. Electrodes are formed supported by the substrate. A minor pattern having a center mirror component and a hinge pattern are formed supported by the substrate. Portions of the substrate are removed in the exposed regions to form a support structure from the unexposed regions such that the support structure supports the minor pattern and hinge pattern.
Another method for fabricating a MEMS minor device is disclosed. A release layer is formed on a first substrate. A minor pattern having a center minor component and a hinge pattern are formed supported by the release layer. Electrodes are formed supported by a second substrate. A support structure is formed. The first substrate is attached with the second substrate using the support structure. The first substrate and the release layer are removed such that the support structure supports the minor pattern and hinge pattern.
Another method for fabricating a MEMS minor device is disclosed. A release layer is formed on a first substrate. A minor pattern having a center minor component and a hinge pattern are formed supported by the release layer. Electrodes are formed supported by a second substrate. A support structure is formed using a third substrate. The first substrate is attached with the second substrate using the support structure. The first substrate and release layer are removed.
Another method for fabricating a MEM gimbaled minor device is disclosed. Electrodes are formed supported by a first substrate. Portions of a second substrate on a bottom side are removed selectively. Portions of the second substrate on a topside are removed selectively to form a mirror, frame pattern, and hinge pattern. The first substrate is attached with the second substrate.
Other features and advantages of the present invention will be apparent from the accompanying drawings, and from the detailed description, which follows below.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention is illustrated by way of example and not limited in the figures of the accompanying drawings in which like references indicate similar elements and in which:
Figure 1 is a top view of a MEMS mirror device according to one embodiment without electrodes and a wiring pattern;
Figure 2 is a top view of a MEMS mirror device according to one embodiment illustrating electrodes and a wiring pattern;
Figure 3 is a cross-sectional side view of one embodiment along the line A-A' such as that shown in Figure 2;
Figures 4a through 4f are cross-sectional side views illustrating process steps of a method for fabricating the MEMS minor device according to a first embodiment;
Figures 5a through 5f are cross-sectional side views illustrating process steps of a method for fabricating the MEMS minor device according to a second embodiment;
Figures 6a through 6f are cross-sectional side views illustrating process steps of a method for fabricating the MEMS minor device according to a third embodiment;
Figure 7a is a top view of a MEMS minor device according to another embodiment without electrodes and a wiring pattern;
Figure 7b is an illustration showing the cross-sectional side views along the lines B-B', C-C, D-D', and E-E' such as that shown in Figure 7a to show the thickness and width for the hinge pattern, frame pattern, mirror, and support structure; and
Figures 8a-8f are cross-sectional side views illustrating process steps of a method for fabricating the MEMS minor device according to a fourth embodiment.
DETAILED DESCRIPTION
A micro-electro-mechanical-system (MEMS) minor device is described that includes a substrate. Electrodes are formed supported by the substrate. A support structure is formed adjacent to the electrodes. A hinge pattern is formed on the support structure. A hinge pattern and a minor pattern having a center minor component are formed such that support structure supports the hinge pattern and minor pattern. The support structure also supports the hinge pattern and minor pattern such that a bottom surface of the center minor component in a stationary non-rotating position is capable of exceeding a height of 50μm above the electrodes. For example, the support structure may support the hinge pattern and minor pattern such that the bottom surface of the center mirror component in a stationary non-rotating position has a height of about lOOμm above the electrodes.
By having a center minor component capable of exceeding a height of 50μm above the electrodes, the center minor component may have a larger angular range of motion that can pivot about an axis. For example, the center minor component is capable of having an angular range of motion exceeding 20 degrees with respect to an axis Because the center minor component may have such a large range of angular motion, the center minor component may redirect light beams at a larger number of positions. Thus, such a MEMS minor device having a large angular motion can provide increased flexibility for optical switching systems, scanning systems, pnnting systems, and display systems that require redirecting beams of light.
The methods for fabncating a MEMS minor device as descnbed herein allow for a large number of minor devices to be ananged on a single substrate. The methods for fabncating a MEMS minor device also allow the center minor component to be at a desired height above the electrodes or substrate dictated simply by a thickness of a substrate or a thickness of a formed support structure.
For a first embodiment, a MEMS mirror device fabncation method exposes selectively a substrate to form exposed regions and unexposed regions. Electrodes are formed supported by the substrate. A minor pattern having a center minor component and a hinge pattern are formed supported by the substrate. Portions of the substrate are removed in the exposed regions to form a support structure from the unexposed regions such that the support structure supports the minor pattern and hmge pattern.
For the first embodiment, a single substrate is used to fabncate a MEMS minor device. The single substrate is used to form the electrodes, minor pattern, hinge pattern, and support structure. The height at which a center mirror component is above the electrodes is dictated by the thickness of the substrate.
For a second embodiment, a MEMS minor device fabncation method forms a release layer on a first substrate. A minor pattern having a center minor component and a hmge pattern are formed supported by the release layer. Electrodes are formed supported by a second substrate. A support structure is formed. The first substrate and the second substrate are attached using the support structure. The first substrate and the release layer are removed such that the support structure supports the minor pattern and hmge pattern
For the second embodiment, two substrates are used to fabncate a MEMS minor device. The height at which the center minor component is above the electrodes is dictated by a thickness of the formed support structure. Thus, to increase the height of the of the center minor component above the electrodes, a thicker support structure is formed. As such, the thickness of the support structure formed dictates the height at which a center component is above the electrodes.
For a third embodiment, a MEMS mirror device fabrication method forms a release layer on a first substrate. A minor pattern having a center minor component and a hinge pattern are formed supported by the release layer. Electrodes are formed supported by a second substrate. A support structure is formed using a third substrate. The first substrate is attached with the second substrate using the support structure. The first substrate and release layer are removed.
For the third embodiment, three substrates are used to fabricate a MEMS minor device. A first substrate is used to form the hinge pattern and minor pattern. A second substrate is used to form the electrodes. A third substrate is used to form the support structure. The thickness of the third substrate used dictates the thickness of the support structure. Thus, the height at which the center mirror component is above the electrodes is simply dictated by the thickness of the third substrate. Thus, to increase the height of the of the center minor component above the electrodes, a thicker third substrate is simply used.
For a fourth embodiment, a MEMS minor device fabrication method forms electrodes supported by a first substrate. Portions of a second substrate are removed selectively on a bottom side. Portions of the second substrate are removed selectively on a topside to form a mirror pattern, frame pattern, hinge pattern, and support structure. The first substrate is attached with the second substrate.
For the fourth embodiment, two substrates are used to fabricate a MEMS minor device. The height at which the center mirror component is above the electrodes is dictated by the thickness of the second substrate used. Furthermore, the minor pattern, frame pattern, hinge pattern, and support structure can be formed from a single substrate.
For all the embodiments, a layer can be selectively patterned on a substrate using any combination of a photolithography and dry or wet etching process or a liftoff process. A liftoff process involves depositing a photosensitive film over a substrate that is then exposed and developed to pattern the photosensitive film. Material is then deposited over the entire surface the substrate and on the patterned photosensitive film. After the material is deposited over the substrate and on the patterned photosensitive film, the patterned photosensitive film is dissolved and any material formed thereon is removed. As a result of this process, the material deposited is selectively patterned. Furthermore, a layer may also be removed or released by using oxygen plasma that reacts with the layer to release or remove the layer from an attached material.
Figure 1 is top view of one embodiment of a MEMS minor device without electrodes and a wiring pattern illustrating a first minor device 9A and a second minor device 9B having a support structure 5, hinge pattern 6, and mirror pattern 7. Mirror
pattern 7 may include a center minor component 7a, frame pattern 7b, and minor component 7c. Center minor component 7a is capable of having an angular range of motion with respect to an axis Frame pattern 7b provides support for center minor component 7a. Mirror component 7c may be used for alignment or bonding purposes Alternatively, mirror component 7c may be omitted from minor pattern 7
Figure 2 is a complete top view of one embodiment of a MEMS minor device such as that shown in Figure 1 further illustrating electrodes 4 and wmng pattern 2 for the first minor device 9A and second minor device 9B.
Figure 3 is a cross sectional side view showing the structure of one embodiment of a MEMS mirror device taken along the line A-A' such as that shown in Figure 2. As shown in Figure 3, a MEMS minor device includes a substrate 1 having wmng pattern 2 formed thereon. Electrodes 4 are formed such that electrodes are coupled with wmng pattern 2. An insulation layer 3 is formed to provide insulation for winng pattern 2 and electrodes 4.
Support structure 5 is formed on insulation layer 3 adjacent from electrodes 4 Support structure 5 may include a post structure to provide support for layers formed thereon or attached therewith. Support structure 5 may define a honeycombed shape Support structure 5 may also define holes such that the holes are centered approximately below the center minor component Support structure 5 provides support for hmge pattern 6 and mirror pattern 7.
Minor pattern 7 includes a center minor component 7a, frame pattern 7b, and mirror component 7c. Alternatively, minor pattern may include center minor component 7a and frame pattern 7b. H ge pattern 6 is attached with minor pattern 7 and support structure 5. Hinge pattern 6 may be a thin and flexible matenal. Hmge pattern 6 provides support for minor pattern 7. Frame pattern 7b provides support for center minor component 7a. Minor component 7c is supported by hinge pattern 6 and may be used for alignment or bonding purposes. Alternatively, minor component 7c may be omitted from mirror pattern 7.
The center minor component 7a is formed such that it is disposed above electrodes 4. Center minor component 7a includes a reflective surface to reflect beams of light Electrodes 4 are located below at opposing edges of center minor component 7a. Center mirror component 7a may also be connected with a ground line (not shown) in substrate 1 for electncal shielding purposes. Electrodes 4 are coupled with a respective wmng pattern 2 located on substrate 1. Alternatively, a ground line may be disposed between electrodes 4 and wmng pattern 2 for purposes of electncal shielding.
Center minor component 7a may move about an axis to have an angular range of motion caused by electrostatic actuation from electrodes 4. Electrostatic actuation is caused by a voltage being applied to electrodes 4 through wiring pattern 2. A voltage applied to electrodes 4 creates an electric field between, for example, electrodes 4 and center minor component 7a. Typically, the electric field is created near the edges of center minor component 7a. The electric field causes center minor component 7a to have an angular range of motion with respect to an axis such as, for example, an axis parallel to hinge pattern 7. The edges of center minor component 7a towards electrodes 4 at which the voltage is applied moves towards such electrodes 4.
By increasing the angular range of motion for center minor component 7a, center minor component 7a can redirect beams of light to a larger number of positions thereby increasing flexibility for optical switching. Increasing the thickness for support structure 5 can increases the angular range of motion for center minor component 7a. Support structure 5 having an increased thickness provides a larger height for center minor component 7a to be off of substrate 1. Because center mirror component 7a may have a large height off substrate 1, center minor component 7a is provided with a larger angular range of motion.
For the following embodiments, the support structure can be fabricated to support the hinge pattern and minor pattern such that a bottom surface of the center minor component in a stationary non-rotating position is capable of exceeding a height of 50μm above the electrodes. Also, in the following embodiments, the support structure may support the hinge pattern and minor pattern such that the bottom surface of the center minor component in a stationary non-rotating position is capable of having a height about lOOμm above the electrodes. At such heights, the following embodiments provide a center minor component that is capable of having an angular range of motion exceeding 20 degrees with respect to an axis.
Figures 4a through 4f are cross-sectional side views illustrating process steps of a method for fabricating the MEMS minor device according to a first embodiment.
Referring to Figure 4a, substrate 10 is exposed selectively on a first side to form exposed regions 11a and unexposed regions 1 lb in substrate 10. A honeycombed mask may be used to expose selectively substrate 10. Alternatively, other masks may be used to form exposed regions on a substrate such that mirror components are centered approximately over the exposed regions. For purposes of illustration, the first side is a topside of substrate 10.
Substrate 10 is a substrate that can be etched more rapidly in the exposed regions than in the unexposed regions. For example, substrate 10 may be a photosensitive glass substrate that can be exposed selectively and etched more rapidly in the exposed regions than in the unexposed regions. After being exposed selectively, substrate 10 may be polished to retain planarity and remove any materials that may have formed on substrate 10 during this process.
Referring to Figure 4b, a first metal layer is formed on a second side of substrate 10 and is selectively patterned and etched to form electrodes 14. For purposes of explanation, the second side is a bottom side of substrate 10. The first metal layer may be a metallic layer such as, for example, an aluminum Al layer. After forming electrodes 14, an oxide layer is then formed over electrodes 14 and substrate 10 on the bottom side and selectively patterned to form insulation layer 13, such that insulation layer 13 exposes portions of electrodes 14. Alternatively, other dielectric layers may be used such as, for example, silicon dioxide SiO2 layer, silicon nitride SixNy layer, or silicon oxynitride SixOyNz layer, that can be selectively patterned and etched to form insulation layer 13.
After forming insulation layer 13, a second metal layer is formed on insulation layer 13 and on exposed portions of electrodes 14 and is selectively patterned and etched to form wiring pattern 12. The second metal layer may also be a metallic layer such as, for example, an Al layer. Wiring pattern 12 is formed such that it is coupled with electrodes 14. Insulation layer 13 provides insulation for wiring pattern 12 and electrodes 14.
Referring to Figure 4c, a polysilicon layer is formed on the topside of substrate 10. The polysilicon layer is selectively patterned and etched to form hinge pattern 16. Alternatively, a polymer layer, oxide layer, nitride layer, silicon nitride SixNy layer, silicon dioxide SiO2 layer, or silicon oxynitride SixOyNz layer may be used that is selectively patterned and etched to form hinge pattern 16. Hinge pattern 16 is formed to be thin and flexible. Hinge pattern 16 is also formed such that portions of substrate 11 are exposed above an area near electrodes 14.
Referring to Figure 4d, at least one layer having light reflective properties is formed on hinge pattern 16 and on the exposed portions of the topside of substrate 11. For example, a metal layer having light reflective properties may be formed on hinge pattern 16 and portions of the exposed substrate 11 and selectively pattern and etched to form minor pattern 17. The metal layer may be a gold Au metal layer, aluminum Al metal layer, or a copper Cu metal layer. Minor pattern 17 includes a center minor component 17a, frame pattern 17b, and mirror component 17c. Frame pattern 17b is supported by hinge pattern 16. Frame pattern 17b provides support for center minor component 17a.
Minor component 17c is supported by hinge pattern 16. Alternatively, mirror component 17c may be omitted from mirror pattem 17.
Multiple layers may also be used to form minor pattern 17. For example, a first metal layer is formed on hinge pattern 17 and on portions of the exposed substrate 11. A support layer is formed on the first metal layer. A second metal layer is formed on the support layer. The three layers are selectively patterned and etched to form minor pattern 17.
The first and second metal layers are layers having light reflective properties. For example, a gold Au metal layer, an aluminum Al metal layer, or a copper Cu metal layer may be used for the first and second metal layers. The support layer is a layer that provides a flat surface and structural support. For example, a silicon dioxide SiO2 layer, silicon nitride SixNy layer, polysilicon layer, silicon oxynitride SixOyNz layer, or a polymer layer may be used for the support layer. Alternatively, the support layer may include the same material as the first and second metal layers.
Referring to Figure 4e, a polymer layer is formed over mirror pattern 17 and hinge pattern 16 and is patterned selectively and etched to form protection layer 18. Alternatively, a polysilicon layer, oxide layer, or nitride layer may be used to form protection layer 18. Protection layer 18 is patterned to protect minor pattern 17 and hinge pattern 16. Protection layer 18 is also patterned such that an etching solution can reach substrate 11. For example, a hydro-fluoric (HF) acid etching solution is used to etch substrate 11. Alternatively, forming protection layer 18 may be optional if minor pattern 17 and hinge pattern 16 are resistant to the etching solution. If, for example, HF acid is used and hinge pattern 16 is made from an oxide material, which etches easily in HF acid, protection layer 18 (not made of an oxide) is then required.
Referring to Figure 4f, the etching solution is deposited over substrate 11 to etch substrate 11. For example, HF acid is used that etches away the exposed regions 11a more rapidly than the unexposed regions 1 lb such that remaining portions of the unexposed regions 1 lb of substrate 11 form support structure 15. If a protection layer is used, then the protection layer is removed using an oxygen plasma, wet, or dry etch process.
The thusly-fabricated MEMS minor device serves to provide a support structure using a single substrate. The single substrate is a photosensitive substrate. For example, the photosensitive substrate is a photosensitive glass substrate that is exposed selectively. Because the photosensitive substrate is exposed selectively, the photosensitive substrate can be etched to form the support structure after forming the hinge pattern and minor pattern. Thus, mounting a minor pattern and a hinge pattern on a support structure is
avoided. Furthermore, the thickness of the photosensitive substrate dictates the height at which a center minor component is above the electrodes.
Figures 5a through 5f are cross-sectional side views illustrating process steps of a method for fabricating the MEMS minor device according to a second embodiment.
Referring to Figure 5a. a polymer layer is formed on a first substrate 20 to form a release layer 21. Release layer 21 may also be a layer that can be etched easily away or is removed easily from first substrate 20. For example, release layer 21 may be a polysilicon layer, oxide layer, or a nitride layer. First substrate 20 may be a silicon substrate, glass substrate, or a borosilicate glass substrate.
Referring to Figure 5b. at least one layer having light reflective properties is formed on release layer 21. For example, a metal layer having light reflective properties may be formed on release layer and selectively pattern and etched to form minor pattern 27. The metal layer may be a gold Au metal layer, aluminum Al metal layer, or a copper Cu metal layer. Minor pattem 27 includes a center minor component 27a, frame pattern 27b, and minor component 27c formed on release layer 21. Alternatively, minor component 27c may be omitted from mirror pattern 27.
Multiple layers may also be used to form mirror pattern 27. For example, a first metal layer is formed on release layer 21. A support layer is formed on the first metal layer. A second metal layer is formed on the support layer. The three layers are selectively patterned and etched to form minor pattern 27.
The first and second metal layers are layers having light reflective properties. For example, a gold Au metal layer, an aluminum Al metal layer, or a copper Cu metal layer may be used for the first and second metal layers. The support layer is a layer that provides a flat surface and structural support. For example, a silicon dioxide SiO2 layer, silicon nitride SixNy layer, polysilicon layer, silicon oxynitride SixOyN2 layer, or a polymer layer may be used for the support layer. Alternatively, the support layer may include the same material as the first and second metal layers.
After minor pattern 27 is formed on release layer 21, a polysilicon layer is formed over mirror pattern 27 and is selectively patterned and etched to form hinge pattern 26. Alternatively, a polymer layer, oxide layer, nitride layer, silicon nitride SixNy layer, silicon dioxide SiO2 layer, or silicon oxynitride SixOyNz layer may be used that is selectively patterned and etched to form hinge pattern 26. Hinge pattern 26 is formed on portions of minor pattern 27. Hinge pattern 26, however, is not formed on center minor component 27a. Hinge pattern 26 is formed to be thin and flexible.
Referring to Figure 5c, a first metal layer is formed on a second substrate 30 and is selectively patterned and etched to form wiring pattern 32. Second substrate 30 may be
may be a silicon substrate, glass substrate, or borosilicate glass substrate. The first metal layer may be a metallic layer such as, for example, an aluminum Al layer. After forming wmng pattern 32, an oxide layer is then formed over wmng pattern 32 and second substrate 30 and is selectively patterned and etched to form insulation layer 33 Insulation 33 is formed such that portions of wmng pattern 32 are exposed. Alternatively, other dielectnc layers may be used such as, for example, silicon dioxide SιO2 layer, silicon nitnde SιxNy layer, or silicon oxynitnde SιxOyNz layer, that can be selectively patterned and etched to form insulation layer 33.
After forming insulation layer 33, a second metal layer is formed over insulation layer 33 and wmng pattern 32 and is selectively patterned and etched to form electrodes
34. The second metal layer may also be a metallic layer such as, for example, an Al layer Electrodes 34 are formed such that they are coupled with wmng pattern 32 Insulation 33 provides insulation for wmng pattern 32 and electrodes 34
Refernng to Figure 5d, a thick patterned film is used to form support structure
35. A metal plating process is used with the thick patterned film to form support structure 35. For example, an electroless metal deposition process may be used to form support structure 25.
Initially, for the electroless metal deposition process, a thick photo resist film is formed on insulation layer 33 and selectively patterned to allow support structure 35 to be formed therein on insulation layer 33. Alternatively, a thick photo resist film may be formed on hinge pattern 26 and selectively patterned to allow support structure 35 to be formed on hmge pattern 26.
Subsequently, an aqueous solution having nickel Ni is deposited over the patterned photo resist film such that nickel Ni is formed in the patterned thick photo resist film After Ni is formed, the remaining photo resist film is removed to form support structure 35 made of Ni. Alternatively, an aqueous solution having copper Cu or gold Au may be used to form support structure 35 using the electroless metal deposition process The remaining photo resist film is then removed.
Alternatively, an electro-platmg process or a metal sputtenng process may be used For the electro-platmg process, a thick photo resist film is formed on insulation layer 33 and selectively patterned to allow support structure 35 to be formed therein on insulation layer 33. Alternatively, a thick photo resist film is formed on hinge pattern 26 and selectively patterned to allow support structure 35 to be formed therein on hmge pattern 26.
Subsequently, an electro-plat g solution having nickel Ni is deposited over the patterned photo resist film and an electnc cunent is passed through the solution such that
Ni is formed in the patterned thick photo resist film. After Ni is formed, the remaining photo resist film is removed to form support structure 35 made of Ni. Alternatively, an electro-plating solution having copper Cu or gold Au may be used to form support structure 35 using the electro-plating process. Depending on where the patterned photo resist film is formed, a thin conductive layer (not shown) may be formed selectively on insulation layer 33 or hinge pattern 26 to assist in the electro-plating process. The photo resist film is then removed.
For the sputtering process, a thick photo resist film is formed on insulation layer 33 and selectively patterned to allow support structure 35 to be formed therein on insulation layer 33. Alternatively, a thick photo resist film is formed on hinge pattern 26 and selectively patterned to allow support structure 35 to be formed therein on hinge pattern 26.
Subsequently, metal is sputtered on the patterned thick photo resist film such that the metal is formed therein. For example, nickel Ni, copper Cu, or gold Au may be sputtered on the patterned thick photo resist film such that metal is formed therein. Subsequently, the remaining patterned thick photo resist film and metal formed thereon are removed to form support structure 35. The thick photo resist film is then removed.
Referring to Figure 5e, first substrate 20 is attached with second substrate 30. If support structure 35 is formed on insulation layer 33, first substrate 20 may be attached with second substrate 30 by flipping first substrate 20 and bonding hinge pattern 26 with a top side of support structure 35. Alternatively, if support structure 35 is formed on hinge pattem 26, first substrate 20 may be attached with second substrate 30 by flipping first substrate 20 and bonding support structure 35 with insulation layer 33.
Support structure 35 can be bonded to insulation layer 33 or hinge pattern 26 using a soldering bond technique that forms a bonding layer. For example, if support structure 35 is formed on insulation layer 33, a bonding layer 38 may be formed to bond support structure 35 with hinge pattern 26. Alternatively, if support structure 35 is formed on hinge pattern 26, a bonding layer may be formed near insulation layer 33 to bond support structure 35 with hinge pattern 26. The bonding layer may include a lead-tin PbSn mixture. Alternatively, a thin metal layer may be formed on hinge pattern 26 or insulation layer 33 to assist in the bonding process.
Referring to Figure 5f, after first substrate 20 is attached with second substrate 30, first substrate 20 and release layer 21 are removed such that support structure 35 supports hinge pattem 26. Hinge pattern 26 supports minor pattern 27. First substrate 20 may be removed using an etching or polishing process. For example, first substrate 20 may be etched away using hydro-fluoric (HF) acid or first substrate 20 may be polished
away. Release layer 21 may be removed using oxygen plasma, wet etch, or a dry etch process.
The thusly fabricated MEMS minor device serves to provide a support structure using a thick film process. In the above process, the thickness of the thick photo resist film used dictates the thickness of support structure 35. Furthermore, the thickness of support structure 35 dictates the height in which a center minor component is above the electrodes that determines angular range of motion for the center minor component.
Figures 6a through 6e are cross-sectional side views illustrating process steps of a method for fabricating the MEMS mirror device according to a third embodiment. Initially, the fabrication steps illustrated by Figure 6a to form release layer 41, minor pattern 47, and hinge pattern 46 are identical to the fabrication steps illustrated by Figures 5a and 5b for a first substrate 40 and accordingly descriptions to Figure 6a will be omitted. Also, the fabrication steps illustrated by Figure 6b to form wiring pattern 52, electrodes 54, and insulation layer 53 using a second substrate 50 are identical to the fabrication steps illustrated by Figure 5c and accordingly descriptions to Figure 6b will be omitted.
Referring to Figures 6c and 6d, a third substrate 60 is used to form support structure 65. Third substrate 60 may be etched selectively to form support structure 65. Third substrate may be a silicon substrate, glass substrate, or a borosilicate glass substrate. Third substrate 60 may be etched selectively in areas 61a of third substrate 60 using a reactive ion etching (RE) process. The RIE etching process forms deep holes in third substrate 60 such that areas 61b of third substrate 60 remain to form support structure 65. Alternatively, deep holes may be formed in third substrate 60 using a wet etch or a laser ablation process such that areas 61a are removed from third substrate 60.
Third substrate 60 may also be a photosensitive substrate that is exposed selectively to form exposed regions 61a and unexposed regions 61b in third substrate 60. Third substrate 60 is a substrate that can be etched more rapidly in the exposed regions than in the unexposed regions. After being exposed selectively, third substrate 60 may be polished to retain planarity and remove any materials that may have formed on third substrate 60 during this process.
Subsequently, an etching solution is used to etch third substrate 60. For example, HF acid etching solution is deposited selectively over third substrate 60 to etch third substrate 60. The HF acid etches away the exposed regions 61a more rapidly than the unexposed regions 61b such that the remaining portions of the unexposed regions 61b of third substrate 60 form support structure 65. Support structure 65 may define a
honeycombed shape or define holes approximately centered with respect to center minor components
Referring to Figure 6e, first substrate 40 is attached with second substrate 50 using support structure 65 For example, support structure 65 is bonded with insulation layer 53 using a solder bond process thus forming a bonding layer 69. Subsequently, hinge pattern 46 is bonded with support structure 65 using a solder bond process thus forming a bonding layer 68. Alternatively, support structure 65 is bonded with hmge pattern 46 using a solder bond process thus forming a bonding layer 68 Subsequently, insulation layer is bonded with support structure 65 thus forming bonding layer 69. Bonding layers 68 and 69 may include a lead-tin PbSn mixture. A thin metal layer may also be formed on insulation layer 53 and hmge pattern 46 to assist in the bonding process
Referring to Figure 6f, after first substrate 40 is attached with second substrate 50 using support structure 65. First substrate 40 and release layer 41 are removed such that support structure 65 supports hmge pattern 46. Hinge pattern 46 supports minor pattern 47. First substrate 40 may be removed using an etching or polishing process. For example, first substrate 40 may be etched away using HF acid or first substrate 40 may be polished away. Release layer may be removed using an oxygen plasma, wet etch, or a dry etch process.
The thusly fabncated MEMS minor device uses three substrates One substrate is used to form minor pattern 47 and hinge pattern 46. A second substrate is used to form electrodes 54, and a third substrate 50 is used to form a support structure 65. The height at which the center minor component is above the electrodes is simply dictated by the thickness of the third substrate used. Thus, to increase the height of the center minor component above the electrodes, a thicker substrate may be used.
Figure 7a is a top view of a MEMS minor device according to another embodiment without electrodes and a wmng pattern. Figure 7a shows a first mirror device 101a and a second minor device 101b having a support structure 95, hmge pattern 96, frame pattem 97, and mirror 97a
Support structure 95, hinge pattern 96, frame pattern 97, and mirror 97a are all formed from a single substrate. Hinge pattern 96 provides support for frame 97b and minor 97a. Frame 97b provides support for minor 97a. Support structure 95 provides support for hinge pattern 96, frame pattern 97b, and minor 97a. Mirror 97a is capable of having an angular range of motion with respect to an axis.
Figure 7b is an illustration showing the cross-sectional side views along the lines B-B', C-C, D-D', and E-E' such as that shown in Figure 7a to show the different thickness and width for the hinge pattern 96, frame pattern 97b, minor 97a, and support
structure 95, respectively, for first minor 101a and second mirror 101b. Refernng to Figure 7b, along the lines B-B', C-C, and D-D', hinge pattern 96 is formed to have a smaller thickness than frame pattem 97b and minor 97a. Alternatively, hinge pattern 96 may be formed to have the same thickness as frame pattern 97b and minor 97a. Frame pattern 97b and mirror 97a are formed to have the same thickness.
Figures 8a-8f are cross-sectional side views illustrating process steps of a method for fabncating the MEMS minor device according to the fourth embodiment Figure 8a illustrates the processing steps to form a winng pattern, electrodes, insulation layer using a first substrate. Refernng to Figure 8a, the fabncation steps illustrated by Figure 8a to form winng pattern 82, electrodes 84, insulation layer 83 using a first substrate 80 are identical to the fabncation steps illustrated by Figures 5c and 6b and accordingly descnptions to Figure 8a will be omitted.
Figures 8b, 8c, and 8d illustrate the processing steps to form the hmge pattern, frame pattern, minor, and support structure individually from a single substrate such as that shown in Figure 7b. The processing steps are illustrated along the lines B-B', C- C, D-D', E-E' such as that shown Figure 7a for minor device 101a and mirror device 101b.
Referring to Figure 8b, a second substrate 90 is etched selectively on a first side to remove large portions of second substrate 90 to define open areas ("windows") 100 such that the open areas 100 are located below where hinge pattern 96, mirror 97a, and frame pattern 97b will be formed. For purposes of illustration, the first side of second substrate 90 refers to a bottom side of second substrate 90. To form open areas 100, a silicon etching process is used to etch selectively the bottom side of second substrate 90. For example, a reactive ion etching (RIE) process may be used to etch selectively a bottom side of second substrate 90 to form open areas 100. Alternatively, a wet etch or a laser ablation process may be used to etch the bottom side of second substrate 90 to form open areas 100.
An oxide layer is deposited on a second side of second substrate 90 to form a mask layer 91. Alternatively, a polymer layer, silicon nitnde SιxNy layer, silicon oxynitnde SixOyNz layer, or a metal layer may be used to form mask layer 91. Mask layer 91 may also be formed pnor to forming open areas 100. For purposes of illustration, the second side refers to the topside of second substrate 90. Mask layer 91 is patterned to define hmge pattern 96, frame pattern 97b, mirror 97a, and support structure 95 from second substrate 90.
Figures 8c and 8d illustrate the processing steps for forming h ge pattern 96, frame pattern 97b, mirror 97a, and support structure 95. The following process steps
descnbe forming hinge pattern 96 such that it has a smaller thickness than frame pattern 97b and mirror 97a. Alternatively, the following processing steps may be modified to form hinge pattern 96 having the same thickness as frame pattern 97b and minor 97a
Refernng to Figure 8c, mask layer 91 is patterned selectively on second substrate 90 to expose portions of second substrate 90. The patterned mask layer 91 defines hinge pattern 96, frame pattern 97b, mirror 97a, and support structure 95. The exposed portions of second substrate 90 are etched using a silicon etching process. For example, a RIE etching process may be used to etch exposed portions of second substrate 90 to a first depth such that a thin portion ("floor") of second substrate 90 remains above open areas 100. Alternatively, a wet etch or a laser ablation process may be used to etch the exposed portions of second substrate 90 to the first depth.
At this depth, an oxide layer is deposited over second substrate 90 and etched selectively to form sidewalls 94. Alternatively, a polymer layer, silicon nitnde SιxNy layer, silicon oxynitnde SιxOyNz layer, or a metal layer may be used to form sidewalls 94. Sidewalls 94 provide protection to selective portions of the topside of second substrate 90 that define hmge pattern 96, frame pattern 97b, mirror 97a, and support structure 95. Layers that have formed on the floor in making sidewalls 94 are the etched to expose the floor.
Subsequently, exposed portions of the floor of second substrate 90 are etched using a silicon etching processes. For example, a RIE etching process may be used to etch exposed portions of the floor such that the floor falls below the sidewalls. Alternatively, a wet etch process or a laser ablation process may be used to etch the exposed portions of the floor to fall below the sidewalls.
Next, a release process is performed to form hmge pattern 96, frame pattern 97b, and minor 97a. The release process is an etching process that undercuts selectively the exposed portions of topside of second substrate 90 that defines hmge pattern 96, frame pattern 97b, and mirror 97a underneath sidewalls 94 such that the floor is separated. If hinge pattern 96 is to have the same thickness as frame pattern 97b and mirror 97a, hmge pattern 96, frame 97b, and minor 97a are released at the same time. Alternatively, if hinge pattern 96 is to have a smaller thickness than frame pattern 97b and minor 97a, frame pattern 97b and mirror 97a are released after hinge pattern 96 at a lower depth.
The following step descnbes the release process. To release frame pattern 97b and mirror 97a at a larger depth than hinge pattern 96, the above steps are repeated such that exposed portions of the topside of second substrate 90 that define frame pattern 97b and mirror 97a underneath sidewalls 94 fall below hinge pattern 96.
A RIE etching process may be used to release the exposed portions of the topside of second substrate that defines hinge pattern 96, frame pattern 97b, and minor 97a underneath sidewalls 94 to form hinge pattern 96, frame pattern 97b, and minor 97a from second substrate 90. Alternatively, a time controlled profile etching process may be used to release hinge pattern 96, frame pattern 97b, and minor 97a from second substrate 96. The release process may undercut frame pattern 97b and mirror 97a underneath sidewalls 94 such that non-straight edge surfaces are formed. Alternatively, the release process may undercut hinge pattern 96 such that non-straight edge surfaces are also formed. Hinge pattern 96, frame pattern 97b, and mirror 97a are thus formed after it has been released from second substrate 90, and the remaining mask layer 91 and sidewalls 94 are removed. Alternatively, mask layer 91 and sidewalls 94 may remain in forming the MEMS minor device.
Referring to Figure 8d, the next step in the process is to remove the floor ("clear the floor"). The floor is etched away to clear the floor such that hinge pattern 96. frame pattern 97b, and minor 97a are suspended about support structure 95 and second substrate 90. For example, the floor of second substrate 90 may be etched away using an RIE etching process. Alternatively, a wet etch or a laser ablation process may be used to etch the exposed portions of the floor to clear the floor. Second substrate 90 may also be flipped and the floor may be cleared from the back side using the same etching processes. After the floor has been cleared, support structure 95 is thusly formed. For purposes of illustration, support structure 95, hinge pattern 96, frame pattem 97b, and minor 97a are illustrated with straight surfaces, but may have non-straight edge surfaces.
Figure 8e is a cross-sectional side of the thusly formed hinge pattern 96, frame pattern 97b, minor 97a, and support structure 95 taken along the line A- A' such as that shown in Figure 7a with showing electrodes. Referring to Figure 8e, support structure 95 provides support for hinge pattern 96, frame pattern 97b, and minor 97a. Hinge pattern 96b provides support for frame pattern 97b. Frame pattern 97b provides support for minor 97a.
A reflective material 97a' may then be formed on a top surface of minor 97a. Reflective material 97a' provides a reflective surface for mirror 97a, which is used to redirect beams of light. Alternatively, reflective material 97a' may be formed on frame pattern 97b and hinge pattern 96. Reflective material 97a' includes at least one layer. For example, reflective material 97a' may include a metal layer such as, for example, a gold Au metal layer, an aluminum metal layer, or a copper Cu metal layer. Alternatively, reflective material 97a' may be formed after the processing steps as illustrated in Figure 8e or after first substrate 80 is attached with second substrate 90.
Figure 8f illustrate attaching first substrate 80 with second substrate 90 to form the MEMS minor device according to the fourth embodiment. Refernng to Figure 8f, first substrate 80 is attached with second substrate 90 using support structure 95 For example, support structure 95 is bonded with insulation layer 83 using a solder bond process thus forming a bonding layer 98. Bonding layer 98 may include a lead-tin PbSn mixture. A thm metal layer may also be formed on insulation layer 83 and a bottom side of support structure 95 to assist in the bonding process.
Refernng to Figure 8f, the MEMS mirror device according to the fourth embodiment includes first substrate 80, wmng pattern 82, insulation layer 83, and electrodes 84 First substrate 80, winng pattern 82, insulation layer 83, and electrodes 84 are constructed and operate in a similar manner as substrate 1, wmng pattern 2, insulation layer 3, and electrodes 4, respectively, of Figure 3.
The MEMS minor device according to the fourth embodiment also includes a support structure 95, hmge pattern 96, frame pattern 97b, and minor 97a Support structure 95, hinge pattern 96, frame pattern 97b, and minor 97a are made from a second substrate, which is separate from first substrate 80. The substrate to form support structure 95, h ge pattern 96, frame pattern 97b, and minor 97a may be a single crystal silicon (SCS) substrate or a substrate in which deep holes may be formed Support stmcture 95, hmge pattern 96, frame pattern 97b, and mirror 97a are formed as a single unit. Support stmcture 95, mirror 97a, frame pattern 97b, and hmge pattern 96 operate in a similar manner as support stmcture 5, center minor component 7a, frame pattern 7b, and hinge pattern 6, respectively, of Figure 3.
The thusly fabncated MEMS minor device uses two substrates. One substrate is used to form electrodes 84, winng pattern 82, and insulation layer 83. A second substrate is used to form support stmcture 95, minor 97a, hmge pattern 96, and frame pattern 97b The height at which the minor is above the electrodes is simply dictated by the thickness of the second substrate used. Thus, to increase the height of the of the center minor component above the electrodes, a thicker second substrate may be used. Also, the mirror, frame pattern, and hinge pattern are formed without using th film layenng, which reduces the number of processing steps.
In the foregoing specification, the invention has been descnbed with reference to specific exemplary embodiments thereof. It will, however, be evident that vanous modifications and changes may be made thereto without departing from the broader spmt and scope of the invention as set forth in the appended claims. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restnctive sense.