MEMS sandwich accelerometer

Abstract

The invention discloses an MEMS (Micro Electro Mechanical System) sandwich accelerometer, and relates to the technical field of MEMS, a lower electrode structure layer comprises lower electrode bulk silicon, and a bottom insulating layer, a wiring layer, a surface insulating layer and a lower electrode bonding ring which are sequentially arranged on the front surface of the lower electrode bulk silicon from bottom to top; the lower electrode bonding ring is used for bonding the lower electrode structure layer and the movable mass block silicon; a lead hole is formed in the surface insulating layer; the lower electrode bonding ring is connected with the wiring layer through a lead hole; the surface insulating layer is provided with a second bonding pad and is connected with the wiring layer through a lead hole; the lower electrode bonding ring horizontally leads an electric signal of the movable mass block silicon to the second bonding pad through the wiring layer; the upper electrode structure layer comprises upper electrode body silicon, and a back insulating layer and an upper electrode bonding ring which are sequentially arranged on the back surface of the upper electrode body silicon from top to bottom; the upper electrode bonding ring is used for bonding the upper electrode structure layer and the movable mass block silicon; the lower electrode bonding ring and the upper electrode bonding ring are metal bonding rings, and the three layers of silicon structures are bonded through metal eutectic. According to the invention, horizontal leading-out of the signals of the movable structure layer is realized, bonding pads on planes with different heights are prevented from being manufactured after bonding of the multilayer structure, and the process difficulty is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of micro-electromechanical systems (MEMS), in particular to a MEMS sandwich accelerometer. Background Art

[0002] The MEMS sandwich accelerometer significantly improves the sensitivity and measurement accuracy of the accelerometer through a multi-layer capacitor differential design. Its symmetrical layout can effectively suppress temperature drift and enhance anti-interference capabilities, ensuring high linearity output.

[0003] However, the signal output of the three-layer structure of the MEMS sandwich accelerometer chip and the production of pads on planes at different heights face process difficulties, which become an obstacle to the development of MEMS sandwich accelerometers.

[0004] Colibrys' process is a typical example of a MEMS sandwich accelerometer chip currently used both domestically and internationally. In this process, a three-layer silicon structure is bonded together via silicon-silicon dioxide bonding. Because silicon-silicon dioxide bonding is incompatible with metal pad processes, metal pads can only be fabricated after wafer bonding. This necessitates the formation of pads on silicon structures at varying heights, significantly complicating the patterned metal deposition process. This can also easily lead to metal deposition on the sidewalls of the three-layer silicon structure, potentially causing short circuits.

[0005] In addition, in order to reduce the impact of imperfectly symmetrical differential capacitance on detection sensitivity and linearity, the spacing between the upper and lower capacitors of the sandwich structure needs to be strictly controlled, which also places high demands on the process. Summary of the Invention

[0006] In order to overcome the above-mentioned defects in the prior art, the present invention provides a MEMS sandwich accelerometer, which can realize the horizontal extraction of the movable structure layer signal, avoids the production of pads on planes of different heights after bonding the multi-layer structure, and reduces the process difficulty.

[0007] To achieve the above object, the present invention adopts the following technical solutions, including:

[0008] A MEMS sandwich accelerometer is characterized by comprising a lower electrode structure layer, a movable mass silicon and an upper electrode structure layer arranged in sequence from bottom to top;

[0009] The lower electrode structure layer includes: a lower electrode body silicon, and an underlying insulating layer, a wiring layer, a surface insulating layer, and a lower electrode bonding ring arranged sequentially from bottom to top on the upper surface, i.e., the front surface, of the lower electrode body silicon; the lower electrode bonding ring is used to bond the lower electrode structure layer to the movable mass body silicon;

[0010] A lead hole is provided in the surface insulating layer; a lower electrode bonding ring is connected to the wiring layer through the first lead hole in the surface insulating layer; a second pad is provided on the surface insulating layer, and the second pad is connected to the wiring layer through the second lead hole in the surface insulating layer; the lower electrode bonding ring leads the electrical signal of the movable mass silicon to the second pad through the wiring layer;

[0011] The upper electrode structure layer includes: an upper electrode body silicon, and a back insulating layer and an upper electrode bonding ring arranged on the lower surface, i.e., the back surface, of the upper electrode body silicon from top to bottom; the upper electrode bonding ring is used to bond the upper electrode structure layer to the movable mass body silicon;

[0012] The lower electrode bonding ring and the upper electrode bonding ring are both metal bonding rings, and the three-layer silicon structure is bonded by metal eutectic.

[0013] Preferably, the lower electrode bonding ring and the upper electrode bonding ring are made of the same material, TiW / Au or Al / Ge, and form a gold-silicon eutectic bond or an aluminum-germanium eutectic bond with the movable mass silicon.

[0014] Preferably, the thickness of the back insulating layer in the upper electrode structure layer is consistent with the total thickness of the bottom insulating layer, the wiring layer and the surface insulating layer in the lower electrode structure layer.

[0015] Preferably, the movable mass block is made of silicon wafer, and comprises a movable mass block, a thinned cantilever beam and a support body; wherein the movable mass block is connected to the support body via the thinned cantilever beam;

[0016] The back side and the front side of the support body are respectively provided with a back side shallow cavity and a front side shallow cavity, and the back side shallow cavity and the front side shallow cavity are respectively annular grooves adapted to the lower electrode bonding ring and the upper electrode bonding ring.

[0017] Preferably, the width of the shallow cavity is greater than the width of the corresponding bonding ring, and before bonding, the depth of the shallow cavity is less than the height of the bonding ring; during bonding, the shallow cavity provides overflow space for the bonding ring; after bonding, the thickness of the bonding ring is compressed until the movable mass block silicon contacts the surface insulating layer and the back insulating layer respectively, at which time the bonding ring thickness is consistent with the depth of the shallow cavity.

[0018] Preferably, the back thinning area and the front thinning area of ​​the silicon wafer are corroded, and after corrosion, the two form a thinned cantilever beam in the silicon of the movable mass block; the back thinning area and the front thinning area are formed in the same silicon etching process, and the sizes of the back thinning area and the front thinning area are consistent, ensuring the symmetry of the upward and downward movement of the movable mass block; the movable structure release area of ​​the silicon wafer is corroded, and after corrosion, a movable mass block in the silicon of the movable mass block is formed; the remaining part of the silicon wafer is the support body; the back and front sides of the support body are silicon etched / corroded respectively, and after etching / corrosion, a back shallow cavity and a front shallow cavity are formed respectively, and the sizes of the back shallow cavity and the front shallow cavity are consistent.

[0019] Preferably, a first pad is provided in a front vacant area of ​​the lower electrode body silicon to achieve electrical connection with the lower electrode body silicon.

[0020] Preferably, a third pad is provided on the front surface of the upper electrode silicon body to achieve electrical connection with the upper electrode silicon body.

[0021] Preferably, the size of the surface insulating layer is larger than the size of the movable mass silicon, and the second pad is arranged in a front vacant area of ​​the surface insulating layer.

[0022] Preferably, the metal eutectic bonding of the three-layer silicon structure is compatible with the metal pad process.

[0023] The advantages of the present invention are:

[0024] (1) The present invention provides a MEMS sandwich accelerometer that can realize the horizontal lead-out of the movable structure layer signal, avoids the production of pads on different height planes after the multi-layer structure is bonded, and reduces the process difficulty. Specifically, the present invention uses gold-silicon eutectic bonding or aluminum-germanium eutectic bonding to achieve the binding of the three-layer silicon structure, which is compatible with the metal pad process, avoids the production of pads after the three-layer silicon structure is bonded, and reduces the process difficulty. In addition, the present invention realizes the lateral lead-out of the middle layer silicon structure signal through the conductive ability of the metal eutectic bonding and the arrangement of the buried layer lead under the metal bonding ring. According to the design of the present invention, the pads of the middle layer and the bottom layer silicon structure can be completed at the same time before the wafer is bonded. After the wafer is bonded, it is only necessary to make the top pad on the surface of the top silicon structure.

[0025] (2) The present invention also limits the compression height of the gold-silicon or aluminum-germanium eutectic bonding ring through the design of the bonding shallow cavity, and can accurately control the gap between the upper and lower electrodes and the movable structural layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The figure is a cross-sectional schematic diagram of a MEMS sandwich accelerometer chip structure of the present invention. DETAILED DESCRIPTION

[0027] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0028] In this embodiment, the chip structure of the MEMS sandwich accelerometer is based on a wafer-level eutectic bonding process with a conductive bonding ring, which reduces the difficulty of manufacturing the electrical connection pads of the intermediate movable mass block and the lower electrode structure. The bonding ring groove design ensures that the gap between the three-layer silicon structure is precisely controllable after bonding. It is more suitable for batch manufacturing of high-precision MEMS sandwich accelerometer chips, and meets the application needs of high-end MEMS accelerometers in military equipment, industrial control, aerospace and other fields.

[0029] Depend on Figure 1 As shown, the MEMS sandwich accelerometer is composed of a lower electrode structure layer, a movable mass silicon 201 and an upper electrode structure layer arranged in sequence from bottom to top, forming a sandwich-like structure.

[0030] The lower electrode structure layer includes: a lower electrode silicon body 101 , a bottom insulating layer 102 , a wiring layer 103 , a surface insulating layer 104 , a first pad 105 , a lower electrode bonding ring 106 and a second pad 108 .

[0031] The bottom insulating layer 102, wiring layer 103, surface insulating layer 104, and bottom electrode bonding ring 106 are arranged sequentially from bottom to top on the upper surface (front face) of the bottom electrode silicon bulk 101. The bottom insulating layer 102 electrically isolates the wiring layer 103 from the bottom electrode silicon bulk 101. The surface insulating layer 104 serves as a cushioning layer for the bottom electrode bonding ring 106, which is used to bond the bottom electrode structure layer to the movable mass silicon bulk 201. Two lead holes 107 are provided in the surface insulating layer 104. The lower electrode bonding ring 106 is connected to the wiring layer 103 through the first lead hole, and the second pad 108 is connected to the wiring layer 103 through the second lead hole. The movable mass silicon 201 is electrically connected to the second pad 108 through the lower electrode bonding ring 106, the first lead hole, the wiring layer 103, and the second lead hole. The lower electrode bonding ring 106 leads the electrical signal level of the movable mass silicon 201 to the second pad 108 through the wiring layer 103. The first pad 105 is electrically connected to the lower electrode silicon 101. The lower electrode silicon 101 and the movable mass silicon 201 form a lower detection capacitor.

[0032] The wiring layer 103 is typically made of a hard, high-temperature-resistant metal (such as W) or heavily doped, low-resistance polysilicon. The bottom electrode bonding ring 106 is typically made of TiW / Au (where TiW (titanium-tungsten alloy) serves as an adhesion barrier) or Al / Ge. Accordingly, the bond between the bottom electrode structure layer and the movable mass silicon 201 is a gold-silicon eutectic bond or an aluminum-germanium-silicon eutectic bond.

[0033] The size of the bottom insulating layer 102 ensures that the wiring layer 103 and the bulk silicon 101 are completely insulated, and the first pad 105 is provided in a spare area on the upper surface (front surface) of the lower electrode bulk silicon 101 .

[0034] The size of the surface insulating layer 104 is larger than that of the movable mass silicon 201 . The second pad 108 is provided in a vacant area on the upper surface (front) of the surface insulating layer 104 and is connected to the wiring layer 103 through a second lead hole.

[0035] The upper electrode structure layer includes: an upper electrode silicon body 301 , a back insulating layer 302 , an upper electrode bonding ring 303 and a third pad 304 .

[0036] The back insulating layer 302 and the top electrode bonding ring 303 are arranged sequentially from top to bottom on the lower surface (back surface) of the top electrode bulk silicon 301. The back insulating layer 302 serves as a cushioning layer for the top electrode bonding ring 303, which is used to bond the top electrode structure layer to the movable mass silicon 201. The third pad 304 is electrically connected to the top electrode bulk silicon 301. The top electrode bulk silicon 301 and the movable mass silicon 201 form the upper detection capacitor.

[0037] The upper electrode bonding ring 303 and the lower electrode bonding ring 106 are made of the same material and have the same dimensions. The upper electrode bonding ring 303 is also typically made of TiW / Au (where TiW serves as an adhesion barrier) or Al / Ge. Accordingly, the bond between the upper electrode structure layer and the movable mass silicon 201 is a gold-silicon eutectic bond or an aluminum-germanium eutectic bond. A third bonding pad 304 is provided on the upper surface (front face) of the upper electrode silicon 301.

[0038] The upper detection capacitor and the lower detection capacitor form a differential capacitor.

[0039] Among them, the thickness of the back insulating layer 302 in the upper electrode structure layer is consistent with the total thickness of the bottom insulating layer 102, the wiring layer 103 and the surface insulating layer 104 in the lower electrode structure layer, and the thickness of the upper electrode bonding ring 303 and the lower electrode bonding ring 106 are consistent, so that the initial spacing between the upper detection capacitor and the lower detection capacitor is consistent, ensuring the symmetry of the differential capacitance.

[0040] The movable mass block silicon 201 is made of silicon wafer, and includes a movable mass block 2011 , a thinned cantilever beam 2012 and a support body 2013 ; the movable mass block 2011 is connected to the support body 2013 via the thinned cantilever beam 2012 .

[0041] Among them, the back thinning area 205 and the front thinning area 206 of the silicon wafer are corroded, and after corrosion, the two form a thinned cantilever beam 202 in the movable mass block silicon 201; the back thinning area 205 and the front thinning area 206 are formed in the same silicon etching process, and the etching dimensions (depth and width) of the two are consistent, ensuring the symmetry of the upward and downward movement of the movable mass block 2011.

[0042] The movable structure release area 207 of the silicon wafer is etched to form a movable mass block 2011 in the movable mass block silicon 201 after etching.

[0043] The remaining part of the silicon wafer is the support body 2013. The back side (lower surface) and the front side (upper surface) of the support body 2013 are silicon etched or corroded. The etching / corrosion dimensions (depth and width) of the two are consistent. After etching / corrosion, the back side shallow cavity 203 and the front side shallow cavity 204 are respectively formed in the movable mass block silicon 201. The back side shallow cavity 203 and the front side shallow cavity 204 are annular grooves adapted to the lower electrode bonding ring 106 and the upper electrode bonding ring 303 respectively. The width of the shallow cavity (the back side shallow cavity 203 and the front side shallow cavity 204) is greater than the width of the corresponding bonding ring. The width of the shallow cavity is less than the height of the bonding ring before gold-silicon bonding or aluminum-germanium bonding; during gold-silicon bonding or aluminum-germanium bonding, the role of the shallow cavity is to provide overflow space for the gold-silicon or aluminum-germanium alloy. After gold-silicon bonding or aluminum-germanium bonding, the bonding ring forms a gold-silicon or aluminum-germanium alloy, and the thickness of the alloy is compressed until the movable mass silicon 201 outside the shallow cavity contacts the surface insulating layer 104 and the back insulating layer 302 respectively. At this time, the alloy thickness is consistent with the depth of the shallow cavity, so that the gap between the movable mass silicon 201 and the lower electrode / upper electrode structure layer can be precisely controlled.

[0044] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A MEMS sandwich accelerometer, characterized in that: It comprises a lower electrode structure layer, a movable mass silicon (201) and an upper electrode structure layer which are arranged in sequence from bottom to top; The lower electrode structure layer comprises: a lower electrode body silicon (101), and a bottom insulating layer (102), a wiring layer (103), a surface insulating layer (104), and a lower electrode bonding ring (106) arranged in sequence from bottom to top on the upper surface, i.e., the front surface, of the lower electrode body silicon (101); the lower electrode bonding ring (106) is used to bond the lower electrode structure layer to the movable mass block silicon (201); A lead hole (107) is provided in the surface insulating layer (104); the lower electrode bonding ring (106) is connected to the wiring layer (103) through the first lead hole in the surface insulating layer (104); a second pad (108) is provided on the surface insulating layer (104), and the second pad (108) is connected to the wiring layer (103) through the second lead hole in the surface insulating layer (104); the lower electrode bonding ring (106) leads the electrical signal of the movable mass silicon (201) to the second pad (108) through the wiring layer (103); The upper electrode structure layer comprises: an upper electrode body silicon (301), and a back side insulating layer (302) and an upper electrode bonding ring (303) sequentially arranged on the lower surface, i.e., the back side, of the upper electrode body silicon (301) from top to bottom; the upper electrode bonding ring (303) is used to bond the upper electrode structure layer to the movable mass block silicon (201); The lower electrode bonding ring (106) and the upper electrode bonding ring (303) are both metal bonding rings, and the three-layer silicon structure is bonded via metal eutectic.

2. A MEMS sandwich accelerometer according to claim 1, characterized in that: The lower electrode bonding ring (106) and the upper electrode bonding ring (303) are made of the same material, TiW / Au or Al / Ge, and form a gold-silicon eutectic bond or an aluminum-germanium eutectic bond with the movable mass silicon (201).

3. A MEMS sandwich accelerometer according to claim 1, characterized in that: The thickness of the back insulating layer (302) in the upper electrode structure layer is consistent with the total thickness of the bottom insulating layer (102), the wiring layer (103) and the surface insulating layer (104) in the lower electrode structure layer.

4. The MEMS sandwich accelerometer according to claim 1, characterized in that: The movable mass block silicon (201) is made of a silicon wafer and comprises a movable mass block (2011), a thinned cantilever beam (2012) and a support body (2013); wherein the movable mass block (2011) is connected to the support body (2013) via the thinned cantilever beam (2012); The back side and the front side of the support body (2013) are respectively provided with a back side shallow cavity (203) and a front side shallow cavity (204), and the back side shallow cavity (203) and the front side shallow cavity (204) are respectively annular grooves adapted to the lower electrode bonding ring (106) and the upper electrode bonding ring (303).

5. A MEMS sandwich accelerometer according to claim 4, characterized in that: The width of the shallow cavity is greater than the width of the corresponding bonding ring, and before bonding, the depth of the shallow cavity is less than the height of the bonding ring; during bonding, the shallow cavity provides overflow space for the bonding ring; after bonding, the thickness of the bonding ring is compressed until the movable mass block silicon (201) contacts the surface insulating layer (104) and the back insulating layer (302) respectively, at which time the bonding ring thickness is consistent with the depth of the shallow cavity.

6. The MEMS sandwich accelerometer according to claim 4, characterized in that: The back thinning region (205) and the front thinning region (206) of the silicon wafer are etched, and after the etching, the thinning cantilever beam (202) in the movable mass block silicon (201) is formed; the back thinning region (205) and the front thinning region (206) are formed in the same silicon etching process, and the sizes of the back thinning region (205) and the front thinning region (206) are consistent, thereby ensuring the symmetry of the upward and downward movements of the movable mass block (2011) ; The movable structure release area (207) of the silicon wafer is corroded to form a movable mass block (2011) in the movable mass block silicon (201) after etching; the remaining part of the silicon wafer is the support body (2013); the back and front sides of the support body (2013) are silicon etched / corroded respectively to form a back shallow cavity (203) and a front shallow cavity (204) after etching / corrosion, and the back shallow cavity (203) and the front shallow cavity (204) have the same size.

7. The MEMS sandwich accelerometer according to claim 1, characterized in that: A first bonding pad (105) is provided in a front vacant area of ​​the lower electrode silicon body (101) to achieve electrical connection with the lower electrode silicon body (101).

8. The MEMS sandwich accelerometer according to claim 1, characterized in that: A third pad (304) is provided on the front surface of the upper electrode silicon body (301) to achieve electrical connection with the upper electrode silicon body (301).

9. The MEMS sandwich accelerometer according to claim 1, characterized in that: The size of the surface insulating layer (104) is larger than the size of the movable mass silicon (201), and the second pad (108) is arranged in a front vacant area of ​​the surface insulating layer (104).

10. The MEMS sandwich accelerometer according to claim 1, characterized in that: The metal eutectic bonding of the three-layer silicon structure is compatible with the metal pad process.

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