CN107064555B - MEMS accelerometer and manufacturing process thereof - Google Patents

MEMS accelerometer and manufacturing process thereof Download PDF

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CN107064555B
CN107064555B CN201710140855.8A CN201710140855A CN107064555B CN 107064555 B CN107064555 B CN 107064555B CN 201710140855 A CN201710140855 A CN 201710140855A CN 107064555 B CN107064555 B CN 107064555B
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silicon
etching
layer
mass block
cover plate
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CN107064555A (en
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胡宗达
李航
于连忠
杨燕
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Institute of Geology and Geophysics of CAS
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Institute of Geology and Geophysics of CAS
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
    • G01P15/00—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
    • G01P15/02—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses
    • G01P15/08—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B81—MICROSTRUCTURAL TECHNOLOGY
    • B81B—MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES
    • B81B7/00—Microstructural systems; Auxiliary parts of microstructural devices or systems
    • B81B7/02—Microstructural systems; Auxiliary parts of microstructural devices or systems containing distinct electrical or optical devices of particular relevance for their function, e.g. microelectro-mechanical systems [MEMS]
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B81—MICROSTRUCTURAL TECHNOLOGY
    • B81C—PROCESSES OR APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OR TREATMENT OF MICROSTRUCTURAL DEVICES OR SYSTEMS
    • B81C1/00—Manufacture or treatment of devices or systems in or on a substrate
    • B81C1/00015—Manufacture or treatment of devices or systems in or on a substrate for manufacturing microsystems
    • B81C1/00134—Manufacture or treatment of devices or systems in or on a substrate for manufacturing microsystems comprising flexible or deformable structures
    • B81C1/00142—Bridges
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B81—MICROSTRUCTURAL TECHNOLOGY
    • B81C—PROCESSES OR APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OR TREATMENT OF MICROSTRUCTURAL DEVICES OR SYSTEMS
    • B81C1/00—Manufacture or treatment of devices or systems in or on a substrate
    • B81C1/00349—Creating layers of material on a substrate
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B81—MICROSTRUCTURAL TECHNOLOGY
    • B81C—PROCESSES OR APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OR TREATMENT OF MICROSTRUCTURAL DEVICES OR SYSTEMS
    • B81C1/00—Manufacture or treatment of devices or systems in or on a substrate
    • B81C1/00436—Shaping materials, i.e. techniques for structuring the substrate or the layers on the substrate
    • B81C1/00523—Etching material
    • B81C1/00531—Dry etching
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B81—MICROSTRUCTURAL TECHNOLOGY
    • B81C—PROCESSES OR APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OR TREATMENT OF MICROSTRUCTURAL DEVICES OR SYSTEMS
    • B81C1/00—Manufacture or treatment of devices or systems in or on a substrate
    • B81C1/00436—Shaping materials, i.e. techniques for structuring the substrate or the layers on the substrate
    • B81C1/00523—Etching material
    • B81C1/00539—Wet etching
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B81—MICROSTRUCTURAL TECHNOLOGY
    • B81C—PROCESSES OR APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OR TREATMENT OF MICROSTRUCTURAL DEVICES OR SYSTEMS
    • B81C2201/00—Manufacture or treatment of microstructural devices or systems
    • B81C2201/01—Manufacture or treatment of microstructural devices or systems in or on a substrate
    • B81C2201/0101—Shaping material; Structuring the bulk substrate or layers on the substrate; Film patterning
    • B81C2201/0128—Processes for removing material
    • B81C2201/013—Etching
    • B81C2201/0132—Dry etching, i.e. plasma etching, barrel etching, reactive ion etching [RIE], sputter etching or ion milling
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B81—MICROSTRUCTURAL TECHNOLOGY
    • B81C—PROCESSES OR APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OR TREATMENT OF MICROSTRUCTURAL DEVICES OR SYSTEMS
    • B81C2201/00—Manufacture or treatment of microstructural devices or systems
    • B81C2201/01—Manufacture or treatment of microstructural devices or systems in or on a substrate
    • B81C2201/0101—Shaping material; Structuring the bulk substrate or layers on the substrate; Film patterning
    • B81C2201/0128—Processes for removing material
    • B81C2201/013—Etching
    • B81C2201/0133—Wet etching
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
    • G01P15/00—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
    • G01P15/02—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses
    • G01P15/08—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values
    • G01P2015/0862—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values being provided with particular means being integrated into a MEMS accelerometer structure for providing particular additional functionalities to those of a spring mass system

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  • Microelectronics & Electronic Packaging (AREA)
  • Computer Hardware Design (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Micromachines (AREA)
  • Pressure Sensors (AREA)

Abstract

The invention relates to the field of sensors, in particular to an MEMS accelerometer, which comprises an upper cover plate, a device layer and a lower cover plate; the device layer includes: the device comprises an anchor point, a mass block, a decoupling beam and an acceleration detection structure; the decoupling beam is used for connecting the anchor point and the mass block, the acceleration detection structure is arranged in the mass block in an axial symmetry manner, and the acceleration detection structure comprises: a resonant beam and a drive electrode; comb teeth are formed on two sides of the resonant beam; the comb teeth on one side of the resonant beam are superposed with the driving electrode; the comb teeth on the other side are superposed with the comb teeth on the mass block; the driving electrode applies an electric driving signal to the resonance beam, and the acceleration detecting structure detects acceleration by detecting a resonance frequency of the resonance beam.

Description

MEMS accelerometer and manufacturing process thereof
Technical Field
The invention relates to a MEMS sensor, in particular to a MEMS accelerometer.
Background
Today, accelerometers are suitable for many applications, such as measuring the intensity of earthquakes and collecting data, detecting the impact strength in a car crash, and detecting the angle and direction of tilt in cell phones and gaming machines. With the continuous progress of micro-electro-mechanical systems (MEMS) technology, many small acceleration meters of nanometer scale have been widely commercialized.
Usually, the accelerometer can only measure the acceleration in one plane direction in X, Y, Z axes, and if the acceleration in three dimensions needs to be measured, three accelerometers need to be arranged respectively. For this reason, the designer should also need to design a three-dimensional acceleration sensor that can directly detect acceleration. For example, chinese patent application publication No. CN102798734 uses three independent masses, and directly forms a comb structure between each mass and the supporting frame, and each mass is responsible for detecting acceleration in one plane direction.
Although the structure can directly detect the acceleration in three directions, three independent mass blocks are required to be arranged, and the mass blocks and the frame cannot be reused, so that the whole chip area is very large. Furthermore, in real-world situations, the acceleration is often a combination of three vectors of the X, Y, Z axis. During detection, the three independent mass blocks can generate displacement, and crosstalk and noise between the mass blocks can influence the precision of a detection result. Furthermore, the accuracy by way of the variation of the spacing and/or the overlapping area of the comb teeth between the proof mass and the frame is inherently low. Due to the arrangement of the three different mass blocks, in order to achieve an accurate detection result, the requirement on the consistency between each mass block and each elastic beam is very high, so that the requirement on the whole machining process is also very high.
Disclosure of Invention
The technical problem to be solved by the present invention is to overcome the defects of the prior art, and to provide a MEMS accelerometer with high accuracy, small detection error and stable performance.
A MEMS accelerometer, comprising: an upper cover plate, a device layer and a lower cover plate; the device layer includes: the device comprises an anchor point, a mass block, a decoupling beam and an acceleration detection structure; the anchor points are fixed with the upper cover plate and the lower cover plate; the decoupling beam is used for connecting the anchor point and the mass block, the acceleration detection structure is arranged in the mass block in an axial symmetry manner, and the acceleration detection structure comprises: a resonant beam and a drive electrode; two tail ends of the resonance beam are respectively connected with the anchor points; comb teeth are formed on two sides of the resonant beam; the comb teeth on one side of the resonant beam are superposed with the driving electrode; the comb teeth on the other side of the resonant beam are superposed with the comb teeth on the mass block; the driving electrode applies an electric driving signal to the resonance beam so that the resonance beam vibrates, and the acceleration detection structure detects acceleration by detecting a vibration frequency of the resonance beam.
The invention also comprises the following additional features:
the electric drive signal of the drive electrode comprises: sine waves, square waves, triangular waves; the frequency of the electrical drive signal is at: between 10 hz and 10 mhz.
The mass block is provided with three acceleration detection structure groups respectively, each acceleration detection structure group comprises at least two acceleration detection structures, and the acceleration detection structure groups detect the displacement of the mass block in three dimensions respectively in a differential mode.
The mass block is provided with a sunken area, comb teeth are formed on the side wall of the mass block in the sunken area, and the acceleration structure is arranged in the sunken area.
The height of the comb teeth of the resonance beam is the same as that of the comb teeth on the side wall of the mass block.
The comb tooth height of the resonance beam is not more than the comb tooth height on the side wall of the mass block, and one end of the comb tooth of the resonance beam is flush with the comb tooth on the side wall of the mass block.
The height of the comb teeth of the resonance beam is half of that of the comb teeth on the side wall of the mass block, and one end of the comb teeth of the resonance beam is flush with the comb teeth on the side wall of the mass block.
The decoupling beam comprises a decoupling beam frame and a tuning fork type decoupling beam; the decoupling beam frame is connected with the anchor point, and the mass block is connected with the decoupling beam frame through the tuning fork type decoupling beam.
A manufacturing process for a MEMS accelerometer, the manufacturing process comprising the steps of:
the first step, forming silicon dioxide layers on the top surface and the bottom surface of the silicon chip on the insulator by using a high-temperature growth or chemical deposition method;
etching a groove which is as deep as an upper silicon layer on the silicon dioxide layer on the top surface of the silicon wafer on the insulator through photoetching and etching;
thirdly, further depositing a silicon nitride layer on the top surface of the silicon wafer on the insulator by a chemical deposition method;
etching the silicon nitride layer and the silicon dioxide layer on the top surface of the silicon wafer on the insulator by photoetching and etching to form a plurality of grooves which are deep to the upper silicon layer;
fifthly, etching the silicon dioxide layer on the bottom surface of the silicon wafer on the insulator through photoetching and etching to form a plurality of grooves reaching the lower silicon layer;
sixthly, further etching the lower silicon layer and the buried oxide layer of the silicon wafer on the insulator to form a sunken area with a certain depth and a groove reaching the upper silicon layer;
seventhly, depositing metal in the groove deep to the upper silicon layer, and leading out an electrode;
eighthly, etching a pattern which is deep to an upper silicon layer at a corresponding position on the bottom surface of the silicon wafer on the insulator through photoetching and etching to form a mass block, a resonant beam and a comb tooth structure;
ninth, removing the silicon dioxide layer on the bottom surface of the silicon wafer on the insulator;
tenthly, carrying out anodic bonding on the bottom surface of the silicon wafer on the insulator and the lower cover plate;
step ten, etching the top surface of the silicon wafer on the insulator, and removing the exposed upper silicon layer to form a freely movable mass block, a resonant beam and a comb tooth structure;
the twelfth step, the silicon nitride layer on the top surface of the silicon wafer on the insulator is removed, and the upper silicon layer exposed outside is further etched to a certain depth;
a tenth step of removing the silicon dioxide layer on the top surface of the silicon-on-insulator wafer;
and fourteenth, bonding the top surface of the silicon wafer on the insulator with the upper cover plate to form the complete accelerometer.
The manufacturing process for the lower cover plate further comprises:
etching a plurality of holes on the bottom surface of the lower cover plate by photoetching and etching;
a second step of depositing a metal in the hole;
etching the top surface of the lower cover plate to form a bonding depressed area;
fourthly, depositing metal in the bonding sunken area and connecting the metal in the hole;
the manufacturing process for the upper cover plate further comprises: and forming a bonding concave area on the bottom layer of the upper cover plate by photoetching and etching.
The etching method is one or more of the following methods: dry etching or wet etching, the dry etching comprising: deep reactive ion, and gaseous xenon difluoride etching of silicon and reactive ion, plasma, and gaseous hydrogen fluoride etching of silicon oxide.
The etchant for wet etching the upper silicon layer and the lower silicon layer is one or the combination of more of the following etchants: potassium hydroxide, tetramethyl ammonium hydroxide, or ethylenediamine pyrocatechol corrosion solutions.
The etchant for wet etching the silicon dioxide layer is one or the combination of more of the following etchants: hydrofluoric acid and buffered hydrofluoric acid.
Compared with the traditional accelerometer, the technical scheme of the invention has the following advantages: first, the present invention detects acceleration by detecting a change in the resonant frequency of the resonant beam. Compared with the mode of detecting the acceleration by detecting the capacitance change in the traditional technology, the method has higher precision, and also reduces the problem of mechanical coupling in the traditional accelerometer. And the mode of detecting the frequency is easier to be converted into a digital signal, and the later signal processing and the interface of a computer are easier. Secondly, the present invention uses a single mass to detect X, Y, Z acceleration in three directions, reducing cross talk and noise between the masses used. In addition, compared with three independent masses, one mass has larger volume and mass, so that the detection sensitivity of the accelerometer is higher, and the crosstalk among the masses is reduced. The accelerometer detects frequency through difference, on one hand, detection precision is improved, and on the other hand, the influence of nonlinear change generated by external acceleration change on the frequency of the resonant beam is reduced.
Drawings
Figure 1 is a side view of an accelerometer.
Figure 2 is a top view of the present accelerometer device layer.
Fig. 3 is an enlarged schematic view of a resonant beam in the accelerometer for detecting acceleration in a horizontal direction.
FIG. 4 is a schematic diagram of a set of resonant beams in an accelerometer detecting acceleration in a vertical direction.
FIG. 5 is a schematic diagram of the mass and resonant beam when no and no acceleration occurs in the vertical direction in the accelerometer.
Figure 6 is a schematic diagram of an initial state and a first step of an accelerometer chip manufacturing process.
FIG. 7 is a schematic diagram of a second step and a third step of an accelerometer chip manufacturing process.
Fig. 8 is a schematic diagram of the fourth step and the fifth step of the accelerometer chip manufacturing process.
Fig. 9 is a schematic diagram of a sixth step and a seventh step of the accelerometer chip manufacturing process.
Fig. 10 is a schematic diagram of the eighth step and the ninth step of the accelerometer chip manufacturing process.
Fig. 11 is a schematic diagram of the tenth step and the eleventh step of the accelerometer chip manufacturing process.
Fig. 12 is a schematic diagram of a twelfth step and a thirteenth step of the accelerometer chip manufacturing process.
FIG. 13 is a fourteenth step of the accelerometer chip manufacturing process.
Fig. 14 is a fifteenth schematic diagram of the accelerometer chip manufacturing process.
Figure 15 is a sixteenth step schematic diagram of an accelerometer chip manufacturing process.
Fig. 16 is a seventeenth schematic diagram of a manufacturing process of an accelerometer chip.
Fig. 17 is a schematic diagram of an eighteenth step of the accelerometer chip manufacturing process.
Fig. 18 is a diagram illustrating a nineteenth step of the accelerometer chip manufacturing process.
Figure 19 is a schematic diagram of a twentieth step in the accelerometer chip fabrication process.
Figure 20 is a schematic diagram of an initial state and a first step of a cover plate manufacturing process in an accelerometer chip.
FIG. 21 is a schematic diagram of a second step and a third step of a cover plate manufacturing process in an accelerometer chip.
Fig. 22 is a schematic diagram of the fourth step and the fifth step of the manufacturing process of the cover plate in the accelerometer chip.
An upper cover plate 1, a device layer 2, a lower cover plate 3, an electrode 4, an upper silicon layer 5, a lower silicon layer 6, a silicon dioxide layer 7, a silicon nitride layer 8, an anchor point 21, a decoupling beam 22, a mass block 23, a hollow part 231, a resonant beam 24, a comb tooth structure 25,
Detailed Description
The present invention will be described in detail below with reference to embodiments and drawings, it being noted that the described embodiments are only intended to facilitate the understanding of the present invention, and do not limit it in any way.
Figure 1 shows a side view of a MEMS accelerometer of the invention comprising an upper cover plate 1, a device layer 2 and a lower cover plate 3. Preferably, the device layer 2 is made of a silicon-on-insulator (SOI wafer) comprising: an upper silicon layer 5 and a lower silicon layer 6, with a silicon dioxide layer 7 disposed between the upper and lower silicon layers 5, 6 to electrically isolate the upper and lower silicon layers 5, 6. This layer 7 of silicon dioxide is also called buried oxide. In fig. 1, a metal electrode 4 is deposited in the lower cover plate 3, but the electrode may also be disposed in the upper cover plate 1, and the device layer 2 may also be adjusted in position accordingly.
Fig. 2 shows the present MEMS acceleration device layer 2, which includes an anchor point 21, a decoupling beam 22 connected to the anchor point 21, and a mass 23 connected to the decoupling beam 22. The decoupling beam 22 is connected with the anchor point 21 to form a peripheral frame, and then is connected with the mass block 22 through the Y-shaped tuning fork type decoupling beam. The main purpose of connecting the masses 22 by Y-tuning fork decoupling beams is to reduce the quadrature coupling error between the three directions X, Y, Z. The preferred Y-tuning fork type decoupling beam 22 has a small degree of inter-axis coupling in the X, Y plane and is able to relieve residual stresses during the bonding process.
Refer to fig. 1 to 4. The resonant beams 24 are symmetrically arranged around the mass 22, a plurality of hollow parts 231 are formed in the mass, and the resonant beams 24 are also arranged in the hollow parts 231. The two ends of the resonant beam 24 are fixed by anchor points 21. Comb tooth structures 25 are formed between the resonant beams 24 and the mass blocks 23, respectively. An electrode 4 is provided at an end of the resonance beam 24 opposite to the mass 23. A comb structure 25 is also formed between the electrode 4 and the resonant beam 24. During operation, the electrode 4 applies an electrical signal to the resonant beam 24 to drive the resonant beam 24 to vibrate at a certain frequency. The resonant beams 24 arranged around the mass 23 are used for detecting acceleration changes in the X, Y horizontal plane. When a horizontal acceleration occurs, the mass 23 is displaced along the direction of the acceleration, and the displacement causes the pitch of the comb teeth 25 between the mass 23 and the resonant beam 24 to change, so that the electrostatic force applied to the resonant beam 24 changes, thereby changing the resonant frequency of the resonant beam 24. As can be seen from fig. 2, the resonant beams 24 are symmetrically arranged in pairs at both ends of the mass. During the acceleration detection, the electrostatic force on the resonant beam 24 at one end of the mass becomes larger, and the electrostatic force on the resonant beam 24 at the opposite end becomes smaller. By the differential detection method, the differential resonance frequency of the two groups of resonance beams 24 can be detected, and the direction and amplitude of the acceleration can be calculated. Common mode errors and interferences are effectively suppressed by a differential detection mode.
Referring to fig. 1, 2, and 4, the group of resonance beams 24 provided in the hollow portion 231 of the mass 23 is for detecting acceleration in the Z-axis direction. When detecting the acceleration in the Z-axis direction, the present invention detects the acceleration by making the heights of the comb teeth 25 between the resonant beam 24 and the mass block 23 different. The height of the comb teeth 24a arranged on the resonant beam 24 is smaller than the height of the comb teeth 23a arranged on the mass block 23, and the height of the comb teeth 24a on the resonant beam 24 is also smaller than the displacement amplitude of the mass block 23 in the vertical direction of the Z axis. In a preferred embodiment, the height of the comb teeth 24a on the resonant beam 24 is half of the height of the comb teeth 23a on the mass block 23. Further, in the two sets of resonance beams 24 for detecting Z-axis acceleration, the bottom ends of the comb teeth 24a of one set of resonance beams 24 are flush with the bottom ends of the comb teeth 23a on the mass block 23. The top ends of the comb teeth 24a of the other group of resonant beams 24 are flush with the top ends of the comb teeth 23a of the mass block 23. Further, the electrostatic force variation experienced by the two resonant beams 24 is different according to the displacement direction of the mass 23 in the Z-axis direction. For example, when the mass 23 is displaced upward by an external acceleration, the comb teeth of the resonant beam 24 and the comb teeth of the mass 23, which are flush with the top end of the comb teeth of the mass 23, do not generate a change in the overlapping area, so that the resonant beam 24, which is flush with the top end of the comb teeth of the mass 23, does not generate any change in electrostatic force. Meanwhile, the resonance beam 24 comb teeth which are flush with the bottom end of the mass block 23 comb teeth can reduce electrostatic force due to the reduction of the overlapping area of the comb teeth, and thus the resonance frequency of the resonance beam 24 is changed. And the acceleration in the Z-axis is derived from the difference in frequency change of the two sets of resonant beams 24.
Next, a manufacturing process of the present accelerometer will be further described with reference to fig. 6 to 19. The device layer 2 of the accelerometer adopts a silicon-on-insulator (SOI) structure, and comprises an upper silicon layer 5, a lower silicon layer 6 and a silicon dioxide layer 7 arranged between the upper silicon layer 5 and the lower silicon layer 6. The silicon dioxide layer 7 may also be referred to as a buried oxide layer, among others. The specific processing steps comprise:
in a first step, a silicon dioxide layer 7 is formed on the top and bottom surfaces of a silicon-on-insulator wafer using high temperature growth or chemical deposition.
And secondly, coating photoresist on the top surface of the silicon-on-insulator wafer, then exposing the bottom surface according to a specific pattern, removing the exposed photoresist by using a developer, and baking the unexposed photoresist. So that the exposed pattern is revealed. And then the silicon dioxide layer 7 on the top surface of the SOI silicon chip is etched by reactive ion or plasma dry etching or hydrofluoric acid, and a part of the upper silicon layer 5 is exposed.
In a third step, a further silicon nitride layer 8 is deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD) on the top surface of the SOI wafer.
And fourthly, coating photoresist on the top surface of the silicon-on-insulator wafer, then exposing the bottom surface according to a specific pattern, removing the exposed photoresist by using a developer, and baking the unexposed photoresist. So that the exposed pattern is revealed. And then the silicon nitride layer 8 and the silicon dioxide layer 7 on the top surface of the SOI silicon wafer are etched by reactive ion or plasma dry etching or hydrofluoric acid to form a plurality of grooves which are deep to the upper silicon layer 5.
And fifthly, coating photoresist on the bottom surface of the SOI silicon wafer, then exposing the bottom surface according to a specific pattern, removing the exposed photoresist by using a developer, and baking the unexposed photoresist. And then the silicon dioxide layer 7 on the bottom surface of the SOI silicon wafer is etched by reactive ion or plasma dry etching or hydrofluoric acid to form a plurality of grooves reaching the lower silicon layer 6.
And sixthly, further etching the groove formed in the fourth step and reaching the lower silicon layer 6 by utilizing deep reactive ion etching, or potassium hydroxide, or tetramethyl ammonium hydroxide, or ethylenediamine phosphorus benzenediol to form a sunken area and a plurality of grooves reaching the buried oxide layer 7.
And seventhly, further etching the exposed buried oxide layer 7 by reactive ion or plasma dry etching or hydrofluoric acid so that the groove is deep to the upper silicon layer 5.
And step eight, depositing metal in the groove and leading out the electrode 4.
And a ninth step of recoating the bottom surface of the SOI silicon wafer with photoresist, then exposing the bottom surface according to a specific pattern, removing the exposed photoresist with a developer, and baking the unexposed photoresist. And then the silicon dioxide layer 7 on the bottom surface of the SOI silicon chip is etched by reactive ion or plasma dry etching or hydrofluoric acid, so that the lower silicon layer 6 is exposed.
And step ten, further etching the lower silicon layer by utilizing deep reactive ion etching, or potassium hydroxide, or tetramethyl ammonium hydroxide, or ethylenediamine phosphorus benzenediol until the sunken area is deep to the buried oxide layer 7.
Eleventh, the exposed buried oxide layer 7 is further etched by reactive ion or plasma dry etching, or hydrofluoric acid, so that the recess region is deep to the upper silicon layer 5.
And step eleven, etching the upper silicon layer 5 and the lower silicon layer 6 exposed outside the SOI silicon wafer to a certain depth by using reactive ion or plasma dry etching or hydrofluoric acid.
And thirteenth, etching the exposed buried oxide layer 7 by reactive ion or plasma dry etching, or hydrofluoric acid.
And fourteenth, removing the silicon dioxide layer 7 on the bottom surface of the SOI silicon wafer by using reactive ion or plasma dry etching or hydrofluoric acid.
And fifteenth step, bonding the bottom surface of the silicon-on-insulator wafer and the prefabricated lower cover plate 3 together by using anodic bonding or metal thermocompression bonding.
Sixthly, removing the exposed upper silicon layer 5 by utilizing deep reactive ion etching, or potassium hydroxide, or tetramethyl ammonium hydroxide, or ethylene diamine phosphorus benzenediol to form a freely movable decoupling beam 22, a mass block 23 and a resonant beam 24.
Seventeenth, the silicon nitride layer 8 on the top surface of the SOI wafer is removed by reactive ion or plasma dry etching, or hydrofluoric acid.
Eighteenth, further etching the exposed upper silicon layer 5 to a certain depth by using deep reactive ion etching, or potassium hydroxide, or tetramethyl ammonium hydroxide, or ethylenediamine phosphorus benzenediol, to form comb tooth structures 25 of different heights.
And nineteenth step, removing the silicon dioxide layer 7 on the top surface of the SOI silicon wafer by reactive ion or plasma dry etching or hydrofluoric acid.
And twentieth, bonding the top surface of the silicon-on-insulator wafer and the prefabricated upper cover plate 1 together by using anodic bonding or metal hot-pressing bonding to form a complete accelerometer structure.
Referring to fig. 20 to 22, the process for manufacturing the lower cover plate 3 according to the present invention further includes the following steps:
in the first step, a photoresist is coated on the bottom surface of the lower cover plate 3, and then the bottom surface is exposed according to a specific pattern, and the exposed photoresist is removed with a developer, and the unexposed photoresist is baked. And etching the bottom surface of the lower cover plate 3 to form a deep hole.
In the second step, a photoresist is coated on the top surface of the lower cover plate 3, and then the bottom surface is exposed according to a specific pattern, and the exposed photoresist is removed with a developer, and the unexposed photoresist is baked. And etching the top surface of the lower cover plate 3 to form a bonding depressed area.
And thirdly, depositing metal in the deep hole on the bottom surface of the lower cover plate 3, and leading out an electrode 4.
The fourth step, the top surface of the lower cover plate 3 is subjected to Chemical Mechanical Polishing (CMP) so that the electrode 4 communicates with the bonding depression.
And fifthly, depositing metal at corresponding positions in the bonding concave regions on the top surface of the lower cover plate 3.
Referring to fig. 6 to 19, the upper and lower cover plates 1 and 3 in the present invention may also be made of glass. The cover plate made of glass has the advantages that: the silicon-glass bonding temperature is low, and the prior metal electrode and lead wire can not be influenced. When the upper and lower cover plates 1 and 3 are made of glass, the fifteenth and twentieth of the above-described manufacturing process steps are silicon-glass bonding, in which the silicon-on-insulator wafer is bonded to the upper and lower cover plates 1 and 3.
The deep etching and the etching method in the invention are one or more of the following methods: dry etching or wet etching, the dry etching comprising: deep reactive ion, and gaseous xenon difluoride etching of silicon and reactive ion, plasma, and gaseous hydrogen fluoride etching of silicon oxide.
The etchant for wet etching the upper silicon layer and the lower silicon layer is one or the combination of more of the following etchants: potassium hydroxide, tetramethyl ammonium hydroxide, or ethylenediamine pyrocatechol corrosion solutions.
The etchant for wet etching the silicon dioxide layer is one or the combination of more of the following etchants: hydrofluoric acid and buffered hydrofluoric acid.
The traditional MEMS accelerometer detects acceleration by detecting capacitance change among comb teeth, while the invention adopts electrostatic negative stiffness effect and detects acceleration by detecting change of resonant frequency on a resonant beam. Compared with the traditional accelerometer, the invention effectively solves the problem of mechanical coupling in the traditional resonant accelerometer with a lever structure, and the method for differentially detecting the vibration frequency also ensures higher detection precision and more stable system. And the detection sensitivity of the whole accelerometer is improved by two times by a differential detection mode. In addition, the detection frequency is easier to convert into a digital signal, the interface with a computer is more convenient, and the influence of nonlinear change generated by external acceleration change on the frequency of the resonant beam is reduced. . In addition, the whole mass block is adopted, so that the volume of the mass block is larger, and the overall detection sensitivity of the accelerometer is improved. On the other hand, coupling and crosstalk between the individual masses are also reduced.
And because the etching process and the silicon bonding process are simpler, the production efficiency of the product is extremely high, and the cost is lower. Therefore, the MEMS accelerometer manufactured by the process has the advantages of high sensitivity, small error, low cost and the like.
Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention, and not for limiting the protection scope of the present invention, although the present invention is described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions can be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims (9)

1. A MEMS accelerometer, comprising: an upper cover plate, a device layer and a lower cover plate; the device layer includes: the device comprises a first anchor point, a mass block, a decoupling beam and an acceleration detection structure; the first anchor point is fixed with the upper cover plate and the lower cover plate; the decoupling beam is used for connecting the first anchor point and the mass block, and is characterized in that the acceleration detection structure is axisymmetrically arranged in the mass block, and the acceleration detection structure comprises: a resonant beam and a drive electrode; two tail ends of the resonance beam are respectively connected with a second anchor point; comb teeth are formed on two sides of the resonant beam; the comb teeth on one side of the resonant beam are superposed with the driving electrode; the comb teeth on the other side of the resonant beam are superposed with the comb teeth on the mass block; the driving electrode applies an electric driving signal to the resonance beam to cause the resonance beam to vibrate, and the acceleration detection structure detects acceleration by detecting a vibration frequency of the resonance beam; the mass block is respectively provided with three acceleration detection structure groups, each acceleration detection structure group comprises at least two acceleration detection structures, and the acceleration detection structure groups respectively detect the acceleration of the mass block in three dimensions in a differential mode; a sunken area is formed on the mass block, comb teeth are formed on the side wall of the mass block in the sunken area, and the acceleration detection structure is arranged in the sunken area; the comb teeth of the resonant beam for detecting the vertical acceleration are half of the height of the comb teeth on the side wall of the mass block, and one end of the comb teeth of the resonant beam for detecting the vertical acceleration is flush with the tail end of the comb teeth on the side wall of the mass block.
2. The accelerometer of claim 1, wherein the electrical drive signal to the drive electrode comprises: sine waves, square waves, triangular waves; the frequency of the electrical drive signal is at: between 10 hz and 10 mhz.
3. The accelerometer of claim 1, wherein the decoupling beams comprise a decoupling beam frame and a tuning fork type decoupling beam; the decoupling beam frame is connected with the first anchor point, and the mass block is connected with the decoupling beam frame through the tuning fork type decoupling beam.
4. A manufacturing process of a MEMS accelerometer is characterized in that: the manufacturing process comprises the following steps:
the first step, forming silicon dioxide layers on the top surface and the bottom surface of the silicon chip on the insulator by using a high-temperature growth or chemical deposition method;
etching a groove which is as deep as an upper silicon layer on the silicon dioxide layer on the top surface of the silicon wafer on the insulator through photoetching and etching;
thirdly, further depositing a silicon nitride layer on the top surface of the silicon wafer on the insulator by a chemical deposition method;
etching the silicon nitride layer and the silicon dioxide layer on the top surface of the silicon wafer on the insulator by photoetching and etching to form a plurality of grooves which are deep to the upper silicon layer;
fifthly, etching the silicon dioxide layer on the bottom surface of the silicon wafer on the insulator through photoetching and etching to form a plurality of grooves reaching the lower silicon layer;
sixthly, further etching the lower silicon layer and the buried oxide layer of the silicon wafer on the insulator to form a sunken area with a certain depth and a groove reaching the upper silicon layer;
seventhly, depositing metal in the groove etched in the sixth step and deep to the upper silicon layer, and leading out an electrode;
eighthly, etching a pattern which is deep to an upper silicon layer at a corresponding position on the bottom surface of the silicon wafer on the insulator through photoetching and etching to form a mass block, a resonant beam and a comb tooth structure;
ninth, removing the silicon dioxide layer on the bottom surface of the silicon wafer on the insulator;
tenthly, carrying out anodic bonding on the bottom surface of the silicon wafer on the insulator and the lower cover plate;
step ten, etching the top surface of the silicon wafer on the insulator, and removing the exposed upper silicon layer to form a freely movable mass block, a resonant beam and a comb tooth structure;
the twelfth step, the silicon nitride layer on the top surface of the silicon wafer on the insulator is removed, and the upper silicon layer exposed outside is further etched to a certain depth;
a tenth step of removing the silicon dioxide layer on the top surface of the silicon-on-insulator wafer;
and fourteenth, bonding the top surface of the silicon wafer on the insulator with the upper cover plate to form the complete accelerometer.
5. The manufacturing process of a MEMS accelerometer according to claim 4, wherein: the manufacturing process for the lower cover plate further comprises:
etching a plurality of holes on the bottom surface of the lower cover plate by photoetching and etching;
a second step of depositing a metal in the hole;
etching the top surface of the lower cover plate to form a bonding depressed area;
and fourthly, depositing metal in the bonding sunken area and connecting the metal in the bonding sunken area with the metal in the hole.
6. The manufacturing process of a MEMS accelerometer according to claim 4, further comprising for the manufacturing process of the upper cover plate: and forming a bonding concave area on the bottom layer of the upper cover plate by photoetching and etching.
7. A process for manufacturing a MEMS accelerometer according to any of claims 4 to 6, wherein: the etching method is one or more of the following methods: dry etching or wet etching, the dry etching comprising: deep reactive ion of silicon, gaseous xenon difluoride etch and reactive ion of silicon oxide, plasma, and gaseous hydrogen fluoride etch.
8. The manufacturing process of a MEMS accelerometer according to claim 7, wherein: the etchant for wet etching the upper silicon layer and the lower silicon layer is one or the combination of more of the following etchants: potassium hydroxide, tetramethyl ammonium hydroxide and ethylenediamine pyrocatechol corrosive liquid.
9. The manufacturing process of a MEMS accelerometer according to claim 7, wherein: and the etchant for wet etching the silicon dioxide layer is hydrofluoric acid.
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