CN107064555B - MEMS accelerometer and manufacturing process thereof - Google Patents

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

A MEMS accelerometer and its manufacturing process

technical field

The invention relates to a MEMS sensor, in particular to a MEMS accelerometer.

Background technique

Today, accelerometers are suitable for many applications, such as measuring the strength of earthquakes and collecting data, detecting the impact strength of a car crash, and detecting the angle and direction of tilt in mobile phones and game consoles. With the continuous advancement of microelectromechanical system (MEMS) technology, many nanometer-scale small accelerometers have been widely used commercially.

Usually, the accelerometer can only measure the acceleration in one plane direction in the X, Y, and Z axes. If you need to measure the acceleration in three dimensions, you need to set up three accelerometers respectively. To this end, the designer should also need to design the acceleration that can directly detect the three dimensions. For example, the Chinese invention patent application with publication number CN102798734 uses three independent mass blocks, and a comb-tooth structure is directly formed between each mass block and the supporting frame, and each mass block is responsible for detecting the acceleration in a plane direction.

Although this structure can directly detect the acceleration in three directions, it requires three independent mass blocks, and the mass blocks and the frame cannot be reused, so that the overall chip area is very large. In addition, in reality, acceleration is often a combination of three vectors of X, Y, and Z axes. During detection, the three independent mass blocks will all generate displacement, and the crosstalk and noise between the mass blocks will also affect the accuracy of the detection results. In addition, the accuracy of detecting changes in the spacing and/or overlapping area of the comb teeth between the proof-mass and the frame is inherently low. Since three different mass blocks are set, in order to achieve accurate detection results, the requirements for the consistency between each mass block and the elastic beam are very high, so that the overall processing technology requirements are also very high.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to overcome the above-mentioned deficiencies of the prior art, and to provide a MEMS accelerometer with high precision, small detection error and stable performance.

A MEMS accelerometer includes: an upper cover plate, a device layer and a lower cover plate; the device layer includes: an anchor point, a mass block, a decoupling beam and an acceleration detection structure; the anchor point and the upper cover plate and The lower cover plate is fixed; the decoupling beam is used to connect the anchor point and the mass block, the acceleration detection structure is axially symmetrically arranged in the mass block, and the acceleration detection structure includes: a resonance beam and a drive two ends of the resonant beam are respectively connected with the anchor point; comb teeth are formed on both sides of the resonant beam; the comb teeth on one side of the resonant beam are superimposed with the driving electrodes; the other The comb teeth on the side are superimposed with the comb teeth on the mass block; the drive electrode applies an electric drive signal to the resonant beam to make the resonant beam vibrate, and the acceleration detection structure detects the vibration frequency of the resonant beam to detect the vibration frequency of the resonant beam. Detect acceleration.

The present invention also includes the following accessory features:

The electric driving signal of the driving electrode includes: sine wave, square wave, triangular wave; the frequency of the electric driving signal is between 10 Hz and 10 MHz.

The mass blocks are respectively provided with three groups of acceleration detection structure groups, each group of acceleration detection structure groups includes at least two acceleration detection structures, and the acceleration detection structure groups respectively detect the three-dimensional acceleration of the mass block in a differential manner. displacement.

A concave area is formed on the mass block, comb teeth are formed on the side wall of the mass block located in the concave area, and the acceleration structure is arranged in the concave area.

The height of the comb teeth of the resonance beam is the same as the height of the comb teeth on the side wall of the mass block.

The height of the comb teeth of the resonance beam is not greater than the height 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 height of the comb teeth of the resonance beam is 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 resonance beam is flush with the comb teeth on the side wall of the mass block.

The decoupling beam includes a decoupling beam frame and a tuning fork type decoupling beam; the decoupling beam frame is connected to the anchor point, and the mass block is connected to the decoupling beam frame through a tuning fork type decoupling beam .

A manufacturing process of a MEMS accelerometer, the manufacturing process comprising the following steps:

The first step is to use high temperature growth or chemical deposition to form silicon dioxide layers on the top and bottom surfaces of the silicon-on-insulator wafer;

In the second step, through photolithography and etching, a groove deep to the upper silicon layer is etched on the silicon dioxide layer on the top surface of the silicon-on-insulator wafer;

The third step is to further deposit a silicon nitride layer on the top surface of the silicon-on-insulator wafer by chemical deposition;

The fourth step is to etch the silicon nitride layer and the silicon dioxide layer on the top surface of the silicon-on-insulator wafer by photolithography and etching to form a plurality of grooves as deep as the upper silicon layer;

The fifth step, through photolithography and etching, the silicon dioxide layer on the bottom surface of the silicon-on-insulator wafer is etched to form a plurality of grooves as deep as the lower silicon layer;

The sixth step, further etching the lower silicon layer and the buried oxide layer of the silicon-on-insulator wafer to form a recessed area with a certain depth and a groove as deep as the upper silicon layer;

The seventh step, depositing metal in the groove as deep as the upper silicon layer, and extracting the electrode;

In the eighth step, through photolithography and etching, a pattern as deep as the upper silicon layer is etched at the corresponding position on the bottom surface of the silicon wafer on the insulator to form a mass block, a resonant beam and a comb-tooth structure;

The ninth step, removing the silicon dioxide layer on the bottom surface of the silicon wafer on the insulator;

The tenth step, anodic bonding the bottom surface of the silicon wafer on the insulator and the lower cover plate;

The eleventh step is to etch the top surface of the silicon-on-insulator chip, and remove the exposed upper silicon layer to form a free-moving mass block, a resonant beam and a comb-tooth structure;

In the twelfth step, the silicon nitride layer on the top surface of the silicon-on-insulator wafer is removed, and the exposed upper silicon layer is further etched to a certain depth;

The thirteenth step, removing the silicon dioxide layer on the top surface of the silicon wafer on the insulator;

In the fourteenth step, the top surface of the silicon-on-insulator chip is bonded to the upper cover plate to form a complete accelerometer.

The manufacturing process for the lower cover plate also includes:

In the first step, through photolithography and etching, a plurality of holes are etched on the bottom surface of the lower cover plate;

the second step, depositing metal in the hole;

In the third step, etching is performed on the top surface of the lower cover plate to form a bonding recessed area;

The fourth step, depositing metal in the bonding recess area, and connecting with the metal in the hole;

The manufacturing process of the upper cover plate further includes: forming a bonding concave region on the bottom layer of the upper cover plate by photolithography and etching.

The etching method is one or more of the following methods: dry etching or wet etching, and the dry etching includes: deep reactive ions of silicon, reactive ions, and gaseous difluorine Reactive ion, plasma, and gaseous hydrogen fluoride etching of xenon and silicon oxide.

The etchant used for wet etching the upper silicon layer and the lower silicon layer is a combination of one or more of the following etchants: potassium hydroxide, tetramethylammonium hydroxide, or ethylenediamine Hydroquinone etchant.

The etchant for wet etching the silicon dioxide layer is a combination of one or more of the following etchants: hydrofluoric acid and buffered hydrofluoric acid.

Compared with the traditional accelerometer, the technical solution of the present invention has the following advantages: First, the present invention adopts the detection of the resonant frequency change of the resonant beam to detect the acceleration. Compared with the traditional method of detecting acceleration by detecting capacitance changes, the accuracy is higher, and the problem of mechanical coupling in traditional accelerometers is also reduced. Moreover, the method of detecting frequency is also easier to convert into digital signal, and it is also easier to process the signal in the later stage and interface to the computer. Secondly, in the present invention, a whole mass block is used to detect the accelerations in the three directions of X, Y and Z axes, which reduces the crosstalk and noise between using multiple mass blocks. In addition, compared with three separate mass blocks, the volume and mass of one mass block are larger, so that the detection sensitivity of the accelerometer is also higher, and the crosstalk between the various mass blocks is also reduced. The accelerometer detects the frequency through the difference, which increases the detection accuracy on the one hand, and reduces the influence of the nonlinear change caused by the external acceleration change on the frequency of the resonant beam.

Description of drawings

Figure 1 is a side view of an accelerometer.

FIG. 2 is a top view of the device layer of the accelerometer.

FIG. 3 is an enlarged schematic diagram of a resonant beam in an accelerometer for detecting acceleration in a horizontal direction.

FIG. 4 is a schematic diagram of a resonant beam group for detecting acceleration in a vertical direction in an accelerometer.

Figure 5 is a schematic diagram of the mass and the resonant beam in the accelerometer when no and no acceleration occurs in the vertical direction.

FIG. 6 is a schematic diagram of the initial state and the first step of the manufacturing process of the accelerometer chip.

FIG. 7 is a schematic diagram of the second step and the third step of the manufacturing process of the accelerometer chip.

FIG. 8 is a schematic diagram of the fourth step and the fifth step of the manufacturing process of the accelerometer chip.

FIG. 9 is a schematic diagram of the sixth step and the seventh step of the manufacturing process of the accelerometer chip.

FIG. 10 is a schematic diagram of the eighth and ninth steps of the manufacturing process of the accelerometer chip.

FIG. 11 is a schematic diagram of the tenth and eleventh steps of the manufacturing process of the accelerometer chip.

FIG. 12 is a schematic diagram of the twelfth and thirteenth steps of the accelerometer chip manufacturing process.

FIG. 13 is a schematic diagram of the fourteenth step of the manufacturing process of the accelerometer chip.

FIG. 14 is a schematic diagram of the fifteenth step of the manufacturing process of the accelerometer chip.

Figure 15 is a schematic diagram of the sixteenth step of the accelerometer chip manufacturing process.

FIG. 16 is a schematic diagram of the seventeenth step of the manufacturing process of the accelerometer chip.

FIG. 17 is a schematic diagram of the eighteenth step of the manufacturing process of the accelerometer chip.

FIG. 18 is a schematic diagram of the nineteenth step of the manufacturing process of the accelerometer chip.

FIG. 19 is a schematic diagram of the twentieth step of the manufacturing process of the accelerometer chip.

FIG. 20 is a schematic diagram of the initial state and the first step of the cover plate manufacturing process in the accelerometer chip.

FIG. 21 is a schematic diagram of the second and third steps of the manufacturing process of the cover plate in the accelerometer chip.

FIG. 22 is a schematic diagram of the fourth and fifth steps of the manufacturing process of the cover plate in the accelerometer chip.

Upper cover 1, device layer 2, lower cover 3, electrode 4, upper silicon layer 5, lower silicon layer 6, silicon dioxide layer 7, silicon nitride layer 8, anchor point 21, decoupling beam 22, mass 23. The hollow part 231, the resonance beam 24, the comb-tooth structure 25,

Detailed ways

The present invention will be described in detail below with reference to the embodiments and the accompanying drawings. It should be noted that the described embodiments are only intended to facilitate the understanding of the present invention, but do not have any limiting effect on it.

FIG. 1 shows a side view of the MEMS accelerometer of the present invention, which includes 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 silicon wafer), and the silicon-on-insulator includes: an upper silicon layer 5 and a lower silicon layer 6, and a layer is disposed between the upper silicon layer 5 and the lower silicon layer 6 The silicon dioxide layer 7 electrically isolates the upper silicon layer 5 and the lower silicon layer 6 . This silicon dioxide layer 7 is also called a buried oxide layer. As described in FIG. 1 , the metal electrode 4 is deposited in the lower cover plate 3 , but the electrode can also be arranged in the upper cover plate 1 , and the device layer 2 can also be adjusted accordingly.

FIG. 2 shows the 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 . Wherein, the decoupling beam 22 is connected with the anchor point 21 to form a peripheral frame, and is then connected with the mass block 22 through a Y-shaped tuning fork type decoupling beam. The main purpose of connecting the mass blocks 22 through the Y-shaped tuning fork-type decoupling beam is to reduce the orthogonal coupling error between the three directions of X, Y, and Z. The preferred Y-shaped tuning fork type decoupling beam 22 is that its coupling degree between axes in the X, Y plane is small, and it can relieve the residual stress during the bonding process.

Referring to Figures 1 to 4 . A group of resonant beams 24 are symmetrically arranged around the mass block 22 respectively, and a plurality of hollow parts 231 are also formed in the mass block, and the resonant beams 24 are also arranged in the hollow parts 231 . Both ends of the resonance beam 24 are fixed by the anchor points 21 . Comb structures 25 are respectively formed between the resonance beam 24 and the mass 23 . An electrode 4 is provided at the end of the resonance beam 24 opposite to the mass 23 . A comb-tooth structure 25 is also formed between the electrode 4 and the resonance beam 24 . During operation, the electrode 4 applies an electrical signal to the resonant beam 24 to drive the resonant beam 24 to vibrate according to a certain frequency. Among them, the group of resonant beams 24 arranged around the mass block 23 is used to detect the acceleration changes in the X and Y horizontal planes. When the horizontal acceleration occurs, the mass block 23 will have a corresponding displacement along the acceleration direction, and the displacement will cause the spacing of the comb teeth 25 between the mass block 23 and the resonant beam 24 to change, so that the applied force on the resonant beam 24 changes. The electrostatic force changes, which in turn changes the resonant frequency of the resonant beam 24 . It can be seen from FIG. 2 that the resonant beams 24 are symmetrically arranged in pairs at both ends of the mass. In the process of detecting the acceleration, the electrostatic force on the resonance beam 24 at one end of the mass block will become larger, while the electrostatic force on the resonance beam 24 at the opposite end will become smaller. Through the differential detection method, the differential resonance frequencies of the two groups of resonance beams 24 can be detected, and then the direction and amplitude of the acceleration can be calculated. The common mode error and interference are effectively suppressed by the differential detection method.

Referring to FIG. 1 , FIG. 2 and FIG. 4 , the group of resonant beams 24 disposed in the hollow part 231 of the mass block 23 is used to detect the acceleration in the Z-axis direction. When detecting the acceleration in the Z-axis direction, the present invention adopts a manner of detecting the height of the comb teeth 25 between the resonance beam 24 and the mass block 23 with different heights. The height of the comb teeth 24a provided on the resonance beam 24 is smaller than the height of the comb teeth 23a provided on the mass block 23, and the height of the comb teeth 24a on the resonance 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 resonance beam 24 is half of the height of the comb teeth 23a on the mass block 23 . In addition, in the two groups of resonant beams 24 for detecting Z-axis acceleration, the bottom ends of the comb teeth 24 a of one group of resonant beams 24 are flush with the bottom ends of the comb teeth 23 a on the mass block 23 . The top ends of the comb teeth 24a of the other group of resonance beams 24 are flush with the top ends of the comb teeth 23a on the mass 23 . Furthermore, according to the direction of displacement of the mass 23 in the Z-axis direction, the electrostatic force changes received by the two groups of resonance beams 24 will be different. For example, when the mass 23 is displaced upward due to the external acceleration, the comb teeth of the resonant beam 24 and the comb teeth of the mass 23 that are flush with the top of the comb teeth of the mass block 23 will not have a change in the overlapping area, so that the comb teeth of the mass 23 and the mass 23 will not change their overlapping area. There is no electrostatic force change from the top of the comb to the flush resonant beam 24 . At the same time, the comb teeth of the resonant beam 24 flush with the bottom end of the comb teeth of the mass block 23 will reduce the electrostatic force due to the reduction of the overlapping area of the comb teeth, thereby causing the resonant frequency of the resonant beam 24 to change. And the acceleration on the Z axis is obtained according to the frequency change difference of the two groups of resonant beams 24 .

Next, the manufacturing process of the present accelerometer will be further described with reference to FIGS. 6 to 19 . The device layer 2 of the accelerometer adopts a silicon-on-insulator (SOI) structure, which includes an upper silicon layer 5 , a lower silicon layer 6 and a silicon dioxide layer 7 disposed between the upper silicon layer 5 and the lower silicon layer 6 . The silicon dioxide layer 7 may also be called a buried oxide layer. Its specific processing steps include:

In the first step, silicon dioxide layers 7 are formed on the top and bottom surfaces of the silicon-on-insulator wafer by high temperature growth or chemical deposition.

In the second step, photoresist is coated on the top surface of the silicon-on-insulator wafer, 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 removed. The exposed photoresist is baked. In this way, the exposed pattern will be revealed. Then, the silicon dioxide layer 7 on the top surface of the SOI silicon wafer is etched by reactive ion or plasma dry etching or hydrofluoric acid to expose a part of the upper silicon layer 5 .

In the third step, a silicon nitride layer 8 is further deposited on the top surface of the SOI silicon wafer by means of plasma chemical vapor deposition (PECVD).

In the fourth step, photoresist is coated on the top surface of the silicon-on-insulator wafer, 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 removed. The exposed photoresist is baked. In this way, the exposed pattern will be revealed. 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 as deep as the upper silicon layer 5 .

In the fifth step, a photoresist is coated on the bottom surface of the SOI silicon wafer, 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. bake. 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 as deep as the lower silicon layer 6 .

The 6th step, utilizes deep reactive ion etching, or potassium hydroxide, or tetramethyl ammonium hydroxide, or ethylenediamine phosphine, further engraves the groove deep to the lower silicon layer 6 formed in the 4th step. etch to form a recessed region and a plurality of trenches as deep as the buried oxide layer 7 .

In the seventh step, the exposed buried oxide layer 7 is further etched by reactive ion or plasma dry etching, or hydrofluoric acid, so that the groove is as deep as the upper silicon layer 5 .

In the eighth step, metal is deposited in the groove, and the electrode 4 is drawn out.

The ninth step, re-coating photoresist on the bottom surface of the SOI silicon wafer, and then exposing the bottom surface according to a specific pattern, removing the exposed photoresist with a developer, and removing the unexposed photoresist. bake. 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 expose the lower silicon layer 6 .

The tenth step is to further etch the lower silicon layer by using deep reactive ion etching, or potassium hydroxide, or tetramethyl ammonium hydroxide, or ethylenediamine phosphoroquinone, until the recessed area is as deep as the buried oxide layer 7 .

In the eleventh step, the exposed buried oxide layer 7 is further etched by reactive ion or plasma dry etching, or hydrofluoric acid, so that the recessed area is as deep as the upper silicon layer 5 .

In the twelfth step, reactive ion or plasma dry etching or hydrofluoric acid is used to etch the exposed upper silicon layer 5 and lower silicon layer 6 of the SOI silicon wafer to a certain depth.

In the thirteenth step, the exposed buried oxide layer 7 is further etched by reactive ion or plasma dry etching, or hydrofluoric acid.

In the fourteenth step, the silicon dioxide layer 7 on the bottom surface of the SOI silicon wafer is removed by reactive ion or plasma dry etching or hydrofluoric acid.

In the fifteenth step, the bottom surface of the silicon-on-insulator wafer and the prefabricated lower cover plate 3 are bonded together using anodic bonding or metal thermocompression bonding.

In the sixteenth step, the exposed upper silicon layer 5 is removed by deep reactive ion etching, or potassium hydroxide, or tetramethyl ammonium hydroxide, or ethylenediamine phosphine, to form a free-moving decoupling beam 22 , the mass block 23 and the resonance beam 24 .

In the seventeenth step, the silicon nitride layer 8 on the top surface of the SOI silicon wafer is removed by reactive ion or plasma dry etching, or hydrofluoric acid.

In the eighteenth step, the exposed upper silicon layer 5 is further etched to a certain depth using deep reactive ion etching, or potassium hydroxide, or tetramethyl ammonium hydroxide, or ethylenediamine phosphine, to form Comb structures 25 of different heights.

In the nineteenth step, the silicon dioxide layer 7 on the top surface of the SOI silicon wafer is removed by reactive ion or plasma dry etching, or hydrofluoric acid.

In the twentieth step, using anodic bonding or metal thermocompression bonding, the top surface of the silicon-on-insulator wafer and the prefabricated upper cover plate 1 are bonded together to form a complete accelerometer structure.

20 to 22, wherein, the processing technology for the lower cover plate 3 in 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 bake. Then, the bottom surface of the lower cover plate 3 is etched to form deep holes.

In the second step, 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 removed. bake. Then, the top surface of the lower cover plate 3 is etched to form a bonding recessed area.

In the third step, metal is deposited in the deep hole on the bottom surface of the lower cover plate 3, and the electrode 4 is drawn out.

In the fourth step, chemical mechanical polishing (CMP) is performed on the top surface of the lower cover plate 3 so that the electrode 4 is connected to the bonding recessed area.

In the fifth step, metal is deposited at the corresponding position in the bonding recessed area on the top surface of the lower cover plate 3 .

6 to 19 , the upper cover plate 1 and the lower cover plate 3 in the present invention can also be made of glass. The advantage of using glass to make a cover plate is that the silicon-glass bonding temperature is low and will not affect the previous metal electrodes and leads. When the upper cover plate 1 and the lower cover plate 3 are made of glass, silicon-glass bonding is used in the fifteenth and twentieth steps of the above manufacturing process, and the silicon-on-insulator wafer is bonded to the silicon-on-insulator wafer. It is bonded with the upper cover 1 and the lower cover 3.

The deep etching and the etching method described in the present invention are one or more of the following methods: dry etching or wet etching, and the dry etching includes: deep reaction of silicon Ion, reactive ion, and gaseous xenon difluoride etch and reactive ion, plasma, and gaseous hydrogen fluoride etch of silicon oxide.

The etchant used for wet etching the upper silicon layer and the lower silicon layer is a combination of one or more of the following etchants: potassium hydroxide, tetramethylammonium hydroxide, or ethylenediamine Hydroquinone etchant.

The etchant for wet etching the silicon dioxide layer is a combination of one or more of the following etchants: hydrofluoric acid and buffered hydrofluoric acid.

The conventional MEMS accelerometer detects the acceleration by detecting the capacitance change between the comb teeth, while the present invention adopts the electrostatic negative stiffness effect and detects the acceleration by detecting the change of the resonant frequency on the resonant beam. Compared with the traditional accelerometer, the present invention effectively solves the mechanical coupling problem in the traditional resonant accelerometer with lever structure, and the method of differentially detecting vibration frequency also makes the detection accuracy higher and the system more stable. The differential detection method also doubles the detection sensitivity of the entire accelerometer. Moreover, the detection frequency is easier to convert into a digital signal, which is more convenient to interface with the computer, and also reduces the influence of the nonlinear change caused by the external acceleration change on the frequency of the resonant beam. . In addition, the present invention adopts a whole mass block, so that the volume of the mass block itself is larger, and on the one hand, the overall detection sensitivity of the accelerometer is increased. On the other hand, the coupling and crosstalk between the various masses are also reduced.

Moreover, since the etching process and the bonding process of silicon are relatively simple, the production efficiency of this product is extremely high and the cost is also low. Therefore, the MEMS accelerometer manufactured by this process has the advantages of high sensitivity, small error and low cost.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, not to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that , the technical solutions of the present invention may be modified or equivalently replaced 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 comprises: a first anchor point, a mass block, a decoupling beam and an acceleration detection structure; the first anchor point and The upper cover plate and the lower cover plate are fixed; the decoupling beam is used to connect the first anchor point and the mass block, and it is characterized in that the acceleration detection structure is axially symmetrically arranged in the mass block , the acceleration detection structure includes: a resonance beam and a driving electrode; two ends of the resonance beam are respectively connected with the second anchor point; comb teeth are formed on both sides of the resonance beam; The comb teeth are superimposed on the driving electrodes; the comb teeth on the other side of the resonant beam are superimposed with the comb teeth on the mass block; the driving electrodes apply an electrical driving signal to the resonating beam, so that the resonating beam vibrates , the acceleration detection structure detects the acceleration by detecting the vibration frequency of the resonant beam; three sets of acceleration detection structure groups are respectively set in the mass block, and each group of acceleration detection structure groups includes at least two acceleration detection structures. The structural groups respectively detect the acceleration of the mass block in three dimensions through a differential method; a concave area is formed on the mass block, and comb teeth are formed on the side wall of the mass block located in the concave area, and the acceleration detection The structure is arranged in the recessed area; the height of the comb teeth of the resonant beam for detecting vertical acceleration is 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 vertical acceleration is the same as the height of the comb teeth on the side wall of the mass block. The ends of the comb teeth on the side walls of the mass are flush with each other. 2 . The accelerometer according to claim 1 , wherein the electric driving signal of the driving electrode comprises: sine wave, square wave, and triangular wave; the frequency of the electric driving signal is between 10 Hz and 10 MHz. 3 . . 3 . The accelerometer according to claim 1 , wherein the decoupling beam comprises a decoupling beam frame and a tuning fork type decoupling beam; the decoupling beam frame is connected to the first anchor point, and the The mass block is connected with the decoupling beam frame through a tuning fork type decoupling beam. 4. a manufacturing process of a MEMS accelerometer, characterized in that: the manufacturing process comprises the following steps: The first step is to use high temperature growth or chemical deposition to form silicon dioxide layers on the top and bottom surfaces of the silicon-on-insulator wafer; In the second step, through photolithography and etching, a groove deep to the upper silicon layer is etched on the silicon dioxide layer on the top surface of the silicon-on-insulator wafer; The third step is to further deposit a silicon nitride layer on the top surface of the silicon-on-insulator wafer by chemical deposition; The fourth step is to etch the silicon nitride layer and the silicon dioxide layer on the top surface of the silicon-on-insulator wafer by photolithography and etching to form a plurality of grooves as deep as the upper silicon layer; The fifth step, through photolithography and etching, the silicon dioxide layer on the bottom surface of the silicon-on-insulator wafer is etched to form a plurality of grooves as deep as the lower silicon layer; The sixth step, further etching the lower silicon layer and the buried oxide layer of the silicon-on-insulator wafer to form a recessed area with a certain depth and a groove as deep as the upper silicon layer; In the seventh step, metal is deposited in the groove deep to the upper silicon layer etched in the sixth step, and the electrode is drawn out; In the eighth step, through photolithography and etching, a pattern as deep as the upper silicon layer is etched at the corresponding position on the bottom surface of the silicon wafer on the insulator to form a mass block, a resonant beam and a comb-tooth structure; The ninth step, removing the silicon dioxide layer on the bottom surface of the silicon wafer on the insulator; The tenth step, anodic bonding the bottom surface of the silicon wafer on the insulator and the lower cover plate; The eleventh step is to etch the top surface of the silicon-on-insulator chip, and remove the exposed upper silicon layer to form a free-moving mass block, a resonant beam and a comb-tooth structure; In the twelfth step, the silicon nitride layer on the top surface of the silicon-on-insulator wafer is removed, and the exposed upper silicon layer is further etched to a certain depth; The thirteenth step, removing the silicon dioxide layer on the top surface of the silicon wafer on the insulator; In the fourteenth step, the top surface of the silicon-on-insulator chip is bonded to the upper cover plate to form a complete accelerometer. 5. The manufacturing process of the MEMS accelerometer according to claim 4, wherein the manufacturing process for the lower cover plate further comprises: In the first step, through photolithography and etching, a plurality of holes are etched on the bottom surface of the lower cover plate; the second step, depositing metal in the hole; In the third step, etching is performed on the top surface of the lower cover plate to form a bonding recessed area; In the fourth step, metal is deposited in the bonding recessed area, and the metal in the bonding recessed area is connected with the metal in the hole. 6 . The manufacturing process of the MEMS accelerometer according to claim 4 , wherein the manufacturing process for the upper cover plate further comprises: forming a bonding recess on the bottom layer of the upper cover plate by photolithography and etching. 7 . Area. 7. The manufacturing process of the MEMS accelerometer according to any one 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 includes: deep reactive ion etching of silicon, gaseous xenon difluoride etching and reactive ion, plasma, and gaseous hydrogen fluoride etching of silicon oxide. 8. The manufacturing process of the MEMS accelerometer according to claim 7, wherein the etchant used for wet etching the upper silicon layer and the lower silicon layer is one or more of the following etchants Combination of species: potassium hydroxide, tetramethylammonium hydroxide, ethylenediamine catechol corrosion solution. 9 . The manufacturing process of the MEMS accelerometer according to claim 7 , wherein the etchant used for wet etching the silicon dioxide layer is hydrofluoric acid. 10 .

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