CN115420907B

CN115420907B - MEMS accelerometer and forming method thereof

Info

Publication number: CN115420907B
Application number: CN202211364537.7A
Authority: CN
Inventors: 李森科·伊戈尔·叶夫根耶维奇; 徐宝; 徐元; 吴刚
Original assignee: Hangzhou Maixinmin Micro Technology Co ltd
Current assignee: Hangzhou Maixinmin Micro Technology Co ltd
Priority date: 2022-11-02
Filing date: 2022-11-02
Publication date: 2023-03-21
Anticipated expiration: 2042-11-02
Also published as: CN115420907A

Abstract

The invention relates to a MEMS accelerometer and a forming method thereof, comprising the following steps: a substrate; a proof mass suspended on the substrate and including a first proof mass portion and a second proof mass portion, the first proof mass portion having a weight greater than that of the second proof mass portion; sensing electrodes including a first moving sensing electrode, a second moving sensing electrode, a first stationary sensing electrode, and a second stationary sensing electrode; and the driving electrodes comprise a first moving driving electrode, a second moving driving electrode, a first fixed driving electrode and a second fixed driving electrode. According to the technical scheme, the Z-axis linear acceleration can be measured by using the compensation type MEMS accelerometer only by using one substrate, the equivalent function which can be achieved by at least two substrates in the related technology is achieved, different directions of the Z-axis linear acceleration can be determined, and the measurement precision is improved.

Description

MEMS accelerometer and forming method thereof

Technical Field

The invention relates to the technical field of micro-electro-mechanical systems, in particular to a micro-electro-mechanical system (MEMS) accelerometer and a forming method thereof.

Background

An inertial sensor is a device that is capable of sensing and/or generating motion. An inertial sensor is a device that includes a microelectromechanical system. Such MEMS devices include accelerometers capable of sensing acceleration. Accelerometers are one of the primary devices of inertial navigation and guidance systems. Compared with conventional mechanical and optical sensors, MEMS sensors are low cost, small, low power consuming, and can be integrated with and use the same manufacturing operations as integrated circuits.

MEMS sensors are widely used in consumer electronics, industrial manufacturing, medical electronics, automotive electronics, aerospace, and military, among other fields. MEMS sensors have great potential for development and commercial value. The operating principle of MEMS accelerometers is the inertial effect. When the object moves, the suspended microstructure is influenced by inertia force, and the change of an accelerometer signal is in direct proportion to linear acceleration. MEMS accelerometers are mainly classified into capacitive, piezoresistive, piezoelectric, and optical types according to the detection method. Meanwhile, the capacitive detection method used in the MEMS accelerometer is widely applied in industry mainly because of the simple structure and the compatibility of the working mode and the semiconductor technology. The MEMS chip may be manufactured by a semiconductor manufacturing method and may contain a single or a plurality of devices as described above. The acceleration can be measured in a number of ways using capacitive methods. One of the methods is to use a differential capacitor formed by two capacitors and to arrange them in such a way that when subjected to acceleration, the capacitance value of one of the capacitors increases while the capacitance value of the other decreases, which allows increasing the variation value of the capacitance and improving the measurement accuracy.

MEMS accelerometers fall into two types: one of the accelerometers is a direct conversion type accelerometer, and the magnitude of the acceleration is determined according to the displacement of an inertial mass from an initial position under the action of inertial force; the other is a compensation type accelerometer, the magnitude of the acceleration depends on the magnitude of the voltage applied to keep the inertial mass in the initial position; compensated accelerometers have higher sensitivity and accuracy than direct conversion accelerometers.

However, the design and manufacture of the compensated MEMS accelerometer have some technical difficulties, and such an accelerometer must have a differential capacitance in its design for measurement accuracy, and an electrostatic driving electrode for holding the inertial mass at an initial position, requires the use of an additional substrate and the application of the electrode thereto, and also requires the operation of connecting the substrate to be performed, which results in a significant increase in the cost and difficulty of manufacturing such a structure.

Disclosure of Invention

The invention aims to provide the MEMS accelerometer, which reduces the manufacturing process cost, can determine different directions of Z-axis linear acceleration, improves the measurement precision and has better applicability.

In order to realize the purpose, the invention adopts the following technical scheme:

a MEMS accelerometer, comprising:

a substrate;

a proof mass suspended above the substrate, the proof mass including a first proof mass portion and a second proof mass portion, the first proof mass portion having a weight greater than a weight of the second proof mass portion;

sensing electrodes including a first moving sensing electrode, a second moving sensing electrode, a first fixed sensing electrode and a second fixed sensing electrode, the first moving sensing electrode being disposed on a lower surface of the first proof mass portion, the second moving sensing electrode being disposed on a lower surface of the second proof mass portion, the first fixed sensing electrode and the second fixed sensing electrode both being fixedly disposed on the substrate, the first fixed sensing electrode being located below the first moving sensing electrode, the second fixed sensing electrode being located below the second moving sensing electrode;

the driving electrodes comprise a first moving driving electrode, a second moving driving electrode, a first fixed driving electrode and a second fixed driving electrode; the first movable driving electrode is arranged on the lower surface of the first detection mass part and is arranged at an interval with the first movable sensing electrode; the second movable driving electrode is arranged on the lower surface of the second proof mass part and is arranged at an interval with the second movable sensing electrode; the first fixed driving electrode and the second fixed driving electrode are fixedly arranged on the substrate, the first fixed driving electrode is positioned below the first movable driving electrode, and the second fixed driving electrode is positioned below the second movable driving electrode.

Preferably, the first proof-mass has a horizontal cross-sectional area equal to a horizontal cross-sectional area of the second proof-mass, the MEMS accelerometer further comprising a first fixed component located between the first and second proof-masses.

Preferably, the first proof-mass portion has a horizontal cross-sectional area greater than a horizontal cross-sectional area of the second proof-mass portion, the MEMS accelerometer further comprising a first fixed component located between the first and second proof-mass portions.

Preferably, the first fixing assembly includes two torsion bars each located between the first and second proof mass portions, and a first fixing anchor fixedly disposed on the substrate, the first and second movement sensing electrodes being connected to the first fixing anchor by corresponding ones of the torsion bars, respectively.

Preferably, the second proof mass portion has a plurality of notches formed therethrough in a thickness direction thereof.

Preferably, the MEMS accelerometer further includes a second fixing component, the second fixing component includes two elastic suspensions and two second fixing anchors fixedly disposed on the substrate, and the first moving driving electrode and the second moving driving electrode are respectively elastically connected to the second fixing anchors through the corresponding elastic suspensions.

Preferably, the proof mass has a plurality of through holes formed therethrough in a thickness direction thereof.

The invention also provides a method for forming the MEMS accelerometer, which comprises the following steps:

depositing a polycrystalline silicon film on a substrate, obtaining a first structural layer with a first fixed sensing electrode, a second fixed sensing electrode, a first fixed driving electrode and a second fixed driving electrode after photoetching and etching drawing, depositing a phosphorosilicate glass layer on the first structural layer, annealing, and etching an anchor hole to obtain a first sacrificial layer;

depositing a polycrystalline silicon thin film and a phosphorosilicate glass layer on the first sacrificial layer, annealing, photoetching, etching and drawing to obtain a second structure layer with a first movable sensing electrode, a second movable sensing electrode, a first movable driving electrode and a second movable driving electrode, depositing the phosphorosilicate glass layer on the second structure layer, annealing, and etching the anchor hole to obtain a second sacrificial layer;

applying a dielectric layer on the second sacrificial layer to obtain a proof mass.

Preferably, before obtaining the first structural layer, the method further comprises: depositing a silicon nitride layer on the substrate; after obtaining the proof mass, the method further comprises: and removing the first sacrificial layer and the second sacrificial layer.

Compared with the prior art, the invention has the beneficial effects that:

according to the MEMS accelerometer provided by the technical scheme, the proof mass block deflects up and down through unequal weights of the first proof mass part and the second proof mass part, so that the movable sensing electrode and the fixed sensing electrode form a differential capacitor, the movable driving electrode and the fixed driving electrode form electrostatic driving compensation to control the proof mass block to be fixed at the initial position, and the Z-axis linear acceleration is measured according to an applied voltage value, the measurement mode greatly improves the measurement precision, the compensation type MEMS accelerometer can be used for measuring the Z-axis linear acceleration only by one substrate, the equivalent function which can be achieved by at least two substrates in the related technology is realized, the structure of the MEMS accelerometer is simplified, and the manufacturing process cost is reduced; meanwhile, due to the fact that voltage is applied to the first fixed driving electrode or the second fixed driving electrode, different directions of the action of the Z-axis linear acceleration are determined, and the acceleration phase acting on the MEMS accelerometer is accurately determined; in addition, the movable sensing electrode and the movable driving electrode are arranged at intervals, so that mutual influence is reduced, noise is reduced, and the measurement accuracy of the Z-axis linear acceleration is improved.

Drawings

FIG. 1 is a schematic diagram of a MEMS accelerometer according to an embodiment of the invention.

Fig. 2 isbase:Sub>A schematic cross-sectional view taken along linebase:Sub>A-base:Sub>A of fig. 1.

Fig. 3 is a schematic cross-sectional view taken along line B-B in fig. 1.

FIG. 4 is a schematic diagram of a MEMS accelerometer reflecting the direction of a sensing signal under the action of acceleration according to an embodiment of the invention.

FIG. 5 is a schematic view of a MEMS accelerometer according to another embodiment of the present invention.

FIG. 6 is a schematic view of a MEMS accelerometer according to another embodiment of the present invention.

Fig. 7 is a schematic view of a first structural layer and a substrate.

Fig. 8 is a schematic diagram of the first structural layer, the first sacrificial layer and the substrate.

Fig. 9 is a schematic view of a first structural layer, a first sacrificial layer, a second structural layer and a substrate.

Fig. 10 is a schematic view of a first structural layer, a first sacrificial layer, a second structural layer, a second sacrificial layer and a substrate.

FIG. 11 is a schematic diagram of a first structural layer, a first sacrificial layer, a second structural layer, a second sacrificial layer, a proof mass, and a substrate.

Description of reference numerals:

1. a substrate; 2. a proof mass; 21. a first proof mass portion; 22. a second proof mass section; 23. a notch; 24. a through hole; 31. a first movement sensing electrode; 32. a second movement sensing electrode; 41. a first fixed sensing electrode; 42. a second stationary sensing electrode; 51. a first moving drive electrode; 52. a second moving drive electrode; 61. a first fixed drive electrode; 62. a second fixed drive electrode; 71. a torsion bar; 72. a first anchor; 81. an elastic suspension; 82. a second anchor; 100. a first structural layer; 110. a first sacrificial layer; 200. a second structural layer; 210. a second sacrificial layer; 300. and (6) anchoring holes.

Detailed Description

The technical solutions of the present invention will be described clearly and completely with reference to the accompanying drawings, and it is to be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.

In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.

The embodiment of the invention provides the MEMS accelerometer, which not only realizes the purpose of measuring the Z-axis linear acceleration by using the compensation type MEMS accelerometer, but also reduces the manufacturing process cost, can determine different directions of the Z-axis linear acceleration, and improves the measurement precision.

Referring to fig. 1-4, in one embodiment, a MEMS accelerometer includes:

a substrate 1;

a proof mass 2 suspended on the substrate 1, including a first proof mass portion 21 and a second proof mass portion 22, the first proof mass portion 21 having a weight larger than that of the second proof mass portion 22;

sensing electrodes including a first moving sensing electrode 31, a second moving sensing electrode 32, a first fixed sensing electrode 41 and a second fixed sensing electrode 42, the first moving sensing electrode 31 being fixedly disposed on a lower surface of the first proof mass portion 21, the second moving sensing electrode 32 being fixedly disposed on a lower surface of the second proof mass portion 22, the first fixed sensing electrode 41 and the second fixed sensing electrode 42 being fixedly disposed on the substrate 1, the first fixed sensing electrode 41 being located below the first moving sensing electrode 31, the second fixed sensing electrode 42 being located below the second moving sensing electrode 32;

driving electrodes including a first moving driving electrode 51, a second moving driving electrode 52, a first fixed driving electrode 61, and a second fixed driving electrode 62; the first moving driving electrode 51 is disposed on the lower surface of the first proof mass portion 21, and is spaced apart from the first moving sensing electrode 31; the second moving driving electrode 52 is disposed on the lower surface of the second proof mass portion 22, and is spaced apart from the second moving sensing electrode 32; a first fixed driving electrode 61 and a second fixed driving electrode 62 are both fixedly disposed on the substrate 1, the first fixed driving electrode 61 is located below the first moving driving electrode 51, and the second fixed driving electrode 62 is located below the second moving driving electrode 52.

It is noted that the substrate 1 may comprise any suitable substrate 1 material known in the art, for example a semiconductor material comprising silicon or any other semiconductor material, or a non-semiconductor material such as glass, plastic, metal or ceramic. The substrate 1 may also include integrated circuits fabricated thereon, if desired. Proof mass 2 may comprise any suitable material known in the art, such as a dielectric material comprising phosphosilicate glass, polyimide, or any other dielectric material, and may have the same or different thickness of about several microns to 100 microns, such as about 5 microns to 20 microns. The first moving sensing electrode 31, the second moving sensing electrode 32, the first moving driving electrode 51, the second moving driving electrode 52, the first stationary sensing electrode 41, the second stationary sensing electrode 42, the first stationary driving electrode 61, and the second stationary driving electrode 62 may be any suitable material known in the art, for example, polysilicon or any other semiconductor material, and may have the same or different thickness of about several micrometers to 100 micrometers, for example, about 2 to 10 micrometers.

The gaps between the first moving sensing electrode 31 and the first stationary sensing electrode 41, and the second moving sensing electrode 32 and the second stationary sensing electrode 42 are independently selected from between about several micrometers to 10 micrometers. The gaps between the first moving driving electrode 51 and the first fixed driving electrode 61, and the second moving driving electrode 52 and the second fixed driving electrode 62 are independently selected from about several micrometers to 10 micrometers.

As shown in fig. 4, one non-limiting MEMS accelerometer of the present invention operates on the following principle: defining the direction vertical to the upper surface of the substrate 1 as a Z-axis direction, the direction close to the upper surface of the substrate 1 as a negative direction, and the direction far away from the surface of the substrate 1 as a positive direction; the X-axis direction is along the horizontal direction, and the Y-axis direction is along the vertical direction.

If linear acceleration is applied to the MEMS accelerometer in the negative Z-axis direction, the proof mass 2 is deflected relative to the Y-axis due to the proof mass 2 being suspended from the substrate 1 and the first proof mass portion 21 having a greater weight than the second proof mass portion 22. In this case, the inertial force moves the first proof mass part 21 upward and the second proof mass part 22 downward, thereby changing the gap between the first moving sensing electrode 31 and the first fixed sensing electrode 41 (increasing the gap) and changing the gap between the second moving sensing electrode 32 and the second fixed sensing electrode 42 (decreasing the gap), thereby changing the value of the differential capacitance.

To hold proof mass 2 in its initial position, a voltage is applied across first fixed drive electrode 61 (the voltage of first fixed drive electrode 61 relative to first moving drive electrode 51) until the change in differential capacitance value is zero. The magnitude of the voltage applied to the first fixed driving electrode 61 is proportional to the magnitude of the acceleration acting in the negative direction of the Z-axis.

If linear acceleration is applied to the MEMS accelerometer in the positive Z-axis direction, the proof mass 2 is deflected relative to the Y-axis due to the proof mass 2 being suspended from the substrate 1 and the first proof mass portion 21 having a greater weight than the second proof mass portion 22. In this case, the inertial force moves the first proof mass part 21 downward and the second proof mass part 22 upward, thereby changing the gap between the first moving sensing electrode 31 and the first fixed sensing electrode 41 (decreasing the gap) and changing the gap between the second moving sensing electrode 32 and the second fixed sensing electrode 42 (increasing the gap), thereby changing the value of the differential capacitance.

To hold proof mass 2 in its initial position, a voltage is applied across second fixed drive electrodes 62 (the voltage of second fixed drive electrodes 62 relative to second moving drive electrodes 52) until the change in differential capacitance value is zero. The magnitude of the voltage applied to the second fixed drive electrode 62 is proportional to the magnitude of the acceleration in the positive direction of the Z-axis. Therefore, the application of a voltage to the first fixed driving electrode 61 or the second fixed driving electrode 62 determines the direction in which the acceleration acts, i.e., the phase thereof.

As can be seen from the above, in the case of only one substrate 1, the proof mass 2 with asymmetric weight is arranged, that is, the weights of the first proof mass part 21 and the second proof mass part 22 are not equal, under the action of the Z-axis linear acceleration, the proof mass 2 moves up and down along the torsion axis, so that the movable sensing electrode and the fixed sensing electrode form a differential capacitor, and the movable driving electrode and the fixed driving electrode form electrostatic driving compensation to control the proof mass 2 to be immobile at the initial position, and the Z-axis linear acceleration is measured according to the applied voltage value, which greatly improves the measurement accuracy, and does not need to additionally arrange an additional substrate 1, so that the compensation type MEMS accelerometer can be used to measure the Z-axis linear acceleration, and the equivalent function that can be achieved by at least two substrates 1 in the related technology can be realized, thereby simplifying the structure of the MEMS accelerometer and reducing the manufacturing process cost; meanwhile, because voltage is applied to the first fixed driving electrode 61 or the second fixed driving electrode 62, different directions of the action of the Z-axis linear acceleration are determined, and the phase of the acceleration acting on the MEMS accelerometer is accurately determined; in addition, the movable sensing electrode and the movable driving electrode are arranged at intervals and are not connected with each other, namely, are not electrically connected with each other, so that the influence of each other is reduced, the noise can be reduced, and the measurement precision of the Z-axis linear acceleration can be improved.

Specifically, as shown in fig. 1, the horizontal cross-sectional area of the first proof mass portion 21 is equal to the horizontal cross-sectional area of the second proof mass portion 22, wherein the second proof mass portion 22 has a plurality of notches 23 formed therethrough in the thickness direction thereof, so that the weight of the first proof mass portion 21 is greater than the weight of the second proof mass portion 22, and it is possible to ensure that the proof mass 2 rotates along the torsion axis at the central position under acceleration, so that the first and second

proof mass portions

21 and 22 move up and down.

In order to suspend the movement sensing electrode on the substrate 1, the MEMS accelerometer further includes a first fixing assembly located between the first proof mass portion 21 and the second proof mass portion 22, the first fixing assembly includes two torsion bars 71 and a first fixing anchor 72 fixedly disposed on the substrate 1, the two torsion bars 71 are disposed at the center of the proof mass 2, each torsion bar 71 is located between the first proof mass portion 21 and the second proof mass portion 22, the first movement sensing electrode 31 and the second movement sensing electrode 32 are connected to the first fixing anchor 72 by corresponding to the torsion bar 71, respectively, such that the first movement sensing electrode 31 and the second movement sensing electrode 32 are suspended above the substrate 1.

In order to suspend the movable driving electrode on the substrate 1, the MEMS accelerometer further includes a second fixed component, the second fixed component includes two elastic suspensions 81 and two second fixed anchors 82 fixedly disposed on the substrate 1, and the first movable driving electrode 51 and the second movable driving electrode 52 are respectively elastically connected to the second fixed anchors 82 through corresponding elastic suspensions 81, so that the first movable driving electrode 51 and the second movable driving electrode 52 are elastically suspended above the substrate 1.

It should be noted that, since the weight of the first proof mass portion 21 is greater than that of the second proof mass portion 22, the left elastic suspension 81 supports the first proof mass portion 21 through the first moving drive electrode 51, and the right elastic suspension 81 supports the second proof mass portion 22 through the second moving drive electrode 52, it is necessary to set the two elastic suspensions 81 on both sides of the proof mass 2 to have different rigidities so as to ensure that the initial positions of the first proof mass portion 21 and the second proof mass portion 22 are maintained in the absence of acceleration, and further ensure that the initial gaps of the first moving sense electrode 31 and the first fixed sense electrode 41 are equal, the initial gaps of the second moving sense electrode 32 and the second fixed sense electrode 42 are equal, the initial gaps of the first moving drive electrode 51 and the first fixed drive electrode 61 are equal, and the initial gaps of the second moving drive electrode 52 and the second fixed drive electrode 62 are equal, thereby further improving the acceleration measurement accuracy of the Z axis.

It will be appreciated that upon application of linear acceleration to the MEMS accelerometer along the Z axis, the torsion bar 71 rotates about its longitudinal axis and the two resilient suspensions 81 deform under the force of inertia, causing the proof mass 2 to deflect from an initial position, the inertial force causing the first and

second proof masses

21, 22 to move in opposite directions, thereby changing the gap between the first moving sense electrode 31 and the first fixed sense electrode 41, and the gap between the second moving sense electrode 32 and the second fixed sense electrode 42, and hence the value of the differential capacitance.

As shown in fig. 2-3, first and second tie-down anchors 72, 82 are comprised of two structural layers; the first moving sensing electrode 31, the second moving sensing electrode 32, the torsion bar 71, the first moving driving electrode 51, the second moving driving electrode 52, the elastic suspension 81, the first fixed sensing electrode 41, the second fixed sensing electrode 42, the first fixed driving electrode 61, and the second fixed driving electrode 62 are formed of one structural layer.

In a preferred embodiment, the proof mass 2 is formed with a plurality of through holes 24 extending therethrough in the thickness direction thereof, so that the damping force along the Z-axis is reduced.

In another embodiment, as shown in figure 5, the main difference is that the proof mass 2 does not have through holes 24, and the damping force along the Z-axis increases, requiring the MEMS accelerometer to be packaged in a vacuum.

In yet another embodiment, as shown in FIG. 6, the primary difference is that the second proof mass 22 does not have a notch 23 and is solid. The two torsion bars 71 are located at the position where the proof mass 2 deviates from the center line, and the horizontal sectional area of the first proof mass portion 21 is larger than the horizontal sectional area of the second proof mass portion 22, so that the weight of the first proof mass portion 21 is larger than the weight of the second proof mass portion 22, and it can be ensured that the proof mass 2 rotates along the torsion axis deviating from the center position under the action of acceleration, so that the first proof mass portion 21 and the second proof mass portion 22 move up and down. The MEMS accelerometer also includes a first fixed component located between the first proof mass 21 and the second proof mass 22.

Referring to fig. 7-11, a method for forming the MEMS accelerometer is further provided in an embodiment of the present invention, including the following steps:

s1: depositing a silicon nitride layer on the substrate 1; in particular, in order to reduce the influence of the electric field generated by other MEMS electrostatic and microelectronic devices on the substrate 1, doping techniques such as doping with phosphorus may be used, and if an n-type silicon substrate 1 is used, a phosphosilicate Glass (PSG) layer is used as a doping source in a standard diffusion furnace. After removing the PSG layer, a 0.6 μm Low-stress silicon nitride layer was deposited as an electrical isolation layer on the substrate 1 by Low Pressure Chemical Vapor Deposition (LPCVD).

S2: as shown in fig. 7, a polysilicon thin film is deposited on a substrate 1 by Low Pressure Chemical Vapor Deposition (LPCVD), patterned by photolithography, which includes coating a wafer with photoresist, exposing the photoresist with an appropriate mask, developing the exposed photoresist to create a desired etch mask for subsequent transfer of the pattern into an underlying layer, and etching in a plasma etching system after patterning the photoresist to obtain a first structural layer 100 having a first anchor 72, a second anchor 82, a first fixed sense electrode 41, a second fixed sense electrode 42, a first fixed drive electrode 61, and a second fixed drive electrode 62.

S3: as shown in fig. 8, a phosphosilicate glass layer is deposited on the first structural layer 100 by a Low Pressure Chemical Vapor Deposition (LPCVD) method, annealed at 1050 ℃ for 1 hour in argon, and etched by Reactive Ion Etching (RIE) after photolithography and patterning are applied to obtain a first sacrificial layer 110, in which a first anchor 72, a second anchor 82, and the like may be disposed in the anchor hole 300.

S4: as shown in fig. 9, a polysilicon film is deposited on the first sacrificial layer 110, a phosphosilicate glass (PSG) layer with a thickness of 200 nm is deposited on the polysilicon film, the polysilicon film is doped with phosphorus from above and below the PSG layer by annealing at 1050 ℃ for 1 hour, the annealing is also used for significantly reducing the net stress of the polysilicon film, the polysilicon film and the phosphosilicate glass layer are subjected to photolithography patterning by using a designed mask to obtain a second structural layer 200, and the PSG layer is etched to generate a hard mask for subsequently etching the polysilicon film. The hard mask is more resistant to chemical etching of the polysilicon than the photoresist and ensures better pattern transfer into the polysilicon. After etching the polysilicon film, the photoresist is stripped and the remaining oxide hard mask is removed by RIE. The second structural layer 200 has a first fixed anchor 72, a second fixed anchor 82, an elastic suspension 81, a first moving sensing electrode 31, a second moving sensing electrode 32, a first moving driving electrode 51, and a second moving driving electrode 52.

S5: as shown in fig. 10, a phosphosilicate glass layer is deposited on the second structural layer 200 and annealed, and a Reactive Ion Etch (RIE) of anchor holes 300 is performed after applying a photolithographic mapping, resulting in a second sacrificial layer 210, the process providing anchor holes 300 for filling proof-mass 2.

S6: as shown in fig. 11, a dielectric layer is applied on the second sacrificial layer 210 to obtain the proof mass 2. The dielectric layer Si3N4 is deposited in a glow discharge at 300 ℃. Next, photoresist is applied to form the proof mass 2, and after etching the Si3N4 layer, the photoresist is removed.

S7: removing the first sacrificial layer 110 and the second sacrificial layer 210 to release the structural layer of the MEMS accelerometer, the method of removing the first sacrificial layer 110 and the second sacrificial layer 210 is as follows: this is achieved by immersing the substrate 1 in a 49% hydrofluoric acid (HF) bath at 25 ℃ for 2 minutes. Then placed in distilled water and alcohol for 2 minutes, respectively, to reduce blocking, and placed in an oven at 110 ℃ for at least 10 minutes.

The method provided by the invention ensures that the MEMS accelerometer for measuring Z-axis linear acceleration in a compensation mode is manufactured in one process flow, an additional substrate 1 with an additional electrode is not needed, the operation of subsequently connecting the substrate 1 is reduced, the cost of the production process is simplified and reduced, and the cost of the MEMS accelerometer manufactured according to the invention is obviously lower than the manufacturing cost of a traditional system due to the reduction of the times of technical operation. In addition, the manufacturing method of the semiconductor can also be adopted in the manufacturing of the MEMS accelerometer, so that the manufacturing cost of the MEMS accelerometer is further reduced.

The above embodiments are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited thereby, and any insubstantial changes and substitutions made by those skilled in the art based on the present invention are within the protection scope of the present invention.

Claims

1. A MEMS accelerometer, comprising:

a substrate;

the driving electrodes comprise a first moving driving electrode, a second moving driving electrode, a first fixed driving electrode and a second fixed driving electrode; the first movable driving electrode is arranged on the lower surface of the first detection mass part, is arranged at an interval with the first movable sensing electrode and is not connected with the first movable sensing electrode; the second movable driving electrode is arranged on the lower surface of the second proof mass part, is arranged at intervals with the second movable sensing electrode and is not connected with the second movable sensing electrode; the first fixed driving electrode and the second fixed driving electrode are fixedly arranged on the substrate, the first fixed driving electrode is positioned below the first movable driving electrode, and the second fixed driving electrode is positioned below the second movable driving electrode;

the MEMS accelerometer further comprises a first fixed component located between the first proof-mass and the second proof-mass;

the MEMS accelerometer also comprises a second fixed component, the second fixed component comprises two elastic suspensions and two second fixed anchors fixedly arranged on the substrate, and the first movable driving electrode and the second movable driving electrode are respectively and elastically connected with the second fixed anchors through the corresponding elastic suspensions; the two elastic suspensions have different rigidities so that the initial gap between the first moving sensing electrode and the first fixed sensing electrode, the initial gap between the second moving sensing electrode and the second fixed sensing electrode, the initial gap between the first moving driving electrode and the first fixed driving electrode, and the initial gap between the second moving driving electrode and the second fixed driving electrode are equal;

the second fixing anchor consists of two structural layers, and the elastic suspension consists of one structural layer; and the first structural layer comprises a part of the second fixed anchor, the first fixed sensing electrode, the second fixed sensing electrode, the first fixed driving electrode and the second fixed driving electrode, and the second structural layer comprises another part of the second fixed anchor, the elastic suspension, the first movable sensing electrode, the second movable sensing electrode, the first movable driving electrode and the second movable driving electrode.

2. The MEMS accelerometer of claim 1, wherein a horizontal cross-sectional area of the first proof mass is equal to a horizontal cross-sectional area of the second proof mass.

3. The MEMS accelerometer of claim 1, wherein the first proof mass has a horizontal cross-sectional area greater than a horizontal cross-sectional area of the second proof mass.

4. The MEMS accelerometer of claim 2 or 3, wherein the first fixing assembly comprises two torsion bars, each located between the first proof mass portion and the second proof mass portion, and a first fixing anchor fixedly disposed on the substrate, the first and second movement sensing electrodes being connected to the first fixing anchor by corresponding torsion bars, respectively.

5. The MEMS accelerometer of claim 2, wherein the second proof mass has a plurality of notches formed therethrough along a thickness thereof.

6. The MEMS accelerometer of claim 1, wherein two of said elastic suspensions are respectively located on both sides of said proof mass, and said first moving driving electrode is located near the elastic suspension on the same side with respect to said first moving sensing electrode, and said second moving driving electrode is located near the elastic suspension on the same side with respect to said second moving sensing electrode.

7. The MEMS accelerometer of any of claims 1-3, wherein the proof mass has a plurality of through holes formed therethrough along a thickness thereof.

8. A method for forming the MEMS accelerometer of claim 1, comprising the steps of:

9. The method for forming a MEMS accelerometer according to claim 8, wherein prior to obtaining the first structural layer, the method further comprises: depositing a silicon nitride layer on the substrate; after obtaining the proof mass, the method further comprises: and removing the first sacrificial layer and the second sacrificial layer.