Capacitive MEMS six-dimensional force sensor chip with structure decoupling and preparation process thereof

Abstract

The invention discloses a structure-decoupled capacitive MEMS six-dimensional force sensor chip and a preparation process thereof, the structure-decoupled capacitive MEMS six-dimensional force sensor chip comprises a top pole plate, a first outer frame and a bottom pole plate, and the first outer frame is located at the outer side of the top pole plate; the top pole plate comprises an upper electrode and silicon columns, and the silicon columns are distributed in the middle of the upper electrode; the bottom pole plate comprises a base body, a lower electrode, anchor points and a bonding pad, the anchor points are distributed in the middle of the lower electrode, and the positions of the anchor points correspond to the positions of the silicon columns. The device has the advantages of full-dimensional physical structure decoupling, small size, high sensitivity, small temperature influence and easiness in manufacturing, and is suitable for severe working environments, such as mechanical hand fingertips, micro medical robots and the like, with small mounting and working spaces and sharp temperature and humidity changes.

Description

Technical Field

[0001] The present invention relates to the technical field of capacitive MEMS six-dimensional force sensor chips, and in particular to a structurally decoupled capacitive MEMS six-dimensional force sensor chip and a preparation process thereof. Background Art

[0002] The six-dimensional force sensor can measure the force signals in the three directions of X, Y, and Z and the torque signals in the three directions of Mx, My, and Mz in space. At present, the MEMS six-dimensional force sensors promoted and produced by six-dimensional force manufacturers at home and abroad are mostly silicon-based strain gauges produced by MEMS technology instead of metal foil strain gauges. The entire sensor body is still a large metal body, which cannot make the six-dimensional force sensor miniaturized and chip-based, and it is not easy to mass produce, and the cost is high. However, the six-dimensional force sensor produced entirely based on the MEMS process can easily realize the miniaturization and mass production of the six-dimensional force sensor. Miniaturized MEMS six-dimensional force sensors have broad application prospects in aerospace, electronic scales, industrial control, robots, medical devices and other fields. For example, in the field of robots, it can accurately sense the force of the robot's fingers and realize fine operation control; in the field of medical devices, it can be installed in interventional surgical instruments and training equipment to provide scientific data support for doctor training and surgical treatment; in the field of aerospace, it can provide key mechanical parameters for attitude control and structural monitoring of micro-aircraft.

[0003] Six-axis force sensors based on MEMS technology are classified according to their working principles, mainly into two categories: piezoresistive and capacitive. MEMS piezoresistive sensors are made by ion implantation on a specific crystal plane to make piezoresistors, metal film deposition to make wires and connect resistors in a specific way to form a Wheatstone bridge. When the sensor is subjected to external force or torque, the resistance value changes, and the strain signal at the piezoresistors is converted into an electrical signal through the Wheatstone bridge to achieve force and torque measurement. The decoupling detection of six-axis force of piezoresistive six-axis force sensors is relatively simple, but the silicon piezoresistive manufacturing process is required to be high and is greatly affected by temperature. The working principle of MEMS capacitive sensors is that when the sensor is subjected to external force or torque, the capacitor plates on the sensor will produce relative displacement, causing the distance or overlapping area between the capacitor plates to change, thereby causing the capacitance value to change, and achieving force and torque measurement. Capacitive mems six-axis force sensors have the advantages of simple structure, easy process implementation, good dynamic response, and good temperature performance. At present, few capacitive six-axis force sensors based on MEMS technology at home and abroad can detect forces of Newtons or tens of Newtons, and most of them have the problem of large inter-axis crosstalk. Summary of the invention

[0004] The object of the present invention is to provide a structurally decoupled capacitive MEMS six-dimensional force sensor chip and a preparation process thereof, so as to solve the problems in the prior art.

[0005] To achieve the above object, the present invention provides the following technical solution: a structurally decoupled capacitive MEMS six-dimensional force sensor chip, comprising a top plate, a first outer frame and a bottom plate, wherein the first outer frame is located outside the top plate;

[0006] The top plate includes an upper electrode and a silicon column, and the silicon column is distributed in the middle of the upper electrode;

[0007] The bottom electrode plate includes a substrate, a lower electrode, an anchor point and a pad. The anchor point is distributed in the middle of the lower electrode, and the position of the anchor point corresponds to the position of the silicon column.

[0008] Preferably, the upper electrode comprises a triangular flat plate upper electrode, a rectangular flat plate upper electrode and a comb-teeth-shaped flat plate upper electrode group, and the silicon pillars are evenly distributed on the triangular flat plate upper electrode.

[0009] Preferably, the lower electrode comprises a triangular flat plate lower electrode, a comb-tooth-shaped flat plate lower electrode group and a rectangular flat plate lower electrode, and the anchor points are evenly distributed at the triangular flat plate lower electrode.

[0010] Preferably, the rectangular flat plate upper electrode and the rectangular flat plate lower electrode overlap by two-thirds of their area, and the comb-teeth-shaped flat plate upper electrode group and the comb-teeth-shaped flat plate lower electrode group overlap by two-thirds of their area.

[0011] Preferably, the area of ​​the upper electrode of the triangular plate is slightly smaller than the area of ​​the lower electrode of the triangular plate.

[0012] Preferably, the four rectangular flat plate upper electrodes are respectively located between two comb-tooth-shaped flat plate upper electrode groups on four sides, and the four rectangular flat plate lower electrodes are respectively located between two comb-tooth-shaped flat plate lower electrode groups on four sides.

[0013] A preparation process of a structurally decoupled capacitive MEMS six-dimensional force sensor chip includes a bottom plate preparation process, a top silicon plate preparation process, gold-gold bonding and a slicing process.

[0014] Preferably, the bottom plate preparation process specifically includes the following steps:

[0015] S11, select a single crystal silicon wafer with an N-type (1 0 0) crystal plane and a thickness of 400 μm;

[0016] S12, placing the silicon wafer in a thermal oxidation furnace for thermal oxidation, forming a SiO2 film with a thickness greater than 200 nm on the surface of the silicon wafer;

[0017] S13, coating one side of the thermally oxidized silicon wafer with a CrAu metal layer by magnetron sputtering, with a Cr layer thickness of 50 nm and an Au layer thickness of 300-500 nm;

[0018] S14. Apply photoresist as a mask on the metal layer, etch the metal layer through a dry etching process, prepare alignment marks, pads, leads and lower electrode patterns, and retain the metal layer in the anchor bonding area.

[0019] Preferably, the top silicon plate preparation process comprises the following steps:

[0020] S21, selecting a low-resistance single-crystal silicon wafer with a thickness of 400 um and a resistivity of less than 0.005 Ω·cm;

[0021] S22, using photoresist as a mask on any one side of the silicon wafer, and dry etching an alignment mark, this side is called the top plate front side;

[0022] S23, using photoresist as a mask on the back of the top plate, etching a groove with a depth of 4 μm through a dry silicon etching process, leaving only the silicon in the anchor bonding area;

[0023] S24, plating a CrAu metal layer on the back of the top plate by magnetron sputtering or evaporation;

[0024] S25, using photoresist as a mask, etching the CrAu metal layer through a dry etching process, leaving only the metal of the upper electrode and the anchor bonding area; the silicon below the metal etching area is also etched away by 3-4um to prepare the entire upper electrode contour opposite to the lower electrode;

[0025] S26. Using photoresist as a mask, silicon pillars are prepared through a deep silicon etching process. It is necessary to precisely control the etching parameters in order to achieve the required etching depth and prevent over-etching.

[0026] Preferably, the gold-gold bonding and dicing process specifically includes the following steps:

[0027] S31, after the bottom plate and the top plate are prepared, gold-gold hot pressing bonding is performed at a temperature of 380°C, and the alignment marks described in S14 and S22 are used for alignment, so that the bottom plate and the top plate are bonded into an integral wafer;

[0028] S32, after the bonding is completed, use the photoresist as a mask to perform deep silicon etching on the front side of the top plate and etch through it, completing the separation preparation of the upper electrode plate structure and the outer frame and the preparation of the entire sensor chip;

[0029] S33, using the dicing mark prepared in S22 as an alignment mark, dicing the bonded whole wafer, so that the sensor chip is divided into several independent units on the wafer and the pads are exposed.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1. The sensor chip is matched with the conditioning circuit and can measure the three-directional forces Fx, Fy, Fz and the three-directional moments Mx, My, Mz respectively through time division multiplexing technology. The sensor consists of two layers of plates, with a total of 16 plate capacitors between the plates. The six-dimensional force is measured based on the differential capacitance detection and plate variable gap capacitance detection principles. The sensor has the advantages of full-dimensional physical structure decoupling, small size, high sensitivity, little temperature influence, and easy manufacturing. It is suitable for mechanical fingertips, micro medical robots, and other harsh working environments with small installation and working space, and rapid changes in temperature and humidity.

[0032] 2. The present invention solves the technical problems that the traditional metal-based six-dimensional force sensor is large in size, easily affected by temperature, and not suitable for low-cost, miniaturized and mass-produced; the MEMS six-dimensional force sensor of the present invention is made into a chip-based six-dimensional force sensor using MEMS process technologies such as photolithography, etching, coating, bonding, etc. on a silicon-based wafer, which is easy to realize miniaturized mass production, and the lower electrode plate can also be made on glass, with low overall cost. Compared with piezoresistive sensors, the capacitance value of MEMS capacitive sensors is independent of the electrode material and is little affected by temperature changes, so MEMS capacitive sensors have good temperature stability.

[0033] 3. The present invention solves the technical problems that the crosstalk in each dimension is large in the structural design of traditional metal-based six-dimensional force and MEMS six-dimensional force sensors, especially the difficulty in decoupling the Mz torque of the MEMS six-dimensional force sensor or the complicated solution method; the structural design of the present invention realizes full-dimensional structural decoupling in principle, and the six detection channels will only detect the capacitance changes caused by the corresponding dimensional forces, and there is basically no cross-axis sensitivity; the present invention adopts 4 flat plate capacitors in Mz torque detection, and the upper and lower electrodes do not completely overlap. The two lower electrodes opposite to each other are divided into a group, and positive and negative excitations are applied respectively, so that a pair of differential capacitors are formed between the upper and lower electrodes. According to the differential capacitance detection principle, the differential output can be detected on the common plate, that is, the mass block, through the capacitance conditioning circuit; the Mz detection structure designed by the present invention is simple in principle, has no crosstalk, and is easy to solve.

[0034] 4. The present invention solves the technical problem that it is difficult for the mems six-dimensional force sensor to achieve detection of tens of Newtons and has low sensitivity; the mems six-dimensional force sensor can easily achieve micro-newton-based measurement, but it is difficult to achieve force detection of Newtons or tens of Newtons and has low sensitivity; the present invention adopts the structural form of upper and lower parallel plates, which has a large basic capacitance, adopts differential capacitance and variable gap capacitance detection principles, and a small force can cause a large change in the corresponding detection capacitance, which can effectively improve the sensitivity. The upper electrode mass block is evenly distributed with many supporting silicon columns, and the sensor sensitivity and range can be optimized and adjusted by changing its diameter and length, so that a six-dimensional force sensor with a range of several Newtons or tens of Newtons can be easily designed. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0036] Figure 1 It is a schematic diagram of the structure of the present invention;

[0037] Figure 2 is an exploded view of the present invention;

[0038] Figure 3 It is a schematic structural diagram of the top electrode plate and the first outer frame of the present invention;

[0039] Figure 4 is a schematic structural diagram of the bottom electrode plate of the present invention;

[0040] Figure 5 It is the spatial force coordinate definition diagram of the present invention;

[0041] Figure 6 It is a schematic diagram of the structure of 16 flat-plate detection capacitors of the present invention;

[0042] Figure 7 It is a schematic diagram of the structure of the chip structure deformed under the action of the force Fx of the present invention;

[0043] Figure 8 It is a schematic diagram of the structure of the chip structure deformed under the action of the force Fy of the present invention;

[0044] Fig. 9 It is a cross-sectional schematic diagram of the chip structure deformation under the action of the force Fz of the present invention;

[0045] Fig.10 is a cross-sectional schematic diagram of the chip structure deformation under the action of the moment Mx of the present invention;

[0046] Fig.11 It is a plane schematic diagram of the chip structure deformation under the action of the moment Mz of the present invention;

[0047] Fig.12 It is a production process flow chart of the present invention.

[0048] In the figure: 1, top electrode plate; 2, first outer frame; 3, bottom electrode plate; 11, upper electrode; 12, silicon pillar; 111, triangular flat plate upper electrode; 112, rectangular flat plate upper electrode; 113, comb-tooth type flat plate upper electrode group; 31, substrate; 32, lower electrode; 33, anchor point; 34, pad; 321, triangular flat plate lower electrode; 322, comb-tooth type flat plate lower electrode group; 323, rectangular flat plate lower electrode. DETAILED DESCRIPTION

[0049] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention.

[0050] See also Figure 1-5 In an embodiment of the present invention, a structurally decoupled capacitive MEMS six-dimensional force sensor chip includes a top plate 1, a first outer frame 2 and a bottom plate 3, wherein the first outer frame 2 is located outside the top plate 1;

[0051] The top electrode 1 includes an upper electrode 11 and a silicon column 12, and the silicon column 12 is distributed in the middle of the upper electrode 11; the upper electrode 11 includes a triangular flat plate upper electrode 111, a rectangular flat plate upper electrode 112 and a comb-tooth-shaped flat plate upper electrode group 113, and the silicon column 12 is evenly distributed on the triangular flat plate upper electrode 111.

[0052] The bottom electrode 3 includes a substrate 31, a lower electrode 32, an anchor point 33 and a pad 34, wherein the anchor point 33 is distributed in the middle of the lower electrode 32, and the position of the anchor point 33 corresponds to the position of the silicon pillar 12; the lower electrode 32 includes a triangular flat plate lower electrode 321, a comb-tooth-shaped flat plate lower electrode group 322 and a rectangular flat plate lower electrode 323, and the anchor points 33 are evenly distributed at the triangular flat plate lower electrode 321.

[0053] The rectangular flat plate upper electrode 112 overlaps with the rectangular flat plate lower electrode 323 by two-thirds of its area, and the comb-tooth-shaped flat plate upper electrode group 113 overlaps with the comb-tooth-shaped flat plate lower electrode group 322 by two-thirds of its area; the area of ​​the triangular flat plate upper electrode 111 is slightly smaller than the area of ​​the triangular flat plate lower electrode 321; the four rectangular flat plate upper electrodes 112 are respectively located between the two comb-tooth-shaped flat plate upper electrode groups 113 on the four sides, and the four rectangular flat plate lower electrodes 323 are respectively located between the two comb-tooth-shaped flat plate lower electrode groups 322 on the four sides.

[0054] The top plate is the force-sensitive area of ​​the sensor, and its substrate is a highly doped silicon wafer. The top plate includes two structures: a silicon column and an upper electrode. The upper electrode can be divided into a comb-tooth-shaped flat plate upper electrode group, a triangular flat plate upper electrode, and a rectangular flat plate upper electrode. The silicon columns are evenly distributed on the triangular flat plate electrode surface of the top plate, playing a role of force support. The silicon column structure is equivalent to adding evenly distributed spring elements between the upper and lower plates, which significantly increases the overload resistance of the six-dimensional force sensor. In actual use, the structural stiffness of the top plate when subjected to force depends on the number, diameter and length of the silicon columns. The outer frame surrounds the top plate and wraps up the entire flat plate capacitor for detecting six-dimensional forces. In the detection circuit, the outer frame is always grounded, which can shield the interference of the external environment on the flat plate detection capacitor and play a protective role. The bottom plate substrate of the sensor is a silicon wafer, and glass and SOI wafers can also be selected as the bottom substrate. The lower electrode structure (such as Figure 4 As shown). The lower electrode can be divided into a comb-shaped flat plate lower electrode group, a triangular flat plate lower electrode and a rectangular flat plate lower electrode, just like the upper electrode. There are many circular anchor bonding areas evenly distributed on the triangular flat plate lower electrode, and their positions correspond to the silicon pillars of the top plate one by one. The silicon pillars and the circular anchors are connected by a gold-silicon eutectic bonding process. If the circular anchor bonding area of ​​the lower electrode is made into a silicon pillar-like structure, the sensitivity of the sensor can be increased. The upper and lower electrodes corresponding to the comb-shaped flat plate electrode group and the rectangular flat plate electrode overlap about two-thirds of the area and are staggered, and there is a gap of several microns between the upper and lower electrodes in the vertical direction. The silicon pillars on the outermost four vertices of the bonding anchors of the top plate and the bottom plate connect the upper electrode to the pad made on the bottom plate substrate. In addition to playing a supporting role, they also play an electrical connection role, which facilitates the electrical connection between the sensor and the conditioning circuit. The area of ​​the triangular plate upper electrode is slightly smaller than that of the lower electrode. When the top plate is subjected to force, the overlapping area of ​​the upper and lower electrodes of the triangular plate remains unchanged, which only causes a change in the distance between the plates. The four rectangular flat plate electrodes arranged in an orthogonal cross are located between the two comb-tooth-shaped electrode groups on the same side. Meanwhile, the upper and lower electrodes of the rectangular flat plate do not completely overlap, but have a certain misalignment.

[0055] The force coordinates of the sensor in space are as follows Figure 5As shown, based on the spatial rectangular coordinate system in the figure, the six-dimensional forces include forces Fx, Fy and moment Mz in the horizontal plane, and forces Fz, and moments Mx and My in the vertical plane.

[0056] The 16 plate capacitors composed of the top plate and the bottom plate of the sensor are distributed as follows: Figure 6 As shown, 8 groups of flat plate capacitors composed of comb-tooth flat plate electrodes are applied with the same positive excitation to the lower plates of capacitors C1 and C3 through the conditioning circuit, and the same negative excitation is applied to the lower plates of capacitors C2 and C4, so that a differential capacitance is formed between the upper and lower plates for measuring Fx; the same positive excitation is applied to the lower plates of capacitors C5 and C7 through the conditioning circuit, and the same negative excitation is applied to the lower plates of capacitors C6 and C8, so that a differential capacitance is formed between the upper and lower plates for measuring Fy. For the four groups of flat plate capacitors composed of triangular flat plate electrodes, a positive excitation is applied to the lower plate of the C9 capacitor and a negative excitation is applied to the lower plate of the C10 capacitor through a conditioning circuit, and a differential capacitor for measuring Mx is formed between the upper and lower plates; similarly, a positive excitation is applied to the lower plate of the C11 capacitor and a negative excitation is applied to the lower plate of the C12 capacitor through a conditioning circuit, and a differential capacitor for measuring My is formed between the upper and lower plates; a positive excitation is applied to the lower plates of the C9, C10, C11, and C12 capacitors and a negative excitation is applied to the top plate through a conditioning circuit, and a variable gap flat plate capacitor for measuring Fz is formed between the upper and lower plates; for the flat plate capacitor composed of four rectangular flat plate electrodes, the same positive excitation is applied to the lower plates of the C13 and C15 capacitors and the same negative excitation is applied to the lower plates of the C14 and C16 capacitors through a conditioning circuit, and a differential capacitor for measuring Mz is formed between the upper and lower plates.

[0057] In the actual measurement process, the conditioning circuit using time-division multiplexing technology applies different positive and negative excitations to the lower electrodes of the capacitors of different measurement channels, and different capacitance outputs can be collected at the upper electrodes, and then the magnitude and direction of the applied force can be obtained by calculation. Each axial force value can be calculated according to the following formula:

[0058] U Fx =C1+C3-C2-C4

[0059] U Fy =C5+C7-C6-C8

[0060] U Fz =C9+C 10 +C 11 +C 12

[0061] U Mx =C9-C 10

[0062] U My =C 11 -C 12

[0063] U Mz =C 13 +C 15 -C 14 -C 16

[0064] like Figure 7-8 As shown, when detecting the Fx tangential force, the shear force causes the silicon column to bend laterally, and the top comb-tooth-shaped upper electrode is displaced horizontally, causing the area of ​​the comb-tooth electrode overlap area to change, thereby causing the capacitance to change. The change in the overlap area is proportional to the applied shear force. At this time, the capacitances of C1 and C3 increase and decrease at the same time, the capacitances of C2 and C4 increase and decrease at the same time, the capacitances of C5 and C6 increase and decrease at the same time, the capacitances of C7 and C8 increase and decrease at the same time, C9, C10, C11, and C12 remain unchanged, the sum of the increase and decrease of C13 and C15 is zero, and the sum of the increase and decrease of C14 and C16 is zero, that is, the outputs of Fy, Fz, Mx, My, and Mz are zero, and the Fx directional force will not cause the Fy, Fz, Mx, My, and Mz crosstalk outputs. The Fx size can be accurately measured by detecting the value of C1+C3-C2-C4 through the conditioning circuit.

[0065] like Fig. 9 As shown in the figure, when detecting the Fz normal force, the top plate is subjected to the vertical force, the silicon column is compressed, the gap between the upper electrode and the lower electrode of the sensor is reduced, the capacitance of C1-C16 increases, and the capacitance increment of the plates with the same area is consistent, so the output of the differential detection output channel of the conditioning circuit is zero, that is, the output of Fx, Fy, Mx, My, Mz is zero, and the Fz direction force will not cause the Fx, Fy, Mx, My, Mz crosstalk output. 10 +C 11 +C 12 The value of Fz can be accurately measured.

[0066] like Fig.10 As shown, when detecting the Mx torque, the top plate is acted upon by the torque Mx, the silicon column in the C9 region is compressed, and the silicon column in the C10 region is stretched, and vice versa. The gaps between the upper and lower electrodes of C9 and C10 will increase or decrease in the opposite direction. C1, C2, C6, C7, and C13 increase (decrease) in the same way, and C3, C4, C5, C8, and C15 decrease (increase) in the same way. The overlapping area of ​​the upper and lower electrodes of C11, C12, C14, and C16 is symmetrical about the X-axis, so when the active gap of one half of the surface increases, the other half must decrease. Compared with the initial capacitance, its capacitance will basically not change, so the capacitance of C11, C12, C14, and C16 remains unchanged. Detecting C9-C through the conditioning circuit 10 The value of Mx can be accurately measured, and the Mx torque will not cause crosstalk output among Fx, Fy, Fz, My, and Mz.

[0067] like Fig.11 As shown in the figure, when detecting the horizontal moment Mz, the silicon column bends laterally along the moment center. Except for the triangular flat electrode, the overlapping area of ​​other electrodes changes. C13 and C15 increase (decrease) at the same time, C14 and C16 decrease (increase) at the same time. The C 13 +C 15 -C 14 -C 16 At this time, C2, C3, C6, and C7 increase (decrease) at the same time, C1, C4, C5, and C8 decrease (increase) at the same time, and the plate gap and overlap area of ​​C9, C10, C11, and C12 remain unchanged, and the capacitance remains unchanged, so the Mz torque will not cause crosstalk output of Fx, Fy, Fz, Mx, and My.

[0068] According to the symmetry of the sensor, the principle and process of Fx and Fy detection are the same, so the value of Fy can be measured by adjusting the circuit to detect C5+C7-C6-C8, and the force in the Fy direction will not cause crosstalk output of Fx, Fz, Mx, My, and Mz. 11 -C 12 The value can be used to measure the size of My, and the size of My torque will not cause crosstalk output of Fx, Fy, Fz, Mx, and Mz.

[0069] In summary, the capacitive sensor can detect six-dimensional forces and has structural decoupling capabilities.

[0070] like Fig.12 A preparation process for a structurally decoupled capacitive MEMS six-dimensional force sensor chip, including a bottom plate preparation process, a top silicon plate preparation process, gold-gold bonding and a slicing process.

[0071] The bottom plate preparation process specifically includes the following steps:

[0072] S11, select a single crystal silicon wafer with an N-type (1 0 0) crystal plane and a thickness of 400 μm;

[0073] S12, placing the silicon wafer in a thermal oxidation furnace for thermal oxidation, forming a SiO2 film with a thickness greater than 200 nm on the surface of the silicon wafer;

[0074] S13, coating one side of the thermally oxidized silicon wafer with a CrAu metal layer by magnetron sputtering, with a Cr layer thickness of 50 nm and an Au layer thickness of 300-500 nm;

[0075] S14, applying photoresist as a mask on the metal layer, etching the metal layer through a dry etching process, preparing alignment marks, pads 34, leads and lower electrodes 32 patterns, and retaining the metal layer in the bonding area of ​​the anchor point 33.

[0076] The top silicon plate preparation process comprises the following steps:

[0077] S21, selecting a low-resistance single-crystal silicon wafer with a thickness of 400 um and a resistivity of less than 0.005 Ω·cm;

[0078] S22, using photoresist as a mask on any one side of the silicon wafer, and dry etching an alignment mark, this side is called the front side of the top plate 1;

[0079] S23, using photoresist as a mask on the back of the top plate 1, etching a groove with a depth of 4 μm through a dry silicon etching process, leaving only the silicon of the bonding area of ​​the anchor point 33 (the outer frame and the silicon column area);

[0080] S24, plating a CrAu metal layer on the back of the top plate 1 by magnetron sputtering or evaporation;

[0081] S25, using photoresist as a mask, etching the CrAu metal layer by dry etching process, leaving only the metal of the upper electrode 11 and the anchor 33 bonding area (outer frame and silicon column area); the silicon below the metal etching area is also etched away by 3-4um to prepare the entire upper electrode 11 outline opposite to the lower electrode 32;

[0082] S26, using photoresist as a mask, preparing silicon pillars 12 through a deep silicon etching process. This process requires precise control of etching parameters to achieve the required etching depth and prevent excessive over-etching.

[0083] The gold-gold bonding and dicing process specifically includes the following steps:

[0084] S31, after the bottom electrode plate 3 and the top electrode plate 1 are prepared, gold-gold hot pressing bonding is performed at a temperature of 380°C, and the alignment marks described in S14 and S22 are used for alignment, so that the bottom electrode plate 3 and the top electrode plate 1 are bonded into an integral wafer;

[0085] S32, after the bonding is completed, use the photoresist as a mask to perform deep silicon etching on the front side of the top electrode plate 1, and etch through it, completing the separation preparation of the upper electrode 11 electrode plate structure and the outer frame and the preparation of the entire sensor chip;

[0086] S33, using the dicing mark prepared in S22 as an alignment mark, dicing the bonded whole wafer, so that the sensor chip is divided into several independent individuals on the wafer, and the pad 34 is exposed; it is convenient for subsequent packaging and testing.

[0087] In the bottom plate preparation process, the silicon wafer, the base material of the bottom plate, can be replaced with glass and SOI wafer. If glass is used as the base material, you can start directly from S13, and the subsequent process steps are the same as the silicon wafer process. If you choose SOI wafer as the base material of the bottom plate, you can also start directly from S13, but in S14, the silicon under the metal layer etching area must also be etched away until the buried oxide layer. The metal layer plating process in S13 can also be prepared by evaporation and other processes during mass production.

[0088] The top plate substrate material can also be replaced with an SOI sheet. The entire processing and production process remains unchanged, except that the SOI buried oxide layer in S26 can be used as a stop layer to prevent over-etching, making it easier to achieve process control of etching depth. At the same time, the SOI buried oxide layer can also be used as an electrical insulation protection layer to provide anti-interference protection for the flat plate detection capacitor.

[0089] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A structurally decoupled capacitive MEMS six-dimensional force sensor chip, It is characterized in that It comprises a top plate (1), a first outer frame (2) and a bottom plate (3), wherein the first outer frame (2) is located outside the top plate (1); The top electrode (1) comprises an upper electrode (11) and a silicon column (12), wherein the silicon column (12) is distributed in the middle of the upper electrode (11); The bottom electrode (3) comprises a substrate (31), a lower electrode (32), an anchor point (33) and a pad (34); the anchor point (33) is distributed in the middle of the lower electrode (32), and the position of the anchor point (33) corresponds to the position of the silicon column (12).

2. A structurally decoupled capacitive MEMS six-dimensional force sensor chip according to claim 1, It is characterized in that The upper electrode (11) comprises a triangular flat plate upper electrode (111), a rectangular flat plate upper electrode (112) and a comb-tooth-shaped flat plate upper electrode group (113), and the silicon pillars (12) are evenly distributed on the triangular flat plate upper electrode (111).

3. The structurally decoupled capacitive MEMS six-dimensional force sensor chip according to claim 2, It is characterized in that The lower electrode (32) comprises a triangular flat plate lower electrode (321), a comb-tooth-shaped flat plate lower electrode group (322) and a rectangular flat plate lower electrode (323), and the anchor points (33) are evenly distributed at the triangular flat plate lower electrode (321).

4. The structurally decoupled capacitive MEMS six-dimensional force sensor chip according to claim 3, It is characterized in that The rectangular flat plate upper electrode (112) and the rectangular flat plate lower electrode (323) overlap by two thirds of their area, and the comb-tooth-shaped flat plate upper electrode group (113) and the comb-tooth-shaped flat plate lower electrode group (322) overlap by two thirds of their area.

5. The structurally decoupled capacitive MEMS six-dimensional force sensor chip according to claim 3, It is characterized in that The area of ​​the triangular flat plate upper electrode (111) is slightly smaller than the area of ​​the triangular flat plate lower electrode (321).

6. The structurally decoupled capacitive MEMS six-dimensional force sensor chip according to claim 3, It is characterized in that The four rectangular flat plate upper electrodes (112) are respectively located between the two comb-tooth-shaped flat plate upper electrode groups (113) on the four sides, and the four rectangular flat plate lower electrodes (323) are respectively located between the two comb-tooth-shaped flat plate lower electrode groups (322) on the four sides.

7. A preparation process for a structurally decoupled capacitive MEMS six-dimensional force sensor chip. It is characterized in that It includes bottom plate preparation process, top silicon plate preparation process, gold-gold bonding and dicing process.

8. The process for preparing a structurally decoupled capacitive MEMS six-dimensional force sensor chip according to claim 7, It is characterized in that The bottom plate preparation process specifically includes the following steps: S11, select a single crystal silicon wafer with an N-type (1 0 0) crystal plane and a thickness of 400 μm; S12, put the silicon wafer into the thermal oxidation furnace for thermal oxidation, and form a layer of SiO2 with a thickness of more than 200nm on the surface of the silicon wafer. 2 film; S13, coating one side of the thermally oxidized silicon wafer with a CrAu metal layer by magnetron sputtering, with a Cr layer thickness of 50 nm and an Au layer thickness of 300-500 nm; S14, applying photoresist as a mask on the metal layer, etching the metal layer through a dry etching process, preparing alignment marks, pads (34), leads and lower electrodes (32) patterns, and retaining the metal layer of the anchor point (33) bonding area.

9. The process for preparing a structurally decoupled capacitive MEMS six-dimensional force sensor chip according to claim 8, It is characterized in that The top silicon plate preparation process comprises the following steps: S21, selecting a low-resistance single crystal silicon wafer with a thickness of 400 um and a resistivity of less than 0.005 Ω·cm; S22, using a photoresist as a mask on any one side of the silicon wafer, and dry etching an alignment mark, this side is referred to as the front side of the top plate (1); S23, using photoresist as a mask on the back of the top electrode plate (1), etching a groove with a depth of 4 μm through a dry silicon etching process, leaving only the silicon of the bonding area of ​​the anchor point (33); S24, plating a CrAu metal layer on the back side of the top electrode plate (1) by a process such as magnetron sputtering or evaporation; S25, using a photoresist as a mask, etching the CrAu metal layer by dry etching process, leaving only the metal of the bonding area of ​​the upper electrode (11) and the anchor point (33); the silicon below the metal etching area is also etched away by 3-4 um, to prepare the entire upper electrode (11) contour opposite to the lower electrode (32); S26, using the photoresist as a mask, preparing the silicon pillar (12) through a deep silicon etching process.

10. The process for preparing a structurally decoupled capacitive MEMS six-dimensional force sensor chip according to claim 9, It is characterized in that The gold-gold bonding and dicing process specifically includes the following steps: S31, after the bottom electrode plate (3) and the top electrode plate (1) are prepared, gold-gold hot pressing bonding is performed at a temperature of 380°C, and the alignment marks described in S14 and S22 are used for alignment, so that the bottom electrode plate (3) and the top electrode plate (1) are bonded into an integral wafer; S32, after the bonding is completed, use the photoresist as a mask to perform deep silicon etching on the front side of the top plate (1), and etch through it, so as to complete the separation preparation of the upper electrode (11) plate structure and the outer frame and the preparation of the entire sensor chip; S33, using the dicing mark prepared in S22 as an alignment mark, dicing the bonded whole wafer, so that the sensor chip is divided into a plurality of independent units on the wafer, and the pad (34) is exposed.

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