Structure and preparation method of MEMS acceleration sensor chip

Abstract

The invention relates to the technical field of micro electro mechanical system accelerometers. The invention particularly relates to a structure and a preparation method of an MEMS acceleration sensor chip. The MEMS acceleration sensor chip structurally comprises a sensitive structure layer which comprises a sensitive mass block unit which comprises a main longitudinal beam, a sensitive mass block and a plurality of movable electrodes located on the two sides of the sensitive mass block; the sensitive mass block is elastically connected with the main longitudinal beam; the sensitive structure layer further comprises fixed electrode units located on the two sides of the sensitive mass block. The fixed electrode unit at least comprises a plurality of fixed electrodes; the movable electrode and the fixed electrode form a differential capacitor structure; wherein the main longitudinal beam is fixedly connected with the substrate layer through the main anchor point; main auxiliary anchor points are further arranged on the two opposite sides of the main anchor point in the extending direction of the main longitudinal beam respectively, and the main longitudinal beam is further fixedly connected with the base layer through the main auxiliary anchor points respectively; the rigidity of the connecting structure of the main auxiliary anchor point and the main longitudinal beam in the sensitive direction of the sensitive mass block unit is smaller than that in the non-sensitive direction.

Description

Technical Field

[0001] The present invention relates to the technical field of micro-electromechanical system accelerometers, and in particular to the structure and preparation method of a MEMS acceleration sensor chip. Background Art

[0002] Micro-Electro-Mechanical Systems (MEMS) devices are micro devices or systems that highly integrate micro-mechanical structures, micro-sensors, micro-actuators, and control circuits on a single or multiple chips. MEMS micro-accelerometer chips are micro-sensors specifically used to measure acceleration, and they play an important role in many fields such as automobiles, aerospace, biomedicine, communications, and consumer electronics. Common inertial acceleration sensor chips are based on Newton's second law, and their systems can be simplified into a second-order system containing a sensitive mass block and a spring structure. The acceleration is first converted into displacement, and then the displacement is converted into an electrical signal through a conversion element, which is often based on piezoelectric, capacitive, and piezoresistive types. Among them, the capacitive comb-tooth variable gap type is considered to be the best configuration for making high-sensitivity, high-temperature range acceleration sensor chips due to its high sensitivity and temperature stability.

[0003] The movable structural part (sensitive mass block, mobile electrode, spring) and fixed electrode of the MEMS acceleration sensor chip are connected to the substrate through the anchor structure. These anchors are the only connection points between the sensitive structure of the acceleration sensor chip and the substrate. The residual stress and thermal stress introduced by the manufacturing process, packaging patch and other processes, as well as the thermal stress generated by the change of ambient temperature, will be transmitted to the acceleration sensor chip structure through the anchor, resulting in structural deformation and detection capacitance change, affecting the output stability of the sensor. There are several schemes in the prior art to improve the thermal stability of capacitive MEMS acceleration sensor chips, but the effect is still difficult to meet the detection and high-precision measurement of acceleration in extreme high temperature environments. Therefore, a scheme is needed to further improve the thermal stability of capacitive MEMS acceleration sensor chips (thermal stability refers to the ability of MEMS acceleration sensor chip performance to remain constant with changes in external temperature, and more specifically refers to whether it can maintain a relatively stable sensitivity under changes in external temperature), reduce the structural deformation of the movable structural part caused by thermal stress and the resulting change in detection capacitance, so that the capacitive MEMS acceleration sensor chip can meet the needs of detection and high-precision measurement of acceleration in extreme high temperature environments. Summary of the invention

[0004] Therefore, the present invention provides a structure and preparation method of a MEMS acceleration sensor chip to improve the thermal stability of the capacitive MEMS acceleration sensor chip, reduce the structural deformation of the movable structure part caused by thermal stress and the resulting change in detection capacitance, so that the capacitive MEMS acceleration sensor chip can meet the needs of acceleration detection and high-precision measurement in extreme high temperature environments.

[0005] The present invention provides a structure of a MEMS acceleration sensor chip, comprising: a sensor substrate, the sensor substrate comprising: a stacked base layer, a functional layer and a sensitive structural layer; the sensitive structural layer comprising a sensitive mass block unit, the sensitive mass block unit comprising a main longitudinal beam, a sensitive mass block and a plurality of movable electrodes located on both sides of the sensitive mass block; the sensitive mass block is arranged around the main longitudinal beam and elastically connected to the main longitudinal beam; the movable electrode is fixedly connected to the sensitive mass block; the sensitive structural layer also comprises fixed electrode units located on both sides of the sensitive mass block; the fixed electrode unit at least comprises a plurality of fixed electrodes extending toward the main longitudinal beam; the fixed electrode unit is fixedly connected to the base layer; the functional layer has a hollow area and a hollow area surrounding the hollow area. The projection of the hollow area on the sensitive structure layer at least covers the sensitive mass block unit and the fixed electrode unit; the edge area is fixedly connected to the base layer and the sensitive structure layer; the movable electrode and the fixed electrode constitute a differential capacitor structure; the sensitive mass block is suitable for displacement along the extension direction of the main longitudinal beam under external acceleration, driving the movable electrode to displace; wherein the main longitudinal beam is connected and fixed to the base layer through the main anchor point; main auxiliary anchor points are respectively arranged on the opposite sides of the main anchor point along the extension direction of the main longitudinal beam, and the main longitudinal beam is also connected and fixed to the base layer through the main auxiliary anchor points; the stiffness of the connection structure between the main auxiliary anchor point and the main longitudinal beam in the sensitive direction of the sensitive mass block unit is less than the stiffness in the non-sensitive direction.

[0006] Optionally, the main auxiliary anchor point is connected to the main longitudinal beam through a main beam decoupling beam; the width of the main auxiliary anchor point is greater than the width of the main longitudinal beam; the main body of the main auxiliary anchor point is perpendicular to the extension direction of the main longitudinal beam; both ends of the main body of the main auxiliary anchor point extend a partial length of connecting parts along the extension direction of the main longitudinal beam, and the connecting parts are connected to the end parts of the main longitudinal beam through the main beam decoupling beam; the main body of the main auxiliary anchor point is connected and fixed to the base layer, and the connecting part of the main auxiliary anchor point and the main beam decoupling beam are suspended above the base layer; the main beam decoupling beam is suitable for deforming along the extension direction of the main longitudinal beam, so that the distance between the position where the main beam decoupling beam is connected to the main longitudinal beam and the main body of the main auxiliary anchor point changes in a sensitive direction when subjected to thermal stress.

[0007] Optionally, the sensitive mass block is provided with an elastic component accommodating groove on the side facing the extension direction of the main longitudinal beam, and an elastic component is provided in the elastic component accommodating groove, and the two ends of the elastic component are respectively connected to the main longitudinal beam and the sensitive mass block, so that the sensitive mass block is suitable for displacement along the extension direction of the main longitudinal beam under external acceleration.

[0008] Optionally, the elastic component is a folding beam spring; the folding beam spring is a serpentine folding structure, extending in a serpentine manner along the extension direction of the main longitudinal beam, with one end connected to the side of the main longitudinal beam and the other end connected to the side of the sensitive mass block.

[0009] Optionally, the sensitive mass block, folded beam spring and movable electrode together constitute a centrally symmetrical figure, and the center of symmetry of the centrally symmetrical figure coincides with the main anchor point; there are multiple fixed electrode units, which are centrally symmetrically distributed with the main anchor point as the center of symmetry; with the extension direction of the main longitudinal beam as the y-axis and the direction perpendicular to the y-axis and passing through the center of the main anchor point as the x-axis, the sensitive mass block, folded beam spring, movable electrode and fixed electrode units are symmetrically distributed along the y-axis, and symmetrically distributed along the x-axis; adjacent movable electrodes and fixed electrodes constitute a capacitor; the capacitors on the same side of the x-axis are connected in parallel; the capacitors on both sides of the x-axis have opposite capacitance changes under external acceleration.

[0010] Optionally, the sensitive mass block and the main longitudinal beam are provided with a plurality of process release holes penetrating through the sensitive mass block and the main longitudinal beam in the thickness direction; the process release holes are arranged in an array, and the process release holes in adjacent columns are arranged in a staggered manner.

[0011] Optionally, the fixed electrode unit also includes a secondary longitudinal beam; the secondary longitudinal beam is parallel to the main longitudinal beam, and is connected and fixed to the base layer through a secondary anchor point; the fixed electrode unit is provided with a secondary auxiliary anchor point on one side along the extension direction of the secondary longitudinal beam, and the secondary longitudinal beam is also connected and fixed to the base layer through the secondary auxiliary anchor point; the connection structure between the secondary auxiliary anchor point and the secondary longitudinal beam has a stiffness in the sensitive direction of the sensitive mass block unit that is less than the stiffness in the non-sensitive direction.

[0012] Optionally, the secondary auxiliary anchor point is connected to the secondary longitudinal beam through a secondary beam decoupling beam; the width of the secondary auxiliary anchor point is greater than the width of the secondary longitudinal beam; the main body of the secondary auxiliary anchor point is perpendicular to the extension direction of the secondary longitudinal beam; both ends of the main body of the secondary auxiliary anchor point extend a partial length of connecting parts along the extension direction of the secondary longitudinal beam, and the connecting parts are connected to the end of the main longitudinal beam through the secondary beam decoupling beam; the main body of the secondary auxiliary anchor point is connected and fixed to the base layer, and the connecting part of the secondary auxiliary anchor point and the secondary beam decoupling beam are suspended above the base layer; the secondary beam decoupling beam is suitable for deforming along the extension direction of the secondary longitudinal beam, so that the distance between the position where the secondary beam decoupling beam is connected to the secondary longitudinal beam and the main body of the secondary auxiliary anchor point changes in a sensitive direction when subjected to thermal stress.

[0013] Optionally, there are multiple fixed electrode units, which are distributed symmetrically with the main anchor point as the center of symmetry; wherein the secondary anchor points of each fixed electrode unit are distributed symmetrically with the main anchor point as the center of symmetry, and at the same time, the secondary auxiliary anchor points of each fixed electrode unit are also distributed symmetrically with the main anchor point as the center of symmetry.

[0014] Optionally, the secondary longitudinal beam is provided with a plurality of process release holes penetrating the secondary longitudinal beam in the thickness direction; the process release holes are arranged in an array, and the process release holes in adjacent columns are arranged in a staggered manner.

[0015] Optionally, the sensitive structure layer also includes a bonding frame; the bonding frame surrounds and defines a main activity space, and the sensitive mass block unit and the fixed electrode unit are arranged in the main activity space; the structure of the MEMS acceleration sensor chip also includes: an upper cover; the upper cover includes a cover plate, and a frame protruding from a surface of one side of the cover plate; the frame and the cover plate together enclose a cover plate activity space; the frame is suitable for connection with the bonding frame, the cover plate activity space corresponds to the main activity space, and together with the hollow space of the functional layer, accommodates the sensitive mass block unit and the fixed electrode unit.

[0016] Optionally, a conductive medium layer is provided on the side of the sensitive structure layer facing the upper cover, and the conductive medium layer at least covers the sensitive structure unit and the fixed electrode unit; the cover plate is provided with a plurality of through holes, the through holes expose the conductive medium layer, the through holes are filled with conductive electrodes, the conductive electrodes are connected to the conductive medium layer, and are exposed on the surface of the cover plate facing away from the base layer; the positions of the through holes correspond to the settings of the main anchor point and the secondary anchor point.

[0017] The present invention also provides a method for preparing the structure of a MEMS acceleration sensor chip, comprising the following steps: forming a sensor substrate, including: providing a substrate layer; forming an initial functional layer on the substrate layer; forming an initial sensitive structural layer on the side of the initial functional layer facing away from the substrate layer; etching the initial sensitive structural layer to form a sensitive structural layer, including: forming a sensitive mass block unit, the sensitive mass block unit including a main longitudinal beam, a sensitive mass block and a plurality of movable electrodes located on both sides of the sensitive mass block; the sensitive mass block is arranged around the main longitudinal beam and elastically connected to the main longitudinal beam; the movable electrode is fixedly connected to the sensitive mass block; and at the same time, fixed electrode units located on both sides of the sensitive mass block are formed; the fixed electrode unit at least includes a plurality of electrodes extending toward the longitudinal beam; and the plurality of electrodes extending toward the longitudinal beam are provided at the same time. A plurality of fixed electrodes extending from the main longitudinal beam; the functional layer is corroded through the sensitive structural layer to form a hollow area and an edge area surrounding the hollow area, and the projection of the hollow area on the sensitive structural layer at least covers the sensitive mass block unit and the fixed electrode unit; the edge area is fixedly connected to the base layer and the sensitive structural layer; wherein the step of etching the initial sensitive structural layer to form the sensitive structural layer also includes: forming a main anchor point connecting and fixing the main longitudinal beam to the base layer; forming main auxiliary anchor points on opposite sides of the main anchor point along the extension direction of the main longitudinal beam, and the main longitudinal beam is also connected and fixed to the base layer through the main auxiliary anchor points; the stiffness of the connection structure between the main auxiliary anchor point and the main longitudinal beam in the sensitive direction of the sensitive mass block unit is less than the stiffness in the non-sensitive direction.

[0018] Optionally, the step of etching the initial sensitive structure layer to form the sensitive structure layer includes: forming a sensitive layer mask on the side of the sensitive structure layer facing away from the base layer; using the sensitive layer mask as a mask, graphically etching the initial sensitive structure layer to form a sensitive mass block unit and a fixed electrode unit; and removing the sensitive layer mask.

[0019] Optionally, the step of forming a sensitive mass block unit includes: forming a main beam decoupling beam connecting the main auxiliary anchor point and the main longitudinal beam; the width of the main auxiliary anchor point is greater than the width of the main longitudinal beam; the main body of the main auxiliary anchor point is perpendicular to the extension direction of the main longitudinal beam; both ends of the main body of the main auxiliary anchor point extend a partial length of connecting parts along the extension direction of the main longitudinal beam, and the connecting parts are connected to the end of the main longitudinal beam through the main beam decoupling beam; the main beam decoupling beam is suitable for deforming along the extension direction of the main longitudinal beam, so that the distance between the position where the main beam decoupling beam is connected to the main longitudinal beam and the main body of the main auxiliary anchor point changes in a sensitive direction when subjected to thermal stress.

[0020] Optionally, the step of forming the sensitive mass block unit includes: forming an elastic component accommodating groove on the side of the sensitive mass block in the extension direction of the main longitudinal beam, an elastic component is arranged in the elastic component accommodating groove, and two ends of the elastic component are respectively connected to the main longitudinal beam and the sensitive mass block, so that the sensitive mass block is suitable for displacement along the extension direction of the main longitudinal beam under external acceleration; the elastic component is a folding beam spring; the folding beam spring is a serpentine folding structure, which extends in a serpentine shape along the extension direction of the main longitudinal beam, one end is connected to the side of the main longitudinal beam, and the other end is connected to the side of the sensitive mass block.

[0021] Optionally, the formed sensitive mass block, folded beam spring and movable electrode together constitute a centrally symmetrical figure, and the center of symmetry of the centrally symmetrical figure coincides with the main anchor point; a plurality of fixed electrode units are formed, which are centrally symmetrically distributed with the main anchor point as the center of symmetry; with the extension direction of the main longitudinal beam as the y-axis and the direction perpendicular to the y-axis and passing through the center of the main anchor point as the x-axis, the sensitive mass block, folded beam spring, movable electrode and fixed electrode units are symmetrically distributed along the y-axis, and symmetrically distributed along the x-axis; adjacent movable electrodes and fixed electrodes constitute a capacitor; the capacitors on the same side of the x-axis are connected in parallel; the capacitors on both sides of the x-axis have opposite capacitance changes under external acceleration.

[0022] Optionally, the step of forming a fixed electrode unit located on both sides of the sensitive mass block also includes: simultaneously forming a secondary longitudinal beam; the secondary longitudinal beam is parallel to the main longitudinal beam, and is connected and fixed to the base layer through a secondary anchor point; a secondary auxiliary anchor point is formed on one side of the fixed electrode unit along the extension direction of the secondary longitudinal beam, and the secondary longitudinal beam is also connected and fixed to the base layer through the secondary auxiliary anchor point; the secondary auxiliary anchor point is an axisymmetric structure with the central axis of the secondary longitudinal beam as the axis of symmetry; the secondary auxiliary anchor point is an axisymmetric structure with the central axis of the secondary longitudinal beam as the axis of symmetry; the connection structure between the secondary auxiliary anchor point and the secondary longitudinal beam has a stiffness in the sensitive direction of the sensitive mass block unit that is less than that in the non-sensitive direction.

[0023] Optionally, the step of forming fixed electrode units located on both sides of the sensitive mass block also includes: simultaneously forming a sub-beam decoupling beam connecting the sub-auxiliary anchor point and the sub-longitudinal beam; the width of the sub-auxiliary anchor point is greater than the width of the sub-longitudinal beam; the main body of the sub-auxiliary anchor point is perpendicular to the extension direction of the sub-longitudinal beam; both ends of the main body of the sub-auxiliary anchor point extend a partial length of the connecting portion along the extension direction of the sub-longitudinal beam, and the connecting portion is connected to the end of the main longitudinal beam through the sub-beam decoupling beam; the main body of the sub-auxiliary anchor point is connected and fixed to the base layer, and the connecting portion of the sub-auxiliary anchor point and the sub-beam decoupling beam are suspended above the base layer; the sub-beam decoupling beam is suitable for deforming along the extension direction of the sub-longitudinal beam, so that the distance between the position where the sub-beam decoupling beam is connected to the sub-longitudinal beam and the main body of the sub-auxiliary anchor point changes in the sensitive direction when subjected to thermal stress.

[0024] Optionally, multiple fixed electrode units are formed, which are centrally symmetrically distributed with the main anchor point as the center of symmetry; wherein the secondary anchor points of each fixed electrode unit are centrally symmetrically distributed with the main anchor point as the center of symmetry, and at the same time, the secondary auxiliary anchor points of each fixed electrode unit are also centrally symmetrically distributed with the main anchor point as the center of symmetry.

[0025] Optionally, the step of corroding the functional layer through the sensitive structure layer includes: forming a release hole mask on the side of the sensitive structure layer facing away from the base layer; using the release hole mask as a mask, etching a process release hole in the sensitive structure layer, the process release hole exposing the initial functional layer at a corresponding position; corroding the initial functional layer through the process release hole to form a hollow area in the initial functional layer; the projection of the hollow area on the sensitive structure layer at least covers the sensitive structure unit and the fixed electrode unit; and removing the release hole mask.

[0026] Optionally, the minimum line width of the process release hole is greater than 3 μm; and the size of the long side of the process release hole is 2-3 times greater than the size of the short side.

[0027] Optionally, before the steps of forming the sensitive mass block unit and simultaneously forming the fixed electrode unit, it also includes: forming a patterned conductive medium layer and a first bonding medium layer on the side of the initial sensitive structure layer facing away from the base layer; the conductive medium layer at least covers the positions where the sensitive mass unit and the fixed electrode unit are predetermined to be formed; the first bonding medium layer covers the positions corresponding to the edge areas; in the steps of forming the sensitive mass block unit and simultaneously forming the fixed electrode unit, it also includes: removing the conductive medium layer corresponding to the portion removed when the sensitive mass block unit is formed, and removing the conductive medium layer corresponding to the portion removed when the fixed electrode unit is formed; when forming the process release hole, removing the conductive medium layer at the position corresponding to the predetermined process release hole.

[0028] Optionally, the method for preparing the structure of the MEMS acceleration sensor chip also includes the following steps: forming an upper cover, including: providing a cover substrate; etching the cover substrate to form a cover, and a frame protruding from the surface of one side of the cover; the frame and the cover together enclose a cover activity space; in the process of forming the sensitive structural layer, it also includes: forming a bonding outer frame, the bonding outer frame surrounds and encloses a main activity space, and the sensitive mass block unit and the fixed electrode unit are arranged in the main activity space; the frame is suitable for connecting to the bonding outer frame, the activity space corresponds to the main activity space, and the sensitive mass block unit and the fixed electrode unit are jointly accommodated.

[0029] Optionally, a blind hole is formed at a preset position of the cover plate, and the blind hole is filled with electroplated metal to form a conductive electrode; the preset position corresponds to the position of the main anchor point and the secondary anchor point in the sensor substrate; after the conductive electrode is formed, a patterned second bonding medium layer is formed on the side of the cover plate where the conductive electrode is exposed; the second bonding medium layer is connected to the conductive electrode.

[0030] Optionally, the sensor base and the upper cover are bonded together through a first bonding medium layer and a second bonding medium layer; after bonding, the conductive electrodes correspond to the main anchor point and the secondary anchor point, and the conductive medium layer is connected through the second bonding medium layer; the frame of the upper cover and the bonding outer frame of the sensor base are bonded together through the first bonding medium layer and the second bonding medium layer; the activity space corresponds to the main activity space, and together with the hollow space of the functional layer, accommodates the sensitive mass block unit and the fixed electrode unit.

[0031] The beneficial effects of the technical solution of the present invention are:

[0032] The structure of the MEMS acceleration sensor chip provided by the present invention comprises a sensitive structural layer including a sensitive mass block unit and a fixed electrode unit; the fixed electrode unit is fixedly connected to the base layer; movable electrodes are arranged on both sides of the sensitive mass block, the fixed electrode unit is arranged with fixed electrodes, and the movable electrodes and the fixed electrodes form a differential capacitance structure. The sensitive mass block is elastically connected to the main longitudinal beam through an elastic member, and the main longitudinal beam is fixedly connected to the base layer through a main anchor point. In this way, the sensitive mass block is suitable for displacement along the extension direction of the main longitudinal beam under the acceleration applied by the outside world, driving the movable electrode to displace, thereby realizing differential capacitance acceleration sensing measurement. Compared with single capacitance acceleration sensing measurement, the capacitance change of the differential capacitance acceleration sensing measurement is doubled for the same plate displacement, the sensitivity is doubled, and the nonlinear error performance is better. On this basis, main auxiliary anchor points are respectively arranged on both sides of the main anchor point along the extension direction of the main longitudinal beam, and the main longitudinal beam is also connected and fixed to the base layer through the main auxiliary anchor points. The main auxiliary anchor point is an axisymmetric structure with the central axis of the main longitudinal beam as the axis of symmetry; the connection structure of the main auxiliary anchor point and the main longitudinal beam has a stiffness in the sensitive direction of the sensitive mass block unit that is less than that in the non-sensitive direction. In this way, through the axisymmetric setting of the main auxiliary anchor point, since the stiffness in the sensitive direction of the sensitive mass block unit is less than that in the non-sensitive direction, it provides support to the main longitudinal beam in the non-sensitive direction (such as the direction other than the extension direction of the main longitudinal beam), so that when the main longitudinal beam is disturbed in the non-sensitive direction, it is not easy for the main longitudinal beam to deform and displace in the non-sensitive direction, thereby making it difficult for the sensitive mass block to deform and displace in the non-sensitive direction. In the sensitive direction, the connection structure of the main auxiliary anchor point and the main longitudinal beam can also eliminate the deformation caused by thermal stress, so that the main longitudinal beam itself is not easy to deform under the influence of thermal stress, and then the displacement of the active electrode affected by acceleration is not easy to be affected by thermal stress, so that the measurement of acceleration is not easy to be disturbed by the influence of thermal stress, thereby improving the thermal stability of the MEMS acceleration sensor chip.

[0033] The method for preparing the structure of the MEMS acceleration sensor chip provided by the present invention can manufacture the structure of the MEMS acceleration sensor chip provided by the present invention. The structure of the formed MEMS acceleration sensor chip, the sensitive structure layer includes a sensitive mass block unit and a fixed electrode unit; the fixed electrode unit is fixedly connected to the base layer; movable electrodes are arranged on both sides of the sensitive mass block, the fixed electrode unit is arranged with fixed electrodes, and the movable electrodes and the fixed electrodes form a differential capacitance structure. The sensitive mass block is elastically connected to the main longitudinal beam through an elastic member, and the main longitudinal beam is fixedly connected to the base layer through a main anchor point. In this way, the sensitive mass block is suitable for displacement along the extension direction of the main longitudinal beam under external acceleration. In this way, the sensitive mass block is suitable for displacement along the extension direction of the main longitudinal beam under external acceleration, driving the movable electrode to displace, thereby realizing differential capacitance acceleration sensing measurement. Compared with single capacitance acceleration sensing measurement, the capacitance change of the differential capacitance acceleration sensing measurement is doubled for the same plate displacement, the sensitivity is doubled, and the nonlinear error performance is better. On this basis, main auxiliary anchor points are respectively arranged on both sides of the main anchor point along the extension direction of the main longitudinal beam, and the main longitudinal beam is also connected and fixed to the base layer through the main auxiliary anchor points. The main auxiliary anchor point is an axisymmetric structure with the central axis of the main longitudinal beam as the axis of symmetry; the connection structure of the main auxiliary anchor point and the main longitudinal beam has a stiffness in the sensitive direction of the sensitive mass block unit that is smaller than that in the non-sensitive direction. In this way, through the axisymmetric arrangement of the main auxiliary anchor point, since the stiffness in the sensitive direction of the sensitive mass block unit is smaller than that in the non-sensitive direction, it provides support to the main longitudinal beam in the non-sensitive direction (such as the direction other than the extension direction of the main longitudinal beam), so that when the main longitudinal beam is disturbed in the non-sensitive direction, it is not easy for the main longitudinal beam to deform and displace in the non-sensitive direction, thereby making it difficult for the sensitive mass block to deform and displace in the non-sensitive direction. In the sensitive direction, the connection structure between the main auxiliary anchor point and the main longitudinal beam can also eliminate the deformation caused by thermal stress, so that the main longitudinal beam itself is not easily deformed under the influence of thermal stress, and the displacement of the active electrode affected by acceleration is not easily affected by thermal stress, so that the acceleration measurement is not easily disturbed by the influence of thermal stress, thereby improving the thermal stability of the MEMS acceleration sensor chip. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0035] Figure 1 It is a simple schematic diagram of the conversion of acceleration into displacement when measuring acceleration of a capacitive acceleration sensor chip;

[0036] Figure 2a It is a schematic diagram of the conversion between displacement and capacitance when measuring acceleration of a single capacitive acceleration sensor chip;

[0037] Figure 2b A schematic diagram of the conversion between displacement and capacitance of a differential capacitive acceleration sensor chip when measuring acceleration;

[0038] Figure 3 A schematic diagram of the structure of a MEMS acceleration sensor chip according to an embodiment of the present invention;

[0039] Figure 4 A schematic top view of a sensitive structure layer of a MEMS acceleration sensor chip according to an embodiment of the present invention;

[0040] Figure 5 It is a structural schematic diagram of a decoupling beam portion of a MEMS acceleration sensor chip according to an embodiment of the present invention;

[0041] Figure 6 It is a schematic diagram of the arrangement of process release holes of a MEMS acceleration sensor chip according to an embodiment of the present invention;

[0042] Figure 7 A schematic diagram of a process for preparing a MEMS acceleration sensor chip according to an embodiment of the present invention;

[0043] Figure 8a-8i It is a schematic diagram of various states in the process of forming a sensor chip substrate in a method for preparing a MEMS acceleration sensor chip according to an embodiment of the present invention;

[0044] Figure 9a-9e A schematic diagram of various states in the process of forming an upper cover in a method for preparing a MEMS acceleration sensor chip according to an embodiment of the present invention;

[0045] Figure 10a-Figure 10c It is a schematic diagram of various states in the bonding process of the sensor substrate and the upper cover in the method for preparing the MEMS acceleration sensor chip according to an embodiment of the present invention;

[0046] Fig.11a This is an optical image of the functional layer remaining after the functional layer is corroded when the process release holes are misaligned;

[0047] Fig.11b This is an optical image of the functional layer remaining when the process release holes are arranged in a non-displaced manner and the functional layer is corroded;

[0048] Fig.11c This is a diagram showing the corrosion of the functional layer when the process release holes are arranged in a non-displaced manner;

[0049] Fig.12 The figure is a graph showing changes in the fully differential capacitance of a MEMS acceleration sensor chip according to an embodiment of the present invention at 20° C. and 100° C. under different accelerations. DETAILED DESCRIPTION

[0050] refer to Figure 1 Since acceleration itself is difficult to measure directly, it needs to be converted into other physical quantities for measurement. The most common method is to convert acceleration into displacement changes of the mass block, and then convert the displacement changes into other quantities for measurement. The principle is simply explained as follows Figure 1 As shown, the second-order inertial system composed of mass block m, spring k and system damping b converts the accelerometer input a into displacement x, and then converts the displacement x into electrical signal output through piezoresistive, piezoelectric or capacitive displacement detection elements. The acceleration can be converted by detecting the electrical signal.

[0051] When the accelerometer input tends to be steady, the displacement of the mass block also tends to be stable. At this time, the relationship between the displacement x and acceleration a of the system can be expressed as:

[0052]

[0053] Displacement sensitivity S x for:

[0054]

[0055] Where ω0 is the natural frequency of the second-order system, which is determined by the mass m of the system mass block m and the stiffness k of the spring k, and is defined as It can be seen that for the second-order mechanical system of the inertial accelerometer, its displacement sensitivity is affected by the natural frequency of the system. The larger the frequency, the smaller the displacement sensitivity. At the same time, the larger the mass of the system, the smaller the spring stiffness, the lower the natural frequency, the greater the displacement sensitivity, but the smaller the quality factor.

[0056] The working principle of capacitive accelerometer is that the change of displacement changes the parameters in the capacitor, thereby realizing the conversion of mechanical physical quantity into electrical quantity and outputting the signal. The basic working principle of the capacitive sensitive part can be explained by a flat plate capacitor. Ignoring the edge effect, the capacitance of the capacitive sensitive part can be expressed as:

[0057]

[0058] Where C is the capacitance, ε is the dielectric constant of the medium between the plates, A is the area between the plates, and d is the distance between the plates. It can be seen that the change in the dielectric constant, the change in the plate area, and the scaling of the plate distance will all lead to changes in the capacitance and form an exact functional relationship with it.

[0059] For example, Figure 2a and Figure 2b As shown, the displacement change of the electrode plate causes the initial gap d0 to change by Δd, and then the acceleration a is measured by the change of the capacitance value C.

[0060] For MEMS acceleration sensor chips, their thermal stability is related to their preparation materials, sensor body structure and measurement circuit. Among them, because MEMS is usually a silicon-based device, the silicon material will undergo thermal expansion as the temperature changes, which will generate stress and strain inside the sensitive structure of the accelerometer chip. If the stress is concentrated on the spring beam, the system stiffness, that is, the spring stiffness k, will change. If the strain becomes accumulated and cannot be reasonably released, this will cause the initial gap d0 of the capacitor comb pair to change, thereby affecting the output ΔC of the capacitance signal. The sensitive structure of the existing technology is limited by the above problems and is difficult to meet the detection and high-precision measurement of acceleration in extreme high temperature environments.

[0061] In order to solve the problem that capacitive MEMS acceleration sensor chips are difficult to meet the requirements of acceleration detection and high-precision measurement in extreme high temperature environments, the inventors of the present application have conducted careful research and proposed a structure and preparation method of a MEMS acceleration sensor chip to improve the thermal stability of the capacitive MEMS acceleration sensor chip, reduce the structural deformation of the movable structure caused by thermal stress and the resulting changes in detection capacitance, so that the capacitive MEMS acceleration sensor chip can meet the requirements of acceleration detection and high-precision measurement in extreme high temperature environments.

[0062] The present invention provides a structure of a MEMS acceleration sensor chip, comprising: a sensor substrate, the sensor substrate comprising: a stacked base layer, a functional layer and a sensitive structural layer; the sensitive structural layer comprising a sensitive mass block unit, the sensitive mass block unit comprising a main longitudinal beam, a sensitive mass block and a plurality of movable electrodes located on both sides of the sensitive mass block; the sensitive mass block is arranged around the main longitudinal beam and elastically connected to the main longitudinal beam; the movable electrode is fixedly connected to the sensitive mass block; the sensitive structural layer also comprises fixed electrode units located on both sides of the sensitive mass block; the fixed electrode unit at least comprises a plurality of fixed electrodes extending toward the main longitudinal beam; the fixed electrode unit is fixedly connected to the base layer; the functional layer has a hollow area and a hollow area surrounding the hollow area. The projection of the hollow area on the sensitive structure layer at least covers the sensitive mass block unit and the fixed electrode unit; the edge area is fixedly connected to the base layer and the sensitive structure layer; the movable electrode and the fixed electrode constitute a differential capacitor structure; the sensitive mass block is suitable for displacement along the extension direction of the main longitudinal beam under external acceleration, driving the movable electrode to displace; wherein the main longitudinal beam is connected and fixed to the base layer through the main anchor point; main auxiliary anchor points are respectively arranged on the opposite sides of the main anchor point along the extension direction of the main longitudinal beam, and the main longitudinal beam is also connected and fixed to the base layer through the main auxiliary anchor points; the stiffness of the connection structure between the main auxiliary anchor point and the main longitudinal beam in the sensitive direction of the sensitive mass block unit is less than the stiffness in the non-sensitive direction.

[0063] The present invention also provides a method for preparing the structure of a MEMS acceleration sensor chip, comprising the following steps: forming a sensor substrate, including: providing a substrate layer; forming an initial functional layer on the substrate layer; forming an initial sensitive structural layer on the side of the initial functional layer facing away from the substrate layer; etching the initial sensitive structural layer to form a sensitive structural layer, including: forming a sensitive mass block unit, the sensitive mass block unit including a main longitudinal beam, a sensitive mass block and a plurality of movable electrodes located on both sides of the sensitive mass block; the sensitive mass block is arranged around the main longitudinal beam and elastically connected to the main longitudinal beam; the movable electrode is fixedly connected to the sensitive mass block; and at the same time, fixed electrode units located on both sides of the sensitive mass block are formed; the fixed electrode unit at least includes a plurality of electrodes extending toward the longitudinal beam; and the plurality of electrodes extending toward the longitudinal beam are provided at the same time. A plurality of fixed electrodes extending from the main longitudinal beam; the functional layer is corroded through the sensitive structural layer to form a hollow area and an edge area surrounding the hollow area, and the projection of the hollow area on the sensitive structural layer at least covers the sensitive mass block unit and the fixed electrode unit; the edge area is fixedly connected to the base layer and the sensitive structural layer; wherein the step of etching the initial sensitive structural layer to form the sensitive structural layer also includes: forming a main anchor point connecting and fixing the main longitudinal beam to the base layer; forming main auxiliary anchor points on opposite sides of the main anchor point along the extension direction of the main longitudinal beam, and the main longitudinal beam is also connected and fixed to the base layer through the main auxiliary anchor points; the stiffness of the connection structure between the main auxiliary anchor point and the main longitudinal beam in the sensitive direction of the sensitive mass block unit is less than the stiffness in the non-sensitive direction.

[0064] The technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. In the description of the present invention, it should be noted that the terms "first", "second" and "third" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0065] Example 1

[0066] refer to Figure 3-Figure 5 The present invention provides a structure of a MEMS acceleration sensor chip, comprising:

[0067] The sensor substrate 1 comprises: a base layer 11 , a functional layer 12 and a sensitive structure layer 13 which are stacked.

[0068] The sensitive structural layer 13 includes a sensitive mass block unit, which includes a main longitudinal beam 132, a sensitive mass block 131 and a plurality of movable electrodes (including 133a, 133b, 133c and 133d) located on both sides of the sensitive mass block; the sensitive mass block 131 is arranged around the main longitudinal beam 132 and is elastically connected to the main longitudinal beam 132; the movable electrode is fixedly connected to the sensitive mass block 131.

[0069] The sensitive structural layer 13 further includes fixed electrode units located on both sides of the sensitive mass block; the fixed electrode units at least include a plurality of fixed electrodes (including 134a, 134b, 134c and 134d) extending toward the main longitudinal beam 132; the fixed electrode units are fixedly connected to the base layer 11;

[0070] The functional layer 12 has a hollow area and an edge area surrounding the hollow area, and the projection of the hollow area on the sensitive structure layer 13 at least covers the sensitive mass block unit and the fixed electrode unit; the edge area is fixedly connected to the base layer 11 and the sensitive structure layer 13;

[0071] The movable electrode and the fixed electrode form a differential capacitor structure; the sensitive mass block 131 is suitable for displacement along the extension direction of the main longitudinal beam 132 under external acceleration, driving the movable electrode to displace.

[0072] The main longitudinal beam 132 is connected and fixed to the base layer 11 through the main anchor point 135; main auxiliary anchor points (including 1351a and 1351b) are respectively arranged on the two opposite sides of the main anchor point 135 along the extension direction of the main longitudinal beam 132, and the main longitudinal beam 132 is also connected and fixed to the functional layer 12 and the base layer 11 through the main auxiliary anchor points; the connection structure of the main auxiliary anchor point and the main longitudinal beam 132 (including Figure 4In the structure at the position indicated by 1352a and 1352b in FIG. 1 , in the sensitive direction of the sensitive mass block unit (i.e., the direction in which the sensitive mass block is displaced, in this embodiment, Figure 4 The rigidity of the middle main longitudinal beam 132 in the extension direction is smaller than that in the non-sensitive direction (i.e. Figure 4 The rigidity in the direction other than the extension direction of the main longitudinal beam 132).

[0073] The structure of the MEMS acceleration sensor chip provided in this embodiment, the sensitive structure layer 13 includes a sensitive mass block unit and a fixed electrode unit; the fixed electrode unit is fixedly connected to the base layer; active electrodes are arranged on both sides of the sensitive mass block 131, and the fixed electrode unit is arranged with fixed electrodes, and the active electrodes and the fixed electrodes form a differential capacitance structure. The sensitive mass block 131 is elastically connected to the main longitudinal beam 132 through an elastic member, and the main longitudinal beam 132 is fixedly connected to the base layer 11 through a main anchor point 135. In this way, the sensitive mass block is suitable for displacement along the extension direction of the main longitudinal beam under the acceleration applied by the outside world, driving the movable electrode to displace, so as to realize differential capacitance acceleration sensing measurement. Compared with the single capacitance acceleration sensing measurement, the differential capacitance acceleration sensing measurement has a doubled capacitance change, doubled sensitivity, and better nonlinear error performance for the same plate displacement. On this basis, main auxiliary anchor points are respectively arranged on both sides of the main anchor point 135 along the extension direction of the main longitudinal beam, and the main longitudinal beam 132 is also connected and fixed to the functional layer 12 and the base layer 11 through the main auxiliary anchor points. The main auxiliary anchor point is an axisymmetric structure with the central axis of the main longitudinal beam 132 as the axis of symmetry; the connection structure of the main auxiliary anchor point and the main longitudinal beam 132 has a stiffness in the sensitive direction of the sensitive mass block unit that is less than that in the non-sensitive direction. In this way, through the axisymmetric setting of the main auxiliary anchor point, since the stiffness in the sensitive direction of the sensitive mass block unit is less than the stiffness in the non-sensitive direction, it provides support to the main longitudinal beam in the non-sensitive direction (such as the direction other than the extension direction of the main longitudinal beam), so that when the main longitudinal beam is disturbed in the non-sensitive direction, it is not easy for the main longitudinal beam to deform and displace in the non-sensitive direction, thereby making it difficult for the sensitive mass block to deform and displace in the non-sensitive direction. In the sensitive direction, the connection structure of the main auxiliary anchor point and the main longitudinal beam 132 can also eliminate the deformation caused by thermal stress, so that the main longitudinal beam 132 itself is not easy to deform under the influence of thermal stress, and then the displacement of the active electrode affected by acceleration is not easy to be affected by thermal stress, so that the acceleration measurement is not easy to be disturbed by the influence of thermal stress, thereby improving the thermal stability of the MEMS acceleration sensor chip.

[0074] refer to Figure 2a and 2b , Figure 2a It is a capacitance schematic diagram of a single capacitive acceleration sensor chip; Figure 2bThe capacitance diagram of the differential capacitive acceleration sensor chip is shown in Table 1.

[0075] Table 1: Comparison of single capacitor operation mode and differential operation mode

[0076]

[0077] By comparing the data in the table, we can find that compared with the single capacitance mode, the capacitance change under the differential working mode is doubled for the same plate displacement, the sensitivity is doubled, and the nonlinear error performance is better. Therefore, the differential capacitance sensor is more effective.

[0078] Furthermore, the main auxiliary anchor points are connected to the main longitudinal beam 132 via a main beam decoupling beam; that is, the connection structure between the main auxiliary anchor points and the main longitudinal beam 132 is a main beam decoupling beam (including 1352a and 1352b in the figure). The width of the main auxiliary anchor points (1351a, 1351b) is greater than the width of the main longitudinal beam 132; the main body of the main auxiliary anchor points (1351a, 1351b) is perpendicular to the extension direction of the main longitudinal beam 132; both ends of the main body of the main auxiliary anchor points (1351a, 1351b) extend a portion of the length of the connecting portion along the extension direction of the main longitudinal beam 132, and the connecting portion is connected to the end of the main longitudinal beam 132 via the main beam decoupling beam (1352a, 1352b); the main auxiliary anchor points (1351a, 1351b) are connected to the main longitudinal beam 132 via the main beam decoupling beam (1352a, 1352b). The main body of the main auxiliary anchor points (1351a, 1351b) is connected and fixed to the base layer 11, and the connecting parts of the main auxiliary anchor points (1351a, 1351b) and the main beam decoupling beam are suspended on the base layer 11; the main beam decoupling beam (1352a, 1352b) is suitable for deforming along the extension direction of the main longitudinal beam, so that the distance between the position where the main beam decoupling beam (1352a, 1352b) is connected to the main longitudinal beam 132 and the main body of the main auxiliary anchor points (1351a, 1351b) changes in a sensitive direction when subjected to thermal stress.

[0079] refer to Figure 5 In this embodiment, both ends of the main body of the main auxiliary anchor point 1351a extend a portion of the length of the connecting portion along the extension direction of the main longitudinal beam 132, and the connecting portion is connected to the end of the main longitudinal beam 132 through the main beam decoupling beam 1352a; the main beam decoupling beam 1352a is suitable for deforming along the extension direction of the main longitudinal beam 132, so that the distance between the position where the main beam decoupling beam 1352a connects the main longitudinal beam 132 and the main body of the main auxiliary anchor point 1351a changes in the sensitive direction when subjected to thermal stress; in other words, the main beam decoupling beam 1352a can deform in the sensitive direction when the structure is affected by thermal stress. In this way, in the sensitive direction of the sensitive mass block 131, that is, the extension direction of the main longitudinal beam 132, the main beam decoupling beams (1352a, 1352b) can undergo the following deformation due to thermal expansion. Figure 5 Deformation shown (no thermal stress at room temperature can refer to Figure 4 state, which is close to the state of being perpendicular to the main longitudinal beam 132), so the deformation of the main beam decoupling beam can reduce the deformation of the sensitive mass block caused by the thermal stress; in the non-sensitive direction, that is, the direction at a certain angle to the extension direction of the main longitudinal beam 132, for example, the direction perpendicular to the extension direction of the main longitudinal beam 132, the direction of the force is consistent with the length direction of the main beam decoupling beam 1352a, and it is not easy to deform. Therefore, it has good rigidity above this direction and is not easy to be disturbed. The situation of the main auxiliary anchor point 1351b and the main beam decoupling beam 1352b on the other side is the same, and will not be repeated here.

[0080] In this way, by setting the main auxiliary anchor points, the connection stability of the main longitudinal beam is improved, and the deformation or strain caused by thermal stress is reduced, thereby improving the thermal stability of the MEMS acceleration sensor.

[0081] For further reference, Figure 4 The sensitive mass block 131 is provided with an elastic component accommodating groove on the side of the extension direction of the main longitudinal beam 132, and an elastic component 136 is provided in the elastic component accommodating groove. The two ends of the elastic component 136 are respectively connected to the main longitudinal beam 132 and the sensitive mass block 131, so that the sensitive mass block 131 is suitable for displacement along the extension direction of the main longitudinal beam 132 under external acceleration.

[0082] By setting the elastic component accommodating groove, the elastic component is accommodated within the structural range of the elastic component 136, which simplifies the overall structure and avoids the effect of reduced sensitivity caused by the need to set the elastic component so that the main longitudinal beam 132 for fixing the elastic component is too far away from the sensitive mass block 131.

[0083] Specifically, in this embodiment, the elastic member 136 is a folding beam spring; the folding beam spring is a serpentine folding structure, which extends in a serpentine shape along the extension direction of the main longitudinal beam, with one end connected to the side of the main longitudinal beam and the other end connected to the side of the sensitive mass block. In this way, the folding beam spring with a serpentine folding structure realizes an elastic connection between the sensitive mass block 131 and the main longitudinal beam 132 at the side of the main longitudinal beam 132, and can be displaced along the extension direction of the main longitudinal beam 132. In some embodiments, the corner of the folding beam spring is an arc shape. The arc-shaped corner has better lateral rigidity interference capability than the fold line corner.

[0084] Furthermore, in the present embodiment, the sensitive mass block 131, the folded beam spring and the movable electrode (including 133a, 133b, 133c and 133d) together constitute a centrally symmetrical figure, and the center of symmetry of the centrally symmetrical figure coincides with the main anchor point; there are multiple fixed electrode units, which are centrally symmetrically distributed with the main anchor point as the center of symmetry; with the extension direction of the main longitudinal beam as the y-axis and the direction perpendicular to the y-axis and passing through the center of the main anchor point as the x-axis, the sensitive mass block, the folded beam spring, the movable electrode and the fixed electrode unit are symmetrically distributed along the y-axis, and symmetrically distributed along the x-axis; adjacent movable electrodes and fixed electrodes constitute capacitors; capacitors located on the same side of the x-axis are connected in parallel; and capacitors located on both sides of the x-axis have opposite capacitance changes under external acceleration.

[0085] Specifically, refer to Figure 4 The movable electrodes are divided into four groups of 133a, 133b, 133c and 133d with the x-axis and y-axis as boundaries, and the fixed electrodes are divided into four groups of 134a, 134b, 134c and 134d with the x-axis and y-axis as boundaries. The adjacent movable electrodes and fixed electrodes constitute capacitors, such as 133a and 134a, 133b and 134b, each constituting a capacitor. The capacitors on the same side of the x-axis are connected in parallel. At the same time, the capacitors located on both sides of the x-axis, such as the capacitors formed by 133a and 134a, and the capacitors formed by 133c and 134c, have opposite capacitance changes under external acceleration. As shown in the figure, on one side of the x-axis in the figure, the movable electrode 133a is the lower electrode plate and the fixed electrode 134a is the upper electrode plate; on the other side of the x-axis, the movable electrode 133a is the upper electrode plate and the fixed electrode 134a is the lower electrode plate; therefore, when the sensitive mass block 131 moves along the extension direction of the main longitudinal beam 132, although the movable electrodes on both sides of the x-axis have the same displacement direction, the capacitance changes generated are opposite: for example, when the sensitive mass block 131 moves upward in the figure, on the side of 133a and 134a, the upper and lower electrodes are close, while on the side of 133c and 134c, the upper and lower electrodes are close. For the 133a and 134a group and the 133b and 134b group on the same side of the x-axis, the changes are the same. In this way, a differential capacitor is formed.

[0086] The capacitors of group 133a and 133b are C1, the capacitors of group 133b and 134b are C2, the capacitors of group 133c and 133b are C3, and the capacitors of group 133d and 134d are C4. The differential capacitance output is ΔC=C1+C2-C3-C4. Since C1, C2, C3, and C4 are completely centrally symmetrically arranged, the initial state is ΔC=C 1初始 +C 2初始 -C 3初始 -C 4初始 If a lateral cross-axis acceleration disturbance is introduced, the capacitance will change due to the change in the position of the electrode plate. The capacitance changes are ΔC1, ΔC2, ΔC3, and ΔC4 respectively. At this time, C1 = C1初始 +ΔC1, C2=C 2初始 +ΔC2, C3=C 3初始 -ΔC3, C4=C 4初始 -ΔC4; Substituting the differential capacitance output into the above equation, we get ΔC = C 1初始 +C 2初始 -C 3初始 -C 4初始 +ΔC1+ΔC2-ΔC3-ΔC4. Since the structure is completely symmetrical, ΔC1=ΔC3, ΔC2=ΔC4. Therefore, when subjected to lateral interference, the differential capacitance output is still ΔC=C 1初始 +C 2初始 -C 3初始 -C 4初始 ; Thus, the completely symmetrical distribution can enhance stability; similarly, when the ambient temperature of the accelerometer changes, the acceleration sensor chip will expand from the center of the anchor point to the surrounding area, driving the electrodes to undergo different degrees of micro-displacement. The capacitance change ΔC1=ΔC2=ΔC3=ΔC4 caused at this time can be eliminated in the differential working mode. Therefore, the completely symmetrical structure can play a role in common mode suppression.

[0087] Furthermore, the sensitive mass block 131 and the main longitudinal beam 132 are provided with a plurality of process release holes h penetrating through the sensitive mass block 131 and the main longitudinal beam 132 in the thickness direction; each process release hole h is arranged in an array, and the process release holes in adjacent rows are arranged in a staggered manner as follows: Figure 6 As shown. The process release holes h can also be arranged without misalignment, such as Figure 4 The process release hole h is used to process the lower functional layer 12 through the process release hole during the preparation process, so as to realize the suspended state of the main longitudinal beam 132, the sensitive mass block 131 and the fixed electrode, so that the sensitive mass block 131 can be displaced. For the distribution of the process release hole h, please refer to Fig.11a , Fig.11b and Fig.11c The same release hole shape and gap, only the arrangement is different. Fig.11b For non-staggered arrangement, Fig.11a For staggered arrangement, it can be seen that the staggered arrangement of the accelerator chip has less residue on the sacrificial layer, indicating that the gas phase hydrofluoric acid corrodes it faster. Fig.11c According to the corrosion situation shown in the figure, it can be explained that when the non-staggered arrangement is used, the corrosion of the sacrificial layer gradually spreads to the surrounding areas with the release hole as the center. Taking the four adjacent release holes as a repeating unit for explanation, it can be seen from the figure that the central area of ​​the four release holes surrounds the area where corrosion is most difficult to occur, leaving a diamond-shaped sacrificial layer residue as shown in the figure. If the arrangement is staggered, it will help to improve this phenomenon.

[0088] For further reference, Figure 4The fixed electrode unit also includes a secondary longitudinal beam (including 137a, 137b, 137c and 137d); the secondary longitudinal beam is parallel to the main longitudinal beam 132, and is connected and fixed to the base layer through secondary anchor points (including 139a, 139b, 139c and 139d); the fixed electrode unit is provided with a secondary auxiliary anchor point (including 1391a, 1391b, 1391c and 1391d) on one side along the extension direction of the secondary longitudinal beam, and the secondary longitudinal beam is also connected and fixed to the base layer 11 through the secondary auxiliary anchor point; the secondary auxiliary anchor point is an axisymmetric structure with the central axis of the secondary longitudinal beam as the symmetry axis; the connection structure of the secondary auxiliary anchor point and the secondary longitudinal beam (including 1392a, 1392b, 1392c, 1392d) has a stiffness in the sensitive direction of the sensitive mass block unit that is less than that in the non-sensitive direction.

[0089] Similar to the structure of the main longitudinal beam 132 and the main auxiliary anchor point, the secondary auxiliary anchor point is arranged axially symmetrically. Since the stiffness of the sensitive mass block unit in the sensitive direction is less than the stiffness in the non-sensitive direction, it provides support for the secondary longitudinal beam in the non-sensitive direction (such as the direction other than the extension direction of the main longitudinal beam), so that when the secondary longitudinal beam is disturbed in the non-sensitive direction, it is not easy for the secondary longitudinal beam to deform and displace in the non-sensitive direction, thereby making it difficult for the fixed electrode to deform and displace in the non-sensitive direction. In the sensitive direction, the connection structure between the secondary auxiliary anchor point and the secondary longitudinal beam can also eliminate the deformation caused by thermal stress, so that the secondary longitudinal beam itself is not easy to deform under the influence of thermal stress, and then the fixed electrode is not easy to be affected by acceleration and deform or displace, so that the acceleration measurement is not easy to be disturbed by the influence of thermal stress, thereby improving the thermal stability of the MEMS acceleration sensor chip.

[0090] Specifically, similar to the main auxiliary anchor point, the auxiliary auxiliary anchor point is connected to the auxiliary longitudinal beam through the auxiliary beam decoupling beam; the width of the auxiliary auxiliary anchor point is greater than the width of the auxiliary longitudinal beam; the main body of the auxiliary auxiliary anchor point is perpendicular to the extension direction of the auxiliary longitudinal beam; both ends of the main body of the auxiliary auxiliary anchor point extend a connection portion of a certain length along the extension direction of the auxiliary longitudinal beam, and the connection portion is connected to the end of the main longitudinal beam through the auxiliary beam decoupling beam; the main body of the auxiliary auxiliary anchor point is connected and fixed to the base layer, and the connection portion of the auxiliary auxiliary anchor point and the auxiliary beam decoupling beam are suspended on the base layer; the auxiliary beam decoupling beam is suitable for deformation along the extension direction of the auxiliary longitudinal beam, so that the distance between the position where the auxiliary beam decoupling beam connects the auxiliary longitudinal beam and the main body of the auxiliary auxiliary anchor point changes in the sensitive direction when subjected to thermal stress. Therefore, the auxiliary beam decoupling beam can provide support to the auxiliary longitudinal beam in the non-sensitive direction, eliminate thermal stress and strain in the sensitive direction, and thus improve the thermal stability of the MEMS acceleration sensor chip.

[0091] Furthermore, there are multiple fixed electrode units, which are distributed symmetrically with the main anchor point as the center of symmetry; wherein the secondary anchor points of each fixed electrode unit are distributed symmetrically with the main anchor point as the center of symmetry, and at the same time, the secondary auxiliary anchor points of each fixed electrode unit are also distributed symmetrically with the main anchor point as the center of symmetry.

[0092] Similar to the aforementioned sensitive mass block 131 and the movable electrode, there are also multiple fixed electrode units, which are correspondingly centrally symmetrically distributed, thereby achieving complete symmetry, and further realizing the common-mode suppression effect of the differential capacitance MEMS acceleration sensor.

[0093] Furthermore, the secondary longitudinal beam is provided with a plurality of process release holes h penetrating the secondary longitudinal beam in the thickness direction; each process release hole is arranged in an array, and the process release holes in adjacent columns are arranged in a staggered manner. Similar to the process release holes h of the aforementioned sensitive mass block 131 and the main longitudinal beam 132, the process release holes are used to process the functional layer thereunder to form a hollow area, thereby realizing the suspension of the secondary longitudinal beam and the fixed electrode.

[0094] Furthermore, the sensitive structure layer 13 also includes a bonding outer frame 1300; the bonding outer frame 1300 surrounds and sets up a main body activity space, and the sensitive mass block unit and the fixed electrode unit are arranged in the main body activity space; the structure of the MEMS acceleration sensor chip also includes: an upper cover 2; the upper cover 2 includes a cover plate, and a frame protruding from the surface of one side of the cover plate; the frame and the cover plate jointly enclose a cover plate activity space; the frame is suitable for connecting with the bonding outer frame 1300, the cover plate activity space corresponds to the main body activity space, and together with the hollow space of the functional layer, the sensitive mass block unit and the fixed electrode unit are accommodated. In a specific embodiment, the frame is connected to the bonding outer frame 1300 through a bonding medium layer.

[0095] Furthermore, a conductive medium layer is provided on the side of the sensitive structure layer 13 facing the upper cover 2, and the conductive medium layer at least covers the sensitive structure unit and the fixed electrode unit; the capacitance change of the sensitive structure layer is derived to the conductive medium layer through the conductive medium layer; the cover plate is provided with a plurality of through holes, the through holes expose the conductive medium layer, the through holes are filled with conductive electrodes, the conductive electrodes are connected to the conductive medium layer, and are exposed on the surface of the cover plate facing away from the base layer; the positions of the through holes correspond to the main anchor point and the secondary anchor point. Through the conductive electrodes, the electrical signal in the conductive medium layer can be led out, so that the external monitoring equipment can measure the acceleration according to the change of the electrical signal inside the MEMS acceleration sensor chip.

[0096] In order to reflect the actual working effect of the structure of the MEMS acceleration sensor chip provided in this embodiment, the same acceleration is applied to it at different temperatures for testing, and the data is collected and plotted. Fig.12At 20°C (normal temperature) and 100°C (unconventional high temperature), under the same acceleration input, the fully differential capacitance and the change amount remain basically consistent, which shows that the structure of the MEMS acceleration sensor chip provided in this embodiment has good temperature stability.

[0097] Example 2

[0098] This embodiment provides a method for preparing a structure of a MEMS acceleration sensor chip, which is used to prepare the MEMS acceleration sensor chip of the above embodiment 1. Figure 7 , including the following steps:

[0099] A sensor substrate is formed, comprising:

[0100] refer to Figure 8a , providing a substrate layer 11; forming an initial functional layer 120 on the substrate layer 11; forming an initial sensitive structural layer 130 on the side of the initial functional layer 120 facing away from the substrate layer 11;

[0101] The initial sensitive structure layer 130 is etched to form a sensitive structure layer 13, including:

[0102] refer to Figure 8b-8f ,as well as Figure 4 , forming a sensitive mass block unit, the sensitive mass block unit includes a main longitudinal beam, a sensitive mass block and a plurality of movable electrodes located on both sides of the sensitive mass block; the sensitive mass block is arranged around the main longitudinal beam and elastically connected to the main longitudinal beam; the movable electrode is fixedly connected to the sensitive mass block;

[0103] Also refer to Figure 8b-8f ,as well as Figure 4 , and at the same time, fixed electrode units are formed on both sides of the sensitive mass block; the fixed electrode units at least include a plurality of fixed electrodes extending toward the main longitudinal beam;

[0104] refer to Figure 8h-Figure 8i , the initial functional layer 120 is corroded through the sensitive structural layer to form a functional layer 12, and a hollow area and an edge area surrounding the hollow area are formed, and the projection of the hollow area on the sensitive structural layer 13 at least covers the sensitive mass block unit and the fixed electrode unit; the edge area is fixedly connected to the base layer 11 and the sensitive structural layer 13;

[0105] Among them, the step of etching the initial sensitive structure layer 130 to form the sensitive structure layer 13 also includes: forming a main anchor point for connecting and fixing the main longitudinal beam to the base layer; forming main auxiliary anchor points on opposite sides of the main anchor point along the extension direction of the main longitudinal beam, and the main longitudinal beam is also connected and fixed to the base layer through the main auxiliary anchor points; the stiffness of the connection structure between the main auxiliary anchor point and the main longitudinal beam in the sensitive direction of the sensitive mass block unit is less than the stiffness in the non-sensitive direction.

[0106] The method for preparing the structure of the MEMS acceleration sensor chip provided in this embodiment can manufacture the structure of the MEMS acceleration sensor chip provided in the above-mentioned embodiment 1. The structure of the formed MEMS acceleration sensor chip, the sensitive structure layer includes a sensitive mass block unit and a fixed electrode unit; the fixed electrode unit is fixedly connected to the base layer; active electrodes are arranged on both sides of the sensitive mass block, the fixed electrode unit is arranged with a fixed electrode, and the active electrode and the fixed electrode form a differential capacitance structure. The sensitive mass block is elastically connected to the main longitudinal beam through an elastic member, and the main longitudinal beam is fixedly connected to the base layer through a main anchor point. In this way, the sensitive mass block can be adapted to be displaced along the extension direction of the main longitudinal beam under the external acceleration. In this way, the sensitive mass block can be adapted to be displaced along the extension direction of the main longitudinal beam under the external acceleration, driving the active electrode to be displaced, thereby realizing differential capacitance acceleration sensing measurement. Compared with single capacitance acceleration sensing measurement, the differential capacitance acceleration sensing measurement has a doubled capacitance change, doubled sensitivity, and better nonlinear error performance for the same plate displacement. On this basis, main auxiliary anchor points are respectively arranged on both sides of the main anchor point along the extension direction of the main longitudinal beam, and the main longitudinal beam is also connected and fixed to the base layer through the main auxiliary anchor points. The main auxiliary anchor point is an axisymmetric structure with the central axis of the main longitudinal beam as the axis of symmetry; the connection structure of the main auxiliary anchor point and the main longitudinal beam has a stiffness in the sensitive direction of the sensitive mass block unit that is smaller than that in the non-sensitive direction. In this way, through the axisymmetric arrangement of the main auxiliary anchor point, since the stiffness in the sensitive direction of the sensitive mass block unit is smaller than that in the non-sensitive direction, it provides support to the main longitudinal beam in the non-sensitive direction (such as the direction other than the extension direction of the main longitudinal beam), so that when the main longitudinal beam is disturbed in the non-sensitive direction, it is not easy for the main longitudinal beam to deform and displace in the non-sensitive direction, thereby making it difficult for the sensitive mass block to deform and displace in the non-sensitive direction. In the sensitive direction, the connection structure between the main auxiliary anchor point and the main longitudinal beam can also eliminate the deformation caused by thermal stress, so that the main longitudinal beam itself is not easily deformed under the influence of thermal stress, and the displacement of the active electrode affected by acceleration is not easily affected by thermal stress, so that the acceleration measurement is not easily disturbed by the influence of thermal stress, thereby improving the thermal stability of the MEMS acceleration sensor chip.

[0107] Furthermore, the step of etching the initial sensitive structure layer to form the sensitive structure layer includes:

[0108] refer to Figure 8f , forming a sensitive layer mask M3 on the side of the initial sensitive structure layer 130 facing away from the base layer 11;

[0109] refer to Figure 8g , using the sensitive layer mask M3 as a mask, patterning and etching the initial sensitive structure layer 130 to form a sensitive mass block unit and a fixed electrode unit;

[0110] refer to Figure 8h , remove the sensitive layer mask.

[0111] Furthermore, the step of forming the sensitive mass block unit includes: forming a main beam decoupling beam connecting the main auxiliary anchor point and the main longitudinal beam; the width of the main auxiliary anchor point is greater than the width of the main longitudinal beam; the main body of the main auxiliary anchor point is perpendicular to the extension direction of the main longitudinal beam; both ends of the main body of the main auxiliary anchor point extend a partial length of connecting parts along the extension direction of the main longitudinal beam, and the connecting parts are connected to the end of the main longitudinal beam through the main beam decoupling beam; the main beam decoupling beam is suitable for deforming along the extension direction of the main longitudinal beam, so that the distance between the position where the main beam decoupling beam is connected to the main longitudinal beam and the main body of the main auxiliary anchor point changes in a sensitive direction when subjected to thermal stress.

[0112] Furthermore, the step of forming the sensitive mass block unit includes: forming an elastic component accommodating groove on the side of the sensitive mass block in the extension direction of the main longitudinal beam, an elastic component is arranged in the elastic component accommodating groove, and the two ends of the elastic component are respectively connected to the main longitudinal beam and the sensitive mass block, so that the sensitive mass block is suitable for displacement along the extension direction of the main longitudinal beam under external acceleration; the elastic component is a folding beam spring; the folding beam spring is a serpentine folding structure, which extends in a serpentine shape along the extension direction of the main longitudinal beam, one end of which is connected to the side of the main longitudinal beam, and the other end of which is connected to the side of the sensitive mass block.

[0113] Furthermore, the formed sensitive mass block, folded beam spring and movable electrode together constitute a centrally symmetrical figure, and the center of symmetry of the centrally symmetrical figure coincides with the main anchor point; the formed fixed electrode units are multiple, with the main anchor point as the center of symmetry and centrally symmetrically distributed; with the extension direction of the main longitudinal beam as the y-axis, and the direction perpendicular to the y-axis and passing through the center of the main anchor point as the x-axis, the sensitive mass block, folded beam spring, movable electrode and fixed electrode units are symmetrically distributed along the y-axis, and symmetrically distributed along the x-axis; adjacent movable electrodes and fixed electrodes constitute capacitors; capacitors on the same side of the x-axis are connected in parallel; capacitors on both sides of the x-axis have opposite capacitance changes under external acceleration.

[0114] Furthermore, the step of forming a fixed electrode unit located on both sides of the sensitive mass block also includes: simultaneously forming a secondary longitudinal beam; the secondary longitudinal beam is parallel to the main longitudinal beam, and is connected and fixed to the base layer through a secondary anchor point; a secondary auxiliary anchor point is formed on one side of the fixed electrode unit along the extension direction of the secondary longitudinal beam, and the secondary longitudinal beam is also connected and fixed to the base layer through the secondary auxiliary anchor point; the secondary auxiliary anchor point is an axisymmetric structure with the central axis of the secondary longitudinal beam as the axis of symmetry; the connection structure between the secondary auxiliary anchor point and the secondary longitudinal beam has a stiffness in the sensitive direction of the sensitive mass block unit that is less than that in the non-sensitive direction.

[0115] Furthermore, the step of forming fixed electrode units located on both sides of the sensitive mass block also includes: simultaneously forming a sub-beam decoupling beam connecting the sub-auxiliary anchor point and the sub-longitudinal beam; the width of the sub-auxiliary anchor point is greater than the width of the sub-longitudinal beam; the main body of the sub-auxiliary anchor point is perpendicular to the extension direction of the sub-longitudinal beam; both ends of the main body of the sub-auxiliary anchor point extend a partial length of connecting parts along the extension direction of the sub-longitudinal beam, and the connecting parts are connected to the end of the main longitudinal beam through the sub-beam decoupling beam; the main body of the sub-auxiliary anchor point is connected and fixed to the base layer, and the connecting part of the sub-auxiliary anchor point and the sub-beam decoupling beam are suspended above the base layer; the sub-beam decoupling beam is suitable for deforming along the extension direction of the sub-longitudinal beam, so that the distance between the position where the sub-beam decoupling beam is connected to the sub-longitudinal beam and the main body of the sub-auxiliary anchor point changes in the sensitive direction when subjected to thermal stress.

[0116] Furthermore, multiple fixed electrode units are formed, which are centrally symmetrically distributed with the main anchor point as the center of symmetry; wherein the secondary anchor points of each fixed electrode unit are centrally symmetrically distributed with the main anchor point as the center of symmetry, and at the same time, the secondary auxiliary anchor points of each fixed electrode unit are also centrally symmetrically distributed with the main anchor point as the center of symmetry.

[0117] Furthermore, the step of corroding the functional layer through the sensitive structure layer includes: forming a release hole mask on the side of the sensitive structure layer facing away from the base layer; using the release hole mask as a mask, etching a process release hole in the sensitive structure layer, the process release hole exposing the initial functional layer at the corresponding position; corroding the initial functional layer through the process release hole to form a hollow area in the initial functional layer; the projection of the hollow area on the sensitive structure layer at least covers the sensitive structure unit and the fixed electrode unit; and removing the release hole mask.

[0118] Furthermore, the minimum line width of the process release hole is greater than 3μm. The process release hole is not a functional structure of the sensor and does not serve the acceleration sensing function. It is only a structure added to realize the preparation of the sensor, and is a non-functional structure; while for example, the capacitor and folded beam spring in the sensitive structure layer of the sensor are structures set to realize the sensing function of the sensor, and are functional structures. The minimum gap size of these functional structures, such as the minimum gap of the capacitor is 3μm, and the length, width, gap, etc. of other functional structures are not less than 3μm, then the minimum line width size in the functional structure can be said to be 3μm;

[0119] In the etching process of semiconductor technology, the minimum line width affects the etching rate. For the same processing parameters, the smaller the minimum line width of the processed graphics, the slower the rate of material removal in the etching process, so a minimum line width needs to be limited.

[0120] Therefore, the minimum line width of the process release hole is greater than 3μm (for example, either the length or the width must be greater than the minimum line width in the original structure layer, which is greater than 3μm according to the above distance). This is to avoid the introduction of the release process hole, which will increase the overall etching time.

[0121] Furthermore, the long side of the process release hole is 2-3 times greater than the short side. When the long side of the process release hole is 2-3 times greater than the short side, the etching rate at the process release hole can be further increased. However, the spacing of the long sides should not be too long. Too long will not only lead to an increase in the area of ​​a single opening, but also lead to an excessively large overall opening rate of the overall structure, which will reduce the mass of the mass block and reduce the sensitivity and stability of the sensor. At the same time, too large an opening rate will also lead to a decrease in structural strength. Therefore, it is preferred that the long side is 2-3 times the short side.

[0122] For further reference, Figure 8b-Figure 8d , before the steps of forming the sensitive mass block unit and simultaneously forming the fixed electrode unit, it also includes:

[0123] A patterned conductive dielectric layer 31 and a first bonding dielectric layer 32 are formed on the side of the initial sensitive structure layer facing away from the base layer; the conductive dielectric layer 31 at least covers the positions where the sensitive mass unit and the fixed electrode unit are predetermined to be formed; and the first bonding dielectric layer 32 covers the position corresponding to the edge area;

[0124] Specifically include:

[0125] refer to Figure 8b , forming a patterned first mask M1 on the side of the initial sensitive structure layer facing away from the base layer;

[0126] refer to Figure 8c , forming a first initial dielectric layer 3, filling the portion not covered by the first mask M1;

[0127] refer to Figure 8d , the first initial dielectric layer 3 is thinned to expose the first mask M1 , and then the first mask M1 is removed, and the remaining first initial dielectric layer 3 forms a patterned conductive dielectric layer 31 and a first bonding dielectric layer 32 .

[0128] In the steps of forming the sensitive mass block unit and the fixed electrode unit at the same time, it also includes: removing the conductive medium layer 31 corresponding to the portion removed when the sensitive mass block unit is formed, and removing the conductive medium layer 31 corresponding to the portion removed when the fixed electrode unit is formed; when forming the process release hole, removing the conductive medium layer 31 at the position corresponding to the predetermined process release hole.

[0129] Furthermore, the method for preparing the structure of the MEMS acceleration sensor chip further includes the following steps: forming an upper cover, including:

[0130] providing a cover plate substrate;

[0131] The cover plate substrate is etched to form the cover plate and a frame protruding from a surface of one side of the cover plate; the frame and the cover plate together enclose a cover plate activity space;

[0132] Fig.9e , including: forming a third cover plate mask M6 on one side of the cover plate substrate; etching the cover plate substrate using the third cover plate mask M6 as a mask to form a frame and enclose an activity space.

[0133] The process of forming the sensitive structural layer also includes:

[0134] A bonding outer frame is formed, the bonding outer frame surrounds and defines a main body activity space, and the sensitive mass block unit and the fixed electrode unit are arranged in the main body activity space; the frame is suitable for connecting with the bonding outer frame, and the activity space corresponds to the main body activity space, and the sensitive mass block unit and the fixed electrode unit are jointly accommodated.

[0135] Furthermore, a blind hole is formed at a preset position of the cover plate, and the blind hole is filled with electroplated metal to form a conductive electrode; the preset position corresponds to the position of the main anchor point and the auxiliary anchor point in the sensor substrate.

[0136] Specifically include:

[0137] refer to Figure 9a , forming a first cover plate mask M4 on one side surface of the cover plate substrate 20;

[0138] refer to Figure 9b , using the first cover plate mask M4 as a mask to etch the cover plate substrate to form a blind hole;

[0139] refer to Fig.9c , forming an electroplated metal layer, which fills the blind hole and covers the surface of the cover plate. Then, the electroplated metal layer on the surface of the cover plate is removed, and the remaining second initial dielectric layer in the blind hole forms a conductive electrode 21.

[0140] After the conductive electrode is formed, a patterned second bonding dielectric layer 33 is formed on the side of the cover plate where the conductive electrode is exposed; the second bonding dielectric layer 33 is connected to the conductive electrode 21 .

[0141] Specifically include:

[0142] refer to Figure 9d A patterned second cover mask M5 is formed on one side of the cover substrate 20; the patterned second cover mask M5 at least exposes the conductive electrode 21. The portion not covered by the second cover mask M5 is filled to form a second bonding dielectric layer 33, and the second bonding dielectric layer 33 is connected to the conductive electrode 21. The second cover mask M5 is then removed.

[0143] In addition, when the third cover mask M6 is subsequently formed, the third cover mask M6 is formed on the surface of the second bonding dielectric layer 33 .

[0144] Furthermore, in some embodiments, after forming the blind hole and before electroplating metal to fill the blind hole, it also includes: forming a composite film layer of an insulating layer, a barrier layer and a seed layer on the side wall of the blind hole (this step is not shown in the drawings). Fig.9e , etching the cover plate substrate to form a cover plate activity space.

[0145] For further reference, Fig.10a , bonding the sensor substrate 1 and the upper cover 2 through the first bonding medium layer 32 and the second bonding medium layer 33;

[0146] After bonding, the conductive electrode 21 corresponds to the main anchor point and the secondary anchor point, and is connected to the conductive medium layer 31 through the second bonding medium layer 33; the frame of the upper cover 2 and the bonding outer frame of the sensor substrate 1 are bonded and connected through the first bonding medium layer 32 and the second bonding medium layer 33;

[0147] The cover plate activity space corresponds to the main body activity space, and together with the hollow space of the functional layer, accommodates the sensitive mass block unit and the fixed electrode unit.

[0148] In addition, in some embodiments, it also includes:

[0149] refer to Figure 8e , a substrate positioning hole is formed on the side of the substrate layer 11 facing away from the sensitive structure layer 13 through a second mask M2. Fig.9e In the step of etching the cover substrate 20 to form the cover activity space, the cover positioning hole is formed simultaneously. Fig.10a In the bonding step, the upper cover and the sensor substrate are positioned by the cover plate positioning holes and the substrate positioning holes.

[0150] refer to Fig.10b , the cover substrate 20 is thinned so that the conductive electrode 21 is exposed on the surface of the cover substrate 20 facing away from the sensor substrate 1 .

[0151] refer to Fig.10c A metal electrode pad 22 is formed on the surface of the conductive electrode 21 exposed on the side of the cover substrate 20 facing away from the sensor substrate 1, so that the conductive electrode 21 can lead out electrical signals. The metal electrode pad 22 can also be formed by positioning through the substrate positioning hole.

[0152] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A structure of a MEMS acceleration sensor chip, characterized in that: include: A sensor substrate, the sensor substrate comprising: a base layer, a functional layer and a sensitive structure layer which are stacked; The sensitive structural layer comprises a sensitive mass block unit, and the sensitive mass block unit comprises a main longitudinal beam, a sensitive mass block and a plurality of movable electrodes located on both sides of the sensitive mass block; the sensitive mass block is arranged around the main longitudinal beam and elastically connected to the main longitudinal beam; the movable electrode is fixedly connected to the sensitive mass block; The sensitive structural layer further comprises fixed electrode units located on both sides of the sensitive mass block; the fixed electrode units at least comprise a plurality of fixed electrodes extending toward the main longitudinal beam; the fixed electrode units are fixedly connected to the base layer; The functional layer has a hollow area and an edge area surrounding the hollow area, and the projection of the hollow area on the sensitive structure layer at least covers the sensitive mass block unit and the fixed electrode unit; the edge area is fixedly connected to the base layer and the sensitive structure layer; The movable electrode and the fixed electrode form a differential capacitor structure; the sensitive mass block is suitable for displacement along the extension direction of the main longitudinal beam under external acceleration, driving the movable electrode to displace; Among them, the main longitudinal beam is connected and fixed to the base layer through a main anchor point; main auxiliary anchor points are respectively arranged on opposite sides of the main anchor point along the extension direction of the main longitudinal beam, and the main longitudinal beam is also connected and fixed to the base layer through the main auxiliary anchor points; the main auxiliary anchor point is an axisymmetric structure with the central axis of the main longitudinal beam as the symmetry axis; the connection structure between the main auxiliary anchor point and the main longitudinal beam has a stiffness in the sensitive direction of the sensitive mass block unit that is less than the stiffness in the non-sensitive direction.

2. The structure of the MEMS acceleration sensor chip according to claim 1, characterized in that: The main auxiliary anchor point is connected to the main longitudinal beam via a main beam decoupling beam; The width of the main auxiliary anchor point is greater than the width of the main longitudinal beam; the main body of the main auxiliary anchor point is perpendicular to the extension direction of the main longitudinal beam; Both ends of the main body of the main auxiliary anchor point extend a portion of the length of the connecting portion along the extension direction of the main longitudinal beam, and the connecting portion is connected to the end of the main longitudinal beam through the main beam decoupling beam; the main body of the main auxiliary anchor point is connected and fixed to the base layer, and the connecting portion of the main auxiliary anchor point and the main beam decoupling beam are suspended on the base layer; The main beam decoupling beam is suitable for deforming along the extension direction of the main longitudinal beam, so that the distance between the position where the main beam decoupling beam connects the main longitudinal beam and the main body of the main auxiliary anchor point changes in a sensitive direction when subjected to thermal stress.

3. The structure of the MEMS acceleration sensor chip according to claim 1, characterized in that: The sensitive mass block is provided with an elastic component accommodating groove on the side facing the extension direction of the main longitudinal beam, and an elastic component is arranged in the elastic component accommodating groove. The two ends of the elastic component are respectively connected to the main longitudinal beam and the sensitive mass block, so that the sensitive mass block is suitable for displacement along the extension direction of the main longitudinal beam under external acceleration.

4. The structure of the MEMS acceleration sensor chip according to claim 3, characterized in that: The elastic component is a folding beam spring; the folding beam spring is a serpentine folding structure, which extends in a serpentine shape along the extension direction of the main longitudinal beam, with one end connected to the side of the main longitudinal beam and the other end connected to the side of the sensitive mass block.

5. The structure of the MEMS acceleration sensor chip according to claim 4, characterized in that: The sensitive mass block, the folded beam spring and the movable electrode together form a central symmetrical figure, and the symmetry center of the central symmetrical figure coincides with the main anchor point; The fixed electrode units are multiple and are symmetrically distributed with the main anchor point as the center of symmetry; Taking the extension direction of the main longitudinal beam as the y-axis and the direction perpendicular to the y-axis and passing through the center of the main anchor point as the x-axis, the sensitive mass block, the folded beam spring, the movable electrode and the fixed electrode unit are symmetrically distributed along the y-axis and symmetrically distributed along the x-axis; The adjacent movable electrodes and the fixed electrodes form a capacitor; The capacitors located on the same side of the x-axis are connected in parallel; The capacitance changes of the capacitors located on both sides of the x-axis are opposite when an external acceleration is applied.

6. The structure of the MEMS acceleration sensor chip according to claim 1, characterized in that: The sensitive mass block and the main longitudinal beam are provided with a plurality of process release holes penetrating through the blocks in the thickness direction; the process release holes are arranged in an array, and the process release holes in adjacent rows are arranged in a staggered manner.

7. The structure of the MEMS acceleration sensor chip according to claim 1, characterized in that: The fixed electrode unit further includes a secondary longitudinal beam; the secondary longitudinal beam is parallel to the main longitudinal beam and is connected and fixed to the base layer through a secondary anchor point; The fixed electrode unit is provided with a secondary auxiliary anchor point on one side along the extension direction of the secondary longitudinal beam, and the secondary longitudinal beam is also connected and fixed to the base layer through the secondary auxiliary anchor point; the secondary auxiliary anchor point is an axisymmetric structure with the central axis of the secondary longitudinal beam as the axis of symmetry; the connection structure between the secondary auxiliary anchor point and the secondary longitudinal beam has a stiffness in the sensitive direction of the sensitive mass block unit that is less than that in the non-sensitive direction.

8. The structure of the MEMS acceleration sensor chip according to claim 7, characterized in that: The secondary auxiliary anchor point is connected to the secondary longitudinal beam via a secondary beam decoupling beam; The width of the secondary auxiliary anchor point is greater than the width of the secondary longitudinal beam; the main body of the secondary auxiliary anchor point is perpendicular to the extension direction of the secondary longitudinal beam; Both ends of the main body of the auxiliary auxiliary anchor point extend a portion of the length of the connecting portion along the extension direction of the auxiliary longitudinal beam, and the connecting portion is connected to the end of the main longitudinal beam through the auxiliary beam decoupling beam; the main body of the auxiliary auxiliary anchor point is connected and fixed to the base layer, and the connecting portion of the auxiliary auxiliary anchor point and the auxiliary beam decoupling beam are suspended on the base layer; The auxiliary beam decoupling beam is suitable for deforming along the extension direction of the auxiliary longitudinal beam, so that the distance between the position where the auxiliary beam decoupling beam connects the auxiliary longitudinal beam and the main body of the auxiliary auxiliary anchor point changes in a sensitive direction when subjected to thermal stress.

9. The structure of the MEMS acceleration sensor chip according to claim 8, characterized in that: The fixed electrode units are multiple and are symmetrically distributed with the main anchor point as the center of symmetry; The secondary anchor points of each of the fixed electrode units are distributed symmetrically with the main anchor point as the center of symmetry. Meanwhile, the secondary auxiliary anchor points of each of the fixed electrode units are also distributed symmetrically with the main anchor point as the center of symmetry.

10. The structure of the MEMS acceleration sensor chip according to claim 9, characterized in that: The secondary longitudinal beam is provided with a plurality of process release holes penetrating the secondary longitudinal beam in the thickness direction; the process release holes are arranged in an array, and the process release holes in adjacent rows are arranged in a staggered manner.

11. The structure of the MEMS acceleration sensor chip according to claim 7, characterized in that: The sensitive structural layer also includes a bonding outer frame; The bonding outer frame surrounds and defines a main body activity space, and the sensitive mass block unit and the fixed electrode unit are arranged in the main body activity space; The structure of the MEMS acceleration sensor chip also includes: Upper cover; The upper cover includes a cover plate and a frame protruding from a surface of one side of the cover plate; the frame and the cover plate together enclose a cover plate activity space; the frame is suitable for connecting to the bonding outer frame, the cover plate activity space corresponds to the main body activity space, and together with the hollow space of the functional layer, accommodates the sensitive mass block unit and the fixed electrode unit.

12. The structure of the MEMS acceleration sensor chip according to claim 11, characterized in that: A conductive medium layer is provided on the side of the sensitive structure layer facing the upper cover, and the conductive medium layer at least covers the sensitive structure unit and the fixed electrode unit; The cover plate is provided with a plurality of through holes, the through holes exposing the conductive medium layer, the through holes are filled with conductive electrodes, the conductive electrodes are connected to the conductive medium layer and exposed on the surface of the cover plate facing away from the base layer; The positions of the through holes are arranged corresponding to the main anchor points and the secondary anchor points.

13. A method for preparing a structure of a MEMS acceleration sensor chip, characterized in that: The following steps are involved: A sensor substrate is formed, comprising: Providing a base layer; forming an initial functional layer on the base layer; forming an initial sensitive structural layer on the side of the initial functional layer facing away from the base layer; Etching the initial sensitive structure layer to form a sensitive structure layer includes: A sensitive mass block unit is formed, wherein the sensitive mass block unit comprises a main longitudinal beam, a sensitive mass block and a plurality of movable electrodes located on both sides of the sensitive mass block; the sensitive mass block is arranged around the main longitudinal beam and elastically connected to the main longitudinal beam; the movable electrode is fixedly connected to the sensitive mass block; At the same time, fixed electrode units are formed on both sides of the sensitive mass block; the fixed electrode units at least include a plurality of fixed electrodes extending toward the main longitudinal beam; The initial functional layer is corroded to form a functional layer; the functional layer is corroded through the sensitive structural layer to form a hollow area and an edge area surrounding the hollow area, wherein the projection of the hollow area on the sensitive structural layer at least covers the sensitive mass block unit and the fixed electrode unit; the edge area is fixedly connected to the base layer and the sensitive structural layer; Among them, the step of etching the initial sensitive structural layer to form a sensitive structural layer also includes: forming a main anchor point for connecting and fixing the main longitudinal beam to the base layer; forming main auxiliary anchor points on opposite sides of the main anchor point along the extension direction of the main longitudinal beam, and the main longitudinal beam is also connected and fixed to the base layer through the main auxiliary anchor points; the main auxiliary anchor points are axially symmetrical structures with the central axis of the main longitudinal beam as the symmetry axis; the connection structure between the main auxiliary anchor points and the main longitudinal beam has a stiffness in the sensitive direction of the sensitive mass block unit that is less than the stiffness in the non-sensitive direction.

14. The method for preparing the structure of the MEMS acceleration sensor chip according to claim 13, characterized in that: The step of etching the initial sensitive structure layer to form a sensitive structure layer includes: forming a sensitive layer mask on the side of the sensitive structure layer facing away from the base layer; Using the sensitive layer mask as a mask, pattern-etching the initial sensitive structure layer to form the sensitive mass block unit and the fixed electrode unit; The sensitive layer mask is removed.

15. The method for preparing the structure of the MEMS acceleration sensor chip according to claim 14, characterized in that: The steps of forming the sensitive mass block unit include: forming a main beam decoupling beam connecting the main auxiliary anchor point and the main longitudinal beam; The width of the main auxiliary anchor point is greater than the width of the main longitudinal beam; the main body of the main auxiliary anchor point is perpendicular to the extension direction of the main longitudinal beam; both ends of the main body of the main auxiliary anchor point extend a portion of the length of the connecting portion along the extension direction of the main longitudinal beam, and the connecting portion is connected to the end of the main longitudinal beam through the main beam decoupling beam; The main beam decoupling beam is suitable for deforming along the extension direction of the main longitudinal beam, so that the distance between the position where the main beam decoupling beam connects the main longitudinal beam and the main body of the main auxiliary anchor point changes in a sensitive direction when subjected to thermal stress.

16. The method for preparing the structure of the MEMS acceleration sensor chip according to claim 15, characterized in that: The steps of forming the sensitive mass block unit include: An elastic component accommodating groove is formed on the side of the sensitive mass block in the extension direction of the main longitudinal beam, an elastic component is arranged in the elastic component accommodating groove, and two ends of the elastic component are respectively connected to the main longitudinal beam and the sensitive mass block, so that the sensitive mass block is suitable for displacement along the extension direction of the main longitudinal beam under external acceleration; The elastic component is a folding beam spring; the folding beam spring is a serpentine folding structure, which extends in a serpentine shape along the extension direction of the main longitudinal beam, with one end connected to the side of the main longitudinal beam and the other end connected to the side of the sensitive mass block.

17. The method for preparing the structure of the MEMS acceleration sensor chip according to claim 16, characterized in that: The formed sensitive mass block, the folded beam spring and the movable electrode together form a central symmetrical figure, and the symmetry center of the central symmetrical figure coincides with the main anchor point; The fixed electrode units are formed in a plurality and are centrally symmetrically distributed with the main anchor point as the symmetry center; Taking the extension direction of the main longitudinal beam as the y-axis and the direction perpendicular to the y-axis and passing through the center of the main anchor point as the x-axis, the sensitive mass block, the folded beam spring, the movable electrode and the fixed electrode unit are symmetrically distributed along the y-axis and symmetrically distributed along the x-axis; The adjacent movable electrodes and the fixed electrodes form a capacitor; The capacitors located on the same side of the x-axis are connected in parallel; The capacitance changes of the capacitors located on both sides of the x-axis are opposite when an external acceleration is applied.

18. The method for preparing the structure of a MEMS acceleration sensor chip according to claim 14, characterized in that: The step of forming fixed electrode units located on both sides of the sensitive mass block further includes: A secondary longitudinal beam is also formed at the same time; the secondary longitudinal beam is parallel to the main longitudinal beam and is connected and fixed to the base layer through a secondary anchor point; A secondary auxiliary anchor point is formed on one side of the fixed electrode unit along the extension direction of the secondary longitudinal beam, and the secondary longitudinal beam is also connected and fixed to the base layer through the secondary auxiliary anchor point; the secondary auxiliary anchor point is an axisymmetric structure with the central axis of the secondary longitudinal beam as the axis of symmetry; the connection structure between the secondary auxiliary anchor point and the secondary longitudinal beam has a stiffness in the sensitive direction of the sensitive mass block unit that is less than that in the non-sensitive direction.

19. The method for preparing the structure of the MEMS acceleration sensor chip according to claim 18, characterized in that: The step of forming fixed electrode units located on both sides of the sensitive mass block further includes: A secondary beam decoupling beam is also formed simultaneously to connect the secondary auxiliary anchor point and the secondary longitudinal beam; The width of the secondary auxiliary anchor point is greater than the width of the secondary longitudinal beam; the main body of the secondary auxiliary anchor point is perpendicular to the extension direction of the secondary longitudinal beam; both ends of the main body of the secondary auxiliary anchor point extend a portion of the length of the connecting portion along the extension direction of the secondary longitudinal beam, and the connecting portion is connected to the end of the main longitudinal beam through the secondary beam decoupling beam; the main body of the secondary auxiliary anchor point is connected and fixed to the base layer, and the connecting portion of the secondary auxiliary anchor point and the secondary beam decoupling beam are suspended on the base layer; The auxiliary beam decoupling beam is suitable for deforming along the extension direction of the auxiliary longitudinal beam, so that the distance between the position where the auxiliary beam decoupling beam connects the auxiliary longitudinal beam and the main body of the auxiliary auxiliary anchor point changes in a sensitive direction when subjected to thermal stress.

20. The method for preparing the structure of the MEMS acceleration sensor chip according to claim 19, characterized in that: The fixed electrode units are formed in plurality, and are centrally symmetrically distributed with the main anchor point as the center of symmetry; wherein the secondary anchor points of each of the fixed electrode units are centrally symmetrically distributed with the main anchor point as the center of symmetry, and at the same time, the secondary auxiliary anchor points of each of the fixed electrode units are also centrally symmetrically distributed with the main anchor point as the center of symmetry.

21. The method for preparing the structure of a MEMS acceleration sensor chip according to claim 13, characterized in that: The step of corroding the functional layer through the sensitive structural layer comprises: forming a release hole mask on the side of the sensitive structure layer facing away from the base layer; Using the release hole mask as a mask, etching a process release hole in the sensitive structure layer, wherein the process release hole exposes the initial functional layer at a corresponding position; The process releases the hole and corrodes the initial functional layer to form a hollow area in the initial functional layer; the projection of the hollow area on the sensitive structure layer at least covers the sensitive structure unit and the fixed electrode unit; The release hole mask is removed.

22. The method for preparing the structure of the MEMS acceleration sensor chip according to claim 21, characterized in that: The minimum line width of the process release hole is greater than 3 μm; The dimension of the long side of the process release hole is 2-3 times greater than the dimension of the short side.

23. The method for preparing the structure of the MEMS acceleration sensor chip according to claim 21, characterized in that: Before the steps of forming the sensitive mass unit and the fixed electrode unit at the same time, the method further includes: A patterned conductive medium layer and a first bonding medium layer are formed on the side of the initial sensitive structure layer facing away from the base layer; the conductive medium layer at least covers the positions where the sensitive mass unit and the fixed electrode unit are predetermined to be formed; and the first bonding medium layer covers the position corresponding to the edge area; In the steps of forming the sensitive mass unit and the fixed electrode unit at the same time, the method further includes: removing together the conductive medium layer corresponding to the portion removed when forming the sensitive mass block unit, and removing together the conductive medium layer corresponding to the portion removed when forming the fixed electrode unit; When forming the process release hole, the conductive medium layer at the position corresponding to the process release hole is removed together.

24. The method for preparing the structure of the MEMS acceleration sensor chip according to claim 23, characterized in that: The following steps are also included: Forming an upper cover, including: providing a cover plate substrate; Etching the cover plate substrate to form a cover plate and a frame protruding from a surface of one side of the cover plate; the frame and the cover plate together enclose a cover plate activity space; The process of forming the sensitive structure layer also includes: Forming a bonding outer frame, wherein the bonding outer frame surrounds and defines a main body activity space, and the sensitive mass block unit and the fixed electrode unit are arranged in the main body activity space; The frame is suitable for being connected to the bonding outer frame, and the activity space corresponds to the main body activity space, and the sensitive mass block unit and the fixed electrode unit are jointly accommodated.

25. The method for preparing the structure of the MEMS acceleration sensor chip according to claim 24, characterized in that: Forming a blind hole at a preset position of the cover plate, and filling the blind hole with electroplated metal to form a conductive electrode; The preset position corresponds to the position of the main anchor point and the auxiliary anchor point in the sensor matrix; After forming the conductive electrode, forming a patterned second bonding dielectric layer on the side of the cover plate that exposes the conductive electrode; The second bonding medium layer is connected to the conductive electrode.

26. The method for preparing the structure of the MEMS acceleration sensor chip according to claim 25, characterized in that: Bonding the sensor substrate and the upper cover through the first bonding medium layer and the second bonding medium layer; After bonding, the conductive electrode corresponds to the main anchor point and the secondary anchor point, and is connected to the conductive medium layer through the second bonding medium layer; The frame of the upper cover and the bonding outer frame of the sensor substrate are bonded and connected through the first bonding medium layer and the second bonding medium layer; the activity space corresponds to the main body activity space, and together with the hollow space of the functional layer, accommodates the sensitive mass block unit and the fixed electrode unit.

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