A micro differential pressure MEMS pressure sensor pressure sensitive chip and its preparation method

Abstract

The present invention relates to a micro differential pressure MEMS pressure sensor pressure sensitive chip and a preparation method thereof, belonging to the field of sensor technology. The pressure sensor pressure sensitive chip includes a five-layer structure, namely, layer one to layer five; the structural features of the "island-film-beam coupling" type micro differential pressure sensor pressure sensitive chip proposed by the present invention include a porous island structure that suppresses deflection deformation, an octagonal arc-shaped pressure-sensitive film structure, a stress-concentrating cross-shaped beam structure, and a highly symmetrical piezoresistive circuit. The pressure-sensitive structure is axisymmetric along the x and y axes of its own center, so that when subjected to pressure in the z-axis direction, the stress on the pressure-sensitive structure is induced to be concentrated in the intersection area between the cross-beam structure above the pressure-sensitive film and the porous mass block island structure (and the supporting frame structure).

Description

Technical Field

[0001] The invention belongs to the technical field of sensors and relates to a micro-differential pressure MEMS pressure sensor pressure-sensitive chip and a preparation method thereof. Background Art

[0002] As the most mature micro-electromechanical system (MEMS) component, MEMS pressure sensor is widely used due to its miniaturization and low manufacturing cost. However, most of the MEMS pressure sensors that have been industrialized are mainly used to measure pressures above 100kPa (one standard atmospheric pressure). However, MEMS sensors that measure pressures below 100kPa are not common due to objective factors such as difficulty in preparation and high cost. However, whether in the medical and biological fields or in military applications, the demand for pressure sensing tests of micro-ranges below 1kPa is increasing. For the design and manufacture of MEMS micro-pressure sensors, the balance between the linearity and sensitivity performance of the sensor has always been the key factor restricting the large-scale application of MEMS pressure-sensitive cores in this field. In order to sense tiny pressure changes, the thickness of the pressure-sensitive film (sensitive structure) of the pressure-sensitive chip must be small enough to meet the sensitivity requirements of the sensor. However, too thin a film thickness will cause the pressure-sensitive film to deflect too much in the pressure-sensitive direction when under pressure, thereby reducing the linearity of the sensor. Summary of the invention

[0003] In view of this, an object of the present invention is to provide a micro-differential pressure MEMS pressure sensor pressure-sensitive chip and a preparation method thereof.

[0004] In order to achieve the above object, the present invention provides the following technical solutions:

[0005] A method for preparing a micro differential pressure MEMS pressure sensor pressure sensitive chip, the method comprising the following steps:

[0006] S1: using a thermal oxidation process, depositing a layer of silicon oxide on both sides of a single crystal silicon wafer as a device layer, etching a piezoresistive structure 5 on the silicon oxide layer on the upper surface of the silicon wafer using an etching process, preparing a varistor strip and an ohmic contact area on the upper surface of the silicon wafer using a light boron doping and a concentrated boron doping process, and repairing the lattice damage caused by the implantation using a rapid annealing RTP process after the implantation is completed;

[0007] S2: using plasma vapor deposition process PECVD to deposit an oxide insulating layer with a thickness of 500 nm on one side of the boron-doped piezoresistive structure 5 of the silicon wafer; and using an etching process to open an electrical contact hole for ohmic contact on the insulating layer; and then using a metal film deposition process to deposit a metal film on the insulating layer, and etching to form a metal interconnection lead 1 through a metal corrosion process to ensure that the piezoresistive structures 5 are electrically interconnected;

[0008] S3: using an etching process to etch the outline of the beam structure 2 on the silicon oxide layer on the upper surface of the silicon wafer, and then using the silicon oxide layer as a mask to etch silicon by reactive ion etching (RIE) to form the beam structure 2, with a depth of 4 um;

[0009] S4: using an etching process to etch a regional pattern of "pressure-sensitive film 3 + island structure 4" on the silicon oxide layer on the lower surface of the silicon wafer; spraying photoresist again on the surface of the silicon oxide layer where the "pressure-sensitive film 3 + island structure 4" pattern is etched, and developing to form an island structure 4 pattern as a mask; etching silicon using a reactive ion deep etching (DRIE) process, the depth of which is the corresponding height of the island structure 4; finally removing the remaining photoresist to expose the silicon oxide layer of the "pressure-sensitive film 3 + island structure 4" pattern;

[0010] S5: using the silicon oxide layer etched with the “pressure-sensitive film 3 + island structure 4” pattern as a mask, the “pressure-sensitive film 3 + island structure 4” region is etched on the bottom surface of the silicon wafer using the reactive ion deep etching (DRIE) bulk silicon process again to form a pressure-sensitive film 3 and an island structure 4 of a target size;

[0011] S6: removing the remaining silicon oxide layer on the back of the silicon wafer, and bonding a glass sheet as a glass base 7 to the back of the silicon wafer by using an anodic bonding process;

[0012] The glass base is selected according to the type of application of the pressure sensor to be prepared:

[0013] If it is a differential pressure type, a through-hole structure is processed on the glass base to ensure that the back of the pressure-sensitive film is connected to the outside world;

[0014] If it is an absolute pressure type, no through hole is processed, and the construction of the vacuum pressure reference cavity between the back of the pressure-sensitive film and the glass base is completed through a high-vacuum anodic bonding process.

[0015] Optionally, the metal film in S2 is Al.

[0016] Optionally, in S3, the silicon wafer is an N-type high-resistance all-silicon wafer or SOI; when SOI is used as the silicon wafer, the DRIE process stops etching when the buried silicon oxide layer is reached, so as to improve the dimensional accuracy and uniformity of the thickness of the pressure-sensitive film.

[0017] A micro differential pressure MEMS pressure sensor pressure-sensitive chip based on the preparation method, the pressure sensor pressure-sensitive chip comprises a five-layer structure, namely, layer one to layer five;

[0018] Layer 1: is the first substrate, which is a metal layer, made of aluminum, copper or chrome-gold alloy, and is made into a metal interconnection lead 1 through a MEMS etching process; the metal interconnection lead 1 electrically conducts the ohmic contact area of ​​the piezoresistive structure 5 in the layer 2 arranged below the layer 1 to form a Wheatstone bridge type piezoresistive circuit; the piezoresistive circuit has the function of converting the measured pressure signal into an electrical signal output;

[0019] Layer 2: It is the second substrate layer, which is made of single crystal silicon and silicon oxide, and includes a beam structure 2 made by etching MEMS silicon etching process and a piezoresistive structure 5 made by boron element doping process; wherein the piezoresistive structure 5 is composed of a high-resistance piezoresistive strip and a low-resistance ohmic contact area; two groups of piezoresistive strips are arranged on the upper surface of the beam structure 2, and the two groups of piezoresistive strips are symmetrically arranged in the stress concentration area on the beam structure 5 relative to the center of the piezoresistive chip structure; the length direction of the first group of piezoresistive strips is perpendicular to the direction of the chip frame, and the length direction of the second group of piezoresistive strips is parallel to the direction of the chip frame;

[0020] Layer 3: It is the third substrate layer, arranged below layer 2, made of single crystal silicon, and constitutes the pressure-sensitive film 3 of the chip;

[0021] Layer 4: It is the fourth substrate layer, made of single crystal silicon, and its upper surface is connected to the pressure-sensitive film 3 of layer 3; an island structure 4 is arranged in the center of layer 4; the lower part and surrounding parts of the island structure 4 are hollow structures, so as to ensure that the pressure-sensitive film 3 and the island structure 4 can be deformed freely when under pressure; a support frame 6 is arranged around layer 4, and the upper and lower parts of the support frame 6 are connected to the pressure-sensitive film 3 and the glass base 7 respectively, and the thickness of the support frame 6 is greater than that of the pressure-sensitive film 3, so as to play a role of fixed support;

[0022] Layer 5: It is the fifth layer of substrate, made of glass, with a through hole in the middle, and the diameter of the through hole is smaller than the supporting frame 6; the upper surface is fixedly connected to the supporting frame 6 of layer 4 through the MEMS bonding process, and serves as the glass base 7 at the bottom of the pressure-sensitive chip; the lower surface of layer 5 serves as the patch surface of the pressure-sensitive chip, and is fixed to the shell through patch glue when the pressure-sensitive chip is packaged in a shell.

[0023] The beneficial effects of the present invention are:

[0024] In view of the structural design contradiction between sensitivity and linearity in the design of existing MEMS micro-differential pressure sensor pressure sensitive chips, the present invention proposes an "island-membrane-beam coupling" type piezoresistive micro-differential pressure sensitive chip structure. Compared with the existing "island-membrane coupling" type pressure sensitive chip, the linearity of the pressure sensitive chip is greatly improved under the same size conditions, and the problems of small stress concentration area and poor stress distribution uniformity of the "island-membrane coupling" type pressure sensitive chip are effectively solved, thereby improving the yield and performance stability of the pressure sensitive chip.

[0025] The structural features of the "island-membrane-beam coupling" type differential pressure sensor pressure-sensitive chip proposed in the present invention include a porous island structure that suppresses deflection deformation, an octagonal arc-shaped pressure-sensitive film structure, a stress-concentrating cross-shaped beam structure, and a highly symmetrical piezoresistive circuit. The pressure-sensitive structure is axisymmetric along the x and y axes of its own center, so that when subjected to pressure in the z-axis direction, the stress on the pressure-sensitive structure is induced to be concentrated in the intersection area between the cross-beam structure above the pressure-sensitive film and the porous mass block island structure (and the supporting frame).

[0026] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0028] Figure 1 This is a process flow chart for single crystal silicon substrates;

[0029] Figure 2 This is the SOI substrate process flow chart;

[0030] Figure 3 It is a three-dimensional diagram of a micro differential pressure sensitive chip;

[0031] Figure 4 It is a top view of the micro differential pressure sensitive chip;

[0032] Figure 5 This is a side view of the micro-differential pressure sensitive chip.

[0033] Figure numerals: 1-metal interconnection lead; 2-beam structure; 3-pressure-sensitive film; 4-island structure; 5-piezoresistive structure; 6-support frame; 7-glass base. DETAILED DESCRIPTION

[0034] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0035] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0036] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0037] The present invention designs a piezoresistive micro differential pressure MEMS pressure sensor pressure sensitive chip and its manufacturing process. The MEMS pressure sensitive chip involved in the present invention is based on the piezoresistive effect of silicon, and uses the silicon diffusion process to implant and diffuse doped element (boron) ions into the silicon wafer to form a sensitive resistor of the Wheatstone bridge, and uses the Wheatstone bridge to convert the pressure signal into a voltage signal, thereby realizing the measurement of pressure. The core lies in the design of the pressure sensitive chip structure and the process scheme that meets the structural manufacturing requirements.

[0038] In order to realize the manufacture of the above-mentioned "island-membrane-beam coupling" type micro-differential pressure sensor pressure-sensitive chip, the present invention proposes the following two sets of MEMS manufacturing process schemes. They are respectively a scheme of using N-type high-resistance all-silicon wafer as the silicon wafer material and a scheme of using SOI (Silicon On Insulator) as the silicon wafer. The process steps of the two are the same. The difference is that when etching the pressure-sensitive film 3 structure, the middle silicon oxide layer of SOI can be used as a self-stop layer to effectively control the etching depth and ensure the consistency of the thickness of the pressure-sensitive film 3. The stability of the performance indicators of the pressure-sensitive chips between batches of mass production is greatly improved, and the yield of the production is improved. However, the disadvantage is that the material cost is higher than that of using all-silicon wafers. The process scheme of the present invention includes the following steps:

[0039] a) Using a thermal oxidation process, a layer of silicon oxide is deposited on both sides of the single crystal silicon wafer as the device layer, and a piezoresistive structure 5 is etched on the silicon oxide layer on the upper surface of the silicon wafer using an etching process. A piezoresistive resistor strip and an ohmic contact area are prepared on the upper surface of the silicon wafer using a light boron doping and a concentrated boron doping process, that is, the piezoresistive structure includes a piezoresistive resistor strip and an ohmic contact area. After the implantation is completed, a rapid annealing RTP process is used to repair the lattice damage caused by the implantation;

[0040] b) Using plasma vapor deposition process PECVD to deposit an oxide insulating layer (thickness of about 500 nm) on one side of the silicon wafer boron-doped piezoresistive structure 5. And using etching process to open an electrical contact hole for ohmic contact on the insulating layer. Then using metal film deposition process to deposit Al or other metal film on the insulating layer, and using metal corrosion process to etch to form metal interconnection leads 1, to ensure electrical interconnection between the piezoresistive structures 5;

[0041] c) etching a beam structure 2 pattern on the silicon oxide layer on the upper surface of the silicon wafer by using an etching process, and then using the silicon oxide layer as a mask, etching silicon by reactive ion etching (RIE) to form the beam structure 2, with a depth of about 4 μm;

[0042] d) Etch the "pressure-sensitive film 3 + island structure 4" area pattern on the silicon oxide layer on the lower surface of the silicon wafer using an etching process. Then spray photoresist again on the surface of the silicon oxide layer where the "pressure-sensitive film 3 + island structure 4" pattern is etched, and develop to form the island structure 4 pattern as a mask. Etch silicon using a reactive ion deep etching (DRIE) process to a depth corresponding to the height of the island structure 4. Finally, remove the remaining photoresist to expose the silicon oxide layer of the "pressure-sensitive film 3 + island structure 4" pattern;

[0043] e) Using the silicon oxide layer etched with the "pressure-sensitive film 3 + island structure 4" pattern as a mask, the "pressure-sensitive film 3 + island structure 4" area is etched on the bottom surface of the silicon wafer using the reactive ion deep etching (DRIE) bulk silicon processing technology again to form a pressure-sensitive film 3 and an island structure 4 of a target size;

[0044] When using SOI as the substrate, the DRIE process will stop etching when it reaches the buried silicon oxide layer, effectively improving the dimensional accuracy and uniformity of the pressure-sensitive film thickness;

[0045] f) removing the remaining silicon oxide layer on the back of the silicon wafer, and bonding a glass sheet as a glass base 7 to the back of the silicon wafer using an anodic bonding process;

[0046] The glass base can be selected according to the application type of the pressure sensor to be prepared. If it is a differential pressure type, a through-hole structure is processed on the glass base to ensure that the back of the pressure-sensitive film can be connected to the outside world. If it is an absolute pressure type, it is not necessary to process the through-hole, and the vacuum pressure reference cavity between the back of the pressure-sensitive film and the glass base is constructed through a high vacuum anodic bonding process.

[0047] Figure 1 This is a process flow chart for single crystal silicon substrates; Figure 2 This is the SOI substrate process flow chart.

[0048] The structural features of the pressure-sensitive chip of the "island-film-beam coupling" type differential pressure sensor proposed in the present invention include a porous island structure that suppresses deflection deformation, an octagonal arc-shaped pressure-sensitive film structure, a stress-concentrating cross-shaped beam structure, and a highly symmetrical piezoresistive circuit. The pressure-sensitive structure is axisymmetric along the x and y axes of its own center, so that when subjected to pressure in the z-axis direction, the stress on the pressure-sensitive structure is induced to be concentrated in the intersection area between the cross-beam structure above the pressure-sensitive film and the porous mass block island structure (and the supporting frame 6).

[0049] like Figure 3 to Figure 5 As shown, the MEMS piezoresistive pressure sensor of the present invention comprises a 5-layer structural substrate according to the spatial structure, including layer 1 to layer 5, which is divided into 7 parts according to function.

[0050] Layer 1: The first substrate is a metal layer, made of aluminum, copper or chrome-gold alloy and other metal raw materials commonly used in MEMS processes, and is made into metal interconnection leads 1 through MEMS etching process. The metal interconnection leads 1 electrically conduct the ohmic contact area of ​​the piezoresistive structure 5 in the second substrate (layer 2) arranged under the first substrate (layer 1) to form a Wheatstone bridge piezoresistive circuit. The piezoresistive circuit has the function of converting the measured pressure signal into an electrical signal output.

[0051] Layer 2: The second layer substrate is made of single crystal silicon and silicon oxide materials, including a beam structure 2 made by etching MEMS silicon etching process and a piezoresistive structure 5 made by boron doping process. The piezoresistive structure 5 is composed of a high-resistance piezoresistive strip and a low-resistance ohmic contact area. Two groups of piezoresistive strips are arranged on the upper surface of the beam structure 2, and the two groups of piezoresistive strips are arranged symmetrically relative to the center of the piezoresistive chip structure in the stress concentration area on the beam structure 2. The length direction of the first group of piezoresistive strips is perpendicular to the direction of the chip frame, and the length direction of the second group of piezoresistive strips is parallel to the direction of the chip frame.

[0052] Layer 3: The third substrate is arranged below the second substrate (layer 2), and is made of single crystal silicon, constituting the pressure-sensitive film 3 of the chip.

[0053] Layer 4: The fourth layer of substrate material is single crystal silicon, and the upper surface is connected to the pressure-sensitive film 3 of the third layer of substrate (layer 5). An island structure 4 is arranged in the center of the fourth layer of substrate (layer 4). The island structure 4 is provided with a cavity structure below and around it, which ensures that the pressure-sensitive film 3 and the island structure 4 can deform freely when under pressure. The fourth layer of substrate (layer 4) is provided with a support frame 6 structure around it, and the upper and lower surfaces of the support frame 6 are respectively connected to the pressure-sensitive film 3 and the glass base 7. The thickness of the support frame 6 is much greater than that of the pressure-sensitive film 3. When subjected to a pressure of 1 to 3 times the range of the pressure-sensitive chip, no obvious deformation occurs, and it plays a role of fixed support.

[0054] Layer 5: The fifth substrate is made of glass with a through hole in the middle. The diameter of the through hole is slightly smaller than the support frame 6. The upper surface is fixedly connected to the support frame 6 of the fourth substrate (layer 4) through the MEMS bonding process, serving as the glass base 7 structure at the bottom of the pressure-sensitive chip. The lower surface of the fifth substrate (layer 5) serves as the patch surface of the pressure-sensitive chip. When the pressure-sensitive chip is packaged in a shell, it is fixed to the shell through patch glue.

[0055] The structural features of the present invention include the following 4 points:

[0056] a) Octagonal arc pressure-sensitive film:

[0057] In order to generate greater stress and strain under tiny pressure and measure tiny pressure changes, the micro-pressure pressure-sensitive chip needs the pressure-sensitive film to be as thin as possible and as large in area as possible. However, large-area films are difficult to make, and it is difficult to control the overall uniformity of the film. The present invention proposes adding large-sized arc chamfers to the four corners of the square support frame and the island structure, so that the pressure-sensitive film has a concentric octagonal arc shape. Compared with the original square frame-type pressure-sensitive film, the pressure-sensitive film of this shape greatly reduces the area of ​​the pressure-sensitive film, but the maximum positive stress on the film remains basically unchanged, which reduces the process difficulty, and reduces the deflection deformation of the pressure-sensitive structure, that is, reduces the nonlinearity of the signal output within the measuring range.

[0058] b) Porous island structure:

[0059] In order to suppress the problem of excessive nonlinearity of the output signal of the pressure-sensitive chip caused by the large deflection of the pressure-sensitive structure, the present invention proposes to make a large-volume axisymmetric island structure on the back of the pressure-sensitive film to suppress the deformation in the z-axis direction, thereby improving the linearity of the pressure-sensitive chip. However, if the mass of the island structure is too large, it will cause excessive prestress on the pressure-sensitive film, which will cause the sensitivity of the pressure-sensitive chip to decrease. In addition, if the mass of the pressure-sensitive structure is too large, the output signal will drift due to the influence of acceleration, reducing the accuracy of the pressure-sensitive chip in an unstable test environment. Therefore, the present invention proposes to effectively improve the problem of the excessive overall mass of the pressure-sensitive structure by drilling small holes evenly arranged on the island structure.

[0060] c) Double beam cross beam structure:

[0061] Since the micro-range MEMS pressure-sensitive chip has a larger area and thinner pressure-sensitive film than the traditional MEMS pressure-sensitive chip, the proportion of the stress concentration area on the pressure-sensitive film is greatly reduced, and the uniformity of the stress distribution in the stress concentration area is also relatively low. The present invention proposes to make a double-beam cross-beam structure on the upper surface of the pressure-sensitive film, and use the stiffness difference between the beam structure and the film structure to readjust the stress distribution on the pressure-sensitive structure, so that the stress is concentrated on the intersection area of ​​the beam structure, the island structure and the film structure, effectively reducing the dissipation of strain energy in the non-stress concentration area, and the uniformity of the stress distribution in the stress concentration area is also improved, which improves the performance degradation of the pressure-sensitive chip caused by the positional offset of the varistor strip and the stress concentration area caused by the manufacturing process error. The precision requirements of the manufacturing process are reduced, and the chip manufacturing yield rate is improved.

[0062] d) Highly symmetrical piezoresistive circuit:

[0063] The stress concentration effect and stress distribution uniformity of the area where the varistor strip on the piezoresistive varistor chip is located have a great influence on the chip performance. The traditional "island-membrane coupling" type varistor chip needs to use double-sided alignment during production because the island structure that determines the stress distribution is on the back of the chip. The double-sided alignment accuracy is limited, which increases the performance error between the actual product and the theoretical model. The present invention designs a highly symmetrical piezoresistive circuit (including piezoresistive strips, ohmic contact areas and metal wiring). The piezoresistive circuit is symmetrically arranged on the double-beam structure on the upper surface. Since the piezoresistive strips and the double-beam structure are both symmetrical structures, the alignment difficulty in the manufacturing process is reduced. And the piezoresistive strip and the double-beam structure are on the same surface, so a single-sided alignment process can be used. The single-sided alignment process has a smaller accuracy error than the double-sided alignment, which improves the position accuracy of the piezoresistive strip. And according to the stress distribution readjustment effect of the double-beam structure designed by the present invention, the influence of the double-sided alignment error of the island structure and the beam structure on the chip performance is reduced when the back island structure is manufactured.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A method for preparing a pressure-sensitive chip of a micro-differential pressure MEMS pressure sensor, characterized in that: The method comprises the following steps: S1: using a thermal oxidation process, depositing a layer of silicon oxide on both sides of a single crystal silicon wafer as a device layer, etching a piezoresistive structure (5) on the silicon oxide layer on the upper surface of the silicon wafer using an etching process, preparing a varistor strip and an ohmic contact area on the upper surface of the silicon wafer using a light boron doping and a concentrated boron doping process, and repairing the lattice damage caused by the implantation using a rapid annealing RTP process after the implantation is completed; S2: using a plasma vapor deposition process PECVD to deposit an oxide insulating layer with a thickness of 500 nm on one side of the boron-doped piezoresistive structure (5) of the silicon wafer; and using an etching process to open an electrical contact hole for ohmic contact on the insulating layer; and then using a metal film deposition process to deposit a metal film on the insulating layer, and etching to form a metal interconnection lead (1) through a metal corrosion process to ensure electrical interconnection between the piezoresistive structures (5); S3: using an etching process to etch the outline of the beam structure (2) on the silicon oxide layer on the upper surface of the silicon wafer, and then using the silicon oxide layer as a mask to etch silicon by reactive ion etching (RIE) to form the beam structure (2) with a depth of 4 μm; the beam structure (2) is a cross beam structure, and two groups of varistor strips are arranged on the upper surface of the beam structure (2), and the two groups of varistor strips are symmetrically arranged relative to the center of the varistor chip structure in the stress concentration area on the beam structure (2); the length direction of the first group of varistor strips is perpendicular to the direction of the chip frame, and the length direction of the second group of varistor strips is parallel to the direction of the chip frame; S4: using an etching process to etch a "pressure-sensitive film (3) + island structure (4)" regional pattern on the silicon oxide layer on the lower surface of the silicon wafer; the pressure-sensitive film (3) is an octagonal arc-shaped pressure-sensitive film structure; the island structure (4) is a porous mass block island structure, and the bottom and surrounding of the island structure (4) are cavity structures to ensure that the pressure-sensitive film (3) and the island structure (4) can deform freely when under pressure; spraying photoresist again on the surface of the silicon oxide layer etched with the "pressure-sensitive film (3) + island structure (4)" pattern, and developing to form an island structure (4) pattern as a mask; etching silicon using a reactive ion deep etching (DRIE) process, the depth of which is the corresponding height of the island structure (4); finally removing the remaining photoresist to expose the silicon oxide layer of the "pressure-sensitive film (3) + island structure (4)" pattern; S5: Using the silicon oxide layer on which the "pressure-sensitive film (3) + island structure (4)" pattern is etched as a mask, the "pressure-sensitive film (3) + island structure (4)" region is etched on the bottom surface of the silicon wafer using a reactive ion deep etching (DRIE) bulk silicon process again, thereby forming a pressure-sensitive film (3) and an island structure (4) of a target size; S6: removing the remaining silicon oxide layer on the back of the silicon wafer, and bonding a glass sheet as a glass base (7) to the back of the silicon wafer using an anodic bonding process; The glass base is selected according to the type of application of the pressure sensor to be prepared: If it is a differential pressure type, a through-hole structure is processed on the glass base to ensure that the back of the pressure-sensitive film is connected to the outside world; If it is an absolute pressure type, no through hole is processed, and the construction of the vacuum pressure reference cavity between the back of the pressure-sensitive film and the glass base is completed through a high-vacuum anodic bonding process.

2. The method for preparing a micro differential pressure MEMS pressure sensor pressure sensitive chip according to claim 1, characterized in that: The metal film in S2 is Al.

3. The method for preparing a pressure-sensitive chip of a micro-differential pressure MEMS pressure sensor according to claim 1, characterized in that: In S3, the silicon wafer is an N-type high-resistance all-silicon wafer or SOI; when SOI is used as the silicon wafer, the DRIE process stops etching when the buried silicon oxide layer is reached, so as to improve the dimensional accuracy and uniformity of the thickness of the pressure-sensitive film.

4. A micro differential pressure MEMS pressure sensor pressure sensitive chip based on the preparation method according to any one of claims 1 to 3, characterized in that: The pressure sensor pressure sensitive chip includes a five-layer structure, namely layer one to layer five; Layer 1: is the first substrate, which is a metal layer, made of aluminum, copper or chrome-gold alloy, and is made into a metal interconnection lead (1) through a MEMS etching process; the metal interconnection lead (1) electrically connects the ohmic contact area of ​​the piezoresistive structure (5) in the layer 2 arranged below the layer 1 to form a Wheatstone bridge type piezoresistive circuit; the piezoresistive circuit has the function of converting the measured pressure signal into an electrical signal output; Layer 2: is the second substrate, which is made of single crystal silicon and silicon oxide, and includes a beam structure (2) made by a MEMS silicon etching process and a piezoresistive structure (5) made by a boron element doping process; wherein the piezoresistive structure (5) is composed of a high-resistance piezoresistive strip and a low-resistance ohmic contact area; two groups of piezoresistive strips are arranged on the upper surface of the beam structure (2), and the two groups of piezoresistive strips are symmetrically arranged relative to the center of the piezoresistive chip structure in the stress concentration area on the beam structure (2); the length direction of the first group of piezoresistive strips is perpendicular to the direction of the chip frame, and the length direction of the second group of piezoresistive strips is parallel to the direction of the chip frame; Layer 3: The third substrate layer is disposed below layer 2 and is made of single crystal silicon, constituting the pressure-sensitive film (3) of the chip. Layer 4: It is the fourth substrate layer, made of single crystal silicon, and its upper surface is connected to the pressure-sensitive film (3) of layer 3; an island structure (4) is arranged in the center of layer 4; the island structure (4) is provided with a cavity structure below and around it, so as to ensure that the pressure-sensitive film (3) and the island structure (4) can deform freely when under pressure; a supporting frame (6) is arranged around layer 4, and the upper and lower surfaces of the supporting frame (6) are connected to the pressure-sensitive film (3) and the glass base (7) respectively; the thickness of the supporting frame (6) is greater than the thickness of the pressure-sensitive film (3), so as to play a role of fixed support; Layer 5: The fifth substrate is made of glass and has a through hole in the middle. The projection of the through hole on the fifth substrate is located in the area surrounded by the support frame (6), within the projection range on the fifth substrate. The upper surface is fixedly connected to the support frame (6) of layer 4 through a MEMS bonding process and serves as a glass base (7) at the bottom of the pressure-sensitive chip. The lower surface of layer 5 serves as a patch surface of the pressure-sensitive chip and is fixed to the shell through patch glue when the pressure-sensitive chip is packaged in a shell.

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