A temperature self-compensating small-range MEMS sensor and its preparation method

Abstract

The present invention discloses a temperature self-compensating small-range MEMS sensor and a preparation method thereof. The sensor includes a packaging shell and a pressure-sensitive chip. The pressure-sensitive chip includes a first substrate, a second substrate, a third substrate, a fourth substrate, a fifth substrate and a sixth substrate from top to bottom; the first substrate is a passivation protection layer, the second substrate is a metal layer, the third substrate includes a peninsula-arc edge beam structure and a piezoresistor; the fourth substrate includes a pressure-sensitive membrane structure, the fifth substrate includes a fixed structure, and the sixth substrate includes a glass base; the metal layer is provided with metal interconnection leads, and the piezoresistor is arranged in the peninsula-arc edge beam structure; the metal interconnection leads electrically conduct the ohmic contact area of ​​the piezoresistor to form a Wheatstone bridge form piezoresistive circuit. The present invention realizes the over-range protection function of the sensor, solves the current situation that the sensitivity and linearity of the small-range MEMS pressure sensor cannot be achieved at the same time, and realizes the self-compensation of temperature drift.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular to a temperature self-compensating small-range MEMS sensor and a preparation method thereof. Background Art

[0002] With the widespread application of robotics in industrial automation, medical assistance, service robots, and flexible tactile sensing, the demand for small-range, high-precision pressure sensors continues to grow. Robots, especially in application scenarios such as flexible manipulators, bionic tactile sensors, and precision grasping, require sensors that can sense tiny pressure changes in order to achieve accurate perception of the environment and highly sensitive interaction. MEMS pressure sensors are widely used in industries such as industry, medical care, and consumer electronics due to their miniaturization, low cost, and high performance. However, most of the existing MEMS pressure sensor technologies focus on high-pressure measurements above 100 kPa, and still face many challenges in achieving micro-range pressure measurements below 1 kPa, especially in complex and changing temperature environments. Their performance is significantly limited, and it is difficult to ensure the stability of sensitivity and accuracy.

[0003] In practical applications, fluctuations in ambient temperature can cause thermal stress in the sensitive structure of the sensor. Thermal stress originates from uneven thermal expansion of the material caused by temperature changes, which in turn affects the piezoresistive effect and film deformation, resulting in nonlinear errors in the output signal and reducing the linearity and accuracy of the sensor. This problem is particularly prominent in small-range sensors, because the film thickness is small and the sensitive structure is more precise, which is more sensitive to changes in the thermal expansion coefficient, making the sensor extremely susceptible to thermal stress and causing output errors.

[0004] Specifically, existing MEMS pressure sensors have the problem of not being able to achieve both linearity and sensitivity. Only a sufficiently small thickness of the pressure-sensitive chip's pressure-sensitive film (sensitive structure) can meet the sensor's sensitivity requirements; however, too thin a film thickness will cause the pressure-sensitive film to deflect too much in the pressure-sensitive direction when under pressure, resulting in reduced linearity of the sensor. At the same time, when the MEMS pressure sensor measures a wide range of pressure, the sensor has no over-range protection design, which can easily damage the chip.

[0005] Based on this, the existing technology generally uses external electronic circuits or multi-point correction algorithms to correct temperature drift, or uses material optimization to reduce thermal stress; among them, reliance on external circuits requires additional electronic components and complex signal processing circuits. Although it can improve the temperature drift problem to a certain extent, it increases the system complexity or manufacturing cost, which not only increases the cost and power consumption of the system, but may also cause time delays in compensation response, making it difficult to meet the needs of real-time dynamic compensation in robotic applications, and it is also difficult to achieve widespread application in small-range MEMS pressure sensors; on the other hand, the existing mechanical design methods are difficult to fundamentally suppress the influence of thermal stress, resulting in the linearity and sensitivity of the sensor being difficult to meet the high requirements of robotic applications within a small range.

[0006] Polysilicon materials have gradually become the preferred material for varistors due to their good thermal stability and matching of linear thermal expansion coefficients. At the same time, studies have shown that the design of special structures using the gravity characteristics of mass blocks can effectively offset the nonlinear output caused by thermal stress. However, the technology for achieving temperature self-compensation in combination with polysilicon varistors based on the design of mass blocks and thermal stress balance is not yet mature, and related research mainly focuses on conceptual discussions and lacks engineering solutions. Summary of the invention

[0007] In order to solve the above problems, the present invention provides a temperature self-compensating small-range MEMS sensor and a preparation method thereof, by designing a specific structure of the MEMS pressure sensor, using the silicon diffusion process to implant and diffuse doping element (boron) ions into the silicon wafer to form a sensitive resistor of the Wheatstone bridge, and using the Wheatstone bridge to convert the pressure signal into a voltage signal, thereby realizing the measurement of pressure. The present invention realizes the over-range protection function of the sensor, solves the current situation that the sensitivity and linearity of the existing small-range MEMS pressure sensor cannot be achieved at the same time, and at the same time uses an adjustable mass block to balance the thermal stress caused by temperature changes, and connects the polysilicon varistor in series to realize the self-compensation of temperature drift.

[0008] The present invention provides a temperature self-compensating short-range MEMS sensor, and the specific technical solution is as follows:

[0009] The sensor comprises a packaging shell and a pressure-sensitive chip, and the pressure-sensitive chip comprises, from top to bottom, a first substrate, a second substrate, a third substrate, a fourth substrate, a fifth substrate and a sixth substrate;

[0010] The first substrate is a passivation protection layer, the second substrate is a metal layer, the third substrate includes a peninsula-arc edge beam structure and a piezoresistor, the piezoresistor is composed of a high-resistance varistor strip and a low-resistance ohmic contact area, including a single-crystal silicon piezoresistor and a polycrystalline silicon piezoresistor; the fourth substrate includes a pressure-sensitive film structure, the fifth substrate includes a fixed structure, and the sixth substrate includes a glass base;

[0011] The metal layer is provided with metal interconnection leads, and the piezoresistor is arranged in the peninsula-arc edge beam structure; the metal interconnection leads electrically conduct the ohmic contact area of ​​the piezoresistor to form a Wheatstone bridge type piezoresistive circuit.

[0012] Furthermore, the first substrate is made of silicon nitride, the second substrate is made of aluminum, copper or chrome-gold alloy, the third substrate is made of single crystal silicon and silicon oxide, the fourth substrate and the fifth substrate are made of single crystal silicon, and the sixth substrate is made of glass.

[0013] Furthermore, two groups of varistor strips are provided on the upper surface of the peninsula-arc edge beam structure, and the two groups of varistor strips are symmetrically arranged in the stress concentration area on the peninsula-arc edge beam structure relative to the center of the varistor chip structure.

[0014] Furthermore, the length directions of the two groups of varistor strips are perpendicular to the direction of the chip frame, and each group of varistor strips includes four varistor strips.

[0015] Furthermore, a hole island structure is provided in the middle of the fifth substrate, and a cavity structure is provided below and around the hole island structure.

[0016] Furthermore, a supporting frame is provided around the fifth substrate, and the upper and lower surfaces of the supporting frame are fixedly connected to the pressure-sensitive membrane structure and the glass base respectively, and the thickness of the supporting frame is greater than the thickness of the hole island structure.

[0017] The present invention also discloses a method for preparing a temperature self-compensating small-range MEMS sensor, the specific process of which is as follows:

[0018] S1: A mask with a piezoresistor structure is made on the front side of a single crystal silicon wafer by photolithography, and a piezoresistive strip and an ohmic contact area are prepared;

[0019] S2: etching metal interconnect leads to form electrical interconnections between the single-crystal silicon piezoresistor and the polycrystalline silicon piezoresistor;

[0020] S3: etching a peninsula-arc edge beam structure on the oxide layer on the upper surface of the substrate;

[0021] S4: depositing a layer of aluminum nitride on the upper surface of the substrate as a passivation layer;

[0022] S5: etching a pattern of a pressure-sensitive membrane structure + a hole island structure on the oxide layer on the lower surface of the substrate;

[0023] S6: using the oxide layer on which the pressure-sensitive film structure + hole island structure pattern is etched as a mask, etching the pressure-sensitive film structure + hole island structure region on the bottom surface of the silicon wafer to form a pressure-sensitive film structure and hole island structure of a target size;

[0024] S7: removing the remaining oxide layer on the back side and bonding a glass sheet as a glass base to the back side of the silicon wafer.

[0025] Furthermore, in step S2, the etching process of the metal interconnection lead is as follows:

[0026] Depositing an oxide insulating layer on one side of a silicon wafer boron-doped single crystal silicon piezoresistor, and etching an electrical contact hole for ohmic contact on the insulating layer;

[0027] Then, a metal film is deposited on the insulating layer, and metal interconnection leads are etched out.

[0028] Furthermore, in step S3, the etching process of the peninsula-arc edge beam structure is as follows:

[0029] The graphic outline of the peninsula-arc edge beam structure is formed on the surface oxide layer of the substrate through an etching process, which is used as a mask, and then silicon is etched through reactive ion etching (RIE) to form the peninsula-arc edge beam structure.

[0030] Furthermore, in step S5, the etching process of the pressure-sensitive membrane structure and the hole island structure is as follows:

[0031] The area pattern of the pressure-sensitive membrane structure + hole island structure is etched out on the oxide layer on the lower surface of the substrate by an etching process;

[0032] Spraying photoresist on the surface of the oxide layer of the regional pattern, and developing to form a hole island structure pattern as a mask;

[0033] The silicon is etched by using a reactive ion deep etching (DRIE) process, and the depth is the height corresponding to the hole island structure;

[0034] The remaining photoresist is removed to expose the oxide layer of the pressure-sensitive film structure + hole island structure pattern.

[0035] The beneficial effects of the present invention are as follows:

[0036] 1. The present invention designs a "peninsula-membrane-arc edge beam coupling" type piezoresistive absolute pressure sensitive chip structure, including an octagonal arc-shaped pressure-sensitive film structure, a stress-concentrating peninsula-arc edge beam structure and a highly symmetrical piezoresistive circuit. The piezoresistive structure is axially symmetrical 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 piezoresistive structure is induced to concentrate on both sides of the opening area on the peninsula-arc edge beam structure above the pressure-sensitive film. Compared with the existing "island-membrane coupling" type piezoresistive chip, the linearity of the piezoresistive 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 piezoresistive chip are effectively solved, thereby improving the yield and performance stability of the piezoresistive chip.

[0037] 2. In the pressure-sensitive structure of the present invention, a hole island structure is provided below the sensing film structure. By designing the thickness of the hole island, a certain over-range protection effect is achieved, and at the same time, the performance of the pressure-sensitive chip is less affected. The hole island structure is arranged below and has a large volume. It can be regarded as a mass block. The gravity effect of the mass block is utilized to make the gravity generated by the mass block counteract the thermal stress, thereby reducing the impact of temperature changes on the pressure-sensitive element and improving the sensitivity and long-term stability of the sensor.

[0038] 3. The present invention connects polysilicon piezoresistors in series through metal interconnection leads, utilizes the good thermal stability and linear thermal expansion coefficient of polysilicon materials to match the thermal expansion characteristics of the sensitive diaphragm, reduces the influence of thermal stress on the output of the varistor, and realizes electrical self-compensation for thermal drift. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a schematic diagram of the three-dimensional structure of the sensor of the present invention.

[0040] Figure 2 It is a schematic top view of the overall structure of the sensor of the present invention.

[0041] Figure 3 It is a schematic side view of the sensor structure of the present invention.

[0042] Figure 4 It is a schematic flow chart of the sensor preparation method of the present invention.

[0043] Figure 5 It is a schematic diagram of the sensor preparation process of the present invention.

[0044] Explanation of the reference numerals: 1-passivation protection layer, 2-single crystal silicon piezoresistor, 3-metal interconnection lead, 4-peninsula structure, 5-pressure-sensitive membrane structure, 6-hole island structure, 7-support frame, 8-glass base, 9-polycrystalline silicon piezoresistor. DETAILED DESCRIPTION

[0045] The following description clearly and completely describes the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0046] In the description of the embodiments of the present invention, it should be noted that the indicated orientation or positional relationship is based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the invention product is usually placed when in use, or the orientation or positional relationship commonly understood by those skilled in the art, or the orientation or positional relationship in which the invention product is usually placed when in use, which is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first" and "second" are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0047] In the description of the embodiments of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection, or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0048] Example 1

[0049] Embodiment 1 of the present invention discloses a temperature self-compensating short-range MEMS sensor, such as Figure 1 and Figure 2 As shown, the specific structure is as follows:

[0050] The sensor includes a packaging shell and a pressure-sensitive chip. The pressure-sensitive chip includes a six-layer structure, including a first substrate, a second substrate, a third substrate, a fourth substrate, a fifth substrate and a sixth substrate from top to bottom, forming Figure 3 Layers 4 to 9.

[0051] Combination Figure 3 As shown, the first substrate is a passivation protection layer 1, which is made of silicon nitride and is made by a vapor deposition process to protect the front of the chip and improve the robustness of the chip;

[0052] The second substrate is a metal layer, and the material is aluminum, copper or chrome-gold alloy. The metal layer is provided with metal interconnection leads 3, and the metal interconnection leads 3 are made by magnetron sputtering process.

[0053] The third substrate is made of single crystal silicon and silicon oxide, including a peninsula-arc edge beam structure made by a MEMS etching process, a single crystal silicon piezoresistor 2 and a polycrystalline silicon piezoresistor 9 made by a boron element doping process; the single crystal silicon piezoresistor 2 is composed of a high resistance varistor strip and a low resistance ohmic contact area;

[0054] As a preferred embodiment, two groups of varistor strips are provided on the upper surface of the peninsula-arc edge beam structure, and the two groups of varistor strips are symmetrically arranged in the stress concentration area on the peninsula-arc edge beam structure relative to the center of the varistor chip structure;

[0055] The length directions of the two groups of varistor strips are perpendicular to the direction of the chip frame, and each group of varistor strips includes four varistor strips.

[0056] Specifically, the metal interconnection lead 3 electrically conducts the ohmic contact region of the single crystal silicon piezoresistor 2 in the layer 6 disposed below the layer 5, forming a Wheatstone bridge type piezoresistive circuit, which converts the measured pressure signal into an electrical signal output.

[0057] Among them, the island structure in the island-beam-membrane coupling structure is at the bottom and has a large volume. It can be regarded as a mass block. Before the device and the substrate are finally bonded, the mass of the island structure can be adjusted according to needs; the gravity effect of the mass block is used to design the mechanical balance compensation for thermal stress in the structure; when the sensor is working, the gravity generated by the mass block offsets the thermal stress caused by temperature changes, thereby reducing the impact of temperature changes on pressure-sensitive elements and improving the sensitivity and linearity of the sensor at different temperatures. Compared with the traditional simple thin film structure design, the introduction of the mass block effectively reduces the nonlinear output error in the stress concentration area of ​​the sensor and improves the sensitivity and long-term stability of the sensor.

[0058] The fourth substrate is arranged below the sixth layer and is made of single crystal silicon to form a pressure-sensitive film structure 5 of the pressure-sensitive chip.

[0059] The fifth substrate includes a fixed structure, and the material is single crystal silicon; the fixed structure is as follows:

[0060] The upper surface is connected to the pressure-sensitive membrane structure 5 of layer seven, and a hole island structure 6 is arranged in the middle. The bottom and surrounding areas of the hole island structure 6 are cavity structures, which ensure that the pressure-sensitive membrane structure 5 and the hole island structure 6 can deform freely when under pressure; a supporting frame 7 is arranged around the layer eight where the fifth substrate is located, and the upper and lower surfaces of the supporting frame 7 are respectively connected to the pressure-sensitive membrane structure 5 and the glass base 8 of the sixth substrate. The thickness of the supporting frame 7 is greater than that of the hole island structure 6, and plays a fixed supporting role.

[0061] The sixth substrate includes a glass base 8 made of glass. Specifically, the upper surface of the layer nine where the sixth substrate is located is fixedly connected to the supporting frame 7 through a MEMS bonding process, and serves as the glass base 8 at the bottom of the pressure-sensitive chip. The lower surface 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.

[0062] Example 2

[0063] Embodiment 2 of the present invention discloses a method for preparing the temperature self-compensating small-range MEMS sensor described in Embodiment 1 above, such as Figure 4 and Figure 5 As shown, the specific preparation process is as follows:

[0064] S1: A mask with a single-crystal silicon piezoresistor 2 structure is made on the front side of the single-crystal silicon wafer by photolithography, and a piezoresistive strip and an ohmic contact area are prepared on the silicon wafer by using a boron doping and a concentrated boron doping process. After the implantation is completed, a rapid annealing process is used to repair the lattice damage caused by the implantation;

[0065] S2: using a plasma vapor deposition process PECVD to deposit an oxide insulating layer on one side of the boron-doped single-crystal silicon piezoresistor 2 of the silicon wafer, and etching to open an electrical contact hole for ohmic contact on the insulating layer; then using a sputtering process to deposit a metal film on the insulating layer, and etching to form a metal interconnection lead 3 by a metal corrosion process, to ensure electrical interconnection between the single-crystal silicon piezoresistor 2 and the polycrystalline silicon piezoresistor 9;

[0066] S3: using an etching process to form a pattern outline of a peninsula-arc edge beam structure on the oxide layer on the upper surface of the substrate as a mask, and then etching silicon by reactive ion etching (RIE) to form a peninsula-arc edge beam structure;

[0067] S4: using a chemical vapor deposition process LPCVD to deposit a layer of aluminum nitride on the upper surface of the substrate as a passivation layer;

[0068] S5: etching the pattern of the pressure-sensitive membrane structure 5 + the hole island structure 6 on the oxide layer on the lower surface of the substrate by using an etching process;

[0069] Spraying photoresist on the surface of the oxide layer where the pattern of the pressure-sensitive film structure 5+hole island structure 6 is etched, and developing to form the pattern of the hole island structure 6 as a mask;

[0070] The silicon is etched by using a reactive ion deep etching (DRIE) process, and the depth is the height corresponding to the hole island structure 6;

[0071] The remaining photoresist is removed to expose the oxide layer of the pressure-sensitive film structure 5 + hole island structure 6 pattern.

[0072] S6: using the oxide layer on which the pressure-sensitive film structure 5 + hole island structure 6 pattern is etched as a mask, etching the pressure-sensitive film structure 5 + hole island structure 6 region on the bottom surface of the silicon wafer by a reactive ion deep etching (DRIE) bulk silicon processing technology to form a pressure-sensitive film structure 5 and a hole island structure 6 of a target size;

[0073] S7: removing the remaining oxide layer on the back side, and using an anodic bonding process, bonding a glass sheet as a glass base 8 to the back side of the silicon wafer.

[0074] The present invention is not limited to the above-mentioned specific embodiments, but extends to any new features or any new combination disclosed in this specification, as well as any new method or process steps or any new combination disclosed.

Claims

1. A temperature self-compensating small-range MEMS sensor, characterized in that: The sensor comprises a packaging shell and a pressure-sensitive chip, and the pressure-sensitive chip comprises, from top to bottom, a first substrate, a second substrate, a third substrate, a fourth substrate, a fifth substrate and a sixth substrate; The first substrate is a passivation protection layer, the second substrate is a metal layer, the third substrate includes a peninsula-arc edge beam structure and a piezoresistor, the piezoresistor is composed of a high-resistance varistor strip and a low-resistance ohmic contact area, including a single-crystal silicon piezoresistor and a polycrystalline silicon piezoresistor; the fourth substrate includes a pressure-sensitive film structure, the fifth substrate includes a fixed structure, and the sixth substrate includes a glass base; The metal layer is provided with metal interconnection leads, and the piezoresistor is arranged in the peninsula-arc edge beam structure; the metal interconnection leads electrically conduct the ohmic contact area of ​​the piezoresistor to form a Wheatstone bridge type piezoresistive circuit.

2. The temperature self-compensating small-range MEMS sensor according to claim 1, characterized in that: The first substrate is made of silicon nitride, the second substrate is made of aluminum, copper or chrome-gold alloy, the third substrate is made of single crystal silicon and silicon oxide, the fourth substrate and the fifth substrate are made of single crystal silicon, and the sixth substrate is made of glass.

3. The temperature self-compensating small-range MEMS sensor according to claim 1, characterized in that: Two groups of varistor strips are arranged on the upper surface of the peninsula-arc edge beam structure, and the two groups of varistor strips are symmetrically arranged relative to the center of the varistor chip structure in the stress concentration area of ​​the peninsula-arc edge beam structure.

4. The temperature self-compensating small-range MEMS sensor according to claim 3, characterized in that: The length directions of the two groups of varistor strips are perpendicular to the direction of the chip frame, and each group of varistor strips includes four varistor strips.

5. The temperature self-compensating small-range MEMS sensor according to claim 1, characterized in that: A hole island structure is arranged in the middle of the fifth substrate, and a cavity structure is arranged below and around the hole island structure.

6. The temperature self-compensating small-range MEMS sensor according to claim 5, characterized in that: The fifth substrate is surrounded by a supporting frame, the upper and lower surfaces of which are fixedly connected to the pressure-sensitive membrane structure and the glass base respectively, and the thickness of the supporting frame is greater than that of the hole island structure.

7. A method for preparing a temperature self-compensating small-range MEMS sensor, characterized in that: include: S1: A mask with a piezoresistor structure is made on the front side of a single crystal silicon wafer by photolithography, and a piezoresistive strip and an ohmic contact area are prepared; S2: etching metal interconnect leads to form electrical interconnections between the single-crystal silicon piezoresistor and the polycrystalline silicon piezoresistor; S3: etching a peninsula-arc edge beam structure on the oxide layer on the upper surface of the substrate; S4: depositing a layer of aluminum nitride on the upper surface of the substrate as a passivation layer; S5: etching a pattern of a pressure-sensitive membrane structure + a hole island structure on the oxide layer on the lower surface of the substrate; S6: using the oxide layer on which the pressure-sensitive film structure + hole island structure pattern is etched as a mask, etching the pressure-sensitive film structure + hole island structure region on the bottom surface of the silicon wafer to form a pressure-sensitive film structure and hole island structure of a target size; S7: removing the remaining oxide layer on the back side and bonding a glass sheet as a glass base to the back side of the silicon wafer.

8. The method for preparing the temperature self-compensating small-range MEMS sensor according to claim 7, characterized in that: In step S2, the etching process of the metal interconnection lead is as follows: Depositing an oxide insulating layer on one side of a silicon wafer boron-doped single crystal silicon piezoresistor, and etching an electrical contact hole for ohmic contact on the insulating layer; Then, a metal film is deposited on the insulating layer, and metal interconnection leads are etched out.

9. The method for preparing the temperature self-compensating small-range MEMS sensor according to claim 7, characterized in that: In step S3, the etching process of the peninsula-arc edge beam structure is as follows: The graphic outline of the peninsula-arc edge beam structure is formed on the surface oxide layer of the substrate through an etching process, which is used as a mask, and then silicon is etched through reactive ion etching (RIE) to form the peninsula-arc edge beam structure.

10. The method for preparing the temperature self-compensating small-range MEMS sensor according to claim 7, characterized in that: In step S5, the etching process of the pressure-sensitive membrane structure and the hole island structure is as follows: The area pattern of the pressure-sensitive membrane structure + hole island structure is etched out on the oxide layer on the lower surface of the substrate by an etching process; Spraying photoresist on the surface of the oxide layer of the regional pattern, and developing to form a hole island structure pattern as a mask; The silicon is etched by using a reactive ion deep etching (DRIE) process, and the depth is the height corresponding to the hole island structure; The remaining photoresist is removed to expose the oxide layer of the pressure-sensitive film structure + hole island structure pattern.

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