A pressure sensor and a method for preparing the same

Abstract

The present invention provides a pressure sensor, which includes a glass base and a silicon strain diaphragm located on the glass base. A concave cavity is provided on one side of the glass base. The silicon strain diaphragm includes an insulating dielectric layer on the front surface and a silicon substrate covered by the insulating dielectric layer. A fishbone-shaped cross-beam film component is provided on the front surface of the silicon strain diaphragm facing the cavity. A group of piezoresistors, a group of heavily doped contact regions and a pair of metal leads are provided at each end of the cross-beam film component. The piezoresistors and the heavily doped contact regions are connected in series, and both ends are led out from the heavily doped contact regions by the metal leads. The metal leads and the heavily doped contact regions form an ohmic contact on the front surface of the silicon strain diaphragm, and a Wheatstone bridge is formed between the piezoresistors; the cost is reduced, the efficiency is improved, the performance of the sensor can be adjusted, and it is applicable to different ranges; the anti-interference ability is strong, and it has excellent stiffness, ultimate yield moment and restoring force characteristics.

Description

Technical Field

[0001] The present invention relates to the technical field of sensors, and particularly to a pressure sensor and a preparation method thereof. Background Art

[0002] A piezoresistive pressure sensor converts an external pressure change into a corresponding electrical signal based on the piezoresistive effect of single crystal silicon, and measures the external pressure through a Wheatstone bridge composed of four equal-value resistors. Piezoresistive pressure sensors are mainly applied to related fields such as industrial control, automotive electronics, consumer electronics, medical electronics, and aerospace. Piezoresistive pressure sensors are designed and developed using technologies, and their internal structure consists of a silicon diaphragm obtained from a silicon wafer as a force-sensitive element, four pairs of equal-value resistors and low-resistance interconnects fabricated through processes such as doping and etching, and a multi-functional layer integrated with various materials such as evaporated metal leads.

[0003] The structure of piezoresistive pressure sensors is mainly flat diaphragm type and beam diaphragm type. In order to pursue high-sensitivity performance requirements, the strain diaphragm of the flat diaphragm structure pressure sensor chip is designed to be thinner and thinner. However, a thinner strain diaphragm will cause a larger membrane deflection, resulting in the maximum displacement value of the diaphragm exceeding the general design standard (one-fifth principle of the beam diaphragm thickness), thereby reducing the linearity of the sensor and having poor shock resistance. Although the beam diaphragm structure pressure sensor has excellent linearity, deep silicon etching is involved in the wafer manufacturing process. At present, the radial depth error of large-size deep silicon etching is relatively large (±10%), which makes it impossible to guarantee the thickness uniformity of the flat diaphragm layer after the front beam diaphragm is etched, increasing the risk of the sensor strain diaphragm breaking. For piezoresistive pressure sensors, the thickness of the strain diaphragm is the most critical. Uneven thickness leads to large performance differences among sensors in the same batch, increasing the difficulty of subsequent debugging and compensation and the manufacturing cost. Summary of the Invention

[0004] The purpose of the present invention is to provide a pressure sensor and a preparation method thereof, which can overcome the problems such as uneven thickness of the flat diaphragm layer, the risk of the sensor strain diaphragm breaking, difficulty in subsequent debugging and compensation, and increased manufacturing cost.

[0005] To achieve the above purpose, the solution of the present invention is as follows:

[0006] A pressure sensor includes a glass base and a silicon strain diaphragm located on the glass base. One side of the glass base is provided with a recessed cavity, and the silicon strain diaphragm includes an insulating dielectric layer on the front surface and a silicon substrate covered by the insulating dielectric layer.

[0007] On the front side of the silicon strain diaphragm facing the cavity, there is a fishbone-shaped cross-beam membrane component. At each end of the cross-beam membrane component, there is a group of piezoresistors, a group of heavily doped contact regions, and a pair of metal leads. The piezoresistors and the heavily doped contact regions are connected in series, and both ends are led out from the heavily doped contact regions by the metal leads. The metal leads and the heavily doped contact regions form an ohmic contact on the front side of the silicon strain diaphragm, and a Wheatstone bridge is formed between the piezoresistors.

[0008] Further, the cross-beam membrane component includes island-shaped beam blocks arranged at equal or unequal intervals and fishbone strips for connecting two adjacent island-shaped beam blocks. The number of island-shaped beam blocks on each beam of the cross-beam membrane component is equal.

[0009] Further, the cross-beam membrane component at the connection with the edge membrane region is straight or linearly tapered.

[0010] Further, each group of piezoresistors includes multiple piezoresistor bars.

[0011] Further, the island-shaped beam blocks are one or more of rectangular, triangular, oval, rhombic, and circular.

[0012] A method for manufacturing a pressure sensor as described in any one of the above, comprising the following steps:

[0013] 1) Fabricate interconnected piezoresistors and heavily doped contact regions on the front side of a silicon substrate to obtain a silicon strain diaphragm (2);

[0014] 2) Fabricate lead holes and metal leads on the front side of the silicon strain diaphragm;

[0015] 3) Define the shape of the cross-beam structure of the cross-beam membrane component on the front side of the silicon strain diaphragm by photolithography, and then etch to fabricate a fishbone-like beam structure;

[0016] 4) Back-etch the SOI wafer / silicon wafer until reaching a preset thickness and stop;

[0017] 5) Anodic bond the silicon strain diaphragm with a fishbone-like beam structure obtained in step 4) to glass with or without a cavity;

[0018] 6) Dice to fabricate a pressure sensor.

[0019] Further, in step 1), the piezoresistors and the heavily doped contact regions are fabricated by ion implantation;

[0020] In step 2), a metal layer is deposited by processes such as evaporation or sputtering, etched to obtain metal leads, and annealed and alloyed to form an ohmic contact;

[0021] In step 3), positive photolithography is used to define the shape of the cross beam, and a fishbone-like beam film is obtained by shallow etching.

[0022] In step 4), deep silicon etching of the back cavity is carried out by positive and negative overlay etching until the buried oxide layer is encountered.

[0023] Furthermore, in step 2), an SiO2 layer or a SiN layer is obtained by LPCVD process, and electrode holes are obtained by photolithography and etching.

[0024] Furthermore, in step 1), a piezoresistor and a heavily doped contact region are obtained by implanting B+ ions and annealing.

[0025] Furthermore, the metal lead can be made of Al, Cr / Au, or Ti / Au materials.

[0026] After adopting the above technical solution, the fishbone-shaped cross beam film can not only ensure the sensitivity of the pressure sensor but also improve the linearity of the sensor; reduce costs, reduce the risk of chip breakage of the strain film caused by large radial depth errors in large-size deep silicon etching; improve efficiency, reduce the risk caused by uneven flat film thickness, reduce the difficulty of subsequent debugging and compensation, and reduce manufacturing costs; can adjust the performance of the sensor and is suitable for different ranges; has strong anti-interference ability and excellent stiffness, ultimate yield moment, and restoring force characteristics. Brief Description of the Drawings

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required to be used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0028] Figure 1 It is a schematic structural diagram of a pressure sensor provided in Embodiment 1 of the present invention;

[0029] Figure 2 It is a partial cross-sectional view of a pressure sensor provided in Embodiment 1 of the present invention;

[0030] Figure 3 It is a top view of a pressure sensor provided in Embodiment 1 of the present invention;

[0031] Figures 4A - 4H It is a preparation flow chart of the pressure sensor in Embodiment 2 of the present invention, where:

[0032] Figure 4A It is a schematic diagram of the wafer preparation and mark alignment process;

[0033] Figure 4B It is a schematic diagram of piezoresistor fabrication;

[0034] Figure 4C Schematic diagram for fabricating a heavily doped contact region;

[0035] Figure 4D Schematic diagram for fabricating an electrode via;

[0036] Figure 4E Schematic diagram for fabricating a metal lead;

[0037] Figure 4F Schematic diagram for fabricating a crossbeam membrane component;

[0038] Figure 4G Schematic diagram for back cavity etching;

[0039] Figure 4H Schematic diagram for silicon - glass bonding;

[0040] Figures 5A - 5C Front - view schematic diagram of silicon strain diaphragms in various structural forms;

[0041] Figures 6A - 6B Front - view schematic diagram of crossbeam membrane components in various structural forms. Detailed implementation manners

[0042] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0043] Embodiment 1:

[0044] As Figure 1 shown, a pressure sensor, a MEMS piezoresistive pressure sensor designed and developed using MEMS technology, includes a glass base 1 and a silicon strain diaphragm 2 located on the glass base 1. The silicon strain diaphragm 2 is a silicon membrane with a front - side beam membrane and a back - cavity structure formed by front - side etching and back - cavity etching processes on an SOI wafer / silicon wafer;

[0045] As Figure 1 or Figure 2As shown, a concave cavity is provided on one side of the glass base 1. The silicon strain diaphragm 2 includes an insulating dielectric layer on the front surface and a silicon substrate covered by the insulating dielectric layer. The silicon substrate is an N-type <100> crystal plane SOI (Silicon-On-Insulator) silicon wafer or an N-type silicon wafer. The silicon strain diaphragm 2 and the glass base 1 with a concave cavity are bonded by anodic bonding. The non-bonding surface of the silicon wafer can be thinned. Since the cavity is made on the glass base 1, the thinned thickness is not affected by the cavity, which can reduce the thickness and other dimensions of the chip and lower the cost of the chip. And because of the process of silicon-glass anodic bonding, the glass plays a role in stress buffering for the silicon strain diaphragm 2, improving the stability of the sensor in subsequent packaging and testing, and having broad application prospects.

[0046] As Figure 1 shown, a fishbone-shaped cross-beam film member 3 is provided on the front surface of the silicon strain diaphragm 2 facing the cavity, and the cross-beam film member 3 is arranged at the center of the silicon strain diaphragm 2, which inhibits large deformation of the silicon strain diaphragm 2 and at the same time enables the pressure sensor to have high linearity.

[0047] As Figure 1 or Figure 3 shown, specifically, the cross-beam film member 3 has four ends, and a set of piezoresistors 4, a set of heavily doped contact regions 5 and a pair of metal leads 6 are provided at each end. The piezoresistors 4 and the heavily doped contact regions 5 at each end are connected in series, and are led out from the heavily doped contact regions 5 by the metal leads 6 at both ends. The metal leads 6 and the heavily doped contact regions 5 form an ohmic contact on the front surface of the silicon strain diaphragm 2, and a Wheatstone bridge is formed between the piezoresistors 4.

[0048] As Figure 1 shown, further, the cross-beam film member 3 is an island-shaped beam block 31 arranged at equal or unequal intervals, and the island-shaped beam blocks 31 are connected in series by fishbone strips. The use of a cross-beam film member 3 in a fishbone shape can reduce costs and reduce the risk of chip breakage of the strain diaphragm caused by large radial depth errors in large-size deep silicon etching.

[0049] And the number of island-shaped beam blocks 31 on each beam of the cross-beam film member 3 is the same, which can reduce the risk caused by uneven flat film thickness, reduce the difficulty of subsequent debugging and compensation, and the thickness of each island-shaped beam block 31 can also be adjusted, which can not only adjust the performance of the sensor, but also be applicable to different ranges.

[0050] In addition, the cross-beam film member 3 with a fishbone-like structure has strong anti-interference ability. The fishbone-like structure has excellent stiffness, ultimate yield moment and restoring force characteristics and is shock-resistant.

[0051] Further, the cross-beam membrane member 3 at the connection with the edge membrane region is straight-bar-shaped or linearly gradually changing. In this embodiment, the straight-bar shape is adopted, making the whole more stable and with strong anti-interference ability.

[0052] As Figure 1 or Figure 3 shown, further, each group of the varistors 4 includes multiple numbers of varistors 4. Specifically, four groups of varistors 4 are symmetrically distributed at the ends of the cross-beam membrane member 3, and the number of varistors 4 in each group is not limited to a specific number, generally 2 - 4, and 4 are adopted in this embodiment.

[0053] Further, the island-shaped beam blocks 31 are one or more of rectangle, triangle, ellipse, rhombus, and circle. Specifically, in this embodiment, rectangular island-shaped beam blocks 31 are adopted and are equally spaced on the beams of the cross-beam. The island-shaped beam blocks 31 on each beam are connected by fishbone strips 32, and the fishbone strips 32 and the island-shaped beam blocks 31 are of an integral structure, making the overall structure more stable, and having better plasticity and flexibility, suitable for different measurement ranges; see Figure 6A , when the island-shaped beam blocks 31 are triangular, the structure is more stable; see Figure 6B , when the island-shaped beam blocks 31 are elliptical, the island-shaped beam blocks 31 are equally spaced from each other, and the overall plasticity and flexibility are better.

[0054] As Figure 5A shown, the end of the cross-beam membrane member 3 in this solution can also adopt a square boss structure, which can improve the overall sensitivity and linearity; as Figure 5B shown, the central part of the cross-beam membrane member 3 in this solution is wider and has better stability; as Figure 5C shown, the end of the cross-beam membrane member 3 in this solution adopts an arc structure, making the whole more stable and suitable for different measurement ranges.

[0055] Specifically, the metal lead 6 can be made of materials such as Al, Cr / Au, Ti / Au, etc. In this embodiment, Cr / Au is adopted as the metal lead to prevent the oxidation of the metal lead by the oxygen generated during anodic bonding.

[0056] Embodiment 2:

[0057] This embodiment discloses a preparation method of a pressure sensor. Multiple groups of varistors 4 are made at the midpoint positions of the side lines of a square diaphragm fabricated by a back cavity etching process. The number of varistors 4 in each group is arbitrary, and in this embodiment, it is 4. A cross-beam structure is etched on the front surface of the silicon strain diaphragm 2. The varistors 4 are located on the cross-beam structure and at the edge of the cross-beam structure, and the varistors 4 are in the stress concentration area. Specifically, the steps of this method include:

[0058] 1) Wafer preparation, marking layer etching: Align and etch the marking on the zero layer of the N-type <100> plane SOI (Silicon-On-Insulator) wafer, and thermally oxidize the silicon wafer surface to form thermal silicon dioxide, as Figure 4A shown;

[0059] 2) Lithography of varistor 4: Lithograph the varistor 4 pattern in the device layer area of the SOI wafer, ion implant B+, and anneal to obtain varistor 4, as Figure 4B shown;

[0060] 3) Lithography of heavily doped contact region 5: Lithograph the pattern of the heavily doped contact region in the device layer area of the SOI wafer, ion implant B+, and anneal to obtain heavily doped contact region 5, as Figure 4C shown;

[0061] 4) Open electrode hole 8: Obtain the SiO2 layer or SiN layer by LPCVD process, and lithograph and etch to obtain electrode hole 9, as Figure 4D shown;

[0062] 5) Fabrication of metal lead 6, ohmic connection: Deposit the metal layer by evaporation or sputtering and other processes, etch to obtain metal lead 6, anneal and alloy to form ohmic contact, as Figure 4E shown;

[0063] 6) Fabrication of the cross-beam membrane component 3 structure: Define the cross-beam shape by front-side lithography, and obtain the fishbone-like structure of the cross-beam membrane component 3 by shallow etching, with a thickness of d1, which determines the thickness of the cross-beam membrane component 3, as Figure 4F shown;

[0064] 7) Back cavity 7 etching: Deep silicon etching of the SOI wafer / silicon wafer by positive and negative alignment until the buried oxide layer is encountered, as Figure 4G shown;

[0065] 8) Punching glass bonding, dicing: Anodically bond the silicon strain diaphragm 2 obtained in step 7) with the punched glass base 1, and dice to obtain the pressure sensor, which can reduce the thickness of the chip and there is no problem of increasing the chip size, and the cavity is fabricated on the glass base 1, which is not restricted by the silicon wafer crystal orientation, as shown in Figure 4H.

[0066] After the chip fabrication is completed, dicing is performed. Through this step, the entire silicon wafer is formed into a large number of individual pressure sensor chips, and each silicon wafer can obtain different numbers of pressure sensor chips according to the designed size.

[0067] The above is only the preferred embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent replacement or improvement made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A pressure sensor, characterized in that, It includes a glass base (1) and a silicon strain diaphragm (2) located on the glass base (1). One side of the glass base (1) is provided with a sunken cavity. The silicon strain diaphragm (2) includes an insulating dielectric layer on the front side and a silicon substrate covered by the insulating dielectric layer; On the front side of the silicon strain diaphragm (2) facing the cavity, there is a fishbone-shaped cross-beam film component (3). At each end of the cross-beam film component (3), there is a group of piezoresistors (4), a group of heavily doped contact regions (5), and a pair of metal leads (6). The piezoresistors (4) and the heavily doped contact regions (5) are connected in series, and both ends are led out from the heavily doped contact regions (5) by the metal leads (6). The metal leads (6) and the heavily doped contact regions (5) form an ohmic contact on the front side of the silicon strain diaphragm (2), and a Wheatstone bridge is formed between the piezoresistors (4); The cross-beam film component (3) includes island-shaped beam blocks (31) arranged at equal or unequal intervals and fishbone strips (32) for connecting the island-shaped beam blocks (31); the number of island-shaped beam blocks (31) on each beam of the cross-beam film component (3) is equal; the cross-beam film component (3) at the connection with the edge film region is straight or linearly tapered, and the end of the cross-beam film component (3) adopts a square boss structure.

2. The pressure sensor according to claim 1, wherein Each group of the piezoresistors (4) includes a plurality of piezoresistor (4) strips.

3. A pressure sensor according to claim 1, characterized in that, The island-shaped beam blocks (31) are one or more of rectangle, triangle, ellipse, rhombus, and circle.

4. A method for preparing a pressure sensor according to any one of claims 1-3, characterized in that, It includes the following steps: 1) Fabricate interconnected piezoresistors (4) and heavily doped contact regions (5) on the front side of the silicon substrate to obtain the silicon strain diaphragm (2); 2) Fabricate lead holes and metal leads (6) on the front side of the silicon strain diaphragm (2); 3) Define the shape of the cross-beam structure of the cross-beam film component (3) by photolithography on the front side of the silicon strain diaphragm (2), and then etch to fabricate a fishbone-like beam structure; 4) Back-etch the SOI wafer / silicon wafer until it stops when encountering a preset thickness; 5) Anodic bond the silicon strain diaphragm (2) with a fishbone-like beam structure obtained in step 4) to the glass base (1) with a cavity; 6) Dicing to fabricate a pressure sensor.

5. The manufacturing method of a pressure sensor according to claim 4, wherein In step 1), the piezoresistors (4) and the heavily doped contact regions (5) are fabricated by ion implantation; In step 2), a metal layer is deposited by processes such as evaporation or sputtering, etched to obtain metal leads, and annealed and alloyed to form an ohmic contact; In step 3), the cross-beam shape is defined by front-side photolithography, and a fishbone-like cross-beam film component (3) is obtained by shallow etching; In step 4), deep silicon etching of the back cavity (7) is performed by positive and negative overlay etching until the buried oxide layer is encountered.

6. The preparation method of a pressure sensor according to claim 5, characterized in that, In step 2), it also includes obtaining a SiO2 layer or a SiN layer by LPCVD process, and photolithographically etching to obtain electrode holes (8).

7. The manufacturing method of a pressure sensor according to claim 6, characterized in that, In step 1), the piezoresistors (4) and the heavily doped contact regions (5) are obtained by implanting B+ ions and annealing.

8. The manufacturing method of a pressure sensor according to claim 7, characterized in that, The metal leads can be selected from materials such as Al, Cr / Au, and Ti / Au.

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