Pressure sensor based on silicon-silicon bonding and preparation method thereof

Abstract

The invention provides a pressure sensor based on silicon-silicon bonding and a preparation method thereof. The preparation method comprises the following steps: providing a low-resistance silicon wafer, forming a silicon deep hole in a first surface of the low-resistance silicon wafer, and depositing an isolation material in the silicon deep hole to form an isolation ring; etching the first surface to form a shallow groove and a conductive silicon column to obtain a low-resistance cap wafer; providing an SOI wafer, performing ion implantation on the first surface of the SOI wafer to form a resistance region, and obtaining a substrate wafer; bonding the low-resistance cap wafer with the substrate wafer; grinding the second surface of the low-resistance cap wafer until the isolating ring is exposed; depositing an insulating layer on the second surface of the low-resistance cap wafer, and forming a metal electrode on the insulating layer; and forming a back cavity structure on the second surface of the substrate wafer, exposing the top silicon of the SOI wafer, and forming a sensitive film layer. The conductive silicon column is made of low-resistance silicon, copper ion pollution is avoided, the preparation process is simple, and the period is controllable; the device obtained based on the silicon-silicon bonding process has high bonding strength and high air tightness.

Description

Technical Field

[0001] The present invention belongs to the field of semiconductor technology, and in particular relates to a pressure sensor based on silicon-silicon bonding and a preparation method thereof. Background Art

[0002] MEMS pressure sensors are sensing devices that combine micromechanical structures with electronic circuits. They primarily utilize chips made from traditional semiconductor materials such as single-crystal silicon wafers. They measure pressure by detecting physical deformation or charge accumulation, converting it into an electrical signal. This allows for sensitive monitoring and precise conversion of pressure changes. They are widely used in various industrial automation environments, such as railway transportation, aerospace, and military industries. Based on their operating principles, they can be categorized into piezoresistive, piezoelectric, capacitive, resonant, and fiber optic pressure sensors. Piezoresistive pressure sensors offer significant advantages in measurement accuracy and stability. Furthermore, they utilize an integrated manufacturing process and lack transmission components, resulting in a compact size, light weight, and ease of installation and portability.

[0003] Piezoresistive pressure sensors measure pressure based on the piezoresistive effect of semiconductor materials. Pressure changes cause changes in the resistance of the piezoresistor and bridge imbalance, and pressure measurement is achieved based on the ratio of the bridge imbalance to the measured voltage. To improve the system integration of MEMS pressure sensors, traditional pressure sensors use a through-silicon-via (TSV) copper plating process to fill lead holes to form conductive columns to connect to the piezoresistor, thereby leading the sensitive unit electrodes to the surface of the wafer-level package, enhancing device reliability while facilitating integrated packaging applications such as flip-chip soldering. However, the TSV copper plating process is complex and prone to copper ion contamination. The electroplating filling of wide and deep TSV holes is costly and time-consuming. At the same time, in pressure sensors prepared using metal bonding processes, the bonding metal and ordinary metal wires are prone to melting under harsh high-temperature conditions, causing device damage.

[0004] Based on the above problems, it is necessary to provide a pressure sensor based on silicon-silicon bonding and a preparation method thereof to improve the bonding strength and high temperature resistance while reducing the process cost. Summary of the Invention

[0005] The present invention is to solve all or part of the problems of the above-mentioned prior art and provides a preparation method of a pressure sensor based on silicon-silicon bonding, comprising the following steps: providing a low-resistance silicon wafer, forming a silicon deep hole on the first surface of the low-resistance silicon wafer, and depositing isolation material in the silicon deep hole to form an isolation ring; etching the first surface to form a shallow groove and a conductive silicon column to obtain a low-resistance cap wafer; providing an SOI wafer, performing ion implantation on the first surface of the SOI wafer to form a resistance area to obtain a substrate wafer; bonding the low-resistance cap wafer to the substrate wafer; grinding the second surface of the low-resistance cap wafer until the isolation ring is exposed; depositing an insulating layer on the second surface of the low-resistance cap wafer, and forming a metal electrode on the insulating layer, the metal electrode can be any one of Pt, Pt-Ir alloy, Pt-Rh alloy, Ir-Rh alloy or W-Re alloy; forming a back cavity structure on the second surface of the substrate wafer to expose the top silicon of the SOI wafer to form a sensitive film layer. Conductive silicon pillars are made of low-resistance silicon to avoid copper ion contamination. The preparation process is simple and the cycle is controllable, which enhances the process adaptability and safety of the device production process and reduces costs. Based on the silicon-silicon bonding process, the pressure sensor has high bonding strength and high airtightness. The use of high-temperature resistant metal (alloy) electrodes allows the device to work normally under harsh high-temperature conditions, thereby improving the high-temperature tolerance of the product.

[0006] The resistivity of the low-resistance silicon wafer ranges from 0.001Ω·cm to 0.05Ω·cm.

[0007] The isolation ring structure is formed by forming a dielectric layer on the surface of the low-resistance silicon wafer and the inner wall of the silicon deep hole, depositing polysilicon on the dielectric layer to fill the silicon deep hole; then removing the polysilicon and dielectric layer from the surface of the low-resistance silicon wafer to expose the surface of the low-resistance silicon wafer. The dielectric layer is made of silicon oxide, which enhances structural stability and electrical performance and reduces crosstalk and capacitive coupling between different layers. Silicon oxide has excellent insulation, thermal stability, and chemical stability. The polysilicon pillars serve as structural support to enhance the mechanical strength of the isolation ring and alleviate stress issues caused by thermal oxygen filling.

[0008] The formation process of the back cavity structure includes: thinning the second surface of the substrate wafer through a grinding process; processing the thinned second surface through a deep silicon etching process until the top silicon of the SOI wafer is exposed, forming a sensitive film layer, and improving the response performance of the device.

[0009] The first surface of the low-resistance silicon wafer is etched by dry etching, which has high etching precision and forms shallow grooves and conductive silicon pillars.

[0010] The first surface of the low-resistance cap wafer is bonded to the first surface of the substrate wafer, achieving efficient and reliable electrical connection while having high bonding strength and maintaining structural stability and integrity.

[0011] During the bonding process, the conductive silicon pillar is bonded to the resistance region, thereby improving the overall conductivity and efficiency of the circuit.

[0012] A pressure sensor based on silicon-silicon bonding is also provided. It is manufactured using the aforementioned method for preparing a pressure sensor based on silicon-silicon bonding and comprises a low-resistance cap wafer and a substrate wafer; a sensitive film layer is formed on the second surface of the substrate wafer, and a resistance region is provided on the first surface of the substrate wafer; the low-resistance cap wafer includes an isolation ring with conductive silicon pillars disposed therein; and an insulating layer is provided on the second surface of the low-resistance cap wafer. A metal electrode is disposed on the insulating layer, passing through the insulating layer and electrically connected to the resistance region via the conductive silicon pillars. This sensor exhibits high bonding strength and airtightness, and can operate normally even under harsh high-temperature conditions, thereby improving the product's high-temperature tolerance and long-term stability.

[0013] The metal electrode and the resistance area form a Wheatstone bridge, output a voltage signal, are easy to integrate, and can accurately detect resistance changes.

[0014] The TSV isolation ring includes a dielectric layer on the inner wall of the isolation ring and filled polysilicon, which enhances structural stability and electrical performance.

[0015] Compared with the existing technology, the beneficial effects of the present invention mainly include the following: low-resistance silicon is used to make conductive silicon pillars, avoiding copper ion contamination, the preparation process is simple and the cycle is controllable, the process adaptability and safety of the device production process are enhanced, and the cost is reduced; the pressure sensor obtained based on the silicon-silicon bonding process has high bonding strength and high airtightness; the use of high-temperature resistant metal electrodes ensures that the device can work normally under high temperature and harsh conditions, thereby improving the high temperature tolerance and long-term stability of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0017] Figure 1 — Figure 2 This is a process flow chart of the method for preparing a pressure sensor using a TSV copper electroplating process.

[0018] Figure 3 — Figure 4 This is a process flow chart of the method for preparing a pressure sensor based on silicon-silicon bonding provided by the present invention.

[0019] Figure 5 This is a schematic structural diagram of the silicon-silicon bonded pressure sensor provided by the present invention. DETAILED DESCRIPTION

[0020] The following description and accompanying drawings fully illustrate specific embodiments of the present invention to enable those skilled in the art to practice them. Other embodiments may include structural, logical, electrical, process and other changes. The examples represent only possible variations. Unless clearly required, separate components and functions are optional, and the order of operation may vary. Parts and features of some embodiments may be included in or replace parts and features of other embodiments.

[0021] In the prior art, the pressure sensor uses TSV copper electroplating process to fill the lead hole to form a conductive column to connect the resistance area, thereby leading the sensitive unit electrode to the surface of the wafer level package. Figure 1 、 2 As shown, the existing preparation process includes: (1) preparing a cap wafer, providing a silicon wafer (resistivity of 1Ω·cm to 100Ω·cm), performing deep silicon etching on the silicon wafer to form silicon vias, electroplating copper in the silicon vias and performing chemical mechanical polishing (CMP), depositing silicon oxide on both sides of the wafer after CMP, and etching the bottom silicon oxide to form grooves, forming a Ge bonding layer in the grooves, and performing deep silicon etching on the bottom surface to obtain a cap wafer; (2) preparing a substrate wafer, providing an SOI wafer, which includes a top silicon layer, an insulating layer and a base silicon layer from top to bottom. Ion implantation is performed on the top silicon of the SOI wafer to form a resistance region. Silicon nitride and silicon oxide are deposited on the ion implantation surface and grooves are etched. An Al bonding layer is formed in the groove to obtain a substrate wafer. (3) The cap wafer is bonded to the substrate wafer, and the Ge bonding layer is bonded to the Al bonding layer. After bonding, the silicon oxide on the top surface of the cap wafer is rinsed with HF. The silicon oxide is then photolithographically etched to form a groove, and a CuNi electrode is electroplated in the groove. The bottom of the substrate wafer is ground and thinned, and the base silicon is photolithographically etched to expose the insulating layer. The insulating layer is then etched to form a sensitive film layer. In the above preparation process, the TSV copper plating process is complex and prone to copper ion contamination. The electroplating filling of wide and deep silicon through-holes is costly and has a long production cycle. At the same time, the bonding strength of the metal bonding process is not high. Under high temperature and harsh conditions, the bonding metal and ordinary metal wires of the pressure sensor prepared are prone to melting, causing device damage.

[0022] Example 1

[0023] This embodiment provides a method for preparing a pressure sensor based on silicon-silicon bonding, the specific steps are as follows: Figure 3 、 4 As shown, a low-resistance silicon wafer is provided, wherein the resistivity of the low-resistance silicon wafer ranges from 0.001Ω·cm to 0.05Ω·cm. Resin coating, exposure, development, deep silicon etching, resist removal, and cleaning processes are performed to form a silicon deep hole 11 on the first surface 101 of the low-resistance silicon wafer 1. Isolation material is deposited within the silicon deep hole 11 to form an isolation ring 12. The isolation ring 12 is formed by forming a dielectric layer on the surface of the low-resistance silicon wafer 1 and the inner wall of the silicon deep hole 11, depositing polysilicon on the dielectric layer to fill the silicon deep hole 11, and removing the polysilicon and dielectric layer from the surface of the low-resistance silicon wafer 1 to expose the surface of the low-resistance silicon wafer 1; the dielectric layer is silicon oxide.

[0024] The first surface 101 is etched by dry etching to form shallow grooves 13 and conductive silicon pillars 14, thereby obtaining a low-resistance cap wafer for subsequent bonding.

[0025] A SOI wafer is provided. The SOI wafer comprises, from top to bottom, a top silicon layer, an insulating layer, and a base silicon layer. The upper surface of the top silicon layer serves as the first surface of the SOI wafer, while the lower surface of the base silicon layer serves as the second surface of the SOI wafer. Ion implantation is performed on the first surface 201 of the SOI wafer to form a resistance region 21, resulting in a substrate wafer. Changes in the resistance of the resistance region 21 reflect changes in pressure.

[0026] The low-resistance cap wafer is bonded to the substrate wafer; the first surface 101 of the low-resistance cap wafer is bonded to the first surface 201 of the substrate wafer. During the bonding process, the conductive silicon column 14 is bonded to the resistance area 21, and the main bonding surface 17 of the low-resistance cap wafer is bonded to the main bonding surface 22 of the substrate wafer to ensure that the device has sufficient bonding strength.

[0027] The second surface 102 of the low-resistance cap wafer is ground until the isolation ring 12 is exposed.

[0028] An insulating layer 15 is deposited on the second surface 102 of the low-resistance cap wafer; a metal electrode 16 is formed on the insulating layer 15. The metal electrode 16 can be made of any of Pt, Pt-Ir alloy, Pt-Rh alloy, Ir-Rh alloy, or W-Re alloy. Using a high-temperature resistant metal (alloy) electrode allows the device to operate normally under harsh high-temperature conditions, improving the product's high-temperature tolerance. The insulating layer 15 is used for insulation, preventing the metal electrode 16 from electrically connecting to areas outside the conductive silicon pillars 14. The process of forming the metal electrode includes forming a contact hole on the insulating layer 15 through photolithography and etching processes, forming the metal electrode 16 within the contact hole, and electrically connecting the metal electrode 16 to the resistor region 21 through the conductive silicon pillars 14 to output a voltage signal.

[0029] A back cavity structure is formed on the second surface 202 of the substrate wafer, exposing the top silicon layer of the SOI wafer and forming a sensitive film layer 23. The thickness of the sensitive film layer 23 is 10μm-100μm. The back cavity structure formation process includes: thinning the second surface 202 of the substrate wafer through a grinding process; processing the thinned second surface 202 through a deep silicon etching process to expose the top silicon layer and form the sensitive film layer 23. The back cavity etching exposes the sensitive film layer 23 containing the resistor region 21. The sensitive film layer 23 is exposed to the external environment. The external pressure causes the sensitive film layer 23 to deform, thereby causing the resistor region 21 on the sensitive film layer 23 to deform. The change in resistance causes a change in the electrical signal.

[0030] In the above preparation method, after the low-resistance cap wafer is bonded to the substrate wafer, there is no dependency between the process of forming the electrode on the second surface 102 of the low-resistance cap wafer and the process of forming the sensitive film layer 23 on the second surface 202 of the substrate wafer, and their order can be adjusted according to actual needs.

[0031] Example 2

[0032] This embodiment provides a pressure sensor based on silicon-silicon bonding, which is manufactured using the preparation method described in Example 1 and has a structure as shown in FIG. Figure 3 As shown, it includes a low-resistance cap wafer and a substrate wafer; a sensitive film layer is formed on the second surface 202 of the substrate wafer, and a resistance region 21 is provided on the first surface 201 of the substrate wafer; the low-resistance cap wafer includes an isolation ring 12, within which a conductive silicon pillar 14 is provided. The low-resistance cap wafer ensures the conductivity of the conductive silicon pillar 14 and reduces signal transmission loss. The second surface 102 of the low-resistance cap wafer includes an insulating layer 15, on which a metal electrode 16 is provided. The metal electrode 16 passes through the insulating layer 15 and is electrically connected to the resistance region 21 through the conductive silicon pillar 14. The metal electrode 16 forms a Wheatstone bridge with the resistance region 21 to output a voltage signal. The TSV isolation ring 12 includes a dielectric layer on the inner wall of the TSV isolation ring 12 and filled with polysilicon. Based on the silicon-silicon bonding process, the pressure sensor has high bonding strength and high airtightness. The use of high-temperature resistant metal (alloy) as the electrode ensures that the device can operate normally under high temperature conditions, improving the product's high temperature tolerance and long-term stability.

[0033] It should be understood that some common English nouns or letters used in this application for the sake of clarity are only used for illustrative reference and not for restrictive interpretation or specific usage, and their possible Chinese translations or specific letters should not be used to limit the scope of protection of this application. It should also be noted that in this article, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations.

Claims

1. A method for preparing a pressure sensor based on silicon-silicon bonding, characterized in that: The following steps are involved: Providing a low-resistance silicon wafer, forming a silicon deep hole on a first surface of the low-resistance silicon wafer, and depositing an isolation material in the silicon deep hole to form an isolation ring; Etching the first surface to form shallow grooves and conductive silicon pillars to obtain a low-resistance cap wafer; Providing an SOI wafer, performing ion implantation on a first surface of the SOI wafer to form a resistance region, thereby obtaining a substrate wafer; bonding the low-resistance cap wafer to the substrate wafer; grinding the second surface of the low-resistance cap wafer until the isolation ring is exposed; Depositing an insulating layer on the second surface of the low-resistance cap wafer, and forming a metal electrode on the insulating layer, wherein the metal electrode can be made of any one of Pt, Pt-Ir alloy, Pt-Rh alloy, Ir-Rh alloy or W-Re alloy; A back cavity structure is formed on the second surface of the substrate wafer to expose the top silicon layer of the SOI wafer and form a sensitive film layer.

2. The method for preparing a pressure sensor based on silicon-silicon bonding according to claim 1, characterized in that: The resistivity of the low-resistance silicon wafer ranges from 0.001Ω·cm to 0.05Ω·cm.

3. The method for preparing a pressure sensor based on silicon-silicon bonding according to claim 1, characterized in that: The isolation ring structure forming process is as follows: forming a dielectric layer on the surface of the low-resistance silicon wafer and the inner wall of the silicon deep hole, and depositing polysilicon on the dielectric layer to fill the silicon deep hole; removing the polysilicon and dielectric layer from the surface of the low-resistance silicon wafer to expose the surface of the low-resistance silicon wafer; The dielectric layer is silicon oxide.

4. The method for preparing a pressure sensor based on silicon-silicon bonding according to claim 1, characterized in that: The formation process of the back cavity structure includes: performing a thinning process on the second surface of the substrate wafer by a grinding process; The thinned second surface is processed by a deep silicon etching process to expose the top silicon layer of the SOI wafer and form a sensitive film layer.

5. The method for preparing a pressure sensor based on silicon-silicon bonding according to claim 1, characterized in that: The first surface of the low-resistance silicon wafer is etched by dry etching.

6. The method for preparing a pressure sensor based on silicon-silicon bonding according to claim 1, characterized in that: The first surface of the low-resistance cap wafer is bonded to the first surface of the substrate wafer.

7. The method for preparing a pressure sensor based on silicon-silicon bonding according to claim 6, characterized in that: During the bonding process, the conductive silicon pillar is bonded to the resistance region.

8. A pressure sensor based on silicon-silicon bonding, characterized in that: The method for preparing a pressure sensor based on silicon-silicon bonding according to any one of claims 1 to 7 comprises a low-resistance cap wafer and a substrate wafer; A sensitive film layer is formed on the second surface of the substrate wafer, and a resistance area is provided on the first surface of the substrate wafer; The low-resistance cap wafer includes an isolation ring, a conductive silicon column is provided in the isolation ring, and an insulating layer is included on the second surface of the low-resistance cap wafer. A metal electrode is provided on the insulating layer. The metal electrode passes through the insulating layer and is electrically connected to the resistance area through the conductive silicon column.

9. The pressure sensor based on silicon-silicon bonding according to claim 8, characterized in that: The metal electrode and the resistance area form a Wheatstone bridge to output a voltage signal.

10. The pressure sensor based on silicon-silicon bonding according to claim 8, characterized in that: The isolation ring includes a dielectric layer on the inner wall of the isolation ring and filled polysilicon.

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