MEMS differential pressure sensor chip structure and preparation method thereof

Abstract

The MEMS differential pressure sensor chip structure comprises a substrate, a silicon wafer is arranged on the substrate, a pressure cavity, a group of isolation grooves and a group of piezoresistors are arranged on the silicon wafer, and a group of metal leads correspondingly matched with the piezoresistors are further arranged on the silicon wafer. A piezoresistor is prepared through photoetching, boron injection, photoresist removal and boron diffusion processes on a silicon wafer, then a pressure cavity and an isolation groove are formed through photoetching, deep silicon etching, RIE and photoresist removal processes, and then a substrate is bonded on the silicon wafer. The chip structure provided by the invention is convenient to prepare and simple in structure, and the influence of static pressure in a non-sensitive direction on the measurement error drift of the differential pressure sensor can be eliminated by arranging a group of isolation grooves in the periphery of the sensitive diaphragm.

Description

Technical Field

[0001] The invention relates to the field of micro-mechanical electronic technology, and in particular to a MEMS differential pressure sensor chip structure and a preparation method thereof. Background Art

[0002] MEMS silicon pressure sensors are the most important type of sensors in industrial production and are widely used in the automotive industry, medical and health care, etc. Piezoresistive differential pressure sensors are the most widely used type of pressure sensors. By utilizing the good mechanical and electrical properties of silicon, varistors are implanted into sensitive films through diffusion or ion implantation to achieve the integration of pressure-sensitive elements and conversion circuits.

[0003] At present, when working in a high static pressure environment, the MEMS differential pressure sensor will have a large measurement error drift due to the stress generated by the static pressure in the direction of the non-sensitive membrane layer, which seriously affects the measurement accuracy and working stability of the MEMS differential pressure sensor. Summary of the invention

[0004] The present invention is to overcome the deficiencies in the prior art and provide a MEMS differential pressure sensor chip structure and a preparation method.

[0005] This application provides the following technical solutions: A MEMS differential pressure sensor chip structure is characterized in that it includes: a substrate, a silicon wafer is provided on the substrate, a group of varistors and a silicon dioxide protective layer are provided on the upper surface of the silicon wafer, metal leads corresponding to the varistors are provided on the silicon dioxide protective layer, a pressure cavity and a group of isolation grooves are provided on the lower surface of the silicon wafer, and the isolation grooves are located outside the pressure cavity.

[0006] On the basis of the above technical solutions, there are also the following further technical solutions: The isolation groove is in the form of a ring with different diameters, and the ring is a rectangular ring or a circular ring The through hole is coaxially distributed with the pressure cavity.

[0007] The pressure cavity is located below the set of varistors.

[0008] The silicon wafer is a double-polished silicon wafer or a SOI silicon wafer.

[0009] The substrate is glass or a double-polished silicon wafer.

[0010] The SOI silicon wafer comprises a top silicon layer, a buried oxide layer and a substrate silicon layer. The pressure cavity and a group of isolation grooves are arranged on the substrate silicon and the buried oxide layer. A group of varistors is arranged on the top silicon layer, and a silicon dioxide protective layer is arranged on the top silicon layer.

[0011] A method for preparing a MEMS differential pressure sensor chip structure, characterized in that it comprises the following steps: S1, taking an SOI silicon wafer, the SOI silicon wafer comprising a top silicon layer, a buried oxide layer and a substrate silicon layer sequentially distributed from top to bottom, a silicon dioxide protective layer formed on the top of the top silicon layer, and sequentially performing photolithography, boron implantation, degumming and boron diffusion processes on the top silicon to form a varistor on the top silicon surface of the SOI silicon wafer; S2, sequentially using photolithography, RIE etching and stripping processes to form lead holes on the silicon dioxide protective layer above the varistor area; S3, using a PVD process to prepare a layer of metal on the silicon dioxide protective layer near the lead hole, and then using photolithography, metal etching, and degumming processes to make the metal layer into a metal lead that is electrically connected to the varistor, and finally using an alloy process to make the metal form an ohmic contact with the varistor under the lead hole; S4, performing photoresist protection on the top silicon surface of the SOI silicon wafer, and then performing photolithography, deep silicon etching, RIE and degumming processes on the substrate silicon layer of the SOI silicon wafer in sequence, and making a pressure cavity and an isolation groove from bottom to top on the substrate silicon layer of the SOI wafer; S5. Take a glass substrate with holes and bond it to the substrate silicon layer.

[0012] Based on the above steps, there are further steps: The pressure cavity and the top of the isolation groove in S4 extend to the lower surface of the top silicon layer.

[0013] The metal etching in S3 is a dry method or a wet method or a dry method followed by a wet method.

[0014] Advantages of the invention: The chip structure provided by the present invention is easy to prepare and has a simple structure. Since a group of isolation grooves are arranged on the periphery of the sensitive diaphragm, the influence of static pressure in a non-sensitive direction on the measurement error drift of the differential pressure sensor is eliminated. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a finished product schematic diagram of the MEMS differential pressure sensor chip structure provided by the present invention; Figure 2 It is a schematic diagram of the structure when the S1 step is completed; Figure 3 It is a schematic diagram of the structure when the S2 step is completed; Figure 4 It is a schematic diagram of the structure when the S3 step is completed; Figure 5 It is a schematic diagram of the structure when the S4 step is completed. DETAILED DESCRIPTION

[0016] like Figure 1-5As shown, a method for preparing a MEMS differential pressure sensor chip structure comprises the following steps: S1. Take an SOI silicon wafer 2. The SOI silicon wafer 2 includes a top silicon layer 2a, a buried oxide layer 2b and a substrate silicon layer 2c which are sequentially distributed from top to bottom. The crystal orientation of the top silicon layer 2a in S1 is N (100).

[0017] A varistor 8 is formed on the top silicon surface of the SOI silicon wafer through photolithography, boron implantation, degumming and boron diffusion processes in sequence. The top silicon and the varistor 8 are covered with a silicon dioxide protective layer 5 that plays an insulating role.

[0018] S2, using photolithography, RIE etching and degumming processes in sequence to make two lead holes 5a on the silicon dioxide protection layer 5 above each varistor 8 area, S3, using PVD process to prepare a layer of metal on the silicon dioxide 5 protective layer near the lead hole, and then using photolithography, metal etching (wet etching), and degumming process to make the metal layer into a metal lead 6 that is electrically connected to the varistor 5, and finally using alloy process to make the metal lead 6 form an ohmic contact with the varistor under the lead hole 5a; S4. Perform photoresist protection on the top silicon surface of the SOI silicon wafer, and then perform photolithography, deep silicon etching, RIE and de-gumming processes in sequence on the substrate silicon layer 2c of the SOI silicon wafer, and make a cylindrical pressure cavity 3 and a group of annular isolation grooves 4 from bottom to top on the substrate silicon layer of the SOI wafer, and the top of the pressure cavity 3 and the isolation groove 4 extend to the lower surface of the top silicon layer 2a.

[0019] S5. Take a glass substrate 1 with a hole and bond it to the substrate silicon layer 2c, so as to obtain a MEMS differential pressure sensor chip structure.

[0020] The photolithography, wet etching, stripping process, deep silicon etching and RIE mentioned in the above steps are all conventional techniques in the art, and those skilled in the art have mastered them, so the specific implementation parameters are not described here.

[0021] A MEMS differential pressure sensor chip structure is obtained through the above steps, which includes: a glass substrate 1, on which is disposed an SOI silicon wafer 2, wherein the SOI silicon wafer 2 includes a top silicon layer 2a, a buried oxide layer 2b and a substrate silicon layer 2c. The glass substrate 1 is connected to the substrate silicon layer 2c.

[0022] A pressure cavity 3 and a group of isolation grooves 4 are provided on the substrate silicon 2c and the buried oxide layer 2b of the SOI silicon wafer 2. The isolation grooves 4 are circular ring-shaped and rectangular ring-shaped structures, and two isolation grooves 4 are coaxially distributed outside the pressure cavity 3, the inner isolation groove 4 is circular ring-shaped, and the outer isolation groove 4 is rectangular ring-shaped.

[0023] Two spaced-apart varistors 5 are provided on the buried oxide layer 2b in the area above the pressure cavity 3, a silicon dioxide protective layer 5 serving as an insulator is provided on the upper surface of the top silicon layer 2a, a pair of lead holes 5a are provided on the silicon dioxide protective layer 5 above each varistor 5, metal leads 6 corresponding to and covering the lead holes 5a are provided on the silicon dioxide protective layer 5, and the lower ends of the metal leads 6 extend into the lead holes 5a to form ohmic contact with the varistor 5.

[0024] A through hole 7 connected to the pressure cavity 3 is provided on the glass substrate 1, so that the buried oxide layer 2b between the two varistors 5 above the pressure cavity 3 forms a sensitive film layer 9. The through hole 7 is coaxially distributed with the pressure cavity 3, but has a smaller area than the pressure cavity 3.

Claims

1. A MEMS differential pressure sensor chip structure, characterized in that: It includes: A substrate (1) is provided on the substrate (1), a silicon wafer (2) is provided on the upper surface of the silicon wafer (2), a group of varistors (8) and a silicon dioxide protective layer (5) are provided on the upper surface of the silicon wafer (2), a metal lead (6) corresponding to the varistor (8) is provided on the silicon dioxide protective layer (5), and a pressure cavity (3) and a group of isolation grooves (4) are provided on the lower surface of the silicon wafer (2), and the isolation grooves (4) are located outside the pressure cavity (3).

2. A MEMS differential pressure sensor chip structure according to claim 1, characterized in that: The isolation groove (4) is in the form of a ring with different diameters, and the ring is a rectangular ring or a circular ring.

3. A MEMS differential pressure sensor chip structure according to claim 1, characterized in that: The through hole (7) is coaxially distributed with the pressure cavity (3).

4. A MEMS differential pressure sensor chip structure according to claim 1, characterized in that: The pressure cavity (3) is located below the group of varistors (8).

5. A MEMS differential pressure sensor chip structure according to claim 1, characterized in that: The silicon wafer (2) is a double-polished silicon wafer or an SOI silicon wafer.

6. A MEMS differential pressure sensor chip structure according to claim 1, characterized in that: The substrate is glass or a double-polished silicon wafer.

7. A MEMS differential pressure sensor chip structure according to claim 5, characterized in that: The SOI silicon wafer comprises a top silicon layer (2a), a buried oxide layer (2b) and a substrate silicon layer (2c); the pressure cavity (3) and a group of isolation grooves (4) are arranged on the substrate silicon (2c) and the buried oxide layer (2b); a group of varistors (8) are arranged on the top silicon layer (2a); and a silicon dioxide protective layer (5) is arranged on the top silicon layer (2a).

8. A method for preparing a MEMS differential pressure sensor chip structure, characterized in that: It includes the following steps: S1. Take an SOI silicon wafer, which includes a top silicon layer, a buried oxide layer and a substrate silicon layer distributed from top to bottom, a silicon dioxide protective layer is formed on the top of the top silicon layer, and a varistor is formed on the top silicon surface of the SOI silicon wafer by photolithography, boron implantation, degumming and boron diffusion processes in sequence; S2, sequentially using photolithography, RIE etching and stripping processes to form lead holes on the silicon dioxide protective layer above the varistor area; S3, using a PVD process to prepare a layer of metal on the silicon dioxide protective layer near the lead hole, and then using photolithography, metal etching, and degumming processes to make the metal layer into a metal lead that is electrically connected to the varistor, and finally using an alloy process to make the metal form an ohmic contact with the varistor under the lead hole; S4, performing photoresist protection on the top silicon surface of the SOI silicon wafer, and then performing photolithography, deep silicon etching, RIE and degumming processes on the substrate silicon layer of the SOI silicon wafer in sequence, and making a pressure cavity and an isolation groove from bottom to top on the substrate silicon layer of the SOI wafer; S5. Take a glass substrate with holes and bond it to the substrate silicon layer.

9. The method for preparing a MEMS differential pressure sensor chip structure according to claim 8, characterized in that: The pressure cavity and the top of the isolation groove in S4 extend to the lower surface of the top silicon layer.

10. The method for preparing a MEMS differential pressure sensor chip structure according to claim 8, characterized in that: The metal etching in S3 is a dry method or a wet method or a dry method followed by a wet method.

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