Manufacturing method of resonant beam type pressure sensor

Abstract

The invention discloses a manufacturing method of a resonant beam type pressure sensor, which belongs to the technical field of micro electro mechanical systems and comprises the following steps of: adopting an SOI (Silicon On Insulator) silicon wafer, and processing a central deep groove and an annular deep groove on the back surface of a substrate silicon layer by utilizing anisotropic dry etching to form a pressure sensing diaphragm and a boundary region; bonding the bottom surface of the boundary area on the base; forming a resonant beam and a clamped region on the device layer by using anisotropic etching; etching through the annular deep groove by using a plasma deep silicon etching process; silicon dioxide at the bottom of the beam is removed through reactive ion etching, and a suspended beam structure and a supporting column are obtained.

Description

Technical Field

[0001] The invention belongs to the technical field of micro-electromechanical systems, and in particular relates to a method for manufacturing a resonant beam pressure sensor. Background Art

[0002] Resonant pressure sensor is a sensor that uses resonant element to convert the measured pressure into frequency signal, and it outputs periodic signal itself; because its accuracy is mainly affected by the mechanical characteristics of the structure, it has strong anti-interference ability and stable performance. Silicon resonant pressure sensor has many advantages such as wide bandwidth, compact structure, low power consumption, small size, low weight, and batch production, and has always been the focus of research and development in various countries.

[0003] After the 1990s, the resonant silicon microstructure pressure sensor made of single crystal silicon material by micromachining technology has developed rapidly, and the resonant pressure sensor has embarked on the road of miniaturization and micro-miniaturization. At present, many related research results have been published abroad, typical of which are Druck Company in the UK and Yokogawa Electric Corporation in Japan. The silicon resonant pressure sensor of Druck Company in the UK adopts the working mode of electrostatic excitation / capacitive vibration pickup. Its resonator is a butterfly structure or two connected rectangular structures obtained by using concentrated boron self-stop body silicon etching technology, and is formed into a whole with two rectangular silicon islands and a rectangular pressure sensitive diaphragm. Finally, the silicon wafer is bonded to a base with electrodes and pressure-conducting holes. Yokogawa Company of Japan launched a silicon resonant differential pressure sensor in the mid-1990s. It was manufactured using epitaxial boron doping technology and reactive sealing technology, and has two electromagnetically excited H-shaped silicon beams for differential measurement. It has excellent performance and is widely used in the industrial field, but it requires a built-in permanent magnet. The above two sensors have basically been commercialized, but their common problem is that their manufacturing process and layout are relatively complex. According to the current micro-machining process technology level in my country, it is very difficult to achieve. In China, Beijing University of Aeronautics and Astronautics has been conducting follow-up research on silicon resonant pressure sensors since the mid-1980s, in the context of developing a new generation of micro-sensors for aviation in my country, and established a micro-sensor technology laboratory. In the early 1990s, it first proposed a silicon resonant beam pressure sensor scheme with electrothermal excitation and piezoresistive detection in China, and roughly proposed a scheme for the overall structure of single crystal silicon using SOI wafer processing of single beam and substrate. Summary of the invention

[0004] The object of the present invention is to provide a method for manufacturing a resonant beam pressure sensor, which overcomes the shortcomings of the prior art, simplifies the process and improves the performance by utilizing the characteristics of SOI silicon wafers.

[0005] To achieve the above object, the present invention provides a method for manufacturing a resonant beam pressure sensor, comprising the following steps: (a) Anisotropic dry etching is used to process a central deep groove and an annular deep groove on the back side of the silicon layer of the SOI silicon wafer substrate to form a pressure-sensitive diaphragm and a boundary area; (b) bonding the bottom surface of the boundary region to the base; (c) using a sputtering deposition process to deposit a metal film on the upper surface of the structure, and using a photolithography process to use a photoresist as a mask to wash away the excess metal film, leaving wires, pad areas and electrodes on the upper surface of the structure; (d) using a photolithography process, with a photoresist as a mask and a buried layer as a stop layer, the device layer is etched to remove the exposed silicon and process the device layer into a series of dumbbell-shaped patterns; (e) using a photolithography process, with a photoresist as a mask and a substrate silicon layer as a stop layer, the buried layer is etched to remove the silicon dioxide in the exposed portion, leaving an isolation layer slightly larger than the dumbbell-shaped pattern; (f) using plasma deep silicon etching to carve a deep annular groove; (g) Using photoresist as a mask for protection, reactive ion etching is performed on the middle part of the isolation layer to obtain the suspended resonant beam structure and support column.

[0006] Preferably, the specific steps of processing the central deep groove and the annular deep groove in step (a) are: spin coating photoresist on the substrate silicon layer, setting a mask on the photoresist after pre-baking, exposing, post-baking, developing, and hardening the mask layer, covering the silicon layer with the photoresist as a mask for subsequent processing, and performing anisotropic dry etching on the substrate silicon layer, wherein the annular deep groove is located outside the central deep groove, and an independent sensitive unit is obtained after the annular deep groove is etched through.

[0007] Preferably, the base in step (b) is made of BF33 glass, and the boundary region and the base are bonded together using silicon-glass anodic bonding technology.

[0008] Preferably, in step (c), the metal film is located on the upper surface of the buried layer exposed around the dumbbell-shaped pattern, and has a thickness of 50-100 nm.

[0009] Preferably, the dumbbell-shaped pattern and the resonant beam are required to consist of a middle portion and two end portions, the middle portion is an elongated rectangle, and the two end portions are block regions with an area much larger than that of the middle portion.

[0010] Preferably, there are one or more dumbbell-shaped patterns on each independent sensitive unit, wherein the center of one dumbbell-shaped pattern is opposite to the center of the central deep groove, and the remaining dumbbell-shaped patterns are placed on the upper surface of the boundary area parallel or perpendicular thereto.

[0011] Preferably, a silicon dioxide layer is processed on the upper surface of the device layer, and the silicon dioxide layer is processed into a dumbbell-shaped pattern using a photolithography process. The dumbbell-shaped pattern is used as a mask and the buried layer is used as a stop layer. The silicon dioxide layer is etched on the device layer by PECVD or thermal oxidation.

[0012] Preferably, the steps of processing the silicon dioxide layer into a dumbbell-shaped pattern using a photolithography process are: first spin-coating photoresist on the surface, exposing and developing to produce a dumbbell-shaped pattern, using the photoresist as a mask and the device layer as a stop layer to remove the exposed part of the silicon dioxide; etching the device layer to process the dumbbell-shaped pattern using a KOH solution or an EDP solution etchant.

[0013] Preferably, the reactive ion etching in step (f) uses CF4, CHF3 or CF4+O2 gas as an etchant.

[0014] Preferably, the side length of the pressure-sensitive diaphragm is 2-4 mm, the thickness is 20-40 μm, the length of the resonant beam structure is 400-2000 μm, the width is 30-100 μm, and the thickness is 4-30 μm.

[0015] Therefore, the present invention adopts the above-mentioned method for manufacturing a resonant beam pressure sensor, and its beneficial effects are: The present invention adopts the overall processing of SOI silicon wafer, simplifies the process flow, increases the yield rate, and improves the processing accuracy, mechanical quality and stability.

[0016] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is an illustration of the material of the present invention; Figure 2 It is a cross-sectional view of a SOI silicon wafer; Figure 3 It is a process flow chart of obtaining a pressure-sensitive membrane by using photolithography and anisotropic wet etching; Figure 4 This is a cross-sectional view of the SOI silicon wafer and BF33 glass after bonding; Figure 5 The process flow chart is to process a dumbbell-shaped pattern on the upper surface of the device layer by using a photoresist as a mask and a buried layer as a stop layer; Figure 6 It is a process flow chart of first processing a silicon dioxide layer on the upper surface of the device layer, and then processing a dumbbell-shaped pattern on the upper surface of the device layer using a photolithography process and an etching process; Figure 7 It is a top view of the SOI silicon wafer after obtaining the dumbbell-shaped pattern; Figure 8It is a top view of the photoresist in which the electrode shape is photoetched on the dumbbell-shaped pattern; Fig. 9 It is a top view of a metal thin film electrode prepared on a dumbbell-shaped pattern; Fig.10 It is a cross-sectional view of an independent sensitive unit after the deep annular groove is cut through; Fig.11 It is a cross-sectional view of the sensitive unit after the slow release of hydrofluoric acid; Reference numerals: 1. Device layer; 2. Buried layer; 3. Substrate silicon layer; 4. Central deep groove; 5. Annular deep groove; 6. Pressure-sensitive diaphragm; 7. Boundary area; 8. Base; 9. Dumbbell-shaped pattern; 10. Resonant beam; 11. Support column; 12. Silicon dioxide layer; 13. Metal film; 14. Wire; 15. Pad area; 16. Electrode. DETAILED DESCRIPTION

[0018] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0019] Unless otherwise defined, technical or scientific terms used in the present invention shall have the common meanings understood by one having ordinary skills in the field to which the present invention belongs.

[0020] In addition, it should be understood that although this specification is described according to the implementation modes, not every implementation mode includes only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation modes that can be understood by those skilled in the art. These other implementation modes are also covered within the protection scope of the present invention.

[0021] The present invention is further described below with reference to the accompanying drawings and specific embodiments.

[0022] A method for manufacturing a resonant beam pressure sensor, the manufacturing process of which is as follows: (a) A SOI silicon wafer is selected, which consists of a device layer 1, a buried layer 2, and a substrate silicon layer 3. The thickness of the device layer 1 is about 6 μm, the thickness of the buried layer 2 is about 3 μm, and the thickness of the substrate silicon layer 3 is about 300 μm; (b) manufacturing a doped layer having specific conductive and piezoresistive properties on the upper surface of the device layer 1 by epitaxy or diffusion; (c) cleaning and drying the SOI silicon wafer, spin coating the photoresist on the substrate silicon layer, setting a mask on the photoresist after pre-baking, exposing, post-baking, developing, and hardening the mask layer, and covering the silicon layer with the photoresist as a mask for subsequent processing; (d) using an etchant such as a KOH solution or an EDP solution to perform anisotropic wet etching on the substrate silicon layer 3, processing a central deep groove 4 and an annular deep groove 5 to form a pressure-sensitive membrane 6 and a boundary area 7, the etching groove depth is about 280 μm, and the size of the pressure-sensitive membrane is about 2000 μm×2000 μm; (e) stripping off the photoresist mask layer, rinsing and drying the SOI silicon wafer; (f) The base 8 is made of BF33 glass, and corresponding through holes are etched on the BF33 glass by laser etching, and the etched SOI silicon wafer is aligned and bonded to the BF33 glass by silicon-glass anodic bonding technology; (g) using the photoresist as a mask and the buried layer 2 as a stop layer, etching the device layer 1 to remove the silicon material in the exposed portion, and processing the device layer 1 into a series of dumbbell-shaped patterns 9, wherein the dumbbell-shaped patterns 9 are required to consist of a middle portion and two end portions, wherein the middle portion is an elongated rectangle, and the two end portions are block regions with an area much larger than that of the middle portion; (h) using plasma deep silicon etching to carve through the annular deep groove 5; (i) Reactive ion etching is used to obtain a suspended resonant beam 10 structure and a support column 11 from the middle portion of the dumbbell-shaped pattern 9. The beam is about 600 μm long, 30 μm wide and 6 μm thick. Reactive ion etching can use CF4, CHF3 or CF4+O2 as an etchant, as long as the etching rate of silicon dioxide is much higher than that of silicon within a certain temperature range; (j) Laser etching of BF33 glass to separate independent sensitive structures.

[0023] In the above embodiment, the dumbbell-shaped image 9 can also be processed in step (g) by the following method: a silicon dioxide layer 12 is processed on the upper surface of the device layer 1, the silicon dioxide layer 12 is processed into a metal film 13 by a photolithography process, and the device layer 1 is etched using the metal film 3 as a mask and the buried layer 2 as a stop layer.

[0024] The steps of processing the silicon dioxide layer 12 into the metal film 13 by photolithography are as follows: first, spin-coat the surface with photoresist, expose and develop to produce a dumbbell-shaped pattern 9, use the photoresist as a mask and the device layer 1 as a stop layer to remove the exposed part of the silicon dioxide; an isotropic or anisotropic etchant can be used.

[0025] The silicon dioxide layer 12 can be obtained by PECVD or thermal oxidation; The device layer 1 can be etched using an etchant such as KOH or EDP solution.

[0026] Therefore, the present invention provides a method for manufacturing a resonant beam pressure sensor, which uses SOI silicon wafer integral processing, simplifies the process flow, increases the yield rate, and improves processing accuracy, mechanical quality and stability.

[0027] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for manufacturing a resonant beam pressure sensor, characterized in that: The following steps are involved: (a) Anisotropic dry etching is used to process a central deep groove and an annular deep groove on the back side of the silicon layer of the SOI silicon wafer substrate to form a pressure-sensitive diaphragm and a boundary area; (b) bonding the bottom surface of the boundary region to the base; (c) using a sputtering deposition process to deposit a metal film on the upper surface of the structure, and using a photolithography process to use a photoresist as a mask to wash away the excess metal film, leaving wires, pad areas and electrodes on the upper surface of the structure; (d) using a photolithography process, with a photoresist as a mask and a buried layer as a stop layer, the device layer is etched to remove the exposed silicon and process the device layer into a series of dumbbell-shaped patterns; (e) using a photolithography process, with a photoresist as a mask and a substrate silicon layer as a stop layer, the buried layer is etched to remove the silicon dioxide in the exposed portion, leaving an isolation layer slightly larger than the dumbbell-shaped pattern; (f) using plasma deep silicon etching to carve a deep annular groove; (g) Using photoresist as a mask for protection, reactive ion etching is performed on the middle part of the isolation layer to obtain the suspended resonant beam structure and support column.

2. The method for manufacturing a resonant beam pressure sensor according to claim 1, characterized in that: The specific steps of processing the central deep groove and the annular deep groove in step (a) are as follows: spin coating photoresist on the substrate silicon layer, setting a mask on the photoresist after pre-baking, exposing, post-baking, developing, and hardening the mask layer, covering the silicon layer with the photoresist as a mask for subsequent processing, and performing anisotropic dry etching on the substrate silicon layer. The annular deep groove is located outside the central deep groove, and an independent sensitive unit is obtained after the annular deep groove is etched through.

3. The method for manufacturing a resonant beam pressure sensor according to claim 1, characterized in that: The base in step (b) is made of BF33 glass, and the boundary area and the base are bonded together using silicon-glass anodic bonding technology.

4. The method for manufacturing a resonant beam pressure sensor according to claim 1, characterized in that: In step (c), the metal film is located on the upper surface of the buried layer exposed around the dumbbell-shaped pattern, and its thickness is 50-100 nm.

5. The method for manufacturing a resonant beam pressure sensor according to claim 4, characterized in that: The dumbbell-shaped figure and the resonant beam are required to consist of a middle portion and two end portions, wherein the middle portion is an elongated rectangle and the two end portions are block-shaped regions with an area much larger than that of the middle portion.

6. The method for manufacturing a resonant beam pressure sensor according to claim 2, characterized in that: There are one or more dumbbell-shaped patterns on each independent sensitive unit, wherein the center of one dumbbell-shaped pattern is opposite to the center of the central deep groove, and the remaining dumbbell-shaped patterns are placed on the upper surface of the boundary area parallel or vertically thereto.

7. The method for manufacturing a resonant beam pressure sensor according to claim 1, characterized in that: A silicon dioxide layer is processed on the upper surface of the device layer, and the silicon dioxide layer is processed into a dumbbell-shaped pattern using a photolithography process. The dumbbell-shaped pattern is used as a mask and the buried layer is used as a stop layer. The silicon dioxide layer is etched on the device layer by PECVD or thermal oxidation.

8. The method for manufacturing a resonant beam pressure sensor according to claim 7, characterized in that: The steps of processing the silicon dioxide layer into a dumbbell-shaped pattern by using a photolithography process are as follows: first, spin-coating a photoresist on the surface, exposing and developing to produce a dumbbell-shaped pattern, and removing the exposed part of the silicon dioxide using the photoresist as a mask and the device layer as a stop layer; KOH solution or EDP solution etchant is used to etch the device layer to process the dumbbell-shaped pattern.

9. The method for manufacturing a resonant beam pressure sensor according to claim 1, characterized in that: The reactive ion etching in step (f) uses CF4, CHF3 or CF4+O2 gas as an etchant.

10. The method for manufacturing a resonant beam pressure sensor according to claim 1, characterized in that: The side length of the pressure-sensitive diaphragm is 2-4 mm, the thickness is 20-40 μm, the length of the resonant beam structure is 400-2000 μm, the width is 30-100 μm, and the thickness is 4-30 μm.

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