SiC wafer processing method, MEMS pressure sensor and preparation method thereof

Abstract

The invention provides a SiC wafer processing method, an MEMS pressure sensor and a preparation method thereof, and relates to the technical field of advanced manufacturing. The invention provides a SiC wafer processing method, which comprises the following steps of sequentially extending an n-type buffer layer, a p-type epitaxial layer and an n-type epitaxial layer on the surface of an original SiC wafer to form a SiC wafer with the n-type buffer layer, the p-type epitaxial layer and the n-type epitaxial layer laminated on the surface; and after a Si wafer and the n-type epitaxial layer are temporarily bonded, the other surface of the original SiC wafer is ground, thinned and polished, and the processed SiC wafer is obtained. According to the method, the original SiC wafer and the Si wafer are ground and thinned after being bonded, so that deep etching processing of the SiC wafer is avoided, and the production cost and difficulty of the SiC wafer are remarkably reduced; and the morphology uniformity of the surface of the SiC wafer is improved through polishing.

Description

Technical Field

[0001] The present invention relates to the field of advanced manufacturing technology, and in particular to a SiC wafer processing method, a MEMS pressure sensor and a preparation method thereof. Background Art

[0002] With the development of the Internet of Things and big data, the Internet of Everything is quietly changing people's lifestyles. Information acquisition is a key link in the Internet of Everything, and sensors play an important role as an effective means of collecting information.

[0003] As a mature means of detecting signals, MEMS pressure sensors are widely used in the automotive industry, aerospace, oil exploration, biomedicine, consumer electronics and other fields. According to different pressure measurement principles, MEMS pressure sensors include capacitive, resonant, fiber optic and piezoresistive types. Among them, piezoresistive MEMS pressure sensors work based on the piezoresistive effect of materials. The process preparation is simple and the cost is low, so they are also the most widely used. However, ordinary silicon-based piezoresistive pressure sensors are usually reverse doped on the silicon substrate to form a PN junction isolation area. Once the temperature of this pressure sensor exceeds 125°C, the leakage current of the PN junction will increase sharply, causing the sensor to fail. In special fields such as aerospace, engine cavity pressure is an important parameter, which is crucial to determining engine safety, but the engine temperature is high and traditional sensors cannot meet the detection requirements.

[0004] With the development of new materials, pressure sensors based on SiC (silicon carbide) have emerged. Since SiC has a higher bandgap than silicon, it is more suitable for working at high temperatures. However, silicon carbide is a very hard material, with a Mohs hardness of nearly 9.5, second only to diamond. For thicker SiC wafers, the commonly used processing method is dry etching, which has high production costs, great difficulty, and uneven etching morphology, all of which have brought difficulties to the commercial application of SiC-based pressure sensors. Summary of the invention

[0005] In view of this, an object of the present invention is to provide a SiC wafer processing method, a MEMS pressure sensor and a preparation method thereof. The surface morphology of the SiC wafer processed by the present invention is uniform.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a method for processing a SiC wafer, comprising the following steps:

[0008] An n-type buffer layer, a p-type epitaxial layer, and an n-type epitaxial layer are sequentially epitaxially grown on the surface of the original SiC wafer to form a SiC wafer having an n-type buffer layer, a p-type epitaxial layer, and an n-type epitaxial layer stacked on the surface;

[0009] After the Si wafer is temporarily bonded to the n-type epitaxial layer, the other side of the original SiC wafer is ground, thinned and polished to obtain a processed SiC wafer.

[0010] Preferably, the thickness of the n-type buffer layer is 1 μm; the thickness of the p-type epitaxial layer is 5 μm; the thickness of the n-type epitaxial layer is 2 μm;

[0011] The thickness of the original SiC wafer is 350 μm.

[0012] Preferably, the temporary bonding temperature is 300° C. and the duration is 60 min.

[0013] Preferably, the polished surface roughness of the processed SiC wafer is 1-10 nm.

[0014] Preferably, the thickness of the SiC wafer in the processed SiC wafer is 14-30% of the thickness of the original SiC wafer.

[0015] Preferably, the resistivity of the SiC wafer in the processed SiC wafer is 0.001-0.01Ω·cm, and the thickness is 50-100 μm.

[0016] The present invention also provides a method for preparing a MEMS pressure sensor, comprising the following steps:

[0017] Depositing a first insulating material on the polished surface of the SiC wafer prepared by the processing method described in the above technical solution to form a first insulating layer;

[0018] Permanently combining the Si substrate with the first insulating layer and removing the Si wafer, and re-exposing the n-type epitaxial layer;

[0019] Performing patterning on the surface of the n-type epitaxial layer using a photoresist and a mask, and then etching the n-type epitaxial layer according to the pattern obtained by the patterning to form a varistor strip and expose a portion of the p-type epitaxial layer;

[0020] Depositing a second insulating material on the surface of the etched n-type epitaxial layer and the exposed surface of the p-type epitaxial layer to form a second insulating layer, and then drilling the second insulating layer on the etched n-type epitaxial layer until the second insulating layer is penetrated, wherein the holes obtained by the drilling are channels connecting the metal electrode and the n-type epitaxial layer;

[0021] According to the design, a patterning process is performed on the surface of the second insulating layer using a negative photoresist and a mask plate, and then sputtering and peeling are performed on the surface obtained by the patterning process to form metal electrodes and metal leads;

[0022] According to the design, the surface of the Si substrate is patterned using photoresist and a mask plate, and then the Si substrate, the first insulating layer and the SiC wafer are etched in sequence according to the pattern obtained by the patterning to form a cavity to obtain the MEMS pressure sensor.

[0023] Preferably, the first insulating material comprises silicon dioxide;

[0024] The second insulating material includes silicon dioxide or silicon nitride.

[0025] Preferably, the permanent bonding method includes anodic bonding;

[0026] The temperature of the anodic bonding is 300-500° C., the voltage is 500-1500 V, and the pressure is 0.1-0.5 MPa.

[0027] The present invention also provides a MEMS pressure sensor prepared by the preparation method described in the above technical solution, comprising a SiC wafer;

[0028] An n-type buffer layer, a p-type epitaxial layer and an n-type epitaxial layer are sequentially stacked on the upper surface of the SiC wafer; the size of the n-type epitaxial layer is smaller than the size of the p-type epitaxial layer;

[0029] A second insulating layer located on the surface of the n-type epitaxial layer and the surface of the p-type epitaxial layer;

[0030] A metal lead and a metal electrode located on the surface of the second insulating layer, wherein the n-type epitaxial layer is connected to the metal electrode through the metal lead;

[0031] Also includes: a first insulating layer and a Si substrate;

[0032] The surface of the SiC wafer, the first insulating layer and the Si substrate form a cavity.

[0033] The present invention provides a method for processing a SiC wafer, comprising the following steps:

[0034] An n-type buffer layer, a p-type epitaxial layer, and an n-type epitaxial layer are sequentially epitaxially grown on the surface of the original SiC wafer to form a SiC wafer having an n-type buffer layer, a p-type epitaxial layer, and an n-type epitaxial layer stacked on the surface;

[0035] After the Si wafer is temporarily bonded to the n-type epitaxial layer, the other side of the original SiC wafer is ground, thinned and polished to obtain a processed SiC wafer.

[0036] The present invention bonds the original SiC wafer and the Si wafer and then grinds and thins them, thereby avoiding deep etching of the SiC wafer, significantly reducing the production cost and difficulty of the SiC wafer, and avoiding damage to the n-type epitaxial layer caused by fixation during the grinding and thinning process; and improving the morphology uniformity of the SiC wafer surface through polishing.

[0037] The present invention adopts SiC to manufacture high temperature resistant MEMS devices. Compared with silicon, its high bandgap width makes the PN junction leakage current based on SiC less affected by temperature; high electron mobility makes the high frequency characteristics of the MEMS device based on SiC better and the conduction loss lower; high thermal conductivity and melting point make the MEMS device based on SiC better in thermal conductivity and smaller in creep range, so the MEMS device based on SiC has better temperature characteristics than silicon-based MEMS devices.

[0038] Furthermore, in the present invention, after the silicon dioxide layer is deposited on the SiC wafer, the wafer is permanently bonded to the Si substrate by using a low-temperature anodic bonding method, thereby reducing the thermal stress generated by high-temperature permanent bonding. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 A side view of the MEMS pressure sensor prepared in Example 1;

[0040] Figure 2 A cross-sectional view of the MEMS pressure sensor prepared in Example 1;

[0041] Figures 3 to 15 Schematic diagram of the structural changes in each step when preparing the MEMS pressure sensor in Example 1. DETAILED DESCRIPTION

[0042] The present invention provides a method for processing a SiC wafer, comprising the following steps:

[0043] An n-type buffer layer, a p-type epitaxial layer, and an n-type epitaxial layer are sequentially epitaxially grown on the surface of the original SiC wafer to form a SiC wafer having an n-type buffer layer, a p-type epitaxial layer, and an n-type epitaxial layer stacked on the surface;

[0044] After the Si wafer is temporarily bonded to the n-type epitaxial layer, the other side of the original SiC wafer is ground, thinned and polished to obtain a processed SiC wafer.

[0045] The present invention sequentially epitaxies an n-type buffer layer, a p-type epitaxial layer and an n-type epitaxial layer on the surface of an original SiC wafer to form a SiC wafer with an n-type buffer layer, a p-type epitaxial layer and an n-type epitaxial layer stacked on the surface.

[0046] Before the epitaxy, the present invention preferably cleans and dries the original SiC wafer.

[0047] The present invention has no special limitation on the cleaning, and the metal particles and organic particles on the SiC wafer can be removed by means well known to those skilled in the art.

[0048] In the present invention, the thickness of the n-type buffer layer is preferably 1 μm; the thickness of the p-type epitaxial layer is preferably 5 μm; the thickness of the n-type epitaxial layer is preferably 2 μm;

[0049] The thickness of the original SiC wafer is preferably 350 μm.

[0050] After forming a SiC wafer with an n-type buffer layer, a p-type epitaxial layer and an n-type epitaxial layer stacked on the surface, the present invention temporarily bonds the Si wafer to the n-type epitaxial layer and then grinds, thins and polishes the other side of the original SiC wafer to obtain a processed SiC wafer.

[0051] Before the temporary bonding, the present invention preferably cleans the Si wafer.

[0052] The present invention has no special limitation on the cleaning, and the metal particles and organic particles on the Si wafer can be removed by means well known to those skilled in the art.

[0053] In the present invention, the temperature of the temporary bonding is preferably 300° C., and the time is preferably 60 minutes.

[0054] In the present invention, the thickness of the SiC wafer in the processed SiC wafer is preferably 14-30% of the thickness of the original SiC wafer. In a specific embodiment, the thickness of the SiC wafer in the processed SiC wafer may be 15%, 20%, 25% or 30% of the thickness of the original SiC wafer. The SiC wafer in the processed SiC wafer refers to the SiC wafer excluding the n-type buffer layer, the p-type epitaxial layer and the n-type epitaxial layer.

[0055] In the present invention, the resistivity of the processed SiC wafer is 0.001-0.01Ω·cm, and the thickness is 50-100μm.

[0056] The present invention also provides a method for preparing a MEMS pressure sensor, comprising the following steps:

[0057] Depositing a first insulating material on the polished surface of the SiC wafer prepared by the processing method described in the above technical solution to form a first insulating layer;

[0058] Permanently combining the Si substrate with the first insulating layer and removing the Si wafer, and re-exposing the n-type epitaxial layer;

[0059] Performing patterning on the surface of the n-type epitaxial layer using a photoresist and a mask, and then etching the n-type epitaxial layer according to the pattern obtained by the patterning to form a varistor strip and expose a portion of the p-type epitaxial layer;

[0060] Depositing a second insulating material on the surface of the etched n-type epitaxial layer and the exposed surface of the p-type epitaxial layer to form a second insulating layer, and then drilling a hole in the second insulating layer on the etched n-type epitaxial layer until the second insulating layer is penetrated;

[0061] According to the design, the surface of the second insulating layer is patterned using a photoresist and a mask, and then sputtering and stripping are performed on the surface obtained by the patterning to form metal electrodes and metal leads;

[0062] According to the design, the surface of the Si substrate is patterned using photoresist and a mask plate, and then the Si substrate, the insulating layer and the SiC wafer are etched in sequence according to the pattern obtained by the patterning to form a cavity to obtain the MEMS pressure sensor.

[0063] The present invention deposits a first insulating material on the polished surface of the SiC wafer prepared by the processing method described in the above technical solution to form a first insulating layer.

[0064] In the present invention, the first insulating material includes silicon dioxide.

[0065] In the present invention, the thickness of the first insulating layer is preferably 300 nm.

[0066] After forming the first insulating layer, the present invention permanently combines the Si substrate with the first insulating layer and removes the Si wafer, and the n-type epitaxial layer is exposed again.

[0067] In the present invention, the permanent bonding method preferably includes anodic bonding; the temperature of the anodic bonding is preferably 300-500°C, and the temperature of the anodic bonding may be 300°C, 350°C, 400°C, 450°C or 500°C; the voltage is preferably 500-1500V, and the voltage of the anodic bonding may be 500V, 800V, 1000V, 1200V or 1500V; the pressure is preferably 0.1-0.5MPa, and the pressure of the anodic bonding may be 0.1MPa, 0.2MPa, 0.3MPa, 0.4MPa or 0.5MPa.

[0068] In the present invention, the method of removing the Si wafer preferably includes pyrolysis, and the temperature of the pyrolysis is preferably 500°C.

[0069] After the n-type epitaxial layer is exposed again, the present invention uses photoresist and a mask plate to perform patterning on the surface of the n-type epitaxial layer, and then etches the n-type epitaxial layer according to the pattern obtained by the patterning to form a varistor strip and expose part of the p-type epitaxial layer.

[0070] After the etching, the present invention deposits a second insulating material on the surface of the etched n-type epitaxial layer and the exposed surface of the p-type epitaxial layer to form a second insulating layer, and then punches the second insulating layer on the etched n-type epitaxial layer until the second insulating layer is penetrated.

[0071] In the present invention, the second insulating material includes silicon dioxide.

[0072] In the present invention, the thickness of the second insulating layer is preferably 300 nm.

[0073] In the present invention, the drilling includes: etching after patterning using photoresist and a mask.

[0074] In the present invention, the diameter of the hole obtained by drilling is preferably 30 μm; the hole is used to connect the metal lead and the n-type epitaxial layer.

[0075] After the drilling, the present invention uses a photoresist and a mask plate to perform a patterning process on the surface of the second insulating layer according to the design, and then sputters and peels off the surface obtained by the patterning process to form metal electrodes and metal leads.

[0076] After forming the metal electrodes and metal leads, the present invention performs patterning on the surface of the Si substrate using photoresist and a mask plate according to the design, and then etches the Si substrate, the first insulating layer and the SiC wafer in sequence according to the pattern obtained by the patterning to form a cavity, thereby obtaining the MEMS pressure sensor.

[0077] In the present invention, the size of the cavity is preferably 1 mm*1 mm*0.35 mm.

[0078] The present invention also provides a MEMS pressure sensor prepared by the preparation method described in the above technical solution, comprising a SiC wafer;

[0079] An n-type buffer layer, a p-type epitaxial layer and an n-type epitaxial layer are sequentially stacked on the upper surface of the SiC wafer; the size of the n-type epitaxial layer is smaller than the size of the p-type epitaxial layer;

[0080] A second insulating layer located on the surface of the n-type epitaxial layer and the surface of the p-type epitaxial layer;

[0081] A metal lead and a metal electrode located on the surface of the second insulating layer, wherein the n-type epitaxial layer is connected to the metal electrode through the metal lead;

[0082] Also includes: a first insulating layer and a Si substrate;

[0083] The surface of the SiC wafer, the first insulating layer and the Si substrate form a cavity.

[0084] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. 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.

[0085] Figure 1 This is a side view of the MEMS pressure sensor prepared in Example 1. In which, 1-piezoresistor strip, 2-metal lead, 3-metal electrode, 4-silicon dioxide insulating layer, 5-p-type SiC epitaxial layer, 6-thinned SiC wafer, 7-silicon dioxide insulating layer, 8-Si substrate;

[0086] Figure 2 A cross-sectional view of the MEMS pressure sensor prepared in Example 1; wherein 9 is a cavity;

[0087] Figures 3 to 15 Schematic diagram of the structural changes in each step when preparing the MEMS pressure sensor in Example 1.

[0088] Among them, 10-n type SiC epitaxial layer, 11-Si wafer, 12-n type SiC buffer layer.

[0089] Example 1

[0090] like Figure 3 As shown, step 1: prepare a Si wafer with a thickness of 350 μm, and use a standard cleaning process to clean the Si wafer to remove metal particles and organic particles on the wafer.

[0091] like Figure 4 As shown, a SiC wafer with a thickness of 350 μm is prepared, and the SiC wafer is cleaned using a standard cleaning process to remove metal particles and organic particles on the SiC wafer.

[0092] like Figure 5 As shown, step three: adopting the epitaxial process to sequentially grow an n-type buffer layer with a thickness of 1 μm, a p-type epitaxial layer with a thickness of 5 μm and an n-type epitaxial layer with a thickness of 2 μm on the SiC wafer, all of which are homogeneous epitaxy.

[0093] like Figure 6 As shown, step four: bonding the Si wafer and the n-type epitaxial layer (temperature is 300° C., time is 60 min).

[0094] like Figure 7 As shown, step five: the SiC wafer is processed by a grinding process, and then the processed SiC is polished to reduce the roughness. The thickness of the SiC wafer is 50 μm, and the surface roughness Ra is 1 to 10 nm.

[0095] like Figure 8 As shown, step six: a silicon dioxide layer with a thickness of 300 nm is grown on the processed SiC using a thin film deposition process.

[0096] like Fig. 9 As shown, step seven: bond the SiC wafer with silicon oxide grown thereon to the Si substrate, the Si substrate and the silicon oxide layer of the SiC wafer are permanently bonded by anodic bonding (temperature of 400°C, voltage of 1000V, pressure of 0.3MPa), and remove the silicon on one side of the epitaxial layer (pyrolysis temperature of 500°C).

[0097] like Fig.10 As shown, step eight: using photoresist and mask, adopting conventional photolithography process to pattern the n-type epitaxial layer, and dry-etching the exposed n-type epitaxial layer to form a varistor strip.

[0098] like Fig.11 As shown, step nine: a 300nm thick silicon dioxide layer is grown on the processed silicon carbide by a thin film deposition process as an insulating layer, and the insulating layer on the varistor strip is photoetched by using a photoresist and a mask, and the exposed insulating layer is etched to form a through hole for electrical connection.

[0099] like Fig.12 As shown, step ten: photolithography patterning of metal electrodes and metal lead structures, using negative photoresist for photolithography, sputtering metal after photolithography, and finally stripping to form metal electrodes and leads.

[0100] like Fig.13 As shown, step eleven: the silicon substrate is subjected to back-side photolithography, and the back-side cavity is etched using a dry process until the silicon dioxide layer;

[0101] like Fig.14 As shown, step twelve: etching the oxide layer, etching the silicon dioxide layer using a dry process.

[0102] like Fig.15 As shown, step thirteen: silicon carbide etching, using a dry process to etch the back silicon carbide. The above steps avoid deep etching of silicon carbide, significantly reducing the production cost and difficulty of SiC devices.

[0103] The resistivity of SiC wafer is 0.001~0.01Ω·cm.

[0104] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for processing a SiC wafer, characterized in that: The following steps are involved: An n-type buffer layer, a p-type epitaxial layer, and an n-type epitaxial layer are sequentially epitaxially grown on the surface of the original SiC wafer to form a SiC wafer having an n-type buffer layer, a p-type epitaxial layer, and an n-type epitaxial layer stacked on the surface; After the Si wafer is temporarily bonded to the n-type epitaxial layer, the other side of the original SiC wafer is ground, thinned and polished to obtain a processed SiC wafer.

2. The processing method according to claim 1, characterized in that: The thickness of the n-type buffer layer is 1 μm; the thickness of the p-type epitaxial layer is 5 μm; the thickness of the n-type epitaxial layer is 2 μm; The thickness of the original SiC wafer is 350 μm.

3. The processing method according to claim 1, characterized in that: The temporary bonding temperature is 300° C. and the duration is 60 min.

4. The processing method according to claim 1, characterized in that: The polished surface roughness of the processed SiC wafer is 1-10 nm.

5. The processing method according to claim 1 or 2, characterized in that: The thickness of the processed SiC wafer is 14-30% of the thickness of the original SiC wafer.

6. The processing method according to any one of claims 1 to 4, characterized in that: The resistivity of the processed SiC wafer is 0.001-0.01Ω·cm, and the thickness is 50-100μm.

7. A method for preparing a MEMS pressure sensor, characterized in that: The following steps are involved: Depositing a first insulating material on the polished surface of the SiC wafer prepared by the processing method according to any one of claims 1 to 6 to form a first insulating layer; Permanently combining the Si substrate with the first insulating layer and removing the Si wafer, and re-exposing the n-type epitaxial layer; Performing patterning on the surface of the n-type epitaxial layer using a photoresist and a mask, and then etching the n-type epitaxial layer according to the pattern obtained by the patterning to form a varistor strip and expose a portion of the p-type epitaxial layer; Depositing a second insulating material on the surface of the etched n-type epitaxial layer and the exposed surface of the p-type epitaxial layer to form a second insulating layer, and then drilling the second insulating layer on the etched n-type epitaxial layer until the second insulating layer is penetrated, wherein the holes obtained by the drilling are channels connecting the metal electrode and the n-type epitaxial layer; According to the design, a patterning process is performed on the surface of the second insulating layer using a negative photoresist and a mask plate, and then sputtering and peeling are performed on the surface obtained by the patterning process to form metal electrodes and metal leads; According to the design, the surface of the Si substrate is patterned using photoresist and a mask plate, and then the Si substrate, the first insulating layer and the SiC wafer are etched in sequence according to the pattern obtained by the patterning to form a cavity to obtain the MEMS pressure sensor.

8. The preparation method according to claim 7, characterized in that: The first insulating material includes silicon dioxide; The second insulating material includes silicon dioxide or silicon nitride.

9. The preparation method according to claim 7 or 8, characterized in that: The permanent bonding method includes anodic bonding; The temperature of the anodic bonding is 300-500° C., the voltage is 500-1500 V, and the pressure is 0.1-0.5 MPa.

10. The MEMS pressure sensor prepared by the preparation method according to any one of claims 7 to 9, characterized in that: Including SiC wafers; An n-type buffer layer, a p-type epitaxial layer and an n-type epitaxial layer are sequentially stacked on the upper surface of the SiC wafer; the size of the n-type epitaxial layer is smaller than the size of the p-type epitaxial layer; A second insulating layer located on the surface of the n-type epitaxial layer and the surface of the p-type epitaxial layer; A metal lead and a metal electrode located on the surface of the second insulating layer, wherein the n-type epitaxial layer is connected to the metal electrode through the metal lead; Also includes: a first insulating layer and a Si substrate; The surface of the SiC wafer, the first insulating layer and the Si substrate form a cavity.

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