A silicon carbide thick epitaxial wafer for high voltage devices

Abstract

The present invention discloses a silicon carbide thick epitaxial wafer for high-voltage devices, which effectively solves the problems of crystal defects and poor ablation resistance of the epitaxial wafer. By coating a modified carbon film on a silicon carbide substrate, carbon atoms of the carbon film migrate during epitaxy and annealing to supplement carbon vacancies in the epitaxial layer, thereby achieving the purpose of repairing carbon vacancies and improving the carrier life of the silicon carbide epitaxial wafer. Secondly, aluminum particles are doped in the modified carbon film to improve its ablation resistance. Al has a high melting point and a large latent heat of phase change, high thermal conductivity, and good high-temperature oxidation resistance. The Al2O3 formed by oxidation has the advantages of high melting point, low thermal expansion coefficient, good mechanical properties and corrosion resistance, etc. It can act as a heat insulation layer and prevent oxygen from diffusing into the internal SiC layer, realizing self-healing of surface cracks, significantly improving the ablation resistance of the silicon carbide thick epitaxial wafer, and is also of great significance to the development of semiconductor devices.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductors and relates to a silicon carbide thick epitaxial wafer for high-voltage devices. Background Art

[0002] The third generation of semiconductor silicon carbide materials has the advantages of high thermal conductivity, high breakdown field strength, high saturated electron drift rate, etc., which can meet the new requirements of modern electronic technology for high temperature, high power, high voltage, high frequency and radiation resistance and other harsh conditions, and is also the strategic direction of my country's semiconductor technology in the future. With the continuous popularization and development of the third generation of semiconductor materials, they have played a key role in power electronics, aerospace, new energy, smart grid, electric vehicles and other industries.

[0003] When light shines on the surface of a semiconductor, it will be absorbed. Photon absorption simultaneously generates a majority carrier and a minority carrier, which are called non-equilibrium carriers. In many semiconductor materials, the number of photogenerated non-equilibrium carriers is far less than the majority carriers generated by doping that already exist in the material. Therefore, when illuminated, the number of majority carriers in the semiconductor remains basically unchanged, while the number of minority carriers increases significantly. The minority carrier lifetime is an important parameter of semiconductor materials and semiconductor devices, which directly reflects the quality of the material and whether the characteristics of the device meet the requirements.

[0004] How to improve the carrier lifetime of silicon carbide epitaxial wafers is a difficult problem faced by the industry. At the same time, high-temperature annealing will cause damage to the surface of the epitaxial wafer. How to improve the ablation resistance of silicon carbide epitaxial wafers is also a difficult problem that the industry urgently needs to solve. Summary of the invention

[0005] The purpose of the present invention is to provide a silicon carbide thick epitaxial wafer for high voltage devices, so as to solve the problems of short carrier lifetime and poor ablation resistance of the silicon carbide epitaxial wafer mentioned in the background art.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] A silicon carbide thick epitaxial wafer for high-voltage devices is prepared by the following steps: coating a modified carbon film on the carbon surface of a silicon carbide substrate, placing the wafer in a reaction chamber of an epitaxial furnace, introducing hydrogen, gradually heating the temperature to 1600-1650°C, introducing a silicon source, a carbon source and a doping source, growing a buffer layer on the silicon surface of the silicon carbide substrate, adjusting the flow values ​​of various sources, growing an epitaxial layer to a specified thickness, annealing, cooling the wafer to room temperature, performing a blue film protection on the silicon surface of the wafer, and polishing off the carbon film to obtain the silicon carbide thick epitaxial wafer for high-voltage devices.

[0008] Furthermore, the modified carbon film has a thickness of 50 μm-500 μm.

[0009] Furthermore, the flow rate of the hydrogen is 80-120 L / min, and the pressure of the hydrogen introduced into the reaction chamber is 80-200 mbar.

[0010] Furthermore, the silicon source is selected from any one of silane, dichlorosilane and trichlorosilane.

[0011] Furthermore, the carbon source is selected from any one of methane, ethylene and propane.

[0012] Furthermore, the doping source is selected from any one of N2 and trimethylaluminum.

[0013] Furthermore, the annealing process is specifically as follows: 1500-1700° C., keeping warm for 20-30 minutes.

[0014] The modified carbon film is prepared by the following steps:

[0015] Step S1, placing the graphene nanosheets into a beaker containing anhydrous ethanol, and performing ultrasonic dispersion at a power of 400-420 W for 1-2 hours to obtain a mixed solution a;

[0016] Step S2, pouring aluminum powder into a beaker containing anhydrous ethanol, stirring at a speed of 180-230 rpm for 50-70 min to obtain a mixed solution b;

[0017] Step S3, mixing the mixed solution a and the mixed solution b, stirring at 58-60° C. and 1400-1500 rpm for 50-60 min, and then vacuum drying for 20-23 h, placing the dried powder in a ball mill in an argon atmosphere, ball milling at 600-700 rpm for 4-5 h, and finally vacuum hot pressing and sintering to obtain prefabricated particles;

[0018] Step S4, dissolving ascorbic acid in distilled water, stirring at 220-250 rpm, then transferring to a reaction kettle, adding prefabricated particles therein, reacting at 200-210° C. for 6-7 hours, centrifuging, washing the precipitate with anhydrous ethanol for 2-3 times, and drying to obtain a semi-finished product;

[0019] Step S5, dissolving the semi-finished product in distilled water to obtain a modified carbon film.

[0020] Furthermore, in step S1, the usage ratio of the graphene nanosheets and anhydrous ethanol is 2.5-3.3 mg: 300-400 mL.

[0021] Furthermore, the usage ratio of the aluminum powder and anhydrous ethanol in step S2 is 13.2-14.1 g: 250-350 mL.

[0022] Furthermore, the vacuum hot pressing sintering conditions in step S3 are a temperature of 440-470° C. and a pressure of 60-70 MPa.

[0023] Furthermore, in step S4, the dosage ratio of ascorbic acid, distilled water, and prefabricated particles is 20-25 mg: 20-25 mL: 1.3-1.5 mg.

[0024] Furthermore, in step S5, the usage ratio of the semi-finished product to distilled water is 10.3-14.1 mg: 50-70 mL.

[0025] Beneficial effects of the invention: The purpose of the invention is to provide a silicon carbide thick epitaxial wafer for high voltage devices, which effectively solves the problems of crystal defects and poor ablation resistance of the epitaxial wafer. By coating a modified carbon film on a silicon carbide substrate, carbon atoms of the carbon film migrate during epitaxy and annealing to supplement carbon vacancies in the epitaxial layer, thereby achieving the purpose of carbon vacancy repair and improving the carrier lifetime of the silicon carbide epitaxial wafer.

[0026] The modified carbon film contains carbon forms such as amorphous carbon film, carbon spheres and graphene, sp 2 、sp 3 The hybridization of carbon bonds greatly improves the stability of the membrane, making it have lower internal stress and better bonding strength, while retaining excellent properties such as high hardness, low friction coefficient, and low wear rate, thereby optimizing the mechanical and thermal stability of the membrane.

[0027] In addition, carbon spheres have a large specific surface area, a high porous structure, and biocompatibility, and can efficiently adsorb a large number of metal and non-metal particles. In order to avoid ablation of the epitaxial wafer surface due to excessively high temperatures during high-temperature annealing, aluminum particles are doped to improve its ablation resistance. Al has a high melting point and a large latent heat of phase change, high thermal conductivity, and good resistance to high-temperature oxidation. It is a good high-temperature phase change material. The Al2O3 formed by oxidation has the advantages of high melting point, low thermal expansion coefficient, good mechanical properties, thermal shock stability, and corrosion resistance. It can act as a heat insulation layer and prevent oxygen from diffusing into the internal SiC layer, achieving self-healing of surface cracks, significantly improving the ablation resistance of silicon carbide thick epitaxial wafers, and is also of great significance to the development of semiconductor devices. DETAILED DESCRIPTION

[0028] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. 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.

[0029] Example 1

[0030] The modified carbon film is prepared by the following steps:

[0031] Step S1, placing 2.5 mg of graphene nanosheets into a beaker containing 300 mL of anhydrous ethanol, and performing ultrasonic dispersion at a power of 400 W for 1 h to obtain a mixed solution a;

[0032] Step S2, pouring 13.2 g of aluminum powder into a beaker containing 250 mL of anhydrous ethanol, stirring at 180 rpm for 50 min to obtain a mixed solution b;

[0033] Step S3, mixing the mixed solution a and the mixed solution b, stirring at 58° C. and 1400 rpm for 50 min, and then vacuum drying for 20 h, placing the dried powder in a ball mill in an argon atmosphere, ball milling at 600 rpm for 4 h, and finally vacuum hot pressing to obtain prefabricated particles, wherein the sintering conditions are a temperature of 440° C. and a pressure of 60 MPa;

[0034] Step S4, dissolving 20 mg of ascorbic acid in 20 mL of distilled water, stirring evenly at 220 rpm, then transferring to a reaction kettle, adding 1.3 mg of prefabricated particles thereto, reacting at 200° C. for 6 h, centrifuging, washing the precipitate twice with anhydrous ethanol, and drying to obtain a semi-finished product;

[0035] Step S5, dissolving 10.3 mg of the semi-finished product in 50 mL of distilled water to obtain a modified carbon membrane.

[0036] Example 2

[0037] The modified carbon film is prepared by the following steps:

[0038] Step S1, placing 2.9 mg of graphene nanosheets into a beaker containing 350 mL of anhydrous ethanol, and performing ultrasonic dispersion at a power of 410 W for 1.5 h to obtain a mixed solution a;

[0039] Step S2, pouring 13.8 g of aluminum powder into a beaker containing 300 mL of anhydrous ethanol, stirring at 200 rpm for 60 min to obtain a mixed solution b;

[0040] Step S3, mixing the mixed solution a and the mixed solution b, stirring at 59° C. and 1450 rpm for 55 min, and then vacuum drying for 21 h, placing the dried powder in a ball mill in an argon atmosphere, ball milling at 650 rpm for 4.5 h, and finally vacuum hot pressing to obtain prefabricated particles, wherein the sintering conditions are a temperature of 460° C. and a pressure of 65 MPa;

[0041] Step S4, dissolving 23 mg of ascorbic acid in 23 mL of distilled water, stirring evenly at 240 rpm, then transferring to a reaction kettle, adding 1.4 mg of prefabricated particles thereto, reacting at 205° C. for 6.5 h, centrifuging, washing the precipitate twice with anhydrous ethanol, and drying to obtain a semi-finished product;

[0042] Step S5, dissolving 12.7 mg of the semi-finished product in 55 mL of distilled water to obtain a modified carbon membrane.

[0043] Example 3

[0044] The modified carbon film is prepared by the following steps:

[0045] Step S1, placing 3.3 mg of graphene nanosheets into a beaker containing 400 mL of anhydrous ethanol, and performing ultrasonic dispersion at a power of 420 W for 2 h to obtain a mixed solution a;

[0046] Step S2, pouring 14.1 g of aluminum powder into a beaker containing 350 mL of anhydrous ethanol, stirring at 230 rpm for 70 min to obtain a mixed solution b;

[0047] Step S3, mixing the mixed solution a and the mixed solution b, stirring at 60° C. and 1500 rpm for 60 min, and then vacuum drying for 23 h, placing the dried powder in a ball mill in an argon atmosphere, ball milling at 700 rpm for 5 h, and finally vacuum hot pressing to obtain prefabricated particles, wherein the sintering conditions are a temperature of 470° C. and a pressure of 70 MPa;

[0048] Step S4, dissolving 25 mg of ascorbic acid in 25 mL of distilled water, stirring at 250 rpm, then transferring to a reaction kettle, adding 1.5 mg of prefabricated particles, reacting at 210° C. for 7 h, centrifuging, washing the precipitate with anhydrous ethanol for 3 times, and drying to obtain a semi-finished product;

[0049] Step S5, dissolving 14.1 mg of the semi-finished product in 70 mL of distilled water to obtain a modified carbon membrane.

[0050] Example 4

[0051] The silicon carbide thick epitaxial wafer for high-voltage devices is prepared by the following steps: coating the carbon surface of the silicon carbide substrate with the modified carbon film prepared in Example 1 with a thickness of 50 μm, placing it in the reaction chamber of an epitaxial furnace, introducing hydrogen, wherein the flow rate of the hydrogen is 80 L / min, and the pressure of the hydrogen introduced into the reaction chamber is 80 mbar, gradually heating up to 1600° C., introducing silane, methane and N2, growing a buffer layer on the silicon surface of the silicon carbide substrate, adjusting the flow values ​​of various sources, growing an epitaxial layer to a specified thickness, annealing at 1500° C., keeping the temperature for 20 minutes, cooling to room temperature, protecting the silicon surface of the wafer with a blue film, and polishing off the carbon film to obtain the silicon carbide thick epitaxial wafer for high-voltage devices.

[0052] Example 5

[0053] The silicon carbide thick epitaxial wafer for high-voltage devices is prepared by the following steps: coating the carbon surface of the silicon carbide substrate with the modified carbon film prepared in Example 2 with a thickness of 300 μm, placing it in the reaction chamber of an epitaxial furnace, introducing hydrogen, wherein the flow rate of the hydrogen is 100 L / min, and the pressure of the hydrogen introduced into the reaction chamber is 150 mbar, gradually heating to 1630° C., introducing silicon dichlorohydride, ethylene and N2, growing a buffer layer on the silicon surface of the silicon carbide substrate, adjusting the flow values ​​of various sources, growing an epitaxial layer to a specified thickness, annealing at 1600° C., keeping the temperature for 25 minutes, cooling to room temperature, protecting the silicon surface of the wafer with a blue film, and polishing off the carbon film to obtain the silicon carbide thick epitaxial wafer for high-voltage devices.

[0054] Example 6

[0055] The silicon carbide thick epitaxial wafer for high-voltage devices is prepared by the following steps: coating the carbon surface of the silicon carbide substrate with the modified carbon film prepared in Example 3 with a thickness of 500 μm, placing the substrate in a reaction chamber of an epitaxial furnace, introducing hydrogen, wherein the flow rate of the hydrogen is 120 L / min, and the pressure of the hydrogen introduced into the reaction chamber is 200 mbar, gradually heating the substrate to 1650° C., introducing trichlorosilane, propane and trimethylaluminum, growing a buffer layer on the silicon surface of the silicon carbide substrate, adjusting the flow values ​​of various sources, growing an epitaxial layer to a specified thickness, annealing at 1600° C., keeping the temperature for 25 minutes, cooling the substrate to room temperature, protecting the silicon surface of the wafer with a blue film, and removing the carbon film to obtain the silicon carbide thick epitaxial wafer for high-voltage devices.

[0056] Comparative Example 1

[0057] Silicon carbide thick epitaxial wafers produced by Nanjing Xianfeng Nanomaterials Technology Co., Ltd.

[0058] Comparative Example 2

[0059] The preparation method of the silicon carbide thick epitaxial wafer of Comparative Example 2 refers to that of Example 4, except that the modified carbon film is not coated.

[0060] Comparative Example 3

[0061] The method for preparing the silicon carbide thick epitaxial wafer of Comparative Example 3 refers to that of Example 4, except that in the method for preparing the modified carbon film, no prefabricated particles are added in step S4.

[0062] The silicon carbide thick epitaxial wafers obtained in Examples 4-6 and Comparative Examples 1-3 were subjected to the following performance tests: (1) defect testing was performed using a Candela 8520 defect tester; (2) ablation resistance performance test was performed with reference to the national military standard GJB 323A-96 "Ablation Test Method for Ablation Materials". The test results are shown in Table 1:

[0063] Table 1

[0064]

[0065] It can be seen from Table 1 that, compared with Comparative Examples 1-3, the silicon carbide thick epitaxial wafers prepared in Examples 4-6 have fewer total defects, lower average mass ablation rates, and better carrier lifetime and ablation resistance.

[0066] In the description of the specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0067] The above contents are merely examples and explanations of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the invention or exceed the scope defined by the claims, they shall all fall within the protection scope of the present invention.

Claims

1. A silicon carbide thick epitaxial wafer for high voltage devices, characterized in that: The silicon carbide thick epitaxial wafer for high-voltage devices is prepared by the following steps: coating a modified carbon film on the carbon surface of a silicon carbide substrate, placing the substrate in a reaction chamber of an epitaxial furnace, introducing hydrogen, heating the substrate, introducing a silicon source, a carbon source and a doping source, growing an epitaxial layer on the silicon surface of the silicon carbide substrate to a specified thickness, annealing, cooling the temperature to room temperature, protecting the silicon surface of the wafer with a blue film, and removing the carbon film to obtain a silicon carbide thick epitaxial wafer for high-voltage devices; The modified carbon film is prepared by the following steps: Step S1, adding graphene nanosheets into anhydrous ethanol and dispersing by ultrasonic to obtain a mixed solution a; Step S2, adding aluminum powder into anhydrous ethanol and stirring evenly to obtain a mixed solution b; Step S3, mixing the mixed solution a and the mixed solution b and drying them, ball milling the dried powder, and finally vacuum hot pressing and sintering to obtain prefabricated particles; Step S4, dissolving ascorbic acid in distilled water, stirring evenly, then transferring to a reaction kettle, adding prefabricated particles therein, reacting at 200-210° C. for 6-7 hours, centrifuging, washing, and drying to obtain a semi-finished product; Step S5, dissolving the semi-finished product in distilled water to obtain a modified carbon film.

2. The silicon carbide thick epitaxial wafer for high voltage devices according to claim 1, characterized in that: The modified carbon film has a thickness of 50 μm-500 μm.

3. The silicon carbide thick epitaxial wafer for high voltage devices according to claim 1, characterized in that: The flow rate of the hydrogen is 80-120 L / min, and the pressure of the hydrogen introduced into the reaction chamber is 80-200 mbar.

4. The silicon carbide thick epitaxial wafer for high voltage devices according to claim 1, characterized in that: The silicon source is selected from any one of silane, dichlorosilane and trichlorosilane, the carbon source is selected from any one of methane, ethylene and propane, and the doping source is selected from any one of N2 and trimethylaluminum.

5. The silicon carbide thick epitaxial wafer for high voltage devices according to claim 1, characterized in that: The annealing process is: 1500-1700° C., heat preservation for 20-30 minutes.

6. The silicon carbide thick epitaxial wafer for high voltage devices according to claim 1, characterized in that: The amount ratio of the graphene nanosheets and anhydrous ethanol in step S1 is 2.5-3.3 mg: 300-400 mL; the amount ratio of the aluminum powder and anhydrous ethanol in step S2 is 13.2-14.1 g: 250-350 mL; the vacuum hot pressing sintering conditions in step S3 are a temperature of 440-470° C. and a pressure of 60-70 MPa.

7. The silicon carbide thick epitaxial wafer for high voltage devices according to claim 1, characterized in that: The dosage ratio of ascorbic acid, distilled water and prefabricated particles in step S4 is 20-25 mg: 20-25 mL: 1.3-1.5 mg; the dosage ratio of the semi-finished product and distilled water in step S5 is 10.3-14.1 mg: 50-70 mL.

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