Method for growing silicon carbide epitaxial wafer

Abstract

The invention provides a silicon carbide epitaxial wafer growth method. The growth method comprises the following steps: placing a silicon carbide substrate in a reaction chamber, introducing carrier gas, and carrying out multiple times of alternate etching and annealing treatment; introducing a first reaction source gas and a first doping source gas for reaction; introducing a second reaction source gas and a second doping source gas for reaction; and stopping introducing the second reaction source gas and the second doping source gas, continuously introducing the carrier gas, cooling, pressurizing and taking out. In the technical scheme of the invention, the crystal quality of the silicon carbide substrate can be improved and defects can be reduced through multiple times of alternate etching and annealing treatment, so that the surface consistency of the silicon carbide substrate is improved, the consistency of the silicon carbide epitaxial wafer prepared when the buffer layer and the epitaxial layer are grown subsequently is relatively good, and the product yield and the process stability can be improved.

Description

Technical Field

[0001] The invention relates to the field of semiconductor technology, and in particular to a growth process of a silicon carbide epitaxial wafer. Background Art

[0002] Silicon carbide material is one of the representative third-generation semiconductors. It is grown by PVT method, and then cut and polished into substrate wafers. Then, single-layer or multi-layer epitaxial functional layers are grown by step flow epitaxy to form silicon carbide epitaxial wafers. Then, the structure design and process manufacturing of the device are carried out. The surface defects of silicon carbide epitaxial wafers are an important indicator of its quality as a semiconductor product, which will affect the electrical performance parameters and service life of the device.

[0003] At present, the CVD chemical vapor deposition method is used for silicon carbide epitaxy, that is, carbon source, silicon source and doping source gas are introduced into the high-temperature reaction furnace chamber, and then a single crystal epitaxial layer is continuously grown on the substrate. There are many defects in the homogeneous CVD epitaxial layer, such as triangle defects, carrot defects, stacking faults, dislocations, point defects, etc., among which most of the stacking faults and dislocation defects are inherited from the substrate. At present, the interface state can be improved by pre-treating the substrate surface, and the buffer layer growth process set between the substrate and the epitaxial layer can regulate the defect conversion ratio from the substrate to the epitaxial layer, thereby reducing the probability of harmful defects in the epitaxial layer. However, due to the difference in temperature field and flow field between the center and edge areas of the epitaxial wafer, the window of the above process is narrow, and it is easy to have surface morphology differences between the center and edge areas, and even show obvious crystal quality differences, which reduces the consistency of the wafer and affects the product yield and process stability.

[0004] From the above, we can see that the current silicon carbide epitaxial wafers still have various defects, which will affect the characteristics of silicon carbide devices, so the epitaxial growth process of silicon carbide needs to be continuously optimized. Summary of the invention

[0005] The object of the present invention is to provide a method for growing a silicon carbide epitaxial wafer, which can solve the problem of wafer consistency, thereby improving product yield and process stability.

[0006] To achieve the above-mentioned object, the present invention provides a method for growing a silicon carbide epitaxial wafer. The growth method comprises:

[0007] (1) Surface treatment

[0008] Placing the silicon carbide substrate in a reaction chamber and introducing a carrier gas to perform multiple alternating etching and annealing processes, wherein the etching and annealing processes use different carrier gases;

[0009] (2) Buffer layer growth

[0010] continuously introducing the carrier gas, and introducing the first reaction source gas and the first doping source gas to react;

[0011] (3) Growth of the outer layer

[0012] Continuously introducing the carrier gas, and introducing the second reaction source gas and the second doping source gas to react;

[0013] (4) Cooling

[0014] Stop introducing the second reaction source gas and the second doping source gas, continue introducing the carrier gas, and remove it after cooling and pressurizing it.

[0015] In the technical solution of the present invention, multiple alternating etching and annealing processes are performed before the growth of the buffer layer, and different carrier gases are used for etching and annealing. Multiple alternating etching and annealing processes can improve the crystal quality of the silicon carbide substrate, reduce defects, and thus improve the surface consistency of the silicon carbide substrate. Therefore, the consistency of the silicon carbide epitaxial wafer obtained when the buffer layer and the epitaxial layer are subsequently grown is better, which can improve the product yield and process stability.

[0016] As a technical solution of the present invention, the carrier gas includes hydrogen or argon.

[0017] As a technical solution of the present invention, the carrier gas used in the etching also includes an auxiliary etching gas, the auxiliary etching gas includes chlorine or hydrogen chloride, and the volume ratio of the auxiliary etching gas to the total amount of the carrier gas is 1:500-5000.

[0018] As a technical solution of the present invention, during the etching, the carrier gas flow ratio between the center and edge areas of the silicon carbide substrate is 0.1-2.0, the temperature of the reaction chamber is 1620-1650°C, the pressure is 80-120 mbar, the time is 10-15 min, and the flow rate of the carrier gas is 80-150 slm.

[0019] As a technical solution of the present invention, during the annealing treatment, the temperature of the reaction chamber is 1600-1620° C., the pressure is 80-120 mbar, the time is 6-12 min, and the flow rate of the carrier gas is 80-150 slm.

[0020] As a technical solution of the present invention, the first reaction source gas and the second reaction source gas are mixed gases of ethylene and trichlorosilane in different proportions.

[0021] As a technical solution of the present invention, the first doping source gas and the second doping source gas are each independently hydrogen-saturated vapor of trimethylaluminum or nitrogen.

[0022] As a technical solution of the present invention, when the buffer layer grows, the temperature of the reaction chamber is 1580-1650°C, the pressure is 80-120mbar, the carrier gas flow rate is 80-150slm, the carrier gas flow ratio between the center and edge areas of the silicon carbide substrate is 0.6-3.0, the C / Si molar ratio in the first reaction source gas is 0.6-1.0, and the buffer layer growth time is 3-10min.

[0023] As a technical solution of the present invention, when the outer edge layer grows, the temperature of the reaction chamber is 1580-1650°C, the pressure is 80-120mbar, the carrier gas flow rate is 80-150slm, the carrier gas flow ratio between the center and edge areas of the silicon carbide substrate is 0.6-3.0, the C / Si molar ratio in the second reaction source gas is 0.8-1.2, and the growth time of the outer edge layer is 5-30min.

[0024] As a technical solution of the present invention, during the cooling, the reaction chamber is cooled to 800-1000°C, the pressure is increased to 1000-1100 mbar, and the carrier gas flow rate is reduced to below 30 slm, taken out from the reaction chamber and then cooled to room temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a process diagram of the silicon carbide epitaxial wafer growth method in Example 1.

[0026] Figure 2 FIG. 4 is a diagram showing the appearance defects of the silicon carbide substrate after step (4) in Example 1.

[0027] Figure 3 This is a defect image of the silicon carbide substrate in comparative example 1 after step (4).

[0028] Figure 4 Figure 2 is the appearance defect image of the silicon carbide substrate after step (4) in comparative example 2 DETAILED DESCRIPTION

[0029] The silicon carbide epitaxial wafer prepared by the silicon carbide epitaxial wafer growth method of the present invention comprises a silicon carbide substrate and a buffer layer and an epitaxial layer that sequentially cover the silicon carbide substrate. The thickness of the buffer layer is 0.5 to 1.5 μm. As an example, the thickness of the buffer layer can be, but not limited to, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, and 1.5 μm. The thickness of the epitaxial layer is 5 to 1000 μm. As an example, the thickness of the epitaxial layer can be, but not limited to, 5 μm, 10 μm, 30 μm, 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 700 μm, 800 μm, 900 μm, and 1000 μm.

[0030] The method for growing a silicon carbide epitaxial wafer of the present invention comprises the steps of (1) surface treatment, (2) buffer layer growth, (3) outer edge layer growth and (4) cooling.

[0031] Wherein, the surface treatment in step (1) comprises placing the silicon carbide substrate in a reaction chamber and introducing a carrier gas to perform multiple alternating etching and annealing treatments. Multiple alternating etching and annealing treatments refer to the first etching, the first annealing, the second etching, the second annealing, the third etching, the third annealing, and so on. Preferably, it is the first etching, the first annealing, the second etching, and the second annealing. The carrier gas used for each etching and annealing is different. The carrier gas includes hydrogen or argon, preferably hydrogen is used for etching, and preferably argon is used for annealing. Furthermore, the carrier gas used during etching also includes auxiliary etching gas, and the auxiliary etching gas includes chlorine or hydrogen chloride. The volume ratio of the auxiliary etching gas to the total amount of the carrier gas is 1:500 to 5000. As an example, the volume ratio of the auxiliary etching gas to the total amount of the carrier gas can be but is not limited to 1:500, 1:1000, 1:1500, 1:2000, 1:2500, 1:3000, 1:3500, 1:4000, 1:4500, and 1:5000.

[0032] During etching, the carrier gas flow ratio between the center and edge regions of the silicon carbide substrate is 0.1-2.0. Since the carrier gas flows in the center and edge regions of the silicon carbide substrate are different, the carrier gas in the center region is less than that in the edge region. By setting the carrier gas flow ratio to 0.1-2.0 and combining the fact that there are more defects in the center region itself, the defects in the center region and the edge region can reach a basic balance after etching, thereby further ensuring the consistency of the morphology of the surface of the silicon carbide substrate before forming a buffer layer.

[0033] During etching, the temperature of the reaction chamber is 1620-1650°C, which can be but not limited to 1620°C, 1630°C, 1640°C, and 1650°C. The pressure is 80-120mbar, which can be but not limited to 80mbar, 85mbar, 90mbar, 95mbar, 100mbar, 1050mbar, 110mbar, 115mbar, and 120mbar. The carrier gas flow rate is 80-150slm, which can be but not limited to 80slm, 90slm, 100slm, 115slm, 120slm, 130slm, 140slm, and 150slm. The etching time is 10-15min, which can be but not limited to 10min, 11min, 12min, 13min, 14min, and 15min.

[0034] The reaction chamber is heated before etching, and during the heating process, 0.3-0.8slm of argon gas is introduced as a rotating gas to rotate the silicon carbide substrate, thereby ensuring subsequent uniform and stable growth of the buffer layer and the epitaxial layer.

[0035] During the annealing treatment, the temperature of the reaction chamber is 1600-1620°C, which can be but not limited to 1600°C, 1610°C, and 1620°C. The pressure is 80-120mbar, which can be but not limited to 80mbar, 85mbar, 90mbar, 95mbar, 100mbar, 1050mbar, 110mbar, 115mbar, and 120mbar. The carrier gas flow rate is 80-150slm, which can be but not limited to 80slm, 90slm, 100slm, 115slm, 120slm, 130slm, 140slm, and 150slm. The etching time is 6-12min, which can be but not limited to 6min, 7min, 8min, 9min, and 10min.

[0036] Step (2) of buffer layer growth includes continuously introducing a carrier gas, and introducing a first reaction source gas and a first doping source gas to react. The carrier gas is the same as the carrier gas for the annealing treatment, which can be hydrogen or argon, preferably argon. The first reaction source gas is a mixed gas of ethylene and trichlorosilane. The first doping source gas is hydrogen saturated steam of trimethylaluminum or nitrogen.

[0037] When the buffer layer is grown, the temperature of the reaction chamber is 1580-1650° C., which may be, but not limited to, 1580° C., 1590° C., 1600° C., 1610° C., 1620° C., 1630° C., 1640° C., and 1650° C. The pressure is 80-120 mbar, which may be, but not limited to, 80 mbar, 85 mbar, 90 mbar, 95 mbar, 100 mbar, 1050 mbar, 110 mbar, 115 mbar, and 120 mbar. The carrier gas flow rate is 80-150 slm, which may be, but not limited to, 80 slm, 90 slm, 100 slm, 115 slm, 120 slm, 130 slm, 140 slm, and 150 slm. The flow ratio of the middle bypass carrier gas is 0.6 to 3.0. As an example, the flow ratio of the middle bypass carrier gas can be, but not limited to, 0.6, 0.8, 1.0, 1.5, 2.0, 2.5, and 3.0. The C / Si molar ratio in the first reaction source gas is 0.6 to 1.0, and can be, but not limited to, 0.6, 0.7, 0.8, 0.9, and 1.0. The growth time of the buffer layer is 3 to 10 minutes, and can be, but not limited to, 3 minutes, 4 minutes, 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, and 10 minutes.

[0038] Step (3) the growth of the outer edge layer includes continuously introducing a carrier gas, and introducing a second reaction source gas and a second doping source gas for reaction. The carrier gas is the same as the carrier gas for the annealing treatment, which can be hydrogen or argon, preferably argon. The second reaction source gas is a mixed gas of ethylene and trichlorosilane. The second doping source gas is a hydrogen saturated vapor or nitrogen of trimethylaluminum. The hydrogen saturated vapor of trimethylaluminum can be obtained by passing trimethylaluminum liquid into a bubbler and bringing out the saturated vapor. The temperature of the reaction chamber during the growth of the outer edge layer is 1580-1650°C, which can be but is not limited to 1580°C, 1590°C, 1600°C, 1610°C, 1620°C, 1630°C, 1640°C, 1650°C. The pressure is 80-120 mbar, which can be but not limited to 80 mbar, 85 mbar, 90 mbar, 95 mbar, 100 mbar, 1050 mbar, 110 mbar, 115 mbar, 120 mbar. The carrier gas flow rate is 80-150 slm, which can be but not limited to 80 slm, 90 slm, 100 slm, 115 slm, 120 slm, 130 slm, 140 slm, 150 slm. The bypass carrier gas flow rate ratio is 0.6-3.0. As an example, the bypass carrier gas flow rate ratio can be but not limited to 0.6, 0.8, 1.0, 1.5, 2.0, 2.5, 3.0. The C / Si molar ratio in the second reaction source gas is 0.8-1.2, which can be but not limited to 0.8, 0.9, 1.0, 1.1, 1.2. The growth time of the outer layer is 5 to 30 minutes, which may be but is not limited to 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, and 30 minutes.

[0039] The temperature, pressure, carrier gas flow rate, middle bypass carrier gas flow rate ratio, and growth time of the buffer layer growth and the outer layer growth can be the same or different. In addition, the C / Si molar ratio in the second reaction source gas is higher than the C / Si in the first reaction source gas. This is based on the different doping levels required for the buffer layer and the epitaxial layer (generally, the buffer layer doping is two or three orders of magnitude higher than the epitaxial layer), and the corresponding growth rates are different (high doping requires low speed to obtain), and the optimal carbon-silicon ratio for high-speed growth is higher than that for low-speed growth, thereby obtaining a good surface defect state.

[0040] Step (4) cooling includes stopping the introduction of the second reaction source gas and the second doping source gas, continuing to introduce the carrier gas and taking it out after cooling and pressurizing. During cooling, the reaction chamber is cooled to 800-1000°C, which may be but not limited to 800°C, 820°C, 840°C, 860°C, 880°C, 900°C, 920°C, 940°C, 960°C, 980°C, 1000°C. The pressure is increased to 1000-1100mbar, which may be but not limited to 1000mbar, 1020mbar, 1040mbar, 1060mbar, 1080mbar, 1100mbar. When the carrier gas flow rate drops below 30slm, take it out of the reaction chamber and cool it to room temperature.

[0041] In order to better illustrate the purpose, technical scheme and beneficial effects of the present invention, the present invention will be further described below in conjunction with specific embodiments. It should be noted that the following implementation method is a further explanation of the present invention and should not be used as a limitation of the present invention.

[0042] Example 1

[0043] This embodiment is a method for growing a silicon carbide epitaxial wafer, which includes the following steps.

[0044] (1) Surface treatment

[0045] A 6-inch silicon carbide substrate with a 4° bevel angle along the <11-20> direction is placed in the loading chamber and the chamber door is closed, and then transferred to a 900°C reaction chamber. The reaction chamber is slowly heated from 900°C to 1630°C, and 0.5slm of argon is introduced as a rotating gas during the heating process to rotate the silicon carbide substrate. The pressure in the reaction chamber is reduced to 100mbar, the carrier gas flow rate is 120slm, and the silicon carbide substrate is etched for 6min. A mixed gas of hydrogen and hydrogen chloride (hydrogen chloride accounts for 0.3vol.‰ of hydrogen) is introduced as a carrier gas, and the carrier gas flow ratio of the center and edge areas of the silicon carbide substrate is 0.25, and the center and edge areas are 24slm and 96slm, respectively. The temperature of the reaction chamber was lowered to 1600°C, the carrier gas was switched to argon and the flow rate was increased to 100 slm, the pressure remained unchanged, and the annealing treatment was performed for 5 minutes. During the annealing treatment, the carrier gas flow ratio between the center and edge regions of the silicon carbide substrate was 1.5, and the center and edge regions were 60 slm and 40 slm, respectively. Then, the etching and annealing treatment was performed again as described above.

[0046] (2) Buffer layer growth

[0047] The carrier gas argon was continuously introduced, and ethylene, trichlorosilane and nitrogen were introduced for reaction, and the C / Si molar ratio of ethylene and trichlorosilane was 0.8. The pressure, carrier gas flow rate and temperature in the reaction chamber remained unchanged, and the hydrogen carrier gas flow ratio in the center and edge areas of the silicon carbide substrate was 1.5, the center and edge areas were 72 slm and 48 slm respectively, the nitrogen flow rate was 150 sccm and the doping concentration was 1.20E18 / cm 3 The buffer layer growth time is 8 minutes.

[0048] (3) Growth of the outer layer

[0049] Argon, ethylene, trichlorosilane and nitrogen were continuously introduced for reaction, and the C / Si molar ratio of ethylene and trichlorosilane was 1.1. The pressure, carrier gas flow rate, temperature in the reaction chamber and the carrier gas flow ratio between the center and edge regions of the silicon carbide substrate remained unchanged, and the outer edge layer growth time was 20 minutes.

[0050] (4) Cooling

[0051] Stop introducing ethylene, trichlorosilane and nitrogen, continue to introduce carrier gas hydrogen and lower the temperature of the reaction chamber to 900°C, then increase the pressure to 1024 mbar, reduce the carrier gas hydrogen flow rate to 30 slm, take it out of the reaction chamber and cool it to room temperature.

[0052] The process of the silicon carbide epitaxial wafer growth method of this embodiment is as follows: Figure 1 As shown, the prepared silicon carbide epitaxial wafer includes a silicon carbide substrate and a buffer layer and an epitaxial layer that sequentially cover the silicon carbide substrate. The thickness of the buffer layer is 1.0 μm, and the thickness of the epitaxial layer is 10 μm. The appearance defects of the silicon carbide substrate after step (4) are detected using a sica88 defect detector, and the results are as follows: Figure 2 As shown by Figure 2 It can be seen from the results that the defects on the surface of the silicon carbide epitaxial wafer obtained by the silicon carbide epitaxial wafer growth method of this embodiment are greatly reduced.

[0053] Example 2

[0054] This embodiment is a method for growing a silicon carbide epitaxial wafer, which includes the following steps.

[0055] (1) Surface treatment

[0056] A 6-inch silicon carbide substrate with a 4° bevel angle along the <11-20> direction is placed in the loading chamber and the chamber door is closed, and then transferred to a reaction chamber at 800°C. The reaction chamber is slowly heated from 800°C to 1650°C, and 0.8slm of argon is introduced as a rotating gas during the heating process to rotate the silicon carbide substrate. The pressure in the reaction chamber is reduced to 80mbar, the carrier gas flow rate is 80slm, and the etching time of the silicon carbide substrate is 5min. A mixed gas of hydrogen and hydrogen chloride (hydrogen chloride accounts for 0.5vol.‰ of hydrogen) is introduced as a carrier gas, and the carrier gas flow ratio of the center and edge areas of the silicon carbide substrate is 0.50, and the center and edge areas are 36slm and 72slm, respectively. The temperature of the reaction chamber was lowered to 1610°C, the carrier gas was switched to argon and the flow rate was increased to 80 slm, the pressure remained unchanged, and the annealing treatment was performed for 10 minutes. During the annealing treatment, the carrier gas flow ratio between the center and edge regions of the silicon carbide substrate was 1.0, and the center and edge regions were 45 slm and 45 slm, respectively. Then, the etching and annealing treatment was performed again as described above.

[0057] (2) Buffer layer growth

[0058] The carrier gas hydrogen was continuously introduced, and the hydrogen saturated vapor of ethylene, trichlorosilane and trimethylaluminum was introduced for reaction, and the C / Si molar ratio of ethylene and trichlorosilane was 1.0. The pressure, carrier gas flow rate and temperature in the reaction chamber remained unchanged, and the hydrogen carrier gas flow ratio in the center and edge areas of the silicon carbide substrate was 2.5, the center and edge areas were 75 slm and 30 slm respectively, the flow rate of hydrogen saturated vapor of trimethylaluminum was 100 sccm and the doping concentration was 1.20E18 / cm 3 , the buffer layer growth time is 5min.

[0059] (3) Growth of the outer layer

[0060] The carrier gas hydrogen, ethylene, trichlorosilane and trimethylaluminum hydrogen saturated vapor were continuously introduced for reaction, and the C / Si molar ratio of ethylene and trichlorosilane was 1.2. The pressure, carrier gas flow rate, temperature in the reaction chamber and the hydrogen carrier gas flow ratio in the center and edge regions of the silicon carbide substrate remained unchanged, and the outer edge layer growth time was 10 minutes.

[0061] (4) Cooling

[0062] Stop introducing ethylene, trichlorosilane and nitrogen, continue to introduce carrier gas hydrogen and lower the temperature of the reaction chamber to 900°C, then increase the pressure to 1024 mbar, reduce the carrier gas hydrogen flow rate to 30 slm, take it out of the reaction chamber and cool it to room temperature.

[0063] Example 3

[0064] This embodiment is a method for growing a silicon carbide epitaxial wafer, which includes the following steps.

[0065] (1) Surface treatment

[0066] A 6-inch silicon carbide substrate with a 4° bevel angle along the <11-20> direction is placed in the loading chamber and the chamber door is closed, and then transferred to a 900°C reaction chamber. The reaction chamber is slowly heated from 900°C to 1630°C, and 0.5slm of argon is introduced as a rotating gas during the heating process to rotate the silicon carbide substrate. The pressure in the reaction chamber is reduced to 100mbar, the carrier gas flow rate is 120slm, and the silicon carbide substrate is etched for 6min. A mixed gas of hydrogen and hydrogen chloride (hydrogen chloride accounts for 0.3vol.‰ of hydrogen) is introduced as a carrier gas, and the carrier gas flow ratio of the center and edge areas of the silicon carbide substrate is 0.25, and the center and edge areas are 24slm and 96slm, respectively. The temperature of the reaction chamber was lowered to 1600°C, the carrier gas was switched to argon and the flow rate was increased to 100 slm, the pressure remained unchanged, and the annealing treatment was performed for 5 minutes. During the annealing treatment, the carrier gas flow ratio between the center and edge regions of the silicon carbide substrate was 1.5, and the center and edge regions were 60 slm and 40 slm, respectively. Then, the etching and annealing treatment was performed again as described above.

[0067] (2) Buffer layer growth

[0068] The carrier gas hydrogen was continuously introduced, and ethylene, trichlorosilane and nitrogen were introduced for reaction, and the C / Si molar ratio of ethylene and trichlorosilane was 0.8. The pressure in the reaction chamber was raised to 120mbar, the carrier gas flow rate was 150slm, the temperature was 1650℃, and the hydrogen carrier gas flow ratio in the center and edge areas of the silicon carbide substrate was 1.5, the center and edge areas were 72slm and 48slm respectively, the nitrogen flow rate was 150sccm and the doping concentration was 1.20E18 / cm 3 The buffer layer growth time is 8 minutes.

[0069] (3) Growth of the outer layer

[0070] The carrier gases hydrogen, ethylene, trichlorosilane and nitrogen were continuously introduced for reaction, and the C / Si molar ratio of ethylene and trichlorosilane was 1.1. The pressure, carrier gas flow rate, temperature in the reaction chamber and the hydrogen carrier gas flow ratio in the center and edge regions of the silicon carbide substrate remained unchanged, and the outer edge layer growth time was 20 minutes.

[0071] (4) Cooling

[0072] Stop introducing hydrogen saturated vapor of ethylene, trichlorosilane and trimethylaluminum, continue to introduce carrier hydrogen and lower the temperature of the reaction chamber to 850°C, then increase the pressure to 1100 mbar, reduce the carrier hydrogen flow rate to 25 slm, take it out of the reaction chamber and cool it to room temperature.

[0073] Comparative Example 1

[0074] This comparative example is a method for growing a silicon carbide epitaxial wafer, comprising the following steps.

[0075] (1) Surface treatment

[0076] A 6-inch silicon carbide substrate with a 4° bevel angle along the <11-20> direction is placed in the loading chamber and the chamber door is closed, and then transferred to a 900°C reaction chamber. The reaction chamber is slowly heated from 900°C to 1630°C, and 0.5slm of argon is introduced as a rotating gas during the heating process to rotate the silicon carbide substrate. The pressure in the reaction chamber is reduced to 100mbar, the carrier gas flow rate is 120slm, and the silicon carbide substrate is etched for 6min. A mixed gas of hydrogen and hydrogen chloride (hydrogen chloride accounts for 0.3vol.‰ of hydrogen) is introduced as a carrier gas, and the carrier gas flow ratio of the center and edge areas of the silicon carbide substrate is 0.25, and the center and edge areas are 24slm and 96slm, respectively. The temperature of the reaction chamber was lowered to 1600°C, the carrier gas was switched to argon and the flow rate was increased to 100 slm, the pressure remained unchanged, and the annealing treatment was performed for 5 minutes. During the annealing treatment, the carrier gas flow ratio between the center and edge areas of the silicon carbide substrate was 1.5, and the center and edge areas were 60 slm and 40 slm respectively.

[0077] (2) Buffer layer growth

[0078] The carrier gas argon was continuously introduced, and ethylene, trichlorosilane and nitrogen were introduced for reaction, and the C / Si molar ratio of ethylene and trichlorosilane was 0.8. The pressure, carrier gas flow rate and temperature in the reaction chamber remained unchanged, and the hydrogen carrier gas flow ratio in the center and edge areas of the silicon carbide substrate was 1.5, the center and edge areas were 72 slm and 48 slm respectively, the nitrogen flow rate was 150 sccm and the doping concentration was 1.20E18 / cm 3 The buffer layer growth time is 8 minutes.

[0079] (3) Growth of the outer layer

[0080] Argon, ethylene, trichlorosilane and nitrogen were continuously introduced for reaction, and the C / Si molar ratio of ethylene and trichlorosilane was 1.1. The pressure, carrier gas flow rate, temperature in the reaction chamber and the carrier gas flow ratio between the center and edge regions of the silicon carbide substrate remained unchanged, and the outer edge layer growth time was 20 minutes.

[0081] (4) Cooling

[0082] Stop introducing ethylene, trichlorosilane and nitrogen, continue to introduce carrier gas hydrogen and lower the temperature of the reaction chamber to 900°C, then increase the pressure to 1024 mbar, reduce the carrier gas hydrogen flow rate to 30 slm, take it out of the reaction chamber and cool it to room temperature.

[0083] The appearance defects of the silicon carbide substrate of this comparative example after step (4) were detected using a sica88 defect detector, and the results are as follows: Figure 3 As shown. Figure 3 It can be seen from the results that the surface defects of the silicon carbide epitaxial wafer obtained by the silicon carbide epitaxial wafer growth method of this comparative example do not change much. This is because only one etching and annealing treatment cannot ensure the consistency of the silicon carbide substrate surface.

[0084] Comparative Example 2

[0085] This comparative example is a method for growing a silicon carbide epitaxial wafer, comprising the following steps.

[0086] (1) Surface treatment

[0087] A 6-inch silicon carbide substrate with a 4° bevel angle along the <11-20> direction is placed in the loading chamber and the chamber door is closed, and then transferred to a 900°C reaction chamber. The reaction chamber is slowly heated from 900°C to 1630°C, and 0.5slm of argon is introduced as a rotating gas during the heating process to rotate the silicon carbide substrate. The pressure in the reaction chamber is reduced to 100mbar, the carrier gas flow rate is 120slm, and the silicon carbide substrate is etched for 6min. A mixed gas of hydrogen and hydrogen chloride (hydrogen chloride accounts for 0.3vol.‰ of hydrogen) is introduced as a carrier gas, and the carrier gas flow ratio of the center and edge areas of the silicon carbide substrate is 0.25, and the center and edge areas are 24slm and 96slm, respectively.

[0088] (2) Buffer layer growth

[0089] The carrier gas argon was continuously introduced, and ethylene, trichlorosilane and nitrogen were introduced for reaction, and the C / Si molar ratio of ethylene and trichlorosilane was 0.8. The pressure, carrier gas flow rate and temperature in the reaction chamber remained unchanged, and the hydrogen carrier gas flow ratio in the center and edge areas of the silicon carbide substrate was 1.5, the center and edge areas were 72 slm and 48 slm respectively, the nitrogen flow rate was 150 sccm and the doping concentration was 1.20E18 / cm 3 The buffer layer growth time is 8 minutes.

[0090] (3) Growth of the outer layer

[0091] Argon, ethylene, trichlorosilane and nitrogen were continuously introduced for reaction, and the C / Si molar ratio of ethylene and trichlorosilane was 1.1. The pressure, carrier gas flow rate, temperature in the reaction chamber and the carrier gas flow ratio between the center and edge regions of the silicon carbide substrate remained unchanged, and the outer edge layer growth time was 20 minutes.

[0092] (4) Cooling

[0093] Stop introducing ethylene, trichlorosilane and nitrogen, continue to introduce carrier gas hydrogen and lower the temperature of the reaction chamber to 900°C, then increase the pressure to 1024 mbar, reduce the carrier gas hydrogen flow rate to 30 slm, take it out of the reaction chamber and cool it to room temperature.

[0094] The appearance defects of the silicon carbide substrate of this comparative example after step (4) were detected using a sica88 defect detector, and the results were as follows: Figure 4 As shown. Figure 4 It can be seen from the results that the surface defects of the silicon carbide epitaxial wafer obtained by the silicon carbide epitaxial wafer growth method of this comparative example have not changed much. This is because only the surface of the silicon carbide substrate is etched and no annealing treatment is performed, and the consistency of the surface of the silicon carbide substrate cannot be guaranteed.

[0095] 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 the scope of protection of the present invention. Although the present invention is described in detail with reference to the preferred embodiments, it is not limited to those listed in the embodiments. Those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A method for growing a silicon carbide epitaxial wafer, characterized in that: include: (1) Surface treatment Placing the silicon carbide substrate in a reaction chamber and introducing a carrier gas to perform multiple alternating etching and annealing processes, wherein the etching and annealing processes use different carrier gases; (2) Buffer layer growth continuously introducing the carrier gas, and introducing the first reaction source gas and the first doping source gas to react; (3) Growth of the outer layer Continuously introducing the carrier gas, and introducing the second reaction source gas and the second doping source gas to react; (4) Cooling Stop introducing the second reaction source gas and the second doping source gas, continue introducing the carrier gas, and remove it after cooling and pressurizing it.

2. The method for growing a silicon carbide epitaxial wafer according to claim 1, characterized in that: The carrier gas includes hydrogen or argon.

3. The method for growing a silicon carbide epitaxial wafer according to claim 1, characterized in that: The carrier gas used in the etching also includes an auxiliary etching gas, the auxiliary etching gas includes chlorine or hydrogen chloride, and the volume ratio of the auxiliary etching gas to the total amount of the carrier gas is 1:500-5000.

4. The method for growing a silicon carbide epitaxial wafer according to claim 1, characterized in that: During the etching, the carrier gas flow ratio between the center and edge areas of the silicon carbide substrate is 0.1-2.0, the temperature of the reaction chamber is 1620-1650° C., the pressure is 80-120 mbar, the time is 10-15 min, and the flow rate of the carrier gas is 80-150 slm.

5. The method for growing a silicon carbide epitaxial wafer according to claim 1, characterized in that: During the annealing treatment, the temperature of the reaction chamber is 1600-1620° C., the pressure is 80-120 mbar, the time is 6-12 minutes, and the flow rate of the carrier gas is 80-150 slm.

6. The method for growing a silicon carbide epitaxial wafer according to claim 1, characterized in that: The first reaction source gas and the second reaction source gas are mixed gases of ethylene and trichlorosilane in different proportions.

7. The method for growing a silicon carbide epitaxial wafer according to claim 1, characterized in that: The first doping source gas and the second doping source gas are each independently hydrogen-saturated steam of trimethylaluminum or nitrogen.

8. The method for growing a silicon carbide epitaxial wafer according to claim 1, characterized in that: When the buffer layer grows, the temperature of the reaction chamber is 1580-1650°C, the pressure is 80-120mbar, the carrier gas flow rate is 80-150slm, the carrier gas flow ratio between the center and edge areas of the silicon carbide substrate is 0.6-3.0, the C / Si molar ratio in the first reaction source gas is 0.6-1.0, and the buffer layer growth time is 3-10min.

9. The method for growing a silicon carbide epitaxial wafer according to claim 1, characterized in that: When the outer edge layer grows, the temperature of the reaction chamber is 1580-1650°C, the pressure is 80-120mbar, the carrier gas flow rate is 80-150slm, the carrier gas flow ratio between the center and edge areas of the silicon carbide substrate is 0.6-3.0, the C / Si molar ratio in the second reaction source gas is 0.8-1.2, and the growth time of the outer edge layer is 5-30min.

10. The method for growing a silicon carbide epitaxial wafer according to claim 1, characterized in that: During the cooling, the reaction chamber is cooled to 800-1000° C., the pressure is increased to 1000-1100 mbar, and the flow rate of the carrier gas is reduced to below 30 slm, and the carrier gas is taken out of the reaction chamber and then cooled to room temperature.

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