A method for improving the quality of SiC single crystal and epitaxial growth

Abstract

The present invention discloses a method for improving the quality of SiC single crystal and epitaxial growth, belonging to the field of semiconductor technology. Before the growth of the SiC crystal, the SiC substrate material is pretreated by electrochemical etching, specifically: the growth surface of the SiC substrate to be pretreated is exposed, and the other side is covered; the covered surface of the substrate is connected to a graphite electrode as the anode, and the cathode is selected from a graphite electrode or a platinum electrode; the anode and the cathode are symmetrically placed, placed in an electrolyte, connected to a power supply and energized to perform electrochemical etching on the growth surface of the substrate; the electrochemically etched substrate is continuously immersed in the electrolyte, then immersed in deionized water and ultrasonically treated, and finally dried with an inert gas. The method for improving the quality of SiC single crystal and epitaxial growth provided by the present invention pretreats the SiC substrate material by electrochemical etching before the growth of the SiC crystal, improves the surface quality of the substrate, avoids the misalignment probability caused by two-dimensional nucleation on the substrate surface, optimizes the nucleation in the initial stage of growth, and thus improves the quality of SiC single crystal and epitaxial growth.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and particularly relates to a method for improving the quality of SiC single crystal and epitaxial growth. Background Art

[0002] Compared with the first- and second-generation semiconductor materials represented by Si and GaAs, the third-generation semiconductor represented by SiC has characteristics such as wide bandgap, high saturated electron mobility, high breakdown electric field strength, and high thermal conductivity. Due to its superior properties such as high frequency, high temperature resistance, chemical etching resistance, high efficiency, strong radiation resistance, and high voltage resistance, it is regarded as one of the most promising materials in the field of semiconductor materials. With the increasing maturity of semiconductor manufacturing technology, SiC has become the supporting material for core electronic devices in fields such as intelligent communication, new energy vehicles, aerospace, Internet of Things, intelligent transportation, smart grid, nuclear energy technology, and oil exploration. Therefore, there is an urgent need for higher-quality and larger-sized SiC crystals to meet the huge application scenarios and market demands. Currently, the mainstream growth methods of SiC single crystal are physical vapor transport method (PVT), top seeded solution growth method (TSSG), and high temperature chemical vapor deposition method (HTCVD), while the mainstream growth method of SiC epitaxy is homo / heteroepitaxial chemical vapor deposition method (CVD).

[0003] The basic principle of single crystal growth by the PVT method is to use a closed or semi-closed crucible system, and the crucible material can be selected from isostatic graphite, tantalum carbide, tantalum carbide coating, or tungsten metal, etc. During growth, the powder sublimates and decomposes at the high-temperature zone, and through the mass transport process in the growth chamber, it condenses to form a single crystal at the low-temperature seed crystal (seed crystal holder).

[0004] The basic principle of single crystal growth by the TSSG method is to use a closed or semi-closed crucible system, with a graphite crucible as the heating component (heating method is not limited), and carbon felt for heat insulation. Through the heating system, the crucible provides the heat source required for crystal growth, and the Si source in the crucible and the C source provided by the graphite crucible are transported by convection and precipitate at the seed crystal interface to form a SiC single crystal.

[0005] The growth of SiC crystals by the HTCVD method is relatively similar to the PVT method. The reaction vessel is a graphite crucible, and the precursor (for example: SiH4 + C3H8) enters the heating zone of the graphite crucible through the gas channel under the crucible. A seed crystal is installed at the top of the crucible, and the gas deposits and grows silicon carbide crystals at the relatively low-temperature seed crystal. The growth temperature of the HTCVD method is generally above 2300°C.

[0006] At present, chemical vapor deposition (CVD) is generally used for silicon carbide epitaxial growth. In an epitaxial furnace, a silicon source gas and a carbon source gas (such as SiH4 + C2H4, TCS + C3H8, etc.) are introduced. Under the action of a carrier gas such as H2, N2 can be used as a doping gas. They are mixed together and introduced into the reactor. The temperature of the reaction chamber is about 1500 °C. The silicon source gas and the carbon source gas react preferentially on the silicon carbide substrate to achieve the growth of the silicon carbide epitaxial layer.

[0007] Different from the growth of traditional Si and GaAs single crystals, whether it is the growth of silicon carbide single crystals by the physical vapor transport (PVT), the thermal sublimation solution growth (TSSG), the hot-wall chemical vapor deposition (HTCVD) method, or the growth of silicon carbide epitaxial layers by the CVD method, crystal growth is carried out on a large-size seed crystal or substrate. The size of the seed crystal is basically the same as the size of the grown crystal. It is impossible to use traditional processes such as necking and shoulder opening with small seed crystals to obtain single crystals with a low defect density. On a large-area silicon carbide seed crystal or substrate, at the initial growth stage, multi-point two-dimensional nucleation often occurs. The single crystal growth starts from these two-dimensional nucleation centers. After growth and coalescence, more defects are often introduced due to misalignment, resulting in a high-defect layer at the initial growth of the silicon carbide single crystal / epitaxy, which severely limits the improvement of the quality of the silicon carbide single crystal / epitaxy. Therefore, the present invention provides a method for improving the quality of SiC single crystal and epitaxial growth. Summary of the Invention

[0008] The purpose of the present invention is to provide a method for improving the quality of SiC single crystal and epitaxial growth, improving the surface quality of the substrate, avoiding the misalignment probability caused by two-dimensional nucleation on the substrate surface, optimizing the nucleation in the initial growth stage, and thus improving the quality of the crystal and epitaxy.

[0009] To achieve the above purpose, the present invention provides a method for improving the quality of SiC single crystal and epitaxial growth. Before the growth of the SiC crystal, the SiC substrate material is pretreated by electrochemical etching to improve the surface quality of the substrate, avoid the misalignment probability caused by two-dimensional nucleation on the substrate surface, and thus improve the quality of SiC single crystal and epitaxial growth.

[0010] Preferably, the specific steps of the electrochemical etching pretreatment of the SiC substrate material are as follows:

[0011] (1) Expose the growth surface of the SiC substrate to be pretreated and cover the other side;

[0012] (2) Connect the covered surface of the substrate to a graphite electrode as the anode, and select a graphite electrode or a platinum electrode as the cathode;

[0013] (3) Place the anode and the cathode symmetrically, place the silicon carbide substrate in the electrolyte, connect the power supply and energize it to perform electrochemical etching on the growth surface of the substrate.

[0014] (4) The electrochemically etched substrate is continuously immersed in the electrolyte, then immersed in deionized water and ultrasonically treated, and finally dried with an inert gas.

[0015] Preferably, in the step (2), the substrate masking surface and the graphite electrode are adhesively connected or vacuum-adsorbed through a conductive adhesive.

[0016] Preferably, in the step (3), the distance between the cathode and the anode is 1 - 20 cm, the power supply voltage is 0 - 50 V, and the current is 0 - 500 mA.

[0017] Preferably, in the step (3), the electrolyte is an HF solution with a concentration of 0 - 60 wt%, a temperature of 0 - 50 °C, and the electrochemically etching time is 0 - 5 h.

[0018] Preferably, in the step (4), it is immersed in the electrolyte for 0 - 12 hours and ultrasonically treated in deionized water for 0 - 10 hours.

[0019] Preferably, in the step (4), the inert gas is Ar or He.

[0020] The process of electrochemical etching basically includes two parts: the first part, holes are generated during the etching process, a current is formed at the SiC - electrolyte interface, and SiC is oxidized into SiO x film, and the second part, the SiO x film is dissolved in the electrolyte. The type / concentration of the electrolyte, the electrochemically etching time / temperature, the externally applied auxiliary conditions (such as: ultraviolet light irradiation, ultrasonic oscillation, etc.), the load voltage / current, and the electrode spacing will all affect the effect of electrochemical etching.

[0021] The main method of the present invention is to perform electrochemical etching pretreatment on the SiC substrate material before crystal growth, and then perform corresponding crystal or epitaxial growth. The basic principle of the electrochemical etching pretreatment is: by using electrochemical etching, defects such as surface damage of the substrate are preferentially removed, the surface quality of the substrate is improved, and the probability of inheriting the original defects and dislocations in the substrate during crystal growth is reduced; during pretreatment, shallow etching pits can be left on the smooth substrate growth surface, which can provide more nucleation sites, reduce the surface nucleation energy, optimize the substrate growth surface, improve the step flow, make the step flow delicate, gentle, and with a small height, which is beneficial to promoting the "flow" of the steps, thereby optimizing the nucleation in the initial stage of crystal growth, avoiding the misalignment probability caused by two-dimensional nucleation on the smooth substrate surface, and enabling the crystal to grow in a step flow manner from the initial stage of crystal growth, improving the crystal growth quality. By applying the principle and advantages of the electrochemical etching pretreatment to the growth of silicon carbide single crystals and epitaxy, the product qualification rate can be effectively improved and the production capacity can be increased.

[0022] Therefore, the present invention provides a method for improving the quality of SiC single crystal and epitaxial growth. Aiming at the sources of defects and dislocations, a suitable substrate pretreatment scheme is selected to etch and remove defects such as surface damage of the substrate, improve the surface quality of the substrate, and cause steps to appear on the surface, avoiding the misalignment probability caused by two-dimensional nucleation on the smooth substrate surface, so that the growth starts from the initial stage of crystal growth in a step-flow manner, thereby improving the crystal quality.

[0023] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Description of the Drawings

[0024] Figure 1 It is a device diagram for the electrochemical etching used in the present invention;

[0025] Figure 2 It is a comparison diagram of rocking curves of the etched area and the unetched area in the single crystal growth experiment of the same crystal;

[0026] Figure 3 It is a comparison diagram of rocking curves of the etched area and the unetched area in the epitaxial growth experiment of the same crystal;

[0027] Reference Numerals in the Drawings

[0028] 1 - Anode electrode; 2 - Cathode electrode; 3 - Teflon cover plate; 4 - Power supply; 5 - Electrolyte; 6 - SiC substrate; 7 - Graphite screw rod; 8 - Wire. Detailed Embodiments

[0029] The present invention provides a method for improving the quality of SiC single crystal and epitaxial growth. Before the growth of the SiC crystal, the SiC substrate material is pretreated by electrochemical etching to improve the surface quality of the substrate, avoid the misalignment probability caused by two-dimensional nucleation on the substrate surface, optimize the nucleation in the initial growth stage, and thus improve the quality of SiC single crystal and epitaxial growth.

[0030] In the present invention, the specific steps for the electrochemical etching pretreatment of the SiC substrate material are as follows:

[0031] (1) Expose the growth surface of the SiC substrate to be pretreated and cover the other side;

[0032] (2) Connect the covered surface of the substrate to a graphite electrode as the anode, and select a graphite electrode or a platinum electrode as the cathode;

[0033] (3) Place the anode and the cathode symmetrically, place the silicon carbide substrate in the electrolyte, connect the power supply and turn on the power to perform electrochemical etching on the growth surface of the substrate;

[0034] (4) Immerse the electrochemically etched substrate in the electrolyte continuously, then immerse it in deionized water and soak it ultrasonically, and finally dry it with an inert gas.

[0035] In the present invention, the device used for electrochemical etching is as follows Figure 1 shown, which includes an anode electrode 1, a cathode electrode 2, a tetrafluoroethylene cover plate 3, a power supply 4, an electrolyte 5, a SiC substrate 6, a graphite screw rod 7, and a wire 8. Among them, the anode and cathode are placed symmetrically up and down. The distance between the two electrodes is fixed and adjusted by a thread between the graphite screw rod 7 and the tetrafluoroethylene cover plate 3. The distance between the cathode and the anode is 1 - 20 cm. The covered surface of the SiC substrate 6 is adhered to the anode electrode 1 through a conductive adhesive or connected by vacuum adsorption. The pre-etched surface is in contact with the electrolyte 5. The distance between the anode electrode 1 (graphite electrode) and the cathode electrode 2 (graphite electrode) is fixed and adjusted by a thread between the graphite screw rod 7 and the tetrafluoroethylene cover plate 3. The graphite screw rod 7 is conductively tightened with the graphite electrodes 1 and 2 through a thread, and the wire 8 is conductively connected to the graphite screw rod 7 through a conductive clip.

[0036] The power supply is energized, the power supply voltage is 0 - 50 V, and the current is 0 - 500 mA. Hydroxide ions (OH - ) are generated by electrolyzing water and accumulate at the anode. The hydroxide ions (OH - ) react with holes (h + ) to form free radicals ( . OH). The free radicals are unstable and easily diffuse between the SiC at the anode and the electrolyte interface, oxidizing SiC into SiO x and CO x . Then, the oxidation products SiO x and CO x dissolve in the HF electrolyte. The process can be expressed as:

[0037] 4OH - -4e - →2H2O+O2;

[0038] OH - +h + → . OH;

[0039] SiC+4 . OH+O2→SiO2+CO2+2H2O;

[0040] SiO2+6HF→2H + +SiF6 2- +2H2O.

[0041] In the present invention, the specific steps of electrochemical etching + single crystal growth of silicon carbide are as follows:

[0042] Step 1: Expose the growth surface of the SiC substrate to be pretreated, and cover the other side of the substrate.

[0043] Step 2: The masking surface of the substrate is connected to a graphite electrode as the anode, and the cathode is selected from a graphite electrode or a platinum electrode;

[0044] Step 3: The anode and the cathode are symmetrically placed. The silicon carbide substrate is placed in an electrolyte with a concentration of 0 - 60 wt%, the power supply is connected and energized, and the growth surface of the substrate is electrochemically etched for 0 - 5 h;

[0045] The temperature of the electrolyte is controlled at 0 - 50 °C. Auxiliary conditions can be selected, such as ultraviolet light irradiation, ultrasonic vibration, etc. The types of electrolytes can be neutral (such as: NaCl solution), alkaline (such as: KOH solution), acidic (such as: HF solution). In the present invention, HF solution is preferably selected as the electrolyte.

[0046] Step 4: The electrochemically etched substrate is first immersed in the electrolyte for 0 - 12 hours, then immersed in deionized water and ultrasonically vibrated multiple times, with the time controlled at 0 - 10 hours. Finally, it is dried with an inert gas such as Ar gas or He gas for standby.

[0047] Step 5: The pretreated SiC substrate and high-purity SiC powder are placed in a corresponding crystal growth crucible. The crucible is tightened, and a reasonable crystal growth thermal field is set (the substrate adhesion method is not limited, for example: adhesive bonding, mechanical fixing, chemical fixing, etc., the type of crystal growth crucible is not limited, for example: graphite crucible, tantalum carbide crucible, graphite crucible coated with tantalum carbide coating, etc., the thermal field structure is not limited).

[0048] Step 6: After the furnace loading is completed, the single crystal growth furnace is evacuated to make the pressure in the furnace reach 10 -6 mbar, and then the corresponding temperature control and pressure control programs are set.

[0049] Step 7: Under vacuum conditions, a heating program is set. After 2 - 6 hours, the temperature is raised to 1100 - 1450 °C, then the argon gas inlet is opened (the gas flow rate is controlled at 0 - 5 L / min). After 0.5 - 3 hours, the pressure is raised to 200 - 900 mbar. Under the condition of constant pressure with flowing argon, after 2 - 6 hours, the temperature is raised to 2000 - 2300 °C, and then under the condition of constant temperature with flowing argon, within 0.5 - 50 hours, the pressure is reduced to 0.1 - 50 mbar. Under the growth conditions of a temperature of 2000 - 2300 °C and a pressure of 0.1 - 50 mbar, the crystal grows for 3 - 15 days.

[0050] Step 8: Before the pressure increase and decrease, keep the argon gas inlet open (the gas flow rate is controlled at 0 - 5 L / min). After 0.5 - 3 hours, the pressure is raised to 200 - 900 mbar. It is cooled to 700 - 1400 °C in 10 - 20 hours, and then cooled naturally, and the entire crystal growth is completed.

[0051] During the process of SiC epitaxial growth, a substrate with a preferred orientation is generally used as a seed crystal, and HCl etching is used before epitaxial growth. The purpose of this is to create steps on the surface to avoid two-dimensional nucleation and misalignment on the smooth substrate surface, thereby improving the epitaxial quality. Through electrochemical etching pretreatment, that is, performing controllable electrochemical etching pretreatment before epitaxial growth, it can replace HCl etching, avoiding the introduction of corrosive gases, reducing the requirements for equipment, being safe, reliable, and pollution-free. At the same time, it can control the depth, size, and distribution of etching pits, thus better forming a step flow, enabling the crystal to grow in a step flow manner from the initial stage of crystal growth, achieving the purpose of improving the epitaxial quality, and having more controllable advantages than HCl etching.

[0052] In the present invention, the specific steps of electrochemical etching + SiC epitaxial growth are as follows:

[0053] Step 1: Expose the growth surface of the SiC substrate to be pretreated and cover the other side of the substrate.

[0054] Step 2: Connect the covered side of the substrate to a graphite electrode as the anode, and select a graphite electrode or a platinum electrode as the cathode;

[0055] Step 3: Place the anode and cathode symmetrically, place the silicon carbide substrate in an electrolyte with a concentration of 0 - 60 wt%, connect the power supply and apply electricity, and perform electrochemical etching on the growth surface of the substrate for 0 - 5 h;

[0056] The temperature of the electrolyte is controlled at 0 - 50 °C. Auxiliary conditions can be selected, such as ultraviolet light irradiation, ultrasonic vibration, etc. The types of electrolytes can be neutral (such as: NaCl solution), alkaline (such as: KOH solution), acidic (such as: HF solution). In the present invention, HF solution is preferably selected as the electrolyte.

[0057] Step 4: Immerse the electrochemically etched substrate in the electrolyte for 0 - 12 hours first, then soak it in deionized water and perform ultrasonic vibration multiple times, with the time controlled at 0 - 10 hours. Finally, dry it with an inert gas such as Ar gas or He gas and set it aside for use.

[0058] Step 5: Fix the pretreated substrate in a CVD epitaxial furnace, heat it up to 1500 - 1700 °C. After reaching the reaction temperature, introduce purified and dried gas raw materials (preferably silane and propane, with the gas flow rate controlled at 0 - 1 L / min), introduce high-purity H2 as a carrier gas (with the gas flow rate controlled at 50 - 150 L / min), introduce high-purity N2 (with the gas flow rate controlled at 0 - 1 L / min) as an N-type doping gas or trimethylaluminum as a P-type dopant, in a flowing gas mode, control the growth pressure at 200 - 500 mbar, and perform epitaxial growth for 0 - 10 hours under the growth conditions of a temperature of 1500 - 1700 °C and a pressure of 200 - 500 mbar.

[0059] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent substitution methods and shall be included in the protection scope of the present invention. In addition, it should be understood that after reading the content of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application and all belong to the protection scope of the present invention.

[0060] Unless otherwise defined, the meanings of the technical terms used herein are the same as those commonly understood by those skilled in the technical field to which this application belongs; the use of the relevant terms herein is only for describing specific embodiments and is not intended to limit this application.

[0061] In the present invention, unless otherwise specified, the reagents, instruments, equipment, etc. used are all reagents, instruments, and equipment commonly used by those skilled in the art.

[0062] Example 1: Electrochemical etching + PVT method for SiC single crystal growth

[0063] Step 1: Expose the C surface of the SiC substrate as the growth surface, and connect the Si surface to the graphite electrode with conductive glue so that there is complete contact between the SiC substrate and the graphite electrode.

[0064] Step 2: The SiC substrate and the graphite electrode are used as the anode and connected to the positive pole of the power supply, and a graphite electrode of the same size and thickness is used as the cathode and connected to the negative pole of the power supply. The distance between the two electrodes is 6 cm, the output voltage of the power supply is 15 V, and the current is 50 mA.

[0065] Step 3: Electrochemically etch the SiC substrate with the exposed C surface in an HF electrolyte with a concentration of 10 wt% for 10 minutes, and control the temperature of the electrolyte at 30 °C.

[0066] Step 4: Immerse the electrochemically etched substrate in the electrolyte for 12 hours first, then ultrasonically immerse it in deionized water for 2 hours, and finally dry it with Ar gas for standby.

[0067] Step 5: Place the pretreated and adhered SiC substrate and high-purity SiC powder in a graphite crucible, tighten the crucible, place it in a reasonable crystal growth thermal field, evacuate the single crystal growth furnace so that the pressure in the furnace reaches 10 -6 mbar, and set the corresponding temperature control and pressure control programs.

[0068] Step 6: Under vacuum conditions, set the heating program. Heat to 1350 °C over 3 hours. At this time, open the argon gas inlet (gas flow rate is 1 L / min) and maintain for 1 hour. Then increase the pressure to 300 mbar. Under the condition of constant pressure with flowing argon, heat to 2100 °C over 3 hours. Then, under the condition of constant temperature with flowing argon, reduce the pressure to 5 mbar within 1 hour. Under the growth conditions of a temperature of 2100 °C and a pressure of 5 mbar, crystal growth is carried out for 5 days.

[0069] Step 7: Before increasing and decreasing the pressure, keep the Ar gas inlet open (gas flow rate is 1 L / min) for 1 hour, increase the pressure to 800 mbar, cool down to 1100 °C over 15 hours, and then cool down naturally to end the entire crystal growth.

[0070] Example 2: Growth of SiC single crystal by electrochemical etching + HTCVD method

[0071] Step 1: Expose the C surface of the SiC substrate as the growth surface, and connect the Si surface to the graphite electrode using conductive glue to ensure complete contact between the SiC substrate and the graphite electrode.

[0072] Step 2: Use the SiC substrate and the graphite electrode as the anode connected to the positive pole of the power supply, and use a graphite electrode of the same size and thickness as the cathode connected to the negative pole of the power supply. The distance between the two electrodes is 6 cm, the output voltage of the power supply is 15 V, and the current is 50 mA.

[0073] Step 3: Electrochemically etch the SiC substrate with the exposed C surface in an HF electrolyte with a concentration of 10 wt% for 10 min, and control the temperature of the electrolyte at 30 °C.

[0074] Step 4: Immerse the electrochemically etched substrate in the electrolyte for 12 hours first, then ultrasonically immerse it in deionized water for 2 hours, and finally dry it with Ar gas for standby.

[0075] Step 5: Fix the pretreated substrate on the top of the graphite crucible, which is provided with gas transmission holes at the bottom. Set the corresponding thermal field, and the graphite components are coated with tantalum carbide coating. Evacuate and leak-check the single crystal growth furnace to make the pressure in the furnace reach 10 -6 mbar for 12 hours, with a leak rate where the pressure fluctuation does not exceed 5 Pa. Set the corresponding temperature and pressure control programs.

[0076] Step 6: Under vacuum conditions, set the heating program. Heat to 2300 °C over 10 hours. After reaching the reaction temperature, adopt the lower-inlet gas supply method, introduce high-purity Ar as the carrier gas (control the gas flow rate at 5 L / min), introduce SiH4 and C3H8 (control the gas flow rate at 0.1 L / min) as the reaction gases, and in the flowing gas mode, control the growth pressure at 200 mbar. Under the growth conditions of a temperature of 2300 °C and a pressure of 200 mbar, crystal growth is carried out for 5 days.

[0077] Step 7: Before boosting the pressure and cooling down, stop introducing the reaction gas, keep the Ar inlet open (gas flow rate controlled at 5 L / min) for 1 hour, boost the pressure to 800 mbar, cool down to 1100 °C in 15 hours, and then cool down naturally, ending the entire crystal growth.

[0078] Example 3: Electrochemical etching + SiC epitaxial growth

[0079] Step 1: Expose the C face of the SiC substrate as the growth surface, and connect the Si face to the graphite electrode using conductive adhesive, ensuring complete contact between the SiC substrate and the graphite electrode.

[0080] Step 2: Use the SiC substrate and the graphite electrode as the anode connected to the positive pole of the power supply, and use a graphite electrode of the same size and thickness as the cathode connected to the negative pole of the power supply. The distance between the two electrodes is 6 cm, the output voltage of the power supply is 15 V, and the current is 50 mA.

[0081] Step 3: Electrochemically etch the SiC substrate with the exposed C face in an HF electrolyte with a concentration of 10 wt% for 10 minutes, and control the temperature of the electrolyte at 30 °C.

[0082] Step 4: Immerse the electrochemically etched substrate in the electrolyte for 12 hours first, then ultrasonically immerse it in deionized water for 2 hours, and finally dry it with Ar gas for standby.

[0083] Step 5: Fix the pretreated and adhered substrate in the CVD epitaxial furnace, heat it up to 1600 °C. After reaching the reaction temperature, introduce high-purity H2 as the carrier gas (gas flow rate controlled at 50 L / min), introduce purified and dried silane and propane as the reaction gases (gas flow rate controlled at 0.1 L / min), introduce high-purity N2 (gas flow rate controlled at 0.05 L / min) as the doping gas, in the flowing gas mode, control the growth pressure at 300 mbar, and under the conditions of temperature: 1600 °C, pressure: 300 mbar, carry out epitaxial growth for 1 hour, and then cool down to end the growth.

[0084] Experimentally test the crystal quality obtained in Example 1. The results of this experiment are from the same furnace of crystal growth, ensuring that the growth conditions and the thermal field are the same, avoiding the errors caused by the poor repeatability of silicon carbide single crystal growth and the fluctuations in growth conditions. The seed crystal is divided into two regions, half of which forms an etched region through electrochemical pretreatment, and the other half is untreated as the unetched region. The results are as Figure 2 shown, and it can be seen from Figure 2 that the full width at half maximum (FWHM) value of the etched region is much smaller than that of the unetched region. The smaller the FWHM value, the better the crystallization quality, indicating that the method of the present invention has achieved the effect of improving the crystal quality.

[0085] Experimentally test the epitaxial quality of SiC obtained in Example 3. The results of this experiment are obtained from epitaxial growth in the same furnace, ensuring that the growth conditions and thermal field are the same, avoiding errors caused by fluctuations in growth conditions. The seed crystal is divided into two regions. Half of it forms an etched region through electrochemical pretreatment, and the other half is untreated as the unetched region. The results are as Figure 3 shown. It can be seen from Figure 3 that the full width at half maximum (FWHM) value of the etched region is much smaller than that of the unetched region. The smaller the FWHM value, the better the crystallization quality. Therefore, it shows that chemical etching can improve the epitaxial quality.

[0086] In summary, electrochemical etching pretreatment reduces the nucleation energy of silicon carbide single crystal and epitaxial growth. Whether it is the growth of silicon carbide single crystal by PVT, HTCVD, or TSSG method, or the epitaxial growth of silicon carbide, it is more conducive to step-flow growth, avoiding the occurrence of two-dimensional nucleation, optimizing the nucleation in the initial growth stage, and improving the quality of silicon carbide crystal and epitaxy.

[0087] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify or equivalently replace the technical solutions of the present invention, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for improving the quality of SiC single crystal and epitaxial growth, characterized in that: Before the growth of SiC crystals, the SiC substrate material is pretreated by electrochemical etching to improve the surface quality of the substrate, avoid the misalignment probability caused by two-dimensional nucleation on the substrate surface, optimize the nucleation in the initial stage of growth, and enable the growth in a step-flow manner from the initial stage of crystal growth, thereby improving the quality of SiC single crystal and epitaxial growth; The specific steps for the electrochemical etching pretreatment of the SiC substrate material are as follows: (1) Expose the growth surface of the SiC substrate to be pretreated and cover the other side; (2) Connect the covered surface of the substrate to a graphite electrode as the anode, and select a graphite electrode or a platinum electrode as the cathode; (3) Place the anode and cathode symmetrically, place the silicon carbide substrate in the electrolyte, connect the power supply and energize it to perform electrochemical etching on the growth surface of the substrate; (4) Immerse the electrochemically etched substrate in the electrolyte continuously, then immerse it in deionized water and soak it ultrasonically, and finally dry it with an inert gas; In step (3), the electrolyte is an HF solution with a concentration of 10 - 60 wt% and a temperature of 30 - 50 °C, and the electrochemical etching time is 10 min - 5 h.

2. The method for improving the quality of SiC single crystal and epitaxial growth according to claim 1, wherein: In step (2), the covered surface of the substrate is connected to the graphite electrode by conductive adhesive adhesion or vacuum adsorption.

3. A method for improving the quality of SiC single crystal and epitaxial growth according to claim 1, characterized in that: In step (3), the distance between the cathode and the anode is 1 - 20 cm, the power supply voltage is 15 - 50 V, and the current is 50 - 500 mA.

4. A method for improving the quality of SiC single crystal and epitaxial growth according to claim 1, characterized in that: In step (4), soak it in the electrolyte for 12 hours, and soak it in deionized water and ultrasonicate it for 2 - 10 hours.

5. A method for improving the quality of SiC single crystal and epitaxial growth according to claim 1, characterized in that: In step (4), the inert gas is Ar or He.

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