A method for growing high-purity 4H-SiC single crystals by the PVT method

Abstract

The present invention discloses a method for growing high-purity 4H-SiC single crystals by the PVT method, belonging to the field of semiconductor technology. Before the growth of the SiC crystal, the Si surface of the SiC substrate is subjected to electrochemical etching pretreatment, specifically: the Si surface of the SiC substrate is exposed and the C surface 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, the SiC substrate is placed in the electrolyte, and the power supply is connected 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 growing high-purity 4H-SiC single crystals by the PVT method provided by the present invention can provide more nucleation sites, reduce the nucleation energy of 4H on the Si surface, provide a window for the nucleation and growth of 4H-SiC, reduce the absorption of nitrogen elements, and stabilize the growth of high-purity 4H-SiC single crystals by performing electrochemical etching pretreatment on the Si surface of the SiC substrate before the PVT method growth of the SiC crystal.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and particularly to a method for growing high-purity 4H-SiC single crystals by the physical vapor transport (PVT) method. Background Art

[0002] SiC has stable physical and chemical properties, and is characterized by a wide bandgap, high saturated electron mobility, high breakdown electric field strength, high thermal conductivity, etc. It is regarded as one of the most promising materials in the field of semiconductor materials. SiC crystals are also ideal substrates for epitaxial films such as gallium nitride and silicon carbide, with characteristics such as high lattice matching and good thermal conductivity. Compared with the first-generation semiconductor materials represented by Si and the second-generation semiconductor materials represented by GaAs, it has obvious advantages and is an ideal semiconductor material for manufacturing optoelectronic devices, high-frequency high-power devices, and high-temperature electronic devices. Currently, it has been widely used in white light illumination, optical storage, screen display, aerospace, high-temperature radiation environment, oil exploration, automation, radar and communication, automotive electronics, etc.

[0003] At present, the physical vapor transport method (abbreviated as PVT) is the mainstream method for growing SiC single crystals. The specific growth method is as follows: a seed crystal is placed at the top of the crucible, powders are added at the bottom of the crucible, the crucible thermal field is placed in a crystal growth furnace, the temperature at the bottom of the crucible is high, and the temperature at the top is low. By controlling the temperature and pressure, the bottom powders are gradually sublimated and transported to the top seed crystal for condensation and crystallization, thereby realizing the growth of SiC single crystals. Currently, this method has become the mainstream method in the industry and has achieved large-scale production of SiC.

[0004] The crystal structure of SiC is diverse and different crystal forms can transform into each other. The most common crystal forms are 3C-SiC, 4H-SiC, 6H-SiC, and 15R-SiC. Due to the differences in crystal structures, there are slightly different physical and chemical characteristics between different crystal forms. Due to the influence of the surface energy of different polar surfaces of SiC, the surface energy of the C surface is lower, which is more suitable for the growth of 4H single crystals with higher nucleation energy, while the surface energy of the Si surface is higher, which is suitable for the growth of 6H single crystals with lower nucleation energy. However, there are partially overlapping growth windows between different crystal forms of SiC, which leads to the phenomenon of coexistence of polytype inclusions during the growth of single crystals. For example, during the growth of 4H-SiC single crystals, 6H and 15R crystal forms are likely to appear; during the growth of 6H-SiC single crystals, 4H and 15R crystal forms are likely to appear, etc. This seriously affects the growth quality of SiC single crystals and increases production costs.

[0005] SiC single crystals generally have N-type conductivity and high-purity semi-insulating type. Gallium nitride and other epitaxial structures are grown on high-purity semi-insulating SiC, which can be applied to the fields of microwave communication and radar. In addition, carbon electronics based on graphene on SiC also require high-purity semi-insulating SiC single crystals. However, the growth of high-purity semi-insulating SiC single crystals is very difficult. This is because high-purity semi-insulation requires the nitrogen concentration in the single crystal to be less than 1E16 cm -3 , but in the process of SiC single crystal growth process (physical vapor transport method, abbreviated as PVT method), the graphite materials, powders, and heat-insulating materials used all belong to porous or powder materials with a large surface area, which will adsorb a large amount of nitrogen (the nitrogen content in the atmosphere exceeds 78%), making it very difficult to prepare high-purity semi-insulating SiC and the cost remains high.

[0006] In order to reduce the incorporation of nitrogen, some people have adopted the method of growing 6H-SiC single crystals on the Si surface. This is because it is more difficult to incorporate nitrogen on the Si surface of the SiC seed crystal. However, in the traditional PVT process, it is impossible to grow 4H-SiC single crystals on the Si surface. Generally, only 6H-SiC single crystals can be grown on the Si surface seed crystal. However, the bandgap width of 6H-SiC single crystals is smaller than that of 4H-SiC, and the performance is slightly worse than that of 4H. To solve this problem, the present invention proposes a method for growing high-purity semi-insulating 4H-SiC single crystals on the Si surface of a SiC seed crystal by the PVT method. Summary of the Invention

[0007] The purpose of the present invention is to provide a method for growing high-purity 4H-SiC single crystals by the PVT method, which can reduce the absorption of nitrogen while ensuring the growth of a single crystal form of 4H-SiC on the Si surface, achieving the purpose of reducing costs and increasing efficiency.

[0008] To achieve the above purpose, the present invention provides a method for growing high-purity 4H-SiC single crystals by the PVT method. Before growing the SiC crystal by the PVT method, the Si surface of the SiC substrate is pretreated by electrochemical etching to provide more nucleation sites, reduce the nucleation energy of 4H on the Si surface, provide a window for the nucleation and growth of 4H-SiC, reduce the absorption of nitrogen elements, and stabilize the growth of high-purity 4H-SiC single crystals.

[0009] Preferably, the specific steps for the electrochemical etching pretreatment of the Si surface of the SiC substrate are as follows:

[0010] (1) Expose the Si surface of the SiC substrate to be pretreated and cover the C surface;

[0011] (2) Connect the C surface of the substrate to a graphite electrode as the anode, and select a graphite electrode or a platinum electrode as the cathode;

[0012] (3) Place the anode and cathode symmetrically, place the SiC substrate in the electrolyte, connect the power supply and energize it to electrochemically etch the Si surface of the substrate;

[0013] (4) Immerse the electrochemically etched substrate in the electrolyte continuously, then immerse it in deionized water and ultrasonicate, and finally dry it with an inert gas.

[0014] Preferably, in the step (2), the C-plane of the substrate is adhered or connected by vacuum adsorption to the graphite electrode through a conductive adhesive.

[0015] 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.

[0016] 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 an electrochemical etching time of 0 - 5 h.

[0017] Preferably, in the step (4), immerse in the electrolyte for 0 - 12 hours, and immerse in deionized water and ultrasonicate for 0 - 10 hours.

[0018] Preferably, in the step (4), the inert gas is Ar or He.

[0019] 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 electrochemical etching time / temperature, the external auxiliary conditions (such as: ultraviolet light irradiation, ultrasonic vibration, etc.), the load voltage / current, and the electrode spacing will all affect the effect of electrochemical etching.

[0020] The main method of the present invention is to perform electrochemical etching pretreatment on the Si - plane of the SiC substrate before crystal growth, before growing SiC crystals by the PVT method. After the electrochemical etching pretreatment, 4H - SiC single crystal growth is carried out on the Si - plane by the PVT method. The basic principle of the electrochemical etching pretreatment is that electrochemical etching can provide more nucleation sites on the substrate, reduce the nucleation energy of 4H on the Si - plane, provide a suitable window for the nucleation and growth of 4H - SiC, break the current situation that only 6H - SiC can grow on the Si - plane and 4H - SiC can only grow on the C - plane, make full use of the characteristic that it is more difficult for nitrogen elements to be incorporated during the growth on the Si - plane, reduce the absorption of nitrogen elements, improve the quality of single crystal growth, avoid the generation of grain boundaries and polytypes, thereby stabilizing the growth of high - purity 4H - SiC single crystals and making it easier to prepare high - purity semi - insulating 4H - SiC.

[0021] Therefore, the present invention provides a method for growing high-purity 4H-SiC single crystals by the PVT method. By selecting a suitable substrate pretreatment scheme and using electrochemical etching to reduce the surface nucleation energy of the Si surface, while ensuring the growth of a single crystal form of 4H-SiC on the Si surface, the absorption of nitrogen is reduced, achieving the purpose of cost reduction and efficiency improvement.

[0022] The following will further describe the technical solutions of the present invention in detail through the accompanying drawings and embodiments. Brief Description of the Drawings

[0023] Figure 1 It is a device diagram for the electrochemical etching used in the present invention;

[0024] Figure 2 It is a thermal field structure diagram for growing high-purity 4H-SiC single crystals by the PVT method in the present invention;

[0025] Figure 3 It is a Raman mapping diagram of a SiC single crystal grown by the PVT method directly on the untreated Si surface of a SiC substrate;

[0026] Figure 4 It is a Raman mapping diagram of a SiC single crystal grown by the PVT method in the same cycle on the etched area and the unetched area formed after the Si surface of a SiC substrate is pretreated by electrochemical etching;

[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; 9 - Upper temperature measurement hole; 10 - Lower temperature measurement hole; 11 - Upper thermal insulation; 12 - Lower thermal insulation; 13 - Side thermal insulation; 14 - Seed crystal holder; 15 - Seed crystal; 16 - Crystal growth crucible; 17 - High-purity SiC powder. Detailed Embodiments

[0029] The present invention provides a method for growing high-purity 4H-SiC single crystals by the PVT method. Before growing SiC crystals by the PVT method, the Si surface of the SiC substrate is pretreated by electrochemical etching to provide more nucleation sites, reduce the nucleation energy of 4H on the Si surface, provide a window for the nucleation and growth of 4H-SiC, reduce the absorption of nitrogen elements, and stabilize the growth of high-purity 4H-SiC single crystals.

[0030] In the present invention, the specific steps for pretreating the Si surface of the SiC substrate by electrochemical etching are as follows:

[0031] (1) Expose the Si surface of the SiC substrate to be pretreated and cover the C surface;

[0032] (2) Connect the C 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) The anode and the cathode are symmetrically placed. The SiC substrate with the exposed Si surface is placed in the electrolyte, and the power supply is connected and energized to electrochemically etch the Si surface of the substrate.

[0034] (4) The substrate after electrochemical etching is continuously soaked in the electrolyte, then soaked in deionized water and ultrasonically treated, and finally dried with an inert gas.

[0035] In the present invention, the device used for electrochemical etching is as Figure 1 shown, and it is composed of 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 the cathode are symmetrically placed up and down. The distance between the two electrodes is fixed and adjusted by the 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 adhesively connected or vacuum-adsorbed to the anode electrode 1 through a conductive adhesive. 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 the 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 the thread, and the wire 8 is conductively connected to the graphite screw rod 7 through a conductive clip.

[0036] When the power supply is energized, the power supply voltage is 0 - 50 V, and the current is 0 - 500 mA. Hydroxide (OH - ) accumulates at the anode. Hydroxide (OH - ) and holes (h + ) 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 . After that, 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 + + SiF62- + 2H2O

[0041] In the present invention, the specific steps of electrochemical etching + high-purity 4H-SiC single crystal growth are as follows:

[0042] Step 1: Expose the Si surface of the SiC substrate to be pretreated and cover the C surface;

[0043] Step 2: Connect the C surface of the substrate to a graphite electrode as the anode, and select a graphite electrode or a platinum electrode as the cathode (the C surface of the substrate is preferably attached to the graphite electrode by conductive glue or vacuum adsorption);

[0044] Step 3: Place the anode and cathode symmetrically, place the SiC substrate with the exposed Si surface in an electrolyte with a concentration of 0 - 60 wt%, connect the power supply and energize, and perform electrochemical etching on the growth surface of the substrate 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: 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 aside for use.

[0047] Step 5: Use the Si surface of the pre-treated seed crystal 15 as the growth surface and fix it on the seed crystal holder 14 (the fixing method is not limited, and can be: adhesive bonding, mechanical fixing, chemical fixing, etc.). Place the high-purity SiC powder 17 at the bottom of the crystal growth crucible 16, tighten the crucible, and place it in the corresponding heat preservation thermal field (the material of the crystal growth crucible can be isostatic graphite, tantalum carbide, tantalum carbide coating, or tungsten metal, etc.).

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

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

[0050] Step 8: Before boosting pressure and reducing temperature, keep the argon inlet path open (gas flow rate controlled at 0 - 5 L / min) for 0.5 - 3 hours, boost the pressure to 200 - 900 mbar, reduce the temperature to 700 - 1400 °C in 10 - 20 hours, and then let it cool naturally to end the whole crystal growth.

[0051] In the present invention, the thermal field device used for crystal growth is as Figure 2 shown, including an upper temperature measurement hole 9; a lower temperature measurement hole 10; an upper thermal insulation 11; a lower thermal insulation 12; a side thermal insulation 13; a seed crystal holder 14; a seed crystal 15; a crystal growth crucible 16; and high-purity SiC powder 17. From top to bottom, there are an upper thermal insulation 11, a side thermal insulation 13, and a lower thermal insulation 12. Among them, the upper and lower temperature measurement holes 9 and 10 are respectively located in the middle of the upper and lower thermal insulations. The crystal growth crucible 16 is placed in the middle of the lower thermal insulation 12. The high-purity SiC powder 17 is placed at the bottom of the crystal growth crucible 16. The seed crystal 15 is fixed on the seed crystal holder 14, and the seed crystal holder 14 is connected to the crystal growth crucible by a threaded knob.

[0052] The following further elaborates the present invention in combination 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 replacement methods and are all 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.

[0053] 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 relevant terms herein is only for describing specific embodiments and is not intended to limit this application.

[0054] In the present invention, unless otherwise specified, the reagents, instruments, equipment, etc. used are all the reagents, instruments, and equipment commonly used by those skilled in the art in this field.

[0055] Example

[0056] This example provides a method for growing high-purity 4H-SiC single crystals on the Si surface of an electrochemically etched and pre-treated SiC substrate by the PVT method. The specific steps are as follows:

[0057] Step 1: Expose the Si surface of the SiC substrate 6, and use a conductive adhesive to connect the C surface to the graphite electrode 1 so that there is full contact between the SiC substrate 6 and the graphite electrode 1.

[0058] Step 2: The SiC substrate 6 and the graphite electrode 1 are used as anodes and connected to the positive pole of the power supply, and the graphite electrode 2 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 4 is 15 V, and the current is 50 mA.

[0059] Step 3: The SiC substrate with the exposed Si surface is electrochemically etched in the HF electrolyte 5 with a concentration of 10 wt% for 10 minutes, and the temperature of the electrolyte 5 is controlled at 30 °C.

[0060] Step 4: The electrochemically etched substrate is first immersed in the electrolyte 5 for 12 hours, then ultrasonically immersed in deionized water for 2 hours, and finally dried with Ar gas for standby.

[0061] Step 5: The Si surface of the pretreated seed crystal 15 is used as the growth surface and fixed on the seed crystal holder 14 (the fixing method is not limited and can be: adhesive bonding, mechanical fixing, chemical fixing, etc.). The high-purity SiC powder 17 is placed at the bottom of the crystal growth crucible 16, the crucible is tightened, and placed in the corresponding heat preservation thermal field.

[0062] 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.

[0063] Step 7: Under vacuum conditions, set the heating program. It takes 3 hours to heat up to 1350 °C. At this time, open the argon gas inlet (gas flow rate is 1 L / min). It takes 1 hour to increase the pressure to 300 mbar. Under the condition of constant pressure with flowing argon, it takes 3 hours to heat up to 2100 °C. Then, under the condition of constant temperature with flowing argon, it takes 1 hour to reduce the pressure to 5 mbar. Under the growth conditions of a temperature of 2100 °C and a pressure of 5 mbar, the crystal grows for 5 days.

[0064] Step 8: Before increasing and decreasing the pressure and temperature, keep the Ar gas inlet open (gas flow rate is 1 L / min). It takes 1 hour to increase the pressure to 800 mbar, and 15 hours to cool down to 1100 °C, and then cool down naturally, and the whole crystal growth is completed.

[0065] SIMS tests were carried out on the high-purity 4H-SiC single crystals grown with the N-type 4H-SiC substrates with two different crystal planes as seed crystals after electrochemical etching pretreatment, and the results are shown in Table 1.

[0066] Table 1

[0067] Growth conditions Nitrogen concentration Growth of 4H-SiC on Si face of N-type 4H seed crystal 3.0E17 - 5.0E17 Growth of 4H-SiC on C face of N-type 4H seed crystal 1.0E18 - 3.0E18

[0068] As can be seen from the data in Table 1, the absorption of nitrogen in the growth of 4H-SiC single crystals on the Si face is one order of magnitude smaller than that in the growth of 4H-SiC single crystals on the C face. If the growth of 4H-SiC single crystals is stabilized on the Si face, it is beneficial to reduce the absorption of nitrogen and conducive to the growth of high-purity semi-insulating 4H-SiC single crystals.

[0069] Raman mapping scanning tests were carried out on SiC single crystals grown by the PVT method directly on the untreated Si face of the SiC substrate and on the SiC single crystals grown by the PVT method on the etched area and the unetched area formed after electrochemical etching pretreatment of the Si face of the SiC substrate.

[0070] Raman mapping scanning tests can determine the SiC crystal form distribution. The same color represents the same characteristic peaks and the same crystal form. Among them, the blue characteristic peaks are: 204, 776 representing 4H-SiC; the green characteristic peaks are: 150, 789 representing 6H-SiC; the red characteristic peaks are: 173, 785 representing 15R-SiC. Figure 3 In the case of directly growing single crystals on the untreated Si face of the SiC substrate, the color of the Raman mapping diagram is not single, indicating the presence of 6H, 4H, and 15R crystal forms and the phenomenon of polytype inclusion. And Figure 4 This is the Raman mapping diagram of the same round of single crystal growth on the etched area and the unetched area formed after electrochemical etching pretreatment of the Si face of the SiC substrate. The color of the etched area is single, indicating that 4H-SiC is the main crystal form in this etched area. However, there are more differently colored points in the unetched area, and the crystal form difference is larger than that in the etched area, showing the phenomenon of polytype inclusion. This indicates that electrochemical etching pretreatment can promote and stabilize the growth of a single crystal form of 4H-SiC on the Si face.

[0071] In summary, before growing SiC crystals by the PVT method, electrochemical etching pretreatment of the Si face of the SiC substrate can provide more nucleation sites, reduce the nucleation energy of 4H on the Si face, provide a window for the nucleation and growth of 4H-SiC, stabilize the growth of a single crystal form of 4H-SiC on the Si face, reduce the absorption of nitrogen elements at the same time, and is conducive to solving the problem of excessive nitrogen content in high-purity semi-insulating SiC single crystals, breaking the technical barrier of growing 4H on the C face and 6H on the Si face, making the preparation of high-purity semi-insulating 4H-SiC simpler.

[0072] 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 growing high-purity 4H-SiC single crystals by a PVT method, characterized in that: Before the PVT SiC crystal growth, the Si surface of the SiC substrate is pre-treated by electrochemical etching to provide more nucleation sites, reduce the nucleation energy of 4H on the Si surface, provide a window for the nucleation growth of 4H-SiC, reduce the absorption of nitrogen, and stabilize the growth of high-purity 4H-SiC single crystals; The specific steps of electrochemical etching pretreatment of the Si surface of the SiC substrate are: (1) Exposing the Si surface of the SiC substrate to be pretreated and covering the C surface; (2) The C-side of the substrate is connected to a graphite electrode as the anode, and a graphite electrode or a platinum electrode is selected as the cathode; (3) The anode and cathode are placed symmetrically, the SiC substrate is placed in the electrolyte, the power supply is connected and the Si surface of the substrate is electrochemically etched; (4) The electrochemically etched substrate is further immersed in the electrolyte, then immersed in deionized water for ultrasonic treatment, and finally dried with an inert gas; In the step (3), the electrolyte is an HF solution with a concentration of 0-60wt%, a temperature of 0-50°C, and an electrochemical etching time of 0-5h.

2. The method for growing high-purity 4H-SiC single crystal by a PVT method according to claim 1, characterized in that: In the step (2), the C surface of the substrate and the graphite electrode are connected by conductive adhesive bonding or vacuum adsorption.

3. The method for growing high-purity 4H-SiC single crystal by PVT method according to claim 1, characterized in that: 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.

4. The method for growing high-purity 4H-SiC single crystal by PVT method according to claim 1, characterized in that: In the step (4), the sample is immersed in the electrolyte for 0-12 hours, and immersed in deionized water for 0-10 hours.

5. The method for growing high-purity 4H-SiC single crystal by PVT method according to claim 1, characterized in that: In the step (4), the inert gas is Ar or He.

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