A cleaning method

Abstract

The present invention relates to the field of silicon carbide cleaning, and provides a cleaning method, which comprises using a cleaning gas to clean a deposit containing silicon carbide located on the surface of a substrate; the substrate comprises a pyrolytic carbon coating located on the surface of the substrate; the pyrolytic carbon coating is obtained by pyrolysis of polyimide and nano-microcrystalline cellulose; and the cleaning gas is chlorine trifluoride. The method can make silicon carbide films or particles fall off from the pyrolytic carbon surface, realize the cleaning of a CVD reactor, and at the same time, can reduce the corrosion of the reactor and the substrate by chlorine trifluoride, thereby increasing the service life of the reactor.

Description

Technical Field

[0001] The invention relates to the field of silicon carbide cleaning, and in particular to a cleaning method. Background Art

[0002] Silicon carbide is an important ceramic material, which is mostly grown epitaxially using chemical vapor deposition (CVD). However, during the epitaxial growth process, due to long-term reaction in the CVD deposition furnace, a certain thickness of SiC coating is deposited on the walls of the reaction chamber, the surface of the base and the gas port. If the coating is too thick, it will block the gas port, and these films often emit small particles that will contaminate the deposited sample and cause lattice defects.

[0003] In order to remove the deposited silicon carbide and maintain the clean conditions of the furnace deposition, chlorine trifluoride (ClF 3 ) gas as a cleaning gas to implement the CVD reactor cleaning process. However, chlorine trifluoride reacts easily with graphite. Therefore, when using chlorine trifluoride for cleaning, although chlorine trifluoride can be used to remove silicon carbide, it is also easy to cause damage to the reaction container and the base due to the high corrosion reactivity of graphite.

[0004] Therefore, it is urgent to develop a method that can clean silicon carbide more safely, so as to reduce damage to the reactor and extend the service life of the reactor. Summary of the invention

[0005] The purpose of the present invention is to overcome the above-mentioned problems existing in the prior art and to provide a cleaning method, which can more safely achieve the purpose of cleaning silicon carbide.

[0006] In order to achieve the above object, the present invention provides a cleaning method, which comprises: using a cleaning gas to clean a deposit containing silicon carbide located on a surface of a substrate; the substrate comprises a pyrolytic carbon coating located on a surface of a substrate;

[0007] The pyrolytic carbon coating is obtained by pyrolysis of polyimide and nano-microcrystalline cellulose;

[0008] The cleaning gas is chlorine trifluoride.

[0009] The present invention adopts the above technical solution to achieve the following beneficial effects:

[0010] (1) The present invention uses chlorine trifluoride (ClF 3) gas is used as the cleaning gas, and PI / NCC pyrolytic carbon film is used as the coating material on the surface of the carbon sensor to implement the CVD reactor cleaning process. Silicon carbide film or particles can fall off from the surface of the pyrolytic carbon film, while the surface of the pyrolytic carbon film is not easily damaged or doped with impurities. By annealing in a nitrogen environment containing trace amounts of oxygen, fluorine atoms are diffused outward, which can further reduce the damage to the CVD reactor and ensure the cleanliness of the CVD reactor.

[0011] (2) The method provided by the present invention can also extend the service life of the reactor.

[0012] The endpoints and any values ​​of the range disclosed in this article are not limited to the precise range or value, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article. Herein, in the absence of special instructions, data ranges include endpoints. DETAILED DESCRIPTION

[0013] The specific embodiments of the present invention are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0014] Unless otherwise defined, all scientific and technical terms used in the present invention have the same meanings as commonly understood by one of ordinary skill in the art to which the present invention relates.

[0015] The present invention provides a cleaning method, which comprises: using a cleaning gas to clean a deposit containing silicon carbide on a surface of a substrate; the substrate comprises a pyrolytic carbon coating on a surface of a base;

[0016] The pyrolytic carbon coating is obtained by pyrolysis of polyimide (PI) and nanocrystalline cellulose (NCC);

[0017] The cleaning gas is chlorine trifluoride.

[0018] In the present invention, the substrate refers to the inner wall of an apparatus for manufacturing, for example, a silicon carbide single crystal (for example, in the form of a silicon carbide epitaxial film) or its auxiliary equipment (for example, a susceptor for placing a semiconductor wafer).

[0019] In the present invention, the substrate may be a material that can withstand the temperature at which a silicon carbide single crystal is formed, such as a carbon material (such as graphite), silicon carbide, or a carbon / silicon carbide material.

[0020] In the present invention, a pyrolytic carbon coating is added to the substrate in order to protect the substrate during the cleaning process. The pyrolytic carbon coating is obtained by pyrolysis of polyimide and nano-microcrystalline cellulose.

[0021] In some embodiments, the thickness of the pyrolytic carbon coating is 30-80 μm, for example, 30, 40, 50, 60, 70, 80 μm and any range between any two values.

[0022] In some embodiments, the polyimide is BTDA-TDI / MDI copolymerized polyimide (ie, P84 polyimide), such as a compound represented by formula (I).

[0023]

[0024] The relative molecular weight of the P84 polyimide may be 80,000-150,000 g / mol, for example, 80,000, 90,000, 100,000, 110,000, 120,000, 130,000, 140,000, 150,000 g / mol and any range between any two values, and may be purchased from HP polymer GmbH, Austria.

[0025] The nano-microcrystalline cellulose can be purchased commercially or prepared at home, and the preparation method thereof can be a conventional method in the art, such as preparing the nano-microcrystalline cellulose by acid hydrolysis.

[0026] In some embodiments, the weight ratio of the polyimide to the nanocrystalline cellulose is 1:0.5-2, such as 1:0.5, 1:0.8, 1:1, 1:1.2, 1:1.5, 1:1.8, 1:2 and any range between any two values, preferably 1:0.8-1.2.

[0027] In some embodiments, the method for preparing the pyrolytic carbon coating further comprises: attaching the polyimide and the nano-microcrystalline cellulose to a substrate before pyrolyzing the polyimide and the nano-microcrystalline cellulose, and then performing a curing treatment.

[0028] In some embodiments, the curing treatment conditions include: a temperature of 200-400°C, such as 200, 220, 240, 260, 280, 300, 320, 340, 360, 380, 400°C and any range between any two values, and a time of 0.5-2h, such as 0.5, 1, 1.5, 2h and any range between any two values.

[0029] In some embodiments, the attachment method includes: contacting a solution containing polyimide and nano-microcrystalline cellulose with a substrate, and then performing a solvent removal treatment, so that the polyimide and nano-microcrystalline cellulose are attached to the substrate.

[0030] In some embodiments, the concentration of polyimide in the solution is 20-30 wt %, for example, 20, 22, 24, 26, 28, 30 wt % and any range between any two values.

[0031] In some embodiments, the solvent of the solution is selected from at least one of N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide and N,N-diethylacetamide.

[0032] In the preparation process, there is no particular restriction on the order of adding the substances, as long as a uniform material can be obtained. For example, nanocrystalline cellulose can be added to the solvent first, and then polyimide can be added. The polyimide can be powder or granules. In this process, operations such as ultrasound and stirring can also be used.

[0033] In the present invention, the desolvation method can be a conventional method in the art, such as vacuum drying (such as drying at 40-80°C in a vacuum environment for 2-6 hours) or inert gas (such as nitrogen) purging.

[0034] In some embodiments, the pyrolysis conditions include: a pyrolysis temperature of 900-1500°C, such as 900, 1000, 1100, 1200, 1300, 1400, 1500°C and any range between any two values; the pyrolysis atmosphere is an inert atmosphere; the pyrolysis time is 1-3h, such as 1, 1.5, 2, 2.5, 3h and any range between any two values.

[0035] In some embodiments, the inert atmosphere is a nitrogen atmosphere, a helium atmosphere, or an argon atmosphere.

[0036] In some embodiments, the heating rate to the pyrolysis temperature is 2-9°C / min, for example, 2, 4, 6, 8, 9°C / min and any range between any two values.

[0037] In some embodiments, during the cleaning process, the concentration of the cleaning gas is above 80%, such as 80, 85, 90, 95, 100% and any range between any two values. It should be understood that the gas introduced during the cleaning process includes cleaning gas and diluent gas, such as inert gas conventionally used in the art.

[0038] In some embodiments, the flow rate of the cleaning gas is 10-100 sccm, for example, it can be 10, 20, 40, 60, 80, 100 sccm and any range between any two values.

[0039] In some embodiments, the cleaning process is performed in a nitrogen atmosphere, wherein the flow rate of the nitrogen can be 1-10 slm, such as 1, 2, 4, 6, 8, 10 slm, and any range between any two values.

[0040] In some embodiments, the cleaning conditions include: a temperature of 300-500° C., such as 300, 350, 400, 450, 500° C., and any range between any two values, a time of 10-40 min, such as 10, 20, 30, 40 min, and any range between any two values. The pressure may be normal pressure.

[0041] Through the above cleaning, silicon carbide on the surface of the pyrolytic carbon film is removed.

[0042] In some embodiments, the method further comprises: performing annealing treatment on the cleaned system.

[0043] In some embodiments, the annealing is performed in the presence of nitrogen and oxygen, and the oxygen content is less than 0.5%. Compared with nitrogen gas without oxygen, the use of nitrogen gas containing low concentration of oxygen for annealing can further improve the discharge effect of fluorine atoms, reduce its corrosion to the reactor, and extend the life of the reactor.

[0044] In some embodiments, the annealing conditions include: a temperature of 800-1000°C, such as 800, 820, 840, 860, 880, 900, 920, 940, 960, 980, 1000°C and any range between any two values, and a time of 10-40 minutes, such as 10, 20, 30, 40 minutes and any range between any two values.

[0045] In some embodiments, during the annealing process, the total gas flow rate is 1-10 slm, for example, 1, 2, 4, 6, 8, 10 slm and any range between any two values. The total gas flow rate includes the nitrogen flow rate and the oxygen flow rate. Through the annealing process, the residual fluorine atoms in the cleaning process are discharged from the reactor.

[0046] In some embodiments, if the furnace wall surface is obviously light yellow, it indicates that most of the formed silicon carbide film has been removed. When it is found that the remaining amount of the formed silicon carbide film is significant, further etching is required. After repeated cleaning operations, the termination of cleaning can be carefully determined based on the appearance color of the substrate.

[0047] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0048] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0049] The present invention is described in detail below in conjunction with specific embodiments, which are used to understand but not to limit the present invention.

[0050] Preparation Example 1

[0051] This preparation example is used to illustrate the preparation method of polyimide-nanocrystalline cellulose pyrolysis carbon film.

[0052] N-methyl-pyrrolidone (NMP) is used as a solvent, an appropriate amount of nanocrystalline cellulose (NCC) is added, and then P84 polyimide powder is added to obtain a PI / NCC solution, wherein the content of PI in the PI / NCC solution is 25wt%, and the content of NCC is 20wt%.

[0053] Step 2: Apply the PI / NCC solution to the inner wall of the reactor, dry it in a vacuum environment at 60°C for 4 h to evaporate the excess solvent, and then cure it at 300°C for 1 h. 2 , and kept at 1000℃ for 2h to obtain a PI / NCC pyrolytic carbon film of about 40μm.

[0054] Comparative Preparation Example 1

[0055] This preparation example is used to illustrate the preparation method of a reference pyrolytic carbon film.

[0056] Methane (CH 4 ) is a carbon source precursor, and a deposition temperature of 1 000 °C is used by chemical vapor deposition (CVD) process. 4 The flow rate was 500 mL / min, the deposition time was 8 h, the deposition pressure was 5 kPa, and a pyrolytic carbon interface layer of about 40 μm was deposited on the inner wall of the reactor.

[0057] Example 1

[0058] This embodiment is used to illustrate a method for cleaning silicon carbide.

[0059] This example is carried out in a reactor where the substrate surface is coated with the PI / NCC pyrolytic carbon film described in Preparation Example 1.

[0060] After 15 cycles of silicon carbide deposition were performed using the reactor, a cleaning operation was performed, and the specific operating conditions were as follows.

[0061] (1) The furnace temperature was set at 400°C and the pressure was at atmospheric pressure. High-purity nitrogen was introduced during the heating process at a nitrogen flow rate of 5 slm. Then, chlorine trifluoride gas was introduced for cleaning at a chlorine trifluoride gas flow rate of 60 SCCM for 30 min.

[0062] (2) The temperature was continued to rise to 900° C., and a mixture of nitrogen and oxygen containing 0.2% oxygen was introduced at a flow rate of 5 slm for 20 min.

[0063] (3) If the surface of the furnace wall is obviously light yellow, it indicates that most of the formed silicon carbide film has been removed. When it is found that the remaining amount of the formed silicon carbide film is significant, further etching is required. After repeating the cleaning operation, carefully determine the termination of cleaning based on the appearance color of the base.

[0064] After the cleaning was completed, the steps (1) and (2) were repeated cyclically. After 10 cleanings, substantially no damage was found on the reactor surface.

[0065] Comparative Example 1

[0066] This comparative example is used to illustrate a reference cleaning method for silicon carbide.

[0067] The operation was carried out according to the method of Example 1, except that the deposition furnace used for cleaning was a deposition furnace in which the substrate surface was covered with the pyrolytic carbon film in Comparative Preparation Example 1, rather than a deposition furnace covered with the PI / NCC pyrolytic carbon film.

[0068] The steps (1) and (2) were repeated cyclically, and the pyrolytic carbon film on the reactor surface fell off after six cleanings.

[0069] It should be noted that, in this article, the terms "comprise", "include" or any other variant thereof are intended to cover non-exclusive inclusion, so that the process, method, article or device including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise one..." do not exclude the presence of other identical elements in the process, method, article or device including the element. In addition, it should be pointed out that the scope of the methods and devices in the embodiments of the present application is not limited to performing functions in the order shown or discussed, and may also include performing functions in a substantially simultaneous manner or in reverse order according to the functions involved, for example, the described method may be performed in an order different from that described, and various steps may also be added, omitted, or combined. In addition, the features described with reference to certain examples may be combined in other examples.

[0070] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A cleaning method, characterized in that: The method comprises: using a cleaning gas to clean a deposit containing silicon carbide on a surface of a substrate; the substrate comprises a pyrolytic carbon coating on a surface of a base; The pyrolytic carbon coating is obtained by pyrolysis of polyimide and nano-microcrystalline cellulose, wherein the polyimide is BTDA-TDI / MDI copolymerized polyimide, and the weight ratio of the polyimide to the nano-microcrystalline cellulose is 1:0.5-2; The cleaning gas is chlorine trifluoride.

2. The cleaning method according to claim 1, characterized in that: The relative molecular weight of the BTDA-TDI / MDI copolymer polyimide is 80000-150000 g / mol.

3. The cleaning method according to claim 1, characterized in that: The weight ratio of the polyimide to the nano-microcrystalline cellulose is 1:0.8-1.

2.

4. The cleaning method according to claim 1, characterized in that: The preparation method of the pyrolytic carbon coating comprises: before pyrolyzing the polyimide and the nano-microcrystalline cellulose, attaching the polyimide and the nano-microcrystalline cellulose to a substrate, and then performing a curing treatment.

5. The cleaning method according to claim 4, characterized in that: The curing treatment conditions include: temperature of 200-400° C. and time of 0.5-2 h.

6. The cleaning method according to claim 4, characterized in that: The attachment method comprises: contacting a solution containing polyimide and nano-microcrystalline cellulose with a substrate, and then performing a solvent removal treatment, so that the polyimide and nano-microcrystalline cellulose are attached to the substrate.

7. The cleaning method according to claim 6, characterized in that: The concentration of polyimide in the solution is 20-30 wt %.

8. The cleaning method according to claim 6, characterized in that: The solvent of the solution is selected from at least one of N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide and N,N-diethylacetamide.

9. The cleaning method according to claim 1, characterized in that: The pyrolysis conditions include: pyrolysis temperature of 900-1500° C., pyrolysis atmosphere of inert atmosphere, and pyrolysis time of 1-3 hours.

10. The cleaning method according to claim 9, characterized in that: The inert atmosphere is a nitrogen atmosphere, a helium atmosphere or an argon atmosphere.

11. The cleaning method according to claim 1, characterized in that: During the cleaning process, the concentration of the cleaning gas is above 80%.

12. The cleaning method according to claim 11, characterized in that: During the cleaning process, the flow rate of the cleaning gas is 10-100 sccm.

13. The cleaning method according to claim 11, characterized in that: The cleaning process is performed under a nitrogen or argon atmosphere.

14. The cleaning method according to claim 1, characterized in that: The cleaning conditions include: temperature of 300-500° C. and time of 10-40 min.

15. The cleaning method according to claim 1, characterized in that: The method comprises: annealing the cleaned system; The annealing is performed in the presence of nitrogen and oxygen, and the content of oxygen is less than 0.5%.

16. The cleaning method according to claim 15, characterized in that: The annealing treatment conditions include: a temperature of 800-1000° C. and a time of 10-40 min.

17. The cleaning method according to claim 15, characterized in that: During the annealing process, the total gas flow rate is 1-10 slm.

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