TWI410516B - Graphite protective film and manufacturing method thereof - Google Patents

Abstract

In this invention, a protection film composed of silicon carbide material is disposed on the graphite substrate surface; wherein a buffer layer and a multi-layered incline layer are disposed between the graphite substrate and the protection film. The buffer layer is disposed between the graphite substrate and the multilayered incline layer. The buffer layer and the multilayered incline layer are made of a silicon compound composite film through chemical vapor permeation process. The composite film may be a composite material of silicon carbide/silicon nitride, and the buffer layer and multilayered incline layer can be utilized to buffer the thermal stress generated between the graphite and silicon carbide protection film due to the mismatch thermal expansion coefficient while rising and decreasing the temperature.

Description

Graphite protective film and method of manufacturing same

The invention relates to a graphite protective film and a manufacturing method thereof, the purpose of which is to improve and alleviate the graphite and the niobium carbide protective film, because the thermal expansion coefficient is not integrated in the thermal stress generated by the temperature rise and fall process, causing cracks in the niobium carbide protective film, or causing The graphite substrate itself is deficient in carbon oxidation or corrosion.

In a semiconductor-related manufacturing process, such as a wafer carrier used in epitaxial growth; a graphite crucible for carrying molten germanium in a process such as C-Z method; and as a crystal alone The necessary consumables such as the support frame for thermal oxidation treatment are made of graphite (generally isotropic graphite) and a protective film on the surface. The reason why graphite is used as the substrate is because it has the advantages of easy processing, excellent electrical and thermal conductivity, and chemical stability.

Generally, graphite materials for industrial use are mostly porous. In order to prevent the carbon or impurities of graphite from volatilizing during the high temperature process and affecting the purity of the finished component, a coating film must be formed on the surface of the graphite. This cover film must be able to cover the graphite densely and not have holes in itself. According to the application process, the combination of the cover film/graphite must also have requirements of thermal shock resistance, oxidation resistance, corrosion resistance and good thermal stability. Common materials used as graphite coating films in the literature include niobium carbide (SiC), tantalum nitride (Si ₃ N ₄ ), boron nitride (BN), niobium carbide (TiC), and boron carbide (B ₄ C). Among them, the material used as the cover film is the first to promote carbonized niobium. The reason is that in addition to the strong mechanical strength, low density (3.2g/cm ³ ) and excellent oxidation resistance of tantalum carbide, tantalum carbide and graphite are carbon-containing. The materials are therefore highly compatible and have similar thermal expansion coefficients to each other. Despite the difference in physical properties, such as the thermal expansion coefficient of tantalum carbide is slightly larger than that of graphite (approximately 10% difference), under the cyclical operation of rapid heating and cooling in the actual process, thermal expansion coefficient will be uncoordinated. Mismatch) in turn causes residual tensile stress of the tantalum carbide coating. It has been reported from relevant literatures that when the residual stress on the tantalum carbide coating film is too large, cracks are generated in the tantalum carbide coating film. The cracks are generated, so that the impurities in the graphite material are diffused and deposited into the epitaxial elements by the cracks of the film, or the oxidizing gas or corrosive gas in the semiconductor process enters through the cracks, causing the carbon of the graphite material itself. Oxidation or corrosion. In addition, the thermal conductivity coefficient of tantalum carbide is much smaller than that of graphite, so that the thermal stress caused by the temperature gradient between the tantalum carbide layer and the graphite material when the carrier is heated is also considered to cause tantalum carbide. One of the causes of cracks in the cover film. It can be seen from the above description that how to overcome the problem of cracks in the surface covering film is the focus of the technical requirements.

The main object of the present invention is to provide an improved and tempered graphite and tantalum carbide protective film, because the thermal expansion coefficient is not integrated in the thermal stress generated by the temperature rise and fall, causing cracks in the tantalum carbide protective film, or causing carbonaceous oxidation of the graphite material itself. Or a graphite protective film that is missing, such as corrosion, and a method for producing the same.

In order to achieve the above, the surface of the graphite substrate of the present invention is provided with a protective film made of a tantalum carbide material; wherein the graphite substrate and the protective film are provided with a buffer layer and a plurality of inclined layers, and the buffer layer is disposed on the graphite. Between the substrate and the multi-layer inclined layer, the buffer layer and the multi-layer inclined layer are formed by a chemical vapor infiltration process using a ruthenium compound composite film, and the composite film may be a composite of tantalum carbide/tantalum nitride, and the buffer is utilized. The layer and the multi-layered inclined layer to alleviate the graphite and the niobium carbide protective film, because the thermal expansion coefficient is not integrated in the thermal stress generated by the temperature rise and fall process to avoid cracks.

The features of the present invention can be clearly understood by referring to the drawings and the detailed description of the embodiments.

In the present invention, a graphite protective film and a method for producing the same are provided. The surface of the graphite substrate 11 is provided with a protective film 12. As shown in the first figure, the protective film 12 may be a tantalum carbide material, if directly on the graphite substrate 11. The protective film 12 for depositing tantalum carbide has a large difference in thermal expansion coefficient (graphite: 4.8×10 ^-6 1/K, niobium carbide: 5.12×10 ^-6 1/K), which is not small in the process of rapid temperature rise and fall. Stress, which in turn causes cracks to occur. Once the cracks are generated, the carbon in the graphite substrate will precipitate from the cracks at high temperatures, which will affect the quality of the film deposition in the process system. Therefore, the present invention is to prepare a buffer layer to alleviate the stress generated during the rapid temperature rise and fall between the tantalum carbide film and the graphite substrate to avoid cracks.

The focus of the present invention is that a buffer layer 13 and a plurality of inclined layers 14 are disposed between the graphite substrate 11 and the protective film 12, and the buffer layer 13 is disposed on the stone. Between the ink substrate 11 and the plurality of inclined layers 14, the buffer layer 13 is formed by a chemical vapor infiltration process using a ruthenium compound composite film, and the multilayer inclined layer 14 is formed by a chemical vapor deposition process using a ruthenium compound composite film. The composite film may be a composite of tantalum carbide/tantalum nitride. A functionally gradient material (FGM) is formed by using the buffer layer 13 and the plurality of inclined layers 14 having different niobium carbide/niobium nitride ratios. The so-called FGM, as the name suggests, is a series of intermediate interlayers whose function gradually changes the physical properties of the substrate to the film. The present invention makes the thermal expansion coefficient of the buffer layer 13 close to that by the progressive change of the thermal expansion coefficient. The thermal expansion coefficient of the graphite substrate 11 further causes the respective inclined layers 14 to have different thermal expansion coefficients, and the thermal expansion coefficient is increased from the thermal expansion coefficient close to the buffer layer 13 to the thermal expansion coefficient close to the protective film 12, thereby achieving the relaxation of graphite and tantalum carbide. The protective film is not integrated with the thermal stress generated by the temperature rise and fall process due to the thermal expansion coefficient.

In the method for manufacturing the graphite protective film of the present invention, the following materials and equipment are prepared: (1) tetramethylsilane, purity 99.99%, boiling point 26.5 ° C, flammable gas or liquid, non-toxic, The molecular formula is Si(CH ₃ ) ₄ .

(2) Argon gas Ar (argon), ultra high purity 99.9995%, non-flammable, non-toxic, but suffocating.

(3) Ammonia NH ₃ (ammonia), purity 99.9995%, corrosive.

(4) Nitrogen N ₂ (nitrogen), purity 99.9995%, non-flammable, non-toxic, asphyxiating gas.

(5) Hydrogen H ₂ (hydrogen), purity 99.9995%, highly flammable gas.

(6) Ethanol (C ₂ H ₅ OH), purity 99.8%. The equipment is used for cleaning and degreasing. Flammable, keep away from fire.

(7) Acetone (CH ₃ COCH ₃ ), purity 99.5%, cleaning of equipment and degreasing of substrates. Flammable, keep away from fire.

(8) graphite (graphite), model CZ5-R6510, ultra-high purity isotropic graphite.

(9) Vertical wall low pressure chemical vapor deposition (LPCVD) system It includes a gas source section, an evaporator, a reaction chamber and a heating system, and an extraction system.

The method for manufacturing the graphite protective film of the present invention, as shown in the second figure, comprises at least the following steps: Step A, providing a graphite substrate, the step A further comprising: a washing step and a step of the step (A-1) (A-2) a preheating step of polishing the graphite substrate with both sides of the sandpaper, and then placing the graphite substrate in acetone and oscillating with an ultrasonic oscillator to remove the graphite substrate. The pre-heating step is to pre-heat the graphite substrate 10 at a temperature of 1000 ° C when the cleaned graphite substrate is placed in a reaction chamber, and the reaction chamber is evacuated to a temperature below 10 ^-5 torr. After a minute, the hydrogen is further cooled by hydrogen for 15 minutes; in step B, the first stage chemical vapor infiltration process is carried out by introducing tetramethyl decane into the reaction chamber under a hydrogen atmosphere with argon as a carrier gas. a reaction chamber is formed with ammonia gas (NH ₃ ) to form a buffer layer composed of a tantalum carbide/rhenium nitride-based composite film on the surface of the graphite substrate, wherein, as shown in the third figure, The graphite substrate 11 is provided with a plurality of open holes 111. The adhesion between the graphite substrate 11 and the surface buffer layer 13 and the thermal stability thereof can be increased. The environmental conditions in the first stage chemical vapor infiltration process of the control step B are as follows: 1. Adding ammonia gas under a hydrogen atmosphere and Tetramethyl decane, and the partial pressure ratio of the tetramethyl decane to ammonia gas may be 3, and the total reaction pressure may be 10 torr.

2. The lower reaction temperature, the reaction temperature can be 700~1000 °C.

3. The reaction time can be 50 to 60 minutes, and preferably 55 minutes.

The reactant formed under the above environmental conditions can penetrate into each open hole 111 to form the buffer layer 13, and can control the reaction space to make the buffer layer 13 form discontinuous on the surface of the graphite substrate 11. a surface structure for improving the adhesion between the graphite substrate 11 and the buffer layer 13 and the buffer layer 13 and the subsequent coating, and thermally expanding the buffer layer 13 by controlling the partial pressure ratio of the tetramethyl decane to the ammonia gas The coefficient is close to the thermal expansion coefficient of the graphite substrate 11 to improve the thermal stability between the graphite substrate 11 and the buffer layer 13.

Step C: performing a second-stage chemical vapor deposition process, wherein a chemical vapor deposition process is performed using tetramethyl decane, ammonia gas, and hydrogen as a raw material gas, and a plurality of inclined layers composed of a ruthenium compound composite film are formed on the surface of the buffer layer. In the embodiment shown in the fourth figure, the first, second, third, fourth, and fifth inclined layers 141, 142, 143, 144, and 145 are sequentially disposed on the surface of the buffer layer 13 for mitigation. The thermal stress between the protective film and the graphite substrate, in this step, a multilayer inclined layer having a thermal expansion coefficient of 4.8 to 5.12 is prepared by the following environmental conditions, and the second stage chemical vapor deposition process of the step C is performed. The conditions are as follows: 1. Ammonia gas and tetramethyl decane are added under a hydrogen atmosphere, and the partial pressure ratio of the tetramethyl decane to ammonia gas may be 3, and the total reaction pressure may be 10 torr.

2. A higher reaction temperature, the reaction temperature being greater than the reaction temperature of step B, which rises from 1000 ° C to about 1200 ° C.

The reactants formed under the above environmental conditions sequentially generate the first, second, third, fourth, and fifth inclined layers 141, 142 from a low temperature (1000 ° C) to a high temperature (about 1200 ° C). 143, 144, 145, and different ratios of niobium carbide/niobium nitride between the inclined layers due to different reaction temperatures, the niobium carbide/niobium nitride molar ratio may be 2.3 to 3.7, and the niobium carbide/nitrogen The ruthenium ratio is increased from the buffer layer 13 toward the protective film 12, that is, the first slanted layer 141 has the smallest proportion of niobium carbide/tantalum nitride, and the fifth inclined layer 145 has the largest proportion of niobium carbide/tantalum nitride.

Step D: providing a protective film 12 on the multi-layer inclined layer 14, as shown in the first figure, to complete the finished product, wherein the thickness of the protective film 12 and the plurality of inclined layers 14 also affect thermal stress, so the protective film 12 Thickness can be controlled to 2.5 to 10 μm (preferably 5 μm), and the thickness of the multilayer inclined layer 14 may be 2.5 to 2.85 μm (preferably 2.8 μm).

In the graphite protective film formed by the manufacturing method of the present invention, the buffer layer 13 provided on the surface of the graphite substrate 11 is formed by a low-temperature chemical vapor infiltration process, so that the buffer layer 13 can penetrate not only the graphite substrate but also the graphite substrate. In the open hole 111, a discontinuous surface structure is also formed to enhance the adhesion of the film layer, and the thermal expansion coefficient of the buffer layer 13 is made close by controlling the partial pressure ratio of the tetramethyl decane to the ammonia gas. The thermal expansion coefficient of the graphite substrate 11 is to improve the thermal stability between the graphite substrate 11 and the buffer layer 13; further, when the multilayer inclined layer is formed, the thermal expansion coefficient of each layer increases as the reaction temperature of the prepared inclined layer increases. Since the ratio of the niobium carbide/niobium nitride is changed to be close to the graphite substrate 11 to approach the protective film 12, a progressive buffer layer is formed, so that the thermal stress caused by the uncoupling of the thermal expansion coefficient at the temperature rise and fall can be buffered. It can also avoid the occurrence of cracks in the tantalum carbide protective film or the loss of carbonaceous oxidation or corrosion of the graphite substrate itself.

The technical content and technical features of the present invention have been disclosed as above, but those skilled in the art can still make various substitutions and modifications without departing from the spirit and scope of the invention. Therefore, the scope of the present invention should be construed as being limited by the scope of the appended claims

Graphite substrate ‧‧11

Open hole ‧‧11111

Protective film ‧‧12

Buffer layer ‧‧13

Inclined layer ‧‧14

The first figure is a schematic structural view of the graphite protective film of the present invention.

The second figure is a schematic flow chart of the method for manufacturing the graphite protective film of the present invention.

The third figure is a schematic structural view of the graphite substrate and the buffer layer of the present invention.

The fourth figure is a schematic structural view of the graphite substrate, the buffer layer and the multi-layer inclined layer of the present invention.

Graphite substrate ‧‧11

Open hole ‧‧11111

Protective film ‧‧12

Buffer layer ‧‧13

Inclined layer ‧‧1

Claims (49)

A graphite protective film having a protective film on the surface of the graphite substrate, wherein a buffer layer and a plurality of inclined layers are disposed between the graphite substrate and the protective film, and the protective film may be a tantalum carbide material, and the buffer layer may be The graphite substrate is formed between the graphite substrate and the multi-layer inclined layer, and the buffer layer is formed by a chemical vapor phase infiltration process using a ruthenium compound composite film, and the multi-layer slant layer is formed by a chemical vapor deposition process using a ruthenium compound composite film. And the composite film may be a composite of tantalum carbide/tantalum nitride. The graphite protective film according to claim 1, wherein each of the inclined layers has a different ratio of niobium carbide to tantalum nitride, and the niobium carbide/tantalum nitride ratio may be 2.3 to 3.7, and the niobium carbide/tantalum nitride ratio It is increased from the buffer layer toward the protective film. The graphite protective film according to claim 1, wherein the graphite substrate is provided with a plurality of open pores, and the buffer layer penetrates into each open pore. The graphite protective film according to claim 1, wherein the buffer layer has a thermal expansion coefficient close to a thermal expansion coefficient of the graphite substrate. The graphite protective film according to claim 1, wherein each of the inclined layers has a different coefficient of thermal expansion, and the coefficient of thermal expansion is increased from a coefficient of thermal expansion close to the buffer layer to a coefficient of thermal expansion close to the protective film. The graphite protective film according to claim 1, wherein the multilayer inclined layer has a thickness of 2.5 to 2.85 μm. The graphite protective film according to claim 6, wherein the multilayer is inclined The thickness of the layer may preferably be 2.8 μm. The graphite protective film according to claim 1, wherein the protective film has a thickness of 2.5 to 10 μm. The graphite protective film according to claim 8, wherein the thickness of the protective film is preferably 5 μm. A graphite protective film is provided with a protective film on the surface of the graphite substrate, wherein a buffer layer and a plurality of inclined layers are disposed between the graphite substrate and the protective film, and the buffer layer is disposed on the graphite substrate and the inclined layer of the plurality of layers. Between the thermal expansion coefficients of the buffer layer is close to the thermal expansion coefficient of the graphite substrate, and each inclined layer has a different thermal expansion coefficient, and the thermal expansion coefficient is increased from a thermal expansion coefficient close to the buffer layer to a thermal expansion coefficient close to the protective film. The graphite protective film according to claim 10, wherein the buffer layer and the plurality of inclined layers are formed by a chemical vapor deposition process and a chemical vapor deposition process, respectively, using a ruthenium compound composite film. The graphite protective film according to claim 10 or 11, wherein the protective film may be a tantalum carbide material, and the composite film may be a composite of tantalum carbide/tantalum nitride. The graphite protective film according to claim 12, wherein each of the inclined layers has a different niobium carbide/tantalum nitride ratio, and the niobium carbide/tantalum nitride ratio may be 2.3 to 3.7, and the niobium carbide/tantalum nitride ratio is It is increased from the buffer layer toward the protective film. The graphite protective film according to claim 10, wherein the graphite substrate is provided with a plurality of open pores, and the buffer layer is infiltrated into each of the openings. Inside the hole. The graphite protective film according to claim 10, wherein the multilayer inclined layer has a thickness of 2.5 to 2.85 μm. The graphite protective film according to claim 15, wherein the thickness of the plurality of inclined layers is preferably 2.8 μm. The graphite protective film according to claim 10, wherein the protective film has a thickness of 2.5 to 10 μm. The graphite protective film according to claim 17, wherein the protective film has a thickness of preferably 5 μm. A method for manufacturing a graphite protective film, comprising at least the following steps: A, providing a graphite substrate; B, performing a first-stage chemical vapor infiltration process, forming a buffer layer composed of a composite film of a ruthenium compound on the surface of the graphite substrate C, performing a second-stage chemical vapor deposition process, forming a plurality of inclined layers composed of a composite film of a ruthenium compound on the surface of the buffer layer: D, providing a protective film on the inclined layer of the plurality of layers to complete the finished product. The method for producing a graphite protective film according to claim 19, wherein the step A further comprises: a step A-1, a washing step, a step A-2, and a preheating step. The method for producing a graphite protective film according to claim 20, wherein the cleaning step is performed by polishing the graphite substrate on both sides with a sandpaper, and then placing the graphite substrate in acetone to oscillate with an ultrasonic oscillator. Removing graphite The impurities remaining in the substrate during processing. The method for producing a graphite protective film according to claim 20 or 21, wherein the preheating step is to put the cleaned graphite substrate into a reaction chamber, and when the reaction chamber is evacuated to 10 ^-5 torr or less, After preheating the graphite substrate at a temperature of 1000 ° C for 10 minutes, hydrogen gas was introduced thereto to cool for 15 minutes. The method for producing a graphite protective film according to claim 19, wherein the step B and the step C are carried out in a reaction chamber under a hydrogen atmosphere, and argon gas is used as a carrier gas to carry tetramethyl decane into the reaction chamber. And introducing ammonia gas (NH ₃ ) to form a composite film of tantalum carbide/tantalum nitride to form a buffer layer. The method for producing a graphite protective film according to claim 19, wherein the reaction temperature of the step C is greater than the reaction temperature of the step B. The method for producing a graphite protective film according to claim 24, wherein the reaction temperature of the step B is 700 to 1000 ° C, and the reaction temperature of the step C is raised from 1000 ° C to about 1200 ° C. The method for producing a graphite protective film according to claim 23, wherein the total reaction pressure in the step B and the step C is 10 torr. The method for producing a graphite protective film according to claim 23 or 26, wherein the partial pressure ratio of tetramethyl decane to ammonia in the step B and the step C may be 3. The method for producing a graphite protective film according to claim 23, wherein the reaction time in the step B is 50 to 60 minutes. The method for producing a graphite protective film according to claim 28, wherein the reaction time in the step B is preferably 55 minutes. The method for producing a graphite protective film according to claim 19, wherein The thickness of the plurality of inclined layers may be 2.5 to 2.85 μm. The method for producing a graphite protective film according to claim 30, wherein the thickness of the plurality of inclined layers is preferably 2.8 μm. The method for producing a graphite protective film according to claim 19, wherein the protective film has a thickness of 2.5 to 10 μm. The method for producing a graphite protective film according to claim 32, wherein the thickness of the protective film is preferably 5 μm. The method for producing a graphite protective film according to claim 19, wherein a thermal expansion coefficient of the buffer layer is close to a thermal expansion coefficient of the graphite substrate, and each inclined layer has a different thermal expansion coefficient, and the thermal expansion coefficient is close to the buffer layer. The coefficient of thermal expansion is increased to approximate the coefficient of thermal expansion of the protective film. The method for producing a graphite protective film according to claim 19, wherein each of the inclined layers has a different cerium carbide/cerium nitride ratio, and the cerium carbide/cerium nitride ratio may be 2.3 to 3.7, and the cerium carbide/nitriding The 矽 ratio is increased from the buffer layer toward the protective film. The method for producing a graphite protective film according to claim 19, wherein the graphite substrate is provided with a plurality of open pores, and the buffer layer penetrates into each of the open pores. A method for manufacturing a graphite protective film, comprising at least the following steps: A, providing a graphite substrate; B, performing a first-stage chemical vapor infiltration process, forming a buffer layer composed of a composite film of a ruthenium compound on the surface of the graphite substrate , the thermal expansion of the buffer layer The expansion coefficient is close to the thermal expansion coefficient of the graphite substrate; C. performing a second-stage chemical vapor deposition process, forming a plurality of inclined layers composed of a composite film of a ruthenium compound on the surface of the buffer layer, each inclined layer having a different thermal expansion coefficient, And the coefficient of thermal expansion is increased from a thermal expansion coefficient close to the buffer layer to a thermal expansion coefficient close to the protective film: D, a protective film is disposed on the plurality of inclined layers to complete the finished product. The method for producing a graphite protective film according to claim 37, wherein the step B and the step C are carried out in a reaction chamber under a hydrogen atmosphere with argon as a carrier gas to carry tetramethyl decane into the reaction chamber. And introducing ammonia gas (NH ₃ ) to form a composite film of tantalum carbide/tantalum nitride to form a buffer layer. The method for producing a graphite protective film according to claim 37 or 38, wherein the reaction temperature of the step C is greater than the reaction temperature of the step B. The method for producing a graphite protective film according to claim 37, wherein the reaction temperature of the step B is 700 to 1000 ° C, and the reaction temperature of the step C is raised from 1000 ° C to about 1200 ° C. The method for producing a graphite protective film according to claim 38, wherein the partial pressure ratio of tetramethyl decane to ammonia in the step B and the step C may be 3. A method for manufacturing a graphite protective film, comprising at least the following steps: A, providing a graphite substrate; B, performing a first-stage chemical vapor infiltration process, using tetramethyl decane, ammonia gas, hydrogen as a raw material gas for chemical gas a phase infiltration process, the surface of the graphite substrate forms a buffer layer composed of a composite film of tantalum carbide/tantalum nitride, The partial pressure ratio of the tetramethyl decane to the ammonia gas may be 3, the reaction temperature may be 700 to 1000 ° C, the reaction time may be 50 to 60 minutes; C, the second stage chemical vapor deposition process is performed, a chemical vapor deposition process is carried out by using methyl decane, ammonia gas and hydrogen as raw material gases, and a plurality of inclined layers composed of a ruthenium compound composite film are formed on the surface of the buffer layer, wherein the partial pressure ratio of the tetramethyl decane to the ammonia gas can be 3, the reaction temperature is raised from 1000 ° C to about 1200 ° C; D, a protective film is placed on the inclined layer of the multilayer to complete the finished product. The method for producing a graphite protective film according to claim 42, wherein the multilayer inclined layer has a thickness of 2.5 to 2.85 μm. The method for producing a graphite protective film according to claim 43, wherein the thickness of the plurality of inclined layers is preferably 2.8 μm. The method for producing a graphite protective film according to claim 42, wherein the protective film has a thickness of 2.5 to 10 μm. The method for producing a graphite protective film according to claim 45, wherein the thickness of the protective film is preferably 5 μm. The method for producing a graphite protective film according to claim 42, wherein the thermal expansion coefficient of the buffer layer is close to a thermal expansion coefficient of the graphite substrate, and each of the inclined layers has a different thermal expansion coefficient, and the thermal expansion coefficient is The coefficient of thermal expansion from the buffer layer is increased to approximate the coefficient of thermal expansion of the protective film. The method for producing a graphite protective film according to claim 42, wherein each of the inclined layers has a different ratio of niobium carbide to tantalum nitride, and the niobium carbide/tantalum nitride ratio may be 2.3 to 3.7, and the carbonization is performed.矽/nitride The ratio is increased from the buffer layer toward the protective film. The method for producing a graphite protective film according to claim 42, wherein the graphite substrate is provided with a plurality of open pores, and the buffer layer penetrates into each of the open pores.