Silicon carbide seed crystal pretreatment method, product and application

Abstract

The invention belongs to the field of silicon carbide single crystal materials, and particularly discloses a silicon carbide seed crystal pretreatment method, a product and application, the silicon carbide seed crystal pretreatment method comprises the following steps: S1, cleaning a silicon surface of a silicon carbide seed crystal, and S2, preparing a composite unit layer, specifically, coating a positive photoresist on the clean silicon surface obtained in the step S1, performing drying to obtain a positive photoresist layer, and then performing drying on the positive photoresist layer to obtain the silicon carbide seed crystal. The method comprises the following steps: S1, preparing a positive photoresist layer on the seed crystal, preparing a graphite coating on the positive photoresist layer, and forming a composite unit layer formed by laminating the positive photoresist and the graphite layer, S4, heating the seed crystal with the composite unit layer formed on the silicon surface, so that the composite unit layer is completely cured and densified, and a prefabricated seed crystal is obtained, and S5, cleaning the carbon surface of the prefabricated seed crystal, and completing pretreatment. The invention also provides the silicon carbide seed crystal pretreated according to the method and a method for growing silicon carbide by adopting the pretreated seed crystal. The method effectively solves the stress problem caused by seed crystal bonding, and can be used for replacing a traditional seed crystal bonding process.

Description

Technical Field

[0001] The present invention belongs to the field of silicon carbide single crystal materials, and more specifically, relates to a pretreatment method and application of a silicon carbide seed crystal. Background Art

[0002] In recent years, silicon carbide has shown great application potential due to its wide bandgap, high breakdown field strength, high thermal conductivity and many other characteristics. In particular, with the application of silicon carbide devices in the field of electric vehicles, the silicon carbide industry has received widespread attention from all walks of life.

[0003] There are many methods for growing silicon carbide single crystals, such as liquid phase method, PVT method, HTCVD method, etc., but the only method that can be used commercially to produce silicon carbide single crystals is physical vapor transport method, that is, PVT method. PVT method (English: Physical Vapor Transport) is a commonly used crystal growth method, mainly used to prepare high-quality crystal materials. This method vaporizes the material at high temperature, and then condenses and sublimates on the substrate through the transport process to form crystals. The PVT method can quickly grow high-quality crystals in a high-temperature environment, and can grow large-sized crystals. Specifically, in the PVT method, silicon carbide raw materials are placed at the bottom of the crucible, and silicon carbide seed crystals are placed on the top. Through the design of the insulation structure, the crucible has a certain axial and radial temperature gradient. The crucible is heated to 2000℃~2400℃ by heating, so that the silicon carbide raw materials evaporate and sublimate to form a gas phase. Under the action of the temperature gradient, the gas phase is transported from the bottom of the crucible to the seed crystal for crystallization, thereby growing a silicon carbide single crystal.

[0004] During the growth process, the silicon carbide seed crystal is usually fixed to the graphite tray at the top of the crucible by bonding. However, due to the difference in thermal expansion coefficients between silicon carbide single crystals and graphite, shear stress parallel to the bonding surface will be generated at high temperatures, resulting in a large number of defects caused by stress, and even causing the ingot to crack. In order to alleviate the stress caused by bonding, the industry has gradually developed a bonding method that inserts a layer of soft graphite paper between the seed crystal and the graphite tray. This not only reduces the difficulty of removing the seed crystal from the graphite tray after the growth is completed, but the soft medium also plays a certain buffering role in the shear stress between the silicon carbide seed crystal and the graphite tray.

[0005] However, although the insertion of graphite paper has played a certain positive role in the bonding of silicon carbide seed crystals, with the development of the industry, especially the lower-level epitaxial plants' requirements for seed crystal stress levels and defect quality have increased, higher requirements have been placed on the seed crystal bonding process.

[0006] Therefore, a new seed crystal pretreatment method or fixing method is urgently needed to replace seed crystal bonding, so as to solve or reduce the shear stress problem caused by bonding. Summary of the invention

[0007] In view of the defects of the prior art, the purpose of the present invention is to provide a pretreatment method, product and application of a silicon carbide seed crystal, aiming to solve the problem that the back of the traditional silicon carbide seed crystal is easily sublimated or ablated, and at the same time solve the stress problem caused by the traditional seed crystal bonding process.

[0008] To achieve the above object, according to one aspect of the present invention, a method for pretreating a silicon carbide seed crystal is provided, which comprises the following steps:

[0009] S1: Clean the silicon surface of the silicon carbide seed crystal,

[0010] S2: preparing a composite unit layer, specifically, first coating a positive photoresist on the clean silicon surface obtained in step S1, performing drying to obtain a positive photoresist layer, then preparing a graphite coating on the positive photoresist layer, performing drying to form a composite unit layer formed by stacking a positive photoresist and a graphite layer,

[0011] S4: heating the seed crystal with the composite unit layer formed on the silicon surface to completely solidify and densify the composite unit layer to obtain a prefabricated seed crystal.

[0012] S5: Clean the carbon surface of the prefabricated seed crystal to complete the pretreatment.

[0013] In the above invention concept, a composite layer of a positive photoresist layer and a graphite layer is prepared on the silicon surface of the silicon carbide seed crystal. The preparation of the composite layer is equivalent to pre-treating the silicon surface of the silicon carbide seed crystal. When the silicon carbide seed crystal is used for crystal growth, the composite unit layer can be converted into graphite, which can well protect the back of the seed crystal. At the same time, this method can replace the seed crystal bonding, and there is no need to bond the seed crystal to the graphite holder, thereby avoiding the shear stress caused by the seed crystal bonding to the graphite holder. The above pre-treatment method is relatively easy to operate and has good operability.

[0014] Furthermore, it also includes step S3, which is to repeat step S2 at least twice to prepare at least two composite unit layers on the silicon surface of the silicon carbide seed crystal, including at least a first composite unit layer attached to the silicon surface and a second composite unit layer stacked on the first composite unit layer. In actual engineering practice, multiple composite layers can be prepared as needed. When the number of composite layers is small, the protective effect of the coating on the seed crystal is reduced, and problems such as sublimation and ablation of the seed crystal are prone to occur; when the number of composite layers is large, the thickness of the sprayed graphite coating is prone to unevenness, and the uniformity of thermal conductivity on the back of the seed crystal will decrease. When preparing multiple composite unit layers, a drying process needs to be performed after each layer of positive photoresist or graphite coating is applied.

[0015] Further, in step S2, the viscosity of the positive photoresist is 1mpa·s to 200mpa·s, and the thickness of the positive photoresist layer is 2μm to 10μm. When the viscosity of the positive photoresist is higher than the above range, it is too viscous and there is a risk of difficulty in coating evenly. The thickness of the positive photoresist layer is limited to 2μm to 10μm. When its thickness is too thin, it is difficult to coat, the film layer is not dense, and vacancies will be generated when it is converted into a graphite film layer at high temperature.

[0016] Further, in step S2, the positive photoresist is heated to a temperature of 50 to 100°C and coated on the silicon surface of the rotating silicon carbide seed crystal, the rotation speed is 2000 to 10000 r / min, and the temperature for drying is 60 to 120°C. After the positive photoresist is heated, its fluidity is better, which is more conducive to the development of the coating process, and it is easy to obtain a photoresist layer with uniform thickness. The rotation speed is limited to 2000 to 10000 r / min. The specific rotation speed is related to the viscosity of the positive photoresist. When the viscosity is large, a higher rotation speed tends to be selected. The drying temperature is limited to 60 to 120°C. If the temperature is too high, it is easy to cause bubbling of the film layer due to too fast evaporation of the solvent.

[0017] Further, in step S2, a graphite spray is sprayed on the positive photoresist layer to prepare a graphite coating, the graphite powder particle size in the graphite spray is 5000 mesh or more, and the temperature of the positive photoresist layer is maintained at 60° C. to 120° C. The graphite powder particle size in the graphite spray is limited to 5000 mesh or more, and the graphite powder particle size is smaller, so it is easier to spray into a fine and uniform graphite coating. The graphite coating is thinner, and the temperature when it falls on the positive photoresist layer can reach 60° C. to 120° C., which is conducive to its rapid film formation.

[0018] Furthermore, in step S2, the graphite spray is sprayed until the first composite unit layer is opaque, which means the spraying is qualified. Opaqueness indicates that the graphite layer is at least evenly spread.

[0019] Furthermore, in step S4, the prefabricated seed crystal obtained in step S3 is heated at a temperature of 120° C. to 200° C. for a duration of 5 min to 30 min. After the prefabricated seed crystal is heated, the bonding and curing of the positive photoresist and the graphite layer can be promoted.

[0020] According to a second aspect of the present invention, there is also provided a pretreated silicon carbide seed crystal prepared by any of the above methods.

[0021] According to a third aspect of the present invention, there is also provided a method for preparing silicon carbide by using the pretreated silicon carbide seed crystal as described above.

[0022] First, the pre-treated silicon carbide seed crystal is directly overlapped or clamped on the graphite part, and the silicon carbide raw material is heated to prepare for crystal growth.

[0023] Next, using a heated high temperature environment, the conformal photoresist layer in the composite unit layer is naturally carbonized in situ into a dense carbon film accompanied by high temperature. The dense carbon film can be used to protect the back of the seed crystal and fill the gaps in the graphite in the first composite unit layer to improve the density of the first unit layer.

[0024] Finally, after the crystal growth is completed, it is directly removed from the overlapping or clamping position.

[0025] Furthermore, the conformal photoresist in the next composite unit layer is filled into the gaps in the graphite layer of the previous composite unit layer to improve the thermal conductivity, thereby making the temperature on the back of the seed crystal uniform. The more uniform the temperature, the less likely it is to sublime and the smaller the stress.

[0026] In general, the above technical solution conceived by the present invention has the following technical advantages compared with the prior art:

[0027] 1. In the method of the present invention, a composite unit layer is prepared on the silicon surface of the silicon carbide seed crystal, and the composite unit layer is formed by stacking a conformal photoresist and a graphite layer. By prefabricating a graphite coating on the back of the silicon carbide seed crystal, it can be used to protect the seed crystal from being sublimated or ablated during the growth process. At the same time, it is convenient to directly overlap or clamp the seed crystal on the graphite part for crystal growth, which effectively solves the stress problem caused by the seed crystal bonding and can be used to replace the traditional seed crystal bonding process.

[0028] 2. The pretreatment method of silicon carbide seed crystal provided by the present invention is simple to operate, does not require expensive equipment and complicated processes, and only requires spin coating. The process cost is low and the process fault tolerance is strong. If there is unqualified coating, the number of coatings can be increased. Since it can be coated multiple times, the yield rate is more controllable and the qualified rate is high, which is very suitable for mass production.

[0029] 3. When using the pretreated seed crystal of the present invention to prepare silicon carbide, the pretreated silicon carbide seed crystal is directly overlapped or clamped on the graphite part, and the silicon carbide raw material is heated to prepare for crystal growth. First, the composite unit layer is in-situ carbonized into a dense carbon film, combined with the natural growth of the crystal. After the growth of the silicon carbide crystal is completed, it is directly removed from the overlapped or clamped position without the need for seed crystal bonding, which simplifies the process and solves the stress problem caused by seed crystal bonding. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a flow chart of a method for pretreating a silicon carbide seed crystal in an embodiment of the present invention;

[0031] Figure 2 is a photograph of the back coating of the silicon carbide seed crystal in an embodiment of the present invention;

[0032] Figure 3This is a photo of the back of the silicon carbide seed crystal prepared in the embodiment of the present invention after being used for silicon carbide crystal growth. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0034] In the description of the present invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0035] In addition, throughout this specification, "one embodiment", "one example" or similar language indicates that a particular feature, structure or characteristic described in conjunction with the embodiment is included in at least one embodiment of the present invention. Therefore, the phrase "in one embodiment" and similar language may, but do not necessarily, refer to the same embodiment.

[0036] The present invention provides a pretreatment method and application of silicon carbide seed crystals, wherein a composite coating formed by a graphite layer and a positive photoresist layer is prefabricated on the back of the silicon carbide seed crystal to protect the seed crystal from being sublimated or ablated during the growth process, and at the same time, the seed crystal is directly overlapped or clamped on the graphite piece for crystal growth. The positive photoresist has a complex composition and can form a continuous, dense and smooth film with the composite graphite layer at high temperature.

[0037] The components of positive photoresist mainly include photodecomposers, alkaline soluble resins, solvents, photosensitizers and dispersants. The photodecomposers in positive photoresists are usually diazo compounds, such as diazophthalic acid esters and linear phenolic acid esters, which play a key role in the exposure process and change the solubility of the material through photochemical reactions. Alkaline soluble resins are mainly composed of linear phenolic resins, which provide the adhesion and chemical resistance of photoresists. In the unexposed state, the resin has a certain solubility in the developer; after exposure, due to the effect of the photosensitive agent, the solubility of the resin will change, which is convenient for selective removal during the development process. Solvents are used to dilute and adjust the viscosity of the photoresist to facilitate the coating and development process. The photosensitizer is usually a photosensitive compound, such as diazonaphthoquinone (DNQ), which exists as a dissolution inhibitor before exposure to reduce the dissolution rate of the resin; after exposure, the photosensitizer chemically decomposes and becomes a solubility enhancer, greatly increasing the solubility factor in the developer. Dispersants are used to adjust the uniformity and stability of photoresists to ensure that no precipitation or agglomeration occurs during the coating process. Given its excellent film-forming properties and high carbon residue rate, it is very suitable as a seed crystal back film to protect the seed crystal from back sublimation or ablation.

[0038] In order to explain the method of the present invention in more detail, it is further explained in detail below in conjunction with specific embodiments.

[0039] Figure 1 : is a flow chart of a pretreatment method of a silicon carbide seed crystal in an embodiment of the present invention. As can be seen from the figure, this embodiment is used to prepare a two-layer composite unit layer, which mainly includes the following steps:

[0040] Step 1: Clean the silicon surface of the silicon carbide seed crystal.

[0041] Step 2: coating a positive photoresist on the clean silicon surface obtained in step S1, and performing drying to obtain a first positive photoresist layer.

[0042] Step 3: Prepare a first layer of graphite coating on the first positive photoresist layer, perform drying, and form a first composite unit layer consisting of a stack of positive photoresist and graphite layers.

[0043] Step 4: Apply positive photoresist again on the first graphite coating layer and perform drying to obtain a second positive photoresist layer.

[0044] Step 5: Spray a second layer of graphite coating on the second positive photoresist layer, and perform drying to form a second composite unit layer consisting of a positive photoresist and a graphite layer.

[0045] Finally, the seed crystal with two composite unit layers formed on the silicon surface is heated to completely solidify and densify the composite unit layers to obtain a prefabricated seed crystal. The carbon surface of the prefabricated seed crystal is cleaned and pretreatment is completed, and it can be sealed and packaged for use.

[0046] Example 1

[0047] The specific embodiments are as follows:

[0048] (1) Place the seed crystal silicon surface upward on a glue machine and clean the surface of the seed crystal with electronic grade isopropyl alcohol;

[0049] (2) Selecting a commercially available DOW SPR 220-4.5 UV positive photoresist, heating it to 80° C., dripping it onto the surface of the seed crystal, and spin coating it at 4000 r / min to form a film; the viscosity of the positive photoresist is 200 mPa·s, and the thickness of the positive photoresist layer is 4 μm to 7 μm;

[0050] (3) drying the seed crystal of the spin-coated adhesive film at 80°C, and then placing it on a heating table and heating it to 120°C and maintaining it;

[0051] (4) using commercially available Contai Graphit 33 as a graphite spray with a particle size of 5000 mesh, spraying it repeatedly on the surface of the seed crystal 8 times, each time for 5 seconds, and visually inspecting that there is no light leakage point. When the graphite spray falls on the positive photoresist layer, the temperature of the positive photoresist layer is maintained at 120°C;

[0052] (5) placing the seed crystal on which the first layer of graphite coating has been sprayed in step (4) back into the coating machine, and using the photoresist heated to 80° C. in step (2) to spin-coat the graphite coating to form a film, and then heating and drying at 80° C.;

[0053] (6) placing the seed crystal heated and dried in step (5) on a heating table, heating it to 120° C. and maintaining it, repeating the operation of step (4) to spray a second layer of graphite coating;

[0054] (7) heating the seed crystal on which the second graphite coating is sprayed in step (6) to 160° C. and maintaining the temperature for 20 min to allow each layer of the film to completely dry and form a continuous and dense graphite coating on the back of the seed crystal;

[0055] (8) Remove the seed crystal that has been dried in step (7), clean the carbon surface of the seed crystal with isopropyl alcohol, and then vacuum package it.

[0056] Figure 2 This is a photograph of the back coating of the silicon carbide seed crystal in an embodiment of the present invention. As can be seen from the figure, the coating is smooth, delicate, and the color is relatively uniform.

[0057] Example 2

[0058] This embodiment includes the following steps:

[0059] S1: Use electronic grade isopropyl alcohol to clean the silicon surface of the silicon carbide seed crystal.

[0060] S2: Prepare a composite unit layer, specifically, first coat a positive photoresist on the clean silicon surface obtained in step S1, perform drying, obtain a positive photoresist layer, and then prepare a graphite coating on the positive photoresist layer to form a composite unit layer composed of a positive photoresist and a graphite layer. The viscosity of the positive photoresist is 1 MPa·s. The positive photoresist is heated to a temperature of 50°C and coated on the silicon surface of a rotating silicon carbide seed crystal at a rotation speed of 2000 r / min. The drying temperature is 60°C, and the thickness of the positive photoresist layer is 2μm to 5μm.

[0061] The graphite spray is sprayed on the positive photoresist layer to prepare a graphite coating, wherein the particle size of the graphite powder in the graphite spray is above 5000 meshes, and the temperature of the positive photoresist layer is maintained at 60° C. when the graphite spray falls on the positive photoresist layer.

[0062] Spraying the graphite spray until the first composite unit layer is opaque is considered qualified.

[0063] S3: coating the positive photoresist on the first graphite coating layer again, performing drying to obtain a second positive photoresist layer, spraying a second graphite coating layer on the second positive photoresist layer, performing drying to form a second composite unit layer formed by stacking the positive photoresist and the graphite layer, wherein the process parameters for preparing the second positive photoresist layer and the second graphite coating layer are the same as those in step S2.

[0064] S4: heating the seed crystal with the composite unit layer formed on the silicon surface to completely solidify and densify the composite unit layer to obtain a prefabricated seed crystal. The prefabricated seed crystal obtained in step S3 is heated at a temperature of 120° C. for 30 minutes.

[0065] S5: Clean the carbon surface of the prefabricated seed crystal to complete the pretreatment.

[0066] Example 3

[0067] S1: Use electronic grade isopropyl alcohol to clean the silicon surface of the silicon carbide seed crystal.

[0068] S2: preparing a composite unit layer, specifically, first coating a positive photoresist on the clean silicon surface obtained in step S1, performing drying to obtain a positive photoresist layer, and then preparing a graphite coating on the positive photoresist layer to form a composite unit layer formed by laminating a positive photoresist and a graphite layer, wherein the viscosity of the positive photoresist is 100 mPa·s, and the thickness of the positive photoresist layer is 3 μm to 8 μm. When the positive photoresist is heated to a temperature of 100° C., it is coated on the silicon surface of a rotating silicon carbide seed crystal, the rotation speed is 10,000 r / min, and the drying temperature is 120° C.

[0069] The graphite spray is sprayed on the positive photoresist layer to prepare a graphite coating, the particle size of the graphite powder in the graphite spray is above 5000 meshes, and the temperature of the positive photoresist layer is maintained at 120° C. when the graphite spray falls on the positive photoresist layer.

[0070] Spraying the graphite spray until the first composite unit layer is opaque is considered qualified.

[0071] S4: heating the seed crystal with the composite unit layer formed on the silicon surface to completely solidify and densify the composite unit layer to obtain a prefabricated seed crystal. The prefabricated seed crystal obtained in step S3 is heated at a temperature of 200° C. for a duration of 5 minutes.

[0072] S5: Clean the carbon surface of the prefabricated seed crystal to complete the pretreatment.

[0073] Example 4

[0074] S1: Use electronic grade isopropyl alcohol to clean the silicon surface of the silicon carbide seed crystal.

[0075] S2: preparing a composite unit layer, specifically, first coating a positive photoresist on the clean silicon surface obtained in step S1, performing drying to obtain a positive photoresist layer, and then preparing a graphite coating on the positive photoresist layer to form a composite unit layer formed by laminating a positive photoresist and a graphite layer, wherein the viscosity of the positive photoresist is 150 mPa·s, and the thickness of the positive photoresist layer is 6 μm to 10 μm. The positive photoresist is heated to a temperature of 75°C and then coated on the silicon surface of a rotating silicon carbide seed crystal, the rotation speed is 8000 r / min, and the drying temperature is 100°C.

[0076] The graphite spray is sprayed on the positive photoresist layer to prepare a graphite coating, wherein the particle size of the graphite powder in the graphite spray is above 5000 meshes, and the temperature of the positive photoresist layer is maintained at 100° C. when the graphite spray falls on the positive photoresist layer.

[0077] Spraying the graphite spray until the first composite unit layer is opaque is considered qualified.

[0078] S3: coating the positive photoresist on the first graphite coating layer again, performing drying to obtain a second positive photoresist layer, spraying a second graphite coating layer on the second positive photoresist layer, performing drying to form a second composite unit layer formed by stacking the positive photoresist and the graphite layer, wherein the process parameters for preparing the second positive photoresist layer and the second graphite coating layer are the same as those in step S2.

[0079] S4: heating the seed crystal with the composite unit layer formed on the silicon surface to completely solidify and densify the composite unit layer to obtain a prefabricated seed crystal. The prefabricated seed crystal obtained in step S3 is heated at a temperature of 150° C. for a duration of 10 minutes.

[0080] S5: Clean the carbon surface of the prefabricated seed crystal to complete the pretreatment.

[0081] Example 5

[0082] S1: Use electronic grade isopropyl alcohol to clean the silicon surface of the silicon carbide seed crystal.

[0083] S2: preparing a composite unit layer, specifically, first coating a positive photoresist on the clean silicon surface obtained in step S1, performing drying to obtain a positive photoresist layer, and then preparing a graphite coating on the positive photoresist layer to form a composite unit layer formed by laminating a positive photoresist and a graphite layer, wherein the viscosity of the positive photoresist is 80 mPa·s, and the thickness of the positive photoresist layer is 2 μm to 7 μm. When the positive photoresist is heated to a temperature of 60°C, it is coated on the silicon surface of a rotating silicon carbide seed crystal, the rotation speed is 5000 r / min, and the drying temperature is 90°C.

[0084] The graphite spray is sprayed on the positive photoresist layer to prepare a graphite coating, wherein the particle size of the graphite powder in the graphite spray is above 5000 meshes, and the temperature of the positive photoresist layer is maintained at 90° C. when the graphite spray falls on the positive photoresist layer.

[0085] Spraying the graphite spray until the first composite unit layer is opaque is considered qualified.

[0086] S3: coating the positive photoresist on the first graphite coating layer again, performing drying to obtain a second positive photoresist layer, spraying a second graphite coating layer on the second positive photoresist layer, performing drying to form a second composite unit layer formed by stacking the positive photoresist and the graphite layer, wherein the process parameters for preparing the second positive photoresist layer and the second graphite coating layer are the same as those in step S2.

[0087] S4: heating the seed crystal with the composite unit layer formed on the silicon surface to completely solidify and densify the composite unit layer to obtain a prefabricated seed crystal. The prefabricated seed crystal obtained in step S3 is heated at a temperature of 130° C. for a duration of 25 min.

[0088] S5: Clean the carbon surface of the prefabricated seed crystal to complete the pretreatment.

[0089] Example 6

[0090] This embodiment uses the above-mentioned pretreatment of silicon carbide seed crystals to prepare silicon carbide, which includes the following steps:

[0091] First, a 6-inch diameter pre-treated silicon carbide seed crystal is directly clamped on the graphite piece, and the silicon carbide raw material is heated to prepare for crystal growth. The growth temperature is 2170°C, the growth pressure is 10mbar, and the growth time is 120h.

[0092] During the heating process, the conformal photoresist layer in the composite unit layer is naturally carbonized into a dense carbon film in situ at high temperature, thereby protecting the back of the seed crystal from sublimation and ablation.

[0093] Finally, after the crystal growth is completed, the silicon carbide seed crystal and the grown crystal are directly removed from the clamping position.

[0094] Figure 3 This is a photograph of the back of the silicon carbide seed crystal prepared in an embodiment of the present invention after being used for silicon carbide crystal growth. As can be seen from the figure, the graphite coating on the back of the seed crystal prepared by this method can well protect the back of the seed crystal during the growth of silicon carbide crystals. Even after being tested in a high-temperature environment for more than one hundred hours, problems such as sublimation and ablation of the seed crystal do not occur.

[0095] It will be easily understood by those skilled in the art that 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 and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for pretreating silicon carbide seed crystals, characterized in that: It includes the following steps: S1: Clean the silicon surface of the silicon carbide seed crystal, S2: preparing a composite unit layer, specifically, first coating a positive photoresist on the clean silicon surface obtained in step S1, performing drying to obtain a positive photoresist layer, and then preparing a graphite coating on the positive photoresist layer to form a composite unit layer composed of a positive photoresist and a graphite layer stacked together, S4: heating the seed crystal with the composite unit layer formed on the silicon surface to completely solidify and densify the composite unit layer to obtain a prefabricated seed crystal. S5: Clean the carbon surface of the prefabricated seed crystal to complete the pretreatment.

2. The method for pretreating silicon carbide seed crystals according to claim 1, characterized in that: It also includes step S3, which is to repeat step S2 at least twice to prepare at least two composite unit layers on the silicon surface of the silicon carbide seed crystal, including at least a first composite unit layer attached to the silicon surface and a second composite unit layer stacked on the first composite unit layer.

3. The method for pretreating silicon carbide seed crystal according to claim 1, characterized in that: In step S2, the viscosity of the positive photoresist is 1 mPa·s to 200 mPa·s, and the thickness of the positive photoresist layer is 2 μm to 10 μm.

4. The method for pretreating silicon carbide seed crystals according to claim 3, characterized in that: In step S2, the positive photoresist is heated to a temperature of 50-100°C and then coated onto the silicon surface of the rotating silicon carbide seed crystal at a rotation speed of 2000-10000 r / min and a drying temperature of 60-120°C.

5. The method for pretreating silicon carbide seed crystals according to claim 4, characterized in that: In step S2, a graphite spray is sprayed on the positive photoresist layer to prepare a graphite coating, wherein the particle size of the graphite powder in the graphite spray is above 5000 meshes, and the temperature of the positive photoresist layer is maintained at 60°C to 120°C when the graphite spray falls on the positive photoresist layer.

6. The method for pretreating silicon carbide seed crystals according to claim 5, characterized in that: In step S2, the graphite spray is sprayed until the first composite unit layer is opaque and the spraying is qualified.

7. The method for pretreating silicon carbide seed crystal according to any one of claims 1 to 6, characterized in that: In step S4, the prefabricated seed crystal obtained in step S3 is heated at a temperature of 120° C. to 200° C. for a duration of 5 min to 30 min.

8. The pretreated silicon carbide seed crystal prepared by the method according to any one of claims 1 to 7.

9. A method for preparing silicon carbide by pretreating silicon carbide seed crystals as claimed in claim 8, characterized in that: First, the pre-treated silicon carbide seed crystal is directly overlapped or clamped on the graphite part, and the silicon carbide raw material is heated to prepare for crystal growth. Then, using the high temperature environment, the conformal photoresist layer in the composite unit layer is naturally carbonized into a dense carbon film in situ with high temperature, and then crystal growth occurs. Finally, after the crystal growth is completed, the silicon carbide seed crystal and the grown crystal are directly removed from the overlapping or clamping position.

10. The method according to claim 9, characterized in that In step S3, the conformal photoresist in the next composite unit layer is filled into the gaps in the graphite layer of the previous composite unit layer to improve the thermal conductivity and further to make the temperature on the back of the seed crystal uniform.

Images