Seed crystal bonding method for inhibiting back sublimation of SiC

Abstract

The invention provides a seed crystal bonding method for inhibiting back sublimation of SiC, and belongs to the technical field of silicon carbide crystal growth treatment. A laser annealing mode is adopted, laser is used as a heat source, after the laser passes through a transmission system, a laser beam with uniform energy distribution can be generated and is projected to the surface of the silicon carbide seed crystal, silicon carbide on the surface layer absorbs the energy of the laser to be melted and then decomposed into carbon and silicon, the melting point of the silicon is low, and the silicon escapes after being melted and gasified; and the left carbon can form a compact carbon film on the surface layer of the silicon carbide. The production cost is reduced, the production efficiency is improved, meanwhile, the problem of back sublimation during SiC growth is solved, and the success rate of seed crystal bonding and the SiC crystal quality are both improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of silicon carbide crystal growth processing, and particularly relates to a seed crystal bonding method for inhibiting SiC back sublimation. BACKGROUND

[0002] SiC material has characteristics of large band gap, high critical breakdown field, high electron mobility, high thermal conductivity and the like, and becomes an ideal material for manufacturing high-temperature, high-frequency, high-power, radiation-resistant, short-wave light-emitting and photoelectric integrated devices. The unique physical properties of SiC material determine its application in important fields such as artificial satellites, rockets, radars, communications, fighter jets, non-interference electronic ignition devices, jet engine sensors and the like. Therefore, developed countries have invested a large amount of manpower and resources in related technical research.

[0003] The patent CN101985773B and the patent CN118932481A adopt the method of coating the back surface of the seed crystal with an organic polymer containing a high amount of carbon, and forming a dense graphite film after high-temperature vacuum treatment to prevent back sublimation of the seed crystal. The patent CN118932481A adopts the method of a magnetron sputtering protective film to prevent back sublimation of the seed crystal, solve the problem of SiC growth back sublimation, and improve the success rate of seed crystal bonding and the quality of SiC crystal. At present, silicon carbide manufacturers all adopt the above-mentioned principle to form a dense C film on the back of the seed crystal to solve the problem of SiC growth back sublimation. However, the above-mentioned two solutions have the problems of complicated process, low production efficiency and difficulty in mass production. At the same time, the two solutions are sensitive to process environment such as treatment vacuum and temperature, and are prone to cause delamination and other defects, resulting in a decrease in the yield of crystal growth. SUMMARY

[0004] The technical problem to be solved by the present application is to provide a seed crystal bonding method for inhibiting SiC back sublimation in view of the above-mentioned deficiencies of the prior art.

[0005] In the laser ablation embodiment, after the silicon carbide absorbs laser energy, amorphous silicon and amorphous carbon are formed, and a black amorphous layer formed at the same time further promotes the absorption of laser energy, so that the surface layer of the silicon carbide is sublimated to form a carbon film. When the silicon carbide crystal is annealed at a temperature higher than 2000 DEG C, the double surface layers are sublimated to form a carbon film.

[0006] Based on this, the purpose of the present application is to use laser annealing as a heat source, and after the laser passes through the transmission system, a laser beam with uniform energy distribution is generated and projected on the surface of the silicon carbide seed crystal. The surface layer of silicon carbide absorbs the energy of the laser and melts and decomposes into carbon and silicon. The melting point of silicon is lower, and after melting and gasification, it escapes, and the remaining carbon forms a dense carbon film on the surface layer of silicon carbide. Not only does it reduce production costs and improve production efficiency, but it also solves the problem of SiC growth back sublimation, the success rate of seed crystal bonding, and the quality of SiC crystals is improved.

[0007] In order to achieve the above-mentioned purpose of the present application, the specific technical scheme adopted is as follows: S1. Pre-treatment of the seed crystal and graphite support; Specifically, the back surface of the seed crystal is mirror polished to reduce surface roughness and ensure uniform absorption of laser energy. The graphite support is cleaned, and high-purity graphite support is used. The surface is ultrasonically cleaned with ethanol or acetone to remove impurities and dust; S2. Parameter setting of the laser system; Specifically, S2.1. Establish a finite element model of laser annealing based on the two-temperature equation; S2.2. Define the critical anti-sublimation depth and optimize the average power and repetition frequency of the laser; S3. Laser-induced carbon film formation; Specifically, S3.1. Initial heating stage: the laser irradiates the back surface of the SiC seed crystal at a low energy density (0-5 J / cm 2 ), and the surface temperature rises above 1410℃ (the melting point of Si), and Si begins to melt.

[0008] S3.2. Melting and decomposition stage: gradually increase the energy density to (2-50 J / cm 2 ), the surface layer of SiC is completely melted, and a decomposition reaction occurs. Gaseous Si (boiling point 2355℃) sublimates and escapes due to high temperature, and the remaining carbon atoms gather on the surface; S3.3. Carbon film densification stage: maintain laser irradiation for 1-3 minutes, and carbon atoms recombine at high temperature to form a continuous and dense carbon film covering the entire back surface of the seed crystal.

[0009] S4. Seed crystal and graphite support bonding; Specifically, S4.1. Bond the seed crystal with the formed carbon film to the graphite support; S4.2. Place the bonded seed crystal on the graphite ring for growth.

[0010] Preferably, it further includes step S5. Process post-processing, specifically: S5.1. Detect the uniformity of the carbon film under a strong light lamp to ensure that there are no cracks or holes; S5.2 High temperature stability test is performed to verify the anti-sublimation performance of the carbon film in a simulated growth environment (e.g., 2000℃ / Ar).

[0011] Preferably, the electron temperature and the lattice temperature in step S2.1 satisfy:

[0012] , where T e is the electron temperature, T ｌ is the lattice temperature, K ｌ and C ｌ are the thermal conductivity and the heat capacity of the lattice, respectively, ▽ is the Hamiltonian operator, G is the electron-lattice coupling coefficient, S is the laser heat, and t is time.

[0013] Preferably, the laser parameters in step S2.2 are specifically: the wavelength is 800-1030 nm, the pulse energy is 0-50 J / cm 2 , the power is 10E10-10E14 W / cm 2 , the repetition frequency is 1-100 kHz, the pulse width is 10-500 fs, the pulse stability is -3- +3, the spatial uniformity is ≤3%, the overlap is 90%-99%, the pitch is 0-20 um, and the environment control is argon.

[0014] Compared with the prior art, the present application achieves the following technical effects: 1. Compared with the traditional magnetron sputtering protective film and the carbonized film formed by an adhesive in a high-temperature vacuum, the laser annealing scheme can improve the production effect and reduce the disadvantages of traditional carbonized protective film preparation.

[0015] 2. Reducing the cost of production materials, using the laser annealing scheme, directly decomposing on the substrate surface layer to form a dense carbonized film. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to facilitate the description, the present application is described in detail by the following specific embodiments and drawings.

[0017] Figure 1 is a flowchart of the process of forming a carbonized film on the surface of a substrate.

[0018] Figure 2 is a schematic diagram of overlap vs pitch.

[0019] Figure 3 is a schematic diagram of the seed crystal adhered to the graphite holder after carbonization.

[0020] Figure 4 is a schematic diagram of the adhered seed crystal placed on the graphite ring for growth.

[0021] Figure 5 This is a schematic diagram of the carbon film formed on the surface of the substrate after annealing.

[0022] Figure 6 This is a schematic diagram of the surface of a carbonized seed crystal under traditional processing. Detailed Implementation

[0023] The following are specific embodiments of the present invention, in conjunction with the appendix. Figures 1-5 The technical solutions of the present invention will be further described below, but the present invention is not limited to these embodiments; in the following description, specific details such as specific configurations are provided only to help to fully understand the embodiments of the present invention. Therefore, those skilled in the art should understand that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of the present invention.

[0024] It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined with each other.

[0025] Unless otherwise specified, the materials, practices, and experimental equipment involved in the embodiments of this invention are all commercially available products in the relevant chemical and biotechnology fields.

[0026] As shown in Figure 1, a seed crystal bonding method for suppressing SiC back sublimation includes the following steps: S1. Pretreatment of seed crystal and graphite support; Specifically, the back of the seed crystal is mirror-polished to reduce surface roughness and ensure uniform absorption of laser energy; the graphite support is cleaned using a high-purity graphite support, and the surface is ultrasonically cleaned with ethanol or acetone to remove impurities and dust. S2. Set the parameters for the laser system; Specific examples Figure 2 As shown in Figure S2.1, a finite element model for laser annealing is established based on the two-temperature equation. S2.2. Define the critical anti-sublimation depth and optimize the average power and repetition frequency of the laser; S3. Laser-induced carbon film formation; Specifically, S3.1. Initial heating stage: The laser uses a low energy density (0-5 J / cm²). 2 Irradiate the back of the SiC seed crystal to raise the surface temperature to above 1410℃ (the melting point of Si), and Si begins to melt.

[0027] S3.2. Melting and decomposition stage: Gradually increase the energy density to (2-50 J / cm³). 2 When the SiC surface layer completely melts and undergoes a decomposition reaction, the gaseous Si (boiling point 2355℃) sublimates and dissipates due to the high temperature, and the remaining carbon atoms accumulate on the surface. S3.3. Carbon film densification stage: maintain laser irradiation for 1-30s, carbon atoms recombine at high temperature to form a continuous dense carbon film covering the entire back of the seed crystal.

[0028] S4. Seed crystal and graphite support are bonded; Specifically as Figures 3-4 S4.1. Bond the carbon film forming seed crystal to the graphite support; S4.2. Place the bonded seed crystal on the graphite ring for growth.

[0029] Preferably, it also includes step S5. Post-process, specifically: S5.1. Detect carbon film uniformity under strong light lamp to ensure no cracks or holes; S5.2. Perform high temperature stability test to verify the anti-sublimation performance of the carbon film in a simulated growth environment (such as 2000℃ / Ar).

[0030] Preferably, the electron temperature and lattice temperature in step S2.1 satisfy:

[0031] ,

[0032] where T e is the electron temperature, T ｌ is the lattice temperature, K ｌ and C ｌ are the thermal conductivity and heat capacity of the lattice respectively, ▽ is the Hamiltonian operator, G is the electron-lattice coupling coefficient, S is the laser heat, and t is time.

[0033] Preferably, the laser parameters in step S2.2 are specifically: wavelength 800-1030 nm, pulse energy 0-50 J / cm 2 , power 10E10-10E14 W / cm 2 , repetition frequency 1-100 kHz, pulse width 10-500 fs, pulse stability -3- +3, spatial uniformity ≤3%, overlap 90%-99%, pitch 0-20um, and environment control is argon.

[0034] Example 1

[0035] Experimental conditions:

[0036] Laser parameters: wavelength 1030 nm, pulse energy 30 J / cm², power density 10¹² W / cm², repetition frequency 50 kHz, pulse width 100 fs, and environment is argon.

[0037] Carbon film formation stage: initial heating energy density 3 J / cm²(1410℃), melting and decomposition stage energy density 30 J / cm²(above 2355℃), densification time 15 s.

[0038] Step execution: mirror-polish the back of the seed crystal (Ra≤0.1 μm), and ultrasonically clean the graphite holder. Optimize the laser parameters through a finite element model to ensure that the critical anti-sublimation depth is ≤5 μm. After laser irradiation, a continuous carbon film (thickness about 2 μm) is formed on the back of the seed crystal. The carbon film is bonded to the graphite holder, and no cracks are observed in the carbon film after testing at 2000℃ / Ar environment, and the anti-sublimation performance is improved.

[0039] Example 2

[0040] Experimental conditions:

[0041] Laser parameters: wavelength 800 nm, pulse energy 10 J / cm², power density 10¹¹ W / cm², repetition frequency 10 kHz, pulse width 200 fs, carbon film densification time: 10 s.

[0042] Step execution: high-purity graphite holders (impurity content <50 ppm) are used, and the surface roughness of the polished seed crystal is Ra≤0.05 μm. Model calculations show that the electron-lattice temperature difference ΔT<100 K (coupling coefficient G=2×10 7 W / m³K). After the formation of the carbon film, the uniformity is >98% as detected by strong light. In high-temperature testing, the carbon film is stable at 2200℃ for 1 hour without SiC sublimation.

[0043] Example 3

[0044] Experimental conditions:

[0045] Laser parameters: pulse energy 50 J / cm², repetition frequency 100 kHz, pitch 10 μm, overlap 95%. Environmental control: argon flow 10 L / min, oxygen content <1 ppm.

[0046] Step execution: optimize the laser spatial uniformity (≤2%), to ensure that the carbon film thickness deviation is <±0.1 μm. Gradient energy (20→50 J / cm²) is used in the melting and decomposition stage to reduce thermal stress cracks. After bonding, the seed crystal is continuously worked in the growth furnace for 100 hours, and the back sublimation rate is reduced.

[0047] Those skilled in the art to which the present application pertains can make various modifications or supplements to the described specific embodiments or use similar ways to replace them, without departing from the inventive concept of the present application or exceeding the scope defined by the appended claims.

Claims

1. A seed crystal bonding method for suppressing SiC back sublimation, characterized in that, Includes the following steps: S1. Pretreatment of seed crystal and graphite support; S2. Set the parameters for the laser system; S3. Laser-induced carbon film formation; S4. Seed crystal bonded to graphite support.

2. The seed crystal bonding method for suppressing SiC back sublimation according to claim 1, characterized in that, Step S1 specifically involves: mirror polishing the back of the seed crystal to reduce surface roughness and ensure uniform absorption of laser energy; cleaning the graphite tray by using a high-purity graphite tray and ultrasonically cleaning the surface with ethanol or acetone to remove impurities and dust.

3. The seed crystal bonding method for suppressing SiC back sublimation according to claim 1, characterized in that, Step S2 specifically involves: S2.

1. Establish a finite element model for laser annealing based on the two-temperature equation; S2.

2. Define the critical anti-sublimation depth and optimize the average power and repetition frequency of the laser.

4. The seed crystal bonding method for suppressing SiC back sublimation according to claim 1, characterized in that, Step S3 specifically involves: S3.

1. Initial heating stage: The laser operates at a low energy density of 0-5 J / cm². 2 Irradiating the back of the SiC seed crystal raises the surface temperature to above 1410℃ (the melting point of Si), causing Si to begin to melt. S3.

2. Melting and decomposition stage: Gradually increase the energy density to (2-50 J / cm³). 2 When the SiC surface layer completely melts and undergoes a decomposition reaction, the gaseous Si (boiling point 2355℃) sublimates and dissipates due to the high temperature, and the remaining carbon atoms accumulate on the surface. S3.

3. Carbon film densification stage: Maintain laser irradiation for 1-3 minutes, and carbon atoms recombine at high temperature to form a continuous and dense carbon film that covers the entire back side of the seed crystal.

5. The seed crystal bonding method for suppressing SiC back sublimation according to claim 1, characterized in that, Step S4 specifically involves: S4.

1. Adhere the seed crystal that forms the carbon film to the graphite substrate; S4.

2. Place the bonded seed crystal on the graphite ring for growth.

6. The seed crystal bonding method for suppressing SiC back sublimation according to claim 1, characterized in that, It also includes step S5. Post-processing, specifically: S5.1 The uniformity of the carbon film is checked under a strong light to ensure that there are no cracks or holes; S5.2 conducts high-temperature stability tests to verify the sublimation resistance of the carbon film in a simulated growth environment (such as 2000℃ / Ar).

7. The seed crystal bonding method for suppressing SiC back sublimation according to claim 3, characterized in that, In step S2.1, the electron temperature and lattice temperature satisfy the following: ， Among them, T e For electron temperature, T ｌ K represents the lattice temperature. ｌ and C ｌ ∠F represents the thermal conductivity and heat capacity of the crystal lattice, ∠H is the Hamiltonian operator, G is the electron-lattice coupling coefficient, S is the laser heat, and t is time.

8. The seed crystal bonding method for suppressing SiC back sublimation according to claim 3, characterized in that, The laser parameters in step S2.2 are specifically: wavelength of 800-1030nm, pulse energy of 0-50J / cm. 2 The power is 10E10-10E14W / cm² 2 The repetition frequency is 1-100kHz, the pulse width is 10-500fs, the pulse stability is -3-+3, the spatial uniformity is ≤3%, the overlap is 90%-99%, the pitch is 0-20um, and the environment is controlled by argon.

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