Silicon-containing large-size aluminum nitride seed crystal and preparation method thereof

Abstract

The invention relates to the technical field of aluminum nitride seed crystals, and particularly discloses a silicon-containing large-size aluminum nitride seed crystal and a preparation method thereof. The silicon-containing large-size aluminum nitride seed crystal sequentially comprises a c-axis oriented aluminum nitride polycrystalline layer, a silicon carbide seed crystal layer and an aluminum nitride seed crystal layer from bottom to top. The aluminum nitride polycrystalline with c-axis orientation serves as the substrate, the stress problem caused by lattice mismatch and thermal mismatch of dissimilar materials is solved, due to the fact that the difference of thermal expansion coefficients of aluminum nitride in the c-axis direction and the a-axis direction is large, large stress can be introduced into any area with the inconsistent orientation, the aluminum nitride polycrystalline has c-axis orientation, and the stress performance of the aluminum nitride polycrystalline is greatly improved. And the stress problem caused by inconsistent orientation of the homologous material can be solved. The silicon-containing large-size aluminum nitride seed crystal is high in crystal quality, large in size, small in impurity content, small in crystal internal stress and not prone to cracking, the size of the silicon-containing large-size aluminum nitride seed crystal can closely follow the development pace of a silicon carbide material, and the inherent problem of low diameter expanding efficiency in follow-up aluminum nitride single crystal growth is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum nitride seed crystals, and particularly to a silicon-containing large-size aluminum nitride seed crystal and a preparation method thereof. Background Art

[0002] The physical vapor transport (PVT) method is currently the main method for preparing large-size aluminum nitride single crystals. The most commonly used and efficient method is: using a large-size silicon carbide as a seed crystal, directly obtaining a large-size aluminum nitride single crystal on its surface through heteroepitaxial growth, then obtaining a large-size aluminum nitride seed crystal through cutting, grinding, polishing, etc., and then further preparing a higher-quality aluminum nitride single crystal through the PVT method. This process method realizes the heteroepitaxial growth of aluminum nitride single crystals on silicon carbide seeds, expanding the size of aluminum nitride seeds to 8 inches.

[0003] However, the existing method for preparing large-size aluminum nitride seeds using silicon carbide seeds has problems such as high crystal impurity content, poor uniformity of seed crystal crystallization quality, poor repeatability of the heteroepitaxial growth process, easy cracking of the crystal, and high operation and maintenance costs of the growth equipment. Silicon carbide seeds are composed of carbon and silicon elements, so it is inevitable that the grown aluminum nitride single crystals have high concentrations of carbon and silicon impurities; since silicon carbide is more volatile than aluminum nitride, high-temperature thermal ablation occurs on the surface of silicon carbide seeds during the heating stage of the high-temperature furnace, and due to the influence of internal defects of the silicon carbide seeds themselves, the degree of thermal ablation on the surface of silicon carbide seeds usually varies greatly, which results in poor uniformity of the crystallization quality of the prepared aluminum nitride single crystals, and the repeatability of the process usually also fails to meet the requirements of subsequent aluminum nitride crystal growth for aluminum nitride seeds; compared with silicon carbide, aluminum nitride has a larger coefficient of thermal expansion. When the growth of the aluminum nitride single crystal is completed and the crystal cools from the high-temperature growth stage to room temperature, the aluminum nitride single crystal will be subjected to tensile stress applied by the silicon carbide seed crystal, making the heteroepitaxially grown aluminum nitride single crystal extremely prone to cracking; the carbon and silicon components volatilized from the silicon carbide seed crystal at high temperature will corrode the vast majority of metal high-temperature systems. Therefore, when using silicon carbide as a seed crystal to grow aluminum nitride single crystals, a graphite high-temperature furnace with a graphite insulation structure must be used. However, the graphite insulation structure is prone to reacting with nitrogen elements at high temperatures, thereby shortening the service life of the graphite insulation structure and significantly increasing the operation and maintenance costs of the graphite high-temperature furnace. Summary of the Invention

[0004] Aiming at problems such as high crystal impurity content, poor uniformity of seed crystal crystallization quality, and easy cracking of crystals, the present invention provides a silicon-containing large-sized aluminum nitride seed crystal and a preparation method thereof. By using c-axis oriented aluminum nitride polycrystal as a substrate, the problem of crystal cracking caused by the difference in thermal expansion coefficients between silicon carbide and aluminum nitride is effectively solved. By controlling the thickness of the silicon carbide seed crystal layer, the impurity content is reduced, the crystallization quality of the silicon carbide seed crystal is improved, and aluminum nitride is orderly arranged on the surface of the silicon carbide seed crystal, obtaining a high-quality aluminum nitride seed crystal.

[0005] To solve the above technical problems, the technical solution provided by the present invention is as follows: In the first aspect, the present invention provides a silicon-containing large-sized aluminum nitride seed crystal, which sequentially includes an aluminum nitride polycrystal layer with c-axis orientation, a silicon carbide seed crystal layer, and an aluminum nitride seed crystal layer from bottom to top; the thickness of the silicon carbide seed crystal layer is 2 μm to 5 μm.

[0006] Due to the lattice mismatch and thermal mismatch between silicon carbide and aluminum nitride, the internal stress is very large when growing aluminum nitride on the surface of silicon carbide. After the crystal growth is completed, the cooling will cause different shrinkage degrees of the two materials. At this time, the grown aluminum nitride is very easy to crack. Compared with the prior art, the silicon-containing large-sized aluminum nitride seed crystal provided by the present invention uses c-axis oriented aluminum nitride polycrystal as a substrate, solving the stress problem introduced by the lattice mismatch and thermal mismatch of dissimilar materials. Since the difference in thermal expansion coefficients of aluminum nitride along the c-axis and a-axis directions is also very large, any region with inconsistent orientation will introduce large stress. The aluminum nitride polycrystal of the present invention has c-axis orientation and can also solve the stress problem introduced by inconsistent orientation of homologous materials.

[0007] The metal system is sensitive to silicon elements. Too high silicon concentration will cause damage to the metal system, and the quality of silicon-free aluminum nitride seed crystals is too poor to meet the requirements of aluminum nitride single crystals. By limiting the thickness of the silicon carbide seed crystal layer, the present invention can significantly reduce the concentrations of carbon and silicon components in the aluminum nitride crystal and the high-temperature growth system, enabling the silicon-containing large-sized aluminum nitride seed crystal to be prepared and used in a metal high-temperature system and improving the process repeatability; at the same time, it can also ensure the stability of the ordered lattice of silicon carbide. If the thickness is too small, the ordered lattice of silicon carbide will be distorted under the action of processing stress, which is not conducive to improving the crystal quality; if the thickness is too large, the elements in the excess silicon carbide will all enter the silicon-containing large-sized aluminum nitride seed crystal in the form of impurities, increasing the impurity content of the crystal.

[0008] The silicon-containing large-sized aluminum nitride seed crystal provided by the present invention has high crystallization quality, large size, small impurity content, and small internal stress in the crystal and is not easy to crack. The size of the silicon-containing large-sized aluminum nitride seed crystal can keep up with the development pace of silicon carbide materials, breaking through the inherent problem of low diameter expansion efficiency in the subsequent growth of aluminum nitride single crystals.

[0009] Preferably, the diameter of the c-axis oriented aluminum nitride polycrystalline layer is 50 mm to 220 mm, and the thickness is 1 mm to 3 mm.

[0010] Through a large number of experiments, the present invention has found that if the thickness of the c-axis oriented aluminum nitride polycrystalline layer (hereinafter referred to as the aluminum nitride polycrystalline layer) is low, the provided supporting force is insufficient, and the absorption capacity of the silicon carbide seed layer (i.e., the bonding capacity between the aluminum nitride polycrystalline layer and the silicon carbide seed layer) is also insufficient, resulting in the risk of silicon element diffusion; if the thickness is large, the wafer yield is reduced, leading to an increase in cost.

[0011] Exemplarily, the aluminum nitride polycrystals in the c-axis oriented aluminum nitride polycrystalline layer are prepared by iterative growth of aluminum nitride powder through physical vapor transport method for 2 to 4 times (preferably 3 times) (see CN117684271A); the full width at half maximum of the rocking curve of the (0002) plane of the aluminum nitride polycrystals is less than 500 arcsec.

[0012] Preferably, the carbon surface of the silicon carbide seed layer is in contact with the c-axis oriented aluminum nitride polycrystalline layer.

[0013] The present invention selects the carbon surface of the silicon carbide seed to be in contact with the c-axis oriented aluminum nitride polycrystalline layer, which can expose the silicon surface of the silicon carbide seed, and is more conducive to growing the aluminum nitride seed layer on the silicon carbide seed.

[0014] Preferably, the thickness of the aluminum nitride seed layer is 20 μm to 50 μm.

[0015] If the thickness of the aluminum nitride seed layer is thin, it is not conducive to completely covering the surface of the silicon carbide seed; if the thickness is thick, the quality of the large-size silicon-containing aluminum nitride seeds will be reduced.

[0016] In a second aspect, the present invention provides a method for preparing the large-size silicon-containing aluminum nitride seeds as described above, comprising the following steps: S1, using the c-axis oriented aluminum nitride polycrystal as a substrate, bonding the carbon surface of the silicon carbide seed to the surface of the aluminum nitride polycrystal with a carbon and nitrogen-containing adhesive to obtain a first layer-like object; the first layer-like object sequentially includes a c-axis oriented aluminum nitride polycrystalline layer, a carbon and nitrogen-containing adhesive layer, and a silicon carbide seed layer from bottom to top; S2, graphitizing the first layer-like object at 1400 °C to 1600 °C to obtain a second layer-like object; the second layer-like object sequentially includes a c-axis oriented aluminum nitride polycrystalline layer, a graphite layer, and a silicon carbide seed layer from bottom to top; S3, thermally bonding the second layer-like object at 1800 °C to 1900 °C to obtain a third layer-like object; the third layer-like object sequentially includes a c-axis oriented aluminum nitride polycrystalline layer and a silicon carbide seed layer from bottom to top; S4. Thin and polish the silicon carbide seed layer of the third layer to obtain a composite substrate; the composite substrate sequentially includes a c-axis oriented aluminum nitride polycrystalline layer and a silicon carbide seed layer from bottom to top; S5. Using aluminum nitride polycrystal as a target, perform magnetron sputtering on the surface of the silicon carbide seed layer of the composite substrate by magnetron sputtering method to obtain a composite seed; the composite seed sequentially includes a c-axis oriented aluminum nitride polycrystalline layer, a silicon carbide seed layer, and an amorphous aluminum nitride thin film layer from bottom to top; S6. Under a protective atmosphere, anneal the composite seed to obtain a silicon-containing large-size aluminum nitride seed.

[0017] In the preparation method of the silicon-containing large-size aluminum nitride seed provided by the present invention, in step S2, the carbon-nitrogen-containing binder is prone to graphitization transformation after denitrification at high temperature (1400°C - 1600°C). When graphite exists in a layered form, the force in the vertical direction is the van der Waals force, so that the stress between layers is small, which can effectively relieve the interaction force between the substrate and the silicon carbide seed. However, the van der Waals force between the graphite layers is weak and is not sufficient to support the thermal stress in the subsequent crystal growth process. Therefore, it is necessary to absorb graphite through the thermal bonding step S3, that is, carbon diffuses into the lattice of aluminum nitride polycrystal under the action of high temperature (1800°C - 1900°C), and aluminum nitride and carbon form a solid solution to form an aluminum-carbon-nitrogen compound, thereby enhancing the interaction force between the silicon carbide seed layer and the aluminum nitride polycrystalline layer. The present invention performs thermal bonding at a specific temperature, and on the basis of complete bonding, it can also ensure that the silicon carbide seed does not decompose.

[0018] In step S4 of the present invention, thinning and polishing the silicon carbide seed layer can significantly reduce the concentrations of carbon and silicon components in the silicon-containing large-size aluminum nitride seed and the high-temperature growth equipment, and at the same time is beneficial to ensuring the stability of the ordered lattice of the silicon carbide seed.

[0019] In step S5, aluminum nitride polycrystal has the advantage of high purity, which can effectively solve the wetting problem caused by the introduction of oxygen impurities and increase the uniformity of the magnetron sputtered aluminum nitride thin film. Usually, magnetron sputtering can only obtain polycrystals (amorphous aluminum nitride thin film), and the orientation of polycrystalline grains is completely random. In step S6, the amorphous aluminum nitride thin film is annealed at high temperature, which can effectively improve the orientation of polycrystals. The annealing process is accompanied by the Ostwald ripening process of amorphous aluminum nitride crystals, and disordered atoms will gradually transform to the state with the lowest energy under the action of high temperature; and the silicon carbide seed provides an ordered lattice under the amorphous aluminum nitride thin film, and the annealing treatment gives the aluminum and nitrogen atoms the energy for molecular thermal motion. Therefore, with the progress of annealing, the quality of the composite seed will gradually improve.

[0020] Preferably, in S1, the carbon-nitrogen-containing binder includes polyacrylonitrile and a solvent.

[0021] Further preferably, in S1, the solvent includes dimethylformamide.

[0022] Further preferably, in S1, the mass concentration of the carbon-nitrogen binder is 25% - 35%.

[0023] In the present invention, the elemental composition of polyacrylonitrile is relatively simple, consistent with the elements of each layer of material, and no other impurities will be introduced; polyacrylonitrile denitrifies under high temperature. Due to the molecular chain structure tending to fold into a hexagon, it is prone to graphitization transformation after denitrification at high temperature; the carbon-nitrogen binder has a good wetting effect on silicon carbide and aluminum nitride, can be evenly tiled on the surface of the substrate, and effectively avoids the generation of cavities.

[0024] Preferably, in S1, the thickness of the carbon-nitrogen binder layer of the first layer-like material is 400 nm - 600 nm.

[0025] It should be noted that the carbon-nitrogen binder can be coated on the substrate by spin coating. After spin coating, silicon carbide seeds are bonded, and the carbon-nitrogen binder will continuously gel and solidify.

[0026] Preferably, in S1, the thickness of the silicon carbide seed layer of the first layer-like material is 200 μm - 300 μm.

[0027] In the prior art, the minimum thickness of silicon carbide seeds can be 200 μm - 300 μm. If the thickness is thinner, the yield will drop significantly.

[0028] Preferably, in S2, it is heated to 1400°C - 1600°C at a rate of 90°C / h - 110°C / h, the pressure for graphitization is 9 GPa - 11 GPa, and the holding pressure time is 40 min - 50 min.

[0029] Through a large number of experiments, the present invention finds that if the heating rate is too fast, the formed air flow is large, and cavities are likely to appear in the graphite layer. If the heating rate is too slow, it will affect production efficiency and process cost; if the holding pressure time is too long, the carbon element after graphitization will diffuse, resulting in bonding failure. If the holding pressure time is too short, the graphitization process will be incomplete.

[0030] Preferably, in S3, it is heated to 1800°C - 1900°C at a rate of 40°C / h - 100°C / h (further preferably 50°C / h - 70°C / h), the pressure for thermal bonding is 9 GPa - 11 GPa, and the holding pressure time is 40 min - 50 min.

[0031] Exemplarily, S2 - S3 are carried out in a high-temperature hot isostatic pressing furnace.

[0032] Exemplarily, in S4, thinning is carried out in a thinning machine, and polishing is carried out by chemical mechanical polishing.

[0033] Preferably, in S4, the surface roughness of the silicon carbide seed layer in the composite substrate is 0.3 nm or less.

[0034] The surface roughness of the specific silicon carbide seed layer provides a basis for the subsequent ordered arrangement of the amorphous aluminum nitride thin film layer during annealing treatment, enabling the formation of an ordered surface lattice. If the roughness is too large, the surface of the silicon carbide seed layer is disordered, and it is difficult to obtain an ordered lattice even after annealing.

[0035] Exemplarily, in S5, the aluminum nitride polycrystal is prepared by a physical vapor transport method from aluminum nitride powder with a purity ≥ 99.99%.

[0036] Aluminum nitride powder is usually amorphous particles. Due to its small grain size and large specific surface area, the oxygen impurity content is relatively high. Even through sintering, it is difficult to completely remove impurities. Aluminum nitride polycrystals have the advantage of high purity, which can effectively solve the wetting problem caused by the introduction of oxygen impurities.

[0037] Exemplarily, in S5, the magnetron sputtering is carried out in a magnetron sputtering instrument.

[0038] Preferably, in S5, the power of the magnetron sputtering is 3 kW to 7 kW, the tray temperature is 500 °C to 600 °C, and the sputtering time is 25 min to 35 min.

[0039] Through a large number of experiments, the present invention finds that if the power of the magnetron sputtering is too high, the sputtering speed is too fast, and the thickness uniformity becomes poor; if the power is too low, the sputtering efficiency is insufficient; the higher the temperature of the sample tray, the better; the sputtering duration corresponds to the thickness of the amorphous aluminum nitride thin film layer.

[0040] Exemplarily, in S6, the annealing treatment is carried out in a high-temperature furnace.

[0041] Exemplarily, in S6, the protective atmosphere includes a nitrogen atmosphere.

[0042] Preferably, in S6, the temperature of the annealing treatment is 1500 °C to 1600 °C, and the holding time is 25 min to 35 min.

[0043] Through a large number of experiments, the present invention finds that too high an annealing temperature will cause the decomposition and diffusion of the silicon carbide seed, resulting in voids inside; too low an annealing temperature is not conducive to the molecular thermal motion of aluminum nitride in the amorphous aluminum nitride thin film layer, resulting in a decrease in crystallization quality. Description of the Drawings

[0044] Figure 1Schematic structural diagrams of the steps in the method for preparing a silicon-containing large-size aluminum nitride seed crystal according to the present invention; in the figure, 1 represents an aluminum nitride polycrystalline layer with a c-axis orientation, 2 represents a carbon-nitrogen-containing adhesive layer, 2* represents a graphite layer, 3 represents a silicon carbide seed crystal layer, 4 represents an amorphous aluminum nitride thin film layer, and 4* represents an aluminum nitride seed crystal layer; Figure 2 Raman test stress distribution diagram of the silicon-containing large-size aluminum nitride seed crystal in Example 1 of the present invention; Figure 3 X-ray diffraction pattern of the (0002) plane double crystal rocking curve of the silicon-containing large-size aluminum nitride seed crystal in Example 1 of the present invention. Specific embodiments

[0045] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0046] In the present invention, materials without special instructions are all commercially available products.

[0047] Example 1 This example provides a silicon-containing large-size aluminum nitride seed crystal (see Figure 1 ), which sequentially includes an aluminum nitride polycrystalline layer 1 with a c-axis orientation, a silicon carbide seed crystal layer 3, and an aluminum nitride seed crystal layer 4* from bottom to top; the carbon surface of the silicon carbide seed crystal layer 3 is in contact with the aluminum nitride polycrystalline layer 1 with a c-axis orientation.

[0048] The aluminum nitride polycrystalline layer 1 with a c-axis orientation has a diameter of 60 mm and a thickness of 1.2 mm; the silicon carbide seed crystal layer 3 has a thickness of 2 μm; the aluminum nitride seed crystal layer 4* has a thickness of 20 μm.

[0049] The method for preparing the above-mentioned silicon-containing large-size aluminum nitride seed crystal includes the following steps: S1, using an aluminum nitride polycrystal with a c-axis orientation as a substrate, bonding the carbon surface of a 200-μm-thick silicon carbide seed crystal to the surface of the aluminum nitride polycrystal with a carbon-nitrogen-containing adhesive (a dimethylformamide solution containing 30 wt% of the carbon-nitrogen-containing adhesive), and the thickness of the carbon-nitrogen-containing adhesive layer 2 is 400 nm to obtain a first-layer object.

[0050] The first-layer object sequentially includes an aluminum nitride polycrystalline layer 1 with a c-axis orientation, a carbon-nitrogen-containing adhesive layer 2, and a silicon carbide seed crystal layer 3 from bottom to top.

[0051] S2, putting the first-layer object into a high-temperature hot isostatic pressing furnace, heating it to 1500 °C at a rate of 100 °C / h, carrying out graphitization at 10 GPa, and holding the temperature and pressure for 45 min to obtain a second-layer object.

[0052] The second layer includes, from bottom to top, a c-axis oriented polycrystalline aluminum nitride layer 1, a graphite layer 2*, and a silicon carbide seed layer 3 in sequence.

[0053] S3. Then, the high-temperature hot isostatic pressing furnace is heated to 1850°C at a rate of 70°C / h, and the second layer is thermally bonded at 10 GPa and kept at temperature and pressure for 45 min to obtain the third layer.

[0054] The third layer includes, from bottom to top, a c-axis oriented polycrystalline aluminum nitride layer 1 and a silicon carbide seed layer 3 in sequence.

[0055] S4. The third layer is placed in a thinning machine, and the silicon carbide seed layer 3 is thinned. The surface roughness of the silicon carbide seed layer 3 is polished to 0.25 nm by chemical mechanical polishing to obtain a composite substrate.

[0056] The composite substrate includes, from bottom to top, a c-axis oriented polycrystalline aluminum nitride layer 1 and a silicon carbide seed layer 3 in sequence.

[0057] S5. The composite substrate is placed in a magnetron sputtering instrument, and polycrystalline aluminum nitride is used as a target to perform magnetron sputtering on the surface of the silicon carbide seed layer 3 at a power of 3.5 kW and a tray temperature of 600°C for 35 min to obtain a composite seed crystal.

[0058] The composite seed crystal includes, from bottom to top, a c-axis oriented polycrystalline aluminum nitride layer 1, a silicon carbide seed layer 3, and an amorphous aluminum nitride thin film layer 4 in sequence.

[0059] S6. The composite seed crystal is placed in an annealing furnace, and annealing treatment is performed at 1510°C in a nitrogen atmosphere and kept at temperature for 34 min, and then cooled to room temperature with the furnace to obtain a 2-inch large-size silicon-containing aluminum nitride seed crystal.

[0060] Example 2 This example provides a large-size silicon-containing aluminum nitride seed crystal (see Figure 1 ), which includes, from bottom to top, a c-axis oriented polycrystalline aluminum nitride layer 1, a silicon carbide seed layer 3, and an aluminum nitride seed layer 4*; the carbon surface of the silicon carbide seed layer 3 is in contact with the c-axis oriented polycrystalline aluminum nitride layer 1.

[0061] The diameter of the c-axis oriented polycrystalline aluminum nitride layer 1 is 110 mm and the thickness is 2 mm; the thickness of the silicon carbide seed layer 3 is 3 μm; the thickness of the aluminum nitride seed layer 4* is 35 μm.

[0062] The preparation method of the above large-size silicon-containing aluminum nitride seed crystal includes the following steps: S1. Using aluminum nitride polycrystal with c-axis orientation as the substrate, the carbon surface of a 250-μm-thick silicon carbide seed crystal is bonded to the surface of the aluminum nitride polycrystal by using a carbon-nitrogen binder (a dimethylformamide solution containing 25 wt% carbon-nitrogen binder). The thickness of the carbon-nitrogen binder layer 2 is 500 nm, obtaining a first layer-like object.

[0063] The first layer-like object successively includes an aluminum nitride polycrystal layer 1 with c-axis orientation, a carbon-nitrogen binder layer 2, and a silicon carbide seed crystal layer 3 from bottom to top.

[0064] S2. The first layer-like object is placed in a high-temperature hot isostatic pressing furnace, heated to 1400 °C at a rate of 93 °C / h, graphitized at 9 GPa, and kept at a constant temperature and pressure for 50 min, obtaining a second layer-like object.

[0065] The second layer-like object successively includes an aluminum nitride polycrystal layer 1 with c-axis orientation, a graphite layer 2*, and a silicon carbide seed crystal layer 3 from bottom to top.

[0066] S3. Then, the high-temperature hot isostatic pressing furnace is heated to 1800 °C at a rate of 80 °C / h, and the second layer-like object is thermally bonded at 9 GPa, kept at a constant temperature and pressure for 50 min, obtaining a third layer-like object.

[0067] The third layer-like object successively includes an aluminum nitride polycrystal layer 1 with c-axis orientation and a silicon carbide seed crystal layer 3 from bottom to top.

[0068] S4. The third layer-like object is placed in a thinning machine, and the silicon carbide seed crystal layer 3 is thinned. The surface roughness of the silicon carbide seed crystal layer 3 is polished to 0.28 nm by chemical mechanical polishing, obtaining a composite substrate.

[0069] The composite substrate successively includes an aluminum nitride polycrystal layer 1 with c-axis orientation and a silicon carbide seed crystal layer 3 from bottom to top.

[0070] S5. The composite substrate is placed in a magnetron sputtering instrument, using aluminum nitride polycrystal as the target material, magnetron sputtering is carried out on the surface of the silicon carbide seed crystal layer 3, with a power of 5 kW and a tray temperature of 550 °C, sputtering for 30 min, obtaining a composite seed crystal.

[0071] The composite seed crystal successively includes an aluminum nitride polycrystal layer 1 with c-axis orientation, a silicon carbide seed crystal layer 3, and an amorphous aluminum nitride thin film layer 4 from bottom to top.

[0072] S6. The composite seed crystal is placed in an annealing furnace, annealed at 1560 °C in a nitrogen atmosphere, kept at a constant temperature for 30 min, and cooled to room temperature with the furnace, obtaining a 4-inch large-size silicon-containing aluminum nitride seed crystal.

[0073] Example 3 This example provides a large-size silicon-containing aluminum nitride seed crystal (see Figure 1),(from bottom to top, successively including an aluminum nitride polycrystalline layer 1 with c-axis orientation, a silicon carbide seed layer 3, and an aluminum nitride seed layer 4*; the carbon surface of the silicon carbide seed layer 3 is in contact with the aluminum nitride polycrystalline layer 1 with c-axis orientation.)

[0074] The diameter of the aluminum nitride polycrystalline layer 1 with c-axis orientation is 210 mm, and the thickness is 2.8 mm; the thickness of the silicon carbide seed layer 3 is 5 μm; the thickness of the aluminum nitride seed layer 4* is 50 μm.

[0075] The method for preparing the above-mentioned large-size aluminum nitride seed crystal containing silicon includes the following steps: S1, using an aluminum nitride polycrystalline with c-axis orientation as a substrate, bonding the carbon surface of a 280-μm-thick silicon carbide seed crystal to the surface of the aluminum nitride polycrystalline by using a carbon and nitrogen-containing binder (a dimethylformamide solution containing 35 wt% of the carbon and nitrogen-containing binder), and the thickness of the carbon and nitrogen-containing binder layer 2 is 600 nm, to obtain a first layer-like object.

[0076] The first layer-like object, from bottom to top, successively includes an aluminum nitride polycrystalline layer 1 with c-axis orientation, a carbon and nitrogen-containing binder layer 2, and a silicon carbide seed layer 3.

[0077] S2, putting the first layer-like object into a high-temperature hot isostatic pressing furnace, heating it to 1600 °C at a rate of 108 °C / h, carrying out graphitization at 11 GPa, and holding the temperature and pressure for 40 min, to obtain a second layer-like object.

[0078] The second layer-like object, from bottom to top, successively includes an aluminum nitride polycrystalline layer 1 with c-axis orientation, a graphite layer 2*, and a silicon carbide seed layer 3.

[0079] S3, then heating the high-temperature hot isostatic pressing furnace to 1900 °C at a rate of 50 °C / h, carrying out thermal bonding on the second layer-like object at 11 GPa, and holding the temperature and pressure for 40 min, to obtain a third layer-like object.

[0080] The third layer-like object, from bottom to top, successively includes an aluminum nitride polycrystalline layer 1 with c-axis orientation and a silicon carbide seed layer 3.

[0081] S4, putting the third layer-like object into a thinning machine, thinning the silicon carbide seed layer 3, and polishing the surface roughness of the silicon carbide seed layer 3 to 0.29 nm by chemical mechanical polishing, to obtain a composite substrate.

[0082] The composite substrate, from bottom to top, successively includes an aluminum nitride polycrystalline layer 1 with c-axis orientation and a silicon carbide seed layer 3.

[0083] S5, putting the composite substrate into a magnetron sputtering instrument, using the aluminum nitride polycrystalline as a target, carrying out magnetron sputtering on the surface of the silicon carbide seed layer 3, with a power of 6.5 kW and a tray temperature of 600 °C, and sputtering for 25 min, to obtain a composite seed crystal.

[0084] The composite seed crystal sequentially includes, from bottom to top, a c-axis oriented aluminum nitride polycrystalline layer 1, a silicon carbide seed crystal layer 3, and an amorphous aluminum nitride thin film layer 4.

[0085] S6. Place the composite seed crystal into an annealing furnace, and under a nitrogen atmosphere, perform annealing treatment at 1590 °C, hold for 26 min, and cool to room temperature with the furnace to obtain an 8-inch large-size silicon-containing aluminum nitride seed crystal.

[0086] Comparative Example 1 This comparative example provides a large-size silicon-containing aluminum nitride seed crystal, which sequentially includes, from bottom to top, a silicon carbide seed crystal layer 3 and an aluminum nitride seed crystal layer 4* (excluding the c-axis oriented aluminum nitride polycrystalline layer 1).

[0087] The thickness of the silicon carbide seed crystal layer 3 is 200 μm; the thickness of the aluminum nitride seed crystal layer 4* is 20 μm.

[0088] The preparation method of the above large-size silicon-containing aluminum nitride seed crystal includes the following steps: S1. Use chemical mechanical polishing to polish the surface roughness of the silicon carbide seed crystal layer 3 to 0.25 nm, place it into a magnetron sputtering instrument, use aluminum nitride polycrystal as the target, perform magnetron sputtering on the surface of the silicon carbide seed crystal layer 3, with a power of 3.5 kW and a tray temperature of 600 °C, and sputter for 35 min to obtain a composite seed crystal.

[0089] S2. The same as S6 in Example 1, which will not be elaborated herein.

[0090] Comparative Example 2 This comparative example provides a large-size silicon-containing aluminum nitride seed crystal, which is similar to Example 2, except that: the thickness of the silicon carbide seed crystal layer 3 is 240 μm. The other conditions are the same as those in Example 2, which will not be elaborated herein.

[0091] The preparation method of the above large-size silicon-containing aluminum nitride seed crystal includes the following steps: S1 - S3. The same as those in Example 2, which will not be elaborated herein.

[0092] S4. Use chemical mechanical polishing to polish the surface roughness of the silicon carbide seed crystal layer 3 of the third layer to 0.28 nm to obtain a composite substrate (i.e., the silicon carbide seed crystal layer 3 is not thinned).

[0093] The composite substrate sequentially includes, from bottom to top, a c-axis oriented aluminum nitride polycrystalline layer 1 and a silicon carbide seed crystal layer 3.

[0094] S5 - S6. The same as those in Example 2, which will not be elaborated herein.

[0095] Comparative Example 3 This comparative example provides a silicon-containing large-sized aluminum nitride seed crystal, which is similar to Example 3, except that: the aluminum nitride polycrystal of the substrate layer does not have a c-axis orientation. The remaining conditions are the same as those in Example 3 and will not be elaborated.

[0096] The preparation method of the above silicon-containing large-sized aluminum nitride seed crystal is the same as that in Example 3 and will not be elaborated.

[0097] The aluminum nitride polycrystal of the substrate layer is prepared by a physical vapor transport method from aluminum nitride powder with a purity of ≥99.99%.

[0098] Verification test Raman tests and X-ray rocking curve tests were performed on the silicon-containing large-sized aluminum nitride seed crystals provided in Examples 1 to 3 and Comparative Examples 1 to 3, and the results are as Figures 2 to 3 shown in Table 1.

[0099] Table 1 Performance test results of silicon-containing large-sized aluminum nitride seed crystals

[0100] Note: In the column of "Residual stress", negative values indicate compressive stress and positive values indicate tensile stress.

[0101] From Figure 2 it can be seen that for the silicon-containing large-sized aluminum nitride seed crystal in Example 1, the E2(high) result has a value of 656.1 cm -1 ~657.6 cm -1 , and the stress-free peak corresponding to aluminum nitride single crystal is 657.4 cm -1 . The gap is small. Referring to the empirical formula (σ = 250×△E2, where σ represents the residual stress, the unit is MPa, and △E2 represents the offset of the Raman peak position relative to the corresponding peak position of the stress-free aluminum nitride crystal, the unit is cm -1 ), the calculated residual stress is -50 MPa to 325 MPa. This shows that the internal stress of the silicon-containing large-sized aluminum nitride seed crystal provided in this example is small and it is not easy to crack. From Figure 3 it can be seen that the full width at half maximum of the (0002) plane double crystal rocking curve of the silicon-containing large-sized aluminum nitride seed crystal is 149 arcsec (≤200 arcsec), indicating that the crystallization quality of the silicon-containing large-sized aluminum nitride seed crystal provided in this example is high.

[0102] It can be seen from Table 1 that: In the case of Comparative Example 1 without aluminum nitride polycrystal, since the stress of silicon carbide cannot be buffered, the residual stress of the prepared silicon-containing large-sized aluminum nitride seed crystal is large and even cracks; the aluminum nitride on the surface of silicon carbide is affected by large stress, and the crystal lattice is distorted, resulting in the quality of the crystal being affected and even peak splitting occurring; In Comparative Example 2, when the silicon carbide was not thinned, due to the limited action distance of the back aluminum nitride polycrystal, the stress applied by the silicon carbide to the aluminum nitride could not be effectively buffered, and the residual stress of the prepared large-size aluminum nitride seed crystal containing silicon was relatively large or even cracked; the aluminum nitride on the surface of the silicon carbide was under great stress, resulting in lattice distortion, which affected the quality of the crystal and even caused peak splitting. In Comparative Example 3, the used aluminum nitride polycrystal did not have a c-axis orientation and could buffer stress to a certain extent. However, due to the isotropy of the polycrystalline aluminum nitride, the ability to buffer stress was lower than that of the aluminum nitride polycrystal with a c-axis orientation. Therefore, the residual stress of the prepared large-size aluminum nitride seed crystal containing silicon was slightly larger than that in the examples; the aluminum nitride on the surface of the silicon carbide was under relatively large stress, resulting in lattice distortion, which affected the quality of the crystal to a certain extent, but no peak splitting occurred.

[0103] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, or improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A large-sized silicon-containing aluminum nitride seed crystal, characterized in that, It includes, from bottom to top, a c-axis oriented aluminum nitride polycrystalline layer, a silicon carbide seed layer, and an aluminum nitride seed layer in sequence; the thickness of the silicon carbide seed layer is 2 μm to 5 μm.

2. The silicon-containing large-sized aluminum nitride seed crystal according to claim 1, wherein The diameter of the c-axis oriented aluminum nitride polycrystalline layer is 50 mm to 220 mm, and the thickness is 1 mm to 3 mm; The thickness of the aluminum nitride seed layer is 20 μm to 50 μm.

3. The silicon-containing large-size aluminum nitride seed crystal according to claim 1, wherein, The carbon surface of the silicon carbide seed layer is in contact with the c-axis oriented aluminum nitride polycrystalline layer.

4. The method for preparing a silicon-containing large-size aluminum nitride seed crystal according to any one of claims 1 to 3, characterized in that, It includes the following steps: S1: Using a c-axis oriented aluminum nitride polycrystal as a substrate, bonding the carbon surface of a silicon carbide seed to the surface of the aluminum nitride polycrystal with a carbon-nitrogen-containing binder to obtain a first layer-like object; the first layer-like object includes, from bottom to top, a c-axis oriented aluminum nitride polycrystalline layer, a carbon-nitrogen-containing binder layer, and a silicon carbide seed layer in sequence; S2: Graphitizing the first layer-like object at 1400 °C to 1600 °C to obtain a second layer-like object; the second layer-like object includes, from bottom to top, a c-axis oriented aluminum nitride polycrystalline layer, a graphite layer, and a silicon carbide seed layer in sequence; S3: Thermally bonding the second layer-like object at 1800 °C to 1900 °C to obtain a third layer-like object; the third layer-like object includes, from bottom to top, a c-axis oriented aluminum nitride polycrystalline layer and a silicon carbide seed layer in sequence; S4: Thinning and polishing the silicon carbide seed layer of the third layer-like object to obtain a composite substrate; the composite substrate includes, from bottom to top, a c-axis oriented aluminum nitride polycrystalline layer and a silicon carbide seed layer in sequence; S5: Using aluminum nitride polycrystal as a target, magnetron sputtering on the surface of the silicon carbide seed layer of the composite substrate by magnetron sputtering to obtain a composite seed; the composite seed includes, from bottom to top, a c-axis oriented aluminum nitride polycrystalline layer, a silicon carbide seed layer, and an amorphous aluminum nitride thin film layer in sequence; S6: Annealing the composite seed under a protective atmosphere to obtain a silicon-containing large-size aluminum nitride seed.

5. The method for preparing a silicon-containing large-sized aluminum nitride seed crystal according to claim 4, wherein, In S1, the carbon-nitrogen-containing binder includes polyacrylonitrile and a solvent; In S1, the thickness of the carbon-nitrogen-containing binder layer of the first layer-like object is 400 nm to 600 nm.

6. The preparation method of the silicon-containing large-size aluminum nitride seed crystal according to claim 5, wherein, In S1, the solvent includes dimethylformamide; In S1, the mass concentration of the carbon-nitrogen-containing binder is 25% to 35%.

7. The preparation method of the silicon-containing large-size aluminum nitride seed crystal according to claim 4, wherein, In S2, it is heated to 1400 °C to 1600 °C at 90 °C / h to 110 °C / h, the pressure for graphitization is 9 GPa to 11 GPa, and the heat preservation and pressure maintenance time is 40 min to 50 min; In S3, it is heated to 1800 °C to 1900 °C at 40 °C / h to 100 °C / h, the pressure for thermal bonding is 9 GPa to 11 GPa, and the heat preservation and pressure maintenance time is 40 min to 50 min.

8. The preparation method of the large-size silicon-containing aluminum nitride seed crystal according to claim 4, wherein, In S4, the surface roughness of the silicon carbide seed layer in the composite substrate is below 0.3 nm.

9. The preparation method of the silicon-containing large-size aluminum nitride seed crystal according to claim 4, wherein, In S5, the power of the magnetron sputtering is 3 kW to 7 kW, the tray temperature is 500 °C to 600 °C, and the sputtering time is 25 min to 35 min.

10. The method for preparing a large-sized silicon-containing aluminum nitride seed crystal according to claim 4, wherein In S6, the temperature for the annealing treatment is 1500 °C to 1600 °C, and the heat preservation time is 25 min to 35 min.

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