Bonding method of silicon carbide seed crystal, silicon carbide single crystal and preparation method and application of silicon carbide single crystal

Abstract

The invention provides a silicon carbide seed crystal bonding method, a silicon carbide single crystal and a preparation method and application of the silicon carbide single crystal, and the bonding method comprises the following steps: firstly, providing a glue solution containing a binder, a silane coupling agent and a solvent, then coating the glue solution on the bonding surface of graphite paper and the silicon carbide seed crystal, and then concentrically pressing and bonding the graphite paper and the silicon carbide seed crystal at one time, carrying out primary hot pressing by adopting the silicon carbide crystal ingot as a pressing block, and carrying out secondary hot pressing by adopting the pressing block according to the sequence of the pressing block, the silicon carbide seed crystal, the graphite paper and the graphite support from top to bottom after the primary hot pressing is finished, so as to finish the bonding of the silicon carbide seed crystal; according to the bonding method, a glue solution containing a silane coupling agent is selected and matched with a silicon carbide crystal ingot to serve as a pressing block for primary hot pressing, so that the problem of poor distribution of a glue layer on a bonding surface of graphite paper and silicon carbide seed crystals is effectively solved, the interface bonding strength of the graphite paper and the silicon carbide seed crystals is also effectively improved, and the preparation requirement of the silicon carbide single crystal is met.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductor materials, and in particular relates to a method for bonding a silicon carbide seed crystal, a silicon carbide single crystal, and a preparation method and application thereof. Background Art

[0002] Silicon carbide (SiC) single crystal is one of the most important third-generation semiconductor materials because of its wide band gap, high breakdown electric field strength and high thermal conductivity. It can meet the high requirements of aerospace, photovoltaic power generation, rail power grid and new energy trams for substrate materials under harsh conditions such as high power, high frequency and high temperature.

[0003] At present, the most mature and mainstream method for growing silicon carbide single crystals is physical vapor transport (PVT). The main steps of this method are: loading silicon carbide powder at the bottom of a graphite crucible, bonding a silicon carbide seed crystal to the top of the crucible, heating the graphite crucible by electromagnetic induction, causing the powder material to sublimate at high temperature, and finally growing a silicon carbide single crystal at the interface of the silicon carbide seed crystal. The bonding effect between the silicon carbide seed crystal and the top of the crucible directly affects the continuity of crystal growth and the quality of the crystal. Polymers such as photoresist, epoxy resin, and phenolic resin are usually used as interface adhesives, and the silicon carbide seed crystal bonding process is mainly divided into two categories: (1) graphite plate fixing; (2) direct bonding.

[0004] Among them, the method of fixing the graphite plate includes: clamping the seed crystal sheet bonded with flexible graphite paper on the top of the crucible through a double-layer graphite plate. This method will reduce the crystal growth area due to the graphite plate structure that fixes the seed crystal, and cannot avoid the problem of uneven distribution of adhesive at the bonding interface. At the same time, the fixing structure is often complex and costly. The above shortcomings make this solution difficult to apply for large-scale production. The direct bonding method includes: first, applying a uniform adhesive layer on the silicon surface of the silicon carbide seed crystal, and after high-temperature pressure carbonization (requires ≥5h), bonding it to the flexible graphite paper through an adhesive, and after pressure heat curing, it is pressure-heat-cured and bonded to the graphite base. This solution is simple to operate and low in cost. It is currently the mainstream bonding method. However, this solution cannot determine the uniformity of the adhesive interface layer between the graphite paper and the seed crystal after carbonization, which will affect the surface temperature distribution of the seed crystal during growth, and crystal ablation or even shedding will occur. At the same time, the adhesive has insufficient wettability with the graphite and silicon carbide seed crystal surfaces, which makes the carbonization layer not dense enough after the adhesive is solidified and then carbonized. In addition, the bonding force between the carbonization layer and the seed crystal mainly depends on the interface Si-C bond, that is, the bonding strength of the adhesive.

[0005] It can be seen that in the above two solutions, the silicon carbide seed crystal needs to be bonded to the flexible graphite paper before bonding with the graphite material. This is because the thermal expansion coefficient of the silicon carbide seed crystal (~4.5×10 -6 / K) and graphite support (~2×10-6 / K) have a large difference in thermal expansion coefficients. The introduction of flexible graphite paper can buffer the difference in thermal expansion between the silicon carbide seed crystal and the graphite holder at high temperature. In addition, the uniformity of the adhesive between the silicon carbide seed crystal and the graphite paper is directly related to the curvature of the wafer, the flatness of the contact surface of the pressing block, the material of the pressing block, the heating rate, and the vacuum degree. Among them, the material of the pressing block is the most important factor. However, the current process mainly uses graphite (~2×10 -6 / K), stainless steel (~15×10 -6 / K) materials are used as pressing blocks, but the thermal expansion coefficient of these materials does not match that of the silicon carbide seed crystal, which causes bubbles, large gas path lines, and virtual adhesion in actual operations, directly affecting production efficiency.

[0006] Therefore, in view of the above problems, there is still a need to develop a method for bonding silicon carbide seed crystals with simple process, no abnormalities on the bonding surface and high bonding strength. Summary of the invention

[0007] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a method for bonding a silicon carbide seed crystal, a silicon carbide single crystal and a preparation method and application thereof. By adding a silane coupling agent to the glue solution and selecting a silicon carbide ingot as a pressing block for the first hot pressing, the bonding method is not only simple in process, but also can effectively improve the problem of poor distribution of the glue layer on the bonding surface of graphite paper and silicon carbide seed crystal, and can effectively reduce the risk of unsmooth growth of silicon carbide crystals and decreased crystal quality caused by low bonding strength between graphite paper and silicon carbide seed crystals.

[0008] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a method for bonding a silicon carbide seed crystal, the bonding method comprising the following steps:

[0010] (1) providing a glue solution containing a binder, a silane coupling agent and a solvent;

[0011] (2) applying the glue obtained in step (1) on the bonding surface of the graphite paper and the silicon carbide seed crystal, and then pressing the two concentrically to bond them together, and then using the silicon carbide ingot as a pressing block, performing the first hot pressing in the order of the silicon carbide ingot, the silicon carbide seed crystal and the graphite paper from top to bottom;

[0012] (3) The composite structure obtained after the first hot pressing in step (2) is bonded to the graphite tray, and then a second hot pressing is performed using a pressing block in the order of a pressing block, a silicon carbide seed crystal, a graphite paper and a graphite tray from top to bottom to complete the bonding of the silicon carbide seed crystal.

[0013] In the bonding method provided by the present invention, firstly, a glue solution containing a binder, a silane coupling agent and a solvent is provided. The added silane coupling agent is a type of dispersing aid with low surface tension and extremely strong wetting ability. The silane alkoxy group (-SiOR') contained in it is easily hydrolyzed to generate silanol group. The silanol group tends to the surface of the inorganic material and can undergo a condensation reaction, while the organic end (R-) tends to the surface of the organic material, thereby forming a coupling effect, which helps to improve the interfacial bonding strength between the graphite paper and the silicon carbide seed crystal; then the above-mentioned glue solution is coated on the bonding surface of the graphite paper and the silicon carbide seed crystal, and it is ensured that the glue solution can be evenly distributed on the bonding surface of the two, and then the two are pressed concentrically and centered. This step needs to ensure that it is placed in place at one time to avoid multiple Placing it easily causes the problem of uneven distribution of the adhesive layer on the bonding surface, and then a silicon carbide ingot is used as a pressing block, and the first hot pressing is carried out in the order of silicon carbide ingot, silicon carbide seed crystal and graphite paper from top to bottom. After the first hot pressing, the composite structure composed of the silicon carbide seed crystal and graphite paper is removed to check whether there are abnormal phenomena such as bubbles, large lines, and virtual adhesion. If there is no abnormality, the silicon carbide seed crystal and graphite paper bonded together can be bonded to the graphite tray again, and concentric bonding is also required. The pressing block is used again, and the second hot pressing is carried out in the order of pressing block, silicon carbide seed crystal, graphite paper and graphite tray from top to bottom, so that the silicon carbide seed crystal, graphite paper and graphite tray can be bonded together to complete the bonding of the silicon carbide seed crystal.

[0014] It should be noted that there are no special requirements for the glue used for bonding in the above step (2). Conventional glue in the art can be used, or the glue provided in step (1) can be directly used, and the glue provided in step (1) is preferred. At the same time, there are no special requirements for the material of the pressing block used for the second hot pressing in the above step (3). Conventional pressing blocks in the art or silicon carbide ingots can be used as pressing blocks, and silicon carbide ingots are preferred.

[0015] On the one hand, the bonding method provided by the present invention simplifies the carbonization process in the traditional bonding process, integrates the carbonization process into the growth process, and can save about 50% of the time of the bonding process before growth; on the other hand, the bonding method provided by the present invention uses a silicon carbide ingot as a pressing block in the first hot pressing process, which has the same thermal expansion coefficient as the silicon carbide seed crystal, and can effectively promote the unobstructed gas path of the organic gas generated by the decomposition of the solvent and the adhesive during the hot pressing process, reduce the appearance of pores, and improve the uniformity of the glue layer distribution between the graphite paper and the silicon carbide seed crystal paper, thereby reducing the mismatch problem of the thermal expansion coefficient between the pressing block material and the silicon carbide seed crystal in the bonding process, and at the same time, a silane coupling agent is added to the glue liquid to effectively improve the interface bonding strength; in addition, the bonding method provided by the present invention can observe the bonding surface after the graphite paper / silicon carbide seed crystal is hot-pressed and cured, and timely remove defective bonding products, which is suitable for the bonding process of 6-inch and 8-inch silicon carbide seed crystals.

[0016] Preferably, the adhesive in step (1) comprises photoresist.

[0017] Preferably, the adhesive in step (1) is a phenolic resin adhesive and / or an epoxy resin adhesive.

[0018] Preferably, the silane coupling agent in step (1) includes any one of γ-aminopropyltriethoxysilane, γ-glycidyloxypropyltrimethoxysilane or γ-aminoethylaminopropyltrimethoxysilane, or a combination of at least two thereof.

[0019] Preferably, based on the amount of the binder in step (1) being 1 g, the amount of the silane coupling agent in step (1) is 0.01 to 0.05 g, for example, 0.01 g, 0.015 g, 0.02 g, 0.025 g, 0.03 g, 0.035 g, 0.04 g, 0.045 g or 0.05 g, etc.

[0020] Preferably, the solvent in step (1) comprises any one of anhydrous ethanol, isopropanol, acetone or ethyl acetate, or a combination of at least two thereof.

[0021] Preferably, the viscosity of the glue in step (1) is 500-2000 mPa·s (for example, 500 mPa·s, 700 mPa·s, 900 mPa·s, 1100 mPa·s, 1300 mPa·s, 1500 mPa·s, 1700 mPa·s, 1900 mPa·s or 2000 mPa·s, etc.) for spin coating, or 10-50 mPa·s (for example, 10 mPa·s, 15 mPa·s, 20 mPa·s, 25 mPa·s, 30 mPa·s, 35 mPa·s, 40 mPa·s, 45 mPa·s or 50 mPa·s, etc.) for spray coating.

[0022] Preferably, the coating method in step (2) is spin coating or spray coating, which can further ensure that the glue is evenly distributed on the bonding surface of the graphite paper and the silicon carbide seed crystal.

[0023] Preferably, the liquid supply rate of the spraying is 20 to 50 μL / s, for example, 20 μL / s, 25 μL / s, 30 μL / s, 35 μL / s, 40 μL / s, 45 μL / s or 50 μL / s.

[0024] Preferably, the spin coating has a rotation speed of 500 to 1500 rpm, for example, 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm, 1000 rpm, 1100 rpm, 1200 rpm, 1300 rpm, 1400 rpm or 1500 rpm.

[0025] Preferably, the coating time in step (2) is 20 to 30 s, for example, 20 s, 21 s, 22 s, 23 s, 24 s, 25 s, 26 s, 27 s, 28 s, 29 s or 30 s.

[0026] Preferably, the thickness of the graphite paper in step (2) is 0.2-0.5 mm, for example, 0.2 mm, 0.25 mm, 0.3 mm, 0.35 mm, 0.4 mm, 0.45 mm or 0.5 mm.

[0027] Preferably, the thickness of the silicon carbide seed crystal in step (2) is 350-1000 μm, for example, 350 μm, 400 μm, 500 μm, 600 μm, 700 μm, 800 μm, 900 μm or 1000 μm.

[0028] Preferably, the first hot pressing in step (2) and the second hot pressing in step (3) are both carried out in a hot pressing furnace.

[0029] Preferably, the vacuum degree of the hot pressing furnace is ≤10Pa.

[0030] Preferably, the applied pressure of the first hot pressing in step (2) and the second hot pressing in step (3) are each independently 0.05 to 0.3 MPa, for example, 0.05 MPa, 0.07 MPa, 0.09 MPa, 0.11 MPa, 0.13 MPa, 0.15 MPa, 0.17 MPa, 0.19 MPa, 0.21 MPa, 0.23 MPa, 0.25 MPa, 0.27 MPa, 0.29 MPa or 0.3 MPa, etc.

[0031] Preferably, the first hot pressing in step (2) and the second hot pressing in step (3) are both performed under the condition of gradient heating, and the step of gradient heating comprises: first heating to 80-130°C (for example, 80°C, 90°C, 100°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, 310°C, 320°C, 330°C, 340°C, 350°C, 360°C, 370°C, 380°C, 390°C, 400°C, 410°C, 420°C, 430°C, 440°C, 450°C, 460°C, 470°C, 480°C, 490°C, 500°C, 510°C, 510°C, 520°C, 530°C, 540°C, 550°C, 560°C, 570°C, 580°C, 590°C, 600°C, 610°C, 610°C, 620°C, 630°C, 640°C, 650°C The temperature is then raised to 10°C, 120°C or 130°C, etc.), and then heated to 170-250°C (e.g., 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C or 250°C, etc.) for a second time for ≥20min (e.g., 20min, 21min, 22min, 24min, 26min, 28min, 30min, 32min, 34min, 36min, 38min or 40min, etc.).

[0032] Preferably, the thickness of the silicon carbide ingot in step (2) is 5 to 15 mm, for example, 5 mm, 7 mm, 9 mm, 11 mm, 13 mm or 15 mm.

[0033] Preferably, the diameter of the silicon carbide ingot in step (2) is greater than the diameter of the silicon carbide seed crystal in step (2).

[0034] Preferably, the silicon carbide ingot in step (2) is obtained by selecting a downgraded silicon carbide block and then grinding and rounding it, thereby reducing production costs, and the specific size specifications can be adjusted according to actual needs.

[0035] In a second aspect, the present invention provides a method for preparing a silicon carbide single crystal, the preparation method comprising the following steps:

[0036] Filling silicon carbide powder at the bottom of a graphite crucible, and using the bonding method described in the first aspect to bond the resulting bonded member as a graphite crucible cover;

[0037] The graphite crucible is placed in a single crystal furnace, and the silicon carbide single crystal is grown by a PVT method.

[0038] It can be seen from the above content that the present invention combines the carbonization step in the traditional bonding process into the growth step, thereby simplifying the preparation process of silicon carbide single crystals.

[0039] Preferably, the growth temperature is 2200-2300°C, for example, 2200°C, 2210°C, 2220°C, 2240°C, 2260°C, 2280°C or 2300°C.

[0040] Preferably, the growth time is 85 to 95 h, for example, 85 h, 87 h, 89 h, 91 h, 93 h or 95 h.

[0041] Preferably, before the temperature of the single crystal furnace reaches 800°C, the heating rate is ≤100°C / h, for example, 100°C / h, 90°C / h, 80°C / h, 70°C / h, 60°C / h, 50°C / h, 40°C / h, 30°C / h, 20°C / h or 10°C / h, so as to avoid the problem of organic gas generated during the formation of the silicon carbide single crystal being unable to be removed in time due to too fast a heating rate, thereby forming pores.

[0042] Preferably, the growth pressure is 150-300 Pa, for example, 150 Pa, 170 Pa, 190 Pa, 210 Pa, 230 Pa, 250 Pa, 270 Pa, 290 Pa or 300 Pa.

[0043] Preferably, the growth is carried out under inert gas protection conditions.

[0044] In a third aspect, the present invention provides a silicon carbide single crystal bonding structure, wherein the silicon carbide single crystal bonding structure is prepared by the preparation method described in the first aspect.

[0045] In a fourth aspect, the present invention provides a silicon carbide single crystal bonding structure as described in the fourth aspect for use as a substrate material in aerospace, photovoltaic power generation, rail power grid and new energy electricity.

[0046] Compared with the prior art, the present invention has the following beneficial effects:

[0047] The bonding method of silicon carbide seed crystal provided by the present invention first provides a glue liquid containing a binder, a silane coupling agent and a solvent, and after the glue liquid is coated on the bonding surface of graphite paper and silicon carbide seed crystal, the two are pressed and bonded at one time by concentric center, and then a silicon carbide crystal ingot is used as a pressing block for the first hot pressing. After the first hot pressing is completed, the pressing block is used again, and the second hot pressing is performed in the order of pressing block, silicon carbide seed crystal, graphite paper and graphite tray from top to bottom, so as to complete the bonding of the silicon carbide seed crystal; the bonding method effectively improves the problem of poor distribution of the glue layer on the bonding surface of graphite paper and silicon carbide seed crystal by selecting a glue liquid containing a silane coupling agent and using a silicon carbide crystal ingot as a pressing block, and also effectively improves the interface bonding strength between the two, thereby meeting the preparation requirements of silicon carbide single crystals. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 A schematic diagram of the hot pressing structure in the second hot pressing in the bonding method provided by the present invention;

[0049] Figure 2 A schematic diagram of the structure of a bonded part obtained by the bonding method provided by the present invention;

[0050] Among them, 20 is a silicon carbide seed crystal, 21 is a graphite paper, 23 is a silicon carbide ingot, and 24 is a graphite tray. DETAILED DESCRIPTION

[0051] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0052] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0053] In the description of the present invention, it should be understood that descriptions involving orientations, such as up, down, front, back, left, right, etc., and orientations or positional relationships indicated are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0054] Unless otherwise specified, the raw materials involved in the following specific embodiments are all conventional materials in the art and can be purchased from commercial products.

[0055] Example 1

[0056] A method for bonding a silicon carbide seed crystal comprises the following steps:

[0057] (1) Weigh 100 g of phenolic resin binder (purchased from Nathanmei, solid content 30%) in a beaker, add an appropriate amount of isopropanol, and measure the viscosity of the solution by a viscometer to find that it is 1000 mPa·s (test temperature is 27° C., rotation speed is 1000 rpm), then dropwise add 3 g of γ-aminopropyltriethoxysilane and stir for 30 min to obtain a glue solution;

[0058] (2) using a spin coating method, the glue obtained in step (1) is evenly coated on the crystalline silicon surface of the carbide seed crystal (thickness of 350 μm) and one side surface of the graphite paper (thickness of 0.2 mm), respectively, at a spin coating speed of 1000 rpm for 25 seconds, and then the two are pressed and bonded at the same time, and then placed in a hot pressing furnace, using a silicon carbide ingot as a pressing block, and hot pressing is performed for the first time in the order of silicon carbide ingot, silicon carbide seed crystal, and graphite paper from top to bottom;

[0059] In the first hot pressing, the vacuum degree in the hot pressing furnace is 10Pa, the thickness of the silicon carbide ingot is 10mm, and the diameter is 5mm larger than the diameter of the silicon carbide seed crystal, the applied pressure is 0.1MPa, and the first hot pressing is carried out under the condition of staged heating, specifically: first heating to 100°C in 40min, and then heating to 200°C in 30min, to complete the first hot pressing;

[0060] (3) After the first hot pressing in step (2), the composite structure consisting of the silicon carbide seed crystal and the graphite paper is removed to check whether there are bubbles, large lines, virtual adhesion and other abnormal phenomena, and then the glue obtained in step (1) is used to bond the graphite paper and the silicon carbide seed crystal to the graphite holder, and then the composite structure is placed in the hot pressing furnace again, and the silicon carbide ingot is used as a pressing block again, and the graphite paper and the graphite holder are bonded together. Figure 1 The hot pressing structure shown in the figure is to place the silicon carbide ingot 23, the silicon carbide seed crystal 20, the graphite paper 21 and the graphite tray 22 in this order, in the vertical direction ( Figure 1Applying pressure in the direction indicated by the middle arrow F) to perform a second hot pressing to complete the bonding of the silicon carbide seed crystal;

[0061] During the second hot pressing, the vacuum degree in the hot pressing furnace was 10Pa, the thickness of the silicon carbide ingot was 10mm, and the diameter was 5mm larger than the diameter of the silicon carbide seed crystal. The applied pressure was 0.1MPa, and the temperature was raised in stages, specifically: first, the temperature was raised to 100°C in 40 minutes, and then the temperature was raised to 200°C in 30 minutes to complete the second hot pressing.

[0062] The structural schematic diagram of the bonded part obtained by the bonding method provided in this embodiment is as follows Figure 2 As shown, it includes a silicon carbide seed crystal 20, a graphite paper 21 and a graphite holder 22 which are stacked.

[0063] Example 2

[0064] A method for bonding a silicon carbide seed crystal comprises the following steps:

[0065] (1) Weigh 100 g of epoxy resin adhesive (purchased from Henkel Loctite) into a beaker, add an appropriate amount of isopropyl alcohol, and measure the viscosity of the solution by a viscometer to find that it is 30 mPa·s (test temperature is 27° C., rotation speed is 1000 rpm). Then, dropwise add 2 g of γ-glycidyloxypropyltrimethoxysilane and stir for 30 min to obtain a glue solution;

[0066] (2) spraying the glue evenly on the crystalline silicon surface of the carbide seed crystal (350 μm thick) and one side surface of the graphite paper (0.2 mm thick), with the liquid supply of the spraying being 25 μL / s for 25 seconds. After the spraying is completed, the two are pressed and bonded at the same time and then placed together in a hot pressing furnace. The silicon carbide ingot is used as a pressing block, and the silicon carbide ingot, the silicon carbide seed crystal and the graphite paper are first hot pressed in the order of from top to bottom.

[0067] In the first hot pressing, the vacuum degree in the hot pressing furnace is 10Pa, the thickness of the silicon carbide ingot is 10mm, and the diameter is 5mm larger than the diameter of the silicon carbide seed crystal. The applied pressure is 0.2MPa, and the temperature is increased in stages, specifically: firstly, the temperature is increased to 100°C in 40min, and then the temperature is increased to 200°C in 35min to complete the first hot pressing;

[0068] (3) after the first hot pressing in step (2), the composite structure consisting of the silicon carbide seed crystal and the graphite paper is removed, and whether there are abnormal phenomena such as bubbles, large lines, and virtual adhesion, and then the graphite paper and the silicon carbide seed crystal bonded together are bonded to the graphite tray by step (1), and then placed in the hot pressing furnace again, and the silicon carbide ingot is used as a pressing block again, and the silicon carbide ingot, the silicon carbide seed crystal, the graphite paper and the graphite tray are placed in the order of from top to bottom, and pressure is applied in the vertical direction for a second hot pressing to complete the bonding of the silicon carbide seed crystal;

[0069] During the second hot pressing, the vacuum degree in the hot pressing furnace was 10Pa, the thickness of the silicon carbide ingot was 10mm, and the diameter was 5mm larger than the diameter of the silicon carbide seed crystal. The applied pressure was 0.2MPa, and it was carried out under the condition of staged heating, specifically: first heating to 100°C in 40 minutes, and then heating to 200°C in 35 minutes to complete the second hot pressing.

[0070] Example 3

[0071] A method for bonding silicon carbide seed crystals, which differs from Example 1 in that the pressure applied in the first hot pressing in step (2) and the second hot pressing in step (3) is 0.05 MPa, and other substances, amounts and preparation methods are the same as those in Example 1.

[0072] Example 4

[0073] A method for bonding silicon carbide seed crystals, which differs from Example 1 in that the pressure applied in the first hot pressing in step (2) and the second hot pressing in step (3) is 0.2 MPa, and other substances, amounts and preparation methods are the same as those in Example 1.

[0074] Comparative Example 1

[0075] A method for bonding silicon carbide seed crystals, which differs from Example 1 in that no γ-aminopropyltriethoxysilane is added to the glue solution in step (1), and other substances, amounts and preparation methods are the same as those in Example 1.

[0076] Comparative Example 2

[0077] A method for bonding silicon carbide seed crystals, which differs from Example 1 in that graphite blocks are used as pressing blocks in both step (2) the first hot pressing and step (3) the second hot pressing, and other substances, amounts and preparation methods are the same as those in Example 1.

[0078] Comparative Example 3

[0079] A method for bonding silicon carbide seed crystals, which differs from Example 1 in that stainless steel blocks are used as pressing blocks in both step (2) the first hot pressing and step (2) the second hot pressing, and other substances, amounts and preparation methods are the same as those in Example 1.

[0080] Comparative Example 4

[0081] A method for bonding silicon carbide seed crystals, which differs from Example 1 in that, before performing step (2), it also includes the step of spin-coating the glue obtained in step (1) on the bonding surface of the silicon carbide seed crystal, and then directly placing it in a hot press furnace and heating it to 800° C. for carbonization, and then performing steps (2) and (3) after carbonization, and other materials, conditions and parameters are the same as those in Example 1.

[0082] Application Examples 1 to 4 and Comparative Application Examples 1 to 4

[0083] A method for preparing a silicon carbide single crystal, specifically comprising: filling silicon carbide powder at the bottom of a graphite crucible, and using the bonding pieces obtained in Examples 1 to 4 and Comparative Examples 1 to 4 as graphite crucible covers, respectively, placing the graphite crucible in a single crystal furnace, and growing the silicon carbide single crystal by a PVT method;

[0084] The growth temperature was set at 2300°C, the heating rate was controlled below 100°C / h before 800°C, high-purity Ar was used as the protective gas, the growth pressure was controlled at 200Pa, and the growth time was 90h.

[0085] Result analysis:

[0086] The bonding conditions of silicon carbide seed crystals and the growth conditions of silicon carbide single crystals are summarized in Table 1 from the following three aspects:

[0087] (1) Visual inspection of the bonding surface refers to the visual inspection of the bonding surface of the bonded parts under ultraviolet light after the first bonding in step (2); (2) Visual inspection of the bonding back side of the single crystal obtained after growth; (3) Visual inspection of the area ratio of hexagonal voids in the single crystal.

[0088] Table 1

[0089]

[0090]

[0091] From the data in Table 1, we can see that:

[0092] The bonding effects of the silicon carbide single crystals subsequently prepared from the bonding parts obtained by the bonding methods provided in Examples 1 to 4 are all good, the water stains on the back of the crystal are uniform as a whole, there is no crystal degradation due to bonding, and the cumulative area of ​​hexagonal voids in the silicon carbide crystals is relatively low.

[0093] However, the bonding effect of the silicon carbide single crystal subsequently prepared by the bonding method provided in Comparative Examples 1 to 4 is poor, ablation occurs, and the cumulative area of ​​hexagonal voids in the silicon carbide crystal is significantly higher than that of Examples 1 to 4.

[0094] The applicant declares that the present invention illustrates a method for bonding silicon carbide seed crystals, silicon carbide single crystals and their preparation methods and applications through the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvement to the present invention, equivalent replacement of the raw materials selected by the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for bonding silicon carbide seed crystals, characterized in that: The bonding method comprises the following steps: (1) providing a glue solution containing a binder, a silane coupling agent and a solvent; (2) applying the glue obtained in step (1) on the bonding surface of the graphite paper and the silicon carbide seed crystal, and then pressing the two concentrically to bond them together, and then using the silicon carbide ingot as a pressing block, performing the first hot pressing in the order of the silicon carbide ingot, the silicon carbide seed crystal and the graphite paper from top to bottom; (3) The composite structure obtained after the first hot pressing in step (2) is bonded to the graphite tray, and then a second hot pressing is performed using a pressing block in the order of a pressing block, a silicon carbide seed crystal, a graphite paper and a graphite tray from top to bottom to complete the bonding of the silicon carbide seed crystal.

2. The bonding method according to claim 1, characterized in that: The binder in step (1) comprises photoresist; Preferably, the adhesive in step (1) is a phenolic resin adhesive and / or an epoxy resin adhesive; Preferably, the silane coupling agent in step (1) includes any one of γ-aminopropyltriethoxysilane, γ-glycidyloxypropyltrimethoxysilane or γ-aminoethylaminopropyltrimethoxysilane, or a combination of at least two thereof; Preferably, based on the amount of the binder in step (1) being 1 g, the amount of the silane coupling agent in step (1) is 0.01 to 0.05 g; Preferably, the solvent in step (1) comprises any one of anhydrous ethanol, isopropanol, acetone or ethyl acetate, or a combination of at least two thereof; Preferably, the viscosity of the glue in step (1) is 500-2000 mPa·s for spin coating, or the viscosity is 10-50 mPa·s for spray coating.

3. The bonding method according to claim 1 or 2, characterized in that: The coating method in step (2) is spin coating or spray coating; Preferably, the liquid supply rate of the spraying is 20 to 50 μL / s; Preferably, the spin coating speed is 500 to 1500 rpm; Preferably, the coating time in step (2) is 20 to 30 seconds.

4. The bonding method according to any one of claims 1 to 3, characterized in that: The thickness of the graphite paper in step (2) is 0.2 to 0.5 mm; Preferably, the thickness of the silicon carbide seed crystal in step (2) is 350 to 1000 μm.

5. The bonding method according to any one of claims 1 to 4, characterized in that: The first hot pressing in step (2) and the second hot pressing in step (3) are both performed in a hot pressing furnace; Preferably, the vacuum degree of the hot pressing furnace is ≤10Pa; Preferably, the applied pressures of the first hot pressing in step (2) and the second hot pressing in step (3) are each independently 0.05 to 0.3 MPa; Preferably, the first hot pressing in step (2) and the second hot pressing in step (3) are both carried out under gradient heating conditions, and the gradient heating step includes: first heating to 80-130°C for ≥30 min, and then heating to 170-250°C for a second time for ≥20 min.

6. The bonding method according to any one of claims 1 to 5, characterized in that: The thickness of the silicon carbide ingot in step (2) is 5 to 15 mm; Preferably, the diameter of the silicon carbide ingot in step (2) is greater than the diameter of the silicon carbide seed crystal in step (2).

7. A method for preparing a silicon carbide single crystal, characterized in that: The preparation method comprises the following steps: The silicon carbide powder is filled at the bottom of the graphite crucible, and the bonding member obtained by bonding with the bonding method according to any one of claims 1 to 6 is used as the graphite crucible cover. The graphite crucible is placed in a single crystal furnace, and the silicon carbide single crystal is grown by a PVT method.

8. The preparation method according to claim 7, characterized in that: The growth temperature is 2200-2300°C and the growth time is 85-95h; Preferably, before the temperature of the single crystal furnace reaches 800° C., the heating rate is ≤100° C. / h; Preferably, the growth pressure is 150-300 Pa; Preferably, the growth is carried out under inert gas protection conditions.

9. A silicon carbide single crystal bonding structure, characterized in that: The silicon carbide single crystal bonding structure is prepared by the preparation method as claimed in claim 7 or 8.

10. An application of the silicon carbide single crystal bonding structure as claimed in claim 9 as a substrate material in aerospace, photovoltaic power generation, rail power grid and new energy electricity.

Images