A special graphite crucible for crystal growth furnace and its preparation method

Abstract

The present invention discloses a special graphite crucible for crystal growth furnaces and a preparation method thereof. Using a semi-coked carbon product with self-bonding properties as the raw material, and graphene powder and pitch coke powder as microstructure regulators, the raw materials are mixed in multiple rounds to form pressed powder. Then, the pressed powder is subjected to pre-forming, isostatic pressing, carbonization, graphitization, and machining to prepare a graphite crucible that meets the requirements of crystal growth furnaces. By introducing nano-scale and micro-scale microstructure regulators, on the one hand, the interfacial bonding of semi-coked raw materials is improved, and the microstructure of the product is optimized; on the other hand, the structure regulators, as reinforcing agents, strengthen the structural support of the graphite crucible and also prevent the intercalation corrosion of the graphite crucible by silicon vapor under high-temperature conditions, effectively improving the structural stability and service life of the graphite crucible. In addition, the main raw materials of the present invention are industrial semi-finished products in the coal chemical or petrochemical industries, with wide sources and low prices, and are suitable for large-scale batch production.

Description

Technical Field

[0001] The present invention relates to the technical field of special graphite, and more specifically to a graphite crucible dedicated to a crystal growth furnace and a preparation method thereof. Background Art

[0002] As a third-generation wide-bandgap semiconductor material, due to its excellent properties such as wide bandgap, high dielectric constant, etc., SiC has become an ideal material for making high-temperature, high-frequency, high-power, and high-voltage electronic devices, with characteristics such as high thermal conductivity, high saturated electron velocity, and strong radiation resistance. The comprehensive performance of the prepared SiC power devices is far superior to that of traditional silicon-based devices, breaking through the physical limitations of silicon-based semiconductor materials. However, due to various defects existing during growth, including microtubes, stacking faults, dislocations, and polytype inclusions, etc., it cannot meet the requirements of current device applications, and the crystal quality needs to be further improved. One of the reasons for the formation of defects in the grown crystal is the corrosion behavior of the graphite crucible wall caused by sublimated gases such as Si and Si 2 C, so the performance requirements for the graphite crucible by the crystal growth furnace are becoming increasingly strict.

[0003] There are very few graphite products in the domestic market that can be well applied to the third-generation semiconductor SiC crystal growth furnace, mainly foreign brands such as German R6510 and Japanese SiC6. With the continuous progress of the semiconductor industry, foreign graphite products are increasingly unable to meet the industrial needs of the crystal growth furnace, mainly reflected in the following aspects: 1. Taking R6510 as an example, it is difficult to resist the corrosion of silicon vapor, and the crucible needs to be replaced about once a month; 2. Foreign graphite products are all developing towards large sizes, calculating the price by weight, which is beneficial to upstream suppliers, but not friendly to downstream customers, and the finishing utilization rate is relatively low. Therefore, developing a dedicated graphite crucible for the third-generation semiconductor crystal growth furnace and breaking through the "stuck-neck" technology to fill the domestic gap is of great significance.

[0004] In recent years, regarding the synergistic effect of nanoparticles and microparticles as microscopic regulators on special graphite, it has mainly been analyzed through particle size grading. Tian Benliang's "Discussion on Several Issues in Batching" analyzed that when small particles and large particles are graded, the optimal ratio of the diameter of small particles to that of large particles is ≤0.225. The particle size grading of the graphene powder, pitch coke powder, and self-sintering raw materials used in this invention also conforms to this theory. In recent years, corresponding progress has also been made in the research and development of low-porosity graphite in China. Yang Cheng et al. (A High-Thermal-Conductivity and Low-Porosity Graphite for Curved Glass Hot Bending Molds and Its Preparation Method, Authorization Publication No. CN112321300B) prepared low-porosity graphite products by mixing modified petroleum coke powder and modified mesophase carbon microspheres, but the mixing process will seriously affect the internal uniformity of the products and is prone to forming defects. Zhai Xuecheng et al. (A Carbon Nanotube-Modified and Reinforced Graphite Electrode and Its Preparation Method, Authorization Publication No. CN110204349A) improved the product density and physical and electrical properties by adding nanoparticles. Although the compounding of nanoparticles and microparticles can effectively conduct microscopic regulation, the smaller the particle size, the more difficult it is to achieve homogeneous dispersion under industrial conditions, and it is prone to agglomeration and forming defects, which instead has a negative effect on the performance of the products. At the same time, the traditional processing method is still used for preparing crucibles in China. Dong Xianhu et al. (A Method for Preparing Graphite Crucibles with Recycled Graphite, Authorization Publication No. CN105272287B) processed the blank into a crucible, resulting in low utilization rate of the raw material blank and low production efficiency as it is time-consuming and laborious. Therefore, how to provide a new graphite crucible to overcome the deficiencies of the existing technology is an urgent problem for those skilled in the art to solve. Summary of the Invention

[0005] In view of this, to solve the above problems, the present invention provides a special graphite crucible for the third-generation semiconductor SiC crystal growth furnace and its preparation method.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] First, the present invention provides a preparation method for a special graphite crucible for a crystal growth furnace, including the following steps:

[0008] S1. High-speed disperse and classify and mix graphene powder and pitch coke powder evenly, where the number of high-speed classification mixing times ≥ 3 times;

[0009] S2. Disperse and classify and mix the mixed powder obtained in step S1 with self-sintering carbon materials evenly, where the number of classification mixing times ≥ 3 times;

[0010] S3. Preform the crucible and isostatically press the powder obtained in step S2, and directly obtain the green crucible sample after demolding;

[0011] S4. First carbonize and then graphitize the green sample obtained in step S3 to obtain a special graphite crucible for a crystal growth furnace.

[0012] Preferably, the mass ratio of the self-sintering carbon material, graphene powder, and pitch coke powder is 85-95:0.1-3:5-15.

[0013] Preferably, the high-speed dispersion and classification mixing in step S1 are specifically as follows:

[0014] S11. Take graphene powder and an equal mass of pitch coke powder and disperse them in a high-speed disperser at a rotation speed of 6000-8000 r / min for 2-10 min;

[0015] S12. Take pitch coke powder with twice the mass of the pitch coke powder in S11 and continue to disperse the mixture obtained in step S11 in a high-speed disperser at a rotation speed of 6000-8000 r / min for 2-10 min;

[0016] S13. Take the remaining pitch coke powder and the mixture in step S12 and disperse them in a high-speed disperser at a rotation speed of 6000-8000 r / min for 2-3 min.

[0017] Preferably, the graphene powder is high-thermal-conductivity reduced graphene oxide powder, with a specific surface area of 500-600 m² / g and a thermal conductivity > 1000 W / mk.

[0018] Preferably, the particle size D50 of the pitch coke powder is 2-12 μm and the ash content ≤ 0.2%.

[0019] Preferably, the high-speed dispersion and classification mixing in step S2 are specifically as follows:

[0020] S21. Take the mixed powder prepared in step S1 and an equal mass of self-sintering carbon material and mix them in a three-dimensional double-motion mixer at a rotation speed of 30-50 r / min for 1-3 h;

[0021] S22. Take self-sintering carbon material with twice the mass of the self-sintering carbon material in S21 and continue to mix the mixture obtained in step S21 in a three-dimensional double-motion mixer at a rotation speed of 30-50 r / min for 1-3 h;

[0022] S23. Take the remaining self-sintering carbon material and the mixture in step S22 and mix them in a three-dimensional double-motion mixer at a rotation speed of 30-50 r / min for 1-3 h.

[0023] Preferably, the self-sintering carbon material includes one or more of pitch green coke, petroleum green coke, α component, and mesophase carbon microspheres. The particle size D50 of the self-sintering carbon material is 10-50 μm and the ash content ≤ 0.2%.

[0024] Preferably, the crucible preforming and isostatic pressing in step S3 are as follows: first, pre-mold at 30 - 50 Mpa, then load it into a rubber sleeve with a steel mold and evacuate under a pumping pressure of 1 - 1.5 L / s for 20 - 30 min, and send it to an isostatic press for forming at 100 - 220 Mpa.

[0025] Preferably, the specific steps of carbonization in step S4 are as follows: heat up to 400 - 450 °C at a heating rate of 1 - 8 °C / h; then heat up to 700 - 850 °C at a heating rate of 0.1 - 5 °C / h; then heat up to 1000 - 1300 °C at a heating rate of 1 - 10 °C / h; finally, cool down at a cooling rate of 5 - 30 °C / h to 200 - 220 °C, open the furnace door, and cool down to 50 - 70 °C for discharging.

[0026] The specific steps of graphitization are as follows: heat the carbonized product to 1000 - 1300 °C at a heating rate of 25 - 35 °C / h, then heat it to 2000 - 2100 °C at a heating rate of 70 - 90 °C / h, then heat it to 2500 - 2800 °C at a heating rate of 100 - 125 °C / h, and then keep it warm for 1 - 2 h.

[0027] In addition, the present invention also provides a graphite crucible prepared by the method described in the above technical solution.

[0028] From the above technical solutions, it can be seen that compared with the prior art, the present invention discloses a special graphite crucible for crystal growth furnace and its preparation method, which has the following beneficial effects:

[0029] The present invention uses self-sintering raw materials as the main material and a composite material of highly thermally conductive graphene and pitch coke powder as the auxiliary material. Highly thermally conductive graphene, as a nanomaterial, composites with micron-sized pitch coke powder to act as an excellent microstructure regulator. However, the dispersion of nanomaterials is difficult. If they cannot be well dispersed, it is easy to have a negative effect on the products. Currently, most of the dispersion applications remain in the laboratory stage and there is no good industrial means. The present invention realizes the uniform dispersion of nanomaterials and micron-sized materials through a hierarchical mixing method and industrial feasible means. By introducing nanoscale and micron-scale microstructure regulators, on the one hand, the interfacial bonding of semi-coked raw materials is improved and the microstructure of the product is optimized; on the other hand, the structure regulator, as a reinforcing agent, strengthens the structural support force of the graphite crucible and also prevents the intercalation corrosion of the graphite crucible by silicon vapor under high-temperature conditions, effectively improving the structural stability and service life of the graphite crucible.

[0030] The process adopted by the present invention belongs to the category of "one-component method" processes, that is, a single main raw material, while the German R6510 adopts a two-component method process, which is mainly sintered through the mixture of coke and pitch. Analyzed from the process, the "one-component method" has inherent advantages, with better product quality uniformity and product stability; and it is a self-sintering raw material, with high sphericity, good shrinkage uniformity, and not prone to internal cracks. Detailed implementation mode

[0031] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work shall fall within the scope of protection of the present invention.

[0032] Embodiment 1

[0033] The crucible for semiconductor SiC crystal growth furnace is mainly prepared from self-sintering carbon material, high thermal conductivity graphene powder, and pitch coke powder; among them, the mass ratio of self-sintering carbon material, high thermal conductivity graphene powder, and pitch coke powder is 90:0.5:9.5;

[0034] The graphene powder is prepared by thermally reducing commercially available graphene oxide powder in a tube furnace at 550 °C for 1.5 min to obtain the required high thermal conductivity graphene powder, with a specific surface area of 550 m² / g and a thermal conductivity of 1100 W / mk;

[0035] The self-sintering carbon material uses mesophase carbon microspheres with a particle size D50 of 35 μm and an ash content of 0.1% for standby.

[0036] The pitch coke powder is high-purity ultrafine coke powder, with a particle size D50 of 8 μm and an ash content of 0.2%;

[0037] S1.

[0038] S11. Disperse 90 g of graphene powder and 90 g of pitch coke powder in a high-speed disperser for 2 min, and the rotation speed of the disperser is 7500 r / min;

[0039] S12. Disperse the mixture and 180 g of pitch coke powder in a high-speed disperser for 2 min, and the rotation speed of the disperser is 6500 r / min;

[0040] S13: Disperse the mixture of S12 and the remaining 540 g of pitch coke powder in a high-speed disperser for 3 min, and the rotation speed of the disperser is 6000 r / min, finally obtaining 900 g of homogenously mixed high thermal conductivity graphene / coke mixture;

[0041] S2.

[0042] S21. Mix 900 g of high thermal conductivity graphene / coke mixture with 900 g of mesophase carbon microspheres in a 30 L three-dimensional motion mixer for 2 h at a rotation speed of 50 r / min;

[0043] S22. Mix more than 1800 g of the mixture with 1800 g of mesophase carbon microspheres in a 30 L three-dimensional motion mixer for 2.5 h at a rotation speed of 50 r / min;

[0044] S23: Mix 3600 g of the above mixture with the remaining 5400 g of mesophase carbon microspheres in a 30 L three-dimensional motion mixer for 3 h at a rotation speed of 40 r / min;

[0045] S3. First pre-mold the above 9000 g of homogeneous mixed material obtained in step S2, load it into a rubber sleeve with a steel mold in the center, and vibrate and compact it; then evacuate for 30 min under a pumping pressure of 1.5 L / s, and send it to an isostatic press for isostatic pressing at 130 MPa, and demold the green body;

[0046] S4. Send the green body sample obtained in step S3 to a box-type carbonization furnace for treatment, landfill the flake graphite, and set the carbonization heating curve as follows: heat up to 400 °C at a heating rate of 2 °C / h; then heat up to 700 °C at a heating rate of 1 °C / h; then heat up to 1000 °C at a heating rate of 2 °C / h; finally, cool down to 200 °C at a cooling rate of 10 °C / h to open the furnace door, and cool down to 50 °C to take out of the furnace;

[0047] Then carry out graphitization treatment: heat the carbonized product to 1000 °C at a heating rate of 30 °C / h, then heat up to 2000 °C at a heating rate of 85 °C / h, then heat up to 2500 °C at a heating rate of 100 °C / h, and then hold for 1 h.

[0048] The density of the sample obtained by graphitization is 1.89 g / cm 3 , the bending strength is 80 Mpa, the porosity is 13%, the average pore diameter is 0.4 μm, and the thermal expansion coefficient is 5.9*10 -6 / °C. The product yield reaches 98%. The silicon infiltration depth of the product is 185 μm, which is 18.5% lower than the silicon infiltration depth of 227 μm of SGL R6510.

[0049] Example 2

[0050] The difference from Example 1 is that the sintering raw material is adjusted to a mixture of green coke and mesophase carbon microspheres with a mass ratio of 1:1.

[0051] The final product yield is 85%. The prepared graphite properties are detected as the bulk density of 1.88 g / cm 3 , the bending strength is 70 Mpa, the porosity is 14.5%, and the thermal conductivity is 120 w(mk).

[0052] Example 3

[0053] It is different from Example 1 in that the final carbonization temperature is adjusted to 1300 °C and the final graphitization temperature is adjusted to 2800 °C.

[0054] The yield of the final product reaches 90%. The performance density of the prepared graphite product is 1.9 g / cm 3 , and the flexural strength is 78 Mpa.

[0055] The basic physical and chemical properties of the products of Examples 1-3 are as shown in Table 1 below

[0056] Table 1 Basic physical and chemical properties of materials

[0057]

[0058] Comparative Example 1

[0059] German R6510 product.

[0060] Comparative Example 2

[0061] Japanese SiC6 product.

[0062] The performance comparison between the products of Examples 1-3 of the present invention and the products of Comparative Examples 1-2 is shown in Table 2 below.

[0063] Table 2 Product performance comparison

[0064]

[0065] The graphite material of the present invention uses self-sintered raw materials as the main material. The product has a small pore size of 0.2-0.6 μm and a small porosity of 13-15%. The pore sizes of R6510 and SiC6 are 1-1.8 μm, and the porosity reaches 19%. The product of the present invention has stronger resistance to silicon vapor corrosion.

[0066] In this specification, the various embodiments are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the description in the method part.

[0067] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a graphite crucible for a crystal growth furnace, characterized in that: The following steps are involved: S1. High-speed dispersion and graded mixing of graphene powder and asphalt coke powder, wherein the high-speed graded mixing number is ≥ 3 times; S2. The mixed powder obtained in step S1 is dispersed and mixed evenly with the self-sintered carbon material, wherein the number of graded mixing is ≥ 3 times; S3. The powder obtained in step S2 is preformed into a crucible, isostatically pressed, and demolded to obtain a crucible green sample directly; S4. The green sample obtained in step S3 is first carbonized and then graphitized to obtain a graphite crucible for a crystal growth furnace; The mass ratio of the self-sintered carbon material, graphene powder and asphalt coke powder is 85-95:0.1-3:5-15; The particle size D50 of the self-sintered carbon material is 10-50 μm; The graphene powder is high thermal conductivity reduced oxide graphene powder, with a specific surface area of ​​500-600 m2 / g and a thermal conductivity greater than 1000 W / mk; The asphalt coke powder has a particle size D50 of 2-12 μm and an ash content of ≤0.2%; The high-speed dispersion and graded mixing described in step S1 are specifically as follows: S11. Take graphene powder and asphalt coke powder of equal mass and disperse them in a high-speed disperser at a speed of 6000-8000r / min for 2-10min; S12. Take twice the mass of the asphalt coke powder in S11 and the mixture obtained in step S11 and continue to disperse in a high-speed disperser at a speed of 6000-8000r / min for 2-10min; S13. Take the remaining asphalt coke powder and the mixture of step S12 and disperse it in a high-speed disperser at a speed of 6000-8000r / min for 2-10min; The high-speed dispersion and graded mixing described in step S2 are specifically as follows: S21. The mixed powder obtained in step S1 is mixed with an equal mass of self-sintered carbon material in a three-dimensional dual-motion mixer at a speed of 30-50r / min for 1-3h; S22. Take twice the mass of the self-sintered carbon material in S21 and the mixture obtained in step S21 and continue mixing at a speed of 30-50r / min in a three-dimensional dual-motion mixer for 1-3h; S23. Take the remaining self-sintered carbon material and the mixture of step S22 and mix them in a three-dimensional double-motion mixer at a speed of 30-50 r / min for 1-3 hours.

2. The method for preparing a special graphite crucible for a crystal growth furnace according to claim 1, characterized in that: The self-sintering carbon material comprises one or more of asphalt green coke, petroleum green coke, α component, and mesophase carbon microspheres. The particle size D50 of the self-sintering carbon material is 10-50 μm, and the ash content is ≤0.2%.

3. The method for preparing a special graphite crucible for a crystal growth furnace according to claim 1, characterized in that: The crucible preforming and isostatic pressing in step S3 are as follows: first pre-molding at 30-50 MPa, then placing it in a rubber sleeve with a steel mold and evacuating it at a vacuum pressure of 1-1.5 L / s for 20-30 minutes, and then sending it to an isostatic press for molding at 100-220 MPa.

4. The method for preparing a special graphite crucible for a crystal growth furnace according to claim 1, characterized in that: The specific steps of carbonization in step S4 are: heating to 400-450°C at a heating rate of 1-8°C / h; then heating to 700-850°C at a heating rate of 0.1-5°C / h; then heating to 1000-1300°C at a heating rate of 1-10°C / h; finally cooling to 200-220°C at a cooling rate of 5-30°C / h, opening the furnace door, cooling to 50-70°C and taking out of the furnace; The specific steps of graphitization are: heating the carbonized product to 1000-1300°C at a heating rate of 25-35°C / h, then heating it to 2000-2100°C at a heating rate of 70-90°C / h, then heating it to 2500-2800°C at a heating rate of 100-125°C / h, and then keeping the temperature for 1-2h.

5. A graphite crucible prepared by the method according to any one of claims 1 to 4.

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