A high-density and low-porosity graphite crucible for a crystal growth furnace and its preparation method

Abstract

The present invention discloses a high-density and low-porosity graphite crucible special for crystal growth furnaces and a preparation method thereof. Graphene powder, graphite powder and ultra-fine pitch coke are used as aggregates. The aggregates and ultra-fine pitch powder are dispersed at low temperature and kneaded at high temperature to prepare a paste, which is crushed into pressed powder. The pressed powder is subjected to pre-forming, isostatic pressing, carbonization, impregnation, graphitization and machining to prepare a graphite crucible meeting the requirements of crystal growth furnaces. By introducing nano-scale and micro-scale microstructure regulators, on the one hand, the interfacial bonding property of 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. In addition, the main raw materials of the present invention are industrial semi-finished products in the coal chemical industry or petrochemical industry, 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 particularly to a high-density and low-porosity graphite crucible for 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 and high dielectric constant, SiC has become an ideal material for fabricating high-temperature, high-frequency, high-power, and high-voltage electronic devices. 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 the growth of SiC, including microtubes, stacking faults, dislocations, and polytype inclusions, etc., it obviously 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 Si2C. Therefore, the performance requirements for the graphite crucible in the crystal growth furnace are becoming increasingly strict.

[0003] The graphite products that can be applied to the third-generation semiconductor SiC crystal growth furnace in the domestic market are mainly foreign brands, such as R6510 from Germany and SiC6 from Japan. With the continuous progress of the semiconductor industry, foreign graphite products are increasingly unable to meet the industrial needs of the crystal growth furnace, which are mainly reflected in the following aspects: 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. Foreign graphite products are all developing towards large sizes, and the price is calculated by weight, which is beneficial to upstream suppliers, but not friendly to downstream customers, and the fine machining utilization rate is relatively low. Therefore, it is of great significance to develop a special graphite crucible for the third-generation semiconductor crystal growth furnace.

[0004] 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 a hot-bending mold of curved glass and its preparation method, authorized announcement number CN112321300B) prepared low-porosity graphite products by mixing modified petroleum coke powder and modified mesophase carbon microspheres. However, the mixing of materials will seriously affect the internal uniformity of the products and is prone to forming defects. Zhai Xuecheng et al. (A carbon nanotube-modified enhanced graphite electrode and its preparation method, authorized announcement number CN110204349B) improved the product density and physical and electrical properties by adding nano-particles. Although the compounding of nano-particles and micro-particles 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 easy to cause agglomeration to form defects, which instead has a negative effect on the performance of the products. Dong Xianhu et al. (A method for preparing a graphite crucible with recycled graphite, authorized announcement number CN105272287B) processed the blank into a crucible, but the blank utilization rate of the raw materials is low, and it is time-consuming and laborious with low production efficiency. Therefore, how to provide a new graphite crucible to overcome the deficiencies of the existing technology is an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0005] In view of this, in order 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] A preparation method of a special high-density and low-porosity graphite crucible for a crystal growth furnace, comprising the following steps:

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

[0009] S2. Disperse and classify the mixed powder obtained in step S1 with ultra-fine pitch coke aggregate to mix them evenly, where the number of classification mixing is ≥3 times;

[0010] S3. Disperse the mixed powder obtained in step S2 with ultra-fine pitch powder at 30 - 100 r / min at room temperature for 1 - 5 h, and then knead it at 120 - 190 °C in a vacuum kneader for 1 - 3 h to obtain a paste. Crush the paste into 10 - 30 μm to obtain pressed powder;

[0011] S4. Perform crucible pre-forming and isostatic pressing on the pressed powder obtained in step S3, and directly demold to obtain a crucible green body sample;

[0012] S5. First carbonize the green body sample obtained in step S4, impregnate it, and then graphitize it to obtain a special high-density and low-porosity graphite crucible for a crystal growth furnace.

[0013] Preferably, the mass ratio of the ultra-fine pitch coke aggregate, graphene powder, graphite powder, and ultra-fine pitch powder is 65-75:0.1-3:5-10:25-35.

[0014] Preferably, the high-speed dispersion and classified mixing in step S1 are specifically as follows:

[0015] S11. Take graphene powder and an equal mass of graphite powder and disperse them in a high-speed disperser at a rotation speed of 6000-8000 r / min for 2-3 min;

[0016] S12. Take twice the mass of graphite powder as that 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 2-3 min;

[0017] S13. Take the remaining graphite 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.

[0018] 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 greater than 1000 W / mk.

[0019] Preferably, the particle size D50 of the graphite powder is 2-10 μm and the ash content is ≤0.2%.

[0020] Preferably, the D50 of the ultra-fine pitch coke aggregate is ≤5 μm and the ash content is ≤0.4%; the particle size of the ultra-fine pitch powder is 200-300 mesh.

[0021] Preferably, the high-speed dispersion and classified mixing in step S2 are specifically as follows:

[0022] S21. Take the mixed powder prepared in step S1 and an equal mass of ultra-fine pitch coke aggregate and mix them in a three-dimensional double-motion mixer at a rotation speed of 30-50 r / min for 1-3 h;

[0023] S22. Take twice the mass of ultra-fine pitch coke aggregate as that 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;

[0024] S23. Take the remaining ultra-fine pitch coke aggregate 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.

[0025] Preferably, the crucible preforming and isostatic pressing in step S4 are as follows: first pre-mold at 30-50 Mpa, then load it into a rubber sleeve with a steel mold and evacuate to vacuum for 20-30 min under a pumping pressure of 1-1.5 L / s, and send it to an isostatic press for forming at 100-220 Mpa.

[0026] Preferably, the impregnation pressure in step S5 is 0.6-0.8 MPa, and the impregnation time is 4-8 h; the specific steps of carbonization are as follows: heat up at a heating rate of 1-10 °C / h to 1000-1300 °C and keep warm for 1-3 h, then cool down at a cooling rate of 5-50 °C / h to 50-70 °C and take out of the furnace;

[0027] The specific steps of graphitization are as follows: heat up the carbonized product at a heating rate of 25-45 °C / h to 1000-1300 °C, and then heat up at a heating rate of 70-125 °C / h to 2500-2800 °C and keep warm for 1-2 h.

[0028] In addition, the present invention also provides a high-density and low-porosity graphite crucible for a crystal growth furnace prepared by the method described in the above technical solution.

[0029] It can be seen from the above technical solutions that, compared with the prior art, the present invention discloses a high-density and low-porosity graphite crucible for a crystal growth furnace and its preparation method, which has the following beneficial effects:

[0030] The present invention uses graphene and graphite powder compound-modified pitch coke as the aggregate. High-thermal-conductivity graphene, as a nanomaterial, is compounded with micron-sized graphite 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. At present, most of the dispersion applications stay at the laboratory stage and there is no good industrial means. The present invention realizes the uniform dispersion problem of nanomaterials and micron-sized materials through an industrial-feasible means of hierarchical mixing. By introducing nanoscale and micron-scale microstructure regulators, on the one hand, the interfacial bonding of 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.

[0031] Compared with traditional crucibles, the advantages of the present invention are as follows:

[0032] The graphite raw materials of the present invention are all fine particles, and the porosity and average pore diameter of the product are both relatively low. The product of the present invention has stronger resistance to silicon vapor corrosion;

[0033] The preparation method of the present invention enables the graphitization qualification rate of this product to reach 90% through a reasonable formula, reasonable control of the heating curve and the effect of sleeve forming;

[0034] The graphite product involved in the present invention is specially developed for the crucible part of the third-generation semiconductor SiC crystal growth furnace. The formed green body is directly in the shape of a crucible, and the utilization rate of finish machining is high. Specific Embodiments

[0035] The technical solutions 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 the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0036] Embodiment 1

[0037] The crucible for the semiconductor SiC crystal growth furnace is mainly prepared from pitch coke aggregate, highly thermally conductive graphene powder, graphite powder, and ultra-fine pitch powder; among them, the mass ratio of pitch coke aggregate, highly thermally conductive graphene, graphite powder, and ultra-fine pitch powder is 63:1:9:27;

[0038] The graphene powder is prepared by thermally reducing commercially available graphite oxide in a tube furnace at 550 °C for 1.5 min to obtain the required highly thermally conductive graphene powder, with a specific surface area of 550 m² / g and a thermal conductivity of 1100 W / (m·K).

[0039] The pitch coke aggregate uses ultra-fine pitch coke aggregate with a particle size D50 of 3 μm and an ash content of 0.2%;

[0040] The ultra-fine pitch powder is 250 mesh and serves as a binder.

[0041] The graphite powder has a particle size D50 of 2 μm and an ash content of 0.12%;

[0042] S1.

[0043] S11. Disperse 90 g of graphene powder and 90 g of graphite powder in a high-speed disperser for 2 min, and the rotation speed of the disperser is 7500 r / min;

[0044] S12. Disperse the mixture and 180 g of graphite powder in a high-speed disperser for 2 min, and the rotation speed of the disperser is 6500 r / min;

[0045] S13: Disperse the mixture of S12 and the remaining 540 g of graphite 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 a homogeneous mixture of highly thermally conductive graphene / graphite mixture;

[0046] S2.

[0047] S21. Mix 900 g of high thermal conductivity graphene / graphite mixture with 900 g of ultra-fine pitch coke aggregate in a 30 L three-dimensional motion mixer for 2 h at a rotational speed of 50 r / min;

[0048] S22. Mix more than 1800 g of the mixture with 1800 g of ultra-fine pitch coke aggregate in a 30 L three-dimensional motion mixer for 2.5 h at a rotational speed of 50 r / min;

[0049] S23: Mix 3600 g of the above mixture with the remaining 2970 g of ultra-fine pitch coke aggregate in a 30 L three-dimensional motion mixer for 3 h at a rotational speed of 40 r / min to obtain 6570 g of modified aggregate;

[0050] S3. Mix 6570 g of the modified aggregate obtained in step S2 with 2430 g of ultra-fine pitch powder (250 mesh) in a three-dimensional mixer at a rotational speed of 80 r / min for 2 h, then transfer it to a vacuum kneader and knead at 180 °C for 1.5 h to obtain a paste, and crush the paste into pressed powder with D50 20 μm;

[0051] S4. First pre-mold 9000 g of the pressed powder, load it into a rubber sleeve with a steel mold in the center, and vibrate and compact it; then evacuate under a pumping pressure of 1.5 L / s for 30 min, and send it to an isostatic press for isostatic pressing at 200 MPa to demold the green body;

[0052] S5. Send the green body sample obtained in step S4 to a box-type carbonization furnace for treatment, landfill the flake graphite, and set the carbonization heating curve as follows: heat up to 1000 °C at a heating rate of 6.5 °C / h, keep it at a constant temperature for 1 hour; finally cool down to 50 °C at a cooling rate of 10 °C / h and take it out of the furnace;

[0053] Then carry out petroleum asphalt impregnation, impregnate in an environment of 0.6 - 0.8 MPa compressed air for 4 - 5 h, and then carry out graphitization treatment: heat the carbonized product to 1000 °C at a rate of 30 °C / h, and then heat it to 2500 °C at a rate of 85 °C / h, and then keep it at a constant temperature for 1 h.

[0054] The density of the sample obtained by graphitization is 1.85 g / cm 3 , the flexural strength is 50 Mpa, the porosity is 15%, the average pore diameter is 0.7 μm, and the thermal expansion coefficient is 5.2*10 -6 / °C. The product yield reaches 85%.

[0055] Example 2

[0056] The difference from Example 1 is that the particle size D50 of the ultra-fine pitch coke aggregate is 2.7 μm, and the particle size of the ultra-fine pitch powder is 300 mesh.

[0057] The final product yield is 86%. The volume density of the prepared graphite is detected to be 1.87 g / cm 3, the bending strength is 55 Mpa, and the porosity is 14.5%.

[0058] Example 3

[0059] The difference from Example 1 is that the final carbonization temperature is adjusted to 1300 °C and the final graphitization temperature is adjusted to 2800 °C.

[0060] The yield of the final product reaches 80%. The performance of the prepared graphite product has a density of 1.88 g / cm 3 , and the bending strength is 42 Mpa.

[0061] The basic physical and chemical properties of the products in Examples 1 - 3 are shown in Table 1 below.

[0062] Table 1 Basic Physical and Chemical Properties of Materials

[0063]

[0064] In this specification, each embodiment is described in a progressive manner. The key point of each embodiment is to illustrate the differences from other embodiments. For the same or similar parts among the embodiments, reference can be made to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and reference can be made to the method part for relevant details.

[0065] 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 the embodiments shown herein, but will be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A preparation method of a high-density and low-porosity graphite crucible special for a crystal growth furnace, characterized in that It includes the following steps: S1. High-speed disperse and classify and mix graphene powder and graphite powder evenly, where the number of high-speed classification and mixing is ≥3 times. Specifically: S11. Take graphene powder and graphite powder of equal mass in a high-speed disperser and disperse at a rotation speed of 6000 - 8000 r / min for 2 - 3 min; S12. Take graphite powder with twice the mass of the graphite 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 - 3 min; S13. Take the remaining graphite powder and the mixture in step S12 and disperse in a high-speed disperser at a rotation speed of 6000 - 8000 r / min for 2 - 3 min; S2. Disperse and classify and mix the mixed powder obtained in step S1 and ultra-fine pitch coke aggregate evenly, where the number of classification and mixing is ≥3 times. Specifically: S21. Take the mixed powder prepared in step S1 and ultra-fine pitch coke aggregate of equal mass in a three-dimensional double-motion mixer and mix at a rotation speed of 30 - 50 r / min for 1 - 3 h; S22. Take ultra-fine pitch coke aggregate with twice the mass of the ultra-fine pitch coke aggregate 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; S23. Take the remaining ultra-fine pitch coke aggregate and the mixture in step S22 and mix in a three-dimensional double-motion mixer at a rotation speed of 30 - 50 r / min for 1 - 3 h; S3. Disperse the mixed powder obtained in step S2 and ultra-fine pitch powder at 30 - 100 r / min at room temperature for 1 - 5 h, and then knead at 120 - 190 °C in a vacuum kneader for 1 - 3 h to obtain a paste. Crush the paste into 10 - 30 μm to obtain pressed powder; S4. Carry out crucible pre-forming and isostatic pressing on the pressed powder obtained in step S3, and directly obtain a crucible green body sample after demolding; S5. First carbonize the green body sample obtained in step S4, impregnate it and then graphitize it to obtain a high-density and low-porosity graphite crucible for crystal growth furnace; The mass ratio of the ultra-fine pitch coke aggregate, graphene powder, graphite powder, and ultra-fine pitch powder is 65 - 75: 0.1-3:5-10：25-35； The particle size D50 of the graphite powder is 2 - 10 μm, and the ash content is ≤0.2%; The D50 of the ultra-fine pitch coke aggregate is ≤5 μm, and the ash content is ≤0.4%; the particle size of the ultra-fine pitch powder is 200 - 300 mesh; The crucible pre-forming and isostatic pressing in step S4 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 to be formed at 100 - 220 Mpa; The impregnation pressure in step S5 is 0.6 - 0.8 MPa, and the impregnation time is 4 - 8 h; the specific steps of carbonization are: heat up at a heating rate of 1 - 10 °C / h to 1000 - 1300 °C and keep it warm for 1 - 3 h, and then cool down at a cooling rate of 5 - 50 °C / h to 50 - 70 °C and take it out of the furnace; The specific steps of graphitization are as follows: the carbonized product is heated to 1000 - 1300 °C at a heating rate of 25 - 45 °C / h, and then heated to 2500 - 2800 °C at a heating rate of 70 - 125 °C / h, and held for 1 - 2 h; 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 greater than 1000 W / mK.

2. A high - density and low - porosity graphite crucible for a crystal growth furnace prepared by the method according to claim 1.

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