Special graphite for ion implantation and preparation method thereof

Abstract

The invention belongs to the field of carbon product production, and particularly relates to special graphite for ion implantation and a preparation method thereof, and the special graphite is composed of aggregate coke, an additive and a binder; the aggregate coke comprises at least one of low-ash petroleum coke, pitch coke, pitch coke green coke, needle coke and artificial high-purity graphite, the ash content is not higher than 0.2%, the water content is not higher than 0.02%, and the prepared special graphite for ion implantation has excellent comprehensive performance indexes. The volume density is 1.85-1.92 g / cm < 3 >, the porosity is smaller than or equal to 7%, the resistivity is 12-14 mu omega m, the breaking strength is larger than or equal to 85 MPa, the compressive strength is larger than or equal to 180 MPa, the Young modulus is 13-15 GPa, the thermal expansion coefficient is smaller than or equal to 5.0 * 10 <-6 > / DEG C, the total impurity content is smaller than or equal to 50 ppm, the key metal element content is smaller than or equal to 5 ppm, and all the properties reach the industry leading level. The harsh requirements of the ion implantation technology on the special graphite material in the aspects of electric heating performance, mechanical performance, thermal stability and purity can be fully met, and stable operation and efficient work of ion implantation equipment are effectively guaranteed.

Description

Technical Field

[0001] The present invention belongs to the field of carbon product production, and specifically relates to a special graphite for ion implantation and a preparation method thereof. Background Art

[0002] Isostatic graphite, as a new type of special graphite material, has the characteristics of high strength, high density, high purity, isotropic and homogeneous and dense structure, and is widely used in many fields such as photovoltaic, electrical discharge machining, metal continuous casting, chemical industry, high-temperature furnace, metallurgical fixture, military, semiconductor, nuclear energy, etc. It is an important strategic basic material to promote economic development, scientific and technological progress and national defense construction. However, the production of isostatic graphite puts extremely high requirements on raw materials, process technology, equipment and personnel, etc. At present, only medium and low-end products can be produced in China, and the application scope is greatly limited.

[0003] The conventional production process of special carbon graphite materials is as follows: first, use a grinding machine to grind coke particles into micron-sized fine powder, and then mix according to a specific formula; the mixed fine powder is preheated, and molten liquid asphalt is added and kneaded into a paste; the paste is cooled to form a paste block with a size less than 10 cm, and then the paste block is ground into fine powder of dozens of microns again; then a green body is obtained by molding through die pressing or isostatic pressing, and the green body is baked into a special carbon material, and further formed into a special graphite material after impregnation, secondary baking and graphitization treatment. Among them, the finer the particle size of the coke fine powder, the more pores, the greater the amount of binder asphalt required, and the higher the performance of the final product.

[0004] In the field of semiconductor manufacturing, ion implantation is the core process to achieve doping of semiconductor wafers. Due to the good high-temperature resistance and excellent electrical conductivity of graphite, it is widely used in ion source components such as arc chambers and electrodes.

[0005] However, as the chip manufacturing process enters below 5 nm, many problems are exposed in the existing isostatic graphite materials, and it is difficult to meet the performance requirements of the ion implantation process for graphite materials:

[0006] First, the purity is insufficient. The content of impurity elements (such as Fe, Na, K, etc.) in traditional graphite exceeds 500 ppm, which is easy to volatilize at high temperature, thus contaminating the ion beam and increasing the defect rate of the wafer;

[0007] Second, the structure is uneven. The grain size difference is large (in the range of 10 - 50 μm) and the porosity is high (greater than 15%), which will cause uneven plasma distribution and reduce the uniformity of ion implantation;

[0008] Third, the thermal shock resistance is poor. Frequent thermal cycles are easy to cause crack propagation, and the service life of the component is only a few hundred hours;

[0009] Fourthly, the surface roughness is not ideal. After machining, the surface Ra > 1.6μm, which will accelerate the loss of plasma etching.

[0010] Fifthly, the material bonding strength is poor. During use, particle shedding and powdering are likely to occur on the surface of the graphite material, which will then contaminate the entire system.

[0011] Therefore, the present invention provides a special graphite for ion implantation and its preparation method. Summary of the Invention

[0012] In order to make up for the deficiencies of the prior art and solve at least one of the technical problems proposed in the background art.

[0013] The technical solution adopted by the present invention to solve its technical problems is as follows: A special graphite for ion implantation according to the present invention, the special graphite is composed of aggregate coke, additives and binders;

[0014] The aggregate coke includes at least one of low-ash petroleum coke, pitch coke, green pitch coke, needle coke, and artificial high-purity graphite, with an ash content not higher than 0.2% and a moisture content not higher than 0.02%;

[0015] The additives include at least one of nano silicon carbide, carbon black, natural flake graphite, elemental sulfur, and boric acid;

[0016] The binder includes high-temperature asphalt with a softening point of 100-180°C, and the ash content of the special graphite is controlled within 50 ppm.

[0017] A preparation method of a special graphite for ion implantation, the preparation method includes the following steps:

[0018] S1. Raw material treatment: Different types of aggregate coke are each divided into coarse particles, medium particles, fine particles, and ultra-fine particles through a powder grinding and classification device;

[0019] S2. Primary and secondary grading and mixing: The fine powders of raw material coke of different types and particle sizes are mixed according to a certain ratio for grading, so that the particle size D50 of the graded powder does not exceed 20μm;

[0020] The graded powder is preheated to 150-250°C by a preheater, the vacuum dehydration device is started to remove moisture, and then it is put into an intermeshing internal mixer for uniform mixing for 10-30 min. The internal mixer rotor has spiral shear teeth, and the rotation speed is adjustable from 10-120 rpm. Melted high-temperature asphalt with a softening point of 100-180°C is added for mixing, the mixing temperature is 150-250°C, the pressure of the internal mixer is 0.5-2 MPa, the pressure mixing time is 10-30 min, the atmospheric open mixing time is 10-20 min, open mixing and pressure mixing are carried out alternately, and the total mixing time is 30-180 min. During the mixing process, the exhaust valve of the flue gas treatment system is started;

[0021] The kneaded paste is put into a kneader with a preheating temperature of 200 - 300 °C for kneading treatment. The kneading time is 30 - 240 min, and the kneading temperature is 200 - 300 °C. The suction valve of the flue gas treatment system of the kneader is adjusted to control the volatile content of the paste to 10% - 15%. After the kneading of the paste is completed, it is put into a cooler and cooled to below 60 °C;

[0022] S3. Paste treatment: The cooled paste is crushed and then subjected to grinding and classification treatment to form pressed powders of coarse particles, medium particles, fine particles, and ultra-fine particles;

[0023] The pressed powders of different particle sizes are proportioned according to a certain ratio so that the particle size D50 range of the proportioned pressed powder is 20 - 50 μm, and then a homogenizing and mixing device is used for mixing;

[0024] S4. Isostatic pressing: The proportioned and mixed pressed powder is loaded into a special mold rubber sleeve, evacuated for 10 - 120 min, and the vacuum degree is not lower than -0.085 MPa. After the evacuation is completed, the mold is lifted into a cold isostatic press, and isostatic pressing is carried out under the conditions of a forming pressure of 160 - 220 MPa and a holding time of the highest pressure of 20 - 40 min, and the density of the green body is controlled at 1.50 - 1.75 g / cm 3 ;

[0025] S5. Post-process treatment: The green body is subjected to high-temperature carbonization treatment, and the carbonization temperature is not lower than 950 °C to form a first-baked product;

[0026] The first-baked product is subjected to ultra-high pressure impregnation with a pressure not lower than 5 MPa, and impregnants such as asphalt and resin are impregnated into the pores to obtain an impregnated product. The impregnated product is then subjected to secondary carbonization treatment, and the carbonization temperature is not lower than 850 °C to form a second-baked product;

[0027] The first-baked product or the second-baked product is treated in a high-temperature graphitization purification furnace, and the temperature is not lower than 2800 °C, and halogen element gas is introduced in the high-temperature stage for purification to control the ash content within 50 ppm to form a purified graphitized product;

[0028] The purified graphitized product is subjected to precision milling and ultrasonic cleaning for finishing treatment.

[0029] Preferably, in step S1, the D50 range of the coarse particles is 30 - 50 μm, the D50 range of the medium particles is 15 - 30 μm, the D50 range of the fine particles is 5 - 15 μm, and the D50 of the ultra-fine particles is less than 5 μm.

[0030] Preferably, in step S3, the D50 range of the coarse particles is 50 - 70 μm, the D50 range of the medium particles is 30 - 50 μm, the D50 range of the fine particles is 10 - 30 μm, and the D50 of the ultra-fine particles is less than 10 μm.

[0031] The beneficial effects of the present invention are as follows:

[0032] 1. For a special graphite for ion implantation and its preparation method according to the present invention, in terms of product performance, the prepared special graphite for ion implantation has excellent comprehensive performance indicators. Its bulk density is in the range of 1.85 - 1.92 g / cm 3 , the porosity is ≤7%, the resistivity is 12 - 14 μΩm, the flexural strength is ≥85 MPa, the compressive strength is ≥180 MPa, the Young's modulus is 13 - 15 GPa, the thermal expansion coefficient is ≤5.0×10-6 / ℃, the total impurity content is ≤50 ppm, and the key metal elements are ≤5 ppm. All performances reach the leading level in the industry, which can fully meet the stringent requirements of the ion implantation process for special graphite materials in terms of electrothermal performance, mechanical performance, thermal stability and purity, and effectively ensure the stable operation and high-efficiency work of ion implantation equipment.

[0033] 2. For a special graphite for ion implantation and its preparation method according to the present invention, in terms of the innovation of the preparation method, the raw material coke grading technology significantly improves the bulk density of the powder (which can be increased by 10% - 20%) and the green body density (which can be increased by 3% - 10%) by reasonably matching different types and particle sizes of coke raw materials, greatly reduces the dimensional shrinkage during the subsequent heat treatment process, and improves the process qualification rate; at the same time, it optimizes the bonding strength between coke powder and pitch, reduces the pore content and pore size, makes the product have lower roughness after finishing, and improves the product quality. The application of additives further optimizes the product performance. By adding carbon black, sulfur, boric acid, etc., the flexural strength is increased by 5% - 10%, the Shore hardness is increased by 5% - 20%, the roasting coke value is increased by 5% - 10%, and the grain size after graphitization is reduced by 5% - 10%, effectively improving the comprehensive performance of the product. The unique mixing process, including preheating, internal mixing, kneading, and cooling links, improves the preheating efficiency of coke powder, realizes the rapid and uniform mixing of coke powder and pitch, promotes the full polycondensation reaction of pitch, and lays a foundation for the improvement of product performance. The paste milling grading technology improves the bulk density of the powder through the scientific ratio of different particle sizes of pressed powder after paste milling, increases the green body bulk density by 5% - 10%, reduces the heat treatment dimensional shrinkage, improves the process qualification rate, and at the same time increases the product bulk density, reduces the porosity and pore size, and prolongs the service life of the product.

[0034] 3. For a special graphite for ion implantation and its preparation method according to the present invention, in terms of production manufacturing and cost control, this preparation method realizes efficient and stable production by optimizing process parameters and equipment linkage control, such as precisely controlling parameters such as vacuum dehydration, pressure plasticization, ultrasonic vibration and low-speed stirring of the mixing equipment, reduces the product defect rate caused by process fluctuations, reduces production costs, improves production efficiency and economic benefits, and enhances the competitiveness of the product in the market. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The present invention will be further described below in conjunction with the accompanying drawings.

[0036] Figure 1 It is the process flow diagram in the present invention. Specific embodiments

[0037] In order to make the technical means, creative features, achieved purposes and effects of the present invention easy to understand, the present invention will be further described below in conjunction with specific embodiments.

[0038] As Figure 1 shown, a special graphite for ion implantation in an embodiment of the present invention, the special graphite is composed of aggregate coke, additives and binders;

[0039] The aggregate coke includes at least one of low-ash petroleum coke, pitch coke, green pitch coke, needle coke, and artificial high-purity graphite, with an ash content not higher than 0.2% and a moisture content not higher than 0.02%;

[0040] The additives include at least one of nano silicon carbide, carbon black, natural flake graphite, elemental sulfur, and boric acid;

[0041] The binder includes high-temperature asphalt with a softening point of 100 - 180 °C, and the ash content of the special graphite is controlled within 50 ppm.

[0042] A preparation method of a special graphite for ion implantation, the preparation method includes the following steps:

[0043] S1. Raw material treatment: Different types of aggregate coke are each divided into coarse particles, medium particles, fine particles, and ultrafine particles through a powder grinding and classification device;

[0044] S2. Primary and secondary grading and mixing: Different types and particle sizes of raw coke powder are mixed according to a certain ratio for grading, so that the particle size D50 of the graded powder does not exceed 20 μm;

[0045] The graded powder is preheated to 150 - 250 °C by a preheater, the vacuum dehydration device is started to remove moisture, and then it is put into an intermeshing internal mixer for uniform mixing for 10 - 30 min. The internal mixer rotor has spiral shear teeth, and the rotational speed is adjustable from 10 - 120 rpm. Melted high-temperature asphalt with a softening point of 100 - 180 °C is added for mixing, the mixing temperature is 150 - 250 °C, the pressure of the internal mixer is 0.5 - 2 MPa, the pressure mixing time is 10 - 30 min, the atmospheric mixing time is 10 - 20 min, and the mixing and pressure mixing are carried out alternately, with a total mixing time of 30 - 180 min. The exhaust valve of the flue gas treatment system is started during the mixing process;

[0046] The kneaded paste is put into a kneader with a preheating temperature of 200 - 300°C for kneading treatment. The kneading time is 30 - 240 min, and the kneading temperature is 200 - 300°C. The exhaust valve of the kneader flue gas treatment system is adjusted to control the volatile content of the paste to 10% - 15%. After the paste kneading is completed, it is put into a cooler and cooled to below 60°C;

[0047] S3. Paste treatment: The cooled paste is crushed and then subjected to grinding and classification to form pressed powders of coarse particles, medium particles, fine particles, and ultra-fine particles;

[0048] The pressed powders of different particle sizes are proportioned according to a certain ratio so that the particle size D50 range of the proportioned pressed powder is 20 - 50 μm, and then a homogenizing and mixing device is used for mixing;

[0049] S4. Isostatic pressing: The proportioned and mixed pressed powder is loaded into a special mold rubber sleeve, evacuated for 10 - 120 min, and the vacuum degree is not lower than -0.085 MPa. After evacuation, the mold is lifted into a cold isostatic press, and isostatic pressing is carried out under the conditions of a forming pressure of 160 - 220 MPa and a holding time of the highest pressure of 20 - 40 min, and the density of the green compact is controlled at 1.50 - 1.75 g / cm 3 ;

[0050] S5. Post-treatment: The green compact is subjected to high-temperature carbonization treatment, and the carbonization temperature is not lower than 950°C to form a first-baked product;

[0051] The first-baked product is subjected to ultra-high pressure impregnation with a pressure not lower than 5 MPa, and impregnants such as asphalt and resin are impregnated into the pores to obtain an impregnated product. The impregnated product is then subjected to secondary carbonization treatment, and the carbonization temperature is not lower than 850°C to form a second-baked product;

[0052] The first-baked product or the second-baked product is treated in a high-temperature graphitization purification furnace at a temperature not lower than 2800°C, and halogen element gas is introduced in the high-temperature stage for purification to control the ash content within 50 ppm to form a purified graphitized product;

[0053] The purified graphitized product is subjected to precision milling and ultrasonic cleaning for finishing treatment.

[0054] In step S1, the D50 range of the coarse particles is 30 - 50 μm, the D50 range of the medium particles is 15 - 30 μm, the D50 range of the fine particles is 5 - 15 μm, and the D50 of the ultra-fine particles is less than 5 μm.

[0055] In step S3, the D50 range of the coarse particles is 50 - 70 μm, the D50 range of the medium particles is 30 - 50 μm, the D50 range of the fine particles is 10 - 30 μm, and the D50 of the ultra-fine particles is less than 10 μm.

[0056] Example 1

[0057] Raw material preparation: Low-ash petroleum coke, pitch coke, and needle coke are selected as the aggregate coke. After testing, their ash content is not higher than 0.2%, and the moisture content is not higher than 0.02%. The additives are carbon black and elemental sulfur. The binders are high-temperature asphalt with a softening point of 120°C as the mixing binder, high-temperature asphalt with a softening point of 110°C as the impregnating agent, and a special resin with a coking value of 60% as the impregnating agent.

[0058] Raw material grinding and classification: The petroleum coke, pitch coke, and needle coke are respectively passed through grinding and classification equipment and divided into coarse particles (D50 range 30 - 50 μm), medium particles (D50 range 15 - 30 μm), fine particles (D50 range 5 - 15 μm), and ultrafine particles (D50 less than 5 μm).

[0059] Primary and secondary grading and mixing: According to the ratio of 5% coarse needle coke, 5% coarse pitch coke, 10% medium pitch coke, 20% fine pitch coke, 30% fine petroleum coke, 20% fine green coke, 5% ultrafine petroleum coke, 2% ultrafine needle coke, and 3% additives (2% carbon black, 1% elemental sulfur), the fine powder of raw material coke and additives are graded to make the particle size D50 of the graded powder 18 μm. The graded powder is preheated to 200°C with a preheater, the vacuum dehydration device is started to remove moisture, and then it is put into an intermeshing internal mixer for uniform mixing for 20 min. The rotor speed of the internal mixer is set at 60 rpm. Melted high-temperature asphalt with a softening point of 120°C is added for mixing. The mixing temperature is 200°C, the pressure of the internal mixer is 1 MPa, the pressure mixing time is 20 min, and the open mixing time at normal pressure is 15 min. Open mixing and pressure mixing are carried out alternately, and the total mixing time is 90 min. The exhaust valve of the flue gas treatment system is started during the mixing process. The mixed paste is put into a kneader with a preheating temperature of 250°C for kneading treatment. The kneading time is 120 min, the kneading temperature is 250°C, and the exhaust valve of the kneader flue gas treatment system is adjusted to control the volatile content of the paste to 12%. After the paste kneading is completed, it is put into a cooler and cooled to below 60°C.

[0060] Paste grinding and grading: The cooled paste is crushed and then subjected to grinding and grading treatment to form pressed powder with coarse particles (D50 range 50 - 70 μm), medium particles (D50 range 30 - 50 μm), fine particles (D50 range 10 - 30 μm), and ultrafine particles (D50 less than 10 μm). According to the ratio of 15% coarse particles, 20% medium particles, 40% fine particles, and 25% ultrafine particles, the pressed powder of different particle sizes is graded to make the particle size D50 of the graded pressed powder 35 μm, and then a homogenizing mixing device is used for mixing.

[0061] Isostatic pressing: The mixed and sized powder is filled into a special mold rubber sleeve, evacuated for 60 minutes until the vacuum reaches -0.09 MPa. After evacuation, the mold is lifted into a cold isostatic press and isostatic pressing is carried out under the conditions of a forming pressure of 180 MPa and a holding time of 30 minutes at the maximum pressure, controlling the green body density to be 1.65 g / cm 3 .

[0062] Post-processing: The green body is subjected to high-temperature carbonization at a carbonization temperature of 1000 °C to form a first-baked product; the first-baked product is subjected to ultra-high pressure impregnation at a pressure of 6 MPa, and high-temperature pitch with a softening point of 110 °C is impregnated into the pores to obtain an impregnated product. The impregnated product is then subjected to secondary carbonization at a carbonization temperature of 900 °C to form a second-baked product; the second-baked product is treated in a high-temperature graphitization purification furnace at a temperature of 2900 °C, and chlorine is introduced during the high-temperature stage for purification to control the ash content within 45 ppm to form a purified graphitized product; the purified graphitized product is subjected to precision milling, ultrasonic cleaning and other finishing treatments.

[0063] Example 2

[0064] Raw material preparation: Pitch coke green coke and artificial high-purity graphite are selected as aggregate coke, and the ash content and moisture meet the requirements; additives include nano-silicon carbide, natural flake graphite, and boric acid; the binder uses high-temperature pitch with a softening point of 150 °C as the mixing binder, high-temperature pitch with a softening point of 130 °C as the impregnating agent, and a special resin with a coking value of 58% as the impregnating agent.

[0065] Raw material grinding and classification: Using the same grinding and classification method as in Example 1, the aggregate coke is divided into powders of corresponding particle size grades.

[0066] Primary and secondary grading and kneading: According to a specific ratio, such as 4% of raw pitch coke coarse particles, 8% of raw pitch coke medium particles, 18% of raw pitch coke fine particles, 32% of artificial high-purity graphite fine particles, 6% of artificial high-purity graphite ultra-fine particles, and additives (1% of nano silicon carbide, 1% of natural flake graphite, 1% of boric acid, totaling 3%), the raw coke fines and additives are graded so that the particle size D50 of the graded powder is 16 μm; the graded powder is preheated to 230 °C with a preheater, the vacuum dehydration device is started to remove moisture, and then it is put into an intermeshing internal mixer for uniform mixing for 25 min. The rotor speed of the internal mixer is set at 80 rpm; molten high-temperature pitch with a softening point of 150 °C is added for kneading, the kneading temperature is 230 °C, the pressure applied to the internal mixer is 1.5 MPa, the pressure kneading time is 25 min, and the open kneading time at normal pressure is 18 min. Open kneading and pressure kneading are carried out alternately, and the total kneading time is 120 min. During the kneading process, the exhaust valve of the flue gas treatment system is started; the kneaded paste is put into a kneader with a preheating temperature of 280 °C for kneading treatment, the kneading time is 180 min, the kneading temperature is 280 °C, and the exhaust valve of the kneader flue gas treatment system is adjusted to control the volatile content of the paste to 13%. After the paste kneading is completed, it is put into a cooler and cooled to below 60 °C.

[0067] Paste grinding and grading: The cooled paste is crushed and then subjected to grinding and classification treatment to form pressed powder of different particle sizes; grading is carried out according to the same pressed powder ratio of particle sizes as in Example 1, and then a homogenizing and mixing device is used for mixing.

[0068] Isostatic pressing: The graded and mixed pressed powder is filled into a special mold rubber sleeve, evacuated for 90 min, and the vacuum degree reaches -0.095 MPa. After the evacuation is completed, the mold is lifted into a cold isostatic press, and isostatic pressing is carried out under the conditions of a forming pressure of 200 MPa and a holding time of 35 min at the maximum pressure, and the green body density is controlled to be 1.70 g / cm 3 .

[0069] Post-process treatment: The green body is subjected to high-temperature carbonization treatment at a carbonization temperature of 1100 °C to form a first-baked product;

[0070] The first-baked product is subjected to ultra-high pressure impregnation at a pressure of 7 MPa, and high-temperature pitch with a softening point of 130 °C and special resin are impregnated into the pores to obtain an impregnated product. The impregnated product is then subjected to secondary carbonization treatment at a carbonization temperature of 950 °C to form a second-baked product;

[0071] The second-baked product is treated in a high-temperature graphitization purification furnace at a temperature of 3000 °C, and fluorine gas is introduced during the high-temperature stage for purification to control the ash content within 40 ppm to form a purified graphitized product; the purified graphitized product is subjected to precision milling, ultrasonic cleaning and other finishing treatments.

[0072] The performance of the special graphite products for ion implantation prepared in Example 1 and Example 2 was tested, and the results are as follows:

[0073] Performance Index Example 1 Example 2 <![CDATA[Bulk density (g / cm 3 )]]> 1.88 1.90 Porosity (%) 6.5 6.2 Resistivity (μΩm) 13 13.5 Flexural Strength (MPa) 90 92 Compressive Strength (MPa) 185 188 Young's Modulus (GPa) 14 14.5 <![CDATA[Coefficient of thermal expansion (×10 -6 / °C)]]> 4.8 4.6 Total Impurity Content (ppm) 48 42 Critical Metal Element Content (ppm) 4.5 4

[0074] The test results show that for the special graphite products prepared by the preparation method of the present invention, all performance indicators reach or exceed the expected targets, meet the use requirements in the field of ion implantation, and verify the effectiveness and reliability of the technical solution of the present invention.

[0075] Special graphite product for ion implantation: bulk density 1.85 - 1.92 g / cm 3 , porosity ≤ 7%, resistivity 12 - 14 μΩm, flexural strength ≥ 85 MPa, compressive strength ≥ 180 MPa, Young's modulus 13 - 15 GPa, coefficient of thermal expansion ≤ 5.0×10-6 / °C, total impurity content ≤ 50 ppm, key metal element ≤ 5 ppm.

[0076] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A special graphite for ion implantation, characterized in that: The special graphite is composed of aggregate coke, additives and a binder; The aggregate coke includes at least one of low-ash petroleum coke, pitch coke, green pitch coke, needle coke, and artificial high-purity graphite, with an ash content not higher than 0.2% and a moisture content not higher than 0.02%; The additives include at least one of nano silicon carbide, carbon black, natural flake graphite, elemental sulfur, and boric acid; The binder includes high-temperature asphalt with a softening point of 100 - 180 °C, and the ash content of the special graphite is controlled within 50 ppm.

2. A preparation method of special graphite for ion implantation, characterized in that, It is used to prepare the special graphite for ion implantation described in claim 1, and the preparation method includes the following steps: S1. Raw material treatment: Different types of aggregate coke are each divided into coarse particles, medium particles, fine particles, and ultra-fine particles through a grinding and classification device; S2. Primary and secondary grading and mixing: The fine powders of raw material coke of different types and particle sizes are mixed according to a certain ratio for grading, so that the particle size D50 of the graded powder does not exceed 20 μm; The graded powder is preheated to 150 - 250 °C by a preheater, the vacuum dehydration device is started to remove moisture, and then it is put into an intermeshing internal mixer for uniform mixing for 10 - 30 min. The internal mixer rotor has spiral shear teeth, and the rotational speed is adjustable from 10 - 120 rpm. Melted high-temperature asphalt with a softening point of 100 - 180 °C is added for mixing, the mixing temperature is 150 - 250 °C, the pressure of the internal mixer is 0.5 - 2 MPa, the pressure mixing time is 10 - 30 min, the atmospheric open mixing time is 10 - 20 min, open mixing and pressure mixing are carried out alternately, and the total mixing time is 30 - 180 min. During the mixing process, the exhaust valve of the flue gas treatment system is started; The mixed paste is put into a kneader with a preheating temperature of 200 - 300 °C for kneading treatment, the kneading time is 30 - 240 min, the kneading temperature is 200 - 300 °C, the exhaust valve of the kneader flue gas treatment system is adjusted to control the volatile content of the paste to 10% - 15%. After the paste kneading is completed, it is put into a cooler and cooled to below 60 °C; S3. Paste treatment: The cooled paste is crushed and then subjected to grinding and classification treatment to form pressed powders of coarse particles, medium particles, fine particles, and ultra-fine particles; The pressed powders of different particle sizes are graded according to a certain ratio so that the particle size D50 range of the graded pressed powder is 20 - 50 μm, and then a homogenizing mixing device is used for mixing; S4. Isostatic pressing: Load the graded and mixed pressing powder into a special mold rubber sleeve, evacuate for 10 - 120 minutes with a vacuum degree not lower than -0.085 MPa. After evacuation, lift the mold into a cold isostatic press and perform isostatic pressing under the conditions of a forming pressure of 160 - 220 MPa and a holding time of the highest pressure of 20 - 40 minutes, and control the green body density to be 1.50 - 1.75 g / cm 3 ; S5. Post-treatment: The green body is subjected to high-temperature carbonization treatment at a carbonization temperature not lower than 950 °C to form a first-baked product; The first-baked product is subjected to ultra-high pressure impregnation with a pressure not lower than 5 MPa, and asphalt and resin impregnants are impregnated into the pores to obtain an impregnated product. The impregnated product is then subjected to secondary carbonization treatment at a carbonization temperature not lower than 850 °C to form a second-baked product; The first-baked product or the second-baked product is treated in a high-temperature graphitization purification furnace at a temperature not lower than 2800 °C, and halogen element gas is introduced in the high-temperature stage for purification to control the ash content within 50 ppm to form a purified graphitized product; The purified graphitized product is subjected to precision milling and ultrasonic cleaning for finishing treatment.

3. The preparation method of a special graphite for ion implantation according to claim 2, characterized in that: In the step S1, the D50 range of the coarse particles is 30 - 50 μm, the D50 range of the medium particles is 15 - 30 μm, the D50 range of the fine particles is 5 - 15 μm, and the D50 of the ultrafine particles is less than 5 μm.

4. The preparation method of a special graphite for ion implantation according to claim 2, characterized in that: In the step S3, the D50 range of the coarse particles is 50 - 70 μm, the D50 range of the medium particles is 30 - 50 μm, the D50 range of the fine particles is 10 - 30 μm, and the D50 of the ultrafine particles is less than 10 μm.

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