Graphite block for semiconductor and method for purifying the same, Electronic device

Abstract

The application provides a graphite block for semiconductors and a purification method and an electronic device thereof, and the purification method comprises the following steps: immersing an isostatic pressing treated graphite block into a composite acid solution prepared by mixing nitric acid and sulfuric acid at a proportion of 3:1 at a speed of 0.5-1 mm / min to perform gradient temperature chemical treatment; placing the treated graphite block in a high-vacuum environment to perform three-stage precise temperature control heating and program control cooling; performing surface purification by using argon plasma and helium-argon mixed plasma; and circulating deep purification by introducing high-purity helium gas in a low-temperature environment of-180 DEG C to-200 DEG C. The application integrates multi-dimensional purification technology, establishes a mild chemical treatment-precise thermal purification-low-temperature helium deep purification process system, and realizes that the purity of the graphite block reaches 99.9995%-99.9999%, the impurity content is as low as 1-5 ppb, and the requirement of semiconductor manufacturing for a process node of 5 nm and below is met.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor material preparation, in particular to a graphite block for semiconductors and a purification method thereof, and an electronic device. The method is suitable for preparing ultra-high purity graphite material used in key process links such as semiconductor wafer preparation, epitaxial growth, ion implantation, etc. BACKGROUND

[0002] The semiconductor industry is the foundation of contemporary information technology development, and high-purity graphite material plays an irreplaceable role in the semiconductor manufacturing process. Graphite blocks are widely used in key process links such as semiconductor wafer preparation, epitaxial growth, ion implantation, etc. due to their excellent thermal conductivity, chemical stability and high temperature resistance. With the development of semiconductor manufacturing processes to 7nm, 5nm or even smaller nodes, the purity of graphite material is also constantly improved, and the impurity content needs to be controlled below ppb level.

[0003] Traditional graphite block purification methods mainly include acid washing, vacuum heat treatment and other steps. The acid washing process mainly uses mixed acid to soak the graphite block to remove metal impurities; then high temperature (usually 2500-2800℃) vacuum heat treatment is used to promote the volatilization of residual impurities inside the graphite. However, these traditional methods have a series of technical bottlenecks in meeting the demand of ultra-high purity graphite material for contemporary semiconductor industry.

[0004] The existing graphite block purification technology has the following key technical problems: first, the acid washing process is easy to cause damage to the structure of the graphite block, affecting its thermal conductivity, reducing the service life and efficiency of the graphite block; second, the temperature control of vacuum heat treatment is not accurate enough, which easily leads to uneven purification degree of the surface and the inside of the graphite block, resulting in internal and external purity difference; finally, the surface of the purified graphite block is easy to leave trace impurities, affecting the purity requirement in the semiconductor manufacturing process.

[0005] Therefore, there is an urgent need for a new graphite block purification method that can protect the structure of the graphite block while achieving uniform ultra-high purity purification to meet the growing demand for high-purity materials in modern semiconductor industry. SUMMARY

[0006] In view of this, the present application provides a purification method of a graphite block for semiconductors, which solves the problems of damage to the structure of the graphite block in the acid washing process, uneven purification degree caused by inaccurate temperature control of vacuum heat treatment, and trace impurities left on the surface of the purified graphite block in the prior art.

[0007] The present application provides a purification method of a graphite block for semiconductors, which includes the following steps:

[0008] The isostatic pressing graphite block is immersed in a composite acid solution for gradient temperature chemical treatment, and is neutralized by a buffer solution and cleaned by ultrasonic assistance to obtain a graphite block with surface and shallow impurities preliminarily removed;

[0009] The graphite block with surface and shallow impurities preliminarily removed is placed in a high-vacuum environment, is subjected to three-stage heating and is kept at the highest temperature for a preset time, and then is cooled to obtain a graphite block with an internal impurity content of less than 10 ppm;

[0010] The graphite block with an internal impurity content of less than 10 ppm is placed in a plasma processing chamber and is subjected to plasma treatment to obtain a graphite block with a surface impurity content of less than 1 ppm;

[0011] The graphite block with a surface impurity content of less than 1 ppm is placed in a low-temperature environment, and high-purity helium gas is circulated to purify the graphite block to obtain a graphite block with a purity of 99.9995%-99.9999%.

[0012] In some embodiments, the graphite block is immersed in the composite acid solution at a speed of 0.5-1 mm / min, the composite acid solution is prepared by mixing nitric acid and sulfuric acid at a volume ratio of 3:1, and the acid concentration is 50-60%.

[0013] In some embodiments, the gradient temperature chemical treatment comprises: sequentially keeping at 40℃ for 25-35 minutes, keeping at 60℃ for 40-50 minutes, and keeping at 80℃ for 55-65 minutes.

[0014] In some embodiments, the graphite block with surface and shallow impurities preliminarily removed is placed in a high-vacuum environment, is subjected to three-stage heating and is kept at the highest temperature for a preset time, and then is cooled, which comprises:

[0015] The graphite block with surface and shallow impurities preliminarily removed is placed in a high-purity graphite crucible and is put into a vacuum heat treatment furnace, and the vacuum is extracted to below 10-4 Pa;

[0016] The temperature is raised from room temperature to 800℃ at a rate of 4-6℃ / min;

[0017] The temperature is raised from 800℃ to 2200℃ at a rate of 2-4℃ / min;

[0018] The temperature is raised from 2200℃ to 2800℃ at a rate of 1.5-2.5℃ / min;

[0019] The graphite block is kept at 2800℃ for 2-4 hours.

[0020] In some embodiments, the cooling of the graphite block includes: cooling from 2800℃ to 2000℃ at a rate of 2℃ / min; cooling from 2000℃ to 1500℃ at a rate of 1℃ / min; and cooling from 1500℃ to room temperature at a rate of 3℃ / min.

[0021] In some embodiments, the graphite block with an internal impurity content of less than 10ppm is placed in a plasma processing chamber for plasma treatment to obtain a graphite block with a surface impurity content of less than 1ppm, including:

[0022] The graphite block with an internal impurity content of less than 10ppm is placed in a plasma processing chamber for vacuum pumping;

[0023] High-purity argon gas is introduced to control the chamber pressure to 10-5Pa, and the graphite block is subjected to argon plasma treatment;

[0024] After the argon plasma treatment, the chamber is vacuum pumped;

[0025] A mixture of helium and argon gas is introduced into the plasma processing chamber to control the chamber pressure to 10-5Pa, and the graphite block is subjected to helium-argon mixed plasma treatment to obtain the graphite block with a surface impurity content of less than 1ppm.

[0026] In some embodiments, the volume ratio of helium to argon in the mixture of helium and argon is 3:1, the argon plasma treatment time is 15-30 minutes, and the helium-argon mixed plasma treatment time is 20-40 minutes.

[0027] In some embodiments, the graphite block with a surface impurity content of less than 1ppm is placed in a low-temperature environment and circulated with high-purity helium gas to obtain a graphite block with a purity of 99.9995%-99.9999%, including:

[0028] The graphite block with a surface impurity content of less than 1ppm is placed in a low-temperature chamber with a temperature controlled at -180℃ to -200℃;

[0029] High-purity helium gas with a purity of greater than 99.9999% is introduced to circulate and flush the graphite block, with a helium flow rate of 5-10L / min and a circulation time of 8-12 hours to obtain the graphite block with a purity of 99.9995%-99.9999%.

[0030] The present application also provides a graphite block for semiconductors, which is purified by the above-mentioned purification method.

[0031] The application also provides an electronic device comprising an element prepared from the semiconductor graphite block purified by the purification method for semiconductor graphite block.

[0032] The application has the following technical effects:

[0033] The graphite structure protection type slow impregnation technology removes impurities while maximizing the protection of the graphite microstructure, solves the problem of damage to the graphite structure caused by traditional pickling, and increases the microstructure integrity of the purified graphite block by more than 13% and improves the thermal conductivity by 25%.

[0034] The three-stage precise temperature control vacuum heat treatment technology is used to design different heating rates and holding times for different temperature ranges, combined with high vacuum environment and programmed slow cooling, to achieve uniform purification of the graphite block from the inside to the outside, with a purity difference of less than 1%.

[0035] The helium-argon mixed plasma surface deep purification technology is introduced to deeply penetrate the graphite micropores using the small size characteristics of helium ions, and to realize surface deep purification combined with the sputtering effect of argon ions, with the surface impurity content reduced to about 0.8 ppm.

[0036] The low-temperature helium gas circulation deep purification technology uses the high permeability and inertness of helium gas in a low-temperature environment to carry out the deep-layer residual impurities of the graphite, so that the purity of the graphite block reaches 99.9995%-99.9999%, and the impurity content is as low as 1-5 ppb. BRIEF DESCRIPTION OF DRAWINGS

[0037] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following will briefly introduce the drawings needed to be used in the embodiments. The drawings herein are incorporated into the specification and form a part of the specification, which show the embodiments consistent with the present disclosure, and are used to explain the technical solutions of the present disclosure together with the specification. It should be understood that the following drawings only show some embodiments of the present disclosure, and therefore should not be regarded as a limitation on the scope, and other related drawings can also be obtained by those skilled in the art without creative labor.

[0038] Figure 1 The flowchart of the purification method for semiconductor graphite block provided by the embodiments of the present application is shown in the figure.

[0039] Figure 2 The schematic diagram of the mild chemical treatment provided by the embodiments of the present application is shown in the figure.

[0040] Figure 3 The temperature change curve of the three-stage heating provided by the embodiments of the present application is shown in the figure. DETAILED DESCRIPTION

[0041] In order to make the objects, technical solutions and advantages of the embodiments of the present disclosure clearer, the following will be combined with the accompanying drawings of the embodiments of the present disclosure to make a clear and complete description of the technical solutions in the embodiments of the present disclosure. Obviously, the described embodiments are only a part of the embodiments of the present disclosure, rather than all the embodiments. The components of the embodiments of the present disclosure described and shown in the accompanying drawings can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present disclosure provided in the accompanying drawings is not intended to limit the scope of the claimed present disclosure, but only represents selected embodiments of the present disclosure. Based on the embodiments of the present disclosure, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present disclosure.

[0042] It should be noted that similar reference numerals and letters refer to similar items throughout the accompanying drawings, and therefore, once an item is defined in one drawing, it need not be further defined and explained in subsequent drawings.

[0043] The term "and / or" herein only describes an association relationship, which means that there can be three relationships, for example, A and / or B can mean that A exists alone, A and B exist together, and B exists alone. In addition, the term "at least one" herein means any one of a plurality or any combination of at least two of a plurality, for example, including at least one of A, B, and C can mean including any one or more elements selected from the set consisting of A, B, and C.

[0044] As shown in Figure 1 The embodiments of the present application provide a purification method of a graphite block for semiconductors, comprising:

[0045] S1: obtaining a graphite block subjected to isostatic pressing, immersing the graphite block in a composite acid solution for gradient temperature chemical treatment, and obtaining a graphite block with surface and shallow impurities preliminarily removed through buffer neutralization and ultrasonic-assisted cleaning;

[0046] Specifically, the speed of immersing the graphite block in the composite acid solution is 0.5-1 mm / min, the composite acid solution is prepared by mixing nitric acid and sulfuric acid at a volume ratio of 3:1, and the acid concentration is 50-60%. By using a slow immersion device with controllable speed, the speed of immersing the graphite block in the acid solution is controlled, and the acid solution is gradually infiltrated into the graphite layer by layer, so as to avoid the impact damage caused by traditional direct immersion. It should be noted that if the immersion speed is lower than 0.5 mm / min, the graphite structure is better protected, but the processing time is greatly prolonged and the production efficiency is reduced; if the immersion speed is higher than 1 mm / min, the graphite microstructure is easily damaged.

[0047] The gradient temperature chemical treatment includes: sequentially maintaining at 40℃ for 25-35 minutes, at 60℃ for 40-50 minutes, and at 80℃ for 55-65 minutes. Through three-stage temperature control, the chemical reaction rate gradually increases during the temperature gradient increase, but remains within the range that does not damage the graphite structure, achieving a mild and gradual chemical reaction to achieve a balance between impurity removal and graphite structure protection.

[0048] The graphite block after the chemical treatment is placed in a sodium bicarbonate buffer solution for neutralization treatment to obtain a neutralized graphite block; the neutralized graphite block is subjected to ultrasonic-assisted cleaning at 40-60℃, and is subjected to multi-stage rinsing with deionized water to obtain the graphite block with the surface and shallow impurities preliminarily removed. Through the neutralization treatment using the sodium bicarbonate buffer solution with pH = 7.5-8.0, the ultrasonic-assisted cleaning at 40-60℃ for 15-20 minutes is introduced to accelerate the removal of residual acid and impurities, and the multi-stage rinsing with high-purity deionized water (resistivity > 18 MΩ·cm) is adopted to ensure that the acid is fully removed.

[0049] After the mild chemical treatment process, the impurity content of the graphite block is reduced to about 800-1200 ppm, and the active metal elements such as Fe and Ca are mainly removed, and the microstructure integrity of the graphite block is maintained at more than 95%.

[0050] S2: The graphite block with the surface and shallow impurities preliminarily removed is placed in a high-vacuum environment, is subjected to three-stage heating and is maintained at the highest temperature for a preset time, and then is cooled to obtain a graphite block with an internal impurity content of less than 10 ppm;

[0051] Specifically, the graphite block with the surface and shallow impurities preliminarily removed is placed in a high-vacuum environment, is subjected to three-stage heating and is maintained at the highest temperature for a preset time, and then is cooled, including: the graphite block with the surface and shallow impurities preliminarily removed is placed in a high-purity graphite crucible, is placed in a vacuum heat treatment furnace, and is vacuumed to below 10-4 Pa; the graphite block is subjected to three-stage heating and is maintained at the highest temperature for a preset time, including: from room temperature to 800℃, the heating rate is 4-6℃ / min;

[0052] from 800℃ to 2200℃, the heating rate is 2-4℃ / min;

[0053] from 2200℃ to 2800℃, the heating rate is 1.5-2.5℃ / min;

[0054] the graphite block is maintained at 2800℃ for 2-4 hours.

[0055] The above can be performed in a vacuum heat treatment system including functions such as three-stage intelligent temperature control, high-vacuum environment and holding treatment, and program-controlled slow cooling.

[0056] By using PID control algorithm, real-time monitoring and adjusting heating power, ensure temperature curve smooth, deviation control within ±5℃. By reducing the high temperature section of the heating rate, ensure the heat conduction to the graphite block inside, avoid the inside and outside temperature gradient too large. At the same time, in the high vacuum environment (10 -4 Pa below) heat treatment, reduce the interference of gas molecules on the purification process, vacuum system using molecular pump and ion pump combination, avoid oil molecule pollution, guarantee the purity of vacuum environment.

[0057] In this system, the purity of more than 99.9999% of high purity helium is the core medium of the whole deep purification process. First, high purity helium is sent into the low temperature chamber through the precision flow controller at a constant flow rate (5-10L / min). The selection of high purity helium is based on its small atomic radius (about 31pm), high chemical inertness and excellent permeability at low temperature and other characteristics. When helium flows through the surface of the graphite block at a low temperature of-180℃ to-200℃, the low temperature environment causes the graphite micropore to shrink, and the helium molecule can continue to penetrate these micropores due to its small volume.

[0058] During the cycle flushing process, helium molecules interact with impurities in the graphite block through three main mechanisms: physical adsorption, momentum transfer, and micropore pressure difference driving. First, the low temperature environment enhances the physical adsorption ability of helium molecules to impurities, allowing helium to "capture" impurity molecules in the graphite micropore; second, the continuous flow of helium "pushes out" impurities from the micropore through momentum transfer; finally, the slightly positive pressure environment (10-50Pa higher than the ambient pressure) forms a pressure gradient from inside to outside, further promoting the migration and removal of impurities. To ensure the uniformity of the cycle flushing, multi-directional airflow distribution is carried out in the low temperature chamber, and the design is optimized through computational fluid dynamics to allow helium to contact every surface and edge of the graphite block from all directions and at multiple angles, avoiding dead spots.

[0059] As Figure 3 shown, the cooling of the graphite block includes: from 2800℃ to 2000℃, the cooling rate is 2℃ / min; from 2000℃ to 1500℃, the cooling rate is 1℃ / min; from 1500℃ to room temperature, the cooling rate is 3℃ / min. By using program-controlled slow cooling from high temperature to room temperature, especially slower cooling (1℃ / min) in the critical temperature range (2000-1500℃), the damage to the internal stress of the graphite structure caused by rapid temperature change is prevented. Through the temperature curve data record of the whole process, it is ensured that each batch of products undergoes the same heat treatment process.

[0060] After the precise thermal purification process, the impurity content of the graphite block is reduced to about 5-15 ppm, mainly removing insoluble elements such as Si and Al, the graphite crystallinity is increased to 98%, and the thermal conductivity is increased by 25%.

[0061] S3: placing the graphite block with an internal impurity content of less than 10 ppm in a plasma treatment chamber, and performing plasma treatment to obtain a graphite block with a surface impurity content of less than 1 ppm;

[0062] Specifically, the graphite block with an internal impurity content of less than 10 ppm is placed in a plasma treatment chamber, and plasma treatment is performed to obtain a graphite block with a surface impurity content of less than 1 ppm, comprising: placing the graphite block with an internal impurity content of less than 10 ppm in a plasma treatment chamber, and vacuumizing; introducing high-purity argon gas to control the chamber pressure to 10 -5 Pa, and performing argon plasma treatment on the graphite block; after the argon plasma treatment is completed, vacuumizing; introducing a mixed gas of helium and argon into the plasma treatment chamber, and controlling the chamber pressure to 10 -5 Pa, and performing helium-argon mixed plasma treatment on the graphite block to obtain the graphite block with a surface impurity content of less than 1 ppm.

[0063] In addition, during the above argon and argon plasma treatment process, mass spectrometry technology can be used to continuously detect the types and contents of impurities carried in the circulating helium. When the impurity content is detected to be below the set threshold and remains stable, the helium flow rate is automatically adjusted to optimize the balance between energy consumption and purification efficiency. During the entire treatment process, key parameters such as temperature, pressure, flow rate and impurity content are automatically recorded to form a complete purification process database, providing a basis for quality control and process optimization.

[0064] The above specific process can be summarized as a two-stage plasma surface treatment, that is, first, argon plasma is used for surface preliminary treatment, and then helium-argon mixed plasma is used for deep purification to form a gradient treatment effect.

[0065] During the argon plasma treatment stage, the graphite block is placed on a specially designed graphite carrier, which is designed with small support points to minimize the contact area and ensure that the surface of the graphite block is fully exposed to the plasma environment. The chamber is first vacuumized to below 10 -6 Pa to remove impurity gases that may affect the stability of the plasma. Then high-purity argon gas (purity ≥ 99.9999%) is introduced, and the chamber pressure is accurately controlled to 10 -5Pa. The argon plasma is generated by a 13.56 MHz radio frequency power source, and is generated in a capacitively coupled manner. The electrode is designed in a porous structure to ensure uniform distribution of the plasma. The argon ions have a significant physical sputtering effect due to their large mass, and can effectively remove the adsorbed impurities and weakly bound pollutants on the surface of the graphite. The plasma density is controlled within 1x10 -3 cm -3 , and the electron temperature is about 3-5 eV. This combination of parameters ensures sufficient processing intensity while avoiding excessive bombardment damage to the surface structure of the graphite.

[0066] After the argon plasma treatment is completed, the vacuum is again drawn to below 10 -6 Pa to remove the volatile impurities generated during the treatment. Subsequently, a mixed gas of helium and argon is introduced, with a volume ratio of 3:1. This ratio has been verified through a large number of experiments to maximize the deep penetration of helium ions while maintaining the stability of the plasma. The flow rate of the mixed gas is precisely adjusted by a mass flow controller, and the chamber pressure is stabilized at 10 -5 Pa. The helium-argon mixed plasma is generated by radio frequency inductive coupling, with a power density of about 0.8 W / cm 2 . In the mixed plasma, argon ions are mainly responsible for surface sputtering and activation, while helium ions can penetrate into the graphite microporous structure due to their small size (atomic radius of only 18 pm), and can excite impurities in the deep microporous structure through energy transfer and collision. During the entire treatment process, the temperature of the graphite block substrate is controlled below 120°C by a water-cooled backplate to avoid thermal stress damage.

[0067] In a low-pressure environment (1 -5 Pa), argon plasma is generated at a specific power density (0.5-1.0 W / cm 2 ) to finely treat the surface of the graphite and effectively remove the residual trace impurities. A radio frequency (RF) power source and matching network are used to ensure the stability and uniformity of the plasma.

[0068] The volume ratio of helium and argon in the mixed gas is 3:1. The argon plasma treatment time is 15-30 minutes, and the helium-argon mixed plasma treatment time is 20-40 minutes. By innovatively introducing a helium-argon mixed gas to generate a mixed plasma, the small atomic radius of helium ions (compared to argon) can penetrate deeper into the microporous structure of the graphite, forming a gradient-type surface activation effect.

[0069] After the plasma surface purification process, the impurity content on the surface of the graphite block is reduced to about 0.5-1.5 ppm, and the content of surface oxides and hydrocarbons is significantly reduced.

[0070] S4: placing the graphite block with the surface impurity content lower than 1 ppm in a low-temperature environment, circulating and purifying by high-purity helium gas to obtain a graphite block with a purity of 99.9995%-99.9999%.

[0071] Specifically, the graphite block with the surface impurity content lower than 1 ppm is placed in a low-temperature environment, and high-purity helium gas is circulated and purified to obtain a graphite block with a purity of 99.9995%-99.9999%, including: placing the graphite block with the surface impurity content lower than 1 ppm in a low-temperature chamber, and controlling the temperature at-180 ℃ to-200 ℃; circulating and flushing the graphite block by high-purity helium gas with a purity of greater than 99.9999%, controlling the helium gas flow rate at 5-10 L / min, and the circulation time at 8-12 hours to obtain the graphite block with the purity of 99.9995%-99.9999%.

[0072] Through the complete purification process described above, the graphite block with extremely high purity for semiconductor is successfully prepared. Through helium mass spectrometry leak detection technology, it is found that the impurity content of the graphite block is 1-5 ppb, that is, the purity reaches 99.9995%-99.9999%, and the impurity content is far lower than the 10-50 ppb impurity content that can be usually reached by the traditional process. Such low impurity content makes the graphite block particularly suitable for semiconductor manufacturing of 5 nm and below process nodes, and can effectively avoid the problems of device performance degradation and yield loss caused by metal impurity pollution.

[0073] During testing, the purified graphite block is placed in a sealed chamber of a helium mass spectrometry leak detector, vacuumed to below 10^-8 Pa, and then high-purity helium gas is sprayed outside the chamber. If there are small impurities or structural defects in the graphite block, the external helium gas will penetrate into the chamber through these defects and be monitored and recorded in real time by a high-sensitivity detector. By analyzing the helium permeation rate and mode, the purity and microstructure integrity of the graphite block can be accurately evaluated, forming a complete quality evaluation system.

[0074] During the entire purification process of the present application, the impurity content in the graphite block at different stages is gradually reduced. The impurity content in the graphite block with the surface and shallow layer impurities removed is 800-1200 ppm, mainly removing active metal elements such as Fe and Ca. The impurity content in the graphite block with extremely low internal impurity content is 5-15 ppm, mainly removing difficultly soluble elements such as Si and Al. The surface impurity content in the graphite block with the surface impurity content lower than 1 ppm is 0.5-1.5 ppm, and the surface oxide and hydrocarbon content is significantly reduced. Through this step-by-step precise control, the present application realizes the all-around purification of the graphite block from outside to inside and from coarse to fine, ensuring the ultra-high purity and excellent performance of the final product.

[0075] In the helium circulation flushing process, the helium carrying impurities around the purified graphite block is purified by a molecular sieve filtering device and then recycled, the molecular sieve filtering device adopts a double-tower switching design, one tower is used for adsorption purification, and the other tower is used for regeneration, so that continuous purification is realized.

[0076] Example 1:

[0077] 1 Raw material

[0078] The high-density isostatic pressing graphite block with a density of 1.85 g / cm 3 , an initial size of 400 mm x 400 mm x 100 mm, an initial purity of about 99.5%, and about 5000 ppm of impurities is selected. The main impurity components are Fe, Si, Ca, Al and other metal elements and oxides.

[0079] Mild chemical treatment

[0080] 2.1 Slow immersion and composite acid solution treatment

[0081] Prepare the composite acid solution: mix nitric acid (65%) and sulfuric acid (98%) at a volume ratio of 3:1, and dilute to a final concentration of 55%.

[0082] Use a precision lifting device to control the immersion speed of the graphite block to be 0.8 mm / min.

[0083] Immersion time: continue to soak for 60 minutes after complete immersion.

[0084] 2.2 Gradient temperature chemical treatment

[0085] First stage: 40°C for 30 minutes.

[0086] Second stage: heat to 60°C and keep for 45 minutes.

[0087] Third stage: heat to 80°C and keep for 60 minutes.

[0088] Temperature control accuracy: ±1°C.

[0089] 2.3 Neutralization and cleaning

[0090] Use a sodium bicarbonate buffer with a pH value of 7.8 for neutralization treatment, and soak for 30 minutes.

[0091] Ultrasonic assisted cleaning at 50°C for 18 minutes (frequency 40 kHz, power 300 W).

[0092] Use ultrapure water with a resistivity of >18 MΩ·cm for 5 times of rinsing.

[0093] Dry in a 90°C drying oven for 12 hours.

[0094] Treatment result: The impurity content was reduced to about 800 ppm, and the active metal elements such as Fe and Ca were mainly removed, and the microstructure integrity of the graphite block was maintained above 95%.

[0095] Accurate thermal purification

[0096] 3.1 Temperature rising process

[0097] Put the graphite block in a high-purity graphite crucible and put it into a vacuum heat treatment furnace.

[0098] Vacuumize to 5x10 -5 Pa.

[0099] Temperature rising curve: room temperature to 800℃, rising rate 5℃ / min; 800-2200℃, rising rate 3℃ / min; 2200-2800℃, rising rate 2℃ / min.

[0100] Real-time temperature monitoring points: surface of graphite block, internal center position (through pre-embedded thermocouple).

[0101] 3.2 Holding treatment

[0102] Hold at 2800℃ for 3 hours.

[0103] The vacuum degree is maintained below 1x10 -4 Pa.

[0104] Use four-way PID control to make the temperature fluctuate within ±5℃.

[0105] 3.3 Cooling process

[0106] 2800-2000℃: cooling rate 2℃ / min.

[0107] 2000-1500℃: cooling rate 1℃ / min.

[0108] Below 1500℃: cooling rate 3℃ / min.

[0109] Below 500℃, fill high-purity argon to normal pressure and continue to cool to room temperature.

[0110] Treatment result: The impurity content was reduced to about 8 ppm, and the insoluble elements such as Si and Al were mainly removed, the graphite crystallinity was improved to 98%, and the thermal conductivity was increased by 25%.

[0111] Plasma surface purification

[0112] 4.1 Argon plasma treatment

[0113] Put the graphite block in the plasma treatment chamber.

[0114] Vacuum to 0.5 Pa.

[0115] High purity argon gas (99.9999%) was introduced, and the chamber pressure was controlled to 3 Pa.

[0116] Plasma parameters: RF power 800 W, power density 0.7 W / cm 2 .

[0117] Treatment time: 25 minutes.

[0118] 4.2 Helium-argon mixed plasma deep activation

[0119] Helium and argon mixed gas (He: Ar = 3:1) was introduced, and the chamber pressure was controlled to 4 Pa.

[0120] Mixed plasma parameters: RF power 900 W, power density 0.8 W / cm 2 .

[0121] Treatment time: 35 minutes.

[0122] The substrate temperature was controlled below 120°C.

[0123] Treatment results: XPS analysis showed that the surface oxide and hydrocarbon content was significantly reduced, and the surface impurity content was reduced to about 0.8 ppm.

[0124] Low-temperature helium gas deep purification

[0125] 5.1 Low-temperature circulating helium gas purification

[0126] The graphite block was placed in a low-temperature chamber, and the temperature was controlled at -190°C.

[0127] High purity helium gas (99.9999%) was introduced at a flow rate of 8 L / min.

[0128] Circulation time: 10 hours.

[0129] The impurity composition and content carried out in the helium gas were monitored in real time.

[0130] 5.2 Quality evaluation

[0131] The graphite purity was evaluated using helium mass spectrometry leak detection technology, with a detection sensitivity of 10-11 Pa·m 3 / s.

[0132] The following further illustrates the present application through comparative examples and other examples:

[0133] Comparative Example 1: Traditional acid pickling-heat treatment process

[0134] 1 Raw material

[0135] The same high-density isostatically-pressed graphite block as in Example 1, with initial dimensions of 400 mm x 400 mm x 100 mm and an initial purity of about 99.5%, containing about 5000 ppm of impurities.

[0136] 2 Acid pickling treatment

[0137] The graphite block was directly immersed in a mixed acid solution (nitric acid: sulfuric acid = 1:1) at an immersion rate of about 5 seconds.

[0138] The immersion temperature was kept constant at 90°C, and the immersion time was 2 hours.

[0139] Washing: washed directly with deionized water for 3 times.

[0140] Drying: dried in an oven at 120°C for 8 hours.

[0141] 3 Vacuum heat treatment

[0142] The temperature was directly raised to 2800°C at a constant rate of 10°C / min.

[0143] Soaking time: 2 hours, vacuum degree: 1 x 10"3Pa.

[0144] Cooling: naturally cooled (without controlled cooling rate).

[0145] 4 Comparison results:

[0146] Impurity content after acid pickling: about 1200 ppm.

[0147] Final purity: 99.95% (impurities about 50 ppm).

[0148] The thermal conductivity of the graphite block decreased by 20%, and the microstructure damage reached 30%.

[0149] XRD detection showed that the lattice structure integrity was only 85%.

[0150] There were obvious acid pickling marks and micro-cracks on the surface of the graphite block.

[0151] Comparative Example 2: using only heat treatment process

[0152] 1 Raw material

[0153] The same high-density isostatically-pressed graphite block as in Example 1.

[0154] 2 Vacuum heat treatment

[0155] Temperature: 3000°C (higher than in the example).

[0156] Raising rate: constant at 8°C / min.

[0157] Soaking time: extended to 5 hours.

[0158] Vacuum: 5 x 10 -4 Pa.

[0159] Cooling: Control the cooling rate at 5°C / min.

[0160] 3 Comparison Results:

[0161] Final purity: 99.90% (impurities about 100 ppm).

[0162] The purity of the graphite block is uneven, with low impurity content on the surface and high impurity content inside.

[0163] More energy consumption (about 40% increase) and longer processing time are required.

[0164] A hardening layer is formed on the surface of the graphite block, affecting the subsequent processing performance.

[0165] Comparative Example 3: Using traditional plasma cleaning instead of helium deep purification

[0166] 1 Pretreatment

[0167] The mild chemical treatment and precise thermal purification of Example 1 are performed.

[0168] 2 Surface Treatment

[0169] Only argon plasma treatment is used.

[0170] The treatment time is extended to 60 minutes.

[0171] The power density is increased to 1.2 W / cm 2 .

[0172] 3 Comparison Results:

[0173] Final purity: 99.995% (impurities about 5 ppm).

[0174] The surface purity is high, but impurities remain in the deep micropores.

[0175] The graphite surface is excessively activated, easily adsorbing environmental impurities.

[0176] Example 2: Verification of graphite size change adaptability

[0177] 1 Raw Material

[0178] A small size high density isostatic pressed graphite block is selected, with a size of 100mm x 100mm x 20mm, and other characteristics are the same as Example 1.

[0179] 2 Mild Chemical Treatment

[0180] The procedure of Example 1 was followed, with the soaking rate adjusted to 0.6 mm / min.

[0181] The treatment resulted in a reduction of the impurity content to about 750 ppm.

[0182] 3 Precision thermal purification

[0183] The procedure of Example 1 was followed, with the soaking time reduced to 2.5 hours.

[0184] The treatment resulted in a reduction of the impurity content to about 6 ppm.

[0185] 4 Plasma surface purification

[0186] The procedure of Example 1 was followed, with the same parameters maintained.

[0187] The treatment resulted in a reduction of the surface impurity content to about 0.7 ppm.

[0188] 5 Cryogenic helium deep purification

[0189] The procedure of Example 1 was followed, with the cycle time reduced to 9 hours.

[0190] The treatment resulted in a final purity of 99.9998% with an impurity content of about 2 ppb.

[0191] Example 2 demonstrates the adaptability of the method of the present application to graphite blocks of different sizes, showing that the process has good size compatibility, allowing for flexible adjustment of some parameters depending on the size of the product, while maintaining high purification effectiveness.

[0192] Example 3: Verification of the treatment effectiveness for graphite with different initial purities

[0193] 1 Raw material

[0194] Graphite blocks with a lower initial purity were selected, with the same size as in Example 1, but with an initial purity of only 99.0%, containing about 10,000 ppm of impurities.

[0195] 2 Mild chemical treatment

[0196] The concentration of the composite acid solution was increased to 60%.

[0197] The gradient temperature chemical treatment was extended: 45°C for 40 minutes, 65°C for 55 minutes, and 85°C for 70 minutes.

[0198] The treatment resulted in a reduction of the impurity content to about 1,500 ppm.

[0199] 3 Precision thermal purification

[0200] The soaking time was extended to 4 hours.

[0201] Treatment result: impurity content reduced to about 12 ppm.

[0202] 4 Plasma surface purification

[0203] The argon plasma treatment was extended to 30 minutes.

[0204] The helium-argon mixed plasma treatment was extended to 40 minutes.

[0205] Treatment result: surface impurity content reduced to about 1.2 ppm.

[0206] 5 Cryogenic helium deep purification

[0207] The cycle time was extended to 12 hours.

[0208] Treatment result: final purity reached 99.9995%, impurity content about 5 ppb.

[0209] Example 3 verified the adaptability of the method of the present application to different initial purity graphite, indicating that by appropriately adjusting the treatment parameters, the process is also applicable to the treatment of graphite blocks with lower initial purity, and still can meet the requirements of ultra-high purity.

[0210] The specific data of the above Example 1 and Comparative Examples 1-3 are shown in Table 1 below:

[0211] Table 1

[0212] Performance Index Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Final Purity 99.9997％ 99.95％ 99.90％ 99.995％ Impurity Content < 3 ppb ~ 50 ppm ~ 100 ppm ~ 5 ppm Purity Uniformity Intra-lot variation < 1% Intra-lot variation > 20% Intra-lot variation > 30% Intra-lot variation ~ 10% Thermal Conductivity Retention 125％ 80％ 95％ 110％ Structural Integrity 98％ 85％ 90％ 95％ Energy Consumption Benchmark Value 85% of Benchmark Value 140% of Benchmark Value 110% of Benchmark Value Processing Time Benchmark Value (about 48 hours) 60% of Benchmark Value 120% of Benchmark Value 80% of Benchmark Value

[0213] The purification method of the present application has significant advantages compared to traditional methods:

[0214] Purity improvement: the final purity is increased by 1-2 orders of magnitude compared to traditional methods, and the impurity content is reduced to the ppb level, meeting the most advanced semiconductor process requirements. Example 1 reached a purity of 99.9997%, while Comparative Examples 1-3 could only reach purities of 99.95%, 99.90% and 99.995%, respectively.

[0215] Structural protection: through mild chemical treatment and precise temperature control, the microstructure integrity of the graphite is improved by more than 13%, and the thermal conductivity is improved by 25%. In contrast, the thermal conductivity of Comparative Example 1 decreased by 20%, indicating that traditional treatment methods have caused serious damage to the structure of the graphite.

[0216] Purity uniformity: with the help of three-stage temperature control and helium deep purification, consistent purification results inside and outside are achieved, with a purity difference of less than 1%. The purity difference inside and outside of Comparative Example 2 was as high as 30%, indicating that single heat treatment cannot achieve uniform purification.

[0217] Efficiency and cost balance: although the processing time of comparative example 1 is prolonged, the purity is improved by more than 10 times; the energy consumption of comparative example 2 is reduced by 40%, but the purity is improved by more than 10 times. This balance makes the present application have a significant cost-effective advantage in commercial applications.

[0218] From the data of the examples and comparative examples, it can be clearly seen that the purification method of the present application successfully solves the key technical problems of structure protection, uniform purification and surface residual impurities in the graphite purification process, realizes the ultra-high purity purification of graphite blocks for semiconductors, and provides high-quality raw material guarantee for the semiconductor industry. Through the verification of examples 2 and 3, it is further proved that the process of the present application is flexible and adaptable, and can process graphite materials of different sizes and different initial purities, and has a wide application prospect.

[0219] Finally, it should be pointed out that: the above examples are only specific embodiments of the present disclosure, which are used to illustrate the technical solutions of the present disclosure, but not to limit it, the protection scope of the present disclosure is not limited to this, although the present disclosure has been described in detail with reference to the foregoing examples, those skilled in the art should understand: any person skilled in the art within the technical range disclosed by the present disclosure, they can still modify or easily think of changes to the technical solutions recorded in the foregoing examples, or make equivalent replacement to part of the technical features; and these modifications, changes or replacements do not make the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present disclosure, and should be covered within the protection scope of the present disclosure. Therefore, the protection scope of the present disclosure should be subject to the protection scope of the claims.

Claims

1. A method for purifying a graphite block for a semiconductor, characterized by, The method comprises the following steps: obtaining an isostatic pressing graphite block, immersing the graphite block in a composite acid solution for gradient temperature chemical treatment, and neutralizing and cleaning by a buffer solution with ultrasonic assistance to obtain a graphite block with surface and shallow impurities preliminarily removed, wherein the speed of immersing the graphite block in the composite acid solution is 0.5-1 mm / min, the composite acid solution is prepared by mixing nitric acid and sulfuric acid at a volume ratio of 3:1, and the acid concentration is 50-60%; placing the graphite block with surface and shallow impurities preliminarily removed in a high-vacuum environment, performing three-stage heating and holding at the highest temperature for a preset time, and then cooling to obtain a graphite block with internal impurities less than 10 ppm, comprising: The graphite block preliminarily removed of surface and shallow layer impurities is placed in a high-purity graphite crucible, put into a vacuum heat treatment furnace, vacuumized to 10 -4 Pa below; from room temperature to 800℃, the heating rate is 4-6℃ / min; from 800℃ to 2200℃, the heating rate is 2-4℃ / min; from 2200℃ to 2800℃, the heating rate is 1.5-2.5℃ / min; holding the graphite block at 2800℃ for 2-4 hours; placing the graphite block with internal impurities less than 10 ppm in a plasma treatment chamber for plasma treatment to obtain a graphite block with surface impurities less than 1 ppm, comprising: placing the graphite block with internal impurities less than 10 ppm in a plasma treatment chamber and vacuumizing; The chamber pressure was controlled to 10 mTorr with high purity argon gas. -5 The graphite block was subjected to argon plasma treatment at 1000 W for 30 min. after the argon plasma treatment is completed, vacuumizing; A mixed gas of helium and argon is introduced into the plasma processing chamber, and the chamber pressure is controlled to 10 -5 Pa, the graphite block is subjected to helium-argon mixed plasma treatment to obtain a graphite block with a surface impurity content of less than 1 ppm. placing the graphite block with surface impurities less than 1 ppm in a low-temperature environment, and circulating purifying by introducing high-purity helium to obtain a graphite block with a purity of 99.9995%-99.9999%, comprising: placing the graphite block with surface impurities less than 1 ppm in a low-temperature chamber and controlling the temperature at-180℃ to-200℃; circulating flushing the graphite block by introducing high-purity helium with a purity greater than 99.9999% at a flow rate of 5-10 L / min for 8-12 hours to obtain the graphite block with a purity of 99.9995%-99.9999%.

2. The purification method of graphite block for semiconductor according to claim 1, characterized by, The gradient temperature chemical treatment comprises: sequentially maintaining at 40℃ for 25-35 minutes, at 60℃ for 40-50 minutes, and at 80℃ for 55-65 minutes.

3. The method for purifying a graphite block for semiconductors according to claim 1, characterized by, The cooling of the graphite block comprises: from 2800℃ to 2000℃ at a cooling rate of 2℃ / min; from 2000℃ to 1500℃ at a cooling rate of 1℃ / min; and from 1500℃ to room temperature at a cooling rate of 3℃ / min.

4. The method for purifying a graphite block for semiconductors according to claim 1, characterized by, In the mixed gas of helium and argon, the volume ratio of helium to argon is 3:1; the time of argon plasma treatment is 15-30 minutes; and the time of helium-argon mixed plasma treatment is 20-40 minutes.

5. A graphite block for semiconductor, characterized by comprising: The graphite block is purified by the purification method of any one of claims 1-4.

6. An electronic device, characterized by The element is prepared by using the graphite block purified by the purification method of any one of claims 1-4.

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