Graphite block for semiconductor, purification method thereof, and electronic device

Abstract

The invention provides a graphite block for a semiconductor, a purification method of the graphite block and an electronic device. The purification method comprises the following steps: immersing the graphite block subjected to isostatic pressing treatment into a composite acid solution prepared from nitric acid and sulfuric acid according to a ratio of 3: 1 at a speed of 0.5-1mm / min for gradient heating chemical treatment; the treated graphite block is placed in a high vacuum environment for three-section type accurate temperature control heating and program control cooling; argon plasma and helium-argon mixed plasma are adopted for surface purification; and introducing high-purity helium in a low-temperature environment of-180 DEG C to-200 DEG C to carry out circulating deep purification. By integrating a multi-dimensional purification technology, a mild chemical treatment-precise thermal purification-low-temperature helium deep purification process system is established, so that the purity of the graphite block reaches 99.9995-99.9999%, the impurity content is as low as 1-5ppb, and the manufacturing requirements of semiconductors with process nodes of 5nm and below are met.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor material preparation, and particularly to a graphite block for semiconductors, a purification method thereof, and an electronic device. This method is applicable to the preparation of ultra-high purity graphite materials used in key process steps such as semiconductor wafer preparation, epitaxial growth, and ion implantation. Background Art

[0002] The semiconductor industry is the foundation of the development of contemporary information technology, and high-purity graphite materials play an irreplaceable role in the semiconductor manufacturing process. Graphite blocks are widely used in key process steps such as semiconductor wafer preparation, epitaxial growth, and ion implantation due to their excellent thermal conductivity, chemical stability, and high-temperature tolerance. As semiconductor manufacturing processes develop towards 7nm, 5nm, and even smaller nodes, the requirements for the purity of graphite materials are constantly increasing, and the impurity content needs to be controlled below the ppb level.

[0003] Traditional graphite block purification methods mainly include steps such as pickling and vacuum heat treatment. In the pickling process, a mixed acid is mainly used to soak the graphite block to remove metal impurities; subsequently, through high-temperature (usually 2500 - 2800 °C) vacuum heat treatment, the remaining impurities inside the graphite are promoted to volatilize. However, these traditional methods have a series of technical bottlenecks in meeting the requirements of the contemporary semiconductor industry for ultra-high purity graphite materials.

[0004] The existing graphite block purification technologies have the following key technical problems: First, the pickling process is prone to causing damage to the structure of the graphite block, affecting its thermal conductivity, and reducing the service life and efficiency of the graphite block; second, the temperature control of vacuum heat treatment is not precise enough, easily leading to uneven purification degrees on the surface and inside of the graphite block, resulting in internal and external purity differences; finally, trace impurities are likely to remain on the surface of the purified graphite block, affecting the purity requirements in the semiconductor manufacturing process.

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

[0006] In view of this, the present application provides a purification method for a graphite block for semiconductors, which solves the problems in the prior art that the pickling process is prone to causing damage to the structure of the graphite block, the temperature control of vacuum heat treatment is not precise enough resulting in uneven purification degree, and trace impurities are likely to remain on the surface of the purified graphite block.

[0007] The embodiments of the present application provide a purification method for a graphite block for semiconductors, including the following steps:

[0008] Obtain an isostatically pressed graphite block, immerse the graphite block in a composite acid solution for gradient temperature rise chemical treatment, and neutralize with a buffer solution and assist cleaning with ultrasonic waves to obtain a graphite block with surface and shallow layer impurities preliminarily removed;

[0009] Place the graphite block with surface and shallow layer impurities preliminarily removed in a high vacuum environment, perform three-stage heating and keep it at the highest temperature for a preset time, and then cool down to obtain a graphite block with an internal impurity content lower than 10 ppm;

[0010] Place the graphite block with an internal impurity content lower than 10 ppm in a plasma treatment chamber for plasma treatment to obtain a graphite block with a surface impurity content lower than 1 ppm;

[0011] Place the graphite block with a surface impurity content lower than 1 ppm in a low-temperature environment, introduce high-purity helium gas for cyclic purification to obtain a graphite block with a purity of 99.9995%-99.9999%.

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

[0013] In some embodiments, the gradient temperature rise chemical treatment includes: maintaining at 40°C for 25-35 minutes, at 60°C for 40-50 minutes, and at 80°C for 55-65 minutes in sequence.

[0014] In some embodiments, placing the graphite block with surface and shallow layer impurities preliminarily removed in a high vacuum environment, performing three-stage heating and keeping it at the highest temperature for a preset time, and then cooling down includes:

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

[0016] From room temperature to 800°C, the heating rate is 4-6°C / min;

[0017] From 800°C to 2200°C, the heating rate is 2-4°C / min;

[0018] From 2200°C to 2800°C, the heating rate is 1.5-2.5°C / min;

[0019] Keep the graphite block at 2800°C for 2-4 hours.

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

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

[0022] Placing the graphite block with an internal impurity content of less than 10 ppm in a plasma processing chamber and evacuating the chamber;

[0023] Introducing high-purity argon gas to control the chamber pressure to 10-5 Pa and performing argon plasma processing on the graphite block;

[0024] After the argon plasma processing is completed, evacuate the chamber;

[0025] Introduce a mixed gas of helium and argon into the plasma processing chamber, control the chamber pressure to 10-5 Pa, and perform helium-argon mixed plasma processing on the graphite block to obtain the graphite block with a surface impurity content of less than 1 ppm.

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

[0027] In some of these embodiments, placing the graphite block with a surface impurity content of less than 1 ppm in a low-temperature environment and introducing high-purity helium gas for cyclic purification to obtain a graphite block with a purity of 99.9995% - 99.9999% includes:

[0028] Placing the graphite block with a surface impurity content of less than 1 ppm in a low-temperature chamber and controlling the temperature at -180°C to -200°C;

[0029] Introduce high-purity helium gas with a purity greater than 99.9999% to perform cyclic flushing on the graphite block, control the helium gas flow rate at 5 - 10 L / min, and the cyclic time at 8 - 12 hours to obtain the graphite block with a purity of 99.9995% - 99.9999%.

[0030] The embodiments of the present application also provide a graphite block for semiconductors, which is purified by using the above purification method for graphite blocks for semiconductors.

[0031] An embodiment of the present application also provides an electronic device, including components prepared from a graphite block for semiconductor use purified by all or part of the purification method of the graphite block for semiconductor use described above.

[0032] The present application has the following technical effects:

[0033] Through the graphite structure protection type slow impregnation technology, while removing impurities, the graphite microstructure is protected to the greatest extent, solving the problem of damage to the graphite structure caused by traditional pickling, increasing the integrity of the microstructure of the purified graphite block by more than 13%, and improving the thermal conductivity by 25%.

[0034] Adopting the three-stage precise temperature control vacuum heat treatment technology, designing different heating rates and holding times for different temperature ranges, and combining a high-vacuum environment and programmed controlled slow cooling, uniform purification of the graphite block from the inside to the outside is achieved, and the purity difference is controlled within 1%.

[0035] Introducing the helium-argon mixed plasma surface deep purification technology, using the small size characteristics of helium ions to penetrate deep into the graphite micropores, and at the same time combining the sputtering effect of argon ions to achieve surface deep purification, and the surface impurity content is reduced to about 0.8 ppm.

[0036] Through the low-temperature helium gas circulation deep purification technology, using the high permeability and inactivity of helium gas in a low-temperature environment, the residual impurities deep in the graphite are carried out, achieving a graphite block purity of 99.9995% - 99.9999%, and the impurity content is as low as 1 - 5 ppb. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the drawings required for use in the embodiments will be briefly introduced below. The drawings here are incorporated into the specification and constitute a part of this specification. These drawings show embodiments consistent with the present disclosure and are used together with the specification to illustrate the technical solutions of the present disclosure. It should be understood that the following drawings only show some embodiments of the present disclosure, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0038] Figure 1 It is a schematic flow chart of the purification method of the graphite block for semiconductor use provided by the embodiment of the present invention;

[0039] Figure 2 It is a schematic diagram of the mild chemical treatment provided by the embodiment of the present invention;

[0040] Figure 3 It is the temperature change curve of the three-stage heating provided by the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0041] To make the objectives, technical solutions, and advantages of the embodiments of the present disclosure clearer, the technical solutions in the embodiments of the present disclosure will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present disclosure. Apparently, the described embodiments are only a part rather than all of the embodiments of the present disclosure. Components of the embodiments of the present disclosure generally described and illustrated in the accompanying drawings herein may 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 merely represents selected embodiments of the present disclosure. All other embodiments obtained by those skilled in the art based on the embodiments of the present disclosure without creative efforts fall within the scope of protection of the present disclosure.

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

[0043] As used herein, the term "and / or" merely describes an association relationship and indicates that three relationships may exist. For example, A and / or B may represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the term "at least one" as used 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 may represent any one or more elements selected from the set composed of A, B, and C.

[0044] As Figure 1 shown, an embodiment of the present application provides a purification method for a graphite block for semiconductors, including:

[0045] S1: Obtain an isostatically pressed graphite block, immerse the graphite block in a composite acid solution for gradient temperature rise chemical treatment, and neutralize with a buffer solution and perform ultrasonic-assisted cleaning to obtain a graphite block with surface and shallow impurities preliminarily removed;

[0046] Specifically, the speed at which the graphite block is immersed in the composite acid solution is 0.5 - 1 mm / min. The composite acid solution is prepared by mixing nitric acid and sulfuric acid in a volume ratio of 3:1, and the acid solution concentration is 50 - 60%. By using a slow impregnation device with a controllable speed, the speed at which the graphite block is immersed in the acid solution is controlled, allowing the acid solution to penetrate into the graphite layer by layer, avoiding the impact damage caused by traditional direct immersion. It should be noted that if the immersion speed is lower than 0.5 mm / min, although the graphite structure is better protected, the treatment time will be significantly prolonged and the production efficiency will be reduced; if the immersion speed is higher than 1 mm / min, it is easy to cause damage to the microscopic structure of the graphite.

[0047] The gradient temperature rise chemical treatment includes: maintaining at 40°C for 25 - 35 minutes, at 60°C for 40 - 50 minutes, and at 80°C for 55 - 65 minutes in sequence. Through a three-stage temperature control, during the process of gradually increasing the temperature gradient, the chemical reaction rate gradually increases, but remains within the range that does not damage the graphite structure, achieving a mild and progressive chemical reaction, and reaching 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 ultrasonically assisted cleaned at 40 - 60°C and multi-stage rinsed with deionized water to obtain the graphite block with surface and shallow-layer impurities preliminarily removed. By using a sodium bicarbonate buffer solution with pH = 7.5 - 8.0 for neutralization treatment, introducing ultrasonic-assisted cleaning at 40 - 60°C for 15 - 20 minutes to accelerate the removal of residual acid liquid and impurities, and using high-purity deionized water (resistivity > 18 MΩ·cm) for multi-stage rinsing to ensure the complete removal of acid liquid.

[0049] After this mild chemical treatment process, the impurity content of the graphite block is reduced to about 800 - 1200 ppm, mainly removing active metal elements such as Fe and Ca, and the integrity of the microscopic structure of the graphite block is maintained above 95%.

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

[0051] Specifically, placing the graphite block with surface and shallow-layer impurities preliminarily removed in a high-vacuum environment, subjecting it to three-stage heating and holding at the highest temperature for a preset time, and then cooling, includes: placing the graphite block with surface and shallow-layer impurities preliminarily removed in a high-purity graphite crucible, putting it into a vacuum heat treatment furnace, and evacuating to below 10-4 Pa; subjecting the graphite block to three-stage heating and holding at the highest temperature for a preset time includes: from room temperature to 800°C, with a heating rate of 4 - 6°C / min;

[0052] From 800°C to 2200°C, the heating rate is 2 - 4°C / min;

[0053] From 2200°C to 2800°C, the heating rate is 1.5 - 2.5°C / min;

[0054] The graphite block is held at 2800°C for 2 - 4 hours.

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

[0056] By using the PID control algorithm, the heating power is monitored and adjusted in real time to ensure a smooth temperature curve with the deviation controlled within ±5°C. By reducing the heating rate in the high-temperature section, the heat is ensured to be evenly conducted into the graphite block to avoid excessive temperature gradient between the inside and outside. Meanwhile, heat treatment is carried out in a high-vacuum environment (below 10 -4 Pa) to reduce the interference of gas molecules on the purification process. The vacuum system adopts a combination of a molecular pump and an ion pump to avoid oil molecule contamination and ensure the purity of the vacuum environment.

[0057] In this system, high-purity helium gas with a purity greater than 99.9999% is the core medium for the entire deep purification process. First, the high-purity helium gas is sent into the low-temperature chamber at a constant flow rate (5 - 10 L / min) through a precision flow controller. The selection of high-purity helium gas is based on its small atomic radius (about 31 pm), high chemical inertness, and excellent permeability at low temperatures. When helium gas flows through the surface of the graphite block in a low-temperature environment of -180°C to -200°C, the low-temperature environment causes the graphite micropores to contract, and the helium molecules can continue to penetrate these micropores due to their small volume.

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

[0059] As Figure 3 shown, cooling the graphite block includes: cooling from 2800°C to 2000°C at a cooling rate of 2°C / min; cooling from 2000°C to 1500°C at a cooling rate of 1°C / min; and cooling from 1500°C to room temperature at a cooling rate of 3°C / min. By adopting a slow cooling with program control from high temperature to room temperature, especially slower cooling (1°C / min) in the critical temperature range (2000 - 1500°C), the internal stress damage of the graphite structure caused by rapid temperature changes is prevented. Through recording the temperature curve data of the entire process, it is ensured that each batch of products undergoes the same heat treatment process.

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

[0061] S3: Place the graphite block with an internal impurity content of less than 10 ppm in a plasma treatment chamber for plasma treatment to obtain a graphite block with a surface impurity content of less than 1 ppm.

[0062] Specifically, placing the graphite block with an internal impurity content of less than 10 ppm in a plasma treatment chamber for plasma treatment to obtain a graphite block with a surface impurity content of less than 1 ppm includes: placing the graphite block with an internal impurity content of less than 10 ppm in a plasma treatment chamber and evacuating; introducing high-purity argon 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, evacuating; introducing a mixed gas of helium and argon into the plasma treatment chamber, 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, in the above argon and argon plasma treatment processes of the present invention, mass spectrometry technology can be used to continuously detect the types and contents of impurities carried in the circulating helium gas. When the detected impurity content drops below the set threshold and remains stable, the helium gas 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 two-stage plasma surface treatment, that is, first using argon plasma for preliminary surface treatment, and then using helium-argon mixed plasma for deep purification to form a gradient treatment effect.

[0065] In the argon plasma treatment stage, the graphite block is placed on a special graphite carrier. The carrier is designed with tiny support points to minimize the contact area and ensure that the surface of the graphite block can be fully exposed to the plasma environment. The chamber is first evacuated to below 10 -6 Pa to remove impurity gases that may affect plasma stability. Subsequently, high-purity argon (purity ≥ 99.9999%) is introduced, and the chamber pressure is precisely controlled to 10 -5Pa. The argon plasma is generated by exciting with a 13.56 MHz radio frequency power supply, using a capacitive coupling method. The electrode has a specially designed porous structure to ensure uniform plasma distribution. Due to its relatively large mass, argon ions have a significant physical sputtering effect, which can effectively remove the adsorbed impurities and weakly bound contaminants on the graphite surface. The plasma density is controlled within 1×10 -3 cm -3 range, and the electron temperature is about 3 - 5 eV. This parameter combination ensures sufficient processing intensity while avoiding over-bombardment damage to the graphite surface structure.

[0066] After the argon plasma treatment, the vacuum is pumped down again to below 10 -6 Pa to remove the volatile impurities generated during the treatment process. Subsequently, a mixed gas of helium and argon is introduced, and the volume ratio is controlled at 3:1. This ratio has been verified by a large number of experiments to be able to maximize the deep penetration effect of helium ions while maintaining plasma stability. 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, and the power density is controlled at 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 microporous structure of graphite due to their small volume characteristics (atomic radius is only 18 pm), and excite the impurities in the deep micropores through energy transfer and collision. During the whole treatment process, the temperature of the graphite block substrate is controlled below 120 °C by a water-cooled backplane to avoid thermal stress damage.

[0067] Under 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 graphite surface and effectively remove the trace impurities remaining on the surface. A radio frequency (RF) power supply and a matching network are used to ensure plasma stability and uniformity.

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

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

[0070] S4: Place the graphite block with surface impurity content lower than 1 ppm in a low-temperature environment, and introduce high-purity helium gas for cyclic purification to obtain a graphite block with a purity of 99.9995%-99.9999%.

[0071] Specifically, placing the graphite block with surface impurity content lower than 1 ppm in a low-temperature environment and introducing high-purity helium gas for cyclic purification to obtain a graphite block with a purity of 99.9995%-99.9999% includes: placing the graphite block with surface impurity content lower than 1 ppm in a low-temperature chamber, controlling the temperature at -180°C to -200°C; introducing high-purity helium gas with a purity greater than 99.9999% to conduct cyclic flushing on the graphite block, controlling the helium gas flow rate at 5-10 L / min, and the cyclic time at 8-12 hours to obtain the graphite block with a purity of 99.9995%-99.9999%.

[0072] Through the above complete purification process, the present invention successfully prepares a graphite block for semiconductors with extremely high purity. After being detected by the helium mass spectrometry leak detection technology, it is found that the impurity content of the graphite block is 1-5 ppb, that is, it reaches a purity of 99.9995%-99.9999%. The impurity content is much lower than the 10-50 ppb impurity content that can usually be achieved by traditional processes. Such a low impurity content makes this graphite block particularly suitable for semiconductor manufacturing at process nodes of 5 nm and below, and can effectively avoid problems such as device performance degradation and yield loss caused by metal impurity contamination.

[0073] During the test, place the purified graphite block in the sealed chamber of a helium mass spectrometry leak detector, evacuate it to below 10^-8 Pa, and then spray high-purity helium gas outside the chamber. If there are tiny impurities or structural defects inside 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 highly sensitive detector. By analyzing the helium gas permeability and pattern, the purity of the graphite block and the integrity of its microscopic structure can be accurately evaluated, forming a complete quality evaluation system.

[0074] During the entire purification process of the present invention, the impurity content in the graphite blocks at different stages gradually decreases. The impurity content in the graphite block with surface and shallow-layer impurities preliminarily 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 insoluble elements such as Si and Al. The surface impurity content in the graphite block with surface impurity content lower than 1 ppm is 0.5-1.5 ppm, and the surface oxide and hydrocarbon content are significantly reduced. Through this step-by-step precise control, the present invention realizes the all-round purification of the graphite block from the outside to the inside and from the rough to the refined, ensuring the ultra-high purity and excellent performance of the final product.

[0075] During the helium circulation and flushing process, the helium carrying impurities around the purified graphite block is purified by a molecular sieve filtration device and then recycled. The molecular sieve filtration device adopts a two-tower switching design, with one tower for adsorption and purification and the other for regeneration to achieve continuous purification.

[0076] Example 1:

[0077] 1 Raw materials

[0078] Select high-density isostatic graphite blocks with a density of 1.85 g / cm 3 , with an initial size of 400 mm × 400 mm × 100 mm, an initial purity of about 99.5%, and containing about 5000 ppm of impurities. The main impurity components are metal elements such as Fe, Si, Ca, Al and oxides.

[0079] Mild chemical treatment

[0080] 2.1 Slow impregnation and treatment with a composite acid solution

[0081] Prepare a composite acid solution: Mix nitric acid (65%) and sulfuric acid (98%) in 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 at 0.8 mm / min.

[0083] Impregnation time: Continue to soak for 60 minutes after complete immersion.

[0084] 2.2 Gradient temperature rise chemical treatment

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

[0086] Second stage: Raise the temperature to 60 °C and maintain for 45 minutes.

[0087] Third stage: Raise the temperature to 80 °C and maintain for 60 minutes.

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

[0089] 2.3 Neutralization and cleaning

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

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

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

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

[0094] Processing result: After detection, the impurity content is reduced to about 800 ppm. Mainly, reactive metal elements such as Fe and Ca are removed, and the integrity of the microstructure of the graphite block is maintained above 95%.

[0095] Precision Thermal Purification

[0096] 3.1 Heating process

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

[0098] Vacuum is pumped to 5×10 -5 Pa.

[0099] Heating curve: From room temperature to 800 °C, the heating rate is 5 °C / min; from 800 - 2200 °C, the heating rate is 3 °C / min; from 2200 - 2800 °C, the heating rate is 2 °C / min.

[0100] Real-time temperature monitoring points: The surface of the graphite block and the internal center position (through embedded thermocouples).

[0101] 3.2 Heat preservation treatment

[0102] Keep the temperature at 2800 °C for 3 hours.

[0103] The vacuum degree is maintained below 1×10 -4 Pa.

[0104] Adopt four-way PID to control the temperature fluctuation within the range of ±5 °C.

[0105] 3.3 Cooling process

[0106] 2800 - 2000 °C: The cooling rate is 2 °C / min.

[0107] 2000 - 1500 °C: The cooling rate is 1 °C / min.

[0108] Below 1500 °C: The cooling rate is 3 °C / min.

[0109] Below 500 °C, fill with high-purity argon to atmospheric pressure and continue to cool to room temperature.

[0110] Processing result: After detection, the impurity content is reduced to about 8 ppm. Mainly, insoluble elements such as Si and Al are removed, the crystallinity of the graphite is increased to 98%, and the thermal conductivity is increased by 25%.

[0111] Plasma Surface Purification

[0112] 4.1 Argon plasma treatment

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

[0114] Vacuum is pumped to 0.5 Pa.

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

[0116] Plasma parameters: radio frequency 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] A mixed gas of helium and argon (He:Ar = 3:1) is introduced, and the chamber pressure is controlled to 4 Pa.

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

[0121] Treatment time: 35 minutes.

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

[0123] Treatment result: After XPS analysis, the contents of surface oxides and hydrocarbons are significantly reduced, and the surface impurity content is reduced to about 0.8 ppm.

[0124] Low-temperature helium deep purification

[0125] 5.1 Low-temperature cyclic helium purification

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

[0127] High-purity helium gas (99.9999%) is introduced, and the flow rate is 8 L / min.

[0128] Cycle time: 10 hours.

[0129] The impurity components and contents carried out in the helium gas are monitored in real time.

[0130] 5.2 Quality assessment

[0131] The helium mass spectrometry leak detection technology is used to evaluate the purity of graphite, and the detection sensitivity is 10-11 Pa·m 3 / s.

[0132] The present invention is further illustrated by the following comparative examples and other embodiments:

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

[0134] 1 Raw materials

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

[0136] 2 Pickling treatment

[0137] Directly immerse the graphite block into the mixed acid solution (nitric acid: sulfuric acid = 1:1), and the immersion is completed in about 5 seconds.

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

[0139] Cleaning: Rinse directly with deionized water 3 times.

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

[0141] 3 Vacuum heat treatment

[0142] Directly raise the temperature to 2800 °C, and the heating rate is kept constant at 10 °C / min.

[0143] Insulation time: 2 hours, vacuum degree: 1×10-3 Pa.

[0144] Cooling: Natural cooling (without controlling the cooling rate).

[0145] 4 Comparison results:

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

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

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

[0149] XRD detection shows that the lattice structure integrity is only 85%.

[0150] There are obvious pickling marks and microcracks on the surface of the graphite block.

[0151] Comparative Example 2: Only use the heat treatment process

[0152] 1 Raw materials

[0153] The same high-density isostatic pressing graphite block as in Example 1.

[0154] 2 Vacuum heat treatment

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

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

[0157] Insulation time: extended to 5 hours.

[0158] Vacuum degree: 5×10 -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 inside and outside the graphite block is uneven, with a low impurity content on the surface and a high impurity content inside.

[0163] It requires more energy consumption (about 40% increase) and longer processing time.

[0164] A hardened layer forms on the surface of the graphite block, affecting subsequent processing performance.

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

[0166] 1 Pretreatment

[0167] Carry out mild chemical treatment and precise thermal purification according to Example 1.

[0168] 2 Surface treatment

[0169] Only use argon plasma treatment.

[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 there are still impurities remaining in the deep micropores.

[0175] The graphite surface is over-activated and easily adsorbs environmental impurities.

[0176] Example 2: Verification of adaptability to graphite size changes

[0177] 1 Raw materials

[0178] Select small-sized high-density isostatic graphite blocks with dimensions of 100 mm × 100 mm × 20 mm, and other characteristics are the same as those in Example 1.

[0179] 2 Mild chemical treatment

[0180] Carry out according to the method of Example 1, and adjust the impregnation speed to 0.6 mm / min.

[0181] Treatment result: The impurity content is reduced to about 750 ppm.

[0182] 3 Precise thermal purification

[0183] Carry out according to the method of Example 1, and shorten the heat preservation time to 2.5 hours.

[0184] Treatment result: The impurity content is reduced to about 6 ppm.

[0185] 4 Plasma surface purification

[0186] Carry out according to the method of Example 1, and maintain the same parameters.

[0187] Treatment result: The surface impurity content is reduced to about 0.7 ppm.

[0188] 5 Deep purification with low-temperature helium

[0189] Carry out according to the method of Example 1, and shorten the cycle time to 9 hours.

[0190] Treatment result: The final purity reaches 99.9998%, and the impurity content is about 2 ppb.

[0191] Example 2 verifies the adaptability of the method of the present invention to graphite blocks of different sizes, indicating that the process has good size compatibility, can flexibly adjust some parameters according to the product size, and at the same time maintain a high purification effect.

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

[0193] 1 Raw materials

[0194] Select an isostatic graphite block with a lower initial purity. The size is the same as that in Example 1, but the initial purity is only 99.0%, and it contains about 10,000 ppm of impurities.

[0195] 2 Mild chemical treatment

[0196] Increase the concentration of the composite acid solution to 60%.

[0197] Prolong the gradient temperature rise chemical treatment: maintain at 45 °C for 40 minutes, 65 °C for 55 minutes, and 85 °C for 70 minutes.

[0198] Treatment result: The impurity content is reduced to about 1500 ppm.

[0199] 3 Precise thermal purification

[0200] Prolong the heat preservation time to 4 hours.

[0201] Processing result: The impurity content is reduced to about 12 ppm.

[0202] 4 Plasma surface purification

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

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

[0205] Processing result: The surface impurity content is reduced to about 1.2 ppm.

[0206] 5 Low-temperature helium deep purification

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

[0208] Processing result: The final purity reaches 99.9995%, and the impurity content is about 5 ppb.

[0209] Example 3 verifies the adaptability of the method of the present invention to graphite with different initial purities, indicating that by appropriately adjusting the processing parameters, this process is also applicable to treating graphite blocks with relatively low initial purities and can still meet the ultra-high purity requirements.

[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 Internal and External Difference < 1% Internal and External Difference > 20% Internal and External Difference > 30% Internal and External Difference ≈ 10% Thermal Conductivity Retention Rate 125％ 80％ 95％ 110％ Structural Integrity 98％ 85％ 90％ 95％ Energy Consumption Reference Value 85% of the Reference Value 140% of the Reference Value 110% of the Reference Value Processing Time Reference Value (≈ 48 hours) 60% of the Reference Value 120% of the Reference Value 80% of the Reference Value

[0213] The purification method of the present invention has significant advantages compared with the traditional method:

[0214] Purity improvement: The final purity is increased by 1-2 orders of magnitude compared with the traditional method, and the impurity content is reduced to the ppb level, meeting the requirements of the most advanced semiconductor processes. The purity of Example 1 reaches 99.9997%, while Comparative Examples 1-3 can only reach 99.95%, 99.90%, and 99.995% respectively.

[0215] Structure protection: Through mild chemical treatment and precise temperature control, the integrity of the graphite microstructure is improved by more than 13%, and the thermal conductivity is increased by 25%. In contrast, the thermal conductivity of Comparative Example 1 decreases by 20%, indicating that the traditional treatment method causes serious damage to the graphite structure.

[0216] Purity uniformity: With the help of three-stage temperature control and helium deep purification, a purification effect that is consistent inside and outside is achieved, and the purity difference is controlled within 1%. The internal and external purity difference of Comparative Example 2 is as high as 30%, indicating that a single heat treatment cannot achieve uniform purification.

[0217] Efficiency and cost balance: Although the processing time is extended compared to Comparative Ratio 1, the purity is increased by more than 10 times; compared to Comparative Ratio 2, the energy consumption is reduced by 40%, but the purity is increased by more than 10 times. This balance gives the present invention a significant cost-performance advantage in commercial applications.

[0218] It can be clearly seen from the data of the examples and comparative ratios that the purification method of the present invention has successfully solved the key technical problems such as structural protection, uniform purification, and surface residual impurities in the graphite purification process, achieving ultra-high purity purification of graphite blocks for semiconductors, and providing high-quality raw material guarantee for the semiconductor industry. Through the verification of Example 2 and Example 3, it further proves the flexibility and adaptability of the process of the present invention, which can process graphite materials of different sizes and different initial purities, and has a wide application prospect.

[0219] Finally, it should be noted that the above-described embodiments are only specific embodiments of the present disclosure, used to illustrate the technical solutions of the present disclosure, rather than limiting them. The protection scope of the present disclosure is not limited thereto. Although the present disclosure has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: Any person skilled in the art within the technical scope disclosed by the present disclosure can still modify the technical solutions recorded in the foregoing embodiments or can easily think of changes, or perform equivalent replacements on some of the technical features; and these modifications, changes or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present disclosure, and should all be covered by 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 purification method for a graphite block used in semiconductors, characterized in that, It includes the following steps: Obtain an isostatically pressed graphite block, immerse the graphite block in a composite acid solution for gradient temperature rise chemical treatment, and neutralize with a buffer solution and assist cleaning with ultrasonic waves to obtain a graphite block with surface and shallow layer impurities preliminarily removed; Place the graphite block with surface and shallow layer impurities preliminarily removed in a high-vacuum environment, perform three-stage heating and hold at the highest temperature for a preset time, and then cool down to obtain a graphite block with an internal impurity content lower than 10 ppm; Place the graphite block with an internal impurity content lower than 10 ppm in a plasma treatment chamber for plasma treatment to obtain a graphite block with a surface impurity content lower than 1 ppm; Place the graphite block with a surface impurity content lower than 1 ppm in a low-temperature environment, introduce high-purity helium for cyclic purification to obtain a graphite block with a purity of 99.9995%-99.9999%; 2. The purification method of the graphite block for semiconductor according to claim 1, characterized in that, The speed at which the graphite block is immersed in the composite acid solution is 0.5-1 mm / min. The composite acid solution is prepared by mixing nitric acid and sulfuric acid according to a volume ratio of 3:1, and the acid solution concentration is 50-60%; 3. The purification method of the graphite block for semiconductor according to claim 1 or 2, characterized in that, The gradient temperature rise chemical treatment includes: maintaining at 40°C for 25-35 minutes, maintaining at 60°C for 40-50 minutes, and maintaining at 80°C for 55-65 minutes in sequence; 4. The purification method of the graphite block for semiconductor according to claim 1, characterized in that, Place the graphite block with surface and shallow layer impurities preliminarily removed in a high-vacuum environment, perform three-stage heating and hold at the highest temperature for a preset time, and then cool down, including: Place the graphite block with the surface and shallow impurities preliminarily removed into a high-purity graphite crucible, put it into a vacuum heat treatment furnace, and evacuate to below 10 -4 Pa; From room temperature to 800°C, the heating rate is 4-6°C / min; From 800°C to 2200°C, the heating rate is 2-4°C / min; From 2200°C to 2800°C, the heating rate is 1.5-2.5°C / min; Hold the graphite block at 2800°C for 2-4 hours; 5. The purification method of the graphite block for semiconductor according to claim 4, wherein Cooling the graphite block includes: cooling from 2800°C to 2000°C, with a cooling rate of 2°C / min; cooling from 2000°C to 1500°C, with a cooling rate of 1°C / min; cooling from 1500°C to room temperature, with a cooling rate of 3°C / min; 6. The purification method of the graphite block for semiconductor according to claim 1, characterized in that, Place the graphite block with an internal impurity content lower than 10 ppm in a plasma treatment chamber for plasma treatment to obtain a graphite block with a surface impurity content lower than 1 ppm, including: Place the graphite block with an internal impurity content lower than 10 ppm in a plasma treatment chamber and evacuate; Introduce high-purity argon gas to control the chamber pressure to 10 -5 Pa, and perform argon plasma treatment on the graphite block; After the argon plasma treatment, evacuate; Introduce a mixed gas of helium and argon into the plasma processing chamber, and control the chamber pressure to 10 -5 Pa, perform helium-argon mixed plasma treatment on the graphite block to obtain a graphite block with a surface impurity content lower than 1 ppm.

7. The purification method of the graphite block for semiconductor according to claim 6, characterized in that, In the mixed gas of helium and argon, the volume ratio of helium to argon is 3:1; the time for argon plasma treatment is 15-30 minutes; the time for helium-argon mixed plasma treatment is 20-40 minutes; 8. The purification method of the graphite block for semiconductor according to claim 1, wherein, Place the graphite block with a surface impurity content lower than 1 ppm in a low-temperature environment, introduce high-purity helium for cyclic purification to obtain a graphite block with a purity of 99.9995%-99.9999%, including: Place the graphite block with a surface impurity content lower than 1 ppm in a low-temperature chamber and control the temperature at -180°C to -200°C; Circulate and flush the graphite block with high-purity helium gas with a purity greater than 99.9999%, control the helium gas flow rate to be 5-10 L / min, and the circulation time to be 8-12 hours to obtain the graphite block with a purity of 99.9995%-99.9999%.

9. A graphite block for semiconductor, characterized in that, It is purified by using the purification method of the graphite block for semiconductor according to any one of claims 1-8.

10. An electronic device, characterized in that, It includes components prepared from the graphite block for semiconductor purified by using the purification method of the graphite block for semiconductor according to any one of claims 1-8, either in whole or in part.

Images