Method for dry cleaning of medium-large size graphite-based disc and bottom flow guide type graphite jig

Abstract

The application discloses a method for cleaning a large-size graphite substrate for silicon-based nitride epitaxy by a dry method and a graphite jig with a bottom flow guide. The method comprises the following stages: bearing preparation, initial replacement, medium-temperature reconstruction, high-temperature cleaning, gradient cooling and final cooling. The graphite substrate is vertically loaded in the jig and placed in a furnace cavity, and is heated in stages under vacuum, and inert gas and reactive gas are sequentially introduced, and alternating gas pressure blowing is performed throughout the process. In the high-temperature cleaning stage, high-temperature vacuum desorption is inserted. When the gradient cooling is performed, the reactive gas is cut off, only the inert gas is introduced and continuous blowing is performed. Finally, the gas supply is stopped and a deep vacuum is maintained, and the vacuum is broken and the furnace is discharged after being cooled to a safe temperature. The graphite jig with the bottom flow guide is used to perform the above method. The application breaks through the macro-mass transfer bottleneck of the medium-large-size substrate, realizes efficient stripping of a deep dense polycrystalline compound, avoids thermal stress damage and deformation of the large-span substrate, and realizes uniform and residue-free cleaning, thereby improving the reusability of the substrate and the epitaxial yield.

Description

Technical Field

[0001] This invention relates to the field of semiconductor epitaxial manufacturing processes and equipment, and more specifically, to a dry cleaning method for medium-to-large-sized graphite-based disks for silicon-based nitride epitaxy, and a bottom-guided graphite fixture for performing the method. Background Technology

[0002] With the widespread application of third-generation wide-bandgap semiconductor materials, represented by gallium nitride (GaN), in optoelectronics and high-power devices, especially the rapid expansion of silicon-based nitride (GaN-on-Si) epitaxial technology, metal-organic chemical vapor deposition (MOCVD) processes have placed extremely high demands on the temperature field uniformity of wafers. To achieve higher single-furnace capacity and production efficiency, the industry widely adopts medium-to-large-sized graphite substrates with huge disk spans. Simultaneously, to match the corresponding equipment, the edges of the substrates have evolved into complex structures such as step differences and skirts. However, in the unique silicon-based nitride epitaxial process, these substrates need to be exposed to high-temperature and high-concentration metal-organic source environments for extended periods. High-hardness, extremely dense polycrystalline composites containing silicon (Si) / aluminum (Al) / gallium (Ga) easily deposit within the micropores of their surface silicon carbide (SiC) coating. If not thoroughly removed, this will lead to particle contamination and thermal field distortion during epitaxial growth, severely reducing the yield of epitaxial wafers.

[0003] Existing dry cleaning technologies for graphite-based disks face significant bottlenecks in heat and mass transfer processes, as well as equipment compatibility issues, when dealing with silicon-based byproducts, medium to large disk sizes, and complex edges. Specifically: First, there is a contradiction between thermal stress control and reaction thermodynamics. Conventional dry cleaning often relies on extreme high temperatures (above 1400℃) to forcibly pyrolyze deposits. This not only places a huge load on the furnace body and accelerates the thermal aging of the substrate, but also makes medium and large-sized substrates prone to huge thermal stress due to the radial temperature difference between the center and the edge during the drastic and continuous temperature rise and fall process. This can lead to warping and deformation of the substrate or tearing and peeling of the SiC coating on the surface. If the process temperature is simply reduced, the etching reaction thermodynamics will decrease sharply, making it impossible to effectively reduce stubborn deposits.

[0004] Secondly, there is the bottleneck of fluid mass transfer resistance in medium and large-sized disks. The large surface area of ​​medium and large-sized disks leads to huge radial airflow diffusion resistance. In conventional constant-pressure dry cleaning, the process gas can often only quickly pass over the surface of the disk, making it difficult to penetrate into the micro-pits of the SiC coating, let alone reach the central area of ​​medium and large-sized disks. This causes severe fluid stagnation of by-products in the central area, resulting in a cleaning rate mismatch of "overwashing at the edges and residue in the center".

[0005] Finally, there is the bottleneck of airflow obstruction and compatibility with the supporting equipment (graphite fixture). Existing vertical cleaning racks mostly use a single-specification solid bottom groove for support. On the one hand, after high-density insertion of medium and large-sized base plates, the solid bottom groove will tightly block the bottom of the base plate, artificially creating an "airflow dead zone" at the bottom, making it impossible for the reactive gas to reach the complex edges of the base plate bottom (e.g., step differences, skirt structures); on the other hand, the single groove type of traditional fixed fixtures cannot be compatible with base plates of various shapes. When forcibly loading heavy medium and large-sized base plates with complex irregular edges, it is very easy to cause local jamming or thermal stress concentration due to interference at the force points. Moreover, once the fixture is damaged or the base plate specification is changed, it can only be completely re-customized, resulting in extremely high material costs.

[0006] In summary, simple process cooling or fixture improvements are insufficient to address the existing technological challenges. The industry urgently needs a novel dry cleaning method that couples "dynamic flow field technology" with "bottom-guided graphite fixtures." This method aims to mitigate the destructive thermal stress accumulated during thermal cycling through stepped temperature management and extended insulation at specific points. Furthermore, it requires not only overcoming the macroscopic gas flow bottleneck of medium-to-large-sized substrates using dynamic pressure differentials, but also introducing a high-temperature vacuum desorption mechanism. This mechanism leverages deep vacuum to break down mass transfer resistance and chemical equilibrium within microscopic pores, thoroughly removing deep-seated, stubborn deposits from large substrates. Finally, combined with bottom-guided and non-destructive bearing capabilities of physical fixtures, this method can completely solve the industry problems of uneven cleaning, susceptibility to thermal damage, and deep-seated residues in medium-to-large-sized graphite substrates during the cleaning process. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention aims to overcome the deficiencies of dry cleaning methods for large-size graphite-based disks, such as high mass transfer resistance, mismatch between center and edge etching rates, susceptibility to thermal stress damage, and poor compatibility of traditional support fixtures that obstruct airflow. This invention provides a dry cleaning method and fixture for medium-to-large-size graphite-based disks used in silicon-based nitride epitaxy. By coupling a multi-temperature zone stepped thermal buffer with an alternating gas pressure purging process, and utilizing a novel bottom-guided graphite fixture, this invention achieves efficient and non-destructive removal of micropores and complex edge polycrystalline deposits on the disk. Specifically, this invention aims to provide a dry cleaning method for medium-to-large-size graphite-based disks used in silicon-based nitride epitaxy, and a bottom-guided graphite fixture for performing this method.

[0008] To solve the above-mentioned technical problems or achieve the above-mentioned objectives, the present invention adopts the following technical solution: According to one aspect of the present invention, a dry cleaning method for medium-to-large-sized graphite-based disks of silicon-based nitride epitaxy is provided, comprising the following steps: Preparation stage: Vertically load multiple graphite substrates onto the bottom-guided graphite fixture, and place the bottom-guided graphite fixture inside the furnace cavity; Initial replacement stage: Under vacuum conditions, the furnace temperature is raised to the first temperature range, and at the same time, an inert gas, which is the process gas, is introduced into the furnace to perform alternating pressure purging. Intermediate temperature reconstruction stage: The furnace temperature is raised from the first temperature range to the second temperature range, and during this period, reactive gas as process gas is introduced, and alternating pressure purging is performed; High-temperature cleaning stage: The furnace temperature is raised from the second temperature range to and maintained in the third temperature range. During this period, the mixture of reactive gas and inert gas is introduced and alternating gas pressure purging is performed. At least one high-temperature vacuum desorption step is performed during this period. Gradient cooling stage: The furnace temperature is gradually reduced from the third temperature range to the fourth temperature range. During this period, the supply of reactive gas is cut off, only inert gas is introduced, and alternating pressure purging is performed. Termination of cooling phase: The furnace temperature is reduced from the fourth temperature range to the fifth temperature range. Then, all process gas supplies are stopped and evacuation is continued to maintain a deep vacuum environment. After the furnace temperature continues to drop to the safe threshold temperature, inert gas is introduced to break the vacuum and the furnace is cooled to room temperature.

[0009] In one embodiment of the present invention, alternating pressure purging includes sequentially performing the following steps: Inflation step: Introduce the appropriate process gas and increase the furnace pressure to the preset absolute pressure limit; Pressure holding step: Keep the furnace vent valve closed and maintain the furnace pressure at the upper limit of absolute pressure. The duration of the pressure holding step is set to 3-10 seconds. Evacuation procedure: Evacuate the air to reduce the furnace chamber pressure to the preset lower absolute pressure limit.

[0010] In one embodiment of the present invention, in each process stage of performing alternating gas pressure purging, the upper limit of the absolute pressure in the furnace cavity is set to 2.0 Torr-10.0 Torr, and the lower limit of the absolute pressure is set to 0.01 Torr-0.5 Torr; and throughout the entire process, the duration of the gas charging step is set to 2 seconds-6 seconds, the duration of the gas extraction step is set to 30 seconds-80 seconds, and the alternating gas pressure purging frequency is changed by adjusting the duration of the gas charging step and the gas extraction step.

[0011] In one embodiment of the present invention, in the initial replacement stage, the furnace cavity temperature is increased at a heating rate of 1.0℃ / min to 6.0℃ / min; in the intermediate temperature reconstruction stage, the furnace cavity temperature is increased at a heating rate of 4℃ / min to 12℃ / min; in the high temperature cleaning stage, the furnace cavity temperature is increased at a heating rate of 4℃ / min to 12℃ / min; and in the gradient cooling stage, the furnace cavity temperature is cooled at a cooling rate of 6℃ / min to 12℃ / min.

[0012] In one embodiment of the present invention, the high-temperature vacuum desorption step includes: during the period of maintaining a constant temperature in the third temperature range, pausing the alternating pressure purging, cutting off the supply of inert gas and reactive gas, and maintaining full-speed evacuation to reduce the absolute pressure of the furnace cavity to ≤1×10⁻⁶. -2 Torr, and maintain the temperature in this state for 15-40 minutes, and the temperature holding time of the desorption step is included in the total temperature holding time of the third temperature range.

[0013] In one embodiment of the present invention, the first temperature range is 150℃-350℃; the second temperature range is 500℃-800℃; the third temperature range is 1000℃-1250℃; the fourth temperature range is 600℃-900℃; the fifth temperature range is 400℃-550℃; and the safety threshold temperature is not higher than 400℃.

[0014] In one embodiment of the present invention, a constant-temperature thermal buffer node is provided in the intermediate-temperature reconstruction stage, the high-temperature cleaning stage, and the gradient cooling stage during the temperature change process, wherein: The isothermal heat buffer node in the intermediate temperature reconstruction stage is set within the range of 450℃-550℃ and kept at a constant temperature for 15 minutes-50 minutes. The constant temperature heat buffer node during the high temperature cleaning stage is set within 950℃-1050℃ and maintained at a constant temperature for 20-60 minutes. The constant temperature thermal buffer node in the gradient cooling stage is first set within 950℃-1050℃ and kept constant for 15-40 minutes, and then set within 800℃-870℃ and kept constant for 15-40 minutes.

[0015] In one embodiment of the present invention, the inert gas includes N2 with a purity ≥ 99.999%, and the reactive gas includes H2 with a purity ≥ 99.999%, wherein the volumetric flow rate ratio of N2 to H2 is (3-8):1 during the intermediate temperature reconstruction stage and the high temperature cleaning stage.

[0016] In one embodiment of the present invention, during the high-temperature cleaning stage, the total time for maintaining a constant temperature in the third temperature range is controlled between 200 and 500 minutes; during the final cooling stage, the absolute pressure of the deep vacuum environment is maintained at ≤1×10⁻⁶. -2 Torr.

[0017] In one embodiment of the invention, the corresponding process gas is preheated to 100°C-1000°C when it enters the furnace cavity.

[0018] In one embodiment of the present invention, the diameter of the graphite substrate disk is 390mm-790mm.

[0019] In one embodiment of the present invention, the graphite substrate includes a disc-type graphite substrate and a skirted graphite substrate.

[0020] According to another aspect of the present invention, a bottom-guided graphite fixture is provided for performing a dry cleaning method for medium-to-large-sized graphite-based disks for silicon-based nitride epitaxy as described above, comprising: Two side panels, which are arranged opposite and parallel to each other; Multiple supporting beams are spanned and detachably fixed between two side plates. The side bearing surfaces of the supporting beams are set at an inclined angle relative to the horizontal plane and are tangent to or attached to the circular periphery of the graphite base plate.

[0021] In one embodiment of the present invention, a plurality of limiting grooves are provided on the support beam at intervals along its axial direction, and the groove width of the limiting groove is greater than the edge thickness of the graphite substrate to be cleaned; the bottom of the limiting groove is provided with a venting hole that connects the upper surface and the lower surface of the support beam; and a venting channel is provided on the top surface of the support beam along its axial direction, and the venting channel passes through each limiting groove sequentially along the axial direction of the support beam.

[0022] In one embodiment of the present invention, the width of the air guide hole is smaller than the groove width of the limiting groove, and the length direction of the air guide hole is parallel to the axial direction of the supporting crossbeam; the bottom of the air guide channel is higher than the bottom of the limiting groove.

[0023] In one embodiment of the present invention, the limiting groove has outwardly expanding chamfered structures or arc-shaped surface structures at both sides of the groove opening; and The internal cross-section of the limiting groove has a stepped structure, consisting of a wider upper groove section and a narrower lower groove section from top to bottom, with a stepped bearing surface at the junction of the upper and lower groove sections; or the internal cross-section of the limiting groove is a straight-walled U-shaped groove structure with a uniform groove width throughout.

[0024] In one embodiment of the present invention, handle holes penetrating the two side plates are respectively provided; the two ends of the supporting beam are respectively integrally formed with a reinforcing assembly part and an external threaded part extending outward from the reinforcing assembly part, the reinforcing assembly parts at both ends are respectively embedded in the two side plates, and the external threaded parts at both ends are respectively protruding out of the two side plates and locked and fixed by graphite nuts.

[0025] The technical solution provided by this invention has the following advantages compared with the prior art: (1) This invention achieves uniform, heat-damaged, and deep-residue-free dry cleaning of medium-to-large-sized graphite substrates for silicon-based nitride epitaxy by using a bottom-guided graphite fixture with vertical support and a five-stage sequential process. This method relies on stepped temperature zone control and alternating air pressure purging throughout the process to effectively eliminate the destructive thermal stress generated by thermal cycling and avoid substrate warping and coating damage; it uses alternating air pressure to forcefully break through the macroscopic airflow mass transfer bottleneck of medium-to-large-sized substrates, achieving uniform cleaning of the entire substrate surface and eliminating the problems of over-cleaning at the edges and residue in the center; it breaks through the mass transfer resistance of micropores through high-temperature vacuum desorption, thoroughly removing deep and stubborn deposits; and it isolates oxygen with deep vacuum during the final cooling stage to prevent substrate oxidation and secondary sublimation of by-products. The overall solution works synergistically from multiple dimensions such as heat transfer, mass transfer, thermal stress, and microscopic desorption to solve the industry pain points such as uneven cleaning, susceptibility to heat damage, deep residue, and difficulty in cleaning edge dead corners in one go, significantly improving the reusability of graphite substrates and the yield of epitaxial production.

[0026] (2) This invention introduces a high-temperature vacuum desorption mechanism to overcome microscopic pore resistance and achieve deep removal of stubborn deposits. Addressing the difficulty in cleaning dense Si / Al / Ga polycrystalline composites generated by silicon-based nitride epitaxy, especially the industry pain point of large-sized graphite disks where the large radial span leads to airflow stagnation and "desorption dead zones" in the central area, this invention specifically designs a high-temperature vacuum desorption step during the high-temperature cleaning stage. By pausing purging and maintaining full-speed evacuation to ≤1×10⁻⁶, -2 The deep vacuum of Torr disrupts the mass transfer resistance and chemical reaction balance within the micropores of the silicon carbide (SiC) coating, causing byproducts and gaseous products in the central region and deep micro-pits of complex edges of medium and large-sized substrates to rapidly diffuse and desorb at high temperatures. This mechanism, combined with isothermal cleaning, achieves thorough and complete removal of dense polycrystalline composites without dead angles, greatly improving the cleanliness of the substrate surface and the yield of epitaxial wafers.

[0027] (3) This invention adopts a multi-temperature zone stepped thermal buffer management to achieve a balance between efficient cleaning and low thermal damage. This invention changes the traditional method of simply relying on extreme ultra-high temperature (e.g., greater than 1400℃) to forcibly pyrolyze deposits, and controls the maximum cleaning temperature within a relatively safe range of 1250℃. Through the synergy of "non-extreme high temperature" and "long-term constant temperature", it ensures excellent temperature field uniformity of medium and large-sized disks. More importantly, this invention innovatively introduces a process gas preheating mechanism to avoid local quenching and thermal shear stress impact caused by cold gas directly blowing on medium and large-sized graphite substrates under high temperature conditions; in conjunction with setting multiple specific constant temperature thermal buffer nodes (e.g., 450℃-550℃, 950℃-1050℃, etc.) in the heating and cooling process, it gives medium and large-sized substrates sufficient thermal equilibrium time, greatly alleviates the severe thermal stress caused by transient radial temperature difference, and effectively prevents substrate warping and tearing and peeling of the surface SiC coating. In addition, a deep vacuum is continuously drawn during the cooling termination phase, which completely eliminates the oxidation and pulverization of the graphite matrix and the secondary sublimation of by-products.

[0028] (4) This invention innovatively couples dynamic alternating air pressure with a bottom-guided graphite fixture, overcoming the macroscopic mass transfer bottleneck of medium and large-sized substrates. Addressing the issues of airflow stagnation in the central region and dead zones at the edges of medium and large-sized substrates, the bottom-guided graphite fixture of this invention constructs a three-dimensional cross-exhaust network on the supporting beam, consisting of "air guide holes + air guide channels + fluid gaps." Combined with the axial penetration effect of the handle holes on the side plate, it eliminates bottom obstruction during high-density loading of traditional fixtures. Simultaneously, in conjunction with alternating air pressure purging in the process, the large pressure difference fluctuation generated by the filling and pumping creates a strong "breathing effect," forcing highly reactive gases (e.g., H2) to laterally penetrate the large-span substrate surface and reach deep into complex edges (step differences, skirts), achieving uniform etching of the entire substrate surface and fundamentally solving the cleaning mismatch problem of "over-washing at the edges and residue at the center."

[0029] (5) The bottom-guided graphite fixture of the present invention adopts a highly tolerant adaptive and guiding design, breaking the equipment compatibility barrier of irregularly shaped base plates. The limiting groove of the bottom-guided graphite fixture adopts an adaptive cross-section design (stepped or straight-walled U-shaped), which can stably support the heavy base plate with step difference, and the width of the groove is greater than the edge thickness throughout, so that the downwardly extending fragile skirt edge can be tolerated in the groove, effectively avoiding rigid compression caused by limited thermal expansion at high temperature. The chamfered or arc-shaped surface structure of the two sides of the groove opening provides excellent physical guidance for manual or automated robotic arm loading, greatly reducing the collision and chipping scrap rate of brittle large-size base plates during the insertion and removal process.

[0030] (6) This invention adopts a fully graphite-based anti-vibration and anti-torsion modular architecture, which significantly reduces the cost of consumables for the production line and extends its life cycle. The specially designed reinforced assembly part at the end of the bottom-guided graphite fixture fits tightly with the corresponding side plate and uses a nut locking system made of pure graphite material. This all-graphite connection eliminates the risk of thermal expansion mismatch under extreme temperature differences, and its high-strength structural connection is more stable and resists the severe mechanical vibration caused by alternating air pressure pulses. The modular and detachable design of this invention breaks the status quo that the entire fixture is scrapped when it is damaged. When individual crossbeams are damaged or different specifications of base plates need to be replaced, only local components need to be replaced, which greatly reduces the customization and maintenance costs of silicon-based epitaxial production lines and has extremely high industrial promotion value. Attached Figure Description

[0031] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure.

[0032] To more clearly illustrate the technical solutions in the embodiments of this disclosure or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, those skilled in the art can obtain other drawings based on these drawings without creative effort.

[0033] Figure 1 This diagram illustrates the overall process flow of a dry cleaning method for medium-to-large-sized graphite-based disks for silicon-based nitride epitaxy, as provided in an embodiment of the present invention. Figure 2 The following is a time sequence and process window curve of alternating gas pressure purging at different temperature stages provided in an embodiment of the present invention; Figure 3 This diagram illustrates the overall three-dimensional structure of a bottom-guided graphite fixture (with a stepped limiting groove on the supporting crossbeam) provided in an embodiment of the present invention. Figure 4 This diagram illustrates the overall three-dimensional structure of a bottom-guided graphite fixture (with a straight-walled U-shaped limiting groove on the supporting beam) according to another embodiment of the present invention. Figure 5 The embodiments of the present invention are shown. Figure 3 A schematic diagram of the structure of the central support beam (with stepped limiting grooves); Figure 6 It shows Figure 5 Enlarged view of point I in the middle; Figure 7 The embodiments of the present invention are shown. Figure 4 A schematic diagram of the structure of the central support beam (with a straight-walled U-shaped limiting groove); Figure 8 It shows Figure 7 Enlarged schematic diagram at point II; Figure 9 The diagram shows the internal cross-section of the stepped limiting groove on the supporting beam in an embodiment of the present invention, and a cross-sectional schematic diagram of its mating state with a graphite base disk with a step difference in edge thickness. Figure 10 The diagram shows the internal cross-section of the straight-walled U-shaped limiting groove on the supporting beam in an embodiment of the present invention, and a cross-sectional schematic diagram of its mating state with a circular graphite base disk with uniform edge thickness. Figure 11 The diagram shows the internal cross-section of the straight-walled U-shaped limiting groove on the supporting beam in an embodiment of the present invention, and a cross-sectional schematic diagram of its engagement with a skirted graphite base disk with a downwardly extending skirt at the edge. Figure 12 A schematic diagram of the overall structure of the graphite substrate disk in an embodiment of the present invention is shown, wherein (a) is a disc-shaped graphite substrate disk with a step difference in edge thickness, (b) is a disc-shaped graphite substrate disk with uniform edge thickness, and (c) is a skirted graphite substrate disk. Figure 13 The diagram shows the PL (photoluminescence) dominant wavelength distribution mapping of the wafers obtained in the embodiments of the present invention and the comparative examples, where (a) is the cleaned group of the embodiments and (b) is the uncleaned group of the comparative examples; Figure 14 A scatter plot comparing the relationship between the wafer optical properties (luminescence intensity and wavelength) obtained from the embodiments of the present invention and the comparative examples is shown. Figure 15 Box line comparison diagrams of the optical properties (wavelength and half-width) of the wafers obtained from embodiments of the present invention and comparative examples are shown, wherein (a) is a box line comparison diagram of wavelength and (b) is a box line comparison diagram of half-width.

[0034] Explanation of reference numerals in the attached figures: 1. Side plate; 1-1. Handle hole; 2. Support beam; 2-1. Limiting groove; 2-2. Air guide hole; 2-3. Air guide channel; 2-4. Reinforced assembly part; 2-5. External thread part; 3. Graphite nut; 4. Graphite base plate. Detailed Implementation

[0035] To better understand the above-described objectives, features, and advantages of this disclosure, embodiments of this disclosure will be further described below. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other.

[0036] Numerous specific details are set forth in the following description in order to provide a full understanding of this disclosure, but this disclosure may also be implemented in other ways than those described herein; obviously, the embodiments in the specification are only some, and not all, of the embodiments of this disclosure.

[0037] like Figure 1 As shown, an embodiment of the present invention provides a dry cleaning method for medium-to-large-sized graphite-based disks with silicon-based nitride epitaxy, the method comprising the following steps: S1. Loading preparation stage: Vertically load multiple graphite substrates onto the bottom-guided graphite fixture, and place the bottom-guided graphite fixture inside the furnace cavity; S2. Initial replacement stage: Under vacuum conditions, the furnace temperature is raised to the first temperature range, and at the same time, inert gas as process gas is introduced into the furnace to perform alternating pressure purging. S3. Intermediate temperature reconstruction stage: The furnace temperature is raised from the first temperature range to the second temperature range, and during this period, a reactive gas as a process gas is introduced, and the alternating gas pressure purging is performed; S4. High-temperature cleaning stage: The furnace temperature is raised from the second temperature range to and maintained in the third temperature range. During this period, the reactive gas and the inert gas are mixed and introduced, and the alternating gas pressure purging is performed. At least one high-temperature vacuum desorption step is performed during this period. S5. Gradient cooling stage: The furnace temperature is gradually reduced from the third temperature range to the fourth temperature range. During this period, the supply of the reactive gas is cut off, and only the inert gas is introduced, and the alternating gas pressure purging is performed. S6. Termination of Cooling Stage: Reduce the furnace temperature from the fourth temperature range to the fifth temperature range, then stop all process gas supply and continue evacuation to maintain a deep vacuum environment. After the furnace temperature continues to drop to the safe threshold temperature, introduce inert gas to break the vacuum and cool to room temperature.

[0038] This invention achieves uniform, heat-damaged, and deep-residue-free dry cleaning of medium-to-large-sized graphite substrates for silicon-based nitride epitaxy using a bottom-guided graphite fixture with vertical support and a five-stage sequential process. This method relies on stepped temperature zone control and continuous alternating air pressure purging to effectively eliminate destructive thermal stress generated by thermal cycling, preventing substrate warping and coating damage. Alternating air pressure forces the way through the macroscopic airflow mass transfer bottleneck of medium-to-large-sized substrates, achieving uniform cleaning across the entire surface and eliminating over-cleaning at the edges and residue in the center. High-temperature vacuum desorption breaks down the mass transfer resistance of micropores, thoroughly removing deep-seated stubborn deposits. During the final cooling stage, deep vacuum isolates oxygen, preventing substrate oxidation and secondary sublimation of byproducts. The overall solution addresses industry pain points such as uneven cleaning, susceptibility to heat damage, deep residue, and difficulty in cleaning edge dead zones through multi-dimensional synergy in heat transfer, mass transfer, thermal stress, and microscopic desorption, significantly improving the reusability of graphite substrates and epitaxial production yield.

[0039] In this embodiment, in step S1, a bottom-guided graphite fixture can be used to vertically support multiple graphite substrates, preferably at least three graphite substrates, and then steps S2-S6 are executed sequentially. Combined with... Figure 2 The time-series curves shown illustrate the flow field synergy mechanism of the five process stages S2-S6 described above: First, during the stepped heating and alternating purging process in stages S2 to S3, the preheated process gas, combined with temperature difference and airflow fluctuations, achieves initial desorption of impurities and induces microscopic cracks in dense deposits by utilizing thermal expansion differences. Subsequently, in stage S4, the alternating pulsed airflow generates a "breathing effect" due to pressure difference fluctuations during charging and pumping. This, combined with the three-dimensional exhaust network of the bottom-guided graphite fixture, guides the reducing gas to overcome the huge radial diffusion resistance of medium and large-sized substrates, penetrating into micropores for chemical etching. Simultaneously, the high-temperature vacuum desorption step breaks down deep mass transfer resistance at the microscopic level. In the cooling stage of S5, continuous gas pulses extract the stripped gaseous byproducts from the furnace cavity, suppressing secondary sublimation caused by supersaturation. Finally, in stage S6, gas supply is stopped and evacuation is performed to maintain a deep vacuum environment, removing residual impurities and completely isolating oxygen to prevent oxidation and pulverization of the graphite matrix at high temperatures. This also provides an absolutely clean background environment for subsequent vacuum breaking by inert gas.

[0040] In the above embodiments, such as Figure 2 As shown, alternating pressure purging includes sequentially performing the following steps: Inflation step: Introduce the appropriate process gas and increase the furnace pressure to the preset absolute pressure limit; Pressure holding step: Keep the furnace vent valve closed and maintain the furnace pressure at the upper limit of absolute pressure. The duration of the pressure holding step is set to 3-10 seconds. Evacuation procedure: Evacuate the air to reduce the furnace chamber pressure to the preset lower absolute pressure limit.

[0041] In this embodiment, the 3-10 second pressure holding step is a key dwell point in the alternating pressure purging process. When the furnace pressure reaches the upper limit of absolute pressure, both the concentration and absolute pressure of the reactant gas in the chamber are at their peak. By closing the exhaust valve to maintain the pressure, sufficient permeation time is provided for the high-pressure reactant gas, allowing it to penetrate deeply into the center of the medium-to-large-sized graphite substrate disk and into the deep gaps of complex edges such as the bottom step difference and skirt, driven by the static pressure difference, and to undergo sufficient adsorption and reduction etching reactions with the dense polycrystalline by-products in the deep dead corners. Without this pressure holding buffer, the gas would be immediately drawn away after being filled, causing the gas flow to only quickly sweep across the surface of the substrate disk, making it difficult to achieve deep mass transfer in the center of medium-to-large-sized graphite substrate disks and other locations.

[0042] In the above embodiments, such as Figure 2As shown, in each process stage of alternating gas pressure purging, the upper limit of absolute pressure in the furnace cavity is set to 2.0 Torr-10.0 Torr, and the lower limit of absolute pressure is set to 0.01 Torr-0.5 Torr. In addition, throughout the entire process, the duration of the gas charging step is set to 2 seconds-6 seconds, and the duration of the gas extraction step is set to 30 seconds-80 seconds. The alternating gas pressure purging frequency is changed by adjusting the duration of the gas charging step and the gas extraction step.

[0043] In this embodiment, the present invention enhances the gas-solid mass transfer and stripping process by constructing a trapezoidal pressure waveform with high amplitude within the furnace cavity. This variable pressure mode utilizes transient high-pressure forced reducing gas to overcome diffusion resistance, cover the entire medium-to-large-sized disk surface, and penetrate into the bottom layer of the deposit; simultaneously, it utilizes low-pressure evacuation to establish a strong gas flow shear force, synergistically generating a "breathing effect," thereby assisting chemical reduction with a purely physical flow field. According to Le Chatelier's principle, the forceful removal of gaseous products will drive the surface reduction reaction continuously in the positive direction. By maintaining a constant upper and lower pressure difference, a consistent "physical shear force" benchmark is ensured for each pulse purging; while the adaptive frequency variation achieved by dynamically adjusting the charging and evacuation times is to precisely match the kinetic requirements of different stages. For example, in the initial replacement stage of S2, the main process requirement is to remove adsorbed water vapor and replace background gas, which can be achieved by using low-frequency gentle purging with a longer filling and evacuation time; in the core high-temperature cleaning stage of S4, the filling and evacuation time is shortened to achieve high-frequency purging, and the high-frequency breathing effect is used to force fresh gas to accelerate the replacement of by-products in the dead corner, completely breaking the fluid stagnation in the central area of ​​medium and large-sized base plates.

[0044] In the above embodiments, the temperature change rate is controlled as follows at each process stage: In step S2, the furnace temperature is increased at a rate of 1.0℃ / min to 6.0℃ / min; in step S3, the furnace temperature is increased at a rate of 4℃ / min to 12℃ / min; in step S4, the furnace temperature is increased at a rate of 4℃ / min to 12℃ / min; and in step S5, the furnace temperature is decreased at a rate of 6℃ / min to 12℃ / min.

[0045] In this embodiment, the stepwise fine control of the heating and cooling slope effectively alleviates the interfacial thermal stress between the polycrystalline composite and the substrate layer, and further reduces the huge radial thermal stress generated by the asynchronous heat transfer between the center and the edge during the heating and cooling process of medium and large-sized substrates. The gentle and progressive heating and cooling curves provide sufficient time for the large substrate surface to homogenize, avoiding microcracks in the SiC coating and substrate deformation caused by extreme thermal shock, while effectively preventing the supersaturated reverse adsorption of gaseous metal byproducts due to excessively rapid condensation.

[0046] In the above embodiment, the high-temperature vacuum desorption step S4 includes: during the period of maintaining a constant temperature in the third temperature range, pausing the alternating gas pressure purging, cutting off the supply of inert gas and reactive gas, and maintaining full-speed evacuation to reduce the absolute pressure of the furnace cavity to ≤1×10⁻⁶. -2 Torr, and maintain the temperature in this state for 15-40 minutes, and the temperature holding time of the desorption step is included in the total temperature holding time of the third temperature range.

[0047] In this embodiment, this high-temperature vacuum desorption step is the core mechanism for overcoming the microscopic mass transfer resistance of the dense residues unique to silicon-based materials. Under high-temperature excitation in the third temperature range (1000℃-1250℃), the deep-seated stubborn residues within the micropores of the SiC coating already possess high molecular kinetic energy. At this point, by pumping air at full speed, a molecular kinetic energy of ≤1×10⁻⁶ can be established. -2 Torr's ultimate high vacuum, based on the gas law and Le Chatelier's principle, significantly increases the pressure difference inside and outside the micropores, disrupts the chemical equilibrium inside the pores, and forces the deep Si / Al / Ga polycrystalline complex and the gaseous products generated by reduction to diffuse outward from the micro-pits and desorb, thereby achieving a deep cleaning that cannot be achieved by ordinary airflow purging.

[0048] In the above embodiments, the temperature range parameters involved in each process stage are set as follows: In step S2, the first temperature range is 150℃-350℃; in step S3, the second temperature range is 500℃-800℃; in step S4, the third temperature range is 1000℃-1250℃; in step S5, the fourth temperature range is 600℃-900℃; in step S6, the fifth temperature range is 400℃-550℃; the safety threshold temperature is not higher than 400℃.

[0049] In this embodiment, the temperature ranges in each of the above process steps are set based on the thermal decomposition threshold of the deposit and the thermal boundary of the SiC coating to alleviate the thermal stress deformation and mass transfer inhomogeneity of medium and large-sized substrates. The first temperature range of 150℃-350℃, combined with inert gas pulses, achieves initial desorption of water vapor and volatile residues. The second temperature range of 500℃-800℃ induces microscopic thermal expansion cracks in the dense polycrystalline deposit, facilitating the infiltration of the initially introduced reactive gas into the micropores and initiating initial reduction. The third temperature range of 1000℃-1250℃ is controlled within the thermal stability domain of the SiC coating. This temperature range provides the activation energy required for the reduction of highly stable composites such as AlN and GaN by H2, while keeping the upper temperature limit below 1250℃ to reduce the risk of SiC coating ablation and substrate aging. To address the slow heat transfer characteristic of medium and large-sized substrates, the isothermal time is extended within this temperature range, providing ample thermal equilibrium cycles for the vast surface area. This ensures that the reaction temperature is consistent between the center and edges of the substrate, achieving a uniform chemical etching rate across the entire surface. Simultaneously, the maximum temperature limit reduces the heating power load required to maintain the temperature field for medium and large-sized substrates. The fourth temperature range of 600℃-900℃ serves as a pressurized cooling transition section, where airflow pulsation promotes the discharge of gaseous byproducts, inhibiting their reverse adsorption or sublimation in the central region of the substrate. The fifth temperature range of 400℃-550℃ isolates oxygen under high vacuum, preventing substrate oxidation etching. Considering the large heat storage and slow cooling of medium and large-sized substrates, a safety threshold is set at no higher than 400℃. When the temperature drops below this threshold, the graphite substrate and silicon carbide coating lose the thermodynamic conditions for rapid oxidation, providing an absolutely clean background environment for the introduction of inert gas (N2) to break the vacuum and prepare for pressure, thus completely eliminating oxidation losses and safety hazards throughout the cooling process.

[0050] In the above embodiments, in steps S3, S4, and S5, a constant-temperature thermal buffer node is provided during the temperature change process, wherein: The isothermal heat buffer node of the intermediate temperature reconstruction stage (S3) is set within 450℃-550℃ and kept at a constant temperature for 15 minutes-50 minutes; The constant temperature heat buffer node of the high temperature cleaning stage (S4) is set within 950℃-1050℃ and kept at a constant temperature for 20 minutes-60 minutes. The isothermal heat buffer node of the gradient cooling stage (S5) is first set at 950℃-1050℃ and kept at a constant temperature for 15-40 minutes, and then set at 800℃-870℃ and kept at a constant temperature for 15-40 minutes.

[0051] In this embodiment, the large-sized graphite substrate has a high heat capacity, and rapid heating can easily lead to a severe radial temperature difference between the center and the edge. A buffer node at 450℃-550℃ effectively homogenizes the surface temperature, allowing the deposit and substrate to smoothly transition through the initial period of thermal expansion differences. A buffer node at 950℃-1050℃ provides deep thermal equilibrium reserves before entering the high-temperature (1250℃) core cleaning stage, ensuring that the temperature of the entire broad substrate surface is essentially uniform before entering the high-activation-energy chemical etching stage, fundamentally eliminating the coating tearing problem caused by thermal stress concentration. The cooling process is crucial for maintaining cleanliness. Two stepped cooling buffer nodes are set up. On the one hand, this allows sufficient time for gaseous silicon-based reaction byproducts to be extracted from the furnace chamber under the influence of gas pulses, preventing them from becoming oversaturated and re-adsorbed onto the substrate surface due to rapid cooling. On the other hand, it effectively releases the residual stress of the graphite substrate and SiC coating during the shrinkage process, achieving safe cooling with low heat loss.

[0052] In the above embodiments, the inert gas includes N2 with a purity ≥ 99.999%, and the reactive gas includes H2 with a purity ≥ 99.999%. In the intermediate temperature reconstruction stage and the high temperature cleaning stage (in the stage of introducing reactive gas), the volume flow ratio of N2 to H2 is (3-8):1.

[0053] In this embodiment, the defined ratio of high-purity reactive gas to inert gas ensures a sufficient concentration of strongly reducing hydrogen radicals during the high-temperature etching stage. Simultaneously, using 3-8 times the volume of high-purity nitrogen as a dilution and transport medium effectively removes locally generated complex metallic gaseous byproducts from the wide exhaust paths of medium-to-large-sized disks, reducing the probability of reverse side reactions caused by excessively high local concentrations.

[0054] In the above embodiment, in step S4, the total time for maintaining the constant temperature in the third temperature range is controlled between 200 and 500 minutes; in step S6, the absolute pressure of maintaining the deep vacuum environment is not greater than 1 × 10⁻⁶. -2 Torr.

[0055] In this embodiment, the isothermal time during the high-temperature cleaning stage is controlled between 200 and 500 minutes, coupled with a cleaning temperature of 1000°C to 1250°C. Considering the physical characteristics of medium-to-large-sized graphite substrates—high heat capacity and slow radial heat conduction—setting the isothermal time to 200-500 minutes provides sufficient heat conduction and thermal equilibrium periods for the large-span substrate surface. This long-term isothermal process ensures a uniform temperature field between the center and edge regions of the substrate, and compensates for the impact of reduced cleaning temperature on chemical etching kinetics, ensuring the synchronous chemical reduction reaction across the entire substrate surface and achieving uniform removal of surface deposits. During the final cooling stage, the absolute pressure of the high-vacuum environment is maintained at ≤1×10⁻⁶. -2Torr keeps the graphite substrate in an oxygen-free passivation state during the high-temperature cooling range, preventing oxidation, etching, and pulverization of the graphite substrate.

[0056] In the above embodiments, the corresponding process gas is preheated to 100°C-1000°C when it enters the furnace cavity.

[0057] In this embodiment, preheating the process gas entering the furnace cavity is an effective thermal management mechanism to reduce thermal stress damage. Due to the large radial span of the surface of medium-to-large-sized graphite substrates, their sensitivity to local temperature gradients is significantly increased. Especially during the core medium-to-high temperature cleaning or isothermal buffering stages, both the furnace cavity and the graphite substrates are at high temperatures. If room temperature gas is directly introduced, the high-velocity cold airflow can easily trigger a local quenching effect upon contact with the vast substrate surface, resulting in enormous transient thermal shear stress. By preheating the process gas to 100℃-1000℃, the temperature difference between the high-velocity airflow and the surface of the medium-to-large-sized substrates can be significantly reduced, effectively suppressing the transient thermal shear stress impact caused by direct cold gas purging. Combined with the aforementioned stepped thermal buffering strategy, this further prevents macroscopic warping deformation of the medium-to-large-sized substrates due to thermal stress concentration, as well as microcracks and peeling of the surface silicon carbide (SiC) coating.

[0058] In the above embodiments, the diameter of the graphite substrate disk is 390mm-790mm.

[0059] In this embodiment, the disk diameter parameter of 390mm-790mm corresponds to the physical specifications of large-size graphite substrate disks in current silicon-based nitride epitaxy. Addressing the physical characteristics of this size range—long radial diffusion distance and tendency for reactive gas to stagnate in the central region—the aforementioned bottom guiding network and alternating pressure purging process work synergistically to force the reactive gas to laterally cover and penetrate the central region of the substrate using alternating pressure differences. This reduces the etching rate deviation between the center and edge regions of large-span disks, maintaining the cleaning uniformity across the entire disk surface. Furthermore, the method and fixture structure disclosed in this embodiment are backward compatible and can also be applied to conventionally sized graphite substrate disks with a disk diameter less than 390mm.

[0060] In the above embodiments, the graphite substrate can be a disc-shaped graphite substrate, a graphite substrate with a stepped difference at the edge, a graphite substrate with uniform edge thickness, or a skirt-shaped graphite substrate with a downward-extending skirt structure at the edge.

[0061] In this embodiment, the present invention is compatible with various graphite substrates, including disc-shaped graphite substrates, graphite substrates with stepped edges, graphite substrates with uniform edge thickness, and skirted graphite substrates with downward-extending skirt structures. Through targeted limiting groove structures and tolerant load-bearing designs, it achieves stable support and non-destructive loading of substrates with different edge shapes, effectively avoiding rigid compression, thermal expansion jamming, and loading collision damage. At the same time, in conjunction with the bottom guiding network and alternating air pressure purging, it ensures that the reactive gas can uniformly reach complex structural areas such as the surface, stepped surface, and inner side of the skirt of various substrates, eliminating cleaning dead corners. This enables medium and large-sized graphite substrates of different structural types to achieve uniform and thorough cleaning of the entire surface, significantly improving cleaning versatility and process compatibility, and meeting the high-efficiency reuse requirements of multi-specification substrates in silicon-based nitride epitaxial production lines.

[0062] like Figure 3 and 4 As shown, embodiments of the present invention also provide a bottom-guided graphite fixture for performing the dry cleaning method for medium-to-large-sized graphite-based disks in silicon-based nitride epitaxy as described above, comprising: Two side panels 1 arranged opposite and parallel to each other; Multiple supporting beams 2 are spanned and detachably fixed between two side plates 1. The side bearing surfaces of the supporting beams 2 are set at an inclined angle relative to the horizontal plane and are tangent to or attached to the circular periphery of the graphite base plate 4.

[0063] In this embodiment, the inclined support surface forms a conformal support with the edge of the medium-to-large-sized, disc-shaped graphite substrate. This geometry evenly distributes the weight of the substrate along the circumferential tangential direction, avoiding localized stress concentration and thermal stress interference caused by traditional right-angle or flat-bottomed supports. Simultaneously, the detachable beam frame allows for flexible replacement of support components with different load-bearing characteristics according to production line process requirements.

[0064] The bottom-guided graphite fixture provided in this embodiment forms a stable load-bearing frame through two relatively parallel side plates and multiple detachably connected support beams. The side load-bearing surfaces of the support beams are designed with an inclination, allowing them to be precisely tangent to or fit against the circumference of the graphite base disk. This ensures that the weight of the base disk is evenly distributed along the circumference, avoiding localized stress concentration and thermal expansion interference caused by traditional right-angle supports. This significantly reduces the risk of warping and edge chipping of medium and large-sized graphite base disks during loading and high-temperature cleaning. Furthermore, the detachable design of the support beams allows for flexible replacement of adaptable components according to the specifications of the graphite base disk, improving the fixture's versatility and modular reusability, reducing production line material costs, and providing a reliable structural guarantee for the vertical load-bearing and stable cleaning of medium and large-sized graphite base disks.

[0065] In the above embodiments, such as Figure 3-8As shown, multiple limiting grooves 2-1 are spaced apart along the axial direction on the supporting beam 2. The width of the groove opening of the limiting groove 2-1 is greater than the thickness of the edge of the graphite base disk 4 to be inserted. A venting hole 2-2 is opened through the bottom of the limiting groove 2-1 to connect the upper and lower surfaces of the supporting beam 2. A venting channel 2-3 is opened along the axial direction on the top surface of the supporting beam 2. The venting channel 2-3 passes through each limiting groove 2-1 in sequence along the axial direction of the supporting beam 2.

[0066] In this embodiment, the groove width is greater than the thickness of the base disk, allowing a physical fluid gap to be reserved between the surface and inner wall of the graphite base disk 4 after it is inserted into the limiting groove 2-1. This fluid gap is spatially connected to the air guide hole 2-2 at the bottom of the supporting beam 2 and the air guide channel 2-3 at the top, forming a fluid exhaust network. In the alternating pressure purging process, the airflow flows laterally through the air guide channel 2-3 and vertically through the limiting groove 2-1 via the air guide hole 2-2. Considering the large radial span of the medium-to-large-sized graphite base disk 4, the reactive gas can enter the bottom edge region of the base disk through the air guide hole 2-2 and the fluid gap, and be guided upwards towards the center of the disk surface along the fluid gap, thereby shortening the diffusion path of the gas to the center of the medium-to-large-sized disk surface, thus participating in the etching reaction of the entire disk surface.

[0067] In the above embodiments, such as Figure 5-11 As shown, the width of the air guide hole 2-2 is less than the groove width of the limiting groove 2-1, and the length direction of the air guide hole 2-2 is parallel to the axis of the supporting beam 2; the bottom of the air guide channel 2-3 is higher than the bottom of the limiting groove 2-1.

[0068] In this embodiment, the width of the air guide hole 2-2 is smaller than the width of the limiting groove 2-1. This ensures that when the bottom edge of the base plate is supported on the bottom surface of the groove, the air guide hole 2-2 still retains a permeable cross section, maintaining the flow of air in the vertical direction. Simultaneously, it ensures the static strength of the supporting beam 2 against bending when fully loaded with multiple graphite base plates (preferably at least three). The height difference structure, where the bottom of the air guide channel 2-3 is higher than the bottom of the limiting groove 2-1, limits the groove depth of the air guide channel 2-3, allowing the lower part of the supporting beam to retain a continuous solid cross section, thus meeting the static strength requirement for bending resistance when fully loaded with multiple graphite base plates (preferably at least three). Furthermore, this height difference structure ensures that after the graphite base plate 4 is seated on the bottom of the limiting groove 2-1, the air guide channel 2-3 maintains unobstructed space above the base plate bearing point. Gas between the surfaces of adjacent base plates is laterally connected through this unobstructed air guide channel 2-3, achieving a physical balance of fluid pressure difference.

[0069] In the above embodiments, such as Figure 9-11 As shown, the limiting groove 2-1 has outwardly expanding chamfered structures or arc-shaped surface structures at both sides of the groove opening; and like Figure 5-6As shown in Figure 9, the internal cross-section of the limiting groove 2-1 has a stepped structure, comprising a wider upper groove segment and a narrower lower groove segment from top to bottom. A stepped bearing surface is present at the junction of the upper and lower groove segments. Optionally, such as... Figure 7-8 As shown in Figures 10-11, the internal cross-section of the limiting groove 2-1 is a straight-walled U-shaped groove structure with a uniform width throughout the groove.

[0070] In this embodiment, the internal cross-section of the stepped limiting groove 2-1 is specifically designed for graphite base disks 4 with stepped edge thickness differences, allowing the edge steps to sit smoothly on the stepped bearing surface and preventing lateral swaying. The straight-walled U-shaped limiting groove 2-1 is suitable for graphite base disks 4 with downwardly extending skirts at the edges and graphite base disks 4 with uniform edge thickness. Its internal structure allows the bottom edge (or skirt) of the base disk to be directly and smoothly supported on the bottom of the groove. Because the entire width of the straight-walled U-shaped limiting groove 2-1 is greater than the thickness of the base edge (or skirt), the edge of the base disk and the fragile skirt are generously contained within the limiting groove 2-1, avoiding rigid compression of the sidewalls or thermal expansion jamming. The chamfered or arc-shaped surface structure of the groove not only provides a generous physical guiding space for automated loading by the robotic arm but also effectively accommodates the local thermal expansion deformation of the graphite base disk 4 under extreme temperature changes, preventing interference and chipping at the edges.

[0071] In the above embodiments, such as Figure 3-8 As shown, each of the two side plates 1 has a handle hole 1-1 that penetrates the two side walls; the two ends of the supporting beam 2 are integrally formed with a reinforcing assembly part 2-4 and an external threaded part 2-5 extending outward from the reinforcing assembly part 2-4. The reinforcing assembly parts 2-4 at both ends are embedded in the two side plates 1 respectively, and the external threaded parts 2-5 at both ends pass through the two side plates 1 respectively and are locked and fixed by graphite nuts 3.

[0072] In this embodiment, the handle hole 1-1 facilitates loading, unloading, and handling, and also serves as an axial passage for lateral airflow in the furnace cavity. The non-cylindrical reinforcing assembly 2-4 is embedded in the side plate 1, effectively limiting the circumferential rotation of the crossbeam under gravity or airflow impact. The entire graphite fixture and graphite nut 3 are made of graphite, ensuring that each component has a consistent coefficient of thermal expansion during heating and cooling, eliminating the risk of high-temperature thermal stress mismatch, and firmly resisting mechanical vibration caused by high-frequency alternating pressure differences. When changing base plates of different specifications, only the graphite nut 3 needs to be unscrewed to replace the corresponding slotted support crossbeam 2, realizing low-cost modular reuse of the graphite fixture on the production line.

[0073] The technical solutions of the present invention will be described and illustrated in detail below through specific embodiments.

[0074] In the following embodiments, in conjunction with Figures 1 to 12The structure and process shown provide a detailed verification of the process control strategy and fixture flow guiding mechanism of the present invention.

[0075] Example 1 This embodiment provides a dry cleaning method for graphite-based disks used in silicon-based nitride epitaxy and a bottom-guided graphite fixture. In this embodiment, taking the cleaning of polycrystalline deposits of conventional thickness as an example, the experimental subject is a 506mm diameter circular graphite-based disk with an edge thickness step difference, as referenced... Figure 12 In example (a), the dimensions are 14×4 inches (i.e., with 14 grooves for supporting 4-inch wafers), the groove depth is 1 mm, the base thickness is 15 mm, and the surface is coated with a dense SiC coating. This embodiment uses a preferred set of process parameters to verify its cleaning effect.

[0076] Specifically, in combination Figure 1 and Figure 2 As shown, in step S1, the bottom-guided graphite fixture containing the graphite substrate disk 4 to be cleaned is pushed into the sealed furnace cavity. The dry cleaning method provided in this embodiment is implemented through the following consecutive stages: In the initial replacement stage of S2, the furnace cavity is first evacuated to a deep vacuum, and then the furnace temperature is gradually increased to the target value of 300°C in the first temperature range at a heating rate of 3.0°C / min. During this heating period, pure N2 preheated to approximately 200°C is introduced into the furnace cavity as an inert gas, and an alternating pressure purging operation is initiated. The duration of the charging step is controlled to be 5 seconds, the pressure holding step to be 10 seconds, and the evacuation step to be 70 seconds, so that the absolute pressure in the furnace cavity forms an alternating trapezoidal fluctuation between a preset upper limit of 4.0 Torr and a lower limit of 0.2 Torr. This low-frequency charging and evacuation cycle, pressure holding and permeation, and low-pressure environment increase the mean free path of molecules, promoting the desorption and discharge of water vapor and volatile organic compounds adsorbed on the surface and micropores of the graphite substrate 4.

[0077] In the S3 intermediate-temperature reconstruction stage, a stepped heating method was adopted. First, the furnace cavity temperature was raised to 500℃ at a heating rate of 8.0℃ / min and held at this temperature for 20 minutes, forming the first thermal buffer node. Subsequently, the temperature was raised to the target value of 700℃ in the second temperature range at the same rate and held for 20 minutes. During this period, a preheated mixed gas (N2 to H2 volume flow ratio controlled at 7:1) was introduced into the furnace cavity, and the frequency of alternating pressure purging was increased: the duration of the gas filling step was shortened to 3.5 seconds, the duration of the pressure holding step was set to 6 seconds, and the duration of the evacuation step was shortened to 50 seconds, maintaining an alternating absolute pressure fluctuation between an upper limit of 4.0 Torr and a lower limit of 0.2 Torr. The "breathing effect" generated by the alternating pressure difference induced microcracks in the dense polycrystalline composite on the surface of the large-size substrate.

[0078] Next, the process enters the S4 high-temperature cleaning stage, continuing the stepped heating. First, the furnace temperature is raised to 1000℃ at a rate of 8.0℃ / min and held at this temperature for 30 minutes, forming the second thermal buffer node and ensuring sufficient thermal equilibrium for the large-span plate. Then, the temperature is raised to the target value of 1250℃ in the third temperature range and held at this target temperature for 400 minutes. During this period, fully preheated (approximately 1000℃) mixed gas is introduced into the furnace cavity, maintaining an absolute pressure of 4.0 Torr (upper limit) and 0.2 Torr (lower limit), and further increasing the alternating frequency: controlling the duration of the gas filling step to 2 seconds, the pressure holding step to 3 seconds, and the evacuation step to 30 seconds. The pulsating alternating air pressure causes the mixed gas to enter the air guide hole 2-2 at the bottom of the limiting groove 2-1; combined with the air guide channel 2-3 opened on the top surface of the supporting beam 2, the airflow is laterally split during the rising process, flows upward along the fluid gap on both sides of the base plate, penetrates the bottom of the fixture and seeps into the micro-pits of the graphite base plate, reducing AlN, GaN and other deposits into gaseous by-products.

[0079] Specifically, while maintaining a constant temperature of 1250℃ for 300 minutes, a high-temperature vacuum desorption step was performed: alternating pressure purging was paused, the supply of N2 and H2 gases was cut off, and full-speed evacuation was maintained to reduce the absolute pressure in the furnace chamber to ≤1×10⁻⁶. -2 The process involves applying a deep vacuum to the Torr coating and maintaining it at a constant temperature for 30 minutes. This step utilizes negative pressure to break down the mass transfer resistance within the micropores of the SiC coating, forcing the deep, dense residues to desorb and leave the field.

[0080] Furthermore, in the S5 gradient cooling stage, a stepped cooling process is performed after cleaning: first, the furnace temperature is lowered to 1000℃ at a cooling rate of 8.0℃ / min and held at that temperature for 30 minutes; then, it is lowered to 850℃ at the same rate and held at that temperature for 30 minutes, forming two thermal buffer nodes in the cooling process; finally, it is lowered to the target value of 750℃ in the fourth temperature range and held for 15 minutes. During this period, the H2 supply is cut off, and only pure N2 preheated to about 600℃ is introduced, while the frequency of alternating gas pressure purging is reduced. Continuous pulses of pure inert gas carry away the residual gaseous byproducts in the furnace cavity, inhibiting their supersaturation and secondary sublimation adsorption on the disk surface.

[0081] Finally, during the S6 cooling termination phase, the furnace cavity temperature is reduced to 500℃ at a rate of 10℃ / min. Then, the gas supply is stopped and the furnace is evacuated at full speed, causing the absolute pressure inside the furnace cavity to rapidly decrease and be maintained at ≤1×10⁻⁶. -2 Torr operates in a deep vacuum environment. Under this vacuum passivation state, continuous cooling is maintained to isolate oxygen and prevent oxidation and pulverization of the graphite at high temperatures. Once the furnace temperature drops below the safe threshold of 400°C, room temperature N2 is slowly introduced to break the vacuum to atmospheric pressure, and finally, the furnace is cooled to room temperature before being opened and the graphite removed.

[0082] The implementation of the above-mentioned dynamic flow field process relies on the bottom-guided graphite fixture provided by this invention. Combined with... Figure 3 , Figure 5-6 and Figure 9 As shown, its load-bearing and assembly structure is described below: To provide a stable load-bearing frame and resist mechanical vibrations from alternating air pressure, the entire bottom-guided graphite fixture is made of isotropic high-purity graphite. The overall weight of the graphite fixture is much greater than the maximum alternating air pressure of the pulsed airflow. During modular assembly, the reinforced mounting parts 2-4 at both ends of the support beam 2 engage with the corresponding mounting holes on the two side plates 1, providing anti-rotation support to limit mechanical vibrations of the fixture under alternating pressure differences from the pulsed airflow. The external threaded parts 2-5 at both ends protrude from the two side plates 1 and are locked in place by corresponding graphite nuts 3. The all-graphite locking system eliminates the risk of thermal stress mismatch under extreme temperature differences and allows for the disassembly and replacement of support beams 2 of different specifications as needed.

[0083] Multiple (several groups) of limiting grooves 2-1 are spaced apart along the axial direction on the supporting crossbeam 2. For example... Figure 9 As shown, for the graphite base disk 4 with stepped difference in this embodiment, the graphite fixture preferably adopts a limiting groove 2-1 with a stepped internal cross section. During loading, the graphite fixture is positioned through the handle holes 1-1 on the two side plates 1. The diameter of the handle holes 1-1 penetrates through the side plates 1 and also serves as a fluid channel for axial airflow in the furnace cavity, eliminating the "airflow dead zone" when the traditional fixture is fully loaded with high density.

[0084] The limiting groove 2-1 has outwardly expanding chamfered edges on both sides of the groove opening, providing physical guidance for the descent of the graphite base disk 4, allowing its edge steps to smoothly settle on the stepped bearing surface. Once the base disk 4 is in place, because the groove width is greater than the base disk thickness, a fluid gap is reserved between the front and back sides of the base disk and the groove wall. This fluid gap, together with the aforementioned air guide hole 2-2 and air guide channel 2-3, constitutes a three-dimensional exhaust network, providing an unobstructed fluid channel for the penetrating and scouring of the "breathing effect" airflow during the core high-temperature cleaning stage.

[0085] Example 2 This embodiment provides a dry cleaning method for graphite-based disks grown using silicon-based nitride epitaxy and a bottom-guided fixture. This embodiment primarily targets graphite-based disks 4 that have undergone epitaxial growth in a relatively short time and have a thin layer of polycrystalline composite material adhering to their surface. By adjusting the temperature and pressure parameters and gas ratio within the process window, heat consumption is reduced and the process cycle is shortened.

[0086] Specifically, in step S1, the bottom-guided graphite fixture containing the graphite substrate disk 4 to be cleaned is pushed into the sealed furnace cavity, and then the following process stages are executed sequentially: During the initial replacement phase of S2, the furnace temperature is raised to the target value of 250°C in the first temperature range at a heating rate of 5.0°C / min. During this period, preheated (approximately heated to 150°C) pure N2 is introduced into the furnace, and alternating pressure purging is initiated. The duration of the charging step is controlled to be 6 seconds, the pressure holding step to be 8 seconds, and the evacuation step to be 60 seconds, so that the absolute pressure forms an alternating trapezoidal fluctuation between the preset upper limit of 3.0 Torr and the lower limit of 0.2 Torr.

[0087] In the S3 intermediate-temperature reconstruction stage, a stepped heating method was adopted: the furnace temperature was increased to 450℃ at a heating rate of 10.0℃ / min, and held at this temperature for 15 minutes to form the first thermal buffer node; then, the temperature was increased to the target value of 650℃ in the second temperature range at the same rate. During this heating, a preheated (approximately 600℃) H2 and N2 mixture with a volumetric flow rate ratio of 8:1 was introduced, and the frequency of alternating gas pressure purging was adjusted: the duration of the gas filling step was controlled to be 4 seconds, the duration of the pressure holding step to be 5 seconds, and the duration of the gas extraction step to be 45 seconds. The physical shear force generated by the trapezoidal pressure difference fluctuation was used to disrupt the thinner surface deposit structure.

[0088] Further, the process proceeds to the S4 high-temperature cleaning stage. To address the etching requirements of thinner deposits, this embodiment balances aging time and thermal uniformity, continuing with a stepped heating method: the furnace temperature is increased to 950°C at a heating rate of 6.0°C / min, and held at this temperature for 20 minutes to form the second thermal buffer node; subsequently, the temperature is increased to the target value of 1250°C in the third temperature range, and the isothermal cleaning time at this target temperature is set to 350 minutes.

[0089] During this period, the alternating frequency is further increased: the inflation step lasts for 3 seconds, the pressure holding step lasts for 4 seconds, and the evacuation step lasts for 35 seconds, continuously performing trapezoidal alternating gas pressure purging with an upper limit of 3.0 Torr and a lower limit of 0.2 Torr. The alternating pressure difference drives the reducing gas through the air guide channel 2-3 opened on the supporting beam 2, the air guide hole 2-2 at the bottom of the limiting groove 2-1, and the fluid gap reserved between the base plate and the tank wall, forming a cross flow field, reducing the attached substances into gaseous by-products and discharging them.

[0090] Specifically, during the aforementioned constant temperature maintenance at 1250℃, a high-temperature vacuum desorption step is interspersed: alternating pressure purging is suspended, all process gas supplies are cut off, and full-speed evacuation is maintained to reduce the absolute pressure in the furnace cavity to ≤8×10⁻⁶. -3 The material is subjected to a deep vacuum under Torr conditions and held at a constant temperature for 15 minutes. Because the deposit in this embodiment is relatively thin, 15 minutes of deep vacuum desorption can effectively break the mass transfer resistance of the micropores and promote the desorption and removal of deep residues.

[0091] Subsequently, in the S5 gradient cooling stage, a step-by-step rapid cooling process is performed: the furnace temperature is reduced to 1000℃ at a cooling rate of 10.0℃ / min and held at that temperature for 15 minutes, then reduced to 850℃ at the same rate and held at that temperature for 15 minutes, forming two thermal buffer nodes in the cooling process; finally, the temperature is reduced to the target value of 750℃ in the fourth temperature range. During this process, the H2 supply is cut off, and only preheated (approximately 600℃) pure N2 is introduced, and the frequency of alternating gas pressure purging is reduced, using a pulsed flow of pure inert gas to remove residual reaction byproducts.

[0092] Finally, during the S6 cooling termination phase, once the temperature drops to 500℃, the gas supply is stopped and full-speed extraction is initiated, causing the furnace chamber pressure to decrease and be maintained at ≤8×10⁻⁶. -3 Torr is continuously cooled in a deep vacuum environment. Once the temperature drops to a safe threshold of no more than 400°C, room temperature N2 is slowly introduced to break the vacuum to atmospheric pressure and the temperature is continuously reduced until it reaches room temperature before the furnace is opened and the parts are removed.

[0093] Regarding the physical load-bearing structure, this embodiment uses a graphite jig (see...). Figure 3 (5-6 and 9) By designing the overall weight of the graphite fixture to be much greater than the maximum alternating gas pressure of the pulsed airflow, and by reinforcing the locking fit between the assembly part 2-4 and the graphite nut 3 to construct an anti-rotation frame, the mechanical vibration of the fixture under the alternating pressure difference of the pulsed airflow is limited. The stepped limiting groove 2-1 with an outwardly expanding chamfered structure provides physical guidance for the graphite base plate 4. Together with the fluid gap on the surface of the base plate and the handle hole 1-1 on the side plate 1, it provides an unobstructed three-dimensional physical fluid channel in both the horizontal and vertical directions for the alternating gas pressure purging process.

[0094] Example 3 This embodiment provides a dry cleaning method for graphite-based disks used in silicon-based nitride epitaxy and a bottom-guided fixture. This embodiment mainly targets flat-bottomed circular graphite-based disks with uniform edge thickness (see reference). Figure 12 (b) and Figure 10 By modularly replacing support components, the paper elucidates the load-bearing mechanism and flow field coordination of the fixture structure on a conventional flat-bottomed base.

[0095] Specifically, in step S1, the bottom-guided graphite fixture containing the graphite substrate disk 4 to be cleaned is pushed into the sealed furnace cavity. Regarding overall process control, the core process parameters in stages S2 to S6 of this embodiment (including target values ​​for each temperature range, stepped thermal buffer nodes, process gas preheating temperature, differential pressure window of the trapezoidal alternating gas pressure, and charging, holding, and evacuation times, volumetric flow rate ratio, and high-temperature vacuum desorption steps, etc.) all follow the settings of Embodiment 1.

[0096] During the S4 high-temperature cleaning stage, the preheated reducing mixed gas, driven by a trapezoidal alternating pressure difference, enters the gas guide hole 2-2 at the bottom of the limiting groove 2-1. After converging through the gas guide channel 2-3, it flows upward along the fluid gap reserved between the substrate surface and the inner wall of the tank. This specific "breathing effect" airflow, combined with sufficient holding time, fully covers the front and back surfaces of the flat-bottomed substrate and the bottom right-angle edge, fully participating in the reduction etching reaction. Simultaneously, in conjunction with the interspersed high-temperature vacuum desorption steps, the microscopic pore resistance is broken, and the generated gaseous byproducts are completely removed from the tank. Finally, in the S6 termination cooling stage, full-speed evacuation is activated to maintain the furnace cavity at ≤1×10 -2 Torr is passivated and cooled in a deep vacuum environment to prevent graphite from oxidizing and pulverizing at high temperatures.

[0097] Regarding the physical load-bearing structure, considering the shape characteristics of the flat-bottomed, disc-shaped graphite base disk, this embodiment replaces the fixture modularly with a support beam 2 featuring a straight-walled U-shaped limiting groove 2-1 by unscrewing the graphite nut 3 on the side plate 1 (in conjunction with...). Figure 4 , Figure 7-8 and Figure 10 (As shown). The anti-rotation assembly mechanism also relies on the cooperation between the reinforcing assembly part 2-4 and the external thread part 2-5 at the end of the supporting beam 2.

[0098] like Figure 10 As shown in the cross-sectional details, the internal cross-section of the limiting groove 2-1 in this embodiment is a straight-walled U-shaped groove structure without steps. The width of the straight-walled U-shaped limiting groove 2-1 remains consistent throughout and is greater than the thickness of the graphite base plate 4. After the graphite base plate 4 is vertically inserted into place, its bottom right-angled edge is stably supported on the bottom surface of the straight-walled U-shaped limiting groove 2-1. Since the groove width is greater than the thickness of the base plate edge, a physical fluid gap is generously reserved between the two sides of the base plate and the inner wall of the U-shaped groove. This physical gap is connected to the bottom air guide hole 2-2 (the air-permeable section is retained after the base plate is seated), the through air guide channel 2-3, and the handle hole 1-1 on the side plate, providing an unobstructed physical fluid channel for the airflow driven by the trapezoidal alternating pressure difference to forcefully penetrate the straight-walled U-shaped limiting groove 2-1. At the same time, the two sides of the groove opening of the straight-walled U-shaped limiting groove 2-1 retain an outwardly expanding chamfered structure, providing physical guidance and preventing collisions for automated loading and unloading of the base plate.

[0099] Example 4 This embodiment provides a dry cleaning method for graphite-based disks with silicon-based nitride epitaxy and a bottom-guided fixture. This embodiment mainly targets skirted graphite-based disks with downwardly extending skirts at the edges (see reference). Figure 12 (c) and Figure 11 By modularly replacing support components, the load-bearing mechanism and flow field coordination of the straight-walled U-shaped limiting groove 2-1 structure of the fixture on the skirted base plate are explained.

[0100] Specifically, in step S1, the bottom-guided fixture containing the graphite substrate disk 4 to be cleaned is pushed into the sealed furnace cavity. Regarding overall process control, the parameters for stages S2 to S6 in this embodiment are basically the same as those in embodiment 1. However, in the high-temperature cleaning stage S4, considering the deep physical dead zones on the inner side of the skirt, the constant-temperature cleaning time in the third temperature range (1250℃) is extended to 450 minutes.

[0101] In the trapezoidal alternating gas pressure purging process, the preheated reducing mixed gas is forced into the gas guide hole 2-2 at the bottom of the limiting groove 2-1 under the combined action of transient high pressure and pressure holding steps. After converging through the gas guide channel 2-3, it flows from bottom to top along the fluid gap reserved between the base plate skirt and the inner wall of the tank, deeply penetrating into the recessed area inside the skirt to participate in the reduction reaction. Combined with the high-temperature vacuum desorption step, it breaks the mass transfer bottleneck and forcefully carries the gaseous by-products out of the tank. In the S6 termination cooling stage, the gas supply is stopped and full-speed extraction is started to maintain the furnace cavity at ≤1×10 -2 Torr was cooled to room temperature in a deep vacuum environment.

[0102] Regarding the physical load-bearing structure, considering the shape characteristics of the skirted graphite base disk, this embodiment replaces the fixture with a support beam 2 featuring a straight-walled U-shaped limiting groove 2-1 by unscrewing the graphite nut 3. The anti-rotation assembly mechanism is also achieved by utilizing the cooperation between the reinforcing assembly part 2-4 at the end of the support beam 2 and the external thread part 2-5.

[0103] like Figure 11 As shown in the cross-sectional details, in this embodiment, the limiting groove 2-1 on the supporting beam 2 is a straight-walled U-shaped groove structure without steps. The groove width of the straight-walled U-shaped limiting groove 2-1 remains consistent throughout and is greater than the maximum thickness of the downward-extending skirt of the graphite base disk 4. After the graphite base disk 4 is vertically inserted into place, its downward-extending skirt rests smoothly on the bottom surface of the straight-walled U-shaped limiting groove 2-1. Because the internal width of the straight-walled U-shaped limiting groove 2-1 is greater than the skirt thickness, the fragile downward-extending skirt body is generously contained within the groove, completely avoiding lateral rigid compression or thermal jamming with the inner walls on both sides due to limited thermal expansion at high temperatures.

[0104] Meanwhile, fluid gaps are reserved between the inner and outer surfaces of the skirt and the inner wall of the straight-walled U-shaped limiting groove 2-1. Combined with the bottom air guide hole 2-2 (since the width of the air guide hole 2-2 is smaller than the groove width, sufficient air permeability is still maintained after the base plate is seated), the through air guide channel 2-3, and the handle hole 1-1 on the side plate, a three-dimensional physical channel is formed for airflow to penetrate laterally and enter vertically into the recessed areas on both sides of the skirt. Furthermore, the two edges of the groove opening of the straight-walled U-shaped limiting groove 2-1 retain an outwardly expanding chamfered structure, providing physical guidance for placing and removing the base plate.

[0105] Example 5 This embodiment provides a dry cleaning method for medium to large-sized graphite-based disks produced by silicon-based nitride epitaxy, along with a bottom-guided fixture. This embodiment primarily targets skirted graphite-based disks with a disk diameter of 400mm (see reference). Figure 12 (c) and Figure 11 These base plates have a downward-extending skirt, the inside of which can easily cause airflow obstruction and fluid stagnation.

[0106] Specifically, in step S1, the bottom-guided fixture containing the graphite substrate disk 4 to be cleaned is pushed into the sealed furnace cavity. Regarding the overall process control parameters, this embodiment basically follows the temperature rise and fall curves, stepped thermal buffer nodes, process gas preheating mechanism, and deep vacuum passivation cooling settings of embodiment 1 in stage S6.

[0107] During the S4 high-temperature cleaning stage, considering the physical dead zones of the recessed structure on the inner side of the skirt, the total isothermal etching time at 1250℃ was extended to 430 minutes. In the trapezoidal alternating gas pressure purging process, the preheated mixed gas, under the synergistic effect of transient high pressure and sufficient pressure holding steps, flows forcefully from bottom to top along the fluid gaps on the substrate surface through the gas guide hole 2-2 and gas guide channel 2-3 at the bottom of the limiting groove 2-1, deeply penetrating into the recessed area on the inner side of the skirt to participate in the reduction reaction.

[0108] Specifically, in order to overcome the mass transfer resistance of deep micropores, during the aforementioned 430-minute isothermal holding period, a 20-minute high-temperature vacuum desorption step was interspersed at the 150-minute and 300-minute marks of the etching process: that is, alternating pressure purging was suspended, the supply of N2 and H2 gases was cut off, and full-speed evacuation was maintained to reduce the absolute pressure of the furnace chamber to ≤1×10⁻⁶. -2 After maintaining the deep vacuum state of the Torr for 20 minutes, the mixed gas is introduced and the alternating gas pressure is purged.

[0109] In terms of the physical load-bearing structure, the graphite fixture in this embodiment adopts a supporting beam 2 with a straight-walled U-shaped limiting groove 2-1. For example... Figure 11 As shown, the internal cross-section of the limiting groove 2-1 is a straight-walled U-shaped groove structure with a uniform width throughout. After loading, the downward-extending skirt of the graphite base disk 4 is stably supported at the bottom of the groove. Because the width of the straight-walled U-shaped limiting groove 2-1 is greater than the thickness of the skirt, the fragile skirt body is generously contained within the limiting groove 2-1, effectively preventing lateral rigid compression or thermal jamming with the inner walls on both sides due to thermal expansion at high temperatures. At the same time, the physical fluid gaps reserved between the two sides of the skirt and the groove wall, together with the handle holes 1-1 on the two side plates 1, constitute a three-dimensional physical fluid channel for airflow to penetrate laterally and enter vertically into the recessed areas on both sides of the skirt.

[0110] Example 6 This embodiment provides a dry cleaning method for medium to large-sized graphite-based disks produced by silicon-based nitride epitaxy, along with a bottom-guided fixture. This embodiment primarily targets circular graphite-based disks with a diameter of 785 mm and uniform edge thickness (see reference). Figure 12 (b) and Figure 10 The base plate of this specification has a very large radial span, which leads to a significant increase in the fluid diffusion path and radial heat transfer hysteresis effect in the central region.

[0111] Specifically, regarding process control in S2-S6, this embodiment specifically adjusted the trapezoidal alternating gas pressure parameters during the high-temperature cleaning stage (S4) to address the radial diffusion resistance of the large-size disk: the upper limit of the absolute pressure was set to 6.0 Torr, and the lower limit was set to 0.1 Torr. Simultaneously, the duration of the inflation step was controlled to 3 seconds, the pressure holding step duration was extended to 8 seconds, and the evacuation step duration was 60 seconds. Furthermore, the volumetric flow ratio of preheated N2 to H2 was adjusted to a 5:1 mixture, and the total isothermal time at 1250°C was set to 500 minutes.

[0112] Under the combined effect of this high-amplitude pressure difference fluctuation and long-term pressure holding (8 seconds), the high-energy mixed gas can overcome the huge radial resistance, flow laterally and fully cover the central area of ​​the 785mm base plate; the long 500-minute isothermal cycle provides ample thermal equilibrium time for the large-span plate surface, effectively reducing the radial temperature difference.

[0113] Specifically, within the aforementioned 500-minute isothermal cleaning cycle, three high-temperature vacuum desorption steps, each lasting 15 minutes, were interspersed at the 120th, 240th, and 360th minutes of etching. During each step, alternating purging was paused and the mixed gas was cut off, utilizing ≤1×10 -2 The deep vacuum of Torr disrupts the mass transfer balance of byproducts generated within the central micropore, promoting their complete desorption and discharge. The isothermal thermal buffer nodes and gas filling / evacuation parameters for the remaining stages S2, S3, and S5, as well as the deep vacuum passivation parameters for stage S6, are basically the same as those in Example 1.

[0114] In terms of the physical load-bearing structure, this embodiment selects a support beam 2 with a straight-walled U-shaped limiting groove 2-1 (refer to...). Figure 4 , Figure 7-8 and Figure 10 After the circular graphite base disk is inserted into the limiting groove 2-1, it is physically supported by the bottom surface of the straight-walled U-shaped limiting groove 2-1. In the above-mentioned alternating gas pressure purging process, the gas guide hole 2-2 and the fluid gap reserved between the base disk and the groove wall serve as gas flow channels, guiding the reactive gas into the bottom of the base disk, participating in the full-disk surface etching, and extracting the generated gaseous byproducts from the furnace cavity.

[0115] Comparative Example 1 To verify the actual technical effect of the dry cleaning method for medium and large-sized graphite-based disks and the bottom-guided fixture for silicon-based nitride epitaxy provided by this invention, a set of epitaxial growth comparison samples were set up for photoluminescence (PL) characterization tests.

[0116] Experimental subjects: selected as follows Figure 12 The disc-shaped graphite substrate shown in (a) has a diameter of 506 mm and a size of 14 × 4 inches (i.e., the surface of the substrate has 14 grooves evenly distributed to support 4-inch wafers). The groove depth is 1 mm, the total thickness of the substrate is 15 mm, and the surface is covered with a dense SiC coating.

[0117] Example 1 (Cleaning Group): The graphite substrate disks of the above specifications were cleaned using the dry cleaning process and bottom-guided fixture of Example 1 of the present invention, and then loaded into an MOCVD machine for silicon-based nitride epitaxial growth. The target wavelength for this batch of epitaxial growth was set to 561nm.

[0118] Comparative group (uncleaned group): The same type of graphite substrate disk with dense polycrystalline byproducts accumulated after long-term service and without cleaning was directly used for growth under the same epitaxial parameters and target wavelength setting of 561nm.

[0119] The statistical data of PL wavelengths of the epitaxial wafers in the two groups (Example 1 group and Comparative Example 1 group) are shown in Table 1 below. Table 1: Statistical Table of PL Wavelengths of Epitaxial Wafers in Example 1 Group and Comparative Example 1

[0120] The statistical data in Table 1 above reflects the difference in the epitaxial process compliance rates between the two groups of substrates. For the target epitaxial wavelength of 561 nm, the uncleaned comparative group exhibited a blue shift in the average wavelength and higher range and standard deviation, indicating a mismatch in the large radial temperature difference across the substrate surface. In contrast, the graphite substrate cleaned using the process of Example 1 of this invention showed an average wavelength of 560.51 nm for the epitaxial wafer, meeting the target value of 561 nm, and the range (2.96 nm) and standard deviation (0.40 nm) converged compared to the comparative group. This data confirms the effectiveness of the cleaning method and fixture for medium-to-large-sized graphite substrates of this invention in eliminating residual impurities and restoring the thermal properties of the substrate.

[0121] Figure 13 The mapping spectrum of the dominant wavelength distribution of the epitaxial wafer is shown. For example... Figure 13As shown in Figure (b), the wafers grown in the comparative group (uncleaned substrate) exhibit significant color gradations and distribution differences on the substrate surface (manifested as local wavelength abrupt changes and irregular color patches). This morphology reflects that residual polycrystalline deposits on the substrate surface and within the grooves caused localized thermal resistance anomalies, which in turn led to temperature field mismatch during epitaxial growth, resulting in a noticeable temperature difference between the center and edge on medium to large-sized substrates. In contrast, as shown in Figure (b), the wafers grown in the comparative group (uncleaned substrate) show significant color gradations and distribution differences on the substrate surface (manifested as localized wavelength abrupt changes and irregular color patches). Figure 13 As shown in (a), the wafer mapping patterns of the substrate grown in Example 1 (after cleaning) exhibit significant convergence characteristics in wavelength data. It should be noted that, although... Figure 13 In (a), a certain color transition from center to edge is still visually apparent, but this is essentially a magnified representation of minute wavelength fluctuations due to the testing software's extremely narrow color gradation dynamic range (approximately 3nm span). Compared to the comparative group... Figure 13 Compared to the severe macroscopic distortion exhibited in (b), the wavelength distribution across the entire disk surface in Example 1 group has eliminated the enormous "bullseye" drift. This characterization result objectively demonstrates that the cleaned graphite substrate effectively removed the residues that caused abnormal local thermal resistance, substantially restored the heat transfer consistency of the graphite substrate, and significantly improved the severe flow field and temperature field mismatch problem in medium and large-sized disk surfaces.

[0122] Figure 14 Scatter plot and Figure 15 ( Figure 15 The box plots in (a) and (b) further reflect the statistical characteristics of the entire data set and the degree of deviation from the target wavelength (561 nm). Combined with the figures, it can be seen that the data in the comparative group exhibits a large discrete distribution, and the average wavelength (553.71 nm) deviates from the set value.

[0123] Under this reference standard, the data points of Example 1 group ( Figure 14 The distribution is concentrated, representing the main data distribution in the bins ( Figure 15 The reduced interquartile spacing in (a) and (b) indicates that the temperature difference over the long radial span of the medium-to-large-sized disk surface has been effectively controlled; at the same time, the average wavelength has not undergone significant drift. The results of small wavelength drift and high data convergence objectively confirm that the dry cleaning technology of this invention removes parasitic deposits on the surface of the graphite-based disk and restores the uniform thermal conductivity of the graphite-based disk.

[0124] The comparative data above shows that using an uncleaned graphite substrate results in a wavelength range as high as 15.74 nm, with a standard deviation of 2.55 nm. In contrast, using the graphite substrate cleaned according to Example 1 of this invention controls the wavelength range to 2.96 nm and reduces the standard deviation to 0.40 nm. The morphological characterization and statistical data above confirm that the dry cleaning method and bottom-guided fixture for medium-to-large-sized graphite substrates used in silicon-based nitride epitaxy provided by this invention can effectively remove residual deposits from the surface and tank area of ​​medium-to-large-sized substrates, restoring the performance of graphite substrates that have failed due to contamination and meeting the production requirements of epitaxial processes.

[0125] In summary, the dry cleaning method for large-sized graphite substrate disks in silicon-based nitride epitaxy and the bottom-guided graphite fixture disclosed in this invention overcome the bottlenecks of existing technologies from multiple dimensions, including heat transfer, mass transfer, thermal stress control, micropore cleaning, and irregular edge adaptation. This is achieved through the synergistic coupling of multi-temperature zone stepped thermal buffer management, full-process alternating gas pressure purging, high-temperature vacuum deep desorption, and bottom-guided graphite fixture. The method completely solves the industrial problems in silicon-based nitride epitaxy processes, such as uneven cleaning of large-sized graphite substrate disks, central residue, edge dead corners, thermal stress warping, SiC coating damage, poor compatibility of traditional fixtures, and high material costs. This invention controls the maximum process temperature below 1250℃, and with the help of a multi-node constant temperature thermal buffer and process gas preheating mechanism, achieves mild thermal cycling at non-extreme high temperatures, effectively eliminating thermal stress caused by radial temperature differences on large disk surfaces and avoiding substrate deformation and coating peeling. Relying on the "breathing effect" formed by alternating gas pressure purging, it forcibly breaks through the macroscopic airflow mass resistance of medium and large-sized substrates. With the help of the three-dimensional air guiding network of the bottom guide fixture, it achieves uniform etching of the entire disk surface and complex edges (step differences, skirts), fundamentally eliminating the cleaning mismatch problem of "over-cleaning at the edges and residue in the center". Through the high-temperature vacuum desorption step, it breaks the microscopic mass transfer resistance in the micropores of the SiC coating, and completely desorbs and removes the deep dense Si / Al / Ga polycrystalline composite, achieving residue-free deep cleaning. At the same time, it adopts a fully graphite modular detachable fixture with adaptive limiting grooves, inclined bearing, air guiding holes and air guiding channel structure, which is compatible with various irregularly shaped substrates such as discs and skirts, to achieve non-destructive loading, airflow without dead angles, and low-cost modular reuse.

[0126] Furthermore, experimental verification shows that the graphite substrates cleaned using this invention can effectively restore a uniform thermal field and surface cleanliness, reducing the wavelength range of epitaxial wafers from 15.74 nm to 2.96 nm and the standard deviation from 2.55 nm to 0.40 nm, significantly improving epitaxial wafer yield and substrate reuse life. This invention features a stable process, strong adaptability, and high industrial applicability, fully meeting the needs of silicon-based nitride epitaxial production lines for efficient, non-destructive, and large-scale cleaning of medium-to-large-sized graphite substrates, demonstrating outstanding technical value and broad prospects for industrial application.

[0127] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to the process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0128] The above descriptions are merely embodiments of this application, which enable those skilled in the art to understand and implement this application. Various modifications to the embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments described herein, but is to be accorded the widest scope consistent with the principles and features disclosed herein.

Claims

1. A dry cleaning method for medium-to-large-sized graphite-based disks with silicon-based nitride epitaxy, characterized in that, Includes the following steps: Preparation stage: Vertically load multiple graphite substrates onto a bottom-guided graphite fixture, and place the bottom-guided graphite fixture inside the furnace cavity; Initial replacement stage: Under vacuum conditions, the furnace temperature is raised to the first temperature range, and at the same time, an inert gas, which is the process gas, is introduced into the furnace to perform alternating pressure purging. Intermediate temperature reconstruction stage: The furnace temperature is raised from the first temperature range to the second temperature range, and a reactive gas as a process gas is introduced during this period, and the alternating pressure purging is performed; High-temperature cleaning stage: The furnace temperature is raised from the second temperature range to and maintained in the third temperature range. During this period, the reactive gas and the inert gas are mixed and introduced, and the alternating gas pressure purging is performed. At least one high-temperature vacuum desorption step is performed during this period. Gradient cooling stage: The furnace temperature is gradually reduced from the third temperature range to the fourth temperature range. During this period, the supply of the reactive gas is cut off, and only the inert gas is introduced, and the alternating gas pressure purging is performed. Termination of cooling phase: The furnace temperature is reduced from the fourth temperature range to the fifth temperature range. Then, all process gas supplies are stopped and the furnace is continuously evacuated to maintain a deep vacuum environment. After the furnace temperature continues to drop to the safe threshold temperature, inert gas is introduced to break the vacuum and the furnace is cooled to room temperature.

2. The dry cleaning method for medium-to-large-sized graphite-based disks of silicon-based nitride epitaxy according to claim 1, characterized in that, The alternating pressure purging includes sequentially and cyclically performing the following steps: Inflation step: Introduce the appropriate process gas and increase the furnace pressure to the preset absolute pressure limit; Pressure holding step: Keep the furnace cavity exhaust valve closed and maintain the furnace cavity pressure at the upper limit of the absolute pressure, and set the duration of the pressure holding step to 3-10 seconds; Evacuation procedure: Evacuate the air to reduce the furnace chamber pressure to the preset lower absolute pressure limit.

3. The dry cleaning method for medium-to-large-sized graphite-based disks of silicon-based nitride epitaxy according to claim 2, characterized in that, In each process stage of the alternating gas pressure purging, the upper limit of the absolute pressure in the furnace cavity is set to 2.0 Torr-10.0 Torr, and the lower limit of the absolute pressure is set to 0.01 Torr-0.5 Torr. In the entire process, the duration of the gas charging step is set to 2 seconds-6 seconds, and the duration of the gas extraction step is set to 30 seconds-80 seconds. The alternating gas pressure purging frequency is changed by adjusting the duration of the gas charging step and the gas extraction step.

4. The dry cleaning method for medium-to-large-sized graphite-based disks of silicon-based nitride epitaxy according to claim 1, characterized in that, In the initial replacement stage, the furnace temperature is increased at a rate of 1.0℃ / min to 6.0℃ / min; in the intermediate temperature reconstruction stage, the furnace temperature is increased at a rate of 4℃ / min to 12℃ / min; in the high-temperature cleaning stage, the furnace temperature is increased at a rate of 4℃ / min to 12℃ / min; and in the gradient cooling stage, the furnace temperature is cooled at a rate of 6℃ / min to 12℃ / min.

5. The dry cleaning method for medium-to-large-sized graphite-based disks of silicon-based nitride epitaxy according to claim 1, characterized in that, The high temperature vacuum desorption step comprises: during the isothermal holding in the third temperature interval, suspending the alternating gas pressure purge, cutting off the supply of the inert gas and the reactive gas, and keeping the full speed pumping, so that the absolute pressure of the furnace chamber is reduced to ≤ 1 × 10 -2 Torr, and isothermally held in this state for 15-40 minutes, and the isothermal holding time of the desorption step is counted into the total isothermal time of the third temperature interval.

6. The dry cleaning method for medium-to-large-sized graphite-based disks of silicon-based nitride epitaxy according to claim 1, characterized in that, The first temperature range is 150℃-350℃; the second temperature range is 500℃-800℃; the third temperature range is 1000℃-1250℃; the fourth temperature range is 600℃-900℃; the fifth temperature range is 400℃-550℃; and the safety threshold temperature is not higher than 400℃.

7. The dry cleaning method for medium-to-large-sized graphite-based disks of silicon-based nitride epitaxy according to claim 1, characterized in that, The intermediate-temperature reconstruction stage, the high-temperature cleaning stage, and the gradient cooling stage all have constant-temperature thermal buffer nodes during temperature changes, wherein: The constant temperature thermal buffer node in the intermediate temperature reconstruction stage is set within 450℃-550℃ and kept at a constant temperature for 15 minutes-50 minutes. The constant temperature heat buffer node of the high temperature cleaning stage is set within 950℃-1050℃ and kept at a constant temperature for 20 minutes-60 minutes. The constant temperature thermal buffer node in the gradient cooling stage is first set at 950℃-1050℃ and kept constant for 15-40 minutes, and then set at 800℃-870℃ and kept constant for 15-40 minutes.

8. The dry cleaning method for medium-to-large-sized graphite-based disks of silicon-based nitride epitaxy according to claim 1, characterized in that, The inert gas includes N2 with a purity ≥ 99.999%, and the reactive gas includes H2 with a purity ≥ 99.999%. In the intermediate temperature reconstruction stage and the high temperature cleaning stage, the volumetric flow rate ratio of N2 to H2 is (3-8):

1.

9. The dry cleaning method for medium-to-large-sized graphite-based disks of silicon-based nitride epitaxy according to claim 1, characterized in that, During the high-temperature cleaning phase, the total time spent maintaining the constant temperature in the third temperature range is controlled between 200 and 500 minutes; during the final cooling phase, the absolute pressure of the deep vacuum environment is maintained at ≤1×10⁻⁶. -2 Torr.

10. The dry cleaning method for medium-to-large-sized graphite-based disks of silicon-based nitride epitaxy according to claim 1, characterized in that, The process gas is preheated to 100°C-1000°C when it enters the furnace chamber.

11. The dry cleaning method for medium-to-large-sized graphite-based disks of silicon-based nitride epitaxy according to claim 1, characterized in that, The diameter of the graphite substrate disk is 390mm-790mm.

12. The dry cleaning method for medium-to-large-sized graphite-based disks of silicon-based nitride epitaxy according to claim 11, characterized in that, The graphite substrate includes a disc-type graphite substrate and a skirted graphite substrate.

13. A bottom-guided graphite fixture for performing a dry cleaning method for medium-to-large-sized graphite-based disks for silicon-based nitride epitaxy according to any one of claims 1-12, characterized in that, include: Two side plates, which are arranged opposite to and parallel to each other; Multiple supporting beams are provided, which span across and are detachably fixed between the two side plates. The side bearing surfaces of the supporting beams are set at an inclined angle relative to the horizontal plane and are tangent to or in contact with the circular periphery of the graphite base disk.

14. The bottom-guided graphite fixture according to claim 13, characterized in that, The supporting crossbeam has multiple limiting grooves spaced along its axial direction, and the width of the groove opening is greater than the edge thickness of the graphite substrate to be cleaned. The bottom of the limiting groove has a through-hole that connects the upper and lower surfaces of the supporting crossbeam. Furthermore, the top surface of the supporting crossbeam has an air guide channel along its axial direction, and the air guide channel passes through each of the limiting grooves sequentially along the axial direction of the supporting crossbeam.

15. The bottom-guided graphite fixture according to claim 14, characterized in that, The width of the air guide hole is smaller than the groove width of the limiting groove, and the length direction of the air guide hole is parallel to the axial direction of the supporting crossbeam; the bottom of the air guide channel is higher than the bottom of the limiting groove.

16. The bottom-guided graphite fixture according to claim 14, characterized in that, The limiting groove has outwardly expanding chamfered or arc-shaped surface structures at both sides of its opening; and The internal cross-section of the limiting groove has a stepped structure, including a wider upper groove section and a narrower lower groove section from top to bottom, and a stepped bearing surface at the junction of the upper and lower groove sections; or the internal cross-section of the limiting groove is a straight-walled U-shaped groove structure with a uniform groove width throughout.

17. The bottom-guided graphite fixture according to claim 13, characterized in that, Each of the two side plates has a handle hole that penetrates the two side walls; each end of the supporting beam has an integrally formed reinforcing assembly part and an external threaded part extending outward from the reinforcing assembly part. The reinforcing assembly parts at both ends are respectively embedded in the two side plates, and the external threaded parts at both ends pass through the two side plates and are locked and fixed by graphite nuts.

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