A method of cleaning a silicon carbide substrate

Abstract

The present application relates to the technical field of silicon carbide semiconductor material preparation, and particularly relates to a cleaning method of a silicon carbide substrate, comprising the following steps: (S.1) placing a silicon carbide substrate to be cleaned in a closed cleaning cavity; (S.2) activating the surface of the substrate by plasma; (S.3) introducing an airflow containing amino-modified graphene quantum dots into the cavity, so that the quantum dots capture surface impurities; (S.4) irradiating the surface of the substrate by using a pulsed energy source, so that the quantum dots adsorbed with impurities are desorbed from the surface of the substrate; (S.5) introducing a purge gas to discharge the desorbed quantum dots and impurities out of the cavity. Through the in-situ three-step method of "plasma activation-nano adsorption-pulsed laser desorption", the present application realizes efficient and uniform removal of surface impurities of 8-inch or larger size substrates, and effectively solves the cleaning consistency problem of the edge and the center area.

Description

Technical Field

[0001] This invention relates to the field of silicon carbide semiconductor material preparation technology, and in particular to a method for cleaning silicon carbide substrates. Background Technology

[0002] With the rapid development of third-generation semiconductor technology, silicon carbide (SiC) substrates, due to their excellent wide bandgap characteristics, high thermal conductivity, and high breakdown field strength, have become the core basic material for manufacturing high-power, high-frequency, and high-temperature electronic devices. However, the microscopic cleanliness of the substrate surface directly determines the quality of subsequent epitaxial films and the final performance of the devices. Any trace amount of surface contaminants, including metallic impurities (such as iron and nickel), organic residues, and particles, can become a fatal defect source, leading to a significant decrease in device yield and reliability. Therefore, substrate cleaning, as a key process at the forefront of the industry chain, is of paramount importance to the entire industry in terms of its technical level.

[0003] Driven by the pursuit of higher device performance and lower manufacturing costs, the semiconductor industry is accelerating its migration to larger substrates, with 8-inch silicon carbide substrates gradually moving towards the forefront of industrialization. However, the increase in size presents unprecedented challenges to traditional cleaning technologies. The increase in surface area is not a simple linear expansion; it dramatically amplifies the process uniformity issues that are easily controlled on smaller substrates. For 8-inch substrates, significant processing differences easily occur between the edge and center regions during cleaning, leading to uneven impurity concentrations or inconsistent surface damage. This non-uniformity directly propagates to the epitaxial growth stage, causing lattice mismatch and defect proliferation, ultimately failing to meet the stringent requirements of high-performance device manufacturing.

[0004] Currently, the mainstream substrate cleaning technologies in the industry can be broadly divided into two categories: wet cleaning and dry cleaning. However, both exhibit significant limitations when dealing with 8-inch silicon carbide substrates. Wet cleaning, especially the series of solution cleaning based on the RCA standard, has long been considered the golden rule in the silicon-based semiconductor field. It relies on a combination of strong oxidizing acids, alkalis, and oxidizing agents to remove various contaminants, and is effective for smaller silicon carbide substrates. However, when faced with large 8-inch substrates, its inherent drawbacks are amplified dramatically: First, to ensure uniformity, a huge amount of high-purity chemical reagents are required, including toxic and harmful concentrated sulfuric acid and hydrogen peroxide, which is not only costly but also brings severe environmental pressure and wastewater treatment problems. Second, during the cleaning process, rinsing with large amounts of deionized water is an essential step, which not only wastes a lot of water resources but also easily leads to secondary pollution due to water residue. More importantly, wet cleaning is essentially an isotropic chemical etching process, which is difficult to control precisely and can easily lead to increased micro-roughness of the substrate surface, or even chemical damage to the silicon carbide lattice structure. This runs counter to the requirements of epitaxial technology, which seeks atomically flat surfaces. In addition, the lengthy multi-tank cleaning process and drying time severely restrict production cycle time, making it difficult to adapt to the efficiency requirements of large-scale mass production.

[0005] To overcome the many drawbacks of wet cleaning, dry cleaning technologies, especially plasma cleaning, are gaining popularity. These technologies typically utilize plasma-activated gases to react physically or chemically with surface contaminants, then extract the reaction products using a vacuum system. The entire process requires no large amounts of chemical liquids, demonstrating advantages in environmental protection and reducing secondary pollution. However, existing dry technologies also fall short when dealing with 8-inch silicon carbide substrates. While conventional plasma treatment can effectively remove some organic contaminants and light oxide layers, its ability to remove strongly bonded metallic impurities and stubborn carbon residues on the substrate surface is often insufficient. More importantly, plasma itself, as a high-energy state substance, is prone to uneven energy distribution due to the "edge effect" when processing large-area substrates. This can cause over-etching or lattice damage in the substrate edge areas, while potentially creating cleaning dead zones in the central area. This spatial non-uniformity of the cleaning effect is unacceptable for large-size, high-performance silicon carbide epitaxy. Another approach is to use physical bombardment, such as argon ion sputtering. However, this method carries a higher risk of damaging the substrate lattice and is highly likely to disrupt the integrity of the atomic structure on the silicon carbide surface. Therefore, it is also unsuitable as the final cleaning process before fabricating high-performance devices.

[0006] Therefore, the current industry dilemma lies in the fact that while traditional wet cleaning is relatively mature, it faces the triple pressure of environmental protection, uniformity, and surface damage; while existing dry technologies struggle to balance cleaning capacity, uniformity, and non-destructive treatment. The industry urgently needs a new cleaning solution truly suitable for 8-inch and larger silicon carbide substrates. Ideally, this solution should be able to complete all cleaning steps in a single environment to avoid cross-contamination, achieve efficient and uniform removal of multiple types of contaminants, absolutely guarantee no damage to the substrate's valuable crystal structure, and be highly efficient and environmentally friendly to meet the demands of modern mass production. Summary of the Invention

[0007] This application aims to overcome the shortcomings of existing technologies in achieving uniform and non-destructive cleaning of 8-inch and larger silicon carbide substrates under the premise of high efficiency and environmental protection. Therefore, it provides a cleaning method for silicon carbide substrates to overcome the above-mentioned deficiencies.

[0008] To achieve the above-mentioned objectives, the present invention is implemented through the following technical solution:

[0009] In a first aspect, the present invention provides a method for cleaning a silicon carbide substrate, comprising the following steps:

[0010] (S.1) Place the silicon carbide substrate to be cleaned into a sealed cleaning chamber;

[0011] (S.2) Introduce process gas into the sealed cleaning chamber and generate plasma to activate the substrate surface;

[0012] (S.3) An airflow containing amino-modified graphene quantum dots is introduced into the cavity, so that the quantum dots are adsorbed on the surface of the activated substrate to capture surface impurities.

[0013] (S.4) The substrate surface is irradiated with a pulsed energy source, and a two-dimensional relative motion is generated between the energy beam and the substrate surface to desorb the quantum dots adsorbed with impurities from the substrate surface.

[0014] (S.5) Purge gas is introduced to remove the desorbed quantum dots and impurities from the cavity.

[0015] As described in the background section, with 8-inch silicon carbide substrates gradually becoming more widely used, the contradictions between traditional wet cleaning and conventional dry cleaning processes regarding uniformity, damage control, and environmental efficiency are becoming increasingly acute. Wet cleaning relies on the isotropic reaction of a large number of chemical reagents. Its inherent fluid dynamics make it difficult to achieve uniform chemical action on large-area surfaces, easily leading to differences in cleaning effects between edges and centers, while also incurring significant chemical waste and the risk of surface lattice damage. Existing dry technologies, such as single-function plasma treatment, while avoiding chemical pollution to some extent, face challenges in controlling the uniformity of high-energy particles, have insufficient selective removal capabilities for specific impurities, and pose a risk of physical damage to sensitive substrate surfaces. It is against this backdrop that an innovative cleaning strategy is urgently needed that can break away from traditional thinking and fundamentally coordinate and solve the three major challenges of uniformity, non-destructiveness, and high efficiency.

[0016] The in-situ three-step method of "plasma activation-nano-adsorption-pulse energy desorption" established in this invention is the first to organically integrate and synergize three different physicochemical principles within the same sealed cavity, producing a synergistic effect greater than the sum of its parts. The first step, plasma activation, does not aim to directly remove stubborn impurities, but rather serves as a gentle "pretreatment." Through plasma bombardment and chemical reactions on the substrate surface, it cleans the surface and increases its surface energy without damaging the crystal lattice, creating an ideal and uniformly active surface environment for the subsequent precise adsorption of nanomaterials. This step lays the first foundation for the uniformity of the entire process.

[0017] The second step introduces amino-modified graphene quantum dots as a nano-adsorption medium. The amino functional groups on their surface can precisely and efficiently coordinate with metal ions and other impurities on the silicon carbide substrate surface, selectively immobilizing them through intermolecular forces. This molecular recognition-based adsorption method is inherently very friendly to the substrate lattice, fundamentally avoiding the risk of physical or chemical damage. Furthermore, these nanoscale adsorbents are transported in the form of an airflow, and with the assistance of substrate rotation, a uniformly thick adsorption film can be formed on a large surface area. This solves the problem of uneven cleaning caused by uneven reactant concentration or energy distribution in traditional technologies, providing a second layer of guarantee for uniformity.

[0018] However, simply achieving gentle adsorption of impurities is insufficient. The key to completing the entire cleaning cycle lies in the complete and uniform removal of the adsorbed quantum dots from the substrate without leaving any residue or causing secondary damage. This invention abandons traditional methods such as thermal annealing or continuous energy irradiation, which are prone to heat accumulation and stress damage. Instead, it creatively employs a pulsed energy source (such as a pulsed laser) and precisely controlled two-dimensional relative motion between the laser and the substrate surface. The pulsed operation means that energy is applied intermittently and transiently. Within a single pulse cycle, energy is preferentially used to rapidly break the bonds between the quantum dots and the substrate surface, causing the adsorbent to desorb along with its captured impurities. Due to the extremely short pulse duration, heat does not have time to diffuse into the depths of the substrate lattice before the pulse ends, thus achieving a "cold" treatment of the surface adsorption layer and effectively protecting the integrity of the substrate material. Simultaneously, the scanning or rotating motion between the energy beam and the substrate ensures that every point on the entire 8-inch substrate surface receives pulse irradiation with a highly consistent energy density, achieving uniformity in the desorption process—something difficult to achieve with traditional fixed-point or scanning methods.

[0019] In summary, the three interconnected processes, each paving the way for the next and collectively mitigating the limitations of any single technology, ultimately form a complete, efficient, and gentle cleaning loop. Because dynamic homogenization measures such as rotation or scanning are incorporated throughout the entire process from activation and adsorption to desorption, the difference in impurity residue between the edge and center of the 8-inch substrate is controlled to an extremely low level, meeting the stringent requirements for substrate surface consistency in large-scale epitaxial growth. Regarding non-destructive testing, based on the mechanism of specific adsorption and instantaneous pulse desorption, the lattice integrity of the substrate surface is maximized, and the surface roughness after cleaning is well maintained or even improved, laying a solid foundation for high-quality epitaxy. In terms of efficiency and environmental friendliness, the entire process can be completed within minutes in the same chamber, eliminating the cumbersome transfer, rinsing, and drying steps of wet processes. This not only significantly shortens the cleaning cycle, adapting to mass production schedules, but also completely eliminates dependence on large amounts of high-risk chemical reagents, making the process greener and safer.

[0020] Preferably, the substrate is kept rotating in at least one of the plasma activation step, nano-adsorption step, and energy desorption step.

[0021] In the plasma activation step, rotation effectively overcomes the uneven gas distribution and energy density in the edge and center regions caused by the cavity geometry and plasma sheath effect, ensuring a uniform activation effect across the entire substrate surface and laying a uniform starting point for subsequent nano-adsorption. In the nano-adsorption step, the rotating substrate disrupts the orientation of the airflow path, allowing the amino-modified graphene quantum dot airflow to contact the surface in a more random and diffuse manner. This effectively suppresses the uneven distribution of quantum dot clouds that may be caused by the inlet position, thus ensuring the uniformity of adsorption layer thickness and density at the atomic scale.

[0022] Furthermore, in the pulsed energy desorption step, the synergy between rotation and energy beam scanning constitutes a two-dimensional homogenization system. This not only avoids the local heat accumulation and damage that may be caused by fixed irradiation, but also achieves the average distribution of thermal stress by periodically and intermittently exposing every point on the substrate surface to pulsed energy. Thus, while ensuring the complete desorption of impurities, the integrity of the silicon carbide lattice is perfectly protected.

[0023] Preferably, in step (S.2), the process gas includes an inert gas and oxygen.

[0024] Preferably, the inert gas is argon, and the volume ratio of argon to oxygen is 9:1.

[0025] Preferably, before step (S.2), the cavity is further evacuated to a pressure below 10 Pa.

[0026] Preferably, in step (S.3), the airflow velocity is 100-300 sccm;

[0027] The concentration of the amino-modified graphene quantum dots is 0.01-0.05 mg / mL;

[0028] The particle size of the amino-modified graphene quantum dots is 5-8 nm.

[0029] In step (S.3), if the flow rate is too slow or the concentration is too low, the adsorption in the edge region will be saturated while the supply in the central region will be insufficient, resulting in a significant radial concentration gradient. If the flow rate is too fast or the concentration is too high, it may cause the quantum dots to agglomerate in the gas flow, or multilayer non-uniform stacking on the substrate surface, or even affect the adsorption stability due to the impact effect. The concentration range of 0.01-0.05 mg / mL and the gas flow rate of 100-300 sccm ensure that the quantum dots can be stably and uniformly spread across the entire surface in a monolayer or sub-monolayer form with the cooperation of substrate rotation, thus laying the foundation for achieving uniform desorption in the future.

[0030] Preferably, the preparation method of the amino-modified graphene quantum dots is as follows:

[0031] (1) Graphene quantum dots were prepared by hydrothermal / solvothermal method using graphene oxide synthesized by Hummers method as a precursor.

[0032] (2) Graphene quantum dots are dispersed in a solvent and 3-aminopropyltriethoxysilane is added dropwise to the dispersion. APTES is hydrolyzed and its silanol groups undergo a condensation reaction with the hydroxyl groups on the surface of the graphene quantum dots. After the reaction, the unreacted 3-aminopropyltriethoxysilane and byproducts are removed by purification to obtain pure amino-modified graphene quantum dots.

[0033] Preferably, in step (S.4), the pulsed energy source is a pulsed laser;

[0034] The two-dimensional relative motion is achieved by scanning the substrate surface with the pulsed laser beam and / or rotating the substrate.

[0035] Preferably, the pulsed laser has a wavelength range of 1064 nm or 532 nm and an energy density range of 0.1-2 J / cm². 2 The pulse frequency range is 1-20 Hz, and the pulse laser irradiation time is 1-2 minutes.

[0036] Preferably, in step (S.4), the purging gas is high-purity nitrogen.

[0037] This application has the following beneficial effects:

[0038] First, through the synergistic effect of the in-situ three-step method of "plasma activation-nano adsorption-pulsed laser desorption", the efficient and uniform removal of impurities on the surface of large-sized substrates such as 8 inches was achieved, effectively solving the problem of cleaning consistency between the edge and center areas.

[0039] Secondly, based on the specific adsorption of amino-modified graphene quantum dots and the precise and controllable desorption of pulsed laser, this process can completely remove metal and carbon residues while greatly avoiding damage to the substrate surface lattice, thus perfectly maintaining its excellent lattice integrity and surface flatness.

[0040] Furthermore, the entire cleaning process is completed quickly within the same sealed cavity, which not only significantly shortens the process time and improves production efficiency, but also fundamentally eliminates chemical pollution and cross-contamination in wet processes, meeting the requirements of green and environmentally friendly manufacturing.

[0041] Ultimately, this technical solution provides a reliable surface treatment guarantee for high-quality epitaxial growth of large-size silicon carbide substrates, and has strong industrial applicability and promotion value. Attached Figure Description

[0042] Figure 1This is a surface defect test image of the silicon carbide substrate before cleaning in Example 1.

[0043] Figure 2 This is a test image of the surface defects of the silicon carbide substrate after cleaning in Example 1. Detailed Implementation

[0044] The present invention will be further described below with reference to specific embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0045] Preparation of amino-modified graphene quantum dots

[0046] The specific preparation method of amino-modified graphene quantum dots is as follows:

[0047] Raw materials: graphene oxide (GO, sheet diameter 0.5-5 μm, purity >99%), 3-aminopropyltriethoxysilane (APTES, purity 98%), ammonia (NH3·H2O, concentration 25-28%), deionized water.

[0048] step:

[0049] 1. Preparation of graphene oxide quantum dots (O-GQDs): 100 mg of graphene oxide powder was dispersed in 100 mL of deionized water and sonicated (500 W) for 2 hours to obtain a brownish-red dispersion. This dispersion was transferred to a 200 mL high-pressure reactor lined with polytetrafluoroethylene and reacted at 180 °C for 8 hours. After natural cooling, the solution was filtered through a 0.22 μm microporous membrane to obtain an aqueous solution of O-GQDs with a concentration of approximately 0.5 mg / mL.

[0050] 2. APTES Amine Modification: Measure 50 mL of the above O-GQDs aqueous solution into a round-bottom flask and adjust the pH to 9-10 with ammonia. Slowly add 1 mL of APTES dropwise while continuously stirring. Heat the reaction system to 70°C and reflux under nitrogen protection for 6 hours.

[0051] 3. Purification: After the reaction is complete, the reaction solution is transferred to a dialysis bag with a molecular weight cutoff of 1000 Da and dialyzed with deionized water for 48 hours to completely remove unreacted APTES and byproducts. Finally, a solid powder is obtained by freeze-drying, or the powder is appropriately concentrated to prepare an aqueous solution of the required concentration for later use. The amino-modified graphene quantum dots (NH2-GQDs) prepared by this method have a uniform particle size distribution of approximately 5-8 nm and an amino grafting rate of over 85%.

[0052] Example 1

[0053] This embodiment provides a cleaning method for an 8-inch silicon carbide substrate, the specific steps of which are as follows:

[0054] (S.1) Substrate Placement: An 8-inch 4H-SiC single crystal substrate (initial surface roughness Ra≈0.4nm) with a diameter of 200mm and a thickness of 400μm was transferred using a robotic arm into a 12L 316L stainless steel sealed cleaning chamber and placed on a three-point vacuum chuck stage with a quartz coating. The vacuum chuck was activated (vacuum degree -0.09MPa) to fix the substrate, and the chamber door was closed. The vacuum pump was started to evacuate the chamber pressure to 1.0 Pa, a process that took approximately 2 minutes.

[0055] (S.2) Plasma Activation: A mixture of high-purity argon (99.999% purity) and high-purity oxygen (99.999% purity) in a volume ratio of 9:1 is introduced into the cavity, with a total flow rate set to 120 sccm. After the cavity pressure stabilizes at 3.0 Pa, the inductively coupled plasma (ICP) generator located at the top of the cavity is activated, with a power set to 300 W. Simultaneously, the substrate stage is driven to rotate at a speed of 15 r / min for 2.0 minutes to ensure uniform activation of the substrate surface by the plasma.

[0056] (S.3) Nano-adsorption: Turn off the plasma generator and maintain the chamber pressure at 3.0 Pa. Open the valve of the nano-adsorption module and steadily introduce a nitrogen suspension of amino-modified graphene quantum dots with a concentration of 0.01 mg / mL, a particle size of 5 nm, and an amino grafting rate of 88% into the chamber at a flow rate of 100 sccm. Continue rotating the substrate stage at 15 r / min and continue the adsorption treatment for 3.0 minutes to form a uniform adsorption layer of quantum dots on the substrate surface.

[0057] (S.4) Pulsed Laser Desorption: Turn off the nano-adsorption module. Start the Nd:YAG pulsed laser (wavelength 1064 nm) and set the laser energy density to 0.1 J / cm². 2The pulse frequency was 10 Hz. At the same time, the two-dimensional scanning galvanometer was turned on (scanning speed 50 mm / s), and the stage was rotated at 15 r / min to irradiate the substrate surface. The desorption process took 2.5 minutes to ensure that the quantum dots adsorbed with impurities were uniformly removed from the substrate surface.

[0058] (S.5) Purging and Impurity Removal: Turn off the laser module and scanning galvanometer. Introduce high-purity nitrogen gas (99.999% purity) at a flow rate of 250 sccm into the cavity, and simultaneously activate the dual exhaust ports located at the bottom of the cavity to purge and remove the desorbed impurities and quantum dot mixture. The purging time is 40 seconds. After purging, slowly introduce clean air into the cavity to atmospheric pressure, open the cavity, and use a robotic arm to remove the cleaned substrate. Figure 1 This is a surface defect test image of the silicon carbide substrate before cleaning in this embodiment. Figure 2 The image shows a surface defect test result of the silicon carbide substrate after cleaning in this embodiment. As can be seen from the image, the defects and impurity content on the surface of the silicon carbide substrate are significantly reduced after cleaning using the method described in this embodiment.

[0059] Example 2

[0060] The difference between this embodiment and Embodiment 1 lies in adjusting the key parameters of nano-adsorption and pulsed laser desorption to optimize cleaning efficiency:

[0061] (S.3) In the nano-adsorption step, the concentration of amino-modified graphene quantum dots used was 0.03 mg / mL, the particle size was 7 nm, and the airflow rate was adjusted to 200 sccm. The adsorption treatment time was shortened to 2.5 minutes.

[0062] (S.4) In the pulsed laser desorption step, the laser energy density is increased to 1.0 J / cm². 2 The pulse frequency was set to 15 Hz, and the desorption treatment time was shortened to 1.5 minutes accordingly.

[0063] The other steps and parameters are the same as in Example 1.

[0064] Example 3

[0065] The difference between this embodiment and Embodiment 1 is that a higher concentration of nanomaterials and energy density are used to target substrates with heavier initial contamination.

[0066] (S.3) In the nano-adsorption step, the concentration of amino-modified graphene quantum dots used was 0.05 mg / mL, the particle size was 8 nm, and the airflow velocity was set to 300 sccm.

[0067] (S.4) In the pulsed laser desorption step, the laser energy density is increased to 2.0 J / cm². 2The pulse frequency was set to 20 Hz, and the desorption treatment time was controlled to 1.0 minute.

[0068] The other steps and parameters are the same as in Example 1.

[0069] Example 4

[0070] This example demonstrates the effects of using lasers of different wavelengths:

[0071] (S.3) In the nano-adsorption step, the quantum dot concentration is 0.025 mg / mL, the gas flow rate is 180 sccm, and the particle size is 6 nm.

[0072] (S.4) In the pulsed laser desorption step, the laser wavelength is changed to 532 nm and the laser energy density is set to 0.7 J / cm². 2 The pulse frequency was 10 Hz, and the desorption time was 1.2 minutes. This wavelength may have a better desorption effect on certain types of carbon residues.

[0073] The other steps and parameters are the same as in Example 1.

[0074] Example 5

[0075] This example demonstrates process adaptability at lower substrate rotation speeds:

[0076] (S.2) In the plasma activation step, the substrate stage rotation speed was set to 5 r / min. To compensate for the potential impact on uniformity caused by the reduced rotation speed, the ICP power was adjusted to 280 W, and the processing time was extended to 2.5 minutes.

[0077] In both the (S.3) nano-adsorption step and the (S.4) pulsed laser desorption step, the substrate stage rotation speed is maintained at 5 r / min. The nano-adsorption gas flow rate is adjusted accordingly to 150 sccm; the scanning mirror speed for pulsed laser desorption is adjusted to 30 mm / s to ensure irradiation uniformity.

[0078] The other steps and parameters are the same as in Example 1.

[0079] Example 6

[0080] This embodiment demonstrates process adaptability at higher substrate rotation speeds, making it suitable for scenarios with more stringent thermal budget control requirements.

[0081] (S.2) In the plasma activation step, the substrate stage rotation speed is set to 30 r / min. The ICP power is adjusted accordingly to 350 W. The high rotation speed improves heat dissipation, and the processing time can be maintained for 2.0 minutes.

[0082] In both the (S.3) nano-adsorption step and the (S.4) pulsed laser desorption step, the substrate stage rotation speed is maintained at 30 r / min. The nano-adsorption gas flow rate is increased to 250 sccm; the pulsed laser desorption uses a higher scanning mirror speed (80 mm / s), which, in conjunction with the high rotation speed, achieves extremely fast thermal cycling.

[0083] (S.4) The laser energy density for pulsed laser desorption is a relatively low 0.5 J / cm². 2 Effective desorption is achieved by utilizing a high repetition frequency (18Hz) and high-speed motion.

[0084] The other steps and parameters are the same as in Example 1.

[0085] Comparative Example 1

[0086] This comparative example uses the industry-standard RCA wet cleaning process, and the cleaning method is as follows:

[0087] SPM cleaning: Immerse the 8-inch silicon carbide substrate in an SPM solution (concentrated sulfuric acid H2SO4: hydrogen peroxide H2O2 = 4:1 volume ratio) at 120°C for 15 minutes to remove organic residues.

[0088] Rinse: Rinse the substrate with ultrapure water for 10 minutes.

[0089] SC-1 cleaning: Immerse the substrate in SC-1 solution (ammonia NH4OH: hydrogen peroxide H2O2: ultrapure water = 1:1:5 volume ratio) at 80℃ for 10 minutes to remove particulates and some metal impurities.

[0090] Rinse: Rinse the substrate with ultrapure water for 10 minutes.

[0091] SC-2 cleaning: Immerse the substrate in an SC-2 solution (hydrochloric acid HCl: hydrogen peroxide H2O2: ultrapure water = 1 : 1 : 6 volume ratio) at 80℃ for 10 minutes to remove metal ions.

[0092] Final rinsing and drying: Rinse thoroughly with ultrapure water for 15 minutes, then dehydrate with isopropanol (IPA), and finally dry with high-purity nitrogen.

[0093] Comparative Example 2

[0094] This comparative example uses another common dry cleaning method, which involves using only plasma for treatment.

[0095] Cleaning method:

[0096] 1. Place the substrate in the same cavity as in this invention and evacuate to 3.0 Pa.

[0097] 2. Introduce an Ar / O2 mixed gas (volume ratio 9:1, total flow rate 120 sccm).

[0098] 3. Turn on the ICP plasma, set the power to 400 W (higher than the present invention, in an attempt to enhance the effect), rotate the stage at 15 r / min, and extend the processing time to 5 minutes.

[0099] 4. After treatment, purge directly with N2 and restore atmospheric pressure.

[0100] Comparative Example 3

[0101] In this comparative example, the core material of the present invention, amino-modified graphene quantum dots, is replaced with ordinary graphene quantum dots.

[0102] Cleaning method: The steps in this comparative example are exactly the same as those in Example 2, with the only difference being:

[0103] Step (S.3): Use unaminated graphene quantum dots with the same concentration (0.03 mg / mL) and particle size (7 nm).

[0104] Comparative Example 4

[0105] Cleaning method: The steps in this comparative example are basically the same as those in Example 2, with the key difference being:

[0106] Steps (S.2), (S.3), (S.4): The substrate stage remains stationary and does not rotate.

[0107] Step (S.4): The pulsed laser is turned off and the scanning mirror is fixed to irradiate the central region of the substrate.

[0108] The silicon carbide substrates obtained from cleaning in Examples 1-6 and Comparative Examples 1-4 were tested. The specific test process and results are summarized below.

[0109] Test methods and procedures:

[0110] 1. Surface Impurity Content and Uniformity Test: A test solution was dropped onto the surface of each 8-inch substrate and manually shaken to ensure uniform distribution across the wafer surface. ICP-MS analysis was then performed on the test solution to accurately determine the atomic concentrations of elements such as Fe, Ni, and C. To eliminate the influence of adsorbed environmental carbon on the surface, each point was subjected to a short-duration argon-ion sputtering etching process (approximately 5 nm depth) followed by measurement to obtain information on the substrate surface's inherent impurities. The measured values ​​for each point were recorded, and the average impurity content (representing cleanliness) and standard deviation (representing uniformity) for all points were calculated.

[0111] 2. Surface Topography and Roughness Testing: Four detection points (top, bottom, left, right) and one detection point (center) were taken at a distance of 5 mm from the edge of the wafer. A surface scan of 10 μm × 10 μm was performed on each scanned area. A three-dimensional topography image of each scanned area was acquired, and the arithmetic mean surface roughness (Ra) of that area was calculated using the instrument software. The average Ra value of the five points was then reported to evaluate the impact of the cleaning process on the overall surface smoothness.

[0112] 3. Process efficiency assessment

[0113] Method: Timing.

[0114] Process: Record the total time from the moment the substrate is placed into the cavity (or immersed in the first tank) until all cleaning steps are completed and the substrate is removed.

[0115] Table 1 Summary of Test Results

[0116] Sample number Total time (minutes) <![CDATA[Fe impurity content (×10 9 atoms / cm 2 )]]> <![CDATA[Impurity uniformity (standard deviation, ×10 9 atoms / cm 2 )]]> Surface roughness Ra (nm) Before cleaning - ~800 >100 (Initially uneven) 0.40 Example 1 ~8.5 10.5 0.25 0.105 Example 2 ~7.0 9.8 0.22 0.098 Example 3 ~6.5 8.5 0.28 0.102 Example 4 ~7.2 9.5 0.24 0.101 Example 5 ~9.0 11.2 0.35 0.108 Example 6 ~6.8 10.8 0.26 0.104 Comparative Example 1 >70 55.0 1.5 0.165 Comparative Example 2 ~8.0 520.0 15.0 0.135 Comparative Example 3 ~7.0 95.0 5.5 0.112 Comparative Example 4 ~6.5 Center: 8.0, Edge: 110.0 45.0 (Extremely uneven) Center: 0.130, Edge: 0.095

[0117] Note: Fe impurity content and roughness are average values ​​from multiple measurements; impurity uniformity is expressed as the standard deviation of Fe content, with smaller values ​​indicating greater uniformity.

[0118] The above test results clearly demonstrate that the silicon carbide substrate cleaning method provided by this invention has significant progress compared with the prior art. As can be seen from the table above, all embodiments (1-6) can reduce the Fe impurity content on the substrate surface to an extremely low level (<12×10). 9 atoms / cm 2 Furthermore, it maintained excellent surface smoothness (Ra ≈ 0.10 nm), achieving a balance between high cleanliness and low damage. Additionally, the standard deviation of impurity content in all examples was less than 0.3 × 10⁻⁶. 9 atoms / cm 2 This demonstrates that the method of the present invention can be perfectly adapted to the cleaning of 8-inch large-size substrates, solving the problem of uneven edges and centers caused by the size increase in traditional technologies (such as Comparative Examples 1 and 4). Finally, the total cleaning time of the embodiments of the present invention is controlled within 10 minutes, and the efficiency is more than 8 times that of Comparative Example 1 (traditional wet method), which greatly improves the production cycle.

[0119] Comparative Example 2 demonstrates that plasma technology alone cannot effectively remove metallic impurities, highlighting the necessity of introducing a nano-adsorption step. Comparative Example 3 shows a significant decrease in the adsorption effect of unmodified graphene quantum dots, clarifying the crucial role of amino modification as a core material characteristic in achieving specific adsorption. Comparative Example 4 most powerfully demonstrates that dynamic processing (rotation / scanning) is the "key" to achieving large-scale uniform cleaning; without it, even with other identical steps, cleaning will completely fail.

[0120] In summary, this invention systematically solves the long-standing technical contradictions in the field of cleaning large-size silicon carbide substrates through a multi-step in-situ synergistic mechanism of "plasma activation-nano-adsorption-pulsed laser desorption" and dynamic homogenization techniques such as rotation / scanning.

[0121] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A cleaning method of a silicon carbide substrate, characterized by, The method comprises the following steps: (S.1) placing a silicon carbide substrate to be cleaned in a closed cleaning cavity; (S.2) introducing a process gas into the closed cleaning cavity and exciting a plasma to activate the surface of the substrate; (S.3) introducing a gas flow containing amino-modified graphene quantum dots into the cavity, so that the quantum dots are adsorbed on the surface of the activated substrate to capture surface impurities; (S.4) irradiating the surface of the substrate with a pulsed energy source, while generating two-dimensional relative motion between the energy beam and the substrate surface, so that the quantum dots adsorbed with impurities are desorbed from the substrate surface; (S.5) introducing a purge gas to remove the desorbed quantum dots and impurities from the cavity.

2. The cleaning method according to claim 1, wherein in at least one of the plasma activation step, the nano-adsorption step and the energy desorption step, the substrate is kept rotating.

3. The cleaning method according to claim 1, wherein in step (S.2), the process gas comprises an inert gas and oxygen.

4. The cleaning method according to claim 3, wherein the inert gas is argon, and the volume ratio of argon to oxygen is 9:

1.

5. The cleaning method according to claim 1, wherein before step (S.2), the cavity is further vacuumed to a pressure lower than 10 Pa.

6. The cleaning method according to claim 1, wherein in step (S.3), the flow rate of the gas flow is 100-300 sccm; the concentration of the amino-modified graphene quantum dots is 0.01-0.05 mg / mL; the particle size of the amino-modified graphene quantum dots is 5-8 nm.

7. The cleaning method according to claim 1 or 6, wherein the preparation method of the amino-modified graphene quantum dots is as follows: (1) using graphene oxide synthesized by the Hummers method as a precursor, and preparing graphene quantum dots by a hydrothermal / solvothermal method; (2) dispersing the graphene quantum dots in a solvent, and adding 3-aminopropyl triethoxysilane dropwise into the dispersion, hydrolyzing APTES and making the silicon hydroxyl group thereof condense with the hydroxyl group on the surface of the graphene quantum dots, and after the reaction, removing unreacted 3-aminopropyl triethoxysilane and by-products by purification to obtain pure amino-modified graphene quantum dots.

8. The cleaning method according to claim 1, wherein in step (S.4), the pulsed energy source is a pulsed laser; the two-dimensional relative motion is realized by scanning the pulsed laser on the substrate surface and / or rotating the substrate.

9. The cleaning method according to claim 8, wherein The wavelength of the pulse laser ranges from 1064 nm or 532 nm, the energy density ranges from 0.1-2 J / cm 2 , the pulse frequency ranges from 1-20 Hz, and the pulse laser irradiation time is 1-2 minutes.

10. The cleaning method according to claim 1, wherein in step (S.4), the purge gas is high-purity nitrogen.

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