A pre-cleaning method for silicon carbide polishing pieces

Abstract

This invention relates to the field of semiconductor manufacturing technology, specifically disclosing a pre-cleaning method for silicon carbide polished wafers. The method first utilizes an organic cleaning solution coupled with polishing and ultrasonication to efficiently remove wax and organic contaminants, and loosen the nano-carbon cluster structure. Then, a hydrogen peroxide-hydrofluoric acid composite system is used to renew the oxide layer and fix metal contaminants in situ. Subsequently, a sulfuric acid-hydrogen peroxide high-temperature strong oxidation system is used to deeply decompose the nano-carbon clusters and complex organic matter. Finally, under the synergistic effect of ultraviolet photocatalysis and pulsed megasonic waves, a composite cleaning solution of oxalic acid and hydrogen peroxide is used to achieve efficient chelation and desorption of metal ions, forming a stable passivation film on the surface. This method can stably control the surface roughness (Ra) of the silicon carbide substrate below 0.2 nm, while completely breaking the vicious cycle of "cleaning-residue-recontamination," significantly improving cleaning efficiency and substrate surface quality.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing technology, and in particular to a pre-cleaning method for silicon carbide polished wafers. Background Technology

[0002] Silicon carbide (SiC), as a core material of third-generation semiconductors, has become an ideal substrate for high-voltage power devices due to its wide bandgap, high breakdown field strength, and excellent thermal conductivity. It has irreplaceable application value in high-end fields such as power electronics and new energy.

[0003] In the fabrication process of silicon carbide polished wafers, chemical mechanical polishing (CMP) is a key step to achieve ultra-precise surface planarization and reduce surface roughness (Ra) to below the nanometer level. However, this process inevitably leads to complex and persistent contaminants on the surface of the polished wafer, mainly including: 1) Abrasive particle residues, such as nanodiamonds or colloidal silica microparticles. These hard particles are easily embedded in the surface microstructure or firmly adsorbed by van der Waals forces under mechanical pressure; 2) Organic contaminants, including additives in the polishing slurry (such as dispersants and complexing agents), polishing pad wear products, and organic matter introduced from the environment. These tend to form a dense organic film on the surface, hindering the effective contact of subsequent cleaning solutions; 3) Metallic impurities, mainly from the wear of process equipment, which may exist in a free state or in the form of bonding with surface hydroxyl groups. Even trace amounts can seriously affect the electrical performance of the device; 4) Non-uniform oxide layers, including SiO2 layers generated by natural oxidation or during the process. The interface between these layers and the silicon carbide substrate is complex, and improper removal can easily lead to substrate damage or new defects.

[0004] Currently, the industry commonly uses a tank-type pre-cleaning process based on the RCA standard. However, this process has significant limitations when processing silicon carbide polished wafers: First, it has a low removal rate for ultrafine nano-carbon clusters and submicron particulate contaminants remaining from cutting and polishing. These carbon-based contaminants are highly hydrophobic and chemically inert, easily agglomerating and tightly adhering to the surface. Their size can be as low as tens of nanometers (e.g., 5~50nm), making them difficult to decompose effectively by conventional chemical oxidation systems. Simultaneously, the submicron-sized (≥0.1μm) particles remaining on the substrate surface are significantly higher than the process requirements, becoming one of the main problems affecting cleanliness. Second, the chelation and desorption efficiency for subsurface metal ions is limited, especially for deeply embedded Fe... 3+ The complexing ability of existing cleaning solutions is insufficient for transition metal ions, which can easily lead to excessive metal ion residues. Finally, the process window is narrow in the etching step to remove the oxide layer. When using hydrofluoric acid, over-etching is likely to occur, which will damage the surface morphology of the substrate and cause the roughness (Ra) to deteriorate to more than 0.2 nm, affecting the quality of epitaxial growth.

[0005] Current technologies suffer from a misconception: prioritizing final cleaning while neglecting pre-cleaning. This often focuses cleaning efforts on subsequent processes, overlooking the crucial role of pre-cleaning in source control. In this approach, stubborn contaminants directly enter later stages, not only increasing the load on final cleaning equipment and reducing overall efficiency, but also potentially leading to secondary migration and re-adsorption of contaminants during multi-step processing. This creates a vicious cycle of "cleaning-residue-recontamination," ultimately resulting in excessive particle counts and metal ion contamination on the substrate surface, severely restricting the product quality and device fabrication yield of silicon carbide substrates. Therefore, developing a pre-cleaning method that can efficiently remove various complex contaminants at the source with controllable process capabilities has become a pressing technical challenge in this field. Summary of the Invention

[0006] To address the problems of difficult removal of nano-carbon-based contaminants, limited metal ion chelation and desorption efficiency, and easy over-etching leading to increased roughness in existing pre-cleaning processes for silicon carbide polished wafers, this invention provides a pre-cleaning method for silicon carbide polished wafers. This invention achieves efficient decomposition of nano-carbon clusters, deep desorption of subsurface metal ions, and controllable stripping of the surface oxide layer by sequentially performing organic liquid cleaning, oxidative etching, high-temperature oxidation, and photoacoustic synergistic cleaning on the silicon carbide substrate. This systematically solves the problem of removing complex contaminants from the source, breaking the vicious cycle of "cleaning-residue-recontamination," reducing the load and process difficulty of final cleaning, and providing a reliable guarantee for the high-quality, large-scale preparation of silicon carbide substrates.

[0007] To solve the above-mentioned technical problems, the technical solution provided by the present invention is as follows: A pre-cleaning method for silicon carbide polished wafers includes the following steps performed sequentially: S1, the silicon carbide polished wafer is placed in an organic cleaning solution for the first cleaning; S2, the silicon carbide polished wafer after S1 is placed in an oxidation etching solution of hydrogen peroxide, hydrofluoric acid and ultrapure water for a second cleaning. S3, the silicon carbide polished wafer after S2 cleaning is placed in an oxidizing solution of concentrated sulfuric acid and hydrogen peroxide for a third cleaning; S4, the silicon carbide polished wafer cleaned in S3 is placed in a composite cleaning solution, and ultraviolet light and pulsed megasonic waves are applied simultaneously for the fourth cleaning. After drying, the cleaned silicon carbide substrate is obtained. The composite cleaning solution is a mixed solution of hydrogen peroxide, oxalic acid and ultrapure water in a volume ratio of 1:(0.8~1.8):(9~13), with a pH of 4.5~5.5.

[0008] Compared to existing technologies, the pre-cleaning method for silicon carbide polished wafers provided by this invention, specifically the S1 organic cleaning method, can quickly remove organic matter such as wax and cutting fluid residue from the substrate surface, while simultaneously loosening the aggregated structure of nano-carbon clusters, laying the foundation for subsequent deep cleaning. The S2 oxidation etching solution uses a hydrogen peroxide and hydrofluoric acid composite system, which, compared to traditional single hydrofluoric acid etching, possesses a unique stripping-regeneration synergistic effect: hydrofluoric acid first selectively etches away the defective or contaminated native oxide layer, exposing a clean silicon carbide surface. Subsequently, hydrogen peroxide reacts with the newly formed surface to generate a new, dense, and uniform oxide film. This process not only achieves gentle renewal of the oxide layer, effectively avoiding surface roughness deterioration caused by over-etching, but also fixes and removes metal impurities encapsulated in the original oxide layer during the regeneration process, thereby significantly reducing metal ion contamination in the pretreatment stage and inhibiting its re-adsorption in subsequent processes.

[0009] The S3 system, composed of concentrated sulfuric acid and hydrogen peroxide, provides a strong oxidizing solution that deeply oxidizes and decomposes residual nano-carbon clusters, converting inert carbon-based pollutants into water-soluble substances and significantly improving the removal rate of nano-carbon clusters. The S4 composite cleaning solution, in synergy with ultraviolet light and pulsed megasonic waves, further enhances the desorption effect of deeply embedded metal ions: hydrogen peroxide generates strong oxidizing species under ultraviolet excitation, disrupting the chemical bonds between metal ions and the substrate surface; oxalic acid, as a highly efficient chelating agent, reacts with Fe... 3+ Transition metal ions form stable and soluble complexes; at the same time, the oxalic acid system can form a dense and stable passivation film on the substrate surface, significantly increasing the contact angle to over 70°, effectively inhibiting natural oxidation and re-adsorption of pollutants, thereby fundamentally breaking the cycle of "cleaning-residue-recontamination".

[0010] Furthermore, by precisely controlling the oxalic acid ratio and the system pH, the chelation reaction efficiency and passivation film formation effect can be balanced. Combined with specific pulsed megasonic conditions, the mechanical and chemical effects of the cleaning process on the substrate surface can be minimized, ensuring that the substrate surface roughness (Ra) after cleaning is stably controlled below 0.2 nm, so as to meet the stringent requirements for surface flatness in subsequent epitaxial growth.

[0011] It should be noted that the pre-cleaning mentioned in this invention refers to the final surface cleaning and preparation step performed on the silicon carbide substrate after chemical mechanical polishing (CMP) and before entering the final cleaning process. Its purpose is to systematically remove various complex contaminants introduced by the CMP process from the source, creating clean and controllable initial surface conditions for final cleaning, thereby improving the overall cleaning process efficiency and the final substrate quality.

[0012] Furthermore, in S1, the organic cleaning solution is a mixed solution of a dewaxing cleaning agent and ultrapure water with a volume ratio of 1:19 to 1:24.

[0013] By controlling the concentration of the dewaxing cleaning agent within the above range, it can quickly and thoroughly remove wax, cutting fluid residue, and most organic additives from the surface of the polishing pad. At the same time, it can effectively wet and penetrate into the interior of the nano-carbon clusters, significantly loosening and swelling their hydrophobic aggregate structure, laying the foundation for subsequent deep cleaning.

[0014] It should be noted that the dewaxing cleaning agent used in this invention is a conventional dewaxing cleaning agent in the art, such as semiconductor-grade solvent-based or water-based dewaxing agents, and its specific components are not the core improvement of this invention. The cleaning effect of this invention does not depend on a specific brand or special formula dewaxing product; any conventional dewaxing cleaning agent in the art is acceptable, and this invention does not impose any special limitations.

[0015] Furthermore, in S1, the temperature of the first cleaning is 60℃~70℃, and the cleaning time is 5min~10min.

[0016] Further, in S1, the first cleaning is carried out in a cleaning tank equipped with a scouring mechanism and an ultrasonic device. The scouring mechanism drives the silicon carbide polishing sheet to be scouring periodically in the organic cleaning liquid. The scouring frequency is 2 to 5 times / min and the scouring stroke is 100 mm to 200 mm. The ultrasonic device generates an ultrasonic frequency of 400 kHz to 800 kHz.

[0017] Periodic agitation effectively washes the surface of silicon carbide substrates, and combined with high-frequency ultrasound, generates a dense cavitation effect at the microscale, which strongly loosens and peels off firmly attached nanoparticles and embedded contaminants, allowing subsequent chemical cleaning solutions to contact and penetrate the substrate surface more fully and evenly, thus improving the cleaning effect.

[0018] Furthermore, in S1, the silicon carbide polishing sheet remains completely submerged below the surface of the organic cleaning solution throughout the entire polishing stroke.

[0019] Preferably, during the upward throwing process, the distance between the highest point of the silicon carbide substrate and the liquid surface is not less than 0.5 cm.

[0020] Further, in S2, the volume ratio of hydrogen peroxide, hydrofluoric acid and ultrapure water is 1:(0.005~0.02):(50~150).

[0021] This ratio ensures extremely low concentrations of hydrofluoric acid and high concentrations of hydrogen peroxide. The trace amounts of hydrofluoric acid, while avoiding corrosion of the silicon carbide substrate, allow for selective and gentle etching of incomplete or contaminated native oxide layers (SiO2). The diluted hydrogen peroxide then reacts immediately with the exposed fresh silicon carbide surface, generating a uniform and dense new oxide film in situ. During this process, some metal ions are captured and chemically bonded to the new film in its early stages of growth. This achieves controllable oxide layer renewal, avoids surface roughening due to over-etching, and effectively fixes or transforms the metal ions encapsulated in the original oxide layer, significantly reducing the risk of metal contaminant residue and re-adsorption.

[0022] This ratio balances the relative relationship between etching rate and oxidation rate, avoiding over-etching (surface roughening) due to excessive HF or incomplete new oxide film due to insufficient H2O2.

[0023] Furthermore, in S2, the temperature of the second cleaning is 30℃~50℃, and the cleaning time is 2min~5min.

[0024] Furthermore, in S3, the volume ratio of concentrated sulfuric acid to hydrogen peroxide is 13:7 to 3:1.

[0025] At this ratio, the cleaning solution can deeply and thoroughly oxidize and decompose the chemically inert nano-carbon clusters and complex organic matter remaining after step S1, ultimately converting them into substances such as carbon dioxide, water, and soluble small-molecule carboxylic acids, thereby achieving highly efficient removal of stubborn carbon-based contaminants that are difficult to remove with conventional cleaning.

[0026] Furthermore, in S3, the cleaning temperature of the third cleaning is 110℃~120℃, and the cleaning time is 5min~10min.

[0027] Furthermore, in S4, the temperature of the fourth cleaning is 28℃~32℃, and the cleaning time is 8min~15min.

[0028] Furthermore, in S4, the wavelength of the ultraviolet light irradiation is 250nm~260nm, and the light intensity is 25mW / cm². 2 ~35mW / cm 2 The carrier frequency of the pulsed megasonic wave is 800 kHz to 1200 kHz, the pulse repetition frequency is 100 kHz to 500 kHz, and the power density is 0.5 W / cm². 2 ~1.0W / cm 2 The duty cycle is 20% to 50%.

[0029] The optimized reaction conditions can further promote the removal of residual organic contaminants and metal ions on the surface of the silicon carbide substrate.

[0030] Furthermore, in S4, the fourth cleaning is carried out in a cleaning tank equipped with a scouring mechanism. The scouring mechanism drives the silicon carbide polishing sheet to be scourned periodically in the organic cleaning liquid. The scouring frequency is 2 to 5 times / min, and the scouring stroke is 100 mm to 200 mm. Throughout the entire scouring stroke, the silicon carbide polishing sheet remains completely submerged below the surface of the organic cleaning liquid.

[0031] Preferably, during the upward throwing process, the distance between the highest point of the silicon carbide substrate and the liquid surface is not less than 0.5 cm.

[0032] Furthermore, in S4, the pH of the composite cleaning solution is adjusted in a timely manner to the range of 4.5 to 5.5 using alkaline water prepared by high-purity CO2 gas or electrolysis of ultrapure water.

[0033] It should be noted that after each cleaning process in the cleaning solution, an ultrapure water rinsing step is also included to remove any residual cleaning solution from the previous process and to prevent the cleaning solution from being carried over into the next cleaning solution with different chemical properties. Specifically, the ultrapure water rinsing time is ≥5 minutes.

[0034] Furthermore, in step S4, the drying process employs a staged rotary drying method, specifically including the following steps: Control the rotation speed of the silicon carbide polishing wafer to 350rpm~550rpm and spin dry for 90s~120s; then increase the rotation speed to 550rpm~850rpm and spin dry for 180s~360s; then reduce the speed until the rotation stops to obtain the cleaned silicon carbide substrate.

[0035] In summary, this invention provides a pre-cleaning method for silicon carbide polished wafers. This method first efficiently removes wax and organic contaminants and loosens the nano-carbon cluster structure through the coupling effect of an organic cleaning solution and polishing-ultrasound. Then, a hydrogen peroxide-hydrofluoric acid composite system is used to renew the oxide layer and fix metal contaminants in situ. Subsequently, a sulfuric acid-hydrogen peroxide high-temperature strong oxidation system is used to deeply decompose the nano-carbon clusters and complex organic matter. Finally, under the synergistic effect of ultraviolet photocatalysis and pulsed megasonic waves, a composite cleaning solution of oxalic acid and hydrogen peroxide is used to achieve efficient chelation and desorption of metal ions, forming a stable passivation film on the surface. This method can stably control the surface roughness (Ra) of silicon carbide substrates below 0.2 nm, while completely breaking the vicious cycle of "cleaning-residue-recontamination," significantly improving cleaning efficiency and substrate surface quality. It provides a clean and smooth surface foundation for subsequent high-quality epitaxial growth and has significant application value for promoting the development of silicon carbide-based power device fabrication processes. Attached Figure Description

[0036] Figure 1This is a particle test image of the silicon carbide substrate obtained by cleaning in Example 1 of the present invention after cleaning by a conventional terminal process; Figure 2 This is a particle test image of the silicon carbide substrate obtained by cleaning in Example 2 of the present invention after being cleaned by a conventional terminal process; Figure 3 This is a particle test image of the silicon carbide substrate obtained by cleaning in Example 3 of the present invention after cleaning by a conventional terminal process. Figure 4 The image shows a particle test pattern of the silicon carbide substrate cleaned in Comparative Example 1 of this invention after being cleaned using a conventional terminal process. Figure 5 The image shows a particle test pattern of the silicon carbide substrate cleaned in Comparative Example 2 of this invention after being cleaned using a conventional terminal process. Figure 6 The image shows a particle test pattern of the silicon carbide substrate cleaned in Comparative Example 3 of this invention after being cleaned using a conventional terminal process. Figure 7 This is a particle test image of the silicon carbide substrate obtained by cleaning in Comparative Example 4 of the present invention after cleaning by a conventional terminal process. Figure 8 The image shows a particle test pattern of the silicon carbide substrate obtained by cleaning in Comparative Example 5 of this invention after cleaning by a conventional terminal process. Figure 9 This is a particle test image of the silicon carbide substrate obtained by cleaning in Example 1 of the present invention after being cleaned using a shortened terminal cleaning process. Figure 10 The image shows a particle test pattern of the silicon carbide substrate obtained by Comparative Example 1 of this invention after being cleaned using a shortened terminal cleaning process. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0038] To better illustrate the present invention, further examples are provided below.

[0039] All reagents used in the examples and comparative examples were USP grade or higher. Specifically, the hydrogen peroxide concentration was 30%, concentrated sulfuric acid was 98%, oxalic acid was 10%, hydrofluoric acid was 40%, ammonia was 27%, and hydrochloric acid was 37%. The resistivity of the ultrapure water was ≥18 MΩ. cm. The dewaxing cleaning agent consists of 1 wt% organic solvent D-limonene, 2 wt% surfactant alkylphenol polyoxyethylene ether, 0.5 wt% metal chelating agent citric acid, and the balance being deionized water.

[0040] The silicon carbide substrates cleaned in the following examples and comparative examples are chemically mechanically polished substrates. The silicon carbide substrates can be 6 inches or larger. A 6-inch silicon carbide substrate was used in the following examples and comparative examples.

[0041] In the following examples and comparative cases, the cleaning effect was verified using the following methods after the terminal cleaning was completed: (1) The number of particles with a diameter ≥ 0.1 μm on the substrate surface was detected using a surface defect detector; (2) The number of Fe metal ions was tested using a plasma-inductively coupled mass spectrometer. 3+ / Al 3+ (3) Surface roughness was tested using an atomic force microscope with a scanning area of ​​5 μm * 5 μm. (4) The wetting angle of the substrate surface was tested using a contact angle meter to characterize the integrity of the passivation film on the substrate surface, and the average value ± standard deviation was taken.

[0042] Example 1 This embodiment provides a pre-cleaning method for silicon carbide polished wafers, comprising the following steps performed sequentially: S1. Place the silicon carbide polishing wafer in an organic cleaning solution of dewaxing cleaning agent and ultrapure water with a volume ratio of 1:24, and ultrasonically clean it at 70°C for 10 minutes. The cleaning tank is equipped with an up-and-down agitator arm with an agitation frequency of 2 times / min, an agitation stroke of 100mm, and an ultrasonic frequency of 800KHz. After cleaning, rinse with ultrapure water overflow for 5 minutes. S2, place the silicon carbide polished wafer in an oxidation etching solution of hydrogen peroxide, hydrofluoric acid and hydrogen peroxide in a volume ratio of 1:0.005:50, immerse and clean it at 50°C for 5 minutes, and after cleaning, rinse it with ultrapure water overflow for 5 minutes. S3. Place the silicon carbide polishing wafer in an oxidizing solution of concentrated sulfuric acid and hydrogen peroxide with a volume ratio of 13:7 and clean it at 120°C for 10 minutes. After cleaning, rinse with ultrapure water overflow for 5 minutes. S4. The silicon carbide polished wafer is placed in a composite cleaning solution of hydrogen peroxide, oxalic acid, and ultrapure water with a volume ratio of 1:0.8:9, and subjected to pulsed megasonic-assisted cleaning for 8 minutes at 28°C. The cleaning tank is equipped with an up-and-down agitator and an ultraviolet irradiation system. The agitation frequency is 2 times / min, the agitation stroke is 100mm, and the ultraviolet irradiation uses a 250nm UV low-pressure mercury lamp with a light intensity of 25mW / cm². 2 The carrier frequency of the pulsed megasonic wave is 800 kHz, the pulse repetition frequency is 100 kHz, and the power density is 0.5 W / cm². 2 The duty cycle is 20%; after cleaning, rinse with ultrapure water overflow for 5 minutes. S5, the silicon carbide polished wafer is dried in stages using a rotary process: Set the rotation speed of the silicon carbide polishing wafer to 350 rpm and dry it by rotation for 120 seconds; Increase the rotation speed to 550 rpm and rotate to dry for 360 seconds; Reduce the rotation speed to a stop, reset the origin, and the process time is 90 seconds to obtain the cleaned silicon carbide substrate.

[0043] The particle test pattern of the silicon carbide substrate obtained after cleaning in this embodiment is shown below. Figure 1 As shown.

[0044] Example 2 This embodiment provides a pre-cleaning method for silicon carbide polished wafers, comprising the following steps performed sequentially: S1. Place the silicon carbide polishing sheet in an organic cleaning solution of dewaxing cleaning agent and ultrapure water with a volume ratio of 1:19, and ultrasonically clean it at 60°C for 5 minutes. The cleaning tank is equipped with an up-and-down agitator arm with an agitation frequency of 5 times / min, an agitation stroke of 200mm, and an ultrasonic frequency of 400KHz. After cleaning, rinse with ultrapure water overflow for 8 minutes. S2, place the silicon carbide polished wafer in an oxidation etching solution of hydrogen peroxide, hydrofluoric acid and hydrogen peroxide in a volume ratio of 1:0.02:150, immerse and clean at 30°C for 2 minutes, and after cleaning, rinse with ultrapure water overflow for 8 minutes. S3. Place the silicon carbide polishing wafer in an oxidizing solution of concentrated sulfuric acid and hydrogen peroxide with a volume ratio of 3:1, and clean it at 110°C for 5 minutes. After cleaning, rinse with ultrapure water overflow for 8 minutes. S4. The silicon carbide polished wafer is placed in a composite cleaning solution of hydrogen peroxide, oxalic acid, and ultrapure water with a volume ratio of 1:1.8:13. Pulsed megasonic assisted cleaning is performed at 32°C for 15 minutes. The cleaning tank is equipped with an up-and-down agitator and an ultraviolet irradiation system. The agitation frequency is 5 times / min, the agitation stroke is 200mm, and the ultraviolet irradiation uses a 260nm UV low-pressure mercury lamp with a light intensity of 35mW / cm². 2 The carrier frequency of the pulsed megasonic wave is 1200 kHz, the pulse repetition frequency is 500 kHz, and the power density is 1.0 W / cm². 2 The duty cycle is 50%; after cleaning, rinse with ultrapure water overflow for 5 minutes. S5, the silicon carbide polished wafer is dried in stages using a rotary process: Set the rotation speed of the silicon carbide polishing wafer to 550 rpm and dry it by rotation for 90 seconds; Increase the rotation speed to 850 rpm and rotate to dry for 180 seconds; Reduce the rotation speed to a stop, reset the origin, and the process time is 120 seconds to obtain the cleaned silicon carbide substrate.

[0045] The particle test pattern of the silicon carbide substrate obtained after cleaning in this embodiment is shown below. Figure 2 As shown.

[0046] Example 3 This embodiment provides a pre-cleaning method for silicon carbide polished wafers, comprising the following steps performed sequentially: S1. Place the silicon carbide polishing wafer in an organic cleaning solution of dewaxing cleaning agent and ultrapure water with a volume ratio of 1:20, and ultrasonically clean it at 65°C for 8 minutes. The cleaning tank is equipped with an up-and-down agitator arm with an agitation frequency of 3 times / min, an agitation stroke of 150mm, and an ultrasonic frequency of 600KHz. After cleaning, rinse with ultrapure water overflow for 5 minutes. S2, place the silicon carbide polished wafer in an oxidation etching solution of hydrogen peroxide, hydrofluoric acid and hydrogen peroxide in a volume ratio of 1:0.01:100, immerse and clean at 40°C for 3 minutes, and after cleaning, rinse with ultrapure water overflow for 5 minutes. S3. Place the silicon carbide polishing wafer in an oxidizing solution of concentrated sulfuric acid and hydrogen peroxide with a volume ratio of 7:3, and clean it at 115°C for 8 minutes. After cleaning, rinse with ultrapure water overflow for 5 minutes. S4. The silicon carbide polished wafer is placed in a composite cleaning solution of hydrogen peroxide, oxalic acid, and ultrapure water (volume ratio 1:1:10) and subjected to pulsed megasonic-assisted cleaning at 30°C for 12 minutes. The cleaning tank is equipped with an up-and-down agitator and an ultraviolet irradiation system. The agitation frequency is 3 times / min, the agitation stroke is 150mm, and the ultraviolet irradiation uses a 254nm UV low-pressure mercury lamp with a light intensity of 30mW / cm². 2 The carrier frequency of the pulsed megasonic wave is 1000 kHz, the pulse repetition frequency is 300 kHz, and the power density is 0.8 W / cm². 2 The duty cycle is 40%; after cleaning, rinse with ultrapure water overflow for 5 minutes. S5, the silicon carbide polished wafer is dried in stages using a rotary process: Set the rotation speed of the silicon carbide polishing disc to 450 rpm and dry it by rotation for 100 seconds; Increase the rotation speed to 750 rpm and dry for 250 seconds. Reduce the rotation speed to a stop, reset the origin, and the process time is 100 seconds to obtain the cleaned silicon carbide substrate.

[0047] The particle test pattern of the silicon carbide substrate obtained after cleaning in this embodiment is shown below. Figure 3 As shown.

[0048] Comparative Example 1 This comparative example provides a pre-cleaning method for silicon carbide polished wafers (traditional RCA process), which specifically includes the following steps: Step a: Add the chemically mechanically polished silicon carbide substrate to a mixed solution of wax remover and ultrapure water with a volume ratio of 1:14, heat to 70°C, and ultrasonically clean for 15 minutes at a power of 800 kHz. The cleaning tank is equipped with an up-and-down agitator arm with an agitation frequency of 3 times / min and an agitation stroke of 150 mm. After cleaning, rinse with ultrapure water overflow for 5 minutes. Step b: Place the silicon carbide substrate in a mixed solution of concentrated sulfuric acid and hydrogen peroxide with a volume ratio of 4:1, heat to 120°C, clean for 15 minutes, and rinse with ultrapure water overflow for 5 minutes after cleaning. Step c: Place the silicon carbide substrate in a mixed solution of ammonia, hydrogen peroxide and ultrapure water in a volume ratio of 1:1:5, heat to 70°C and clean with megasonic wave for 15 minutes at a power of 800 kHz. After cleaning, rinse with ultrapure water overflow for 5 minutes. Step d: Place the silicon carbide substrate in a mixed solution of hydrochloric acid, hydrogen peroxide and ultrapure water with a volume ratio of 1:1:5, heat to 70°C and clean with megasonic waves for 10 minutes at a power of 800 kHz. After cleaning, rinse with ultrapure water overflow for 5 minutes. Step e: Place the silicon carbide substrate in a mixed solution of hydrofluoric acid and ultrapure water with a volume ratio of 1:60, immerse it at 30°C for 3 minutes, and rinse it with ultrapure water overflow for 5 minutes after cleaning. Step f: The silicon carbide substrate is dried under nitrogen at 600 rpm for 10 min to obtain the cleaned silicon carbide substrate.

[0049] The particle test pattern of the silicon carbide substrate obtained by this comparative cleaning is shown below. Figure 4 As shown.

[0050] Comparative Example 2 This comparative example provides a pre-cleaning method for silicon carbide polished wafers. The only difference from Example 3 is the omission of oxalic acid in step S4; the remaining steps are exactly the same. The specific steps are as follows: S1~S3 are the same as in Example 3, and will not be described again here; S4. The silicon carbide polishing wafer is placed in a composite cleaning solution of hydrogen peroxide and ultrapure water at a volume ratio of 1:10, and subjected to pulsed megasonic-assisted cleaning at 30°C for 12 minutes. The cleaning tank is equipped with an up-and-down agitator and an ultraviolet irradiation system. The agitation frequency is 3 times / min, the agitation stroke is 150mm, and the ultraviolet irradiation uses a 254nm UV low-pressure mercury lamp with a light intensity of 30mW / cm². 2 The carrier frequency of the pulsed megasonic wave is 1000 kHz, the pulse repetition frequency is 300 kHz, and the power density is 0.8 W / cm². 2 The duty cycle is 40%; after cleaning, rinse with ultrapure water overflow for 5 minutes. S5 is the same as in Example 3, and will not be described again here.

[0051] The particle test pattern of the silicon carbide substrate obtained by this comparative cleaning is shown below. Figure 5 As shown.

[0052] Comparative Example 3 This comparative example provides a pre-cleaning method for silicon carbide polished wafers. The only difference from Example 3 is that there is no ultraviolet light irradiation in S4; the rest are exactly the same. The specific steps are as follows: S1~S3 are the same as in Example 3, and will not be described again here; S4. The silicon carbide polished wafer is placed in a composite cleaning solution of hydrogen peroxide, oxalic acid, and ultrapure water (volume ratio 1:1:10) and subjected to pulsed megasonic assisted cleaning at 30°C for 12 minutes. The cleaning tank is equipped with an up-and-down agitator arm with an agitation frequency of 3 times / min and an agitation stroke of 150mm. The carrier frequency of the pulsed megasonic wave is 1000kHz, the pulse repetition frequency is 300kHz, and the power density is 0.8W / cm². 2 The duty cycle is 40%; after cleaning, rinse with ultrapure water overflow for 5 minutes. S5 is the same as in Example 3, and will not be described again here.

[0053] The particle test pattern of the silicon carbide substrate obtained by this comparative cleaning is shown below. Figure 6 As shown.

[0054] Comparative Example 4 This comparative example provides a pre-cleaning method for silicon carbide polished wafers. The only difference from Example 3 is that oxalic acid in S4 is replaced with citric acid; the rest are exactly the same. The specific steps are as follows: S1~S3 are the same as in Example 3, and will not be described again here; S4. The silicon carbide polished wafer is placed in a composite cleaning solution of hydrogen peroxide, citric acid, and ultrapure water (volume ratio 1:1:10) and subjected to pulsed megasonic-assisted cleaning at 30°C for 12 minutes. The cleaning tank is equipped with an up-and-down agitator and an ultraviolet irradiation system. The agitation frequency is 3 times / min, the agitation stroke is 150mm, and the ultraviolet irradiation uses a 254nm UV low-pressure mercury lamp with a light intensity of 30mW / cm². 2 The carrier frequency of the pulsed megasonic wave is 1000 kHz, the pulse repetition frequency is 300 kHz, and the power density is 0.8 W / cm². 2 The duty cycle is 40%; after cleaning, rinse with ultrapure water overflow for 5 minutes. S5 is the same as in Example 3, and will not be described again here.

[0055] The particle test pattern of the silicon carbide substrate obtained by this comparative cleaning is shown below. Figure 7 As shown.

[0056] Comparative Example 5 This comparative example provides a pre-cleaning method for silicon carbide polished wafers. The only difference from Example 3 is that the proportion of oxalic acid in the S4 composite cleaning solution is increased; otherwise, the methods are identical. The specific steps are as follows: S1~S3 are the same as in Example 3, and will not be described again here; S4. The silicon carbide polished wafer is placed in a composite cleaning solution of hydrogen peroxide, oxalic acid, and ultrapure water with a volume ratio of 1:3:9. It is then subjected to pulsed megasonic-assisted cleaning at 30°C for 12 minutes. The cleaning tank is equipped with an up-and-down agitator and an ultraviolet (UV) irradiation system. The agitation frequency is 3 times / min, and the agitation stroke is 150mm. The UV irradiation uses a 254nm UV low-pressure mercury lamp with a light intensity of 30mW / cm². 2 The carrier frequency of the pulsed megasonic wave is 1000 kHz, the pulse repetition frequency is 300 kHz, and the power density is 0.8 W / cm². 2 The duty cycle is 40%; after cleaning, rinse with ultrapure water overflow for 5 minutes. S5 is the same as in Example 3, and will not be described again here.

[0057] The particle test pattern of the silicon carbide substrate obtained by this comparative cleaning is shown below. Figure 8 As shown.

[0058] The silicon carbide substrates of Examples 1 to 3 and Comparative Examples 1 to 5 were pre-cleaned and then terminally cleaned according to conventional terminal cleaning processes. The metal ion residue, roughness, number of particles ≥0.1μm and average contact angle of the cleaned silicon carbide surface are shown in Table 1.

[0059] The specific steps of a traditional terminal cleaning process are as follows: Step 1: Place the pre-cleaned silicon carbide substrate in a mixed solution of concentrated sulfuric acid and hydrogen peroxide with a volume ratio of 4:1, clean it at 120°C for 15 minutes, and then rinse it with ultrapure water for 5 minutes after cleaning. Step 2: Place the silicon carbide at the bottom in a mixed solution of ammonia, hydrogen peroxide and ultrapure water with a volume ratio of 1:2:7, and clean it at 70℃ for 12 minutes. The cleaning tank contains megasonic waves with a fluctuation frequency of 1MHz and a power density of 0.9W / cm². After cleaning, rinse with ultrapure water for 5 minutes. Step 3: Place the silicon carbide substrate in a mixed solution of hydrochloric acid, hydrogen peroxide and ultrapure water with a volume ratio of 1:1:6, and clean it at 70°C for 12 minutes. After cleaning, rinse with ultrapure water for 5 minutes. Step 4: Place the silicon carbide substrate in a mixed solution of hydrofluoric acid and ultrapure water with a volume ratio of 1:40, immerse and clean at room temperature for 10 minutes, rinse with ultrapure water for 5 minutes after cleaning, and then rinse with ultrapure water overflow for 3 minutes. Step 5: Purge the silicon carbide substrate with strong hot nitrogen gas at a speed of 600 rpm for 600 s, with a nitrogen flow rate of 100 mL / min and a nitrogen temperature of 50 ℃. Then reset the silicon carbide substrate to its origin for 30 s.

[0060] Table 1

[0061] To demonstrate the significant advantages of the pre-cleaning process of this invention, silicon carbide polished wafers of the same specifications were pre-cleaned using Example 1 and Comparative Example 1 (traditional RCA pre-cleaning), respectively. Subsequently, both were subjected to final cleaning under the same conditions but with a significantly shortened process time. The specific final cleaning process is as follows (shortened final cleaning process): Step 1: Place the pre-cleaned silicon carbide substrate in a mixed solution of concentrated sulfuric acid and hydrogen peroxide with a volume ratio of 4:1, clean it at 120°C for 10 minutes, and rinse it with ultrapure water for 5 minutes after cleaning. Step 2: Place the silicon carbide at the bottom in a mixed solution of ammonia, hydrogen peroxide and ultrapure water with a volume ratio of 1:2:7, and clean it at 70℃ for 8 minutes. The cleaning tank contains megasonic waves with a fluctuation frequency of 1MHz and a power density of 0.9W / cm². After cleaning, rinse with ultrapure water for 5 minutes. Step 3: Place the silicon carbide substrate in a mixed solution of hydrochloric acid, hydrogen peroxide and ultrapure water with a volume ratio of 1:1:6, clean it at 70°C for 8 minutes, and rinse it with ultrapure water for 5 minutes after cleaning. Step 4: Place the silicon carbide substrate in a mixed solution of hydrofluoric acid and ultrapure water with a volume ratio of 1:40, immerse and clean at room temperature for 5 minutes, rinse with ultrapure water for 5 minutes after cleaning, and then rinse with ultrapure water overflow for 3 minutes. Step 5: Purge the silicon carbide substrate with strong hot nitrogen gas at a speed of 600 rpm for 600 s, with a nitrogen flow rate of 100 mL / min and a nitrogen temperature of 50 ℃. Then reset the silicon carbide substrate to its origin for 30 s.

[0062] The number of particles with a surface diameter ≥ 0.1 μm, residual metal ions, and surface roughness of the cleaned silicon carbide substrate are shown in Table 2.

[0063] Example 1: Particle cleaning effect after using shortened terminal process as shown in Example 1 Figure 9 As shown, the particle effect after cleaning using the shortened terminal process in Comparative Example 1 is as follows: Figure 10 As shown.

[0064] Table 2

[0065] The results show that, under conditions where the subsequent terminal cleaning time is significantly shortened, the substrate pre-cleaned by the method of this invention maintains excellent and stable key indicators such as surface particle number, residual metal ion content, and surface roughness, comparable to the effect after traditional full-process terminal cleaning. In contrast, the substrate of Comparative Example 1, pre-cleaned by traditional RCA, shows a significant increase in surface particle number (up to 25.99%) and metal ion concentration (up to 34.96%) after the same short-time terminal cleaning, and a certain degree of increase in surface roughness (Ra).

[0066] This comparison demonstrates that the pre-cleaning process provided by the present invention can remove contaminants more thoroughly from the source, which not only significantly reduces the process load of subsequent terminal cleaning and improves the overall efficiency, but more importantly, ensures that the substrate has a higher level of cleanliness and flatness before entering the terminal, thereby providing a reliable guarantee for subsequent high-quality epitaxial growth. It has outstanding advantages in improving the yield and performance consistency of silicon carbide device fabrication.

[0067] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A pre-cleaning method for silicon carbide polished wafers, characterized in that, This includes the following steps performed sequentially: S1, the silicon carbide polished wafer is placed in an organic cleaning solution for the first cleaning; S2, the silicon carbide polished wafer after S1 is placed in an oxidation etching solution of hydrogen peroxide, hydrofluoric acid and ultrapure water for a second cleaning. S3, the silicon carbide polished wafer after S2 cleaning is placed in an oxidizing solution of concentrated sulfuric acid and hydrogen peroxide for a third cleaning; S4, the silicon carbide polished wafer cleaned in S3 is placed in a composite cleaning solution, and ultraviolet light and pulsed megasonic waves are applied simultaneously for the fourth cleaning. After drying, the cleaned silicon carbide substrate is obtained. The composite cleaning solution is a mixed solution of hydrogen peroxide, oxalic acid and ultrapure water in a volume ratio of 1:(0.8~1.8):(9~13), with a pH of 4.5~5.

5.

2. The pre-cleaning method for silicon carbide polished wafers as described in claim 1, characterized in that, In S1, the organic cleaning solution is a mixed solution of a dewaxing cleaning agent and ultrapure water with a volume ratio of 1:19 to 1:24; and / or In S1, the temperature of the first cleaning is 60℃~70℃, and the cleaning time is 5min~10min.

3. The pre-cleaning method for silicon carbide polished wafers as described in claim 1 or 2, characterized in that, In S1, the first cleaning is carried out in a cleaning tank equipped with a shoveling mechanism and an ultrasonic device. The shoveling mechanism drives the silicon carbide polishing sheet to shove periodically in the organic cleaning liquid. The shoveling frequency is 2 to 5 times / min and the shoveling stroke is 100 mm to 200 mm. The ultrasonic device generates an ultrasonic frequency of 400 kHz to 800 kHz.

4. The pre-cleaning method for silicon carbide polished wafers as described in claim 3, characterized in that, In S1, the silicon carbide polishing sheet remains completely submerged below the surface of the organic cleaning liquid throughout the entire polishing stroke.

5. The pre-cleaning method for silicon carbide polished wafers as described in claim 1, characterized in that, In S2, the volume ratio of hydrogen peroxide, hydrofluoric acid, and ultrapure water is 1:(0.005~0.02):(50~150).

6. The pre-cleaning method for silicon carbide polished wafers as described in claim 1, characterized in that, In S2, the temperature of the second cleaning is 30℃~50℃, and the cleaning time is 2min~5min.

7. The pre-cleaning method for silicon carbide polished wafers as described in claim 1, characterized in that, In S3, the volume ratio of concentrated sulfuric acid to hydrogen peroxide is 13:7 to 3:1; and / or In S3, the cleaning temperature of the third cleaning is 110℃~120℃, and the cleaning time is 5min~10min.

8. The pre-cleaning method for silicon carbide polished wafers as described in claim 1, characterized in that, In S4, the temperature of the fourth cleaning is 28℃~32℃, and the cleaning time is 8min~15min; and / or In S4, the wavelength of the ultraviolet light irradiation is 250nm~260nm, and the light intensity is 25mW / cm². 2 ~35mW / cm 2 The carrier frequency of the pulsed megasonic wave is 800 kHz to 1200 kHz, the pulse repetition frequency is 100 kHz to 500 kHz, and the power density is 0.5 W / cm². 2 ~1.0W / cm 2 The duty cycle is 20% to 50%.

9. The pre-cleaning method for silicon carbide polished wafers as described in claim 1 or 8, characterized in that, In S4, the fourth cleaning is carried out in a cleaning tank equipped with a shredding mechanism. The shredding mechanism drives the silicon carbide polishing sheet to shred periodically in the organic cleaning liquid. The shredding frequency is 2 to 5 times / min, and the shredding stroke is 100 mm to 200 mm. Throughout the entire shredding stroke, the silicon carbide polishing sheet remains completely submerged below the surface of the organic cleaning liquid.

10. The pre-cleaning method for silicon carbide polished wafers as described in claim 1, characterized in that, In step S4, the drying process employs a staged rotary drying method, specifically including the following steps: Control the rotation speed of the silicon carbide polishing wafer to 350rpm~550rpm and spin dry for 90s~120s; then increase the rotation speed to 550rpm~850rpm and spin dry for 180s~360s; then reduce the speed until the rotation stops to obtain the cleaned silicon carbide substrate.

Images