A composite polishing pad for SiC wafer CMP and its preparation and use method

Abstract

The application relates to the field of semiconductor material processing, and discloses a composite grinding disc for SiC wafer CMP and a preparation and use method thereof. The composite grinding disc comprises a base disc and a grit area arranged on the base disc, the grit area is spliced by at least one CeO2 grit disc and at least one GO grit disc, the total area ratio of the CeO2 grit disc to the GO grit disc is 2:1-4:1, the surface of the grit area is provided with grooves, the groove density is 0.28-0.32, the CeO2 grit disc is composed of CeO2 grits and a bonding agent in a weight ratio of 0.8:1-1.2:1, and the GO grit disc is composed of GO grits and a bonding agent in a weight ratio of 1:7-1:10. Through the innovative design of the component ratio and the structure, the four advantages of high material removal rate (MRR up to 448.3 nm / h), low surface roughness (Sa down to 0.35 nm), low subsurface damage (SSD down to 2.3 nm) and good process cleanness are realized, and the technical problem that high efficiency and high quality processing cannot be considered in the SiC wafer polishing field is solved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor material processing technology, and more specifically, to a composite polishing disk for SiC wafer CMP and its preparation and use methods. Background Technology

[0002] With the development of third-generation semiconductors, SiC wafers, with their advantages of large bandgap, high electron mobility, high breakdown electric field, and high thermal conductivity, are widely used in electric vehicles, 5G communications, and other fields, becoming one of the most promising semiconductor materials. However, SiC wafers are a hard and brittle material with high brittleness and low fracture toughness. They also have high hardness (Mohs hardness 9.2) and strong chemical inertness. Traditional chemical mechanical polishing (CMP) still suffers from low material removal rate and easy surface damage. Therefore, achieving high-efficiency and planarized ultra-precision machining of SiC wafers is extremely difficult.

[0003] Polishing with a grinding disc can achieve planarization of SiC wafers. However, during the sintering of the grinding disc, the distribution of abrasive grains exhibits considerable randomness, resulting in uneven material removal from the workpiece surface, which affects the quality of the polishing process. While some in the art have proposed techniques using fixed-grain grinding discs, most employ a single abrasive grain (such as diamond or CeO2). Diamond discs, although exhibiting high material removal rate (MRR), are prone to scratches and deep subsurface damage (SSD), while CeO2 discs suffer from low efficiency due to insufficient mechanical removal capacity. Some patents have also proposed using free abrasive grains, where GO is added to the polishing slurry to generate a SiO2 passivation layer using the oxygen-containing functional groups of GO. However, this method results in a low MRR, significant passivation layer residue, and complex subsequent processing.

[0004] Furthermore, the groove structure on the surface of the grinding disc is crucial for slurry delivery, grinding heat dissipation, and chip removal. If the groove density is too low, the slurry distribution will be uneven, leading to chip accumulation and scratches; if it is too high, the effective grinding area will decrease, and the grinding radius (MRR) will drop. Existing grinding disc groove designs are mostly based on empirical selection, lacking synergistic optimization with the abrasive grain structure.

[0005] Therefore, there is an urgent need to provide a polishing pad and its process method for SiC wafer CMP that can simultaneously achieve high material removal rate, low surface roughness, low subsurface damage and good process cleanliness, so as to break through the technical bottleneck of "efficiency and quality being difficult to balance" in SiC wafer polishing. Summary of the Invention

[0006] To address at least one of the aforementioned problems, this invention provides a composite polishing disc for SiC wafer CMP and its preparation and application method. This invention involves mixing cerium dioxide (CeO2) powder and graphene oxide (GO) powder with a binder to form an abrasive disc, then assembling the disc according to a specific area ratio to prepare a composite polishing disc. Concentric spiral grooves are designed on the composite polishing disc to achieve efficient synergy between chemical softening and mechanical removal.

[0007] In a first aspect, the present invention provides a composite polishing disk for CMP of SiC wafers, comprising a base disk and an abrasive region disposed on the base disk, wherein the abrasive region is composed of at least one CeO2 abrasive disk and at least one GO abrasive disk spliced ​​together, the ratio of the total area of ​​the CeO2 abrasive disk to the total area of ​​the GO abrasive disk being 2:1 to 4:1; the surface of the abrasive region is provided with grooves, the groove density being 0.28 to 0.32; the CeO2 abrasive disk is composed of CeO2 abrasive particles and a binder mixed in a weight ratio of 0.8:1 to 1.2:1, and the GO abrasive disk is composed of GO abrasive particles and a binder mixed in a weight ratio of 1:7 to 1:10.

[0008] Optionally, the groove has a concentric spiral pattern; the groove density is 0.29~0.31.

[0009] Optionally, the Raman spectral defect ratio of the GO abrasive grains is ID / IG ≥ 1.26.

[0010] Optionally, the particle size D50 of the CeO2 abrasive is 1.2~1.8μm; the particle size D50 of the GO abrasive is 7~10μm.

[0011] Optionally, the adhesive is one or more of resin binders, ceramic binders, or metal binders.

[0012] Secondly, the present invention provides a method for preparing a composite polishing disk for SiC wafer CMP, comprising the following steps:

[0013] Preparation of GO abrasive particles: Expanded graphite was oxidized using the modified Hummers method. After centrifugation, washing, and drying, the graphite was ultrasonically treated for 5-15 minutes and then pulverized and sieved to obtain GO abrasive particles with uniform particle size.

[0014] Preparation of GO abrasive discs: The prepared GO abrasives and binder are mixed evenly at a weight ratio of 1:7 to 1:10, injected into a mold, cured and shaped, and then removed to obtain GO abrasive discs;

[0015] Preparation of CeO2 abrasive disc: CeO2 abrasive particles and binder are mixed evenly at a weight ratio of 0.8:1 to 1.2:1, injected into a mold, cured and shaped, and then removed to obtain CeO2 abrasive disc;

[0016] Assembly: The CeO2 abrasive disc and the GO abrasive disc are bonded and fixed to the base disc at an area ratio of 2:1 to 4:1 to obtain the first grinding disc;

[0017] Post-processing: Place the first grinding disc on a processing device and process concentric spiral grooves on the surface of the first grinding disc. When the groove density reaches 0.28~0.32, stop processing to obtain a composite grinding disc.

[0018] Optionally, the curing of the GO abrasive disc and the CeO2 abrasive disc adopts a two-step curing method: first, it is left to stand at room temperature for 24 h, and then cured at 50-80 ℃ for 1-3 h; the GO abrasive and the CeO2 abrasive are pre-stirred before being mixed with the adhesive, and the stirring time is 15-40 min.

[0019] Compared with the prior art, the composite grinding disc of the present invention has at least the following beneficial effects:

[0020] 1. This invention optimizes the abrasive composition ratio and surface structure of the grinding disk, enabling CeO2 abrasives to selectively remove the passivation layer. It utilizes GO oxygen-containing functional groups to generate a CeO2 chemical passivation layer in situ, effectively suppressing subsurface damage on the SiC surface. At the same time, it achieves the triple advantages of high material removal rate, low surface roughness, and low subsurface damage, completely solving the technical problem of the inability to achieve both high efficiency and high quality processing in the field of SiC wafer polishing.

[0021] 2. The present invention adopts a fixed abrasive type grinding disc structure, which is more environmentally friendly and requires less subsequent waste liquid treatment compared with the traditional free abrasive type grinding disc. It eliminates the process pollution risk caused by free abrasive from the structure and improves the controllability and environmental protection of the processing process.

[0022] 3. The grinding disc of the present invention has a simple manufacturing process, requires no additional equipment, is easy to use and has a wide range of applications. It can be used for multiple purposes, is inexpensive, and is easy to use in batches.

[0023] Thirdly, the present invention provides a method for using a composite polishing disc, wherein the composite polishing disc is installed on a dual-plane polishing machine, the polishing speed is set to 50~90 rpm, the polishing pressure is set to 35~60 psi, and the polishing time is set to 40~60 min; and the SiC wafer is polished by introducing a prepared polishing fluid into the grooves on the surface of the polishing disc.

[0024] Optionally, the grinding fluid includes grinding powder, dispersant, and solvent; the grinding powder has a weight percentage of 0.2~0.4wt% and a particle size of 0.4~0.6μm; the weight ratio of the dispersant to the grinding powder is 5:1; the dispersant is a nonionic water-soluble polymer selected from at least one of polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), polyethylene glycol (PEG), or hydroxypropyl methylcellulose (HPMC); and the solvent is deionized water.

[0025] Optionally, the pH of the grinding slurry is 4-9; the temperature of the grinding slurry is 30-50°C.

[0026] Compared with the prior art, the method for preparing and using the composite grinding disc of the present invention has the same advantages as the grinding discs described above, and will not be repeated here. Attached Figure Description

[0027] Figure 1 This is a top view of the composite grinding disc of the present invention;

[0028] Figure 2 This is a schematic diagram of a partial cross-section of the grooves of the composite grinding disc of the present invention;

[0029] Figure 3 This is a flowchart illustrating the manufacturing process of the composite grinding disc of the present invention.

[0030] Reference numerals: 1. GO abrasive disc; 2. CeO2 abrasive disc; 3. Base disc; 31. Groove. Detailed Implementation

[0031] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0032] See Figure 1 and Figure 2This application provides a composite polishing disk for SiC wafer CMP, including a base disk 3 and an abrasive region disposed on the base disk 3. The abrasive region is composed of at least one CeO2 abrasive disk 2 and at least one GO abrasive disk 1 spliced ​​together. The ratio of the total area of ​​the CeO2 abrasive disk 2 to the total area of ​​the GO abrasive disk 1 is 2:1 to 4:1. The surface of the abrasive region is provided with grooves 31, and the groove density is 0.28 to 0.32. The CeO2 abrasive disk 2 is composed of CeO2 abrasive particles and binder mixed in a weight ratio of 0.8:1 to 1.2:1, and the GO abrasive disk 1 is composed of GO abrasive particles and binder mixed in a weight ratio of 1:7 to 1:10. In this embodiment, a single CeO2 abrasive disc 2 and a single GO abrasive disc 1 are manufactured using the same mold. The abrasive zone is composed of six identical CeO2 abrasive discs 2 and two identical GO abrasive discs 1 joined together, with an area ratio of CeO2 abrasive discs 2 to GO abrasive discs 1 of 3:1. The two GO abrasive discs 1 are symmetrically arranged at 180° on the base disc 3 to ensure that the chemical softening effect is evenly distributed along the circumferential direction during polishing. The base disc 3 is made of stainless steel. In this embodiment, the grooves 31 are concentric spiral grooves with a groove density of 0.28~0.32. The concentric spiral grooves 31 ensure that the polishing fluid forms a uniform and continuous liquid film on the disc surface and transports and discharges grinding debris along the spiral path, avoiding secondary scratches. Within the above groove density range, the effective coverage of the polishing fluid on the surface of the grinding disc can reach 40~45%, and a stable liquid film thickness can be maintained within a wide speed range (50~90 rpm), ensuring both sufficient chemical reaction contact and sufficient effective mechanical grinding area. When the groove density is below 0.28, insufficient liquid film coverage and poor chip removal easily lead to scratches. When the groove density is above 0.32, the effective grinding area is too small, and the material removal rate decreases significantly. In this application, the groove density is defined as the ratio of the groove width to the groove pitch, and can be expressed by the following formula:

[0033] (Equation 1)

[0034] In the formula, ρ is the groove density, W is the groove width (mm), and P is the pitch between adjacent grooves. When W=1mm and P=3.3mm, ρ=1 / 3.3≈0.303, which is the preferred groove density in this application. The concentric spiral structure, compared to grid-like or radial grooves, ensures continuous radial delivery and uniform distribution of the polishing fluid on the disk surface, while also facilitating chip discharge along the spiral path and preventing localized accumulation.

[0035] Specifically, the weight ratio of GO abrasive to binder is 1:7 to 1:10. As an example, the weight ratio of GO abrasive to binder can be any of 1:7, 1:8, 1:9, or 1:10, or any ratio between the two. The high binder content in the CeO2 abrasive disk in this application gives the disk surface appropriate elasticity and adaptability, enabling it to better conform to the micro-contours of the workpiece surface. After abrasive grains detach, the binder can promptly "replenish" the exposed new abrasive grains, which is beneficial for achieving sub-nanometer surface quality. The weight ratio of CeO2 abrasive to binder is 0.8:1 to 1.2:1. As an example, the weight ratio of CeO2 abrasive to binder can be any of 0.8:1, 0.9:1, 1:1, or 1.2:1, or any ratio between the two. GO abrasive grains and the binder form a dense two-dimensional barrier structure, effectively blocking the transfer of water molecules and heat. Simultaneously, the high thermal stability of GO itself inhibits the softening and decomposition of the binder at high temperatures, allowing the grinding disc to maintain high bonding strength even under wet grinding conditions. The binder is at least one of resin, ceramic, or metal binders. In this application, epoxy resin is selected as the binder. After curing, epoxy resin exhibits excellent wear resistance, chemical stability, and bonding strength, enabling it to stably hold the abrasive grains.

[0036] Specifically, the particle size D50 of CeO2 abrasive grains is 1.2~1.8μm; the particle size D50 of GO abrasive grains is 7~10μm. This grinding disc adopts a coarse and fine particle size gradation technology. The coarse particle size is used for efficient removal, and the fine particle size is used for surface finishing. The synergistic effect of the two different particle sizes gives the grinding disc the advantages of high processing efficiency and low surface scratches.

[0037] See Figure 3 This application provides a method for preparing a composite grinding disc, comprising the following steps:

[0038] Preparation of GO abrasive particles: Expanded graphite was oxidized using the modified Hummers method. After centrifugation, washing, and drying, it was treated with high-power ultrasound for 5-15 minutes, then pulverized and sieved to obtain GO abrasive particles with a particle size D50 of 7-10 μm. High-power ultrasound treatment can reduce the particle size of GO abrasive particles and increase the uniformity of powder size, resulting in more uniform dispersion.

[0039] Preparation of GO abrasive discs: The prepared GO abrasives and binder are mixed evenly at a weight ratio of 1:7 to 1:10, injected into a mold, cured and shaped, and then removed to obtain GO abrasive discs;

[0040] Preparation of CeO2 abrasive disc: CeO2 abrasive particles and binder are mixed evenly at a weight ratio of 0.8:1 to 1.2:1, injected into a mold, cured and shaped, and then removed to obtain CeO2 abrasive disc;

[0041] Assembly: The CeO2 abrasive disk and the GO abrasive disk are bonded and fixed on the base disk at an area ratio of 2:1 to 4:1 to obtain the first grinding disk; the contact area of ​​the GO abrasive disk in the first grinding disk is smaller to avoid excessive oxidation of the SiC surface and resulting in an excessively thick passivation layer;

[0042] Post-processing: The first grinding disc is placed on a processing device, and concentric spiral grooves are machined on the surface of the first grinding disc. When the groove density reaches 0.28~0.32, processing is stopped, and the composite grinding disc is obtained. In this application, the composite grinding disc reacts better with the silicon carbide passivation layer. Therefore, reducing the GO disc surface area results in a moderate amount of passivation layer formation, and using CeO2 with lower hardness as the disc material reduces damage to the deep silicon carbide.

[0043] Specifically, the GO abrasive grain ID / IG ratio is ≥1.26. After treatment, the GO in this application exhibits significantly improved defect density and oxygen-containing functional group content. The increased oxygen-containing functional groups endow GO with good hydrophilicity, ensuring uniform dispersion without agglomeration in the binder. The defect edges mechanically anchor to the binder, resulting in significantly improved abrasive grain retention compared to untreated GO, and a longer grinding disc lifespan. The curing temperature for both GO and CeO2 abrasive discs is 50–80℃, and the curing time is 1–3 hours. Both GO and CeO2 abrasive grains are pre-stirred before mixing with the binder for 15–40 minutes. This application employs a two-step curing process: standing at room temperature for 24 hours followed by curing at 60°C for 2 hours. This two-step process balances the dispersibility of the abrasive particles and the complete cross-linking between the abrasive particles and the binder. At room temperature, the low viscosity allows the GO and CeO2 abrasive particles to be evenly distributed and their internal stress to be fully released. After curing at 60°C, the binder is fully cross-linked, ensuring that the grinding disc does not produce microcracks under wet grinding and high-temperature conditions. The abrasive particle shedding rate is significantly reduced compared to traditional curing methods.

[0044] This application also provides a method for using the aforementioned composite polishing disc. The specific steps involve installing the composite polishing disc on a dual-plane polishing machine, setting the polishing speed to 50-90 rpm, the polishing pressure to 35-60 psi, and the polishing time to 40-60 min. The SiC wafer is polished by introducing a prepared polishing slurry into the grooves on the disc surface. By setting appropriate parameter ranges, groove density, and abrasive grain size, this application avoids the problems of scratch deepening caused by high speed and subsurface damage caused by high pressure. The continuous introduction of polishing slurry into the grooves allows it to fully penetrate the grinding zone, reducing the temperature and effectively suppressing thermal damage to the SiC wafer. The polishing time of 40-60 min ensures both the removal volume and surface roughness stability. Before operation, a diamond dressing ring is used to dress the disc surface to reduce height differences and increase flatness.

[0045] Specifically, the polishing slurry includes polishing powder, dispersant, and solvent. The pH of the slurry is 4-9, a weakly acidic to weakly alkaline environment chemically compatible with the SiC wafer surface, facilitating synergistic chemical and mechanical removal and improving material removal rate. The slurry temperature is 30-50℃, the polishing powder weight percentage is 0.2-0.4 wt%, and the dispersant-to-polishing powder weight ratio is 5:1. The dispersant is a non-ionic, water-soluble polymer selected from at least one of polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), polyethylene glycol (PEG), or hydroxypropyl methylcellulose (HPMC), and the solvent is deionized water. The polishing powder weight percentage is controlled within the range of 0.2-0.4 wt%, ensuring sufficient cutting power while avoiding excessive abrasive accumulation that could deepen scratches. The non-ionic dispersant forms a steric hindrance layer on the polishing powder surface, ensuring uniform dispersion of the polishing powder in the slurry without agglomeration, thus preventing surface scratches caused by localized abrasive particle aggregation.

[0046] The synergistic mechanism of this invention is as follows: When the composite polishing disk rotates, the CeO2 abrasive region and the GO abrasive region periodically and alternately contact the same area of ​​the SiC wafer. The GO abrasive region, through its oxygen-containing functional groups, undergoes an interfacial reaction with the SiC surface, catalyzing the formation of a soft SiO2 passivation layer; the CeO2 abrasive region that follows it then undergoes an interfacial reaction with the SiC surface through CeO2 abrasive particles. 4+ / Ce 3+ The valence state change of GO catalyzes the oxidation of the SiC surface, while its micron-sized particles efficiently remove the softened layer mechanically. This serial cyclic mechanism of "GO softening—CeO2 removal" can be characterized by the following simplified reaction:

[0047] (Equation 2)

[0048] (Equation 3)

[0049] This application elaborates on relevant performance parameters, such as material removal rate (MRR), through examples and comparative examples. h (nm / hr), surface roughness Sa (nm), and subsurface damage SSD (nm). All reagents used in the embodiments of this application are commercially available analytical grade, and the instruments, equipment, and testing methods used are as follows:

[0050] (1) Particle size test: The particle size was measured using a Malvern Mastersizer 3000 laser particle size analyzer;

[0051] (2) Raman spectroscopy: A Horiba LabRAM HR Evolution Raman spectrometer was used with an excitation wavelength of 532 nm to measure the ID / IG ratio of GO. ID is the intensity of the D peak and IG is the intensity of the G peak.

[0052] (3) Material Removal Rate (MRR): The difference in wafer thickness Δh before and after polishing was measured using a CCI-Lite white light interferometer and calculated using the following formula:

[0053] (Equation 4)

[0054] In the formula, Δh is the thickness change (nm) and t is the polishing time (h).

[0055] (4) Surface roughness Sa: The average value was obtained from 5 random areas using a Zygo NewView 9000 optical profilometer;

[0056] (5) Subsurface damage (SSD): The thickness of the damage layer was observed using a Mueller matrix spectroscopy combined with cross-sectional TEM.

[0057] Example 1

[0058] This embodiment includes the following steps:

[0059] Preparation of GO abrasive particles: Place 5g of expanded graphite in a three-necked flask, and slowly add 120mL of concentrated sulfuric acid and 30mL of concentrated phosphoric acid at a solid-liquid ratio of 1:24g / mL under ice bath conditions; after stirring for 5-15min, add 15g of potassium permanganate in batches, strictly controlling the temperature to ≤5℃; then raise the temperature to 50℃ and react for 12h; slowly add deionized water to dilute to twice the original amount of acid added, controlling the temperature to ≤90℃; after cooling, add 30wt% hydrogen peroxide until the system turns bright yellow to terminate the reaction. The resulting suspension was centrifuged at 10,000 rpm for 15 min, washed three times with 5 wt% dilute hydrochloric acid, and washed with deionized water until pH=6. It was then vacuum dried at 80℃ for 25 h. The dried powder was dispersed in deionized water and treated in an ultrasonic instrument with a power of 1000 W, a frequency of 40 kHz, and an ice bath temperature of <30℃ for 15 min. The treated liquid was freeze-dried to obtain GO powder, which was then passed through a 200-400 mesh sieve to obtain GO abrasive particles with a particle size D50 of 10 μm and ID / IG=1.31.

[0060] Preparation of GO abrasive discs: The above-mentioned GO abrasives and E-44 type bisphenol A epoxy resin were mixed at a weight ratio of 1:8, and 5 wt% polyamide relative to the weight of E-44 type bisphenol A epoxy resin was added; the mixture was pre-stirred at 50°C for 30 min using a ceramic heated magnetic stirrer; the mixture was poured into a fan-shaped mold with a central angle of 45°, and allowed to stand at room temperature for 24 h to allow the resin to initially crosslink, and then transferred to a forced-air drying oven at 60°C for 2 h to cure, and then cooled and demolded to obtain GO abrasive discs;

[0061] Preparation of CeO2 abrasive discs: CeO2 abrasive particles with a particle size D50 of 1.8 μm were mixed with E-44 type bisphenol A epoxy resin at a weight ratio of 1.2:1. Then, 5 wt% polyamide relative to the weight of E-44 type bisphenol A epoxy resin was added. The mixture was pre-stirred at 50°C for 30 min using a ceramic heated magnetic stirrer. The mixture was then poured into a fan-shaped mold of the same specifications as in step 2. The mixture was first allowed to stand at room temperature for 24 h to allow the E-44 type bisphenol A epoxy resin to undergo preliminary cross-linking. Then, it was transferred to a forced-air drying oven and cured at 60°C for 2 h. After cooling and demolding, the CeO2 abrasive discs were obtained.

[0062] Assembly: The prepared CeO2 abrasive disc and GO abrasive disc are alternately and symmetrically spliced ​​at an area ratio of 2:1. The GO abrasive area is adjusted to be evenly and symmetrically distributed in the circumferential direction. It is then bonded and fixed to a stainless steel base disc with a diameter of 240mm using two-component polyurethane adhesive. After curing at room temperature for 24 hours, the first grinding disc is obtained.

[0063] Post-processing: The first grinding disc is placed on a CNC grooving machine and a diamond forming wheel is used to machine concentric spiral grooves with a pitch P=3.3mm and a width W=1mm. The groove depth is 1.5mm. After machining, the groove density ρ≈0.303 is measured, and machining is stopped. Finally, a diamond dressing ring is used to dress the disc surface to eliminate unevenness, thus obtaining the finished composite grinding disc.

[0064] Preparation of grinding slurry: CeO2 powder with a particle size D50 of 0.5μm was selected as the grinding powder, and PVP was selected as the dispersant. The weight percentage of CeO2 in the grinding powder was 0.4wt%, and the weight percentage of PVP was 2wt%. First, PVP and deionized water were mixed evenly, and then the CeO2 powder was added and stirred evenly. HNO3 or NaOH was added to precisely adjust the pH to 4. After preparation, the mixture was placed in a magnetic heating stirrer and stirred for 1 hour. The temperature of the grinding slurry was 30℃. After stirring, it was allowed to stand for 30 minutes to confirm that there was no obvious sedimentation before subsequent use.

[0065] Polishing: In this embodiment, SiC wafers were used as test pieces. The prepared composite polishing pad was mounted on a dual-plane polishing machine, with the pad surface in contact with the SiC wafer (4-inch 4H-SiC, Si surface). The polishing speed was set to 90 rpm, the polishing pressure to 36 psi, and the polishing time to 50 min. The SiC wafer was polished by introducing the prepared polishing slurry into the grooves on the surface of the polishing pad at a flow rate of 50 mL / min.

[0066] In this embodiment, the SiC wafer material removal rate was measured using a CCI-Lite white light interferometer, the surface roughness Sa was measured using a Zygo NewView 9000 optical profilometer, and the subsurface damage (SSD) was evaluated using a Mueller matrix ellipsometer. Specific test data are shown in Table 1.

[0067] Example 2

[0068] This embodiment includes the following steps:

[0069] Preparation of GO abrasive particles: The same preparation method as in Example 1 was used, except that the particle size D50 of the GO abrasive particles was 8 μm.

[0070] Preparation of GO abrasive discs: The same preparation method as in Example 1 was used, except that GO abrasives and E-44 type bisphenol A epoxy resin were mixed at a weight ratio of 1:9.

[0071] Preparation of CeO2 abrasive disc: The same preparation method as in Example 1 was used, except that the particle size D50 of CeO2 abrasive was 1.5 μm, and CeO2 abrasive was mixed with E-44 type bisphenol A epoxy resin at a weight ratio of 1:1.

[0072] Assembly: The same assembly method as in Example 1 is used, except that the ratio of the total area of ​​CeO2 abrasive disk to the total area of ​​GO abrasive disk is 3:1;

[0073] Post-processing: The composite grinding disc was obtained using the processing method described in Example 1;

[0074] Preparation of the polishing slurry: The same preparation method as in Example 1 was used, except that the particle size D50 of the polishing powder CeO2 was 0.5 μm, the weight percentage of polishing powder CeO2 was 0.4 wt%, and the weight percentage of PVP was 2 wt%.

[0075] Polishing: The same test piece and polishing steps as in Example 1 were used, except that the grinding speed was 90 rpm and the grinding pressure was 44 psi.

[0076] The SiC wafer was tested using the same equipment as in Example 1. The specific data are shown in Table 1.

[0077] Example 3

[0078] This embodiment includes the following steps:

[0079] Preparation of GO abrasive particles: The same preparation method as in Example 1 was used, except that the particle size D50 of the GO abrasive particles was 7 μm.

[0080] Preparation of GO abrasive discs: The same preparation method as in Example 1 was used, except that GO abrasives and epoxy resin were mixed at a weight ratio of 1:10.

[0081] Preparation of CeO2 abrasive disc: The same preparation method as in Example 1 was used, except that the particle size D50 of CeO2 abrasive was 1.2 μm, and CeO2 abrasive was mixed with E-44 type bisphenol A epoxy resin at a weight ratio of 1:1.

[0082] Assembly: The same assembly method as in Example 1 is used, except that the ratio of the total area of ​​the CeO2 abrasive disk to the total area of ​​the GO abrasive disk is 4:1;

[0083] Post-processing: The composite grinding disc was obtained by the processing method described in Example 1, except that the groove density was 0.305;

[0084] Preparation of polishing slurry: The same preparation method as in Example 1 was used, except that the particle size D50 of the polishing powder CeO2 was 0.4 μm, the weight percentage of polishing powder CeO2 was 0.2 wt%, the weight percentage of PVA was 1 wt%, the polishing slurry temperature was 50 °C, and the pH of the polishing slurry was 4.

[0085] Polishing: The same test piece and polishing steps as in Example 1 were used, except that the grinding speed was 90 rpm and the grinding pressure was 55 psi.

[0086] The SiC wafer was tested using the same equipment as in Example 1. The specific data are shown in Table 1.

[0087] Example 4

[0088] The same method for preparing the polishing disc as in Example 2 was used, except that the trench density was 0.305; the polishing object was a single-crystal silicon wafer; the polishing powder was SiO2 powder with a particle size of D50=0.5μm; the dispersant was PVA; the polishing pressure was 36psi; and the performance of the single-crystal silicon wafer was tested using the same instruments and equipment as in Example 2. The specific data are shown in Table 1.

[0089] Example 5

[0090] The same method for preparing the grinding disc as in Example 4 was used, except that the trench density was 0.303 and the dispersant was PVP. The same instruments and equipment as in Example 4 were used to test the performance of the single crystal silicon wafer. The specific data are shown in Table 1.

[0091] Example 6

[0092] The same method for preparing the polishing disc as in Example 2 was used, except that the trench density was 0.302; the polishing object was a single-crystal silicon wafer; the polishing speed was 70 rpm; the polishing pressure was 55 psi; and the same instruments and equipment as in Example 2 were used to perform performance tests on the single-crystal silicon wafer. The specific data are shown in Table 1.

[0093] Comparative Example 1

[0094] The specific steps of this comparative example are the same as those of Example 2, except that in Comparative Example 1, the CeO2 abrasive disk and the GO abrasive disk are bonded and fixed to the base disk in a 1:1 area ratio to obtain the first polishing disk. Subsequent use of the polishing disk is the same as in Example 2. The performance of the polished SiC wafer is tested using the same instruments and equipment as in Example 2, and the specific data are detailed in Table 1.

[0095] Comparative Example 2

[0096] The specific steps of this comparative example are the same as those of Example 2, except that the CeO2 abrasive grains in Example 2 are replaced with SiO2 abrasive grains with the same grain size as the CeO2 abrasive grains in Example 2. The SiO2 abrasive disc is prepared using the same method as in Example 2. In Comparative Example 2, the SiO2 abrasive disc and the GO abrasive disc are bonded and fixed to a stainless steel base at a 1:1 area ratio to obtain the first grinding disc. Subsequent use of the grinding disc is the same as in Example 2, and the performance of the SiC wafer is tested using the same instruments and equipment as in Example 2. Specific data are shown in Table 1.

[0097] Comparative Example 3

[0098] The specific steps of this comparative example are the same as those of Example 5, except that the CeO2 abrasive grains in Example 5 are replaced with SiO2 abrasive grains with the same grain size as the CeO2 abrasive grains in Example 5. The SiO2 abrasive disc is prepared using the same method as in Example 5. In Comparative Example 3, the SiO2 abrasive disc and the GO abrasive disc are bonded and fixed to the base disc at a 1:1 area ratio. Subsequent use of the grinding discs is the same as in Example 5. The performance of the single-crystal silicon wafer is then tested using the same instruments and equipment as in Example 5, and the specific data are shown in Table 1.

[0099] Comparative Example 4

[0100] The specific steps of this comparative example are the same as those of Example 5, except that the particle size D50 of GO abrasive is 12 μm, the particle size D50 of CeO2 abrasive is 5 μm, and the particle size D50 of SiO2 grinding powder is 1.8 μm. The same instruments and equipment as in Example 5 are used to test the performance of SiC wafers, and the specific data are shown in Table 1.

[0101] Comparative Example 5

[0102] The specific steps of this comparative example are the same as those of Example 2. The difference is that the trench density is 0.5 in the post-processing step, and the same instruments and equipment as in Example 2 are used to perform performance testing on the SiC wafer. The specific data are shown in Table 1.

[0103] Comparative Example 6

[0104] This comparative example uses a traditional grinding wheel, entirely composed of CeO2 abrasive grains, with other parameters identical to those in Example 2. Performance testing of the SiC wafer was performed using the same equipment as in Example 2; specific data are shown in Table 1.

[0105] Comparative Example 7

[0106] The specific steps of this comparative example are the same as those of Example 2, except that PVP is not added to the polishing slurry, and the same instruments and equipment as in Example 2 are used to perform performance testing on the SiC wafer. The specific data are shown in Table 1.

[0107] The performance test results of Examples 1-6 and Comparative Examples 1-7 of the present invention are shown in Table 1.

[0108] Table 1. CMP performance test results of Examples 1-6 and Comparative Examples 1-7

[0109] As shown in Table 1, Examples 1-3 demonstrate that the material removal rate (MRR) for SiC wafer polishing reaches 448.3 nm / h, an improvement of approximately 167% compared to the traditional CeO2 free abrasive method (Comparative Example 6, material removal rate MRR is 168.5 nm / h). Simultaneously, the surface roughness (Sa) is as low as 0.35 nm, and the subsurface damage (SSD) is ≤3.5 nm, achieving mirror-level flatness. Examples 4-6 further demonstrate that this invention is also applicable to CMP of single-crystal silicon wafers, achieving a material removal rate (MRR) as high as 328.5 nm / h and a surface roughness (Sa) as low as 0.48 nm. This design achieves multiple uses for a single plate, demonstrating good process versatility. The results of Comparative Example 1 (area ratio 1:1), Comparative Example 4 (oversized particles), Comparative Example 5 (excessively high groove density), Comparative Example 6 (no GO plate), and Comparative Example 7 (no dispersant) collectively prove that the five core technical characteristics—CeO2:GO area ratio 2:1 to 4:1, CeO2 particle size 1.2 to 1.8 μm, GO particle size 7 to 10 μm, groove density 0.28 to 0.32, and the presence of PVP / PVA dispersant in the grinding slurry—are synergistic and indispensable. Deviation from any one of these characteristics will lead to significant performance degradation. When the GO (Gross Grinding) ratio is too high, the mechanical removal capacity is insufficient, the Material Removal Rate (MRR) decreases, and the surface roughness (Sa) increases significantly, resulting in a marked deterioration in polishing performance. When the abrasive grain size is too large, although the MRR increases slightly, the surface roughness (Sa) and subsurface damage (SDD) deteriorate significantly, and surface scratches become obvious, which is not conducive to obtaining mirror polishing quality. When the groove density is too high, the effective grinding area decreases, leading to a decrease in the MRR. In summary, the composition of the grinding disc, the abrasive grain size, and the groove density all work together to affect the overall performance of the grinding disc. A balance must be achieved among these three factors to obtain the optimal polishing effect.

[0110] This invention optimizes the abrasive composition ratio and surface structure of the grinding disk, enabling CeO2 abrasives to selectively remove the passivation layer. It utilizes GO oxygen-containing functional groups to generate a CeO2 chemical passivation layer in situ, effectively suppressing subsurface damage on the SiC surface. Simultaneously, it achieves the triple advantages of high material removal rate, low surface roughness, and low subsurface damage, completely solving the technical problem of the inability to achieve both high efficiency and high quality processing in the field of SiC wafer polishing.

[0111] Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first," "second," etc., may explicitly or implicitly include at least one of that feature. In the description of this disclosure, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0112] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0113] The above embodiments merely illustrate several implementation methods of this disclosure, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the inventive concept of this disclosure, and these all fall within the protection scope of this disclosure.

Claims

1. A composite grinding disk for CMP of SiC wafers, characterized in that, The abrasive includes a base disk and an abrasive region disposed on the base disk. The abrasive region is composed of at least one CeO2 abrasive disk and at least one GO abrasive disk spliced ​​together. The ratio of the total area of ​​the CeO2 abrasive disk to the total area of ​​the GO abrasive disk is 2:1 to 4:

1. The surface of the abrasive region is provided with grooves, and the groove density is 0.28 to 0.

32. The CeO2 abrasive disk is composed of CeO2 abrasive and binder mixed in a weight ratio of 0.8:1 to 1.2:1, and the GO abrasive disk is composed of GO abrasive and binder mixed in a weight ratio of 1:7 to 1:

10.

2. The composite grinding disc according to claim 1, characterized in that, The groove has a concentric spiral pattern; the groove density is 0.29~0.

31.

3. The composite grinding disc according to claim 1, characterized in that, The Raman spectral defect ratio of the GO abrasive grains is ID / IG≥1.

26.

4. The composite grinding disc according to claim 3, characterized in that, The particle size D50 of the CeO2 abrasive is 1.2~1.8μm; the particle size D50 of the GO abrasive is 7~10μm.

5. The composite grinding disc according to claim 3, characterized in that, The adhesive is one or more of resin adhesives, ceramic adhesives, or metal adhesives.

6. A method for preparing a composite grinding disc as described in any one of claims 1-5, characterized in that, Includes the following steps: Preparation of GO abrasive particles: Expanded graphite was oxidized using the modified Hummers method. After centrifugation, washing, and drying, the graphite was ultrasonically treated for 5-15 minutes and then pulverized and sieved to obtain GO abrasive particles with uniform particle size. Preparation of GO abrasive discs: The prepared GO abrasives and binder are mixed evenly at a weight ratio of 1:7 to 1:10, injected into a mold, cured and shaped, and then removed to obtain GO abrasive discs; Preparation of CeO2 abrasive disc: CeO2 abrasive particles and binder are mixed evenly at a weight ratio of 0.8:1 to 1.2:1, injected into a mold, cured and shaped, and then removed to obtain CeO2 abrasive disc; Assembly: The CeO2 abrasive disc and the GO abrasive disc are bonded and fixed to the base disc at an area ratio of 2:1 to 4:1 to obtain the first grinding disc; Post-processing: Place the first grinding disc on a processing device and process concentric spiral grooves on the surface of the first grinding disc. When the groove density reaches 0.28~0.32, stop processing to obtain a composite grinding disc.

7. The method for preparing the composite grinding disc according to claim 6, characterized in that, The curing of the GO abrasive disc and the CeO2 abrasive disc adopts a two-step curing method: first, it is left to stand at room temperature for 24 hours, and then cured at 50-80 ℃ for 1-3 hours; the GO abrasive and the CeO2 abrasive are pre-stirred before being mixed with the adhesive, and the stirring time is 15-40 min.

8. A method of using the composite grinding disc as described in any one of claims 1-5, characterized in that, The composite polishing disc is installed on a dual-plane polishing machine, and the polishing speed is set to 50~90 rpm, the polishing pressure to 35~60 psi, and the polishing time to 40~60 min. The SiC wafer is polished by passing the prepared polishing fluid through the grooves on the surface of the polishing disc.

9. The method of using the composite grinding disc according to claim 8, characterized in that, The grinding fluid comprises grinding powder, dispersant, and solvent; the grinding powder has a weight percentage of 0.2~0.4wt% and a particle size of 0.4~0.6μm; the weight ratio of the dispersant to the grinding powder is 5:1; the dispersant is a nonionic water-soluble polymer selected from at least one of polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), polyethylene glycol (PEG), or hydroxypropyl methylcellulose (HPMC); and the solvent is deionized water.

10. The method of using the composite grinding disc according to claim 8, characterized in that, The pH value of the grinding slurry is 4~9; the temperature of the grinding slurry is 30~50℃.

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