Polished Silicon Carbide Research Articles

Influence of Binding Agent on the Cutting Performance and Friction Wear Characteristics of Catalytic Composite Abrasive Cluster

To improve the polishing efficiency and process stability of catalytic composite abrasive clusters (CCAC), CCAC containing different binding agent ratios was investigated. Five groups of CCAC with different binding agent ratios were prepared for friction chemical polishing of silicon carbide (SiC), respectively. Based on material removal rate (MRR) and surface roughness (Ra) as evaluation metrics, the polishing performance of five groups of CCAC were compared. Subsequently, wear experiments were carried by block shaped CCAC with diameter of 1.6 mm, as well as single crystal diamond (SCD) abrasives with the same particle size. The friction coefficient and the cross-sectional area at the worn area of wear were measured to evaluate the effect of binding agent content on the continuous cutting performance of the abrasive as well as on the tribological properties. The experimental results showed that #3 abrasive exhibited the highest machining efficiency (MRR reaches 330.535 nm min−1) and better surface roughness (Ra reaches 22.741 nm). Excessive or insufficient bonding agent in CCAC will affect the processing performance of the abrasive. When the proportion of binding agent in the abrasive is 25%, CCAC has better processing ability and can realize efficient polishing of SiC wafers.

Application of the Fenton reaction in silicon carbide polishing and its oxidative active center

The Fenton reaction is known for generating highly reactive hydroxyl radicals that are applied to accelerate the polishing removal rate of chemically inert SiC substrates. However, previous research primarily focuses on the polishing removal rate acceleration on the C surfaces of SiC substrates, and very limited studies have been conducted to investigate whether the hydroxyl radicals produced by the Fenton reaction serve as the primary agents of oxidative activity. Furthermore, the oxidation ability of hydroxyl radicals on the C surface and its relationship with their concentration are still not well-established. Therefore, more extensive research is needed to gain comprehensive understanding on the role of hydroxyl radicals in the oxidative activity on the C surface and their concentration-dependent effects. In this study, the polishing results of alumina, cerium oxide, and silica containing polishing slurries with and without Fenton reaction were compared and analyzed. The material removal rate (MRR) of the C surfaces of SiC substrates was significantly improved after the introduction of the Fenton reaction in alumina-containing slurry at pH 4, resulting in a smoother surface. Low-field nuclear magnetism, atomic force microscopy (AFM), ultraviolet spectrophotometry, and X-ray photoelectron spectroscopy (XPS) were employed to gain insights on inter-particle interactions and oxidation mechanisms of C face of SiC in presence of Fenton reaction. The results revealed that while hydroxyl radicals demonstrated potent oxidation ability, they alone were incapable of oxidizing C face of SiC.

Atomistic Removal Mechanisms of SiC in Hydrogen Peroxide Solution.

To elucidate the atomic mechanisms of the chemical mechanical polishing (CMP) of silicon carbide (SiC), molecular dynamics simulations based on a reactive force field were used to study the sliding process of silica (SiO2) abrasive particles on SiC substrates in an aqueous H2O2 solution. During the CMP process, the formation of Si-O-Si interfacial bridge bonds and the insertion of O atoms at the surface can lead to the breakage of Si-C bonds and even the complete removal of SiC atoms. Furthermore, the removal of C atoms is more difficult than the removal of Si atoms. It is found that the removal of Si atoms largely influences the removal of C atoms. The removal of Si atoms can destroy the lattice structure of the substrate surface, leading the neighboring C atoms to be bumped or even completely removed. Our research shows that the material removal during SiC CMP is a comprehensive result of different atomic-level removal mechanisms, where the formation of Si-O-Si interfacial bridge bonds is widespread throughout the SiC polishing process. The Si-O-Si interfacial bridge bonds are the main removal mechanisms for SiC atoms. This study provides a new idea for improving the SiC removal process and studying the mechanism during CMP.

Effects of ultrasonic vibration-assisted machining methods on the surface polishing of silicon carbide

Effects of ultrasonic vibration-assisted machining methods on the surface polishing of silicon carbide

Center-injected Polishing for Efficient Slurry Utilization

Polishing is one of the most crucial finishing processes and usually consumes a sufficient slurry to achieve an ultra-fine surface. However, excess slurry consumption is environmentally costly, as it generates a large amount of wastewater. Given the growing environmental concerns, it is essential to improve the process efficiency and minimize the environmental burdens. Considering this, a novel polishing system, herein referred to as center-injected polishing, is proposed by injecting slurry into the center of the polishing pad. Here, it is aimed to utilize the centrifugal force of the rotating pad, with the aim of efficient slurry utilization. The slurry is directly introduced between the pad and the workpiece, then dispersed across the pad by centrifugal force. A simple experiment was conducted with computational analysis using the specially designed polishing tool to prove the concept; slurry was distributed more uniformly in center-injected polishing when compared to the conventional process. The polishing system was then constructed to evaluate polishing performances. Based on sets of experiments in the polishing of silicon carbide (SiC), slurry efficiencies and productivity were analyzed with respect to different rotational speeds and slurry supply rates. The material removal rate (MRR) was more than twice the rate achieved by conventional polishing at the same processing conditions; whereas the slurry consumption was approximately 60% less at the same MRR. The extended Preston equation was used to predict the MRR of the new process. It is expected that efficient slurry utilization will reduce the environmental footprint of abrasive processes.

Synthesis of Al2O3@MnO2 composite abrasives and their chemical mechanical polishing performance on silicon carbide (SiC)

The effectiveness of silicon carbide (SiC) planarization mostly relies on the chemical and mechanical effects during chemical mechanical polishing (CMP). Nevertheless, the alumina (Al2O3) abrasive only provides a mechanical effect and is incapable of achieving a high-efficiency polishing of SiC. To address this issue, a series of novel Al2O3@MnO2 composite abrasives were prepared by encapsulating varying amounts of manganese dioxide (MnO2) on Al2O3 abrasive, and the polishing performance on SiC wafers was evaluated. The X-ray diffraction (XRD) and scanning electron microscope (SEM) images, along with the size and zeta potential data, show that MnO2 is successfully coated on the surface of Al2O3, and the dispersion of Al2O3@MnO2 composite abrasive is significantly improved when compared with the pure Al2O3. Furthermore, the CMP experiment and surface profile analysis demonstrate that the material removal rate (MRR) can reach a maximum value of 640.47 nm/h when using a 0.05 wt% MnO2-coated Al2O3 composite abrasive, which is 76 % higher than that of traditional Al2O3 abrasive. Furthermore, the average surface roughness (Sa, arithmetic mean height) of SiC is reduced to 0.73 nm. X-ray photoelectron spectroscopy results reveal that the surface of SiC is oxidized and forms a chemical bond known as Mn–O–Si after CMP. The results of the friction coefficient test and contact angle test indicate that slurries containing composite abrasive have exceptional wettability and a higher friction coefficient. Under the synergistic chemical and mechanical effects, SiC is oxidized to soft oxide and then removed circularly to reach excellent flatness.

Effects of polishing media on the surface chemical and micromechanical properties of SiC

Hydrogen peroxide(H2O2) has been widely used to improve polishing performance in chemical mechanical polishing(CMP) of silicon carbide(SiC), but the reaction processes and mechanism of the generated hydroxyl radicals during CMP have not yet been reported in detail. In this paper, the reactions of H2O and H2O2 molecules with SiC were simulated by ReaxFF-MD model. The results show that H-Si and O-Si bonds are formed when H2O reacts with SiC surface and however, suppressed with the introduction of H2O2. Meanwhile, it is successfully observed the whole processes of forming and breaking bonds of the peroxy bonds on the surface of SiC. The indentation hardness, elastic modulus, bond energy and bond length were obtained by LAMMPS and ReaxFF-MD model. The results indicate that, compared with unreacted SiC, the physical and bonding properties of SiC after being reacted with H2O and H2O2 are significantly altered. The performance improvement of SiC polishing is attributed to the reduction of indentation hardness and bond energy caused by chemical reaction.

Chemical mechanical polishing of silicon carbide (SiC) based on coupling effect of ultrasonic vibration and catalysis

Polishing SiC is a difficult task due to its exceptional chemical stability and high hardness. While the strong catalytic performance resulting from the coupling effect of ultrasonic vibration and catalysis is well-known, there have been limited studies on its effectiveness for SiC chemical mechanical polishing. To address this gap, we present a novel approach that utilizes the coupling of ultrasonic vibration and catalysis for SiC polishing. The hydroxyl free radical (*OH) generated by coupling effect is analyzed using ultraviolet-visible spectrophotometry (UV–VIS) to screen for a catalyst that matches ultrasonic vibration and establish a high-performance catalytic coupling system. The use of ultrasonic vibration in SiC polishing results in a significant increase in catalytic efficiency, with a doubling effect observed. Additionally, the catalyst itself increases ultrasonic efficiency by 43.1 %, leading to a substantial improvement in material removal rate (MRR). We study the impact of the placement of the ultrasonic vibration device on MRR and evaluate the performance of the coupling system used for polishing. Also, we delved into the removal mechanism of SiC by utilizing XPS and nyquist plots. Our findings reveal a maximum MRR of 214.6 nm/h, which improves the efficiency of commercial slurry by 80.0 %. Furthermore, the proposed strategy increases the MRR of commercial slurry by more than 70 % in the time range of 0–1 h, 1–2 h, and 0–2 h. The surface roughness (Ra) measured by AFM using a scanning area of 1 × 1 µm2 at sub-angstrom scale (Ra=0.0627 nm) is achieved. This study significantly improves the polishing efficiency of commercial slurry and has great application prospects.

Multi-Objective Optimization in Ultrasonic Polishing of Silicon Carbide via Taguchi Method and Grey Relational Analysis.

As high-level equipment and advanced technologies continue toward sophistication, ultrasonic technology is extensively used in the polishing process of difficult-to-process materials to achieve efficiently smooth surfaces with nanometer roughness. The polishing of silicon carbide, an indispensable difficult-to-machine optical material, is extremely challenging due to its high hardness and good wear resistance. To overcome the current silicon carbide (SiC) ultrasonic polishing (UP) process deficiencies and strengthen the competitiveness of the UP industry, the multi-objective optimization based on the Taguchi-GRA method for the UP process with SiC ceramic to obtain the optimal process parameter combination is a vital and urgently demanded task. The orthogonal experiment, analysis of variance, grey relational analysis (GRA), and validation were performed to optimize the UP schemes. For a single objective of roughness and removal rate, the influence degree is abrasive size > preloading force > abrasive content > spindle speed > feed rate, and spindle speed > abrasive size > feed rate > preloading force > abrasive content, respectively. Moreover, the optimal process combination integrating these two objectives is an abrasive content of 14 wt%, abrasive size of 2.5 μm, preloading force of 80 N, spindle speed of 8000 rpm, and feed rate of 1 mm/s. The optimized workpiece surface morphology is better, and the roughness and removal rate are increased by 7.14% and 28.34%, respectively, compared to the best orthogonal group. The Taguchi-GRA method provides a more scientific approach for evaluating the comprehensive performance of polishing. The optimized process parameters have essential relevance for the ultrasonic polishing of SiC materials.

Tribological Study on Photocatalysis-Assisted Chemical Mechanical Polishing of SiC

Silicon carbide (SiC) is widely used as a power semiconductor substrate material, even if it takes a large amount of processing time to secure an appropriate surface as a wafer for devices after chemical mechanical polishing (CMP). Therefore, studies on SiC CMP have focused on shortening the processing time by increasing material removal efficiency. Among the methods of SiC CMP that have been widely studied recently, the photocatalysis-assisted CMP (PCMP) method is known to efficiently increase the material removal rate (MRR) of SiC under UV light and photocatalysts. However, a limited number of comparative studies have been conducted on PCMP from a tribology perspective. In this article, a comparative study was conducted from a tribology perspective on CMP, mixed abrasive slurry CMP (MAS CMP), and PCMP. The experimental results demonstrated that SiC PCMP has higher friction and processing temperature than MAS CMP and general CMP, which may be caused by photocatalytic oxidation and the TiO2 particles used as photocatalysts.

Research on Abrasive Water Jet Polishing of Silicon Carbide Based on Fluid Self-Excited Oscillation Pulse Characteristics

A self-excited oscillating pulsed abrasive water jet polishing method is proposed to solve the problems of low removal efficiency in traditional abrasive water jet polishing and the influence of an external flow field on the material surface removal rate. The self-excited oscillating chamber of the nozzle was used to generate pulsed water jets to reduce the impact of the jet stagnation zone on material surface removal and increase the jet speed to improve processing efficiency. ANSYS Fluent was employed to simulate the processing flow field characteristics for different lengths of oscillation cavities. The simulation results indicate that the velocity of the jet shaft reached a maximum of 178.26 m/s when the length of the oscillation cavity was 4 mm. The erosion rate of the material is linear with the processing angle. A nozzle with a length of 4 mm of the self-excited oscillating cavity was fabricated for SiC surface polishing experiments. The results were compared with those of ordinary abrasive water jet polishing. The experimental results showed that the self-excited oscillation pulse fluid enhanced the erosion ability of the abrasive water jet on the SiC surface and significantly improved the material-removal depth of the abrasive water jet polishing SiC. The maximum surface erosion depth can be increased by 26 μm.

Influence of surface morphology and processing parameters on polishing of silicon carbide ceramics using femtosecond laser pulses

In this paper, silicon carbide (SiC) ceramics were polished using a high-frequency femtosecond laser (fs-laser). The influence of different laser incidence angles on the machined surface were investigated in detail, and the processing morphologies for different laser processing parameters were analyzed and optimized. The theoretical simulation and experimental results indicated that the original surface defects of pits prior to processing of the SiC surface remarkably affects the ablation effect. When fs-laser polishing at vertical incidence, the effect of light trapping occurred in the pits due to multiple reflections, enhancing the absorption of laser energy to enlarge the size of pits. The small incidence angle can eliminate the effects of light trapping in the pits and obtain the smooth surface of the material. In addition, the degree of oxidation and graphitization decrease significantly with a decrease of incidence angle. The optimal processing parameter combination under the incidence angle of 10°, laser frequency of 100 kHz, scanning speed of 200 mm/s, single pulse energy of 60 μJ was obtained. The polished SiC ceramic exhibited a smooth, flat and pit-free surface with the average Sa of 0.187 μm and Sz of 2.313 μm. Finally, the formation of typical features such as pits, particles and debris deposition, was explained in detail. Our work provides new research ideas for understanding the polishing mechanisms concerning the removal of surface defects and depositions from the SiC ceramics.

Study on material removal mechanism in ultrasonic chemical assisted polishing of silicon carbide

An ultrasonic chemical assisted polishing (UCAP) method exploiting the recombination mechanism of ultrasonic vibration, Fenton oxidation and mechanical impact is proposed for efficient finishing of silicon carbide (SiC). Experiments and theoretical analyses were performed to explore the effect of H2O2 content, FeSO4 content and ultrasonic amplitude on removal rate and surface roughness of UCAP and material removal mechanism. The combined interactions of ultrasonic and Fenton oxidation achieved superior polished efficiency and quality with a 19.51 % improvement in MRR and a 18.3 % increase in Ra compared to MP. This originates from the synergistic effect of oxidation of OH generated by chemical polishing slurry and the promotion of mechanical removal of abrasives and oxidation rate of SiC by ultrasonic vibration. Excessive FeSO4 and insufficient H2O2 can induce flocculent precipitates, thus reducing the MRR of SiC UCAP. Moreover, a larger ultrasonic amplitude generated a greater MRR, but with a smaller deterioration of the machined surface. This investigation reveals that UCAP is a progressive precision machining approach for optical ceramic materials polishing. The proposed polishing process will promote hybrid processing technologies research and simplify the existing SiC machining process to achieve extremely efficient polishing of SiC.

X-ray Diffraction Analysis of Damaged Layer During Polishing of Silicon Carbide

X-ray Diffraction Analysis of Damaged Layer During Polishing of Silicon Carbide

Low Shear Force Defect Removal from SiC Using Megasonic Enhanced Cleaning

Wide band gap (WBG) materials (i.e., Silicon Carbide (SiC)) have attracted much attention in the semiconductor arena because of their intrinsic properties (i.e. high capacitance, thermal stability, and wear resistance). In order to achieve the desired removal rate and surface planarity during the Chemical Mechanical Planarization (CMP) process of SiC substrates high shear force and chemically aggressive conditions are employed. Although effective this process can result in significant surface contamination/defectivity (i.e., organic residue, abrasive particles, etc.) post-polish. Current methods of post-CMP cleaning for SiC substrates implement a Polyvinyl Alcohol (PVA) brush scrubbing to aid in surface contaminate removal. A balance of controlled shear force and interfacial adsorption/redox reactions are necessary to effectively remove rouge contaminates without any generation of secondary defects. This research focuses on development of a “soft” (low-shear force) post-CMP cleaning process for SiC which uses transient cavitation effects via megasonic energy coupled with catalytic complexes to enhance reactive oxygen species (ROS) generation. More specifically, hydroxyl radical (*OH) generating organometallic complexes were incorporated into the cleaning fluid to increase ROS and provide additional surface-active chemistries to disrupt the defects non-covalent surface binding energy. Initial results show increased ROS generation (which is complex structure dependent) improved defect removal efficiency under static megasonic conditions with no changes to the surface energy of the final polished SiC substrate.

Effect of Particle Size Distribution, pH, and Na+ Concentration on the Chemical Mechanical Polishing of Sapphire and 4H-SiC (0001)

As two typical representatives of super-hard materials, sapphire and silicon carbide, their processing has always been a hot spot. Chemical mechanical polishing (CMP) technology is the only way to achieve global planarization, and it has also become one of the most important processes for precision machining of sapphire and silicon carbide. This paper introduced the relationship between the removal rate and surface roughness of sapphire and 4H-SiC (0001) and the size distribution and pH of alumina slurry. More importantly, this paper explored the negative effect of Na+ on the removal rate of alumina-based sapphire polishing slurry, and the more negative effect of Na+ on the removal rate of alumina-based silicon carbide polishing slurry and the surface state of SiC(0001). At the end of the article, the polishing mechanism of sapphire with alumina as a brasive was given.

Charge Utilization Efficiency and Side Reactions in the Electrochemical Mechanical Polishing of 4H-SiC (0001)

Slurryless electrochemical mechanical polishing (ECMP) is very effective in the polishing of silicon carbide (SiC) wafers. To achieve a high material removal rate (MRR) of SiC wafer using ECMP with low electrical energy loss, charge utilization efficiency in the anodic oxidation of the SiC surface was investigated and the underlying mechanism was clarified by modeling the anodic oxidation system of SiC in 1 wt% NaCl aqueous solution. The charge utilization efficiency in the anodic oxidation of SiC was found to be constant when the current density was less than 20 mA cm−2 and significantly decreased when the current density was greater than 30 mA cm−2, resulting in a significant reduction in the MRR. Modeling of the anodic oxidation system indicates that the charge utilization efficiency depended on the potential applied on the SiC surface: the oxidation of SiC occupied the dominant position in the anodizing system when the potential is lower than 25 V vs Ag∣AgCl, charge utilization efficiency greatly decreased when the applied potential was greater than 25 V owing to the occurrence of oxidations of the H2O and Cl−. This research provides both a theoretical and practical foundation for using ECMP to polish SiC wafers.

Development and characterization of silicon dioxide clad silicon carbide optics for terrestrial and space applications

Silicon carbide (SiC), a non-oxide ceramic with superior thermo-mechanical stability, chemical and radiation resistive properties, finds extensive utilization in optical instruments for terrestrial and space applications. However, its inherent porous texture (α-HCP) becomes a deterrent for high-performance optical telescopes, although several techniques of surface alterations over sintered or reaction-bonded SiC are available. In the present work, the physical vapour deposition (PVD) technique is adopted to deposit a thick (∼5 μm) Silicon dioxide (SiO 2 ) clad layer on a sintered and optically polished SiC (SSiC) substrate. SiO 2 clad layer coated SSiC (SDO-SSiC) substrate reduces the surface porosity of SSiC which is found to be suitable for optical mirror application. Finally, an Al based reflective and oxides protective coatings are deposited on SiO 2 clad layer to achieve reflective behaviour. The surface figure of 75 nm PV (peak-to-valley) and less than 2 nm surface micro-roughness values are achieved which meets the stringent optical telescope specifications for terrestrial and space applications. The structural and nano-mechanical properties of presently developed SiO 2 clad layer-based SiC telescopic mirror have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-Ray Analysis (EDX), atomic force microscopy (AFM), and nanoindentation techniques. The optical properties are investigated by optical profilometry and wavelength based spectrometric (both in visible and infrared ranges) techniques. Finally, space worthiness studies viz., thermo-vacuum, thermal storage, thermal shock and relative humidity tests have been carried out successfully. The process of cleaning, grinding and polishing at each substrate preparation stage and coatings are also reported comprehensively.

High efficiency polishing of silicon carbide by applying reactive non-aqueous fluids to fixed abrasive pads

In pursuing high precision and high-quality surface of silicon carbide (SiC) substrates for electronic applications, however, the processing efficiency on Si-face has long been a difficult challenge compared to that of the C-face. Conventional polishing slurries are aqueous-based due to its unparalleled compatibility with most of chemical reagents, and have been widely studied and well understood. The chemical reactivity of all added accelerating agents in aqueous polishing systems is constrained by the prevalent presence of water as a solvent. On the other hand, non-aqueous polishing systems have not been well explored. In this report, reactive non-aqueous organic systems containing polar hydroxyl groups are evaluated as a high efficiency processing vehicle for Si-face polishing of SiC on fixed abrasive pads (FAPs). The surface quality of SiC is surprisingly improved while the polishing efficiency is accelerated on a diamond FAP in presence of methanol compared to those using water, and are further improved when organic acids are introduced to the reactive non-aqueous fluids. Contact angle measurement and X-ray photoelectron spectroscopy (XPS) analysis on the polished SiC surface are completed to assist us to shed light on the removal behavior and to explore and elucidate the removal mechanism of non-aqueous system fluids on FAPs. The initial positive results from this reactive non-aqueous polishing system serves our community as a promising approach for the ultra-precision polishing on other hard-to-process semiconductor and ceramic materials.

Accelerated C-face polishing of silicon carbide by alkaline polishing slurries with Fe3O4 catalysts

As a third-generation semiconductor material, Silicon carbide (SiC) excels in extraordinary physical and chemical properties, which makes, in turn, it hard to process. The strong oxidizing species·OH produced by the Fenton reaction has been effectively applied in the chemical mechanical polishing (CMP) of single-crystal SiC. In order to expand the applicable pH range of Fenton reaction, magnetic recoverable Fe3O4 nanocatalysts were prepared in this paper, and the Fenton system was successfully applied to SiC polishing in alkaline silica slurry, which significantly improved the material removal rate (MRR). UV–vis spectroscopy curves prove that in a H2O2 containing slurry, more·OH radicals were produced at pH 2.5 than that at pH 9.0 during Fe3O4 catalyst-assisted polishing, which is consistent with conventional wisdom about Fenton Reaction. Surprisingly, MRR of SiC wafer up to 632 nm/h was achieved at pH 9.0 instead of 2.5 using the same slurry. A detailed hypothesis is presented to elucidate the material removal mechanism of the Fenton reaction system on SiC polishing.