A Review on Precision Polishing Technology of Single-Crystal SiC

Single-crystal SiC is a typical third-generation semiconductor power-device material because of its excellent electronic and thermal properties. An ultrasmooth surface with atomic surface roughness that is scratch free and subsurface damage (SSD) free is indispensable before its application. As the last process to reduce the surface roughness and remove surface defects, precision polishing of single-crystal SiC is essential. In this paper, precision polishing technologies for 4H-SiC and 6H-SiC, which are the most commonly used polytypes of single-crystal SiC, such as chemical mechanical polishing (CMP), photocatalytic chemical mechanical polishing (PCMP), plasma-assisted polishing (PAP), electrochemical mechanical polishing (ECMP), and catalyst-referred etching (CARE), were reviewed and compared with emphasis on the experimental setup, polishing mechanism, material removal rate (MRR), and surface roughness. An atomically smooth surface without SSD can be obtained by CMP, PCMP, PAP, and CARE for single-crystal SiC. However, their MRRs are meager, and the waste treatment after CMP is difficult and expensive. Moreover, PAP’s operation is poor due to the complex polishing system, plasma generation, and irradiation devices. A high MRR can be achieved by ECMP. In addition, it is an environmentally friendly precision polishing process for single-crystal SiC since the neutral salt solution is generally used as the electrolyte in ECMP. However, the formation of the egglike protrusions at the oxide/SiC interface during anodic oxidation would lead to a bigger surface roughness after ECMP than that after PAP is processed. The HF solution used in CARE was toxic, and Pt was particularly expensive. Ultrasonic vibration-assisted single-crystal SiC polishing and electrolyte plasma polishing (EPP) were discussed; furthermore, the research direction of further improving the surface quality and MRR of single-crystal SiC was prospected.

Effect of Particle Size and pH Value of Slurry on Chemical Mechanical Polishing of SiO2 Film

This study investigated the effects of particle size and pH of SiO2-based slurry on chemical mechanical polishing for SiO2 film. It was found that the removal rates and surface roughness of the material was highly dependent on the particle size and pH. As the particle size varied, the main polishing mechanism provided the activation energy to mechanical erasure. In addition, pH affected the particle size and Zeta potential, which had an important effect on the strength of the mechanical and chemical action of the chemical mechanical polishing. The change in mechanical action greatly influenced the removal rate. According to the experimental results, the best polishing of SiO2 film was achieved with 40 nm particle size SiO2 abrasives when the pH was 4.

High-Efficiency Chemical Mechanical Polishing of Ti-6Al-4V Alloy via the Synergistic Action of H2O2 and K+ Under Alkaline Conditions

Ti-6Al-4V (TC4) alloy has been widely used for implants, and excellent surface quality is required for satisfactory performance. In this study, chemical mechanical polishing (CMP) was introduced to process TC4 alloy. H2O2 and K+ were used to enhance the CMP efficiency. It is revealed that, at pH 10, the material removal rate (MRR) of TC4 alloy increases with the increasing H2O2. A synergistic action between H2O2 and K+ exists under alkaline conditions. With H2O2 and at pH 10, as the K+ concentration increases, the MRR of TC4 alloy first increases and then levels off. The anions have little influence on the CMP performance. After polishing, the surface is smooth without scratches, and the substrate underneath the surface film has no processing damage. For the synergistic action, K+ ions are adsorbed on the Stern layer of the TC4 alloy surface and the silica particles, screening the surface negative charge. Firstly, OOH- produced from H2O2 and OH- can approach the TC4 alloy surface easily, promoting the corrosion. Secondly, more silica particles come into contact with the TC4 alloy surface, enhancing the interactions. Therefore, the MRR increases. The research work brings about a promising high-efficiency CMP process for titanium alloys.

Polishing Characteristics and Mechanism of Polishing Glass Substrate Using Suede Pad with Fine Micrometer-Sized Pores

Chemical mechanical polishing (CMP) using a suede polishing pad is an essential fabrication process for glass substrates that require ultra-high planarization. However, the effect of surface asperities of the suede pad on its polishing characteristics is not completely understood because the structure of the suede pad in the thickness direction is not constant, and its surface asperities can easily change during the pad conditioning or marathon polishing processes. In addition, many previous studies have discussed the polishing mechanism using a suede pad; however, these studies used suede pads with a pore size of approximately 100 μm. This paper discusses the polishing characteristics of a suede pad with fine micrometer-sized pores by clarifying the relationships between the removal rate, friction coefficient, pore parameters, and roughness as the pad surface asperities. In this study, a series of marathon polishing tests were performed with and without conditioning. It was discovered that the removal rate was affected not only by the pore parameters but also by the surface roughness of the suede pad with fine pores. The relationship between the removal rate and the friction coefficient changed owing to the influence of pad conditioning, and this change is significant when the break-in conditioning time is short.

A New Chemical-Mechanical Polishing Method Based On Colloids Silica and MgO Was Developed For Polishing Y3Al5O12 Material

The material yttrium aluminum oxide (Y3Al5O12) is one of the materials commonly used in laser devices. For application in optical devices, it is necessary to produce ultra-precise surface quality, however, Y3Al5O12 material belongs to the group of difficult-to-machine materials with high brittleness and hardness. Therefore, it is very difficult to ensure that the main criterion when finishing this material to produce a quality surface in the nanometer form with the ability to remove the material is very difficult. To solve this problem, this work provided a new chemical - mechanical polishing mixture. The proposed polishing mixture of ZrO2, Na2SiO3–5H2O, and MgO abrasives has a weight ratio of 8%, 5% and 1% respectively, with the remainder being deionized water. The surface result after polishing is obtained with a material removed rate of 38 (nm/min) along with an ultra-smooth surface produced with Ra = 0.41 nm. With the help of X-ray photoelectron spectroscopy (XPS) method before and after polishing by CMS, the reaction mechanisms were elucidated. Analytical results show that Y3Al5O12 material produces YOOH and AlOOH in Na2SiO3 solution, then combines with –Si–OH to form (Y-Si) and (Al-Si) with significantly reduced hardness compared to other Y3Al5O12 materials, these products combine with MgO to form montmorillonites (3MgO–Al2O3–3SiO2–3Y2O3–5Al2O3). With this formation, the surface layer of Y3Al5O12 material becomes soft and is easily removed by ZrO2 abrasive particles under the influence of mechanical polishing, resulting in superfine surfaces are generated from the proposed CMS model.