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To realize the damage-free finishing of CVD-SiC substrates, which are used as materials for space telescope mirrors and glass lens molds, plasma chemical vaporization machining (PCVM) and plasma-assisted polishing (PAP) were combined. In this study, the properties of such CVD-SiC substrates, including their surface morphology, composition and crystalline orientation, were investigated. Lapping using diamond abrasives and conventional chemical mechanical polishing (CMP) using CeO 2 slurry were conducted for comparison with the proposed atmospheric-pressure-plasma-based finishing process. Many scratches and a subsurface damage (SSD) layer were formed by the diamond lapping of CVD-SiC. Conventional CMP using CeO 2 slurry was conducted for the damage-free finishing of CVD-SiC. However, the polishing efficiency was very low. In the proposed process, PCVM, which is a noncontact dry etching process, was performed to remove the SSD layer while PAP, which combines plasma modification and soft abrasive polishing, was performed for damage-free surface finishing. PCVM was conducted on a diamond-lapped CVD-SiC surface. After PCVM for a short duration of 5 min, the scratches and SSD layer formed by lapping were completely removed, although the surface roughness was slightly increased. PAP using a resin-bonded CeO 2 grindstone was conducted to decrease the surface roughness of CVD-SiC processed by diamond lapping and PCVM for 5 min, for which a loose-held-type grindstone was demonstrated to be very useful. A flat and scratch-free surface with an rms roughness of 0.6 nm was obtained after PAP finishing. [ABSTRACT FROM AUTHOR]

Abstract: Plasma-assisted polishing (PAP), which combined the irradiation of atmospheric-pressurewater vapor plasma and ceria abrasive polishing, was proposed for the finishing of difficult-to-machine materials, such as single crystal SiC, GaN, sapphire and diamond. In the case of PAP was applied to a 4H-SiC-Si face, an oxide layer (SiO2) was generated after plasma irradiation and it was removed by polishing using soft abrasives. In this way, a damage-free and atomically-flat 4H-SiC-Si face could be obtained. In this study, soft abrasive polishing (CeO2)of a plasma-oxidized SiC-Si face and a thermally oxidized SiC-C face was respectively conducted. The generation of a well-ordered one-bilayer step-terrace structure on both of the polished Si face and C face was confirmed by atomic force microscopy (AFM). However, due to the high temperature of thermal-oxidation, many pits were generated on SiC-C face after polishing. [Copyright &y& Elsevier]

Thermal oxidation (TO) and abrasive polishing were combined for atomic-scale planarization of 4H-SiC. It was found that the oxide/SiC interface was atomically flat regardless of the thickness of the oxide. The specimen prepared by TO was dipped in HF solution to remove the oxide. However, owing to the residual silicon oxycarbide (Si-C-O), the step/terrace structure of 4H-SiC could not be observed. Nanoindentation tests revealed that the hardness of Si-C-O was much lower than that of SiC. A thermally oxidized SiC surface was polished using CeO2 abrasives, which resulted in an atomically flat surface with a well-ordered two-bilayer step/terrace structure. [ABSTRACT FROM AUTHOR]

Single-crystal silicon carbide (4H-SiC) has a range of useful physical, mechanical and electronic properties that make it a promising material for fabrication of next-generation semiconductor devices. In this work, we report a hybrid polishing process combining thermal oxidation pretreatment and soft abrasive polishing to realize the damage-free and atomic-scale smooth finishing of the carbon face of 4H-SiC. By thermal oxidation pretreatment, the hardness of the carbon face has been reduced from 4.6 GPa to 1.7 GPa, which enables highly efficient polishing using CeO 2 slurry. For conventional CeO 2 slurry polishing without pretreatment, scratches still existed after a long polishing duration for 16 h. The probable scratch removal mechanism in CeO 2 slurry polishing has been proposed based on surface morphology changes during polishing. Whereas a scratch-free surface with well-ordered SiC atomic steps was obtained within a short polishing duration of only 3 h when polishing was conducted on a thermally oxidized surface. Our results demonstrate that hybrid polishing combining surface pretreatment and soft abrasive polishing is a promising approach to realize the damage-free and atomic-scale smooth finishing of the carbon face of 4H-SiC. [ABSTRACT FROM AUTHOR]

Electro-chemical mechanical polishing (ECMP), which combines anodic oxidation and soft abrasive polishing, was applied to single-crystal SiC. Ceria (CeO 2 ) slurry was used as an electrolyte for anodic oxidation as well as a polishing medium to remove the oxide layer. As a result of anodic oxidation, the surface hardness decreased from 34.5 GPa to 1.9 GPa, which made it possible to polish the oxidized SiC surface using a very soft abrasive such as CeO 2 . It was found that the material removal rate (MRR) of ECMP for a diamond-abrasive-polished surface was 3.62 μm/h. ECMP using CeO 2 slurry was conducted for 30 min on a diamond-abrasive-polished surface. All the scratches were completely removed and a smooth surface with a root mean square (RMS) roughness of 0.23 nm was obtained. [ABSTRACT FROM AUTHOR]

Abstract: Damaged layers and polishing haze exist on substrate surfaces owing to abrasion during figuring processes, which deteriorate surface integrity. We have developed a novel damage-free ultraprecision figuring technique and obtained atomically flat and damage-free SiC(0001) surfaces with a domain size of 300–500nm. Using ultraprecision-figured 0°-off 4H-SiC(0001) surfaces as substrates, we demonstrated the formation of graphene layers upon them and successfully produced atomically flat monolayer graphene with a domain size of over 300nm on entire ultraprecision-figured SiC surfaces by annealing in ultra high vacuum without any Si flux. The quality of the graphene layers on the ultraprecision-figured SiC surfaces was markedly higher than that of layers on non-figured SiC surfaces. This indicates that the damaged surface layers with scratches, defects, and so on, enhance roughness on SiC surfaces, and reduce the quality of graphene films. In addition, we found a new phenomenon:step terraces of 500nm width exhibited erosion at step edges, leading to the creation of hexagonal pits at terraces, while step terraces of 300nm width exhibited hardly any erosion. A graphitization mechanism was discussed. [Copyright &y& Elsevier]