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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]

For the finishing of some difficult-to-machine materials, such as silicon carbide, diamond, and so on, a novel polishing technique named plasma-assisted polishing (PAP) was proposed, which combined with the irradiation of atmospheric pressure water vapor plasma and polishing using soft abrasives. In this article, application of PAP to 4H-SiC (0001) substrate was conducted. We used helium-based water vapor plasma to modify the mechanical and chemical properties of the SiC surface. The results of X-ray photoelectron spectroscopy measurements indicate that the surface was efficiently oxidized after plasma irradiation, and the main product was SiO. CeO was used as the abrasive material in PAP, the hardness of which was near to that of the oxidized surface. The scanning white light interferometer images of the PAP processed surface showed us that scratches disappeared and surface roughness also decreased from 4.410 nm p-v, 0.621 nm root mean square (rms) to 1.889 nm p-v, 0.280 nm rms. From the atomic force microscopy images, step and terrace structure was observed on the surface after PAP, which means an atomically flat surface was obtained. The PAP processed surface was observed using cross-sectional transmission electron microscope, which indicated that almost no crystallographical defects were introduced. [ABSTRACT FROM AUTHOR]

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]