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Since SiC is hard and brittle, dicing by normal grinding process not only requires a long time for processing, but also reduces chip strength due to microcracks. The use of highly efficient and damage-free etching with high-pressure plasma as a chemical processing method for dicing rather than mechanical processing was investigated. The results of groove processing using a combination of a metal mask with slit-like apertures and plasma etching with high-pressure SF6 plasma showed that the processing speed decreased with decreasing slit width and increasing groove depth. The results of electrostatic field calculations suggest that this is due to a decrease in plasma intensity caused by electric field decreasing.

In addition to silicon carbide (SiC) and gallium nitride (GaN), gallium oxide (Ga2O3) is attracting attention as a widegap semiconductor material. Ga2O3, unlike SiC and GaN, is not as hard, but has strong cleavage properties, making highly effective mechanical machining difficult. Thus, the processing of Ga2O3 by high-speed etching employing atmospheric-pressure plasma was studied. An extremely high removal rate of 60 μm/min was obtained due to basic processing experiments using hydrogen gas instead of toxic and corrosive chlorine gas as the reaction gas.

Catalyst-referred etching (CARE) is an abrasive-free and damage-free polishing method that involves applying a catalytic reaction at the contact point of the catalyst surface and workpiece in a chemical solution. An atomically flat silicon carbide (SiC) wafer surface can be obtained by the CARE process. Recently, it was found that water can be used as a chemical solution, even in the case of SiC polishing. However, its current removal rate of 4H-SiC (0001) 4°off-axis substrate is only 2 nm/h and is expected to increase. In this study, the use of photoelectrochemical oxidation in combination with the CARE process using water was investigated, successfully increasing the removal rate up to approximately 100 nm/h.

We developed a new etching technique using plasma generated at high pressure up to 9 atm. Operating at 9-atm pressure with a 30-μm-diameter wire electrode, we demonstrated the generation of well-ordered plasma at a narrow gap of ∼10 μm between the electrode and workpiece, and realized a high spatial resolution of <40 μm during processing. This technique should allow for the processing of high-precision X-ray crystal optical devices with compact and complex structures, such as a micro channel-cut crystal monochromator with an extremely narrow (sub-100 μm width) groove for realization of Fourier-transform-limited X-ray lasers with high intensity.

Photoelectrochemical (PEC) oxidation is currently employed to improve the removal rates of surface polishing methods applied to gallium nitride (GaN) wafers, such as PEC mechanical polishing (PECMP) and PEC catalyst-referred etching (PEC-CARE). The use of PEC along with these methods has successfully achieved removal rates as high as 720 nm h−1while still ensuring the highly ordered step-and-terrace structures generated by the same methods when PEC-oxidation is not employed. However, the atomic-scale phenomena induced by PEC oxidation to assist the polishing process of GaN surfaces remain unclear. To address such a question, this study investigates the role of PEC oxidation during CARE as an example. The results demonstrate that PEC oxidation selectively occurs at the step edge and advances through the GaN (0001) surface laterally rather than in the depth direction, thus enabling high-speed polishing and resulting in a highly ordered surface, both crystallographically and geometrically.

Atmospheric-pressure plasma etching of a gallium nitride (GaN) substrate using hydrogen radicals instead of chlorine radicals was investigated toward the backside thinning of GaN vertical power devices to reduce on-resistance. As a basic experiment, a pipe-shaped electrode was placed facing the GaN substrate to generate atmospheric-pressure plasma of a gas mixture of helium and hydrogen and high-speed etching of approximately 4 μm min−1was achieved. Although many spherical Ga metal particles were observed on the surface after processing, the addition of oxygen gas was found to be able to suppress them.

A comprehensive study of the physicochemical interactions and the reaction mechanism of SiC etching with water by Pt catalysts can reveal key details about the surface treatment and catalytic phenomena at interfaces. Therefore, density functional theory simulations were performed to study the kinetics of Pt-assisted water dissociation and breaking of a Si-C bond compared to the HF-assisted mechanism. These calculations carefully considered the elastic and chemical interaction energies at the Pt-SiC interface, activation barriers of Si-C bond dissociation, and the catalytic role of Pt. It was found that the Pt-catalyzed etching of SiC in water is initiated via hydrolysis reactions that break the topmost Si-C bonds. The activation barrier strongly depends on the elastic and chemical interactions. However, chemical interactions are a dominant factor and mainly contribute to the lowering of the activation barrier, resulting in an increased rate of reaction.