Nearly isotropic etching of 6H-SiC in NF₃ and O₂ using a remote plasma

Nearly isotropic etching of the 6H-SiC carbon face has been achieved in a remote plasma at 330°C using a mixture of O₂ and NF₃ in argon. Using evaporated aluminum as a mask, undercutting has been observed to a distance equal to the etch depth. The etch rate is a function of the ratio of O₂ to NF₃ flow rates and of temperature, peaking strongly to 220 nm/min at 82% oxygen for 330°C. Smooth surfaces were obtained for gas ratios leading to the maximum etch rate, and also for a NF₃-argon mixture, with significant roughening observed for other O₂-NF ₃-argon mixtures. In the absence of a practical wet etch for SiC, this procedure is promising for isotropic etching in SiC device processing.