Fast, smooth, and anisotropic etching of SiC using SF6/Ar

Abstract

Using magnetically enhanced reactive ion etching and an etch chemistry containing sulfur hexafluoride and argon we have dry etched silicon carbide (SiC) with etch rates as large as 1900 Å/min and obtained smooth etched surfaces and good etch anisotropy. Such etch processes are useful for a variety of SiC devices, including vertical UMOSFETs. Etch chemistry was found to greatly affect etch rate and final surface roughness. Etching in mixtures of sulfur hexafluoride (SF6) and oxygen, for example, resulted in relatively rough etched surfaces (typically 25 Å rms) with a maximum etch rate near 800 Å/min. Etching in SF6/Ar gave smoother surfaces and larger etch rates, most likely because physical sputtering by Ar+ ions helps to remove nonvolatile or low-volatility fluorocarbon and carbon-rich etch products. For example, using equal SF6 and Ar flow rates of 40 sccm, a process pressure of 10 mTorr, and a rf power density near 2.5 W/cm2, etch rates near 1000 Å/min are obtained. Atomic force microscopy indicates that the surface roughness of SiC etched under these conditions actually decreased slightly (from 6.1 Å to 4.4 Å rms). Scanning electron microscopy indicates good etch anisotropy with slight trenching at feature edges. Increasing the rf power density to 3.5 W/cm2 increases the etch rate to 1900 Å/min with only slightly increased surface roughness. The combination of large etch rate, smooth etched surfaces, and good etch anisotropy make magnetically enhanced reactive ion etching in SF6/Ar attractive for SiC device fabrication.