Codeposition on diamond film surface during reactive ion etching in SF6 and O2 plasmas

Abstract

The surface of polycrystalline diamond films during reactive ion etching in electron cyclotron resonance SF6 and O2 plasmas has been examined by scanning electron microscopy, Raman spectroscopy, and x-ray photoelectron spectroscopy. A SF6 plasma required a high voltage in negative substrate biasing in order to achieve an equivalent etching rate to an O2 plasma. This was ascribed to the codeposition effects and the low mean energy of ions upon impact in a SF6 plasma. The elemental composition of the amorphous layer formed at the etched film surface in the two plasmas was almost equivalent and mainly composed of carbon and oxygen, except a low concentration (⩽1%) of sulfur and fluorine in the case of a SF6 plasma. The significant codeposition on diamond surface was the most likely the result of plasma–wall interactions induced by the fragments from SF6, and highly responsible for suppressing the ratio of lateral to vertical etching rate leading to anisotropic etching in a SF6 plasma, in contrast with the little or no codeposition leading to isotropic etching in an O2 plasma. The results give the substantial implications for the etching process in practical SF6/O2 plasmas utilized in device fabrication.