Profile Evolution during Cold Plasma Beam Etching of Silicon

Abstract

Processing characteristics of cold, directional plasma beams have been studied by numerical simulation of the profile evolution of trenches etched in silicon with chlorine, where the cold plasma beams were characterized by highly directional fluxes of neutrals as well as ions with their low temperatures or random thermal energies. The model included ion and neutral transport in microstructures and ion-assisted surface chemistry for the chlorine-silicon system. The numerical results demonstrate that the cold plasma beams achieve high etch anisotropy and microscopic uniformity: a tapered profile, inversely tapered profile, and reactive-ion-etching (RIE) lag, which often occur in usual plasma etching environments, are significantly suppressed owing to preferential incidence of neutral reactants as well as ions onto the bottom of microstructural features. In addition, the increased directionality of neutral fluxes not only offsets the RIE lag, but also further causes a weak inverse RIE lag without relying on surface inhibitors. Experimental techniques are also discussed for generation of such cold, directional beams of reactive plasmas.