Planar Plasma Etching of Polysilicon Using CCl4 and NF 3

Abstract

A comparison is made between carbon tetrachloride and nitrogen trifluoride as etchants for plasma etching phosphorus‐doped polysilicon over silicon dioxide. The comparison is based upon optimal gas pressures and flow rates of and for a commercial planar plasma etcher. The etch rates of doped polysilicon and silicon dioxide were measured as a function of power density for both and . Polysilicon to silicon dioxide etch rate ratios of 15 to 1 were found for with accompanying very high etch rates (1–2 μm/min). Ten to one etch rate ratios were obtained with using low power densities and low etch rates (400 Å/min). Line edge profiles were examined and found to be quite isotropic for polysilicon etched with and anisotropic . Also studied was the effect on etch rates due to varying wafer loads and the rates of photoresist erosion.