Etching of Tungsten and Tungsten Silicide Films by Chlorine Atoms

Abstract

Thin films of tungsten and tungsten silicide were etched both within and downstream from a plasma discharge at 200 mtorr pressure and temperatures below 150°C. When samples were positioned downstream from the discharge, etching proceeded solely by chemical reaction of the film with chlorine atoms. Without a discharge, molecular chlorine did not etch tungsten or tungsten silicide. Downstream and in‐plasma tungsten etch rates were approximately equal at 110°C, but the chlorine atom etch rate dropped more rapidly than the in‐plasma etch rate as temperature decreased. The chemical reaction between chlorine atoms and the tungsten film was proportional to the gas phase Cl atom mole fraction. A pretreatment consisting of either a dilute hydrofluoric acid dip or a short plasma etch cycle was necessary for atom etching of tungsten silicide films. The etch rates of tungsten silicide in plasmas were approximately an order of magnitude higher and less temperature sensitive than those in the downstream (atom) configuration.