Plasma-enhanced etching of tungsten, tungsten silicide, and molybdenum in chlorine-containing discharges

Thin films of tungsten, tungsten silicide, and molybdenum were etched both within and downstream from Cl2 discharges. Without a discharge, molecular chlorine did not etch the films. Experimental conditions ranged from 0.1 to 1.0 Torr pressure, 30 to 180 degree C electrode temperature, 0.2 to 1.0 W/cm2 power density, and 3 to 200 sccm flow rate. In-discharge etch rates varied from 10 to 90 nm/min for tungsten (W), 10 to 450 nm/min for tungsten silicide (WSix), and 1 to 8 nm/min for molybdenum (Mo). Small additions of BCl3, during W and WSix etching, significantly increased the etch rates and improved the reproducibility. When samples were positioned downstream from a Cl2 discharge, etching proceeded solely by chemical reaction of the film with chlorine atoms. Downstream and in-plasma tungsten etch rates were approximately equal at 110 degree C, but the chlorine atom etch rate dropped more rapidly than the in-plasma etch rate as temperature decreased. In contrast, molybdenum etched faster by atoms alone than in the plasma, although atom etching was not observed below 100 degree C. Reactions of tungsten with a modulated beam of chlorine atoms and molecules were also studied