Catalyzed gaseous etching of silicon

Traces of copper and silver are shown to accelerate the etching of silicon by molecular fluorine. Copper residue formed by aqueous HF etching of sputter-deposited aluminum (0.5% Cu) produces a 100-fold increase in the etching rate of an underlying (100) silicon, compared to unmetallized samples, at temperatures above 80 °C. Above 180 °C, F2 exhibits a higher absolute etch rate than equivalent concentrations of fluorine atoms. The temperature dependence of the reaction is interpreted in terms of a Cu-CuF(x=1,2) catalytic cycle in which CuF(x=1,2) is the active intermediate. Preliminary results for other gases and metals are presented, and the origin of discrepancies in published rate data for the F2/Si reaction are discussed.