HYDROFLUOROCARBON PLASMA SUBMICRON SILICON DIOXIDE ETCH IN AN AXISYMMETRICAL STATIC MAGNETRON

A low pressure (50 m Tr) discharge is generated in an axisymmetric, static magnetron (400 kHz). As additives to CF4, a series of hydrofluorocarbon gases with a single carbon atom (CHF3, CH2F2 and CH3F) and with double carbon atoms (C2HF5, C2F4H2 and C2H4F2) are studied to determine the fluorine-hydrogen feed gas composition dependence of submicron thermal oxide contact etch and oxide/silicon selectivity. For a particular carbon series, a simple linear relationship between feed gas flows and fluorine/hydrogen or carbon/hydrogen molar flow ratios establishes the loci in parameter space for the oxide etch to stop on the underlying silicon with a minimal polymer build-up. As a consequence, an understanding of the relationship between the silicon etchants, principally atomic fluorine, and polymerizing precursors is found. RIE lag is also discussed.