Is a far more selective etchant for silicon than when excited to a plasma discharge. This applies to good advantage in parallel plate reactors where under given conditions of rf power and pressure the etch ratio of silicon to is 30:1 but with only 7:1. In contrast to the deposition of carbon in a process sulfur has not been found on a silicon surface etched in . The selectivity of an etching process cannot be shifted sufficiently in favor of by adding hydrogen, it can also not be increased much in favor of silicon by adding oxygen. The reaction product is . No other silicon compound than appeared in the mass spectrum. 1% in argon achieves etch rates of more than 100 nm/min with moderate rf energy. is also a useful etchant for with etch rates of 100 nm/min.