Precision plasma etching of Si, Ge, and Ge:P by SF6 with added O2

The impact of the O2 content in SF6-O2 gas mixtures on the etch rate and sidewall profile of silicon (Si), germanium (Ge), and phosphorous doped germanium (Ge:P) in reactive ion etching has been studied. The characteristics of etch rate and sidewall profile are greatly affected by the O2 content. Below 50% of O2 content, a large variation in Ge etch rates is found compared to that of Si, but for O2 content above 50% the etch rates follow relatively the same trend. Lightly doped Ge shows the highest etch rate at a O2 concentration up to 20%. Sidewall angles range from a minimum of 80° to a maximum of 166°, with O2 concentration of 20% yielding perfect anisotropic mesa etch. Also at this O2 concentration, reasonable Si/Ge selectivity is possible. These observations indicate that by adjusting the O2 concentration, precision plasma etching of Si, Ge, and Ge:P is possible.