Alternative etching gases to SF6 for plasma enhanced chamber cleaning in silicon deposition systems

The aim of this study is to reduce the amount of harmful substances in the effluent gas in the plasma cleaning process of vacuum chambers by substituting the greenhouse gas SF6. We present comparative studies for the optimised cleaning rates which are based on C4F8/O2 and NF3 diluted with He, Ar and N2 in comparison to SF6/O2. Since the deposition of amorphous silicon (a-Si) requires a temperature of 200–250 °C in the vacuum chamber, the cleaning process has to match with these conditions, creating especially limitations on the maximum plasma power that can be used. The results for C4F8/O2 turn out to be unsatisfactory. NF3 however appears to be more promising. We find that the utilisation of NF3 as etching gas in the vacuum chamber approaches up to 90% and the dilution can be up to 80%. This high dilution and utilisation demonstrates also that cleaning with NF3 can be cheaper than cleaning with SF6 even though NF3 is much more expensive than SF6.