Low temperature etching of Si in high density plasma using SF6/O2

Low temperature etching of Si with SF"6 has been studied, using a DECR system and a special Helicon type plasma source. In contrast to the current understanding of low temperature etching, we did not observe a ''freezing'' of the lateral etching reaction, but obtained isotropic etch profiles, even at temperatures below -120^o C. Anisotropic etch profiles are obtained by an addition of O"2. We therefore propose a sidewall passivation mechanism to explain the reduction of the lateral etching. Si etch rates of [email protected]/min at selectivities Si/SiO"2 well above 100/1, with anisotropic profile have been obtained.