LOW-TEMPERATURE ETCHING OF SI IN HIGH-DENSITY PLASMA USING SF6/O-2

Low temperature etching of Si with SF6 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-degrees-C. Anisotropic etch profiles are obtained by an addition of O2. We therefore propose a sidewall passivation mechanism to explain the reduction of the lateral etching. Si etch rates of 5 mum/min at selectivities Si/SiO2 well above 100/1, with anisotropic profile have been obtained.