Low temperature SF6/O2 electron cyclotron resonance plasma etching for polysilicon gates

The use of SF6/O2 chemistry for polysilicon gate etching at a low temperature in an electron cyclotron resonance plasma etcher is considered. Sidewall angle, polysilicon etch rate, and selectivity to gate oxide and photoresist are reported as functions of temperature in the range -125 deg. C to 25 deg. C. The addition of oxygen to the plasma allows anisotropic etching to be obtained at higher temperatures than with pure SF6. 0.3 μm long gates were formed at -100 deg. C using an etch process with ≅3:1 selectivity to photoresist and ≅14:1 selectivity to oxide