Reactive-ion etching of tungsten silicide using NF3 gas mixtures

Abstract

We report in this paper the reactive-ion etching of WSix films using gas mixtures containing NF3. A combination of NF3/H2 or NF3/He was used to anisotropically etch WSix films as thick as 4000 Å with photoresist masks. They yielded satisfactorily high etch rates and good selectivities with respect to photoresist and III–V materials. The NF3/He mixture yielded higher etch rates for both WSix and photoresist but a lower selectivity with respect to photoresist. CHF3 was used with NF3 for thicker films and/or submicron features in order to form polymer to protect the sidewalls. Metal masks have to be used in this etch since the etch rates are very low and the selectivity with respect to photoresist is no longer high. A low percentage of NF3 and a low pressure were necessary for successful etches using the NF3/CHF3 plasma. Etched lines as narrow as 0.18 μm are shown. In addition to the optimal etch conditions, data will also be presented for the effects of variations of cathode coverage, rf power, gas pressure, and gas composition.