Effects of etch chemistry on SF6-based tungsten etching by electron cyclotron resonance reactive ion etching

Abstract

Studies of etch chemistry effects on SF6-based tungsten etching have been performed in an electron cyclotron resonance microwave reactive ion etching system. The etch chemistry and, therefore, reactive species concentrations were varied in several ways and the effect of these variations on etch rate and anisotropy of etched features were evaluated. Reactive species concentrations were altered by varying the residence time in a pure SF6 plasma or by introducing argon or nitrogen in the SF6 plasma under constant residence time. For pure SF6 and under conditions similar to those in a parallel plate radio frequency system, the tungsten etch rate was more than three times greater—presumably the results of higher dissociation efficiencies. As residence time was increased from 1 to 30 s the etch rate was decreased by greater than a factor of 2 and linewidth loss was reduced from better than 50 to 5%. Addition of argon to the plasma reduced the etch rate while maintaining short residence times. The addition of nitrogen to SF6 resulted in a complex behavior that provided optimum etch rate with minimum linewidth loss for a 50/50 mixture. In evaluating the behavior, sidewall passivation processes and competitive reactions in the gas phase are discussed.