Tungsten silicide and tungsten polycide anisotropic dry etch process for highly controlled dimensions and profiles

Highly anisotropic dry etching of tungsten silicide and tungsten polycides is required for the realization of submicron low resistance gates and interconnects for use in high performance complementary metal–oxide–semiconductor ~CMOS! and BiCMOS technologies. The current etch chemistries are not anisotropic, i.e., lateral etching of the tungsten silicide takes place which results in undesirable CD loss. In many applications a spacer needs to be formed on the polycide sidewall ~Fig. 1!. Undesirable undercutting can result in nonideal spacer formation for further device fabrication. Tungsten silicide etching has been described in literature using mixtures of SF6 , Cl2 , or CF4 . 2–4 However, all these chemistries have excessive undercutting, no end point detection, and poor control of sidewall profile. It is the purpose of this brief to describe an etch chemistry using C2F6 , Cl2 , and O2 which forms polymer on the sidewall of the tungsten silicide during the etch in order to avoid undercutting. In addition, the etch chemistry allows increase of the critical dimension by controlling the polymer deposition on the sidewall.