Anisotropy and kinetics of the etching of tungsten in SF6 multipolar microwave plasma

An experimental study of the etching of tungsten with SF6 has been performed in a microwave multipolar plasma using an electron cyclotron resonance excitation with an independent low dc biasing. The anisotropy and etch rate of tungsten have been measured as a function of atomic fluorine concentration in the plasma and compared with silicon characteristics. The etching mechanisms of tungsten are analyzed in light of published data on the fluorine-tungsten interaction, and the results are explained in terms of the diffusion model for plasma etching developed for the Si-F system. Atomic fluorine adsorption on tungsten appears to be monolayerlike, whereas it is of multilayer type on silicon, and associative desorption of WF6 occurs from WF3 and/or WF4 adspecies in nearest-neighbor positions.