TUNGSTEN ETCHING IN PULSED SF6 PLASMAS

Tungsten etching in pulsed plasmas has been investigated in a helicon plasma source reactor. The time dependence of the fluorine atom concen tration has been measured using the time-resolved actinometry techniqu e and related to the etch rate. According to our observations, it appe ars that fluorine adsorption on the tungsten substrate surface continu es in the post-discharge period until the surface saturates. Moreover, it appears that two etching regimes exist. For short discharge off pe riods, the etching is limited by the fluorine adsorption ability of th e surface, whereas for long periods, the etching is limited by the des orption rate of the etch products. Experiments were performed at diffe rent substrate temperatures and plasma gas pressures. An empirical mod el has been developed, in good agreement with the experimental data.