A method of analysis of the F base strip process effect on the polycide film

In VLSI technology, photoresist is used as a mask for the pattern transfer by the etch processes, and also for the electrical regime defining processes performed by the ion implantation process. An oxygen plasma ashing process is usually implemented subsequently for the photoresist removal. In the ashing processes involving a high current/high dosage implantation process, a gas with extra F ions, like CF₄ and C₂F₆, needs to be added into the O₂ plasma to increase the strip ability. Among the F base gases, CF₄ is the most powerful gas. However, the addition of the fluorine based gases could damage the integrity of the exposed tungsten silicide layer, which is deposited on the top of the poly gate to reduce the polysilicon film contact resistance. In this paper, the addition of the CF₄ gas in the plasma ashing processes was studied for the effect on the WSix integrity. This study is done by collecting the correlation of loss rate on the WSix film and on the PE oxide film during the ashing processes containing the CF4 gas. The correlation is then reviewed with the final electrical data, and summarizes the fluorine ashing gas effect on the electrical outcomes. Through this study, the effect of the ashing processes on the device performance can be predicted before setting up the new ashing recipes for production