Dummy Poly Silicon Gate Removal by Wet Chemical Etching

Abstract

For the gate last integration scheme, dummy poly silicon gate removal is one of the indispensable processes either for a high-k first or a high-k last route. In this paper, experimental results of dummy poly silicon gate removal using TetraMethyl Ammonium Hydroxide (TMAH) chemical etching are presented. The preliminary results show that the poly silicon removal rate was highly sensitive to the wet etch conditions. By optimizing the wet etch conditions, high selectivity of poly silicon with respect to SiO2, Si3N4 and hafnium silicon oxynitride (HfSiON) was obtained. A gate trench of critical dimension (CD) of about 70 nm without poly silicon residue was fabricated using optimized conditions. The excellent etch capability of the optimized wet etch process was also demonstrated by controlling trench profiles.