Etching of polysilicon in inductively coupled Cl2 and HBr discharges.: III.: Photoresist mask faceting, sidewall deposition, and microtrenching

The etching artifacts observed during the high density Cl-2 plasma etching of photoresist-masked polysilicon [A. P. Mahorowala and H. H. Sawin, J. Vac. Sci. Technol. B 20, 1055 (2002)] were analyzed using a 2 1/2-dimensional Monte Carlo profile evolution simulator [A. P. Mahorowala and H. H. Sawin, J. Vac. Sci. Technol. B 20, 1064 (2002)]. A set of profile evolution simulations for the Cl etching of photoresist-masked polysilicon features, including plasma deposition of two representative etching byproducts (C and SiCl2) were performed. The extent of deposition and the formation of facets, straight sidewalls, and microtrenches were strongly affected by the competing etching and deposition. The simulations suggested that the top facet angle was controlled by the surface composition at the top of the photoresist lines and the angular dependence for etching of the deposited material; the facet being less steep when there was more deposition of Si-based byproducts. The lower facet angle and the polysilicon sidewall profile were governed by the feature aspect ratio, the sticking probabilities, and fluxes of the depositing material and the depositing material etching angular dependence. Feature bottom microtrenching was strongly linked to sidewall curvature, i.e., bowing. Microtrenching was found to begin when the sidewalls bowed sufficiently. Scattering of the ions from the curved sidewalls exhibited a focusing effect on the directional ions concentrating them at a point near the sidewall, thereby causing the microtrenching. (C) 2002 American Vacuum Society.