Pattern Density Effect in 65nm Logic BEOL Al-Pad Etch

Abstract

As semiconductor devices are being scaled down to critical dimensions of 65nm and below, the control of the pattern density effect in back end of line (BEOL) etch, in particular the corresponding loading effect, becomes crucial to ensure the on-target production. This paper addresses the challenges and solutions to reduce the influence of pattern density variation in 65nm BEOL logic Al-pad etch processes. Challenges include the impact of pattern density from the corrosion window with different Al-pad photo transmission rates (TR) and the within-wafer profile loading between Al-line (dense feature) and Al-pad (iso feature). Polymer deposition was found to be linked to these issues. The corresponding solutions focus on the adjustment of polymer gas ratio for any product based on its actual pattern density and the optimized combination of etch gases and bias power to reduce the within-wafer dense and iso loading.