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

As semiconductor device is being scaled down to 65nm node and below, the control of pattern density effect in back end of line (BEOL) etch becomes more crucial to ensure the on-target production delivery. Pattern density difference normally stems from the specific design of various products. 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 on A) corrosion window with different Al-pad photo transmission rates (TR); B) within-wafer profile loading between Al-line (dense feature) and Al-pad (iso feature). Polymer mode has been proven as one of potential mechanisms for these issues. The corresponding feasible solutions focus on A) the adjustment of polymer gas ratio for any product based on its actual pattern density. B) the optimized combo of chemicals and bias power to reduce the within-wafer dense and iso loading.