Within Wafer & Wafer to Wafer Thickness Uniformity Controllable Study on ILD-CMP Via Polishing Pad’s Physical Property Analysis and Linear Interval Feedback APC’s Implementation

Abstract

The CMP post thickness profile became so critical for ILD-CMP. The WTW (wafer to wafer) thickness variation, WiW (within wafer) thickness range control, especially for WEE (wafer extreme edge) TK are key production indices in the fab. ILD-CMP, as a stop-in process, is processed with APC (auto processing feedback) normally to control WTW. In this research, linear Interval feedback mode APC was studied to cover ILD-CMP wafer to wafer (WTW) thickness variation. After the bulk removal step and planarization was completed, then turn on APC. It is showed that APC feedback simulation curve was more close to the real removal rate decay curve. After the linear interval feedback APC was implemented, the WTW thickness variation can be reduced by 35.57% than the initial feedback mode. For WiW improvement, 4 different types of pads with different rigidity, thickness and compression ratio were tested to check the WEE thickness’s response to the CMP tuning parameters, such as pressure, slurry flow rate, and head/platen rotation speed, etc. The results indicated that CIPC pad can be demonstrated the linear correlation between WEE thickness and wafer edge pressure, as well as the thickness’s stability through retaining ring’s lifetime. The hardness and compression ratio of polishing sub-pad were so critical for ILDCMP WEE thickness uniformity’s tuning and stability maintenance.