Impact of Rework Process to ETCH Bias and the Corresponding Solution

Etch bias is a key parameter to determine AEICD performance, and the photo rework is a routine method if photo process abnormal. Dependence of etch bias on photo rework is firstly found and studied in this work. By theoretical analysis and experimental verification, the model of the this dependence is proposed, which mainly attributes to the new dense OX film left below Barc after rework and the high selectivity of Barc to OX for Barc open step. Under the above two conditions, part of plasma convert its etch direction from vertical to horizontal during the OX open period, which attributes to trimming Barc CD, and thus changing etch bias. This dependence gets weaker when transmission rate increases due to macro-loading effect. Besides, it also gets stronger for dense pattern than for iso pattern, which attributes to micro-loading effect. While this dependence may induce AEICD and thus the WAT shift, solution to weaken the side effect of etch bias shift is proposed.