Evaluation on metal photo rework scheme for yield improvement

Metal photo rework scheme which consists of NBA resist strip and ashing result to yield loss for 0.25 mum CMOS product. The failure pattern is cluster failures at the wafer center and mild failure at the wafer edge. Investigation showed that the frequency of heat treatment from 220degC to 250degC promotes the severity of sort failure. It indicates that there is insufficient thermal budget. Thus, the solution for yield improvement is either to buy margin for thermal budget or to reduce heat treatment process. Evaluation on different metal photo rework schemes as well as the metal scheme was undertaken. This paper described on the journey to characterizing a more robust rework scheme with minimal change in the process flow. Considering the yield result, cost and throughput of production, a more robust metal rework scheme is finalized on NBA only with nothing change on the metal scheme.