The Process Challenges from Silicon Rich Polymers: A Case Study on Yield Loss Induced by Consecutive Etch and Stripping Processes

This paper discusses a case of random yield loss observed in multiple production lots due to leakage failures. Failure analysis (FA) revealed polysilicon bridging and short circuits caused by poly etch blocking, linked to various etch and strip processes. The issue stemmed from the formation of silicon-rich polymers during hard mask etching and poly etching processes, which were inadequately removed in subsequent plasma and chemical resist stripping processes. These polymers accumulated, causing blocked etch in the later poly etch layer and resulting in leakage failures. The analysis identified differences in equipment and process chemistry as the root cause of the polymer formation and removal inefficiency. Experiments to optimize polymer formation and removal are discussed as a reference to future process improvements and enhance wafer yield.