A study on directional damaged defect in photomask manufacturing process

The wafer industry is quickly moving to the high-end technology nodes to meet the demands of advanced semiconductor applications, mask makers focus on pattern fidelity control. However, it poses additional challenges to professional mask makers in terms of process window control of pattern diversity. In this article, a reproducible pattern damaged defect is recently observed by KLA mask inspection that is unrepairable due to the large defect size. This defect, so called directional damaged defect in this paper, is distributed among multiple die in array mask and shows pinhole and LCE (Local CD Error) at the pattern line end through SEM (Scan Electron Microscope). Moreover, this defect is highly directional and positional dependence. A step-by-step analysis of the process flow via SEM is conducted and it shows that LCE and damage is caused by low conductivity chemicals during clean process. This paper proposes that the root cause is the frictional accumulation of charges by chemical flowing large size pattern so as to result in directional damaged defect. A special any-angle radial shape layout is designed to verify process window of this type defect, as a result, all the process window of wet chemical solutions can be verified.