It is well known that with the development of advanced semiconductor technology, the phase shift mask (PSM) has been widely utilized in the semiconductor lithography process. Usually, the PSM blank coated with negative chemically amplified resist (NCAR) was used for fabrication of AA (Active area) layer and Poly layer mask which utilized in the logic semiconductor products. Under the electron beam (EB) writing systems, this NCAR resist showed better opaque pattern forming ability for complex OPC pattern and sub-resolution assist bar features[1]. In this contribution, a kind of defect so-called tiny MoSi defect that was captured by KLA inspection tool during NCAR mask fabrication process would be described. This kind of defect randomly scattered over the whole mask and located on quartz surface where photo resist was developed for not exposure by electron beam and Cr/MoSi was removed after dry etching process. In order to figure out this problem, we investigated the root cause of tiny MoSi defect by split condition test and cross validation, especially focused on the interaction between each process unit. According to the verification result, we would propose the possible formation mechanism and modify the recipe based on this understanding. The long-term inspection monitoring result showed that this kind defect density could be reduced from two hundred to less than twenty counts after recipe optimization.
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