18 December 1998 Method to determine printability of photomask defects and its use in phase-shift mask evaluations
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Abstract
Typically all defects found on a photomask are repaired, despite the fact that many of the defects would not cause problems on the wafer. Ideally, if the lithographic process does not image the defect onto the wafer in such a way as to adversely affect the performance of the device, then the mask maker should not be required to repair the defect -- saving time and money. It is difficult to classify defects in this manner, however, as the impact of the defect depends on various factors, including: lithography process parameters, proximity of defect to a critical feature, feature type and the size, shape, phase and transmission of the defect. These effects are further complicated by shrinking critical feature sizes and the use of resolution enhancement techniques, such as PSM and OPC. To address this problem, a new method of determining the printability of defects on all types of photomasks was developed. This method involves characterizing the aerial image of the defect and assigning an equivalent mask CD error to the defect. The equivalent CD error is then compared to the mask CD error specification to determine if the defect should be repaired. This methodology ties the mask defect specification directly to the device performance specifications and accounts for the multitude of factors that influence the defect printability in a real lithography process. This technique has been used to evaluate attenuated and alternating PSM.
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Scott M. Mansfield, Richard A. Ferguson, Lars W. Liebmann, Antoinette F. Molless, Alfred K. K. Wong, "Method to determine printability of photomask defects and its use in phase-shift mask evaluations", Proc. SPIE 3546, 18th Annual BACUS Symposium on Photomask Technology and Management, (18 December 1998); doi: 10.1117/12.332867; https://doi.org/10.1117/12.332867
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