Data preparation ofphotomask layout has become a major issue ofmask making. As model-based OPC becomes a compulsory technology for advanced manufacturing processes, photolithography engineers encounter the issue in data preparation ofphotomask layout-the file size after-OPC treatment is much larger than original file size (without OPC treatment). Consequence oflarge file size leads to difficult manipulation of database such as longer OPC run time and larger disk space, which challenges computer systems and software tools, etc. Part of file-size expansion arises from the nature ofcurrent methodology, which is caused by fragmentation ofpolygon edges. However, still part of expansion is unnecessary, because some unintentional layout is sent into an OPC engine. If any given OPC engine is fed with unintentional layout features, frequently very bad, in terms ofphotolithography target and file size, post-OPC layout is produced. To avoid the unnecessary file size expansion and unintentional features produced after OPC is applied on layouts, a systematic "smoothing" algorithm is developed to apply on a real chip. Any algorithms that scan through polygons for each type of defects would be unavoidable to scan the whole layout many times. The algorithm introduced here does not try to fix different kinds ofpolygon "defects" one by one. The key is different kinds of defects are reduced to a few categories. The performance can be expected because polygons are scanned through fewer times. After the treatment, the numbers ofpolygon vertices becomes less. The new database is also more OPC friendly.