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The OASIS (Open Artwork System Interchange Standard) format is a new standard format for describing LSI layout data and it has begun to be used for photomask data. One of the greatest features of OASIS format is its conciseness of expressing pattern data and it has been proven that the size of GDS2 files can be significantly reduced down by converting them to OASIS format. It is widely believed that OASIS will replace the position of GDS2 format which is currently most frequently used. In general, OASIS has two aspects for the mask industry. One is OASIS format as a new replacement of GDS2. The other is OASIS.VSB, which is a unified format to be defined for the description of fractured EB data.

However, the mask industry has not shifted completely into OASIS and sometimes software operation for both OASIS and GDS2 is required. In the environment of OASIS and GDS2 mixture, bi-directional data conversion between OASIS and GDS2 is a key issue. When GDS2 data is converted to OASIS format, the file size always gets smaller and there is no file size problem. But when OASIS data is converted to GDS2 format, the file size can be more than one hundred times larger than the OASIS file, which sometimes causes hard disk space problems.

In order to cope with this problem, we have developed a file size estimation tool for OASIS to GDS2 conversion. The name of the tool is "o2gest" and it is a member of SmartOASIS, which provides comprehensive practical functions to enable easy transition of data processing flow from conventional GDS2 or EB formats to OASIS. The processing speed and the calculation accuracy is a key issue for an estimation tool.