Efficient mask data preparation for variable shaped e-beam writing system focusing on memory devices

摘要

To cope with sub-100nm technology in the mask making industry, a variable shaped e-beam(VSB) writing system is one of the solutions through its high-electron voltage. The VSB writing system, however, requires a different mask data preparation comparing to the traditional raster scan writing system. Due to the differences, mask making industries are confronted with difficult problems, such as explosively increasing data volume and unpredictably growing mask making time especially for memory devices. VSB system's writing time is determined by the conversion from CAD data to VSB data. The conversion time, especially for the critical layers of memory devices, mostly depends on to what extent optimize CAD data to enhance writing system throughput. For this reason, to shorten the unpredictably growing mask making time, a data conversion tool must consider the throughput of data conversion and mask writing at the same time. To reduce the data conversion time while retaining the optimal writing time, we propose the mixed-mode data processing method, in which the hierarchical data operation is applied on memory cells and the flat data operation is applied on peripheral circuits. For each area, different fracturing strategies are applied, too. The polygon-aware fracturing method is applied to improve the CD control within memory cells, and the selective one-directional fracturing method is applied to reduce the writing time within peripheral circuits.