Pattern-data preparation method to enhance high-throughput mask fabrication in variable-shaped e-beam writing system

We have developed a new method of preparing pattern data to increase throughput of an EB writing system. The main idea is to expand cells smaller than a threshold size to the corresponding upper level cells during hierarchical shape data operations, which leads to reduction of the number of subfields and shots in our EB writing system. The cell expansions, however, could cause increase in the data volume and data conversion time as a result of destroying the hierarchy of CAD data. Therefore, we have introduced an additional rule, that is, not to expand cell arrays which have more elements than a threshold number. The new data conversion processor, which adopts the above-mentioned cell expansion algorithm, has been applied to a 64Mbit and a 256Mbit DRAM. The new module was applied to three layers, that is, the trench layer, the gate poly layer and metal layer of each DRAM. As a result, we found that the number of subfields and the number of shots were reduced by about 60% and 35%, respectively, for the average of 6 layers. Resulting throughput was evaluated as 1.8 times for the average of 6 layers. Performance change in the conversion processor has been examined in terms of data volume and data conversion time, and is discussed in the paper.