FEASIBILITY STUDY OF NEW GRAYBEAM WRITING STRATEGIES FOR RASTER SCAN MASK GENERATION

The simplicity of the raster scan beam technology has made it the dominant choice for maskmaking production tools. Nevertheless, building patterns on a grid resolution determined by the address of the raster scan mask generator places limitations on the location of pattern edges. Furthermore, as pattern dimensions shrink to 0.5 mum, and eventually to 0.15 mum, the standard technique of decreasing the address unit size decreases write time throughput. One promising approach to avoid this throughput bottleneck is pixel-level intensity and position modulation (graybeam plus pixel deflection to displace edge locations of patterns at a resolution smaller than the address grid size. In this article, methods for modulating the intensity and position of writing pixels are shown, along with simulation and experimental results using test patterns. Simulation results are presented that show the relationship between grid size and the discrete intensity levels needed to achieve a given edge placement requirement. Intensity and position modulation opens the possibility of using fewer pixels per pattern (larger address size) for a given edge placement requirement in comparison to conventional raster scan exposure techniques. Sensitivity of the displacement to lithography parameters and patterns are also determined and compared to experimental results. Finally, feasibility for hardware implementation on a raster scan e-beam system is presented.