Extending a multi-beam laser writer for optical and EUV masks

While laser mask pattern generators (MPGs) continue to serve the application spaces for legacy-node chip production and second-level writing for advanced masks, they also capture some masks with large data volumes resulting from optical proximity corrections. To improve throughput and print performance for these masks, a software-based data path has been implemented on the ALTA (R) multi-beam MPG platform. Running on a multicore architecture, the new data path provides more than an order of magnitude increase in processing speed for data preparation and rasterization compared to the existing hardware solution. The programs performing the data preparation and rasterization, along with the general-purpose computers on which they run, are referred to as the raster engine (RE). The RE accepts MEBES (R), OASIS (R), and GDSII (TM) formats, optimizes the data on a 0.1-nm grid, and applies both system and user-defined critical dimension (CD) corrections prior to printing. During mask printing, the prepared data are rasterized out to a 0.5-nm writing grid while applying additional corrections required by the ALTA architecture. A beam engine (BE) converts the rasterized data to radio frequency (RF) signals that drive the 32-channel acousto-optical modulator. The edge-placement resolution in the scan direction is controlled using timing, whereas the stripe-axis resolution is achieved using fixed beam spacing with 80 gray intensity levels. Significant improvements are observed in the scan-axis print performance and the consistency of corner rounding. This paper also examines the effects of the number of passes used in multi-pass printing on the tradeoff between print quality and mask write times. Finally, the capability to align to the fiducials defined by the SEMI P48 standard for EUV masks has been added to the ALTA system.