Lossless layout compression for maskless lithography systems

Future lithography systems must produce more dense chips with smaller feature sizes, while maintaining throughput comparable to today's optical lithography systems. This places stringent data-handling requirements on the design of any maskless lithography system. Today's optical lithography systems transfer one layer of data from the mask to the entire wafer in about sixty seconds. To achieve a similar throughput for a direct-write maskless lithography system with a pixel size of 25 nm, data rates of about 10 Tb/s are required. In this paper, we propose an architecture for delivering such a data rate to a parallel array of writers. In arriving at this architecture, we conclude that pixel domain compression schemes are essential for delivering these high data rates. To achieve the desired compression ratios, we explore a number of binary lossless compression algorithms, and apply them to a variety of layers of typical circuits such as memory and control. The algorithms explored include the Joint Bi-Level Image Processing Group (JBIG), Ziv-Lempel (LZ77) as implemented by ZIP, as well as our own extension of Ziv-Lempel to two-dimensions. For all the layouts we tested, at least one of the above schemes achieves a compression ratio of 20 or larger, demonstrating the feasibility of the proposed system architecture.