Optical UV lithography has probably the best chance to become the production technique for 256MB complexity devices [M. Rothschild, Proceedings of the 37th International Symposium on Electron, Ion, and Photon Beams, Orlando, FL, 26-29 May, 1992 (unpublished). N. Nomura et al., Microcircuit Engineering Conference, Erlangen, Germany, Date 1992 (unpublished) 1. X-ray lithography (XRL) is still a promising alternative, but this technology is in an earlier state of development [S. Yoshida, MicroProcess Conference, Kawasaki, Japan, Date 1992 (unpublished)]. Many research centers are putting effort into this to accelerate the development. Maskmaking is one of the critical issues in XRL. With increasing pattern complexity, not only the accuracy of the lithographic tool, but the whole path from computer-aided design conversion to lithography tool optimization to exposure becomes important. 256MB complexity pattern data have been converted by using both a flattening and a hierarchical convertor. The total conversion time from both convertors is similar. By maintaining the hierarchy during the fracturing, the hierarchical convertor has more flexibility for pattern manipulation. The Leica Cambridge EBPG5-HR was optimized and the exposure time of a 256MB complexity mask was less than 7 h. Four masks were exposed and fully analyzed. After correcting for substrate drift in the first two exposures, the overlay between the second pair of masks was 41 nm (3sigma). Pattern placement in all masks was better than 25 nm (3sigma).