Status and issues of electron projection lithography

Abstract

Electron projection lithography (EPL) is a viable candidate for moderate-volume production of systems on a chip (SOC) for the 65-nm node and beyond. Making EPL a realistically applicable technology depends strongly on how well its infrastructure is developed. Many developments related to EPL, including those by Selete, are currently under way. The world's first full-field EPL exposure tool, the Nikon EB stepper, NSR-EB1A, was shipped to Selete. In the installation stage, the tool produced 70-nm line and space, 50-nm isolated line, and 80-nm contact hole resolution. EPL resist performance is approaching 50-nm resolution, 5-µC/cm2 sensitivity, and commercial availability. Sample EPL stencil masks are also available from three mask suppliers in Japan. Beta mask defect inspection and repair are also available, as is data processing software for EPL mask making. Such software has reduced processing time and data volume using PC clusters and hierarchical processing. The results of the first of EPL trial device fabrication showed good resolution for hole patterns at about 70 nm and the usefulness of EPL in hole delineation. EPL is thus being steadily improved and elements are commercially available, underscoring EPL's feasibility as a practical technology. Issues that remain to be solved include better EB stepper performance, faster resist, more accurate masks, the demonstration of practical inspection and repair tools, and verification software. These issues are, it should be noted, engineering issues rather than basic EPL issues. EPL remains the most promising candidate for the 65-nm node and beyond, especially for hole delineation. Selete is continuing EPL development, working with suppliers of exposure tools, resist, masks, inspection and repair tools, and software targeting lithography for 65-, 45-, and 32-nm nodes.