Alignment mark materials for projection electron lithography

Abstract

Recent advances in projection electron lithography have led to the development of a non-imaging mark detection scheme for alignment and registration that uses backscatter electron (BSE) contrast. The detection scheme is referred to as the beamlet method and uses the measured BSE emission to detect the correct alignment condition when the image of a mask mark is scanned over a corresponding wafer mark When applied to a SCALPEL system (i.e. SCattering with Angular Limitation in Projection Electron Lithography) mark detection accuracy of better than 10 nm has been reported. Incident electrons with approximately 100 keV energy will be used in a practical SCALPEL lithography tool. In this study we compare theoretical BSE ratios with quantitative measurements in a prototype SCALPEL machine. From these results we are able to predict the suitability of materials used for conductive links in very large scale integrated (VLSI) circuits.The theory for BSE emission from thin deposited films has been developed from work on thin self supporting films.