Application of Sector Fresnel Zone Plates to Video Based Alignment in X-ray Lithography

Abstract

Fresnel zone plate patterns have been widely applied to mask to wafer alignment because the fresnel beam spots are unaffected by poor edge definition or by rough surfaces arising from variation in processing. This paper describes a video-based alignment using a sector fresnel zone plate (SFZP) which is unique among the zone plates in having an oblique line focus. SFZPs printed on both X-ray mask and wafers are illuminated with collimated He-Ne laser beam. The bright image formed on an oblique line focus shows high contrast better than 11-15dB in signal to background ratio. With SFZPs, position sensing repeatability better than 9 nm (3σ) has been obtained in four processed wafer types.