Half wavelength pattern replication using a projection lens with an ultra high numerical aperture and thin resist process

Applicability of a projection lens with an ultra high numerical aperture of 0.85 is investigated. Shorter wavelength exposure systems and various reso lution enhancement techniques such as phase shifting masks, off-axis illumi nation and multi reticle exposure methods are researched. However, minimiza tion of LSI patterns following the conventional trends is becoming increasi ngly difficult. Hence, various other ideas should be introduced and put to practical use simultaneously. When applying such a lens, it is anticipated that the depth of focus will become very small, especially for short wavele ngth exposure. For this reason, a thin resist with a thickness of 0.15-0.2 mum is adopted. A manufactured test exposure system is used for the experim ents, and wafers are exposed by a halogen lamp illumination system with a c entral wavelength of 480 nm. As a result, half-wavelength 0.24 mum line-and -space patterns are printed successfully and significantly better than thos e obtained by the conventional trends, and 0.21 mum patterns are almost res olved. Depth of focus for the 0.24-mum patterns is about 1 mum. The combina tion of ultra high numerical aperture exposure and thin resist process will be a superior option for further minimization of LSIs.