Half Wavelength Pattern Replication Using a Projection Lens with an Ultra High Numerical Aperture and Thin Resist Process

Abstract

Applicability of a projection lens with an ultra high numerical aperture of 0.85 is investigated. Shorter wavelength exposure systems and various resolution enhancement techniques such as phase shifting masks, off-axis illumination and multi reticle exposure methods are researched. However, minimization of LSI patterns following the conventional trends is becoming increasingly 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 wavelength exposure. For this reason, a thin resist with a thickness of 0.15–0.2 µm is adopted. A manufactured test exposure system is used for the experiments, and wafers are exposed by a halogen lamp illumination system with a central wavelength of 480 nm. As a result, half-wavelength 0.24 µm line-and-space patterns are printed successfully and significantly better than those obtained by the conventional trends, and 0.21 µm patterns are almost resolved. Depth of focus for the 0.24-µm patterns is about 1 µm. The combination of ultra high numerical aperture exposure and thin resist process will be a superior option for further minimization of LSIs.