Resolution enhancement by oblique illumination optical lithography using a transmittance-adjusted pupil filter

This paper describes the resolution enhancement by oblique illumination optical lithography using a transmittance-adjusted pupil filter that has a conjugate shape to the secondary light source. The resolution enhancement depends on the amplitude transmittance distribution of the pupil filter in the lens aperture. Thus, the optimum transmittance distribution attaining the highest resolution at a practical depth of focus is investigated, and superior performance is verified experimentally using an actual i-line stepper, that is, the actual resolution improvement is comparable to the simulation results. Despite this improvement, two problems must be addressed. Pattern profiles degrade at the ends of periodical patterns, and the opaque pattern widths of middle-pitch patterns become a little narrow. These two problems are solved by optimizing the transmittance distribution of the filter such that there is no significant deterioration in the high-resolution performance.