Performance of single sideband optical lithography using a pupil filter in replicating isolated patterns

This paper describes how oblique illumination optical lithography using a transmittance-adjusted pupil filter is efficient for isolated patterns as well as periodical patterns. This method is successful for the following reasons. When a pupil filter has a small transmittance in the area where 0th-order diffraction light image of secondary light source is made, the 0th-order diffraction light is selectively attenuated. From this attenuation, the ratio of the light components with a middle and high spatial frequency becomes larger than it would without a pupil filter. As a result, because the light intensity curves for isolated line patterns and space patterns are sharpened, high resolution and large focus latitude are obtained. Lines-and-spaces patterns and both types of isolated patterns with a critical size near the resolution limit are replicated into the designed width simultaneously with the same exposure dose.