Three-dimensional aerial images of periodic patterns and the depth of focus for lines-and-spaces patterns

Abstract

A prescription for obtaining the three-dimensional irradiance of any periodic pattern is given and applied to obtaining the irradiance and the depth of focus (DOF) for linesand-spaces patterns. As is well known, the DOF for such patterns can be made large by restricting the angular spread of the illuminating light. At a fixed k 1 , the so-called tip-to-tip distance between two opposing line-ends can be made smaller if the numerical aperture of the imaging optics is increased.

Exploring the limits of high contrast contact imaging using split pupil exposures in high-NA EUV lithography

“…The DoF generally drops with an increased range of illumination angles σ x inside an illumination pole. 24,25 Comprehensive simulation studies for different pitch combinations, mask absorber materials and source fillings have demonstrated that split pupil exposures enable not only a mitigation of the image blur, but also a compensation of best focus shifts between different pitches. The best imaging performance was achieved for a combination of split pupil exposures with low-n/low-k absorbers.…”