Directional Difference of Patterns Printed by Scan-Projection Lithography Using a Gradient Index Lens Array

Abstract

Peculiar patterning characteristics of scan projection lithography using a gradient index lens array were investigated. When a lens array with two-line lenses was used, pattern widths of line-and-space patterns differed according to the pattern directions. Parts of the light rays diffracted in the direction perpendicular to the lens line are lost without passing through the lenses, because only two lenses are available in that direction. As a result, the resolution of patterns parallel to the lens line slightly degrades. On the other hand, light rays parallel to the lens line are sufficiently used for imaging. For this reason, the widths of line patterns printed in a positive resist slightly decrease. However, if the two-line lens array was replaced by a four-line lens array, the peculiar patterning characteristics were almost lost, and patterns were printed almost without directional differences. This is because the lens array width becomes sufficient.

Investigation into causes of resolution degradation in projection exposure using a gradient-index lens array

“…For this reason, the authors developed two handmade prototype exposure systems using a commercial GRIN lens array, in the past research. [4][5][6].…”