Layer thickness-induced lens distortions during thermal nanoimprint

Abstract

Arrays of convex spherical lenses with heights in the micrometer range and diameters of 100 and 200μm⁠, respectively, were imprinted into thin layers of polystyrene by thermal imprint. The masters were prepared by gray tone lithography and dry etching. They feature three distinct lens heights, so that during imprint into medium layer thickness three different situations prevail: imprint into thick layers, imprint into thin/adequate layers, and imprint into highly thinned layers. Only during imprint in such highly thinned layers slight recovery was detected combined with stretching-induced polymer layer breakup. For all other cases the replication quality was good and did not show recovery effects. This is in contrast to the imprint of flat stamps into layer thickness of similar sizes. Differences detected in height of the replicated lenses compared to the master are due to thermal expansion in the thermal nanoimprint lithography process. Negligible residual layers were obtained at only slightly changed curvature radius.