Demolding force dependence on mold surface modifications in UV nanoimprint lithography

Abstract

Nanoimprint lithography (NIL) has attracted broad interests in nano/micropatterning of photonic structures, however, one of the major challenges in NIL is the defect rate due to a large demolding force which causes difficult demolding. In this work, adhesion and friction stresses were obtained from the overall demolding force through measurements of the total demolding force and the geometries of the mold patterns. The friction stress on the sidewalls is generally larger than the adhesion stress between the mold and the resist. In addition, a conformal Al2O3 layer grown via atomic layer deposition was introduced to cover the imprint mold and reduce the surface roughness on the sidewalls. Together with the coating of an anti-adhesion layer for easy mold releasing, both adhesion and friction stresses were reduced, leading to a lower total demolding force compared to the conventional mold with merely a hydrophobic surfactant layer or mold without any surface modification. The results obtained from this work will help the design and optimization of the NIL molds to mitigate the defect rate in UV-NIL.