Sidewall-angle dependent mold filling of three-dimensional microcavities in thermal nanoimprint lithography

Abstract

Nanoimprint stamp cavities with vertical and sloped sidewalls show different filling behaviors during thermal nanoimprinting resulting from the varying ability of the viscous polymer to wet the surface during the thermal imprint step. In this paper, the authors describe the formation of prefill states already in the pressure-less contact phase, before squeeze flow begins to fill the cavities. These stable states are created by a constant contact angle formed at the sidewall, and the states themselves generate surface topographies in the resist below the imprint cavities which are dependent upon the surface energy, the geometry of the stamp cavities, and the resist thickness. Therefore, prefilling topographies, formed once a stamp is in contact with a liquid polymer surface and resulting in a transformation of the resist layer with homogeneous thickness into a thickness modulated film, have to be considered as the standard case in molding. Furthermore, due to the local balance of material pinning and wetting mechanisms, cavities preferentially fill from the sloped sidewall and, therefore, this observed phenomenon is highly relevant for the defect-free replication of 3-D surface topographies.