Nanoimprint combination techniques

Abstract

The combination of nanoimprint with optical lithography in a conventional mask aligner, both low-cost techniques, provides a number of novel but simple options for pattern definition with photoresists beyond nanoimprint or optical lithography. The effects exploited are based on two issues related to the interfaces at the bottom (substrate/resist) and at the top (resist/air); the bottom interface leads to a specific exposure situation with a reflective substrate like silicon, resulting in standing waves and a swing of the mean intensity in the resist; the top interface represents a pre-patterned surface providing phase shifting and diffraction when exposed. Both facts can be used to realize specific patterning results. We will show ‘residual layer free imprint’, frequency doubling with ‘residual layer lithography’, ‘hybrid lithography’ to overcome the pattern size dependence of nanoimprint as well as ‘multi-level structures’ resulting from diffraction patterns along the walls of lithography-defined grooves or inside the resist when thick layers are used. Major parameters for all effects are the resist thickness as well as the geometries of the stamp, in particular the stamp height. Furthermore, hierarchical wrinkling patterns can be induced by adding an exposure in the deep ultraviolet range to the hybrid process. The physical background of the effects will be addressed and examples of the single techniques are shown, indicating the requirements. With the physical understanding at hand the engineer is able either to make use of the effects shown or to avoid them, simply by choosing the boundary conditions of the combination process accordingly. The successful combination of nanoimprint with optical lithography relies on the fact that the imprint process does not change the properties of the imprinted material, in this case the optical ones, so that these can be exploited in a further processing step, namely lithography.