Mr-NIL 6000LT – Epoxy-based curing resist for combined thermal and UV nanoimprint lithography below 50 °C

Abstract

The aim of the work presented here was to develop curing polymers for nanoimprint lithography (NIL) enabling short cycle time, low imprint temperature, and an isothermal imprint process. The result is mr-NIL 6000LT: A photochemically curing polymer system for isothermal imprinting by combined thermal and UV nanoimprint lithography. It allows a lower imprint temperature than materials presented previously [C. Schuster, M. Kubenz, F. Reuther, M. Fink, G. Grützner, mr-NIL 6000 – New epoxy-based curing resist for efficient processing in combined thermal and UV nanoimprint lithography, in: Proceedings of SPIE 6517 2007, 65172B.; D.W. Johnson, H. Miller, M. Kubenz, F. Reuther, G. Grützner, Nanoimprinting with SU-8 Epoxy Resists, in: Proceedings of SPIE 6517 2007, 65172A.]. The material system chosen is based on a blend of epoxy resins and a photo acid generator. Such epoxy resists cure during the imprint step in combined thermal and UV nanoimprint lithography. Initiated by UV exposure the cationic polymerisation occurs at elevated temperature forming a polymer pattern with significantly increased thermal stability compared to the uncured system. Apart from the material development leading to mr-NIL 6000LT the correlations between the parameters imprint temperature, exposure time and post exposure hold time are investigated in this work. With the applied resin combination a T g of −15 °C is obtained. This enables the formation of solid films at room temperature after spin-coating and prebake and nevertheless imprint temperatures in the range of 45–50 °C, which is a distinct decrease compared to the 100–110 °C needed for the previously introduced mr-NIL 6000 [C. Schuster, M. Kubenz, F. Reuther, M. Fink, G. Grützner, mr-NIL 6000 – New epoxy-based curing resist for efficient processing in combined thermal and UV nanoimprint lithography, in: Proceedings of SPIE 6517 2007, 65172B.] or the 65–70 °C necessary for defect-free imprinting of the epoxy-based polymer described in [D.W. Johnson, H. Miller, M. Kubenz, F. Reuther, G. Grützner, Nanoimprinting with SU-8 Epoxy Resists, in: Proceedings of SPIE 6517 2007, 65172A.]. mr-NIL 6000LT exhibits good dimensional stability at 120 °C after curing during the imprint process. This is sufficient for an isothermal imprint process as well as subsequent processes, e.g. metallization or etching.