Development of thermosets for thermal nanoimprint lithography at decreased temperatures

Abstract

Prepolymers formed from multifunctional allyl monomers can beneficially used in nanoimprint lithography (NIL), since they cure as a consequence of heating during the imprint process. Thus they have the potential to enable NIL at comparatively low temperatures while the imprinted patterns concurrently show high thermal stability, in contrast to thermoplastic polymers, where the thermal behaviour of the imprinted patterns is closely related to the glass transition temperature (T_g) of the polymers. The use of allyl prepolymers for NIL was previously described, but only very few experimental data are known. In recent investigations on the application of allyl prepolymers for NIL a displacement of the patterns on the wafer has been observed after cooling down the imprinted polymer in the press. This could be avoided by detaching the stamp at the imprint temperature, i.e. without cooling down the press, which requires the polymer to be crosslinked to a great extent in this stage. Since high temperatures are necessary (150 °C - 190 °C), and the imprint time is still long, allyl prepolymers to be reported here have been modified aiming at a reduction of imprint temperature and time. The admixture of free-radical initiators increases the polymerization rate and allows the polymerization to start at lower temperatures. A reduced imprint temperature (100 °C) and shorter imprint time (10 min) are achieved. Additional polymer modification by plasticizers improves the material flow during the imprint due to a lower T_g. Recipes for polymer modifications have been found out, which result in thermally stable imprints under the specified processing conditions.