Viscosity Measurement of Spin-coated UV Nanoimprint Resin

Despite of the importance for understanding or predicting resin filling in UV nanoimprint, viscosities of UV curable resins used in UV nanoimprint were not well known and considered as same as those of UV curable resins in the bulk state. In UV nanoimprint, UV curable resin is commonly spin-coated on a wafer and a thin UV curable resin film is created. The ratio of surface to volume of a spin-coated film is extremely large in comparison to that in the bulk status. Therefore, it is possible that the viscosity of the spin-coated UV curable resin is changed by evaporation of some volatile components, for example. We constructed viscosity measurement apparatus for a thin liquid film, simply based on laminar shear of fluid between two plates. By using the viscosity measurement apparatus, it was found that the viscosity of UV curable resin supplied on a wafer by a droplet or by spin-coating with thickness larger than 2.3 mu m showed almost the same viscosity as that in the bulk state, however, when a thin film was created by spin-coating with a thickness smaller than that, the viscosity clearly increased. It was also found that viscosity of spin-coated UV curable resin increases with time or by heating and becomes 6 times of that in the bulk state for PAK-01. We succeeded in viscosity measurement of PAK-01 with a thickness of 0.58 pm prepared from diluted PAK-01 (PAK-01-1000) and found that the UV curable resin was exactly Newtonian fluid in these thickness ranges.