Numerical analysis of pattern shape deformation in UV imprint considering thermal deformation with UV shrinkage and curing

A novel numerical method for analyzing the deformation of molding patterns on UV imprint with soft molds considering thermal deformation in addition to UV shrinkage and curing is presented. In the case of UV imprint using an easily deformable mold-like PDMS, transfer error on UV resin is caused by thermal expansion/contraction arising from UV reaction heat and by UV shrinkage. Specifically, when a UV resin with high reaction heat such as cation polymerization-type UV resin is used, thermal deformation has a nonnegligible effect on pattern shape deformation. Therefore, it is necessary to consider thermal deformation caused by UV reaction heat in the numerical deformation analysis of UV imprint requiring high surface accuracy, such as optical devices. The present method newly adopts the theory of reaction rate to consider the temperature-dependent UV reaction rate and introduces an advanced idea of virtual temperature as a measure of UV reaction progress. By defining the time histories of thermal deformation and UV shrinkage as a function of virtual temperature, the effects of both are considered simultaneously. In order to apply the present method to actual imprints, temperature measurement experiments and various rheometry experiments are conducted on a target UV resin to identify its model parameters. A validation analysis of the present method is performed on an actual micromirror array imprint and shows that the simulation accuracy of transfer error can be significantly improved by considering thermal deformation.