Inclination of mold pattern’s sidewalls by combined technique with photolithography at defocus-positions and electroforming

We succeeded in achieving inclined sidewalls in a positive-tone photoresist structure by adjusting the focus offsets in a projection ultraviolet (UV) lithography system. In our experiments, highly precise patterns on Ni-electroformed mold were replicated from a photoresist master. The practicality of the mold was then evaluated by thermal nanoimprint experiments on polycarbonate (PC). When the focus offsets became small by moving the UV image plane (defined by wafer surface) closer to the lens the inclined angles of the photoresist walls increased. In this work, the release force was measured using a desktop nanoimprint system equipped with a load cell that measured not only the compression power but also the tensile force in the de-molding process. Starting from the glass transition temperature T _g (144°C) of PC, the heating temperature in the molding process was changed by increments of 10°C resulting in T _g + 10, T _g + 20, and T _g + 30°C. The result showed that the release force decreased with increasing incline angles. It was observed that the more inclined the sidewalls of the mold pattern were, further small the release forces became, and the mold pattern became to be defended from deformation.