Elimination of pattern defects of nanoimprint under atmospheric conditions

We studied generation mechanism of bubble defects in air using molds having many recessed square patterns and photo-curable liquid polymer with a viscosity of 64 mPa s. The liquid polymer films with an initial thickness of 620–2000 nm were pressed with an imprint pressure of 0.1–0.5 MPa and cured. We found that air trapped in mold recesses is partially evacuated when liquid polymer flows out during the pressing. Bubble defects decrease with increasing liquid polymer outflow and fewer bubble defects are generated for smaller patterns. The initial polymer thickness exceeding 1 µm produces sufficient outflow to evacuate almost all the bubbles. We propose a method of condensing trapped gas, which should work well even if the liquid polymer outflow amount is small. We demonstrate this method's effectiveness experimentally using trichrolofluoromethane as the ambient gas. No bubble defects are observed in the sample imprinted using this method.