Meniscus behavior under helium exposure for rapid resist spreading during nanoimprint lithography

Nanoimprint lithography under helium exposure plays an important role in realizing rapid resist spreading. It is expected that the reduction in the surface tension of the resist due to the diffusion of helium would have an impact on the spreading behavior of the resist. By assuming van der Waals potential, the surface tension of the resist under helium exposure is estimated to be reduced by 70%. In our experiment, we obtain an 83% reduction in the surface tension of a resist under helium exposure by evaluating the meniscus shape at the corner of a rectangular imprinted area after UV curing. Furthermore, the C/O composition ratio of the resist after UV curing is found to change due to the exposure. Our study confirms that helium strongly affects the surface tension of the resist. The result also suggests the possibility of the supercritical fluidic behavior of helium in the resist. The resist spreading velocity can be increased by 2.5 times by helium exposure.