Improvement of imprinted pattern uniformity using sapphire mold

In order to improve the adhesion property between a mold and photocurable polymer film in photosolidified imprint lithography, a sapphire plate was used which has advantages such as large Young's modulus, large Knoop hardness value, and large ultimate compressive and tensile forces compared with a quartz plate. The contact angle of water on the sapphire surface is considerably larger than that on the quartz surface and comparable with that on the quartz surface with hydrophobic treatment. As the number of imprinting experiments increases, the contact angle for the sapphire remains, constant although that for the surface-treated quartz gradually decreases. From the 40 imprinting experiments using the same sapphire mold, no degradation of the replicated pattern in the photocurable polymer is observed. On the other hand, thin polymer residues are observed to remain at the edge of the protruding mold patterns, probably due to the rough side wall structures which made them easy to adhere to the polymer. It is considered that such a residual polymer film on the mold is too thin to be replicated in the imprinting experiment.