Fabrication Processes for Capacity-Equalized Mold with Fine Patterns

Abstract

The variation of residual layer thickness (RLT) by the difference of pattern density is a difficult problem in UV nanoimprint lithography (NIL). A capacity-equalized mold was proposed to solve the problem, and the effectiveness of the concept was validated using a mold with various pattern sizes of hundreds of micrometers. However, the effectiveness should be evaluated at nanometer scales to prove the concept. Here the first challenge has been to fabricate and evaluate a two-step-depth mold with tens of nanometer patterns for the capacity-equalized mold. A two-step-depth mold with sub-100 nm patterns was fabricated by a combination of electron beam lithography and laser beam lithography. We succeeded in fabricating a two-step-structure with a width of around 40 nm, and the widths of the deeper grooves were found to have slightly increased during the second RIE process. The differences in widths were found to vary approximately from 10 to 30 nm. UV nanoimprint was carried out using the two-step-depth mold in order to examine its depth modulation, and to judge whether it could be applied to a NIL process, including a residual-layer-removal process. Fine patterns of 40 nm width were successfully transferred onto the underlying Si wafer from two-step-height resin patterns that were fabricated by UV nanoimprint.