Residual layer uniformity using complementary patterns to compensate for pattern density variation in UV nanoimprint lithography

Abstract

How to form a thin and uniform residual layer, which is difficult to be created for a feature with nonuniform pattern densities, is of critical importance in nanoimprint lithography since residual layer removal by a reactive ion etching process will result in poor pattern transfer fidelity for nonuniform residual layers. A capacity-equalized mold using complementary cavity patterns to balance the imprinted volume of the feature with pattern density variation was verified to be a good method against pattern density variation for producing a uniform residual layer. To obtain an insight into the validity of the capacity-equalized mold, the effects of the introduced complementary patterns for capacity equalization on the residual layer, at locations that were not only at a distance away from the introduced complementary patterns but also the ones that were very close to the introduced complementary patterns, were carefully studied. It was found that a capacity-equalized mold with even very coarse complementary patterns as large as 10 times the minimum width of original patterns could result in a good uniform residual layer. It showed that the residual layer thickness was mainly determined by the volume of the capacity of the pattern trench with varied depths per unit area, but not by the size of the complementary patterns. Furthermore, the local nonuniformity induced by the complementary patterns themselves was also studied. The authors found that this local nonuniformity had little influence on producing a uniform residual layer that contributed to the low viscosity of the UV-curable resin. The authors also found that the nonuniformity of the residual layer was produced even by using a capacity-equalized mold due to the presence of air bubbles.