Mixed micro- and nanoscale structures are gaining popularity in various fields due to their rapid advances in patterning. An investigation in stamp resist filling with multiscale cavities via ultraviolet (UV) nanoimprint lithography (UV-NIL) is necessary to improve stamp design. Here, simulations at the level of individual features were conducted to explain different filling behaviors of micro- and nanoscale line patterns. There were noticeable interactions between the micro-/nanoscale cavities. These delayed the resist filling process. Several chip-scale simulations were performed using test patterns with different micro/nano ratios of 1:1, 1:2, and 1:3. There were some minor influences that changed the micro/nano ratios on overall imprint qualities. During the imprinting process, the pressure difference at the boundary between micro- and nanoscale patterns became obvious, with a value of 0.04 MPa. There was a thicker residual layer and worse cavity filling when the proportion of nanoscale structures increased.
Pattern density is an important factor in UV nanoimprint stamp design. Various pattern densities may affect the thickness of the residual layer and its uniformity. This work investigated the effect of pattern density as well as other stamp parameters, including stamp material, stamp thickness and cavity height, on residual layer thickness (RLT), contact pressure, and imprint quality. Two kinds of stamps were designed for simulation, one with detached uniform lines and the other with adjacent non-uniform lines. Results show that areas near the edges of the imprint field in all stamps are the first to achieve high contact pressure. The study observed that long imprint time enables a reduction of RLT after a stable period, particularly obvious with high density. For a long-term imprint of patterns with various densities, flowing behaviour of the residual resist was revealed. These conclusions are beneficial for making guidelines for stamp design in UV nanoimprint lithography.
High aspect ratio three-dimensional micro- and nanopatterns have important applications in diverse fields. However, fabricating these structures by a nanoimprinting method invites problems like collapse, dislocation, and defects. Finite-element analysis (FEA) is a good approach to help understand the filling process and stress distribution. The FEA method was employed to simulate the nanoimprinting process using positive and negative molds with aspect ratios of 1:1, 3:1, 5:1, and 7:1. During the filling process, the resist adjacent to boundaries has the maximum displacement. The corners of contact areas between the protruding part of the mold and the resist has the maximum Von Mises stress. For both positive and negative molds, the maximum stress in the mold increases with aspect ratio. However, filling up negative molds is more difficult than positive ones. With the same aspect ratio, the maximum stress in a negative mold is approximately twice as large as that in a positive one.
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