Reflow of supported sub-100 nm polymer films as a characterization process for NanoImprint lithography

Abstract

In this paper, we address the reflow behavior of polymer thin films, focusing our effort on the accuracy of surface shape recognition. Although much work was already performed to control resist reflow during lens manufacturing for instance, our approach is significantly different since no contact line (substrate/ polymer/atmosphere) needs to be considered. Here, a linear stability approach is successfully developed to describe the thin film evolution which is also compared with experiments. Polystyrene films, with thickness ranging from few tens of nanometers up to several hundred of nanometers were patterned with NanoImprint lithography technique. Atomic force microscopy measurements were used to characterize smooth or steep shapes, respectively. Mechanical measurements of earlier stages of pattern reflow were directly accessible without any assumption, contrary to the diffraction method usually employed. We show that by controlling the reflow process of any complex surface shape during the course of time, measurements of material parameters such as thin film viscosity, surface tension, or even Hamaker constant can be made possible.

Symmetry plays a key role in the erasing of patterned surface features

“…Topographic perturbations can also be used to directly pattern homogeneous thin films, as is the case in nanoimprint lithography [13][14][15][16][17], and is applicable as a data storage technique with dense memory capabilities [18,19], in self-cleaning surfaces [20], and organic optoelectronics [21,22]. The relaxation of thin film perturbations has been used to study glassy polymer dynamics [23][24][25], film viscosity [26][27][28][29], and viscoelastic properties [30][31][32]. In essence, topographic perturbations can be used not only in patterning films for applied technologies, but as a way to study material properties on small length-scales that are inaccessible with bulk measurement techniques.…”

Thermal Reflow Simulation for PMMA Structures with Nonuniform Viscosity Profile

“…Two methods of thermal reflow simulation for polymeric structures were used in this study. The first is the analytical reflow simulation method proposed by Leveder [ 11 , 13 ] for periodic structures obtained in polystyrene via nanoimprint lithography. This method is based on a two-dimensional Navier–Stokes equation coupled to a continuity equation considering Laplace pressure and Hamaker energy with the assumption of no slip length and no Marangoni effect.…”

Interfacial Interactions during Demolding in Nanoimprint Lithography

“…The dry etching technique, such as ICP, may be performed after imprinting to control the structural height of the micro/nanopattern and remove residual materials [ 24 ]. Further, the internal stress relaxation (e.g., stress induced during molding and demolding) may cause reflowing of the imprinted resist [ 25 , 26 ], which is usually undesirable during pattern replication. Recently, we found that the strong chain entanglement in certain polymers seems beneficial to pattern stability and fidelity, and good thermal stability of the nanoscale patterns on polycarbonate is successfully demonstrated at a temperature above its T g [ 24 ].…”