Nanoimprint Lithography and the Role of Viscoelasticity in the Generation of Residual Stress in Model Polystyrene Patterns

Abstract

Understanding polymer deformation during the nanoimprinting process is key to achieving robust polymer nanostructures. Information regarding this process can be extracted from monitoring the decay of the imprinted polymer patterns during thermal annealing. In the present work, the effect of both the molar mass and the imprinting temperature on the pattern decay behavior during thermal annealing is investigated. Previously, it was found that the decay rate is fastest for a highly entangled polymer due to the elastic recovery caused by the residual stress created during the imprinting process. The present paper demonstrates that this residual stress level can be modified through control of the imprinting temperature. These results are contrasted with those for an unentangled polymer over a similar range of imprinting temperatures, where it is found that the pattern decay is controlled by simple Newtonian flow. In particular, the pattern decay is well described by surface‐tension‐driven viscous flow, and no imprinting‐temperature effect is observed during thermal annealing. It is shown that the stability of the film against pattern decay can be optimized for moderately entangled polymer films. This effect is attributed to the competition between the effect of increased viscosity with increasing molar mass and increased residual stresses with entanglements. These observations provide guidance for the optimization of imprinting process in terms of selection of molar mass and processing temperatures.

Surface patterning of polymeric membranes and its effect on antifouling characteristics

“…Note that different levels of residual stress can be imparted depending on the processing conditions and polymer properties. [77][78][79] Using the conventional NIL process, i.e. imprinting the membranes at T > T g (or T m ) of the polymer, can indeed create surface patterns with high fidelity to the features on the mold ( Fig.…”

“…[73][74][75][76] For the thermal embossing route of NIL processes, the pattern replication mechanism is normally based on the "squeeze flow" of viscous polymer that is supported on a rigid substrate. [73,[77][78][79][80] Specifically, a viscous polymer film is first squeezed into the cavities of a rigid (silicon) mold under a relatively high pressure (a few MPa) at a temperature above the glass transition temperature (T g ), or melting temperature (T m ), of the polymer, and then solidified at a temperature below T g (or T m ) before the release of pressure.…”

Viscoelastic properties measurements of thin polymer films from reflow of nanoimprinted patterns

“…Despite a huge development of imprinting equipments, stamp manufacturing processes, imprint processes, dedicated materials, and metrology approaches, a complete simulation toolbox of NIL is still lacking. [10][11][12][13][14] The dynamics is probed using x ray photon correlation microscopy, or more generally by light scattering techniques. However, in NIL processes, resist film thickness is ranging from several tens of nanometer up to several hundreds of nanometer.…”

Viscoelastic effects and anomalous transient levelling exponents in thin films

“…Thin viscoelastic films have been studied experimentally by dewetting [38,39], and relaxation of nanoimprinted patterns [40,41], in particular. From the theoretical point of view, viscoelastic thin film equations have been derived, using the linear Jeffreys model [3,[42][43][44][45].…”