Thin polymer films viscosity measurements from nanopatterning method

Abstract

Polystyrene films, with thickness ranging from a few tens of nanometers up to several hundreds of nanometers and molecular weight of 27.5 kg mol−1, were patterned with nanoimprint lithography (NIL) technique. A rigid silicon stamp containing nanoscale features was printed into a thin spin coated polystyrene film. Then these patterns were annealed above the glass transition temperature in order to characterize the viscous reflow of the topography. Special attention was paid to provide, at initial times, imprinted nanoscale patterns with a very small aspect ratio and amplitude/wavelength as well as to avoid the nucleation of holes during imprinting or during the course of the reflow. This allowed the authors to process topography data with a high degree of accuracy from a linear viscous stability model. Atomic force microscopy measurements, with a spatial resolution lower than 1 nm, were used to characterize smooth or steep shapes. The mechanical measurements of earlier stages of pattern reflow were directly accessible without any assumption, contrary to the diffraction method usually employed. Our results clearly demonstrate that even the earliest stages of pattern reflow are driven by simple viscous effects and that relaxation dynamics, which is usually considered as following exponential laws, could be more complex. This article also demonstrates that the NIL process can be used for viscosity measurements for ultrathin resist film.

On using the levelling of the free surface of a Newtonian fluid to measure viscosity and Navier slip length

“…This requires a preliminary knowledge of the fluid viscosity, which can be obtained by applying the same method with a different geometry. Actually, levelling has already been used to measure viscosity [13,14], assuming no slip at the fluid-solid interface and referring to the analytical solution for free-surface profiles with infinitesimal amplitudes, but without an evaluation of the approximations involved. This point is analysed here.…”

Influence of thermal diffusion and shear thinning during the leveling of nanoimprinted patterns in a polystyrene thin film

“…The two latter steps are repeated until the amplitude reaches a few nanometers in order to record the evolution of the amplitude versus the annealing time. As it has been already shown by Leveder et al [17], the square wave profile is progressively transformed into a sinusoidal one, which corresponds to the main mode of the initial profile in the Fourier series, and finally to a flat surface.…”

“…An initial examination of the mean viscosity of the film can be performed by using the method of Leveder et al [17]. This method consists in evaluating the characteristic decreasing time τ of the pattern amplitudes and computing the viscosity with the following equation…”

“…Quantitative rules have been established by Gilormini and Teyssèdre [22] who also demonstrated that, as the amplitude is reduced during the leveling, their rules are fulfilled after a certain time. As τ is a parameter of equation (6) that can be deduced from experiments and that helped [17,18,21,20] to derive the physical properties of the materials, we focus on the quantity…”

“…This method has been applied to polystyrene (PS) by Leveder et al [17] and Rognin et al [18,19], and to poly(methyl methacrylate) (PMMA) by Jones et al [20] and Teisseire et al [21]. The polymer films are patterned with the thermal nanoimprint process in order to preserve the physical and chemical properties of the polymers.…”