Leveling of Polymer Grating Structures upon Heating: Dimension Dependence on the Nanoscale and the Effect of Antiplasticizers

Abstract

The transition temperatures of nanoscale polymeric films are measured from a leveling experiment where a designed nanostructure is heated from below. Surface tension forces drive the relaxation of the polymeric features, allowing direct measurement of the critical temperature of collapse, T, and indirect measurement of the glass transition temperature, T. Small-angle X-ray scattering and atomic force microscopy are used to follow the leveling dynamics, whereas a mathematical model for the momentum balance is implemented to extract the viscosity of the polymer film as a function of temperature. Our methodology is illustrated in the context of films of poly(methyl methacrylate) that are patterned via nanoimprint lithography into dense gratings. We study how the glass transition temperature and the critical temperature of collapse vary as a function of the film size and the inclusion of the antiplasticizer, tris(2-chloropropyl) phosphate. The grating periods are varied consistently between 80 and 240 nm, whereas the antiplasticizer concentrations are 1, 3, 5, and 10 wt %. The solution of the momentum balance allows the detailed correlation between stresses, curvature, heating, and shear rates during leveling. We found that both temperatures, T and T, decrease as the film size decreases or as the concentration of the antiplasticizer increases. In addition, antiplasticizer concentrations between 3 and 5 wt % stabilize the size dependence of T. We show that the nature of the antiplasticizer is effectively to increase the low-temperature viscosity of the film. However, during leveling, the antiplasticized film sustains its curvature, thereby driving a sudden relaxation, once T is reached, and increasing the possibilities of defects.

Burger Model as the Best Option for Modeling of Viscoelastic Behavior of Resists for Nanoimprint Lithography

“…Observed decrease of viscosity with increase in temperature is in line with what was observed previously in numerous publications [35,36]. From comparing the values obtained by us to other works [17,35,36] we can see that the SLS-Kelvin model is closest to other research, although this might be caused due to similarity of the measurement method used, as the Burger model can be used to predict the behaviour during dwell with the highest accuracy. The change in viscosity with the depth of indentation can be attributed to the same change in mobility as described above when analysing Young's modulus.…”

Solvent Vapor Annealing, Defect Analysis, and Optimization of Self-Assembly of Block Copolymers Using Machine Learning Approaches

“…11,[63][64][65][66][67][68] The ideal thickness for a given BCP is unique, and depends upon the composition of the BCP and factors such as surface functionalization and energy, the use of a topcoat and other factors. 8,10,42,62,64,69 Both experimental and computational results strongly link initial film thickness with the resulting self-assembled structure and persistent defects. 18,70,71 Small fluctuations of thickness within a monolayer film can lead to different self-assembled structures as unfavorably thin domain thicknesses frustrate packing due to the buildup of strain.…”

“…To achieve the desired nanopattern via self-assembly, not only are the annealing parameters critical but the initial thickness of the applied BCP monolayer must be precise, typically within one or two nanometers. ,− The ideal thickness for a given BCP is unique and depends upon the composition of the BCP and factors such as surface functionalization and energy, the use of a topcoat, and other factors. ,,,,, Both experimental and computational results strongly link initial film thickness with the resulting self-assembled structure and persistent defects. ,, Small fluctuations of thickness within a monolayer film can lead to different self-assembled structures as unfavorably thin domain thicknesses frustrate packing due to the buildup of strain. , The periodicity of structures formed from self-assembled BCP nanopatterns may be dependent upon film thickness and other processing parameters, as has been recently shown with bottlebrush BCPs. , …”