Scaling of correlation length in lamellae forming PS-b-PMMA thin films upon high temperature rapid thermal treatments

Abstract

Perpendicularly oriented lamellar forming block copolymers are promising candidates for the fabrication of high aspect ratio nanostructures either by means of direct pattern transfer to the underlying substrate or by sequential infiltration processes. In this work, highly ordered lamellar grains (ξ > 500 nm) were produced by thermally treating the samples at high temperature (T_target > 250 °C) in a Rapid Thermal Processing (RTP) machine. The variation of the lateral order of the nanostructures during the annealing process was investigated in detail, by decoupling the effect of the transients and of the isothermal step of the thermal treatment. Moreover, the self-assembly process was studied as a function of the annealing time and temperature in order to identify the processing parameters that maximize the lateral order avoiding, and at the same time, any degradation of the macromolecules. From this study the activation energy (E_a ∼ 55 kJ mol⁻¹) of the lamellar grain coarsening process on featureless substrates was determined. The specific process conditions that promote the self-assembly of lamellar thin films reaching a level of lateral order that is suitable for nanostructure fabrication were established.