Suppression of roughness replication in bilayer films prepared by spin-coating

Utilizing the high resolution of a reflection ultrasmall-angle scattering setup, the roughness replication in polymer single-layer and bilayer samples is probed. Single films of fully brominated polystyrene (PBrS) as well as bilayer films of polystyrene on top of PBrS and of PBrS on top of polyamide-6I are investigated. Three different methods are presented to suppress the replication: the use of thick films, the use of films of laterally heterogeneous thickness, and the preparation from a solvent such that the polymer has only a weak interaction with the substrate. For single-layer samples of PBrS with increasing film thickness, the long-range correlation is decreased. Conformal roughness was detected up to a film thickness of 18R(g) (1349 Angstrom) At a film thickness of 26R(g) (1989 Angstrom), an individual scattering of the interfaces was observed. Irrespective of the roughness replication behavior of the individual sublayers, the methods presented are able to suppress the constraint of a morphology replication in bilayer films.