Evolution of Order in Thin Block Copolymer Films

Abstract

The organization of thin films of symmetric poly(styrene-b-methyl methacrylate) diblock copolymers on silicon is investigated by neutron and X-ray reflectivity. The surface and internal structure as a function of annealing time is compared for two sets of films 680 and 800 Å in thickness. For the thicker films the equilibrium morphology shows no surface features since the film thickness is 2.5L where L is the period of the lamellar microdomain morphology. The thinner films, 2.1L in thickness, exhibit hole formation over 40% of the surface. In both cases the multilayer organization proceeds from the substrate upward by chain transport through channels which perforate the developing layers. For short annealing times a sharp increase in surface roughness is seen, which may be linked with the wetting of PMMA-rich surface regions by polystyrene. At longer times these height fluctuations decay or grow into holes, depending on the initial film thickness. © 1994, American Chemical Society. All rights reserved.