We have examined, with tapping mode atomic force microscopy(AFM), the effect of post-exposure bake times and developer on surface roughness using model bilayer interfaces of deuterium-labeled poly(tert-butyloxycarbonyloxy styrene) and poly(hydroxystyrene). The AFM results demonstrate the evolution of the resulting surface morphology, representative of a line edge, as the width of the deprotection front increases. As bake time increases, the average surface roughness increases from (1 to 4-5) nm, however the surfaces are not laterally homogeneous. Initially, the bilayer is smooth with residual particulates remaining from the developing stage. After short bake times, the surface possesses a dual morphology with deep pits within a shallow variable topology. The variable topology is characteristic of developed surfaces in uniformly deprotected films, independent of the level of deprotection. A histogram of depth analysis of the AFM images demonstrates that as the width of the deprotection profile increases, the profile broadens asymmetrically, producing a bimodal distribution. However, at long bake times, the overall width of the distribution has doubled the initial, unbaked, roughness and recovered a symmetrical shape. The images demonstrate that the deprotection front is spatially inhomogeneous during short bake times and evolves into a homogeneous broad front. The origin of the spatial inhomogeneity and the dual morphology are still unknown.
Citation: Polymeric Materials: Science & Engineering
Pub Type: Journals
atomic force microscopy, photoresist, reaction front, roughness