MECHANISM FOR THE LOCAL PLANARIZATION OF MICROSCOPICALLY ROUGH SURFACES BY DRYING THIN-FILMS OF SPIN-COATED POLYMER SOLVENT SOLUTIONS

When thin films of polymer/solvent solutions are spin coated onto microscopically rough substrates, the dry film profile tends to smooth or planarize those features of the substrate that have lateral dimensions on the order of micrometers and less. A mathematical model is used to explain the physical mechanisms that are responsible for this local planarization. The governing equations are those of conservation of species and overall mass. The finite element method is employed to handle this transient, two-dimensional, free boundary problem. It is found that local planarization is driven by large lateral concentration gradients that develop during drying, and by the presence before drying of a greater total mass of nonvolatiles per unit area where the film is thicker. The model is applied to isolated grooves and ridges and to a periodic array of grooves/ridges. © 1990, The Electrochemical Society, Inc. All rights reserved.