Flow and evaporation of a thick polymer film on a rotating disk

Flow, mass transfer and film thickness variation during a thick photoresist film formation on a wafer spin coating process are numerically studied. Governing equations and boundary conditions for the cylindrical coordinates are simplified using the von Karman similarity transformation and solved by the finite difference method. The viscosity and binary diffusion coefficient are assumed to be functions of solvent concentration and the mass transfer coefficient is used to model the solvent evaporation from a free surface. The velocity components for the coating liquid and the film thickness variation with time are analyzed according to the various process parameters such as spin speeds and the initial photoresist concentrations. When the evaporation is considered, the velocity components are small due to the increase of viscosity and resultant decrease of outflow rate. The final film thickness is predicted from the wet film thickness, the thickness at the end of the spin coating process and the initial solute concentrations.