Finite element analysis of nonuniformities in spin casting of polymer films

Spin casting of polymers is a simple technique of applying centrifugal force, shear stress, and evaporation of a polymer slab on a rotating disk or a substrate 1,2 . It is widely used for producing very thin organic films, from dielectrics and protective coatings to microelectronics devices. When the thin films are used for precision membrane structures, uniform properties are critical 3'4. The purpose of the reported investigation is to develop a finite element model to investigate nonuniformity in the spin casting process. At first, nonuniformity has been created by assigning different values of elasticity or viscosity to the polymer slab in certain regions of the model. Rigid inclusions at different locations have also created nonuniformity in the model. The model containing nonuniformity has been found to offer different radial and vertical displacements compared to the uniform model. The radial displacement of the polymer interface changed at the boundary of the nonuniform region and remained changed beyond the nonuniformity. In the vertical displacement case, the effect of nonuniformity has been found to be locally confined to its original position. Models with rigid elements at different surface locations also affect the displacements.