Analysis of the spincoating of thickness gradient polymer films
By dropping a polystyrene (PS) solution at a position displaced radially from the axis of rotation during spincoating, PS films with a radial dependence of the film thickness can be produced. The radial thickness profiles of the PS thickness gradient films were measured using a combination of techniques. We present a calculation of the radial dependence of the film thickness. Using the resulting expression, we have performed fits of the measured radial film thickness profiles for a variety of PS thickness gradient films prepared under different deposition conditions. We also present the results of measuring the intensity of light reflected from the films during spincoating. The resulting plots of photodiode voltage with time reveal an oscillation in intensity as the film thickness decreases during spincoating. The light reflectivity experiment allowed the determination of the film drying time as well as the tracking of the film thickness as a function of time during spincoating.