A pulsed laser, a microscope, and a 35-mm camera are used to stroboscopically create and image interference fringes around surface features during spin coating. The measured film thickness profiles are compared to predictions from a lubrication model. This model has been extended to two dimensions so that the surface contours around features of any width and length may be calculated, and preliminary results are reported. Profile asymmetry, or 'pile- up,' is caused by surface tension forces near the edges of the feature that accelerate flow where the channel (the film thickness) narrows and retard flow where the film thickness widens.
Loni M. Manske,
David B. Graves,
"Origins of asymmetry in spin-cast films over topography", Proc. SPIE 1463, Optical/Laser Microlithography IV, (1 July 1991); doi: 10.1117/12.44800; https://doi.org/10.1117/12.44800