Dependence of Film Thickness on Speed in Spin Coating

The observed variation of film thickness with spin speed (Ω) in spin coating is summarized for resists, spin‐on glasses (SOGs), and polyimides. While the thickness measurements of resists and SOGs show an dependence, the data for polyimides show a wide variation in speed dependence, from Ω⁻¹ to . The possible non‐newtonian nature of the fluid (modeled as a truncated power law) cannot explain this behavior since predictions indicate that non‐newtonian effects are always accompanied by a variation in the thickness with radial position, a variation which has not been observed experimentally. However, the type of evaporation model used for the fluid can cause the thickness to vary with speed in the observed fashion. This suggests that the polyimide behavior is a result of differences in the evaporation rate of the solvent.