Investigation of the solvent-evaporation effect on spin coating of thin films

A simple empirical relationship exists between the thickness and the solvent-evaporation rate of spin-coated thin films. The thickness of a film formed from an organic solvent solution can be approximated by the relationship\documentclass{article}\pagestyle{empty}\begin{document}$ D = K_0 \mu ^{0.36} \omega ^{ - 0.50} (E\lambda /C_p)^{0.60} $\end{document}, where μ is the viscosity of the coating solution, ω is the rotation speed, E is the solvent-evaporation rate, λ is the latent heat of evaporation, C_p is the heat capacity of the solvent, and K₀ is a constant for volatile organic solvents. A similar relationship for aqueous polymer solutions is\documentclass{article}\pagestyle{empty}\begin{document}$ D = K_0 \mu ^{0.36} \omega ^{ - 0.50} (1.0 - RH)^{0.60} $\end{document}, where RH is the relative humidity of air around the spin coater and K_a is a constant for aqueous solutions. These relationships are helpful in understanding the mechanism of thin-film formation in spin coating.