Laser interferometric measurement of the fluid thinning behavior was performed for a sampling of different coating solutions during spinning. This technique was validated before for pure solvents and has also been applied to mixtures.

        The present paper used the technique to determine if the solvent evaporation that really applies to coating deposition is happening fast enough to actually create a "skin" layer that is relatively depleted of solvent at times when some amounts of the coating solution is less intensively perturbed by the evaporation process.

        Our thinning rate data showed that the evaporation rate (at least for those times when it is accessable by our measurement) is SLOW with respect to diffusion of the solvent within the thin precursor layer. This means that the solution is NOT developing a skin during most of the coating formation.

        Our work was presented at the SPIE meeting on Sol-Gel Optics, in January 2000. It also appears in this SPIE proceedings volume:

D. E. Haas, J. N. Quijada, S. J. Picone, and D. P. Birnie, III, “Effect of Solvent Evaporation Rate on “Skin” Formation During Spin Coating of Complex Solutions”, in Sol-Gel Optics V, B. S. Dunn, E. J. A. Pope, H. K. Schmidt, and M. Yamane Eds., Proc. SPIE 3943, 280-284 (2000).