Journal of the Electrochemical Society, Vol.147, No.2, 699-705, 2000
Effect of air shear on film planarization during spin coating
In some spin-coating processes such as antireflective coating and E-beam resist for nanometer patterning, the effect of air shear on film planarization becomes significant. Here analytical solutions of film profiles and the degree of planarization over isolated and periodic features under the effect of air shear are presented. For the cases of high Ohm(2) or d/h(f) << 1, a new governing parameter, Ohm(a)(2) (=Ohm(2)[1 + 2/(3 beta)]), can be used as Ohm(2) in the existing results without air shear effect. The governing parameter Ohm(2) represents the ratio of centrifugal force to surface tension force and beta represents that of centrifugal force to air shear force. The feature height or depth is d and the liquid film thickness far from the feature is h(f). Compared to the curve of the degree of planarization without air shear effect. the curve with air shear effect shifts toward the lower Ohm(2) directions. The effect of air shear tends to make the film profile's maximum higher and minimum lower for both isolated and periodic features.