Effects of aging on the thickness of a homogeneous film fabricated using a spin coating process

The thickness of the film produced by spin coating is different from the theoretically calculated thickness based on the Newtonian fluid equation. In this study, the rotational time and rotational speed (in revolutions per minute [RPM]) were used as the control parameters, and the thickness differences between the actual and theoretical results were analyzed based on statistical analyses. Furthermore, we investigated the effects of the aging time (i.e., time after spin coating before heat treatment curing) independently from the parameters of the theoretical equation for spin coating of Newtonian fluids mentioned above. The thickness of the film formed by the spin coater within a period of 300 s was smaller than the theoretically predicted thickness at all rotation speeds irrespective of aging. Based on statistical analyses of the measured thickness values, we confirmed that rotational speeds in the range of 2000–6000 RPM within a period of 300 s did not yield thickness differences owing to aging time. However, below 1500 RPM, the thickness without aging time was smaller than the thickness with aging time. In addition, the thicknesses of the edge and center of the substrate were unequal but became uniform as the aging time increased. Additionally, the estimated thickness based on the constructed plots yielded completely different results from those predicted by the existing equation about Newtonian fluids. Based on the analyses of the thickness as a function of aging time and speed, we confirmed that the aging time—which was not accounted for in the conventional equation—was the parameter that primarily affected the thickness.