Flow of a Gravity Driven Thin Liquid Film over One-dimensional Topographies A Detailed Comparison of Experiments,Analytical and Numerical Models

Spin-coating, one of Philips’ widespread wet-chemical coating technologies, is sensitive to substrate inhomogeneities. That leads sometimes to coating imperfections that are much larger than their causes. In order to understand how some of these imperfections affect the coating procedure, some experiments are going to be studied. In this case, a gravity-driven set-up will be used. The phenomenon is comparable to that ocurring in spin-coating, with the advantage that the lower speed allows better observation and analysis of the situation. One dimensional topographies are studied. With special attention to the case of a step-up topography, different experiments are performed varying the thikness of the flow and the height of the topography. The empiric profiles are compared to analytical predictions and numerical simulations of the problem. Conclusions: • the work performed by Messé (NL-UR030/97) has been continued : 1. the optical path is now correct 2. the image processing software has been improved and made more user-friendly and robust 3. a complete set of experimental data about the sharp variation of the slope of the liquid surface at a step-up is available • the lubrication theory describing the flow has been augmented with a nonlinear correction • numerical simulations of the flow have been performed with FIDAP • experimental, analytical and numerical results compare very well, and confirm that the numerical and present analytical tools are appropriate • a small discrepancy remains about the fast variation of slope, that is not encompassed in any model c Philips Electronics N.V. 1998 iii