Investigation of liquid film evolution on a rotating wafer through optical calibration

Many industries including semiconductor processing and rotating disk reactors use a process that involves dispensing various chemical solutions onto a rotating plate. During this process, a thin liquid film forms on the surface and spreads radially driven by the disk rotation (inertia) and surface tension, creating distinct and complex wave patterns. Analyzing the shape, thickness, and wavelength of these wave patterns is critical to understanding the characteristics of the liquid film. In this study, we present a high-speed photography technique combined with an optical thickness correction method that allows us to accurately measure the film thickness distribution in a relatively larger area. With this approach, detailed wave information can be obtained by placing only a single camera above the disk. We have validated that this correction method is accurate to within 10%. By systematically varying the disk rotation speed from 200 to 500 rpm and the flow rate from 0.5 to 2.0 LPM, we characterized the wave patterns of the liquid film. Depending on the conditions, the wave patterns were analyzed as concentric or spiral, and the thickness of the waves was measured. The results of this research are expected to significantly improve the efficiency and quality of both semiconductor and reactor processes.