Liquid Film Structure Formed by Two-Fluid Jet Impingement on a Rotating Disk

The two-fluid jet method is a widely utilized cleaning technique for single-wafer processing. In this method, the liquid film structure formed by a swinging nozzle on a rotating wafer significantly affects both cleaning and etching performance. However, the film structure formed by two-fluid jet impingement, particularly when the nozzle is positioned off-center relative to the wafer center, is poorly understood. This study measures the distribution of liquid film thickness formed by a two-fluid jet using a laser focus displacement meter. We varied several parameters, including the disk rotational speed, airflow rates, and nozzle positioning. We found that the two-fluid jet produces a thinner liquid film near the injection region, with thicknesses less than half that of liquid jets using a single liquid. Moreover, in the off-center case, two-fluid jets effectively reduce the peak thickness of the liquid film around the nozzle. The airflow causes this reduction, additionally helping to minimize the formation of dry spots on the wafer center.