Modeling Liquid Splash for Defect Reduction in Single Wafer Cleaning Process

In the single wafer cleaning process, liquid splash during the liquid dispense step can generate droplets that redeposit onto the wafer surface, leading to watermark defects. This study presents a three-dimensional computational fluid dynamics (CFD) model to investigate the mechanisms of liquid splash and its dependence on key process parameters. The model employs the Volume of Fluid (VoF) method and adaptive mesh refinement (AMR) to accurately resolve liquid splash and droplet formation. Simulations were validated against experimental data and successfully reproduced liquid splash and deposition regimes. Parametric studies show that a higher wafer spin speed and nozzle flow rate promotes splash by increasing the kinetic energy of the impinging liquid in the rotating wafer reference frame. A nonlinear dependence on liquid viscosity was observed, where intermediate viscosity promoted splash, while both low and high viscosity suppressed it. Hydrophobic wafer surface and low liquid surface tension enhanced splash. These findings provide mechanistic insights into splash formation and offer quantitative guidance for optimizing single wafer cleaning processes to minimize defect generation.