Control of Electrostatic Charge Generated during Two-Fluid Spraying of Pure Water Using an Inductive Charging Method†

This study presents a technique designed to prevent electrostatic discharge during the cleaning of semiconductors using a two-fluid spray composed of pure water. The current generated by spraying pure water with a prototype Faraday cage was measured. Furthermore, a shadow Doppler particle analyzer was used to measure the velocity and size of the airborne droplets, clarifying the relationship between the generated current and droplet characteristics. The results confirmed that the current generated during two-fluid spraying exhibits positive polarity and that the droplet charge increases with droplet velocity. We further demonstrated that the charging of pure-water droplets can be controlled by installing an inductive charging element immediately downstream of the pure-water jet. This phenomenon is believed to occur because the electrons induced by the charging element flow through the continuous fluid region along the nozzle wall toward the ground. © 2025 Institute of Electrical Engineers of Japan and Wiley Periodicals LLC.