This study was performed to investigate how the nozzle design parameters affect the spray characteristics of a twin-fluid nozzle used in wafer cleaning. External mixing-type twin-fluid nozzles, which had various design parameters that could be changed, were used to understand the effects of each parameter. Deionized water (DIW) and N2 gas were used as the working fluids. Various design parameters of the twin-fluid nozzle, such as the liquid nozzle diameter, gas slit angle, and the number of nozzles, critically affected the spray behavior in terms of both the macroscopic and microscopic spray characteristics. Measurements were made using a Nd: YAG laser and an ICCD camera. Additionally, the droplet size and velocity were determined using a phase Doppler particle analyzer (PDPA) in order to optimize the microscopic spray characteristics in terms of the spatial distribution and Sauter mean diameter (SMD). Experimental results show that the macroscopic spray characteristics did not change significantly as the gas slit angle was altered; however, the microscopic spray behaviors (e.g., the droplet diameter and mean velocity) were distinctly varied. By identifying the effects of independent design parameters, it appears that wafer the cleaning performance can be improved. (C) 2015 The Electrochemical Society. All rights reserved.