Particle deposition velocity onto EUVL masks in vertical airflow

Extreme ultraviolet lithography (EUVL) masks are vulnerable to particulate contamination due to the unavailability of pellicles. Particle deposition velocity is used to assess the level of particulate contamination. The particle deposition velocity onto a circular disk or a square flat plate situated perpendicular to the airflow was investigated. The numerical and experimental methods employed in this paper were validated by comparing the numerically simulated mean Sherwood numbers or the experimentally determined particle deposition velocities with the theoretically predicted values for the circular disk, representing a wafer, exposed to vertical airflow. Then, an equation for predicting the particle deposition velocity onto a square flat plate, simulating a EUVL mask, in vertical airflow was suggested by numerically obtaining the mean Sherwood number correlation, and validated through experiments.