Splashing Drops

The outcome of a drop impact event depends on many parameters. In this thesis, we focused on how three different substrate properties influence the splashing behavior of impacting drops. These properties can be used to control splashing in the extreme ultraviolet (EUV) source chamber of lithography machines produced by ASML. We measured and modeled how the substrate orientation changes the outcome of a drop impact event onto a deep liquid pool. Both the splashing threshold and the direction at which the splashed droplets are ejected can be controlled by tuning the substrate orientation, the drop size and velocity. The temperature of a solid substrate is also found to influence drop impact behavior. On cold substrates, drop solidification limits its spreading diameter. For the drop splashing a two-fold behavior is observed: On the one hand the last observed deposition event is found at higher impact velocities as compared to isothermal impact due to energy loss by solidification. On the other hand the impact velocity at which the first splashing event is found decreases, as the solidified liquid forms irregularities on the substrate. Finally, we investigated how substrate elasticity can be used to suppress drop splashing, by studying the impact of drops onto an elastic membrane. The splashing threshold was found to increase with decreasing membrane tension. The velocity at which the membrane deforms and the maximal membrane deformation were measured from simultaneous profilometry measurements. These properties are then used in a model for drop splashing to explain the experimentally determined splashing threshold. In the EUV source chamber one can exploit these substrate properties to suppress drop splashing. Thereby, contamination formed by splashed drops can be minimized such that the source will operate at higher efficiency