The effect of assist liquid on the hole taper improvement in femtosecond laser percussion drilling

Absence of debris or spatters on the periphery of laser micromachining area is crucial in semiconductor applications due to reduction of line width and line space of silicon (Si) devices. We studied the role of different types of volatile liquid films in reducing debris formation and taper improvement during femtosecond (fs) laser drilling of Si. It was found that more volatile liquids, i.e. liquids with lower boiling points were more effective in reducing debris formation during the fs laser drilling process. Plasma confinement in liquid and shock waves are believed to be the main causes for the reduction of debris formation. The more volatile liquids also led to reduction in hole taper angles.