Role of volatile liquids in debris and hole taper angle reduction during femtosecond laser drilling of silicon

The absence of debris or spatters on the periphery of laser micromachining area is critical 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 during femtosecond (fs) laser drilling of Si. It was found that more volatile liquids, i.e. liquids with lower boiling points and lower number of carbon atoms in the molecular formula, 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 the formation of debris. The more volatile liquids also led to reduction in hole taper angles.