Ablation plume effects on high precision excimer laser-based micromachining

Abstract.

The observation of systematic variations of the shape of holes drilled along a line into polyimide by excimer laser-based mask imaging and ablation stimulated this investigations. Despite homogeneous illumination of the total line of holes in the mask, the exit diameters of the holes drilled in the inner part of the line were smaller with respect to those of holes situated near both ends of the line; the entrance diameters were all equal within experimental variation. It was found that plasma plume ejection from the holes leads to a cloud of material which is optically denser above the inner holes so that the excimer laser radiation is attenuated there stronger than above the outer holes.