<title>High-efficiency microdrilling of silicon wafer using excimer laser</title>

Abstract

Drilling rate of thin silicon wafer of 50(mu) thickness was determined as a function of beam diameter and laser fluence of KrF excimer laser with a pulse width of approximately 30ns FMHW. Analysis of drilling process indicated that decreasing beam diameter and laser fluence enhanced the drilling rate with improved quality of the drilled hole. The extent of debris and molten particles ejected from the hole was also reduced as the laser fluence was decreased. The drilling rate, approximately 0.6(mu) per pulse at beam diameters larger than 100(mu) , increased significantly as the beam diameter decreased especially below 20(mu) , reaching approximately as large as 4(mu) per pulse at 10(mu) in diameter under constant laser fluence. On the other hand, only very small increase in drilling rate was observed as the laser fluence was increased. A simple formula was derived where the drilling rate is proportional to the fourth root of the laser fluence and inversely proportional to the square root of the beam diameter, assuming that the silicon is removed in a liquid state out of the hole.