Dicing of Thin Silicon Wafers with Ultra-Short Pulsed Lasers in the Range from 200 fs up to 10 ps

Abstract

In this paper the influence of the pulse duration in a range of 200 fs up to 10 ps on the cutting process of thin silicon is investigated. The experiments are carried out with a Light Conversion Pharos with various pulse durations between 200 fs and 10 ps. The laser is operated at the second harmonic wavelength of 515 nm and a repetition rate of 200 kHz. Although the ablation threshold, which is determined with the method of Liu [1], amounts 0,27 J/cm² for 0,2, 1 and 10 ps, one can find extremely different ablation behavior during the cutting experiments. It turns out that independent from pulse energy and pulse overlap, the shortest pulse duration at 200 fs leads to a deeper cutting depth and furthermore to a higher cutting speed. This difference can be explained with higher pulse peak intensities and shorter interaction time between laser and material for the 200 fs pulse duration. Nevertheless the general ablation geometry is very similar for all tested pulse durations. We explain this with a simple geometric model. This model considers the projection from a Gaussian beam profile in an existing cutting kerf.