Through-hole energy-density threshold of silicon induced by combined millisecond and nanosecond pulsed laser

We report herein the experimental investigation of the through-hole energy-density threshold of silicon irradiated by a double-pulse laser. The double pulse consists of a 1 ms pulse and a time-delayed 5 ns pulse and is referred to as a combined-pulse laser (CPL). A modified level-set method is used to calculate the process of millisecond laser drilling, and we study how the time delay affects the CPL. The results show that the through-hole energy-density threshold decreases with increasing delay time between the CPL pulses. In addition, the energy density of the nanosecond pulse strongly affects the through-hole energy-density threshold. We also consider the thickness and the doping concentration of the silicon wafers. Compared with the results for single-ms-pulse irradiation, the CPL produces a better through-hole energy-density threshold because the surface ablation caused by the nanosecond pulse increases the energy absorbed by the silicon wafer from the millisecond pulse.