HIGH SPEED LASER DRILLING: PARAMETER EVALUATION AND CHARACTERISATION

Laser drilling of via- holes is one of the key processes in the production of MWT- and EWT- solar cells. Both cell concepts have their specific boundary conditions regarding hole diameter and number of holes per cell area but in both cases the processing time and the laser induced damage should be as small as possible. In this paper we investigate the influence of laser fluence and pulse width on the laser induced damage as well as the processing speed. We compare ultra short laser pulses of only 12 ps with longer pulses in the range of 250 ns up to 1.6 µs. We observe a decreasing processing time with increasing pulse width. At the same time the process stability increases due to a decreasing dependence of the drilling efficiency of the laser fluence. For the evaluation of laser induced damage, lifetime samples are prepared and the recombination velocity SVia at the holes is determined. As an alternative method for damage analysis µ- photo-luminescence measurements and µ- Raman spectroscopy measurements were performed.