Femtosecond laser delamination of thin transparent layers from semiconducting substrates [Invited]

Transparent dielectric layers of typically 100 nm thickness can be delaminated from strongly absorbing, semiconducting substrates selectively and without noticeable damage at the opened surface by irradiation with fs laser pulses at photon energies above the semiconductor band gap. We have studied this very special ablation process on silicon wafers coated by SiO2, SixNy and Al2O3, using pulse durations from 50 fs to 2000 fs, and the laser wavelengths 1030, 800, 515, and 400 nm. By help of a precise determination of ablation thresholds and detailed inspection of ablation craters by optical and atomic force microscopy, we conclude that a very short penetration depth of the laser light due to charge carriers generated in the silicon by the pulse itself is the key for the quasi damage-free delamination process.