Depth profiling of multi-layer samples using femtosecond laser ablation

An all solid-state femtosecond laser (lambda (o) similar to 775 nm, pulse duration similar to 170 fs. maximum pulse energy similar to 0.5 mJ) with a Gaussian beam profile was used for depth profiling of Cu Ag and TiN-TiAlN multi-layers on silicon and iron substrates. Laser-induced breakdown spectroscopy (LIBS) in argon was used for characterisation of the Cu-Ag samples. while laser ablation in a Vacuum with time-of-flight mass spectrometry (TOF-MS) was applied for the characterisation of the TiN-TiAlN samples. The thickness of the individual Cu and Ag layers was 600 nm. Each individual TiN and TiAlN layer was 280 nm thick. The LIES experiment was performed in the pressure range 10-1000 mbar. Variation of the pulse fluence from 0.8 to 1.5 J cm(-2) caused a change of the ablation rate from 15 to 30 nm per pulse. The first layers of Cu and Ag could be satisfactorily resolved by LIES. In femtosecond laser ablation TOF-MS a lower fluence (about 0.3 J cm(-2)) than in LIBS could be applied. The TiN-TiAlN multi-structures were well resolved. The Caussian-type beam of the femtosecond laser limited the contrast of the detected depth profiles in both schemes. The complementary sensing techniques enable study of technical and physical limitations in the use of femtosecond laser ablation.