Depth profiling of multi-layer samples using femtosecond laser ablation

An all solid-state femtosecond laser (lambda (o) similar to 775 nm, pulse d uration similar to 170 fs. maximum pulse energy similar to 0.5 mJ) with a G aussian beam profile was used for depth profiling of Cu Ag and TiN-TiAlN mu lti-layers on silicon and iron substrates. Laser-induced breakdown spectros copy (LIBS) in argon was used for characterisation of the Cu-Ag samples. wh ile laser ablation in a Vacuum with time-of-flight mass spectrometry (TOF-M S) was applied for the characterisation of the TiN-TiAlN samples. The thick ness 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 pre ssure 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 fem tosecond 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 techniq ues enable study of technical and physical limitations in the use of femtos econd laser ablation.