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An all solid-state femtosecond laser (l 0 y775 nm, pulse duration y170 fs, maximum pulse energy y0.5 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 LIBS experiment was performed in the pressure range 10-1000 mbar. Variation of the pulse fluence from 0.8 to 1.5 J cm 22 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 LIBS. In femtosecond laser ablation TOF-MS a lower fluence (about 0.3 J cm 22 ) than in LIBS could be applied. The TiN-TiAlN multi-structures were well resolved. The Gaussian-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.

A femtosecond laser system was used in combination with a time-of-flight mass spectrometer (TOF-MS) for in-depth profiling of semiconductor and metal samples. The semiconductor sample was a Co-implanted (10(17) ions/cm3) silicon wafer that had been carefully characterized by other established techniques. The total depth of the shallow implanted layer was 150 nm. As a second sample, a thin film metal standard had been used (NIST 2135c). This standard consisted of a silicon wafer with nine alternating Cr and Ni layers, each having a thickness of 56 and 57 nm, respectively. An orthogonal TOF-MS setup was implemented. This configuration was optimized until a sufficient mass resolution of 300 (m/delta m) and sensitivity was achieved. The experiments revealed that femtosecond-laser ablation TOF-MS is capable of resolving the depth profiles of these demanding samples. The poor precision of the measurements is discussed, and it is shown that this is due to pulse-to-pulse stability of the current laser system. Femtosecond-laser ablation TOF-MS is shown to be a promising technique for rapid in-depth profiling with a good lateral resolution of various multilayer thin film samples.

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