Ž . Applied Surface Science 154–155 2000 659–663 www.elsevier.nlrlocaterapsusc Femtosecond pulse laser processing of TiN on silicon J. Bonse ) , P. Rudolph, J. Kruger, S. Baudach, W. Kautek ¨ Laboratory for Thin Film Technology, Federal Institute for Materials Research and Testing, Unter den Eichen 87, D-12205 Berlin, Germany Received 1 June 1999; accepted 21 July 1999 Abstract Ž . Ultrashort pulse laser microstructuring pulse duration 130 fs, wavelength 800 nm, repetition rate 2 Hz of titanium Ž . nitride TiN films on silicon substrates was performed in air using the direct focusing technique. The lateral and vertical precision of laser ablation was evaluated. The TiN ablation threshold changed with the number of pulses applied to the surface due to an incubation effect. An ablation depth per pulse below the penetration depth of light was observed. Columnar structures were formed in the silicon substrate after drilling through the TiN layer. q 2000 Elsevier Science B.V. All rights reserved. PACS: 79.20.D; 78.66; 78.47 Keywords: Femtosecond laser ablation; Titanium nitride; Silicon; Optical properties 1. Introduction Ž . Titanium nitride TiN plays an important role in many industrial applications because of its hardness, Ž . high evaporation temperature 29508C , good chemi- w x cal stability and metallic brightness 1,2 . Mechanical machining of this coating material is difficult due to its large brittleness and hardness. A solution of this problem may be the application of ultrashort laser pulses to avoid mechanical tool wear and to mini- mize thermal and mechanical stress during the struc- turing process. Laser ablation is associated with material- and laser-dependent parameters. If the laser fluence ap- Ž plied to the sample exceeds a certain material-de- ) Corresponding author. Tel.: q 49-30-8104-2594; fax: q 49-30- 8104-1827. Ž . E-mail address: joern.bonse@bam.de J. Bonse . . pendent fluence f , ablation occurs. The diameters th and the depths of the ablated areas are influenced by the radial beam profile of the laser and can be used to characterize the ablation process. In this work, the lateral dimensions were investigated to estimate the ablation threshold fluence. 2. Experimental Ž . A TiN film thickness 3.2 mm was deposited by Ž unbalanced magnetron sputtering Hauzer, HTC 625 . Multilab in nitrogen atmosphere at a pressure of 5.5 = 10 y5 mbar on a single crystalline silicon wafer. A commercial Ti:sapphire femtosecond-laser-sys- Ž . tem Spectra Physics, Spitfire with a wavelength of 800 nm, based on chirped pulse amplification tech- Ž . nique CPA , was used for the ablation experiments. The system provides variable output energies up to 0169-4332r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. Ž . PII: S0169-4332 99 00481-X