Picoseconds-Laser Modification of Thin Films

The interaction of a Nd:YAG laser, pulse duration of 40 ps, with a titanium nitride (TN) and tungsten-titanium (W-Ti) thin films deposited at silicon was studied. The peak intensity on targets was up to 10(12) W/cm2. Results have shown that the TiN surface was modified, by the laser beam, with energy density of > or = 0.18 J/cm2 (lambdalaser = 532 nm) as well as of 30.0 J/cm2 (lambdalaser= 1064 nm). The W-Ti was surface modified with energy density of 5.0 J/cm2 (lambdalaser= 532 nm). The energy absorbed from the Nd:YAG laser beam is partially converted to thermal energy, which generates a series of effects such as melting, vaporization of molten materials, dissociation and ionization of the vaporized material, appearance of plasma, etc. The following morphological changes of both targets were observed: (i) The appearance of periodic microstructures, in the central zone of the irradiated area, for laser irradiation at 532 nm. Accumulation of great number of laser pulses caused film ablation and silicon modification. (ii) Hole formation on the titanium nitride/silicon target was registered at 1064 nm. The process of the Nd:YAG laser interaction with both targets was accompanied by plasma formation above the target.