Effects of the pulse duration in laser modification of nano-sized WTi film on Si substrate

A study of morphological and composition changes of the WTi/Si system induced by nanosecond and picosecond laser pulses is presented. A 190 nm thick WTi film was deposited on a silicon substrate of n-type (100). The pulsed laser systems used were: nanosecond TEA CO(2) laser (emission, 10.6 mu m; pulse FWHM; pulse duration 120 ns) and picosecond Nd:YAG laser (emission, 532 nm; pulse FWHM; pulse duration 40 ps). During experiments the used fluences (Phi) had similar values, Phi(1) = 20 J cm(-2) in case of the TEA CO(2) laser and Phi(2) = 16 J cm(-2) for the Nd: YAG laser. The laser-induced morphological and composition modifications showed a dependence on pulse duration. Generally, the following morphological changes were observed: (i) ablation/exfoliation of the WTi thin film, (ii) appearance of hydrodynamic features such as resolidified material, and (iii) formation of nano-sized grains and globules. Overall morphological modifications were more pronounced after the picosecond laser action. The surface composition analysis showed a quite different distribution of sample components depending on the pulse duration. Formation of the silicon dioxide (SiO(2)) was recorded only in the case of irradiation of the WTi/Si system by picosecond laser pulses.