Evaluation of the composition and morphology of a WTi/Si system processed by a picosecond laser

Abstract

In this work we studied the influence of laser radiation on the composition, structure and morphology of WTi thin films deposited on n-type (100) silicon wafers. The films were deposited by d.c. sputtering from a 70:30 at% W-Ti target, using Ar ions, to a thickness of ∼190 nm. Irradiation was performed with a pulsed Nd:YAG laser operating at 1064 nm, whereas the pulse duration was 150 ps. Laser fluences of 3.2 and 5.9 J/cm2 were found to be sufficient for modification of the WTi/silicon target system. The results show: (i) ablation of WTi thin film and a Si substrate in the central zone of spots, (ii) appearance of hydrodynamic features like resolidified material, (iii) partial ablation of the WTi thin film at the periphery and (iv) appearance of thin film cracks at the far periphery. On the non-ablated areas, the laser modification induced changes in composition, such as inter-mixing of components at the WTi/Si interface with formation of silicides in both metals. Surface oxidation was the dominant process in the ablated areas, which is demonstrated by the presence of a SiO2 phase.