Elastic behavior of tin thin-films

Thin films are increasingly being used in many technological areas. One of the problems in practical applications is the level of internal film stress, which, in severe cases, can lead to coating failure. In our laboratories we are currently studying the effect of deposition parameters and of post-deposition treatments on the stress behaviour of some coatings obtained by magnetron sputtering techniques and by ion beam assisted deposition (IBAD). In this work we concentrate on TIN since this compound is particularly valuable as a study system, in view of the good understanding of its physical properties and its wide range of applications, ranging from barrier layers in microelectronics to gas diffusion inhibition, and from optical coatings to sliding wear reduction. We have deposited thin films (ranging in thickness from 100 nm up to a few microns) of TiN in different experimental conditions, by d.c. magnetron reactive sputtering and by IBAD, and we have characterized the coatings with respect to composition, structure and microstructure by scanning electron microscopy, Auger electron spectroscopy and X-ray diffraction. The elastic response of the films has been studied in detail by surface Brillouin light scattering. Our results are in general agreement with other works in the literature; however, the Rayleigh wave velocities for IBAD samples are much lower than expected. Some preliminary explanations of this fact are presented.