Mechanical Properties of Thin Films

The mechanical properties of thin films are different from those of bulk materials because of their unique microstructure, large surface-to-volume ratio, reduced dimensions, and the constraints caused by the substrate. Since the substrate is a key factor in the mechanical properties of single and multilayered thin film structures, this paper will limit itself to the mechanical properties of thin films on substrates. The mechanical prop­ erties of free-standing thin films were previously reviewed by Hardwick ( 1 ) . Because of the diversity of the subject and the sheer volume of pub­ lications, a complete review of the area of mechanical properties of thin films is impossible. Focus will be on thin metal and ceramic films with thickness less than I J-lm. Measurement techniques and recent results will be reviewed and areas of future work will be identified. Understanding the processes controlling the mechanical properties of thin film structures is important in a variety of scientific and technological applications. In the last few decade� the �cientific arena has seen the development of dry deposition processes, such as physical vapor deposition (PVD) and chemical vapor deposition (CVD), as well as the appearance of improved in situ characterization and analysis techniques: i.e. X-ray photoemission spectroscopy (XPS); Auger spectroscopy; low energy elec­ tron diffraction (LEED); and Brillouin scattering that allows relatively easy deposition of unusual microstructures, both crystalline and amorphous, as well as layered structures with controlled and reproducible periods of a few monolayers. Laminated thin film structures have been produced with tailored elastic and plastic properties. Detailed characterization and