ABSTRACT
In contrast to free-standing films, films attached to a substrate may be stressed in tension or compression. The film stress can be obtained from the bending of the film/substrate composite by measuring the radius of curvature and using the Stoney equation. Frequently, measurements of stress are also carried out using the X-ray diffraction sin2 ψ method. In general, growth processes proceed far from thermodynamic equilibrium and are mainly kinetically controlled. This results in many different types of defects which create stresses. The most important of these defects have been described. Extrinsic stress of thermal origin arises when the deposition temperature is different from room temperature and the thermal expansion coefficients of the substrate and the film are different. Through control of the deposition parameters — substrate temperature and the energy and flux of energetic particles bombarding the growing film — the stress can be tailored to applications which require specific tensile or compressive stresses. Interface stresses play a role in thin films and multilayers with small bilayer lengths. An example of the measurements of interface stress has been presented. Finally, the importance of controlling stress relaxation has been emphasised and an example of stress relaxation in amorphous Ta54Cr46 film has been given.
