A comprehensive model of stress generation and relief processes in thin films deposited with energetic ions

摘要

Levels of intrinsic stress in thin films deposited using energetic condensation of ions and/or atoms are known to depend strongly on the energy of the depositing species. At low energies (up to a few eV) thin films are often observed to have a large number of voids and show tensile stress. As the energy increases, the stress is observed to rise to a maximum at all intermediate energy-usually at a few tens to a few hundreds of eV. Thereafter as the energy is increased further, the intrinsic stress is found to decrease. Variations on this "universal" behaviour occur when species of two quite different energies are deposited whereupon the higher of the two energies seems to determine the level of intrinsic stress even when the fraction of ions at that energy is comparatively small. This finding has led to the use of the plasma immersion ion implantation (Pill) method during film deposition to produce coatings with low stress. Although 98-99% of the ions impacting the substrate have energies in the range which produces very high intrinsic stress, the intrinsic stress in the film is determined predominantly by the 1-2% of ions with high energy (kV and above).