Structure and internal stress in ultra-thin silver films deposited on MgF 2 and SiO substrates

Abstract

A substantially improved bending-beam technique combined with the capacitance method was used for the continuous determination of the internal stress during vacuum deposition of ultra-thin silver films. With this method a sensitivity improvement of about two orders of magnitude was achieved compared with results reported previously. By proper experimental design all radiation interference on the stress-measuring appratus except the unavoidable direct heat radiated from the evaporators was eliminated. With this improved method it was possible to determine continuously the internal stress of silver films deposited onto fresh MgF 2 or SiO substrate films under varying experimental conditions ( i.e. evaporation rate, residual gas pressure). Based on correlations between internal stress and the structure of the films observed using an electron microscope a model is proposed that explains the origin of the alternately compressive and tensile stress in such ultra-thin films.