The internal stress in thin silver, copper and gold films

The internal stress of silver, copper and gold films was measured as a function of film thickness during deposition and as a function of time after deposition under ultrahigh vacuum conditions. A model for the origin of the internal stress was used to interpret each stress curve in terms of the corresponding film structure. During the deposition of the three metals onto MgF 2 substrate films tensile as well as compressive stresses are found as the film thickness increases and the maximum tensile stress occurs at the thickness at which the metal films become completely continuous. A compressive strain, built up at the metal substrate interface during the coalescence stage, is assumed to be the origin of the compressive stress in the continuous metal film. The tensile stress change after deposition of these metals is attributed to recrystallization and annealing processes that occur in the films. The compressive interface strain, which is maintained during this recrystallization, again determines the compressive stress measured during the deposition of a second metal layer. The growth of this second metal film is a continuation of the growth of the first film without renewed nucleation.