Internal stress of thin silver, copper, gold and chromium films—a comparison

A model previously developed to account for internal stress of evaporated films of Au, Ag, and Cu low melting metals with similar, high mobilities, can be applied to metals with higher melting points and therefore smaller mobilities. Thus the stress measuring technique together with the model for the interpretation of the stress curves constitutes a valuable new method for the in situ investigation of the structure of thin films. The principle advantage of this method is the fact that the measuring technique itself does not influence the growth processes of the deposited film. In contrast to the metals of the copper group, the intrinsic stress of Cr deposited under standard conditions is only tensile. In terms of the stress model the large tensile stress and the lack of changes in incremental stress indicate a small average grain size, which remains more or less constant as the film thickness increases. Thus owing to the low mobility of the chromium atoms columnar grain growth is representative of the growth of the chromium film. However, the mobility of the chromium atoms can be increased by a higher substrate temp. At temp. higher than 350 deg C tensile as well as compressive stresses are found. As a further application of this technique one can also investigate possible changes in film stress after the film deposition. In these experiments again considerable differences between the metals of the copper group on one side and chromium on the other side have been found. As a last application, the technique can also be used to study the effect of gas adsorption on the internal stress of films deposited under best vacuum conditions. The adsorption of gases on the surface of the metal film generally gives rise to a compressive stress depending on the strength of the interaction between the metal and the respective gas. A special behavior is observed in the case of oxygen adsorption on chromium films. Upon exposure of the film to oxygen a small compressive stress is observed which on further exposure changes to tensile stress. 2 ref.--AA