Note on the origin of intrinsic stresses in films deposited via evaporation and sputtering

Abstract

An attempt is made to provide a broad and brief review (with a sufficient number of references) of the question of intrinsic stresses in films deposited via evaporation and sputtering. Films deposited via evaporation are usually found initially in a disordered state, at the limit in an amorphous condition. Very broad thermodynamic principles imply that disorder is usually accompanied by an increase in volume (with few exceptions, e.g. water). Any relaxation from a disordered state to a more ordered state will, therefore, be accompanied by a decrease in volume and the formation of tensile stresses. The situation is modified in films deposited in the presence of impurities. Then one often finds the formation of compressive stresses. Several mechanisms may account for this result: (a) direct diffusion of interstitial impurities in the bulk of the underlying film: (b) surface and grain boundary diffusion of the impurities leading to compound formation (and swelling) in the grain boundaries, and at low temperatures in intergranular voids; (c) some attention is paid to a third model where compressive stresses could result from impurity adsorption not at the top surface of the growing films, but one monolayer below. The presence of compressive stresses in films deposited via sputtering is briefly reviewed in terms of the atomic peening mechanism. An experiment exploring the interrelationship between the purification effect of ion bombardment, thus causing tensile stresses, and the more normal formation of compressive stresses is discussed. © 1989.