Mechanics of compressive stress evolution during thin film growth

Based on recent in situ measurements, Chason et al. (2002) proposed that the evolution of compressive stress during thin film growth by vapor deposition is due to an increase in surface chemical potential in the presence of growth flux and the consequent exchange of adatoms between the free surface and the grain boundaries. Based on this hypothesis, we present a model for grain boundary stress evolution during thin film growth. To illustrate the mechanics of the problem, first it is assumed that the local normal stress on the grain boundary is proportional to the local grain boundary opening only. The resulting "linear spring" model captures all essential features of the experimental observations. A more accurate description of the grain boundary stress evolution is presented by modeling the stress field due to the material inserted into the grain boundary as that resulting from a continuous distribution of dislocations along the grain boundary. The adatom flux between the grain boundary and the free surface is assumed to be proportional to the difference in chemical potential between the two. This model successfully explains a wide range of experimental observations, including the development of compressive stress during room temperature growth, effect of growth rate on the kinetics of compressive stress evolution and the continued tensile stress generation during low-temperature growth. (C) 2003 Elsevier Ltd. All rights reserved.