Influence of segregation on the measurement of stress in thin films

Abstract

The force that a deposited film A exerts on its substrate B is usually written as the sum of volumetric and surface (and interface) contributions. In the simplest case (pseudomorphous film, absence of segregation), volumetric and surface contributions can be easily separated through simple force measurements. In this article, we show that, in the presence of segregation, only simultaneous in situ stress, strain, and composition measurements allow the proper analysis of stress establishment in thin films. For this purpose, we discuss how segregation influences both volumetric and surface stresses. More precisely, we show that (1) the separation between a surface and a volumetric stress can be meaningless when segregation occurs; (2) one should carefully distinguish between the true physical thickness and the deposited thickness; (3) surface strain should be accounted for in the analysis of the experimental diffraction data; and (4) when the elastic modulus misfit between film and substrate cannot be neglected the total stress depends explicitly on the shape of the concentration profile.