Residual stress determination in thin films by X-ray diffraction and the widespread analytical practice applying a biaxial stress model: An outdated oversimplification?

Abstract Compressive stresses are commonly desired in thin films and the stress state in layers and coatings is in general evaluated assuming a biaxial nature of stress. But how thin is thick enough, or how many atom layers are necessary until this model assumption fails and a hydrostatic term joins in? In order to provide an answer molybdenum has been magnetron sputtered on display glass in layer thicknesses from 100 nm up to 2000 nm and afterwards investigated by X-ray diffraction to determine the residual stress state in the [1 1 0] fiber-textured sputtered films. It will be demonstrated that the use of a biaxial stress model might only be justified for thin layers if at all.