Modelling of Structure Formation and Mechanical Stresses during Growth of Vapor Deposited Amorphous Thin Films

Abstract

Independent of the details of the applied materials system, the growth of amorphous thin films can be characterized in dependence of the film thickness by the presence of a strong structure formation and intrinsic mechanical growth stresses. After substrate dependent early stages, film growth in the medium film thickness regime (typ. 100nm) is smooth under continuous evolution of compressive stresses. In the late stages of growth, the films roughen markedly, accompanied by strong tensile stresses. Using systematically varied film preparation parameters, it is possible to identify the main atomic processes for the mesoscopic structure formation and the macroscopic growth stresses, and to correlate both ascpects. In the framework of continuum growth models, assuming surface diffusion, self shadowing and hill coalescence as main processes on an atomic level, even a quantitative understanding of structure formation and tensile stresses in the high film thickness regime is possible. A surface reconstruction mechanism is able to explain compressive stresses in the medium film thickness regime.