High temperature stability and relaxation of UHV/CVD SiGe thin films

Abstract

High temperature (950°C) annealing is used to stimulate relaxation in UHV/CVD SiGe thin films. It is found that the films are stable to thicknesses which exceed the stability criterion of Matthews and Blakeslee [1] by a small amount. In unstable films, the misfit dislocation density increases with annealing time, reaching a maximum value. For films which exceed the empirical stability criterion by a relatively small amount, the misfit dislocations relax the film to a strain given by the film thickness and the empirical stability criterion. However, large remnant strains are observed when the relaxation process introduces relatively high dislocation densities (≳5 misfits/nucron). Associated with large remnant strains are a marked propensity for dislocation banding and looping deep into the substrate with extended annealing. These results are discussed with respect to the magnitude of the misfit dislocation nucleation barrier and the energy associated with interactions among misfit dislocations.