Ab-initio Calculations of Shear Stress Effects on Defects and Diffusion in Silicon

In recent years a lot of attention has been given to engineering the stress state in ULSI devices to enhance device performance. As a result the stress conditions inside state-of-the-art devices are significantly more complex than simple hydrostatic or biaxial stress situations. In this paper we extend previous work on normal stress effects on point-defect equilibrium concentrations as well as point-defect and dopant diffusion to also include shear. We find there is little effect of shear stress on point-defect equilibrium concentrations. However shear is important for vacancy (V), interstitial (I), and boron (B) migration since it introduces anisotropies and off-diagonal elements in the diffusivity tensor. Diffusivity can no longer be view as a diagonal tensor, but instead a general tensor needs to be used to describe I, V, and B diffusion correctly