Nonhydrostatic stress effects on boron diffusion in Si

The thermodynamics of diffusion under hydrostatic pressure and nonhydrostatic stress is developed for single crystals free of extended defects and is applied to the case of boron diffusion in silicon. The thermodynamic relationships obtained permit the direct comparison of hydrostatic and biaxial stress experiments and of atomistic calculations under hydrostatic stress. Assuming various values for the anisotropy in the migration strain, a currently unknown parameter, comparison is made between various measurements under hydrostatic pressure and nonhydrostatic stress, and various atomistic calculations of the volumetrics of B and Si diffusion by an interstitial-based mechanism. An independent determination of the anisotropy of the migration strain would permit a parameter-free determination of the predominant diffusion mechanism and would permit the prediction of the ratio of the diffusivity normal to the free surface to the diffusivity parallel to the surface for biaxially strained films. Procedures for measuring and calculating the anisotropy in the migration strain are described.