Thermally activated dopant diffusion in crystalline silicon at 200 degree C.

Recently, anomalous, asymmetric diffusion of dopants in silicon during silicidation at temperatures as low as 200degreeC has been reported. This observation has not been explained satisfactorily so far and presents, therefore, a formidable challenge to present Fickian-type diffusion theories. In this letter, the structure of the asymmetric diffusion is analyzed and it is shown that the anomalous diffusion can be explained consistently by postulating the existence of an inhomogeneous stress field as an external driving force in conjunction with stress relaxation mechanisms due to the silicon self-interstitial diffusion. However, at the same time, it is demonstrated conclusively that the hypothesized diffusion in stress fields cannot be effectuated by thermal activation.