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Substitutional Diffusion of Transition Metal Impurities in Silicon

Near-surface Cu and Ni rich layers are observed by secondary ion mass spectroscopy (SIMS) in intentionally contaminated silicon wafers after thermal oxidation at 950°C for 35 min. The diffusivities of Cu and Ni obtained from their respective SIMS profiles are almost 9 orders of magnitude smaller than documented which are widely believed of interstitials, but comparable to that of Group III and V atoms which are known as substitutional. According to the experimental results, a model is proposed for in-diffusion of transition metal atoms contaminated on the surface of a silicon wafer during thermal oxidation. In this model, the interstitial and substitutional atoms diffuse independently and the slow substitutional diffusion gives rise to a near-surface impurity-rich layer.