Diffusion, solubility and gettering of copper in silicon

The feasibility of quantitative predictive modeling of gettering of Cu in silicon, which requires quantitative understanding of its diffusivity and precipitation behavior, is discussed. Investigations of diffusion of Cu at low temperatures enabled us to determine the pairing constants of copper with boron, re-evaluate its diffusivity at room temperature in p-Si, and to predict its diffusivity in p+-Si substrates. We demonstrate that copper may either precipitate in the bulk of the wafer or diffuse to its surface, depending on the position of Fermi level in the sample. It is suggested that the Fermi level position determines the sign and magnitude of the electrostatic charge on the growing copper precipitates, and thus enhances or suppresses precipitation of interstitial copper ions. Modeling of p/p+ segregation gettering of copper shows that while the copper can be gettered in p+ layer during or after high-temperature anneals, it eventually will be released and will precipitate in the device region within the first few months of operation, unless more stable gettering (precipitation) sites for copper are utilized. An n-type layer is predicted to be an effective gettering site.