Oxidation enhanced diffusion in Si B-doping superlattices and Si self-interstitial diffusivities

A special thin film structure has been grown by low temperature molecular beam epitaxy for an investigation of the properties of self-interstitials in Si. It consists of a doping superlattice made from B spikes separated from each other by 100 nm of Si. After dry oxidation, the width of each spike is directly proportional to the interstitial concentration at that depth. The superlattice as a whole thus gives a depth profile of the time-averaged interstitial concentration, allowing the direct determination of the diffusion coefficient of interstitials. The abrupt dopant concentration transitions possible in low-temperature molecular-beam-epitaxy-grown films allow this investigation in the temperature range 750–900 °C. At 800 °C we find a value of DI=(1.4±0.4)10−13 cm2/s. Performing the experiments as a function of temperature yields DI = D0eEa/kT with D0=102±2 cm2/s and Ea=(3.1±0.4) eV.