Enhanced diffusion of platinum in electron-irradiated silicon

Platinum has been diffused at 600, 700 and 800°C into n-type epitaxial silicon samples with and without prior 2 MeV electron irradiation at doses of 1×1014–1×1017 cm−2. Without prior electron irradiation, diffusion at 700 and 800°C for 30 min resulted in the presence of a single deep level in the DLTS (Deep Level Transient Spectroscopy) spectrum, which is attributed to the platinum acceptor level at 0.23 eV below the conduction band edge. At lower diffusion temperatures no deep level was detected. However, after prior electron irradiation and subsequent in-diffusion at 600°C this platinum level is again present in the DLTS spectrum. Depth profiling shows, that the platinum concentration increases with electron dose. Its value after in-diffusion without prior irradiation at 750°C is comparable to the one after in-diffusion at 600°C following a dose of 1×1017 cm−2. A tentative explanation of this enhanced diffusion is proposed and the influence of the irradiation induced vacancies and silicon self-interstitials is discussed.