Dopant redistribution during the solid-phase growth of CrSi₂ on Si(100)

The results of an investigation into the redistribution of dopants - As, B, and P - during the solid-phase reaction of Cr with Si substrates to form CrSi₂ are presented. Cr layers, 47 nm thick, were evaporated onto B-doped Si substrates which had previously been implanted with one of the three dopants. Two implant doses were investigated for each dopant. Following heat treatment at 500 °C, doping profiles were determined by secondary-ion mass spectrometery (SIMS) and, for arsenic-doped samples, by Rutherford backscattering spectroscopy (RBS). Both SIMS and RBS were also used to measure the extent of silicide formation. The results demonstrate that B and P are transported from the Si substrate to the surface of the growing CrSi₂ layer while As accumulates at the CrSi₂/Si interface. The silicide formation reaction is shown to be inhibited by large As concentrations. No other dopant-concentration-related effects were observed. A model, based on dopant segregation driven by the relative free energies of CrSi₂ and Cr-dopant compounds, is proposed to explain the results.