On the migration behavior of metal impurities in Si during secondary ion mass spectrometry profiling using low-energy oxygen ions

Secondary ion mass spectrometry (SIMS) was used to investigate the segregation of several metal impurities in Si under low-energy oxygen ion bombardment. Our results suggested that both the segregation of Ca, Cr, and Ta at the SiO₂/Si interface, and the antisegregation of Ti, Hf, and Zr into the oxide were thermodynamically driven. The migration behavior of Ca indicates that CaO, having a higher heat of formation than Si, was most probably formed under oxygen bombardment. Sharper in-depth profiles were obtained for Ti, Zr, and Hf (metals with lower heat of oxide formation than Si) by bombarding at angles of incidence for which a stoichiometric surface oxide is formed. The effect of impurity diffusivity is demonstrated through SIMS measurements at elevated temperatures (∼350-380°C) for Cr, Zr, Ta, and Ti.