Enhancement of boron diffusion through gate oxides in metal-oxide-semiconductor devices under rapid thermal silicidation

Abstract

It has recently been reported that there is anomalous enhanced diffusion of B through the gate oxide in metal-oxide-semiconductor (MOS) structures from B-implanted, p+-polycrystalline silicon gates upon annealing in the presence of H or F. This letter discusses the effects of TiSi2 formation on B penetration through the gate oxide in p+ polycrystalline silicon gate MOS devices. From secondary-ion mass spectrometry analyses, it is found that B penetration effect is enhanced by TiSi2 formation, for 950 and 1100 °C rapid thermal annealing, in spite of the fact that the F concentration in the gate oxide for samples with silicide is lower than that for samples without silicide. Furthermore, samples with a one-step TiSi2 formation process exhibit more serious B penetration effects than those with a two-step process. This indicates that the effect of silicide on B penetration is more complicated than simply acting as a sink for F. Pileup of B at the silicide/polycrystalline silicon interface, the generation of point defects such as Si vacancies and interstitials during silicide formation, and B-defect interactions must be taken into account to explain the results.