Caterina Riva

Niobium Contamination in Silicon

In this paper niobium is characterized as a silicon contaminant. It is shown that niobium is a relatively slow diffuser, with an intermediate diffusivity between very slow diffusers such as molybdenum and fast diffusers such as iron. Niobium is found to be very effective as a recombination center, and in addition prone to surface segregation. In addition, niobium shows optical activation, but no thermal activation. Three deep levels are revealed in niobium contaminated silicon, plus an additional level observed in high contamination dose samples only. One of these levels is located very close to midgap, and consistently niobium was also found very effective in degrading the generation lifetime.

Analysis of Contaminated Oxide-Silicon Interfaces

Methods for the analysis of the oxide-silicon interface were compared for their ability to reveal metal segregation at the interface and organic contamination. The impact of these contaminations on surface recombination velocity measurements, on capacitance vs. voltage, conductance vs. voltage and capacitance vs. time measurements and on MOS-DLTS spectra was studied. Niobium-contaminated wafers were used as an example of metal surface segregation, because it was previously shown that niobium is prone to surface segregation. Interface state density measurements obtained by the conductance method showed a limited impact of niobium implantation. Vice versa significant effects were found in MOS-DLTS spectra. For what concerns organic contamination, MOS-DLTS showed the most significant effects from the point-of-view of the intrinsic properties of the silicon oxide - silicon interface, and GOI tests demonstrate a clear impact of the organic contamination on MOS capacitors oxide breakdown events.