Role of hydrogen: Formation and passivation of meta-stable defects due to hydrogen in silicon

Abstract

Hydrogen is well known for its ability to effectively passivate defects in silicon. However, it has been recently proposed that it can also be detrimental, with susepected involvement in light and elevated temperature induced degradation (LeTID). The role of rapid firing processes in the passivation of B-O defects and activation of LeTID indicate a similar involvement of hydrogen in the passivation of B-O defects and LeTID related reactions. While B-O passivation rate is suppressed by dark annealing in Czochalski mono-crystalline silicon, both mono-crystalline silicon and multi-crystalline wafer types showed a similar formation rate of LeTID. It has been recently demonstrated that interstitial hydrogen can migrate to the surface by annealing. Thermal annealing suppressed B-O passivation rate significantly while the LeTID formation rate was not changed significantly. The implication is that as the B-O defect is present uniformly in the bulk of silicon, while hydrogen must either be readily present in bulk, or diffuse to the entire bulk region to passivate B-O defect, the LeTID may not necessarily occur throughout the bulk like B-O passivation. During the first 300 hours of light soaking on mc-Si samples, Cz-Si samples showed improvement in lifetime, which can be explained by the passivation of the B-O defect. However, the full recovered lifetime was similar to the lifetime after firing. The lifetime curve showed no shockley-read-hall component when the lifetime was fully recovered, which confirms the LeTID, which is independent defect to B-O defect, was no longer present. This implies that while B-O defect was passivated, the LeTID defect may have also been recovering at the same rate. It may be that hydrogen initially contributing to the recombination as LeTID, is contributing to B-O passivation, which leads to a recovery in lifetime with a reduction in LeTID and B-O defect.