Light and Elevated Temperature Induced Degradation in Mono-Like and Float-Zone Silicon: Correlations to Material Types, Silicon Nitride Films, and Dopant Diffusion

We compare light and elevated temperature induced degradation (LeTID) in four different silicon substrates, namely p-type boron-doped and n-type phosphorus-doped mono-like Si and float zone silicon, and study the dependence of the degradation behaviors on silicon nitride (SiNx) film properties and dopant diffusions. The materials exhibit different degradation kinetics, but show a similar dependence on the SiNx deposition conditions, correlating strongly with the Si-N bond density and the refractive index of the SiNx films, measured using Fourier-transform infrared spectroscopy and ellipsometry. It is observed that the degradation severity is reduced by decreasing SiNx deposition temperature and power, revealing a potential solution to mitigate LeTID. Moreover, p-type materials are found to generally suffer a higher degradation extent than their n-type counterparts. Our experimental results are consistent with LeTID depending on the hydrogen concentration in the Si bulk. This model can explain the larger degradation observed in the p-type Si wafers, the dependence of LeTID on the SiNx films, and also the presence of heavily doped regions, all of which affect the diffusion of hydrogen and its final concentration in the bulk after firing.