SiGe composition and thickness effects on NBTI in replacement metal gate / high-κ technologies

The dependence of NBTI on SiGe thickness and composition for epitaxially grown layers on (100) and (110) Si substrates is studied in detail. It is found that SiGe thickness has no significant impact on NBTI at lower Ge%. However, lower NBTI degradation was observed with increasing Ge%, even though the interface state densities (N
it
) increase with respect to Si. This improved NBTI is due to band offset limited V
T
, indicating that the improvement is substrate related rather than interface related. The physical mechanism is then discussed in terms of Ge%-induced variation in the band alignment.