Impacts of a buffer layer and hydrogen-annealed wafers on the performance of strained-channel nMOSFETs with SiN-capping layer

In this study, the effects of Si₃N₄ layer capping and TEOS buffer layer inserted prior to the Si₃N₄ deposition on the NMOS device characteristics as well as correlated hot-electron degradations were investigated. The devices were built on two kinds of the substrates, namely, Cz and hydrogen-annealed (Hi) wafers. More importantly, we found that hydrogen species is the primary culprit for aggravated reliabilities in strained devices. By exerting the accelerated stress test, we could study the hot-electron degradation thoroughly in terms of threshold voltage shift (ΔV_TH), transconductance degradation (ΔGm) and so on. The TEOS buffer layer could effectively block the diffusion of hydrogen species from the Si₃N₄ capping layer into the channel and the Si/SiO₂ interface during the Si₃N₄ deposition as well as subsequent thermal cycles.