Positive bias temperature instability in p -type metal-oxide-semiconductor devices with HfSiON/SiO₂ gate dielectrics

We present a detailed investigation on positive-bias temperature stress (PBTS) induced degradation of nitrided hafnium silicate (HfSiON)/SiO₂ gate stack in n+-poly crystalline silicon (polySi) gate p-type metal-oxide-semiconductor (pMOS) devices. The measurement results indicate that gate dielectric degradation is a composite effect of electron trapping in as-fabricated as well as newly generated neutral traps, resulting a significant amount of stress-induced leakage current and generation of surface states at the Si/SiO₂ interface. Although, a significant amount of interface states are created during PBTS, the threshold voltage (V_T) instability of the HfSiON based pMOS devices is primarily caused by electron trapping and detrapping. It is also shown that PBTS creates both acceptor- and donor-like interface traps via different depassivation mechanisms of the Si₃ ≡SiH bonds at the Si/SiO₂ interface in pMOS devices. However, the number of donor-like interface traps Δ NitD is significantly greater than that of acceptor-like interface traps Δ N^A_it, resulting the PBTS induced net interface traps as donor-like.