A new degradation mechanism and its role on negative bias temperature instability in metal-oxide-semiconductor devices

For the first time, an experimental investigation of dopant passivation/depassivation in the silicon substrate of metal-oxide-semiconductor (MOS) devices is presented during and after negative bias temperature stress (NBTS). It is believed that dopant passivation/depassivation is caused by hydrogen diffusion into the substrate forming complex with the dopant during NBTS and back diffusion of hydrogen from the passivated dopant atom during relaxation phase, respectively. The source of the diffusing hydrogen species responsible for dopant passivation during NBTS is the atomic hydrogen (H^o) liberated during interface state (N_it) generation by the hot electron impact with the Si₃ ≡ SiH bonds at the Si/SiO₂ interface. Dopant passivation mechanism significantly contributes in the measured threshold and flatband voltage shifts ΔV_T and ΔV_fb, respectively during NBTS. We propose that the experimentally observed new degradation phenomena should be taken into account in evaluation of the NBTI induced oxide charge trapping and interface trap creation.