Impact of Si/N ratios in a pre-metal SixNy:H z dielectric film on NMOS channel hot carrier reliability

The effect of silicon to nitrogen ratios in a pre-metal silicon nitride dielectric film on NMOSFET channel hot carrier (CHC) reliability is studied. Si_xN_y:H_z films are deposited with Si/N ratios of 0.9 and 0.7. Wafer level hot carrier data shows transistors built with a silicon rich liner have a 4.5× higher CHC lifetime. Charge pump measurements are carried out and indicate an increase in D_it for a wafer with a nitrogen rich liner. It is shown that the nitrogen rich film releases less hydrogen during subsequent processing resulting in less hydrogen passivation of the Si/SiO₂ surface and increased D_it. The observed lifetime reduction is a result of the increase in D_it. Finally, it is demonstrated that despite an end-of-line anneal in a hydrogen ambient, hydrogen exposure early in the fabrication process can play an important role in Si/SiO₂ surface passivation, affecting CHC reliability