Reliability of Metal-Insulator-Metal (MIM) after Electrostatic Discharge (ESD) Stress

The lifetime and degradation mechanism of a metal- insulator-metal (MIM) on GaAs MMIC after electrostatic discharge (ESD) stress have been investigated. The mean-time- to-failure (MTTF) of MIM after applying ESD stress using a machine model (MM) is experimentally obtained by the time- dependent-dielectric-breakdown (TDDB) method. The nondestructive MIM remaining after ESD stress shows almost the same MTTF as the no-stress MIM. The obtained MTTF extrapolated by the electric field dependence is 3.6times10¹² hours at an actual operating voltage. Therefore, we found that stressed MIM has sufficient MTTF for practical use. Moreover, initial failure rate is decreased by a screening effect. To investigate the degradation mechanism, we have analyzed electrical conductance in detail. The insulator of silicon nitride (SiN) has a charge trap site with a barrier height of 1.8 eV, and its conduction mechanism is Poole-Frenkel (PF) emission. When moderate ESD stress is applied, some induced carriers are trapped in the trap site, and PF emission is suppressed. With increasing stress, PF emission is enhanced by newly generated traps, and finally shows catastrophic breakdown when trapped carriers accumulate until reaching the limit of breakdown, Q_bd. These phenomena resemble those in the case of a long-time stress study. Therefore, we can explain the ESD stress by the continuous percolation model, which considers the defect path across SiN films, even at a very short stress time of about 100 ns.