Effect of mobile charge on hot-carrier degradation in lateral diffused MOSFET

Hot carrier-induced device degradation in n-type lateral diffused MOSFETs with mobile charges in gate oxide has been studied. Abnormal decrease-then-increase in V-th during hot-carrier stress was observed. The decrease was found to be caused by movement of mobile charges while the increase was the normally observed hot-electron degradation. The hot-electron degradation was drastically accelerated with the presence of mobile charges and easily recovered after baking or negative gate bias. The magnitude of degradation linearly increases with mobile charge density. The acceptable limits of mobile charge density have been estimated. The observed behaviors are very similar to positive charging processes found in other n-MOSFETs that were attributed to hot-hole effects, suggesting mobile charge induced degradation must be carefully excluded in hot-hole injection studies.