The role of hydrogen in defect formation and passivation in bipolar and MOS oxides
Hughart, David Russell
Ambient hydrogen has been shown to enhance the degradation of several types of linear bipolar devices. Recently, it has been seen that hydrogen exposure can cause increased degradation at high dose rates. This has created interest in investigating the possibility of an accelerated hardness assurance test involving irradiation at high dose rates during a hydrogen soak. This thesis investigates the various factors that determine the effects of hydrogen on bipolar and MOS devices and discusses the risks involved in using hydrogen screening as an accelerated hardness assurance test. Hydrogen soaking experiments are performed to evaluate the dependence of defect buildup and annealing in gated lateral bipolar transistors on hydrogen exposure. Comparisons of the radiation responses of transistors tested in 2009 to identical devices from the same wafer tested in 2003 show that aging has reduced the amount of radiation-induced interface trap and oxide trapped charge formation in most cases. These results demonstrate that hydrogen has a dual role and that the way in which the radiation response of a hydrogen-sensitive device evolves with age depends on whether hydrogen is diffusing into or out of the device, and whether the initial defect concentration favors passivation or depassivation reactions. These results strongly suggest that hydrogen exposure cannot replace low-dose-rate irradiation in ELDRS tests for bipolar devices and ICs without extensive characterization testing.