Hydrogen, in its various forms, has an important and sometimes critical impact on the radiation response and long term reliability of semiconductor integrated circuits (ICs). At present, a relatively large density of hydrogen species is present in even the driest and cleanest of all IC fabrication and packaging processes.

High levels of molecular hydrogen are found to be trapped inside certain hermetically sealed IC packages after encapsulation. This is shown to severely degrade the performance of ICs fabricated in both Metal-Oxide-Semiconductor (MOS) and bipolar technologies after ionizing radiation exposure. Furthermore, it is also demonstrated that excess molecular hydrogen dramatically changes the radiation response of bipolar ICs when they are exposed at different dose rates. In particular, it changes the transition dose rates and low dose rate enhancement factor in circuits exhibiting Enhanced Low Dose Rate Sensitivity (ELDRS).

Characterization and modeling of the effects of molecular hydrogen on the Total Ionizing Dose (TID) and dose rate response of linear bipolar ICs are presented in this work. By deliberately introducing and controlling molecular hydrogen concentration in test bipolar transistors, enhanced radiation-induced degradation in terms of interface trap and oxide-trapped-charge buildup are characterized at different dose rates. Moreover, annealing experiments are performed at different biases and temperatures after irradiations. From the experimental results, physical models are proposed and implemented through computer simulations to describe the effects of molecular hydrogen. The models incorporate molecular hydrogen cracking and electron/hole recombination reactions to describe the impact of molecular hydrogen on TID and dose rate responses of bipolar ICs.

The results of this work should stimulate changes in recipes used during IC fabrication and packaging to ensure proper control of hydrogen contamination. They also suggest that hardness assurance test methods used to qualify radiation tolerant electronic parts need to include the measure of hydrogen content in IC packages. Moreover, molecular hydrogen and its effects on bipolar IC dose rate response, particularly on ELDRS, may help to predict the low dose rate response of target ICs and reduce or even eliminate costly procedures of selecting and qualifying parts for use in the space radiation environment.