Co-60 gamma irradiation effects on electrical characteristics of HfO2 MOSFETs and specification of basic radiation- induced degradation mechanism

We have studied the effects of Co-60 gamma irradiation on electrical characteristics of metal oxide semiconductor field effect transistors (MOSFETs) with radio-frequency-sputtered Hafnium Oxide (HfO2) gate dielectric, and possible interaction mechanisms between irradiation and HfO2/Si gate stack. The electrical response of the HfO2 devices has been compared with those of experimental and commercial MOSFETs with conventional Silicon Dioxide (SiO2) dielectrics of the similar thickness. We have observed only small threshold voltage shifts during irradiation of the HfO2 MOSFETs; the SiO2 MOSFETs exhibit more than 10 times larger shifts. We have found interesting radiation-induced charge trapping mechanisms by analysis of X-ray photoelectron spectroscopy (XPS) measurements of HfO2/Si gate dielectric stack. The XPS analyses before and after different irradiation doses indicate that both the passivation and charge trapping occurs under radiation exposure. The passivation of dangling bonds significantly decreases the sensitivity of the HfO2 MOSFETs to irradiation. The small threshold shift is predominantly due to the breaking oxygen bonds, especially in HfOx and SiOx core levels. The obtained results demonstrate that the HfO2 based devices are almost insensitive to the irradiation compared to the conventional SiO2 gate and passivation effects significantly decrease radiation sensitivity of HfO2- based device.