Radiation tolerance, charge trapping, and defect dynamics studies of ALD-grown Al/HfO2/Si nMOSCAPs

Abstract

The radiation response, long-term performance, and reliability of HfO2-based gate dielectric materials play a critical role in metal oxide semiconductor (MOS) technology for space device applications. Al/HfO2/Si atomic layer-deposited devices were irradiated by gamma and swift heavy ions. An increase in the leakage current and charge trapping has been observed as the gamma irradiation dose varied from 25 to 100 krad. The density of oxide traps is found to increase with an increase in the gamma dose while the interface trap density is found to decrease. Another set of samples were irradiated by 120 MeV Au ions to study the SHI-induced defect annealing/creation of defects and intermixing effects in HfO2/Si-based devices. The formation of an interfacial layer of HfSiO at a fluence of at 5 × 1013 cm−2 is revealed by X-ray reflectivity analysis. The densities of interface- and oxide-trapped charges are found to decrease up to a critical fluence of 1 × 1012 cm−2 and then increase with further increase in fluence to 5 × 1013 cm−2. The presence of the interlayer, due to the swift heavy ion-induced intermixing, has been confirmed by X-ray photoelectron spectroscopy measurements. Various current conduction mechanisms in both substrate and gate injection cases were used to understand the basic mechanisms of direct, Fowler–Nordheim, and Poole–Frenkel tunneling, as well as Schottky emission in these devices. These studies elucidated the radiation tolerance and charge-trapping behavior of Al/HfO2/Si nMOS capacitors.