Effect of zero bias Gamma ray irradiation on HfO₂ thin films

Hafnium dioxide was proposed by the researchers as one of the dielectric materials that could be used as dielectric layer in the fabrication of capacitor in MOS-based devices and capacitive RF MEMS switches. In the current work, HfO₂ dielectric layer has been fabricated using ALD technique and the fabricated layers have been investigated under Co-60 gamma irradiation doses up to 1500 krad (SiO₂). Crystal structures and the phase of the HfO₂ thin films were studied before and after irradiation using GI-X-ray diffraction, elemental composition was investigated by energy-dispersive X-ray spectroscopy. Capacitance–Voltage (C–V) and Conductance–Voltage (G–V) measurements were measured before and after irradiation at 1 MHz AC frequency. The density of the interface states (D_it) was calculated from measured C–V and G–V characteristics. Dependency of flat band voltage on irradiated dose was obtained from the C–V measurements. Slight decrease in series resistance (R_S) was observed with increase in irradiation dose, which is crucial for the conductance of the device characteristics. D_it features improved for higher irradiation doses but still in the order of 10¹¹ eV/cm². Calculated values of D_it were not found to be high enough for Fermi level pinning and so it’s not corrupting the device operation over the given dose range. The effect of irradiation on HfO₂ thin films and MOS system were determined from analysis of measured XRD spectra, C–V and G–V curves.