White X-Ray Radiation Effects in MOS Capacitors With Atomic Layer Deposited HfO2/Al2O3 and Al2O3/HfO2/Al2O3 Gate Dielectric Stacks for High Total Doses

Abstract

White x-ray radiation effects in metal-oxide- semiconductor (MOS) capacitors with HfO2/Al2O3 (H/A) two-layer and Al2O3/HfO2/Al2O3 (A/H/A) three-layer gate dielectric stacks are investigated at high total dose levels of approximately 10, 50, and 100 Mrad(Si), based on capacitance-voltage (C-V) and current-voltage (I-V) measurements before and after irradiations, and the annealing behaviors at ambient temperature of the irradiated MOS capacitors are also observed over a long time. The H/A and A/H/A stacks are grown by atomic layer deposition (ALD), and have the same physical and equivalent oxide thicknesses. The C-V results indicate that the H/A and A/H/A-stack capacitors have almost an identical radiation response up to 50 Mrad(Si), and hole trapping is the main damage mechanism for the stacks. An anomalous C-V rebound for the A/H/A-stack capacitor after 100 Mrad(Si) is attributed to the existence of the potential well in the A/H/A stack, considering the continuously increased C-V shift for the H/A-stack capacitor with doses. In addition, radiation-induced interface traps lead to a significant C-V stretch-out even after 10 Mrad(Si), and multi-photon absorption is proposed for the production of the interface traps due to white x-ray irradiation at a high dose rate. Meanwhile, the I-V results show that the leakage current of the tested capacitors is increased after irradiation, and the A/H/A-stack capacitor has a much smaller leakage current than the A/H-stack capacitor, both before and after irradiation, because of its stack structure advantage in suppressing the leakage current. The primary mechanism for the leakage current is analyzed using the Frenkel-Poole model.