Analysis of Total Ionizing Dose Effects Using Electron Holography

The ability to directly image charge accumulation in the irradiated oxide film of the metal-oxide-semiconductor capacitor is demonstrated using the electron holography technique. Capacitors with 100 nm thickness of oxide film are fabricated and irradiated using a ⁶⁰Co gamma source to a target total dose of 450 krad(SiO₂). Electric and materials analyses are performed before and after irradiation to study the total ionizing dose (TID) effect. The observed leftward shift in the capacitance-voltage (C-V) curve and a larger potential drop near the Si/SiO₂ interface mapped by electron holography indicate charge buildup at the irradiated oxide layer. Technology computer-aided design simulations are performed to analyze and validate the electrostatic potential data from holography, and also quantify the charge distributions across the oxide layer for both pre- and post-irradiated devices. A larger amount of positive volumetric charges is added near the oxide/silicon interface for the irradiated sample in order to fit both C-V measurement data and electron holography profiles. The good matching between the experimental and simulation results shows evidence that electron holography provides the ability to directly image the charge accumulation at the irradiated oxide layer due to TID effects.