Radiation-Induced Charge Trapping in Shallow Trench Isolations of FinFETs

We provide comprehensive experimental data and technology computer-aided design simulations to clarify total-ionizing-dose mechanisms in 16-nm Si FinFETs. In n-channel FinFETs irradiated to ultra-high doses the transconductance evolution rebounds (increase up to 3-10 Mrad followed by a decrease), while the drain-to-source leakage current steadily augments until reaching a plateau at very large doses. These effects result from positive charge trapping deep in the sidewalls of the shallow trench isolation (STI) and negative trapped-charge accumulation localized in the upper STI corners. Larger sizes of inter-fin STI enhance the leakage current degradation of transistors with smaller numbers of fins. Hydrogen-induced border-trap and/or interface-trap generation at the Si/oxide interface at the STI corners leads to increased low-frequency noise at doses > 10 Mrad(SiO ₂ ). These results show that the quality of oxides and interfaces in the upper region of the STI adjacent to the device channel is crucial for the tolerance to ultra-high radiation of modern FinFET technologies.