A study of the effects of tunneling currents and reliability of sub-2 nm gate oxides on scaled n-MOSFETs

This work examined various components of direct gate tunneling currents and analyzed reliability of ultrathin gate oxides (1.4-2 nm) in scaled n-metal -oxide-semiconductor field effective transistor (MOSFETs). Direct gate tunn eling current components were studied both experimentally and theoretically . In addition to gate tunneling currents, oxide reliability was investigate d as well. Constant voltage stressing was applied to the gate oxides. The o xide breakdown behaviors were observed and their effects on device performa nce were studied. The ultrathin oxides in scaled n-MOSFETs used in this stu dy showed distinct breakdown behavior and strong location dependence. No "s oft" breakdown was seen for 1.5 nm oxide with small area, implying the impo rtance of using small and more realistic MOS devices for ultrathin oxide re liability study instead of using large area devices. Higher frequency of ox ide breakdowns in the source/drain extension to the gate overlap region was then observed in the channel region. Possible explanations to the observed breakdown behaviors were proposed based on the quantum mechanical effects and point-contact model for electron conduction in the oxide during the bre akdown. It was concluded that the source/drain extension to the gate overla p regions have strong effects on the device performance in terms of both ga te tunneling currents and oxide reliability. (C) 2001 Elsevier Science Ltd. All rights reserved.