Reduction of channel hot-electron-generated substrate current in sub-150-nm channel length Si MOSFET's

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Abstract
Channel hot-electron-generated substrate currents were measured in MOSFET devices with channel lengths down to 0.09 mu m, and a family of characteristic plots of substrate current, normalized to drain current, I/sub SUB//I/sub D/, rather than (V/sub DS/-V/sub DSAT/)/sup -1/ was obtained. For channel lengths greater than 0.5 mu m, the characteristics are independent of channel length. For channel lengths in the range of 0.15 mu m, the characteristics are independent of channel length. For channel lengths in the range of 0.15 mu m, the normalized substrate current at constant V/sub DS/ increases with decreasing channel length. However, as the channel length is decreased below 0.15 mu m, a decrease of the normalized substrate current is observed. The decrease is larger at 77 K than at 300 K. This decrease accompanies the onset of electron velocity overshoot over a large portion of the channel. It is suggested that the decrease is due either to a decrease of carrier energy because energy relaxation and transit times become comparable, to a relative decrease of the carrier population in the channel, or to both.