Threshold-voltage instability in MOSFET's due to channel hot-hole emission

Abstract

Hydrogen introduced and trapped in the gate oxide of MOSFET's by the silicon-nitride capping process can be activated by emitted holes from the MOSFET channel to produce a large threshold-voltage shift. This effect requires avalanche multiplication in the channel for the production of holes when a dc voltage is applied to the gate. For the pulsed-gate case, the magnitude of the threshold-voltage shift depends significantly on the gate-pulse fall time, cycle time, and duty cycle. In both cases the electric field normal to the Si/SiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> interface near the drain aids the emission of holes across that interface. A semiquantitative model is proposed which says that holes can recombine at H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> molecules and release sufficient energy to cause dissociation. The atomic hydrogen created can participate in electrochemical reactions at the gate oxide/channel interface which create nonuniform distributions of trapped charge and interface states along the channel. Model calculations of the time, temperature, and voltage dependences of this threshold instability agree well with measured results.