COMPARISON BETWEEN DIRECT-CURRENT AND SINUSOIDAL CURRENT STRESSING OFGATE OXIDES AND OXIDE SILICON INTERFACES IN METAL-OXIDE-SILICON FIELD-EFFECT TRANSISTORS/

It was recently reported that plasma process-induced damage to metal-o xide-silicon field-effect transistors (MOSFETs) comprises a damage mec hanism that involves alternating-current (ac) stressing of the oxide a nd the oxide/silicon interface. The study reported herein is aimed at establishing signatures of MOSFET damage induced by ac stressing appli ed at conditions that emulate plasma processing environment. We apply sinusoidal ac voltage stress signals to 0.5 mu m n-channel or p-channe l MOSFETs with 90-Angstrom-thick gate oxides. We assess damage on MOSF ETs by measuring transconductance, threshold voltage, and subthreshold swing. We find that the onset of damage to devices subjected to ac st ressing occurs at voltage amplitudes as low as 4 V, whereas in dc stre ssing, applied for the same time, damage becomes significant only at d e voltages larger than 10 V. We also show that damage from ac stressin g attains a maximum at frequencies in the range 1-100 kHz and decrease s at frequencies above 5 MHz. It is proposed that carrier hopping is p rimarily responsible for oxide current and, hence, device damage obser ved following the ac stress. This hopping current is insignificant dur ing high-field de stress when Fowler-Nordheim tunneling becomes the do minant conduction mechanism. (C) 1997 American Institute of Physics.