Wear‐out and breakdown of thermally grown Ta2O5 insulating films on plasma oxynitrided Si substrates

Abstract

AbstractWear‐out and breakdown at constant current stress (J = 10 mA/cm2) were studied for Ta2O5 insulating layers (30 nm thick) thermally grown over plasma oxynitrided (5 to 15 s at room temperature) Si substrates. For injected charges Qinj lower than 100 C/cm2 hard breakdown occurs, while for Qinj higher than 100 C/cm2 it appears that only progressive breakdowns are possible. An optimum of the dielectric properties was found for oxynitridation times as long as 10 s, simultaneously for the hard breakdown charge (33 C/cm2 on a capacitors with an area of 2.5 × 10–3 cm2), the equivalent thickness (8.24 nm) and the wear‐out (variation of the gate voltage smaller than 50 mV, during the stress up to 100 C/cm2). The observed optimum was attributed to a defect free relaxed interfacial structure containing approximately 1 × 1014 cm–2 nitrogen atoms in the first atomic monolayer adjacent to the Si substrate, as one with a significant improvement of the SiOxNy interfacial layer relative permittivity (5.5) without considerable reduction of the tunneling barrier heights. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)