Abstract
Wearβout and breakdown at constant current stress (J = 10 mA/cm^2^) were studied for Ta~2~O~5~ insulating layers (30 nm thick) thermally grown over plasma oxynitrided (5 to 15 s at room temperature) Si substrates. For injected charges Q~inj~ lower than 100 C/cm^2^ hard breakdown occurs, while for Q~inj~ higher than 100 C/cm^2^ 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/cm^2^ on a capacitors with an area of 2.5 Γ 10^β3^ cm^2^), the equivalent thickness (8.24 nm) and the wearβout (variation of the gate voltage smaller than 50 mV, during the stress up to 100 C/cm^2^). The observed optimum was attributed to a defect free relaxed interfacial structure containing approximately 1 Γ 10^14^ cm^β2^ nitrogen atoms in the first atomic monolayer adjacent to the Si substrate, as one with a significant improvement of the SiO~x~N~y~ interfacial layer relative permittivity (5.5) without considerable reduction of the tunneling barrier heights. (Β© 2006 WILEYβVCH Verlag GmbH & Co. KGaA, Weinheim)