Wear‐out and breakdown of thermally grown Ta 2 O 5 insulating films on plasma oxynitrided Si substrates

Wear‐out 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 × 10 –3 cm 2 ), 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/cm 2 ). The observed optimum was attributed to a defect free relaxed interfacial structure containing approximately 1 × 10 14 cm –2 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. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)