The effects of post-thermal annealing in N2 and/or forming gas (FG) on the electrical characteristics and Fowler-Nordheim (FN) current stress resistance were investigated for Si oxynitride grown in helicon-wave excited O2–N2–Ar plasma. The X-ray photoelectron spectroscopic data indicated growth of the Si oxynitride. The capacitance-voltage characteristics were measured to evaluate the electrical qualities of the grown Si oxynitride. The minimum interface state density D it,min had the smallest value when the Si oxynitride sample was post-thermally annealed in FG (3% H2) at 300°C followed by annealing in N2 at 700°C. However, D it,min was approximately 3.5 ×1011 eV-1cm-2, still higher than that for thermal Si oxide. The shift of the threshold voltage (V th) after the stressing (±10 V, 100 min) was also the smallest for the Si oxynitride sample continuously annealed in FG (3% H2) and N2. The FG annealing does not necessarily improve the electrical characteristics and FN stress resistance. The N2 annealing after FG annealing is required to improve the electrical properties and FN reliability, in contrast with the case of Si oxide.

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The effects of the gas-flow-rate ratio on the electrical characteristics and the Fowler-Nordheim (FN) current stress resistance were investigated for Si oxynitride grown with helicon-wave excited (HWP) N2–Ar plasma. The flow-rate ratio of N2 [N2/(N2+Ar)] was varied from 100% (N2 only) to 60%. The X-ray photoelectron spectroscopic data (XPS) indicated that uniform Si oxynitride (probably Si2N2O) was formed through the entire film thickness when the N2 gas-flow-rate ratio was 100% (N2 only), though a small amount of Si suboxide was included. The capacitance–voltage (C–V) measurements revealed that the interface-state density was the lowest in this flow-rate ratio case, as the grown layer was postannealed at moderate temperatures (300–500°C). Fowler-Nordheim current injection was performed using the metal/Si-oxynitride/Si capacitors thus fabricated. The shift of the threshold voltage was the lowest for the sample grown without Ar mixing. It was smaller than that for the thermal Si oxide (SiO2) grown at 900°C. The results of FN current stress resistance experiments were explained in terms of the surface plasmon and avalanche breakdown models.