Metal–oxide nitride–oxide–Si (MONOS) structure was fabricated using the oxidation-nitridation series with helicon-wave O2–Ar and N2–Ar plasmas, respectively. The detrimental effect of Ar ion etching was minimized during the fabrication process by controlling the plasma–sheath width. The top oxide was very thin (∼1–2 nm) as compared with nitride (∼12–13 nm) and bottom oxide (∼7–8 nm). Fowler–Nordheim tunneling electron injection was performed in this MONOS diode for both dc and pulsed stress voltages with the electrical polarity being changed. For the positive stress voltage, the shift of the threshold voltage Vth was negative and larger for the smaller stress voltage. It was higher for the pulsed stress than for the dc one. On the other hand, Vth shift is positive and smaller for the pulsed stress than for the dc one for the negative stress bias. These findings can almost be explained by the avalanche breakdown model together with the effect of the total amount of the injected carries. Terman analysis indicated that the interface state density did not increase after both positive and negative stresses, which was probably due to film structure and the presence of a small amount of Si oxynitride (or Si–N–O bonds) at the insulator/Si interface. Write/erase characteristics were also briefly discussed.
Si was oxynitrized (and/or nitrized) in both helicon-wave-excited and inductively-coupled N2 or N2+Ar mixed plasma. Fairly good capacitance-voltage (C–V) characteristics were obtained after post-thermal annealing at 400°–500°C for 30 min in nitrogen ambient. X-ray photoelectron spectroscopic (XPS) measurements showed that chemically stoichiometric Si oxynitride, Si2 N2 O, was uniformly formed throughout the whole film thickness at a flow-rate ratio of N2 of 80% in a N2 + Ar mixed plasma (N2:Ar = 8:2). On the other hand, SiO2 was formed at the outer surface while Si2 N2O was formed in the middle portion of the film and near the interface between the grown film and Si, when the flow-rate ratio of N2 was less than about 80%. The growth rate and the degree of “nitridation" were maximum at flow-rate ratio of N2 of 80%. The leakage current in the film was found to be mainly the Fowler-Nordheim-type tunneling current.
Pulsed Fowler–Nordheim (FN) current stress resistance was investigated for the Si oxynitride grown in the helicon-wave excited N2–Ar plasma. The shift of the gate threshold voltage Vth increased with an increase in the pulse frequency for both polarities of the applied stress voltage. At low frequencies (<1 kHz), the Vth shift was larger for the negative gate-voltage stress than for the positive one. However, as the frequency exceeds about 1 kHz, the Vth shift become much higher for the positive stress than for the negative one. The Vth shift was smaller as the pulse duty ratio was larger. These findings could be explained with the surface–plasmon and avalanche breakdown models combined with the effect of the total amount of the injected carriers to the oxynitride from the Si substrate or the gate electrode. The effect of Ar ion etching during plasma processing on the FN stress resistance was also investigated. The Ar ion etching effect was found to be substantially reduced as the plasma-sheath width was large and Si oxynitride samples were grown under this condition. The mean time to failure was highly improved by the Si oxynitride samples grown under the condition of reduced Ar ion etching effect.
Si was oxynitrided with helicon-wave excited \Nii and Ar mixed plasma. The flow-rate ratio (\Nii :Ar) was kept constant (8:2). Oxynitridations were performed in two growth geometries in which plasma was either concentrated on the substrate or diverged from the substrate using permanent magnets. In the case of plasma concentration, relatively uniform Si oxynitride (probably \Sii \Nii O) was formed throughout the entire depth of the film. In the case of plasma divergence, however, only Si oxide was grown. Therefore, the presence of nitrogen ions is concluded to be essential for oxynitridation of Si.
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