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Oxynitrides can suppress the diffusion of boron from the polycrystalline silicon gate electrode to the channel region of an ultralarge scale integrated device, and are therefore important potential substrates for thin SiO2 gates. Direct oxynitridation of Si in N2O is a simple and manufacturable N incorporation scheme. We have used rapid thermal oxidation to grow O2- and N2O-oxides of technological importance (∼10 nm thick) in the temperature range 800–1200 °C. Accurate measurements of the N content of the N2O-oxides were made using nuclear reaction analysis. N content increases linearly with oxidation temperature, but is in general small. A 1000 °C N2O-oxide contains about 7×1014 N/cm2, or the equivalent of about one monolayer of N on Si (100). Nonetheless, this small amount of N can retard boron penetration through the dielectric by two orders of magnitude as compared to O2-oxides. The N is contained in a Si-O-N phase within about 1.5 nm of the Si/SiO2 interface, and can be pushed away from the interface by O2-reoxidation. We have measured Si/SiO2 interfacial roughness by x-ray reflectometry, and found that it decreases with increasing oxidation temperature for both O2- and N2O-oxides, although the N2O-oxides are smoother. The enhanced smoothness of N2O-oxides is greater the greater the N content. N2O-oxides are promising candidates for thin ultralarge scale integrated circuit gate dielectrics.

Thermally grown Si(001)/SiO2 samples were studied by x-ray reflectivity. Fits of model electron density profiles to the data reveal the existence of an interfacial layer at the Si/SiO2 interface up to 15-Å-thick, with density higher than either the crystalline Si or the main oxide layer. This density of the layer is reduced by a postoxidation anneal.

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We have examined fluctuations in the tunneling current of 3.5 nm SiO2 barriers for voltages in the direct tunneling regime. We find a 1/f power law for the spectral density of the fluctuations where f is the frequency. This 1/f noise can be attributed to fluctuations of a trap assisted tunneling current through the oxide that causes current noise but is not evident in the I–V curves. We suggest that this noise may be a more sensitive probe of trap assisted tunneling and degradation in thin oxides than other measures. At voltages above a threshold of 2.5 V, we observe the reversible onset of non-Gaussian current transients in the noise. The onset of these current transients can be related to a transition in the spacial uniformity of the tunneling current density that may result in eventual breakdown of the oxide.

The growth temperature dependence of the thin thermally oxidized Si(001)/SiO2 interface width was studied using synchrotron x-ray diffraction. Nine samples with oxide thickness of about 100 Å were studied, with growth temperatures ranging from 800 to 1200 °C. The oxides were prepared by rapid thermal oxidation. We found that interfacial roughness decreases linearly with increasing growth temperature, with a measured interface width of 2.84 Å for the sample grown at 800 °C, and 1.76 Å when grown at 1200 °C.