No abstract

Interface defects generated by negative-bias temperature stress (NBTS) in an ultrathin plasma- nitrided SiON/Si(100) system were characterized by using D2 annealing, conductance-frequency measurements, and electron-spin resonance measurements. D2 annealing was shown to lower negative-bias temperature instability (NBTI) than H2 annealing. Interfacial Si dangling bonds (Pb1 and Pb0 centers), whose density is comparable to an increase in interface trap density, were detected in a NBTS-stressed sample. The NBTI of the plasma-nitrided SiON/Si system was thus shown to occur through Pb depassivation. Furthermore, the nitridation was shown to increase the Pb1/Pb0 density ratio and modify the Pb1 structure. Such a predominance and structural modification of Pb1 centers are presumed to increase NBTI by enhancing the Pb–H dissociation. Although we suggest that NBTS may also induce non-Pb defects, nitrogen dangling bonds do not seem to be included in them.

We investigated transition layers at the interface of the thin SiO2 film successively etched back by diluted HF, using infrared reflection-absorption spectroscopy. The etching rate of the oxide film reveals that there is a Si-rich transition layer within 0.6 nm of the interface. However, frequency shift in the longitudinal optical phonon due to Si-O-Si asymmetric stretching toward lower wave numbers takes place less than 1.5 nm from the interface. We propose a model in which the transition layer is assumed to be Si-rich suboxide layers caused by the compositional roughness of the SiO2/Si interface. Through estimating the phonon frequencies which depend on the composition of the suboxide structure in this model, we found that the phonon frequency apparently starts to shift at around 1.5 nm from the interface, even if there are suboxide-rich layers within 0.6 nm, which can be caused by 1–2 monolayers of roughness.

We investigated bonding configurations of nitrogen atoms in silicon oxynitride films, resulting in a 960 cm−1 absorption peak, which is a higher frequency than that for Si3N4 (840 cm−1). The 960 cm−1 peak was observed in the films for which an N 1s x-ray photoemission peak was observed with a binding energy of about 398.6 eV, which has been reported as a binding energy associated with the ≡Si–N–Si≡ structure. However, the 960 cm−1 peak was absent in the films for which the N 1s peak was observed at about 397.8 eV, being close to the binding energy associated with the Si3≡N structure. We conclude that the absorption peak at 960 cm−1 arises from the ≡Si–N–Si≡ structure of doubly bonded N atoms with two Si atoms, not affected by any oxygen atoms.

Employing hydrogen depth-profiling via 1H(15N,αγ)12C nuclear reaction analysis (NRA), the “native” H concentration in thin (19–41.5 nm) SiO2 films grown on Si(100) under “wet” oxidation conditions (H2+O2) was determined to be (1–2)×1019 cm−3. Upon ion-beam irradiation during NRA this hydrogen is redistributed within the oxide and accumulates in a ∼8-nm-wide region centered ∼4 nm in front of the SiO2/Si(100) interface. Annealing in H2 near 400 °C introduces hydrogen preferentially into the near-interfacial oxide region, where apparently large numbers of hydrogen trap sites are available. The amount of incorporated H exceeds the quantity necessary to H-passivate dangling Si bonds at the direct SiO2/Si(100) interface by more than one order of magnitude. The H uptake is strongly dependent on the H2-annealing temperature and is suppressed above 430 °C. This temperature marks the onset of hydrogen desorption from the near-interfacial oxide trap sites, contrasting the thermal stability of the native H, which prevails homogeneously distributed in the SiO2 films after oxidation at 900 °C. Hydrogen bound in the near-interface oxide region is not redistributed by the ion-beam irradiation, further emphasizing its different chemical interaction with the SiO2 network as opposed to the native oxide H. The mechanism of the irradiation-induced H redistribution and its possible relation to the degradation of electrically stressed electronic devices are discussed.