Attenuated Total Reflection Spectra of Nitrided SiO2/Si Structures

The behavior of nitrogen in silicon dioxide films on single-crystal silicon substrates was studied by attenuated total reflection (ATR) and time-of-flight secondary ion mass spectrometry. Nitrogen was introduced into a dielectric formed by pyrogenic oxidation at 850°C in an atmosphere of wet oxygen by implantation of N+ ions of energy 40 keV at doses of 2.5·1014 and 1.0·1015 cm–2 followed by rapid thermal annealing at 1000 or 1050°C for 15 s in air. Some of the samples were nitrided during thermal annealing in an N2 atmosphere with the addition of a small amount of O2 at 1200°C for 120 min. It was established that the majority of N atoms diff used during the heat treatments to the SiO2/Si interface and accumulated near the boundary region of the oxide. ATR spectra showed an absorption band with maxima at ~2320 and 2360 cm–1 that was probably due to vibrations of double cumulative bonds of the O=Si=N– type. These bonds formed through the interaction of N with dangling bonds at the Si-dielectric interface, as a result of which uncompensated or strained bonds were replaced by more stable ones. The resulting stronger chemical bonds prevented charge accumulation on the surface of the SiO2/Si interface.