Infrared ellipsometric study on the initial stages of oxide growth on Si(001)

The initial stages of native oxide growth on an etched Si(001) surface have been studied by infrared (IR) spectroscopic ellipsometry. The mid-infrared ellipsometric spectra show characteristic vibrational bands of Si–H stretching vibrations between 2100 and 2200 cm−1, and bands of silicon oxide between 1000 and 1290 cm−1. The most intense band in the range of Si–H stretching vibrations is assigned to a vibration of SiH2 groups, while the most prominent bands from the oxide interface can be assigned to bands originating from different Si–O stretching vibrations. By monitoring these bands during degradation of the passivated surface in atmospheric conditions different steps of the oxide growth at the interface are identified. The frequencies of the Si–O bands differ from those in thicker films. It is concluded that at the very beginning the top Si atoms are oxidized by replacement of the hydrogen bonds allowing the subsequent oxidation of the back bonds.