Vibrational study of the SiO2/Si interface by high resolution electron energy loss spectroscopy

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Abstract
By using high resolution electron energy loss spectroscopy (HREELS) the surface phononspectra of SiO2(0001) and of thick amorphous SiO2 layers have been measured. The spectra recorded on the crystalline surface are characterized by three first order peaks at 498, 798, and 1176 cm− 1. The HREELS data could be interpreted by the dielectric theory applied to anisotropicmaterial, and the optical constants were compared to infrared spectroscopy values. HREELS spectra as a function of oxide thickness could be obtained from oxidized Si(100) wafers by sputter erosion. Peak positions shifted to lower frequencies and intensities decreased regularly with decreasing oxide thickness. At the interface a transition layer of about 25 Å was observed and carbon contamination was identified. The dielectric theory applied to a thin homogeneous supported film cannot account for the observed frequency shift.

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