Optical dispersion analysis within the IR range of thermally grown and TEOS deposited SiO2 films

SiO₂ thin films, with thickness ranging between approximately 13 and 95 nm, have been thermally grown at 950°C in dry oxygen and chemically vapor deposited at low pressures (0.3 Torr) by decomposition of tetraethylorthosilicate (TEOS) at 710°C, on Si (100) substrates. Dispersion analysis was performed on Fourier transform infrared (FTIR) transmission spectra of these films within the range 900–1400 cm⁻¹. It was found that the spectra were best described within this range, by four Lorentz oscillators located near 1060, 1089, 1165 and 1220 cm⁻¹ almost independent of film thickness. The polarization of the oscillators (proportional to their strength) was found to increase slightly, and their widths to decrease, with film thickness. From the study of the FTIR spectra obtained at room temperature, it was suggested that at this temperature, a considerable number of Si–O–Si angles in these SiO₂ films are distributed in a way expected at higher temperatures and that the distribution of the Si–O–Si angles depends on the thermal history of the film and the method of growth.