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 degrees C in dry oxygen and chemically va por deposited at low pressures (0.3 Torr) by decomposition of tetraethylort hosilicate (TEOS) at 710 degrees C, on Si (100) substrates. Dispersion anal ysis was performed on Fourier transform infrared (FTIR) transmission spectr a of these films within the range 900-1400 cm(-1). It was found that the sp ectra were best described within this range, by four Lorentz oscillators lo cated near 1060, 1089, 1165 and 1220 cm(-1) almost independent of film thic kness. The polarization of the oscillators (proportional to their strength) was found to increase slightly, and their widths to decrease, with film th ickness. From the study of the FTIR spectra obtained at room temperature, i t 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 temp eratures and that the distribution of the Si-O-Si angles depends on the the rmal history of the film and the method of growth. (C) 1999 Elsevier Scienc e Ltd. All rights reserved.