Oxygen to silicon ratio determination of SiOxHy thin films

The oxygen to silicon ratio of several SiOxHy thin films deposited by the electron cyclotron resonance plasma method was studied by several methods (heavy ion elastic recoil detection analysis, energy dispersive X-ray spectroscopy, Auger spectroscopy and infrared spectroscopy). Among these methods, other groups found that x scales linearly with the wavenumber of the Si-O-Si stretching vibration (vst) by the relation x = 0.020vst − 19.3. This equation has been used by many different groups to determine x of SiOx thin films, but we have found that in our ECR deposited films the above mentioned formula gives accurate results for x values higher than 1.5, but for Si richer films the formula overestimates the x value, with values well outside the 20% accuracy range. A possible explanation of this discrepancy may be the bonded hydrogen of the films: in the plasma deposited samples used in this study the hydrogen content was high, above 20 at.% for silicon-rich samples. As a consequence, the Si-O-Si groups were immersed in a more electronegative matrix than in the usual case (SiOx with a low hydrogen concentration) and thus the variation of the position of the stretching peak was less pronounced.