Thermodynamic study, compositional and electrical characterization of LPCVD SiO2 films grown from TEOS/N2O mixtures

The theoretical phase diagram describing the growth of SiO₂ films from TEOS and N₂O mixtures within the temperature range 500–1100°C and pressure 0.3 Torr has been obtained, minimizing the total Gibbs energy of the chemical system involved in the deposition. It was found that at temperatures up to 900°C and N₂O/TEOS molar ratios up to approximately 7, the SiO₂ films deposited contained carbon impurities. For higher N₂O/TEOS molar ratios the obtained films are carbon free. SiO₂ films were grown from TEOS/N₂O mixtures in a conventional horizontal low pressure chemical vapor deposition reactor at temperatures of 710°C and 820°C and at a pressure of 0.3 Torr. These films were analyzed using X-ray photoelectron spectroscopy, Rutherford backscattering spectroscopy, atomic force microscopy and C–V measurements taken on metal–insulator–semiconductor structures formed with the deposited films as insulators. It was found that the films contain carbon impurities the concentration of which decreases with the increase of N₂O/TEOS molar ratio, in agreement with the results of the thermodynamic study. Carbon atoms were 90% bonded to other carbon atoms and only 10% to oxygen. It was found that the films are substoichiometric in oxygen with O/Si atomic ratios ranging between 1.95 and 1.80. The films were found to be positively charged, the charge increasing with N₂O flow and decreasing with deposition temperature.