Investigation of low temperature SiO₂ plasma enhanced chemical vapor deposition

Low temperature (<270 °C) plasma enhanced chemical vapor deposition (PECVD) of SiO₂ thin films using tetraethylorthosilicate (TEOS) and O₂ plasma was investigated. Depositions were carried out in a PECVD reactor with a helical resonator discharge source. Transmission infrared spectroscopy, spectroscopic ellipsometry, and wet etch rate measurements were used to characterize the deposited films as a function of rf power, gas composition, and substrate temperature. Most pronounced effects were observed when the substrate temperature and TEOS:O₂ flow ratio R-fraktur sign were varied. Good quality SiO₂ films can be obtained at high temperature and/or low R-fraktur sign. For R-fraktur sign>0.1, while the deposition rate was weakly dependent on temperature between 260 and 100 °C, it increased almost by a factor of 2 between 100 and 45 °C. This is also accompanied by drastic changes in film properties such as refractive index, increase in OH and -OC₂H₅ content, and decrease in film density. Studies using in situ attenuated total reflection Fourier transform infrared (ATR FTIR) spectroscopy indicated that stable good quality SiO₂ films without any SiOH at higher temperature (250 °C) and with very little SiOH at room temperature could be deposited using very low R-fraktur sign. Based on the understanding provided by ATR FTIR, films with properties approaching to those of thermal oxide have been deposited at room temperature.