Low temperature (<270 degrees C) plasma enhanced chemical vapor deposition (PECVD) of SiO2 thin films using tetraethylorthosilicate (TEOS) and O-2 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:O-2 flow ratio R were varied. Good quality SiO2 films can be obtained at high temperature and/or low R. For R>0.1, while the deposition rate was weakly dependent on temperature between 260 and 100 degrees C, it increased almost by a factor of 2 between 100 and 45 degrees 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 degrees C) and with very little SiOH at room temperature could be deposited using very low R. Based on the understanding provided by ATR FTIR, films with properties approaching to these of thermal oxide have been deposited at room temperature.