Gas and surface phase chemistries of CF4 plasma were studied in an inductively coupled modified gaseous electronics conference reference cell, using in situ Fourier transform infrared spectroscopy enhanced by a multipass White cell and in situ spectroscopic ellipsometry. The self-bias dc voltage, densities of gaseous species, fluorocarbon film thickness on Si substrate, as well as etch rates of SiO2 and Si were measured during plasma processing as functions of the pressure, CF4 gas flow rate, rf source power, platen bias power, and source-platen gap. The gaseous molecules and radicals monitored included CF4, CF3, CF2, SiF4, and COF2, among which CF4 and SiF4 were found to be the two dominant species, combining for about 80% of the total concentration. The density ratio of SiF4 and COF2 was about 2:1 with no bias on the substrate and increased up to ∼ 8:1 when Si substrate etching took place. Specifically, as the Si etch rate increased, the COF2 density dropped, likely due to suppressed etching of the quartz source window, while the density of SiF4 increased. Comparisons between the gas phase data and etch rate results of Si and SiO2 indicate that the gas phase chemistry is strongly influenced by surface reactions on the substrate, wall, and quartz source window. The thickness of fluorocarbon reaction layer on Si substrate is mainly determined by densities of fluorocarbon radicals and fluorine atoms in the bulk plasma as well as the self-bias voltage on the substrate, and a thicker film is usually associated with a lower etch rate.