The OH(X2 Pi) radical in a 20:80 tetraethoxysilane (TEOS)/O-2 plasmas has been characterized during deposition of SiO2 using the imaging of radicals interacting with surfaces (IRIS) method, The reactivity of OH at the surface of a growing SiO2 film has been determined as a function of the applied radio-frequency (rf) plasma power (P) and the substrate temperature (T-S). The reactivity (R) of OH during deposition of SiO2 on a 300 K Si substrate is 0.4 +/- 0.04. R decreases as substrate temperature increases but is unaffected by Increasing rf power. Translational and rotational temperatures (Theta(T) and Theta(R), respectively) of the OH radical an also determined. For a 20:80 TEOS/O-2 plasma (P = 85 W), Theta(T) = 912 +/- 20 K and Theta(R) = 450 +/- 20 K. Theta(T) is significantly higher than Theta(R) and increases with increasing rf power. Using isotopically labeled O-18(2) as a precursor, the source of the oxygen in OH is identified as the O-2 gas, dot oxygen from the ethoxy groups on TEOS. With these data, the role of OH in deposition of SiO2 from TEOS-based plasmas and the effects of plasma deposition parameters on film formation are discussed.