The effect of various processing conditions on the extent of adsorption of organics and incorporation of carbon in Si/SiO2 during thermal oxidation is investigated. The key parameters studied are preoxidation cleaning, temperature-ramp rate and ambient, gas-phase impurity concentration, and the presence of moisture. A novel method based on the catalytic oxidation of organics is developed to monitor and characterize the outgassing of organics. Results show that SC1-last surfaces adsorb more polar organics than do HF-last surfaces; this results in a higher amount of carbon incorporation. HF-last surfaces, however, retain a larger fraction of the adsorbed organics. Addition of oxygen to the temperature-ramp ambient reduces the extent of carbon incorporation. The kinetics and mechanisms of carbon incorporation in Si/SiO2 substrates are investigated. A reaction model based on the competitive processes of desorption, readsorption, decomposition, oxidation, and chemisorption of the adsorbed organics is developed. This model provides a better understanding of one of the key aspects of defect formation in silicon-based dielectric thin films.