Tungsten-carbon thin films have been reactively sputter deposited in various Ar-CH4 gas mixtures and the growth kinetics of the reactive deposition process have been elucidated. The films are amorphous as-deposited with partial crystallization of W2C and WC occurring following a 1100 degreesC-1 min rapid thermal anneal. Carbon incorporation within the W-C films is attributed to the flux of CH3 radicals impinging on the growth surface. Although they have a significantly lower concentration (similar to0.1%) than the CH4 molecules contained within the plasma, their sticking coefficient is significantly larger than that of CH4. In addition, the change in the incorporation rate of carbon in the W-C films at higher CH4 (and subsequently CH3) concentrations has been shown to be due to the changes in the growth surface; as the CH3 flux increases, the growth surface becomes carbon terminated and decreases the incorporation of carbon because of the low CH3-C sticking coefficient.