The chemical properties of titanium nitride-carbide (TiNC) and titanium nitride (TiN) films deposited on silicon are investigated comparatively, showing that the surface reactivity of nitridebased films can be modified precisely and reversibly by controlling the surface elemental composition. These materials are used as diffusion barrier films, and therefore understanding their surface chemistry is key for controlling further deposition steps during interconnect metallization. Chemical vapor deposition (CVD) using Ti[N(CH3)2]4 leads to the formation of TiNC, and nitridation of this film through postannealing under NH3 decreases significantly the carbon content on the surface, leaving essentially a TiN surface, as characterized through the use of spectroscopic, depth-profiling, and microscopic techniques. As determined by the temperature-programmed desorption (TPD) studies of ethylene (carbidization reagent) and dimethylamine (decomposition product of the deposition precursor), the TiN surface is more reactive toward these compounds than the original TiNC film. The role of carbon as a surface reactivitymodifier is explained by its ability to decrease the acidity of Ti surface atoms.Moreover, the test reaction of ethylene on the TiN surface is accompanied by a decomposition process that progressively incorporates carbon onto the surface, reducing the surface reactivity to the point where it resembles that of the starting TiNC film. The ability to control the reactivity of a deposited film offers unique opportunities in designing chemical modification schemes for a successful deposition onto these barrier films. © 2009 American Chemical Society.