We report a multi-element, multi-edge and multi-detection mode X-ray photoabsorption study of a series of Al/TiNx/Si(100) thin films as a function of the TiNx film thickness (100Å-500Å) and of the annealing temperature (400°C-600°C). The Si K- and L-edge results show that Si does not diffuse to the surface for all the films. The high resolution Ti L-edge and N K-edge spectra show that the TiNx layer undergoes a dramatic chemical reaction with the gradual increase in the annealing temperature. This chemical reaction stabilizes at 560°C at which the TiNx film is known to fail to act as an effective diffusion barrier between Al and Si.