A comparative study of reactively‐ion‐sputtered (RIS) and low pressure chemical‐vapor‐deposited (LPCVD) TiN, and sputter‐deposited TaN thin films as diffusion barriers for Cu has been done using Auger electron spectroscopy, Rutherford backscattering spectrometry, x‐ray diffraction, scanning electron microscopy, and sheet resistance measurements. For the RIS TiN and sputtered TaN diffusion barriers, the integrity of the individual layers was preserved and there was no evidence of interdiffusion for samples annealed up to 500 °C in N2–H2ambient for 1 hour. The LPCVD TiN was stable up to 450 °C for 30 minutes only, after which Cu started to diffuse into the TiN layer. The reasons for the higher thermal stability of RIS TiN compared to LPCVD TiN can be deduced from the microstructural differences in the two films, as observed with x‐ray diffraction technique.