It is proposed that the plasma enhanced chemical vapor deposited tungsten nitride (PECVD‐W–N) thin film is used as a diffusion barrier to prevent the interdiffusion between Al and Si during postannealing process. The atomic concentration of N in W–N film deposited with NH3/WF6partial pressure ratio of 0.5 is about 33 at. % and its resistivity is 90–110 μΩ cm. The Rutherford backscattering spectrometry, Auger electron depth profiles, x‐ray diffraction, and scanning electron micrographs show that 900 Å PECVD‐W67N33film interposed between Al and Si is more impermeable than PECVD‐W film due to N atoms and it also keeps its chemical integrity during the postfurnace annealing at 600 °C for 30 min in Ar ambient.