Characteristics of reactively sputtered niobium nitride thin films as diffusion barriers for Cu metallization

NbN films were prepared by radio frequency reactive magnetron sputtering and then employed as diffusion barriers between Cu and Si. The microstructure of the NbN films was an assembly of very small columnar crystallites with a cubic structure. To investigate the properties as diffusion barriers, we performed metallurgical reactions of Cu/NbN 0.8 /Si, Cu/Nb/Si and Cu/TaN 0.7 /Si for comparisons. The sheet resistance increased dramatically after annealing above 750°C for Cu/NbN 0.80 /Si, and above 500°C for both Cu/Nb/Si and Cu/TaN 0.7 /Si. The interfaces were deteriorated seriously and formation of Cu 3 Si was observed when the sheet resistance was significantly increased. The diffusion coefficient of Cu in NbN barrier films was estimated by using the change of resistance (Δ R s / R s %). Compared with TaN 0.7 , NbN 0.8 films possess larger grain size and lower Cu diffusion coefficient. Our results suggest that the NbN film can be used as a diffusion barrier for Cu metallization as compared to the well-known TaN film.