Growth, Thermal Stability and Cu Diffusivity of Reactively Sputtered NbN Thin Films as Diffusion Barriers between Cu and Si

NbNx films were prepared by RF reactive magnetron sputtering from a Nb target in N2/ Ar gas mixtures and then used as diffusion barriers between Cu and Si substrates. Material characteristics of the NbNx, films were investigated and were correlated with the N2/Ar flow ratio. The variations in film resistivity is correlated with the change of phases and chemical compositions from α-Nb, β-Nb2N, γ-Nb4N3, δ-NbN + δ′-NbN as the N2/Ar ratio is increased. The thermal stability of Cu (60 nm)/NbNx (25 nm)/Si multilayers were investigated and our results indicated that the barrier performances were significantly affected by the chemical composition of NbNx films. The diffusion coefficient of Cu in NbNx was measured by four-point probe analysis after annealing Cu/NbNx/Si multilayered samples in the temperature range of 600-850°C. Cu diffusion in NbNx had components from the grain boundaries and the lattice. In addition, our results suggest that the NbNx can be used as a potential diffusion barrier for Cu metallization as compared to the conventional TaN.