Characteristics of DC Reactively Sputtered (Ti,Zr)N Thin Films as Diffusion Barriers for Cu Metallization

(Ti,Zr)N films were prepared by dc reactive magnetron sputtering from a Ti-5 atom % Zr alloy target in N2/Ar gas mixtures and then employed as diffusion barriers between Cu thin films and Si substrates. Material characteristics of the (Ti,Zr)N film were investigated by X-ray photoelectron spectroscopy and cross-sectional transmission electron microscopy (XTEM). The (Ti,Zr)N film microstructure was an assembly of very small columnar crystallites with a rock-salt (NaCl) structure. Metallurgical reactions of Cu/(Ti,Zr)N0.95/Si, Cu/(Ti,Zr)N0.76/Si, and Cu/TaN0.71/Si were studied by X-ray diffraction and sheet resistance measurements. The variation percentage of sheet resistance for all Cu/barrier/Si systems stayed at a constant value after annealing up to 500DGC for 30 min. However, the sheet resistance increased dramatically after annealing above 750DGC for Cu/(Ti,Zr)N0.95/Si, and 500DGC for both Cu/(Ti,Zr)N0.76/Si and Cu/TaN0.71/Si. For these samples, the interface deteriorated seriously and formation of Cu3Si was observed by XTEM. Our results suggest that the refractory binary metal nitride film, (Ti,Zr)N, can be used as a diffusion barrier for Cu metallization as compared to the well-known TaN film.