Sputtered copper films with insoluble Mo for Cu metallization: A thermal annealing study

The thermal annealing behavior of Cu films containing insoluble 2.0 at.% Mo magnetron co-sputtered on Si substrates is discussed in the present study. The Cu-Mo films were vacuum annealed at temperatures ranging from 200 degreesC to 800 degreesC. X-ray diffraction (XRD) and scanning electron microscopy (SEM) observations have shown that Cu4Si was formed at 530 degreesC, whereas pure Cu film exhibited Cu4Si growth at 400 degreesC. Twins are observed in focused ion beam (FIB) images of as-deposited and 400 degreesC annealed, pure Cu film, and these twins result from the intrinsically low stacking-fault energy. Twins appearing in pure Cu film may offer an extra diffusion channel during annealing for copper silicide formation. In Cu-Mo films, the shallow diffusion profiles for Cu into Si were observed through secondary ion mass spectroscopy (SIMS) analysis. Higher activation energy obtained through differential scanning calorimetry (DSC) analysis for the formation of copper silicide further confirms the beneficial effect of Mo on the thermal stability of Cu film.