A study of intermetallic compound formation at the interface between copper thin film and silicon substrate is presented in this work. Two systems; Cu/Si and Cu-(5at%) Nb/Si, were studied. From the intermetallics formed at the interfaces of two systems; as a model, formation mechanisms of Cu0.83Si0.17 with and without niobium impurity were examined. Variations in values of parabolic rate constants and activation energies with Nb impurity content were determined. The samples were annealed at different temperatures and time intervals after vacuum deposition of the films. X-Ray, Scanning Electron Microscopy (SEM), and Energy Dispersive Spectroscopy (EDS) analysis showed the sequential formation of several intermetallic phases at the interfaces. Using this data, a model had been given about the formation of the observed intermetallic phases.