Deposition of copper films on silicon substrates: Film purity and silicide formation

Deposition of copper films on silicon substrates by the radio-frequency plasma reduction of spin-coated copper formate films in hydrogen and oxygen plasma discharges has been investigated further. The atomic compositions of these films, determined by Auger electron and x-ray photoelectron spectroscopy, were found to be a strong function of the processing conditions, especially power density and temperature. Rutherford backscattering studies (RBS) of the silicon–copper interface revealed the formation of copper silicide at deposition temperatures that are nominally as low as 40 °C. The silicide formation was further investigated by depositing pure copper films on silicon substrates by thermal evaporation. The Cu/Si interface was analyzed before and after in situ annealing at 300 °C and 10−8 Torr and compared with the results for the plasma deposited films. RBS data show that diamondlike carbon films are excellent diffusion barriers between Si and Cu.