LOW-TEMPERATURE PASSIVATION OF COPPER BY DOPING WITH AL OR MG

The doping of copper with Al and Mg is discussed as a method of passivating the exposed surface of copper films proposed for use as a conductor in microelectronics. Doping by co-deposition and by diffusion from Cu/M/SiO2 bilayers, where M = Al or Mg, is discussed. Annealing such doped films in an ambient containing small amounts of oxygen produces a thin surface barrier layer of dopant oxide which stops further oxidation. In good cases, the conductivity of these films approaches that of films of pure sputtered copper. Such doping also improves adhesion to SiO2 and stability on SiO2. Improvements in stability include both decreased roughening due to grain growth and decreased diffusion transport into SiO2.