Ultrathin amorphous Ni-Ti film as diffusion barrier for Cu interconnection

5-nm-thick amorphous Ni-Ti films deposited on Si by magnetron sputtering, annealed at various temperatures in high vacuum, have been studied as diffusion barriers for Cu interconnection using X-ray diffraction, atomic force microscopy and four-probe methods. Although no Cu silicide peaks are found from X-ray diffraction patterns of the samples annealed up to 750 °C, it is found that the sheet resistance of Cu/Ni-Ti/Si decreases with the increase of annealing temperature and then slightly increases when the annealing temperature is higher than 700 °C. Root mean square roughness of Cu/Ni-Ti/Si increases with the increase of annealing temperature and many island-like grains present on the surface of the 750 °C annealed sample, which is ascribed to dewetting and agglomeration.