Stability of interfaces in Mo/Cu multilayered metallization

Mo/Cu multilayered metallizations with less than or equal to 10 Cu conducting layers of various thicknesses separated by Mo diffusion barriers 20 nm thick were deposited, by magnetron sputtering onto oxidized Si wafers. The samples were annealed for 1 h in the vacuum of 10(-3) Pa at temperatures between 400 degrees C and 800 degrees C and in a N-2 atmosphere at temperatures up to 700 degrees C. Rutherford backscattering spectroscopy, X-ray diffraction in both standard and grazing incidence configurations, scanning electron microscopy, electron diffraction spectroscopy and resistometry were employed to analyse the samples. Two mechanisms are assumed to be responsible for intermixing in immiscible Mo/Cu multilayers: grain boundary diffusion and the formation of Mo and Cu nitrides in nitrogen environment. In the nitrogen ambient the multilayer intermixed completely even at 500 degrees C, In vacuum the 20 nm thick Mo layer was found to be an effective barrier against Mo/Cu intermixing up to 600 degrees C/1 h annealing. Only a small increase (less than or equal to 20%) of the multilayer resistance was recorded in the samples annealed in vacuum. Cu-enriched hillocks appeared on the surfaces of samples annealed at greater than or equal to 500 degrees C.