The major sources of impurities in sputtered Al alloy films for interconnects prepared by physical vapor deposition (PVD) include those originating from the target material, residual gases present in the vacuum system, and those introduced through the gas delivery system. In this study, we report the effect of impurities incorporated from residual gases present in vacuum systems on the properties of Al-Cu interconnects, in particular, electromigration performance of 0.6-mu m-wide Al-1% Cu Lines. Controlled leaks of isotope gases H2O18, N-2(15), O-2(18), and (CH4)-H-13, in the 10(-6)-10(-9) Ton range, were introduced into a PVD tool during the sputtering process. Using these isotope gases, the impurities originating from residual gases were distinguished from those originating from other sources of impurities. The sputtering target was found to be the major source of H and O impurities in the film, whereas N atoms are introduced in the film mainly through the gas phase. The microstructural properties of blanket Al-Cu films deposited with intentionally introduced residual gas phase contaminants were also investigated using transmission electron microscopy, x-ray diffraction, and secondary ion mass spectroscopy. Controlled leaks of N-2 during the sputtering process were found to affect the distribution of Cu in the blanket AI-Cu films as;well as the electromigration behavior of the patterned structures to a larger extent than O-2, CH4, and H2O. On the other hand, upon controlled exposures of the above mentioned residual gases to blanket Al-Cu films, N-2 was found to have the lowest sticking coefficient to a clean AI-Cu surface.