The chemical and structural changes occurring in aluminum alloy/titanium layered metallizations and their implications are discussed. Characterization of Ti/Al–Cu/Si films was performed by secondary ion mass spectrometry (SIMS), Rutherford backscattering spectrometry, and transmission electron microscopy. Silicon and/or copper additions to aluminum produce a retarded reaction rate between aluminum and titanium upon annealing. SIMS measurements of annealed films show titanium diffusion throughout the entire aluminum film. In the absence of either silicon or copper, the titanium content is homogeneous at a level of ∼6×1018 atoms/cm3. Addition of silicon does not prevent titanium diffusion, but reduces the Ti concentration in the bulk of the film while producing a higher concentration in the near-surface region. Copper additions produce a similar, but much less dramatic effect.