Co-evaporated Cu-Ti films on thermally-oxidized Si substrates were annealed in vacuum at temperatures between 300 and 700°C. Reactions within the films and between film and substrate were monitored by Rutherford backscattering spectrometry, X-ray diffraction, transmission electron microscopy and sheet resistance. We found that, despite the competition from intermetallic compound formation, the Cu-Ti films react with SiO2 beginning at 400°C, with Ti migrating to the SiO2 interface to form both a suicide, Ti5Si3, and an oxide and to the free surface to form additional oxide. The reaction leaves relatively pristine Cu. Above 600°C, however, Cu begins to react with the underlying suicide. By comparison, pure Ti reacts with SiO2 only above ∼700°C.