Cu passivation: A method of inhibiting copper-polyamic acid interactions

The use of passivation metals to protect Cu from interacting with polyamic acid precursor has been investigated by means of cross-sectional transmission electron microscopy, Rutherford backscattering spectroscopy, and resistivity measurements. Palladium or platinum, each 100 nm in thickness, was electron-beam evaporated onto Cu surface. Although not a good diffusion barrier against Cu outdiffusion, these metals can still effectively inhibit the Cu-polyamic acid interactions and, consequently, prevent the formation of Cu oxide precipitates in the polymer film. The trade-off is that, since Pd and Pt both diffuse into Cu and form solid solution alloys, the resistivity of Cu is raised significantly due to the enhanced electron-impurity scattering. In contrast, Cr serves both as a passivation metal and a good diffusion barrier without raising Cu resistivity. This is probably due to the lack of mutual solubility between Cr and Cu.