Stabilization of alumina slurry for chemical-mechanical polishing of copper

Stabilization of alumina slurries containing Fe(NO3)(3) and benzotriazole (BTA) for chemical-mechanical polishing (CMP) of copper in acidic media was investigated. Slurry stability was evaluated from the initial settling rate of alumina particles in well-dispersed slurries. zeta. potential and FTIR spectroscopy were employed to elucidate the observed effects. Fe3+, used as an etchant for copper, did not affect the slurry stability significantly, especially at low concentrations (<0.05 M). However, BTA worsened the stability, especially at higher concentrations, by reducing the electrostatic repulsion between alumina particles. This was confirmed by a drop in the measured zeta potential. FTIR spectra showed that BTA is chemisorbed onto alumina particle surfaces. Finally, the addition of poly(ethylene glycol) (MW = 1 000 000) improved the slurry stability significantly and a stable alumina slurry for the CMP of copper was obtained. Preliminary data on the removal rates of copper and the selectivities of removal between SiO2 and Cu using these slurries are reported.