Stabilization of Alumina Slurry for Chemical−Mechanical Polishing of Copper

Abstract

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. ζ 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 ζ 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 betw...