Ammonium Persulfate and Potassium Oleate Containing Silica Dispersions for Chemical Mechanical Polishing for Cobalt Interconnect Applications

We investigated the suitability of ammonium persulfate (APS) and potassium oleate (PO) containing silica dispersions for polishing Co interconnects based on removal and dissolution rates, corrosion, post-polish surface quality, and post-polish particle contamination. A slurry consisting of 3 wt% silica, 1 wt% APS and 0.2 mM PO produced a removal rate of ∼465 nm/min at pH 9, along with removal rate selectivity of >100:1 between Co and TiN. The same composition but without abrasives reduced the ΔEcorr between Co and TiN to ∼7 mV and Igc to ∼0.04 μAcm−2, indicating minimal galvanic corrosion. Addition of PO led to no measurable dissolution of the Co films. Surface analysis showed very good post-polish surface quality and minimal contamination with silica particles. These and results obtained with similar H2O2 containing slurries suggest that the APS and PO-based silica slurry is more suitable for the Co bulk CMP process. The roles of persulfates ions, pH, and PO on the removal process and passivation behavior of Co are discussed and a removal mechanism is proposed.