Formation of Cobalt-BTA Complexes and Their Removal from Various Surfaces Relevant to Cobalt Interconnect Applications

The use of benzotriazole (BTA) during Co film planarization leads to the undesirable formation of insoluble Co-BTA complexes, which can be observed as organic residues on various surfaces after polishing. Here, we investigated the formation of Co-BTA complexes at different pH values and their adsorption and removal from Co, TiN, SiN, and SiO 2 film surfaces relevant to Co interconnect applications. The stability constant, log K eq , of Co 2+ -BTA complex was determined from its spectroscopic properties and log K eq was found to lie between 2.7 and 3.9 in the pH range of 6 ∼ 12, much smaller than that of Co 3+ -ethylenediaminetetraacetic acid (EDTA) complexes (log K eq = 36.0). Using this data, and recognizing that potassium persulfate (K 2 S 2 O 8 ) and EDTA can lead to oxidation and ligand exchange of Co 2+ -BTA complexes, respectively, we were able to remove Co-BTA complexes adsorbed on all films by exposing them to aqueous solutions of 50 mM EDTA, 1.5 wt% K 2 S 2 O 8 , and 1 mM sodium dodecylbenzenesulfonate (SDBS) at pH 12. SDBS was helpful in lowering ΔE corr to about 10 mV for the Co/TiN couple as well as the corrosion currents of Co film.