A colloidal silica-based slurry with H 2 O 2 (1 wt%) as the oxidizer and arginine (0.5 wt%) as the complexing agent was found to polish cobalt (Co) with superior performance (better post-polish surface quality and no pit formation) at pH 10 compared to pH 6 and 8. At pH 10, there is no measurable dissolution of Co and an open circuit potential (E oc ) difference of ∼20 mV between Cu and Co, suggestive of reduced galvanic corrosion. Our results also suggest that, during polishing, the Co film surface was covered with a passive film, possibly of Co(III) oxides. Addition of 5 mM BTA to this slurry inhibited Cu dissolution rates and yielded a Co/Cu removal rate ratio of ∼1.2 while further reducing the E oc difference between Cu and Co to ∼10 mV, both very desirable attributes. The roles of H 2 O 2 , arginine, and silica abrasives as well as the pH on the Co material removal process are discussed and a removal mechanism is proposed.

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Further development of a novel cobalt-Al-based metal fill scheme that can be scaled to 11 nm requires the planarization of the metal overfill overburden while also protecting it from corrosion. Very recently, we showed that KMnO4 and sucrose-based aqueous solutions can reduce the ΔEcorr between Al and Co to ∼10 mV. The present work describes the development of the associated silica-based slurry compositions for polishing the Al-Co alloy films. The influence of dodecyl benzene sulfonic acid (DBSA) in tuning the selectivity of the slurry to achieve the desired gate height control and on corrosion currents will also be described.

Co, a candidate material for barrier and capping layers in 10 nm and smaller Cu interconnects, is prone to corrosion and galvanic corrosion during chemical mechanical planarization (CMP) and wet cleaning in aqueous environments posing a serious challenge to its use since the Co liner in the advanced nodes is desired to be only ∼2 to 3 nm thick. We show that E corr between Cu and Co (2 nm) films can be reduced to <10 mV, with Cu being more noble, in an aqueous solution of 6.6 mM (0.05 wt%) Glycine + 15 mM 1,2,4 Triazole, while maintaining an excellent surface finish making it an excellent cleaning solution for Cu/Co (2 nm) structures. We also show that such thin Co films behave electrochemically very differently from thicker (physical vapor deposited 200 nm and even 20 nm) films, perhaps due to differences in deposition methods, differences in surface interactions as determined by XPS and in grain sizes as revealed by SEM imaging, and that (post-CMP) cleaning solutions available for the thicker films do not work for them.