Cleaning Solutions for Ultrathin Co Barriers for Advanced Technology Nodes

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 ΔEcorr 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.