Competitive Anion/anion Interactions on Copper Surfaces Relevant for Damascene Electroplating

The competitive interaction of chloride and SPS (bis-(sodium-sulfopropyl)-disulfide) at Cu(1 0 0)/electrolyte model interfaces was studied by means of cyclic voltammetry in combination with in situ STM and DFT. This specific anion/anion interaction is of paramount importance for the suppressor ensemble deactivation in the context of the industrial Cu Damascene process used for the state-of-the-art on-chip metallization. It is the interplay between chemisorbed chloride and SPS which regulates the dissociative SPS adsorption on copper as the key step in the course of the surface-confined MPS (mercaptopropane sulfonic acid) production. The latter species is considered as the actual anti-suppressor (depolarizer) in context of the Cu Damascene process.Under competitive conditions the chloride adsorbs and orders much faster on Cu(1 0 0) than the SPS. The resulting c(2 x 2)-Cl adlayer acts as an effective barrier for the dissociative SPS adsorption, at least under non-reactive conditions. Defect sites within the chloride matrix are identified as crucial pre-requisites for the dissociative SPS adsorption. Defects are generated under reactive conditions during copper dissolution or copper deposition due to rapid anion adsorption/desorption dynamics. As consequence of the SPS dissociation a mixed, defect-rich c(2 x 2)-Cl-MPS co-adsorption phase forms on Cu(1 0 0) where every second chloride species of the pristine c(2 x 2)-Cl adlayer is displaced by MPS units. This co-adsorption phase reveals an apparent p(2 x 2) symmetry in the STM experiment since only the sulfonic head groups of the MPS units are imaged while the S and the Cl species chemisorbed on the copper surface remain invisible at the "buried" interface.The relevance of this surface reaction for the Cu Damascene process is discussed in detail. (C) 2012 Elsevier Ltd. All rights reserved.