Electrochimica Acta 70 (2012) 286–295 Contents lists available at SciVerse ScienceDirect Electrochimica Acta j ourna l ho me pag e: www.elsevier.com/locate/electacta Competitive anion/anion interactions on copper surfaces relevant for Damascene electroplating N.T.M. Hai a , T.T.M. Huynh a , A. Fluegel b , M. Arnold b , D. Mayer b , W. Reckien c , T. Bredow c , P. Broekmann a,b,∗ a Department of Chemistry and Biochemistry, University of Bern, Freiestr. 3, Bern, Switzerland b BASF SE, Global Business Unit Electronic Materials, 67056 Ludwigshafen, Germany c Mulliken Center for Theoretical Chemistry, University of Bonn, Beringstr. 4, 53115 Bonn, Germany a r t i c l e i n f o Article history: Received 13 March 2012 Accepted 15 March 2012 Available online 23 March 2012 Keywords: Copper Damascene process Electroplating Additive STM a b s t r a c t 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 combina- tion 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 × 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 × 2)-Cl–MPS co-adsorption phase forms on Cu(1 0 0) where every second chloride species of the pristine c(2 × 2)-Cl adlayer is displaced by MPS units. This co-adsorption phase reveals an apparent p(2 × 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. © 2012 Elsevier Ltd. All rights reserved. 1. Introduction One of the key steps in today’s mass fabrication of logic and memory devices is the void-free metallization of vias and trenches by means of additive-assisted copper electroplating [1]. For that an unconventional growth mode is mandatory that is in liter- ature often referred to as super-fill [1]. This process requires a low copper deposition rate at the wafer surface and the upper side-walls of those features in combination with an “accelerated” copper deposition at the feature bottom. The most common con- cept in the context of the so-called Cu Damascene process relies on the use of a two component additive package. It is typically the ∗ Corresponding author at: Department of Chemistry and Biochemistry, Univer- sity of Bern, Switzerland. Tel.: +41 31 631 4317. E-mail addresses: peter.broekmann@iac.unibe.ch, broekman@thch.uni-bonn.de (P. Broekmann). non-uniform surface coverage of a suppressor additive ensemble (polarizer) and its specific antagonist (depolarizer) which regulates the differential copper deposition velocity inside and outside of those features. Such non-uniformity in the additive surface cov- erage results from a combination of shape evolution effects upon feature fill (anti-suppressor dominated effect) [2–5] in combination with the sophisticated additive transportation/adsorption kinetics (suppressor-dominated effect) [6,7]. Poly-alkylated glycols (PAGs) are the most common suppres- sor precursors [1,8–10] which, however, require chloride [10–13] and most likely Cu(I) [12] as co-additives in order to show a suppressing effect on the copper deposition kinetics. SPS (bis-(3- sulfopropyl)disulfide) is commonly used as specific antagonist for the PAG/Cl/Cu(I) suppressor ensemble. When accumulated at the surface SPS is capable to avoid the formation of the PAG/Cl/Cu(I) suppressor ensemble. One possible approach to gain more insights into the under- lying molecular-level mechanism of this suppressor deactivation 0013-4686/$ – see front matter © 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2012.03.054