Competitive anion/anion interactions on copper surfaces relevant for Damascene electroplating

• Published in: Electrochimica acta 2012-05, Vol.70, p.286-295
• Main Authors: Hai, N.T.M., Huynh, T.T.M., Fluegel, A., Arnold, M., Mayer, D., Reckien, W., Bredow, T., Broekmann, P.
• Format: Article
• Language: English
• Subjects: Additive; Anions; Applied sciences; Chemistry; CHLORIDES; Copper; Copper Damascene process; Electrochemistry; Electrodeposition; Electrolytes; ELECTROPLATING; Exact sciences and technology; General and physical chemistry; INLAYS; Metallic coatings; METALLIZING (FOR PLATING); Metals. Metallurgy; Production techniques; SINTERING; Spark plasma sintering; SPARK SINTERING; STM; Study of interfaces; Sulfonic acid; Surface chemistry; Surface treatment
• ISSN: 0013-4686; 1873-3859
• DOI: 10.1016/j.electacta.2012.03.054

The competitive interaction of chloride and SPS (bis-(sodium-sulfopropyl)-disulfide) at Cu(100)/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(100) 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(100) 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.