Combined Secondary Ion Mass Spectrometry Depth Profiling and Focused Ion Beam Analysis of Cu Films Electrodeposited under Oscillatory Conditions Nguyen T. M. Hai, [b] David Lechner, [b] Florian Stricker, [b] Julien Furrer, [b] and Peter Broekmann* [a] 1. Introduction The metallization of vias and trenches for state-of-the-art mi- croprocessor fabrication relies on an additive-assisted Cu elec- trodeposition. [1] Plating additives are typically used to redistrib- ute the local current densities on the wafer substrate in such a way that a bottom–up fill of trenches and vias with copper is achieved. It is actually the antagonistic interplay among a sup- pressor ensemble (polarizer) and its specific antagonist (depo- larizer, anti-suppressor) that accelerates copper deposition at the bottom of those features even beyond their fill, whereas the wafer surface remains largely blocked for the Cu deposi- tion. A non-uniform distribution of suppressor ensembles and their antagonists across the trenches and vias is required for such a bottom–up fill to occur. The particular transportation and adsorption kinetics of both the suppressor and the antag- onist (or precursors thereof) into those trenches and vias has been identified as an important factor for the resulting non- uniformity in the additive surface coverage, in particular during the early stage of the fill process. [2] In addition, there are shape evolution effects that become operative upon fea- ture fill, further amplifying the desired non-uniformity in the additive surface concentration, thus leading to an antagonist accumulation at the feature bottom. In addition to these purely physical effects (additive trans- portation, shape evolution), there are particular chemical reac- tions involved that also contribute to the required appearance of gradients in the concentration of suppressors and their an- tagonists. [3] Detailed knowledge about the chemical aspects of the superfill process is mandatory for a more rational design of new suppressor concepts. This is particularly important for an- other type of suppressor additive that is also present in com- mercial plating baths. These additives are meant to disturb the antagonistic interplay between the so-called type-I suppressor (typically based on polyalkylene glycols, PAGs) and bis- (sodium-sulfopropyl)-disulfide (SPS) in the final stage of the su- perfill process. This is how undesired over-plating (momentum plating) after the successful feature fill is prevented. The most important electrochemical characteristic of this second type of suppressor additive (denoted as type-II suppressors) [4] is the absence of deactivation pathways through SPS. This feature has been identified as a mechanistic prerequisite for their use as leveling reagents in the context of Damascene copper plating. Classical leveling concepts rely on mass-transfer limitations of these polymeric levelers in conjunction with their consump- tive inclusion into the deposit. [5] The required time-delayed ar- rival of these additives at the wafer surface after the feature fill is typically achieved by the use of high-molecular-mass poly- mers that are highly diluted in the plating bath. [6] A more advanced approach towards leveling beyond this classical transportation/inclusion concept was discussed re- cently. [7] Prototypical model additives of this concept are poly- The recrystallization behavior of Cu films electrodeposited under oscillatory conditions in the presence of plating addi- tives was studied by means of secondary ion mass spectrome- try (SIMS) and focused ion beam analysis. When combined with bis-(sodium-sulfopropyl)-disulfide (SPS), Imep levelers (polymerizates of imidazole and epichlorohydrin) show charac- teristic oscillations in the galvanostatic potential/time transient measurements. These are related to the periodic degradation and restoration of the active leveler ensemble at the interface. The leveler action relies on adduct formation between the Imep and MPS (mercaptopropane sulfonic acid)-stabilized Cu I complexes that appear as intermediates of the copper deposi- tion when SPS is present in the electrolyte. SIMS depth profil- ing proves that additives are incorporated into the growing film preferentially under transient conditions during the struc- tural breakdown of the leveler ensemble and its subsequent restoration. In contrast, Cu films electrodeposited in the pres- ence of a structurally intact Imep–Cu I –MPS ensemble remain largely contamination free. [a] Dr. P. Broekmann Department of Chemistry and Biochemistry University of Bern, Freiestrasse 3, 3012 Bern (Switzerland) Fax: (+ 41) (0)31 631 39 94 E-mail : peter.broekmann@dcb.unibe.ch [b] Dr. N. T.M. Hai, D. Lechner, F. Stricker, Dr. J. Furrer Department of Chemistry and Biochemistry University of Bern, Freiestrasse 3, 3012 Bern (Switzerland) Supporting Information for this article is available on the WWW under http://dx.doi.org/10.1002/celc.201402427. ChemElectroChem 2015, 2, 664 – 671 # 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 664 Articles DOI: 10.1002/celc.201402427