The recrystallization behavior of Cu films electrodeposited under oscillatory conditions in the presence of plating additives was studied by means of secondary ion mass spectrometry (SIMS) and focused ion beam analysis. When combined with bis-(sodium-sulfopropyl)-disulfide (SPS), Imep levelers (polymerizates of imidazole and epichlorohydrin) show characteristic 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 deposition when SPS is present in the electrolyte. SIMS depth profiling proves that additives are incorporated into the growing film preferentially under transient conditions during the structural breakdown of the leveler ensemble and its subsequent restoration. In contrast, Cu films electrodeposited in the presence of a structurally intact Imep-Cu-I-MPS ensemble remain largely contamination free.

An extraordinarily strong suppressor additive (IPEG) for copper plating has been synthesized by the copolymerization of imidazole and poly(ethylene glycol) diglycidyl ether (PEG-DGE). This new IPEG polymer contains the typical functional groups of both PAG (poly(alkylene glycol)) and IMEP (polymerizate of imidazole and epichlorohydrin) polymers. The new IPEG polymer combines the properties of PAG (typical suppressor for Damascene applications) and IMEP (state-of-the-art leveler for Damascene applications). The combination of two suppressing modes of action in a single polymer results in significant enhancement of the suppressing capacity of this new IPEG polymer over that of conventional suppressors and levelers. (C) 2013 The Electrochemical Society. All rights reserved.

The particular mechanistic role of halides in the additive-assisted copper electrodeposition is studied by means of combined potential/time transients, in situ STM (scanning tunneling microscopy) experiments, DFT (density functional theory) calculations and ICP-MS (inductively coupled plasma mass spectroscopy) analysis. More specifically, we studied the competitive interaction of bromide and SPS (bis-sodium-sulfopropyl-disulfide). The latter additive is commonly used in the Damascene process as specific antagonist (anti-suppressor, depolarizer) of the polyalkylene glycol (PAG) suppressor additives whereas halides are essential co-additives of the suppressors.Galvanostatic potential transient experiments indicate a substantial stabilization of the PAG suppressor complexes at the copper/electrolyte interface under reaction conditions when the chloride is displaced by the bromide in the formed PAG-Cu(I)-X (X = halide) ensemble. Those bromide containing suppressor complexes reveal substantially improved barrier properties with respect to inter-diffusion of cupric and cuprous ions. Furthermore they are more robust against degradation by the MPS (mercaptopropane sulfonic acid) which is formed under reactive conditions from the SPS as the actual anti-suppressor species in the course of a surface-confined SPS dissociation.Our combined STM and DFT work demonstrates that identical halide/MPS co-adsorption phases are formed when the SPS interacts with either the chloride or the bromide modified copper surfaces. The MPS production gets, however, substantially decelerated when the bromide is present. This effect is discussed as one important reason among others why the antagonistic interaction between the PAG suppressor ensembles and the SPS (MPS) is disturbed when the chloride is displaced by the bromide. We further demonstrate by means of an ICP-MS analysis the capability of the free MPS ligands to dissolve less soluble Cu(I) aggregates. (C) 2012 Elsevier Ltd. All rights reserved.

The full 3D structure of a copper/electrolyte interface is studied by means of in situ surface X-ray diffraction (SXRD) methods. Chloride anions chemisorb on Cu(100) in 10 mM HCI at high potentials under formation of a p(1 X 1)-Cl adlayer: This anionic chemisorption layer serves as a structural template for the lateral ordering of water molecules and hydronium cations in the near-surface liquid electrolyte. Evidence for this interfacial geometry is mainly derived from the intensity distribution of surface-sensitive X-ray diffraction data along the (10L)-adlayer rod. The characteristic oscillating intensity distribution along the (10L) rod is due to a centered bilayer system consisting of the anionic inner Helmholtz layer (IHL) of chemisorbed chloride and the cationic outer Helmholtz layer (OHL). The latter is constituted in the present case by hydronium cations that preferentially populate 4-fold hollow sites of the underlying chloride lattice. IHL and OHL are separated by an extra interfacial water layer. Anions and cations in the IHL and OHL compete for these water species as part of their solvation shell. The Cl/water/hydronium bilayer can be considered as a prototypical model system where the anions and cations in the coupled bilayer system are sharing the interfacial water as part of their solvation shell. In this respect, the Cl-/water/hydronium bilayer considerably differs from the previously studied Cl-/water/K+ system where the interfacial water was clearly assigned to the solvation shell of the alkali metal cation in the OHL. The absence of strongly solvated alkali metal cations in the OHL leads to an increase in the in-plane and out-of-plane exchange dynamics of water and hydronium cations as manifested by an isotropic atomic displacement parameter that is notably higher for the Cl-/water/hydronium than for the more static Cl-/water/K+ system. A comprehensive comparison of our results with other state-of-the-art SXRD studies strongly suggests that the adsorption of partly solvated cations on-top of an anion-modified metal electrode surface has to be considered as a specific cation adsorption phenomenon since the particular structure of the formed bilayer system as well as the involved interfacial dynamics clearly depend on the chemical nature of the anions and cations involved in the structure formation.

Polymerizates of imidazole and epichlorohydrin (Imep) serve as one of the benchmarks for today's chemistry development of leveler additives in context of the industrial copper Damascene process. We therefore studied the synergistic and antagonistic interplay of the Imep polymer with other additives, commonly present in copper plating baths used for the state-of-the-art IC manufacturing. Characteristic oscillations in the applied electrode potential appear in galvanostatic copper electrodeposition when Imep is used in combination with SPS (bis(sodium sulfopropyl) disulfide). We identified the reversible Cu(I) coordination chemistry of the Imep polymer as a second prospective driving force beyond interfacial anion/cation pairing toward the formation of such suppressor/leveler ensembles at the interface. OH groups of the pristine Imep polymer coordinate with H2O-Cu(I)-MPS units (primary effect) that appear as side products of the copper electrodeposition in the presence of SPS. The latter transforms during copper deposition into monomeric MPS (mercaptopropanesulfonic acid/sulfonate) as result of the adsorptive SPS dissociation on the copper surface. Electrostatic coupling between the anionic sulfonate of the MPS and the cationic imidazolium group in the formed linear, bidentate Imep-Cu(I)-MPS complex results into a neutral, hydrophobic species that finally precipitates (secondary effect). The presence of diamagnetic Cu(I) species in those precipitates is proven by elementary analysis in combination with magnetic SQUID measurements. The observed potential oscillations under galvanostatic conditions are discussed in terms of an alternating precipitation and dissolution of the Imep-Cu(I)-MPS suppressor ensemble at the copper/electrolyte interface. Linear sweep experiments prove a partially hidden, N-shaped negative differential resistance (HN-NDR) as physical origin for the observed instabilities under galvanostatic conditions. SIMS (secondary ion mass spectroscopy) depth profiling of copper films deposited under such oscillatory conditions reveals periodic modulations in the contamination level parallel to the surface normal. Cross-sectional FIB analysis of the grown copper deposit reveals periodically repeating lines of grain boundaries in the copper deposit.

This study reinvestigates the electrochemical characteristics of three different suppressor additives that are used in context of industrial copper plating (Damascene, Through-Silicon-Via). It is the particular aim of this contribution to further substantiate our recently introduced classification scheme of suppressor chemistries that relies on their antagonistic and synergistic interplay with MPS (mercaptopropane sulfonic acid/sulfonate). The latter appears as intermediate species in the course of copper electrodeposition in the presence of SPS (bis-(sodium-sulfopropyl)-disulfide).Both the linear sweep voltammetry and potential transient experiments reveal a purely antagonistic interaction between PAG (polyalkylene glycol) based suppressor ensembles and the SPS (MPS precursor) which is rationalized in terms of the coordinative dissolution of a hyper-branched PAG-Cu(I)-Cl coordination network by the MPS. Such purely antagonistic suppressor/MPS interplay is our criterion for a so-called type-I suppressor. A purely synergistic suppressor/MPS interaction is observed for the PEI (polyethylene-imine) which can be considered as a prototypical type-II suppressor. Beyond classical interfacial anion/cation pairing the partly protonated, poly-cationic PEI is capable to form MPS-stabilized Cu(I) adducts. Their suppressing effect relies on an in situ hyper-branching achieved by a combination of Cu(I) coordination and an inner salt formation.Polymerizates of imidazole and epichlorohydrin (Imep) actually show both an antagonistic and a synergistic MPS/suppressor interaction. While free MPS acts as antagonist with respect to the formed Imep-Cu(I)-MPS suppressor adduct it is the MPS coordinated to Cu(I) which serves as crucial co-additive for the Imep suppressor ensemble. It is this interplay of antagonistic and synergistic MPS/suppressor interactions which introduces an extra feedback loop into the reaction cycle of those plating additives thus giving rise to the appearance of non-linear temporal instabilities into the plating characteristics under galvanostatic control. (C) 2012 Elsevier Ltd. All rights reserved.

We present an in situ surface x-ray diffraction study on the structuring impact of an anion-modified electrode surface on the near-surface liquid electrolyte. This templating effect of the so-called inner Helmholtz layer of specifically adsorbed anions affects not only the interfacial structure parallel to the surface normal by layering the liquid in the near-surface regime but induces moreover a lateral ordering of water dipoles and solvated counter ions in the so-called outer Helmholtz layer. In this respect, we observe a symmetry transfer from the inner Helmholtz layer into the liquid electrolyte next to the electrode surface. Our prototypical model system is a Cu(100) surface on which chloride adsorbs under the formation of a simple p(1x1) adlayer phase (this notation refers to the fcc unit cell of Cu) that serves as structural template for the coadsorption of monovalent potassium and hydronium cations from the acidified supporting electrolyte. A layer of interfacial water is interpreted as a part of the remaining solvation shell of potassium cations in the outer Helmholtz layer.

The structure and reactivity of a Cu(100) single crystal electrode surface covered with free base meso-tetra (N-methyl-4-pyridinium) porphyrin (abbreviated as H(2)TMPyP) as a function of electrode potential have been investigated with cyclic voltammetry (CV), electrochemical scanning tunneling microscopy (ECSTM), and UV-Vis and Raman spectroscopy. The well-ordered self-assembled layer of the porphyrin is consistent with the adsorption of the reduced porphyrin species after the first two-electron reduction step. The copper dissolution reaction in the presence of the stable self-assembled porphyrin layer starts at step edges on both upper and lower terraces and coincides with the preferential oxidation of reduced porphyrin species at step sites. The dissolved copper cations are incorporated into the free base porphyrin molecules leading to the formation of CuTMPyP. As a consequence this new species accumulates in the solution with time and a copper redeposition in the cathodic potential scan is lacking.

The self-assembly of 5-(12-cyano-dodecyloxy)-isophthalic acid has been investigated at the Au(111)/aqueous electrolyte interface by means of electrochemical scanning tunneling microscopy (ECSTM). At potentials below the potential of zero charge (pzc), the molecules form a row type pattern, both on the reconstructed Au(111) surface (Au(111)-(22 × √3)) as well as on the unreconstructed Au(111) surface (Au(111)-(1 × 1)). On both surfaces the isophthalic acid groups arrange commensurately along the √3 direction of the surface. The cyano containing alkyl chains are interdigitated leading to the formation of cyano functional rows on the surface. The self-assembled layers show a strong dependency on the electrode potential. The potential induced phase transition of the organic layer, the lifting of the Au(111)-(22 × √3) surface reconstruction in the presence of this molecular layer, as well as the growth of an ordered layer from a disordered phase, have been potentio-dynamically investigated.

Combined voltammetric and in-situ STM studies were employed to gain information about the structure of a sulfate-modified Cu(111) electrode surface exposed to an acidic electrolyte containing a redox-active porphyrin (meso-tetra(N-methyl-4-pyridyl)-porphine, abbreviated as [H2TMPyP](4+)). A particular focus of this study lies on the characterization of the interfacial structure under reactive conditions, for example, during an ongoing electron transfer reaction. The oxidized form of [H2TMPyP](4+) cannot be stabilized within the narrow potential window of copper. A two-electron, transfer reduction affects the central porphine core even at the anodic limit of the copper potential window close to the onset of the oxidative copper dissolution reaction. This porphyrin-related electron transfer reaction can take place even in the presence of a preadsorbed sulfate/ water coadsorption layer. The latter causes a charge inversion at the metal/anion interface with an excess of negative charges within the sulfate/water layer. Enhanced electrostatic interactions between this sulfate/water coadsorption layer and the cationic porphyrin reactants and reaction products. are discussed as the physical origin for the formation of a paired anion-cation layer at the interface that retains its structural integrity even during the ongoing electron transfer reaction, at least on the time scale of the STM experiment. It is the starting sulfate desorption at more negative potentials that causes the loss of lateral order within this paired anion-cation layer. Highly water-soluble cationic porphyrin species coadsorb/codesorb together with the sulfate anions onto/from the Cu(111) electrode.

The initial stage of oxidative CuI film formation on Cu(111) has been studied in an electrochemical environment by means of cyclic voltammetry (CV), in situ scanning tunneling microscopy (STM) and ex situ synchrotron X-ray photoemission spectroscopy (SXPS). Cyclic voltammetric studies indicate a significant acceleration of copper oxidation in the presence of iodide. The reason for that is the iodide-mediated stabilization of cuprous species resulting in a downward shift of the onset potential for copper oxidation. Reactive sites for the copper oxidation followed by iodide complexation are exclusively defects such as substrate step edges. It is the surface-confined supersaturation of mobile CuI species that leads to the two-dimensional (21)) CuI film formation via nucleation and growth of a Cu/I bilayer on top of the preadsorbed iodide phase. In an advanced stage of copper oxidation, however, terraces are directly transformed into the 2D CuI film at the reactive boundary between metallic copper and the growing 2D CuI film. Structurally, this 2D CuI film is closely related to the (111) plane of crystalline CuIbulk (zinc blende type). There is no significant passivation of the copper surface against the oxidative dissolution reaction in the presence of the 2D CuI film. Copper dissolution in the presence of the 2D CuI film proceeds also via an inverse step flow mechanism involving the concerted receding of four atomic layers. A model of this process will be discussed on the basis of STM results. The transition from 2D to a three-dimensional (3D) CuI growth mode is observed for an advanced stage of copper oxidation.

The surface redox-chemistry of adsorbed viologens is studied by means of cyclic voltammetry (CV) in combination with in situ scanning tunneling microscopy (STM). 1,1'-Dibenzyl- 4,4'-bipyridinium molecules (DBV2+) adsorb on a chloride modified Cu(100) electrode surface under formation of a laterally well ordered 2D array of supramolecular cavitand ensembles. Each cavitand consists at least of 4 individual DBV2+ sub-units which are arranged in a certain circular manner making this supramolecular cavitand chiral. Both possible enantiomeric forms are found in two mirror domains at the surface. Reducing the di-cationic DBV(ads)2+ species to the corresponding radical mono-cation DBV(ads).+ causes a phase transition from the pre-existing DBV 2+ ( ads) cavitand phase to a stripe pattern following a nucleation and growth mechanism. DBV(ads).+ species are adsorbed with their main molecular axis parallel to the surface in a side-on adsorption geometry. Enhanced intermolecular pi - pi-interactions are identified as the main driving force for the formation of 1D oligomer and polymer chains as the characteristic structural motif of the DBV(ads).+ phase. These structural motifs are generally independent of the electronic and structural substrate properties. Chloride desorption through the viologen film is discussed as the reason for an order - disorder transition within the viologen film at even more negative potentials.