We investigate the effect of amine-based leveler additives on the catalytic function of the accelerator at the Cu-electrolyte interface. In the presence of the bis-(sodium sulfopropyl)-disulfide (SPS) accelerator, chronopotentiometric measurements show the potential changes from inhibition of the levelers increased with molecular weight and were greater to those of glycol-based suppressors. In situ surface-enhanced Raman spectroscopy (SERS) revealed significant conformational changes of the surface-adsorbed SPS in the presence of the amine-based levelers. This leveler-induced conformational perturbation of SPS diminishes the activity of SPS. SERS also revealed decreased coverages of surface-adsorbed SPS in the presence of the high molecular weight amine-based levelers at negative potentials, indicating that the leveler limits direct contact of SPS with the surface. Decreased coverages were also found for adsorbed chloride in the presence of all levelers considered, likely contributing to the deactivation of the accelerative effect of SPS. Secondary-ion mass spectrometry (SIMS) analysis of Cu electrodeposited from solutions comprised of a linear polyethyleneimine (PEI), SPS, and Cl– show increased S, Cl, and C content in the deposit relative to solutions absent PEI, indicating the presence of PEI results in co-incorporation of these additives. This leveler-assisted incorporation of SPS and Cl– also serves to mitigate SPS acceleration.

The electrochemical nitrate reduction reaction (NO3 –RR) offers two-fold advantagesrestoring balance to the global nitrogen cycle and a less energy intensive pathway to the production of ammonia. We report the results of voltammetric and spectroscopic measurements examining NO3 –RR on Cu and Cu-alloyed electrodes (CuAg, CuSn, and CuPt) in an alkaline medium. Electrochemical results demonstrate that the overpotential for the NO3 –RR is ∼120 mV less on the CuAg catalyst as compared to the Cu-only catalyst. In situ surface enhanced Raman spectroscopy (SERS) obtained from these two Cu samples shows that the presence of dilute Ag maintains the Cu surface in a more reduced state (Cu(I)) during the course of NO3 –RR, while the neat Cu surface is heavily oxidized during NO3 –RR in an alkaline medium. Consistent with this behavior, the CuSn alloy also stabilizes Cu(I) on the electrode surface and results in increased NO3 –RR rates. Alternatively, the CuPt alloy does not yield a stabilized Cu(I) component and consequently results in NO3 –RR rates lower than those for neat Cu. These results indicate that alloying Cu with different metals can tune the nitrate reduction activity by making the Cu atoms more resistant to oxidation to Cu(II) and stabilizing the Cu atoms in lower oxidation states.

Electrodeposition of copper constitutes a key process for fabrication of modern microelectronic devices. [1][2][3][4] Commonly, the deposition process is required to fill recessed structures with metal. The size scales of such recessed structures range from nanometer-sized dual damascene structures for production of microprocessors, [5,6] to micrometer-sized through-silicon vias (TSVs) for 3D integration of different components within a package. [7,8] Despite the huge differences with regard to the dimensions, the various filling applications share the requirement of different local deposition rates to fill the recessed structures with copper. In order for filling to occur, the deposition needs to be accelerated at the bottom of the features, whereas it should be suppressed at the top. [9][10][11][12][13] These differential deposition rates may be obtained by the addition of suitable organic additives to the electrolyte. [1,6,[9][10][11][12][13][14][15] Electrolytes for electrolytic copper deposition typically consist of a cupric ion source, sulfuric acid, and halides such as chloride. Deposition of metallic copper from cupric ions is generally accepted to take place via cuprous ion intermediates. [6,[16][17][18] Industrially relevant plating electrolytes further contain a set of typically three organic additives, which provide the differential deposition rates to allow feature filling. [1,6,[9][10][11][12][13][14][15] Local acceleration of copper electrodeposition at the feature bottom is achieved by the accelerator and inhibition at the feature top by the suppressor. [10,11,13,14,19,20] The leveler further supports filling by local inhibition at exposed areas and may, thereby, prevent mounding over the recessed features. [14,21] Leveler additives typically consist of (poly) cationic alkylamines, e.g., PEI, which are supposed to interact with the surface by hydrophobic and interfacial anion/cation pairing effects. [15,21,22] Previous and recent spectroelectrochemistry investigations further supported interaction of this class of molecules to surface-confined halides. [23,24] An additional contribution to the adsorption by the formation of insoluble complexes with cuprous ions was proposed. [22] However, no direct evidence for interaction of the hydrophobic alkyl moieties with the bare or halide-covered copper surface, electrostatic interactions between halide anions and cationic ammonium ions, or complex formation with cuprous ions is available. Furthermore, the exact mechanism of the inhibition of the deposition is unclear and has been ascribed to the formation of a physical barrier for cupric ions by either adsorption or precipitation. [15,21,22] Recently, computational modeling and comparison of the results with electrochemical and spectroelectrochemical data was shown to be a suitable approach to reveal the detailed mechanism of the adsorption and inhibition of polyethylene glycol (PEG)-based suppressors. [25] Here, we use this approach to address PEI, which serves as reference compound for leveler additives...