Superconformal electrodeposition of copper in 500 nm deep trenches ranging from 500 to 90 nm in width has been demonstrated using an acid cupric sulfate electrolyte containing chloride (Cl), polyethylene glycol (PEG), and 3-mercapto-1-propanesulfonate (MPSA). In contrast, similar experiments using either an additive-free electrolyte, or an electrolyte containing the binary combinations Cl-PEG, Cl-MPSA, or simply benzotriazole (BTAH), resulted in the formation of a continuous void within the center of the trench. Void formation in the latter electrolytes is shown to be reduced through the geometrical leveling effect associated with conformal deposition in trenches or vias with sloping sidewalls. The slanted sidewalls also counterbalance the influence of the differential cupric ion concentration that develops within the trenches. Examination of the i-E deposition characteristics of the electrolytes reveals a hysteretic response associated with the Cl-PEG-MPSA electrolyte that can be usefully employed to monitor and explore additive efficacy and consumption. Likewise, resistivity measurements performed on corresponding blanket films can be used to quantify the extent of additive incorporation and its influence on microstructural evolution. The films deposited from the Cl-PEG-MPSA electrolyte exhibit spontaneous recrystallization at room temperature that results in a 23% drop in resistivity within a few hours of deposition.

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In situ stress measurements were made during copper electrodeposition onto ͑111͒-textured Au from acidic sulfate electrolyte using the wafer curvature method. In the Cu underpotential deposition region, the intermediate (ͱ3 ϫ ͱ3)R30°Cu-sulfate honeycomb structure creates a surface stress that is tensile when compared to that of the sulfate-adsorbed electrode at positive potentials or the complete (1 ϫ 1) Cu monolayer at more negative potentials. This behavior is consistent with surface-induced charge redistribution models that appear in the literature. During the bulk deposition of Cu, there is a rapid increase in tensile stress during the first 20 nm of growth that we attribute to nuclei coalescence and grain boundary formation. The magnitude of the tensile stress as well as the film thickness at which the maximum stress occurs are both dependent upon the electrode potential due to its influence on the nucleation density. When the films are continuous, the total stress is the superposition of the coalescence-induced tensile stress and a compressive stress which we attribute to the incorporation of mobile adatoms on the surface into the grain boundaries. The tensile stress component dominates thin films deposited at high overpotential, whereas thick films deposited at low overpotential have a net compressive stress. When deposition is interrupted both tensile and compressive components of the stress relax somewhat but are quickly reestablished when deposition is resumed. The development of the growth stress that we describe here is very similar to that which has been reported for Cu deposition from the vapor phase.

The chemical and electrochemical behavior of titanium was examined in the Lewis acidic aluminum chloride-1-ethyl-3methylimidazolium chloride (AlCl 3 -EtMeImCl) molten salt at 353.2 K. Dissolved Ti͑II͒, as TiCl 2 , was stable in the 66.7-33.3% mole fraction ͑m/o͒ composition of this melt, but slowly disproportionated in the 60.0-40.0 m/o melt. At low current densities, the anodic oxidation of Ti͑0͒ did not lead to dissolved Ti͑II͒, but to an insoluble passivating film of TiCl 3 . At high current densities or very positive potentials, Ti͑0͒ was oxidized directly to Ti͑IV͒; however, the electrogenerated Ti͑IV͒ vaporized from the melt as TiCl 4 (g). As found by other researchers working in Lewis acidic AlCl 3 -NaCl, Ti͑II͒ tended to form polymers as its concentration in the AlCl 3 -EtMeImCl melt was increased. The electrodeposition of Al-Ti alloys was investigated at Cu rotating disk and wire electrodes. Al-Ti alloys containing up to ϳ19% atomic fraction ͑a/o͒ titanium could be electrodeposited from saturated solutions of Ti͑II͒ in the 66.7-33.3 m/o melt at low current densities, but the titanium content of these alloys decreased as the reduction current density was increased. The pitting potentials of these electrodeposited Al-Ti alloys exhibited a positive shift with increasing titanium content comparable to that observed for alloys prepared by sputter deposition.

Epitaxial LiCoO2 (LCO) thin films of different orientations were fabricated by pulsed laser deposition (PLD) in order to model single-crystal behavior during electrochemical reaction. This paper demonstrates that deposition of conductive SrRuO3 between a SrTiO3 (STO) substrate and an LCO film allows (1) epitaxial growth of LCO with orientation determined by STO and (2) electrochemical measurements, such as cyclic voltammetry and impedance spectroscopy. Scanning transmission electron microscopy (S/TEM and SEM) has demonstrated an orientation relationship between LCO and STO of three orientations, (111), (110) and (100), and identified a LCO/electrolyte surface as consisting of two crystallographic facets of LCO, (001) and {104}. The difference in the orientation of LCO accounts for the difference in the exposed area of {104} planes to the electrolyte, where lithium ions have easy access to fast diffusion planes. The resistance for lithium ion transfer measured by electrochemical impedance spectroscopy had inverse correlation with exposed area of {104} plane measured by TEM. Chemical diffusivity of lithium ions in LCO was measured by fitting electrochemical impedance spectroscopy data to a modified Randles equivalent circuit and allowed us to determine its dependence on film orientation.