A model for predicting leveling during electrodeposition in the presence of an inhibiting additive is presented. Based on a diffusion-adsorption mechanism, the model assumes that the additive is consumed at the cathode by electroreduction. Using the approximation of a flat, stagnant diffusion layer, leveling during metal electrodeposition into triangular and semicircular grooves is simulated. The variation of the leveling agent concentration along the groove profile is determined by solving a concentration field problem with a boundary element method, and the advancement of the groove profile is simulated with a flexible moving-boundary algorithm. Leveling performance depends on three dimensionless groups characterizing leveling-agent reduction, metal-ion reduction, and the geometrical ratio of the diffusion layer thickness to the groove depth.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see ABSTRACT A model for cathodic leveling based on a diffusion-adsorption-reduction mechanism for the leveling agent was tested experimentally by electrodepositing nickel into a semicircular groove in the presence of coumarin. The inhibition of nickel by coumarin was measured on a rotating disk electrode, and kinetics for the reduction of coumarin and Langmuir adsorption coefficient were obtained from polarization data. Satisfactory agreement was found between experimentally measured and simulated leveling for groove depths on the order of the diffusion layer thickness or smaller.

Pb02 is one of the most prominent anode materials, but it has to be protected from chemical reduction by applying an external trickle current. Platinum is also a good material but does not have a high current efficiency for ozone and is consumed due to a large wear rate. Carbon materials are also good candidates for ozone evolution but are easily corroded in acid solution. On the basis of these comparisons, it is also expected to be used as a special material for an ozone generator that is suitable for the semiconductor industry or medical field, where high purity of the product would be required.

Through-mask electrochemical micromachining (EMM) involves high speed selective metal dissolution from unprotected areas of a photoresist-patterned workpiece that is made an anode in an electrolytic cell. Compared to chemical etching, electrochemical dissolution offers higher rates and better control on a micro-and macro-scale of shape and surface texture of anodically dissolved materials. 1,2 EMM is receiving considerable attention in the electronics industry for thin film patterning. 3 In recent years, there has been an increasing demand for the micromachining of titanium. Due to their good mechanical properties and chemical inertness, titanium and titanium alloys have attracted considerable interest in the chemical process, aerospace, and biomedical industries. Fabrication of well-defined microstructures with controlled surface finish on titanium has become key in the biomedical industry for producing implants with improved biocompatibility 4-7 as well as miniaturized implantable devices. 8 For such applications, electrochemical micromachining (EMM) is promising in view of its flexibility and cost effectiveness.EMM has been used in the past for machining chemically resistant metals like Ti, Ta, Zr, and Nb. 9 Allen and Gillbanks 10 performed EMM of Ta in a solution of 5% by volume sulfuric acid in methanol. A uniform etch rate over the anode surface was obtained for an applied cell voltage of 10 V. These studies, however, give very little information on the role of prevailing electrochemical conditions. Rosset et al. 11,12 studied shape change during the dissolution of a type 304 stainless steel through an unevenly spaced pattern of lines into a 6 M NaNO 3 electrolyte. Using a flow-channel cell, they investigated the influence of current density and hydrodynamic conditions on the profile shapes and surface finish. The current distribution between anodes and hence the etch rate was found to be more uniform when dissolution is mass-transport controlled. The maximum current that could be applied was limited by Joule heating of the electrolyte in the developing etch grooves. Datta 13 employed EMM to fabricate an array of precision nozzles in copper and stainless steel foils for application in ink-jet printer heads. Nozzles of desired shape with microsmooth surfaces were obtained by dissolving at the limiting current plateau or at high voltages. The use of pulsating voltage provided a better control over the nozzle fabrication process because of the possibility of applying high instantaneous current density while maintaining a low average current. Shape evolution during the electrochemical etching of lines and holes into thin metal films sandwiched between a photoresist mask and an insulating support has been simulated by West et al. 14 assuming the primary current distribution approximation. Both small and large aspect ratio of photoresist thickness to cavity width were considered. The calculated shapes were compared with the experimental results of Rosset et al. 12 The fair agreement obtained between theory and ex...

A model for cathodic leveling based on a diffusion-adsorption-reduction mechanism for the leveling agent was tested experimentally by electrodepositing nickel into a semicircular groove in the presence of coumarin. The inhibition of nickel by coumarin was measured on a rotating disk electrode, and kinetics for the reduction of coumarin and Langmuir adsorption coefficient were obtained from polarization data. Satisfactory agreement was found between experimentally measured and simulated leveling for groove depths on the order of the diffusion layer thickness or smaller.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see ABSTRACT Electrical impedance of aging porous silicon layers (PS) was studied applying the regime of temperature cycling (from -50 to +150°C) in a range of alternating current (a.c.) frequencies 0.2 to 105 Hz (amplitude 1 V). Freshly obtained PS exhibits changes of electrical properties at temperatures above 50°C, presumably associated with the escape of electrolyte from the pores. A.C. electrical conductivity of PS is very sensitive to its postanodizing treatments (heat-treatment, pore filling by inert electrolyte, evacuation at increased temperatures, annealing in nitrogen). Activation energy for the electrical conduction ranges from 0.1 to 0.23 eV depending on a.c. frequency and postanodizing treatments. An electric equivalent circuit was designed to fit the experimental data acquired at differently treated PS samples. The components of the equivalent circuit were assigned to physical elements of PS (a surface phase on top of PS and a layer of underlying bulk material). Based on the measurements of the electrical impedance and chemical composition of PS films the mechanism of electrical conduction is assumed to be a charge carrier migration through the localized states associated with the surface impurities (hydrides and/or oxides of silicon). The obtained impedance data show the strong influence of residuals of the electrolyte inside the pores of freshly prepared PS on its aging stability.

Shape change simulations of the electrochemical etching of lines and holes into thin metal films sandwiched between a photoresist mask and an insulating support are presented. For the moving-boundary simulations, which use a boundaryelement method, it is assumed that the primary current distribution is applicable. The Appendix explains how formulating the current distribution problem in terms of a stream function instead of an electric potential can improve the efficiency of the numerical procedure. Two aspect ratios of photoresist thickness to cavity width are considered. In one case, large aspect ratios are assumed, and various metal film thicknesses are investigated. At long times, but before the insulating support is first exposed to the electrolyte, the shapes of the profiles can be fit to an ellipse. The simulations are continued following exposure of the support, and these results are summarized by a design curve that gives the cavity width necessary to etch a groove of a desired width or a hole of a desired radius into a metal of a given thickness. The second case that is investigated was studied experimentally by Rosset et al. [17]. The aspect ratio of this geometry is 0.08, and the thickness of the metal is large compared to the cavity widt~h. The argeement between theory and experiment is discussed in terms of the likelihood of achieving in practical situations the modeling assumptions.The fabrication of electronic devices may require the etching of thin metal films that are coverd by a photoresist mask and supported by an insulating material. This is accomplished by dry or wet etching processes, with the latter being done either chemically or electrochemically. Datta and Romankiw (1) reviewed the advantages of different wet-etching procedures, and Allen (2) discussed many of the practical considerations. Figure 1 shows the initial, unetched assembly that is considered here. As indicated, both two-dimensional lines and axisymmetric holes are investigated. The thickness of the photoresist mask is d, and b is the metal film thickness. The half-width of the initial, unetched two-dimensional line is L, and r0 is the radius of the unetched axisymmetric hole.The prediction of the final shape requires a moving boundary simulation where, at each time step, the reaction rate distribution on the surface is determined. Dukovic (3) reviewed the developments in the 1980's in movingboundary calculations for electrodeposition. Electrochemical etching has received less attention from a theoretical viewpoint. In nearly all of the studies, which are reviewed briefly below, the local etch rate along the metal is assumed to be mass-transfer controlled. Kuiken et al. (4,5) studied by a perturbation analysis shape changes near the edge of the photoresist for masstransfer controlled etching. Their work, which is valid for infinitesimally thin masks (i.e., d/L = 0), was verified experimentally (6). Vuik and Cuvelier (7) also investigated diffusion-controlled etching through a thin photoresist mask. They discuss two numerical ...