Copper Electropolishing Research Articles

Effect of eco-friendly organic additives on copper electropolishing and process parameter optimization

The type of organic additives significantly affects copper electropolishing performance, including glossiness and surface smoothness. Therefore, developing efficient and eco-friendly additives is crucial for advancing this technology. This study investigates the effects of glycerol and ascorbic acid on copper electrochemical properties and surface morphology. Using the Box- Behnken Design (BBD), we examined the interaction effects of polishing time (A), current density (B), and polishing temperature (C) while optimizing the process parameters. The results demonstrate that glycerol and ascorbic acid additives effectively reduce the critical current density and limiting current density, synergistically enhancing copper surface glossiness and smoothness while slowing down the dissolution rate of the copper. Interaction analysis revealed a prioritized sequence of effects: AB > BC > AC. Under optimal conditions (1.5 min of polishing time, 12 A dm−2 of current density, and 27 °C of polishing temperature), copper surface roughness decreases from 1.2 μm to 37 nm, representing a 97% reduction, along with enhanced corrosion resistance.

Physico-Chemical Studies of Almond Shell Extracts Potential on the Electropolishing and Electrorefining of Copper

Addition of almond shell extract to electrochemical process bath such as electropolishing and electrorefining of copper was investigated using potentiodynamic polarization and surface investigation. Addition of several concentrations of the extracts provide a sharp decline in electrorefining rate, but gave augmentation in electropolishing rate. Surfce investigation provided the confirmatory evidence of improved surface texture by almond shell extract addition to copper electropolishing and electrorefining electrolyte. Kinetic investigation and activated constraints were calculated for the electrochemical processes. A distinct improvement in the surface texture was observed where surface irregularity, roughness (Ra) diminishs from 0.95 to 0.43, 0.32, 0.22 and 0.06 μm in the presence of 25, 100, 150 and 200 ppm extract.

Surface Characterization of High-Purity Copper Electropolishing and Electrodeposition Treatments in an Ionic Liquid

High purity (>99.9% composition) copper metal specimens were used in electropolishing treatments with an acid-free ionic liquid electrolyte prepared from quaternary ammonium salts as a green polishing solution. A prominent ionic liquid composed of ethylene glycol (HOCH2CH2OH) and choline chloride (HOC2H4N(CH3)3 +Cl−), sometimes abbreviated as 2EG:1VB4, has been used in other studies to successfully electropolish various metal alloys, but has only been used in limited capacity to polish pure rare earth metals (1-5), like copper, the focus of this study. Voltammetry and chronoamperometry tests were conducted to determine the optimum conditions for electrochemical polishing, while Atomic Force Microscopy (AFM) revealed nanoscale effectiveness of the ionic liquid relative to an industry standard acid polishing treatment of 1 Mol Phosphoric Acid (H3PO4). Surface morphology comparisons summarized electrochemical polishing efficiency of these relative treatments by providing root mean square roughness prior to and post-electrochemical polishing.Electropolishing using the ionic liquid revealed a mirror finish >10 times smoother than the same copper metal surface prior to electropolishing. This transition manifested in a marked change in root mean squared roughness from 167.15 nm to 14.744 nm and resulted in a mass loss of 0.0535 g for an electropolishing rate of 59.444 µg/s when subjected to a 900 second treatment with an average voltage of 1.5 V. By comparison, the phosphoric acid electropolishing treatment yielded an improvement in root mean squared roughness of 85.019 nm, resulted in a mass loss of 0.067 g for a higher electropolishing rate of 74.444 µg/s when subjected to the same treatment conditions. However, the it can be noted that while the elctropolishing rate via the acid solutionis greater, there are extreme peaks and troughs etched on the smoothed surface due to pitting at low current densities (Figure 1). Hydrogen contamination can be observed to affect the overall root mean square average of the region, which may be remedied via a relatively costly degassing treatment at temperatures up to 800 deg C to achieve more comparable results to the ionic liquid solution.After these electropolishing pretreatments, the resulting copper surfaces were subsequently electroplated during a 1 hour treatment at 2 V with an 2EG:1VB4 ionic liquid solution that had previously been used to electropolish high-purity niobium metal. A thin film of niobium metal coated the polished copper during electrodeposition resulting in an average mass gain of 0.002 g, and a root mean squared roughness of increase of -2.101 nm for the ionic liquid pretreated sample, compared to the -2.417 nm resulting roughness from the phosphoric acid pretreatment.As a result, pretreatments revealed a cheaper, recyclable, and environmentally-friendly approach to electopolishing pure copper was demonstrated to be more effective than an acidic industry standard electrolyte. Additionally, electrodeposition of niobium metals on each pretreatment sample provides a reasonably cost-effective method to combine the electroconductivity benefits of copper and ferroelasticity attributes of niobium metals. References Derek Lofis and Tarek M Abdel-Fattah, International Journal of Minerals, Metallurgy and Materials, 26(5), 649–656 (2019)Derek Lofts and Tarek M. Abdel-Fattah, Colloids and Surfaces A: Physicochemical and Engineering Aspects, 511C, 113-119 (2016)Tarek M. Abdel-Fattah, Derek Loftis and Anil Mahapatro, Nanoscience and Nanotechnology, 5(2), 36-44 (2015)Tarek M. Abdel-Fattah, Derek Loftis and Anil Mahapatro, Journal of Surfaces and Interfaces of Materials, 3, 67-74 (2015)Tarek M. Abdel-Fattah, Derek Loftis and Anil Mahapatro, Journal of Biomedical Nanotechnology, 7(6) 794-800 (2011) Figure 1

Effect of methanolic plant extract on copper electro-polishing in ortho-phosphoric acid

The behavior of copper electro-polishing in ortho-phosphoric acid using the galvanostatic polarization method was ascertained. This was examined via measuring and comparing anode potential –limiting current relationship in solution of regularly mounting concentrations (from 50 to 1800 ppm of methanolic Allium sativum (garlic extract), Tilia cordata (Tilia leafs), Foeniculum vulgare (fennel seeds), and Lablab purpureus (Dolichos lablab extract) and weight loss method. Influence of temperature on the dissolution kinetics were investigated. First order kinetic is applicable to the copper dissolution in solution containing plant extracts. Surface morphologies, brightness and roughness of polished specimens were examined with a scanning electron microscope (SEM), reflectance and atomic force microscope (AFM). Addition of methanolic plant extract to electro-polishing solution produce a lesser limiting current. According to SEM, UV–VIS-NIR spectra and surface roughness measurements, addition of high concentration (1800 ppm) of methanolic plant extract to the electrolytic solution is highly effective to enhance surface quality. High reflection property is obtained when the different type of methanolic plant extract is added to the electro-polishing electrolyte. The minimum Ra and PV values are achieved by garlic extract, which records the highest reflectance value and inhibition efficiency. Weight loss data obtained is excellent conformity with the result obtained by electrochemical measurements.

Copper Electropolishing in Phosphoric Acid under Normal and Forced Convection Conditions in Presence of Some Pharmaceutical Drugs

Some pharmaceutical drugs namely valsartan, hydrocholorothiazide, erythromycin thiocynate and diclofenac potassium were studied as chemical additions for enhancing the finished copper surface attained. Anode potential-limiting current relationship was measured and comparing of gradually increasing pharmaceutical compound concentrations (from 1 × 10-4 to 7 × 10-4 M). Copper dissolution behaviour in presence of pharmaceutical compounds was studied under natural convection [rotating cylinder (RCE) and rotating disc electrode (RDE)] as forced convection. The limiting current was found to diminish with enlarging additives concentration and increase with increasing temperature (293-313 K). Activation energies values confirm that reaction rate was diffusion controlled. The results showed that the improvement produced in electropolishing in presence of pharmaceutical compounds occurs through adsorption of their molecules above metal surface. All the pharmaceutical compounds adsorption process obey kinetic-thermodynamic model. The data under different conditions were controlled by dimensionless correlations viz. Sherwood, Schmidt and Reynolds numbers. Surface morphology also confirmed that an addition of pharmaceutical compound to copper dissolution bath enhance surface appearance and its texture quality to great extent.

Studying Copper Electropolishing Inhibition in Presence of Some Organic Alcohols

Studying Copper Electropolishing Inhibition in Presence of Some Organic Alcohols

Studying Copper Electropolishing Inhibition in Presence of Some Organic Alcohols

Electro polishing is defined as anodic corrosion. The issue of the effects of corrosion on structural integrity of metal surfaces has been a question of concern for some time. The uses of chemical corrosion inhibitors are common in production and processing operations. Nevertheless, the challenge is to develop a new class of corrosion inhibitors to protect the materials, due to the economic importance of copper there are several researches deals with acceleration and inhibition of this process. In this paper the electropolishing process inhibited with different ratio by addition of some organic alcohols(methanol, ethanol,propanol, and isopropanol) by addition with concentration (2, 5, 10, 15, 20, 25 and 30 %) .The results reveal that these organic alcohols have a strongest inhibitive effect ranging from8. 7 – 53.8 % and the thermodynamic parameters were present.

Copper Electropolishing in the Presence of Purine Derivatives

Copper Electropolishing in the Presence of Purine Derivatives

An in-situ Study of Copper Electropolishing in Phosphoric Acid Solution

An in-situ Study of Copper Electropolishing in Phosphoric Acid Solution

Mechanistic Study of Copper Electropolishing

Electropolishing of copper in phosphoric acid was investigated through mathematical modeling, using a model based on thermodynamics and transport theory. The electropolishing process consists of two distinct regimes: the copper-accumulation regime and the salt-film-growth regime. The concentrations of cupric ion and a certain anion at the anode surface increase in the first regime as a result of transport limitations, until the saturation level of a certain cupric salt is reached. In the second regime, the salt film forms and grows on the anode surface because of thermodynamic requirements. The model can be used to calculate the onset point of film formation, the growth rate of the film, and the thickness of the film.

Electrochemical Equilibria of Copper in Aqueous Phosphoric Acid Solutions

The electrochemical behavior of copper in aqueous solutions containing phosphoric acid (orthophosphoric acid) and phosphate salts is important in a variety of industrial applications. This study presents aqueous solubility diagrams and potential-pH diagrams for a copper–phosphoric-acid–water system at a wide range of total dissolved copper, , and phosphoric acid activities, . and were used as the cupric-phosphate solid species in the constructions of the diagrams. The stability domains of these two solids were similar, but had a relatively narrower predominance region. The diagrams showed that a higher amount of is required to form the copper-phosphate solids when is increased. For the combinations of lower and higher values, phosphoric acid is expected to increase the solubility range of copper through the formation of aqueous copper-phosphate complexes. Increasing the temperature broadens the stability domain of . The aqueous solubility diagram constructed for copper electropolishing rules out the formation of any anodic solid films on the copper electrode during electropolishing in 85 wt % phosphoric acid. The predictions of the diagrams agree with the experimental data from the literature.

A Mechanistic Model for Copper Electropolishing in Phosphoric Acid

Copper electropolishing in phosphoric acid has been characterized using electroanalytical methods, primarily potential transient techniques. An uncommon voltage response, consisting of two distinct steps, was noted when the current was stepped to the limiting current. A slow (, depending on agitation) and relatively small initial potential increase was followed by a fast and large potential rise. The latter always reached the oxygen evolution potential , irrespective of the process conditions. While the first, slow potential transient can be correlated in terms of a diffusion process, the second, rapid potential rise suggests the buildup of a highly resistive component, most likely a surface film. The nearly instantaneous potential relaxation upon current interruption further supports the resistive film model rather than a transport-related process. A two-stage mechanism is proposed and analytically modeled. Accordingly, the cupric ion concentration at the anode increases during the initial stage of the dissolution process due to transport limitations, until a saturation level is reached and a resistive surface film forms. During the second stage, the continuing imbalance between the rate of cupric ion formation and transport into the bulk leads to increasing film thickness and, consequently, to a rapid buildup in resistance. The model quantitatively correlates the experimentally measured transients and is consistent with all other observations relating to the copper electropolishing process.

Thermodynamics of Copper Electropolishing in Phosphoric Acid

not Available.

Roles of Additives in Damascene Copper Electropolishing

This study explores how the dissolution of damascene Cu depends on accelerators of organic acids in alcohol-containing electropolishing electrolytes. Four two-additive electrolytes that contain different accelerators, acetic, citric, citrazinic, and benzoic acids, are evaluated. At the bottom of damascene features, an esterification reaction between alcohols and organic acids efficiently forms a highly resistive layer and reduces the acidity of the solution. Accordingly, outside the damascene features, the rate of removal of Cu is dominated by the acidity of electrolytes but, inside the features, it is also determined by the resistance of the viscous layer. For a weak acidic additive, acetic acid, an extremely high additive concentration is introduced to sustain the moderate acidity of the solution to initiate intense esterification. Therefore, acetic-acid-based two-additive electrolytes exhibit excellent Cu planarization capability.

Electrochemical Characterization of Copper Electropolishing in Phosphoric Acid

not Available.

Water diffusion coefficients during copper electropolishing

Cu electropolishing was studied using a rotating disc electrode in a variety of phosphoric acid-based electrolytes, including several with ethanol and other species added as diluents. Diluents allow a wider range of water concentrations and electrolyte viscosities to be accessed and also reduce the removal rate during Cu electropolishing, simplifying possible application to damascene processing. Transient and steady state currents in the mass transfer limited regime are shown to depend on both the number of water acceptor molecules associated with each dissolving Cu ion and on the effective diffusion coefficient of water. Transient analysis samples the bulk transport properties, whereas steady state analysis integrates them through the diffusion layer. Assuming that the effective diffusion coefficients appropriate to transient and steady state behavior are the same, about one water molecule is associated with each dissolving Cu ion. This analysis yields effective diffusion coefficients for water on the order of 10−9cm2s−1. However, the data is also consistent with an assumption that six water molecules are associated with each dissolving Cu ion, but the effective diffusion coefficient appropriate for a Levich analysis is somewhat lower than that in the bulk electrolyte. This analysis yields effective diffusion coefficients for water on the order of 10−8–10−7cm2s−1. The latter interpretation, that six water molecules are associated with each dissolving Cu ion, appears more likely since it provides almost exact agreement with the effective diffusion coefficient reported previously by Vidal and West. In combination with previously published impedance results ruling out a salt film mechanism, the good agreement between the transient and steady state analyses confirm that water is the acceptor species that complexes dissolving Cu ions in phosphoric acid-based electropolishing baths.

Effects of applied voltages on planarization efficiency of Cu electropolishing

Copper electropolishing (Cu-EP) was recently investigated to be a next generation technology for planarizing damascene copper interconnections. In this study, effects of applied voltages on microscaled planarization efficiency (PE) of Cu-EP are discussed. It was found that the initial polishing rate and the formation time of a viscous layer were crucial for the PE of Cu-EP because only a thin copper film should be removed. A higher polishing rate outside of a feature and a more resistive diffusion layer covered inside of a feature resulted in a higher step-height reduction on a copper film.

Roles of copper mechanical characteristics in electropolishing

We investigated the effect of film stress, hardness, and grain size of copper films on copper electropolishing, which was considered as a next-generation technique in copper multilevel interconnects. The copper electropolishing rate was found to increase with an increase in the tensile stress of copper films. It was suggested that the tensile stress weakened metallic bonds between copper atoms and assisted the copper electropolishing rate, whereas the hardness and grain size of polished copper films did not relate directly to the copper electropolishing rate due to a negligible etching effect and no mechanical stress applied during copper electropolishing in a concentrated phosphoric acid electrolyte.

Copper Electropolishing in Concentrated Phosphoric Acid: II . Theoretical Interpretation

A theory for copper electropolishing in concentrated phosphoric acid is compared to ac‐impedance and electrohydrodynamic (EHD)‐impedance spectra. A water‐acceptor mechanism is hypothesized. Agreement between experiment and theory is good. Curve fits of the EHD‐impedance data estimate that the Schmidt number of the system is at room temperature. At temperatures near 90°C, . The plausibility of these high values of is discussed. These estimates of the Schmidt number are obtained without any assumptions about the bulk concentration of the acceptor. With a known viscosity and diffusion coefficient, the Levich analysis of the variation of the limiting current with rotation speed is subsequently used to estimate the bulk concentration of acceptor. The value obtained is in agreement with the known water content in phosphoric acid which indicates that water is the acceptor species.

Copper Electropolishing in Concentrated Phosphoric Acid: I . Experimental Findings

The electropolishing of rotating copper‐disk electrodes in concentrated phosphoric acid is studied by steady‐state measurements, ac‐impedance spectroscopy, and flow‐modulation spectroscopy. The effects of applied potential, rotation speed, and temperature on the response of the system are investigated at the mass‐transfer‐limited plateau. Both the Arrhenius behavior of the limiting current and the ac‐impedance data suggest that the rate of reaction is controlled by mass transfer of an acceptor to the copper surface and not by precipitation of a salt film. It is not possible to determine from steady‐state measurements the diffusion coefficient of the acceptor because its identity and bulk concentration are not known with certainty. Therefore, the steady‐state measurements are complemented with flow‐modulation spectra which allow an estimation of the diffusion coefficient of the acceptor without knowledge of its bulk concentration.