Copper Plating Bath Research Articles

Influence of bath composition and pH on the electrocodeposition of alumina nanoparticles and copper

The electrocodeposition of alumina particles (primary particle size 13 nm) in a copper matrix was investigated. Three copper plating baths covering a wide pH range were used: an acidic copper sulphate, a neutral pyrophosphate, and an alkaline sorbitol based bath. The highest amount of incorporated particles (ca. 11 wt.% alumina) was found for the pyrophosphate bath. From zeta potential measurements in diluted solutions we concluded that the particles are charged negatively in this electrolyte. A tentative electrostatic model is proposed to explain qualitatively the relation between the surface charge of the particles and the amount of incorporated particles. Furthermore, the microstructure, microhardness and electric conductivity of the layers were characterized.

New and clean strategy for the determination of Cu 2+ in electroless copper plating baths

This article concerns a new and clean strategy for the determination of Cu 2+ in electroless copper plating baths with differential spectrophotometry. With this strategy, the problem of too high absorbance of Cu 2+ under plating conditions has been solved. We investigated the influence of copper sulfate, sodium hypophosphite, nickel sulfate, sodium citrate, polyglycol, temperature and pH on the absorption spectrum of Cu 2+ in electroless copper plating baths. Five grams per litre of CuSO 4·5H 2O solution was selected as the reference solution. Experimental results prove that, this strategy has the merits of fast and high accuracy compared to the traditional techniques. Linearly dependent coefficient of the working curve is 0.9999 and the components in the formula have no obvious effect on the detection of Cu 2+ under experimental conditions. Therefore, we can directly move solutions from the EC plating baths for detection, after that the sample can still go back to the baths without any pollution from the plating process to the environment.

Influence of the Anode and the Accelerator on Copper Bath Aging in the Damascene Process

Electrochemical impedance spectroscopy and cyclic voltammetry were used to characterize the aging of copper plating baths used in damascene process for superfilling of trenches and vias in the semiconductor industry. The effects of copper anode composition, anodic current density, and accelerator nature and concentration were studied. Phosphorus added to copper anodes has a prominent impact on the evolution of current/voltage curves and impedance spectra during bath aging. The observed evolutions were explained by the formation of a -accelerator complex in the bulk of the bath that adsorbs at the copper surface to act as an accelerating species, and by the increase of its concentration during aging with undoped copper anode. The -accelerator complex formation is limited by the phosphorus contained in the Cu-P anode, which traps electrogenerated cuprous ions in the black anodic film. Differences observed between baths containing SPS (bis(3-sulfopropyl)disulfide) or MPSA[(3-mercaptopropane)sulfonic acid] are also attributed to the existence of two different -accelerator complexes, both of which exhibit different formation equilibrium constants.

Performance evaluation of acid copper plating films for via filling

The acid copper plating process has been extensively applied in the formation of high density interconnections in build-up printed circuit boards (PCBs). However, deposited films obtained by acid copper plating are greatly affected by additives, and sometimes physical properties are weakened in codeposition with additives present in the deposited films. In order to avoid such a breakdown, the authors evaluated the physical properties of the copper films plated in two types of conformal acid copper plating baths that have been in use for general application and two types of acid copper plating baths for via filling. Proper selection of additives was considered to be of great importance for the acid copper plating baths for via filling. The use of additives that easily codeposit with copper was likely to cause the reduction in physical properties of the film. On the other hand, it was confirmed that a copper film with excellent physical properties can be obtained from the conformal type acid copper plating baths by selection of a suitable additive.

Applications of Metal Surface Modification in Microdevice Fabrication

EFAB{trade mark, serif} is a multilayer electrochemical microfabrication technology for the manufacture of truly 3-demensional (3-D) metal microdevices. Metal surface modification techniques can be applied to not only the EFAB process but also EFAB products. This paper first briefly introduces the applications of surface modification techniques in EFAB and then reports and discusses a surface treatment method for extending the use life of copper instant-masks (Cu-IM) used for instant-mask plating in EFAB. In this surface treatment process a copper substrate is immersed in a benzotriazole (BTA) solution to form a protective film on the copper substrate prior to the application of a patterned insulator layer. This protective film increases the delamination resistance of insulator layers on Cu-IMs in copper plating baths. Therefore the use life of Cu-IMs can be extended.

Involvement of a metastable surface state in the electrocatalytic, electrodeposition and bath additive behaviour of copper in acid solution

Copper in aqueous sulphuric acid solution at room temperature displays a low level active (metastable) surface state redox transition well within the double layer region, at ca. −0.7±0.1 V (SMSE). The latter is an important feature of this electrode system as it apparently coincides with (a) the transition from activation to transport control in acid sulphate copper plating baths, (b) a major change in the inhibiting properties of several plating bath additives, and (c) the onset/termination potential of electrocatalytic processes, e.g. nitrate reduction, at copper in acid. The nature and influence of this active surface state behaviour, which is assumed to be relevant to Damascene copper plating, is discussed.

Monitoring of Additives in Copper Plating Bath by Cyclic Voltammetric Stripping with a Microelectrode

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The Importance of Defect (MMS) Surface States in Additive Effects in Damascence Copper Plating Baths

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Detection of Organic Electroactive Species in Acidic Copper Plating Baths by HPLC with an Electrochemical Detector

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Practical Monitoring of Filling Performance in a Copper Plating Bath

A method for monitoring the filling performance of a copper plating solution for microvia metallization was examined by a continuous operation in a pilot plating bath. The monitoring method was carried out using a simple galvanostat measurement. A potential difference between two polarization curves obtained from the galvanostatic measurements at different flow rates can serve as an effective indicator of filling performance, because a linear function can correlate the potential difference with the filling performance. The shift of the polarization curve of the working solution after a period of operation can be regarded as the occasion of accumulation of by-products.

Fabrication of patterned polypyrrole on fluoropolymers for pH sensing applications

Patterns of polypyrrole (PPy) have been fabricated on flexible poly(tetrafluoroethylene) (PTFE) films using a combination of micro-contact printing, electroless deposition of copper and electropolymerisation of pyrrole. A patterned elastomeric stamp was used to deliver a nitrogen-containing silane coupling agent to an argon plasma-pretreated PTFE surface. The surface was subsequently activated by PdCl 2 and immersed in an electroless copper plating bath allowing selective metallisation. Electropolymerisation of pyrrole was performed on copper-patterned PTFE resulting in the formation of micrometer-scale PPy structures. Each modification and deposition step was characterised by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS). Potentiometric measurements have demonstrated that PPy-patterned PTFE has potential application as a pH sensor. The response times of the sensors have also been investigated. This study offers an interesting alternative to conventional polymer-based pH sensors in terms of production and mechanical support.

SPE-HPLC Detection of Organic Additives in Acidic Copper Plating Baths : I. Sulfopropyl Disulfide-Based Brighteners

A technique has been developed for the study of reaction mechanism and the monitoring of copper electroplating baths utilizing a combination of solid phase extraction (SPE) and high-performance liquid chromatography (HPLC). This method appears suitable for live plating bath control as well as for organic identification, concentration measurement, and reaction mechanism studies. While in the past the total amount of carbon (TOC) present in the deposition bath was used to quantify the decomposition of organics and to determine the plating bath quality, a strong correlation between the TOC measurement and effective plating bath composition was not possible. Moreover, a direct way to thoroughly analyze the organic components of the bath is not commonly available using current electrochemical techniques. However, the results from experiments conducted with the technique described in this paper show how the monitoring of a few diagnostic peaks recovered from a live bath sample can be used directly for this purpose. The identification and quantification of by-products is also proven. Two copper sulfuric plating baths at different acidity were used for this study, and the stability of bis(sodiumsulfopropyl) disulfide and polyethylene glycol additive components, as well as their degradation mechanism and by-products, are studied in this work.

Ion-pair chromatography of bis (sodium-sulfopropyl) disulfide brightener in acidic copper plating baths

Quantitative analysis of the brightener component bis (sodium-sulfopropyl) disulfide (SPS) in acidic copper plating baths poses a real challenge due to the complex chemical matrix containing large amounts of Cu(II) ion and sulfuric acid together with other organic additives and additive decomposition products. We developed a new ion-pair chromatography method to analyze micro-molar amounts of SPS directly in plating bath samples without the need for sample pre-treatment. Addition of tetra- N-methylammonium cation as ion-pairing agent to a methanol–sulfuric acid–water eluent increases the retention time of the anionic SPS 2− on a C 18 column sufficiently to separate this compound from Cu(II) ion and additive by-products.

The chemistry of additives in damascene copper plating

Copper plating baths used for forming integrated circuit interconnects typically contain three or four component additive mixtures which facilitate the superfilling of via holes and trench lines during damascene plating. Extensive study over the last two decades has provided researchers with an understanding of the underlying mechanisms. The role of cuprous intermediates in the copper deposition reaction has long been acknowledged, but it is not yet fully understood. In this paper we describe the results of an electrochemical study of the interaction of the organic additives used with copper and copper ions in solution. It is shown that cuprous intermediates near the copper surface affect the overpotential and the kinetics of plating. The additives regulate the presence of cuprous species on the surface; levelers and suppressors inhibit Cu <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> formation, whereas accelerating additives enhance Cu <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> formation. Acceleration by the bis(sodiumsulfopropyl) disulfide (SPS) additive results from accumulation of cuprous complexes near the surface. Adsorbed cuprous thiolate [Cu(I)(S(CH <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> ) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> SO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> H) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ad</inf> ] is formed through interaction of Cu <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> ions and SPS rather than Cu <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> and mercaptopropane sulfonic acid (MPS).

Environmentally friendly natural polyhydroxylic compounds in electroless copper plating baths: application of xylitol, D-mannitol and D-sorbitol as copper(II) ligands

The possibility of using xylitol, D-mannitol and D-sorbitol as Cu(II) ligands in electroless copper baths was demonstrated. The ligands mentioned showed good chelating properties for Cu(II) ions in alkaline media (pH > 11.5), i.e. under conditions of the use of traditional formaldehyde-containing solutions. Electroless copper plating solutions containing the chelators xylitol, D-mannitol and D-sorbitol are stable and, under the optimal conditions selected, copper coatings up to 3 μm thick can be obtained in 1 h at ambient temperatures.

Various carbon nanofiber–copper composite films prepared by electrodeposition

Carbon nanofiber–copper composite films with different types of nanofibers were fabricated by an electrodeposition process. Four types of carbon nanofibers, vapor-grown carbon nanofibers without heat treatment, vapor-grown carbon nanofibers with heat treatment, vapor-grown carbon nanofibers with smaller diameters, and vapor-grown carbon nanofibers with a cup-stacked nanostructure were used. The carbon nanofibers were homogeneously dispersed in sulfate copper plating baths in the presence of polyacrylic acid. Electrodeposition was carried out under galvanostatic conditions using these copper plating baths. The deposition resulted in electrodeposited copper films containing the carbon nanofibers distributed homogeneously. The surface morphology of the carbon nanofiber–copper composite films was observed to be affected by the type of carbon nanofiber used.

Microcontact printing of copper and polypyrrole on fluoropolymers

This paper describes the use of microcontact printing (μCP) to form micrometer-scale patterns of copper on poly(tetrafluoroethylene) (PTFE), and illustrates the use of these patterned surfaces as substrates for electrodeposition of polypyrrole (PPy) sensor structures. A patterned elastomeric stamp was used to deliver a nitrogen-containing silane coupling agent to the argon plasma-pretreated PTFE surface. The surface was subsequently activated by PdCl 2, allowing the selective activation via the formation of Pd–N complex. Patterning of copper structures with feature sizes of 50–200 μm was achieved by immersing the activated surface into an electroless copper plating bath. Surface chemistry was investigated after each surface modification and deposition step using X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS). This study demonstrates a soft lithography approach for the fabrication of patterned copper and PPy structures on flexible PTFE films, offering new opportunities for the creation of polymer-based electronic devices and sensor arrays.

Characterising nonuniform electrodeposition and electrodissolution using the novel wire beam electrode method

An electrochemically integrated multi-electrode system namely the wire beam electrode (WBE) has been applied as a new method of characterising nonuniform electrodeposition and electrodissolution, by measuring and identifying characteristic patterns in electrodeposition and electrodissolution current distribution maps. Various patterns of electrodeposition current distribution have been obtained from Watts nickel plating and bright acid copper plating baths with the effects of several affecting factors such as bath concentration, temperature, agitation and electrolyte flow. Typical patterns of electrodissolution current distribution have also been detected over a WBE surface under anodic dissolution. This work suggests that the WBE method can be used as a new tool for monitoring, characterising and optimising electrodeposition and electrodissolution processes in the laboratory, and can also be applied as an experimental method to verify the accuracy and completeness of mathematical models for electrodeposition and electrodissolution.

Selective electroless copper deposition on aluminum nitride substrate with patterned copper seed layer

A novel process is presented for the formation of well-defined and fine copper pattern with reliable bonding onto a smooth aluminum nitride substrate by selective electroless deposition of copper in fully additive-based manner without any costly instruments and materials. The process relies on patterning CuO overlayer by photolithographic method and reducing CuO to metallic copper followed by immersing in electroless copper plating bath. The CuO overlayer is composed of the corresponding nanosized particles that allow us to etch them smoothly and selectively. The patterned metallic copper overlayer having chemical interaction with the substrate can act as seeds for initiation of electroless deposition. The minimum width of copper pattern obtained was 25 μm.

The behavior of organic components in copper recovery from electroless plating bath effluents using 3D electrode systems

An electrochemical method was applied for the recovery of copper both from the spent solutions and from the rinse waters of electroless copper plating baths, containing copper sulfate, formaldehyde, quadrol, and NaOH. Experiments were conducted in a rotating packed cell (Rollschichtzelle ®) to investigate the effects of current density, electrolyte composition, temperature, and pH on the copper recovery. All the copper (final C Cu = 0.1 ppm) was recovered from the waste and rinse waters of chemical copper plating plants with 70% current efficiency by the electrochemical treatment in a rotating packed cell at 130 A/m 2 current density, room temperature, with 5 mm diameter cathode granules, with the presence of formaldehyde, and with a specific energy consumption of 3.2–3.5 kW h/kg Cu. On the other hand, final copper concentrations of 5 ppm were reached with 62% current efficiency and 5.5–5.8 kW h/kg Cu specific energy consumption, with electrolytes containing no formaldehyde.