The adhesion between electrolessly deposited copper and a photoimageable polymer

We investigated the relationship between the peel adhesion of copper, deposited by electroless plating, to a photoimageable polymer and the time of chemical etching before plating. Mechanical interlocking is generally considered as being the adhesion mechanism between deposited metals and substrates. However, we found that the peel strength decreased with an increase in the etching time though the polymer roughness did not change. The glass transition temperature of the photoimageable polymer became lower as the etching time increased. The pretreatment not only roughened the surface of the photoimageable polymer, but also affected the bulk polymer and the adhesion.     

Aqueous pretreatments of polyetherimide to facilitate the bonding of electrolessly deposited copper

A chemical method for pretreating polyetherimide substrates to promote adhesion to copper is described. The process consists of cleaning the polymer surface followed by surface normalization, debris solubilization, and adhesion promotion via chemical modification of the polymer surface. Classes of candidates for each of the major steps are described and the optimal agents assembled into a recommended procedure. Peel strengths between 150-210 g mm^-1 for copper to polyetherimide were achieved utilizing the suggested scheme. Scanning electron microscopic and X-ray photoelectron spectroscopic analyses were employed to investigate changes in the polymer surface and chemistry during processing. Metallized specimens were examined after 90° peel testing and the failure locus found to be within the polymer layer.     

Surface modification of poly(tetrafluoroethylene) films by graft copolymerization for adhesion enhancement with electrolessly deposited copper

The surface modification of Ar plasma-pretreated poly(tetrafluoroethylene) (PTFE) films via UV-induced graft copolymerization with either 3-(trimethoxysilyl)propyl methacrylate (TM-SPMA) or glycidyl methacrylate (GMA) was carried out to enhance their adhesion to electrolessly deposited copper. The surface compositions of the PTFE films at various stages of surface modification and electroless plating were studied by X-ray photoelectron spectroscopy (XPS). The adhesion strength of the graft-copolymerized PTFE film to the electrolessly deposited copper was affected by the type of monomer used for graft copolymerization, the graft concentration, the plasma post-treatment time after graft copolymerization, and the extent of thermal post-treatment after metallization. The maximum T-peel strength achieved between the electrolessly deposited copper and the GMA graft-copolymerized PTFE film was about 11 N/cm. This adhesion strength represented a more than 20-fold increase over what could be achieved when the PTFE film was treated by Ar plasma alone. The mechanisms of the adhesion strength enhancement and the failure mode in the metal-polymer laminates were also investigated. It was found that the failure was cohesive in nature within the PTFE film.     

石英光纤表面镍-磷-硼化学镀层上电镀厚镍

采用瓦特电镀液在石英光纤表面Ni-B化学镀层上制备了厚镍镀层.考察了硫酸镍,十二烷基硫酸钠、电流密度以及氧化镧对镍沉积速率和镀层质量的影响,确定了其最适宜值分别为180 g/L、0.08 g/L、0.8 A/dm2和0.9 g/L.用扫描电镜、体视显微镜对镀层的表面形貌进行了表征和分析.结果表明,稀土氧化镧细化了晶粒尺寸、提高了镀层的致密程度和显微硬度.制得的样品厚度约为840 μm,显微硬度为334 HV,电阻率为21μΩ·cm,致密程度为96.4%,润湿时间为2 s.     

Influence of the interface width on the adhesion strength of copper films deposited on negatively biased carbon steel substrates

In order to improve the adhesion of copper films deposited by DC magnetron sputtering on carbon steel substrates, a negative bias voltage was applied to the substrate during the film deposition process. The scratch test was used to evaluate the adhesion strength of the films on the substrates. Chemical element identification and interface width measurement were carried out by Auger electron spectroscopy. The experimental results show that a variation of the bias voltage causes a change in the behaviour of the interface width similar to that of the critical load. The size of the interface width is obtained from Auger elemental depth profiles by measuring the depth of the interface between the coating and the substrate. It had a value of 45 min for an unbiased substrate and increased to 310 min at a bias of 450 V. In the latter case, the interface is relatively wide and the effects of diffusion and physical mixing of materials at the interface become preponderant. Then, the interface width decreased to 130 min at 600 V in which case it gets narrower and the phenomenon of film densification becomes prominent. In all cases, the substrate temperature generated by the bias voltage also has an effect. Moreover, it was observed in this study that the critical load increases with the size of the interface width. As a result, the application of a bias voltage contributes positively to the enlargement of the interface and consequently enhances the adhesion strength.     

Electroless copper on refractory and noble metal substrates with an ultra-thin plasma-assisted atomic layer deposited palladium layer

Electroless Cu was investigated on refractory metal, W and TaN_X, and Ir noble metal substrates with a plasma-assisted atomic layer deposited palladium layer for the potential back-end-of-the-line (BEOL) metallization of advanced integrated devices. The sodium and potassium-free Cu electroless bath consisted of: ethylenediamine tetraacetic acid (EDTA) as a chelating agent, glyoxylic acid as a reducing agent, and additional chemicals such as polyethylene glycol, 2,2′-dipyridine and RE-610 as surfactant, stabilizer and wetting agent respectively. The growth and chemical characterization of the Cu films was carried out with a field emission scanning electron microscope (FE-SEM), X-ray photoelectron spectroscopy (XPS), and Rutherford backscattering spectrometry (RBS). Group VIII metals such as Pt, Pd, etc., are stable in the electroless bath and catalytic towards the oxidation of glyoxylic acid and therefore work well for the electroless deposition of Cu. From RBS analysis, the amount of carbon and oxygen in Cu films were less than 1-3%. The Cu films were electroless deposited at 45-50 °C on patterned tantalum nitride with plasma-assisted atomic layer deposited (PA-ALD) Pd as a catalytic layer. Electroless Cu trench fill was successful with ultrasonic vibration, RE-610, and lowering the temperature to 45-50 °C on TaN_X with the PA-ALD Pd catalytic layer.     

Activation of Ag/Pd triangular nanoshells with different sizes on depositing electrolessly copper

Ag/Pd triangular nanoshells of different sizes are prepared for catalyzing electroless copper deposition. As supported by the analysis of quartz crystal microbalance and mixed potential theory, the alloy nanoshells can be successfully used as new activators and have the excellent activity for electroless copper bath. For a comparison of deposition rates with a system of triangular Ag/Pd nanoshells, the large Ag/Pd nanoshell is found to have the maximum activity toward electroless bath.     

First stages of the formation of copper electrodeposits and copper sputtered deposits on amorphous carbon and polycrystalline silver substrates

The first stages of the development of copper deposits on amorphous carbon and polycrystalline silver substrates are compared when the deposits are produced by electrodeposition under galvanostatic conditions and by high rate magnetron-enhanced sputtering. It is shown that the first stages of the formation of the metallic deposits are influenced by the deposition rate, the substrate-to-deposit interaction and by the deposition technique. These factors have a particular influence on the growth mode and on the nucleation stage of the deposit. When an island growth mode is observed, an increase of the deposition rate induces thinner covering films because the island density is higher and the islands are smaller for a given quantity of deposited matter. In electrodeposition, an island growth mode is observed on the two types of substrate, but for equivalent experimental conditions the superficial cluster density is higher on silver than on carbon substrates. Dissolution of some copper clusters occurs a short time after the onset of electrolysis. This can be explained by local changes of the supersaturation due to a current microdistribution at the cathode surface. In magnetron-enhanced sputtering, an island growth mode is observed on amorphous carbon substrates, while a layer-by-layer growth mode is detected on polycrystalline silver substrates. On silver substrates two different growth modes are thus observed depending on the deposition technique. In contrast, on carbon substrates, where an island growth mode is observed in both cases, the copper cluster superficial density is a factor 10⁶ to 10⁸ higher in sputtering than in electrodeposition for the same deposition rate. This paper shows that these differences can only be explained by physical and chemical mechanisms specific to each deposition technique taking place during the condensation process.     

Electrochemically deposited gallium oxide nanostructures on silicon substrates

We report a synthesis of β-Ga₂O₃ nanostructures on Si substrate by electrochemical deposition using a mixture of Ga₂O₃, HCl, NH₄OH, and H₂O. The presence of Ga³⁺ ions contributed to the deposition of Ga₂O₃ nanostructures on the Si surface with the assistance of applied potentials. The morphologies of the grown structures strongly depended on the molarity of Ga₂O₃ and pH level of electrolyte. β-Ga₂O₃ nanodot-like structures were grown on Si substrate at a condition with low molarity of Ga₂O₃. However, Ga₂O₃ nanodot structures covered with nanorods on top of their surfaces were obtained at higher molarity, and the densities of nanorods seem to increase with the decrease of pH level. High concentration of Ga³⁺ and OH^- ions may promote the reaction of each other to produce Ga₂O₃ nanorods in the electrolyte. Such similar nature of Ga₂O₃ nanorods was also obtained by using hydrothermal process. The grown structures seem to be interesting for application in electronic and optoelectronic devices as well as to be used as a seed structure for subsequent chemical synthesis of GaN by thermal transformation method.     

Development and thermal durability of an interfacial bond between electrolessly deposited metals and a fluorinated polyimide

The oxygen content of a fluorinated polyimide surface can be increased by exposure to an oxidant such as an alkaline permanganate solution. Deposition of an electroless metal layer on this oxidized surface results in the formation of an interfacial bond which is predominantly chemical in nature. The level of adhesion achieved depends both on the surface oxidation conditions and post-plating heating. Adhesion maxima are obtained by heating to 200°C for an electroless Cu deposit and to 300°C, the cure temperature for the polyimide film, for deposited electroless Ni. The fluorinated polyimide used in this study was derived from the reaction of 2,2-bis(4-(4-aminophenoxy)phenyl)hexafluoropropane with pyromellitic dianhydride and was obtained from Ethyl Corporation as Eymyd® L30N resin.     

New developments in corrosion and blister formation in coatings

Many polymers take up more water at equilibrium at higher temperatures than they do at lower temperatures. Water exposure with cycling temperatures can lead to excess free water when films saturated with water at a higher temperature are quenched or rapidly cooled. This mechanism has been called microfogging with soluble water exuded at lowered temperatures (SWEAT) being the undesired result. The water freed by this process can cause microcavities, blisters, and even total delamination. Means to counteract these failures include increasing permeation coefficients using micaceous iron oxide or other void-containing filler, for example. The intended incorporation of microvoids (microsponges) also allows the SWEAT water to collect in the coating without causing excess damage. A polymeric binder which dissolves the same amount of water at all temperatures would eliminate this effect at its source.     

Synthesis and characterization of poly-(allylbenzene p-sulphonate) films incorporating electrolessly deposited Ni–P

The preparation of a novel electrode material is described. The ionic exchange properties of polymer films electrochemically prepared from the allyl ether of the p-benzenessulphonic acid monomer were explored with an incorporated ion of metallic crystallites in the polymeric matrix. The autocatalytic activity of the pristine and modified polymer for the electroless deposition of Ni–P from a hypophosphite containing solution was analyzed and conditions for the use of the deposition method to modify the nature and the size of the metal particles established. The performance of typical electrodes prepared by this route, e.g., polymer/Cu/Ni–P, towards the proton reduction reaction in buffer solution, when contrasted to polymer/Ni, revealed promising electrocatalytic activity. This behaviour, along with the simplicity of the preparation route makes these modified electrodes strong candidates to replace other systems for electrohydrogenation purposes.     

Fretting wear of thin diamond films deposited on steel substrates

The dominant wear mechanism of thin diamond films deposited onto steel substrates and the effect of film thickness on their lifetime under fretting conditions were studied by analyzing the running-in and the main period of the coatings wear life. Steel plate and steel ball specimens for the present study were both coated with diamond by chemical vapor deposition (CVD). The wear tracks resulting from the fretting tests were investigated by various surface analysis methods. The results showed that the dominant wear mechanism of the diamond coatings, when both surfaces are coated, is an abrasive form of fretting wear. Under these conditions, the lifetime of the diamond films increased with increasing film thickness. It was found that the wear rate during the main period is independent on the initial thickness of the diamond film and therefore its life depends on the residual thickness at the end of the running-in period.     

Resistance of magnesite refractories to smelting products of blister copper

Conclusions An improved method of assessing the results and testing refractories for slag resistance was described.It was established that the most resistant materials to the action of converter slags are periclase-spinel refractories.Magnesia articles are destroyed at the bond owing to the passage of thin periclase constituent into the fusible magnesia-iron silicates.To reduce the rate of wear and increase the resistance of refractories in these melting conditions for blister copper, it is necessary in the production of magnesia articles to use magnesite and chromite ore with a minimum content of SiO₂ and iron oxides.     

A comparative study of three adhesion tests (EN 582, similar to ASTM C633, LASAT (LASer Adhesion Test), and bulge and blister test) performed on plasma sprayed copper deposited on aluminium 2017 substrates

The aim of this study was to compare three adhesion tests carried out on plasma-sprayed copper coatings on aluminium substrates. The first test, the bond pull test, designated EN 582 or ASTM C633, involves a uniaxial static stress and is commonly used in the coating industry. The second test, the LASAT (LASer Adhesion Test), is a recently developed technique based on spallation phenomenon due to laser induced shock waves. In this test, the coating delamination results from spallation at the coating/substrate interface due to uniaxial tensile stress. The last test, the bulge and blister test, involves a quasi-static measurement of the crack propagation energy at the coating/substrate interface. These three techniques have been used to evaluate the influences of different process parameters involved in the coating adhesion such as aluminium surface roughness, substrate pre-heating and plasma spray conditions.     

Diamond deposition on copper treated hardmetal substrates

The adhesion of diamond coatings onto hardmetal substrates is improved by a copper deposition produced by a cementation from aqueous CuSO₄ solutions. During this reaction Co is dissolved from the substrate surface and copper is deposited. To obtain homogeneous Cu deposits, the influence of CuSO₄ concentration and reaction time on cementation were investigated.During diamond deposition, Cu reduces the surface mobility of Co, which is necessary to decrease deposition of non-diamond carbon and therefore increase adhesion. Indentation tests showed the good adhesion of the diamond coatings qualitatively.Cu precipitation and diamond deposition were examined by scanning electron microscopy (SEM). The diamond quality was detected by Raman spectroscopy. Using secondary ion mass spectroscopy (SIMS) depth profiles the interface and the Cu distribution were characterized indicating that during diamond deposition Cu is dissolved and forms an intermetallic Co–Cu mixed crystal.     

Aqueous pretreatment of polyetherimide to facilitate the bonding of electrolessly deposited metals. Part 2. Solubilizer-free systems

An aqueous method for chemically pretreating polyetherimide substrates to promote adhesion to electrolessly deposited copper or nickel is described. The process consists of cleaning the polymer surface followed by surface normalization and debris removal. In contrast to previously developed processes, no separate adhesion promotion step is required. Peel strengths between 150-250 and 120-150 g/mm were achieved for copper and nickel, respectively. Scanning electron microscopy and X-ray photoelectron spectroscopy were utilized to investigate changes in the polymer surface morphology and chemistry during processing. Possible candidates for the different steps are presented, as are analyses of the failure loci following peel strength assessment.     

Effect of benzotriazole (BTA) addition on Polypyrrole film formation on copper and its corrosion protection

Benzotriazole (BTA) was added in a conducting Polypyrrole (PPy) film prepared on copper in oxalic acid aqueous solution containing pyrrole monomer to improve corrosion protection by the PPy film and reduce copper corrosion. When BTA was added in the preparation solution, the copper surface was covered by a BTA–Cu complex layer before the anodic polymerization of PPy was started. On the copper surface with the BTA layer, the initial dissolution of copper was inhibited and the PPy polymerization-deposition was started immediately after the anodic current was imposed. The PPy film thus formed was doped with oxalic ions and ionized BTA and was homogeneous in thickness and strongly adhesive. The PPy film containing BTA protected the copper from corrosion in 3.5 wt.% NaCl solution. In 400 h of immersion, copper dissolution was inhibited with 80% protection efficiency relative to that of bare copper.     

Reduction of hexavalent chromium by polypyrrole deposited on different carbon substrates

Pollution due to toxic hexavalent chromium has reached dangerous levels in some parts of the world, especially in Third World countries. This work focuses on the reduction of Cr(vi) ions in aqueous media by polypyrrole deposits on porous, high area three-dimensional carbon electrodes. Since many properties of deposited polymers are known to depend on the method of synthesis we performed the electropolymerization of pyrrole either at varying potential scan rates or at constant potential on different high area carbon materials. The deposits thus obtained were then put in contact with acidic hexavalent chromium solutions; high reduction yields were obtained (up to 80%). In addition, the possibility of repeating this cycle was studied as well as the wear resistance of these deposits. Finally, the morphology of the deposits was monitored at different stages of the process by scanning electron microscopy.     

Oriented overgrowth of vapour deposited tin on highly oriented PTFE substrates

The vapour deposition of tin on highly uniaxially oriented PTFE causes an oriented overgrowth of tin islands. The origin of this orientation is not clear. Classic epitaxy as well as graphoepitaxy seems to be an explanation for the occurring orientation. The appearance of this orientation was observed in a temperature range from −80 °C to 90 °C. An orientation by crystallization from the melt could not be achieved so far. In this short communication, a metal/polymer system is introduced which offers new possibilities to investigate the origin of oriented overgrowth. Received: 19 September 1997/Revised version: 30 October 1997/Accepted: 31 October 1997