Showing papers on "Electroplating published in 2006"

Ag/AgCl microelectrodes with improved stability for microfluidics

Abstract: A method for fabricating Ag/AgCl planar microelectrodes for microfluidic applications is presented. Micro-reference electrodes enable accurate potentiometric measurements with miniaturized chemical sensors, but such electrodes often exhibit very limited lifetimes. Our goal is to construct Ag/AgCl microelectrodes reliably with improved potential stability that are compatible with surface mounted microfluidic channels. Electrodes with geometric surface areas greater than or equal to 100 m 2 were fabricated individually and in an array format by electroplating silver, greater than 1 m thickness, onto photolithographically patterned thin-film metal electrodes. The surface of the electroplated silver was chemically oxidized to silver chloride to form Ag/AgCl micro-reference electrodes. Characterization results showed that Ag/AgCl microelectrodes produced by this fabrication method exhibit increased stability compared with many devices previously reported. Electrochemical impedance spectroscopy allowed device specific parameters to be extracted from an equivalent circuit model, and these parameters were used to describe the performance of the microelectrodes in a microfluidic channel. Thus, stable Ag/AgCl microelectrodes, fabricated with a combination of photolithographic techniques and electroplating, were demonstrated to have utility for electrochemical analysis within microfluidic systems. Published by Elsevier B.V.

Atomic Layer Deposition of Ultrathin Copper Metal Films from a Liquid Copper(I) Amidinate Precursor

Abstract: We report a method for producing thin, completely continuous and highly conductive copper films conformally inside very narrow holes with aspect ratios over 35:1 by atomic layer deposition (ALD). Pure copper thin films were grown from a novel copper(I) amidinate precursor, copper(I) N,N'-di-sec-butylacetamidinate, and molecular hydrogen gas as the reducing agent. This copper precursor is a liquid during vaporization because its melting point (77°C) is lower than its vaporization temperature (90-120°C). Thus, the transport of the precursor vapor is very reproducible and controllable. Carbon and oxygen impurities were below 1 atom %. The growth per cycle varied from 1.5-2 A/cycle on SiO 2 or Si 3 N 4 surfaces but was only 0.1-0.5 A/cycle on metallic Ru, Cu, and Co surfaces. On oxide surfaces, copper atoms form isolated copper crystallites that merge into rough polycrystalline films after more deposition cycles. On Ru and Co metal surfaces ALD Cu nucleates densely, forming smooth and strongly adherent films that are continuous even for films as thin as 4 atomic layers. With 4 nm Cu deposited on 2 nm Ru substrates, the sheet resistance is below 50 Ω/□, which is low enough for making seed layers for electroplating Cu interconnect wires.

High corrosion-resistance nanocrystalline Ni coating on AZ91D magnesium alloy

Abstract: Nanocrystalline (nc) Ni coating was direct-current electrodeposited on the AZ91D magnesium alloy substrate aimed to improve its corrosion resistance using a direct electroless plating of nickel as the protective layer. As comparison, two electroless Ni coatings on the magnesium alloy with different thickness were also presented in the paper. The surface morphologies of the coatings were studied by SEM and FESEM. The nc Ni coating had an average grain size of about 40 nm and an evident {200} preferred texture revealed by XRD. The hardness of the nc Ni coating was about 580 VHN, which was far higher than that (about 100 VHN) of the AZ91D magnesium alloy substrate. The electrochemical measurements showed that the nc Ni coating on the magnesium alloy had the lowest corrosion current density and most positive corrosion potential among the studied coatings on the magnesium alloy. Furthermore, the nc Ni coating on the AZ91D magnesium alloy exhibited very high corrosion resistance in the rapid corrosion test illustrated in the paper. The reasons for an increase in the corrosion resistance of the nc Ni coating on the magnesium alloy should be attributable to its fine grain structure and the low porosity in the coating.

Electroplating of mild steel by aluminium in a first generation ionic liquid: A green alternative to commercial Al-plating in organic solvents

Abstract: In this paper we report on the electroplating of mild steel by aluminium in a first generation ionic liquid [EMIm]Cl/AlCl3 (40/60 mol.-%). The study was performed by means of cyclic voltammetry and galvanostatic polarization complemented by SEM/EDAX and optical microscopy. The results show that the pretreatment of the substrates plays a key role in the coating adhesion. The aluminium coating made on a conventionally pretreated mild steel substrate is of high quality but it does not exhibit good adherence to the substrate. However, we have found that an in situ electrochemical etching of the substrate by anodic polarization prior to electrodeposition leads to well adherent Al coatings of mild steel which resist even mechanical scratching. This is due to dissolution of the pre-formed iron oxide layer and the subsequent re-deposition of iron or Fe–Al alloy formation prior to Al bulk deposition resulting in excellent adhesion. It is also shown that with the electrochemical pretreatment in the ionic liquid not only steel sheets but also complex shapes like e.g. screws can be coated with well adherent aluminium.

Aspect-Ratio-Dependent Copper Electrodeposition Technique for Very High Aspect-Ratio Through-Hole Plating

Abstract: Copper electrodeposition in high-aspect-ratio through-holes micromachined by deep reactive ion etching is one of the most essential processes for fabricating through-wafer interconnects, which will be used in developing future generation high-speed, compact 3D microelectronic devices. Although copper electrodeposition is a well-established process, completely void-free electroplating in very deep and narrow through-holes remains a challenge, where local current distribution does not remain uniform, resulting in void formation in the via. In this paper, we report the fabrication of very high aspect ratio through-wafer copper interconnects by an innovative copper electroplating technique. Completely void-free electroplating in very deep (∼500 μm) and narrow through-holes was accomplished by a proposed "aspect-ratio-dependent electroplating technique." In this technique, electroplating parameters were continuously varied along with changing unfilled via depth. Continuously varying current density improves the local distribution of current as per the changing depth and helps in minimizing void formation. The hydrophilic nature of the via surface was also enhanced by wet surface treatment to improve the interaction between the copper electrolyte and via surface. Very fine pitch (∼80 μm), through-wafer copper interconnects having an aspect ratio as high as 15 were fabricated by the above innovative technique.

The development of Cu bonding wire with oxidation-resistant metal coating

Abstract: Although Cu bonding wire excels over Au bonding wire in some respects such as production costs, it has not been widely used because of its poor bondability at second bonds due to surface oxidation. We conceived an idea of electroplating oxidation-resistant metal on the Cu bonding wire to prevent the surface oxidation. The electroplating of Au, Ag, Pd, and Ni over Cu bonding wire all increased bond strengths as expected, but it caused problematic ball shapes except Pd-plated Cu bonding wire. The wire could produce the same ball shape as that of Au bonding wire. It was also proved to have excellent bondability sufficient to replace Au bonding wire. That is, it excelled in bond strengths, defective bonding ratio, and wideness of "Parameter Windows". It also showed the same stability as Au bonding wire in reliability tests, while bonds of Cu bonding wire were deteriorated in a few of the tests. In short, the Pd-plated Cu bonding wire can realize excellent bonding similar to Au bonding wire, while having much lower production costs.

Photovoltaic contact and wiring formation

Abstract: A method and apparatus for fabricating a solar cell and forming metal contact is disclosed. Solar cell contact and wiring is formed by depositing a thin film stack of a first metal material and a second metal material as an initiation layer or seed layer for depositing a bulk metal layer in conjunction with additional sheet processing, photolithography, etching, cleaning, and annealing processes. In one embodiment, the thin film stack for forming metal silicide with reduced contact resistance over the sheet is deposited by sputtering or physical vapor deposition. In another embodiment, the bulk metal layer for forming metal lines and wiring is deposited by sputtering or physical vapor deposition. In an alternative embodiment, electroplating or electroless deposition is used to deposit the bulk metal layer.

Electroplating preparation of Ni–Al2O3 graded composite coatings using a rotating cathode

Abstract: In order to develop a new technique for fabricating Ni–Al2O3 graded coatings, a polyhedron cathode was used, which is composed of eight pieces of copper foil fixed on the side faces of a regular octagonal nylon prism. The stirring rate was 350 rpm. For pure nickel deposition, the coating thickness difference between different side faces is increased when the electrolyte is stirred. The particle concentration has no evident effect on the coating thickness, but affects the particle content in different coatings. The largest difference of particle contents appears while the Al2O3 particle concentration of the electrolyte is 80 g/L. Based on these results, the graded composite coating was fabricated through rotating the cathode.

Thin, Continuous, and Conformal Copper Films by Reduction of Atomic Layer Deposited Copper Nitride†

Abstract: Thin and continuous copper films serve as seed layers for electrodeposition of interconnects in microelectronic devices. Gaps in the continuity of these Cu films must be avoided, because they can generate voids that later lead to failure of the devices. It is difficult to sputter completely continuous copper-seed layers into the increasingly narrow trenches and holes in modern interconnects. Here we report a method for producing thin, completely continuous, and highly conductive copper films conformally inside very narrow holes with aspect ratios of over 40:1. The first step in our process is atomic layer deposition (ALD) of copper(I) nitride, Cu3N, by the alternating reactions of copper(I) N,N′-di-sec-butylacetamidinate vapor and ammonia on surfaces heated to approximately 160 °C. At this temperature, Cu3N is thermally stable, but is readily reduced to copper metal by exposure to molecular hydrogen gas (H2). Copper layers as thin as 0.8 nm (about 3 monolayers) are electrically continuous and show the electrical resistivity predicted by a grain-boundary-scattering model for continuous films of that thickness. 3 nm thick copper films on 2 nm of ruthenium have a sheet resistance of less than 50 Ω/□, a value low enough to serve as seed layers for advanced electroplating techniques.

Method of metallizing a solar cell substrate

Abstract: Embodiments of the invention contemplate the formation of a low cost solar cell using a novel high speed electroplating method and apparatus to form a metal contact structure having selectively formed metal lines using an electrochemical plating process. The apparatus and methods described herein remove the need to perform one or more high temperature screen printing processes to form conductive features on the surface of a solar cell substrate. The resistance of interconnects formed in a solar cell device greatly affects the efficiency of the solar cell. It is thus desirable to form a solar cell device that has a low resistance connection that is reliable and cost effective. Therefore, one or more embodiments of the invention described herein are adapted to form a low cost and reliable interconnecting layer using an electrochemical plating process containing a common metal, such as copper.

Pulse plating of a low stress film on a solar cell substrate

Abstract: Embodiments of the invention contemplate the formation of a low cost solar cell metal contact structure that has improved electrical and mechanical properties through the use of an electrochemical plating process. The resistance of interconnects formed in a solar cell device greatly affects the efficiency of the solar cell. It is thus desirable to form a solar cell device that has a low resistance connections that is reliable and cost effective. One or more embodiments of the invention described herein are adapted to form a low cost and reliable interconnecting layer using an electrochemical plating process containing common metal, such as copper. However, generally the electroplated portions of the interconnecting layer may contain a substantially pure metal or a metal alloy layer. Methods are discussed herein that are used to form a solar cell containing conductive metal interconnect layer(s) that have a low intrinsic stress.

Use of the reverse pulse plating method to improve the properties of cobalt–molybdenum electrodeposits

Abstract: Conditions leading to cobalt–molybdenum (Co–Mo) electrodeposits with high Mo percentages were studied Deposits prepared by means of direct current electroplating showed a large amount of cracks Maximum amount of Mo in the films was attained by applying deposition potentials in the − 1200 mV to − 1300 mV range Reverse pulse plating mode has been proved useful for obtaining nanocrystalline, low stressed Co–Mo deposits with similar Mo percentages as in direct current conditions (35–40 wt%) The coatings were exposed to a static microindentation test, which highlighted that the pulse plated samples were more compact and less fragile than the direct current plated ones

A zinc transition layer in electroless nickel plating

Abstract: A new process, which is characterized with zinc transition layer obtained by combining immersing zinc in an improved zinc bath containing FeCl3 and electroplating zinc, is used to plate Magnesium alloy AZ91D. Corrosion testing and SEM images indicate that the immersion zinc layers obtained in zinc immersion baths with FeCl3 are more compact. Peel testing shows that there is good adhesion to the subsequent electrodepositing layer. The electroplating zinc can further promote the coverage of zinc transition layer on the magnesium alloy substrate before electroless nickel plating and reduce the galvanic corrosion effect between Mg alloy and Ni–P alloy. The good zinc deposit can be obtained by electroplating zinc in pH 9∼10 zinc pyrophosphate bath at 40 °C under the current density of 2∼3 A/dm2. The developed new process of electroless nickel plating greatly improves the adhesion and coverage of Ni–P coating. The zinc transition layer obtained by the developed process can supersede copper transition layer obtained by cyanide plating process in electroless nickel plating on magnesium alloy.

Analysis of electroplating baths by capillary electrophoresis with high voltage contactless conductivity detection

Abstract: A new design of a contactless conductivity detector for capillary electrophoresis is demonstrated for the detection of compounds of relevance in metal plating baths. Galvanic baths for the deposition of Zn, Cu, Ni and Ag were analysed. The compounds related to the zinc plating system contained Zn2+, Na+, Mg2+ and NH4+, the copper plating system CuEDTA2−, SO42−, oxalate−, EDTA2− and glyoxylate, the nickel plating system Ni2+, Co2+ and NH4+ and the silver plating system included AgCN−, NO3− and CN−. Concurrent determinations of the compounds could be carried out in less than 10 min.

Effects of Electroplating Variables on the Voltammetric Properties of Bismuth Deposits Plated Potentiostatically

Abstract: An attempt is made to describe the electrochemical properties of bismuth films, plated in-situ on glassy carbon in acetic buffer, over a broad range of deposition potentials. It is shown that accumulation during anodic stripping voltammetric determination of lead and zinc at the bismuth film electrode depends to a large extent on the electrolyte composition and the plating parameters. The influence of the plating potential on Pb deposition is moderate, but it could not be disregarded during Zn quantification. The sources of electrode poisoning effects are discussed in detail. Voltammetric studies are complemented by AFM microscopic observations.

Platinum electrode surface coating and method for manufacturing the same

Abstract: An electrode surface coating and method for manufacturing the electrode surface coating comprising a conductive substrate; a surface coating of platinum having a rough configuration and an increase in the surface area of 5 times to 500 times of the corresponding surface area resulting from the basic geometric shape of the electrode. A method for electroplating an electrode surface with platinum coating having a rough surface, comprising electroplating the surface of a conductive substrate at a rate such that the metal particles form on the conductive substrate faster than necessary to form shiny platinum and slower than necessary to form platinum black.

Negative electrode for nonaqueous electrolyte secondary battery

Abstract: A negative electrode 10 for nonaqueous secondary batteries has an active material layer 12 containing active material particles 12a and having a metallic material 13 having low capability of forming a lithium compound deposited between the particles 12a by electroplating. The surface of the active material layer 12 is coated continuously or discontinuously with a surface layer 14 having an average thickness of 0.25 µm or less and made of a metallic material that is the same as or different from the metallic material 13. The particles 12a inside the active material layer 12 are preferably coated with the metallic material 13 while leaving voids between the particles 12a coated with the metallic material 13. The average thickness of the metallic material 13 coating the particles 12a is preferably 0.05 to 2 µm.

Method of preparing copper plating layer having high adhesion to magnesium alloy using electroplating

Abstract: Disclosed is a method of preparing a copper electroplating layer having high adhesion to a magnesium alloy, which is advantageous because the usability of the magnesium alloy, having the highest specific strength among actually usable metals, can be increased through the development of a process of forming a uniform copper plating layer upon electroplating of the magnesium alloy. The method of preparing a copper electroplating layer having high adhesion to a magnesium alloy of this invention is characterized in that the magnesium alloy is pretreated with a plating pretreatment solution to form a film for electroplating, serving as a magnesium alloy pretreatment layer, exhibiting a uniform current distribution, which is then electroplated with copper to form the copper plating layer. According to this invention, through the pretreatment of the magnesium alloy, the adhesion of the copper plating layer to the film for electroplating formed on the magnesium alloy can be increased.

Low-Temperature Bonding of Copper Pillars for All-Copper Chip-to-Substrate Interconnections

Abstract: A copper-to-copper bonding process was developed for an all-copper, chip-to-substrate interconnect technology. High aspect ratio polymer molds for electroplating were formed using a photodefinable polymer on both the chip and the substrate surfaces. Copper pillars were fabricated by electroplating metal in the polymer molds. The chip-to-substrate all-copper connections were formed by joining the two pillars with electroless copper plating followed by an anneal process. The copper-to-copper bonding of the high aspect ratio pillars does not require the use of solder or other noncopper metals. Mechanical shear force measurements were used to characterize the bonding process as a function of annealing conditions. Excellent bond strength of the electrolessly joined pillars was achieved with a 250°C anneal, with the bond strength of the copper pillar interconnects exceeding 148 MPa. High aspect ratio pillars can provide mechanical compliance, and the electroless fabrication method compensates for pillar misalignment and nonplanarity of the bonded surfaces.

Fabrication of high aspect ratio 35 μm pitch through-wafer copper interconnects by electroplating for 3-D wafer stacking

Abstract: We report the fabrication of high aspect ratio (-15) ultradense (∼80000/cm 2 ) through-wafer copper interconnects by a special aspect ratio dependent electroplating technique. In this approach, electroplating process parameters were continuously varied along with varying unfilled via depth, to maintain the uniform current distribution and thus uniform metal deposition. Copper interconnects, with diameters as small as 12 μm and a pitch of 35 μm, were electroplated without any voids. Due to ultrafine pitch and extremely high number of I/Os per cm 2 , these interconnects were found to have significant potential in three-dimensional (3-D) wafer stacking and other high-density electronic packaging applications.

Electrodeposition of decorative and protective Zn-Fe coating onto low-carbon steel substrate

Abstract: Cyclic voltammetry and chronoamperometry were performed in conjunction with SEM technique to study the electroplating process of Zn-Fe alloys. The technological parameters for Zn-Fe electroplating have been optimized and the smooth Zn-Fe coatings with high corrosion resistances were obtained. The results also show that, under our experimental conditions, the deposition of Zn-Fe behaved anomalously and followed the mechanism of three-dimensional (3D) nucleation. With the increase of deposition potential, the grain growth changed from progressive to instantaneous. Meanwhile, a new viewpoint was proposed to explain the anomalous co-deposition behavior of Zn-Fe coatings. (c) 2005 Elsevier B. V. All rights reserved.

Silicon micromachining of high aspect ratio, high-density through-wafer electrical interconnects for 3-D multichip packaging

Abstract: This paper presents a novel silicon micromachining method, which combines tetra methyl ammonium hydroxide (TMAH) etching and deep-reactive ion etching (DRIE) along with bottom-up copper electroplating, to fabricate high-density and high-aspect ratio through-wafer electrical interconnects (TWEIs) for three-dimensional multichip packaging. The silicon wafer was locally etched with TMAH from the backside until the desired membrane thickness was reached, and then DRIE was performed on the membrane until the holes were etched through. TMAH etching preserved large areas of the wafers at the original thickness, thus, ensuring relatively strong mechanical strength and manipulability. DRIE made it possible to realize high-aspect ratio holes with minimized wafer area consumption. A new bottom-up copper electroplating technique was developed to fill the high-aspect ratio through-wafer holes. This method can avoid seams and voids while achieving attractive electrical features. Through-wafer holes, as small as 5 mum in diameter, have been realized by using the combination of TMAH and DRIE, and have been completely and uniformly filled by using bottom-up copper electroplating

Simultaneously depositing Pd-Ag thin membrane on asymmetric porous stainless steel tube and application to produce hydrogen from steam reforming of methane

Abstract: Thin Pd−Ag alloy composite membranes were simultaneously deposited on commercial asymmetric porous stainless steel (APSS) tubes, using a combined method of electroless plating and electroplating under mild conditions. The X-ray diffraction patterns proved that the Pd−Ag alloy structure was formed at room temperature. The permeation behavior was investigated in detail, revealing that the hydrogen permeation flux, which was as high as 0.28 mol/(m2 s), and the infinite hydrogen selectivity versus argon were achieved at a temperature of 773 K with a pressure difference of 100 kPa. The good membrane stability was proven by the temperature-changing cycles (11) and the gas-exchanging cycles (20). Electron probe microanalysis indicated that the Pd−Ag alloy composite membranes had a stable structure and a homogeneous Pd−Ag alloy layer. In addition, the membrane reactor for methane steam reforming was constructed and the reaction performance was tested. The methane conversion, which was as high as 80.72%, was achie...