Cu electrodeposition from methanesulfonate electrolytes for ULSI and MEMS applications

Methanesulfonic acid (MSA) is an alternative to sulfuric acid electrolyte for metal deposition. The electrochemical nucleation and growth of Cu on a glassy carbon electrode in methanesulfonate was compared with sulfate baths. The overpotential for Cu deposition was much smaller in the MSA bath compared to the traditional sulfuric acid bath, and Cu nucleation occurred at a higher rate in the MSA bath. The measured diffusion coefficient value for Cu deposition from the MSA bath was 6.82x10(-6) cm(2)/s. UV-visible spectroscopic results confirmed that the coordination of Cu species was the same in both electrolytes. Cu electrodeposition on Ni sputtered Si substrate from the high efficiency MSA bath was photoresist-compatible with no void formation. One-dimensional Cu nanorods were also deposited through an anodized aluminum oxide template on a Ni evaporated seed layer substrate, showing potential applications as electrical interconnects in ultralarge scale integration (ULSI) and microelectromechanical systems (MEMS)

Investigation of DMAB oxidation at a gold microelectrode in base

A gold microdisk has been used to determine the diffusion coefficient Formula for dimethylamine borane (DMAB) in concentrated alkaline solution. Two steady-state oxidation waves were resolved through the use of microelectrodes. Using the Formula value determined, the coulomb number for both oxidation waves was shown to be 3. The first wave may be further resolved in dilute solutions revealing three one-electron steps. The concentration range wherein the maximum coulombic efficiency for DMAB oxidation on gold may be achieved is demonstrated. An oxidation pathway with a variable coulomb number is suggested

Fabrication of three-dimensional substrates for Li microbatteries on Si

Lithographic techniques for patterning planar substrates to achieve microbattery materials compatible three-dimensional (3D) Ni substrates for sequential deposition of active battery materials are described. A single spin negative photoresist is used to achieve 100 mu m pattern heights. After patterning, Ni is electroplated on the substrates from a low stress Ni sulphamate bath to a maximum of 100 mu m. The sidewall angle achieved yields a thinner Ni feature at the surface level than at the base which is a key parameter to facilitate subsequent active battery materials deposition by vacuum deposition techniques. An aspect ratio of 1.5:1 has been achieved and the surface area is increased by comparison with planar electrodes

Nanoporous gold anode catalyst for direct borohydride fuel cell

Nanoporous gold (NPG) electrodes were fabricated in film and wire array formats by selectively dealloying Ag from Au0.18Ag0.82. Borohydride oxidation reaction (BOR) was studied by cyclic voltammetry at the NPG electrodes. The onset potential for the oxidation at NPG in a wire array format shifted to more negative potentials that than observed at an Au disc and higher currents were realized. An onset potential of −1.07 V vs SCE which is 0.207 V lower than that at an Au disc was recorded. The oxidation current for 20 mM borohydride in 1 M NaOH increased to 73.6 mA cm−2 from 3.17 mA cm-2 at an Au disc. An n value of 7.49 was determined for the oxidation peak at high potential (−0.49 V) while a value of 4.26 was determined at low potential for the oxidation plateau centered at −0.05 V. NPG presents an attractive alternative to gold nanoparticle-based catalysts for use in direct borohydride fuel cells. NPG can establish intimate contact with an electrical substrate and eliminates the need for a carbon support

Ammonia borane oxidation at gold microelectrodes in alkaline solutions

Borane-based electroless plating baths are of interest in many microelectronics applications such as barrier and capping layers for copper integrated circuit interconnect. To optimize the plating baths a thorough understanding of the role of the bath constituents is required. To this end we have employed microelectrodes to investigate the oxidation mechanism of boranes in alkaline solutions. In this paper we present data for the simpler ammonia borane (AB) oxidation and compare it with the previous analysis of dimethylamine borane (DMAB) oxidation. Both AB and DMAB are shown to oxidize in two steady-state mass transport-controlled oxidation waves for specific concentration ranges. Particular emphasis is placed on the analysis of the second oxidation wave observed at less negative potentials and the differences observed in the analysis of AB and DMAB in this potential region. The potential range for oxidation, the optimum concentration, and a suggested mechanism for oxidation are shown

Aligned carbon nanotube-Pt composite fuel cell catalyst by template electrodeposition

Solution phase deposition of aligned arrays of carbon nanotubes (CNTs) in a platinum (Pt) matrix cornposite is demonstrated. The catalyst material is electrodeposited in an oriented manner on the nanoscale using anodised aluminium oxide (AAO) templates. The catalyst performance of the composite for the oxidation of methanol is shown. The carbon monoxide (CO) tolerance is increased and the catalyst function is improved by minimising the influence of adsorbed CO on the kinetics of the methanol oxidation reaction

Nanoporous gold catalyst for direct ammonia borane fuel cells

Nanoporous gold (NPG) electrodes were fabricated in film and wire array formats by selectively dealloying Ag from Au0.18Ag0.82. The ammonia borane (AB) oxidation reaction was studied by cyclic voltammetry at the NPG electrodes. The onset potential for the oxidation at NPG in a wire array format shifted to more negative potentials than that observed at a Au disc and higher currents were realised. An onset potential of -1.30 V vs. SCE was recorded which is 0.28 V lower than that at a Au disc. The oxidation current for 20 mM AB in 1 M NaOH increased from 2.65 mA cm(-2) at a Au disc to 13.1 mA cm(-2) at a NPG wire array. NPG is a viable candidate as an anode catalyst for a direct ammonia borane fuel cell

Nanotemplated platinum fuel cell catalysts and copper-tin lithium battery anode materials for microenergy devices

Nanotemplated materials have significant potential for applications in energy conversion and storage devices due to their unique physical properties. Nanostructured materials provide additional electrode surface area beneficial for energy conversion or storage applications with short path lengths for electronic and ionic transport and thus the possibility of higher reaction rates. We report on the use of controlled growth of metal and alloy electrodeposited templated nanostructures for energy applications. Anodic aluminium oxide templates fabricated on Si for energy materials integration with electronic devices and their use for fuel cell and battery materials deposition is discussed. Nanostructured Pt anode catalysts for methanol fuel cells are shown. Templated CuSn alloy anodes that possess high capacity retention with cycling for lithium microbattery integration are also presented

Zincate-free, electroless nickel deposition on aluminum bond pads

A zincate-free electroless nickel deposition on aluminum bond pads is investigated. A three-step, etch, rinse, and electroless plating, is demonstrated for deposition on aluminum bond pads patterned with polyimide. The chemicals used are compatible with this dielectric material. The deposition has been achieved with good selectivity, uniformity, and deposition rate at 40 × 40   μ m aluminum bond pads. The adhesion and contact resistance were also determined and improved through anneals in the range 200-400°C for 1 h. The optimized condition for adhesion and contact resistance was an anneal at 400°C. The combination of a nickel hypophosphite reducing agent and the additives used leads to an active plating bath in the early stages of deposition, by comparison with commercial solutions, and hence, good coverage of the aluminum bond pad using the simplified process