Yung-Yun Wang

Mechanistic Study of Ag/Pd-PVP Nanoparticles and Their Functions as Catalyst for Electroless Copper Deposition

Ag/Pd nanoparticles stabilized by poly(vinylpyrrolidone) (PVP) have been successfully synthesized in various molar ratios. An ex situ UV-visible spectral analysis was employed to elucidate the growth mechanism of Ag/Pd-PVP nanoparticles, and it revealed that the reduction of Ag ions is much easier than Pd ions in our system. X-ray photoelectron spectroscopy data and mixed potential analysis confirm the effect of the amount of PVP protecting agent to the Ag/Pd-PVPs alloy structure. The growth mechanism of Ag/Pd-PVP nanoparticles is affected by the amount of PVP and forms an inhomogeneous alloy structure. Furthermore, the higher the PVP content, the more inhomogeneous the alloy structure, which is silver-rich in the core and palladium-rich on the surface. The catalytic activity of Ag/Pd-PVP nanoparticles for electroless copper was measured by direct plating on a FR-4 substrate, quartz crystal microgravimetry, and linear scan voltammetry. The performance of Ag/Pd-PVP nanoparticles was also compared with the conventional Sn/Pd activator. Ag/Pd-PVP nanoparticles show the potential for a new activator for electroless copper deposition.

Behavior of Copper Removal by CMP and Its Correlation to Deposit Structure and Impurity Content

Knowledge of the removal behaviors of various electroplated copper films during chemical mechanical polishing (CMP) is important for thickness control and defect generation. In this paper, we investigate the effect of current density and impurities incorporated in blanket and pattern wafer by potentiodynamic polarization method, X-ray diffraction, and secondary ion mass spectroscopy. Defect count was decided by the optical scan method and scanning electron microscopy reviewing. Removal rate and corroded pits were found to decrease with increasing (111)/(200) ratio because (111), the close-packed plane of the face-centered cubic structure, has strong chemical resistance during polishing. Furthermore, incorporated impure atoms, such as carbon, chloride, and sulfur, tend to weaken grain boundaries to generate more corroded pits but do not affect removal rate. Besides, geometric constraint induces concentrated impurities to restrict copper grain growth and induce fast oxide growth rate, resulting in high dishing performance.

Selectivity Enhancement of Electroless Co Deposition for Cu Capping Process via Spontaneous Diazonium Ion Reduction

A one-step, room temperature route to form carbon-metal bonds via spontaneous reduction of diazonium ion in an acid solution has been developed. This property was later employed to design a new process for self-activated electroless Co deposition on Cu without Pd activation. X-ray photoelectron spectroscopy and IR analysis show the evidence of direct organic molecule attachments on Cu. From scanning electron microscopy, electrical resistance, and line-to-line leakage current observations, the selectivity of Co deposition on the modified Cu surface has been greatly improved. Impedance measurements indicated that the charge transfer of electroless reaction was partially blocked by a highly covalent bond to the Cu surface.

Improvement of Pt-Catalyst Dispersion and Utilization for Direct Methanol Fuel Cells Using Silane Coupling Agent

Better catalyst utilization is essential to improve cell performance and to reduce catalyst loading of polymer electrolyte fuel cells. The current function of perfluorosulfonic ionomer (PFSI) in the catalyst paste is to serve as an ionic conducting agent and binder in the catalyst layer. In this study, we have successfully used the PFSI to stabilize dispersed Pt particles in addition to its original function as ionic conducting agent and binder. This results in an electrode with fine Pt cluster, high ionic conductivity, and high catalyst utilization. Silane coupling agent 3-aminopropyltrimethoxysilane (APTMS) was employed to graft PFSI on Pt surface resulting in significant steric stabilization. Electron spectroscopy for chemical analysis and nuclear magnetic resonance results had been verified the occurring of coupling reaction. The transmission electron spectroscopy/energy-dispersive spectroscopy image showed the PFSI indeed grafted on the Pt surface. The primary particle of Pt was 1.9 nm, which was examined by extended X-ray absorption fine structure. The cell performances of the membrane electrode assembly (MEA) made with APTMS-modified Pt cathode and the MEA without treatment were compared. About 15% utilization increase can be achieved by the APTMS treatment.

Impurities Induced Localized Corrosion Between Copper and Tantalum Nitride during Chemical Mechanical Planarization

Using chemical mechanical planarization, the reaction which causes the formation of localized defects between the interface between the copper (Cu) deposit and the tantalum nitride (TaN) barrier layer were studied. The experimental results of potentio-dynamic polarization and secondary ion mass spectroscopy demonstrate that galvanic corrosion was not the dominant factor for such localized defects in our system, most impurities, such as carbon (C) and chloride ion (Cl - ), aggregated near the interface between Cu deposit and TaN barrier layer. As a result, the correlation between localized defects at the Cu/TaN interface and the distribution of impurities is proposed herein.

Electrochemical Investigation of Pd-Free Electroless Co-Based Capping Layers on Cu Surfaces

Electroless Co-based capping layers with dimethylamine borane (DMAB) and hypophosphite as reductants on Cu lines were achieved without Pd activation. The oxidation process of electroless Co-based deposition was characterized by cyclic voltammetry and electrochemical impedance spectroscopy. The oxidation of DMAB was greatly suppressed with the addition of hypophosphite during electroless CoBP deposition. At low [OH - ], an obvious oxidation peak of hypophosphite was attained due to insufficient formation of BH 3 OH - , which showed slow charge transfer on the Cu surface; at high [OH - ], distinct competition between hypophosphite and OH - and sufficient BH 3 OH - formed enhanced the oxidation of DMAB, indicating fast charge transfer. The selectivity of electroless Co-based deposition was also strongly influenced by [DMAB], [hypophosphite], and [OH - ].

Catalyst Improvement of Utilization for Direct Methanol Fuel Cell Using Silane Coupling Agents

A method to prepare improved Pt-based catalyst for direct methanol fuel cell is described in this study. Silane coupling agents (3-aminopropyl) trimethoxysilane (APTMS) (3-glycidyloxy propyl) trimethoxysilane, and N-[3(trimethoxysilyl) propyl] ethylenediamine (3-glycidyloxy) were used to graft perfluorosulfonic ionomer on Pt to stabilize the dispersion and therefore to obtain an electrode with fine Pt cluster and high catalyst utilization. From extended X-ray absorption fine structure examination, Pt nano-particle can be successfully confined to smaller size with the help of APTMS. Polarization test shows improved membrane electrode assembly (MEA) performance while using APTMS. From hydrogen adsorption/desorption cyclic voltammotric analysis, about 15% catalyst utilization increase can be achieved.