Oh Joong Kwon

Effects of the Functional Groups of Complexing Agents and Cu Oxide Formation on Cu Dissolution Behaviors in Cu CMP Process

Cu dissolution behaviors with select reagents (malonic acid, glycine, malic acid, citric acid) were investigated in terms of the functional groups of complexing agents. Based on the results of Cu dissolution rate testing at various pH values, as well as UV-visible analysis with the addition of cupric ions, reaction mechanisms and effects of each functional group are proposed. The effect of Cu oxide formation on the Cu dissolution rate was also investigated by monitoring Cu dissolution rates with various H 2 O 2 concentrations and complexing agent concentrations. Additionally, the effect of the addition of corrosion inhibitor (5-aminotretrazole) on Cu dissolution was investigated. By combining the experimental results, we interpreted the Cu dissolution behaviors based on a competitive contribution from Cu oxide formation and complex formation between Cu (Cu oxide) and the complexing agent.

Development of a Copper Chemical Mechanical Polishing Slurry at Neutral pH Based on Ceria Slurry

We investigated the applicability of ceria-based copper (Cu) chemical mechanical polishing slurry based on commercial ceria slurry, which contained the anionic dispersing agent. Through the zeta-potential and particle size measurements, the neutral pH condition was verified to be favorable to maintain the dispersion stability and glycine was selected as a main complexing agent. Cu polish rate tests with varying glycine concentrations and solid contents of ceria were performed and the possible reaction mechanisms were discussed. Variation in the H 2 O, concentration with a fixed amount of glycine affected the maximum polishing rate, whereas variation in the glycine concentration changed the H 2 O 2 concentration that resulted in the maximum polishing rate. The relationship between Cu oxide thickness and the polishing rate was investigated using coulometric reduction method analysis and X-ray photoelectron spectroscopy analysis. Surface improvement was successfully achieved with the addition of 5-aminotetrazole. According to these experiments, suggestions for ceria-based Cu slurry formulations that have high Cu removal rates and smooth polished surfaces are provided.

Improvement in the Oxidation Resistance of Cu Films by an Electroless Co-Alloy Capping Process

c KC Tech Company, Limited, Kyonggi 456-843, Korea Co-alloy films with various solution compositions CoB, CoWB, and CoWBP were deposited with an electroless technique on Cu films without Pd activation, and their oxidation barrier performance was analyzed. The degrees of oxidation of all films were intensively studied. CoB showed excellent capping performance as an oxidation barrier, whereas CoWB and CoWBP exhibited even poorer oxidation resistance than the case of bare Cu at 400°C. The depth profile of the film compositions and chemical states of the CoB film before and after oxidation was investigated, the results of which suggested that the oxidation of the B component in the film had a clear role in the prevention of continuous Cu diffusion to the surface. The multilayer structure of CoB/ CoWBP/Cu for obtaining both electromigration and oxidation resistance was optimized, showing excellent oxidation resistance In the fabrication of Cu metal lines using the damascene process in ultralarge-scale integration technology, the upper Cu surface ex- posed after a chemical mechanical polishing CMP process must be shielded with a diffusion barrier. Dielectric materials such as SiNx and SiCxNy have been used for this purpose, and these are deposited on the whole substrate without a selective etching process. However, the dielectric constants of these materials are higher than those of the low-k materials used for the interlevel dielectric, which leads to an increase in the effective dielectric constant between the metal lines and the increment in resistor-capacitor delays. 1 Furthermore, a continuous increase in integrity has promoted an increase in the current density of the metal lines, which induces serious electromi- gration issues. 2 It has been reported that the high interfacial energy between metallic-dielectric interfaces Cu-dielectric capping layer is the region where the electromigration phenomenon occurs. 2,3 Electroless deposition of a thin Co-based alloy film on top of the exposed Cu metal line is the most promising solution to these problems. 4 Selective electroless deposition of Co-alloy layers, which act as diffusion barriers, also reduces the total volume of the capping layer and therefore decreases the effective dielectric constant of the entire metal line structure. 1 Furthermore, the interface of the Cu-Co alloy is metal-metal, which may have a lower interfacial energy than the previous metal-dielectric construction. This scheme signifi- cantly increases the lifetime of the metal line and also clearly in- creases the activation energy for the interfacial diffusion of Cu. 5 Capping layers based on Co or Ni with the addition of boron or phosphorus during electroless deposition have been widely re- searched for various applications, including wear-resistive coating and magnetic materials. These capping layers have also included further ternary refractory alloy metals such as tungsten or molybde- num. The incorporation of boron or phosphorus is known to result from the chemical reduction of reducing agents. 6 Boron, phos- phorus, and tungsten are considered to be elements capable of blocking the diffusion of Cu at the grain boundary of Co or Ni, thereby playing a vital role as a diffusion barrier. 7 Recent studies showed that the addition of a small amount of dimethylamine borane DMAB induces Pd-free electroless deposition on a Cu surface from a CoWP electrolyte, whereas using only hypophosphite re- quires Pd activation to deposit an alloy film. 8 Another property that is expected to improve with the electroless capping process is the oxidation resistance of the Cu line. Cu does not form a self-passivation layer like Al, and continuous oxidation occurs when it is exposed to an oxidizing environment. The forma- tion of an oxide layer between Cu and the diffusion barrier interface increases the effective resistivity of the metal line and is also a major cause of the electromigration phenomenon. In previous stud- ies, an improvement in the oxidation properties was mainly achieved by the injection of alloy elements during the deposition of Cu, which diffused to the surface to form a permanent passivation layer.

Deposit profiles characterized by the seed layer in Cu pulse-reverse plating on a patterned substrate

The Cu deposit profile from pulse-reverse plating is affected by the characteristics of the Cu seed layer. When a reverse current is applied to a patterned structure, the sidewall Cu film was dissolved preferentially in comparison to the top film. This is associated with the position-dependent film characteristics of a physical vapor deposition (PVD) seed layer. The sidewall seed layer tends to be less dense and has smaller grains than the top seed layer. It was found that a 90°-tilted oblique angle PVD Cu film, which serves as the sidewall seed layer, is less dense and has smaller grains, and is therefore more likely to be dissolved than an untilted film. This preferentiality led to a heavy deposit at the top of the trench in pulse-reverse plating. Thermal pretreatment of the PVD seed layer or electroless deposition of the seed layer help to reduce the preferentiality, and thus the heavy deposition on the trench top that occurs during pulse-reverse plating.

Silver Direct Electrodeposition on Ru Thin Films

Electrodeposition of Ag was performed on Ru thin films following electrochemical reduction of native Ru oxide. Oxide reduction in a tetramethylammonium hydroxide solution was critical for the formation of continuous Ag film, and a large overpotential was important for high-density nucleation. From a kinetics viewpoint, the thermal stability of the Ag film was improved by the application of a more negative potential, which suggested that better nucleation density at the initial stage of growth induced better substrate adhesion. Suppression of growth by addition of an organic additive generated a larger and more uniformly distributed initial population of Ag particles, and as a result a smooth film was obtained.

Dopamine-induced Pt and N-doped carbon@silica hybrids as high-performance anode catalysts for polymer electrolyte membrane fuel cells

We report a simple and bio-friendly method to synthesize platinum (Pt) and nitrogen (N)-doped carbon@silica using polydopamine (PDA). This silica-based composite permits greater humidifying capacity to sufficiently hydrate membrane electrode assemblies (MEAs), thus improving electrochemical properties for polymer electrolyte membrane fuel cells (PEMFC).

A facile synthetic strategy for iron, aniline-based non-precious metal catalysts for polymer electrolyte membrane fuel cells

The development of a low cost and highly active alternative to the commercial Pt/C catalysts used in the oxygen reduction reaction (ORR) requires a facile and environmentally-friendly synthesis process to facilitate large-scale production and provide an effective replacement. Transition metals, in conjunction with nitrogen-doped carbon, are among the most promising substitute catalysts because of their high activity, inexpensive composition, and high carbon monoxide tolerance. We prepared a polyaniline-derived Fe-N-C catalyst for oxygen reduction using a facile one-pot process with no additional reagents. This process was carried out by ultrasonicating a mixture containing an iron precursor, an aniline monomer, and carbon black. The half-wave potential of the synthesized Fe-N-C catalyst for the ORR was only 10 mV less than that of a commercial Pt/C catalyst. The optimized Fe-N-C catalyst showed outstanding performance in a practical anion exchange membrane fuel cell (AEMFC), suggesting its potential as an alternative to commercial Pt/C catalysts for the ORR.

Nitrogen-rich hollow carbon spheres decorated with FeCo/fluorine-rich carbon for high performance symmetric supercapacitors

A novel approach to fluorine-rich carbon (FC) shell formation on an electron-rich metal surface based on the electronegativity concept is reported. Basically, highly electronegative elements are strongly attracted by low electronegative/electron-rich elements through dipole interaction, which leads to the formation of fluorine-rich carbon shells on metals at various fluorine quantities. Herein, nitrogen-rich hollow carbon spheres decorated with fluorine-rich carbon shell covered metals (FC@M/NHCS, M = Fe, Co, and FeCo) were synthesized by co-polymerization on SiO2, adsorption of metal precursors, and etching of the SiO2, followed by sintering. The fluorine content, quantified by XPS and SEM-EDS studies, decreased according to FeCo > Fe > Co in FC@M/NHCS. HAADF-STEM elemental mapping studies clearly confirmed fluorine-rich carbon shell formation on the metal surface. The influence of fluorine content order in the as-synthesized materials was reflected in their capacitance performances. FC@FeCo/NHCS electrode depicted the maximum specific capacitance of 302.0 F g−1 at 0.2 A g−1 in 6 M KOH medium, delivering excellent stability with no losses over 5000 cycles at 5 A g−1. The symmetric supercapacitor (SSC) devices operated at 1.5 V by delivering maximum device specific capacitance of 51.2 F g−1 at 0.2 A g−1. It exhibited 81.3% of capacitance retention at 10 A g−1 with the FC@FeCo/NHCS. The maximum energy density of 15.3 W h kg−1 at 0.2 A g−1 and the maximum power density of 5100 W kg−1 at 10 A g−1 were delivered by the FC@FeCo/NHCS device. This study provides an ideal way for synthesizing fluorine-rich carbon materials for high energy storage/conversion applications.

Gallic Acid as a Complexing Agent for Copper Chemical Mechanical Polishing Slurries at Neutral pH

Gallic acid was investigated as a new complexing agent for copper (Cu) chemical mechanical polishing slurries at neutral pH. Addition of 0.03 M gallic acid and 1.12 M H2O2 at pH 7 resulted in a Cu removal rate of 560.73±17.49 nm/min, and the ratio of the Cu removal rate to the Cu dissolution rate was 14.8. Addition of gallic acid improved the slurry performance compared to glycine addition. X-ray photoelectron spectroscopy analysis and contact angle measurements showed that addition of gallic acid enhanced the Cu polishing behavior by suppressing the formation of surface Cu oxide.

Preparation of Pt-Ru-Co Ternary Catalyst on Carbon Paper for PEMFC with Electrodeposition and Galvanic Displacement

The Pt-Ru-Co ternary catalyst was prepared on the carbon paper with electrodeposition and galvanic displacement. The carbon paper without PTFE (polytetrafluoroethylene) was used as the substrate for catalyst deposition. The catalyst was prepared with Co electrodeposition on carbon paper through the change of deposition potential and time. The Co nucleation on carbon paper was investigated by using the electrochemical techniques of linear sweep voltammetry (LSV), cyclic voltammetry (CV), chronoamperometry (CA) and field emission scanning electron microscopy (FESEM). Then Pt and Ru galvanic displacement were carried out by control of displacement time. Consequently, the Pt-Ru-Co ternary catalyst was successfully formed using electrodeposition and galvanic displacement, and it showed competitive catalytic activity compared to other reported results in electrochemical analysis.