CHEMICAL-MECHANICAL PLANAIZATION
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Several new experiments, also with SRC/Intel support, are being performed to explore at a fundamental level the relationship between particle/surface interactions and removal rate as well as contamination using a column technique well known for investigating particle adhesion, defects, and delamination phenomena. Professor Matijevic' 's group has already done extensive work with this technique. The slurry is fed into a small vertical column, packed with beads of glass, copper, etc., that are large enough both to avoid filtration of the slurry particles and to simulate the appropriate wafer surface. Since the flow occurs under essentially hydrostatic conditions, it represents the dynamic situation in a polishing tool at low applied pressures. The smaller slurry particles pass through the packed column, unless attached to the larger glass or copper collector beads. Hence, analysis of the time dependent composition of the effluent can provide valuable information about abrasive-film surface interactions. In addition, subsequent rinsing of the loaded column with solutes at different pH and/or with additives will permit evaluation of particle removal. These measurements can be performed in different chemical environments. Indeed, it was already observed that adhesion between silica abrasives and copper is strongly influenced by H₂O₂ concentration in the slurry, with a peak in silica particle retention observed around 0.5 to 1% H₂O₂ in the slurry. This corresponds with the peak in the removal rate of copper. By altering the pH and other conditions, and by subjecting the column to an external sonication energy source, it is also possible to identify conditions that will facilitate particle removal from the film surface. Professor Babu and his group are also investigating the behavior of copper particles coated with polymeric films. Babu is also collaborating with Professor Roy (refer to Roy's section) to investigate the role of various complexing agents during Cu and Ta planarization.

Professor Roy uses Time Resolved Electrochemical Impedance Spectroscopy to Study Novel Materials for CMP and Fuel Cell Applications

CAMP Professor Dipankar Roy's research group at Clarkson University is using time resolved Fourier Transform Electrochemical Impedance Spectroscopy (FT-EIS) to investigate novel materials for a variety of applications. Currently, this work focuses on two specific areas. The first one involves development of efficient polishing slurries for chemical mechanical planarization (CMP) of certain metals like ruthenium (a promising electrode metal for random access memory cells), silver (a potential replacement for copper as wires) and platinum (for electrodes in stacked capacitor cells). Relatively more conventional CMP systems involving copper, tantalum, and tantalum nitride are also studied in Professor Roy's laboratory. The main objective of this research is to investigate the detailed surface reactions that govern the CMP efficiencies in different chemically and/or electrochemically designed slurry environments. This work is funded by NYSTAR and SRC, and is conducted in collaboration with CAMP Director S.V. Babu.

The second area where Professor Roy is using FT-EIS involves exploration of novel materials for highly efficient direct methanol fuel cells (DMFCs). The traditional anode materials (Pt and Pt-based composites) used in DMFCs often limit the efficiency of the fuel cell due to their chemical affinity toward adsorbing "site poisoning" intermediates like CO and methanol fragments. Certain nanomaterials involving noble metals have been tested as possible alternatives of these Pt-based anodes. In particular, composite (alloy and core-shell) nanoparticles of platinum-gold, platinum-ruthenium and titanium dioxide-gold are promising materials for such applications. Fabrication and optical characterization of these catalysts are done in collaboration with CAMP Professor J. H. Fendler. To study the detailed kinetics of methanol oxidation on various anode materials, the Clarkson researchers have successfully combined FT-EIS with a number of time resolved optical techniques such as surface plasmon resonance spectroscopy, polarization modulation infrared reflection absorption spectroscopy, and infrared spectroscopic ellipsometry.

A complete list of recently published research reports from Professor Roy's group can be found at the following Website: http://www.clarkson.edu/~samoy/pub.htm.

For further information about Professor Roy's research, please call him at 315-268-6676 or send e-mail to samoy@clarkson.edu.

NanoDynamics and Clarkson Collaborate on Multiple Levels

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More recently, Professor Egon Matijevic' (the Victor K. LaMer Chair in Colloid and Surface Science) has joined the NanoDynamics Board of Advisors and has already lectured to the company's research and engineering team in Buffalo on the fundamentals of colloidal chemistry and nanotechnology.

In May of this year, NanoDynamics and Clarkson entered into a multi-year arrangement to support the addition of Dr. Benjamin Dorfman to Clarkson's faculty. Dorfman is a leading scientist in the area of diamond-like nanocomposites and quasiamorphous carbon structures and has numerous patents and publications in the field. His patented composition of matter -Dylyn was originally licensed by ART, Inc. Blakely's first advanced material company and is currently produced commercially around the world by N.V. Bekaert s.a., a multibillion dollar European materials company.

Furthermore, a team of Clarkson faculty including Professors Suni, Rengasamy, and Pillay are working on a collaborative proposal to the U.S. Department of Defense for a diesel-powered solid oxide fuel cell to be used by combat soldiers. The FY05 Defense Appropriation includes funding for this initiative.