AND BIOMEDICAL WORK
Professor Anja Mueller, of Clarksn University's Department of Chemistry, is carrying out research that makes use of polymers in biomedical work. Her postdoctoral research was on liposomes as drug delivery agents. It included the characterization of controlled release upon a light signal, liposome fusion with membranes, and characterization of the bahavior of liposomes in a cell culture. Professor Mueller's current and future research projects include the development of a biological fuel cell for medical sensors, synthesis of hydrophilic polymers with enzymes and their surface characterization for the development of a heart valve coating. In addition she will investigate the use of polymers for biosensors and waste water treatment.
Professor Raymond Mackay and graduate student Florentina Pavel have used w/o microemulsions stabilized by a polymerizable surfactant to produce polymethacrylate nanolatexes on the order of 5-10 nanometers in diameter. Recently, these studies have been extended to systems in which the oil itself is a polymerizable monomer. Nanoparticles have been synthesized in-situ in the liquid microemulsions, which are subsequently polymerized to form transparent polymer-nanoparticle composites. Studies are underway to explore the range of composition to which this process can be applied. Professor Mackay has demonstrated a "one-pot"process for producing a nanoparticle / polymer composite which is transparent with optical applications. The composite contains unaggregated and randomly dispersed particles.
Research in Professor Devon Shipp's laboratories centers on novel polymerization techniques and polymer materials. It has produced several exciting discoveries in the past year.
Two developments in the materials area are the production of polymer-silicate nanocomposites, and the development of photo-responsive and photon-harvesting polymers. The nanocomposite materials offer improved tensile strength, reduced flammability, and improved gas permeability properties. Professor Shipp's research has focused on in situ polymerization, initiated from within the silicate layers of clays. The goal is to produce novel polymers with a variety of compositions (e.g. block copolymers) and architects (e.g. star polymers), and to examine their properties. It is envisaged that such polymers will offer enhanced properties compared to simple linear analogues, through greater exfoliation of the silicate layers.
The second materials project is based on the synthesis of well-defined and functionalized polymers bearing chromophores, thus allowing either energy or electron transfer events to occur along the polymer chains. These polymers have potential applications in organic light emitting diodes, photo-catalyzed reactions, photo-stabilization of polymers or photonic materials. In particular, his research group is looking at synthesizing materials such as block or surface-attached (co)polymers
Another advancement, made by Professor Shipp and his group, is in the analysis of atom transfer radical polymerization kinetics. Careful reaction design and procedures, along with the use of an all-encompassing kinetic model, have allowed for the determination of radical-radical termination rate coefficients. Such data are invaluable in predicting polymerization behavior, yet have proved exceedingly difficult to measure with accuracy in the past. Thus, this new method opens up a unique avenue for studying an enduring Achilles' heel of polymer chemistry.
CHEMICAL-MECHANICAL POLISHING AND THIN FILMS
Professor Babu's research group is continuing the investigation of various aspects of chemical-mechanical polishing (CMP) of metal and dielectric films and deposition and characterization of silicon-containing diamondlike carbon films (DLC). Along with the polishing of silicon dioxide films, the CMP research is focused on the planarization of Cu and Ta films, using both alumina and silica abrasives as well as more recently, mixed abrasives and 'engineered' particles in different chemical environments. Also new results have been obtained with very high selectivity novel ceria based slurries for STI planarization, with and without special additives. Several patents have been filed to cover some of the discoveries.
The changes in the film surface hardness in the presence of different oxidizing chemicals are being measured using nanoindentation. These changes have a strong influence on the quality of the planarized film surface and the choice of an abrasive. Measurements, both in air and in the chemical environments of interest to CMP, are being perfomed. Electrochemcial measurements, both in situ and ex situ, are providing valuable insights into material removal mechanisms. Ionic strength and pH have been shown to play an important role in determining removal rates of Cu and Ta films in different polishing environments
The effects of abrasive shape, size and morphology in CMP are being investigated in collaboration with Professor Matijevic'. With support from SRC, well-defined dispersions using monodispersed spherical silica particles, silica particles coated with aluminum (hydrous) oxide, ellipsoidal hematite particles of different anisometries coated with silica, and silica particles coated with ceria are being prepared and evaluated as abrasives for CMP. The effects of particle size and shape are also being evaluated.
It was discovered that some of the problems associated with the use of a single abrasive slurry, such as poor polish selectivity, surface defects and slurry instability, can be overcome by combining two or more different abrasives. It was shown that by using different particle sizes and taking advantage of differing surface charges on the abrasives, both selectivity and polished surface roughness can be improved systematically.
A large number of polishing experiments have been performed using fixed abrasive pad systems for achieving planarization of STI and similar related structures. The pattern density has a very large effect on removal rates and it was also shown that different patterns densities from different parts of the wafer are coupled in their role in pad "activation" and the associated particle generation. These results are very useful in determining the planarization end point and controlling dishing and erosion.
Finally, the CMP facilities now consist of several polishers, a Westech 372, a Westech 4100 polisher/cleaner, and a Speedfam-IPEC 676 orbital tool. Each tool will be deicated to a specific process. Several metrology tools for full wafer mapping have also been acquired and are in use, expanding CAMP's capabilities significantly. Current research sponsors include SRC/Intel, Grace Davison, St. Gobain, PPG, Nyacol, Rodel, and Kodak, Inc. Professor Babu's research group now consists of five Ph.D. and two M.S. students.