Spring 2002 Departmental Distinguished Seminar Series

Brian G. Willis

Chemical-Physical Mechanisms of Aluminum and Copper Metalization Technology
February 22, 2002

The regular advances in silicon integrated circuit technology have required continuous research and development of new materials and processing methods. Dr. Willis's presentation focused on interconnect technology, an area of particular emphasis in the past ten years. Interconnect refers to the tiny sub-micron metal wires and surrounding dielectric materials that provide the connections for signal, power, and ground to the transistor devices. Aggressive shrinking of interconnect structures has required intensive research and development of metalization and dielectric materials. Additionally, the complexity of interconnect designs has required a greater understanding of the chemistry and physics of the materials processing methods. Aluminum, and more recently copper, have been the metals of choice for interconnect metalization in silicon technology. The recent introduction of copper interconnects has created new issues for materials processing and reliability. In particular, "barrier layer" materials are needed to provide an adhesion layer for the copper seed film and act as barriers against copper diffusion into the interlayer dielectric materials. Dr. Willis argued that if the electrical resistance advantage of copper over aluminum interconnects is to be preserved, it is necessary that these liner materials scale to a minimum thickness without compromising adhesion promotion and barrier effectiveness. To design such materials and processing methods, it is necessary to understand the chemistry and physics of copper diffusion within dielectric materials. Results will show that investigations of the copper transport process provide a chemical-physical basis for development of advanced dielectric and liner materials for copper interconnects. Dr. Willis's visit was hosted by Dr. Lisa Podlaha.

Sachin Velankar

(University of Minnesota)

Dynamics of Immiscible Polymer Blends with Compatibilizer
March 4, 2002

Blending of immiscible polymers is a common means of realizing materials with properties that are difficult to obtain with individual polymers. Examples include rubber-toughened thermoplastics, barrier materials for packaging, and highly reflective mirrors composed of several layers of different polymers. Surface-active block copolymers are often added as compatibilizers during processing of these blends in order to promote mixing and control the morphology and properties of the final material. The effects of such a compatibilizer on the dynamics and the rheological properties of droplet-matrix blends were the primary concern of Dr.Velankar's presentation. Dr. Velankar's visit was hosted by Dr. K.T. Valsaraj.

Anthony Dixon

(Worcester Polytech Institute)

CFD Fluid Flow and Heat Transfer for Fixed Bed Reactor Design
March 8, 2002

Computational fluid dynamics (CFD) is a tool that is becoming more realistic for use in the description of the detailed flow fields within fixed beds of low tube?to?particle diameter ratio (N). Prevailing models of fluid flow invoke either a constant velocity (plug-flow) profile, or make use of a single axial velocity component with radial variation across the tube diameter. However, according to Dr. Dixon, difficulties in predicting packed bed performance and the wide disagreement between correlations for effective heat transfer coefficients suggest that these are oversimplified pictures of the real flow situation, especially near the tube wall. To prove this point, Dr. Dixon presented CFD simulations for both a full bed and for near-wall segments of a fixed?bed reactor tube and discussed the importance of such simulations. Dr. Dixon's visit was hosted by Dr. Douglas Harrison.

Roland Horst

(University of Massachusetts)

Compression of Flexible Foams under Simultaneous Shearing and Long Term Stress Relaxation
March 15, 2002

The focus of Dr. Horst's presentation was foam, which, as he pointed out, covers a broad range of materials from shaving cream to flexible polyurethanes that cushions our seats. In particular, Dr. Horst discussed solid foams with an elastomeric matrix from a mechanical point of view. These highly structured materials exhibit rich mechanical response under shear and elongational strain. The shear strain causes a normal stress whose dependence on the applied shear strain is very different from that of the solid rubber forming the matrix of the foam. For example, at low compression the normal stress decreases with increasing shear strain in contrast to solid elastic materials that show an increase of normal stress. The stress relaxation behavior of these heterogeneous systems also deviates from that of solid elastomers and extends over very long times with many modes. Dr. Horst presented a custom-built device that allows the measurement of the stress and also the incremental modulus, i.e. the slope of stress versus strain curve, without applying loading-unloading cycles and so without disturbing the aging process. Dr. Horst's visit was hosted by Dr. Kerry Dooley.

Ben J. McCoy

(University of California, Davis)

Perspectives on Distribution Kinetics and Its Applications
March 22, 2002

Dr. McCoy's presentation examined the engineering importance of size distribution. For example, polymers are distributed in molecular weight, particles in mass, and phase-change clusters in number of molecules. Dr. McCoy explained how the kinetics and dynamics of such systems can be quantitatively described by population dynamics equations. Applications discussed included polymer degradation and pyrolysis; particle fragmentation and agglomeration; and phase-transition dynamics, including nucleation, growth, and ripening for vapor-liquid (aerosol) or liquid-solid (crystallization) systems. Dr. McCoy's visit was hosted by Dr. Carl Knopf.

Jerry Spivey

(North Carolina State University)

Environmental Catalysis: Multifunctional Catalysts for Aldol Condensation Reactions
April 26, 2002

Dr. Spivey discussed the development of heterogeneous catalysts for aldol condensation reactions as an example of environmental catalysis. His particular focus was the synthesis of methyl isobutyl ketone (MIBK) from acetone. In this process, solid catalysts can replace aqueous base homogeneous catalysts that produce a significant wastewater stream. However, these solid catalysts must have a proper balance of acid/base and selective hydrogenation properties. In Spivey's study, the condensation/selective hydrogenation reactions leading to MIBK from acetone were studied on a series of hydrotalcite (HTC)-supported noble metal catalysts in a liquid-phase batch microreactor. A 0.1wt.% Pd/HTC catalyst gave the highest acetone conversion (38%) and selectivity to MIBK (82%), which is among the highest reported in the literature. The HTC catalyzes the condensation of acetone to diacetone alcohol (DAA) and its subsequent dehydration to mesityl oxide (MO), whereas the noble metal selectively hydrogenates the C=O bond in MO to MIBK. Dr. Spivey's visit was hosted by Dr. Carl Knopf.

^ Top