3

Chemistry of Manufacturing and Processing

A large fraction of the processes used in current and projected manufacturing are chemical in nature, ranging from polymer molding, through chemical vapor deposition of semiconductors, to the preparation of precursors and the sintering of fine ceramics. Fundamental understanding of the chemistry of these complex manufacturing processes will pace the availability of the advanced materials and systems required for the 21st-century Navy. Recent scientific and engineering advances make the time ripe for increased emphasis on fundamental research in processing and manufacturing.

Electronic materials research offers rich opportunities for improved chemical processing and preparation techniques. The processing demands brought about by requirements for ever smaller designs and the need to keep yields high make advances in processing key to future generations of semiconductor circuitry. Although the silicon integrated circuit community has done an outstanding job in this context, the other areas of semiconductor electronics have invested too little in the understanding of process chemistry for manufacturing. Even with silicon devices, the technology is reaching a critical point that will require significantly new process chemistry, a situation that opens opportunities with high return. Studies of the fundamentals of metal organic chemical vapor deposition of conductors, semiconductors, and insulators, basic mechanisms of etching, and plasma processing are examples of opportunities in silicon and gallium arsenide (GaAs) processing where increased understanding could pay off in the development of new processes.

Advanced processes such as MBE have not been applied to many materials other than semiconductors, and yet, their application ought to provide new classes of engineered materials with unique properties, such as on-demand acentric structures leading to new ferroelectrics, piezoelectrics, and nonlinear optical materials built one atomic layer at a time. Sol-gel processes have advanced to the point that they should provide a new, highly homogeneous, low-temperature sinterable source of precursors for the preparation of both electronic and structural ceramics.

Drawing on increased computer power, new physical insights, and careful ties to experiment, process modeling is beginning to pay dividends in polymer molding and extrusion. This area is moving rapidly as a result of increased computer power, improved understanding of polymer rheology, and greater emphasis on the relationship between processing and properties. Sophisticated software packages are the product of this research. The generation of these packages requires a new level of collaboration between chemical and mechanical engineering disciplines. There is also a need for careful experimental verification of these models. Application of these models enables a designer to predict the feasibility of a particular process and to make design improvements prior to investing the considerable time and money involved in preparing tooling (e.g., molds and extruder screws that often cost many tens of thousands of dollars). Application of these models has demonstrated that extra efforts expended to improve the design pay large dividends in reducing overall development time. In many cases, the prototype round of tooling can be eliminated. Recently, efforts have been made to extend these process models to describe fiber-filled composite systems. This is a



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ONR Research Opportunities in Chemistry 3 Chemistry of Manufacturing and Processing A large fraction of the processes used in current and projected manufacturing are chemical in nature, ranging from polymer molding, through chemical vapor deposition of semiconductors, to the preparation of precursors and the sintering of fine ceramics. Fundamental understanding of the chemistry of these complex manufacturing processes will pace the availability of the advanced materials and systems required for the 21st-century Navy. Recent scientific and engineering advances make the time ripe for increased emphasis on fundamental research in processing and manufacturing. Electronic materials research offers rich opportunities for improved chemical processing and preparation techniques. The processing demands brought about by requirements for ever smaller designs and the need to keep yields high make advances in processing key to future generations of semiconductor circuitry. Although the silicon integrated circuit community has done an outstanding job in this context, the other areas of semiconductor electronics have invested too little in the understanding of process chemistry for manufacturing. Even with silicon devices, the technology is reaching a critical point that will require significantly new process chemistry, a situation that opens opportunities with high return. Studies of the fundamentals of metal organic chemical vapor deposition of conductors, semiconductors, and insulators, basic mechanisms of etching, and plasma processing are examples of opportunities in silicon and gallium arsenide (GaAs) processing where increased understanding could pay off in the development of new processes. Advanced processes such as MBE have not been applied to many materials other than semiconductors, and yet, their application ought to provide new classes of engineered materials with unique properties, such as on-demand acentric structures leading to new ferroelectrics, piezoelectrics, and nonlinear optical materials built one atomic layer at a time. Sol-gel processes have advanced to the point that they should provide a new, highly homogeneous, low-temperature sinterable source of precursors for the preparation of both electronic and structural ceramics. Drawing on increased computer power, new physical insights, and careful ties to experiment, process modeling is beginning to pay dividends in polymer molding and extrusion. This area is moving rapidly as a result of increased computer power, improved understanding of polymer rheology, and greater emphasis on the relationship between processing and properties. Sophisticated software packages are the product of this research. The generation of these packages requires a new level of collaboration between chemical and mechanical engineering disciplines. There is also a need for careful experimental verification of these models. Application of these models enables a designer to predict the feasibility of a particular process and to make design improvements prior to investing the considerable time and money involved in preparing tooling (e.g., molds and extruder screws that often cost many tens of thousands of dollars). Application of these models has demonstrated that extra efforts expended to improve the design pay large dividends in reducing overall development time. In many cases, the prototype round of tooling can be eliminated. Recently, efforts have been made to extend these process models to describe fiber-filled composite systems. This is a

OCR for page 7
ONR Research Opportunities in Chemistry difficult task because the rheology and flow behavior of long-fiber composites are complex and not yet fully understood. The panel encourages research in this area because the product could facilitate the injection molding of advanced composites. If this work were successful, it would enable molding of composites, which would be far more cost-effective than the manual lay-ups that are employed currently in the aeronautical industry. Many of the traditional fabrication and assembly processes used in manufacturing are not understood well at a fundamental level. What happens at the tip of a tool bit? What limits drilling speed and bit life? Opportunities to improve forming and joining processes by better choices and applications of adhesives depend on better understanding of the adhesion process. Better fundamental understanding of the chemistry of oxide formation and fluxing could pay dividends in welding, brazing, and soldering with improvements in process speed, cost, and reliability. Basic research in these and other areas of processing science is encouraged by the panel. A severe limitation to the rapid development of processes and systems is a lack of emphasis on prototyping. Research activity should be backed up by and coupled to process and manufacturing prototyping for rapid feedback on problems inherent in process and design before they are embedded in a costly, marginally producible system. Not responding to the opportunities offered here carries a significant risk of jeopardizing future U.S. leadership in the area of process science.