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INTRODUCTION
Modern materials applications (e.g., integrated circuits, optoelectronic devices, advanced engines for aerospace and ground transportation, cutting tools, and wear-resistant bearing surfaces) require increasingly precise control of the structure and composition of matter over smaller and smaller dimensions. This has led to the evolution of new, refined synthesis techniques, which allow the requisite control. Many of these techniques utilize the directional transfer of matter or energy through a vacuum or vapor phase. Examples of such techniques are molecular beam epitaxy (MBE), chemical vapor deposition (CVD), evaporation, and sputtering. These and other related technologies, referred to as beam technologies, are the subject of this report.
While some of these techniques go back to the nineteenth century (e.g., evaporation, CVD), others are quite new (e.g., MBE); all are evolving rapidly in response to the demands that applications place on the materials. Utilization of beams in electronic materials that require small complex structures has resulted in further development of beam processing methods. The additional requirements of a continuous fabrication line for a fully integrated process will no doubt lead to further development and sophistication of beam systems that include incorporation of on-line sensing devices that can control the process. In engineered materials, beam technologies have been used extensively for coatings and surface modifications. More recently, beams have been used for the formation of continuous fiber, net shapes, and composites. These applications are the outgrowth of technology demands on beam processing.
Beyond this normal outgrowth, and also of vast importance, is the ability of some of the beam techniques to prepare new structures and compositions of matter that lead to new applications. Examples are the ability to prepare materials monolayer by monolayer, which has led to the development of quantum-well devices for optoelectronic applications, and the ability to prepare diamond films by several different beam technologies, which has led to the availability of diamond in plate and cone shapes, something that was not previously possible. Yet another area in which beam technologies are playing an important role is in the preparation of nanophase materials, an area of increasing interest because of the unique properties of these materials. This latter synthesis of small building-block particles presents a challenge for the development of a high-yield beam process for generating nanosize powders similar to other powder forming processes, which subsequently can be incorporated into a fully integrated process.
A potentially important feature, which all these beam technologies have in common, is that they are all ''dry'' processes that are carried out in a vacuum or a controlled gaseous ambient. As such, they are closed system operations readily adapted to being joined to other dry processes. This capability makes these technologies candidates for components in the integration of materials processing technologies. The potential for shorter lead times, higher productivity, and improved quality, reliability, and performance makes process integration an attractive opportunity. The rapid advances being made in sensor technology, process control, and information processing have created new opportunities for integrated processing of materials.
A large capital investment, appropriate planning, and education of the work force will be required to implement beam or beam-assisted integrated processing. Inexpensive capital will probably be needed to fund this advancement, as is now done in Japan. Second, equipment manufacturers need to provide standard interfaces between machines (both software and hardware are needed for this) to allow the viability of an acceptable integrated process. Again, the Japanese are doing well in this area of development. A primary thrust of the present study was to evaluate the suitability of beam technologies for process integration and to identify the needs and barriers to their successful incorporation into such systems. This necessarily leads to consideration of the needs (e.g., technical development, computer-integrated manufacturing system) that will be required to allow economical processing.
In the following chapters, a summary and the major recommendations are described first, followed by a review of various beam technologies. This is followed by a review of the applications of some techniques to the processing of various materials. Here elemental and compound semiconductors are separated from other materials because of the already important applications that beam technologies have to microelectronic manufacturing. Additionally, the development of beam technologies for microelectronic manufacturing was originally conceived to be an example of integrated processing that could be applied to the study of engineered materials (metals, ceramics, polymers) and their susceptibility to beam-assisted integrated processing. However, fully integrated processing was found not to be well established in microelectronics. Therefore, a study is required in this area similar to that for the engineered materials. Examples of integrated materials processing using beam processing are reviewed, followed by a discussion of the needs and barriers for further integration.
