Plasma processing has emerged as an important technology for the deposition and etching of thin solid films in the manufacture of microelectronic devices. In fact, much of the progress achieved to date in device miniaturization would have been much more difficult without the unique characteristics of plasma processes. It is anticipated that future progress will continue to rely heavily on plasma technology. Although plasma chemical reactors are widely used, a lack of fundamental understanding has resulted in heavy reliance on empiricism in process design and control. The complexities inherent in any chemical reactor are compounded in plasma processing by the presence and active participation of the discharge in both gas phase and surface chemical processes. This has resulted in a technology that is sensitive to many design and operating parameters. A large parameter space gives process engineers flexibility in tailoring process conditions to meet objectives. However, without fundamental insight into the key physical and chemical processes, reactor design and control cannot be based on systematic, rational procedures. The purposes of this review are to introduce chemical engineers to plasma processing practice and phenomenology; to outline the progress made to date in fundamental studies of discharge physics and chemistry; to indicate areas in which chemical engineers must expand their traditional training to participate in plasma processing research; and finally to suggest how established chemical engineering methodology can be applied to plasma chemical reactors.
David B. Graves
Department of Chemical EngineeringUniversity of California Berkeley, CA 94720Introduction to Plasma Processing History, motivation, and future prospects Molecular gas plasmas are currently widely used in the microelectronics industry for the deposition and etching of thin solid films. Plasma processing is one of many techniques and processes used in the manufacture of integrated circuits (Doane et al., 1982), but the importance of plasma processing to present and future developments in microelectronics, coupled with the growing interest in this technology by chemical engineers, justifies a closer look at industrial practice and the underlying science. Simply stated, microelectronics manufacturing amounts to the growth, patterning, and doping of multiple layers of insulating, semiconducting, and conducting thin films (Hess, 1979). Consequently, deposition and selective etching of films is fundamental to many of the steps involved in this industry. It happens that chemically reacting, weakly ionized gas discharges are particularly powerful tools for depositing and removing thin films.Plasma etching is the more important process industrially, with VLSI (very large scale integration) relying upon the superior pattern transfer fidelity possible with plasma etching (a more or less equivalent term is reactive-ion etching). The utility of plasmas for etching hinges on their ability, under certain conditions, to remove material in the direction p...
