Plasma Processing of Materials:

Scientific Opportunities and Technological Challenges

Panel on Plasma Processing of Materials

Plasma Science Committee

Board on Physics and Astronomy

Commission on Physical Sciences, Mathematics, and Applications

National Research Council

National Academy Press
Washington, D.C. 1991



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Plasma Processing of Materials: Scientific Opportunities and Technological Challenges Plasma Processing of Materials: Scientific Opportunities and Technological Challenges Panel on Plasma Processing of Materials Plasma Science Committee Board on Physics and Astronomy Commission on Physical Sciences, Mathematics, and Applications National Research Council National Academy Press Washington, D.C. 1991

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Plasma Processing of Materials: Scientific Opportunities and Technological Challenges NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance. This report has been reviewed by a group other than the authors according to procedures approved by a Report Review Committee consisting of members of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. Upon the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical matters. Dr. Frank Press is president of the National Academy of Sciences. The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. Robert M. White is president of the National Academy of Engineering. The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, upon its own initiative, to identify issues of medical care, research, and education. Dr. Stuart Bondurant is acting president of the Institute of Medicine. The National Research Council was established by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy's purposes of furthering knowledge and of advising the federal government. Functioning in accordance with general policies determined by the Academy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both Academies and the Institute of Medicine. Dr. Frank Press and Dr. Robert M. White are chairman and vice chairman, respectively, of the National Research Council. This project was supported by the National Science Foundation under Grant No. ECS-8922375, the Office of Naval Research under Contract No. N00014-89-J-1728, the Defense Advanced Research Projects Agency under Contract No. N60921-91-M-3233, and the Air Force Office of Scientific Research through the National Science Foundation under Grant No. PHY-8814509. Library of Congress Catalog Card No. 91-66812 International Standard Book Number 0-309-04597-5 Additional copies of this report are available from: National Academy Press 2101 Constitution Avenue, NW Washington, DC 20418 S465 Printed in the United States of America

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Plasma Processing of Materials: Scientific Opportunities and Technological Challenges PANEL ON PLASMA PROCESSING OF MATERIALS JOSEPH PROUD, GTE Laboratories Incorporated, Chair RICHARD A. GOTTSCHO, AT&T Bell Laboratories, Vice Chair JAMES BONDUR, Applied Materials, Inc. ALAN GARSCADDEN, Wright Research and Development Laboratory JOACHIM V. HEBERLEIN, University of Minnesota G. KENNETH HERB, AT&T Bell Laboratories MARK J. KUSHNER, University of Illinois JAMES E. LAWLER, University of Wisconsin MICHAEL A. LIEBERMAN, University of California, Berkeley THOMAS M. MAYER, Sandia National Laboratories ARTHUR V. PHELPS, Joint Institute for Laboratory Astrophysics WARD ROMAN, United Technologies Research Center HERB SAWIN, Massachusetts Institute of Technology HAROLD F. WINTERS, International Business Machines National Research Council Committee Liaison Representatives JOHN H. PEREPEZKO, University of Wisconsin, Solid State Sciences Committee ANDREW U. HAZI, Lawrence Livermore Laboratory, Committee on Atomic, Molecular, and Optical Sciences CHARLES F. KENNEL, University of California at Los Angeles, Plasma Science Committee Government Liaison Representatives JAMES B. GERARDO, Sandia National Laboratories LAWRENCE S. GOLDBERG, National Science Foundation JERRY J. PERRIZO, Air Force Office of Scientific Research CHARLES W. ROBERSON, Office of Naval Research JAMES R. ROBERTS, National Institute of Standards and Technology RONALD D. TAYLOR, Senior Program Officer

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Plasma Processing of Materials: Scientific Opportunities and Technological Challenges PLASMA SCIENCE COMMITTEE FRANCIS PERKINS, Princeton University, Chair JONATHAN ARONS, University of California, Berkeley MAFIA ASHOUR-ABDALLA, University of California, Los Angeles IRA B. BERNSTEIN, Yale University E. M. CAMPBELL, Lawrence Livermore National Laboratory RONALD C. DAVIDSON, Princeton University ALAN GARSCADDEN, Wright Research and Development Center RICHARD A. GOTTSCHO, AT&T Bell Laboratories ROY GOULD, California Institute of Technology ROBERT L. McCRORY, University of Rochester JOSEPH PROUD, GTE Laboratories Incorporated NORMAN ROSTOKER, University of California, Irvine RAVI SUDAN, Cornell University Former Members of the Plasma Science Committee Who Were Active During Formation of the Panel on Plasma Processing of Materials (1988-1991) CHARLES F. KENNEL, University of California, Los Angeles, Chair DAVID E. BALDWIN, University of Texas JOHN M. DAWSON, University of California, Los Angeles JOHN H. MALMBERG, University of California, San Diego RONALD D. TAYLOR, Senior Program Officer

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Plasma Processing of Materials: Scientific Opportunities and Technological Challenges BOARD ON PHYSICS AND ASTRONOMY FRANK D. DRAKE, University of California, Santa Cruz, Chair LLOYD ARMSTRONG, Johns Hopkins University HOWARD C. BERG, Harvard University WILLIAM F. BRINKMAN, AT&T Bell Laboratories PRAVEEN CHAUDHARI, IBM T.J. Watson Research Center GEORGE W. CLARK, Massachusetts Institute of Technology JEROME I. FRIEDMAN, Massachusetts Institute of Technology HAROLD P. FURTH, Princeton University MARTHA P. HAYNES, Cornell University CHARLES F. KENNEL, University of California, Los Angeles GILLIAN KNAPP, Princeton University STEVEN E. KOONIN, California Institute of Technology ALBERT NARATH, Sandia National Laboratories GEORGE W. PARSHALL, E.I. du Pont de Nemours & Company, Inc. JOSEPH M. PROUD, GTE Laboratories Incorporated VERA RUBIN, Carnegie Institution of Washington DAVID N. SCHRAMM, University of Chicago DANIEL TSUI, Princeton University DONALD C. SHAPERO, Director ROBERT L. RIEMER, Associate Director RONALD D. TAYLOR, Senior Program Officer SUSAN M. WYATT, Administrative Associate MARY RIENDEAU, Administrative Secretary ANNE K. SIMMONS, Senior Secretary

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Plasma Processing of Materials: Scientific Opportunities and Technological Challenges COMMISSION ON PHYSICAL SCIENCES, MATHEMATICS, AND APPLICATIONS NORMAN HACKERMAN, Robert A. Welch Foundation, Chair PETER J. BICKEL, University of California, Berkeley GEORGE F. CARRIER, Harvard University DEAN E. EASTMAN, IBM T.J. Watson Research Center MARYE ANNE FOX, University of Texas PHILLIP A. GRIFFITHS, Institute for Advanced Study NEAL F. LANE, Rice University ROBERT W. LUCKY, AT&T Bell Laboratories CLAIRE E. MAX, Lawrence Livermore National Laboratory CHRISTOPHER F. McKEE, University of California, Berkeley JAMES W. MITCHELL, AT&T Bell Laboratories RICHARD S. NICHOLSON, American Association for the Advancement of Science ALAN SCHRIESHEIM, Argonne National Laboratory KENNETH G. WILSON, Ohio State University NORMAN METZGER, Executive Director

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Plasma Processing of Materials: Scientific Opportunities and Technological Challenges Preface In 1989, the Executive Committee of the Division of Plasma Physics (DPP) of the American Physical Society (APS) made a presentation to the Board on Physics and Astronomy (BPA) arguing that a Plasma Science Committee should be established by the National Research Council (NRC). Shortly thereafter, the new committee was formed under the auspices of the BPA. Among its first projects, the Plasma Science Committee (PLSC) launched a study of plasma processing of materials by convening an informational meeting at which representatives of the materials processing community provided technical background and identified issues and priorities. It was noted that low-temperature plasma science is vitally important to the industrial sector in areas such as materials processing and semiconductor fabrication. Yet the basic research and education efforts in this area are inadequate and are not nearly commensurate with its technical and economic importance. Accordingly, the PLSC called for the formation of a panel of specialists to carry out a science and technology assessment with the following specific charge: Evaluate the potential impact of advances in low-temperature plasma science on surface processing technology, with emphasis on semiconductor applications. Identify key research problems in plasma physics and chemistry and the interaction of plasmas with surfaces. Recommend means to bring to bear the strengths of the plasma science community on the scientific, technological, and educational issues identified in the study. The Panel on Plasma Processing of Materials (PPPM) was organized in 1990 and met several times to address this charge. The panel was selected to provide representation from industry as well as from academic institutions, and liaison members were appointed who concurrently served on the Plasma Science Committee, the Solid State Sciences Committee (SSSC), and the Committee on Atomic, Molecular, and Optical Sciences (CAMOS). A daunting problem for the panel stemmed from the diversity of industrial applications of plasma-based systems used in the processing of materials. In its deliberations and its effort to focus the study, the panel concerned itself with two major areas of industrial applications, namely, microelectronics and aerospace. Three subpanels were formed to assess (1) applications of plasma processing of materials in the electronics and aerospace industries, (2) the basic plasma science that supports the applications, and (3) the related educational needs. The subpanels were charged to confront issues affecting the future health of the technology and science, the competitive position of the U.S. technology, identification of emerging technologies, the role of funding and coordination of research goals, and cooperation among industrial, academic, and national laboratory resources. A two-day workshop was held early in 1991 to bring together some two dozen additional experts from the low-temperature plasma community for the purpose of soliciting their review of the panel's draft findings and to obtain additional input. Workshop participants reviewed a preliminary report by the panel and followed the topical approach of the subpanels. The workshop presentations and breakout groups emphasized identification of issues. The acknowledged diversity of subject matter was indeed matched by the diverse views of the

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Plasma Processing of Materials: Scientific Opportunities and Technological Challenges participants, which led to lively debate but also to consensus on many of the key issues. This report, prepared by the Panel on Plasma Processing of Materials, is intended to summarize the views of the working panel members, the input received as a result of the workshop, the useful comments of numerous colleagues contacted by the panel, and many helpful suggestions contributed by the report's NRC-appointed peer reviewers. The Panel on Plasma Processing of Materials finds that plasma processing of materials is a technology critical to implementing some of the key recommendations of the NRC study Materials Science and Engineering for the 1990s (National Academy Press, Washington, D.C., 1989) and to enhancing the health of the technologies identified in the Report of the National Critical Technologies Panel (U.S. Government Printing Office, Washington, D.C., 1991), specifically in the areas of materials synthesis and processing and microelectronic processing. Although the work of the panel is now complete, it is the hope of its members that this report will clarify the critical importance of low-energy plasma science in materials processing and that a coordinated national focus will be developed to meet the demanding technological challenges that lie ahead. The diversity and emerging nature of plasma processing suggest that this will not be an easy task, but it is one that must not fail, given the economic importance of the technology and its enormous potential for stimulating economic growth.

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Plasma Processing of Materials: Scientific Opportunities and Technological Challenges Acknowledgments The panel is grateful to R. McGrath for his extensive contributions to the chapter on education in plasma science, to J. Verdeyen for his input on the history of low-energy plasma science, and to R. Matula for his extensive literature searches. It is also indebted to J. Fincke and D. E. Ibbotson for their contributions to the basic science section, to A. Kornblit for his contribution to the applications section, and to J. T. Herron for his work on chemical kinetics and data base requirements. Contributions from E. S. Aydil, K. Ceraso, D. Economou, D. B. Graves, C. Jurgensen, L. E. Katz, S. Marshall, J.P. McVittie, G. Oehrlein, K. Olasupo, G. S. Selwyn, and D. Vitkavage are gratefully acknowledged. The panel could not have completed its work without the help of its NRC staff officer, Ronald D. Taylor. Thanks are also due to the editor, Susan Maurizi, and Anne Simmons, who prepared the manuscript.

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Plasma Processing of Materials: Scientific Opportunities and Technological Challenges Contents 1   Summary, Findings, Conclusions, and Recommendations   1     Summary   1     Findings, Conclusions, and Recommendations   2 2   Plasma Processing and Low-Energy Plasma Science   6     Classification of Plasmas   7     Brief History of Low-Energy Plasma Science and Technology   8     Industrial Applications of Plasma Processing of Materials   9     Interface Between Basic Plasma Science and Applications   11     Scope of This Report   11 3   Plasma Processing in the Electronics Industry   13     Microelectronics Fabrication   18     Plasma Etching   21     Anisotropy   21     Selectivity   22     Uniformity   22     Damage   23     New Materials   24     Plasma Deposition   24     Planarization, Filling, and Interconnection   25     Surface Modification   26     New Materials   26     Plasma Cleaning   28     Low-Pressure Plasma Reactor Technology   28     Single-Wafer Processing   29     Process Control   30     New Plasma Sources   30     Magnetic Confinement   30     Downstream Processing   31     Modulated Processing   31     Clustered Processing   33     Thermal Plasma Reactor Technology   33     Toward Flexible Microelectronics Manufacturing   34     Findings and Conclusions   35 4   Scientific Foundation of Plasma Processing   37     Surface Processes   39     Theory and Simulation   39     Experimental Studies   41     Beam-Surface Experiments   41

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Plasma Processing of Materials: Scientific Opportunities and Technological Challenges     Ex Situ Analysis   43     Plasma Generation and Transport   44     Low-Pressure Plasma Modeling   45     Analysis   45     Fluid Simulations   46     Particle-in-Cell and Kinetic Simulations   46     Thermal Plasma Modeling   47     Toward CAD Tools and Expert Systems   49     Chemical Kinetics   49     Multidimensional Modeling and Magnetic Effects   49     Stability of Processing Plasmas   50     Accuracy and Reliability of Numerical Simulation Methods   50     Plasma Diagnostics   51     Positive Ions and Neutrals   51     Electron Density and Energy Distribution   53     Fields   53     Negative Ions   53     Particulates   55     Reference Reactors   55     Data Base for Plasma Generation and Transport   55     Present Status   56     Needs   56     Distribution of Information   57     Plasma-Surface Interactions   57     Boundary Conditions   58     Passive Surfaces   59     Particulates   59     Microstructure Evolution   60     In Situ Analysis   60     Funding for Plasma Processing Research   61     Japanese Research   61     French Research   63     Findings and Conclusions   63 5   Educational Issues   65     Educational Requirements for Undergraduates   66     Laboratory Courses and the Scientific Method   67     Research Experiences and Cooperative Programs   67     U.S. Graduate Education   67     Texts and Computer-aided Instruction   69     Faculty Development   69     Continuing Education   69     Foreign Educational Offerings   70     Japan   70     France   71     Findings and Conclusions   72     Appendix: Participants in Workshop on Plasma Processing of Materials   75