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`Chemical Mechanical
`Planarization of
`Microelectronic
`Materials
`
`JOSEPH M. STEIGERWALD
`SHYAM P. MURARKA
`RONALD J. GUTMANN
`
`W)
`
`‘WILEY-
`VCH
`
`WILEY-VCH Verlag GmbH & Co. KGaA
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`Chemical Mechanical
`Planarization of
`Microelectronic
`Materials
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`Chemical Mechanical
`Planarization of
`Microelectronic
`Materials
`
`JOSEPH M. STEIGERWALD
`SHYAM P. MURARKA
`RONALD J. GUTMANN
`
`WILEY-
`VCH
`
`WILEY-VCHVerlag GmbH & Co. KGaA
`
`All books published by Wiley-VCH are carefully prodteced.
`Nevertheless, authors, editors, and publisher do mot warrant the information
`contained in these books, including this book, to be free of errors.
`Readers are advised to keep in mind that statements, data, illustrations,
`mocedural details or other items may inadvertently be inaccurate.
`
`Library of Congress Card No.:
`Aoplied far
`
`British Library Cataloging-in-Publication Data:
`A catalogue record for this book is availeble from the British Library
`
`Bibliographic information published by
`Die Deutsche Bibliothek
`
`Die Dewsche Bibliothek lists this publication in the Dewsche Nationalbibliogra fie;
`detailed bibliographte data is available in the Internet at <hitp:dine.ddb.de>.
`
`© 1997 by John Wiley & Sons,Inc.
`© 3004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
`
`AMl rights reserved (including those of translation inte other languages}.
`No part ef this book maybe reproduced in any form — nor transmitted or translated
`inte machine language withoul written permission trom the publishers.
`Registered names, trademarks, etc. used in this book, even when not speciiically
`marked a3 such, are not to be considered unprotected by law.
`
`Printed in the Federal Republic of Germany
`Printed on acid-free paper
`
`Printing Strauss GmbH, Morlenbach
`Bookbinding Litges & Dopt Buchhinderei Cimbl!, Heppenheim
`
`[5SBN-13: 978-0-471-13827-3
`ISBN-10: O-471-19827-4
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`107
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`vi
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`CONTESTS
`
`Smoothing and Local Planarization
`2.2.1
`2.2.2 Global Planarization
`CMPPlanarization
`
`2.3
`
`2.3.1 Advantages of CMP
`2.3.2 Disadvantages of CMP
`2.3.3 The Challenge of CMP
`References
`
`CMPVariables and Manipulations
`3.1
`32
`
`Output Variables
`lnguit Variables
`References
`
`Mechanical and Electrochemical Concepts for CMP
`41
`42
`43
`
`Preston Equation
`Fluid Layer Interactions
`Boundary Layer Interactions
`
`Fluid Boundary Layer
`4.3.1
`4.3.2. Double Layer
`4.3.3 Metal Surface Films
`4.3.4 Mechanical Abrasion
`
`44
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`4.5
`
`4.6
`
`Abrasion Modes
`4.4.1
`Polishing vs. Grinding
`4.4.2 Hertzian Indentation vs. Fluid-Based Wear
`The Polishing Pad
`4.5.1
`Pad Materials and Properties
`4.5.2
`Pad Conditioning
`Electrochemical Phenomena
`
`4.6.1 Reduction-Oxidation Reactions
`4.6.2 Pourbaix Diaprams
`4.6.3 Mixed Potential Theory
`4.6.4 Example: Copper CMP in NHj-Based Slurries
`4,6.5 Example: Copper-Titantum Interaction
`Role of Chemistry in CMP
`
`47
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`CONTENTS
`
`
`Preface
`
`1 Chemical Mechanical Planarization—An Introduction
`
`Introduction
`1.1
`1.2 Applications
`1.3 The CMP Process
`1.4 CMP Tools
`1.5 Process Integration
`1.6 Conclusion and Book Outline
`References
`
`Historical Motivations for CMP
`
`2.1 Advanced Metallization Schemes
`2.1.1
`Interconnect Delay Impact on Performance
`2.1.2 Methods of Reducing Interconnect Delay
`2.1.3. Planarity Requirements for Multilevel
`Metallization
`
`2.2 Planarization Schemes
`
`xl
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`_—_——_
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`11
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`PREFACE
`
`xiii
`
`have also contributed during the research at Rensselaer and in preparation
`of the manuscript. Professors M. Tomozawa and D. Duquette have pro-
`vided insights and reviews very valuable in the preparation of the book.
`Discussions with L. Cook, M. Fury, K. Holland, B. Jairath, arid several
`graduate students working in CMP-related research at Rensselaer have
`been very fruitful.
`Many thanks are due and sincerely given to Mrs. Lori Wilson for
`putting the manuscript together. Without her several hours of hard work,
`the production of this book would not have been possible. We also wish to
`note our appreciation to Mr. Jan Neirynck for helping us diligently in
`finding referenced materials.
`We are grateful to many authors whose papers we have followed
`closely in various parts of the book and who allowed us to use their work
`in this book. We are also thankful to Academic Press, Adam Hilger,
`American Institute of Physics, American Ceramic Society, Butterworth-
`Heinemann, The Electrochemical Society, Institute of Electrical and
`Electronics Engineers, Japan Intemational Conference on Solid State De-
`vices and Materials, John Wiley & Sons, Journal of Cellular Plastics,
`Journal of Crystalline Growth, Macmillan Publishing Company, Materi-
`als Research Society, and the University of South Florida (T.E. Wade),
`which publishes Proceedings of the VLSI Multilevel Inteconnection Con-
`ference, for the use of copyrighted materials.
`Most ofall, we would like to thank our families for the understand-
`ing and love that made writing of this book possible.
`
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`23 CMP PLANARIZATION
`
`29
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`HISTORICAL MOTIVATIONS FOR CMP
`
`2.2.2 Global Planarization
`
`As mentioned previously, global planarization is required to
`meet the depth of field requirements of lithography tools in the
`sub-0.5 pm regime. Very few other planarization schemes obtain
`the global planarity offered by CMP, the most widely accepted
`method of achieving global planarization®” Recent studies have
`demonstrated the ability to maintain global planarization using a
`blocking mask and an isotropic resist-oxide etch back.“ However,
`process latitude with this scheme remains uncertain and in addit-
`ion,
`the achievement of global planarization requires a globally
`planarized TLD at the previous layer. Thus, a process that creates
`global planarity, such as CMP,
`is required before the blocking
`mask, and an isotropic etch scheme may be performed. Fundamen-
`tally, CMP obtains higher degrees of planarity because planarity is
`imposed due to the extreme flatness of the polishing table. In
`contrast, other planarization schemes rely on the addition of
`planarizing layers and consequently are highly pattem dependant
`leading to a lower degree of planarity. While the CMP processis
`still in its infancy, its promise of global planarity and relative low-
`cost/low-complexity processing has sparked considerable interest
`in the process,°”
`
`2.3
`
`CMP PLANARIZATION
`
`The use of CMP techniques is not unique to planarization.
`Polishing of glass pieces is a long-established practice in the fabri-
`cation of lenses. Indeed, as we shall see in Chapter 5, much of the
`understanding of glass polishing may be applied to oxide CMP. In
`the fabrication of ICs, silicon polishing as a final step in the
`preparation of starting wafers has been in use for several decades.
`However, CMP used for planarization differs from lens fabrication
`and wafer preparation in one important respect.
`In all
`three
`applications, a high degree of planarity or flamess is required;
`however, in CMP, the same degree of flatness must be achieved
`with far less material removal.
`In addition,
`the tolerances for
`material remowal are much tighter for CMP. Water thicknesses, for
`
`
`
`(b)
`
`Figure 2.6
`
`Schematic representation of a wafer polishing tool. (a) Polish
`table with wafer carier assembly. (b) Schematic view of
`water-slury-pad system.
`
`example, may vary by several mils while ILD thicknesses must
`vary less than ~100 om from wafer to wafer. Thus, CMP used for
`planarization demands much tighter process control.
`Figure 2.4 shows a schematic representation of a polishing
`tool. The wafer is pressed against the polishing surface, termed the
`polishing pad, and che wafer and pad are both rotated. A polishing
`
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