HANDBOOK OF VLSI MICROLITHOGRAPHY Principles, Technology and Applications Edited by William B. Glendinning Microlithography Consultant Nobleboro, Maine John N. Helbert Advanced Technology Center Motorola, Inc. Mesa, Arizona Reprint Edition np NOYES PUBUCATIONS Westwood, New Jersey, U.S.A. Copyright © 1991 by Noyes Publications No part of this book may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording or by any informa- tion storage and retrieval system, without permission in writing from the Publisher. Library of Congress Catalog Card Number: 90-23646 ISBN: 0-8155-1281-3 Printed in the United States Printed in the United States of America by Edwards Brothers Transferred to Digital Printing, 2010 Library of Congress Cataloging-in-Publication Data Handbook of VLSI microlithography: principles« technology, and applications / edited by William B. Qlendinning, John N. Helbert. p. cm. Includes bibliographical references and index. ISBN 0-8155-1281-3 : 1. Integrated circuits-Very large scale integration. 2. Microlithography. I. Glendinning, William B. II. Helbert, John N. TK7874.H3494 1991 621.381 '531~dc20 90-23646 CIP MATERIALS SCIENCE AND PROCESS TECHNOLOGY SERIES Editors Rointan F. Bunshah, University of California, Los Angeles (Series Editor) Gary E. McGuire, Microelectronics Center of North Carolina (Series Editor) Stephen M. Rossnagel, IBM Thomas J. Watson Research Center (Consulting Editor) Electronic Materials and Process Technology DEPOSITION TECHNOLOGIES FOR FILMS AND COATINGS: by Rointan F. Bunshah et al CHEMICAL VAPOR DEPOSITION FOR MICROELECTRONICS: by Arthur Sherman SEMICONDUCTOR MATERIALS AND PROCESS TECHNOLOGY HANDBOOK: edited by Gary E. McGuire HYBRID MICRCCIRCUrr TECHNOLOGY HANDBOOK: by James J. Ucari and Leonard R. Enlow HANDBOOK OF THIN FILM DEPOSniON PROCESSES AND TECHNIQUES: edited by Klaus K. Schuegraf KDNIZECMXUSTER BEAM DEPOSITION AND EPITAXY: by Toshinori Takagi DIFFUSION PHENOMENA IN THIN FILMS AND MICROELECTRONIC MATERIALS: edited by Devendra Gupta and Paul S. Ho HANDBOOK OF CONTAMINATION CONTROL IN MICROELECTRONICS: edited by Donald L. Tolliver HANDBOOK OF ION BEAM PROCESSING TECHNOLOGY: edited by Jerome J. Cuomo, Stephen M. Rossnagel, and Harold R. Kaufman CHARACTERIZATION OF SEMICONDUCTOR MATERIALS-Volume 1: edited by Gary E. McGuire HANDBOOK OF PLASMA PROCESSING TECHNOLOGY: edited by Stephen M. Rossnagel, Jerome J. Cuomo, and William D. Westwood HANDBOOK OF SEMICONDUCTOR SILICON TECHNOLOGY: edited by William C. O'Mara, Robert B. Herring, and Lee P. Hunt HANDBOOK OF POLYMER COATINGS FOR ELECTRONICS: by James J. Ucari and Laura A. Hughes HANDBOOK OF SPUTTER DEPOSITION TECHNOLOGY: by Kiyotaka Wasa and Shigeru Hayakawa HANDBOOK OF VLSI MICROLJTHOGRAPHY: edited by William B. Glendinning and John N. Helbert CHEMISTRY OF SUPERCONDUCTOR MATERIALS: edited by Terrell A. Vanderah CHEMICAL VAPOR DEPOSmON OF TUNGSTEN AND TUNGSTEN SIUCIDES: by John E.J. Schmitz (continued) v vi Series Titles Ceramic and Other Materials-Processing and Technology SOL-GEL TECHNOLOGY FOR THIN RLMS, FIBERS. PREFORMS, ELECTRONICS AND SPECIALTY SHAPES: edited by Usa C. Klein FIBER REINFORCED CERAMIC COMPOSITES: by K.S. Mazdiyasni ADVANCED CERAMIC PROCESSING AND TECHNCtOGY-Votume 1: edited by Jon G.P. Binner FRICTION AND WEAR TRANSITIONS OF MATERIALS: by Peter J. Blau SHOCK WAVES FOR INDUSTRIAL APPLICATIONS: edited by Lawrence E. Murr SPECIAL MELTING AND PROCESSING TECHNOLOGIES: edited by G.K. Bhat CORROSION OF GLASS. CERAMICS AND CERAMIC SUPERCONDUCTORS: edited by David E. Clark and Bruce K. Zoitos Related Titles ADHESIVES TECHNOLOGY HANDBOOK: by Arthur H. Landrock HANDBOOK OF THERMOSET PLASTICS: edited by Sidney H. Goodman SURFACE PREPARATION TECHNKXJES FOR ADHESIVE BONDING: by Raymond F. Wegman FORMULATING PLASTICS AND ELASTOMERS BY COMPUTER: by Ralph D. Hermansen PREFACE The chapter topics of this lithography handbook deal with the critical and enabling aspects of the intriguing task of printing very high resolution and high density integrated circuit (IC) patterns into thin resist process pattern transfer coatings. Circuit pattern density or resolution drives Dynamic Random Access Memory (DRAM) technology, which is the principal circuit density driver for the entire Very Large Scale Integrated Circuit (VLSI) industry. The book's main theme is concerned with the special printing processes created by workers striving to achieve volume high density IC chip production, with the long range goal being pattern features sizes near 0.25 μιπ or 256 Mbit DRAM lithography. The text is meant for a full spectrum of reader types spanning university, industrial, and government research and development scientists and production-minded engineers, technicians, and students. Specifically, we have attempted to consider the needs of the lithography-oriented student and practicing industrial engineers and technicians in developing this handbook. The leadoff chapter focusses on the view that lithography methods (printing patterns) are pursued for the singular purpose of manufacturing IC chips in the highly competitive commercial sector, and attempts to delineate the factors determining lithographic tool selection. The reader's perspective is drawn to consider IC device electrical performance criteria versus plausible and alternative energetic, or circuit density limited, particle printing methods-visible or shorter UV optical, electron, X-ray, and ion beams. The criteria for high quality micrometer and submicrometer lithography is very simply defined by the three major patterning parameters: line/space resolution, line edge and pattern feature dimension control, which when combined with pattern to pattern alignment capability determine lithographic overlay accuracy. Patterning yield and throughput further enter in as dependent economic factors. Resist technology has a logical, prominent, second-chapter position indicative of resist's overall importance in lithography, i.e., the end product of any IC lithography process is the patterned resist masking layer needed to delineate the VLSI circuit level. Example coverage of optical resist process optimization assures the reader a grasp of the most commonly and widely used (world- vii viii Preface wide) lithographic process technologies. The basic resist design concepts and definitions are thoroughly covered as well as advanced lithographic processes. Basic metrology considerations (Chapter 3) are absolutely imperative to rendering a total description of lithography methodology. The task of precisely measuring printed line width, or, space artifacts at submicron dimensions must be performed at present without the use of a traceable reference source-National Institute of Standards and Technology. These desirable and necessary standards must be made available in the future. However, critical and sufficient physical modelling of varied resist and IC material topological structures requires funding support and completion. Nevertheless, elucidation of optical, scanning-electron-microscope (SEM), and electrical test device linewidth measurements data present the reader with key boundary conditions essential for obtaining meaningful linewidth characterization. The portrayal of energetic particle microlithography is totally incomplete without some detail of the actual printing tool concepts, design, construction, and performance. The printing tools are presented and described in chapters 4-7 as to their usage in the IC manufacturing world. Clearly optical lithography has been the backbone and mainstay of the world's microchip production activity and will most likely continue in this dominant role until about 1997. In the optical arena, it is found that 1X, 5X, and 10X reduction printers of the projection scanned and unscanned variety must be described in subsets according to coherent and non-coherent radiation, as well as, by wavelengths ranging from visible to deep ultraviolet. Higher resolution or more energetic sourced tools are also well described. Next in world manufacturing usage, electron beam (e- beam) pattern printing has been vital, mostly because of its application in a pattern generation capacity for making photo masks and reticles, but also because of direct-write on-wafer device prototyping usage. The writing strategy divides e-beam printers, in general, into two groups: Gaussian beam raster scan, principally for pattern generation, and fixed or variable-shaped beam vector scan for direct-write-on-wafer applications. Subsets of the latter groups depend upon site-by-site versus write-on-the-fly substrate movements. The sophistication and complexity of e-beam printers requires diverse expertise in many technical areas such as: electrostatic and electromagnetic beam deflection, high speed beam blanking, intense electron sources, precise beam shapers, and ultra fast data flow electronics and storage. Interestingly, important special beam relationships Preface ix of maximum current, density, and writing pattern path-speed require the observance of unique boundary conditions in meeting printing criteria. On a worldwide basis, X-ray printing does not yet have high volume IC device production background examples, but high density prototype CMOS devices have been fabricated by IBM and feasibility demonstrated. The X-ray chapter presents X-ray lithography as a system approach with source, mask, aligner, and resist components. Of the competing volume manufacturing printing methods (optical and X-ray), the X-ray process is unique as a proximity and 1:1 method. As such, in order to meet the IC patterning quality criteria, extreme demands are placed on the mask fabrication process, much more so than for masks or reticles produced for the optical analogue. For economically acceptable IC production, laser/diode plasma and synchrotron ring X-ray sources must be presented as high density photon emitters. In the second part of Chapter 6, synchrotron is given special attention and presented as a unique X-ray generator with an X-ray flux collimation feature. In spite of the synchrotron's massive size and very large cost, it's multiport throughput capacity makes it viable for the very high production needs of certain industrial IC houses or possibly for multi-company or shared-company situations. In the last of the printing tool chapters, Chapter 7, the energetic ion is depicted in a controllable, steerable, particle beam serial pattern writer performing lithography at a high mass ratio compared to an e-beam writer. The focussed ion beam not only can deposit energy to form IC pattern latent resist images, but offers as another application the direct implant of impurity ions into semiconductor wafers, obviating completely the need for any resist whatsoever and greatly simplifying the IC chip processing sequence. The versatile energetic ion plays yet another and possibly its most significant role in a "steered-beam" tool, indispensable for optical and X-ray mask repair through the precise localized oblation and/or deposition of mask absorber material. The goal of establishing 0.35 μητι IC chip production by 1995 is plagued by the constraints of yield-defect models. A small fractlonal-submicron mask defect population is adversely catastrophic to the mask-and-reticle-dependent energetic lithographies (optical, X-ray), and especially so for the case of 1:1 parallel reduction printing. The modernization of photo mask and reticle fabrication methods and facilities paves the way for achieving extremely accurate and defect free optical masks and x Preface reticles ( <0.1/cm2). With defects of fractional-submicron sizes, mask and reticle repairs require fully automated "steered- beam" inspection/mapping equipment to work under full computer automation with compatible focussed ion beam repair tools. One of the editors' purposes in assembling this book has been to accurately disseminate the results of many and varied microlithography workers. Since it is not possible in any one book to satisfy enough detail for every reader's full curiosity, we consider at least that the reader is enabled to perform his own valid analysis and make some meaningful conclusions regarding the status and trends of the vital technical thrust areas of submicron iC pattern printing technology. The editors wish to extend appreciation to various colleagues for helpful discussions and encouragement: A. Oberai, J.P. Reekstin, M. Peckerar, and many others as the lengthy lists of chapter references attest. In addition, many individuals representing industrial, government, and university sectors have been extremely helpful in providing technical discussions, data, and figures to the chapter authors of this book. Gratitude is further extended here to those persons and their organizations. Gratitude also has been expressed via courtesy annotations in the figure captions. Finally, we commend and thank Judy Walsh for her compilation and editing skills. Nobleboro, Maine William B. Glendinning Mesa, Arizona John N. Helbert June, 1991 CONTRIBUTORS Phillip D. Blais John Melngailis Westinghouse Electric Corp. Research Laboratory of Advanced Technology Labs Electronics Baltimore, MD Massachusetts Institute of Technology Franco Cerrina Cambridge, MA University of Wisconsin Madison, Wl Michael E. Michaels Westinghouse Electric Corp. William B. Glendinning Advanced Technology Labs U.S. Army ETDL Baltimore, MD Fort Monmouth, NJ Michael T. Postek John N. Helbert National Institute of Motorola, Inc. Standards and Technology Advanced Technology Center Gaithersburg, MD Mesa, AZ Lee H. Veneklasen Robert D. Larrabee KLA Instruments, Inc. National Institute of San Jose, CA Standards and Technology Gaithersburg, MD Whitson G. Waldo Motorola, Inc. Loren W. Linholm Chandler, AZ National Institute of Standards and Technology Gaithersburg, MD NOTICE To the best of the Publisher's knowledge the information contained in this publication is accurate; however, the Publisher assumes no responsibility nor liability for errors or any consequences arising from the use of the information contained herein. Final determination of the suitability of any information, procedure, or product for use contemplated by any user, and the manner of that use, is the sole responsibility of the user. The book is intended for informational purposes only. The reader is warned that caution must always be exercised when dealing with VLSI microlithography chemicals, products, or procedures which might be considered hazardous. Expert advice should be obtained at all times when implementation is being considered. Mention of trade names or commercial products does not constitute endorsement or recommendation for use by the Publisher. xii