Chemical_Vapor_Deposition_of_Tungsten_and_Tungsten_Silicides_for_VLSI__ULSI_Applications__Materials_

需完整版本 发邮件：wzxidian@gmail.com Doc uCo m P DF Tria l ww w.pd fwiz ard. com CHEMICAL VAPOR DEPOSITION OF TUNGSTEN AND TUNGSTEN SILICIDES 需完整版本 发邮件：wzxidian@gmail.com Doc uCo m P DF Tria l ww w.pd fwiz ard. com 需完整版本 发邮件：wzxidian@gmail.com Doc uCo m P DF Tria l ww w.pd fwiz ard. com CHEMICAL VAPOR DEPOSITION OF TUNGSTEN AND TUNGSTEN SILICIDES For VLSIjULSI Applications by John E.J. Schmitz Thin Film Division Genus, Inc. Mountain View, California Reprint Edition r;:;:::1 NOYES PUBLICATIONS~ Westwood, New Jersey, U.S.A. 需完整版本 发邮件：wzxidian@gmail.com Doc uCo m P DF Tria l ww w.pd fwiz ard. com Copyright © 1992 by lohn E.l. Schmitz No part of this book nlay 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: 91-18643 ISBN: 0-8155-1288-0 Printed in the United States Published in the United States of America by Noyes Publications Fairview Avenue, Westwood, New Jersey 07675 10 987 6 5 43 Library of Congress Cataloging-in-Publication Data Schnlitz, John EJ. Chemical ve:.por deposition of tungsten and tungsten silicides for VLSI/ULSI applications / by John E.J. Schmitz p. em. Includes bibliographical references and index. ISBN 0-8155-1288-0 1. Integrated circuits--Very large scale integration--Materials. 2. Tungsten. 3. Vapor-plating. I. Title. TK7871.15.T85S36 1991 621.39'5--dc20 91-18643 CIP 需完整版本 发邮件：wzxidian@gmail.com Doc uCo m P DF Tria l ww w.pd fwiz ard. com To Pieternel and Lucas v 需完整版本 发邮件：wzxidian@gmail.com Doc uCo m P DF Tria l ww w.pd fwiz ard. com 需完整版本 发邮件：wzxidian@gmail.com Doc uCo m P DF Tria l ww w.pd fwiz ard. com 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 ALMS 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 MICROCIRCUIT TECHNOLOGY HANDBOOK: by James J. Licari and Leonard R. Enlow HANDBOOK OF THIN FILM DEPOSITION PROCESSES AND TECHNIQUES: edited by Klaus K. Schuegraf IONIZED-CLUSTER BEAM DEPOSITION AND EPITAXY: by Toshinori Takagi DIFFUSION PHENOMENA IN THIN ALMS 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 SIUCON TECHNOLOGY: edited by William C. O'Mara, Robert B. Herring, and Lee P. Hunt HANDBOOK OF POLYMER COATINGS FOR ELECTRONICS: by James J. Licari and Laura A. Hughes HANDBOOK OF SPUTTER DEPOSITION TECHNOLOGY: by Kiyotaka Wasa and Shigeru Hayakawa HANDBOOK OF VLSI MICROUTHOGRAPHY: edited by William B. Glendinning and John N. Helbert CHEMISTRY OF SUPERCONDUCTOR MATERIALS: edited by Terrell A. Vanderah CHEMICAL VAPOR DEPOSITION OF TUNGSTEN AND TUNGSTEN SIUCIDES: by John E.J. Schmitz (continued) vii 需完整版本 发邮件：wzxidian@gmail.com Doc uCo m P DF Tria l ww w.pd fwiz ard. com Ceramic and Other Materials-Processing and Technology SOL-GEL TECHNOLOGY FOR THIN ALMS. ABERS, PREFORMS, ELECTRONICS AND SPECIALTY SHAPES: edited by Lisa C. Klein ABER REINFORCED CERAMIC COMPOSITES: by K.S. Mazdiyasni ADVANCED CERAMIC PROCESSING AND TECHNOLOGY-Volume 1: edited by Jon G.P. Binner FRICTION AND WEAR TRANSITIONS OF MATERIALS: by Peter J. Blau SHOCK WAVES FOR INDUSTRIAL APPUCATIONS: 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 TECHNIQUES FOR ADHESIVE BONDING: by Raymond F. Wegman FORMULATING PLASTICS AND ELASTOMERS BY COMPUTER: by Ralph D. Hermansen viii 需完整版本 发邮件：wzxidian@gmail.com Doc uCo m P DF Tria l ww w.pd fwiz ard. com PREFACE The acceptance of the chemical vapor deposition of tungsten (CVD- W) is such that it is finding its way more and more into high volume production of ULSI circuits. Unfortunately, bringing up a CVD-W process is not a trivial exercise. New equipment configurations (cold wall reactor), new deposition chemistries (not to mention the chemistries of precleaning and/or etching), adhesion layers, etc. all contribute to the complexity of this process. In addition, the maintenance of a tungsten process in terms of reactor cleaning, maintenance and trouble shooting requires a solid background in CVD-W technology. Extensive literature has been published on blanket and selective CVD-W, in which a vast amount of (sometimes conflicting) information can be found. What is clearly needed is a book where all relevant and pertinent material is gathered in a condensed format. It is the intention of this book to provide such a compilation of the literature with emphasis on the material which has appeared in the last 10 years. In addition, unpublished material obtained in the laboratory of the author is included. After reading this work, the reader will have all the necessary background to bring up, fine tune and maintain successfully a CVD-W process in a production line. Others seeking a quick overview of the current status of CVD-W will also benefit from this book. The nine chapters of this book can be read in any order. No background other than basic physics and chemistry is assumed. Where appropriate, rule of thumb calculations are included to increase further insight into the subject. The author has also provided personal opinion and insight on certain subjects where appropriate. Chapter I gives a description of the driving forces behind the introduction of CVD-W in Ie manufacturing. Chapter II treats the issues of blanket CYD-W for plug applications. In this chapter the etch back of blanket tungsten is also briefly summarized. Selective tungsten is described in chapter III with the emphasis again on plug applications. Chapter IV compares the benefits of selective and blanket CYD-W for plug applications. Another important application of blanket CYD-W, namely that of the use of tungsten as interconnect material, is extensively discussed in chapter V. Important properties of the gases and chemistries used and of tungsten itself are evaluated in chapter VI. Chapter VII is especially important because it ix 需完整版本 发邮件：wzxidian@gmail.com Doc uCo m P DF Tria l ww w.pd fwiz ard. com treats the principles of cold wall reactors where much attention is paid to wafer temperature and its effect on the process. Chapter VIII lists several subjects which might become important future applications of CVD-W but are now still in the R&D stage. Additionally, some alternative plug processes are discussed. The chemical vapor deposition of tungsten silicide (WSix) is also covered in this book in chapter IX. This material was included since the chemistry and equipment are so similar to blanket tungsten. Additionally, it allowed the coverage of the SiH2Cl2 based tungsten silicide process which is relatively new today. For the convenience of the reader a comprehensive reference list of over 260 references is included at the end of the book. The literature references are grouped according to their subject. In addition, a subject and an author index will be found which facilitates the use of the book as a reference tool for CVD-Wand CVD-WSix' A statement about the units used in this book is in order. The unit system as used in each specific piece of literature under discussion is maintained. Sunnyvale March, 1991 x J.E.J. Schmitz 需完整版本 发邮件：wzxidian@gmail.com Doc uCo m P DF Tria l ww w.pd fwiz ard. com ACKNOWLEDGMENTS During the preparation of this book many people were consulted for advice or asked for original SEM micrographs. The following persons have to be mentioned: Larry Bartholomew, Ray Chow, Russell Ellwanger, Janet Flanner, Clark Fuhs, Dr. Mart Graef, Dr. Albert Hasper, Sien Kang, Dr. H. Korner, Gareth Patten, Dr. Ivo Raaijrnakers, Dr. Ed Rode, Steve Selbrede and Dr. Evert van de Yen. Special thanks to Jim Dodsworth and Norm Zetterquist who carefully read the manuscript and gave many suggestions and to Doree Swanson who helped with the preparation of the manuscript. Thanks also to the Genus executive management for the support given during the period of preparation of the manuscript, especially William W.R. Elder. The Electrochemical Society, The Materials Research Society, Wiley and Sons Inc., Lake Publishing Corporation, The Institute of Electrical and Electronics Engineers, Inc. (IEEE), Solid State Technology, Elseviers Science Publishers BV, Cahners Publishing Co. and The American Institute of Physics graciously allowed the reprint of numerous pictures from their publications. Finally I would like to thank Noyes Publications, in particular George Narita, for the support given and for his consideration of the viability of this publication. xi 需完整版本 发邮件：wzxidian@gmail.com Doc uCo m P DF Tria l ww w.pd fwiz ard. com xii NOTICE To the best of the Publisher's knowledge the information contained in this book 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. Tungsten deposition raw materials and processes could be potentially hazardous and due caution should always be exercised in the handling of materials and equipment. Expert advice should be obtained at all times when implementation is being considered. 需完整版本 发邮件：wzxidian@gmail.com Doc uCo m P DF Tria l ww w.pd fwiz ard. com CONTENTS PREFACE ix ACKNOWJ..,EDGMENT xi TABLE OF CONTENTS xiii CHAPTER I: INTRODUCTION 1 1.1 Scaling down 1 1.2 Electrical contacts 3 1.3 Device reliability 4 1.4 Contact planarization and design rules 6 CHAPTER II: THE BLANKET TUNGSTEN APPROACH 10 2.1 Principal steps 10 2.2Tungsten adhesion 11 2.2.1 Adhesion layers 12 2.2.2 Chemical resistance 15 2.2.3 Contact resistance 15 2.2.4Step coverage 17 2.2.5 Manufacturability 18 2.3 Blanket deposition of tungsten 19 2.3.1 Chemistry 19 2.3.2Step coverage 21 2.3.3 Film thickness requirements 38 2.3.4 Film thickness uniformity 41 2.4 Etch back of blanket tungsten 42 2.4.1 Etch back without a sacrificial layer 42 2.4.2 Etch back using a sacrificial layer 47 2.5 Degree of planarization and the contact diameter 47 2.6 Blanket tungsten material characterization 50 xiii 需完整版本 发邮件：wzxidian@gmail.com Doc uCo m P DF Tria l ww w.pd fwiz ard. com CHAPTER III: THE SELECTIVE TUNGSTEN APPROACH 51 3.1 Principal steps 52 3.2 rr)rpes of substrates 53 3.3 Types of dielectric layers 54 3.4 Chemistry of selective tungsten 55 3.4.1 Hz/WF6 chemistry 56 3.4.2 SiH4/WF6 chemistry 63 3.5 Mechanisms of selectivity loss 73 3.6 Electrical characterization 81 CHAPTER IV: BLANKET VERSUS SELECTIVE TUNGSTEN 87 4.1 Feasibility of selective and blanket contact or via fill 87 4.2 Costs of the contact/via fill process 90 4.3 World wide status of CVD of tungsten 93 4.3 Conclusions 93 CHAPTER V: TUNGSTEN AS INTERCONNECT MATERIAL 95 5.1 Weaknesses of aluminum interconnects 95 5.2 Tungsten interconnects 97 5.3 Issues of tungsten interconnects 98 5.3.1 Tungsten film stress 98 5.3.2 Origin of the stress in CVD-tungsten films 99 5.3.3 Determination of film stress 102 5.3.4 Roughness of tungsten films 102 5.3.5 ResistivityofCVD-W 105 5.3.6 Determination of the resistivity 109 CHAPTER VI: THE CHEMISTRY OF CVD-W AND PROPERTIES OF TUNGSTEN 110 6.1 CVD tungsten source material. , 111 6.2 Experinlental deposition rate relations obtained for the Hz/WF6 chemistry 114 6.3 Some properties of tungsten 117 xiv 需完整版本 发邮件：wzxidian@gmail.com Doc uCo m P DF Tria l ww w.pd fwiz ard. com 6.4 Contamination issues in CVD-W 120 CHAPTER VII: THE DEPOSITION EQUIPMENT 123 7.1 Hot wall reactors 123 7.2 Cold wall reactors 125 7.2.1 Heat transfer 125 7.2.2 Temperature and thickness uniforrnity 135 7.2.3 Thermal diffusion 136 7.2.4 Distribution of temperature, concentrations and gas velocity in a cold wall reactor 141 7.3 Industrial reactors 142 7.3.1 rrypeofequipment 142 7.3.2 Backside deposition 144 7.3.3 Particle contamination 145 7.4 Future reactor developments 146 CHAPTER VIII: MISCELLANEOUS 150 8.1 Tungstengates 150 8.1.1 Problems of Poly-Si gate electrodes 150 8.1.2 Tungsten as the gate material. 151 8.2 Selective growth on implanted oxide 154 8.2.1 Tungsten growth using silicon implants 156 8.2.2 Tungsten growth using tungsten implants 156 8.3 Buried tungsten 157 8.4 Alternative deposition techniques 158 8.4.1 Plasma enhanced CVD-W 158 8.4.2 Photo enhanced CVD-W 160 8.5 Alternative plug processes 163 8.5.1 Conversion of Poly-Silicon into W 164 8.5.2 SOGffiW plugs 167 8.5.3 The pillar approach 170 xv 需完整版本 发邮件：wzxidian@gmail.com Doc uCo m P DF Tria l ww w.pd fwiz ard. com CHAPTER IX: CHEMICAL VAPOR DEPOSITION OF TUNGSTEN SILICIDE 171 9.1 Introduction 172 9.2 WSix for polycide applications 172 9.3 Silicide deposition methods 175 9.4 CVD ofWSix..........................•.......................................................................176 9.5 CVD-WSix based on SiH4/WF6 chemistry 182 9.5.1 Deposition process and film properties 182 9.5.2 Electrical performance of WSix in devices 186 9.5.3 Si content in WSix.............•...................•........................•.............188 9.5.4 Thin film resistivity of WSix 190 9.5.5 EtchingofWSix...•..•..•.................................................................•191 9.6 WSix based on SiHzClz/WF6 chemistry 192 9.7 Fluorine content in CVD-WSix films 199 9.8 Stress in CVD-WSix films 203 9.9 Step coverage of CVD-WSix films 207 9.10 Conclusions 208 REFERENCES 209 AUTHOR INDEX 228 SUBJECT INDEX 231 APPENDIX: UNIT CELLS OF W AND WSi2 235 xvi 需完整版本 发邮件：wzxidian@gmail.com Doc uCo m P DF Tria l ww w.pd fwiz ard. com CHAPTER I INTRODUCTION 1.1 SCALING DOWN There are two basic reasons for the ongoing increase of component integration in integrated circuits (IC's): (a) better performance: the smaller size of the devices (ie. transistors, diodes etc.) often results in a better performance and higher speed of these components and (b) cost savings: more components can be integrated per unit area or, from another perspective, the size of the IC's can be considerably snlaller, thus allowing more of them on each wafer. It is possible that the latter provides higher yields because the risk of particle contamination resulting in defects is lower. Higher yields obviously equate to lower cost per die. When design rules invade the sub-micron regime, new process problems will occur. These problems are partly caused by the increased aspect ratios which are inherent to sub-micron design rules. For example, low temperature oxides such as SiH4/Oz-LTO or plasma enhanced Si3N4 1 需完整版本 发邮件：wzxidian@gmail.com Doc uCo m P DF Tria l ww w.pd fwiz ard. com Introduction tend to result in void formation in the dielectric layer when the aspect ratio becomes larger than 1. Another example of a common problem associated with the deposition of thin films on sub-micron features is that the step coverage of sputtered aluminum is not acceptable in sub- micron contacts (see below). The general approach to reduce problems asso~iated with high aspect ratios is planarization of the steps. Planarization of contacts (or vias) can be accomplished by filling them with a conducting material. The main emphasis of this book is to show how this can be achieved by Chemical Vapor Deposition of Tungsten (CVD-W) either in the blanket or in the selective mode. In addition, other important applications of CVD-W will be Figure 1.1. Cross section of a multi-level metallization system. In this situation the contacts and the via's are already filled. 2 需完整版本 发邮件：wzxidian@gmail.com Doc uCo m P DF Tria l ww w.pd fwiz ard. com Introduction Al .. -: .. " ... ", ....- :.0' , . ...: . Figure 1.2. A high aspect ratio sub-micron contact filled with sputtered aluminum. Note the thinning of the aluminum at the side walls. discussed as well as film properties and cold wall reactor fundamentals. 1.2 ELECTRICAL CONTACTS An Ie design with multi-level metallization contains at least two types of contacts: a) the contact to the active areas hereafter referred to as "contact" and 3 需完整版本 发邮件：wzxidian@gmail.com Doc uCo m P DF Tria l ww w.pd fwiz ard. com Introduction b) the connection between two overlying metal layers hereafter named as "via" (see figure 1.1). In most types of Ie's, the contacts can end on n+ or p+ mono-crystalline silicon, pOly-silicon, various types of sUicides, and other materials such as TiN. One of the most important properties of the contact and the via is the contact resistance (Rc): (1.1) The determination of Rc is not trivial and care should be taken that the appropriate device (Kelvin) is used (see for more details chapter III). Values of Rc found in the literature for contacts direct to silicon are in the range of 10-7 ncm2 and vias are in the range of 10-8 Ocm2. 1.3 DEVICE RELIABILIlY Consider the ramifications when a sub-micron, high-aspect ratio contact will be filled in the conventional way using sputtered aluminum (see figure 1.2). When the step coverage is only minimally acceptable, the aluminum can still provide continuous conductance and electrical contact. In fact, Rc from such a contact, as measured from a Kelvin structure, can still be excellent under such conditions. 1\vo problems, however, remain with this approach: (a) During current passage a very high current density is seen at the bottom of the contact hole where the sputtered aluminum tends to be thinnest. This can result in Joule heating and, even more serious, in increased electromigration of the aluminum in the contact. Eventually this electromigration can lead to an open contact and the loss of the integrity of the cirellit or a dead circuit. (b) Due to the poor step coverage of the aluminum layer, very high aspect ratios usually remain after aluminum deposition. Since in the following step, a dielectric layer must be deposited, void formation in this 4 需完整版本 发邮件：wzxidian@gmail.com Doc uCo m P DF Tria l ww w.pd fwiz ard. com Introduction Figure 1.3. The same situation as in figure 1.2 but now after the deposition of a dielectric layer (for example plasma enhanced CVD- oxide). layer can easily occur (see figure 1.3). Such voids are generally considered to be a reliability hazard. For instance, crack formation or enhanced aluminum mobility can occur. Moreover, when a resist etch back (REB) is used for dielectric planarization such voids can cause intra-metal shorts. Although several attempts have been made to improve the step coverage of sputtered aluminum, the results have not been optimal because other properties (such as elec