THIN FILMS SCIENCE AND TECHNOLOGY Advisory Editor: G. Siddall Vol. 1 Langmuir-Blodgett Films (Barlow, Editor) Vol. 2 Size Effects in Thin Films (Tellier and fosser) Vol. 3 Langmuir-Blodgett Films, 1982 (Roberts and Pitt, Editors) Vol. 4 Passivity of Metals and Semiconductors (Froment, Editor) Vol. 5 Growth of Crystalline Semiconductor Materials on Crystal Surfaces (Aleksandrov) Vol. 6 Coatings on Glass (Pulker) Vol. 7 Thin Films by Chemical Vapour Deposition (Morosanu) THIN FILMS SCIENCE AND TECHNOLOGY, 7 Thin Films by Chemical Vapour Deposition C .E. MOROSANU Electronic Components Research and Development Centre, 72996 Bucharest 30 Romania ELSEVIER, Amsterdam —Oxford—New York—Tokyo 1990 Distribution of this book is being handled by the following publishers: for the U.S.A and Canada ELSEVIER SCIENCE PUBLISHERS, Inc. 655 Avenue of the Americas New York, NY 10010 for the East European Countries, China, Northern Korea, Cuba, Vietnam and Mongolia EDITURA TEHNICA Pia-fa Scinteii nr. 1 R-71341 Bucuresti 33, Romania for all remaining areas ELSEVIER SCIENCE PUBLISHERS 25, Sara Burgerhartstraat P.O.Box 211, 1000 AE Amsterdam, The Netherlands Library of Congress Cataloguing-in-Publication Data: Morosanu, C.E. Thin Films by Chemical Vapour Deposition (Thin Films Science and Technology: vol. 7) Rev., updated, and enl. translation of: Depunerea chimicä din vapori a straturilor subjiri Includes bibliographical references and indexes. ISBN 0-444-98801-7 1. Vapour plating. 2. Thin films. 3. Semiconductors. I. Title. II. Series: Thin films science and technology: 7. TS 695. M6713 1990 671.7*35 dc20 ]$BN 0-444-98801-7 (vol.7) ISBN 0-444-41903-9 (series) With 135 illustrations and 36 tables ©EDITURA TEHNICA, 1990 ©Translation, C.E. MOROSANU, 1990 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system,, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise without prior written permission of the copyright owner. PRINTED IN ROMANIA Preface The explosive growth of the semiconductor industry has caused a rapid evolution of thin-film materials that lend themselves to the fabrication of state-of-the-art semiconductor devices. Beginning with the decade of the 60s, an old research tech- nique named chemical vapour-phase deposition (CVD), which shows several unique advantages, has developed into the most widely used technique for thin film preparation in electronics technology. In the last thirty years, tremendous advances have been made in the science and technology of thin films prepared by means of CVD. The scope of this book is to present, in a single volume, an up-to-date overview of the important field of CVD processes which has never been completely reviewed, previously. The topic of the present volume has been organized into three main parts, i.e. fundamental considerations (Chapters 2—10), thin film preparation and charac- terization (Chapters 11 — 15) and applications (Chapter 16). Thus an attempt is made to provide a comprehensive treatment of both theoretical and practical aspects of all classes of CVD thin films, i.e. semiconductors, insulators, metals, superconductors, and magnetics. It is hoped that the book will be useful to both beginning and advanced special- ists as .well as to workers in related fields, thus contributing to the further deve- lopment of CVD thin films. C.E. Morosanu Acknowledgements I am grateful to the authors acknowledged in the figure captions and table headings, to the publishers of Applied Physics Letters, Electronics, Electronics Letters, Hewlett-Packard Jour- nal, IBM Journal of Research and Development, IEEE Transactions on Electron Devices, the Japanese Journal of Applied Physics, the Journal of Applied Physics, the Journal of Crystal Growth, the Journal of the Electrochemical Society, the Journal of Electronic Materials, the Journal of Vacuum Science and Technology, Metallurgical Transactions of the AIME, Philips Research Reports, Physics of Thin Films, Proceedings of the IEEE, RCA Review, Revue Rou- maine de Chimie, Revue Technique Thomson-CSF, Scientific American, Semiconductor Inter- national, Solar Energy Materials, Solid-State Electronics, Solid State Technology, and Thin Solid Films and to the following book publishers—Academic Press, McGraw-Hill Book Co., North- Holland Physics Publishing, Pergamon Press, Plenum Publishing Corp., Springer Verlag, and Wiley for permission to copy figures and data for tables. I have also been helped by numerous colleagues throughout the world who have sent me most of their important published articles and whose work I have used. I gratefully acknowledge the support of the Electronic Components Research and Develop- ment Centre. 1 Evolution of CVD Films 1.1 Introductory Remarks Thin films have been the topic of a large number of investigations during the past quarter century since these films became technologically important particularly in the field of semiconductor electronics [1 — 10]. Thin films can be prepared by using a variety of methods, among which chemical vapour deposition (CVD) has received widespread acceptance [11 — 93]. CVD involves the formation of a solid film on a heated substrate sur- face by means of a chemical reaction in a gas or in the vapour phase. This process employs various gaseous, liquid and solid chemicals as sources of the elements of which the thin film is to be made. In comparison with most thin film preparation methods, CVD has a number of unique advan- tages such as the versatility, adaptability, compatibility, quality, simplicity, reproducibility, productivity and cheapness. For these reasons, CVD has expanded continuously and developed into the most important method for producing films for solid-state devices. In the present book, an attempt has been made to cover all aspects of CVD thin films. Both early and recent developments, especially of materials used in the semiconductor industry (where the majority of high quality CVD films are extensively applied), are surveyed. The material pre- sented is organized in five parts, i.e. an introduction, fundamentals, techni- ques, applications and conclusions. In the introductory part, a brief presenta- tion of the historic development of CVD thin films is also included. The second part begins with a comparison between CVD and other modern film formation methods and then covers fundamental aspects of CVD films such as thermodynamics, kinetics, thickness, nucleation, structure, analysis and properties. Reactor systems and process techniques for preparing semicon- ducting, insulating, conducting, superconducting and magnetic films are then discussed. Next, the applications of CVD films primarily in the field of microelectronics are discussed briefly. Finally, a brief concluding part, 19 INTRODUCTION which also contains a presentation of the present status and future trends in CVD films, is provided. Numerous excellent general and specialized reviews are available on theoretical and practical aspects of CVD thin films [11—22]. Many general aspects of the growth of thin films by means of CVD have been summarized in books by Powell et al. (published in 1966) [11] and Vossen and Kern (1978) [2]. General reviews available dealt with all CVD thin film materials — e.g. Feist et al. (1969) [14], Campbell (1970) [16], Haskell and Byrne (1972) [17] and Bryant (1977) [19] — or only the elec- tronic CVD thin film materials —e.g., Chu(1969) [20], Amick and Kern (1970) [92], Wang and Bracken (1972) [4821], Chu and Schmeltzer (1973) [21], Tietjen (1973) [22], and Watts (1973) [52]. There are also two general bibliogra- phies by Agajanian (1976) [41] and Hawkins (1981) [42] covering several as- pects of CVD. Proceedings of international [23—31] or European [32—36] conferences on CVD held generally bi-annually and tri-annually, respectively, contain a collection of original papers describing almost all CVD topics. Other symposia, such as Electrochemical Society Meetings [37] (held semi- annually), Electronic Materials Conferences [39] (held annually), Interna- tional Conferences on thin films [38] (held tri-annually), etc. [40] include in their topics many papers on CVD films. Patent literature on CVD films is also very rich. A large body of important patents can be retrieved from various sources: Chemical Abstracts, RCA Rev., IBM J. Res. Dev., Solid State Technol., the Official Gazette of the US Patent Office, etc. An important specialized subject, i.e. epitaxial semiconductor films [43—54], has also been partly covered in books by Mathews (1975) [4], and Cullen and Wang (1978) [44]. There are also general reviews by Glang and Wajda (1962) [49], Francombe and Johnson (1969) [51], Shaw (1975) [46], Arizumi (1978) [48], and Pogge (1980) [45] and special reviews by Cave and Czorny (1963) [2349), Doo and Ernst (1967) [2254), Gupta and Wang (1968) [2324], Runyan (1969) [2325], Gupta (1971) [2326], Watts (1973) [52], Barry (1976) [53], Hammond (1978) [2255], Bloem and Giling (1978) [47], Bollen (1978) [2329], Pearce (1983) [2338] and Liaw and Rose (1986) [2340] (for silicon growth); by Holonyak et al. (1962) [2577], Minden (1973) [2585], Hollan (1978) [2587], Hollan et al. (1980) [54] and Ludowise (1985) [2595] (for III - V material growth); by Hartmann (1975) [3225] (for II - VI material growth), and by Hiscocks (1972) [3370] (for IV—VI material growth). A bibliography on epitaxial films was presented by Grünbaum (1975) [83]. There is also a bibliography on silicon epitaxial growth [2326]. Inter- national Conferences on Semiconductor Silicon [55—59], Vapour Growth and Epitaxy [60—65], MOVPE [66—68], GaAs and Related Compounds [69—80], and II-VI compounds [81, 82] provide much information on recent advan- ces in CVD epitaxial films. Another specialized topic, i.e. insulating films, has been thus far summarized less extensive [84—93]. A book by Milek (1971 — 1972) [84], reviews by Amick et ah (1977) [100], Morosanu (1980) [89], and Kern (1982) [90] as well as bibliographies by Agajanian (1977) [4034] and Morosanu (1980) [93] have been published on some aspects of CVD insulating films. 20 EVOLUTION OF CVD FILMS A detailed discussion of all aspects of CVD thin film technology is diffi- cult to deal with in a single book in view of extremely abundant works publi- shed on this subject. The information on various aspects of CVD films is often dispersed in the technical literature. Numerous journals contain CVD articles, e.g. J. Electrochem. Soc, Thin Solid Films, J. Cryst. Growth, J. Electron. Mater., J. Vac. Sei. Technol., Phys. Thin Films, J. Appl. Phys.> IBM J.Res. Dev., RCA Rev., Appl. Phys. Lett., Jpn. J. Appl. Phys., Philips Res. Rep., Solid State Technol., Semiconductor International, IEEE Trans. Electron Dev., Proc. IEEE, Solid State Electron., and others. It has been attempted to collect together the most relevant and useful data, which frequently are presented in the form of tables. More detailed informa- tion on any aspect of CVD films can be obtained by consulting the exten- sive bibliography listed at the end of the book [1—5370]. 1.2 Short History of CVD Thin Films In this section an attempt is made to present an historical review of the literature on CVD films. However, only the significant developments in the evolution of these films during the past 30 years, i.e. 1960—1989, are emphasized. The first examples of CVD thin films were recognized as such in the latter part of nineteenth century. These were of pyrolitic carbon (Sawyer and Man, 1880 [94]) and metals (Aylsworth, 1896 [95], and de Lodyguine, 1897 [96]) used for coating the carbon filaments of incandescent lamps as well as nickel (Mond, 1890—1891 [97]) obtained in high purity using chemical transport by means of nickel carbonyl. In about the same period, chemists began to study the formation of high-purity metallic thin films produced by using chemical transport as a matter of both scientific and technological interest. Little further progress was made until the 1930s, when the deposition of refractory compounds (metal borides, carbides, nitrides, oxides and suicides), pigments (silicon dioxide and titanium dioxide), and other materials (sulphides, selenides, tellurides, and alloys) became of industrial importance. In the 1950s, CVD materials entered the field of electronics, for example carbon films were used for coating graphite susceptors in the zone- refining process of germanium or indium antimonide and bulk germanium or silicon. In the same decade, when germanium was the sole semiconductor material, homoepitaxial layers of Ge were first obtained. In about 1960, two important developments in electronic technology caused a tremendous expansion of interest in CVD thin films. The first of these was the replacement of Ge with Si as the basic semiconductor mate- rial for device fabrication and the second was the introduction of the so-called planar technology, invented by Hoerni in 1959. The first major breakthrough in the field of CVD films dates from 1960, when homoepitaxial films of silicon of device quality were first obtained by Theuerer. These films soon achiev- ed industrial importance, being applied in the manufacture of nearly all 21 INTRODUCTION types of silicon semiconductor devices and integrated circuits. In the same years, homoepitaxial films of III —V compounds (e.g. GaAs), heteroepitaxial films on oxide substrate as well as heterojunctions, were first obtained. Starting in the mid 1960s, other CVD films of electronic materials such as dielectrics were intensively investigated. At the same time, the study began of thin films of metals and conductive materials applicable to electronics as well as of superconductors and magnetic materials applicable in related fields. Technological needs resulted in the development of polycrystalline semiconductor films (mainly of silicon in 1968 by Sarace et al.). Films of doped amorphous semiconductors especially of <z-Si:H (developed later in 1975 by Spear), have been found to be very important in the field of opto- electronics. In addition to preparation techniques, significant developments have been achieved later in the fields of fundamentals and application of CVD films. A. The main emphasis during the evolution of CVD films has been on their preparation techniques. CVD films have been prepared primarily by using the conventional method at atmospheric pressure and high temperature (HTCVD). However, a few improved variants such as LTCVD, SP and MOCVD proved to be useful in various situations. New variants such as PECVD, UVCVD, LCVD and EBCVD soon appeared. LTCVD, a CVD process operating under normal pressure at tem- peratures below 500° C, was described in 1967 by Goldmith and Kern for obtaining Si0 layers. 2 SP (spray pyrolysis), a CVD process occurring in the open air which lends itself to a high degree of continuous, cheap and voluminous preparation of thin films, was originally described for the preparation of Si0 films 2 and extended later to other semiconductor, metal and oxide films (Viguie and Spitz, 1975). MOCVD is an open-tube vapour-phase thin film growth process that employs either organometallic plus inorganic compounds or only organome- tallies as sources of the elements of which the thin film is to be made. This process was first demonstrated by Manasevit in 1968 for the growth of III—V compound semiconductor films. An important development was the prepara- tion of GaAs films of device quality in 1977 by Dupuis and Dapkus. LPCVD was reported by Sandor in 1962 and by Kern in 1965 for the deposition of undoped Si0 . This process was perfected in 1973 by 2 Tanikawa et al. who used an arrangement of closely packed vertical wafers for obtaining uniform deposition. LPCVD has now become an industrial process for obtaining polysilicon. Early PECVD work was reported by Sterling and Swann in 1965 for depositing a-Si, Si0 and Si N films. This process also achieved industrial 2 3 4 acceptance in the preparation of Si N films. In addition, it has been exten- 3 4 sively used for preparing doped a-Si layers, beginning with the works of Chittick et al. in 1969 and Spear and LeComber in 1975. The earliest works in the field of UVCVD appear to be the growth of epitaxial silicon by Nishizawa in 1961 and Frieser in 1968 and silicon nitride by van den Brekel and Severin in 1972. This process is presently 22