The MATERIALS SCIENCE Of THIN FILMS Milton Ohring
The Materials Science of Thin Films Milton orin Stevens institute of Technology Department of Materials Science and Engineering Academic Press San Diego New York Boston London Sydney Tokyo Toronto
I I I The Materials Science of Milton Ohring Stevens Institute of Technology Department of Materials Science and Engineering Hoboken, New Jersey Academic Press San Diego New York Boston London Sydney Tokyo Toronto
This book is printed on acid-free paper. o Copyright e 1992 by Academic Press All rights reserved. No part of this publication may be reproduced or or mechanical, including photocopy, recording, or any information storage and retrieval system, without permission in writing from the publisher Designed by Elizabeth E. Tustin ACADEMIC PRESS A Division of Harcourt Brace& Company 525 B Street, Suite 1900. San Diego. Califomia 92101.4495 United Kingdom Edition published b ACADEMIC PRESS LIMITED 24-28 Oval Road, London NWI 7DX Library of Congress Cataloging-in-Publication Data The materials science of thin films/ Milton Ohrin Includes bibliographical references and index ISBN 0-12-524990-X (Alk. paper) 1. Thin fIms. 1. Title TA4189.T450471991 62044-dc20 Printed in the United States of Amenca 9900020Mv10987
This book is printed on acid-free paper. @ Copyright 0 1992 by Academic Pres No pari of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording. or any information storage and retrieval system, without permission in writing from the publisher. Designed by Elizabeth E. Tustian ACADEMIC PRESS A Division of Harcouri Brace d; Company 525 B Street, Suite 1900. San Diego, California 92101-4495 United Kingdom Uition published by ACADEMIC PRESS LIMITED 24-28 Oval Rod. London NWI 7DX All rights reserved. Library of Congress Cataloging-in-Publication Data Ohring. Milton, date. The materials science of thin films / Milton Ohring. Includes bibliograpbical references and indcx. ISBN 0-12-524990-X (Alk. paper) 1. Thin films. I. Title. TA418.9.T45oQ7 1991 p. cm. 620'.44-&20 91-9664 CIP Printed in the United States of America 99 00 01 02 03 MV11 10 9 8 7
Contents Acknowledgments Thin Films-A Historical Perspective A Review of Materials Science I 1. Introduction 1. 2. Structure 1. 3. Defects in Solids 10 1. 4. Bonding of Materials 1.5. Thermodynamics of Materials 21 neues 1. 7. Nucleation 40 1. 8. Conclusion 43 Exercises Referer Vacuum Science and Technology 49 2.1. Kinetic Theory of Gases 2. 2. Gas Transport and Pumping 55
+ Contents Foreword ............................................. xi Preface .............................................. xiii ... Acknowledgments ..................................... xvii Thin Films - A Historical Perspective ........................ xix Chapter 1 A Review of Materials Science ......................... 1 1.1. Introduction ........................................ 1 1.2. Structure .......................................... 2 1.3. Defects in Solids .................................... 10 1.4. Bonding of Materials ................................. 14 1.5. Thermodynamics of Materials ........................... 21 1.6. Kinetics .......................................... 33 1.7. Nucleation ......................................... 40 1.8. Conclusion ........................................ 43 Exercises ......................................... 43 References ........................................ 46 Chapter 2 Vacuum Science and Technology ..................... 49 2.1. Kinetic Theory of Gases ............................... 49 2.2. Gas Transport and Pumping ............................. 55 V
Contents 2.3. Vacuum Pumps and Systems Excercise References 257 Chapter 3 Physical Vapor Deposition 3. 1. Introduction 3.2. The Physics and Chemistry of Evaporation 3. 3. Film Thickness Uniformity and Purity 3. 4. Evaporation Hardware and Techniques 988%0 3.5. Glow Discharges and Plasmas 3.6. Sputtering 3.7. Sputtering Processes l18 3.8. Hybrid and Modified PVD Processes Exercises References Chapter 4 Chemical Vapor Deposition 147 4. 1. Introduction 147 4. 2. Reaction Types 4.3. Thermodynamics of CVD 155 4,4. Gas Transport ..... 162 4. 5. Growth Kinetics 4.6. CVD Processes and Systems Exercises 190 References Chapter 5 Film Formation and Structure 195 5. 1. Introduction 5.2. Capillarity Theory 5.3. Atomistic Nucleation Processes 206 5. 4. Cluster Coalescence and Depletion 213 5.5. Experimental Studies of Nucleation and Growth 219 5.6. Grain Structure of Films and Coatings 5.7. Amorphous Thin Films Exercises References
vi Contents 2.3. Vacuum Pumps and Systems ............................ 62 Excercises ......................................... 75 References ........................................ 77 Chapter 3 3.1. Introduction ........................................ 79 Physical Vapor Deposition ........................... 79 3.2. The Physics and Chemistry of Evaporation ................... 81 3.3. Film Thickness Uniformity and Purity ...................... 87 3.4. Evaporation Hardware and Techniques ..................... 96 3.5. Glow Discharges and Plasmas ........................... 101 3.6. Sputtering ........................................ 109 3.7. Sputtering Processes ................................. 118 3.8. Hybrid and Modified PVD Processes ...................... 132 Exercises ......................................... 140 References ........................................ 144 Chapter 4 Chemical Vapor Deposition ......................... 147 4.1. Introduction ....................................... 147 4.2. Reaction Types ..................................... 149 4.3. Thermodynamics of CVD ............................. 155 4.4. Gas Transport ..................................... 162 4.5. Growth Kinetics .................................... 167 4.6. CVD Processes and Systems ............................ 177 Exercises ......................................... 190 References ........................................ 193 Chapter 5 Film Formation and Structure ........................ 195 5.1. Introduction ....................................... 195 5.2. Capillarity Theory .................................. 198 5.3. Atomistic Nucleation Processes .......................... 206 5.4. Cluster Coalescence and Depletion ....................... 213 5.5. Experimental Studies of Nucleation and Growth .............. 219 5.6. Grain Structure of Films and Coatings ..................... 223 5.7. Amorphous Thin Films ............................... 234 Exercises ......................................... 243 References ........................................ 246
Contents Chapter 6 Characterization of thin Films 249 6. 1. Introduction 249 6.2. Film Thickness 6.3. Structural Characterization 6.4. Chemical Characterization 275 References Chapter 7 Epitaxy 7. 1. Introduction 307 7. 2. Structural Aspects of Epitaxial Films 7.3. Lattice Misfit and Imperfections in Epitaxial Film 316 7. 4. Epitaxy of Compound Semiconductors 322 7.5. Methods for Depositing Epitaxial Semiconductor Films 331 7.6. Epitaxial Film Growth and Characterization 77. Conclusion References 353 Interdiffusion and Reactions in Thin Films 355 8. 1. Introduction 355 8. 2. Fundamentals of Diffusion 8.3. Interdiffusion in Metal Alloy Films 372 8.4. Electromigration in Thin Films 379 8. 5. Metal-Semiconductor Reactions 8.6. Silicides and Diffusion barriers 8.7. Diffusion During Film Growth Referer 401 Chapter 9 Mechanical Properties of Thin Films 403 9. 1. Introduction 403 9.2. Introduction to Elasticity, Plasticity, and Mechanical Behavior 9. 3. Internal Stresses and Their Analysis 9. 4. Stress in Thin Films 420 9. 5. Relaxation Effects in Stressed Films
Contents vii Chapter 6 Characterization of Thin Films ....................... 249 6.1. Introduction ....................................... 249 6.2. Film Thickness ..................................... 252 6.3. Structural Characterization ............................. 265 6.4. Chemical Characterization ............................. 275 Exercises ......................................... 300 References ........................................ 305 Chapter 7 Epitaxy .......................................... 307 7.1. Introduction ....................................... 307 7.2. Structural Aspects of Epitaxial Films ...................... 310 7.3. Lattice Misfit and Imperfections in Epitaxial Films ............. 316 7.4. Epitaxy of Compound Semiconductors ..................... 322 7.5. Methods for Depositing Epitaxial Semiconductor Films ......... 331 7.6. Epitaxial Film Growth and Characterization ................. 339 7.7. Conclusion ....................................... 350 Exercises ......................................... 351 References ........................................ 353 Chapter 8 Interdiffusion and Reactions in Thin Films ............. 355 8.1. Introduction ....................................... 355 8.2. Fundamentals of Diffusion ............................. 357 8.3. Interdiffusion in Metal Alloy Films ....................... 372 8.4. Electromigration in Thin Films .......................... 379 8.5. Metal-Semiconductor Reactions ......................... 385 8.6. Silicides and Diffusion Barriers .......................... 389 Exercises ......................................... 398 References ........................................ 401 8.7. Diffusion During Film Growth .......................... 395 Chapter 9 Mechanical Properties of Thin Films .................. 403 9.1. Introduction ....................................... 403 9.2. Introduction to Elasticity. Plasticity. and Mechanical Behavior ..... 405 9.3. Internal Stresses and Their Analysis ....................... 413 9.4. Stress in Thin Films ................................. 420 9.5. Relaxation Effects in Stressed Films ...................... 432
9.6. Adhesion 439 Exercises References Chapter 10 Electrical and Magnetic Properties of Thin Films 451 10. 1. Introduction to Electrical Properties of Thin Films 10.2. Conduction in Metal Films 10.3. Electrical Transport in Insulating Films 464 10. 4. Semiconductor Contacts and MOS Structures 10.5. Superconductivity in Thin Films 10.6. Introduction to Ferromagnetism 10.7. Magnetic Film Size Effects- M, versus Thickness and Temperature 10.8. Magnetic Thin Films for Memory Applications 493 Exercises References Chapter 11 Optical Properties of Thin Films 11. 1. Introduction 11. 2. Properties of Optical Film Materials 11.3. Thin-Film Optics 11.4. Multilayer Optical Film Applications References Chapter 12 Metallurgical and Protective Coatings 547 12.1. Introduction 547 12. 2. Hard Coating Materials 12.3. Hardness and Fracture 561 12. 4. Tribology of Films and Coatings 570 12,5. Diffusional, Protective, and Thermal Coatings 580 Exerc Chapter 13 Modification of Surfaces and Films 589 13. 1. Introduction 13. 2. Lasers and Their Interactions with Surfaces
viii Contents 9.6. Adhesion ......................................... 439 Exercises ......................................... 446 References ........................................ 449 Chapter 10 Electrical and Magnetic Properties of Thin Films ....... 451 10.1. Introduction to Electrical Properties of Thin Films ............ 451 10.2. Conduction in Metal Films ............................ 455 10.3. Electrical Transport in Insulating Films ................... 464 10.4. Semiconductor Contacts and MOS Structures ............... 472 10.5. Superconductivity in Thin Films ........................ 480 10.6. Introduction to Ferromagnetism ......................... 485 Temperature .................................... 489 10.8. Magnetic Thin Films for Memory Applications .............. 493 Exercises ........................................ 502 References ....................................... 505 10.7. Magnetic Film Size Effects - M, versus Thickness and Chapter 11 Optical Properties of Thin Films ...................... 507 11.1. Introduction ...................................... 507 1 1.2. Properties of Optical Film Materials ...................... 508 1 1.3. Thin-Film Optics .................................. 524 1 1.4. Multilayer Optical Film Applications ..................... 531 Exercises ........................................ 542 References ....................................... 544 Chapter 72 Metallurgical and Protective Coatings ................. 547 12.1. Introduction ...................................... 547 12.2. Hard Coating Materials .............................. 551 12.3. Hardness and Fracture ............................... 561 12.4. Tribology of Films and Coatings ........................ 570 12.5. Diffusional, Protective, and Thermal Coatings ............... 580 Exercises ........................................ 585 References ....................................... 587 Chapter 13 Modification of Surfaces and Films ................... 589 13.1. Introduction ...................................... 589 13.2. Lasers and Their Interactions with Surfaces ................. 591
Contents 13.3. Laser Modification Effects and Applications 13. 4. lon-lImplantation Effects in Solids ,..,... 13.5. Ion-Beam Modification Phenomena and Applications 616 Exercises..' References 626 Chapter 14 Emerging Thin-Film Materials and Applications 629 14.1. Film-Patterning Techniques 14.2. Diamond Films 635 14.3. High-T Superconductor Films 641 14.4. Films for Magnetic Recording 14.5. Optical Recording 14.6. Integrated Optics 14.7. Superlattices 14.8. Band-Gap Engineering and Quantum Devices 669 14.9. Conclusion 678 Exercises 678 Refer 681 Appendix 1 Physical Constants 685 Appendix 2 Selected Conversions 687 Index
Contents ix 13.3. Laser Modification Effects and Applications ................ 602 13.4. Ion-Implantation Effects in Solids ....................... 609 13.5. Ion-Beam Modification Phenomena and Applications .......... 616 Exercises ........................................ 624 References ....................................... 626 Chapter 14 Emerging Thin-Film Materials and Applications ......... 629 14.1. Film-Patterning Techniques ........................... 630 14.2. Diamond Films .................................... 635 14.3. High-T, Superconductor Films ......................... 641 14.4. Films for Magnetic Recording .......................... 645 14.5. Optical Recording .................................. 650 14.6. Integrated Optics ................................... 654 14.7. Superlattices ...................................... 661 14.8. Band-Gap Engineering and Quantum Devices ............... 669 14.9. Conclusion ....................................... 678 Exercises ........................................ 678 References ....................................... 681 Appendix 1 Physical Constants ................................ 685 Appendix 2 Selected Conversions ... ....................... 687 index .............. .................. 689
It is a distinct pleasure for me to write a foreword to this new textbook by my long-time friend, Professor Milt Ohring There have been at least 200 books written on various aspects of thin film science and technology, but this is the first true textbook, specifically intended for classroom use in universities. In my opinion there has been a crying need for a real textbook for a long time most thin film courses in universities have had to use many books written for relatively experienced thin film scientists and engineers, often supplemented by notes prepared by the course instructor The Materials Science of Thin Films, a true textbook, complete with problems after each chapter, is available to serve as a nucleus for first courses in thin film science and technology In addition to his many years of experience teaching and advising graduate udents at Stevens Institute of Technology, Professor Ohring has been the coordinator of an on-premises, M.S. degree program offered by Stevens at the AT&T Bell Laboratories in Murray Hill and Whippany, New Jersey. This ongoing cooperative program has produced over sixty M.s. graduates to date Several of these graduates have gone on to acquire Ph. D. degrees. The combination of teaching, research, and industrial involvement has provided Professor Ohring with a broad perspective of thin film science and technology and tremendous insight into the needs of students entering this exciting field His insight and experience are quite evident in this textbook John L. vossen
Foreword It is a distinct pleasure for me to write a foreword to this new textbook by my long-time friend, Professor Milt Ohring. There have been at least 200 books written on various aspects of thin film science and technology, but this is the first true textbook, specifically intended for classroom use in universities. In my opinion there has been a crying need for a real textbook for a long time. Most thin film courses in universities have had to use many books written for relatively experienced thin film scientists and engineers, often supplemented by notes prepared by the course instructor. The Materials Science of Thin Films, a true textbook, complete with problems after each chapter, is available to serve as a nucleus for first courses in thin film science and technology. In addition to his many years of experience teaching and advising graduate students at Stevens Institute of Technology, Professor Ohring has been the coordinator of an on-premises, M.S. degree program offered by Stevens at the AT&T Bell Laboratories in Murray Hill and Whippany, New Jersey. This ongoing cooperative program has produced over sixty M.S. graduates to date. Several of these graduates have gone on to acquire Ph.D. degrees. The combination of teaching, research, and industrial involvement has provided Professor Ohring with a broad perspective of thin film science and technology and tremendous insight into the needs of students entering this exciting field. His insight and experience are quite evident in this textbook. John L. Vossen xi
Preface Thin-film science and technology play a crucial role in the high-tech industries that will bear the main burden of future American competitiveness, While the major exploitation of thin films has been in microelectronics, there are numerous and growing applications in communications, optical electronics coatings of all kinds, and in energy generation and conservation strategies. A great many sophisticated analytical instruments and techniques, largely devel- oped to characterize thin films and surfaces, have already become indispens- able in virtually every scientific endeavor irrespective of discipline. When I was called upon to offer a course on thin films, it became a genuine source of concern to me that there were no suitable textbooks available on this unques- tionably important topic. This book, written with a materials science flavor, is a response to this need. It is intended for Science and engineering students in advanced undergraduate or first-year graduate level courses on thin films 2. Participants in industrial in-house courses or short courses offered by professional societies 3. Mature scientists and engineers switching career directions who require overview of the field Readers should be reasonably conversant with introductory college chem istry and physics and possess a passive cultural familiarity with topics com- monly treated in undergraduate physical chemistry and modern physics courses xiii
+ Preface Thin-film science and technology play a crucial role in the high-tech industries that will bear the main burden of future American competitiveness. While the major exploitation of thin films has been in microelectronics, there are numerous and growing applications in communications, optical electronics, coatings of all kinds, and in energy generation and conservation strategies. A great many sophisticated analytical instruments and techniques, largely developed to characterize thin films and surfaces, have already become indispensable in virtually every scientific endeavor irrespective of discipline. When I was called upon to offer a course on thin films, it became a genuine source of concern to me that there were no suitable textbooks available on this unquestionably important topic. This book, written with a materials science flavor, is a response to this need. It is intended for 1. 2. 3. Science and engineering students in advanced undergraduate or first-year graduate level courses on thin films Participants in industrial in-house courses or short courses offered by professional societies Mature scientists and engineers switching career directions who require an overview of the field. Readers should be reasonably conversant with introductory college chemistry and physics and possess a passive cultural familiarity with topics commonly treated in undergraduate physical chemistry and modem physics courses
