The
Materials Science
of
Thin
Films

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.
@
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
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
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
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
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
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

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
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 chem-
istry and physics and
possess
a passive cultural familiarity with topics com-
monly treated in undergraduate physical chemistry and modem physics courses.
xiv
Preface
It is worthwhile to briefly elaborate on this book’s title and the connection
between thin films and the broader discipline of materials science and engineer-
ing. A dramatic increase in our understanding of the fundamental nature of
materials throughout much of the twentieth century has led to the development
of materials science and engineering. This period witnessed the emergence of
polymeric, nuclear, and electronic materials, new roles for metals and ceram-
ics, and the development of reliable methods to process these materials in bulk
and thin-film form. Traditional educational approaches to the study of materi-
als have stressed
structure-property
relationships in bulk solids, typically
utilizing metals, semiconductors, ceramics; and polymers, taken singly or

collectively as illustrative vehicles to convey principles. The same spirit is
adopted in this book except that
thin solid films
are the vehicle. In addition,
the basic theme has been expanded to include the multifaceted
processing-
structure-properties-performance
interactions. Thus the original science
core is preserved but enveloped by the engineering concerns of
processing
and
performance.
Within this context,
I
have attempted to weave threads
of
commonality among seemingly different materials and properties, as well as to
draw distinctions between materials that exhibit outwardly similiar behavior. In
particular, parallels and contrasts between films and bulk materials are recur-
ring themes.
An optional introductory review chapter on standard topics in materials
establishes a foundation for subsequent chapters. Following a second chapter
on vacuum science and technology, the remaining text is broadly organized
into three categories. Chapters
3
and
4
deal with the principles and practices of
film deposition from the vapor phase. Chapters
5-9

deal with the processes
and phenomena that influence the structural, chemical, and physical attributes
of films, and how to characterize them. Topics discussed include nucleation,
growth, crystal perfection, epitaxy, mass transport effects, and the role of
stress. These are the common thin-film concerns irrespective of application.
The final portion of the book (Chapters
10-14)
is largely devoted to specific
film properties (electrical, magnetic, optical, mechanical) and applications, as
well as to emerging materials and processes. Although the first nine chapters
may be viewed as core subject matter, the last five chapters offer elective
topics intended to address individual interests. It is my hope that instructors
using this book will find this division of topics a useful one.
Much of the book reflects what is of current interest to the thin-film research
and development communities. Examples include chapters on chemical vapor
deposition, epitaxy, interdiffusion and reactions, metallurgical and protective
coatings, and surface modification. The field is evolving
so rapidly that even
the classics of yesteryear, e.g., Maissel and Glang,
Handbook
of
Thin
Film
Preface
xv
Technology
(1970) and Chopra,
Thin Film Phenomena
(1969), as well as
more recent books on thin films, e.g., Pulker,

Coatings
on
Glass
(1984), and
Eckertova,
Physics
of
Thin Films
(1986),
make little or no mention of these
now important subjects.
As every book must necessarily establish its boundaries,
I
would like to
point out the following:
(1)
Except for coatings (Chapter
12)
where thicknesses
range from several to as much as hundreds of microns (1 micron or
1
pm
=
lop6
meter), the book
is
primarily concerned with films that are less
than 1 pm thick.
(2)
Only films and coatings formed from the gas phase by

physical
(PVD)
or chemical vapor deposition
(CVD)
processes are considered.
Therefore spin and dip coating, flame and plasma spraying of powders,
electrolytic deposition, etc., will not be treated.
(3)
The topic of polymer films
could easily justify a monograph of its own, and hence will not be discussed
here. (4) Time and space simply do not allow for development of all topics
from first principles. (Nevertheless,
I
have avoided using the unwelcome
phrase “It can be shown that
. . .
,”
and have refrained from using other
textbooks or the research literature to fill in missing steps of derivations.)
(5)
A
single set of units (e.g., CGS, MKS,
SI,
etc.) has been purposely avoided to
better address the needs of a multifaceted and interdisciplinary audience.
Common usage, commercial terminology, the research literature and simple
bias and convenience have all played a role in the ecumenical display
of
units.
Where necessary, conversions between different systems of units are provided.

At the end of each chapter are problems of varying difficulty, and
I
believe a
deeper sense of the subject matter will be gained by considering them. Three
very elegant problems (Le. 9-6,
-7,
-8)
were developed by Professor W.
D.
Nix, and
I
thank him for their use.
By emphasizing immutable concepts,
I
hope this book will be spared the
specter
of
rapid obsolescence. However, if
this
book will in some small
measure help spawn new technology rendering it obsolete, it will have served a
useful function.
Milton Ohring