Table Of ContentPULSED AND PULSED BIAS
SPUTTERING
Principles and Applications
PULSED AND PULSED BIAS
SPUTTERING
Principles and Applications
by
Edward V. Barnat
Sandia National Laboratories
Albuquerque, NA1
Toh-MingLu
Rensselaer Polytechnic Institute
Troy,NY
SPRINGER SCIENCE+BUSINESS MEDIA, LLC
Library of Congress Cataloging-in-Publication Data
A C.I.P. Catalogue record for this book is available
from the Library of Congress.
Pulsed and Pulsed Bias Sputtering: Principles and Applications.
By Edward V. Barnat amd Toh-Ming Lu.
ISBN 978-1-4020-7543-8 ISBN 978-1-4615-0411-5 (eBook)
DOI 10.1007/978-1-4615-0411-5
Copyright© 2003 by Springer Science+Business Media New York
Originally published by Kluwer Academic Publishers in 2003
Softcover reprint of the hardcover 1s t edition 2003
Ali rights reserved. No part ofthis work may be reproduced, stored in a retrieval
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Printed on acid-free paper.
TABLE OF CONTENTS
PREFACE IX
ACKNOWLEDGMENTS Xl
Chapter 1 INTRODUCTION
OVERVIEW OF SPUTTERING FOR
TECHNOLOGICAL APPLICATIONS
2 PLASMA-SURF ACE 6
INTERACTIONS
3 CHARGING OF INSULATING SURFACES 7
4 OVERVIEW OF THE MONOGRAPH ............. 9
Chapter 2 BASIC PLASMA PHENOMENON 11
THE PLASMA STATE 11
2 BASIC PLASMA STRUCTURE 13
3 COLLISIONS 22
4 SUMMARY 26
Chapter 3 PLASMA SOURCES USED FOR 29
SPUTTER DEPOSITION
1 DIRECT CURRENT (DC) SOURCES ............. 29
2 ALTERNATING CURRENT (AC) SOURCES ... 38
3 SUMMARY 42
Chapter 4 RESPONSE OF A PLASMA . . . . . .. . . . . . ... 45
TO AN APPLIED BIAS
GENERAL CONSIDERATIONS ................. ... 46
AND APPROXIMATIONS
2 QUASI-STATIC APPROXIMATION OF .......... 49
THE SHEATH
3 BREAKDOWN OF THE QUASI-STATIC 54
APPROXIMATION
4 TRANSIENT NATURE OF THE SHEATH 57
5 SUMMARY 62
VI
Chapter 5 SINUSOIDAL WAVEFORM . ... . .. . . . . .. 65
1 QUASI-STATIC REGIME ..................... 65
2 TRANSIENT SHEATH REGIME 69
3 SUMMARY 72
Chapter 6 PULSED WAVEFORM ..................... 75
DEFINITION OF THE PULSE 76
2 QUASI-STATIC RESPONSE OF THE ............. 76
SYSTEM TO AN APPLIED PULSE
3 APPROXIMATED PREDICTIONS OF ........ .... 89
ENERGY SPECTRA
4 HIGHER FREQUENCY RESPONSE OF THE ... 95
SYSTEM TO THE PULSED WAVEFORM
5 COMPARISON BETWEEN SINUSOIDAL 104
AND PULSED WAVEFORMS
6 SUMMARY 106
Chapter 7 APPLICATION OF A PULSED 109
WAVEFORM TO A TARGET:
PULSED REACTIVE SPUTTERING
INTRODUCTION . . .... . . .. ... . .. . .. . .. . . . . ... .. ... . ... 110
2 APPLICATION OF A PULSE FOR ARC .......... 112
SUPPRESSION (PREDICTIONS)
3 APPLICATION OF A PULSE TO 121
REACTIVE SPUTTERING (PRACTICE)
4 SUMMARY ......................................... .... 127
Chapter 8 APPLICATION OF A PULSED 129
WAVEFORM TO A SUBSTRATE:
PULSED BIAS SPUTTERING
1 INTRODUCTION ...................................... 129
2 CONSIDERATIONS FOR PULSED 130
BIASING OF THE SUBSTRATE
3 OBSERVED FLUX OF CHARGE TO A 133
PULSED SUBSTRATE
4 APPLICATION OF A PULSED BIAS TO 138
FILM GROWTH
5 SUMMARY ......................................... .... 143
Vll
Chapter 9 CONCLUSIONS AND FUTURE .......... 145
DIRECTIONS
1 CONCLUSIONS ....................................... 145
2 FUTURE DIRECTIONS 146
REFERENCES 149
INDEX 157
PREFACE
As thin film technology evolves, more stringent requirements are
placed on the techniques and the materials employed to bring about the next
generations of applications. It is typically the role of the research scientists
and industrial engineers to bring about innovations to meet these stringent
requirements. This is done through not only an understanding of a broad
range of disciplines, such as physics, chemistry, and materials science, but
the application of that understanding as well.
Sputter deposition is a very popular technique to coat thin films for
many diverse high tech applications such as semiconductor integrated
circuits, optical films, and hard coatings. Typically the technique utilizes a
plasma generated under a vacuum condition, and ions are extracted from the
plasma (direct current (DC)) to bombard the target. Atoms would be
sputtered out of the target and would travel to the substrate for coating. For
reactive sputtering to form insulating films, the target can get charged up
quickly and arcing would occur (target poisoning). To overcome this
problem, an oscillatory potential source can be used so that the target would
be neutralized during sputtering. Typically it is in the range of radio
frequency (RF). Normally RF sputtering would require higher power and
would give a slower deposition rate. Recently an alternative strategy called
the pulsed sputtering technique was developed to address the charging
problem. The technique utilizes a pulsing potential to neutralize the target in
the kilohertz regime and can produce much higher deposition rate than that
of the RF sputtering.
Also, in the sputtering of a metal film, if a bias potential is applied to
the substrate, one can control the film properties such as adhesion, texture,
morphology, and density of the film. This is because one can extract ions to
bombard the growth front during growth. However, if the substrate is an
insulator, it can get charged up very quickly and one would lose the benefit
of ion bombardment, particularly during the initial stages of growth. Initial
stages of film nucleation very often can affect the properties of the film
subsequently grown. RF potential can be used to neutralize the substrate.
However, the ion energy distribution generated by a RF power is not
uniform and is not well controlled. Recently, it is recognized that using a
pulsed bias potential on the substrate in the kilohertz regime one can
overcome this difficulty and can produce better controlled and superior film
quality.
Both pulsed sputtering and pulsed bias sputtering mentioned above
are considered to be advanced sputtering techniques and are developed only
in recent years. Our monograph will give a detailed account on these newly
developed concepts. The basic principles of the charging and discharging
phenomena at the target and substrate, and the methods of neutralizing them
x
using pulsing techniques are described in detail. In addition, we will present
in a coherent manner the basic physics of DC plasma formation and the
utilization of the plasma in the sputtering environment. This monograph will
not only be useful for academic researchers but also for industrial scientists
interested in sputter coatings of high quality metal and insulator.
ACKNOWLEDGMENTS
The authors would like to acknowledge the SRC (Semiconductor
Research Corporation), the FRC (Marco Interconnect Focus Center for
Research), the New York State Science and Technology Foundation, and the
Intel Foundation for support. The authors are also very grateful for the
contributions of the many who had made the work presented in this
monograph possible, including Dr. Matthew Nielsen (General Electric
CRD), Dr. Jin-Young Kim (Texas Instruments), Dr. Pei-I Wang (RPI), Dr.
Jason Drotar (Naval Research Lab), Dr. Atul Kumar (DSI), and Diaki
Nagakura (RPI).
We would like to thank the authors who have allowed us to use their
work that appears in this monograph. The authors would like to thank Carol
Day and Greg Franklin of Kluwer Academic Publishers for the opportunity
to present this work to the broader scientific community. Finally, we would
like to thank Angela Eaton for her many hours reviewing and editing the
monograph.
Edward V. Bamat would also like to express his deep appreciation
to both Dr. Toh-Ming Lu and Dr. Gwo-Ching Wang for their
encouragement, guidance, and support throughout his doctoral studies. Ed
would also like to thank both Dr. Gerry Hays and Dr. Greg Hebner (Sandia
National Laboratories) for their support during the finishing stages of this
monograph at Sandia. Finally, he would like to express his gratitude to both
his friends and family for their love and support.
Edward V. Bamat
Toh-Ming Lu
Rensselaer Polytechnic Institute
Troy, NY
October 2002
Chapter 1
INTRODUCTION
This monograph is a guide for those interested in improving sputter
based thin film technology through the use of a pulse-based technology. Of
critical importance to the discussion that will be offered in this monograph
are the effects energetic-charged particles have on surfaces and how an
applied waveform can be applied to control these energetic-charged
particles. It is hoped that through a discussion of the response of a plasma to
an applied waveform, an understanding can be gained as to the factors that
influence the effectiveness of the applied waveform for controlling these
charged particles.
The chapter begins with a simple description of the sputtering
phenomenon and an out line of some of the technological applications of the
sputtering process. The chapter continues with a discussion of the
importance of the interactions that occur between charged particles from the
plasma and the surface exposed to the plasma. Section 3 considers the case
when the surface exposed to the plasma is non-conducting, and how
charging of this surface can adversely impact interactions between the
plasma and the surface. The chapter closes with an overview of the
remaining monograph.
1 OVERVIEW OF SPUTTERING FOR
TECHNOLOGICAL APPLICATIONS
1.1 What is sputtering?
Sputtering is the physical removal of atoms from a surface due to
energetic particle bombardmene. This removal occurs from momentum
transfer between the ejected atoms and adjacent surface atoms. Momentum
is transferred to theses atoms through a series of collisions from other atoms
that had been set into motion through collisions with the bombarding
particle. Sputter based deposition techniques use these ejected atoms as the
source material for growth. For the deposition-based processes that we are
discussing here, the energetic particle is an ion that has been accelerated
from an ionized gas, or a plasma.
E. V. Barnat et al., Pulsed and Pulsed Bias Sputtering
© Kluwer Academic Publishers 2003
