Table Of ContentTHIN-FILM CAPACITORS FOR
PACKAGED ELECTRONICS
THIN-FILM CAPACITORS FOR
PACKAGED ELECTRONICS
by
Pushkar Jain
Rensselaer Polytechnic Institute
Troy, NY
Eugene J. Rymaszewski
Rensselaer Polytechnic Institute
Troy, NY
Library of Congress Cataloging-in-Publication
Thin-Film Capacitors for Packaged Electronics
By Pushkar Jain and Eugene J. Rymaszewski
ISBN 978-1-4020-7705-0 ISBN 978-1-4419-9144-7 (eBook)
DOI 10.1007/978-1-4419-9144-7
Copyright ©2004 by Springer Science+Business Media New York
Originally published by Kluwer Academic Publishers in 2004
Softcover reprint ofthe hardcover 1st edition 2004
Ali rights reserved. No part of this publication may be reproduced, stored in a retrieval
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Printed on acid-free paper.
This bookis dedicatedto
ourfamiliesfor their love and encouragement
throughout all our endeavors
CONTENTS
PREFACE
Xl
ACKNOWLEDGEMENTS
xv
CHAPTER 1
INTRODUCTION 1
1.1 CapacitorFundamentals 4
1.1.1 Capacitance 4
1.1.2 Dielectric Dispersion and Loss Factor 5
1.1.3 Equivalent Series Inductance and Resistance 6
1.1.4 DC Leakage and Breakdown Voltage 7
1.2 Application Domains 7
1.2.1 DecouplingCapacitors 7
1.2.2 BlockingCapacitors 10
1.2.3 Precision Capacitors 10
1.3 Physical Structures/Embodiments 11
1.3.1 Surface-mount and Through-hole Discrete Capacitors 11
1.3.2 State-of-the-artThick-Film Capacitors 15
1.3.3 EmbeddedThin-FilmCapacitors 16
1.4 CapacitorIntegration Drivers 18
1.4.1 Cost Leverages 18
1.4.2 Easy Integration and HigherPackaging Densities 18
1.4.3 Improved Electrical Performance 18
1.5 Thin-FilmCapacitorTechnology 19
1.5.1 FabricationTechniques 20
1.5.2 Dielectrics for Thin-Film Capacitors 21
Vlll Contents
1.6 Summary 24
1.7 References 24
CHAPTER 2
DESIGN FUNDAMENTALS 27
2.1 BreakdownVoltage and Capacitance DensityDesign Limits 27
2.1.1 Interdependencybetween E and e, 28
BR
2.1.2 BreakdownVoltage and Capacitance Density 30
2.1.3 Capacitors with Ta20s Thin Films 32
2.2 Tolerance in Capacitance Density 34
2.2.1 Dielectric Dispersion 35
2.2.2 Temperature CoefficientofCapacitance 35
2.2.3 CapacitorAging 36
2.2.4 Dimensional Accuracy 36
2.3 DC Leakage 36
2.4 CapacitorLosses 37
2.5 Series Inductance and Resistance 38
2.6 References 40
CHAPTER 3
PERFORMANCE DETRACTORS
43
3.1 Interfacial Micro-roughness 43
3.2 Deviation from Optimal Stoichiometry 53
3.2.1 Selection ofDeposition technique 53
3.2.2 Reactive Sputtering: Issuesand Challenges 54
3.2.3 Reactive SputteringModel for Ta-O, Deposition 56
3.2.4 Experimental Methodology 60
3.2.5 Model Prediction and Experimental Results 63
3.2.6 Effects ofSubstrateTemperature 75
3.3 FilmMicrostructure 87
3.4 References 88
Contents
IX
CHAPTER 4
ELECTRICAL CHARACTERIZATION
91
4.1 Thin Film DecouplingCapacitors 92
4.2 Characterization Methodologies 95
4.2.1 DC and Low Frequency Characterization 96
4.2.2 High FrequencyCharacterization 97
4.3 Test Vehicle:Design and Fabrication 98
4.3.1 High FrequencyTest Vehicle Design 98
4.3.2 Test Vehicle Fabrication 101
4.4 Dielectric Constant and Loss 103
4.4.1 Low Frequency Characterization 103
4.4.2 High Frequency Characterization 105
4.5 Total Series Inductance 112
4.6 Leakage CurrentDensity 114
4.7 Capacitance Densityand Breakdown Field 115
4.8 Summaryand Conclusion 117
4.9 References 118
CHAPTERS
INTEGRATION ISSUES AND CHALLENGES
121
5.1 Metal Diffusion intoDielectrics 121
5.1.1 MIS CapacitorTest Structures 122
5.1.2 C-V Characteristics ofMIS Capacitors 123
5.1.3 Bias-Temperature-Stress(BTS) Technique 125
5.1.4 TriangularVoltage Sweep (TVS) Technique 126
5.1.5 Metal Ion Penetration into Ta20s:A Detailed Example 127
5.2 Interlayer Stresses and Adhesion 141
5.3 Low Thermal Budget 142
5.4 References 143
CHAPTER 6
APPLICATIONS 145
6.1 2D Interconnections in ICs 146
x Contents
147
6.2 Integration into 2D Packaging
6.3 FlexCircuits 148
149
6.4 Large Area PowerDistribution
150
6.5 Integration into 3D Structures
6.6 Electromagnetic Considerations 151
6.7 PowerElectronics 152
6.8 References 153
INDEX 155
PREFACE
Capacitors were invented in 1745 [1] and have served as portable
electrical charge storage devices ever since.During the 19thcentury a general
understanding of electro-magnetism was gradually developed. Electronic
zo"
devices and circuits were pioneered in the early century and, by its end,
revolutionized the generation, processing, storage and transmission of
information. No evolutionary limits have yet been approached. "Rare is an
electronic circuit which doesnot employ at leastonecapacitor" [1].
Strictly speaking, all circuits have capacitors;often not wanted, considered
parasitic capacitors, such as capacitance of signal interconnections. A great
deal of effort in academia and industry attempts to reduce the value of the
parasitic capacitors by means ofnovelmaterials and structures with the lowest
dielectric constant. This book deals with the capacitors ofa wanted kind, still
needed and capable ofkeeping pace with the demands posed by ever greater
levels ofintegration.
The measure ofcapacitance is a Farad (F)- a very large quantity, seldom
needed and requiring extraordinary technology to produce, especially if the
operating voltage must be high [2]. The practical values range from
picofarads (pF), to nanofarads (nF), to microfarads (JlF); 10,12F, 10.9 F and
10'6 F, respectively. In digital electronics the operating voltages are usually
below 5 V, in automotive electronics they are 12 V to 42 V, and in power
electronics they canreach several kV.
The capacitor properties depend on the design geometry and on the
properties ofthe dielectric material and, to a lesser degree, on the properties
oftheconductor material ofitsplates and leads.
The basic equation isC=Eoe,A/d,where:
12
Eo dielectric constant offree space(permittivity) 8.85xlO· F/m
s, relative dielectric constant ofthe dielectric dimensionless
A area ofthe capacitor plates m2
d spacing (distance) between theplates m
Thus, ifthe dielectric material ofa capacitor isreplaced with another one,
whose relative dielectric constant is 100 times greater, then the capacitance
will increase by thesame factor 100.
Xli Preface
An intriguing and important question now is: ..What happens to the
breakdown voltage. VBR.. ofthe new capacitor as compared to the original
one? Willitstay thesame,go uporcome down?Andby whatfactor?"
The quantitative answer is of particular importance in the design of thin
film capacitors. Ifthe breakdown voltage, VBR = EBR d, goes up, indicating a
higher breakdown field E of the new film material, then the film can be
BR
made thinner (smaller d) resulting in the same breakdown voltage but with an
additional capacitance increase, with the total capacitance increase being
greater than the ratio ofthe two dielectric constants. Ifthe V comes down,
BR
then a thicker film is needed to preserve the value ofthe breakdown voltage,
thus offsetting the gain from the higher dielectric constant. An answer can be
found in acorrelation between the dielectric constant and the breakdown field
of a dielectric. Until now, such correlations were not widely available and
probablyonly seldom used [3].
The authors of this book have developed an empirical and quantitative
answer to this question in terms ofthe "best one can achieve," or "BOCA",
based on data for the breakdown fields of a range of relative dielectric
constants between about 2 and 1000. Given the dielectric thickness, d, ofthe
equation above, the BOCA breakdown voltage can be derived and related to
the capacitance density, CIA. They are presented in Chapter 2 for the
dielectric constants between 3 and 3,000 and for the dielectric thickness
between 0.01 urn and 10urn.
An important byproduct ofthis work was an assessment ofthe feasibility
ofa flat thin film capacitor operating at about I kV to achieve capacitance
density (CIA) on the order of5,000 f.lF/cm2•
In their investigations the authors had to cope with numerous obstacles
(performance detractors) when they tried to approximate the BOCA values of
capacitance density and breakdown voltage with various thickness thin
dielectric films oftantalum oxide,silicon oxide and silicon nitride.
The published data seems to indicate that other investigators were
confronted with similarproblems.The causes ofmany ofthese problems with
the deposition of our films were understood and brought under control in
manufacturing ofthe films in the thickness range from about 0.1 urn to about
5 urn, They are discussed in Chapter 3, the most voluminous chapter ofthis
book.
Another set of "performance detractors" is the electrical response of an
actual capacitor as compared to performance expectations of an "ideal"
capacitor, which has no losses in its dielectric and/or its plates; and has no
magnetic field. An actual capacitor has dielectric losses. The value of the
dielectric constant diminishes at higher frequencies. The plates and
connection leads have a finite resistance and a finite inductance. The
inductive reactance interacts with that of the capacitor, modifying its
frequency response.
