Low Dielectric Constant Materials for IC Applications

322 Pages·2003·5.222 MB·English

by  P. S. Ho, J. Leu, W. W. Lee (auth.), Professor Paul S. Ho, Jihperng Jim Leu, Wei William Lee (eds.)

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advanced microelectronics
9
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Serieseditors: K.Itoh T.Lee T.Sakurai D.Schmitt-Landsiedel
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Editors:P.S.Ho,J.Leu,W.W.Lee
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P.S. Ho J. Leu W.W. Lee (Eds.)
Low Dielectric
Constant Materials
for IC Applications
With163Figures
1 3
ProfessorPaulS.Ho WeiWilliamLee
TexasMaterialsInstitute TaiwanSemiconductorManufacturingCo.
TheUniversityofTexasatAustin (TSMC),No.9,CreationRoad1
Austin,TX78712,USA Science-BasedInd.Park,Hsin-chu,Taiwan
e-mail:[email protected] e-mail:[email protected]
Jihperng(Jim)Leu
IntelCorp.,MS:RA1-204
5200N.E.ElamYoungParkway
Hillsboro,OR97214,USA
e-mail:[email protected]
SeriesEditors:
Dr.KiyooItoh
HitachiLtd.,CentralResearchLaboratory,1-280Higashi-Koigakubo
Kokubunji-shi,Tokyo185-8601,Japan
ProfessorThomasLee
StanfordUniversity,DepartmentofElectricalEngineering,420ViaPalouMall,CIS-205
Stanford,CA94305-4070,USA
ProfessorTakayasuSakurai
CenterforCollaborativeResearch,UniversityofTokyo,7-22-1Roppongi
Minato-ku,Tokyo106-8558,Japan
ProfessorDorisSchmitt-Landsiedel
TechnischeUniversita¨tMu¨nchen,Lehrstuhlfu¨rTechnischeElektronik
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ISSN1437-0387
ISBN 978-3-642-63221-1 ISBN 978-3-642-55908-2 (eBook)
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Dieelectrics.3.Integratedcircuits.I.Ho,P.S.II.Lee,WeiWilliam.III.Leu,J(Jihperng),1958–IV.Series.
TK3401.L692002 621.3815–dc21 2002066982
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Preface
This book addresses issues on development, characterization and integration
of low dielectric constant (k) materials for advanced on-chip interconnects.
The implementation of low-k dielectrics was first identified as a key enabling
technologyforthedevelopmentofon-chipinterconnectsinthe1994National
TechnologyRoadmapforSemiconductors.Researchanddevelopmentforlow-
k dielectrics for microelectronics applications can be traced back further by
a number of years. While the need for low-k dielectrics for improving the
performance and density of advanced interconnects is clear, the progress in
implementation of low-k materials has been slower than anticipated. With
the announcement of copper metallization in 1997, the implementation of
low-k dielectrics was highlighted in the 1997 Technology Roadmap with a
k of 2.5–3.0 to be implemented for the 180-nm node in 1999. This was not
fulfilleduntil2000whenIBMannouncedthedevelopmentofCuinterconnects
for the 130-nm node with SiLKTM, a low-k dielectric material developed by
the Dow Chemical Company with a k of about 2.7. At this time, there is
intense effort in the industry to develop Cu/low-k interconnects with porous
dielectrics with a k of 2.2 or less.
Thedelayinimplementationoflow-kILDcanbelargelyattributedtothe
many challenges associated with the integration of these materials into the
dual-damasceneCuinterconnectstructures.Aparticularlydifficultchallenge
has been to obtain the combination of low dielectric constant and good ther-
malandmechanicalpropertiesincomparisontoSi O.Thisrequiresmaterial
2
design with molecular structures to optimize the bonding strength but re-
duce the electronic polarizability. This is a conflicting goal challenging low-k
development and will become more difficult for porous materials as porosity
is incorporated to further reduce the dielectric constant. This book begins
with an overview in Chap. 1 by Ho et al. summarizing the basic issues for
low-k material development and integration. The difficulty of balancing the
electronicpolarizabilitywithbondingstrengthformaterialdevelopmentwas
emphasized together with characterization of low-k materials in thin-film
form, the impact of material reactions on reliability and the integration of
low-k dielectrics into Cu damascene structures.
Aftertheoverview,thisbookisorganizedintotwopartswithChaps.2to
6 discussing material development and characterization and Chaps. 7 to 10
VI Preface
discussingmaterialreactionandprocessintegration.Withintenseeffortsfrom
industryanduniversities,significantprogresshasbeenmadeinthesynthesis
of fully dense low-k materials with molecular structures to optimize material
properties for integration into copper interconnects.
Material characterization has been an integral part of low-k development
and extensive efforts have been made in metrology development to evaluate
material properties for process integration. Since low-k materials are inte-
grated as thin films, their properties can differ appreciably from bulk or
thick-film materials. This challenges metrology development for measuring
materialpropertiesofthinfilmsonawafer,particularlyforporousmaterials
wheretheporosityfurthercomplicatesmaterialcharacterization.InChap.2,
Ryan et al. describe characterization techniques developed for measuring di-
electric, thermal, and mechanical properties of low-k thin films. In Chap. 3,
Lin et al. review two new techniques: specular X-ray reflectivity (SXR) and
small-angle neutron scattering (SANS) for characterization of porous low-k
materials.
Two general approaches for synthesis of low-k materials are discussed: in
Chap. 4 by Gill et al. on vapor deposition and in Chap. 5 by Endo et al. on
plasma-enhanced chemical vapor deposition of polymeric low-k dielectrics.
For development of porous low-k materials, the “porogen” approach using a
thermally degradable template appears promising in that it can be applied
to a wide range of inorganic and organic materials and has good control of
the pore size and morphology. The application of the porogen technique to
synthesize porous low-k materials is described in Chap. 6 by Volksen et al.
In the past several years, significant progress has been made by the semi-
conductorindustrytointegratelow-kdielectricsintocopperinterconnects.In
Chap. 10, Waterloos describes process integration of SiLKTM into Cu dam-
ascene structures. Complementing the integration chapter, Oehrlein et al. in
Chap.9discusstheplasma-etchingprocess,akeystepinintegrationoflow-k
structures. The weak thermal and mechanical properties have raised reliabil-
ityconcernsonthermalstabilityandstructuralintegrityoflow-k structures.
Distinct failure mechanisms have been observed in low-k structures during
processing or reliability tests, where more work is clearly required to fully
understand the impact of low-k integration on interconnect reliability. Two
basic issues related to reliability are discussed in this book: in Chap. 7 by
Martini and Kelber on metal/polymer interfacial reaction and in Chap. 8 by
Faupel et al. on metal diffusion in polymers.
Continuingeffortsinlow-kintegrationwillundoubtedlyadvanceourknowl-
edge on material development, characterization, process integration, and re-
liability for this exciting class of materials and its technology. While new
knowledge and developments are to be expected, we hope that this book
provides a basis for readers to understand the current advances in low-k
dielectrics for interconnect applications. We sincerely appreciate the efforts
from all the authors for their valuable contributions to make this book pos-
Preface VII
sible. We would like to thank Claus Ascheron from Springer-Verlag for his
patience in letting us complete this book properly and Jo Ann Smith for her
efforts in working with the manuscript.
Austin, TX, U.S.A. Paul S. Ho
Hillsboro, OR, U.S.A. Jihperng (Jim) Leu
Hsin-chu, Taiwan William W. Lee
March 2002
Contents
1 Overview on Low Dielectric Constant Materials
for IC Applications
P.S. Ho, J. Leu, and W.W. Lee ................................... 1
1.1 Introduction............................................... 1
1.2 Dielectric Constant and Bonding Characteristics ............... 4
1.3 Material Properties and Integration Requirements.............. 8
1.4 Characterization of Low-k Dielectrics ......................... 11
1.5 Porous Low-k Materials..................................... 14
1.6 Conclusion ................................................ 18
References ..................................................... 19
2 Materials Issues and Characterization
of Low-k Dielectric Materials
E.T. Ryan, A.J. McKerrow, J. Leu, and P.S. Ho .................... 23
2.1 Introduction............................................... 23
2.2 Thin-Film Material Characterization ......................... 26
2.3 General Structure–Property Relationships..................... 37
2.3.1 Dielectric Constant .................................. 37
2.3.2 Thermal Properties .................................. 43
2.3.3 Moisture Uptake .................................... 46
2.3.4 Thermomechanical and Thermal Stress Properties ....... 46
2.4 Fluorinated Polyimide:
Effect of Chemical-Structure Modifications on Film Properties ... 48
2.5 Crosslinked and Thermosetting Materials ..................... 51
2.6 Parylene Polymers: Effect of Thermal History
on Film Properties ......................................... 56
2.7 Future Challenges.......................................... 64
References ..................................................... 68
X Contents
3 Structure and Property Characterization
of Low-k Dielectric Porous Thin Films Determined
by X-Ray Reflectivity and Small-Angle Neutron Scattering
E.K. Lin, H. Lee, B.J. Bauer, H. Wang, J.T. Wetzel, and W. Wu...... 75
3.1 Introduction............................................... 75
3.2 Two-Phase Methodology .................................... 76
3.2.1 Experimental ....................................... 77
3.2.2 Two-Phase Analysis Using the Debye Model ............ 79
3.2.3 Results and Discussion ............................... 80
3.3 Three-Phase Methodology................................... 83
3.4 Films with Ordered Porous Structure......................... 86
3.5 Limits of SANS Characterization Methods .................... 87
3.6 Future Developments ....................................... 88
3.6.1 Contrast Variation SXR .............................. 88
3.6.2 Inhomogeneous Wall Composition ..................... 89
3.7 Conclusion ................................................ 92
References ..................................................... 92
4 Vapor Deposition of Low-k Polymeric Dielectrics
W.N. Gill, S. Rogojevic, and T. Lu................................ 95
4.1 Introduction............................................... 95
4.2 Vapor-Phase Deposition and Polymerization on Substrates ...... 97
4.3 Parylenes ................................................. 98
4.3.1 Synthesis Review .................................... 99
4.3.2 Properties of Parylene-N ............................. 100
4.3.3 Mechanisms and Models of Parylene Polymerization ..... 101
4.3.4 Integration Issues with Parylene-N..................... 106
4.3.5 Synthesis and Properties of Parylene-F ................. 107
4.3.6 Integration Issues with Parylene-F ..................... 110
4.4 Polynaphthalene and Its Derivatives.......................... 111
4.4.1 Experimental System for Polynaphthalene Synthesis ..... 111
4.4.2 Properties of Polynaphthalene
and Fluorinated Polynaphthalene...................... 113
4.5 Teflon and Its Derivatives ................................... 114
4.5.1 Synthesis of Teflon-AF ............................... 114
4.5.2 Properties of Teflon-AF .............................. 115
4.5.3 Integration Issues with Teflon ......................... 115
4.6 Vapor-Deposited Polyimides................................. 116
4.7 Prospects for Vapor-Depositable Low-k Polymers .............. 117
References ..................................................... 117
Contents XI
5 Plasma-Enhanced Chemical Vapor Deposition
of FSG and a-C:F Low-k Materials
K. Endo, K. Kishimoto, Y. Matsubara, and K. Koyanagi............. 121
5.1 Introduction............................................... 121
5.2 FSG Films ................................................ 122
5.2.1 Introduction ........................................ 122
5.2.2 General Characteristics............................... 122
5.2.3 HDP-CVD FSG Film ................................ 128
5.3 a-C:F Films ............................................... 144
5.3.1 Introduction ........................................ 144
5.3.2 Deposition of a-C:F by PE-CVD
and Controlling Fluorine Concentration ................ 145
5.3.3 Control of F/C Ratio by Helicon-Wave HDP-CVD....... 146
5.3.4 Mechanism of the Reduction of the Dielectric Constant
of a-C:F ............................................ 151
5.3.5 Signal-Delay Measurements of CMOS Circuits........... 156
5.3.6 Conclusion.......................................... 162
References ..................................................... 163
6 Porous Organosilicates for On-Chip Applications:
Dielectric Generational Extendibility by the Introduction
of Porosity
W. Volksen, C.J. Hawker, J.L. Hedrick, V. Lee, T. Magbitang,
M. Toney, R.D. Miller, E. Huang, J. Liu, K.G. Lynn, M. Petkov,
K. Rodbell, and M.H. Weber ..................................... 167
6.1 Introduction............................................... 167
6.2 Porous Silica .............................................. 171
6.3 Organosilicates ............................................ 173
6.4 Porogens.................................................. 175
6.5 Porous Organosilicate Matrix Resins.......................... 180
6.6 Formation of Nanohybrids................................... 183
6.7 Porous Organosilicates...................................... 186
6.8 Characterization of Porous Organosilicates .................... 187
6.9 Conclusion ................................................ 196
References ..................................................... 198
7 Metal/Polymer Interfacial Interactions
D.M. Martini, and J.A. Kelber ................................... 203
7.1 Introduction............................................... 203
7.2 Experimental Methods...................................... 204
7.2.1 XPS and AES Analysis............................... 205
7.2.2 XPS for Nucleation Modes............................ 206
7.2.3 Other Surface-Science Techniques...................... 207
7.2.4 Metal-Deposition Techniques.......................... 207