OXALIC ACID BASED CHEMICAL SYSTEMS FOR ELECTROCHEMICAL MECHANICAL ...

237 Pages·2006·2.1 MB·English

O A B C S F
XALIC CID ASED HEMICAL YSTEMS OR
E M P C
LECTROCHEMICAL ECHANICAL LANARIZATION OF OPPER

by

Viral Pradeep Lowalekar

A Dissertation Submitted to the Faculty of the

DEPARTMENT OF MATERIALS SCIENCE AND ENGINEERING

In Partial Fulfillment of the Requirements
For the Degree of

DOCTOR OF PHILOSOPHY

In the Graduate College

THE UNIVERSITY OF ARIZONA

2 0 0 6
THE UNIVERSITY OF ARIZONA
GRADUATE COLLEGE

As members of the Dissertation Committee, we certify that we have read the dissertation

prepared by Viral Pradeep Lowalekar

entitled Oxalic Acid Based Chemical Systems for Electrochemical Mechanical

Planarization of Copper

and recommend that it be accepted as fulfilling the dissertation requirement for the

Degree of Doctor of Philosophy

Date: 06/30/06
_______________________________________________________________________
Srini Raghavan

Date: 06/30/06
_______________________________________________________________________
William Davenport

Date: 06/30/06
_______________________________________________________________________
David Poirier

Final approval and acceptance of this dissertation is contingent upon the candidate’s
submission of the final copies of the dissertation to the Graduate College.

I hereby certify that I have read this dissertation prepared under my direction and
recommend that it be accepted as fulfilling the dissertation requirement.

________________________________________________ Date: 06/30/06
Dissertation Director: Srini Raghavan
3
STATEMENT BY AUTHOR

This dissertation has been submitted in partial fulfillment of requirements for an
advanced degree at the University of Arizona and is deposited in the University Library
to be made available to borrowers under rules of the Library.

Brief quotations from this dissertation are allowable without special permission,
provided that accurate acknowledgment of source is made. Requests for permission for
extended quotation from or reproduction of this manuscript in whole or in part may be
granted by the head of the major department or the Dean of the Graduate College when in
his or her judgment the proposed use of the material is in the interests of scholarship. In
all other instances, however, permission must be obtained from the author.

SIGNED: Viral P. Lowalekar
4
ACKNOWLEDGEMENTS

First and Foremost, I would like to sincerely thank my advisor, Prof. Srini Raghavan
for his guidance and support in the completion of this dissertation. I want to send my
deepest appreciation to Prof. Raghavan for his advice and encouragement. Prof.
Raghavan has been very kind, patient and has always given me opportunity to explore
areas outside my research. Over the years, I have learned a lot from him for which I
would always remain indebted to him.
I would also like to thank my committee members: Prof. William Davenport and Prof.
David Poirier for being on my committee and taking time to read my dissertation. I would
also like to thank Dr. Jeffrey Sczechowski for proof reading my dissertation. I want to
acknowledge Dr. Kenneth Nebesny and Dr. Paul Lee with chemistry department for
helping me with the XPS characterization. My thanks and appreciations are also due to
Dr. Wayne Huang and Dr. Subramanian Tamilmani. As a friend and former fellow
graduate student, they taught me a lot during the early part of my graduate life and helped
me throughout. I would like to appreciate the help of Mr. Ashok Muthukumaran in
performing certain experiments. I would like to thank all my current and past research
colleagues and fellow graduate students who have made my graduate experience a
memorable one.
I must also acknowledge the financial support provided NSF/SRC Engineering
Research Center for Environmentally Benign Semiconductor Manufacturing.
I would like to thank all my friends in and around Tucson to making my stay here, an
enjoyable one. Finally, and most importantly, I want to convey my love and gratitude to
my parents, Mr. Pradeep Lowalekar and Mrs. Prerna Lowalekar, my brother, Mr. Vishal
Lowalekar, and my grandparents, for their unconditional love, affection, support, and
prayers, without which this would not have been possible. Last but not the least, I would
like to thank God for everything.
5
TABLE OF CONTENTS

TABLE OF CONTENTS....................................................................................................5

LIST OF ILLUSTRATIONS..............................................................................................8

LIST OF TABLES............................................................................................................13

ABSTRACT......................................................................................................................16

CHAPTER 1: INTRODUCTION.....................................................................................18
1.1. Introduction............................................................................................................18
1.2. Research Objectives...............................................................................................24

CHAPTER 2: BACKGROUND.......................................................................................25
2.1. Chemical Mechanical Planarization......................................................................25
2.1.1. CMP Tools......................................................................................................30
2.1.2. CMP Consumables – Pads..............................................................................33
2.1.3. CMP Consumables – Slurries.........................................................................36
2.1.4. CMP Mechanisms...........................................................................................38
2.1.4.1. Oxide CMP..............................................................................................38
2.1.4.2. Tungsten CMP.........................................................................................39
2.1.5. Copper CMP...................................................................................................43
2.1.5.1. Nitric Acid Based Chemistries.................................................................43
2.1.5.2. Ammonia Based Chemistries...................................................................46
2.1.5.3. Hydrogen Peroxide Based Chemistries...................................................49
2.1.5.4. Hydroxylamine Based Chemistries..........................................................50
2.1.5.5. Iodate Based Chemistries.........................................................................54
2.2. Integration Issues in Copper CMP for 65 nm Technology Node and Beyond......59
2.2.1. Need for Low-k Materials...............................................................................59
2.2.2. Integration Challenges for Copper/Low-k Interconnects...............................65
2.3. Electrochemical Mechanical Planarization (ECMP).............................................71
2.3.1. Introduction.....................................................................................................71
2.3.2. The ECMP Process.........................................................................................71
2.3.3. Topographic Control.......................................................................................74
2.3.4. Line Resistance...............................................................................................75
2.3.5. Environmental Advantages.............................................................................75
2.4. Pads/Electrodes for ECMP....................................................................................78
2.5. Chemistries for ECMP...........................................................................................82
2.6. Importance of Static Etching in ECMP.................................................................87
2.7. Inhibitors for Copper..............................................................................................91
2.8. Oxalic Acid Based Chemistries.............................................................................97
6
TABLE OF CONTENTS - Continued

CHAPTER 3: EXPERIMENTAL SET-UP AND MATERIALS..................................100
3.1. Theoretical Work.................................................................................................100
3.1.1. Potential – pH Diagrams...............................................................................100
3.2. Experimental Methods.........................................................................................103
3.2.1. Laboratory Scale Electrochemical Mechanical Abrasion Cell (EC-AC).....103
3.2.2. ECMP Experiment in EC-AC Tool..............................................................106
3.2.3. Static (no abrasion) Experiment in EC-AC Tool..........................................109
3.3. Electrochemical Measurements...........................................................................110
3.3.1. Potentiodynamic Polarization.......................................................................110
3.3.2. Anodic Polarization......................................................................................116
3.3.3. Potentiostatic Experiments............................................................................117
3.3.4. Galvanostatic Experiments...........................................................................118
3.4. Cyclic Voltammetry.............................................................................................119
3.5. Quartz Crystal Microbalance (QCM)..................................................................124
3.6. Chemical and Physical Analysis..........................................................................128
3.6.1. Atomic Absorption Spectrophotometry (AAS)............................................128
3.6.2. Surface Profile Measurements......................................................................129
3.6.3. Four Point Probe...........................................................................................133
3.6.4. X-ray Photoelectron Spectroscopy (XPS)....................................................136
3.6.5. pH Measurements.........................................................................................136

CHAPTER 4: RESULTS AND DISCUSSION..............................................................138
4.1. Potential-pH Diagrams.........................................................................................138
4.1.1. Copper–Oxalic Acid–Water System.............................................................138
4.1.2. Copper–Oxalic Acid–BTA–Water System...................................................141
4.1.3. Copper–Oxalic Acid–TSA–Water System...................................................144
4.2. Anodic Dissolution of Copper in Oxalic Acid Solutions.....................................147
4.2.1. Etch Rate of Copper in Oxalic Acid Solution at Different Applied
Potentials.......................................................................................................147
4.2.2. Identification of Inhibitors............................................................................151
4.3. ECMP of Copper in the Presence of Abrasive Particles......................................154
4.3.1. Removal Rates of Copper during Abrasion in Oxalic Acid Solution –
Need for Inhibitors........................................................................................154
4.3.2. Removal Rates of Copper during Abrasion in Oxalic Acid Solution –
Effect of BTA as Inhibitor............................................................................156
4.3.3. Removal Rates of Copper during Abrasion in Oxalic Acid Solution
– Effect of TSA as Inhibitor..........................................................................159
4.3.3.1. Removal Rates of Copper in Oxalic Acid Solution Containing TSA –
Effect of Particle Concentration.............................................................162
4.3.3.2. Removal Rates of Copper in Oxalic Acid Solution Containing TSA –
Effect of solution pH..............................................................................164
7
TABLE OF CONTENTS - Continued

4.3.3.3. Galvanostatic Study of Copper Removal in Oxalic Acid Solution
Containing TSA – Effect of Current Density........................................167
4.3.3.4. Galvanostatic Study of Copper Removal in Oxalic Acid Solution
Containing TSA – Effect of Particles....................................................170
4.3.3.5. Galvanostatic Study of Copper Removal in Oxalic Acid Solution
Containing TSA – Effect of Time before Polishing..............................172
4.4. ECMP of Copper in the Absence of Abrasive Particles......................................175
4.4.1. Removal Rates of Copper during Abrasion in Oxalic Acid Solution –
Effect of Concentration.................................................................................176
4.4.2. Galvanostatic Study of Copper Removal in Oxalic Acid Solution
Containing TSA– Effect of Current Density................................................178
4.4.2. Galvanostatic Study of Copper Removal in Oxalic Acid Solution
Containing TSA – Effect of TSA Concentration..........................................181
4.4.3. Galvanostatic Study of Copper Removal in Oxalic Acid Solution –
Comparison of BTA and TSA as Inhibitor...................................................184
4.5. Passivation Kinetics of Copper in Oxalic Acid Solution Containing TSA.........187
4.5.1. Dissolution of Copper in Oxalic Acid..........................................................187
4.5.2. Copper Dissolution in Oxalic Acid Containing TSA...................................188
4.5.3. Effect of TSA Concentration on Copper Dissolution in Oxalic Acid..........191
4.5.4. Comparison of TSA and BTA as Inhibitors for Copper in Oxalic Acid
Chemistry......................................................................................................192
4.5.5. Inhibition Efficiency.....................................................................................196
4.6. Cyclic Voltammetry (CV)....................................................................................199
4.6.1. Oxidation of Oxalic Acid..............................................................................199
4.6.2. Oxidation of Thiosalicylic Acid (TSA)........................................................200
4.6.3. Cyclic Voltammetry (CV) and Quartz Crystal Microbalance (QCM)
Studies in Cu/TSA System............................................................................203
4.7. XPS Characterization of Passive Film.................................................................206
4.8. Mechanism of Passivation...................................................................................216

CHAPTER 5: CONCLUSIONS AND FUTURE WORK..............................................219
5.1. Conclusions..........................................................................................................219
5.2. Future Work.........................................................................................................224

REFERENCES...............................................................................................................225
8
LIST OF ILLUSTRATIONS

Figure 1.1: Trends in logic and memory devices [1.4]................................................19

Figure 1.2: Cross sectional view of MOSFET device with three levels of metal
interconnects: a) Surface topography without any planarization,
b) planarized surface without topography buildup [1.7]...........................22

Figure 2.1: Schematic of copper damascene process.(1) Electrodeposition of
copper to fill vias and trenches. (2) Bulk copper removal. (3) Barrier
metal removal and overpolish....................................................................28

Figure 2.2: Measurement of planarity [2.5].................................................................29

Figure 2.3: Schematic of CMP tools: (a) rotary, and (b) orbital [2.7 -2.9]..................32

Figure 2.4: Mechanism of tungsten CMP proposed by Kaufman et al. [2.31]............41

Figure 2.5: Pourbaix diagram for W-H O system.......................................................42
2

Figure 2.6: Pourbaix diagram for Cu-H O system. [Activities of dissolved copper
2
species = 0.1 M, 10-3 M and 10-6 M]........................................................45

Figure 2.7: Polish rate and etch rate of copper in nitric acid slurries [2.39]................45

Figure 2.8: Effect of NH OH concentration on copper removal rate [2.41]................47
4

Figure 2.9: Pourbaix diagram for Cu-NH -H O system..............................................48
3 2

Figure 2.10: Pourbaix diagram for Cu-hydroxylamine-H O system overlaid on
2
hydroxylamine-H O system......................................................................53
2

Figure 2.11: Removal rate of copper in 0.5 M hydroxylamine solution as a
function of pH...........................................................................................53

Figure 2.12: Removal rates of copper disk with slurry containing 3% MoO and
2
varying concentration of KIO at pH 4 [2.58]..........................................57
3

Figure 2.13: Schematic of interconnect.........................................................................60

Figure 2.14: Variation of time delay as a function of device generation [2.60]............62
9
LIST OF ILLUSTRATIONS - Continued

Figure 2.15: (a) Cross-section SEM micrograph showing delamination of low-k film
undergone CMP [2.66] and (b) Variation of time to CMP-induced
delamination as function of modulus of low-k film [2.65, 2.66]..............67

Figure 2.16: Relation between copper removal rate and applied charge [2.73]............73

Figure 2.17: Schematic representation of an ECMP process.........................................73

Figure 2.18: Effect of downforce on low-k (k<2.5) wafers, shows peeling at high
downforce and no peeling under ECMP...................................................77

Figure 2.19: Schematic of pad/electrode structure used by Wada et al. [2.78].............79

Figure 2.20: Carbon polishing pad used by Kondo et al. [2.79]. [Inset: Electro-cell
structure fabrication in carbon pad]..........................................................80

Figure 2.21: Mechanism for electropolishing of copper in DI water as
proposed by Wada.....................................................................................84

Figure 2.22: Change in topography of copper by planarization in presence of
inhibitor during ECMP process................................................................89

Figure 2.23: Change in topography of copper while polishing in aggressive
chemistry with high static etch rate...........................................................90

Figure 2.24: Chemical structure of various copper corrosion inhibitors.......................96

Figure 2.25: Speciation diagram for oxalic acid - water system....................................99

Figure 3.1: Typical setup of the laboratory scale electrochemical abrasion cell
(EC-AC tool)............................................................................................104

Figure 3.2: Cross-sectional view of the EC-AC tool.................................................105

Figure 3.3: Schematic showing the offset between the pad and the copper sample..107

Figure 3.4: Tafel plot for simple system shown Tafel relationships and
Tafel slopes [3.17]..................................................................................113

Figure 3.5: Tafel plot of mixed electrode system of hydrogen and zinc
electrodes [3.17]......................................................................................114
10
LIST OF ILLUSTRATIONS - Continued

Figure 3.6: Schematic of potential sweep during cyclic voltammtery.......................120

Figure 3.7: Cyclic voltammogram for a reversible single electron transfer reaction.120

Figure 3.8: Influence of potential scan rate on voltammogram of a reversible
reaction....................................................................................................123

Figure 3.9: Cyclic voltammogram for an irreversible reaction..................................123

Figure 3.10: Schematic of the front and rear side of the gold coated quartz
crystals [3.19]..........................................................................................126

Figure 3.11: Schematic of the QCM interfaced with a potentiostat to study the
mass change of the sample with simultaneous electrochemical
measurements [3.19]...............................................................................127

Figure 3.12: Schematic diagram of a Alpha Step 200 surface profiler........................131

Figure 3.13: Preparation of abraded sample for step height measurement using
profilometery...........................................................................................132

Figure 3.14: Schematic representation of a four point probe technique......................135

Figure 4.1: Potential-pH diagram for copper-oxalic acid-water system for
dissolved copper activity of 10-6 M. Note: indicate different
overpotential values (0, 300 mV, 500 mV and 750 mV) for copper
exposed to 0.1 M oxalic acid at pH 4.......................................................140

Figure 4.2: Potential-pH diagram for copper-oxalic acid-BTA-water system:
(a) BTA concentration of 0.005 M, and (b) 0.01 M BTA.
Note: indicate different overpotential values (0, 300 mV, 500 mV
and 750 mV) for copper exposed to 0.1 M oxalic acid at pH 4..............143

Figure 4.3: Potential-pH diagram of copper-TSA-water system overlapped on
copper-oxalic acid-water system. Note: indicate different
overpotential values (0, 300 mV, 500 mV and 750 mV) for copper
exposed to 0.1 M oxalic acid at pH 4.......................................................146

Figure 4.4: Static etch rate of copper in oxalic acid solution as a function of
concentration and overpotential...............................................................149