ISBN-10:
9814273325
ISBN-13:
9789814273329
Pub. Date:
08/25/2010
Publisher:
World Scientific Publishing Company, Incorporated
Electromigration In Ulsi Interconnections

Electromigration In Ulsi Interconnections

by Cher Ming Tan

Hardcover

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Overview

Electromigration in ULSI Interconnections provides a comprehensive description of the electromigration in integrated circuits. It is intended for both beginner and advanced readers on electromigration in ULSI interconnections. It begins with the basic knowledge required for a detailed study on electromigration, and examines the various interconnected systems and their evolution employed in integrated circuit technology. The subsequent chapters provide a detailed description of the physics of electromigration in both Al- and Cu-based Interconnections, in the form of theoretical, experimental and numerical modeling studies. The differences in the electromigration of Al- and Cu-based interconnections and the corresponding underlying physical mechanisms for these differences are explained.The test structures, testing methodology, failure analysis methodology and statistical analysis of the test data for the experimental studies on electromigration are presented in a concise and rigorous manner. Methods of numerical modeling for the interconnect electromigration and their applications to the understanding of electromigration physics are described in detail with the aspects of material properties, interconnection design, and interconnect process parameters on the electromigration performances of interconnects in ULSI further elaborated upon. Finally, the extension of the studies to narrow interconnections is introduced, and future challenges on the study of electromigration are outlined and discussed.

Product Details

ISBN-13: 9789814273329
Publisher: World Scientific Publishing Company, Incorporated
Publication date: 08/25/2010
Series: International Series On Advances In Solid State Electronics And Technology Series
Pages: 312
Product dimensions: 6.10(w) x 9.00(h) x 0.90(d)

Table of Contents

Foreword vii

Preface xiii

1 Introduction 1

1.1 What is Electromigration" 1

1.2 Importance of Electromigration 2

1.3 Outlines of this Book 6

2 History of Electromigration 11

2.1 Understanding the Physics of Electromigration 11

2.1.1 Quantum mechanical theory of electromigration 11

2.1.2 Practical engineering electromigration formulation 16

2.1.3 Concept of flux divergence 20

2.2 Electromigration Lifetime Modeling 22

2.3 Electromigration Lifetime Improvement 29

2.4 Electromigration Aware IC Design 30

3 Experimental Studies of Al Interconnections 37

3.1 Introduction 37

3.2 Process-Induced Failure Physics 38

3.2.1 Microstructural in homogeneities of metallization 38

3.2.1.1 Grain size 40

3.2.1.2 Grain size distribution 40

3.2.1.3 Texture of a metal line 41

3.2.2 Presence of impurity 42

3.2.3 Mechanical stress in the film 43

3.2.4 Presence of defect 45

3.2.4.1 Length dependence of lifetime 45

3.2.4.2 Length dependence of the standard deviation of EM lifetime distribution 46

3.2.5 Temperature gradient 46

3.2.6 Material differences 51

3.2.7 Temperature 52

3.3 Design-Induced Failure Mechanisms 54

3.3.1 Proximity of metal lines 54

3.3.2 Inter-metal dielectric (IMD) thickness between metal lines and oxide thickness underneath the first metallization 54

3.3.3 Number of metallization levels 54

3.3.4 Use of barrier layers 55

3.3.5 Via separation length 58

3.3.6 Cornering of metal line and Step height of metal lines 59

3.3.7 Use of passivation layer 59

3.3.8 Metal width variation 61

3.3.9 Reservoir effect 61

3.4 Self-Induced Process During EM 63

3.4.1 Self-induced stress gradient 63

3.4.2 Self-induced temperature gradient 64

3.4.3 Microstructure change of interconnect 65

3.5 Electromigration Test Structure Design 67

3.5.1 NIST test structure 68

3.5.2 Test structure for multi-level metallization 73

3.5.3 Test structure for bamboo structure 77

3.6 Package-Level Electromigration Test (PET) 77

3.7 Rapid Electromigration Test 79

3.7.1 TRACE method 80

3.7.2 Standard Wafer-level Electromigration Accelerated Test (SWEAT) 83

3.7.3 Wafer-level isothermal Joule-heated electromigration test (WIJET) 85

3.7.4 Wafer level constant current electromigration test (Lee, Tibel and Sullivan 2000) 87

3.7.5 Breakdown energy of metal (BEM) 87

3.7.6 Pitfalls of SWEAT 90

3.7.7 Potential pitfalls of constant current test method 99

3.7.8 Potential pitfall of breakdown energy method (BEM) 100

3.7.9 Potential pitfalls of WIJET 100

3.7.10 Summary 101

3.7.11 Highly accelerated electromigration test 101

3.8 Practical Consideration in Electromigration Testing 103

3.8.1 Failure criteria used in EM testing 103

3.8.2 Interpretation of the measured δ R/R0 105

3.8.3 Actual temperature of test strips 108

3.8.4 Test structure used 109

3.8.5 Current density used 109

3.8.6 Short length effect 109

3.8.7 Failure model used in EM accelerated testing (deviation from Black equation) 111

3.9 Failure Modes in Electromigration 113

3.9.1 Open/resistance increase 113

3.9.2 Short 115

3.10 Test Data Analysis 115

3.11 Failure Analysis on EM Failures 125

3.12 Conclusion 133

4 Experimental Studies of Cu Interconnections 143

4.1 Different in Interconnect Processing and its Impact on EM Physics 144

4.2 Process-induced Failure Physics 152

4.2.1 Interface between Cu and surrounding materials 152

4.2.1.1 Surface engineering 153

4.2.1.2 Alternative cap-layer materials 156

4.2.2 Microstructure 162

4.2.3 Presence of impurity 173

4.2.4 Mechanical stress 180

4.2.5 Barrier metal 191

4.2.6 Presence of defects 199

4.2.7 Temperature gradient 200

4.2.8 Material differences 200

4.2.9 Temperature 201

4.3 Design-Induced Failure Mechanism 202

4.3.1 Line width dependence of EM lifetime 202

4.3.2 Current crowding 208

4.3.3 Line width transition 211

4.3.4 Reservoir effect 212

4.3.5 Current direction dependence of EM lifetime 217

4.3.6 Blech short length effect 221

4.3.7 Via structure design 224

4.4 Electromigration Testing 225

4.5 Statistics of Cu Electromigration 228

5 Numerical Modeling of Electromigration 243

5.1 ID Continuum Electromigration Modeling 245

5.2 2D EM Modeling 246

5.2.1 Sharp interface model 248

5.2.2 Phase field model 251

5.3 Electromigration Simulation Using Atomic Flux Divergence and Finite Element Analaysis 253

5.3.1 Computation methods for Atomic Flux Divergence (AFD) 254

5.3.1.1 Formulation of AFD 254

5.3.1.2 Voiding mechanism simulation 257

5.3.1.3 Lifetime prediction 258

5.4 Monte Carlo Simulation of Electromigration 260

5.4.1 Monte Carlo simulation of the movement of atoms during EM 260

5.4.2 Monte Carlo simulation of void movement during EM 262

5.4.3 Holistic EM simulation 263

5.5 Resistance Change Modeling 264

6 Future Challenges 269

6.1 Electromigration Modeling 269

6.2 EDA Tool Development 271

6.3 Physics of Electromigration 274

6.4 Electromigration Testing 274

6.5 New Failure Mechanism for Interconnects 275

6.6 Alternative Interconnect Structure 277

6.7 Alternative Interconnect System 278

Index 285

Biography 291

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