Copper Interconnect Technology

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1 Tapan Gupta Copper Interconnect Technology i Springer

2 Contents 1 Introduction Trends and Challenges Physical Limits and Search for New Materials Challenges Choice of Materials Why Copper (Cu) Interconnects? New Technologies Multilayer Metal Architecture Substrate Engineering An Alternate Technology for Interconnects Materials Used in Modern Integrated Circuits Properties of Copper Grain Size Melting Temperature Barrier Layer Low-K Dielectric Materials Polymers Semiconductors Silicon (Si) Challenges and Accomplishments Challenges Accomplishments Technologies of the 21 st Century, and the Plan to Meet the Challenges Ultra-Shallow Junction (USJ) Circuit Design and Architecture Improvements Performance and Leakage in Low Standby Power (LSTP) Systems Introduction of New Materials and Integration Processes Nano-Materials Superconductors Integration Processes 47 > 1.18 Summary 53 References 55 xiii

3 xiv Contents 2 Dielectric Materials Introduction Interlayer Dielectric (ILD) Introduction Mathematical Model Selection Criteria for an Ideal Low-K Material Search for an Ideal Low-K Material Achievement Impact of Low-K ILD Materials on the Cu-Damascene Process Deposition Techniques High-K Dielectric Materials Introduction Impact on Scaling and Requirements Search for a Suitable High-K Dielectric Material Deposition Technology for High-K Materials Summary 102 References Diffusion and Barrier Layers Ill 3.1 Diffusion Ill Introduction Ill Transitional Effects Mathematical Modeling of Diffusion in Cu-Interconnects Grain Boundary (GB) Diffusion Vacancy Diffusion Drift Diffusion Interdiffusion Diffusion of Copper and Its Consequences Precipitation Barrier Layer for Cu-Interconnects Theory Ideal Barrier Layer Barrier Layer Architecture Interlayer Reactions Influence of the Barrier Layer Properties on the Reliability of Cu-Interconnects Low-K Dielectric-Barrier Layer Reaction Rates Influence of the Barrier Layer on the Electrical Conductivity of Cu-Lines Influence of Barrier Layer Thermal Conductivity on Cu-Line Classification of Barrier Layer 144

4 XV Properties of Different Barrier Layer Materials Cap-Layer, Its Properties and Functions Summary 150 References Pattern Generation Photolithography Introduction Resolution Limits of Optical Lithography Deep Ultraviolet (DUV) Lithography Reticles Enhancement Techniques for Resolution nm Lithography Chemically Amplified Resist (CA) Extreme Ultraviolet (EUV) Lithography e-beam Lithography (EBL) Electron-Beam Resist e-beam Reticle Step and Flash Imprint Lithography (SFIL) Etching and Cleaning of Damascene Structures Etching Cleaning Summary 214 References Deposition Technologies of Materials for Cu-Interconnects Introduction Emerging Technologies Cu-Damascene Process Barrier Layer Requirements Deposition Requirements Thin Film Growth and Theory of Nucleation Nucleation Theory Instrumentation Physical Vapor Deposition Sputtering Ionized Physical Vapor Deposition (IPVD) Chemical Vapor Deposition (CVD) Plasma Enhanced CVD (PECVD) System Metal-Organic Vapor Deposition (MOCVD) Low Temperature Thermal CVD (LTTCVD) System Atomic Layer Deposition (ALD) Plating 243 > History of Electroplating and Printed Circuit Boards (PCBs) 243

5 xvi Contents DC Bath Chemistry Electroplating of Copper Inside Damascene Architecture Process Chemistry for Superconformal Electrodeposition of Copper Electrochemical Mechanical Deposition (ECMD) Influence of the Seed Layer on Electroplating Electroless Deposition of Copper Stress in Cu-Interconnects Summary 253 References The Copper Damascene Process and Chemical Mechanical Polishing The Copper Damascene Process Introduction Conventional Metallization Technology Cu-Damascene Metallization Technology General Objectives and Challenges Chemical Mechanical Polishing (CMP) and Planarization Introduction Chemical Mechanical Polishing (CMP)Technology Copper Dishing Model Slurry Chemistry Particle Size Inside the Slurry Relative Velocity of the Pad and Wafer Pad Pressure Pad-Elasticity Pad Conditioning Shallow Trench Isolation (STI) Abrasive Free Polishing End-Point Detection Dry In Dry Out Multi-Step Processing Post-CMP Cleaning CMP Pattern Density Issues Summary 296 References Conduction and Electromigration Conduction Introduction Conduction Mechanism and Restrictions Effect of Grain Boundary (GB) Resistance on the Conductivity of Cu-Interconnects Effect of Grain Size and Morphology of the Substrate 311

6 Contents xvii Morphology of the Cu-Film and Its Influence on the Conduction (Electrical) Mechanism of Cu-Interconnects Effect of Film Thickness on the Conductivity of Cu-Interconnects Diffusion Related Impacts on the Conductivity of a Cu-Line Cu-Line Stress and Its Consequences Conduction of Heat Through Cu-Interconnects Thermal Cycling (Annealing) Related Phenomena Electromigration (EM) Electromigration (EM) Mechanism of Electromigration (EM) and Its Effects Void Formation Analytical Model on Stress Related EM Effect of Microstructure of the Film on Mass Migration Effect of Solute on Electromigration Melting Temperature of a Metal and Its Effect on Grain Growth Effect of Temperature on EM Current Density and Its Effect on EM Summary 336 References Routing and Reliability Routing Introduction Methods of Improving Interconnect Routings Interconnect Routing Design Challenges with High Density Routing Cascaded Driver Transmission Line Coupling Clocking of High-Speed System Reliability Introduction Reliability Issues Related to Cu-Interconnects Measurements Summary 393 References 394 Glossary (Copper Interconnects) 405 Index 415 >