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Spie Press Book

EUV Lithography
Editor(s): Vivek Bakshi
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Book Description

Editorial Review

Dr. Bakshi has compiled a thorough, clear reference text covering the important fields of EUV lithography for high-volume manufacturing. This book has resulted from his many years of experience in EUVL development and from teaching this subject to future specialists. The book proceeds from an historical perspective of EUV lithography, through source technology, optics, projection system design, mask, resist, and patterning performance, to cost of ownership. Each section contains worked examples, a comprehensive review of challenges, and relevant citations for those who wish to further investigate the subject matter. Dr. Bakshi succeeds in presenting sometimes unfamiliar material in a very clear manner. This book is also valuable as a teaching tool. It has become an instant classic and far surpasses others in the EUVL field. --Dr. Akira Endo, Chief Development Manager, Gigaphoton Inc.


Extreme ultraviolet lithography (EUVL) is the principal lithography technology aiming to manufacture computer chips beyond the current 193-nm-based optical lithography, and recent progress has been made on several fronts: EUV light sources, optics, optics metrology, contamination control, masks and mask handling, and resists.

This comprehensive volume is comprised of contributions from the world's leading EUVL researchers and provides all of the critical information needed by practitioners and those wanting an introduction to the field.

Interest in EUVL technology continues to increase, and this volume provides the foundation required for understanding and applying this exciting technology.

About the editor of EUV Lithography

Dr. Vivek Bakshi previously served as a senior member of the technical staff at SEMATECH; he is now president of EUV Litho, Inc., in Austin, Texas.

Book Details

Date Published: 11 December 2008
Pages: 702
Volume: PM178

Table of Contents
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Chapter 1: EUV Lithography: A Historical Perspective
1.1 Introduction
1.2 The Early Stage of Development—1981 to 1992
1.3 The Second Stage of Development—1993 to 1996
1.3.1 Two-Mirror Imaging System Development
1.3.2 Three-Mirror Imaging System Development
1.3.3 MOS Device Demonstration Using EUVL
1.4 Other Developments in Japan and Europe
1.5 The Development of Individual Technologies
1.5.1 Selection of the Exposure Wavelength
1.5.2 Design of Reflective Imaging Systems
1.5.3 Fabrication and Evaluation of Aspherical Mirrors
1.5.4 Multilayer Coatings and Reflection Masks
1.5.5 EUV Resist Development
1.5.6 EUV Light Source Development
1.6 EUVL Conferences
1.7 Summary
1.8 Acknowledgements
1.9 References
Chapter 2: EUV LLC: A Historical Perspective
2.1 Introduction
2.1.1 Background
2.1.2 Need for a Revolutionary Approach
2.2 Formation of the LLC
2.2.1 Vision
2.2.2 Implementation
2.2.3 Organizational Structure
2.3 Program Structure 2
2.3.1 Organization
2.3.2 Risk Management
2.3.3 Reporting
2.3.4 Documentation
2.4 Program Results
2.4.1 Technical accomplishments
2.4.2 IP Portfolio
2.4.3 Program Statistics
2.4.4 Delays
2.5 Retrospective observations
2.5.1 Improvements
2.5.2 External Issues
2.5.3 Benefits
2.6 Status of EUV Development at the end of LLC 2
2.6.1 Risk Reduction
2.6.2 Industry involvement
2.7 Summary
2.8 Acknowledgements
2.9 Appendix A - Major Accomplishments
2.10 Appendix B - Patents
2.11 References
Chapter 3: EUV Source Technology
3.1 Introduction
3.2 EUV Source Requirements
3.2.1 Definition of EUV Source
3.2.2 Joint Specifications
3.2.3 Throughput Model
3.3 DPP and LPP Source Technologies
3.3.1 Discharge-Produced Plasma (DPP)
3.3.2 Laser-Produced Plasma (LPP)
3.4 EUV Source Performance
3.4.1 Conversion Efficiency of EUV Sources
3.4.2 EUV Source Performance Results
3.4.3 Source Components and Their Lifetimes
3.5 Summary and Future Outlook
Chapter 4A: Optics and Multilayer Coatings for EUVL Systems
4A.1 Introduction
4A.2 Properties of EUVL Systems
Chapter 4B: Projection Systems for Extreme Ultraviolet Lithography
4B.1 General EUVL Optical Design Considerations
4B.2 EUV Microsteppers
4B.2.1 "10X" Microstepper
4B.2.2 Microexposure Tool (MET)
4B.3 Engineering Test Stand (ETS)
4B.4 Six-Mirror EUVL Projection Systems
4B.4.1 Feasibility
4B.4.2 Concepts with Concave/Primary Mirrors
4B.4.2 Concepts with Convex Primary Mirrors
Chapter 4C: Specification, Fabrication, Testing, and Mounting of EUVL Optical Substrates
4C.1 Introduction
4C.2 Specification
4C.3 Projection Optics
4C.4 Effect of Substrate Errors on Imaging Performance
4C.5 Low-Frequency (Figure) Errors
4C.7 High-Spatial-Frequency Errors
4C.8 Influence of Coatings on Roughness Specification
4C.9 Calculation of Surface Errors
4C.10 Uniformity
4C.11 Substrate Materials
4C.12 Fabrication
4C.13 Metrology
4C.14 Mounting and Assembly
4C.15 Alignment
4C.16 Condenser Optics
Chapter 4D: Multilayer Coatings for EUVL
4D.1 Overview and History of EUV Multilayer Coatings
4D.2 Choice of ML Materials and Wavelength Considerations
4D.3 Multilayer Deposition Technologies
4D.4 Theoretical Design
4D.5 High Reflectivity, Low Stress, and Thermal Stability Considerations
4D.6 Optical Constants
4D.7 Multilayer Thickness Specifications for Imaging and Condenser EUVL Mirrors
Chapter 5: EUV Optical Testing
5.1 Introduction
5.2 Target Accuracy
5.3 Techniques for Angstrom-scale EUV Wavefront Measurement Accuracy
5.3.1 Spherical-Wave Illumination
5.3.2 Basic Testing Requirements
5.3.3 Knife-Edge Test
5.3.4 Point-Diffraction Interferometer
5.3.5 Phase-Shifting Point-Diffraction Interferometer
5.3.6 Shearing Interferometery
5.3.7 Hartmann Wavefront Sensor
5.3.8 EUV Interferometry Examples
5.3.9 Aerial Image Monitors
5.3.10 Calibration Techniques
5.4 Intercomparison
5.4.1 Visible-Light and EUV Interferometry
5.5 Future Directions
5.5.1 At-Wavelength Optical Testing in Commercial Lithography Applications
5.5.2 EUV Optical Testing in Other Areas
Chapter 6A: Optics Contamination
6A.1 Introduction
6A.1.2 Survey of Recent Lifetime Results
6A.2 Fundamentals of Optics Contamination
6A.2.1 Causes of Projection Optics Contamination
6A.2.2 Theoretical Models of Optics Contamination
6A.3 Optics Contamination Control
6A.3.1 Measurements of Optics Lifetime
6A.3.2 Measurement of Optics Contamination (In-Situ Metrology)
6A.3.3 Environmental Control Strategy
6A.3.4 Development of Contamination-Resistant Capping Layers
6A.3.5 Cleaning of Optics Contamination
6A.3.6 Novel Approaches to Contamination Control
6A.4 Summary and Future Outlook
Chapter 6B: Grazing Angle Collector Contamination
6B.1 Introduction
6B.1.1 EUV Lithography Challenges
6B.1.2 EUV Sources
6B.1.3 EUV Collector Optics
6B.2 Collector Lifetime Status and Challenges
6B.2.1 Mechanism of Reflectivity Degradation
6B.2.2 Erosion and Deposition: A Binary Collision Approximation Study of Sn Interaction with Ru Surfaces
6B.2.3 Sn Chemical Removal
6B.3 Summary
Chapter 6C: Collector Contamination: Normal Incidence (Multilayer) Collectors
6C.1 Introduction
6C.2 Overview of Normal-Incidence Collector Mirrors
6C.3 Collector Performance
6C.3.1 Erosion by Fast Ions and Lifetime Calculation
6C.3.2 Contamination and Optics Cleaning
6C.3.3 Thermal Load and Layer Intermixing
6C.4 Summary
Chapter 7: EUV Mask and Mask Metrology
7.1 Introduction
7.2 EUV Mask Structure and Process Flow
7.3 Mask Substrate
7.3.1 Mechanical Property Requirements
7.3.2 Surface Figure Requirement
7.3.3 Defect Requirements
7.4 Mask Blank Fabrication
7.4.1 Multilayer Deposition Process
7.4.2 Multilayer Characterization
7.4.3 Multilayer Performance Improvement Techniques and Defect Mitigation
7.4.4 Multilayer Defect Inspection
7.4.5 Multilayer Defect Repair
7.4.6 Multilayer Defect Compensation
7.5 Absorber Stack and Backside Conductive Coating
7.5.1 Absorber Layer
7.5.2 Buffer Layer
7.5.3 Antireflection Coating
7.5.4 Shadowing Effect
7.5.5 Bossung Curve Assymetry and Focus Shift
7.5.6 Backside Conductive Coating and Mask Handling
7.6 Mask Patterning
7.6.1 E-Beam Writing
7.6.2 Absorber Stack Etch
7.6.3 Absorber Defect Inspection
7.6.4 Absorber Defect Repair
7.6.5 Buffer Layer Etch
7.6.6 Buffer Layer Defect Inspection and Repair
7.7 Mask Cleaning
7.8 Advanced Mask Structure
7.8.1 Etched Binary Mask
7.8.2 Attenuated Phase Shift Mask
7.8.3 Alternating Phase Shift Mask
7.8.4 Modified Alternating Phase Shift Mask
7.9 Summary and Future Outlook
Chapter 8: Photoresists for Extreme Ultraviolet Lithography
8.1 Introduction
8.2 Earliest EUV Resist Imaging
8.3 Absorption Coefficients of EUV Photoresists
8.3.1 Absorption Coefficient Definitions
8.3.2 Absorption Cross-Sections of the Elements
8.3.3 Methods for Determining EUV Absorbance
8.4 Multilayer Resists and Pattern Transfer
8.4.1 Multilayer Resist Approaches
8.4.2 Defects in Ultrathin Resist Films
8.4.3 Pattern Transfer of UTR into Hard Masks
8.4.4 Integration of UTRs into Integrated Circuit Manufacturing Processes
8.5 Resist Types
8.5.1 Environmentally Stable Chemically Amplified Photoresists (ESCAP)
8.5.2 KRS Photoresists
8.5.3 PMMA
8.5.4 Negative Resists
8.5.5 Resists with Silicon or Boron
8.6 PAGs and Acids
8.6.1 Acid Diffusion
8.6.2 New PAGs for EUV
8.6.3 Exposure Mechanisms
8.7 Line Edge Roughness
8.7.1 Added Base
8.7.2 Polymer Size
8.7.3 Shot Noise
8.7.4 Film Quantum Yield
8.8 Summary and Future Outlook
Notes and References
Chapter 9: High-Resolution EUV Imaging Tools for Resist Exposure and Aerial Image Monitoring
9.1 Introduction
9.2 EUV Tool Design Considerations
9.3 EUV Microstepper
9.3.1 MS-13 Tool Concept
9.3.2 EUV Source
9.3.3 EUV Optics
9.3.4 Tool Subsystems
9.3.5 Tool Subsystems testing
9.4 Reticle Imaging Microscope
9.4.1 RIM-13 Tool Architecture
9.4.2 EUV Source
9.4.3 EUV Illumination
9.4.4 Reticle Imaging
9.4.5 EUV Microscope
9.4.6 Visible Microscope
9.4.7 Tool Subsystems
9.4.8 EUV Reticle Aerial Image Capture Results
9.4.9 Software
9.5 Summary and Future Outlook
Chapter 10: Fundamentals of the EUVL Scanner
10.1 Introduction
10.2 Illumination Optics
10.2.1 Illumination Optics Design
10.2.2 Source Requirements
10.2.3 Thermal Loading of Illuminator
10.3 Projection Optics
10.3.1 Numerical Aperture
10.3.2 Magnification and Field Size
10.4 Stages
10.4.1 Reticle Stage and Wafer Stage
10.4.2 Reticle Chuck
10.4.3 Wafer Chuck
10.5 Sensors
10.5.1 Reticle Focus Sensor
10.5.2 Wafer Focus Sensor
10.5.3 Wafer Alignment Sensor
10.5.4 Aerial Image Sensor
10.5.5 Dose Sensor
10.6 Handling Systems
10.6.1 Reticle Handling System
10.6.2 Wafer Handling System
10.7 Vacuum and Environment System
10.8 Budgets
10.8.1 Overlay Budget
10.8.2 Focus Budget
10.8.3 Wafer Throughput Budget
10.9 Summary
Chapter 11: EUVL System Patterning Performance
11.1 Introduction: The Benefits of EUV Imaging
11.2 Imaging with the 0.1-NA ETS Optic
11.2.1 Static Imaging Characterization of the 0.1-NA ETS Optic
11.2.2 Low-k1 Printing With Modified Illumination
11.2.3 Determining the Impact of Limited Resist Resolution
11.2.4 Early Demonstration of Chromeless Phase-Shift-Mask Printing in the EUV Range
11.2.5 Buried Programmed Defect Printability Study
11.3 Imaging with the 0.3-NA MET Optic
11.3.1 Predicted Performance
11.3.2 Demonstrating Resist-Limited Performance
11.4 System Contributors to Line-Edge Roughness
11.4.1 LER Transfer from the Mask to the Wafer
11.4.2 Mask Roughness Effects on LER
11.4.3 Mask Roughness Effects on Printed Contact Size Variations
11.5 Flare in EUVL Systems
11.5.1 Sources of Flare and Estimating Flare from Surface Roughness
11.5.2 Flare Characterization of the Intel MET
11.5.3 Impact of Flare on Patterning Performance and Flare Variation Compensation
11.6 Summary
Chapter 12: Lithography Cost of Ownership (CoO)
12.1 CoO Overview
12.1.1 SEMATECH Lithography CoO Historical Activities
12.1.2 General CoO Equations and Input Relationships
12.1.3 Lithography Global CoO Input Assumptions
12.1.4 Lithography Specific Product Parameters
12.2 Lithography Historical Cost and Price Trends
12.2.1 Historical Completed Wafer, Die, and Function Costs to Manufacture
12.2.2 Historical Photolithography Exposure Tool Price Trends
12.2.3 Historical Reticle Costs and Mask Usage Trends
12.3 Major Lithography CoO Parameter and Productivity Drivers
12.3.1 Example of 100nm Litho Patterning Metal 1 Level CoO within a 90nm Half Pitch Logic Device Manufacturing
12.3.2 Exposure Tool Cell Throughput (TPT)
12.3.3 Exposure Level Product Requirements (Yield, Send Aheads, and Rework)
12.3.4 DUV Source Consumables and Running Costs
12.3.5 Photoresist Cost Drivers and Photoresist Process Complexity
12.3.6 Reticle Cost Drivers
12.3.7 Litho Cell Equipment Reliability, Availability, and Maintainability (RAM)
12.4 General Observations on Litho Cell and CoO Improvements (past decade)
12.4.1 Exposure Tool Supplier CoO Improvement Factors
12.4.2 Optical Laser Source Improvements
12.4.3 Photoresist and Photoresist Processing
12.4.4 Reticle Improvements
12.4.5 FAB Automation Processing and Yield Controls
12.5 Brief CoO Considerations for Near Future Lithography Technologies
12.5.1 193nm Immersion Lithography (193i)
12.5.2 Extreme Ultraviolet Lithography (EUVL)
12.5.3 Maskless Lithography (ML2)
12.5.4 Nano Imprint Lithography (NIL)
12.6 Summary
12.7 Example Case Studies of Litho CoO Calculations
12.7.1 Example Case 1: Improved Yield at Expense of System Cost and/or TPT Performance
12.7.2 Example Case 2: Slight Improved Laser Source Power at Expense of Specialty Gas Costs
12.7.3 Example Case 3: Product Lots Reroute To Different Tool vs. Lot Hold
Appendix: Reference Data for the EUV Spectral Region

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