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SPIE Handbook of Microlithography, Micromachining and Microfabrication

Volume 1: Microlithography

Chapter 2 is presented on this Web site, below. The complete table of contents is at the bottom of this page and the book can be ordered through SPIE.


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Chapter 2 Table of Contents

Mark A. McCord, Stanford University
Michael J. Rooks, Cornell University

2.1 Introduction 2.1.1 Definition and historical perspective
2.1.2
Applications
2.1.3
Alternative techniques

2.2 Elements of electron optics 2.2.1 Introduction
2.2.2
Electron sources
2.2.3
Electron lenses
2.2.4
Other electron optical elements 2.2.4.1 Apertures
2.2.4.2
Electron beam deflection
2.2.4.3
Beam blanking
2.2.4.4
Stigmators
2.2.5 Other column components
2.2.6
Resolution

2.3 Electron-solid interactions 2.3.1 Forward scattering
2.3.2
Backscattering
2.3.3
Secondary electrons
2.3.4
Modeling

2.4 Proximity effect 2.4.1 Introduction
2.4.2
Proximity effect avoidance
2.4.3
Proximity effect correction 2.4.3.1 Dose modulation
2.4.3.2
Pattern biasing
2.4.3.3
GHOST
2.4.3.4
Software

2.5 Systems 2.5.1 Environment
2.5.2
SEM and STEM conversions
2.5.3
Commercial SEM conversion systems 2.5.3.1 Nanometer Pattern Generation System (NPGS)
2.5.3.2
Raith pattern generators
2.5.3.3
Leica EBL Nanowriter
2.5.4 Gaussian vector scan systems 2.5.4.1 JEOL systems
2.5.4.2
Leica Lithography Systems
2.5.4.3
Leica Lithographie Systeme Jena (Jenoptik) LION
2.5.5 Gaussian spot mask writers 2.5.5.1 Etec MEBES systems
2.5.5.2
Lepton EBES4
2.5.6 Shaped Spot and Cell Projection Systems 2.5.6.1 IBM EL-4
2.5.6.2
Etec Systems Excaliber and Leica Lithographie Systeme Jena ZBA 31/32
2.5.6.3
JEOL shaped spot systems
2.5.6.4
Cell projection
2.5.7 SCALPEL
2.5.8
Other e-beam system research 2.5.8.1 STM writing
2.5.8.2
Parallel beam architectures - microcolumns
2.5.9 Electron beam fabrication services

2.6 Data preparation 2.6.1 Pattern structure
2.6.2
Avoiding trouble spots
2.6.3
Alignment marks
2.6.4
CAD Programs
2.6.5
Intermediate formats 2.6.5.1 GDSII Stream
2.6.5.2
CIF
2.6.5.3
DXF
2.6.5.4
PG3600
2.6.6 Low-level formats

2.7 Resists 2.7.1 Charge dissipation
2.7.2
Positive resists 2.7.2.1 PMMA
2.7.2.2
EBR-9
2.7.2.3
PBS
2.7.2.4
ZEP
2.7.2.5
Photoresists as e-beam resists
2.7.3 Negative resists 2.7.3.1 COP
2.7.3.2
Shipley SAL
2.7.3.3
Noncommercial negative resists: P(SI-CMS) and EPTR
2.7.4 Multilayer systems 2.7.4.1 Low/high molecular weight PMMA
2.7.4.2
PMMA/copolymer
2.7.4.3
Trilayer systems
2.7.5 Inorganic and contamination resists
2.7.6
Other research: scanning probes and thin imaging layers

2.8 Acknowledgements

2.9 Appendix: GDSII Stream Format

2.10 References


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SPIE Handbook of Microlithography, Micromachining and Microfabrication

THE COMPLETE TABLE OF CONTENTS

CHAPTER 1 Optical Lithography

Harry J. Levinson, Advanced Micro Devices
William H. Arnold, Advanced Micro Devices

1.1 Introduction / 13

1.2 Imaging / 13 1.2.1 The contributions of physics and chemistry / 17
1.2.2 Aerial image considerations / 24
1.2.3 PhotoresistsCoperational considerations / 38
1.2.4 Thin film optics / 42
1.2.5 Focus / 57
1.2.6 Optical proximity effects / 68
1.2.7 Off-axis illumination / 71
1.2.8 Pupil plane filtering and Super-FLEX / 73
1.2.9 Phase-shifting masks / 74

1.3 Wafer Steppers / 82 1.3.1 Overview / 82
1.3.2 National Technology RoadmapCstepper requirements / 83
1.3.3 Overview of the stepper as a system / 83
1.3.4 Reduction lenses / 86
1.3.5 Illumination systems / 91
1.3.6 The wafer stage / 92
1.3.7 Alignment systems / 94
1.3.8 Stepper total overlay / 97
1.3.9 Stepper productivity and cost of ownership / 101
1.3.10 Mix-and-match strategies / 108

1.4 Steppers for the 0.35 :m to 0.18 :m Generations / 109 1.4.1 0.35 :m/64 Mbit generation: high NA i-line and DUV introduction / 109
1.4.2 0.25 :m/256 Mbit generation: KrF step-and-scan / 111
1.4.3 0.18 :m optical lithography / 117

1.5 Yield / 119

1.6 The Limits of Optical Lithography / 120

1.7 Summary / 126

1.8 Acknowledgments / 126

1.9 References / 127


Chapter 2 Table of Contents

Mark A. McCord, Stanford University
Michael J. Rooks, Cornell University

See list above


CHAPTER 3 X-Ray Lithography

Franco Cerrina, University of Wisconsin

3.1 Introduction / 253 3.1.1 X-ray properties / 255 3.1.1.1 Optical constants / 256 3.1.2 Image formation and modeling / 257 3.1.2.1 Cascaded systems / 259
3.1.2.2 Geometrical image / 260
3.1.2.3 Fresnel diffraction / 261
3.1.2.4 Mask transmission / 262
3.1.2.5 Computational models / 264
3.1.3 Patterning ability / 265

3.2 Implementation: Systems and Components / 267 3.2.1 X-ray sources / 267 3.2.1.1 Point sources / 268
3.2.1.2 Synchrotron radiation sources / 269
3.2.1.3 Beam delivery systems / 276
3.2.1.4 Synchrotrons and lithography / 278
3.2.2 Masks / 280 3.2.2.1 Stress and distortion / 281
3.2.2.2 Intrinsic distortions / 282
3.2.2.3 Extrinsic distortions / 283
3.2.2.4 Mask fabrication process / 286
3.2.2.5 Pattern inspection and repair / 289
3.2.2.6 X-ray mask design variations / 289
3.2.2.7 Global mask optimization / 291
3.2.2.8 Optimal exposure conditions / 295
3.2.2.9 Suppliers / 297
3.2.3 X-ray steppers or aligners / 297 3.2.3.1 Alignment error detection system / 299
3.2.3.2 Suppliers / 300
3.2.4 Resists / 300 3.2.4.1 Resist types / 301

3.3 Applications / 301 3.3.1 High-resolution lithography / 302 3.3.1.1 ULSI / 302
3.3.1.2 Nanolithography / 303
3.3.1.3 Diffractive optics / 304
3.3.1.4 High penetrating power / 304

3.4 Status of X-Ray Lithography / 305

3.5 Conclusions / 307

3.6 Suggested Reading / 307

3.7 Bibliography / 308


CHAPTER 4 Deep-UV Resist Technology: The Evolution of Materials and Processes for 250-nm Lithography and Beyond

Robert D. Allen, IBM Almaden Research Center
Willard E. Conley, IBM Microelectronics Division
Roderick R. Kunz, MIT Lincoln Laboratory

4.1 Introduction / 323 4.1.1 Evolutionary/revolutionary changes in microlithography of the 1990s / 323
4.1.2 Chemically amplified photoresists: a brief history and description / 327

4.2 DUV (248-nm) Resist Materials / 330 4.2.1 Newer concepts in positive resists / 330
4.2.2 Negative DUV resists / 333

4.3 Properties of DUV (248-nm) Resist Materials / 334 4.3.1 Acid diffusion in CA resists / 334
4.3.2 Environmental stability: divergence in DUV resists / 335
4.3.3 Image thermal stability / 338
4.3.4 Reflection control / 340
4.3.5 Etch resistance in DUV resists / 345

4.4 DUV Process Considerations / 346 4.4.1 Process ideology / 346
4.4.2 Positive-tone process considerations / 347
4.4.3 Negative-tone process considerations / 347
4.4.4 Reflection suppression process / 349

4.5 Facilities Considerations / 349

4.6 Materials Manufacturing and Quality Considerations / 350 4.6.1 Manufacturing considerations / 350
4.6.2 Quality control considerations / 350

4.7 Cost and Market Considerations / 351

4.8 193-nm Lithography / 352 4.8.1 Introduction / 352
4.8.2 193-nm acrylic single-layer resists / 357 4.8.2.1 Tool evaluation resist / 357
4.8.2.2 Etch resistant resists / 359
4.8.3 Recent advances in materials for 193-nm single-layer resists / 365 4.8.3.1 New polymers / 365
4.8.3.2 New high-performance resists / 366
4.8.4 Plasma etching of 193-nm resists / 366
4.8.5 Reflectivity control at 193 nm / 367
4.8.6 Top-surface imaging and multilayer resists for 193-nm lithography / 369

4.9 Conclusion / 371

4.10 References / 372


CHAPTER 5 Photomask Fabrication Procedures and Limitations

John G. Skinner, JGSA Inc.
Timothy R. Groves, IBM Semiconductor Research and Development Center
Anthony Novembre, Bell Laboratories, Lucent Technologies
Hans Pfeiffer, IBM Semiconductor Research and Development Center
Rajeev Singh, Intel Corporation, Technology and Manufacturing Group

5.1 Introduction / 380

5.2 Photomasks, Masks, and Reticles: Terminology / 381

5.3 Photomask Specifications / 381 5.3.1 Mask parameters / 381 5.3.1.1 Pattern position / 382
5.3.1.2 Critical dimension control / 382
5.3.1.3 Defects and pattern fidelity / 383
5.3.2 Specifications: 1994 SIA Roadmap / 383
5.3.3 Combined feature placement and CD specification / 385

5.4 Mask Types / 385 5.4.1 Binary masks / 385
5.4.2 Proximity effect correction masks / 386
5.4.3 Optical proximity correction masks / 387
5.4.4 Phase shift masks / 388
5.4.5 Halftone and embedded phase shift masks / 389

5.5 Photomask Substrates / 390 5.5.1 Substrate size / 390
5.5.2 Substrate material / 393
5.5.3 Substrate surface quality and flatness / 393
5.5.4 Opaque films / 394

5.6 Pattern Generation for Masks: Challenges and Projections / 395 5.6.1 Introduction / 395
5.6.2 Challenges / 400 5.6.2.1 Performance parameters / 400
5.6.2.2 Performance drivers / 401
5.6.2.3 Physical limitations / 403
5.6.2.4 Practical limitations / 406
5.6.3 Meeting the challenges / 411 5.6.3.1 Present state of the art / 411
5.6.3.2 System calibration / 416
5.6.3.3 Performance of the EL- 4 system / 417
5.6.3.4 Future challenges / 418
5.6.4 Conclusions / 420

5.7 Mask Fabrication: Resists and Processing / 420 5.7.1 Selection of exposure tool / 421
5.7.2 Imaging material considerations / 421
5.7.3 Commercially available electron beam resists / 425 5.7.3.1 Positive acting resists / 425
5.7.3.2 Negative acting resists / 432
5.7.4 Resist processing issues / 435 5.7.4.1 Process sequence and its influence on CD control / 435
5.7.4.2 Process control techniques / 437
5.7.5 Conclusions / 442

5.8 Metrology / 442 5.8.1 Pattern placement / 443
5.8.2 Feature measurement / 443

5.9 Mask Defects and Inspection / 447 5.9.1 Printability of defects / 447
5.9.2 Hard vs soft defects / 447
5.9.3 Types of hard defects / 448
5.9.4 PSM defects / 448
5.9.5 Minimum defect requirement / 448
5.9.6 Inspection of defects / 449

5.10 Mask Processing and Automation / 453

5.11 Photomask Cleaning / 455 5.11.1 Requirements / 455
5.11.2 Adhesion mechanisms / 457
5.11.3 Development of cleaning methods / 459
5.11.4 Common wet cleaning equipment for photomasks / 462
5.11.5 Common wet cleaning methods for photomasks / 462
5.11.6 Conclusions / 463

5.12 Mask Error Analysis / 464 5.12.1 Pattern placement errors across mask / 464
5.12.2 CD variation across a mask / 464

5.13 Summary / 466

5.14 References / 469


CHAPTER 6 Metrology Methods in Photolithography

Laurie J. Lauchlan, IBM SSD
Diana Nyyssonen, IBM Microelectronics
Neal Sullivan, DEC

6.1 Introduction / 477

6.2 Standards and Artifacts / 478 6.2.1 Calibration: a reality check / 483
6.2.2 When no standards exist / 485 6.2.2.1 Pitch / 486
6.2.2.2 Linewidth / 488
6.2.2.3 Overlay / 494
6.2.3 Standards summary / 496

6.3 Overlay Metrology / 496 6.3.1 Measurement system overview / 501 6.3.1.1 Wafer handling / 502
6.3.1.2 Optical components / 502 6.3.1.2.1 Lens effects / 503
6.3.1.2.2 Resolution and depth of field / 505
6.3.1.2.3 Illumination / 505
6.3.1.2.4 Focus methods / 507
6.3.1.3 Camera, image processing, and pattern recognition / 508
6.3.2 Data analysis: accuracy and precision / 509 6.3.2.1 Precision / 510
6.3.2.2 Accuracy: tool-induced shift / 512
6.3.3 Process and tool interactions: target asymmetry and measurement algorithms / 515 6.3.3.1 Process asymmetries / 518
6.3.3.2 Measurement algorithms / 519
6.3.3.3 Overlay target design / 522
6.3.4 Overlay discussion / 523 6.3.4.1 Measurement optimization / 523
6.3.4.2 Current issues in overlay registration measurement / 525
6.3.4.3 Process control / 526

6.4 Linewidth Metrology / 527 6.4.1 Optical linewidth metrology / 530 6.4.1.1 Diffraction and scattering effects on optical profiles / 530
6.4.1.2 System and material effects on optical waveforms / 536
6.4.2 Electrical linewidth metrology / 543
6.4.3 SEM linewidth metrology / 547 6.4.3.1 SEM resolution/sharpness / 549
6.4.3.2 CD SEM system overview / 553 6.4.3.2.1 Electron sources / 553
6.4.3.2.2 Electron lens and detector designs / 557
6.4.3.2.3 Improved electron gun designs / 559
6.4.3.2.4 Magnification/field of view / 562
6.4.3.2.5 Electron image formation / 564
6.4.3.3 Specimen effects / 566
6.4.3.4 Automation / 568
6.4.4 Advanced probe linewidth metrology / 571
6.4.5 Linewidth discussion / 581

6.5 A 250-nm metrology strategy / 582

6.6 Acknowledgments / 584

6.7 References / 585


CHAPTER 7 Optical Lithography Modeling

Andrew R. Neureuther, University of California at Berkeley
Chris A. Mack, Finle Technologies, Inc.

7.1 Introduction / 599 7.1.1 Overview / 599
7.1.2 Overview of the modeling and simulation process / 599

7.2 Models for Imaging / 601 7.2.1 Exposure systems and key parameters / 601
7.2.2 Images in projection printing / 605
7.2.3 Wave- space view of projection printing / 612
7.2.4 Images at the small feature limit / 615

7.3 Models for Wafer/Resist Interactions / 619 7.3.1 Substrate interactions / 619
7.3.2 Exposure and the latent image / 623
7.3.3 Development / 627

7.4 Role of Simulation in Practical Characterization / 632 7.4.1 Focus effects / 632
7.4.2 Aerial image optimization / 637
7.4.3 Lumped parameter model / 642
7.4.4 Modified illumination / 644
7.4.5 High-numerical-aperture effects / 648 7.4.5.1 Zero-order scalar model / 648
7.4.5.2 First-order correction to the scalar model / 649
7.4.5.3 Second-order correction to the scalar model / 649
7.4.5.4 Full scalar model / 650
7.4.5.5 Other issues in scalar modeling / 651
7.4.5.6 Vector model / 652

7.5 Modeling Technology Innovations / 653 7.5.1 Resist post-exposure bake and chemical amplification / 654
7.5.2 Defect printability / 658
7.5.3 Exposure tool tuning and imperfections / 662
7.5.4 Mask transmission and edge effects / 663
7.5.5 Substrate topography / 663
7.5.6 3D process modeling / 664

7.6 Information on Models and Simulators / 664

7.7 Future Perspective / 667

7.8 References / 668


CHAPTER 8 Issues in Nanolithography for Quantum Effect Device Manufacture

Martin C. Peckerar, F. Keith Perkins, Elizabeth A. Dobisz, Orest J. Glembocki
Naval Research Laboratory

8.1 Introduction / 683

8.2 Impossible Feats: Fundamental Limits in Process Technology / 685 8.2.1 Optical lithography / 686
8.2.2 Charged particle approaches to lithography / 691 8.2.2.1 E-beams for direct-write and mask-making applications: throughput considerations / 692
8.2.2.2 Multibeam direct-write systems and stochastic effects / 694
8.2.2.3 Beam heating, charging, and other miscellaneous effects / 696
8.2.2.4 Alignment / 696
8.2.2.5 Ultimate resolution / 697
8.2.2.6 Particle projection tools / 702
8.2.3 X-ray lithography / 704
8.2.4 Proximal probe electron lithography / 710
8.2.5 Extreme ultraviolet lithography / 717
8.2.6 Resists for quantum device manufacture / 720
8.2.7 The limits of metrology / 728
8.2.8 Summary / 729

8.3 Unlikely Events: Quantitative Techniques for Yield Assessment / 730 8.3.1 Quantifying process latitude / 730
8.3.2 Particle-limited defect yield statistics / 731
8.3.3 Summary / 737

8.4 Self-Defeating Purposes: Process-Induced Damage in Device Manufacture / 738 8.4.1 Ionizing radiation effects / 738
8.4.2 Dry-etch damage in compound semiconductors / 740
8.4.3 Summary / 743

8.5 Novel Approaches to Advanced Manufacture: Self-Assembling Systems / 744

8.6 Conclusions / 745

8.7 Acknowledgments / 746

8.8 Appendix: Derivation of Key Equations / 746 8.8.1 Resolution of a projection optical system / 746
8.8.2 The depth-of-focus relationship / 748
8.8.3 Minimum resolved period in proximity printing / 749
8.8.4 Derivation of key statistical formulas / 751 8.8.4.1 Basic yield formula / 751
8.8.4.2 The standard deviation of a Poisson distribution / 752

8.9 References / 754


How to order the complete book from SPIE

Cornell NanoScale Facility

Stanford Nanofabrication Facility

Please send us your comments, corrections, and submissions.



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