Nano-Cmos Circuit and Physical Design Nano-Cmos Circuit and Physical Design
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NANO-CMOS CIRCUIT AND PHYSICAL DESIGN NANO-CMOS CIRCUIT AND PHYSICAL DESIGN Ban P. Wong NVIDIA Anurag Mittal Virage Logic, Inc. Yu Cao University of California–Berkeley Greg Starr Xilinx A JOHN WILEY & SONS, INC., PUBLICATION Copyright 2005 by John Wiley & Sons, Inc. All rights reserved. Published by John Wiley & Sons, Inc., Hoboken, New Jersey. Published simultaneously in Canada. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning, or otherwise, except as permitted under Section 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, 978-750-8400, fax 978-646-8600, or on the web at www.copyright.com. 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For general information on our other products and services please contact our Customer Care Department within the U.S. at 877-762-2974, outside the U.S. at 317-572-3993 or fax 317-572-4002. Wiley also publishes its books in a variety of electronic formats. Some content that appears in print, however, may not be available in electronic format. Library of Congress Cataloging-in-Publication Data: Nano-CMOS circuit and physical design / Ban P. Wong ... [et al.]. p. cm. Includes bibliographical references and index. ISBN 0-471-46610-7 (cloth) 1. Metal oxide semiconductors, Complementary–Design and construction. 2. Integrated circuits–Design and construction. I. Wong, Ban P., 1953– TK7871.99.M44N36 2004 621.39732–dc22 2004002212 Printed in the United States of America. 10987654321 CONTENTS FOREWORD xiii PREFACE xv 1 NANO-CMOS SCALING PROBLEMS AND IMPLICATIONS 1 1.1 Design Methodology in the Nano-CMOS Era 1 1.2 Innovations Needed to Continue Performance Scaling 3 1.3 Overview of Sub-100-nm Scaling Challenges and Subwavelength Optical Lithography 6 1.3.1 Back-End-of-Line Challenges (Metallization) 6 1.3.2 Front-End-of-Line Challenges (Transistors) 12 1.4 Process Control and Reliability 15 1.5 Lithographic Issues and Mask Data Explosion 16 1.6 New Breed of Circuit and Physical Design Engineers 17 1.7 Modeling Challenges 17 1.8 Need for Design Methodology Changes 19 1.9 Summary 21 References 21 v vi CONTENTS PART I PROCESS TECHNOLOGY AND SUBWAVELENGTH OPTICAL LITHOGRAPHY: PHYSICS, THEORY OF OPERATION, ISSUES, AND SOLUTIONS 2 CMOS DEVICE AND PROCESS TECHNOLOGY 24 2.1 Equipment Requirements for Front-End Processing 24 2.1.1 Technical Background 24 2.1.2 Gate Dielectric Scaling 26 2.1.3 Strain Engineering 33 2.1.4 Rapid Thermal Processing Technology 34 2.2 Front-End-Device Problems in CMOS Scaling 41 2.2.1 CMOS Scaling Challenges 41 2.2.2 Quantum Effects Model 43 2.2.3 Polysilicon Gate Depletion Effects 45 2.2.4 Metal Gate Electrodes 48 2.2.5 Direct-Tunneling Gate Leakage 49 2.2.6 Parasitic Capacitance 52 2.2.7 Reliability Concerns 56 2.3 Back-End-of-Line Technology 58 2.3.1 Interconnect Scaling 59 2.3.2 Copper Wire Technology 61 2.3.3 Low-κ Dielectric Challenges 64 2.3.4 Future Global Interconnect Technology 65 References 66 3 THEORY AND PRACTICALITIES OF SUBWAVELENGTH OPTICAL LITHOGRAPHY 73 3.1 Introduction and Simple Imaging Theory 73 3.2 Challenges for the 100-nm Node 76 3.2.1 κ-Factor for the 100-nm Node 77 3.2.2 Significant Process Variations 78 3.2.3 Impact of Low-κ Imaging on Process Sensitivities 82 3.2.4 Low-κ Imaging and Impact on Depth of Focus 83 3.2.5 Low-κ Imaging and Exposure Tolerance 84 3.2.6 Low-κ Imaging and Impact on Mask Error Enhancement Factor 84 3.2.7 Low-κ Imaging and Sensitivity to Aberrations 86 CONTENTS vii 3.2.8 Low-κ Imaging and CD Variation as a Function of Pitch 86 3.2.9 Low-κ Imaging and Corner Rounding Radius 89 3.3 Resolution Enhancement Techniques: Physics 91 3.3.1 Specialized Illumination Patterns 92 3.3.2 Optical Proximity Corrections 94 3.3.3 Subresolution Assist Features 101 3.3.4 Alternating Phase-Shift Masks 103 3.4 Physical Design Style Impact on RET and OPC Complexity 107 3.4.1 Specialized Illumination Conditions 108 3.4.2 Two-Dimensional Layouts 111 3.4.3 Alternating Phase-Shift Masks 114 3.4.4 Mask Costs 118 3.5 The Road Ahead: Future Lithographic Technologies 121 3.5.1 The Evolutionary Path: 157-nm Lithography 121 3.5.2 Still Evolutionary: Immersion Lithography 122 3.5.3 Quantum Leap: EUV Lithography 124 3.5.4 Particle Beam Lithography 126 3.5.5 Direct-Write Electron Beam Tools 126 References 130 PART II PROCESS SCALING IMPACT ON DESIGN 4 MIXED-SIGNAL CIRCUIT DESIGN 134 4.1 Introduction 134 4.2 Design Considerations 134 4.3 Device Modeling 135 4.4 Passive Components 142 4.5 Design Methodology 146 4.5.1 Benchmark Circuits 146 4.5.2 Design Using Thin Oxide Devices 146 4.5.3 Design Using Thick Oxide Devices 148 4.6 Low-Voltage Techniques 150 4.6.1 Current Mirrors 150 4.6.2 Input Stages 152 4.6.3 Output Stages 153 4.6.4 Bandgap References 154 4.7 Design Procedures 155 4.8 Electrostatic Discharge Protection 157 viii CONTENTS 4.8.1 Multiple-Supply Concerns 157 4.9 Noise Isolation 159 4.9.1 Guard Ring Structures 159 4.9.2 Isolated NMOS Devices 161 4.9.3 Epitaxial Material versus Bulk Silicon 161 4.10 Decoupling 162 4.11 Power Busing 166 4.12 Integration Problems 167 4.12.1 Corner Regions 167 4.12.2 Neighboring Circuitry 167 4.13 Summary 168 References 168 5 ELECTROSTATIC DISCHARGE PROTECTION DESIGN 172 5.1 Introduction 172 5.2 ESD Standards and Models 173 5.3 ESD Protection Design 173 5.3.1 ESD Protection Scheme 173 5.3.2 Turn-on Uniformity of ESD Protection Devices 175 5.3.3 ESD Implantation and Silicide Blocking 177 5.3.4 ESD Protection Guidelines 178 5.4 Low-C ESD Protection Design for High-Speed I/O 178 5.4.1 ESD Protection for High-Speed I/O or Analog Pins 178 5.4.2 Low-C ESD Protection Design 180 5.4.3 Input Capacitance Calculations 183 5.4.4 ESD Robustness 185 5.4.5 Turn-on Verification 186 5.5 ESD Protection Design for Mixed-Voltage I/O 190 5.5.1 Mixed-Voltage I/O Interfaces 190 5.5.2 ESD Concerns for Mixed-Voltage I/O Interfaces 191 5.5.3 ESD Protection Device for a Mixed-Voltage I/O Interface 192 5.5.4 ESD Protection Circuit Design for a Mixed-Voltage I/O Interface 195 5.5.5 ESD Robustness 198 5.5.6 Turn-on Verification 199 5.6 SCR Devices for ESD Protection 200 5.6.1 Turn-on Mechanism of SCR Devices 201 CONTENTS ix 5.6.2 SCR-Based Devices for CMOS On-Chip ESD Protection 202 5.6.3 SCR Latch-up Engineering 210 5.7 Summary 212 References 213 6 INPUT/OUTPUT DESIGN 220 6.1 Introduction 220 6.2 I/O Standards 221 6.3 Signal Transfer 222 6.3.1 Single-Ended Buffers 223 6.3.2 Differential Buffers 223 6.4 ESD Protection 227 6.5 I/O Switching Noise 228 6.6 Termination 232 6.7 Impedance Matching 234 6.8 Preemphasis 235 6.9 Equalization 237 6.10 Conclusion 238 References 239 7 DRAM 241 7.1 Introduction 241 7.2 DRAM Basics 241 7.3 Scaling the Capacitor 245 7.4 Scaling the Array Transistor 247 7.5 Scaling the Sense Amplifier 249 7.6 Summary 253 References 253 8 SIGNAL INTEGRITY PROBLEMS IN ON-CHIP INTERCONNECTS 255 8.1 Introduction 255 8.1.1 Interconnect Figures of Merit 258 8.2 Interconnect Parasitics Extraction 259 8.2.1 Circuit Representation of Interconnects 260 8.2.2 RC Extraction 263 8.2.3 Inductance Extraction 267 x CONTENTS 8.3 Signal Integrity Analysis 271 8.3.1 Interconnect Driver Models 272 8.3.2 RC Interconnect Analysis 274 8.3.3 RLC Interconnect Analysis 277 8.3.4 Noise-Aware Timing Analysis 281 8.4 Design Solutions for Signal Integrity 283 8.4.1 Physical Design Techniques 284 8.4.2 Circuit Techniques 288 8.5 Summary 293 References 294 9 ULTRALOW POWER CIRCUIT DESIGN 298 9.1 Introduction 298 9.2 Design-Time Low-Power Techniques 300 9.2.1 System- and Architecture-Level Design-Time Techniques 300 9.2.2 Circuit-Level Design-Time Techniques 300 9.2.3 Memory Techniques at Design Time 305 9.3 Run-Time Low-Power Techniques 311 9.3.1 System- and Architecture-Level Run-Time Techniques 311 9.3.2 Circuit-Level Run-Time Techniques 313 9.3.3 Memory Techniques at Run Time 316 9.4 Technology Innovations for Low-Power Design 320 9.4.1 Novel Device Technologies 320 9.4.2 Assembly Technology Innovations 321 9.5 Perspectives for Future Ultralow-Power Design 321 9.5.1 Subthreshold Circuit Operation 322 9.5.2 Fault-Tolerant Design 322 9.5.3 Asynchronous versus Synchronous Design 323 9.5.4 Gate-Induced Leakage Suppression Schemes 323 References 324 PART III IMPACT OF PHYSICAL DESIGN ON MANUFACTURING/YIELD AND PERFORMANCE 10 DESIGN FOR MANUFACTURABILITY 331 10.1 Introduction 331 10.2 Comparison of Optimal and Suboptimal Layouts 332 CONTENTS xi 10.3