Ultraclean Surface Processing of Silicon Wafers Springer-Verlag Berlin Heidelberg Gmbh Takeshi Hattori (Ed.)

Ultraclean Surface Processing of Silicon Wafers Springer-Verlag Berlin Heidelberg GmbH Takeshi Hattori (Ed.)

Ultraclean Surface Processing of Silicon Wafers

Secrets of VLSI Manufacturing

With 464 Figures

, Springer Dr. Takeshi Hattori ULSI R&D Laboratories Sony Corporation Semiconductor Company Atsugi 243-8585, Japan E-mail: [email protected]

Translators: Dr. Takeshi Hattori Stefan Heusler ULSI R&D Laboratories Blumenthalstr. 83 Sony Corporation Semiconductor Co. D-50668 KOln, Germany

Jason P. Webb 12107 Lake Carrol Drive Tampa, FL 33618-3729, USA

Library of Congress Cataloging-in-Publication Data. Ultraclean surface processing of silicon wafers: secrets of VLSI manufacturing 1 Takeshi Hattori (ed.). p. cm. ISBN 3-540-61672-1 (alk. paper) 1. Semiconductor wafers-Cleaning. 2. Silicon-Surfaces. 3. Surface preparation. l. Hattori, Takeshi, 1945-. TK7871.85.U48 1998 621.3815'2-DC21 98-10353

ISBN 978-3-642-08272-6 ISBN 978-3-662-03535-1 (eBook) DOI 10.1007/978-3-662-03535-1

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SPIN 10543602 57/3144 - 5 4 3210 - Printed on acid-free paper Preface

Advances in large-scale integration (LSI) and the reduction in device geome• tries have been accompanied by more-complicated silicon-wafer processes and an increased number of process steps. Furthermore, micro-contamination, such as particles, metallic impurities, and organic contaminants has come to exert an ever-increasing impact on device yield, quality, and reliability. Con• trolling such micro-contamination is the crucial element of the present and future success in very large scale integration (VLSI) manufacturing. It is not too much to say that the process equipment and processes themselves are the source of the contamination. For this reason, making the total VLSI process cleaner - that is, preventing contamination from the surface of silicon wafers and maintaining clean surface in the full range of processes - has become even more essential. Traditional approaches to contamination control, such as cleanroom-air filtration or, as an extension, the purification of cleanroom-utility materials - that is, methods stemming from the notion of "cleanroom environment cleanliness" have been all important. However, "silicon surface cleanliness", an approach concerned with how to keep the wafer surface clean or make it cleaner, is more essential and more effective. In other words, the fundamental stance of this book will be "concepts drawn from the wafer surface" . This book focuses on ultraclean processing of silicon-wafer surfaces. It is intended for engineers and technicians involved in research, development, and manufacturing of VLSI chips, those concerned with equipment, materi• als, facilities, and utilities in the semiconductor and related industries, and scientists in academia. Unlike many other books on contamination control, we deal with VLSI wafer processing and related issues by starting from the wafer surface. The result is a practical reference to be used widely from research and devel• opment labs to the volume production fabs. This book is a reorganized, updated, English version of the Japanese book "Silicon Wafer Hyoumen no Clean-ka Gijutsu" published in 1995 by Realize Inc., Tokyo, Japan. The orig• inal book has been very well received by the Japanese semiconductor de• vice/equipment/materials industries and by the academic community. I hope that this new edition will be of use for not only the Japanese industry but also the world-wide semiconductor and related industries. VI Preface

Part I introduces "ultraclean technology" for VLSI manufacturing from the starting point of the wafer surface. Part II describes the influence of contamination on VLSI devices and also refers to the influence of micro• roughness. Part III comments on mechanisms of particle adhesion to the surface of silicon wafers in air, plasma, vacuum, and liquid and also touches on the influence of static charges. Because monitoring the contamination levels on the wafer surfaces is fundamental to contamination control, Parts IV and V are concerned with analysis and evaluation of the wafer surfaces with remarks extending from the basics to application to the VLSI processing lines. Part VI describes, from the view point of ultraclean processing of silicon surfaces, issues of each VLSI process and their countermeasures and also touches on clustering for process integration. Parts VII and VIII deal with wafer cleaning and related technologies, the most important process from the standpoint of removing contamination, and thoroughly explains the technologies from all angles. Also, throughout the book, we do not try to avoid redundancy of description in different chapters if the items repeated are deemed essential and important. This book is composed of these eight closely related parts. In order to in• clude in detail as much as possible of the latest knowledge and data on clean processing of the surface of silicon wafers, some 50 engineers/professors, re• garded as top in their fields in Japan, have contributed to this book. Until re• cently in Japan, the fields discussed here have been treated as the confidential technical knowledge of each company. Therefore, there are many occasions when technical opinions in this field have not yet reached consensus. All the Japanese references listed in the original edition have been deleted; but some new English references have been added to this English edition instead. In this book, no attempt has been made to force unity in the various opinions presented by the authors. In this still developing field of ultraclean processing of silicon surfaces, there are many problems that remain unsolved, and we eagerly anticipate research progress. We look forward to the arrival of the day in the near future when "ultraclean technology" will be established as a scientific and systematic, and therefore universal, "processing science" . I would like to thank Professor Eicke Weber for reading the manuscript and making valuable suggestions.

Atsugi, Japan Takeshi Hattori July 1998 Table of Contents

Part I. Introduction

1. Ultraclean Technology for VLSI Manufacturing: An Overview Takeshi Hattori, Sony...... 3 1.1 Introduction...... 3 1.2 Importance of Particle Reduction ...... 4 1.3 Sources of Particle Generation and Their Control ...... 7 1.3.1 Environment (Cleanroom) ...... 7 1.3.2 Personnel...... 9 1.3.3 Process Materials...... 10 1.3.4 Manufacturing Equipment/Process...... 11 1.4 Controlling Metallic Contaminants...... 14 1.5 Controlling Airborne Impurities...... 14 1.6 The Future of Ultraclean Technology ...... 16 References ...... 17

Part II. Influence of Contamination on Silicon Device Characteristics

2. Influence of Silicon Crystal Quality on Device Characteristics Yoshinobu Monma, Fujitsu...... 21 2.1 Introduction...... 21 2.2 Influence of Crystalline Defects and Device Characteristics. .. 21 2.2.1 Stacking Faults...... 21 2.2.2 Oxide Precipitation...... 23 2.2.3 Bipolar Transistor Failures...... 23 2.2.4 Refresh Failure of the DRAM...... 24 2.3 Influence of Crystal Quality on Oxide Film Perfection ...... 25 2.4 Influence of Silicon Crystal Quality on Device Processes...... 26 2.5 Issues for the Future...... 27 References ...... 27 VIII Table of Contents

3. Influence of Contaminants on Device Characteristics Jun Sugium, Hitachi ...... 29 3.1 Introduction...... 29 3.2 Trends in LSI Technology...... 29 3.3 How Contaminants Degrade Device Performance...... 30 3:3.1 Device Characteristic Degradation Due to Particulate Contaminants ...... 33 3.3.2 Device Characteristic Degradation Due to Metallic Contaminants...... 36 3.3.3 Device Characteristic Degradation Due to Organic Contaminants...... 39 3.4 Issues for the Future...... 40 References ...... 41

4. Influence of Metallic Contamination on Dielectric Degradation of MOS Structures Makoto Takiyama, Nippon Steel ...... 42 4.1 Dielectric Degradation Mechanisms of the Oxide Film Caused by Metallic Contamination...... 42 4.1.1 Formation of Metal Oxides and Metal Silicates...... 43 4.1.2 Dissolution of Metallic Contaminants in the Oxide Film ...... 43 4.1.3 Local Thinning of the Oxide Film Due to Metal Silicide Formation ...... 44 4.1.4 Accelerated Decomposition and Evaporation of Oxide Film ...... 46 4.1.5 Enhancement of Surface Micro-Roughness...... 47 4.2 Correlation Between Metallic Contamination Levels and Yield of Oxide Breakdown Strength ...... 49 4.2.1 Metallic Contamination Levels and In-Depth Profile, and Their Influence on Oxide Film Breakdown Strength (Time Zero Dielectric Breakdown) ...... 49 4.2.2 Influence on Time-Dependent Dielectric Breakdown Characteristics ...... 52 4.2.3 Influence of Other Metallic Contaminants on Dielectric Degradation...... 52 4.3 Influences on Other Electrical Characteristics and on Thermal Oxidation ...... 52 4.3.1 Influence on Thermal Oxidation...... 53 4.3.2 Influence on the Shift of Flat-Band Voltage (VFB ) . . . .. 53 4.3.3 Influence on Generation Lifetime of Minority Carriers (Tg) ...... 54 4.3.4 Influence on Interface State Density (Did...... 54 4.4 Issues for the Future...... 55 References ...... 55 Table of Contents IX

5. Influence of Micro-Roughness on Device Characteristics Takashi Futatsuki, Organo ...... 57 5.1 Influence of Micro-Roughness on Device Characteristics...... 57 5.2 Methods of Measuring Micro-Roughness...... 60 5.3 Increases in Micro-Roughness Due to Wafer Cleaning...... 61 5.4 Toward Micro-Roughness Reduction...... 63 References ...... 64

Part III. Mechanisms of Particle Adhesion on Wafer Surfaces

6 .. Particle Deposition in Air Motoaki Adachil and Kikuo Okuyama2 1Osaka Prefecture University /2 Hiroshima University...... 67 6.1 Dynamics of Particles in the Gas Phase ...... 67 6.1.1 Brownian Motion...... 69 6.1.2 Inertial Motion...... 69 6.1.3 Motion in an External Force Field...... 70 6.2 Basic Formula for Particle Deposition...... 72 6.3 Adhesion Forces Between a Wafer and a Particle...... 73 6.3.1 Electrostatic Force...... 74 6.3.2 Van der Waals Force...... 74 6.3.3 Born Repulsion...... 75 6.4 Particle Deposition under Various Flow Fields...... 75 6.4.1 Deposition in Stationary and Convective Fields...... 75 6.4.2 Deposition in Laminar Flow...... 76 6.4.3 Deposition in Turbulent Flow ...... 77 References ...... 81

7. Particle Deposition in Plasma Motoaki Adachil and Kikuo Okuyama2 1Osaka Prefecture University /2 Hiroshima University...... 82 7.1 Dynamics of Particles...... 82 7.1.1 Effect of Pressure ...... 82 7.1.2 Effect of Temperature Gradient ...... 85 7.1.3 Effect of Electric Field ...... 86 7.2 Particle Deposition...... 87 7.2.1 RF Plasma ...... 87 7.2.2 ECR Plasma...... 90 References ...... 91 X Table of Contents

8. Particle Deposition in Vacuum Tetsuro Kodama, ULVAC ...... 92 8.1 Particle Adhesion Forces...... 92 8.2 The Behavior of Particles in Vacuum...... 93 8.2.1 Particle Descent...... 93 8.2.2 Particle Swirl ...... 94 8.2.3 Cleaning of Vacuum Chambers...... 95 8.3 Influence of Static Electricity...... 98 8.4 Particle Generation...... 99 8.4.1 Particles Generated by Ball Bearings ...... 100 8.4.2 Particles Generated by Process Equipment ...... 102 8.5 Issues for the Future ...... 103 References ...... 104

9. Particle Adhesion in Liquids Akio Saito and Katsuhiro Ota, Hitachi ...... 105 9.1 Models and Theories of Particle Adhesion ...... 105 9.2 Test Results Using Standard Polystyrene Particles ...... 107 9.2.1 Adhesion in Laminar Flows ...... 107 9.2.2 Adhesion in Baths ...... 108 9.3 Relationship Between Various Parameters and Adhesion ..... 109 9.3.1 Ionic Strength of Solution ...... 109 9.3.2 Zeta Potential ...... 110 9.3.3 Particle Diameter ...... 111 9.4 Considerations of Non-stationary State Deposition ...... 112 9.5 Issues for the Future ...... 113 References ...... 114

10. Particle Adhesion and Removal on Wafer Surfaces in RCA Cleaning Mitsushi Itano and Takehiko Kezuka, Daikin Industries ...... 115 10.1 Interactions Between Particles and Wafers in Liquids ...... 115 10.2 Relationship Between pH in Solution and Particle Adhesion on the Wafer ...... 119 10.3 Controlling Particle Adhesion with Surfactants ...... 123 10.3.1 Controlling Particle Adhesion on the Si Surface ...... 123 10.3.2 Controlling Particle Adhesion on an Si3N4 Surface .... 126 10.3.3 Preventing Re-adhesion of Particles from the Back Surface of a Wafer ...... 129 10.3.4 Controlling Particle Adhesion with Surfactants ...... 129 10.4 Removing Particles Deposited on a Wafer by Alkaline Solutions ...... 130 10.4.1 Etching Rate and Particle Removal Efficiency ...... 130 Table of Contents XI

10.4.2 Comparison with Acidic Solutions ...... 133 10.4.3 Oxidation of Organic Particles Using an Alkaline/Hydrogen Peroxide Solution ...... 134 References ...... 136

11. Effects of Electrostatic Charge on Particle Adhesion on Wafer Surfaces Hitoshi Inaba, Takasago Thermal Engineering 137 11.1 Introduction ...... 137 11.2 Particle Adhesion Caused by Static Electricity ...... 137 11.2.1 Results of Measuring Particle Adhesion Speed On a Charged Wafer Surface ...... 137 11.2.2 Calculated Comparison of Floating Range for Particles to Adhere to a Charged Wafer Surface ...... 138 11.3 Actual Wafer Charging Situations in Production Processes ... 140 11.4 Electrostatic Charging Prevention Techniques ...... 142 11.4.1 Neutralization with Soft X-Ray Radiation ...... 143 11.4.2 Neutralization with UV Irradiation in Vacuum ...... 146 11.5 Issues for the Future ...... 149 References ...... 150

Part IV. Analysis and Evaluation of Silicon Wafer Surfaces: Fundamentals

12. Measurement of Particles on Wafer Surfaces Motosuke Miyoshi, Toshiba ...... 153 12.1 Introduction ...... 153 12.2 Principles and Theory of Light Scattering ...... 153 12.3 Light Scattering by Particles On the Wafer ...... 157 12.4 Configuration of the Particle Detection System ...... 159 12.4.1 Configuration of the Particle Detection System and the Beam Scanning Method ...... 159 12.4.2 Data Processing for Particle Mapping ...... 159 12.4.3 The Sensitivity of Particle Detection and Its Calibration ...... 162 12.5 The Detection of Particles On Patterned Wafers ...... 164 12.6 Issues for the Future ...... 167 References ...... 167 XII Table of Contents

13. Analysis and Evaluation of Impurities on Wafer Surfaces Ayako Shimazaki, Toshiba ...... 168 13.1 Analysis Technology for Impurities on Wafer Surfaces ...... 168 13.2 Chemical Analysis ...... 169 13.2.1 Metallic Impurities ...... 170 13.2.2 Other Impurities ...... 173 13.3 Physical Analysis ...... 174 13.3.1 Total Reflection X-Ray Fluorescence Analysis ...... 174 13.4 Issues for the Future...... 177 References ...... 177

14. Analysis and Evaluation of Molecules Adhered to Wafer Surfaces Norikuni Yabumoto, NTT ...... 179 14.1 Methods of Wafer Surface Analysis ...... 179 14.2 Thermal Desorption Spectroscopy ...... 180 14.3 Analysis of Adsorbed Molecules ...... 183 14.3.1 Hydrogen ...... 184 14.3.2 Water ...... 187 14.3.3 Hydrocarbons ...... 188 14.3.4 Ammonia ...... 191 14.4 Issues for the Future ...... 192 References ...... 193

15. Electrical Evaluation of Metallic Impurities on Wafer Surfaces Morimasa Miyazaki, Sumitomo Sitix ...... 194 15.1 Introduction ...... 194 15.2 Wafer Evaluation ...... 194 15.2.1 I-£-PCD Method ...... 194 15.2.2 Spy Method ...... 202 15.3 Evaluation with a pn Junction ...... 208 15.3.1 Reverse Bias Leakage Current ...... 208 15.3.2 Step Recovery Method ...... 212 15.4 Evaluation with a MOS Structure ...... 214 15.4.1 MOS C-t Method ...... 214 15.4.2 Gate Oxide Reliability Evaluation ...... 218 15.5 Issues for the Future ...... 221 References ...... 221 Table of Contents XIII

16. Analysis of Microscopic Areas on Wafer Surfaces Using STM/AFM Sumio Hosaka, Hitachi ...... 223 16.1 Introduction ...... 223 16.2 STM and AFM ...... 223 16.2.1 STM ...... 224 16.2.2 AFM ...... 224 16.3 Atomic Observation Using STM and AFM ...... 225 16.3.1 In situ Dynamic Observation with STM ...... 225 16.3.2 In situ Observation During Crystal Growth ...... 227 16.3.3 In situ Observation During Annealing ...... 227 16.3.4 In situ Observation During the Initial Oxidation Process ...... 228 16.3.5 Inspecting Hydrogen-Terminated Si Surfaces ...... 228 16.3.6 Observation with Atomic Resolution Using AFM ..... 228 16.4 Semiconductor Surface Measurements at the nm Level ...... 228 16.4.1 Evaluation of Insulator Surface Morphology ...... 229 16.4.2 Dependence of Native Oxide Breakdown Voltage on Si Facet Surface ...... 229 16.4.3 Evaluation of Poly-Si Gates-Si02 Interface ...... 232 16.4.4 Distribution of Impurities on Poly-Si Surfaces (STM-TBI Measurement) ...... 233 16.4.5 Observation of Silicon pn Junctions (STM-CITS Measurement) ...... 234 16.4.6 Other Measurement Techniques ...... 236 16.5 Advice on STM and AFM Operation ...... 236 16.6 Issues for the Future ...... 238 References ...... 238

Part V. Analysis and Evaluation of Wafer Surfaces: Applications to Semiconductor Manufacturing Lines

11. Detection and Analysis of Particles in Production Lines Takeshi Hattori, Sony ...... 243 17.1 Introduction ...... 243 17.2 Detecting Particles on Wafers ...... 244 17.2.1 Measuring Particles on Polished Wafers ...... 244 17.2.2 Measuring Particles on Patterned Wafers ...... 247 17.2.3 Measuring Particles in the LSI Manufacturing Lines ... 248 17.3 Analyzing Particles on Wafers ...... 250 17.3.1 Methods for Analyzing Particles on Wafers ...... 251 17.3.2 Background to the Development of Systems for Analyzing Particles Adhered to Wafer Surfaces .... 252 XIV Table of Contents

17.3.3 Structure of Systems for Analyzing Particles Adhered to Wafer Surfaces ...... 253 17.3.4 Analyzing and Identifying Particles in VLSI Manufacturing...... 254 17.3.5 Examples of Particle Analysis During Wafer Processing ...... 254 17.4 Issues for the Future ...... 257 References ...... 258

18. Pattern Defect Monitoring in Production Lines Yoshiki Suzuki, KLA Tencor Japan...... 259 18.1 Introduction ...... 259 18.2 In-Line Monitoring ...... 259 18.3 Importance of Process Monitoring in Product Wafer Inspection ...... 260 18.4 Wafer Inspection Systems Used for In-Line Defect Monitors and Their Advantages ..... 260 18.5 Goals and Benefits of In-Line Defect Monitoring ...... 263 18.6 Quick Detection of Excursions ...... 264 18.7 Pulse Monitoring ...... 265 18.8 Correlation Between Yield and Defectivity ...... 266 18.9 Examples of Successful In-Line Monitoring of Excursions ..... 266 18.10 Requirements for Successful In-Line Monitoring of More Advanced Devices ...... 269 References ...... ' ...... 270

19. Clean Level Monitoring in Production Lines K enji Yoneda, Matsushita Electronics ...... 271 19.1 Introduction ...... 271 19.2 Clean Level Evaluation Using MOS Capacitors ...... 272 19.2.1 Detection of Particles and Heavy Metals ...... 273 19.2.2 Detection of Fixed Charge and Mobile Ions ...... 276 19.2.3 Charge Build-up Evaluation Using MOS Capacitors ... 277 19.3 In-Line Process Cleanliness Evaluation Technique ...... 279 19.3.1 Heavy Metal Evaluation Using Minority Carrier Lifetime (MCLT) ...... 280 19.3.2 Contamination Evaluation Using TRXRF ...... 281 19.3.3 CV Evaluation Using Non-contact CV Measurement Equipment ...... 281 19.4 Summary ...... 284 References ...... 284 Table of Contents XV

20. Analysis of Defects in Devices and Silicon Crystals in Production Lines Tomohisa Kitano and Kazuko Ikeda, NEC ...... 286 20.1 Introduction ...... 286 20.2 Analyzing Process-Induced Defects ...... 286 20.2.1 Stress-Induced Crystal Defect Formation Due to Device Structures ...... 286 20.2.2 Thermal Stress-Induced Defects ...... 290 20.2.3 Ion Implantation-Induced Defects ...... 291 20.2.4 Oxidation-Induced Defects ...... 292 20.2.5 Contaminant-Induced Defects ...... 292 20.3 Analyzing Defects in the Si Substrate ...... 294 20.3.1 Gettering and Grown-In Defects ...... 294 20.3.2 Surface Flatness and Surface Defects ...... 296 20.4 Analyzing Defects in Specific Micro-Regions ...... 299 20.5 Issues for the Future ...... 300 References ...... 301

Part VI. Ultraclean Technology for Wafer Processes and Equipment

21. Oxidation and Diffusion Kikuo Yamabe, Toshiba ...... 305 21.1 Introduction ...... 305 21.2 Thermal Oxidation of Silicon ...... 305 21.3 Activation and Diffusion of Dopant Impurities ...... 306 21.4 Furnaces for High-Temperature Treatments ...... 309 21.4.1 Heaters ...... 311 21.4.2 Linear Tubes ...... 311 21.4.3 Reaction Tubes ...... 312 21.5 Behavior of Heavy Metal Impurities in Si ...... 312 21.6 Issues for the Future ...... 314 References ...... 316

22. CVD (Part 1): Atmospheric Pressure/Low-Pressure CVD Kazuo Maeda, Semiconductor Process Laboratory ...... 317 22.1 Particle Generation Due to CVD ...... 317 22.2 Overview of Atmospheric Pressure and Low-Pressure CVD ... 318 22.2.1 Atmospheric Pressure CVD ...... 318 22.2.2 Low-Pressure CVD ...... 319 22.3 Particle Generation ...... 321 XVI Table of Contents

22.3.1 Characteristics of Particles in Atmospheric Pressure and Low-Pressure CVD ...... 321 22.3.2 Sources of Particle Generation ...... 321 22.3.3 Hardware Sources ...... 321 22.3.4 Process Sources ...... 323 22.4 Particle Reduction Strategies ...... 325 22.4.1 Particle Reduction Strategies for Atmospheric Pressure and Low-Pressure CVD . . . . . 325 22.4.2 Hardware Revision ...... 326 22.4.3 Process Control ...... 327 22.5 Issues for the Future ...... 330 References ...... 330

23. CVD (Part 2): Plasma CVD Masashi Asami, Applied Materials Japan ...... 331 23.1 Introduction ...... 331 23.2 Principles and Features of Plasma CVD ...... 331 23.3 Sources of Particle Generation and Particle Behavior ...... 334 23.3.1 Sources of Particle Generation ...... 334 23.3.2 Particle Behavior ...... 335 23.4 Particle Reduction ...... 337 23.4.1 Eliminating Sources of Particle Generation ...... 337 23.4.2 Preventing Particle Adhesion ...... 339 23.4.3 Managing Particles ...... 339 23.5 Reducing Charge-up ...... 340 23.6 Issues for the Future ...... 340 References ...... 341

24. CVD (Part 3): Metal CVD Makoto Bekine, NEC ...... 342 24.1 Cleaning Methods for Metal CVD ...... 342 24.2 Reactions Used for Metal CVD ...... 342 24.2.1 W-CVD ...... 342 24.2.2 TiN/Ti CVD ...... 344 24.3 Particle Generation Due to Metal CVD ...... 344 24.3.1 Non-selective Growth During Selective W-CVD ...... 345 24.3.2 Particles Generated During Blanket W-CVD ...... 345 24.3.3 Particles Generated Due to TiN/Ti CVD ...... 347 24.4 Electrical Characteristics and Surface Reaction ...... 347 24.4.1 Dependence of the Surface Structure and the Surface Reaction ...... 348 24.4.2 Characteristics of the Device and Pre-treatment ...... 349 24.5 Issues for the Future ...... 350 Table of Contents XVII

24.5.1 Pre-treatment Techniques ...... 350 24.5.2 Cleaning Technique ...... 350 24.5.3 Clustering ...... 351 References ...... 351

25. Physical Vapor Deposition Tsuyoshi Takahashi, Anelva ...... 352 25.1 Introduction ...... 352 25.2 Clean Technology for the Sputtering Process ...... 352 25.2.1 Improved Step Coverage and Clean Sputtering ...... 352 25.2.2 Improvement of Film Quality by Clean Sputtering .... 354 25.2.3 Barrier Layer Formation by Clean Sputtering ...... 355 25.3 Strategies for Particles in Sputtering Equipment ...... 356 25.3.1 Techniques for Reducing Particles in the Sputtering Process ...... 356 25.3.2 Countermeasures Relating to Transport ...... 359 25.4 Issues for the Future ...... 359

26. Dry Etching (Part 1): Particulate Contamination Due to Dry Etching Katsumi Ukai, Anelva ...... 361 26.1 Contaminants in Dry Etching ...... 361 26.2 Factors in Particle Generation ...... 362 26.2.1 Mechanical Causes ...... 363 26.2.2 Chemical Causes ...... 365 26.3 Particle Control ...... 366 26.3.1 Effectiveness of In Situ Monitoring ...... 366 26.3.2 Control Through Particle Monitoring ...... 367 26.3.3 Control Through In-Process Gas Monitoring ...... 368 26.4 Issues for the Future ...... 369 References ...... 370

27. Dry Etching (Part 2): Influence of Chemical Contamination and Defects on Dry Etching Moritaka Nakamura, Fujitsu ...... 371 27.1 Introduction ...... 371 27.2 A Simple Model of Surface Reactions ...... 372 27.3 Carbon-Eliminated RIE ...... 373 27.4 In Situ Surface Analysis in a Carbon-Eliminated System ...... 375 27.5 A Model of Electronic Excitation for the Effects of Impurities or Contaminants ...... 376 27.6 In Situ Analysis in a Contaminated System ...... 378 XVIII Table of Contents

27.7 Model for Etching Si02 Where Defects and Radiation Damage Promote Etching ...... 379 27.8 Experiments on Vacuum UV Irradiation from Plasmas or X-Ray Irradiation ...... 380 27.9 Issues for the Future ...... 382 References ...... 383

28. Ion Implantation Yasutsugu Us ami, Hitachi ...... 384 28.1 Introduction ...... 384 28.2 Trends in Ion Implantation Technology ...... 384 28.3 Contamination During Ion Implantation ...... 387 28.3.1 Particle Adhesion on the Wafer ...... 388 28.3.2 Particle Adhesion on the Wafer Back Side ...... 390 28.3.3 Heavy Metal Contamination ...... 392 28.3.4 Energy Contamination ...... 394 28.3.5 Contamination Due to Residual Gas ...... 397 28.4 Issues for the Future...... 397 References ...... 397

29. Lithography Pumio Mizuno, Hitachi ...... 398 29.1 Clean Technology in Lithography ...... 398 29.2 Pattern Defects Due to Optical Aligners ...... 401 29.3 Pattern Defects Due to Resist Process ...... 403 29.4 Pattern Dimension Imprecision Due to the Resist Process .... 404 29.5 Wafer Contamination in Lithography ...... 407 29.5.1 Wafer Contamination Caused by Lithographic Equipment ...... 407 29.5.2 Wafer Contamination Caused by Resists ...... 408 29.6 Radiation Damage Caused by Electron Beam Direct-Writing . 412 References ...... 412

30. CMP Yoshihiro Hayashi, NEC ...... 414 30.1 Introduction ...... 414 30.2 Interlayer Dielectric Film CMP ...... 414 30.2.1 CMP Process Overview ...... 414 30.2.2 Slurry Composition and CMP Characteristics ...... 415 30.3 Metal CMP ...... 420 30.3.1 Metal CMP Using Slurries Without Polishing Materials ...... 421 30.3.2 Electrolytic Ionized Water Cleaning ...... 423 Table of Contents XIX

30.4 Issues for the Future ...... 424 References ...... 425

31. Cluster Tools Atsuyoshi Koike, Hitachi ...... 426 31.1 Introduction ...... 426 31.2 Necessity for Cluster Tools ...... 426 31.2.1 Gate Oxide Films ...... 427 31.2.2 Ultrathin Dielectric Films for Capacitors ...... 429 31.2.3 Low-Resistance Contacts ...... 430 31.2.4 High-Reliability Interconnects ...... 431 31.3 Disadvantages of Cluster Tools ...... 432 31.4 Issues for the Future ...... 433 References ...... 434

Part VII. Cleaning Silicon Wafer Surfaces

32. Trends in Wafer Cleaning Technology Takeshi Hattori, Sony ...... 437 32.1 Introduction ...... 437 32.2 Wet Cleaning ...... 437 32.2.1 RCA Cleaning ...... 439 32.2.2 Re-examining RCA Cleaning ...... 441 32.2.3 Preventing Contamination During Cleaning Processes. 442 32.3 Re-examining Wet Cleaning Equipment ...... 443 32.4 Wafer Drying ...... 445 32.5 Dry Cleaning ...... 445 32.6 Measuring and Evaluating Contaminants ...... 447 32.7 Issues for the Future...... 449 References ...... 450

33. Wet Cleaning (Part I): Removal of Particulate Contaminants Hiroyuki Kawahara, Matsushita Electronics ...... 451 33.1 Particle Removal by Wet Cleaning ...... 451 33.2 Particle Removal by SC-l Cleaning ...... 453 33.3 Particle Removal Mechanisms ...... 457 33.4 The Future of Particle Removing Through Wet Cleaning ..... 459 References ...... 460 XX Table of Contents

34. Wet Cleaning (Part 2): Removal of Metallic Contaminants Yuji Fukazawa, Toshiba ...... 462 34.1 Removal of Metallic Contaminants by Wet Cleaning ...... 462 34.2 Metallic Contaminant Removal Characteristics of Acidic Solutions ...... 462 34.3 Metallic Contamination by Wet Cleaning Itself ...... 464 34.3.1 SC-1 Solution ...... 464 34.3.2 HF Cleaning ...... 467 34.4 Future Metallic Contaminant Removal Technology ...... 471 34.4.1 Cleaning Solutions...... 471 34.4.2 DI Water Rinse ...... 472 34.4.3 Drying ...... 472 References ...... 473

35. Wet Cleaning (Part 3): Removal of Organic Contaminants Shinichi Yasui, Shinko Pantec ...... 474 35.1 The Effects of Organic Contaminants and Methods for Their Removal...... 474 35.2 Addition of Ozone to DI Water ...... 475 35.3 Removal of Organic Contamination ...... 475 35.3.1 Evaluation Methods ...... 475 35.3.2 Comparison of Contaminant Removal Efficiency of Cleaning Chemicals ...... 476 35.3.3 Mechanisms of Organic Contaminant Removal ...... 477 35.3.4 Problems with the Static Cleaning Method ...... 478 35.3.5 Dynamic Cleaning ...... 479 35.3.6 Organic Removal with Spin Cleaning ...... 480 35.4 Issues for the Future ...... 481 References ...... 481

36. Wet Cleaning (Part 4): Micro-Roughness and COPs Created by SC-I E. Morita, H. Okuda, F. Inoue, and K. Akiyama Mitsubishi Materials Silicon ...... 482 36.1 Introduction ...... 482 36.2 Etching Action of SC-1 ...... 482 36.3 Relationship Between SC-1 Cleaning and COP ...... 484 36.4 Relationship Between SC-1 Cleaning and Micro-Roughness ... 488 36.5 Relationship Between SC-1 Cleaning and Haze Appearance ... 490 36.6 Relationship Between Micro-Roughness and Haze ...... 491 References ...... 493 Table of Contents XXI

37. Wafer Drying After Wet Cleaning Katsuhiko Itoh and Yoshio Saito, Hitachi ...... 494 37.1 Introduction ...... 494 37.2 Spin-Drying ...... 495 37.3 IPA Vapor Drying ...... 496 37.4 Other Drying Techniques ...... 498 37.5 Evaluation of Dry Wafers ...... 499 37.6 Issues for the Future ...... 502 References ...... 502

38. Watermarks: Generation, Control, and Removal Haruo Itoh, Hitachi ...... 503 38.1 The Mechanism of Watermark Creation ...... 503 38.2 Control and Removal of Watermarks ...... 506 References ...... 507

39. Physical Cleaning Kenji Sugimoto, Nobuyasu Hiraoka, and Masahiro Nonomura Dainippon Screen ...... 508 39.1 Introduction ...... 508 39.2 Brush Scrubbing ...... 508 39.2.1 Brush Characteristics ...... 509 39.2.2 Problems with Brushes ...... 510 39.3 High-Pressure Jet Scrubbing ...... 510 39.3.1 Problems with High-Pressure Jets ...... 511 39.4 Ultrasonic Scrubbing ...... 511 39.4.1 Removal Mechanism ...... 511 39.4.2 Process Factors ...... 512 39.4.3 Problems Caused by Megasonics ...... 513 39.5 Issues for the Future ...... 513

40. Dry Cleaning Takashi Ito, Fujitsu Labs ...... 514 40.1 Dry Cleaning ...... 514 40.2 Removal of Metallic Contaminants ...... 516 40.2.1 Ultraviolet Excitation Cleaning ...... 516 40.2.2 Chemical Vapor Cleaning ...... 519 40.3 Native Oxide Film Removal ...... 520 40.3.1 HF Gas Etching ...... 520 40.3.2 Ultraviolet Excitation F2/H2 Treatment ...... 522 40.4 Removal of Organic Contaminants ...... 523 40.5 Hydrogen Termination of the Surface ...... 526 40.6 Issues for the Future ...... 528 References ...... 528 XXII Table of Contents

Part VIII. Wafer-Cleaning-Related Issues

41. HF Vapor Cleaning Technology Tsutomu Takeuchi and Akira Izumi Dainippon Screen ...... 531 41.1 Introduction ...... 531 41.2 Hydrogen Fluoride (HF) Vapor Cleaning ...... 532 41.2.1 The Role of HF Vapor Cleaning ...... 532 41.2.2 Merits of HF Vapor Cleaning ...... 532 41.2.3 Problems with HF Vapor Cleaning ...... 533 41.2.4 Applications of HF Vapor Cleaning ...... 533 41.2.5 The Necessity of Organic Contaminant Removal in HF Vapor Cleaning ...... 534 41.2.6 Native Oxide Removal in HF Vapor Cleaning ...... 534 41.3 HFjCH3 0H Vapor Cleaning (HAVe) ...... 535 41.3.1 Merits of HF jCH3 0H Vapor Cleaning ...... 535 41.3.2 Particle Evaluation ...... 537 41.3.3 Wafer Surface Condition After HAVC Processing ..... 538 41.3.4 Contact Resistance Evaluation ...... 540 41.4 Issues for the Future ...... 541 References ...... 541

42. Native Oxide Films and Chemical Oxide Films Mizuho Morita, Osaka University ...... 543 42.1 Introduction ...... 543 42.2 Types of Native Oxide ...... 543 42.3 Measurement of Ultrathin Film Thicknesses ...... 544 42.4 Clean Si Surfaces After Wafer Cleaning ...... 545 42.5 Native Oxide Growth Processes ...... 546 42.5.1 Growth in Air ...... 546 42.5.2 Growth in Ultrapure Water ...... 549 42.6 Structure of Native Oxides and Chemical Oxides ...... 552 42.7 Mechanisms of Native Oxide Growth ...... 554 42.7.1 Growth in Air ...... 554 42.7.2 Growth in Ultrapure Water ...... 555 42.8 Issues for the Future ...... 556 References ...... 557 Table of Contents XXIII

43. Hydrogen Termination: The Ideally Finished Silicon Surface Hiroto Izumi, Stella Chemifa ...... 559 43.1 Passivation of the Si Surface ...... 559 43.2 Hydrogen Termination of the Surface ...... 560 43.2.1 Si Surface Passivation Using HF/BHF ...... 560 43.2.2 Si Surface Passivation Using Hydrogen Annealing ..... 562 43.3 Storage and Transport of Ultraclean Wafers ...... 562 References ...... 565

44. Adsorption of Organic Volatiles on Silicon Surfaces and Their Removal by Wet Cleaning Koichiro Saga and Takeshi Hattori, Sony ...... 566 44.1 Introduction ...... 566 44.2 Analytical Methods of Organic Contamination Adsorbing on Silicon Surfaces ...... 567 44.3 Analytical Methods of Outgassing from Plastic Boxes ...... 568 44.4 Identification of Organic Contaminants Adsorbing on Silicon Wafers ...... 569 44.5 Removal of Organic Contamination by Wet Cleaning ...... 574 44.6 Adsorption Property of the Organic Volatiles After Cleaning . 576 44.7 Acceleration of Organic Adsorption in the Presence of Residual Fluorine ...... 579 44.8 Conclusions ...... 581 References ...... 582

45. Wafer Carrier Cleaning Takeshi Hattori, Sony ...... 584 45.1 Introduction ...... 584 45.2 Problems with Carriers Made of Fluorocarbon Resin ...... 584 45.2.1 Generation of Chemical Contamination ...... 584 45.2.2 Particle Generation ...... 585 45.3 Evaluating Particle Contamination from Carriers ...... 588 45.4 The Effectiveness of Carrier Cleaning ...... 589 45.5 Development of New Carrier Cleaners ...... 591 45.6 Issues for the Future ...... 593 References ...... 593

46. Goals for Next-Generation Wafer Cleaning Technology Nahomi Aoto, NEC ...... 594 46.1 Functions Necessary in Next-Generation Cleaning ...... 594 46.2 High-Performance Cleaning ...... 594 XXIV Table of Contents

46.3 Issues with Cleaning Processes in Advanced Device Manufacturing...... 596 46.4 Currently Proposed Cleaning Techniques: Problems and Prospects ...... 600 46.5 Next-Generation Cleaning Technology for Better Device Manufacturing ...... 603 46.6 A Development Framework for the Future ...... 605 References ...... 606

Index ...... 609 List of Contributors

Motoaki Adachi Takeshi Hattori Osaka Prefecture University ULSI R&D Laboratories Sakai, Osaka 599-8570 Sony Corporation Japan Semiconductor Company E-mail: Atsugi 243-8585 [email protected] Japan E-mail: [email protected] Nahomi Aoto ULSI Device Development Labs. Yoshihiro Hayashi NEC Corporation Silicon Systems Research Labs. Sagamihara 229-1198 NEC Corporation Japan Sagamihara 229-1198 E-mail: aoto@lsi.nec.co.jp Japan E-mail: [email protected] Masashi Asami Applied Materials Japan Inc. Sumio Hosaka Narita, Chiba 286-0825 Advanced Research Laboratories Japan Hitachi Limited (retired) Kogubunji, Tokyo 185-0014 Yuji Fukazawa Japan Integrated Circuit Advanced Process E-mail: [email protected] Engineering Department Hitoshi Inaba Toshiba Corporation Takasago Thermal Engineering Isogo, Yokohama 235-8522 Corporation, Limited Japan Atsugi 243-0213 E-mail: Japan [email protected] Fax: ++81-(0)462-48-2290 Takashi Futatsuki Japan Organo Corporation Mitsushi Itano Koto, Tokyo 136-8631 Daikin Industries Limited Japan Settsu, Osaka 566-8585 E-mail: Japan [email protected] E-mail: [email protected] XXVI List of Contributors

Takashi Ito Tetsuro Kodama Fujitsu Laboratories Limited ULVAC Japan, Limited Atsugi 243-0197 Chigasaki 253-0071 Japan Japan E-mail: [email protected] Atsuyoshi Koike Haruo Itoh Semiconductor & Integrated Semiconductor & Integrated Circuits Division Circuits Division Hitachi Limited Hitachi Limited Kodaira, Tokyo 187-8588 Ome, Tokyo 198-0023 Japan Japan E-mail: Fax: ++81-(0)428-33-2092 [email protected]

Katsuhiko Itoh Kazuo Maeda Semiconductor Manufacturing Semiconductor Process Technology Center Laboratories Co. Ltd. Hitachi Limited Minato, Tokyo 108-0075 Ome, Tokyo 198-0023 Japan Japan E-mail: [email protected] E-mail: [email protected] Morimasa Miyazaki Sumitomo Sitix Corporation Hiroto Izumi Kishima, Saga 849-0506 Stella Chemifa Corporation Japan Sakai, Osaka 590-0982 E-mail: [email protected] Japan E-mail: [email protected] Motosuke Miyoshi Integrated Circuit Advanced Hiroyuki Kawahara Process Engineering Department ULSI Process Technology Toshiba Corporation Development Center Isogo, Yokohama 235-0032 Matsushita Electronics Corporation Japan Minami, Kyoto 601-8413 E-mail: [email protected] Japan E-mail: [email protected] Fumio Mizuno Instrument Division Tomohisa Kitano Hitachi Limited ULSI Device Development Labs. Hitachinaka, Ibaraki 312-8504 NEC Corporation Japan Sagamihara 229-1198 E-mail: Japan [email protected] E-mail: [email protected] List of Contributors XXVII

Yoshinobu Monma Makoto Sekine Fujitsu LSI Technology Limited NEC Electronics Inc. Kawasaki 213-0013 Roseville, CA 95661-9022 Japan USA E-mail: [email protected] E-mail: [email protected]

Etsuro Morita Ayako Shimazaki Mitsubishi Materials Integrated Circuit Advanced Process Silicon Corporation Engineering Department Noda, Chiba 278-0015 Toshiba Corporation Japan Isogo, Yokohama 235-0032 E-mail: [email protected] Japan E-mail: [email protected] Mizuho Morita Kenji Sugimoto Department of Precision Science Dainippon Screen Manufacturing and Technology Corporation, Limited Osaka University Fushimi, Kyoto 612-8486 Suita, Osaka 565-0871 Japan Japan E-mail: [email protected] E-mail: [email protected] Jun Sugiura Semiconductor & Integrated Moritaka Nakamura Circuits Division ULSI Development Division Hitachi Limited Fujitsu Limited Kodaira, Tokyo 187-8588 Nakahara, Kawasaki 211-8588 Japan Japan E-mail: [email protected] Yoshiki Suzuki KLA Tencor Japan Limited Koichiro Saga Hodogaya, Yokohama 240-0005 ULSI R&D Laboratories Japan Sony Corporation E-mail: [email protected] Semiconductor Company Tsuyoshi Takahashi Atsugi 243-8585 Anelva Corporation Japan E-mail: [email protected] Fuchu, Tokyo 183-8507 Japan Akio Saito E-mail: [email protected] Production Engineering Tsutomu Takeuchi Research Laboratories Dainippon Screen Manufacturing Hitachi Limited Corporation, Limited Totsuka, Yokohama 244-0817 Kamigyo, Kyoto 602-8585 Japan Japan E-mail: [email protected] E-mail: [email protected] XXVIII List of Contributors

Makoto Takiyama Norikuni Yabumoto NSC Electron Corporation NTT Advanced Technology Hikari, Yamaguchi 743-0063 Corporation Japan Atsugi 243-0122 E-mail: [email protected] Japan E-mail: [email protected] Katsumi Ukai Anelva Corporation Shinichi Yasui Yamanashi 401-0397 Shinko Pantec Corporation, Limited Japan Chuo, Kobe 651-0072 E-mail: [email protected] Japan E-mail: [email protected] Yasutsugu Usami Instrument Division Kenji Yoneda Hitachi Limited ULSI Process Technology Hitachinaka, Ibaraki 312-8504 Development Center Japan Matsushita Electronics Corporation E-mail: [email protected] Minami, Kyoto 601-8413 Japan Kikuo Yamabe E-mail: [email protected].meLco.jp Tsukuba University Tsukuba, Ibaraki 305-0004 Japan Fax: 0298-55-7440