handbook of physical vapor deposition

HANDBOOK OF PHYSICAL VAPOR DEPOSITION (PVD) PROCESSINGFilm Formation, Adhesion, Surface Preparation and Contamination Controlby

Donald M. MattoxSociety of Vacuum Coaters Albuquerque, New Mexico

np

NOYES PUBLICATIONSWestwood, New Jersey, U.S.A.

Copyright 1998 by Noyes Publications No part of this book may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording or by any information storage and retrieval system, without permission in writing from the Publisher. Library of Congress Catalog Card Number: 97-44664 ISBN: 0-8155-1422-0 Printed in the United States Published in the United States of America by Noyes Publications 369 Fairview Avenue, Westwood, New Jersey 07675 10 9 8 7 6 5 4 3 2 1

Library of Congress Cataloging-in-Publication Data Mattox, D. M. Handbook of physical vapor deposition (PVD) processing / by Donald M. Mattox. p. cm. Includes bibliographical references and index. ISBN 0-8155-1422-0 1. Vapor-plating--Handbooks, manuals, etc. I. Title. TS695.M38 1998 671.7' 35--dc21 97-44664 CIP

DedicationTo my wife VivienneWithout Viviennes constant support, encouragement, and editorial assistance, this book would not exist. Her wide spectrum of contacts within the vacuum equipment and PVD technology industries has made the accumulation of information in some sections of this book possible.

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NOTICETo the best of our knowledge the information in this publication is accurate; however the Publisher does not assume any responsibility or liability for the accuracy or completeness of, or consequences arising from, such information. This book is intended for informational purposes only. Mention of trade names or commercial products does not constitute endorsement or recommendation for use by the Publisher. Final determination of the suitability of any information or product for use contemplated by any user, and the manner of that use, is the sole responsibility of the user. We recommend that anyone intending to rely on any recommendation of materials or procedures mentioned in this publication should satisfy himself as to such suitability, and that he can meet all applicable safety and health standards.

Preface

The motivation for writing this book was that there was no single source of information which covers all aspects of Physical Vapor Deposition (PVD) processing in a comprehensive manner. The properties of thin films deposited by PVD processes depend on a number of factors (see Sec. 1.2.2), and each must be considered when developing a reproducible process and obtaining a high product throughput and yield from the production line. This book covers all aspects of PVD process technology from characterizing and preparing the substrate material, through the deposition process and film characterization, to post deposition processing. The emphasis of the book is on the aspects of the process flow that are critical to reproducible deposition of films that have the desired properties. The book covers both neglected subjects, such as film adhesion, substrate surface characterization, and the external processing environment, and widely discussed subjects, such as vacuum technology, film properties and the fundamentals of individual deposition processes. In this book, the author relates these subjects to the practical issues that arise in PVD processing, such as contamination control and substrate property effects on film growth, which are often not discussed or even mentioned in the literature. By bringing these subjects together in one book, the author has made it possible for the reader to better understand the interrelationships between various aspects of the processing and the resulting film properties. The author draws upon his long experience in developing PVD processes, teaching short courses on PVD processing, to not only present the basics but

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also to provide useful hints for avoiding problems and solving problems when they arise. Some examples of actual problems and solutions (war stories) are provided as foot notes throughout the text. The organization of the text allows a reader who is already knowledgeable in the subject to scan through a section and find subjects that are of particular interest. Extensive references allow the reader to pursue subjects in greater detail if so desired. An important aspect of the book is the useful reference material presented in the Appendices. A glossary of over 2500 terms and acronyms will be especially useful to those individuals that are just entering the field and those who are not fully conversant with the English language. Many of the terms are colloquialisms that are used in the field of Surface Engineering. The author realizes that covering this subject is a formidable task, particularly for one person, and that this effort is incomplete at best. He would like to elicit comments, corrections, and additions, which may be incorporated in a later edition of the book. In particular, he would like to elicit war stories of actual problems and solutions. Credit will be given for those which are used. Please contact the author at (ph.) 505-856-6810, (fax) 505856-6716, or e-mail [email protected]. Albuquerque, New Mexico August, 1997 Donald M. Mattox

Table of Contents

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Table of Contents

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Introduction .......................................................................... 291.1 SURFACE ENGINEERING .......................................................... 29 1.1.1 Physical Vapor Deposition (PVD) Processes .................. 31 Vacuum Deposition .................................................... 32 Sputter Deposition ...................................................... 33 Arc Vapor Deposition ................................................. 34 Ion Plating................................................................... 34 1.1.2 Non-PVD Thin Film Atomistic Deposition Processes .... 35 Chemical Vapor Deposition (CVD) and PECVD ...... 35 Electroplating, Electroless Plating and Displacement Plating...................................................................... 36 Chemical Reduction ................................................... 37 1.1.3 Applications of Thin Films.............................................. 38 THIN FILM PROCESSING ........................................................... 39 1.2.1 Stages of Fabrication ....................................................... 39 1.2.2 Factors that Affect Film Properties ................................. 40 1.2.3 Scale-Up and Manufacturabilty ...................................... 43 PROCESS DOCUMENTATION ................................................... 44 1.3.1 Process Specifications ..................................................... 44 Laboratory/Engineering Notebook ............................. 46 1.3.2 Manufacturing Process Instructions (MPIs) .................... 46 1.3.3 Travelers .......................................................................... 47 1.3.4 Equipment and Calibration Logs..................................... 48 1.3.5 Commercial/Military Standards and Specifications ........ 48 SAFETY AND ENVIRONMENTAL CONCERNS ...................... 50

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Handbook of Physical Vapor Deposition (PVD) ProcessingUNITS............................................................................................. 50 1.5.1 Temperature Scales ......................................................... 51 1.5.2 Energy Units .................................................................... 51 1.5.3 Prefixes ............................................................................ 51 1.5.4 Greek Alphabet ............................................................... 52 1.6 SUMMARY .................................................................................... 52 FURTHER READING ................................................................................ 53 REFERENCES ............................................................................................ 54

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Substrate (Real) Surfaces and Surface Modification .... 562.1 2.2 INTRODUCTION .......................................................................... 56 MATERIALS AND FABRICATION ............................................ 57 2.2.1 Metals .............................................................................. 57 2.2.2 Ceramics and Glasses ...................................................... 59 2.2.3 Polymers .......................................................................... 61 ATOMIC STRUCTURE AND ATOM-PARTICLE INTERACTIONS ........................................................................ 63 2.3.1 Atomic Structure and Nomenclature ............................... 63 2.3.2 Excitation and Atomic Transitions .................................. 64 2.3.3 Chemical Bonding ........................................................... 66 2.3.4 Probing and Detected Species ......................................... 67 CHARACTERIZATION OF SURFACES AND NEAR-SURFACE REGIONS ..................................................... 69 2.4.1 Elemental (Chemical) Compositional Analysis .............. 71 Auger Electron Spectroscopy (AES) .......................... 72 Ion Scattering Spectroscopy (ISS and LEISS) ........... 73 Secondary Ion Mass Spectrometry (SIMS) ................ 75 2.4.2 Phase Composition and Microstructure .......................... 75 X-ray Diffraction ........................................................ 75 Electron Diffraction (RHEED, TEM) ........................ 76 2.4.3 Molecular Composition and Chemical Bonding ............. 76 Infrared (IR) Spectroscopy ......................................... 76 X-ray Photoelectron Spectroscopy (XPS) or Electron Spectroscopy for Chemical Analysis (ESCA) ............ 79 2.4.4 Surface Morphology ........................................................ 80 Contacting Surface Profilometry ................................ 82 Scanning Tunneling Microscopy (STM) and Atomic Force Microscopy (AFM) ....................................... 83 Interferometry ............................................................. 84 Scanning Near-Field Optical Microscopy (SNOM) and Photon Tunneling Microscopy (PTM) .................... 84 Scatterometry .............................................................. 85 Scanning Electron Microscope (SEM) ....................... 85 Replication TEM ........................................................ 85 AdsorptionGases and Liquids ................................. 86

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2.4.5 Mechanical and Thermal Properties of Surfaces............. 87 2.4.6 Surface Energy ................................................................ 88 2.4.7 Acidic and Basic Properties of Surfaces ......................... 90 2.5 BULK PROPERTIES ..................................................................... 91 2.5.1 Outgassing ....................................................................... 91 2.5.2 Outdiffusion .................................................................... 92 2.6 MODIFICATION OF SUBSTRATE SURFACES ........................ 92 2.6.1 Surface Morphology........................................................ 92 Smoothing the Surface ................................................ 92 Roughening Surfaces .................................................. 95 Vicinal (Stepped) Surfaces ....................................... 100 2.6.2 Surface Hardness ........................................................... 100 Hardening by Diffusion Processes ........................... 100 Hardening by Mechanical Working ......................... 102 Hardening by Ion Implantation ................................ 102 2.6.3 Strengthening of Surfaces ............................................. 103 Thermal Stressing ..................................................... 103 Ion Implantation ....................................................... 104 Chemical Strengthening ........................................... 104 2.6.4 Surface Composition ..................................................... 104 Inorganic Basecoats .................................................. 105 Oxidation .................................................................. 105 Surface Enrichment and Depletion ........................... 107 Phase Composition ................................................... 107 2.6.5 Surface Activation ..................................................... 108 Plasma Activation ..................................................... 108 Corona Activation..................................................... 109 Flame Activation ...................................................... 110 Electronic Charge Sites and Dangling Bonds........... 110 Surface Layer Removal ............................................ 111 2.6.6 Surface Sensitization.................................................. 111 2.7 SUMMARY .................................................................................. 112 FURTHER READING .............................................................................. 112 REFERENCES .......................................................................................... 113

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The Low-Pressure Gas and Vacuum Processing Environment ....................................................................... 1273.1 3.2 INTRODUCTION ........................................................................ 127 GASES AND VAPORS ............................................................... 128 3.2.1 Gas Pressure and Partial Pressure ................................. 129 Pressure Measurement .............................................. 131 Identification of Gaseous Species............................. 135

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Handbook of Physical Vapor Deposition (PVD) Processing3.2.2 Molecular Motion .......................................................... 136 Molecular Velocity ................................................... 136 Mean Free Path ......................................................... 136 Collision Frequency .................................................. 136 Energy Transfer from Collision and Thermalization ............................................ 137 3.2.3 Gas Flow ........................................................................ 138 3.2.4 Ideal Gas Law ................................................................ 140 3.2.5 Vapor Pressure and Condensation ................................. 141 GAS-SURFACE INTERACTIONS ............................................. 143 3.3.1 Residence Time ............................................................. 143 3.3.2 Chemical Interactions .................................................... 144 VACUUM ENVIRONMENT ...................................................... 146 3.4.1 Origin of Gases and Vapors .......................................... 147 Residual Gases and Vapors ...................................... 147 Desorption ................................................................ 148 Outgassing ................................................................ 149 Outdiffusion .............................................................. 151 Permeation Through Materials ................................. 151 Vaporization of Materials ......................................... 152 Real and Virtual Leaks ............................................. 153 Brought-in Contamination .................................... 154 VACUUM PROCESSING SYSTEMS ........................................ 155 3.5.1 System Design Considerations and Trade-Offs ......... 157 3.5.2 Processing Chamber Configurations ............................. 157 Direct-Load System .................................................. 159 Load-Lock System .................................................... 159 In-Line System ......................................................... 161 Cluster Tool System ................................................. 162 Web Coater (Roll Coater) ......................................... 162 Air-To-Air Strip Coater ............................................ 163 3.5.3 Conductance .................................................................. 163 3.5.4 Pumping Speed and Mass Throughput ......................... 165 3.5.5 Fixturing and Tooling .................................................... 166 Substrate Handling ................................................... 171 3.5.6 Feedthroughs and Accessories ...................................... 171 3.5.7 Liners and Shields ......................................................... 171 3.5.8 Gas Manifolding ............................................................ 172 Mass Flow Meters and Controllers ........................... 173 3.5.9 Fail-Safe Designs .......................................................... 175 What-If Game ....................................................... 178 VACUUM PUMPING .................................................................. 179 3.6.1 Mechanical Pumps ........................................................ 179 Oil-Sealed Mechanical Pumps .................................. 180 Dry Pumps ................................................................ 181 Diaphragm Pumps .................................................... 182

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Momentum Transfer Pumps .......................................... 182 Diffusion Pumps ....................................................... 182 Turbomolecular Pumps ............................................ 185 Molecular Drag Pumps ............................................. 186 3.6.3 Capture Pumps .............................................................. 186 Sorption (Adsorption) Pumps ................................... 186 Cryopanels ................................................................ 187 Cryopumps................................................................ 188 Getter Pumps ............................................................ 190 3.6.4 Hybrid Pumps ................................................................ 191 3.7 VACUUM AND PLASMA COMPATIBLE MATERIALS ....... 191 3.7.1 Metals ............................................................................ 192 Stainless Steel ........................................................... 193 Low-Carbon (Mild) Steel ......................................... 196 Aluminum ................................................................. 196 Copper ...................................................................... 198 Hardenable Metals .................................................... 198 3.7.2 Ceramic and Glass Materials ......................................... 198 3.7.3 Polymers ........................................................................ 199 3.8 ASSEMBLY ................................................................................. 199 3.8.1 Permanent Joining ......................................................... 199 3.8.2 Non-Permanent Joining ................................................. 200 3.8.3 Lubricants for Vacuum Application.............................. 203 3.9 EVALUATING VACUUM SYSTEM ............................................... PERFORMANCE ......................................................................... 204 3.9.1 System Records ............................................................. 204 3.10 PURCHASING A VACUUM SYSTEM FOR PVD PROCESSING ........................................................................... 205 3.11 CLEANING OF VACUUM SURFACES .................................... 208 3.11.1 Stripping ........................................................................ 208 3.11.2 Cleaning......................................................................... 209 3.11.3 In Situ Conditioning of Vacuum Surfaces ................. 210 3.12 SYSTEM-RELATED CONTAMINATION ................................ 212 3.12.1 Particulate Contamination ............................................. 212 3.12.2 Vapor Contamination .................................................... 215 Water Vapor ............................................................. 215 3.12.3 Gaseous Contamination................................................. 216 3.12.4 Changes with Use .......................................................... 216 3.13 PROCESS-RELATED CONTAMINATION ............................... 216 3.14 TREATMENT OF SPECIFIC MATERIALS .............................. 217 3.14.1 Stainless Steel ................................................................ 217 3.14.2 Aluminum Alloys .......................................................... 218 3.14.3 Copper ........................................................................... 220 3.15 SAFETY ASPECTS OF VACUUM TECHNOLOGY ................ 221 3.16 SUMMARY .................................................................................. 222 FURTHER READING .............................................................................. 222 REFERENCES .......................................................................................... 225

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Handbook of Physical Vapor Deposition (PVD) Processing The Low-Pressure Plasma Processing Environment ...... 2374.1 4.2 INTRODUCTION ........................................................................ 237 THE PLASMA ............................................................................. 239 4.2.1 Plasma Chemistry .......................................................... 239 Excitation .................................................................. 239 Ionization by Electrons ............................................. 241 Dissociation .............................................................. 242 Penning Ionization and Excitation............................ 242 Charge Exchange ...................................................... 243 Photoionization and Excitation ................................. 243 Ion-Electron Recombination .................................... 243 Plasma Polymerization ............................................. 243 Unique Species ......................................................... 244 Plasma Activation ................................................. 244 Crossections and Threshold Energies ....................... 244 Thermalization .......................................................... 244 4.2.2 Plasma Properties and Regions ..................................... 245 Plasma Generation Region ....................................... 246 Afterglow or Downstream Plasma Region ........... 246 Measuring Plasma Parameters .................................. 246 PLASMA-SURFACE INTERACTIONS ..................................... 247 4.3.1 Sheath Potentials and Self-Bias ..................................... 247 4.3.2 Applied Bias Potentials ................................................. 248 4.3.3 Particle Bombardment Effects ....................................... 248 4.3.4 Gas Diffusion into Surfaces .......................................... 249 CONFIGURATIONS FOR GENERATING PLASMAS............. 249 4.4.1 Electron Sources ............................................................ 249 4.4.2 Electric and Magnetic Field Effects .............................. 250 4.4.3 DC Plasma Discharges .................................................. 252 Pulsed DC ................................................................. 257 4.4.4 Magnetically Confined Plasmas .................................... 258 Balanced Magnetrons ............................................... 258 Unbalanced Magnetrons ........................................... 261 4.4.5 AC Plasma Discharges .................................................. 262 4.4.6 Radio Frequency (rf) Capacitively-Coupled Diode Discharge .................................................................. 262 4.4.7 Arc Plasmas ................................................................... 264 4.4.8 Laser-Induced Plasmas .................................................. 265 ION AND PLASMA SOURCES.................................................. 265 4.5.1 Plasma Sources .............................................................. 265 End Hall Plasma Source ........................................... 266 Hot Cathode Plasma Source ..................................... 266 Capacitively Coupled rf Plasma Source ................... 267 Electron Cyclotron Resonance (ECR) Plasma Source 268

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Inductively Coupled rf Plasma (ICP) Source ........... 268 Helicon Plasma Source ............................................. 271 Hollow Cathode Plasma Source ............................... 271 4.5.2 Ion Sources (Ion Guns) ................................................. 271 4.5.3 Electron Sources ............................................................ 272 4.6 PLASMA PROCESSING SYSTEMS .......................................... 273 4.6.1 Gas Distribution and Injection ...................................... 274 Gas Composition and Flow, Flow Meters, and Flow Controllers ..................................................................... 275 4.6.2 Electrodes ...................................................................... 275 4.6.3 Corrosion ....................................................................... 276 4.6.4 Pumping Plasma Systems.............................................. 276 4.7 PLASMA-RELATED CONTAMINATION ................................ 276 4.7.1 Desorbed Contmination................................................. 277 4.7.2 Sputtered Contamination ............................................... 277 4.7.3 Arcing ............................................................................ 277 4.7.4 Vapor Phase Nucleation ................................................ 278 4.7.5 Cleaning Plasma Processing Systems ........................... 278 4.8 SOME SAFETY ASPECTS OF PLASMA ........................................ PROCESSING .............................................................................. 279 4.9 SUMMARY .................................................................................. 279 FURTHER READING .............................................................................. 280 REFERENCES .......................................................................................... 281

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Vacuum Evaporation and Vacuum Deposition ............... 2885.1 5.2 INTRODUCTION ........................................................................ 288 THERMAL VAPORIZATION .................................................... 289 5.2.1 Vaporization of Elements .............................................. 289 Vapor Pressure .......................................................... 289 Flux Distribution of Vaporized Material .................. 292 5.2.2 Vaporization of Alloys and Mixtures ............................ 295 5.2.3 Vaporization of Compounds ......................................... 296 5.2.4 Polymer Evaporation ..................................................... 296 THERMAL VAPORIZATION SOURCES ................................. 296 5.3.1 Single Charge Sources................................................... 297 Resistively Heated Sources....................................... 297 Electron Beam Heated Sources ................................ 301 Crucibles ................................................................... 304 Radio Frequency (rf) Heated Sources ...................... 305 Sublimation Sources ................................................. 305 5.3.2 Replenishing (Feeding) Sources.................................... 306 5.3.3 Baffle Sources ............................................................... 307 5.3.4 Beam and Confined Vapor Sources .............................. 307 5.3.5 Flash Evaporation .......................................................... 307 5.3.6 Radiant Heating ............................................................. 308

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Handbook of Physical Vapor Deposition (PVD) ProcessingTRANSPORT OF VAPORIZED MATERIAL ............................ 309 5.4.1 Masks ............................................................................. 309 5.4.2 Gas Scattering ................................................................ 309 CONDENSATION OF VAPORIZED MATERIAL .................... 310 5.5.1 Condensation Energy .................................................... 310 5.5.2 Deposition of Alloys and Mixtures ............................... 311 5.5.3 Deposition of Compounds from Compound Source Material ..................................................................... 313 5.5.4 Some Properties of Vacuum Deposited Thin Films ...... 314 MATERIALS FOR EVAPORATION ......................................... 314 5.6.1 Purity and Packaging ..................................................... 314 Purchase Specifications ............................................ 315 5.6.2 Handling of Source Materials ....................................... 315 VACUUM DEPOSITION CONFIGURATIONS ........................ 315 5.7.1 Deposition Chambers .................................................... 316 5.7.2 Fixtures and Tooling ..................................................... 316 5.7.3 Shutters .......................................................................... 317 5.7.4 Substrate Heating and Cooling ...................................... 318 5.7.5 Liners and Shields ......................................................... 318 5.7.6 In Situ Cleaning ............................................................. 319 5.7.7 Getter Pumping Configurations .................................... 319 PROCESS MONITORING AND CONTROL ............................. 319 5.8.1 Substrate Temperature Monitoring ............................... 320 5.8.2 Deposition MonitorsRate and Total Mass ................. 320 5.8.3 Vaporization Source Temperature Monitoring ............. 322 5.8.4 In Situ Film Property Monitoring .................................. 322 CONTAMINATION FROM THE VAPORIZATION SOURCE 323 5.9.1 Contamination from the Vaporization Source .............. 323 5.9.2 Contamination from the Deposition System ................. 325 5.9.3 Contamination from Substrates ..................................... 325 5.9.4 Contamination from Deposited Film Material .............. 325 ADVANTAGES AND DISADVANTAGES OF VACUUM DEPOSITION ............................................................................ 326 SOME APPLICATIONS OF VACUUM DEPOSITION ............. 327 5.11.1 Freestanding Structures ................................................. 327 5.11.2 Graded Composition Structures .................................... 328 5.11.3 Multilayer Structures ..................................................... 328 5.11.4 Molecular Beam Epitaxy (MBE) .................................. 328 GAS EVAPORATION AND ULTRAFINE PARTICLES .......... 329 OTHER PROCESSES .................................................................. 330 5.13.1 Reactive Evaporation and Activated Reactive Evaporation (ARE) ................................................... 330 5.13.2 Jet Vapor Deposition Process ........................................ 331 5.13.3 Field Evaporation .......................................................... 331

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5.14 SUMMARY .................................................................................. 331 FURTHER READING .............................................................................. 331 REFERENCES .......................................................................................... 332

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Physical Sputtering and Sputter Deposition (Sputtering)3436.1 6.2 INTRODUCTION ........................................................................ 343 PHYSICAL SPUTTERING ......................................................... 345 6.2.1 Bombardment Effects on Surfaces ................................ 346 6.2.2 Sputtering Yields ........................................................... 349 6.2.3 Sputtering of Alloys and Mixtures ................................ 352 6.2.4 Sputtering Compounds .................................................. 353 6.2.5 Distribution of Sputtered Flux....................................... 354 SPUTTERING CONFIGURATIONS .......................................... 354 6.3.1 Cold Cathode DC Diode Sputtering .............................. 356 6.3.2 DC Triode Sputtering .................................................... 357 6.3.3 AC Sputtering ................................................................ 357 6.3.4 Radio Frequency (rf) Sputtering ................................... 358 6.3.5 DC Magnetron Sputtering ............................................. 358 Unbalanced Magnetron ............................................ 361 6.3.6 Pulsed DC Magnetron Sputtering ................................. 362 6.3.7 Ion and Plasma Beam Sputtering .................................. 362 TRANSPORT OF THE SPUTTER-VAPORIZED SPECIES ...... 363 6.4.1 Thermalization............................................................... 363 6.4.2 Scattering ....................................................................... 364 6.4.3 Collimation .................................................................... 364 6.4.4 Postvaporization Ionization ........................................... 364 CONDENSATION OF SPUTTERED SPECIES ......................... 365 6.5.1 Elemental and Alloy Deposition ................................... 365 6.5.2 Reactive Sputter Deposition .......................................... 366 6.5.3 Deposition of Layered and Graded Composition Structures .................................................................. 371 6.5.4 Deposition of Composite Films ..................................... 372 6.5.5 Some Properties of Sputter Deposited Thin Films ........ 372 SPUTTER DEPOSITION GEOMETRIES .................................. 373 6.6.1 Deposition Chamber Configurations............................. 373 6.6.2 Fixturing ........................................................................ 373 6.6.3 Target Configurations ................................................... 374 6.6.4 Ion and Plasma Sources................................................. 376 6.6.5 Plasma Activation Using Auxiliary Plasmas................. 376 TARGETS AND TARGET MATERIALS .................................. 376 6.7.1 Target Configurations ................................................... 377 Dual Arc and Sputtering Targets .............................. 378 6.7.2 Target Materials ............................................................ 378 6.7.3 Target Cooling, Backing Plates, and Bonding .............. 380

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Handbook of Physical Vapor Deposition (PVD) Processing

6.7.4 Target Shielding ............................................................ 381 6.7.5 Target Specifications ..................................................... 381 6.7.6 Target Surface Changes with Use ................................. 382 6.7.7 Target Conditioning (Pre-Sputtering) ........................... 383 6.7.8 Target Power Supplies ................................................... 383 6.8 PROCESS MONITORING AND CONTROL ............................. 384 6.8.1 Sputtering System .......................................................... 384 6.8.2 Pressure ......................................................................... 385 6.8.3 Gas Composition ........................................................... 385 6.8.4 Gas Flow ........................................................................ 386 6.8.5 Target Power and Voltage ............................................. 387 6.8.6 Plasma Properties .......................................................... 387 6.8.7 Substrate Temperature ................................................... 387 6.8.8 Sputter Deposition Rate ................................................. 388 6.9 CONTAMINATION DUE TO SPUTTERING............................ 389 6.9.1 Contamination from Desorption .................................... 389 6.9.2 Target-Related Contamination ...................................... 389 6.9.3 Contamination from Arcing .......................................... 390 6.9.4 Contamination from Wear Particles .............................. 390 6.9.5 Vapor Phase Nucleation ................................................ 390 6.9.6 Contamination from Processing Gases ......................... 390 6.9.7 Contamination from Deposited Film Material .............. 391 6.10 ADVANTAGES AND DISADVANTAGES OF SPUTTER DEPOSITION ............................................................................... 391 6.11 SOME APPLICATIONS OF SPUTTER DEPOSITION ............. 393 6.12 SUMMARY .................................................................................. 394 FURTHER READING .............................................................................. 394 REFERENCES .......................................................................................... 396

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Arc Vapor Deposition .............................................. 406INTRODUCTION ........................................................................ 406 ARCS ............................................................................................ 407 7.2.1 Vacuum Arcs ................................................................. 407 7.2.2 Gaseous Arcs ................................................................. 408 7.2.3 Anodic Arcs ................................................................... 408 7.2.4 Cathodic Arcs ................................................................ 410 7.2.5 Macros ....................................................................... 411 7.2.6 Arc Plasma Chemistry ................................................... 412 7.2.7 Postvaporization Inization ............................................. 412 ARC SOURCE CONFIGURATIONS ......................................... 413 7.3.1 Cathodic Arc Sources .................................................... 413 Arc Initiation ............................................................. 413 Rancom Arc Sources ................................................ 413 Steered Arc Sources .................................................. 413

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Pulsed Arc Sources ................................................... 415 Filtered Arcs .......................................................... 415 Self-Sputtering Sources ......................................... 415 7.3.2 Anodic Arc Source ........................................................ 416 7.4 REACTIVE ARC DEPOSITION ................................................. 417 7.5 ARC MATERIALS ...................................................................... 417 7.6 ARC VAPOR DEPOSITION SYSTEM ...................................... 418 7.6.1 Power Supplies .............................................................. 418 7.6.2 Fixtures .......................................................................... 418 7.7 PROCESS MONITORING AND CONTROL ............................. 419 7.8 CONTAMINATION DUE TO ARC VAPORIZATION ............. 419 7.9 ADVANTAGES AND DISADVANTAGES OF ARC VAPOR DEPOSITION ............................................................................... 419 7.9.1 Advantages .................................................................... 419 7.9.2 Disadvantages................................................................ 419 7.10 SOME APPLICATIONS OF ARC VAPOR DEPOSITION ........ 420 7.11 SUMMARY .................................................................................. 420 FURTHER READING .............................................................................. 421 REFERENCES .......................................................................................... 421

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Ion Plating and Ion Beam Assisted Deposition ................ 4268.1 8.2 INTRODUCTION ........................................................................ 426 STAGES OF ION PLATING ....................................................... 429 8.2.1 Surface Preparation (In Situ) ......................................... 430 8.2.2 Nucleation ..................................................................... 431 8.2.3 Interface Formation ....................................................... 431 8.2.4 Film Growth .................................................................. 432 8.2.4 Reactive and Quasi-Reactive Deposition ...................... 432 Residual Film Stress ...................................................... 433 Gas Incorporation .......................................................... 433 Surface Coverage and Throwing Power ....................... 434 Film Properties .............................................................. 434 SOURCES OF DEPOSITING AND REACTING SPECIES ....... 435 8.3.1 Thermal Vaporization ................................................... 435 8.3.2 Physical Sputtering ........................................................ 436 8.3.3 Arc Vaporization ........................................................... 436 8.3.4 Chemical Vapor Precursor Species ............................... 437 8.3.5 Laser-Induced Vaporization .......................................... 437 8.3.6 Gaseous Species ............................................................ 438 8.3.7 Film Ions (Self-Ions) ..................................................... 438 SOURCES OF ENERGETIC BOMBARDING SPECIES ........... 438 8.4.1 Bombardment from Gaseous Plasmas........................... 439 Auxiliary Plasmas.......................................................... 440 8.4.2 Bombardment from Gaseous Arcs ................................ 440

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Handbook of Physical Vapor Deposition (PVD) ProcessingBombardment by High Energy Neutrals ....................... 440 Gaseous Ion and Plasma Sources (Guns) ...................... 441 Film Ion Sources ........................................................... 441 Postvaporization Ionization ...................................... 442 8.4.6 High Voltage Pulsed Ion Bombardment ....................... 444 8.5 SOURCES OF ACCELERATING POTENTIAL ........................ 444 8.5.1 Applied Bias Potential ................................................... 444 8.5.2 Self-Bias Potential ......................................................... 446 8.6 SOME PLASMA-BASED ION PLATINGCONFIGURATIONS . 446 8.6.1 Plasma and Bombardment Uniformity .......................... 447 8.6.2 Fixtures .......................................................................... 448 8.7 ION BEAM ASSISTED DEPOSITION (IBAD) ......................... 450 8.8 PROCESS MONITORING AND CONTROL ............................. 451 8.8.1 Substrate Temperature ................................................... 452 8.8.2 Gas Composition and Mass Flow .................................. 453 8.8.3 Plasma Parameters ......................................................... 453 8.8.4 Deposition Rate ............................................................. 454 8.9 CONTAMINATION IN THE ION PLATING PROCESS .......... 454 8.9.1 Plasma Desorption and Activation ................................ 455 8.9.2 Vapor Phase Nucleation ................................................ 455 8.9.3 Flaking ........................................................................... 456 8.9.4 Arcing ............................................................................ 456 8.9.5 Gas and Vapor Adsorption and Absorption .................. 456 8.10 ADVANTAGES AND DISADVANTAGES OF ION PLATING 457 8.11 SOME APPLICATIONS OF ION PLATING .............................. 458 8.11.1 Plasma-Based Ion Plating .............................................. 458 8.11.2 Vacuum-Based Ion Plating (IBAD) .............................. 459 8.12 A NOTE ON IONIZED CLUSTER BEAM (ICB) DEPOSITION . 459 8.13 SUMMARY .................................................................................. 460 FURTHER READING .............................................................................. 460 REFERENCES .......................................................................................... 461 8.4.3 8.4.4 8.4.5

9

Atomistic Film Growth and Some Growth-Related Film Properties ............................................................................ 4729.1 9.2 INTRODUCTION ........................................................................ 472 CONDENSATION AND NUCLEATION ................................... 477 9.2.1 Surface Mobility ............................................................ 477 9.2.2 Nucleation ..................................................................... 478 Nucleation Density ........................................................ 480 Modification of Nucleation Density .............................. 482 9.2.3 Growth of Nuclei ........................................................... 483 9.2.4 Condensation Energy .................................................... 486 INTERFACE FORMATION ........................................................ 487 9.3.1 Abrupt Interface ............................................................ 487 Mechanical Interlocking Interface ................................ 488

9.3

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xxi

9.4

9.5

9.6

9.3.2 Diffusion Interface ........................................................ 489 9.3.3 Compound Interface ...................................................... 490 9.3.4 Pseudodiffusion (Graded or Blended) Interface .... 492 9.3.5 Modification of Interfaces ............................................. 493 9.3.6 Characterization of Interfaces and Interphase Material 494 FILM GROWTH .......................................................................... 496 9.4.1 Columnar Growth Morphology..................................... 497 Structure-Zone Model (SZM) of Growth ................. 498 9.4.2 Substrate Surface Morphology Effects on Film Growth502 Surface Coverage ...................................................... 503 Pinholes and Nodules ............................................... 504 9.4.3 Modification of Film Growth ........................................ 505 Substrate Surface Morphology ................................. 505 Angle-of-Incidence ................................................... 505 Modification of Nucleation during Growth .............. 505 Energetic Particle Bombardment .............................. 506 Mechanical Disruption ............................................. 509 9.4.4 Lattice Defects and Voids ............................................. 509 9.4.5 Film Density .................................................................. 510 9.4.6 Residual Film Stress ...................................................... 510 9.4.7 Crystallographic Orientation ......................................... 514 Epitaxial Film Growth .............................................. 514 Amorphous Film Growth.......................................... 515 Metastable or Labile Materials ................................. 516 9.4.8 Gas Incorporation .......................................................... 516 REACTIVE AND QUASI-REACTIVE DEPOSITION OF FILMS OF COMPOUND MATERIALS.................................................. 517 9.5.1 Chemical Reactions ....................................................... 518 Reaction Probability ................................................. 518 Reactant Availability ................................................ 520 9.5.2 Plasma Activation.......................................................... 521 9.5.3 Bombardment Effects on Chemical Reactions.............. 521 9.5.4 Getter Pumping During Reactive Deposition................ 522 9.5.5 Particulate Formation .................................................... 523 POST DEPOSITION PROCESSING AND CHANGES ............. 523 9.6.1 Topcoats ........................................................................ 523 9.6.2 Chemical and Electrochemical Treatments ................... 525 9.6.3 Mechanical Treatments ................................................. 526 9.6.4 Thermal Treatments ...................................................... 527 9.6.5 Ion Bombardment.......................................................... 528 9.6.6 Post-Deposition Changes .............................................. 529 Adhesion (See Ch. 11) .............................................. 529 Microstructure .......................................................... 529 Void Formation......................................................... 529

xxii

Handbook of Physical Vapor Deposition (PVD) ProcessingElectrical Resistivity ................................................. 531 Electromigration ....................................................... 531 9.7 DEPOSITION OF UNIQUE MATERIALS AND STRUCTURES 533 9.7.1 Metallization .................................................................. 533 9.7.2 Transparent Electrical Conductors ................................ 535 9.7.3 Low Emissivity (Low-E) Coatings ................................ 536 9.7.4 Permeation and Diffusion Barrier Layers ..................... 537 9.7.5 Porous Films .................................................................. 537 9.7.6 Composite (Two Phase) Films ...................................... 537 9.7.7 Intermetallic Films ........................................................ 539 9.7.8 Diamond and Diamond-Like Carbon (DLC) Films ...... 539 9.7.9 Hard Coatings ................................................................ 541 9.7.10 PVD Films as Basecoats ................................................ 543 9.8 SUMMARY .................................................................................. 544 FURTHER READING .............................................................................. 544 REFERENCES .......................................................................................... 545

10 Film Characterization and Some Basic Film Properties . 56910.1 10.2 10.3 INTRODUCTION ........................................................................ 569 OBJECTIVES OF CHARACTERIZATION ............................... 571 TYPES OF CHARACTERIZATION ........................................... 571 10.3.1 Precision and Accuracy ................................................. 572 10.3.2 Absolute Characterization ............................................. 573 10.3.3 Relative Characterization .............................................. 573 10.3.4 Functional Characterization .......................................... 573 10.3.5 Behavorial Characterization .......................................... 574 10.3.6 Sampling ........................................................................ 574 STAGES AND DEGREE OF CHARACTERIZATION.............. 575 10.4.1 In Situ Characterization ................................................. 575 10.4.2 First Check .................................................................... 575 10.4.3 Rapid Check .................................................................. 576 10.4.4 Postdeposition Behavior ................................................ 577 10.4.5 Extensive Check ............................................................ 578 10.4.6 Functional Characterization .......................................... 578 10.4.7 Stability Characterization .............................................. 578 10.4.8 Failure Analysis ............................................................. 579 10.4.9 Specification of Characterization Techniques ............... 579 SOME FILM PROPERTIES ........................................................ 580 10.5.1 Residual Film Stress ...................................................... 580 10.5.2 Thickness ....................................................................... 583 10.5.3 Density ........................................................................... 585 10.5.4 Porosity, Microporosity, and Voids .............................. 586 10.5.5 Optical Properties .......................................................... 589 Optical Reflectance and Emittance ........................... 590 Color ......................................................................... 593

10.4

10.5


xxiii

Mechanical Properties ................................................... 594 Elastic Modulus ........................................................ 594 Hardness ................................................................... 595 Wear Resistance........................................................ 595 Friction ...................................................................... 596 10.5.7 Electrical Properties ...................................................... 596 Resistivity and Sheet Resistivity .............................. 596 Temperature Coefficient of Resistivity (TCR) ......... 597 Electrical Contacts .................................................... 597 10.5.8 Chemical Stability ......................................................... 598 Chemical Etch rate .................................................... 598 Corrosion Resistance ................................................ 598 10.5.9 Barrier Properties .......................................................... 599 Diffusion Barriers ..................................................... 599 Permeation Barriers .................................................. 600 10.5.10 Elemental Composition ................................................. 600 X-ray Fluorescence (XRF) ....................................... 601 Rutherford Backscatter (RBS) Analysis ................... 603 Electron Probe X-ray Microanalysis (EPMA) and SEM-EDAX .......................................................... 606 Solution (Wet Chemical) Analysis ........................... 607 10.5.11 Crystallography and Texture ......................................... 607 10.5.12 Surface, Bulk and Interface Morphology ...................... 607 Transmission Electron Microscopy (TEM) and Scanning Transmission Electron Microscopy (STEM) ............................................. 607 10.5.13 Incorporated gas ............................................................ 608 10.6 SUMMARY .................................................................................. 608 FURTHER READING .............................................................................. 608 REFERENCES .......................................................................................... 609

11 Adhesion and Deadhesion .................................................. 61611.1 11.2 INTRODUCTION ........................................................................ 616 ORIGIN OF ADHESION AND ADHESION FAILURE (DEADHESION) .......................................................................... 617 11.2.1 Chemical Bonding ......................................................... 617 11.2.2 Mechanical Bonding ..................................................... 617 11.2.3 Stress, Deformation, and Failure ................................... 618 11.2.4 Fracture and Fracture Toughness .................................. 619 11.2.5 Liquid Adhesion ............................................................ 620 Surface Energy ......................................................... 621 Acidic-Basic Surfaces ............................................... 621 Wetting and Spreading ............................................. 621 Work of Adhesion .................................................... 622

xxiv

Handbook of Physical Vapor Deposition (PVD) ProcessingADHESION OF ATOMISTICALLY DEPOSITIED INORGANIC FILMS........................................................................................... 622 11.3.1 Condensation and Nucleation ........................................ 623 Nucleation Density ................................................... 623 11.3.2 Interfacial Properties that Affect Adhesion ................... 623 11.3.2 Types of Interfaces ........................................................ 623 11.3.2 Interphase (Interfacial) Material .................................... 624 11.3.3 Film Properties that Affect Adhesion ............................ 625 Residual Film Stress ................................................. 625 Film Morphology, Density and Mechanical Properties .......................................... 625 Flaws ......................................................................... 626 Lattice Defects and Gas Incorporation ..................... 626 Pinholes and Porosity ............................................... 627 Nodules ..................................................................... 627 11.3.4 Substrate Properties that Affect Adhesion .................... 627 11.3.5 Post-Deposition Changes that Can Improve Adhesion . 628 11.3.6 Post-Deposition Processing to Improve Adhesion ........ 628 Ion Implantation ....................................................... 628 Heating ...................................................................... 629 Mechanical Deformation .......................................... 629 11.3.7 Deliberately Non-Adherent Interfaces .......................... 629 ADHESION FAILURE (DEADHESION) ................................... 629 11.4.1 Spontaneous Failure ...................................................... 630 11.4.2 Externally Applied Mechanical StressTensile and Shear .................................................................. 631 11.4.3 Chemical and Galvanic (Electrochemical) Corrosion ... 633 11.4.4 Diffusion to the Interface .............................................. 634 11.4.5 Diffusion Away from the Interface ............................... 634 11.4.6 Reaction at the Interface ................................................ 634 11.4.7 Fatigue Processes .......................................................... 635 11.4.8 Subsequent Processing .................................................. 635 11.4.9 Storage and In-Service .................................................. 636 11.4.10 Local Adhesion FailurePinhole Formation ............... 636 ADHESION TESTING ................................................................ 636 11.5.1 Adhesion Test Program ................................................. 637 11.5.2 Adhesion Tests .............................................................. 637 Mechanical Pull (Tensile, Peel) Tests ...................... 638 Mechanical Shear Tests ............................................ 640 Scratch, Indentation, Abrasion, and Wear Tests ...... 640 Mechanical Deformation .......................................... 641 Stress Wave Tests ..................................................... 641 Fatigue Tests ............................................................. 641 Other Adhesion Tests ............................................... 642

11.3

11.4

11.5


xxv

Non-Destructive Testing ............................................... 642 Acoustic Imaging ...................................................... 642 Scanning Thermal Microscopy (SThM) ................... 643 11.5.4 Accelerated Testing ....................................................... 643 11.6 DESIGNING FOR GOOD ADHESION ...................................... 644 11.6.1 Film Materials, Glue Layers, and Layered Structures 645 11.6.2 Special Interfacial Regions............................................ 646 Graded and Compliant Interfacial Regions .............. 646 Diffusion Barriers ..................................................... 646 11.6.3 Substrate Materials ........................................................ 647 Metals ....................................................................... 647 Oxides ....................................................................... 647 Semiconductors ........................................................ 648 Polymers ................................................................... 649 11.7 FAILURE ANALYSIS ................................................................. 650 11.8 SUMMARY .................................................................................. 650 FURTHER READING .............................................................................. 651 REFERENCES .......................................................................................... 652

12 Cleaning ............................................................................... 66412.1 12.2 INTRODUCTION ........................................................................ 664 GROSS CLEANING .................................................................... 667 12.2.1 Stripping ........................................................................ 667 12.2.2 Abrasive Cleaning ......................................................... 667 12.2.3 Chemical Etching .......................................................... 670 12.2.4 Electrocleaning .............................................................. 671 12.2.5 Fluxing........................................................................... 672 12.2.6 Deburring ...................................................................... 672 SPECIFIC CLEANING ................................................................ 672 12.3.1 Solvent Cleaning ........................................................... 673 Water ......................................................................... 673 Petroleum Distillate Solvents ................................... 674 Chlorinated and Chlorofluorocarbon (CFC) Solvents 674 Alternative to CFC Solvents ..................................... 677 Supercritical Fluids ................................................... 678 Semi-Aqueous Cleaners ........................................... 679 12.3.2 Saponifiers, Soaps, and Detergents ............................... 681 12.3.3 Solution Additives ......................................................... 682 12.3.4 Reactive Cleaning.......................................................... 684 Oxidative CleaningFluids ..................................... 684 Oxidative CleaningGaseous ................................. 686 Hydrogen (Reduction) Cleaning ............................... 688 12.3.5 Reactive Plasma Cleaning and Etching ......................... 688

12.3

xxvi


12.4

APPLICATION OF FLUIDS ....................................................... 692 12.4.1 Soaking .......................................................................... 693 12.4.2 Agitation ........................................................................ 693 Hydrosonic Cleaning ................................................ 694 12.4.3 Vapor Condensation ...................................................... 694 12.4.4 Spraying ........................................................................ 694 12.4.5 Ultrasonic Cleaning ....................................................... 695 12.4.6 Megasonic Cleaning ...................................................... 699 12.4.7 Wipe-Clean .................................................................... 700 12.5 REMOVAL OF PARTICULATE CONTAMINATION ............. 700 12.5.1 Blow-Off ....................................................................... 700 12.5.2 Mechanical Disturbance ................................................ 701 12.5.3 Fluid Spraying ............................................................... 701 12.5.4 Ultrasonic and Megasonic Cleaning ............................. 701 12.5.5 Flow-Off ........................................................................ 702 12.5.6 Strippable Coatings ....................................................... 702 12.6 RINSING ...................................................................................... 702 12.6.1 Hard Water and Soft Water ........................................... 703 12.6.2 Pure and Ultrapure Water .............................................. 703 12.6.3 Surface Tension ............................................................. 707 12.7 DRYING, OUTGASSING, AND OUTDIFFUSION ................... 707 12.7.1 Drying ............................................................................ 707 12.7.2 Outgassing ..................................................................... 709 12.7.3 Outdiffusion .................................................................. 710 12.8 CLEANING LINES ...................................................................... 711 12.9 HANDLING AND STORAGE/TRANSPORTATION................ 713 12.9.1 Handling ........................................................................ 713 12.9.2 Storage/Transportation .................................................. 715 Passive Storage Environments.................................. 715 Active Storage Environments ................................... 716 Storage and Transportation Cabinets ........................ 716 12.10 EVALUATION AND MONITORING OF CLEANING............. 717 12.10.1 Behavior and Appearance ............................................. 717 12.10.2 Chemical Analysis ......................................................... 719 12.10.3 Particle Detection .......................................................... 720 12.11 IN SITU CLEANING ................................................................... 720 12.11.1 Plasma Cleaning ............................................................ 721 Ion Scrubbing ........................................................... 721 Reactive Plasma Cleaning/Etching ........................... 721 12.11.1 Reactive Ion Cleaning/Etching ...................................... 722 Reactive Cleaning in a Vacuum ............................... 723 12.11.2 Sputter Cleaning ............................................................ 724 12.11.3 Laser Cleaning ............................................................... 724 12.11.4 Photodesorption ............................................................. 725 12.11.5 Electron Desorption ....................................................... 725

Table of Contents

xxvii

12.12 CONTAMINATION OF THE FILM SURFACE ........................ 725 12.13 SAFETY ....................................................................................... 726 12.14 SUMMARY .................................................................................. 727 12.14.1 Cleaning Metals............................................................. 727 12.14.2 Cleaning Glasses and Ceramics .................................... 727 12.14.3 Cleaning Polymers ........................................................ 727 FURTHER READING .............................................................................. 727 REFERENCES .......................................................................................... 729

13 External Processing Environment .................................... 74413.1 13.2 INTRODUCTION ........................................................................ 744 REDUCTION OF CONTAMINATION ...................................... 745 13.2.1 Elimination of Avoidable Contamination ..................... 745 Housekeeping ........................................................... 745 Construction, Materials, and Furniture ..................... 746 Elimination of Vapors .............................................. 747 13.2.2 Containing Contamination-Producing Sources ......... 747 13.2.3 Static Charge ................................................................. 748 MATERIALS ............................................................................... 748 13.3.1 Cloth, Paper, Foils, etc. ................................................. 748 13.3.2 Containers, Brushes, etc. ............................................... 750 13.3.3 Chemicals ...................................................................... 750 13.3.4 Processing Gases ........................................................... 751 Dry Gases.................................................................. 751 High Pressure Gases ................................................. 752 Toxic and Flammable Gases..................................... 753 BODY COVERINGS ................................................................... 753 13.4.1 Gloves............................................................................ 754 13.4.2 Coats and Coveralls ....................................................... 756 13.4.3 Head and Face Coverings.............................................. 756 13.4.4 Shoe Coverings ............................................................. 756 13.4.5 Gowning Area ............................................................... 757 13.4.6 Personal Hygiene ........................................................... 757 PROCESSING AREAS ................................................................ 758 13.5.1 Mechanical Filtration .................................................... 759 13.5.2 Electronic and Electrostatic Filters ................................ 759 13.5.3 Humidity Control .......................................................... 760 13.5.4 Floor and Wall Coverings ............................................. 760 13.5.5 Cleanrooms.................................................................... 760 13.5.6 Soft-Wall Clean Areas................................................... 761 13.5.7 Cleanbenches ................................................................. 762 13.5.8 Ionizers .......................................................................... 762 13.5.9 Particle Count Measurement ......................................... 762 13.5.10 Vapor Detection ............................................................ 763

13.3

13.4

13.5

xxviii Handbook of Physical Vapor Deposition (PVD) Processing13.5.11 Reactive Gas Control ..................................................... 763 13.5.12 Microenvironments ....................................................... 763 13.5.13 Personnel Training ........................................................ 764 13.6 SUMMARY .................................................................................. 764 FURTHER READING .............................................................................. 764 REFERENCES .......................................................................................... 765

Appendix 1: Reference Material ............................................. 768A1.1 A1.2 A1.3 A1.4 A1.5 A1.6 A1.7 TECHNICAL JOURNALS AND ABBREVIATIONS ................ 768 PERIODICALS AND ABBREVIATIONS .................................. 770 OTHER ......................................................................................... 770 BUYERS GUIDES, AND PRODUCT AND SERVICES ........... 771 DIRECTORIES ......................................................................... 771 SOCIETIES, ASSOCIATIONS, AND OTHER ........................... 772 ORGANIZATIONS ................................................................... 772 PUBLISHERS .............................................................................. 777 WEB SITE INDEX ....................................................................... 779

Appendix 2: Transfer of Technology from R&D to Manufacturing .................................................................... 782Stages of Technology Transfer ..................................... 783 Organization .................................................................. 783 Management ............................................................. 783 R&D group ............................................................... 784 Analytical Support Group ......................................... 784 Manufacturing Development .................................... 784 Manufacturing .......................................................... 785 Quality Control ......................................................... 785 Other Specialties ....................................................... 785 A2.3 R&D and Manufacturing Environments .................... 786 A2.4 Communication ............................................................. 788 A2.5 Styles of Thinking ......................................................... 788 A2.6 Training ......................................................................... 789 REFERENCES .......................................................................................... 790 A2.1 A2.2

Glossary of Terms and Acronyms used in Surface Engineering ........................................................... 791 Index .......................................................................................... 906

Introduction

29

1 Introduction

1.1

SURFACE ENGINEERING

Surface engineering involves changing the properties of the surface and near-surface region in a desirable way. Surface engineering can involve an overlay process or a surface modification process. In overlay processes a material is added to the surface and the underlying material (substrate) is covered and not detectable on the surface. A surface modification process changes the properties of the surface but the substrate material is still present on the surface. For example, in aluminum anodization, oxygen reacts with the anodic aluminum electrode of an electrolysis cell to produce a thick oxide layer on the aluminum surface. Table 1-1 shows a number of overlay and surface modification processes that can be used for surface engineering. Each process has its advantages, disadvantages and applications. In some cases surface modification processes can be used to modify the substrate surface prior to depositing a film or coating. For example a steel surface can be hardened by plasma nitriding (ionitriding) prior to the deposition of a hard coating by a PVD process. In other cases, a surface modification process can be used to change the properties of an overlay coating. For example, a sputter-deposited coating on an aircraft turbine blade can be shot peened to densify the coating and place it into compressive stress. 29

30


Table 1-1. Processes for Surface Engineering Atomistic/Moleular DepositionElectrolytic Environment Electroplating Electroless plating Displacement plating Electrophoretic deposition Vacuum Environment Vacuum evaporation Ion beam sputter deposition Ion beam assisted deposition (IBAD) Laser vaporization Hot-wire and low pressure CVD Jet vapor deposition Ionized cluster beam deposition Plasma Environment Sputter deposition Arc vaporization Ion Plating Plasma enhanced (PE)CVD Plasma polymerization Chemical Vapor Environment Chemical vapor deposition (CVD) Pack cementation Chemical Solution Spray pyrolysis Chemical reduction

Bulk CoatingsWetting Processes Dip coating Spin coating Painting Fusion Coatings Thick films Enameling Sol-gel coatings Weld overlay Solid Coating Cladding Gilding

Surface ModificationChemical Conversion Wet chemical solution (dispersion & layered) Gaseous (thermal) Plasma (thermal) Electrolytic Environment Anodizing Ion substitution Mechanical Shot peening Work hardening Thermal Treatment Thermal stressing Ion Implantation Ion beam Plasma immersion ion implantation Roughening and Smoothing Chemical Mechanical Chemical-mechanical polishing Sputter texturing Enrichment and Depletion Thermal Chemical

Particulate DepositionThermal Spray Flame Spray Arc-wire spray Plasma spraying D-gun High-vel-oxygen-fuel (HVOF) Impact Plating

Introduction

31

An atomistic film deposition process is one in which the overlay material is deposited atom-by-atom. The resulting film can range from single crystal to amorphous, fully dense to less than fully dense, pure to impure, and thin to thick. Generally the term thin film is applied to layers which have thicknesses on the order of several microns or less (1 micron = 10-6 meters) and may be as thin as a few atomic layers. Often the properties of thin films are affected by the properties of the underlying material (substrate) and can vary through the thickness of the film. Thicker layers are generally called coatings. Atomistic deposition process can be done in a vacuum, plasma, gaseous, or electrolytic environment.

1.1.1

Physical Vapor Deposition (PVD) Processes

Physical Vapor Deposition (PVD) processes (often just called thin film processes) are atomistic deposition processes in which material is vaporized from a solid or liquid source in the form of atoms or molecules, transported in the form of a vapor through a vacuum or low pressure gaseous (or plasma) environment to the substrate where it condenses. Typically, PVD processes are used to deposit films with thicknesses in the range of a few nanometers to thousands of nanometers; however they can also be used to form multilayer coatings, graded composition deposits, very thick deposits and freestanding structures. The substrates can range in size from very small to very large such as the 10' x 12' glass panels used for architectural glass. The substrates can range in shape from flat to complex geometries such as watchbands and tool bits. Typical PVD deposition rates are 10100 (110 nanometers) per second. PVD processes can be used to deposit films of elements and alloys as well as compounds using reactive deposition processes. In reactive deposition processes, compounds are formed by the reaction of depositing material with the ambient gas environment such as nitrogen (e.g. titanium nitride, TiN) or with a co-depositing material (e.g. titanium carbide, TiC). Quasi-reactive deposition is the deposition of films of a compound material from a compound source where loss of the more volatile species or less reactive species during the transport and condensation process, is compensated for by having a partial pressure of reactive gas in the deposition environment. For example, the quasi-reactive sputter deposition of ITO (indium-tin-oxide) from an ITO sputtering target using a partial pressure of oxygen in the plasma.

32


The main categories of PVD processing are vacuum evaporation, sputter deposition, and ion plating as depicted in Fig. 1-1.

Figure 1-1. PVD processing techniques: (1a) vacuum evaporation, (1b and 1c) sputter deposition in a plasma environment, (1d) sputter deposition in a vacuum, (1e) ion plating in a plasma environment with a thermal evaporation source, (1f) ion plating with a sputtering source, (1g) ion plating with an arc vaporization source and, (1h) Ion Beam Assisted Deposition (IBAD) with a thermal evaporation source and ion bombardment from an ion gun.

Vacuum DepositionVacuum deposition (Ch. 5) which is sometimes called vacuum evaporation is a PVD process in which material from a thermal vaporization source reaches the substrate with little or no collision with gas molecules in the space between the source and substrate . The trajectory of the vaporized material is line-of-sight. The vacuum environment also provides the ability to reduce gaseous contamination in the deposition system to a low level. Typically, vacuum deposition takes place in the gas pressure range of 10-5 Torr to 10-9 Torr depending on the level of gaseous contamination that can be tolerated in the deposition system. The thermal

Introduction

33

vaporization rate can be very high compared to other vaporization methods. The material vaporized from the source has a composition which is in proportion to the relative vapor pressures of the material in the molten source material. Thermal evaporation is generally done using thermally heated sources such as tungsten wire coils or by high energy electron beam heating of the source material itself. Generally the substrates are mounted at an appreciable distance away from the evaporation source to reduce radiant heating of the substrate by the vaporization source. Vacuum deposition is used to form optical interference coatings, mirror coatings, decorative coatings, permeation barrier films on flexible packaging materials, electrically conducting films, wear resistant coatings, and corrosion protective coatings.

Sputter DepositionSputter deposition (Ch. 6) is the deposition of particles vaporized from a surface (target), by the physical sputtering process. Physical sputtering is a non-thermal vaporization process where surface atoms are physically ejected from a solid surface by momentum transfer from an atomic-sized energetic bombarding particle which is usually a gaseous ion accelerated from a plasma. This PVD process is sometimes just called sputtering, i.e. sputtered films of which is an improper term in that the film is not being sputtered. Generally the source-to-substrate distance is short compared to vacuum deposition. Sputter deposition can be performed by energetic ion bombardment of a solid surface (sputtering target) in a vacuum using an ion gun or low pressure plasma (10 at% for light elements. Mass resolution is poor for mixtures of heavy elements, and surface morphology can distort the analysis results since the scattering angle can change over the surface.

Substrate (Real) Surfaces and Surface Modification Secondary Ion Mass Spectrometry (SIMS)

75

Secondary Ion Mass Spectrometry (SIMS) is a surface analytical technique that utilizes the sputtered positive and negative ions that are ejected from a grounded surface by ion bombardment. The ejected ions are mass analyzed in a mass spectrometer.[25]-[28] The ions may be in an atomic or molecular form and may be multiply charged. For instance, the sputtering of aluminum with argon, yields Al+, Al2+, Al 3+ Al2+ Al3+ and Al4+. When molecules are present, the sputtering produces a complex distribution of species (cracking pattern). The technique can analyze trace elements in the ppm (parts per million) and ppb (parts per billion) range. The degree of ionization of the ejected particles is very sensitive to surrounding atoms (matrix effect) and the presence of more electronegative materials such as oxygen. For example, the aluminum ion yield per incident ion from an oxide-free surface of aluminum is 0.007, but if the surface is covered with oxygen the yield is 0.7. To quantify the analysis requires the development of standards. The problem of low ion yield and matrix effect can be avoided by post-vaporization ionization of the sputtered species. This technique is called Secondary Neutral Mass Spectrometry (SNMS). Since the detected species are sputtered from the surface, the technique is very surface-sensitive. The matrix effect and the ability of atoms to move about on the surface makes sputter profiling through an interface with SIMS very questionable. Since ion beams cannot be focused as finely as electron beams the lateral resolution of SIMS is not as good as that of AES.

2.4.2

Phase Composition and Microstructure

In some applications the crystallographic phase composition, grain size, and lattice defect structure of a surface can be important. Phase composition is generally determined by diffraction methods.

X-ray DiffractionWhen a crystalline film is irradiated with short wavelength X-rays the crystal planes can satisfy the Bragg diffraction conditions giving a diffraction pattern. This diffraction pattern can be used to determine the

76


crystal plane spacing (and thus the crystal phase), preferential orientation of the crystals in the structure, lattice distortion, and crystallite size.[29]

Electron Diffraction (RHEED, TEM)The diffraction of electrons can be used to determine the lattice structure.[30] The diffraction can be of a bulk (3-dimensional ) material or can be from a surface. Reflection High Energy Electron Diffraction (RHEED) is used in epitaxial film growth to monitor film structure during deposition. Electron diffraction can be used in conjunction with Transmission Electron Microscopy (TEM) to identify crystallographic phases seen with the TEM. This application is called electron microdiffraction or Selected Area Diffraction or TEM-SAD.[31]

2.4.3

Molecular Composition and Chemical Bonding Infrared (IR) Spectroscopy

A polymer is a large molecule formed by bonding together numerous small molecular units, called monomers. The most common polymeric materials are the organic polymers which are based on carbon-hydrogen (hydrocarbon) monomers which may or may not contain other atoms such as nitrogen, oxygen, metals, etc. In building a polymer, many bonds are formed which have various strengths and separations (bond lengths) between atoms. Infrared spectroscopy uses the adsorption of infrared radiation* by the molecular bonds to identify the bond types which can absorb energy by oscillating, vibrating and rotating.[32] The adsorption spectrum is generated by having an continuum spectrum of infrared radiation pass through the sample and comparing the emerging spectra to that of a reference beam that has not passed through the sample. In dispersive infrared spectrometry a monochromator separates light from a broad-band source into individual narrow bands. Each narrow band is then chosen by a mechanical slit arrangement and is passed through the sample. In Fourier Transform infrared spectrometry (FT-IR) the need for a mechanical slit is

*Infrared radiation is electromagnetic radiation having a wavelength greater than 0.75 microns.

Substrate (Real) Surfaces and Surface Modification

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eliminated by frequency modulating one beam and using interferometry to choose the infrared band. This technique gives higher frequency resolution and a faster analysis time than the dispersive method. By having a spectrum of adsorption vs infrared frequency, the type of material can often be identified. If the material cannot be identified directly, then the types of individual bonds can be identified giving a good indication of the type of polymer material. It can also be used to characterize polymer substrate materials as to their primary composition and such polymer additives as plasticizers, anti-slip agents, etc. The IR spectrum of many materials are cataloged and a computer search is often used to identify the material. Sample collection is an important aspect of IR analysis. Bulk materials can be analyzed but if they are thick, the sensitivity of the technique suffers. Often the sample is prepared as a thin film on the surface of an IR transparent material (window) such as potassium bromide (KBr). The film to be analyzed can be formed by condensation of a vapor on the window, dissolving the sample in a solvent, then drying to a film or by solvent extraction from a bulk material followed by evaporation of the solution on an IR window. Figure 2-8 shows an IR spectra of a phythale plasticizer extracted from a vinyl material by extraction using acetone. This type of plasticizer is often used in polymers to make them easier to mold and is a source of contamination by outgassing, outdiffusion and extraction of the low molecular weight materials by solvents such as alcohol (Sec. 13.3.1). Reflection techniques can often be used to analyze surface layers without using solvent extraction. A reflection technique is shown in Fig. 8 where the sample is sandwiched between plates of a material having a high index of refraction in the infrared so as to have a high reflectivity from the surface. In PVD technology, IR spectroscopy is used in a comparative manner to insure that the substrate material is consistent. Quite often it is found that a specific polymer material from one supplier will differ from that of another in the amount of low-molecular weight constituents present. This can affect the outgassing and outdiffusion of material from the bulk during processing and the postdeposition behavior of the film surface.* The

*The producer metallized web materials for labeling applications but sometimes the users complained that they couldnt print on the metallized surface. The problem was the low molecular weight species in the web was diffusing through the metallization and forming a low-energy polymer surface on the metallization. The manufacturer needed to have a better web material.

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low-molecular weight materials can originate from an additive material or from differing curing of the monomer materials. A procedure to characterize a polymeric material might consist of: A swipe or solvent clean of the surface of the asreceived material to determine if there is a surface layer of lo

handbook of physical vapor deposition

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