Handbook of Deposition Technologies for Films and Coatings-Rointan F.Bunshah

Electronic Materials and Process TechnologyHANDBOOK OF DEPOSITION TECHNOLOGIES FOR FILMS AND COATINGS, Second Edition: edited by Rointan F.. Bunshah CHEMICAL VAPOR DEPOSITION FOR MICROEL

DEPOSITION TECHNOLOGIES FOR FILMS AND COATINGS

Science, Technology

and Applications Second Edition

np NOYES PUBLICATIONS Park Ridge, New Jersey, U.S.A.

Edited by

Rointan F Bunshah

University of California at Los Angeles

Los Angeles, California

utilized in any form or by any means,

elec-tronic 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: 93-30751

ISBN: 0-8155-1337-2

Printed in the United States

Published in the United States of America by

Noyes Publications

Mill Road, Park Ridge, New Jersey 07656

10 9 8 7 6 5 4 3 2 1

Library of Congress Cataloging-in-Publication Data

Handbook of deposition technologies for films and coatings / edited by Rointan F Bunshah 2nd ed.

This volume is dedicated to Professor John Thornton for his many pioneering contributions to thin film science and technology which have inspired so many of the scientists and engineers working in this field.

vii

Electronic Materials and Process Technology

HANDBOOK OF DEPOSITION TECHNOLOGIES FOR FILMS AND COATINGS, Second Edition: edited by Rointan F Bunshah

CHEMICAL VAPOR DEPOSITION FOR MICROELECTRONICS: by Arthur Sherman SEMICONDUCTOR MATERIALS AND PROCESS TECHNOLOGY HANDBOOK: edited by Gary E McGuire

HYBRID MICROCIRCUIT TECHNOLOGY HANDBOOK: by James J Licari and Leonard R Enlow

HANDBOOK OF THIN FILM DEPOSITION PROCESSES AND TECHNIQUES: edited by Klaus

K Schuegraf

IONIZED-CLUSTER BEAM DEPOSITION AND EPITAXY: by Toshinori Takagi

DIFFUSION PHENOMENA IN THIN FILMS AND MICROELECTRONIC MATERIALS: edited by Devendra Gupta and Paul S Ho

HANDBOOK OF CONTAMINATION CONTROL IN MICROELECTRONICS: edited by Donald

HANDBOOK OF CHEMICAL VAPOR DEPOSITION: by Hugh O Pierson

DIAMOND FILMS AND COATINGS: edited by Robert F Davis

ELECTRODEPOSITION: by Jack W Dini

HANDBOOK OF SEMICONDUCTOR WAFER CLEANING TECHNOLOGY: edited by Werner Kern

CONTACTS TO SEMICONDUCTORS: edited by Leonard J Brillson

HANDBOOK OF MULTILEVEL METALLIZATION FOR INTEGRATED CIRCUITS: edited by Syd R Wilson, Clarence J Tracy, and John L Freeman, Jr.

HANDBOOK OF CARBON, GRAPHITE, DIAMONDS AND FULLERENES: by Hugh O Pierson

Ceramic and Other Materials—Processing and Technology

SOL-GEL TECHNOLOGY FOR THIN FILMS, FIBERS, PREFORMS, ELECTRONICS AND SPECIALTY SHAPES: edited by Lisa C Klein

FIBER REINFORCED CERAMIC COMPOSITES: edited by K S Mazdiyasni

ADVANCED CERAMIC PROCESSING AND TECHNOLOGY, Volume 1: edited by Jon G P Binner

FRICTION AND WEAR TRANSITIONS OF MATERIALS: by Peter J Blau

SHOCK WAVES FOR INDUSTRIAL APPLICATIONS: edited by Lawrence E Murr SPECIAL MELTING AND PROCESSING TECHNOLOGIES: edited by G K Bhat

CORROSION OF GLASS, CERAMICS AND CERAMIC SUPERCONDUCTORS: edited by David E Clark and Bruce K Zoitos

HANDBOOK OF INDUSTRIAL REFRACTORIES TECHNOLOGY: by Stephen C Carniglia and Gordon L Barna

CERAMIC FILMS AND COATINGS: edited by John B Wachtman and Richard A Haber

Related Titles

ADHESIVES TECHNOLOGY HANDBOOK: by Arthur H Landrock

HANDBOOK OF THERMOSET PLASTICS: edited by Sidney H Goodman

SURFACE PREPARATION TECHNIQUES FOR ADHESIVE BONDING: by Raymond F Wegman

FORMULATING PLASTICS AND ELASTOMERS BY COMPUTER: by Ralph D Hermansen HANDBOOK OF ADHESIVE BONDED STRUCTURAL REPAIR: by Raymond F Wegman and Thomas R Tullos

CARBON–CARBON MATERIALS AND COMPOSITES: edited by John D Buckley and Dan

D Edie

CODE COMPLIANCE FOR ADVANCED TECHNOLOGY FACILITIES: by William R Acorn

Los Angeles, California

Arthur Sherman

ConsultantPalo Alto, California

Rointan F Bunshah

Department of Materials Science and

Engineering

University of California at Los Angeles

Los Angeles, California

Coordinated Science Laboratory

University of Illinois at

Urbana-Champaign

Urbana, Illinois

Bret L Halpern

Jet Process Corporation

New Haven, Connecticut

xiii

John A Thornton*

Coordinated Science Laboratory

University of Illinois at

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.

i x

A decade after the first edition of this volume was published, a secondedition is being brought out partly due to the excellent response to the firstedition and also to update the many improvements in deposition technologies,the mechanisms and applications

The entire volume has been extensively revised and contains 50% ormore new material Five entirely new chapters have been added Theorganization of the book has also been changed in the following respects:

1 Considerably more material has been added in Plasma

Assisted Vapor Deposition Processes

2 A new chapter on Metallurgical Coating Applications has

been added

The chapter in the first edition on Polymeric Coating techniques hasbeen omitted as it deserves a volume by itself Large topics such as coatingstechnology in microelectronics, diamond films, etc., have been treated inseparate volumes in this series

Although there are some new competing volumes dealing with selectedtopics on the materials science of thin films, this volume remains the onlycomprehensive treatment of the entire subject of Deposition Technology.Applications of films and coatings spans the entire gamut of science andtechnology Generic application areas include electronic, magnetic, optical,mechanical, chemical and decorative applications New deposition technolo-gies such as arc evaporation, unbalanced magnetron sputtering, ion beamassisted deposition, and metal-organic CVD have come on stream for criticalapplications In this post cold war era, many economic solutions toengineering problems will necessarily involve coatings, e.g., battery materialsfor the emerging electric car industry

The core subjects are the basic technologies for the deposition of filmsand coatings These are the Physical Vapor Deposition (PVD) Processesconsisting of Evaporation, Sputtering, and Ion Plating; Chemical VaporDeposition (CVD) and Plasma-Assisted Chemical Vapor Deposition (PACVD);Electrodeposition and Electroless Plating; Thermal Spraying, Plasma Spray-ing and Detonation Gun Technologies Chapters on other subjects common

to the above technologies are included These are: Adhesion of Coatings,Cleaning of Substrates, Role of Plasmas in Deposition Processes, Structure

of PVD Deposits, Growth and Structure of PVD Films, Mechanical andTribological Properties of PVD Deposits, Elemental and Structural Character-ization Techniques, and Metallurgical Coatings A relatively new develop-ment, Jet Vapor Deposition Process, was added as the last chapter in thebook during the page proof stage because of its novelty

We hope that this volume will be useful to the multitude of disciplinesrepresented by the workers in this field and provide a source for futuredevelopments

Los Angeles, California

June, 1993

Almost universally in high technology applications, a composite material

is used where the properties of the surface are intentionally different from those

of the core Thus, materials with surface coatings are used in the entire section of applications ranging from microelectronics, display devices, chemi-cal corrosion, tribology including cutting tools, high temperature oxidation/corrosion, solar cells, thermal insulation and decorative coatings (includingtoys, automobile components, watch cases, etc.)

cross-A large variety of materials is used to produce these coatings They aremetals, alloys, refractory compounds (e.g., oxides, nitrides, carbides),intermetallic compounds (e.g., GaAg) and polymers in single or multiplelayers The thickness of the coatings ranges from a few atom layers to millions

of atom layers The microstructure and hence the properties of the coatingscan be varied widely and at will, thus permitting one to design new materialsystems with unique properties (A material system is defined as thecombination of the substrate and coating.)

Historically, coating technology evolved and developed in the last 30years in several industries, i.e., decorative coatings, microelectronics andmetallurgical coatings They used similar techniques but only with thepassage of time have the various approaches reached a common frontierresulting in much useful cross-fertilization That very vital process isproceeding ever more strongly at this time

With this background in mind, a short course on Deposition gies and their applications was developed and given on five consecutiveoccasions in the last three years This volume is based on the material used

Technolo-in the course

x i

It comprises chapters dealing with the various coating techniques, theresulting microstructure, properties and applications The specific techniquescovered are evaporation, ion plating, sputtering, chemical vapor deposition,electrodeposition from aqueous solution, plasma and detonation gun coatingtechniques, and polymeric coatings In addition several other chapters areadded Plasmas are used in many of the deposition processes and therefore

a special chapter on this topic has been added Cleaning of the substrate andthe related topic of adhesion of the coating are common to many processesand a brief exposé of this topic is presented Characterization of the films, i.e.,composition, impurities, crystal structure and microstructure are essential tothe understanding of the various processes Two chapters dealing with thisarea are included Finally, a chapter on application of deposition techniques

in microelectronics is added to give one example of the use of several of thesetechniques in a specific area This volume represents a unique collection ofour knowledge on Deposition Technologies and their applications up to andincluding the state-of-the-art It is hoped that it will be very useful to students,practicing engineers and managerial personnel who have to learn about thisessential area of modern technology

Los Angeles, California

April 1982

x v

Contents

1 Deposition Technologies: An Overview 27

Rointan F Bunshah 1.0 THE MARKET 27

2.0 INTRODUCTION 28

3.0 AIM AND SCOPE 30

4.0 DEFINITIONS AND CONCEPTS 31

5.0 PHYSICAL VAPOR DEPOSITION (PVD) PROCESS TERMINOLOGY 32

6.0 CLASSIFICATION OF COATING PROCESSES 34

7.0 GAS JET DEPOSITION WITH NANO-PARTICLES 36

8.0 MICROSTRUCTURE AND PROPERTIES 38

9.0 UNIQUE FEATURES OF DEPOSITED MATERIALS AND GAPS IN UNDERSTANDING 40

10.0 CURRENT APPLICATIONS 41

10.1 Decorative/Functional Coating 41

10.2 High Temperature Corrosion 42

10.3 Environmental Corrosion 42

10.4 Friction and Wear 42

10.5 Materials Conservation 43

10.6 Cutting Tools 43

10.7 Nuclear Fuels 44

10.8 Biomedical Uses 44

10.9 Electrical Uses 44

11.0 “FRONTIER AREAS” FOR THE APPLICATION OF THE PRODUCTS OF DEPOSITION TECHNOLOGY 44

12.0 SELECTION CRITERIA 46

13.0 SUMMARY 48

APPENDIX 1: DEPOSITION PROCESS DEFINITIONS 49

Conduction and Diffusion Processes 49

Chemical processes 50

Wetting Process 50

Spraying Processes 51

REFERENCES 54

2 Plasmas in Deposition Processes 55

John A Thornton and Joseph E Greene 1.0 INTRODUCTION 55

2.0 PARTICLE MOTION 56

2.1 Mean Free Path and Collision Cross Sections 56

2.2 Free Electron Kinetic Energy in a Plasma 58

2.3 Electron Energy Distribution Functions 59

2.4 Collision Frequencies 61

3.0 COLLECTIVE PHENOMENA 68

3.1 Plasma Sheaths 69

3.2 Ambipolar Diffusion 74

3.3 Plasma Oscillations 75

4.0 PLASMA DISCHARGES 76

4.1 Introduction 76

4.2 Ionization Balances and the Paschen Relation 77

4.3 Cold Cathode Discharges 82

4.4 Magnetron Discharges 84

4.5 RF Discharges 85

5.0 PLASMA VOLUME REACTIONS 87

5.1 Introduction 87

5.2 Electron/Atom Interactions 87

5.3 Electron/Molecule Interactions 88

5.4 Metastable Species 90

5.5 Applications of Volume Reactions 92

6.0 SURFACE REACTIONS 93

6.1 Introduction 93

6.2 Ion Bombardment 93

6.3 Electron Bombardment 100

6.4 Glow Discharge Surface Cleaning and Activation 100

REFERENCES 103

3 Surface Preparation for Film and Coating Deposition

Processes 108

Donald M Mattox 1.0 INTRODUCTION 108

2.0 CONTAMINATION 110

2.1 Recontamination 111

3.0 ENVIRONMENT CONTROL 113

4.0 CLEANING PROCESSES 119

4.1 Particulate Removal 120

4.2 Abrasive Cleaning 121

4.3 Etch Cleaning 121

4.4 Fluxing 122

4.5 Alkaline Cleaners 122

4.6 Detergent Cleaning 122

4.7 Chelating Agents 123

4.8 Solvent Cleaning 123

4.9 Oxidation Cleaning 128

4.10 Volatilization Cleaning 130

4.11 Hydrogen Reduction Cleaning 130

4.12 Electrolytic Cleaning 131

5.0 DRYING AND OUTGASSING 132

6.0 MONITORING OF CLEANING 133

7.0 IN SITU CLEANING 134

7.1 Ion Scrubbing 134

8.0 PLASMAS 134

8.1 Generation of Plasmas 135

8.2 Plasma Chemistry 140

8.3 Bombardment Effects on Surfaces 141

8.4 Sputter Cleaning and Etching 143

9.0 STORAGE AND HANDLING 147

10.0 ACTIVATION AND SENSITIZATION 148

11.0 SURFACE MODIFICATION 150

12.0 PASSIVATION AND PRESERVATION 151

13.0 SAFETY 152

REFERENCES 152

4 Evaporation: Processes, Bulk Microstructures and Mechanical Properties 157

Rointan F Bunshah 1.0 GENERAL INTRODUCTION 157

2.0 SCOPE 159

3.0 PVD PROCESSES 159

3.1 Preamble 159

3.2 PVD Processes 160

3.3 Advantages and Limitations 165

4.0 THEORY AND MECHANISMS 166

4.1 Vacuum Evaporation 166

5.0 EVAPORATION PROCESS AND APPARATUS 169

5.1 The System 169

6.0 EVAPORATION SOURCES 172

6.1 General Considerations 172

6.2 Resistance Heated Sources 175

6.3 Sublimation Sources 176

6.4 Evaporation Source Materials 178

6.5 Induction Heated Sources 180

6.6 Electron Beam Heated Sources 181

6.7 Arc Evaporation 189

7.0 LASER INDUCED EVAPORATION/LASER ABLATION/PULSED LASER DEPOSITION (PLD) 192

8.0 DEPOSITION RATE MONITORS AND PROCESS CONTROL 194

8.1 Monitoring of the Vapor Stream 194

8.2 Monitoring of Deposited Mass 196

8.3 Monitoring of Specific Film Properties 196

8.4 Evaporation Process Control 199

9.0 DEPOSITION OF VARIOUS MATERIALS 201

9.1 Deposition of Metals and Elemental Semiconductors 201

9.2 Deposition of Alloys 201

9.3 Deposition of Intermetallic Compounds 205

9.4 Deposition of Refractory Compounds 209

9.5 Reactive Evaporation Process 213

9.6 Activated Reactive Evaporation (ARE) 213

9.7 Materials Synthesized by Evaporation-based Processes 223

10.0 MICROSTRUCTURE OF PVD CONDENSATES 224

10.1 Microstructure Evolution 224

10.2 Texture 236

10.3 Residual Stresses 237

10.4 Defects 237

11.0 PHYSICAL PROPERTIES OF THIN FILMS 241

12.0 MECHANICAL AND RELATED PROPERTIES 241

12.1 Mechanical Properties 241

13.0 PURIFICATION OF METALS BY EVAPORATION 256

APPENDIX 258

On Progress in Scientific Investigations in the Field of Vacuum Evaporation in the Soviet Union 258

REFERENCES 261

5 Sputter Deposition Processes 275

John A Thornton and Joseph E Greene 1.0 INTRODUCTION 275

1.1 Sputter Deposition Systems 278

1.2 Sputter-Deposition Applications 279

1.3 Process Implementation 282

1.4 History of Sputter Deposition and Background Reading 283

2.0 SPUTTERING MECHANISMS 284

2.1 Sputtering Rate 285

2.2 Momentum Exchange 289

2.3 Alloys and Compounds 292

2.4 Sputtering with Reactive Species 295

2.5 The Nature of Sputtered Species 296

2.6 Energy Distribution of Sputtered Species 298

3.0 SPUTTER DEPOSITION TECHNIQUES 301

3.1 Planar Diode and the DC Glow Discharge 301

3.2 Triode Discharge Devices 305

3.3 Magnetrons 306

3.4 RF Sputtering 318

3.5 Ion-Beam Sputtering 327

4.0 SPUTTER DEPOSITION MODES 328

4.1 Reactive Sputtering 328

4.2 Bias Sputtering 332

REFERENCES 337

6 Ion Plating 346

Donald M Mattox 1.0 INTRODUCTION 346

2.0 PROCESSING PLASMA 351

3.0 GENERATION OF PLASMAS 351

3.1 DC Diode Discharge 351

3.2 RF Discharge 355

3.3 Microwave Discharges 356

3.4 Electron Emitter Discharge 356

3.5 Magnetron Discharges 357

3.6 Plasma Enhancement 358

4.0 PLASMA CHEMISTRY 359

5.0 BOMBARDMENT EFFECTS ON SURFACES 360

5.1 Collisional Effects 363

5.2 Surface Region Effects 368

5.3 Near Surface Region Effects 369

5.4 Bulk Effects 369

6.0 SOURCES OF DEPOSITING ATOMS 369

6.1 Thermal Vaporization 370

6.2 Sputtering 371

6.3 Vacuum Arcs 371

6.4 Chemical Vapor Precursors 373

7.0 REACTIVE ION PLATING 373

8.0 BOMBARDMENT EFFECTS ON FILM PROPERTIES 373

8.1 Effects: Adatom Nucleation 373

8.2 Effects: Interface Formation 374

8.3 Effects: Film Growth 374

8.4 Film Adhesion 376

8.5 Film Morphology/Density 376

8.6 Residual Film Stress 378

8.7 Crystallographic Orientation 378

8.8 Gas Incorporation 380

8.9 Surface Coverage 380

8.10 Other Properties 381

9.0 ION PLATING SYSTEM REQUIREMENTS 381

9.1 Vacuum System 381

9.2 High Voltage Components 381

9.3 Gas Handling System 383

9.4 Evaporation/Sublimation Sources 383

9.5 Sputtering Sources 383

9.6 Plasma Uniformity 384

9.7 Plasma Generation Near the Substrate Surface 384

9.8 Substrate Fixturing 384

10.0 PROCESS MONITORING AND CONTROL 385

10.1 Plasma 385

10.2 Substrate Temperature 385

10.3 Specifications 385

11.0 PROBLEM AREAS 386

12.0 APPLICATIONS 389

13.0 SUMMARY 389

REFERENCES 391

7 Chemical Vapor Deposition 400

Jan-Otto Carlsson 1.0 INTRODUCTION 400

2.0 IMPORTANT REACTION ZONES IN CVD 401

3.0 DESIGN OF CVD EXPERIMENTS 402

3.1 Classification of CVD Reactions 403

3.2 Thermodynamics 405

3.3 Adhesion 409

3.4 Substrate Cleaning Procedures 410

3.5 The CVD system 410

3.6 The Gas Dispensing System 411

3.7 The Reactor 413

3.8 The Exhaust System 415

3.9 Analysis of the Vapor in a CVD Reactor 417

4.0 GAS FLOW DYNAMICS 417

4.1 Gas Flow Patterns 420

4.2 Boundary Layers 423

4.3 Mass Transport Processes Across a Boundary Layer 428

5.0 RATE-LIMITING STEPS DURING CVD 428

6.0 REACTION MECHANISMS 436

7.0 NUCLEATION 438

8.0 SURFACE MORPHOLOGY AND MICROSTRUCTURE OF CVD MATERIALS 442

9.0 SELECTIVE DEPOSITION 445

9.1 Area-Selective Growth 446

9.2 Phase-Selective Deposition 452

10.0 SOME APPLICATIONS OF THE CVD TECHNIQUE 453

11.0 OUTLOOK 455

REFERENCES 456

8 Plasma-Enhanced Chemical Vapor Deposition 460

Arthur Sherman 1.0 INTRODUCTION 460

2.0 REACTOR INFLUENCE ON PLASMA BEHAVIOR 461

2.1 DC/AC Glow Discharges 461

2.2 AC Discharges with Unequal Area Electrodes 464

2.3 Frequency Effects on RF Plasma Reactor Behavior 466

2.4 Adjusting DC Bias for Fixed Electrode Geometry 467

2.5 Plasma-Enhanced CVD (PECVD) Reactors 467

3.0 FILMS DEPOSITED BY CVD 472

3.1 Silicon Nitride 472

3.2 Silicon Dioxide 478

3.3 Conducting Films 481

REFERENCES 482

9 Plasma-Assisted Vapor Deposition Processes: Overview 485

Rointan F Bunshah 1.0 INTRODUCTION 485

2.0 PLASMA-ASSISTED DEPOSITION PROCESSES 488

3.0 MODEL OF A DEPOSITION PROCESS 488

4.0 MATERIALS DEPOSITED BY REACTIVE VAPOR DEPOSITION

PROCESSES 491

5.0 KEY ISSUES IN PLASMA-ASSISTED REACTIVE VAPOR DEPOSITION PROCESSES 492

5.1 Plasma Volume Chemistry 492

5.2 Type and Nature of the Bombardment of the Growing Film 493 6.0 PLASMA-ASSISTED DEPOSITION TECHNIQUES IN CURRENT USAGE 495

6.1 Plasma-Assisted Chemical Vapor Deposition 495

6.2 Sputter Deposition 496

6.3 Activated Reactive Evaporation (ARE) 497

7.0 LIMITATIONS OF CURRENT PLASMA-ASSISTED TECHNIQUES 499 8.0 HYBRID PROCESSES 501

9.0 CONCLUSIONS 501

REFERENCES 505

10 Deposition from Aqueous Solutions: An Overview 506

Morton Schwartz 1.0 INTRODUCTION 506

2.0 GENERAL PRINCIPLES 508

3.0 ELECTRODEPOSITION 520

3.1 Mechanism of Deposition 520

3.2 Parameters 526

4.0 PROCESSING TECHNIQUES 536

5.0 SELECTION OF DEPOSIT 539

5.1 Individual Metals 539

5.2 Alloy Deposition 543

6.0 SELECTED SPECIAL PROCESSES 550

6.1 Electroless Deposition 550

6.2 Electroforming 557

6.3 Anodizing 560

6.4 Plating on Plastics 570

6.5 Plating Printed Circuit Boards 571

7.0 STRUCTURES AND PROPERTIES OF DEPOSITS 574

8.0 SUMMARY 596

APPENDIX A - Preparation of Substrates for Electroplating 597

APPENDIX B - Representative Electroless Plating Solution Formulation 599

APPENDIX C - Comparison of Aluminum Anodizing Processes (Types I, II and III) 602

REFERENCES 605

11 Advanced Thermal Spray Deposition Techniques 617

Robert C Tucker, Jr. 1.0 INTRODUCTION 617

2.0 EQUIPMENT AND PROCESSES 618

2.1 Plasma Spray Process 618

2.2 Detonation Gun Deposition Process 626

2.3 High Velocity Oxy-Fuel Deposition 628

2.4 Thermal Control 629

2.5 Auxiliary Equipment 630

2.6 Equipment-Related Coating Limitations 631

3.0 TOTAL COATING PROCESS 632

3.1 Powder 632

3.2 Substrate Preparation 632

3.3 Masking 633

3.4 Coating 633

3.5 Finishing 635

4.0 COATING STRUCTURE AND PROPERTIES 636

4.1 Surface Macrostructure and Microstructure 636

4.2 Microstructure 637

4.3 Bond Strength 643

4.4 Residual Stress 644

4.5 Density 645

4.6 Mechanical Properties 647

4.7 Wear and Friction 653

4.8 Corrosion Properties 660

4.9 Thermal Properties 662

4.10 Electrical Characteristics 664

5.0 SUMMARY 665

REFERENCES 665

12 Non-Elemental Characterization of Films and Coatings 669

Donald M Mattox 1.0 INTRODUCTION 669

2.0 CHARACTERIZATION 671

3.0 FILM FORMATION 677

4.0 ELEMENTAL AND STRUCTURAL ANALYSIS 681

5.0 SOME PROPERTY MEASUREMENTS 682

5.1 Adhesion 682

5.2 Film Thickness 689

5.3 Film Stress 691

5.4 Coefficient of Thermal Expansion 695

5.5 Mechanical Properties 695

5.6 Electrical Resistivity 696

5.7 Temperature Coefficient of Resistivity (TCR) 696

5.8 Electromigration 697

5.9 Density 697

5.10 Porosity 698

5.11 Chemical Etch Rate (Dissolution) 701

6.0 SUMMARY 701

REFERENCES 702

13 Nucleation, Film Growth, and Microstructural Evolution 707

Joseph E Greene 1.0 INTRODUCTION 707

2.0 NUCLEATION AND THE EARLY STAGES OF FILM GROWTH 708

2.1 Three-Dimensional Nucleation and Growth 710

2.2 Two-Dimensional Nucleation and Growth 721

2.3 Stranski-Krastanov Nucleation and Growth 728

3.0 COMPUTER SIMULATIONS OF MICROSTRUCTURE EVOLUTION 730

3.1 Film Growth in the Ballistic Aggregation, Low-Adatom Mobility, Limit 732

3.2 Effects of Adatom Migration 734

4.0 MICROSTRUCTURE EVOLUTION AND STRUCTURE-ZONE 736

5.0 EFFECTS OF LOW-ENERGY ION IRRADIATION DURING FILM GROWTH 743

5.1 Effects of Low-Energy Ion/Surface Interactions on Nucleation Kinetics 743

5.2 Effects of Low-Energy Ion/Surface Interactions on Film Growth Kinetics 750

REFERENCES 760

14 Metallurgical Applications 766

Rointan F Bunshah 1.0 INTRODUCTION 766

2.0 CORROSION 766

3.0 GALVANIC CORROSION 767

3.1 Galvanic Cells 768

4.0 EMF AND GALVANIC SERIES 770

5.0 COATINGS FOR GALVANIC CORROSION 770

6.0 METHODS OF DEPOSITION OF METALLIC COATINGS 772

7.0 EXAMPLES OF CORROSION-RESISTANT COATINGS 7737.1 Preamble 7738.0 HIGH TEMPERATURE OXIDATION/CORROSION 7769.0 FRICTION AND WEAR 7819.1 Adhesive Wear 7819.2 Fretting Wear 7819.3 Abrasive Wear 7829.4 Fatigue Wear 7829.5 Impact Erosion Wear by Solid Particles and Fluids 7829.6 Corrosive Wear 7839.7 Electric Arc Induced Wear 7839.8 Solution Wear (Thermodynamic Wear) 78310.0 COATINGS TO REDUCE FRICTION AND WEAR 78310.1 Friction 78310.2 Lubrication 78510.3 Wear 785REFERENCES 787

15 Characterization of Thin Films and Coatings 789

Gary E McGuire

1.0 INTRODUCTION 7892.0 SURFACE ANALYSIS TECHNIQUES 7892.1 Auger Electron Spectroscopy 7892.2 Photoelectron Spectroscopy 7972.3 Secondary Ion Mass Spectroscopy 8032.4 Rutherford Backscattering Spectroscopy 8123.0 IMAGING ANALYSIS TECHNIQUES 8223.1 Scanning Electron Microscopy 8223.2 Transmission Electron Microscopy 8284.0 OPTICAL ANALYSIS TECHNIQUES 8344.1 Ellipsometry 8344.2 Fourier Transform Infrared Spectroscopy 8384.3 Photoluminescence Spectroscopy 841REFERENCES 845

16 Jet Vapor Deposition 848

Bret L Halpern and Jerome J Schmitt

1.0 INTRODUCTION 8482.0 PRINCIPLES AND APPARATUS OF JVD 8493.0 DISCUSSION 8533.1 Jet Structure, Behavior, and Vapor Transport 8533.2 Substrate Motion 856

4.0 EXAMPLES OF JVD FILMS AND APPLICATIONS 8574.1 Cu, Au Multilayer Electrodes; Al, Al2O3 Microlaminates 8574.2 PZT: Ferroelectric FRAM Nonvolatile Memories 8584.3 Electronic Grade Silicon Nitride 8594.4 Fiber Coating for Composite Materials 8594.5 Coating of Thermally Sensitive Membranes 8604.6 “Ceramic Host–Organic Guest” Films 8604.7 Polymer Deposition: Parylene 8615.0 SUMMARY 861REFERENCES 862

Index 864

$600 billion Just one industry, semiconductors, has changed entire productionlines every 5 to 6 years It is further estimated that only 10% of all items whichcan benefit from surface modifications are being processed today.

Surface engineering will remain a growth industry in the next decade,because surface-engineered products increase performance, reduce costs,and control surface properties independently of the substrate, thus offeringenormous potential due to the following:

! Creation of entirely new products

! Solution of previously unsolved engineering problems

! Improved functionality of existing products—engineering or decorative

! Conservation of scarce materials

! Ecological considerations—reduction of effluent output and powerconsumption

Research and development expenditures in surface engineering are veryextensive It is reported that Japan is spending $100 to $150 million for R/D

in diamond and diamond-like carbon coatings The payoff is estimated at $16billion by the end of this decade In advance thermal barrier coatings by PVDmethods for high temperature operation of turbine blades, it is estimated thatmore than $10 million have been spent in the United States alone Wear-resistant coatings for disc and heads has attracted much more than $10million in R/D expenditures worldwide The list continues to expand

2.0 INTRODUCTION

Most materials used in high technology applications are composites,i.e., they have a near-surface region with properties differing from those of thebulk materials This is caused by the requirement that the material exhibit

a combination of various, and sometimes conflicting, properties For example,

a particular engineering component may be required to have high hardness andtoughness (i.e., resistance to brittle crack propagation) This combination ofproperties can be obtained by having a composite material with high surfacehardness and a tough core Alternately, the need may be for a hightemperature, corrosion-resistant material with high elevated-temperaturestrength as is the case with the hot stage blades and vanes in a gas turbine.The solution again is to provide the strength requirement from the bulk and thecorrosion requirement from the surface

In general, coatings are desirable, or even necessary, for a variety ofreasons including economics, materials conservation, unique properties, orthe engineering and design flexibility which can be obtained by separating thesurface properties from the bulk properties

This near-surface region is produced by depositing a coating onto it (i.e.,

overlay coating) by processes such as physical or chemical vapor deposition,

electrodeposition, and thermal spraying, or by altering the surface material by

the in-diffusion of materials (i.e., diffusion coating or chemical conversion

coating), or by ion implantation of new material so that the surface layer now

consists of both the parent and added materials

“Coatings” may also be formed by other processes such as melt/solidification (e.g., laser glazing technique), by mechanical bonding of asurface layer (e.g., roll bonding), by mechanical deformation (e.g., shotpeening), or other processes which change the properties without changingthe composition

As stated above, the coating/substrate combination is a compositematerials system The behavior of this composite system depends not only

on the properties of the two components (i.e., the coating material and thesubstrate material), but also on the interaction between the two (i.e., thestructure and properties of the coating/substrate interface) which is integral tothe very important factor of adhesion of coatings In some cases, such as foroverlay coatings, this is a distinct region For others, such as ion implantation

or diffusion coatings, it is not a discrete region

Historically, most solid metallic and some ceramic materials wereproduced by melting/solidification technology Since the advent of depositiontechnologies (i.e., production of solid materials from the vapor), the diversity

of materials that can be produced has more than doubled because theproperties of solid materials produced from the vapor phase can be varied over

a much wider range than the same material produced from the liquid phase.This is because melt techniques produce solid materials with properties close

to equilibrium properties whereas the deposition conditions may be so chosen

as to produce materials from the vapor phase with properties close toequilibrium (similar to their melt-produced counterparts), or properties far

removed from equilibrium properties (non-equilibrium properties) Moreover,

a much greater variation in microstructure is possible with vapor sourcematerials For example, a copper-nickel alloy produced by solidification fromthe melt will always consist of a single phase solid solution, whereas the samealloy produced by alternate deposition from two sources may consist ofalternate layers of nickel and copper, i.e., a laminate composite or a solidsolution depending on the deposition temperature

A large number of materials are used for coatings today These mayrange from the naturally occurring oxide layer which protects the surfaces ofmany metals such as aluminum, titanium, and stainless steel, to those withvery deliberate and controlled alloying additions to the surface to producespecific properties, as exemplified by techniques such as molecular beamepitaxy or ion implantation Other examples with increasing degree ofcriticality range from paint coatings applied to wood and metals, electrostaticallypainted golf balls, the print in the daily newspaper, optical coatings on lensesand other elements, vapor deposited microcircuit elements such as resistors,diffusion or overlay coatings on superalloys used in gas turbines for hightemperature corrosion protection, hard overlay coatings of engineeringcomponents and machine tools, etc

3.0 AIM AND SCOPE

The aim of this volume is to give the reader a perspective on severalcoating techniques with emphasis on the techniques which are used in critical

or demanding (i.e., high technology) applications Consequently, some of thetechniques such as painting, dip coating, or printing will not be emphasizedexcept as they pertain to some special application like thick film electricalcomponents Nevertheless, a wide variety of techniques and their applicationswill be covered The material is intended to present a broad spectrum ofdeposition technologies to those who may be familiar with only one or twotechniques Hopefully, this will help them to select and weigh variousalternatives when the next technological problem involving coatings facesthem

The specific deposition technologies to be covered are:

1 Physical Vapor Deposition including evaporation, ion plating andsputtering

2 Chemical Vapor Deposition and Plasma-Assisted ChemicalVapor Deposition

3 Electrodeposition and Electroless Deposition

4 Plasma Spraying as well as a very special variant calledDetonation Gun Technology

There are some generic areas common to several of the depositiontechnologies, the most prominent example being the use of plasmas in many

of the deposition technologies Therefore, a chapter on plasmas in depositionprocesses is included Another common topic is cleaning of the substrate andadhesion of the coating A chapter is included on that topic

A further common topic is the characterization of the chemical compositionand the microstructure of the coating at various levels of resolution A chapter

is included to satisfy this need

New chapters are added dealing with Metallurgical Applications (Corrosion,Function and Wear), Overview of Plasma-Assisted Deposition Processes,Plasma-Assisted Chemical Vapor Deposition, and Nucleation/Growth of ThinFilms

It is realized that all specific applications cannot be satisfied within thisframework For example, specific applications such as coatings for optical ormagnetic applications are not addressed per se At the other end of thespectrum, coatings for the first wall of thermo-nuclear reactors cannot bediscussed since the development of the subject is in an embryonic stage

In each of the chapters on deposition technologies, the theory,methodology, advantages, limitations and applications are discussed.

4.0 DEFINITIONS AND CONCEPTS

In order to avoid potential problems, it is necessary to clarify certaindistinctions which are common and pertinent to deposition technologies.These are as follows:

1 Diffusion vs.Overlay Coatings—Diffusion coatings are produced

by the complete interdiffusion of material applied to the surfaceinto the bulk of the substrate material Examples of this are thediffusion of oxygen into metals to form various sub-oxide andoxide layers, the diffusion of aluminum into nickel base alloys toform various aluminides, etc A characteristic feature of diffusioncoatings is a concentration gradient from the surface to theinterior, as well as the presence of various layers as dictated bythermodynamic and kinetic considerations Ion implantationmay be considered to be a special case where the coatingmaterial is implanted at a relatively shallow depth (a few hundredangstrom units) from the surface

An overlay coating is an add-on to the surface of the part, e.g.,gold-plating on an iron-nickel alloy, or titanium carbide onto acutting tool, etc Depending upon the process parameters, aninterdiffusion layer between the substrate and the overlay coatingmay or may not be present

2 Thin Films vs Thick Films—Historically, the physical dimension

of thickness was used to make the distinction between thick filmsand thin films Unfortunately, the critical thickness value depended

on the application and discipline In recent years, a "Confucian"solution has been advanced It states that if a coating is used forsurface properties (such as electron emission, catalytic activity),

it is a thin film; whereas, if it is used for bulk properties, corrosionresistance, etc., it is a thick film Thus, the same coating material

of identical thickness can be a thin film or a thick film dependingupon the usage This represents a reasonable way out of thesemantic problem

3 Steps in the Formation of a Deposit—There are three steps in theformation of a deposit:

a Synthesis or creation of the depositing species

b Transport from source to substrate

c Deposition onto the substrate and film growth

These steps can be completely separated from each other or be imposed on each other depending upon the process under consideration Theimportant point to note is that if, in a given process, these steps can beindividually varied and controlled, there is much greater flexibility for such aprocess as compared to one where they are not separately variable This isanalogous to the degrees of freedom in Gibbs phase rule For example,consider the deposition of tungsten by CVD process It takes place by thereaction:

considerations of throwing power, i.e., the ability to coat irregularly shaped

objects, since high vacuum evaporation is basically a line-of-sight technique

5.0 PHYSICAL VAPOR DEPOSITION (PVD) PROCESS TERMINOLOGY

The basic PVD processes are those currently known as evaporation,sputtering and ion plating In recent years, a significant number of specializedPVD processes based on the above have been developed and extensivelyused, e.g., reactive ion plating, activated reactive evaporation, reactivesputtering, etc There is now considerable confusion since a particularprocess can be legitimately covered by more than one name As

an example, if the activated reactive evaporation (ARE) process is used with

a negative bias on the substrate, it is very often called reactive ion plating Simple evaporation using an RF heated crucible has been called gasless ion

plating An even worse example of the confusion that can arise is found in the

chapter on ion plating in this volume (Ch 6) where the material is convertedfrom the condensed phase to the vapor phase using thermal energy (i.e.,evaporation) or momentum transfer (i.e., sputtering) or supplied as a vapor(very similar to CVD processes) Carrying this to the logical conclusion, onemight say that all PVD processes are ion plating! On the other hand, the mostimportant aspect of the ion plating process is the modification of themicrostructure and composition of the deposit caused by the ion bombardment

of the deposit resulting from the bias on the substrate, i.e., what is happening

Step 1: Creation of Vapor Phase Specie There are three ways to put a

material into the vapor phase-evaporation, sputtering or chemical vapors andgases

Step 2: Transport from Source to Substrate The transport of the vapor

species from the source to the substrate can occur under line-of-sight ormolecular flow-conditions (i.e., without collisions between atoms andmolecules); alternately, if the partial pressure of the metal vapor and/or gasspecies in the vapor state is high enough or some of these species are ionized(by creating a plasma), there are many collisions in the vapor phase duringtransport to the substrate

Step 3: Film Growth on the Substrate This involves the deposition of the

film by nucleation and growth processes The microstructure and composition

of the film can be modified by bombardment of the growing film by ions fromthe vapor phase resulting in sputtering and recondensation of the film atomsand enhanced surface mobility of the atoms in the near-surface and surface

of the film

Every PVD process can be usefully described and understood in terms

of these three steps The reader is referred to Chapter 9 for a morecomprehensive treatment

6.0 CLASSIFICATION OF COATING PROCESSES

Numerous schemes can be devised to classify or categorize coatingprocesses, none of which are very satisfactory since several processes willoverlap different categories For example, the Appendix contains a list anddefinitions of various deposition processes based upon those provided byChapman and Anderson with some additions These authors classify theprocesses under the general heading of Conduction and Diffusion Processes,Chemical Processes, Wetting Processes and Spraying Processes Here, theChemical Vapor Deposition process falls under the Chemical Processes, andthe Physical Vapor Deposition Process (Evaporation, lon Plating and Sputtering)falls under the spraying processes The situation can easily get confused as,for example, when Reactive and Activated Reactive Evaporation, and Reactivelon Plating are all classified as Chemical Vapor Deposition processes byYee[3] who considers them thusly because a chemical reaction is involved and

it does not matter to him whether evaporated metal atoms or stable liquid orgaseous compounds are the reactants Another classification of the methods

of deposition of thin films is given by Campbell.[4] He considers the overlapbetween physical and chemical methods, e.g., evaporation and ion plating,sputtering and plasma reactions, reactive sputtering and gaseousanodization.[5] He classifies the Chemical Methods of Thin Film Preparation

as follows:

Chemical Methods of Thin Film Preparation

Formation from the Medium Electroplating

lon PlatingChemical ReductionVapor PhasePlasma Reaction

Formation from the Substrate Gaseous Anodization

ThermalPlasma Reduction

In addition, he considers the following as chemical methods of thick filmpreparation: Glazing, Electrophoretic, Flame Spraying and Painting.

In contrast to the chemists’ approach given above, the physicists’approach to deposition processes is shown in the following classification ofvacuum deposition techniques by Schiller, Heisig and Goedicke[6] and byWeissmantel.[7]

Figure 1.1 Survey of vacuum deposition techniques (Schiller[6])

A different classification comes from a materials background where theconcern is with structure and properties of the deposits as influenced byprocess parameters Thus, Bunshah and Mattox[8] give a classification based

on deposition methods as influenced by the dimensions of the depositingspecie, e.g., whether it is atoms/molecules, liquid droplets or bulk quantities,

as shown in Table 1.1

In atomistic deposition processes, the atoms form a film by condensing

on the substrate and migrating to sites, where nucleation and growth occurs.Further, adatoms do not achieve their lowest energy configurations and theresulting structure contains high concentrations of structural imperfections.Often the depositing atoms react with the substrate material to form a complexinterfacial region

Another aspect of coatings formed by atomistic deposition processes is

as follows The sources of atoms for these deposition processes can be bythermal vaporization (vacuum deposition) or sputtering (sputter deposition) in

a vacuum, vaporized chemical species in a carrier gas (chemical vapordeposition), or ionic species in an electrolyte (electrodeposition) In lowenergy atomistic deposition processes, the depositing species impinge on thesurface, migrate over the surface to a nucleation site where they condense andgrow into a coating The nucleation and growth modes of the condensingspecies determine the crystallography and microstructure of

the coating For high energy deposition processes, the depositing particlesreact with or penetrate into the substrate surface.

Particulate deposition processes involve molten or solid particles and theresulting microstructure of the deposit depends on the solidification orsintering of the particles Bulk coatings involve the application of largeamounts of coating material to the surface at one time such as in painting.Surface modification involves ion, thermal, mechanical, or chemical treatments,which alter the surface composition or properties All of these techniques arewidely used to form coatings for special applications

Table 1.1 Methods of Fabricating Coatings

7.0 GAS JET DEPOSITION WITH NANO-PARTICLES

One of the chapters in this volume (Ch 11) deals with Plasma Sprayingand Detonation Gun Techniques where a high velocity stream of macro-particles (µm dimensions) impinge on a substrate to form a coating With the

Figure 1.2 Schematic diagram of gas deposition apparatus.

advent of evaporation[9] and sputtering processes[10] to produce particles (nm dimensions), the same concept can be used to producecoatings by carrying nano-particles in a gas stream and impinging them on

nano-a substrnano-ate.[11][12] Figure 1.2 shows a schematic of this process wheremetallic nano-particles produced by evaporation are carried in a gas stream,accelerated through a nozzle and impinged on a substrate to produce acoating Single nozzles or multiple nozzle configurations can be used, thelatter producing an array of dots, for example The attributes of this processare:

1 Direct write maskless processing to produce dots, lines, andother shapes

2 High deposition rate, 10 - 20 µm per second over a small area

3 Low temperature (room temperature) deposition

4 Metals, alloys, ceramics, and organic materials can bedeposiited

5 Multiphase films with uniform mixing can be produced

6 The collection officiency is very high, ~90%, i.e very little waste

or scatter

Examples of applications of this technique are:

1 Electrical connecting lines in circuits including the repair aspect

2 Fabrication of microelectrodes

3 Oxide superconductor contacts

4 Capacitors

5 Implantation of virus into plants for the bio industry

6 Cell-gene processing technology

8.0 MICROSTRUCTURE AND PROPERTIES

In electrodeposition, typically the growth process involves condensation

of atoms at a kink site on the substrate surface, followed by layered growth

of the deposit Adatom mobility is increased by the hydrated nature of the ionsand the adatom mobility may vary with crystal orientation Field ionmicroscopy stripping studies of copper electrodeposited on tungsten hasshown that there is surface rearrangement of the tungsten atoms during theelectrodeposition process Electrodeposited material does not grow in auniform manner; rather it becomes faceted, develops dendrites and othersurface discontinuities Thus the microstructure of electrodeposited coatingsmay vary from relatively defect-free single crystals usually grown on singlecrystal substrates, to highly columnar and faceted structures In theelectroplating process, organic additives may be used to modify the nucleationprocess and to eliminate undesirable growth modes This results in amicrostructure more nearly that of bulk material formed by conventionalmetallurgical processes Electrodeposition from a molten salt electrolyteallows the deposition of many materials not available from aqueous electrolytes

In vacuum processes, the depositing species may have energies rangingfrom thermal (a few tenths of an electron volt) for evaporation to moderateenergies (ten to hundreds of electron volts) for sputtered atoms to highenergies for accelerated species such as those used in ion implantation.These energies have an important but poorly understood effect on interfacialinteraction, nucleation and growth Where there is chemical reaction betweenthe substrate atoms and the depositing atoms, and diffusion is possible, adiffusion or compound interfacial region is formed composed of compoundsand/or alloys which modify the effective surface upon which the deposit grows.Low energy electron diffraction studies have shown that this interfacial reaction

is very sensitive to surface condition and process parameters If the coatingand substrate materials are not chemically reactive and are insoluble, theinterfacial region will be confined to an abrupt discontinuity in composition.This type of interface may be modified by bombardment with high energyparticles to give high defect concentrations and implantation of ions resulting

in a “pseudodiffusion” type of interface The type of interface formed willinfluence the properties of the deposited coating In many circumstances,these interfacial regions are of very limited thickness and pose a challenge tothose interested in compositional, phase, microstructural and propertyanalysis

The microstructure of the depositing coating in the atomic depositionprocesses depends on how the adatoms are incorporated into the existingstructure Surface roughness and geometrical shadowing will lead topreferential growth of the elevated regions giving a columnar type microstructure

to the deposits.[13] This microstructure will be modified by substratetemperature, surface diffusion of the atoms, ion bombardment during deposition,impurity atom incorporation and angle of incidence of the depositing adatomflux The structure zone model of Movchan and Demchishin[14] for vacuumdeposited films is discussed in later chapters

In chemical vapor deposition, the chemical species containing the filmatoms is generally reduced or decomposed on the substrate surface, often athigh temperatures Care must be taken to control the interface reactionbetween coating and substrate and between the substrate and the gaseousreaction products The coating microstructure which develops is very similar

to that developed by the vacuum deposition processes, i.e., small-grainedcolumnar structures to large-grained equiaxed or oriented structures.Each of the atomistic deposition processes has the potential of depositingmaterials which vary significantly from the conventional metallurgicallyprocessed material The deposited materials may have high intrinsicstresses, high point defect concentration, extremely fine grain size, orientedmicrostructures, metastable phases, incorporated impurities, and macro andmicro porosity These properties may be reflected in the physical properties

of the materials and by their response to applied stresses such as mechanicalloads, chemical environments, thermal shock or fatigue loading Metallurgicalproperties which may be affected include elastic constants, tensile strength,fracture toughness, fatigue strength, hardness, diffusion rates, friction/wearproperties, and corrosion resistance In addition, the unique microstructure

of the deposited material may lead to such effects as anomalously lowannealing and recrystallization temperatures where the internal stresses andhigh defect concentration aid in atomic rearrangement

The high value of grain boundary area to volume ratio found in fine graineddeposited material means that diffusion processes may be dominated by grainboundary rather than bulk diffusion The fine grained nature of the materialsalso affects the deformation mechanisms such as slip and twinning For thinfilms, the free-surface to volume ratio is high, and the pinning of dislocation bythe free surface leads to the high tensile strengths often measured in thin films

of materials

In vapor deposition processes, impurity incorporation during depositioncan give high intrinsic stresses or impurity stabilized phases which are notseen in the bulk forms of the materials Reactive species allow the deposition

of compounds such as nitrides, carbides, borides and oxides Gradeddeposits can be formed

Vapor deposition processes have the capability of producing unique and/

or nonequilibrium microstructures One example is the fine dispersion ofoxides in metals, where the oxide particle size and spacing is very small (100

- 500 Å) Alternately, metals and alloys deposited at high substratetemperatures have properties similar to those of conventionally fabricated(cast, worked and heat treated) metals and alloys A more recent example

is the nano-scale laminate composites consisting of alternate layers ofrefractory compounds with unusually high hardness values

9.0 UNIQUE FEATURES OF DEPOSITED MATERIALS AND GAPS IN UNDERSTANDING

It is useful to state at this point some of the unique features of materialsproduced by deposition technologies They are:

1 Extreme versatility of range and variety of deposited materials

2 Overlay coatings with properties independent of thethermodynamic compositional constraints

3 Ability to vary defect concentration over wide limits, thus resulting

in a range of properties comparable to, or far removed fromconventionally fabricated materials

4 High quench rates available to deposit amorphous materials

5 Generation of microstructures different from conventionallyprocessed materials, e.g., a wide range of microstructures—ultrafine (submicron grain or laminae size) to single crystal films

6 Fabrication of thin self-standing shapes even from brittle materials

7 Ecological benefits with certain techniques

The first edition lists some of the areas where our understanding

of basic processes and phenomena is lacking and which obviously arethe areas where research activities are essential These are:

1 Microstructure and properties in the range of 500 to 10,000 Å—particularly important for submicron microelectronics, reflectivesurfaces and corrosion.

2 (a) Effect of the energy of the depositing species on

interfacial interaction, nucleation and growth of deposit

(b) Effect of “substrate surface condition,” i.e.,

contamination (oxide) layers, adsorbed gases,

surface topography

3 Residual stresses—influence of process parameters

Considerable progress and understanding has developed in the lastdecade

10.0 CURRENT APPLICATIONS

The applications of coatings in current technology may be classed intothe following generic areas:

Optically Functional—Laser optics (reflective and transmitting),

architectural glazing, home mirrors, automotive rear view mirrors,reflective and anti-reflective coatings, optically absorbing coatings,selective solar absorbers

Electrically Functional—Electrical conductors, electrical contacts,

active solid state devices, electrical insulators, solar cells

Mechanically Functional—Lubrication films, wear and erosion

resistant coatings, diffusion barriers, hard coatings for cutting tools

Chemically Functional—Corrosion resistant coatings, catalytic

coatings, engine blades and vanes, battery strips, marine useequipment

Decorative—Watch bezels, bands, eyeglass frames, costume

replaced with lightweight plastic, overcoated with chromium by sputtering forthe appearance to which the consumer is accustomed.

Another extensive application is aluminum-coated polymer films for heatinsulation, decorative and packaging applications

A rapidly growing application is the use of a gold-colored wear-resistantcoating of titanium nitride on watch bezels, watch bands and similar items

A new application is black wear-resistant hard carbon films

10.2 High Temperature Corrosion

Blades and vanes used in the turbine-end of a gas turbine engine aresubject to high stresses in a highly corrosive environment of oxygen-, sulfur-and chlorine-containing gases A single or monolithic material such as a hightemperature alloy is incapable of providing both functions The solution is todesign the bulk alloy for its mechanical properties and provide the corrosionresistance by means of an overlay coating of an M-Cr-AI-Y alloy where Mstands for Ni, Co, Fe or Ni + Co The coating is deposited in production byelectron beam evaporation and in the laboratory by sputtering or plasmaspraying With the potential future use of synthetic fuels, considerableresearch will have to be undertaken to modify such coating compositions forthe different corrosive environments as well as against erosion from theparticulate matter in those fuels

10.3 Environmental Corrosion

Thick ion plated aluminum coatings are used in various

irregularly-shaped parts of aircraft and space-craft as well as on fasteners: (a) to replace

electroplated cadmium coatings which sensitize the high-strength parts to

hydrogen embrittlement or (b) to prevent galvanic corrosion which would occur when titanium or steel parts contact aluminum or (c) to provide good

brazeability New alloy coatings in the micron thickness range have beendeveloped

10.4 Friction and Wear

Dry-film lubricant coatings of materials such as gold, MoS2, WSe2 andother lamellar materials are deposited on bearings and other sliding parts bysputtering or ion plating to reduce wear Such dry-film lubricants are

especially important for critical parts used in long-lifetime applications sinceconventional organic fluid lubricants are highly susceptible to irreversibledegradation and creep over a long time.

10.5 Materials Conservation

Aluminum is continuously coated on a steel strip, 2 feet wide and 0.006inches thick to a 250 micro-inch thickness in an air-to-air electron-beamevaporator at the rate of 200 feet/minute The aluminum replaces tin, which

is becoming increasingly scarce and costly The strip then goes to the lacquerline and is used for steel can production With the change in Eastern Europe,this line has switched to deposition of Cr and Cu on steel

10.6 Cutting Tools

Cutting tools are made of high-speed steel or cemented carbides Theyare subject to degradation by abrasive wear as well as by adhesive wear Inthe latter mode, the high temperatures and forces at the tool tip promotemicrowelding between the steel chip from the workpiece and the steel in thehigh-speed steel tool or the cobalt binder phase in the cemented carbide Thesubsequent chip breaks the microweld and causes tool surface cratering andwear A thin layer of a refractory compound such as TiC, TiN, Al2O3 preventsthe microwelding by introducing a diffusion barrier Improvements in tool life

by factors of 300 to 800% are possible as well as reductions in cutting forces.The coatings are deposited by chemical vapor deposition or physical vapordeposition Some idea of the importance of such coatings can be assessedfrom the fact that the yearly value of cutting tools purchased in the U.S is $1billion and the cost of machining is approximately $60 billion

The last decade has seen major advances in this area and some of theseare:

! Ti alloy nitrides, e.g., (Ti, Al) N

! Ti carbonitrides, e.g., Ti (C,N)

! Multilayer coatings of different nitrides

! Diamond coated tools by CVD and PACVD processes formachining of non-ferrous metals and polymer-matrixcomposites A bond layer such as silicon nitride has to be used

to attach the diamond coating to the carbide cutting tool