diffusion phenomena in in thin films and microelectronic materials

8/16/2019 Diffusion phenomena in IN THIN FILMS AND MICROELECTRONIC MATERIALS

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D I F F U S I O N

P H E N O M E N

IN TH IN FILM S N D

MICROELECTRONIC

M TERI LS

Edited by

D e v e n d r a G u p t a a n d P a u l S. H o

IBM Thomas J. Watson Research CenterYorktown Heights, New York

np NOYES PUBLICATIONSPark Ridge New Jersey U S A



Contents

1. SOME FORMAL ASPECTS OF DIFFUSION: BULK SOLIDSAND THIN FILMS 1

Devendra Gupta

Introduction 1Mathematical Basis of Diffusion 2Single Crystals 2

Fick s First Law 2Fick s Second Law 3Instantaneous Source Geom etry 4Thick Layer Geom etry 4Infinite Couple with Surface Com position Constant 5Boltzmann-Matano Analysis 5

Structurally Inhom ogeneous Samples 7Experimental Techniques 13

Microsectioning Diffusion Measurements 14Surface Accumulation Techniques 16

Thermodynam ical Considerations 20Driving Force F on Individual Atoms Is Zero 20Pressure and Mass Dependence of Diffusion 25

Pressure Dependence 25Mass Dependence 26

Driving Force F on Individual Atoms Is Finite-Linear ChemicalDiffusion Regime 28

Non Linear Chemical Diffusion Regime 31Structure of Grain Boundaries, Mobile Defects and Diffusion

Hierarchy 33Grain Boundary Structu re and State of Mobile Defects 33Mechanism of Grain Boundary Diffusion 38An isotropy and Orientation of Grain-Boundary Diffusion 40

IX



x Contents

Diffusion Data in Grain Boundaries and Thin Films:Diffusion Hierarchy 41

Relationsh ip Among GB Diffusion Lattice Diffusion and GBEnergy 49

Influence of Solu te Segregation on GB Self-Diffusion and ItsRelationship with GB Energy Solute Segregation and GBDiffusion 52

Thermal Behavior of KSDJ 55Composition Dependence of K8l \y 58Estimating Grain Boundary Segregation Parameters from

Diffusion Measurements 61Variable Effects of Solutes on GB Diffusion 62

Concluding Rem arks 65

References 65

2. ANELASTIC RELAXATION AND DIFFUSION IN THIN-LAYERMATERIALS 73

Brian S BerryIntroduction 73Anelastic Relaxation Behavior 74

Quasi-Static Response Functions 75Dynamic Anelastic Behavior: The Internal Friction Peak 79Anelastic Behavior with Multiple or Distributed Relaxation

Times 83Thermally-Activated Relaxation Behavior 84

Experimental Methods 88Vibrating-Reed Apparatus 89The Mandrel Method for Quasi-Static Measurements 94Accom modation Stress and the Bending Bilayer 97

Interstitial Solute Diffusion in BCC Metals 99The Snoek Relaxation 100Experimental Results 104

Hydrogen Diffusion in Metallic Glasses I l lThe Hydrogen Reorientation Relaxation 112The Gorsky Relaxa tion. . 117

Other Therm ally-Activated Processes in Metallic Glasses 121Grain-Boundary Diffusion in Pure and Alloyed Aluminum Films . . 123Point-Defect Relaxations in Ion-Implanted Silicon 128Structural Relaxation in Silicon Monoxide 133Concluding Rem arks 136Appendix: Frequencies and Internal Friction of Multilayered

Reed 137References 141

3. DIFFUSION IN ARTIFICIALLY MODULATED Т Н Ш FILMS 146A Lindsay Greer

Introduction 146Theory 147



Contents xi

Interdiffusion in a Steep Concentration Gradient 147Gradient Energy Effects 149Strain Effects 158Non-Linear Diffusion Effects 163

Measurement Techniques 167Relationship to Other Diffusion Measurements 171Stability of Modulated Structures 174

Experimental Results on Crystalline Metals 175Early Work 175Gold-Silver 175Copper-Palladium 176Gold-Nickel 178Copper-Gold 182Copper-Nickel 183Silver-Palladium 185Ternary Systems 186

Experimental Results on Am orphous Metals 187Introduc tion to Amorphous Metals 187Interdiffusion Measurements 188Discussion 192

Experimental Results on Semiconductors 193GaAs-AlAs 193GaSb-InSb 194

Amorphous Si-Ge 195Discussion 196Conclusions 196References 198

4. DIFFUSION AND GROWTH IN OXIDE FILMS 204Alan Atkinson

Introduction 204Experimental Techniques 205

Secondary Ion Mass Spectroscopy (SIMS) Sectioning 205Nuclear Reaction Depth Profiling 207Sputter-Sectioning of Radioactive Tracers 208Chemical Dissolution 208Gaseous Exchange 208Diffusion in Growing Oxide Films 209

Lattice Diffusion in Oxides 211Point Defects in Oxides 211Self-Diffusion 213

Cation Self-Diffusion 214

Oxygen Ion Self-Diffusion 215Diffusion in Doped Oxides 215Heterovalent Doping 216Homoyalent Doping 216

Solute Diffusion 217Tracer Solute Diffusion 217



xii Contents

Dilute Limit 217Non-Dilute 218

Am orphous Oxides 218

Theoretical Estimates of Diffusion Parameters 220Short-Circuit Diffusion 222Dislocation Diffusion 222Grain Boundary Diffusion 22 3Surface Diffusion 224Theoretical Studies of Dislocations, Grain Boundaries and

Surfaces 224Dislocations 224Grain Boundaries 224

Oxide Film Grow th by Thermal Oxidation 225

Theory of Oxide Film Growth 225Thick Films 225Thin Films 226

Defects Injected at the Metal/Oxide Interface 228Defects Injected at the Oxide/Gas Interface 229

Oxide Films Growing by Outward Cation Transport 23 1Growth of CoO 231Growth of NiO 231Growth of Other Oxides by Cation Transport 234

Oxide Films Growing by Inward Oxygen Transport 234Growth of Highly Protective Films 235

Oxidation of Alloys 235Protection by Incorporated Coatings 237

Concluding Remarks 239References 239

5. DIFFUSION-INDUCED GRAIN BOUNDARY MIGRATION INTHIN FILMS 245

arol A. Handwerker

Introduction 245Morphology and Kinetics of DIGM, DIR, and Liquid FilmMigration 253

Systems Exhibiting DIGM and DIR 253Grain Morphology of DIGM 256Crystallographic Orientation of Alloyed Regions 257Surface Relief 260Kinetics of Migration 261Com positions of Alloyed Regions 26 3Nucleation of New Grains—Diffusion-Induced

Recrystallization 267Liquid Film Migration 270

Driving Force for Grain Boundary /Interface Motion 272Distinctions Between Free Energy Changes and Driving

Forces 272Diffusional Transport in Polycrystals with Migrating Grain

Boundaries 273



Contents xiii

Driving Force for DIGM, DIR, and LFM 274Effect of Coherency Strain on Interface Migration 276

Model for Coherency Strain Energy 277Migration of Liquid Films 279Migration Regimes for Liquid Films 282Stress Relaxation Mechanisms 283Migration Velocities and Morphology of the Migrating

Interface 284Controlled Variation of Strain 285Tests of the Coherency Strain Theory for liquid Film

Migration 286Migration Velocities 287Controlled Variation of Strain 288Morphology of Migrating Interfaces 288Other Driving Forces for Boundary Migration 289

liq u id Film Migration in Ceramics 290Effect of Diffusion-Induced Strain on Grain Boundary

Migration 291Distinctions Between Grain Boundaries and liq u id Films 29 1Qualitative Test of the Coherency Strain Theory for DIGM. . . . 292Critical Values of Dg/V 295Features of Grain Boundaries Required to Quantitatively

Model DIGM 297

Unequal Grain Boundary Diffusivities 297Unequal La ttice Diffusivities of the Solute and SolventSpecies 298

Grain Boundaries as Sources/Sinks for Vacancies 299Geom etrical Constraints 300Grain Boundary Structure Effects in DIGM 301Relative Rates of Grain Boundary and Lattice Diffusion. . . . 30 1Stress Relief Mechanisms 302Other Driving Forces 303

Mechanism Maps for DIGM and DIR 303Special Considerations for Thin Films 312

References 314

6. EFFECTS OF AMBIENTS ON THIN FILM INTERACTIONS 323Chin An hang

Introduction 323Observed Am bient Effects 324

Enhanced Interactions 324Reduced Interactions 325

Mechanisms for the Am bient Effects 326Sinking Effect Model 326Surface Energy Model 327Interface Oxide Model 327Surface Potential Model 327

Observation of Other Ambient Effects from the SurfacePotential Model 330



xiv Contents

Reduced Interaction in Au Systems by CO 330Reduced Interactions in Pt Systems by Oxygen 332Reduced Interactions by Oxygen for the Ni and Cu Systems . . . 333Com peting Am bient Effects 335Diffusion Through a Less-Electronegative Metal Layer 340Ambient Effects on Competing Interactions and on

Preferential Reac tions 344Oxidation Effects of the Outdiffused Species 346

Effect of Oxygen on the Suicide Formation 4 7

Applications and Fu ture Studies. 354Summary 365References 366

7. ELECTROMIGRATION IN METALLIC THIN FILMS 369Thomas Kwok and Paul S HoIntroduction 369Electromigration in Bulk Metals 37 1

Phenomenological Description 37 1Theory of Electromigration 375Techniques of Measurement 378Electromigration in Substitutional Systems 382

Electromigration in Metallic Thin Films 385Nature of Electromigration in Metallic Thin Films 385Damage Form ation and Kinetics 387Structural and Thermal Effects 389Lifetime Measurement 392Methods to Improve Electromigration Resistance 393

Electromigration in Fine Lines 397Scaling Trends 397Process and Material Related Aspects 399Effect of Microstructure 400Effect of Metal Line Geom etry 403

Linelength Dependence 403Linewidth Dependence 407Effect of Film Thickness 40 9

Pulsed Current Powering Characteristics 41 2Electromigration in Multilevel Interconnec tion 416

Electromigration at Contacts 416Current Crowding and Local Heating in Studs and Vias 420

Summary 423References 425

8. DIFFUSION BARRIERS IN SEMICONDUCTOR CONTACTMETALLIZATION 432

Hannu P. Kattelus and Marc A. NicoletIntroduction 432

General Considerations. 43 2Functions of a Diffusion Barrier 434



Contents xv

Electrical Requirements in Contacts 43 5Summary 437

Importance of the Choice of the Material and of theDeposition Process 438

Basic Considerations 43 8Single Crystalline Versus Non-Single Crystalline Films 440Summary 440

Polycrystalline Films Consisting of One Single Layer 441Elemental Metallic Films 441Effect of Impurities—Stuffed Barrier 44 3Compound Film—Inert Barrier 44 5

From Elemental to Compound Films 445Single Phase Com pounds 44 8

Multiphase Com pounds 462Summary 462Am orphous Films Consisting of One Single Layer 463

General Observations 463Examples of Am orphous Diffusion Barriers 46 8Summary 475

Multilayer Configurations 475Sacrificial Barrier 476Contacting Layers 477Tandem Barriers 480Summary 489

References 491

9. THERMAL STABILITY OF Pb-ALLOY JOSEPHSON JUNCTIONS. . . . 499Masanori M urakami

Introduction 499Thermal Strain of Films on Rigid Substrates 501Thermal Stability Below Room Tem perature 504

Pb Thin Films 504Strain Behavior 504Microstructure Changes After Repeated Thermal Cycling . . . 507Reduction of Strain Relaxation 514

Pb-In-Au Base Electrode Material 517Strain Behavior 518Microstructure Change After Repeated Thermal Cycling. . . . 518Correlation Between Device Reliability and Micro-

structure Change 520Pb-Bi Counterelectrode Material 524

Strain Behavior 525

Microstructure Change After Repeated Thermal Cycling. . . . 525Correlation Between Device Reliability and Micro-

structure Changes 530Thermal Stability Above Room Tem perature 532

Strain Behavior 533Primary Strain Relaxation Process 534



xvi Contents

Secondary Relaxation Process 538Hillock Form ation of Pb-In-Au Base Electrode 538

Mechanism 538Reduction of Hillock Form ation 540

Summary 542References 543

10. DIFFUSION AND ELECTROMIGRATION OF IMPURITIES INLEAD SOLDERS 546

Chao-Kun Н и and Hillard B HuntingtonIntroduction 546Fast Diffusers in Pure Lead 548

Diffusion 548Electromigration 551

Dilute Impurities in Lead-Tin Solders 554Impurities Subjected to Trapping by the Added Tin 555

Diffusion 555Electromigration 564

An Impurity Not Subject to Trapping—Silver 567Diffusion 567Electromigration 569

Experiments With 1000 ppm Nickel 569Diffusion 570

Electromigration 572Dilute Impurities in Lead-Indium Solders 573

Diffusion in Lead-Indium Alloys 573Electromigration 577

Conclusion 578References 579

INDEX 582

diffusion phenomena in in thin films and microelectronic materials

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