THIN FILM PHENOMENA KASTURI L. CHOPRA. Staff Scientist, Ledgemont Laboratory, Kennecott Copper Corporation Lexington, Massachusetts

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1 THIN FILM PHENOMENA KASTURI L. CHOPRA Staff Scientist, Ledgemont Laboratory, Kennecott Copper Corporation Lexington, Massachusetts Adjunct Professor of Mechanical Engineering Northeastern University Boston, Massachusetts McGRAW-HILL BOOK COMPANY New York St. Louis San Francisco London Sydney Toronto Mexico Panama

CONTENTS Preface vii 1 INTRODUCTION 1 П THIN FILM DEPOSITION TECHNOLOGY 10 1. Introduction 10 2. Thermal Evaporation 11 2.1 General Considerations 11 2.

2 CONTENTS Preface vii 1 INTRODUCTION 1 П THIN FILM DEPOSITION TECHNOLOGY Introduction Thermal Evaporation General Considerations Evaporation Methods 14 Resistive Heating; Flash Evaporation; Arc Evaporation; Exploding-wire Technique; Laser Evaporation; RF Heating; Electron-bombardment Heating 3. Cathodic Sputtering Sputtering Process Glow-discharge Sputtering 29 Pressure; Deposit Distribution; Current and Voltage Dependence; Cathode; Contamination Problem; Deposition Control 3.3 Sputtering Variants 34 xi

XÜ Contents 3.4 Low-pressure Sputtering 36 Magnetic Field; Assisted (Triode) Sputtering; RF Sputtering; Ion-beam Sputtering 3.5 Reactive Sputtering 41 3.6 Sputtering of Multicomponent Materials 42 4.

3 XÜ Contents 3.4 Low-pressure Sputtering 36 Magnetic Field; Assisted (Triode) Sputtering; RF Sputtering; Ion-beam Sputtering 3.5 Reactive Sputtering Sputtering of Multicomponent Materials Chemical Methods Introduction Electrodeposition 44 Electrolytic Deposition; Electroless Deposition; Anodic Oxidation 4.3 Chemical Vapor Deposition (CVD) 46 Pyrolysis (Thermal Decomposition); Hydrogen Reduction; Halide Disproportionation; Transfer Reactions; Polymerization 4.4 Miscellaneous Methods Vacuum-deposition Apparatus Vacuum Systems Substrate-deposition Technology 61 Substrate Materials; Substrate Cleaning; Uniform and Nonuniform Deposits; Masks and Connections; Multiple-film Deposition 6. Conclusions Appendix 69 References 76 III THICKNESS MEASUREMENT AND ANALYTICAL TECHNIQUES Thickness Measurement Electrical Methods 84 Film Resistance; Capacitance Monitors; Ionization Monitors 1.2 Microbalance Monitors 90 Microbalances; Quartz-crystal Monitor 1.3 Mechanical Method (Stylus) Radiation-absorption and Radiation-emission Methods Optical-interference Methods 99 Photometric Method; Spectrophotometry Method; Interference Fringes; X-ray Interference Fringes 1.6 Summary of Methods Analytical Techniques Chemical Analysis Structural Analysis Surface Structure 110 Optical Methods; Low-energy Electron Diffraction (LEED); Auger-electron Spectroscopy; Field-emission, Field-ion, and

$Contents xiii Sputter-ion Microscopy; Reflection Electron Diffraction; Replica Electron Microscopy 2.$

4 Contents xiii Sputter-ion Microscopy; Reflection Electron Diffraction; Replica Electron Microscopy 2.4 Volume Structure 121 X-ray Diffraction; X-ray Microscopy (Topographic Methods); Transmission Electron-diffraction and Electron-microscope Methods 3. Conclusions 129 References 130 IV NUCLEATION, GROWTH, AND STRUCTURE OF FILMS Nucleation Condensation Process Langmuir-Frenkel Theory of Condensation Theories of Nucleation 142 Capillarity Theory; Statistical or Atomistic Theory; Miscellaneous Models; Further Deductions of the Nucleation Theories 1.4 Experimental Results 149 Sticking Coefficient; Observations on Nucleation; Condensation Centers; Condensate Temperature 2. Growth Processes General Description Liquid-like Coalescence 166 Experimental Observations; Coalescence Model 2.3 Influence of Deposition Parameters 171 General Aspects; Kinetic-energy Effect; Oblique Deposition; Electrostatic Effects 3. Some Aspects of the Physical Structure of Films 182 Crystallite Size; Surface Roughness; Density of Thin Films 4. Crystaflographic Structure of Films Lattice Constant of Thin Films 191 Size Effect; Surface Pseudomorphism 4.2 Disordered and Amorphous Structures 195 Impurity Stabilization; Vapor Quenching (VQ): Codeposit Quenching 4.3 Abnormal Metastable Crystalline Structures 199 Amorphous-Crystalline Transformation; Codeposit Quenching of Metastable Alloys; Deposition-parametercontrolled and Nucleated Metastable Structures; Pseudomorphs and Superstructures; Conclusions; Metastabilization Mechanisms 4.4 Two-dimensional Superstructures Fiber Texture (Oriented Overgrowth) Alloy Superlattices 223

xiv Contents 5. Epitaxial-growth Phenomenon 224 5.1 Influence of Substrate and Deposition Conditions.

5 xiv Contents 5. Epitaxial-growth Phenomenon Influence of Substrate and Deposition Conditions Substrate; Substrate Temperature; Deposition Rate; Contamination; Film Thickness; Electrostatic Effects; Deposition Methods; Summary 5.2 Theories of Epitaxy 238 Royer Hypothesis; van der Merwe Theory; Brück-Engel Theory; Nucleation Theories; Summary 6. Structural Defects in Thin Films Concluding Remarks 252 References 254 V MECHANICAL EFFECTS IN THIN FILMS Introduction Internal Stresses Experimental Techniques 267 Bending-plate or-beam Methods; X-ray and Electrondiffraction Methods; Other Techniques 2.2 Experimental Results 271 Thermal Stress; Intrinsic Stress; Substrate Temperature Dependence; Thickness Dependence; Deposition Rate and Angle-of-incidence Dependence; Annealing Effects; Anisotropic Stresses; Stresses in Chemically Prepared Films 2.3 Origin of Intrinsic Stress 287 Thermal Effect; Volume Changes; Surface Layer; Surface Tension; Electrostatic Effects; Lattice-misfit Accommodation Model; Structural-defect Hypothesis; Crystalliteboundary Mismatch Model; Anisotropic Growth 3. Mechanical Properties Experimental Techniques 296 High-speed Rotor; Bulge Test; Tensile Test; Electronmicroscope Devices; Direct Measurement of Strain 3.2 Experimental Results 298 Stress-Strain Curves; Tensile Strength; Microhardness 3.3 Origin of the Tensile-strength Effects 306 Structural-defect Hypothesis; Surface Effects; Volume Effects; Phenomenological Approach 3.4 Films vs. Whiskers Stress Relief Adhesion of Films Measurement of Adhesion Experimental Results Origin of Adhesion 321

Contents XV 5. Concluding Remarks 322 References 323 VI ELECTRON-TRANSPORT PHENOMENA IN METAL FILMS 328 1. Introduction 328 2. Electrical Conduction in Discontinuous Films 329 2.

6 Contents XV 5. Concluding Remarks 322 References 323 VI ELECTRON-TRANSPORT PHENOMENA IN METAL FILMS Introduction Electrical Conduction in Discontinuous Films Conduction Mechanisms 329 Thermionic (Schottky) Emission; Quantum-mechanical Tunneling; Activated Tunneling; Tunneling between Allowed States; Tunneling via Substrate and Traps 2.2 Experimental Results Temperature Coefficient of Resistivity (TCR) Network (Porous) Films Elastoresistance Electrical Conduction in Continuous Films Theories of Size Effect Experimental Results 355 Thickness Dependence; Low-temperature Results; Size-effect Anisotropy; Magnetic Boundary Scattering; Superimposed Films 3.3 Temperature Coefficient of Resistivity (TCR) 365 Theory; Experimental Results 3.4 Specular Scattering Field Effect Influence of Absorption and Adsorption on Conductivity Conductivity Changes Due to Annealing High-resistivity Films Galvanomagnetic Size Effects in Thin Films Introduction Longitudinal Magnetoresistance Transverse Magnetoresistance (Field Perpendicular to the Film Surface-Hl) Transverse Magnetoresistance (Field Parallel to the Film Surface-H ) Hall Effect in Thin Films The Anomalous Skin Effect Eddy-current Size Effects Transport of Hot Electrons Thermal Transport Thermal Conductivity Thermoelectric Power Heat Transport across Film - Insulator Interface 423

Contents 7. Concluding Remarks 425 References 425 TRANSPORT PHENOMENA IN SEMICONDUCTING FILMS 434 1. Introduction 434 2.

7 Contents 7. Concluding Remarks 425 References 425 TRANSPORT PHENOMENA IN SEMICONDUCTING FILMS Introduction Theoretical Considerations 435 Mobility; Galvanomagnetic Surface Effects; Anisotropy Effects; Quantum Size Effects 3. Experimental Results Size Effects Transport Properties of Thick Films Photoconduction in Semiconductor Films Activation Process Photoconductivity Mechanisms High-voltage Photovoltaic Effect Field Effect - Thin-film Transistor (TFT) Concluding Remarks 459 References 460 TRANSPORT PHENOMENA IN INSULATOR FILMS Introduction Dielectric Properties Thin Films Thick Films Dielectric Losses Piezoelectric Films Electrical Conduction in Insulator Films Conduction Mechanisms Thermionic (Schottky) Emission Quantum-mechanical Tunneling 483 Theories; Image-force Correction; Temperature-field (TF) Emission; Temperature Dependence; Experimental Results; Conclusions 4.4 Bulk-limited Conduction 499 Space-charge-limited Current (SCLC) Flow; Trap and Impurity Effects 4.5 Voltage-controlled Negative Resistance (VCNR) Current-controlled Negative Resistance (CCNR) Tunnel Emission (Hot-electron Transport) Tunnel Spectroscopy Photoeffects in Tunnel Structures Electroluminescence 516

Contents xvii 5.2 Photoconduction and Photoemission 518 6. Concluding Remarks 522 References 522 IX SUPERCONDUCTIVITY IN THIN FILMS 529 1. Introduction 529 2. Basic Concepts 530 3.

8 Contents xvii 5.2 Photoconduction and Photoemission Concluding Remarks 522 References 522 IX SUPERCONDUCTIVITY IN THIN FILMS Introduction Basic Concepts Transition Temperature of Thin-film Superconductors Introduction Thickness Dependence Superconductivity-enhancement Phenomenon Mechanisms of Enhanced Superconductivity Influence of Stress Influence of Impurities Electrostatic-charge (Field) Effect Proximity Effects in Superimposed Films Critical Magnetic Field Type I Films Type II Films Mean-free-path Dependence of Яр Transverse Critical Field Critical Current Propagation of Normal and Superconducting Phases Superconductive Tunneling Experimental Results 576 General; Tunneling in Superimposed Films; Gapless Superconductivity 7.2 Supercurrent (Josephson) Tunneling Infrared Transmission through Thin Films Superconductive Thin-film Devices Cryotrons 588 Wirewound Cryotron; Crossed-film Cryotron (CFC); The Shielded CFC; In-line Cryotron; Multicrossover Cryotron (MCC); Ferromagnetic Cryotron Configuration 9.2 Computer Memory Devices 593 Crowe Cell; Persistor, Persistatron, and Continuous-film Memory (CFM) 9.3 Superconducting Magnets Low-frequency Devices Bolometers Radiation Detectors Tunnel Devices Concluding Remarks 599 References 600

XVÜi Contents X FERROMAGNETISM IN FILMS (by M. H.Cohen) 608 1. Introduction 608 2. Magnetization vs. Thickness 610 3. Stoner-Wohlfarth Model (A First Approximation) 614 4. Magnetic Anisotropy 619 4.

9 XVÜi Contents X FERROMAGNETISM IN FILMS (by M. H.Cohen) Introduction Magnetization vs. Thickness Stoner-Wohlfarth Model (A First Approximation) Magnetic Anisotropy Shape Anisotropy Magnetocrystalline Anisotropy Strain-Magnetostriction Anisotropy M-induced Uniaxial Anisotropy Oblique-incidence Uniaxial Anisotropy Unidirectional Anisotropy Perpendicular Anisotropy Magnetization Ripple Anisotropy-dispersion Model Micromagnetic Model 639 Hoffmann's Theory; Harte's Theory 6. Quasi-static Manifestations of Ripple Rotational Hysteresis HA Domain Splitting (HA Fallback) Initial Susceptibility Effects of High KD/K U Domain Walls Structure of Walls 659 Bloch Walls; Ne'el Walls; Crosstie Walls; Other Wall Calculations; Experimental Results 7.2 Wall Motion 666 Domain Nucleation and Growth; Coercive Force; Wall Velocity; Magnetic Viscosity; Creep; Wall Streaming 8. Resonance Ferromagnetic Resonance Spin-wave Resonance Energy-loss Mechanisms Switching Coherent Rotation Theory Experimental Results Interpretation Complex Magnetization Configurations M Normal to Film Plane 693 MnBi Films (К ] _ < 0); Stripe Domains (K i > 0) 10.2 Multilayer Films 696 Interaction Mechanisms; Domain Wall Interactions 10.3 Cylindrical Films 698

Contents XIX 11. Measurement Techniques 699 11.1 Microscopic Observations 699 Bitter Technique; Kerr and Faraday Magneto-optical Effects; Lorentz Electron Microscopy 11.

10 Contents XIX 11. Measurement Techniques Microscopic Observations 699 Bitter Technique; Kerr and Faraday Magneto-optical Effects; Lorentz Electron Microscopy 11.2 Macroscopic Measurements 702 Mechanical Detection (Torque Magnetometer); Fluxpickup Detection; Magneto-optic Detection; Magnetoresistive or Hall-effect Detection; Ripple-independent H Determinations 12. Applications Flat-film Memory Cylindrical-film Memory Future Developments 710 References 710 XI OPTICAL PROPERTIES OF THIN FILMS Introduction Thin Film Optics Reflection and Transmission at an Interface Reflection and Transmission by a Single Film Anisotropic and Inhomogeneous Films Multilayer Films Optical Absorption Optical Constants of Thin Films Experimental Methods 732 Reflection Methods; Reflectance and Transmittance Methods; Interferometric Methods; Spectrophotometric Methods; Critical-angle Method; Polarimetrie Methods (Ellipsometry); Summary 3.2 Results on Optical Constants 741 General Remarks; Metal Films; Abnormal Absorption Phenomenon; Maxwell-Garnett Theory of Abnormal Absorption; Dielectric and Semiconducting Films 3.3 Size Effects in Optical Properties 757 Semiconductor and Dielectric Films; Metal Films 4. Thin Film Absorption and Photoemission Phenomena Infrared Absorption 761 Optical Modes; Surface Modes 4.2 Magneto-optical Absorption Plasma-resonance Absorption Ultraviolet Absorption Photoemission from Metal Films 767

XX Contents 5. Multilayer Optical Systems 769 5.1 Antireflection Coatings 770 Inhomogeneous Films; Homogeneous Single Films; Multilayer Films; Infrared Antireflection Coatings 5.

11 XX Contents 5. Multilayer Optical Systems Antireflection Coatings 770 Inhomogeneous Films; Homogeneous Single Films; Multilayer Films; Infrared Antireflection Coatings 5.2 Reflection Coatings 777 Metal Mirrors; All-dielectric System 5.3 Interference Filters 781 Reflection Filters; Transmission Interference Filters; Frustrated Total-re flection Filter 5.4 Absorptance and Thermal Emittance of Coatings Thin-film Polarizers Concluding Remarks 786 References 787 Author Index 795 Subject Index 827

and Technology of Thin Films

An Introduction to Physics and Technology of Thin Films This page is intentionally left blank An Introduction to Physics and Technology of Thin Films Alfred Wagendriste1 Institute of Applied and Technical