THIN FILM MATERIALS TECHNOLOGY

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THIN FILM MATERIALS

TECHNOLOGY

Sputtering of

Compound Materials

by

Kiyotaka Wasa

Yokohama City University

Yokohama, Japan

Makoto Kitabatake

Matsushita Electric Industrial Co., Ltd.

Kyoto, Japan

Hideaki Adachi

Matsushita Electric Industrial Co., Ltd. Kyoto, Japan

YMam Andrew

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2.1 THIN FILM GROWTH PROCESS 17 2.1.1 Structural Consequences of the Growth Process 23 2.1.1.1 Microstructure 24 2.1.1.2 Surface Roughness and Density 26 2.1.1.3 Adhesion 29 2.1.1.4 Metastable Structure 31 2.1.2 Solubility Relaxation 33 2.2 THIN FILM DEPOSITION PROCESS 33 2.2.1 Classification of Deposition Processes 33 2.2.1.1 PVD Processes 33 2.2.1.1 CVD Processes 44 2.2.2 Deposition Conditions .. 47 2.3 CHARACTERIZATION .' 60 REFERENCES 66

3 Sputtering Phenomena 71

3.1 SPUTTER YIELD 71 3.1.1 Ion Energy 72 3.1.2 Incident Ions, Target Materials 78 3.1.3 Effects of Incidence Angle 79

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aw Contents

3.1.4 Crystal Structure of Target 84 3.1.5 Sputter Yields of Alloys 87 3.2 SPUTTERED ATOMS 90 3.2.1 Features of Sputtered Atoms 90 3.2.2 Velocity and Mean Free Path 91 3.2.2.1 Velocity of Sputtered Atoms 91 3.2.2.2 MeanFreePath 97 3.3 MECHANISMS OF SPUTTERING 97 3.3.1 Sputtering Collisions 98 3.3.2 Sputtering 100 3.3.2.1 Classical Empirical Formula of Sputtering Yield.... 101 3.3.2.2 Linear Cascade Collision Theory 103 3.3.2.3 Simplified Model and Modern Yield Formula 109 REFERENCES I l l

4 Sputtering Systems 115

4.1 DISCHARGE IN A GAS 115 4.1.1 Cold Cathode Discharge 115 4.1.2 Discharge in a Magnetic Field 124 4.1.2.1 Spark Voltage in a Magnetic Field 124 4.1.2.2 Glow Discharge in a Magnetic Field 127 4.1.2.3 Glow Discharge Modes in a Transverse

Magnetic Field 129 4.1.2.4 Plasma in a Glow Discharge 133 4.2 SPUTTERING SYSTEMS 135 4.2.1 DC Diode Sputtering 136 4.2.2 RF Diode Sputtering 137 4.2.3 Magnetron Sputtering 139 4.2.4 Ion Beam Sputtering 151 4.2.5 ECRPlasma 153 4.2.6 Medium-Frequency Sputtering 154 4.3 PRACTICAL ASPECTS OF SPUTTERING SYSTEMS 156 4.3.1 Targets for Sputtering 157 4.3.1.1 Compound Targets 157 4.3.1.2 Powder Targets 160 4.3.1.3 Auxiliary Cathode 161 4.3.2 Sputtering Gas 162 4.3.3 Thickness Distribution 168 4.3.4 Substrate Temperature 173 4.3.5 Off-Axis Sputtering; Facing-Target Sputtering 173 4.3.6 Monitoring ' 177 4.3.6.1 Gas Composition 177

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4.3.6.2 Sputtering Discharge 178 4.3.6.3 Plasma Parameters 179 4.3.6.4 Substrate Temperature Monitoring 183 4.3.6.5 Thickness Monitoring 184 4.3.6.6 Film Structure 185 REFERENCES 187

Deposition of Compound Thin Films 191

5.1 OXIDES 219 5.1.1 ZnO Thin Films 219 5.1.1.1 Deposition of ZnO 221 5.1.1.2 Electrical Properties and Applications 236 5.1.2 Sillenite Thin Films 248 5.1.2.1 Amorphous/Polycrystalline Films ..249 5.1.2.2 Single-Crystal Films .252 5.1.3 Perovskite Dielectric Thin Films 254 5.1.3.1 PbTiO3 Thin Films 255

5.1.3.2 PLZTThinFilms 271 5.1.4 Perovskite Superconducting Thin Films 295 5.1.4.1 Studies of Thin Film Processes 301 5.1.4.2 Basic Thin Film Processes 302 5.1.4.3 Synthesis Temperature 308 5.1.4.4 Low-Temperature Processes, In-Situ Deposition 309 5.1.4.5 Deposition of Rare-Earth, High~rc Superconductors .311

5.1.4.6 Deposition of Rare-Earth-Free, High-rc

Superconductors 320 5.1.4.7 Structure and Structural Control 324 5.1.4.8 Phase Control by Layer-by-Layer Deposition 329 5.1.4.9 DiamagnetizationProperties 332 5.1.4.10 Passivation of Sputtered High-rc Thin Films 334

5.1.4.11 Multilayers and Superconducting Devices 338 5.1.5 Transparent Conducting Films 340 5.2 NITRIDES 342 5.2.1 TiN Thin Films 342 5.2.2 Compound Nitride Thin Films 343 5.2.3 Si-N Thin Films .'. 344 5.3 CARBIDES AND SILICIDES 345 5.3.1 SiC Thin Films 346 5.3.2 Tungsten Carbide Thin Films 355 5.3.3 Mo-Si Thin Films 359 5.4 DIAMOND 359 5.5 SELENIDES 365 5.6 AMORPHOUS THIN FILMS 368

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xiv Contents

5.6.1 Amorphous ABO3 371

5.6.2 Amorphous SiC 374 5.7 SUPERLATTICE STRUCTURES 375 5.8 ORGANIC THIN FILMS 378 5.9 MAGNETRON SPUTTERING UNDER A STRONG

MAGNETIC FIELD 380 5.9.1 Abnormal Crystal Growth 380 5.9.2 Low-Temperature Doping of Foreign Atoms into

Semiconducting Films 382 REFERENCES 389

6 Structural Control of Compound Thin Films:

Perovskite and Nanometer Oxide Thin Films 405

6.1 FERROELECTRIC MATERIALS AND STRUCTURES 406 6.1.1 Ferroelectric Materials 406 6.1.2 Microstructure of Heteroepitaxial Thin Films 410 6.2 CONTROL OF STRUCTURE 417 6.2.1 Growth Temperature 418 6.2.2 Buffer Layers and Graded Interfaces 422 6.2.3 Cooling Rate 429 6.2.4 Vicinal Substrates 432 6.2.5 Dielectric Properties of Structure-Controlled Thin Films 443 6.3 NANOMETER STRUCTURE 448 6.3.1 Nanometer Materials 448 6.3.2 Nanometer Superlattice 452 6.4 INTERFACIAL CONTROL 455 REFERENCES 460 7 Microfabrication by Sputtering 465

7.1 CLASSIFICATION OF SPUTTER ETCHING 465 7.2 ION-BEAM SPUTTER ETCHING 469 7.3 DIODE SPUTTER ETCHING 482 7.4 DEPOSITION INTO DEEP-TRENCH STRUCTURES 487 REFERENCES 490

Appendix 493

Table A. 1. Electric Units, Their Symbols and Conversion Factors . 493 Table A.2. Fundamental Physical Constants 495

THIN FILM MATERIALS TECHNOLOGY