Handbook of physical vapor deposition (PVD) processing : film formation, adhesion, surface, prepartion and contamination control

Table of Contents ix ix 1 Introduction .......................................................................... 29 1.1 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 1.2 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 1.3 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 1.4 SAFETY AND ENVIRONMENTAL CONCERNS ...................... 50 Table of Contents x Handbook of Physical Vapor Deposition (PVD) Processing 1.5 UNITS............................................................................................. 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 2 Substrate (“Real”) Surfaces and Surface Modification .... 56 2.1 INTRODUCTION .......................................................................... 56 2.2 MATERIALS AND FABRICATION ............................................ 57 2.2.1 Metals .............................................................................. 57 2.2.2 Ceramics and Glasses ...................................................... 59 2.2.3 Polymers .......................................................................... 61 2.3 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 2.4 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 Adsorption—Gases and Liquids ................................. 86 Table of Contents xi 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 3 The Low-Pressure Gas and Vacuum Processing Environment ....................................................................... 127 3.1 INTRODUCTION ........................................................................ 127 3.2 GASES AND VAPORS ............................................................... 128 3.2.1 Gas Pressure and Partial Pressure ................................. 129 Pressure Measurement .............................................. 131 Identification of Gaseous Species............................. 135 xii Handbook of Physical Vapor Deposition (PVD) Processing 3.2.2 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 3.3 GAS-SURFACE INTERACTIONS ............................................. 143 3.3.1 Residence Time ............................................................. 143 3.3.2 Chemical Interactions .................................................... 144 3.4 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 3.5 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 3.6 VACUUM PUMPING.................................................................. 179 3.6.1 Mechanical Pumps ........................................................ 179 Oil-Sealed Mechanical Pumps .................................. 180 Dry Pumps ................................................................ 181 Diaphragm Pumps .................................................... 182 Table of Contents xiii 3.6.2 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 xiv Handbook of Physical Vapor Deposition (PVD) Processing 4 The Low-Pressure Plasma Processing Environment ...... 237 4.1 INTRODUCTION ........................................................................ 237 4.2 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 4.3 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 4.4 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 4.5 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 Table of Contents xv 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 5 Vacuum Evaporation and Vacuum Deposition ............... 288 5.1 INTRODUCTION ........................................................................ 288 5.2 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 5.3 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 xvi Handbook of Physical Vapor Deposition (PVD) Processing 5.4 TRANSPORT OF VAPORIZED MATERIAL ............................ 309 5.4.1 Masks ............................................................................. 309 5.4.2 Gas Scattering ................................................................ 309 5.5 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 5.6 MATERIALS FOR EVAPORATION ......................................... 314 5.6.1 Purity and Packaging ..................................................... 314 Purchase Specifications ............................................ 315 5.6.2 Handling of Source Materials ....................................... 315 5.7 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 5.8 PROCESS MONITORING AND CONTROL ............................. 319 5.8.1 Substrate Temperature Monitoring ............................... 320 5.8.2 Deposition Monitors—Rate and Total Mass ................. 320 5.8.3 Vaporization Source Temperature Monitoring ............. 322 5.8.4 In Situ Film Property Monitoring .................................. 322 5.9 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 5.10 ADVANTAGES AND DISADVANTAGES OF VACUUM DEPOSITION ............................................................................ 326 5.11 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 5.12 GAS EVAPORATION AND ULTRAFINE PARTICLES .......... 329 5.13 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 Table of Contents xvii 5.14 SUMMARY.................................................................................. 331 FURTHER READING .............................................................................. 331 REFERENCES .......................................................................................... 332 6 Physical Sputtering and Sputter Deposition (Sputtering)343 6.1 INTRODUCTION ........................................................................ 343 6.2 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 6.3 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 6.4 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 6.5 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 6.6 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 6.7 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 xviii 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 7 Arc Vapor Deposition .............................................. 406 7.1 INTRODUCTION ........................................................................ 406 7.2 ARCS ............................................................................................ 407 7.2.1 Vacuum Arcs ................................................................. 407 7.2.2 Gaseous Arcs ....................