Table of Contents

Typical Equipment for Optical Coating Production

• 1.1. INTRODUCTION 1
• 1.2. GENERAL REQUIREMENTS 2
• 1.2.1. The Vacuum 5
• 1.2.2. Deposition Sources 27
• 1.2.3. Fixturing and Uniformity 61
• 1.2.4. Temperature Control 73
• 1.2.5. Process Control 78
• 1.3. TYPICAL EQUIPMENT 81
• 1.4. ALTERNATIVE APPROACHES 86
• 1.5. UTILITIES 90

Measurements

• 2.1. INTRODUCTION 103
• 2.2. SPECTROPHOTOMETERS 104
• 2.2.1 Dispersive Spectrometers and Spectrophotometers 104
• 2.2.2 Interferometric Spectrometers and Spectrophotometers 108
• 2.2.3 Fourier Transform Infrared versus Grating Instruments 116
• 2.2.4 Types of Reflecting Surfaces 119
• 2.2.5 The Original Recording Spectrophotometer 120
• 2.2.6. Measuring Transmittance 122
• 2.2.7. Potential Measurement Problems 125
• 2.2.8. Measuring Reflectance 127
• 2.2.9. Checking Linearity of Reflectance Measurements 131
• 2.2.10. Other Reflectance Measurements 135
• 2.2.11. Photodiode Array Spectrometers 138
• 2.3. COLOR MEASUREMENTS 141
• 2.3.1. Typical Color Filters 141
• 2.3.2. Plotting Colors on a C.I.E. 1976 Diagram 142
• 2.3.3. Comparing Gels and Optical Thin Film Coatings 144
• 2.3.4. Tolerancing the Production of Color Filters 147
• 2.3.5. Tolerancing and MacAdam Ellipses 148
• 2.3.6. Illuminants and Metameric Matches 149
• 2.3.7. Caution With Respect to Light Sources 151
• 2.4. INDEX & THICKNESS DETERMINATION 153
• 2.4.1. Index of Refraction Determination 154
• 2.4.2. Fitting Values for High Index Materials 154
• 2.4.3. Fitting Values for Low Index Materials 159
• 2.4.4. Using the FilmStar Software Package for Index Fitting 160
• 2.4.5. Tuning-In the Thickness of a Four-Layer AR 164
• 2.4.6. Another Index Test Method 166

Materials and Processes

• 3.1. PROCESS KNOW-HOW 173
• 3.1.1. Film Growth Models and Observations 175
• 3.1.2. Chiral and Sculptured Coatings 184
• 3.1.3. Stress in Coatings 184
• 3.1.4. Laser Damage in Coatings 187
• 3.1.5. Rain Erosion of Coatings 191
• 3.2. MATERIALS 192
• 3.2.1. Silicon Compounds 194
• 3.2.2. Titanium Oxides, TiO through TiO2 201
• 3.2.3. Magnesium Compounds 210
• 3.2.4. Germanium 223
• 3.2.5. Thorium Fluoride 224
• 3.2.6. Zinc Sulfide 225
• 3.2.7. Zinc Selenide 228
• 3.2.8. Lead Telluride 229
• 3.2.9. Hafnium Compounds 230
• 3.2.10. Niobium and Neodymium Compounds 231
• 3.2.11. Yttrium Compounds 232
• 3.2.12. Zirconium Dioxide 234
• 3.2.13. Tantalum Pentoxide 236
• 3.2.14. Aluminum Compounds 238
• 3.2.15. Cerium Compounds 241
• 3.2.16. Scandium Oxide 242
• 3.2.17. Zinc Oxide 243
• 3.2.18. Lead Fluoride 244
• 3.2.19. Calcium Fluoride 245
• 3.2.20. Barium Fluoride 245
• 3.2.21. Ytterbium Fluoride 246
• 3.2.22. Lanthanum Compounds 246
• 3.2.23. Rhodium 248
• 3.2.24. Chromium 249
• 3.2.25. Aluminum 250
• 3.2.26. Silver 251
• 3.2.27. Gold 253
• 3.2.28. Indium-Tin Oxide 254
• 3.2.29. Electrochromic Materials, Tungsten Oxide, Etc. 257
• 3.2.30. Cubic Boron Nitride 259
• 3.2.31. Bismuth Oxide 261
• 3.2.32. Gadolinium Fluoride 262
• 3.2.33. Lithium Fluoride 262
• 3.2.34. Toxicity of Coating Materials 263
• 3.2.35. Relative Cost of Coating Materials 263
• 3.3. MIXED MATERIALS and TERNARY OXIDES 264
• 3.4. CRYSTAL MONITOR CONTROLLER SETUP 268
• 3.4.1 The Problem 268
• 3.4.2 The Solution 269
• 3.4.3 Setting Ramp and Soak Times 270
• 3.4.5 Soak Level Before Shutter Opens 274
• 3.4.6 Control Delay After Shutter Opens 275
• 3.5. IONS AND ION SOURCES 276
• 3.5.1. Ion to Atom Arrival Ratio (IAAR) and Its Implications 276
• 3.5.2. Kaufman Gridded Source 280
• 3.5.3. Cold Cathode Source 282
• 3.5.4. End-Hall Source 284
• 3.5.5. IS1000/PS1500 Plasma/Ion Source 287
• 3.5.6. Behavior of Three Types of Plasma/Ion Sources 290
• 3.5.7. Ion/Plasma Sources with Fluoride Coatings 302
• 3.6. OTHER PROCESSES TO CONSIDER 302
• 3.6.1. Physical Vapor Deposition 303
• 3.6.2. Dip, Spin, and Spray Coatings 304
• 3.6.3. Chemical Vapor Deposition 305
• 3.6.4. Plasma-Enhanced CVD 306
• 3.6.5. Plasma Polymerization 307
• 3.6.6. Hard Carbon Coatings 307
• 3.6.7. Atomic Layer Deposition 309

Thin Film Monitoring and Control

• 4.1 OVERVIEW 345
• 4.2 SIMPLE MONITORS 350
• 4.2.1. "Eyeball" and Measured Charge 351
• 4.2.2. Optical Thickness Monitors 355
• 4.2.3. Automation versus Manual Monitoring 358
• 4.3 CRYSTAL MONITORS 360
• 4.3.1. Crystal Thickness Controllers 360
• 4.3.2. Crystal Control of Eyeglass Coatings 363
• 4.3.3. Calibrations and Variations 368
• 4.3.4. Tooling Factors 369
• 4.3.5. Variations 370
• 4.4 DIRECT VERSUS INDIRECT 371
• 4.5 CHIP CHANGERS 372
• 4.6 SENSITIVITY TO ERRORS 375
• 4.6.1. Geometrical Factors 375
• 4.6.2. Spectral Requirement Factors 376
• 4.7 ERROR COMPENSATION AND DEGREE OF CONTROL 382
• 4.7.1. Narrow Bandpass Filter Monitoring 382
• 4.7.2. Broad Band AR Coating Monitoring 386
• 4.8 ERROR ACCUMULATION 389
• 4.9 NBP FILTER MONITORING 390
• 4.9.1. Signal to Noise in Monitoring 392
• 4.9.2. Special Layers in NBP Monitoring 393
• 4.10 LAST TWO LAYERS OF NBP FILTERS 394
• 4.10.1 Types of Final Layer Monitoring Techniques 395
• 4.10.2 Basis of Predicted Thickness 397
• 4.10.3 Summary of the Last Two Layers of a NBP Filter 404
• 4.11 MORE ON SENSITIVITY 404
• 4.11.1 Effects of Errors on the Average Transmission 404
• 4.11.2 Sensitivity of Turning Points in Monitoring 406
• 4.11.3 Total Error Sensitivity of the Average Transmission 408
• 4.11.4 Error Compensation in the Monitoring 409
• 4.12 OTHER EFFECTS ON OPTICAL MONITORS 413
• 4.12.1 Error Due to Drift in the Monitoring Wavelength 413
• 4.12.2. Effects of Thin Film Wedge on the Monitor Chip 414
• 4.12.3. Error Due to Width of the Monitoring Passband 416
• 4.13 TURNING POINT DETECTION 418
• 4.13.1. Precision versus Accuracy 418
• 4.13.2. Optical Monitor with the Method of Schroedter 418
• 4.13.3. Suggestion for Monitoring of DWDM Filters, Etc. 420
• 4.13.4. More on Turning Point Detection 421
• 4.13.5. Terminations by the Last Maximum and Minimum 422
• 4.14 CONSTANT LEVEL MONITORING 423
• 4.15 SENSITIVITY AND CORRECTION STRATEGIES 425
• 4.15.1. Sensitivity versus Layer Termination Point 425
• 4.15.2. Sensitivity Versus g-Value 427
• 4.15.3. Constant Level Monitoring Strategies 431
• 4.16 PASSIVE VERSUS ACTIVE, STEERING 436
• 4.16.1. Passive Versus Active Optical Monitoring 436
• 4.16.2. Steering the Monitoring Signal Result 436
• 4.17 PRECOATED MONITOR CHIPS 445
• 4.17.1. Eliminating the Precoated Chip 445
• 4.17.2. General Design Procedure 447
• 4.17.3. Specific Design Procedure 447
• 4.17.4. Results of the Procedure 451
• 4.18 DESENSITIZING FOR %T/%R ERRORS 453
• 4.19 OVERCOMING ABSORPTION 463
• 4.20 REVERSE & FORWARD ENGINEERING 465
• 4.20.1. A Narrow Bandpass Filter 465
• 4.20.2. A Special "Multichroic" Beamsplitter 466
• 4.20.3. A Very Broadband Antireflection Coating 467
• 4.20.4. The Rest of the Story 473
• 4.21 FENCEPOST MONITORING 474
• 4.21.1 Monitoring in General Cases 475
• 4.21.2 Monitoring Non-QWOT NBP Filters 479
• 4.21.3 New Approach to NBP Monitoring and Control 484
• 4.21.4 Preliminary Conclusions on Fencepost Monitoring 493
• 4.21.5 Simulation of Error Effects in FP Monitoring 493
• 4.22 DIRECT DOUBLE BEAM MONITORING 502
• 4.22.1 Single Beam versus Double Beam Optical Monitors 502
• 4.22.2. Intermittent Monitoring 503
• 4.23 ELLIPSOMETRIC MONITORING 505
• 4.24 BROAD BAND OPTICAL MONITORING 512

Process Development

• 5.1. INTRODUCTION 529
• 5.2. DESIGN OF EXPERIMENTS METHODOLOGY 533
• 5.2.1. Process Flow Diagram 533
• 5.2.2. Cause-and-Effect Diagram 534
• 5.2.3. Control, Noise, or Experiment 535
• 5.2.4. Screening and Pareto Ranking 536
• 5.2.5. Standard Operating Procedures 538
• 5.3. DESIGN OF THE EXPERIMENTS: EXAMPLES 538
• 5.3.1. A Central Composite Design for Aluminizing 540
• 5.3.2. A Box-Behnken Design for IAD Deposition of TiO2 544
• 5.4. REAL LIFE EXAMPLE PROBLEM SOLVING 551
• 5.5. ANOTHER REAL LIFE EXAMPLE 556