PRACTICAL DESIGN AND PRODOCTION OF OPTICAL THIN FILMS

Transcription

1 PRACTICAL DESIGN AND PRODOCTION OF OPTICAL THIN FILMS RONALD R.WILLEY LexaLite International Corporation Charlevoix, Michigan Marcel Dekker, Inc. New York Basel Hong Kong

2 Contents From the Series Editor Preface in v 1 Fundamentals of Thin Film Optics and the Use of Graphical Methods in Thin Film Design INTRODUCTION REVIEW OF THIN FILM OPTICS PRINCIPLES REFLECTANCE DIAGRAMS Low Reflectors, Antireflection Coatings High Reflectors Narrow Bandpass Pass Filters Beamsplitters Three Layer AR Coating on Germanium, Example Four Layer Broad Band AR Coating in Visible, Example ADMITTANCE DIAGRAMS TRIANGLE DIAGRAMS APPROXIMATIONS OF INDICES AND DESIGNS INHOMOGENEOUS INDEX FUNCTIONS LowlndexLimitations A Fourier Approach SUMMARY REFERENCES 44 vu

3 mil Contents 2 Estimating What Can Be Done Before Designing INTRODUCTION ANTIREFLECTION COATINGS Procedure The Formula Results Summary of Antirefiection Coating Estimation BANDPASS AND BLOCKER COATINGS Estimating the Width of a Blocking Band Estimating the Optical Density of a Blocking Band Estimating the Number of Layers and Thickness Needed Estimating More Complex Coatings DICHROIC REFLECTION COATINGS CHAPTER SUMMARY REFERENCES 66 3 Fourier Viewpoint of Optical Coatings INTRODUCTION FOURIER CONCEPTS Background Some Limitations A Method to Determine the Multiple Reflections Overcoming Low Index Limitations With Thickness Low Index Limitations Benefit of Extra Thickness Observations of Extra Thickness Characteristics Fourier View of the Characteristics Conclusions with Respect to More Thickness CONCLUSIONS REFERENCES 86 4 Typical Equipment for Optical Coating Production INTRODUCTION GENERAL REQUIREMENTS The Vacuum How Good a Vacuum is Needed? How Can We Create the Vacuum Needed? 91 Types of Pumps 94 Mechanical Pumps 95 Diffusion Pumps 96

4 Contents Roots Blowers Cryopumps Other Pumps Evaporation Sources Resistance Sources Electron Beam Sources Sputtering Sources Chemical Vapor Sources Fixturing and Uniformity Fixturing Configurations Protection from Back Coating Fixture Temperature Considerations Uniformity Source Positioning Masking Ion Sources and Uniformity Temperature Control Heating Cooling Temperature Sensors and Control Process Control 4.3. TYPICAL EQUIPMENT 4.4. ALTERNATIVE APPROACHES 4.5. UTILITIES 4.6. REFERENCES 5 Materials and Process Know-How 5.1. INTRODUCTION Index of Refraction Determination 5.2. MATERIALS Some Specific Materials Silicon Oxides, SiO to Si Titanium Oxides, TiO to Ti Magnesium Fluoride Germanium, Ge Thorium Fluoride Zinc Sulfide Zinc Selenide Lead Telluride Hafnium Dioxide Niobium and Neodymium Compound Yttrium Oxide Zirconium Dioxide Tantalum Pentoxide Aluminum Oxide

5 X Contents Cerium Dioxide Scandium Oxide Magnesium Oxide Zinc Oxide Aluminum Fluoride Cerium Fluoride Lead Fluoride Calcium Fluoride Barium Fluoride Chromium Aluminum Silver Gold Indium-Tin Oxide and Electrochromic Materials Toxicity of Coating Materials Relative Cost of Coating Materials PROCESS KNOW-HOW ION SOURCES OTHER PROCESSES TO CONSIDER Physical Vapor Deposition Dip and Spray Coatings Chemical Vapor Deposition Plasma Enhanced CVD Plasma Polymerization Hard Carbon Coatings SUMMARY REFERENCES Process Development INTRODUCTION DESIGN OF EXPERIMENTS METHODOLOGY Process Flow Diagram Cause & Effect Diagram Control, Noise, or Experiment Standard Operating Procedures DESIGN OF THE EXPERIMENTS, EXAMPLE A Central Composite Design for Aluminizing SUMMARY REFERENCES 211

6 Contents XI 7 Monitoring and Control of Thin Film Growth INTRODUCTION EFFECTS OF ERRORS WAYS TO MONITOR Measured Charge Time/Rate Monitoring Crystal Monitoring Optical Thickness Monitors Single Wavelength Monitoring 222 Turning Point Monitoring 223 Level Monitoring 223 Constant Level Monitoring Broad Band Optical Monitors Ellipsometric Monitors Trade-offs in Monitoring ERROR COMPENSATION AND DEGREE OF CONTROL Narrow Bandpass Monitoring Error Compensation in Edge Filters Broad Band Monitoring Compensation Effects of Thin Film Wedge on the Monitor Chip Effects of Monochromator Bandwidth on Optical Monitoring CALIBRATIONS AND VARIATIONS Tooling Factors Variations The Optical Monitor with Crystal Method of Schroedter SENSITIVITY AND STRATEGIES Sensitivity versus Layer Termination Point in Reflectance Sensitivity versus g-value Precoated Monitor Chips Eliminating the Precoated Chip Constant Level Monitoring Strategies Steering the Monitoring Signal Result Departures from Ideal Steering Concept Algorithm More on Photometries Example Case Lessons Learned Results Almost Achromatic Absentee Layers 260

7 XU 7.7. PRACTICAL CONSIDERATIONS A Narrow Bandpass Filter A Special "Multichroic" Beamsplitter A Very Broadband Antireflection Coating Single Beam versus Double Beam Optical Monitors Automation versus Manual Monitoring CHAPTER SUMMARY REFERENCES 274 Index 277