Beam Effects, Surface Topography, and Depth Profiling in Surface Analysis Edited by Alvin W. Czanderna National Renewable Energy Laboratory Golden, Colorado Theodore E. Madey Rutgers, The State University ofnew Jersey Piscataway, New Jersey and Cedric J. Powell National Institute of Standards and Technology Gaithersburg, Maryland PLENUM PRESS NEW YORK AND LONDON
Contents 1. Photon Beam Damage and Charging at Solid Surfaces John H. Thomas III 1. Introduction 1 2. Electrostatic Charging of Samples in Photoemission Experiments 2 2.1. Electrostatic Surface Charging 2 2.2. Differential Surface Charging 8 2.3. Lateral and In-Depth Charge Effects 10 2.4. Small-Spot Analysis Charging Effects 13 3. Energy Scale Calibration 13 4. The Auger Parameter: Charge-Independent Chemical Identification 18 5. Photon Damage 20 5.1. Photon Absorption Processes 20 5.2. Radiation Damage to Inorganic Materials 25 5.3. Photon Damage to Polymers 29 6. Closing Comments 34 References 35 2. Electron Beam Damage at Solid Surfaces Carlo G. Pantano, Andrew S. D'Souza and Alan M. Then 1. Introduction 39 2. Fundamentals 41 2.1. Electronic Excitation Processes 41 2.1.1. Electron-Stimulated Desorption 41 2.1.2. Electron-Stimulated Adsorption 45 2.1.3. Decomposition of Surface Layers and Thin Films 49 xiii
xiv Contents 2.1.4. Oxidation of Surface Layers and Thin Films... 53 2.1.5. Thresholds for Sample Damage Resulting from Electronic Excitation 54 2.2. Charging Insulators 58 2.3. Electromigration in Insulators 60 2.4. Electron-Beam-Induced Heating 64 3. Electron Beam Effects in Auger Surface Analyses 65 3.1. Physical Effects 65 3.2. Contaminated, Oxidized, or Coated Surfaces 69 3.3. Polymers 74 3.4. Glasses 74 3.5. Sputter Depth Profiles 80 3.6. Microanalyses 83 4. Recommendations 85 5. References 87 5.1. Review of Beam Damage in Electron Microscopy... 87 5.2. General Discussions of Electron Beam Damage in Surface Analysis 87 5.3. Fundamentals of Electron-Stimulated Desorption 87 5.4. Studies of Electron Beam Interactions at Solid Surfaces 88 5.5. Charging of Insulators Resulting from Electron Beam Irradiation 92 5.6. Electron Beam Damage in Glasses 93 5.7. Electron Beam Damage during Surface Analysis 94 3. Ion Beam Bombardment Effects on Solid Surfaces at Energies Used for Sputter Depth Profiling L. S. Dake, D. E. King, J. R. Pitts, anda. W. Czanderna 1. Introduction 97 1.1. Overview 97 1.2. Ion Beams and Solids: Topics Not Covered 102 1.3. Definitions and Nomenclature 103 1.4. Overview of lon-surface and Ion-Solid Interactions... 105 2. Ion Beam-Solid Interactions 108 2.1. Introduction 108 2.2. Ion Beam 110 2.2.1. Reflection/Backscattering 110 2.2.2. Penetration and Trapping 111 2.3. Ion-Substrate Interactions 116
2.4. Mixing and Implantation of Material 118 2.4.1. Ballistic Mixing 118 2.4.2. Diffusional Mixing Processes 122 2.5. Removalof Material 123 2.5.1. Physical Sputtering 124 2.5.2. SputterYields 125 2.5.3. Differential Sputtering 131 2.6. Altered Layer (Zone of Mixing) 133 Structural Changes Resulting from Ion Beam Bombardment... 139 3.1. Bond Stretching, Bond Breaking, and Surface Reconstruction from Ion Beam Bombardment 140 3.2. Structural Changes as Nanotopography from Ion Beam Bombardment 143 3.3. Surface Defect Formation from Ion Beam Bombardment 149 3.4. Damage Depth and Defect Density from Ion Beam Bombardment 154 3.5. Enhanced Diffusion and Changes in Electrical Properties from Ion Beam Bombardment 163 Physical Effects: Ion-Beam-Induced Topography 168 4.1. Introduction 168 4.2. Mechanisms for Topography Development 169 4.3. Microscopic and Macroscopic Roughness 173 4.4. EtchPits 176 4.5. Pyramids 181 4.6. Cones 182 4.7. Whiskers 189 4.8. Ripples and Corrugation 189 4.9. Sputter-InducedRecrystallization 193 4.10. Coalescence to Form Islands 193 4.11. Swelling 194 4.12. Smoothing 194 4.13. Miscellaneous Results 197 4.13.1. Topographical Differences in the Same Sample 197 4.13.2. Topography of Kapton and Teflon after Atom Beam Bombardment 198 4.13.3. Sputtering with Non-Noble-Gas Ions 198 4.13.4. Annealing Sputter Damage 201 4.14. Concluding Remarks 201 Compositional Changes and Chemical Effects 201 5.1. Introduction 201 XV
xvi Contents 5.2. Organic Materials 203 5.3. Alloys 206 5.3.1. Ternary Alloys 210 5.4. Semiconductors 211 5.5. Metal Oxides 213 5.5.1. Simple Metal Oxides 213 5.5.2. Complex Oxides: Perovskites 217 5.5.3. Complex Oxides: Glasses 218 5.6. Compounds 221 5.7. Calculations and Simulations 226 6. Depth Resolution: Sample, Beam, and Instrumental Effects 227 6.1. Introduction 227 6.2. Nature and Condition of the Sample 227 6.3. Ion Beam Bombardment Effects 231 6.4. Instrumental Effects 239 6.5. Ultimate and Practical Limits on Az 247 7. Combined Beam Effects 249 8. Applications 251 9. Summary and Concluding Remarks 252 References 255 Appendix 1. Acronyms and Abbreviations 273 4. Characterization of Surface Topography T. V. Vorburger, J. A. Dagata, G. Wilkening, and K. lizuka 1. Introduction 275 2. Results Obtainable with Profiling Instruments 279 2.1. Profile Recordings and Dimensional Measurement... 279 2.2. Surface Statistics 281 2.2.1. Surface Parameters 282 2.2.2. Statistical Functions 285 2.2.3. Other Statistical Descriptors 290 2.3. B and width Limits 290 3. Stylus Instruments 291 3.1. Height Resolution and Range 291 3.2. Lateral Resolution and Range 293 3.3. Stylus Load and Surface Deformation 296 3.4. Other Distortions 297 3.5. Calibration 299
Contents xvii 3.6. Applications 300 3.7. Area Profiling with Stylus Instruments 300 4. Optical Profiling Techniques 302 5. Scanned Probe Microscopy 307 5.1. Short History of Scanned Probe Microscopy 307 5.2. Calibration and Characterization 311 5.2.1. Instruments for Displacement Calibration 311 5.2.2. Calibration Specimens for Displacement 314 5.2.3. Instruments for Critical Dimensions and High Resolution 315 5.2.4. Specimens for Critical Dimensions 318 5.3. Other Types of Scanned Probe Microscopes 319 5.3.1. Force-Based Methods (Mechanical) 321 5.3.2. Methods Based on Other Probe-Sample Interactions 323 5.4. Applications of SPM Measurements 325 5.4.1. Data Storage Industries 325 5.4.2. Microelectronics Industries 326 5.4.3. Polymers and Coatings Industries 327 5.4.4. Optical Element Industries 327 5.4.5. Mechanical Parts Industries and Materials Science 328 5.4.6. Electrochemical Science 329 5.5. Future Directions: Techniques and Instrumentation... 330 6. Intercomparisons 334 7. Conclusions 339 References 341 5. Depth Profiling Using Sputtering Methods H. W. Werner and P. R. Boudewijn 1. Introduction 355 1.1. Principle of Sputter Depth Profiling 357 1.2. Methods for Sputter Depth Profiling 359 1.3. Different Modes of Sputter Depth Profiling 360 1.3.1. Planar Sputter Depth Profiling 360 1.3.2. Crater-Wall, Tapered-Section, or Angular-Mapping Depth Profiling 362 1.4. Comparison of Sputter Depth Profiling with Other Methods 362 1.4.1. Consumptive Methods for Depth Profiling 362
1.4.2. Nonconsumptive Methods and Modes for Depth Profiling 363 2. Physical Basis of the Sputtering Process 366 2.1. Introduction 366 2.2. Theory of the Sputtering Process 366 2.2.1. Binary Collision Theory 366 2.2.2. Classification of Sputtering Events 367 2.2.3. Sputtering from Linear Collision Cascades... 367 2.3. Sputtering Yields (Experimental) 371 2.4. Information Depth 373 2.5. Processes Related to Sputtering 376 3. Experimental Aspects 378 3.1. Introduction 378 3.2. Ion Beam Sources 378 3.3. Time Needed to Obtain a Depth Profile 381 4. Analysis of Sputter Depth Profiles 382 4.1. Introduction 382 4.2. Conversion of the Sputter Depth Profile of an Element X, /(X, t), into a Concentration Depth Profile c(z) 382 4.2.1. Determination of the Depth Scale 382 4.2.2. Conversion of the Measured Signal / into an Elemental Concentration c 383 4.3. Artifacts in Sputter Depth Profiles 386 4.3.1. Artifacts Related to the Interaction Process between Energetic Projectiles and the Solid... 386 4.3.2. Artifacts Related to the Properties of the Sample. 389 4.3.3. Artifacts Related to Instrumental Parameters... 391 4.4. Evaluation of a Measured Depth Profile 394 4.4.1. Depth Resolution 394 4.4.2. Detection Limit for a Given Element 396 5. Application of Sputter Depth Profiling to Various Thin-Film Materials 397 5.1. Stable Isotope Tracers 397 5.2. Thin-Film Interdiffusion and Multilayer Analysis 398 5.3. Corrosion and Oxidation 398 5.4. Catalysts 402 5.5. Polymer-Metal Interfaces 402 5.6. Insulating Materials 403 5.7. Semiconductor Materials 405 5.8. Miscellaneous Applications 409 5.9. Newcomers to Sputter-Depth-Profiling Techniques... 411
Contents xix 6. Summary and Future Prospects 412 Acknowledgment 412 References 412 Index 421