Practical Surface Analysis SECOND EDITION Volume 1 Auger and X-ray Photoelectron Spectroscopy Edited by D. BRIGGS ICI PLC, Wilton Materials Research Centre, Wilton, Middlesbrough, Cleveland, UK and M. P. SEAH Division of Materials Metrology, National Physical Laboratory, Teddington, Middlesex, UK JOHN WILEY & SONS Chichester New York Brisbane Toronto Singapore SALLE + SAUERLÄNDER Aarau Frankfurt am Main Salzburg
Contents Preface to First Edition Preface to Second Edition 1. A Perspective on the Analysis of Surfaces and Interfaces 1 M. P. Seah and D. Briggs 1.1 Introduction 1 1.2 The background to electron beam techniques 5 1.2.1 Auger electron spectroscopy 5 1.2.2 Other techniques 6 1.3 The background to photon beam techniques 7 1.3.1 X-ray photoelectron spectroscopy 7 1.3.2 Other techniques 9 1.4 The background to ion beam techniques 10 1.4.1 Secondary ion mass spectrometry 10 1.4.2 Secondary neutral mass spectrometry 11 1.4.3 Medium and low energy ion scattering spectroscopies 12 1.4.4 Other techniques 12 1.5 Conclusions 13 References 16 2. Instrumentation 19 J. C. Riviere 2.1 Introduction 19 2.2 Vacuum requirements 19 2.2.1 Attaining UHV 20 2.3 Sample handling and treatment 36 2.3.1 Sample introduction 37 2.3.2 Sample manipulation 40 2.3.3 Sample treatment 41 2.4 Sources 51 2.4.1 X-ray sources 51 2.4.2 Electron sources 61 2.4.3 Ion sources 66 xiii xv
vi Contents 2.5 Electron energy analysers 69 2.5.1 Energy resolution 70 2.5.2 Cylindrical mirror analyser (CMA) 71 2.5.3 Concentric hemispherical analyser (CHA) 75 References 83 3. Spectral Interpretation 85 D. Briggs and J. C. Riviere 3.1 Introduction 85 3.2 Nomenclature 85 3.2.1 j-j coupling 86 3.2.2 LS coupling 87 3.3 The electron-excited secondary electron spectrum 90 3.3.1 Auger electron spectra 92 3.4 The X-ray photoelectron spectrum 112 3.4.1 Primary structure 112 3.4.2 Information from primary structure 119 3.4.3 Secondary structure 127 3.4.4 Time-dependent spectra 133 3.5 Angular effects 134 3.5.1 Enhancement of surface sensitivity 134 3.5.2 Single-crystal studies 136 References 139 4. Depth Profiling in AES and XPS 143 S. Hofmann 4.1 Introduction 143 4.1.1 Non-destructive techniques 143 4.1.2 Destructive techniques 144 4.2 Practice of sputter depth profiling with AES and XPS 145 4.2.1 Vacuum requirements 146 4.2.2 Ion gun." 146 4.2.3 Analysing mode: comparison of AES and XPS 147 4.3 Quantification of sputtering profiles: principles 148 4.3.1 Calibration of the depth scale (z = f(t)) 149 4.3.2 Calibration of the concentration scale (x =/(/)) 151 4.3.3 Quantitative depth profiles of the chemical State 156 4.4 Sputtering profile compared to the original concentration profile: the concept of depth resolution 156 4.4.1 Depth resolution 156 4.4.2 Factors limiting depth resolution and accuracy of profiles. 161 4.4.3 Superposition of different contributions to depth resolution 173 4.4.4 Depth dependence of the depth resolution 174 4.4.5 Optimized depth profiling conditions 177
Contents 4.5 Special profiling techniques 180 4.5.1 Destructive methods using SAM 180 4.5.2 Non-destructive profiling by Variation of the electron emission angle or the electron energy 183 4.6 Deconvolution of sputtering profiles 186 4.7 Standard materials for depth profiling 192 4.8 Summary and conclusions 193 Acknowledgement 194 References 194 5. Quantification of AES and XPS 201 M. P. Seah 5.1 Introduction 201 5.2 Quantification of AES for homogeneous binary solids 202 5.2.1 Basic formalisms 202 5.2.2 Spectrometer terms 213 5.2.3 The measurement of intensity 214 5.3 Quantification of XPS for homogeneous binary solids 223 5.3.1 Basic considerations 223 5.3.2 Spectrometer terms 229 5.3.3 The measurement of intensity and reference data banks... 233 5.4 Quantification of inhomogeneous samples 241 5.4.1 Imaging and microscopy in AES and XPS 241 5.4.2 Thin or monoatomic overlayers 244 5.4.3 Angle-resolved analysis, inelastic scattering and composition-depth profiles 248 5.5 Quantification in sputter-depth profiles and thicker overlayers.. 250 References 251 6. Applications of AES in Microelectronics 257 D. W. Harris and R. S. Nowicki 6.1 Introduction 257 6.2 Incoming inspection 259 6.2.1 Particle identification 260 6.2.2 Solder preforms and lids 265 6.3 Processing 265 6.3.1 Cleaning 265 6.3.2 Passivation 267 6.3.3 Plasma etch residue 273 6.3.4 Layered aluminium alloys 275 6.3.5 Aluminium/gold wire bonds 276 6.4 Packaging 280 6.4.1 Gold 280 6.4.2 Solderability 282 vii
Vlll Contents 6.4.3 Die attach failure 287 6.5 Failure analysis 289 6.5.1 Refractory metal silicides 289 6.5.2 Diffusion barriers 293 6.5.3 Bonding problems 299 6.5.4 Aluminium spiking 302 6.6 Conclusion: process characterization and quality control 302 Glossary 304 References 307 7. AES in Metallurgy 311 M. P. Seah 7.1 Introduction 311 7.2 Characterization of segregation 317 7.2.1 Measurements on grain boundaries 319 7.2.2 Measurements on free surfaces 326 7.3 Theory of segregation 328 7.3.1 The Langmuir-McLean theory for surface and grain boundary segregation in binary Systems 328 7.3.2 The free energy of grain boundary segregation in binary Systems, AG gb 330 7.3.3 The free energy of surface segregation in binary Systems... 332 7.3.4 Site competition in simple ternary Systems 334 7.3.5 More complex binary Systems 336 7.3.6 Segregation in ternary Systems 337 7.3.7 Surface segregation in ternary Systems; one species from the gas phase 341 7.3.8 The kinetics of segregation 341 7.4 Materials effects of segregation 344 7.4.1 Segregation and basic materials parameters 344 7.4.2 Temper brittleness 348 7.4.3 Stress corrosion cracking; hydrogen and liquid metal embrittlement 349 7.4.4 Stress relief cracking and creep embrittlement 350 7.5 Conclusion 351 References 351 8. Applications of Electron Spectroscopy to Heterogeneous Catalysis... 357 T. L. Barr 8.1 Introduction 357 8.2 Fundamentals of electron spectroscopy as applied to catalysis. 359 8.2.1 Introduction 359 8.2.2 Comparative energy and intensity surveys 360 8.2.3 Novel techniques and topics 362 8.2.4 Chemisorption and basic catalytic studies 372
Contents 8.3 Electron spectroscopy and applied catalysis 373 8.3.1 Reviews related to this subject 373 8.3.2 Problems and techniques in the application of electron spectroscopy to catalysis 374 8.3.3 XPS studies of support materials 380 8.3.4 Platinum metal catalysis 385 8.3.5 Zeolites catalytic cracking and other processes 407 8.3.6 Desulphurization and related catalysts 423 8.4 Conclusion 428 References 430 9. Applications of XPS in Polymer Technology 437 D. Briggs 9.1 Introduction 437 9.2 Sample handling 437 9.3 Instrumentation 440 9.4 Spectral Information 443 9.4.1 The information depth 443 9.4.2 Core level binding energies 444 9.4.3 Shake-up satellites 448 9.4.4 Valence band spectra 448 9.4.5 Functional group labelling (derivatization) 448 9.5 Application of XPS to polymer surface analysis problems 455 9.5.1 Some general considerations 455 9.5.2 Polymer surface modification 461 9.6 Conclusions 477 References 477 Bibliography 480 10. Uses of Auger Electron and Photoelectron Spectroscopies in Corrosion Science 485 N. S. Mclntyre and T. C. Chan 10.1 Introduction 485 10.2 Special aspects of XPS and AES for corrosion studies 487 10.2.1 Surface sensitivity 487 10.2.2 Elemental sensitivities 488 10.2.3 Quantitative analysis 489 10.2.4 Spatial resolution 493 10.2.5 Depth profiling 496 10.2.6 Experimental techniques 498 10.2.7 Chemical effects 500 10.3 Review of XPS and AES applications in corrosion science 506 10.3.1 Light metals 506 10.3.2 First-row metals and their alloys 507 10.3.3 Second- and third-row transition metals 515 ix
x Contents 10.3.4 Protective coatings and inhibitors 517 10.4 Conclusion 521 References 521 Appendix 1. Spectrometer Energy Scale Calibration 531 M. P. Seah and G. C. Smith ALI Introduction 531 AI.2 The relation between voltage and energy in electrostatic electron spectrometers 532 AI.3 Calibration in XPS 534 A1.4 Calibration in AES 535 Acknowledgements 539 References 539 Appendix 2. Charge Referencing Techniques for Insulators 541 M. P. Seah, P. Swift and D. Shuttleworth A2.1 Introduction 541 A2.2 XPS 541 A2.2.1 General 541 A2.2.2 Reference via adventitious carbon-based contamination 543 A2.2.3 Deposited surface layers 544 A2.2.4 Implanted noble gas ions 545 A2.2.5 Mixtures 546 A2.2.6 Internal Standards 547 A2.2.7 Low-energy electron flood guns 547 A2.3 AES 550 References 552 Appendix 3. Data Analysis in XPS and AES 555 P. M. A. Sherwood A3.1 Introduction 555 A3.2 Data collection Systems 556 A3.3 Simple data Operations 557 A3.4 Signal-to-noise considerations 558 A3.5 The fitting of data 559 A3.6 Smoothing 561 A3.6.1 Curve fitting 562 A3.6.2 Convolutional algorithms 563 A3.6.3 Fourier transform frequency filtering 565 A3.7 The analysis of overlapping spectral features 565 A3.7.1 Derivative spectra 566 A3.7.2 Deconvolution methods 568 A3.7.3 Maximum entropy methods 569 A3.7.4 Factor analysis method 569 A3.7.5 Pattern recognition method 570
Contents A3.7.6 Spectral ratioing method 571 A3.7.7 Difference spectra 571 A3.7.8 Addition spectra 572 A3.7.9 Curve synthesis and curve fitting 572 A3.7.10 Fitting theoretical calculations to valence band spectra 575 A3.8 Background removal 581 A3.8.1 Linear backgrounds 581 A3.8.2 Integral (non-linear) backgrounds 582 A3.8.3 Backgrounds based upon elastic and inelastic loss processes 582 References 583 Appendix 4. Auger Chemical Shifts and the Auger Parameter 587 S. D. Waddington A4.1 Introduction 587 A4.2 The Auger parameter 587 A4.3 Extra-atomic relaxation energies 588 A4.4 Determination of chemical State from the AP 590 A4.4.1 Chemical State plots 590 A4.5 Practical points in the determination of APs and AP shifts 593 References 593 Appendix 5. Photoelectron and Auger Energies and the Auger Parameter: A Data Set 595 C. D. Wagner Data Set 598 Acknowledgement 625 References 625 Appendix 6. Empirically Derived Atomic Sensitivity Factors for XPS... 635 Appendix 7. (a) Line Positions from Mg X-rays, by Element 639 (b) Line Positions from AI X-rays, by Element 641 Appendix 8. (a) Line Positions from Mg X-rays, in Numerical Order... 643 (b) Line Positions from AI X-rays, in Numerical Order... 644 Appendix 9. Kinetic Energies of Auger Electrons: Experimental Data from Spectra Acquired by X-ray Excitation 645 C. D. Wagner Acknowledgement 650 References 650 Index 651 Contents of Volume 2 xi