Advanced Scanning Electron Microscopy and X-Ray Microanalysis

463 Pages·1986·21.835 MB·English

by  Dale E. Newbury, David C. Joy, Patrick Echlin, Charles E. Fiori, Joseph I. Goldstein (auth.)

Advanced
Scanning Electron
Microscopy and
X-Ray Microanalysis
Advanced
Scanning Electron
Microscopy and
X-Ray Microanalysis
Dale E. Newbury
National Bureau of Standards
Gaithersburg, Maryland
DavidC. Joy
A T & T Bell Laboratories
Murray Hill, New Jersey
Patrick Echlin
University of Cambridge
Cambridge, England
Charles E. Fiori
National Institutes of Health
Bethesda, Maryland
and
Joseph I. Goldstein
Lehigh University
Bethlehem, Pennsylvania
Springer Science+Business Media, LLC
Library of Congress Cataloging in Publication Data
Main entry under title:
Advanced scanning electron microscopy and X-ray microanalysis.
Includes bibliographies and index.
I. Scanning electron microscope. 2. X-ray microanalysis. I. Newbury, D. E. [DNLM:
I. Electron Probe Microanalysis. 2.Microscopy, Electron, Scanning. QH 212.53 A244)
QH212.S3A38 1986 502./8/25 85-28261
ISBN 978-1-4757-9029-0 ISBN 978-1-4757-9027-6 (eBook)
DOI 10.1007/978-1-4757-9027-6
© 1986 Springer Science+Business Media New York
Originally published by Plenum Press, New York in 1986.
Softcover reprint of the hardcover 1s t edition 1986
All rights reserved
No part of this book may be reproduced, stored in a retrieval system, or transmitted
in any form or by any means, electronic, mechanical, photocopying, microfilming,
recording, or otherwise, without written permission from the Publisher
Preface
This book has its origins in the intensive short courses on scanning elec
tron microscopy and x-ray microanalysis which have been taught
annually at Lehigh University since 1972. In order to provide a textbook
containing the materials presented in the original course, the lecturers
collaborated to write the book Practical Scanning Electron Microscopy
(PSEM), which was published by Plenum Press in 1975. The course con
tinued to evolve and expand in the ensuing years, until the volume of
material to be covered necessitated the development of separate intro
ductory and advanced courses. In 1981 the lecturers undertook the
project of rewriting the original textbook, producing the volume Scan
ning Electron Microscopy and X-Ray Microanalysis (SEMXM). This vol
ume contained substantial expansions of the treatment of such basic
material as electron optics, image formation, energy-dispersive x-ray
spectrometry, and qualitative and quantitative analysis. At the same
time, a number of chapters, which had been included in the PSEM vol
ume, including those on magnetic contrast and electron channeling con
trast, had to be dropped for reasons of space. Moreover, these topics had
naturally evolved into the basis of the advanced course. In addition, the
evolution of the SEM and microanalysis fields had resulted in the devel
opment of new topics, such as digital image processing, which by their
nature became topics in the advanced course.
Thus, following this progression of development, the lecturers of the
advanced course have collaborated to produce a book containing the
principal topics covered in that course. In comparison to the introductory
SEMXM volume, the topics covered in this book are undergoing rapid
development. Our current efforts represent a snapshot of the field at this
point in time. We fully expect these areas to develop quite substantially,
v
vi
PREFACE
and we hope that our efforts to assemble these chapters may be of aid to
our readers in making their own contributions to a most exciting field of
work.
Dale E. Newbury
David C. Joy
Patrick Echlin
Charles E. Fiori
Joseph I. Goldstein
Contents
1. Modeling Electron Beam-Specimen Interactions. . . . . . . . . . 3
1.1. Introduction................................... 3
1.2. Cross Sections for Scattering Processes . . . . . . . . . . . . . 3
1.2.1. General Properties ..................... . . 3
1.2.2. Elastic Scattering. . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2.3. Inelastic Scattering . . . . . . . . . . . . . . . . . . . . . . . 7
1.3. Analytic Modeling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
1.3.1. X-Ray Generation in Thin Foils. . . . . . . . . . . . 16
1.3.2. X-Ray Generation in Thick Targets. . . . . . . . . 17
1.4. Monte Carlo Electron Trajectory Simulation ........ 19
1.4.1. Formulation............................ 19
1.4.2. Applications of the Monte Carlo Method. . . . . 26
Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
2. SEM Microcharacterization of Semiconductors ........... 45
2.1. Introduction................................... 45
2.2. Voltage Contrast ............................. . . 45
2.3. Voltage Measurements .......................... 52
2.4. Stroboscopic Microscopy ........................ 56
2.5. Charge Collection Microscopy. . . . . . . . . . . . . . . . . . . . 59
2.6. Charge Collection Images of Semiconductor
Materials. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
2.7. Quantitative Measurements in Charge Collection
Microscopy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
2.8. Practical Aspects of Charge Collection Microscopy ... 75
2.9. Cathodoluminescence Studies. . . . . . . . . . . . . . . . . . . . . 77
2.10. Thermal Wave Microscopy. . . . . . . . . . . . . . . . . . . . . . . 82
3. Electron Channeling Contrast in the SEM ............... 87
3.1. Introduction................................... 87
3.2. Origin of Electron Channeling Contrast. . . . . . . . . . . . . 87
vii
viii
CONTENTS
3.3. Characteristics of Electron Channeling Contrast. . . . . . 89
3.4. The Electron Channeling Pattern . . . . . . . . . . . . . . . . . . 92
3.4.1. Coarse Structure . . . . . . . . . . . . . . . . . . . . . . . . . 92
3.4.2. Fine Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
3.5. Electron Optical Conditions to Observe Electron
Channeling Contrast . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
3.5.1. Beam Divergence . . . . . . . . . . . . . . . . . . . . . . . . 99
3.5.2. Beam Current. . . . . . . . . . . . . . . . . . . . . . . . . . . 100
3.5.3. Choice of Detectors ...................... 101
3.5.4. Signal Processing. . . . . . . . . . . . . . . . . . . . . . . . . 103
3.5.5. Beam Energy. . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
3.5.6. Backscattered Electron Energy. . . . . . . . . . . . . . 105
3.5.7. Specimen Tilt. . . . . . . . . . . . . . . . . . . . . . . . . . . 105
3.5.8. Specimen Condition. . . . . . . . . . . . . . . . . . . . . . 106
3.6. Channeling Micrographs. . . . . . . . . . . . . . . . . . . . . . . . . 107
3.6.1. Polycrystalline Samples . . . . . . . . . . . . . . . . . . . 107
3.6.2. Limit of Spatial Resolution in Channeling
Contrast Images ............... . . . . . . . . . . 111
3.6.3. Limit of Misorientation Detection .......... 113
3.7. Selected Area Electron Channeling Patterns .... . . . . . 113
3.8. Orientation Determination with ECPs. . . . . . . . . . . . . . 117
3.8.1. Determining Orientation . . . . . . . . . . . . . . . . . . 118
3.8.2. Channeling Maps . . . . . . . . . . . . . . . . . . . . . . . . 118
3.9. Deformation Effects on Channeling Contrast. . . . . . . . 123
3.9.1. Channeling Patterns. . . . . . . . . . . . . . . . . . . . . . 123
3.9.2. Deformation Effects in Channeling Contrast
Images. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
Appendix 1: Electron Channeling Maps. . . . . . . . . . . . . . . . . . 137
Appendix 2: Worked Example of Orientation
Determination ........................... 142
4. Magnetic Contrast in the SEM ........................ 147
4.1. Introduction................................... 147
4.2. Magnetic Microstructures. . . . . . . . . . . . . . . . . . . . . . . . 147
4.2.1. Magnetic Domains. . . . . . . . . . . . . . . . . . . . . . . 147
4.2.2. Types of Magnetic Materials . . . . . . . . . . . . . . . 149
4.3. Type I Magnetic Contrast: External Deflection of
Secondary Electron Trajectories . . . . . . . . . . . . . . . . . . . 150
4.3.1. Physical Origin.......................... 150
4.3.2. Characteristics of Type I Magnetic Contrast .. 151
4.3.3. Quantitative Theory of Type I Magnetic
Contrast. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
CONTENTS ix
4.3.4. Strategy for Observing Type I Magnetic
Contrast. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
4.4. Type II Magnetic Contrast: Internal Deflection of
Primary Electron Trajectories. . . . . . . . . . . . . . . . . . . . . 158
4.4.1. Physical Origin . . . . . . . . . . . . . . . . . . . . . . . . . . 158
4.4.2. Characteristics of Type II Magnetic Contrast. . 161
4.4.3. Calculation of Type II Magnetic Contrast .... 168
4.4.4. Strategy for Observing Type II Magnetic
Contrast. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170
4.5. Type III Magnetic Contrast: Polarization of Secondary
Electrons. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173
4.5.1. Physical Origin . . . . . . . . . . . . . . . . . . . . . . . . . . 173
4.5.2. Experimental Techniques. . . . . . . . . . . . . . . . . . 174
4.6. Dynamic Experiments. . . . . . . . . . . . . . . . . . . . . . . . . . . 175
5. Computer-Aided Imaging and Interpretation. . . . . . . . . . . . . . 181
5.1. Introduction................................... 181
5.2. Some Perceptual Limitations and Artifacts Due to
Prejudice. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182
5.3. Some Perceptual Limitations and Artifacts of the Eye
and Mind . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183
5.4. The Image Acquisition and Display System . . . . . . . . . 186
5.5. General Considerations for a Computer and Its
Microscope Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188
5.5.1. Considerations for the Microscope. . . . . . . . . . 189
5.5.2. Considerations for the Computer. . . . . . . . . . . 190
5.6. Color Display Systems .......................... 192
5.7. The Photography of Color Displays. . . . . . . . . . . . . . . . 195
5.8. Satellite Processors ............................. 196
5.9. Ways to Obtain Quantitative Intensity Information
from Digital Images. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197
5.9.1. LineScans.............................. 197
5.9.2. Image Intensity Histograms. . . . . . . . . . . . . . . . 199
5.9.3. Histogram Stretching. . . . . . . . . . . . . . . . . . . . . 200
5.9.4. Histogram Normalization ............... . . . 200
5.9.5. Density Slicing ... . . . . . . . . . . . . . . . . . . . . . . . 201
5.9.6. Primary Coloring and Pseudocoloring ....... 201
5.10. Transformations for Electron and X-Ray Micrograph
Processing: The Contrast Problem . . . . . . . . . . . . . . . . . 202
5.10.1. Some Preliminaries. . . . . . . . . . . . . . . . . . . . . . . 203
5.10.2. Derivative Transformations. . . . . . . . . . . . . . . . 204
5.10.3. The First Derivative. . . . . . . . . . . . . . . . . . . . . . 205
X CONTENTS
5.10.4. The Space Gradient . . . . . . . . . . . . . . . . . . . . . . 206
5.10.5. The Space Laplacian. . . . . . . . . . . . . . . . . . . . . . 206
5.10.6. Isotropic, Nonlinear, Differential Operators. . . 206
5.11. Application of the Derivative Transforms to the
Contrast Problem. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207
5.12. Discrete Approximations to Several of the Derivative
Operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208
5.13. "Smoothing" Kernels. . . . . . . . . . . . . . . . . . . . . . . . . . . 210
5.14. The Acquisition and Display of X-Ray Images in
Scanning Electron Column Instruments ............ 214
5.14.1. Statement of the Problem. . . . . . . . . . . . . . . . . . 215
5.14.2. Discussion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216
5.15. Methods to Separate the Characteristic and
Continuum Radiation: EDS . . . . . . . . . . . . . . . . . . . . . . 218
5.16. Deadtime Correction for Digitally Acquired EDS
Images. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220
5.17. Methods to Separate the Characteristic and
Continuum Radiation: WDS ..................... 220
5.17.1. Regional Variance in Background-Corrected
Images. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222
5.17.2. Choice of Scale for Background-Corrected
Images. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222
5.17.3. Conversion of Background- and Deadtime-
Corrected Intensity Maps to Quantitative
Maps.. ... ...... ..... ... . .. . ... . . . ..... 224
5.18. An Example of Computer-Aided Imaging and
Interpretation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224
5.19. Contrast Criteria for Images. . . . . . . . . . . . . . . . . . . . . . 236
5.20. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240
Appendix. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240
6. Alternative Microanalytical Techniques ................. 243
6.1. Introduction................................... 243
6.2. Strengths and Weaknesses ofSEM/XM. . . . . . . . . . . . . 243
6.3. General Observations on Analysis Methods. . . . . . . . . 247
6.3.1. Quantitative Analysis Procedures. . . . . . . . . . . 247
6.3.2. Detection Limits. . . . . . . . . . . . . . . . . . . . . . . . . 254
6.4. High-Spatial-Resolution Microanalysis . . . . . . . . . . . . . 257
6.4.1. Thin Specimens: Analytical Electron
Microscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257
6.4.2. Analysis at Atomic Resolution ............. 262
6.4.3. Analysis of Bulk Samples. . . . . . . . . . . . . . . . . . 263
6.4.4. Surfaces................................ 266