The Use of the Scanning. Electron Microscope

BY

J. W. S.(!IEARLE

J. T. SPARROW AND

P. M. CROSS

PERGAMON PRESS OXFORD · NEW YORK • TORONTO

SYDNEY • BRAUNSCHWEIG

Contents

L1sT oF CoNTRIBUTORS

1. Introduction to Scanning Electron Microscopy J. w. s. HEARLE

1.1 . The background 1.1.1. History of microscopy 1.1.2. Direct and indirect images

1.2. The scanning electron microscope 1.2.1. The instrument 1.2.2. The practical advantages

1.3. The logic of scanning electron microscopy 1.3.1. Imageformation 1.3.2. The analogy with the refiected light microscope 1.3.3. Detail, contrast and resolution 1.3.4. 'Some numbers 1.3.5. The transmission scanning electron microscope: reciprocity 1.3.6. The formal advantages of the scanning system

2. The Interaction of Electrons with Solids D. C. NoRTHROP

2.1. Introduction

2.2. Electron range

2.3. Secondary electron emission 2.3.1. The energy distribution of emitted secondaries 2.3.2. Selection of secondaries in the SEM 2.3.3. Secondary electron yield 2.3.4. The effect of angle of incidence on secondary electron emission 2.3.5. Specimen charging effects 2.3.6. Voltage and field contrast

2.4. Specimen currents and voltages induced by the primary electron beam

2.5. Cathodoluminescence

2.6. X-ray emission

2.7. Auger electron emission

2.8. S~mmary and conclusions

3. The Design and Use of the Scanning Electron Microscope J. E. CASTLE

3.1. Introduction

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3.2. The formation of an electron beam 3.2.1. The electron gun 3.2.2. The cathode 3.2.3. The lens system

CONTENTS

3.3. Resolution and contrast in the scanning electron microscope 3.3.1. The display system 3.3.2. The electron probe 3.3.3. The specimen 3.3.4. The collector

3.4. The basic facilities required in.an operating microscope 3.4.1. The vacuum system 3.4.2. The specimen stage 3.4.3. The electron-optical column 3.4.4. Data treatment

3.5. Mainfeatures of commercially available microscopes 3.5.1. High-resolution microscopes 3.5.2. Simplified instruments

~ J,5.3. Scanning attachments for transmission electron microscopes 3.5.4. Optional extras

3.6. Conclusion

4. Specimen Preparation MRS. p. M. CROSS

4.1. lntroduction 4.1.1. Simple preparation 4.1.2. More complex preparation

4.2. Specimen coating 4.2.1. Coating with a thin layer of metal or carbon 4.2.2. Practical coating procedure 4.2.3. The use of antistatic agents

4.3. Low beam energy work

4.4. Replication

4.5. Conclusion

S. Procedures for Using a Scanning Electron Microscope MRS. P. M. CROSS

5.1. lntroduction 5.1.1. Techniques to gain topographical information 5.1.2. Techniques to gain chemical composition information 5.1.3. Techniques to gain other information 5.1.4. Learning how to use the instrument

5.2. Use procedure of the emissive mode 5.2.1. Conditions for optimum topographical detail 5.2.2. Operational sequence 5.2.3. Photography 5.2.4. Summary of procedure 5.2.5. Y-modulation of data 5.2.6. Electric and magnetic field mapping 5.2.7. Use of Auger electrons

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5.3. Use procedure of the reftective mode 5.3.1. General observation 5.3.2. Electron chamrelling patterns

5.4. Cathodoluminescent mode

5.5. X-ray spectroscopy

5.6. Specimen current mode

5.7. The mirror mode

5.8. The transmission mode

5.9. Conclusions

6. Applications to Metallurgy J. E. CASTLE

6.1. Introduction

CONTENTS

6.2. Fractography in the study of failure mechanisms 6.2.1. Introduction 6.2.2. Cleavage fracture 6.2.3. Ductile f ailure 6.2.4. Fatigue failure 6.2.5. Stress corrosion cracking 6.2.6. Embrittlement 6.2.7. Conclusions

6.3. Physical structure of metals, alloys and composite materials 6.3.1. Physical structure revealed by fracture 6.3.2. Deep etching techniques: eutectic alloys 6.3.3. Study of composite materials 6.3.4. Structure of sinters and compacts

6.4. Studies of surface morphology 6.4.1. Pitting, etching and surface damage 6.4.2. Electrodeposits 6.4.3. Adhesion and orientation of metal films

6.5. Chemical metallurgy 6.5.1. Products of high-temperature oxidation 6.5.2. Porosity of oxide layers 6.5.3. The oxide/metal interface 6.5.4. Other areas of chemical metallurgy

6.6. Conclusions

7. Applications to Fibres and Polymers J. T. SPARROW

7.1 . Introduction

7.2. Operating conditions for polymers and fibres

7.3. Coating materials

7.4. Textile fibres 7.4.1. lntroduction 7.4.2. Surface studies 7.4.3. Fracture studies 7.4.4. Studies of cross-sections 7.4.5. Studies of internal structure

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7.5. Textile yarns and fabrics 7.5.1. Introduction 7.5.2. Preparation techniques 7.5.3. Use of X-ray microanalysis

7.6. Bulk polymers 7.6.1. Introduction 7.6.2. Powders 7.6.3. Large specimens 7.6.4. Thin films

7.7. Dynamic and special experiments 7.7.1. Introduction 7.7.2. Special stages 7.7.3. Recording of information 7.7.4. Coating for dynamic experiments

7.8. Conclusions

CONTENTS

8. Applications to Solid-state Electronics D. C. NoRTHROP

8. 1. Introduction

8.2. Investigation of materials 8.2.1. Interna[ specimen currents 8.2.2. Specimen voltages 8.2.3. Total specimen current 8.2.4. Cathodoluminescence

8.3. Investigation of semiconductor devices 8.3.1. Measurements on devices

9. Applications to Biological Materials P. ECHLIN

9 .1. Introduction

9.2. Modes of examination 9.2.1. Topographical detail 9.2.2. Cathodoluminescence· 9.2.3. X-ray microanalysis 9.2.4. Transmissive operating mode

9.3. Ancillary techniques 9.3.1. Introduction 9.3.2. Low-voltage operation 9.3.3. Ion beam etching 9.3.4. Examination of specimens at low temperatures

9.4. Preparation of labile biological material 9.4.t. Introduction 9.4.2. Minima[ preparation 9.4.3. Fixation and dehydration techniques 9.4.4. Sectioned material 9.4.5. Freeze drying 9.4.6. Critical point drying 9.4.7. Examination of living material 9.4.8. Examination of materials at low temperatures 9.4.9. Surface coating 9.4.10. Surface replication

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10. Faults MRS. P. M. CROSS

10.1. Introduction

CONTENTS

10.2. Faults which result in no image on the display tube 10.2.1. Electronic faults 10.2.2. Vacuum faults

10.3. Faults which result in an obvious distorted image or image of low quality 10.3.1. Poor electron emission 10.3.2. Charging 10.3.3. Beam damage 10.3.4. Vacuum damage 10.3.5. Poor image quality due to a magnetized specimen 10.3.6. Faults in the column and collector system 10.3.7. Electronicfaults

10.4. Faults which may not be obvious on the final photomicrograph 10.4.1. Faults due to the condition and position of the specimen 10.4.2. Faults due to instrument conditions

11. Dimensional Measurements G. S. LANE

11. 1. Introduction 11.2. Three-dimensional viewing

11.2. 1. Unaided viewing 11.2.2. Optical stereoscopes 11.2.3. The viewing of stereopairs of electron micrographs

11.3. Simple quantitative measurement techniques 11.3.1. Lateral measurements using a single micrograph 11 .3.2. Measurement of height differences

t 1.4. lügorow treatment t 1.4.t. The two-dimensional case 11.4.2. The three-dimensional case 11.4.3. The effects of measurement errors

t t.S. The use of stereographic equations 1 t.S.1. Measurement of parameters 1 t.S.2. The use of the computer

t 1.6. Extension of the basic theory to the low magnification case 11. 7. Further applications of stereographic techniques

11. 7 .1. The equation of a plane 11. 7 .2. The angle between two planes 11. 7 .3. The angle between two lines

11.8. Miscellaneous measurement techniques 11.8.1. Contour mapping 11.8.2. The production of three-dimensional models 11.8.3. The estimation of lengths and areas

12. Management of the SEM A. J. SHERRlN

12. 1. Introduction 12.2. Organi:iation

12.2.1. Planning and policy 12.2.2. Supervisor

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12.3. Location and facilities 240 12.3.1. Accommodation and installation 240 12.3.2. SEM accommodation 241 12.3.3. Specimen preparation 242 12.3.4. Office accommodation 242 12.3.5. Photographie Jacilities 243

12.4. Operation 243 12.4.1. Usage 243 12.4.2. Operators 244 12.4.3. Operator training 244 12.4.4. Operating procedures 245 12.4.5. Instrument allocation 245 12.4.6. Specimen processing 245 12.4.7. Examination procedure 246 12.4.8. Filing and dispatching 248

12.5. Maintenance 248 12.5.1. SEM 248 12.5.2. Ancillary apparatus 249

12.6. Rental service 249

12. 7. Photography 249

12.8. Visitors 250 12.9. Conclusion 250

13. The Future of Scanning Electron Microscopy ]. W. S. HEARLE and D . C. NoRTHROP

13 .1. The pattern of development

13.2. Instrument developments 13 .2.1. High-resolution version$ of current instruments 13.2.2. Crewe's microscopes 13.2.3. A high-voltage SEM

13.3. Techniques 13.3.1. Dynamic viewing 13 .3 .2. Environmental stages 13 .3 .3. Element identification 13.3.4. Electron channelling 13.3.5. Stroboscopic techniques

13.4. Signal processing 13.4.1. The range of the SEM 13.4.2. The isolation of potential contrast from surface topology

13.5. Conclusions 13.5.1. Sources of information 13.5.2. Review of 1971 Chicago Symposium

LIST OF MANUFACTURERS AND SUPPLIERS

AUTHOR INDEX

SUB]ECT INDEX

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