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  • SECONDARY ION MASS

    SPECTROMETRY

  • SECONDARY ION MASS

    SPECTROMETRYApplicAtions for Depth profiling AnD

    surfAce chArActerizAtion

    FRED A. STEVIEAnalytical Instrumentation Facility,

    North Carolina State University

    MOMENTUM PRESS, LLC, NEW YORK

  • Secondary Ion Mass Spectrometry: Applications for Depth Profiling and

    Surface Characterization

    Copyright Momentum Press, LLC, 2015.

    All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means electronic, mechanical, photocopy, recording, or any otherexcept for brief quotations, not to exceed 400 words, without the prior permission of the publisher.

    First published by Momentum Press, LLC222 East 46th Street, New York, NY 10017www.momentumpress.net

    ISBN-13: 978-1-60650-588-5 (print)ISBN-13: 978-1-60650-589-2 (e-book)

    Momentum Press Materials Characterization and Analysis Collection

    Collection ISSN: 2377-4347 (print)Collection ISSN: 2377-4355 (electronic)

    Cover and interior design by Exeter Premedia Services Private Ltd., Chennai, India

    10 9 8 7 6 5 4 3 2 1

    Printed in the United States of America

  • This book is dedicated to my wife, Eileen, whose encouragement and support throughout my career helped make possible

    my contribution to science.

  • AbstrAct

    Secondary ion mass spectrometry (SIMS) is a mass spectrometric tech-nique for solid materials that can provide elemental analysis at parts per million sensitivity and lateral resolution of 50 nm. When those capabili-ties are combined with the ability to provide that analysis as a function of depth, SIMS has proved to be a valued technique for a wide range of applications. This book was written to explain a technique that requires an understanding of many details in order to properly obtain and interpret the data. It also will serve as a reference for those who need to provide SIMS data. The book has over 200 figures and the references allow one to trace the development of SIMS and help understand the technique.

    KEYWORDS

    depth profiling, magnetic sector mass analyzer, mass spectrometry, secondary ion mass spectrometry, time-of-flight mass analyzer, quadrupole mass analyzer

  • contents

    List of figures xiii

    List of tabLes xxi

    Preface xxiii

    1 comParison of surface anaLyticaL techniques 11.1 Common Elemental Surface Analysis Techniques 11.2 Introduction to Mass Spectrometry 31.3 Brief History of Mass Spectrometry and SIMS 51.4 Types of Mass Spectrometry 71.5 Rationale for SIMS 81.6 Types of SIMS Data 11References 12

    2 sims technique 192.1 Interaction of Ions with Matter 192.2 Sputtering Process 192.3 Sputtering Yield 232.4 Preferential Sputtering 282.5 Secondary Ion Yield 282.6 Oxygen Flood (Oxygen Leak, Oxygen Backfill) 30

    2.7 Matrix Effects 32References 34

    3 anaLysis Parameters 393.1 Parameters of Interest for Depth Profiling 39

    3.2 Primary Beam Polarity and Species 39

  • x COntEntS

    3.3 Secondary Ion Polarity and Species 433.4 Primary Beam Energy 473.5 Primary Beam Angle of Incidence 483.6 Primary Beam Current, Raster Size 493.7 Secondary Beam Energy DistributionVoltage Offset 493.8 Mass Interferences, Mass Resolution 52

    References 58

    4 instrumentation 614.1 Vacuum System 614.2 Overall Instrument 624.3 Ion Sources 634.4 Primary Ion Column 664.5 Sample Chamber and Sample 664.6 Secondary Ion Column and Mass Analyzers 674.7 Detectors 754.8 Focused Ion Beam SIMS (FIB-SIMS) 764.9 Computers and Data Manipulation 774.10 Related Instruments 77

    References 78

    5 DePth ProfiLing (Dynamic sims) 815.1 Raster and Gate 815.2 Depth Resolution 835.3 Sputtering Rate 965.4 Nonuniform Sputtering, Sample Rotation 965.5 Detection Limit, Dynamic Range, Memory Effect 1005.6 Count Rate SaturationDetector Dead Time 1045.7 Small Area Analysis 1055.8 Nonuniform Distribution 1095.9 Image Depth ProfileLateral Resolution 111

    5.10 Movement of Species Due to Chemical Effect 111

    References 112

  • COntEntS xi

    6 quantification 1216.1 Need for Secondary Standards 1216.2 Depth Profile QuantificationRelative Sensitivity

    Factors 1216.3 Ion Implanted Standards 1246.4 Bulk Standards 1316.5 Matrix and Trace Quantification 132

    6.6 Useful Yield 1346.7 Precision and Accuracy 1356.8 Quantification in Multiple MatrixesCesium

    Cluster Ions 1376.9 Static SIMS Quantification 138

    6.10 RSF Relationship with Ionization Potential and Electron Affinity 140

    References 143

    7 surfaces, interfaces, muLtiLayers, buLk 1497.1 Sample Considerations 1497.2 SurfaceStatic SIMS 1497.3 Interfaces 1517.4 Multilayers 1567.5 Back Side Analysis 1577.6 Bulk Analysis 160References 162

    8 insuLators 1658.1 Sample Charging 1658.2 Charge Compensation Methods 1688.3 Electron Beam Neutralization 1698.4 Species Mobile Under Ion Bombardment 1828.5 Buried Insulators 1858.6 Electron Stimulated Desorption 1858.7 Summary 186References 187

  • xii COntEntS

    9 resiDuaL anD rare gas eLements 191 9.1 Residual Gas Elements, Raster Reduction 191 9.2 Rare Gas Elements 200 References 201

    10 aPPLications 20510.1 Semiconductors 20510.2 Organic Materials 22310.3 Minerals, Ceramics, Catalysts 22710.4 Metals 229References 230

    11 anaLysis aPProach 23511.1 Initial Considerations 23511.2 Analysis Sequence 236

    aPPenDix 239

    inDex 253

  • list of figures

    Figure 1.1. Isotopic abundances. 3Figure 1.2. High mass resolution mass spectrum of 700 Da. 4Figure 1.3. Mass spectrometer block diagram. 4Figure 1.4. AES depth profile. 9

    Figure 1.5. SIMS depth profile. 9

    Figure 1.6. SIMS mass spectrum y-axis display. 10Figure 1.7. Zinc oxide mass spectrum. 11Figure 1.8. SIMS depth profile of BPSG layers. 12

    Figure 1.9. Carbon segregation in niobium bicrystals. 12Figure 2.1. Interaction of ions with matter. 20Figure 2.2. SIMS process. 20Figure 2.3. Energy distribution of sputtered particles. 20Figure 2.4. TRIM simulation at two impact energies. 21Figure 2.5. Simulation of particle surface interaction. 22Figure 2.6. Sputtering simulations for SF5

    +. 22Figure 2.7. Sputtering simulation of C60

    + versus Ga+ on Ag(111). 23Figure 2.8. Sputtering yield versus primary energy. 23Figure 2.9. Sputtering yield versus primary energy. 24Figure 2.10. Penetration versus incidence angle. 24Figure 2.11. Distribution of implanted species. 25Figure 2.12. Sputtering yield versus incidence angle. 25Figure 2.13. Penetration depth versus energy and incidence angle. 26Figure 2.14. Angular distribution of sputtered material. 26Figure 2.15. Sputtering yield versus primary ion atomic number. 27

  • xiv LiSt Of figuRES

    Figure 2.16. Sputtering yield versus target atomic number. 27Figure 2.17. Secondary ion yield versus primary energy. 29Figure 2.18. Secondary ion yield versus incidence angle. 30Figure 2.19. O2

    + and oxygen flood remove matrix effect. (a) Yield enhancement in SiO2 and discontinuity at interface and (b) added oxygen flood removed yield difference between SiO2 and Si. 31

    Figure 2.20. Matrix effect: P in Si versus SiO2. 32Figure 2.21. Matrix effect: P in Si versus SiO2. (a) Raw data:

    apparent P peaks, (b) referenced to P in Si, and (c) referenced to P in SiO2. 33

    Figure 2.22. Matrix effect and yield enhancement for Pt analysis. (a) Pt+ in profile of PtSi/Si is enhanced by oxygen because Si is present through the PtSi layer and (b) Pt+ in profile of Pt/Si is enhanced when Si is encountered below the Pt layer. 33

    Figure 3.1. Positive secondary ion yields for O2+ impact on Si. 41

    Figure 3.2. Negative secondary ion yields for Cs+ impact on Si. 42Figure 3.3. Positive secondary Cs-molecular ion yields for

    Cs+ bombardment of Si. 43Figure 3.4. Periodic table summary of optimum primary

    beam choices. 44Figure 3.5. AlGaN mass spectrum, 2.8% Al, O2

    + bombardment. 46Figure 3.6. Choice of primary beam for detection limit. 47Figure 3.7. Choice of secondary species: Molecular ions.

    (a) Impurity + primary beam species, (b) impurity + matrix. 47

    Figure 3.8. Angle of incidence dependence on sample voltage. 48Figure 3.9. Angle of incidence dependence on sample voltage. 49Figure 3.10. Secondary ion energy distribution. 50Figure 3.11. Voltage offset. 50Figure 3.12. Voltage offset. 51Figure 3.13. Voltage offset on mass spectrum. 52Figure 3.14. Mass resolution. (a) Completely separated,

    (b) partial separation, (c) mass regions measured, (d) trapezoidal peak shape. 54

  • LiSt Of figuRES xv

    Figure 3.15. Mass interferences. 55

    Figure 3.16. High mass resolution separates mass interferences in Si. 56

    Figure 3.17. High mass resolution. 56Figure 3.18. Mass interference for Cu in 0.3 m SiO2 film on Si. 57Figure 4.1. SIMS instrument block diagram. 62Figure 4.2. Duoplasmatron. 63

    Figure 4.3. Cesium microbeam source. 65Figure 4.4. Liquid metal ion source (LMIS). 65Figure 4.5. Primary ion column components. 67Figure 4.6. Quadrupole analyzer. 68

    Figure 4.7. Double focusing magnetic sector analyzer. 69Figure 4.8. Ion trajectories for magnetic sector. 69Figure 4.9. CAMECA IMS 7f magnetic sector analyzer. 71Figure 4.10. CAMECA NanoSIMS 50L magnetic sector analyzer. 71Figure 4.11. Time of flight analyzer. 73

    Figure 4.12. TOF-SIMS timing diagram. 74Figure 4.13. TOF-SIMS reflectron analyzer. 74

    Figure 4.14. TOF-SIMS electrostatic analyzer. 75

    Figure 4.15. Faraday cup and electron multiplier responses. 76

    Figure 5.1. Raster and gate relationship with depth profile shape. 82

    Figure 5.2. Beam diameter effect o