Scanning Auger Electron Microscopy - Hardcover

Hardcover

ISBN 10: 0470866772 ISBN 13: 9780470866771

Verlag: Wiley, 2006

Inhaltsangabe

This book concentrates upon a form of scanning electron microscopy in which electrons are focused onto the surface of a solid sample and Auger electrons are emitted into an energy analyzer in which their kinetic energy is established.
 
Following an introductory chapter setting the scene on the topic, chapters 2 and 3 are concerned respectively with the theory of the Auger process and the instrumentation needed in Auger microscope. Chapters 4 and 5 discuss the limits to the spatial resolution of the microscopy and the methods used to separate the chemical information in an Auger image from potentially confusing effects (referred to as imaging artefacts) due to other properties of the sample, the experimental geometry employed or the methods used for collecting or displaying the data. Chapter 6 presents the software tools useful to interpret the information in an Auger image. Chapter 7 discussed methods that can convert the intensities of the pixels in a set of images using different Auger peaks from the same area of a sample into a set of maps revealing the atomic concentrations at each point in the surface - image quantification. Chapters 8 and 9 describe some of the most important applications of Auger microscopy in the fields of metallurgy and of semiconductor device characterization.
 
The material in the book is intended as a guide to the subject of Auger electron microscopy and so it is hoped that it will be of interest to researchers in this field as well as to others who wish to discover what can be achieved with this technique and what are its limitations. In addition, it will be useful to analysts working with SAMs who are hard pressed to measure many samples and have little time to work on other aspects of the behaviour of their instrument or the problems that they may, perhaps unwittingly encounter.

Über diesen Titel

Über die Autorin bzw. den Autor

Martin Prutton is the editor of Scanning Auger Electron Microscopy, published by Wiley.

Mohamed M. El Gomati is the editor of Scanning Auger Electron Microscopy, published by Wiley.

Von der hinteren Coverseite

This book concentrates upon a form of scanning electron microscopy in which electrons are focused onto the surface of a solid sample and Auger electrons are emitted into an energy analyzer in which their kinetic energy is established.

Following an introductory chapter setting the scene on the topic, chapters 2 and 3 are concerned respectively with the theory of the Auger process and the instrumentation needed in Auger microscope. Chapters 4 and 5 discuss the limits to the spatial resolution of the microscopy and the methods used to separate the chemical information in an Auger image from potentially confusing effects (referred to as imaging artefacts) due to other properties of the sample, the experimental geometry employed or the methods used for collecting or displaying the data. Chapter 6 presents the software tools useful to interpret the information in an Auger image. Chapter 7 discussed methods that can convert the intensities of the pixels in a set of images using different Auger peaks from the same area of a sample into a set of maps revealing the atomic concentrations at each point in the surface – image quantification. Chapters 8 and 9 describe some of the most important applications of Auger microscopy in the fields of metallurgy and of semiconductor device characterization.

The material in the book is intended as a guide to the subject of Auger electron microscopy and so it is hoped that it will be of interest to researchers in this field as well as to others who wish to discover what can be achieved with this technique and what are its limitations. In addition, it will be useful to analysts working with SAMs who are hard pressed to measure many samples and have little time to work on other aspects of the behaviour of their instrument or the problems that they may, perhaps unwittingly encounter.

Auszug. © Genehmigter Nachdruck. Alle Rechte vorbehalten.

Scanning Auger Electron Microscopy

John Wiley & Sons

Copyright © 2006 John Wiley & Sons, Ltd
All right reserved.
ISBN: 978-0-470-86677-1

Chapter One

Introduction

M. M. El Gomati and M. Prutton

The region near to the surface of a solid material can play important-roles in the properties of that solid. Should an atom or molecule arrive at such a surface, be it in vacuo, in air, in a liquid or in contact with the surface of a different material, then the crystallographic structure, the atomic type, the electronic structure, the vibrations of surface atoms and the bonding forces between the arrival and the surface may all affect what happens next. Thus, for example, the arrival may adhere to the solid surface or be scattered off of it, or the arrival may react with the surface forming a new compound locally. Should the temperature, the structure and the binding energies of the atoms in the surface have appropriate values then the arrival may diffuse into the solid or even cause atoms in the solid to diffuse out to the surface. For these reasons solid surfaces are important in many processes in a wide variety of different parts of science, including biology, chemistry, materials science and physics. Further, they are important in many areas of technology such as semiconductor device fabrication and characterisation, the design of catalysts to speed up chemical reactions, and the development of anti-corrosion layers on alloys and metals. The subject of surface science is thus very broad indeed, having scientific and commercial implications in the effects that it has on large industries. Introductions to the subject include books by Prutton, Walls, Woodruff and Delchar and Zangwill. The whole area has been reviewed, for instance, by Duke and by Duke and Plummer.

What is meant by the surface of a solid? The answer to this question depends upon what surface properties are under investigation and what experimental techniques are being used for their measurement. The theoretical physicist may be interested in the wave functions of atoms in the outermost layer of the solid. Most extremely, interest may be on the wave functions and their properties in the region in a vacuum outside the solid surface. The experimental scientist may be measuring the properties of the topmost few atomic layers of the solid or the topmost few hundred layers depending upon the methods being used. Most experimental methods involve the bombardment of the surface under study by particles or photons and the detection of scattered particles or photons. If visible photons are incident and reflected photons are detected then the depth of the region of the solid being probed is of the order of the wavelength of the light being used - the information depth is of the order of many hundreds of nanometers. If energetic X-rays are incident and detected then this depth may be of the order of microns. If energetic X-rays are incident and photoelectrons are detected this depth can be as small as a fraction of a nanometer - only a few atom layers are being probed. A similar information depth is obtained when energetic electrons are incident and Auger electrons are emitted from the atoms in the solid. In this book the surface is taken to be the region of a solid within a depth of a few (<20) atomic layers from its free surface.

This information depth depends upon the relative sizes of the depth penetrated by the incident photons or particles - the penetration depth and the depth from which the stimulated particles or photons can arrive at the detector with properties unchanged - the escape depth. If the penetration depth is small compared with the escape depth then it is the penetration depth that determines the information depth. This is the case, for example, in energy dispersive X-ray (EDX) detection where electrons are focused onto a solid sample and may penetrate to a depth of the order of a micron and characteristic X-rays are emitted and detected. The X-rays may reach their detector unchanged from such a relatively small depth so the information depth is the penetration depth. At the other extreme, in Auger electron spectroscopy (AES), energetic (say 10 keV) electrons may be focused onto the solid and low energy Auger electrons are detected. The ingoing electrons may penetrate a micron or so but the Auger electrons have much lower kinetic energies and can only escape from the solid with their energies unchanged if they originate from very near the surface. In this case the escape depth determines the information depth and may be very small - about 0.5nm depending upon the kinetic energy of the Auger electrons. The information depths for X-ray photoelectron spectroscopy are very similar to those of Auger spectroscopy - particularly when the kinetic energies of the photoelectrons are below about 1 keV. This subject is dealt with more completely in Chapter 2.

When the intention is to study the topmost atomic layer in a solid the environment in which the sample is immersed becomes of critical importance. Even in a 'vacuum', in every second many atoms or molecules in the ambient atmosphere will strike the surface. This rate depends upon the pressure of the ambient gas - the lower the pressure the lower the rate of impact. Since these events may change the surface by knocking off atoms expected to be present, by sticking to the surface or by reacting with the surface then the surface may be changed from whatever state it was intended to be in - atomically clean, covered with specific atoms of a different kind or whatever the investigator required. The kinetic theory associated with contamination from the ambient atmosphere is discussed in more detail in Chapter 3. Most surface science measurements are conducted in ultra-high vacuum (UHV) in which the total pressure is less than about [10.sup.9] mbar. In such pressures the arrival rate of molecules from the ambient gas can allow measurement times of several hours before the surface under study is covered with a single layer (a monolayer) of contaminating molecules.

One question that usually needs to be answered about a surface is 'what is it composed of?' The answer is revealed with those measurements that can be chemically specific and yet have sufficient sensitivity to detect the small amount of material in the topmost atomic layer. The techniques available to a surface analyst are summarised in Table 1.1 where a rough guide to the sensitivity of each method is given.

This book concentrates upon a form of scanning electron microscopy in which electrons are focused onto the surface of a solid sample and Auger electrons are emitted into an energy analyser in which their kinetic energy is established. These electrons were first described as a theoretical possibility in 1923 by Rosseland and were identified by Meitner and independently by Auger from the results of cloud chamber experiments. Photographs of Auger and Meitner are reproduced in Figure 1.1 and the story of Lise Meitner's scientific struggles is described by Sime. All their work was directed at the explanation of sharp spectral features in -ray spectroscopy arising from internal conversion in [gamma] irradiation. The subject is described in the book by Burhop. The use of Auger electrons in the analysis of surfaces was first described by Lander as early as 1953. As can be seen in the caption to Figure 1.2, the kinetic energy of an Auger electron is determined by the differences between the electronic energy levels in the atoms involved in the process. This energy depends upon the element emitting Auger electrons and is independent of the energy of the ionising beam of electrons. The...

Details zur Ausgabe

• Verlag: Wiley
• Erscheinungsdatum: 2006
• Sprache: Englisch
• ISBN 10: 0470866772
• ISBN 13: 9780470866771
• Einband: Gebundene Ausgabe
• Auflage: 1
• Anzahl der Seiten: 384
• Herausgeber: Prutton Martin, El Gomati Mohamed
• Kontakt zum Hersteller: Wiley-VCH GmbH; product_safety@wiley.com; ; Boschstrasse 12; Weinheim; 69469; Deutschland