Material Characterization Using Ion Beams

Transcription

1 Material Characterization Using Ion Beams

2 N ATO ADVANCED STUDY INSTITUTES SERIES A series of edited volumes comprising multifaceted studies of contemporary scientific issues by some of the best scientific minds in the world, assembled in cooperation with NATO Scientific Affairs Division. Series B: Physics RECENT VOLUMES IN THIS SERIES Volume 19 - Volume 20 - Volume 21 _. Volume 22 - Volume 23 - Volume 24 - Volume 25 - Volume 26 - Volume 27 - Volume 28 - Volume 29 - Defects and Their Structure in Nonmetallic Solids edited by B. Henderson and A. E. Hughes Physics of Structurally Disordered Solids edited by Shashanka S. Mitra Superconductor Applications: SQUIDs and Machines edited by Brian B. Schwartz and Simon Foner Nuclear Magnetic Resonance in Solids edited by Lieven Van Gerven Photon Correlation Spectroscopy and Velocimetry edited by E. R. Pike and H. Z. Cummins Electrons in Finite and Infinite Structures edited by P. Phariseau and L. Scheire Chemistry and Physics of One-Dimensional Metals edited by Heimo J. Keller New Developments in Quantum Field Theory and Statistical Mechanics-Cargese 1976 edited by Maurice Levy and Pronob Mitter Topics in Theoretical and Experimental Gravitation Physics edited by V. De Sabbata and J. Weber Material Characterization Using Ion Beams edited by J. P. Thomas and A. Cachard Electron-Phonon Interactions and Phase Transitions edited by Tormod Riste The series is published by an international board of publishers in conjunction with NATO Scientific Affairs Division A Life Sciences Plenum Publishing Corporation B Physics New York and London C Mathematical and D. Reidel Publishing Company Physical Sciences Dordrecht and Boston D Behavioral and Sijthoff International Publishing Company Social Sciences Leiden E Applied Sciences Noordhoff International Publishing Leiden

3 Material Characterization Using Ion Beams Edited by 1. P. Thomas Nuclear Physics Institute Universite Gaude Bernard (Lyon I) Villeurbanne, France and A. Cachard Department of Physics of Materials Universite Claude Bernard (Lyon I) Villeurbanne, France PLENUM PRESS LONDON AND NEW YORK Published in cooperation with NATO Scientific Affairs Division

4 Library of Congress Cataloging in Publication Data Nato Advanced Study Institute on Material Characterization Using Ion Beams, Aleria, France, Material characterization using ion beams. (NATO advanced study institutes series: Series B, Physics; v. 28) "Lectures presented at the NATO Advanced Study Institute on Material Characterization Using Ion Beams held in Aleria, Corsica, August 29-September 12,1976." Includes index. 1. Ion bombardment-addresses, essays, lectures. 2. Materials-Analysis-Addresses, essays, lectures. 3. Solid state physics-addresses, essays, lectures. I. Thomas, J. P. II. Cachard, A. III. Title. IV. Series. QC702.7.B65N ISBN ISBN (e8ook) DOl / Lectures presented at the NATO Advanced Study Institute on Material Characterization Using Ion Beams held in Aleria, Corsica, August 19-5eptember 12, Plenum Press, New York Sof'tcover reprint of the hardcover 1 st edition 1978 A Division of Plenum Publishing Corporation 227 West 17th Street, New York, N.Y 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

5 A.S.I.M.S. ACTIVITIES The Advanced Study Institute on Materials Science was created in 1973 in the Departement de Physique des Materiaux of the University of Lyons. The aim of this Institute was to organize specialized courses on material science at a doctoral level in Lyons and International Summer Schools on the same subject at a post-doctoral level in Corsica. Here is the list of the Summer Schools which have been done with NATO as the main sponsor: Radiation Damage Processes in Materials 1-15 September, 1973 Director: C.H.S. Dupuy Proceedings edited by C.H.S. Dupuy (Noodhoff International Publishing Company) Physics of Nonmetallic Thin Films 29 August - 12 September, 1974 Director: C.H.S. Dupuy Proceedings edited by C.H.S. Dupuy and A. Cachard (Plenum Publishing Company) Electrode Processes in Solid State Ionics Theory and Application to Energy Conversion and Storage 28 August - 9 September, 1975 Director: M. Kleitz Proceedings edited by M. Kleitz and J. Dupuy (D. Reidel Publishing Company) v

6 PREFACE The extensive use of low-energy accelerators in non-nuclear physics has now reached the stage where these activities are recognized as a natural field of investigation. Many other areas in physics and chemistry have undergone similarly spectacular development: beam foil spectroscopy in atomic physics, studies in atomic collisions, materials implantation, defects creation, nuclear microanalysis, and so on. Now, this most recent activity by itself and in its evident connection with the others has brought a new impetus to both the fundamental and the applied aspects of materials science. A summer school on "Material Characterization Using Ion Beams" has resulted from these developments and the realization that the use of ion beams is not restricted to accelerators but covers a wide energy range in the developing technology. The idea of the ion beam as a common denominator of many act1v1t1es dealing with surface and near-surface characterization was enthusiastically received by many scientists and a school on this subject received the positive endorsement of NATO. The Advanced Study Institute on Materials Science has assumed for us the status of an "institution" leading to better contact among the many laboratories engaged in this field. The fourth Institute in this series was held in Aleria, Corsica, between August 22 and September 12, It is a pleasure to acknowledge the efforts of all the people who participated in making this summer school a success. First of all, we must cite not only the lecturers but also all those who acted as efficient discussion leaders during the panels: they managed to maintain the constant interest of the attendees. We are very grateful to the local authorities in Aleria, the mayor, Mr. Carlotti, and Mr. V. Carlotti, general councilor, who made it vii

7 viii PREFACE possible for the school to take place under the best of conditions. The "Mission Regionale" and especially Mr. J. de Rocca Serra was of great help to the organization, together with Miss M. L. Carlotti, who took care of social events, among them a trip to Bavella and a Corsican evening. The penitentiary administration, and especially Mr. Talbert and Mr. Bona1di, did their best to make our stay in the "Village de Vacances" as fruitful as possible. Many thanks are due to them and to all the staff of the V.l.V.E. of Casabianda. As noted above, NATO was the main sponsor of this meeting, and once again we are very grateful to it. Our respective departments, the "Departement de Physique des Materiaux" and "l'lnstitut de Physique Nuc1eaire" of the University of Lyons were also of great help in the organization. The Organizing Committee J. P. Thomas A. Cachard C.H.S. Dupuy M. Fallavier G. Chassagne J. Remilleux

8 CONTENTS Introduction J.P. Thomas xi PART I ION BEAMS: PRODUCTION AND INTERACTION WITH MATTER Energy Loss of Charged Particles W.K. Chu Some General Considerations of Ion Beam Production and Manipulation J.H. Freeman 3 35 PART II SURFACE STUDIES: kev RANGE IONS Applications of Low-Energy Ion Scattering H.H. Brongersma, L.C.M. Beirens, and G.C.J. van der Ligt Ion Beam Induced Light Emission: Mechanisms and Analytical Applications \tl. F. van der Weg Complementary Analysis Techniques: AES, ESCA 101 J. Tousset PART III IN-DEPTH ANALYSIS Fundamental Aspects of Ion Microanalysis 143 G. Blaise ix

9 x Ion Induced X-rays: General Description F. Follanann The Evolving Use of Electrons, Protons and Heavy Ions in the Characterisation of Materials.... J.A. Cairns Backscattering of Ions With Intermediate Energies H. Verbeek Backscattering Analysis With MeV 4He Ions J.W. Mayer, M-A. Nicolet, and W.K. Chu Microanalysis by Direct Observation of Nuclear Reactions A. Cachard, J.P. Thomas, and E. Ligeon CONTENTS PART IV SOLID STATE STUDIES USING CHANNELING EFFECTS Channeling: General Description J.A. Davies Flux Peaking - Lattice Location P. Mazzoldi Analysis of Defects by Channeling E. Rimini Application of MeV Ion Channeling to Surface Studies J.A. Davies GENERAL CONCLUSIONS General Conclusions Participants Index

10 INTRODUC TION J.P. THOMAS Institut de Physique Nucleaire and IN2P3 Villeurbanne, France The idea to hold a summer school devoted to the use of ion beams in material science carne for the people of our two departments, from the acknowledgement of a favorable local and international context. The local context concerned obviously the continuity of the spirit of the ASIMS meetings, previously invoked in the preface, and, more than that, the mutual interest in this field of research of the Institut de Physique Nucleaire and the Departement de Physique des Materiaux. The international context, certainly more significant, showed evidence of a strong need to have a full review of well established techniques dealing with ion beams. As a matter of fact, following an increasing period of meetings on the subject, a more didactic presentation and discussion of these techniques seemed very feasible at this time in the form of a summer school. Taking account of my feeling on the subject before the conference and my observations during this event, I still realise that the task of such an introduction is not an easy one. Nevertheless I will keep the way I followed at the opening session, trying to make several comments about the title, about the topic s, and probabl y the most difficult, about what should remain from such a gathering of speciali sts. About the title first : necessarily short, it so appears as somewhat ambitious especially if we intend to discuss the use of ion beams in a large energy range. Instead of setting an arbitraxi

11 xii J. P. THOMAS ry upper limit to it, we will not consider in these lectures the activation analysis techniques in the sense of radioactive isotope formation (generally dealing with high energy). Nevertheless it is rather difficult to introduce other techniques without referring somehow to the one which is certainly the starting point of the extensive use of ion beams for material characterization. As characteristics of activation analysis we will particulary mention that the determination of impurities at the substra te level, with very high sensitivity, applies mainly for the bulk of the material. If this feature is still of great value in characterization, recent years have shown that interest has shifted from bulk problems to surfaces and thin films, and more than average composition three dimensional profiles are more and more required. These new needs must, be considered as enhancing, in the definition of the characterization (I), the determination of the structure aside those of the composition. Similarly it is worthwhile to note the acknowledgement of the whole concept of defect, more and more related to a discontinuity of the material, and, in which the physical aspect is as important as the chemical one. Still referring to activation analysis, the other methods, often qualified of "prompt" at low energy (MeV range and less) point out the first evolution concerning the "appliedtl use of ion beams. This evolution can be related to those of nuclear and atomic physics. In the good old days of nuclear physics, the basic instrument was the cyclotron, in the 10 to 100 MeV range, and very limited shifts of protons, deuterons and ex-particles were available for activation analysis. By comparison, the electrostatic accelerator V. D. G type is operating in the MeV range, with an increasing variety of projectiles, and nuclear physicists are no more the majority of users. The conjunction of the availability of such machines with these new needs we discussed previously explains the development of material resea.rch teams using these accelerators. As pointed our by the book of J.F. ZIEGLER "New uses of ion accelerators"(2) or more recently by the french prospect report on non-nuclear developed through the use of accelerators(3). this field of research has shown is maturity. Nuclear physics going up to higher energy, it is easy to caricature showing the opposite evolution of the methods of material characterization. In fact it is true that there is a tremendous development of low energy machines (down to several key) but the explanation must be found in technological improvement, ahowing with this decrease in energy surface studies with easier to handle device s. Thus, opposite directions seem the ways nuclear physics and our field of interest are taking. Nevertheless if interactions are

12 INTRODUCTION xiii PHOTONS AAS IRS UVS / IONS--- EPM ELECTRONS Fig. AES: Auger electron spectroscopy; BILE: Beam induced light emission; EPM: Electron probe microscopy; ESCA: Electron spectroscopy for chemical analysis; HEHlXE: High energy heavy ions X-rays emission; IBSCA: Ion beam spectrochemical analysis; IIAES: Ion induced Auger electron spectroscopy; IILE: Ion induced light emission; lixe: Ion induced X-ray emission; IPM: Ion probe microscopy; IRS: Infra-red spectroscopy; ISS: Ion scattering spectroscopy; LEED: Low energy electron diffraction; LETS: Low energy ion scattering; LMSA: Le Gressus Massignon-Sopizet-Auger; MEIS: Medium energy ion scattering; PES: Photo electron spectroscopy; PIXE: Particle induced X-ray emission; PRA: Prompt radiation analysis; RBS: Rutherford backscattering; RHEED: Reflection high energy electron diffraction; SCANIR: Surface composition by analysis of neutral and ion impact radiation; SEM: Scanning electron microscopy; SHEED: Secondary high energy electrons diffraction; SAM: Scanning Auger microscopy.

13 xiv J. P. THOMAS TARGET l EMERGING BEAM INCIDENT ION BEAM CHANGES IN TEMPERATURE PROPERTIES CHANGES IN STRUCTURE (INDUCED DEFECTS) ENERGY DlflECTION OF MOTION CHARGE STATE IONIZATION e;photons SPECIES ; PRODUCTS SPUTTERED TARGET ATOMS Fig. 2 : Schematic picture of basic radiation-induced effects. still existing and fruitful, more connections exist now with atomic physics which is very active in the same energy region. More than that, there is now a constant exchange between fundamental and applied features of particle matter interaction and very often the same people do the two kinds of experiments with the same equipment. This becomes apparent from the communications presented at the meetings on atomic collisions (4) and ion beam surface layer analysis (5). About the topics now : although described as ambitious our title suffers, on the other hand, to be somewhat restrictive especially after having emphasized the interest of surface analysis. In this matter, it must be recognized that more than ion beams the general term of radiation would be adequate to give a good picture of the present universe of characterization. As a pictorial representation of the techniques so involved we can adopt the allegorical form of the bright sun appearing on Figure 1. Although the means of characterization are not so numerous as suggested by the thirty-one initials found in the current literature, a coherent meeting cannot afford to treat all of them. Nevertheless extending the discussion to the most significant methods not related to ion beams is obviously of great interest. If we want now to practice this esoteric vocabulary for characterization, a sim-

14 INTRODUCTION xv pier picture based on basic physical processes may help. In this way, radiation-induced effects can be described in terms of changes as represented in Figure 2. The most important of these changes concerns of course the emerging beam (not taken in the restrictive sense of transmitted beam) because this is the matter of the methods of characterization. Nevertheless the changes induced in the target itself have always to be considered, either, as another means of characterization, as a possible perturbation for the analysis, or at last as a way to obtain a new material to be characterized. It is hardl y conceivable to not consider, among these changes, the slowing down of the beam as one of fundamental importance for the matter of this book and especially for in-depth analysis. Thus, elements of the stopping theory will naturally be given prior to go into details of the techniques and methods. Since exhaustive reviews have been done about the wide subject of collisions (6), the lectures of Dr. CHU will be more concerned with the practical aspect of the energy loss and related phenomena. In this way, a presentation of usable theory combined with useful references will have the ambition to offer relevant data for analysis. Ion beam production and manipulation will also appear in the first chapter, since, despite the variety of set-ups, the problem of the quality of ion beams is common to all the techniques. In Dr. FREEMAN's lecture, the discussion will go from general accelerator concepts to a detailed description of the phenomena occurriag in ion beam production and transport leading to a scope for substantial improvements. For the central subject, methods and techniques of characterization, we decided to have two chapters - surface and in-depth analysis - simply following an increasing of the incident beam energy. Of these two key words, one tnust be aware that the first one, though commonly used, is somewhat ambiguous and it may deserve some comment. As a. matter of fact, the questions related to the concept of surface are numerous, but among them the physical question of how deep is the surface phase studied is primordial. Defining the surface as the outermost layer bounding the solid suggests a minimum probing depth as the criterion but is it not then a too restrictive definition? When doing in-depth analysis, the methods being destructive or nondestructive, does the depth resolution lead to the same information in each case? In order to answer these fundamental questions and particularly the first one, it must be recognized that some techniques not directl y related to ion beams can hardly be ignored due to their impact on the

15 xvi J. P. THOMAS discipline. Auger spectroscopy and ESCA, the most representative, will appear in the lecture as "complementary techniques" which is of course a fairly egocentric point of view ~ Dr. TOUSSET will present these techniques of electron spectroscopy to end the surface studies chapter following Dr. BRONGERSMA who will make the first reference to the scattering process and Dr. VAN DER WEG who will introduce the use of light emission. As a first contribution to the in-depth analysis chapter, Dr. BLAISE's lecture - ion microanalysis - will make the transition surface - near surface - since the sputtering phenomenon is part of the ion emission mechanism. This phenomenon will be discussed with its complement, the ionization, through this lecture where fundamental aspects of the technique will be treated in great detail. The principles of ion-induced X-ray emission as well as the general analytical applications will appear in Dr. FOLKMANN's lecture while Dr. CAIRNS will present more generally the relative merits of these particles but also of the electrons in the characterization. The remaining interest of electrons will more precisely appear in the description of a new sophisticated complementary technique: controlled atmosphere electron microscopy. The back scattering technique as well as the use of nuclear reactions for analysis do not require special comments at this place since they are probably the best known techniques of characterization developed using ion accelerators. Dr. MAYER will present Rutherford backscattering emphasizing its easy use for applications and restricting it to alpha-particles in the MeV range. Dr. VERB EEK will describe the extension of the technique to lower energies with the subsequent advantages and disadvantages. For nuclear reactions, Dr. RIGO's lecture will particularly emphasize the specificity of light element determination (including isotopic analysis). Thus, X-ray emission, backscattering and nuclear reactions, as complementary techniques, constitute the trilogy of the powerful means of characterization accelerators can offer. Concerning the determination of the elemental composition of the surface and near surface, as well as the identification of the species attached to these surfaces, nearly all the significant techniques are represented. For crystalline materials one may obtain unique structural information when channeling effects of ion beams occur. A general and comprehensive description of a phenomenon which has turned from a specifically fundamental interest to a widely applied one will be given by Dr. DAVIES. Two other lectures will be devoted to specific applications : Dr. MAZZOLDI will be in charge of the description of the impurities location in

16 INTRODUCTION xvii crystal lattices while the analysis of defects will be given in Dr. RIMINI's lecture. (The channeling technique has strongly contributed to the impact of ion implantation (7) in material science). We must also particulary emphasize the recent sophisticated use of channeling in surface studies reported by Dr. DAVIES in the last lecture. With the improvement of vacuum conditions, the possibility of single and double alignment of the technique has led to new data on surface atoms which deserve to be compared to other surface techniques. Since the lectures, briefly presented here, will remain the only witnesses of a two weeks summer school, the introduction may suffer last additional comments arising from personal appraisal of the live meeting. As a main remark, it is quite clear that the development of the techniques and methods of characterization is strongly oriented by current problems of materials of economic interest. As the most representative of these materials, silicon, must still be reported, most of the development of ion implantation and ion analysis having been done since the beginning of the sixties for its applications. Compound semiconductors, amorphous glasses and more generally nonmetallic thin films (8), as existing or potential components of electronics technology, follow the same way. Research in metals and alloys (9) is important in nuclear reactor technology due to crucial concerns in energy production : most of the characterization is then devoted to induced-defect analysis and light-element profiling on suitable materials for irradiation. As a consequence of this increase of the means of characterization there is a revival of some fundamentals in particle-matter interaction. An unusually large part of atomic collision people have allowed spirited discussions on the basis of these techniques. These discussions like those dealing with the previous aspects or with the respective merits of the techniques were expressed through numerous panels : the concluding lecture will try to summarize the trends which appeared since no publications have been possible for these informal presentations. Exciting and controversial results are now appearing at a tremendous rate from the different techniques and the necessary background on each of them is more and more difficult to acquire. If this book can contribute to an easier communication between specialists of sophisticated (and expensive) techniques, we think that it is worth our efforts. Despite or perhaps because of the expensive character of these techniques and also considering their complementarity there is a strong indication of a concentration

17 xviii J. P. THOMAS for an in-situ multicharacterization, in the future. According to the respective quality of the systems described here, a personal feeling is that there will still be little room to connect an accelerator to these new devices. REFERENCES (l) Characterization of materials. Publication MAB-229-M National Academy of Sciences, Washington, D. C. (March 1967) (2) "New uses of ion accelerator sit, Ed. by J. F. ZIEGLER Plenum Press, N. Y., (l975) (3) Rapport de prospective : "Physique autour des accelerateurs dans des domaines autres que nucleaires. Applications". DGRST Report 1977, edited by "La Documentation Fran~aise", 29-31, quai Voltaire, Paris Cedex 07 (4) "Atomic Collisions in Solids", ed. by F. W. SARIS and W.F. VAN DER WEG, North-Holland Publ. Co., Amsterdam, (1976) (5) "Ion Beam Surface Layer Analysis", ed. by O. MEYER G. LINKER, F. KAPPELER, Plenum Press, N. Y., (1976) (6) For example P. SIGMUND in "Radiation Damage Processes in Material", ed. by C. H. S. DUPUY, Noordhoff Intern. Publ., Leyden, The Netherlands, (1975) (7) "Ion Implantation, Sputtering and their Applications", P.D. TOWNSEND, J.C. KELLY and N.E. W. HARTLEY Academic Press, London, (1976) (8) "Physics of Non-Metallic thin Films", ed. by C. H. S. DUPUY and A. CACHARD, Plenum Press, N. Y., (I97~ (9) "Applications of Ion Beams to Metal", ed. by S. T. PICRAUX, E. P. EERNISSE, F. L. VOOK, Plenum Press, N. Y., (l974)