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In situ characterization of thin film growth
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Related titles: Electromigration in thin films and electronic devices (ISBN 978-1-84569-937-6) Electromigration is a significant problem affecting the reliability of microelectronic devices such as integrated circuits. Recent research has focused on how electromigration affects the increasing use by the microelectronics industry of lead-free solders and copper interconnects. Part I reviews ways of modelling and testing electromigration. Part II discusses electromigration in copper interconnects, while Part III covers solder. Thin film growth (ISBN 978-1-84569-736-5) Thin film technology is used in many applications such as microelectronics, optics, magnetics, hard and corrosion-resistant coatings and micromechanics. This book provides a review of the theory and techniques for the deposition of thin films. Thin film growth will help the reader understand the variables affecting growth kinetics and microstructural evolution during deposition. Part I covers the theory and modelling of thin film growth while Part II describes the techniques and mechanisms of film growth. This section covers examples such as silicon nanostructured thin films, colloidal crystal thin films and graphene thin films. It also contains discussion of pliable substrates and thin films for particular functions. Advanced piezoelectric materials (ISBN 978-1-84569-534-7) Piezoelectric materials produce electric charges on their surfaces as a consequence of applying mechanical stress. They are used in the fabrication of a growing range of devices such as transducers, actuators, pressure sensor devices and increasingly as a way of producing energy. This book provides a comprehensive review of advanced piezoelectric materials, their properties, methods of manufacture and applications. It covers lead zirconate titanate (PZT) piezo-ceramics, relaxor ferroelectric ceramics, lead-free piezoceramics, quartz-based piezoelectric materials, the use of lithium niobate and lithium in piezoelectrics, single crystal piezoelectric materials, electroactive polymers (EAP) and piezoelectric composite materials. Details of these and other Woodhead Publishing materials books can be obtained by:
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In situ characterization of thin film growth Edited by Gertjan Koster and Guus Rijnders
Oxford
Cambridge
Philadelphia
New Delhi
© Woodhead Publishing Limited, 2011
iv Published by Woodhead Publishing Limited, 80 High Street, Sawston, Cambridge CB22 3HJ, UK www.woodheadpublishing.com Woodhead Publishing, 1518 Walnut Street, Suite 1100, Philadelphia, PA 19102-3406, USA Woodhead Publishing India Private Limited, G-2, Vardaan House, 7/28 Ansari Road, Daryaganj, New Delhi – 110002, India www.woodheadpublishingindia.com First published 2011, Woodhead Publishing Limited © Woodhead Publishing Limited, 2011 The authors have asserted their moral rights. This book contains information obtained from authentic and highly regarded sources. Reprinted material is quoted with permission, and sources are indicated. Reasonable efforts have been made to publish reliable data and information, but the authors and the publisher cannot assume responsibility for the validity of all materials. Neither the authors nor the publisher, nor anyone else associated with this publication, shall be liable for any loss, damage or liability directly or indirectly caused or alleged to be caused by this book. Neither this book nor any part may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, microfilming and recording, or by any information storage or retrieval system, without permission in writing from Woodhead Publishing Limited. The consent of Woodhead Publishing Limited does not extend to copying for general distribution, for promotion, for creating new works, or for resale. Specific permission must be obtained in writing from Woodhead Publishing Limited for such copying. Trademark notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation, without intent to infringe. British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library. Library of Congress Control Number: 2011935503 ISBN 978-1-84569-934-5 (print) ISBN 978-0-85709-495-7 (online) The publisher’s policy is to use permanent paper from mills that operate a sustainable forestry policy, and which has been manufactured from pulp which is processed using acidfree and elemental chlorine-free practices. Furthermore, the publisher ensures that the text paper and cover board used have met acceptable environmental accreditation standards. Typeset by Replika Press Pvt Ltd, India Printed by TJI Digital, Padstow, Cornwall, UK
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Contents
Contributor contact details
Part I Electron diffraction techniques for studying thin film growth in situ
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1
1
Reflection high-energy electron diffraction (RHEED) for in situ characterization of thin film growth
G. Koster, University of Twente, the Netherlands
1.1
Reflection high-energy electron diffraction (RHEED) and pulsed laser deposition (PLD) Basic principles of RHEED Analysis of typical RHEED patterns: the influence of surface disorder Crystal growth: kinetics vs thermodynamics Variations of the specular intensity during deposition Kinetical growth modes and the intensity response in RHEED RHEED intensity variations and Monte Carlo simulations Conclusions Acknowledgements References
18 23 25 26 26
2
Inelastic scattering techniques for in situ characterization of thin film growth: backscatter Kikuchi diffraction
29
N. J. C. Ingle, University of British Columbia, Canada
2.1 2.2 2.3
Introduction Kikuchi patterns Kikuchi lines in reflection high-energy electron diffraction (RHEED) images Dual-screen RHEED and Kikuchi pattern collection
1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 1.10
2.4
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3 5 8 12 13
29 30 33 37
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Contents
2.5 2.6 2.7 2.8 2.9 2.10
Lattice parameter determination Epitaxial film strain determination Kinematic and dynamic scattering Epitaxial film structure determination Conclusion References
Part II Photoemission techniques for studying thin film growth in situ
40 41 42 45 48 49
53
3
Ultraviolet photoemission spectroscopy (UPS) for in situ characterization of thin film growth
K. M. Shen, Cornell University, USA
3.1 3.2
Introduction Principles of ultraviolet photoemission spectroscopy (UPS) Applications of UPS to thin film systems Future trends References
56 63 72 73
4
X-ray photoelectron spectroscopy (XPS) for in situ characterization of thin film growth
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H. Bluhm, Lawrence Berkeley National Laboratory, USA
4.1 4.2 4.3
Introduction In situ monitoring of thin film growth Measuring the reaction of thin films with gases using ambient pressure X-ray photoelectron spectroscopy (XPS) In situ measurements of buried interfaces using high kinetic energy XPS (HAXPES) Conclusions Acknowledgments References
92 94 95 96
5
In situ spectroscopic ellipsometry (SE) for characterization of thin film growth
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J. N. Hilfiker, J.A. Woollam Co., Inc., USA
5.1 5.2 5.3 5.4 5.5 5.6
Introduction Principles of ellipsometry In situ spectroscopic ellipsometry (SE) characterization In situ considerations Further in situ SE examples Conclusions
3.3 3.4 3.5
4.4 4.5 4.6 4.7
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75 83 88
99 100 109 119 132 143
Contents
5.7 5.8 5.9
Sources of further information and advice Acknowledgments References
Part III Alternative in situ characterization techniques 6
In situ ion beam surface characterization of thin multicomponent films
L. V. Goncharova, The University of Western Ontario, Canada
6.1 6.2
Introduction Background to ion backscattering spectrometry and time-of-flight (TOF) ion scattering and recoil methods Experimental set-ups Studies of film growth processes relevant to multicomponent oxides Conclusions Acknowledgments References
6.3 6.4 6.5 6.6 6.7
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144 146 146 153 155 155 157 161 165 176 176 176
7
Spectroscopies combined with reflection high-energy electron diffraction (RHEED) for real-time in situ surface monitoring of thin film growth
P. G. Staib, Staib Instruments, Inc., USA
7.1 7.2
180
7.5 7.6 7.7
Introduction Overview of processes and excitations by primary electrons in the surface Recombination and emission processes Descriptions and results of in situ spectroscopies combined with reflection high-energy electron diffraction (RHEED) Conclusion and future trends Sources of further information and advice References
8
In situ deposition vapor monitoring
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V. Matias, Los Alamos National Laboratory, USA and R. H. Hammond, Stanford University, USA
8.1 8.2 8.3 8.4 8.5
Introduction Overview of vapor flux monitoring Quartz crystal microbalance (QCM) Vapor ionization techniques Optical absorption spectroscopy techniques
7.3 7.4
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181 188 191 206 209 209
212 212 214 217 223
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Contents
8.6 8.7 8.8 8.9 8.10
Summary of techniques and resources Case studies Conclusions Acknowledgments References
230 231 235 236 236
9
Real-time studies of epitaxial film growth using surface X-ray diffraction (SXRD)
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G. Eres, J. Z. Tischler, C. M. Rouleau, B. C. Larson and H. M. Christen, Oak Ridge National Laboratory, USA and P. Zschack, Argonne National Laboratory, USA
9.1 9.2
9.4 9.5 9.6
Introduction Growth kinetics studies of pulsed laser deposition (PLD) using surface X-ray diffraction (SXRD) Real-time SXRD in SrTiO3 PLD: an experimental case study Future trends Acknowledgment References
Index
9.3
239 245 250 267 269 269 274
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Contributor contact details
(* = main contact)
Editors
Chapter 1
Gertjan Koster MESA+ Institute for Nanotechnology University of Twente Carre 3247 PO Box 217 NL-7500AE Enschede The Netherlands
Gertjan Koster MESA+ Institute for Nanotechnology University of Twente Carre 3247 PO Box 217 NL-7500AE Enschede The Netherlands
E-mail:
[email protected] E-mail:
[email protected] Guus Rijnders University of Twente Faculty of Science & Technology Carre, 3243 PO Box 217 NL-7500 AE Enschede The Netherlands E-mail:
[email protected] Chapter 2 N. J. C. Ingle Advanced Materials and Process Engineering Laboratory University of British Columbia 2355 East Mall Vancouver BC V6T 1Z4 Canada E-mail:
[email protected] © Woodhead Publishing Limited, 2011
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Contributor contact details
Chapter 3
Chapter 6
Kyle M. Shen Laboratory of Atomic and Solid State Physics 532A Clark Hall Department of Physics Cornell University Ithaca NY 14853 USA
L. V. Goncharova Department of Physics and Astronomy The University of Western Ontario 1151 Richmond Street London Ontario N6A 3K7 Canada
E-mail:
[email protected] E-mail:
[email protected] Chapter 4
Chapter 7
H. Bluhm Chemical Sciences Division Lawrence Berkeley National Laboratory Mail Stop 6R2100 Berkeley CA 94720 USA
P. G. Staib Staib Instruments, Inc. 101 Stafford Court Williamsburg VA 23185 USA
E-mail:
[email protected] Chapter 8
Chapter 5
V. Matias Los Alamos National Laboratory Mail Stop T004 Los Alamos NM 87545 USA
J. N. Hilfiker J.A. Woollam Co., Inc. 645 M Street Suite 102 Lincoln NE 68508 USA E-mail:
[email protected] E-mail:
[email protected] E-mail:
[email protected] R. H. Hammond* Stanford University Stanford CA 94305 USA E-mail:
[email protected] © Woodhead Publishing Limited, 2011
Contributor contact details
Chapter 9 G. Eres*, J. Z. Tischler, C. M. Rouleau, B. C. Larson and H. M. Christen Materials Science and Technology Division Oak Ridge National Laboratory Oak Ridge TN 37831 USA E-mail:
[email protected] P. Zschack X-Ray Science Division Advanced Photon Source Argonne National Laboratory USA
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Reflection high-energy electron diffraction (RHEED) for in situ characterization of thin film growth G. K o s t e r, University of Twente, the Netherlands
Abstract: In this chapter reflection high-energy electron diffraction (RHEED) is described in combination with pulsed laser deposition (PLD). Both the use of RHEED as a real-time rate-monitoring technique as well as methods to study the nucleation and growth during PLD are discussed. After a brief introduction of RHEED and demonstration of typical surface diffraction patterns, a case will be made for the step-density model to describe the intensity variations encountered during deposition. Finally, an overview of these intensity variations, the intensity response during a RHEED experiment as a result of various kinetic growth modes, will be given. Key words: thin films, pulsed laser deposition, surface electron diffraction, reflection high-energy electron diffraction (RHEED).
1.1
Reflection high-energy electron diffraction (RHEED) and pulsed laser deposition (PLD)
Reflection high-energy electron diffraction (RHEED) was limited to low background pressures only until the development of high-pressure RHEED, which made it possible to monitor the surface structure in situ during the deposition of oxides at higher pressures, presented new possibilities (Rijnders et al., 1997). Figure 1.1 is a schematic picture of a typical high-pressure RHEED set-up. Besides observed intensity oscillations due to layer-by-layer growth, enabling accurate growth rate control, it has become clear that intensity relaxation observed due to the typical pulsed way of deposition leads to a wealth of information about growth parameters (Blank et al., 1998). Pulsed laser deposition (PLD) has become an important technique in the fabrication of novel materials. Starting in the mid-1960s (Ready, 1963), when the first attempts to produce high-quality thin films showed the promise of this technique, it has taken the discovery of high-Tc superconductors for PLD to become widespread. The main advantages of PLD are the relatively easy stoichiometric transfer of material from the target to the substrate and an almost free choice of (relatively high) background pressure. For instance, 3 © Woodhead Publishing Limited, 2011
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In situ characterization of thin film growth
(a) Laser beam
Load lock
Substrate holder heater Phoshor screen + camera
Electron gun ø 1 mm
0–3°
Filament ø0.5 mm Target holder
10 over the current speed. If in addition the lens design were modified so that the acceptance area of the lens is increased to 4 mm2, another factor of 10 in acquisition speed could be gained, making it possible to collect 10 spectra per second. Even though these improvements are challenging, they are merely technical in nature; monitoring film growth with a time resolution of 0.1 s should therefore be possible in the future.
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4.3
In situ characterization of thin film growth
Measuring the reaction of thin films with gases using ambient pressure X-ray photoelectron spectroscopy (XPS)
In the following we will focus on the reaction of gases with thin films. Ultrathin oxide, metal, organic as well as semiconductor films play an everincreasing role in technological applications, including industrial catalysis and data storage devices. The interaction of these systems with reactants as well as environmental gases (such as water vapor) has great influence on their performance and longevity. In particular in the field of heterogeneous catalysis the correlation between the yield and conversion in a catalytic reaction (measured by the composition of the gas phase) with the chemical nature of the active catalyst surface is of great importance for a better understanding of the basic, atomic scale processes in a catalytic reaction, and may lead to a rational design of more efficient catalytic materials. On the other hand, thin film systems can also be used to study surface reactions, in particular phase transitions and volatilization processes21 that are difficult to quantify in a bulk system. This is illustrated in Fig. 4.11. The upper panel shows the scenario for a bulk sample that interacts with the gas environment and forms a reacted layer at its surface. Photoelectrons with a certain escape depth (symbolized by the length of the arrow) are used to monitor the reaction. If the reaction also involves volatilization, this process Less volatilized e– Reacted layer
More volatilized e–
Bulk substrate
e– Reacted layer
e–
Thin film Bulk substrate
4.11 Volatilization and phase transition reactions are easier to quantify in a thin film system than for a bulk sample. For details see text.
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is not detectable in an experiment on a bulk sample: the sample on the left will give an identical signal in an XPS experiment as the sample on the right in the upper panel. However, if one uses a thin film sample instead (lower panel, Fig. 4.11) where the film thickness is of the order of the escape depth of the electrons, the attenuation of the substrate electrons can be used to gauge the degree of volatilization of the film, or of its partial conversion into another phase. In addition, since the sample under investigation has a finite thickness of the order of the escape depth of the electrons, the signal of the sample itself can be used to measure the volatilization or conversion of the material into another phase. In essence, thin film samples are, under certain circumstances, superior to bulk samples to monitor gas/surface interactions. It is, however, necessary to point out two caveats. It has been shown that thin film systems can show markedly different properties from their bulk counterparts; this is in part their appeal for the tuning of reaction properties in catalysis.22 In addition, all the above considerations hold only true in the absence of morphological changes (i.e. deviations from a strictly twodimensional model) to the film and substrate–film interface; such changes would make the quantitative analysis of thickness changes challenging. The investigation of the reaction of surfaces with gas phase species needs to bridge the so-called ‘pressure gap’ in surfaces science. In the case of XPS this is hampered by the strong interaction of electrons with gas phase molecules, as pointed out in the section above. The differentially pumped electrostatic lens designed by Kelly et al. afforded measurements at pressures in the mtorr range.17 Many reactions, in particular in environmental science, require higher pressures: in order to measure, e.g., the surface of neat liquid water the water vapor pressure in the experimental chamber has to be at least 4.6 torr, which is the equilibrium water vapor pressure at the triple point. To achieve higher pressures in an XPS experiment, the path length of the electrons through the high-pressure region has to be kept as short as possible. In addition, several differential apertures are necessary to keep the electron analyzer in a high-vacuum environment. This basic concept (see Fig. 4.12a and b) was developed more than 30 years ago in the original designs by Hans & Kai Siegbahn and collaborators, which allowed experiments of up to 1 torr.23,24 Several other groups built instruments based on this concept.25–27 To overcome the trade-off between an increase in detection efficiency through larger apertures on one hand, and better differential pumping through smaller apertures on the other hand, the latest generation of these instruments uses electrostatic lenses that are placed between the apertures, raising the pressure limit to more than 5 torr.28–31 The increase in the pressure limit is also partly due to the use of synchrotron radiation, which offers higher photon flux and tighter focused X-ray beams. Since the instruments operate at realistic environmental humidities, the technique is often called ambient pressure
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In situ characterization of thin film growth To pump To pump p1
