Properties of Metal Silicides PDF
Preview Properties of Metal Silicides
P R O P E R T I ES OF M e t al S i l i c i d es E d i t ed by KAREN MAEX and MARC VAN ROSSUM MI EC, Leuven, Belgium IEE Published by: INSPEC, the Institution of Electrical Engineers, London, United Kingdom © 1995: INSPEC, the Institution of Electrical Engineers Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the Copyright, Designs and Patents Act, 1988, this publication may be reproduced, stored or transmitted, in any forms or by any means, only with the prior permission in writing of the publishers, or in the case of reprographic reproduction in accordance with the terms of licences issued by the Copyright Licensing Agency. Inquiries concerning reproduction outside those terms should be sent to the publishers at the undermentioned address: Institution of Electrical Engineers Michael Faraday House, Six Hills Way, Stevenage, Herts. SG1 2AY, United Kingdom While the editor and the publishers believe that the information and guidance given in this work is correct, all parties must rely upon their own skill and judgment when making use of it. Neither the editor nor the publishers assume any liability to anyone for any loss or damage caused by any error or omission in the work, whether such error or omission is the result of negligence or any other cause. Any and all such liability is disclaimed. The moral right of the authors to be identified as authors of this work has been asserted by them in accordance with the Copyright, Designs and Patents Act 1988. British Library Cataloguing in Publication Data A CIP catalogue record for this book is available from the British Library ISBN 0 85296 859 0 Printed in England by Short Run Press Ltd., Exeter Foreword Modern electronics technology has changed the world in a short time span. A good share of the credit should go to microelectronics. From the invention of the first transistor we have come a long way towards integrating billions of components on a single chip. Continuous advancements in technology have resulted in integrated circuits with smaller device dimensions and larger area and complexity. The trends show that process and device technology evolution is proceeding towards lateral dimensions below 0.1 |im. The number of components per chip increased at a rate of 100% per year during the sixties and 59% during the seventies and eighties. Will these trends continue in the future? Experts have examined various limits to the evolution of microelectronics: fundamental limits imposed by physics as well as practical limits imposed by the device structure, circuit and system configuration. It is believed that we are far from encountering the fundamental limits of physics and for the foreseeable future the scaling of the device dimensions will continue and IC chips with increasing complexity will be built in the future. Overall circuit performance in the past has depended primarily on device properties. To enhance the circuit and system speed the primary effort had been on improving the device speed. During the last decade that has changed. The parasitic resistance, capacitance and inductance associated with interconnections and contacts are now beginning to influence circuit performance and will be one of the primary factors in the evolution of deep submicron ULSI technology. It is now a foregone conclusion that for submicron feature size the impact of parasitics seriously hurts circuit and system performance. RC time delay, IR voltage drop, power consumption and crosstalk noise due to these parasitics are becoming increasingly significant. Thus even with very fast devices the overall performance of a large circuit could be seriously affected by the limitations of interconnections and contacts. During the last few years a great deal of work has been done on new and innovative materials, device structures and fabrication technology to overcome the problems of conventional ULSI circuits. In order for a certain conductor to be used to form multilayer interconnections, several requirements must be met which are imposed by fabrication technology and required circuit performance. The main requirements are good conductivity, reliability and manufacturability. In general, several requirements are imposed on interconnection materials by fabrication technology. In a multilayer interconnection structure, the layers incorporated early in the process sequence might be subjected to several fabrication steps, to which layers incorporated later might not be subjected. The most rigorous set of requirements are: low resistivity; ease of formation of thin films of the material; ability to withstand the chemicals and high temperatures required in the fabrication process; good adhesion to other layers; ability to be thermally oxidised; stability of electrical contacts to other layers; ability to contact shallow junctions; good MOS properties; resistance to electromigration; and ability to be defined into fine patterns. The materials which have been used or proposed for forming interconnections can be broadly classified into four categories: low temperature metals; heavily doped polysilicon; high temperature refractory metals; and metal silicides. Since the main requirement for interconnections specified by circuit performance is good conductivity aluminium and its alloys have long been used for this application. However, as device dimensions are scaled down, its reliability has become a major issue. In general, several other requirements are imposed by fabrication technology, device compatibility, reliability, etc. Refractory metals and silicides are playing increasingly important roles in meeting these requirements. It must be pointed out that these materials will not replace aluminium but complement it in a multilayer structure. During the last few years, use of refractory metal silicides has been heavily investigated for many applications, such as ohmic contacts, MOS gate electrodes, and silicidation of diffusions, and the results have been very exciting. Silicides of platinum, palladium, tungsten, molybdenum, titanium, cobalt, nickel, tantalum and other metals have reasonably good compatibility with IC fabrication technology for one or more applications cited above. They have fairly high conductivity and resistance to electromigration, they can make low resistance and reliable contacts to shallow p-n junctions, they can withstand the chemicals normally encountered during the fabrication process, thermal oxidation of most of the silicides can be conducted in oxygen and steam to produce a passivating layer of SiO , and fine features can be 2 formed in these materials. However, to incorporate the silicides in a microelectronics structure many problems must be solved for proper functioning of the device. Important issues are that the silicides involve non-homogeneous materials, grains and grain boundaries, and often they contain secondary and metastable phases. Equally important is the presence of adjoining layers and the interfaces between them, and the role they play in the different processes and mechanisms. As the semiconductor structures get smaller, other layers and interfaces can dominate the various phenomena in interconnect processing. Reactions and interactions with other layers in these structures are common. In addition, the interfaces themselves can act as separate phases and greatly affect the film properties and processing. Low resistivity silicide layers are obtained by depositing the silicide directly, or by depositing the metal on silicon and reacting the materials to form the silicide. In either case, a relatively high temperature anneal is needed - in the second case to react the metal and silicide, and in both cases to allow crystallisation/grain growth to occur. In all of these cases a detailed knowledge of the formation techniques, properties of as-formed films and changes during the subsequent processing is absolutely necessary. The electrical properties of silicide interconnects and contacts are determined by factors such as phase formation (including reactions, recrystallisation, grain growth, transformation, and agglomeration), and dopant redistribution and segregation. Properties which are important during processing of the layers may depend on the topography, morphology, and composition of the as-deposited films. Properties such as dopant diffusion, phase transformation, physical stress characteristics, and many others may depend heavily on the grain size, structure, doping, composition, and texture of each layer. This book brings leading experts in this field together to share the results of their research and experience. It will be a valued reference source to other researchers, manufacturing engineers and academicians working on further development and use of silicides. Krishna C. Saraswat Department of Electrical Engineering Stanford University, Stanford, CA 94305, USA September 1995 Introduction Silicides have been for many decades a fruitful subject of metallurgical studies. The large variety of compounds and their complex phase transitions were amply sufficient reasons to motivate a continuing effort in fundamental investigations, resulting in a steady stream of publications and by now an impressive body of metallurgical literature. Moreover, the growing interest for microelectronic applications over the last twenty years has widened the scope of silicide work and has opened new research avenues, aiming at a better understanding of the behaviour of silicides when combined with other device materials. Today, several silicides belong to the category of strategic materials for the electronics industry, having been introduced in the production of virtually all advanced silicon integrated circuits (see the Foreword by Professor K. Saraswat for more examples). Applications in so-called "niche markets" such as sensors, detectors and other electronic devices are also developing at a fast pace, their success being mainly based on the excellent compatibility of silicides with the basic silicon material. Nevertheless, the silicidation process remains very complex and reflects how closely materials properties are influencing technological developments. The unusual width and diversity of our subject creates special problems in reviewing the data. It has been impossible to provide an exhaustive coverage of all relevant materials aspects for the many silicide compounds which have been listed in the literature. Moreover, a special difficulty with silicides is the problem of phase identification, since many of the compounds mentioned in research papers have not been unambiguously identified. Although the main categories of silicides (near-noble metal, refractory metal and rare earth metal) have been treated in some detail, our overall approach has been synthetic rather than analytical. As a result, this book is organised along the main categories of materials properties, as they can be found in most solid-state textbooks: structural and thermal properties (ch.l), growth and phase transformations (ch.2), thermochemical properties and phase diagrams (ch.3), electronic properties (ch.4), electrical transport (ch.5), optical properties (ch.6), diffusion (ch.7) and hyperfine interactions (ch.8). All chapters try to introduce a sense of perspective to the wealth of available data by separating the essential from the accessory. We hope that this book will become a useful working tool for the many researchers who today contribute to the development of the silicide field. It is our pleasure to thank all experts who were involved in this enterprise by writing review articles. We also acknowledge the refereeing support of numerous researchers and in particular would like to thank the following: Dr. S. Mantl, Forschungszentrum Julich, Germany Dr. S. Ogawa, Matsushita Electric, Japan Dr. A. Vantomme, Physics Department, Leuven University, Belgium Dr. K. Larsen, University of Catania, Italy Finally, a special word of thanks is due to John Sears (Managing Editor of the EMIS Datareviews Series) for his support and encouragement during the whole editing process. Karen Maex Marc Van Rossum IMEC September 1995 Contributing Authors M. Affronte Universita Degli Studi di Modena, Dipartimento 5.1 di Fisica, Via G. Campi, 213/A, 41100 Modena, Italy T. Barge SOITEC SA, Site Technologique Astec, 7.2 15 Avenue des Martyrs, 38054 Grenoble, France L. A. Clevenger IBM Thomas J. Watson Laboratory, PO Box 218, 2.1,2.2 Yorktown Heights, NY 10598, USA J. Derrien CRMC2-CNRS, Case 913, Campus de Luminy, 4.1,4.2,4.4 13288 Marseille Cedex 09, France P. Gas CNRS, Laboratoire de Metallurgie, Faculte des 7.1-7.3 Sciences et Techniques de Saint Jerome, Avenue Escadrille Normandie-Niemen, 13397 Marseille, France U. Gottlieb ENSPG, Laboratoire des Materiaux et du Genie 5.1, 5.2 Physique, BP46, Domain Universitaire, 38402 St. Martin d'Heres Cedex, France and CNRS, Centre de Recherches sur les Tres Basses Temperatures, BP166, 38042 Grenoble Cedex 9, France G. Guizetti Dipartimento di Fisica 1A. Volta1, Universita di 6.1-6.8 Pavia, via Basi 6,1-27100 Pavia, Italy FM. d'Heurle IBM Thomas J. Watson Laboratory, PO Box 218, 7.1-7.3 Yorktown Heights, NY 10598, USA CC. Hsu Chinese Academy of Sciences, Institute of 1.4,2.3-2.6, Semiconductors, PO Box 912, Beijing 100083, 4.3,4.5,5.3 (Xu Zhenjia) China 6.9 CNRS, Centre de Recherches sur les Tres Basses Temperatures, BP166, 38042 Grenoble Cedex 9, France O. Laborde and at the same address 5.1,5.2 Laboratoire des Champs Magnetiques Intenses IKS, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium G. Langouche 8.1-8.4 R. Madar Laboratoire des Materiaux et du Genie Physique, 3.4,3.5 Ecole Nationale Superieure de Physique de Grenoble, BP46, 38402 St. Martin d'Heres Cedex, France K. Maex IMEC, Kapeldreef 75, B-3001 Leuven, Belgium 1.1 RW. Mann IBM Thomas J. Watson Laboratory, PO Box 218, 2.1,2.2 Yorktown Heights, NY 10598, USA F. Marabelli Dipartimento di Fisica 1A. Volta', Universita di •6.1-6.8 Pavia, via Basi 6, 1-27100 Pavia, Italy F. Nava Universita Degli Studi di Modena, Dipartimento 5.1, 5.2 di Fisica, Via G. Campi, 213/A, 41100 Modena, Italy M. Ostling Royal Institute of Technology, Electrum 229, 1.2, 1.3 Solid State Electronics, PO Box 1298, S-16440Kista, Sweden A. Reader Philips Research Laboratories, Building WAM, 1.1 Prof. Hostlaan 4, 5656 AA Eindhoven, The Netherlands M. Setton Lam Research Sari, EUROPOLE, Batiment 3.7 Eurennepolis, 4, Place R. Schumann, 38000 Grenoble, France R. Sinclair Stanford University, Department of Materials 3.1-3.3, Science and Engineering, Building 550, 3.6,3.8 Stanford, CA 94305, USA 0. Thomas MATOP, associe au CNRS, Faculte des 7.3 Sciences et Techniques de Saint Jerome, Avenue Escadrille Normandie-Niemen, 13397 Marseille, France M. Van Rossum IMEC, Kapeldreef 75, B-3001 Leuven, Belgium 1.1 C. Zaring Royal Institute of Technology, Electrum 229, 1.2, 1.3 Solid State Electronics, PO Box 1298, S-16428Kista, Sweden Abbreviations The following abbreviations are used in this book. AES Auger electron spectroscopy ASTM American Society for Testing and Materials BIS Bremsstrahlung isochromat spectroscopy CSS complete solid solubility C-V capacitance-voltage CVD chemical vapour deposition DDS dominant diffusing species DMR deviation from Mathiessen's rule DOS density of states DVM discrete vibrational method EDC energy distribution curve EDX energy dispersive X-rays EFG electric field gradient EHT extended Huckel-theory EMP electron microprobe EPR electron paramagnetic resonance FEBA fast e-beam annealing FIR far infrared FWHM fUll width at half maximum H hexagonal H|! micro hardness HP high pressure HRA Rockwell hardness HRTEM high resolution transmission electron microscopy HT high temperature HV Vickers hardness IBS ion beam synthesis IC integrated circuit IPC inverse photoemission spectroscopy IR infrared I-V current-voltage JCPDS Joint Committee on Powder Diffraction Standards LA laser annealing LDF local density formalism LEED low energy electron diffraction LP low pressure LPE liquid phase epitaxy LT low temperature MBE molecular beam epitaxy MBT metal base transistor MIGS metal-induced gap states ML monolayer MS Mossbauer spectroscopy NIR near infrared NMR nuclear magnetic resonance NO nuclear orientation NOS number of states O orthorhombic PAC perturbed angular correlations PBT permeable base transistor PECVD plasma-enhanced chemical vapour deposition PES photoemission spectroscopy R reflectance RBS Rutherford back-scattering RDE reactive deposition epitaxy RE rare earth RH resistive heating RHEED reflection high energy electron diffraction RRR residual resistance ratio RS Raman scattering RT room temperature RTA rapid thermal annealing RTP rapid thermal processing SALICIDE self-aligned process SB Schottky barrier SC single crystal SE ellipsometric spectroscopy SEM scanning electron microscopy SIMS secondary ion mass spectrometry SOI silicon-on-insulator SPE solid phase epitaxy SR synchrotron radiation T tetragonal or transmittance TDOS thermodynamic density of states TE thermal evaporation TEM transmission electron microscopy TM transition metal TT template technique UHV ultra high vacuum ULSI ultra large scale integration UPS ultraviolet photoemission spectroscopy UV ultraviolet VLSI very large scale integration VUV vacuum ultraviolet WF work function minimum channelling yield Xm.n XAES X-ray induced Auger electron spectroscopy XARS X-ray absorption resonance spectroscopy XPD X-ray photoelectron diffraction XPS X-ray photoemission spectroscopy XRD X-ray diffraction XTEM X-ray cross-section transmission electron microscopy
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