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Atomic Layer Deposition for Semiconductors Cheol Seong Hwang Editor Atomic Layer Deposition for Semiconductors Cheol Seong Hwang Editor Atomic Layer Deposition for Semiconductors 123 Editor Cheol Seong Hwang Department of Materials Science and Engineering and Inter-university Semiconductor Research Center Seoul National University Seoul Korea ISBN 978-1-4614-8053-2 ISBN 978-1-4614-8054-9 (eBook) DOI 10.1007/978-1-4614-8054-9 Springer New York Heidelberg Dordrecht London Library of Congress Control Number: 2013951501 Ó Springer Science+Business Media New York 2014 This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. Exempted from this legal reservation are brief excerpts in connection with reviews or scholarly analysis or material supplied specifically for the purpose of being entered and executed on a computer system, for exclusive use by the purchaser of the work. Duplication of this publication or parts thereof is permitted only under the provisions of the Copyright Law of the Publisher’s location, in its current version, and permission for use must always be obtained from Springer. Permissions for use may be obtained through RightsLink at the Copyright Clearance Center. Violations are liable to prosecution under the respective Copyright Law. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. While the advice and information in this book are believed to be true and accurate at the date of publication, neither the authors nor the editors nor the publisher can accept any legal responsibility for any errors or omissions that may be made. The publisher makes no warranty, express or implied, with respect to the material contained herein. Printed on acid-free paper Springer is part of Springer Science+Business Media (www.springer.com) Foreword Atomic Layer Deposition (ALD) is not a new technique, since the first experi- ments were carried out over 40 years ago. Industrial use began in 1983 with the production of thin film electroluminescent displays. In these displays, the dielectric-luminescent layer-dielectric thin films stack is made in a continuous process. Interestingly, this stack is 1–1.5 micron thick. Other industrial appli- cations of ALD remained limited for 20 years, but during the past 10–15 years microelectronics has been the major driver for ALD technology. In the late 1990s, it became obvious that the continuation of Moore’s law would require introduction of new materials into microelectronics. Additionally, new deposition methods were needed in IC technology since materials had to be deposited with atomic level accuracy as very thin films uniformly over the increasing wafer sizes and conformally over the increasingly demanding three- dimensional (3D) device structures. New interest was paid to ALD and enormous research activities went into the development of processes to manufacture high-k dielectric materials, metals, and materials for barrier layers. High-k dielectric materials for both gate oxides in metal–oxide–semiconductor field effect transistors (MOSFET) and capacitor dielectrics in Dynamic Random Access Memories (DRAM) have been the most important topics in ALD research during last 10–15 years. Especially, DRAMs require complex 3D capacitor struc- tures and no other thin film technology than ALD can be employed in their pro- duction. ALD has been used in these high-k applications already for some time. Furthermore, at the moment the dielectrics used in DRAMs are ZrO2–Al2O3–ZrO2 nanolaminates the preparation of which on a 3D structure is even more challenging. The DRAMs contain electrodes which also need to be conformal. ALD TiN is the material of choice for this application. About 6 years ago, it was announced that the first microprocessors using MOSFETs containing high-k dielectrics were coming to the market. These revo- lutionary new devices contained ALD-made hafnium-based oxides as dielectrics and metals as gate electrodes. The current MOSFETs are still planar devices and as such not so much dependent on ALD as the 3D DRAMs. On the other hand, the replacement gate approach and the future 3D transistor structures will also make MOSFET processing a 3D task and thereby involve ALD. v vi Foreword A third semiconductor application area where ALD has been extensively stu- died is interconnects. Apparently, the first real application was tungsten seed layers for tungsten chemical vapor deposition (CVD) contact plug fill using a process based on reduction of WF6 with either diborane or silanes. For copper inter- connects ALD has been explored for years but its implementation has been delayed. Copper appears to be a challenging material to find good ALD chemistry and the problem has not been solved yet. Development of ALD processes for platinum group metals has been successful and they may be employed in semi- conductor applications as electrodes or barriers. There are also many other application areas in microelectronics for which ALD have been explored and where it could be used. These include non-volatile memories such as ferroelectric RAM (FeRAM), flash, and phase change memories. This book Atomic Layer Deposition for Modern Semiconductor Devices focuses on its topic ALD in semiconductor industry, but presents also fundamentals of ALD technology and ALD reactors. This book consists of chapters written by prominent scientists and engineers in the field. It is timely since there are enough research and results on the use of ALD in microelectronics for reviewing. This book nicely covers the existing application areas of ALD in microelectronics and presents the emerging areas such as phase change memories. This book is useful for scientists, students, and engineers to achieve an overview of the present situation, as well as the future and challenges in ALD for microelectronic materials and device fabrication. Helsinki, Finland, April 30, 2012 Markku Leskelä Preface How will our world and society look in 100 years? This may be a question that no one can answer clearly. Perhaps, it is even difficult to say how our world and society will look in 10 years. There can be, however, many plausible answers to the question about our future even at this moment. ‘‘It will be a world that uses better information technology than now’’ without a doubt. The basic hardware for the information technology will be certainly take the form of a computer, no matter which level they are at; from supercomputer to small hand-held electronic appliances. Better computers, however, do not simply mean calculation machines with higher speed processors and higher density memories. They must be envi- ronmentally benign and sustainable. In addition, the main stream semiconductor technology based on Si-chips will most likely not be radically changed within 10–20 years although there are several potential technology contenders such as carbon-based electronics. On the other hand, it is forecast that pursuit of the present technology trend in computer and semiconductor chips will necessitate too much energy consumption in 10 years. Therefore, computers with better perfor- mance but low energy consumption are necessary. Lighter weight and longer battery life time are the key market requirements for portable appliances. These impose a significant challenge to all scientists, engineers, and designers in the information technology field and semiconductor industry. Two basic strategies could be adopted to accomplish such a demanding goal; one is following Moore’s law, and the other is surpassing it (or pursuing goals beyond- Moore’s law). The enormous improvement in computing technology over the last *50 years has been accomplished according to Moore’s law. This has been achieved by appropriate collaborations among and competitions between people working in the fields of design technology (such as recent multi-core architecture of microprocessors), material innovations, and chip fabrication technology. As the dimensions of modern semiconductor chips have shrunk to *20 nm, further miniaturization became extremely challenging due to the complexities of related processes and resultant costs. Therefore, alternatives to blind miniaturization are indispensable; those would include new functional materials, new device structures, and new thin film processes including deposition, etching, and cleaning. There have been innovative approaches differing from the conventional com- puting technologies based on the binary digits which have been so successfully implemented on complementary metal oxide semiconductor field effect transistors. vii viii Preface The so-called quantum computing is one of these new directions although it faces critical challenges due to the uncertainty principle. These approaches are usually called more-Moore or beyond-Moore technology. No matter which research trend becomes the main stream in 10–20 years in the field of microelectronics or nanoelectronics, new functional materials processed by an innovative process technology for new innovative devices must be pursued. Confining the scope of discussion
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