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Advances in Silicon CarbideProcessing and ApplicationsStephen E. SaddowAnant AgarwalEditorsArtech House, Inc.Boston Londonwww.artechhouse.comLibrary of Congress Cataloguing-in-Publication DataA catalog record for this book is available from the Library of Congress.British Library Cataloguing in Publication DataAdvancesinsiliconcarbideprocessingandapplications.(ArtechHousesemiconductormaterials and devices library).1. Silicon carbide 2. Silicon carbideIndustrial applicationsI. Saddow, Stephen E. II. Agarwal, Anant321.38152ISBN 1-58053-740-5Cover design by Igor Valdman 2004 ARTECH HOUSE, INC.685 Canton StreetNorwood, MA 02062All rights reserved. Printed and bound in the United States of America. No part of this bookmay be reproduced or utilized in any formor by any means, electronic or mechanical, includ-ing photocopying, recording, or by any information storage and retrieval system, withoutpermission in writing from the publisher.All terms mentioned in this book that are known to be trademarks or service marks havebeen appropriately capitalized. Artech House cannot attest to the accuracy of this informa-tion. Use of a term in this book should not be regarded as affecting the validity of any trade-mark or service mark.International Standard Book Number: 1-58053-740-510 9 8 7 6 5 4 3 2 1To our wives, Karen and Suman, for their love and patienceContentsPreface xiAcknowledgments xiiiCHAPTER 1Silicon Carbide Overview 11.1 General Properties 11.1.1 Mechanical and Chemical Properties 21.1.2 Bandgap 21.1.3 Critical Field 21.1.4 Saturated Drift Velocity 31.1.5 Thermal Conductivity 31.1.6 Figures of Merit 41.2 History 41.2.1 Berzelius and Acheson 41.2.2 The Discovery of Polytypism 61.2.3 The First LED and the Lely Process 61.2.4 The Lost Decades 71.2.5 The Second Wave 71.2.6 The Third Wave 71.3 Crystalline Structure 81.3.1 Basic Structure 81.3.2 Polytypism 81.3.3 Impurities in Different Polytypes 91.4 Crystal Growth 111.4.1 Seeded Sublimation Growth 111.4.2 High Temperature Chemical Vapor Deposition 141.5 Epitaxial Growth 181.5.1 Chemical Vapor Deposition 181.6 Defects 211.6.1 Micropipes 211.6.2 Stacking Faults 221.7 Commercial Outlook 221.7.1 High-Frequency Applications 231.8 Summary 25References 26viiCHAPTER 2High-Temperature SiC-FET Chemical Gas Sensors 292.1 Introduction 292.2 Detection Mechanism of Field-Effect Gas Sensors 302.2.1 Gas Sensing Principle 302.2.2 Detection of Different Molecules 312.2.3 Influence of Oxygen 342.2.4 Influence of Different Metals 352.2.5 Influence of Temperature 362.2.6 Sensor Arrays 362.3 Field-Effect Chemical Gas Sensor Devices 382.3.1 Capacitors 382.3.2 Schottky Diodes 382.3.3 The P-N Junction Diode 432.3.4 Field-Effect Transistors 442.4 Sensor Properties at Elevated Temperatures, Influence of Hydrogen 492.4.1 Influence of Hydrogen on Capacitors 502.4.2 Influence of Hydrogen on Schottky Diodes 512.5 More Sensor Properties 532.5.1 Speed of Response 532.5.2 Long-Term Stability 562.6 Experimental 572.6.1 Sample Preparation 572.6.2 Gate Metal Deposition 572.6.3 Mounting 582.6.4 Device Operation 582.7 Applications 592.7.1 Petrol Engine Exhausts 592.7.2 Diesel Engine Exhausts 602.7.3 Flue Gas Monitoring 612.8 Outlook and Conclusions 62Acknowledgments 63References 63CHAPTER 3Silicon Carbide Technology and Power Electronics Applications 693.1 DC-DC Conversion 693.1.1 SMPC Circuit Topologies and Operation 703.1.2 Silicon Carbide Devices in SMPC Applications 733.1.3 Other SiC Switches 783.1.4 SiC AC-DC Inverter Example 793.2 DC-AC Power Conversion 803.2.1 DC-AC Power Inverter 803.2.2 Inverter Control Techniques 813.2.3 SiC DC-AC Inverter Example 823.3 Pulsed-Power Applications 913.3.1 Thyristor Basics 92viii Contents3.3.2 Evaluation of SiC Thyristors for Pulsed-Power Switching 943.4 Thermal Management and High-Voltage Packaging 973.4.1 Hybrid Si-SiC Half-Bridge Module 983.4.2 Implementation Analysis of a High-Voltage SiC BridgeRectifier Module 1003.4.3 Electrostatic Analysis of a High-Voltage Package for SiCDevices 1033.5 Summary 106References 106CHAPTER 4Advances in Selective Doping of SiC Via Ion Implantation 1094.1 Introduction 1094.2 As-Implanted Profiles 1144.2.1 Diagnostic Techniques 1144.2.2 Random Implants 1154.2.3 Channeled Implants 1244.3 Implant Annealing 1284.3.1 Annealing Concepts 1284.3.2 Silane Overpressure Annealing Process 1304.3.3 Implanted Ion Profiles After Annealing 1364.3.4 Defect Evolution 1404.3.5 Results of Electrical Activation 1434.4 Technology Barriers and Suggestions for Future Work 147References 148CHAPTER 5Power SiC MOSFETS 1555.1 Introduction 1555.2 SiC UMOSFET 1565.3 SiC DIMOSFET 1635.4 SiC LDMOS 1695.5 Summary and Future Development 171References 172CHAPTER 6Power and RF BJTs in 4H-SiC: Device Design and Technology 1776.1 Introduction 1776.2 Device Structures and Operation of Power BJTs 1776.3 Design of the Epitaxial Power BJT 1816.3.1 Design of the Collector Layer 1816.3.2 Design of the Base Layer 1836.3.3 Design of the Unit Cell 1846.4 Process Integration 1866.4.1 Process Sequence 1866.5 1.2-kV Power BJTs 1886.6 Design and Fabrication of UHF Transistors 192Contents ix6.7 Future Work 199References 200About the Editors 203Index 205x ContentsPrefaceRecently there have been numerous books written on SiC, which is a testament tothe importance of this technology and its potential impact on society. A majority ofthese books attempt to comprehensively cover a specific aspect of the technologyand do this by a set of in-depth chapters on a particular research topic, concept, orresult. While this is an excellent means to convey important aspects of the technol-ogy, the intent of Advances in Silicon Carbide Processing and Applications is to beless expansive and focus in on two of the most promising applications of SiC tech-nology: gas and chemical sensing and electric vehicle motor drive and control. Hav-ing made this decision, we realized that the underlying device and processing issuesthat enable these application areas to be served by SiC technology should also beaddressed. Hence a major portion of the book involves aspects of SiC technology inthis key area, again with the intent (and hope) that the reader will be able to gain abroad and deep insight into the pacing issues of the technology as of this date. Whilethere is no way to predict the wisdom of this strategy a priori, we have nonethelesstried to put ourselves into the shoes of potential readers of this book and carefullyselected chapter topics that would best support this strategy.We hope that all who read this book will benefit from the somewhat differentapproach we have taken. We begin with an overview of SiC as of 2003, with anattempt to provide some predictions as to the market for the technology. We thenimmediately jump into the application chapters, first on gas sensors, which is clearlyan area where SiC can gain a significant market share compared with traditional Sitechnology, followed by advances in electric motor drive where, again, SiC clearlyhas an advantage over Si due to its robust material properties. We then step backand discuss the all-important area of SiC ion implantation technologythis is keysince the properties of the SiC lattice precludes the use of thermal diffusion toachieve planar selective doping over the surface of single-crystal wafers. After dis-cussing this topic, we then finish up with a discussion of recent advances in both SiCMOS and bipolar technology, both of which directly impact the sensor and motordrive applications. Attention was made to provide a large number references in therecognition that no single book can be fully exhaustive of such a broad subject suchas SiC.xiAcknowledgmentsIt is with the most sincere gratitude that the editors of this book thank all of thechapter authors for their dedication and hard work in bringing this idea to fruition.Just as a work of art can be immediately appreciated by the viewer, without anyunderstandingoftheeffortsexpendedtobringitabout,sotooisawell-writtenbook easy to appreciate by the reader without an appreciation of the long hours ofhard work that is involved. Special thanks go to our colleagues who reviewed spe-cific chapters of the book; their contribution has certainly improved the quality ofeach chapter. In particular, we thank John Wolan of the University of South Floridafor his review of Chapter 2, Omar Manasreh for his review of Chapter 3, NelsonSaks of the Naval Research Laboratory for his review of Chapter 4, and Paul Chowof RPI for his review of Chapter 6. We wish to thank all of the SiC pioneers whohave come before us and all of the present researchers in the field who have pushedthe technology to the point where such a book project was warranted. Stephen E.Saddow would like to personally thank all of his current and former students, espe-cially in the SiC Group at the University of South Florida, for all of their dedicationand hard work that made this book possible.Stephen E. SaddowTampa, FloridaAnant AgarwalDurham, North CarolinaJune 2004xiiiC H A P T E R 1Silicon Carbide OverviewOlle Kordina and Stephen E. Saddow1.1 General PropertiesSilicon carbide (SiC) is a semiconductor material with highly suitable properties forhigh-power, high-frequency, and high-temperature applications. This almostworn-out opening statement may be found in many papers dealing with SiC. Yet, itcannotbeleftoutbecauseitreallybringsforwardtheessenceofthematerialspotential. Siliconcarbideisawidebandgapsemiconductormaterial withhighbreakdown electric field strength, high saturated drift velocity of electrons, and ahigh thermal conductivity. In combination with these properties, a native substrateof reasonable size exists, and one may readily grow the material and dope it both n-and p-types. In addition, SiC, like silicon (Si), has SiO2 as its stable, native oxide.This fact is often overlooked but is key to any semiconductor technology, both froma processing perspective as well as opening up metal-oxide-semiconductor (MOS)device opportunities fo