NEW APPLICATIONS OF EXCIMER LAMPS TO THE LOW TEMPERATURE PHOTO-DEPOSITION OF THIN FILMS A thesis submitted to the University of London for the degree of Doctor of Philosophy PHILIPPE BERGONZO Department of Electronic and Electrical Engineering UNIVERSITY COLLEGE LONDON ProQuest Number: 10055371 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest. ProQuest 10055371 Published by ProQuest LLC(2016). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code. Microform Edition © ProQuest LLC. ProQuest LLC 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106-1346 à Karine, à mes parents, Abstract Over the last decade, the requirement for low temperature processing in the semiconductor industry has become apparent due to the continued reduction in device geometry and the emergence of temperature sensitive materials. Of the low temperature techniques available, photo-enhanced processing of materials is very promising since the growing films are not subject to damaging ionic bombardment which is present in plasma assisted systems. Here is presented the development of a flexible large area, low temperature photo enhanced chemical vapour deposition reactor (photo-CVD) for apphcations to low temperature thin films processing. The development of novel excimer lamps has opened up the field of direct photo- CVD. Such lamps are a cheap and intense source of visible, UV and vacuum ultraviolet radiation (YUV: below 200nm), The major breakthrough with the development of these lamps is that they offer a large number of wavelengths that can be used for selective photo-CVD. The fabrication and characterisation of those light sources were conducted, and various devices generating up to a few watts are presented. Applications of the available radiation are also presented such as for the direct VUV enhanced generation of ozone and various metal-organic depositions (MOD). For the first time, the 172nm radiation of a xenon excimer lamp has been used to deposit silicon dioxide (Si 0 2 ), silicon nitride (SigN^), and silicon oxynitride films from the photo-CVD of gas mixtures of silane with nitrous oxide and anunonia, and at temperatures as low as 300°C. Fast deposition (up to 500Â/min) of Si 0 2 was also achieved by irradiating silane and oxygen gas mixtures. Investigations into the deposition photochemistry are reported, together with the characterisation of the deposited material properties. Good Si 0 2 and SigN^ film quality was obtained, as well as a very good control of the stoichiometry in the case of silicon oxynitride film deposition, therefore providing interesting perspectives for electronic and optical applications. Abstract Acknowledgements The completion of this project would not have been possible without the help and assistance from a number of people, all of whom contributed in their own special way, and rightly deserve their mention here. I am grateful to all the persons who allowed me to use their equipment, such as Prof. M. Green for the ellip some try measurements. Dr. S. Best and Miss E. Lloyd for the FTIR analyses, and Dr. S.J.B. Corrigan who lent me a vacuum ultraviolet monochromator without expecting it back. I would also like to acknowledge Dr. M. Dubois for the SIMS analysis, and Dr. V. Craciun and his Romanian compatriots who did the XPS measurements. I am deeply indebted to Dr Frank Beech and Dr. Glenn C. Tyrrell for proof­ reading the manuscripts of this thesis, and dealing with my written French accent. Their constructive suggestions and advices were invaluable in the making of this dissertation, as well as their help on many occasions during this research, in spite of the numerous arguments I had with Glenn. I shall also recognise the support of the Service Science and Technology of the French Embassy, and namely of Mrs. V. Fleurette, who managed to make possible my military service as a researcher at UCL. I am also indirectly very thankful to Parthiv Patel, who let me take over his project. Many thanks are also due to all the people from room 919, and in particular to the great colleagues and friends who are R. Duncan Marshall and Tim H. York, for having shared so many technical problems, as well as so many late night discussions and social events. Since they had to cope with my French arrogance, I forgive Duncan for cycling faster than I, and Tim for smoking all my cigarettes. I am also deeply grateful to Dr U. Kogelschatz, from ABB, who, further to sponsor this work, also let me learn all the necessary knowledge involved with excimer lamps technologies in his laboratory. I greatly appreciate how he often solved my problems at the other end of the fax machine. I am also indebted to Prof. P. Pinard, who further to recommending me for this PhD and always trying his best for my grant applications, was indeed like a second supervisor, especially in terms of motivation and moral support. Finally, I would like to thank my supervisor Ian W. Boyd, for accepting me as a research student in his laboratory. I recognise that I owe him very much, for his understanding and encouragement, his scientific advice, his moral support, and his financial contribution. In fact, in spite of tremendous efforts to find a grant for this project, no success was ever gained from almost 12 applications for an EEC studentship over the last three years. Ian managed to sort out my financial difficulties by juggling with contracts, other grants, and arranging financed periods during the completion of this project. January 1994 UCL, London Table of Contents Abstract Preface and Acknowledgements Table of Contents 1 Introduction 4 Chapter I ...................... Photo-CVD, Apparatus and Methods 8 1- Introduction to photo-CVD processing 9 1.1- ..................The need for low temperature techniques 9 1.2- ...........................A brief outline on other techniques 9 1.3 - Photo-enhanced Chemical Vapour Deposition 10 1.4- .........................Sources of Vacuum Ultraviolet light 13 2.- ..................................Design of a photo-CVD reactor 17 2.1- Stipulations 17 2 .2 r General diagram of the photo-CVD reactor 18 2.3- Safety requirements 25 2.4- M aintenance 26 3.-.... ................... Characterisation of the deposited films 27 3.1 - Ellipsometry 27 3.2- ............................................... Infra-red spectrometry 31 4.- C o n c lu sio n 34 References to chapter 1 35 C hapter! .............................................................. Excimer Lamps 38 1.- ................Silent discharges for excimer generation 39 1.1- Electrical discharges for UV generation 39 1.2 - .......The silent discharge or dielectric barrier discharge 42 1.3- ..............................Application to rare gas molecules 49 2.- Excimer lamps {X > 160nm)54 2.1- ................................. Construction of excimer lamps 54 2.2- .................................................Power measurements 58 3 - ..................................................VUV excimer lamps 64 3.1- Introduction 64 3.2 ...............................Initial VUV excimer lamp design 64 3.3- Improvements 66 3.4- Incorporation to a CVD reactor 69 4.- Conclusion 70 References to chapter 2 71 Contents page 1 Chapters ................. Initial Applications of Excimer Lamps 74 1.- .........................Photochemical generation of ozone 75 1.1- ............................Fundamentals of ozone generation 75 1.2- .........................Ozone generation with UV radiation 79 1.3- The VUV enhanced ozone reactor 82 1.4- Conclusion 90 2.- ....................Application of excimer lamps to MOD 91 2.1- ....................................................Experimental set-up 91 2.2- ..................................UV induced metal depositions 93 2.3- ................ UV induced dielectric material depositions 96 2.4- ..................................................................... Conclusion 100 References to chapter 3 101 Chapter 4 ....................... The Photochemical Deposition and Characterisation of Silicon Dioxide Layers 103 1 -................................ The photo-CVD of silicon dioxide from silane and nitrous oxide gas mixtures 104 1.1- ............................................ Experimental conditions 104 1.2- .............................................. Results and discussion 110 1.3- Conclusion 118 2- .......................... The photo-CVD of silicon dioxide from silane and oxygen gas mixtures 120 2.1- ...................................................................Introduction 120 2.2- ..............Experimental details and sample preparation 121 2.3- .............................................. Results and discussion 125 2.4- ..................................................................... Conclusion 135 References to chapter 4 137 Chapters ........................The Photochemical Deposition and Characterisation of Silicon Nitride and Oxynitride Layers 140 1.- The photo-CVD of silicon nitride from silane and ammonia gas mixtures 141 1 .1 - ..... ............................................................Introduction 141 1.2- .................................................. Experimental details 142 1.3- .... ..............................The window