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Growth of Low Work Function Materials Using Aerosol-Assisted Metalorganic Chemical Vapor Deposition

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Growth of Low Work Function Materials Using Aerosol-Assisted Metalorganic Chemical Vapor Deposition GROWTH OF LOW WORK FUNCTION MATERIALS USING AEROSOL-ASSISTED METALORGANIC CHEMICAL VAPOR DEPOSITION By YONG SUN WON A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQURIEMENT FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2006 This document is dedicated to my deceased father. ACKNOWLEDGEMENTS The author appreciates Dr. Olga Kryliouk and Dr. Lisa McElwee-White for their service as committee members and precious academic advice. He also thanks Dr. Tim Anderson, his committee chair, for the encouragement and support all the time in every situation. The author wants to express his gratitude to his colleagues too, Young Seok Kim and Byung Jin Chun. It was a great pleasure and relief to have them besides the author throughout his study. So many people helped the author as well; Dr. Chatu Sirimanne and Seth Dumbree (from the Chemistry department) for the synthesis of ZrC precursors, Laurel Reitfort (from the Chemistry department) for the synthesis of LaB6 precursors, Dr. Omar Bchir, Hiral Ajmera, and Andrew Heitsch (from the Dr. Anderson’s group) for the LaB6 MOCVD growth, Dr. Venu Varanasi (from the Dr. Anderson’s group) for the ThermoCalc simulation, Dr. Adrian Roitberg (from the QTP group) for the Gaussian simulation, Rob Holoboff (A&N Corporation), James Hinnant and Dennis Vince (the staffs of Chemical Engineering department) for the construction of the MOCVD system. Finally, the author would like to give all the credit for his achievements to his family. iii TABLE OF CONTENTS ACKNOWLEDGMENTS ................................................................................................. iii LIST OF TABLES............................................................................................................ vii LIST OF FIGURES ........................................................................................................... ix ABSTRACT...................................................................................................................... xii CHAPTER 1 INTRODUCTION ............................................................................................................1 1.1 Field Emitter Arrays (FEAs) ..................................................................................2 1.1.1 Gated Emitter (Spindt Emitter) ....................................................................2 1.1.2 Fowler-Nordheim Equation..........................................................................2 1.1.3 Tip Failure ....................................................................................................3 1.1.4 Applications..................................................................................................4 1.2 Emitter Materials ....................................................................................................5 1.2.1 General Requirements for Emitter Tip Materials.........................................5 1.2.2 Advantages of ZrC and LaB6 as Emitter Tip Materials ...............................5 1.2.3 Gated Si and Mo FEAs.................................................................................5 1.2.4 Crystal Structure of ZrC ...............................................................................7 1.2.5 Crystal Structure of LaB6 .............................................................................9 1.3 Equilibrium Thermodynamics of the Zr-C System ..............................................10 1.3.1 Cystal Chemistry of Transition Metal Carbides and Nitrides ....................10 1.3.2 Analysis of Themodynamic Properties and Phase Stability in the Zr-C System..............................................................................................................13 1.3.3 Cohesive Properties and Vibrational Entropy of 3d Transition Metal Compounds ......................................................................................................18 1.4 Computational Thermochemistry .........................................................................21 1.4.1 Density Functional Theory and Effective Core Potentials .........................22 1.4.2 Ensemble Properties and Statistical Themodynamics................................23 1.5 Film Growth..........................................................................................................25 1.5.1 Physical Methods........................................................................................26 1.5.2 Chemical Methods......................................................................................27 1.5.3 Aerosol-Assisted MOCVD (AA-MOCVD)...............................................28 1.6 Thin Films and Bulk Materials for FEAs .............................................................29 1.7 Summary...............................................................................................................31 iv 2 EQULIBRIUM ANALYSIS OF ZIRCONIUM CARBIDE CVD GROWTH ..............39 2.1 Introduction...........................................................................................................39 2.2 Calculations and Themochemical Properties........................................................39 2.3 Results and Discussion .........................................................................................40 2.3.1 Phase Change as a Function of Temperature and Pressure ........................41 2.3.2 Phase Change as a Function of Temperature and the Inlet H/Zr Ratio......42 2.3.3 Phase Change as a Function of Temperature and the Inlet C/Zr Ratio ......44 2.3.4 The Addition of Chlorine to the System.....................................................45 2.4 Summary...............................................................................................................47 3 STUDY OF PRECURSOR DECOMPOSITION USING COMPUTATIONAL THERMOCHEMISTRY ............................................................................................53 3.1 Introduction...........................................................................................................53 3.2 Experimental Methods..........................................................................................53 3.3 Decomposition of Tetraneopentyl and Tetrabenzyl Zirconium Precursors for the CVD of Zirconium Carbide .............................................................................54 3.3.1 Comparison of Decomposition Behaviors of ZrNp4 and ZrBn4.................55 3.3.2 Initial Stage of the Decomposition of ZrNp4..............................................56 3.3.3 Isobutene Cleavage.....................................................................................58 3.3.4 Summary.....................................................................................................60 3.4 Decomposition of Alkyl- and Arylimido Precursors for CVD of Tungsten Nitride ....................................................................................................................61 3.4.1 Overview on the Tungsten Nitride MOCVD Growth ................................61 3.4.2 NMR Kinetics of Acetonitrile Exchange in 2 ............................................63 3.4.3 Optimized Geometries................................................................................64 3.4.4 Dissociation of Acetonitrile........................................................................65 3.4.5 Cleavage of W-Cl Bonds............................................................................67 3.4.6 Bond Dissociation Energies for W-N(imido) and N(imido)-C in Complexes 1-3 .................................................................................................69 3.4.7 Interpretation of Positive Ion EI MS Data..................................................72 3.4.8 Feasibility of Alkyl- and Arylimido Precursors for Tungsten Nitride ALD .................................................................................................................73 3.4.9 Summary.....................................................................................................74 4 GROWTH OF ZrC THIN FILMS BY AEROSOL-ASSISTED MOCVD ....................89 4.1 Introduction...........................................................................................................89 4.2 AA-MOCVD System Description and Growth Procedure...................................90 4.3 Precursor Synthesis...............................................................................................93 4.3.1 Precursor Candidates..................................................................................93 4.3.2 General .......................................................................................................93 4.3.3 Tetraneopentyl Zirconium (ZrNp4) ............................................................93 4.3.4 Trineopentyl Zirconium Monochloride (ZrNp3Cl) ....................................94 4.4 Optimization of Growth Conditions .....................................................................94 4.4.1 Comparison with Equilibrium Analysis .....................................................94 v 4.4.2 Summary of the Suggested Growth Conditions .........................................97 4.5 Film Charactrization .............................................................................................97 4.5.1 General .......................................................................................................98 4.5.2 Structural Analysis .....................................................................................98
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