Hafnium Alkylamides and Alkoxide Adsorption And
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HAFNIUM ALKYLAMIDES AND ALKOXIDE ADSORPTION AND REACTION ON HYDROGEN TERMINATED SILICON SURFACES IN A FLOW REACTOR by KEJING LI A DISSERTATION Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Chemical and Biological Engineering in the Graduate School of The University of Alabama TUSCALOOSA, ALABAMA 2010 Copyright Kejing Li 2010 ALL RIGHTS RESERVED ABSTRACT This work is a study of the gas phase and surface chemistry of three metalorganic Hf (IVB) precursors – tetrakis(dimethylamido) hafnium (TDMAH), tetrakis(ethylmethylamido) hafnium (TEMAH), and hafnium tert-butoxide (HTB) adsorption and reaction onto hydrogen terminated Si(100), Si(111) and Ge surfaces during low pressure chemical vapor deposition (CVD) in a temperature range of 25 ºC to 300 ºC in a flow reactor. The main methods used include in-situ attenuated total reflectance Fourier transforms infrared spectroscopy (ATR-FTIR), transmission IR, quadrupole mass spectrometer (Q-MS), ab inito density functional theory (DFT), photoelectron spectroscopy (XPS), finite element analysis (FEA), computational fluid dynamics (CFD), and atomic force microscopy (AFM). Possible gas phase decomposition and surface adsorption reactions were surveyed. Reaction energies, vibrational spectra and transition states were calculated for the three precursors and especially the two alkylamido hafnium precursors to support experimental observations. Interfacial bonding and surface catalyzed reaction processes initiated by the adsorption of precursors were detected. For TDMAH and TEMAH, β-hydride elimination and insertion reactions were calculated to be not favorable thermodynamically at these low experimental temperatures. Interfacial bonding during adsorption between the Si was through N-Si and/or C-Si. Decomposition products containing Hf-H species were observed on the surface at room temperature and 100 ºC and the peak assignment was confirmed by deuterated water experiments. The gas phase by-products were mostly dimethylamine (DMA) and a small amount of methylmethleneimine (MMI) or ethylmethylamine (EMA) and methylethyleneimine (MEI). A surface three-member cyclo species was tentatively identified. ii For HTB, interfacial bonding was Si-O or Ge-O. Another β-hydride elimination generated Hf-OH on the surface and t-butene in the gas phase. A monodentate and bidentate model was proposed for chemisorption of HTB with different concentration on two Si surface orientations at temperatures below 150 ºC. Carbonate was found to form in the film at higher temperatures. The effect of HTB buoyancy driven flow in the ATR flow through cell on thin film topography was observed using AFM of thin films deposited from HTB at 250 ºC. The images showed a wavy surface at the downstream end of the substrate due to roll-type flow predicted by CFD calculations. iii LIST OF ABBREVATIONS AND SYMBOLS ALD Atomic layer deposition ATR Attenuated total reflectance C Capacitance CAE Constant analyzer energy mode CB Conductance band CFD Computational fluid dynamics CRR Constant retard ratio d Film thickness dp Depth of penetration DTGS Duterated triglycine sulphate e Electron charge EBE Binding energy EF Evanescent field Eg Band gap EKIN Kinetic energy EOT Equivalent oxide thickness EPL Effective path length ESCA Electron spectroscopy for chemical analysis ESI Electron spray ionization FEA Finite element analysis GGA Generalized gradient approximation iv Gr Grasholf number GTO Gaussian type orbital HTB Hafnium tert-butoxide IRE Internal reflectance element ISD Source drain current ITRS International technology roadmap for semiconductors κ Dielectric constant k Conductivity coefficient Kn Knudsen number L Channel length LCAO Linear combination of atomic orbitals LDA Local density approximation MEI Methylethyleneimine MMI Methylmethyleneimne MOSFET Metal oxide semiconductor field effect transistor N Number of molecular orbitals n Number of electrons in a molecule N-S Navier-Stokes equation PDA Personal digital assistant RBS Rutherford backscattering PPM Parts per million Ra Raleigh number Re Reynolds number RMS Root-mean-square SCF Self-consistent field v SLD Soft laser desorption STO Slater type orbital S/N Signal to noise ratio ss Stainless steel TDEAT Tetrakis(dimethylamido) hafnium TDMAH Tetrakis(dimethylamido) hafnium TEMAH Tetrakis(methylethylamido) hafnium TM Transition metal UHV Unltra high vacuum VB Valence band Cv Constant volume heat capacity m Reduced ion mass MS Mass spectrometry N Number of ions per unit volume n Refractive index P Polarization t IRE thickness VD Voltage between source and drain VG Gate voltage VFB Flat band voltage VTh Threshold voltage ZT* Ion's transverse effective charge ε Absorption coefficient ωTO Frequency of the transverse optical phonon Hˆ Hamiltonian vi η Plank constant χ µ Contracted Gassian basis functions vii ACKNOWLEDGEMENTS I am grateful to have been admitted to the Chemical & Biological Engineering Department in The University of Alabama four and half a year ago where I spent a very meaningful journey during which I owe my sincere gratitude to many persons. They have accompanied me and helped me through achieving this thesis. This is one of the most beneficial fortunes that God has blessed in my life. It is a privilege for me to acknowledge these people and wish I have listed all of them. I would like to thank my advisor Dr. Tonya Klein for her passionate guidance, training, and support in my work. She has trained me in every aspect from a very dependent fresh undergraduate with bare idea about research to a self-motivated Ph.D who is willing to devote to this field. I appreciate the open opportunities she granted me to dig in subjects that I felt interested in. The subconscious beneficial learning from her is tremendous. She has taught me knowledge, creative way of thinking, techniques and skills that would be useful in my career; and she also taught me the optimistic philosophy to life and people. Her independence, persistence, confidence, patience and sense of humor have enlightened her students including me, with feeling full of hope and not running away from problems. I still remember the day when I first got frustrated with some experimental results and we were leaving after talking a long time in the late afternoon, she turned around and said to me across the hall way, “do you know what does Ph.D. stand for?” she asked and then stood there, answered her question loudly “P means persistency.” I remember these words when I really felt lost in solving these mechanism puzzles and got the courage to persist, never give up. Without her guidance and help, this journey would be a very high mountain for me to climb. I would like to thank Dr. David Dixon and Dr. Shengang Li for training me half core viii of this thesis in density functional theory and hands-on teaching in many ways one page may not be enough. I feel fortunate to have met them and benefited from their smartness, solid chemistry knowledge, critical way of thinking, and preciseness in study. I always breathed a lot of inspiration after talking with them and felt learnt a lot. I really appreciate their continuous offering of guidance and help in this work and my improvement as a researcher. I will always remember Dr. Dixon’s advice – “it is this tiny thing that makes a difference.” Without their positive catalytic help, this thesis would be taking much longer. I would like to express my gratitude to my committee and members in their groups who have added indispensable bricks to this thesis work. Dr. Alan Lane and his student Dr. Wei Li have helped a lot in the mass spectrometry work. Dr. Lane was my teaching assistant advisor for two semesters and I was impressed by his leading style. I was also encouraged when Wei toured us passionately about his laboratory and his work; Dr. C. Heath Turner and his student Dr. Zheng Hu has led my way in using Gaussian software and intrigued my interest in modeling. I also thank his later post doc associates Dr. Wei An and Dr. Xian Wang for their friendship and beneficial discussion about chemistry. Dr. Shane Street and his students Dr. Litao Bai and Mr. Cliffton Watkins helped me with the transmission IR in their lab and they were very patient and we had pleasant discussions about IR every time. I can’t forget my appreciation to my labmates Shilpa Dubey, Ning Li, Gihan Kwon, and Jinwen Wang. Shilpa spent half a year with me before graduation, who taught me step by step about manipulating instruments and handling experiments. Her detail oriented style has laid the basis of my experimental attitude a lot. Ning is a diligent co-worker and quick learner with whom I got much encouragement in solving problems professionally and had fun in the lab when we discussed our projects from different perspects. Gihan had four years here as my labmate and officemate. He was like a big brother in the lab who was willing to offer assistance. I was amazed about the complex Matilda he built and his instrumental sense is the ix best I have ever seen. Jinwen was also like a big brother who worked very diligently from morning until midnight almost every day, which was somewhat a little pressure for me but has been a role model for all of us. I would also like to thank two earlier labmates Harish Bhandari and Lucas Falco for their friendship. I feel proud to have ever worked with these people and in this lab. I also would like to thank Dr. Alfred Waterfeld and Dr. Joseph Thrasher who several times provided me with materials that I was in dire need of, which have been so important to accomplish this thesis. The help from Dr. Huzhen Zhu, Mr. David Drab, Mr. Scott Brown, Dr. Kevin Shaughnessy, Dr. Myrna Hernandez and Dr. Ken Belmore with the X-ray crystallography, discussions about transition states and Khimera, and NMR analysis is greatly appreciated.