GROWTH OF THE TRANSITION METAL SILICIDES FILMS FROM SINGLE SOURCE PRECURSORS BY MOCVD

Abstract

This thesis reports the synthesis and MOCVD deposition of new single-source precursors namely Co(CO)4SiCl3, Mn(CO)5SiCl3 and Fe(CO)4(SiCl3)2, which lead to the formation of silicides films. UPS studies and DFT calculations of these precursors and CVD reactions are reported as well. The thesis is divided into six chapters. Chapter 1 reviews the MOCVD of various precursors leading to the formation of transition metal silicides. Chapter 2 gives a brief introduction of the characterization techniques used in this work. Chapter 3 contains the experiment details of all the studies reported here. Chapter 4 presents and discusses the results of the UPS studies and density functional theory (DFT) calculations of Co(CO)4SiCl3, Co(CO)4GeCl3, Mn(CO)5SiCl3 and cis-Fe(CO)4(SiCl3)2. He(I) photoelectron spectra (UPS) of these complexes have been measured and interpreted on the basis of empirical arguments and DFT calculations. For cis/trans-Fe(CO)4(SiCl3)2 isomers the calculations predict the trans-isomer to be more stable than cis by 15.2 kJmol-1. The cis-isomer is exclusively present in the solid state and in the gas phase. UPS results show the importance of charge polarization effects and the lack of ?-back donation along the TM-Si bonds. The calculated M-Si bond distances are as follows: 2.34 Å (Co-Si), 2.43 Å (Co-Ge), 2.47 Å (Mn-Si), 2.41 Å (trans-Fe-Si) and 2.45 Å (cis-Fe-Si), respectively. For Co(CO)4SiCl3, the DFT calculated Co-Si bond dissociation energy is 317.7 kJmol-1, compared to 222.2 k.Jmol-1 for Co-C energy in Co(CO)4CCl3. Chapter 5 deals with the growth and characterization or metal silicides films. cis-Fe(CO)4(SiCl3)2, Co(CO)4SiCl3 and Mn(CO)5SiCl3 have been synthesized and employed as new single source precursors for the formation or metal silicides films at 500 °C by low pressure chemical vapour deposition (LPCVD). In the case or cis- 500 °C by low pressure chemical vapour deposition (LPCVD). In the case of cis Fe(CO)4SiCl3)2 as precursor, the influence of substrates is obvious. On Pyrex glass substrate, porous polycrystalline (cubic) FeSi films were obtained whereas epitaxial films of orthorhombic ?-FeSi2 were formed on Si(100) substrate. For Co(CO)4SiCl3 and Mn(CO)5SiCl3, the influence of substrate is not evident. CoSi and MnSi films have been obtained on both glass and Si(100) substrate. The films have been investigated by an array of techniques : x-ray photoelectron spectroscopy (XPS)and x-ray diffraction (XRD) to determine chemical composition, scanning electron microscopy (SEM) to observe the morphological properties and atomic force microscopy (AFM) to obtain a 3-dimension perspective of the film surface. Chapter 6 covers an in-situ UPS study of the cis-Fe(CO)4(SiCl3)2 pyrolysis. In order to gain better insight into this reaction mechanism, the deposition in the temperature range between 30.1 and 600.0 °C has been studied by UPS in the kinetically controlled regime at 10-6 mbar. A decomposition pathway of cis-Fe(CO)4(SiCl3)2 via elimination of SiCl4 and formation of Fe(CO)4=SiCl2 is proposed, in which Fe(CO)4=SiCl2 is assumed to remain adsorbed on the surface, and after further elimination of CO and Cl2, to undergo nucleation to polycrystalline FeSi. The mechanism of SiCl4 elimination has been modelled by DFT calculations with a DZVP/(Al) basis set.