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Introduction
A silicide is a compound of silicon and another metal from the periodic table. Over the past few decades, silicides have been investigated extensively [1-7] due to their potential use in microelectronic devices. They have been used as contacts, barrier contacts, gate electrodes, local interconnects and diffusion barriers [8].
Metal silicide thin films are formed by a reaction between a silicon substrate and a deposited metal layer, usually as a result of thermal treatment. The interactions between metal film layers and silicon typically take place at temperatures well below the melting point of the product and the reactants. The phase diagrams for binary metal-silicide-forming systems usually show several equilibrium phases [9]. Some of these phases are present as detectable growth phases under steady-state annealing conditions. However, alternative methods such as sputtering [10, 11] or co-evaporation [12] are also employed to form these compounds. Reaction between the metal and the silicon substrate can also be achieved by depositing the metal onto a heated substrate in reactive deposition [13, 14] or reactive deposition epitaxy [15]. Moreover, silicides may also be produced by ion beam mixing [16] or by laser irradiation [17]. Amongst the metal silicides, epitaxial silicides have received considerable attention due to their thermal stability, lower electrical resistivity, and, more importantly, the potential to epitaxially overgrow the silicide layer with more silicon [18]. These features could potentially open the way to the creation of new classes of devices based on semiconductor-metal-semiconductor multilayer structures.
In thin film systems, only one compound phase usually forms between two components, silicon and metal. It is believed that phase formation in thin films is dictated by kinetics rather than by thermodynamics. After the metal layer has been totally consumed whilst forming the first phase, a second phase, when present in the phase diagram, will form at higher temperature and longer annealing times [9]. For a new phase to form, it is necessary for the atoms of the metal and silicon to get together near the interface and form a nucleus of the appropriate composition and structure.
One of the epitaxial silicides that have been the subject of many studies is CoSi2, which has replaced titanium in silicon technology to form highly conductive narrow lines on the gate stack of modern metal-oxide-semiconductor devices [19, 20].
CHAPTER 1: INTRODUCTION
1.1 Introduction
1.2 Cobalt silicides .
1.3 Objectives and scope of research
1.4 Thesis outline
CHAPTER 2: THEORETICAL BACKGROUND AND LITERATURE REVIEW
2.1 Introduction
2.2 Diffusion .
2.2.1 Solid-state diffusion
2.2.2 Diffusion mechanisms in solids .
2.2.3 Lattice diffusion .
2.2.4 The diffusion coefficient .
2.3 Heats of reaction .
2.4 Effective heat of formation model
2.5 Cobalt silicides formation .
2.5.1 Cobalt silicides formation on a Co-Si system .
2.5.2 Cobalt silicides formation through diffusion barrier
CHAPTER 3: EXPERIMENTAL TECHNIQUES
3.1 Introduction .
3.2 Barrier layer fabrication
3.2.1 CrZr by arc-melting
3.2.3 FeZr by co-evaporation
3.3 Annealing of samples
3.4 Rutherford backscattering spectrometry
3.4.1 Kinematic factor
3.4.2 Depth scaling of thin film systems
3.4.3 Energy loss
3.4.4 Scattering cross-section
3.5 Scanning electron microscope (SEM) .
3.6 X-ray diffraction (XRD)
3.7 Auger electron spectroscopy (AES) .
CHAPTER 4: RESULTS AND ANALYSIS
4.1 Introduction
4.2 Si/CrZr/Si system by arc melting
4.3 Si/FeZr/Co system by solid-state diffusion
4.4 Si/FeZr/Co system by MBE
4.5 Annealed Si<100>/FeZr(33 nm)/Co(126 nm) sample .
4.6 Annealed Si<100>/FeZr(43nm)/Co(126 nm) Sample
4.7 Annealed Si<100>/FeZr(48 nm)/Co(126 nm) sample .
4.8 Annealed Si<100>/FeZr(53 nm)/Co(126 nm) sample
4.9 Annealed Si<100>/FeZr(63 nm/Co(126 nm) sample .
4.10 Annealed Si<100>/FeZr(83 nm)/Co(126 nm) Sample
