Organic and metal-organic reactions on functionalized silicon surfaces

With scaling down the size of features in modern electronic devices, it becomes essential to control the reactions at the interfaces for clean deposition on semiconductor substrates. Thus, there is a need to understand and tune the interfacial properties. Atomic layer deposition (ALD), a known process to fabricate ultra-thin films using a self-limiting layer-by-layer growth mechanism, can eliminate ligand contamination from the metal-organic precursor's reaction with surface functional groups. These functionalities can sometimes be used not only to control the layer-by-layer growth through their reactivities but also to manipulate surface nanostructuring. The formation of the first layer in film growth is relevant for both ALD and chemical vapor deposition (CVD) schemes, as the reaction of the metal-organic precursor on various surfaces is the first step in both processes. Analyzing surface modification approaches using a variety of functionalized silicon surfaces that can model technologically relevant solid substrates, the fundamental reactivities and ability to form nanostructures starting with the selected precursor molecules, can be understood by investigating the surface chemistry at the molecular level.;This work combines our investigation of multifunctional organic and metal-organic molecules on clean silicon surfaces prepared in vacuum and on functionalized silicon both in vacuum and ex situ. The clean Si(100)-2x1 is well defined and has a rich history of serving as a model for understanding multiple reactions. The reactions of a bifunctional molecule, a beta-diketone, used as a ligand in metal-organic precursors, set a foundation for the reactivity investigation of silicon summarized in this work. In addition to the reactivity of multifunctional molecules on a clean silicon surface, the reactivity of the surface itself can be altered by functionalization with different reacting groups. Here the silicon surfaces were functionalized, both by wet chemical methods and vacuum deposition, to create H-Si(100), NH-Si(100), NH2-Si(100), NHx-Si(100) and OH-Si(100) surfaces. These surfaces were then reacted with a promising copper metal-organic precursor, Copper(hexafluoroacetylacetonato)vinyltrimethylsilane or Cu(hfac)VTMS, used for depositing clean copper films by CVD. Surface hydrogen was removed in the reaction of Cu(hfac)VTMS with the functionalized silicon surfaces, a process that suggests the reduction of copper producing copper nanoparticles with minimal surface contamination from the hfac ligand. Non-thermal methods using ultra-violet (UV) light were also tested to photoactivate hfac ligand removal on silicon oxide surfaces providing evidence for surface mediated photodesorption. The model system of Cu(hfac)VTMS on functionalized surfaces provides a platform for growing copper nanostructures by self-limiting reactions and is controlled by the surface substrate design.;A variety of surface analytical techniques are used to probe the surface properties. Spectroscopic techniques such as multiple internal reflection Fourier-transform infrared spectroscopy (MIR-FTIR), temperature programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS) are used to probe the surface structure and reactivity to follow the thermodynamics and kinetics of surface processes. These spectroscopic techniques are supported by density functional theory (DFT) computations of model surface reactions and prediction of infrared frequencies. Microscopic techniques, such as scanning electron microscopy (SEM) and atomic force microscopy (AFM) are used to observe copper nanostructure growth on the functionalized silicon substrates.;The surface chemistry developed here leads to the formation of the nanostructures that could further be used as models in electron transfer processes, thin film growth, or catalytic reactions. Thus, understanding the molecular mechanisms of these processes would help control the surface reactions at the surface/nanoparticle interface and possibly design novel catalytic schemes based on copper nanostructures.