Percolated Si:SiO2 Nanocomposite: Oven- vs. Laser-Induced Crystallization of SiOx Thin Films

Autor: Schumann, Erik
Jazyk: angličtina
Rok vydání: 2021
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Druh dokumentu: Text<br />Doctoral Thesis
Popis: Silizium basierende Technologie bestimmt den technologischen Fortschritt in der Welt und ist weiterhin ein Material für die weitere Entwicklung von Schlüsseltechnologien. Die Änderung der Silizium-Materialeigenschaft der optischen und elektronische Bandlücke durch die Reduktion der Materialdimension auf die Nanometerskala ist dabei von besonders großem Interesse. Die meisten Silizium-Nanomaterialien bestehen aus Punkt-, Kugel- oder Drahtformen. Ein relativ neues Materialsystem sind dreidimensionale, durchdringende, Nano-Komposit Netzwerke aus Silizium in einer Siliziumdioxid Matrix. Die vorliegende Arbeit untersucht die Entstehung von dreidimensionalen Silizium-Nanokomposit-Netzwerken durch Abscheidung eines siliziumreichen Siliziumoxids(SiOx, mit x
Silicon-based technology determines the technological progress in the world significantly and is still a material of choice for further development of key technologies. In particular the reduction of silicon structure sizes to a nanometer scale are of great interest. Most silicon nano structures are based on spherical, dot-like or cylindrical, wire-like geometries. A relatively new material system are three dimensional percolated nanocomposite networks of silicon within a silica matrix. To form any of these nano structures fast, room temperature processes are desired which also offer the possibility of structure modification by different process management. The present work studies the formation of three-dimensional silicon nanocomposite networks by the deposition of a silicon rich silicon oxide (SiO x, with x < 2) and subsequent thermal treatment. Thereby, reactive ion beam sputter deposition (IBSD) as well as reactive magnetron sputtering (RMS) was compared. As well, the differences between a conventional oven and a millisecond line-focused diode laser were studied. As-deposited and thermally treated thin films were characterized with regard to the overall mean composition, homogeneity, morphology and structure by Rutherford backscattering, Raman spectroscopy, X-ray diffraction, spectroscopic ellipsometry, photospectrometry as well as cross-sectional and energy-filtered transmission electron microscopy. Depending on the deposition method as well as the thermal treatment process different structure sizes and degrees of crystallization were achieved. Most notably it was found, that during 13 ms laser processing (oven: min. 90 min), much bigger structures (laser: ≈ 50 nm; oven: ≈ 10 nm) with a notably higher degree of crystallization (laser: ≈ 92-99%; oven: ≈ 35-80%) evolve. Moreover, the structure morphology after deposition is preserved during oven treatment but diminishes following laser processing. This was explained by a process via the liquid phase for laser processing in contrast to a solid state process during oven treatment. Finally it was shown, that intentional introduced vertical and horizontal composition fluctuations can be used to form well-defined silicon nano-networks with a three dimensional square mesh structure.:1 Introduction 2 Fundamentals 2.1 The silicon - silicon oxide system 2.1.1 The Si-O phase diagram 2.1.2 Chemical reaction consideration 2.2 Phase separation of binary systems 2.2.1 Phase separation regimes 2.2.2 Diffusion in solids 2.3 Different types of silicon nanostructures 2.3.1 0D - Silicon nanoparticles 2.3.2 1D - Silicon nanowires 2.3.3 3D - Silicon nanonetworks 3 Experimental methods 3.1 SiOx thin film deposition 3.1.1 SiOx thin films by ion beam sputter deposition 3.1.2 SiOx thin films by reactive magnetron sputter deposition 3.1.3 Comparison of ion beam and magnetron sputter deposition 3.2 Thermal processing of as-deposited SiOx thin films 3.2.1 Oven treatment 3.2.2 Laser treatment 3.3 Thin-film characterization 3.3.1 Rutherford backscattering 3.3.2 Spectroscopic ellipsometry and photospectrometry 3.3.3 Raman spectroscopy 3.3.4 X-ray diffraction 3.3.5 Transmission electron microscopy 4 Results 4.1 Accessible SiOx compositions as a function of deposition and annealing method 4.2 Structure and properties of ion beam sputter deposited SiOx thin films before and after thermal processing 4.2.1 Phase- and microstructure of SiO0:6 thin films deposited by ion beam sputter deposition at 450°C 4.2.2 Phase- and microstructure of SiO0.6 thin films deposited by ion beam sputter deposition at room temperature 4.3 Structure and properties of reactive magnetron sputter deposited SiOx thin films before and after thermal processing 4.4 Multilayer SiOx films for the generation of defined squared mesh structures 5 Discussion 5.1 Compositional homogeneity of SiO0:6 thin films before and after thermal treatment 5.2 Phase structure of as-deposited SiOx thin films 5.3 Influence of the thermal treatment on the structural properties of percolated Si:SiO2 nanostructures 5.3.1 Observed structural properties 5.3.2 Origin of different structure sizes - liquid vs. solid state crystallization 5.4 Influence of the deposition temperature during ion beam sputtering on the structural properties of percolated Si:SiO2 nanostructures before and after thermal processing 5.5 Influence of the deposition method on the structural properties of percolated Si:SiO2 nanostructures 5.6 Formation of interface layers and electrical characterization 6 Summary and outlook 6.1 Summary 6.2 Outlook A EFTEM imaging
Databáze: Networked Digital Library of Theses & Dissertations
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