| Summary: | 碩士 === 國立成功大學 === 材料科學及工程學系碩博士班 === 91 === The material characterizations of various TiO2-SiO2 composite oxide thin films prepared with low pressure chemical vapor deposition, using titanium tetra-iso-propoxide(TTIP) and tetraethoxysilane(TEOS) as precursors, before and after annealing were investigated. The characterizations of TiO2-SiO2 composite thin films as gate dielectrics were investigated by I-V and C-V measurement.
In this study, Rutherford backscattering spectrometry (RBS) analysis was used to determine the composition of TiO2-SiO2 thin films. The structure and crystallography of the composite oxide thin films were characterized by glancing incident angle X-ray diffraction (GIAXRD) and transmission electron microscope (TEM) diffraction patterns. The morphology of TiO2-SiO2 thin films before and after annealing were observed with scanning electron microscope (SEM) and transmission electron microscope (TEM). The chemical bonding of TiO2-SiO2 thin films were investigated with X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). Spectroscopic ellipsometry was carried out to measure the refraction index and thickness of TiO2-SiO2 thin films. Finally the electrical properties (I-V, C-V) were measured by PA meter /dc voltage source(HP4140) and LCR meter(HP4284).
From RBS results, the composition ratios of Si/(Ti+Si) in the oxide thin films increased with the increasing carrier flow rates through TEOS. However, the stoichiometry of (Ti+Si):O maintained 1:2 for all films. Pure TiO2 thin film revealed the anatase phase before and after annealing. The as-deposited composite oxide thin films with altering SiO2 ratios were amorphous. The composite oxide thin films with altering SiO2 ratios crystallized after annealing at 600, 700, and 800℃, but the diffraction intensities were much smaller compared with pure TiO2. The morphology of TiO2-SiO2 composite thin films were much smoother than pure TiO2 thin films before and after annealing. The binding energy of O 1s core level electron of TiO2-SiO2 composite thin films were shifted to lower energy as the SiO2 ratio in the composite thin films increased. The binding energy of Ti 2p and Si 2p of TiO2-SiO2 composite thin films remains constant with different SiO2 ratio. The intensity of FTIR signal were much stronger after annealing, indicating that the atoms in the annealed thin films were arranged much uniformly than those as-deposited. The refractive indexes decreased by increasing SiO2 ratio in the thin films. The relative dielectric constants were almost the same with various SiO2 ratios after 600 and 700 ℃ annealing. The relative dielectric constants of high SiO2 composition were smaller than the pure TiO2 films after 800℃ annealing. The leakage current densities decreased as annealing temperature increased. The leakage current densities of various TiO2-SiO2 composite thin films did not exhibit an obvious tendency with the ratio of SiO2 in the thin films.
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