The effects of microwave plasma treatments on the physical and electrical characteristics of silicon dioxide films are discussed. Plasma treatments significantly improve the characteristics at low temperatures. Differences in the type of inert gas, O2 partial pressure, and total pressure cause differences in the plasma energy and active species concentrations, which affect reduction in the impurity concentrations, generation of dangling bonds, and effective working depth of the plasma. The changes in the electrical characteristics of the plasma-treated oxide films are consistent with those in the physical characteristics. The plasma conditions that result in the best improvements are determined.
Electric-stress hardening of silicon dioxide (SiO 2 ) films under high electric field stresses was studied. SiO 2 films were formed by two-step oxidation utilizing thermal oxidation and plasma oxidation. This process has the advantages of both oxidation processes: the low degradation rate of thermal oxidation and the flat SiO 2 surface and SiO 2 /Si interface obtained by plasma oxidation. Time-dependent dielectric breakdown and stress-induced leakage current were measured to evaluate the degradation rate and the breakdown lifetime of the oxides. Atomic force microscopy was used to evaluate the roughnesses of the SiO 2 surface and interface. The two-dimensional degradation distribution under a current stress was investigated by the stress-induced etched-oxide surface roughness method. Atomically uniform SiO 2 was found to suppress the generation of local weak spots under current stress. We conclude that using an appropriate combination of the oxidation processes can reduce the degradation and enhance the breakdown lifetimes of SiO 2 films. #
Vitreous silicon oxide (v-SiO 2 ) shows anomalous phonon properties such as the positive temperature coefficient of velocity (TCV). Variation of the Si-O-Si bond angle between SiO 4 tetrahedrons has been recognized to be the key, but the origin of TCV still remains unclear. In this study, we controlled the bond angle by doping nitrogen and measured TCV of vitreous silicon oxynitride thin films with various nitrogen concentrations using picosecond ultrasonics. TCV significantly decreases by adding a small amount of nitrogen, and it shows positive to negative values as the nitrogen concentration increases. We evaluated the bond-angle change by Fourier-transform infrared spectroscopy, which decreases with the increase in the nitrogen content. We also find that the temperature rise in nondoped v-SiO 2 decreases the bond angle, leading to an increase in the sound velocity. We then reveal theoretically that the bond-angle change dominates the origin of the positive TCV. This study indicates the existence of a zero-TCV single material, and we discover that the specific content of v-SiO 1.71 N 0.19 achieves this.
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