Investigation of Anodic Oxidation Technique for the Preparation of Ultra-thin Gate Dielectrics on Si and SiC Substrates
Date Issued
2010
Date
2010
Author(s)
Chuang, Kai-Chieh
Abstract
This dissertation was focused on the anodic oxidation (anodization) process. First, the anodization is used to improve the electricsl characteristics of high-k Al2O3 on Si substrate. Second, we grow SiO2 on n-type 4H-SiC substrate by anodization.
An anodic field was added in aqueous nitric acid for the improvements of high-k Al2O3 on Si in both current density and reliability. After being annealed in furnace at 650℃ in N2, Al2O3 with equivalent oxide thickness (EOT) of 24-25Å are prepared. It was found that the leakage current, breakdown field, and stress induced leakage current were much improved without sacrificing the interfacial property. This improvement can be ascribed to the compensation oxidation process. On the other hand, MOS solar cells with different Al2O3 thickness are investigated. The best case can achieve an efficiency of 7.2% when the incident light intensity equals 5 mW/cm2.
Also, room-temperature anodization is introduced to prepare ultra-thin SiO2 on n-type 4H–SiC. Both the interfacial layer and carbon cluster are not observed. The capacitance equivalent thickness (CET) is about 27-48 Å, and the breakdown field of the grown oxide is higher than 5 MV/cm. The hysteresis of capacitance-voltage curves can be negligible. The positive current conduction is mainly dominated by the Schottky emission, while negative-biased current is limited by carrier generation-recombination. Furthermore, the frequency parameters of anodization were investigated. It is shown that the SiO2 on n-type 4H–SiC substrate by scanning frequency anodization has higher oxide breakdown field and better interfacial properties than that by DC anodization. It is suggested that both the bulk and interface traps in the oxide can be compensated since the scanning frequencies are in close proximity to the response times of interface states. The energy conveyed from the scanning frequency can rebuild the defect bonds in the interfacial region.
Subjects
High-k gate dielectrics
anodization
SiC
MOS solar cell
frequency dispersion
Type
thesis
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