| Because the size of the Silicon based MOS devices continues to scale, the quality of SiO2/Si interface, to some degree, determine how a MOS device performance. It is valuable for improving the reliability of ultrathin gate MOS devices by studying the property of SiO2/Si interface and its defects to improve its quality. When conventional experiment tools are not enough to explain some of the properties the micro-nano devices, by establishing the SiO2/Si structure model and simulating with computer has become an important way to study the influence of which on MOS device. While there are still some problems when building the c-SiO2/Si model, this work focuse on the modeling mothed of a-SiO2/Si structurel and study the difference with c-SiO2/Si model, the influence of different defects on the photoelectric properties of both model and the influence of interface transition zone on the gate leakage of ultrathin MOS device.Study the modeling method about a-SiO2/Si structure. First analysis structure composition and the common bonding defects of Si in SiO2/Si, clearing the modeling requirement. Based on comparing the advantages and disadvantages of common modeling methods, ascertain the theoretical foundation of modeling is combination of molecular dynamics simulation and optimization with DFT, discuss its basic theory, and describe some related parameters and the application in simulation especially. In view of the different structure between various layers near the interface, we built an a-SiO2/Si model layer by layer based on the theoretical foundation of modeling method, and study the method of modeling a-SiO2 from α-quartz and some common interface topologies, descripte the modeling mind, process and key issues completely, analysis and optimize the key parameters about modeling process, such as cutoff energy, k-point.A comparative study the photoelectric properties between c-SiO2/Si(001) model and a-SiO2/Si(001) model is made. The photoelectric properties of the established a-SiO2/Si(001) model and c-SiO2/Si(001) model are alculated and compared. Results show that the bandgaps of two models are basically equal, but due to the introduce of a-SiO2 when modeling a-SiO2/Si model, generate two defects energy level in the band gap of a-SiO2/Si(001), which main introduced by Si 3p orbital, and make dielectric and absorption coefficient of a-SiO2/Si(001) more larger than c-SiO2/Si(001) when wavelength are larger than 300 nm.A comparative study of the influence of Si atomic bonding defects on photoelectric properties of a-SiO2/Si(001) and c-SiO2/Si(001) model is made. We first build several defective SiO2/Si(001) model via introducing horizontal hanging bond, Pb0 defect and vertical hanging bond at defect free SiO2/Si interface, then calculate the properties before and after the defect passivated by H atom. The results show that the Si atoms defects can make the energy band of both models move towards low energy direction, reduce the bandgap, and generate defects energy level, while the influence on a-SiO2/Si(001) is much stronger. When wavelength are longer than 600 nm, the defects will increase the absorption coefficient of both models, and the influence of horizontal hanging bond and Pb0 are greater than vertical hanging bond, and Si atoms defect in a-SiO2/Si(001) make its absorption coefficient bigger when wavelength blong 250 nm to 350 nm. H atoms passivating the horizontal hanging bond and Pb0 can eliminate the defect energy level in a-SiO2/Si(001) and its influence on the absorption coefficient when wavelength is longer than 600 nm, increase the absorption coefficient when wavelength blong 250 nm to 350 nm, but the vertical hanging bond passivated by H will decrease the absorption coefficient in this rang. While Pb0 defects in c-SiO2/Si(001) passivated by H atoms does not eliminate the influence on band structure and the absorption coefficient of c-SiO2/Si(001).Study the influence of silicon sub-oxide near SiO2/Si interface on the reliability of Si-based ultrathin gate MOS device. By modeling abrupt and contain transition zone a-SiO2/Si model, calculate the energy and tunneling current through SiO2 layer of both models. Results show that the silicon sub-oxide in the interfacial transition zone reduce the number of strained Si-Si bond and improve the stability of the device, but make tunneling current through the SiO2 layer increase 13 times.The method of modeling a-SiO2/Si proposed in this work can be used to modeling varieties of SiO2/Si model according to the different modeling requirements, and also fits for establishing high K/Si model, and has certain reference value to theoretically research on the reliability of ultra-thin gate MOS interface. |
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