Influence of Oxygen Vacancies and Strain on Electronic Reliability of SiO 2-x Films
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Influence of Oxygen Vacancies and Strain on Electronic Reliability of SiO2-x films Ken Suzuki, Yuta Ito, Hideo Miura, and Tetsuo Shoji Fracture and Reliability Research Institute, Graduate School of Engineering, Tohoku University Aramaki Aoba 6-6-11, Aoba-ku, Sendai 980-8579, Japan ABSTRACT We performed a quantum chemical molecular dynamics analysis for SiO2-x structure under strain to make clear the effect of the strain and intrinsic defects on both electronic and structural characteristics of SiO2-x. The SiO2-x showed a large change of the structure during the simulation. This is mainly because that the Si-O bonds near an oxygen vacancy were broken and a free silicon monoxide molecule was generated in the SiO2-x structure. The magnitude of the band gap of the SiO2-x decreased drastically due to the formation of the free monoxide. In addition, the band gap decreased further under large tensile strain of about 10%. We can conclude therefore, that both the existence of oxygen vacancies and tensile strain in SiO2-x films deteriorate the electronic reliability of the oxide film seriously. INTRUDCTION Miniaturization of the microelectronic devices in modern integrated circuits has enabled the system performance improved dramatically for the past decades. In addition to the miniaturization, the structure of the devices has become very complicated and thus, the mechanical stress and strain have been increasing drastically. Large mechanical stress or strain in the gate oxide film decreases the band gap of the gate oxide film and thus, increases the leakage current through the film [1-4]. Local defects in thin gate oxide films used for sub 100-nm devices also play a very important role on both the electronic performance and reliability of the devices because the localized states within the band gap of the gate oxides with intrinsic defects are sources of the leakage current and the degradation of the dielectric properties. One of the most important local defects in the gate oxides is the compositional fluctuation caused by oxygen or silicon vacancies. They are mainly introduced near the interface between the thermally oxidized Si-dioxide and the remained Si. Such an interface also has a large intrinsic stress and distortion of atomic bonding structures caused by the lattice mismatch between the adjacent layers. Therefore, the effect of strain and defects on the leakage current should be clarified to improve both the electronic characteristics and the reliability of the devices. In this study, we applied the tight-binding quantum chemical molecular dynamics simulation to make clear the effect of the strain and intrinsic defects on dielectric characteristics of SiO2-x. METHOD Tight-binding quantum chemical molecular dynamics simulations were performed using the colors code [5]. The formalization of this program is based on the extended Hückel approximation. This method enables us much faster simulations than those based on the regular
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first principle calculation. Thus, the complex systems requiring large s
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