First-principles Study of Ge/GeO2 Interface and Bulk GeO2 and Calculation of Electron Mobility in SiGe FinFETs

• Main Authors: Shang-Chun Lu, 呂尚濬
• Other Authors: 劉致為
• Format: Others
• Language: en_US
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/65314294473854328457

碩士 === 國立臺灣大學 === 光電工程學研究所 === 101 === Due to the aggressive scaling of CMOS technology, applying high mobility materials to channel of metal-oxide-semiconductor field-effect transistors (MOSFETs) is an important way to preserve the validity of Moore''s Law. Among all the choices, Ge has been regarded as a promising candidate for p-channel device. However, an important issue concerning Ge MOSFETs is the electrical condition of the germanium/dielectric interface. As a result, germanium oxide (GeO2) is used as the potential passivation layer since the densities of interface states (Dit) can be reduced effectively by the methods of thermal oxidation. Nevertheless, one of the remaining puzzles is that the electronic structure of Ge/GeO2 interface models including a defect-free suboxide transition region did not reveal any gap states within the Ge band gap, suggesting that the suboxide itself should not be invoked as the cause of any electrical degradation. Therefore, in this work, by employing first-principle density functional theory (DFT) method, we investigate the electronic structure of Ge/GeO2 with Ge dangling bonds at different oxidation states to show the origin of the defect states at different energy locations and the shift of defect states within the bandgap due to higher oxidation state, and also explain the source of the positive fixed charges in defective GeO2 for the first time by calculating formation energy. Expecting the future high-k dielectric integration with Ge MOSFET, we also take a look at the impact of several kinds of high-k metal impurities on the gap states at Ge/GeO2 interface. This helps pave a way to find the optimal high-k oxides for Ge transistors. In the second phase of this work, we switch the focus to another approach which can also keep Moore''s law going: FinFET. We simulate the electron mobility of SiGe FinFETs with different [Ge]/[Si] ratios, while taking into account three scattering mechanisms: phonon scattering, surface roughness scattering, and SiGe alloy scattering. We extract the alloy scattering potential from experimental data. In addition, the enhancement of mobility under stress along fin-width and channel direction as well as the fin-width effect on mobility are also investigated. Our results demonstrate a possible strategy to optimize the mobility of SiGe FinFETs via strain engineering at certain Ge concentration.