Atomic-scale calculations of interfacial structures and their properties in electronic materials
With the tremendous increase in computational power over the last two decades as well as the continuous shrinkage of Si-based Metal Oxide Semiconductor Field Effect Transistors (MOSFET), quantum mechanically based ab initio methods become an indispensable tools in nano-scale device engineering. The following atomistic simulations, including ab initio, nudged elastic band (NEB) and kinetic Monte Carlo methods, have been presented in this work. Using VASP, an ab initio simulation package, we calculated B segregation energy at different atomic sites in perfect and defected Si/SiO2 interfaces and arsenic segregation energy in Si/LaAlO3 structures. With the presence of O vacancies and H in B doped systems, the predicted segregation energy is 0.85 eV for neutral systems and 1.12 eV for negatively charged systems, which is consistent with experimental measurements (0.51 to 1.47 eV). Focussing on the La deficient Si/LaAlO3 interfacial structure, we find that the arsenic prefers energetically not to segregate into LaAlO3 nor does it pile up in front of the interface. In combation of atomic-resolution Z-contrast imaging and electron energy loss spectroscopy (EELS), we theorectically calculated the band structure and EELS of a Ge/SiO2 interface. we actually found a chemically abrupt Ge/SiO2 interface, which has never been reported before and which is quite desirable for applications. Furthermore, we formulated a kinetic Monte Carlo model to simulate the oxidation process of Ge ion-implanted Si, which explained the formation of abrupt Ge/SiO2 interface. Using nudged elastic band (NEB) method, we systematically calculate the vacancy formation, diffusion activation energy and pre-exponential diffusion factor at pure and Cu doped Al grain boundaries. Though grain boundary diffusion is still much faster than that of bulk, adding small amounts of Cu can dramatically improve the electromigration reliability of Al interconnects. A comparison of the vacancy formation energy at Al, Al(Cu) and strained Al grain boundaries, in which all the Al atoms keep their positions as they are in the Al(Cu) structure, highly indicates that the increase of the vacancy formation energy at the Al(Cu) grain boundary is a combined result of electronic and strain effects from the impurity-atom segregation to the grain boundaries.
School:The Ohio State University
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:ab initio first principles neb monte carlo mosfet electronic devices segregation high k laalo3 oxidation strained interface diffusion grain boundary interconnects
Date of Publication:01/01/2005