Dynamics of defects and dopants in complex systems: si and oxide surfaces and interfaces
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Precise control of dopant redistribution and activation in the vicinity of the semiconductor-dielectric interface has become crucial for fabrication of deep sub-micron metal-oxide -semiconductor field-effect transistor devices. During the process of ion implantation and thermal oxidation a great number of native defects (such as vacancies and interstitials) can be created in the substrate. These defects are known to be mainly responsible for transient enhanced diffusion and electrical activation/deactivation of dopant impurities. In this work we seek to develop a detailed understanding of the exact mechanisms of defect annihilation, and dopant diffusion and in complex systems such as Si surfaces and amorphous-crystalline Si-Si and Si-SiO2 interfaces using density functional theory total energy calculations. • Si(001) surface −We examine structure, energetics, and bonding of vacancies and interstitials on the clean and terminated Si(001) surface and its subsurface layers. − We propose mechanism of vacancy stabilization at the surface and subsurface layers. − We find Si(001) surface to be an effective sink for vacancies and interstitials, irrespective of surface passivation. − We present diffusion pathways and barriers of vacancies at and in the vicinity of the clean surface. − We have demonstrated that the stability of native defects within the topmost three subsurface layers is greatly influenced by surface passivation. • Amorphous-crystalline Si interface −We present native defect configurations, energetics and the origin of their stabilization at amorphous-crystalline Si interface and in amorphous Si. −A continuous random network model is employed in the construction of a realistic a-c interface structures. −We propose the ’sponge-like’ behavior of the amorphous phase toward native defects. • Si/SiO2 interface −We present stable Si interstitial structures at interface and in the oxide. −We propose mechanism of interstitial diffusion from Si into a-SiO2. −We consider Boron-Interstitial pair behavior in vicinity of interface. −We propose a novel mechanism of vacancy stabilization and vacancy clusterviii ing at interface. We believe the findings we present here show the importance of understanding the role of surfaces and interfaces in affecting defect and dopant behavior in their vicinity. This research leads to an understanding of the broad range of phenomena applicable to modern microelectronics device fabrication and process modeling.