Behavior of Si Interstitials and Boron-Interstitial Pairs at the Si/SiO 2 Interface
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BEHAVIOR OF Si INTERSTITIALS AND BORON-INTERSTITIAL PAIRS AT THE Si/SiO2 INTERFACE. Taras A. Kirichenko1, Decai Yu 2, Sanjay K. Banerjee 1 and Gyeong S. Hwang 2* 1 2
Microelectronics Research Center, University of Texas, Austin, Texas 78712 Department of Chemical Engineering, University of Texas, Austin, Texas 78713
ABSTRACT Using density functional theory calculations within the generalized gradient approximation, we have investigated the structure, energetics, bonding, and diffusion behavior of Si interstitials and boron-interstitial pairs at the Si/SiO2 interface. We find that interstitials are significantly stabilized at the Si/SiO2 interface and prefer to reside on the SiO2 side rather than the Si side. Due to the interstitial stabilization, boron-interstitial pairs are likely to be easily dissociated in the vicinity of the Si/SiO2 interface. This study provides valuable insight into interstitial annihilation and boron precipitation at the interface. INTRODUCTION The Si surface [1,2] and Si/SiO2 interface [3,4] have been considered effective sinks for interstitials and vacancies, but a detailed study of the interactions of defects with the surface and interface is still lacking. The surface/interface annihilation will directly influence the population of defects in the substrate, which in turn affects the redistribution and electrical activation of injected dopant impurities [5,6]. In addition, the precipitation of dopant impurities at the surface and interface is also an important issue in untrashallow junction formation. With continued scaling of devices these proximity effects are becoming more important, but the annihilation and precipitation mechanisms are still unclear. In this study, we examine the structure, energetics, and diffusion of interstitials and boron-interstitial pairs in the vicinity of the Si/SiO2 interface using density functional theory slab calculations. Here, we consider two different interface structures: i) c-Si and c-SiO2 and ii) c-Si and a-SiO2. For amorphous SiO2 construction, we use a continuous random network [7] model based on Keating-like potentials [8]. COMPUTATIONAL DETAILS All atomic and electronic structures and total energies were calculated using the plane-wave-basis pseudopotential method within the generalized gradient approximation (GGA) to density functional theory (DFT) [9,10], as implemented in the Vienna Ab-initio Simulation Package (VASP) [11,12]. We used a cutoff energy of 300 eV for planewave expansion and a (2×2×1) mesh of k points in the scheme of Monkhorst-Pack [13] for Brillouin zone (BZ) sampling. All atoms are fully relaxed using conjugate gradient method to minimize the total energy until all residual forces on the atoms are less than 5×10-2 eV/Å. We have calculated diffusion pathways and barriers under the static
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approximation using the climbing nudged elastic band method (NEBM) method [14]. The bonding mechanisms of defect systems considered here were analyzed based on charge density topologies and electron localization functions (ELF
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