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Author: search.filters.author.Wang, YHas files: Yes

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    Effect of fluorine implantation dose on boron transient enhanced diffusion and boron thermal diffusion in Si/sub 1-x/Ge/sub x
    (IEEE, 2005-03-21) Mubarek, HAW El; Bonar, J M; Dilliway, G D; Wang, Y; Hemment, Peter L F; Willoughby, A F; Ashburn, Peter; Karunaratne, M. S. A
    This paper studies how boron transient enhanced diffusion (TED) and boron thermal diffusion in Si/sub 1-x/Ge/sub x/ are influenced by a high-energy fluorine implant at a dose in the range 5 /spl times/ 10/sup 14/ cm/sup -2/ to 1 /spl times/ 10/sup 16/ cm/sup -2/. Secondary ion mass spectroscopy (SIMS) profiles of boron marker layers are presented for different fluorine doses and compared with fluorine SIMS profiles and transmission electron microscopy (TEM) micrographs to establish the conditions under which boron diffusion is suppressed. The SIMS profiles show that boron thermal diffusion is reduced above a critical F/sup +/ dose of 7 - 9 /spl times/ 10/sup 14/ cm/sup -2/, whereas boron TED is suppressed at all doses. Fitting of the measured boron profiles gives suppressions of boron TED diffusion coefficients by factors of 6.8, 10.6, and 12.9 and of boron thermal diffusion coefficient by factors of 1.9, 2.5, and 3.5 for F/sup +/ implantation doses of 9 /spl times/ 10/sup 14/, 1.4 /spl times/ 10/sup 15/, and 2.3 /spl times/ 10/sup 15/ cm/sup -2/ respectively. The reduction of boron thermal diffusion above the critical fluorine dose correlates with the appearance of a shallow fluorine peak on the SIMS profile in the vicinity of the boron marker layer, which is attributed to vacancy-fluorine clusters. This reduction of boron thermal diffusion is explained by the effect of the clusters in suppressing the interstitial concentration in the Si/sub 1-x/Ge/sub x/ layer. The suppression of boron TED correlates with a deep fluorine peak around the range of the fluorine implant and TEM micrographs show that this peak is due to a band of dislocation loops. This suppression of boron TED is explained by the retention of interstitials in the dislocation loops, which suppresses their backflow to the surface. The fluorine SIMS profiles show that the fluorine concentration in the Si/sub 1-x/Ge/sub x/ layer increases with increasing germanium concentration and that the fluorine concentration in the Si/sub 1-x/Ge/sub x/ layer after anneal is much higher than after implant. This indicates that fluorine is transported into the Si/sub 1-x/Ge/sub x/ layer from the adjacent silicon, and is explained by the lower formation energy for vacancies in Ge than in Si. This accumulation of fluorine in the Si/sub 1-x/Ge/sub x/ layer during anneal is advantageous for devices like SiGe heterojunction bipolar transistors, where the boron must be kept within the Si/sub 1-x/Ge/sub x/ layer.
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    Green's functions for transversely isotropic elastic half space
    (American Society of Civil Engineers, 1993-09) Rajapakse, R. K. N. D; Wang, Y
    This paper presents a comprehensive analytical treatment of the three‐dimensional response of a transversely isotropic elastic half space subjected to time‐harmonic excitations. General solutions for equations of equilibrium expressed in terms of displacements are derived by applying Fourier expansion with respect to the circumferential coordinate and Hankel integral transforms with respect to the radial coordinate. The general solutions are used to derive the explicit solutions for Green's functions (displacements and stresses) corresponding to a set of time‐harmonic circular ring loads acting inside a half space. The circumferential variation of the ring loads are assumed to be cosmθ for loadings in the vertical and radial directions and sinmθ for the loading in the circumferential direction. These Green's functions can be used as the kernel functions of the boundary‐integral‐equation method and in the development of solutions for a variety of elastodynamic boundary value problems. Comparisons with existing numerical solutions for an isotropic half space are presented to confirm the accuracy of the present solutions. Selected numerical results for displacements and stresses are presented to portray the dependence of the response of the half space on the frequency of excitation and the degree of anisotropy of the medium.