ENHANCED DIFFUSION AND ELECTRICAL BEHAVIOR OF MISFIT DISLOCATIONS IN EPITAXIAL Si/Si(Ge)

AUTOR(ES)
FONTE

IBICT - Instituto Brasileiro de Informação em Ciência e Tecnologia

DATA DE PUBLICAÇÃO

1994

RESUMO

This dissertation addresses enhanced or \"pipe\" diffusion of dopants along localized misfit dislocations (MD) using a \"model\" misfit dislocation structure at epitaxial Si/Si(Ge) interfaces and provides basic information on the merits of applicability of novel bandgap engineered devices. Pipe diffusion is modeled and explored to create pipe-like one dimensional junctions, or doped dislocation diodes. Buried conical diodes surrounding misfit dislocations are formed using photolithography, anisotropic etching and ion implantation/annealing and then imaged using conventional Scanning Electron Microscopy (SEM) and its Electron Beam Induced Current mode (EBIC/SEM). Transmission Electron Microscopy (TEM) was also used to examine the dislocation core structure in some detail. Although these studies are performed on specially designed trench/mesa structures and not on actual heterojunction bipolar transistor structures, the implication is clear that electrical pipes could arise from pipe diffusion. The diffusion of arsenic and antimony was dramatically enhanced while pipe diffusion is not detected for phosphorus, boron and gallium. This result is consistent with an enhancement influenced by injected vacancies and shows a dopant enhanced diffusion dependence similar to that of high temperature diffusion under Si nitridation, known to inject vacancies. The diffusion enhancement is not uniform for each dislocation as detected by EBIC/SEM and SEM investigations of polished and etched samples. Interactions between MD\ s account for large apparent non uniformities but do not explain some other irregularities in the diffusion process. Possible causes for such irregularities include (1) the presence of precipitates or decoration along dislocations and (2) differences in the core structure of different dislocations resulting in varying amounts of diffusion enhancement. EBIC/SEM micrographs reveal a dark recombination contrast in the vicinity of the dislocation core and a white generation signal within the space charge region of the surrounding n/p diode. The dark contrast at room temperature suggests that dislocations are decorated. TEM analysis detected evidence of variations in the core structures of, as well as precipitates at, dislocations after the mesa/trench structure fabrication process. A two-dimensional mathematical model describing the isoconcentration profiles surrounding individual dislocations delineated by concentration dependent etching is used to show that the arsenic diffusivity, Dd, along dislocations is up to five orders of magnitude larger than the diffusivity in the host crystal, Dv, in the temperature range studied. The access to the isoconcentration profile around individual dislocations also permits the experimental determination of the effective \"pipe\" radius a, a parameter that could not be experimentally obtained in investigations by other authors. The average value obtained for a from drive-in diffusion experiments at four different temperatures in the 950C to 1026C range is 4.4 nm. This value indicates that enhanced diffusion occurs via an impurity atmosphere around dislocations. Using the average value for a, both the activation energy Ead and the pre-exponential factor D ad for pipe diffusion of arsenic were found through numerical fitting of isoconcentration profiles to the two-dimensional mathematical model to be Ead= 1.7 eV and Dod= 3.4 x 10-4 cm2/s. A similar analysis performed for antimony at 1026C results in a diffusion enhancement in excess of six orders of magnitude.

ASSUNTO(S)

silicon-germanium heterostructures misfit dislocations pipe diffusion enhanced diffusion dopant diffusion engenharia eletrica

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