Dopant diffusion in Si and SiGe

نویسنده

  • Jens S. Christensen
چکیده

Dopant diffusion in semiconductors is an interesting phenomenon from both technological and scientific points of view. Firstly, dopant diffusion is taking place during most of the steps in electronic device fabrication and, secondly, diffusion is related to fundamental properties of the semiconductor, often controlled by intrinsic point defects: self-interstitials and vacancies. This thesis investigates the diffusion of P, B and Sb in Si as well as in strained and relaxed SiGe. Most of the measurements have been performed using secondary ion mass spectrometry on high purity epitaxially grown samples, having in-situ incorporated dopant profiles, fabricated by reduced pressure chemical vapor deposition or molecular beam epitaxy. The samples have been heat treated both under close-to-equilibrium conditions (i. e., long time annealings in an inert ambient) and conditions which resulted in non-equilibrium diffusion (i. e., vacuum annealing, oxidation, short annealing duration, and proton irradiation). Equilibrium P and B diffusion coefficients in Si as determined in this thesis differ from a substantial part of previously reported values. This deviation may be attributed to slow transients before equilibrium concentrations of point defects are established, which have normally not been taken into account previously. Also an influence of extrinsic doping conditions may account for the scattering of the diffusivity values reported in literature. B and Sb diffusion in Si under proton irradiation at elevated temperatures was found to obey the so-called intermittent model. Parameters describing the microscopic diffusion process were derived in terms of the intermittent diffusion mechanism, and it was found also that the presence of Sb strongly affected the B diffusion and vice versa. In relaxed Si1-xGex-alloys, which has the same lattice structure as Si but a larger lattice constant, P diffusion is found to increase with increasing Ge content (x ≤ 0.2). In Si/SiGe/Si heterostructures, where the SiGe layer is biaxially strained in order to comply with the smaller lattice parameter of Si, P diffusion in the strained layer is retarded as compared with relaxed material having the same Ge content. In addition, P is found to segregate into the Si layer via the Si/SiGe interface and the segregation coefficient increases with increasing Ge content in the SiGe layer.

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تاریخ انتشار 2004