This letter investigates the effect of a deep F ϩ implant on the diffusion of boron in silicon. The effects on boron thermal diffusion and transient enhanced diffusion are separately studied by characterizing the diffusion of a buried boron marker layer in wafers with and without a 185 keV, 2.3 ϫ10 15 cm Ϫ2 F ϩ implant, and with and without a 288 keV, 6 ϫ10 13 cm Ϫ2 P ϩ implant. In samples given both P ϩ and F ϩ implants, the fluorine completely eliminates the transient, enhanced boron diffusion caused by the P ϩ implant, and in samples implanted with F ϩ only, the fluorine suppresses the boron thermal diffusion by 65%. These results are explained by the effect of the fluorine on the vacancy concentration in the vicinity of the boron profile.

This paper investigates how the thermal diffusion of boron in silicon is influenced by a high energy fluorine implant with a dose in the range 5 ϫ 10 14 -2.3ϫ 10 15 cm −2 . Secondary Ion Mass Spectroscopy (SIMS) profiles of boron marker layers are presented for different fluorine doses and compared with fluorine profiles to establish the conditions under which thermal boron diffusion is suppressed. The (SIMS) profiles show significantly reduced boron thermal diffusion above a critical F + dose of 0.9-1.4ϫ 10 15 cm −2 . Fitting of the measured boron profiles gives suppressions of the boron thermal diffusion coefficient by factors of 1.9 and 3.7 for F + implantation doses of 1.4 ϫ 10 15 and 2.3ϫ 10 15 cm −2 , respectively. The suppression 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. This shallow fluorine peak is present in samples with and without boron marker layers, and hence it is not due to a chemical interaction between the boron and the fluorine. Analysis of the (SIMS) profiles and cross-section Transmission Electron Microscope micrographs suggests that it is due to the trapping of fluorine at vacancy-fluorine clusters, and that the suppression of the boron thermal diffusion is due to the effect of the clusters in suppressing the interstitial concentration in the vicinity of the boron profile.

The control of phosphorus (P) diffusion in germanium (Ge) is essential for the realisation of ultrashallow n-type junctions in Ge. This work reports a detailed study of the effect of fluorine (F) co-implantation on P diffusion in Ge. P and F profiles were characterized by secondary ion mass spectroscopy. The ion implantation damage was investigated using cross sectional transmission electron microscopy. It is shown that F co-implantation reduces the implanted P profile width and reduces both intrinsic and extrinsic P diffusion in Ge. A defect mediated mechanism for the strong influence of F co-implantation on P diffusion in Ge is proposed and invokes the formation of FnVm clusters in the F-amorphized Ge layer. A fraction of these FnVm clusters decorate the interstitial type end-of-range defects in the re-grown Ge layer and the rest react during re-growth with interstitial germanium atoms diffusing back from the amorphous crystalline interface. The Ge vacancies are then annihilated and mobile interstitial F is released and out diffuses from the surface. This results in a re-grown Ge layer which has a low vacancy concentration and in which the P diffusion rate is reduced. These results open the way to the realization of enhanced Ge n-type devices.

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Abstract-A technology is described for fabricating SiGe heterojunction bipolar transistors (HBTs) on wafer-bonded silicon-oninsulator (SOI) substrates that incorporate buried tungsten silicide layers for collector resistance reduction or buried groundplanes for crosstalk suppression. The physical structure of the devices is characterized using cross section transmission electron microscopy, and the electrical properties of the buried tungsten silicide layer are characterized using sheet resistance measurements as a function of bond temperature.