Use this URL to cite or link to this record in EThOS:
Title: Suppression of boron transient enhanced and thermal diffusion in silicon and silicon germanium by fluorine implantation
Author: El Mubarek, Huda Abdel Wahab Abdel Rahim
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 2004
Availability of Full Text:
Access from EThOS:
Full text unavailable from EThOS. Please try the link below.
Access from Institution:
In this thesis a study is made of the growth of buried boron marker layers with sharp and narrow boron profiles and of the effect of fluorine implantation on the diffusion of boron in buried marker layers in silicon and silicon germanium. Initial experiments investigate the effect of varying F⁺ implantation energy on boron thermal diffusion and boron transient enhanced diffusion (TED) in Si1-xGex. In samples implanted with 185keV F⁺, the fluorine suppresses boron transient enhanced diffusion completely and suppresses thermal diffusion, whereas in samples implanted with 42keV F⁺, the fluorine does not reduce boron transient enhanced diffusion. These results indicate that a high energy F⁺ implant is much more effective than a low energy implant for suppressing boron diffusion. The effect of F+ implantation dose on the diffusion of boron in silicon and silicon germanium is then studied. In silicon samples implanted with P⁺ and 2.3x1015cm⁻² F⁺, the fluorine completely suppresses boron transient enhanced diffusion. Reduction of boron thermal diffusion is observed for F⁺ doses at and above a dose of 1.4x1015cm⁻². In Si1-xGex a reduction of boron thermal diffusion is observed for F⁺ doses at and above a dose of 9x1014cm⁻², whereas a suppression of boron transient enhanced diffusion is observed for all F⁺ doses. For F⁺ doses of 1.4x1015cm⁻² and 2.3x1015cm⁻² the fluorine reduces the boron thermal diffusion coefficient by factors of 1.9 and 3.7 in silicon and factors of 2.5 and 3.5 in Si1-xGex respectively. The reduction of boron thermal diffusion correlates with the appearance of shallow fluorine peaks in the silicon layers and Si1-xGex layers at and above the critical doses of 1.4x1015cm⁻² and 9x1014cm⁻² respectively. These shallow fluorine peaks are present in samples with and without boron marker layers in both silicon and Si1-xGex and hence are not due to a chemical interaction between the fluorine and boron. Transmission electron microscopy (TEM) micrographs show that there are no extended defects in both the silicon and Si1-xGex layers, and hence it is proposed that the shallow fluorine peaks are due to vacancy-fluorine clusters. The reduction in boron thermal diffusion above the critical F⁺ dose is then explained by the presence of the vacancy-fluorine clusters, which suppress the interstitial concentration in the silicon and Si1-xGex layers. The suppression of boron transient enhanced diffusion 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. The suppression of TED by fluorine is then explained by the influence of the loops in suppressing the backflow of interstitials to the surface. Analysis of the SIMS profiles shows that fluorine is transported from the adjacent silicon into the Si1-xGex layer during anneal, and reaches concentrations that are much higher than observed after implant. This mechanism would give benefits in devices like Si1-xGex heterojunction bipolar transistors (HBTs), since a high fluorine concentration is automatically obtained in the vicinity of the boron profile, which maximises the effect of fluorine in suppressing boron diffusion.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available