Parry, Carl Patrick (1991) Incorporation of elemental boron during silicon and silicon germanium molecular beam epitaxy. PhD thesis, University of Warwick.

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Abstract

Most of the improvements in silicon devices over recent years have been brought about by reductions in the lateral geometry of devices, owing to developments in processing technology. Structures featuring reduced vertical dimensions are of considerable interest because they will show novel electronic properties, compared with their conventional Si equivalents, though these impart stringent demands on profile control. Using low temperature processes, such as Molecular Beam Epitaxy, it may be possible to fabricate such devices, though improvements in our present understanding of dopant incorporation will be necessary before the technique can realise its full potential for the production of doping profiles featuring atomically abrupt doping interfaces.

A key area addressed in the present study is the incorporation behaviour of boron in Si and Si₁₋Gex using co-evaporation of the element. It is shown here that although elemental boron is a relatively well behaved dopant during MBE, it can show severe profile smearing in Si, depending on the growth temperature, by forming a surface-accumulated phase of boron. This collects at the growing surface at coverages of up to 0.25 ML, with any attempt to exceed this amount leading to the rapid formation of inactive boron precipitates. The surface phase is shown to modify dopant incorporation behaviour, leading to badly smeared doping profiles. The incorporation properties of the surface phase have been used to determine equilibrium solid solubilities of boron that show good agreement with previously published bulk data. The present study has been extended to 450°C. The low temperature incorporation of boron in Si is quite different as the processes causing profile smearing become increasingly kinetically limited. This is observed as a strong reduction in profile smearing and an associated rise in boron solubility limits.

For the case of boron incorporation during Si₁₋xGex, MBE, it is found that boron shows a complex dependency on temperature, growth rate, and Ge fraction. A mechanism for this behaviour is elucidated, involving the influence of both the change in matrix, and the availability of favourable incorporation sites, during co-evaporation of Ge.

Previously observed dopant incorporation behaviour has been discussed in terms of segregation of dopant from underlying layers, though the work presented in this thesis is qualitatively consistent with models for dopant incorporation considering only processes occurring at the immediate surface.

Item Type:	Thesis or Dissertation (PhD)
Subjects:	Q Science > QC Physics
Library of Congress Subject Headings (LCSH):	Molecular beam epitaxy, Boron, Semiconductor doping, Silicon alloys, Germanium alloys
Official Date:	September 1991
Dates:	Date Event September 1991 Submitted
Institution:	University of Warwick
Theses Department:	Department of Physics
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Parker, E. H. C.
Format of File:	pdf
Extent:	x, 108 leaves : illustrations, charts
Language:	eng

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