Effect of fluorine on boron diffusion under interstitial

zhangcunbiao

Effect of fluorine on boron diffusion under interstitial
injection from the surface
M.N. Kham *, H.A.W. El Mubarek, J.M. Bonar
1
, D. Chivers
2
, P. Ashburn
School of Electronics and Computer Science, University of Southampton, Highfield, Southampton, SO17 1BJ, UK
Available online 9 November 2006
Abstract
In this paper, a point defect injection study is performed to investigate the effect of fluorine on boron diffusion when interstitials are
injected from the surface. 185 keV, 2.3 · 1015
cm2
F+ is implanted into silicon with a boron marker layer located at about Rp/2 of the
fluorine implant. This is followed by rapid thermal annealing at 1000 C for times 15–120 s in an oxygen ambient. The wafers are covered
with different layers prior to anneal to introduce different point defect injection effects. When interstitials are injected from the surface,
fluorine strongly suppresses boron diffusion for anneal times of 15 and 30 s. For longer anneal times, fluorine becomes progressively less
effective and the boron diffusion coefficient approaches the value obtained in samples without fluorine. This effect of fluorine on boron
diffusion suppression correlates with the presence of a shallow SIMS fluorine peak at Rp/2. These results support earlier work showing
that vacancy–fluorine clusters at Rp/2 are responsible for the suppression of boron diffusion and that these clusters anneal out during
long anneal times. An issue of boron cross contamination during the fluorine implant is also identified.
 2006 Elsevier B.V. All rights reserved.
PACS: 61.72.Ji; 61.72.Tt
Keywords: Fluorine; Boron; Point defect injection
1. Introduction record fT of 110 GHz [4] and in metal-oxide-semiconduc-