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BORON-ENHANCED-DIFFUSION OF BORON:
THE LIMITING FACTOR FOR ULTRA-SHALLOW JUNCTIONS
Aditya Agarwall,2, D. J. Eagleshami, H.-J. Gossmannl, L. Pelazl, S. B. Herneri, D. C. Jacobsonl,
T. E. Haynes2, Y. Erokhin3, and R. Simonton3
1Bell Laboratories, Lucent Technologies, Murray Hill NJ 07974
2Solid State Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831
3Semiconductor Equipment Operations, Eaton Corporation, Beverly MA 01915
OC 2 C1 97
OCT 2 1 g
Reducing implant energy is an effective way to eliminate
transient enhanced diffusion (TED) due to excess interstitials
from the implant. It is shown that TED from a fixed Si dose
implanted at energies from 0.5 to 20 keV into boron doping-
superlattices decreases linearly with decreasing Si ion range,
virtually disappearing at sub-keV energies. However, for sub-
keV B implants diffusion remains enhanced and xj is limited
to >100 nm at 1050 C. We term this enhancement, which
arises in the presence of B atomic concentrations at the surface
of =6%, Boron-Enhanced-Diffusion (BED).
It is currently projected that 0.07 pim technology will require
junction depths, x1, = 30 nm. This places severe restrictions
on the amount of transient enhanced diffusion (TED) which
can be tolerated. If dopants are to be introduced by
implantation, TED is inevitable due to the excess interstitials
from the implant. However, it is hoped that TED can be
reduced by reducing the implantation energy, thus placing the
dopant and the implantation-induced excess interstitials closer
to the surface which is a sink for interstitials. Consequently,
ultra-low energy implantation is being widely pursued for
shallow junctions for future device technologies (1), and a
new generation of ultra-low energy commercial implanters is
being designed. In this work, we show that reducing implant
energy is an effective way to eliminate TED due to
interstitials from the implant. However, for sub-keV B
implants diffusion remains enhanced and xj is limited to 100
nm at 1050 C. This enhancement is also observed from
evaporated B layers arising in the presence of B atomic
concentrations at the surface of =6%.
TED from low-energy Si+ implants
We have quantified the reduction in TED with reduced implant
energy using implantation of Si into boron-doping
superlattices (B-DSL) containing B marker layers grown by
molecular beam epitaxy (MBE) (2). Diffusion of the B
marker layers (e.g. Fig.l) is profiled using SIMS and the
diffusivity enhancement (ratio of observed diffusivity to
S10 Implanted w/ 1x10a cm2, 5 keV Si
m 10 i
0 100 200 300 400
500 600 700
Fig.I SIMS profiles comparing diffusion of B spikes during
600 s at 810 C in unimplanted and 5 keV Si+ implanted B-
DSL's. The Si+ dose was 1x1014 cm-2.
0 100 200 300 400 500 600 700
Fig.2(a) Diffusivity enhancement of B markers from a
1x1014 cm-2 Si+ implant at 1-, 2-, and 5-keV, following
1050 C, 10 s annealing, as a function of marker layer depth.
equilibrium diffusivity) is extracted for each marker layer
using the process simulator PROPHET (3), which takes into
account the standard concentration-dependence of B diffusion.
(a) DB* (1050 C) = 5.2x10'4 cm2s1
- 1' - -- --_ .. 2 keV
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Agarwal, A.; Eaglesham, D.J.; Gossmann, H.J.; Pelaz, L.; Herner, S.B.; Jacobson, D.C. et al. Boron-enhanced-diffusion of boron: The limiting factor for ultra-shallow junctions, article, December 1, 1997; Tennessee. (digital.library.unt.edu/ark:/67531/metadc693298/m1/1/: accessed November 14, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.