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High Conductivity, Shallow, Tailless Phosphorus and Boron Profiles

IP.com Disclosure Number: IPCOM000122684D
Original Publication Date: 1991-Dec-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 2 page(s) / 83K

Publishing Venue

IBM

Related People

Morehead, FF: AUTHOR

Abstract

Although the electrical solubility of phosphorus is greater than that of As, the As profile is much steeper because of the characteristic phosphorus "plateau, kink, and tail" that occurs during in-diffusion. These P tails are due to the supersaturation of Si self-interstitials produced by the diffusion process itself. Arsenic has no tail because of its much lower diffusivity and because its diffusion is not dominated by the interstitial component (vacancies contribute more) as in the case of P.

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High Conductivity, Shallow, Tailless Phosphorus and Boron Profiles

      Although the electrical solubility of phosphorus is
greater than that of As, the As profile is much steeper because of
the characteristic phosphorus "plateau, kink, and tail" that occurs
during in-diffusion.  These P tails are due to the supersaturation of
Si self-interstitials produced by the diffusion process itself.
Arsenic has no tail because of its much lower diffusivity and because
its diffusion is not dominated by the interstitial component
(vacancies contribute more) as in the case of P.

      The phosphorus tail can be eliminated by preamorphizing the
silicon wafer to a desired depth with several calculated doses of Si
ions implanted at different energies. Preamorphizing eliminates
undesirable channeling of the subsequent P implant, reduces or
eliminates any transient diffusion from the implantation damage (also
undesirable), and, most importantly, leaves a narrow zone of
dislocation loops to the right of the amorphous-crystalline boundary
in the Si wafer after the amorphous region has recrystallized (a few
seconds after the start of the annealing during the drive-in).  These
dislocations pin the concentration of the Si interstitials that tend
to build up during diffusion at their equilibrium or surface value,
eliminating the phosphorus tail, and yielding an arsenic like profile
for the P.

      This effect is displayed in the figure, in which P is
indiffused into crystalline silicon from a P-implanted polysilicon
layer at 850~C for 16 hours.  Without an amorphous layer beyond the
interface, the usual P tail results with an 1100 nm junction depth.
The relative concentration of the Si self-interstitials is also shown
for this case, starting with their equilibrium value at the surface
and supersaturating at 30 times equilibrium in the tail region.  With
an amorphous- crystalline boundary at the indicated depth, 200 nm, a
junction at less than 400...