Ja. Van Der Berg et al., Medium energy ion scattering for the characterisation of damage profiles of ultra shallow B implants in Si, NUCL INST B, 183(1-2), 2001, pp. 154-165
High depth resolution medium energy ion scattering (MEIS) in the double ali
gnment mode has been used to determine the pre- and post-annealing damage d
istributions following 0.1-2.5 keV B+ implantation into Si(100) at differen
t substrate temperatures. Samples were irradiated to doses ranging from 1 x
10(14) to 2 x 10(16) cm(-2) at substrate temperatures of -150 degreesC, 25
degreesC and 300 degreesC. Rapid thermal processing (RTP) was carried out
to temperatures ranging from 400 degreesC to 1000 degreesC for 10 s, to mon
itor the annealing of damage caused by the B+ implant.
For the room temperature (RT) implants, two distinct damage distributions w
ere observed. The first was a narrow, near-surface damage peak which grows
out from the virgin Si surface peak to a maximum depth of 3 nm, much shallo
wer than the TRIM predicted mean projected range of e.g, 1 keV B+ ions (R-p
approximate to 5.3 nm), The width of this damage layer showed only a weak
dependence on the B+ ion energy and strong dependence on the dose. The numb
er of displaced atoms in this layer for dilute damage conditions is in good
agreement with modified Kinchin Pease predictions. For 1 keV B+, a second,
deeper damage peak appeared only after a B dose of 1 x 10(15) cm(-2), havi
ng a maximum at a depth of approximate to7.5 nm, well beyond the R-p of 5.3
nm. MEIS showed that this post-implant damage structure which develops for
irradiations performed at 25 degreesC and 300 degreesC, is the result of d
ynamic annealing processes that are highly effective in the region in betwe
en the two peaks, in which Frenkel defects have their maximum production ra
tes. The observed growth of the surface damage layer with implant dose is a
scribed to the migration of point defects, created along the bombardment ca
scade, to the Si/SiO2 interface. For 500 eV B+ implants, due to proximity o
f this surface sink, the residual damage is greater even at 300 degreesC. I
mplantations at -120 degreesC resulted in a single, heavily damaged layer s
tretching from the surface to the position of the deep damage. These damage
profiles show a direct correlation between the displaced Si and the implan
ted B distributions. MEIS yields approached random level, showing near or t
otal amorphisation of the Si lattice: epitaxial regrowth, even after 30 s R
TP at 600 degrees, was however only partial, apparently arrested at B conta
ining I clusters formed near R-p of the B distribution.
RTP at 400 degreesC and 500 degreesC of the samples implanted at room tempe
rature leads to substantial reduction in the Si damage. especially in the w
idth of the near-surface peak, it suggests a substantial rearrangement of S
i atoms in the lattice that occurs without the release of Si interstitials,
in view of the absence of TED at these temperatures and may involve a degr
ee of realignment of the damage structure with the channelling direction. T
he annealing behaviour measured by MEIS at higher temperatures is consisten
t with XTEM observations, showing the formation and growth in size of exten
ded interstitial defects and their ultimate dissolution at high temperature
. As well as moving into the bulk where they cause TED, a fraction of the r
eleased interstitials migrate to the surface and increase the width of the
surface damage region. MEIS studies also indicates the occurrence of revers
e annealing for high temperature implant conditions. (C) 2001 Elsevier Scie
nce B.V, All rights reserved.