Rapid isothermal annealing of As-, P-, and B-implanted silicon Page: 4,165
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tions of a wafer annealed for 30 sec with a heater set point
temperature of 1150 "C. There is substantial diffusion to-
ward the surface and into the bulk in both cases. As was seen
in Ref. 12, the half of the wafer that was not capped lost
- 30% of the implanted As. This is in good agreement with
the 27% rise in sheet resistance shown in Fig. 3(a). The half
of the wafer that was capped shows that no loss of As has
Both (100) and (111) Si wafers were implanted with 75As
(100 keV) to doses ranging from 1.0X 1014 to 1.0X 1016/cm2
to determine any effects of wafer orientation on rapid isoth-
ermal annealing. A 0.05-pm sputtered SiO2 cap was deposit-
ed on the wafer prior to the anneal. Figure 4 compares the
sheet resistance versus anneal time for As doses of 1.0 x 10>5
and 1.0 X 10'6/cm2 in (100) and (111) oriented wafers. The
graphite heater set point temperature was 1200 'C in all
cases. The sheet resistance for the (111) wafers implanted to a
dose of 1.0 x 10'5/cm2 is always higher than (100) wafers
implanted to the same dose. After a 15-sec exposure the two
orientations differ by 40% in sheet resistance. The sheet re-
sistances differ by more than 10% after a 25-sec exposure.
Comparable differences between (100) and (111) wafers were
observed for implant doses of 1.0 and 5.0 X 10'4/cm2. How-
ever, for doses of 1.0 X 1016/cm2, the sheet resistances for the
two different orientations agree to within 10% for each ex-
posure time. A similar trend was observed on wafers which
were implanted to a dose of 5.0 X 1015/cm2 and isothermally
annealed with a heater temperature of 1200 C.
The RBS channeling spectra for a (111) Si wafer which
was implanted with As to a dose of 1.0 X 101'/cm2 and isoth-
ermally annealed for 15 sec with a graphite heater tempera-
ture of 1200 C are presented in Fig. 5(a). The scattering yield
from the silicon shows that the first 0.08 pm of Si is still
defective and has not completely annealed. This is in con-
trast to the 100 wafer shown in Fig. 2 of Ref. 12 which was
implanted to 1.0 X 10'5/cm2 and annealed for 15 sec with an
1.0 x 101'/cm2 (111)
.' ' " 1.0 x 10'5cm2(
1.0 x 1016,cm2(
- 1.0 x 1016'cm2(
0 5 10 15 20 25 30
FIG. 4. Sheet resistance vs exposure time for As implanted (100) and (111) Si
annealed with a heater set point temperature of 1200 C.
1150 C heater temperature and no damage detectable by
RBS remained. The scattering from As with the beam in the
random direction [shown in Fig. 5(a)] implies minimal diffu-
sion of the dopant has occurred. In addition, the reduction in
scattering yield from the As with the beam in the aligned
direction is so slight as to imply that less than 40% of the As
is located on a substitutional lattice site. A (100) wafer an-
nealed under the same condition showed -97% of the As
was located on a substitutional lattice site. This difference is
residual defects and percent of substitutional arsenic ex-
plains the differences we observed in sheet resistance (Fig. 4)
for the two orientations.
The RBS data for a (111) wafer implanted to 1.0 X 1016/
cm2 with As and annealed for 15 sec with a 1200 C heater
temperature is presented in Fig. 5(b). The scattering yield
from the arsenic with the He+ beam in a random direction
indicates significant diffusion of the As has occurred both
toward the surface and into the bulk of the wafer. This is
considerably different from the 1.0 X10'5/cm2 sample
where only minimal movement of the dopant occurred. This
rapid diffusion will be discussed further in the next section.
The scattering yield from both the As (y1min = 7.3%) and the
Si (Xmin = 3.5%) indicates that essentially all of the defects
have been annealed and the As is 96% substitutional in the Si
lattice. These results compare favorably with those obtained
on (100) Si wafers which were implanted and annealed under
identical conditions (mn Si = 2.6% and Xmi, As = 4.5%).
In summary we have seen that the anneal quality of
(100) As implanted wafers is quite good independent of the
dose. However, the crystal quality after annealing of (111)
wafers is highly dependent upon the dose. Good anneals
were obtained for doses >5.0 x 1015/cm2. Similar results
have been reported by Chu et al.'7 for conventional furnace
anneals at 1100 C in N2. They observed better anneals for
(111) wafers implanted to doses of 1.0 X 10'6/cm2 than for
wafers implanted to 1.0>X 10'5/cm2. The low growth veloc-
ity of (111) Si relative to (100)18 is probably the reason for the
poor anneals of the 1.0 x 10'5/cm2 implanted wafers. How-
ever, this growth velocity can be enhanced at high dopant
concentrations by the impurity enhanced self-diffusivity of
silicon.'9 This may explain why the wafers implanted to
1.0X 10'6/cm2 have better crystal quality after annealing.
As mentioned in the previous paragraphs, the As diffu-
sion is dependent upon the As concentration. As profiles,
after rapid isothermal annealing, with a heater temperature
of 1200 'C, are shown in Figs. 6(a) and 6(b) for As implant
doses of 1.0 x 105/cm2 and 1.0 X 10'6/cm2, respectively.
The 1.0 x 10'5/cm2 implants show a decrease in the peak
concentration of - 50% after a 15-sec exposure with some
As having diffused into the bulk. The peak concentration
decreases further and the depth of diffusion into the bulk
increases with increasing exposure time. After a 30-sec expo-
sure the dopant concentration is relatively constant to a
depth of - 0.2 pm and then decreases more than an order of
magnitude between 0.2 and 0.3 pm. However, the wafers
which were implanted to a dose of 1.OX 10'6/cm2 and an-
nealed with a 1200 C heater temperature [Fig. 6(b)] show a
substantial diffusion of the As toward the surface and into
the bulk after 15 sec. After 30 sec. the As concentration is
4165 J. App. Phys., Vol. 55, No. 12, 15 June 1984
_I 1 1 t .I.
Wilson et al 4165
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Wilson, Scott R.; Paulson, W. M.; Gregory, R. B.; Hamdi, A. H. & McDaniel, Floyd Del. (Floyd Delbert), 1942-. Rapid isothermal annealing of As-, P-, and B-implanted silicon, article, June 15, 1984; [College Park, Maryland]. (digital.library.unt.edu/ark:/67531/metadc139472/m1/4/: accessed June 18, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT College of Arts and Sciences.