Evolution of Defect and Impurity Profile During High Dose Co Implantation into Si at Elevated Temperatures
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gated by RBS and channeling using a 1.4 MeV He' beam at backscattering angles of 1300 and 170'. For the calculation of the depth profiles of the Co concentration and the backscattering minimum yield the computer code RUBSODY [5] was applied. Additionally, typical samples were examined by cross section transmission electron microscopy. RESULTS AND DISCUSSION Evolution of the defect p2rofile
-Si samples implanted to Co doses ranging from IX1014
cm-2
to 2x 1017
cm-2
were
investigated by RBS and channeling. By dividing the spectrum obtained with the ion beam aligned to the direction by the spectrum accumulated with the analyzing beam incident in random direction the depth profile of the minimum yield Xmin (Xmin profile) has been calculated. The shape of this profile allows to draw conclusions about the kind and concentration
of lattice imperfections in the sample.IX04C-
I11
M2
The Xmin profiles of samples implanted to doses between 1x0 4 c 2 and 1x0 5 c 2 are identical to the Xmnin profile of an unimplanted sample. Therefore, the damage created by the 15 Co implantation was annealed out (within the detection limits of RBS). At a dose of 2x1 0 cm-2 a step appears in the Xmin profile at a depth of 200 nm (see fig. 1). This depth corresponds to the maximum of the Co concentration profile. The step height AXmnin increases with increasing dose and reaches its level of saturation (AXmin = 40%) at a dose of 2x10 1 6 cm-2 . Moreover, there is a shoulder in the profile immediately behind the step. The Xmnin value in the region between the surface and the maximum of the Co profile remains the same as in the case of an unimplanted sample up to a dose of 5x 1015 cm-2 . However, the high surface peak of the 120
300
10 z[nm]
200
100
0 Si
80 00
Z
E
60
00
0060 0 _X
8 40
XXxXX~ý,XX
0co
0
00
X
XX0
X
X
0 X 00o~o
20
2 lxO' X111cm 21 5 + 2x 101' CM 5 10" cm-' ~XA~ 5x 1X10 16 c 2
0
XXKX XX
XXX
+
2x10 17
cm-
x0'
m
C&
,X
2
00 50
0
100
150
200
channel Fig. 1:
Depth profiles of the minimum yield (in the Si part of the spectrum) after Co2 implantation at E =250 keV and Ti.. = 350'C with doses between 1 X 1015 cm-
and 2 X10 17
CM-2 .p
180
2 15 Xmin, profile (with a maximum value of 30% for the implantation with 5x 10 cm- ) shows that2
damage accumulation occurs also at the surface. At doses equal to or higher than
IX 1016
cm-
rises, but the step at a depth of 200 nm is still present. the Xmin value in the near surface region 2 17 Only at very high doses (1 and 2x 10 cm- ) this step becomes less pronounced. The Xmin profiles presented are completely different from Xmin profiles obtained for implantation at room temperature (RT) where Gaussian defect distributions with a maximum at -2/3 of the projected range of the Co ions are observed and where amorphization takes place already at doses below 1 X 1014 cm-2 . Thus, the xM profiles show clearly that dynamic annealing occurs at the target temperature of 350'C 23' that the radiation damage produced by the Co implantation is converted into
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