JAEA-Review-2010-065.pdf:15.99MB - 日本原子力研究開発機構

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Analysis of Radiation Damage at a Si Surface
Bombarded with a Single 10-, 50- and 400-keV C60 Ion
K. Narumi a) , H. Naramoto a) , Y. Takahashi a) , K. Yamada b) , A. Chiba b) ,
Y. Saitoh b) a, c)
and Y. Maeda
a) Advanced Science Research Center, JAEA, b) Department of Advanced Radiation Technology,
TARRI, JAEA, c) Department of Energy Science and Technology, Kyoto University
Bombardment effects of 10-to-100-keV C60 ions on a Si
surface have been investigated in order to understand the
unique sputtering phenomenon induced by C60-ion 1, 2)
bombardment: carbon build-up at the surface and energy
3)
dependence of Si sputtering yield . In this report, the
volume affected by single-C60-ion bombardment was
evaluated by investigating C60-ion fluence dependence of
the areal density of disordered Si atoms.
Pieces of Si(100) wafer, which had been treated with a
wet chemical method to remove an oxide layer and to
reduce organic contaminants on a surface, were irradiated
+ 2+
with 10- and 50-keV C60 and 400-keV C60 ions from the
400-kV ion implanter of TIARA. The fluence of the C60 ion was 10 11 to 10 14 C60/cm 2 . After the irradiation, the
number of disordered Si atoms was evaluated by
Rutherford-backscattering spectrometry (RBS) using
2-MeV 4 He + ions incident along a -axial channel.
RBS spectra for Si samples irradiated with 400-keV
2+
C60 ions are shown in Fig. 1. The number of Si atoms
displaced from the lattice site can be determined by the
integrated yield of a surface damage peak around 1.13 MeV.
Obtained areal density of the disordered Si atoms is plotted
as a function of C60-ion fluence as shown in Fig. 2: The
areal density increases with the fluence, then seems to
reach a constant at a certain fluence.
In order to analyze the result, two conditions were
assumed: 1) A volume affected by irradiation with one C60 ion is cylindrical, and 2) all Si atoms in the volume are
displaced with the same probability from the lattice site.
[10 3 ]
Yield (arb. units)
2
1
Random
1.210 14 /cm 2
1.810 13 /cm 2
2.210 12 /cm 2
1.710 11 /cm 2
Unirradiated
0
0.9 1 1.1 1.2
Energy (MeV)
Fig. 1 RBS spectra for 2.0-MeV 4 He + ions incident
along a -axial channel of Si samples irradiated
with 400-keV C 60 2+ ions. A random RBS spectrum is
also shown.
JAEA-Review 2010-065
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The areal density N (/cm 2 ) of Si atoms displaced from the
lattice site at the fluence (/cm 2 ) is given by,
N b ( b N0
) exp( a),
(1)
where a is the area of the cross section of the volume, b the
upper limit of N, and N0 the areal density of disordered Si
atoms at an unirradiated surface, which could be caused by
natural oxidation after irradiation. The obtained fluence
dependence is reproduced well by eq. (1) as shown in Fig. 2,
and the fitted parameters are listed in Table 1: The
thickness of the disordered layer, which is the height of the
volume, derived from b assuming the bulk density of Si is
also shown as L. The results so far indicate that a and L of
the volume affected by single-C60-ion bombardment
increase with the ion energy. Further analysis is in
progress.
References
1) K. Narumi et al., JAEA Takasaki Ann. Rep. 2006
(2008) 166.
2) K. Narumi et al., JAEA Takasaki Ann. Rep. 2007
(2008) 175.
3) K. Narumi et al., JAEA Takasaki Ann. Rep. 2008
(2009) 163.
Disordered Si Atoms (10 17 /cm 2 )
3
2
1
0
10 10
2+
400 keV C60 +
50 keV C60 +
10 keV C60 10 11
10 12
10 13
10 14
Fluence (C 60/cm 2 )
10 15
10 16
Energy (keV) a (nm 2 ) b (/cm 2 ) L (nm)
10 18 3.910 16 7.8
50 45 6.310 16 13
400 90 1.910 17 Table 1 Fitting parameters in eq. (1) obtained from the
results shown in Fig. 2.
38
60
40
20
0
Corresponding Si Thickness (nm)
Fig. 2 Fluence dependence of areal density of disordered
Si atoms. A broken line shows N 0. Results from
fitting with eq. (1) are shown by solid lines. The
right-hand ordinate shows Si thickness derived from
the left-hand ordinate assuming the bulk density of Si.