J. Plasma Fusion Res. SERIES, Vol. 9 (2010)

Effect of Energetic Helium ion Implantation on Hydrogen Isotope Retentionin Silicon CarbideYasuhisa Oya1, Sachiko Suzuki1, Masanori Hara2, Masao Matsuyama2 and Kenji Okuno1
1

Radioscience Research Laboratory, Faculty of Science, Shizuoka University,836, Ohya, Suruga-ku, Shizuoka 422-8529, Japan

2Hydrogen Isotope Research Center, University of Toyama, 3190, Gofuku, Toyama 930-8555, Japan(Received: 26 October 2009 / Accepted: 2 April 2010)

The effects of He retention and damage introduction on the D retention in SiC were studied by changing theimplantation energy of He+ from 0.75 keV to 4.0 keV. The D and He retentions in SiC and chemical behavior ofSiC were evaluated by means of thermal desorption spectroscopy (TDS) and X-ray photoelectron spectroscopy(XPS). It was found that the D retention decreased by the He retention in the same implantation depth with D2+,
although that increased if the implantation depth of He+ is larger than that of D2+. In addition, free C formation
would make the higher retention of D bound to C. These facts indicate that not only the introduction of damaged
structures but also the He retention would govern the hydrogen isotope retention in SiC.
Keywords: Tritium retention Helium ion implantation effect, silicon carbide, XPS, TDS(implantation depth of 10 nm) was implanted. The effect ofHe implantation on deuterium retention was studied by
X-ray photoelectron spectroscopy (XPS) and thermal
desorption spectroscopy (TDS).

1. Introduction

Silicon carbide (SiC) is thought to be one ofcandidates for an insulating insert in the Pb-Li channels of
the dual-coolant breeding blanket concept, due to its
minimal activation, good compatibility with Pb-Li, goodthermal conductivity and thermal stability [1-4]. One of thecritical issues is the evaluation of hydrogen isotope
retention and its helium implantation effects for evaluating
the tritium transport in the blanket system. In our previousstudies, it was found that the deuterium was preferentiallytrapped by C and, thereafter, it was trapped by Si, which
was the major deuterium trapping state in SiC  [5].
However, in the case of helium implantation, it wastrapped by both of Si and C even in the low hydrogenisotope ion fluence, indicating the helium implantation
would make a large influence on hydrogen isotope trapping[6-9]. In addition, helium pre-implantation andpost-implantation experiments show that the retention ofdeuterium bound to C was almost constant even in thehelium
pre-implantation
andpost-implantation
experiments, although that bound to Si largely decreased
especially in the helium post-implantation. These facts
indicate that helium would correlate with the deuterium
bound to Si and this would be the results of the conjunctionof helium retention and damage introduction. This
motivates us to understand more detail interaction
mechanism of helium and damaged structures on hydrogenisotopes in SiC.
In this study, the helium ion (He+) implantationenergy was systematically changed from 0.75 keV to 4.0
keV, which corresponded to the implantation depth of 5 40 nm, and, thereafter, 1.0 keV of deuterium ion (D2+)

2. Experimental$ SRO\FU\VWDOOLQH VLOLFRQ FDUELGH ȕ-SiC) wafer(ROICERAM-HS) supplied by Asahi Glass Co. Ltd., witha size of 10 mmI×0.5 mmt was used as a sample. Thesample was heated at 1300 K for 10 minutes in a vacuum
below 1 × 10-6 Pa to remove residual hydrogen andimpurities as a pretreatment. After cooling, He+ wasimplanted with an energy of 0.75 - 4.0 keV using an ion
flux of 1.3 × 1018 He+ m-2 s-1 and an ion fluence of 1.0 ×
1022 He+ m-2 at room temperature. Thereafter, 1.0 keV D2+implantation was performed using the same ion flux andfluence. The implantation depth of 0.75 - 4.0 keV He+ by
SRIM calculation was evaluated to be about 5 - 40 nm,
although that of 1.0 keV D2+, 10 nm [10]. This fact showsthat He+ with an energy of 0.75 keV retains in the nearsurface region and deuterium, beneath the He+ retention
region, although in case of He+ with an energy of 4.0 keV,
the retention region of He+ and D2+ was replaced and thedeuterium is retained in the surface region. After theseexperimental sequences, the chemical states of Si and C
were evaluated by XPS (ESCA1600 system, ULVAC-PHIInc.) [5-9]. To evaluate the D and He retentions, TDSexperiments using a high resolution mass spectrometer
were performed at a heating rate of 0.5 K s-1 and at heating
temperature up to 1300 K.

author’s e-mail: syoya@ipc.shizuoka.ac.jp322©2010 by The Japan Society of Plasma
Science and Nuclear Fusion ResearchY. Oya et al., Effect of Energetic Helium Ion Implantation on Hydrogen Isotope Retention in Silicon Carbide

3. Results and discussion

6.0
5.0
4.0
3.0

1.3 keV He+-D2+ imp.

1.04006008001000 1200 1400

Temperature/K㻌

7.04.0 keV He+-D2+ imp.
6.0
1.3 keV He+-D2+ imp.
0.75 keV He+-D2+ imp.
5.0
4.0(b)
3.0
2.0
1.0
0.0
400
600
800 1000

Temperature / K

1200

0.9

3.0

0.6

1.5

Undefined
D desorption

0D2+ imp.
only

0.75

㻌

1.3

4
4.0

0.3

He retention / arb. unit

D retention / 1020 m-2

2.0
0.0

4.5

0.0

although those for the 0.75 keV and 1.3 keV He+ implanted
SiC samples were almost constant, indicating that the He
retained near surface region would interfere D trapping.
Fig. 3 shows the XPS spectra of Si 2p and C 1s as afunction of He+ implantation energy and peak positions ofSi 2p and C 1s were summarized in Fig. 4. It was foundthat the peak positions of C 1s for 1.3 keV and 4.0 keV He+
implanted SiC samples were shifted toward higher energyside, although that for 0.75 keV was moved to lower
energy side, indicating that the damaged structures wereintroduced in the near surface region by high energy He+
implantation. In the case of 0.75 keV He+ implantation, notonly the damage introduction but also He retention would
make the negative peak shift. However, after the D2+
implantation, the peak positions for all the samples wereshifted toward higher energy side, showing the D retentionin SiC. For Si 2p, which is largely influenced by the defectaround the Si atom, the negative peak shift was observed,indicating the introduction of C defects. By the D2+
implantation, the peak positions were slightly shifted
toward the original position. This would be the indicationof Si-D formation. The peak areas of C 1s and Si 2p weresummarized in Fig. 5. It was found that the peak areas of C
1s decreased by He+ and D2+ implantation, although thoseof Si 2p were almost constant. This indicates that the
selective chemical sputtering of C was occurred for SiC
and free C would be formed.
Based on these experimental results, the interaction
between hydrogen isotopes and helium, and damaged
structures in SiC are discussed. As mentioned in ourprevious paper [5], it is considered that most of hydrogenisotopes implanted with high energy are bound to Si and Cwith forming Si-D and/or C-D bonds. According to theSRIM calculation, the 4.0 keV He+ was retained beneaththe D retained region because the implantation depth of He
was much higher than that of D, indicating that only thedamaged structures would make a large influence on the Dretention, although both of the introduction of damage

C-D(a)

1.2Fig. 2 Summary of D and He retentions for the He+
implanted SiC with the implantation energy of 0.75 keV,
1.3 keV and 4.0 keV.

Si-D

0.75 keV He+-D2+ imp.

1.5Total
Si-D bondC-D bond

He+ implantation energy / eV㻌
4.0 keV He+-D2+ imp.

㻌

6.00.0

㻌

7.0

7.5

㻌He desorption rate / arb. unit

D2 desorption rate / 1017 m-2 s-1

Fig. 1 shows D2 and He TDS spectra obtained for SiC
with various He+ implantation energies. It was found that
D2 TDS spectra for the 0.75 keV and 1.3 keV He+
implanted SiC consisted of two desorption peaks, andtrapping state is almost the same as that of non- He+
implantation experiment as shown in our previous paper,
where the desorption temperature was slightly shifted tolower temperature side. However the desorption stages arealmost consistent with the previous paper [5]. For the 4.0
keV He+ implanted SiC, an additional desorption peak wasobserved at the temperature around 1200 K, which has notobserved for the He+ implantation with the same
implantation depth with D2+. In addition, the FWHM (fullwidth at half maximum) was quite narrow, indicating thatthe desorption process was quite different from the otherdesorption stages of Si-D and C-D bonds. It was confirmedthat this desorption peak was clearly associated by thedesorption of D2, not He and the reproducibility wasconfirmed. The He TDS spectra in Fig. 1(b) indicated thatlarge amount of He was desorbed for the 4.0 keV He+
implanted SiC at the desorption temperature of about 1200
K, indicating that the D desorption would be accompaniedwith the He desorption. However, no large desorption peak
was observed for the 0.75 keV and 1.3 keV He+ implanted
SiC samples, which lead to the direct interaction between
He and D. From the TDS spectra, the D and He retentions
were summarized in Fig. 2, indicating that the large Dretention was found for the 4.0 keV He+ implanted SiC,

1400

Fig. 1 The (a) D2 and (b) He TDS spectra for the He+
implanted SiC with the implantation energy of 0.75 keV,
1.3 keV and 4.0 keV. The implantation energy of D2+
was set to be 1.0 keV.

323

Y. Oya et al., Effect of Energetic Helium Ion Implantation on Hydrogen Isotope Retention in Silicon Carbide㻌

1.00.5Si 2p binding㻌energy /eV96-0.4-0.6

Pre-heating

0.3

C 1s peak shift / eV(b)㻌㻌Intensity / Arb. unit1.0-0.294㻌

4.0 keV He+ imp.
1.3 keV He+ imp.
0.75 keV He+ imp.
After heating

4.0 keV
1.3 keV
0.75 keV-0.8

0.0
110 108 106 104 102 100 98

1.5

0.0

㻌

(a)

0.5

After He+ imp. After He+-D2+ imp.
㻌4.0 keV
1.3 keV
0.75 keV

0.2
0.1

㻌

1.5

4.0 keV He+ imp.
1.3 keV He+ imp.
0.75 keV He+ imp.
After heating㻌Intensity / 㻌Arb. unit

2.0

Si 2p peak shift / eV

㻌0.0-0.1
Pre-heating

0.0294 292 290 288 286 284 282 280 278 276

C 1s binding energy /eV

After He+ imp. After He+-D2+ imp.

Fig. 4 Summary of peak shifts of (a) Si 2p and (b) C 1sfor the He+ implanted SiC.

Fig. 3 XPS spectra of (a) Si 2p and (b) C 1s for the He+
implanted SiC with the implantation energy of 0.75 keV,
1.3 keV and 4.0 keV.

By the He+ implantation with higher energy, large
amount of damaged structure was introduced and the D
was trapped in SiC, making negative peak shift of Si 2pand positive peak shift of C 1s. In addition, in case of C 1s,
free C formation would induce the positive peak shift of C
1s by the He+ implantation. More peak shift toward higher
binding energy side was found by the D2+ implantation,
showing the formation of C-D bond and induction of thechemical sputtering of C. It is also reported that the carbon
interstitials can freely migrate while the Si interstitials areimmobile around room temperature [12]. This fact wasalso consistent with our experimental results that the free C
was aggregated on the surface by heating after the He+
and/or D2+ implantations. In case of low He+ implantation,
large amount of He was retained in the same project rangeof D. This He retention prevents the D trapping by Si as
shown in our previous paper [6-9]. In addition, the Heretention in SiC would prevent the D retention. This would
be explained by the Si-Si clusterization and/or He retention
in the diffusion path of D in SiC, which induce the high D
de-trapping efficiency.
In summary, the 4 keV He+ implantation, which
penetration depth is higher than that of 1 keV D2+,
introduces the damaged structure in SiC, which explains
the higher D retention compared to that of 0.75 keV He+
implantation . This fact indicates that the He retention
would be one of the key factors for the evaluation ofhydrogen isotopes retention in SiC.

structures and He retention govern the D retention in caseof 0.75 keV and 1.3 keV He+ implantation as mention
above. Therefore, it can be said that the D retention in SiC
increased by the introduction of the damaged structures,
although the amorphization did not confirm in the present
study. It is reported that the Si-Si bonds were formed after
electron irradiation, while the no C-C bonds formation wasobserved in the reference papers by S. Muto et al., which
was explained by simple molecular orbital calculations[11-12]. This result is also consistent with our experimental
results, showing that the retention of D bound to Si wasalmost the same as that for the non-He+ implanted SiC,
although the retention of D bound to C was increased byhigh energy He+ implantation. In addition, some papers
mentioned that the recrystallization would be preceded at
the temperature above 2000 K. Therefore the damaged
structure would remain in the sample even if the deuterium
is desorbed [13,14]. According to Si 2p XPS spectra, there
was no large difference between just after He+ implantation
and additional D2+ implantation, indicating that Si-Si
cluster was formed by He+ implantation. It can be said thatthe free C would be formed by He+ implantation and madethe C-D formation at room temperature. In addition, theundefined desorption stage was found at the temperature of1200 K, which is the same temperature of He desorption
from He bubble, indicating that the He bubble
decomposition triggered the this D desorption. However,the detailed mechanism is still not clear and further studies
will be required to elucidate this desorption process.

4. Conclusion

The effect of He retention and damage introduction
on the D retention in SiC were studied as a function of the324

Y. Oya et al., Effect of Energetic Helium Ion Implantation on Hydrogen Isotope Retention in Silicon Carbide

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[3]

Si 2p peak area / arb. unit

㻌

1.0

0.5

Pre-heating

8.0

C 1s peak area / arb. unit

4.0 keV
1.3 keV
0.75 keV(a)After He+ imp.

After He+-D2+ imp.

㻌(b)

6.0

4.0 keV
1.3 keV
0.75 keV4.0
2.0
Pre-heating++
After He+ imp. After He -D2 imp.

Fig. 5 Summary of peak areas of (a) Si 2p and (b) C 1sfor the He+ implanted SiC.
implantation energy of He+ from 0.75 keV to 4.0 keV. The
D and He retentions in SiC and chemical behavior of SiC
were evaluated by means of XPS and TDS. It was foundthat the D retention decreased by the He retention in thesame implantation depth with D2+, although that increased
if only the damaged structures were introduced. It can besaid that the energetic D2+ was directly interacted with theretained He near the surface region and both of He and D
would be quickly desorbed, which induced the low He andD retentions in SiC. However, in the case of He retention
beneath the D retention region, large He retention wasobserved. In addition, free C formation would make thehigh retention of D bound to C. These facts indicate that
not only the damage introduction but also the He retention
governs the hydrogen isotope retention in SiC.

Acknowledgement

This study was supported by a Grand-in-aid forscientific research in fusion by Ministry of Education,
Science and Culture, Japan, by the joint usage/research
program of the Hydrogen Isotope Research Center,
University of Toyama (No.HRC2009-02 &03) and by theCenter for Instrumental Analysis at Shizuoka University.

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