RIKEN Accel. Prog. Rep. 50 (2017)

Ⅲ-1. Atomic & Solid State Physics (Ion)

Behavior of Cu impurity in Si studied by the β-NMR of 58 Cu
M. Mihara,∗1,∗2 M. Tanaka,∗1,∗2 Y. Tanaka,∗1,∗2 H. Du,∗1,∗2 T. Sugihara,∗1,∗2 K. Ohnishi,∗1,∗2 S. Yagi,∗1,∗2T. Hori,∗1,∗2 S. Nakamura,∗1,∗2 R. Yanagihara,∗1,∗2 Y. Ishibashi,∗2 Y. Abe,∗2 H. Ueno,∗2 K. Yamada,∗2D. Nagae,∗2 Y. Ichikawa,∗2 M. Fukuda,∗1,∗2 K. Matsuta,∗1,∗2 A. Ozawa,∗3,∗2 T. Izumikawa,∗4 T. Ohtsubo,∗5M. Takechi,∗5 S. Momota,∗6,∗2 D. Nishimura,∗7,∗2 T. Suzuki,∗8 T. Yamaguchi,∗8,∗2 T. Nagatomo,∗2T. Minamisono,∗1 K. Matsukawa,∗9 K. Shirai,∗10 and T. Fujimura∗10Cu impurities in Si devices are known as serious
contaminants because of the unique diﬀusivity of Cu,
which is the fastest among transition-metal impurities,enabling them to easily spread over a Si wafer of standard size only in a few hours.1) Short-lived β emitter
58
Cu (I π = 1+ , T1/2 = 3.2 s) is an attractive option
for a β-NMR probe nucleus for studying the behaviorof Cu impurities in Si, which will provide unique information on the mechanism of fast Cu diﬀusion or theproperties of the Cu-dopant complex which is related
to the gettering technique.2) Using the β-NMR technique, which relies on magnetic dipole moment μ andelectric quadrupole moment Q of the probe nucleus,
local internal magnetic ﬁelds or electric ﬁeld gradients(EFGs) at a probe nucleus can be observed. In thepresent case of 58 Cu in Si, measurement of the staticEFG is essential for examining the structure of a complex such as a B-Cu pair or of oﬀ-center substitutional(S) site of implanted Cu ions suggested by β-ray emission channeling.3)
We have been performing the 58 Cu β-NMR experiments since 2010 using the Riken Projectile Fragment
Separator (RIPS) at the RIBF operated by the RIKEN
Nishina Center and CNS, University of Tokyo. In previous works, we have shown NMR signals of 58 Cu in Si
at 15 K in 20104) and signals implying a quadrupole
splitting νQ , detected in 2013.5) In the present study,
we have tried to conﬁrm the reproducibility and a beta
nuclear quadrupole (β-NQR) spectrum was obtained,as shown in Fig. 1. In the case of 58 Cu, which has
a nuclear spin I = 1, the quadrupole interaction generates a splitting into two NMR lines with frequencies of ν0 ± νQ /2, where ν0 and νQ are described asν0  μB0 /h and νQ = (3/4)eqQ/h(3cos2θ − 1), respectively. The spectrum in Fig. 1 was obtained byapplying multi RF pulses as a function of νQ . Owing to the remarkable progress in the recent μ andQ measurements for 58 Cu by laser spectroscopy,6) thecenter frequency ν0 of approximately 4.04 MHz at B0∗1Department of Physics, Osaka University
RIKEN Nishina Center∗3 Department of Physics, University of Tsukuba∗4 Radioisotope Center, Niigata University∗5 Department of Physics, Niigata University∗6 School of Environmental Science and Engineering, Kochi
University of Technology∗7 Department of Physics, Tokyo University of Science∗8 Department of Physics, Saitama University∗9 SUMCO, Co.
∗10 ISIR, Osaka University∗2- 230 -= 0.93 T was estimated, and our result supports thevalue of μ[58 Cu] = +(0.570 ± 0.002)μN in Ref.
Ref. 6).
6. A
νQ of approximately 2.5 MHz was obtained from thepresent νQ spectrum. This supports the idea that implanted Cu atoms in the Si lattice are not located in a
spatially symmetric conﬁguration, as proposed by theβ-ray emission channeling.3) The EFG (q) cannot bedetermined because the angle between the main axisof the EFG and the direction of B0 is unknown. The
EFG for 58 Cu in Si is determined from the crystal orientation dependence of νQ relative to B0 and the valueof Q = (15 ± 3) efm2 in Ref. 6.
6).

Fig. 1. β-NQR spectrum of 58 Cu in Si.

References
1) E. R. Weber, Appl. Phys. A30, 1 (1983).
2) S. M. Myers et al., J. Appl. Phys. 88, 3795 (2000).
3) U. Wahl et al., Phys. Rev. Lett. 84, 1495 (2000).
4) M. Mihara et al., Hyperﬁne Interact. 197, 143 (2010).
5) M. Mihara et al., JPS Conf. Proc. 6, 030114 (2015).
6) P. Vingerhoets et al., Phys. Lett. B703, 34 (2011).