Difference of Irradiation Effects between Ar Cluster Ion
and Ar+ for DLC film formation
T. Kitagawa1,2,3), K. Miyauchi1), K. Kanda1), S. Matsui1), N. Toyoda1), H.
Tsubakino4), J. Matsuo5), and I. Yamada1,3)
1) Lab. of Adv. Sci. and Tech. for industry, Himeji Inst. of Tech., Ako-gun, Hyogo, JAPAN, 2) Nomura Plating Co.
Ltd., Nishiyodogawa, Osaka, JAPAN, 3) Collaborative Research Center for Cluster ion Beam Process Tech., 4)
Faculty of Eng., Himeji Inst of Tech., Shosha, Himeji Hyogo, JAPAN, 5) Ion Beam Eng. Exp. Lab. Kyoto University,
Sakyo, Kyoto, JAPAN
Abstract. In order to study the influences of Ar monomer ion (Ar+) on carbon film properties induced by ion beams
assisted deposition, Ar cluster ion, Ar+, and their mixed ions (Ar cluster ion and Ar+) irradiated surface during
evaporation and deposition of C60. From Near Edge X-ray Absorption Fine Structure (NEXAFS) and Raman
spectroscopy measurements, lower sp2 content in carbon films was obtained via Ar cluster ion beam bombardment in
comparison with bombardment by Ar+ and mixed ion beams. Furthermore higher hardness and smoothness of surface
were demonstrated via Ar cluster ion bombardments. Thus, it was important to irradiate using higher fraction Ar cluster
ions in the beam, in order to obtain hard DLC films with flat surface.
irradiation of Ar cluster ion beam during evaporating
used C60 as a carbon source. In this study, various ionassisted depositions were carried out, in order to
understand differences in irradiation effects obtained
by Ar cluster and Ar+. That is useful to develop a new
deposition method for hard DLC fabrication.
Characteristics of DLC films deposited simultaneously
with Ar cluster ion, Ar+ and their mixed ions (Ar
cluster and Ar+) surface bombardment by an
evaporation of C60 were studied using the Near Edge
X-ray Absorption Fine Structure (NEXAFS) and
Raman spectroscopy. Both hardness and the surface
morphology were investigated.
INTRODUCTION
Diamond-Like Carbon (DLC) films have been used
as protective coatings for various applications.
Especially hard-DLC films are expected for disks and
heads coatings of hard disk drives [1]. Development of
magnetic media and sensors of reading head such as
GMR and TMR is very fast. Modern trends claim that
floating space between head and media should be
lower than 15 nm to obtain higher recording density.
The floating space can be reduced by depositing DLC
films with thinner thickness. However thinner
thickness induces the degradation of film durability.
Thus, high wear-resistance DLC films, possessing
higher hardness (> 20~30 GPa) compared with present
DLC films formed by plasma CVD deposition, are
required. In order to satisfy these demands, hard DLC
deposition realized simultaneously with cluster ion
beam assisted deposition was proposed.
EXPERIMENT
Figure 1 shows the various Ar ions assisted DLC
deposition system. Ar cluster ion, Ar+ and their mixed
ions bombarded the target during evaporation of C60.
The experimental procedures of these ion beam
irradiations are described as follows. In the case of Ar
cluster ion irradiation, Ar cluster was generated by
supersonic expansion of high-pressure gas (3000 torr)
through a small orifice of the nozzle. The neutral Ar
In the previous study, we’ve demonstrated that Gas
Cluster Ion Beam (GCIB) assisted deposition was
useful for forming DLC films with high hardness (~50
GPa), smooth surface, and low content of sp2 orbital at
room temperature [2, 3]. DLC films were formed by
CP680, Application of Accelerators in Research and Industry: 17th Int'l. Conference, edited by J. L. Duggan and I. L. Morgan
© 2003 American Institute of Physics 0-7354-0149-7/03/$20.00
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(Ultra-Violet Synchrotron Radiation) facility of
Institute for Molecular Science (beam-line 8B1) in
Japan. Soft X-ray generated from synchrotron
radiation irradiated to a film at normal incidence with
photon energy from 275 to 320 eV. Total electron
yield mode, where applied to count all electrons
emitted from the surface by X-ray radiation, was
applied. The energy resolution of the monochromator
having grating was better than ~0.5 eV. The
normalization of spectra was performed by the spectra
of an Au sheet. Each normalization was done before
and after measurement on carbon films. The sp2
content in carbon films was analyzed by using near
edge peak of π* resonance (285.5 eV), which was
referred from spectrum of graphite. As it is very
difficult to determine absolute values of sp2 contents of
DLC films, the relative values of the contents were
estimated. The DLC films deposited with RF plasma
method were used as a standard sample to determine
those values. Also C60 film was investigated with
NEXAFS measurement as standard carbon films.
Furthermore Raman spectroscopy was applied to study
the bonding structures of the films (JASCO Corp.,
Laser Raman Spectroscope, NRS-2100). A wavelength
of Ar laser to measure Raman spectroscopy was 514
nm. In this measurement, the resolution of the Raman
shift was better than 20 cm-1. This resolution is
sufficiently higher, if the spectra of the DLC films
were broad. Hardness of the DLC films was measured
by nano-indentation technique (Hysitron Inc. (TriboScope)). Maximum indentation depth of the tip was
below 30 nm. The substrate hardness of Si wafer did
not affect on the film hardness, because this depth was
much shallower than film thickness (0.3 µm). The
hardness of the each film was obtained by averaging 5
times measurements of hardness. Surface morphology
for films was observed with non-contact mode by
Atomic Force Microscope (AFM; JEOL, JSPM-4200,
scanning area of 1 µm2).
FIGURE 1. Schematic diagram of the apparatus for DLC
films formed with various Ar ion beams assisted deposition.
clusters were inserted into ionizer, and ionized by 150
eV electrons. The current of electron emission was 120
mA. After acceleration, Ar cluster ions irradiated a
substrate. The mean size of the Ar cluster was
approximately 1000 atoms/ion, which was estimated
from retarding potential technique [2]. Thus, if Ar
cluster ion is accelerated at 5 keV, the each
constitutional atom of Ar cluster has energy of only 5
eV. For Ar+ extraction, Ar gas was supplied from a
tube, which was installed near the ionizer as shown in
figure 1. In the case of Ar+ irradiation, Ar cluster beam
was not used. The ionization condition where kept the
same for both Ar monomer and Ar cluster. For
generation of ‘mixed ion beam’, introduction of both
Ar cluster beam and Ar gas to the ionizer was applied.
The content of the Ar monomer ion in the beam was
more than 50 %. Acceleration voltage of these ion
beams was fixed at 5 kV, to obtain maximum hardness
by Ar cluster ion beam assisted deposition [3]. The
energy of cluster constitutional atoms and monomer
were 5 eV and 5 keV, respectively. Thus, the energy of
Ar+ was substantially higher in comparison with the
energy per atoms in cluster. C60 used as a carbon source
was evaporated from a heated crucible with the
deposition rate of 3.5 nm/min. In this evaporation rate,
crucible temperature was approximately 400 degree of
C. The C60 molecules and incident ions where in 1.5
proportion. This proportion was considered as an
optimum DLC deposition condition to obtain hard film
properties with Ar cluster ion beams [2]. The thickness
of each film was 0.3 µm. Si wafers used as substrates
were kept at room temperature during the deposition.
RESULTS AND DISCUSSIONS
Figure 2 shows NEXAFS spectra of carbon films
formed by various ion beams assisted deposition. C60
film and RF plasma DLC film were also examined.
The NEXAFS spectrum of C60 film showed three π*
peak of the carbon K edge (284.5eV, 285.5 eV, and
287.4 eV). This result demonstrates a good agreement
with the previous theoretical study [5]. Spectra of our
films were different from standard spectrum of C60
film. It indicates that C60 molecules were broken by
the ion irradiations, then amorphous film was created.
However the spectrum of the film formed with Ar+
Bonding structures of the films were studied with
NEXAFS and Raman spectroscopy. NEXAFS
measurement was used to obtain information of
containing sp2-hybridized orbital in DLC films [3, 4].
NEXAFS measurements were performed at UVSOR
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(1350cm-1) and G (1550-1600cm-1) peaks for a rough
estimation of sp2 contents. D peak is usually assigned
to A1g zone-edge mode because of the finite size of the
graphic domains. G peak is originated from the zonecenter E2g photon, which indicates the existence of
lattice vibrations in the plane of the graphite-like rings
[6-9]. I(D)/I(G) peak ratios were obtained from the
peak separation of Raman spectra. When the I(D)/I(G)
ratio was small, it indicates that small amount of sp2
content in the DLC film is exist[10]. Table 2 shows the
I(D)/I(G) peak ratio of carbon films deposited with
various ion beams. The films by Ar+ and mixed ion
had the peak ratio around 1.5~1.6. The films formed
with Ar cluster ion had lower peak ratio of 0.58. From
both Raman and NEXAFS spectra studies, it could be
estimated that the films formed with Ar cluster ion
irradiation had lower sp2 contents than those formed
by assisted irradiation of ion beams with higher
fraction of Ar+ contents.
FIGURE 2. NEXAFS spectra of carbon films formed with
various Ar ion beams assisted deposition. The C60 film and
DLC film formed by RF plasma method were mesured to
obtain standard spectra.
TABLE 1. Integrals of π* peak (285.3 eV) extracted from
NEXAFS spectra of the films irradiated with various ion
beam irradiation. The integrals were normalized with
that of the films by RF plasma method as a standard.
Incident Ion
Ar cluster
Ar cluster
Ar+
species
ion
and Ar+
Integral of π*
0.68
0.99
1.18
peak
irradiation have a small peak at 287eV, which is at the
same position with the third peak of C60. The similarity
also is observed on σ* broad peak around 294 eV.
Thus, the structures of C60 were still remained in the
film formed by Ar+ assisted deposition. On the other
hand, films irradiated with Ar cluster ions and mixed
ions had no structure of C60. However, a slightly lager
peak at 285.3 eV was obtained from the film with
mixed ion irradiation. This peak at 285.3 eV was
originated from sp and sp2 hybridized orbital of carbon
bonding [4]. The peak was usually identified as sp2
orbital because the sp orbital is not stable. Integral of
this peak in the spectra that is useful to discuss sp2
contents in films was shown in table 1. The integrals
of the peaks were normalized using that of RF plasma
DLC as a reference. The smallest integral of the peak
was obtained from the films by cluster ion beam
assisted deposition. With increasing Ar cluster ion
content in the beam, the integral of the peak decreased.
It indicated that, when fraction of Ar+ was high, sp2
contents also became larger due to graphitization of
carbon.
FIGURE 3. Raman spectra of films deposited with various
assisted ion bombardments. The spectra was sparated into D
and G band (D band: 1350cm-1, G band: 1550-1600cm-1).
I(D)/I(G), that was the ratio of the integral of the each peak,
was estimated for rough evaluation of DLC film quality.
TABLE 2. I(D)/I(G) peak ratio of the films with various
ion beam bombardments.
Incident Ion
Ar cluster
Ar cluster
Ar+
species
ion
and Ar+
I(D)/I(G)
0.58
1.51
1.60
peak ratio
Figure 3 shows Raman spectra of films formed
with various ion-assisted deposition. Raman spectra of
the DLC films were generally discussed using D
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Also higher hardness and smoother surface were
obtained by the higher fraction cluster ions. Therefore,
it was important to increase the Ar cluster ion ratio in
the beam to obtain hard DLC films with flat surface.
Furthermore, it was difficult to fabricate DLC films
with high hardness and smooth surface only with Ar+
bombardment.
ACKNOWLEDGMENTS
This work is supported by New Energy and
Industrial Technology Development Organization
(NEDO).
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FIGURE 4. Hardness of the films formed with various
assisted ion bombardments. Hardness values increased with
increasing the fraction of Ar cluster ion in the beam.
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CONCLUSIONS
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Ar cluster ion, Ar+ (Ar monomer), and their mixed
ion (Ar cluster and Ar+) irradiated surface during the
evaporation of C60, in order to study the differences of
the irradiation effects of Ar cluster ion and Ar+ on
DLC film fabrication. From NEXAFS and Raman
spectroscopy measurements, higher fraction of Ar
cluster ion in the beam brought lower sp2 contents.
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