Research Activities

Development of Tera-Hertz Light Sources at Compact
Electron Linear Accelerator LEENA
S.Hashimoto, S. Chin, K. Kawata, Y. Minagawa#, Y. Takemura#, D. Li*, S. Amano, S. Miyamoto
LASTI, University of Hyogo
#
JASRI
*
Institute for Laser Technology
Abstract
We have been upgrading the 15 MeV compact electron linear accelerator LEENA since last year.
As a result, the electron beam transport efficiency and beam currents have been greatly improved.
We have also succeeded in measuring both the synchrotron radiation from a bending magnet andSmith-Purcell radiation in a terahertz regime.
Introduction
The compact electron linear accelerator LEENA (Laser
Emitted ElectroN Accelerator) is located in the
NewSUBARU synchrotron light facility. Because of its
old-fashioned control system and insufficient beam
monitors, the accelerator could not show good performanceat recent. In order to make it possible for NewSUBARU
facility users to use radiation in terahertz regime for industry,
we are regenerating the accelerator and developing terahertz
sources using the accelerator [1,2]. As the terahertz
sources we are planning both the synchrotron radiation forma bending magnet and Smith-Purcell radiation. When theelectron beams pass through near a metal grating, theinduced surface current on the grating radiates
electromagnetic waves (Smith-Purcell effect). The main
parameters of LEENA are shown in Table. I.

Table ILEENA main parameters

Beam Energy
Macro pulse
RF frequency
Repetition rate
Macro pulse width
Gun
CathodeCharge per bunch
Bunch length

15MeV
100 mA (Max.)
2856 MHz
1-10 Hz5µs
rf gunthermal35 pC
30 ps (design)

Upgrade of the old-fashioned accelerator
The control system of the accelerator was based on PLC, potentiometers and touch-panel. This
old-fashioned system made difficult for operators to beam-handle with high precision and highreproducibility. For the flexible tuning of the accelerator, all equipments such as power-supplies are
required to be controlled by a PC. Using the OPC server we made it possible for the PC to communicate
with the PLC, and beam-operations become easier by using Graphical User Interface programs developed by

Fig.1 Macro-pulse current measured by several Current Transformers. Beam transport
efficiency was improved after the system upgrades and the fine-tuning.

11

LabVIEW.
As for vacuum, a few sputtering ionization pumps and vacuum gauges were newly added and after theleak detection and the baking, the vacuum pressure became one digit better than before.
A new screen monitor was installed at the entrance of the alpha magnet for the beam to be injected withthe right position and angle to reduce the beam loss at the magnet.
By the above mentioned upgrades the beam transport efficiency was greatly improved as shown in Fig. 1[3]. The macro-pulse averaged current measured at CT1 (just after Linac) was 95mA, and 65mA at Faraday
Cup (FC). The maximum current is limited to 100mA at 15 MeV by the radiation safety regulation.
Measurement of Terahertz radiation from a bend and Smith-Purcell radiation
The schematic drawing of the terahertz measurement is shown in Fig. 2. The synchrotron radiation froma bending magnet and Smith-Purcell radiation were measured with Zero Bias Diode (VDI WR6.5, 110-170
GHz, 2000V/W) through quartz windows [4].
In the case of Smith-Purcell radiation, the measured peak power was about 9.3 µW with the electron
beam of 15MeV, 40mA. Considering the macropulse width of 3.5 µs and the ZBD antenna aperture of
78.5mm2, the energy per mm2 per macropulse is 0.4 pJ/mm2/pulse. The measured radiation is “incoherent”,
because the measured wavelength (110-170 GHz) is shorter than the expected bunch length of 30 ps.

Fig.2 The generation and measurement of Terahertz
radiations at LEENA; The synchrotron radiation from thebending magnet and the Smith-Purcell radiation.

Fig.3 Waveform of Smith-Purcell
radiation measured by a Zero Bias Diode.

Undergoing and future plans for developing terahertz sources at LEENA
Although we have succeeded in the first observation of the Smith-Purcell radiation and the synchrotron
radiation at LEENA, those radiation intensities were relatively weak because of the incoherent radiation
which intensity is proportional to the number of electron in a bunch N. If the bunch length of the electron
beam is less than radiation wavelength, the radiation is coherent and proportional to N2. The generation of
the coherent radiation by short electron bunches is the next important topic in LEENA.
To measure radiation spectrum and estimate bunch length, the Martin-Puplett interferometer is underconstruction. And BPM (Beam Position Monitors) for nondestructive measurement of beam position andthe solenoid coil to focus and guide low energy electron beam just after RF gun are under design and will be
installed in near future.
References[1] S.Hashimoto et al., Lasti Annual Report, 10, pp.13-14 (2010).
[2] S.Hashimoto et al., The 8th Annual Meeting of Particle Accelerator Society in Japan (2011).
[3] S.Hashimoto et al., The 9th Annual Meeting of Particle Accelerator Society in Japan (2012).
[4] S.Chin et al., The 9th Annual Meeting of Particle Accelerator Society in Japan (2012).

12

Laser-plasma extreme ultraviolet source at 6.7 nm

using a rotating cryogenic Xe target
S.Amano, and T.Inoue
LASTI/UH
Abstract
A laser-plasma source comprising a rotating cryogenic solid-state Xe target has been studied foruse in extreme ultraviolet lithography (EUVL) systems equipped with La/B4C mirrors. The laserto-EUV power conversion efficiency (CE) of the cryogenic Xe target was improved to achieve amaximum CE of 0.15% at 6.7 nm with 0.6% bandwidth. We successfully demonstrated thecontinuous generation of EUV light with an average power of 80 mW at 6.7 nm with 0.6%
bandwidth using a Nd:YAG slab laser at a repetition rate of 320 Hz and an average power of 100
W.
Introduction
Recently, a new lithography system that uses
La/B4 C mirrors having a reflectivity peak at 6.7
nm has been proposed as a next-generation
candidate to supersede the current EUVL
projection lithography system, which relies on
Mo/Si mirrors having a reflectivity peak at 13.5
nm [1]. This means that a light source emitting
around 6 nm will be required for use in future
lithography systems for industrial mass
production of semiconductors. To achieve a highCE around 6 nm, LPX sources based on targets ofhigh-Z metal elements such as Gd and Tb, havebeen studied. However, these LPX sources cannot
be used effectively for industrial EUVL
applications until a number of difficult problems
have been resolved, including the high cost of thetargets, establishing a way to continuously supply
the targets, and the plasma-debris problem
associated with such metals, etc.
Here, we propose the use of our Xe LPX
source as a 6 nm light source because it emits
broadly in the 5–17 nm range and does notexhibit the problems highlighted above. Thus, wecharacterized the Xe LPX as a source emitting at
6.7 nm with 0.6% bandwidth required for use
with La/B4C mirrors. In this letter, we describe
the characteristics of EUV at 6.7 nm using our
LPX source.

radiation. By changing the position of the focus
lens to change a laser spot, laser intensity on thetarget was adjusted to find an optimized intensity.

Figure 1. Experimental setup to obtain data of
EUV emissions from a cryogenic rotating Xetarget. FC represents the Flying Circus III energy
generator, and TG is a transmission grating.
To measure the generated EUV emission, we
employed an energy detector calibrated at 13.5
nm with 2% bandwidth (SCIENTEC Engineering,
Flying Circus III) and a spectrometer having a
resolution of 0.76 nm, which is equipped with atransmission grating (50 mm diameter and 1000
line/mm) and a back-illuminated 2D-CCD camera.
At first, the 13.5 nm light with 2% bandwidth in
the emission spectrum was calibrated using theenergy detector. Next, the required 6.7 nm lightwith 0.6% bandwidth in the emission spectrum
was compared with the 13.5 nm light with 2%
bandwidth to obtain an absolute CE for the 6.7
nm light with 0.6% bandwidth, taking into
account the sensitivity of the CCD camera. To
achieve the highest CE at 6.7 nm with 0.6%
bandwidth, we attempted to control the plasma

Experiments
Our LPX source uses the developed targetsystem described in ref [2]. Figure 1 shows anexperimental setup to obtain data for the EUV
emission from the cryogenically cooled rotating
Xe target. Here, a conventional Q-switched
Nd:YAG rod laser (Spectra-Physics, PRO-230)
was used in single-shot operation, which coulddeliver pulses at wavelengths of 1ω (1064 nm).
The laser pulse width was about 10 ns. The pulses
were expanded using a beam-expander andfocused on the target with an f = 500 mm lens sothat plasma was produced and emitted EUV

13parameter by changing the driving laser
conditions. We investigated the dependence of
the CE on the drum rotation and laser intensity.

Though the obtained power is still low, oursource is the only LPX source at present that cangenerate an emission continuously at 6.7 nm.

Results
Under certain operating conditions, humps
around 6 nm were observed in the emission
spectra (see Fig. 2). The emission spectra in Fig.
2 were obtained using a 1ω pulse in the rotation
and rest condition. In previous experiments for
the EUV emission at 13.5 nm with 2% bandwidth,
we observed an increase in CE and a lower
production of fast ions when the drum was rotated,as compared with conditions when the drum wasat rest [3]. In the present study for the EUV
emission at 6.7 nm, the same phenomena wereobserved as shown in Fig. 2, that is, a hump wasobserved at around 6 nm, which had a higher
intensity in the EUV emission spectrum
corresponding to the rotating drum as comparedwith the EUV emission spectrum corresponding
to the drum at rest. This result is explained by thefollowing exploration. The Xe gas vaporized on
the target surface by the wipers during therotation produces an optically thick plasma
having an optimized density and a temperature
suitable for emitting EUV radiation, where thesatellite lines of the plasma contribute effectively
to increasing the EUV intensity. As a result in thiswork, it was found that a maximum CE at 6.7 nmwith 0.6% bandwidth was obtained for the 1ω
laser irradiation and the rotating drum target (Fig.
2), and its CE was estimated from this emission
spectrum to be 0.15%. The CE was spatiallyintegrated taking into account its EUV angular
distribution. Because the bandwidth of 0.6% for
the La/B4C mirror reflectivity is narrower thanthe 2% for the Mo/Si mirror, the availablereflected power is intrinsically small. In the caseof 13.5 nm light, a maximum CE was also
obtained for the 1ω laser irradiation and therotating drum target, however, the laser intensity
in this case was 1×1010 W/cm2 at a laser energy of
0.8 J. On the other hand, the maximum CE at 6.7
nm with 0.6% bandwidth was obtained for thehigher laser intensity of 4×1012 W/cm2 at a laser
energy of 0.8 J. Because the Xe[XI] ion mainly
emits 13.5 nm light and the Xe[XLIV] ion emits
6.7 nm light, it is considered that a higher laser
intensity is required to achieve a higher charge
state.
Because CE is dependent on the laser intensity,a CE at 6.7 nm with 0.6% bandwidth wasestimated to be 0.08% for a laser intensity of
1.5×1010 W/cm2 at a laser energy of 0.3 J.
Therefore, when our developed slab laser having
an average power of 100 W (0.3 J@320 Hz) wasused to irradiate the rotating target, a continuous
EUV generation was achieved with an average
power of 80 mW at 6.7 nm with 0.6% bandwidth.

Figure 2. EUV radiation spectra with a hump at 6
nm emitted from the cryogenically cooled Xe
drum target. The lines represent 13.5 nm lightwith 2% bandwidth and 6.7 nm light with 0.6%
bandwidth, respectively.1ω pulse irradiation (0.8
J/10 ns) for both the rotating drum and the drumat rest. The laser intensity was 4×1012 W/cm2.
References[1] J. Benschop, EUV: past, present and prospects,
Keynote I, 2009 International Symposium on
Extreme Ultraviolet Lithography, Prague Czech,
October 2009, International Sematech, Available
from:<http://www.sematech.org/meetings/archivs/litho/ index.htm>.
[2] K. Fukugaki, S. Amano, A. Shimoura, T.
Inoue, S. Miyamoto, and T. Mochizuki: Rev. Sci.
Instrum. 77, 063114 (2006).
[3] S. Amano, K. Masuda, A. Shimoura, S.
Miyamoto, and T. Mochizuki: Appl. Phys. B. 101,
213-219(2010).

14Effective collision cross section of xenon plasma debris inargon buffer gas
Tomoaki Inoue, Takayasu Mochizuki, Kazuya Masuda, Sho Amano, and Kazuhiro Kanda
Abstract
Mitigation of fast debris and soft x-rays generated from laser-produced xenon
plasmas were studied in an argon buffer gas in laser intensities of 109–1011 W/cm2 using
a cryogenic drum target. Considerable mitigation of debris was confirmed bymeasurements of material sputtering. From the experimental results, an attenuation
parameter of sputtering by the debris σ 1 and an absorption cross section of soft x-rays
at 13.5 nm σ2(13.5nm) were derived to be 2.2 × 10−20 m2 and 1.8 × 10−22 m2, respectively.
Moreover, σ 1 is concluded to be equivalent to the effective collision cross section σ1of a debris particle at a kinetic energy of 1–4 keV. Sufficient debris mitigation can beobtained together with low soft x-ray absorption (less than 10%). These parametersprovide a useful design tool for realizing a practical soft x-ray source because they
predict the effect of the buffer gas well.
when the argon buffer gas was present. The argon gas
at room temperature was introduced into the chamber
through a nozzle on an upper wall of the chamber.
The sputtering rate and the absorption rate at 13.5
nm were measured using the QCM and soft x-ray
calorimeter, respectively, as a function of the argon
gas pressure, which was varied by adjusting the flowrate of the argon gas.

Introduction
Soft x-rays from high-temperature, high-density
plasmas produced by focusing a high-intensity laser
on target materials are expected to be useful as acompact high-brightness soft x-ray source for avariety of applications [1]. However, debris emitted
from the plasmas remains one of the most serious
problems that must be solved before the source canbe used for practical applications. The debris
generally causes sputtering and/or deposition on thesurfaces of condenser mirrors [2], degrading themirrors’ reflectivity and thus reducing the usable
x-ray output power. Chemically inert xenon debris
from a xenon plasma target will not be deposited on
the mirror surface [2]. Thus, mitigation of fast xenon
debris by the buffer gas is a technical issue to beresolved. However, a trade-off between mitigation of
the fast debris and absorption of the soft x-rays, bothof which are caused by the buffer gas, remains to bestudied.
In this paper, we report the experimental
results and discuss the effective attenuation
cross-sections of plasma debris and soft x-rays inargon buffer gas. We find an effective debris
mitigation parameter that is useful for realizing apractical laser-produced soft x-ray source.

Results and discussions
X-ray emission experiments were performed
with the rotating drum cryogenic xenon target. We
obtained the laser intensity dependence of the soft
x-ray CEs at 5–17 nm. The laser intensity range at
which the CE is significant is found to be 109–1011
W/cm2 , and the maximum CE was about 25%/2πSr.
The circles and triangles in figure 1 represent
the sputtering rate Nsputter(nl) and transmission ofsoft x-rays T(nl) at 13.5 nm, respectively. Here, nl
should be expressed more precisely by ∫dnl, but
we assumed that n was uniform in a spatial range ofinterest for observing the buffering effect.
Note that the experimentally observed Nsputter(nl)decreased in an approximately exponential form as nl
increased. Thus, we assume that Nsputter(nl) is welldescribed by(1)
N sputter ( nl ) = N sputter ( 0 ) exp( − σ 1 nl ) ,Experimental
A rotating drum cryogenic solid xenon target wasused. A Q-switched 1.06-µm Nd:yttrium aluminium
garnet laser (Quantel YG980) pulse was focusedthrough a f/500 lens on the target surface at an angleof 5° to normal incidence. The laser pulse duration
was 8 ns at full width at half maximum with anenergy of 300 mJ/pulse for either single shot orrepetitive shots at 10 Hz. The laser intensity was
adjusted in a range of 109–1011 W/cm2 by changing
the lens position. The target chamber was evacuatedby a turbo-molecular pump that maintained a xenonpressure in the chamber of less than 0.2 Pa except

where σ 1 is the attenuation parameter of sputtering
for the argon gas buffer. It has the same unit as across section. .
Similarly, T(nl) is expressed by(2)
T ( nl ) = exp (− σ 2 (13 .5 nm )nl ) ,where σ2(13.5nm) is the absorption cross section ofsoft x-rays at 13.5 nm for an argon molecule. From
figure 1, σ 1 and σ2(13.5nm) were derived to be 2.2
× 10−20 m2 and 1.8 × 10−22 m2, respectively.
On the other hands, the relationship between thecollision cross section of a debris particles σ1(E,Z)

15

Line integral of Ar Pressure [Pa m]

and the attenuation parameter of sputtering σ 1 isexpressed by∑ ∫ σ ( E, Z )s(m, E ) N (nl , E, Z )dE
1

Xe

Z =0

∞

, (3)

∑ ∫ s(m, E ) N (nl , E, Z )dE
Xe

Z =0

where NXe(nl,E,Z) is the number of debris particles
per unit energy interval arriving at the observation
point which is located at a distance l from the sourcewith a buffer gas of density n and s(m,E) is theaverage number of particles sputtered by a debris
particle having a mass m and kinetic energy E. Notethat s(m,E) depends on the mass m and kinetic energy
E of the colliding debris, and also on the bombarded
target material, but not on the charge number Z. We
assume the effective charge number in the target
material [3].
To evaluate σ 1 , the kinetic energy dependenceof s(m,E) was calculated by the numerical code The
Stopping Range of Ions in Matter (SRIM), as shownin figure 2. The values of s(m,E) for the above
sputtered materials were normalized by those at a
kinetic energy of 4 keV.
Figure 2 shows that s(m, E) ⋅ N Xe (0, E, Z ) has
significant values only at energies of 1–4 keV. Thus,
we can take a representative average value-3

10Transmission

σ1 =Nsputter(nl) [nm/shot@Au]

∞

-4

10

-5

10

-6

10

0
1
2
3
4
5
-2
Line integral of Ar density [m ]Figure 1 Mitigation of Au sputtering by fast xenon
debris (○) and transmission of 13.5 nm soft x-rays(△; experimental, dotted line; Henke et al [4]) as afunction of the line integral of the argon pressure.

s(m, E)⋅ NXe(nl, E,Z) as s(m, E) ⋅ NXe(nl, E, Z ) in (3) for
each mirror material in this energy range. The valueof σ1(E, Z) averaged over 1–4 keV should beequivalent to σ 1 :σ1 ≈ σ1 .
(4)Hereafter, we define σ 1 as the effective collision

10

11

Normalized s(m,E) [arb. unit]

Normalized s(m,E) Nxe(0,E,Z), Nxe(0,E,Z) [arb. unit]

10

10

9

10

8

10

300

cross section of a debris particle colliding with abuffer argon gas molecule.

1000

2000

3000

4000

5000

Kinetic energy [eV]

Figure 2 Kinetic energy dependences of the numberof xenon ions N Xe (0, E, Z ) and the sputtering rates

Conclusion
The attenuation parameter of sputtering by thedebris σ 1 is concluded to be equivalent to theeffective collision cross section σ1 of a debris particle
at kinetic energies of 1–4 keV. From figure 1, σ 1
and σ2(13.5nm) were evaluated as 2.2 × 10−20 m2 and1.8 × 10−22 m2, respectively.
Therefore, sufficient debris mitigation and low
absorption of soft x-rays (less than 10%) can beobtained. The obtained parameters are useful as adesign tool for realizing a practical laser-produced
plasma soft x-ray source because they predict theeffects of a buffer gas well.

s(m,E).
Reference
Tomoaki T, Mochizuki T, Kazuya M, Amano S,
Sekioka T and Kanda K 2011 J. Phys. B: At. Mol. Opt.
Phys. 45 115401[1] Bakshi V 2005 EUV Source for Lithography(SPIE, Bellingham, WA) p. 4[2] Mochizuki T 2000 Proc. SPIE 3886 306[3] Ziegler J F, Biersack J P and Littmark U The
Stopping and Range of Ions in Solids (The Stopping
and Ranges of Ions in Matter vol 1) ed J F Ziegler, p
5[4] Henke B L, Gullikson E M and Davis J C 1993
X-ray interactions: photoabsorption, scattering,transmission, and reflection at E=50-30000 eV,
Z=1-92, Atomic Data and Nuclear Data Tables 54
181 http://henke.lbl.gov/optical_constants/

16

EUV Interference Lithography for 1X nm
Takuro Urayama, Takeo Watanabe, Yuya Yamaguchi, Naohiro Matsuda,
Yasuyuki Fukushima, Takafumi Iguchi, Tetsuo Harada, and Hiroo Kinoshita
Center for EUVL, Laboratory of Advanced Science and Technology for Industry,
University of Hyogo
3-1-2 Koto, Kamigori-cho, Ako-gun, Hyogo, 687-1205, Japan
EUV interference lithographic exposure tool was developed to evaluate hp 20 nm and below.
The transmission diffraction grating with hp 30-nm absorber pattern was succeeded to fabricate.
In the fabrication process of the transmission diffraction grating, SiO2 hard mask process andthe center stop process were applied to obtain high contrast of the interference fringes toreplicate resist fine pattern. In addition, the vibration effect was succeeded to reduce. As results,
hp 22.5 nm, hp 20 nm, hp 17.5 nm, and hp 15 nm resist patterns were succeeded to replicate by
the two-luminous-flux interference exposure using the two-window transmission diffraction
grating in EUV-IL. In addition, the hole pattern of hp 35 nm and hp 28-nm thefour-luminous-flux interference exposure using the four-window transmission diffraction
grating was succeeded to replicate.
Keywords: EUVL, interference lithography, grating, resist, non-chemical amplified
1.Introduction
Extreme ultraviolet lithography (EUVL) [1] is themost promising technology to be used in high volume
manufacturing of the semiconductor devices around2012 [2]. In EUVL for 22 nm node, the top threetechnical issues which are listed in order of amount of
the problems are defect-free EUV mask, EUV lightsource with high power and high stability, and EUV
resist which satisfies with high resolution, highsensitivity, low line width roughness (LWR), and low
outgas.[3] For the extending EUVL to 1x nm node,
EUV resist is the top issue.[3] High sensitivity, low
LWR, and low outgas should be achieved
simultaneously. The resist platform should be changedfor 16 nm node and below.[4,5] Thus, EUV resist
development for 16 nm node is not so easy. However,there is no exposure tool which can evaluate the resist
pattern width of 1X nm. Therefore, we developed theexposure tool based on the EUV interference
lithography (EUV-IL) [6]. Previously we demonstrated
hp 25 nm resist pattern using EUV-IL.[7-9]This paper focuses on the pattern replication of 1X
nm by the improvement of the transmission grating
and the EUV-IL exposure tool.

The beamline-setup configuration of the EUV-IL isshown in Fig. 1. The EUV-IL exposure tool was
installed in the class 100 clean room at the end stationof BL9 beamline in NewSUBARU synchrotron
radiation facility [10] which belongs to the Universityof Hyogo. The 10.8-m-long undulator was employed
as a light source of the BL9 beamline. By tuning theundulator gap, the EUV monochromated wavelengthof 13.5 nm can be produced by the undulator, and theflux intensity of the EUV light is approximately 1,000
times higher than that from the bending magnet as alight source [10].

2.Experimental
2.1 EUV interference lithography

In the optics design concept of the EUV-IL beamline,
to increase the exposure throughput of the EUV-IL, theFig. 1 View of interference lithography system

17

mem
mbrane. RF power, bias power, and totaltpressureewerre 100 W, 25
2 W, and 11.3 Pa, respectively. Theereacctive gas flow
w rate and thhe dry-etching time periodd
are shown in Tab
ble. 1.

m
reducced as muchh as
number of tthe optical mirrors
possible. And then, reduccing the expo
osure time, itt can
prevent fromm the vibrationn effect.
lithography [11]The principle of the interferenceibased on thee two-luminoous-flux interfference expoosureusing the twoo-window traansmission grrating is show
wn in
Fig.2 By onee grating, cohherent EUV lightlis diffraacted
to the 0th, ±1st, ±2st, …. orrder lights. As shown in Fiig.2,
at the interfference poinnt of 1st-ordeer and -1st-oorderdiffracted ligghts, the interrference fring
ges were creaated.
Since the piitch the interference frinnges have a half
pitch size off the diffractioon grating, reeplication patttern
pitch of the resist patternn has a half pitch size off thediffraction grrating.[11]Table 1. Etching prrocess conditiions
Mask
M
lay
yer/Etchedlayyer
Reesist/SiO2
Reesist
SiO2/TaN

Gas

Gas flow rate
(sccm)

CF4
O2
Cl2+He60 sccm
20 sccm
25 sccm+
+75
sccm

Etch
time
(s)
50
20
170

In order to increase thhe light con
ntrast of thee
inteerference frinnges, the trannsmitted lightt between theetwoo-window graating have too be cut off. “Center“stop””
process was ap
pplied after the back-etching siliconn
subbstrate. A polymer type chemically amplifiedaEBB
resiist was employed in insteead of ZEP520A resist of
the center stop layer becausee of the beneffit of the EUVVlighht attenuation
n. The resistt thickness forf the centeer
stop
p was 2 μm because of tthe enough absorbanceaof
EUV wavelengthh.

Fig. 2 Principle off interference exposure
2.2 Fabricatioon of the trannsmission diffffraction gratinng
The key element of EUV-IL is the transmisssion
diffraction grating.[7] In the fabrrication of thetransmission diffraction gratinggfor thhe replicationn of
20 nm widthh resist patteern and below
w, the SiO2 hhardmask processs was optiimized and the center stop
processes waas improved.
Figure 3 shows the fabrication process of thetransmission diffraction grating.
g
It is preparedpthat 100–nm-thick Sii3N4 coating with low film
m stress on ffront
and back suurface of 4-innch Si waferr. Electron bbeam
resist ZEP5220A (Nippon Zeon) was coated on it anddiffraction ggrating patternrn was repliccated by elecctron
beam lithogrraphy using by
b 50 kV elecctron beam diirect
writing systeem (ELS-75000, Elionix).. Then the S
SiO2
grating patteern was repplicated usin
ng the inducctive
coupled plasm
ma of reactivve ion etchingg (ICP-RIE, T
TCP
9400SE, Laam Researchh) method employing CF4
reactive gas bby ZEP520A
A resist patternn as a mask. And
the TaN diffrraction gratinng pattern wass replicated uusing
ICP-RIE dryy etching meethod employ
ying Cl2 reacctive
gas and SiO
O2 grating patttern as a maask. The etchhing
time of TaN was increaseed to 170 s tot obtain the finestructure diiffraction grrating TaN pattern. A
Afterremoving thee residual resiist, silicon su
ubstrate back etchby KOH sollution was appplied to obttain a memb rane
structure of the TaN diffraction patttern on a S
Si3N4

Fig. 3 Fabrication processs of the transmissionn
difffraction gratinngFigure 4 shows the fabricateed transmissio
on diffractionn
gratting. The transmission diiffraction graating has fouursetss of the two
o-window diiffraction graating patternn,such as hp 45 nm
m, hp 40 nm,, hp 35 nm, anda hp 30 nm
m.
Usiing this gratinng, resist patttern of hp 22
2.5 nm, hp 200
nm,, hp 17.5 nm
m, and hp 15 nnm can be reeplicated on awaffer. The distaance betweenn the grating
g and a wafeer
wass set to be app
proximately 1 mm.

18

(a)
(

plicating resiist pattern piitch is 2/22
systtem, the reppof thee transmissio
on diffractionn
times by the pitch
plicated resisst
gratting. Figures 9(a) and 9(b)) show the repit.
pattterns before and after thhe vibration improvement
ment as shownn in Fig.9 (b)),
After the vibration improvem
was replicateed with highh
35 nm hole ressist pattern w
ntrast.
con(b)
hp
p 45 nmhp
p 40 nm(c)
hp 35 nmhp
p 30 nmFig. 4 Fabriccated transm
mission diffracction grating ; (a)ment
top view of the transmisssion grating, (b) arrangemof four sets oof the two-w
windows of diffraction gratting,and (c) cross sectional vieew of the hp 30
3 nm diffracction
bstrate.
gratings befoore back etchiing the Si sub
2.3 Vibrationn removal
Since the vvibration affeects with the replication off theresist patternn, the vibration has to be reeduced.
stages w
were
The vibrattions on the ggrating and wafer
w
on Co., Ltd.)). As
measured usiing an acceleerometer (Rioa result of tthe vibrationn measurement, the vibraation
originates too the pumpping system. And prevvious
ystem and a gap
grating stagee had a tilt aadjustment sy
adjustment syystem with a long range. Since adjustm
mentom, stages w
system had a large degrree of freedo
werennoveleasily to afffect with vvibrations. Therefore,Tgrating stages were dessigned and installed in the
EUV-IL expposure tool. Tilt adjustm
ment system wasremoved andd increased thhe rigidity off the stages. The
setup of the sstages is show
wn in Fig.5.
Figure 6 sshows the vibbration measu
urement resuult of
the vibrationn displacemennt of the gratiing and the w
wafer
stages beforee and after thhe improvemeent of the graatingstage. After the improvem
ment of the gratinggstage,, thelow frequenccy vibration can be redu
uced. Beforee theimprovementt of the ggrating stagee, the vibraation
displacementt between thee grating and the wafer staages
m in maxiimum. How
was 30 nm
wever, after the
improvementt of the ggrating stagee, the vibraation
displacementt was reducedd to be 5 nm ini maximum..
Figures 7((a) and 7(b) show 25 nm
m line and sppace
pattern beforre and after the vibratio
on improvem
ment,
respectively. As shownn in Fig. 7(b), after the
improvementt, L/S resist patternwith highhcontrast waspn Fig.8, by the
replicated. IIn addition, as shown inosure using thefour-luminouus-flux interference expo
on diffractio
on grating, holew transmissio
four-windowdgraating
pattern can bbe replicated. In the four diffraction

ge setup in thee EUV-IL exp
posure toolFig. 5 Stag

Fig. 6 Vibration off exposure staage

Fig. 7 CD-SEM images of 255-nm-width liine and spacee
resiist (ZEP520Ab) after theA) pattern (a) before and (bstage.
provement off the grating st
imp

19

3. Results
R
and DiscussionsD
ows the repliccated L/.S ressist pattern ofF
Figure10 shoamplifiedd
nonresistusing
theen-chamicallytwoence exposurre using theeo-luminous-flux interferentwo
wn in Fig.10
0, hp 22.5 nmm,o-window graating. As show
hp 20
2 nm, hp 17.5 nm and hpp 15 nm resistt pattern weree
repllicated after thent. For 15 nm
mt vibrationn improvemen
L/S
S pattern, pattern strippinng was obseerved for theenonn-chemically amplified ressist (Inpria).
A results, it was confirm
med that the EUV-IL
E
has a
As
cap
pability to replicate the resiist pattern wiith of 1X nm.
F
as shown in Figs. 9(b) and 11, by thee
Furthermore,
four-luminous-fllux interfereence exposurre using theefour-window trransmission diffraction grating,holeegpatttern width of 35 nm andd 28 nm resist pattern of
ZEP
P520A resist were replicatted. In this caase, B
by thet grating paatterns of hp 50 nm and hp
h 40 nm L/SS,
holee patterns ofm and hp 28
2 nm wereeo hp 35 nm
repllicated, respeectively.
In the near future, the resisst pattern rep
plication of 111
nm would be achieved byy the fabriccation of theeing pattern off hp 22 nm.
ffraction gratin
nsmission difftran

Fig. 8 H
theHole patteern replicaation byosure using thefour-luminouus-flux interference expo
w diffraction ggrating.
four-window

Fig. 9 CD-S
SEM image of 35-nm-w
width hole reesist
d (b) after the(ZEP520A) pattern (a) before andvibration impprovement.
(a)

(b)

(c)

(d)

mically ampliified negativee-tone resist
Fig. 10 CD
D-SEM imagges of the rep
plicated resistt images of thet non-chem(Inpria); (aa) hp 22.5 nm
m, (b) hp 20 nm, (c) hp 17. 5 nm, and (d) hp 15 nm.

20Kinoshita andd S. Yusa, Jpnn.
Ohnishi, S. Suzuki, H. K
J. Appl. Phy
ys. 46 (9B) (22007) 6118.
otopolym. Scii.
5. T. Watanabee and H. Kinooshita, J. Pho
Technol. 21 (2008) 777.
gh-Gasson, FF.
k, D. He, W. Li, S. Shing
6. H. H. Solak
M. Yang, P. Nealey,
N
Appll.
Cerrina, B. H. Sohn, M
Phys. Lett. 75
7 (1999) 23228.
ukushima, T.. Iguchi, HH.
uchi, Y. Fuk
7. Y. Yamagu
W
JJ.
Kinoshita T. Harada, and T. Watanabe,
Photopolym
m. Sci. Technool. 23 (2010) 681.
T
8. Y. Fukushima, Y. Yam
maguchi, T. Kimura, T.
JJ.
Harada, T. Watanabe, and H. Kinoshita,K
mer Sci. Technnol 23 (2010)) 673.
Photopolymura, Y. Kamajji,ma, N. Sakagaami, T. Kimu
9. Y. Fukushim
T
T. Iguchi, Y.
Y Yamaguchi
hi, M. Tada, T. Harada, T.
Phys. 49
9
Watanabe, anda H. Kinoshhita, Jpn. J. Appl.
A
D06.
(2010) 06GD
YY.
10. S. Hashimotto, A. Ando, M. Nibe, S. Miyamoto,M
ukuda, T. Tannaka and Y. Goemi, Nucll.
Shoji, Y. Fu
Instrum. Meethods Phys. Res., Sect. A 467 (2001)
141.
Y Fukushimaa, R. Ohnishi, T. Watanabee
11. S. Suzuki, Y.
oshita, J. Phootopolym. Scii. Technol. 21
and H. Kino
1
(2008) 435.

Fig.11 Replicate hole ressist pattern (ZZEP520A) o f hp
28 nm by thee four-luminoous-flux interrference expoosureusing the fouur-window difffraction grating.
4. Conclusioons
d in the class 100
EUV-IL exxposure tool was installedBbeamlinee inclean room at the end station of BL9
RU. The fabricationfa
processpof theNewSUBAR
and the vibration wastransmission diffraction gratinggment of the grating stage. The
reduced by tthe improvem
nterference
andtwo-luminouus-fluxintheosures using thefour-luminouus-flux interfference expo
EUV-IL expoosure tool weere used for the resist pattternreplication oof line andd space andd hole patteerns,
respectively. As results, hhp 22.5 nm, hp 20 nm, hp 17.5
nm, and hp155 nm L/S pattterns and hp 35 nm and hpp 28
nm hole patteerns were repplicated.
m can replicaated resist forr hp
As resultss, this systemo open use forr the
1X nm. Accoordingly, the EUV-IL is toevaluation oof the resoluution of thee EUV resisst to
ment for 1X nm
n in EUVL
accelerate ressist developmr
In the nearr future, for hp 11 nm resist
patternning,fabrication oof the transsmission graatings wouldd be
improved and we will reaalize evaluation of EUV reesist
for 11 nm.
Acknowledggments
G
This work was supporrt by the Grant-in-Aid
for
Research(B) (22360146),(
Scientific R
Society for the
Promotion oof Science, the Ministry
y of Educattion,
Culture, Spoorts, Science and Technollogy, Japan. And
also we wouuld like to thaank Dr. Andreew Grenville andStowers of Inpria
I
Dr. Jason S
oration for ttheir
Corpo
support to prrovide the resist materials.
References
1. H. Kinosshita, K. Kurrihara, Y. Ishiii and Y. Tori
rii, J.
Vac. Sci.. Technol. B 7 (1989) 1648
8.
2. ITRS Rooadmap 2010 update [http///www.itrs.neet/].
mmaries of thee Internationaal Symposium
3. The sum
m of
L
2
2010
Extreme Ultraviolet LithographyF
4. T. Wataanabe, Y. Fukushima,
H. Shiotanii, R.

21

Imaging of EUV-mask patterns using coherent EUV
scatterometry microscope based on coherent diffraction
imaging
Tetsuo Harada1,2, Masato Nakasuji1,2, Teruhiko Kimura1,2, Yutaka Nagata2,3, Takeo Watanabe1,2, and Hiroo
Kinoshita1,2
1 Center for EUV Lithography, Laboratory of Advanced Science and Technology for Industry, University of
Hyogo, Kamigori, Hyogo 678-1205, Japan
2 Core Research for Evolutional Science and Technology, Japan Science and Technology Agency, Kawaguchi,
Saitama 332-0012, Japan
3 Laser Technology Laboratory, RIKEN, Wako, Saitama 351-0198, Japan
Abstract
In extreme-ultraviolet (EUV) lithography, defect-free mask production is a critical issue forhigh-volume manufacturing. For mask inspection and metrology, we have developed a coherent
EUV scatterometry microscope (CSM). It is a simple lensless system. An aerial image of the mask
pattern is reconstructed with iterative calculation based on coherent diffraction imaging. Periodic
patterns, aperiodic patterns and phase structures were reconstructed well by the CSM. A defect in aline-and-space pattern was detected as a diffraction signal. The aerial image of the defect is also
reconstructed. This paper demonstrates the capability of the CSM to observe complex diffraction
amplitudes directly from the pattern and the defect.
they inspect only the top surface of themultilayer. The multilayer is sufficiently
thick at about 300 nm that small buried
structures would not propagate to thesurface.5 The multilayer could contain
printable phase defects despite having a flat
top
surface.
Thus,anactinic(at-wavelength) EUV inspection tool isrequired to investigate buried defects in themultilayer. SELETE has developed an
actinic blank inspection (ABI) tool using
Schwarzschild optics and a laboratory
source.6,7 ABI is a dark-field microscope for
specialized defect inspection of blank masks,
including detection of phase defects. As abright-field microscope, we have developed
an EUV microscope using Schwarzschild
optics and an X-ray zooming tube,8,9 whichisinstalledattheNewSUBARU
synchrotron facility. It has a high numericalaperture (NA) of 0.3 and a large field with adiameter of 50 um. This bright-fieldmicroscope observes an aerial image of apattern directly with high resolution. We
have also developed a repair method formask defects using a focused ion beam.10,11
The LBNL group has developed an actinic
imaging tool (AIT) using a Fresnel zone
plate as an optical component.12 The AIT
inspects for pattern defects and phase
defects on blank masks.13
In general, EUV exposure tools or EUV
microscopes illuminate the EUV mask,collect the diffraction from the mask, andproject an aerial image. The diffraction from

Introduction
In extreme-ultraviolet (EUV) lithography,
defect-free mask production is one of thecriticalissuesforhigh-volume
manufacturing. A mask is a master patternof a semiconductor device, and there must
be no defects on the mask. The repair of thedefect feature is also important. In EUV
lithography, the EUV mask is a reflective
type mask, which is different from thetransparent
type
mask
used
for
conventional 193 nm lithography. An EUV
mask consists of a glass substrate of
150×150 mm2 in size, a Mo/Si multilayer
and absorber patterns. A phase structuresuch as a bump or pit on the substrate, andparticles in the multilayers could beprintable as a defect. For example, ashallow structure of 1 nm on the surface ofa mask substrate causes 53 degrees of large
reflection-phase shift in =13.5 nm light,
which is the working wavelength of EUV
lithography. Also, this buried defect isprintable. The illumination of the mask is
at an oblique angle of 6 degrees in thepresent EUV scanner. This causes a
shadowing effect because of the height of
the absorber pattern, which affects the acritical dimension (CD) value and thereflection phase from the pattern with anazimuthdirection
relativetotheillumination.1
For defect inspection, ultraviolet (UV)andelectron-beam4
based
laser2,3
microscopes have been developed. However,22the mask is important for mask evaluation.
However, the aerial image contains not only
the mask information but also theproperties of the optics. To evaluate themask alone, we have developed the coherent
EUV scatterometry microscope (CSM),
which is a lensless type microscope.14-16 An
EUV mask is exposed with coherent EUV
light, and the CSM records the EUV
diffraction intensity from the pattern
directly. The diffraction intensity contains
only the amplitude information in thefrequency
space,
where
the
phase
informationismissed.
This
phaseinformation is retrieved via iterative
calculations with Fourier transforms andinverse Fourier transforms.
Thus, theCSM
observes
complexdiffraction
amplitude from the mask. The aerial imageof the mask pattern with aberration-free
optics is reconstructed by using an inverse
Fourier transform. The CSM system is very
simple,andiscomposedofacharge-coupled-device (CCD) camera, amask stage, and focusing optics, and does
not require high-precision optics, or a highprecisionalignment
system.
We
demonstrated the observation of periodic
line-and-space (L/S) and hole patterns as
aerial images. We also demonstrated a first
method of CD measurement for periodic
patterns. An actinic CD value wasestimated from the intensity of the 0th and1st diffraction orders.15 This method iscapable of CD evaluation over the wholemask area.
The image reconstruction method using
the diffraction intensity with coherent
illumination is called coherent diffraction
imaging (CDI). In 1998, Miao, et al. first
demonstrated CDI in the hard X-ray
region17 , where CDI is a powerful method
to achieve a high NA for imaging. Various
CDI algorithms have been developed inrecent years.18,19 Takahashi et al. reported ahigh resolution of less than 10 nm in three
dimensional imaging.20 In this paper, weused ptychographical CDI21 to reconstruct
an aperiodic structure in the CSM.

CSM system, respectively. A pinhole with adiameter of 5 um is exposed to thecollimated beam, which reduces the beam
diameter. Then, a concave spherical mirror
reflects the beam and a planar mirror
reflects it onto the EUV mask. The concave
mirror projects the pinhole image onto themask. The radius of the curvature of theconcave mirror is 200 mm, and the distancefrom the pinhole to the concave mirror is
200 mm, which is the same as the distancefrom the concave mirror to the mask. The
mirrors are coated with 40 pairs of Mo/Si
multilayers. Diffraction from the mask isrecorded using a back-illuminated CCD
camera (Roper Scientific MTE-2048B). Thiscamera can operate in a high-vacuum
environment. The CCD camera is cooled toa temperature of -50°C. The surface of the
CCD is placed parallel to the mask surface.
The imaging area is 27.6×27.6 mm2, whichcontains 2048×2048 arrays of imaging
pixels with an area of 13.5×13.5 um2. The
mask x-y stages can move ±75 mm by using
stepping motors to enable observation of thewhole area of the EUV mask. The minimum
step size of the stage is 100 nm. Two
Magnescale LASERSCALER noncontact
opticaltype
encoders
monitorthe
movements in the x- and y-directions. The
minimum signal step is 34.5 nm. The maskz stage can move 1.5 mm using a stepping
motor to focus the exposure light on themask.
The angle of incidence from normal is 6°
on the EUV mask, which is the same as
those of the current EUV lithographyscanners. The spatial coherence length of
the incident beam is about 90 um, as
estimated from the divergence. This issubstantially larger than the CSM-field sizeof 5 um. The distance from the mask to the
CCD camera is about 100 mm, which isequivalent to a numerical aperture of 0.14.
The estimated spatial resolution is 50 nm at
half pitch.
Figure 3 shows examples of thediffraction images of the CSM, and theirscanning electron microscope (SEM) images.
Figure 3(a) shows a diffraction image with a
176-nm L/S pattern. The center signal of
the white region is directly reflected fromthe pattern of the 0th diffraction order,
where the diffraction fringes of Fraunhofer
diffraction are recorded. The two signals
other than the center signal are diffractionsof the ±1st order. Figure 3(b) shows adiffraction image of a hole pattern with aExperiment
The CSM system has been installed at
the BL-3 beamline of the NewSUBARU
synchrotron radiation facility,22 which uses
bending magnet as a light source. Twotoroidal mirrors collimate the white light to
the CSM system. Figures 1 and 2 show aphotograph and a schematic view of the23

112-nm half pitch. The center signal of thewhite region is also directly reflected fromthe pattern of the 0th diffraction order. The
8 signals other than the center are
diffractions of horizontal, vertical anddiagonal 1st orders.
The z stage aligns the focusing positionof the pinhole image, which is the probe
using EUV coherent illumination in the
CSM system. Divergence from the pinhole isabout 3 mrad, estimated from the
Fraunhofer diffraction, and the depth offocus (DOF) of the probe is about 0.8 mm.
Thus, re-alignment of the z-axis is not
required, even when sample is moved andchanged. This long DOF is suitable forquick measurements such as the CD
metrology. In a previous paper, we reported
the evaluation results of the CD
distribution over the whole mask area
without focus alignment.15 The CD
uniformity corresponded well with that
evaluated using CD-SEM.

Fig. 3 Diffraction images from the CSM of (a) a176-nm L/S pattern, and (b) a 112-nm half
pitch hole pattern. (c) and (d) are same
patterns measured by SEM.
Image Reconstruction Algorithm
We reconstructed an aerial image of
EUV mask patterns15 from the diffraction
intensity by using a hybrid-input-output(HIO) algorithm23, which is widely used for
retrieving algorithms of missing phase
information in the hard X-ray region. In
HIO algorithms, the illumination of thesample is assumed to be a plane wave,
where a large area with a small isolated
sample is exposed. In the CSM, the probe
size of 5 um is much smaller than a sample
mask size of 150×150 mm2. Because theexposed area size is equal to the probe size,
the pattern was not illuminated with aplane wave. The diffraction includes thepattern and the probe information. However,the degraded amplitude at the outside
region of the probe made the reconstruction
error large. Although the periodic patterns
were reconstructed, aperiodic structures
were not reconstructed. A suitable method
to reconstruct the EUV mask pattern isneeded.
Ptychography21 is one of the CDI
algorithms, in which the sample isilluminated locally with position scanning.
Ptychography has been demonstrated toachieve a large field-of-view in the hard
X-ray region.24 The probe is scanned tooverlap the illumination area, anddiffractions are recorded at each probe
position. In the iterative calculations of
ptychography,
revisedamountsofFig. 1 Photograph of the CSM system.
The arrows show the light path ofsynchrotron radiation. The CCD camera
records diffraction from the EUV-mask
pattern.

Fig. 2 Schematic view of the CSM system.

24

reconstruction are weighted using the probe
amplitude. A non-uniform probe distribution
is applicable for image reconstruction. Thus,
we used ptychographical CDI in the CSM,
which consists of a small probe and a large
sample.

30 s. The elbow was scanned in 5×5
overlapping
elbow
positions.
The
illuminatedpositionwasmeasuredprecisely using the encoders. Duringexposure, we turned off the encoder toprevent detection of its laser light by the
CCD camera. If the stage drifts thermally,
the reconstructed image quality would be
degraded. In ptychography, precise controlof the probe position is crucial for highquality imaging. Thus, we also turn off thestage motor power when the stage has
halted to prevent thermal drift.
Figure 5(a) shows the reconstructed
image of the probe, and Figure 5(b) shows
the horizontal and vertical profiles. The
probe size is about 4 um at full width half
maximum. The vertical profile has a notchin the center, and the notch position
corresponded with the edge position of theelbow pattern, which indicated that thenotch was a probe reconstruction error.
There was weak amplitude around thecenter, and the asymmetric probe shape dueto the focusing optics was also wellreconstructed. For another reconstruction
result for the same probe, the notch shapeand the weak amplitude were slightly
different.
B. Image reconstruction result
Reconstructed images of the absorberpatterns using the CSM are shown in
Figure 6. Figure 6(a) is that of a 128-nm L/Spattern, which was illuminated in 5×5
points with a 1 um step. The probe exposure
time at each position was 100 s. The
periodic structure of the L/S pattern and theaperiodic structure of the angular shape are
well reconstructed. The CCD camera
recorded up to 2nd order diffraction fromthe 128 nm L/S pattern, and the phase of
not only the 1st diffraction order but also
the 2nd diffraction order was retrieved wellusing ptychography. In the pattern region,
the intensity distribution is not uniform,
and would be affected by the reconstructed
error of the probe or the scattering noise of
the focused optics. Figure 6(b) is areconstructed image of the crossed line with
2-um width. The cross shape was wellreconstructed. The non-uniformity of thepattern region was also reconstructed, andthe left line was blurred. The residual stagedrift causes these blurring errors.
Exact and reliable control of the probe is
crucial for high-quality imaging in
ptychography.26 We are developing a newstage to improve the stage precision, which

10 mFig. 4 The schematic of the elbow pattern toreconstruct the illumination probe. The
circles indicate the illumination positions.

Fig. 5(a) The reconstructed image, and (b)the horizontal and vertical profile of theprobe.

EUV Mask Sample
In ptychography, the complex amplitude
distribution of a probe is required for phaseretrieval. We reconstructed the probe with aprior pattern with a known shape andstructure. The known pattern andilluminated position are shown in Figure 4.
The pattern which was chosen toreconstruct the two-dimensional profile isan elbow with 10 um width. The gray color
region is covered with an absorber layer of
50 nm thick TaN, and the elbow is areflective region. The absorption and phaseshift were calculated with Henke’s opticalconstant25, where the shadowing effect was
ignored. The circle in Figure 4 indicates theilluminated position of the probe. The
scanning step was constant at 5 um in bothx and y directions.
The exposure time at each position was25

is composed of a pulsed-motor stage withlaser encoders and a piezo flexure stage
withstrain-gauge
sensors.
The
pulsed-motor stage moves 150 mm toobserve whole area of an EUV mask. The
optical encoder is chosen to measure longstrokes. The piezo flexure stage moves for
ptychographicalmeasurement.
Thestrain-gauge sensor is not an optical type,which could measure the position duringexposure. In near future, we intend toobserve the EUV mask by ptychographical
CDI with this new hybrid stage.
C. Phase structure reconstruction result
We observed a phase structure of bump
structures on a glass substrate. The bumps
were 5 nm in height, and 0.15×0.5 mm2 insize. The angular edge of the bump wasobserved with a scanning position of 4×4
points and step of 1.5 um. The intended
exposure time at each position was 120 s.
The observation results for intensity andthe phase images are shown in Figure 7. In
the intensity image of Figure 7(a), the edgeof the phase structure was detected as adark line due to destructive interference. In
the phase image of Figure 7(b), the phasestructure was clearly reconstructed. The
phase
difference
wasquantitatively
estimated to be 0.84 waves, which isdifferent from the calculated value of 0.74
waves by virtue of the height. Thisdifference could be caused by thickness
errors for the bump or for the multilayer
deposition. Thus, the CSM can observe thephase, which is very important for the
EUV-mask evaluation.
D. Defect reconstruction result
We also observed an amplitude defect in
the absorber patterns. Figure 8(a) shows
the SEM image of the defect, which is a line
defect in an 88-nm L/S pattern. This defectline is 30 nm narrower than the other lines.
The defect size varied from 2 nm to 40 nm,
in which the width of the line was ranging
from 44 to 86 nm. Figure 8(b) shows thediffraction image from the defect and theL/S patterns. The exposure time was 100 s.
The diffraction from the L/S pattern was
similar to that shown in Figure 3(a), anddiffraction from the defect was clearlyrecorded as a line diffraction in the lateral
direction. To decrease the shadowing effect,
the plane of incidence of the probe waschosen to be parallel to the lines. The line
diffraction has symmetrical intensity
around the 0th diffraction order, whichshows that the phase distribution of thedefect line is symmetrical. When the plane
was chosen to be perpendicular to the line,
the diffraction intensity was asymmetrical.
The diffraction phase from a defect depends
on the azimuth of the probe, and the CSM
can observe the phase effect. The defectsignal for a defect size of up to 10-nm in
width was detected at the diffraction image.
Thus, the CSM detects the defect as thedifference of the calculated diffraction
signal without reconstruction of the aerial
image. Also, this CSM inspection using thediffraction image quickly detects theexistence of defects in the field of view.
Image reconstruction is still needed todetect the defect position. Theoreticaldetection limits for the defect sizes dependon the signal-to-noise ratio of the detector
noise, the source brightness and thesubstrate
roughness.
The
substrate
roughness generates speckle noise on thesignal. If the detector noise is at imaginary
zero, then the detection limit is estimated toabout 30-nm with a current EUV mask.
Figure
8(c)
shows
the
image
reconstruction result for the line defect byptychographical CDI. The defect was
illuminated at 7×2 points with a 1 um step.
There is a bright line from the defect in the
L/S pattern. However, the periodic L/Spattern around the defect has a blurred
shape due to the noise in the image
reconstruction. We filtered out diffraction
from the periodic L/S signal andreconstructed the aerial image, as shown in
Figure 8(d). The defect was clearly detectedwithout a periodic structure. Thus, the CSM
can inspect the defect positions by using
ptychographical CDI.

Fig. 6 Reconstructed images of absorberpatterns using the CSM. (a) 128-nm L/Spattern. (b) 2-um width crossed lines.

26

Conclusions
The We have developed the CSM for
EUV mask inspection and metrology. The
CSM is an actinic and lensless typemicroscope, which records diffraction froman EUV mask directly. The EUV mask
patterns
wereobservedusing
ptychographical CDI. Ptychography is asuitable CDI method for the CSM, andconsists of a small probe and a large sample.
The aerial images of the periodic L/Sstructure and the aperiodic angular edge
structure were well reconstructed. The
amplitude and phase images of the bump onthesubstrate
werereconstructed
quantitatively. Also, a line defect with
10-nm width was detected as a diffraction
image, and the defect position was also
inspected in the reconstructed image. Thus,
it is demonstrated that the CSM canobserve complex diffraction amplitudes inthe EUV mask pattern.
In the near future, we intend to install alaboratory EUV laser source of high-orderforpractical
harmonic
generation27
inspection. The power will be 1,000 times
stronger than that of our present source,which wastes most of the light to achieve ahigh spatial coherence.

Fig. 7 Reconstructed image of the phasestructure of (a) intensity, and (b) phase
distribution.

Fig. 8 (a) SEM image and (b) diffraction
image of the 30-nm size line defect. (c)Reconstructed image, and (d) that with theperiodic signal filtered out.

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[8] K. Hamamoto, Y. Tanaka, T. Yoshizumi, N. Hosokawa, N. Sakaya, M. Hosoya, T. Shoki, T. Watanabe, H.
Kinoshita, Jpn. J. Appl. Phys. 45, 5378 (2006).
[9] K. Takase, Y. Kamaji, N. Sakagami, T. Iguchi, M. Tada, Y. Yamaguchi, Y. Fukushima, T. Harada, T.
Watanabe, H. Kinoshita, Jpn. J. Appl. Phys. 49, 06GD07 (2010).
[10] T. Amano, N. Takagi, H. Shigemura, T. Terasawa, O. Suga, K. Shiina, F. Aramaki, A. Yasaka, Y. Inazuki,
N. Hayashi, SPIE Proc. 7823, 782323 (2010).
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Gullikson, E. H. Anderson, H. Han, Proc. SPIE 6730, 67305E (2007).
[13] I. Mochi, K. A. Goldberg, B. La Fontaine, A. Tchikoulaeva, C. Holfeld, SPIE Proc. 7636, 76361A(2010).
[14] T. Harada, J. Kishimoto, T. Watanabe, H. Kinoshita, D.G. Lee, J. Vac. Sci. Technol. B 27, 3203 (2009).
[15] T. Harada, M. Nakasuji, M. Tada, Y. Nagata, T. Watanabe, H. Kinoshita, Jpn. J. Appl. Phys. 50, 06GB03(2011).
[16] T. Harada, M. Nakasuji, T. Kimura, Y. Nagata, T. Watanabe, H. Kinoshita, Proc. SPIE 8081, 80810K

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(2011).
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28

Critical Dimension Measurement of an Extreme-Ultraviolet
Mask Utilizing Coherent Extreme-Ultraviolet Scatterometry
Microscope at NewSUBARU
Tetsuo Harada1,2, Masato Nakasuji1,2, Masaki Tada1,2, Yutaka Nagata2,3, Takeo Watanabe1,2, and Hiroo
Kinoshita1,2
1 Center for EUV Lithography, Laboratory of Advanced Science and Technology for Industry, University of
Hyogo, Kamigori, Hyogo 678-1205, Japan
2 Core Research for Evolutional Science and Technology, Japan Science and Technology Agency, Kawaguchi,
Saitama 332-0012, Japan
3 Laser Technology Laboratory, RIKEN, Wako, Saitama 351-0198, Japan
Abstract
We have developed a coherent extreme ultraviolet scatterometry microscope (CSM) for actinic
inspection and metrology of an extreme ultraviolet (EUV) mask. It was installed at the BL-3
beamline of the NewSUBARU synchrotron radiation facility. The CSM is a lens-less system withno objective, and aerial images and critical dimension (CD) values are estimated using therecorded diffraction image. A method of measuring CD values by reconstruction of aerial images
using diffraction intensity has been developed. A repeatability of 0.3 nm (3) with a high precision
is achieved with the actinic method. We also evaluate the CD uniformity of the 88 nm
lines-and-spaces patterns on the finished EUV mask, which corresponds well with that obtained by
critical-dimension scanning electron microscopy (CD-SEM) results.
We have developed a coherent EUV
scatterometry microscope (CSM), which is alens-less system for actinic inspection andmetrology.7) For CSM, the mask is exposedtoacoherent
EUV
light.
A
charge-coupled-device(CCD)
camerarecords diffraction and scattering from themask directly, which contains amplitude
information in the frequency space. CD is
estimated using diffraction intensity, and an
aerial image of the pattern is reconstructedwith iterative calculation. We observed line
patterns and hole patterns, and the aerial
images of these patterns were wellreconstructed. This paper focuses on an
actinic and quick CD-measurement method
using diffraction intensity, and the resultsof evaluation of CD uniformity for thefinished EUV mask.

Introduction
In extreme ultraviolet (EUV) lithography,
the mask is of the reflective type composedof a glass substrate of 150×150 mm2 in size,a Mo/Si multilayer, and absorber patterns.
EUV mask fabrication has specific issues in
EUV lithography such as phase defects ofthe multilayer and the shadowing effect due
to the oblique illumination.1-5) Thus, EUV
inspection and metrology are required toevaluate the actinic feature of defectprintability and critical dimension (CD)values. A poor CD uniformity influences theelectric properties of semiconductor devices.
On the international technology roadmap
for semiconductors,6) the required CD
uniformity is 3.3 nm (3), and theacceptable uncertainty of CD metrology toolis 0.69 nm (3) for dense lines of the 22 nm
node. The conventional tool of CD metrology
is critical-dimension scanning electron
microscopy (CD-SEM). In the process ofmask-pattern writing by electron beamlithography (EBL), the proximity effect
could
make
the
CD
distribution
non-uniform. EBL controls exposure dose tocompensate for the effect. Thus, the CD
evaluation of the whole mask area isrequired to detect local CD errors. However,mask-pattern CDs for about 100 points aremeasured typically by CD-SEM, because
only a limited size can be observed by
CD-SEM and it takes a long time to observe
the whole mask area.

Design of the Coherent EUV Scatterometry
Microscope
The CSM system has been installed at
the BL-3 beamline of the NewSUBARU
synchrotron radiation facility,8) which
employed a bending magnet as a lightsource. Two toroidal mirrors collimate thewhite light to the CSM system. Figures 1
and 2 show a photograph and a schematic
view of the CSM system, respectively. A
pinhole with a diameter of 5 um is exposedto the collimated beam, which reduces thebeam diameter. Then, a concave sphericalmirror reflects the beam and a planar

29

mirror reflects it onto an EUV mask. The
concave mirror projects the pinhole image
onto the mask. The radius of the curvatureof the concave mirror is 160 mm, anddistance from the pinhole to the concave
mirror is 160 mm, which is the same as the
distance from the concave mirror to themask. The mirrors are coated with 40 pairsof Mo/Si multilayers. Diffractions from themask are recorded with a back-illuminated
CCD (Roper Scientific MTE-2048B) camera.
This camera can operate in a high-vacuum
environment. The CCD camera is cooled toa temperature of ±50 °C. The surface of the
CCD is placed parallel to the surface of themask. The imaging area is 27.6 × 27.6 mm2,
which contains imaging pixels of 2048×2048
arrays with an area of 13.5×13.5 m2. The
mask x-y stages can move ±75 mm throughstepping motors to enable observation of thewhole area of the EUV mask. The minimum
step size of the stage is 100 nm. Two
encoders of Magnescale LASERSCALER of
the noncontact optical type monitor the
movements in the x- and y-directions. The
minimum signal step is 34.5 nm. The maskz stage can move 1.5 mm through a
stepping motor to focus the exposure lighton the mask.
The angle of incidence on the EUV maskfrom normal is 6°, which is the same as
those of the present EUV lithographyscanners. Owing to the oblique illuminationof the exposure tools, CD includes the
shadowing effects caused by absorberpattern height. The shadowing effect causesa horizontal-vertical bias, which means a
CD value difference between horizontal andvertical line-and-space (L/S) directions.1)
Thus, CSM can evaluate actinic CD value
including the shadowing effect. The spatial
coherence length of the incident beam is 18
m, as estimated from the divergence. Thisis substantially larger than the CSM-fieldsize of 5 m. The distance from the mask to
the CCD camera is about 100 mm, which isequivalent to a numerical aperture of 0.14.
The estimated spatial resolution is 50 nm at
half pitch. Figure 3 shows an example of adiffraction image recorded using the CCD
camera. The sample was a L/S pattern witha 176 nm pitch. The center signal of thewhite region is directly reflected from thepattern of the 0th diffraction order, wherediffraction fringes of Fraunhofer diffraction
are recorded. The two signals besides thecenter are diffractions of the ±1st order.

Fig. 1 Photograph of the CSM system.
The arrows show the light path ofsynchrotron radiation. The CCD camera
records diffraction from the EUV-mask
pattern.

Fig. 2 Schematic view of the CSM system.

Fig. 3 Diffraction pattern image recorded with
the CCD camera from an L/S pattern with 176
nm pitch.
CD Analysis
We develop a method to measure the CD
value based on the scalar diffraction theory.
At the exposure tool, an EUV mask isilluminated, and diffractions from the mask
pattern are generated. The projection optics
propagates the diffractions from a mask to
the focal plane as aerial images on a wafer.
In this study, an aberration-free system is30

assumed, since the wave front error of the
projection should be very small inlithography. The imaging optics do not add
wave front error to the diffraction from themask, but filter the diffraction with thepupil. At CSM, the CCD camera records
diffraction intensity. If the phase of thediffraction is known, aerial images can becalculated. For the L/S pattern, aerial
images can be calculated using CSM data
and the phases of the diffraction orders.
For small-pitch patterns, only a few
diffraction orders make it through theimaging optics. Near the resolution limit,
only the 0th and the 1st diffraction orders
are transmitted through the imaging optics.
For imaging with the 0th and 1st diffraction
orders, an intensity profile of an aerial
image can be calculated using thediffraction intensities. The aerial image is
generated by the interference of the threediffracted waves of the 0th and ±1st orders.
The phase difference between the 0th and1st diffraction orders causes defocus, which
can be ignored at the in-focus position. The
phase difference between the +1st and -1stdiffraction orders causes defocus andposition shift of the aerial image. Thus, theintensity profile of the aerial image at the
in-focus position can be calculated by thediffraction intensities of the 0th and ±1st
diffraction orders. The 0th diffraction ordermeans the bias component of theinterference, and the 1st diffraction ordermeans the modulation component. We
describe the intensity profile of the L/Saerial image as follows:

the profile with a wide reflection area (small
CD value) has a high peak intensity. The
other profile with narrow area (large CD
value) has a low intensity.
On the wafer of the image plane, theaerial image interacts with the photoresist
to create a binary structure in ideal. The
width of the resist pattern is influenced byresist sensitivity, dose, intensity profile, andthe resist process. For simple evaluation, weapply a constant-intensity threshold to theaerial image profile, which determines theimage CD value.9) Thus, the image CD
corresponds to the reflection region as thespace width in CD-SEM results, not to the
CD value of the absorber region. For
example, the threshold is determined tomake the image CD value 88 nm for the CD
88 nm L/S pattern (L/S ratio of 1:1). The
same threshold determines the image CDwith other profiles. As shown in Fig. 4, theimage CD values are 101.3 and 74.9 nm forthe patterns that have absorber widths of
64 and 112 nm, respectively.
Aerial Image Intensity

CD value
64 nm
88 nm
112 nm

88 nm

Ith
0

2

88

176 264 352
Position (nm)

440

528

Fig. 4 Calculated intensity profiles of 88 nm
L/S patterns, which have varied absorber
widths of 64, 88, and 112 nm.

  2x 
  2x  (1)I  x   u0  u1 exp
i   u1 exp
i  .
 p 
 p 

The amplitudes of the 0th and ±1st
diffraction order are denoted as u0, u+1 and
u-1, respectively. p means the pitch of the
L/S pattern, and x means the position in theimage plane. Calculated intensity profiles of
L/S patterns with 176 nm pitch (22 nmnode) are shown in Fig. 4. The
TaN-absorber width was varied at 64 nm(black dashed line), 88 nm (black line, 1:1
L/S ratio), and 112 nm (gray line), which isequal to CD value for CD-SEM. The
diffraction intensities of these patterns arecalculated on the basis of the scalar
diffraction theory. The intensity profiles of
the aerial images shown in Fig. 4 arecalculated using eq. (1). As shown in Fig. 4,

EUV Mask Sample
The sample EUV mask is a finishedmask (Dai Nippon Printing), which is a
glass substrate with 40 periods of the Mo/Si
multilayer structure. The top layer of themultilayer is a 11-nm-thick silicon capping
layer. The absorber is composed of a
10-nm-thick CrN layer (buffer layer) and a
70-nm-thick tantalum-based layer.
Various types of L/S pattern are locatedon the mask. The L/S patterns have five L/Sratios of 1:1, 1:2, 2:1, 1:4, and 4:1.
Twenty-two types of the vertical L/S pattern,horizontal L/S pattern, wiring pattern and
bit-line pattern are located. Each pattern
type has ten pattern widths ranging from31

80 to 600 nm, which are equivalent to thepatterns on the wafer with widths from 20
to 150 nm. Therefore, the number ofpatterned areas in one region is 220. Eachpatterned area is 35×35 m2. The areas arelocated with 50 m steps. One patterngroup has seven pattern regions withvarious mask biases ranging from -12 to+12 nm. 21×21 pattern groups are locatedon the EUV mask with 6.5 mm steps. In
this study, we measured the L/S patterns
that have 88 nm hp, 1:1 ratio, and 0 nm
mask bias. The incidence plane of EUV
illumination was parallel to the L/S
direction; this configuration caused no
shadowing effect. We evaluated the image
CD uniformity of the 10×9 patterns with 13
mm steps. The distribution was alsomeasured by CD-SEM (Vistec LWM9000),
which has an average CD value of 91.9 nm
and a uniformity of 7.7 nm (3). The
magnificationwas
75,000×.
The
acceleration voltage was 1,500 V. The
number of signal integrations was 128. The
field of view was 1.9×1.9 m2. Figure 5
shows a CD-SEM image of a 88 nm L/Spattern.

than the center. Thus, the absorber width at
the center region is smaller than that at theedge, which is caused by the proximity
effectoftheEBL
process.
The
backscattering of the electrons at thepattern edge affects the center position as
the bias component, and makes the resist
width small. The radius of a uniform regionof the image CD within 0.1 nm is less than
2.5 m from the center. CSM can measure
the uniform center region of 35×35 m2 insize, since the alignment precision of thestage position is less than 1 m.
Next, we evaluated the repeatability ofimage CD. The repeatability for the 88 nm
L/S pattern was measured at the same
position 20 times. The image CD values areshown in Fig. 6 (black points). The
fluctuation is large, about 1.1 nm (3).
However, all the diffraction intensities of
the 0th and ±1st orders fluctuated at thesame ratio. Thus, the image CD fluctuationiscausedbythefluctuationofexposure-light dose. In this study, we
compensate for the dose fluctuation using
the intensity ratio of the 0th and 1st
diffraction orders. If the reflectivity of themask is uniform in the whole area, then theintensity ratio depends on the CD value
only. Image CD value can be calculatedusing intensity ratio. In practice, we
calculate diffraction intensity from the L/Spattern with various absorber widths,
which has a rectangular pattern anddesigned absorber thickness. Image CD
value is determined by comparing between
the experimental and calculated intensity
ratios. The image CD fluctuation with thedose compensation is shown in Fig. 6 (graypoints), and the repeatability is greatly
improved from 1.1 nm to 0.3 nm (3).
The exposure time dependence ofrepeatability for 20 measurements is also
shown in Fig. 7, where the time is varied
from 1 to 100 s. The repeatability is low at 2
nm (3) for 1 s, which is improved withincreasing time; 0.3 nm for 20 s and 0.13
nm for 100 s. The image CD value ismarkedly stable even for different and longexposure times. We choose 20 s forevaluating
image
CD
uniformity,
considering the balance between exposure
time and repeatability. The dark current
noise of the CCD camera is about 0.02
electrons/s/pixel, and the readout noise isabout 5.0 electrons/pixel at 100 Hz. Since
the readout noise is dominant with lessthan 250 s of exposure time, theFig. 5 CD-SEM image of an 88 nm L/S pattern.
Results and Discussion
The intensity threshold discussed in §3
is determined by a reference L/S patternthat has an almost 88 nm CD value of 1:1
L/S ratio. An aerial image is calculatedusing diffraction intensities from thereference pattern. The threshold isdetermined to make the reference image CD
value 88 nm. The exposure time was 20 s.
We determine the diffraction intensity ofeach order as the integral of CCD signalsthat distribute around the diffraction center
within ±0.5°.
First, we evaluated the image CD profile
in one pattern area of 35×35 m2. The
profile was not uniform, where the edge
region had a 4 nm larger image CD value

32

Image CD (nm)repeatability
islimitedbythesignal-to-noise ratio of exposure dose andreadout noise. Thus, the low repeatability ofthe short exposure time will be improved
using a large dose. The high-brightness
source of coherent EUV provides high-speed
and high-precision measurement of image
CD by CSM.
The results of evaluation of image CD
uniformity of the EUV mask are shown in
Fig. 8. For this measurement, we did only
position alignment to move the mask. The
gray contrast shows the image CD value.
The horizontal and the vertical axes
indicate the x and y positions of the mask,
respectively. The image CD values of theleft side region are larger than those of theright side. This distribution is almost thesame as that of CD-SEM results. To
compare with the CD-SEM results, therelationship between CSM and CD-SEM
results is shown in Fig. 9. The vertical axis
indicates the image CD value obtained by
CSM, and the horizontal axis indicates thespace width obtained by CD-SEM. Since therelationship is almost linear, CSM resultscorrespond well to CD-SEM results. The
deviation of CSM results from CD-SEM
results is approximately 1.4 nm (3), whichis comparable to the uncertainty of the
CD-SEM results in this study. The gradientof the relationship is 0.7, which means thatthe image CD is not equal to the space
width obtained by CD-SEM. Thus, CSM canevaluate the actinic CD uniformity of thewhole mask area with high speed and nocomplex alignment.
no correction
with dose correction

85.5

3: 0.3 nm

81.76 nm±0.13 nm (3)Image CD (nm)

82.5
82.0
81.5
81.0
80.5
1

10
Exposure Time (s)100Fig. 7 Repeatability of CSM at various
exposure times from 1 to 100 s. The error
bar means the three-sigma deviation fromthe average.

40

90.5
90.5
89.0
87.5
86.0
84.5
83.0
81.5
80.0

30

Y (mm)

20
10
0
-10
-20
-30
-40
-60

-40

-20
0
X (mm)

20

40

Fig. 8 Results of evaluation of image CD
uniformity for CSM. The number ofsampling points is 10 × 9, where the 88 nm
L/S patterns fabricated by the same process
are located with 13 mm steps.
92
90
CSM Image CD (nm)

86.0

83.0

88
86
84
82
80

78

80

82

84

86

88

90

92

94

85.0

SEM Space Width (nm)84.5

Fig. 9 CD value relationship measured
using CSM and by CD-SEM of the EUV
mask.

3: 1.1 nm

84.0
0

5

10
Number15

Conclusions
We have developed the coherent EUV
scatterometry microscope for actinic inspection
and metrology of the EUV mask. The CD
measurement method by estimation of theaerial image using the diffraction intensities
has been developed. A high repeatability of 0.3
nm (3) is achieved. We evaluate the CD
uniformity of the 88 nm L/S pattern, whichcorresponds well to that obtained by CD-SEM.

20

Fig. 6 CD value fluctuation measured by
CSM 20 times at the same position of an 88
nm L/S pattern, which shows repeatabilityof CSM. The two data series show
measurements with and without dosecorrection.

33

In the near future, we will install a laboratory
EUV laser source of high-order harmonic
generation (HHG) for practical inspection. The
power will be 1000 times greater than that ofour present source, which wastes most of thelight to achieve a high spatial coherence. The
target scanning time for the whole mask is lessthan 90 min.

References[1] K. Otaki: Jpn. J. Appl. Phys. 39 (2000) 6819.
[2] T. Terasawa, T. Yamane, T. Tanaka, T. Iwasaki, O. Suga, and T. Tomie: Jpn. J. Appl. Phys. 48 (2009)
06FA04.
[3] E. M. Gullikson, C. Cerjan, D. G. Stearns, P. B. Mirkarimi, and D. W. Sweeney: J. Vac. Sci. Technol. B 20
(2002) 81.
[4] K. A. Goldberg, I. Mochi, and P. Naulleau: J. Vac. Sci. Technol. B 27 (2009) 2916.
[5] Y. Kamaji, K. Takase, T. Yoshizumi, T. Sugiyama, T. Uno, T. Watanabe, and H. Kinoshita: Jpn. J. Appl.
Phys. 48 (2009) 06FA07.
[6] Semiconductor Industry Association: International Technology Roadmap for Semiconductors: 2009
Lithography (International SEMATECH, Austin, TX, 2009) .
[7] T. Harada, J. Kishimoto, T. Watanabe, H. Kinoshita, and D.G. Lee: J. Vac. Sci. Technol. B 27 (2009)3203.
[8] T. Watanabe, T. Haga, M. Niibe, and H. Kinoshita: J. Synchrotron Rad. 5 (1998) 1149.
[9] Chris Mack: Fundamental Principles of Optical Lithography (Wiley, Chichester, U.K., 2008) Chap. 3.8.

34

Fabrication of Carbon X-ray Mask for High Aspect Ratio
X-ray Diffraction Grating
Daiji Noda1, Atsushi Tokuoka1, Megumi Katori2, Yasuto Minamiyama2, and Tadashi Hattori1
1
Laboratory of Advanced Science and Technology for Industry, University of Hyogo,
2
Nanocreate Co., Ltd.
Abstract
For X-ray lithography, the accuracy of the fabricated structure depends largely on the accuracy of
the X-ray mask. Conventionally, a resin material is used for the support membrane for large area
X-ray masks. However, resin membranes have the disadvantage that they can sag after several
cycles of X-ray exposure due to the heat generated by the X-rays. Therefore, we proposed thincarbon wafers for the membrane material because carbon has an extremely small thermal
expansion coefficient. This new type of X-ray mask is very easy to process, and it is expected that
it will lead to more precise X-ray masks. We succeeded in fabricating X-ray masks with large
effective areas up to 100  100 mm2 on carbon membranes. Au, with a height of about 4 m and apitch of 5.3 m, was used as the X-ray absorber material.
Introduction
X-ray lithography technique is one of the most promising technologies for fabricating micrometer level
three-dimensional microstructures. This is used a highly directional synchrotron radiation light, which makes aprocess suitable for high accuracy, high aspect ratio microstructure fabrication. For X-ray lithography, theaccuracy of the fabricated structure depends largely on the accuracy of the X-ray mask pattern, that is, a bottom
surface and side wall configurations of structure. Since, in X-ray lithography, the radiation is highly directional,a micro-fabrication technology that produces un-tapered and high aspect ratio highly absorbent structures on a
low absorbent membrane is required.
X-ray mask generally consists of X-ray absorber, membrane and frame. An effective area of X-ray mask
should be as large as possible to improve
production efficiency and reduce cost. Here, we
focus on the membrane material. The membranematerial should have high transmittance, sincelithography requires high contrast between absorberand blank pattern. And, it is also important informing a high accuracy mask pattern. In order to
I. Seed layer deposition
having these requirements, a resin material isconventionally used for a membrane of large
effective area pattern of X-ray masks [1-2].
However, resin membrane has a great disadvantage,that is, sag due to X-ray derived heat after several
cycles of X-ray exposure. In this study, we haveproposed that carbon wafer was used as membranematerial because carbon has an extremely small
II. Resist patterningthermal expansion coefficient [3].
Fabrication of carbon X-ray mask
The conventional X-ray mask fabrication
process using Si wafer has bonding process of aframe and etching process of Si wafer because the
X-ray transmittance is not good. On the other hand,the newly X-ray mask fabrication process is very
easy, as shown in Fig. 1. The thickness of carbon
wafer was used at 200 m to ensure necessarytransmittance and strength. Therefore, thin carbon
wafer also has role of frame. Thus, bonding andetching processes was disused in conventional
fabrication process.

III. Au electroforming

CarbonFabrication of X-ray grating
X-ray radiographic imaging techniques have

Ti

Au

SU-8

Fig. 1: New fabrication process of X-ray mask.

35

been applied in many fields. Previously, we
proposed a method for X-ray phase imaging using
X-ray Talbot interferometry [4], which requires
the use of X-ray gratings with high aspect ratio
structures. Therefore, we have fabricated a new
X-ray mask on 6 inch carbon wafer having 1:1
line and space patterns at 5.3 m intervals, with
an Au absorber height of 4 m. This mask has alarge effective area of 100  100 mm2, as shownin Fig. 2.
For the deep X-ray lithography, we used
NewSUBARU, which is the synchrotron
radiation facility owned by our university.
Beamline 2 has the potential to pattern large areas
up to A4 size with highly uniform pattern
thickness. Using the newly fabricated X-ray
mask, we have fabricated microstructure patterns
with 35 m thick photoresist by X-ray
lithography technique. Figure 3 shows a pictureof an X-ray grating pattern on a 6 inch Si
substrate made using the new carbon X-ray mask.
The structure of the patterned photoresist over thewhole area is excellent.
For the X-ray diffraction grating, gold wasformed between the photoresist structure byelectroforming.

Fig. 2: Picture of carbon X-ray mask.

Conclusions
The purpose of this research was to develop
an X-ray mask to be used in the production of Xray gratings for phase tomography imaging with
an X-ray Talbot interferometer. A conventional Xray mask was fabricated using a large area resin
membrane. However, the patterned area became
warped after several X-ray exposures. As a result,
we proposed and fabricated a new X-ray maskusing a carbon wafer to serve as the support
Fig.3: Picture of resist microstructure on 6 inch wafer.
membrane. This overcame the problem of thermal
deformation during X-ray exposure that usuallyoccurs when using masks based on resin membranes.
We successfully fabricated a large area X-ray mask on a thin carbon wafer with Au lines with a pitch of 5.3
m and a height of about 4 m covering a large effective area of 100  100 mm2. Using this new carbon X-ray
mask, large area X-ray gratings were fabricated on 6-inch Si substrates.
These results give us confidence that the spatial resolution of phase tomography imaging using X-ray Talbot
interferometry can be significantly improved using gratings produced using carbon membrane-based X-ray
masks.
Acknowledgment
This research was supported by the research project “Development of Systems and Technology for
Advanced Measurement and Analysis” from the Japan Science and Technology Agency (JST).
References[1] D. Noda, M. Tanaka, K. Shimada, and T. Hattori, Jpn. J. Appl. Phys., 46, 2, pp. 849-851 (2007).
[2] D. Noda, M. Tanaka, K. Shimada, W. Yashiro, A. Momose, and T. Hattori, Microsyst. Technol., 14, 9-11, pp.
1311-1315 (2008).
[3] N. Takahashi, H. Tsujii, D. Noda, and T. Hattori, Proc. 2008 IEEE Int. Symp. Micro-Nano Mech. Human Sci.
Nagoya, Japan, pp. 414-419 (2008).
[4] A. Momose, Jpn. J. Appl. Phys., 44, 9A, pp. 6355-6367 (2005).

36

Fabrication of High Aspect Ratio Au microstructures using
Direct Electroforming on Si microstrucutures
Atsushi Tokuoka, Daiji Noda, and Tadashi Hattori
Laboratory of Advanced Science and Technology for Industry, University of Hyogo,
Abstract
Our research study combines the capabilities of Silicon deep reactive ion etching technology with
UV lithography in order to fabricate high precision X-ray masks consisting of rectangular patterns,
which cannot be achieved by UV lithography alone. Silicon deep reactive ion etching technology
using inductively coupled plasma has attracted the attention of engineers working in this field, andthis is a very effective technology for fabricating Si microstructures. We developed a fabrication
method in which metallic microstructures are fabricated by electroforming directly into grooves
etched in the Si after the sidewalls of the grooves have been coated with an insulating film. Au
electroforming was accomplished from the bottoms of grooves etched into silicon. It is expectedthat this technology can be used in the production of a wide variety of devices.
Introduction
Nanotechnology is attracting attention as a technology that will play a key role in miniaturization and theincreased sophistication of parts in the future. In particular, remarkable developments are being made in microelectro mechanical systems (MEMS) technology and this is contributing to downscaling and enhancing theperformance of various components. Silicon deep reactive ion etching (DRIE) technology using an inductively
coupled plasma (ICP) has attracted the attention of engineers working in this field [1], and this is a very effective
technology for fabricating Si microstructures as shown in Fig. 1. Our research study combines the capabilities of
Si dry etching technology with UV lithography in order to fabricate high precision X-ray masks consisting ofrectangular patterns, which cannot be
achieved by UV lithography alone. For the
study, the X-ray mask to be fabricated wasconfigured as a rectangular line-and-spacemask comprising 5.3μm pitch narrow lines[2-3].
We considered the method to fabricate
Au microstructures in grooves fabricated in
the Si substrate. In this method, the Au iselectroplated directly onto the Si. However,in that alone the Au microstructures obtained
are poor as shown in Fig. 2. This is due to thefact that electroplating takes place fromamong the bottoms, the top and the sidewalls
5.3 µm52 µmof the grooves. It is necessary thatelectroplating take place from the bottoms ofthe groove only. If Au doesn't extract it only
Fig. 1: SEM image of Si microstructures using ICP-RIE.
from the bottom of the structure, the cave canbe done in the structure, and an excellent Au
microstructure cannot be obtained as shownin Fig. 2.
New fabrication process
The new method for fabricating Au
microstructures by directly electroplating ona structured Si substrate is shown in Fig. 3.
The fabrication process consists of five steps:(1) applying resist to the Si substrate andforming a mask pattern in it using UVlithography, (2) etching grooves into thesilicon by Si dry etching using an ICP
etching system, (3) covering the Si
microstructure and the remaining resist witha polymer film, (4) removing the polymer

Fig. 2: SEM image of defective Au microstructures.

37

film from the bottoms only of the grooves byvertical anisotropic etching (5) depositing Au
in the grooves by electroplating up from thebottoms of the grooves only. This new Au
microstructure fabrication method uses thepolymer coating process normally used in the
Bosch process [4]. It is necessary that growth
take place from the bottoms of the grooves
only in order to form good quality Au
microstructures. The polymer coating forms
aninsulating
layer
that
prevents
electroplating on the sidewalls.
Fabrication of high aspect ratio structures
The grooves were fabricated to a depthof 20μm in first trial. After coating the
sidewalls with polymer film the grooves werefilled with Au to a depth of 18μm byelectroplating. A cross section of thecompleted microstructure is shown in Fig. 4.
Thus, we successfully demonstrated thefabrication of high aspect ratio Au
microstructures using the new fabrication
method. Following this, we attempted tocarry out the process on even higher aspectratio grooves. However, it was difficult toform a sufficiently good quality polymer filmon the sidewalls of the higher aspect ratio
grooves using the process used on the lower
aspect ratio grooves. We believe that changes
to the experimental conditions are needed toenable us to fabricate Au microstructures inhigher aspect ratio grooves.

Fig. 3: Fabrication process of Au microstructures.

Fig. 4: SEM image of high aspect ratio microstructures.
Conclusions
Silicon dry etching technology makes it
possible to fabricate precise high aspect
structures. If these high aspect ratio grooves can be filled with Au then it becomes feasible to fabricate astructure that can be used as an X-ray mask. The Au structures were fabricated by electroplating directly on the
Si. However, good quality Au microstructures cannot be obtained by electroplating in etched grooves since
growth takes place from both the bottoms and the sidewalls of the grooves. In order to fabricate good quality
microstructures, i.e. to completely fill the grooves with void-free Au, the sidewalls of the grooves need to be
insulating, so that growth takes place from the bottoms only.
This can be achieved by coating the sidewalls with polymer. As a result, grooves 20μm deep filled to a depthof 18μm were successfully fabricated. However, it was difficult to form a sufficiently good quality polymer filmon the sidewalls of the higher aspect ratio grooves.
From these results, we believe that changes to the electroplating conditions are needed to enable us tofabricate high-quality Au microstructures in these deeper grooves.
Acknowledgment
This research was supported by the research project “Development of Systems and Technology for
Advanced Measurement and Analysis” from the Japan Science and Technology Agency (JST).
References[1] C. K. Chung, H. C. Lu, and T. H. Jaw, Microsyst. Technol., 6, 3, pp. 106-108 (200).
[2] H. Tsujii, K. Shimada, M. Tanaka, D. Noda, and T. Hattori, J Advanced Mech. Design, Systems, Manuf., 2, 2,
pp. 246-251 (2008).
[3] D. Noda, H. Tsujii, N.Takahashi, and T. Hattori, Microsyst. Technol., 16, 8-9, pp. 1309-1313 (2010).
[4] F. Lamer, A. Schilp, K. Funk, and M. Offenberg, Techl. Digest MEMS ’99, pp. 211-216 (1999).

38

SERS Active Three Dimensional Gold Nanostructure
Fabrication for Optofluidic Device
R.Takahashi*Laboratory of Advanced Science and Technology for Industry, University of Hyogo, JAPAN*Introduction. Recently, surface enhanced Raman scattering (SERS) is attracting attention asa detection method suitable for micro region of microfluidic devices. In this study, we aimed
at in situ, label-free and high sensitivity measurement by applying SERS to detection unit of
microfluidic devices. In SERS measurement of fluidics, conventional colloid type is themainstream. Such detection method using colloid, however, has resulted in problem ofquantitativity because it is difficult to control colloidal particles in flow channel. To resolve
this problem, we have developed and demonstrated the three dimensional gold
nanostructure (Au3D).
Fabrication of Au3D. We prepared the well for construction of gold nanostructure by the way that thesilicone sheet with a 6 mm through hole was stuck on the slide glass. Approximately 18 µl of gold
nanoparticle (AuNP, 20 nm) and 1 µl of polystyrene latex beads (PS, 600 nm) dispersion liquid weremixed. 5 µl of the mixed solution was dropped into the well and dried under 75 % relative humidity.
The self-assembled three dimensional PS structure was formed by casting method of convective
self-assembly [1], where AuNPs were simultaneously accumulated in the gaps of the PS. Finally, inorder to remove PS, the self-assembly structure was soaked in dichloromethane for 5 min. Thus,
Au3D was obtained (Fig.1).
SERS measurement. At first, in situ SERS measurement was performed in the form of a batchusing Au3D and 4,4’-Bipyridine (4bpy) as the Raman active molecule as following steps:
Step 1, a measurement well was made of a clean silicone sheet with about 6 mm hole and
Au3D on the slide glass. Step 2, 30 µl of 4bpy aqueous solution was dropped into the well,and covered with a cover glass so as to prevent drying of 4bpy solution and changing of 4bpy
concentration. Step 3, 1 s irradiation of 785 nm (100 mW) laser focused on the Au3D wasstarted. As shown in Fig.2, characteristic enhanced Raman spectrum of 4bpy (1000 cm-1,
1200 cm-1, 1280 cm-1, 1600 cm-1) was observed within 1 min after dropping 4bpy. The peak of
1 nM 4bpy solution was, however, weak although it was detectable without drying nor
concentration.
Next, in situ and flow SERS measurement in microfluidic device with Au3D was performed
as shown in Fig.3. The polydimethylsiloxane (PDMS) with microchannel was set on the slide
glass where Au3D had been fabricated. The composed microfluidic device was fixed to the jig,
and 50 µl of 4bpy aqueous solution was injected by a syringe. As results, we succeeded inhighly sensitive detection of 1 nM with extreamly improved S/N ratio as shown in Fig.4.
This enhancement was estimated 10 times larger than that of batch measurement andreached over 107 compared with the normal Raman spectroscopy without Au3D. Highsensitive improvement using microfluidic device like this didn’t occur in the case of the twodimensional SERS substrate which was used in our laboratory [2]. The reason of thisexcellent result was as follows. In regard to two dimensional SERS substrate effective
thickness of gold is less than 10 nm, while Au3D thickness is about 3 µm. Since adsorption
surface area of the molecule becomes very large in being three dimensional, Au3D sterically
produces many SERS activity spots. Furthermore, as explicit decrease in the peak intensity
was not observed even by washing repeatedly as shown in Fig.5, Au3D has strongly
absorbed 4bpy molecules. Thus, it was considered Au3D enabled trapping and accumulationof coming 4bpy molecules in a flow, and as a result, the excellent SERS was achieved. We
demonstrated sufficiently that Au3D was effective for SERS measurement in microfluidic
devices.
Conclusion. We have fabricated Au3D as SERS active substrate by casting method of
convective self-assembly and demonstrated that Au3D is successful for optofluidic devices
using SERS by comparing batch measurement and flow measurement.

39

Fig.1: SEM image of Au3D. The diameter ofthe holes is about 600 nm.
Fig.2: Characteristic enhanced Raman spectraof 4bpy with different concentration (100 nM,
10 nM, 1 nM, Blank) by batch measurement.

ab

Fig.3: (a) Photo image of microfluidic device. (b) Cross section of microchannel in the
microfluidic device (a). Au3D width is 6 mm, height is about 3 µm. Slide glass thickness
is 1 mm. PDMS thickness is about 2 mm.

Fig.4: SERS spectra of 4bpy with different
concentration (10 nM, 1 nM, Blank) byflow measurement.

Fig.5: Evaluation of adsorption effect by
washing Au3D. Au3D was repeatedly
soaked in ultrapure water for 5 min after
SERS measurement of 500 nM 4bpy.

Reference[1] Y. Mori, N. Shinohara, and T. Fukuoka, in International Workshop on Nanomechanical Cantilever
Sensors 2008 (Mainz, Germany, 19 May 2008)[2] T. Fukuoka, M. Yoshida, R. Takahashi, M. Suzuki, Y. Utsumi, IEEE-NEMS W5D-3, (Kyoto, Japan, 7March 2012).

40

Fabrication of Integrated Magneto Impedance Sensor
for Medical Monitoring
Y. Yoritama1), T. Yamamoto1), T. Uchiyama2), A. Yamaguchi3), Y. Utsumi1)
1)
University of Hyogo, 2)Nagoya University, 3)Keio University
Abstract
For medical monitoring, we fabricate integrated Magneto Impedance (MI) sensor. The sensor ismagnetic sensor using skin effect. The fabricate process is complex consisting lithography
process, sputtering process and electroplating process. Therefore, we optimize the process
through repeated study of the chemical resistance of various materials and procedures, aimed atcompletion of the sensor.
effect occurs, when high-frequency current isapplied to the zero magnetostrictive amorphous
metal in which spin is arranged circumferentially.
The impedance of a thin film, having length l andwidth w, is expressed as following formulas. The
low frequency impedance corresponds to the DC
resistance, while the high frequency impedance is
proportional to the skin depth δ which is function of
the dc magnetic fields. The sensing elements
utilizing significant change in impedance due to theskin effect are easy handling devices. Our sensors
detecting only the inductance component ofimpedance, is operating based on a pickup coilmethod (Fig.1).

Introduction
In recent years, the people's concern about theirhealth is increasing under the influence of aging
society in advanced nations. It is said that humanhealth state is determined by the homeostasis of the
body. Physical changes occur pulled by external
factor will be offset by the action of the autonomic
nerve system. This means that, the human healthstate depends on the autonomic nervous system. So
if the system malfunctions, the state of the body
can’t be control. And the owner is ill. Therefore, wefabricate un-invasive healthy monitoring system
consisted by near-infrared spectroscopic device fordetection the amount of substance inside blood andintegration magnetometric sensor to measure thedynamic characteristics of human’s circulatoryorgan system as one of the function of theautonomic nervous system in same time. And the
dynamic fluctuation of the circulatory system at thetime of quiet and stress, and the characteristic ofconstant
maintenanceareinvestigatedsystematically. From the measurement results, dothe mathematical modeling of the circulatory
system response. And estimation and control of
health status will be possible by this model applied
to the signal obtained from the sensor.

Theoretical formulas.
: Space permeability,
J: Magnetic polarization,
δ:Skin depth of skin effect,
ρ: Electric resistivity,
ω: Angular frequency of current,l:Sheet length, w: Sheet width.

The Principle of MI Sensor
Our present study aims at to fabricate ultra-highsensitivity magnetic sensor for medical monitoring
system. This sensor is to be measured biomagnetic
field, and its value size is about 10 -10 ~10-13T. Thisvalue is very small than the magnetic field in theexternal environment such as geomagnetism, theminimum magnetic field like this could bemeasured by SQUID (Supercondacting Quantum
Interference Device) which is one of the mostsensitive magnetic sensors. On the other hand, MI
sensor using a magnetic impedance (MI) element
has been attracting attention for improved theresolution of up to 10 -12T in late year [1].
The change in the high frequency impedance ofvery soft ferromagnetic materials upon the action of
external dc fields, known as magneto-impedance(MI) effect, has been intensively studied formagnetic sensor applications [2]. The sensitive MI

Fig.1 Outline of MI sensor. The number of turns on
the coil was 20. The width of the Au wire is 20µm.

41currently under investigation.
In this way, we have succeeded in fabricate a novel
integrated MI sensor using UV lithography. This
integrated sensor can be applied for healthmonitoring system using the results of thismeasurement. From the standpoint of maintaining
health it can be applied in the prevention oflifestyle-related diseases. In addition, this device isalso expected to apply to measure human stress ordevelop the some industrial technology.

Fabrication of Prototype Sensor
In this study, integrated MI sensor is fabricatedusing UV lithography and succeeding packaging
method to improve productivity. In detail, we
fabricated it by building up SU-8 layers shown in
Fig.2. The sensor is in Fig.3. One side of sensor thatwas removed from the brass substrate is covered
with Kapton film for insulation. Its size is 1.5mm inlength, 1.0mm in width, and the thickness is 35μm
(Without Kapton film). Its characteristics are

Fig.2 Outline our process.
SU-8 layer thickness of one is about 70µm.
Ni-Fe plate thickness is 60nm.
Fig.3 The completed sensor.

References[1] T. Uchiyama, A. Yamaguchi, Y. Utsumi, Noise Characterization of Coil Detection Type Magnetic Field
Sensor Utilizing Pulse Excitation Amorphous Wire Magneto-Impedance Element, in J. Magn. Soc. Jpn.,
34(Japan, 2010),533-536.
[2] K. Mohri, Magnetic Sensors (Tokyo, Japan, 1998)

42

Blood separation chip for automated biological analysis
Hiroki Nose a, Kazahisa kuroda a, Masatoshi Kataoka b and Yuichi Utsumi aaLaboratory of Advanced Science and Technology for Industry, University of Hyogo,
Kamigori,Ako,Hyogo,678-1205,Japanb
Health Technology Research Center, AIST, Hayashi, Takamatsu, Kagawa 761-0395, Japane-mail: hiroki@lasti.u-hyogo.ac.jp
Abstract

We present a chip for the blood separation using centrifugal force and capillary force. We
expect that this chip can perfome overall assay with high-efficiency and significantly shorten
the analysis time by integrate our proposed 3D lab-on-a-CD. The material of the chip which isfabricated by using X-ray lithography is SU-8 and Si. Blood separation is done using
centrifugal force by spinning the chip at a frequency of 40Hz and transport to collection
chamber from separation chamber using capillary force. It is necessary for capillary force totreat surface condition. We succeed in liquid transportaion by only control spin speed.
Centrifugal force exceeds capillary force, theplasma stays in the 1st chamber. When capillary
force exceeds centrifugal force by acceleration ofspin, the plasma is transported to the next chamber.
The frequency which starts transportation of theplasma is shown below.

Introduction
The lab-on-a-CD is promising for the automationof multiple microreactor systems. Recently, highperformance immunoassay based on lab-on-a-CD
has been proposed [1]. The extraction of plasma
from whole blood is the first preparative step inmany assay protocols and major importance in
medical diagnosis [2]. We present a chip for the
extraction of blood plasma from whole blood using
centrifugal force of spin and capillary force. We
expect that this chip can be overall assay with highefficiency and significantly shorten the analysis
time by integrate our proposed 3D lab-on-a-CD [3].
Separation of the plasma from the blood cell isdone using centrifugal force by spinning the chip at
a frequency of 40Hz. Phase separation is caused ina centrifugal field by a difference in mass density.
Only plasma is transported to collection chamberfrom whole blood separation chamber by capillary
force. We designed chip show fig, 1. We expectthat proposed chip would be able to extract only
plasma from whole blood by only control spin
speed.

Experiments and Results
This preparation chip made from a photoresist
SU-8(an epoxy-negative-tone resist) and Si wafer isfabricated by using X-ray lithography. X-ray
photoresist SU-8 was applied to Si wafer and was
exposed to x-ray and the exposed resist wasdeveloped by immersing into the SU-8 developer.
Fig, 2 shows the preparation chip fabricated byusing X-ray lithography. PDMS(polydimethylsiloxane) is used as the cover to seal microchannel.
According to affect capillary force, surface
modification is important process. Contact angle ofcapillary are about 75° with normal condition. In
order to increase capillary force, we control contact
angle by the surface modification. The surface
modification was done with UV ozone cleaner. We
examined the optimum modification for capillary
force. Optimum UV irradiation time which is ideal
for liquid transportation is 7min.
We performed liquid transportation by using awater colored red (not blood) and we observed the
behaviour of liquid transportation with ahydrophilic device. Fig, 3 which shows flow
sequence in the chip was obtained by using strobe
scope system. Thus, we succeeded in transporting
the liquid to the 2nd chamber from the 1st chamber.

Capillary force
Fca=Tcosθ∙2πr
induced surface tension T and contact angle θ andbore diameter r.
Centrifugal force
Fce=ρπr2hR (2πν)2induced density of fluid mass ρ, frequency of spin ν,
the height of the rise of liquids h, and radial
position to raised liquid center position fromspinning center position R.

43

Figure 2 Photo of the fabricated chip
The microchannels are fabricated by patterning
photoresist SU-8 by x-ray lithography. The fabricatedSU-8 chip is locally hydrophilized by exposure
UV.

Figure 1 Schematic layout of blood separation
1. We inlet the whole blood to 1st chamber(separation chamber).
2. Separate plasma and blood cells by spinning chipat a frequency of 50Hz.
3. Separated blood plasma by sedimentation ofwhole blood transported to 2nd chamber(separation chamber) using capillary force.
4. Transported plasma in 2nd chamber again
separated by spinning chip as well as 1st chamber
and transport to 3rd chamber.
5. Transported plasma in 3rd chamber transported tocollection chamber using capillary force.
6. Bottom of Collection chamber is pillar form forcollection plasma using only capillary force.

44

(a)

(b)

(c)

(d)

Figure 3 The figure shows the transportation from the
1st chamber to the 2nd chamber.
We observed the behaviour of liquid transportation
with a hydrophilic device. (a) First we spun chip withhigh frequency. (b) Liquid transportation to 2nd
chamber is begun at a requency of about 25Hz. (c) The
liquid passes the top of microchannel at a frequency of
about 17Hz.(d)After the liquid passes the top, we riserotation to the high frequency. The liquid transported to
2nd chamber rapidly. Thus, the transportation from the
1st chamber to the 2nd chamber succeeded.
References
1. Design of a Compact Disk-like Platform for
Enzyme-Linked Immunosorbent Assay, S. Lai, S.
Wang, J. Luo, L. J. Lee, S. T. Yang, and M. J.
Madou, Analytical Chemistry, 76, 1832 (2004)
2. Centrufugal extraction of plasma from whole bloodon rotation disk, Stefan Haebelre, Thilo Brenner, Roland Zengerle, and Jens
Ducree, lab chip, 2006, 6, 776 -781
3. Vertical liquid transportation through capillarybundle structure using centrifugal force, Saki
Kondo, Tsukasa Azeta, Yoshiaki kita, Yuichi
Utsumi, Microsyst Technol, 2010, 16, 1577-1580

Fabrication of fluorocarbon resin micro fluidic chipfor processing of amino acid derivatization
Hideki Kido a, Hajime Mita b, and Yuichi Utsumi a
University of Hyogo, 3-1-2 Kouto, Kamigori, Ako, Hyogo, 678-1205, Japanb
Fukuoka Institute of Technology, 3-30-1 Wajiro-Higashi, Higashi-Ku, Fukuoka, 811-0295, Japana

Abstract
Polytetrafluoroethylene (PTFE) is very attractive material for various fields. But, micro fabricationof PTFE is difficult from its high stability. However, synchrotron radiation (SR) induces thescission of polymer chain of PTFE. In this study, we succeeded the fabrication of PTFE micro
fluidic chip by SR dry etching and thermal compression bonding. In the derivatization process,prevention of leaks is important to this device. Thus, we measured the liquid holding force bypressurizing of the channel while applying a load. In addition, we confirmed that breaking pressurechanges with the capillary diameter of the PTFE filter.
Introduction
Polytetrafluoroethylene (PTFE) is very attractive material for various fields, because of its chemical
resistance and heat resistance, etc. But, micro fabrication of PTFE is very difficult from its high stability.
Therefore, PTFE has never been applied to micro fluidic device. However, it is known that synchrotron
radiation (SR) induces scission of polymer chain of PTFE [1 2]. We have been fabricated PTFE
microstructures such as micro filter by dry etching using SR [3]. As a next step, we have been considering
application of PTFE micro fluidic chip for amino acid derivatization process. In this study, we succeeded in
the fabrication of PTFE micro fluidic chip by SR dry etching and thermal compression bonding. PTFE is an
ideal material for performing the derivatization process. Because, this process using some strong acid such ashydrochloric acid, and some processes such as extraction and hydrolysis require high temperature heating
operation.
Experiments and Results
Figure 1 shows the schematic diagram of amino acid derivatization device. This device consists of two
microchips, and the function of valve is performed by sliding of the chip. And it’s also includes micro filters
for filtration and hold the liquid during the heating operation. In this study, we demonstrate the fabrication of
PTFE micro fluidic chip which include two simple micro channels. The PTFE chip is fabricated by the SR
dry etching and the thermal compression bonding. In the SR dry etching, PTFE evaporates from the surface
by irradiation of high energy X-ray and leads to the etching of micro patterns. In the assembly, we bonded
PTFE substrates by the thermal compression bonding to form the PTFE micro fluidic chip. We haveconfirmed that the bond strength of this method is approximately 10 MPa (Fig. 2). Figure 3 shows theoverview of assembly of PTFE chip. This chip is formed by laminating of three PTFE substrates. Size ofPTFE chip is 1.2×20×60mm and dimensions of included channel is 600μm width and 400μm height. Figure 4
shows the fabricated PTFE micro fluidic chip, which has been filled in the channel with dye solution.
The derivatization device shown in Figure 1, upper chip has not bonded with lower chip. Therefore,
prevention of leaks is very important to this device. Thus, we measured the liquid holding force bypressurizing of the channel while applying finite load. In this experiment, we used fabricated PTFE micro
fluidic chip. Figure 5 shows the measurement result of the liquid holding force. In the derivatization process,approximately 30 kPa of liquid holding force is required for respond to pressure rise when the heating
operation. From the measurement results, we have confirmed that sufficient holding force can be obtained bymore than 15 MPa of applying load. In addition, we confirmed that breaking pressure changes with thecapillary diameter of the PTFE filter as shown in Fig. 6. This micro filter consists from the bundle ofcapillaries. This measurement was performed using fabricated PTFE micro fluidic chip.
As mentioned above, we have proposed a micro fluidic chip for amino acid derivatization process. In thisstudy, we succeeded in fabrication of PTFE micro fluidic chip. And we measured the fluid characteristic
performance in the PTFE chip.

45

Upper chip

14

Bond
strength
[MPa]
接合強度
[MPa]

Valve channel

Reagent reservoir
Sample outlet
Vapor removal filter
Compressed air inlet

12
10
8
6
4
2

Lower chip

Reaction cell

0

Sample inlet
Extraction cell0

Filtration filter

10

20

30

40

圧着荷重
[kPa][kPa]
Impressedpressure

Figure 1. Schematic diagram of amino acidderivatization device.

Figure 2. Measurement results of bond strength.

チップサイズ
Chip size
1.2×60×20 mm

Thermal compression

Figure 3. Overview of thermal compression bonding.

流路径
Channel size
0.4×0.6 mm

Figure 4. Fabricated PTFE micro fluidic chip.

10

50

Breakingpressure
[kPa]
破断圧力
[Pa]

保持圧力
[kPa] [kPa]
Holdingpressure

45
40
35
30
25
20
15
10

8

Calculated
計算値 value
Experimental
実験値 value

6
4
2

5

0

0
0

2

4

6

8

10

12

14

16

0

18

50

100

150

200

フィルター径［mm］
Capillarydiameter of thefilter [mm]

Load
[MPa]
荷重 [MPa]

Figure 5. Measurement results of holding pressure ofslide valve.

Figure 6. Measurement results of breaking pressureof PTFE micro filter.

References[1] Y.Zhang, T.Katoh, M.Washio, H.Yamada, S.Hamada, Appl.Phys.Lett.67 (1995) 872-874[2] Yuichi Utsumi, Takefumi Kishimoto, Tadashi Hattori Hirotsugu Hara, Jpn. J. Appl. Phys., 44,7B (2005)
5500-5504[3] Yoshiaki Ukita, Kazuhiro Kanda, Shinji Matsui, Mitsuyoshi Kishihara, Yuichi Utsumi, Microsyst Technol
14 (2008) 1567-1572

46

Contamination-Free Internally-Triggered

Automatic Flow Sequencing for MicrofluidicsaM. Ishizawaa*, H. Nosea, Y. Ukitab, and Y. Utsumia
Laboratory of Advanced Science and Technology for Industry, University of Hyogo, Japanb
School of Materials Science, Japan Advanced Institute of Science and Technology, Japan

Abstract
Automation of micro-scale chemical system (MicroTAS) using centrifugal microfluidics has been
intensively investigated [1-3]. Conventional valving methods using centrifugal microfluidics does
not require complex external machines, however the device requires hand operations to do
chemical process. We propose a simple liquid flow sequencing method which can carry out fully
automated chemical process by just spinning the device at constant speed.
Introduction
Automation of micro-scale chemical system (MicroTAS) has been realized using a external control
system consist of multiple components such as syringepump, pneumatic valve, reagent stock, many tubing,and computer controllers, therefore the whole system become huge and expensive and result in a problem
so-called ‘chip in a lab’. The centrifugal microfluidics realize liquid pumping with relatively simple control
system. For the automation of multistep liquid handling on a centrifugal microfluidics, microvalves havebeen studied as follows. B. S. Lee et al have proposed the wax based microvalve [1]. The operation of thevalve is realized by irradiating a laser from outside. S. Lay et al realized multi-step flow sequencing to use apassive valve that holds the liquid by surface tension, multi step flow sequencing is realized by accelerating
the disk [2]. G. Welte realized multi-step flow sequencing by combining the principle of the siphon and thecapillary action [3]. These studies report successful flow sequencing, however none of them realize low-cost,reliable, and simple automation due to the requirement of external-triggered control. This paper reports a
fluidic circuit design which realize on-chip controlling of multi-step flow sequencing on a steadily spinning
CD.
Experiments and Results
Figure 1 shows the principle of valving method, which applied in our method. Considering microfluidic
channel on a disk as shown in fig. 1(a), the liquid reservoirs, which are arranged in a radial direction on adisk and be connected with vent. When one of vent is closed as shown in fig. 1(b, c) the loaded liquid in areservoir cannot flow in the waste even the disk is spun at high speed. On the other hand, when both of thevents are opened the liquid can flow and be injected in the waste reservoir, when the disk is spun as shown infig. 1(d). In other words, by controlling the air supply to the reservoirs, can be controlled liquid flowing.
Figure 2 shows schematic illustration of designed flow sequencer. The device has two liquid stock reservoirs.
Both of them are connected to waste reservoir having air out vent, however only 1st reservoir is connected toair in vent. On the other hand, vent channel of 2nd reservoir is connected to the outlet of the 1st reservoir via
dummy reservoir. When the device is spun, the liquids will move toward to the edge of the disk due tocentrifugal force, however the liquid from 1st reservoir will flows in the venting channel of 2nd reservoir andblock the vent channel of 2nd reservoir. Because this state is same as fig. 1(b), therefore the liquid in the 2 ndreservoir cannot move and retained until the 1st reservoir become empty as shown in fig. 2(b). We observedthat the dropped pressure in 2nd reservoir aspirates liquid plug, therefore the dummy reservoir is located in
middle of the venting channel, to prevent the contamination in 2nd reservoir. The vent channel will be opened(a)2 (c). Then
when the 1st reservoir become empty, then the liquid in 2nd reservoir starts to flow as shown in fig.
finally the liquid sequencing will be completed. In this concept, the first liquid behaves like ‘clepsydra’ tocontrol the timing of injection of other reservoir(s).
To demonstrate the concept, we fabricated a device based on the design shown in fig. 2. The microchannel
structure is patterned on poly-dimethylsiloxane (PDMS) by conventional soft lithography process. ThisPDMS is attached on the spin coater. For the visualization of the flow sequencing the colorized waters (redand blue) are loaded in the reservoirs and reservoirs are sealed with flat PDMS having vent hole made withsyringe needle. The device is placed in custom-made machine and spun at constant frequency of 2000 rpm
for 10 sec. Flow image is recorded by strobe scope system. Figure 3 shows the images of flow sequencing.
As shown in the fig. 3, automatic flow sequencing at constant and high rate spinning is successfully
demonstrated. The method is expected to be effective realizing simple automated internally-triggered liquidhandling for multi-step chemical process.

47

(

(a)

(b)

(c)

Rotation
center(d)

Rotation
centerRotation
center

Air in vent
Open

Waste

Open

Waste

Waste

Spinning

Centrifugal force

Centrifugal force

Close

Liquidreservoir

Open

Liquidreservoir

Centrifugal force

Open

Waste

Air out ventTransfer channel

Liquidreservoir

Liquidreservoir

Close

Spinning

Spinning

Figure 1: Principle of valving. (a) Initial state of the liquid (liquid is loaded in the liquid reservoir) (b)liquid injection with closed air in vent (liquid does not flow due to lack of air supply from air in vent) (c)with closed air out vent (liquid does not flow due to blocking of air exit) (d) with opened vents (liquid
flows and get transported to waste reservoir)

(b)

(a)
Rotation center
Air in Vent

2nd
reservoir(c)

1streservoir

Channel opend andvent the 2nd reservoir

2nd liquid injection

1st liquid injection

Centrifugal force

Channel blockedby liquid

Air out
Vent

Before spinning

Empty

Empty

Centrifugal force

Via dummy
reservoir(d)Venting channel

Empty

Retaining liquidplug

The end of injection

Figure 2: Sequencing method (a) initial state of flow sequencing (b) 1 st liquid injection (vent channel ofthe 2nd reservoir is blocked by 1st liquid) (c) 2nd liquid injection (following 1st liquid injection) (d)sequencing completed (both reservoirs are empty)

Figure 3: (a) Initial state of spinning (both reservoirs are filled with water) (b) 1st liquid injection (air ventchannel of 2nd reservoir is blocked by 1st liquid) (c) 1st liquid injection completed and 2nd liquid injection
starts (e) during 2nd liquid injection (e) 2nd liquid injection completed
References[1] B. S. Lee et al., Lab Chip, 2009, 9, pp. 1548-1555[2] S. Lai et al., Anal. Chem., 2004, 76, pp. 1832-1837[3] G. Welte et al., Proc. of Micro TAS 2010, pp. 818-820

48Reflected Surface Acoustic Wave Actuator Using Micro
GrooveTsunemasa Saikia,b, Hikaru Tomitab, Yasuto Arisueb, Hiroo Shizukab, Koichi Okudab, Kazusuke Maenakab,
Yuichi UtsumibaHyogo Prefectural Institute of Technology, Kobe, 654-0037, Japanb
University of Hyogo, Himeji, 671-2280, Japane-mail: saiki@hyogo-kg.go.jp

Abstract
Surface acoustic wave (SAW) devices with very simple structures have attracted attention. Therefore, we studied SAW
actuators that could enable a. high efficiency microfluidic mixing chip [3].On the other hand, we considered that powdertransport is also possible by using the SAWs. However, in powder transport that is different from continuous liquid flowin channels, it is difficult to move object in directions other than one of the SAW propagation. Then, a novel SAW
actuator based on these results was designed and fabricated, and its possibility of powder transport by the SAW reflectedfrom the micro-groove was evaluated.

Introduction
The manufacturing process for each component device in a lab-on-a-chip must be simplified for multiple functional
devices to be integrated. Surface acoustic wave (SAW) devices with very simple structures have attracted attention.
Therefore, we have studied a high efficiency microfluidic chip that consists of SAW pumps, a SAW mixer, a Y-type flow
channel, and so on [1-3]. Moreover, we considered that using SAWs can not only flow liquid but also transport powder,because solid moving by the SAWs had been reported [4]. If powder can be transported, we can establish a dissolution
process consisting of powder movement, powder injection into liquid, and themselves mixing operated only by the
SAWs on one-chip. However, unlike continuously flowing liquid in a channel, spatially controlling powder transport byusing the SAWs is difficult, because the powder transport direction must be aligned with an axis direction of aninterdigital transducer (IDT) that generates the SAWs. We thus proposed and fabricated a novel SAW actuator using areflection wave from a micro groove and evaluated its ability to move powder.

Experiments and Results
Figure 1 shows our experimental setup for observing the powder movement caused by a reflected SAW actuator. In theexperiment, a function generator created 1-kHz burst waveforms consisting of 1000 cycles of 19.2-MHz sine waves, andan amplifier boosted the burst waveform voltage. When the burst waveform voltage was applied to an IDT electrode (a200-μm stripline pitch, a 5-mm aperture, and 20 stripline pairs) patterned on a piezoelectric wafer (127.8-degree
y-rotated x-propagating LiNbO3), SAWs were generated. The SAWs propagated in the perpendicular direction against
orientation flat of the wafer. The SAWs were then reflected by a micro groove (a 30-degree inclination angle, a 100-μm
depth, a 100-μm width, a 5-mm length) located 20-mm from the IDT and fabricated by cutting work. We chose thisinclination angle because the SAWs reflected by the micro groove can propagate efficiently. Note that Figure 2 shows
our other experimental results for the relationship between SAW propagation angle against orientation flat and SAWtransfer characteristic (SAW amplitude / electric power applied to IDT). Here, the SAW amplitudes were measured by alaser Doppler vibrometer. The SAWs of a 60-degree propagation angle, i.e. the reflected SAWs of a 30-degree
inclination angle, had good transfer characteristics. On the other hand, we chose this micro groove depth because we
considered that the SAW reflection ratio increases as the micro groove deepens in theory. The reflected SAWs arrived atcopper powder, which has an 8.9 specific gravity and an average particle about 10-μm in diameter. The powder was thenenergized by the reflected SAWs and moved to the upper stream of the SAWs, i.e. the micro groove, as shown in thephotographs taken using a high-definition camera in Figure 3. Here, the electric power applied to the IDT was about
1.7-W. This fact reveals that the reflected SAW actuator can transport the powder. Moreover, to investigate the powder
moved by transmitted SAWs, we also carried out another powder movement experiment for different a micro grove
shape (a 15-deg. inclination angle, a 10-μm depth). Figure 4 shows photographs of powder moved by transmitted SAW.
These results reveal that not only reflected but also transmitted SAWs can transport the powder.
The above mentioned facts prove that the powder transport using the reflected and transmitted SAWs can be controlled
by adjusting the inclination angle and depth of the micro groove. In our future work, we will develop high-performancereflected and transmitted SAW actuators by using multiple micro grooves in order to fabricate lab-on-a-chips forsynthesis and analysis including the dissolution process.

49

Function
generator

Distance
L

AmplifierIncl ination anglePerpendicular
direction

Power
meter

Incident SAW


Micro
grooveReflecti ve SAW

IDT

Powder

Amplitude / Applied electric power [nm/W ]Orientation flatdi rection50
SAW prop agation
direction

40
30
20

LiNbO 3 wafer(1 28 deg. y-rotated
x-p ropag ating)

Propagation
an gle 

IDT

Orientation flat

1000

10 20 30 40 50 60 70 80 90
Propagation angle  [degrees]

Figure 2. Relationship between SAW
Figure 1. Experimental setup for
propagation angle against orientation flat
observing powder moved by reflected
and SAW amplitude / electric power
SAW actuator.

Incident
SAW

PowderMicrogroovePowderMovingIncident
SAW

MovingMicrogroove5mm(a) t = 0s

5mm(a) t = 0s(b ) t = 30s(b) t = 2s

Figure 3. Photographs of powder moved Figure 4. Photographs of powder moved
by reflected SAW.
by transmitted SAW.
References[1] Y. Utsumi, T. Saiki and K. Okada, “Proposal of a Novel Continuous Flow Pumping Operated by Surface Acoustic
Wave,” 12th International Conference on Miniaturized Systems for Chemistry and Life Sciences (μTAS2008), 715(2008).
[2] T. Saiki, K. Okada and Y. Utsumi, “Micro Liquid Rotor Operated by Surface-acoustic-wave”, Micro System
Technology, Vol.16, pp.1589-1594 (2010).
[3] T. Saiki, K. Okada and Y. Utsumi, “High Efficiency Mixing and Pumping of Continuous Liquid Flow using
Surface-Acoustic-Wave”, 13th International Conference on Miniaturized Systems for Chemistry and Life Sciences(µTAS2009), 58 (2009).
[4] M. Kurosawa, M. Takahashi and T. Higuchi, “Ultrasonic Linear Motor Using Surface Acoustic Waves”, IEEE
Transactions on Ultrasonics, Ferroelectronics, and Frequency Control, 43, 901 (1996).

50

Damage Analysis of n-GaN Etched with He and N2 Plasmas
Masahito Niibe1, Takuya Kotaka1, Retsuo Kawakami2, Yoshitaka Nakano3, and Takashi Mukai4
1
Univ. Hyogo, 2Univ. Tokushima, 3Chubu Univ., 4Nichia Co.

Abstract
To understand the details of etching-induced damage on a GaN surface, n-GaN crystals were
plasma-etched with He and N2 gases. The etched surfaces were analyzed by XPS and soft X-ray
absorption spectroscopy (XAS) methods. The shape of the near-edge absorption fine structure(NEXAFS) of the N-K edge deformed with increasing gas pressure and processing time. The
deformation can be explained by the increase of the band widths of a number of peaks constructing
the NEXAFS spectra due to the increase of structural disorder in the crystal. The increase in band
widths for the surface etched with N2 plasma was larger than that for the surface etched with He
plasma.
Introduction
GaN-based semiconductors are widely applied to photoemission devices or high-frequency power electronics
devices because of their excellent characteristic features. To further improve the performance of these devices, it
is highly desirable to develop plasma-etching processes that are damage-free. However, control ofplasma-etching damage is currently insufficient because of the complicated relationships between the
non-equilibrium plasma behavior and reactions on the semiconductor surfaces in plasma processes.
To understand the mechanism of defect creation by physical etching, we have etched n-GaN crystals using acapacitively coupled radio frequency (RF) plasma reactor with rare gases of Ar, Kr, or Xe and evaluated various
characteristics, such as the surface morphology, surface composition, and electronic properties [1]. Helium (He)is a rare gas with very light mass; it is expected to have a much larger preferential etching ratio than other raregases for the two constructing atoms, Ga and N, in a GaN binary alloy. On the other hand, N2 has the capability
to compensate for the composition deviation induced by preferential etching because it contains the component
element of GaN crystal. In this paper, n-GaN crystals were plasma-etched with He and N2 gases, and theirsurfaces were analyzed from the viewpoint of structural disordering. The result of nitrogen-K near edge X-ray
absorption fine structure (NEXAFS) spectroscopy [2] is reported.
Experiments
Plasma etching of n-GaN crystals was carried out using a capacitively coupled RF plasma reactor with anunbalanced electrode structure at the constant self-bias voltage of -200 V. He and N2 gases were used as theplasma source gas. GaN samples were Si-doped GaN crystals grown on a sapphire substrate with 4 μm thickness
by the metal-organic chemical vapor deposition (MOCVD) method (n-GaN, Nichia Co.). The etching gas
pressure was changed in the range of 10 – 100 mTorr with the processing time changing up to 200 min. The
etching rates for He and N2 plasmas were 0.77 and 0.36 nm/min at gas pressure of 10 mTorr and 0.59 and 0.17
nm/min at 50 mTorr, respectively.
The composition change in the plasma-etched GaN surface was evaluated by the X-ray photoelectron
spectroscopy (XPS) method (Shimadzu, ESCA-1000). The N/Ga ratio on the surface was determined by the
integrated intensities of N1s and Ga3s peaks. The relative composition deviation was calculated with an N/Ga
ratio of the as-grown sample equaling one.
NEXAFS spectroscopy at nitrogen K-edge soft X-ray absorption (~400 eV) was conducted for analyzing theetching damage. The NEXAFS measurement was carried out at the analyzing station of beamline 9 at the
NewSUBARU synchrotron radiation facility. The measurement was carried out using the total electron yield(TEY) method in a sample current mode and the total fluorescence yield (TFY) method [3], which included
measuring the amount of fluorescence with an Al-coated photodiode to avoid yellow-band (secondary) emission.
TEY and TFY measurements were carried out simultaneously for the same sample at the same position. It is wellknown that the TEY method can yield information in a shallow region from the sample surface because of thesmall escape length of photo-generated electrons of less than about 5 nm [2]. Meanwhile, the TFY method canyield information of a deeper region (bulk) of a sample of more than 100 nm [3] because of the much longer
penetration depth of soft X-ray photons.
Results
Figure 1 shows the typical NEXAFS spectra at the N-K edge of n-GaN crystals etched with N2 plasma. Figure1(a) shows the gas pressure dependence of the spectral changes in NEXAFS at the processing time of 100 min
obtained by the TEY method. The spectrum of the as-grown sample agrees well with that previously reported for51

wurtzite-type crystal [4]. According to Katsikini et al. [4], thecomplicated absorption shape at a photon energy of 400 –414 eV can be explained by the superposition of six Gaussian
peaks, i.e., G1- G6 as indicated in Fig. 1(a).
As shown in Fig. 1(a), the complicated peak shape becamesmoother or blunter with increasing N2 gas pressure from 10
to 100 mTorr. The same tendency was observed withincreasing processing time from 5 to 200 min. This isbecause of the increases in defect density as well as theamorphous-like structures at the crystal surface withincreasing gas pressure or processing time.
Deenapanray et al. reported [5] that new pre-edge andpost-edge absorption peaks called RL1 and RL2 wereobserved in the NEXAFS spectra by high-energy Ar ion
bombardment of 0.4 – 2.5 keV on a GaN surface. After the
analysis by Katsikini et al. [6], these new peaks wereassigned to the absorption of N atoms at the interstitial sitefor RL1 and to that of the nitrogen molecules in the crystal
for RL2, respectively. However, in this study, the appearanceof a remarkable peak corresponding to RL1 or RL2 was notobserved even in the most damaged sample etched at 100
mTorr and 200 min.
The NEXAFS spectra of the nitrogen K-edge of n-GaN
crystals etched with N2 plasma measured by the TFY(fluorescence) method are shown in Fig. 1(b). As adistinctive result different from the TEY measurement shownin Fig. 1(a), almost no change in the NEXAFS spectra
depending on the processing time was observed for the
spectra obtained by the TFY method even though themeasurements were carried out for the same samples. This
result is related to the fact that the TFY measurement is a
Fig.1 NEXAFS spectra of nitrogen K-edge ofbulk-sensitive method. Namely, the etching damage detected
n-GaN crystals etched with N2 plasma obtained byby the TEY method in this study could be restricted only in(a):TEY and (b):TFY method at the angle ofshallow regions of less than about 5 nm from the surface [3].
incidence of 90° from the surface.
Furthermore, in regions deeper than 5 nm, a rigid crystalline
structure could be maintained containing light defects in the etched n-GaN crystal. The result of particle model(PIS) calculation indicates that the thickness of heavily damaged layer (N/Ga ratio is not equal to one) is about 5– 6 nm. The above result agrees well with the PIS calculation.
Figure 2 shows the NEXAFS spectra of the nitrogen K-edge of n-GaN samples etched with He plasma
obtained by the TEY method. Figure 2 represents normalized data at the G2 (the highest) peaks. The N-K
absorption intensity decreased with increasing gas pressure. The result indicates that the surface density ofnitrogen atoms decreases because of the preferential etchingof nitrogen atoms on the GaN crystal. On the other hand, thedegree of peak shape smoothening in He-etched samples wasmuch smaller than that in the N2-etched one, althoughblunting of the peak shape was certainly observed. These
results can be mainly attributed to the difference of theelastic energy transfer ratios by the collision of the He+ andN2+ ions in plasma to the GaN solid surface.
References[1] M. Niibe et al.: Phys. Status Solidi, C8 (2011) 435.
[2] J. Stohr, ‘NEXAFS Spectroscopy’ Springer, Berlin (2003).
[3] T. Kotaka and M. Niibe: Adv. X-ray Chem. Analysis, 43(2012) 175.
[4] M. Katsikini et al.: J. Appl. Phys., 83 (1998) 1437.
[5] P. N. K. Deenapanray et al.: Appl. Phys. Lett., 83, (2003)
4948.
[6] M. Katsikini et al.: J. Phys. Conf. Series, 190 (2009)
012065.

52

Fig.2 NEXAFS spectra of nitrogen K-edge ofn-GaN crystals etched with He plasma obtained by
the TEY method.

Investigation of analyzing depth of N-K absorption spectra
measured using TEY and TFY methods
Takuya Kotaka, Masahito Niibe, and Tohru Mitamura
LASTI, University of Hyogo

Abstract
In order to investigate the analyzing depth of N-K absorption spectra measured using the TEY and
TFY methods, the spectra of Si3N4 crystals covered with Cr thin films were measured. The
thicknesses of Cr films were 1 – 100 nm. The N-K absorption intensity of Si3N4 measured using
the TEY method was observed at Cr thickness of less than 3 nm, while that measured with the TFY
method was observed for more than 100 nm. The decrease in the TFY peak intensity was explainedby the transmittance of Cr film.
Introduction
In near edge X-ray absorption fine structure (NEXAFS) spectroscopy at soft X-ray region, the total electron
yield (TEY) method with the sample current mode is widely used because it can be obtained using relatively
simple equipment. The partial electron yield (PEY) method is also often used to examine photoelectron yields
with a simple energy discrimination detector. However, because the escape depth of an electron in solids is abouta few to a few tens angstrom [1], information obtained by TEY or PEY is restricted in a sample surface. To
obtain information from sample bulk, the total fluorescence yield (TFY) method is employed with detection offluorescent X-rays that can penetrate from deeper region of the sample.
Although, the energy dependence of the typical mean free path of an electron [2] or the X-ray penetration
depth [3] in solids has been already reported, such data are rather distributed, and, therefore, precise informationof analyzing depth for individual energy and material is insufficient. In this paper, we propose a convenientmethod to investigate the analyzing depth of the TEY and TFY methods for individual photon energy.
Absorption intensity at the N-K edge (~400 eV) of Si3N4 crystals covered with Cr thin film was obtained by the
TEY and TFY methods. A photodiode was used as a fluorescence X-ray detector for the TFY measurement; thisdetector had wide energy range of sensitivity, including visible lights, but was very simple to use. The analyzing
depth at the N-K edge for both methods was evaluated.
Experiments
The sample used to investigate the analyzing depth was Si3N4
crystal grown on a Si wafer with thickness of 200 nm (NTT-AT
Co.). A part of the Si3N4 sample was covered with Cr thin filmsof thickness ranging from 1 to 100 nm, which was deposited bymagnetron sputtering. Cr was not coated on the entire surface
because, to compensate for an absorption intensity difference
arising from the surface state difference of the individual
samples (about 5%), the N-K absorption intensity was
normalized with the intensity of the non–coated area. Cr is asuitable material for uniformly covering the Si3N4 surface
Fig. 1 Photodiode detector. The
because Cr film is less likely to island-grow [4]. The thicknesses
electrode leads were covered with an Alof Cr films were controlled with the deposition time because theplate.
deposition rate of the sputtering system was very stable.
NEXAFS spectroscopy at the N-K edge was carried out at
the end station of the beamline BL9A in the NewSUBARU SR facility at the University of Hyogo [5]. The
measurements were carried out using the TEY and TFY methods. The TEY measurement was conducted withmonochromated soft X-rays incident on the Cr thin film, and the amount of secondary electrons emitted from the
Si3N4 layer underneath was detected by means of the sample current mode.
The TFY measurement was conducted by detecting the fluorescence emitted from the Si3N4 layer underneaththe Cr thin film. The X-ray detector used for TFY method was a photodiode (AXUV-100, IRD), which wasplaced at the angle of 30° from the sample normal and a distance of 3 cm. To prevent the inflow of secondary
electrons from a sample into the electrodes, the surrounding of electrode leads were covered with Al plate, as

53

shown in Fig.1. Because electrons flow into the acceptance surface of the photodiode run down to the earth
trough a cathode lead, they are not detected by a pico-ammeter inserted in the anode lead. The photodiode,whose acceptance surface was coated with Al thin film of 40 nm thickness, was used to prevent the influence of
secondary emission of visible light.
(a)Absorption intensity [a.u.]

0.8

0.6

Si3N4

0.4

0.2

1 nm

0.0

4 nm

2 nm

390

400

410

420

3 nm

430

440

Photon energy [eV]

0.10
(b)
0.08

Absorption intensity [a.u.]

Results and discussion
Figure 2 shows the N-K absorption spectra of Si3N4 crystal
covered with Cr thin film of various thicknesses measured using the(a): TEY and (b): TFY methods. In Fig. 2(a), the spectra of thesamples covered with Cr thicknesses of 0 – 4 nm are shown. Thereis no change in spectra for the sample with Cr thickness greater than
4 nm. The peak intensity near 405 eV originated from Si3N4 crystal
decreased with increasing Cr thickness and was observed to a Cr
thickness of 2 nm. A slight peak was detected for the Cr thickness of
3 nm, and none was detected at 4 nm. Another peak near 400 eV
was observed for the samples with Cr thickness greater than 3 nm.
Because the peak was observed only at the Cr-deposited part, the400 eV peak must arise from a native chromium nitride film. From
the result above, the N-K absorption spectra obtained by the TEY
method reflected the information at a shallow region of less thanabout 3 nm from the surface. An electron mean free path in solids at
400 eV is about 1 nm as previously reported [1,2]. Therefore, theanalysing depth obtained by the TEY method in this study can bealmost explained with the electron mean free path.
As shown in Fig. 2(b), the peak intensity near 405 eV measured
with the TFY method decreased with increasing Cr thickness.
However, it was detected even from the sample with Cr thickness of
100 nm with an intensity of about 30% of that detected at the
non-coated Si3N4 surface. From the result above, the N-K absorption
spectra obtained by the TFY method was found to reflect the
information from the sample bulk, and the amount of contribution
from a region of a few nm depth from the surface was relatively
small.
Figure 3 shows the thickness dependence of the peak intensity
near 405 eV calculated with the transmission coefficient of Cr film

Si3N4
1 nm
5 nm
10 nm

0.06

20 nm
0.04

50 nm
70 nm

0.02

100 nm

0.00
390

400

410

420

430

440

Photon energy [eV]Fig. 2 N-K absorption spectra of Si3N4
crystal covered with Cr thin film ofvarious thicknesses measured using the(a): TEY and (b): TFY methods.

[3] and the peak intensity measured using the TFY method.
According to a previous report [6], the N-K fluorescent photon
energy of Si3N4 is mainly about 393 eV. Therefore, thetransmission coefficient was calculated with incident photon
energy of 405 eV and with output photon energy of 393 eV. The
angle of output light (30°) was also considered to calculate thelight path length. The experimental intensity agrees well with thecalculated value for various Cr thickness samples. Therefore, thepeak intensity obtained by the TFY method can be explained
almost fully by the absorption of the upper Cr layer.
Fig. 3 Thickness dependence of peakAcknowledgements
intensity at 405 eV of N-K edge of Si3N4
The authors express their thanks Dr. H. Takenaka at NTT-AT Co.
covered with Cr film measured with thefor providing a SiN wafer for sample material.
TFY method (circle) and calculated
Referenceswith transmittance of Cr film (line).
[1] J. Stohr: “NEXAFS Spectroscopy” Springer Berlin, (2003)
p.123.
[2] I, Lindau and W.E. Spicer: J. Electron Spectrosc. 3, 409 (1974). C.J. Powell: Surf. Sci. 44, 29 (1974).
[3] http://www.cxro.lbl.gov/.
[4] M. Niibe et al.: Rev. Laser Engineer. 24, 48 (1996).
[5] M. Niibe et al.: AIP Conf. Proc. No.705 (AIP, New York, 2004) p.576.
[6] G. Wiech and A. Simunek: Phys. Rev. B 49, 5398 (1994).

54

Characterization of Electronic States of Ion-irradiatedMulti-walled Carbon Nanotubes and Multi-layer Graphenes using
Soft X-ray Absorption Spectroscopy
S. Honda1,7, Y. Nosho1,7, A. Tsukagoshi1,7, M. Niibe2, and M. Terasawa2,71
Univ. of Hyogo, 2LASTI Univ. of Hyogo
R. Hirase3, H. Yoshioka3, and H. Izumi3
3
Hyogo Pref. Inst. of Tech.
K.-Y. Lee4
4
National Taiwan Univ. of Sci. and Tech.
K. Niwase55
Hyogo Univ. of Teacher Education
E. Taguchi6
6
Research Center for Ultra-High Voltage Electron Microscopy, Osaka Univ.
M. Oura7
7
RIKEN SPring-8 Center
Abstract
Low energy Ar ions (0.5 - 5 keV) were irradiated to vertically aligned multi-walled carbon nanotube(MWCNT) films and multi-layer graphene films. The electronic states and structural properties of theirradiated MWCNT films and graphene films were characterized by x-ray absorption spectroscopy (XAS)
and Raman spectroscopy, respectively. It was found that strong dependence of the intensity of π∗ peak on theincident angle of soft x-ray (α) was observed, not for the MWCNT films as-prepared. This should be due tohighly oriented orbitals of π∗ of multi-layer graphene films as-prepared. On the other hand, after the Ar ion
irradiation to the graphene films, with increasing the ion accelerated energy and dose, dependence of heightof π∗ peak on the incident angle (α) is changed. This implies degradation of the alignment of layers of themulti-layer graphene films induced by the irradiation.
Introduction
Nanostructured carbon materials such ascarbon nanotubes (CNTs)[1] and graphenes[2]have been extensively studied toward realizationof potential nanodevice applications. Irradiationof nanostructured carbon materials with energetic
particles is thought to modify their structure andproperties, and are applied to process of
nanodevice fabrication[3,4]. It was reported thatspatially localized Ar ion irradiation of individual
MWCNTs deposited on SiO2 substrates was used
for fabrication of quantum dots[5]. Moreover, Ar
ion irradiation of MWCNTs enhanced thefield-emission properties due to defects
introduced by the ion irradiation[6]. Several
analytical techniques can be used to characterize
irradiated nanostructured carbon materials.
Especially, XAS can characterize defects in
MWCNTs introduced by the irradiation. Since
XAS gives information on the density of states, it
is a powerful tool to characterize change of thelocal electronic states of target materials[7,8]. In
this study, 0.5 - 5 keV Ar ions were used toirradiate the vertically aligned MWCNT films andmulti-layer graphene films, and their electronic
states and structural properties were characterized
by XAS and Raman spectroscopy, respectively. In
addition, scanning electron microscopy (SEM)
and transmission electron microscopy (TEM)(a)

GIntensity (a.u.)

(b)

2D

1200

1600
2000
2400
Raman Shift (cm-1)

2800

Fig. 1. (a) TEM image of a MWCNT. The inset of(a) shows selected area electron-diffraction pattern.
(b) Typical Raman spectrum of multi-layer graphenefilms.
55

デ タ

were utilized to characterize structural propertiesof the MWCNT films and the multi-layer
graphene films.

(a) π∗

Intensity (a.u.)

Experiments and Results
Vertically aligned MWCNT films andmulti-layer graphene films were synthesized bythermal catalytic chemical vapor deposition.
Figure 1(a) shows a transmission electron
microscopy (TEM) image of the MWCNT. The
inset of Fig. 1(a) shows a selected area
electron-diffraction pattern of the MWCNT. The
average length and the diameter of MWCNTs
were 160 µm and 23 nm, respectively. We
employed electron cyclotron resonance ion source(Pantechnik, Nanogan) at SPring-8 BL17SU[9] toirradiate the MWCNT films at room temperature(RT) with Ar ions. The incident energy ranged
from 0.5 to 5 keV and the dose varied between
1×1013 and 1×1017 cm-2. Micro-Raman spectra
were taken with Ar ion laser (514.5 nm) using a
Raman spectroscope (JASCO, NRS-2100). Figure1(b) shows a typical Raman spectrum of
as-prepared multilayer graphene films. In the
spectrum, G peak (∼1580 cm-1) and 2D peak(∼2700 cm-1) are clearly seen. Number of layersof graphene films used in this study was estimatedto be 3 to 5 from 2D peak position and shape ofRaman spectra of graphene films as-prepared. The
carbon K-edge XAS measurement was performed
using BL09 of the 1.5 GeV synchrotron radiation
source NewSUBARU at the University of
Hyogo[10]. The total electron yield method wasused for the measurement.
XAS spectra of vertically aligned MWCNT
films as-prepared are shown at in Fig. 2(a). The
spectra were measured at different angles ofincident soft x-ray to the substrate surface (α),
and normalized to their intensity at ∼320 eV. In all
the spectra, π∗ peak at 285 eV and σ∗ peak at 292
eV are clearly seen. Both the peaks relate to
sp2-hybridized carbon (sp2-C) atoms. One shouldnote that the intensity of π∗ peak does not strongly
depend on the incident angle (α). This should be
due to a wavy form of the MWCNTs with anaveraged orientation perpendicular to thesubstrate surface. Figure 2(b) shows XAS spectraof multi-layer graphene films as-prepared. Strong
dependence of the intensity of π∗ peak on theincident angle (α) was observed, not for verticallyaligned MWCNT films as-prepared. This should
be due to highly oriented orbitals of π∗. On theother hand, after the Ar ion irradiation to thegraphene films, with increasing the ion
accelerated energy and dose, dependence ofheight of π∗ peak on the incident angle (α) ischanged. This implies degradation of thealignment of layers of the multi-layer graphenefilms induced by the irradiation.

σ

∗

α=45°
α=60°
α=75°
α=90°
280

285 290 295 300 305
Energy (eV)310

315 320デ タ

σ∗Intensity (a.u.)(b) π∗

α=45°
α=60°
α=75°
α=90°
280

285 290 295 300 305
Energy (eV)310

315 320

Fig.2. XAS spectra of (a) vertically aligned
MWCNT films and (b) multi-layer graphenefilms at different angles of incident soft x-ray.

References[1] S. Iijima, Nature 354, 56 (1991).
[2] K. S. Novoselov et al., Science 306, 666 (2004).
[3] A. V. Krasheninnikov and F. Banhart, Nature
Mater. 6, 723 (2007).
[4] A. V. Krasheninnikov and K. Nordlund, J. Appl.
Phys. 107, 071301 (2010).
[5] M. Suzuki et al., Appl. Phys. Lett. 81, 2273
(2002).
[6] D. -H. Kim et al., Chem. Phys. Lett. 378, 232(2003).
[7] J. Schiessling et al., J. Phys.: Condens. Matter.
15, 6563 (2003).
[8] T. Hemraj-Benny et al., Small 2, 26 (2006).
[9] M. Oura et al., J. Synchrotron Rad. 5, 1058
(1998).
[10] M. Niibe et al., AIP Conf. Proc. 705, 576(2004).

56

Electronic structure of fluorinated diamond-like carbon
thin films as a function of annealing temperature using
photoelectron spectroscopy
Yuichi Haruyama, Yuji Kang, Makoto Okada, and Shinji Matsui
Laboratory of Advanced Science and Technology for Industry, University of Hyogo
Abstract
The electronic structure of fluorinated diamond-like carbon (F-DLC) thin films was investigatedby the photoelectron spectroscopy. The photon energy dependence of the photoelectron spectrain the valence band region was measured from 70 to 420 eV and the orbital components of thephotoelectron spectra in the valence band region were clarified. In addition, the chemicalcomposition of the F-DLC thin films as a function of the annealing temperature were determinedby the measurements of photoelectron spectra in the F 1s and C 1s core-levels. Based on the
results of the photoelectron spectroscopy measurements as a function of the annealing temperature,
the electronic structure of the F-DLC thin films is discussed.
Introduction
The study of diamond-like carbon (DLC) thin films has attracted much attention for wide applications
because of the films’ interesting properties, such as low friction coefficient, high hardness, and chemical
inertness [1]. Since doping the fluorine into DLC thin films reduces the surface free energy, the fluorinateddiamond-like carbon (F-DLC) thin films have an additional property such as high detachability, as well as
high hardness and chemical inertness. In the field of nanoimprint lithography, F-DLC thin films have beenused as an anti-sticking layer of nanoimprint mold, for example [2]. In the previous study, the hardness andthe contact angles of a water drop in the F-DLC thin films were evaluated. In addition, the chemicalcomposition and components of the F-DLC thin films were also evaluated by the measurements of X-ray
photoelectron spectrum. However, it was pointed out that the thermal stability in the F-DLC thin films waschanged, depending on the temperature. Although the temperature of the F-DLC thin films is one of thecritical parameters to control their property, the annealing effect on the F-DLC thin films has not been fully
understood at present. Therefore, it is important to clarify the electronic structures such as the chemicalcomposition and components on the F-DLC thin films as a function of the annealing temperature.
Experiments and Results
All photoelectron measurements were performed on a BL7B end station at the NewSUBARU facility,
University of Hyogo. The photoelectron spectra were measured in an analysis chamber mounted with ahemispherical electrostatic spectrometer (VSW Ltd, CL150). The synchrotron radiation with h between 70
and 420 eV and the Mg K line (h = 1253.6 eV) were used as the excitation source and were incident at 45°
with respect to the surface normal. The total energy resolutions were about 0.7 eV for the C 1s core-level
regions. Gold films evaporated on copper sample holders and F-DLC films were used for the Fermi levelmeasurements and the total energy resolution reference. The F-DLC thin films were formed on the Si wafers
using the RF plasma methods with the RF frequency of 13.56 MHz. he trifluoromethane gas was usedduring the deposition of the F-DLC thin films. The thickness of F-DLC films was ~0.3 µm. The F-DLC films
were exposed once in air and led to the photoelectron analysis chamber for photoelectron measurements.
Sample annealing was performed in the sample preparation chamber, which was connected to thephotoelectron analysis chamber via a manual valve. The F-DLC films were annealed from RT up to 700 °C
with the electron bombardment behind the sample and the annealing temperature of the F-DLC films wasmeasured with the thermocouple.
Fig. 1(a) shows the photoelectron spectra of the valence band region in F-DLC thin films as a function ofh. Five peaks at ~36, ~20, ~16, ~12, and ~7 eV were observed at h = 70 eV. Two peaks at ~16 and ~12eV were larger than three peaks at ~36, ~20, and ~7 eV. With increasing hfrom 70 to 420 eV, the intensityof two peaks at ~36 and ~20 eV increased gradually while the intensity of the peak at ~7 eV decreased.
According to Yeh and Lindau, the photoionization cross section of the F 2p state at h = 70 eV is larger thanthat of the C 2s, C 2p, and F 2s states. Therefore, two peaks at ~16 and ~12 eV are predominantly derived
from the F 2p state. With increasing h, the photoionization cross section of the C 2s and F 2s states
increased gradually as compared to that of the F 2p state. At h = 420 eV, the photoionization cross section of
the F 2s state became larger than that of the F 2p state. These indicate that the two peaks at ~36 and ~20 eV
are predominantly derived from the F 2s and C 2s states, respectively. On the other hand, the peak at ~7 eV is57

predominantly derived from the C 2p state since the C 2p state increased gradually as compared to that of theF 2p state with increasing h. In Fig. 1(b), the photoelectron spectrum of the valence band region in F-DLC
thin films was compared with that of the DLC thin films and of the polytetrafluoroethylene (PTFE).
Although the spectral feature in F-DLC thin films resembles that of PTFE, the intensity of the peaks at ~20
and 7 eV is larger than that of PTFE. The spectral feature in F-DLC thin films is different from that of the
DLC thin films. The difference of the spectral feature between F-DLC and DLC thin films is related to thecontribution of the F 2s and 2p states since the photoionization cross section of the F 2s and F 2p states waslarger than that of the C 2s and C 2p states in this photon energy. In the previous photoelectron spectroscopy
study in DLC thin films, the spectral features between 22 and 12 eV and between 12 and 0 eV werepredominantly derived from the C 2s and C 2p states, respectively. It is considered that the larger intensity at~20 and 7 eV in F-DLC thin films as compared to PTFE is probably due to the contribution of the C 2s and2p states, respectively.
Fig. 2 shows the photoelectron spectra of F-DLC thin films as a function of the annealing temperature.
The annealing temperatures of F-DLC thin films are denoted beside each spectrum. There are several peaks
originating from the C and F atoms in each photoelectron spectrum. Three peaks at ~690, ~290, ~40 eV are
assigned to the F 1s, C 1s and F 2s core-levels, respectively while a peak at ~600 eV is assigned to Auger
electrons caused by F KLL decay process. The O 1s and N 1s peaks appeared at ~530 eV and at ~400 eV was
not observed at RT although the F-DLC thin films were exposed in air before photoelectron spectroscopy
measurements. This indicates that the surface of the F-DLC thin films is inactive for air. After annealing at
120-400 °C, no clear change was observed as compared to the photoelectron spectrum at RT. With increasing
the annealing temperature at 500 °C, the intensity of the F 1s peak at ~690 eV decreased. With further
increasing the annealing temperature at 600-700 °C, the F 1s peak at ~690 eV decreased rapidly. In ourprevious photoelectron spectroscopy study of PTFE, the chemical composition ratios of the F atoms to C
atoms (F/C) were estimated from the relative intensity of the F 1s peak to the C 1s peak. Using the identicalmethod, the F/C chemical composition ratio at RT was estimated to be 1.36. The F/C chemical composition
ratio is plotted as a function of the annealing temperature. After annealing up to 400 °C, the F/C chemicalcomposition ratio was retained between 1.27 and 1.42. With increasing the annealing temperature at 500 °C,
the F/C chemical composition ratio decreased to 1.17. After annealing at more than 600 °C, the F/Cchemical composition ratio decreased markedly. The F/C chemical composition ratio decreased to 0.14 at
700 °C. These results indicate that the F-DLC thin films were stable at less than 400 °C and that the content
of the F atoms in the F-DLC thin films decreased at more than 500°C.
(a)

Valenceh = 1253.6 eV

o

700 C
o

600 C

h =
420 eVo

500 C
Intensity (arb. units)

Intensity (arb. units)

240 eV216 eV180 eV|F 2s|

130 eV|F 2p |
C 2p
C 2s
|

(b)
h = 216 eV
|

70 eV

o

400 C
o

300 C
o

200 C

|

o

DLC

C
(Auger)

|
|
|

F-DLC

F 1s

120 C
F
(Auger)

C 1s

RT

PTFE
50

40

30
20
10
Binding energy (eV)

1000

0

800

600
400
200
Binding energy (eV)0

Figure 2. Wide scan of the photoelectron spectraof the F-DLC thin films as a function of thetemperature. The photoelectron spectra in thisfigure were normalized by the C 1s peak intensity.

Figure 1. (a) Photoelectron spectra of the valenceband region in F-DLC thin films as a function of
the photon energy. (b) Photoelectron spectrumof the valence band region in F-DLC thin film
was compared with that of the DLC thin film andof PTFE.

References[1] J. Ullmann, Nucl. Instrum. Methods Phys. Res., Sect. B 127 (1997) 910-917.
[2] N. Yamada et al., Jpn. J. Appl. Phys. 46 (2007) 6373-6374.

58

K and L-edge Spectra of Several Sulfur Compounds
T. Hasegawa1, M. Uemura1, T. Tanikawa2, S. Fukushima3, M. Motoyama4 and K. Kanda4
1 Synchrotron Analysis L.L.C., 3-2-24 Wadamiya-dori, Hyogo-ku, Kobe, Hyogo 652-0863 Japan
2 Kansai Research Center, Forestry and Forest Products Research Institute, Nagaikyutaro-68, Momoyama,
Fushimi, Kyoto 612-0855 Japan
3 National Institute for Materials Science, 1-2-1 Sengen, Tsukuba-shi, Ibaraki, 305-0047 Japan
4 LASTI, University of Hyogo, 3-1-2 Koto Kamigori, Ako, Hyogo 678-1205 Japan
Abstract
Sulfur can occur in many chemical forms in the bio-materials or environment, etc. Therefore,chemical state of sulfur which relates to fundamental properties is an important factor in thesefields. We has tried Near Edge X-ray absorption fine structure (NEXAFS) measurement of sulfur
K and L-edge of several sulfur compounds by the beamline BL05 at New SUBARU for the
preliminary study of the practical analysis technique. The spectra provided a good deal of
information related to oxidation state of sulfur. The usefulness of NEXAFS spectroscopy as amethod of sulfur chemical state analysis was demonstrated at BL05.
Introduction
Sulfur is one of the key elements for realizing useful properties of the advance materials, and is importantelement in the field of bio-materials or environment, etc. However, it is also well known that the chemical state
analysis, especially oxidation state analysis, for sulfur is not so easy, even by the X-ray absorption fine structure(XAFS) measurement. Because sulfur K-edge exists on the soft X-ray region (around 2.47 keV), the example ofpractical analysis using K-edge XAFS has not been reported so frequently. In addition, the measurement of
L-edge which one can expect to get the more close information about the chemical state is seldom reported.
Based on these points, we has tried NEXAFS measurement of K and L-edge of sulfur by the beamline BL05
(beamline for industrial use) at New SUBARU, University of Hyogo [1], for establishing the base of practicalanalysis technique. BL05 will be managed and maintained by the Synchrotron Analysis L.L.C. (SALLC), whichis composed of the industrial companies, in cooperation with the staffs of the Laboratory of Advanced Scienceand Technology for Industry in University of Hyogo.
Experiments
BL05 consists of two branch lines, one is a double crystal monochromator beamline (BL05A) for the use in
the higher-energy region (1300-4000 eV) and the other is a varied line spacing plane grating (VLSPG)
monochromator beamline (BL05B) for the use in the lower-energy region (50-1300 eV). The NEXAFS spectra
were measured by fluorescent X-ray yield (FLY) method for K-edge in BL05A, and total electron yield (TEY)method for L-edge in BL05B. For the FLY measurement, silicon drift detector (SII, Vortex) was used. The highpurity powdered reagents were used as the measured samples, and were diluted with the hexagonal boron nitride(h-BN) powder so that the concentration of S atoms may consist with 2% or less for the measurement of K-edge.
The powdered samples were mounted to the holder with indium foil or double side adhesive conductive carbon
tape.
Results
In Fig.1-2, the measured sulfur K and L-edge NEXAFS spectra of several sulfur compounds are shown.
These spectra have been normalized to I0 and had a linear pre-edge background removed. K-edge NEXAFS
spectra are shown good correspondence of strong peak position to the oxidation state of sulfur. The changes ofenergy position and spectral shape corresponding to the environments of sulfur atom can be seen in L-edge
NEXAFS spectra. We inferred from K and L-edge NEXAFS spectra that sulfur in sodium sulfite are partially
oxidized, and changes to sulfate (S6+ state) due to the radiation damage. In addition, it turned out DL-methionine
sulfoxide (S4+) is hard to received the radiation damage, so this compound should be good practical referencematerials of S4+ state. Considering the circumstances mentioned above, the chemical state analysis of sulfur inorganic materials should be possible practically by means of the measurement of both K and L-edge spectra.

59

2+

S

Troilite

L-Methionine
2-

S

PyriteDL-Methionine
sulfoxide

S22-

4+

Normalized absorption (a.u.)

Normalized absorption (a.u.)S
Sulfur
S0
L-Methionine
S2+
DL-Methionine
sulfoxide
S4+

Sodium sulfite

Sodium dodecyl
sulfate2480
2500
Photon energy (eV)Phenyl ethyl
sulfone6+

S

L-Cysteic acid

L-Cysteic acid

2460

Sodium sulfite

6+

S

Sodium dodecyl
sulfate
160
170
180
190
Photon energy (eV)2520

Incident angle at sample surface :45 degIncident angle at sample surface :90 degFig 1. S K-edge NEXAFS spectra recorded in
FLY of sulfur compounds.

Fig 2. S L-edge NEXAFS spectra recorded in
TEY of sulfur compounds.

Reference[1] T.Hasegawa et al., Advances in X-ray Chem. Anal. Jpn., 41, pp.99-106 (2010) [in Japanese].

60Crystallization Mechanism of a-SiGe Graded Filmby Soft X-ray Irradiation
Shota Kino, Yuki Maruyama, Akira Heya, Kazuhiro Kanda and Naoto Matsuo
University of Hyogo
Abstract
We proposed novel low-temperature crystallization of a-Ge, a-Si and a-SiGe films by the SR soft
X-ray irradiation at storage-ring current of 25-220 mA and dose quantity of 50 mA ･ h.
Crystallization mechanism of SiGe graded film by soft X-ray irradiation was investigated ascompared with crystallization of 50nm Si1-xGex film. It is found that SiGe graded film wasindicated the same pattern for SiGe film with 50nm thickness.
Introduction
It is important to fabricate high-quality semiconductor materials on plastic substrate at low temperature for seatcomputer. Thin-film transistors (TFTs) are popularly applied to a switching device for flatpanel displays (OLED
displays). Recently, germanium is expected as an attractive material to realize the TFT with a high mobility [1].
Crystallization methods induced exicimer laser, Ar+ laser, green laser and hard X-ray have been reported for low
temperature crystallization. So far, the relationship between electron excitation followed by atom migration
process, thermal process and the storage-ring current has reported to previous work [2, 3]. In this study, weinvestigated crystallization of SiGe with different Ge fraction and crystallization of SiGe graded film.

2cm

Experiments and Results
Amorphous Si (a-Si) films were deposited by plasma-enhanced chemical vapor deposition (PECVD) method
and a-Ge and a-Si1-xGex(x=0.2 0.4 0.5 0.6 and 0.8) were deposited by molecular beam deposition (MBD) method(deposition rate: 0.02 nm/s, base pressure: ~10-10 Torr). The thickness of a-Si, a-Ge and a-SiGe film was 50 nm.
In addition, we prepared a-SiGe graded film by MBD. Graded film was deposited different composition ofSi1-xGex(x=0.2, 0.4, 0.6 and 0.8) with each 50nm film thickness, and the total film thickness was 200nm. The
irradiation of soft X-ray was carried out at BL07A of NewSUBARU. The light source of BL07A was the 3m
undulator. The electron energy of the NewSUBARU ring was 1.0 GeV during this experiment. The storage-ringcurrent, photon energy and dose quantity were 100 mA, 50 eV and 50 mA･h respectively. The characteristics ofthe film were measured by X-ray diffraction (XRD), reflection high energy electron diffraction (RHEED) and
Raman spectroscopy.
The crystalline fraction of Si0.2Ge0.8, Si0.4Ge0.6 and Si0.6Ge0.4
were 85%, 70% and 21%, respectively. When the fraction of Ge
in SiGe film was high, crystalline fraction was high andcrystallization area was large. Si0.8Ge0.2 did not crystallize.
Figure 1 shows the optical image of a-SiGe graded film
irradiated by same conditions. Crystallization area was center ofcolor changed area and the color-changed area separated to 3
parts. The top layer (Si0.8Ge0.2) did not crystallize in the result of
XRD and RHEED. From these results, the crystallized area foreach layer was different as shown in Fig. 2. It is considered that Fig. 1 Optical image of SiGe graded film
SiGe graded film was indicated the same pattern for SiGe film after soft X-ray irradiation.
with 50nm thickness. In generally, the temperatures of
Low Xc region
crystallization for Si and Ge using conventional thermal
annealing are 680°C and 500°C [4], respectively. And Ge has
Si Ge
higher photoionization cross-section than Si. Therefore,
crystallization of bottom layer with high fraction of Ge wasenhanced. It is expected that the SiGe graded film with various
Si Ge
composition of a-SiGe and poly-SiGe will become excellent
Quartz substrate
Crystallization
High Xcarea
material for solar cells.
regionFig. 2 Cross sectional diagram for
References
crystallization area of SiGe graded film by[1] T. Sadoh et al., Jpn. J. Appl. Phys., 46 (2007), pp. 1250-1253.
soft X-ray irradiation.
[2] Y. Nonomura et al., AM-FPD’11 (2011) pp.193-196[3] S. Kino et al., AM-FPD’12 (2012) pp.223-226[4] I. Nakao et al., IEICE SDM2008-17, pp.83-88, 2008.

61

0.8

0.2

0.2

0.8

Thermal Durability of FIB-DLC Films Containing W
Akihiro Fujimotoa, Makoto Okadaa, Yuji Kanga, Shinji Matsuia, Tsuneo Suzukib, and Kazuhiro Kandaaa
LASTI, University of Hyogo, Kamigori, Hyogo 678-1205, Japan,bExtreme Energy-Density Research Institute, Nagaoka University of Technology,
Nagaoka, Niigata 940-2188, Japan
Abstract
Diamond-like carbon film containing W (W-DLC) was fabricated by focused-ion-beamchemical-vapor deposition (FIB-CVD), and its thermal durability was investigated using x-ray
absorption fine structure near the carbon K-edge (C−K NEXAFS) spectroscopy and a combinationof Rutherford backscattering and elastic recoil detection analysis in comparison with those ofcommercial DLC and W-DLC films. The concentration of W in the films did not decrease when
the annealing temperature was increased, while the concentration of H did. The W-DLC film
fabricated by FIB-CVD unchanged after annealing for 32 h at 873 K in vacuum. Its thermal
durability was comparable to that of the commercial films.
Introduction
Use of diamond-like carbon (DLC) devices fabricated by focused-ion-beam chemical-vapor deposition(FIB-CVD) for electrochemical applications requires high electrical conductivity and high thermal durability
because Joule heating is occurs when electric current passes through a nano-device. Incorporation of W into
DLC film was known to improve the film’s thermal durability. Previous work showed that the electricalconductivity of W-DLC fabricated by FIB-CVD using W(CO)6 as the W source is in the range 2.5 to 6.3×103
Sm−1.1) . It sufficiently high for W-DLC to be used for fabricating three-dimensional nano-devices. Therefore,
the thermal durability of W-DLC fabricated by FIB-CVD must be improved for it to be in electrochemical
applications. In the present study, we investigated the effect of annealing in vacuum at three temperatures
ranging from 673 to 873 K on W-DLC film fabricated by FIB-CVD. The metric used for thermal durability
was the residual film thickness after. The elementary composition analysis was performed using a
combination of RBS and ERDA techniques. The effect of annealing on the W-DLC films fabricated by
FIB-CVD was compared to the effect on commercial DLC films for industrial use.
Experiments
The W-DLC films were fabricated on to Si substrates using a FIB-CVD apparatus (SII Nano Technology
Inc.; SMI2050MS2).2,3) Phenanthrene (C14H10) and tungsten carbonyl (W(CO)6) were used as starting
materials. The ion source was Ga+, and the beam current was 20 nA. Several commercial DLC and W-DLC
films were fabricated for comparison. The samples were annealed in a furnace (Thermo RIKO Co. Ltd;GFA430) under vacuum conditions (Pa ≤ 10−4). The annealing temperature was 673, 773, or 873 K, and theannealing time was 32 hours. RBS and ERDA with MeV-He+ irradiation were performed using anelectrostatic accelerator (Nisshin-High Voltage Co. Ltd.; NT-1700HS) located in the Extreme Energy Density
Research Institute at the Nagaoka University of Technology.4) The He+ beam was accelerated to 2.5 MeV, andthe incident beam angle with respect to the surface normal was 72°. The film thickness was determined bymeasurement of the of RBS spectrum.
Results and Discussions
The residual Ga in nanodevices fabricated by FIB-CVD istransferred to the surface, where it produces Ga spheres that arevaporized from the film by annealing.5−8) Fig. 1 shows thedependence of the Ga concentration in the W-DLC and DLC films
fabricated by FIB-CVD on the annealing temperature, as
determined by RBS measurement. “FIB-CVD W-DLC1” indicates
the W-DLC film prepared by FIB-CVD in the present work and“FIB-CVD W-DLC2” and “FIB-CVD DLC” indicate the W-DLC
film and DLC film prepared by FIB-CVD in the previous work.9)
Figs. 2 (a)−(c) show the dependence of the H concentration in the
DLC and W-DLC films on the annealing temperature, as estimatedusing a combination of ERDA and RBS techniques. The Ga and W
concentrations in the as-deposited W-DLC film fabricated by
FIB-CVD in the present work were ≈5.5% and ≈0.1%, respectively.
The W concentration in the commercial UBMS W-DLC was

62

Fig. 1 Dependence on annealing temperature of
Ga concentration in W-DLC and DLC films
fabricated by FIB-CVD. Circles represent data
for FIB-CVD W-DLC1 film fabricated inpresent work, squares represent data for
FIB-CVD W-DLC2 film fabricated in previous
work, and triangles represent data for FIB-CVD
DLC film fabricated in previous work. Points at
273 K indicate Ga content as-deposited.

≈4.5%, ≈20 times that in the W-DLC films fabricated by
FIB-CVD.
As shown in Fig. 1, the Ga concentration in the W-DLC
films and DLC films fabricated by FIB-CVD decreased withan increase in the annealing temperature, which is consistent
with previous findings.7,10,11) The Ga concentration decreased
from ≈4−8 % to ≈2 % after annealing at 773 K, and most of
the Ga had evaporated after annealing at 873 K. The W
concentration in the W-DLC films fabricated by FIB-CVD andin the UBMS W-CVD film did not depended on the annealing
temperature. This is attributed to the very high boiling point oftungsten, 5828 K.
H concentration in the as-deposited W-DLC and DLC films
in the present work was ≈20 %, except for PE-CVD DLC film,(≈40 %), as shown in Fig. 2. The H concentration in the
PE-CVD DLC film decreased after annealing at 673 K anddecreased steeply when the annealing temperature wasincreased from 773 to 873 K. The H concentration in other
W-DLC and DLC films kept that of as-deposited after
annealing at 673 K and it decreased when the annealing
temperature exceeded 773 K. The desorbed H was considered
to be emitted from C−H bonding rather than hydrogenmolecules in the film, because the desorption starts at a hightemperature, ≈773 K. In other words, the exodus of H from the
DLC film is considered to lead to the graphitization of DLC
film due to the decoupling of the C−H bonding and subsequent
coupling of C=C bonding in films.12−14)
The dependence of the film thickness on the annealing
temperature obtained from RBS measurement is shown in Fig.
3. The thickness of the W-DLC film fabricated by FIB-CVD
increased when the annealing temperature was slightly
increased from as-deposited to 673 K. This small increase wasconsidered to due to the variation of film thickness
as-deposited films. The thickness decreased steeply when thetemperature was increased from 673 to 773 K and this film
remained when it was increased to 873 K. This demonstrates
that the thermal durability of W-DLC film fabricated by
FIB-CVD is higher than that of PE-CVD DLC film and lower
than those of W-DLC and DLC films fabricated by UBMS.
However, a part of the W-DLC film fabricated by FIB-CVD
remained after annealing at 873 K.
References[1] S. Matsui, Nucl. Instrum. Methods. Res., Sect. B 257(2007) 758.
[2] J. Igaki et al., Microelectron. Eng. 83 (2006) 1221.
[3] K. Nakamatsu et al., J. Vac. Sci. Technol. B 23 (2005)
2801.
[4] J. Igaki et al., Jpn. J. Appl. Phys. 46 (2007) 8003.
[5] J. Fujita et al., Jpn. J. Appl. Phys. 41 (2002) 4423.
[6] R. Kometani et al., Jpn. J. Appl. Phys., 47, (2008) 5032.
[7] K. Kanda et al., Radiat. Phys. Chem. 75 (2006) 1850.
[8] K. Kanda et al., Trans. Mat. Res. Soc. Jpn, 36 (2011) 71.
[9] A. Wada et al., Jpn. J. Appl. Phys. 50 (2011) 06GG05.
[10] J. Igaki et al., Jpn. J. Appl. Phys. 46 (2007) 8003.
[11] T. Nagata et al., Jpn. J. Appl. Phys. 47 (2008) 9010.
[12] K. Kanda et al., Jpn. J. Appl. Phys. 41 (2002) 4295.
[13] A. Saikubo et al., New Dia. Front. Carbon Tech. 16(2006) 235.
[14] A. Saikubo et al., Dia. Relat. Mater. 17 (2008) 1743.

63

Fig. 2 Dependence on annealing temperature of H
concentration: a) Circles represent data for
FIB-CVD W-DLC1 film fabricated in present
work, squares represent data for FIB-CVD
W-DLC2 film fabricated in previous work, andtriangles represent data for FIB-CVD DLC film
fabricated in previous work; b) Closed circles
represent data for UBMS W-DLC film and Closed
squares represent data for UBMS DLC film; c)
Diamonds represent data for IP DLC film andcrosses represent data for PE-CVD DLC film.

Fig. 3 Dependence on annealing temperature of
film
thickness
obtainedfromRBS
measurement. Circles represent data for
FIB-CVD W-DLC1 film fabricated in present
work, closed circles represent data for UBMSW-DLC film, closed squares represent data for
UBMS DLC film, diamonds represent data for
IP DLC film, and crosses represent data for
PE-CVD DLC film.

Comparison of Photon Flux of a BL06 with that of the Sun
Yukinori Kawamotoa, Kensei Kobayashia, Ryou Imaib, and Kazuhiro KandabaGraduate School of Engineering, Yokohama National University, Hodogaya-ku, Yokohama 240-8501, Japanb
LASTI, University of Hyogo, Kamigori, Hyogo 678-1205, Japan,
Abstract
Photon flux at the sample stage of BL06 was estimated for the comparison of the solar system withthe simulation experiment using BL06. Photon flux was almost 1.0×1010 photons/s/0.1%bw/mm2
at the sample stage in the region of photon energy under 1000 eV.

Introduction
A wide variety of complex organic compounds including precursors of amino acids have been detected incarbonaceous chondrites and comets. It was suggested that organics in them were formed in quite cold
environments, such as interstellar space. Irradiation of frozen mixture of possible interstellar molecules
including CH3OH, NH3 and H2O with high-energy particles gave complex amino acid precursors with highmolecular weights. Such interstellar complex molecules would be altered by cosmic rays and solar light (UV,
soft X-rays) in proto-solar nebula and interplanetary space before the delivery to the Earth by such
extraterrestrial bodies as space dusts. 1-3) We are planning to examine possible alteration of amino acids andtheir precursors by irradiation with photons.
BL06 in NewSUBARU was constructed for the irradiation of white beam in the soft X-ray region. The
novel functional surface, whose surface properties, such as wettability, refractive index, and so on, aremodified by the exposure to the SR. In addition, experiments in the astrobiology were performed toinvestigate the irradiation effect of soft X-ray on the molecules in the space. For the discussion on thealteration of organic compounds of interstellar origin in the solar system by the simulation experiments using
SR beamline on the ground, estimation of the energy-dependent photon flux was demanded. In the present
study, we calculated the photon flux in the square of 1 mm2 at the sample stage of BL06.
Calculation
A bending magnet was used as a light source of BL06. The white radiation beam from a bending magnet
was introduced to the sample stage using a pair of mirrors, M0 and M1, whose incident angle was 3°.
Therefore, the photon flux at the sample stage of BL06 was represented by,

N = F SR ⋅ ε AC ⋅ R0 ⋅ R1

(1)

where FSR was photon flux at the light source position in the bending magnet and εAC was the accepting
efficiency. R0 and R1 were the reflectivity of M0 and M1, respectively. The photon flux at the light source
position was estimated by the production of the brilliance of NewSUBARU4) and beam size at the lightsource position of BL06, which was calculated to σx = 0.17 mm and σy = 0.27 by Prof. Ando. The angles atthe light source position corresponding to the square of 1 mm2 at the sample stage were estimated by opticaltrace calculation to 0.41 mrad and 0.40 mrad in the horizontal and vertical direction, respectively. These
angles were much smaller than the acceptance of mask and/or M0. The reflectivity of mirror was determinedusing the web calculation in the Center for X-ray Optics of the Berkeley Lab. Mirror constants of BL06 weretabulated in Table I.
Table I Mirror constants of BL06

Mirror
Incident angle
Material
Shape
Coating material
Coating thickness

M0
3°
SiO2
Sagittal cylinder
Pt
50 nm

Surface roughness

0.299 nm RMS

64

M1
3°
SiO2
TroidalPt
50 nm
0.295 nm RMS

Results and Discussions
The determined energy-dependent
photon flux was showed in Fig. 1.
Photon flux was almost 1.0×1010
photons/s/0.1%bw/mm2 at the sample
stage in the region of photon energy
under 1000 eV. In addition, thephoton flux in the 1.0 GeV of ring
electron energy is almost same that in
the 1.5 GeV. Photon flux decreased
steeply with increasing photon energy
beyond 1000 eV. This decreasing was
dominantly ascribable to the decreasein the mirror reflectivity.
We can compare the simulation
experimental results using SR
beamline with the solar system in thevarious conditions, by the use of thepresent calculation results. As sample,
Fig. 2 shows the luminance at the sample stageof BL06 with that in the revolution orbit of the
Earth from the sun of the present age. As
shown in Fig. 2, the simulation experimentusing BL06 has a large acceleration factor.

Fig. 1 Photon flux in the BL06

Acknowledgement
The authors thank Prof. Miyamoto for his
polite instruction for the calculation on thephoton flux.

Fig.2 Luminance of BL06 and the sun
References[1] K. Kobayashi, T. Ogawa, et. al., Electr. Eng. Jpn., 91 (3), 293-298 (2008).
[2] G. A. Gusev, K. Kobayashi, et. al., Origins Life Evol. Biosph., 38, 509-515 (2008).
[3] J. Takahashi, K. Kobayashi, H. Mita et. al., Int. J. Mol. Sci. 10(5), 3044-3064 (2009).
[4] A. Ando et. al., 1997 Proc. IEEE Particle Accelerator Conf. (Vancouver) 757.

65

Stability and alteration of amino acids and related
compounds against soft X-rays in interplanetary space
Yukinori Kawamoto 1 , Takuto Okabe 1 , Midori Eto 1 , Yumiko Obayashi 1 , Takeo Kaneko 1 ,Jun-ichi Takahashi 2 , Hajime Mita 3 , Kazuhiro Kanda 4 , Kensei Kobayashi 1
1Yokohama National University, Yokohama, Japan, 2NTT, Isehara, Japan,
3Fukuoka Institute of Technology, Fukuoka, Japan, 4University of Hyogo, Kamigori, Japan
Abstract
In order to examine stability and possible stability of bioorganic compounds in space environments,
target molecules (amino acids, amino acid precursors, nucleic acid bases) were irradiated with soft
X-rays from NewSUBARU BL-6 in a solid state under high vacuum. Free amino acids were lessstable than their precursors. Water-insoluble products were produced by irradiation. Changes
in structure by irradiation was studied by C-XANES with NewSUBARU BL05.
Introduction
Prebiotic organic matters such as amino acids have been found in extraterrestrial bodies. It was suggested
that they were formed in cold space environment, and were delivered to the early Earth. Interplanetary dust
particles (IDPs) were promising carriers since they could deliver organics safer than large meteorites orcomets. On the other hand, IDPs are so small that they are directly exposed to the solar radiation, which may
decompose or alter organic molecules in IDPs. In the present study, we evaluated the stability of amino acids,
their precursors, and RNA bases against soft X-rays and extreme ultraviolet light (EUV): Irradiation was
performed at NewSUBARU BL-06 (Univ. Hyogo), and the irradiation products were analyzed by several
methods including HPLC and C-XANES.
Experiments and Results
Six amino acid-related samples - Glycine (Gly), alanine (Ala), hydantoin (Hyd: precursor of glycine),
isovaline (Ival), 5-Ethyl-5-methylhydantoin (EMHyd: precursor of isovaline) and complex organic
compounds synthesized by proton irradiation of a mixture of CO, NH3 and H2O (referred to as CAW) – and 4
RNA bases were irradiated with continuous light from soft X-rays to IR (hereafter referred as to soft X-rays)
at NewSUBARU BL-06 (University of Hyogo) under high vacuum condition. After collecting the irradiatedsample with pure water, we measured the recovery ratio of each compound by using ion exchange orreversed-phase HPLC systems. In some cases, CaF2 window was used to cut soft X-rays and EUV (referred
as to VUV irradiation; cut-off wavelength is ca. 130 nm).
Amino acids or their precursors were gradually decomposed by soft X-rays irradiation, and water-insolubleorganics were formed. The water-insoluble products could mostly dissolved in dichloromethane. Recoveryof the amino acid precursors (Hyd, EMHyd, and CAW) was much more than that of the free amino acids(Gly, Ival) after soft X-rays irradiation. Thus, we could suggest that the precursor amino acids are likely topresent more stable than free amino acids in space environment such as meteorite surface and in IDPs.
Neither racemization nor formation of glycine was observed even after 99 % of the initial L-alanine wasdecomposed. RNA bases were more stable than amino acids and their precursors against irradiation.
When CaF2 window was used, little insoluble matters were formed. Thus, soft X-rays (including EUV) areresponsible for the formation of insoluble organics. Soft X-rays fraction in the solar radiation is small in thepresent time, but it is supposed that the strong X-rays were emitted from the young Sun before the formationof planetesimals. It should be examined the possible formation of insoluble organic matter, that is now foundin carbonaceous chondrites and comets, by the irradiation with high-energy photons from the young Sun.
After irradiation, amino acids and their precursors gave water-insoluble products. We measured
C-XANES spectra of the isovaline and CAW before and after soft X-rays irradiation to see possible alteration
processes in space. C=O peaks in C-XANES spectra of both materials decreased after irradiation, while
C=C peaks increased.
Amino acids and their precursors are going to be exposed to actual space environment by utilizing the
Exposed Facility of JEM, ISS. The mission named the Tanpopo is now scheduled to start in June, 2014 [1].
References[1] A. Yamagishi, et al., Trans. JSASS Space Tech., 7, Tk49-55 (2009).

66

Effective Modification in Silica-Based Films
by Synchrotron Radiation
K. Moriwaki, T.Haraguchi, Graduate School of Eng./ Kobe Univ.,
K.Kanda, S.Matsui, LASTI/Univ. Hyogo, and K.Watanabe, Photonics Labs/NTT

Abstract
Undulator radiation (UR) or synchrotron radiation (SR) by the NewSUBARU is used to change
the refractive index in silica-based films for optical waveguide devices. Irradiated samples areshown to have a large refractive-index change of 10-2 order. Defects in the glass induced by theirradiation are characterized by optical absorption measurements as the major causes for therefractive-index change. As the results, UR with peak energy of 50eV or 60eV in the first order isfound to be more effective to induce the defects in GeO2-doped SiO2 sputtered-films than any
other peak energies of 80 or 100 eV. In addition, those UR-induced defects are found toconcentrate within a 200nm-deep layer from the surface. Those defects are stable up to around
300℃ annealing, although they disappear after 800℃ annealing.
Introduction
We use synchrotron radiation (SR) and undulator radiation (UR) for photo-induced refractive-index
modifications in silica-based glasses for optical waveguide devices1). Our main objectives are to induce large
refractive-index changes more effectively using SR without a spectrometer or UR, and to investigate their
origins depending on wavelengths of SR or UR spectra. Especially, UR would be a very useful tool for thematerials modifications, because it can select a useful wavelength and it has very high intensity. Their UR
characteristics would make materials modified effectively with a very short processing time. For thosereasons we mainly use UR for the materials modifications in this report. Our previous results1) showed that ahigh refractive index change by SR irradiation was obtained, but the origins are not so clear at the present
stage. As one of the major causes of the refractive-index change is defects induced by SR or UR,
we characterized the optical absorption changes by SR or UR induced defects, and their depth
distributions. This report shows the results related to the defects for GeO2-doped SiO2 glass
which is used for optical waveguide devices.
Experiments and Results
Experimental conditions are almost the same as in the previous experiments1). UR (from the
NewSUBARU BL-7A) was used to investigate irradiation-wavelength effects. SR (from the NewSUBARU
BL6) was also irradiated on samples directly without a spectrometer. The electron energy of the SR was
1GeV. GeO2-doped SiO2 fabricated by sputtering on Si or on pure silica substrate were used in our
experiments. Optical absorption measurement (wavelength range of 190-400nm) was used to characterize
defects induced by SR or UR. Pure silica substrate was used for an optical absorption measurement.
Reference:Air

1.1

sample1
sample2
sample3
sample4

Absorbance

1.0

sample1 1500mAh
sample2 500mAh
sample3 500mAh
sample4 500mAh

0.9
0.8

Absorbance

1.2

Reference:before irradiation

1.0

0.8
0.6
0.4

0.7
0.6
0.5
0.4
0.3
0.2

0.2

0.1

0.0

0.0

200

250

300

350

400

200

250

300

350

wavelength (nm)wavelength (nm)(a) Before irradiation(b) After irradiation

400

Fig.1 Optical absorbance for (a) before and (b) after UR-irradiated samples (from 1 to 4) of GeO2-doped SiO2
film on silica substrate. The UR peak energy is 50eV. Each sample has different amount of original defects
which are shown in the spectra in (a). The amount of defects after the irradiation depends on the original
ones.

67

Typical optical absorption spectra for samples of GeO2 doped SiO2 films on silica substrates are shown in
Fig.1. The spectra in Fig.1 are by four samples which have different amount of original defects before theirradiation. The original defects can be seen in Fig.1(a) which shows that the number 1 sample has the largest
amount of defects. Basically large amount of original defects makes the absorbance difference after theirradiation higher as shown in Fig.1(b). Figure 1 (b) also shows that a peak of 242nm is decreased and two
peaks around the 242 nm (higher and lower one) appear. The 242nm peak would be attributed as GODC
(Germanium Oxygen deficient-type center). The lower peak near 242nm would be attributed as a
combination of GEC (Ge Electron trapped Center, 215nm) peak and Ge E’ center (193nm) peak which
originates from a lone-pair-related defect. In order to characterize an amount of the defects, thecombination-peak heights of 193nm and 215nm are used and plotted in Fig.2 with various UR peak energy
and dose, including a reference by SR irradiation. Figure 3 shows that the most effective peak energy to
induce defects in the experimental data is 50 eV or 60eV. SR irradiation is not so effective in the Fig.3,
because the SR intensity is relatively weak compared to that by UR.
In Fig.3, Ar ion etching is used to remove the surface layer for depth-profile characterizations. After a 200
nm-deep etching, absorbance spectra are decreased drastically, but further etching up to 500 nm does notchange the absorbance as shown in Fig.3. As the results, the UR-induced defects have been found toconcentrate within a 200nm-deep layer from the surface.

1

1500mA･h

0.8500mA･h2.0

UR irradiated
200nm etched
500nm etched
before irradiation

1.5

Absorbance

ΔAbsorbance

1.2

0.6
0.4

1.0
0.5

0.2

0.0

0

SR

50eV

60eV

80eV

peak energy(1st)

200

100eV

250

300

350

400

Wavelength(nm)Fig.2 The amount of defects appeared in theabsorbance spectra for four samples with two
doses after UR-irradiation of 50-100 eV peakenergies with reference by SR irradiation.

Fig.3 Absorbance spectra for samples before,
after UR-irradiation of 50eV peak energy andafter etching (270nm and 500nm-deep fromthe surface).

Thermal stability and relaxation characteristics for the UR-induced defects were also measured by annealing
the irradiated samples at temperature range from 300 to 1000℃. The absorbance of the glass films wereincreased a little bit but almost stable by an annealing at 300℃ or 400℃ after UR irradiation. Afterannealing more than 800℃, the absorption spectra became almost the same as the original ones before theirradiation because of relaxation.
Conclusions
An effective tool for refractive index change is investigated for an application of SiO2 based materials to
optical waveguide devices. SR or UR-induced defects are the causes of refractive index change. UR withpeak energy of 50eV or 60eV in the first order was found to be more effective to induce the defects in
GeO2-doped SiO2 sputtered-films than that with any other peak energies of 80 or 100 eV. Those UR-induced
defects were found to concentrate within a 200nm-deep layer from the surface. Those defects were stable up
to around 300℃ annealing, so that thermally-stable devices could be fabricated.
From those results, UR is expected to be an effective irradiation source for the refractive-index change in
optical waveguide devices
References[1] K.Moriwaki et al., LASTI Annual Report vol.10 (2008).

68

Release property of thin PDMS layer
for UV nanoimprinting
Makoto Okada, Yuichi Haruyama, Kazuhiro Kanda, and Shinji Matsui
Laboratory of Advanced Science and Technology for Industry, University of Hyogo, Japan
Abstract
UV-nanoimprint lithography (NIL) is used to fabricate high-throughput, low-cost, high-resolution
nanostructure devices. The nanoimprint mold is typically coated with an antisticking layer toensure easy separation of the mold from the UV nanoimprint resins. This layer must be highly
durable to meet the demands of a manufacturing environment, and F-ASL is the standard type used.
In this study, we focused on using PDMS as the antisticking layer for nanoimprinting andexamined its antisticking capabilities. Experimental results showed that the thin PDMS layer
functions comparably to the fluorinated-antisticking layer as an antisticking layer.
Introduction.
Nanoimprint lithography1-3) is a promising andcost-effective ultrafine lithography technique. The
nanoimprint molds come into direct contact withthe resins used, so an antisticking layer is coatedon the molds to prevent resin adhesion. Generally,a fluorinated antisticking layer (F-ASL) is usedfornanoimprinting.
Polydimethylsiloxane(PDMS) has heat durability, chemical stability,
and a release property, and we focused on using athin PDMS layer4, 5) as the antisticking layer fornanoimprinting. In this study, we examined thethin PDMS layer's antisticking capabilities.

zero of the force curve indicates the adhesion
force. In the case of a low-friction surface, thetorsional displacement of the cantilever was small
because the cantilever was able to move smoothly
over the surface. On the other hand, there was alarge torsional displacement of the cantileverwhen the surface had a high friction. The
frictional curve was obtained from the torsional
displacement of the cantilever. The upper andlower sides of the frictional curve are themeasurement results of the approach and returnroutes, respectively. We determined the frictional
force from the difference between the upper andlower sides of the frictional curve. A large
difference between the upper and lower sides
indicates a high frictional force, and in the reverse
case, the frictional force is low. We used an
E-sweep/NanoNavi Station (SII NanoTechnologyInc.) as the SPM system and a cantilever with a
SiO2 glass micro-particle with a 1-m diameter.
The spring constant of the cantilever was 0.95
N/m and the contact force was approximately 10
nN. Figures 1(a), (b), and (c) show the force cu
rves of the Si substrate, F-ASL, and thin PDMS
layer, respectively.

Evaluation of thin PDMS layer
We used P7266-DMS (Polymer Source Inc.)for the thin PDMS layer coating. The coatingprocess is as follows.: (1) The substrate surface
was cleaned with an ozone cleaner (SKB401Y-01:
SUN ENERGY Co.), this producing the hydroxyl
groups. (2) The P7266-DMS was spin-coated on
the substrate. (3) The substrate was annealed at
200 C in a vacuum at 1.0 × 10-3 Pa for 10 h. (4)After annealing, the substrate was rinsed withtoluene to remove the excess P7266-DMS.
We compared the thin PDMS layer to a F-ASL
formed by using OPTOOL HD1100-TH (Daikin
Industries). First, we measured the water contact
angles of the F-ASL and thin PDMS layers with acontact angle meter (Drop Master 500: Kyowa
Interface Science Co.). Results showed they were115 and 106, respectively. Although the contact
angle of the PDMS was about 10 less than that of
the F-ASL, the fact that it was still over 100 was
significant. Next, we measured the adhesion andfrictional forces6, 7) on the Si substrate, F-ASL,
and thin PDMS layer by scanning probe
microscopy (SPM).
The force curve was obtained from the amountof the cantilever's deflection. The difference from

Fig. 1 Force curves of (a) Si substrate, (b)F-ASL, and (c) PDMS. (d) Adhesion forces of Si
substrate, F-ASL, and PDMS.

69

Figure 3 shows the scanning electron
microscopy (SEM) image of the imprinted pattern.
The line- and space-widths were 80 and 190 nm,
respectively. This result indicates that ahigh-resolution pattern can be obtained when
PDMS is used as the antisticking layer.

The adhesion forces of both the F-ASL andthe thin PDMS layer were lower than that of the
Si substrate, although for the thin PDMS layer it
was slightly higher than for the F-ASL (Fig. 1(d)).
Figures 2(a), (b), and (c) show the frictional
curves of the Si substrate, F-ASL, and thin PDMS
layer, respectively. Measurement of the frictional
forces by SPM revealed significant characteristicsof the thin PDMS layer. The frictional forces of
the F-ASL and thin PDMS layer were lower thanthat of the Si substrate  in fact, the PDMS had avanishing low value.

Conclusion
We examined the suitability of PDMS as anantisticking layer by using a contact angle meterand SPM. The release property of the thin PDMS
layer was sufficient to carry out UVnanoimprinting. Significantly, the frictional forceof the PDMS had a vanishing low value. The
demolding force is related to adhesion and friction
between the antisticking layer and thenanoimprint resin, and we therefore expect thatthe demolding force will be reduced when we use
the thin PDMS layer.
Acknowledgements
The authors thank Prof. S. Hosaka from
Gunma University for his helpful discussions.
References[1] S. Y. Chou, P. R. Krauss, and P. J. Renstrom:Appl. Phys. Lett. 67, 3114 (1995).
[2] S. Y. Chou, P. R. Krauss, and P. J. Renstrom:
Science 272, 85 (1996).
[3] J. Haisma, M. Verheijen, and K. Heuvel: J.
Vac. Sci. Technol. B 14, 4124 (1996).
[4] I. Bita, J. K. W. Yang, Y. S. Jung, C. A. Ross,
E. L. Thomas, and K. K. Berggren: Science, 321,
939 (2008).
[5] Y. S. Jung and C. A. Ross: Nano Lett., 7, 2046
(2007).
[6] H. A. Mizes, K.-G. Loh, R. J. D. Miller, S. K.
Ahuja, and E. F. Grabowski: Appl. Phys. Lett., 59,
2901 (1991).
[7] C. M. Mate, G. M. McClelland, R. Erlandsson,
and S. Chiang: Phys. Rev. Lett. 59, 1942 (1987).

Fig. 2 Frictional curves of (a) Si substrate, (b)F-ASL, and (c) PDMS. (d) Frictional forces ofSi substrate, F-ASL, and PDMS.
UV nanoimprinting using mold coated withthin PDMS layer
We performed UV nanoimprinting using aquartz mold coated with the thin PDMS layer.
PAK-01 (Toyo Gosei Co.) was used as a
UV-curable resin and NM-0901HB (Meisyo KikoCo.) was used as a nanoimprint apparatus. The
imprinting pressure, UV wavelength, UV intensity,and UV irradiation time were 3 MPa, 365 nm, 40
mW/cm2, and 30 sec, respectively.

Fig. 3 SEM image of imprinted pattern.

70