Laser-Compton Gamma-Ray Source
by using 2P
Pm Tm-Laser
Sho Amano, Shuji Miyamoto
LASTI/UH
Abstract
In order to expand energy range of the Compton gamma-ray, we considered to introduce a Tmfiber laser operating at 2 Pm to generate gamma rays in the energy range of 4–21 MeV, using alaser-focusing design to generate the maximum flux. The generated luminosity is calculated to be
6400 photons/(W·mA·s) with a laser power of 4 W and a beam current of 200 mA. This is at thesame level as for the Nd:YVO4, and CO2, laser. Tm-fiber laser is also capable of operating in ahigh-power regime and can generate kW-level output power. At present, the maximum gamma-ray
flux is limited only by the laser power. When operating the laser at 1 kW of output power with abeam current of 200 mA, we expect a flux of up to ~109 photons/s. At NewSUBARU, up to several
dozen MeV gamma-ray sources are capable of generating such high power.
with beamline 1 (BL1). The Nd:YVO4 and CO2
lasers are installed in the experimental hall, andonly the beam transport path for the Nd: YVO4 or
CO2 laser is shown in Fig.1. The beam transport
paths for the Nd:YVO4 and CO2 laser are called
the N-path and the C-path, respectively. The
transmittance of each path corresponds to eachlaser wavelength and each path has an optimized
collision point (A or B) for laser beam andelectron. Figure 2 shows the RMS size of theelectron beam calculated from Twiss parameters,
and the laser beam radii (1/e2) in the straightsection. To maximize the interaction length, thefocusing optic in the N-path of the Nd:YVO4 laser(1.064 Pm) is designed to create a laser spot witha radius of 0.5 mm at position A at the center ofthe straight section, which is one advantage
offered by NewSUBARU. At position A, the laser
beam collides with the electron beam, which is ofnearly equal size. However, in the C-path thefocusing optics were redesigned to focus the laserat position B near the laser window; because
diffraction is an order of magnitude greater thanfor the Nd:YVO4 laser. Considering the effective
hard apertures along the C-path, we find that theradius of the laser spot is 1.2 mm at position B,
which is about twice the size of the electron beam.

Introduction
Initially, we generated gamma rays in the range of
17–37 MeV by using a Nd:YVO4 laser operating
at 1.06 Pm. The gamma-ray source is used forvarious studies. Several applications, however,demand gamma-ray energies of several MeV,
prompting us to install a CO2 laser operating at
10.6 Pm to generate gamma rays in the range of
1–4 MeV. In addition to the Nd:YVO4 and theCO2 lasers, the installation of a third laser with awavelength of approximately 2 Pm is planned togenerate gamma rays in the energy range that is
not currently attainable. With the addition of the
2-Pm laser, we will have the capacity to generate
gamma rays with a continuously tunable energy
range from 1 to 37 MeV. The Tm-doped fiber
laser is a candidate for the 2-Pm laser. Recently, ahigh-power Tm-doped fiber laser has beendeveloped with an output power at the kW level.
In general, both Nd:YVO4 and CO2 lasers arecapable of operating in a high-power regime, andoutput powers exceeding the kW level havealready been achieved. Because the laserCompton gamma-ray flux is proportional topower of the driving laser, these high power
lasers make it possible to generate a high flux of
gamma rays. Thus, by using the high power lasers,
the gamma-ray source in NewSUBARU will becapable of producing a high flux of gamma raysin the energy spectrum from 1 to 37 MeV.
In this paper, we present a theoretical predictionof the performance expected using a 2-Pm laser.

Calculated results
By introducing a 2-Pm laser, we expect to be able
to generate gamma rays with energies spanningthe 4- to 21-MeV range, with electron energies
tuned to 0.7–1.5 GeV. Thus, driving with such alaser will enable us to generate gamma rays
spanning an energy range that is not attainable
using the present lasers. We proceeded byconsidering a beam transport path for a 2-Pmlaser and calculating the expected gamma-ray
luminosity. The first case considered entailed
passing the 2-Pm laser beam through the N-path
so that it collides with the equal-sized electron

Compton gamma-ray beamline (BL1a)
Figure 1 shows the experimental setup of thelaser-Compton
gamma-raysourcein
NewSUBARU, which is an electron storage ringwith stored energies from 0.7 to 1.5 GeV. LaserCompton gamma-ray experiments are conducted
on one of the straight sections in combination13

beam at point A. However, this design proved
unsatisfactory because of diffraction losses for the
2-Pm laser. We next considered the following twocases (Fig. 2): (1) At point A, the 2-Pm laser
beam that has passed through the N-path collides
with the electron beam. The laser beam radius atpoint A is 1.2 mm (twice as large as the radius of
the electron beam). (2) At point B, a laser beamthat has passed through the C-path collides withthe electron beam. The laser beam radius at point
B is 0.6 mm, which is the same size as theelectron beam. From the same calculation that
produced results for the case of the Nd:YVO4 andCO2 lasers, we estimate a luminosity for cases (1)and (2) to be 6400 photons/(W·mA·s) and 3500
photons/(W·mA·s), respectively. We conclude
that higher luminosity can be obtained for case(1), with the collision at point A, where the longinteraction zone may be used with advantage
even with a large laser beam radius. Under these
conditions, the luminosity of the gamma rays
generated by a 2-Pm laser should be at the samelevel as for the Nd:YVO4 and CO2 lasers.

At present, gamma-rays with energies of 17–37
MeV and 1.7–3.9 MeV are achieved using an
Nd:YVO4 and a CO2 laser, respectively, and theluminosities obtained in both cases are 6000–
7000 photons/(W·mA·s). The maximum gammaray flux is currently 5×106 photons/s, obtainedusing a laser power of 4 W and an electron-beamcurrent of 200 mA. We also estimate that the
gamma-ray luminosity produced by a 2-Pm laser
should be 6400 photons/(W·mA·s), with energies
covering the range of 4–21 MeV.
Nd:YVO4, CO2, and Tm-doped fiber lasers (thelatter as a 2-Pm laser) are all capable ofgenerating kW-level output power. Using thislevel laser power with an electron-beam currentof 200 mA allows a gamma-ray flux of 109
photons/s to be achieved. Thus, the laserCompton gamma-ray source in NewSUBARU
has the potential to generate such high fluxes overa continuously tunable energy range from 1 to 37
MeV.
References[1] S.Amano et al., AIP Conf. Proc, 1234, pp.489(2010).

Shield tunnel
e

e

A

B

collimator

Shield
hutch

lens

Laser

BL-1

14m

Laser beam radius (mm)Electron beam size (mm)FIG1.

detector

Experimental setup of laser Compton gamma-ray

1.0

a

0.8

rx =0.3 mm

Vx =0.3mm
ry =0.18Vy
mm=0.18mm

Vx

0.6
0.4

Vx =Vy =0.3mm

Vy

0.2
0

-10

10
8

B

A
-5

0
s(m)

10

b
CO2

6

Nd

4

Tm
Z=1.2mm205Z=0.6mm

-10

-5

0

5

10

FIG2. (a) Electron bean size and (b) laser beam radius of the Nd:YVO4, CO2 and Tm lasers in theinteraction zone. The zero value on the horizontal axis refers to the center of the long straight section.
Summary

14

Imaging for Stress Corrosion Cracking in Stainless Steelwith Laser Compton Scattering Gamma Ray
T.Hasegawa1), S.Nakahigashi1), T.Fujishiro2), K.Horikawa3), M.Terasawa3) and S.Miyamoto3)
Japan Power Engineering and Inspection Corporation, 2)University of Hyogo, 3)LASTI, University of Hyogo

1)

Abstract
In order to detect SCC non-destructively, laser compton scattering gamma ray imaging was
examined. As a result, imaging with 1.76MeV gamma ray was available to detect artificial slit for
30mm thick stainless steel and SCC for 10mm thick stainless steel.
was generated by collision between CO2 laser andelectron. This     was 1.76MeV. Imaging
plate (IP) which had 50um resolution was utilized todetect the image. Table 1 shows the examination
condition and fig.2 shows experimental equipment,
respectively.

Introduction
The simulation technique for ultrasonicpropagation is very useful as a support tool toanalyze the result of practical ultrasonic testing(UT). In Japan power Engineering and Inspection
Corporation (JAPEIC), large-scale ultrasonicsimulation system used finite element method has
been developed and put to practical use [1-3].
In ultrasonic simulation, the information, such as
specimen shape, physical properties of specimen,
three-dimensional defect shape and distribution, isnecessary. Particularly, the information about defectis very important to evaluate the validity ofsimulation model and to simulate more accurately.
Stress corrosion cracking (SCC), known as adefect occurred in the structure in nuclear power
plant or chemical plant, has very intricate
ramification and narrow crack width. Therefore, it
has been difficult to observe actual 3D SCC shape inthe specimen so far.
Recently, the authors have succeeded for the
first time to observe 3D SCC image occurred instainless steel and nickel-based alloy by synchrotron
radiation used Spring-8, synchrotron radiation
facility [4-5]. Fig.1 shows the 3D CT image of
SCC in stainless steel as an example [6]. However, it
was impossible to compare the actual result of UT
since the size of specimen was very small (a few mm
diameters) and UT was not available.
Therefore, we tried to perform imaging
experiment by gamma(Ȗ) ray for larger size of
specimen (a few dozens of millimeter thick).

SCC
ĳ


Fig.1 Three dimensional CT image of SCC instainless steel observed by synchrotron radiation [6].
15mm
10mm

10mm

SCC
Fig.2 SCC specimen for imaging experiment.
Table 1. Experimental condition.
1.0 GeVElectron energy
Laser
CO2 laser ( :10.54um)
Gamma ray energy
1.76MeV
Irradiation time
1h, 3h, 6h, 9h
Image detection
Imaging plate
Specimen thickness
10-50mm
Artificial slit
Width:0.245mm
Depth:1mm~5mm

Experiments
SUS316L stainless steels were used as
specimens in this imaging experiment. For eachspecimen, SCC was artificially developed in highpressure pure hot water at 300Υ. SCC specimen
size was 10x10mm and the thickness was from 10 to50mm. Fig.1 shows the SCC specimen. Some of
SUS316L blocks were prepared as standard
specimen machined the slit artificially. We also
prepared the weld joint specimen with SCC. Thebase metal was SUS304 and filler metal was
SUS308. The thickness of specimen was 10mm.
Imaging experiment was performed by Ȗ ray in
NEW SUBARU BL01A. In this experiment, Ȗ ray

IP
Ȗ ray
Specimen 

15

Fig.2 Experimental equipment.

(2004), P10 (in Japanese).
[3] I.Komura et al., JAPEIC NDE Center Technical
Review, Vol.4 (2001), P10 (in Japanese).
[4] S.Nakahigashi et al., Proc. 2007 Spring Meetingof AESJ (2007), P36 (in Japanese).
[5] S.Nakahigashi et al., Proc. 2008 Fall Meeting of
AESJ (2008), P929 (in Japanese).
[6] S.Nakahigashi et al., Maintenology, Vol.8 No.3
(2009), P69 (in Japanese).

Experimental results
Imaging experiment was performed for 10mm
thick standard specimen which had 21 slits (width:
0.245mm, depth: ~1.7mm) at 2mm intervals. Fig.3
shows the image for standard specimen. 7 slits wereconfirmed both sides of beam center on the image.
The slit images between third and sixth from beam
center were clear. The energy of Ȗ ray at the position
from third to sixth slit was estimated at 0.6 ~1.0MeV
in calculation.
In order to examine effects of specimen
thickness and irradiation time for the image contrast,
imaging experiments for two kinds of standard
specimen with 10mm and 30mm thick were carriedout. Irradiation times were 3hrs, 6hrs and 9hrs. Fig.4
shows the result of 3hrs irradiation as an example. In
cases of slit size in this experiment, there was noremarkable difference in the slit image contrast
between 10mm and 30mm thick specimen. The
image resolution was saturated above 6hrs
irradiation although the image was clearer withincreasing with irradiation time until 6hrs.
Imaging experiment was also performed for the
10mm thick SUS316L specimen with SCC.
Irradiation time was for 3hrs and the beam center of ray was located at 5mm distance from the crack.
Fig.5 shows the image of SCC in SUS316L. Yshaped crack was confirmed on the image although
the contrast was not so clear. In cases ofmeasurement by optical microscope, the size ofcrack width near the specimen surface was about
250um. On the other hands, the width near the crack
tip was 50~100um.
Moreover, the experiment was carried out for
weld joint specimen with SCC. The irradiation time
was for 3hrs. Fig.6 shows the image of weld joint
specimen. It was confirmed by the figure that thecrack was occurred at heat affected zone (HAZ) andpropagated toward the specimen depth. It was notedthat the crack penetrated into filler metal from HAZ,
with its propagating. The crack depth was measured
about 13mm.

SUS316L
Beam center

2.0mm
0.245mmFig.3 The  image of standard specimen.
SUS316L

10mmt

30mmt

Fig.4 The effect of specimen thickness.

SCC

Conclusions
Imaging measurements by 1.76MeV   were
performed for stainless steels which had SCC or
artificial slit. Clear slit image was confirmed forstainless steel specimen up to 30mm thick. On theother hands, SCC image was confirmed for 10mm
thick specimen although the image was not so clear.
Laser compton scattering gamma ray imaging
may be good tool as non-destructive defect detection
technique to compare with the result of UT since thedefect detection for 10mm thick stainless steel by
UT is available.

Fig.5 The image of SCC in SUS316L specimen.
SUS304

SCC penetrates into
filler metal from HAZ.
Crack depth: ~13mm

References[1] I.Komura et al., ULTRASONIC TECHNO,
Vol.13, No.2 (2001), P10 (in Japanese).
[2] T.Furukawa et al., Maintenology, Vol.3, No.3

Fig.6 The image of SCC penetrated into
filler metal from heat affected zone (HAZ).

16

Study of 12C(J,2D)4He with NewSUBARU
laser Compton scattered J-ray beam
Tatsushi Shimaa, Yasuki Nagaib, Shuji Miyamotoc, Sou Amanoc, Ken Horikawac,
Takayasu Mochizukic, Hiroaki Utsunomiyad and Hidetoshi AkimunedaResearch Center for Nuclear Physics, Osaka University
Nuclear Science and Engineering Directorate, Japan Atomic Energy Agencyc
Laboratory of Advance Science and Technology for Industry, The University of Hyogod
Department of Physics, Konan Universityb

Abstract
The 16O(J,2D)4He reaction cross section was measured at the J-ray energies between 16 MeV and
39 MeV using an active target method and a quasi-monochromatic J-ray beam provided at theLaboratory of Advanced Science and Technology for Industry (LASTI) of the University of Hyogo.
The cross section is found to be rather small in the energy region corresponding to the 2+ and 4+
excited states of the intermediate 8Be nucleus, while it becomes large above the energy
corresponding to the 8Be 1- state, being in contrast to the latest result reported by Afanas'ev andKhodyachikh. The present result suggests the cross sections are dominated by the contributions of
the 1- states in 8Be and 12C excited with the E1 transition.

Introduction
The triple-alpha reaction and the 12C(D,J)16O
reaction are considered to play essential roles inthe evolution and the nucleosynthesis of the stars
in the He-burning phase [1]. It has been discussed
that the triple-alpha reaction plays important roles
also in various processes such as the He-ignition
in Type I X-ray bursts [2] and the break out fromthe H-burning in the rp-process in neutrino-driven
wind [3]. To study those processes in detail,accurate data of the triple-alpha reaction rate aredemanded. The cross section of the reaction,
however, is hardly measured by a laboratory
experiment, because it is a fusion reaction of
three alpha-particles, and the reaction rate must
be calculated with some reliable theoretical modelfor the three-alpha system. To develop such a
reliable theory, the information about the inverse
reaction, i.e., the photodisintegration of 12C is
expected to be helpful. For that purpose we madea new measurement of the 12C(J,2D)4He reaction
cross section with use of an active target and aquasi-monochromatic J-ray beam. In thiscontribution the preliminary result is presented.

Electron Storage Ring "NewSUBARU"

Gamma-raycollimatore-Plastic
counter
Colliding region
Time Projection
Chamber
Focusing lensMirrors

10kHz Nd:YVO4 laser

Fig. 1. A schematic drawing of the experimental
setup (top view).
The LCS J-ray was generated by the head-on
collision of the electron beam and the laser lights
with the wavelengths of 1064nm (fundamentalwave) and 532nm (second harmonics) of a
Nd:YVO4 pulse laser. The 180° backscattered Jray was extracted by using a collimator made of
10 cm thick lead brick. Using a collimator withthe collimation angle of 0.081 mrad, the J-ray
energy spread of 4.5% (FWHM) was achieved.
The intensity of the incident J-ray was
20000~40000 photons/s, which was measured
online by using a plastic scintillation counter
whose detection efficiency was calibrated with a
BGO counter with the absolute efficiency better
than 99%. The energy distribution of the incident
g-rays was determined so as to reproduce thepulse height spectrum measured with a 6”I u 5”
NaI(Tl) scintillation counter using its response
functions calculated with the EGS5 Monte Carlocode. Fig. 2 shows an example of the J-ray pulse
height spectrum and the intrinsic J-ray energy
distribution.

Experiment
The experiment was performed at theLaboratory of Advanced Science and Technology
for Industry (LASTI) at the University of Hyogo.
A quasi-monochromatic J-ray beam in the energy
range of between 16 MeV and 39 MeV wasgenerated at the BL01 beam line of the
NewSUBARU storage ring in LASTI using thelaser Compton-backscattering (LCS) method[4,5]. Figure 1 shows a schematic view of theexperimental setup.

17

1600
FWHM=4.5%
800

0

10

20
EJ [MeV]30

35

Cross Section [mb]

50

100

150

200
250
z [mm]

x [mm]

30

-30
0

50

100

150

200
250
z [mm]

Fig. 5. An example of the track of the backgrounddue to the D-decay of a radioactive isotope
contained in the TPC gas. It can be easily
distinguished from the 12C(J,2D)4He events
because of the absence of the three tracks
originating in the J-ray beam axis.
12

C(J,2D)4He cross section
The cross section was obtained from thenumbers of the observed 12C(J,2D)4He events as afunction of the incident J-ray energy. Figure 6
shows the preliminary result from the present
experiment together with the existing data
including our previous data measured by using
the LCS J-ray source at the National Institute ofAdvanced Industrial Science and Technology(AIST). Compared to the latest result [15], thepresent cross section is significantly smaller inthe energy region below ~20 MeV where the 2+
and 4+ excited states of the intermediate 8Be
nucleus exist. As shown in Tables 1 and 2, there
are few 1- states below EJ ~20MeV in 8Be and 12C,
while many 1- states with relatively large widths
exist above ~20MeV. Therefore the present result
suggests the reaction is dominated by the E1
transition to the 1- excited states of the target 12C
nucleus and the intermediate 8Be nucleus.

0.4

25

0

0

0.8

20

0

Fig. 4. An example of the tracks of the D-particles
from the 12C photodisintegration. The box showsthe edge of the effective volume of the TPC (sideview). The J-rays are injected from the left.

ENDF/B-VII
Arenhoevel&Sanzone

15

J-ray beam

-30

The J-ray beam was introduced into a timeprojection chamber (TPC) which contained a gas
mixture of 80% He and 20% CD4 [6]. The 12C
nuclei in the CD4 gas worked as an active target,
provided a detection efficiency better than 98.5%
and an acceptance of the solid angle of 4S for the
12
C(J,2D)4He reaction events. The overallsensitivity for the photodisintegration waschecked by the simultaneous measurement of theD(J,p)n reaction, whose cross section has been
well known both experimentally and theoretically.
As shown in Fig. 3, the present result on theD(J,p)n reaction cross section is in a good
agreement with the existing data [6,7,8,9] as well
as a theoretical calculation [10] and the ENDF/BVII evaluation [11].

0
10

30

30

Fig. 2. A typical pulse height spectrum of the LCS
g-ray measured with a NaI(Tl) scintillation
counter (histogram) and the reproduced pulse
height spectrum (black solid curve) assuming the
intrinsic distribution (gray solid curve) of the Jray energy.

1.2

x [mm]Count

The 12C(J,2D)4He events were identified byrequiring the existence of the three tracks of thecharged fragments emitted from the J-ray beamaxis and their large energy losses in the TPC gas.
Figures 4 and 5 show the examples of the tracksof three D-particles from the 12C(J,2D)4He
reaction and the major background probably due
to the D-decays of the radon isotopes contained in
the TPC gas, respectively.

EJ(max) =33.4MeV

2400

40

EJ [MeV]Fig. 3. D(J,p)n reaction cross section. The open
circles and double circles indicate our previous
data measured at AIST and the present ones,
respectively. The triangles, filled circles, andboxes denote the data from Refs. [7], [8], and [9],respectively. The solid curve and dashed curve
are the theoretical calculation with the potential
model [10] and the evaluated data [11],respectively.

18

C(J,2D)4He Cross Section [mb]12experimentally. The spin and parity of each
excited state are to be determined from theangular distribution and analyzing power at therelevant excitation energy, and the LCS J-ray will
be a promising tool for such measurements
because of its nice features such as a very highpolarization, a small energy spread and a small
angular spread.

0.6

0.4

0.2

0

10

15

20
25
30
J-ray Energy [MeV]

Summary and Discussion
The 12C(J,2D)4He reaction cross section wasmeasured by means of a quasi-monochromatic Jray beam for the first time. Using an active target
technique, the absolute cross section wasdetermined with high accuracy, and it will be
useful to develop a reliable theoretical method to
calculate the triple-alpha fusion reaction.

35

Fig. 6. 12C(J,2D)4He reaction cross section. The
open circles and double circles indicate ourprevious data measured at AIST and the present
ones, respectively. The filled triangles, graydownward triangles, diagonal crosses, and dots
denote the data from Refs. [12], [13], [14] and[15], respectively.

Acknowledment
This work was supported in part by Grant-inAid for Specially Promoted Research of the Japan
Ministry of Education, Science, Sports andCulture and in part by Grant-in-Aid for Scientific
Research of the Japan.

Table 1. Excited states of 8Be [16]. Ex, JS and *stand for the excitation energy, spin-parity, andthe total width of a state.
Ex [MeV]* [MeV]JS
00+
5.57u10-6
+
3.040
2
1.5
11.4004+
3.5
19.40010.65
19.8604+
0.7
20.1002+
1.1
20.90041.6
21.5003+
1.0
22.00014
24.000(1,2)7

References[1] A.Bcdefg et al., J. Lasti Rev., 34,2, pp.1234-1244(2000).
[1] E.E. Salpeter, ApJ 115, 326 (1952); F. Hoyle, ApJ
Supp. 1, 121 (1954).
[2] K. Nomoto, F.-K. Thielemann, and S. Miyaji,
A&A 149, 239 (1985); F.-K. Thielemann et al., Prog.
Par. Nucl. Phys. 46, 5 (2001).
[3] S. Wanajo, ApJ 647, 1323 (2006).
[4] K. Aoki et al., Nucl. Instr. Meth. in Phys. Res. A
516, 228 (2004).
[5] S. Miyamoto et al., Radiation Meas. 41, S179S185 (2006).
[6] T. Kii, T. Shima, T. Baba, and Y. Nagai, Nucl.
Instr. Meth. in Phys. Res. A 552, 329 (2005).
[7] D.M. Skopik et al., Phys. Rev. C 9, 531 (1974).
[8] R. Bernabei et al., PRL 57, 1542 (1986).
[9] C. Dupon et al., Nucl. Phys. A 445, 13 (1985).
[10] H. Arenhövel and M. Sanzone, Few-Body
Systems Suppl. 3: Photodisintegration of theDeuteron (Springer-Verlag, Wien,1991).
[11] ENDF/B-VII data file for 1H (MAT=125). 2006,
evaluated by G.M. Hale.
[12] V.N. Maikov, Zh. ekper. teor. Fiz. 34, 1406
(1958) (Soviet Physics-JETP 7, 973 (1958)).
[13] A. Murakami, J. Phys. Soc. Japan 28, 1 (2008).
[14] E.A. Kotikov et al., Izv. Ross. Akad. Nauk, Ser.
Fiz. 66, 445 (2002).
[15] S.N. Afanas’ev and A.F. Khodyachikh, Phys.
Atomic Nuclei 71, 1827 (2008).
[16] ENDSF file for 8Be, edited by J.H. Kelley, J.L.
Godwin, C.G. Sheu, et al., 2004.
[17] ENDSF file for 12C, edited by F. AjzenbergSelove and J.H. Kelley, Nucl. Phys. A 506, 1(1990).

Table 2. Excited states of 12C [17].
Ex [MeV]* [MeV]
JS
0
0+
0
4.439
2+
1.08u10-87.654
0+8.50u10-6
9.641
3
0.034
10.300(0+)
310.84410.31517.23011.15
19.200(1-)~1.1
22.65013.2
25.40012
27.000(1-)
1.4
28.200
11.6
On the other hand, a large strength wasobserved in the energy region above 29 MeV
where a lot of excited states with unknown JS
exist. It will be important for better understandingof the mechanism of the 12C(J,2D)4He reaction todetermine JS of those excited states19Laser-plasma debris from a rotating
cryogenic––solid-Xe target
S.Amano, Y.Inaoka, H.Hiraish, S.Miyamoto, T.Mochizuki
LASTI/UH
Abstract
We investigate the characteristics of laser plasma debris that is responsible for damaging optics.
The debris is composed of fast ions, neutral particles, and fragments, and originates from a solid
Xe target on a rotating drum that we developed as an extreme ultraviolet (EUV) source. The ice
fragments appear to be a problem most notably with solid Xe targets; however, we find that thedamage induced by Xe ice fragments can be avoided by simply reducing the laser pulse energy.
We find the number of fast neutral particles to be an order of magnitude less than the number ofions, and we clarify that the plasma debris is primarily composed of fast ions. In addition, we findthat the number of fast ions having a few dozen keV’s of energy decreases when using the rotatingtarget compared with the rest target. We attribute this to a gas curtain effect from the Xe gas
localized at the rotating target surface. We estimate the sputtering rate of the Mo/Si mirror, whichis caused primarily by the fast ions, to be 104 nm/1 M shots at 190 mm from the source plasma
and at an 11.25° angle from the incident laser beam. Up to the 1M shots exposure, remarkabledegradation of the mirror reflectivity is not observed though the sputtering damages the mirror.
Mitigation of the ions by using gas and/or magnetic fields will further improve the mirror lifetime.
By comparing with a liquid jet Xe target, we conclude that the sputtering rate per conversion
efficiency when using the solid Xe targets on the rotating drum is the same as that when using theliquid Xe targets. The high conversion efficiency of 0.9% in the rotating drum solid Xe target
makes this technique useful for developing laser plasma EUV sources.
intensity on the target was optimized to be~1×1010 W/cm2 to maximize the EUV radiation
around 13.5nm.
Ions from the plasma were detected using acharge collector (CC) with an applied bias
voltage of –100 V, and their kinetic energies were
estimated from time of flight (TOF) signals. The
CC was fixed 190 mm from the plasma and at a
22.5° angle with respect to the incident laserbeam.
We used a double micro-channel plate (MCP)(Hamamatsu, F4655-10) to detect neutral
particles, after an electrical field repelled the ions.
We positioned the MCP at 45° with respect to thelaser beam, and mounted it inside a small vacuum
chamber that was connected via a vacuum tube to
the main vacuum chamber. The tube included apair of electrodes and a 0.75 mm diameter
pinhole. The pinhole allowed us to differentiallypump the MCP chamber and keep the vacuum
pressure below 10-4 Pa. The distance from theplasma target point to the MCP was 1050 mm.
To observe damages by fragment impact, weplaced a Si substrate 100 mm from the plasma
target point and at a 22.5° angle with respect tothe incident laser beam.
Next, we conducted multi-shot laser experiments
to study mirror damage caused by the total
plasma debris (ions, neutrals, and fragments)using a high-repetition-rate Nd:YAG pulsed slab
laser developed in-house. The slab laser was
configured to generate 1064 nm pulses with pulse
widths of 20 ns at a repetition rate of 320 Hz. In

Introduction
Laser plasma radiation from high density, hightemperature plasma constitutes an attractive, highbrightness point source for producing EUV to xray radiation. It is achieved by illuminating atarget with high-peak-power laser irradiation.
We originally developed a fast rotating
cryogenic drum system, which can continuously
supply a solid Xe target. Using the drum system,a maximum CE of 0.9% was demonstrated at 13.5
nm and with the 2% bandwidth required for an
EUVL source. The source operated continuouslywith an output power of 1W.
We investigated the plasma debris from thedrum target system, that is responsible fordamaging optics. The debris consists of fast ions,fast neutrals, and ice fragments. In this article, wereport in detail the characteristics of the debris
and discuss the damage it causes on a Mo/Si
mirror.
Experiments
Figure 1 shows the experimental setup used toobtain data on the characteristics of the plasma
debris from a cryogenic solid Xe target on arotating drum. Initially, data characteristic of fastions, neutrals, and fragments, which were thought
to be main elements of plasma debris, wereobtained in single-shot laser experiments using a
conventional Nd:YAG rod laser with awavelength of 1064 nm and a 10 ns pulse width.
By adjusting the focal lens position, laser

20the experiments, a Mo/Si mirror sample and agold-coated quartz crystal microbalance (QCM)
sensor (Sigma, SQM-160) were placed 100 mm
from the plasma at 22.5° and 45° angles,
respectively, to measure total erosion rates upon
extended multi-shot plasma operation.
EUV energy from the plasma was also
monitored by an EUV energy monitor placed 190
mm from the plasma at an 11.25° angle withrespect to the incident laser beam. The energy
monitor consisted of an X-ray diode with a Mo/Si
filter (IRD, AXUV-20) and a Mo/Si mirror to
select the wavelength band around 13.5 nm.
Mirror damage leading to reduced reflectivity isdetected by monitoring the decrease in EUV
energy during multi-shot laser operation.

The sputtering of the Mo/Si mirror is mainly
caused by fast ions, and the sputtering rate isestimated to be 104 nm/1 M shots with the mirror
190 mm from the plasma at 11.25° from theincident laser beam. If a Mo/Si multilayer mirror
having more than 40 layers pairs is used, thedegradation of its reflectivity under suchconditions will be kept under 10% for an
exposure of up to 1M shots.
The major plasma debris component is ions, andwe believe its mitigation to be comparatively
simple. To reduce the debris and improve themirror lifetime, we are now developing ionmitigation techniques that involve using gas.
The measured sputtering rate per CE at 51° fromthe incident laser beam is essentially equal to thatobtained when using the liquid Xe jet. Assumingthat the debris distribution for both solid andliquid targets is identical, we conclude that the
sputtering rate per CE for solid Xe rotating targets
is the same as for liquid Xe targets. Considering
the higher efficiency (0.9%) obtained using asolid Xe rotating target compared with a liquid
Xe jet target (0.3%), we conclude that a solid Xe
rotating target is advantageous for laser plasma
EUV sources.

Results
Being an inert gas at room temperature, Xe is
deposition-free compared with other metal targets.
However, damage to mirror surfaces occurs due
to sputtering. In particular, damage by Xe ice
fragments was considered problematic for solid
Xe targets. We find, however, that this damage
can be avoided simply by reducing the laser pulse
energy. We find that the number of fast neutral
particles is approximately an order of magnitudeless than the number of ions, and we demonstratethat the major plasma debris component is fastions. We also find that the number of the fast ionshaving㻌 a few dozen keV’s of energy decreases
when using the rotating target compared to thatobserved when using the stationary target. We
attribute this to the gas curtain effect of Xe gas
localized on the rotating target surface.

P

Faraday
Isolator

References[1] S.Amano et al., Rev. Sci. Instrum., 81,023104(2010).

laser pulse

CC
QCM

Nd:YAGrod or
slab
Laser

EM
TS

HV

MCP

Xe cryogenic DrumEM

MoSi Mirror

X-ray Diode
Fig.1 Experimental setup.

21

Mitigation by argon buffer gas of fast debris fromcryogenic xenon laser plasma EUV light source
T. Sekioka1, S. Amano2, T. Inoue2, and T. Mochizuki2
Graduate School of Engineering, University of Hyogo,
2
LASTI, University of Hyogo

1

Abstract
One of the serious problems in the laser-produced plasma for an extreme ultraviolet (EUV) lightsource used for the next generation lithography is the generation of fast ions that damage the EUV
collector optics. Gas curtain method is regarded as one of the most efficient methods for mitigationof fast debris without serious loss of EUV light. We have investigated the mitigation of fast ionsfrom laser-produced xenon plasma on the rotating drum xenon cryogenic target by argon gas
curtain. Energy spectra of fast Xe+, Xe2+, Xe3+ ions from the xenon plasma were obtained at background pressure of 410-4 Pa, before argon gas was introduced into the chamber. Argon gas flowrate was increased by 100 ml/min step to the extent of 800 ml/min. We have obtained the pressure
dependence of the energy spectra of xenon ions for each charge state. These data on theattenuation of xenon ions by argon buffer gas are indispensable for designing a gas curtain debris
mitigation system.

Introduction
An extreme ultraviolet (EUV) light source isunder development for use in EUV lithography.
However, in general, these targets emit particle debris
that produce mechanical damage and/or depositionon the mirrors degrading their reflectivity in a shortperiod. Mirror cleaning will become a serious
problem. In this study, we investigated the mitigationby argon gas curtain of the fast xenon ions from thecryogenic xenon target.
Fig.1. Experimental setup.

Experiments and results
A schematic diagram of the experimental setup is
shown in Fig. 1. A xenon cryogenic target on therotating drum[1] was irradiated in a target chamber bya pulsed 1.06 Pm Nd:YAG slub laser[2] with a energyof 0.3 J at incident normal. The back ground pressure
inside the target chamber was 410-4 Pa. Fast ionswere measured with a Thomson parabola (TP) ion
analyzer which was set at an angle of 45rwith
respect to the laser axis. The fast ions werecollimated with double pinholes of 0.3mm indiameter, and travel on species-dependent trajectories
determined by electric and magnetic deflections andthen impinge upon the micro channel plate (MCP).
Both the magnetic field and electric field wereapplied between 1-cm-thick and 5-cm-length space.
Figure 2 shows the luminescent image of thefluorescent screen which was set at the output of the
MCP, from a single laser shot. Thomson parabolas of
Xe+, Xe2+ and Xe3+ were confirmed.

Xe3+
Xe+
Xe2+

Fig.2. A typical image of Thomson
parabola ion analyzer.
Figs.3, 4 and 5 show the energy spectra of Xe+,
Xe2+ and Xe3+ at several argon gas flow rates. The
response of MCP for ions was not considered in
the analysis. Above argon gas flow rate of 500
ml/min, only Xe+ ions could be observed.
Above 800 ml/min, where the argon partialpressure was 0.56 Pa, the Xe+ ions
intensity was so week that they wereburied in the back ground.

Argon gas was introduced into the target
chamber, and the argon gas flow rate wasincreased by 100 ml/min step. For each argon
gas flow rate, we obtained the energy spectraof xenon ions resolving their charge state.

22

Data analysis is on the progress for determining
the argon column density that is required to stop
the fast xenon ions to the level where no
sputtering occurs without serious loss of X-ray[3].

;H (QHUJ\VSHFWUD
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

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100 and 200 ml/min.




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Fig.3. Energy spectra of fast Xe+ deburis ions atseveral argon gas flow rates. The flow rates are 0,200, 500 and 800 ml/min.

References[1] K.Fukugaki et al., Rev. Sci. Instrum. 77, 063114(2006)[2] S.Amano et al., Rev. of Laser Engineering, Vol.
29, pp.679-682 (2001)[3] T.Inoue et al., Lasti Annual Report, Vol.10, pp2728 (2008)



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Fig.4. Energy spectra of fast Xe2+ deburis ions atseveral argon gas flow rates. The flow rates are 0,100, 200 and 300 ml/min.

23

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Propose of Three-dimensional Micro Fluidics Device Using
Centrifugal ForceYuichi Utsumi*, Tsukasa Azeta*, Yoshiaki Ukita**and Saki Kondo**Laboratory of Advanced Science and Technology for Industry, University of Hyogo, Japan**School of Materials Science, Japan Advanced Institute of Science and Technology, Japan
AbstractLab-on-a-CD enables automation of chemical operations for overall assay protocol [1, 2], however there isstrong restriction to the lab-on-a-CD, due to limited area for integration of multiple and multiple reactor units
and different modules. This paper reports a new concept of lob-on-a-CD with three-dimensional (3D)
microchannel interconnection, which enables fast, high-sensitive and high-throughput analysis.
driving force arisen from spinning speed from 0 rpm
to 2000 rpm. As shown in fig. 3(a), the liquid is heldby surface tension with spinning speed less than
1000rpm and it becomes transported throughcapillary bundle structure with spinning speed greaterthan 1000rpm. The results suggest possibility ofvertical liquid transportation through vertical
capillary bundle structure by converting the planar
centrifugal driving force into isotropic pressure todrive the liquid in vertical direction.

Introduction
There have been paid much attention to the labon-a-CD for the use of enazyme-linked
immunosorbent assay (ELISA), due to its
convenience for the automation of multiple
microreactors. However it is difficult tosimultaneously realize the performance andintegration of multiple reactor units due to thelimited chip area. One of the biggest problem
arise from the limitation is inadequate sensitivity
due to shortage of surface area for theimmobilization of antibody. To resolve these
problems, we propose a new type lab-on-a-CD
concept based on three-dimensional (3D)
microchannel network.
The important contributions of the 3D structure aresummarized in two types of benefits as listed in
below.
1.

As shown in fig.1, stack concept of lab-on-a-CD
contributes to the large-scale integration ofvarious modules and reactor systems by stacking
various layers of disks with different functions.
Seven multiple reservoirs with different
functions are integrated and connected eachother with 3D microchannel network. It isnotable that we succeeded in to increase thedensity of integrated microreactor unites byutilizing three-dimensionally stacked layers.

2.

Flexibility of structural design, arises from 3D
microstructure, enhances of performance ofvarious modules. For example our device has 3D
scaffolds for the immobilization of antibody onto
the surface [3], and stacked structure of 3D
detection reservoir resulting in the increase of
signal-to-noise ratio as shown in fig. 2.

Experiments and Results
The poly-dimethylsiloxane (PDMS) disks withplaner microchannels are fabricated by conventional
rapid prototyping and poly-methylmethachryrate(PMMA) disks are fabricated by deep X-ray
lithography as shown in fig. 4[3]. To construct 3D
microchannel network, these disks are aligned andreversibly bonded.
To demonstrate the automatic sequencing in 3D CD
platform, we loaded pure water and stained into thereservoirs and CD platform is spun for thesequencing. The burst frequency and flow behaviors
are measured and observed by using strobe scope
system. The four step flow sequencing involving
vertical liquid flow around reaction reservoir are
successfully demonstrated. As shown fig. 5, thereproducibility is indeed good between 8 individual
measurements.
Achieved flow sequencing driven by controlled
centrifugal force in 3D fluidic interconnection is
expected to realize high-efficiency and highthroughput total assay on one platform.

To realize the concept, the most important keytechnology is a controlling of “vertical” liquidtransportation which enables transfer of regents
between different layers of the stacked CD.
To investigate the feasibility of the valving andliquid transportation by centrifugal force,computational fluid dynamics (CFD) using“FLUENT” software is carried out. We assumed the26Sample loading andseparation chamber (top layer)
3D microchannel network
Buffer solution reservoir (bottom layer)
Mixing chamber (middle layer)

3D bio-chemical
reaction chamber
Optical detection chamber

Figure 4. Potographs of desighed andfabricated CD platform consist of three layers

3D CD platform device
Closeupedmicroreactors diagram
Figure1.Schematicof new CD-likefor full automatic immunoassay
microfluidic platform with three-dimensional fluid
network

To spectrometer

Vent
Top layer
Middle layer
Bottom layer

Flow inlight

Waste reservoir

Optical detection
reservoir withstacked structure

Planer microchannels(c)㪣㫀㫈㫌㫀㪻㩷
Transported
through

㪘㫀㫉㩷

㪍㪇㪇
㪋㪇㪇
㪉㪇㪇
㫉㪼㫊㪉

㫉㪼㫊㪊

㫉㪼㫊㪋

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. “A fully automated immunoassay fromwhole blood on a disk” B. S. Lee et al., Lab
Chip, 9, 1548, (2009)
3. " Proposal of a new microreactor for verticalchemical operation," Y. Utsumi, T. Asana,
and Y. Ukita, Japanese Journal of Applied
Physics, 45, 2606 (2006).

㪟㫆㫃㪻㩷㪣㫀㫈㫌㫀㪻

(b)

㪏㪇㪇

Figure 5.(a)Images of flow sequencing ofwater(b)Measured burst frequency

Vertical valve㪚㪼㫅㫋㪼㫉

㪈㪇㪇㪇

㫉㪼㫊㪈

(a)

Verticalpressure㪈㪉㪇㪇㪇
Three dimensional
reaction chamber

Figure 2.Cross sectional view of three-dimensional
microchannel interconnection㪚㪼㫅㫋㫉㫀㪽㫌㪾㪸㫃 㪽㫆㫉㪺㪼㩷㪙㫌㫉㫊㫋㩷㪽㫉㪼㫈㫌㪼㫅㪺㫐㩿㪩㪧㪤㪀㪈㪋㪇㪇㪣㫀㫈㫌㫀㪻㩷

Figure 3. Analysis model of three-dimensional
structure by centrifugal force.
(a)Liquid is held by surface tension.[500rpm](b),(c)Centrifugal force was over surface
tension[over1000rpm].

27

Fabrication of electrodes for multiplex nerval interface
Mitsuhiro Yoshida*, Yoshiaki Ukita*, Kunihiko Mabuchi**, Yuichi Utsumi*Laboratory of Advanced Science and Technology for Industry, University of Hyogo**Dept. of Information physics & Computing, Grad. School of Info. Sci. & Tech. The University of Tokyo
Abstract“Microneurography” developed by Karl-Erik Hagbarth and Ake B.Vallbo, is a technique for reading
and manipulating nerve signals by tools, acting as “nerve signal interfaces”[1]. The “flexible
regeneration type nerve electrode” is an interface device for nerves, connecting nerve fibers to signal
conducting lines on a macro structure, making it usable for “Microneurography” [2]. Our chips buildup
is based on multiple stacked SU-8-layers.
DesignFig.2 (a) shows the outline of the nerve regenerationelectrode. To increase the number of electrodes we
propose stacked type electrode structure. It isdifficult to integrate many electrodes by using single
layer due to small area. Thus the electrode shape isdesigned to be stacked allowing three-demensional(3D) crossing of multiple electrode lines. For the firstattempt, designed electrode structures have 12channels electrode on a single layer and total 24channels are realized by stacking two layers. Fig.2(b) shows the designed nerve reproduction electrodes.

Introduction
Infomation on the nerval system in expressed by theacion potential transmitted in the neuronal cell. This
neural coding can be measured by mounting theelectrode in the neighborhood of the neuronal cell or
the neuronal cell. More, it is also possible tostimulate the neuronal cell oppositely, and to
generate the neural coding. Such an electrode iscalled a nerve electrode. It becomes possible toanalyze the function of the nerval system bymeasuring the neural coding. And, a multi activity ofa cell simultaneous metrology that records theactivity of two or more neuronal cells at the sametime is paid to attention. There is a nerve
regeneration type electrode using the ability ofregeneration for the peripheral nerve to make theaction potential transmitted in the neuronal cell amulti channel. The model of the nerve regenerationelectrode is shown Fig.1 Flexible regeneration typenerve electrode relies on the regeneration ability ofnerves. By putting a pair of cut nerves at both ends ofa capillary, they grow through the capillary toreconnect. When an electrode is embedded inside of
the capillary, it become possible to detect thepotential of nerves by the electrode. This method issuitable to detect signals inside and outside of thenerve fiber. The development of implantable nervalinterface will realize brain-driven prosthetic limb andthe artificial organ, or its also possible to apply toscientific application such as understanding of
biological functions of nerves.

(a)

3mm

30μm, 60μm, 90μm

55mm

20μm

20µm

(b)

electro code
silicon tube

proximalnerve stump

regenerating axons

distalnerve stumpBlack hexagon: capillary layer
White: electrode layer 1
Black: electrode layer 2hole with recording site

Fig.2 (a) Outline of electrode(b) Designed nerve reproduction electrodes

Fig.1 Model of nerve reproduction electrode28

Experiments
Our chips buildup is based on multiple stacked SU8-layers. The prepared single layer electrode chips
are piled up together with the precise alignment andbonding process. Fig.3 shows the fabrication process
image of bonding. For the bonding process theunique characteristic of SU-8 is utilized for thepatterning of capillaries and bonding[].

(a)

(ϸ)

pattern䐟SU-8pattern䐠(b)

Alignment of two electrode layers(Ϲ)
pressure

Bonding with pressure(Ϻ)

Development of inter layer

Fig.4 (a) Outer view fablication electrodes(b) Zoom up of structure of electrodes

Fig.3 Fabrication process image of bonding

Results
Fig.4(a) shows photographs of outer view fabricatedelectrodes. Fig.4(b) shows photographs of zoom up
of structure of electrodes. As shown in Fig.4(b) the
three-dimensionally stacked electrodes and throughcapillary for nerve growth are successfully aligned
and patterned in monolithic SU-8 chip. We inspected
the method to manufacture it for three-dimensions torealize the multi channel of the flexible regeneration
type nerve electrode in this study and demonstrated
that it was possible for the first time. We will aim at
the optimization of the structure parameter and themultistage of the stacking step and the advancementof the fabrication process in future. Moreover, it isnecessary to verify it by measuring an actual neuralcoding by mounting.

References[1] Åke B. Vallbo, Karl-Erik Hagbarth, and B.
Gunnar Wallin : “Microneurography: how thetechnique developed and its role in the investigationof the sympathetic nervous system”, J Apply Physiol
96, p.1262-1269 (2004)[2] Takafumi Suzuki, Takashi Saito, Kunihiko
Mabuchi : “Development of a multi-channel nerve
electrode for peripheral nervous system”, Technicalreport of IEICE, Vol. 100, No. 479 pp.63 -66 (2000)[] F J Blanco, M Agirregabiria, J Garcia, J Berganzo,
M Tijero, M T Arroyo, I Aramburu and Kepa
Mayora : “Novel three-demensional embedded SU-8
microchannels fabricated using a low temperature
full
wafer
adhesive
bonding”,
J.Micromech..Microeng, Vol. 14, pp.1047 -1056(2004)

29

HIGH EFFICIENCY MICROFLUIDIC REACTOR
CHIP OPERATED ONLYUSING SURFACE-ACOUSTIC-WAVE
Takeshi Komoto*, Tsunemasa Saiki*,**, and Yuichi Utsumi**Laboratory of Advanced Science and Technology for Industry, University of Hyogo, Japan** Hyogo Prefectural Institute of Technology, JAPAN
Abstract
Surface acoustic wave (SAW) devices are expected for micro total analysis systems, because theirstructures are simple. We studied flow actuators driven by SAWs. We then fabricated a micromixer driven by the SAWs. In this study, on the basis of the mixer and the flow actuator, we
proposed and fabricated a novel micro-reactor driven by the SAWs, and investigated its reaction
property. As a result, we found that the local rapid mixing of micro solutions was possible by using
the SAWs, and high availability of our micro reactor was demonstrated.
Introduction
The manufacturing process for each component
device in a lab on a chip must be simplified tointegrate multiple functional devices. Surface
acoustic wave (SAW) devices with very simple
structures have attracted attention. Therefore, we
studied SAW actuators that could enable acontinuous liquid to flow with high efficiency [1] andenable a small amount of liquid to be rotated at highrevolution [2]. The knowledge obtained from ourprevious research enabled us to fabricate a highefficiency microfluidic mixing chip [3]. In this study,
we evaluated the chemical reactivity of the chip.

Interdigitaltransducer(IDT)

A
Side wall

Inlet

A'
OutletLiquidflow

Surface acoustic
waves (SAWs)
Piezoelectric
substrate(a) Top view

Structure of our reactor
The top view and magnified sectional view of our
micro reactor operated using SAWs are shown in
Figure 1 (a) and (b). SAWs are generated from the
IDTs when high frequency voltage is applied tointerdigital transducers (IDTs). The SAWs
propagate in the surface layer of the substrate andpass through a sidewall to the bottom plate of theflow channel. The liquid in the flow channel thenbecomes energized due to longitudinal pressure wave
radiation from the SAWs and flows in the propagateddirection of the SAWs. Overall, the liquid in thereactor flows with some rotation in a stream from theinlet to the outlet through external pumps.

Longitudinal pressure wave
Side wall
Interdigitaltransducer (IDT)

Surface acoustic
Liquid flow
waves (SAWs) Piezoelectric substrate(b) Magnified sectional view (A-A')
Figure 1. Overview of micro reactor operated using
SAWs.
Experiments
Our experimental setup for investigating the reaction
characteristic of the microfluidic chip is shown in
Figure 3. Before starting the experiment, we filled
reservoir 1 with solution A, which was a mixture of
10% NaOH water solution of 15 μL and 0.075 mg of
luminol reagent, and filled reservoir 2 with solution
B, which was a mixture of 7.5 vol% H2O2 water
solution of 15 μL and 0.45 mg of potassium
ferricyanide. In the experiment, these solutions
flowed through the two pumps, which operated
simultaneously. We then took photographs of theliquid behavior in the reaction area using a highly
sensitive camera.

A photograph of a microfluidic reactor (mixing) chip
operated using SAWs is shown in Figure 2. The
chip consists of one y-type flow channel, threereservoirs, one reactor, and two pumps. Not only the
micro reactor but also the pumps were driven in the
microfluidic chip using SAWs. The flow channel
widths upstream and downstream of the merging
point were 0.5 mm and 1 mm. The depth of the flow
channel was approximately 250 μm. The IDTs of thereactor and the pumps had pitches of 200 μm, 20
pairs, and apertures of 0.5 mm.

30

Inte rdigit al t ra nsducer (IDT)Al / Cl

Bonding Pad
Wire

Li quid
Reservoir

Side wall
SU-8
0.5mm

Piezoele ctric
substrate(LiNbO3)

React or(a) Non-operation of reactor(PR=0mW)

Pum ps10 mm
Photographing a re a0.5mm(b) Operation of reactor(PR=250mW )Flow cha nne lFigure 4. Photographs of luminescences with luminol
reactions.

Figure 2. Photograph of microfluidic reactor chip
operated using SAWs.

REFERENCES:
1. "Proposal of a Novel Continuous Flow Pumping
Operated by Surface Acoustic Wave," Y. Utsumi,
T. Saiki, K. Okada, 12th International
Conference on Miniaturized Systems for
Chemistry and Life Sciences (μTAS2008), 715(2008).
2. "Fabrication and Estimation of Novel Micro
Liquid Rotor that Operates with Surfaceacoustic-wave," T. Saiki, K. Okada, Y. Utsumi,
12th International Conference on Miniaturized
Systems for Chemistry and Life Sciences(μTAS2008), 387 (2008).
3. "High Efficiency Mixing and Pumping ofContinuous Liquid Flow using SurfaceAcoustic-Wave," Y. Utsumi, T. Saiki, K. Okada,
13th International Conference on Miniaturized
Systems for Chemistry and Life Sciences(μTAS2009), 58 (2009).

Highly sensitive
cameraEyeMicroscope
Function
generator
C h. 2

Ch .1

Liquidreservoir 1

Amplifier 1
for pumps

Pump 1
Flow channel

Power
meter

Amplifier 2
for mixer

Flow

Liq uidreservoir 3

Liquidreservoir 2
Pump 2

ReactorFigure 3. Experimental setup.
Results
The photographs of luminol luminescence in thereaction area are shown in Figure 4. Here, the flow
velocities in the channels were about 5 mm/sec, anddriving power PR of the micro reactor was 250 mW.
When the micro reactor did not operate, only one lineof luminescence was observable near the center ofthe flow channel. However, when the micro reactor
did operate, luminescence occurred in the whole flow
channel. These observations demonstrated that
local and rapid mixing of these solutions was
possible by using the SAWs. Moreover, our micro
reactor demonstrated high applicability.

31

High-sensitive enzyme-linked immunosorbent assay inthree-dimensional lab-on-a-CD
Yoshiaki Ukita, Laboratory of advanced science and technology for industry
Tsukasa Azeta, Laboratory of advanced science and technology for industry
Saki Kondo, Laboratory of advanced science and technology for industry
Yuichi Utsumi, Laboratory of advanced science and technology for industry
Abstract
This paper reports a new lab-on-a-CD with three-dimensional(3D) microchannel network for thehighly versatile and automatic immunoassay system. The lab-on-a-CD is consist of disks withplaner microchannels and vertical channels, which fabricated by using conventional rapid
prototyping method and x-ray lithography. The three dimensional lab-on-a-CD is applied to ELISA
with standard sandwich protocol. The results suggest quite low detection limit (the several ng/ml
order detection limit of immune globlin G of mouse).
Introduction
The lab-on-a-CD is promising for the automationof multiple microreactor systems. Recently, highperformance systems based on lab-on-a-CD has
been proposed [1, 2]. However it is difficult tosimultaneously realize the integration of many
reactor units and various modules due to therestriction of chip size. In fact, the lab-on-a-CDs
proposed by the references are integrating a few
systems [1, 2].
To resolve this problem, we propose a new typelab-on-a-CD concept based on three-dimensional(3D) microchannel network. Figure 1 shows
schematic illustration of 3D lab-on-a-CD consistsof multiple layers of CD-like disks with different
functions. By stacking multiple layers of lab-ona-CD, it can compactly be integrated microreactor
systems. It is also notable that the use of threedimensional structure enhances the performanceof modules. For example, it can be realized to
improve the sensitivity of ELISA by increasing
surface area for the immobilization of antibody,and optical path length is also increased byutilizing stacked structure as shown in fig. 1(b).

(a)
Sample loading andseparation chamber (top layer)
3D microchannel network
Buffer solution reservoir (bottom layer)
Mixing chamber (middle layer)

3D bio-chemical
reaction chamber
Optical detection chamber
3D CD platform device
for full automatic immunoassay

Closeuped microreactors(b)
To spectrometer

Vent
Top layer
Middle layer
Bottom layer

Flow inlight

Waste reservoir

Stacked opticaldetection reservoir

Vertical flow

Bundle-like capillary
structure (for antibody
immobilization)
Planar flow

Figure 1: The schematic illustration of threedimensional lab-on-a-CD. (a) Multiple layerswith different functions are stacked andintegrated together, to construct highperformance assay system. (b) Cross section of
the 3D reaction chamber and optical detection
reservoir.

Experiments and Results
To demonstrate the ELISA, we carried out the
sandwich ELISA by means of standard sandwich
ELISA in fabricated 3D lab-on-a-CD. Planer
PDMS lab-on-a-CD and through-hole PMMA
lab-on-a-CD are fabricated by rapid prototyping
and deep X-ray lithography respectively, and figs.
2(a, b) show the photograph of the disks and SEM
images of bundle-like capillary structures.
To estimate the immobilization and specificity ofantibody, we compared three different reaction
conditions in the lab-on-a-CD. As shown in fig. 4,
the absence of 1st antibody or absence of analyte
result in low level signal, and presence ofimmobilized 1st antibody and analyte result in thehigher signal. This result suggests successful
immobilization of antibody with sufficient
activity on the capillary bundle structure. It is also

notable that we succeeded in on-chip detection bymeans of absorption spectroscopy in threedimensionally stacked detection reservoir with
optical path of 700μm.
It is also very important to realize the on-chip
washing for the automation. Prof. Madou’s groupreports the consumed volume of wash is threetimes of the reaction reservoir, however it isconcerned that the complex flow behavior inbundle-like capillary structure result in the
difficulty of the washing. Thus we demonstrated
and compared the results of ELISA by on-chip

32

(a)

㻌
1.0

Back side disk
(PDMS with planer channel)

0.9

(b)

Off chip washing
On chip washing

0.8
0.7
0.6
0.5

㻌

Middle layer disk
(PMMA with through-hole)

Absorbance at 450nm

Top disk(PDMS with planer channel)

0.4
0.3
0.2
0.1
0.0

0.1

1

10

100

1000

10000

Mouse IgG conc. (ng/ml)

Figure 5. Obtained calibration curve by using
three-dimensional lab-on-a-CD. The mouse IgG(analyte) is sandwitched by anti mouse IgG goat IgGand enzyme conjugated(HRP) anti-mouse IgG goat
IgG. The signal of the enzyme reaction is amplified
by high-sensitive peroxidase substrate(TMBZ).
Closed plots are taken by off-chip washing protocol,
and opened plots are taken by on-chip washingprotocol.

Figure 2. (a)Photographs of fabricated disks of
3D lab-on-a-CD. (b)SEM image of bundle-like
capillary structure for antibody immobilization.

believe that the on-chip washing is effectively
controlling the back ground due to nonspecificbinding of proteins.

㻭㼎㼟㼛㼞㼎㼍㼚㼏㼑㻌㼍㼠㻌㻠㻡㻜㻌㼚㼙

0.8
0.7
0.6

References[1] B. S. Lee et al., 1. “A
fully
automated
immunoassay from whole blood on a disk”, Lab Chip,
9, 1548, (2009)[2] S. Lay et al., 2. “Design of a compact disk-likemicrofluidic
platformfor
enzyme-linked
immunosorbent assay”, Anal. Chem., 76, 1832,(2004)

0.5
0.4
0.3
0.2
0.1
0.0

(a)

(b)

(c)

Figure 3. Comparison of three different reaction
conditions. (a) with 1st antibody, and without analyte(Mouse IgG) (b) without 1st antibody, and withanalyte (10μg/ml of Mouse IgG) (c) with 1st
antibody, and with analyte(10μg/ml fo Mouse IgG)
and off-chip washing step.
As shown in fig. 5, we successfully detected
reasonable dose response of the signal reflecting
the concentration of analyte. The corresponding
assays to the each plot in the fig. 5 were
simultaneously carried out and detected by onchip absorption spectroscopy and the result alsosuggests stable filling of capillary bundle bycentrifugal pumping. The estimated detection
limit is quite sensitive less than several ng/ml andoval reaction time is less than 25 min. By
comparing the results of on-chip washing and offchip washing, it is very encouraging that theresult of on-chip washing also exhibit clear dose
response and plot of 1ng/ml analyte is quite close
to the back ground level of off-chip washing. We

33

Mask Observation Results using a Coherent EUV
Scattering Microscope at NewSUBARU
Tetsuo Haradaa), Junki Kishimoto, Takeo Watanabe, Hiroo Kinoshita
LASTI, University of Hyogo, 3-1-2, Koto, Kamigori, Ako, Hyogo, Japan 678-1205
JST, CREST, Japan
Dong Gun Lee
Samsung Electronics Co., LTD., San #16 Banwol-Dong, Hwasung-City, Gyeonggi-Do, Korea, 445-701
a)Electronic mail: harada@lasti.u-hyogo.ac.jp

A coherent scattering microscope for extreme ultraviolet (EUV) light has been developed for the actinic
inspection of EUV lithography masks. It was installed at the NewSUBARU synchrotron facility. It provides
aberration-free, diffraction-limited imaging and a high numerical aperture. Coherent EUV light scattered(diffracted) from a mask is recorded using a CCD camera with a numerical aperture of 0.15. An image of thesample is reconstructed using a hybrid input-output algorithm, which retrieves the phase from the intensity data.
Masks containing periodic line-and-space and hole patterns with a half pitch ranging from 100 nm to 400 nm
were fabricated in our laboratory and imaged. The reconstructed images correlate well with images obtainedwith a scanning electron microscope (SEM). The actinic critical dimension of the line width of TaN absorberpatterns on a mask was measured and was consistently found to be 25 nm larger than that obtained from theSEM data.

I.

and a field diameter of 5 Pm, and can estimate CDs
ranging from 100 nm to 500 nm. However, aberration
makes it difficult to obtain a high NA at the Fresnel
zone plate. We have developed an EUV microscopethat employs Schwarzschild optics and an X-ray
zooming tube,5,6 and installed it at the NewSUBARU
synchrotron facility. It has a high NA of 0.3 and alarge field with a diameter of 50 Pm. Because of the
low magnification (30u) of the Schwarzschild optics,
the zooming tube uses electromagnetic lenses tomagnify a projected mask image by 10-200u. The
optics for these actinic inspection tools are difficult to
produce and align, and they become more complex as
the NA and magnification become higher.

INTRODUCTION

Extreme ultraviolet (EUV) lithography is apromising technology for the production ofsemiconductor devices at the 32-nm node. The
fabrication of a defect-free mask is a critical issue.
An EUV mask consists of a glass substrate with areflective multilayer coating and a patterned absorbercoating. A Mo/Si multilayer exhibits a highreflectivity of 70% at O= 13.5 nm, which is theworking wavelength of EUV lithography. The
required accuracy of the critical dimension (CD) for
the 32-nm node is less than 2.6 nm.1 To achieve thatlevel of accuracy, it is necessary to be able toprecisely determine the line width of a mask pattern.
Thus, at-wavelength observations with an EUV
microscope is essential for estimating the actinic CDof the reflection profile. There are two types ofdefects in EUV lithography masks: amplitude defects,
which are caused by particles on the surface of amask, and phase defects, which are caused by defects
in the substrate and particles in the multilayer. To
detect phase defects on mask blanks, SELETE hasdeveloped a dark-field inspection tool employing
Schwarzschild optics and a laser plasma source2. To
inspect finished (patterned) masks, the LBNL group
has developed an actinic inspection tool that employsa Fresnel zone plate as an optical component.3,4 It is
installed at the ALS synchrotron facility. This
microscope has a numerical aperture (NA) of 0.0875

This paper describes a coherent EUV scattering
microscope (CSM) based on X-ray diffraction
microscopy.7,8 It requires no objective and uses only
coherent EUV light. The scheme is simple: Coherent
EUV light illuminates a region of a patterned EUV
mask, and an EUV CCD camera records the intensity
distribution of the scattered (diffracted) light. In a
conventional diffraction imaging setup, an objective
collects both phase and amplitude information fromthe sample. In contrast, the CSM records only thediffraction intensity of the sample, which contains
only amplitude information. The missing phase
information is retrieved by using a hybrid
input-output (HIO) algorithm,9 which iteratively

34

calculates the Fourier transform and the inverse
Fourier transform, subject to constraints.

higher diffraction orders, which makes the CSM a
useful tool for quickly estimating the CD. The zerodiffraction order means direct reflection from themask.

The CD for a periodic mask can be determinedfrom the intensity ratios of the zero, 1st, 2nd, andII.

DESIGN OF COHERENT EUVSCATTERING MICROSCOPE(incident angle: 3q) and a planar mirror reflects it(incident angle: 39q) onto an EUV mask. The twomirrors are coated with 40 pairs of Mo/Si layers,which have a peak reflectivity of 43% at O = 13.4 nm,
and 52% at O = 13.5 nm. The Zr filter, the three
Mo/Si multilayers of the branching mirror, and thetwo mirrors of the CSM monochromatize the beam
striking the EUV mask at a wavelength of 0.3 nm.
When the CSM is used for estimating the CD, theresults accurately take the shadowing effects of theabsorber pattern into account because the angle ofincidence on an EUV mask is 6q, which is the sameas that for the alpha EUV exposure tools ADT(ASML) and EUV1 (Nikon).

The CSM is installed on the BL-3C beamline10 of
the NewSUBARU synchrotron facility, which has abending-magnet source. Two toroidal mirrors
collimate the white light, and a Mo/Si multilayer
deflects the beam at the C station by a designed angleof 0.75 mrad. This multilayer has a peak reflection
wavelength around 13.5 nm at an angle of incidenceof 10q. Figures 1 and 2 show a schematic and aphotograph, respectively, of the CSM at the end
station of the BL-3C; and Table 1 lists the
specifications. The optical path in the CSM chamber
begins with a 5-Pm-diameter pinhole and a
200-nm-thick Zr filter, which reduces the beam
diameter and partially monochromatizes the beam.
Next, a concave spherical mirror reflects the beam

Back-illuminated CCDcameraMo/Si(concave,
I3°)

Pinhole(I5 Pm)Mo/Si(flat)

Zr filterSR

I6°

EUV mask

Figure 1. Schematic diagram of coherent EUV scattering microscope (CSM). All the optics, including
the CCD camera, are inside the vacuum chamber.

35

surface of the mask. The imaging area is 27.6 mm
square; it contains a 2048 u 2048 array of imaging
pixels, each of which is 13.5 Pm square. The CCD
camera has a quantum efficiency of 42% for EUV
photons and a 16-bit analog-to-digital converter. The
camera is cooled to –50qC. The RMS noise of the
CCD was estimated to be 7 counts from counting
dark frames for 5 minutes. The dynamic range wasestimated to be 4 orders of magnitude. The distancefrom the mask to the CCD camera is about 92 mm,
which is equivalent to an NA of 0.15. The estimatedspatial resolution for this NA and coherent
illumination is 90 nm. It can be improved by shifting
the CCD camera so that it records higher diffraction
orders. A 200-nm-thick Zr filter was placed just after
the pinhole to remove the UV–visible components ofthe specular reflection from the Mo/Si multilayers.
The CSM has a shadowgraph mode that uses visible
light to align the mask. In this mode, a linear-stage isused to replace the Zr filter and the 5-Pm-diameter
pinhole with a visible ND filter and a 4-mm-diameter
pinhole. The mask X-Y stage can move ±60 mm toenable observation of the whole area of an EUV
mask of 6025 size with encoders. The step resolution
for movement is 4 Pm. The CSM chamber has a load
lock apparatus for sample exchange, which takes
about one hour.

Due to the off-axis illumination of the alpha tools, theCD includes the effects of shadowing by the absorberpattern. The concave mirror (radius of curvature: 163mm) projects the pinhole image onto the mask. It is
163 mm from the pinhole and the same distance fromthe mask. Due to aberrations inherent in the use of apinhole for imaging, the size of the pinhole was madesignificantly larger than the wavelength. The beam
divergence is equal to the calculated diffraction angle.
The area of the concave mirror that is exposed is lessthan a millimeter in diameter. The spot size
calculated by means of a ray-tracing program that
traced rays from the pinhole to the mask is 1 Pm. The
pinhole image is almost the same size as the object,which limits the field size of the CSM. To obtain
good contrast for the reconstruction of mask images,
the diffraction field should be at least 5 Pm across to
produce interference at the position of the CCD
camera. The spatial coherence length of the incident
beam is 18 Pm, as estimated from the divergence.
This is substantially larger than the required fieldsize.

Table 1. Specifications of coherent EUV scattering
microscope.

50 mm

Figure 2. Photograph of coherent EUV scattering
microscope (CSM). The solid line is the optical pathof the SR light.

The CCD camera (MTE-2048B, Roper Scientific)
can operate in a high vacuum and has aback-illuminated CCD without an anti-reflection
coating. The surface of the CCD is parallel to the36

Light source

White SR light (Bending)Center wavelength13.5 nm

Bandwidth

0.3 nmField sizeI5 PmIncident angle

6q

Numerical aperture

0.15

Spatial resolution

45 nm hp

Mask size

6025 glass substrate

Imaging device

Back-illuminated CCD

ZEP520A resist. Electron beam lithography(ELS-7500, ELIONIX) is used to write the pattern in
the resist; and the mask is etched by ICP dry etching(TCP 9400SE Alliance, Lam Research). Three typesof patterns were fabricated: horizontal and vertical
L/S patterns, and holes. The half pitch (hp) ranged
from 50 to 500 nm. Each pattern was formed on a
20-Pm-square area, which is larger than the field size
(I 5 Pm). Forty-eight patterns were fabricated in each
300-Pm-square block (Fig. 4). Nine blocks were
fabricated on a 4-inch Si wafer, along with alignment
marks to make alignment of the mask easy. The
alignment marks are useful for locating the positionof a pattern in the shadowgraph mode of the CSM.
Regarding the fabrication results, the 50-nm-hp
patterns collapsed due to the high aspect ratio of theresist. The 60-nm-hp and 200-nm-hp patterns were
fabricated successfully (Fig. 5). A half pitch of 60 nm
on a mask is equivalent to a half pitch of 15 nm forsemiconductor devices.

III. FABRICATION OF EUVL MASKPATTERNS
Test EUV masks were fabricated to evaluate theCSM specifications. Since coherent EUV scattering
microscopy is a new technique for observing EUV
masks, various types of masks with a variety ofpatterns and phase defects are needed for theevaluation. In this study, we fabricated standard
line-and-space (L/S) and hole patterns to develop our
fabrication technique. The masks consist of a Si
substrate, a Mo/Si multilayer coating, and a TaN
absorber layer. The Mo/Si multilayer has 40
6.9-nm-thick periods; and the ratio of the Mo layer
thickness to the period thickness is 0.4. The TaN
layer is 80 nm thick and has a calculated reflectivityof less than 0.1%. In the mask fabrication process(Fig. 3), first a Si substrate is coated with a Mo/Si
multilayer by magnetron sputtering (MPS-4500,
ULVAC). Next, the TaN layer is deposited; and aspin coater covers it with a 200-nm-thick layer of

Mo/Si multilayer
deposition

TaN deposition

EB lithograpy

ICP dry etching

Figure 3. Fabrication process for EUV mask.

37

Resist coating

Resist removal

Half pitch (nm)
50

60

70

80
VerticalHorizontal
Hole

VerticalHorizontal
Hole
150

180

200

250

Figure 4. SEM image (top view) of fabricated EUV mask. Each square is about 20 Pm on a side. There are 48
squares containing vertical L/S, horizontal L/S, and hole patterns with half pitches ranging from 50 nm to 500
nm.

(a)

(b)

(c)

(d)

800 nmFigure 5. SEM images of fabricated EUV mask: (a) 60-nm-hp L/S, (b) 60-nm-hp holes, (c) 200-nm-hp L/S, (d)200-nm-hp holes.
be 1.5%, assuming the reflectivity of the Mo/Si
multilayer to be about 60%. Since the reflectivity of
the absorber layer was higher than the calculated
value (< 0.1%), the thickness and/or the absorption
coefficient of that layer must be different from thevalues used in the calculation.

IV. RESULTS
To obtain a contrast image of the mask, the CCD
camera signal was measured at two positions, namely,on the surface of the Mo/Si multilayer and on thesurface of the absorber layer, with a ratio of 39. The
reflectivity contrast was found to be as high as 0.95.
The reflectivity of the absorber layer was estimated to38

Figure 6 shows images obtained with the CSM of
the 200-nm-hp L/S pattern in Fig. 5(c): (a) CCD
image, (b) reconstructed image, (c) magnified imageof (b), and (d) profile at the center of thereconstructed pattern. The shadowing effects of theabsorber pattern are negligible because the incident
light was parallel to the L/S pattern. The exposure
time was limited to 12 minutes so that the CCD

signal would not be saturated with zero-order light.
Figure 6(a) is the diffraction intensity recorded by the
CCD camera. The center signal is zero-order light,
and up to 4 diffraction orders were recorded. The
aura around the zero order is due to the Fraunhofer
diffraction of the pinhole. The signal counts for thezero, 1st, 2nd, 3rd, and 4th diffraction orders were
44300, 17955, 915, 1803, and 527, respectively.

(a)

(b)

5 Pm

(d)

1 Pm

㩷

㪈㪅㪇
㪇㪅㪏
㪇㪅㪍
㩷

㪥㫆㫉㫄㪸㫃㫀㫑㪼㪻㩷㪠㫅㫋㪼㫅㫊㫀㫋㫐㩷㩿㪸㪅㫌㪅㪀

(c)

㪇㪅㪋
㪇㪅㪉
㪇㪅㪇

㪇

㪈

㪉

㪊
㪋
㪧㫆㫊㫀㫋㫀㫆㫅㩷㩿P㫄㪀

㪌

㪍

㪎

Figure 6. CSM results for 200-nm-hp L/S pattern: (a) CCD image, (b) reconstructed image obtained with HIO
algorithm, (c) magnified image of (b), and (d) profile of center of (c).
nm, which is smaller than that obtained with the CSM.
The SEM detects secondary electrons at the surfaceof the absorber, and the CSM detects the distributionof the reflectance. Thus, the CD for absorber patterns
obtained with the SEM is smaller because thepatterns have sloping edges. The dependence of CD
on absorber shape will be investigated in the future.

The CD of the absorber thickness was found to be
224.2 ± 2.6 nm by fitting the peak diffraction
intensities to the Fraunhofer diffraction distribution.
On the other hand, a one-minute exposure yielded a
CD of 224.8 ± 3.7 nm. Since these values are
virtually the same, we can conclude that a one-minuteexposure is sufficient for estimating the CD. The
exposure time could be further reduced by increasing
the field of view and by developing a peak detection
algorithm. The CD obtained with the SEM was 199

In reconstructing a diffraction image, thesignal-to-noise (S/N) ratio is improved by resampling
the CCD data to reduce the size of the pixel array39

from the original 2048u2048 pixels to 512u512
pixels, where the estimated oversampling ratio7 is 16.
A threshold is also put on the CCD signal to further
reduce the noise. The images in Fig. 6(b-c) arereconstructions obtained with 200 iterations of the
HIO algorithm. They correlate well to the SEM
image in Fig. 5(c). For the reconstruction, the phasein real space was not constrained to be real andpositive because the target of the CSM contained aphase defect. In addition, the absorber patternproduces a phase shift corresponding to its thickness.
The constraint used in reconstruction was the size ofthe support area (that is, the illuminated area). The
support area was optimized so as to reduce the error
signal in real space (mask image) in theunilluminated area. A loose support constraint was
initially applied, but the bright image of the 5-Pm
field moved around in the support area as theiteration proceeded. For optimization, a tight support
size was chosen, with a step-by-step increase in the
support size to reduce the error. The CD of thereconstructed image profile is about 219 nm, which isabout the same as the fitting results for the diffraction
peaks.
Figures 7 and 8 show a 100-nm-hp L/S pattern anda 400-nm-hp hole pattern, respectively, taken with
the CSM using exposure times of 8 and 10 minutes.
Estimation of the CD requires not only zero- and1st-order diffraction images but also 2nd-order ones.
At present, the CSM cannot record 2nd-orderdiffraction for patterns with a half pitch of less than
100 nm because of the limited NA. However,
1st-order diffraction was clearly recorded for half
pitches from 60 nm to 90 nm. Thus, the pattern withthe smallest hp (60 nm) fabricated in our laboratory
exhibited a periodic structure when observed with
EUV light. In Fig. 7, the reconstruction for the
100-nm-hp L/S pattern is very good. The CD
obtained from the SEM image is 95 nm; that from the
CSM image is 120.7 ± 2.1 nm; and that from thereconstructed image profile is 119 nm. The CD fromthe CSM is larger than that from the SEM.

(b)

(a)

Figure 7. 100-nm-hp L/S pattern: (a) reconstructed image obtained with CSM and (b) SEM image.

(b)

(a)

Figure 8. 400-nm-hp hole pattern: (a) reconstructed image obtained with CSM and (b) SEM image.
The count for the zero-order signal was about 3,000,
which is only 1/10 of that for the L/S pattern. The L/Sand hole patterns were fabricated on the same
substrate, but the absorber layer was not completely
etched off the holes, even though the dry etching

For the hole pattern in Fig. 8, the reconstructed
image corresponds to the SEM image. However,there is a reconstruction error in the absorber region,
possibly due to the low reflectivity of the EUV mask.

40

process was identical. The etching conditions for theV.

absorber layer need to be optimized.

CONCLUSION

In the near future, we will develop a tabletop
high-order harmonic generation (HHG) laser EUV
source11 for the practical inspection of EUV masks.
The power will be 1000 times greater than that of ourpresent source, which wastes most of the light inachieving high spatial coherence. The target defectdetection sensitivity of this actinic inspection tool isless than 20 nm for the 22-nm node, which translates
into a feature size of 5 nm on a wafer. The target
sensitivity for the CD is about 0.1 nm, and the target
scanning time for a whole mask is less than 90
minutes.

A CSM has been developed for the actinic
inspection of EUV lithography masks, and it has been
installed at the NewSUBARU synchrotron facility.
To evaluate its performance, EUV masks containing
L/S and hole patterns with half pitches ranging from50 nm to 500 nm were fabricated, and the CSM wasused to image them. EUV mask patterns with half
pitches down to 100 nm were successfullyreconstructed. For L/S patterns, the image shapes
were well reconstructed and matched those in the
SEM images. The actinic CD of an L/S pattern was
estimated from a one-minute exposure with the CSM,
and was found to be only 25 nm wider than the CD
obtained with a SEM. Our results demonstrate that
the CSM can be used to image EUV masks andobtain the actinic CD. Thus, the CSM is a practical
tool for inspecting EUV masks.

Acknowledgement
This work was partially supported under the
JST-CREST project “Development of Ultra-Fine
Structure Metrology System using Coherent EUV
Source.”References1.

Semiconductor Industry Association, “International Technology Roadmap for Semiconductors: 2007
Lithography”, Austin, TX, International SEMATECH.

2.

T. Terasawa, Y. Tezuka, M. Ito and T. Tomie, SPIE Proc. 5446, 804 (2004).

3.

A. Barty, Y. Liu, E. Gullikson, J. S. Taylor, and O. Wood, SPIE Proc. 5751, 651 (2005).

4.

K. A. Goldberg, P. P. Naulleau, A. Barty, S. B. Rekawa, C. D. Kemp, R. F. Gunion, F. Salmassi, E. M.
Gullikson, E. H. Anderson and H. Han, SPIE Proc. 6730, 67305E (2007).

5.

T. Haga, H. Takenaka and M. Fukuda, J. Vac. Sci. Technol. B 18, 2916 (2000).

6.

K. Hamamoto, Y. Tanaka, H. Kawashima, S. Y. Lee, N. Hosokawa, N. Sakaya, M. Hosoya, T. Shoki, T.
Watanabe and H. Kinoshita, Jpn. J. Appl. Phys. 44, 5474 (2005).

7.

J. Miao, P. Charalambous, J. Kirz and D. Sayre, Nature 400, 342 (1999).

8.

J. Miao, Y. Nishino, Y. Kohmura, B. Johnson, C. Song, S. H. Risbud and T. Ishikawa, Phys. Rev. Lett. 95,
085503 (2005).

9.

J. R. Fienup, Appl. Opt. 21, 2758 (1982).

10.

T. Watanabe, T. Haga, M. Niibe and Hiroo Kinoshita, J. Synchrotron Rad. 5, 1149 (1998).

11.

E. J. Takahashi, Y. Nabekawa and K. Midorikawa, Appl. Phys. Lett. 84, 4 (2004).

41

Imaging Performance Improvement of an Extreme
Ultraviolet Microscope
Kei Takase, Yoshito Kamaji, Naoki Sakagami, Takafumi Iguchi, Masaki Tada, Yuya Yamaguchi, Yasuyuki
Fukushima, Tetsuo Harada, Takeo Watanabe, and Hiroo Kinoshita
Laboratory of Science and Technology for Industry, University of Hyogo
1-1-2 Kouto, Kamigori, Ako-gun, Hyogo 678-1205, JapanThe extreme ultraviolet microscope (EUVM) has been developed for an actinic mask inspection of a EUV
finished mask and a EUV blank mask. Using this microscope, amplitude defects on a finished mask and phase
defects on a glass substrate are observed. However, it has a problem of low contrast, which originates from 1)
thermal noise of a charge coupled device (CCD) camera, 2) wave aberrations of an optical component, and 3) anonuniform illumination intensity. To resolve these issues, EUVM was improved. 1) To reduce a thermal noise,a cooled CCD camera is installed. 2) To remove wave aberrations of a back-end turning mirror, a Mo/Si
multiplayer-coated thick glass substrate with a high surface accuracy is employed instead of a Si wafer substrate.
Furthermore, in situ alignment was carried out to remove wavefront aberrations for a Schwarzschild imaging
optics. In addition, 3) by installing a scanning system on the front-end turning mirror, a highly uniform
illumination intensity was achieved.㻌 As a result, images of less than 100 nm without astigmatism were obtained.
the actinic EUVM installed at the BL-3 beamline of the
NewSUBARU synchrotron radiation (SR) facility. It
consists of Schwarzschild optics (NA, 0.3; magnification,30x) as the illumination and imaging optics, an X-Y-Z
sample stage, an X-ray zooming tube connected to a CCD
camera, and an image processing computer. It is installed ina vacuum chamber (pressure, 1×10-5 Pa) on a vibration
isolation table. Figure 2 shows the mechanism of phase
defect inspection with EUVM. When the multilayer
fulfills the Bragg condition, the EUV light thatpenetrates into the multilayer is normally reflected.
However, if there is a defect pattern on a substrateunder the multilayer, the Bragg condition is notsatisfied in the multilayer, the light on the defectcould not reflect in the right direction to
Schwarzschild optics and makes no imaged on the
X-ray zooming tube. Thus, an image of a phase
defect is observed by a EUVM. EUVM can image
phase defects directly, even on a multilayer with aflat surface.
We have observed the finished mask with theabsorber pattern and the mask blanks with
programmed phase defects to identify the criticaldimensions of phase defects on mask blanks.7)
However, there were nonuniform intensity
distribution and wave aberrations. In this paper,
image quality improvement technologies are
discussed.

1. Introduction
In Accordance with the ITRS roadmap, extreme
ultraviolet lithography (EUVL) is expected to be
introduced into the high-volume manufacturing
process from the 22-nm half-pitch node from 2013.1)
The fabrication of a defect-free mask is the first issue
of EUVL technology.2) There are two types of defects
on EUVL masks. One is an amplitude defect and theother is a phase defect.3-7) An amplitude defectoriginates from either a particle on the surface of themultilayer or a flaw in the multilayer.8,9) On the other
hand, a phase defect is produced when the multilayer
is deposited over either a bump or a pit on thesubstrate. Since the intensity of reflected lightdecreases owing to a phase shift, the projection imageof the mask area with the phase defect is affected.
There are two techniques of detecting a small
defect on an EUVL mask: using deep ultraviolet(DUV) light10) and using EUV light at the exposure
wavelength.11-19) Mask defect inspection using DUVlight is a conventional method that is used in opticallithography. However, this inspection has a difficulty
in detecting a phase defect inside the Mo/Si
multilayer of an EUVL mask because the DUV lightis reflected on the surface of a mask. Thus, the atwavelength mask inspection method is necessary forphase defect inspection of an EUV mask. Therefore,
we constructed an extreme ultraviolet microscope(EUVM) system.3-5,20) Figure 1 shows the configuration of42

Fig. 1 Setup configuration of the EUVM system. (a) front-end turning mirror (b) back-end turning mirror (c)CCD camera.

Fig. 2 Mechanism of phase defect inspection.

flatness of the substrate of the back-end turning
mirror and the wavefront error of the Schwarzschild
optics. Furthermore, this image includes nonuniform
intensity, which reduces the resolution of the imaging.
This nonuniformity also resulted from the surface
figure error of the front-end mirror.

2. Issue of Imaging Quality
Figure 3 shows an image of a 300-nm-half-pitch (hp)
elbow pattern observed using EUVM in our previous
work21). Since the image includes remarkable
wavefront aberrations, the resolution in the horizontal
direction and that in the vertical direction are
different. These aberrations resulted from the surface

43

Fig. 3 EUVM image of 300-nm-hp elbow pattern in our previous work (magnification: 1800x).

Figure 4 shows the surface flatness of the Si
wafer substrate of the back-end turning mirror. As
shown in Fig. 4, the surface figure of the back-end
turning mirror was about 166 nm (rms). To reducewave aberrations, a lower-figure-error substrateshould be employed. In addition, in situ alignment of
Schwarzschild optics is required to reduce wavefront
aberrations.

Fig. 4 The surface flatness of Si wafer substrate of back-end turning mirror was about 166 nm (rms).

noise of CCD camera is observed at themagnification of 6000x. To reduce the thermal noiseof CCD camera, a cooling CCD camera is effective.

Figures 5(a) and 5(b) show images of the
300-nm-half pitch(hp) pattern taken using EUVM attotal magnifications of (a) 1800x and (b) 6000x,
respectively. The noise considered to be thermal

44

Fig. 5 EUVM images of 300-nm-hp pattern taken at total magnifications of (a) 1800x and (b) 6000x.

images of high contrast at a maximum magnificationof 200x. Figures 7(a) and 7(b) show the EUVM
images of a 150-nm-hp pattern at a magnification of
6000x before and after the updating the CCD camera.
The contrast of the 150-nm-hp pattern was increased
from 0.22 to 0.38 when using a cooling CCD camera.
The contrast can be calculated using the following
equation:

3. Imaging Quality Improvement
3.1 Thermal noise reduction utilizing cooling CCD
cameraThe conventional CCD camera was replaced with acooling CCD to increase a high S/N ratio of the
EUVM images by reducing thermal noise. Table䊠
shows the performance of the CCD camera andcooling CCD camera. Figure 6 shows the backgroundimages taken by the conventional (a) and cooling (b)CCD cameras without the optical input observed by
EUVM and the intensity distribution of the image.
The cooling CCD temperature was set at a minimum
cooling temperature of -27 ºC. The thermal noise of
the cooling CCD camera disappeared, as shown Fig.
6(b), and the camera enabled the acquisituion of
uniform-background images. Therefore, the cooling
CCD camera also enabled the acquisition of EUVM

Contrast

I max  I min,
I max  I max

where I max and I min are the average maximum
value and the average minimum value of the EUV
intensity distributions of the line and space pattern,
respectively.

Table䊠. The performance of a CCD camera and a cooling CCD camera.
CCD camera

Cooling CCD camera

Imaging area (Pm )9.0㽢6.7

14.8㽢10.0

Pixels1392㽢1040

2184㽢1472

Pixel size (Pm)

6.45㽢6.45

6.8㽢6.8

Minimum cooling temp. (ºC)

䇷

-27

2

45

Fig. 6 EUVM background images without optical input and the intensity profiles of each image. (a) taken with a
CCD camera, (b) taken with a cooling CCD camera.

Fig. 7 EUVM images of 150 nm Line and Space (L/S) pattern (a) taken with a CCD camera, (b) taken with acooling CCD camera (magnification: 6000x).

3.2 Reduction of wave aberration to improve opticalcomponents
To reduce the wavefront aberration, in general, asmooth and flat mirror surface and highly accuratealignment of the optical system are necessary for theimaging. In the EUVM system, a Mo/Si multilayer
coated on the Si wafer was employed as the back-end
turning mirror. As shown in Fig. 4, this mirror has asurface figure error of 166 nm (rms), it causes a large
wavefront aberration and defocusing. Furthermore, in
the alignment of an optical system (carried out by
wavefront measurement using a laser interferometer)in the atmosphere, alignment accuracy changes after
a period time. It causes imaging aberrations.

The Mo/Si multilayer coated on a thick glass
substrate with a smooth surface was employed as a
back-end turning mirror in the EUVM system, as
indicated by (b) in Fig. 1 instead of the Mo/Si
multilayer coated on a Si wafer substrate to improve
wave aberrations. The wavefront error of the updated
mirror was measured using a Fizeau interferometer(ZYGO GPI) and has a flatness of 3.7 nm (rms), as
shown Fig. 8. In addition, we also carried out in situ
alignment of the Schwarzschild imaging optics to
reduce wave aberrations. Namely, an X-Y-Z-axisalignment mechanical system for each mirror of theimaging optics, which enables movement in vacuumis installed in the optical housing.

46

Fig. 8 The surface flatness of thick glass substrate of back-end turning mirror was about 3.7 nm (rms).
Figures 9(a) and 9(b) show the observed imagesof a 480-nm-hp elbow pattern before and after
reducing wavefront aberrations, respectively. As aresult of changing a thick mirror and introducing insitu alignment, the wavefront aberrations andresolution were improved.

Fig. 9 EUVM images of 480-nm-hp elbow pattern. (a) before upgrading of imaging optics. (b) after upgrading ofimaging optics (magnification: 600x).
3.3 Achievement of uniform illumination intensity
It was difficult to recognize the existence of phase
defects from the intensity distribution on an EUVM
image recorded using the static illumination as shown
Fig. 10(a), because the signal of the defects is hiddenby the noise that causes the nonuniform illumination
intensity. This nonuniform illumination intensity
distribution seems to be caused by the figure error offront-end mirrors. Then, in order to average anonuniform illumination intensity distribution, thefront-end turning mirror [as indicated by (a) in Fig. 1]
was scanned. A piezo actuator was employed forscanning a mirror.
A uniform illumination was successfully obtained
after the front-end-turning-mirror scanning. Figures
10(a) and 10(b) show the EUVM images of aprogrammed bump defect of 160 nm width recorded
by static illumination and scanning illumination.
Figures 10(c) and 10(d) show the illumination
intensity distributions along the imaginary lines47

between two arrows in Fig. 10(a) and Fig. 10(b),respectively. By reducing noise intensity by afront-end-turning-mirror scanning method, the phase

defect signal was recognized clearly, as shown in Fig.
10(d).

Fig. 10 EUVM images of programmed bump defect width of 160 nm size recorded with (a) static illuminationand (b) scanning illumination. (magnification: 600x) (c) and (d) show the illumination intensity distributions
along the imaginary lines between two arrows in (a) and (b) images.

intensity distribution of the EUVM images. Although
the resolution and contrast of the EUVM images were
improved, the resolution and contrast were still not
sufficient for the 22-nm-node requirement. Further
studies are required for the improvements ofresolution and contrast.

4. Imaging performance of EUVM
After the improvement as described in 㼲 3, theresolution and image contrast of line and spaceabsorber patterns were evaluated. Figure 11 shows
the images of 150-, 130-,120-, 110-, and 100-nm-hp
patterns obtained by EUVM. Then, the contrast as
shown Fig. 11, was calculated from the illumination

Fig. 11 EUVM images of 150, 130, 120, 110 and, 100-nm-hp patterns and there contrast values (magnification:
3000x).

48

good-alignment of Schwarzschild imaging optics.
Utilizing a scanning system on a front-end turning
mirror, the phase defect was recognized clearly in
EUVM owing to reduction of background intensity
noise. By these improvements EUVM image quality
was improved.

5. Conclusions
EUVM images of high contrast at a highmagnification were obtained using the cooling CCD
camera. Wavefront aberrations were reduced andresolution was improved by employing a Mo/Si
multiplayer-coated thick glass substrate of highsurface accuracy on a back-end turning mirror andReferences
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49Development of the Extreme Ultraviolet Interference
Lithography System*Yasuyuki Fukushima, Naoki Sakagami, Teruhiko Kimura,
Yoshito Kamaji, Takafumi Iguchi, Yuuya Yamaguchi, Masaki Tada,
Tetsuo Harada, Takeo Watanabe, and Hiroo Kinoshita
Laboratory of Advanced Science and Technology for Industry, University of Hyogo,
3-1-2 Koto, Kamigori, Hyogo 678-1205, Japane-mail: yasuyuki@lasti.u-hyogo.ac.jp

Extreme ultraviolet interference lithography was carried out at the long undulator beamline in NewSUBARU. It
was confirmed that the spatial coherence length is 1.1 mm using a 10-Pm-wide slit in the Young’s double slit
experiment. A 25-nm half pitch (hp) resist pattern was successfully replicated by extreme ultraviolet interference
lithography (EUV-IL) utilizing a two-window transmission grating pattern of a 50-nm line and space (L/S). For
the replication of a 20-nm L/S resist pattern by EUV-IL, we contrived a fabrication process that is suitable for atransmission grating pattern of 40-nm L/S and smaller. Employing a hard-mask process with a silicon dioxide(SiO2) layer on a tantalum-nitride (TaN) layer in the fabrication of a two-window transmission grating, we
successfully achieved five times larger dry-etch selectivity in comparison with a non-hard-mask process. As aresult, we confirmed the ability this process to apply to a 40-nm hp grating.

1. Introduction
Extreme ultraviolet lithography (EUVL)1) is the mostpromising technology for a 22-nm half-pitch (hp) andit will be required for high-volume-manufacturinglithographic technology by the year 2013.2) Resist
materials and process technologies are two of thethree top issues. In addition, according to the ITRS
roadmap, EUVL is strongly predicted to be expanded
to the 20-nm node by the year 2017 and to the 11-nm
node by the year 2022. For the 20-nm node and the
11 nm-node, the requirements of line widthroughness (LWR) are 0.8 nm (3V) and 0.6 nm (3V),
respectively. Because the required size of LWR issmaller than the molecular size of a resist, asatisfying the LWR criterion is not easy. Thus,

because the development of resist material should bestarted earlier than the development of the EUV
exposure alpha tool, extreme ultraviolet interference
lithography (EUV-IL) 3-12) should be recognized as animportant part in the evaluation of resist materials at
20-nm and smaller.
The EUVL interference exposure tool was
installed at the BL-9 long undulator beamline in the
NewSUBARU synchrotron radiation facility. The
EUV-IL exposure tool including a two-windowtransmission grating was installed at the end stationof the BL9C beamline. In this report, we focus on thecoherence length measurement, exposure result, andfabrication process using a hard-mask process for asilicon dioxide (SiO2) layer on a transmission grating.

2. Beamline Setup for EUV-IL in NewSUBARU
EUV-IL was constructed at the BL9 long undulator(LU) beamline in NewSUBARU. Figure 1 shows thebeamline setup of the EUV-IL. An LU source
spectrum with the peak at a specific wavelength canbe obtained by tuning the gap between the magnets of
the undulator.13) Because the long undulator in
NewSUBARU has a total length of 10.8 m and has
200 periods for high-brilliance radiation, thebrilliance of EUV light with the undulator as a source
is approximately 50,000 times higher than that with abending magnet as a source.14) To achieve a 20-nm
L/S pattern and smaller on a wafer by EUV-IL, alarge spatial coherence length can be increased byenlarging the distance between the pinhole and thetransmission grating. Thus, a large spatial coherence
length and a low exposure time can be realized
simultaneously by increasing the light intensity
employing the long undulator. As described in §4, aspatial coherence length of more than 1 mm can beachieved. Figure 2 shows the light spectrum used inthis experiment. The EUV light was focused on apinhole using an optical component. At the pinhole
position, the beam is focused to a size of 10 Pm in they-direction. Because the distance from the pinhole to
the resist is maintained at approximately 3.3 m and50

the high wavelength range beyond 20 nm is removed
by a 0.2-Pm-thick zirconium (Zr) filter, the light ismonochromated with a wavelength of 13.4 nm on theresist sample.ᴾ(a)X

Monochromator
M8
M6 M7
M5
M4

M0

M1
Z

Grating & wafer
Pinhole

Slit

(b)
Y

M0

Slit M4

M1
Z

M5M6

M7
M8

PinholeMonochromator

Grating&wafer

Fig. 1. BL9 beamline setup of EUV-IL: (a) top view and (b) side view.

Current
intensity(nA)(nA)
Current intensity

500

398.5nA@13.38nm
399 nA@ 13.4 nm
400

300

200

100

61 nA@ 7.24 nm
61.4nA@7.24nm

0
4

6

8

10

12

14

16

Wavelength(nm)
Wavelength (nm)Fig. 2. Spectrum of long undulator at the BL9 beamline used for EUV-IL.

order ray diffracted from another window of thegrating. The diffraction condition of the grating canbe expressed as mO d (sin T f  sin T i ) , wherem , d , T f , and T i are the number of thediffraction order, the pitch size of the grating pattern,
the angle of transmitted light, and the angle of

3. Principle of EUV
Figure 3 shows the principle of EUV-IL. In the dual
beam interference system, double periodic
interference fringes are created at a position fitting
two phases when the +1st order ray diffracted fromone window of the grating interferes with the -1st51

incident light, respectively. In addition, the pitch size
p is expressedof interference fringes
as p O /( 2 sin T ) , where T is half of the angle
between the propagating directions of the two beamsof the +1st and -1st diffraction orders. Consideringnormal incident light, an incident light angle may be
expressed as T i 0 . Then, the pitch size ofinterference fringes p is expressed as p d / 2 .
Thus, the half-size of the grating pattern size can be
replicated on a wafer. In EUV-IL the distance

between the two windows has to be smaller than thecoherence length. In addition, if the grating pitch
pattern d becomes smaller, the diffraction angle
T f of the -1st and +1st diffraction orders becomeslarger. If the distance between two windows of atransmission grating is constant, the distance between
the grating and the wafer becomes smaller. Thus, alarger coherence length may relax the distance
between the grating and the wafer.

Pattern is replicated in this area
+ 1st order light

EUV light

0th order light㼼 1st order light
0th order light+ 1st order light

Resist Wafer

Grating

Fig. 3. Principle of EUV interference lithography.

photodiode position in the vertical direction, as
shown in Fig. 4(b). Two single slits of 3 mm(horizontal)㽢25 Pm (vertical) in size and 3 mm (h)㽢10 Pm (v) in size were prepared. The size of eachslit in the double slit was 3 mm (h)㽢25 Pm (v). Four
double slits with separations of 40, 160 320, and 640
Pm were prepared for Young’s double slit
experiment.

4. Spatial Coherence Measurement
The spatial coherence of the light source can be
determined by Young’s double slit experiment.
Figure 4 shows the experimental setup for the spatial
coherence measurement.15, 16) The distance between
the single slit and the double slit was 0.9 m, and the
distance between the double slit and the photodiodeinstalled in the exposure chamber was 2.4 m. The
light intensity was measured by changing the

Photodiodeinside ofExp. Chamber
Shutter

Double slit

M7 concave
mirrorM6 concave
mirrorM8 planemirrorSlit

Fig. 4. Experimental setup for spatial coherence measurement.

(
52

(

(a)

(b)

2.80E-09
2.80E-09

3.50E-09㻟㻚㻡㻜㻱㻙㻜㻥
3.30E-09㻟㻚㻟㻜㻱㻙㻜㻥

Photodiode Current (A)Photodiode Current (A)2.60E-09
2.60E-09

2.40E-09
2.40E-09

2.20E-09
2.20E-09

2.00E-09
2.00E-09

1.80E-09
1.80E-09

1.40E-09
1.40E-09

(
(c)
0

1000
1000

2000
2000

㻞㻚㻣㻜㻱㻙㻜㻥
2.70E-09
2.50E-09㻞㻚㻡㻜㻱㻙㻜㻥
2.30E-09㻞㻚㻟㻜㻱㻙㻜㻥

(2.10E-09㻞㻚㻝㻜㻱㻙㻜㻥

㻝㻚㻣㻜㻱㻙㻜㻥
1.70E-09
3000
3000

4000
4000

5000
5000

6000
6000

7000
7000

㻝㻚㻡㻜㻱㻙㻜㻥
1.50E-09

8000
8000

㻜

2000
㻞㻜㻜㻜

(d)

Position (Pm)

7.00E-10

4000
㻠㻜㻜㻜

6000
㻢㻜㻜㻜

8000
㻤㻜㻜㻜

10000
㻝㻜㻜㻜㻜

12000
㻝㻞㻜㻜㻜

14000 㻝㻢㻜㻜㻜
16000
㻝㻠㻜㻜㻜

18000
㻝㻤㻜㻜㻜

Position (Pm)

4.00E-11

6.00E-10

2.00E-11

5.00E-10

0.00E+00

Photodiode Current (A)Photodiode Current (A)㻟㻚㻝㻜㻱㻙㻜㻥
3.10E-09
2.90E-09㻞㻚㻥㻜㻱㻙㻜㻥

㻝㻚㻥㻜㻱㻙㻜㻥
1.90E-09

1.60E-09
1.60E-09

4.00E-10
3.00E-10
2.00E-10
1.00E-10
0.00E+00-2.00E-11-4.00E-11-6.00E-11-8.00E-11-1.00E-10-1.20E-10-1.00E-10-1.40E-10

0

200

400

600

800

1000

0

200

Position (Pm)

400

600

800

1000

Position (Pm)

Fig. 5. Examples of light intensity measurement
at the grating position: (a) slit width 25 Pm anddouble slit separation 40 Pm, (b) slit width 25 Pm
and double slit separation 160 Pm, (c) slit width
25 um and double slit separation 320 Pm, and (d)slit width 10 um and double slit separation 640
Pm.
1.0

Normalized Contrast

The spatial coherence was calculated by thefollowing method. The contrast of the spatial
coherenceisexpressedas2
2
Contrast exp( d s / 2 Rc ),where
Rc ( 2 u l c ), l c , and d s are the coherence
radius, the spatial coherence length at the double slit
position, and the double slit separation, respectively.
The spatial coherence length is defined for thecondition where Contrast 0.88 . Furthermore,
the measured value of Contrast is expressed asContrast ( I max  I min ) /( I max  I min ) , where
I min and I max are the minimum photodiode current
and the maximum photodiode current, respectively.
When the distance between the single slit and the
double slit and the distance between the double slit
and the photodiode are taken into account, the spatial
coherence length ( Lc ) at the grating position isexpressed as Lc 2.4 u l c / 0.9 .
Figures 5(a), 5(b), and 5(c) show the results oflight intensity measurements using a 25-Pm slit withdouble slit separations of 40, 160, and 320 Pm,
respectively. In addition, Fig. 5(d) shows the result oflight intensity measurements using a 10-Pm slit witha double slit separation of 640 Pm. In this figure, thevertical axis is the measured current from a
photodiode, and the horizontal axis is the distance tothe double slit in the y-direction. Contrast can beobtained using eq. (5) by substituting the maximum
and minimum values obtained form these graphs.
Figure 6 shows results. The vertical axis isnormalized Contrast , and the horizontal axis is the
double slit separation. Using 25-Pm and 10-Pm
single slits, the spatial coherence lengths ( l c ) at the
double slit position were 204 and 440 Pm,
respectively. Thus, it was confirmed that spatial
coherence ( Lc ) using a 25-Pm slit and a 10-Pm slit
was 544 and 1173 Pm at the transmission grating
position, respectively. As a result, a large spatial
coherence length was achieved for replicating a
20-nm L/S pattern and smaller.

0.8

0.6

0.4

0.2

25 Pm-width slit
10 Pm-width slit

0.0
0

100

200

300

400

500

600

Double slit separation distance (Pm)

Fig. 6. Results of spatial coherence length
measurement.

50 nm, and the prebake was carried out at 180 ºC for
180 s. The exposure conditions were as follows:
using a 25-Pm (vertical) slit, the distance between thewafer and the transmission grating was 250 Pm, thecurrent was 560 nA after transmission grating, andthe exposure time was 12 s. Development was carriedout at 23 ºC for 90 s with o-xylene, and the wafer wasrinsed at 23 ºC for 30 s with isopropyl alcohol.
Figure 7 shows a photograph of a replicated
ZEP520A resist pattern of a 34-nm line and a 16-nm

5. Resist Patterning by EUV-IL
25 nm hp resist pattern was replicated by EUV-IL
using the 100-nm-pitch transmission grating. A wafer
stage and a grating stage were installed in the
EUV-IL exposure chamber. The wafer stage consistsof x-, y-, and z-stages and a tilt stage. The gratingstage consists of x- and y- stages and a tilt stage.
Using these stages, the light axis was adjusted. A
nonchemically amplified resist ZEP520A was
spin-coated on a 4-in. wafer. The resist thickness was53

space (25-nm hp) pattern observed using a criticaldimension scanning microscope (CD-SEM; Hitachi
S8840). In the near future, various types ofchemically amplified resist will be evaluated. In
addition, in future studies, we will approach
replicating 20-nm hp resist patterns and smaller.

Fig. 7. SEM image of replicated ZEP520A resist pattern of a 25-nm hp.

Using a two-dimensional transmission grating, asshown in Fig. 8(a), with a four-beam diffraction, adot or hole pattern can be replicated. In this case, fora 50-nm L/S grating pattern, a 35-nm hp dot resist
pattern was replicated, as shown in Fig. 8(b). The

resist was ZEP520A. The resist thickness was 50 nm.
The resist development and rinse conditions were thesame as those used in replicating the L/S resist
pattern.

(b)(a)

Fig. 8. (a) Configuration of two-dimensional transmission grating and (b) SEM image of replicated ZEP520A
resist pattern of 35-nm hp dot resist pattern.

Si3N4 layer is 7.4%. For the grating absorber, a TaN
layer with 70 nm thick was coated on a Si3N4 layer,
which has a good absorbance of 99.6% for EUV
light.18) Considering the dry-etch selectivity between
a resist and TaN, to fabricate 30-nm and 40-nm L/S
TaN patterns with 70 nm thick, the resist should be
200 nm thick. Therefore, it is impossible to make 30and 40-nm L/S resist patterns with 200 nm thick,because the resist pattern collapses. On the other
hand, if a 20-nm-thick silicon dioxide (SiO2) layer is

6. Transmission Grating Fabrication by Applying
a Hard-Mask Process
The fabrication of a transmission grating17) is a key
technology for EUV-IL. For replicating resist
patterns of 20-nm hp and smaller, it is necessary to
make a transmission grating of a 40-nm L/S pattern.
Figure 9 shows the fabrication of a transmission
grating. A 4-in. silicon wafer coated on both sides
with a silicon nitride (Si3N4) layer in 300 nm thick
was prepared. The transmittance of a 300-nm-thick54

deposited on a TaN layer used for a hard-mask
process, the required thickness of the resist is about
60 nm. The dry-etch selectivity of a resist and of TaN
was approximately 0.32. However, in the case ofusing a hard-mask process for a SiO2 layer, thedry-etch selectivity of the resist and the TaN was
approximately 1.7. The dry-etch selectivity of theresist and the TaN is improved fivefold by employing
a hard-mask process.

method assisted by chlorine (Cl2) gas. The etch
conditions of assisted-gas flow-rate, ICP RF power,
and bias power are 25 sccm, 100 W, and 25 W,
respectively. As shown in Fig. 10(b), because theetching selectivity between a ZEP520A resist and a
SiO2 layer was 0.51, and that between SiO2 and TaN
was 3.4, the selectivity between a ZEP520A resist
and a TaN layer was 1.7. Thus, as shown in Fig. 10,
the etch selectivity between a ZEP520A resist and a
TaN layer using a hard-mask process is five times
larger than that using a non-hard-mask process. A
backside Si3N4 layer of a desired aperture wasremoved by a reactive-ion-etch (RIE) method assisted
by CF4 gas using a metal mask. The silicon substrateof a desired aperture was removed by a wet-etch
process using an aqueous solution of potassiumhydroxide (KOH) at a temperature of 80 ºC.19) Figure11(a) shows a photograph of a finished TaN
transmission grating on a 4-in. Si wafer after a
wet-etch process. Nine transmission gratings can be
fabricated per wafer. Using this method, because a
60-nm L/S grating pattern was successfully formed,
as shown in Fig 11(b), we will try to make a 40-nm
L/S grating pattern in the next stage.

TaN and a SiO2 layers are deposited on a Si3N4
layer using a magnetron sputtering system. As aresult, it is possible to make a 40-nm L/S grating
pattern and smaller using two metal layers that havegreatly different dry-etch rates, as shown in Fig. 10.
A ZEP520A resist was spin-coated on a wafer, and a
resist pattern was replicated by electron beam (EB)lithography. The resist pattern was transferred to a
SiO2 layer by an inductively coupled plasma (ICP)dry-etch system (TCP9400SE, Lam Research)assisted by a fluorocarbon (CF4) gas. The etch
conditionofassisted-gas
flow-rate,
ICP
radio-frequency (RF) power, and bias power are 60
sccm, 100 W, and 25 W, respectively. A SiO2 pattern
was transferred to a TaN layer by an ICP dry-etch
SiO2
Si3N4
Si
Si3N4

TaN

Si3N4 Coatedon Si substrate

Deposition of TaN
and SiO2

Coating ZEP520A resist

Electron beam exposure

Dry etching by CF4 gas

Dry etching by Cl2 gas

Dry etching by CF4 gas

Wet etching by KOHaq

Coating ZEP520A resist

Electron beam exposure

Dry etching by CF4 gas

Completion

Fig. 9. Fabrication of a transmission grating.

55

CF4

selectivity
CF4 0.51

Resist selectivity
0.32
220 nmResistCF4
30 nm
SiO2 15 nm

CF4selectivity
3.4
Cl
2

Cl2

TaN 70 nm

TaN 70 nm

Selectivity of resist and TaN
0.32

Selectivity of resist and TaN
1.7

Fig. 10. Dry-etching selectivities of SiO2 and TaN.

(a)

(b)
2mm
2mm

20mm

20mm

Fig. 11. (a) Photograph of a finished TaN transmission grating on a 4-in. silicon wafer after wet-etching, and (b)SEM image of the cross-sectional view of a 60-nm L/S grating pattern.
Furthermore, to improve the contrast of theinterference fringes, the intensity of EUV lighttransmitted from outside a TaN grating patterned area
has to be reduced with an additional resist absorberlayer. Thus, a 1-Pm-thick ZEP520A resist was
spin-coated on a TaN grating pattern, but only the
TaN grating patterned area was exposed by the EB
writing tool. After the development of the resist, theresidual resist on the TaN grating pattern wasremoved completely by a CF4 dry-etch process. Thus,
70-nm-thick TaN and a 1-Pm-thick resist were used
as an additional absorbers for the outside of a TaN
grating patterned area, which has a total absorbanceof 99.998% including the TaN and the additional
resist layer of ZEP520A.

7. Conclusions
Extreme ultraviolet interference lithography was
carried out at the long undulator beamline in
NewSUBARU. It was confirmed in Young’s double
slit experiment that the spatial coherence length is 1.1
mm using a 10-Pm-wide slit. A 25-nm half-pitch (hp)
resist pattern was successfully replicated by EUV-IL
utilizing a two-window transmission grating patternwith a 50-nm line and space (L/S). For the replicationof a 20-nm L/S resist pattern and smaller by EUV-IL,
we developed a fabrication process suitable for atransmission grating pattern of 40-nm L/S andsmaller. Employing a hard-mask process using asilicon dioxide (SiO2) layer on a tantalum-nitride(TaN) layer in the fabrication of a two-windowtransmission grating, a fivefold larger dry-etch56selectivity in comparison with the non-hard-mask
process was successfully achieved. As a result, we

confirmed the ability to apply this method to a 40-nm
hp grating.

Acknowledgment
We would like to thank the Japan Society for the Promotion Science for the Grant-in-Aid for Scientific
Research.

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57

High-Precision Analysis for Material Analysis Beamline
at BL05 for Industrial Enterprises
T. Hasegawa1, M. Uemura1, M. Motoyama2, S. Matsui2 and K. Kanda2
1 Synchrotron Analysis L.L.C., Hyogo-ku, Kobe, Hyogo 652-0863 Japan
2 University of Hyogo, Kamigori, Ako, Hyogo 678-1205 Japan
Abstract
A material analysis beamline for the industrial enterprises’ use was completed at BL05 in March
2008. 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), which cover the whole energy range of the soft X-ray region from 50 eV to4000 eV. These two branch lines can be operated simultaneously. The X-ray absorption finestructure (XAFS) measurements in the total electron yield (TEY) and fluorescence yield (FLY)
can be performed at BL05A and BL05B. In addition, the X-ray photoelectron spectra (XPS) canbe measured at BL05B.
Introduction
Recently, the needs for material analysis in thesoft X-ray region using synchrotron radiation has
increased in the analysis industry. A material analysis
beamline for the industrial enterprises’ use wascompleted at BL05 in March 2008. The whole usefulenergy range of the BL05 is the soft X-ray region
from 50 to 4000 eV and X-ray absorption spectrum
can be measured with a high-energy resolution. BL05
will be managed and maintained by the Synchrotron
Analysis L.L.C. (SALLC), which is composed of theindustrial companies, in cooperation with the staffs of
the Laboratory of Advanced Scienece andTechnology for Industry in University of Hyogo.
Industrial users can be assisted by staffs of SALLC in
the measurement at BL05. In this paper, we will
introduce BL05 and report recent activities.
Layout of BL05
Bending magnet beamline BL05 consists of two
branch lines (BL05A, BL05B) for the use in the wide
range from 50 eV to 4000 eV. Photo.1 shows aphotograph of BL05. BL05A, which is mounted witha double crystal monochromator, can be used in theenergy range of 1300-4000 eV by exchanging several
monochromatizing crystals. On the other hand,
BL05B is mounted with a varied line spacing planegrating (VLSPG) monochromator, which is designed
to cover the energy range 50-1300 eV with threegratings. Because the incident beam from the bending
magnet is provided for two branch lines through thedifferent windows of mask, these lines can be
operated simultaneously.

Photo.1 Photograph of beamline BL05.
(TEY) and fluorescence yield (FLY) using SDD (SII,
Vortex) can be performed. The fluorescence XAFS
spectra can be measured samples at the under an
atmospheric pressure by the replacement of an end
station to He using Be window. The chamber canmaintain 8 samples of 25 mm corner because ofindustrial use.
Specifications of BL05B
The constant-deviation monochromator consistingof a demagnifying spherical mirror and VLSPG,
which can provide to high resolution, simple
wavelength scanning with fixed slits, was mounted
on BL05B. The including angle of themonochromator is 175q. VLSPG consists of threegratings (100-, 300- and 800-lines/mm). Fig.1 showsa calculated diffraction efficiency of each grating.
Expected resolution (E/'E) is 3,000. Two

Specifications of BL05A
Toroidal mirrors are used as a pre-mirror and afocusing mirror of BL05A, for the purpose to
introduce a high-photon flux to the end station. InSb
(111) crystals and Si (111) crystals are prepared for a
Golovchenko-type double crystal monochromator.
The XAFS measurements in the total electron yield58

unoccupied B2p *, the spectrum was the same shapeas the one Jiménez et al. reported [1]. Additionally,
the calcium L3,2-edge spectral shape of CaF2 almost
corresponds to the spectrum reported by Naftel et al.
[2]. The nickel L3,2 absorption peaks are observed at
853 and 871 eV, respectively [3].

N
= 100,
100, 300,N=
300, 800
800 l/mm
l/mm

5050

Intensity (%)
Intensity (%)

4040

G1

G1
G1 (100(100l/mm)l/mm)
G2 (300G2(300l/mm)
l/mm)
G3
l/mm)
G3 (800(800 l/mm)

G2

G3

3030
2020

L2

345

350
355
360
Photon Energy (eV)
Grating=300 lines/mm
Slit Width=200 Ǵm, Incident Angle=90 q

1010
00
00

L3

Intensity (arbitrary unit)

measurement chambers are prepared at the end
station of BL05B. The XAFS spectra in the total
electron yield and fluorescence XAFS spectra using
SSD (EDAX) can be measurement in the highvacuum chamber. In addition, the X-ray
photoelectron spectra (XPS) using spherical electron
analyzer (VG Scienta, R3000) can be measured in theultra high vacuum chamber. These chambers can be
replaced each other within 1 hour. Each chamber canmaintain 16 samples of 25 mm corner.

200
200

400

600

800

1000 1200 1400
1400

Photon Energy
Energy (eV)(eV)
PhotonFig.3 CaF2 Ca L3,2-edge NEXAFS spectrum.

Fig.1 Diffraction efficiency of BL05B.

Intensity (arbitrary unit)

L3

Intensity (arbitrary unit)

Measurement
We measured standard samples by means of the 
TEY method at BL05B and obtained absorption
spectrain each grating, 100- or 300- or 800-lines/mm.
Fig.2-4 show boron K-edge, calcium and nickel
L3,2-edge near-edge X-ray absorption fine structure(NEXAFS) spectra of h-BN, CaF2 powder and Ni
sheet. The spectrum have been normalized to I0 and
had a linear pre-edge background removed. For h-BN,
an intense peak at 191 eV appeared clearly in Fig.3,
which is assigned to transition from B1s to the

L2

840

850
860
870
880
Photon Energy (eV)
Grating=800 lines/mm
Slit Width=200 Ǵm, Incident Angle=45 q

Fig.4 Ni L3,2-edge NEXAFS spectrum.

190

200
Photon Energy (eV)
Grating=100 lines/mm
Slit Width=300 Ǵm, Incident Angle=45 q
Fig.2 h-BN B K-edge NEXAFS spectrum.

59

References[1] I.Jiménez, A.F.Jankowski, L.J.Terminello, D.G.J.
Sutherland, J.A.Carlisle, G.L.Doll, W.M.Tong, D.K.
Shuh, F.J.Himpsel: Phys. Rev., B55, 12027 (1997).
[2] S.J.Naftel, T.K.Sham, Y.M.Yiu, B.W.Yates: J.
Synchrotron Rad., 8, 255 (2001).
[3] J.A.Bearden, A.F.Burr: Rev. Mod. Phys., 39, 125(1967).

Effect of the Soft X-ray on the Highly-HydrogenatedDiamond-Like Carbon Film
1

Kazuhiro Kanda1, Kumiko Yokota2, Masahito Tagawa2, Mayumi Tode3, Yuden Teraoka3, Shinji Matsui1
Laboratory of Advanced Science and Technology for Industry, University of Hyogo, 2 Graduate School ofEngineering, Kobe University, 3 Japan Atomic Energy Agency
E-mail: kanda@lasti.u-hyogo.ac.jp; Tel.: +81-791-58-0476
Abstract
Hydrogen was found to emit from the highly-hydrogenated Diamond-Like Carbon (H-DLC) films
by the irradiation of synchrotron radiation (SR) even in the vacuum. The hydrogen content in the
H-DLC film decreased exponentially with a soft X-ray exposure dose. In addition, the decrementof hydrogen content was found to decrease with increasing of the initial hydrogen content in the
H-DLC film. It was interpreted that the etching rate of H-DLC increased with its hydrogen content.
exposure was discussed on the basis of themeasurements of etching depth and thermal
desorption spectra.

Introduction
Diamond-Like Carbon (DLC) films generally
have durability against the synchrotron radiation(SR) in the absence of oxygen gas.1) Recently,hydrogen was emitted from the highly-hydrogenated
DLC (H-DLC) films by the irradiation of soft x-ray
even in the vacuum, and increase in the film density,
hardness and refractive index were reported.2) In thepresent study, we investigated the departure processof hydrogen from the highly-hydrogenated DLC filmby the exposure to soft X-ray in the vacuum using
three kinds of highly-hydrogenated DLC thin films,
which contained difference hydrogen contents.

H/(C+H) /%

60

40

20

0

Experiments and Results
Highly-hydrogenated DLC thin films were
deposited on Si wafer with 200 nm thickness byamplitude-modulated RF plasma-CVD method.3) We
called these films H-DLC50, H-DLC40 and HDLC30, in order of hydrogen content. The irradiationof SR against DLC films was carried out at BL-6 of
NewSUBARU.4) The SR at the BL-6 sample stage
had a continuous spectrum from IR to soft X-ray,which was lower than 1 keV. Rutherford
backscattering spectrometry (RBS) and elastic recoil
detection analysis (ERDA) are available for
evaluating quantitative determination for all
elemental composition, specially hydrogen, of thinfilms with high accuracy, being unnecessary forstandard samples. In this study, the hydrogen content
of DLC film has been determined by RBS and ERDA
techniques using a tandem Pelletron accelerator,
5SDH-2 in the Kobe University. Figure 1 depicts the
SR dose dependences of hydrogen content estimatedusing ERDA/RBS techniques. The hydrogen content
in the low-hydrogenated DLC film kept constant
independent on a soft X-ray exposure dose. On theother hand, that in the high-hydrogenated DLC film
decreases exponentially with a soft X-ray exposure
dose. Thus, the departure of the hydrogen wasobserved from high-hydrogenated DLC films, while
was not observed from the low-hydrogenated DLC
film by soft X-ray irradiation. The mechanism of thedeparture process of hydrogen from DLC film by SR

0

2000
4000
SR dose / mA h

6000

Fig. 1 The SR dose dependences of thehydrogen content. Circle, square, and triangle
indicate H-DLC50, H-DLC40 and H-DLC30
respectively. Open circle indicates lowhydrogenated DLC film synthesized using
PBII/D method.
References[1] H. Kyuragi and T. Urisu, Appl. Phys. Lett., 50(1987) 1254
[2] H. Matsuura, et. al., SEI Technical Review, 171(2007) 39 (Japanese)[3] T. Nakahigashi, et. al., Tribology International,
37 (2004) 907[4] K. Kanda, et. al., Jpn. J. Appl. Phys., 42 (2003)
3983
Acknowledgements: A part of this work was
supported by the New Energy and Industrial
Technology Development Organization (NEDO)
under the work entitled “Advanced Fundamental
Research Project on Hydrogen Storage Materials”.
We also thank to use 5SDH-2 of Accelerator andParticle Beam Experimental Facility, Faculty of
Maritime Sciences, Kobe University for the RBS
measurement.

60

Photoemission Study of Hydrogenated Amorphous Carbon
Thin Films as a Function of Annealing Temperature
1

Yuichi Haruyama 1, Masahito Tagawa 2, Kumiko Yokota 2, and Shinji Matsui 1
Laboratory of Advanced Science and Technology for Industry, University of Hyogo
2
Graduate School of Engineering, Kobe University

Abstract
The electronic structure in hydrogenated amorphous carbon (a-C:H) thin films was investigated asa function of the annealing temperature using photoemission spectroscopy. The photoemission
results of the valence band and the C 1s core level suggested that the graphitization of the a-C:H
film proceeds by annealing at more than 400 °C. From the photoemission spectra of the C 1s
core level, the coordination of C atoms in the a-C:H film were evaluated as a function of theannealing temperature. Based on the evaluations, the electronic structure of the a-C:H film as afunction of the annealing temperature is discussed.
comparison. After annealing at 200 °C, no clear
change was observed as compared to thephotoemission spectrum at RT. With increasing
the annealing temperature at 400 °C, a small peakat 3.0 eV appeared. With increasing the annealing
temperature at 600 °C, several peaks were clearlyobserved at 19.0, 13.0, 10.0, 7.8, 5.5 and 3.0 eV.
With further increasing the annealing temperature
at 800-950 °C, a peak at 6.7 eV in addition to theseveral peaks at 19.0, 13.0, 10.0, 7.8, 5.5 and 3.0
eV were observed. The photoemission spectra
after annealing at 600-950 °C are similar to thatof graphite except for the peak at 6.7 eV.
Therefore, the several peaks at 19.0, 13.0, 10.0,
7.8, 5.5 and 3.0 eV are derived from graphite
although the origin of the peak at 6.7 eV is notclear at present. This indicates that the annealing
at 600-950 °C causes the graphitization of a-C:H
film. In addition, the observation of the peak at
3.0 eV after annealing at 400 °C suggests that thegraphitization of a-C:H film starts to arise below
this temperature.

Introduction
Since amorphous carbon thin films haveinteresting properties such as high hardness, lowfriction coefficient, and chemical inertness, the studyof amorphous carbon thin films has attracted a great
deal of attention for wide applications [1-2]. Due totheir properties, amorphous carbon films are mainly
used in industrial products as coatings for themagnetic heads and media of hard disk drives, themachine parts for mold, the cutting tools, etc. In
order to produce good amorphous carbon films,
various vapor phase methods have been extensively
attempted so far, and the properties of thehydrogenated amorphous carbon (a-C:H) films
formed by vapor phase methods have been studied.
In the previous studies using Raman and Auger
electron spectroscopy, the a-C:H films were
thermally stable up to 260 °C. However, it was
pointed out that the thermal stability in the a-C:H
films was not good at more than 300-400 °C due tothe hydrogen desorption and the graphitization of aC:H films.
Although photoemission spectroscopy studies areimportant to investigate the electronic structure suchas the density of states, the orbital characteristic, thesp2 and sp3 contents, etc., there are few reports on
photoemission spectra of the valence band region andC 1s core level in the a-C:H films [3-4]. In particular,
the evolution of photoemission spectra of the valenceband region and C 1s core level in the a-C:H films asa function of the temperature has not been clarified.
In this study, we investigated the electronic structurein the a-C:H film as a function of the annealing
temperature using photoemission spectroscopy.

|
|
|
|
|

Intensity (arb. units)

|

|

|
|
|

|
|

|

|
|

graphite
|

|

|

70 eV

| |

|

|

|

|
|

950 ͠

|
|

|

|
|

|

|

600 ͠

|

|
|

|

800 ͠

|

|

400 ͠

|

200 ͠

ValenceResults and discussion
Figure 1 shows the photoemission spectra of
the valence band region in the a-C:H film as afunction of the annealing temperature. The
annealing temperatures of a-C:H film are denoted
beside each spectrum. In the top, thephotoemission spectrum in graphite is located for

25

20
15
10
5
Binding energy (eV)RT0

Fig.1 Photoemission spectra of the valence band
region in the hydrogenated amorphous carbon
film as a function of the annealing temperature.

61

Figure 2 shows the photoemission spectra (dots)of the C 1s core level in the a-C:H film as a functionof the annealing temperature. A shift of the peak
position to the lower binding energy side wasobserved with increase the annealing temperature. In
addition, the width of the photoemission spectra of
the C 1s core level in a-C:H films were observed tobe narrower with increase the annealing temperature.
In the photoemission spectrum in graphite, a peak at~284.4 eV with a wide tail to the higher binding
energy side was observed. The photoemission
spectrum of the C 1s core level in the a-C:H film
after annealing at 950 °C is similar to that ofgraphite. The broader spectral feature at lower
temperature suggests that there are some C 1scomponents in different chemical environments. In
the previous photoemission study of unhydrogenatedamorphous carbon films, the photoemission spectraof the C 1s core level were essentially composed of
two components positioned at 284.4 and 285.2 eV[5-6]. From the position of the binding energy ingraphite and diamond, the two components at 284.4
and 285.2 eV were assigned to the C 1s electrons
originating from the sp2 and sp3 hybridized carbon
atoms, respectively. In the case of a-C:H films, thecontribution from the C-H bonded carbon atoms in
addition to the sp2 and sp3 hybridized carbon atoms
would be needed. In the previous photoemission
spectrum of the C 1s core level in the hydrogenterminated C(111) surface, only a single peak was
observed, indicating that the binding energy of thebulk C 1s component is same as that of C-H bonded
C 1s component [7]. This also suggests that theelectro-negativity of carbon atoms is similar to thatof hydrogen atoms on the hydrogen terminatedC(111) surface. Therefore, the C 1s electrons
originating from the C-H bonded carbon atoms weretentatively assigned to the component at 285.2 eV. In
this case, it is difficult to reliably distinguishbetween the sp3 hybridized and the C-H bonded
carbon atoms from the photoemission spectra. In
the previous study of a-C:H films formed by thevapor phase methods such as the ion plating and
ECR plasma methods [4], the sp2 contents estimatedfrom the XPS spectra were in good correspondence
to those estimated from the EXAFS spectra although
there is an influence of the C-H bonded carbon
atoms on the photoemission spectra of the C 1s corelevel. This result suggests that there is almost no
influence on the estimation of the sp2 hybridized
carbon atoms using the XPS spectra. Therefore, thecontents of the sp2 hybridized carbon atoms and thecontents of the sum of the sp3 hybridized and the CH bonded (sp3 + C-H) carbon atoms could be
estimated using the XPS spectra. For this reason, acurve fitting analysis was performed on thephotoemission spectra of the C 1s core level using
two components positioned at 284.4 and 285.2 eV.
In Fig. 2, the best fitting results (lines) for a-C:H
films are shown. The sp2 and sp3 + C-H carbon

contents in a-C:H films, which are evaluated fromthe area intensity of each component, aresummarized in Ref. 8.
The error range for
evaluation of the sp2 and sp3 + C-H carbon contents
was ±5%. After annealing at 200 °C, almost nochange was observed.
With increasing theannealing temperature at 400 °C, the sp2 carbon
content increased by 5%. With increasing theannealing temperature at 600 °C, the sp2 carbon
content increased rapidly by 18%. With further
increasing the annealing temperature at 800-950 °C,
the sp2 carbon content increased gradually. The sp2
content in the a-C:H film after annealing at 950 °C
was shown to be highest as compared with thoseafter annealing at less than 800 °C. These results
indicate that the graphitization of a-C:H films starts
below 400 °C and proceeds with increasing theannealing temperature.

C 1s

1253.6 eV

Intensity (arb. units)

Graphite
950 ͠
800 ͠
600 ͠
400 ͠
200 ͠
RT

292

288
284
Binding energy (eV)280

Fig.2 Photoemission spectra (dots) of the C 1s
core level in the hydrogenated amorphous carbon
film as a function of the annealing temperature.
In the top, the photoemission spectrum ofgraphite is located for comparison. The fitting
results (lines) are also plotted in each spectrum.
References[1] J. Ullmann, Nucl. Instrum. Methods Phys. Res.,
Sect. B 127 (1997) 910.
[2] H. Tsai and D. B. Bogy, J. Vac. Sci. Technol. A 5(1987) 3287.
[3] J. Schafer et al., Phys Rev B 53 (1996) 7762.
[4] Y. Haruyama et al., Jpn. J. Appl. Phys. 47 (2008)
3380.
[5] P. Merel et al., Appl. Surf. Sci. 136 (1998) 105.
[6] J. Diaz et al., Phys. Rev. B 54 (1996) 8064.
[7] J. F. Morar et al., Phys. Rev. B 33 (1986) 1340.
[8] Y. Haruyama et al., Jpn. J. Appl. Phys. 48 (2009)055505-3.

62

Control of Oxygen Contamination in BN Thin Film Prepared byReactive Magnetron Sputtering
Masahito Niibe and Yoshie Maeda
LASTI, University of Hyogo
Abstract
To control oxygen contamination in BN thin film prepared by sputtering technique, high purity
gases of Ar:6N and N2:6N5 were used for magnetron sputtering as well as inserting purifier into
the gas line. The vacuum chamber was baked at low temperature of 60 OC for about 17 hrs before
thin film preparation. Oxygen concentration was evaluated by B-K edge X-ray absorption
spectroscopy (XAS) as well as XPS and XAS analyses. It was found that the amount of oxygen
contamination was controlled to be less than 1.4 % in the prepared BN thin film.
oxygen gas contained in the sputtering gases from thegas cylinders. The purity of used gas was improved
from 99.999% to 99.9999% (6N) for Ar and from99.9995% to 99.99995% (6N5) for N2 gas in thecylinder. Gas purifiers (PURERON GP-05) were also
inserted into the gas introduction lines. The vacuum
chamber was baked at low temperature of 60
OC
for about 17 hrs before thin film
preparation.
Oxygen concentration in the prepared film wasevaluated by X-ray photoemission spectroscopy(XPS, Shimazu ESCA-1000) and B-K edge X-ray
absorption spectroscopy (XAS) at the BL9 [2] in the
NewSUBARU SR facility. The XAS measurement
was carried out by total electron yield (TEY) modewith measuring sample current when thephotoelectron emitted by soft X-ray absorption. An
Auger electron spectroscopy (AES) was also
employed for depth analysis.

Introduction
For fabrication of metal nitride thin films byreactive sputtering, oxygen contamination becomes
often problematic. For example, ultra high vacuum
system was proposed to use for preparation oftitanium nitride thin film [1]. However, in the thinfilm fabrication system practically used for coating of
mechanical tools, it is necessary to develop thetechnique to control oxygen contamination for openair thin film fabrication system. We examined thecontamination control technique in preparation ofboron nitride (BN) thin film which is one of theeasily oxidizing materials.
Experiments
The BN thin films were fabricated by an RF
magnetron sputtering system with open-air typesample changing. The cross-sectional schematic viewof the system is shown in Fig. 1. The back groundpressure of the preparation chamber was about 2×10 4
Pa. Mixed gas of Ar and N2 with mixing ratio of 1:1
was used for sputtering. The target was a sintered hBN with 125 mm in diameter. The substratetemperature was not controlled and was less than 50
OC during the sample preparation. We supposed thatthe origins of oxygen contamination were residual
water vapor in the chamber and also water and

Results
Figure 2 shows a B-K edge XAS spectrum of aprepared BN thin film, the oxygen concentration ofwhich was comparatively high. The structure of theBN film was hexagonal (h-BN). Four sharp *
resonance peaks were observed at the photon energy
from 192 to 194eV. These peaks were formerly


0QTOCNK\GFCDUQTRVKQP=CW?

DC biasAr gasSubstrates
Cryo-pumpevacuation

N2 gasMass flow
controller

Target 1

Target 2

Shutter

Cooling water

Magnetron
cathodeMatching box
























2JQVQPGPGTI[=G8?

RF power supply

Fig. 2 Typical B-K edge XAS spectrum of aprepared BN thin film.

Fig. 1 Cross-sectional schematic view of the RF
magnetron sputtering system.

63

identified by the authors [3] as B atoms coordinatedby three N atoms (192.0 eV), and B atoms bound to
one-to-three oxygen atoms substituted for three
nitrogen atoms surrounding for higher energy threepeaks as shown in the figure.
Figure 3 shows the QMS intensity change ofresidual H2O(18) and O2(32) components inthe chamber during the long term baking.
Although, the data scattered day by day, theaverage amounts of residual gases in thechamber decreased 79% for H2O and 92% for
O2 during four months operation.

analysis was not provided yet for XPA and XAS
equipments. Figure 5 show the AES spectra of
prepared BN thin film before and after the Ar ion
etching. Some amounts of oxygen and carbon wereobserved on the surface of the thin film as-depositedand exposed to open air. The oxygen concentration
at the surface evaluated by AES measurement was
about 5 atomic %. However, after the 100 sec
etching with Ar ion, the oxygen concentration
decreased rapidly to about 1.4%.
㪋㩷㪈㪇㪋

㪈㪇㪄㪎

㪠㫅㫋㪼㫅㫊㫀㫋㫐㩷㪲㪸㪅㫌㪅㪴㪄㪐㪈㪇㪠㫆㫅㩷㪪㫋㫉㪼㫅㪾㫋㪿㪲㪘㪴

㪥

㪙

㪈㪇㪄㪏

㪈㪇㪄㪈㪇

㪦

㪚
㪊㩷㪈㪇㪋

㪈㪅㪋㩷㩼

㪈㪇㪄㪈㪈
㪈㪇㪄㪈㪉

㪉㩷㪈㪇㪋
㪑㩷㪈㪏
㪑㩷㪊㪉

㪈㪇㪄㪈㪊
㪈㪇㪄㪈㪋

㪈㪇㪇
㪈㪇㪆㪇㪍

㪈㪇㪆㪉㪐

㪛㪸㫋㪼

㪈㪈㪆㪈㪏

㪈㪉㪆㪈㪇

㪊㪇㪇

㪋㪇㪇

㪌㪇㪇

㪍㪇㪇

Fig. 5 AES spectra of BN thin film prepared
before and after the Ar ion etching.
Conclusion
The oxygen contamination was successfully
controlled by using high purity sputtering gas andlong term baking with low temperature for open air
type magnetron sputtering system.

B-K edge XAS spectra of prepared BN thinfilms before and after improvement in vacuum
atmosphere is shown in Fig. 4. The intensity of three
* peaks at the higher energy side decreased
remarkably after the improvement. A curve fitting
calculation indicates that ratio N and O atoms
bonding to the B atoms for the sample of before theimprovement was 73% and 27%, respectively.
However, the values changed for the sample after
improvement as 92% and 8%, respectively.
Depth analysis of the prepared sample was carriedout by AES analyzer at the Faculty of Engineering,
University of Hyogo, because etching gun for depth

Acknowledgment
The authors thank to Prof. Shozo Inoue at the
University of Hyogo for his support to measure the
AES depth profile and the spectra.
References[1] K. Hoshi et al., Proc. ISSP2007 Kanazawa Japan.
[2] M. Niibe et al., AIP Conf. Proc. 705 576 (2004).
[3] M. Niibe et al., Bulletin Soc. Discrete ValiationalX, 21, 179 (2008).

㪉㪇

㪈㪌

㪈㪇

After improve.

㪌

Before improve.
㪇
㪈㪏㪌

㪉㪇㪇

㪢㫀㫅㪼㫋㫀㪺㩷㪼㫅㪼㫉㪾㫐㩷㪲㪼㪭㪴㪇㪐㪆㪇㪐

Fig. 3 QMS intensity change of residual H2O(18)and O2(32) components in the chamber during thelong term baking.

㪥㫆㫉㫄㪸㫃㫀㫑㪼㪻㩷㪸㪹㫊㫆㫉㫇㫋㫀㫆㫅㩷㪲㪸㪅㫌㪅㪴㪑㩷㪙㪼㪽㫆㫉㪼㩷㪼㫋㪺㪿㫀㫅㪾㪑㩷㪘㪽㫋㪼㫉㩷㪼㫋㪺㪿㫀㫅㪾

㪈㪐㪇

㪈㪐㪌

㪉㪇㪇

㪉㪇㪌

㪉㪈㪇

㪉㪈㪌

㪉㪉㪇

㪧㪿㫆㫋㫆㫅㩷㪜㫅㪼㫉㪾㫐㩷㪲㪼㪭㪴

Fig. 4 B-K edge XAS spectra of prepared BN
thin films before and after the improvement invacuum atmosphere.

64Semi-quantitative analysis of carbon contamination
on MLMs using high power EUV light
Takahiro Nakayamaa, Hiroyoshi Kuboa, Akira Miyakea, Hiromitsu Takasea, Shigeru Terashimaa,
Shintaro Kawatab, Takashi Aokib, Shuichi Matsunarib,
Hiroo Kinoshitac, Takeo Watanabec, Masahito NiibecaCanon, 23-10, Kiyohara-Kogyodanchi, Utsunomiya-shi, Tochigi-ken, 321-3298, Japanb
Nikon, 1-10-1, Asamizodai, Sagamihara-shi, Kanagawa-ken, 228-0828, Japanc
Laboratory of Advanced Science and Technology for Industry (LASTI), Univ. of Hyogo, 3-1-2, Kouto,
Kamigori-cho, Ako, Hyogo 678-1205, Japan
Abstract
It is very important to mitigate oxidation of multilayer mirrors (MLMs) and carbon deposition
onto MLMs to extend the lifetime of EUV exposure tool. In this study we focused on carbon
deposition on Si-capped multilayer mirror. We made experiments of EUV irradiation to the MLMs
using apparatuses connected to an undulator beamline (BL9) of synchrotron radiation facility New
SUBARU in the University of Hyogo. This undulator beamline stably gives us high-power EUV
light. As the result of experiments, we found that carbon deposition rate was constant until carbon
thickness became 2.5 nm.
Introduction
HVM (High Volume Manufacturing) EUV Scanner is needed to operate for several years without highmaintenance cost. In order to estimate a lifetime for HVM, we have to figure out scaling law. We focus on thescaling law of contaminations on multilayer mirrors (MLMs). Carbon deposition on MLMs causes a damageof optical performances. We have to elucidate a photochemical reaction of EUV irradiation to the MLMs andestimate carbon deposition rate for HVM. We have found dependences of carbon deposition rate on average
EUV intensity, hydrocarbon partial pressure, characteristics of EUV source1-3. We have elucidated thesedependences by carbon deposition rate. But we do not know whether carbon deposition rate is constant or not.
So we need to make sure if carbon deposition rate is constant to understand the reaction quantitatively.
Experiments and Results
We made experiments using an apparatuses connected to an undulator beamline (BL9) in NewSUBARU
synchrotron radiation facility in the University of Hyogo. Figure 1 shows schematic diagram of theapparatus.
mirrors
C coated

TMP(Incident angle=80 deg.)

TMPLong undulator
Beamline

Photo diodeReflected light
Orifices(4 mmf)QMS
Direct light

TMP

MLM sample
I100 mm Pinhole/I 2 mm Pinhole
Mirror chamber

HxC YMain chamber

Figure 1. Schematic diagrams of EUV irradiation apparatus
We used X-ray photoelectron spectroscopy (XPS) and obtained carbon deposition quantity fromphotoelectron intensity of C(1s). We converted photoelectron intensity of C(1s) into a carbon film thickness.
Furthermore, we calculated carbon deposition rate by dividing the carbon film thickness by the total
irradiation time. The average EUV intensity distribution is shown in Fig. 2. Figure 2 also shows carbon
thickness distribution as an example. Dependence of carbon deposition rate on average EUV intensity was
figured out using these data. Figure 3 shows the dependence of carbon deposition rate on average EUV
intensity. Decane (C10H22) was injected at the partial pressure of 1E-6 Pa. The carbon deposition rate does
not increase proportionally to the average EUV intensity.

65

carbon depotision rate(nm/hr.)

250

150
100

0.5

50
0.0

average EUV

200
1.0

intensity(mW/mm2)

carbon thickness(nm)

1.5

0
-1.0

-0.5

0.0

0.5

1.5
1.0
0.5
0.0
0

1.0

50

100

150

200

250
2

average EUV intensity(mW/mm )distance from irradiation center(mm)Figure 3. Dependence of carbon deposition rate
on average EUV intensity

Figure 2. Distribution of Carbon
thickness and average EUV intensity

carbon thickness(nm)A standing wave on MLMs affects on generating secondary electrons4. It is considered that carbon isdeposited by interaction between secondary electrons and adsorbed molecules. So carbon deposition rate
must be changed by the standing wave. We made3
experiments to figure out if carbon deposition rate
200mW/mm^2changes depending on time during EUV irradiation.
30䌭W/mm^2
Experimental results show time dependence of carbon
2
thickness in fig. 4. The result is comparing between two
different EUV intensities. Carbon thickness wasincreasing constantly until it became 2.5 nm. We fitted
1experimental data by least square method and it was good
agreement.
0

Table 1. Experimental conditions.
Decane partial pressure (Pa)
Irradiation time (min.)
1E-5
5
1E-5
15
1E-5
30

0

20

40

60

80

time(min.䋩

Figure 4. Time dependence of carbon thickness

In conclusion, we made experiments using an undulator beamline (BL9) in NewSUBARU synchrotron
radiation facility and figured out dependence of carbon deposition rate on average EUV intensity up to high
EUV intensity. We also figured out if carbon deposition rate is constant. The carbon deposition rate does notdepend on carbon thickness until it becomes 2.5 nm. The standing wave does not affect on carbon depositionon our MLMs so much. As future works, we need to calculate amount of secondary electrons depending oncarbon thickness and compare simulation with experimental results.

ACKNOWLEDGMENT
A part of this work was supported by the Ministry of Economy Trade and Industry (METI) and New Energy
and Industrial Technology Development Organization (NEDO).

REFERENCES[1] H. Takase, “Study of Ruthenium-capped Multilayer Mirror for EUV Irradiation Durability”, Proc. of SPIE
Vol. 6151, 35, 2006
[2] T. Nakayama, “Phenomenological analysis of carbon deposition rate on the multilayer mirror”, Proc. of SPIE
Vol. 6921, 3B, 2008[3] T. Nakayama, et. al., “Analysis of carbon deposition on multilayer mirrors by using two different beamlines”,
Proc. of SPIE 7271(2009) 72713P.
[4] S. B. Hill et. al., "Accelerated lifetime metrology of EUV multilayer mirrors in hydrocarbon environments",
Proc. of SPIE 6921,42 , 200866

Electronic State of Ti in
Ultra-fine Grained SUS316L-1%TiC
M. Terasawa, T. Mitamura, M. Niibe, LASTI, University of Hyogo
T. Yamasaki, Dept. of Materials and Chemistry, Graduate School of Engineering, University of Hyogo
H. Kurishita, Institute for Materials Research (IMR), Tohoku University
M. Kawai, Institute of Material Structure Science, High Energy Accelerator Research Organization (KEK)
Abstract
Ultra fine grained (UFG) materials of SUS316L were fabricated by mechanical alloying (MA) and
hot isostatic pressing (HIP) treatments. It was found that addition of about 1 % TiC powder was
effective to reduce the grain size down to 100 nm, and the materials exhibited superior irradiation
resistance and mechanical properties. The electronic states of the TiC in the UFG materials wereanalyzed by XANES spectroscopy at NewSUBARU BL9.
ultra-fine grained materials than standard 316L is
also found in 1 MeV electron irradiation, as shown in
Fig.2.[1,2]Introduction
In the J-PARC program, which is a large
accelerator development project in Japan to promoteuse of secondary particles, such as neutron, pi- andmyu-particles, neutrino and so on, very high energy
and high current proton beams are utilized. For theneutron source in the J-PARC facility, liquid mercury
target enveloped with metallic container is planned tobe adopted. The container materials must be toughfor heavy irradiation induced by intense proton andneutron flux, in addition to severe erosion due tomercury exposure. One of the candidate materials
is ultra fine grained (UFG) SUS316L-1%TiC.
It is strongly expected that the materials aredeveloped so as to show tough resistance for suchphenomena.
We are developing ultra-fine grained materials of
austenitic stainless steel (316L) with addition ofsmall amount of TiC powder. In this work, electronic
state analysis of TiC in the UFGSUS316L-TiC
materials was investigated by XANES spectroscopy
in order to elucidate the effect of TiC addition.

Fig.1 Vickers microhardness of the UFG316L-TiC as a function ofneutron irradiation dose (En>0.1 MeV)

Experiments and Results
Fabrication of ultra-fine grained materials
Ultra-fine grained materials of austenitic stainlesssteel (SUS316L) were fabricated by mechanicalalloying (MA) and hot isostatic pressing (HIP)
treatments. Powder of SUS316L (an average particle
size: 44 – 105Ǵm), combined with TiC (0.57Ǵm),was used as the starting materials.
The SUS316L-1.0wt.% TiC materials with theaverage grain sizes of 100 nm were obtained by 80 %cold roll and annealing at the temperature of 800͠,
after MA and HIP (800͠) treatment. The fabricatedmaterials have exhibited superior resistance toneutron irradiation examined in JMTR up to 1.14 x1024 n/m2 (En>0.1 MeV). The hardness increase of
the materials after the irradiation is only 6.0 %,though much higher increase (73 %) is shown in thesimultaneous irradiation of the standard SUS316L
specimens. (Fig.1) The lower void swelling of theFig.2 Void swelling of the UFG316L-TiC irradiated by 1 MeV
electrons at 400͠The ultra-fine grained W-1.1wt.% TiC materials withthe grain size of 50 – 100 nm have been also obtainedby the same fabrication method, and exhibited
excellent resistance to the irradiation with neutrons
and helium ions. [3,4]Electronic state analysis of TiC in UFG materials
In the fabrication of the UFG materials, small amount(about 1 wt.%) of TiC addition is found extremely
effective to control the grain size, as described above67

in both SUS316L and W. Although it is suggested
that TiC nano particles act so as to pin the grainboundary during the fabrication process, what kind ofinteraction of TiC with matrix materials is concerned,
and by what mechanism the pinning is governed are
not clear.
We tried to measure the electronic states of Ti in the
SUS316L-1.0wt.% TiC consolidates, as a preliminary
step to elucidate the behavior of Ti or TiC in the
fabrication process. XANES spectroscopy was
performed at the end-station of the long undulator
beamline BL9 in the NewSUBARU SR facility using
a high resolution monochrometor. The data werecollected by a total electron yield (TEY) mode inwhich the sample current was measured when thephotoelectron emitted by soft x-ray absorption. The
values were normalized with a simultaneously
recorded photoemission signal from a gold mesh,which indicates the soft x-ray intensity incident into
the sample. At the present time, XANES spectra of
Ti-L and C-K absorption edge of TiC in the SUS316L-1.0wt.% TiC consolidates were measured.

Fig.4 shows XANES spectra of Ti-L2,3 for the UFG
SUS316L-1.0wt.% TiC specimens. Three kinds ofmaterials, that is, as HIPed, high temperaturecompressed, and cold-rolled, are examined. The
XANES spectra observed show characteristic twin
peak structures for both L2 and L3, which are in
general agreement with the spectra shown in TiC
powders. The NEXAFS spectra are decomposed for
TiC powder and for SUS316L-TiC (as HIPed) as
shown in Fig.5a and Fig.5b, respectively. The 2p
spectra of TiC powder are separated to two peaks(463.4 eV and 465.5 eV) for L2, and other two peaks(458.1 eV and 460.0 eV) for L3. On the other hand,the 2p spectra of SUS316L-TiC (as HIPed) are
separated to two peaks (463.9 eV and 465.9 eV) for
L2, and other two peaks (458.4 eV and 460.3 eV) for
L3. The lower energy peak in L2 is due to t2g (Ǹbonding), and higher energy peak eg (ǻ-bonding).
Likewise the lower energy peak in L3 is due to t2g ,and higher energy peak eg. The energies of the peaksin the UFG materials coincide with the corresponding
peaks in the TiC powder. However, the eg peaks are
smaller than the t2g peaks for both L2 and L3 in
SUS316L-TiC compared with TiC powder. The realreason of this feature is not known at present. It may
be concluded almost of all Ti atoms exist in the formof TiC in the UFG materials, but, in the same time, it
is suggested other kind of precipitates exist withscarce concentration in the matrix.

0QTOCNK\GFCDUQTRVKQP=CW?




㪣㪊



6K%RQYFGT6KOGVCN

㪣㪉





t2g egt2g eg












2JQVQPGPGTI[=G8?

Fig.3. Ti-L2,3 edge XANES spectra of Ti and TiC

Fig.3 shows Ti-L2,3 absorption spectra for pure Ti(99.99 %) metal and TiC powders measured forreference before the XANES study for the fabricated
SUS316L-TiC materials. A peak of Ti-L2 (2p1/2) andL3 (2p3/2) was observed at 465.9 eV and 461.4 eV,
respectively, in the Ti specimen. On the other hand,each of L2 and L3 spectral line exhibits twin peakstructure with an additional line with a separation of
about 1.5 eV for the TiC powder specimen. The
spectral variation is reflected by electronic structure
due to different chemical state.

L3

L2

Fig.5a. Ti-L2,3 NEXAFS for TiC powder
t2g egt2g eg0QTOCNK\GFCDUQTRVKQP=CW?



L3

㩷 L2



Fig.5b. Ti-L2,3 NEXAFS for SUS316L-TiC

References[1]Y. Z. Cheng et al,Material Science Forum, 426432,pp.1065-1070 (2003).
[2] H. Matsuoka et al, Proc. ICAPP’05, Seoul, Korea(2005) paper 5687
[3] H. Kurishita et al, Phys. Scr. T128 (2007) 76-80[4] H. Kurishita et al, IWSMT-8 (2006)



㪣㪊









㪣㪉

4QNNGF
%QORTGUUGFCU*+2GF




2JQVQPGPGTI[=G8?

Fig.4. Ti-L2,3 edge XANES spectra of UFG316L -TiC materials

68Fabrication of High Aspect Ratio Microcoils
Daiji Noda, Masaru Setomoto, and Tadashi Hattori
Laboratory of Advanced Science and Technology for Industry, University of Hyogo
Abstract
Recently, there has been a growing requirement to reduce their size of actuators. Actuators, which
held big volume and weight with a part of a product, have been required to reduce their size.
However, the miniaturization of electromagnetic actuators has made little progress since it requires
three-dimensional micro-fabrication processing and new technologies. We have forcused on the
fabrication of electromagnetic type microactuators that could be driven at low voltage and withhigh efficiency but it is well known that existing technologies for miniaturization of these devices
are unsuitable because the allowable current path would be too small in microscopic
applications.Therefore, we have fabricated a spiral microcoil with narrow pitch and high aspectratio coil line structures using X-ray lithography and metallization techniques. We have fabricatedspiral microcoils at a pitch of 60 m. Thus, an aspect ratio of coil lines was achieved about 5 ascoil lines of 30 m. By using these techniques, microcoils with narrow pitch and high aspect ratio
can be achieved, which are expected to yield high performance.
allowing a greater current path. Then, the magneto
motive force is proportional to the squares of current
path in the microcoil in this model [3]. This
microactuator having the high aspect ratio of coil line
is also expected a high performance in spite ofminiature size.

Introduction
Recently, reductions in size and increases insophistication have become desirable for many
parts and devices. Actuators, which hold bigvolume and weight with a part of a product, havebeen required to reduce their size. However, theminiaturization of actuators has made little progresssince it requires three-dimensional (3D) microfabrication processing and new technologies. On theother hand, LIGA (German acronym for
Lithographite Galvanoformung and Abformung)process [1] can be fabricated nano and micro partsfor devices. This technique is possible to make highaspect ratio structure fixed the narrow pitch of coilline and space. For the deep X-ray lithography
involved in the LIGA process, we used the
NewSUBARU Beamline 11 (BL11), which is asynchrotron radiation (SR) facility owned byour university. The x-ray exposure at BL11
was carried out with the workpiece held in a
specially manufactured ‘nine parts operation’
exposure stage [2]. Thus, this stage makes it
feasible to do 3D deep X-ray lithography for
microcoils. Therefore, we have fabricated a spiralmicrocoil with high aspect structure on pipe surface
for electromagnetic type microactuators using a 3D
deep X-ray lithography and metallization techniques.

Fabrication process of microcoil
The surface of acrylic pipe for a screw thread
structure, this is the coil part, has made using LIGA
process. Figure 1 shows the fabrication process of
microcoil. First, a cylindrical structure was formedon the surface of acrylic pipe by X-ray lithography.
Next, copper was thinly deposited on pipe surface by
sputtering in order to use as a seed layer in theelectroforming. And, copper was formed into narrow
pitch spiral structure by electroforming. Then, pipe
surface was completely covered with copper film.
X-ray

X-ray mask

X-ray lithography

Cu sputtering

Formation of seed layer

Design of electromagnetic actuator
As the structure of the magnetic circuit, we used
the type called open frame solenoid, which is open
on the sides [3]. The material of electromagnetic core(fixed core and plunger) and shield parts (yoke) wereused Permalloy that is a nickel iron alloy, because it
has the largest permeability among soft magnetic
metals. When the electrical supply to the coil isturned on, a magnetic flux forms in the gap,
deforming the magnetic field and producing suction
force on the plunger. If the aspect ratio is increased,
the cross section area of coil lines is also increased

Electroforming of copper

Chemical etching

Fig. 1: Process flows of microcoil

69

Finally, forming Cu layer over the pipe surface wasetched until the isotropic portions of wiring were
exposed. We have fabricated a spiral microcoil at a
pitch of 20 m, as shown in Fig. 2. Thus, an aspectratio of coil lines was achieved about 5 as coil linesof 30 m. Following the seed layer deposition, we

magnetic type actuators. This system is very simple
structure and easy to exchange the coil part. The gap
between plunger and fixed core was adjusted X-, Ystage. The theoretical values by simulation and actual
measurement results of suction force generated by
the microcoil were compared, as shown in Fig. 5.
These results are relatively in good agreement withtheoretical values.
Aspect Ratio: 330

Suction force (mN)

Expermental value
Calculated value

60 mFig. 2: SEM image of coil lines on acrylic pipewith aspect ratio of 5

20

10

0

formed uniform copper electroplating for the current
path of microcoils. Here, we proposed and introduced
the new technique of reverse pulse current forelectroforming in order to form high aspect ratio
structures. In this result, it was able to be confirmedthat plating developed to reach the bottom surface ofthe grooves, as shown in SEM image of Fig. 3.
Finally, Isotropic copper etching was performed until
the insulated portions of the wiring were exposed, as
shown in Fig. 4.

1

2

3

Gap (mm)Fig. 5: Suction force comparison between
measurement values and simulation
results
Conclusions
We have fabricated microcoils with high aspectratio using a 3D X-ray lithography and metallization
technique in order to produce electromagnetic
microactuators. We succeeded in producing athreaded structure with 30 m in coil lines width andabout 5 in the maximum aspect ratio.
On the other hand, we developed a measurement
system to measure a suction force. In measurement
results, theoretical values by simulation values andactual measurement of suction force were compared.
By using these techniques, microcoils with highaspect ratio can be achieved, which are expected toyield high performance. It is anticipated that highperformance microcoils could also be manufactured,in spite of their miniature size.

Measurement of suction force
We have also fabricated a measurement system tomeasure the suction force of designed electro-

30 μm

Acknowledgment
This research is partially supported by the Grantin-Aid for Scientific Research on Priority Area, No.
438,"Next-Generation
Actuators
Leading
Breakthroughs", from the Ministry of Education,
Culture, Sports, Science and Technology, Japan.

Fig. 3: SEM image of coil lines after copper
electroforming

References[1] E. W. Becker, W. Ehrfeld, P. Hagmann, A. Maner,and D. Munchmeyer, Microelectron. Eng., 4, pp.
35-56 (1986).
[2] H. Mekaru, S. Kusumi, N. Sato, M. Yamashita, O.
Shimada, and T. Hattori, Jpn. J. Appl. Phys., 43,
6B, pp. 4036-4040 (2004).
[3] Y. Matsumoto, M. Setomoto, D. Noda, and T.
Hattori, Microsyst. Technol., 14, 9-11, pp. 13731379 (2008).

30 μm

Fig. 4: SEM image of coil lines by isotropic
copper etching70

Fabrication of X-ray Grating Using X-ray Lithography
for X-ray Talbot Interferometry
Daiji Noda1, Naoki Takahashi1, Megumi Katori2, Yasuto Minamiyama2, and Tadashi Hattori1
1
Laboratory of Advanced Science and Technology for Industry, University of Hyogo,
2
Nanocreate Co., Ltd.
Abstract
X-ray radiographic imaging technique is very important in medical, biological, inspection,material science, and so on. However, it is not enough to obtain clear X-ray images of samples
with low absorbance materials, such as biological soft tissues. Then, we have used an X-ray phaseimaging method of an X-ray Talbot interferometer. In this method, X-ray gratings were required tohave narrow pitch and high aspect ratio structure. Therefore, we have developed and fabricatedhigh aspect ratio X-ray gratings with a pitch of 5.3 m, a height of 30 m, and a large effective
area of 60 mm × 60 mm using X-ray lithography and narrow electroforming technique. In thispaper, we discuss the fabrication process of new X-ray mask and results of X-ray gratings of X-ray
lithography technique.
in making new X-ray mask with pitch pattern of 5.3
m and large effective area of 60  60 mm2, asshown in Fig. 2. In contrast to conventional silicon
substrates, the newly devised mask fabrication
process does not require further membrane
application, frame adhesion or substrate etching.
Thus, this is very simple process.

Introduction
X-ray radiographic imaging technique is very
important in medical, biological, inspection, materialscience, and so on. However, it is not enough toobtain clear X-ray images of samples with low
absorbance materials, such as biological soft tissues.
On the other hand, several methods for generating
radiographic contrast from the information of X-ray
phase shift have been investigated. It is improvementin the high sensitivity by about 1000 times higher
than by conventional absorption contrast. Numerous
researchers have studied a variety of methods ofphase imaging [1,2]. X-ray Talbot interferometer(XTI) is one of the methods of X-ray phase imaging[1]. In order to use 10-40 keV X-ray irradiation, theAu thickness of absorptive material must be over 20
m. But, it is not straightforward to make thisstructure with high aspect ratio by conventional
techniques. Then, we have tried in fabricating such
X-ray gratings particularly with a large area using Xray lithography technique.

I. Seed layer deposition

II. Resist patterning

III. Au electroforming

Fabrication of X-ray mask
The conventional X-ray mask fabrication process
was used on Si wafer [3]. In this case, we have used
SU-8 as membrane because of large effective area Xray mask. Therefore, X-ray masks comprising a resin
membrane have the disadvantage that, after several
cycles of X-ray exposure, they crease and sag due to
X-ray-derived heat. As a substitute for theconventional resin membrane, we proposed tofabricate a new X-ray mask using a carbon wafer
membrane that has an extremely small thermal
expansion coefficient and is easy to process.
Figure 1 shows fabrication process using carbon
wafer for membrane material. The fabrication
process consists of three steps: (a) depositing a seedlayer on the carbon wafer, (b) applying resist over theseed layer to perform patterning by irradiation with
UV and development, (c) forming an X-ray absorber,
i.e. an Au film, by electrolytic plating, We succeeded

Carbon

Ti

Au

SU-8

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

60mm

Fig. 2: Picture of carbon X-ray mask

71

Au absorbing part for the X-ray grating wasformed by electroforming. In electroforming,
chromium was used as seed film. A non-cyanic based
solution was used for Au electroforming. From theseresults, the designed pitch of 5.3 m and height ofabout 40 m of X-ray grating are realized, as shownin Fig. 5.

Fabrication of X-ray grating
X-ray lithography using synchrotron radiation has
been utilized for 2.5-dimensional applications on flat
substrate. Therefore, we took advantage of thistechnology to fabricate a high aspect ratio structure
required for X-ray gratings with a pitch of several
micrometers. For X-ray lithography, we used
NewSUBARU beamlines 2, which is the synchrotron
radiation facility owned by our university [4]. The
beamline 2 has a potential of large area patterning
across an A4-size area with a highly uniform pattern
thickness.
A target specification of the X-ray grating was 5.3
m pitch pattern and large effective area of 60  60
mm2. For the deep X-ray lithography, we used anegative photo-resist SU-8. This SU-8 was originallydesigned for UV lithography. However it could also
be used in deep X-ray lithography of high accuracy
and high aspect ratio pattern. The pattern quickly
collapses when the rinse solution is dried in thedevelopment and washing process. In order to solve
this problem, we confirmed that line width of aprovided cash register strike structure body became
big with increase of an exposure a membrane came tobe formed overexposure by the space top surface ofline & space, as shown in Fig. 3. The X-ray grating
was completed by gilding the resist structure of Xray grating. And, we removed top surface layer using
O2 plasma, as shown in Fig. 4.

Fig. 5: SEM image of X-ray grating in crosssectionConclusions
We have fabricated X-ray gratings having a pitchof 5.3 m and a large effective area of 60  60 mm2
for X-ray Talbot interferometry. We were new anddevised that we used a carbon wafer as membranematerials of X-ray mask was used to break off aproblem by the heat transformation of the membrane
which happened at the time of X-rays exposure. To
make a higher aspect ratio X-ray grating, wedeveloped the fabrication process composed of X-ray
lithography and micro electroforming method. In Xray lithography, sticking was observed because of
surface tension. Therefore, we formed on top surface
layer by overexposure. In this result, the resist
structure with high aspect ratio and narrow pitch was
obtained without surface tension in large area. After
Au electroforming, large area and narrow pitch X-ray
grating could be fabricated.
This result suggests that XTI is a novel andsimple method for phase sensitive X-ray radiography,
and promising method for many imaging applications.

45μm

Fig. 3: SEM image of narrow pitch structurewith top surface layer

Acknowledgment
This research was supported by the research
project “Development of Systems and Technology
for Advanced Measurement and Analysis” from theJapan Science and Technology Agency (JST).
References[1] A. Momose, Jpn. J. Appl. Phys., 44, 9A, pp.
6355-6367 (2005).
[2] C. David, B. Nöhammer, H. H. Solak and E.
Ziegler, Appl. Phys. Lett., 81, pp. 3287-3289(2002).
[3] D. Noda, M. Tanaka, K. Shimada, and T. Hattori,
Jpn. J. Appl. Phys., 46, 2, pp. 849- 851 (2007).
[4] Y. Utsumi, T. Kishimoto, T. Hattori, and H. Hara,
Microsyst. Technol., 13, 5-6, pp. 417-423 (2007).

Fig. 4: SEM image of narrow pitch structure
without top surface layer

72

Fabrication of High Hardness Ni Mold with Electroless
Ni-B Thin Layer
Yoshitaka Sawa1, Kenji Yamashita2, Satoshi Nishida2, Daiji Noda3, and Tadashi Hattori3
1
Sawa Plating Co., Ltd., 2Nanocreate Co., Ltd.,
3
Laboratory of Advanced Science and Technology for Industry, University of Hyogo
Abstract
The nickel electroforming method using a high-concentration nickel sulfamate bath is commonlyused to fabricate micro metal molds in the LIGA process; however, this method does not produce
micro metal molds of sufficient hardness. In this research, we used a nickel-boron (Ni-B)
electroless alloy plating method to obtain a hard nickel plated film having hardness of 832 Hv. It
was also ascertained that Ni-B electroless alloy plated film retains its high hardness even during
heat treatment in conditions of 250 C for 1 hour. To deal with the high stresses developed in highhardness plated films, we proposed double-layer nickel electroforming. This method is covered
and used on conventional nickel electroforming layer by high hardness micro mold. High hardness
micro metal mold using double-layer was fabricated by nickel electroforming and Ni-B electrolessalloy plating method.
other elements. Numerous reports are available on
improving the mechanical properties of Ni electroforming film. In this study, not all the 4-mm-thickmicro metal molds were created using hard Ni plated
film; we used double-layer Ni plating to form thinmembranes of hard Ni plating as a film to cover thecamber-free surface of an existing Ni micro mold, in
an attempt to make a micro mold that exhibits
minimum camber, yet has high mold surface
hardness.

Introduction
Recently, strong demand for the sophistication,
downsizing and intensified integration of systems
used in such cutting-edge areas industries asadvanced information communications, medical care,bioscience, environment and energy has been sharply
accelerating microsystem applications. In connection
with this market demand, a manufacturing method
based on transfer technology using micro metal
molds has recently been in the spotlight. In particular,
the LIGA (acronym for the German words
Lithographie, Galvanoformung, and Abformung)process, based on exposure technologies using
ultraviolet (UV) rays or synchrotron radiation (SR),is receiving attention. In the LIGA process, a masterof the mold that will be formed into a threedimensional structure is fabricated by lithography
technology, and the master mold is then used tofabricate the micro metal mold by electroforming.
This micro metal mold is then used for the molding
operation.
The mainstream method for manufacturing micro
metal molds using the LIGA process [1] is based on
the nickel electroforming method. Because Ni
electroforming uses electrolytic deposition dependingon the Ni electroforming conditions during micro
mold creation, a camber can occur on the plated film
due to electrode position stress, rendering the micro
mold unsuitable for use in making molds. However,
the Ni electroforming layer prepared using thisadditive-free bath exhibits a low surface hardness
value of approximately 200 Hv, which is not
sufficiently high, since the injection mold hardness
requirement is approximately 400 Hv or more, in
common practice.
Suggested ways of improving the Ni electroforming layer hardness are to introduce additives into
the plating bath to downsize the crystal grains in theelectroforming film, and Ni-based alloy plating basedon a eutectic process involving phosphorus, boron or

Investigation of plating bath
We investigated Ni plating baths that can be used
to produce the high-hardness Ni plating layer. In thisstudy, we examined Ni-alloy-based plating baths ofthree types: commonly known nickel-phosphorus(Ni-P) electroless alloy plating, Ni-P alloy
electroforming and nickel-boron (Ni-B) electrolessalloy plating. Figure 1 shows a SEM image of themold master after Ni-B electroless alloy plating (bathtemperature: 60 C). The mold master was madeunder the same conditions as Ni-P electroless alloy
plating. Wrinkles creases did not develop on thephotoresist structure side of the Ni-B electroless alloy
plating layer. The plating temperature of the Ni-P
electroless alloy plating bath, which can be as high as

Fig. 1: SEM image of Ni-B electroless plating73

90 C, was considered responsible for thedevelopment of wrinkle creases on the plating layer.
In response to this problem, this study examined useof a Ni-B electroless alloy plating layer to produce a
hard Ni plating layer, since that plating process
enabled a lower bath temperature. We assessed thislayer mechanical property as a metal mold covering
layer.

solution for one minute as surface activation
treatment. This was followed by electroforming in an
additive-free bath to enable deposition of a Nielectroforming layer to be 4 mm thick. Figure 3
shows SEM images of the Ni electroforming moldwe prepared and of the truncated-cone-shapedreflecting protrusions of the light guide plate. Also
shown are SEM images of a cross section of thetruncated-cone-shaped reflecting protrusions.

Results and discussions
The Ni-B electroless alloy plated film wasassessed by internal stress, surface hardness, andabrasion examination test. Test samples ofapproximately 40 μm thick plated film, depositedfrom the 50 and 60 C baths, were used.
Figure 2 shows the results of the hardness
measurement of Ni-B electroless alloy plated film.
The hardness of the plated film deposited from theplating bath at a temperature of 50 C was 808 Hv
and that from the plating bath at a temperature of 60
C was 832 Hv. The Ni-B electroless alloy plated
film did not exhibit any reduction in hardness as aresult of heat treatment below 300 C. The heat
treatment at 300 C yielded hardness values of 904
Hv (for bath temperature of 50 C) and 960 Hv (forbath temperature of 60 C), both values being higher
than that obtained immediately after deposition
without heat treatment.

Fig. 3: SEM image of fabricated Ni micro moldwith Ni-B double layer
Conclusions
We have studied electroforming molds based on
the LIGA process as a technology for manufacturing
3D fine micro-structures. Since nickel electroforming
molds fabricated using an additive-free bath do notmeet the hardness requirement associated with
injection molding, we studied methods of increasing
hardness by means of alloy plating. Thanks to theplated film deposited from the Ni-B electroless alloy
plating solution, we successfully obtained a hardplated film with a hardness of 800 Hv or more. These
results show that we succeed in producing doublelayer plating consisting of a hard plated film andelectroformed film in an additive-free bath, verifyingthat the hard Ni plated film that served as a moldcovering layer covered the entire mold pattern, and insuccessfully fabricating molds that accuratelytransfer mold master patterns prepared by UV
lithography.
Furthermore, we will apply the current technology to large electroformed molds, with the aim ofestablishing a process for making large-area micro
metal molds.

Fig. 2: Measurement results of Vickers hardness

Fabrication of high hardness micro moldWe prepared a Ni micro mold using the doublelayer plating method, which combines a hard Ni
plated film, with mold covering layer composed of a
Ni-B electroless alloy plated film, and a Nielectroforming layer produced in an additive-freebath. In the present study we used a light guideplate pattern with fine reflecting protrusions [2].
We used a Ni-B electroless alloy plating bath at atemperature of 60 C to deposit a hard Ni plated film
approximately 1 μm thick on this mold master. The
surface of the hard Ni plated film, deposited before
electroforming in an additive-free bath, was soaked
in an organic degreasing agent for one minute as
pretreatment, and then soaked in a 10% sulfuric acid

References[1] E. W. Becker, W. Ehrfeld, P. Hagmann, A. Maner,and D. Munchmeyer, Microelectron. Eng., Vol. 4,
pp. 35-56 (1986)[2] T. Tanaka, T. Nomura, Y. Funabiki, T. Kitadani, K.
Idei, K. Yamashita, D. Noda, and T. Hattori, Proc.
2006 IEEE Int. Sympo. on Micro-Nano
Mechatronics and Human Science, Nagoya, Japan,
pp. 480-485 (2006).

74

Fabrication of Light Guide Plate for Ultraviolet Range
Yuta Okayama1, Takaya Fujimoto1, Kenji Yamashita1, Satoshi Nishida2, Yoshitaka Sawa3,
Daiji Noda1, and Tadashi Hattori1
1
Laboratory of Advanced Science and Technology for Industry, University of Hyogo,
2
Nanocreate Co., Ltd., 3Sawa Plating Co., Ltd.
Abstract
The light guide plate, as part of the backlight unit in a cellular phone or liquid crystal display, has
evolved to meet market demands for low power consumption, high-luminance and high-quality
displays. Along with the advance of the light guide plate, light emitting diodes have undergone
development as light source for light guide plates. In recent years, the ultraviolet light are used as asource of light of the air cleaner, and it is used as a source of light to activate the titanium dioxide
which is photocatalyst. However, common ultraviolet light sources are either line or point lightsources. Therefore, we studies surface illuminators that incorporate diffusers in the visible light
range. Applying our existing technology, we constructed an unprecedented ultraviolet surface
illuminator and measured it using a photocatalyst.
achieving uniform surface illumination with a lightguide plate alone, the shape and allocation ofreflective bumps are of much importance.
Optimization of bump shape and allocation enables
the creation of a light guide plate for uniform
illumination. First, the optimal bump shape wasobtained. The bump shape was transformed from acylindrical column to a truncated cone, using fixed
dimensions of 30 μm height and 52 μm base diameter.
Comparisons were made among cylindrical column,
from 50 to 80 degree tapered truncated cones, taking
heed of visible-light diffuser conditions that thelaboratory has studied. Simulation results revealed
that strong light was emitted near 60 to 70 degree
taper angles, as in the visible light range.
In the next step, optimal bump allocation wasderived for the 70 degrees taper angle. In this study,
the light guide plate we fabricated had bumps in a 48
mm  88 mm area on a 52 mm  96 mm  2.6 mmboard. The optimal bump allocation was determinedby thinning filled bumps, on the basis of simulation
results. From simulation results, the fully uniform
placement of bumps was obtained [3]. Before bumpallocation optimization, output characteristics weresuch that the maximum value was 6.39 W/m2 and theminimum value was 1.15 W/m2. After optimization,
the maximum value was reduced to 3.23 W/m2, while
the minimum value was increased to 1.82 W/m2. The
uniformity ratio, which is an indicator of the degreeof illumination uniformity, improved from 35 % to91 %.

Introduction
In recent years, liquid crystal displays (LCDs)
have come to be widely used in cellular phones andTV sets. This popularity has led to growing demand
for a higher performance light guide plate as an LCD
component. In the light guide plate, light is guided
from a light emitting diode (LED) or other point lightsource to desired locations via total internal reflection
rendered by index of refraction differential between
air and diffuser material. The light in light guide platetears a total reflection condition by reflecting in aninternal projection (dot) and irradiates the surface [1].
The light guide plate, converts point light source tosurface illumination. Figure 1 shows a schematic
diagram of a light guide plate. One advantage of thelight guide plate is its efficient use of light throughthe conversion of point light source to surface
illumination. To apply our technology to surface
illuminators using ultraviolet (UV) light, which havebegun to be used recently in home air cleaners andthe like, we have embarked on fabricating a lightguide plate specifically designed for UV-LEDs.
In this study, optimal bump shape and allocation
were derived for UV surface illuminators. Indeed, alight guide plate was fabricated using the molding
technology.

Fabrication of light guide plate
Since the shape was micro sized, the UV-LIGA
process was used to fabricate an UV light guide plate,designed as above. As regards the master pattern, astructure was created by lithography, painting withresist that is photosensitive resin wafer. Next, copper
was sputtered onto the surfaces of the created master
pattern. A mold was then fabricated through Nielectroforming. Consequently, the Ni thickness was
set at approximately 4 mm for electroforming. Lastly,

Fig. 1: Schematic diagram of light guide plate
Design of light guide plate by simulation
The reflection dot of the bottom of light guideplate influences irradiation of the light. Therefore, in75

the light guide plate was produced through injection
molding using the mold as a cavity [3]. The achievedbump shape was obtained at 10 m in top diameter,
52 m in base diameter, 70 degrees in taper angle
and 30 m in height.

gas was again added so as to achieve 100 ppm. This
cycle was repeated several times. Figure 3 shows
experiment results. Since no UV light was irradiatedin the initial period, the activated carbon came close
to saturation after several cycles, diminishing intoluene-processing capacity. However, after a few
hours of UV irradiation, the processing capacity ofphotocatalyst and activated carbon recovered fromapproximately 50 % to approximately 90 %.

Evaluation of light guide plate
Using a photodiode, the emission characteristicsof the fabricated light guide plate were measured toverify that the light guide plate would provide
uniform illumination. Energy values were calculated
from the spectral response characteristics of thephotodiode and the wavelength of the light emitted
by the LED. The energy distribution was obtained as
closely simulation result, as shown in Fig. 2. In thesimulation, the maximum and minimum values were
3.23 W/m2 and 1.82 W/m2, respectively, while themolded light guide plate provided maximum andminimum values of 4.25 W/m2 and 3.10 W/m2,
respectively. The maximum value increase from thesimulation results was probably due to some entry
angle deviation that occurred at LED mounting.
However, the higher minimum value suggests thatthe fabricated light guide plate was better than thesimulated one used for analysis.

(a) Simulation result

UV Irradiation

Density of Gas [ppm]

Only activated Carbon

100
Ability Recovery

80
Ability Fall

60
40
20

Less Than 10ppm

0
0

300

600

900

1200

1500

1800

T ime [min]Fig. 3: Results of deodorization measurement for
toluene gas
Conclusions
We fabricated an unprecedented UV surface
illuminator and assessed its capacity as a light source
for reactivating photocatalysts. Bump shape andallocation for uniform illumination of UV light were
derived through simulation, achieving uniformity
ratio improvement from 35 % to 91 %. The lightguide plate for UV light was fabricated using UVLIGA process. The fabricated light guide plate
presented performance comparable to simulation
results, with a minimum value exceeding analysis
results, though the uniformity ratio did not reach thesimulation results.
We intend to conduct processing measurements
similar to the toluene gas decomposition experiment,
and to closely assess the relationships between
energy value and photocatalyst processing capacity.
Moreover, for additional increases in emitted energy
value, we will review the UV-light diffuser design
through simulation.

(b) Measurement result

Fig. 2: Energy distribution of light guide plate
Measurement of photocatalyst
In light of such trends, using the light guide platefabricated in this study we conducted an experiment
involving the processing of toluene gas discharged
during printing, or from adhesives. We performed
what the repetition experiment that we used an active
carbon and photocatalyst for, experiment by thechange of the irradiation energy and experiment onlyby photocatalyst. Deodorization measurements usinga photocatalyst are conducted either dynamically, byincorporating an external force to generate air flow,or statically, by using a closed space allowing no air
flow. In our study, the experiment of the latter typewas in a static environment.
In the first experiment, 100 ppm of toluene gas
was injected to the container, and the toluene gas
concentration was measured 60 minutes later. On thebasis of concentration measurement results, toluene

References[1] T. Tanaka, T. Nomura, Y. Funabiki, T. Kitadani, K.
Idei, K. Yamashita, D. Noda, and T. Hattori, Proc.
of the 2006 IEEE Int. Symp. on Micro-Nano
Mechatronics and Human Science, Nagoya, Japan,
pp. 480-485 (2006).
[2] Y. Sawa, T. Tanaka, T. Kitadani, H. Ueno, Y.
Itoigawa, K. Yamashita, D. Noda, and T. Hattori,
Microsyst. Technol., 14, pp. 1559-1565 (2008).
[3] Y. Okayama, K. Yamashita, D. Noda, and T.
Hattori, Proc. the 2008 IEEE Int. Symp. on
Micro-Nano Mechatronics and Human Science,
Nagoya, Japan, pp. 408-413 (2008).

76

Fabrication of Micro Capacitive Inclination Sensor
by Resin Molding Method
Hiroaki Miyake1, Kazufumi Nishimoto1, Satoshi Nishida2, Daiji Noda1, and Tadashi Hattori1
1
Laboratory of Advanced Science and Technology for Industry, University of Hyogo,
2
Nanocreate Co., Ltd.
Abstract
In various leading-edge technology industries, there is a growing need to reduce the weight andincrease the energy saving performance of various electronics products. It is now underdevelopment to enable the production of less expensive MEMS devices for low costly production
technology. Then, the LIGA process is a technology, which is considered to be suited for mass
production, enabling the creation of a microstructure by transferring a pattern from this mastermold to a resin. In this study, we fabricated a micro capacitive inclination sensor by using
combination of a resin forming method and a mold. We could fabricate and successfully package aresin sensor by molding technique that can be made at low cost production. If a small inclination
sensor, having a size of several millimeters, could be made using a resin forming method,
production costs could be substantially reduced compared to sensors made with the conventional
MEMS process.
values. Capacitance change of the capacitor on the
one side of the electrodes C is expressed the
proportional inclination angle [2].

Introduction
In various leading-edge technology industries,
there is a growing need to reduce the weight andincrease the energy saving performance of various
electronics products. Although MEMS (Micro
Electro Mechanical Systems) technology [1] is notsuited for mass-produced sensors since silicon isbrittle and expensive and its processing iscomplicated, involving many processes. On the other
hand, the LIGA process is a technology, which isconsidered to be suited for mass production, enabling
the creation of a microstructure by transferring apattern from this master mold to a resin.
In this study, we fabricated a micro capacitive
inclination sensor [2] by using combination of a resin
forming method and a mold. If a small inclination
sensor, having a size of several millimeters, can bemade using a resin forming method, production costs
can be substantially reduced compared to sensors
made with the conventional MEMS process. Since
the dimensions of its sensing region are 7 × 7 × 3
mm3, which are much smaller than the dimensions ofconventional sensors, this inclination sensor is
expected to be widely used in the field where
efficient and reliable attitude control is a primaryfactor to be considered.

Fabrication process of sensor
Figure 1 shows the fabrication process for the
micro capacitive inclination sensor. In the firststep, a mold to be used for forming was
prepared by UV (ultraviolet) lithography andNi electroforming (Figs. 1(A) to (F)). The
spacer part of this mold was transferred to aresin by hot embossing molding (Figs. 1(G)and (H)) [3]. The common electrode wasformed on a structure having projections andrecesses (Figs. 1(I) to (M)). The opposing
electrodes, formed by transferring the pattern,
were then attached to the common electrode,
oil was injected, and the injection port wasthen sealed to complete the fabrication of theinclination sensor (Figs. 1(N) to (P)).
Specifically, an electrode film was formed, only at
the recesses on the slit-structured surface having
projections and recesses. A patterning method using amask would be a viable method for forming anelectrode at a specified position. Using this method,
however, it is very difficult to bring a mask into
proper alignment with a non-flat surface; this method
also has a drawback in respect of cost. In the case of
the process that is the subject of this paper, asignificant cost reduction is possible, since anelectrode film can be formed without using a mask.

Micro capacitive inclination sensor
This is working principle of a micro capacitive
inclination sensor that two semicircular opposing
electrodes are set above one circular common
electrode [2]. Therefore, two capacitors are formed.
The region between the opposing electrodes andcommon electrode is half filled with oil. The oil
inside maintains its level due to gravity when thesensor inclines, so that the amount of oil changes ineach capacitor. As a result, the capacitances change,
and the angle of inclination of the sensor can bedetected, based on this change in the capacitanceFormation of electrode on resin molding
The inclination sensor comprises two electrodes,
i.e., a common electrode and opposing electrode, toform a capacitor. Figure 2 shows images of the crosssection of a molding on which resist had been coated,using a spin/spray coating system. As shown in this77

and then conduct performance evaluations, as shownin Fig. 3.

Fig. 3: Picture of completed sensor
Conclusions
Based on low cost molding techniques suited formass production, we have fabricated a micro
capacitive inclination sensor by using a resin moldedcomponent. We prepared a mold by UV lithography
and Ni electroforming. In addition, using the hot
embossing molding technique, we fabricated astructure in which our pre-designed projections andrecesses were realized.
We proposed a new process for forming
electrodes, only in the recesses in a fabricated resin
molded component, without using a mask, andsuccessfully fabricated the common electrode of an
inclination sensor. The process proposed andestablished in this study requires no alignment andmakes possible a substantial cost reduction. Although
we faced a difficult task of planarizing resist in thisprocess, we used solvent vapor for planarization withsatisfactory results. We successfully fabricated a
micro inclination sensor as a molded product. In
future, we will carry out wiring to complete thisinclination sensor, and then conduct performance
evaluations.
The techniques using resin-molded parts have thepotential to be applied to the production of, not only
inclination sensors, such as the one fabricated in thisstudy, but also MEMS devices. If the techniques
using resin-molded parts are introduced to the massproduction of MEMS devices, including sensors, at
low cost, the range of their applications will further
expand to new areas of technology and industry.

Fig. 1: Fabrication process for sensor using
molding

Electrode region

Junction region

Electrode region

Junction region

100μm(a) after resist coating

100μm(b) resist had been planerFig. 2: SEM image of pattern in cross section
image, resist smoothly followed the projections andrecesses in the pattern. After resist coating, thethickness of the resist film on the electrode region
was the same at that of the film on the junction
region. Therefore, if O2 ashing were performed on amolding having a uniform thickness of resist, resist
could not remain only in the recess in the electroderegion. Therefore, we placed a resist-coated sample
in a container filled with solvent vapor so that resist,
exposed to solvent vapor, would melt and be planar
zed. As is evident from Fig. 2b, the resist coating on
the junction part was very thin, compared with asample, shown in Fig. 2a, which had not yet beenplanar. Cu electrode was thus formed successfully,
only in the recess in the structure, using the proposed
new process.
We successfully fabricated a micro inclination
sensor as a molded product [4]. In future, we will
carry out wiring to complete this inclination sensor,

References[1] F. Kohsaka, J. Liang, T. Matsuo, and T. Ueda,
IEEJ Trans. SM, 127, 10, pp. 431-436 (2007).
[2] H. Ueda, H. Ueno, K. Itoigawa, and T. Hattori,
IEEJ Trans. SM. 126, 12, pp. 637-642 (2006).
[3] N. Ishizawa, K. Idei, T. Kimura, D. Noda, and T.
Hattori, Microsyst. Technol., 14, 9-11, pp. 13811388 (2008).
[4] H. Miyake, K. Nishimoto, H. Ueda, H. Ueno, K.
Itoigawa, S. Nishida, D. Noda, and T. Hattori,
IEEJ Trans. SM, 129, 9, pp. 283-288 (2009).

78