Research Activities

Investigation of Spectral Recovery of Etching Damage
Observed in XAS spectra of TiO2 Thin Films
Keiji Sano1, Masahito Niibe1, Retsuo Kawakami2, Yoshitaka Nakano3(Univ. Hyogo 1, Univ. Tokushima 2, Chubu Univ. 3)
Abstract
We analyzed TiO2 thin films etched with capacitively coupled plasma etching apparatus by nearedge X-ray absorption fine structure (NEXAFS) method. As a result, spectral change due todisordering of the crystalline structure was observed by TFY method (including visible light) inthe sample treated with higher gas pressure. We also found that disordered Ti-L2,3 spectra of etchedsample recovered to as-grown-like by irradiation with soft X-rays. Furthermore, the spectra ofrecovered samples were returned to disordered shape by exposing the sample to air or keeping in
vacuum for a long time. On the other hand, the spectra that measured by TFY method excluding
visible light emission was not changed due to the etching and the soft X-ray irradiation.
Introduction
TiO2 is known not only photocatalytic material but also high dielectric constant material. Therefore, TiO2 is
expected to apply as MOS gate oxide film because of its high dielectric constant. To use TiO2 as MOS gate film,
it has to be processed by etching. However, there are a few reports about the effect of etching damage to TiO2
thin films by etching process. Therefore, we analyzed the effect of etching damage to TiO2 samples by NEXAFS
method. We have found the phenomenon during the analyzing process that disordered NEXAFS spectra of theetched film recovered to as-grown-like by irradiation with soft X-rays[1],[2].
The purpose of this study is the elucidation of the phenomenon that NEXAFS spectra of etched TiO2 thin film
recovered by soft X-ray irradiation. We investigated the spectral recovery condition of the etching damage. For
example, recovery of the spectra was studied for irradiation condition, and compared between the presence andabsence of visible light emission.
Experiments
TiO2 thin films (anatase) were deposited on a glass substrate (Corning 1737) by facing cathodes DC
magnetron sputtering system. We used capacitively coupled plasma etching apparatus (Tokushima Univ.) to etchthe samples. The etching gas was N2, and its pressure and etching time were 100 mTorr and 60 minutes,
respectively. These samples were analyzed by NEXAFS method conducted at the beamline BL09A in the
NewSUBARU synchrotron radiation facility[3]. NEXAFS method can obtain the information of chemical state or
local structure around the element selectively and non-destructively by measuring an absorption edge of any
element in the sample. The measurements were carried out with total electron yield (TEY) method (surface
sensitive) and total fluorescence yield (TFY) method (bulk sensitive) at the Ti-L2,3 edges (443 ~ 496 eV)[4]. TFY
measurement was carried out with two types of photodiodes. One can cut off visible light by aluminum coating(PD-1), another is uncoated (PD-2). Therefore, it can investigate presence or absence of visible light emission.
Results
As shown in Fig.1 (a), the spectra of etched sample measured by TEY method changed that the peak near 467
eV became lower compared with as-grown sample. However, the spectra of the etched sample recovered toas-grown-like by soft X-ray irradiation (undulator light source, tens of W/cm2) for 1 minute. As shown in Fig.1(b), the spectra of as-grown sample and etched sample measured by TFY (PD-1) method changed that the peakbecame lower on the whole absorption region. And the spectra of etched sample were not changed by soft X-ray
irradiation. The spectra of etched sample measured by TFY (PD-2) method were the same spectra measured byPD-1 as shown in Fig.1 (c) (middle). However, the spectra of the etched sample recovered to as-grown-like bysoft X-ray irradiation for 3 minutes as shown in Fig.1 (c) (higher).
The spectra of as-grown sample and etched sample measured by TFY (PD-1) method were affected by
self-absorption which was specific to TFY method. On the other hand, the spectra of etched sample measured by
TFY (PD-2) method (middle) was affected by self-absorption, but spectra of as-grown sample (lower) andirradiated sample (higher) were TEY-like without the influence of self-absorption. Thus, we found that the
spectra of the etched sample recovered to as-grown-like by soft X-ray irradiation. Fig.2 shows the recovery
process of the NEXAFS spectra by soft X-ray irradiation measured with TFY (PD-2) method. The spectrum ofetched sample gradually became as-grown-like by soft X-ray irradiation (496 eV, tens of mW/cm2) for 5 ~ 25
minutes.

19

The recovered spectra of the samples were returned to disordered shape by exposure to air or keeping about
three days in vacuum. After returning to the disordered shape, the spectrum changed to as-grown-like again by
re-irradiation with soft X-rays. Therefore, the recovery phenomenon is not a permanent change but is areversible change.
In the etched sample, the bonding orbital around the Ti atoms should be disturbed by generation of oxygen
vacancies. The spectra should be disturbed by disarray of crystalline structure. Presumably, the spectra should berecovered by trapped electrons to compensate the defective part. Based on these speculation, we considered thatthe mechanism of recovery phenomenon is related to the influence of secondary emission. First, we thought
about the recovery in TEY method as follows. Electrons from electron-hole pairs generated by the soft X-ray
irradiation should be trapped in oxygen vacancies (defects) generated by plasma etching. As a result, it became
easier to emit photoelectron by decreases of scattering by the defects. Second, we thought about recovery in TFY
method as follows. Spectra of etched sample change to spectra of self-absorption type by suppression of
secondary photoemission from as-grown sample. However, the spectra became non-self-absorption (normal)
type by change to easily emit light again due to the influence of electrons trapped in the oxygen vacancies. Fromthe measured results of PD-1 and PD-2, the light emissions should be the visible and ultraviolet region, whichwere cut off by aluminum coating. We considered that the recovery phenomenon is not a permanent change, it
returned to disturbed spectra again due to the trapped electrons react with water and oxygen in air or lifetime ofthe electrons trapped by oxygen vacancies.
References[1] K.Sano et al., LASTI. Annual Report vol.14, 43-44 (2012).
[2] M.Niibe et al., J. Appl. Phys., 113, 126101 (2013).
[3] M.Niibe et al., AIP Conf. Proc. No.705 (AIP, New York, 2004), p.576[4] T.Kotaka and M.Niibe: Adv. X-ray Chem. Analysis, 43 (2012) 175.

(a)

(b)

TFY (PD-2)

Irradiation ofundulator 1min

After Etching

Absorption Intensity [a.u.]

TFY (PD-1)

Absorption Intensity [a.u.]

Absorption Intensity [a.u.]

TEY

(c)

Irradiation ofundulator 3min

After Etching

As-grown

Irradiation ofundulator 3min
After Etching

As-grown

As-grown

445 450 455 460 465 470 475 480 485

445 450 455 460 465 470 475 480 485

445 450 455 460 465 470 475 480 485

Photon Energy [eV]Photon Energy [eV]Photon Energy [eV]Fig.1 Ti-L2,3 NEXAFS spectra of etched TiO2 thin films(a): TEY method and (b): TFY (PD-1, Al coated) method and (c): TFY (PD-2, non-coated) method.

0.35
TFY (PD-2)

25min

Absorption Intensity

0.3
0.25

15min

0.2

10min

0.15
5min
0.1
0.05
After Etching
0
445

450

455

460

465

470

475

480

485

Photon Energy [eV]Fig.2

Recovery of Etching Damage by Soft X-ray Irradiation.

20

Oxidation State Analysis by Soft X-ray Absorption
Fine Structure Using M4,5 edge of Tin
Takumi Yonemura1, Junji Iihara1, Koji Yamaguchi1, and Masahito Niibe2.
1
Sumitomo Electric Industries, Ltd. 2 University of Hyogo

Abstract
We found that soft x-ray absorption fine structure for M4,5 edge of Tin was effective forinvestigating the oxidation states on the surface. Using this method, we have investigated theoxidation state of Sn plate whose surface was processed by the wet thermal oxidation and havefound that the oxidation state on the surface became SnO.
Introduction
Tin (= Sn) is widely used for contact materials such as the electroplated layer on the connector and solder.
The solder, for example, is an alloy whose main component is Sn. The solder is often used for the connection
between the electric parts and the printed circuit in the electric products. The resistivity on that connected
regions influences the electric properties. This resistivity depends on the oxidation states of the solder.
Therefore, to investigate the oxidation state on the surface region is necessary to develop the process for
decreasing the resistivity.
There are some methods for analyzing the oxidation states, for example, the x-ray photoelectron
spectroscopy (XPS), the cyclic voltammetry (CV), and so on. XPS can detect the several nm thickness
oxidation layers on the surface. However, it is difficult to distinguish the oxidation states between SnO andSnO2, because the peak positions of the photoelectron spectra for these Sn compounds are very close to eachother. CV also can detect the oxidation states. However, it is difficult to investigate the particular region likethe surface layer.
We focused on x-ray absorption fine structure (XAFS) which is useful to investigate the chemical state.
XAFS spectrum is obtained by measuring the absorbance for the incident x-ray. The absorbance is obtainedby measuring the number of the auger electrons, the photo currents, the fluorescence x-ray intensity, and soon, because these signals are in proportion to the absorbance. In addition, the effective depth of the signal forthese probes are different each other. This indicates that the analysis depth can be controlled by using themproperly.
We tried to investigate the native oxide of Sn plate at BL16B2 of SPring-8 by the conversion electron yield(CEY) which is the surface sensitive method in XAFS and utilizes the auger electrons. Although we obtained
the Sn K edge XAFS spectrum, it was almost the same to that of Sn metal. The native oxide couldn’t be
detected because the energy of the auger electrons was probably high. Therefore, XAFS measurement using
the Sn M4,5 absorption edge in soft x-ray region could be effective for overcoming that issue and investigating
the oxidation state on the surface more sensitive.
In this report, we have considered the XAFS measurement with Sn M4,5 absorption edge for the oxidation
state analysis on the surface region, using the highly brilliant soft x-ray of NewSUBARU.
Experiments and Results
Five samples were prepared, as listed in Table I.
Table I. Prepared Samples
Sample A1 and A2 were SnO and SnO2 powder as
SampleDetails
standard, which were fixed on the carbon tape,SnO
powderfixed
oncarbon tape (standard)
A1
respectively. Sample B1 and B2 were Sn powder and Sn
SnO2 powder fixed on carbon tape(standard)
A2
plate, respectively. Sample C was Sn plate whose
Sn powder fixed on carbon tapeB1
surface was processed by the wet thermal oxidation.
Sn plate
B2
This process imitated a use environment. The surface ofSn plate with the wet thermal oxidation processC
the sample B2 and C was connected to the ground byusing the carbon tape to prevent the charge-up
phenomenon.
We performed the XAFS measurements using soft x-ray from the synchrotron radiation source at BL9A of
NewSUBARU. Figure 1 was the schematic picture of BL9A measurement system. We used the Sn M4,5
absorption edge (= 484 eV). Therefore, the excited x-ray energy was varied between 480 and 505 eV with aninterval of 0.12 eV. The undulator gap was set to 34.5 mm so that the incident x-ray intensity became
stronger in the above energy regions. The grating and exit slit were set to 1200 lines/mm and 50 m,
respectively. The incident x-ray intensity (I0) was monitored with the photo currents on the gold-mesh using
Keithley6514 type picoammeter. XAFS measurements were performed in a total electron yield (TEY) which21

1.2× 1013 (photons/sec)
SR(0001)

Rear focusing mirror (M2)Gold mesh

Insulated holder
Sample(a) Standard

MirrorθGold-mesh

Undulato
LU light r

LU
光源sourceExit
Exitslit
slit

Grating
Plane VLS
grating（300本/mm、900/mm、1200/mm）

I0

PhotodiodePico-ammeter

I1I(b) Sample B1

電流法（TEY）と蛍光法（TFY）のFig. 1. The measurement system
at 測定が可能
BL9A

is the surface sensitive mode and utilizes the photo currents.
(c) Sample B2
The current (I1) was monitored with a Keithley6517A typepicoammeter.
Figure 2 (a) shows the Sn M4,5-XAFS spectra of standard
I. Sample Preparation(d) Sample C
sample A1 and A2 obtained by TEY. Comparing with these
two spectra, the XAFS spectrum of SnO has thecharacteristic peak at 486 eV. On the other hand, that of
SnO2 has the characteristic peak at 490 and 501 eV. These
characteristic peaks indicate that the oxidation states of Sn
are distinguished clearly by using M4,5-XAFS spectra.
Fig. 2. Sn M4,5-XAFS spectra of (a) SnO
Figure 2 (b) and (c) show the Sn M4,5-XAFS spectra ofpowder and SnO2 powder, (b) Sn powder, (c)sample B1and B2. We found that the XAFS spectrum of
Sn plate, and (d) Sn plate with the wet
sample B1 has three characteristic peaks at 486, 490, andthermal oxidation process
501 eV. While, that of sample B2 has only one characteristic
peak at 486 eV. This indicates that the surface oxidation state of Sn powder, sample B1, was mixed with SnO
and SnO2. On the other hand, that of Sn plate, sample B2, was only SnO. These surface oxidation states
probably show the native oxide layer. Above results indicate that Sn M4,5 XAFS measurement in TEY iseffective for the investigation of the oxidation states on the surface of Sn compounds.
Finally, we have applied the above method to sample C. Figure 2 (d) shows the Sn M4,5-XAFS spectra
obtained by TEY. We found that the spectrum was almost the same to that of SnO. In short, the oxidation
state became SnO by the wet thermal oxidation process.
In summary, we have considered how to investigate the surface oxidation states of the Sn compounds, andhave found that the XAFS measurement by TEY with Sn M4,5 absorption edge was effective. We havesuccessfully obtained the Sn M4,5-XAFS spectra from the native oxide layer of Sn plate and Sn powder. The
oxidation state of Sn plate and Sn powder were SnO and the mixture with SnO and SnO2, respectively.
Using this method, the effect of the wet thermal oxidation process to Sn plate has been investigated. It has
been found that the surface oxidation state became SnO.
References[1] M. Niibe, M. Mukai, S. Miyamoto, Y. Shoji, S. Hashimoto, A. Ando, T. Tanaka, M. Miyai, and H.
Kitamura, Synchrotron Radiation Instrumentation, AIP Conf. Proc. 705, 576-579 (2004).

22

Surface analysis of GaN treated by Ar ion beam etching
Shodai Hirai1, Masahito Niibe2
Graduate School of Eng1. and LASTI2 , University of Hyogo.
Abstract
To understand how would change the surface composition and the etching depth, the surface ofn-GaN was etched by Ar ion beam. The etched surfaces were analyzed by two-beam interference
microscope, X-ray photoelectron spectroscopy (XPS) and soft X-ray absorption spectroscopy(XAS) methods. The etching rates of n-GaN were about 0.13 nm/min and 0.97 nm/min at theacceleration voltage of 0.5 kV and 1.0 kV, respectively. The surface composition of etched n-GaN
changed to Ga-rich as the N/Ga ratio shifts to about 0.5. The relative oxygen content increased
about 3 times. The shape of the Near Edge X-Ray Absorption Fine Structure (NEXAFS) of the
N-K edge measured by TEY method changed with increasing acceleration voltage and processing
time. The appeared peak around 402 eV is explained by formation of N2 molecules on the sample
surface. The disturbance of crystal structure did not occur in deeper region greater than 5 nm.

Introduction

etching. Further, we investigated the etching depth ofGallium Nitride (GaN) is expected as semiconductora Si wafer to compare the etching rate. After thematerials used for power electronic devices and lightetching, n-GaN was exposed to atmosphere. We

emitting devices because the band gap of GaN is

measuredlarge and interatomic distance is short. In order tointerference microscope.

etch

depth

with

using

two-beam

improve the performance of the devices, suppression

The composition change of the etched n-GaN

of etching damage to a circuit during processing issurface was analyzed by an XPS method. All XPS

important. However, understanding of reducing thespectra were obtained using Shimadzu ESCA-1000

damage to the surface by etching is still insufficient.

System with a Mg-Kα radiation (hν=1253.6 eV). The

On the other hand, it is necessary to know the

N/Ga ratio on the surface was determined from thechanges in properties of the material by ion beam

integrated intensities of Ga3s and N1s peaks. The

etching, because ion beam etching is used for depth

relative composition deviation was calculated withanalysis in materials. Therefore, in this study, we

the N/Ga ratio of the as-grown sample is one.

surface

NEXAFS spectroscopy was conducted at nitrogencomposition, the etching depth, and surface structure

K-edge soft X-ray absorption to analyze etchingwhen n-GaN was etched by ion beam.

damage. The NEXAFS measurement was carried out

investigated

how

would

changetheat the analyzing station of beamline 9, at theExperimental Methods

NewSUBARU synchrotron radiation facility at the

The sample was Si dope n-type GaN grown on a

University of Hyogo. The measurement was carried

sapphire substrate by MOCVD. Etching of n-GaN

out by total electron yield (TEY) method in a sample

was carried out using Ar ion beam, the gas pressure

current mode and total fluorescence yield (TFY)

of which was 50 μTorr. Filament current of the ion

method. In TFY method, we measured the amount of

gun was 25 mA. Acceleration voltage was changed influorescence with an Al-coated photodiode in order tothe range of 0.5-1.0 kV. Processing time was changed

cut off visible light emission[1]. Both measurements

up to 3 hours. A part of the n-GaN sample surface

were carried out simultaneously for

was covered with metal mask to make a step by23

Etching depth(nm)2.0● n-GaN 1kV

200

Acceleration Voltage:1kV▲ n-GaN 0.5kV

1.5◆ Si 1kV

N/Ga ratio

150

1.0

100

0.5

50
0

0.0 0
0

0.5
1
1.5
2
2.5
Processing time(hours)

3

4
Relative oxygen content

Fig.1. Time dependence of theetch depth of the Si and n-GaN.
the same sample at the same position. TEY method
can get information on a shallow region of less thanabout 5nm from the sample surface because of theshort escape length of photogenerated electrons. On
the other hand, TFY method can get information on a
deeper area (bulk) of the sample of more than 100 nm
because X-ray fluorescence comes out from deeper
place in the sample compared to electrons.

1
2
3
Processing time(hours)

3
2
1
Acceleration Voltage:1kV

0

1
2
3
Processing time(hours)
Fig.2. Etching time dependence of N/Ga ratio
and the relative amount of oxygen of n-GaN
etching time.
Figure 3 shows the NEXAFS spectra of N-K edgeof the n-GaN sample measured by TEY method at thesoft X-ray incident angle of 90° from the surface.
Figure 3 (a) and (b) show the NEXAFS spectra at theacceleration voltage of 0.5 kV and 1.0 kV,
respectively. As shown in Fig. 3, the peak at 403 eV
and the spectral shape of other peaks are smoothened
when processing time is increased. It indicates thatthe crystal structure of the n-GaN surface wasdistorted. In addition in the case of 1.0 kV, a change
in the spectral shape was greater than that of 0.5 kV.
In TFY method, the spectral shape of overall was notchanged with changing in the accelerating voltage(not shown here). It indicates that the disturbance of
crystal structure was restricted at the surface.
As shown in Fig. 3 (b), a new peak was formed atthe vicinity of 402 eV with increasing in the etchingtime of 1 and 2 hours. The peak decreased when
etching time is increased to 3 hours. The peak around402 eV is a spectrum derived from N2 molecules [4].
N2 molecules were produced on the sample at theearly stage of etching, and desorbed when etchingtime increased.

Results
Figure 1 shows the time dependence of the etch depthof the n-GaN and Si. The etch depth of the n-GaN
samples increased almost linearly with increasing theprocessing time. The etching rate of n-GaN wereabout 0.13 nm/min at the acceleration voltage of 0.5
kV and about 0.97 nm/min at 1.0 kV. The etching rateof Si was about 0.38 nm/min at the acceleration
voltage of 1.0 kV. In the n-GaN samples, the etchingrate of 1.0 kV was 7.3 times greater than the case of
0.5kV. The etching rate of n-GaN was 2.5 times
greater than that of Si. Binding energy of Ga-N and
Si-Si are about 9.0 eV [2] and 3.5 eV [3], respectively.
Therefore, we have expected that Si would be etchedwith higher rate. However, in this study, it was foundthat the etching rate of n-GaN was higher than that of
Si. This is a very interesting result. We will continue
to clarify the reason why the etching rate of n-GaN ishigher than that of Si, in the future.
Figure 2 shows the composition (N/Ga ratio) andthe relative oxygen content of the n-GaN surfaces at
the acceleration voltage of 1.0 kV, obtained by XPS
method. N/Ga ratio was about 0.5 comparing withthat of the as-grown sample in all the etching time.
The relative amount of oxygen was about 3 times
greater comparing with the as-grown sample in all the

24

0

2.5

Dicussion
Absorption intensity [arb. unit]

We consider the changes in the structure of n-GaN
by Ar ion beam etching. First, N was selectively
etched from the surface of the sample by ion beametching, and the sample surface became gallium rich.
After that, N/Ga ratio became constant at about 0.5
becausetheselective

etching of

nitrogen is

suppressed by the impinging of Ar ion to more Ga.
From the results of TEY method, the disturbance of
crystal structure of the sample surface occurs when
n-GaN surface is etched. From the results of TFY

(a)

2.0

as-grown

1.5

1hour

1.0

2hours0.53hours0.0
390

method, the disturbance does not occur in the deep
place from the surface.

2.5

References
Absorption intensity [arb. unit][1] T. Kotaka, M. Niibe, and T. Mitamura, Adv. X-ray.
Chem. Analysis, Jap. 43 175-180 (2012).
[2] I. Grzegory, J. Phys: Condens. Matter. 13
6875-6892 (2001).
[3] Eric J. Lee, et al, J. Am. Chem. Soc. 118
5375-5382 (1996).
[4] M. Katsikini, et al, J Phys: Conference Series. 190
012065 (2009)

400 410 420 430
Photon energy[eV]

(b)

2.0

as-grown

1.5

1hour

1.0

2hours0.53hours

0.0
390

400
410
420
Photon energy[eV]430

Fig.3. NEXAFS spectra of nitrogen K-edge of n-GaN
etched by Ar ion beam, obtained by the TEY method
at the soft X-ray incident angle of 90°from thesurface. (a)Acceleration voltage of 0.5kV.
(b) Acceleration voltage of 1.0kV.

25

NEXAFS Study on Soft X-ray Irradiation Effect on
Highly Hydrogenated Diamond-like Carbon Films
Ryo IMAI, Kazuhiro KANDA
Laboratory of Advanced Science and Technology for Industry, University of Hyogo
Abstract
Structure changes of a hydrogenated diamond-like carbon (H-DLC) film exposed to synchrotron
radiation (SR) in the soft X-ray region were investigated by near-edge X-ray absorption finestructure (NEXAFS) spectroscopy using synchrotron radiation. We found that structure of H-DLC
films by the SR exposure is greatly modified. The sp2/(sp2+sp3) ratio of C atoms in the H-DLC
films, which is quantitatively analyzed from NEXAFS spectra, increased with SR dose.
Introduction
Diamond-like carbon (DLC) films have excellent properties including high hardness, a low friction
coefficient, high abrasion quality, a gas barrier, chemical inertness, and surface lubrication and are therefore
being utilized as coating materials on automobile parts, hard disks, artificial blood vessels, edged tools, andfood containers. Film-forming methods affect the properties of DLC films differently, and thus a wide varietyof DLC films have been developed. DLC films are expected to be used in outer space as a lubrication
substitution for oil, which cannot be used in space because it disappears in vacuums [1-2].
DLC films are generally known to be durable against X-ray exposure [3]. However, it has recently beenreported that soft X-ray exposure on highly hydrogenated DLC (H-DLC) films leads to desorption ofhydrogen and an increase in film density and refractive index [4-5]. Clarification of the effect of soft X-ray
exposure on DLC films is necessary to ensure that DLC films can be used in outer space safely.
In this study, we investigated the modification processes by soft X-ray exposure on H-DLC films.
Specifically C-K edge NEXAFS spectra of H-DLC films were measured using SR, and the sp2/(sp2+sp3) ratioof C atoms in the H-DLC films were obtained.
Experiments
200-nm-thick H-DLC films were deposited on Si wafers by using an amplitude-modulated RF
plasma-enhanced CVD method. This method enables the deposition of DLC films containing a lot ofhydrogen. The hydrogen content of H-DLC films was estimated to be 50 at.% by using the combination of
Rutherford backscattering spectrometry (RBS) and elastic recoil detection analysis (ERDA) techniques [6].
The SR irradiation of the H-DLC films was carried out at BL06 of the NewSUBARU synchrotron facility.
The SR at the BL06 sample stage had a continuous spectrum from IR to soft X-rays, lower than 1 keV. This
includes 300 eV, which is the ionization energy of a carbon K shell. As a result, the K-shell electrons of the C
atoms could be excited by the SR at BL06. During this experiment, the electron energy of the NewSUBARU
ring was 1.0 GeV. The BL06 sample stage was room temperature and the pressure in the chamber was theorder of 10-5 Pa. An SR dose [mA･h] is derived from the product of the ring current [mA] and exposure time[h].
NEXAFS spectra were measured by total electron yield (TEY) method at BL09A of the NewSUBARU.
This measurement enabled us to know information on the local structure near surface of sample. The SR
exposure to sample carried out at magic angle (54.7) with respect to the surface of the sample. The
measured energy range in the experiment was 270-330 eV of C-K edge, and the energy resolution was about
0.5 eV.
Results and discussion
Figure 1 shows C-K edge NEXAFS spectra of H-DLC films exposed to the SR, that of the H-DLC film
before exposure and that of a commercial DLC film as a typical DLC films. This commercial DLC film waswere deposited on 200 nm-thick on Si wafers by using ion plating method and it was named an IP-DLC film.
A sharp π* peak observed at 285.38 eV is ascribed to C1s→π* resonance transition originating from carbon
double bonding. A broad σ* peak observed at about 285-310 eV is ascribed to C1s→σ* resonance transition.
In the C-K edge NEXAFS spectrum of H-DLC before exposure, specific peaks were observed at around
290 eV and 300-305 eV unlike IP-DLC as shown in Fig. 1. Intensity of these specific peaks in spectrum of
H-DLC films became to decrease with increasing of the SR dose, and these peaks in spectrum of the H-DLC
films after 200 mA･h SR dose exposure disappeared. As a result, this spectral feature of the H-DLC films
after the SR exposure of more than 200 mA･h became to resemble that of IP-DLC film. That means the SR
exposure to H-DLC films led to the structural change close to typical DLC films. These changes of C-K edge

26

NEXAFS spectra are considered to correspond to hydrogen desorption from films. In addition, these change
occurred at the SR exposure less than 200 mA･h. Specific peaks observed in the C-K edge NEXAFS
spectrum of H-DLC films before exposure are ascribable to hydrogen bond in H-DLC films.
Figure 2 shows the SR dose dependence of sp2/(sp2+sp3) ratio of H-DLC films. These ratios were
quantitatively estimated by C-K edge NEXAFS spectra of H-DLC films in Fig. 1. The amount of sp2 bonded
carbon atoms can be extracted by normalizing the area of the resonance corresponding to 1s→π* transitionsat 285.4 eV with the area of a large section of the spectrum. The absolute sp2/(sp2+sp3) ratio was determinedby the comparison with that from the NEXAFS spectrum of graphite.
The sp2/(sp2+sp3) ratio of H-DLC films before exposure was 0.33 and it increased rapidly with SR dosein the region less than 200 mA･h. However the SR dose above 200 mA･h, the sp2/(sp2+sp3) ratio wasapproximately constant at 0.50.
Conclusions
In the C-K edge NEXAFS spectra of H-DLC films before exposure, specific peaks were observed. The
structure of this spectra greatly changed in the SR dose region less than 200 mA･h. As a result, the C-K edge
NEXAFS spectra of H-DLC films became to resemble that of IP-DLC film, which can be regarded as a
typical DLC film.
The sp2/(sp2+sp3) ratio increased rapidly from 0.33 to 0.50 by the SR exposure to H-DLC of 200 mA･h.
It was constant at 0.50 in the SR dose region over 200 mA･h.

σ*

IP-DLC
1500mA·h

200mA·h

0.7100mA·h

40mA·has-grownsp2/(sp 2 + sp 3)

Normarized Absorption [a. u.]

π*

0.6
0.5
0.4

0.2

280

290
300
310
Energy [eV]

as-grown
irradiated

0.3
0

1000
2000
SR dose [mA·h]

3000

Fig. 2. SR dose dependence of sp2/(sp2+sp3) of
H-DLC films calculated by their C-K edge
NEXAFS spectra

Fig. 1. C K-edge NEXAFS spectra of H-DLC
films before and after exposure to Soft X-ray
and IP-DLC

References[1] C. Donnet et al., Tribology of Diamond-like Carbon, Springer (2008).
[2] C. Donnet et al., Surf. Coat. Technol. 68-69 (1994) 626.
[3] H. Kyuragi et al., Appl. Phys. Lett. 50 (1987) 1254.
[4] K. Kanda et al., Jpn. J. Appl. Phys. 50 (2011) 055801.
[5] H. Matsuura et al., SEI Tech. Rev. 171 (2007) 36 [in Japanese].
[6] R. Imai et al., Diamond Relat. Matter. 44 (2014) 8-10.

27

Atomic Oxygen Beam Irradiation Effecton the Si-doped DLC Film
Kengo Kidena1), Minami Endo1), Ryo Imai1), Masahito Niibe1), Kumiko Yokota2),Masahito Tagawa2), and Kazuhiko Kanda1
1)
Laboratory of Advanced Science and Technology for Industry, University of Hyogo
2)
Faculty of Engineering, Kobe University
Abstract
Irradiation effect of an atomic oxygen beam on Si-doped Diamod-Like Carbon (Si-DLC) films
was investigated by the measurements of near edge X-ray absorption fine structure (NEXAFS)
spectra and X-ray photoelectron spectra (XPS). We found that carbon atom in the Si-DLC film
was desorbed from surface and silicon oxide was formed on the Si-DLC surface by the irradiationof atomic oxygen. On the other hand, it was concerned that no change in the thickness of Si-DLC
film occurred by the irradiation of atomic oxygen from the Rutherford backscattering
spectrometry (RBS) study.
Introduction
Diamond-like carbon (DLC) films are expected to use as lubrication materials in space, where oil cannot
used, because they exhibit excellent low friction properties both in a vacuum and in air. The region less than2000 km above the ground, where almost artificial satellites are positioned, are called “low Earth orbit (LEO)”.
In this orbit, artificial satellites and spacecrafts are exposed to atomic oxygen, which is the dominant specie inthe upper atmosphere of the Earth. However, it was found that DLC films were etched by the collision withatomic oxygen in our previous work1). Recently, Si-doped DLC films have been widely used due to theiroxidation resistance. In the present study, we investigated the resistance of Si-DLC film against atomic oxygenand elucidated the mechanism of this durability, to use Si-DLC film as lubrication material in LEO.
Experiments
Si-DLC films were deposited on a Si substrate by plasma-enhanced chemical vapor deposition (PE-CVD).
These Si-DLC films consist of ≈50 % hydrogen and ≈10 % Si. We exposed Si-DLC films to an atomic oxygen
beam with an collisional energy of 5.46 eV, which corresponded to the collisional energy at LEO, by laser
detonation-type beam apparatus (Kobe University)2). In the present study, the fluence of atomic oxygen beam
exposed to Si-DLC film corresponded to 1.16 × 1017, 3.52 × 1017, 1.16 × 1018, and 1.16 × 1019 atoms cm-2.
We investigated the effect of atomic oxygen exposure on the Si-DLC films by measuring the NEXAFS
spectra and RBS spectra. The measurement of NEXAFS spectra werecarried out at beamline 09A in the NewSUBARU synchrotron
radiation facility. Film thickness of the Si-DLC surfaces wasestimated by RBS measurement using electrostatic tandem foundationgraph accelerator 5SDH (Kobe University).
Results
Variations in the local structure of the Si-DLC film due to the
exposure to an atomic oxygen beam are discussed on the basis of the
NEXAFS measurements. Fig. 1 shows the C K-edge NEXAFS
spectra of Si-DLC films exposed to an atomic oxygen beam with thatof a Si-DLC film before exposure. The spectrum of SiC powder isalso shown for a reference. The resonance peak at 285.4 eV was
ascribed to the transition from the C 1s level to unoccupied π* orbit
principally originated from sp2(C=C) sites. The broad band observedin the photon energy region of 290-320 eV was ascribed to thetransitions from C 1s level to unoccupied σ* states.
With increasing of fluence of atomic oxygen, the intensity of the
sharp peak at 285.4 eV decreased, and spectral shape of broad peak at
290-320 eV became sharper. When the fluence of atomic oxygen was
beyond 1.16 × 1019 atoms cm-2, the C K NEXAFS spectrum of
Si-DLC film resembled well the spectrum of SiC powder. From thisobservation, the dominant species bonding to C atom in the Si-DLC
can be considered to change from C=C sites from Si-C sites.

28

Fig. 1 C K-edge NEXAFS spectraof Si-DLC films and SiC powderThis conclusion was supported from the measurement results of O K-edge and Si L-edge NEXAFS spectra.
From the measurement of O K-edge NEXAFS spectrum, intensity of the peak derived from SiO2 increased withfluence of atomic oxygen. After the irradiation of atomic oxygen beyond 1.16 × 1019 atoms cm-2, the spectralfeatures of O K NEXAFS spectrum of Si-DLC film changed into a similar shape with the spectrum of SiO2. In
the Si L-edge NEXAFS spectrum of the Si-DLC film before exposure, most of structural peak was not observed
as well as that of SiC powder. With fluence of atomic oxygen, structural peaks were observed in the Si L-edge
NEXAFS spectrum. After the irradiation of atomic oxygen beyond 1.16 × 1019 atoms cm-2, the spectral featuresof Si L NEXAFS spectrum of Si-DLC film changed into a similar shape with the spectrum of SiO2. From these
NEXAFS study, the Si atoms almost bonded with C atoms before exposure to an atomic oxygen beam and the Siatom bonding to O atom increased with the fluence of the atomic oxygen beam on the surface of Si-DLC films.
Elementary composition of the surface of
Si-DLC films due to the irradiation of an atomic
oxygen beam was estimated by the measurementof the XPS spectra. Fig. 2 shows the XPS spectraof the Si-DLC films before and after exposure to
an atomic oxygen beam. Several peaks
originating from C, Si, and O atoms, wereobserved in the spectrum of Si-DLC films before
exposure. The peaks at 532, 235, 153, and 102
eV were assigned to the O1s, C1s, Si2s, and Si2p,
respectively. After exposure to an atomic oxygenbeam, the intensity of the peaks originating fromthe Si and O atoms increased and thoseoriginating from the C atoms decreased. The
results of elementary analysis are listed in Table Fig. 2 XPS spectra of Si-DLC films before and after
1. The amounts of Si and O atom in the Si-DLC exposure to atomic oxygen beam.
films increased with the fluence of the atomic
oxygen beam. However, that of C atoms Table 1
Elementary composition of the surface of Si-DLC films
decreased monotonically.
beforeand after exposure to atomic oxygen beam.
These variation of elementary composition of
the surface of Si-DLC films by the exposure to
FluenceCO
Si
atomic oxygen beam can be considered as atomscm-2
at.%follows: C atoms decreased due to desorption
0
10
54
37
from Si-DLC film by the irradiation of atomic
1545
40
1.2×10 17
oxygen, to form gas species, CO and/or CO2. O
16
39
44
3.5×10 17
and Si atoms increased due to the formation of Si
18
21
28
51
1.2×10oxide by the irradiation of atomic oxygen. Si
oxide was not eliminated from Si-DLC film
22
24
55
1.2×10 19
because it is solid, unlike oxide of C.
Variations in thickness of Si-DLC films due tothe irradiation of an atomic oxygen beam were
estimated by the measurement of RBS. Fluence
dependence of film thickness was depicted inFig. 3. Film thickness of DLC film, which did
not include Si atom, was reported to decrease
with atomic oxygen fluence1), whereas that of
Si-DLC film was constant after the exposure toatomic oxygen beam.
From these results, the C atoms on the
Si-DLC surface were desorbed as the CO and/or
CO2, but Si atoms were remained on the Si-DLC
surface as the SiOx. It was interpreted that thisSiOx layer disturbed the erosion of bulk film
Fig. 3 Fluence dependence of Film thickness
against atomic oxygen.
Reference[1] M. Tagawa et al., Appl. Surf. Sci., 256, pp. 7678-7683 (2010).
[2] K. Yokota et al., J. Spacecraft Rockets, 40, pp. 143 (2002).

29

Molecular Orientation at the Near-surface of Photoaligned
Films Determined by NEXAFS
Yuichi Haruyama1, Makoto Okada1, Emi Nishioka2, Mizuho Kondo2, Nobuhiro Kawatsuki2, and Shinji Matsui1
1
Laboratory of Advanced Science and Technology for Industry, University of Hyogo
2
Department of Materials Science and Chemistry, Graduate School of Engineering, University of Hyogo
Abstract
Near-edge X-ray absorption fine structure (NEXAFS) spectra of polymethacrylate, which has ahexamethylene spacer group terminated with a 4-oxycinnamic acid in its side chain (P6CAM),
were measured at the C K-edge region. Several peaks in the NEXAFS spectra of photoalingned
P6CAM films were observed and the resonances at 285 eV, 288 eV, and 293-305 eV were assigned
to carbon 1s to À* of the phenyl rings, carbon 1s to À* of C=O, and carbon 1s to Ã* transitions,
respectively. From the dependence on the incident angle of the linear polarized synchrotron
radiation in the NEXAFS spectra of photoalingned P6CAM films, it was found that the liquid
crystals orient perpendicular to the polarization direction of the UV light.
Introduction
Studies on the photoinduced orientation of the polymeric films have attracted significant attention for apotentially wide range of applications such as birefringent optical devices, the photo alignment layer of liquid
crystal displays, optical memories, and holographic data storage devices [1-2]. Optical anisotropy of thepolymeric films is created by irradiating the polarized UV light to the films. The polymethacrylate, which has
a hexamethylene spacer group terminated with a 4-oxycinnamic acid in its side chain (P6CAM), is aphotoreactive liquid crystalline polymer comprised of cinnamic ester side groups as shown in Fig. 1. It wasobserved that the molecular orientation of photoreactive liquid crystalline polymer controlled by the linearlypolarized UV radiation and the subsequent annealing procedure [3-5]. In this study, we obtained the C
K-edge NEXAFS spectra of P6CAM in order to investigate the molecular orientation at the near-surface ofthe photoreactive liquid crystalline polymers.
Experiments
P6CAM were synthesized as described in a previous paper [3]. Thin films of P6CAM were prepared byspin-coating a tetrahydrofuran (THF) solution of polymers onto ITO coated SODA glasses. The thickness ofthe thin films was 170 nm. The photoaligned thin films of P6CAM were prepared by irradiating the linear
polarized UV light to the films and by subsequently annealing at 180 °C for 10 minutes. After the procedures,the liquid crystal part of P6CAM reorients to the vertical to the polarization direction of the linear polarized
UV light.
All NEXAFS spectra measurements were carried out using the BL-7B beamline of the NewSUBARU
synchrotron radiation facility at the University of Hyogo. As an excitation source, linear polarizedsynchrotron radiation with photon energy (hν) range from 280 to 330 eV was used and the total energy
resolution was about 0.5 eV. NEXAFS spectra were measured by the total electron yield method. The basepressure in the NEXAFS measurements chamber was 2×10-8 Pa. The sample could be rotated around a
vertical axis to change the incident angle θ of the synchrotron radiation to the sample surface. The directionof the polarization in the synchrotron radiation was horizontal. To reduce the irradiation damage of thesamples, the samples were cooled at about 80 K and NEXAFS spectra were recorded at this temperature. In
addition, the sample was shifted to a different position after each measurement of the NEXAFS spectrum.
Results
Figure 2 shows the C K-edge NEXAFS spectra of photoaligned P6CAM films as a function of incident
angle θ of the synchrotron radiation. NEXAFS spectra are aligned in increasing order of the incident angle θfrom the bottom. The reoriented direction of the liquid crystal in P6CAM was parallel to the incident plane of
the synchrotron radiation. The NEXAFS spectra were normalized by the edge-jump intensity. Two sharp
peaks were observed at 285 and 288 eV wereobserved. In addition, two broad peaks werevisible at 293-305 eV. With increasing the incident
O
OOH
angle θ, the intensity of the peak at 285 eV wasn4remarkably decreased while the intensities of theOOpeaks at 293-305 eV were increased. In the casethat the reoriented direction of the liquid
Figure 1. Chemical structure of P6CAM.

30

Figure 2. C K-edge NEXAFS spectra ofphotoaligned P6CAM films as a function of theincident angle θ, relative to substrate surface.
The reoriented direction of the liquid crystal in
P6CAM was parallel to the incident plane of thesynchrotron radiation.

Figure 3. C K-edge NEXAFS spectra ofphotoaligned P6CAM films as a function of theincident angle θ, relative to substrate surface.
The reoriented direction of the liquid crystal in
P6CAM was perpendicular to the incident planeof the synchrotron radiation.

crystal in P6CAM was perpendicular to the incident
plane of the synchrotron radiation, the C K-edge
NEXAFS spectra of photoaligned P6CAM thinfilms as a function of incidence angle θ of thesynchrotron radiation was shown in Fig. 3. With
increasing the incident angle θ, the intensity of thepeaks at 285 eV was not changed while theintensities of the peaks at 293-305 eV were slightly
increased. Thus, from the difference on the angulardependence of the NEXAFS spectra, it was
confirmed the anisotropy of photoaligned P6CAM
thin films. In the C K-edge NEXAFS spectrum,transitions from the C 1s orbital to the unoccupied
π* and Ã* orbitals are observed at specified sites. In
P6CAM, the resonances at 285 eV, 288 eV, and293-305 eV correspond to carbon 1s to À* of the
Figure 4. Angular dependence of the resonancephenyl rings, carbon 1s to À* of C=O, and carbon 1s
intensity in the parallel and perpendicularto Ã* transitions, respectively. Figure 4 shows thegeometries for photoaligned P6CAM thin films.
angular dependence of the π* resonance intensity inthe parallel and perpendicular geometries for photoaligned P6CAM thin films. From the angular dependeceof the π* resonance intensity, it was found that the liquid crystals orient perpendicular to the polarization
direction of the UV light.
References[1] N. Kawatsuki and H. Ono: Org. Electron. Photonics 2 (2007) 301.
[2] N. Kawatsuki, H. Ono, H. Takatsuka, T. Yamamoto, and O. Sangen: Macromolecules 30 (1997) 6680.
[3] N. Kawatsuki, T. Kawanishi, and E. Uchida: Macromolecules 39 (2006) 9357.
[4] M. Okada, S. Manabe, M. Kurita, M. Kondo, Y. Haruyama, K. Kanda, A. Emoto, H. Ono, N. Kawatsuki,
and S. Matsui: Jpn. J. Appl. Phys. 49 (2010) 128004.
[5] M. Okada, S. Manabe, M. Kurita, M. Kondo, Y. Haruyama, K. Kanda, N. Kawatsuki, and S. Matsui:
Microelectronic Engineering 88 (2011) 2079.

31

EUV Resist Chemical Reaction Analysis using SR
Takeo Watanabe 1) , Kazuya Emura 1) , Daiju Shiono 3) , Yuichi Haruyama 1) , Yasuji Muramatsu2) ,Katsumi Ohmori3) , Kazufumi Sato3) , Tetsuo Harada 1) , and Hiroo Kinoshita 1)
1

Center for EUVL, LASTI, University of Hyogo,
3-1-2 Kouto, Kamigori, Ako-gun, Hyogo 678-1205, Japan.
2
Graduate School of Engineering, University of Hyogo,
2167 Shosha, Himeji, Hyogo 671-2280.
3
Tokyo Ohka Kogyo,
1590 Tabata, Samukawa, Koza, Kanagawa, 253-0114, Japan.

The chemical reaction in EUV irradiation of the several photoacid generators (PAGs) which
employed triphenylsulfonium (TPS) salts as the cation of PAG, is discussed on the basis of theanalysis using the SR absorption spectroscopy in the soft x-ray region. The fluorine atoms of theanion PAGs which have the chemical structure of the imidate type such as TPS-Imidate-1, and
TPS-Imidate-2 strongly decomposed under EUV exposure. In the case of these PAG type, it isfound that in addition to the ionization reaction, the anion decomposition reaction originated by thephoto excitation of the photoacid generator might occur under EUV exposures. Thus thesensitivity seemed to be high comparison to tri-phenylsulfonium perfluorobutanesulfonate(TPS-Nonaflate) under EUV exposure. In the case of tri-phenylsulfonium camphorsulfonate(TPS-Cs), the anion which does not contain fluorine seemed to be very stable under EUV exposureand the sensitivity is lower than TPS-Nonaflate.
Keyword: EUVL, chemically amplified resist, photoacid generator,
decomposition of anion of PAG, SR absorption spectroscopy

activation energy chemically amplified3-5) resist
were performed for the high sensitive resist, but
the LWR not refined.6) The LWR is one of theresist issues to maintain the device electricperformance. There are many reports to improved
LWR from resist material development. One is theapplication of compounds of low molecular weight
and/or narrow polymer dispersity7-11) and monomer
resist12-17) may be one of the key concepts toresolve this issue due to its reduced molecular size
compared with linear polymers against theintended feature print size.
There is a trade-off relationship between resolution,
sensitivity, and LWR; so called RLS trade-off.18,19)
Now the resolving this trade-off relationship 1X
nm node and below becomes very significant anddifficult issue.20,21) Thus more fundamental resist
studies for 1X nm and below is required to clarify
the chemical reaction under EUV exposure.
To increase the sensitivity and decrease the

1. Introduction
The extreme ultraviolet lithography (EUVL)1)will be used from 16-nm node for the
manufacturing semiconductor electronic devices
such as memory and MPU devices. And according
to the International Technology Roadmap for
Semiconductors (ITRS), 8-nm node lithography isrequired from 2025.2)
The top three issues of EUV lithography forhigh volume manufacturing (HVM) are 1) theachievement of the high power and a long term
stable EUV source, 2) the fabrication of the defectfree mask and its defect inspection and repair, and3) the development of the EUV resist which has
the high resolution, the high sensitivity, low line
width roughness (LWR), and low outgassing andlow carbon contamination, simultaneously.
To relax the specification of the EUV power andmaintain the high-lithographic throughput, the highsensitive EUV resist is required. The low

32

LWR, the acid production yield should increase.
Although the acid production yield of thephotoacid generator (PAG) of the chemically
amplified resist had been studied22,23), therequirement of the EUV resist was still notsatisfied yet. Thus, more effective fundamental
work should require to be clarified the chemical
reaction
under
EUV
exposure.
Thephoto-ionization (ionization) reaction might bedominant and the secondary electron plays theimportant role in the chemical reaction under EUV
exposure23). In addition, we had found out that thedecomposition reaction was occurred near the large
photo absorption atom in the solvent, so called“solvent effect” 24). In the case of the PAG
chemical reaction analysis in EUV irradiation, notonly ionization reaction but also the direct
excitation in EUV irradiation might be needed toachieve the high sensitive EUV resist. In theprevious report, for resists which employedtri-phenylsulfonium cyclo(1,3-perfluoropropanedisulfone)
imidate(TPS-Imidate-1)
andtri-phenylsulfonium perfluorobutane- sulfonate(TPS-Nonaflate) as
PAGs, the peak at theabsorbance at 1156 cm-1 in the fourier transform
infrared (FT-IR) spectra increased after EUV
exposure.25-29) As a results of the electron orbital
calculation using perturbation theory by thesoftware code Gaussion0330), the peak at
approximately 1156 cm-1 in FT-IR spectra of resist
A corresponds to the C-F bonding of the anion of
TPS-Imidate-1. However, there was no change inthe FT-IR spectra of resist which include
TPS-Nonaflate, between before and after EUV
exposure. As a result, the outgassing measurements
SampleBasepolymerTable 1.
Resist A

and the FT-IR spectra measurements indicated that
the EUV-induced reaction of TPS-Imidate-1
occurred more efficiently than that of
TPS-Nonaflate. To clarify the difference of theanion decomposition, the analysis using SR
spectroscopy is performed. This paper focused on
the chemical reaction analysis of the model
chemically amplified resists which contains several
PAG on the basis of tri-phenylsulfonium by the SR
absorption spectroscopic method32).
2. Experimental
2.1. Materials for the Model Resists
The model resists which were employed in thisstudy are shown in Table 1. The resists A, B, C,
and D employed poly (hydroxystyreneco-t-butylacrylate) (PHS-TBA) as the basepolymer,
andpropyleneglycol
monomethyletheracetate (PGMEA) as a solvent.
The model resists A does not include any
photoacid generator. Model resists, A, B, C and D
employed TPS-Imidate-1 and TPS-Imidate-2,
TPS-Nonfalte, and TPS-Cs as the photoacid
generator, respectively. The PAG content#1 andcontent#2 ratio to the base resin such as PHS-TBA
is approximately 2 mol% and 6 mol% of the basepolymer for the sensitivity measurement and theSRabsorption
spectroscopy
experiment,
respectively. In sensitivity measurement, the PAG
content#1 of 2 mol% is a normal value. However,the PAG content for SR absorption spectroscopy
experiment should be larger than that forsensitivity measurement, because in SR
spectroscopy experiment the signal from theatomic elements of the resist film is too small

Chemical structure and contents of the model resists.
Resist B
Resist C

Resist Dnmpoly (vinylphenol-co-tert butylacrylate)(PHS-TBA)OOOHPhotoacidgenerator

TPS-Imidate-1
O2S(content#1)(content#2)
Solvent

TPS-Nonaflate

TPS-Cs

CF2

S+ -N
O2S

TPS-Imidate-2

CF2

S+ C4F9SO3-

CF2(2.04 mol%)(6.11 mol%)(1.34 mol%)(4.03 mol%)(2.02 mol%)(6.06 mol%)

propylene glycol monomethylether acetate (PGMEA)

33(2.09 mol%)(6.18 mol%)is approximately 3.0×10 11 photons/s/100mA.
The absorption signal was obtained from the ratioof the photocurrent from the sample to thephotocurrent from the gold mesh. The total energy
resolution was approximately 0.1 eV. The
photocurrent was measured by the electrometer(6514, Keithley).
The photon energy calibration was carried out
by measuring the photon absorption spectrum of
highly oriented pyrolytic graphite (HPOG). The
photon energy at the absorption peak of the carbon
π∗-bonding was adjusted at the photon energy of
285.5 eV.
For the absorption measurement of carbon
1s core level, the measured energy region is280-330 eV and 1200 lines/mm VLSPG was
employed with the undulator gap of 48.0 mm.
For the absorption measurement of fluorine 1s
core level, the measured energy region is685-735 eV and 2400 lines/mm VLSPG was
employed with the undulator gap of 52.0 mm.
The electron current generated on the sample
is measured in the SR absorption experiment
during the SR light exposure.

when the PAG content is 2 mol%.
The resist solution was spin coated on a
4-inches silicon wafer and the prebake was carriedout on a hot plate at the temperature of 130ºC in
the time period of 90 s. The film thickness wasmeasured by Nanometrics 6100A (NANOmetrics)
and the resist film thickness was spin-coated to be
50 nm on a wafer. The EUV exposure to obtain thesensitivity curve in high accuracy, the resist
sensitivity evaluation8) system which can simulatetheEUV
exposure
spectrumofthesix-mirror-imaging optics was installed at the BL3
beamline in NewSUBARU synchrotron radiation
facility31) was utilized. This EUV spectrum whichis same as the practical exposure tool such as
ASML NXE3100B can be produced by theseven-time reflection by three-mirror optics.
2-2. SR photo absorption spectroscopy32)
X-ray spectroscopy (XPS) is a beneficial
measurement method to analyze the atomic
chemical behavior of the material. However, forthe absorption spectroscopy measurement of theatomic which is a small content such as thephotoacid generator of the EUV resist, the highbrilliance light source such as synchrotron
radiation (SR) light is beneficial in absorption
spectroscopy. Thus, soft x-ray of the SR absorption
spectroscopy was employed for the chemical
reaction analysis for the EUV resist materials.
TheSR
absorption
spectroscopy
measurements were performed at the end
station of the BL07B beamline at the
NewSUBARU synchrotron radiation facility.
The short undulator was employed as a lightsource of this beamline. This beamline
consists of three glancing mirrors such as M 0 ,M 1 and M 2 , the monochromater (G), theentrance (S 1 ) and exit (S 2 ) slits and the end
station exposure and analyzing chambers. The
loadlock chamber was adapted to thesechambers to exchange the sample. The
variable-line-spacing plane gratings (VLSPG)
were employed as monochromator. Threedensity types such as 600, 1200, and 2400
lines/mm were installed in the monochromator
vacuum chamber. The photon energy region isfrom 80 eV and 800 eV in the SR spectroscopy.
The exit slit size is 20 µm(H)×20 µm(V) andthe SR light spot size on a sample is 1
mm(H)×1 mm (V). The energy resolution
E/ ∆ E is approximately 1000. The photon fluxof the photon energy of 91.8 eV (λ=13.5 nm)

3. Results and Discussions
3.1 Sensitivity
The sensitivities curves of the resists A, B, C
and D under EUV are shown in Fig. 1. The E0
values which is the exposure dose to clear the
resist remained thickness after the development, ofresists A, B, C and D are 1.1 mJ/cm2, 2.7 mJ/cm2,
3.8 mJ/cm2, and 6.0 mJ/cm2, respectively. The
sensitivity differences of resists A, B, C, and D
under EUV exposure would be discussed by the
analysis of the SR photo absorption spectroscopy
in the soft x-ray region.

A
B
C
D

Fig.1 Sensitivity curves under EUV exposure formodel resist A, B, C, and D.

34

3.2 SR absorption spectroscopy
The absorption spectra of carbon 1s core level
for resists A, B, C and D were measured as shownin Fig.s 2, 3, 4 and 5, respectively. For each sample
the measured energy range was from 280 eV to
330 eV. To highlight the peak height changes, theSR absorption spectra were plotted in the energy
region from 280 eV to 295 eV. The absorption peakat 285.5 eV is corresponding the π∗-bonding of the
benzyl group in the cation of PAG (TPS). From theoutgassing results25-29), this changes correspond tothe cation of PAG such as TPS decomposition
occurred by the secondary electron originated by
the EUV irradiation as shown in Fig. 6. As theincreasing the EUV dose, the absorption spectra ofthe π∗-bonding became smaller. Furthermore, theabsorption peak at 287 eV corresponds to the
σ-bonding of the protection group of
tert-butylacrylate (TBA) of the base polymer. From
the outgassing results25-29), this changes correspond
only to the protecting group decomposition
reaction of TBA in base polymer occurred by thesecondary electron originated by the EUV
irradiation as shown in Fig. 7.

σ*
π*
(TBA)
(TPS)

Anion of
PAG

π*
(TPS)

σ*
(TBA)

Fig. 4 SR absorption spectra of carbon 1s corelevel in resist C.

Anion of
PAG
π*
(TPS)

σ*
(TBA)

Fig. 5 SR absorption spectra of carbon 1s corelevel in resist D; (a) 280 eV-330eV, and (b) 285
eV-295 eV.

Anion of
PAG

Fig. 2 SR absorption spectra carbon 1s core levelin resist A.

Fig. 6 Decompostion reaction of thetriphenylsunfonium employed as the cation of PAG
by the secondary electron.

Anion of
PAG
π*
(TPS)

σ*
(TBA)
Fig. 7 Decomposition reaction of PHS-TBA.
The absorption spectra of fluorine 1s core level
for resists A, B and C were measured by the SR
absorption spectroscopic method. Figures 8, 9, andFig. 3 SR absorption spectra carbon 1s core levelin resist B.

35

10 show the EUV exposure dose dependency of
the absorption of fluorine 1s core level in resists A,
B, and C, respectively. Comparison of Fig.s 8, 9,
and 10, the fluorine of the anion of the PAG in
resists A and B decompose easily rather than thatof the anion of PAG in resist C.

As the results, the resist including imidate typein the anion of PAG which is easy to decompose in
EUV irradiation has higher sensitivity rather thanothers. On the other hand, for TPS-Cs, there is notchanges in the oxygen 1s core spectra as increasing
EUV exposre dose. Thus as the anion of TPS-Cs isvery stable, resist including TPS-Cs has lowest
sensitivity.
In addition, to control the line edge roughness,
generally shortening the acid diffusion inchemically amplified resist during PEB might bebeneficial by increasing the molecular size of theanion of PAG. However, if the decomposition
reaction of the anion of PAG in EUV irradiation is
occurred strongly, the acid diffusion length might
become large. Thus, the simultaneous achievementof the high sensitive and the shortening LWR, theanion decomposition reaction based on the direct
excitation of PAG should be considered andanalyzed.
Figure 11 shows two scheme of thedecomposition reaction of the Imidate type PAG
reaction under EUV irradiation. In Fig. 11(a), R Ph,
and X- indicate the base polymer such as PHS
polymer, the benzyl group of the cation of PAG,
and the anion of PAG, respectively. In Fig. 10(b),X- is the anion of PAG, and X1-, X2-, and X3- aredecomposition species from the anion of X-.which
has a negative charge. N1, N2, and N3 aredecomposition component which have a neutral
charge. The dominant chemical reaction of the
EUV light is ionization and the cation of the PAG
decomposes by secondary electron as shown in Fig.
11(a).

Fig. 8 SR absorption spectra of fluorine 1s corelevel for resist A.

e-

Fig. 9 SR absorption spectra of fluorine 1s corelevel for resist B.

(a) Ph3S+X- → Ph2S + Ph + X- →Ph2S + PhH + H+X-

(for PAG)hν(b) X- → H+ + X1- + H+ + X2- + N1
orhν
X- → H+ + X3- + N2 + N3
Fig. 11 (a) The decomposition reaction by thesecondary electron generated from the ionization
reaction and (b) the decomposition reaction of theanion of PAG by the direct excitation reaction
under EUV irradiation.
For the decomposition reaction of the anion of
PAG, it seems to not occur by the secondary
electron. In the case of Imidate of PAG, the anion
of PAG decomposes by the direct excitation of
PAG as shown in Fig. 11(b). Therefore, the EUV

Fig. 10 SR absorption spectra of fluorine 1s corelevel for resist C.

36

sensitivity of the model resists which contain
Imidate as the anion of PAGs are higher than that
contains Nonaflate and Cs as the anion of PAGs.
Therefore, the low sensitivity of the model resist
contains TPS-Cs depends on the stable chemical
structure of the anion of PAG. Otherwise, the highsensitivity of the model resist contains
TPS-Imidate-1 and TPS-Imidate-2 depend on thedecomposition reaction of the anion of PAG.

5. H. Ito, G. Breyta, D. Hofer, R.
Sooriyakumaran, K. Petrillo, and D. Seeger, J.
Photopolym. Sci. Technol., 7 (1994) 433.
6. J. W. Thackeray, R. A. Nassar, K.
Spear-Alfonso, T. Wallow, B LaFontaine, J.
Photopolym. Sci. Technol., 19 (2006) 525.
7. D. C. Tully, A. R. Trimble and J. M. J. Frechet,Adv. Mater. 12 (2000) 1118.
8. J.B. Kim, H. J. Yun and Y.-G. Kwon, Chem.
Lett., 10 (2002), 1064.
9. M. Ishida, J. Fujita, T. Ogura, Y. Ochiai, E.
Ohshima and J. Momoda: Jpn. J. Appl. Phys.,
42 (2003) 3913.
10. T. Kadota, M. Yoshiiwa, H. Kageyama, F.
Wakaya, K. Gamo and Y. Shirota, Proc. SPIE,
4345 (2001) 891.
11. J. B. Kim, Y.-G. Kwon, T. Fujigaya, Y.
Shibasaki and M. Ueda, J. Mater. Chem., 12(2002) 53.
12. T. Hirayama, D. Shiono, H. Hada and J.
Onodera, J. Photopolym. Sci. Technol., 17(2004) 435.
13. H. Hada, T. Hirayama, D. Shiono, J, Onodera,
T. Watanabe, S. Y. Lee and H. Kinoshita, Jpn. J.
Appl. Phys., 44 (7B) (2005) 5824.
14. Daiju Shiono, Hideo Hada, Kazufumi Sato,
Yasuyuki Fukishima, Takeo Watanabe, andHiroo Kinoshita, J. Photopolym. Sci. Technol.,22, (2009) 737.
15. H . Kudo, R. Hayashi, K. Mitani, T. Yokozawa,
N. C. Kasuga, and T. Nishikubo, Angew. Chem.
Int. Ed., 45, (2006) 7948.
16. H. Seki, S. Kuwabara, H. Kudo and T.
Nishikubo, Chemistry Letters, 40, (2011) 464.
17. Hiroto Kudo, Nobumitsu Niina, Tomoharu
Sato, Hiroaki Oizumi, Toshiro Itani, Takuro
Miura, Takeo Watanabe and Hiroo Kinoshita, J.
Photopolymer Sci. Technol, 25 (2012) 587.
18. T. Watanabe, H. Kinoshita, H. Nii, K.
Hamamoto, H. Hada, H. Komano, and S. Irie,
J. Vac, Sci. Technol., B19 (2001) 736.
19. K. Hamamoto, T. Watanabe, H. Hada, H.
Komano and H. Kinoshita, J. Photopolym. Sci.
Technol., 15 (2002) 361.
20. Yasuyuki Fukushima, Naoki Sakagami,
Teruhiko Kimura, Yoshito Kamaji, Takafumi
Iguchi, Yuya Yamaguchi, Masaki Tada, Tetsuo
Harada, Takeo Watanabe, and Hiroo Kinoshita,
Jpn. J. Appl. Phys., 49 (2010) 06GD06-1.
21. Takuro Urayama, Takeo Watanabe, Yuya
Yamaguchi, Naohiro Matsuda, Yasuyuki
Fukushima, Takafumi Iguchi, Tetsuo Harada,and Hiroo Kinoshita, J. Photopolymer Sci.

4. Conclusions
The chemical reaction in EUV irradiation of theseveral photoacid generators (PAGs) which
employed triphenylsulfonium (TPS) salts as thecation of PAG, is discussed on the basis of theanalysis using the SR absorption spectroscopy inthe soft x-ray region. The fluorine atoms of theanion PAGs which have the chemical structure of
the imidate type such as TPS-Imidate-1, and
TPS-Imidate-2 strongly decomposed under EUV
exposure. In the case of these PAG type, it is foundthat in addition to the ionization reaction, the anion
decomposition reaction originated by the photoexcitation of the photoacid generator might occur
under EUV exposures. Thus the sensitivity seemed
to be high comparison to tri-phenylsulfonium
perfluorobutanesulfonate (TPS-Nonaflate) under
EUV exposure. In the case of tri-phenylsulfonium
camphorsulfonate (TPS-Cs), the anion which does
not contain fluorine seemed to be very stable under
EUV exposure and the sensitivity is lower than
TPS-Nonaflate.
The SR absorption spectroscopy is a powerful
analysis method to analyze the decomposition
reaction of the anion of PAG. To satisfy the
specification of the EUV resist which require forhigh volume manufacturing, all the chemical
reaction should be taken in account, such as theionization and the direct excitation reactions.
Increasing the sensitivity, it might have more space
to achieve the low LWR resist.
References
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37

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K. Hamamoto and H. Komano Jpn. J. Appl.
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Tanaka, H. Shiotani, Y. Fukushima and H.
Komano: Proc. SPIE, 6153 (2006) 615343-1.
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Shiotani, H. Kinoshita and H. Komano,
Synchrotron Radiation Instrumentation: Ninth
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Kinoshita, J. Photopolymer Sci. Technol., 25(2012) 569.

38

Phase defect characterization on an extreme-ultraviolet
blank mask using micro coherent extreme-ultraviolet
scatterometry microscope
Tetsuo Harada, Yusuke Tanaka, Takeo Watanabe, Hiroo Kinoshita
Center for EUV Lithography, LAST, University of Hyogo, Kamigori, Hyogo 678-1205, Japan
Abstract
Defect-free mask production is a critical issue in extreme-ultraviolet (EUV) lithography. On EUV
masks, phase defects are buried by multilayer coating, which is a serious EUV-specific issue.
These defects should be hidden or be compensated completely by the absorber pattern for the
production of defect-free masks. A phase image of the phase defects at the EUV lithography
exposure wavelength is essential to characterize the defects. For characterization of phase defects,
we have developed the micro coherent EUV microscope (micro-CSM). This system is lensless andis based on a coherent diffraction imaging method, which records diffraction images. The intensityand phase images of the defects are reconstructed through iterative calculations. The micro-CSM
system has focusing optics of a Fresnel zone plate to observe small defect. The detection size
limits of the phase defects were a width of 25 nm and a depth of 1.4 nm. Diffraction images froman asymmetric phase defect were related well to the defect shapes and volumes. The defectposition was also inspected by mapping image that was measured using by step-and-repeat
observation. The actinic defect signals were observed by the micro-CSM system.
Introduction
In extreme-ultraviolet (EUV) lithography, defect-free mask production is a critical issue forhigh-volume manufacturing of semiconductor devices. The mask is a master pattern for
manufacture of a semiconductor device, and there must be no defects on this mask. The EUV
mask is a reflective-type mask, unlike the transparent-type mask that is used for conventional
193 nm lithography. The EUV mask is coated with a Mo/Si multilayer followed by an absorberlayer, in which patterns are printed to form the device pattern. However, phase structures
such as bumps or pits on the substrate or particles in the multilayer can form printable defects
in EUV exposure tools. For example, a shallow structure of 1 nm depth on the surface of amask substrate can cause a large reflection phase shift of 53° at the 13.5-nm EUV wavelength.
As a result, this buried defect is printable. The printability has been evaluated by some groups
using EUV actinic microscopes. Buried defects can be detected efficiently at the mask blankstate of manufacture.
We have developed a coherent EUV scatterometry microscope for phase defectcharacterization.[1–5] The sample phase defect was exposed using coherent EUV light, andthe diffracted light was recorded using a CCD camera. To reconstruct the pattern image, thephase information of the diffraction image is required, but this information is not recorded. We
use a coherent diffraction imaging (CDI) method[6-8] to retrieve the missing phase. With
coherent illumination, the phase is embedded in the oversampled diffraction image. This phase
information is then retrieved via iterative calculations using Fourier transforms and inverse
Fourier transforms. The periodic structures of the line-and-space (L/S) and hole patterns andthe aperiodic structures were reconstructed well.[2] In addition to the conventional intensity
images, the phase images were also acquired by the CSM.[5] The EUV-phase shift value of anabsorber structure and the phase difference in the L/S pattern with shadowing effects were
evaluated, because they could cause actinic critical-dimension changes. The phase distributionof a 1 μm square-sized phase defect was also reconstructed, from which the phase value wasquantitatively evaluated.[5] This EUV-phase distribution is the basic information required to
predict defect printability at the EUV exposure tools. Because the defect shape on a glass
substrate is different to the defect shape on a multilayer surface, the conventional atomic force
microscope (AFM) tool cannot be used to evaluate the printability.
The illumination spot size of the CSM system was about 5 μm, which is too large for
evaluation of a target defect that is less than 50 nm wide and 1 nm high. Therefore, the defectsignal was much weaker than the background signals. The sources of these backgroundsignals were the CCD camera noise and scattering from the mask. The scattering noiseproblem in this system is an intrinsic problem, which cannot be avoided. For example, high39EUV illumination flux or even an ideal detector cannot improve the detection limit. Thus, we
proposed the micro-CSM system with a focused illumination probe, which has a probe size ofseveral hundred nm.[10] The phase distributions of small defects (< 50 nm wide, < 1 nm high)will be evaluated by the CDI method using the micro-CSM system. It is difficult tocharacterize such small defects using conventional EUV microscopes with objective lenses.
Because the micro-CSM is a lensless system, the diffraction image is aberration-free andallows us to characterize the defect accurately. In this paper, we show preliminary results ofthe micro-CSM, which includes observation result of various phase defects.
Experiments and Results
Defect-free mask production is a critical issue in extreme-ultraviolet (EUV) lithography. On EUV masks,
phase defects are buried by multilayer coating, which is a serious EUV-specific issue. These defects should
be hidden or be compensated completely by the absorber pattern for the production of defect-free masks. A
phase image of the phase defects at the EUV lithography exposure wavelength is essential to characterize thedefects. For characterization of phase defects, we have developed the micro coherent EUV microscope(micro-CSM). This system is lensless and is based on a coherent diffraction imaging method, which records
diffraction images. The intensity and phase images of the defects are reconstructed through iterative
calculations. The micro-CSM system has focusing optics of a Fresnel zone plate to observe small defect. The
detection size limits of the phase defects were a width of 25 nm and a depth of 1.4 nm. Diffraction images
from an asymmetric phase defect were related well to the defect shapes and volumes. The defect position was
also A schematic view of the micro-CSM system is shown in Fig. 1. The coherent EUV illumination is
focused on the mask by a Fresnel zone plate (FZP). Diffraction from defects is recorded directly by a CCD
camera. The focusing layout of the FZP is off-axis to use the reflection signal, and has a window that enables
it to accept reflected EUV light.

Figure 1. Schematic view of micro-CSM system.
The EUV illumination light is focused by theoff-axis FZP. Diffraction from defects is recorded
directly by the CCD camera.

Figure 2. Optical microscope image of the
FZP. The half FZP is patterned on the SiC
membrane. The focal length is 750 μm. This
was taken by the sample side.

Figure 2 shows an optical microscope image of the FZP that was fabricated by NTT Advanced Technology
Corporation. The designed focal length is approximately 750 μm. The diameter of the original on-axis FZP isapproximately 300 μm. Half of the FZP region was patterned on the membrane. A circular region of 120 μm
in diameter, indicated as a bold line, is used to focus the EUV illumination, which is equivalent to aneffective numerical aperture of 0.08. The expected focusing size determined by the NA is approximately 100
nm. The support membrane is made from 200 nm-thick SiC. The absorber material is 100 nm-thick Ta. The
narrowest line width at the outermost FZP region is approximately 34 nm. A 1 μm square rectangular window
was also patterned to accept the reflected EUV rays. The angle of incidence of the main focused EUV ray isapproximately 6.8°, which is near the angle of the EUV scanner.
The micro-CSM system is located on beamline 10 of the NewSUBARU synchrotron radiation facility26,27.
The entrance slit design is slitless. The monochromator type is that described by Hettrick and Underwood29
in which the mechanically ruled, plane varied-line-space grating operating the converging light produced bya concave spherical mirror. The spectral resolution is approximately 1300 at the EUV wavelength 13.5 nm.
The exit slit is relayed up to 5.2 m downstream at unity magnification by a vertical refocusing mirror, where
the focusing size is approximately 0.05 × 0.8 mm2. A 400 μm-diameter pinhole was inserted at the refocusing40

position to improve the spatial coherence. The FZP in the micro-CSM system was located 2.1 m downstream
from the pinhole.

Figure 3. CCD camera images from the micro-CSM
system. The sample was a programmed-defect mask. The
intensity is shown in log scale. Direct reflection of the
focused EUV (by the FZP pupil) and diffraction(scattering) were recorded. The observation positions
were on (a) the no-defect region and (b) a 70 nm-wide
defect.

Figure 4. The signal profile of a phase
defect with variable width. The
horizontal axis indicates the angle fromthe chief ray of the focusing EUV.

The diffraction signal from a defect is recorded using a back-illuminated CCD camera (Roper Scientific
MTE-2048B). This camera can operate in a high-vacuum environment, and is cooled to a temperature of-50°C. The CCD surface is placed parallel to the mask surface. The imaging area is 27.6 × 27.6 mm2, and2. The CCD chip is locatedcontains 2048 × 2048 arrays of imaging pixels with areas of 13.5 × 13.5μm
parallel to the mask, and the distance from chip to mask is approximately 50 mm. Therefore, the numericalaperture of the micro-CSM system is approximately 0.28. The acceptance angle of the main ray is ±16°. The
estimated spatial resolution is 30 nm at half pitch. The sample mask was a blank EUV mask containing
programmed bump structures on a glass substrate. The bumps were located with about 10 μm pitch. The
designed bump height was 7 nm, while the bump width was varied in a range from 70 to 420 nm, and thebumps were square in shape.
Figure 3 shows the observation results for the programmed defect mask, which are diffraction images
recorded by the CCD camera. Figure 3(a) shows an area without a defect, and (b) shows an area with a 70
nm-wide defect. The image intensity is shown in log scale in both cases. The exposure time was 10 s. The
CCD pixels were binned 4 × 4 to a pixel, and the array count of the CCD chip was 512 × 512. The brightsignal of the center region is caused by the direct reflection of the focused beam, which corresponds to the
FZP pupil. The signal had approximately 40,000 counts in the pupil. The lack of signal on the left side of thepupil is caused by the shadow of the folding mirror. The strong diffraction signal from the defect wasrecorded around the pupil shown in Fig. 3(b), where the signal was 10 times stronger than that without adefect. Figure 4 shows the signal profiles of phase defects with varied widths of 70, 90, 130, and 160 nm.
The vertical axis indicates the detector intensity, and the horizontal axis indicates the angle from the chief ray.
The diffraction signal increased with increasing defect width. The pupil signal decreased with increasing
defect width, which was caused by the destructive interference of the defects. The defect signal decreased
with increasing diffraction angle; the signal from a 70-nm-wide defect was the same as that without any
defect at around 16°. The diffraction signal without any defects was not zero between 4° and 10°, because of
the scattering signal caused by the mask roughness. This signal is the background signal of the micro-CSM
system, which determines the defect size detection limit. This background signal did not depend on theillumination size. However, the diffraction signal from the defects depended on the illumination size. Thus,
the position of the focus is very important for the micro-CSM system, which changes the illumination size.
The distance from the FZP to the mask is measured by a capacitive sensor, and the best focus position was
once evaluated using the 70 nm defect to maximize the defect signal.

41

Figure 5. Mapping image of the diffraction intensity withstep-and-repeat measurements. The diffraction images areshown in the left figure as differences from the diffraction imageat the no-defect position. The intensity of each pixel in the rightfigure shows the integral diffraction signal of the diffraction
images. The programmed defects and actual phase defect wereclearly observed.

Figure 6. Mapping diffraction
image of a 70 nm-wide phase
defect. The focus size of the
EUV illumination was estimatedto be 230 nm (FWHM).

For defect position inspection, we perform mapping measurements of the diffraction image, which arecomposed of step-and-repeat observations in both the X and Y directions. A 40 × 40 pixel mapping image isshown in Fig. 5. The diffraction images on the left were recorded with step distances of 400 nm, withmovements performed by the piezo stage, and are shown as differences from the diffraction image of
no-defect position. The center image is located on the defect. Each pixel of the figure on the right shows theintegral diffraction signal. The diffraction images on the left correspond to the rectangular region indicated by
the dashed line, which is the diffraction intensity around the 90-nm-wide programmed defect. The right-handpart of Fig. 5 includes 40 × 40 pixels of the 16 × 16 μm2 region. In this measurement, the 400 -µm-diameter
pinhole at the beamline refocusing position was not used to increase the illumination size and intensity. The
exposure time for each observation was very short at 0.1 s, which indicates strong illumination intensity.
In the mapping image, there were four programmed defects: two 90-nm-wide defects and two 80-nm-wide
defects. All defect positions were clearly inspected during the mapping measurement. In addition to theprogrammed defects, there was also a diffraction signal from an actual defect. We measured the actual defecton the multilayer surface by AFM, which showed that the defect was 90 nm wide and 2.2 nm high. This AFM
result indicates that the defect is a phase-type defect, because the defect volume is small. The micro-CSM
system detected both the programmed defect and the actual phase defect.

Figure 7. The observation results of the asymmetrically-shaped phase defects. (a)-(d) show the AFM results,and (e)-(h) show the micro-CSM diffraction images of the same defects.
We observed a 70-nm-wide defect by mapping measurements around a best-focus position. The mapping
image at the best focus position is shown in Fig. 6, where the illumination size is minimized. The step
distance was 50 nm, and the exposure time was 0.5 s. Because the defect width was much smaller than theillumination size, this image shows the illumination profile. The focused profile is almost circular, and waswell focused. The scattering signal profile had a full width at half maximum (FWHM) of 250 nm. The
illumination size was 230 nm, as evaluated by deconvolution of the defect width measured by AFM. In thisdeconvolution, the illumination profile and the defect profile were estimated to have Gaussian shapes. The

42

measured illumination size was 2 times larger than the size expected for the NA of 0.08. We will improve the
FZP focusing conditions in future work to minimize the illumination size, which will then enlarge the defectsignal.
Figure 7 shows the diffraction images of asymmetrically-shaped phase defects. Figure 7(a)-(d) show the
AFM results, and Fig. 7(e)-(h) show the micro-CSM results for the same defects. Defects #19, #20, and #22
had oval shapes where the ratio of the long and the short axes was about 1:2. Defect #23 was the smallest
phase defect on this programmed mask and was 60 nm wide and 2.2 nm high. The micro-CSM images wereshown as differences from the diffraction image at a no-defect position. The diffraction signals of the oval
defects had asymmetric diffraction, where the major axis corresponded perfectly to the minor axis of the
AFM result. The diffraction signal is reciprocal space information of the defect. Therefore, the diffraction
distribution of the micro-CSM system corresponds to the defect shapes. At the smallest defect, #23, thediffraction signal was also very small, and this was related to the phase defect volume. Thus, the micro-CSM
measured both defect shape and defect volume. Because the diffraction orientation would be strongly
dependent on the defect shape, the printability of the defect is also dependent on the defect shape.

Figure 8. S/N ratio of the defect signal andbackground noise caused by scattering from thesubstrate.

Figure 9. Mapping diffraction image of thesmallest detectable defect with width of 25
nm and height of 1.4 nm on the glassbt t

To evaluate the size detection limit of the micro-CSM, we observed another programmed phase defect mask.
The mask had programmed pit structures on the glass substrate. The designed defect size range and depth
were 10 – 400 nm and 1 nm, respectively. We performed mapping measurements around the pit defects with50 nm step distances, exposure times of 5 s, and 10 × 10 measurement points. Figure 8 shows the S/N ratio
for each defect size. The horizontal axis indicates the defect width on the glass substrate as measured by
AFM, which was completely different to that on the multilayer surface. The vertical axis indicates the S/Nratio of the defect signal and noise. Noise in this case means the standard deviation that was evaluated fromthe signal fluctuation of the no-defect region. The size detection limits for the phase defect were 25 nm in
width and 1.4 nm in height. The mapping image of the smallest detectable defect is shown in Fig. 9. The
diffraction signal of this defect was clearly observed. The integral intensity of the diffraction on the no-defectregion fluctuated, and this determines the noise level.
The micro-CSM system with FZP focusing optics was developed to characterize defects on EUV masks,
with a focusing size of approximately 230 nm in diameter. The micro-CSM is a lensless system; thediffraction signals from defects are recorded directly with a CCD camera. The phase defect size detection
limits were approximately 25 nm in width and 1.4 nm in depth. An actual phase defect with a width of 90 nm
and a height of 2.2 nm was also detected. The diffraction image was related to both the defect volume and thedefect shape. The actinic defect printability can be estimated from the diffraction image without any opticalaberrations. At the oval phase defects, the defect orientation corresponded perfectly with the diffraction
image. The defect position was also inspected via mapping image measurements composed ofstep-and-repeat observations.
ACKNOWLEDGMENTS
This work is re-contracted research from the EUVL Infrastructure Development Center (EIDEC). EIDEC
programs are supported by the New Energy and Industrial Technology Development Organization (NEDO).
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06F503 (2011).
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[5] T. Harada, M. Nakasuji, Y. Nagata, T. Watanabe, and H. Kinoshita, Jpn. J. Appl. Phys. 52, 06GB02, 2013.
[6] J. Miao, D. Sayre, and H. N. Chapman, J. Opt. Soc. Am. A 15, 1662 (1998).
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06FB08 (2012).

44

Low-Temperature Activation of Boron in B10H14-doped
Si wafer by Soft X-ray Irradiation
Akira Heya1, Shota Hirano1, Fumito Kusakabe1, Naoto Matsuo1, Kazuhiro Kanda2
1

University of Hyogo, 2167 Shosha, Himeji, Hyogo 671-2280, Japan
Phone: +81-79-267-4909 E-mail: heya@eng.u-hyogo.ac.jp
2
LASTI, University of Hyogo, 3-1-2 Koto, Kamigori, Hyogo 678-1205, Japan
Abstract
Novel activation method of B dopant in Si wafer using a soft X-ray undulator was investigated. As
the photon energy closed with the energy of the core level of Si 2p, the activation was enhanced.
The sheet resistance of soft X-ray irradiated sample was low in comparison with that of annealed
sample. The low sheet resistance of 60 Ω/sq was obtained using a mixture of B10H14+ cluster andsoft X-ray irradiation even at temperatures as low as 500 C. The B activation occurred by theatomic migration of Si atoms due to the composition of lattice vibration and Coulomb force via theelectron excitation.
Introduction
Low-temperature activation is required for the fabrication of an ultra-shallow junction below 10 nm. A
novel activation method of B dopant using a soft X-ray undulator at low temperature was developed [1]. The
cluster-ion beam is expected to realize the ultra-shallow doping because the energy a dopant atom is low. In thisstudy, we tried to obtain the low-sheet resistance using B10H14+ cluster as a B source. The photon energy
dependence of sheet resistance and the mechanism of soft X-ray activation was discussed in comparison with athermal activation.
Experimental
B ion clusters (B10H14+) were implanted to Si (100) wafer (n-type, 10-25 Ωcm) with an energy of 47.8 keV
and a dose of 6×1015 cm-2 (0 tilt).
The irradiation of soft X-ray was carried out at BL07A of NewSUBARU (Fig. 1). The storage-ring energy
and storage-ring current were 1 GeV and 300mA, respectively. The photon energy was changed from 50 to 250
eV, with the dose quantity of 50 mA h. The irradiation time was 600 s. The pressure during irradiation was
6×10-5 Pa. A part of sample was cooled using Cu holder with refrigerant of -20C. The surface temperature of Si
wafer was measured via a ZnSe window by a pyrometer. The emissivity was 0.6. For the comparison, theannealing in N2 atmosphere was carried out in the 100 - 800C range for 900 s.
The sheet resistance was measured by a four-point probe method at room temperature. In this study,
correction factor of the four-point probe method was not used. The activation ratio is given by Irvin curve andimplantation dose.
Results and discussion
The temperature and the sheet resistance of Si wafer as a function of photon energy are shown in Figs. 2
and 3, respectively. The temperature at the photon energy of 100 eV, which corresponds to the energy level of Si
2p core-electron (99.8 eV), shows the highest value. The Si 2p core-electrons are excited by soft X-ray
irradiation and they relax resulting in a temperature increase. The activation was enhanced around 100 eV.
According to Fermi golden role, the electron excitation is enhanced by closing with the energy of core level. It isfound that the sheet resistance after soft X-ray irradiation strongly depended on the irradiated photon energy. In
the case of cooled sample, the sheet resistance was decreased from 880 to 430 Ω/sq after soft X-ray irradiation. It
is found that the sheet resistance depend on not only thermal effect but also soft X-ray effect. It is considered thatthe dopant activation was enhanced by the electron excitation in core energy level during the soft X-ray
irradiation.
The relationship between the sheet resistance and the treatment temperature is shown in Fig. 4. The sheet
resistance of soft X-ray irradiated Si was lower than that of annealed Si. The tendency was as same as B+-doped
Si wafer [2]. The sheet resistance for B10H14+ implant was low compared with B+ implant at treatment
temperature around 500C. The sheet resistance was reduced from 410 to 60 Ω/sq by using B10H14+ instead of B+.

45

Under this condition, the activation ratio is estimated to 36 %. Although the dose of B10H14+ implantation is
only three times larger than B+ implantation, the sheet resistance was decreased to one sixth. It isconsidered that the amorphization during implantation is enhanced by using B10H14+. Therefore, the repair of ion
implant damage within Si is easy to occur in comparison with B+ implantation.
Conclusions
1) The activation of B dopant depends on photon energy because the B activation is enhanced by electron
excitation and atomic movement.
2) The low sheet resistance of 60 Ω/sq was obtained using B10H14+ cluster and soft X-ray irradiation even at
temperatures as low as 500 C. The soft X-ray activation occurs by not only the thermal effect but also theexcitation of the core electrons followed by the atomic migration.
Acknowledgments
The authors are grateful to Dr. M. Tanjo of Nissin Ion Equipment Co. Ltd. for supply of the B10H14+-doped
Si wafer and comments.
References[1] T. Fukuoka, A. Heya, N. Matsuo, K. Kanda and T. Noguchi: Extended Abstracts of the 2011 International
Conference on Solid State Devices and Materials, pp.40-41 (2011).
[2] A. Heya, N. Matsuo, K. Kanda and T. Noguchi: 2014 International Workshop on Junction Technology (IWJT)
Extended Abstracts, pp.23-26 (2014).

Fig. 1. A schematic diagram of soft X-ray activation
apparatus and setup for measuring the sample
temperature using a pyrometer. Soft X-ray is generated
from a 2.28m-undulator at BL07A.
Fig. 3. Sheet resistance of B10H14+-doped Si wafer after
soft X-ray irradiation as a function of photon energy ofsoft X-ray.

Fig. 2. Maximum sample temperature of B10H14+-doped
Si wafer during irradiation as a function of photon
energy of soft X-ray. A part of sample was cooled byrefrigerant.

Fig. 4. Sheet resistance as a function of treatment
temperature for B10H14+-doped Si wafer. Open symbols
show the annealed sample.

46

Two Modified Layers in the surface ofSilica-Based Films by Undurator Radiation
K. Moriwaki, H.Umeji, Graduate School of Eng., Kobe Univ.,
K.Kanda, and S.Matsui, LASTI/Univ. Hyogo

Abstract
Undurator radiation (UR) by the NewSUBARU is used to modify the surface in silica-based
films for optical waveguide devices. It is found that the modifications are different between
surface thin layers and inner layers for the samples irradiated by UR with the 1st peak energy
ranging from 20 to 110eV. The thin layers with less than 5 nm thickness from the surface show
strong reduction for both thermally-grown SiO2 and synthetic silica glass by analyzing XPS (X-ray
Photoelectron Spectroscopy) results. Amounts of the surface reduction show a clear dependence
on the peak-energy of UR. Refractive index measurements before and after etching the surface
reduction layers reveal that the higher refractive-index changes on the surface are mainly due tothe surface reduction layer, and relatively lower refractive-index is also induced in the inner layer
under the reduction layer.
Introduction
We use synchrotron radiation (SR) and undurator radiation (UR) for radiation-induced refractive-index
changes in silica-based glass for optical devices1,2). Our main objectives are to induce large refractive-index
changes more effectively using SR or UR without a spectrometer, and to investigate their origins depending
on wavelengths of SR or UR spectra. Especially, UR would be a very useful tool for the materials
modifications, because it can select a useful wavelength and has very high intensity. For those reasons wemainly use UR for the present modification experiments. In this report, we investigate the modification
effects on the surface of silica-based glasses irradiated with UR.

4 112 110 108 106 104 102 100 98 96 94

Intensity (arb.unit)
m
(n
h

ed
ch

Et

7
9.5

de

2
4.5

)

Si‐O Si‐Si

pt

UR
20eV

Si-Si XPS Peak intensity (arb.unit)

Experiments and Results
Experimental conditions are almost the same as in the previous experiments1,2). UR (from the
NewSUBARU BL-7A) was mainly used to investigate irradiation-wavelength effects. The electron energy of
the SR was 1GeV. The UR with the first peak energy ranging from 20 to 110eV was used. The samples were
thermally grown SiO2 films (0.5 m thickness) on Si substrates or pure synthetic silica-glass. XPS
measurements including in-situ etching were used to investigate the surface modification effects and depth
profiles for the modification. Refractive index was measured by spectroscopic ellipsometry before and afteretching the surface layer. Optical absorption spectroscopy was also used for analyzing irradiation defects andthereby the cause of the refractive index changes.
It is shown in Fig.1 that Si-Si bonds are generated on the surface of thermally-grown SiO2 films, after
irradiating UR with peak energy of 20eV by measuring Si2p peaks in XPS. Figure 1 also shows depth
profiles of the S-Si 2p peaks by in-situ etching. From the depth profiles, the Si-Si bond peaks disappear
gradually within 5nm thickness, which shows a presence of a very thin reduction layer on the surface.
Figure 2 shows that the amounts of the Si-Si bonds are increased by decreasing the UR peak energy from 90
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1

20

30

40

50

60

70

80

90 100 110

UR Peak Energy (eV)Binding energy (eV)FIG.1. Si 2p XPS spectra with in-situ etching up
to a depth of 10nm in thermally-grown SiO2
films after irradiating UR with a peak energy of
20 eV. The UR dose is 500 mAh.

FIG.2. Si-Si bond peak-intensity in the XPS
spectra in thermally-grown SiO2 films as afunction of the irradiating UR peak energy. The
UR dose is 500mAh.

47

1.52

After etching
Before etching

1.51

Refractive index

Si-Si XPS Peak intensity (arb.unit)

to 20eV. After irradiating UR with peak energy over 100eV, Si-Si bonds were not found on the samples.
By measuring refractive indices after UR irradiation with peak energies from 20 to 110eV, highrefractive-index changes (10-2-10-1) were found. Figure 3 indicates that there is a correlation between therefractive index and the amounts of Si-Si bonds appeared in Fig.2. The refractive-index changes wereincreased by decreasing the UR peak energy. Figure 4 shows that the higher refractive-index changes are
decreased abruptly by removing the surface reduction layer by 20nm from the surface, while the lower
refractive-indices (10-2) remain after the surface etching. The refractive-index changes after the etching were
nearly independent of the irradiation peak energy (in Fig.4).

Data
Fitting
1.46

1.47

1.48

1.49

1.50

1.51

1.50
1.49
1.48
1.47
1.46

Reference

1.45

20 30 40 50 60 70 80 90 100 110

1.52

UR Peak energy (eV)

Refractive index

FIG.4. Measured refractive index for thermallygrown SiO2 films irradiated by UR, and also
after etching by 20nm from the surface. The UR
dose was 500mAh.The reference indicates thatof an initial sample.

FIG.3. A correlation between the Si-Si bonds
peak-intensity and refractive-indices for the
samples used in Fig.2 irradiated by UR with apeak energy from 20 to 110eV.

Absorbance

Optical absorption spectroscopy revealed that many defects were in the UR-irradiated samples as shown in
Fig.5. The surface defects might be caused by breaking of Si-O bonds and following desorption of O atoms.
It was also found by the surface etching experiments that the most of the defects in Fig.5 were in the layer
shallower than at least 20nm from the surface, while some defects remained after the etching. It is suggested
that the remained defects after the etching are a major cause of the refractive-index changes in inner layer
under the surface reduction layer.
From the results by the ellipsometry and the opticalabsorption measurements, it is found that the
UR
0.30
30eV
modification layers are separated into two parts of
0.25
40eV
the surface (with less than 5nm thickness) and the inner
0.20
layer in the samples by UR irradiation (Fig.6).
60eV
0.15

50eV
High n layer

0.10

SiO2

0.05

Low n layer

Reference

0.00
3.5

4.0

4.5

5.0

5.5

6.0

Si substrate

6.5

Photon energy (eV)FIG.5. Optical absorbance for silica glass
samples irradiated by UR with a peak energy
from 30 to 60 eV. The UR dose was 500mAh.

FIG.6. Two modification-layers model irradiatedby UR with a peak energy from 20 to 110eV.
Each layers show higher (10-2-10-1) and lower(10-2) refractive-index changes.

Conclusions
Refractive-index changes obtained by UR irradiation in silica-based films were found to be separated into
two parts which were a higher refractive-index layer by surface reduction with less than 5nm thickness andrelatively lower refractive-index layer by probably some irradiation defects. From our results, the higher
refractive-index changes on the surface depended strongly on the irradiated UR peak energy. UR is expected
to be a useful irradiation source for modifying materials effectively and controllably.
References[1] K.Moriwaki et al., LASTI Annual Report vol.14 (2012).
[2] K.Moriwaki et al., LASTI Annual Report vol.13 (2011).

48

Microprocessing using Soft X-ray from Laser Produced
Xe Plasma
S. Amano
LASTI/UH
Abstract
Microprocessing of poly(tetrafluoroethylene) (Teflon) and poly(methyl methacrylate) (PMMA)
samples was carried out using soft X-ray from a laser produced Xe plasma source we developed.
In the Teflon sample, a contact angle of a modified surface with a water drop increased from 90°
to 110° to by an irradiation without a mirror and a mask, while the angle decreased to 50° by anirradiation with them. Scanning electron microscopy showed numerous microprotuberances and amasked pattern having micro-concavities on the each sample surface. These suggested that thechanges of the contact angle were ascribable to the microstructures of the Teflon surface. We
succeeded in controlling the wettability of the Teflon surface from hydrophobic to hydrophilic by
microprocessing using the laser plasma X-ray. In the PMMA sample, its etching rate wasinvestigated using an irradiation with a large number of pulses (192000 pulses) and a low power
density of 8×104 W/cm2. The etching rate was calculated to be 5 pm/pulse and this was concluded
to be a result by only photo-etching without thermal effect. We demonstrated pure photo-etching
depth of ~1 µm.
Laser plasma X-ray is generated from high temperature and high density plasma produced by high intensity
laser. This is useful for industrial applications as a compact light source with high intensity comparing tosynchrotron radiation sources. In industrial uses of the X-ray, high average power is also required and wedeveloped a laser produced Xe plasma source to satisfy this demand and started to study for microprocessing
using this source. The developed soft X-ray source with a wavelength rage of 5~17 nm consists of a rotating
drum system supplying cryogenic Xe target and a high repetition rate pulse Nd:YAG slab laser. Fig. 1
shows a soft X-ray irradiation system to microprocess samples.
	
  	
  	
  	
 

Fig.1 Experimental setup of the soft X-ray irradiation system.

The drum target system we developed has a cylindrical drum filled with liquid nitrogen, which cools its
copper surface to the temperature of liquid nitrogen. Xe gas is directed onto the surface and condenses toform a solid Xe layer. The solid Xe-layer coated drum rotates about the vertical z-axis and moves verticallyalong the z-axis, resulting in a spiral motion, supplying a fresh target surface continuously for every laser
shot. Emission spectrum from the Xe plasma has a very broad bandwidth (5~17 nm), so it was expected to bea high efficient soft X-ray source. When a Nd:YAG laser irradiated the target with a laser energy of 800 mJ
and 300 mJ, a conversion efficiency in bandwidth of 5~17 nm was found to be 30 % and 21 %, respectively.
The irradiation laser with a high average power (100 W) and a high repetition rate pulse (320 Hz) was also
developed originally. It is a PCM-MOPA (Phase Conjugated Mirror – Master Oscillator and Power
Amplifier) Nd:YAG slab system. High average output soft X-ray of 20 W at the wavelength range of 5~17nm was achieved by using both the target system and the laser.

49

In order to increase an intensity of this soft X-ray, we used a focusing mirror. The mirror has a shape of acylinder with three pieces of cylindrical Ru coated mirror. The piece with an angle of 101 degrees had acurvature radius of 26 mm. The X-ray energy intensity at a focal plane was measured to be 0.8 mJ/cm2 using
an X-ray diode. A beam pattern had a 1.8 mmf (FWHM) peak in a circle with a diameter of 24 mm[1].
Teflon PTEF: poly(tetrafluoroethylene) and PMMA: poly(methyl methacrylate) samples were irradiated tothe soft-focused X-ray and their microprocessing was investigated[2].
In a Teflon sample, a contact angle of a modified surface with a water drop increased from 90° to 110° to byan irradiation without the mirror and a mask, while the angle decreased to 50° by an irradiation with themirror and a Ni mesh (2000/inch) mask. Scanning electron microscopy showed numerous
microprotuberances and a masked pattern having micro-concavities on the each sample surface (Fig.2).
These suggested that the changes of the contact angle were ascribable to the microstructures of Teflon
surface. We succeeded in controlling the wettability of the Teflon surface from hydrophobic to hydrophilicby microprocessing using the laser plasma X-ray.
PMMA is used for a resist in LIGA process and its etching rate for the laser plasma soft X-ray wasinvestigated. After a large number of pulses (192000 pulses) with a low power density of 8×104 W/cm2
irradiated a PMMA sample through the Ni mesh, an etched depth was measured using a laser microscope.
The etching rate was calculated to be 5 pm/pulse and this was concluded to be only photo-etching without
thermal effect. We demonstrated pure photo-etching of the PMMA surface with the depth of ~1µm using thelaser plasma X-ray.

Fig.2 SEM pictures of the Teflon surface (left) and photographs of a water drop on it (right). The sample was irradiatedwithout the mirror and the mask (upper), irradiated with them (lower).

References[1] S.Amano et al., IEEJ Trans, 130, pp.1768 (2010).
[1] S.Amano et al., IEEJ Trans, 134, pp.489 (2014).

50

Broadband spectroscopy of magnetic response in a
nano-scale magnetic wire
A. Yamaguchi1, K. Motoi2, H. Miyajima2 and Y. Utsumi1
Laboratory of Advanced Science and Technology for Inductry, University of Hyogo, Koto Kamigori, Ako,
Hyogo 678-1205
2
Department of Physics, Keio University, Hiyoshi, Yokohama, Kanagawa 223-8522

1

Abstract
We measure the broadband spectra of magnetic response in a single layered ferromagnetic
nano-scale wire in order to the size effect on ferromagnetic resonance. The resonance frequency
difference between 300-nm- and 5-µm wide wires was varied by about 5 GHz. We detected themagnetization precession induced by the thermal direct current by using Wheatstone bridge circuit.
Our investigation renders that the shape anisotropy is of great importance to control the resonancefrequency and to provide thermal stability of the microwave devices
Introduction
The investigation on magnetization dynamics at gigahertz frequency in artificial nano-magnets is a great
important subject for many applications of magnetic materials, examples of which include magnetoresistive
random access memory, microwave detector and oscillator. [1] Up to now, these studies, by using not only
electrical detection but also magnetic imaging techniques such as time-revolved Kerr microscopy and micro
focus Brilloin light scattering, have been reported. In particular, the electrical detection, which allows theindirect detection of the resistance oscillation as a function of the input microwave signal frequency for thedevices, provides high sensitive detection for magnetization dynamics on these devices below the several
hundred nanometer scale. When we use a nano-scale magnet as a microwave device in a radio-frequency region,
the magnetization fluctuation noise plays an important role. [2, 3] Several kinds of noise may restrict thesignal-to-noise ratio, since the high-frequency thermal fluctuation of magnetization increases with the inverse of
the device volume and it substantially limits both in the nano-scale device size and in the increase of theoperating frequency. The theoretical and experimental understanding of the fundamental limitation is of practicalimportance.
The investigation on the non-equilibrium behavior of these systems is of great interest from a viewpoint ofcomplicated magnetic processes; for example, the thermal nucleation of magnetic domain and the magnetization
damping accompanied with the spin wave excitation. These problems have been investigated by the approachthrough simplifications that have proved successful in the theory of the stochastic processes. [3, 4]
Experiments and Results
We measure the broadband spectra of magnetic response in a single layered ferromagnetic nano-scale wire inorder to investigate the size effect on the ferromagnetic resonance. We found that the resonance frequency
difference between 300-nm- and 5-µm-wide wires was varied by about 5 GHz due to the shape anisotropy.
Furthermore, we experimentally detected the magnetization precession induced by the thermal fluctuation via therectification of a radio-frequency (rf) current by incorporating an additional direct current (dc) by using
Wheatstone bridge circuit. Our investigation renders that the shape anisotropy is of great importance to control
the resonance frequency and to provide thermal stability of the microwave devices.
We investigate electrical broadband spectroscopy for magnetic response including the noise in a single
layered Ni 81 Fe 19 (Permalloy: Py) wire. The soft-ferromagnetic Py nano-scale wires are fabricated onto apolished MgO (100) substrate by means of high-resolution electron beam lithography with a standard lift-off
technique. The thickness t, width W and length L of the Py wires prepared in this study are summarized in Table I.
The coordinate systems are defined as shown in Fig. 1(a). Here, we assume that the wire system is asingle-domain magnetic particle. The longitudinal axis and short axis of the wire are parallel to the x- and y-axes
andare the hard and easy axis anisotropy constants in the out-of-planein the plane, respectively. The
and in-plane directions, respectively. The wires are placed between the center strip-line of the coplanar
waveguide (CPW) comprising Au conductive strip with thickness of 100 nm. The ground-signal-ground (GSG)
typed microwave probe is connected to the system. The real part of S11 is measured by a vector network
analyzer (VNA), and dc voltage difference induced by the rf current flowing through the wire is detected by thebias tee circuit which can separate the dc and rf components of the current. The optical micrograph image isshown in Fig. 1(b). In addition, the broadband spectroscopy under the application of the dc current is measured
by Wheatstone bridge circuit as shown in Fig. 1(b). An external magnetic field H ext is applied in the substrate51

plane along the angle φ H from the longitudinal axis of the Py wire. All experimental measurements are
performed at room temperature.

Sample

#1
#2
#3
#4
#5
1000

Table 1. Summary of sample structure
Length (µm)
Width (nm)

20
20
20
100

300
650
2200
5000

Thickness (nm)

50
50
50
30
100
3 0

Fig. 1(a) Schematic of system coordinate and notation definition. m is the unit vector of the magnetic
moment. (b) Schematic diagram of the broadband magnetic response measurement circuit using Wheatstonebridge.
to the longitudinal axis of the wire #2 in plane. Figures
The magnetic field was applied at angle φ H =2(a) and 2(b) show the magnetic field dependence of real part of S11 and rectifying spectra in the wire #2,
respectively. For clarity, the measured spectra are vertically shifted. As shown in the S11 spectra, we can see astationary peak positions at 9 GHz and a shift towards the higher frequency with increasing the magnetic field.
The former stationary peak corresponds to the natural FMR mode in the absence of the magnetic field in thiscase, because we calibrate the S11 spectrum of the wire in the magnetic field of 0 G. The later shift represents theferromagnetic resonance.

52

Fig. 2(a) Real Part of S11 as a function of frequency in various magnetic fields. (b) Field dependence ofrectifying spectra.
The resonance frequencies determined by the measurements of S11 and rectifying effect are the almost sameas shown in Figs. 2(a) and 2(b). The response signal from the intrinsic ferromagnetic resonance in the S11 isoverlapped the extrinsic signal which gives the stationary peak. On the other hand, the rectifying effect canreveal the only intrinsic response signal as shown in Fig. 2(b). The results suggest that the rectifying effect ismore suitable to detect the spin dynamics in the nano-scale magnets.
The magnetic field dependence of the resonance frequency of each wire is shown in Fig. 3(a). The resonancefrequency increases with increasing magnetic field, as expected by the following extended Kittel equation givenby [5, 6],(1)

where γ is the gyromagnetic ratio andis the magnetic permeability. Generally assuming that the present
system is treated as the single-domain magnetic particle, the easy and hard anisotropic fields are given byand. When a static magnetic field is applied at the angle

from the longitudinal

axis of the wire in the plane, the resonance frequency is modified as the following: [5, 6]
,

(2)

where
(3)
and
.
(4)
Here, M S is the saturation magnetization, N α (α = x, y, z) the demagnetizing factors in the Cartesian coordinate, andthe angle between the longitudinal axis of the wire and the effective magnetic momentsystemvector (see Fig. 1(a)). The Equation (2) enables us to determine the demagnetizing factors and to control theresonance frequency by shape of the sample. The demagnetizing factors can be analytically calculated byfor theAharoni’s theory. [7] Using the calculated demagnetizing factors summarized in Table II,
Py and, we plot the fitting curves given by Eq. (2) as a function of magnetic field as shown in Fig.
3(a). The fitting curves are in fairly good agreement with the experimental data. Concurrently with the fitting
results, this fact indicates that the effective magnetization in the wire is not aligned in the parallel direction of theapplied magnetic field because of the strong magnetic shape anisotropy. In the absence of the magnetic field, thecannot be neglected. These results indicate that the shape anisotropy
anisotropy field of the width direction
enables us to control the resonance frequency and to provide the design guideline for the microwave devices.

53

Fig. 3(a) Magnetic field dependence of Ferromagnetic resonance. (b) Resonance frequency as a function of line
width in the magnetic field of 100 G.

We investigate the excitation of magnetization precession due to the application of the dc current. Figure 4(a)shows the dc current dependence of the rectifying spectra peak height in the magnetic field of 100 Oe at. The dc current dependence of the spectra is shown in the inset of Fig. 4(b). As shown in the inset,
the dc current excited the resonance peak. The full width at half maximum (FWHM) is plotted as a function ofdc current as shown in Fig. 4(b). We found that the spectrum amplitude (peak height at the FMR state) is
proportional to the dc current and the FWHM increases with the increment of the dc current. This dc current
dependence of the FWHM correlates well with the parabolic fitting curve as shown in Fig. 4(b). These results
indicate that the Joule heating due to the dc current [8, 9] induces the thermal excitation of magnetization
precession and produces the rectifying spectra due to the excitation of the higher dipole-spin wave mode.

Fig. 4 (a) Peak strength and (b) Full width at half maximum (FWHM) of rectifying spectra excited by dc + rf currents as afunction of dc current. The applied field of 100 G was fixed at φH=45°in the plane. The inset of Fig. 4(a) shows the dc current
dependence of the rectifying spectra.

54

Conclusion
Thus, the present experimental results reveal that our electrical Wheatstone bridge measurement technique is
useful for the high sensitive detection of the small magnetization precession in a nano-scale magnetic wire under
the application of the dc current. This measurement technique and investigation open the door to the fundamental
spin dynamics of nano-scale magnets with very easy operation and design guideline of the rf-devices using thenano-scale magnets.
References[1] B. Hillebrands and K. E. Ounadjela, Spin Dynamics in Confined Magnetic Structures (Springer, Berlin,2003), Vols. 1 - 3.
[2] W. F. Brown, Jr. Phys. Rev. 130, 1677 (1963).
[3] N. Smith and P. Arnett, Appl. Phys. Lett. 78, 1448 (2001).
[4] V. Safonov and N. Bertram, Phys. Rev. B 65, 172417 (2002).
[5] A. Yamaguchi, K. Motoi, A. Hirohata, H. Miyajima, Y. Miyashita, and Y. Sanada, Phys. Rev. B 78, 104401(2008).
[6] A. Yamaguchi, K. Motoi, M. Miyajima and Y. Utsumi, J. Magn. Magn. Matter. 364, 34 (2014).
[7] A. Aharoni, Demagnetizing factors for rectangular ferromagnetic prisms, J. Appl. Phys. 83, 3432 (1998).
[8] A. Yamaguchi, S. Nasu, H. Tanigawa, T. Ono, K. Miyake, K. Mibu and T. Shinjo, Effect of Joule heating incurrent-driven domain wall motion. Applied Physics Letters 86, 012511-1-3 (2005); A. Yamaguchi, A.
Hirohata, T. Ono and H. Miyajima, Temperature estimation in a ferromagnetic Fe-Ni nanowire involving acurrent-driven domain wall motion, Journal of Physics Condensed Matter 24, 024201-1-9 (2012).
[9] H. Fangohr, D. S. Chernyshenko, M. Franchin, T. Fischbacher and G. Meier, Joule heating in nanowires,
Physical Review B 84, 054437-1-12 (2011).

55

Dihedral Corner Reflector Array for floating image
manufactured by Synchrotron radiationaT.Yamanea, S.Maekawaa,b, I.Okadaa ,Y.Utsumia, A.Yamaguchia
Laboratory of Advanced Science and Technology for Industry, University of Hyogo,
3-1-2 Koto, Kamigori, Hyogo 678-1205, Japanb
Parity Innovations, 3-5 Hikaridai, Seika, Soraku, Kyoto, Japan
E-mail: t.yamane@lasti.u-hyogo.ac.jp, Phone/Fax: +81-791-58-0232

ABSTRACT
We have made a new imaging optics called the Dihedral Corner Reflector Array (DCRA) which is designed tomake the floating image by using synchrotron radiation. DCRA consists of numerous micro-mirrors placed
perpendicular to the surface of substrate. The micro-mirror is implemented by the side of minute square pillar.
The primordial is based on two reflections by a pair of adjacent mutually perpendicular mirrors, i.e., a dihedral
corner reflector. Although the principal of operation is based on reflection by mirrors, the device is alsotransmissive and deflects light. Primordial of DCRA is not so complicated. However, it is too difficult tofabricate the DCRA by usual machining because of high aspect ratio micromachining. Therefore, in thismanuscript, we fabricated the device by deep X-ray lithography due to synchrotron radiation. The characteristicsof the fabricated DCRA are evaluated by the optical transmission and reflection measurements.
1. INTRODUCTION
We have made a new imaging optics called the Dihedral Corner Reflector Array (DCRA) which is designed tomake the floating image by using synchrotron radiation. DCRA as shown in Figure.1 (a), it consists of numerous
pare of perpendicular micro-mirrors i.e., a dihedral corner reflector (DCR) placed perpendicular to the surface of
substrate [1]. DCR on the substrate can converge all the light from a light source onto the reflection-symmetricpoint of the source.(Fig 1(b)) As a result, floating image issue the same light when observing the light source, thearray of numerous dihedral corner reflectors, namely DCRA, can realize the floating image. The DCR is
implemented by the side of minute square pillar. Therefore it is impossible to polish them in pre- or postprocesses. And, the micro-fabrication of high precision is required for the fabrication of DCRA. The fabrication
process using the SR enables us to fabricate the DCRA structure within the limit of accuracy of about 10 nm. [2]Therefore, in this manuscript, we fabricated the device by deep X-ray lithography due to synchrotron radiation.
The characteristics of the fabricated DCRA are evaluated by the DCRA transmittance.
2. EXPERIMENTIn this manuscript, we fabricated the pillar patterned DCRA made of Poly-methyl methacrylate (PMMA) byusing synchrotron radiation. The pillar pattern DCRA utilizing the light from the light source passes through theinterior of the PMMA, and totally reflected by the difference in refractive index between air. Figure 2 shows
schematic of dimensions of our DCRA device. And Table 1 shows dimension of DCRA. Here, we postulate thatthe transmittance of DCRA is the percentage of incident light through the reflection-symmetric point. The
transmittance is given by
Transmittance = I × 𝑅 2 × 𝑇,

(1)

where I is the ideal transmittance, R is reflectance of micro-mirror, and T is the losses, which is defined as
the attenuation of intensity of the incident light after passing through the DCRA.
Reflectance of micro-mirrors is the most important factor in imaging by DCRA. In this study, we evaluate thecharacteristics of the fabricated DCRA by measuring the dimension, perpendicularity of the reflector,
fractional and reflection. The reflection ratio are measured by measurement system as shown in Fig.3. In order toevaluate the angle ϕ dependence of the single reflection of the DCRA at 700 nm in wavelength, we fixed the
DCRA at the angle θ = 25° . As shown in Fig. 4, two reflection peaks are observed. The peak with the larger
amplitude (at about ϕ = 0° ) corresponds to the refractive incident light. The other is the single reflection of
the light by the DCRA. If the ideal DCRA was fabricated, we would obtain the single reflection peak at
ϕ = 50° in this experimental setup. And reflection of our devise is 15%. However, we found the single
reflection was extended in the ϕ range between 40° and 70° because the reflected light was spread by the
0T

0T

0T

0T

0T

0T

56

0T

distortion due to the taper. The actual fraction transmitted is estimated to be 5.4% by substituting the measured
value into Equation (1). Figures 5(a) and 5(b) show a typical optical microscope image of top view and crosssection of the micro-pillars in the fabricated DCRA, respectively. The measured average dimensions of the
DCRA are summarized in Table 2. The measured dimensions except the perpendicularity are almost in good
agreement with the design dimensions. The perpendicularity of the fabricated pillars have about 6 minute taper.
3. CONCLUSION
We proposed novel imaging optics with micro-dihedral corner reflector arrays (DCRA) which can form areflection-symmetric image as a real image in the air. Although the performance of the DCRA was not good, thefabricated DCRA enables us to observe a floating image. Now, we couldn’t measure the perpendicularity andreflectance of a single pillar. Our main work to improve imaging in the future is to increase transmittance andestablish the quantitative measurement method of resolution and reflection ratio.
REFERENCE[1]. S. Maekawa. “Transmissive Optical Imaging Device with Micromirror Array” The International Society for
Optical Engineering, Vol.6392, 63920E-1, (2006)[2] M.Ishikawa, “A proposal to create the impression of a miniature garden, and the development of a
glasses-free small 3d display”, Pioneer R&D 12(3), pp.47-58, 2003. In Japanese(a)(b)
angle[deg]70reflection[%]

60
50
40
30
20
10
0
0

Figure 1. outlook of DCR

20

40

60

80

Figure.4. the single reflectance of the sidewalls of our device.
(y axis angle means φ)Figure 2. schematic of our DCRA device
Table.1.Dimension of DCRA
position
dimension
Pillar dimension[µm]150Pillar height [µm]300
Pitch[µm]25Aperture ratio[%]64.9
Perpendicularity[deg]90
Roughness[nm]10

Figure.5. optical microscope image of pillars
Table.2. dimension of manufactured DCRA
Pillar dimension [μm]Figure 3. the reflectance of side walls of thetransmitted light measuring instrument57

150.92151.42

Pitch [μm]25.87

Pillar height [μm]326.78Perpendicularity[minute]

5.8

Evaluation of localized friction for antisticking layer byatomic force microscopy
Makoto Okada1, Yuichi Haruyama1, and Shinji Matsui1
1
Laboratory of Advanced Science and Technology for Industry, Univ. of Hyogo,
Ako, Hyogo, 678-1205, Japan
E-mail address: m.okada@lasti.u-hyogo.ac.jp
Nanoimprint lithography (NIL)1) is able to produce the nanostructures with highprecision. The nanoimprint mold is usually coated with an antisticking layer (ASL)
because NIL is a contact process and it is necessary to prevent the adhesion of resin. It is
known that the ASL deteriorates with repeated nanoimprinting. Hence, we have to study
the cause of ASL deterioration induced by repeated nanoimprinting. However, this is adifficult issue because NIL includes several factors such as localized movement,chemical reaction, and UV irradiation, etc. and these factors influence the ASL
deterioration. One of the factors that ASL deteriorates during nanoimprinting is alocalized friction between the ASL and nanoimprint resin, as shown in Fig. 1. Atomic
force microscope (AFM) is a useful tool to observe the sub-nm- and nm-ordermorphology. In AFM observation, there are three types of mode, contact mode, dynamic
force mode (also called tapping mode), and non-contact mode. We focused on thecontact mode-AFM because a cantilever is in direct contact with a sample and isscanning on the sample during observation. This means that the localized friction
between the cantilever tip and sample occurs during contact mode-AFM observation.
Furthermore, we can measure the adhesion and frictional forces on the sample by AFM.
In previous work, we reported the abrasion test of ASL formed using (3 3 3trifluoropropyl)trimethoxysilane (FAS-3) by AFM2). However, FAS-3 is rarely used as
the nanoimprint ASL due to a worse release property and the number of rubbing was
only about 600 times in the measurement. In this study, we used ASL formed using(tridecafluoro-1,1,2,2-tetrahydrooctyl)trimethoxysilane (FAS-13) which has a good
release property, and carried out abrasion test by AFM with rubbing over 5000 times.
We used a sphere tip (NanoWorld AG) instead of a standard cantilever which has a
sharp tip to avoid scratching. The sphere diameter was 0.8 m. Figure 2 shows theillustration diagram of abrasion test by AFM using the sphere tip. The ASL was coatedon SiO2/Si substrate with mesa structure. The mesa structure was 1.6 m  1.6 m. The
continuous contact-mode AFM was carried out on the mesa structure, and the adhesion
and frictional forces were intermittently measured on the rubbed area. The subbed area
was 1 m  1 m. The contact force and scanning speed were 200 nm and 10 Hz,
respectively. We defined a one scan as a one rubbing time. Figures 3(a) and 3(b) show
the adhesion and frictional forces on the rubbed ASL as a function of number of rubbing
times. The adhesion force before abrasion test was the highest in the measurement. We
assumed that the ASL was contaminated before starting the test. Contrary to our
expectations, the adhesion and frictional forces increased and decreased during the test.
After abrasion test, we observed the ASL by dynamic force mode-AFM, as shown in Fig.
4. The ASL surface state was affected by rubbing of sphere tip. We assumed from theseresults that the contamination attached to the top of sphere tip and removed during
rubbing and affected the adhesion and frictional force measurements.

58

Acknowledge
This work was partially supported by Kawanishi Memorial ShinMaywa Education
Foundation.
References
1) S. Y. Chou, et al.: Appl. Phys. Lett., 67 (1995) 3114.
2) M. Okada, et al.: Abstr., MNC2013, 8P-11-79 .

Figure 1 Illustration diagram ofdemolding process.

Figure 2 Illustration diagram ofabrasion test by AFM.

(a)

(b)
Figure 3 (a) Adhesion and (b) frictional forces on ASL during abrasion test by AFM.

(a)(b)
Figure 4 (a) Topographic and (b) phase images of FAS-13 after abrasion test by AFM.

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