Takahiro Kozawa1, Julius Joseph Santillan2, and Toshiro Itani2

1The Institute of Scientific and Industrial Research, Osaka University2Evolving nano process Infrastructure Development Center, Inc. (EIDEC)

Analysis of metal resist used for extreme ultraviolet lithography

1000 coresServer

Material design

Establishment of scientific foundation and technology for resist characterization of EUV lithography

Analysis of resist materials

NanopatterningTime-resolved spectroscopy

Modeling

Ultrashort electron beamElectron linear accelerator

Spatial resolution

Pattern formation in metal resist

Density

Absorption coefficientInelastic mean free path (IMFP)

W-valueBand gapIonization energy

Thermalization distance

Particle size (volume)

Redox potentialHole mobilityElectron mobility

NP

Nanoparticle: ZrO2Ligand: Methacrylic acid (MAA)

Chemical reactions

DensityAbsorption coefficient

W-value

IMFP

Ligands

ConcentrationConcentration

Metal resist

1.E-071.E-061.E-051.E-041.E-031.E-021.E-011.E+001.E+01

0 1 2 3 41.E-071.E-061.E-051.E-041.E-031.E-021.E-011.E+001.E+01

0 1 2 3 4

X-ray reflectivity measurement

101

100

10-1

10-2

10-3

10-4

10-5

10-6

10-7

101

100

10-1

10-2

10-3

10-4

10-5

10-6

10-7

2q (degree)

X-r

ay in

tens

ity (a

rb. u

nit)

2q (degree)

X-r

ay in

tens

ity (a

rb. u

nit)

Fig. X-ray reflectivity curves of metal resist film on Si substrate. The film thickness was approximately 60 nm. q is the incident and detector angle.

(a) Measured (b) Measured + Calculated

To estimate the density of resist film, the fitting procedure was repeated for different n-m ratios of (ZrO2)n(C4H6O2)m.

Density

0.0

0.5

1.0

1.5

2.0

2.5

0.0 0.2 0.4 0.6 0.8 1.0Ratio of ZrO2, n/(n+m)

Den

sity

(g c

m-3

)

Fig. Film density estimated from X-ray reflectivity curve.

0.01550.01560.01570.01580.01590.01600.01610.0162

0.0 0.2 0.4 0.6 0.8 1.0Ratio of ZrO2, n/(n+m)

c2

[fitt

ing

erro

r]

InitialBest fit

(ZrO2)n(C4H6O2)m

EDSEELS

Fig. Relationship between ratio of ZrO2 and fitting error.

Best fit

M. Toriumi, Y. Sato, M. Koshino, K. Suenaga, and T. Itani, Appl. Phys. Express 9, 031601 (2016).

Fig. EDS spectra of a freestanding film of ZrOx.MAA and TiOx.MAA resists.

Fig. EELS spectra of a freestanding filmof ZrOx.MAA and TiOx.MAA resists.

1.93

Absorption coefficient

01234567

0.0 0.2 0.4 0.6 0.8 1.0Ratio of ZrO2, n/(n+m)

Abs

orpt

ion

coef

ficie

nt (m

m-1

)

0

2

4

6

8

10

0 200 400 600 800 1000Photon energy (eV)

Abs

orpt

ion

coef

ficie

nt (m

m-1

)

Fig. Absorption spectra of metal resist calculated with the film density of 1.93 g cm-3 and n:m=1:0.98.

Fig. Relationship between absorption coefficient and ratio of ZrO2, calculated with the film density of 1.93 g cm-3. Note that this result does not mean that the absorption coefficient decrease with the increase of ZrO2.

5.14 mm-1@92.5eV

Density: 1.93 g cm-3

InitialBest fit

EDSEELS

Density and absorption coefficient of components

ZrO2 MAA

0

5

10

15

20

0 200 400 600 800 10000

5

10

15

20

0 200 400 600 800 1000

Bulk density: 5.87 g cm-3 Density: 1.02 g cm-3

Effect of surface

Photon energy (eV)

Abs

orpt

ion

coef

ficie

nt (m

m-1

)

3.9 mm-1@92.5eV

Photon energy (eV)

Abs

orpt

ion

coef

ficie

nt (m

m-1

)

Fig. Absorption spectra of ZrO2 calculated with the density of 5.87 g cm-3.

Fig. Absorption spectra of MAA calculated with the density of 1.02 g cm-3.

11.2 mm-1@92.5eV

Grain size (nm)Fig. Experimental and calculated correlation of density as a function of grain size for the nano-ZrO2. [A. Opalinska et al., Beilstein J. Nanotechnol. 6, 27.35 (2015).]

Band gap and ionization potential for estimation of secondary electron yields

Methods Band gap (eV) Referenece

PES/IPS 5.68 S. Sayan et al., Phys. Status Solidi B 241, 2246 (2004).5.5 E. Bersch et al., Phys. Rev. B 78, 085114 (2008).

EELS 5.65 R. Puthenkovilakam et al., Appl. Phys. Lett. 84, 1353 (2004).5.50 S. Miyazaki, J. Vac. Sci. Technol. B 19, 2212 (2001).5.6 H. Nohira et al., J. Non-Cryst. Solids 303, 83 (2002).5.0 N. Ikarashi et al., J. Appl. Phys. 94, 480 (2003).

SE 5.8 M. Balog et al., Thin Solid Films 41, 247 (1977).5.25 L. Zhu et al., Mater. Sci. Semicond. Process. 9, 1025 (2006).

Average 5.5

PES/IPS: Photoemission spectroscopy/inverse photoemission spectroscopyEELS: Electron-energy-loss spectroscopySE: Spectroscopic ellipsometry

Table. Band gap of ZrO2 [H. Jiang et al. Phys. Rev. B 81, 085119 (2010)]Band gap of ZrO2

Photoemission spectrum of MAAUnavailable

Fig. Photodegradation of PMMA measured by UPS. VUV photons (hn=40 eV) were used to degrade PMMA. Irradiation doses are: (a) none (pristine), (b) 6.5x1016 photons/cm2, (c) 1.2x1017photons/cm2, (d) 2.1x1017 photons/cm2, and (e) 2.6x1017 photons/cm2. Intensity of UPS spectra were normalized to ring current at 100 mA. [K. K. Okudaira et al. J. Appl. Phys. 83, 4292 (1998).]

Alternative data for approximation

C. A. Klein, J. Appl. Phys. 39, 2029 (1968).

Average energy required to produce an ion pair (W-value)Relationship between band gap and W-value

5.5 eV

>16.1 eV

ZrO2 MAA

Authors

Jesse

and

Sadauskis

Weiss

and

Bernstein

Leblanc

and

Herman

Meisels

Cooper

and

Mooring

Adler and

BotheSchulze

Gas （1955a） (1956) (1966) (1964) (1968) (1965) (1966) (Wa±s )/eV

CH₄ 27.3 26.8 27.6 26.94 27.5 27.4 27.3±.3

C₂H₂ 25.9 26.3 25.3 (25.7) 25.8±.4

C₂H₄ 26.2 26.4 25.5 25.9 24.6 26.3 25.8±.6

C₂H₆ 24.8 24.6 24.18 25.4 26.0 25.0±.6

C₃H₈ 23.5 23.68 24.6 24.3 24.0±.5

C₄H₁₀ 22.9 23.20 23.8 23.7 23.4±.4

C₅H₁₂ 23.2 22.83 23.5 23.2±.3

C₆H₁₄ 22.63 23.4 23.0±.4

CH₃OH 23.6 25.02 25.5 24.7±.8

C₂H₅OH 24.50 25.1 24.8±.3

C₆H₆ 23.3 20.9 22.1±1.2

H₂ 36.3 36.3 37.0 (36.6) 36.5±.3

N₂ 35.0 34.6 (34.6) (34.6) 34.9 34.8±.2

O₂ 30.9 31.2 31.0 30.1 30.9 30.8±.4

N₂O 32.2 32.9 32.6 32.6±.3

SO₂ 30.4 30.4

H₂O 29.15 29.6 29.9 29.6±.3

CO₂ 32.8 32.6 32.1 33.5 34.5 33.0 32.8 33.0±.7

He 42.3 40.3 (42.3) 41.3±1.0

Ne 35.6 35.3 34.3 (36.5) 35.4±0.9

Ar (26.4) 25.8 25.7 (26.2) (26.4) 23.8 -

Kr 24.2 24.7 (24.2) 24.4±0.3

Xe 22.2 22.0 22.1±0.1

Hg 23.6 23.6

NH₃ 26.5 26.5 26.7 26.6±0.1

Air 33.9 (33.9) (33.8) (34.0) (33.73) (33.9)

Values used as reference values are given in parentheses and are not included in the average of experimental values, W a, given in the last column.

W-value of moleculesTable. W-values for photons and electrons in various gases.

W-value of PHS (film): 22.2 eVT. Kozawa et al., JVST B24, 3055(2006).

ICRU report 31

Size (volume) and concentration

Fig. (a) Low- and (b) high-magnification ADF-STEM images of ZrOx. MAA resist and (c) low-and (d) high-magnification ADF-STEM images of TiOx.MAA resist supported on amorphous carbon. Dotted circles show the diameters of (a, b) 2.0 nm and (c, d) 2.3 nm determined by optical scattering methods. [M. Toriumi, Y. Sato, M. Koshino, K. Suenaga, and T. Itani, Appl. Phys. Express 9, 031601 (2016).]

Diameter: 2 nm

For rough estimation, cubic close-packed structure was assumed.

4.48 nm

3.17 nm

1.17 nm

Volume ratio

NP conc.: 0.0445 nm-3Data from XRD

ZrO2:MAA = 19:81

Radiation chemistry – pulse radiolysis

0.00

0.05

0.10

0.15

0.20

300 500 700 900Wavelength (nm)

Opt

ical

den

sity

(arb

. uni

t)

Fig. Transient absorption spectra, obtained in the pulse radiolysis of metal resist solution in PEGMEA. [Courtesy from Dr. K. Okamoto of Hokkaido University]

Immediately after EB pulse

50 ns

150 ns

300 ns

The details are under investigation.

Ultrashort EB pulse

White light for spectroscopy

Time-resolved spectroscopy

Metal resist solution in PEGMEA

Related information – pulse radiolysis in water

e-hyd + CH2C(CH3)COOH →e-hyd + CH2C(CH3)COO- →

Reduction2.8 x 1010 M-1s-13.0 x 109, 4.5 x 109 M-1s-1

Rate constantE. Hayon et al.

P.N. Moorthy et al., Radiat. Eff. 10,

129 (1971), E. Hayon et al.

Reference

OH. + CH2C(CH3)COO- →Oxidation

1.6 x 1010 M-1s-1 P. Maruthamuthu, Makromol. Chem., Rapid Commun. 1: 23-5 (1980)

Inelastic mean free path (IMFP)Table. Calculated IMFPs (Å) as a function of electron energy for 27 elements. [S. Tanuma et al., Surf. Interface Anal. 17, 911 (1991)]

Electron energy

(eV)C

a Mg Al Si Ti V Cr

50 5.9 4.0 3.2 4.1 4.5 4.2 4.4

100 6.4 5.4 4.2 5.3 5.1 4.9 4.3

Electron energy

(eV)Fe Ni Cu Y Zr Hb Mo

50 4.3 4.9 5.0 5.0 4.4 6.0 5.1

100 4.4 4.6 5.0 5.5 4.8 6.0 4.5

Electron energy

(eV)Ru Rh Pd Ag Hf Ta W

50 4.9 4.8 4.8 6.2 5.8 4.8 5.0

100 4.2 4.1 4.8 4.9 6.2 4.5 4.1

Electron energy

(eV)Re Os Ir Pt Au Bi

50 5.2 5.5 5.3 5.0 6.7 4.9

100 3.8 4.3 4.3 4.2 4.8 5.5

Table. Inelastic mean free paths (Å) as a function of energy for 14 organic compounds. [S. Tanuma et al., Surf. Interface Anal. 21, 165 (1993)]

Electron energy

(eV)26-n -Paraffin Adenine β-Carotene BPA DNA

Diphenyl-

hexatrieneGuanine

50 7.0 6.4 6.4 7.3 7.3 6.4 6.2

100 7.6 6.6 7.0 7.2 7.3 7.0 6.2

Electron energy

(eV)Kapton

Poly-

acetylene

Poly(butene-

1-sulfone)Poly-ethylene PMMA Poly-styrene

Poly(2-

vinylpyridine)

50 7.0 5.3 7.1 6.9 7.8 6.9 6.9

100 6.8 5.7 7.2 7.2 7.9 7.3 7.3

Patterning – line-and-space patterns32 30 28 26 24 22 20 18 17 16 15 14 13

7

8

9

10

11

12

13

14

15

16

17

Half-pitch (nm)

Expo

sure

dos

e (m

J cm

-2)

Rough estimation of hole-electron pair yield

4.48 nm

0.58 nm

ZrO2

MAA

MAA

Exposure dose: 10 mJ cm-2

1.8

1.4

0.6

1 nm

Closest MAA shell

Assuming that holes and electrons generated in zirconia nanoparticles can oxidize and reduce MAA, the maximum number of decomposable MAA molecules in the closest shell was estimated. The radical chain reaction is not taken into account at this stage of investigation.

Distribution of decomposable MAA in the closest MAA shell

0

2

4

6

8

10

12

-32 -16 0 16 32

Fig. Distribution of maximum value of the number of decomposable MAA in the closest MAA shell.

Distance (nm)

Num

ber o

f MA

A m

olec

ules

0

2

4

6

8

10

12

-32 -16 0 16 32Distance (nm)

Num

ber o

f MA

A m

olec

ules

17 mJ cm-2

12 mJ cm-2

7 mJ cm-2

17 mJ cm-2

12 mJ cm-2

7 mJ cm-2

13 n

m h

alf-

pitc

h

32 n

m h

alf-

pitc

hThe number of destroyed MAA ligands required for insolubilization is considered to be approximately 4 or less.

Distribution of decomposable MAA in the closest MAA shell

0

2

4

6

8

10

12

-32 -16 0 16 32

Fig. Distribution of maximum value of the number of decomposable MAA in the closest MAA shell.

Distance (nm)

Num

ber o

f MA

A m

olec

ules

0

2

4

6

8

10

12

-32 -16 0 16 32Distance (nm)

Num

ber o

f MA

A m

olec

ules

17 mJ cm-2

12 mJ cm-2

7 mJ cm-2

17 mJ cm-2

12 mJ cm-2

7 mJ cm-2

13 n

m h

alf-

pitc

h

32 n

m h

alf-

pitc

h

Corresponding acid yield in typical CAR

Distribution of decomposable MAA in the closest MAA shell

0

2

4

6

8

10

12

-32 -16 0 16 32

Fig. Distribution of maximum value of the number of decomposable MAA in the closest MAA shell.

Distance (nm)

Num

ber o

f MA

A m

olec

ules

0

2

4

6

8

10

12

-32 -16 0 16 32Distance (nm)

Num

ber o

f MA

A m

olec

ules

17 mJ cm-2

12 mJ cm-2

7 mJ cm-2

17 mJ cm-2

12 mJ cm-2

7 mJ cm-2

13 n

m h

alf-

pitc

h

32 n

m h

alf-

pitc

h

Corresponding deprotected unit yield in typical CAR

Summary

○ The distribution of the maximum value of the numberof decomposable MAA molecules in the closest MAAshell was roughly estimated on the basis of radiation-material interaction and radiation chemistry.

○ A simulation code strictly based on the reactionmechanism of metal resist is under construction forobtaining the material design.

This work was partially supported by Ministry of Economy, Trade and Industry (METI) and the New Energy and Industrial Technology Development Organization (NEDO).

Acknowledgement