Dissolution Dynamics of Chemically Amplified Resists for Extreme
Ultraviolet Lithography Studied by Quartz Crystal Microbalance
Masaki Mitsuyasu, Hiroki Yamamoto, Takahiro Kozawa
The Institute of Scientific and Industrial Research, Osaka University,
8-1 Mihogaoka, Ibaraki,Osaka 567-0047, Japan
2
Introduction
Lithography roadmap
Year of production
2015
2016
2017
2018
2019
2020
Line pattern size
24 nm
22 nm
20 nm
18 nm
17 nm
15 nm
Exposure source
ArF (193 nm)
Extreme ultraviolet (13.5 nm)
(ITRS2013)
Ionization potential of resist material
Energy deposition of EUV photons
EUV photon
Energy (eV)
1000
100
g line
Radiation chemistry
i line
KrF ArF
EUV
Ionization potential
Ionization
photon
electron
Thermalization
e-
+
Radical cation
+
of resist materials
+
10
ePhotochemistry
428 328
249 193
13.5
Wavelength (nm)
AG
Excitation
+
Ionization
e-
AG Acid Generator
Thermarization
Resist
H+X-
photoacid
2
Introduction
Exposure tool
Specification of DRAM 1/2 pitch = 16 nm
Sensitivity (5-15 mJ/cm2)
Accumulated
energy profile
Latent acid
image
Resolution
(16 nm)
Acid catalyzed
image
LER (3 σ = 0.9 nm)
Development
Dissolution contrast
Development
LER
Zoom Zoo
in
m
Resist film for EUV
Pattern collapse
or
Film thickness thin (<100 nm)
Effect of Low-Molecular Weight Resist Components
Acid concentration (TPS-tf)
Abs. Coefficient
5
10
20
3.8±0.2 3.8±0.2
Quantum efficiency
1.7
2.5
3.8±0.2
3.1
Quantum efficiency increases with increase in acid
generator concentration
Hirose et al. Jpn, J. Appl. Phys., 46. No. 40, 2007.
Acid generator concentration
Simulation
Resist film
Acid generator
Increase
Si wafer
LER
Sensitivity
With the increase in acid generator
concentration,
the concentration of
The details in the effects of low-molecular
weight
unreacted acid generator increses.
T. Kozawa. Jpn. J. Appl. Phys. 51 resist
(2012) 06FC01
components should be investigated.
3
Measurement of Dissolution Behavior of Resist Film
Optical interference method
development
Pattern collapse
beam splitter
laser
wafer
Film thickness thin
(<100 nm)
detector
resist
Quartz crystal microbalance (QCM) method
Fitting
W. Hinsberg, et al. J. Electrochem. Soc. 133 14481451(1986)
Frequency
Mass change
Au electrode
Frequency change
Quartz crystal
Resist
Mass
Time
Time
We can measure the change of film thickness less than 100nm.
4
Objective
5
To understand the effect of each resist components on dissolution behavior,
the dissolution dynamics of chemically amplified resist after EUV
exposures was investigated.
Acid catalytic reaction doesn’t work
Acid catalytic reaction work
PHS films
Chemically amplified resist films
Acid generator
Quencher
EUV irradiation effect
Acid generator
Quencher
Dissolution behavior of resist films
The dissolution behavior of resist film with less than 100 nm was
investigated from the standpoint of a systematic understanding
of resist dissolution.
Samples
6
Polymer
Solvent
m
n
OH
OH
n
O
O
O
PHS
tBOC-PHS
PGMEA
poly(4-hydroxystyrene)
Mw : 11000
poly(4-hydroxyl-co-t-butoxycarbonyloxy)styrene
Mw : 10400, protecting ratio : 30.7%
(propylene glycol monomethyl
ether acetate)
Photoacid generator (PAG)
S
TPS-tf
O
C4F9 S O
O
TPS-nf
Quencher
Development
N
TOA
(triphenylsulfonium triflate) (triphenylsulfonium nonaflate) (trioctylamine)
TMAH
(tetramethylammonium hydroxide)
2.38% aqueous solution
Experimental
7
EUV
Bake
(90°C, 90 sec)
Spin-coating
c. a. 100 nm
EUV exposure
Post exposure bake
(90 °C, 60 sec)
Development
(EQ-10M, Energetic)
Result / Dependence on PAG concentration
Deprotonation
Unexposed films
100
PHS 0-25 wt% TPS-tf
Thickness (nm)
80
8
+ OH-
+ H2O
+
Solvation
60
40
n
25 wt%
+ mH2O
20
(H2O)m
10
20
O
0
-
Interaction
0
0
1
2
Development time (s)
3
H
O
Polymer chain
Z. Yan. et all Macromolecules. 31, 1998, 7723-7727
Result / Dependence on Exposure Dose
100
100
80
80
Thickness (nm)
Thickness (nm)
+
60
40
0 mJ/cm2
0
20
5 mJ/cm2
10 mJ/cm2
15
0
1
2
Development time (s)
+
PAG
e-
20 wt% TPS-tf
+
60
40
0 mJ/cm2
5 mJ/cm2
10 mJ/cm2
0
20
mJ/cm2
15 mJ/cm2
15
0
PHS
10 wt% TPS-tf
PHS
3
+
Secondary Counter anion
electron
9
0
15
0
1
2
Development time (s)
3
+
Photoproducts
Acid generator is decomposed by EUV
exposure, and counter anion is generated
H2O
+
H
-
OH
10
Result / Quencher and PAG
PHS
80
60
5 wt% TOA
O
+
PHS
0 mJ/cm2
40
20
0
TOA
Trap acid
15 mJ/cm2
0
0.2
100
0.4
0.6
0.8
Development time (s)
PHS
80
Thickness (nm)
O
5 mJ/cm2
10 mJ/cm2
O
F3 C S O
O
+
+ F3C S OH
1
100
+
+
60
0 mJ/cm2
0
5 mJ/cm2
10 mJ/cm2
15 mJ/cm2
15
0
0
1
2
Development time (s)
3
20 wt% TPS-tf
+
80
5 wt%
TOA
40
20
PHS
10 wt% TPS-tf
Thickness (nm)
Thickness (nm)
100
+
60
5wt%
TOA
40
0 mJ/cm2
0
20
5 mJ/cm2
10 mJ/cm2
15 mJ/cm2
15
0
0
1
2
Development time (s)
3
11
Result / Dissolution Rate
Effects of resist components
on dissolution rate
Effects of anions
700
PHS only
600
1 wt% TOA
600
5wt% TOA
10 wt% TPS-tf
400
10 wt% TPS-tf
+ 1 wt% TOA
10 wt% TPS-tf
+ 5 wt% TOA
200
20 wt% TPS-tf
0
0
5
10
15
20
25
Exposure dose (mJ/cm2)
z Some resist components have the inhibition
effect on dissolution.
z The solubility in the developer depends on
the remaining acid generator.
Dissolution rate (nm/s)
Dissolution rate (nm/s)
800
TPS-nf
500
400
300
200
100
TPS-tf
0
0
5
10
Exposure dose (mJ/cm2)
TPS-nf is faster than TPS-tf
15
Result / Dissolution behavior of tBOC films
n
m
Developer
+
OH
O
12
O
O
TPS-tf 10 wt%
tBOC-PHS
Swelling layer
180
160
0.6 mJ/cm2 0.2 mJ/cm2
140
0 mJ/cm2
120
Normalized thickness
Thickness (nm)
bridge
0.8 mJ/cm2
100
80
0.4
60
mJ/cm2
1 mJ/cm2
40
3 mJ/cm2
20
5
mJ/cm2
1
0.8
The change of
dissolution behavior
0.6
0.4
0.2
0
0.1
0
0
10
20
30
40
Development time (s)
50
1
10
2
Exposure dose (mJ/cm )
z The sensitivity is 0.8-1.0 mJ/cm2
Conclusion
zThe dissolution behavior of less than 100 nm resist films was
investigated from the standpoint of a systematic understanding of the
effects of each resist component on dissolution using QCM.
zThe solubility in the developer depends on the remaining PAG
concentration and the structure of acid generators.
zIn tBOC-PHS films, the swelling of resist film containing 10 wt% TPS-tf
was observed before and after EUV exposure.
zThe dissolution speed became slower with increase of TPS-tf
concentration in PHS and tBOC-PHS. It is important for the EUV resist
design to take into account the concentration of undecomposed PAG.
14
Acknowledgment
We are grateful to Tokyo Ohka Kogyo Co. Ltd. for
supplying the polymer.
Thank you for your kind attention