Status and Challenge of Chemically Amplified Resists … · Status and Challenge of Chemically...
Transcript of Status and Challenge of Chemically Amplified Resists … · Status and Challenge of Chemically...
The Institute of Scientific and Industrial Research, Osaka University
Status and Challenge of Chemically Amplified Resists
for Extreme Ultraviolet Lithography
Takahiro Kozawa
1. Status and challenge
2. Anion-bound resist
3. Wavelength diffusion
Lithography roadmap
1
10
100
1000
g line i line KrF ArF EUV EB
Ener
gy
(eV
)
Exposure tool
Sensitivity
Resolution
LWR(LER)
Trade-off Ionization energy (~10eV)
Radiation chemistry
Two keywords in the development of resist materials and processes
1.2
ITRS2010 Update
2001 04 07 10 13 16 19 22
130 90 65 45
Year
Line width (nm)
LWR (nm)
Lithography
Solution
KrF excimer
(248 nm)
ArF excimer
(193 nm)
ArF excimer
Immersion (+DP)
32
2.2 1.6
EUV
(13.5 nm)
22
EB for mask production
1.1
16 11
0.8
Transition of basic science for material design
Photochemistry
Trade-off relationships between resolution, sensitivity, and LER
Chemically amplified resist In
tensi
ty
Typical components: Polymer, Acid generator, Quencher
0.0
0.2
0.4
0.6
0.8
1.0
0 1 2 3 4 5 SEM image of resist Position
Role: Conversion of energy modulation to binary image
Development Formation of latent image
Formation of acid image
Energy deposition
Acid diffusion, deprotection
Decomposition of acid generator
Exposure source
Photon/electron interaction with matter
Dissolution of molecules
Resist image
Thermal energy
Energy modulation of quantum beam
Si
Solubility change through chemical reaction
LER ∝ width of intermediate region ≒ Chemical gradient
1
EUV
Relationship between LER and chemical gradient
Aerial image
Acid Image Latent image
Pattern
Insoluble
Soluble
(Spatially) partially soluble
OH
CH CH2
Mixture of soluble and insoluble molecules
LER formation
OR
CH CH2
Cross section
Top-down view
After development
OH
CH CH2
OR
CH CH2
+ Absolutely stochastic
Can not be controlled
Can be controlled
dxdm
fLER LER
/
Protected unit
Resist screening
IMEC
Selete (later EIDEC)
Sematech
A large number of resist materials have been tested in these sites.
IMEC, Sematech, and Selete (EIDEC) have supported the development of
EUV lithography including resist material and processes.
Sensitivity
Resolution
LWR(LER)
Trade-off Evaluation of resist performance is tricky
because of the trade-off relationship.
Performance (efficiency) of resist
①How many photons can be absorbed?
②How many acids can be generated by a single photon?
Quantum efficiency: 2-3
Absorption coefficient: ~4 /mm
③How many dissolution inhibitor (protecting group) can be removed by a
single acid during the diffusion of unit length?
Effective reaction radius
The number of incident photons is limited because of the sensitivity requirement.
④How smoothly are the polymers dissolved in developer?
Relationship between LER and chemical gradient, fLER
dxdm
fLER LER
/
The chemical gradient is determined by ①-③
Generally, resists are evaluated using resolution, LER, and sensitivity.
We in collaboration with Selete evaluated the effective reaction radius and fLER
to understand the current status of chemically amplified resists.
Small Field Exposure Tool : SFET
Source (Xe DPP)
Exposure
chamber
Mask loader
Wafer loader
Wafer
track
Items Target
Specifications
NA 0.3
Illumination
mode
Annular(0.3/0.7),
x-slit
Field size 0.2 x 0.6 mm
Magnification 1/5
Wavefront error <0.9 nm rms
Flare <7% (MSFR)
Source power 0.5W @IF
Wafer size 300 mm
Selete Standard Resists (SSR1 to SSR7)
Resist screening at Selete (EIDEC)
Selete has reported highest performance resists among
those tested using SFET as
Representative patterning results SSR4
SSR5
24 nmHP, 10 mJ cm-2
(Top down)
26nmHP, 10 mJ cm-2
32nmHP, 10 mJ cm-2
32nmHP, 11 mJ cm-2
32nmHP, 8.5 mJ cm-2 Line width, LER
(0 degree)
Thickness
Changing HP
Chan
gin
g d
ose
24nmHP, 10 mJ cm-2 26nmHP, 10 mJ cm-2 32nmHP, 10 mJ cm-2
32nmHP, 8 mJ cm-2 32nmHP, 12 mJ cm-2
(b) SSR5
22 23 24 25 26 28 30 32 35 40 45 50 60
Exposure dose (mJ cm-2)
-30
30
Dev
iati
on
fro
m h
alf-
pit
ch
(no
min
al l
ine
wid
th)
(nm
)
-10
-20
0
20
10
0
15
LE
R (
nm
)
10
5
LER
Line width
7.9 mJ cm-2
22 23 24 25 26 28 30 32 35 40 45 50 60
Exposure dose (mJ cm-2)
(a) SSR4
22 23 24 25 26 28 30 32 35 40 45 50 60
Exposure dose (mJ cm-2)
9.4 mJ cm-2
22 23 24 25 26 28 30 32 35 40 45 50 60
Exposure dose (mJ cm-2)
Hal
f-p
itch
(n
m)
Hal
f-p
itch
(n
m)
Hal
f-p
itch
(n
m)
Hal
f-p
itch
(nm
)
(b) SSR5
22 23 24 25 26 28 30 32 35 40 45 50 60
Exposure dose (mJ cm-2)
-30
30
Dev
iati
on
fro
m h
alf-
pit
ch
(no
min
al l
ine
wid
th)
(nm
)
-10
-20
0
20
10
0
15
LE
R (
nm
)
10
5
LER
Line width
22 23 24 25 26 28 30 32 35 40 45 50 60
Exposure dose (mJ cm-2)
(a) SSR4
22 23 24 25 26 28 30 32 35 40 45 50 60
Exposure dose (mJ cm-2)
22 23 24 25 26 28 30 32 35 40 45 50 60
Exposure dose (mJ cm-2)
Hal
f-p
itch
(n
m)
Hal
f-p
itch
(n
m)
Hal
f-p
itch
(n
m)
Hal
f-p
itch
(nm
)
Footing
Top loss
Simulation result
0.0
0.2
0.4
0.6
0.8
1.0
0 10 20
Reconstruction of latent images from does-pitch matrices of line width and LER
24 nm
13.5mJ
11.5mJ
27.8, *
26.3, 8.1 26.5, 6.9 24.2, 6.4
22.5, *
Dissolution point
No
rmal
ized
pro
tect
ed u
nit
co
nce
ntr
atio
n
Distance (nm)
32.6, 7.6 28.0, 6.6 23.8, 6.4
19.7, 6.9 Bridge (Line width, LER)
dxdmLER
/
31.0
Chemical gradient
2.4 nm s-1
Dissolution rate
11.5
12.0 12.5 13.0
13.5
(SSR3)
Evaluated parameters
SSR3
SSR4
SSR5
SSR7
0.1
0.08-0.1
0.09
0.06
0.24-0.31
0.17-0.24
0.20
0.14
Matrix
Polymer
Polymer
Polymer
Fullerene
Resist Effective reaction radius (nm) fLER
0
2
4
6
8
10
-16 -8 0 8 16
Distance, x (nm)
Nu
mb
er o
f pro
tect
ed u
nit
, C
Average
-0.4s
+0.4s
s
Dissolution line
dx dx
dC/dx: 0.48 dx: 5.6
dC/dx
Q conc.: 0.02
LER Chemical reaction
0.3 nm
Anion
Proton
Reaction site
0
1
2
3
4
5
0 20 40 60 80 100
Challenges Half-pitch: 16 nm
Optical contrast: 0.8
Eff. reaction radius: 0.1 nm
fLER: 0.2
AG 5wt%
AG 10wt% AG 20wt%
AG 30wt%
Required LER
Target
LE
R (
nm
)
Exposure dose (mJ/cm2)
15 nm features has been reported to be resolved with 30 mJ/cm2 sensitivity.
Absorption coefficient: Sum of absorption cross section of atoms
Quantum efficiency: Acid generator concentration
Effective reaction radius: Activation energies for deprotection and diffusion
Required sensitivity
Summary (1)
We have investigated resist patterns fabricated using an EUV exposure
tool on the basis of reaction mechanisms. To simultaneously meet the
requirements of resolution, LER, and sensitivity, it is essential to
enhance the absorption coefficient of the resist, the quantum efficiency
of acids, and the effective reaction radius of catalytic chain reaction.
Especially, the absorption enhancement is the most important factor.
Actually, it is not difficult to increase the absorption coefficient of the
polymer, because the absorption coefficient against EUV is determined,
not by chemical bonds but the photoabsorption cross sections of atomic
elements. The problem is that the introduction of new atomic elements
to the polymer significantly changes the chemistry induced in the resist
films. It is not an easy task to increase the effective reaction radius of
chemical reactions in the new resist platform to the same level as that
in well-studied organic resist polymers.
Anion bound resist
It has been considered that the acid diffusion is the most serious problem for the improvement of resist performance in terms of trade-off relationship.
Recently, a chemically amplified resist with anion-bound acid generator attracted much attention.
Promising material for 16 nm node and beyond
Reaction mechanism is unknown.
An acid diffusion model in a chemically amplified resist with anion-bound acid generator
New simulation code was developed on the basis of radiation chemistry.
For the development of resist materials, particularly, used in the 16 nm node and beyond, it is important to understand the reaction mechanism of catalytic reactions induced in the anion-bound resists.
Basic idea
Similar sensitivity to that of blend type resists
Protons can diffuse. (Experimentally confirmed)
High resolution
Protons cannot diffuse freely.
24 nm 18.16 mJ cm-2 22 nm 20 nm
SFET
Annular
The efficiency of acid catalytic reaction is not bad.
Initial distribution
Proton Anion
PEB PEB
- + -
+
- + - + -
+
-
+
-
+ - +
-
+
-
+
×
Proton diffusion model
○
Protons diffuse under the electric
field produced by anions.
Anion-bound resist
H. Yamamoto et al., Jpn. J. Appl. Phys. 43 (2004) L848.
Representative patterning results
26 nmHP, 18.16 mJ cm-2
Line width, LER
Changing HP
Chan
gin
g e
xposu
re d
ose
22 nmHP 18.16 mJ cm-2
Chemically amplified resist with anion-bound AG
32 nmHP 18.16 mJ cm-2
45 nmHP 18.16 mJ cm-2
28 nmHP 16.50 mJ cm-2
28 nmHP 17.33 mJ cm-2
28 nmHP 18.16 mJ cm-2
Conventional dose-pitch analysis Relationship between LER and chemical gradient
-20
20
Dev
iati
on
fro
m h
alf-
pit
ch
(no
min
al l
ine
wid
th)
(nm
)
0
0
10
LE
R (
nm
)
5
(b) LER (a) Line width
22 23 24 25 26 28 30 32 35 40 45 50 60
Exposure dose (mJ cm-2)
Hal
f-p
itch
(n
m)
22 23 24 25 26 28 30 32 35 40 45 50 60
Exposure dose (mJ cm-2)
Hal
f-p
itch
(n
m)
Analysis of dose-pitch matrices of anion-bound resist
-20
20
Dev
iati
on
fro
m h
alf-
pit
ch
(no
min
al l
ine
wid
th)
(nm
)
0
0
10
LE
R (
nm
)
5
22 23 24 25 26 28 30 32 35 40 45 50 60
Exposure dose (mJ cm-2)
Hal
f-p
itch
(nm
)
22 23 24 25 26 28 30 32 35 40 45 50 60
Exposure dose (mJ cm-2)
Hal
f-p
itch
(nm
)
Exp
erim
en
tal
Sim
ula
tion
dxdmLER
/
20.0
m: normalized protected unit concentration
EUV photon
Ionization
Ionization Next ionization or excitation
Resist
Thermalization
photon
electron
E < Eth
E > Eth
hn
hn-Ie
-Ie
Sensitization mechanism of EUV resists
+
-
+
+
- - Acid generator
(1) Absorption
(2) Deceleration
Eth < E < hn-Ie
(3) Deceleration
25 meV < E < Eth
Eth: Threshold energy for electronic excitation
Ie: Ionization energy
Simulation processes
(4) Electron diffusion and reaction
E=25 meV
Proton generation
Anion generation Post exposure baking (PEB)
Simulation of proton diffusion and deprotection
+
nE
r tDtkT
eDddd 6
Electric field
Random vector Displacement of proton
Monte Carlo simulation
+
+
+
+
+
Fixed
Mobile
Coulomb interaction
Immediately after exposure, protons are separated from anions because of their different origins.
Protected unit (polymer)
If a proton reaches a protected unit within the reaction radius, Rp, the deprotection is induced. Rp
Rq
If a proton reaches a quencher within the reaction radius, Rq, the proton is neutralized.
Quencher
Deprotection
Neutralization
0.0
0.5
1.0
1.5
2.0
-22 -11 0 11 22
Comparison with SFET exposure (22 nm half-pitch)
0.0
0.5
1.0
1.5
2.0
-22 -11 0 11 22
0.025 nm-3
0.01 nm-3
Distance (nm)
Pro
tect
ed u
nit
co
nc.
(n
m-3
) Dose: 18.16 mJ cm-2
PEB 50 s
PEB 100 s
PEB 150 s
Distance (nm)
Pro
tect
ed u
nit
co
nc.
(n
m-3
)
Dissolution point
Chemical gradient(Exp.)
Pattern boundary (Exp.)
PEB time dependence
0.025 nm-3
0.020 nm-3
0.015 nm-3
Quencher concentration dependence
0.010 nm-3
Quencher concentration
PEB time
Space Line Line
Space Line Line
0.0
0.5
1.0
1.5
2.0
-26 -13 0 13 26
0.0
0.5
1.0
1.5
2.0
-26 -13 0 13 26
Dose dependence of latent image (26 nm half pitch)
Distance (nm)
Pro
tect
ed u
nit
con
c. (
nm
-3)
Distance (nm)
Pro
tect
ed u
nit
con
c. (
nm
-3)
Dose: 18.16 mJ cm-2
Dose: 17.33 mJ cm-2 Dose: 18.99 mJ cm-2
0.0
0.5
1.0
1.5
2.0
-26 -13 0 13 26
Dissolution line
Chemical gradient(Exp.)
Pattern boundary (Exp.)
LER (Exp.)
Distance (nm)
Pro
tect
ed u
nit
co
nc.
(n
m-3
)
Space Line Line
Space Line Line Space Line Line
0.0
0.5
1.0
1.5
2.0
-22 -11 0 11 22
0.0
0.5
1.0
1.5
2.0
-25 -12.5 0 12.5 25
0.0
0.5
1.0
1.5
2.0
-24 -12 0 12 24
0.0
0.5
1.0
1.5
2.0
-23 -11.5 0 11.5 23
Half-pitch dependence of latent image
Distance (nm)
Pro
tect
ed u
nit
con
c. (
nm
-3)
Distance (nm)
Pro
tect
ed u
nit
con
c. (
nm
-3)
24 nm HP 25 nm HP
Distance (nm)
Pro
tect
ed u
nit
co
nc.
(n
m-3
)
Distance (nm)
Pro
tect
ed u
nit
co
nc.
(n
m-3
)
22 nm HP 23 nm HP
Dissolution line
Chemical gradient
(Exp.)
Pattern boundary (Exp.)
Dose: 18.16 mJ cm-2
LER (Exp.)
Space Line Line Space Line Line
Space Line Line Space Line Line
The catalytic chain reaction induced in a chemically
amplified resist with anion-bound AG was modeled.
The calculated latent images were compared with the
resist patterns fabricated using SFET of EIDEC. In the
preliminary examination, the calculated images well
agreed with the experimental results. The detailed
analysis of resist patterns using the developed
simulation code is ongoing to obtain the material
design strategy for 16 nm node and beyond.
Summary (2)
This work was partially supported by the New Energy and
Industrial Technology Development Organization (NEDO).
Acknowledgement
EUV photon
Ionization
Ionization Next ionization or excitation
Resist
Thermalization
photon
electron
E < Eth
E > Eth
hn
hn-Ie
-Ie
Reduction of wavelength
+
-
+
+
- - + Acid generator
The electron with thermal energy can sensitize acid generators.
Activation energy for dissociative electron attachment : ~0
(1) Absorption
(2) Deceleration
Eth < E < hn-Ie
(3) Deceleration
25 meV < E < Eth
Eth: Threshold energy for electronic excitation
Ie: Ionization energy
Simulation processes
Wavelength dependent
(4) Electron diffusion and reaction
E=25 meV
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
0 10 20 30
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
0 10 20 30
Distance, (nm) 222 zyx Distance, x (nm)
Pro
bab
ilit
y d
ensi
ty (
nm
-1)
×
qu
antu
m e
ffic
ien
cy
Pro
bab
ilit
y d
ensi
ty (
nm
-1)
×
qu
antu
m e
ffic
ien
cy
2 nm
13.5 nm
12 nm
2 nm
13.5 nm
e- e-
e-
e-
+ + + +
EUV photon
Multiple scattering at <Eth
line & space
Wavelength dependence of resolution blur caused by secondary electrons
Spherical coordinate x coordinate
Spherically symmetric
Electron migration after thermalization
per unit spherical
shell thickness
0
1
2
3
4
5
6
7
8
0 5 10 15
0
1
2
3
4
5
0 5 10 15
Wavelength (nm)
Res
olu
tio
n b
lur
(nm
)
Optical
Secondary electron
Total
Wavelength (nm)
Res
olu
tio
n b
lur
(nm
) Optical
Secondary electron
Total
Acid image resolution (acid diffusion length does not depend on wavelength)
Performance of conventional chemically amplified resists –Resolution-
Optical blur, boptical
Secondary electron blur, belectron
NAkCD
1
22
electronopticalt bbb
2
CDboptical
Total blur,
11 NA
k5.01
NA
k
Average distance
0
1
2
3
4
5
6
0 5 10 15
Wavelength (nm)
Lin
ear
abso
rpti
on
co
effi
cien
t (m
m-1
)
G v
alu
e [(
10
0 e
V)-1
]
0
1
2
3
4
5
6
Inner shell excitation
Performance of conventional chemically amplified resists –Sensitivity-
Absorption coefficient
Acid generation efficiency per unit absorbed dose (G value)
Auger electron (light element)
Fluorescence X-rays (heavy element)
Photoelectron emission
Compton scattering
Carbon K-edge
Acid concentration (acid diffusion length does not depend on wavelength)
Positively affect resolution
Negatively affect resolution
The W-value increases by 10-20% at the absorption edge of the inner shell.
0
1
2
3
4
5
0 5 10 15
0
2
4
6
8
10
0 10 20 30
Distance, x (nm) Wavelength (nm)
Pro
bab
ilit
y d
ensi
ty
×
qu
antu
m e
ffic
ien
cy (
nm
-1)
Res
olu
tio
n b
lur
(nm
) 0
5
10
15
20
25
0 5 10 15
Wavelength (nm)
Rat
io (
%)
Optical
Secondary electron
Total
e-
e-
e-
e-
+ + +
+
EUV photon
E > Eth
E > 25 meV
5.01 NA
k
High-resolution conventional resist such as PMMA
utilize this part for the chemical reaction for pattern
formation (main chain scission).
Non-chemically amplified resists
Chemically amplified resists utilize this part for
the decomposition of acid generators.
Distribution of radical cation Resolution blur of L&S pattern
Summary (3)
The wavelength dependence of lithography resolution was
investigated in the wavelength region of extreme
ultraviolet. The resolution is expected to be highest at a
wavelength of 3-5 nm, depending on NA of exposure tools.
In the case of low-NA tools, the merit of wavelength
reduction from 13.5 nm is significant. However, the merit
of wavelength reduction is lost in the case of high-NA
tools, particularly when the increase in transparency of the
resist with the reduction in wavelength is taken into
account. One of the keys to the realization of 6.67nm
lithography is the development of high-absorption resists.
This work was partially supported by the New Energy and
Industrial Technology Development Organization (NEDO).
Acknowledgement