assessment and extendibility of chemically amplified
TRANSCRIPT
1The Institute of Scientific and Industrial Research, Osaka University2Semiconductor Leading Edge Technologies, Inc. (Selete)
Assessment and extendibility of chemically amplified resists for extreme ultraviolet lithography
Takahiro Kozawa1, Hiroaki Oizumi2, Toshiro Itani2, and Seiichi Tagawa1
Resolution, LER, Sensitivity, Exposure latitude
The extraction of basic parameters related to pattern formation efficiency is essential for resist assessment.
Resolution
LER
Sensitivity
EL
Pattern formation efficiencyInterchangeable To fully extract the resist potential,
users must carefully consider the allocation of pattern formation efficiency.
LER
Sensitivity
EL
Pattern formation efficiencyInterchangeable
Actually, there is no room for the negotiation on resolution.
The balance among sensitivity, LER, and EL is important for the enhancement of productivity.
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
11.5mJ27.8, *
26.3, 8.1 26.5, 6.9 24.2, 6.4
22.5, *
Dissolution point
Nor
mal
ized
pro
tect
ed u
nit
conc
entra
tion
Distance (nm)
32.6, 7.6 28.0, 6.6 23.8, 6.4
19.7, 6.9Bridge(Line width, LER)
dxdmLER
/31.0
=
Chemical gradient
2.4 nm s-1Dissolution rate
11.5
12.0 12.5 13.0
13.5
EUV Symp. 2009
Accuracy: ~20%
(SSR3, R=0.1)
Objective
The incorporation of a simple model for acid-base equilibrium
2. To evaluate the resist performance upon exposure using a high NA tool.
3. To discuss the extendibility of chemically amplified resists.
1. To enhance the accuracy of parameter extraction from ~20% to <10%
( )[ ]ββ
×−−= DoseDose exp11'
Dose-pitch matrix
Dose correction using
Dose-pitch matrix with cross sectional SEM image
NA 0.35 with conventional illumination (σ = 0.8)
Resist requirement for 16 nm node
Small Field Exposure Tool : SFET
Source(Xe DPP)
Exposure chamber
Mask loader
Wafer loader
Wafertrack
Items Target Specifications
NA 0.3
Illumination mode
Annular(0.3/0.7), x-slit
Field size 0.2 x 0.6 mmMagnification 1/5Wavefront error <0.9 nm rmsFlare <7% (MSFR)
Source power 0.5W @IFWafer size 300 mm
Experimental condition
SEM: Hitachi S-9380II
Resist: Selete Standard Resists (SSR4 and SSR5)
Pattern: Line and space (HP: 22-60 nm)
Simulation
line & space
Aerial image of incident EUV
( ) ( )zFp
xCAzyxI απ−
+
+= expcos1
21,,
2/1
Pattern
SFETK. Tawarayama et al. Jpn. J. Appl. Phys. 47 (2008) 4866.
FlareContrast
e-
e-
e-
e-
++++
EUV photon
Secondary electronsDeprotonation
Electron migration
Latent images were calculated on the basis of reaction mechanisms of chemically amplified EUV resists.
Chemical gradient was evaluated at the half-depth of developed pattern.
Effective reaction radius for deprotection, Reff
Quencher concentration
Fitting parameter
The number of acids participating in chemical reaction
The efficiency of chemical reaction per unit diffusion length
Acid diffusion constant
Dissolution point
Acid
Diffusion Diffusion after successful reaction.
Diffusion without inducing reaction.Protected unit(Reaction site)
The amount of chemical reactions required for the dissolution of resist polymer
*Quantum efficiency of acids
Activation energy for acid diffusion
Acid-base equilibriumExposure latitude, sensitivity
Representative patterning resultsSSR4
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-2Line width, LER
(0 degree)Thickness
Changing HP
Cha
ngin
g do
se
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
22232425262830323540455060
Exposure dose (mJ cm-2)
-30
30
Dev
iatio
n fr
om h
alf-
pitc
h (n
omin
al li
ne w
idth
) (nm
)
-10-20
0
2010
0
15
LER
(nm
)
10
5
LER
Line width
7.9 mJ cm-2
22232425262830323540455060
Exposure dose (mJ cm-2)
(a) SSR4
22232425262830323540455060
Exposure dose (mJ cm-2)
9.4 mJ cm-2
22232425262830323540455060
Exposure dose (mJ cm-2)
Hal
f-pi
tch
(nm
)H
alf-
pitc
h (n
m)
Hal
f-pi
tch
(nm
)H
alf-
pitc
h (n
m)
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.00 0.05 0.10 0.15
Erro
r
Effective reaction radius (nm)
Fitting error
∑
−+
−+
−=
i isim
isimi
isim
isimi
isim
isimi NT
TTLER
LERLERWidth
WidthWidtherror /
2
,
,exp,
2
,
,exp,
2
,
,exp,
SSR4SSR5
T: Thickness of remaining resist, N: Total number of data
0.000
0.005
0.010
0.015
0.020
0.00 0.05 0.10 0.15
01234567
0.00 0.05 0.10 0.15 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14
0.00 0.05 0.10 0.15
0.0
0.2
0.4
0.6
0.8
1.0
0.00 0.05 0.10 0.15
Dis
solu
tion
poin
t
Effective reaction radius (nm)(a) Dissolution point (b) Quencher concentration
(c) Acid diffusion constant
Que
nche
r con
c. (n
m-3
)
Effective reaction radius (nm)
Diff
usio
n co
nsta
nt (n
m2
s-1)
Effective reaction radius (nm)
Extracted parameters
(d) Acid-base equilibriumEffective reaction radius (nm)
β
SSR4SSR5
SSR4SSR5
SSR4SSR5
SSR4SSR5
0.00
0.05
0.10
0.15
0.20
0.25
0.00 0.05 0.10 0.15
f LER
Effective reaction radius, Reff (nm)
Relationship between chemical gradient and LER
Determined by factors such as the aerial image quality of incident photons, exposure dose, absorption coefficient, the quantum efficiency of acids, and the effective reaction radius of deprotection.
Determined by material and process factors associated with development and rinse processes.dxdm
fLER LER
/≈
SSR4SSR5
Because LER is inversely proportional to the chemical gradient, the process and material optimizations are equivalent to a task to maximize the chemical gradient.
The chemical gradient also has a maximum value here.
(b) SSR5
22232425262830323540455060
Exposure dose (mJ cm-2)
-30
30
Dev
iatio
n fr
om h
alf-
pitc
h (n
omin
al li
ne w
idth
) (nm
)
-10-20
0
2010
0
15
LER
(nm
)
10
5
LER
Line width
22232425262830323540455060
Exposure dose (mJ cm-2)
(a) SSR4
22232425262830323540455060
Exposure dose (mJ cm-2)
22232425262830323540455060
Exposure dose (mJ cm-2)
Hal
f-pi
tch
(nm
)H
alf-
pitc
h (n
m)
Hal
f-pi
tch
(nm
)H
alf-
pitc
h (n
m)
Simulation result
(b) SSR5
22232425262830323540455060
Exposure dose (mJ cm-2)
-30
30
Dev
iatio
n fr
om h
alf-
pitc
h (n
omin
al li
ne w
idth
) (nm
)
-10-20
0
2010
0
15
LER
(nm
)
10
5
LER
Line width
7.9 mJ cm-2
22232425262830323540455060
Exposure dose (mJ cm-2)
(a) SSR4
22232425262830323540455060
Exposure dose (mJ cm-2)
9.4 mJ cm-2
22232425262830323540455060
Exposure dose (mJ cm-2)
Hal
f-pi
tch
(nm
)H
alf-
pitc
h (n
m)
Hal
f-pi
tch
(nm
)H
alf-
pitc
h (n
m)
0
10
20
30
40
50
60
70
20 30 40 50 60
20 nm
21 nm
22 nm
23 nm
24 nm
25 nm
26 nm
28 nm
30 nm
32 nm
35 nm
40 nm
45 nm
50 nm
60 nm
Half-pitch (nm)Th
ickn
ess (
nm)
Cross-sectional view of SSR5 at 8 mJ cm-2
BottomTop
Simulation
0
10
20
30
40
50
60
70
20 30 40 50 60
BottomTop
20 nm
21 nm
22 nm
23 nm
24 nm
25 nm
26 nm
28 nm
30 nm
32 nm
35 nm
40 nm
45 nm
50 nm
60 nm
Half-pitch (nm)Th
ickn
ess (
nm)
Cross-sectional view of SSR5 at 10 mJ cm-2
Simulation
0
10
20
30
40
50
60
70
20 30 40 50 60
20 nm
21 nm
22 nm
23 nm
24 nm
25 nm
26 nm
28 nm
30 nm
32 nm
35 nm
40 nm
45 nm
50 nm
60 nm
Half-pitch (nm)Th
ickn
ess (
nm)
Cross-sectional view of SSR5 at 11 mJ cm-2
BottomTop
Simulation
0
10
20
30
40
50
60
70
20 30 40 50 60
20 nm
21 nm
22 nm
23 nm
24 nm
25 nm
26 nm
28 nm
30 nm
32 nm
35 nm
40 nm
45 nm
50 nm
60 nm
Half-pitch (nm)Th
ickn
ess (
nm)
Cross-sectional view of SSR5 at 12 mJ cm-2
BottomTop
Simulation
0.0
0.2
0.4
0.6
0.8
1.0
0 10 20 30 40
SFET
NA 0.35 with conventional illumination
(σ = 0.8)
High NA exposure toll
NA 0.3 with annular illumination
(σ = 0.3/0.7)
Half pitch (nm)
Con
trast
Resist performance upon exposure using a high NA tool.
15161718192021222324
Exposure dose (mJ cm-2)
-30
30
Dev
iatio
n fr
om h
alf-
pitc
h (n
omin
al li
ne w
idth
) (nm
)
-10-20
0
2010
0
15
LER
(nm
)
10
5
LER
Line width
Hal
f-pi
tch
(nm
)
15161718192021222324
Exposure dose (mJ cm-2)
Hal
f-pi
tch
(nm
)(b) High NA(a) SFET
Resist performance (SSR5) upon exposure using a high NA tool
15161718192021222324
Exposure dose (mJ cm-2)
Hal
f-pi
tch
(nm
)
15161718192021222324
Exposure dose (mJ cm-2)
Hal
f-pi
tch
(nm
)
Extendibility of chemically amplified resist
Absorption coefficient
Quantum efficiency
Effective reaction radius
~4 10
~2.4
~0.1
~16
~64
0.5 ~0.5
Quencher concentration
Dissolution point Optimized at 10 mJ cm-2 and 16 nm HP*
*Optimum dissolution point and quencher concentration depend on sensitivity and half-pitch because of RLS trade-off relationship.
Current status Technical limit Physical limit
(maybe more)
Optimized at 10 mJ cm-2 and 16 nm HP*
(with ultrathin resist process)(µm-1)
(nm)
15161718192021222324
Exposure dose (mJ cm-2)
-30
30
Dev
iatio
n fr
om h
alf-
pitc
h (n
omin
al li
ne w
idth
) (nm
)
-10-20
0
2010
0
3
LER
(nm
)
2
1
LER
Line width
Hal
f-pi
tch
(nm
)
15161718192021222324
Exposure dose (mJ cm-2)
Hal
f-pi
tch
(nm
)
(b) High NA(a) SFET
Resist performance at technical limit
15161718192021222324
Exposure dose (mJ cm-2)
Hal
f-pi
tch
(nm
)
15161718192021222324
Exposure dose (mJ cm-2)
Hal
f-pi
tch
(nm
)
By increasing pattern formation efficiency, not only LER but also exposure latitude and linearity were significantly improved.
Summary
The resist performance of current EUV resists upon exposure to a high NA tool (NA 0.35) was estimated. LER is away from the requirement.
Assuming the technical limit of the parameters associated with pattern formation efficiency, the extendibility of chemically amplified resists was examined. The resist requirements for 16 nm are achievable at NA=0.35, but comparable to the technical limit.
By improving the resist modeling, the accuracy of parameter extraction was successfully reduced from ~20% to <10%.
1.
2.
3.
Acknowledgement
Dr . Hiroshi Chiba and Dr. Takuro Ono of Nikon Corporation for the calculation of optical images