Proc. of SPIE Vol. 10146 101460G-1Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 19 Apr 2019Terms of Use: https://www.spiedigitallibrary.org/terms-of-use
UV floodexposure
1 /
Coating andPAB
ResistCoating
L J
PSCART.PhotosensitizedChemicallyAmplifiedResistTM
EUV patternexposure
Acid and I Additional acidphotosensitizes generation by
** PSCARTM and Photosensitized Chemically Amplified ResistTM are trademarks of Tokyo Electron Ltd. and Osaka University.
1. INTRODUCTION
In order to lower the cost of ownership of extreme ultraviolet lithography (EUVL) in high volume manufacturing
(HVM), high sensitivity EUV resists enabling high throughput are being sought intensely 1-4. Nonetheless, stochastic
events like photon and chemical shot noise significantly limit lithography performance of EUV resists5-12. Thus,
sensitivity enhancement while keeping lithographic performance in EUV lithography is considered extremely difficult.
The concept of a Photosensitized Chemically Amplified ResistTM (PSCARTM) has been proposed by Tagawa et al.,13 of
Osaka University. This concept can be a promising solution to achieve increased resist sensitivity while maintaining
other high performance characteristics of the material (i.e., resolution, line edge roughness (LER), exposure latitude).
PSCAR uses a flood exposure subsequent to an EUV pattern exposure to sensitize the decomposition of a photo acid
generator (PAG). The preliminary results have been discussed in previous papers13-17.
This paper introduces a new concept for PSCAR (“PSCAR 2.0”). PSCAR 2.0 enhances resist sensitivity and latent
image contrast by using the sensitization of not only the PAG decomposition but also the quencher decomposition during
the flood exposure. The contrast enhancement is realized by the flexibility of increasing the quencher loading while
simultaneously optimizing the flood exposure dose.
In section 2 of this paper, the conventional PSCAR concept which photosensitizes acid generation is reviewed with
relation to simulation results. In section 3, the new PSCAR 2.0 concept is introduced with simulation and experimental
results. Then in section 4, stochastic simulation results are shown to elucidate PSCAR behavior with relation to line
width roughness (LWR).
2. PSCAR: PHOTOSENSITIZATION OF ACID GENERATION
In this section, we will review the basic PSCAR concept13,14, 16,17 as background information for PSCAR 2.0 shown in the
following section. PSCAR photosensitizes acid generation in order to obtain higher sensitivities and enhanced contrast.
Figure 1 schematically shows the basic PSCAR process flow. In the PSCAR process, simply a UV flood exposure step is
added for PSCAR sensitization. By using an inline process flow from coating to development, we assume that the post
EUV exposure delay time effects can be escaped.
Figure 1. PSCAR process flow.
Proc. of SPIE Vol. 10146 101460G-2Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 19 Apr 2019Terms of Use: https://www.spiedigitallibrary.org/terms-of-use
In Figure 1, it is shown that after coating the wafer with resist and post apply bake (PAB), an EUV pattern exposure is
executed. During the EUV exposure step, an acid product and a photosensitizer (PS) are generated. After the EUV
pattern exposure, an ultraviolet (UV) flood exposure creates additional acids in the resist by photosensitization. After
generating enough acids in the resist, a post exposure bake (PEB) is performed to change resist polarity. Finally,
development of the resist completes the resist patterning process.
In the flow shown in Figure 1, it is clear that the PSCAR material itself and the flood exposure module are key for the
successful development and introduction of PSCAR in semiconductor mass fabrication.
PSCAR is based on chemically amplified resists (CAR). A photosensitizer precursor (PP) is added into the PSCAR in
addition to the ordinary CAR components such as a protected polymer, a photo acid generator (PAG), and a quencher. In
PSCAR, the PAG needs the ability of being photosensitized during UV flood exposure. A “PAG which can be
photosensitized by the flood exposure” is abbreviated as “PS-PAG” in this paper.
The typical chemical structures of a PP and a PS are shown in Figure 2. PP is converted to PS by a catalytic chain
reaction induced by the acid generated during the EUV exposure. This chemical structure change allows for selective UV
absorption at the EUV pattern exposed areas. The PP does not have absorption at 365 nm which is the flood exposure
wavelength while the PS has significant absorption at this wavelength. Through this conversion, PS selectively absorbs
UV light to sensitize PS-PAG decomposition and generate more acids.
PSCAR absorption properties at the EUV and UV flood exposure wavelengths are summarized in the table shown in
Figure 2. For EUV resists, EUV absorption is not very selective for each component. During EUV pattern exposure, acid
is generated and the PS can be generated by the reaction with acid at room temperature. The PP to PS reaction is
designed to occur at room temperature due to the low PP deprotection activation energies. On the other hand, the PS in
PSCAR selectively absorbs UV flood exposure light as shown in the table in Figure 2. PS excitation in the EUV pattern
exposed area during a UV flood exposure induces further acid generation by photosensitization.
Figure 2. Left: UV spectrum shift by photosensitizer (PS) generation from a photosensitizer precursor (PP).
Right: PSCAR absorption properties for EUV pattern exposure and UV flood exposure.
Figure 3 shows a simple model equation that describes the line edge roughness (LER).18 From the equation, one can
deduce that the LER of a resist can be reduced by enhancing chemical contrast of the resist for each dose. PSCAR aims
to break the resolution (R), line-edge-roughness (LER), and sensitivity (S) trade-off (RLS trade-off) relationships by
contrast enhancement.
Proc. of SPIE Vol. 10146 101460G-3Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 19 Apr 2019Terms of Use: https://www.spiedigitallibrary.org/terms-of-use
EUV dose j
LERsimple model
Variation in deblocked polymer concentration(EUV shot noise, etc.)
dm /dx%U°
Finite size of a resist molecule
Q LER =
Gradient of blocked polymer concentrationCha lenge of chemicalcont ast enhancement
Reg. QCAR
After EUV exposure(20 mJ /cm2)
Of
oyy
0.6
0.4
E 0.2z
0
-18124 d 0 4 8 1218x Position(nm)
Quencher loading:0.0724
Acid neutralization
1
@ 0.8
8s
2
0.6
0.4
0.2
0.8
08
04
0.2
Flood exposure(No flood)
0 o --16 -124 -4 0 4 8 1216 -18-124 .4 0 4 8 1218
x Position (nm) x Position(nm)
After PEB
0.2 -
'2'
-1812 -8 -4 0 4 8 1216x Position (nm)
-Acid-Base
PAG
-m
dm/dx = 0.055
Figure 3. LER simple model18: PSCAR tries to mitigate roughness of patterns by contrast enhancement.
The detailed behavior of PSCAR is modeled and analyzed using TEL’s internal lithography simulator called
LITHOLAB19 with the optical simulation by KLA Tencor’s PROLITH20, 21. The simulations aim to predict PSCAR
performance and optimize resist formulation. Further details of the simulation are explained elsewhere.19
With the simulated results, the resist system differences are compared between a conventional CAR (Figure 4) and a
PSCAR (Figure 5) with a conventional non-decomposable quencher (a regular quencher such as amines).
In the conventional CAR system (Figure 4), the acid, base (non-decomposable quencher), PAG, and protected polymer
(m) concentrations are simulated. Quencher loading is adjusted based on the acid amount in the resist at 20 mJ/cm2 EUV
dose in this case. The quencher loading in the conventional CAR cannot be higher than the acid amount to be able to
image the resists. Remaining acids after acid quenching (acid neutralization) by bases can catalyze the deprotection of
polymer during PEB. This polymer deprotection causes polarity change to solvate the resist during development.
Figure 4. Normalized concentrations of the chemical species in a CAR with a non-decomposable quencher (regular
quencher) for 16 nm HP L/S. Acid concentration (red), base (quencher) concentration (blue), and PAG concentration
(orange) are normalized to an initial PAG concentration. Blocked polymer concentration (m) (purple) is normalized to an
initial m concentration.
Simulation results of a PSCAR with a non-decomposable quencher (PSCAR 1.0) are shown in Figure 5. Similar to the
conventional CAR with a non-decomposable quencher (Figure 4), the resist component’s relative concentrations are
calculated for the PSCAR 1.0 system at 20 mJ/cm2 EUV dose in Figure 5.
In the case of conventional PSCAR 1.0, the acid generated by EUV pattern exposure is used to generate PS as shown in
Figure 5. This PS photosensitizes PS-PAG decomposition and creates additional acid products. This photosensitization
most likely occurs through electron transfer from excited states of PS to PAG17, 22. The PS image can be improved by
acid quenching in the first step and therefore the PS can create an improved acid image by photosensitization.
The quencher loading in the case of PSCAR 1.0 in Figure 5 can also be increased as compared to the conventional CAR
because the acid amount in the PSCAR can be enhanced by a flood exposure. With the increased quencher loading,
larger amplitude of acids in the resist is realized by photosensitization. The quenching of the unnecessary acid by
increased amount of quencher creates an improved acid image.
Proc. of SPIE Vol. 10146 101460G-4Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 19 Apr 2019Terms of Use: https://www.spiedigitallibrary.org/terms-of-use
After EUV exposure Acid neutralization(20 mJ /cm2) PS generation
An enhanced image is obtained with the PSCAR system according to our simulation results in Figure 5. The chemical
contrast of the protected polymer (dm/dx) becomes roughly twice as the amount of quencher and flood exposure dose are
increased to generate enough acid in the system. Using this contrast enhancement technique, the sensitivity of the resist
can be improved by mitigating shot noise effects on roughness with reduced EUV doses.
Figure 5. Normalized concentrations of the chemical species in a PSCAR with a non-decomposable quencher (regular
quencher) (PSCAR 1.0) for 16 nm HP L/S. Acid concentration (red), base (quencher) concentration (blue), and
photosensitizer (PS) concentration and PAG concentration (orange) are normalized to an initial PAG concentration.
Blocked polymer concentration (m) (purple) is normalized to an initial m concentration.
3. PSCAR 2.0: PHOTOSENSITIZATION OF ACID GENERATION AND QUENCHER
DECOMPOSITION
The benefit of PSCAR as described in section 2 is to be enhanced by introducing additional chemistry. The new version
of PSCAR (PSCAR 2.0) utilizes photosensitization of not only acid generation but also quencher decomposition.
Instead of using non-decomposable quenchers (regular quencher) such as amines, a photo-decomposable base (PDB)
type quencher23-26 can be used in the PSCAR system. The PDB can be onium salts with OH- anion or –COO- anion to
quench super strong acids by anion exchange.23, 24 Resists with a PDB are designated as “PSCAR 1.5” in this paper.
PSCAR 1.5 has the advantage of improving the image contrast due to the decomposition of the quencher (Figure 6)
during an EUV exposure. However, PSCAR 1.5 has one disadvantage. If the PDB does not decompose by
photosensitization during a UV flood exposure (Figure 7), the contrast gained by the PDB will be reduced in the case of
high sensitization of a PSCAR 1.5 when using lower EUV doses.
To escape this situation, a “PDB which can be photosensitized by the flood exposure” (PS-PDB) is introduced to
improve the contrast in a PSCAR. The new PSCAR type is designated as a “PSCAR 2.0.” The PS-PDB decomposes
during EUV pattern exposure (Figure 6) and creates a quencher image in the resist. In addition, the PS-PDB decomposes
during a UV flood exposure by photosensitization (Figure 7). Similar to the PS-PAG, the PS-PDB should not absorb UV
flood exposure wavelengths to escape direct decomposition of the PS-PDB. Photosensitization induced decomposition of
the PS-PDB (most likely by an electron transfer17, 22) should proceed through the excitation of PS. To make the
photosensitization possible, the reduction potential of the onium salt PDB should be higher than the threshold, as it is in
the case of PAG sensitization17, 22. The PS-PDB decomposition though PS excitation during the flood exposure is
expected to create higher quencher image contrast.
Figure 6. EUV pattern exposure induced reactions of quenchers: PDB vs. PS-PDB.
Proc. of SPIE Vol. 10146 101460G-5Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 19 Apr 2019Terms of Use: https://www.spiedigitallibrary.org/terms-of-use
Substrateiesist film stagy
iattern exposa
(EUV etc.)iV food expos
iPEBi
DevelopmersEtching
cks
ure
sure
It
r
PS -PAG
PS -PDBquencher
PS -PDBquencher
PS -PAG +
PS -PDB +quencher
Polymer +(Nonpolar)
PS -PDBquencher +
Polymer -
$611 wprkc yt;
QueeoGlwr
Irleet fu resisF
rn exposure
:m exposure
Acid catalytic re
No bake or low ten
Neutralizatic
UV flood exposu
'composes by photos
UV flood expost
composes by photos
:atalytic reaction
feat (FEB)
Neutralization
PTD or
EUV patte
EUV patte
Via + Acid
+ Acid
PS
PS
De
De
Acid
Acid
Acid c
H
Development
Acid
Inert to resist(Weak acid)
:action
np bake
Ph
Inert IC
:ensitizationiiensitáation
P
Inert
Polymer +(Polar)
9 Inert to resist
NTD
iotosensitizer(PS)
D resist
kcid + PS
to resist + PE
Acid
PSCAR 2.0 r
In the EUV
decompositio
decompositio
increases. Aft
acid catalytic
the PP to PS
PAG and PS-
During the U
excitation.
During the P
improved ima
Finally, durin
tone developm
Figure
eaction steps
pattern expo
on creates an
on, acid quenc
fter pattern exp
c reactions at
conversion, a
-PDB decomp
UV flood expo
PEB in Figure
age of protect
ng developme
ment (NTD). T
e 7. UV flood
are summariz
sure step in
acid product
ching functio
posure, the PS
room tempera
a sharper imag
position.
osure in Figur
e 8, the acid i
ed polymers.
ent in Figure 8
The simulatio
exposure indu
zed in Figure 8
Figure 8. P
Figure 8, bot
t. PS-PDB d
onality is lost
S-PDB quench
ature. When t
ge of the PS is
re 8, PS-PAG
is used to de
8, the resist pa
on examples in
uced reaction
8.
PSCAR 2.0 rea
th of PS-PAG
ecomposition
and the effe
hes a strong ac
the acid quenc
s formed. This
G and PS-PDB
-protect polym
atterns are for
n this paper as
s of quencher
action steps.
G and PS-PD
creates the
ective acid co
cid. In paralle
ching process
s image of the
B decompose
mers. In para
rmed by posit
ssume PTD.
s: PDB vs. PS
DB decompose
inert materia
oncentration in
el, the convers
s occurs at a r
e PS is used fo
in the EUV p
llel, quenchin
tive tone deve
S-PDB.
e in PSCAR
l products. W
n the pattern
sion of PP to P
relatively quic
or photosensit
patterned area
ng of the acid
elopment (PTD
2.0. PS-PAG
With the PDB
exposed area
PS happens by
cker pace than
tization of PS
as through PS
d results in an
D) or negative
G
B
a
y
n
-
S
n
e
Proc. of SPIE Vol. 10146 101460G-6Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 19 Apr 2019Terms of Use: https://www.spiedigitallibrary.org/terms-of-use
PDBCAR
Q
yy
g
ß
After
0.8
0.6
0-10.12
EUV exposure(20 mJ /cm2)
p@
8
Acid neutralization
É 0.8
a oe
0.4H
0.2
.10.12
Flood exposure(No flood)
I
88
_
After PEB
08
08
0.4
0.2
-Acid-Base
PAG
-m
b-4 0 4 8x Position (nm)
1218
Quencher loading:0.0793
dm/dx = 0.058.8 .4 0 4 8 1218
x Position (nm)
0r.18-12 -0 < 0 4 0 12 18
x Positim (nm)
'.18.12 .4 0 4 e 12s Position (nm)
16
PS-PDB áPSCAR 2.0á
2
After
1
O8
0.8
04
0.2
0
EUV exposure(20 mJ /cm2)
s
z
Acid
0.8 -
0.4 -
0.2 -
a
neutralizationPS generation
&
S8
0.2
o-18 -12 -8 -4 0 4 8 1218
x Position (nm)
-18-1241<0 4 8 12 18x Position(nm)
Flood exposure(1510 mJ /cm2)
-18 -12 -8 -4 0 4 8 12 18x Position (nm)
2
0.8
0.2
o
After PEB
-18-12 -8 -4 0 4 8 12 18x Position 1nm)
- Acid-Base-Ps-PAG-M
dm/dx = 0.125
In Figures 9 and 10, the reactions of a conventional CAR with a PDB and a PSCAR 2.0 (a PSCAR with a PS-PDB) are
compared with LITHOLAB simulation results.
Figure 9. Normalized concentrations of the chemical species in a CAR with a PDB for 16 nm HP L/S. Acid
concentration (red), base (quencher) concentration (blue), and PAG concentration (orange) are normalized to an initial
PAG concentration. Blocked polymer concentration (m) (purple) is normalized to an initial m concentration.
The simulation results in Figure 9 show the concentrations of chemical species in a CAR with a PDB for each process
step. With the use of the PDB, the base (quencher) profile is generated by an EUV exposure (20 mJ/cm2) in addition to
the acid profile. Therefore, slight chemical gradient improvement dm/dx is seen compared to a conventional CAR as
shown in Figure 4.
Figure 10 shows the normalized concentrations of the chemical species after an EUV exposure (20 mJ/cm2) in a PSCAR
with a PS-PDB (PSCAR 2.0). In the PSCAR 2.0, quencher concentration can be increased greatly because additional
acids are generated by a flood exposure and additional quenchers are decomposed during the flood exposure. Figure 10
shows the case of quencher concentration of 0.6 compared to PAG. As shown in Figure 10, the protected polymer
gradient dm/dx of PSCAR 2.0 is much higher than dm/dx for the conventional CAR with a PDB in Figure 9 (more than
twice the dm/dx value).
Figure 10. Normalized concentrations of the chemical species in a PSCAR with a PS-PDB (PSCAR 2.0) for 16 nm HP
L/S. Acid concentration (red), base (quencher) concentration (blue), and photosensitizer (PS) concentration and PAG
concentration (orange) are normalized to an initial PAG concentration. Blocked polymer concentration (m) (purple) is
normalized to an initial m concentration.
Figure 11 shows the protected polymer gradient (dm/dx) for different resist types and different EUV exposure doses.
Proc. of SPIE Vol. 10146 101460G-7Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 19 Apr 2019Terms of Use: https://www.spiedigitallibrary.org/terms-of-use
0.16
0.14
0.12
0.10
0.08
0.06
0.04
0.02
0.00
PSCAR
PSCAR 0
15 20 25 30
EUV Exposure Dose (mJ /cm2)
- * -PSPDB PSCAR (Q =0.8)
-H-PDB PSCAR (1=0.6)
4-Reg. Q PSCAR (Q= 0.45 -0.55)
e-PDB CAR (Q= 0.049 -0.122)
4-Reg. Q CAR (Q= 0.0456 -0.122)
Figure 11. Chemical gradient for different resist types with the change of EUV exposure doses for 16 nm HP L/S.
Quencher concentrations (relative to PAG) (Q) used in the simulation are described in parentheses. For the CARs, the
quencher concentration was changed to get the target CD for each EUV dose. For regular quencher PSCAR, Q is
changed to get the best dm/dx. For PDB PSCAR (PSCAR1.5), fixed Q amount was used (roughly the max dm/dx). For
PS-PDB PSCAR (PSCAR 2.0), Q =0.8 was used as a selected value. The calculated dm/dx will be further increased with
increased Q in the case of PSCAR 2.0 (See Fig. 12).
In Figure 11, for the conventional CARs (a regular quencher CAR and a PDB CAR), the resist sensitivities are changed
by changing the quencher amount. To achieve higher resist sensitivity (= less EUV dose to target), the quencher loading
needs to be reduced in the case of conventional CARs. With the reduced amount of quencher, acid amplitude goes down
to get target CD. As a result, chemical gradient in the resists degrades with sensitivity increase in the case of
conventional CARs.
On the other hand, PSCARs can exhibit higher freedom to increase the quencher loading concentration. The best
quencher loading can be selected to get higher contrast in the resist because more acid can be obtained during the flood
exposure.
The PSCAR 1.0 in Figure 11 provides a better chemical contrast than a conventional CAR. A PSCAR with a PDB
(PSCAR 1.5) in Figure 11 has better performance than PSCAR 1.0. However, in the case of PSCAR 1.5, the chemical
gradient tends to decrease with sensitization due to the reduction of PDB decomposition by EUV exposure dose
reduction as shown in Figure 11. The PSCAR 2.0 concept solves this issue and keeps the high contrast at lower doses in
Figure 11. The PS-PDB (quencher) decomposition during the flood exposure seems to help contrast enhancement when
higher quencher loading concentrations are used.
Figure 12 shows the plot of dm/dx for different quencher loading concentrations and EUV exposure doses for PSCAR
1.5 and PSCAR 2.0. In the case of PSCAR 1.5, the quencher loading for maximum dm/dx decreases with reduced EUV
doses. The extremely high quencher loading concentrations (>0.7) tend to decrease chemical contrast as shown in Figure
12.
On the other hand, in Figure 12, PSCAR 2.0 is shown to have a higher capability of improving chemical gradient by
adding higher quencher concentrations. This capability is realized by quencher decomposition with the flood exposure-
induced photosensitization. Higher quencher loading with quencher image by PS-PDB decomposition may also be
beneficial for blocking acid diffusion in the non-pattern exposed area. In addition, higher quencher loading may be
beneficial for reducing quencher-induced chemical shot noise.
As shown in the simulation results (Figures 11 and 12), the potential of contrast enhancement is the highest in PSCAR
2.0. The possibility of increased loading of PS-PDB needs to be confirmed via experiments in the future.
Proc. of SPIE Vol. 10146 101460G-8Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 19 Apr 2019Terms of Use: https://www.spiedigitallibrary.org/terms-of-use
0.16
0.14
0.12
0.10
0.08
0.06
0.04
0.02
0.0003 0.4 0.5 0.6 0.7 0.3 as 1 1.1 1.2 13
Quencher (PDB or PS -PDB) loading relative to PAG
Solid Une PS-POS PSCM
-.-ssM/all2- - . «. rLIM/2
v.. . -2M/rn2N e 1 +30M/an2
PSCAR 1.5`1Y '`.,Dashed Line =PwMAR
]SM/Gn2-. roM/un2- 25 ml/cm2-30 MAT'
PSCAR 2.0
(Refereewith PD
MIN L/S 1:1Ref.
PDB CAR
UV 0 -1/cm' UV 0 J/em2 W 3 Jlcm' UV 6 Jim?
ill 11111
PSCAR .
PDB PSCAR 1.5ice CARB + PP)
Dose to size (mJ /an`)
Sensitivity vs. ref.
PS -PDB PSCAR 2.0(Reference CAR
with PS -PDB + PP)
22.6 18.6
x1.15 x1.37 x2.02
Dose to size (mJ /cm2) 30.8 22.8 16.2 10.4
Sensitivity vs. ref. x1.22 x1.64 x2.31 x3.61
Figure 12. Chemical gradient for PSCAR 1.5 and PSCAR 2.0 with the change of quencher loading and EUV exposure
doses (15 – 30 mJ/cm2 in the graph) for 16 nm HP L/S. The flood exposure doses are adjusted to get 16 nm HP L/S with
different quencher loadings.
The preliminary PSCAR 2.0 experimental results are shown in Figure 13. PSCAR 1.5 results are also shown in Figure 13
for comparison. These results show the preliminary tests without quencher concentration increase to get better contrast.
EUV exposures are performed with ASML’s NXE:3300 with TEL’s stand-alone flood exposure tool at imec.
Figure 13. PSCAR 1.5 and PSCAR 2.0 preliminary sensitization tests with EUV exposures with ASML NXE:3300 and
UV flood exposures with TEL’s pre-alpha UV (365 nm) flood exposure tool (stand-alone) at imec. Patterns are 16 nm
HP L/S. Quencher concentrations are the same for all samples (not optimized to get the best contrast with the flood
exposure).
As can be seen in Figure 13, the sensitivity is enhanced with increased flood exposure doses for both PSCAR 1.5 and
PSCAR 2.0. With 3 J/cm2 flood exposure, 1.37 times sensitivity enhancement compared to the reference base resist is
seen for PSCAR 1.5 and 1.64 times sensitivity enhancement is obtained for PSCAR 2.0. With 6 J/cm2 and 9 J/cm2 flood
exposures in Figure 13, higher sensitization results are shown. For the higher sensitization, roughness increase is
observed so far nonetheless. The roughness at higher sensitization needs to be reduced by quencher concentration
increase in the future tests.
Proc. of SPIE Vol. 10146 101460G-9Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 19 Apr 2019Terms of Use: https://www.spiedigitallibrary.org/terms-of-use
PSCAR 1.5 (PSCAR with PDB) PSCAR 2.0 (PSCAR with PS -PDB)
The corresponding LWR values have not been shown as these values are not reliable due to delay time effects in the
experimental set-up with the stand-alone flood exposure tool with manual wafer handling in clean room air. As a
reference values, the LWR values (3σ) for PSCAR 1.5 example are 4.37 nm (at UV 0 J/cm2), 4.85 nm (at UV 3 J/cm2),
5.41 nm (at UV 6 J/cm2), 6.39 nm (at 9 J/cm2). LWR values (3σ) for PSCAR 2.0 example are 4.39 nm (at UV 0 J/cm2),
5.22 nm (at UV 3 J/cm2), 6.47 nm (at UV 6 J/cm2). To completely break the RLS tradeoff relationship, further
improvement and adjustment of resist materials and formulation are needed.
The focus of the future work will be maximizing contrast by quencher loading optimization and by having higher
efficiency of photosensitization to reduce the reactions of the non-EUV exposed area during flood exposure. In addition,
inline operation in a newly developed flood exposure tool in TEL’s CLEAN TRACKTM is expected to solve the delay
time issues in the future.
For the EUV doses with very high photon shot noises, the contrast enhancement by PSCAR system will not be sufficient
to mitigate the roughness increase. Therefore, in the future tests, we need to elucidate how much sensitization is possible
with keeping roughness performance by experiments.
Figure 14 shows the sensitization test results for the resists with PP and PS with 365 nm UV flood exposure. PSCAR 1.5
and PSCAR 2.0 results are compared. In Figure 14, the non-EUV exposed area is assumed by a PSCAR itself (with PP).
The EUV exposed area is assumed by a PSCAR with replacing PP by PS (deprotected ketone PS is added in the resist).
Figure 14. PSCAR 1.5 and PSCAR 2.0 remaining film thickness with UV flood exposures (365 nm wavelength) after
development. Only the quencher type is changed between PSCAR 1.5 (with a PDB) and PSCAR 2.0 (with a PS-PDB).
The rest of the resist components (a protected polymer, a PS-PAG and a PS/PP) are the same. The same quencher
concentrations are used for all samples. No EUV exposure was done for this test. The EUV exposure effect is mimicked
by replacing PP by PS in the resist film.
In the tests of the non-EUV exposed area (with PP), unwanted gradual film thickness loss is seen with flood exposure
dose increase for both PSCAR 1.5 and PSCAR 2.0. This background reaction is assumed to be due to base resist
absorption at UV flood exposure wavelengths. One option to reduce this effect is to improve the transparency of the base
polymer. Another option is to sensitize faster to mitigate the background absorption effects.
For the resists with PS and PP in Figure 14, it is clearly found that the flood-exposure-induced sensitization is happening
for both PSCAR 1.5 and PSCAR 2.0 with PS selectively. The sensitivity of the resist is enhanced for the PSCAR 2.0 by
more than double of the PSCAR 1.5 (Dose of the PSCAR 2.0 is less than half of the PSCAR 1.5). The results also
support the conclusion that the PSCAR 2.0 photosensitization can be accelerated by decomposition of the PS-PDB
during flood exposure.
4. PSCAR STOCHASTIC SIMULATION
The stochastic resist simulator has been developed to predict PSCAR behavior under photon and chemical shot noise.
The stochastic simulations have been performed by using Synopsys’ Sentaurus Lithography (S-Litho) 27, 28. The model
Proc. of SPIE Vol. 10146 101460G-10Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 19 Apr 2019Terms of Use: https://www.spiedigitallibrary.org/terms-of-use
Photon Acid amplificationDistribution by photosensitization
Acid.. after EUV exposure after photosensitization
Inhibitor Final resistconcentration profile
after PEB 16 nm 1:1 L/S
I/O I JaIIIC
SynopsysS -Litho Prototype
ach wit
Le4J 3
2
1
Regular quencher PDB (Photo Decomposable Base)t t quencher
takes into account the roughness effects due to the shot noise and secondary electron effects during exposure, and the
interaction among the finite number of chemical molecules27. In a prototype implementation of PSCAR, it is possible to
simulate each step of the process, as shown in Figure 15.
Figure 15. PSCAR 2.0 stochastic simulation examples using Synopsys S-Litho prototype for 16 nm HP L/S. Photon and
chemical shot noises and secondary electron effects during exposure are taken into account. Each step of the process can
be simulated.
As a side note, the parameters used in S-Litho stochastic simulations are similar but not the same as the continuum
LITHOLAB simulation model discussed in Section 2 and 3.
Figure 16. LWR values (3σ) of 16 nm HP L/S patterns obtained by stochastic simulator for different resist types. The
EUV exposure dose is fixed at 20 mJ/cm2 for all the resists. Flood exposure doses for sensitization are fixed at 5 J/cm2
for PSCARs. For CARs, no flood exposure is assumed. Quencher amounts are optimized to get 16 nm HP L/S at the
fixed EUV and flood exposure doses. The lowest (best) LWR is obtained for PSCAR 2.0.
As shown in Figure 16, using the lithography stochastic simulation, LWR values for each resist type are simulated for
16 nm L/S using the same EUV exposure condition as in imec’s set up. Each LWR value is derived from 40 different
seeds and the obtained values for each simulation are accumulated to get the final LWR values using all the calculated
values. In the simulation in Figure 16, the EUV dose is fixed at 20 mJ/cm2 for all the resists. The flood exposure doses
are set to be zero for CAR and 5 J/cm2 for PSCARs. The quencher loadings for each resist are adjusted to get 16 nm L/S
pattern size.
Proc. of SPIE Vol. 10146 101460G-11Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 19 Apr 2019Terms of Use: https://www.spiedigitallibrary.org/terms-of-use
35
29.5 mJ/cm230
-31% dose
25 22.5 mJ/cm2
20 -
15PDB PS -PDBCAR PSCAR2.0
From the simulation result in Figure 16, the highest (worst) LWR value is observed when the CAR with the regular
quencher is used. A PSCAR with the regular quencher improved the image in Figure 16. Among PDB CAR, PSCAR 1.5,
and PSCAR 2.0, PSCAR 2.0 realized the lowest LWR around 3 nm when PDB CAR induces roughly 5 nm LWR. From
the stochastic simulation in Figure 16, it is confirmed that PSCAR 2.0 can provide the best LWR value under the same
EUV dose and flood exposure dose condition.
Figure 17 shows dose to size values for PDB CAR and PSCAR 2.0 for 16 nm L/S while keeping LWR performance the
same.
Figure 17. Dose to size for PDB CAR and PSCAR 2.0 for 16 nm L/S while keeping LWR performance the same.
Quencher amount is set the same for both resists and not optimized (not increased) to get best contrast with PSCAR 2.0.
Flood exposure dose: 0 J/cm2 for PDB CAR, 5 J/cm2 for PS-PDB PSCAR2.0.
Quencher amount is set to the same value for both resists and is not optimized (not increased) to get the best contrast
with PSCAR 2.0. In this condition, 31% dose reduction is confirmed. With the quencher loading and flood exposure co-
optimization, further improvement of sensitivity while keeping LWR performance is expected and will be the focus of
future work. The current simulation results suggest that PSCAR 2.0 has the capability of sensitivity enhancement while
keeping similar LWR.
SUMMARY
PSCAR performance when different types of quenchers are used is examined by simulation and experiments. PSCAR
uses “selective” photo sensitization during the flood exposure. The chemical contrast is further enhanced by the
simultaneous optimization of quencher loading and UV flood exposure dose.
A PSCAR continuum model simulator (by TEL) and stochastic simulator (by Synopsys) have been developed to help
predict PSCAR performance. Among the PSCARs with different quencher types, the best performance was found when
PSCAR 2.0 with PS-PDB was used. This PSCAR 2.0 had the highest possible chemical gradient and the lowest LWR.
From these results, it is concluded that the dual sensitization of PS-PAG and PS-PDB in PSCAR 2.0 enables the highest
sensitization with improved contrast for EUV lithography.
Finally, the performance of both PSCAR 1.5 and PSCAR 2.0 has been confirmed on ASML’s NXE:3300 with TEL’s
standalone pre-alpha flood exposure tool at imec. It was found in these preliminary experiments that PSCAR 2.0 indeed
shows an enhanced photosensitization capability in comparison to PSCAR 1.5. Further optimization of the PSCAR
material formulation is needed, but the initial results are promising to already elucidate the potential of PSCARs.
ACKNOWLEDGEMENT
We would like to acknowledge all of our collaborative partners and colleagues who supported this work. We also thank
ASML for fruitful discussions related to this work. We also thank Dr. Wolfgang Demmerle and Mr. Hironobu Taoka of
Proc. of SPIE Vol. 10146 101460G-12Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 19 Apr 2019Terms of Use: https://www.spiedigitallibrary.org/terms-of-use
Synopsys for valuable discussions. We would also like to thank Japan Science and Technology Agency (JST) for partial
support on this work.
REFERENCES
[1] Martin van den Brink, “Cost-effective shrink with Holistic Lithography, extended by EUV,” EUVL Symposium
(2015).
[2] Anna Lio, “EUV resists: What's next?” Proc. SPIE 9776, 97760V (2016).
[3] Takahiro Kozawa, Julius Joseph Santillan and Toshiro Itani, “Relationship between sensitizer concentration and
resist performance of chemically amplified extreme ultraviolet resists in sub-10 nm half-pitch resolution region,”
Tagawa, “Challenge toward breakage of RLS trade-off for EUV lithography by Photosensitized Chemically
Amplified Resist (PSCAR) with flood exposure” Proc. SPIE, 9776, 977607 (2016).
[18] Chris A. Mack, “A Simple Model of Line-Edge Roughness,” Future Fab International, Vol. 34 (2010).
Proc. of SPIE Vol. 10146 101460G-13Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 19 Apr 2019Terms of Use: https://www.spiedigitallibrary.org/terms-of-use
[19] Michael A. Carcasi, Seiji Nagahara, Gosuke Shiraishi, Tomohiro Iseki, Yukie Minekawa, Kosuke Yoshihara,
Proc. of SPIE Vol. 10146 101460G-14Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 19 Apr 2019Terms of Use: https://www.spiedigitallibrary.org/terms-of-use
![Synthesis of non-chemically amplified 193nm photo-resists ...€¦ · was the major driving force for advances in semiconductor fabrication during 1980s and 1990s [3]. DNQ/Novolac](https://static.documents.pub/doc/80x56/60486d2c359f494acc756277/synthesis-of-non-chemically-amplified-193nm-photo-resists-was-the-major-driving.jpg)
