Acid Amplifier - Sematech

Acid Amplifiers Designed For EUV Resists
Can Help Beat the RLS Trade-off
Seth Kruger, 1 Craig Higgins, 1 Srividya Revuru, 1 Sara Cruz, 2
Vaida Auzelyte, 3 Pratap Sahoo, 3 Harun Solak, 3 and Robert Brainard 1
1. College of Nanoscale Science and Engineering, University at Albany, NY 12203
2. Undergraduate summer intern from Mexico
3. Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland
I. Introduction
II. Kinetics
III. Modeling
IV. Lithography
V. Conclusions
II.
Kinetics
III.
Modeling
Synthesis
1
IV.
Lithography

Resolution
Sensitivity
I. EUV Resist Goals
Minimize:
LER
Resolution
Line Edge Roughness (LER)
Sensitivity
RLS Tradeoff
(Resolution) 3 x (LER) 2 x Esize = Z-Parameter
T. Wallow, C. Higgins, R. Brainard et al. Proc. SPIE 6921 (2008)
2

Resolution
Film
Quantum
Yield
How to Simultaneously Improve
Resolution, LER and Sensitivity?
Sensitivity
≡
LER
Moles of Acids
Generated in the Film
Moles of Photons
Absorbed by the Film
We propose that higher
quantum yield will allow us to
go from…
Here
3
to
Here
…with no penalty to sensitivity.

Acid Amplifiers
One possible way to effectively increase the quantum yield
of the resist is through the use of acid amplifiers (AAs).
HA
∆
T A
X
Trigger
(T)
Body
Body
3HB
Body
Activated
Acid Precursor (A)
A
∆
H +
4
Body +
Autocatalysis
H +
H +
HA
H +
H +
H +
H +

Acid Catalyzed
-
RSO3 OH
RSO 3H
3HB
O
O 2
S
R
U = Uncatalyzed
T = Trigger Pull
A = Acid Generation
U
Proposed Mechanism
OH 2
CAT
OH
O
Uncatalyzed
O 2
S
CH2
R
+
O
-H +
-H 2O
T
O 2
S
R
UNCAT
O
5
O 2
S R
A
+
R =
HO3S R
+
O
CH2
O 2
S R
CF 3

AA Decomposition and Behavior in Resist
AA Decomposition
Kinetics
∆
Thermal
No Acid
(slow)
UNCAT
AA
H +
Acid Catalyzed
(fast)
CAT
Acid Diffusion
(slow)
Acid Behavior
in Resist
6
H +
H +
P
Acid Catalyzed
ESCAP Deprotection
(fast)

II. AA Decomposition Kinetics using
19 F-NMR Spectroscopy
Solvent system is a good model for resist environment
OH
3HB
Solvent System for Kinetics
O
d 6
O 2
S
R
Add base to
absorb the acid
CAT
Fast
Catalyzed
Slow
Uncatalyzed
UNCAT
50 / 50 wt %
δ+
δ+
OH 2
OH
δ+
O
O 2
S
O
δ−
R
O 2
S
R
Resist Polymer
7
δ+
O
δ−
O 2
S R
65/20/15
+
HO3S R

ln(AA [M])
-2.5
-3
-3.5
-4
-4.5
-5
-5.5
-6
With and Without Base
CAT
Without Base
Autocatalyzed
0 100 200 300 400 500 600 700 800
Time [min]
UNCAT
8
With Base
(Uncatalyzed
& First-Order)
1.2 eq.
Decomposition
at 100 °C

Reaction Rates Ratios
at 100 °C
k CAT
k UNCAT
1425
1359
25
OAc
O
O
S
OH
O
O
S
9
O
O
CF 3
CF 3
k CAT
k UNCAT
490
1

Uncatalyzed
(Thermal)
OH
UNCAT
δ+
III. Kinetic Modeling
T
Trigger
Pull
Ea Thermal –Ea Trigger
Acid
Formation
O2 S
δ+
δ+
O R
OH2 δ− δ+
O O
2
S
O R
OH
3HB
O
O 2
S
R
10
A
CAT
δ−
O 2
S R
+
HO3S R

Thermal Stability Test
Thermal Acid Generator (TAG)
∆ 150 s
Passed 110 °C
Passed 70 °C
Failed
H + H +
H +
H +
H +
H +
H + H +
H +
H + H +
H + H +
H + H H+
+
H +
H +
H +
H +
H +
H +
Develop
H + H +
Bake 13.4 pH
11

OH
OH
OAc
OH
3AB
O O
S
O
3HB
11HB
O O
S
O
4HB
O O
S
O
O
S
O O
Acid Amplifier Examples
CF 3
CF 3
CF3
CF 3
OH
OH
O O
O
S
3HA
OAc
O O
O
S
3AA
OH
4HA
O
S
O O
8HB
O O
S
O
Unexposed Film
Thickness Loss (UFTL)
Test Results
CF 3
OH
8HA
O O
S
O
Passed 110 °C
Passed 70 °C
Failed
OH
O O
3HD
O
S
CH3
OH
O O
O
S
3HF
CF 3
12
OAc
OH
O S
O O
5AB
OAc
O
S
O O
OH
6AB
6HB
O S
O O
5HB
O S
O O
CF3
CF3
CF3
CF3

Ea (Thermal) - Ea (Trigger)
(kcal/mol)
10
5
0
-5
-10
-15
5HB
k CAT /k UNCAT
6HB
1
Modeling Results
4HA
8HA
4HB
8HB
25
Passed 110 °C
Passed 70 °C
Failed
11HB
3HA
3HF
3HD
13
3HB
5AB
3AA
3AB
6AB
1360 1425 490

Thermal Stability and Modeled III. Computer Activation Modeling Energy
Uncatalyzed Ea (kcal/mol)
65
55
45
35
25
15
Robust
Unstable
Thermal
8HF
-35 -25 -15 -5 5 15
6HB
8HD
8HB
11HB
8HA
3HD
3HB
14
3HA
3HF
3AB
6AB
7AB
3AA
2AA
Passed 110 °C
Passed 70 °C
Failed
Acid Catalyzed
Uncatalyzed Ea – Trigger Pull Ea (kcal/mol)

PAG + hν
Acid Amplifier (AA)
OH
IV. Lithography
Resist Chemistry and Process
H + H +
H + H+
H +
O O
65/20/15
Polymer
H + H +
H +
H +
H +
Resist Thickness 125 nm
PEB
H +
H + H +
H +
H +
H +
H +
H +
H +
H + H +
H +
H +
H + H +
H +
H + H +
H +
H +
H +
7.5 wt% PAG
H + H +
H +
H +
H +
H +
H +
H +
15
Develop
OH
O O
S
O
3HB
~2 wt% 70 mM
OH -
AA
CF 3
0.5 or 1 wt % Base

Fluorinated AAs Give Better
Sensitivity than Nonfluorinated
E 0 (mJ/cm 2 )
4
3.5
3
2.5
2
1.5
1
0.5
Process:
Tool: BMET
7.5 wt% PAG
No AA
10X
Faster
5X
Faster
0
0.05 0.1 0.15 0.2 0.25 0.3
PAB: 130˚C / 60
PEB: 130˚C / 90
Develop: 45 sec
[Base]/[PAG]
O O
16
AA-1A
O O
AA-1B
O
O S
O
O
O S
O
310 mM AA
7.5 wt%
8.8 wt%
CH 3
CF 3

Fluorinated Tosic Acid Shows Better Controlled
Acid Diffusion than Tosic Acid
O O
Ec ≡ Critical Dose
Dose resist starts to clear
outside the open frame
O
O S
CH3 1A O
1B
Base
(wt %)
0.35
0.5
0.8
1.1
1.1
1.2
Ec E0
1A 1B
O O
6.8
> 3.5*
> 1.9*
O
O S
O
*Did not reach Ec
CF 3
Using AA-1A
2-3 wafers cleared completely
Diffusion
Issue?
17
Ec =

# of molecules/cm 2 X 10 14
14
12
10
8
6
4
2
0
Outgassing vs. Dose
6HB
8HB
3HF
3HB
2 3 4 5 6 7
Dose (mJ/cm 2 )
18
No AA
6AB
Outgassing increases with dose as expected

70 mM
Normalized
Film Thickness
1
0.8
0.6
0.4
0.2
OH
Acid Amplifiers Improve Sensitivity
And Are Not Photosensitive
Eo = 1.6 mJ/cm 2
0
0.1 1 10
Tool: AMET
Base 0.5 wt %
PAB 110 °C / 60 s
PEB 110 °C / 60 s
O(p-CF 3 Ts)
Dose (mJ/cm 2 )
Control
No Acid Amplifier
Eo = 6.4 mJ/cm 2
Normalized
Film Thickness
1.2
1
0.8
0.6
0.4
0.2
0
AA resists without PAG
No change in dissolution
rate ≤ 20 mJ/cm 2
OH
19
OA c
O(p-CF 3 TS)
O(p-CF 3 Ts)
OH
OAc
O(p-CF 3 TS)
1 10
Dose (mJ/cm 2 )
OTs

Effect of Trigger
and Acid Precursor No AA
60 nm L/S
Acid Precursors:
-CF 3 gives better sensitivity,
LER and exposure latitude
E size (mJ/cm 2 )
LER (nm)
Z-Parameter
Triggers: -OH vs. -OAc
-OH gives better sensitivity
than -OAc
Process:
Tool: BMET
Base 0.5 wt%
70 mM AA
PAB: 130˚C / 60
PEB: 130˚C / 90
Develop: 45 sec
7.6
4.0
26
E size (mJ/cm 2 )
LER (nm)
Z-Parameter
O
OH
20
O
O
O
O
S
O
5.4
4.7
26
O
S
O
3.5
9.1
63
CH 3
CH 3
O
OH
O
O
O S
O
O
4.9
4.2
19
O
S
O
1.9
7.9
26
CF 3
CF 3

Esize (mJ/cm 2 )
Secondary-Trigger
Acid Amplifier
20
15
10
5
0
AA Loading
0 0.05 0.1 0.15 0.2 0.25
Tool: BMET
Base 1 wt %
PAB 110 °C / 60 s
PEB 110 °C / 60 s
50 nm
Lines/Spaces
6.7 wt%
AA Loading (mol/kg)
LER (nm)
OH
21
O
O
S O
Increased sensitivity without penalty to LER.
8
7
6
5
4
3
2
1
0
50 nm
Lines/Spaces
AA Loading
CF 3
6 8 10 12 14
Esize (mJ/cm 2 )

EL & Z-Parameter O
O
Exposure Latitude (%)
30
25
20
15
10
5
0
Tool: BMET
Base 1 wt %
PAB 110 °C / 60 s
PEB 110 °C / 60 s
50 nm
Lines/Spaces
AA Loading
6 8 10 12 14
Esize (mJ/cm 2 )
Z-parameter (10 -8 mJ nm 3 )
22
OH
Despite some loss in exposure latitude,
Overall gains in Z-parameter quite strong.
30
25
20
15
50 nm
Lines/Spaces
S O
AA Loading
CF 3
0 0.05 0.1 0.15 0.2 0.25
AA Loading (mol/kg)

No AA
With AA
Tool: BMET
Base 1 wt %
PAB 90 °C / 60 s
PEB 90 °C / 60 s
Acid Amplifier: Improved Image Quality
Resolution
40 nm 38 nm 36 nm
E size (mJ/cm 2 )
LER (nm)
21.7
8.6
9.4
Esize (mJ/cm 16.6
4.9
2 )
LER (nm) 5.8
23
32 nm 30 nm
OAc
CF 3
O
S
O O 6AB

Improved Combined Performance
Z-Parameter = (Resolution) 3 x (LER) 2 x Esize
LER 2 (nm 2 )
100
80
60
40
20
Z = 54
OAc
O S
OH
CF 3
O O
S
O
3HB
CF 3
AAs Improve
Z-Parameter
No AA
Z = 74
O O Z = 25
0
0 0.5 1 1.5 2 2.5
Half Pitch 3 X Esize (10 -8 mJ nm)
24

Kinetics
Lithography
• Fluorinated acids give better
performance than non-fluorinated acids.
• No outgassing problems.
V. Conclusions
• Added base allows the comparisons between catalyzed and uncatalyzed
reactions.
• AA triggers significantly modify reactivity of AAs.
Modeling
• Predictions of the chemical reactivity.
Diffusion vs.
Catalysis
Acid Amplifiers are Capable of Simultaneously Improving
Resolution, LER and Sensitivity in EUV Resists
25
H +
H +
P

Group Members
Brian Cardineau
ROX Team
Greg Denbeaux
Acknowledgments
Financial Support from:
Intel Corporation
Additional Help From
Todd Younkin
Wang Yueh
Steve Putna
AMET and BMET Teams
Thanks to duPont for supplying polymers.
26