Photons, Electrons and Acid Yields in
EUV Photoresists: A Progress Report
Robert Brainard, Elsayed Hassanein, Juntao Li, Piyush Pathak, Tao Wang,
Brad Thiel, Franco Cerrina, Richard Moore, Miguel Rodriguez, Boris Yakshinskiy,
Elena Loginova, Theodore Madey, Richard Matyi, Matt Malloy, Anwar Khurshid,
Andrew Rudack, Patrick Naulleau, Andrea Wüest and Kim Dean
Funded by
College of Nanoscale Science and Engineering
SEMATECH
University at Albany
University of Wisconsin-Madison
Rutgers University
SEMATECH
10/29/07
1
I.
Introduction
II.
Experimental Approach
III.
Results
IV.
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A.
Resists and Test Materials
B.
X-ray Photoelectron Spectroscopy
C.
Molecular Modeling of Spectroscopic Results
D.
EUV Photoelectron Results
Summary
2
I.A. Motivation
We propose that the best
way to beat the RLS
Trade-off is with higher
quantum yield since it will
allow us to go from…
EUV Resists
Must Have Better:
•
Resolution
•
LER
•
Sensitivity
Here
Resolution
(RLS Trade-Off)
Here
to
LER
Sensitivity
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See:
Gallatin RE-8
Naulleau RE-P4
3
…with no penalty to
sensitivity.
Quantum Yield of EUV-2D =
2.1 acids/photon absorbed
Quantum
Yield
≡
Number of Acids Generated
Number of Photons Absorbed
by Resist Film
Kozawa and Tagawa1
determined Φ ≈ 2
Why isn’t more acid created?
PAG
92 eV
EUV
Photon
C, H & O
Polymer
eee-
PAG
PAG
H+
H+
H+
In principle, there is enough energy in an
EUV photon to activate ~20-30 PAGs
1) Kozawa, Tagawa, Kai, Shimokawa J. Photopoly 2007
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Program Objectives:
1. Determine how many electrons are made
and at what energy.
PAG
hν
C, H & O
Polymer
eee-
PAG
PAG
H+
H+
H+
2. Determine the sequential mechanisms:
– Photons Æ Electrons
– Electrons Æ Multiple Daughter Electrons
– Electrons Æ Acids
3.
Ultimately, discover methods for increasing quantum yield
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II. Experimental Approach
Qualitative Description of Exposure Mechanism
hν
e- couples
to the
material
O
OOO
O
= hν
= Polymer
X X X X
O = Specific Atoms
X
X
X
X
A
= e-
B
Electrons lose energy as they scatter:
• Where does the energy go?
• If it excites an atomic orbital,
– Which atom, which orbital?
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O O
6
Probability
= PAG
O
Electron
Trajectory
A
B
ΔE
One possible
energy loss
event
II. Material – Measure - Model
Spectroscopic
Measurements
Resist
Model
Vacuum
Output
hν
e-
Filled
Orbitals
Input
Energy
Empty
Orbitals
hν
e-
Absorbance
PES:
X-Ray
EUV
EELS
Density of
States (DoS)
Map all transitions,
energies and
probabilities
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7
Oscillator
Model
Monte
Carlo
Simulations
II. Generating the Oscillator Model
Electron Energy
Loss Spectroscopy
(EELS)
All Transitions
Photoelectron
Spectroscopy
Absorption
Spectroscopy
Ionization Transitions
eee-
hν
5-12 eV
Optical Transitions
Oscillator
Model
Molecular Modeling
Structure
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Monte Carlo
Simulation
Spectra
8
Electron Energy Loss Spectra (EELS)
e-
e-
“zero loss”
ΔE = 0
Excitation
Transitions
N(ΔE)
Electron
gun
Monochromators
Specimen
Location
Energy loss (ΔE)
Analyzer
μ-metal
magnetic
shields
Channeltron
Spectra will
include all
processes:
12”
12” flange
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9
hν
eee-
e-
eee-
Monte Carlo
Modeling
Oscillator
Model
Thousands of Monte Carlo
Simulations will determine
probabilities of:
•
•
•
•
Trajectory profiles
Identification of
electronic transitions
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Ionization
Excitation
Large–angle scattering
Plasmon creation
III. Results:
Experimental Roadmap
Materials
Published Resist
HomoPolymers
Pure TerPolymer
Advanced Materials
Resist
+ Additive
Resist
Modeling
Electronic
Spectra
Quantum
Yield
EELS,
ABS
PES
EELS,
ABS
PES
EELS,
ABS
PES
EELS,
ABS
PES
SemiEmpirical
Spectral
Model
SE
Spectral
Model
SE
Spectral
Model
SE
Spectral
Model
Key:
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Quantum
Yield
Monte
Carlo
Model
Complete
In Progress
11
Monte
Carlo
Model
III. Results
A. Resists and Test Materials
Published resist formulation2-5
O
O
Pure Polymers
O
Polymer
O
OH
OH
OH
65/20/15
I+
7.5%
Photo-Acid
Generator
(PAG)
O
F3CF2CF2CF2C S OO
O
O
OH
2. J. Roberts et.al. SPIE 61533U (2006)
O
+
N
OOH
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0.5%
Base
12
3. T. Fedynyshyn et.al. SPIE 6519OX (2007)
4. J. Woodward et.al. SPIE 651915 (2007)
5. T. Fedynyshyn et.al. SPIE 651917 (2007)
Quantum Yield Increases
with PAG Concentration
6
0.085
C-Parameter
0.075
0.07
4.5
0.065
4
0.06
Eo
3.5
Quantum Yield
5
2.95
3
0.08
C-Parameter
Eo (mJ/cm2)
5.5
2.5
2.30
2
0.055
3
1.80
0.05
2.5
4
5
6
7
8
9
10
0.045
11
[PAG] (wt%)
Quantum
Yield
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=
1.5
4
5
6
7
8
9
10
11
[PAG] (wt%)
Number of Acids Generated
Number of Photons Absorbed
See Poster RE-P2
for more details
13
# Acids
Generated
= [PAG](1 – e(-CE))(6.02 x 1023)
IIB. X-ray Photoelectron Spectroscopy
(XPS)
C 1s
XPS of
EH-33B-127
4.00E+04
Al Kα
hν
(1486 eV)
3.00E+04
Counts / s
e-
OS-1 Resist
O 1s
O1s
2.00E+04
F 1s
0.00E+00
13d5
1000
Counts / s
100
80
Published Resist
OS-1
60
40
20
O
0
25
0
Binding Energy (eV)
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500
Binding Energy (eV)
XPS Valence Spectra
C-pt 3
of OS-1
Resist
50
EUV
F1s
1.00E+04
120
C1s
OH
14
O
0
XPS of Polymer Components
XPS of polymer components assists in identification of spectral features
Ter-Polymer
π ring
O 2s in
PHS & TBA
PHS/TBA
structure in
PS & PHS
O
PHS
O
Sty
Counts/sec (a.u.)
OH
Ter-polymer
O
O
OH
PHS/TBA
40
35
30
25
20
15
10
5
0
Binding Energy
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OH
PHS
PS
IIB. X-ray Photoelectron Spectroscopy
Characterizing Resist Components
OS1 Resist
F 2s
O 2s
15% PAG
C 2s
7.5% PAG
Polymer
Counts/sec (a.u.)
C 2p
I+
O
F3CF2CF2CF2C S OO
Resist
15% PAG
7.5% PAG
S?
40
35
30
25
20
15
10
5
0
O
Binding Energy (eV)
Polymer
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OH
O
Spectroscopic Modeling of
Styrene and Hydroxystyrene
Styrene
Hydroxy-Styrene (PHS)
HOMO: -8.2 eV
LUMO: 0.87 eV
LUMO: 0.78 eV
Empty Orbitals
HOMO: -8.6 eV
Filled Orbitals
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Filled Orbitals
Empty Orbitals
OH
IID. EUV Photoelectron Results
Energy of Photoelectrons Produced by EUV Photons
EUV hν
EUV spectrum of
High PAG resist (15% PAG)
e-
hv = 92 eV
High energy
photoelectrons
resulting from direct
photoionization
processes
valence band
XPS Intensity (arb. units)
XPS Intensity (arb. units)
Low energy secondary
electrons resulting from
energy cascade processes
×103
1 .5 h r
0 .5 h r
0hr
60
70
80
K in e tic E n e rgy (e V )
0
20
40
60
80
K in e t ic e n e r g y ( e V )
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100
90
IV. Summary
Investigating the mechanism by which EUV photons are converted to
multiple photoelectrons.
Determined three resist quantum yields: 1.8, 2.3, 3.0
Evaluating and modeling resists using X-ray and EUV photoelectron
spectroscopy.
Building a high-resolution EELS instrument to characterize all allowed
electronic transitions available to EUV photoelectrons.
Developing a Monte Carlo Model for the EUV exposure mechanism that
should allow us to determine:
- Number and energy of photoelectrons
- Material components that influence quantum yields
- Effect that new elements and new chromophores have on exposure
mechanism and quantum yield.
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Acknowledgements
Sematech for financial support
duPont Electronic Materials for
supplying polymers
Advanced Materials Research Center, AMRC, International SEMATECH Manufacturing Initiative, and
ISMI are servicemarks of SEMATECH, Inc. SEMATECH, the SEMATECH logo, Advanced Technology
Development Facility, ATDF, and the ATDF logo are registered servicemarks of SEMATECH, Inc. All
other servicemarks and trademarks are the property of their respective owners
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