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EUV Radiation Chemistry Fundamentals: Novel Experiments and Simulations
Molecular Foundry D. Frank Ogletree, Paul Ashby, Kristina Closser, Yi Liu, David Prendergast, Deirdre Olynick
CSD/ALS Musa Ahmed, Oleg Kostko, Bo Xu, CXRO Suchit Bhattarai, Patrick Naulleau,
Lawrence Berkeley National Lab Berkeley CA USA
EUVL 2015 Maastricht D. Frank Ogletree LBNL
Limitations of EUV Resists ♦ Sensitivity ♦ Control of Line-edge Roughness ♦ Resolution for sub-10 nm Patterning
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We need to be able to LOOK at what is happening to UNDERSTAND new radiation chemistry
EUVL 2015 Maastricht D. Frank Ogletree LBNL
The Problem
“…it is technically nearly impossible to directly observe the reactions induced in ultrathin resist films
by 92.5 EUV radiation…”
Kozawa & Tagawa EUV CAR review Jpn J Appl Phys 2010
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EUVL 2015 Maastricht D. Frank Ogletree LBNL
Our Program ♦ “New” ways to THINK about EUV reactions
• Concepts from the Electron Spectroscopy and Radiation Biology communities that are less familiar to the Lithography community
♦ New ways to LOOK at EUV reactions • Single Molecule Gas-Phase Experiments at X-ray
Synchrotrons • Follow individual reaction steps in detail
♦ New ways to UNDERSTAND EUV Reactions • ab-initio theoretical calculations of: • Molecular Photoemission cross-sections • Post-excitation Auger Relaxation processes • Molecular Dynamics of post-excitation events
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EUVL 2015 Maastricht D. Frank Ogletree LBNL
THINK: Excitation and Relaxation
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Step 1 Photoionization
M + hν è M+ + e-
e- γ
M+ Step 2 Electronic Relaxation
Auger process ? M+ è M++ + e-
e-
M++
Step 3 Atomic Relaxation
Fragmentation? M+ è R1�+ + R2�
R1�+ R2�
e-
M+
e-
e- Step 4
Inelastic Scattering
M + e- è M+ + 2 e-
and more steps…
EUVL 2015 Maastricht D. Frank Ogletree LBNL
THINK: Molecular Photoemission
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EUV can ionize any molecular orbital
Methanol Photoelectron energy between 57 and 80 eV
Molecules with N, O, F have
2s orbitals bound by 30-40 eV
accessible 4d levels give atoms like Sn, Sb, Te, I much larger EUV
cross-sections, and make Auger relaxation likely
0 eV
10 eV
20 eV
30 eV
40 ev
Photoemission spectrum of gas-phase methanol CH3OH
Kai Siegbahn
1969
14 valence electrons in 7
molecular orbitals give 7 XPS peaks
#1
EUVL 2015 Maastricht D. Frank Ogletree LBNL
THINK: Molecular Relaxation
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0 eV
10 eV
20 eV
30 eV
40 ev
#1 Suppose a deep MO is ionized,
ejecting a relatively slow e- #2
The molecule is left in a highly excited state, and the
valence electrons adjust within 1 fs
An Auger process can fill the deep core hole, ejecting a very slow electron, leaving the molecule doubly ionized
#2
The molecule is still in a highly excited state, it may
undergo a second Auger process or fragment…
#3
EUVL 2015 Maastricht D. Frank Ogletree LBNL
LOOK: Gas-phase Photoemission
Electron energy and angular distributions calculated from maps
Auger and Photo electrons have different
distributions 8
Velocity Map Electron Imaging Spectrometer
VMI trajectories
#1
#2
EUVL 2015 Maastricht D. Frank Ogletree LBNL
LOOK: Synchrotron Mass Spec
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Ionized Molecules and Fragments are
detected by time-of-flight MS
Variable Energy Photons or Electrons excite
gas-phase molecules
#1 #4
Experiment Details: Poster P-RE-10 Oleg Kostko, Bo Xu
EUVL 2015 Maastricht D. Frank Ogletree LBNL
LOOK: Model Compounds
Advanced resist materials will also be investigated • Brainard Group, SUNY, Inpria Inc.
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2-methylphenol 4-chloro-
2-methylphenol 4-iodo-
2-methylphenol 4-bromo-
2-methylphenol
Explore role of high cross-section
4d elements (iodine)
Nanoparticle Organic
Hybrid Resists
Metal Organic Resists for EUV
(MORE)
EUVL 2015 Maastricht D. Frank Ogletree LBNL
LOOK: VMI Electron Spectra
0 10 20 30 40 50 60 70 80 900
1x106
2x106
3x106
4x106
4-Iodo-2-methylphenol
I 4d
Auger electronsInte
nsity
Binding energy (eV)
30 eV 45 eV 60 eV 75 eV 85 eV 92 eV
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As x-ray energy increases toward EUV, I 4d levels increase cross section, clear signature of Auger relaxation
#1 #2
EUVL 2015 Maastricht D. Frank Ogletree LBNL
LOOK: VMI Electron Spectra
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Calculated energies of I-related orbitals (2e- except for 4d with 10)
Kinetic Energy [eV]
0 eV
10 eV
20 eV
30 eV
40 ev
50 eV 4d
5s
σ π
π* 5p
I 4d is excited, one 92 eV photon in, one 35 eV photoelectron out
~ 55 eV potential energy remains!
#2
92 eVAuger
EUVL 2015 Maastricht D. Frank Ogletree LBNL
LOOK: VMI Electron Spectra
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0 eV
10 eV
20 eV
30 eV
40 ev
50 eV 4d
5s
σ π
π* 5p
#2 35 eV photoelectron
16 eV Auger
6 eV Auger
EUVL 2015 Maastricht D. Frank Ogletree LBNL
LOOK: Molecular Fragmentation
PHOTONS ELECTRONS
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(I-MePh)+ I� + (MePh)+
I� + R� + R+
ring-breaking events
#3
EUVL 2015 Maastricht D. Frank Ogletree LBNL
UNDERSTAND: Ionized Molecules
I 4d level is ionized, Molecular orbital density
increases (blue) or decreases (green)
This generates forces on the
atoms (red arrows) and fragmentation, (probable
loss of I radical)
other orbitals produce OH radicals or stable ions
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#3
Theory Details: Poster P-RE-12 Kristi Closser
EUVL 2015 Maastricht D. Frank Ogletree LBNL
Condensed Resist Films?
♦ Photoemission and Auger relaxation processes are almost unchanged • dielectric environment reduces binding
energies ~ 4 eV • sharp lines are broadened
♦ Electrons are elastically scattered before leaving the electric field of the photo-ion • Photoelectrons may be recaptured by primary
or other ions
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EUVL 2015 Maastricht D. Frank Ogletree LBNL
Condensed Resist Films?
♦ Inelastic electron scattering • plasmon excitation in condensed films
(~ 20 eV) • followed by decay to hot electrons, which
interact with molecules ♦ Molecular fragmentation changes • fragments are trapped in polymer matrix,
may recombine or generate secondary reactions…
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EUVL 2015 Maastricht D. Frank Ogletree LBNL
Condensed Phase Resist Studies
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Nanoparticles ≥ 50 nm can be coated with resist films of varying thickness and analyzed by VIM and MS
Dynamically-coated size-selected particles are analyzed
EUVL 2015 Maastricht D. Frank Ogletree LBNL
Summary and Outlook
♦ New ways to THINK about EUV
♦ New tools to LOOK at EUV molecular processes
♦ Theoretical methods to UNDERSTAND these processes
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#1 #3 #2
#4
EUVL 2015 Maastricht D. Frank Ogletree LBNL
Summary and Outlook
♦ We have confirmed that 4d Iodine, has a higher EUV cross-section
♦ One EUV photon generates multiple secondary electrons in the PRIMARY event
♦ Our theoretical and experimental tools can be applied to more “realistic” resist molecules
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EUVL 2015 Maastricht D. Frank Ogletree LBNL 21
This work was supported by the LBNL Laboratory Directed Research and Development Program. Portions of this work were carried out at the Molecular Foundry and at the Advanced Light
Source under U.S. Department of Energy contract No. DE-AC02-05CH11231