s5.2_buitrago
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Elizabeth Buitrago1, O. Yildirim2, R. Fallica1, Andreas Frommhold3, C. Verspaget2, N. Tsugama2,
R. Hoefnagels2, G. Rispens2, M. Meeuwissen2 M. Vockenhuber1 and Y. Ekinci1
1Paul Scherrer Institute, Switzerland 2ASML, Netherlands
3University of Birmingham, UK
The road towards single digit nanometer resolution
patterning in mass production: State-of-the-art EUV
resists platforms
Outline
EUV Interference lithography
XIL-II: EUV-IL tool at PSI
Diffraction grating mask fabrication
EUV resist challenges
State-of-the-art resist platforms:
Positive tone organic chemically amplified resist (CAR)
Negative tone Sn-based resist
Negative tone chemically amplified molecular resist
Conclusions
Slide 2
EUV-IL
XIL-II beamline at Swiss Light Source (SLS):
EUV lithography: 13.5 nm wavelength
Undulator source:
Spatially coherent beam
Temporal coherence: Δλ/λ=4%
Diffractive transmission gratings written
with EBL on S3N4 membranes (~100 nm)
Diffracted beams interfere
Interference pattern printed in resist
Slide 3 m
gp
2sin2
p: period on wafer
g: grating period on mask
m: diffraction order
Advantages of EUV-IL
Stable source: Swiss light synchrotron source (SLS)
Stable interferometer
Infinite depth of focus: Mask-to-wafer (0.3-10 mm)
High resolution:
Theoretical limit = 3.5 nm
Current limit = 7 nm modulation down to 6 nm
Limited by resists and mask writing/quality
Well defined image: pitch independent areal image
Large area for cross-section analysis
Low-cost technique for resist testing
Slide 4
Large Scale Facility with Nanotechnology Infrastructure
Slide 5
Swiss Light Source Laboratory for Micro and Nanotechnology
XIL-II: EUV-IL@SLS
XIL-II: EUV-IL @ PSI
Slide 6
On-site clean room:
Spin-coater, wet-bench, hot-plates, microscope,
developer, optical thickness measurement
In clean room environment with amine filters.
Control
room
Process
room
Exposure
room
Mask Fabrication
Slide 7
direct patterning
two lithography steps
relatively fast, simple process
Silicon nitride membrane, 100 nm
Electron beam lithography HSQ gratings
Masking gratings with PMMA
Cr/Au seed evaporation and liftoff
Au electroplating of photon-stop
Si Si 3 N
4 HSQ PMMA Au
(Fallica et al., MNE 2015) Mask: 11, 12, 13, 14, 16, 18 nm HPs
EUV Chemically Amplified Resist (CAR)
Challenges-Future Resolution (R, HP in nm), line width roughness (LWR, 3σ in nm) and sensitivity
(S, dose in mJ/cm2) cannot be improved simultaneously
RLS trade-off
Higher photon density better LWR high dose (S)
Small Blur better resolution (R) high dose (S)
Larger Blur lower roughness (L) loss of resolution (R)
Low power EUV sources high sensitivity resists required to get high throughput
CARs research and development still dominate, impending need for further R&D and
exploration of state-of-art resist platform alternatives
XIL powerful method in development of EUV resists (CAR and non-CAR)
Different state-of-art EUV resists platforms tested under same process conditions (Mask, UL, resist
thickness, etc., when possible)
Slide 8
Slide 9 Different CAR Resists Compared, HP= 16 nm
HP=16nm-UL1(15nm thk), R1(20nm thk)
HP=16nm-UL1(15nm thk), R2(25nm thk)
HP=16nm-UL1(15nm thk), R3(25nm thk)
HP=16nm-UL1(15nm thk), R1(25nm thk)
29.8mJ/cm2 32.7mJ/cm2 34.5mJ/cm2 36.0mJ/cm2 37.9mJ/cm2 39.6mJ/cm2 41.7mJ/cm2 43.5mJ/cm2 47.8mJ/cm2
36.4mJ/cm2 38.1mJ/cm2 40.0mJ/cm2 41.9mJ/cm2 44.0mJ/cm2 46.1mJ/cm2 48.4mJ/cm2 50.7mJ/cm2
19.4mJ/cm2 20.2mJ/cm2 21.4mJ/cm2 22.3mJ/cm2 23.5mJ/cm2 24.5mJ/cm2 25.8mJ/cm2 26.9mJ/cm2
34.6mJ/cm2 36.2mJ/cm2 38.0mJ/cm2 39.8mJ/cm2 43.8mJ/cm2 46mJ/cm2 50.6mJ/cm2 48.1mJ/cm2
High exposure latitude (EL) for both HP 16 and
18 nm ≥ 24% for all CAR resists
Comparable Z-factors @ 25 nm LRS trade-off
(figure of merit)
UL1R3 has smallest BE = 21mJ/cm2
Name BE (mJ/cm2) EL (%)
LWR (nm) z-factor
UL1R1-25nm 38.4 34.1 6.6 3.4E-08 UL1R1-20nm 43.4 27.4 8.7 6.7E-08 UL1R2-25nm 43.0 24.0 6.4 3.6E-08 UL1R3-25nm 21.0 26.5 6.2 1.6E-08
𝑍 = 𝐵𝐸 × 𝐿𝐸𝑅 2 × 𝐻𝑃 3
Slide 9
CARs 14 and 13 nm HP comparison
Slide 10
HP=13nm-UL1(15nm thk), R1(20nm thk)
HP=13nm-UL1(15nm thk), R2(25nm thk)
HP=13nm-UL1(15nm thk), R3(25nm thk)
HP=13nm-UL1(15nm thnk), R1(25nm thk)
36.6mJ/cm2 38.3mJ/cm2 40.3mJ/cm2 42.1mJ/cm2
37mJ/cm2 38.8mJ/cm2 42.7mJ/cm2 47mJ/cm2
20.7mJ/cm2 21.6mJ/cm2 22.8mJ/cm2
44mJ/cm2
35mJ/cm2 36.9mJ/cm2 38.4mJ/cm2 40.5mJ/cm2
Well resolved patterning down to 13 nm for all CARs.
Small EL ≥ 4.5% @ HP14 for all highly performing CARs
tested and up to 9.7% (UL1R3)
UL1R3 has smallest BE = 22.6mJ/cm2, low LWR (6.7nm)
and high EL down to 14 nm HP (9.7%)
Small EL (3-6%) @ HP13 nm for all except for UL1R3
due to significant pinching, necking and pattern collapse.
UL1R1 @ 20 nm thickness has high EL≥6.5% for
HP=13nm but LWR is high = 11.3 nm
Elevated LWR values also due to bad SEM contrast
extremely thin resist layers
Name HP BE (mJ/cm2) EL (%)
LWR (nm) z-factor
UL1R1-25nm 14 40.1 4.0 7.5 3.1E-08 UL1R1-20nm 14 43.5 8.7 9.6 5.6E-08 UL1R2-25nm 14 44.4 4.5 7.1 3.0E-08
UL1R3-25nm 14 22.6 9.7 6.7 1.4E-08 UL1R1-25nm 13 47.5 3.2 7.9 3.2E-08 UL1R1-20nm 13 58.2 6.5 11.3 8.1E-08
UL1R2-25nm 13 64.5 6.1 8.6 5.2E-08 UL1R3-25nm 13 24.8 0 6.1 1.0E-08
11nm HP, different CARs- Ultimate resolution
Slide 11
HP=11nm-UL1(15nm thk), R1(20nm thk)
HP=11nm-UL1(15nm thk), R2(25nm thk) HP=11nm-UL1(15nm thk), R3(25nm thk)
HP=11nm-UL1(15nm thk), R1(25nm thk)
56.7mJ/cm2 51.2mJ/cm2
40.8mJ/cm2 30.4mJ/cm2
All resists @ 25 nm thickness
are resolved with some
pattern collapse and bridging
down to 11 nm HP.
UL1R1 @ 20 nm thickness
only modulation can be seen
at the dose range tested
Patten collapse still limits
resolution and EL for CARs
Negative tone Chemically Amplified
Molecular Resist: xMT
Slide 12
Resin: Polymer matrix with functional
side-groups, the bulk of the resist
Photo acid generator (PAG):
photoactive compounds that produce
an acid product after interaction with
secondary electrons/photons
Quencher: base neutralizes acid,
improves contrast of the resist (~2%
of PAG)
Solvent: ~90% removed by bake
Crosslinker: to form crosslinks with
the xMT molecule as it cannot do this
by itself. Historically this comes from
previous fullerene-based resists that
are very hard to functionalize with
epoxies
(Frommhold et al., SPIE 2015) Cleaner formulation process, does not require extensive purification
processes to obtain good resists in comparison to Fullerene based resist.
Molecular Resin Crosslinker
PAG Quencher
xMT-0614:
0.2:2:1 xMT:CL06-14:TPS SbF6 PAG + 5% Quencher
Slide 13
PAG Quencher Molecular Resin (xMT) CL06-14
TPS SbF6: triphenyl sulfonium hexafluoroantimonate
xMT-0801:
0.2:2:1 xMT:CL08-01:TPS SbF6 PAG + 5% Quencher
Molecular Resin (xMT) CL08-01 PAG Quencher
(Frommhold et al., SPIE 2015)
2 different crosslinker (CL) molecules tested, same mixing ratio
HP=16nm-Carbon Underlayer(15nm thk)-xMT-0801(25nm thk)
HP=16nm-Carbon Underlayer(15nm thk)-xMT-0614(25nm thk)
Slide 14
Molecular Resists (xMT) compared HP=16 nm
34.3mJ/cm2 35.9mJ/cm2 37.3mJ/cm2 39.2mJ/cm2 40.7mJ/cm2 42.7mJ/cm2 44.4mJ/cm2 52.7mJ/cm2 30.3mJ/cm2
26.4mJ/cm2 28.8mJ/cm2 29.8mJ/cm2 31.4mJ/cm2 32.5mJ/cm2 34.2mJ/cm2 35.4mJ/cm2 38.6mJ/cm2 42.1mJ/cm2
Both xMT materials show well resolved line-spaces down to 16 nm HP.
High exposure latitude (EL) for HP 16 and 18 nm 15% > for both xMT
resists. LWRs as low as 3.1 nm.
xMT-0801 shows low best energy (BE or dose-to-size) ~ 26.6 mJ/cm2
for 16 nm HP. LWRs, overall comparable.
Name BE (mJ/cm2) EL (%) LWR (nm) z-factor
xMT-0614 32.1 17.6 4.3 1.5E-08 xMT-0801 26.6 23.6 5.3 1.2E-08
11nm 12nm HP=14nm
Carbon Underlayer(15nm thk)-xMT-0801(25nm thk)
Carbon Underlayer(15nm thk)-xMT-0614(25nm thk)
Slide 15
Molecular Resists (xMT) compared HP=14 nm and below
xMT-0614 shows well resolved line-spaces down to 12 nm HP with slight
bridging and pattern collapse.
xMT-0801 can resolve down to 12nm HP as well but has prevalent pattern
collapse even at 14 nm HP
xMT-0801 has still lower BE @ 25.9 mJ/cm2 @ 14 nm HP.
No EL <16 nm HP for either due to bridging and pattern collapse
High potential to expand EL down to 11 nm HP features, pattern mitigation
strategy needs to be explored
Great potential for high resolution patterning @ 13 nm HP and below!
13nm 39.5mJ/cm2
11nm 43.2mJ/cm2
12nm 34.9mJ/cm2
30.2mJ/cm2
HP=14nm
13nm 30.9mJ/cm2 41mJ/cm2
36mJ/cm2
Name HP BE (mJ/cm2)
LWR (nm) z-factor
xMT-0614 14 33.4 4.8 1.3E-08 xMT-0801 14 25.9 6.1 1.1E-08 xMT-0614 13 32.5 5.0 8.5E-08 xMT-0801 13 42.7 4.7 1.0E-08 xMT-0614 12 45.2 7.2 2.1E-08
xMT-0801 12 42.9 7.3 2.0E-08
31.6mJ/cm2
Sn-based Resist
Slide 16
Inpria YA
negative tone
organo-oxo molecule
stable after exposure
Sn-based
forms SnO2
high absorption (Sn)
L* = radiation sensitive
ligand
(Fallica et al., MNE 2015)
Sn-based Resist- 16 and 14 nm HP
Slide 17
HP=16nm-YA(25nm thk)
HP=16nm-YA(32nm thk)
30mJ/cm2 35.6mJ/cm2 38.8mJ/cm2 42.3mJ/cm2 46.1mJ/cm2 54.8mJ/cm2 59.7mJ/cm2 70.9mJ/cm2 77.3mJ/cm2
38.6mJ/cm2 42.0mJ/cm2 45.7mJ/cm2 49.8mJ/cm2 54.2mJ/cm2 59.0mJ/cm2 64.2mJ/cm2 70.0mJ/cm2 76.2mJ/cm2
Two different thicknesses of same resist tested (25, 32 nm).
Super high EL >30% down to 14 nm HP nm for thin resist, EL
decreases to ~13.8% for thick resist @ 14 nm HP
BE increases (54.969 mJ/cm2 @ 16 nm HP) with thickness.
But LWR decreases drastically (2.91.4 nm @ 16 nm HP)with
increasing thickness (as expected).
Thickness HP BE (mJ/cm2) EL (%)
LWR (nm) z-factor
25 nm 16 54.9 31.3 2.9 9.3E-09 32 nm 16 68.9 31.4 1.4 2.8E-09 25 nm 14 67.3 31.8 3.0 8.5E-09 32 nm 14 75.2 13.8 1.7 3.0E-09
Sn-based Resist-ultimate resolution
EL reduced to 11.8% for HP 13 nm (25 nm thickness), super high
for this HP.
12 and 11 nm HPs are well resolved and even small EL ~2% is
possible @ 25 nm thickness for 12 nm HP
Even @ 32 nm thickness 12 and 11 nm HP also look very
promising but pattern collapse limits the EL. Slide 18
HP=12nm-YA(25nm thk) HP=11nm-YA(25nm thk)
HP=12nm-YA(32nm thk) HP=11nm-YA(32nm thk) 74.2mJ/cm2 58.0mJ/cm2 63.2mJ/cm2 68.8mJ/cm2 74.9mJ/cm2
58.1mJ/cm2 63.3mJ/cm2 69.0mJ/cm2 75.2mJ/cm2 45.4mJ/cm2 49.4mJ/cm2 53.9mJ/cm2 58.7mJ/cm2 64.0mJ/cm2 69.7mJ/cm2 76.0mJ/cm2
Thickness HP BE (mJ/cm2) EL (%)
LWR (nm) z-factor
25 nm 13 77.7 11.8 3.3 9.3E-09 32 nm 13 85.0 4.1 1.5 2.0E-09 25 nm 12 86.8 2.4 3.6 9.7E-09
Sn-based resist can be
resolved down to 10 nm HP
with minimum pattern collapse
@ 22 nm thickness.
Thickness reduction is feasible
for this resist due to superior
etch resistance.
Low LWR and high EL at HPs ≤
14 nm makes this resist very
interesting for future high
volume manufacturing needs.
Slide 19
Sn-based Resist-ultimate resolution, 10 nm HP
HP=10nm-YA(22nm thk)
* Different mask used for this exposure
Z-factor used as global resist performance figure of merit, measure of the RLS trade-off-relationship
Each state-of-the-art resist platform shows different high performance characteristics: BE, EL, LWR, R, z-values comparable for all resists
Slide 20
Z-factors compared for different state-of-art resist platforms @
different HPs
𝑍 = 𝑆𝑒𝑛𝑠𝑖𝑡𝑖𝑣𝑖𝑡𝑦, 𝐵𝐸 × 𝐿𝐸𝑅 2 × 𝐻𝑃 3
Constant Z intersecting smallest Z per HP
Patterning down to 11 nm and 10 nm HP can be done, several resist platforms need to
be further explored for HVM.
EUV photons can do it
EUV-sensitive materials available (CAR and non-CAR)
Tools available for testing
Each state-of-the-art resist platform shows different high performance characteristics, z-
values comparable for all resists
CAR: UL1R3 (25 nm thk) resist demonstrated to be highly performing with high EL > 9.7%, low BE=22.6
mJ/cm2 and low LWRs ~ 6.7 nm down to 14 nm HP.
Sn-based resist (25 nm thk) also high performing with super high EL down to 13 nm ~ 11.8%, and low LWR
~ 3.3 nm
xMT resist with further optimization to widen EL has potential for 14 and 13 nm HP, has low LWR~5nm and
low BE ~ 35 mJ/cm2
Pattern collapse still limiting performance of most resists research ongoing.
Sn-based resist pattern collapse can be mitigated by use of thinner resist due to superior
etch resistance
Conclusions
Slide 21
Acknowledgments
Slide 22
XIL-II team
Members of LMN and SLS
Collaborators
http://www.psi.ch/sls/xil
We thank all of our resist and underlayer suppliers
Thank you for your attention!
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