Nanofabrication using thermal probes

cQOM, February 2013
Nanofabrication using thermal probes
Urs Duerig, IBM Research – Zurich
Thermo-Mechanical Patterning:
Microfabrication:
Directed Assembly:
Armin Knoll, Felix Holzner, Philip Paul, Urs Duerig
Ute Drechsler, Michel Despont
Cyrill Kuemin, Heiko Wolf
Polymer Synthesis:
Jim Hedrick (IBM Almaden)
Urs Duerig, [email protected]
Agenda
IBM Research - Zurich
State of the art direct write lithography
e-beam lithography
AFM methods
Thermal Scanning Probe Lithography
Resolution and throughput
In-situ metrology
3D nanofabrication
Applications
Directed particle assembly
High resolution patterning of Si
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IBM Research - Zurich
1956 in Adliswil
Since 2011
1963 in Rueschlikon
Binnig-Rohrer Nanotechnology Center
Private-public partnership with ETHZ
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Urs Duerig, [email protected]
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Urs Duerig, [email protected]
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Urs Duerig, [email protected]
Direct Write Lithography Using Thermal Probes
Writing relief structures
into polymer films using
hot Si tips
Si tip at 900oC
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Urs Duerig, [email protected]
E-Beam Lithography
Challenge: High energy of incident e-:
Monte Carlo simulation of electron scattering in resist
on a silicon substrate at a) 10 kV and b) 20 kV.
D. F. Kyser and N. S. Viswanathan, J. Vac. Sci. Technol. 12, 1305 (1975).
Proximity effect
20 kV electron beam, positive resist
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Courtesy of Leica Lithography Systems Ltd.
SPIE Handbook of Microlithography, Micromachining and Microfabrication
Volume 1: Microlithography
© 2009 IBM Corporation
Scanning Probe Lithography (SPL)
STM (Tunneling Microscope)
Local Anodic Oxidation
Field-induced Deposition
Garcia et al., Nano Lett. 2007, 7, 1846.
Dagata 1990
A. Fuhrer et al., Nature 2001, 413, 822.
IBM Research Almaden, Don Eigler, 1990
Nano-Scratching
Dip-Pen Nanolithography
Main issues of SPL:
- only specific applications
- slow
- contact method
Dong et al., small, 2010
Mirkin et al., Science 1999, 283, p661
IBM
© 2009 IBM Corporation
Nano/Micro Fabrication Landscape:
Throughput – Resolution – Scaling
- Single lever throughput competitive to e-beam
- Massive parallelism required for mask/volume
production
High throughput
mask lithography
optical
VSB
Chemically amplified resists
EUV?
(NIL?)
parallelization
?
?
Low throughput
mask-less lithography
electron beam
(E-beam)
probe based
Adapted from:
C. Marrian, D. Tennant, J. Vac. Sci. Technol., A, 2003, 21, S207
S.V. Sreenivasan, MRS Bulletin, Sept. 2008;
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Mask production: Wafer scale litho:
0.005 cm2/s
1 – 20 cm2/s
1 mask in 8h
5 – 100 wph
3 µm
© 2009
2 IBM Corporation
5ˣ104 µm
/h
Thermal probes for patterning
IBM’s probe storage project:
- Density: 15 nm feature size
- Rate: 1 µs per probe
- Tip endurance: 1010 bits corresponding to 1 km of travel
- Scalable using probe arrays
( 64 x 64 probe array fabricated)
Physical nano-indentation (volume preserving)
No chemical modification
Probe patterning by local evaporation:
- direct write
- creates relief in polymeric resist
- pattern can be used as etch mask
- in-situ inspection
Need high temperatures to overcome
activation barriers on a 1 µs time scale
excess ΔT ~ 200 – 300 oC for an acceleration by 108
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© 2009 IBM Corporation
Thermal probe technology for µs – time scale patterning and
imaging
10 µm
write resistor
hinge
read resistor
capacitive platform
Current design:
•Stiffness ~ 0.1…1 N/m
•Resonance frequency ~ 50..150 kHz
•Thermal time constant ~ 5 µs
•Apex radius of tip ~ 5 nm
•Tip height ~ 500 nm
tip
Thermo-mechanical writing:
• Efficient electrostatic actuation: up to 1 µN
• Resistive tip heating: up to 700 C
• no feedback => fast
Thermo-resistive reading:
• Read resistor heated to ~ 200C
• Sensitivity ~ 0.1 nm @ 50 kHz BW
• Measures height and not lever deflection
• in contact
• no feedback => fast
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hot heater  low current
cold heater  high current
© 2009 IBM Corporation
Early attempts using a Diels-Alder polymer resist
Reversible chemical cross-links:
Thermal decomposition
DA activation energy 2.8 eV
High tip temperatures and long
contact times needed
100 nm
B. Gotsmann et al, Adv. Funct. Mater 16, 1499 (2006).
Diels Alder chemistry: chemical bonds
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polymer indentation (PMMA, SU8)
© 2009 IBM Corporation
Material Strategy
Direct removal of organic
material
– Versatile
– Compatible to
CMOS
– In-situ inspection
Molecular glass
Unzip polymer
OH
HO H C
3
n
OH
700 C, 2-15 µs
CH3
HO
CH3
OH
HO
n
Polyphthalaldehyde (PPA)
Efficient thermally
activated process
– Thermal process
active at ~ 150 C
• Mw = 715 g/mol
• physical intermolecular bonds
• complete molecules
are removed
• thermodynamically
unstable backbone
• synthesis at -78 °C
• unzips into monomers
upon bond breakage
Stability
– Imaging and etching
• H-bonds: Tg 126 °C
• Tg = Tunzip ≈ 150 °C
A. De Silva; J. Lee, X. André, N. Felix,
H. Cao, H. Deng & C. Ober
Chem. Mater., 20, 1606 (2008)
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H. Ito, C. G. Willson,
Technical Papers of SPE
Regional Technical Conference
on Photopolymers, 1982, 331
© 2009 IBM Corporation
Thermo-Mechanical Direct Write Patterning
Principle
 Local thermo-mechanical removal of organic resist
using a heated tip (nano-chisel)
 Pattern defined as Bitmap
 Heated tip is pulled into contact by electrostatic force
at each pixel
 Organic resist material is locally decomposed and
evaporated
5.5 µs pulses
Temperature (°C)
400
8 7
0 9
11 1
500
6
pix
300
patterning
regime
el d
ept
h
(nm
)
5
200
mechanical
indentation
4
3
100
Evaporation
Patterning
2
1
Embossing
Data storage
50
100
22
200
300
400
Force (nN)
500
600
Materials challenge:
- low evaporation temperature
- chemically inert fragments
- efficient depolymerization
Urs Duerig, [email protected]
Molecular Glass: Patterning Results
High resolution patterning
2 nm
-10 nm
15 nm half pitch line pattern
6 nm deep lines
no proximity effects
large area patterning
uniform patterning depth
10 µs per pixel writing time
1µm
Ma
te
rial
c
in b ontain
ed
ox
Tip after patterning
several fields:
same scale:
100nm
Pitch 29 nm
8 nm depth
Parameters:
# Pixels: 4 104
Heater temperature: 300°C
Load force: 80nN
Pulse duration: 5.5µs
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0.2 µm3
SEM of the tip
after 2∙105 written pixels
© 2009 IBM Corporation
Self Amplified Depolymerization Polymer
Phthalaldehyde (“unzip”) polymer
Mw = 36 kDa
n ~ 200
Tdec~ 150 C
O
ROH +
(n+1)
H
final polymer
stabilized by
end groups
Th = 700 C;
2-14 us
O
H
RO
IMes
THF/-78°C
O
O
n
O
OH
NEt3
O
RO
O
n
O
O
O
O
Cl
≥ RT (thermodynamically unstable backbone)
Polymer synthesis by
J. Hedrick, ARC
H. Ito, IBM
Self amplified depolymerization
- thermally activated breaking of
one single bond in the backbone
 spontaneous unzipping of the entire polymer chain
 n x amplification of the effect of the thermal stimulus
H. Ito, C. G. Willson,
Technical Papers of SPE Regional Technical Conference
on Photopolymers, 1982, 331
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Urs Duerig, [email protected]
Adv. Mater. 22, 3361-3365 (2010)
700
10
650
0
600
depth / nm
τpulse = 5.5 μs
Ts,h ~ 580 C
550
1
temperature (°C)
Extremely efficient 3-D patterning
500
3
4 5
6
2
5
450
1
400
4
100
3
200
300
force ( nN))
400
500
TH = 700ºC
tF = 14 μ s
-10
-20
-30
-40
-50
-60
0
1
2
ΔF / nN
3
Patterning depth
controlled by
cantilever deflection
and not by polymer
compliance
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Black line: Static lever deflection (k=0.1 N/m)
Tip endurance:
3×106 written pixels = 40 µm3
2 µm
500'000 pixels, 143 s writing time,
lateral scale: 1 : 2'000'000'000'000
vertical scale: 1 : 125'000'000'000
(8 nm / 1000 m)
Comparison:
V(tip cone) ≈ 0.13 µm3
no contamination
Urs Duerig, [email protected]
3-D patterning: Image gallery
300 x 600 pixels
Patterning depth ~ 50 nm
Appr 40” patterning time
Urs Duerig, [email protected]
Nanotechnology 22 275306 (2011)
High speed writing
Large and small
scale fidelity and
uniformity
15 nm pixel size
500 kHz, 7.5 mm/s
ca. 5 nm deep
880X880 pixels
Read: 10x slower
reveals distortions / no
time constant
compensation
~1 Mpixels
<12s write time
No errors
<1min overall
turnaround
Urs Duerig, [email protected]
Application: Particle Placement
Collaboration w. H. Wolf, C Kuemin, IBM-Zurich
Process flow:
- Write shape
matching structures
Ttip ˜ 350°C
90 nm
substrate
Design:
- V-shaped profiles => centering of particles
- Arms designed to hold 3 rods
- Arms written at different width to study
confinement effects
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F. Holzner, et al , Nano Lett. 11, 3957 (2011).
© 2009 IBM Corporation
Application: Particle Placement
Process flow:
Phase images
Ttip ˜ 350°C
substrate
- Capillary assembly
of Au nanorods
(25 x 80 nm)
Tevap = 215°C
- Evaporate template
Experiment:
20 fields with 30 micron distance
Capillary assembly: Moving suspension droplet
across the written fields
Evaporation => increasing concentration =>
high yield assembly
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Topography
Red: SEM outline after
PPA decomposition
F. Holzner, et al , Nano Lett. 11, 3957 (2011).
© 2009 IBM Corporation
Application: Particle Placement
Result:
 Accurate (σ=10 nm)
Ttip ˜ 350°C
substrate
 and directed
(entire angular range,
σ = 24˚)
 Generic process:
- placement on
substrate of choice
- in registry with
underlying features
SEM and analysis of assembled particles
500nm
100 nm
Tevap = 215°C
α
d
# Au nanorods
60
~ 10 nm
accuracy
60
40
40
20
0
30
80
20
0
20
40
α (°)
60
80
0
0
F. Holzner, et al , Nano Lett. 11, 3957 (2011).
10
20 30
d (nm)
40
50
© 2009 IBM Corporation
Application: High Performance Optical Micro-Cavities
Simulation: >10 x improvement
Gaussian structures by tSPL:
A
B
1 µm
C
D
20
d (nm)
15
10
5
0
0
Final structure:
- Two DBR mirrors for high Q cavity
- Light confining envelope written
by tSPL for minimal mode volume V
- Quantum rod positioned and aligned
1
2
3
x (μ m)
4
5
top DBR
h
spacer with curved
surface profile
nano-object
bottom DBR
In collaboration with Fei Ding, Lijian Mai, Thilo Stoeffele and Rainer Mahrt, IBM
IBM
© 2009 IBM Corporation
High resolution patterning of Si
SiO2 hard mask transfer process
4 nm sputtered SiO2
hard mask layer
50 nm HM8006
Si etch mask
most critical step
1 O2 + 4 N2 RIE
thinning of PPA
3-4 nm PPA as etch mask
low etch rate is crucial
CHF3 RIE transfer
of pattern into SiO2
hard mask
1:2 PPA-SiO2 etch
contrast
20 nm PPA
6-8 nm patterning depth
Poly-phthalaldehyde resist for thermal
patterning
n
Mw~40k, n~300, synthesized by ARC
700 C, 2-15 µs
Thermal probe patterning:
n
Raster scanning at a pixel and line pitch of 9.2 nm
Write pulse 5µs per pixel
Scan speed ~1 mm/s
Tip temperature 630oC
Details of the RIE sequence
O2 RIE transfer of
hard mask pattern
into HM8006 resist
© 2009 IBM Corporation
Transfer result
AFM image of patterned PPA: depth of structures is 6-8 nm (black corresponding to -8nm)
line width in pixels
1
2
3
5
10
14
nested L, half pitch
27 nm
36 nm
46 nm
27 nm
36 nm
46 nm
inverted nested L
SEM image after transfer into 50 nm thick HM8006 Si etch mask
thin free standing lines collapsed because of under-etching
nested L, half pitch
27 nm
36 nm
46 nm
27 nm
36 nm
46 nm
inverted nested L
© 2009 IBM Corporation
Final Patterns in Silicon
45o
~ 60 nm
95 nm
55 nm
72 nm
top view
45o
inverse lines
55 nm
45o
~ 15 nm
55 nm
55 nm
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© 2009 IBM Corporation
Line edge roughness
Deviation from straight line
Correlated deviation
=
Uncorrelated deviation
+
Due to position error of the
mechanical scan system used
for thermal patterning
Genuine line edge roughness.
Roughness is extremely sensitive
to contamination in the first
O2 RIE step
upper edge
lower edge
→ 0.6 .. 0.8 nm rms roughness
after transfer
SEM image of transferred pattern
© 2009 IBM Corporation
Why important
ITRS 2011 mask-less lithography requirements:
half pitch (nm)
32
20
12
3σ CD control
(nm)
3.3
2.0
1.2
Oct. 2012
Potential for acceleration
of mask less lithography
road map
10 nm half pitch pattern in PPA resist
200 nm
depth (nm)
2020
2012 + 3Y
2016
2012 + 1Y
2012
1
0
-1
-2
-3
-4
-5
requires optimization of
polymer resist and transfer layer
0.1 0.2 0.3 0.4
y-position (µ m)
within reach with process
fine tuning and PPA+PPA-acid resist
27 nm half pitch patterns
successfully transferred into
50 nm HM8006 resist
0.6...0.8 nm rms line
edge roughness
© 2009 IBM Corporation
Thermal robe patterning is becoming a competitive tool
Mechanics:
• Fast scanning > 10 mm/s
• Position accuracy better 10 nm
• Large fields ~50 µm x 50 µm
Imaging:
• Integrated fast imaging
• In-situ inspection (accelerates overall turn around time)
Patterning:
• Fast and ultra-reliable write ~µs / pixel
• Competitive with e-beam for writing
• No development required (enables in-situ inspection)
• Rapid turnaround time (minutes not hours)
• Flexibility of patterns (no proximity effects)
• Seamless stitching of scan fields
• Unique 3-d patterning capability
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• Huge opportunity for novel materials and applications
Urs Duerig, [email protected]
Acknowledgements
Nano-Patterning at IBM Research Zurich:
Felix Holzner, Armin Knoll, Michel Despont, Philip
Paul, Urs Duerig
References
D. Pires et al., Science, 238, 732, (2010)
A. Knoll et al., Advanced Materials, 22, 31, (2010)
P. Paul et al., Nanotechnology, 22, 275, (2011)
F. Holzner et al., Appl. Phys. Lett., 99, 023110, (2011)
F. Holzner et al., Nanoletters, 11, 3957 (2011)
Thank You!
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Synthesis of PPA at IBM Research Almaden:
James L. Hedrick, Mellany Ramaekers
Microfabrication at IBM Research Zurich:
Ute Drechsler
Capillary Assembly at IBM Research Zurich:
Cyrill Kuemin, Heiko Wolf
Optical Microcavities at IBM Research Zurich:
Fei Ding, Lijian Mai, Thilo Stoeffele, Rainer Mahrt
ToF-SIMS at Empa, Zurich:
Peggy Rossbach
Various at IBM Research Zurich:
Abu Sebastian, Evangelos Eleftheriou, Walter Riess
Collaboration ETH Zurich:
Nicholas Spencer
Funding:
Schweizer National Fonds (SNF)
© 2009 IBM Corporation