nil for small volume production of leds, laser diodes and ... · 20.10.2011 · nil for small...
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NIL for small volume production of LEDs, laser diodes and thin-film PVLEDs, laser diodes and thin-film PV
NNT 2011 Korea, October 2011
Marc VerschuurenPhilips Research, Photonic Materials & Devices
15 years NIL: from lab to R&D. Production?
Mold‐assisted nanolithography: A process for reliable pattern replicationJan Haisma, Martin Verheijen, Kees van den Heuvel,
and Jan van den BergJ. Vac. Sci. Technol. B 14, 4124 (1996)
Nanoimprint lithography
UV-NIL at Philips Research
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Nanoimprint lithographyStephen Y. Chou, Peter R. Krauss, and Preston J. Renstrom
J. Vac. Sci. Technol. B 14, 4129 (1996)
Soft lithographyY. Xia and G.M. Whitesides
Annu. Rev. Mater. Sci. 28, 153 (1998)
The “problem” of NIL
• NIL is not “easy / simple” as many claim• “Low cost” imprint tools turn out to be “expensive”
• Tremendous progress booked• Technology development takes time
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• Aim at the correct early adaptor (proper application)• Production:
– Non-ideal world, substrates with bow, defects, etc.– Chicken & egg problem e.g. (yield, throughput, ...)– Supply chain
Outline
• Substrate Conformal Imprint Lithography
• SCIL in applications
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• SCIL in applications
Imprint techniques = contact techniques
Rigid stamps Soft rubber stampRigid quart
z stamp
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+ resolution+ low pattern deformation- need for release layer- small contact area- only organic resists- sensitive to particles- expensive stamps
+ wafer scale conformal contact+ low cost rubber stamp
(silicone rubber, PDMS)+ intrinsic non-stick+ freedom of imprint resist - resolution- pattern deformation
Addressed by SCIL
High resolution soft stamps.
0
3·10-9
Min
imal
(2U
e–
2Us)
(J·
m-1)
0
3·10-9
Min
imal
(2U
e–
2Us)
(J·
m-1) 40 MPa
X-PDMS: soft & nm Tri-layer, flexible composite stamp
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• Collapse if: decrease of Esurface < Emechanical deformation
• X-PDMS silicone rubber with Young’s modulus 60-80 Mpa(conformal contact)
0 100 200
Grating pitch (nm)
min. (2Ue-2Us)40 MPamin. (2Ue-2Us)11 MPa
-3·10-9
Min
imal
(2U
0 100 200
Grating pitch (nm)
min. (2Ue-2Us)40 MPamin. (2Ue-2Us)11 MPa
-3·10-9
Min
imal
(2U
11 MPa
Thin X-PDMSsoft-PDMSThin glass
SCIL process for wafer scale patterning
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Attach stamp on grooved plate by vacuum.
Spin resist on wafer.Position wafer parallel to stamp~100 µm distance.
Sol-gel
Sequential low pressure imprint cycle. Capillary force driven.
Sequential low force stamp release
1.
2.
5.
6.
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3.7.
4. UV resist curing 8.
SCIL imprinted silica sol-gel resistSilica sol-gel imprint resist• UV curing 30sec. imprint time• Room temperature process• Full inorganic cross-linking• No post-cure needed• Selective stamp cleaning
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High aspect ratio features• The rubber conforms during
release of features
200 nm
SCIL provides nm resolution
200 nm
100 nm
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Our X-PDMS soft stamps replicate nm size features
50 nm pitch 35 nm pitch
SCIL high densitypatterns
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50 nm pitch
40 nm pitch
35 nm pitch
Dot placement errors due to e-beam writing and drift in SEM
Substrate conformal
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SCIL patterned sol-gel resist
The soft rubber conforms to the substrate. Patterns are imprinted over particle contaminants and distortions are dissipated in the soft rubber layer.Stamp lifetime > 3000 imprints
Sol-gel is a perfect hard mask
Pattern transfer into:• Silicon• Al, Ti, Cr, W, Mo, …• Organic layers• GaP, InP
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• GaP, InP• Ge• GaN• GaAs• Lift-off for Au / Ag
SCIL nano-alignment
5 nm steps
Piezo signals
external
external
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• Quartz chuck• Al frame• 3 piezo actuators
(1 nm resolution)• Flexure guidance• No active temperature
control (clean room)• No vibration isolation
Overlay alignment with SCIL (tabletop setup)2 separately aligned imprints on a substrate with imprinted markers. SEM inspection for overlay error.
200 nm 200 nm
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“aligned” (imprint # ~40)X= 20 nm Y= 25 nm
“misaligned” (imprint # ~12)
Overlay alignment with SCILMethod: align + imprint patterns, coat metal. 2nd imprint, (same stamp) align and imprint over 1st patterns. SEM inspection to determine offset between the two imprints.
Substrate size 100x100mm. The square represents 30x30 mm. Measurements at 25 points (group of 5 vectors over 2x2 mm area).
Imprint direction
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Average error single alignment:
X = 40 nmY = 6 nm
The misalignment in X is mostly due to particle contaminants
Imprint direction
SCIL supply chain
• Tooling from Suss MicroTec– SCIL– Stamp manufacturing tools
• Process support– Suss MicroTec
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– Suss MicroTec– Philips Innovation Services / MiPlaza
• Sol-gel resist (available from Philips)– Commercializing
• X-PDMS (available from Philips)– Commercializing
SCIL applied
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SCIL applied
Efficient plasmonic TF a-Si:H solar cells10x5 cm96 cells 6x6 mm
• a-Si:H: promissing for 25 years• Electrical: thin layer• Optical: thick layer
• Plasmonic back-reflector
19Philips research Ferry, Verschuuren, et.al, Optics Express V18 A237 (2010)
H. A. Atwater and A. Polman. Nature Materials, in press.K. R. Catchpole and A. Polman. Appl. Phys. Lett. (2008).V. E. Ferry, et al. Nano Lett. (2008).P. N. Saeta, et al. Opt. Express (2009).
• Plasmonic back-reflector couple light into wave-guide modes � enhanced absorption
• Production:• a-Si:H = time determining• 300 nm � 100 nm =
production x3
2nd gen. plasmonic patterns
123456789
10
Cel
l effi
cien
cy
90 nm intrinsic Si
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01
400 / M
400 / M = 9.6 % efficiency
Angular dependence EQE, 90nm a-Si:H
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400nm pitch, 125nm diameter pillars.Evidence of coupling to waveguide modes in a-Si layer.
Random pattern, 90,125, 175nm diameter pillars, equal density to 400nm pitch regular.Isotropic response.
Vivian E. Ferry, Marc A. Verschuuren, et. al. Nano Letters 2011
Note: optimal efficiency ~5°
Light extraction from InGaN LEDs
Blue LEDs• Internal QE 70-80%• Roughened surface
extraction• Air: 60% Extreme process control required
- LED emission +/- 5 nm � binning
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• Dome: 80%• Photonic crystal
• Beamed light• 75% extraction
into air• 2x brightness
Wierer, David, Megens, Nature Photonics 3, 163 - 169 (2009)
- LED emission +/- 5 nm � binning- Thickness +/- 10 nm- Hole dept & diameter +/- 10nm
Photonic crystal power LEDs
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• Sub-mount with LEDs(>20 µm height variations)
• Imprint on top of LEDs• Patterns reach LED edge• RIE etch GaN
Photonic crystal power LEDs
80°
θ
ϕ
0°
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0° 80°
0°
θ
θ
120°
Far field light distributionwith photonic modes (480 nm)
EL: Photonic crystal emission patterns
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Square array of holes“thick LED” weak coupling
Hexagonal array of holes“thin LED” strong coupling
Wavelength scans are normalized.
VCSELs
Single-mode polarization-locked VCSELs for laser mice
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3” GaAs substrate80.000 lasers
Nano-grating on VCSEL exit aperture
Mix-match process flow
GaAs + MBE laster stack@ Ulm, Germany
Income controlShip to MiPlaza, NL
SCIL imprint grating +alignment markers
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@ Ulm, Germany alignment markers
Break-through RIE etchGaAs RIE etchoptical litho (mask aligner),mesa etching, contact deposition, dicing, testing
Quality controlShip to ULM, DE
Typical growth defects on GaAs substrates
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Conventional E-beam
Source: Philips Photonics ULM
Benchmark: E-beam vs. SCIL (550 nm pitch)
SCIL
1
2
Vol
tage
(V
)
1 Optical pow
er (mW
)
0P
ower
(dB
)
1
2
Vol
tage
(V
)
1 Optical pow
er (mW
)
0
Pow
er (
dB)
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• Split EPI run• Patterning by
SCIL and E-beam• Processing into single
mode VCSELs
Characterization• SRSM• Peak wavelength• Pol. suppression
• Threshold• Slope• Power• Lifetime
0
1
0 1 2 3
Current (mA)
Vol
tage
(V
)
0
Optical pow
er (mW
)
-25
852 853 854Wavelength (nm)
Pow
er (
dB)
0
1
0 1 2 3
Current (mA)V
olta
ge (
V)
0
Optical pow
er (mW
)
-25
852 853 854
Wavelength (nm)
Pow
er (
dB)
Accepted: Marc A. Verschuuren, et. al. Nanotechnology 2011
Improved performance with SCIL
1
2
Vol
tage
(V
)
1
2
Optical pow
er (mW
)
0
Rel
ativ
e sp
ectr
al
pow
er (
dB)
2.5
Vol
tage
(V
)
2
Optical pow
er (mW
)
0
Rel
ativ
e sp
ectr
al
Source: Philips Photonics ULM
E-beam 550 nm SCIL 150 nm
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0
0 1 2 3
Current (mA)
Vol
tage
(V
)
0
Optical pow
er (mW
)
-20855 856 857
Wavelength (nm)
Rel
ativ
e sp
ectr
al
0
0 1 2 3
Current (mA)
Vol
tage
(V
)
0
Optical pow
er (mW
)
-25
855 856 857Wavelength (nm)
Rel
ativ
e sp
ectr
al
pow
er (
dB)
• Sub-wavelength @ same cost
• Efficiency: + 30 - 50% (threshold ↓ & slope ↑)• Production running from 2008 in Philips MiPlaza
SCIL processed VCSELs
• Production ramping from 2008• Processed over 750 wafers, >60 million VCSELs• From 1 product in 2008 to 3 in 2011• Stable processes
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• Yield– equal or better than ebeam lithography– Failure analysis: SCIL does not determine failure
• Lifetime: equal to ebeam lithography• Cost is lower than e-beam
150
200
250
300
0 20 40 60 80 100 120 140 160 180 200 220 240 260
solg
el th
ickn
ess
[nm
]
Wafers #
solgel thickness for the 550nm process
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0
20
40
60
80
0 50 100 150 200 250 300 350 400 450 500solg
el th
ickn
ess
[nm
]
Wafer #
solgel thickness for the 150nm process
1st + 2nd
3rd 4th design
Conclusions
• SCIL is a robust wafer scale nano-imprint process• Flexible process applicable to different fields
• Promising results for LEDs, PV and nano-technology
• Supply chain in place• SCIL expertise available at
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• SCIL expertise available at Philips Innovation services / MiPlaza for:testing, prototyping, (small scale) production
• NIL products are successfully running from 2008
Acknowledgements:
Philips:Robert van de LaarRemco van BrakelMischa Megens
Ulm Photonics:Philipp Gerlach
Questions?
Alexander Weigl
Suss MicroTec:Michael HornungRan Ji