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