Demonstration of Sub-Rayleigh Lithography

Using aMulti-Photon Absorber

Heedeuk Shin, Hye Jeong Chang*, Malcolm N. O'Sullivan-Hale, Sean Bentley# , and Robert W. Boyd

The Institute of Optics, University of Rochester, Rochester, NY 14627, USA* The Korean Intellectual Property Office, DaeJeon 302-791, Korea

# Department of Physics, Adelphi University, Garden City, NY

Presented at OSA annual meeting, October 11th, 2006

Motivation

Quantum lithography

Proof-of-principle experiments

Multi-photon lithographic recording material

Experimental results

Non-sinusoidal 2-D patterns

Conclusion & future work

Outline

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Motivation

In optical lithography, the feature size is limited by diffraction, called the ‘Rayleigh criterion’.- Rayleigh criterion : ~ /2

Quantum lithography using an N-photon lithographic recording material & entangled light source was suggested to improve optical lithography.

We suggest PMMA as a good candidate for an N-photon lithographic material.

2/16

Advantage : high visibility is possible even with large resolution enhancement.

Classical interferometric lithography

- , where K = /(2sin)

Resolution : ~ /2 at grazing incident angle

Quantum interferometric lithography uses entangled N-photon light source.

-

Resolution : ~ /2N

Quantum lithography

phase shifter

)cos(12

1KxI

phase shifter

PDC

)cos(12

1NKxI

Boto et al., Phys. Rev. Lett. 85, 2733, 2000

1

1

0,2

2,0

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Fringe patterns on an N-photon absorber with M laser pulses.

The phase of mth shot is given by 2m/M.

The fringe pattern is

Example

Enhanced resolution with a classical light source

S.J. Bentley and R.W. Boyd, Optics Express, 12, 5735 (2004)

M

m

NMmKxI1

)]/)1(2cos(1[

Phase-shifted-grating method

One photon absorberSingle shot

Two-photon absorberTwo shots

4/16

PMMA is a positive photo-resist, is transparent in visible region and has strong absorption in UV region.

3PA in PMMA breaks chemical bonds, and the broken bonds can be removed by developing process. (N = 3 at 800 nm)

UV absorption spectrum of PMMA

PMMA is excited by multi-photon absorption

PMMA as a multi-photon absorber

800 nm

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Experiment – material preparation

Sample preparation 1) PMMA solution PMMA (Aldrich, Mw ~120,000) + Toluene : 20 wt% 2) PMMA film : Spin-coat on a glass substrate Spin coating condition : 1000 rpm, 20 sec, 3 times Drying : 3 min. on the hot plate

Development 1) Developer : 1:1 methyl isobutyl ketone (MIBK) to Isopropyl

Alcohol 2) Immersion : 10 sec 3) Rinse : DI water, 30 sec 4) Dry : Air blow dry

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Experimental setup

Ti:sapphire fs-laser

f1M1

f2M2

PMMA

BS

M3Pol.WP

PR

WP : half wave plate; Pol. : polarizer; M1,M2,M3 : mirrors; BS : beam splitter; f1,f2 : lenses; PR : phase retarder (Babinet-Soleil compensator)

with regenerative amplifcation

120 fs, 1 W, 1 kHz, at 800 nm

(Spectra-Physics)

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Substrate (Glass)

Phase retarder

PMMA

Developing

Path length difference /2

Interference pattern shifted by /4

Experimental process

/2

/4

8/16

Demonstration of writing fringes on PMMA

Recording wavelength = 800

nm Pulse energy = 130 J per

beam Pulse duration = 120 fs

Recording angle, θ = 70

degree

Period λ/(2sinθ) = 425 nm425 nm

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Sub-Rayleigh fringes ~/4 (M = 2)

Recording wavelength = 800 nm Two pulses with phase shiftPulse energy = 90 J per beam Pulse duration = 120 fsRecording angle, θ = 70 degree Fundamental period λ/(2sinθ) = 425 nmPeriod of written grating = 213 nm

213 nm

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Threefold enhanced resolution (M = 3)

Recording wavelength = 800 nm Three pulses with 2π/3 & 4π/3 phase shiftPulse energy = 80 J per beam Pulse duration = 120 fsRecording angle, θ = 8.9 degree Fundamental period λ/(2sinθ) = 2.6 mPeriod of written grating = 0.85 m

213 nm

2.6 m

1.67 m

0.8 m

11/16

Non-sinusoidal fringes PMMA is a 3PA at 800 nm. (N=3)

Illumination with two pulses. (M=2)

If the phase shift of the second shot is

, where ,

the interference fringe is

Numerical calculation is similar to the experimental result.

This shows the possibility of non-sinusoidal fringe patterns.

33 ))cos(1(85.0))cos(1( KxKxI

10

7

141 nm

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Non-sinusoidal Patterns

Different field amplitudes on each shot can generate more general non-sinusoidal patterns.

M

m

Nmm KxAI

1

)]cos(1[

For example, if N = 3 , M = 3

A1 = 1 A2 = 0.75 A3 = 0.4

∆1 = 0∆2 = π/2∆3 = π

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Two Dimensional Patterns Method can be extended into two

dimensions using four recording beams.

M

mymx

Nmymy

Nmxmx KyAKxAthicknessPattern

1,

)]cos(1[)]cos(1[

For example,N=8, M=14

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Conclusion The possibility of the use of PMMA as a multi-photon

lithographic recording medium for the realization of quantum lithography.

Experimental demonstration of sub-Rayleigh resolution by means of the phase-shifted-grating method using a classical light source.

- writing fringes with a period of /4

Quantum lithography (as initially proposed by Prof. Dowling) has a good chance of becoming a reality.

Future work Higher enhanced resolution (M = 3 or more)

Build an entangled light source with the high gain optical parametric amplification.

Realization of the quantum lithography method.15/16

Acknowledgement

Supported by - the US Army Research Office through a MURI grant- the Post-doctoral Fellowship Program of Korea Science and Engineering Foundation (KOSEF) and Korea Research Foundation (KRF)

Dr. Samyon Papernov &

16/16

Thank you for your attention!

http://www.optics.rochester.edu/~boyd

Two Dimensional Patterns Experimental 2-D pattern

1)Illuminate one shot, N = 3, M = 12)Rotate the sample3)Illuminate the second shot, N = 3, M = 1