Demonstration of Sub Rayleigh Lithography Using a Multi-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 11 th , 2006

Outline

 Motivation  Quantum lithography  Proof-of-principle experiments  Multi-photon lithographic recording material  Experimental results  Non-sinusoidal 2-D patterns  Conclusion & future work 1/16

Motivation

 In optical lithography, the feature size is limited by diffraction, called the ‘Rayleigh criterion’.

-

Rayleigh criterion

: ~ l /2 

Quantum lithography

lithography.

using an

N-photon lithographic recording material & light source entangled

was suggested to improve optical  We suggest PMMA as a good candidate for an N photon lithographic material.

2/16

Quantum lithography

  Classical interferometric lithography -

I

 1 2  1  cos(

Kx

)  , where K = l /(2sin q ) Resolution : ~ l /2 at grazing incident angle   Quantum interferometric lithography uses entangled N-photon light source.

I

 1 2  1  cos(

NKx

)  PDC Resolution : ~ l /2 N phase shifter q 1 2 , 0 phase shifter q 1 0 , 2  Advantage : high visibility is possible even with large resolution enhancement.

Boto et al., Phys. Rev. Lett. 85, 2733, 2000 3/16

Enhanced resolution with a classical light source

Phase-shifted-grating method     Fringe patterns on an N-photon absorber with M laser pulses .

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

The fringe pattern is

I



m M

  1 [ 1  cos(

Kx

 2 (

m

 1 ) p /

M

)]

N

Example One photon absorber Single shot Two-photon absorber Two shots S.J. Bentley and R.W. Boyd, Optics Express, 12, 5735 (2004) 4/16

PMMA as a multi-photon absorber

 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) 800 nm PMMA is excited by multi-photon absorption UV absorption spectrum of PMMA 5/16

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 6/16

Experimental setup

Ti:sapphire fs-laser with regenerative amplifcation 120 fs, 1 W, 1 kHz, at 800 nm (Spectra-Physics) WP Pol.

M3 BS PR M1 M2 f1 f2 PMMA WP : half wave plate; Pol. : polarizer; M1,M2,M3 : mirrors; BS : beam splitter; f1,f2 : lenses; PR : phase retarder (Babinet-Soleil compensator) 7/16

Experimental process

Path length difference l /2 l /4 PMMA Substrate (Glass) Phase retarder 8/16

Demonstration of writing fringes on PMMA

Recording wavelength =

800 nm

Pulse energy = 130 m J per beam Pulse duration = 120 fs Recording angle, θ = 70 degree Period λ/(2sinθ) =

425 nm

425 nm 9/16

Sub-Rayleigh fringes ~

l

/4 (M = 2)

Recording wavelength = p Pulse energy = 90 m J per beam Pulse duration = 120 fs 800 nm Recording angle, θ = 70 degree Fundamental period λ/(2sinθ) = 425 nm Period of written grating =

213 nm

213 nm 10/16

Threefold enhanced resolution (M = 3)

0.8 m m Recording wavelength = 800 nm Three pulses with 2 π/3 & 4π/3 phase shift Pulse energy = 80 m J per beam Pulse duration = 120 fs Recording angle, θ = 8.9 degree Fundamental period λ/(2sinθ) = 2.6 m m Period of written grating = 0.85 m m 1.67 m m 2.6 m m 213 nm 11/16

Non-sinusoidal fringes

141 nm

 PMMA is a 3PA at 800 nm. (N=3)  Illumination with two pulses. (M=2)  If the phase shift of the second shot is p   7 p 10 the interference fringe is

I

 ( 1  cos(

Kx

)) 3  0 .

85 ( 1  cos(

Kx

 p   )) 3  Numerical calculation is similar to the experimental result.

 This shows the possibility of non-sinusoidal fringe patterns.

12/16

Non-sinusoidal Patterns

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

I



m M

  1

A m

[ 1  cos(

Kx

 

m

)]

N

For example, if N = 3 , M = 3 A 1 A 2 A 3 = 1 = 0.75

= 0.4

∆ 1 ∆ 2 ∆ 3 = 0 = π /2 = π 13/16

Two Dimensional Patterns

 Method can be extended into two dimensions using four recording beams.

Pattern



thickness



mx

,

M

 

my A mx

1 [ 1  cos(

Kx

 

mx

)]

N A my

[ 1  cos(

Ky

 

my

)]

N

For example,

N

=8,

M

=14 14/16

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 l /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

& Dr. Samyon Papernov 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) 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 = 1 2)Rotate the sample 3)Illuminate the second shot, N = 3, M = 1