Plasmonic Imaging for Optical Lithography

X-ray Wavelengths at Optical Frequencies

Experiments: Progress and Plans

Yunping YangJosh Conway

Eli Yablonovitch

The Problem

Classically the resolution limit is determined by the Rayleigh Criterion:

Various schemes have been developed to push this to finer resolution than the wavelength itself, but the scale will always be set by wavelength

dSin

Constant Energy CurvesBy adiabatically tapering the thin film thickness,

very small (<50nm) plasmon wavelengths are attainable for in plane imaging.

0 20 40 60 80 1000

100

200

300

400 1.5 eV

2.0 eV

2.5 eV

0

100

200

300

20 40

400

60 80

Plas

mon

Wav

elen

gth

in n

m

Silver Film Thickness in nm

Silver Film on Sapphire

t

p

SapphireAg Air

0 0 . 0 2 0 . 0 4 0 . 0 6 0 . 0 8 0 . 1 0 . 1 2 0 . 1 4 0 . 1 6 0 . 1 8 0 . 2 0 . 2 2 0 . 2 4 0 . 2 6 0 . 2 8 0 . 3 0 . 3 2 0 . 3 4 0 . 3 6 0 . 3 8 0 . 4 0 . 4 2 0 . 4 4 0 . 4 6 0 . 4 8 0 . 5 0 . 5 2 0 . 5 4 0 . 5 6 0 . 5 8 0 . 6 0 . 6 2 0 . 6 4W a v e n u m b e r ( r a d / n m )0

0 . 5

1

1 . 5

2

2 . 5

3

3 . 5

4

w(eV)

t=1nm

t=20nm t=5nmt=2nm

0 0.1 0.2 0.3 0.4 0.50

1

2

3

4 200 100 50 20 15 30 40 10

0.6

Plasmon Wavelength in nm

Plasmon Wave-Vector (2/wavelength in nm)

Plas

mon

Ene

rgy

in e

Vh

k

t=thickness of metal film

Optical frequencies, but with X-ray wavelengths!

SapphireAg Air

Dispersion Relation: Constant Thickness Curves

Grating Coupler

Silver

Glass

Grating

• Design and fabricate gratings to maximize the coupling efficiency;• Verify the DR with constant thickness;• Find some material parameters

Launching of Surface Plasmons: ATR Coupler

Optical Setup for ATR Coupler

Laser/2

PBS

BeamExpander

Iris Mirror

Detector Lens LensLens

Lens

4f

4f

SapphireHemisphere

Ag Thin Film

Optical Setup for ATR Coupler

• Characterize thin film, such as roughness, thickness;• Experimentally verify the dispersion relation;• Launching a standing wave for Plasmon Wavelength Measurement

A Possible Solution

This permits X-ray wavelengths at optical frequencies

photoresistsilicon

light h=2.5eV

plas

mon

wav

epl

asm

on w

ave

sapphire plas

mon

wav

e+

++

+-

--

-

sapphire plas

mon

wav

e+

++

+-

--

-

grat

ing

coup

ler

Plasmon Wavelength Measurement

Antonello Nesci, Rene Dandliker, Hans Peter Herzig, “Quantitative amplitude and phase measurement by use of a heterodyne scanning near-field optical microscope,” Optics Letters, Volume 26, Issue 4, 208-210.

Resolution: 1.6 nm

Taper Motivation

dimple lens

out-coupling slot

far-field fromconventional lens

taper

Taper design will be a trade

between absorption

(joule heating),

scattering (an adiabatic

profile), and maintaining a high enough

effective index at all points of

propagation to maintain

features

n9> n8> >n1>n0

Criteria

0 50 100 1500.0

0.1

0.2

0.3

0.4

Loss

/

Wavelength (nm)

It is clear that Loss/ becomes

prohibitively large at

short wavelengths

Thus we change are adiabatic criteria

accordingly

/ = constant

Length (nm)

Silv

er F

ilm T

hick

ness

(nm

)

100 200 300 400 500 600

10

20

30

40

50

60

Taper Profile