Approaching the NA of Water:Immersion Lithography at 193nm

Bruce Smith

Y. Fan, A. Bourov, L. Zavyalova, J. Zhou, F. Cropanese, N. Lafferty

Rochester Institute of TechnologyM. Gower, D. Ashworth

Exitech Inc.J. Webb

Corning Tropel

Outline

- 193nm immersion lithography to 38nm p/2

- Interferometric vs. projection lithography

- 1.05NA projection microstepper

- Homogeneous immersion and increasing refractive index

Increasing NA with Immersion

θ1

θ2

θ3

Airn1 = 1.0 n2 > n1 n3 > n2

NA = n1 sin (θ1) =n2 sin (θ2)= n3 sin (θ3)

Increasing NA with Immersion

θ1

θ2

θ3

Airn1 = 1.0 n2 > n1 n3 > n2

NA = n1 sin (θ1) =n2 sin (θ2)= n3 sin (θ3)

Increasing NA with Immersion193nm or 134nm

θ1

θ2

θ3

Airn1 = 1.0 n2 > n1 n3 > n2

λ

Scaling of NA or wavelength?

ArF Immersion Talbot LithographyBreadboard “Half-ball” system

+/- 1 Order Talbot interferometer preserves spatial coherence

Unstable excimer resonator for 0.5mm coherence length

Beam expansion increases length to 2mm (field size)

Dual etalons provide 6pm FWHM

Half ball interface allows NA to 1.35

Wafer Stage

40mm Half-Ball

Water Meniscus

Turning mirrors

Phase Grating

Turning Mirror

Polarizer

Beam Expander

Wafer Stage

40mm Half-Ball

Water Meniscus

Turning mirrors

Phase Grating

Turning Mirror

Shutter

Polarizer

Beam Expander

Modified ArF laserfor temporal and spatial coherence

Wafer Stage

40mm Half-Ball

Water Meniscus

Turning mirrors

Phase Grating

Turning Mirror

Polarizer

Beam Expander

Wafer Stage

40mm Half-Ball

Water Meniscus

Turning mirrors

Phase Grating

Turning Mirror

Polarizer

Beam Expander

Modified ArF laser

spatial coherence

80nm 1:1.5

0.5NA

65nm 1:1

0.7NA

60nm 1:1

0.8NA

55nm 1:1.5

0.7NA

55nm 1:1

0.9NA

193i Resist Images 55-80nm ResolutionShipley XP1020 over AR, 50-100nm film thickness, TOK topcoat, TE polarization

50nm 1:3

0.5NA

45nm 1:2

0.7NA

45nm 1:1.5

0.8NA

45nm 1:1 70nm Shipley XP1020

1.0NA

45nm 1:1 80nm TOK ILP012

1.0NA

193i Resist Images 45-50nm ResolutionShipley XP1020 over AR, 50-100nm film thickness, TOK topcoat, TE polarization

38nm p/250nm XP1020

38nm 1:170nm XP1020

1.25NA1.25NA

193i Resist Images 38nm Resolution1.25NA Interference Lens, TE polarization

76nmEarly results show good optical contrast and resist potential

Compact Talbot LensEntire 193nm Talbot system incorporated into compact lens

600nm phase grating produces +/-1st diffraction orders at 18.8°

Talbot lens angle increases NA up to 1.35

Line/space and contact patterns are possible

2/4 beam interference allow for large tolerances

Combined with beam expander and MgF2 polarizer

193 Prism Lens DesignsNA half-pitch_________________0.8 60nm1.05 45nm1.20 40nm1.35 36nm

Excimer Radiation

Phase Grating

Talbot

Prism

Image Plane

Excimer Radiation

Phase Grating

Talbot

Prism

Image Plane

Excimer Radiation

Phase Grating

Talbot

Prism

Image Plane

Excimer Radiation

Phase Grating

Talbot

Prism

Image Plane

Talbot Immersion Research Tool

193nm MgF2 Rochonpolarizer

Smith-Talbot prism (1.0NA – 1.35NA)

Phase shift mask (600nm 3.1 – 4.2X)

5X 193nm fused silica beam expander

Beam from ArF laser

Optical ColumnWorkstation

- Linear guide bearing stage- 200mm X-Y stage travel- 6-8” robotic wafer handling- Compact GAM ArF excimer

5 mJ pulse energy6pm linewidth (FWHM)200 Hz rep. rate

Water Handling at the Wafer Plane

Contact with water Stepping with water

45nm p/2 at 1.05NA

Interferometric Immersion vs. Projection Immersion Lithography

How well can 2-beam interference lithography predict projection

lithography?

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Interferometric Lithography (IL) 2-42% single beam exposure

Images normalized to mask intensityResist Image Intensity Comparisons

Projection vs. Interferometric Lithography of 100nm 1:1 lines

Resist index = 1.7, α=0Vector Simulation

IL Images leveled to mean2-42% best fit to annular

Contrast range 0.25 to 0.75

2%

42%

2%

42%

Projection Lithography0.75NA, annular (0.85/0.55)

Defocus 0-240nmContrast range 0.22 to 0.74

Best Focus

240nm Defocus

Prolith 8.02

Full modulation(Best Focus)

30% demodulation (150nm defocus)

50% demodulation(220nm defocus)

LPM simulation

LPM simulation

Immersion IL Images with demodulation

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Interferometric Lithography (IL) 25-65% single beam exposure

Images normalized to mask intensityResist Image Intensity Comparisons

Projection vs. Interferometric Lithography of 100nm 1:3 lines

Resist index = 1.7, α=0Vector Simulation

IL Images leveled to mean25-65% best fit to annular

Contrast range 0.12 to 0.4022% overexposure vs. 1:1

25%

65%

25%

65%

Projection Lithography0.75NA, annular (0.85/0.55)

Defocus 0-240nmContrast range 0.14 to 0.42

Best Focus

240nm Defocus

Prolith 8.02

Illumination System

AquaCAT 1.05NA

WaferXYZ Stages

Mask

PartialCoherence Aperture

Switch-In Mirror

WaferXY Stages

Open FieldSystem

Beam Delivery System

Dose Monitor Diode

Autofocus System

Illumination System

AquaCAT 1.05NA

WaferXYZ Stages

Mask

PartialCoherence Aperture

Switch-In Mirror

WaferXY Stages

Open FieldSystem

Beam Delivery System

Dose Monitor Diode

Autofocus System

StepperLaser

193nm Immersion MicroStepperExitech PS3000 / 1.05NA Corning Tropel AquaCAT

AquaCAT 193i Catadioptric LensLens SpecificationsNA 1.05 Reduction 90XImage field 0.1 mmWavelength 193.3 nmBandwidth 700 pmTrack length 210 mm +/- 10 mmEntrance Pupil distance 210 mm +/- 10 mmMaterial SiO2Immersion fluid H2OWorking distance >0.5 mm # of elements 8% Obscuration <15%Measured wavefront <0.05 waves rms

(SPIE 5377-74)

4.00 mm

20.0°

Final glass surfaceBottom of assembly

Water Introduction Considerations1. Method – micro syringe pipette ~0.01 ml

immersion volume in 3.5 sec using 10ml/hr Baxter APII syringe pump

2. Retention – surface tensioning to hold meniscus

Meniscus retention testing using final element mock-upa) 20° surface angleb) 90° surface angle

Micro-pipette ported into mechanics

Fluid Injection and Meniscus

Water Meniscus RetentionExperimental Test Approach

Early Image Results

Binary mask 0.70σUnpolarized illlumination

200-240nm pitch TOK ISP topcoat

80nm TOK ILP03 resist AR29 BARC

Remaining system action items:

Field stop and sigma apertures, environmental audit, PSM, system qualification, polarization control

100nm p/2 120nm p/2

Homogeneous Immersion Increasing refractive indices – the defocus effect

Defocus OPD ∝ sin2θ

sinθ

ba

The defocus wave aberration is proportional to sin2θ

Higher indices reduce defocus OPD at equivalent NA values

Small NA/n is desirable

Low index (air) imaging High index imaging

Homogeneous Immersion Increasing refractive indices – the refractive effect

Resist > Media Media > Resist

media nm

resist nr

glass ng

The glass index is not a concern unless surface is planar

The maximum NA is limited to min[nm,nr]

Reflectivity is determined by index disparity

Matched indices is desirable

nmsinθm= nrsinθr

RR

Increasing Water Index in the UVInorganic approach

- UV-vis absorption involves excitation of e- from ground

- Solvents provide “charge-transfer-to-solvent” transitions (CTTS)

- CTTS and λmax for halide ions is well documented [1]

F- < (OH)- < Cl- < Br- < I-

- Alkalai metal cations can shift λmax lower [2]

Cs+ < Rb+<K+<Li+<Na+<NH4+<H3

+O

- d λmax/dT is positive (~500ppm/°C), d λmax/dP is negative

- Goal to approach “anomolous dispersion” with low absorbance

[1] E. Rabinowitch, Rev. Mod. Phys., 14, 112 (1942)

[2] G. Stein and A. Treinen, Trans. Faraday Soc. 56, 1393 (1960)

Effect of Anion on Absorption of Water

Anion in water Absorption Peak [3]______________________________________

I- 5.48eV 227nm

Br- 6.26 198

Cl- 6.78 183

ClO4-1 6.88 180

HPO42-1 6.95 179

SO42-1 7.09 175

H2PO4- 7.31 170

HSO4- 7.44 167

[3] Various including M.J. Blandamer and M.F. Fox, Theory and Applications of Charge-Transfer-To-Solvent Spectra, (1968).

Measured Absorbance Spectra of Sulfates and Phosphates in Water

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Na2SO4 at 17% (a=0.80/mm)K2SO4 at 8% (a=1.03/mm)Cs2SO4 at 40% (a=0.70/mm)H2SO4 at 20% (a=0.087/mm)Gd2(SO4)3 at 1.5% (a=0.09/mm)MgSO4 at 5% (a=1.98/mm)NaHSO4 at 44% (a=0.28/mm)

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Na2HPO4 at 16% (a=0.096/mm)

KH2PO4 at 16% (a=0.501/mm)

NaH2PO4 at 16% (a=0.455/mm)

H3PO4 at 16% (a=0.002/mm)

- Solutions normalized to mole concentration of cation- Fluids with absorbance < 0.1/mm become interesting - Mixtures follow EMA behavior

Fluid Refractive Index and Dispersion

Refractive index @ Cauchy parameters193nm 248nm A B C

HCl@37% 1.583 1.487 1.3997 0.0032 0.000134

CsCl@60% 1.561 1.466 1.3912 0.0020 0.000160

H2SO4@20% 1.472 1.418 1.3635 0.0022 0.000068

H2SO4@96% 1.516 1.469 1.4151 0.0027 0.000040

NaHSO4@44% 1.473 1.418 1.3643 0.0021 0.000074

Cs2SO4@40% 1.481 1.422 1.3685 0.0020 0.000083

Na2SO4@30% 1.479 1.423 1.3667 0.0023 0.000069

H3PO4@20% 1.452 1.398 1.3486 0.0018 0.000077

H3PO4@40% 1.475 1.420 1.3723 0.0015 0.000085

H3PO4@85% 1.538 1.488 1.4316 0.0028 0.000042

H2O (DI) 1.435 1.373 1.3283 0.0021 0.000067

Fluids

*Data obtained by Cauchy model fit are labeled red. Experimental data are not available due to high absorption

Hydrogen Phosphates

Pure and Doped Water Comparisons

59nm 1:1 (50nm resist) 39nm 1:2 (50nm resist)

65nm 1:1 (100nm resist) 45nm 1:2 (70nm resist)

Water (HPLC grade)~100µm gap130nm pitch

Water with40 wt% Cs2SO4

~100µm gap117nm pitch

Summary- 193nm immersion lithography to 38nm p/2- Early optical results of water are promising for n ~1.6 - Resolution limit with 1.6n fluid is 30nm p/2

248nm Water Immersion Lithography

75nm half-pitch0.82NA

Acknowledgements: DARPA / AFRL, International SEMATECH, SRC, IBM, Exitech, Corning Tropel, ASML, Intel, Shipley, TOK,

Photronics, Brewer Science, GAM Laser Inc.