Cost Effective Single Exposure Immersion Lithography

With Second Generation Immersion Fluids For Numerical Apertures of 1.55

and 32 nm Half Pitches

R. H. French1, H. V. Tran1, D. J. Adelman1, N. S. Rogado1, W. Qiu1, J. Feldman1, O. Nagao2, M. Kaku2, M. Mocella3, R. C. Wheland1, M. K. Yang1,

M. F. Lemon1, L. Brubaker1, B. Fones1, B. E. Fischel1, C. Y. Chen4

1. DuPont Co. Central Research, Wilmington DE, 19880-04002. DuPont K. K., NBD-J, Utsunomiya-shi, Japan 321-32313. DuPont Co., Electronic Technologies, Wilmington DE, 198804. DuPont-EKC, Hayward CA, 94545

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2

Acknowledgements

MIT Lincoln Labs•Vlad Liberman•Keith Krohn•Mordy Rothschild

IMEC•E. Hendrickx, R. Gronheid,

Previous Work: • SPIE Proceedings on Optical Microlithography XVII, SPIE Vol. 5377-173, (2004). • Journal of Vacuum Science And Technology B, 22, 6, 3450-3, (2004). • SPIE Proceedings on Optical Microlithography XVIII, ML5754-76, (2005).• Journal of Microlithography, 4, 3, 031103, (2005). • SPIE Proceedings on Optical Microlithography XIX, ML6154-42, (2006). • SPIE Proceedings on Optical Microlithography XX, ML6520-59, (2007).

NIST•Simon Kaplan•John Burnett

Sematech•Bryan Rice

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Introduction

Three Elements For High Index Immersion•High Index Immersion Fluids With Recycle Technology •High Index Last Lens Element (HILLE)•High Index Scanners

Single Patterning With High Index Immersion Lithography• Intrinsically Lower Cost Of Ownership

•Versus Double Patterning With Water•Current Technological Gate Due To HILLE

Development Of Immersion Fluids And Active Recycle•Optimize High Index Immersion Imaging Performance•Minimize High Index Immersion Defectivity

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Outline

High-n Immersion Imaging and Defectivity•Leaching And Residues

Fluid Lifetimes and Daily Fluid Dose

Radiation Durability•Three Gen2 Immersion Fluids•Active Recycle Ver. 3 & 4 Performance

Conclusions

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High Index Immersion Fluids

193 nm Index• IF173: 1.679*• IF175: 1.664• IF169: 1.655• IF132: 1.644• IF131: 1.639• IF137: 1.638

Rad. Dur. Test Of Three Fluids• IF137, IF132, IF169• Compare Radiation Durability Of Different High-n Fluids

Current High Index Fluid Candidates

1.45

1.5

1.55

1.6

1.65

1.7

190 290 390 490 590Wavelength (nm)

Inde

x of

Ref

ract

ion

"n"

IF173-12015IF175-12107IF169-12722IF132-12790IF131-12610IF137-12022

IF173: extrapolated index at 193 and 206 nm

**

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Gen2a Type Immersion Fluid Candidates 193 nm Index• IF173: 1.679*• IF175: 1.664

• IF132: 1.644

Define Gen2a Fluids • Indices > 1.66

Current Optical Abs.

IF175• Abs/cm ~2/cm

IF173• Abs/cm >20/cm

Increased Numerical Aperture Possible• With A High Index Last Lens Element• And A Gen2a Fluid

But May Require Relaxed Absorbance Specification

1.45

1.5

1.55

1.6

1.65

1.7

190 290 390 490 590Wavelength (nm)

Inde

x of

Ref

ract

ion

"n" IF173-12015

IF175-12107IF132-12790

* IF173: extrapolated index at 193 and 206 nm

**

High Index Immersion Imaging and Defectivity

PAG Leaching

Materials Of Construction, Filters

Residues: Particles and Film Formers

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Issues In High Index Lithography: IF Lifecycle

Image Formation

High-n Imaging High-n Defectivity

From Immersion Fluid

From 193nm Laser Irradiation

Materials In Contact With IF:

Soluble: Film Former

Insoluble:Particles

Optical Absorbance

Impact

Source

Define Controlling Factors In High-n Imaging And Defectivity

Optimize Active Recycle To Address These High-n Immersion Issues

Fluid Handling System

Image Formation

High-n Imaging High-n Defectivity

Initial ProductionFrom Immersion Fluid

With Oxygen UptakePhotochemical Degradation

From 193nm Laser IrradiationFilters

Materials Of ConstructionResist PAG, Base

Materials In Contact With IF:

Soluble: Film Former

Insoluble:Particles

Optical Absorbance

Impact

Source

PossiblePossiblePossiblePossibleFluid Handling System

Possible

PossiblePossible

Possible

Image Formation

High-n Imaging High-n Defectivity

PossiblePossiblePossibleInitial ProductionFrom Immersion Fluid

PossiblePossibleWith Oxygen UptakePossiblePossiblePhotochemical Degradation

From 193nm Laser IrradiationPossiblePossiblePossibleFilters

PossiblePossibleMaterials Of ConstructionPossiblePossibleResist PAG, Base

Materials In Contact With IF:

Soluble: Film Former

Insoluble:Particles

Optical Absorbance

Impact

Source

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DuPont Joint

Leaching – Matching of Leaching MethodsProtocol Established With IMEC

Match The Analytical Methods•All Samples Were Split In Half•The Analysis Was Done At DuPont And At RIC (IMEC Analytical Lab)

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Leaching – PAG From PAR-817 Into Water / HILUnexposed PAG Leaching•Good Reproducibility At Two Sites

More Leaching Into Water, Than Into IF132 Or IF169PAG Leaching into Fluids at 6 Minutes

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

Water IF132 IF169

Fluid

Det

ecte

d PA

G (m

ol/m

L x

10-1

0 )

DuPont (MS/MS Method)IMEC (SIM Method)

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Leaching – PAG From PAR-817 Into IF132Good Repeatability• Each Bar Represents Average Of 5 Runs

Leaching Occurs Within First MinuteLevels Well Below Stepper Manufacturer PAG Limits

0.00

0.50

1.00

1.50

2.00

2.50

0 1 3 6Time (min)

Det

ecte

d PA

G (m

ol/m

L x

10 -1

0 )

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Residues Can Arise From Droplet Drying

Sources Of DefectivityFrom Fluid

•Soluble Impurities From Fluid (a)From Stepper

•Materials Of Construction • Insoluble Particles In Fluid (b)•Filters (c)•Photoresist• Irradiated byproducts•Resist / topcoat contaminants

Optical Images: Olympus LEXT Laser Confocal Microscope

Types of Residuing Seen From High Index Fluids

Initially Clean Fluid For Use

(a)

Active Recycle For In-Situ Cleaning

(b) (c)

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PTFE Pipe Tape : Absorbing, Not Film Former

Need To ControlFluid Contamination•From Materials Of Construction

Increases In Opt. Abs.•Can Degrade Imaging

•By High NA Apodization

Optical Absorbance Increased Due To Contact

But No Film Forming Residues Were Introduced

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PTFE Pipe Tape : Absorbing, Not Film Former

Need To ControlFluid Contamination•From Materials Of Construction

Increases In Opt. Abs.•Can Degrade Imaging

•By High NA ApodizationBefore Pipe Tape After Pipe Tape

Optical Absorbance Increased Due To Contact

But No Film Forming Residues Were Introduced

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Filters: Film Former, Yet Optically Transparent

Clean Fluid• Initially

PTFE Filter•Recirculate InFluid Handling System

Reduced Particles

Constant Abs/cm

No Increase In Optical Absorbance

But Film Formation Seen•Some Filters Also Cause Increased Optical Absorbance

No Residue Seen•Of 1mm Fluid Droplet

Film Forming Residue Seen•Of 1mm Filtered Fluid Droplet

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Filters: Film Former, Yet Optically Transparent

Clean Fluid• Initially

PTFE Filter•Recirculate InFluid Handling System

Reduced Particles

Constant Abs/cm

No Increase In Optical Absorbance

But Film Formation Seen•Some Filters Also Cause Increased Optical Absorbance

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Droplet Test Conditions

Droplet Dispense• 1-2 mm Diameter Fluid Droplet Dispensed Onto Bare Si Wafer• With A Clean Plastic Pipette

Droplet Evaporation• Droplet Evaporated By Baking At 100C To 400-500 um In Diameter

Confocal Microscope Analysis• Droplet Evaporation Monitored Under Microscope• Time Sequential Images Taken Of Droplet Evaporation At Room Temperature• For Some, Final Residue Baked At 100C For 1 min• Final Image Taken

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Heavier Particles Drop Out First During Evaporation

Soluble Contaminants Left Over In Center

Defectivity From Contaminated Fluid

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Film Forming Residues And Particles in Dirty Fluid1-2 mm

Diameter Droplet Of Dirty Fluid Evaporated On Bare Si Wafer

Particles Left Behind Along Edges And On Center Of Drying Droplet

Film Forming Residues Left In Center

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Cleaner Fluid1-2 mm

Diameter Droplet Of Cleaner Fluid Evaporated On Bare Si Wafer

No Particles Or Films Left Behind At Edges Of Drying Droplet

Still See Some Particle Collection In Center –Requires Further Optimization

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IF132 Drying on 150 nm PAR-817 Resist FilmIF132 Droplet

Dispensed On 150nm PAR-817

Worst Case Scenario: No Topcoat, Unmatched Resist And Fluid

Component Extraction From Film Leaves Stains On Film As Fluid Dries At Room Temp

Dried Center Shows Residuing

Baking At 100C Makes Residue Disappear

Fluid Lifetimes and Daily Fluid Dose

Factors Which Determine Fluid Lifetime

High Index Immersion Exposure Doses

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Factors Which Determine Fluid Lifetimes

Fluid Lifetime Determined By Many Stepper and Lithography Factors• e.g. Fluid Dose Of 193 nm Laser Radiation, Contaminants From Resist Exposure, etc.

System Design And Lithography Process Definition Required• For Quantitative Fluid Lifetimes

Contamination From UseResist Exposure

Materials Of ConstructionPhotodegradation, Oxygen

Stepper Design ParametersFluid Layer Thickness

Liters Of Fluid In PackageFluid Dose

Fluid Specification LimitsMaximum Absorbance Spec

Index Variation

Fluid Lifetime In Use

Wafer Level CharacteristicsResist Sensitivity

Clear Or Dark Field Level

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Expose A Day’s Wafers: What Is The Delivered Dose?

“Stepper Down” Perspective• Using Standard Stepper Tool1

• 6 kHz Laser• 0.8 mJ/cm2/pulse Laser• 28mm x 7 mm x 3mm Irradiated Volume

• 1.568 mJ/pulse• 0.5 Duty Cycle

Total Daily Dose = 406 kJ/Day

Fluid Dose Is 1.2 J/cm2

• For 3 mm Fluid Thickness• And 100 liter Reservoir

Real Values Dependent On Many Factors• Clear Field Or Dark Field Mask, Wafers/Hour, Resist Sensitivity, etc.

Since Stepper And Lithography Process Are “Owned” By Others• We’ll Use Relative, or Comparative Basis For Fluid Lifetimes

“Wafer Up” Perspective• For A Resist Sensitivity Of 30 mJ/cm2• 3000 Wafers Per Day• 300 mm Wafers

Total Daily Dose = 64 kJ/Day

Fluid Dose Is 0.2 J/cm2

• For 3mm Fluid Thickness• And 100 Liter Reservoir

1. SPIE Proceedings on Optical Microlithography XX, ML6520-59, (2007).

Radiation Durability Results

Three Gen2 Immersion Fluids

Active Recycle Ver. 3 & 4 Performance

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Schematics of Fluid Recirculation System

The Induced Absorbance Aindcell

•Of The Exposure Cell

Two Critical ContributionsAind

fluid : Induced Fluid Absorbance •Measured Downstream In Spectrometer Cell

Aindwindow : Induced Window Absorbance

Flow Rate 115 ml/min•=> 1 l/min Stepper Flow Rate

Energy Density: 0.8 mJ/cm2

fluidind

windowind

cellind AAA +=

Flow

Laser

VentN2

N2

Pump

Fluid Cylinder

Spectrometer Cell

Laser Exposure Cell

Active Recycle Package

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0

0.05

0.1

0.15

0.2

0.25

0 0.2 0.4 0.6 0.8 1Fluid Dose (J/cm2)

Indu

c. F

luid

Abs

/cm IF169

IF137IF132

3 Fluids, No ARP: Comparative Radiation Durability

Relative DifferencesIn Radiation Durability•Set IF169 = 1

IF137: 2.5X Increased•Radiation Durability

IF132: 48X Increased•Radiation Durability

Radiation Durability Test Conditions•All Fluids Had Comparable Absorbances: ~ 0.09/cm•Two Samples Of Each Fluid Tested•No Active Recycle Used

Different Gen2 Fluids Show Very Different Radiation Durabilities

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Compare IF132 Active Recycle Performance

Radiation Durability Testing With•No ARP, Version 3 ARP, Version 4 ARP•5 Replicates, 15 Total Experiments

Exposure Time Chosen To Supply

Average Fluid Dose = 8.4 J/cm2

•14 Days Of Fluid Usage •At 0.6 J/cm2 Daily Fluid Dose

Average Window Dose = 18 kJ/cm2

•Approximately 1 Day Of Use In Scanner

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00.050.1

0.150.2

0.250.3

0.350.4

0.450.5

0 1 2 3 4 5 6 7 8 9 10

Fluid Dose (J/cm2)

Indu

c. F

luid

Abs IF169 No ARP

IF137 No ARPIF132 No ARPIF132 Ver. 3 ARPIF132 Ver. 4 ARP

No ARP

With ARP

00.050.1

0.150.2

0.250.3

0.350.4

0.450.5

0 1 2 3 4 5 6 7 8 9 10

Fluid Dose (J/cm2)

Indu

c. F

luid

Abs IF132 No ARP

IF132 Ver. 3 ARP

IF132 Ver. 4 ARP

No ARP

With ARP

IF132 Active Recycle: Fluid Life

Relative DifferencesIn Radiation Durability•Set No ARP = 1

ARP Version

Ver. 3: 3X Increased•Radiation Durability

Ver. 4: 9X Increased•Radiation Durability

Induced Fluid Absorbance Rate•Fit With Simple Linear Model•Observe Sub-linear Increase In Absorbance

Average 5 Radiation Durability Experiments

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0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

0 2 4 6 8 10 12 14Window Dose (kJ/cm2)

Indu

c. W

indo

w A

bs

IF132 No ARP

IF132 Ver. 4 ARP

IF132 Active Recycle: Window Life

0.01 Abs / Window•With Ver.4 ARP•After 14 kJ/cm2

2.3% Trans. Drop

Not Optimal Window Test •Dose ~1 Day Window Use

But In This Test•Only 1 liter Of Fluid•So Fluid Absorbance

Climbs During Test

Induced Window Abs. For Two WindowsLow Window Contamination Below 6 kJ/cm2

•Suggestive Of Incubated Process

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ConclusionsHigh Index Immersion Lithography Status• High-n Fluid and Active Recycle: Good• High-n Last Lens Element: ?

•Awaiting LuAG, BaLiF, etc.• High-n Scanners Status: Await Announcement

High-n Immersion Imaging and Defectivity• PAG Leaching Low• Materials Of Construction, Filters

•Can Cause Absorbance Increases, Removed By Active Recycle•Film Forming Residues, Avoided By Proper Materials Choices

• For Droplets Which Dry On Wafer

Radiation Durability Of Different High-n Fluids• Can Vary Dramatically

IF132 Active Recycle Ver. 4 Has Improved Performance• 9X Increase In Fluid Lifetime Compared To No ARP• Window Contamination Exhibits Incubation Period

Active Recycle Important For Reduced Window Contamination