New Developments in
Second Generation 193 nm
Immersion Fluids For Lithography
with 1.5 Numerical Aperture
S. Peng, R. H. French, W. Qiu, R. C. Wheland,
M. K. Crawford, M. F. Lemon, M. K. Yang
DuPont Co. Central Research,
E356-384, Experimental Station, Wilmington DE 19880-0356
2
Immersion Lithography Roadmap
Immersion Fluid
A/cm < 0.15
Projection
Lens
MITLL
Photoresist Coated
Silicon Wafer
3 Generations
Of Immer. Fluids
1st Gen = Water
• n193 = 1.436: λeff = 135 nm
2nd Generation IF
• n193 > 1.65: λeff = 117 nm
3rd
Generation IF
• n193 > 1.9: λeff = 102 nm
1st
Year
2001
2004
2006-8
2009-11
2011
2011
FS hp
nm
130
90
65 - 45
38
32
32
λ nm
248
193
Dry
193i H2O
193i Gen2
EUV
13.4
193i
Gen3
index
1
1
1.436
1.65
1
1.9
NA
0.75
0.85
0.93 – 1.3
1.5
0.3
1.8
k1
0.39
0.40
0.31
0.30
0.72
0.30
Immersion Fluid Index Determines Lens Performance!
2005/09/30 Roger H. French © 2005
3
Critical Issues For Post Water Immersion Lithography
Need High Index Throughout the Imaging Stack1
High Index Last Lens Element
• To Avoid Curved Last Lens Element
• And The Tight IF Abs. and dn/dT Spec
Immersion Fluids
• 2nd Generation (n>1.65)
• For 38 nm hp And Below
• Low Absorbance, High Index
• Radiation Durable
• Process Compatible
• 3rd Generation (n>1.9)
• For 32 nm hp And Below
Wafer Materials
• High Index Topcoats
• High Index Resists
1. R. H. French, H. Sewell, et al., JM3, 4(3), 031103, Jul–Sep 2005.
2005/09/30 Roger H. French © 2005
4
Immersion Fluid Property Requirements1
Three Candidate Immersion Fluids
• IF131, IF132 and IF169
1. R. H. French, H. Sewell, et al., JM3, 4(3), 031103, Jul–Sep 2005.
2005/09/30 Roger H. French © 2005
5
Outline
Candidate 2nd Gen. Immersion Fluids
Fluid Refractive Index
• Fluid dn/dT
Fluid Optical Absorbance/cm
• Best Absorbance To Date
• Environmental Effects: Oxygen
Candidate
Immersion
Fluid
193
nm
Index
dn/dT
(ppm/K)
Best
193 nm
Abs/cm
Water1
1.436
-100 ppm/K
0.01/cm
IF131
1.6418
-155 ppm/K 0.169/cm
IF132
1.6468
-145 ppm/K 0.047/cm
IF169
1.6524
-145 ppm/K 0.082/cm
Imaging Performance
Additional Fluid Properties
Preliminary Radiation Durability Results
Conclusion
2005/09/30 Roger H. French © 2005
6
Index Of Refraction By Minimum Deviation
The fluid refractive index, nfluid(λ)
• is given by
Prism Minimum Deviation Angle Experiment
⎡α + δ (λ ) ⎤
sin ⎢
2 ⎥⎦
n fluid (λ ) = ⎣
ngas (λ )
⎛α ⎞
sin⎜ ⎟
⎝2⎠
• where α = prism apex angle
• δ(λ) = measured minimum deviation angle
• ngas(λ) = index of the N2 ambient
• Reproducibility ~ 5 x 10-4
Measure deflection angle
through liquid-filled prism.
Developed With NIST & Woollam
For Current dn/dT Measurements
• Measure On Two Instruments
• VUV-Vase Temperature = ~32oC
• DUV-Vase Temperature = ~22oC
R. H. French, et. al.SPIE 5377-173, (2004), R. A. Synowicki, et. al. Journal of Vacuum Science And Technology B, 22, 6, 3450, (2004).
2005/09/30 Roger H. French © 2005
7
IF132: 2nd Gen. IF: Index of Refraction
1.7
• IF132 To Water
n(d-line)
• Increased To 1.483
Dispersion Δn
• Increased To 0.164
n(193 nm) = 1.647
Index of Refraction:n
Compare
1.65
IF132: n(193 nm)=1.647
1.6
IF132: Δ n = 0.164
Δn ≡ n(193 nm) − nd (589.3 nm)
1.55
n(d-line) = 1.483
1.5
1.45
Water: n(193 nm)=1.437
1.4
Water: Δn = 0.103
1.35
1.3
190
n(d-line) = 1.334
240
290
340
390
440
490
540
Wavelength (nm)
Define Dispersion Δn
2005/09/30 Roger H. French © 2005
Δn ≡ n(193 nm) − nd (589.3 nm)
n193nm = nd + Δn
590
8
dn/dT From Spectral Indices At Two Temperatures
IF108-12804 Water (dn/dT= - 108ppm/K)
IF131-11909 (dn/dT = -155ppm/K)
1.44
n (21C)
1.42
n (33C)
1.4
1.38
1.36
1.34
1.32
190
290
390
490
Wavelength (nm)
Index of refraction "n"
Index of refraction "n"
1.46
590
2005/09/30 Roger H. French © 2005
index (23oC)
index (34oC)
290
390
490
Wavelength (nm)
n
(22
290
390
490
Wavelength (nm)
590
IF169-12722 (dn/dT = -145 ppm/K)
590
Index of refraction "n"
Index of refraction "n"
IF32-12790 (dn/dT = -145 ppm/K)
1.66
1.64
1.62
1.6
1.58
1.56
1.54
1.52
1.5
1.48
1.46
190
1.66
1.64
1.62
1.6
1.58
1.56
1.54
1.52
1.5
1.48
1.46
190
1.68
1.66
1.64
1.62
1.6
1.58
1.56
1.54
1.52
1.5
1.48
1.46
190
n (21C)
n (32C)
290
390
490
Wavelength (nm)
590
9
dn/dT Results
Low dn/dT Needed To Minimize Imaging Artifacts In Stepper
Dispersion
Δn
= n193 – nd
Candidate
Immersion
Fluid
193 nm
Index
Water (NIST)
1.4367
Water
1.4366
0.103
-108 ppm/K
IF131
1.6418
0.167
-155 ppm/K
IF132
1.6468
0.164
-145 ppm/K
IF169
1.6524
0.164
-145 ppm/K
IF175
1.6640
0.166
dn/dT
ppm/K
-100 ppm/K
Compare Water Results Using Our Vase Prism
• To NIST
• Confirm These Results With John Burnett, Simon Kaplan Of NIST
Our Fluids Have dn/dT Below -250 ppm/K Specification
2005/09/30 Roger H. French © 2005
10
Long Path Length Absorbance Measurements
Relative Transmission Measurements
log10 (T1 ) − log10 (T2 )
A / cm =
t 2 − t1
For Accurate Absorbance/cm Values
• Three To FivePath Lengths
• Calculate Abs. And Std. Dev.
• Statistical Analysis of Reproducibility
Tn (λ ) = T0 (λ )e
−α ( λ ) t n
10cm Path Length Abs. Cell
• For Very Low Absorbance Fluids
2005/09/30 Roger H. French © 2005
11
Immersion Fluid Optical Absorbance: Best To Date
IF131: 0.17/cm
.4
.1
IF131-11319 Abs @193 nm = 0.17/cm +/- 0.016
0
180
200
220
240
260
280
Wavelength (nm)
IF169: 0.091/cm
.3
.2
IF132-12790 Abs @193 nm = 0.072+/-0.004/cm
IF132-12387 Abs @193 nm = 0.064+/-0.01/cm
IF132-12238 Abs @193 nm = 0.047+/-0.005/cm
.1
.3
0
180
193 nm
Absorbance per cm, base 10 (A/cm)
.4
IF132: 0.047/cm
193 nm
.2
Absorbance per cm, base 10 (A/cm)
.3
193 nm
Absorbance per cm, base 10 (A/cm)
.4
.2
200
220
240
Wavelength (nm)
IF169-12270 Abs @193 nm = 0.091+/-0.012/cm
.1
Low Absorbance Immersion Fluids
• Reproducible Results
0
180
200
220
240
Wavelength (nm)
2005/09/30 Roger H. French © 2005
260
280
260
280
12
Urbach Edge Positions
Extrinsic Absorptions
• Typically Have
=>Negative Rad. Of Curvature
Intrinsic Absorption Edge
• Has An Exponential Shape
W
Urbach Edge Analysis
• Fits This Exp. Edge Shape
Position Of Abs. Edge
• Water UEP = 185.2 nm1
• IF131: UEP = 190.2 nm
• IF169: UEP = 186.5 nm
• IF132: UEP = 186.2 nm
Fluids Meet FLE Abs. Spec.
• Close To Meeting CLE Abs. Spec.
193 nm
E − E0
Absorbance per cm, base 10 (A/cm)
α (E) = e
−
.4
Urbach Edge Position:cm
IF131: UEP = 190.2
IF169: UEP = 186.5
IF132: UEP = 186.2
.3
.2
FLE Abs. Spec
.1
CLE Abs. Spec
0
186
1. R. H. French, H. Sewell, et al., JM3, 4(3), 031103, Jul–Sep 2005.
2005/09/30 Roger H. French © 2005
190
194
198
202
206
Wavelength (nm)
210
214
13
Reversible Effects Of Environmental Oxygen
2
Oxygen Exposure Experiment
• Initial IF Abs = 0.12/cm
100
1.8
90
1.6
80
• 1 ppm O2
1.4
• Sparge With Nitrogen
• IF Abs. Drops to 0.2/cm
IF Abs. Increases With O2
This Abs. Increase Is Reversible
• By Sparging With Nitrogen
193 nm Abs./cm
• 86 ppm O2
193nm A/cm
O2 ppmw
1.2
60
1
50
0.8
40
0.6
30
0.4
20
0.2
10
0
0
Initital IF
2005/09/30 Roger H. French © 2005
70
Air Expose Sparge 1
Sparge 2
O2 ppmw
• Expose To Air
• IF Abs. Increases to 1.88
14
Imaging 32 nm L/S with 2nd Gen Fluids1
Two Beam Interference Lithography
• Version 1 & 2 Imagers
• 193 nm Excimer Laser
• 3 mm Thick Immersion Fluid
Using Gen 2 Immersion Fluids
Version 1 Imager
With H. Sewell, D. McCafferty, L. Markoya, Wilton
1. R. H. French, H. Sewell, et al., JM3, 4(3), 031103, Jul–Sep 2005.
2005/09/30 Roger H. French © 2005
Version 2 Imager
15
32nm Imaging with IF131 & IF132 High-n Immersion Fluids
32nm Lines And Spaces: Pitch 64nm
IF131
IF132
Using ASML Version 1 Interference Imager
Corresponding To
• NA = 1.5
• k1 = 0.25
With H. Sewell, D. McCafferty, ASML Wilton
R. H. French et al., JM3, 4(3), 031103, Jul–Sep 2005.
2005/09/30 Roger H. French © 2005
16
IF169 Imaging Of 32 nm L/S
Imaging With Our Third Immersion Fluid
32 nm L/S
• Using IF169 Immersion Fluid
• Commercial 193 nm Resist and Topcoat
• On ASML Version 1 Interference Imager
With H. Sewell, D. McCafferty, ASML Wilton
2005/09/30 Roger H. French © 2005
17
32 nm L/S Using IF132 On The ASML Version 2 Imager
Second Tool Imaging 32 nm 1:1
• With IF132
With H. Sewell, D. McCafferty, ASML Wilton
2005/09/30 Roger H. French © 2005
18
Additional Fluid Properties
Rheology And Viscosity
• Comparable To Water
Surface Tension and Contact Angles1
• Lower Than Water
• On Topcoats:
• Compare 90-120o For Water
• To 50-66o For IF132
Fluid-Resist Interactions2
• Beginning Studies Of Linewidth Uniformity and CD Variation
• Using 193 nm Dry Lithography
• Post Exposure Soak Of Wafer Before Develop
• Report On Results At SPIE06
1. R. H. French et al., JM3, 4(3), 031103, Jul–Sep 2005.
2. With ASML
2005/09/30 Roger H. French © 2005
19
193 nm Radiation Durability: IF131
How Does Abs./cm Change Over Time
• Upon IF Irradiation
IF131: Preliminary Rad. Durability Test
Use A Flowing IF System
1
• With Repeated Uses Of The Fluid
• With In-Situ 193 nm Ratiometry
• Of Stepper Exposure
• At Standard Flow Rates
IF131: 193 nm Abs./cm
Post
Before
Irradiation Irradiation:
Clean Up
0.25
0.26
193 nm Optical Absorbance
• Does Not Grow Dramatically
• Can Be Remediated
• Original Fluid Properties Achieved
More Results At SPIE06
2005/09/30 Roger H. French © 2005
In Situ Ratiometry: Abs/cm
Comparable To 12 Hour Lifetime
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
1
Time (Arb. Units)
With J. Sedlacek, V. Liberman, R. Kunz & M. Rothschild, MIT-LL
2
20
193 nm Radiation Durability: IF132
IF132 Shows
IF132: Preliminary Rad. Durability Test
0.6
Irradiation Induced Absorbance
0.5
• Can Be Remediated
IF132: 193 nm Abs./cm
Post
Before
Irradiation Irradiation:
Clean Up
0.09
0.09
In Situ Ratiometry: Abs/cm
• Lower Induced Absorbance
• Fluid Had Lower Initial Absorbance
0.4
0.3
0.2
0.1
Initial Results Promising
• More Experiments In Progress
• More Results At SPIE06
0
0
1
2
3
4
Time (Arb. Units)
With J. Sedlacek, V. Liberman, R. Kunz & M. Rothschild, MIT-LL
2005/09/30 Roger H. French © 2005
5
21
Effect of Fluid Index On Effective Wavelength
Effective Lithography Wavelength
• Determined By Litho Wavelength & Immersion Fluid Index of Refraction
Immer.
Fluid
Water
IF131
IF132
IF133
193 nm
Index
1.436
1.6418
1.6468
1.6524
λeffective
λ eff ≈ λlitho n
IF
134.7 nm
117.8 nm
117.4 nm
117.0 nm
Maximum Wet Numerical Aperture = 1.54
• Using These 2nd Gen. Immersion Fluids
• Assuming A Dry NA Of 0.93
Minimum Feature Size Half Pitches
• k1= 0.30 =>
• k1= 0.28 =>
• k1= 0.27 =>
• k1= 0.25 =>
2005/09/30 Roger H. French © 2005
37.7 nm 1:1 Lines/Spaces
35.2 nm 1:1 Lines/Spaces
33.9 nm 1:1 Lines/Spaces
31.4 nm 1:1 Lines/Spaces
22
Conclusions
2nd Generation 193 nm Immersion Fluids
Candidate
Immersion
Fluid
193 nm
Index
(ppm/K)
Best
193 nm
Abs/cm
IF131
1.6418
-155 ppm/K
0.169/cm
IF132
1.6468
-145 ppm/K
0.047/cm
IF169
1.6524
-145 ppm/K
0.082/cm
dn/dT
These 2nd Gen. Fluids Meet Most Stated Requirements
• 193 nm Index of Refraction
• Temperature Dependence Of the Index: dn/dT
• Optical Absorbance For Flat Last Lens Element
• Close To Curved Lens Element Requirement
Interference Imaging Of 32 nm 1:1 Lines And Spaces
• Demonstrated With All Three Fluids
• Using Two Different Imagers
Preliminary Radiation Durability Results
• Tested Over 12 Hour Equivalent Stepper Lifetime
• With Ability To Remediate The 193 nm Induced Absorption
These 2nd Gen. Immersion Fluids Enable
• 38 nm hp Imaging with k1=0.3
• And 34 nm hp with k1=0.27
2005/09/30 Roger H. French © 2005
23
IF175: Highest Index Candidate IF
IF175: n(193 nm)=1.664
Compare
1.66
n(d-line)
• Increased To 1.498
Dispersion Δn
• Increased To 0.166
n(193 nm) = 1.664
Index of Refraction: n
• IF175 To Water
1.61
IF175: Δ n = 0.166
1.56
1.51
1.498 = n(d-line)
1.46
n(193 nm)=1.437
1.41
Water: Δ n = 0.103
1.36
1.31
190
1.334 = n(d-line)
290
390
Wavelength (nm)
2005/09/30 Roger H. French © 2005
490
590