Sub-diffraction-limited multilayer coatings for the 0.3 numerical aperture micro-exposure tool for extreme ultraviolet lithography
Regina Soufli, Russell M. Hudyma, Eberhard Spiller, Eric M. Gullikson, Mark A. Schmidt, Jeff C. Robinson, Sherry L. Baker, Christopher C. Walton, and John S. Taylor
Regina Soufli,1,*
Russell M. Hudyma,1,2
Eberhard Spiller,1
Eric M. Gullikson,3
Mark A. Schmidt,1
Jeff C. Robinson,1
Sherry L. Baker,1
Christopher C. Walton,1
and John S. Taylor1
1Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, California 94550
2Hyperion Development LLC, 358 South Overlook Drive, San Ramon, California 94582
3Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720
Regina Soufli, Russell M. Hudyma, Eberhard Spiller, Eric M. Gullikson, Mark A. Schmidt, Jeff C. Robinson, Sherry L. Baker, Christopher C. Walton, and John S. Taylor, "Sub-diffraction-limited multilayer coatings for the 0.3 numerical aperture micro-exposure tool for extreme ultraviolet lithography," Appl. Opt. 46, 3736-3746 (2007)
Multilayer coating results are discussed for the primary and secondary
mirrors of the micro-exposure tool (MET): a 0.30 NA lithographic
imaging system with a
field of view at the wafer plane, operating in the
extreme ultraviolet (EUV) region at an illumination wavelength around
. Mo∕Si
multilayers were deposited by DC-magnetron sputtering on large-area, curved MET
camera substrates. A velocity modulation technique was implemented to consistently
achieve multilayer thickness profiles with added figure errors below
rms
demonstrating sub-diffraction-limited performance, as defined by the classical diffraction
limit of Rayleigh (0.25 waves peak to valley) or Marechal (0.07 waves
rms). This work is an experimental demonstration of sub-diffraction-
limited multilayer coatings for high-NA EUV imaging systems, which resulted in the highest resolution microfield EUV images to date.
Claude Montcalm, R. Frederick Grabner, Russell M. Hudyma, Mark A. Schmidt, Eberhard Spiller, Christopher C. Walton, Marco Wedowski, and James A. Folta Appl. Opt. 41(16) 3262-3269 (2002)
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The results for two sets of MET substrates are shown with their respective specifications. All numbers are given in units of nm rms.
Measured at Carl Zeiss, Oberkochen, Germany (see also Ref. 11).
Table 3
Spatial Frequency Ranges Relevant to Flare in the MET Optical System and the Roughness Achieved in These Bands by the Manufacturer of the Set 1 and Set 2 Substrates
Spatial Frequency Range Relevant to Flare
Substrate Roughness (nm rms)
Set 1
Set 2
MET primary
0.11–160 mm−1
0.43
0.27
MET secondary
0.031–50 mm−1
0.35
0.20
Table 4
Decomposition of the MET System Wavefront Error in Fringe Zernike Polynomial Terms Computed for Ideal and Experimental Multilayer Coatings at the Central Field Point (F1)
Term
Description
F1 (Ideal)
F1 (Experimental)
Term by Term Difference
Z1
Piston
−0.0332
−0.0963
0.0631
Z2
x tilt
0.0000
0.0000
0.0000
Z3
y tilt
0.0002
0.0003
−0.0002
Z4
Focus
−0.0404
−0.0521
0.0117
Z5
Third-order astigmatism
0.0001
0.0003
−0.0002
Z6
Third-order 45° astigmatism
0.0000
0.0000
0.0000
Z7
Third-order x coma
0.0000
0.0000
0.0000
Z8
Third-order y coma
0.0000
0.0004
−0.0004
Z9
Third-order spherical
0.0105
0.0290
−0.0185
Z10
x trifoil
0.0000
0.0000
0.0000
Z11
y trifoil
0.0000
0.0000
0.0000
Z12
Fifth-order astigmatism
−0.0001
0.0002
−0.0003
Z13
Fifth-order 45° astigmatism
0.0000
0.0000
0.0000
Z14
Fifth-order x coma
0.0000
0.0000
0.0000
Z15
Fifth-order y coma
0.0001
0.0006
−0.0005
Z16
Fifth-order spherical
0.0098
−0.0233
0.0331
Z25
Seventh-order spherical
−0.0094
−0.0096
0.0002
Z36
Ninth-order spherical
−0.0018
−0.0018
0.0000
RMS wavefront error
0.024
0.034
0.010
The effect of the actual substrate figure error was not included in these calculations.
Table 5
RMS Wavefront Error (WFE) Computed at Eight Points (F1–F8) Across the MET Field for Ideal and Experimental Multilayer Coatings
Field Point
X (μm)
Y (μm)
WFE (nm rms) Ideal
WFE (nm rms) Experimental
Difference (nm rms)
F1
0.00
0.00
0.024
0.034
0.010
F2
0.00
100.00
0.048
0.055
0.007
F3
300.00
100.00
0.019
0.028
0.009
F4
300.00
0.00
0.024
0.027
0.003
F5
300.00
−100.00
0.055
0.053
−0.002
F6
0.00
−100.00
0.017
0.024
0.007
F7
210.00
−70.00
0.024
0.027
0.003
F8
210.00
70.00
0.024
0.033
0.009
Average = 0.006
Table 6
HSFR of the MET Substrates Measured by Atomic Force Microscopy, Calculated EUV Reflectance Loss (ΔR, Given in Absolute %) Due to Light Scattered Outside of the Detector Acceptance Angle in the Reflectometer, and Measured Peak EUV Reflectance (R)
SET 1
SET 2
Primary
Secondary
Primary
Secondary
Substrate HSFR (nm rms)
0.54
0.38
0.38
0.37
Predicted loss ΔR
10.5%
5.5%
6.1%
5.2%
Measured R
58%
62.5%
61.2%
62.4%
R + ΔR
68.5%
68%
67.3%
67.6%
The sum of R and ΔR is consistent within 1% with the experimental Mo∕Si reflectance (N = 40, Γ = 0.4) on an ideally smooth substrate shown in Fig. 3(b), thus demonstrating consistency between all aforementioned results.
Tables (6)
Table 1
Optical Design Parameters for the MET Two-Mirror Camera
MET Primary
MET Secondary
Best-fit-sphere radius (mm)
−312.63 (convex)
340.05 (concave)
Peak aspheric departure (μm)
3.82
5.61
Maximum aspheric slope (μm∕mm)
−1.18
−0.47
Clear aperture radius (mm)
8.4–27
11.4–91.6
Range of incidence angles
2.54°–8.67°
0.67°–1.98°
Table 2
Metrology Results for the Roughness in the Low (Figure), Mid (MSFR), and High (HSFR) Spatial Frequenciesa
The results for two sets of MET substrates are shown with their respective specifications. All numbers are given in units of nm rms.
Measured at Carl Zeiss, Oberkochen, Germany (see also Ref. 11).
Table 3
Spatial Frequency Ranges Relevant to Flare in the MET Optical System and the Roughness Achieved in These Bands by the Manufacturer of the Set 1 and Set 2 Substrates
Spatial Frequency Range Relevant to Flare
Substrate Roughness (nm rms)
Set 1
Set 2
MET primary
0.11–160 mm−1
0.43
0.27
MET secondary
0.031–50 mm−1
0.35
0.20
Table 4
Decomposition of the MET System Wavefront Error in Fringe Zernike Polynomial Terms Computed for Ideal and Experimental Multilayer Coatings at the Central Field Point (F1)
Term
Description
F1 (Ideal)
F1 (Experimental)
Term by Term Difference
Z1
Piston
−0.0332
−0.0963
0.0631
Z2
x tilt
0.0000
0.0000
0.0000
Z3
y tilt
0.0002
0.0003
−0.0002
Z4
Focus
−0.0404
−0.0521
0.0117
Z5
Third-order astigmatism
0.0001
0.0003
−0.0002
Z6
Third-order 45° astigmatism
0.0000
0.0000
0.0000
Z7
Third-order x coma
0.0000
0.0000
0.0000
Z8
Third-order y coma
0.0000
0.0004
−0.0004
Z9
Third-order spherical
0.0105
0.0290
−0.0185
Z10
x trifoil
0.0000
0.0000
0.0000
Z11
y trifoil
0.0000
0.0000
0.0000
Z12
Fifth-order astigmatism
−0.0001
0.0002
−0.0003
Z13
Fifth-order 45° astigmatism
0.0000
0.0000
0.0000
Z14
Fifth-order x coma
0.0000
0.0000
0.0000
Z15
Fifth-order y coma
0.0001
0.0006
−0.0005
Z16
Fifth-order spherical
0.0098
−0.0233
0.0331
Z25
Seventh-order spherical
−0.0094
−0.0096
0.0002
Z36
Ninth-order spherical
−0.0018
−0.0018
0.0000
RMS wavefront error
0.024
0.034
0.010
The effect of the actual substrate figure error was not included in these calculations.
Table 5
RMS Wavefront Error (WFE) Computed at Eight Points (F1–F8) Across the MET Field for Ideal and Experimental Multilayer Coatings
Field Point
X (μm)
Y (μm)
WFE (nm rms) Ideal
WFE (nm rms) Experimental
Difference (nm rms)
F1
0.00
0.00
0.024
0.034
0.010
F2
0.00
100.00
0.048
0.055
0.007
F3
300.00
100.00
0.019
0.028
0.009
F4
300.00
0.00
0.024
0.027
0.003
F5
300.00
−100.00
0.055
0.053
−0.002
F6
0.00
−100.00
0.017
0.024
0.007
F7
210.00
−70.00
0.024
0.027
0.003
F8
210.00
70.00
0.024
0.033
0.009
Average = 0.006
Table 6
HSFR of the MET Substrates Measured by Atomic Force Microscopy, Calculated EUV Reflectance Loss (ΔR, Given in Absolute %) Due to Light Scattered Outside of the Detector Acceptance Angle in the Reflectometer, and Measured Peak EUV Reflectance (R)
SET 1
SET 2
Primary
Secondary
Primary
Secondary
Substrate HSFR (nm rms)
0.54
0.38
0.38
0.37
Predicted loss ΔR
10.5%
5.5%
6.1%
5.2%
Measured R
58%
62.5%
61.2%
62.4%
R + ΔR
68.5%
68%
67.3%
67.6%
The sum of R and ΔR is consistent within 1% with the experimental Mo∕Si reflectance (N = 40, Γ = 0.4) on an ideally smooth substrate shown in Fig. 3(b), thus demonstrating consistency between all aforementioned results.
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