multilayer optics for next-generation euvl systems workshop/oral 10 op-1...2009/07/16 · euv...
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Multilayer optics for next-generation EUVL systems
Regina [email protected]
Lawrence Livermore National Laboratory
July 16, 2009
This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
2009 International Workshop on EUV Lithography, Honolulu, Oahu
Regina Soufli, 07/15/09
Eberhard Spiller
Russell Hudyma
Eric Gullikson (LBNL)
John S. Taylor
Gary Sommargren
Michael A. Johnson
Jim Folta
Don Sweeney
Chris Walton
Andy Aquila (LBNL)
Franklin Dollar (LBNL)
Jeff C. Robinson
Sherry Baker
Jay Ayers
Shannon Ayers
Susan Ratti
Mark Schmidt
Fred Grabner
Rick Levesque
Key Contributors
Regina Soufli, 07/15/09
Presentation Outline
• General principles of EUVL optical substrates, multilayer coatings, roughness and scattering, precision surface metrology
• Example #1: 0.30-NA Micro-Exposure Tool (MET) (two-mirror micro-field system)
• Example #2: 0.1-NA Engineering Test Stand (ETS) (four-mirror scanning system)
• Example #3: EUVL collector substrates, polyimide smoothing• EUV multilayer optics for solar physics• Diffraction limited x-ray mirrors for free-electron lasers
Regina Soufli, 07/15/09
EUVL requires all-reflective optical systems
ETS POB1 - 20000.1 NA
Full-field scanner
SES POB2 - 20010.1 NA
Static fieldMET
2002-today0.3 NA
µstepper
10x1 - 199610x2 - 1999
0.1 NA“Microstepper”
ETSCondenser
Ripple-PlateCondenser WaferM1
M2M3
M4
M5
M6Mask
High NAProjection System
EUV AIMs ToolProposed 2001
Regina Soufli, 07/15/09
In the EUV/x-ray range, the reflective performance of materials is governed by the effect of total external reflection
EUV/x-ray region coincides with core electron binding energies →strong absorption. Refractive index n is expressed as a complex number: n = 1- δ + iβ, where δ, β << 1
For grazing incidence angles θ ≤ θc ≈√2δ, total external reflection occurs (similar to the “total internal reflection” effect at visible wavelengths, per Snell’s law)
θc ~ λ√Z
0.0001
0.001
0.01
0.1
1
0 30 60 90θ (deg)
Ref
lect
ance
SiO2, ideal case
hν = 91.8 eV (λ = 13.5 nm)
D. T. Attwood, Soft X-rays and Extreme Ultraviolet Radiation, Principles and Applications, Cambridge University Press (1999).
E. Spiller, Soft X-ray Optics, SPIE Press, Bellingham, WA (1994).
Regina Soufli, 07/15/09
Multilayer interference coatings
θδθλ 20 sin
21sin2 −= dm
λ0
(2)(1) ( ) ( ) ( )λβλδλ 111 1 in +−=
( ) ( ) ( )λβλδλ 222 1 in +−=
d
°→= 90,1 θm
d20 ≈λ
θ
Bragg equation for multilayers:
(near-normal incidence)
For N bilayers: Electric field amplitude is increased by ~ N, intensity is increased by N2
Regina Soufli, 07/15/09
Multilayer materials selection is driven by optical properties
0.0001
0.001
0.01
0.1
1
100 200 500 1000
hν = 91.8 eV Molybdenum (Mo)
β
δ
Photon Energy (eV)
-0.025
0
0.025
0.050
100 200 500 1000
hν = 91.8 eV Silicon (Si)
β
δ
Photon Energy (eV)
Multilayer materials need to:
have good optical contrast in the desired energy region of operation
be chemically compatible with each other
form stable interfaces
Regina Soufli, 07/15/09
Multilayer microstructure and stress properties depend on deposition method, Γ-ratio and layer thicknesses
R. Soufli, D. L. Windt, J. C. Robinson, et al, “Development and testing of EUV multilayer coatings for the atmospheric imaging assembly instrument aboard the Solar Dynamics Observatory”, Proc. SPIE 5901, 59010M (2005).
-900
-800
-700
-600
-500
-400
0.1 0.2 0.3 0.4 0.5
.. st
ress
=0 d
irec
tion.
.
↓
↓
↓
↓
Mo/Si multilayers
131 Å171 Å193.5 Å211 Å
Γ ratio of Mo
Mea
sure
d St
ress
(MPa
)DC-magnetron sputtered Mo/Si multilayer with Γ=0.16 at 19.35 nm
Γ = dMo / dtotdMo
Regina Soufli, 07/15/09
0
0.2
0.4
0.6
160 170 180
Γ=0.175 Γ=0.165Γ=0.155
Γ=0.23
θ = 85 degMo/Si, N=40
Wavelength (Å)
Ref
lect
ance
0
0.25
0.50
0.75
125 130 135 140
Γ = 0.40Γ =0.45
Γ=0.32Γ = 0.36
θ = 85 degMo/Si, N=50
Wavelength (Å)
Ref
lect
ance
0
0.1
0.2
0.3
0.4
0.5
180 185 190 195 200 205
Γ = 0.19Γ = 0.17Γ = 0.16Γ = 0.135
θ = 85 degMo/Si, N=40
Wavelength (Å)
Ref
lect
ance
Γ-ratio also affects multilayer reflectivity, bandwidth and out-of-band suppression
Regina Soufli, 07/15/09
Highly reflective and precise multilayer optics enable normal-incidence imaging at EUV wavelengths
DC-magnetron sputtered Mo/Si projection optics for a 0.1-NA, 24 mm x1.5 mm ring field EUV step-and-scan system operating at 13. 35 nm (EUVL program)
Performance requirements for
multilayer-coated EUVL optics
• Wavefront control
• Spectral matching
• High + uniform reflectance
• Lifetime stability
M1
M2
M3R. Soufli et al, SPIE Vol. 4343, p.51-59 (2001)
Regina Soufli, 07/15/09
C1
C2
C4
ProjectionOptics
C3
CondenserOptics
M1
M2
Mask
M4
M3
PlasmaSource
Wafer
The Engineering Test Stand (ETS) employs a 0.1-NA ring-field imaging system for a 24-mm field of view
AssembledCamera
D. A. Tichenor et al., “System integration and performance of the EUV Engineering Test Stand,” Proc. SPIE 4343, 19–37 (2001).
Regina Soufli, 07/15/09
Four ETS Set 2 camera substrates on their mounting fixtures
M3
M2M1
M4
Figure = 0.25 nm rms Figure = 0.35 nm rms
Figure = 0.22 nm rms Figure = 0.25 nm rms
ETS substrates made by Tinsley
Regina Soufli, 07/15/09
Mask
Primary
Secondary
Wafer
Source Condenser (2 & 3)
Condenser 1
Micro-Exposure Tool (MET) System Characteristics
• 5x reduction• NA 0.30 (20 nm resolution)• 600 μm x 200 μm field• Residual WFE 0.42 nm rms• Aspheric departure
• M1: 3.8 μm• M2: 5.6 μm
• Obscuration: 10%
The Micro-Exposure Tool (MET ) provides early learning with a high-NA imaging system
Carl Zeiss manufactured the MET camera substrates
Regina Soufli, 07/15/09
EUVL substrates need to satisfy stringent figure and finish specifications
SET 1 SET 2Figure MSFR HSFR Figure MSFR HSFR
MET 1 (primary) 0.43 0.23 0.49 0.18 0.28 0.370.43 0.33 0.54 0.22 0.25 0.38
MET 2 (secondary) 0.25 0.34 0.38 0.22 0.30 0.32— 0.46 0.38 — 0.28 0.37
Specification 0.33 0.30 0.50 0.25 0.20 0.40
— measured by Carl Zeiss— measured by LLNLAll numbers given in nm rms
U. Dinger, G. Seitz, S. Schulte, et al., “Fabrication and metrology of diffraction-limited soft x-ray optics for the EUV microlithography,” Proc. SPIE 5193, 18–28 (2004).
R. Soufli, R. M. Hudyma, E. Spiller, et al., “Sub-diffraction-limited multilayer coatings for the 0.3 numerical aperture micro-exposure tool for extreme ultraviolet lithography,” Appl. Opt. 46, 3736–3746 (2007).
Figure errors lead to imaging aberrations –loss of resolution
MSFR leads to flare, loss of contrast
HSFR leads to loss of reflectance (throughput)
Regina Soufli, 07/15/09
10-2
102
106
1010
1014
10-8 10-6 10-4 10-2
Spatial frequency f (nm-1)PS
D (n
m4 )
Si test substrate by Vendor 2Si test substrate by Vendor 1
0.37 mm2.95 mmZygo 2x Zygo 20x
10 μmAFM
2 μm
σ = 0.16 nm rmsσ = 0.36 nm rms
σ = 0.19 nm rmsσ = 0.19 nm rms
~ 0.16 μrad rms
~ 0.3 μrad rms
Full-
aper
ture
inte
rfer
omet
ry
AFM
EUVL optics require state-of-the-art surface metrology for the figure, mid- and high spatial frequency ranges
Regina Soufli, 07/15/09
Zeiss measurement (MET M1)flipped and rotated to register
0.22 nm rms when clipped and binned
LLNL measurement (MET M1) by Phase Shifting Diffraction Interferometry (PSDI)
magnification adjusted fractionally by 1.7x10-5
0.29 nm rms when clipped and binned
-1 nm +1 nm
Visible-light, phase-shifting diffraction interferometry was used at LLNL to measure EUVL camera optics
G. E. Sommargren, D. W. Phillion, M. A. Johnson, N. Q. Nguyen, A. Barty, F. J. Snell, D. R. Dillon, L. S. Bradsher, “100-picometer interferometry for EUVL”, Proc. SPIE 4688 316-328 (2002).
Sommargren, G.E., “Phase shifting diffraction interferometry for measuring extreme ultraviolet optics,” OSA Trends in Optics and Photonics Vol. 4, Extreme Ultraviolet Lithography, Kubiak and Kania, eds. (Optical Society of America, Washington, DC 1996), pp. 108-112.
Regina Soufli, 07/15/09
DC-magnetron sputtering is a proven deposition technique for the multilayer-coating of EUVL camera and collector optics
R=660 mm
R=1016 mm
Mo 559 X 127 mm2Si
M1
M3 M2
M4
Underneath view of LLNL chamber lid with 5 sputtering targets
70.0% N=60
Γ=0.34
68.9% N=60
Γ=0.34
67.5%N=40 Γ=0.4
Regina Soufli, 07/15/09
LLNL cleaning facility for optical substrates
Custom-developed process includes: rinsing in a water-based solution, followed by drying in N2 environment using semiconductor-grade system (YieldUp™, pictured). Located next to multilayer deposition system.
LLNL AFM images on a Zerodur AIA flight substrate: (i), (ii) as-received and (iii), (iv) after cleaning.
R. Soufli, S. L. Baker, et. al, Appl. Opt. 46, 3156-3163 (2007).
Regina Soufli, 07/15/09
The reflectometry and scattering beamline 6.3.2 at the ALS synchrotron (LBNL) is used for at-wavelength characterization of EUV/x-ray optics
LG156
Beamline Specifications• Wavelength precision: 0.007%• Wavelength uncertainty: 0.013%• Reflectance precision: 0.08%• Reflectance uncertainty: 0.08%• Spectral purity: 99.98%• Dynamic range: 1010
12.5 13.0 13.5 14.00
10
20
30
40
50
60
70
12.90 12.95 13.0067.5
68.0
68.5
69.0
Ref
lect
ance
(%)
Wavelength (nm)
PTB CXRO
Cross-calibration results are shown between beamline 6.3.2 (CXRO) and PTB, BESSY synchrotron (Berlin, Germany)
Beamline scientist = Eric M. Gullikson
1-50 nm wavelength range
For large optic stage:• 40 μm (v) × 300 μm (h) beam size• 100 μm positioning precision (x,y,z)• 0.05 deg θ-precision• 0.5 deg ϕ-precision• Photodiode acceptance = 2.4 deg
2 filter wheels 4 gratings
Regina Soufli, 07/15/09
1. Simulate deposition process
2. Select optimum (v2/v1, θ1), to achieve desired thickness profile
3. Measure results on test optic and iterate
Chamber center
Target
Optic
θ = 0o
v2
v1
v2
θ = θ1θ = - θ1
vspin
10x Schwarzchild primary
Secondary
Achieved using velocity modulation. Until recently, such steep thickness gradients were believed to be possible only by positioning hardware masks over the optical substrate
Velocity modulation is a rapidly converging method used for ultra-precise multilayer film thickness control
Regina Soufli, 07/15/09
DC-magnetron sputtered coatings using velocity modulation demonstrate excellent process stability
Multilayer thickness profiles deposited over a period of 11 months using identical coating recipes
SET 1, 05/01/01SET 2, 03/20/02
MET primary MET secondary
SET 1, 05/01/01SET 2, 03/20/02
Regina Soufli, 07/15/09
Coating profile for EUVL camera optics is optimized for lowest added figure error, rather than peak-to-valley thickness variation
Normalized film thickness as determined by EUV reflectance measurements
Non-compensablemultilayer-added figure error
Added figure error = 0.037 nm rms
RMS of the figure error, weighting the data by illuminated area
subtract best-fit spherical term, compensable during alignment
λ0
Regina Soufli, 07/15/09
We have developed projection optics with sub-diffraction-limited performance during the EUVL program
39-nm, 3:1 elbows (Patrick Naulleau, LBNL)
Added figure error = 0.032 nm rms
M1 mirror, PO Box 2 SES at ALS
M2 mirror, MET Set 1MET camera
Added figure error = 0.044 nm rms
Measured wavefront = 0.55 nm rmsK. A. Goldberg et al, J. Vac. Sci. Technol. B 22(6), 2956-2961 (2005)
Printed 20 nm equal-line, and 21 nm isolated-line features P. P. Naulleau et al
R. Soufli et al., Proc. SPIE 4343, 51-59 (2001)
R. Soufli et al., Appl. Opt. 46, 3736-3746 (2007)
Regina Soufli, 07/15/09
Substrate roughness “propagates” through the multilayer stack and causes flare and loss in mirror reflectance due to scattering in non-specular directions
D.G. Stearns, D. P. Gaines, D. W. Sweeney and E. M. Gullikson, “Non-specular x-ray scattering in a multilayer-coated imaging system”, J. App. Phys. 84, 1003-1028 (1998).
Regina Soufli, 07/15/09
LLNL precision surface metrology lab
• Digital Instruments Dimension 5000™ Atomic Force Microscope (AFM) includes acoustic hood and vibration isolation. Noise level = 0.03 nm rms
• Zygo NewView™ Optical Profiling Microscope
• LEO 1560 ™ Scanning Electron Microscope (SEM)
Zygo AFM
SEM
Regina Soufli, 07/15/09
1 101E-5
1E-4
1E-3
0.01
0.1
1
10
10010 100
MET M2
1/P 0d
P/d
Ω
Scattering Angle (deg)
Measured Calculated
Displacement in image plane (mm)
1E-7 1E-6 1E-5 1E-4 1E-3 0.01 0.110-2
100
102
104
106
108
1010
1012MET M2-2a
PS
D (n
m4 )
Frequency (1/nm)
Zeiss LLNL
MET 1 (primary) MET 2 (secondary)
Substrate HSFR 0.37 nm rms 0.32 nm rms
Expected loss ΔR 6.1% 5.2%
Measured R 61.2% 62.4%
R + ΔR 67.3% 67.6%
Detailed models have been developed and validated experimentally for the scattering from multilayer-coated EUV optics
D. G. Stearns, “Stochastic model for thin film growth and erosion,” Appl. Phys. Lett. 62, 1745-7 (1993). E. M. Gullikson, “Scattering from normal incidence EUV optics”, Proc. SPIE 3331, 72-80 (1998). D.G. Stearns et al, “Non-specular x-ray scattering in a multilayer-coated imaging system”, J. App. Phys. 84, 1003-1028 (1998).
LLNL / Zeiss metrology validation
LLNL metrology / scattering model / ALS scattering measurements validation
R. Soufli et al., Appl. Opt. 46, 3736-3746 (2007)
Regina Soufli, 07/15/09
133.75 Å
133.37 Å
contour sep.= 0.1 Å
65.8 %
63.3 %
contour sep.= 0.3 %
contour sep.= 0.1 Å
contour sep.= 0.3 %
2D EUV reflectance maps serve as an additional method for verifying substrate finish uniformity
2D contour maps of ETS optic M2 obtained at ALS beamline 6.3.2
HSFR non-uniformity leads to EUV reflectance variations on the multilayer-coated optic
Regina Soufli, 07/15/09
We have developed EUV multilayer optics and precision metrologies for next-generation EUV solar physics and space weather satellites
Multilayer-coated flight mirrors for NASA’s Solar Dynamics Observatory (SDO). Launch date: November 2009
R. Soufli, et al, Appl. Opt. 46, 3156-3163 (2007).
R. Soufli, et al, Proc. SPIE 5901, 59010M (2005).
Multilayer-coated test mirrors for NASA/NOAA’s GOES-R space weather satellite. 6 EUV wavelengths , 9.4 nm to 30.4 nm. Launch date: 2014
7 EUV wavelengths (9.4 nm to 33.5 nm)
Regina Soufli, 07/15/09
10-2
100
102
104
0.0001 0.001 0.01 0.1
AIA-1001-002 (Tinsley)
Spatial frequency (nm-1)
PSD
(nm
4 )
0.1
10
1000
100000
0.0001 0.001 0.01 0.1
Primary 04R0416 (Sagem)
Spatial frequency (nm-1)
PSD
(nm
4 )
LLNL AFM measurements on NASA flight substrates reveal surface morphology related to specific polishing techniques
dffSff
f
)(22
1
2 πσ ∫= where S(f) ≡ PSD (nm4), f1= 10 -3 nm-1 , f2 = 5×10-2 nm-1
2×2 μm2, locs. A, B, C, D
10×10 μm2, locs. A, B, C, D
2×2 μm2, locs. A, B, C, D, E
10×10 μm2, locs. A, B, C, D, E
10×10 μm2, loc. B 2×2 μm2, loc. B σ = 0.14 nm rms 10×10 μm2, loc. E 2×2 μm2, loc. E
σ = 0.51 nm rms
Vendor 1, Zerodur™ substrate Vendor 2, Zerodur™ substrate Atmospheric Imaging Assembly (AIA) instrument, Solar Dynamics Observatory (SDO)
R. Soufli, S. L. Baker, D. L. Windt, E. M. Gullikson, J. C. Robinson, W. A. Podgorski, L. Golub, Appl. Opt. 46, 3156-3163 (2007)
Regina Soufli, 07/15/09
0
10
20
30
40
50
60
70
120 125 130 135 140
Mo/Si, Γ = 0.36N=50
θmeas= 87 deg
M4-051116
A4 (witness, Si wafer substrate)
A2 (secondary, Sagem 0420 substrate)
A3 (primary, Sagem 416 substrate)
A1 (witness, Si wafer substrate)
Wavelength (Å)
Ref
lect
ance
(%)
Flight mirror Primary (A3) Secondary (A2)
Substrate roughness (Å
rms)5.0 5.2
Rpeak (%) 56.2 58.8∆R*
(%, absolute) 8.5 8.4
Rpeak +∆R 64.7 67.2
*∆R = predicted reflectance loss due to high-spatial frequency roughness, based on AFM measurements of the substrate and on a multilayer growth model. Calculation performed by E. M. Gullikson, LBNL.
Measured EUV reflectance of multilayer-coated NASA mirrors is consistent with substrate roughness measured by AFM at LLNL
A1 (Si wafer
substrate)
A2 (secondary)
A3 (primary)
A4 (Si wafer substrate)
Regina Soufli, 07/15/09
EUVL collector optics require special substrate materials and polishing techniques
1.08 nm
-1.90 nm -3.38 nm
2.77 nm
(i) (ii) 2 μm 10 μm
(iii) (iv) 2 μm 10 μm
3.06 nm
-4.51 nm -3.47 nm
2.74 nm
HSFR0.05 μm < Λ < 2 μm
Process 1 0.30 nm rmsProcess 2 0.84 nm rms
SiC, Process 1
SiC, Process 2
D. S. Martínez-Galarce, P. Boerner, R. Soufli, B. De Pontieu, N. Katz, A. Title, E. M. Gullikson, J. C. Robinson, S. L. Baker, “The high-resolution lightweight telescope for the EUV (HiLiTE)”, Proc. SPIE 7011 , 70113K (2008).
Regina Soufli, 07/15/09
EUVL collector optics have more relaxed figure specs compared to camera optics and could be fabricated using low-cost techniques
• Aspherical mirrors made by conventional figuring / finishing are very expensive
• Diamond-turned (metal) or ground (ceramic) mirrors are much cheaper and meet EUVL collector figure specs but have insufficient high-spatial frequency roughness (HSFR)
Proposed solution:
• Fabricate diamond-turned metal (e.g. Al) or ground ceramic (e.g. SiC) mirrors
• Reduce HSFR with smoothing film
• Follow with appropriate coating (single-layer or multilayer) for EUV reflectance
J. A. Folta, C. Montcalm, J. S. Taylor, E. A. Spiller, “Low-cost method for producing extreme ultraviolet lithography optics”, U.S. Patent No. 6,634,760.
Regina Soufli, 07/15/09
10-2
103
108
1013
1018
10-8 10-6 10-4 10-2 100
diamond-turned Alpolyimide on Al, ML-coated
Frequency (nm-1)
PSD
(nm
4 )
Polyimide-smoothing of diamond-turned EUVL collector substrates dramatically improves HSFR while maintaining figure
Slope error = 100 μrad rms
σ = 2.7 Ǻ rms
σ = 17.6 Ǻ rms
AFM
Diamond-turned Aluminum surface, after polyimide and Mo/Si multilayer coating
Polyimide smoothes high spatial frequency roughness, including 10 μm-range diamond turning marks
180 μm
140
μm
Measurements obtained with a Zygo New ViewTM optical profiling microscope operated at 40× objective lens magnification
Diamond-turned Aluminum surface, as-received from manufacturer
100 nm
-200 nm
0 nm
Visible light interferometry results from multilayer-coated, diamond-turned condenser mirror
Height map Slope map
R. Soufli, E. Spiller, M. A. Schmidt, J. C. Robinson, S. L. Baker, S. Ratti, M. A. Johnson, E. M. Gullikson, Opt. Eng. 43(12), 3089-3095 (2004).
Acknowledgement: TOPO software by D. L. Windt
Regina Soufli, 07/15/09
R. Soufli, at al, Proc. SPIE 7077, 707716 (2008). A. Barty et al, Optics Express (2009).
10-6
10-4
10-2
100
0 20 40 60 80
IMD calc., dB4C= 50.5 ± 0.2 nm
λ = 13.5 nm (hν = 92.8 eV)
r = 90 mmr = 50 mmr = 30 mm
θ (deg)
Ref
lect
ance
We have developed diffraction-limited, damage-resistant x-ray mirror coatings for the LCLS free-electron laser
50.5 nm-thick B4C on Si substrate. Coating variation = 0.14 nm rms (spec = 1 nm rms) across 175 mm CA
50 nm-thick SiC on Si substrate. Coating variation = 0.34 nm rms (spec = 1 nm rms) across 385 mm CA
450 mm
Regina Soufli, 07/15/09
100
101
102
103
104
105
10-4 10-3 10-2 10-1
1 mTorr, HSFR = 0.15 nm rms10 mTorr, HSFR = 0.47 nm rms
B4C films
Spatial frequency (nm-1)
PSD
(nm
4 )
500×500 nm2 detail from 2x2 μm2 AFM scan
where S(f) ≡ PSD (nm4), f1= 5×10-4nm-1
f2 = 5×10-2 nm-1( )∫= 2
1
22 f
f dfff Sπσ
500×500 nm2 detail from 2x2 μm2 AFM scan
Stress = -1.1 GPa
Stress = -2.3 GPa
B4C thin film deposition parameters were especially modified to reduce coating stress
50 nm-thick B4C films
Regina Soufli, 07/15/09
Acknowledgements
• The EUVL results in this presentation have been obtained through collaboration between researchers at Lawrence Livermore, Lawrence Berkeley and Sandia National Laboratories. Funding was provided by the EUV LLC (through a Cooperative Research and Development Agreement) and by Sematech
• Funding for the AIA / SDO EUV multilayer optics was provided by the Smithsonian Astrophysical Observatory
• Funding for the SUVI / GOES-R EUV multilayer optics was provided by Lockheed Martin Corporation
• LCLS work was funded by DOE Contract DE-AC02-76SF00515. This work was performed in support of the LCLS project at SLAC.
• This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.