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Fiber Lasers for EUV Lithography
A. Galvanauskas, Kai‐Chung Hou*, Cheng ZhuCUOS, EECS Department, University of Michigan
P. AmayaArbor Photonics, Inc.
* Currently with Cymer, Inc
2009 International Workshop on EUV Lithography, Sheraton Waikiki, July 13‐17, 2009
EUVL Source Power Requirement
180 W~500W EUV Power
CE~2% Required Laser Power ~25kW
U. Hinze et al. , Laser Zentrum Hannover e.V., EUVL Symposium 2007
Spectral Purity Filter T~0.9
Collector 5sr and R=50%
Debris ShieldT~1
Advantages of Fiber Laser Technology
• E‐>O efficiency is highest
• Robust and compact
• Long lifetime/reliable
• High repetition rate capability
• High beam quality
• Superior power scalability
Pulsed Laser ArchitectureCommercial Product Electrical-to-Optical
EfficiencyQ-Switched Yb:Glass fiber 25% - 30%
Q-Switched DPSS or Thin Disc 12 –16 %
RF Excited CO2 8.5-10%
High power fiber laser revolutionHistorical trend in diffraction‐limited
cw fiber laser power
YLR-50000
Commercial incoherently combined50kW cw fiber laser system(non diffraction‐limited: M2 = 33)
Fiber lasers constitute a new and developing technology:‐Continuous improvement in fiber and component technology‐Continuing advances in power
Summary of 13.4nm EUV generation results with pulsed fiber lasers
• First proof‐of‐principle demonstration with a solid‐Sn target
• 2% efficient 13.4nm in‐band EUV generation using Sn‐droplet source
• Kai‐Chung Hou et al, Optics Express 16, 965 – 975 (2008)
• Simi A. George et al, Opt. Express 15, 13942‐13948 (2007)
• A. Mordovanakis et al, Optics Letters 31, 2517 – 2519 (2006)
Main trade‐off for high power pulsed fiber laser drivers for EUVL
• Practical droplet source can not exceed certain maximum repetition rate – For Sn‐droplet source it is considered to be at 80kHz – 100kHz
• Maximum pulse energy from a single fiber is limited by extractable energy and fiber nonlinearities– For 3ns‐10ns pulses max energies are 4mJ‐10mJ respectively
• Consequently, maximum power from single‐fiber EUVL driver can not exceed ~1kW– Practical considerations restricts to much less (approximately to 200W – 500W range)
Single‐Emitter FiberIntegrated Module (SEFIM)200 ‐ 500W (~80‐100kHz, 2‐6ns)
Power Scaling Strategy for 25‐kW Fiber‐Laser EUV Driver
λ1
λ2
λn
Spectrally CombinedModules (SCM)5 ‐ >10kW
~500W EUV
Spatially multiplexed SCM blocks >25kW
Conventional Spectral combining using diffraction gratings
• Based on spatial spectral dispersion of diffraction gratings:
λ1λ2λn
Combined Beam
Fiber Laser Channels
Transform Lens
f f
Linewidth considerations in a MW peak power fiber amplifier
• SPM‐induced spectral broadening:
• Example:– 1MW peak 1ns pulse in 100μm core PCF fiber
Δωmax ≈ 18 GHz*
1 2max 0
1 ( )
1 exp( )20.86n
i ii
i eff i i
g LnT PA gπδω
λ−
=
−=∑
*Consistent with experimental results:Christopher D. Brooks and Fabio Di Teodoro, Appl. Phys. Lett. 89, 111119 (2006)
Beam‐size and bandwidth trade‐off in diffraction‐grating based SBC
Tradeoff • Linewidth and beam‐width requirement to retain mode quality
Small beam‐width • high‐power density on grating
Small linewidth• MW peak power can not achieved, limited by SPM
Example• 20GHz linewidth 1mm beam‐width • 25kW (targeted power) 1000 kW/cm2
• Thermal distortion or damage
102
103
104
105
0.1 1 10
10
100
Beamwidth 1/e2 radius (mm)
Line
width (G
Hz)
Intensity (kW/cm
2)
Design Trade for M2~1.2
Spatial dispersion‐free spectral combining based on sharp‐edge spectral filters
Initial experimental results:•2nm inter‐channel separation, 0.5 nm spectral linewidth•91% combining efficiency, 52 W combined•Combined ns‐duration pulses with 4mJ output energy
• No trade‐off between beam size and channel bandwidth –power scalability per channel and for total power
Commercially available LWP Filters
• No limitation on linewidth and beamwidth
• Sharp transition ‐> high channel density– ~0.8 nm measured on sample– ~0.3 nm available from mfg– Yb3+ has 60 nm gain bandwidth
• Tunability– Measured 50 nm shift in cut‐off
with 28⁰ change of angle– Same sharpness in broad tuning
range
00.10.20.30.40.50.60.70.80.91.0
1058.5 1059.0 1059.5 1060.0 1060.5 1061.0 1061.5
~0.8nm
Wavelength (nm)
Tran
smis
sion
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1000 1010 1020 1030 1040 1050 1060 1070 1080
0º 14º 28º
Wavelength (nm)
Tran
smis
sion
99.7% average R
Commercially available LWP Filters
0.80
0.82
0.84
0.86
0.88
0.90
0.92
0.94
0.96
0.95 0.96 0.97 0.98 0.99 1.00
98.6% 99.4%
99.7%
96.8%
N=40N=20N=10
N=5
ReflectanceO
vera
ll C
ombi
ning
Effi
cien
cy (η
)
High damage threshold:•Energy =1J/cm2 (measured by manufacturer)•Power = 100kW/cm2
Measured performance:•Transmission = 95%, Reflectivity = 99.7%
Residual absorption in this type of coatings:• 2 – 10 ppm
Combining Demonstration Setup
Channel‐Amplifiers
SplitterPump1
Pump2
Pump3
Input BeamCombined Output
F1 F2 F3 F4
Delay Lines
Combiner
80μm core Yb‐doped LMAfibers
Spatial Beam Overlapping
a
dc
b
Combined BeamRed Channel
Blue Channel Green Channel 0
200
400
600
800
1000
0 50 100 150 200 250 300 350
Position (mm)
FWH
M B
eam
Dia
met
er (μ
m)
0
200
400
600
800
1000
1200
0 100 200 300 400
Position (mm)
FWH
M B
eam
Dia
met
er (μ
m)
M2~1.85
M2~1.82
Output Beam Mode QualityBeam Profiles after Combiner
M2~1.85
M2~1.82
Horizontal axis
Vertical axis
0
0.03
0.06
0.09
-2 -1 0 1 2 3 4 5 6 7 8
τ (ns)
Nor
mal
ized
Am
plitu
de (a
.u.)
Seed Pulse
~2ns
Combined Pulses
0
0.03
0.06
0.09
-2 -1 0 1 2 3 4 5 6 7 8
τ (ns)
Nor
mal
ized
Am
plitu
de (a
.u.)
Combined Pulse @52W
0.1 ns = 3cm
Temporal Pulse Overlap
Combined power 52 W
Combined pulseenergy 4 mJ
λ1λ2
λn
Spectrally CombinedModules (SCM) 5‐10kW
Demonstrated Feasibility of SBC for multi‐kW EUVL Sources
Non‐spatially dispersive combining scheme
• Combines concurrent high peak power and average power
• Practical scheme for fiber laser based EUVL source
• Current filters allow up to 40 channels combined with 90% combining efficiency
• >92% efficiency, 52W combined power, M2~1.85 demonstrated
• 4.6mJ combined demonstrated
K. Regelskis, K. Hou, G. Raciukaitis, and A. Galvanauskas, "Spatial‐Dispersion‐Free Spectral Beam Combiningof High Power Pulsed Yb‐Doped Fiber Lasers,“ in CLEO 2008, paper CMA4.http://www.opticsinfobase.org/abstract.cfm?URI=CLEO‐2008‐CMA4
ARBOR PHOTONICS, Inc. Powering advanced laser processing Slide 18ARBOR PHOTONICS, Inc. Powering advanced laser processing Slide 18
Size, Efficiency, Reliability & CostComparison of Continuous Wave Industrial Lasers
ARBOR PHOTONICS, Inc. Powering advanced laser processing Slide 19
Power Scaling & Cost ProjectionsProjected Trend for Short‐pulse Fiber Lasers
Acknowledgements
• This work is partially supported by SRC:
– Task ID 1180.001 Feasibility study of a compact and efficient 1‐kW fiber laser source for EUV generation
– Task ID 1779.001 Demonstration of Power Scalability of LPP EUV Lithography Sources Using Fiber Laser Technology with Spectral Multiplexing
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