Session 4, P5
Rare-Earth Plasma EUV Source at 6.7 nm for Future Lithography Takeshi Higashiguchi1,2 Takamitsu Otsuka1, Noboru Yugami1,2, Deirdre Kilbane3, Thomas Cummins3, Colm O’Gorman3, Tony Donnelly3, Padraig Dunne3, Gerry O'Sullivan3, Weihua Jiang4, and Akira Endo5 1Utsunomiya
University Science and Technology Agency 3University College Dublin 4Nagaoka University of Technology 5Waseda University 2Japan
2011 International Workshop on EUV Lithography Makena Beach Golf Resort , Maui, Hawaii, USA Wednesday, June15, 2011
Why 6.X nm EUV source? Beyond EUV (BEUV) source
From ASML presentation shows as follows: (1) extensive (beyond 8 nm@~2017) (2) 6.X nm choice: Best transmission & Easier Manufacturing (3) Source: New fuel is needed (4) R ~ 80% (cal), R ~ 40% (exp)@La/B4C MLM (5) Total throughput for 6.7 nm & 13.5 nm is comparable!!!
Why 6.X nm EUV source? 1,000
Wavelength (nm)
1,000
100
100
10
10 Present day
1 1990
2000
2010
2020
1 2030
Half-pitch feature size (nm)
Beyond EUV (BEUV) source
G. Tallents et al., NATURE PHOTONICS, 4, 809 (2010).
What’s new for high power and high CE
1064 nm 532 nm 355 nm
250 200 150 100 50 0 5.5
6
6.5
7
7.5
8
8.5
Wavelength (nm)
9
9.5
10
Experiment Calculation
350
0.8
300
0.7
250
0.6 0.5
200
0.4
150
0.3
100
0.2
50 0 6
6.5
7
7.5
Wavelength (nm)
0.1 0 8
Intensity (arb. units)
Intensity (arb. units)
300
Intensity (arb. units)
n Laser color dependence n Resonant line appearance in low-density plasma n Enhancement condition of the 6.7-nm emission
Introduction… from previous spectral reports 6.7 nm: Gd, Tb plasmas Mo/B4C mirror
6.7
6.9
7.1
Reflectivity
6.5
Reflectivity at 3 deg. inc. angle
0.4 N=23 N=200 0.3
0.2
0.1
0.0 6.2
6.4
6.6
6.8
6.7 nm
7.0
Wavelength, nm
Wavelength (nm) 6.3
6.5
6.7 S. S. Churilov et al.,Phys. Scr. 80, 045303 (2009).
Previous & recent observations We observed continuum due to satellite lines
Intensity (arb. units)
for absorption spectroscopy
for high power source by us 400 300 200 100 0 5.5
6
6.5
7
7.5
8
8.5
9
9.5
10
Wavelength (nm)
G. O’Sullivan & P. K. Carroll, JOSA 71, 227 (1981). T. Otsuka et al., APL 97, 111503 (2010).
Objective
We demonstrate the efficient BEUV source at 6.7 nm by rare-earth (Gd) LPP and DPP .
Ionic population of Gd ions We should produce 50-200 eV plasma.
9./:+0;.35)4,:./
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()*+,-./01*23*-4,5-*06*78 T. Otsuka et al., APL 97, 111503 (2010).
gf spectra of Gd ions We confirm the UTA resonant lines around 6.7 nm 70 70 70
gf
70 70 70 70
12+
35
13+
35
14+
35
15+
35
16+
35
17+
35
18+
35
Gd Gd Gd Gd Gd Gd Gd
Gd19+ Gd20+ 21+
Gd
22+
Gd
Gd23+ Gd24+ Gd25+
0 0 6.0 6.5 7.0 7.5 8.0 6.0 6.5 7.0 7.5 8.0 Wavelength (nm) Wavelength (nm) T. Otsuka et al., APL 97, 111503 (2010).
Experimental setup
Intensity (arb. units) Intensity (arb. units)
Spectra from Gd & Tb plasmas 400
Gd
300 200 100 0 400
Tb
300 200 100 0 5.5
6
6.5
7
7.5
8
8.5
Wavelength (nm)
9
9.5
10
Laser wavelength dependence n Spot diameter: 50 um (FWHM) n Laser energy: 320 mJ n Laser intensity: 1.6 x 1012 W/cm2
Intensity (arb. units)
300
EUV CEs (in 2% BW)
1064 nm 532 nm 355 nm
250 200
1064 nm: 1.1% 532 nm: 0.7% 355 nm: 0.5%
150 100 50 0 5.5
6
6.5
7
7.5
8
8.5
Wavelength (nm)
9
9.5
10
Laser wavelength dependence n Spot diameter: 50 um (FWHM) n Laser energy: 320 mJ n Laser intensity: 1.6 x 1012 W/cm2
250
UTA resonant lines
200
Self-absorption
150
Critical surface
1064 nm 532 nm 355 nm
ne
Electron density
Intensity (arb. units)
300
nc2
nc1 Laser
100
0
z
Distance
50 0 5.5
nc3
Satellite emissions 6
6.5
7
7.5
8
8.5
Wavelength (nm)
9
9.5
10
Dual laser pulse irradiation
In-band-EUV energy (arb.units)
Gd Tb 1.2 1.0 0.8 0.6 0.4 0.2 0 -400
-200
0
200
400
600
Pulse separation time (ns)
800
1000
Trade off 1 Effective ions vs self-absorption Electron (ion) density decreases, but absorption length increases. For large opacity material (high-Z), such as Xe & Sn Electron density decreased: absorption effect decreased Density gradient increased: absorption effect increased
For small opacity material (low-Z), such as Li & low initial density target Electron density decreased: absorption effect more decreased Density gradient increased: large volume effect increased
Physical summary for high-Z plasmas from 13.5-nm Sn plasmas
Low density plasmas for reducing self-absorption effects Suppression of satellite emission & higher spectral purity Long wavelength (low critical density): CO2 laser@1019 /cc Short laser pulse duration: ~1-2 ns@YAG laser (1064 nm) Low density targets Discharge plasmas (low density plasmas)
Effective dual pulse scheme
We require the use of: low initial density target & DPP or
longer laser wavelength laser
in the self-absorption effect suppression point of view.
Discharge experiments To reduce the satellite lines for low density plasma
Discharge experiments To reduce the satellite lines for low density plasma 350
DPP plasma
7.8% 300
250
Intensity (arb. units)
Intensity (arb. units)
300
200 150 100 50 0 5.5 6 6.5 7 7.5 8 8.5 9 9.5 10 Wavelength (nm)
250
LPP plasma
5.7%
200 150 100 50 0 5.5 6 6.5 7 7.5 8 8.5 9 9.5 10
Wavelength (nm)
Experiment Calculation
350
0.8
300
0.7
250
0.6 0.5
200
0.4
150
0.3
100
0.2
50 0 6
6.5
7
7.5
Wavelength (nm)
0.1 0 8
Intensity (arb. units)
Intensity (arb. units)
Low density plasma by DPP
140
100 Experiment Calculation
120
80
100 60
800 600
40
400 20
200 0 6
6.5
7
7.5
0 8
Wavelength (nm)
calculated by Bowen Li & Gerry O’Sullivan (UCD)
Intensity (arb. units)
Low density plasma by use of low-initial density targets 10% 30% 100%
400 300 200 100 0 5.5
6
6.5
7
7.5
8
8.5
Wavelength (nm)
9
9.5 10
Conversion efficiency (%)
EUV CEs by use of low-initial density targets 10% 30% 100%
2.0 1.5 1.0 0.5 0 0
1
2
3
4
5
6
7
Laser intensity (x 1012 W/cm2)
8
Conversion efficiency (%)
Enhancement of EUV CE by use of dual laser pulse technique 30% 100%
2.0 1.5 1.0 0.5 0 -100
0
100
200
300
Pulse separation time (ns)
400
500
Question, problem, and definition… n CO2 laser-produced plasma behavior? n High temperature (30-50 eV to 50-150 eV): high energy particle generation n CE bandwidth (2% to less than 0.1%?) n Regenerative target supply method (melting point: 1313 OC)
Summary
We have demonstrated the efficient EUV source around 6.7 nm using Gd & Tb (rare-earth). - Spectral behavior at different laser wavelength - Low density target to suppress the self-absorption in plasma - Conversion efficiency: ~ 1.8% before optimizing parameters - Question, problem, and definition
