Transmission Grating Spectrometer for EUV
Lithography
Nathan Gray
Advisors: Alexander Shevelko,
Larry Knight, and Scott Bergeson
Student Group Members:
Matthew Harrison, Jeff Kemp,
Bryce Allred, Jershon Lopez
Extreme Ultraviolet (EUV)
1-1000 Å
Image modified from: NASAexplores Models of the Electromagnetic
Spectrum student sheet. lot.astro.utoronto.ca/spectrum.html
Extreme Ultraviolet (EUV)
1-1000 Å
Absorbed by
Everything:
•Air
Image modified from: NASAexplores Models of the Electromagnetic
Spectrum student sheet. lot.astro.utoronto.ca/spectrum.html
Extreme Ultraviolet (EUV)
1-1000 Å
Absorbed by
Everything:
•Air
•Glass
Image modified from: NASAexplores Models of the Electromagnetic
Spectrum student sheet. lot.astro.utoronto.ca/spectrum.html
Extreme Ultraviolet (EUV)
1-1000 Å
Absorbed by
Everything:
•Air
•Glass
•Plastic
Image modified from: NASAexplores Models of the Electromagnetic
Spectrum student sheet. lot.astro.utoronto.ca/spectrum.html
Extreme Ultraviolet (EUV)
1-1000 Å
Absorbed by
Everything:
•Air
•Glass
•Plastic
•Ponies
Image modified from: NASAexplores Models of the Electromagnetic
Spectrum student sheet. lot.astro.utoronto.ca/spectrum.html
Extreme Ultraviolet (EUV)
Must operate under
vacuum (our chamber is at
30-100 mtorr)
Absorbed by
Everything:
•Air
•Glass
•Plastic
Must use mirrors in place
of conventional optics.
This makes spectroscopy
in the EUV range
complicated.
EUV range
transmission
gratings:
EUV range
transmission
gratings:
Recent transmission
grating development
allows for EUV range
gratings
200 nm period
(5000 lines/mm)
EUV range
transmission
gratings:
Recent transmission
grating development
allows for EUV range
gratings
200 nm period
(5000 lines/mm)
Transmission grating
spectrometers are superior
to reflection grating
spectrometers
Possible Configurations
Simple Transmission Grating Spectrometer
Entrance Slit
Detector
Grating
Possible Configurations

Single Mirror Geometry
Spherical Mirror
Entrance Slit
Detector
•High spectral resolution and luminosity
•Mirror collects large solid angle
Grating
Our Configurations

Double Mirror Geometry
Detector
Entrance Slit
Flat Mirror
Spherical Mirror
Designed by Dr. Alexander Shevelko
Grating
Knight/Shevelko Group
Spectrometer Configuration
Intensity (counts)
4000
3000
5000
0
2000
50
1000
100
Wavelength (Ǻ)
6000
OVI 2s-3p 150.1Ǻ
OVI 2p-4d 129.8Ǻ
OVI 2s-4p 115.83Ǻ, 2p-5d 115.83Ǻ
2
BIV 1s -1s2p 60.3Ǻ
2
2
BIV 1s -1s3p 52.7Ǻ, 1s -1s4p 50.4 Ǻ
BV 1s-2p 48.6Ǻ
B
7000
#002
EL=405 mJ
40 shot sum
150
OVI 2p-3d 173Ǻ
8000
Grating 5000 ℓ/mm
Entrance Slit 250 μm
0
200
FeXVI 3d-4f, FeXVII 3d-4p
Fe
20000
FeXV 3d-4f
#006
FeXIV 3p-4d
FeXVII 3d-4f
EL=300 mJ
40 shot sum
Intensity (counts)
15000
Grating 5000 ℓ/mm
Entrance Slit 250 μm
FeXV 3p-4d
FeXVI 3p-4d
10000
FeXVI 3s-4p
5000
FeXVI 3d-5f
FeXVII 3s-4p
FeX-FeXIII
0
0
50
100
Wavelength (Ǻ)
150
200
Electron Temperature Study
Tungsten
4000
4000
WXXVIII-WXXX 4-4 transitions 48-65 Ǻ
W
#015
Grating 5000 ℓ/mm
Entrance Slit 250 μm
3000
3000
2500
2500
440mJ
300mJ
200mJ
150mJ
2000
Intensity (counts)
Intensity (counts)
W
3500
#024
2000
1500
1500
1000
1000
500
500
EL=440 mJ
1 shot
WXXII-WXXIX 4-5 transitions 25-38 Ǻ
3500
Grating 5000 ℓ/mm
Entrance Slit 250 μm
0
0
0
50
100
150
Wavelength (Ǻ)
200
250
300
0
50
100
150
Wavelength (Ǻ)
200
250
300
Efficiency Calculation
Major advantage of transmission grating over reflection grating
Must take transmission through wires into account (phase shift)
Materials:
Au 25 nm
Au 25 nm
Radiation
Si4N3 200 nm
Formulae
Efficiency Calculation
total efficiency
Efficiency
Total Grating Efficiency
0.006
0.006
0.005
0.005
0.004
0.004
0.003
0.003
0.002
0.002
0.001
0.001
0
0
5
10
15
20
25
30
35
wavelength (nm)
Schopper et al. Method
40
45
0
0
5
10
15
20
25
30
Fujikawa et al. Method
H. W. Schopper et al., Appl. Opt. 16, 1088 (1977).
C. Fujikawa et al., Rev. Sci. Instrum. 69, 2849 (1998).
35
40
45
Absolute Calibration
grating efficiency X spherical mirror reflectivity X flat mirror reflectivity
= total spectrometer efficiency
Absolute Calibration
grating efficiency X spherical mirror reflectivity X flat mirror reflectivity
= total spectrometer efficiency
total spectrometer efficiency X detector calibration
= absolute calibration
Absolute Calibration
grating efficiency X spherical mirror reflectivity X flat mirror reflectivity
= total spectrometer efficiency
total spectrometer efficiency X detector calibration
= absolute calibration
absolute calibration = Intensity scaled to units of actual photon flux,
instead of just relative intensity.
Absolute Calibration
grating efficiency X spherical mirror reflectivity X flat mirror reflectivity
= total spectrometer efficiency
total spectrometer efficiency X detector calibration
= absolute calibration
absolute calibration = Intensity scaled to units of actual photon flux,
instead of just relative intensity.
Detector calibration: completed at Lebedev Physical Institute by Oleg
Yakushev
EUV Lithography
International Technology Roadmap for
Semiconductors printable patterns with 32
nm between features are required by the
semiconductor industry by 2009
EUV Lithography
Main limitation is wavelength of light
source
Higher Resolution requires a source with
smaller wavelength
Typical EUV wafer scanner

V. Bakshi, EUV Sources for Lithography, SPIE Press Book, 2006.
EUV Lithography
Typical EUV Lithography apparatus:
 11 mirror multilayer Mo/Sn multilayer
mirrors with reflections around 66% each.
 The overall transmission in the EUV
scanner is less than 1%,
 The mirrors reflect a bandwidth of 2%
around a central wavelength of 135 °A.
EUV Lithography
Source candidates: Lithium and Tin plasmas
1200
350
Sn (4d-4f) UTA
Li III 1s-2p
Sn
Li
300
EL=450 mJ
100 shot avg
EL=425 mJ
1 shot
250
150
Intensity (counts)
Li III 1s-3p
200
Grating 5000 ℓ/mm
Entrance Slit 250 μm
800
Grating 5000 ℓ/mm
Entrance Slit 250 μm
Li III 1s-4p, 5p
Intensity (counts)
#025
1000
#001
600
400
100
50
200
0
75
85
95
105
115
125
Wavelength (Ǻ)
135
145
155
165
175
0
0
50
100
150
Wavelength (Ǻ)
200
250
300
EUV Lithography




Mirror heating
Unwanted radiation
Target purity
Plasma parameters (electron
temperatures, absolute outputs, etc.)
Current WRS
Planned WRS with multiple gratings
Acknowledgements




Dr. Shevelko
Dr. Knight
Matt Harrison and the other members of
my group
The chemists (especially Dr. Asplund)