RC-P04
Cleaning of
SiliconSilicon-Containing Carbon Contamination
Toshihisa Anazawa, Noriaki Takagi,
Osamu Suga, Iwao Nishiyama
MIRAI-Semiconductor Leading Edge Technologies, Inc.
Koichi Yamawaki, Hirotsugu Yano, Akira Izumi
Kyushu Institute of Technology
Toshinori Miura, Mitsuru Kekura
MEIDENSHA CORPORATION
Contamination and Cleaning
unirradiated
200 µm
EUV masks and mirrors are
contaminated by EUV irradiation
in an usual vacuum condition.
40
nm
40 nm
These XPS are measured by Canon.
Mg Ka
Mo 3d
O KLL
C KLL
Si 2s
Si 2p
O 1s C 1s
1 k 800 600 400 200 0
Binding Energy (eV)
Contamination deteriorates
lithographic performance.
→ It must be cleaned.
(R~13%↓)
100
80
C
Si
60
40
H
O
20
0
0
5 10 15 20
Depth (nm) Substrate
Surface
1
Reflectivity
/Threshold
/EDarea
Intensity
Contamination
mainly consists
of carbon
and hydrogen.
Ratio (atomic %)
irradiated
0.9
Reflectivity
0.8
Threshold
0.7
ED Area
0.6
hp22nm(x5) Iso //
0.5
0
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10
15
Film Thickness (nm)
20
2
Reported Cleaning Studies
Advanttages
Problems
Institution [Reference]
<0.1 nm/min
• Low speed
• Reflectivity down
SNL [SPIE,4688,431(2002)]
EUV + O2
0.24 nm/min
• Easy to apply
• Low speed
LASTI [MNC2003]
UV/O3
~1 nm/min
• readily available
• Difficulty in UV Irradiation
LASTI [JVSTB, 23, 247 (2005)]
Hydrogen Radical
(Hot Filament)
~1 nm/min
• Recovery from Ru oxidation
• Heat load
ASET-Kyutech [JJAP, 46, L633 (2007)]
Selete-Kyutech [EIPBN2008]
5 nm/min
• Modest speed
• Sputter damage
TNO [EUVL Symp. 2008]
• Damageless
• Low speed
TNO [EUVL Symp. 2009]
• Extremely high speed
Selete-MEIDENSHA [EUVL Symp. 2009]
Technique
Rate
Oxygen Plasma
Hydrogen Plasma
Shielded Plasma
0.19 nm/min
Pure O3
90 nm/min
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Our Previous Studies
Hydrogen radical cleaning
H2
Shower head
IR pyrometer
View Port
to Power Supply
H2 H2
H H
H
H
H
H
H H
Vac. Gauge
Hot W wire
Thermal Shield
Sample
to TMP
Sample Stage
(Water-Cooled)
•Simple hot W filament efficiently
decomposes hydrogen molecule to
hydrogen radical.
•Not only carbon contamination but
also oxidation of Ru-capping layer
can be recovered.
•Carbon removal rate ~ 1 nm/min.
Pure ozone cleaning (alkene-gas assisted)
MEIDEN Pure Ozone Generator
condensation
evaporation
generation
Pure O3
～100 %
Ethylene
Exhaust
•Pure ozone is activated by the
alkene assist gas.
•It needs no heating nor irradiation
of any light (UV or EUV, etc.) and
the removal rate is extremely high.
•Carbon removal rate ~ 90 nm/min.
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Problem Caused by Contained Si
Reflectivity
Using the pure O3 cleaning,
the reflectivity degradation of
SR* contaminated multilayer
mask brank is almost recovered.
*Synchrotron Radiation
70%
60%
50%
40%
30%
20%
10%
0%
13
Reflectivity
However, the reflectivity recovery
of strongly contaminated or
multiple contaminated sample
is not good enough.
We investigated the cleaning residue.
13.5
14
Wavelength (nm)
70%
60%
50%
40%
30%
20%
10%
0%
Note that Si capping layer is stable to pure O3 cleaning.
The cause of accumulating
degradation is
cleaning residue SiO2.
1. Initial
2. Contami
3. O3
3. O3
4. Re-Contami
5. 2nd O3
13
13.5
14
Wavelength (nm)
Chemical states of surface Si (XPS)
Atomic %
SiO2 SiOx Si0
After 1st cleaning
38
4
58
After 2nd cleaning
73
0
27
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Where Does Si Come from ?
Almost all carboneous contamination we investigated
(SR, DPP, LPP) contains several parcents of Si species.
Other groups also reported Si in contaminations.
Intel MET
N1 mirror: C : O : Si ~70
70 % : 20 % : 10 %
G1, G2 mirror: C : O : Si ~ 85 % : 10 % : 5 %
Manish Chandhok,
IEUVI Optics Contamination /
Lifetime TWG (1st Mar. 2007)
Albany MET
G2: C : O : Si : P : N = 74 : 20 : 2 : 2 : 1
Andrea Wüest et al.,
IEUVI Optics Contamination /
Lifetime TWG (1st Nov. 2007)
Clean
Contami
After O3
Al2O3
Al2O3
Al2O3
The result clearly shows that
Si comes from vacuum.
Intensity (arb. units)
The origin of Si was unclear. No Si species has been detected by QMS or GC-M.
So we deposited contamination
Clean
Al Kα XPS
on sapphier (Al2O3) substrates.
Contami
after O3
Si 2s
C 1s
Si 2p
Al 2s Al 2p
320 280 240 200 160 120
In addition, this Si species seem
hard to remove by oxidative cleaning.
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40
Binding Energy (eV)
6
Cleanablity Studies of Si:C
Experimental flow:
Si doped C (Si:C) sputter-deposited film → Characterization
↓
Cleaning processing (Pure O3, H-radical)
↓
XPS: Xray Photoelectron Spectroscopy
Characterization (XPS, HFS/RBS) HFS: Hydrogen Forward Schattering spectrometry
RBS: Rutherford Back Scattering spectrometry
Cleaning process condition:
Pure O3 — assist gas = ethylene ~100 Pa
room temperature
H radical — gas pressure ~10-2 Pa
filament temperature ~1780 oC
Characterization:
1. Si concentration
Si concentration dependence of
3. Si and O distributions
film removal rate.
2.area densities
Process time dependence of
of C and Si etc.
Si:C
Si distribution.
Si substrate
(natural oxide)
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Sample Characterization of Si:C
C and Si are co-sputter-deposited on Si wafers.
Doping rate is controlled by area of Si pieces placed on C target.
RBS/HFS
Si Dope (%)
15.2
61.9
11.1
15.2 13.8 7.7
66.3
6.2
11.1 14.1 7.1
69
4.2
6.2 16.7 6.8
73.8
4.2 15.3 5.2
83.3
0
0%
20%
40%
12.2
60%
Atomic Ratio
80%
100%
C
Si
H
O
Ar
Fe
Si
Initial Area Density
(1015atom/cm2)
Film Thickness
(nm)
0%
1435
146
4.2 %
1607
161
6.2 %
1532
153
11.1 %
1361
138
15.2 %
1282
128
Converted from area density with bulk densities:
C (amorphous) = 9.02~10.53×1022 atoms/cm3
SiO2 (amorphous) = 6.62×1022 atoms/cm3
Si = 5.00×1022 atoms/cm3
XPS
~70 % of C is C-C or C-H; π-π* satellite is also observed.
Si mainly exists as SiOx (x<2); Si-C is not observed.
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SiSi-Ratio Dependence for Pure O3
RBS Result
Normalized*Removal Rate
250
Data at initial 30 sec
200
~30 nm/min
150
~50 nm/min
Sputter-deposited carbon
is harder to remove than
CVD deposited carbon.
100
C
Si
50
* Decresed amount
par time
par ratio of element
~10 nm/min
0
0
5
10
15
20
Initial Si Ratio (%)
Contained Si is also removed at initial stage.
C removal rate decreses with Si concentration.
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C Area Density (cm-2 )
We observed time dependence of
depth profile of Si 4.2 % sample.
C decreses with time but removal
rate gradually slow down.
Si also decreses but forms
condensed layer at surface region.
O increases and final ratio Si:O=1:2.
1400
140
1200
120
1000
100
800
80
600
60
400
40
200
20
0
Si/O Area Density (cm-2 )
Change by Processing Time of Pure O3
0
0
1 2
3 4
5 6
7 8
9 10
Thickness (nm)
Time (min)
180
160
140
120
100
80
60
40
20
0
Initial
30 s
1 min
2 min
5 min
10 min
Carbon
Hydrogen
Silicon
Oxygen
0 20 40 60 80 1000 20 40 60 80 1000 20 40 60 80 1000 20 40 60 80 1000 20 40 60 80 1000 20 40 60 80 100
At. Ratio (%)
At. Ratio (%)
At. Ratio (%)
At. Ratio (%)
At. Ratio (%)
At. Ratio (%)
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SiSi-Ratio Dependence for HH-radical
RBS Result
Normalized*Removal Rate
600
Data at initial 30 min
500
~1.2 nm/min
400
300
200
C
Si
100
* Decresed amount
par time
par ratio of element
~0.3 nm/min
0
0
5
10
15
20
Initial Si Ratio (%)
Rate decrease with Si seems smaller than O3.
Si removal rate seems higher than O3.
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140
Thickness (nm)
C Area Density (cm-2)
1400
We observed time dependence of
1200
depth profile of Si 4.2 % sample.
1000
800
120 min H-radical processing
600
seems correspond to 2~3 min
400
prosessing of pure O3.
200
Si decreses faster than pure O3 but
0
SiO2 condensed layer is also formed.
180
160
140
120
100
80
60
40
20
0
Initial
30 min
120
100
80
60
40
20
0
30
60
90
Si/O Area Density (cm-2 )
Change by Processing Time of HH-radical
0
120
Time (min)
120 min
Carbon
Hydrogen
Silicon
Oxygen
0 20 40 60 80 1000 20 40 60 80 100
At. Ratio (%)
At. Ratio (%)
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0 20 40 60 80 100
At. Ratio (%)
12
Comparison between H and Pure O3
Both of techniques removes a little Si but SiO2 layers are
formed at surface region.
Absolute removal rate is several tens faster for pure O3.
Rate decrease by Si containing is smaller for H-radical.
Relative Removal Rates (arb. units)
H ― Si
H―C
1.2
O3 ― Si
1.0
O3 ― C
0.8
0.6
0.4
0.2
0
0
5
10
Si Ratio (%)
15
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13
Recovery from SiO2 Formation
SiO2 SiOx Si0 SiO2 (nm)
73
0
27
3.8
After wet etching
29
0
71
1.1
Si0 is Si in capping layer.
Using wet etching process, SiO2
residue has successfully removed and
reflectivity was completely recoverd.
Note that SiO2 removal process removes not only
cleaning residue but also natural oxide of Si capping
then mutiple application will damage the multilayer.
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13.5
14.0
Wavelength (nm)
70%
65%
60%
55%
50%
45%
Wet
After 2nd cleaning
0%
13.0
2nd O33
58
1. Initial
4. Re-Contami
5. 2nd O3
6. Wet
20%
Re-Contami
4
30%
O3
38
40%
Contami
After 1st cleaning
50%
10%
Peak Reflectivity
Atomic %
60%
Initial
Chemical states of surface Si (XPS)
70%
Reflectivity
Once SiO2 is formed, it seems hard
to remove it by mild-dry process.
Thus we tried wet etching.
14
It seems no Si is contained
in a contamination
on a mask of EUV1.
For such contamination,
both of H radical and
pure O3 can be applied
without wet SiO2 removal.
It's important to operate
in such vacuum conditions.
Al Kα
α XPS
O 1s
C
Si 2s
Si 2p
O KLL
Contami
Ta 4p
Ta 4d
Ta 4f
Clean
1000
Intensity (arb. units)
Contamination of EUV1
Intensity (arb. units)
Favorable Solution
800
600
400
200
Binding Energy (eV)
Al Kα
α XPS
0
Si 2p
Contami
Clean
Difference
110
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106 104 102 100
Binding Energy (eV)
98
96
15
Conclusion
C
C w/Si
SiO2
Si-cap
Ru-cap
☺
(needless)
☺☺☺
☺
☺
☺
☺
(needless)
☺
☺
H
w/ wet
Pure O3
w/ wet
(needless)
☺ = Suitable
= Applicable
(no info)
= Incompatible
For Si free contamination on Si-cap, pure O3 is the best.
For Si containing contamination, pure O3 does not work well.
For SiO2 containing contamination, H-radical is also no good.
Residual SiO2 species can be removed and rescued by wet
etching without apparent damege.
Si free vacuum condition is essential.
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Summary
Origin of Si contained in carboneous contamination
is investigated.
Cleanability of pure O3 and H-radical cleaning,
and behaviour of Si while cleaning is examined.
Rescue process for degradation by residual SiO2
is demonstrated.
In some case, contamination contains little Si.
It's important to operate in such a vacuum conditions.
Acknowledgment
SR contamination samples are prepared
by H. Ikeda at SR center of Ritsumeikan University.
This work was supported by New Energy and
Indastrial Technology Development Organization.
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