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EUVEUV LITHOGRAPHYLITHOGRAPHY2005 EUVL Symposium, 7-9 November 2005ASET, Takeichi 1
High-precision (<1ppb/℃) optical heterodyne interferometric dilatometer for
low thermal expansion materials
Yoshimasa Takeichi, Iwao Nishiyama Association of Super-Advanced Electronics Technologies
(ASET)EUV Process Technology Research Laboratory
Naofumi YamadaNational Institute of Advanced Industrial Science and Technology
(AIST) National Metrology Institute of Japan(NMIJ)
EUVEUV LITHOGRAPHYLITHOGRAPHY2ASET, Takeichi 2005 EUVL Symposium, 7-9 November 2005
Acknowledgement
This work was supported by the New Energy and
Industrial Technology Development Organization (NEDO).
EUVEUV LITHOGRAPHYLITHOGRAPHY3ASET, Takeichi 2005 EUVL Symposium, 7-9 November 2005
Outline
1. Background CTE characteristics, CTE metrology
2. Goal Target performance of dilatometer
3. Methodology Principle & design of the dilatometer
4. Results Evaluation of the performance of the dilatometer
5. Summary
EUVEUV LITHOGRAPHYLITHOGRAPHY4ASET, Takeichi 2005 EUVL Symposium, 7-9 November 2005
1. Background
EUVEUV LITHOGRAPHYLITHOGRAPHY5ASET, Takeichi 2005 EUVL Symposium, 7-9 November 2005
(Change in substrate temperature)
Exposure
Before After
Expansion(Shrinkage)
Background (1): CTE of EUVL Mask Substrate
Mask stage
source
λ:13nm
Waferstage
Illumination Optics
Projection Optics λ:13.5 nm
Reflective Optics
ML,Reflectance :<70%)
Exposure under vacuum
Exposure deforms mask.
Configuration of EUVL system
CTE: Coefficient of Thermal Expansion
Difficult requirement to meet
No commercial dilatometer that meets EUVL requirements
Obstacle to the development of LTEMs
SEMI standards (Class A)0±5 ppb/゚C(19-25゚C)1ppb = 0.1nm (@10cm)
Strong demand for a metrology that meet EUVL
requirement
EUVEUV LITHOGRAPHYLITHOGRAPHY6ASET, Takeichi 2005 EUVL Symposium, 7-9 November 2005
Background (2): Metrology Development Project
Metrology andpatent ownership
EUVL technologyLTEM developer
Metrology user
Research organizationsLTEM suppliers
DevelopmentDevelopmentteamteam
Equipment supplierEquipment supplierOptical heterodyne interferometer,
Thermal control technique
SpecificationsPerformance
evaluation
Manufacture of equipment
Equipment design
EUVEUV LITHOGRAPHYLITHOGRAPHY7ASET, Takeichi 2005 EUVL Symposium, 7-9 November 2005
2. Goal
EUVEUV LITHOGRAPHYLITHOGRAPHY8ASET, Takeichi 2005 EUVL Symposium, 7-9 November 2005
Goal and targets
Overall Goal• To establish a CTE metrology tailored to meet EUVL
requirements and help bring EUVL closer to the stage of practical use
Target
• Resolution: 1 ppb/゚C or less
• Repeatability(σ): 1 ppb/゚C or less
• Making practical dilatometer: marketable
• Metrology standardization
EUVEUV LITHOGRAPHYLITHOGRAPHY9ASET, Takeichi 2005 EUVL Symposium, 7-9 November 2005
3. Methodology
EUVEUV LITHOGRAPHYLITHOGRAPHY10ASET, Takeichi 2005 EUVL Symposium, 7-9 November 2005
AOM
AOM
APD1
He-Ne laser
Spec
imen
Reflector
PBS
Referencelight
Measurementlight
Light frequency 1
Light frequency 2
APD2
Change in length due to change in temperature
Vacuum chamber
Ther
mal
con
trol b
lock
Ther
mal
con
trol b
lock
AOM
AOM
APD1
He-Ne laser
Spec
imen
Reflector
PBS
Referencelight
Measurementlight
Light frequency 1
Light frequency 2
APD2
Change in length due to change in temperature
Vacuum chamber
Ther
mal
con
trol b
lock
Ther
mal
con
trol b
lock
Phase difference between APD1 and APD2 at T1: ( φAPD2 -φAPD1)T1
Phase difference between APD1 and APD2 at T2: ( φAPD2 -φAPD1 )T2
( )λπφφ L
APDAPDΔ
=−Δ2
12
Change in phase difference between T1 and T2:
Methodology (1): Principle of Measurement
ΔL:Change in length
(Quadruple - sensitivity)
Optical heterodyne interferometry
Intensity of superimposed light
Electric field intensity
( )1111 2cos φπ += tfaE
( )2222 2cos φπ += tfaE
221 EEI +=
{ }φπ Δ+++
= tfaaaab2cos2
2 21
22
21
( ) ( ){ }212121
22
21 2cos2
2φφπ −+−+
+= tffaaaa
EUVEUV LITHOGRAPHYLITHOGRAPHY11ASET, Takeichi 2005 EUVL Symposium, 7-9 November 2005
APD2
AOM APD1
Spec
imen
Reflector
PBS
Referencelight
Measurementlight
Light frequency 2
Change in length due to change in temperature
Vacuum chamber
Ther
mal
con
trol b
lock
Ther
mal
con
trol b
lock
AOM
AOM
APD1
He-Ne laser
Spec
imen
Reflector
PBS
Light frequency 1
Vacuum chamber
Ther
mal
con
trol b
lock
Ther
mal
con
trol b
lock
Methodology (1): Optical Path of the Dilatometer
EUVEUV LITHOGRAPHYLITHOGRAPHY12ASET, Takeichi 2005 EUVL Symposium, 7-9 November 2005
AOM
AOM
APD1
He-Ne laser
Spec
imen
Reflector
PBS
Referencelight
Measurementlight
Light frequency 1
Light frequency 2
APD2
Change in length due to change in temperature
Vacuum chamber
Ther
mal
con
trol b
lock
Ther
mal
con
trol b
lock
AOM
AOM
APD1
He-Ne laser
Spec
imen
Reflector
PBS
Referencelight
Measurementlight
Light frequency 1
Light frequency 2
APD2
Change in length due to change in temperature
Vacuum chamber
Ther
mal
con
trol b
lock
Ther
mal
con
trol b
lock
Phase difference between APD1 and APD2 at T1: ( φAPD2 -φAPD1)T1
Phase difference between APD1 and APD2 at T2: ( φAPD2 -φAPD1 )T2
( )λπφφ L
APDAPDΔ
=−Δ2
12
Change in phase difference between T1 and T2:
Methodology (1): Principle of Measurement
ΔL:Change in length
(Quadruple - sensitivity)
Optical heterodyne interferometry
Intensity of superimposed light
Electric field intensity
( )1111 2cos φπ += tfaE
( )2222 2cos φπ += tfaE
221 EEI +=
{ }φπ Δ+++
= tfaaaab2cos2
2 21
22
21
( ) ( ){ }212121
22
21 2cos2
2φφπ −+−+
+= tffaaaa
EUVEUV LITHOGRAPHYLITHOGRAPHY13ASET, Takeichi 2005 EUVL Symposium, 7-9 November 2005
Methodology (2): To Meet EUVL Requirement
Determination of sample length
Determination of change in sample length due to thermal expansion
Stability of thermo control and determination of temperature
This term has a large influence.
This term has little influence.
This term has little influence.
Consideration of uncertainty factors
TLL
Δ⋅
Δ=
1
0
α
( ) ( ) αδδαδδαTLsp
total TT
TLL
LL
⎥⎦⎤
⎢⎣⎡ΔΔ
+Δ⎥
⎦
⎤⎢⎣
⎡ Δ+⎟⎟
⎠
⎞⎜⎜⎝
⎛=
1
00
0
α:low
EUVEUV LITHOGRAPHYLITHOGRAPHY14ASET, Takeichi 2005 EUVL Symposium, 7-9 November 2005
Sample inclination prevention ・ Thermal isolation・ Thermal control・ LTEM pedestal
Vibration isolation・ Stone plate・ Vibration isolation table
Compact interferometer
Methodology (3): KEY Design Consideration
Thermal-shield
Stone plateVibration isolation table
interferometer
Frame
Water
sample
LTEM
Inver
Peltier device
Structure of dilatometer
How to reduce magnitude of uncertainty factors affecting ΔL measurement
Frequency-stabilized laser
Design guidelines
EUVEUV LITHOGRAPHYLITHOGRAPHY15ASET, Takeichi 2005 EUVL Symposium, 7-9 November 2005
Methodology (4): Design Guideline
Pertier Device
Con
stan
t tem
pare
ture
blo
ckradiation radiation
conduction
Con
stan
t tem
pare
ture
blo
ck
conduction
Configuration of thermo-control system
How to reduce magnitude of uncertainty factors affecting ΔT measurement
To achieve uniform temperature distribution in sample
・ Employment of two heat sources Efficiency: Constant temp. blocksUniformity: Peltier device
EUVEUV LITHOGRAPHYLITHOGRAPHY16ASET, Takeichi 2005 EUVL Symposium, 7-9 November 2005
Methodology (5): Practical Dilatometer, Sample
Equipment supplier:
Reference
Displacement
Optical path
Arrangement of laser spot
CTE-01
EUVEUV LITHOGRAPHYLITHOGRAPHY17ASET, Takeichi 2005 EUVL Symposium, 7-9 November 2005
4. Results
EUVEUV LITHOGRAPHYLITHOGRAPHY18ASET, Takeichi 2005 EUVL Symposium, 7-9 November 2005
Evaluation Items
• Determination of measurable range of CTE and types of materials that could be measured
• ReproducibilityRepeatability (Static) : Reproducibility obtainable from measurements of the same sample without moving it .Resetability (Dynamic) : Reproducibility obtainable from measurements involves changing the sample
• Accuracy of measurements: Under evaluation
EUVEUV LITHOGRAPHYLITHOGRAPHY19ASET, Takeichi 2005 EUVL Symposium, 7-9 November 2005
Results (1): Measurable CTE range and materials
• Alumina
• SiC
• Silica glass
• Ti-doped silica glass (LTEM)
• Glass ceramics (LTEM)
CTE-01 can handle a wide variety of materials
Measurable CTE range: from ppm/°C to ppb/°C
several ppm/ °C
hundreds ppb/ °C
EUVEUV LITHOGRAPHYLITHOGRAPHY20ASET, Takeichi 2005 EUVL Symposium, 7-9 November 2005
-700
-500
-300
-100
100
0 10 20 30 40 50 60 70 80
Time [hr]
Phas
e D
iffer
ence
[de
g]
18.0
20.0
22.0
24.0
26.0
0 10 20 30 40 50 60 70 80
Time [hr]
Avg
. tem
pera
ture
[℃
]Change in sample temperature
Change in phase difference176
88
0
-88
-176 Cha
nge
in S
ampl
e Le
ngth
[ nm
]
Results (2): Measured CTE of Silica Glass
EUVEUV LITHOGRAPHYLITHOGRAPHY21ASET, Takeichi 2005 EUVL Symposium, 7-9 November 2005
Results (2): Measured CTE of Silica Glass
Results of measurement for CTE of silica glass
[ppm/゚C]
T1 T2 Meas.1 Meas.2 Δ (Meas.2-Meas.1)
19 22 0.460 0.464 0.004
22 25 0.470 0.471 0.001
These values tell us that the measurement reproducibility is about several ppm per degree.
EUVEUV LITHOGRAPHYLITHOGRAPHY22ASET, Takeichi 2005 EUVL Symposium, 7-9 November 2005
-30
-20
-10
0
10
20
30
0 10 20 30 40 50 60 70 80 90 100 110 120
Time [hr]
Phas
e diff
eren
ce [d
eg.]
Results (3): Measured CTE of Ti-doped silica glass
18
20
22
24
26
0 10 20 30 40 50 60 70 80 90 100 110 120
Time [hr]
Avg
. tem
pera
ture
[ ℃]
13.2
0
-13.2
Change in sample temperature
Change in phase difference
Cha
nge
in S
ampl
e Le
ngth
[ nm
]
EUVEUV LITHOGRAPHYLITHOGRAPHY23ASET, Takeichi 2005 EUVL Symposium, 7-9 November 2005
Results (3): Measured CTE of Ti-doped silica glass
Results of measurement for CTE of LTEM
[ppb/゚C]
T1 T2 Meas.1 Meas.2 Δ (Meas.2-Meas.1)
19 22 -19.95 -19.42 0.53
22 25 -13.06 -13.88 -0.83
19 25 -17.32 -17.68 -0.36
These values indicate that the measurement reproducibility is less than 1 ppb per degree.
EUVEUV LITHOGRAPHYLITHOGRAPHY24ASET, Takeichi 2005 EUVL Symposium, 7-9 November 2005
Results (4): Reproducibility of Measurements
-20-10
01020304050
0 6 12 18 24 30 36 42 48 54 60 66 72 78 84 90 96 102
Time [hr]
Phas
e D
iffer
ence
[de
g]
(a)
18.0
20.0
22.0
24.0
26.0
0 6 12 18 24 30 36 42 48 54 60 66 72 78 84 90 96 102
Time [hr]
Tem
para
ture
(Ave
rage
) [ ℃
] (b)Change in sample temperature
Change in phase differencea
a
EUVEUV LITHOGRAPHYLITHOGRAPHY25ASET, Takeichi 2005 EUVL Symposium, 7-9 November 2005
Results (4): Reproducibility of Measurements
Calculated CTE values (Test No.1)
Average: -26.8 ppb/°C , σ: 0.80 ppb/°C
EUVEUV LITHOGRAPHYLITHOGRAPHY26ASET, Takeichi 2005 EUVL Symposium, 7-9 November 2005
Results (4): Reproducibility of Measurements
Repeatability
Resetability
[ppb/゚C]
Repeatability (Static) : reproducibility obtainable from measurements of the same sample
without moving it .
Resetability (Dynamic) : reproducibility obtainable from measurements involves changing the
sample.
Reproducibility of measurements
ΔCTE: ±0.85 ppb/°C
σ: 0.80 ppb/°C
EUVEUV LITHOGRAPHYLITHOGRAPHY27ASET, Takeichi 2005 EUVL Symposium, 7-9 November 2005
Results (5): Case of CTE Measurements
Tuesday, November 8
Development of Zero Expansion Glass for EUVL Substrate
EUVEUV LITHOGRAPHYLITHOGRAPHY28ASET, Takeichi 2005 EUVL Symposium, 7-9 November 2005
Results (5): Case of CTE Measurements
EUVEUV LITHOGRAPHYLITHOGRAPHY29ASET, Takeichi 2005 EUVL Symposium, 7-9 November 2005
5. Summary
EUVEUV LITHOGRAPHYLITHOGRAPHY30ASET, Takeichi 2005 EUVL Symposium, 7-9 November 2005
Summary・ An optical heterodyne interferometric dilatometer (CTE-01)
tailored to meet EUVL requirements has been developed.
・The CTE-01 can handle a wide variety of materials, including LTEMs.
・Reproducibility of dataRepeatability, σ: < 1 ppb/°CResetability, ΔCTE: < ±1 ppb/°C
These values meet the target specifications.
・We confirm that the CTE-01 will be useful for the precise measurement of the CTEs of EUVL-grade LTEMs.