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WISE 2000, International Workshop on Spectroscopic Ellipsometry,8 – 9 May 2000
DUV (150 – 350nm )Characterization of Materials:
A new instrument, the Purged UVSpectroscopic Ellipsometer ,
Pierre BOHER,,SOPRA S.A., 26 rue Pierre Joigneaux, 92270 Bois-Colombes, France,
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Outline of the talk:
•Introduction.•Presentation of the purged UV spectroscopic ellipsometer.•Experimental results:
•CaF2 substrate•LaF3 film on CaF2 substrate•Photoresists and antireflective coatings •Cr and CrOx layers on glass•Transmittance of SiOF substrate•Extended PUV range
•Conclusion
3
introduction:
• 157nm lithography successor of 193nm generation.• Need to characterize accurately new materials (resists, ARC) and optics at this new wavelength.• Strong correlation between thickness and indices due tolow thickness values.
� Good candidate --> spectroscopic ellipsometry• Need of additional photometric measurements(transmittance of the optics for example).
� New instrument: Purged UV ellipsometer
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SE Basic theoryEllipsometry determines and analyzes the change of the polarization state of light after reflection on a sample
incidence plan
s
EEpEs
N = n - jk
surface
θ0 E Ep rpEs rs
elliptical polarization
ρ ψ= =rr
ep
s
jtan ∆
S
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Advantages of ellipsometry
• Ellipsometry is an absolute technique ( no need of reference spectrum or reference sample ) • Ellipsometry gives twice more informations than reflectometry( ψ and ∆ instead of R )• The phase ∆ is very sensitive to surface layers• As ellipsometry measures the polarization state and not the intensity, it is less sensitive to light intensity fluctuations.
Ellipsometry allows to characterize directly the optical indices (n,k) of bulk materials :
( )N n jk2 2 20
22
0111
= − = +−+
�
��
�
��
�
�
���
sin tanθρρ
θ
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Ellipsometer setup
�Minimized beam path.�Deuterium lamp as source.�Double monochromator included in the polariserarm (avoid photobleaching)�MgF2 Rochon polarizers on stepper motors. �Detection by a photomultiplier in photon counting mode.
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Ellipsometer characteristics
�Rotating analyser instrument.�Spectral range 145-350nm extendable in the visible range.�3 measurement modes possible:
>variable angle spectroscopic ellipsometry >Photometry (reflectance or transmittance)>Scatterometry
8Purged UV spectroscopic ellipsometer
Goniometer
Polariser arm + spectrometer
Analyser arm
Mapping stage
9Schematic view of the purged UV spectroscopic ellipsometer
Sample
Rotatinganalyser
PM tube in photoncounting mode
Fixedpolariser
Deuteriumlamp
GratingPrism
Retarder
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Purged glove box
�SE system is installed inside a glove box with continuous H2O and O2 purification. �Dry nitrogen is injected continuously with automatic pressure adjustment.�Filters can be regenerated automatically every 3-month.
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Purged glove box
�One working face with three gloves to adjust sample and replace deuterium lamp.�Samples up to 200mm diameter introduced with load lock�Residual H2O and O2 measured continuously (in the ppm range during normal working conditions ).
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Purged Glove Box
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0.75
0.8
0.85
0.9
0.95
1
150 175 200 225 250Wavelength (nm)
Tran
smis
sion
ExperimentSimulation
CaF2
Transmittance measurement on a CaF2 substrate
14
0
0.1
0.2
0.3
0.4
50 52 54 56 58 60 62 64 66 68 70
Angle of incidence (deg)
Tan
Psi
-1
-0.6
-0.2
0.2
0.6
1
Cos
Del
ta
Experiment
Simulation
Wavelength 157.6nm
Roughness 5.4nm
CaF2 n=1.600±0.001
Analysis of the SE measurement at 157.6nm on the CaF2 substrate
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1.44
1.48
1.52
1.56
1.6
1.64
140 190 240 290 340Wavelength (nm)
Ref
ract
ive
inde
x n
Refractive index of the CaF2 substrate compared to the literature
16
0
0.1
0.2
0.3
0.4
0.5
0.6
40 45 50 55 60 65 70
Incidence angle (deg)
Tan
Psi
157nm193nm227nm262nm298nm
SE measurements on LaF3/CaF2 sample
17SE measurements on LaF3/CaF2 sample
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
40 45 50 55 60 65 70
Incidence angle (deg)
Cos
Del
ta
157nm193nm227nm262nm298nm
18Analysis of the SE measurement at 157.6nm on the LaF3/CaF2 sample
0
0.1
0.2
0.3
0.4
0.5
0.6
40 45 50 55 60 65 70
Angle of incidence (deg)
Tan
Psi
-1
-0.6
-0.2
0.2
0.6
1
Cos
Del
ta
ExperimentSimulation
LaF3 Layer 400nmn = 1.713
CaF2 Subtrate
Roughness 3.3nm
Wavelength 157.6nm
19Measured dielectric constants of SiO2 and SiN layers
1.4
1.9
2.4
2.9
150 250 350 450
Wavelength (nm)
Inde
x of
refr
actio
n n
SiO2
SiN
0
0.5
1
1.5
150 250 350 450
Wavelength (nm)
Extin
ctio
n co
effic
ient
k
SiO2
SiN
x100
20Variable angle measurement on a photoresist film
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
140 160 180 200 220 240 260 280 300 320Wavelength (nm)
Cos
Del
ta
75deg
70deg
65deg
21Variable angle measurement on a photoresist film
0
1
2
3
4
5
140 160 180 200 220 240 260 280 300 320Wavelength (nm)
Tan
Psi
75deg
70deg
65deg
22
1.2
1.4
1.6
1.8
2
2.2
150 200 250 300Wavelength (nm)
Ref
ract
ive
inde
x n
KrF resistArF resisti-line resistARC F2 resist
F2 KrFArF
Refractive index of different resists and antireflective coatings
23
0
0.25
0.5
0.75
1
150 200 250 300Wavelength (nm)
Abs
orpt
ion
k
KrF resistArF resisti-line resistARCF2 resist
F2 KrFArF
Extension coefficients of different resists and antireflective coatings
24
1.5
1.6
1.7
1.8
1.5 2.5 3.5 4.5 5.5 6.5 7.5 8.5Energy (eV)
Ref
ract
ive
inde
x n
0
0.07
0.14
0.21
Extin
ctio
n co
effic
ient
k
GESP
PUV
157.6nm
Dielectric constants of photoresist 1 measured with the GESP and PUV instruments
25
1.2
1.45
1.7
1.95
2.2
1.5 2.5 3.5 4.5 5.5 6.5 7.5 8.5Energy (eV)
refr
activ
e in
dex
n
0
0.25
0.5
0.75
1
Extin
ctio
n co
effic
ient
k
GESP
PUV
157nm
Dielectric constants of photoresist 2 measured with the GESP and PUV instruments
26
* Reduction of the notching effect
---> lower line width fluctations
Incident angle
AR C
PHOTOR E SISTCanceled by A R C
SUB ST RAT E
* Reduction of the « swing » effect
---> periodic behaviour of the reflectivity
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* Spectroscopic Ellipsometry provides :- Thickness : T- Refractive index : n(λλλλ)- Extinction coefficient : k(λλλλ )
* The index profile : quality of the material
* The knowledge of N and K allows to simulate theR E F L E C TIVIT Y of the material for any thicknesses, anyangles of incidence and at any photolithographic wavelengths.
→The best conditions for the deposition process can be predicted
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R E F L E C TIVIT Y SIMULATION S
Normal incidence
Wavelength : 157.6 nm
Ambient : Photoresist
R
AR C
PHOTOR E SIST
SUB ST RAT E
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Reflectivity at 157.6 nm versus n & k using photoresist 1Thicknes s =150 Å
Refractive index
Extinction coefficient
1.5 1.75 2.0 2.25 2.50.05
0.1
0.15
0.2Reflectance
30
0.7
1.2
1.7
2.2
2.7
3.2
150 170 190 210 230 250 270 290 310 330 350Wavelength (nm)
Opt
ical
indi
ces
n (CrOx)k (CrOx)n (Cr)k (Cr)
Measured Refractive Indices of Cr oxide and Cr versus Wavelength.
31
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0 0.01 0.02 0.03 0.04 0.05 0.06Thickness (µm)
Refle
ctan
ce (%
)
SimulatedreflectanceMeasuredreflectance
Measured and Simulation of reflectance of Cr Oxide on Cr on Glass at 157.6 nm.
32
0.00%
25.00%
50.00%
75.00%
100.00%
152 157 162 167 172 177 182 187 192Wavelength (nm)
Tran
smitt
ance
(%)
Transmission of SiOF versus wavelength.
33
0
1
2
3
4
5
6
7
8
100 200 300 400 500 600 700Wavelength (nm)
Tan
Psi
-1
-0.75
-0.5
-0.25
0
0.25
0.5
0.75
1
Cos
Delta
S E on SiO2/ Si samples using extended PUV range
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1
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
0 1 2 3 4 5 6 7 8 9 10Energy (eV)
Refr
activ
e in
dex
n
-0.01
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
Extin
ctio
n co
effic
ient
k
PUVDatabase
Optical indices of SiO2 compared to litterature using extended PUV range
35
Conclusion:
•A new purged UV spectroscopic ellipsometer has been presented.
•Experimental results on:–CaF2 substrate. –LaF3 layer on CaF2 substrate–CrOx/Cr/glass structures.–Photoresists and antireflective coatings –SiOF transmittance
–Now the range is extended to 145-630nm
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