spectroscopic ellipsometer , a new instrument, the purged...

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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

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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

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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

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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

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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

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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

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* 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

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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.

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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.

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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.

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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

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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