development status of euv wavefront metrology system...

1EUVL Symposium, October 31, 2007, K. Murakami

Development status of EUV wavefront Development status of EUV wavefront metrology system (EWMS)metrology system (EWMS)

October 31, 2007

Katsuhiko Murakami, Katsumi Sugisaki, Masashi Okada, Katsura Ohtaki, Zhu Yucong, Zhiqian Liu, Jun Saito, Chidane Ouchi, Seima Kato,

Masanobu Hasegawa, Takayuki Hasegawa, Hideo YokotaEUVA

Masahito NiibeUniversity of Hyogo

Mitsuo TakedaUniversity of Electro-Communications


OutlineOutline

Introduction

EUV wavefront metrology methods

EUV wavefront metrology using EWMS

Summary


IntroductionIntroduction

EUV wavefront system (EWMS) was developed by EUVA in NEDO project.

We have developed EUV wavefront metrology methods using EUV experimental interferometer (EEI). These metrology methods were applied to EWMS. We have obtained the first EUV wavefront data of full-field projection optics using EWMS with DTI (digital Talbot interferometry) method.

Non-EUV wavefront metrology systems installed in the factories will be used in the manufacturing of EUV lithography tools. EWMS will play an important role as a standard system of EUV wavefront metrology.


Wavefront of high NA (0.25) full-field projection optics can be measured.

Concept of EUV wavefront metrology system (EWMS)Concept of EUV wavefront metrology system (EWMS)

grating

stage

CCD

vacuum chamber

pinhole/window

PO-boxholder

pinhole

stage

vibration isolator

vacuum pump

metrology frame

EUV light(provided fromSR undulator) PO-box


Difficulties and solutions of EUV wavefront metrologyDifficulties and solutions of EUV wavefront metrology

No coherence light sourceCommon-path type interferometer

Limitation of optical elementsSimple interferometer design using pinholes and gratings

Extremely high accuracy requiredNo mechanical reference surface


Principles of interferometers using EUV radiationPrinciples of interferometers using EUV radiation

Test optic

WindowsCCD

(b) CGLSI (c) DTI

1st Pinhole

Grating

CCDCCD

1st Pinhole

Window and2nd Pinhole

Grating

(a) PDI

Point Diffraction Interferometer Shearing Interferometer


EUV experimental interferometer (EEI) at New SubaruEUV experimental interferometer (EEI) at New Subaru

Clean chamberEEI

Illuminator(NA:0.01) EUV beamline

Test optics

EUV beam

Inside of EEI

Entire view of EEI


EUV interference fringes obtained with EEI EUV interference fringes obtained with EEI PDI

DTICGLSIDLSI

SLSILSILDI

EUV interference fringes were obtained for 7 different wavefront metrology methods.


(a) PDI (b) LDI (c) CGLSI (f) DLSI(e) LSI1.29 nmRMS 0.95 nmRMS1.26 nmRMS 1.52 nmRMS1.21 nmRMS

(d) DTI

1.20 nmRMS

Diffraction typeinterferometers

Shearing typeinterferometers

Measured EUV wavefront using EEIMeasured EUV wavefront using EEI

EUV wavefront was measured using 6 different metrology methods.Good agreement between deferent metrology methods.


EUV wavefront metrology system (EWMS)EUV wavefront metrology system (EWMS)

3.8m

Metrology frameOptical element stage

Illumination optics stagePO rotation stage

Optical element stageProjection optics (PO)PO loader

PO loading crane

EUV light


EWMS at New Subaru synchrotron facility EWMS at New Subaru synchrotron facility

Vacuum pump

Main vacuum chamber Vacuum chamber forillumination optics

PO loader

Undulatorbeamline


EUV wavefront metrology using EWMS startedEUV wavefront metrology using EWMS startedThermal clean chamber was installed. Temperature fluctuation is less than +/-0.1K.Prototype full-field EUV projection optics was installed in EWMS and metrology experiments started. However, EUV intensity through pinhole was very low.→ Illumination optical system was upgraded.


BeamlineBeamline optics layout for EWMSoptics layout for EWMS

LU M0 M1 G S1

M4

M5M6

PO

MaskCCD

PH Mask

M8

M7

LU M0 M1

G

S1

M4M5

M6

Top View

Side View

F

F

PO

M7

M8Schwarzschild

Schwarzschild

：Illuminator optics. These mirrors were upgraded.

STOP

STOP


M6 M8M7

MSFR (mid-spatial frequency roughness) of old mirrors were not small enough to collect synchrotron radiation light onto a pinhole.New mirrors with improved MSFR were polished.

Mirrors for illumination optics for EWMS were upgradedMirrors for illumination optics for EWMS were upgraded

0.13nmRMS0.79nmRMSM8



New mirrorsOld mirrors




New mirrorsOld mirrors

MSFR of mirrors


Illumination spot on a pinholeIllumination spot on a pinhole

800μm 800μm

Before upgrade After upgrade

Illumination spot on a pinhole mask was much reduced with upgraded illumination optics .Radiation intensity through the pinhole increased about thousand times.


DTIDTI （（ddigital Talbot igital Talbot iinterferometrynterferometry））

CCD

PH

G

PO

Pinhole mask

Gratings

When the distance between gratings and image is equals to 2nd2/λ, high contrast interferogram is observed.（d: grating pitch, λ: wavelength, 2n: integer, n: Talbot order）


InterferogramInterferogram obtained with EWMSobtained with EWMS

Clear interferogram was obtained with EWMS in DTI configuration.


Wavefront reconstruction processWavefront reconstruction process

DZF: differential Zernike polynomial fittingRM: Rimmer method**M. P. Rimmer, Appl. Opt. 13 (3) 623 (1974)

fft Data

400 450 500 550 600

400

450

500

550

600

9

10

11

12

13

14

15

16

17

X-Shear

Y-Shear

ReconstructedWavefront

InterferogramResult

Removing Tilt & Power

Reconstructingby DZF or RM

FFT

i FFT

Spectrum


Measured wavefront (differential Zernike polynomial fitting)Measured wavefront (differential Zernike polynomial fitting)

0.70 λ RMS

1.67 λ RMS

1.01 λ RMS

1.76 λ RMS

0.88 λ RMS

4.9 λ-5.4 λ

CT

UR

LR

UL

LL CT

UR

LR

UL

LLUL

LR

UR

CT

LL


Measured Measured wavefrontswavefronts ((RimmerRimmer method)method)

0.72 λ RMS

1.67 λ RMS

1.02 λ RMS

1.53 λ RMS

0.79 λ RMS

4.9 λ-5.4 λ

CT

UR

LR

UL

LL CT

UR

LR

UL

LL

UL UR

LR

CT

LL


Comparison of wavefront reconstruction methodComparison of wavefront reconstruction method

-2

-1.5

-1

-0.5

0

0.5

1

1.5

5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35

Zern

ike

coef

ficie

nt (w

ave) Dfferential Zernike Polynomial Fitting

Rimmer Method

Differential Zernikepolynomial fitting

1.013 λ RMS 1.017 λ RMS

Rimmer methodCT

UR

LR

UL

LLCT

UR

LR

UL

LL


SummarySummary

EUV wavefront metrology using EWMS was started.

Mirrors for illumination optics were upgraded and collection efficiency of EUV radiation onto a pinhole was much improved.

The first EUV wavefront data of full-field projection optics using EWMS with DTI (digital Talbot interferometry) method were successfully obtained. Wavefront data reconstructed with DZPF and RM were in good agreement.

Future workWavefront metrology with CGLSI method.Comparison of EUV and visible-light wavefront.


AcknowledgmentAcknowledgment

The authors would like to thank the operation staff of New Subaru

synchrotron facility for their help.

This work was supported by NEDO

(New Energy and Technology Development Organization) .

development status of euv wavefront metrology system...

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