Evaluation of aberration controllability of the full-field ...

October 18, 2011

EUVL Symposium 2011

K. Otaki, T.Yahiro, K.Matsumoto, O.Arai, Y.Kohama and K. Murakami

Evaluation of Aberration Controllability of the Full-Field Exposure System

2EUVL Symposium 2011

BackgroundPrinciple of the MetrologyMISTI@UECMISTI@SeleteAberration controllabilityAberration adjustment and verificationSummary

Outline


Former EUV interferometers we have developed need a high-brightness light source, such as undulator of synchrotron facility.

source brightness[photons/mm2/mrad2/0.1%BW]

undulato r

~1017

DPP ~1011

~106

Illuminator

Beam line

Vacuum chambers

Vacuum pumps

Optics Loader

However, such an interferometry is not applicable to wavefront measurement on practical exposure tools, due to insufficient brightness of their light sources (LPP or DPP).

We developed a novel interferometry system suitable for low-brightness plasma sources in exposure tools.

EUV interferometerat NewSUBARU (undulator)

Because EUV projection optics is very sensitive to the mirror displacement, the aberration monitoring like interferometer at the exposure tool is required.

Background



Outline


Talbot interferometer

Aberrated plane wave

grating

N=0.5

N=1.0λ

2NPZ2

High contrast interferogram appears at the position of Z=2NP2 /λfrom the grating. Wavefront error can be analyzed by the distortion of this fringes using Fourier transform method.

FFT Inv-FFT

Interferogram

W(x,y)

ΔX=W(X+s,Y) - W(X-s,Y) ΔY=W(X,Y+s) - W(X,Y-s)

Sheared wavefront

Wavefront retrieving

Talbot interferometer


* Multi Incoherent Source Talbot Interferometer

Multi incoherent sources made of pinhole clusters make fringe brightness 10^6 times larger.

Talbot Interferometer Fringe contrast 1.0Brightness 10^3x

Fringe contrast 0.6Brightness 10^6 x

Point source Periodic point sources Periodic Incoherent sources

Z

Each source is composed of several 100 pinholes.

Principles of MISTI



Outline


MISTI @ UEC,TokyoY. Ichikawa et. al., 2010 International Symposium on Extreme Ultraviolet Lithography, Kobe, Japan

EUVSource

Pump

ControlUnit

HiNA-3

Vacuumchamber

IU

CC D

Grating

SPF

Mask

Test optics (HiNA-3)NA 0.3. Mag. 1/5

Pin-hole mask

DPP source

First demonstration of MISTI was conducted at UEC in collaboration with Canon and its accuracy was evaluated. We have presented these results at the last EUVL Symposium at Kobe.

MISTI@UEC


W0= T + EW30= + ET

T=-1T=+1

W+1= T + EW-1= -T + E

(i) P.O. rotation (ii) +/- Talbot order (iii) Incoherent mask

incoherently illuminated mask.

W= E

Deviation ≒ 0.2 nmRMS

+/- Talbot images.Systematic error can be separated usingP.O rotation.

Accuracy evaluation of MISTIThree calibration procedures were used.



Outline


Wafer

Reticle

Second MISTI has installed to the EUV1 at Selete, Tsukuba.We have tried to evaluate aberration controllability and aberration adjustment.

EUV1@Selete MISTI@UECWavelength 13.5 nm ←Field size 26x33mm2 0.2x0.5mm2

NA and Mag. 0.25 ,1/4x 0.30, 1/5xIL. Sigma 0.80 0.80IL. system Koeler IL. Critical IL.EUV Source DPP ←

MISTI of EUV1@Selete


Diameter 120nmφInterval 200nm

104mm

Exposure Field

Pinhole groupsDiameter 2.4 umφInterval 4 um

120-140nm

100-120nm

Absorber 100-150nmｔ

ML

Tapered sidewall is better

Metrology reticle

Grating g=1umZ=N*74um

80 fringes @ CCD

Discharge Produced Plasma EUV source

Koeler Illumination

Area 200-300umφ

Metrology reticle for MISTI of EUV1


Stray light 10e3 to 50e3

Dark 6e3 FE-image 15e3

Signal 1e3 count

Signal=1000Noise=50000S/N=1/50

SignalStray

Stray data Oct.18, '10 Exposure time=2sec

CCD noise

set-1 set-2

Interval = 1hour.Deviation = 0.036 nmrms (Z5-36)

In spite of strong stray light, high accurateprecision has been achieved.

-0.1

-0.05

0

0.05

0.1

Z5 Z6 Z7 Z8 Z9 Z10 Z11 Z12 Z13 Z14 Z15 Z16 Z17 Z18 Z19 Z20

set1

set2

dev

Precision = 0.04 nmRMS

Interferogram and retrieved wavefront


K. Sugisaki et. al., Int. Symposium on EUVL , Kobe (2010).

W+1= T + EW-1= -T + ET= (W+1-W-1)/2

T=-1

T=+1

T=WFE to be measured E=Systematic error

b. Intrinsic error

a. Tilt-induced error

W+ W- T E

Calibration using +/- Talbot order

-0.4

-0.3

-0.2

-0.1

0

0.1


W+

- W-

-0.3

-0.2

-0.1

0

0.1


T

Error

before calib.Unit=λ

Example of calibration

Unit=λ

Systematic error calibration

Grating

CCD



Outline


Shearograms at full field

Retrieved wavefront

L2 LC C RC R2

① Initial state 2set② Mirrors have displaced (several-um) 2set ③ Mirrors have been returned to initial position 2set

①set1 - ①set2 →

Repeatability of measurement①-③ → Reproducibility of mirror position①-② measured - predicted → Abberation controllability

L2 LC C RC R2

Mirror displacing

Aberration change

Measured Predicted

compare

Aberration controllability of EUV1 POProcedure of the experiment


0

0.02

0.04

0.06

0.08

0.1

L2 LC C2 RC R2

Field position

Err

or

(nm

RM

S)

Precision set1-set2

Piezo controlability ①-③

Aberration controlｌability error

Aberration change

0.396 0.383 0.366 0.377 0.427 nmrms

0.432 0.385 0.368 0.385 0.432 nmrms

Measured

Predicted

0.055 0.032 0.030 0.032 0.047 nmrms

Aberration controllability

Scale 10x

L2 LC C RC R2

・

Precision of measurement ・

Piezo controllability・

Aberration controllabilityachieved as 0.03 nmrms !

●

High accurate aberration controllability

●

High accurate measurement

Aberration can be predicted completely !

L2 LC C RC R2

Aberration controllability of EUV1 PO



Outline


LC RC

● Aberration has been reduced as expected.●

Prediction errors are about 0.1-0.2 nmrms.●

Most of errors are astigmatism.●

These will be caused of the temperature drift.

Aberration measured

Optics optimized

Mirror displaced

Aberration measured

Step of adjustment

ΔW = M ΔX

0

0.5

1

1.5

L1 L2 L3 LC C1 C2 C3 RC R1 R2 R3

0

0.05

0.1

0.15

0.2

0.25

L1 L2 L3 LC C1 C2 C3 RC R1 R2 R3

Total

Total-2θ

２θ

L1-L3 C1-C3 R1-R3

agreement !

①Before adjustment

②After adj.

③Prediction

Unit=nm rms Unit=nm rms

Prediction error

Aberration adjustment of EUV1 PO


Wav

efro

nt e

rror

(nm

rm

s)

1θ=coma aberration was reduced after the adjustment.

C1L1 R1

Before

After

0

0.2

0.4

0.6

0.8

L1 C1 R1

０θ

1θ

２θ

０θ

1θ

２θ

Aberrations before and after adjustment


CD

(nm

)

ΔCD= CDLeft-CDRight

38nmL/S

Reduction of coma aberration was verified.

-5

0

5

10

L1 C1 R1

before

after

C1L1 R1

CDLeft CDRight

0

0.2

0.4

0.6

0.8

L1 C1 R1

before

after

Coma measured with MISTI

ΔCD W

avef

ront

err

or (n

m r

ms)

Verification by 2-line exposure experiment


On-machine measurement system, MISTI, have been developed and installed to the full-field EUVL exposure tool, EUV1. A lack of source power has been solved by using pinhole clusters and 106 times of power increase has been achieved.

We intentionally produced aberration change by displacing the mirrors of EUV1 projection optics and compared the measured and the predicted aberration. As a result, aberration controllability of 0.03nm in RMS was confirmed.

We have tried to adjust aberration of projection optics on EUV1 using MISTI and reduction of coma aberration was confirmed.

Completeness of EUV1 projection optics has been proved.

Summary


We would like to thank to

S.Ishiyama, S.Ogata, T.Miyachi, A.Hayakawa K.Sugisaki and other staffs of Nikon.

Selete for time consuming of our experiment.

Staffs of Canon Inc. and Prof. M.Takeda, UEC for exploiting the useful results of the joint study.

Acknowledgment

Evaluation of aberration controllability of the full-field ...

Documents

Transcript of Evaluation of aberration controllability of the full-field ...