Study on inspection property of EUV mask defects by ...euvlsymposium.lbl.gov/pdf/2005/poster/1-DI-02 Park...Samsung confidentialPUBLIC 10/16 2005 EUV Symposium, San Diego California10/1410

1/ total1/14Samsung confidentialSamsung confidential1/16 2005 EUV Symposium, San Diego California Nov. 07. 2005PUBLIC

Jinhong Park*, Seong-Sue Kim, SukJoo Lee, Sang-Gyun Woo,Han-Ku Cho and Joo-Tae Moon

Semiconductor R&D Center, SAMSUNG ELECTRONICS

Study on inspection property of EUV Study on inspection property of EUV mask defects by simulation and mask defects by simulation and

experimental approachexperimental approach


Contents

Introduction

Confocal inspectionExperiments

Defect modeling for simulation

Non-actinic pattern inspectionComparison of ARC effect on image contrast

Simulation of CD error

PropertyComparison of sidewall effect on imaging performance

Summary


Introduction

In EUV lithography, defects on mask are one of the critical issues for high volume manufacturing.

The defects can be classified into two categories such as phase and amplitude defects.

In view of mask making, the patterned mask inspection is important to qualify EUV mask as well as the multilayer inspection.

Simulation tools for the confocal and non-actinic pattern inspection are developed by RCWA method.

The experiment of confocal inspection is performed with programmed phase defects and modeled for simulation.

Some properties of non-actinic pattern inspection are also studied in terms of image contrast.


Fabrication of Programmed Phase Defects

Programmed Phase Defect for verifying the inspection simulation(h : 17nm ~ 70nm, w : 46nm ~ 423nm)

SEM image (top-view)

h : 16nm

after ML depo+

substrate

multilayer(Mo/Si 40 pairs)

programmed defect...

wh

patternbefore ML depo

AFM image

w : 46nm

Small smoothing effect is observed after multilayer deposition. The profile of programmed defects on substrate are maintained to top surface of multilayer.The smoothing can be controlled during multilayer deposition with smoothing techniques.


Defect Inspection by Confocal System

marking point

defect(programmed)

defect

Programmed defect Real defect

The programmed defect can be detected by confocal inspection system. (cf. the sensitivity of inspection system is 100nm.)The detected defects are marked after inspection for further analysis.Some real defects as well as programmed defects also are detected.


Programmed defect Real defect

Defect Analysis by SEM and AFM

h : 16nm h : 38nm

SEM

AFM


Defect Modeling for Confocal Inspection Simulation

Modeling of programmed phase defect

The Programmed phase defects are modeled to simulate defect printability and detectability with RCWA method.The rigorous simulations are performed and compared to experimental results.


Reflectivity of EUV blank – EUV, DUV wavelength

0 50 100 150 2000

0.05

0.1

0.15

absorber thickness(nm)

refle

ctiv

ity @

13.

5nm

0 50 100 150 2000.55

0.6

0.65

0.7

refle

ctiv

ity @

257

nm

0 10 20 30 40 50

1

2

3

4x 10

-4

AR layer thickness(nm)

refle

ctiv

ity @

13.

5nm

0 10 20 30 40 500.2

0.25

0.3

0.35

0.4

0.45

0.5

0.55

0.6

0.65

0.7

refle

ctiv

ity @

257

nm

Reflectivity w/o AR layer Reflectivity with AR layer

The optimum thickness of absorber and AR layer should be determined for maximum absorption of EUV and inspection wavelength.The optimum thickness for each layers can be changed in case of applying different materials for absorber and AR layer.

Optimum thickness of absorber and AR layer for EUV blank


Effect of ARC on Wafer Image

-150 -100 -50 0 50 100 1500

0.2

0.4

0.6

0.8

1

distance(nm)

inte

nsity

w/ ARCw/o ARC

There are little effects of AR layer on wafer imaging.Although reflectivity can be increased with different AR layer thickness, the amount of increment is relatively smaller than reflectivity of multilayer.

* Normalized to w/ARC


Effect of ARC on Inspection Image

-600 -400 -200 0 200 400 6000

0.2

0.4

0.6

0.8

1

mask(nm)

inte

nsity

w/ ARCw/o ARC

The AR layer has largely effects on image contrast at inspectionwavelength.The reflectivity of absorber is close to 60% of that of multilayer and it is near a couple of reflectivity of AR layer.The higher reflectivity of absorber and AR layer is, the worse the inspection image contrast be.

* Normalized to w/ARC


Inspection Images w/ and w/o ARC

mask X(nm)

mas

k Y

(nm

)

inspection image w/ ARC

-600 -400 -200 0 200 400 600

-600

-400

-200

0

200

400

6000

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

mask X(nm)

mas

k Y

(nm

)

inspection image w/o ARC

-600 -400 -200 0 200 400 600

-600

-400

-200

0

200

400

6000

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

As applying AR layer on absorber, the image quality could be improved at inspection wavelength. The improved image contrast can give better resolution to image processing for inspectability and detectability.Most of false defects due to the blurred inspection images can be reduced.

w/ AR layer w/o AR layer


Simulation of Defect - CD error

-40 -30 -20 -10 0 10 20 30 400

0.2

0.4

0.6

0.8

1

wafer(nm)

inte

nsity

no CD errorCD error 2nm(1x)CD error 4nm(1x)CD error 8nm(1x)

-160 -120 -80 -40 0 40 80 120 1600

0.2

0.4

0.6

0.8

1

mask(nm)

inte

nsity

no CD errorCD error 8nmCD error 16nmCDerror 32nm

HP 32nm wafer

inspection

As increasing mask CD error, the CD variation on wafer as well as inspection system is increased.The inspection system should discriminate small intensity variation.In EUV lithography, the MEEF is relatively smaller than photo lithography.

* Normalized to no CD error

CD error


Requirement of Inspection for CD error

0 5 10 15 20 25 30 350

1

2

3

4

5

mask CD error (nm,4x)

CD

var

iatio

n @

waf

er (n

m,1

x)

0 5 10 15 20 25 30 350

3

6

9

12

15

CD

var

iatio

n @

insp

ectio

n (n

m,4

x)

Within ±10% CD error, the mask CD error should be less than 23nm in case of HP 32nm HP node.For that case, the inspection system should make a distinction at least more than 11nm CD variation on mask.It should be about less than 10% of mask linewidth.As the linewidth is decreased, the inspection become more difficult.


Pattern Sidewall Effect on Imaging and Inspection

80 82 84 86 88 900.5

0.55

0.6

0.65

0.7

0.75

0.8

0.85

0.9

0.95

1

sidewall angle(deg)

cont

rast

contrast @ inspectioncontrast @ EUV

-40 -30 -20 -10 0 10 20 30 400

0.2

0.4

0.6

0.8

1

wafer(nm)

inte

nsity

90deg88deg86deg84deg82deg80deg

AbsorberBuffer

ML(MoSi)

Substrate

θ

oblique incidence(6°)

-200 -150 -100 -50 0 50 100 150 2000

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

mask (nm)

inte

nsity

90deg88deg86deg84deg80deg

As the mask pattern has small sidewall angle, the image contrast of wafer and inspection can be improved.If pattern has large sidewall angle, the image will be worse because the effect of reduction of absorber become more dominant.If the sidewall is not uniform in whole mask area, it can make CD uniformity error.

* Normalized to 90deg sidewall

wafer

inspection


Summary

The inspection properties of EUV mask are studied in case of confocal inspection and non-actinic pattern inspection.

The experimental results of confocal inspection are performed and modeled for rigorous simulations

The effects of AR layer on imaging and inspection are more important to enhance inspection performance.

Although the MEEF is small in EUV lithography, the sensitivity of inspection requires more tight control to make a distinction for small intensity changes on mask.

As the mask pattern has small sidewall angle, the wafer imaging and inspection performance can be improved.


References

S. Kim, et. al, “Defect printability and defect inspection simulations of patterned EUVL mask using rigorous coupled-wave analysis,” SPIE vol. 5751, pp. 678, 2005.

P. Yan, “EUVL Alternating Phase Shift Mask Imaging Evaluation,” SPIE vol. 4889, pp. 1099, 2002.

A. Stivers, et. al, “Evaluation of the Capability of a Multibeam Confocal Inspection System for Inspection of EUVL Mask Blanks,” SPIE vol. 4889, pp. 408, 2002.

T. Liang, et. al, “Enhanced Optical Inspectability of Patterned EUVL Mask,” SPIE vol. 4562, pp. 288, 2002.

T. Liang, et. al, “Pattern Inspection of EUVL Masks Using DUV Light,” SPIE vol. 4889, pp. 1065, 2002.

Documents

Study on inspection property of EUV mask defects by ...euvlsymposium.lbl.gov/pdf/2005/poster/1-DI-02 Park...Samsung confidentialPUBLIC 10/16 2005 EUV Symposium, San Diego California10/1410