Control technology of EUV Optics Contaminationclient.blueskybroadcast.com/SPIE/EUV08/content/pdf/04...

EUVL WorkshopJune. 11-12, 2008 1

Control technology of EUV Optics Contamination:

Modeling, mitigation and cleaning

for lifetime extension

EUVL Workshop, Maui, HawaiiWednesday, June 11, 2008

Iwao Nishiyama


Outline

1.

IntroductionRequirement for optics lifetime

2.

Modeling-

Two sources of contamination-1. Model for Carbon Growth2. Model for Oxidation

3.

Mitigation & Prevention1. Environmental control2. Capping Layer Development

4.

Cleaning1. Oxidation cleaning2. Atomic hydrogen cleaning

5.

Summary


Contamination related issues in EUV Lithography

Illumination Optics

Collector Optics

Source

Projection Optics Mask

Resist

Mechanics

Reticle Stage

Source

λ:13nm

Wafer stage

Illumination Optics

Projection Optics

Plasma assisted contamination growth

Erosion

Plasma Debris

Carbon Growth,Oxidation

Particle,Carbon Growth

Resist OutgassingOutgassing from

vacuum component


2007 EUV Critical Issues Ranking

Critical Issue Rank*Reliable high power source & collector module 1.2

Resist resolution, sensitivity & LER met simultaneously 2.1

Availability of defect free masks 2.8

Reticle protection during storage, handling and use 4.1

Projection and illuminator optics quality and lifetime 4.8

*) Average of 20 steering committee member votes Significant concern: Timing and cost / business case for EUVL development

Nov. 1st, EUVL Symposium Steering Committee


Requirement and approach for Projection Optics Lifetime

Requirement for production toolLifetime > 30,000 hoursReflectivity loss < 1.6%

Conditionunder unbaked vacuum( H2O, HC)Outgassing from resist materialsEUV irradiation: IEUV ≤ 10 mW/mm2

ApproachModeling:

Understanding of contamination growthMitigation

Environmental control & Capping layer developmentCleaning

Oxidation or Reduction


Modeling

1. Model for Carbon Growth

2. Model for Oxidation


Two degradation mechanism of EUVL mirror

Cx

Hy

EUV photonH2

O

carbon growth on surface oxidization of subsurface

• Reduction of contaminants from vacuum components and resist

• Cleaning technologies are known.

• Oxidation resistant Capping layer• Novel cleaning technology is

required

~ 1 x 10-9

Pa ~ 1 x 10-7

Pa

~ 10 mW/mm2


Surface Model for contamination growth

molecular flux

thermal desorption

photodesorption

photoreaction

Elec.-induced desorption

Elec.-induced reaction

surpERsurpEDsurpPRsurpPDdes

surav

sur cIcIcIcIcSnvdt

dc γσγσσστ

−−−−−= 41

avnv41

des

surcτ

surpPD cIσ

surpPR cIσ

surpED cIγσ

surpER cIγσ

Sticking coefficient

S

Nishiyama et al. SPIE 2006Nishiyama et al. SPIE 2006

[ ASET ]

Rate equation model was applied to atomic oxygen formation on Ru as the measure of surface oxidation.


Fundamental understanding of Ru oxidization from surface chemistry

Helbert Over et al. Science 297Helbert Over et al. Science 297

Chemistry of water molecule adsorbed on Ru and RuO2

Dissociative attachment has a large cross section on Ru Ted Madey et al. EUVL Symposium 2004Ted Madey et al. EUVL Symposium 2004

[ U. Gießen/U.Rutgers ]

Residence time of H2

O on Ru surface can be evaluated from TPD data


Pressure and EUV dependences of H2

O-induced oxidation rate

1.E- 091.E- 081.E- 071.E- 061.E- 051.E- 041.E- 031.E- 021.E- 011.E+001.E+01

1.E- 09 1.E- 08 1.E- 07 1.E- 06 1.E- 05 1.E- 04 1.E- 03 1.E- 02Contaminant pressure/ Torr

Productionrate/(monolayers/s) accelerated testing

production tool10 W/cm2

1.0 0.10.01

1.E- 091.E- 081.E- 071.E- 061.E- 051.E- 041.E- 031.E- 021.E- 011.E+00

1.0E- 03 1.0E- 02 1.0E- 01 1.0E+00 1.0E+01 1.0E+02EUV intensity/ (W/cm2)

Productionrate

1 x 10-04 Torr

1 x 10-06 Torr

1 x 10-08 Torr

Growth rates are linear with contaminant pressure and EUV intensity in typical experimental conditionsContaminant pressure and EUV intensities are good scaling parameters for lifetime estimation.

Repetition rate 2 kHz、Pulse width 8 nsPressure dependence Intensity dependence

5 mW/mm2


[ ASET ]


0.E+00

2.E- 05

4.E- 05

6.E- 05

8.E- 05

1.E- 04

1.E- 04

1.E- 10 1.E- 09 1.E- 08 1.E- 07 1.E- 06 1.E- 05 1.E- 04 1.E- 03Pusle width/ s

Production rate(monolayers/s)

Pulse width & repetition rate dependence of growth rateAverage power = 5 mW/mm2, H2

O pressure = 2 x 10-6

Torr

100 Hz

100 & 10 kHz

1 kHz

Growth rate decreases when repetition rate becomes low and pulse width becomes short.

Loss of adsorbed layer by photo-desorption is negligible in this range

[ ASET ]



Modeling for Carbon growth on EUV mirror

[ Sandia ]


Mass Dependence of deposition rate [ EUVA ]

Tested contaminant molecules

Heavier molecules show larger carbon deposition rates.

This fact should be explained by the adsorbate mass dependence of residence time.

Aoki et al. EUVL Symposium 2005Aoki et al. EUVL Symposium 2005


Insufficiencies in theoretical modeling

Non-linear dependences on pressure and intensity were observed in carbon deposition rate.

Nakayama et al. SPIE 2008Nakayama et al. SPIE 2008

ORuO2

Ru

Current surface models have not counted followings；Interface reaction of oxidation Surface change in carbon growth

Original surface C-covered surface

Ru Ru

C


Mitigation

1. Environmental

control1. Reduce contaminant levels [ HC and water ]1. Reduce contaminant levels [ HC and water ]2. Active blending of oxidation preventing gas2. Active blending of oxidation preventing gas

2. Capping Layer Development1. Oxidation resistant capping layer1. Oxidation resistant capping layer


ES1：Ultra High Vacuum3.7x 10-7

PaES2：O-ring sealed vacuum

4.5 x 10-5

Pa

H2

O+EUV oxidation was suppressed by high background chamber.Prevention of oxidization by background gas was suggested.

Difference of degradation speed with vacuum condition [ U. Hyogo ]

Kakutani et al. EUVL Symposium 2005Kakutani et al. EUVL Symposium 2005


-2.0

-1.0

0.0

0 2 10-8 4 10-8

1x10-6 Torr H2O

5x10-7 Torr H2O

No Added H2O

(R-R

0) x 1

00

Methanol Partial Pressure (Torr)

10 hrs at ~6 mW/mm2

Mitigation by mixing of methanol

Small amount of methanol in ambient background gas mitigate H2O+ EUV oxidization

[ NIST ]

Shannon Hill et al. SPIE 2006Shannon Hill et al. SPIE 2006


[ EUVA ]Capping Layer Screening

Matsunari et al. EUVL Symposium 2005Matsunari et al. EUVL Symposium 2005


Capping Layer Screening [ LLNL ]

65.8%

65.5%

TiO2

-capped MLΔR = -

0.3%

Ruthenium capping layer still a leading candidate for oxidation protection.Sasa Bijt et al. Sasa Bijt et al. EUVL Symposium 2004EUVL Symposium 2004

TiO2 capped MLs are extremely TiO2 capped MLs are extremely stable in air and under accelerated stable in air and under accelerated lifetime testing lifetime testing

Sasa Bijt et al. Sasa Bijt et al. EUVL Symposium 2005EUVL Symposium 2005


Cleaning Technology

1.1.

Oxidation cleaning for carbon Oxidation cleaning for carbon O3, O, EUV + O2

2.2.

Reductive cleaning for carbon and oxideReductive cleaning for carbon and oxideAtomic hydrogen


Atomic-H Cleaning of Carbon Contamination

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

12.5 13 13.5 14 14.5

Reflectivity recovery

As sputtered：

62.4%

C contamination：

58.9%

Atomic H cleaning:

61.9%

[ ASET ]

Oizumi et al. SPIE 2005Oizumi et al. SPIE 2005

0246

4 -6 2 -4 0 -2

7 mm 5 mm

Car

bon

thic

knes

s(n

m)

Carbon area

0246

4-62-40-2

7 mm 5 mm

Car

bon

thic

knes

s(n

m)

Carbon area

After cleaning

Before cleaning

Thickness:5.6 nm

Thickness:negligible


As sputtered：

62.3 %

Oxidation：

59.6 %

Atomic H cleaning:

62.0 %

0

10

20

30

40

50

60

70

12.5 13 13.5 14 14.5Wavelength (nm)

Ref

lect

ivity

(%)

as-depo.oxidizedH-treated

Binding energy/eV280285290

Reflectivity recovery

Binding energy/eV280285290

Before H-treatment(Ru Oxide)

After H-treatment(Ru Metal)

Atomic-H Cleaning of Oxide Layer [ ASET ]

Nishiyama et al. EIPBN 2006Nishiyama et al. EIPBN 2006

Reduction of Ru oxide


Carbon cleaning of patterned mask

5 min 30 minH-treatment

Cleaning rate = 0.37 nm/min

16,00

012,00

08,0004,0002,000

electron dose on carbon deposition (×1015

cm-

2)

1.4 2.8 5.6 8.4 11.2thickness

(nm)

[ Selete ]


Repeated carbon cleaning [ ASML ]

Hans Meiling et al. SPIE 2006Hans Meiling et al. SPIE 2006


Summary

Optics contamination and lifetime is a big concern in EUVL technologyModeling

Models for carbon growth and oxidation are proposed.Lifetime scaling on contaminant-pressure and EUV-intensity are carried out.

Mitigation; Two approaches are developing. 1.

Vacuum environmental control2.

Capping layer development

Cleaning; Two methods are developing1.

Oxidization removal for carbon contamination2.

Reductive removal for carbon and oxide layer by atomic hydrogen

There are still remaining more than one-order-of- magnitude lack in satisfying optics lifetime (without

cleaning). Further efforts and total approaches are necessary.

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