contamination control in euv exposure tools · nikon corporation contamination control in euv...

June 12, 2013

Katsuhiko Murakami Noriaki Kandaka, Takashi Yamaguchi, Atsushi Yamazaki,

Tsuneyuki Hagiwara, Tetsuya Oshino, Jiro Inoue and Kazuya Ota

Nikon Corporation

Contamination control in EUV

exposure tools

2013 EUVL Workshop Katsuhiko Murakami

Contamination control in EUV exposure tools

June 12, 2013 2 2013 EUVL Workshop Katsuhiko Murakami

EUV-induced contamination

• Carbon contamination

• Surface oxidation

Particles in vacuum






Particles in vacuum

EUV + O2 mitigation

On-body UV dry cleaning

Contamination study using a synchrotron facility


Branch chamber

Exposure chamber

Folding mirror

Gate valve with Zr filter

Neutral density filter

Neutral density filter

Rotational photo diode

Sample stage

Load rock chamber

Transfer rod Gas inlet

Synchrotron radiation

0.8

0.85

0.9

0.95

1

0 200 400 600Cumulative dose [J/mm

2]

Re

lative

re

fle

cta

nce

0.88

0.9

0.92

0.94

0.96

0.98

1

0 2 4 6 8 10

Cumulative dose [J/mm2]

Re

lative

re

fle

cta

nce

8W/cm21W/cm2

0.1W/cm2

8W/cm2

1W/cm2

0.1W/cm2

0.01W/cm2

0.002W/cm2

0.8

0.85

0.9

0.95

1

0 200 400 600Cumulative dose [J/mm

2]

Re

lative

re

fle

cta

nce

0.88

0.9

0.92

0.94

0.96

0.98

1

0 2 4 6 8 10

Cumulative dose [J/mm2]

Re

lative

re

fle

cta

nce

8W/cm21W/cm2

0.1W/cm2

8W/cm2

1W/cm2

0.1W/cm2

0.01W/cm2

0.002W/cm2

Contamination growth with perfluorohexane (C6F14)

BL 18 at SAGA LS SR facility

EUV + O2 mitigation of carbon contamination


1E-5

1E-4

1E-3

1E-2

1E-1

1 10 100 1000 10000

E , irradiance [mW/cm2]

V , c

on

tam

ina

ting/c

lean

ing r

ate

[n

m/s

]

C6F14 (5E-5Pa) O2 cleaning (2E-2Pa)

7 8 9 10 11 12 13 14 15 16

Number of pulses irradiated to IU [billion pulses]IU

tra

nsm

itta

nce

[a

rb. u

nit

]

Modeled

Actual

Oxygen flow optimized

History of IU transmittance of EUV1 Contamination growth rate

and O2 cleaning rate

O2 cleaning rate exceeds carbon contamination growth rate in appropriate condition.

Degradation of IU (Illumination Unit) transmittance of EUV1 was stopped after

optimization of O2 flow rate.

EUV + O2 mitigation is very effective to carbon contamination.

Position on mirror

Reflectivity

UV dry cleaning of carbon contamination


Before cleaning After cleaning

● Before cleaning, ■ After cleaning UV dry cleaner using a low pressure mercury lamp

Carbon contamination on a illumination optics of EUV1 can be removed

with UV dry cleaning. Initial reflectivity was recovered.

UV dry cleaning in depressurized atmosphere


1 atm1 atm1/100 atm1/100 atm

◆ measured

--- calculation

Cleaning rate of carbon contamination with UV dry cleaning increases

with reduced pressure.

UV dry cleaning was applied to an on-body cleaning method in EUV1.

低圧水銀ランプ

洗浄サンプル

Low pressure mercury lamp

Sample

真空チェンバー

低圧水銀ランプ

Vacuum chamber

Low pressure mercury lamp

On-body UV dry cleaning for IU of EUV1


FE1

FE2

Con1

Con2

Low pressure mercury lamps placed near each mirror

enabled on-body cleaning of illumination optics.

FM






Particles in vacuum

EUV + O2 mitigation


Metal-oxide capping layer

0.8

0.85

0.9

0.95

1

0.0E+0 5.0E+4 1.0E+5 1.5E+5 2.0E+5

Dose [J/cm2]

Si

MoOx

NbOx

Ru

Metal oxide capping layer


Si

Si

Si

Mo

Mo

Si

Si

Si

Mo

Mo

Metal oxide capping layer

Reflectivity change of Mo/Si multilayers with several different capping layer materials

during EUV exposure in water vapor was measured.

H2O: 1x10-3 Pa, 8 W/cm2

Rela

tive c

hange o

f re

flectivity

Metal oxide capping layers have much higher oxidation durability

compared with conventional Ru capping layer.






Particles in vacuum

EUV + O2 mitigation


Metal-oxide capping layer

Particle capture using silica aerogel

Particles in vacuum: Materials


• Potential particle generating events

– Physical contact

• Collisions: wafer/reticle transfer, pod open/close,

valve o/c, grounding pin contact, …

• Rubbing: bearings, ultrasonic motors, …

– Physical reaction

• Sputtering: corona ionizers, EUV sources, …

• Evaporation and condensation: pumping down in load lock

– Electrical discharge/spark

• EUV sources

• Discharge between reticle and pod during a transitional region in load lock

• Micro-discharge between wafer/reticle backsides and e-chucks.

• Potential materials

– Metal/metalloid: Na, Al, Si, K, Ca, Ti, Cr, Fe, Ni, Mo, Ru, Sn, Ta, …

– Inorganic: SiO2, …

– Organic: CxHyOz

+V -V

HEAVY! > 7 g/cm3

cf. PSL~1 g/cm3

Particle in vacuum: Velocities

June 12, 2013 13

• Interaction with surfaces “bounce or stick” depends on the

relationship between the particle impact velocity Vi and the

critical velocity Vc.

– Vi < Vc: stick

– Vi > Vc: bounce

– Vi >> Vc: split and stick/bounce

S. Wall, et al., Aerosol Science and Technology, Volume 12, Issue 4, 1990, Pages 926 – 946

Critical velocity vs. particle diameter

96 m/s 76 m/s

457 m/s

• Vc is determined by the surface

material, the particle material,

the particle size, etc.

• Particles that have lower

velocities than the critical

velocity cannot continue to fly.

100 nm

FAST! Typical Vc :

100 m/s for 100-nm particles

2,000 m/s for 10-nm particles

2013 EUVL Workshop Katsuhiko Murakami

Particles in vacuum: Flying range


• Forces acting on particles in vacuum

– Gravity: r 3, dominant force but not decelerating force

– Drag force: r 2, weak, depends on the gas pressure

– Coulomb force: weak, depends on E and amount of electric charge

– Thermophoretic force: very weak, depends on the thermal gradient

Flying range vs. Initial velocity

Mo particles in 0.01-Pa O2 gas 1

10

100

1,000

10,000

100,000

1,000,000

10 100 1,000 10,000

Fly

ing

ra

ng

e (

m)

Initial velocity (m/s)

10 nm 100 nm 1,000 nmParticle diameter

below Vc

LONG!

> 100 m

Particle reduction system


To simplify the models, gravity is neglected and the same coefficient of restitution (COR) is used for both the vertical

component and the parallel component to the wall.

Particle source at the top.

Shield between the particle source and the

mask.

Performance of shield is insufficient.

Particle source at the top.

Particle catcher on the shield.

Particle catcher can drastically reduce

the number of flying particles.

Mask

Shield

Mask

Particle shield Particle catcher

Particle catcher

Silica aerogel as particle catcher


STARDUST : NASA’s comet sample return mission, 1999 - 2011

Comet particles

Velocity: ~ 6.5 km/s

Diameter: 40 - 300 µm

Dust Collector with aerogel February 7, 1999

Stardust Launch

Aerogel In Hand

Particle Tracks in Aerogel

(experiment)

Comet Ejecta in Aerogel Photos from jpl.nasa.gov

Vacuum tool particles

Velocity: 10 m/s - 1 km/s

Diameter: 1 µm - 10 nm

Kinetic

energy

10 –13 - –15

1

Thinner sheet is enough

for EUV tools.

Structure of silica aerogels


SiO2

Pore size micro pores: < 2 nm

mesopores: 2-50 nm

macro pores: > 50 nm

Silica particle diameter

2-5 nm

Apparent density: 0.003-0.35 g/cm3

Pore network

Density of air: 0.0012 g/cm3 at 20 °C

Experimental setup of particle catcher


MPE Tool

Particle generator installed

in ESC chamber

High voltage

feedthroughs

Induction coil

Lead wire: +V Particles were generated by discharging

(Air pressure ~5E-3 Pa) Lead wire: V

Photos of aerogel tested:

bare (left) and covered by a foil (right)

Size: 100 mm (W), 100 mm (D), 15 mm (H)

Density: 0.012 g/cm3

Aerogel in ESC chamber

Metal Plate having a through hole

A quarts substrate for particle adhesion

evaluation (not shown in the photo)

Cover plate

Aerogel Aerogel holding plate

10-20% of particles can

go out through the gap

Experimental conditions of particle catcher


#2: Bare aerogel sheet

• The foil was removed.

• Discharging was continuously and the total time was

about 8 seconds.

#1: Aerogel sheet covered with a foil

• An aerogel sheet covered by a foil on the holding plate

was put between the quarts substrate and the particle

generator.

• Discharging was continuously and the total time was

about 8 seconds. Particles are not captured.

Particles are captured.

Experimental results #1: Covered with foil


157

20,431

83,262

53,683

79,865

22,982

3,839

13,137

14,289

Total = 291,645

Pixel Histogram

41 ...

… 40

… 20

… 10

… 7

… 5

… 3

… 2

… 1

117

13,266

59,354

49,915

90,868

29,952

4,452

16,635

19,063

Total = 283,622

Pixel Histogram

41 ...

… 40

… 20

… 10

… 7

… 5

… 3

… 2

… 1

Almost

the same

density

Particle density: 1,331 particles/cm2 Particle density: 1,368 particles/cm2

Up Down

26- >=300 nm

22-25 200 nm

17-21 100 nm

14-16 80 nm

11-13 70 nm

7-10 60 nm

1-6 pix =< 50 nm

Experimental results #2: Bare aerogel


74

519

3,730

4,288

8,317

2,856

412

1,663

1,812

Total = 23,671

Pixel Histogram

41 ...

… 40

… 20

… 10

… 7

… 5

… 3

… 2

… 1

8

184

1,456

2,285

5,546

2,119

274

1,201

1,414

Total = 14,487

Pixel Histogram

41 ...

… 40

… 20

… 10

… 7

… 5

… 3

… 2

… 1

Particle density: 68 particles/cm2 Particle density: 111 particles/cm2

#1 1/20 #1 1/12

Up Down

The aerogel sheet caught almost all particles that impacted it !!

26- >=300 nm

22-25 200 nm

17-21 100 nm

14-16 80 nm

11-13 70 nm

7-10 60 nm

1-6 pix =< 50 nm

Summary


Oxygen introduction during EUV exposure effectively mitigates

carbon contamination growth on optical elements in EUV exposure

tools.

Carbon contamination on optical elements can be removed by UV

dry cleaning. It can be applied to an on-body cleaning method in

EUV exposure tools.

Surface oxidation of multilayer mirrors during EUV exposure can be

prevented by using metal-oxide capping layer.

Particles in a vacuum chamber fly very long distance. Silica aerogel

is suitable material to capture such flying particles in EUV exposure

tools.

Acknowledgements


• EUVA

• NEDO

• METI

• Selete & EIDEC

• SAGA Light Source

• Chiba University

• Panasonic Corp.

Thank you for your attention.

contamination control in euv exposure tools · nikon corporation contamination control in euv...

Documents