euv multilayer coatings: potentials and limits© fraunhofer iof euv multilayer coatings: potentials...

© Fraunhofer IOF

EUV multilayer coatings: potentials and limits

2012 International Workshop on EUV

Lithography

Sergiy Yulin, Torsten Feigl, Viatcheslav Nesterenko,

Mark Schürmann, Marco Perske, Hagen Pauer, Tobias

Fiedler and Norbert Kaiser

Fraunhofer-Institut für Angewandte Optik und

Feinmechanik Jena, Germany

Thursday, 7 June 2012, Maui, Hawaii

© Fraunhofer IOF

Seite 2

Outline

Introduction

High-reflective Mo/Si MLs

High-temperature Si-based MLs

Radiation stable Mo/Si MLs

B-based MLs for future generation of EUVL

Summary and outlook

© Fraunhofer IOF

Seite 3

Some highlights of R&D for EUVL @ Fraunhofer IOF

1999 First R&D work on interface engineering

2002 Transfer of Mo/Si technology to Schott Lithotec AG

2003 Design and realization of NESSY-1 system for EUVL optics

2004 Development of high-temperature MLs for Cymer Inc.

2005 First high-temperature collector with 320 mm for Cymer Inc.

2006 Development of TiO2 and Nb2O5 capping layers for Intel Corp.

2007 Development of optics cleaning technologies for Intel Corp.

2008 Development of new capping layer strategy for Intel Corp.

2008 First collector with 660 mm for Cymer Inc.

2010 Design and realization of NESSY-2 system for EUVL optics

2012 Design and realization of NESSY-3 system for R&D

© Fraunhofer IOF

Seite 4

High-reflective Si-based multilayer mirrors at 13.5 nm D.G. Stearns and R.S. Rosen: High-performance multilayer mirrors for soft-X-ray projection lithography:

Proc. SPIE 1547 , 1991

12,5 13,0 13,5 14,0 14,50

10

20

30

40

50

60

70

80

Ca

lcu

late

d r

efle

ctivity, %

Wavelength, nm

Mo/Si

Nb/Si

Ru/Si

Henke , 1991

AOI = 5o,

s-pol.

R = 75.3%

R = 74.6%

R = 72.1% Mo/Si couple was selected due to:

1) Max. theoretical optical performance

2) Minimum structural defectiveness

System R13.5,

%

FWHM,

nm

Mo-Si 75.4 0.58

Nb-Si 74.6 0.53

Ru-Si 72.1 0.69

© Fraunhofer IOF

Seite 5

Main imperfections in Mo/Si multilayer mirrors

Si

S U B S T R A TE

Mo

Si

Si

Mo

d

Mo

Si

Mo

Si

Si

Mo

MoxSiy

Mo/Si

Diffusion intermixing Interface roughness

Mo/Si

Surface oxidation

Cr/Sc

~8 nm

5 nm 5 nm

The gap between theoretical and experimental reflectivity is integrated effect

of all multilayer defects. Internal and surface defects should be mitigated.

© Fraunhofer IOF

Seite 6

Defect mitigation strategy for Mo/Si mirrors at the IOF

Mitigation strategy for

multilayer defects includes:

• Interface-engineering:

• diffusion barriers (X)

• capping layer (Y)

• buffer layer (Z)

• Optimized deposition process:

• deposition parameters

• deposition tools

Si

S U B S T R A TE

Mo

Si

Si

Mo

d

Mo

Si

Mo

Si

Si

S U B S T R A TE

Mo

Si

Si

Mo

d

Mo

Si

Mo

Si

Conventional design Interface - engineered

X

barriers

Y

capping

layer

Z

buffer

layer

Transition from conventional (2-materials) to interface-engineered design

(at least 5 materials) is general mitigation strategy of multilayer defects used at IOF.

© Fraunhofer IOF

Seite 7

Magnetron sputtering systems at the IOF

2 X MRC (1998): R&D system NESSY 1 (2003): 3 x 300mm (with load lock)

NESSY 2 (2010): up to 650mm NESSY 3 (2012): R&D system

© Fraunhofer IOF

Seite 8

Outline

Introduction




Broadband / narrowband Mo/Si MLs


Summary and outlook

© Fraunhofer IOF

Seite 9

Enhanced reflectivity with diffusion barriers

S. Bait et al. Improved reflectance and stability of Mo/Si multilayers: Opt. Engin., 41(8), pp. 1797 – 1804

(2002).

Si

S U B S T R A TE

Mo

Si

Si

Mo

d1

Mo

Si

Mo

Si

Si

S U B S T R A TE

Mo

Si

Si

Mo

d2

Mo

Si

Mo

Si

Conventional design Interface-engineered design

Barriers

(X)

Main material requirements:

• Minimum absorption at 13.5 nm

• Low diffusion mobility

• Continuous film growth

Currently used barrier materials:

• Boron carbide (B4C)

• Carbon (C)

• Silicon carbide (SiC)

Typical thickness: 0.2 – 0.5 nm

Maximum reflectivity benefit: < 2.0%

© Fraunhofer IOF

Seite 10

Enhanced reflectivity of Mo/C/Si/C multilayer mirrors calculation

0,0 0,2 0,4 0,6 0,8

68

70

72

74

76

[Si/MoSi2/Mo/MoSi

2]60

+Si

-6.8 %

-5.4 %

-1.2 %

[Si/C/Mo/C]60

+Si

Reflect

ivity

(13,5

nm

), %

Thickness of carbon, nm

C on Si

C on Mo

C on both

[Mo/Si]60 [Si/C (0.4 nm)/Mo]60+Si + 0.8%

12,6 12,8 13,0 13,2 13,4 13,6 13,8 14,00

10

20

30

40

50

60

70

R = 69.6 %

= 13.36 nm

FWHM = 0.52 nm

R = 68.8 %

= 13.5 nm

FWHM = 0.50 nm

R = 67.4 %

= 13.1 nm

FWHM = 0.47 nm

without

0.4 nm C on Si

0.4 nm C on Mo

[Si/C/Mo/C]60

+Si

Reflect

ivity,

%

Wavelength, nm

© Fraunhofer IOF

Seite 11

Enhanced reflectivity of Mo/SiC/Si/SiC multilayer mirrors calculation

0,0 0,2 0,4 0,6 0,868

70

72

74

76

-3.8 %

-4.5 %

-0.8 %

[Si/MoSi2(1.4 nm)/Mo/MoSi

2(0.6nm)]

60+Si

[Si/SiC/Mo/Si/SiC]60

+Si+SiO2

Reflect

ivity

(13,5

nm

), %

Thickness of SiC, nm

SiC on Mo-on-Si

SiC on Si-on-Mo

SiC on both

Mo/Si

12,8 13,0 13,2 13,4 13,6 13,8 14,00

10

20

30

40

50

60

70

[Si/SiC/Mo]60

+Si

tSiC

= 0.5 nm

0.0 nm SiC

0.5 nm SiC on Mo-on-Si

[Si/SiC/Mo]60

R = 69.1 %

= 13.44 nm

FWHM = 0.52 nm

[Si/Mo]60

R = 68.8 %

= 13.5 nm

FWHM = 0.5 nm

Re

fle

ctivity, %

Wavelength, nm

[Mo/Si]60 [Si/SiC(0.5 nm)/Mo]60+Si + 0.3%

© Fraunhofer IOF

Seite 12

Material selection for diffusion barriers (C, B4C, Mo2C...) calculation

0.0 0.2 0.4 0.6 0.8

68

70

72

74

76

78

[Si/B4C/Mo/B

4C]

60+Si

[Si/MoSi2/Mo/MoSi

2]

60+Si

[Si/C/Mo/C]60

+Si

Re

fle

ctivity (

13

,5 n

m),

%

Barrier thickness, nm

C on Si

C on Mo

C on both

Mo/Si

B4C on Si

B4C on Mo

B4C on both

Carbon or B4C ?

0.0 0.2 0.4 0.6 0.868

70

72

74

76[Si/B

4C/Mo/B

4C]

60+Si

[Si/MoSi2/Mo/MoSi

2]

60+Si

[Si/Mo2C/Mo/Mo

2C]

60+Si

Re

fle

ctivity (

13

,5 n

m),

%

Barrier thickness, nm

Mo/Si

B4C on Si

B4C on Mo

B4C on both

Mo2C on Si

Mo2C on Mo

Mo2C on both

B4C or Mo2C ? Or ... ?

B4C is more preferable than carbon. Mo2C is more preferable than B4C.

© Fraunhofer IOF

Seite 13

Current state and prospects for reflectivity enhancement

The highest reflectivity at 13.5 nm & AOI ≤ 5:

Further prospects:

• Transition from Mo/Si to Nb/X/Si/X, Ru/X/Si/X …. multilayer mirrors

• Application of new promising diffusion materials

• Application of new oxidation resistant capping layers

Maximum reflectivity benefit is 1.0 - 2.0%...

System Rexp.

%

FWHM,

nm

Ref.

Mo/X/Si/X 70.15 0.54 FOM

Mo/B4C/Si/B4C 70.0 0.53 LBLL

Mo/B4C/Si/C 69.9 0.54 IWS

Mo/Si/C 69.6 0.53 IOF

© Fraunhofer IOF

Seite 14

Outline

Introduction





Summary and outlook

© Fraunhofer IOF

Seite 15

Thermal stability of conventional Mo/Si multilayer mirrors

V.V. Kondratenko et al: Thermal stability of soft X-ray Mo/Si and MoSi2/Si multilayer mirrors, Appl. Opt, 1993.

H. Takenaka et al.: Thermal stability of Mo/C/Si/C multilayer soft X-ray mirrors: J. Elect. Spectroscopy, 1996.

12,3 12,6 12,9 13,2 13,5 13,8 14,10

10

20

30

40

50

60

70

Mo/Si (M744)

N = 50

= 2 h

as-deposit

T=100 oC

T=200 oC

T=300 oC

T=400 oC

Reflect

ivci

ty, %

Wavelength, nm

Mo/Si multilayer mirrors:

Max. reflectivity: ~ 69.0%

Max. temperature: ~ 100oC

Structure damage: ~ 700oC

50 nm

© Fraunhofer IOF

Seite 16

Mo/Si multilayers with enhanced thermal stability

First request: Cymer Inc. @ EUVL Symposium in Miyazaki (2004)

Requirements: R > 60% @ 13.5 nm and T ≤ 500oC

Application: Collector EUVL optics (lithium cleaning: Tm = 108oC)

© Fraunhofer IOF

Seite 17

Enhanced thermal stability of MoSi2/Si mirrors

MoSi2/Si multilayer mirrors:

Temperature: 20 - 600oC

Reflectivity: 41.2%@13.5 nm

FWHM: 0.26 nm

12,5 13,0 13,5 14,00

10

20

30

40T = 500°C

[Si/MoSi2]60+Si

q = 1.5°

Reflect

ivity,

%

Wavelength, nm

As-deposited

=1 h

=10 h

=100 h

V.V. Kondratenko et. al: Thermal stability of soft X-ray Mo/Si and MoSi2/Si multilayer mirrors, Appl. Opt, 1993.

© Fraunhofer IOF

Seite 18

Enhanced thermal stability of Mo/C/Si/C mirrors

12,5 13,0 13,5 14,00

10

20

30

40

50

60 T = 500°C

[Si/C/Mo/C]60

+Si

q = 1.5°

Reflect

ivity,

%

Wavelength, nm

As-deposited

=1 h

=10 h

=100 h

[Mo/C(0.8 nm)/Si/C(0.8nm)]60 As-dep. 500oC, 100h

[Mo/C(0.8)/Si/C(0.8)]60 R = 60% @ 13.5 nm but… T < 400oC

10 nm 10 nm

© Fraunhofer IOF

Seite 19

Mo/Si multilayers with enhanced thermal stability

12,9 13,2 13,5 13,8 14,10

10

20

30

40

50

60

[Si/X/Mo/Si/X]60

+Si

= 100 hours

q = 1.5°

Reflect

ivity,

%

Wavelength, nm

As-deposited

T = 400°C

T = 500°C

T = 600°C

2 nm 2 nm

As-deposited 600oC, 100h

Combination: R 60.0% @ 13.5 nm & T 600oC

[Mo/X/Si/X]60

© Fraunhofer IOF

Seite 20

Reflectance of the first high-temperature collector optics 2005

0%

10%

20%

30%

40%

50%

60%

12.9 13.1 13.3 13.5 13.7 13.9 14.1

wavelenght, nmre

fle

cta

nce

r = 40mm

r = 50mm

r = 60mm

r = 70mm

r = 80mm

r = 90mm

r = 100mm

r = 110mm

r = 120mm

r = 130mm

Combination: R 56.0% @ 13.5 nm & T 600oC

© Fraunhofer IOF

Seite 21

Rs > 65 %

= (13.5 ± 0.03) nm

Dd = 0.015 nm = 15 pm

Diameter: > 660 mm

Lens sag: > 150 mm

Tilt: > 45 deg

Weight: > 40 kg

Current LPP collector coating challenges

2012

© Fraunhofer IOF

Seite 22

Current state and prospects for enhanced thermal stability

Experimental reflectivity & thermal stability of Si-based multilayers:

Further prospects:

• Development of HT multilayers mainly focuses on the improvement of optical

performance.

Our limits:

• Development of HT- multilayers with Tmax > 600oC is limited by temperature of

crystallization of Si-layers (T cryst. ~ 650oC).

System Tmax, oC

R max,

%

FWHM,

nm

Mo/Si < 100 69 0.51

Mo2C/Si ≤ 350 67 0.48

Mo/C/Si/C ≤ 400 60 0.50

MoSi2/Si ≤ 600 42 0.26

Mo/X/Si/X ≤ 600 60 0.47

© Fraunhofer IOF

Seite 23

Outline

Introduction





Summary and outlook

© Fraunhofer IOF

Seite 24

Degradation of Si-capped Mo/Si multilayer mirrors

Industry goal (imaging optics ):

EUV intensity: I EUV ~ 10 mW/mm2

Pressure: PH2O < 10-7 Torr

PHC < 10-9 Torr

Reflectivity loss: D R < 1%

(over 30.000 hours)

12,8 13,0 13,2 13,4 13,6 13,8 14,00

10

20

30

40

50

60

70

Rp = 68.0%

Rp = 45.6%

- 22.7 %

[Si/Mo]60

+Si

PH2O

= 5x10-7 Torr

DEUV

= 165J/mm2

Reflectivity, %

Wavelength, nm

unexp. exposed

~10 hours

Damage caused by two main mechanisms:

• potentially irreversible surface oxidation

• demonstrably reversible surface contamination (mainly carbon growth)

© Fraunhofer IOF

Seite 25

Development of oxidation resistant capping layers

[Mo/Si]59

Mo

Si

Substrate

Ru

[Mo/Si]59

Mo

Si

Substrate

TiO2/Nb2O5

1999 - 2005 2005 - 2010

Three capping layer conceptions:

1) Low-oxidation materials: (Ru, Au, Pt …)

2) Stable oxides: (TiO2, Nb2O5, ZrO2…)

3) Multilayer conception: more than two layers

• Thickness < 2.0 nm

• Good optical properties

• Chemically inert to oxygen

• Amorphous structure

• Compatible with Mo/Si stack

10 nm

~ 103 ~ 104

© Fraunhofer IOF

Seite 26

Reflectivity and temporal stability of TiO2-capped mirrors

0 20 40 60 80 100 120 140 160 1800,965

0,970

0,975

0,980

0,985

0,990

0,995

1,000

Time after deposition, days

No

rmaliz

ed

re

fle

ctivity (

R/R

o)

SiO2

TiO2

Ru

Si: - 0.2%

TiO2: - 0.3%

Ru: - 2.6%

12,8 13,0 13,2 13,4 13,6 13,8 14,00

10

20

30

40

50

60

70 without barriers

with barriers

+ 1.6 %

Rp = 68.50 %

( = 13.42 nm)

FWHM = 0.51 nm

Rp = 66.9%

( = 13.44 nm)

FWHM = 0.48 nm

PTB

[Mo/Si/B4C]

60+TiO

2

tB

4C ~ 0.4 nm

tTiO

2

~ 1.5 nm

Re

fle

ctivity, %

Wavelength, nm

R = 68.5 % @ 13.42 nm Reflectivity loss of 0.3% within 6 months

© Fraunhofer IOF

Seite 27

Synchrotron exposure set-up:

Synchrotron: SAGA-LS BL18

Water pressure: 7*10-6 mbar

EUV intensity: ~ 8.0 W/cm2

Total dose: 150 kJ /cm2

60.0

61.0

62.0

63.0

64.0

65.0

66.0

67.0

68.0

0 50000 100000 150000

Dose/(J/cm2)

Reflectivity/%

TiO2

Nb2O5

Ru

PH2O = 7*10-6 mbar

• Nb2O5 and TiO2: no degradation

• Ru: degradation by surface oxidation

S. Yulin et al., EUVL Symposium, Prague, 2009

Enhanced radiation stability of TiO2- and Nb2O5-capped mirrors

© Fraunhofer IOF

Seite 28

New Exposure Test Stand (ETS) & Xe-gas discharge

ETS requirements:

• Source: DPP / Xe

• Repetition rate: 4 kHz

• In-band power: ≤ 50W/2

• Background pressure 10-8 Torr

• Contaminant inlet 10-2 Torr

• Pressure control in-situ

• EUV-intensity > 25 mW/cm2

• Irradiation area > 15x15 mm2

• EUV intensity 5%

Simultaneous exposure up

to 4 samples is possible with

similar dose ( 5%)

Condenser

Chamber

(P ~ 10- 2 Torr )

EUV-source

Exposure

Chamber

(P < 10 -8Torr)

200 mm

R > 67%

© Fraunhofer IOF

Seite 29

Further prospects for enhanced radiation stability

Currently developed capping layers (for imaging optics):

Further studies/prospects:

• Developed capping layer materials should be tested for EUVL optics

• Application of new multilayer capping layer systems

Our limits:

• Considerable reflectivity losses of EUVL optics due to application of oxide capping

layer with d >> 2.0 nm (collector optics)

• Capabilities for lifetime studies with high-radiation power are still limited

Material Rmax,

%

Oxidation resistance Carbon cleaning

by EUV

Synchrotron Pulsed O2 H2

Ru 68.7

TiO2 68.5

Nb2O5 68.5

© Fraunhofer IOF

Seite 30

Outline

Introduction




B-based multilayers for future generation of EUVL

Summary and outlook

© Fraunhofer IOF

Seite 31

Next generation of lithography (NGL)

Wavelength selection

3 4 5 6 7 8 9 10 11 12 13 140

10

20

30

40

50

60

70

80

Co/C La/B Mo/Sr

Mo/Be Mo/Si

Cr/Sc

Ma

xim

um

re

fle

ctivity, %

Wavelength, nm

Reflectivity requirements:

(R > 70%)

• Mo/Si 12.4 nm

• Mo/Be 11.4 nm

• La/B 6.67 nm

© Fraunhofer IOF

Seite 32

Theoretical reflectivity at 6.7 nm

Reflectivity of La/B vs Mo/Si multilayers

6 7 12 13 14 150

20

40

60

80

R = 76.2%@ 13.5 nm

FWHM = 0.6 nm

Ma

xim

um

re

fle

ctivity, %

Wavelength, nm

[La/B]300

[Mo/Si]60

Henke, 1991

= 5 deg

R = 79.4%@ 6.7 nm

FWHM = 0.058 nm

Mo/Si La/B Issue

R,% 76.1 79.5 ~

d, nm 6.95 3.4 x 2

N 60 ≥ 200 x 3

D, nm 0.60 0.07 x10

• La/B multilayer mirrors are extremely narrowband (FWHM = 0.07 nm)

• Higher reflectivity losses can be predicted due to interface defects (d = 3.4 nm)

© Fraunhofer IOF

Seite 33

Experimental reflectivity at 6.7 nm (2012)

Y. Platonov et al: Status of multilayer coatings for EUVL: EUVL Workshop 2011, Maui, Hawaii.

Champion data is 49.8% @ 6.66 nm

(Rigaku, Japan )

Reflectivity level > 45 % was shown

by few other multilayer suppliers

© Fraunhofer IOF

Seite 34

La and B are not the best materials for multilayer mirrors

1) Polymorphismus in La:

• α- La = 2.46 g/cm3

• - La = 2.35 g/cm3

• - La = 2.52 g/cm3

La-layer is not stable

2) Three lanthanum boride:

• LaB4,

• LaB6

• LaB9

Considerable diffuse intermixing

3) La and B have extreme oxidation

Considerable surface oxidation

Currently only Mo/B4C (not La/B) are commercially used for XRF !!!

© Fraunhofer IOF

Seite 35

6,55 6,60 6,65 6,70 6,75 6,800

10

20

30

40

50

60

70

80

La/B

La/B4C

La/BN

Ma

xim

um

re

fle

ctivity, %

Wavelength, nm

Henke, 1991

= 6.7 nm

= 5 deg

R = 79.5%@ 0.064 nm

R = 74.0%@ 0.058 nm

R = 57.2%@ 0.046 nm

Replacement of boron by boron carbide (B4C)

System R,

%

FWHM,

nm

La/B 79.5 0.064

La/B4C 74.1 0.058

La/BN 57.2 0.046

Transition from La/B to La/B4C results in reflectivity loss of 5.4 % @ 6.7 nm.

© Fraunhofer IOF

Seite 36

B4C-based multilayers with La-, Ru- and Mo-absorber layers

Theory Experiment

6,55 6,60 6,65 6,70 6,75 6,800

10

20

30

40

50

60

70

80

Re

fle

ctivity, %

Wavelength, nm

Henke, 1991

= 6.7 nm

= 5 deg

N = 300

R = 74,1%

FWHM = 0.058 nm

R = 58.7%

FWHM = 0.055 nm

R = 54.1%

FWHM = 0.047 nm

La/B4C

Mo/B4C

Ru/B4C

6,55 6,60 6,65 6,70 6,75 6,80

0

10

20

30

40

50

60

70

80

La/B4C

Mo/B4C

Ru/B4C

Wavelength, nm

Re

fle

ctivity, %

PTB, Berlin

H = 3.38 nm

N = 200

= 10 deg

R = 32,1% @ 6.67 nm

FWHM = 0.036 nm

R = 26.0% @ 6.68 nm

FWHM = 0.039 nm

R = 18.0% @ 6.70 nm

FWHM = 0.039 nm

S. Yulin et al. Reflective optics for next generation lithography, EUVL Symposium, Miami (2011)

La/B4C: R = 32.1% @ 6.67 nm

Rexp/Rth. ~ 0.42…0.44 ( ~ 0.8 nm)

Target of this study: • interface performance

• temporal stability

• thermal stability

© Fraunhofer IOF

Seite 37

Summary and outlook

Remarkable progress has been made in the field of Mo/Si multilayer mirrors for EUVL

application

Interface engineering (barriers, capping layers…) was successfully used for:

improvement of optical properties:

Mo/Si/C: R = 69.6% @ 13.5 nm

Mo/Si/SiC: R = 69.1% @ 13.4 nm

enhanced thermal stability:

Mo/C/Si/C R = 60.0% & T 400 °C

Mo/X/Si/X R = 60.0% & T 600 °C

enhanced radiation stability:

Mo/Si/B4C +TiO2 R = 68.5% @ 13.5 nm

Mo/Si/B4C + Nb2O5 R = 68.5% @ 13.5 nm

Lifetime of EUVL optics is still actual issue for multilayer community

© Fraunhofer IOF

Seite 38

Support: Cymer Inc. and Intel Cor.

EUV: Ch. Laubis, Ch. Buchholz, J. Puls, A. Barboutis,

Ch. Stadelhoff, M. Biel, B. Dubrau and F. Scholze (PTB Berlin)

TEM: U. Kaiser (University, Ulm)

IOF: M. Scheler, T. Müller, St. Schulze (IOF)

Acknowledgements

euv multilayer coatings: potentials and limits© fraunhofer iof euv multilayer coatings: potentials...

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