optics for euv lithographyeuvlsymposium.lbl.gov/pdf/2007/op-01-lowish.pdflithography optics division...

Lithography Optics Division

Optics forEUV Lithography

Martin Lowisch, Peter Kuerz, Thure Boehm,Hans-Juergen Mann, Stephan Muellender, Wolfgang Bollinger, Manfred Dahl, Michael Muehlbeyer, Siegfried Rennon, Frank Rohmund, Udo Dinger, Thomas Stein, and Winfried Kaiser

2007 EUVL Symposium


The optical train – Introduction

Reticle-stage

Wafer stage

Source-Collector module

(SoCoMo)

Collector

Source

• λ 13.5 nm • NA 0.25• Field 26 x 33 mm2

• Magnification 4x

Design Example

Intermediate focus

illuminator

Projection optics


overlay

throughput

CDUniformity

Coatingsreflectivity

Wavelength matching

Impact of optics on tool performance

ToolRequirements

Usable DoF

Exposurelatitude

Flare (MSFR)

aberrations

DesignNumber of mirrorsNumerical aperture

Illumination

mirrors are thekey components

DesignNumerical aperture

Illumination


2D-isotropic PSD(example)

Lateral Frequency [μm-1]

figure

aberrations

CDU, overlay

Figure

MSFR

Optics Technology: Fabrication of EUV mirrors

HSFR

MSFR

in field of view scattering: flare

CDU

HSFR

reduced reflectivity

system throughput


The “right” combination of fabrication technologies…

Computer ControlledPolishing for Deterministic Processes

Ion Beam Figuring:Atomic Level Figure Control

Fast Magneto Rheological Figuring

•The challenge for optics fabrication:Reduction of the Mid Spatial Frequency Roughness MSFR… and at the same time reduction of the figure ( aberration

control) and the HSFR (mirror reflectivity system transmission)


… and improvements in mirror metrology

20 pm RMS Reproducibility

• statistical errors (repeatability):ES = 12 pm RMS surface figure !!!

• statistical errors + adjustment errors (reproducibility):EJ = 20 pm RMS surface figure !!!

12 pm RMS Repeatability

… enable very low figure values and reduced long wavelength MSFR contributions

New result on EUV mirrorFigure = 0.04 nm rmsMSFR = 0.13 nm rmsHSFR = 0.07 nm rms


Optics Fabrication: Flare is determined by the Mid Spatial Frequency roughness

• Due to the small wavelength EUV is extremely sensitive to flare

2)(MSFR/λ⋅∝ mirrorsnFlare

Power spectral density (example)

MSFRFigure HSFR

Definition: All wavelengthsof the Power SpectralDensity which generate in-field scattering contribute to the MSFR


flare reduces overlapof process windowsdue to dose offsets

proximity effects in dependence of thelocal reticletransmission

largest impact of flare on isolatedfeatures on bright-field masks

sensitivity of CD to dose errorsbecomes larger

Dose-to-targetchange

No flareWith flare

Main challenge: flare reduction

CD

Intensity cross-section


Progress in flare reduction

Development focuses on material, polishing, and figuring

POB = Projection Optics Box

8% flare

Flare is calculated for a 2 µm line in a bright field

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.55

2000 2001 2002 2003 2004 2005 2006 2007 2008 2009

MS

FR [n

m rm

s](e

valu

ated

ove

r 4.6

dec

ades

)

test mirror

Set 3

Set 1

Set 2

test mirror(MSFR opt.)

MET2 mirrors

on-axis

AD-tool6 mirrorsoff-axis

setup POB mirrors

16% flare tools

New result on EUV mirrorsupports flare level < 8%Figure = 0.04 nm rmsMSFR = 0.13 nm rms

(0.06 nm rms in 3 decades)HSFR = 0.07 nm rms

2)(MSFR/λ⋅∝ mirrorsnFlare


Coating Technology: EUV requires (almost) perfect nanolayers…

Challenges

Mo Si

substrate

θ

d

γ

EUV coatings:Mo/SiBragg reflectors

> 50 bilayers

high peakreflectance and large FWHM

wave-lengthmatching

> 70% shown < 0.2% shown


Wave-length matching: transmission of a 10-mirror system

matchingTransmission

(integral)

± 0.0% 1.00± 0.1% 0.99± 0.2% 0.95± 0.3% 0.90± 0.4% 0.83± 0.5% 0.75

one mirror

10 mirrors

trans

mis

sion

Impact on a generic 10-mirrorsystem


EUV Optics: The future

The next step:0.25 NA projection optics with sigma > 0.7 illumination systems (with

oblique illumination) enables: – 32 nm half pitch production– 22 nm half pitch R+D

Node ¥ NA 0.25 0.35 0.5

32 nm 0.59 0.83 1.19

22 nm 0.41 0.57 0.81

16 nm 0.30 0.41 0.59

11 nm 0.20 0.29 0.41

EUV is introduced as a high k1 technology

opportunity

NAkRES λ

1=

constant k1

k1 reduction


Image log-slope is key parameter

How much contrast (image slope) do we have?

CDdxdI

INILS 1

=

dxdI

I CD

NILS is proportional to exposure latitude

CDCDNILS

EE Δ=

Δ2

Imag

e in

tens

ity

Lateral position

Aerial image cross section


Dense lines 22 nm with conventional and annular illumination

0.2 0.3 0.40.3

0.4

0.5

0.6

0.7

0.8

0

0.5

1

1.5

2

2.5

3

0.2 0.3 0.40.3

0.4

0.5

0.6

0.7

0.8

0

0.5

1

1.5

2

2.5

3

0.2 0.3 0.40.3

0.4

0.5

0.6

0.7

0.8

0

0.5

1

1.5

2

2.5

3

0.2 0.3 0.40.3

0.4

0.5

0.6

0.7

0.8

0

0.5

1

1.5

2

2.5

3

0.2 0.3 0.40.3

0.4

0.5

0.6

0.7

0.8

0

0.5

1

1.5

2

2.5

3

0.2 0.3 0.40.3

0.4

0.5

0.6

0.7

0.8

0

0.5

1

1.5

2

2.5

3best focus 50 nm defocus 100 nm defocus

Par

tial c

oher

ence

Annu

lar r

ing

radi

us

NA NA NA

NILS NILS NILS

Conventional illumination

Annular illumination

annular illumination enables R&D with NA=0.25


30 nm and 22 nm dense contacts – conventional illumination

0.2 0.3 0.40.3

0.4

0.5

0.6

0.7

0.8

0

0.5

1

1.5

2

2.5

3

0.2 0.3 0.40.3

0.4

0.5

0.6

0.7

0.8

0

0.5

1

1.5

2

2.5

3

0.2 0.3 0.40.3

0.4

0.5

0.6

0.7

0.8

0

0.5

1

1.5

2

2.5

3

0.2 0.3 0.4

0.3

0.4

0.5

0.6

0.7

0.8

0

0.5

1

1.5

2

2.5

3

0.2 0.3 0.40.3

0.4

0.5

0.6

0.7

0.8

0

0.5

1

1.5

2

2.5

3

0.2 0.3 0.4

0.3

0.4

0.5

0.6

0.7

0.8

0

0.5

1

1.5

2

2.5

3

best focus 50 nm defocus 100 nm defocus

NA NA NA

Par

tial c

oher

ence

Par

tial c

oher

ence

30 nm contacts

22 nm contacts

Conventional illumination requires higher NA when shrinking contact pitch and CD

NILS NILS NILS


dense contacts with conventional and quasar illumination

best focus 50 nm defocus 100 nm defocus

NA NA NA

Cen

ter r

adiu

s of

qua

sar

Par

tial c

oher

ence

0.2 0.3 0.4

0.3

0.4

0.5

0.6

0.7

0.8

0

0.5

1

1.5

2

2.5

3

0.2 0.3 0.40.3

0.4

0.5

0.6

0.7

0.8

0

0.5

1

1.5

2

2.5

3

0.2 0.3 0.4

0.3

0.4

0.5

0.6

0.7

0.8

0

0.5

1

1.5

2

2.5

3

0.2 0.3 0.40.3

0.4

0.5

0.6

0.7

0.8

0

0.5

1

1.5

2

2.5

3

0.2 0.3 0.40.3

0.4

0.5

0.6

0.7

0.8

0

0.5

1

1.5

2

2.5

3

0.2 0.3 0.40.3

0.4

0.5

0.6

0.7

0.8

0

0.5

1

1.5

2

2.5

3NILS NILS NILS

30 nm contacts conventional illumination

22 nm contacts quasar illumination

Quasar illumination significantly enhances the process space at moderate NA with excellent image contrast


And another step: Extendibility of EUV – design concepts

Design Examples

Possible production tool concept

for 22nm half pitch with

R&D extension towards 16 nm

US 6,710,917 B2

NA=0.25 NA>0.3 NA<0.5 NA>0.5

WO 2006/069725


Summary

• key technologies are progressing towards production tool requirements– mirror figure– flare– coating technology (reflectivity, wavelength matching)

• Improved NA = 0.25 systems will address32 nm half pitch (production)22 nm half pitch (R+D)

• optical designs with NA > 0.3 support 22 nm half pitch production

• with designs for even higher NA´s (≥ 0.5) resolutions down to 16 nm and beyond arise at the horizon


Thanks to a huge team effort at…

• FOM-Rijnhuizen• TNO TPD• PTB-BESSY• IWS Dresden• Philips• Heidenhain• The teams at ASML and Zeiss• …and many others

Part of this work was supported by:

Acknowledgment

German Federal Ministry of Education and Research projects 13N8088 and 13N8837, MEDEA+ projects "EXTATIC" and "EAGLE", European Commission project "More Moore" (IST-507754-IP).

optics for euv lithographyeuvlsymposium.lbl.gov/pdf/2007/op-01-lowish.pdflithography optics division...

Documents