Modeling EUV mask using alternative materials for Mask 3D...

Modeling EUV mask using alternative

materials for Mask3D effect compensation

Vu Luong (imec, KU Leuven)

Vicky Philipsen, Eric Hendrickx (imec)

Erik Verduijn, Obert Wood II (GlobalFoundries)

Frank Scholze (PTB)

October 7, 2015

International Symposium on Extreme Ultraviolet Lithography, Maastricht, Netherlands

Mask3D effects

Model calibration of alternative mask

Imaging impact at current NA0.33

Imaging impact at future NA0.52

Conclusion & Outlook

Mask3D effects

CONFIDENTIAL - LIMITED USE

Mask technology for current 17nm half-pitch node

4

Standard 70nm Ta-based absorber

Ru-capping layer

Standard 40 bilayer Mo/Si multilayer mirror

Mask3D effects are caused by “thick” mask, i.e. absorber dimensions are similar to EUV wavelength.

EUV λ=13.5nm

Mask3D effects are observed on wafer level as...

Horizontal-Vertical printing bias

Pattern shifts through Focus

Best Focus shifts through Pitch

Two Bar Asymmetry

Vu Luong et al. / EUVL Symposium 2015

Mask3D effects are inherent to current EUV mask technology and will increase in future nodes.

CONFIDENTIAL - LIMITED USEVu Luong et al. / EUVL Symposium 2015

Absorber height impact on Mask3D effects

5

Vertical Lines

1) Horizontal-Vertical printing bias

= Orientation dependent printing

difference, due to shadowing effect

2) Pattern shift through Focus

aka Telecentricity error

non-uniform angular reflection apodization

φ

Diffraction Spectrum [sin(α)/λ]

Inte

nsity

0+1

-1

shadowing effect ±order imbalance

Diffraction orders recombine in shifting aerial image

through focus

Thinner absorber height improves shadowing related Mask3D effects. Alternative materials can compensate for EUV absorbance loss.

Kirchhoff binary mask

α

θ

CONFIDENTIAL - LIMITED USE6 Vu Luong et al. / EUVL Symposium 2015

Absorber material impact on Mask3D effects

3) Best Focus (BF) shift through Pitch

- cause challenges for overlapping Process Windows

- due to phase difference between incident+reflected light and between diffraction orders

Diffraction Spectrum [sin(α)/λ]

Phase

0

+1

-1

Kirchhoff binary mask

Intensity of incident light (w/o effect of ML mirror)

ML mirror

Ph

ase

fron

t of in

cid

en

t ligh

t

(w/o

effe

ct o

f ML m

irror)

Best Focus shift mitigation:- Similar optical density (n-coefficient=1) between

absorber and vacuum

- Darker absorber (k-coefficient ↑) to reduce intensity near absorber/vacuum interface

- Reduce absorber height

CONFIDENTIAL - LIMITED USE7

Multilayer mirror impact on Mask3D effects


ML

mir

ror

Re

fle

cti

vit

y

Shallow effective plane of reflectance improves shadowing.

Uniform angular reflectivity improves Pattern shifts through Focus.

NA

0.5

2 / 4

x

NA

0.3

3 / 4

x

NA

0.5

2 / 8

x

Incidence Angle (degree)

Ideal Mo/SiIdeal Ru/SiExp. Ru/Si

However, first mirror sample reflectivity is lower than ideal Ru/Si multilayer.

Imaging impact simulation of a real alternative mask requires model calibration, based on experimental samples.

@ Obert Wood et al. SPIE 2015

Model calibration of alternative mask


Model calibration of Ni-based multilayer absorber


Multilayer structure with TiN spacers to suppress crystallinity and reduce reflectivity

Sample preparation and TEM by GlobalFoundries. EUV reflectometry by PTB.

Thick[nm] n k

Mat1 5.23 n k

TiN 1.72 0.9349 -0.0192

Mat1 4.39 n k

TiN 1.31 0.9349 -0.0192

Mat1 4.76 n k

TiN 1.49 0.9349 -0.0192

Mat1 2.64 n k

TiN 1.15 0.9349 -0.0192

Mat1 3.61 n k0

0,002

0,004

0,006

0,008

0,01

0 10 20 30

Reflect

ivity

Incidence Angle [degree]

PTB data Model

Mat1

TEM

5nm

Fixed thickness, fit n and k.

Bulk Ni

(CXRO)

Thin Ni

(Modeled)

Bulk Ta

(CXRO)

0,02

0,03

0,04

0,05

0,06

0,07

0,08

0,09

0,10

0,92 0,94 0,96 0,98 1,00

Extinct

ion c

oeffic

ient

k

Refraction coefficient n

Thin film Ni shows more EUV absorbance to bulk Ni.


Model calibration of Ru/Si multilayer mirror


Sample preparation and TEM by GlobalFoundries. EUV reflectometry by PTB.

0

0,2

0,4

0,6

0,8

12 12,5 13 13,5 14 14,5 15

Reflect

ivity

Wavelength [nm]

0

0,2

0,4

0,6

0,8

0 10 20 30

Reflect

ivity

Incidence Angle [degree]

5nm

TEM

C

Ru

Ru2Si

Si

Now we have a model to begin imaging simulations of the real alternative mask.

Thick[nm]

Ru Top 4.8

Ru2Si Top 1.123

Si Top 2.116

C 0.464

Ru 2.393

Ru2Si 2.107

Si 2.061

Bilayer period [nm]

5n

m

Si

Ru2Si

Ru

C

First sample contains an interfacial layer of C-on-Ru to suppress silicide formation


Mask stack:


Std Mask id Alt Mask exp Alt Mask

Absorber 70nm Ta 24nm 3.5x Ni/TiN 24nm 3.5x Ni/TiN

Mirror 40.5x Mo/MoSi2/Si/MoSi2 20.5x Ru/Si 20.5x Ru/Ru2Si/Si/C

Imaging only (no resist effect)

Illumination: Quasar45

outer_sigma 0.9

inner_sigma 0.2

pole angle 45deg

Features NA0.33 NA0.52

Trench thr Pitch 16nm CD; P32100

4x; CRA6°

11nm CD; P2270

V4x/H8x; CRA6°

TwoBar Trench 18nm CD; PS=36nm; PL=180nm

4x; CRA6°

12nm CD; PS=24nm; PL=180nm

4x/CRA9° vs 8x/CRA6°

Simulation setup

11

Imaging Impact at current NA0.33


Trenches 16nm CD NA0.33

0

1

2

3

4

5

30 40 50 60 70 80 90 100

Pitch [nm]

Horizontal-Vertical Bias [nm]

Std Mask

id Alt Maskexp Alt Mask

70nm

25nm

Superior shadowing with thinner absorber.

better HV-bias

-4

-2

0

2

4

6

8

30 40 50 60 70 80 90 100

Pitch [nm]

Pattern shift per100nm Defocus [nm]

Std Mask

id Alt Mask

exp Alt Mask

-0,020

-0,015

-0,010

-0,005

0,000

0,005

0,010

30 40 50 60 70 80 90 100

Pitch [nm]

Best Focus shift through Pitch [μm]

Std Mask

id Alt Mask

exp Alt Mask

better Pattern shift through Focus

Superior Best Focus shift through Pitch

with ideal Alternative Mask only.

P32 P100


Ideal Alternative Mask exhibits better Pattern shift through Focus due to less intensityapodization and less intensity imbalance between the diffraction orders.

Only 0 and ±1 orders shown.

-4

-2

0

2

4

6

8

30 40 50 60 70 80 90 100

Pitch [nm]


-4

-2

0

2

4

6

8

30 40 50 60 70 80 90 100

Pitch [nm]


Std Mask

id Alt Mask

exp Alt Mask

P32 P100

0

0,05

0,1

0,15

0,2

-0,66 -0,33 0 0,33 0,66

Inte

nsi

ty

Diffraction Spectrum [sin(α/λ)]

0

0,05

0,1

0,15

0,2

-0,66 -0,33 0 0,33 0,66

Inte

nsi

ty


NA circle

+1-1

0

Pattern shift through Focus

P48

Explanation through Diffraction Spectrum intensity


-60

-40

-20

0

20

40

60

-0,66 -0,33 0 0,33 0,66

Ph

ase

[deg

ree]


15 Vu Luong et al. / EUVL Symposium 2015

Ideal Alternative Mask exhibits better Best Focus shift through Pitch due to less phase

imbalance between the diffraction orders.

-0,020

-0,015

-0,010

-0,005

0,000

0,005

0,010

30 40 50 60 70 80 90 100

Pitch [nm]


-60

-40

-20

0

20

40

60

-0,66 -0,33 0 0,33 0,66

Ph

ase

[deg

ree]


NA circle

+1

-1

0

P32

-0,020

-0,015

-0,010

-0,005

0,000

0,005

0,010

30 40 50 60 70 80 90 100

Pitch [nm]


Best Focus shift through Pitch

Std Mask

id Alt Mask

exp Alt Mask

P32 P100

Explanation through Diffraction Spectrum phase


-0,020

-0,015

-0,010

-0,005

0,000

0,005

0,010

30 40 50 60 70 80 90 100

Pitch [nm]


-0,020

-0,015

-0,010

-0,005

0,000

0,005

0,010

30 40 50 60 70 80 90 100

Pitch [nm]


tuned AltMask

id Alt Mask

exp Alt Mask

-60

-40

-20

0

20

40

60

-0,66 -0,33 0 0,33 0,66

Ph

ase

[deg

ree]


-60

-40

-20

0

20

40

60

-0,66 -0,33 0 0,33 0,66

Ph

ase

[deg

ree]


NA circle

+1

-1

0

P32

Best Focus shift through Pitch

Height

tuning

Further optimization through multilayer absorber tuningP32 P100

Multilayer absorbers can be tuned tocompensate for Best Focus shift throughPitch.


Two Bar Trench 18nm CD NA0.33

-90

0

90

-250 -125 0 125 250

Posi

tio

n [

nm

]

Focus [nm]

-90

0

90

-250 -125 0 125 250

Posi

tio

n [

nm

]

Focus [nm]

Std

Mask

exp

Alt

Mask


0,14

0,16

0,18

0,2

-150 -100 -50 0 50 100 150

Inte

nsi

ty T

hre

sho

ld

Focus [nm]

overlapping Process Windows

Top bar

Bottom bar

0,21

0,23

0,25

0,27

-150 -100 -50 0 50 100 150In

ten

sity

Th

resh

old

Focus [nm]

Better symmetry and 2Bar PW overlap with the Alternative Mask.

Top bar

Top bar

Bottom bar

Bottom bar

Imaging Impact at future NA0.52


-0,020

-0,015

-0,010

-0,005

0,000

0,005

0,010

20 30 40 50 60 70

Pitch [nm]

Best Focus shift through Pitch [nm]

-1

0

1

2

3

4

20 30 40 50 60 70

Pitch [nm]

Horizontal-Vertical Bias [nm]

19 Vu Luong et al. / EUVL Symposium 2015

Trenches 11nm CD NA0.52

Std Mask

id Alt Maskexp Alt Mask

70nm

25nm

Superior shadowing with thinner absorber.

better HV-bias

70nm

better Pattern shift through Focus

Best Focus shift through Pitch notably smaller,

but also smaller DoF at high NA.

Anamorphic 8x reduction improves Mask3D effects significantly for Std Mask and Alt Mask.

-4

-2

0

2

4

6

8

20 30 40 50 60 70

Pitch [nm]

Pattern shift per 100nm Defocus [nm]

Std Mask

id Alt Mask

exp Alt Mask

Std Mask

id Alt Mask

exp Alt Mask

P22 P70


Two Bar Trench 12nm CD NA0.52 8x/CRA6°

-90

0

90

-100 -50 0 50 100

Posi

tio

n [

nm

]

Focus [nm]

-90

0

90

-100 -50 0 50 100

Posi

tio

n [

nm

]

Focus [nm]

Std

Mask

exp

Alt

Mask


0,13

0,15

0,17

0,19

0,21

-80 -40 0 40 80

Inte

nsi

ty T

hre

sho

ld

Focus [nm]


Top bar

Bottom bar

0,2

0,22

0,24

0,26

0,28

-80 -40 0 40 80In

ten

sity

Th

resh

old

Focus [nm]

8x reduction improves both Std Mask and Alt Mask performance at NA0.52.

Top bar

Top bar

Bottom bar

Bottom bar


Two Bar Trench 12nm CD NA0.52 4x/CRA9°

-90

0

90

-100 -50 0 50 100

Posi

tio

n [

nm

]

Focus [nm]

-90

0

90

-100 -50 0 50 100

Posi

tio

n [

nm

]

Focus [nm]

Std

Mask

exp

Alt

Mask


0,12

0,14

0,16

-80 -40 0 40 80

Inte

nsi

ty T

hre

sho

ld

Focus [nm]


Top bar

Bottom bar

0,14

0,16

0,18

-80 -40 0 40 80In

ten

sity

Th

resh

old

Focus [nm]

At 4x reduction Mask3D mitigation remains challenging at NA0.52.

Top bar

Top bar

Bottom bar

Bottom bar0

20

40

60

80

100

120

140

160

Std Mask exp Alt Mask

oDoF [nm]

NA0.33 NA0.52_8x/CRA6° NA0.52_4x/CRAQ9°

Conclusion & Outlook


Conclusion

We have a model for a real alternative mask stack, based on characterization ofexperimental samples.

Imaging simulation study with this model shows viability of alternative materials in EUVreticles for current lithography systems with NA0.33 to mitigate Mask3D effects.

With NA0.52, reducing these Mask3D effects will be paramount for imaging due to theinherently smaller Process Windows (DoF↓). To this end, anamorphic scanning at 8xreduction offers the best solution. Otherwise, at lower 4x reduction, alternativematerials will be required to reduce Mask3D effects for high NA.

What we have done:


Outlook

Further optimization by layer-tuning the multilayered absorber based on diffractionspectrum study, to compensate for non-ideal amplitude and phase behavior.

Further screening of other alternative materials, in combination with manufacturabilityassessment of current alternative material, e.g. absorber etchability.

What we are planning to do:


Acknowledgement


Patrick Kearney (Sematech)

Aditya Kumar, Suraj Patil (GlobalFoundries)

Christian Laubis, Victor Soltwisch (PTB)

Weimin Gao, and the S-Litho team (Synopsys)

Marc Heyns (imec, KU Leuven)

Lieve Van Look, Iacopo Mochi, Rik Jonckheere, Emily Gallagher, Kurt Ronse,

Greg McIntyre (imec)

Thank you for your attention!

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