Pushing the resolution limits of photolithography: Understanding the fundamentals of the EUV resists

Yasin Ekinci Paul Scherrer Institute, SwitzerlandAdvanced Lithography and Metrology Group

EUV Lithography

Page 2

9m3m

3m

n EUV lithography: n Reflective optics and maskn Plasma source

n EUV in high-volume production delayed mainly due to source power

n Planned for HVM production in 2017n Planned for HVM production in 2018

XIL-II: EUV-IL @ Swiss Light Source, PSI

Page 3

• Undulator source+ Switchable mirror+ pinhole- High brightness- High spatial coherence- 4% bandwidth- tunable wavelength (λ=2.5-18 nm)

• On-site cleanroom- Spin-coater, wet-bench, hot-plates, microscope,

developer, optical thickness measurement

EUV interference lithography

Quasi-crystals

D. Fan

CONCEPT:n EUV: 13.5 nm wavelength

n Spatially coherent n Temporal coherence: Δλ/λ=4%

n Diffractive transmission gratings:n Metal gratings written with EBLn on Si3N4 membranes (~100 nm)

n diffracted beams interferen interference pattern printed in resist

Incident EUV light

Silicon nitride membrane

Diffraction grating

Absorber thin film

First-order diffraction beam

Interference fringes

Silicon frame

Page 4

Record resolution in photolithography

22 nm

14 nm

16 nm

12 nm

10 nm

9 nm

11 nm

8nm

hp 7 nm

hp 30 nm hp 22 nm

hp 17 nm hp 11 nm

Page 5

Science with EUV-ILSi nanowires

• EUV resist development

• Nanoimprint stamps

• Fluidic confinement structures• Plasmonics and Metamaterials

• Polymer grafting

• Biomaterials

• Catalysis

• Templated assembly • Cell growth templates

• Nanomagnetism

• Fresnel Zone Plates

• etc.

Page 6

lw 20 nm

length ~1 µm

lw 6.5 nm

Si fins16 nm 11 nm

Height 88 nm

EUV resists LER

Resolu)on Sensi)vity

n A major challenge is EUV resists with the best performance

n Resolution, HP (nm)

n Sensitivity, dose (mJ/cm2)

n Line edge roughness, 3σ (nm)

n XIL is a powerful method in development of EUV resists

n High resolution and well defined image, pitch independent.

n Enabling research before tools are available.

n Low-cost

n Flexible: outgassing, contamination

Page 7

EUV resists: State of the art @ SPIE 2013

HP 14 nmResist-B

HP 16 nmResist-B

HP 18 nmResist-A

HP 12 nmInpria/JB

HP 8 nmInpria/IB

HP 13 nm2018 typical

How does EUVL work?

• Absorption mechanism• Secondary electrons: - How many are generated?- How do they interact?- How many of them are “useful” electrons?- What are the loss mechanisms?- How far they travel?

• Chemical reactions:- How many acids are generated?

Page 9

e-

e-e-e-

3eV>E>10eV E>10 eV

0 20 40 60 800

2x107

H

HeLi

Be

BC

NO

FNe

NaMg

Al

Si

PS

ClAr

KCa

Sc

TiV

CrMn

FeCo

Ni

CuZnGa

GeAsSe

BrKr

Rb

SrY

Zr

Nb

Mo

Tc

Ru

Rh

Pd

AgCd

In

SnSb

Te

I

Xe

Cs

Ba

LaCe

Pr

Nd

Pm

Sm

Eu

Gd

Tb

Dy

Ho

Er

Tm

Yb

Lu

Hf

Ta

WRe

Os

Ir

Pt

AuHg

TlPb

BiPo

AtRn

Atom

ic a

bsor

ptio

n cr

oss

sect

ion

s a [

cm2 /

mol

]

Atomic Number Z

Atomic absorption cross section at EUV (13.5 nm)

alkaline metals alkaline earths transition metals basic metals semimetals non metals halogen noble gases lantanides

Method:

!" = ΦΦ%

= &&%= '()*

---------- Dill B(unbleachable)

α à/ Dill C(exposure rate)

↑Dill A = B – α(bleachable)↓

Slide 10

+,-

Resist thickness d measurement:§ Woollam M2000 spectroscopic ellipsometer§ 250-1000 nm spectral range§ focusing probe (Φ 30 μm), automatic stage§ Cauchy + B-spline ellipsometric model

Absorption coefficient of EUV resists

Page 11

Previous studies:For PMMA, αPMMA = 5 μm-1 [1][2] (transmission).For most organic polymers, calculated α ≈ 3 - 5 μm-1 [3].EUV backbone polymers, α ≈ 2.1 – 4.4 μm-1 [2] (grazing angle reflectivity).Fluorinate EUV resists α = 6.54 μm-1 [4] (transmission).

[1] G . D . Kubiak et al., Journal of Vacuum Science & Technology B 10 , 2593 (1992). [2 ] Y .-J. Kw ark et al., J. Vac. Sci. Technol. B 24 , 1822 (2006).[3 ] N . N . M atsuzaw a et al., M icroelectronic Engineering 53 , 671 (2000).[4 ] A . Sekiguchi et al., Proc. of SPIE Vol. 9422 94222L-1 .

M etal-containing

† PMMA: formula C5 O2 H8 , density 1.2 g/cm3 .‡ HSQ: formula Si8 O1 2 H8 , density 1.4 g/cm3 .* Source: Manufacturer.

PMM

AH

SQEU

V 1

EUV

2EU

V 3

EUV

3+S

YABA YF

xMT-

213

PBPM

ML3

56H

B1-2

13

05

1015

20a

(µm

-1)

0 5 10 15 200

5

10

15

20

PMMAHSQEUVInpriaIM

a (c

alcu

late

d) [µ

m-1]

a (measured) [µm-1

]

Sn-M Sn-A Sn-F Sn-S Sn-OHZr-M1 Zr-M2 Hf Typ.0

5

10

15

20

14.7 14.2

11.6 11.1

13.5

5.56.4

9.8

4.8

Abso

rptio

n C

oeffi

cien

t (µm

-1)

Absorption of metal-based photoresists

Slide 12

The actual absorption α can be to substantially different than predicted, thus affecting the real sensitivity and lithographic performance.

0 5 10 15 200

5

10

15

20

Sn-MSn-A

Sn-FSn-S

Sn-OH

Zr-M1Zr-M2

Hf

a, m

easu

red

(µm

-1)

a, calculated (µm-1)

PMMAHSQ

EUV 1EUV 2EUV 3

EUV 3+SYABA

YFxMT-213

PBPMML356

HB1-213

0 5 10 15 20B (µm-1)

Results: Dill Parameters

Page 13

A bleachable coefficient

• A > 0• A << α for EUV resist

Bunbleachable coefficient

• B ≈ α at EUV

Cexposure rate constant

• UV 0.022 ≈ 0.008 cm2/mJ [1]• DUV ≈ 0.005 cm2/mJ [2]• higher in EUV 3+S

[1 ] M ic ro C h e m ica ls , O p t ica l P ro p e rt ie s o f P h o to re s ists . A p p lica t io n N o te , 2 0 1 3 .[2 ] Y.-S . S o h n e t a l. , JV S T B 1 9 (6 ), 2 0 7 7 (2 0 0 1 ).

PMMAHSQ

EUV 1EUV 2EUV 3

EUV 3+SYABA

YFxMT-213

PBPMML356

HB1-213

0.0 0.3 0.6 0.9A (µm-1)

0.0 0.1 0.2 0.3 0.4 0.5C (cm2/mJ)

Role of Dill parameter C in CAR

[1] C. Mack et al., Applied Optics 27(23), 4913 (1988)

!"#(%) = !"#( )*+,-

Slide 14

/ Dill C(exposure rate)

./ = #!"1#234. 6ℎ. = # 89ℎ:

; ln 10 @ ⁄BC D

EUV CARs: Absorption

Page 15

Polymer 1 Polymer 1 Polymer 1 Polymer 1 Polymer 1 Polymer 1 Polymer 2 Polymer 20

1

2

3

4

5

64.8 4.7 4.7 4.7 4.9 4.9 4.8 4.9

Ab

sorp

tion

Co

effic

ien

t (µ

m-1)

no PAG PAG A PAG A PAG A PAG B PAG B no PAG PAG A0% 100% 120% 140% 100% 120% 0% 100%

1. effect of PAG loading2. effect of PAG molecule3. effect of backbone polymer

No significant changes due to different components of the resistsBecause they are similar organic molecules

EUV CARs: Sensitivity

Page 16

Polymer 1 Polymer 1 Polymer 1 Polymer 1 Polymer 1 Polymer 1 Polymer 2 Polymer 20

20

40

6051.3

5.4 5.7 6.2 3.8 4.0

33.9

6.5

Do

se-t

o-C

lea

r (m

J/cm

2)

no PAG PAG A PAG A PAG A PAG B PAG B no PAG PAG A0% 100% 120% 140% 100% 120% 0% 100%

Dependence on PAG loading, PAG type and backbone polymer type

PAGs makes the resist much more sensitive as expectedPolymer 2 is more sensitivePAG-B is more sensitive

Quantum yield

Page 17

0.0 1.0 1.2 1.4

0.000

0.005

0.010

0.015

0.020

0 100 120 140

0.0 1.0 -- --

0.000

0.005

0.010

0.015

0.020

(a)

(b)

Dill

Para

met

er C

(cm

2 /mJ)

Polymer 1 PAG A Polymer 1 PAG B

PAG Concentration (%)

Polymer 1 PAG A Polymer 2 PAG A

0.0 1.0 1.2 1.4

0

2

4

6

8

0 100 120 140

0.0 1.0 -- --

0

2

4

6

8

(a)

(b)

Quan

tum

Yiel

d

Polymer 1 PAG A Polymer 1 PAG B

PAG Concentration (%)

Polymer 1 PAG A Polymer 2 PAG A

Without PAG: QY is close to 1PAG loading has little effect: saturation regimePAG B has higher QY due to higher ionizabilityPolymer 2 increases the QY

Proximity effects in EUVL

Page 18

Torok et al,

J. Photopolym. Sci. Technol., Vol. 26, No. 5, 2013

Electron mean free path

e-

e-e-e-

3eV>E>10eV E>10 eV

How to measure the secondary electron blur?

Page 19

We define Chemical Sensitivity as:

Lithographic sensitivity is the reciprocal of the Dose-to-Clear, measured from contrast curve:

!" =$

%×'(!

)*+ℎ- ./01*+*2*+3 =4

567=8× 9:,9<, =>,… [ ⁄BC DBE]

=. =1

8[HBI4]×J+=[ ⁄BC DBE]= [ ⁄BK C] = [ L0BK <MNO6OP]

CS indicates the volume of resist cleared by each absorbed EUV photon.

§ CS is thickness independent: can be compared across different resist platform.

§ Larger CS indicate a higher chemical reactivity, due to chemical amplification, QY, QE, etc...

§ Can be measured by measuring contrast curves and absorption

V

RESIST

ph

0.1 1 10 100

0.0

0.2

0.4

0.6

0.8

1.0

PMMA ZEP520A mrPosEBR

Thic

knes

s (n

orm

.)

Dose (mJ/cm2)

Plot Thickness Thickness ThicknessA1 0 ± 0 0 ± 0 0 ± 0A2 1 ± 0 1 ± 0 1.17186 ± 0.05857LOGx0 22.81965 ± 0.26052 14.62096 ± 0.21021 5.70293 ± 0.42013p -0.13825 ± 0.00973 -0.13712 ± 0.0076 -0.13949 ± 0.01315Reduced Chi-Sqr 0.00252 0.00262 0.00278R-Square(COD) 0.98697 0.97629 0.97761Adj. R-Square 0.98664 0.97567 0.97672

PMMAHSQ

EUV 1EUV 2EUV 3

EUV 3+SYABA

YFxMT-213

PBPMML356

HB1-213

0 10 20 30 40 50 60CS [nm3/Eph]

Chemical Sensitivity

Page 20

ß non-CA CA à

PMMAHSQ

EUV 1EUV 2EUV 3

EUV 3+SYABA

YFxMT-213

PBPMML356

HB1-213

0 1 2 3Clearing Radius [nm/E

ph]

PA diffusionSEB

Another interpretation is derived from the radius of a sphere having the CS volume.

The clearing radius is a measure of the total resist blur (SE blur + PA diffusion blur + etc…):

Effect of SEB from the substrate (the theory)

Page 21

Optical attenuation of Si@ different energies:

Intensity profileIn resist and substrate

Secondary electron densityIn resist and substrate with 3 nm blur

Dose-to clear curve@ different energies

SED=I(z)* exp [-λz]

Effect of SEB from the substrate (the experiment)

Page 22

Best fit to the data: 2.3 nm

Summary

Page 23

• It is good news that EUV photons can make down to 7 nm hp.

• But we need to understand the fundamentals and reaction pathways

• Macroscopic parameters à Microscopic parameters

(dose, absorption, Dill’s parameters) (SEB, QE)

• For a state-of-the-art CAR: QY is 3-8• PAG-backbone interaction could be exploited to increase QY• SEB: For non-CAR=~1-2 nm and for CAR=4-5 nm

• To push the resolution limits of EUV lithography

• we need to understand the fundamentals

• We need to employ many analytical tools

280 285 290 295 300 305 3100.0

0.5

1.0

1.5

Opt

ical

Den

sity

Energy (eV)

S2 best fit

MMA

280 285 290 295 300 305 3100.0

0.5

1.0

1.5O

ptic

al D

ensi

ty

Energy (eV)

S2 exposed best fit

NEXAFS:

Acknowledgments

Hard work: ALMLMNPSIMaterial vendorsFinancial support:SNFSwiss Nanoscience InstituteEuropean CommissionVarious companies

Thank you for your attention!

Advanced lithography and metrology groupwww.psi.ch/sls/xil