Assessment and extendibility of chemically amplified

1The Institute of Scientific and Industrial Research, Osaka University2Semiconductor Leading Edge Technologies, Inc. (Selete)

Assessment and extendibility of chemically amplified resists for extreme ultraviolet lithography

Takahiro Kozawa1, Hiroaki Oizumi2, Toshiro Itani2, and Seiichi Tagawa1

Resolution, LER, Sensitivity, Exposure latitude

The extraction of basic parameters related to pattern formation efficiency is essential for resist assessment.

Resolution

LER

Sensitivity

EL

Pattern formation efficiencyInterchangeable To fully extract the resist potential,

users must carefully consider the allocation of pattern formation efficiency.

LER

Sensitivity

EL

Pattern formation efficiencyInterchangeable

Actually, there is no room for the negotiation on resolution.

The balance among sensitivity, LER, and EL is important for the enhancement of productivity.

0.0

0.2

0.4

0.6

0.8

1.0

0 10 20

Reconstruction of latent images from does-pitch matrices of line width and LER

24 nm

13.5mJ

11.5mJ27.8, *

26.3, 8.1 26.5, 6.9 24.2, 6.4

22.5, *

Dissolution point

Nor

mal

ized

pro

tect

ed u

nit

conc

entra

tion

Distance (nm)

32.6, 7.6 28.0, 6.6 23.8, 6.4

19.7, 6.9Bridge(Line width, LER)

dxdmLER

/31.0

=

Chemical gradient

2.4 nm s-1Dissolution rate

11.5

12.0 12.5 13.0

13.5

EUV Symp. 2009

Accuracy: ~20%

(SSR3, R=0.1)

Objective

The incorporation of a simple model for acid-base equilibrium

2. To evaluate the resist performance upon exposure using a high NA tool.

3. To discuss the extendibility of chemically amplified resists.

1. To enhance the accuracy of parameter extraction from ~20% to <10%

( )[ ]ββ

×−−= DoseDose exp11'

Dose-pitch matrix

Dose correction using

Dose-pitch matrix with cross sectional SEM image

NA 0.35 with conventional illumination (σ = 0.8)

Resist requirement for 16 nm node

Small Field Exposure Tool : SFET

Source(Xe DPP)

Exposure chamber

Mask loader

Wafer loader

Wafertrack

Items Target Specifications

NA 0.3

Illumination mode

Annular(0.3/0.7), x-slit

Field size 0.2 x 0.6 mmMagnification 1/5Wavefront error ＜0.9 nm rmsFlare ＜7% （MSFR）

Source power 0.5W @IFWafer size 300 mm

Experimental condition

SEM: Hitachi S-9380II

Resist: Selete Standard Resists (SSR4 and SSR5)

Pattern: Line and space (HP: 22-60 nm)

Simulation

line & space

Aerial image of incident EUV

( ) ( )zFp

xCAzyxI απ−

+

+= expcos1

21,,

2/1

Pattern

SFETK. Tawarayama et al. Jpn. J. Appl. Phys. 47 (2008) 4866.

FlareContrast

e-

e-

e-

e-

++++

EUV photon

Secondary electronsDeprotonation

Electron migration

Latent images were calculated on the basis of reaction mechanisms of chemically amplified EUV resists.

Chemical gradient was evaluated at the half-depth of developed pattern.

Effective reaction radius for deprotection, Reff

Quencher concentration

Fitting parameter

The number of acids participating in chemical reaction

The efficiency of chemical reaction per unit diffusion length

Acid diffusion constant

Dissolution point

Acid

Diffusion Diffusion after successful reaction.

Diffusion without inducing reaction.Protected unit(Reaction site)

The amount of chemical reactions required for the dissolution of resist polymer

*Quantum efficiency of acids

Activation energy for acid diffusion

Acid-base equilibriumExposure latitude, sensitivity

Representative patterning resultsSSR4

SSR5

24 nmHP, 10 mJ cm-2

(Top down)

26nmHP, 10 mJ cm-2

32nmHP, 10 mJ cm-2

32nmHP, 11 mJ cm-2

32nmHP, 8.5 mJ cm-2Line width, LER

(0 degree)Thickness

Changing HP

Cha

ngin

g do

se

24nmHP, 10 mJ cm-2 26nmHP, 10 mJ cm-2 32nmHP, 10 mJ cm-2

32nmHP, 8 mJ cm-2 32nmHP, 12 mJ cm-2

(b) SSR5

22232425262830323540455060

Exposure dose (mJ cm-2)

-30

30

Dev

iatio

n fr

om h

alf-

pitc

h (n

omin

al li

ne w

idth

) (nm

)

-10-20

0

2010

0

15

LER

(nm

)

10

5

LER

Line width

7.9 mJ cm-2

22232425262830323540455060


(a) SSR4

22232425262830323540455060


9.4 mJ cm-2

22232425262830323540455060


Hal

f-pi

tch

(nm

)H

alf-

pitc

h (n

m)

Hal

f-pi

tch

(nm

)H

alf-

pitc

h (n

m)

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.00 0.05 0.10 0.15

Erro

r

Effective reaction radius (nm)

Fitting error

∑

−+

−+

−=

i isim

isimi

isim

isimi

isim

isimi NT

TTLER

LERLERWidth

WidthWidtherror /

2

,

,exp,

2

,

,exp,

2

,

,exp,

SSR4SSR5

T: Thickness of remaining resist, N: Total number of data

0.000

0.005

0.010

0.015

0.020

0.00 0.05 0.10 0.15

01234567

0.00 0.05 0.10 0.15 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14

0.00 0.05 0.10 0.15

0.0

0.2

0.4

0.6

0.8

1.0

0.00 0.05 0.10 0.15

Dis

solu

tion

poin

t

Effective reaction radius (nm)(a) Dissolution point (b) Quencher concentration

(c) Acid diffusion constant

Que

nche

r con

c. (n

m-3

)


Diff

usio

n co

nsta

nt (n

m2

s-1)


Extracted parameters

(d) Acid-base equilibriumEffective reaction radius (nm)

β

SSR4SSR5

SSR4SSR5

SSR4SSR5

SSR4SSR5

0.00

0.05

0.10

0.15

0.20

0.25

0.00 0.05 0.10 0.15

f LER

Effective reaction radius, Reff (nm)

Relationship between chemical gradient and LER

Determined by factors such as the aerial image quality of incident photons, exposure dose, absorption coefficient, the quantum efficiency of acids, and the effective reaction radius of deprotection.

Determined by material and process factors associated with development and rinse processes.dxdm

fLER LER

/≈

SSR4SSR5

Because LER is inversely proportional to the chemical gradient, the process and material optimizations are equivalent to a task to maximize the chemical gradient.

The chemical gradient also has a maximum value here.

(b) SSR5

22232425262830323540455060


-30

30

Dev

iatio

n fr

om h

alf-

pitc

h (n

omin

al li

ne w

idth

) (nm

)

-10-20

0

2010

0

15

LER

(nm

)

10

5

LER

Line width

22232425262830323540455060


(a) SSR4

22232425262830323540455060


22232425262830323540455060


Hal

f-pi

tch

(nm

)H

alf-

pitc

h (n

m)

Hal

f-pi

tch

(nm

)H

alf-

pitc

h (n

m)

Simulation result

(b) SSR5

22232425262830323540455060


-30

30

Dev

iatio

n fr

om h

alf-

pitc

h (n

omin

al li

ne w

idth

) (nm

)

-10-20

0

2010

0

15

LER

(nm

)

10

5

LER

Line width

7.9 mJ cm-2

22232425262830323540455060


(a) SSR4

22232425262830323540455060


9.4 mJ cm-2

22232425262830323540455060


Hal

f-pi

tch

(nm

)H

alf-

pitc

h (n

m)

Hal

f-pi

tch

(nm

)H

alf-

pitc

h (n

m)

0

10

20

30

40

50

60

70

20 30 40 50 60

20 nm

21 nm

22 nm

23 nm

24 nm

25 nm

26 nm

28 nm

30 nm

32 nm

35 nm

40 nm

45 nm

50 nm

60 nm

Half-pitch (nm)Th

ickn

ess (

nm)

Cross-sectional view of SSR5 at 8 mJ cm-2

BottomTop

Simulation

0

10

20

30

40

50

60

70

20 30 40 50 60

BottomTop

20 nm

21 nm

22 nm

23 nm

24 nm

25 nm

26 nm

28 nm

30 nm

32 nm

35 nm

40 nm

45 nm

50 nm

60 nm

Half-pitch (nm)Th

ickn

ess (

nm)


Simulation

0

10

20

30

40

50

60

70

20 30 40 50 60

20 nm

21 nm

22 nm

23 nm

24 nm

25 nm

26 nm

28 nm

30 nm

32 nm

35 nm

40 nm

45 nm

50 nm

60 nm

Half-pitch (nm)Th

ickn

ess (

nm)


BottomTop

Simulation

0

10

20

30

40

50

60

70

20 30 40 50 60

20 nm

21 nm

22 nm

23 nm

24 nm

25 nm

26 nm

28 nm

30 nm

32 nm

35 nm

40 nm

45 nm

50 nm

60 nm

Half-pitch (nm)Th

ickn

ess (

nm)


BottomTop

Simulation

0.0

0.2

0.4

0.6

0.8

1.0

0 10 20 30 40

SFET

NA 0.35 with conventional illumination

(σ = 0.8)

High NA exposure toll

NA 0.3 with annular illumination

(σ = 0.3/0.7)

Half pitch (nm)

Con

trast

Resist performance upon exposure using a high NA tool.

15161718192021222324


-30

30

Dev

iatio

n fr

om h

alf-

pitc

h (n

omin

al li

ne w

idth

) (nm

)

-10-20

0

2010

0

15

LER

(nm

)

10

5

LER

Line width

Hal

f-pi

tch

(nm

)

15161718192021222324


Hal

f-pi

tch

(nm

)(b) High NA(a) SFET

Resist performance (SSR5) upon exposure using a high NA tool

15161718192021222324


Hal

f-pi

tch

(nm

)

15161718192021222324


Hal

f-pi

tch

(nm

)

Extendibility of chemically amplified resist

Absorption coefficient

Quantum efficiency

Effective reaction radius

~4 10

~2.4

~0.1

~16

~64

0.5 ~0.5

Quencher concentration

Dissolution point Optimized at 10 mJ cm-2 and 16 nm HP*

*Optimum dissolution point and quencher concentration depend on sensitivity and half-pitch because of RLS trade-off relationship.

Current status Technical limit Physical limit

(maybe more)

Optimized at 10 mJ cm-2 and 16 nm HP*

(with ultrathin resist process)(µm-1)

(nm)

15161718192021222324


-30

30

Dev

iatio

n fr

om h

alf-

pitc

h (n

omin

al li

ne w

idth

) (nm

)

-10-20

0

2010

0

3

LER

(nm

)

2

1

LER

Line width

Hal

f-pi

tch

(nm

)

15161718192021222324


Hal

f-pi

tch

(nm

)

(b) High NA(a) SFET

Resist performance at technical limit

15161718192021222324


Hal

f-pi

tch

(nm

)

15161718192021222324


Hal

f-pi

tch

(nm

)

By increasing pattern formation efficiency, not only LER but also exposure latitude and linearity were significantly improved.

Summary

The resist performance of current EUV resists upon exposure to a high NA tool (NA 0.35) was estimated. LER is away from the requirement.

Assuming the technical limit of the parameters associated with pattern formation efficiency, the extendibility of chemically amplified resists was examined. The resist requirements for 16 nm are achievable at NA=0.35, but comparable to the technical limit.

By improving the resist modeling, the accuracy of parameter extraction was successfully reduced from ~20% to <10%.

1.

2.

3.

Acknowledgement

Dr . Hiroshi Chiba and Dr. Takuro Ono of Nikon Corporation for the calculation of optical images

Documents

Assessment and extendibility of chemically amplified