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Effect of UV-wavelength on Hardening Process of

Porogen-containing and Porogen-free Ultra-low-

k

Porogen-containing and Porogen-free Ultra-low-

k

PECVD Glasses

AVS 2010

17-22 October

A.M. Urbanowicz*, K. Vanstreels, P. Verdonck, E. Van Besien,

Ch. Trompoukis, D. Shamiryan, S. De Gendt and M.R. Baklanov

*also at Semiconductor Physics Department ,

Katholieke Universiteit Leuven

(2)

Outline

Introduction

Ultra low-

k

dielectrics fabricated by PECVD and porogen residue problem

New PECVD curing approach: UV-curing of porogen-free films

UV-curing as a photochemical process

Experimental setup

Results

2

Results

Organic residues content in low-

k

matrix studied by UV-spectrocopic

ellipsometry

Effect of UV-curing wavelength on mechanical properties of porogen-free films

Effect of UV-curing wavelength on dielectric constant of the films

(3)

Ultra-low-

k

PECVD dielectric and porgen residue challange

Film hardening

Porogen removal

UV curing

Prior Art

k

<2.3

k

~ 2.5

Porogen residue removal degrades mechanical

properties of ultra-low-

k

PECVD

Porogen

Porogen residue

(4)

Ultra-low-

k

PECVD dielectric and porgen residue challange

PECVD (k=2.3) – high residue content

Porogen residue degrades electrical properties

4

E. Van Bensien, L. Zhao, M. Pantouvaki, D. De Roest, I. Ciofi, K. Croes, A. M. Urbanowicz et. al Electrical Evaluation of Low-k Dielectrics with

Various Degree of Porosity in Planar Capacitor Structures, in Core Partner Workshop, IMEC, Leuven (2010).

PECVD (k=2.3)+ H

2

-AFT - no residue

PECVD (k=2.5) – low residue content

(5)

Film hardening

Porogen removal

UV curing

Prior Art

New curing technology of PECVD ultra-low-

k

dielectrics

New curing technology

UV curing

Porogen removal

Gas inlet Plasma area He/H2

Porogen fully

removed

Skeleton

hardening

?

Porogen

Porogen residue

Reactive species Grid : electrical neutralization

Wafer at 280

°

C

H

H

H

A.M. Urbanowicz, K. Vanstreels, P. Verdonck, D. Shamiryan, S. De Gendt and M. Baklanov,

(6)

0.10

0.12

0.14

0.16

0.18

0.20

0.22

as deposited

e

x

ti

n

c

ti

o

n

c

o

e

ff

ic

ie

n

t

>200 nm

~172 nm

Porogen

Laws of Photochemistry:

Only light that is absorbed can be effective in

producing photochemical change. (Grotthus-Draper

Law: 1817, 1843).

One particle is excited for each quantum of radiation

(photon) absorbed (Stark-Einstein Law: 1912)

Goal: Study of the effect of the UV-curing wavelength on

porogen-free films

600

500

400

300

200

-0.02

0.00

0.02

0.04

0.06

0.08

0.10

e

x

ti

n

c

ti

o

n

c

o

e

ff

ic

ie

n

t

Wavelenght [nm]

6

H

2

-AFT

(photon) absorbed (Stark-Einstein Law: 1912)

Energy of an absorbed photon must be equal to or

greater than the weakest bond in the molecules

(Bolton)

Si-CH

3

Photodissotiation

threshold

L. Prager, P. Marsik, L. Wennrich, M. R. Baklanov, S. Naumov, L. Pistol, D.

Schneider, J. W. Gerlach, P. Verdonck and M. R. Buchmeiser,

Microelectronic

Engineering

, 85, 2094 (2008).

S. Eslava, F. Iacopi, A. M. Urbanowicz, C. E. A. Kirschhock, K. Maex, J. A.

Martens and M. R. Baklanova,

Journal of the Electrochemical Society

,

155

, G231

(2008).

A. M. Urbanowicz, B. Meshman, D. Schneider and M. R. Baklanov,

Physica

Status Solidi a-Applications and Materials Science

,

205

, 829 (2008).

(7)

Experimental setup

Deposition of

130 nm films

1

2a

UV curing (166 s)

172

±

15 nm

Porogen removal

Gas inlet Plasma area He/H2

350 s

NB

Experimental setup

Porogen

Skeleton

hardening

2b

>200 nm

Reactive species Grid : electrical neutralization

Wafer at 280

°

C

H

H

H

BB

BB= broad band

NB= narrow band

(8)

1.55

1.60

1.65

r

e

fr

a

c

ti

v

e

i

n

d

e

x

0.16

0.18

0.20

0.22

as deposited

as deposited

e

x

ti

n

c

ti

o

n

c

o

e

ff

ic

ie

n

t

Porogen

Porogen

residue

As

deposited

UV-cured

Curing of porogen-containing films results in porogen

residues generation

Porogen residue (a-C) contains sp

2

orbitals (C=C) which have transition

band ~4.5 eV (275 nm)

UV Spectrocopic Ellipsometry

8

900

750

600

450

300

150

1.20

1.25

1.30

1.35

1.40

1.45

1.50

UV ~ 172 nm

UV ~ 172 nm

r

e

fr

a

c

ti

v

e

i

n

d

e

x

Wavelenght [nm]

900

750

600

450

300

150

-0.02

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

UV>200 nm

UV>200 nm

as deposited

e

x

ti

n

c

ti

o

n

c

o

e

ff

ic

ie

n

t

Wavelenght [nm]

(9)

1.55

1.60

1.65

0.18

0.20

0.22

as deposited

Porogen

As

deposited

Curing of porogen-free films results in

porogen-residue-free films

UV curing

Porogen removal

Gas inlet Plasma area Reactive species Grid : electrical neutralization Wafer at 280 °C H H H He/H2

Porogen fully

removed

Skeleton hardening

900

750

600

450

300

150

1.20

1.25

1.30

1.35

1.40

1.45

1.50

1.55

H

2

-AFT+ UV ~ 172 nm

H

2

-AFT+ UV ~ 172 nm

UV ~ 172 nm

UV ~ 172 nm

r

e

fr

a

c

ti

v

e

i

n

d

e

x

Wavelenght [nm]

900

750

600

450

300

150

-0.02

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

H

2

-AFT + UV>200 nm

H

2

-AFT + UV>200 nm

UV>200 nm

UV>200 nm

as deposited

e

x

ti

n

c

ti

o

n

c

o

e

ff

ic

ie

n

t

Wavelenght [nm]

(10)

Greater thickness loss after 172 nm NB UV than for

>200 nm BB UV

10

12

14

16

18

T

h

ic

k

n

e

s

s

l

o

s

s

(

s

h

ri

n

k

a

g

e

),

%

UV ~ 172 nm

UV > 200 nm

cured without

porogen (after H

2

-AFT)

cured with

porogen

(conventional)

Observations:

More thickness loss for films without porogen for 172 nm UV curing (improved cross-linking)

0

2

4

6

8

10

T

h

ic

k

n

e

s

s

l

o

s

s

(

s

h

ri

n

k

a

g

e

),

%

H

2

-AFT

(11)

172 nm UV curing of porgen-free low-

k

results in greater YM than

200 nm UV

5 . 5

6 . 0

6 . 5

7 . 0

7 . 5

8 . 0

F i l m s c u r e d

w i t h o u t p o r o g e n

1 7

2 n

m

U V

Y

o

u

n

g

's

M

o

d

u

lu

s

[

G

P

a

]

F i l m s c u r e d

w i t h p o r o g e n

Nano-indentation and Ellipsometric porosimetry

2 0

2 5

3 0

3 5

4 0

4 5

5 0

2 . 0

2 . 5

3 . 0

3 . 5

4 . 0

4 . 5

5 . 0

5 . 5

2 0 0

n m

U V

Y

o

u

n

g

's

M

o

d

u

lu

s

[

G

P

a

]

O p e n p o r o s i t y [ % ]

H

2

-AFT

(12)

15

20

25

H2-AF

H2-AFT + UV >200 nm

H2-AFT + UV ~ 172 nm

d

V

/d

r

Pore radius is greater for 172 nm UV due to more

efficient Si-O-Si matrix cross-linkage

Ellipsometric porosimetry

12

1.0

1.5

2.0

2.5

3.0

0

5

10

Pore radii [nm]

micropores

(13)

0.20

0.25

H

2

-AFT

H

2

-AFT + UV~172 nm

H

2

-AFT + UV>200 nm

N

o

rm

a

liz

e

d

a

b

s

o

rb

a

n

c

e

,

a

.u

.

Improved cross-linkage of Si-O-Si skeleton for ~172 nm

UV-cure

CH

3

Si

O

O

O

CH

3

T

D

cross-linking

with D-groups

optimal cross-linking

only T-groups

Si-CH

3

FTIR

1300

1290

1280

1270

1260

1250

0.00

0.05

0.10

0.15

N

o

rm

a

liz

e

d

a

b

s

o

rb

a

n

c

e

,

a

.u

.

Wavenumber, cm

-1

Si

CH

3

O

O

CH

3

D

Methyl

Oxygen

Silicon

(14)

UV-curing of porogen-free films results in its lower

k

-values

1.8

2.0

2.2

2.4

2.6

2.8

3.0

k

-v

a

lu

e

k

at 100 kHz (metal dots)

k

at 4 GHz (near-field probe)

cured without

porogen (after H

2

-AFT)

cured with

porogen

(conventional)

14

1.0

1.2

1.4

1.6

1.8

k

Observation for porogen free-films:

(15)

2.8

3

3.2

k

v

a

lu

e

10

100

P

o

re

s

iz

e

(

n

m

)

50

10

E

la

s

ti

c

m

o

d

u

lu

s

(

G

P

a

)

20

30

40

50

IMEC’s data base for various organo-silica low-

k

Summary: UV-curing wavelength vs achieved characteristics

of the porogen-residue-free films

UV >200 nm

UV>200 nm

UV>200 nm

UV ~172 nm

1.8

2

2.2

2.4

2.6

0

10

20

30

40

50

60

Porosity (vol. %)

0.1

1

1.8

2

2.2

2.4

2.6

2.8

3

P

o

re

s

iz

e

(

n

m

)

k

value

5

0.5

1

10

1.8

2

2.2

2.4

2.6

2.8

3

E

la

s

ti

c

m

o

d

u

lu

s

(

G

P

a

)

k

value

2

3

4

5

8

Green area – ITRS requirements

UV>200 nm

UV ~172 nm

UV ~172 nm

W. Volksen, D. M. Miller and G. Dubois,

Chem. Rev.,

110, 56 (2010).

(16)

Conclusions

UV-curing in the presence of porogen results in:

porogen residue generation

comparable mechanical properties and

k

-values for both UV-sources

used

UV-curing after porogen removal with H

2

-AFT results in:

narrow band (~172 nm)

YM of 6.64

±

0.61 GPa

Conclusions

curing technology

16

YM of 6.64

±

0.61 GPa

k

of 2.2

±

0.01

broad band (<200 nm)

YM of 3.85

±

0.38 GPa

k

of 2.0

±

0.01

(17)

Conclusions

Optimization of porogen residue-free ultra low-

k

PECVD films

different UV-cure times

combined narrow-band and broadband UV-curing

Electrical evaluation of achieved films using planar capacitor structures

CMP tests of porogen-residue-free films

References

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