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
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
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
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
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/H2Porogen 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,
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]
6H
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
3Photodissotiation
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).
Experimental setup
Deposition of
130 nm films
1
2a
UV curing (166 s)
172
±
15 nm
Porogen removal
Gas inlet Plasma area He/H2350 s
NB
Experimental setup
Porogen
Skeleton
hardening
2b
>200 nm
Reactive species Grid : electrical neutralizationWafer at 280
°
C
H
H
H
BB
BB= broad band
NB= narrow band
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
8900
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]
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/H2Porogen fully
removed
Skeleton hardening900
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]
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
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
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
121.0
1.5
2.0
2.5
3.0
0
5
10
Pore radii [nm]
micropores
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
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)
141.0
1.2
1.4
1.6
1.8
k
Observation for porogen free-films:
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).
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