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© 2018 IBM Corporation
Advanced Low Dielectric Constant MaterialsLearning and
Perspectives
Geraud Dubois
IBM Almaden Research Center, San Jose, CA
Department of Materials Science and Engineering, Stanford
University, CA
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© 2018 IBM Corporation
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Outline
FEOL, MEOL, BEOL & Packaging
Low-k materials: why do we need them?
Ultra low-k materials (ULK) mechanical properties
Chip Package Interaction (CPI) – lessons learned
Ultra low-k materials (ULK) – challenging our thinking
Conclusion
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FEOL, BEOL and PACKAGING T. Wiggins
T. Wiggins
Cu Vias
M1
M2
M3
M4
V1
FET’s (gates)
Cu Wires
Tungsten Studs
ILDBEOL
FEOL
MEOL
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5
0
5
10
15
20
25
30
35
40
45 Gate delay
Interconnect delay, Al & SiO2
Sum of delays, Al & SiO2
100130180250350500
De
lay (
ps)
Technology node (nm)
650
Al 3.0 µm-cmSiO
2 k = 4.0
Al 0.8 µm thickAl line 43 µm long
1997
TransistorsInterconnect
Calculated gate and interconnect delay vs technology node
according to
the National technology roadmap for semiconductor (NTRS) in
1997
20% performance increase
RCdelay
Why did we introduce low-k materials?
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1997 2000 2002 2004 2006 2008
250nm(6 Cu levels)
180nm(7 Cu levels)
130nm(9 Cu levels)
90nm(10 cu levels)
65nm(10 Cu levels)
45nm(10 Cu levels)
SiO2 F-SiO2 F-SiO2 SiCOH SiCOH SiCOH
k= 4.3 k= 3.6 k= 3.0 k= 2.7 k= 2.4k= 3.8
MICROPROCESSORS HISTORICAL EVOLUTION
80 nm80 nm
Cu ILD
480 nm480 nm
ILDCu
W. Volksen, R. Miller, G. Dubois. Chem Rev 2010, 110,
56-110.
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IBM Technology Roadmap
SiO2 (250 nm)
F-SiO2 (180 nm)
F-SiO2 (130 nm)
SiCOH (90 nm)
SiCOH (65 nm)
SiCOH (45 nm)
SiCOH (32 nm)
1996 2000 2004 2008 2012 20162.0
2.5
3.0
3.5
4.0
4.5
DIE
LE
CT
RIC
CO
NS
TA
NT
YEAR OF PRODUCTION (TECHNOLOGY NODE)
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Major Challenges for the Integration of ULK (k
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CPI and ULK MATERIALS
BEOL PACKAGING
ULK Young’s
modulus
ULK Cohesive strength
ULK levels
C4 Stiffness Substrate Flexibility
Preferred ↑ ↑ ↓ ↓ ↓
Reality ↓ ↓ ↑ ↑ ↑
P. Brofman, ICEP 2009, Kyoto, Japan, April 14-16, p1-6.
Packaging BEOL
Technology node n
Pro
ce
ss w
ind
ow
Packaging BEOL
Technology node n+1
Pro
cess w
ind
ow
More thermo-mechanical stress is applied to the BEOL whereas
theoverall fracture resistance of the BEOL has been reduced
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PSPI
Oxide Low K
Shear due to package applies moment to C4
Tension due uplift of the solder bump edge
Tension due to Stretching of upper levels of BEOL Films.
Eoxide > EPSPI > ElowK
WHITE BUMP ISSUES
Acoustic microscopy image of white bumps Cross-section of white
bump
T. Wiggins
R.A. Susko et al. ECS Trans 16 (19) 2009, 51-60.
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MODELING OF CHIP-PACKAGING INTERACTION
C.J. Uchibori et al. AIP Proceedings, Stress-Induced Phenomena
in Metallization, 10th Int Workshop, 2009, 185.G. Wang et al.
Microelectronics Reliability 2005, 45, 1079-1093.
ILD E (GPa)
MSQ-A 2
MSQ-B 5
MSQ-C 10
MSQ-D 15
CVD-OSG 17
ERR at crack 6 vs ILD moduli (CTE~10ppm/K)
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MODELING OF CHIP-PACKAGING INTERACTION
E=23 GPa
E=70 GPa
Influence of higher levels material E
observed
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Parameters Variables Effect on ERR Conclusion
Solder materials - Traditional lead eutectic
- Lead-free
2-3 times higher forlead free solder
Lower E and smaller CTEmismatch with underfill
Underfill CTE: 28, 34 and 41 ppm Factor of 3 increasebetween 28
and41ppm
Lower the underfill CTE
Die attach process - Ceramic vs organic
- With or without underfill
Up to 8x
Up to 3x
Ceramic preferred
OBAR type process
Die size - 8 x 7 mm2
- 14.4 x 13.4 mm215% increase for thebiggest one
Not such a determining factor
Interfaces in the interconnect structures parallel to the die
surfaceare more prone to the packaging effect
G Wang et al. Microelectronics Reliability 2005, 45,
1079-1093.
MODELING OF CHIP-PACKAGING INTERACTION
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Si
C
CC
OQ
T
D
M
50 0 -50 -100 -150
29Si Chemical Shift (ppm)
DEMS/BCHD
k = 2.2, 36SJA3Si
C
OC
O
Si
O
OC
O
Si
O
OO
O
DH TH
OMCTS 2.7
Si
O
O
O
O
Si
Me
O
O
O Si
Me
Me
O
O
Si
H
O
O
O Si
H
Me
O
O
Traditional Building Blocks
Ultra low-k Materials Chemistry ESAWS = 7 GPaPorosity (N2) =
17%
The hybrid network connectivity dictates:
A) thin-film mechanical properties
B) mechanical response to the introduction
of porosity
Si
Me
Me
O
Me
O
Si
O Si
O
Si
OSi
Me
Me
Me
Me
Me
Me
MeMe
OMCTS
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Si
C
CC
OQ
T
D
M
50 0 -50 -100 -150
29Si Chemical Shift (ppm)
DEMS/BCHD
k = 2.2, 36SJA3Si
C
OC
O
Si
O
OC
O
Si
O
OO
O
DH TH
OMCTS 2.7
Si
O
O
O
O
Si
Me
O
O
O Si
Me
Me
O
O
Si
H
O
O
O Si
H
Me
O
O
Traditional Building Blocks
Ultra low-k Materials Chemistry ESAWS = 7 GPaPorosity (N2) =
17%
The hybrid network connectivity dictates:
A) thin-film mechanical properties
B) mechanical response to the introduction
of porosity
Si
Me
Me
O
Me
Si Si
O
O
O
O
O
O
1,2
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HOI Mechanical Properties
0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5
0
2
4
6
8
10
12
14
16
18
20
y = 19.425ρ-11.381
y = 19.52ρ-10.149
y = 2.6633ρ3.3829
MSSQ-SiO2
Et-OCS Me-OCS
ES
AW
S (
GP
a)
Density (g.cm-3)
Si
Si
O
O
O
O
O
O
CH3
Si O
O
O O Si
O
O
Ox y
Si Si
O
O
O
O
O
O
HOI
0
2
4
6
8
10
12
0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4
1.9 4.53.52.5 3 4Dielectric Constant, k
Str
ain
En
erg
y R
ele
ase
Ra
te,
G (
J/m
2)
Density, ρ (g/cm3)
2.2
4 pt. bend Gc
Dense SiO2
k ~ 2.3
2.0
CDO (PECVD)
MSSQ (SOD)
15-17
E.P. Guyer et al. J. Mater. Res. 2006, 21, 882.Dubois et al.,
Adv. Mat. 2007, 19, 3989.
Dubois et al., Journal of Sol-gel Science and Technology, 2008,
48, 187.
Dubois et al., US 7,229,943 (2007)
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ULK Mechanical Properties Landscape
o New Materials have emerged
o Engineering solutions have been found
- UV treatment has been implemented (1.5x improvement in E)
- New designs have helped with chip packaging interaction
(CPI)
+ BCHD – Si (OEt)2Me
D. Edelstein et al. IITC 2012
(EtO)3Si Si(OEt)3
k=2.55
Higher mechanical properties
E ~ 10 GPa
Spin-on
Parameter POCS V2 POCS V2
Porogen No Yes
Dielectric constant ~ 2.4 ~ 2.2
E (GPa) by SAWS 10.0 7.9
Lowest k integrated until now is ~ 2.4
PECVD
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Major Challenges for the Integration of ULK k < 2.55
SiO2 CDO p-SiCOH k < 2.4F-SiO2
POROSITY
AR
BIT
RA
RY
UN
ITS
Mechanical
PropertiesPr
oces
s
Dam
age
Mechanical properties: Young’s modulus, hardness, fracture
resistance, and adhesion
Process damage: plasma, wet chemistries
SiO2 CDO p-SiCOH k < 2.4F-SiO2
POROSITY
AR
BIT
RA
RY
UN
ITS
Mechanical
PropertiesPr
oces
s
Dam
age
Mechanical properties: Young’s modulus, hardness, fracture
resistance, and adhesion
Process damage: plasma, wet chemistries
Mechanical properties: Young’s modulus, hardness, fracture
resistance, and adhesion
Process damage: plasma, wet chemistriesW. Volksen and G. Dubois,
Advanced Interconnects for ULSITechnology, M. Baklanov, P.S. Ho, E.
Zschech, Eds., Wiley,2012, Chapter 1.
Plasma Induced Damage (PID)(Ions, Radicals, VUV…)
Si
Me
OO
O
Si
O O
O
Si
H
O
O
Si
OSi
O
O
O
SiO
O
Si
Me Me
O
Si
O Si
O
O
OH
O
Si
OO
Me
Si O
Si
HO
Si
O
OSi
O
Si
O
OSi
O
O
Si
OO
Me
O
Si
O
O
O
Si
Si
O
O
HSi
MeO
Si
O
Si
OO
OO
Si
O
O
O Si
OO
Me
O
Si
H
O O
Me
Me
Me
H
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Major Challenges for the Integration of ULK k < 2.4
SiO2 CDO p-SiCOH k < 2.4F-SiO2
POROSITY
AR
BIT
RA
RY
UN
ITS
Mechanical
PropertiesPr
oces
s
Dam
age
Mechanical properties: Young’s modulus, hardness, fracture
resistance, and adhesion
Process damage: plasma, wet chemistries
SiO2 CDO p-SiCOH k < 2.4F-SiO2
POROSITY
AR
BIT
RA
RY
UN
ITS
Mechanical
PropertiesPr
oces
s
Dam
age
Mechanical properties: Young’s modulus, hardness, fracture
resistance, and adhesion
Process damage: plasma, wet chemistries
Mechanical properties: Young’s modulus, hardness, fracture
resistance, and adhesion
Process damage: plasma, wet chemistriesW. Volksen and G. Dubois,
Advanced Interconnects for ULSITechnology, M. Baklanov, P.S. Ho, E.
Zschech, Eds., Wiley,2012, Chapter 1.
Plasma Induced Damage (PID)(Ions, Radicals, VUV…)
k increases
Moisture absorption
Electrical properties degraded
Si
OH
OO
O
Si
O O
O
Si
H
O
O
Si
OSi
O
O
O
SiO
O
Si
HO Me
O
Si
O Si
O
O
OH
O
Si
OO
Me
Si O
Si
HO
Si
O
OSi
O
Si
O
OSi
O
O
Si
OO
Me
O
Si
O
O
O
Si
Si
O
O
HSi
MeO
Si
O
Si
OO
OO
Si
O
O
O Si
OO
OH
O
Si
H
O O
HO
Me
Me
H
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ULK Dilemma
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1.POREFILL
2.OVERBURDEN
REMOVAL
6. BURN-OUT
3. PATTERNING
4. METALLIZATION
5. CMP
SUBSTRATE SUBSTRATE
SUBSTRATESUBSTRATE
CuCu Cu Cu
US 8,314,005 , US 8,492,239, US 8,541,301
T. Frot et al. Future Fab Int. 2011, 39, p.67T. Frot et al. Adv.
Mater. 2011, 23, p.2828T. Frot et al. Adv. Funct. Mater. 2012, 22,
3043
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Conclusion
o Culture of Roadmap
o Engineering Solution vs Materials Innovation
o The syndrome of 1 “Material”, many properties
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Acknowledgements
Willi Volksen Teddie Magbitang
Theo Frot Krystelle Lionti
Reinhold Dauskardt
