7/25/2016
Elastic and Thermal Expansion Asymmetry
in
Organosilicate Dielectric Materials
Joe Burg and Reinhold H. Dauskardt
Materials Science and Engineering
Stanford University
Research supported by the Department of Energy under Contract No. DEFG02-07ER46391
Thermomechanical Reliability of Hybrid OrganicInorganic Materials
Numerous Applications
light-weight vehicle
wearables
Low-Cost Processing
AR coatings
microelectronics
energy
Thermomechanical Reliability:
accurate mechanical properties
compressive
stresses
blistering
Z = 0.6014
Hybrid film
Si substrate
channeling
Z = 1.976
atmospheric plasma
roll-to-roll
surface cracks
Z = 3.951
hybrid film
tensile
stresses
Si substrate
2
1
7/25/2016
MD Modeling of Oxycarbosilanes (OCS)
Simulation Elements
Bonded Interactions
Oxygen:
OCS:
H atoms are modeled implicitly
(united atom approach)
Enforce all bond lengths, angles and
dihedral angles
Non-Bonded Interactions: Stillinger-Weber Potential
Oxygen
Silicon
Carbon
3
Network Connectivity Controls the Elastic Properties
T1
To
OH
OH
T2
Si
O
Si O Si
HO Si
OH
OH
OH
T3
Si
O
Si O
Si
terminal O
bridging O
O
Si
q=
CH3
Et-OCS(Me)
Et-OCS
Si
Si
Si
Si
1,3,5 Benzene
4
2
7/25/2016
Simulating Bulk Modulus of Bridged Hybrid ULK
Et-OCS
O
Et-OCS(Me)
CH2
CH3
Si
Oxygen
Silicon
Si
O
CH2
CH2
40
fused SiO2
Experimental Values
Bulk Modulus, K (GPa)
Bulk Modulus, K (GPa)
40
30
20
K = a(q-qc)
qc = .467
a = 99.98
1.92
Et-OCS
qc = .56
a = 70.45
10
0
0.5
Et-OCS(Me)
0.6
0.7
0.8
0.9
1.0
Experimental Values
30
20
fused SiO2
mean-field
elastic model
K = 173.7(p-0.6)
1.92
Et-OCS
10
Et-OCS(Me)
pC= 0.6
0
0.5
0.6
0.7
0.8
0.9
1.0
Si-X-Si Connectivity, p
Condensation Degree, q
rigidity percolation
Oliver, Dauskardt, et.al. Adv. Funct. Mat., 2010.
Simulations Predict 1,3,5-Benzene Stiffer than SiO2
hyperconnected glass network
Si
q = 0.80
α-SiO2
Si
O
O
Si
1,3,5-Benzene
Si
O
O
1,4-Benzene
Si
Si
Si
Si
Si
Si
Methane
Si
Ethane
1,3-Benzene
Si
3
7/25/2016
Network Connectivity Controls the Elastic Properties
where
Si
Si
Si
O Si O Si
Si
Si
O Si O Si
O
O
Si
Si
“hyperconnected” architecture: mSi > CN
Model Glasses Calibrated with Experiments
NMR calibrated
MD prediction
Si
Si
Si
+
Si
1,3,5-Benzene
1,3,5-Benzene
fragmentation
Si
Si
Si
Si
Si
Si
experiment
Si
Si
Si
Si
Si
TT2
2
T-group
T-group
O
O
O
Si
Q-group
C
O SiO C
T
T3
3
O
T1
T1
O
Q-group
O
O
Q33
Q
Q22 Q
Si
O O
Si
Si
O
O
Si
O
Si
QQ4 4
0
0
29
-50
-50
-100
-100
Si Chemical
Shift (ppm)
29
Si Chemical Shift (ppm)
Si
-150
-150
Si
Si
Si
+
Si
Si
Si
hyperconnected
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7/25/2016
Hyperconnected Architectures Significantly Stiffen Highly
Nanoporous Materials
1,3,5-Benzene
w/o fragmentation
Si
1,3,5-Benzene
Si
1,3,5-Benzene
fragmentation
Si
Si
Si
Si
Si
Si
+ Si
mechanically
enhanced
1,3,5-Benzene
fragmentation
Si
Si
Si
+
Si
Si
Si
Si
Si
Si
Elastic and Thermal Expansion Asymmetry
in
Organosilicate Dielectric Materials
Burg and Dauskardt, Nature Materials, 2016.
5
7/25/2016
Dielectric Glasses are Elastically Asymmetric in
Compression and Tension
experiment
compression
tension
11
Burg and Dauskardt, Nature Materials, 2016.
Accessible Atomic Volume During Elastic Deformations
compression
tension
terminal O
C
Et-OCS
Si
terminal O
bridging O
bridging O
Burg and Dauskardt, Nature Materials, 2016.
12
6
7/25/2016
Asymmetric Thermal Expansion Properties
40
compression
30 ■■
compression
20
■
■
■■
■■
■ ■■
■■ ■ ■■ ■
■ ■
tension
■
■■■■■■ ■■■
hea1ng
10
heating
0
a)
0.11
tension
■
■■ ■
■■
■
■
cooling
- 0.5
■
■
■
■
0.0
0.5
Pressure, P (GPa)
Entropic Force, f (nN/bond)
CTE, α (10- 6 K- 1)
compression
■
■
εth
0.10
fentropic εth
εth
■
fentropic
0.09
0.08
■ ■
0.07
b)
tension
fentropic
■
■■ ■
■ ■■ ■■■
- 0.5
■
■
■ ■■
■■ ■
0.0
0.5
Pressure, P (GPa)
Δ
cooling
13
Model Nanoporous Glasses
Model porogen:
Sample pore:
Glass w/o porogen
Rgyration = 0.6 nm
~1.2 nm
Burg and Dauskardt, Nature Materials, 2016.
14
7
7/25/2016
Nanoscale Porosity Decreases Elastic Asymmetry
terminal O
compression
tension
15
Burg and Dauskardt, Nature Materials, 2016.
Model for the Degree of Elastic Asymmetry
terminal O cluster
terminal O-O interaction
terminal O-C interaction
β = 0.33
Burg and Dauskardt, Nature Materials, 2016.
β = 1.0
16
8
7/25/2016
Model for the Degree of Elastic Asymmetry
terminal O cluster
p = 0.86
β = 1.0
terminal O-O interaction
terminal O-C interaction
17
Burg and Dauskardt, Nature Materials, 2016.
Designing Elastically Asymmetric Materials
bridging O
Density, ρ (g/cc)
terminal O
O
O Si O
O
1,3,5-Benzene
Et-OCS
Et-OCS(Me)
increasing
asymmetry
1.6
Degree of Asymmetry, EC / ET
α-SiO2
1.4
1.2
1.0
Mean Si Network Connectivity, mSi
Burg and Dauskardt, Nature Materials, 2016.
18
9
7/25/2016
Elastic Asymmetry Produces Different Crack Driving Forces
surface cracks
Z = 3.951
tensile
stresses
~24%
Eavg
channeling
Z = 1.976
terminal
O
bridging O
(p ~ 0.86)
ET
Et-OCS
Eavg
Si substrate
surface cracking
ET
EC
channeling
compressive
stresses
~24%
~47%
Eavg
blistering
Z = 0.6014
blistering
Et-OCS
Si substrate
Eavg
ET
Eavg
•
•
•
•
assume h = 200nm
simple blanket film
processing temperatures : ΔT = 360K
Eexp ~ Eavg = 0.5(EC + ET)
surface cracking
channeling
ET
EC
Eavg
blistering
19
Thermomechanical Asymmetries
in ULK Dielectric Glasses
Joe Burg and Reinhold H. Dauskardt
Materials Science and Engineering
Stanford University
Research supported by the Department of Energy under Contract No. DE-FG02-07ER46391
10