characterization of mechanical properties of thin film using residual compressive stress
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Characterization of Mechanical Properties of Thin Film Using Residual Compressive Stress
2004. 2. 16.
Sung-Jin Cho, Jin-Won Chung, Myoung-Woon Moon and Kwang-Ryeol Lee
Korea Institute of Science and Technology
미세구조 Workshop, 강원도 평창군 피닉스파크
Residual Stress of Thin Films
• Thin films typically support very high stresses due to the constraint of the substrate to which they are attached
Residual Compressive Stress of DLC Film
Film Deposition
Telephone Cord Buckling
M.W.Moon et al , Acta Mater., 50 (2002) 1219.
Off-Piste Run in Hoghfügen
Buckling Configurations
Quantitative Analysis
K.-R. Lee et al , Diam. Rel. Mater., 2 (1993) 218.
What can we do with this phenomenon?
• Can be a useful tool to estimate the fundamental interface toughness (adhesion) and the mechanical properties of thin films
What can we do with this phenomenon?
1
E
For Isotropic Thin Films
Measurement of Residual Stress
f
s
s
s
d
dE
R
2
21
1
Curvature (R)
DsDf
What can we do with this phenomenon?
1
E
For Isotropic Thin Films
DLC Bridges by Micro Fabrication
DLC film Deposition ( on SiO2 )
DLC PatterningSiO2 Isotropic Wet Etching
Wet Cleaning
Strain Estimation
C6H6, 10mTorr, -400V, 0.5m
150m
Microstructure of DLC Bridges
Strain of the Buckled Thin Films
xco
E
)1(
Z
X
2A0
2
2
2
2
11
2
1
2
2
o
x
x
A
dxx
W
x
W
cooA
E
2
1
ooA
E
2
1
Effect of Bridge Length
60 80 100 120 140 1600
40
80
120
160
200
E/(
1-)
(G
Pa)
Bridge Length (m)
m
Dependence of Film Thickness
0.0 0.3 0.6 0.9 1.2 1.50
40
80
120
160
200
E/(
1-)
(G
Pa)
Thickness (m)
V
V V
V
DLC Bridges
Biaxial Elastic Modulus
0 100 200 300 400 500 600
0
50
100
150
200
SiO2 etching techniqueE
/(1-
) (
GP
a)
Negative Bias Voltage (V)
DLC film Deposition
Cleavage along [011] Direction
Si Etching (by KOH Solution) Wet Cleaning
Strain Measurement
Preparation of Free Overhang
Free Overhang Method
• Biaxial elastic modulus
• Strain of the free overhang
2
0
)(1 A
E
20 )( A
A0 / λof Free-hang at 546 nm
4 8 12 16 20 24
0.02
0.04
0.06
0.08
0.10
0.12
0.14
A0
/
Etching Depth (m)
I II III
a-C:H, C6H6 -400V
5.6 ㎛ 11.3 ㎛
2 ㎛ 11 ㎛
Effect of Etching Depth
546 nm
55 nm
Elastic Modulus for Various Ion Energies
0 100 200 300 400 500 600 700 800
0
50
100
150
200
250
Pla
ne
Str
ain
Mod
ulus
(G
Pa
)
Negative Bias Voltage (V)
Nanoindentation t>1.0 ㎛
100 200 300 400 500 600
0
50
100
150
200
Bridge Method
Freehang Method
E/(1
-)
(GPa
)
Negative Bias Voltage (V)
Advantages of This Method
• Simple Method• Completely Exclude the Substrate Effect• Can Be Used for Very Thin Films
Nano-indentation
Substrate Effect is Significant.
The elastic strain field >> the plastic strain field
Substrate
Substrate Effect on the Measurement
0 50 100 150 200 250 300 350
100
200
300
400
500
600
700 500nm ta-C on Si 500nm ta-C on Al
CSM
Elas
tic M
odul
us (G
Pa)
Displacement (nm)0 50 100 150 200 250 300 350
100
200
300
400
500
600
700 200nm ta-C on Si 200nm ta-C on Al
CSM
Elas
tic M
odul
us (G
Pa)
Displacement (nm)
Advantages of This Method
• Simple Method• Completely Exclude the Substrate Effect• Can Be Used for Very Thin Films
0 200 400 600 800 1000 1200
25
50
75
100
on Si on W / Si on SiO
2/ Si
Bia
xial
Ela
stic
Mod
ulus
(G
Pa
)
Thickness (nm)
a-C:H, C6H6 -400V
J.-W. Chung et al, Diam.Rel. Mater. 10 (2001) 2069.
ta-C (Ground)
Elastic Modulus of Very Thin Films
Biaxial Elastic Modulus
0 100 200 300 400 500 6000
50
100
150
200
Bia
xial
Ela
stic
Mod
ulus
(GP
a)
Thickness (nm)
0 50 100 150 200 250
0.5
1.0
1.5
2.0
2.5
3.0
Res
idua
l Com
pres
sive
Str
ess
(GP
a)
Vb / P1/2 (V/mTorr1/2)
20
233
166
100
0 300 600 900 12001520
1530
1540
1550
1560
G-p
eak
Pos
ition
(cm
-1)
Thickness (nm)
233
166
100
20
Structural Evolution of DLC Films
Si Substrate
Si Substrate
Si Substrate
0 100 200 300 400 500 6000
50
100
150
200
Bia
xial
Ela
stic
Mod
ulus
(GP
a)
Thickness (nm)
J.-W. Chung et al, Diam.Rel. Mater., 11, 1441 (2002).
0 100 200 300 400 500 6000
1
2
3
4
5
6
7
Res
idua
l Com
pres
sive
Str
ess
(GP
a)Negative Bias Voltage (V)
Residual Stress of ta-C film
0 100 200 300 400 500 600 7000
100
200
300
400
500
600
700
800
900
Bia
xia
l Ela
stic
Mo
du
lus
(GP
a)
Thickness (nm)
Biaxial Elastic Modulus of ta-C film
Conclusions
• Can be a useful tool to estimate the fundamental interface toughness (adhesion) and the mechanical properties of thin films
What can we do with this phenomenon?
• Can be a useful tool to estimate the fundamental interface toughness (adhesion) and the mechanical properties of thin films
Fundamental Adhesion
B fsT
B f sU
s f fs
B fs B s f
B B
T U
T U
22
2)1(3
B
B
B
ut
tE
22
2)1(3
B
B
B
ut
tE
0.22 0.24 0.26 0.28 0.30 0.32 0.34 0.36-10
-5
0
5
10
15
20
25
30
(J
/m2 )
Thickness(m)
Fundamental Adhesion
DLC on Glass
Conclusions
• Can be a useful tool to estimate the fundamental interface toughness (adhesion) and the mechanical properties of thin films
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