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 Technolog y 미미미미 Workshop, 미미미 미미미 미미미미미
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
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
DLC Bridges by Micro Fabrication
DLC film Deposition ( on SiO2 )
DLC PatterningSiO2 Isotropic Wet Etching
Wet Cleaning
Strain Estimation
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
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)
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
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
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