Residual Stress Behavior of DLC Film
in Humid Environment
Young-Jin Lee a),b), Tae-Young Kim a),Kwang-Ryeol Lee a), In-Sang Yang b)
a) Future Technology Research Division, KISTb) Department Of Physics, Ewha Womans Univ.
Introduction
Low friction and high wear resist
Chemical inertness
Various application
Artificial Knee Joint
Artificial Hip Joint
High hardness
VCR head drum
Hard disk
Disadvantage
T. Ohana at al. Diamond Rel. Mater., 13 (2004) 1500
Environment dependence of DLC film.
Tribo test under aqueous condition
Tribo test under dry condition
S. J. Park at al. Diamond Rel. Mater., 12 (2003) 1517
Two Possibilities of Film Delamination
Residual stress is changed by water molecules.
Interfacial energy is changed
by water environment.
Film delamination enhanced.
Possibility 2.
Film delamination enhanced.
Possibility 1.
Purpose of This Work
• To investigate the residual stress behavior of various DLC films in humid environment systematically.
• To find the reason for the humidity dependence of DLC film in the point of residual stress.
Stress Measurement
• In Situ stress measurement : kMOS (Multi-beam Optical Sensing). (k-space Associate, Inc.)
• Humidity control : 10 ~ 90 % in air (± 5%). step control.
• Temperature : room temperature(19~26°C).
• Measurement time : about 600sec for each step.
• Stress measurement resolution : maximum 4Km in radius (In this system 1MPa)
Synthesis of DLC Films
• r.f. PACVD (13.56 MHz)
• Precursor Gas : C6H6, CH4
• Deposition Pressure : 1.33 Pa
• Bias Voltage : -100V ~ -800V
• Substrate :
P-type (100) Si-wafer 525 ㎛
P-type (100) Si-wafer 200 ㎛ (5×50
㎜ )
• Film Thickness : 500 ㎚
Residual Stress & Film Structure
1000 1250 1500 1750 20000
5000
10000
15000
20000
25000
Benzene -100V
Methane -150V
Methane -500V
Inte
nsity
(a.
u.)
Wave Number (cm-1)
0 -200 -400 -600 -8000.0
0.5
1.0
1.5
2.0
S
tres
s(G
Pa)
Bias Voltage (V)
0 -200 -400 -600 -800
1.0
1.5
2.0
2.5
3.0
3.5
Str
ess(
GP
a)
Bias Voltage (V)
C6H6 CH4
C6H6 -100V
Polymeric film
CH4 –500V
Graphitic film
CH4 –150V
Diamond-like film
Polymeric FilmPolymeric Film in Humid Condition
-10
0
10
20
30
Elapsed Time
(
MP
a)
20%50%90%80%50%20%
R.H. 20%→ 90%
16MPa↑
Immediate & reversible stress response
Compressive residual stress ∝ Relative humidity
-10
0
10
20
30
(
MP
a)
Elapsed Time
75% 20%90%55%
20%
Diamond-like FilmDiamond-like Filmin Humid Condition
R.H. 20%→ 90%
No change
Compressive residual stress has no relationship with humidity.
-10
0
10
20
30
(
MP
a)
Elapsed Time
25%90%40%20%
Graphitic FilmGraphitic Filmin Humid Condition
R.H. 20%→ 90%
12MPa↑
Immediate & reversible stress response
Compressive residual stress ∝ Relative humidity
Summary Ⅰ
• Residual Stress of DLC film has a humidity dependence.
• This is related with the film structure.
• Especially in polymeric and graphitic film, the compressive residual stress increase as humidity increases.
• Diamond-like film is no relationship with humid condition.
Effect of Water Molecule
F1 F1
>
F2
=
substrate substrate
substrate substrate
F1
Case 1.Reaction at surface
Case 2.Water penetration
Thickness Effectin Humid Condition
20 40 60 80 100
0
10
20
30
(
MP
a)
Relative Humidity (%)
400nm 500nm 1000nm
Polymeric DLC film
R.H. 20%→ 90%
400nm film : 27 MPa↑500nm film : 16 MPa↑1000nm film : 9 MPa↑
400 600 800 1000
0
10
20
30
(
MP
a)Thickness (nm)
Effect of Water Molecule
F1 F1
>
F2
=
substrate substrate
substrate substrate
F1
Case 1.Reaction at surface
Case 2.Water penetration
Effect of Water Molecule
F1 F1
>
substrate substrate
Case 1.Reaction at surface
s o f so
f f
F t F
t t
0
sF
ft
: Initial residual stress
: added force
: film thickness
In the case of polymeric DLC film, added surface force is
9.4±1.4 Nm-1
Conclusion
• Residual stress of DLC film has a relationship with humid condition. It is related with the film structure. Especially in polymeric and graphitic DLC film, compressive residual stress increase as the humidity increases.
• It is possible to enhance the stability of DLC films by structure control.
• This is due to the reaction between water molecules and film surface.
• During residual stress is changed, the structure or chemical composition is not changed.
• Humidity dependence of residual stress could be controled by surface treatment.