Mechanical Properties of diamondlike carbon films grown by plasma CVD

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Mechanical Properties of diamond-like carbon
films grown by plasma CVD
By Liwei Wang Instructor Dr. Y. Tzeng For ELEC
7730 Date Oct 17, 2003
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Questions

• How the hydrogen incorporation induced in the
  DLC film deposition effect the mechanical
  properties?
• What is the synergetic effect on the surface
  roughness of DLC films?

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Outline

• Background Introduction
• ---What is Diamond-like carbon (DLC) film?
• ---Why DLC film?
• DLC deposition techniques
• ---How DLC films grow?
• Mechanical Properties
• ---What is the correlation between mechanical
  properties and the deposition condition?

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What is DLC?
Carbon usually exists in several forms graphite,
diamond, and the new form of fullerines. All
three of these forms are crystalline in structure
but have varying properties based on the bonding
order of the carbon atoms. Diamond-like carbon
(DLC), on the other hand, is amorphous in
structure, containing both SP2 and SP3 bonded
carbon. As such, DLC has both diamond-like and
graphitic properties. Hence the name diamond-like
carbon (DLC).
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What is DLC?
http//www.nippon-itf.co.jp/dlcen.html
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Why DLC film?
High hardness.
Due to the low temperature coating process,
which makes them particularly attractive for
applications where the substrate cannot
experience elevated temperatures. it can be
deposited not only on carburized steel or
aluminum alloy, but also on many kinds of rubber
and resin!
Low friction coefficient (about0.1) even
without lubrication!
http//www.nippon-itf.co.jp/dlcen.html
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Why DLC film?
High optical transparency.
High dielectric strength.
High thermal conductivity.
High chemical inertness, biocompatibility
High surface smoothness. Etc.
The unique combination of those desirable
characteristic and material properties make the
DLC films attract widespread attention in both
industrial and technical applications.
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DLC deposition techniques

• DLC films have been prepared by a variety of
  methods and precursors, such as
• RF-Plasma assisted CVD (RF-PACVD)
• DC-Plasma assisted CVD (DC-PACVD)
• Plasma Enhanced CVD (PECVD)
• Electron cyclotron resonance microwave plasma
  CVD
  
  
  (ECR-PACVD)
• Sputtering
• Vacuum arc deposition
• Filtered - cathodic vacuum arc (FCVA) deposition
• Ion beam deposition
• From a variety of solid and gaseous source
  materials.

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The ECR-MPCVD Process

• Lower, broad range of operating pressures.
• High ionization efficiency
• Wide range of achievable ion energies
• ----Intrinsic ion energies below values that
  can induce
• radiation damage.
• ----Higher energies can be achieved easily
  with assistance
• of extraction grids, or substrate bias.
• Electrodeless coupling of the electric power to
  the plasma
• Directionality of the ion and even neutral beam.

Alfred Grill, Gold Plasma in materials
fabrication, IEEE Press, 1994
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The ECR-MPCVD system

• Microwave generator
• ---2.45Ghz
• Permanent magnets
• ---875gauss
• RF generator
• ---13.56Mhz
• Additional magnets
• Turbo pump

http//www2.eng.cam.ac.uk/www-edm/equip.html
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The ECR-MPCVD system
A schematic of the commercial ECR-MPCVD system
from ASTeX ASTeX AX2040
http//www.eng.uc.edu/rsingh/pvd.htm
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ECR-MPCVD Process parameters
Different process parameters such as
-- substrate bias, -- plasma gas composition, --
substrate temperature, -- pressure and plasma
-- density
Have great influence on the composition, crystal
quality, properties of the deposited films.
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ECR-MPCVD Process parameters used in the DLC
deposition
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Characterization of DLC film-Mechanical properties
Raman spectroscopy
Phase structural determination
Atomic force microscope (AFM)
Surface roughness
Measured by
Film Harness
Nanoindenter
Tribological behaviors
Tribometer
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Phase structural determination by Raman analysis
Highly crystalline perfect graphite exhibits a
sharp peak at 1580cm-1 ----G-peak
Diamond exhibits a sharp peak at 1332cm-1
----D-peak
Raman sensitivity for sp2-C was reported to be
more than a hundred times higher than that for
sp3-C Therefore, most Raman analysis about DLC
film is concerned with G-band (a band around
1580cm-1 )
P.L. Chen et al./Applied Surface Science 92
(1996) 30-34
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Raman spectra
A broad skewed peak centered at 1580cm-1
D-peak shifted from 1410cm-1 to 1365cm-1
G-peak shifted from 1585cm-1 -1545cm-1 when
the magnitude of the bias voltage was increased.
K.Y. Li et al. / Diamond and Related Materials 10
(2001) 1855 - 1861
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Surface roughness

• Generally, DLC film surface roughness
• Range from 2rms to 10rms.
• Decrease with increasing negative bias voltage.

• Because the surface roughness is a synergetic
  effect of
• Ion bombardment
• Formation of volatile hydrocarbon compounds.

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Surface roughness measured by AFM
AFM image of DLC prepared in (a) -120 V and (b)
-60 V
K.Y. Li et al. / Diamond and Related Materials 10
(2001) 1861 - 1867
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Film Hardness

• DLC films have a wide range of hardness
• Range from 3GPa to 80GPa.
• Increase with increasing negative bias voltage
  to certain level.

• These differences are interrelated with
• Kinetic energy of plasma constituents impinging
  on
• substrate surface.
• Subsequent hydrogen incorporation into carbon
  films.

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Film Hardness
Monovalent hydrogen can serve as the terminating
atoms in a carbon network.
Develop softer and polymeric-like films with
hardness below 4 GPa.
Higher concentration of hydrogen will induce more
hydrogen incorporation.
K.Y. Li et al. / Diamond and Related Materials 10
(2001) 1861 - 1867
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Film Hardness
Most mechanical properties of DLC films strongly
depended on the kinetic energy of impinging
particles.
Higher substrate bias leads to intense
impingement distorting the carbon planes and then
reinstating by cross-linked sp3 carbon bonding
Increase the fraction of sp3 sites and develop
more diamond-like bonding environment.
K.Y. Li et al. / Diamond and Related Materials 10
(2001) 1861 - 1867
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Film Hardness
DLCA Acetylene/Argon 3sccm /60sccm
DLCM Methane/Argon 6sccm /60sccm
K.Y. Li et al. / Diamond and Related Materials 10
(2001) 1861 - 1867
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Conclusions

• DLC film describes a variety of amorphous carbon
  materials.
• Exhibit a wide range of mechanical and
  tribological behaviors controlled by the
  deposition process.
• Provide great potential in both industrial and
  technology applications.

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Answers

• Monovalent hydrogen can serve as the terminating
  atoms in a carbon network, which will help
  develop polymeric like films.
• It is a synergetic effect of ion bombardment
  and formation of volatile hydrocarbon compounds.