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Vapor Deposited Diamond Thin Films

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Diamond treasured for centuries as a gemstone. Extreme properties 'biggest and the best' ... unsuitable as gemstones. used as cutting tools and drill bits. ... – PowerPoint PPT presentation

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Title: Vapor Deposited Diamond Thin Films


1
Vapor Deposited Diamond Thin Films
  • Review by
  • Vivek Krishnan
  • Materials Research and Education Center
  • Auburn University, AL

2
Presentation Outline
  • Introduction diamond and graphite
  • Diamond Synthesis
  • Nucleation and growth
  • Substrate choice
  • Applications
  • Conclusions

3

Introduction
  • Diamond treasured for centuries as a gemstone
  • Extreme properties biggest and the best.

'Synthetic Diamond - Emerging CVD Science and
Technology', Spear and Dismukes, Wiley, NY, 1994
4
Questions
  • Why is atomic hydrogen important for growth of
    diamond thin films by CVD?
  • What is Bias Enhanced Nucleation?

5
Properties
  • Extreme mechanical hardness (90 GPa).
  • Strongest known material, highest bulk modulus
    (1.2 x 1012 N/m2), lowest compressibility (8.3 x
    10-13 m2/ N).
  • Highest known value of thermal conductivity at
    room temperature (2 x 103 W/m/ K).
  • Thermal expansion coefficient at room temperature
    (0.8 x 10-6 K) is comparable with that of invar.
  • Broad optical transparency from the deep UV to
    the far IR region of the electromagnetic
    spectrum.

http//www.chm.bris.ac.uk/pt/diamond/end.htm
6
Properties contd.
  • Good electrical insulator (room temperature
    resistivity is 1016 ohm cm).
  • Diamond can be doped to change its resistivity
    over the range 10-106 ohm cm, so becoming a
    semiconductor with a wide bad gap of 5.4 eV.
  • Very resistant to chemical corrosion.
  • Biologically compatible.
  • Exhibits low or 'negative' electron affinity.

http//www.chm.bris.ac.uk/pt/diamond/end.htm
7

Carbon Chemistry
  • Ability of carbon to bond with itself.
  • Allotropes diamond, graphite and amorphous
    carbon.
  • Single element carbon atoms arranged in a
    lattice.
  • Directional covalent bonds.

http//invsee.asu.edu/nmodules/Carbonmod/bonding.h
tml
8
Structures - Graphite
http//www.nyu.edu/pages/mathmol/modules/carbon/ca
rbon1.html
9
Structures - Diamond
http//www.nyu.edu/pages/mathmol/modules/carbon/ca
rbon1.html
10
Carbon Phase Diagram

F.P. Bundy, The P,T Phase and Reaction diagram
for elemental Carbon, 1979 J. Geophys. Res. 85
(B12) (1980) 6930
11
Diamond Synthesis
  • High Pressure High Temperature synthesis (HPHT)-
    ASEA and General Electric (1950s)
  • Graphite- hydraulic press at high temperatures
    and pressures- metallic catalyst - converts to
    diamond over a period of a few hours.
  • P50-100 kbar and T1800-2300K.
  • mm sized crystals
  • unsuitable as gemstones
  • used as cutting tools and drill bits.

http//www.chm.bris.ac.uk/pt/diamond/end.htm
12
Low Pressure Diamond
  • Metastable diamond phase at low pressures first
    deposited by William Eversole of the Union
    Carbide Corp. (1962)
  • Ability to produce polycrystalline diamond films
    with excellent properties using simple
    hydrocarbon mixtures.
  • Techniques present economical alternative to HPHT
    and the promise of synthesizing other metastable
    phases.

Thin Film Diamond Growth Mechanisms, James E.
Butler and Richard L. Woodin, Thin Film Diamond,
Ed. Lettington and Steeds, Pub. Chapman and Hill,
1994
13
Chemical Vapor Deposition
  • Involves a gas-phase chemical reaction occurring
    above a solid surface, which causes deposition
    onto that surface.
  • Requires gas-phase activation.
  • Thermal, plasma activation or combustion flame.

http//www.sandia.gov/1100/CVDwww/cvdinfo.htm
14
Vapor Phase Diamond Deposition
P.W. May, "Diamond Thin Films A 21st Century
Material" Phil. Trans. R. Soc. Lond. A, 358
(2000) 473-495.      
15
Growth of Carbon Lattice
Reduction of carbon from hydrocarbons to form
diamond.
P.W. May, "Diamond Thin Films A 21st Century
Material" Phil. Trans. R. Soc. Lond. A, 358
(2000) 473-495.
16
Film deposition
  • Compromise between growth rate and quality of
    film.
  • Quality- ratio between sp2 and sp3 species,
    crystallinity.
  • Combustion methods - high rates (upto 200 µm/hr,
    respectively), very small, localized areas, poor
    quality films.
  • The hot filament and plasma methods have much
    slower growth rates (0.1-10 µm/hr), but produce
    high quality films.
  • Microwave deposition rate increases linearly
    with microwave power.

P.W. May, "Diamond Thin Films A 21st Century
Material" Phil. Trans. R. Soc. Lond. A, 358
(2000) 473-495.
17
Common Gas- Activation Methods
Hot Filament CVD Pressure of 20-30 torr using
rotary pump. Gas flow rates of few hundred
sccm. Substrate heated to 700-900C. Filament (W)
heated to more than 2200C.
P.W. May, "Diamond Thin Films A 21st Century
Material" Phil. Trans. R. Soc. Lond. A, 358
(2000) 473-495.
18
Microwave Plasma CVD
Microwave power coupled to chamber via quartz
window to create discharge. Microwaves couple
their energy to gas phase electrons, energy
transferred to gas which dissociates to form
reactive species. Using 2.45GHz frequency. 20-200
mbar pressure
P.W. May, "Diamond Thin Films A 21st Century
Material" Phil. Trans. R. Soc. Lond. A, 358
(2000) 473-495.
19
Plasma Jet Methods
  • Gas at high flow rates passes through electrical
    discharge- forms jet of ionized particles.
  • Strike substrate in secondary chamber (100 torr
    to 1 atm).
  • DC arc jet used to pass high currents through
    ionized flowing process gases.
  • Exceedingly high growth rates (900 microns/hr).
  • Very small deposition area

P.W. May, "Diamond Thin Films A 21st Century
Material" Phil. Trans. R. Soc. Lond. A, 358
(2000) 473-495.
20
Summary of Deposition Techniques
Low Pressure Diamond Synthesis Techiques and
Results, Peter K. Bachmann, Thin Film Diamond,
Ed. Lettington and Steeds, Pub. Chapman and Hill,
1994
21
Film growth and nucleation
  • Phase diagram shows diamond is metastable.
  • Atomic hydrogen crucial role.
  • Undergo H abstraction reactions, yield reactive
    methyl radicals, help propagate diamond lattice.
  • Terminate dangling carbon bonds, stop
    graphitization.

22
Effect of mixture concentration and temperature
  • Low CH4 partial pressure and low temperature
    microcrystalline (111) triangular faces with
    twins.
  • At higher concentrations and/or temperature
    rectangular (100) faces- columnar growth

P.W. May, "Diamond Thin Films A 21st Century
Material" Phil. Trans. R. Soc. Lond. A, 358
(2000) 473-495.
23
Parameter effects contd.
  • At higher partial pressures crystalline
    morphology disappears disordered graphite with
    nano crystalline diamond.
  • Gas composition film quality from acetylene
    mixtures inferior to that from methane mixtures.

24
C-H-O composition diagram
Synthetic Diamond Emerging CVD Science and
Technology, Edited by K.E. Spear and J.P.
Dismukes (Wiley, 1994)
25
Choice of Substrate
  • Single crystal Si wafers are most common.
  • Should have high melting point.
  • Good carbide formers. Mo, W, Ti
  • Low C diffusion.

Synthetic Diamond Emerging CVD Science and
Technology, Edited by K.E. Spear and J.P.
Dismukes (Wiley, 1994)
26
Enhanced Nucleation
  • Substrate preparation Scratching surface using
    abrasive film enhances nucleation.

W. A. Yarbrough, J. Am. Ceram. Soc., 7512
3179-200 (1992)
27
Bias Enhanced Nucleation
  • Deposition conditions altered by biasing the
    substrate.
  • Negative potential(100-200V) applied for the
    first few minutes.
  • Carbon rich layer on top- high nucleation rate
    and preferred orientation.

Huimin Liu and David S. Dandy, Diamond Chemical
Vapor Deposition, Noyes Pubilications, New
Jersey, USA, 1995 M. Katoh, M. Aoki and H.
Kawarada, Jpn. J. Appl. Phy., 33(2A)L194-L196
(1994)
28
Characterization
  • Difficult to distinguish between diamond,
    graphite and diamond like carbon
  • X Ray Diffraction show pattern for cubic
    diamond.
  • Raman Spectroscopy shows characteristic Raman
    absorption peaks unique signature- best
    technique.

W. A. Yarbrough, J. Am. Ceram. Soc., 7512
3179-200 (1992)
29
Some Other Reactions and Models
  • Diamond deposited without using hydogen using
    fluorocarbon chemistry.
  • CS2 reacted with fluorine to give diamond with
    SF6.
  • Thermodynamics proves mechanism is possible with
    no necessary activation stages although further
    experimentation needed.

D.E. Patterson, C.J.Chu, B.J. Bai, N.J. Komplin,
R.H. Hauge and J.L. Hargrave pp. 569-576 in
Applications of Diamond Films and Related
Materials. Ed. Y.Tzeng, M. Yoshikawa, M. Murukawa
and A. Feldman, Elsevier, Amsterdam, 1991
30
Charged Cluster Model
  • Cluster formation during nucleation could also
    explain diamond formation.
  • Capillary pressures during cluster formation
    could result in high pressures stabilizing
    diamond over graphite.
  • Charge- most important factor in low pressure
    diamond synthesis.
  • Inhibit Brownian coagulation between clusters.
  • Form an electrical double layer at the cluster
    surface stabilizing dielectric diamond over
    conducting graphite clusters.

I.D. Jeon, C. J. Park, D. Y. Kim, N.M. Hwang, J.
Crys. Growth 223 (2001) 6-14
31
Thermodynamic Paradox
32
Nucleation of Clusters
33
Applications
  • Thermal dissipation in microelectronic packages
    high thermal conductivity.
  • Composite reinforcement extreme stiffness
    metal-matrix composites.

W. A. Yarbrough, J. Am. Ceram. Soc., 7512
3179-200 (1992) http//www.chm.bris.ac.uk/pt/diamo
nd/end.htm
34
Conclusions
  • Diamond is being widely researched because of
    its excellent properties and wide applications.
  • Plasma Chemical Vapor Deposition promises to be a
    commercial technique to grow industrial diamond.
  • Thermodynamic and kinetic studies are needed not
    only to improve diamond deposition but also to
    understand deposition of other metastable phases.

35
Reference List of Deposition Techniques
Low Pressure Diamond Synthesis Techiques and
Results, Peter K. Bachmann, Thin Film Diamond,
Ed. Lettington and Steeds, Pub. Chapman and Hill,
1994
36
Answers
  • Atomic hydrogen is thought to etch graphite and
    aid in diamond deposition. It satisfies the
    dangling bonds at the surface and stops the
    forming of double bonds which result in graphite.
  • Substrate is given a bias which accelerates
    charged particles like ions and electrons to
    produce reactive species and to increase
    nucleation density.

37
Discussion
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