Chemical Vapor Deposition (CVD)

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Chemical Vapor Deposition (CVD)

• NANO54
• Foothill College

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Overview

• What is CVD?
• Types of CVD
• MO-CVD, PE-CVD, etc
• CVD process / applications
• PVD process / applications
• CVD vs. PVD
• Plasma Polymerization

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Family of CVD Technologies
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What is CVD?

• Chemical vapor deposition (CVD) is a chemical
  process used to produce high-purity,
  high-performance solid materials. The process is
  often used in the semiconductor industry to
  produce thin films. In a typical CVD process, the
  wafer (substrate) is exposed to one or more
  volatile precursors, which react and/or decompose
  on the substrate surface to produce the desired
  deposit. Frequently, volatile by-products are
  also produced, which are removed by gas flow
  through the reaction chamber.

http//en.wikipedia.org/wiki/Chemical_vapor_deposi
tion
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CVD Process Applications

• Microfabrication processes widely use CVD to
  deposit materials in various forms, including
  monocrystalline, polycrystalline, amorphous, and
  epitaxial. These materials include silicon,
  carbon fiber, carbon nanofibers, filaments,
  carbon nanotubes, SiO2, silicon-germanium,
  tungsten, silicon carbide, silicon nitride,
  silicon oxynitride, titanium nitride, and various
  high-k dielectrics. The CVD process is also used
  to produce synthetic diamonds.

http//en.wikipedia.org/wiki/Chemical_vapor_deposi
tion
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What is CVD Process?

• Chemical Vapor Deposition is the formation of a
  non-volatile solid film on a substrate by the
  reaction of vapor phase chemicals (reactants)
  that contain the required constituents.
• The reactant gases are introduced into a reaction
  chamber and are decomposed and reacted at a
  heated surface to form the thin film.

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Chemical Vapor Deposition

• CVD gt Chemical Vapor Deposition
• PE-CVD gt Plasma Enhanced CVD
• MO-CVD gt Metal Organic CVD
• Atmospheric pressure CVD (AP-CVD)
• Low-pressure CVD (LP-CVD)
• Ultrahigh vacuum CVD (UHV-CVD)
• Aerosol assisted CVD (AA-CVD)
• Direct liquid injection CVD (DLICVD)

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Plasma Enhanced CVD

• Microwave plasma-assisted CVD (MP-CVD)
• Plasma-Enhanced CVD (PE-CVD)
• Remote plasma-enhanced CVD (RPE-CVD)

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Other Types of Chemical Vapor Deposition

• Atomic layer CVD (ALCVD)
• Combustion Chemical Vapor Deposition (CCVD)
• Hot wire CVD (HWCVD)
• Metal organic chemical vapor deposition (MOCVD)
• Hybrid Physical-Chemical Vapor Deposition (HPCVD)
• Rapid thermal CVD (RTCVD)
• Vapor phase epitaxy (VPE)

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Applications of CVD
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CVD Reactors
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Thermal CVD Reactor
Chemical Vapor Deposition Apparatus http//en.wiki
pedia.org/wiki/Chemical_vapor_deposition
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Chemical Vapor Deposition
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CVD Growth Model
The flow of reactants F is F ? DG ?-1
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Plasma Enhanced (PE)CVD
As the thermal budget gets more constrained while
more layers are added for multi-layer
metallization, we want to come down with the
temperature for the oxide ( or other) CVD
processes. One way for doing this is to supply
the necessary energy for the chemical reaction by
ionizing the gas, thus forming a plasma.
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PVD Apparatus
Physical Vapor Deposition Apparatus http//en.wiki
pedia.org/wiki/Physical_vapor_deposition
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PVD Film Properties

• Benefits

• Trade-offs

• Low substrate temperature
• Conformal film
• Relatively fast process
• Comparatively low cost

• Not stoichiometric film
• By-products incorporated
• Outgassing
• Cracking
• Peeling

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CVD vs. PVD

• Chemical Vapor Deposition (CVD) relies on
  chemical reactions between reactants in the gas
  phase and/or on the substrate surface.
• Physical Vapor Deposition (PVD) is a thermal
  evaporation driven or energy driven process.

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(PVD) Apparatus
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Silicon CVD Epitaxy

• When SiH4 gas is used in a CVD reactor, a Si
  layer is deposited on the wafer surface. The size
  of the crystallites depends on the deposition
  temperature.
• At high enough temperature, the ad-atoms have
  enough kinetic energy to move on the surface and
  align themselves with the underlying Si.
• This is an epitaxial layer, and the process is
  called Epitaxy instead of CVD.
• At lower deposition temperatures, the layer is
  poly-crystalline Si (consisting of small
  crystallites)

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Silicon Epitaxy Process
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CVD Used in Semiconductors
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Silicon Oxide CVD Process
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MO-CVD

• A technique for growing thin layers of compound
  semiconductors in which metal organic compounds,
  having the formula MRx, where M is a group III
  metal and R is an organic radical, are decomposed
  near the surface of a heated substrate wafer, in
  the presence of a hydride of a group V element.
  Abbreviated MOCVD.

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Figure 1 Fabrication of (a) IIIV-OI on Si
substrate by DWB and (b) InGaAs-OI MOSFETs with
metal S/D structure using NiInGaAs alloy.

• A first demonstration of a new metal source/drain
  technology for extremely thin body (ETB) indium
  gallium arsenide (InGaAs) transistor channels on
  insulator (OI) with silicon substrates has been
  reported by University of Tokyo, National
  Institute of Advanced Industrial Science and
  Technology and Sumitomo Chemical Co Ltd
  SangHyeon Kim et al, Appl. Phys. Express, vol4,
  p114201, 2011.

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MO-CVD TMG Arsine gt GaAs
http//www.hlphys.jku.at/fkphys/epitaxy/mocvd.html
The various techniques of growing epitaxial
layers from the vapor phase can be divided
roughly into two categories depending on whether
the species are transported physically or
chemically from the source to the substrate. In
the physical transport techniques (Physical Vapor
Deposition - PVD), the compound to be grown or
its constituents are evaporated and subsequently
transported through the relevant reactor toward
the substrate. In the chemical transport
techniques (Chemical Vapor Deposition - CVD),
volatile species containing the constituent
elements of the layer to be grown are produced
first in- or outside the reactor and transported
as streams of vapor towards the reaction zone
near the substrate. These gaseous species
subsequently undergo chemical reactions or
dissociate thermally to form the reactants which
participate in the growth of the film. The
practical demand to decrease the growth
temperature generated an intensive development
trend of CVD processes based on metal organic
compounds, decomposing at lower temperatures.
This process is referred to as Metal Organic
Chemical Vapor Deposition (MOCVD) or
Organometallic Vapor Phase Epitaxy. The classical
example is the growth of GaAs from
Trimethylgallium (TMG) and Arsine (AsH3). In our
laboratory we apply this technique to grow GaN
from TMG and Ammonia. However, this technique is
based on a very precise control of the gas flow
as can be estimated from the look into the gas
mixing cabinet.
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Planetary MOCVD reactor in an industrial setup
(Photo courtesy of Aixtron)

• http//www.hlphys.jku.at/fkphys/epitaxy/mocvd.html

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Metal Organic Vapor Phase Epitaxy MO-VPE

• Metal organic vapor phase epitaxy (MOVPE), also
  known as organometallic vapor phase epitaxy
  (OMVPE) or metal organic chemical vapor
  deposition (MOCVD), is a chemical vapour
  deposition method of epitaxial growth of
  materials, especially compound semiconductors,
  from the surface reaction of organic compounds or
  metalorganics and metal hydrides containing the
  required chemical elements. For example, indium
  phosphide could be grown in a reactor on a
  substrate by introducing Trimethylindium
  ((CH3)3In) and phosphine (PH3). Formation of the
  epitaxial layer occurs by final pyrolysis of the
  constituent chemicals at the substrate surface.
  In contrast to molecular beam epitaxy (MBE) the
  growth of crystals is by chemical reaction and
  not physical deposition.

http//en.wikipedia.org/wiki/Metalorganic_vapour_p
hase_epitaxy
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MO-CVD Apparatus
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PE-CVD

• Plasma-enhanced chemical vapor deposition
  (PECVD) is a process used to deposit thin films
  from a gas state (vapor) to a solid state on a
  substrate. Chemical reactions are involved in the
  process, which occur after creation of a plasma
  of the reacting gases. The plasma is generally
  created by RF (AC) frequency or DC discharge
  between two electrodes, the space between which
  is filled with the reacting gases

http//en.wikipedia.org/wiki/Plasma-enhanced_chemi
cal_vapor_deposition
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PE-CVD Apparatus

• Thermal - chemical vapor deposition
• A thermal-CVD system was built for carbon
  nanotubes production via gas phase or on
  substrate surface. The sketch of thermal-CVD
  system consists of quartz tube furnace which can
  operate till 1200 degree centigrade. The sketch
  of our equipment is shown in figure 1. Main
  advantages of a thermal-CVD are the absolute
  ability for mass production of nanotubes material
  and the controllable growth of carbon nanotubes
  at a specific location on a substrate for
  incorporation in electronic device.
• Plasma Enhanced - chemical vapor deposition
• A controllable method for carbon nanotubes
  production is plasma enhanced-CVD. Such a system
  is often used to grow free standing vertically
  aligned MWCNT. The set-up which our laboratory is
  equipped with is a glow discharged type. Briefly,
  two electrodes are placed in a stainless-steel
  chamber. The grounded cathode plays the role of a
  substrate holder and Ohmic heater. On the anode
  is applied aprox.400V.

http//www.fy.chalmers.se/atom/research/nanotubes/
experimental.xml
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Low Pressure RF Plasma for PECVD of TiO2 on
Plastics

• http//www.ipe.ethz.ch/laboratories/ltr/research/i
  ndex_EN

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Plasma Polymerization

• Plasma polymerization deposits molecules onto a
  surface as a conformal coating
• The molecules deposited are part of a network,
  often highly cross-linked
• Chemistry is tuned by the gas composition
  mixture, flow rate, and energy conditions
• A variety of very novel molecular networks can be
  formed in a straightforward manner

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Plasma Deposition

• Plasma polymerization (or glow discharge
  polymerization) uses plasma sources to generate
  a gas discharge that provides energy to activate
  or fragment gaseous or liquid monomer, often
  containing a vinyl group, in order to
  initiate polymerization. Polymers formed from
  this technique are generally highly branched and
  highly cross-linked, and adhere to solid surfaces
  well. The biggest advantage to this process is
  that polymers can be directly attached to a
  desired surface while the chains are growing,
  which reduces steps necessary for
  other coating processes such as grafting. This is
  very useful for pinhole-free coatings of 100
  picometers to 1 micrometer thickness with
  insoluble polymers.

http//en.wikipedia.org/wiki/Plasma_polymerization
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Plasma Polymerization
Schematic representation of bicyclic step-growth
mechanism of plasma polymerization
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Plasma Polymerization
Hypothesized model of plasma-polymerized ethylene
film (Wikipedia)
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Plasma Polymerization Mechanism and Species

• Plasma contains many species such as ions, free
  radicals and electrons, so it is important to
  look at what contributes to the polymerization
  process most. The first suggested process by
  Westwood et al. was that of a cationic
  polymerization, since in a direct current system
  polymerization occurs mainly on the cathode.
  However, more investigation has led to the belief
  that the mechanism is more of a radical
  polymerization process, since radicals tend to be
  trapped in the films, and termination can be
  overcome by reinitiation of oligomers. Other
  kinetic studies also support this theory. In
  polymerization, both gas phase and surface
  reactions occur, but mechanism differs between
  high and low frequencies. At high frequencies it
  occurs in radical intermediates, whereas at low
  frequencies polymerization happens mainly on
  surfaces.

http//en.wikipedia.org/wiki/Plasma_polymerization
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Summary

• CVD is a family of techniques
• CVD, PVD, PE-CVD, MO-CVD
• Chemistry in the vapor phase
• Surface reactions on the substrate
• Plasma can enhance reaction conditions
• Used principally in semiconductor industry

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References

• Microelectronics Processing Course - J. Salzman -
  Jan. 2002 . Microelectronics Processing Chemical
  Vapor Deposition
• Microelectronics Processing Course - J. Salzman
  Fall 2006 . Microelectronics Processing . Ion
  Implantation
• Wikipedia, CVD, PVD, PE-CVD, MO-CVD
• American Vacuum Society (AVS)