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Title: Aurustussadestatud pinded / Vapour Deposited Coatings /

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(No Transcript)
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Aurustussadestatud pinded / Vapour Deposited
Coatings / ????????, ?????????? ???????
??????????? ? ??????? Loengukonspekt
Koostas Andrei Surženkov
3
Process definition.

vapour deposition (either physical or chemical)
is a coating
process, where coating material is condensed
in vacuum
at the substrate from vapour phase, forming a
thin
( 10 µm in the case of physical deposition and
1000 µm
in the case of chemical deposition) film.
Sometimes
the deposited material further reacts with
the gaseous substances to form a final compound
coating.
Generally as metals, as non-metals can be
deposited,
certain case depends on the applied metod.

4
Comparison of the coating processes.
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Development of vapour deposition technology.
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Process features.
Process type Material is introduced in
Thermochemical Solid / liquid / gaseous form
Chemical Solution form
Electrodeposition Solution form
Hot-dip Liquid melt
Cladding Solid form
Sol-gel Solution form
Thermal spraying Liquid form (except for cold spraying)
Vapor deposition Vapor (gaseous) form only

process is carried out in vacuum only
low productivity (several hours)
high price
but properties of the coatings (hardness, CoF,
etc.),
which can't be obtained by other methods.

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Process application fields.

electrical devices (LCDs, touch panels,
microelectronic
devices, solar cells, etc.)
magnetic devices (magnetic storage media)
optics (laser mirrors, antireflection coatings,
etc.)
tool industry (plastic molds, cutting tools,
blanking tools,
etc.)
aerospace devices (turbine blades, etc.)
decorative purposes (watches bands, etc.).

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Process limitations.

as the coatings are very thin, they can't
improve bulk
properties (tensile strength, fracture
toughness, etc.),
that is why good mechanical properties of the
substrate
are needed
as vapour deposition is mostly a
high-temperature process,
the ability of the substrate to withstand high
temperatures
is required
vapour deposition is a low production process
vapour deposition equipment is relatively
expensive
(tens of thousands euros).

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Part I. Physical Vapour Deposited (PVD) Coatings
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General features.

absence of chemical reaction during the
deposition process
relatively low temperatures (250 600 ºC) in
comparison
with chemical vapour deposition (CVD) processes
electric and magnetic field is applied
the variety of PVD technologies can be
classified into three
types evaporation, sputtering and arc
evaporation.

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1. Evaporation technology. 1.1 Thermal
evaporation.

in the simpliest variant the material of the
future coating
is resistance heated up to the evaporation
temperature,
and atoms of the material move towards the
substrate by a
straight trajectory and deposit on it, producing
a film.
in this case, only metals and metal alloys with
a low
melting points can be applied (for example, Zn,
Al, etc.)
such technology is used, for instance, for
metallisation
of fabrics.

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1. Evaporation technology. 1.2 Electron / laser
beam evaporation.

coating material is ablated by a focused
electron or laser beam at a
small spot at the target, made of the coating
material
the ablated atoms / atom layers travel through
the vacuum chamber
and deposit at the substrate, forming the
coating
in contrast with thermal evaporation, all metals
and metal alloys,
as well as ceramics and polymers, can be applied
as coating materials,
whereas the temperature of the process can be as
low as room temperature
the main disadvantage of this method is the high
price of the
equipment (electron beam gun or laser)
this method is applied, for example, for
magnetic data storage media
production, but for ultra-high rate
aluminization of fabrics and
transparent barrier coatings, as well.

Ablation removal of material by vaporization,
bypassing the liquid phase.
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Fig. 1. Pulsed laser deposition
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2. Sputtering. 2.1 General principles.

the process finds place in a low vacuum (0.0005
0.12 torr ?
0.07 16 Pa) with a presence of inert gas atoms
(usually Ar)
a high voltage (1 5 kV) is applied between the
target, made of
the sputtered material and the substrate to be
coated
due to high voltage, the inert gas atoms ionize,
forming
a plasma cloud near the surface of the sputtered
material
the ions become accelerated in the electric
field between the substrate
to be coated and the target of the sputtered
material
sputtered material is bombarded by accelerated
inert gas ions from
a plasma cloud, which is situated close to its
surface
as a result, atoms and atomic layers are
extracted from the sputtered
material, which are then directed to the
substrate to be coated
sputtered atoms form a coating.

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2. Sputtering. 2.2 Sputtering technologies.

direct current (DC) diode sputtering (direct
voltage is applied between
the target (cathode) and substrate (anode))
2. triode sputtering (heated filament is used as
a source
of secondary electrons to help ignite and
sustain the plasma)
radio frequency (rf) sputtering (an alternative
voltage at a high
frequency (13.6 MHz) is applied between the
target and the substrate)
magnetron sputtering (an electron trap is formed
by magnetic fields,
what make electrons, extracted during the
ionization and bombardment
process, to arrive back at the target).

Conductive materials only
All materials
If the sputtered and deposited material further
reacts with gases, intentially introduced to the
vacuum chamber after the deposition process, the
process is called reactive sputtering.
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2. Sputtering. 2.2 Sputtering technologies. 2.2.1
Magnetron sputtering.

distinct advantages of magnetron sputtering in
comparison with other
sputtering technologies are higher available
deposition rates (10 times
DC diode sputtering) and lower substrate
heating
both DC and AC current sources can be applied
for magnetron
sputtering (in other words, it can be eiter
direct current magnetron
sputtering or radio frequency magnetron
sputtering)
balanced and unbalanced magnetrons are used for
sputtering
magnetron sputtering is used in, for example,
semiconductive industry,
tool industry, etc..

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Fig. 2. Magnetron sputtering process.
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3. Arc evaporation. 3.1 General principle.

a high-current low-voltage strikes at the
surface of the target, made of
the material of the future coating
due to arc striking, a highly energetic emitting
area (so-called cathode
spot) appears at the surface of the target
the temperature inside the cathode spot is
extremely high (around
15000 ºC), causing the evaporation of the target
material with
the formation of a highly ionized quasi-plasma
cloud
this quasi-plasma cloud is directed towards the
substrate and
is deposited onto it, forming a film
if necessary, a reactive gas is introduced after
this, so that gas molecules
react with the deposited film, creating a
coating.

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Fig. 3. Schematic representation of the arc
evaporation process.
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3. Arc evaporation. 3.2 Technological features.

in comparison with other PVD technologies, arc
evaporation is
the most productive one in addition to that, it
casually allows to deposit
denser coatings with highest mechanical
properties
also arc evaporation provides the highest target
utilization among
the PVD technologies
the main disadvantage of arc evaporation is the
formation of
macrodroplets during the evaporation process,
what leads to higher
surface roughness of the coatings (highest among
all PVD technologies)
and lowers their adhesion to the substrate
one possible solution to the problem of
macrodroplets is seen in magnetic
filtering systems, however, their application
lowers the deposition range.

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4. Comparison of PVD technologies.
Process Deposition rate, µm/s Pressure, Pa Particle energy, eV Adhesion
Evaporation 0.05 25 10-3 lt 2
Sputtering 0.0001 0.7 10-1 ... 10 10 100
Arc evaporation 0.0003 1.85 0.5 10-2 1.510-2 10 100
Unbalanced magnetron sputtering
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Part II. Chemical Vapour Deposited (CVD) Coatings
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General features.

chemical reaction is applied to deposit a
coating
precursor is decomposed, and the decomposition
products
form a coating at the substrate
relatively high process temperature in
comparison with
the PVD processes (600 1100 ºC)
the three main CVD technologies are thermal CVD,
plasma-enhanced CVD (PECVD), and laser CVD
(LCVD).

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Fig. 4. Example scheme of a CVD process (TiC
deposition).
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Comparison of CVD processes.
Process name Precursor decomposition Decomposition process Process temperature
Thermal CVD In contact with hot substrate Dissociation
PECVD In contact with plasma Dissociation
LCVD In contact with laser heated substrate Photochemical process / pyrolysis
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III Applications.
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Cutting tools.