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Aurustussadestatud pinded / Vapour Deposited Coatings /
Покрытия, полученные методом конденсации в вакууме
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Loengukonspekt
Koostas: Andrei Surženkov
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.

Comparison of the coating processes.
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
processspraying
is carried
Liquid
form (except for cold
out in vacuum
only;
spraying)
 low productivity (several hours);
deposition
Vapor (gaseous) form only
Vapor
high price;
 … but properties of the coatings (hardness, CoF, etc.),
which can't be obtained by other methods.

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.).

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).

Part I. Physical Vapour Deposited (PVD)
Coatings
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.

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.

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.
Fig. 1. Pulsed laser deposition
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.
All materials
Conductive materials
only
2. Sputtering.
2.2 Sputtering technologies.
1. direct current (DC) diode sputtering (direct voltage is applied between
2. 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);
1. radio frequency (rf) sputtering (an alternative voltage at a high
frequency (~13.6 MHz) is applied between the target and the substrate);
1. 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).
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.
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..

Fig. 2. Magnetron sputtering process.
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.
Fig. 3. Schematic representation of the arc evaporation process.
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.

4. Comparison of PVD technologies.
Process
Deposition
rate, μm/s
Pressure,
Pa
Particle
energy, eV
Adhesion
Evaporation
0.05 … 25
10-3
<2
+
Sputtering*
0.0001 …
0.7
10-1 ... 10
10 … 100
++
Arc
evaporation
0.0003 …
1.85
0.5 ×10-2-2
… 1.5×10
10 … 100
+++
* Unbalanced magnetron sputtering
Part II. Chemical Vapour Deposited
(CVD) Coatings
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).

Fig. 4. Example scheme of a CVD process (TiC deposition).
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
+
III Applications.
Cutting tools.
TiN, TiAlN, AlTiN, CROMVIc® (Platit AG), ALCRONA
(Balzers), etc.

Fig. 5. Comparison of uncoated and coated drills.
Punching and forging tools.

CrN, TiAlCN, ALCRINVIc® (Platit AG), etc.
Fig. 6. Comparison of uncoated and coated forging tools.
Injection molding.

TiCN, CrN, nACRo® (Platit AG, etc.)
1
Fig. 8. Comparison of nitrided and coated molds.
Diamond-like carbon (DLC) CVD coating.
Low-friction hard chemically inert coating, used for coating
tools, machine parts and for decorative purposes.

References.
Coatings Technology Handbook. Ed. By A. A. Traction.
Taylor & Francis Group, Boca Raton, 2006.
 Modern Surface Technology. Ed. By F.-W. Bach, A. Laarmann,
T. Wenz. Wiley-VCH Verlag GmbH & Co. KgaA, Weinheim,
2006.
th edition. Platit AG, 2011.
 Platit Compendium 2012, 49
 C. Donnet, A. Erdemir. Historical Developments and New Trends
in Tribological and Solid Lubrication Coatings. Surf. Coat. Tech.,
180 – 181, 2004, 76 – 84.
 Loengukonspekt Surface Engineering (1). Vapor Deposition.
Koostajad: Priit Kulu, Eron Adoberg.

Smooth deposition!