physical vapor deposition

1. Physical Vapor
Deposition
Asep Ridwan Setiawan
Prodi Teknik Material

2. Learning outcomes
learners will be able to:
• tell what is physical vapor deposition
• describe how to measure thin film deposition
thickness
• explain what thermal evaporation is used for
• describe the basic principles of e‐beam
evaporation.
• describe the basic principles of sputter evaporation

3. Physical Vapor Deposition (PVD)
Family of processes in which a material is converted to its
vapor phase in a vacuum chamber and condensed onto
substrate surface as a very thin film
• Coating materials: metals, alloys, ceramics and other
inorganic compounds, even some polymers
• Substrates: metals, glass, and plastics
• Very versatile coating technology
• Applicable to an almost unlimited combination of coatings and
substrate materials

4. Processing Steps in PVD
• All physical vapor deposition processes consist of
the following steps:
1. Synthesis of coating vapor
2. Vapor transport to substrate
3. Condensation of vapors onto substrate surface
• These steps are generally carried out in a vacuum
chamber, so evacuation of the chamber must
precede PVD process

5. Physical Vapor Deposition
• Setup for vacuum evaporation, one form of PVD, showing
vacuum chamber and other process components

6. Chemical Vapor Deposition (CVD)
Involves chemical reactions between a mixture of gases and the heated
substrate, depositing a solid film on the substrate
• Reaction product nucleates and grows on substrate surface to form the
coating
• Most CVD reactions require heat

7. Thin film Vacuum deposition
• Use vacuum systems to deposit
thin layers of materials (metals
/insulators) onto substrates.
• The thicknesses of vacuum‐
deposited layers are very thin, 5‐
250 nm.
• The three most common thin
film vacuum deposition
techniques are:
• thermal evaporation,
• electron beam evaporation
• sputtering.
10‐6 torr

8. Thin film Vacuum Deposition
Why vacuum :
• Vacuum systems are used to deposit thin layers of ultra
high purity materials onto samples and substrates
because air molecules that are present during
deposition will become impurities in our deposited
films.
• So we remove the air from the chamber in which we
are doing the film deposition using vacuum pumps.
• Vacuum deposition is any process in which a thin layer
of material is deposited onto a surface in a high vacuum
environment.

9. • The atoms come from an UHP material that we call the
source.
• Atoms from this source travel through the vacuum in
the vacuum chamber and are deposited onto the
surface of our substrate.
• This process is called physical vapor deposition or PVD,
and requires vacuum environments with pressures on
the order of 10‐6 torr = 1.3 x 10‐4 pascals.
• We also require high purity source materials, typically
99.999% pure, >5N.
• These high purity materials include metals such as gold
or aluminum, or an insulator or dielectric, such as
silicon dioxide or silicon nitride.
Thin film Vacuum Deposition

10. Thermal evaporation
• Thermal evaporation uses heat to evaporate the
ultra high purity source so that it goes from solid to
liquid to gas.
• The gas atoms travel through the vacuum in the
vacuum chamber, and when these atoms hit the
substrate, they condense and form a thin film on
the surface of the substrate.
• Metals and dielectrics can both be deposited using
this vacuum thermal evaporation technique.

12. Process characteristics
• Thermal evaporation is typically used most for
metals. Tm metal low, and produce very steady
deposition rates.
• To conduct a thermal evaporation, a small amount
of our source material is placed into a container
called a boat.
• The boat is heated by passing a large electrical
current through it to heat it up in a process called
resistive heating.
• The boats that we use are typically tungsten

13. Boat and Heating

14. Why tungsten boat
• If we want to melt a metal, its container, the boat,
must remain intact during heating.
• It shouldn't melt along with the source.
• We need to conduct a large amount of current
through this boat as well.
• Tungsten boats was used because tungsten has a
higher melting point than source metals, and it's
very electrically conductive, allowing resistive
heating to occur.

15. Mechanism
• The tungsten boat is clamped between two electrodes.
• An electric current as high as several hundred amps
passes through that tungsten boat, which undergoes
resistive heating.
• Just like an incandescent light bulb filament, it heats up
and glows.
• As the boat heats up, the metal source material in the
boat melts, and then evaporates.
• These evaporated metal atoms travel through the
vacuum chamber, strike the surface of the substrate,
and condense, forming our thin layer of the source
material on our substrate.

16. Thickness monitoring
• When should we stop depositing our source
material onto the substrate?
• We typically have a target thin film thickness for
each of our processes that we conduct.
• So that means that we want to monitor the
thickness of our deposited film on that substrate in
real time during the deposition.
• How to do this?

18. • To monitor the film thickness, we place a crystal
sensor in the vacuum chamber so that the source
material is deposited onto the sensor at the same
rate as onto our substrate.
• This crystal sensor vibrates.
• The vibration frequency changes as the film is
deposited onto the crystal, enabling us the sense
this change in vibration and calculate that
deposited film thickness as the deposition is taking
place in real time.
• When the desired thickness is reached, we stop the
flow of electrical current through the boat, which
stops the heating of the source and halts the
deposition.

19. Electron beam evaporation
• This technique is similar to thermal evaporation but
the material is heated up a little bit differently.
• In thermal evaporation, electrical current is used to
heat a boat so that the source material in the boat
melts and evaporates.
• In electron beam evaporation, a stream of
electrons or an electron beam is aimed at a high
purity source material that we want to evaporate.

20. E‐beam
• This beam of electrons heats the material to its
melting point and then evaporates the source
material.
• This electron beam is well confined.
• The advantages of e‐beam evaporation is that we
can rotate different source materials into the path
of that electron beam.
• So that we can deposit multiple material
sequentially without opening the vacuum system
which is also called a breaking vacuum or venting.

22. Component e‐beam evaporator
1. The electron source or electron gun which
produces the beam of electrons.
2. The crucible is where the source material that we
want to evaporate is contained. This is like the
boat for thermal evaporation.

24. Electron gun
• Contained within that electron gun is a filament, the
source of the electrons.
• And magnets for focusing that electron beam and
directing it towards the crucible.
• The electron beam is generated by heating the metal
filament to the point that it glows bright, about 2,500
degrees centigrade.
• At this temperature, electrons are so energetic that
some of them leave the surface of the filament.
• These electrons are then accelerated toward the source
material using a high voltage electrode.

25. • And a set of magnets steer and focus the beam
onto the source material to be evaporated.
• The power level can be to control by adjusting the
filament current.
• This is very important, since some materials require
lower power to melt and can burn at higher power,
while others require higher power just to melt.

26. Crucible
• The source material is contained in a small crucible.
• Depending upon the material being evaporated,
the crucible may be made of tungsten, copper, or
even a ceramic for very high temperature
deposition.
• Because that electron beam is well confined in
space, only a small area of the source material is
heated.
• This means that there's room for multiple small
source materials in the vacuum chamber.

27. Multi deposition system
• Systems that hold four materials are very common
and they are called four pocket hearths.
• There are four crucibles that fit into the hearth, and
each crucible can hold a different source material.
• So that you can have up to four layers of different
materials deposited without breaking vacuum.
• The hearth is a rotated holder of copper which is
water‐cooled.

28. Multi deposition system
• The water cooling prevents the crucible material
from melting and mixing with the source material
or with the hearth itself.
• In this configuration, several different materials can
be deposited or sequential back and forth can also
be deposited of multi‐layer materials.

29. Sputter deposition (sputtering)
• Sputtering is an entirely different process compared to
the other types of thin film deposition.
• Sputtering uses energized atoms that hit the source
which are the blue atoms.
• The source material is in the form of a flat plate which
we call a target.
• Those energetic atoms hit the target and propel source
material atoms off of the target and into the vacuum
system. These are the yellow atoms.
• Some of these source atoms, hit the target up here and
become the thin film.

30. 1
2

31. 3

32. Plasma
• The energetic atoms used in sputter deposition are
created in a plasma.
• You've probably heard of those three common
states of matter, liquid, solid, and gas.
• Well, plasma is a fourth state of matter. But don't
let that scare you.
• We use plasmas in our everyday lives. One common
use of plasma is in fluorescent lights.
• The plasma in a light bulb is used to generate light.

33. States of matter

34. Sputter system
• In our sputter system we will use in argon plasma
which has energetic argon atoms that hit the target
and remove source material from that target.
• Sputtering is performed in a vacuum system.
• After load the target, and substrate, we evacuate
the chamber using vacuum pumps to about 5 x 10‐6
torr.
• Then we leak a small amount of argon gas into that
vacuum chamber.
• Argon will be the gas that forms the plasma.

35. Sputtering mechanism
• Argon is used because it's inert, it's not reactive,
and will not result in unwanted chemical reactions
during our process.
• When the argon gas is in the chamber, we apply a
high negative electrical voltage to the target.
• This high voltage is strong enough to strip an
electron from the argon atoms close to the target.
• That means that the argon atoms are now ionized
and each argon atom has a positive charge.

36. 1
2
3
4

37. Sputtering mechanism
• These positive argon atoms are attracted to that
negatively charged target and they have enough speed
to physically knock off individual atoms of the target
material.
• This is the sputtering process.
• These sputtered atoms fly off in all directions including
toward the substrate that we want to coat.
• The process continues until the substrate is coated with
the desired thickness of material.
• Then we turn the voltage off on the target and the
sputtering stops.

38. Comparison of process