PHYSICAL VAPOUR DEPOSITION CHEMICAL VAPOUR DEPOSITION ATOMIC FORCE MICROSCOPY

1. 21PYB102J
SEMICONDUCTOR PHYSICS AND COMPUTATIONAL
METHODS
MODULE 5
PVD,CVD AND AFM
BY
Dr.T.BEENA
ASSISTANT PROFESSOR
DEPARTMENT OF PHYSICS
SRM IST, RAMAPURAM, CHENNAI – 600089

2. Chemical Vapour Deposition,
Physical Vapour Deposition,
ATOMIC FORCE MICROSCOPY
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3. Chemical Vapour Deposition
(CVD)
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4. Chemical Vapour Deposition
depositing a solid material from a
gaseous phase.
CVD to deposit materials in various forms, including:
monocrystalline, polycrystalline, amorphous.
These materials include: silicon, carbon fiber, carbon
nanofibers, filaments, carbon nanotubes, SiO2, silicon-
germanium, tungsten, silicon carbide, silicon nitride,
silicon oxynitride and titanium nitride.
GAS form
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Precursors GAS form

5. PRINCIPLE
 Material is heated to form a gas and then it is
allowed to deposit as a solid, to form nano
powders(new product) which differ from the
raw material or precursors.
 Control of thermodynamics and kinetics
through temperature, pressure, and
concentrations yields the desired deposit.
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6.  Metal deposition
metal halide (g) → METAL(s) +
byproduct (g)
 Ceramic deposition
metal halide (g) +
oxygen/carbon/nitrogen/boron source (g)
→ CERAMIC(s) + byproduct (g)
g- gas; s-solid
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7. UNIT IV LECTURE 3 7
CVD REACTION

8. Steps:
a predefined mix of reactant gases and inert gases
are introduced at a specified flow rate into the
reaction chamber;
the gas species move to the substrate;
the reactants get adsorbed on the surface of the
heated substrate;
the reactants undergo chemical reactions with the
substrate to form the film; and
the gaseous by-products of the reactions are
desorbed and evacuated from the reaction
chamber.
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9. During the process of chemical vapor deposition, the
reactant gases not only react with the substrate material at
the wafer surface (or very close to it), but also in gas phase
in the reactor's atmosphere.
Reactions that take place at the substrate surface are known
as heterogeneous reactions, and are selectively occurring
on the heated surface of the wafer where they create good-
quality films.
Reactions that take place in the gas phases are known as
homogeneous reactions.
Homogeneous reactions form gas phase aggregates of the
depositing material, which adhere to the surface poorly and
at the same time form low-density films with lots of
defects.
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10. A typical CVD system consists of the following parts:
sources of and feed lines for gases;
mass flow controllers for metering the gases into the
system;
a reaction chamber or reactor;
a system for heating up the wafer on which the film is to
be deposited; and
temperature sensors.
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11. Types of CVD
According to the heating element used to heat the
substrate
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Cold wall Hot wall

12. For instance, a reactor is said to be 'hot-wall' if it uses a
heating system that heats up not only the wafer, but the walls
of the reactor itself, an example of which is radiant heating
from resistance-heated coils.
'Cold-wall' reactors use heating systems that minimize the
heating up of the reactor walls while the wafer is being
heated up, an example of which is heating via IR lamps
inside the reactor.
In hot-wall reactors, films are deposited on the walls in
much the same way as they are deposited on wafers.
so this type of reactor requires frequent wall cleaning.
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13. According to the range of operating pressure
Atmospheric pressure CVD (APCVD) reactors operate
at atmospheric pressure, and are therefore the
simplest in design.
Low-pressure CVD (LPCVD) reactors operate at
medium vacuum (30-250 Pa) and higher temperature
than APCVD reactors.
Plasma Enhanced CVD (PECVD) reactors also operate
under low pressure, but do not depend completely on
thermal energy to accelerate the reaction processes.
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14. The glow discharge used by a PECVD reactor is created by
applying an RF field to a low-pressure gas, creating free
electrons within the discharge region.
The electrons are sufficiently energized by the electric field
that gas-phase dissociation and ionization of the reactant
gases occur when the free electrons collide with them.
Energetic species are then adsorbed on the film surface,
where they are subjected to ion and electron bombardment,
rearrangements, reactions with other species, new bond
formation, and film formation and growth.
Table compares the characteristics of typical APCVD,
LPCVD, and PECVD reactors.
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15. CVD Process Advantages Disadvantages Applications
APCVD
Simple,
Fast Deposition,
Low Temperature
Poor Step Coverage,
Contamination
Low-temperature
Oxides
LPCVD
Excellent Purity,
Excellent
Uniformity,
Good Step
Coverage,
Large Wafer
Capacity
High Temperature,
Slow Deposition
High-temperature
Oxides, Silicon
Nitride, Poly-Si
PECVD
Low Temperature,
Good Step
Coverage
Chemical and
Particle
Contamination
Low-temperature
Insulators over
Metals, Nitride
Passivation
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APCVD, LPCVD, and PECVD Comparison

16. CVD Coatings
containing
On to various substrates Properties
Chromium Solid solution alloys
(i) with Iron, Nickel and Cobalt
(ii) on Iron as carbides and nitrides
(i) Corrosion / oxidation
resistance
(ii) Wear / corrosion
resistance
Aluminium As Aluminides with Iron, Cobalt and Nickel High temperature oxidation
resistance
Boron As Borides with Iron, Cobalt and Nickel Wear / erosion resistance
Silicon As Silicides with Iron, Tungsten and
Molybdenum
High temperature oxidation
resistance
Titanium As Carbides, nitrides and carbonitride on
ferrous and non-ferrous alloys
Wear resistance
Manganese Solid solution alloys on carbon steels Wear resistance
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CVD Coatings and their properties.

17. Advantages of CVD
 Can be used for a wide range of metals and ceramics
 Can be used for coatings or freestanding structures
 Is self-cleaning—extremely high purity deposits (>99.995% purity)
 Conforms homogeneously to contours of substrate surface
 Has controllable thickness and morphology
 Forms alloys
 Can simultaneously coat multiple components
 Coats powders
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18. Applications
 Aircraft
 land gas turbine blades,
 Surface modification to prevent or promote adhesion
 Photoresist adhesion for semiconductor wafers
Silane/substrate adhesion for microarrays (DNA, gene,
protein, antibody, tissue)
 MEMS coating to reduce stiction
 Promote biocompatibility between natural and synthetic
materials Copper capping Anti-corrosive coating
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19. Physical Vapour Deposition
1. alternative process to electroplating
2. The process is similar to chemical vapour deposition
(CVD) except that the raw materials/precursors, i.e. the
material that is going to be deposited starts out in solid
form, whereas in CVD, the precursors are introduced to
the reaction chamber in the gaseous state.
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Precursors SOLID form

20. UNIT IV LECTURE 3 20
Working Concept
PVD processes are carried out under vacuum conditions. The process
involved four steps:
1. Evaporation
2. Transportation
3. Reaction
4. Deposition

21. Evaporation
During this stage, a target, consisting of the material to be deposited is
bombarded by a high energy source such as a beam of electrons or ions. This
dislodges atoms from the surface of the target, ‘vaporising’ them.
Transport
This process simply consists of the movement of ‘vaporised’ atoms from the
target to the substrate to be coated and will generally be a straight line affair.
Reaction
In some cases coatings will consist of metal oxides, nitrides, carbides and
other such materials.
In these cases, the target will consist of the metal.
The atoms of metal will then react with the appropriate gas during the
transport stage.
For the above examples, the reactive gases may be oxygen, nitrogen and
methane.
In instances where the coating consists of the target material alone, this step
would not be part of the process.
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22. Deposition
This is the process of coating build up on the substrate surface.
Depending on the actual process, some reactions between target materials and the
reactive gases may also take place at the substrate surface simultaneously with the
deposition process.
Fig. shows a schematic diagram of the principles behind one common PVD method.
The component that is to be coated is placed in a vacuum chamber. The coating
material is evaporated by intense heat from, for example, a tungsten filament.
An alternative method is to evaporate the coating material by a complex ion
bombardment technique.
The coating is then formed by atoms of the coating material being deposited onto the
surface of the component being treated.
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23. UNIT IV LECTURE 3 23
The vacuum evaporation PVD process

24. Evaporative Deposition: In which the material to be deposited is heated to a high vapor
pressure by electrically resistive heating in "high" vacuum.
Electron Beam Physical Vapor Deposition: In which the material to be deposited is heated
to a high vapor pressure by electron bombardment in "high" vacuum.
Sputter Deposition: In which a glow plasma discharge (usually localized around the
"target" by a magnet) bombards the material sputtering some away as a vapor
.
Cathodic Arc Deposition: In which a high power arc directed at the target material blasts
away some into a vapor.
Pulsed Laser Deposition: In which a high power laser ablates material from the target into
a vapor.
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25. Method Merits Demerits
E-Beam Evaporation
1. high temp
materials
2. good for liftoff
3. highest purity
1. alloys difficult
2. poor step coverage
Filament Evaporation
1. simple to
implement
2. good for liftoff
1. limited source material (no high temp)
2. alloys difficult
3. poor step coverage
Sputter Deposition
1. better step
coverage
2. alloys
3. high temp
materials
4. less radiation
damage
1. possible grainy films
2. porous films
3. plasma damage/contamination
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Summary of Merits and Demerits of evaporation methods

26. Importance of PVD Coatings
 Improved hardness and wear resistance
 Reduced friction
 Improved oxidation resistance
 longer component life.
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27. Advantages
 Materials can be deposited with improved
properties compared to the substrate material
 Almost any type of inorganic material can be
used as well as some kinds of organic materials
 The process is more environmentally friendly
than processes such as electroplating
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28. Disadvantages
 It is a line of sight technique meaning that it is
extremely difficult to coat undercuts and similar
surface features.
 High capital cost.
 Some processes operate at high vacuums and
temperatures requiring skilled operators.
 Processes requiring large amounts of heat -
require appropriate cooling systems.
 The rate of coating deposition is usually quite
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29. Applications
PVD coatings are generally used to improve
hardness, wear resistance and oxidation resistance.
 Aerospace
 Automotive
 Surgical/Medical
 Dies and moulds for all manner of material
processing
 Cutting tools
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30. UNIT IV LECTURE 6 30

31.  Scanning probe microscopy (SPM) is a new branch
of microscopy that forms images of surfaces using a
physical probe that scans the specimen.
 An image of the surface is obtained by mechanically
moving the probe in a raster scan of the specimen, line
by line, and recording the probe-surface interaction as
a function of position.
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32. Some important types of scanning probe
microscopy
AFM, atomic force microscopy
EFM, electrostatic force microscope
FMM, force modulation microscopy
MFM, magnetic force microscopy
STM, scanning tunneling microscopy
SVM, scanning voltage microscopy
SHPM, scanning Hall probe microscopy
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33. Atomic Force Microscope (AFM)
Similar to other scanning probe microscopes, the AFM
raster scans a sharp probe over the surface of a
sample and measures the changes in force
between the probe tip and the sample.
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34. Working Concept
The physical parameter probe is a force resulting from different
interactions.
The origin of these interactions can be ionic repulsion, van der
Waals, capillary, electrostatic and magnetic forces, or elastic and
plastic deformations.
Thus, an AFM image is generated by recording the force
changes as the probe (or sample) is scanned in the x, y and z
directions.
The sample is mounted on a piezoelectric scanner, which ensures
three-dimensional positioning with high resolution.
The force is monitored by attaching the probe to a pliable
cantilever, which acts as a spring, and measuring the bending or
"deflection" of the cantilever.
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35. The larger the cantilever deflection, the higher the force that
will be experienced by the probe.
Most instruments today use an optical method to measure
the cantilever deflection with high resolution; a laser beam is
focused on the free end of the cantilever, and the position of
the reflected beam is detected by a photodiode.
AFM cantilevers and probes are typically made of silicon or
silicon nitride( nano)by micro fabrication techniques.
Stress directly proportional to strain
Force (deflection)directly proportional to height
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36. UNIT IV LECTURE 6 36
Working concept of AFM

37. Basic set-up of an AFM
The ability of an AFM to achieve near atomic scale
resolution depends on the three essential
components:
(1) a cantilever with a sharp tip,
(2) a scanner that controls the x-y-z position, and
(3) the feedback control and loop.
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38.  Cantiliever with a sharp tip. The stiffness of the
cantilever needs to be less the effective spring constant
holding atoms together, which is on the order of 1 - 10
nN/nm.
 The tip should have a radius of curvature less than 20-50
nm (smaller is better) a cone angle between 10-20 degrees.
 2. Scanner. The movement of the tip or sample in the x, y,
and z-directions is controlled by a piezo-electric tube
scanner.
 For typical AFM scanners, the maximum ranges for are 80
mm x 80 mm in the x-y plane and 5 mm for the z-direction.
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39. 3. Feedback control.
The forces that are exerted between the tip and the
sample are measured by the amount of bending (or
deflection) of the cantilever.
By calculating the difference signal in the
photodiode, the amount of deflection(force) can be
correlated with a height .
Because the cantilever obeys Hooke's Law for small
displacements, the interaction force between the
tip and the sample can be determined.
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40. A summary of the different modes of operation is found below.
Mode of Operation Force of Interaction
Contact mode strong (repulsive) - constant force or constant distance
Non-contact mode weak (attractive) - vibrating probe
Tapping mode strong (repulsive) - vibrating probe
Lateral force mode frictional forces exert a torque on the scanning
cantilever
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41. Applications
three-dimensional topographic information of insulating
and conducting structures with lateral resolution down to 1.5
nm and vertical resolution down to 0.05 nm.
These samples include clusters of atoms and molecules,
individual macromolecules, and biological species (cells,
DNA, proteins).
AFM can operate in gas, ambient, and fluid environments
and can measure physical properties including elasticity,
adhesion, hardness, friction .
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42. Metals: roughness measurements, corrosion studies..
Solid powder catalysts: aggregate structural determination,
Polymers: determination of morphology and surface
properties, kinetic studies, aging phenomena, surface
treatment modifications, adhesion force measurement and
indentation,
Biological samples, biomaterials: macromolecules
association and conformation studies, adsorption kinetic
of molecules on polymer surfaces.
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43. Advantages
The AFM has several advantages over the scanning electron
microscope (SEM).
Unlike the electron microscope which provides a two-
dimensional projection or a two-dimensional image of a
sample, the AFM provides a true three-dimensional surface
profile.
Additionally, samples viewed by AFM do not require any
special treatments (such as metal/carbon coatings) that
would irreversibly change or damage the sample.
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44. While an electron microscope needs an expensive vacuum
environment for proper operation, most AFM modes can
work perfectly well in ambient air or even a liquid
environment.
This makes it possible to study biological macromolecules
and even living organisms.
In principle, AFM can provide higher resolution than SEM.
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45. Disadvantages
A disadvantage of AFM compared with the scanning electron
microscope (SEM) is the image size.
The SEM can image an area on the order of millimetres by
millimetres with a depth of field on the order of millimetres.
The AFM can only image a maximum height on the order of
micrometres and a maximum scanning area of around 150 by 150
micrometres.
Another inconvenience is that at high resolution, the quality of an
image is limited by the radius of curvature of the probe tip, and an
incorrect choice of tip for the required resolution can lead to image
artifacts.
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46. Traditionally the AFM could not scan images as fast as an
SEM, requiring several minutes for a typical scan, while an
SEM is capable of scanning at near real-time (although at
relatively low quality) after the chamber is evacuated.
AFM images can be affected by hysteresis of the piezoelectric
material .
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47. 
 Thank you
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