1. Presented by: -Priyasi Singh -Pooja Singh
CVD & PVD
Presented by:
-Priyasi Singh
-Pooja Singh

2. Chemical Vapour Deposition (CVD)

3. Definition:
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.

4. Principle:
Fundamental principle is that a chemical reaction takes place between the source gases.
The product of that is a solid material that condenses on all surfaces inside the reactor
Precursor gases (often diluted in carrier gases) are delivered into the reaction chamber at approximately ambient temperatures.

5. Sequential Steps: Transport of reacting to the substrate surface
Absorption of species on the substrate surface
Heterogeneous surface reaction catalyzed by the substrate surface.
Desorption of gaseous reaction byproducts
Transportation of reaction by-products away from the substrate

6. These steps for the CVD process are sequential; so the one that occurs at the slowest rate will determine the deposition rate and is called the rate-limiting step
If the deposition process is dominated by step-2,3, or 4as numbered above, it is a surface controlled process
If a deposition process is dominated by step-1, it is called a mass-transport controlled process

7. Coating Characteristics
CVD coatings are typically:
Fine grained
Impervious
High purity
CVD coatings are usually only a few microns thick and are generally deposited at fairly slow rates, usually of the order of a few hundred microns per hour.

8. CVD Apparatus
A CVD apparatus will consist of several basic components:
Gas delivery system – For the supply of precursors to the reactor chamber
Reactor chamber – Chamber within which deposition takes place
 Substrate loading mechanism – A system for introducing and removing substrates, mandrels etc
Energy source – Provide the energy/heat that is required to get the precursors to react/decompose.
Vacuum system – A system for removal of all other gaseous species other than those required for the reaction/deposition.
Exhaust system – System for removal of volatile by-products from the reaction chamber.
Exhaust treatment systems – In some instances, exhaust gases may not be suitable for release into the atmosphere and may require treatment or conversion to safe/harmless compounds.
Process control equipment – Gauges, controls etc to monitor process parameters such as pressure, temperature and time. Alarms and safety devices would also be included in this category.

9. Energy Sources
There are several suitable sources of heat for CVD processes. These include:
Resistive Heating e.g. tube furnaces
Radiant Heating e.g. halogen lamps
Radio Frequency Heating e.g. induction heating
Lasers
Other energy sources may include UV-visible light or lasers as a source of photo energy.

10. Precursors
Materials are deposited from the gaseous state during CVD. Thus precursors for CVD processes must be volatile, but at the same time stable enough to be able to be delivered to the reactor.
Typical Precursor Materials: Halides - TiCl4, TaCl5, WF6, etc
 Hydrides - SiH4, GeH4, AlH3(NMe3)2, NH3, etc
Metal Organic Compounds –
Metal Alkyls - AlMe3, Ti(CH2tBu)4, etc
Metal Alkoxides - Ti(OiPr)4, etc
Metal Dialylamides - Ti(NMe2)4, etc
Metal Diketonates - Cu(acac)2, etc
Metal Carbonyls - Ni(CO)4, etc
Others – include a range of other metal organic compounds, complexes and ligands

11. CVD Reactors CVD atmospheric Hot wall tube Cold wall Tube
Continuous motion
Batch
Low pressure
Hot wall tube
PECVD
Hot wall batch
Cold wall single wafer
Vertical flow

12. Hot wall
Cold wall

13. Types of CVD process APCVD (atmospheric pressure CVD)
LPCVD (low Pressure CVD)
PECVD (plasma enhanced CVD)
Hot wall
Parallel type
Single wafer
MOCVD (metal organic CVD)
LCVD (laser CVD)
PCVD (photochemical CVD)
CVI (chemical vapor infiltration)
CBE (chemical beam epitaxy)

14. 1. APCVD APCVD reactors operate in mass transport limited region
So they are designed such that equal flow of reactants is delivered
This ensures uniform film deposition
This is done by placing the wafer horizontally and then moving them under gas stream
They are used for depositing low temperature oxide films
Samples are carried through the reactor on a conveyer belt
Reactant gases flowing through the centre of the reactor are containing by gas curtains formed by fast flow of nitrogen
Advantages:
Simple
High deposition rate
Low temp
Disadvantages:
Poor step coverage
Particle contamination
Require excess wafer handling
Application:
Doped & undoped low temp oxides

15. 2. LPCVD
The reactor consists of a quartz tube heated by a three zone furnace
Gas introduced from one end & pumped out from the other end
Wafers stand vertically, perpendicular to the gas flow
They are placed in a quartz holder
It operates in a surface reaction rate limited mode
Therefore supply of equal flux of reactants is not required
Therefore geometry can be such that it can accommodate a large no. of wafers approx 200 wafers at a time
Advantages:
Excellent purity
Comfortable step coverage
Large wafer capacity
Disadvantage
High temp
Low deposition rate
Application
Doped & undoped high temp oxides
Silicon nitride
polysilicon

16. 3. PECVD
PECVD system use an ‘RF induced’ glow discharge to transfer energy into reactant gases
This procedure allows the substrate to remain at a low temp than APCVD & LPCVD
Types:
Parallel plate type
Hot wall type
Single wafer type

17. a) Parallel plate type
Reaction chamber is cylinder & constructed of Al- coated stainless steel
There are Al plates on the top & bottom
Samples lie on the grounded bottom electrode
RF is applied to the top electrode which creates a glow discharge between 2 plates
Gases flow radially through the discharge
Resistance heater heat the bottom, grounded electrode to a temp b/w °C
Gases are flowing from outer edges to the center
Advantages:
Low temp deposition
Disadvantages
Wafer must be loaded & unloaded indiviually
Chance of contamination
Application:
Silicon dioxide
Deposition on silicon nitride

18. b) Hot wall type
The reaction takes place in a quartz tube heated by a furnace
Samples are held parallel to the gas flow
The electrode assembly contains long graphite or al slabs to support the wafers
Alternating slabs are connected to power supply to generate discharge in the space between the electrode (long slabs serve both as electrode & holder)
Advantage:
Uniformity
Large no. of wafer deposition
Disadvantage:
Contamination while loading and unloading

19. c)Single wafer type The reactor is load locked
It offers cassette to cassette operation
It offers rapid radiant heating of each wafer
Wafer larger than 200mm can be loaded

20. 4. MOCVD
MOCVD stands for Metal- Organic Chemical Vapour Deposition. This is a technique for depositing thin layers of atoms onto a semiconductor wafer. Using MOCVD you can build up many layers, each of a precisely controlled thickness, to create a material which has specific optical and electrical properties
Principle: Atoms that you would like to be in your crystal are combined with complex organic gas molecules and passed over a hot semiconductor wafer.
The heat breaks up the molecules and deposits the desired atoms on the surface, layer by layer.
By varying the composition of the gas, you can change the properties of the crystal at an almost atomic scale.
It can grow high quality semiconductor layers 

21. 5. LCVD
The production of physical parts using LCVD involves generating solid deposits on the surface of a substrate by inducing localized chemical reactions in a suitable vapor reactant through the use of a laser beam.
Materials prepared by CVD, and presumably by LCVD, typically possess high purity, low porosity, and a high degree of crystallinity. These attributes are the result of deposition occurring one atom at a time, leading to materials having excellent mechanical properties and thermal stability.
The deposition happens on a pyrolytic chemical reaction which occurs in the focus of a laser beam.

22. 6. PCVD
Photo-Chemical CVD Reactor uses ultraviolet light as an energy source for activating process gases for the deposition of dielectric films at low temperatures (<150ºC).
Films of silicon dioxide (SiO2), silicon nitride (Si3N4), silicon oxy-nitride (SiON) and others can be deposited.
Minimal stress is observed in these films due to the low deposition temperature.
Since the UV photon energy used does not ionize the process gases, no radiation damage from charged particles has been observed

23. 7. CVI
Chemical Vapor Infiltration method of Ceramic Matrix Composites fabrication is a process, in which reactant gases diffuse into an isothermal porous preform made of long continuous fibers and form a deposition. Deposited material is a result of chemical reaction occurring on the fibers surface. The infiltration of the gaseous precursor into the reinforcing ceramic continuous fiber structure (preform) is driven by either diffusion process or an imposed external pressure.
The deposition fills the space between the fibers, forming composite material in which matrix is the deposited material and dispersed phase is the fibers of the preform.
Commonly the vapor reagent is supplied to the preform in a stream of a carrier gas (H2, Ar, He). Silicon carbide (SiC) matrix is formed from a mixture of methyltrichlorosilane (MTS) as the precursor and Hydrogen as the carrier gas. Methyltrichlorosilane is decomposed according to the reaction: CH3Cl3Si → SiC + 3HCl The gaseous hydrogen chloride (HCl) is removed from the preform by the diffusion or forced out by the carrier stream. Carbon matrix is formed from a methane precursor (CH4)

24. 8. CBE
Chemical beam epitaxy (CBE) forms an important class of deposition techniques for semiconductor layer systems, especially III-V semiconductor systems. This form of epitaxial growth is performed in an ultrahigh vacuum system. The reactants are in the form of molecular beams of reactive gases, typically as the hydride or a metal organic.
CBE combines the advantages of both metalorganic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE) systems, which have been widely used for the preparation of nitride-based compounds.

25. Applications
CVD has applications across a wide range of industries such as:
•         Coatings – Coatings for a variety of applications such as wear resistance, corrosion resistance, high temperature protection, erosion protection and combinations thereof.
•         Semiconductors and related devices – Integrated circuits, sensors and optoelectronic devices
•         Dense structural parts – CVD can be used to produce components that are difficult or uneconomical to produce using conventional fabrication techniques. Dense parts produced via CVD are generally thin walled and maybe deposited onto a mandrel or former.
•         Optical Fibres – For telecommunications.
•         Composites – Preforms can be infiltrated using CVD techniques to produce ceramic matrix composites such as carbon-carbon, carbon-silicon carbide and silicon carbide-silicon carbide composites. This process is sometimes called chemical vapour infiltration or CVI.
•         Powder production – Production of novel powders and fibres
•         Catalysts
•         Nanomachines

26. PHYSICAL VAPOR DEPOSITION
PVD is a process by which a thin film of material is deposited on a substrate acc to following steps:
The material to be deposited is converted into vapour by physical means
The vapor is transported across a region of low pressure from its source to the substrate
Vapor undergoes condensation on the substrate to form the thin film

27. PVD
Evaporation
thermal
E-beam
Sputtering DC RF
Magnetron

28. EVAPORATION
Thermal
A metal is evaporated by passing a high current through a highly refractory material contaminant structure
Once the metal is evaporated, its vapour undergoes collisions with the surrounding gas molecules inside the evaporation chamber.
As a result a fraction is scattered within a given distance during their transfer through the ambient gas.
Therefore pressure lower than 10¯⁵ is necessary to maintain for a straight line path for evaporated molecules.

29. II) E-beam Evaporation
In this mode of operation high intensity electron beam gun is focused on the target material i.e. placed in a water cooled copper.
The process begin under a vacuum. A tungsten filament is heated so that it will give e¯ which forms a beam i.e. deflected & focus on the material to be evaporated by the magnetic field.
When E-beam strikes the target material, the kinetic energy of the motion is transferred into thermal energy.

30. SPUTTERING Sputtering is a deposition tech consist of basic 4 steps;
Ions are generated & directed at the target material
The ion sputter atoms from the target material
The sputter atom get transported to the substrate through a region of reduced pressure
This sputter atom condense on the substrate forming a thin film

31. I)RF SPUTERRING
RF sputtering will allow the sputtering of target that are electrical insulator.
The target attracts Ar ions during one half of the cycle.
The electrons are more mobile & build up a negative charge called as self bias which helps in attracting Ar ions which does the sputtering.

32. II) DC SPUTTERING
Sputtering can be achieved by applying a large DC voltage (approx 2000v).
A plasma discharge is established & the argon ion will be attracted to an impact sputtering of the target atoms.
In DC sputtering the target must be electrically conducted otherwise the target surface will charge with the collection of ion & repels other Ar ion.

33. III)MAGNETRON SPUTTERING
In this technique, a magnetic field, mainly parallel to the target surface, is superimposed to the applied electric field so that the secondary electrons (emitted by the target during its bombardment) are trapped near the target surface.
Thus, one single electron can induce several argon ionizations before being lost by recombination on the chamber walls.
This results in a large increase of the plasma ionization rate at the target surface and then in a significant increase of the deposition rate .

34. 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.
Great variety of coating.
High wear resistance.
Low frictional co-efficient
NO toxic reaction product
Excellent adherence
Uniform coating thickness

35. 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 slow

36. APPLICATIONS
PVD coatings are generally used to improve hardness, wear resistance and oxidation resistance. Thus, such coatings use in a wide range of applications such as:
Aerospace
Automotive
Surgical/Medical
Dies and moulds for all manner of material processing
Cutting tools
Fire arms

37. PVD CVD Deposition occur by condensation.
The material that is introduced onto the substrate is introduced in solid form
Atoms are moving and depositing on the substrate
PVD coating is deposited at a relatively low temperature (around 250°C~450°C)
Deposition occur by chemical reaction.
Introduced in a gaseous form
The gaseous molecules will react with the substrate.
CVD uses high temperatures in the range of 450° C to 1050° C.

38. Cont….
CVD
PVD
5. PVD is suitable for coating tools that are used in applications that demand a tough cutting edge.
High capital cost
7. Coating thickness up to 20micrometer
5. CVD is mainly used for depositing compound protective coatings.
6. Low capital cost
7. Coating thickness micrometer