1. PVD AND CVD PROCESS
Muhammed Labeeb

2. CONTENTS PHYSICAL VAPOUR DEPOSITION CHEMICAL VAPOUR DEPOSITION
REFERENCES

3. WHY VAPOUR DEPOSITION ?
Vapour deposition is a coating technique, involving transfer of material on an atomic level
It is used for
Improved hardness and wear resistance
Reduced friction
Improved oxidation resistance
Components to operate in special environments 

4. PHYSICAL VAPOUR DEPOSITION
Deposition of a material in the vapor phase onto a solid in a vacuum.
The coating method involves purely physical processes such as high-temperature vacuum evaporation with subsequent condensation, or plasma sputter bombardment
Evaporated atoms travel through the evacuated space between the source and the sample and stick to the sample
Usually no chemical reactions take place
Carried out in a vacuum atmosphere
Used for thin and uniform coating or films

5. PHYSICAL VAPOUR DEPOSITION
Evaporation rely on thermal energy supplied to the crucible or boat
Electrical resistance or electric beam can be used as source of heat
Source materials melts and vaporizes which is then deposited on the substrate placed directly above
A shield is usually provided between source metal and substrate

6. PHYSICAL VAPOUR DEPOSITION

7. ADVANTAGES
 PVD coatings are harder and more corrosion resistant than coatings applied by the electroplating process
Coatings have high temperature and good impact strength, excellent abrasion resistance and are so durable
More environmentally friendly process
More than one technique can be used to deposit a given film

8. DISADVANTAGES PVD needs high capital cost
It is a line of sight technique meaning that it is extremely difficult to coat undercuts and similar surface features
The rate of coating deposition is usually quite slow
Processes requiring large amounts of heat require appropriate cooling systems

9. CHEMICAL VAPOUR DEPOSITION
Chemical vapor deposition (CVD) is a chemical process used to produce high- purity, high-performance solid materials or coatings
In a typical CVD process, the substrate is exposed to one or more volatile precursors which react and decompose on the substrate surface to produce the desired deposit
Precursers include Halides (eg TiCl4), Hydrides (eg SiH4) and other componds etc
During this process, volatile by-products are also produced, which are removed by gas flow through the reaction chamber.

10. CHEMICAL VAPOUR DEPOSITION SYSTEM
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
Process control equipment – Gauges, controls etc to monitor process parameters such as pressure, temperature and time

11. CHEMICAL VAPOUR DEPOSITION-STEPS
Transport of reactants by forced convection to the deposition region
Transport of reactants by diffusion from the main gas stream to the substrate surface.
Adsorption of reactants in the wafer (substrate) surface.
Chemical decomposition and other surface reactions take place.
Desorption of by-products from the surface
Transport of by-products by diffusion
Transport of by-products by forced convection away from the deposition region.

12. CHEMICAL VAPOUR DEPOSITION - TYPES
Plasma Enhanced CVD (PE-CVD)
Metal Organic CVD (MO-CVD )
Atmospheric pressure CVD (AP-CVD)
Low-pressure CVD (LP-CVD)
Ultrahigh vacuum CVD (UHV-CVD)
Aerosol assisted CVD (AA-CVD)
Direct liquid injection CVD (DLICVD)

13. CHEMICAL VAPOUR DEPOSITION - TYPES
Plasma enhanced CVD

14. CHEMICAL VAPOUR DEPOSITION - TYPES
Metal organic CVD

15. ADVANTAGES
Variable shaped surfaces, given reasonable access to the coating powders or gases, such as screw threads, blind holes or channels or recesses, can be coated evenly without build-up on edges.
Versatile –any element or compound can be deposited.
High Purity can be obtained.
High Density – nearly 100% of theoretical value.
Material Formation well below the melting point
Economical in production, since many parts can be coated at the same time.

16. 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.

17. APPLICATIONS 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

18. REFERENCE
ASM Metals Hand Book, 9th edn, Vol 4, Heat Treating, ASM, Metals Park, (1983)