PVD AND CVD PROCESS Muhammed Labeeb

CONTENTS PHYSICAL VAPOUR DEPOSITION CHEMICAL VAPOUR DEPOSITION REFERENCES

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 

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

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

PHYSICAL VAPOUR DEPOSITION

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

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

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.

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

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.

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)

CHEMICAL VAPOUR DEPOSITION - TYPES Plasma enhanced CVD

CHEMICAL VAPOUR DEPOSITION - TYPES Metal organic CVD

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.

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.

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

REFERENCE ASM Metals Hand Book, 9th edn, Vol 4, Heat Treating, ASM, Metals Park, (1983) http://www.azom.com/article.aspx?ArticleID=1558 http://www.azom.com/article.aspx?ArticleID=1552