Chemical Vapor Deposition Systems
Types of CVD Processes
CVD covers processes such as:
• Atmospheric Pressure Chemical Vapour Deposition (APCVD)
• Low Pressure Chemical Vapour Deposition (LPCVD)
• Metal-Organic Chemical Vapour Deposition (MOCVD)
• Plasma Assisted Chemical Vapour Deposition (PACVD) or Plasma Enhanced Chemical Vapour Deposition (PECVD)
• Laser Chemical Vapour Deposition (LCVD)
• Photochemical Vapour Deposition (PCVD)
• Chemical Vapour Infiltration (CVI)
• Chemical Beam Epitaxy (CBE)
How Does CVD Work?
Precursor gases (often diluted in carrier gases) are delivered into the reaction chamber at approximately ambient temperatures. As they pass over or come into contact with a heated substrate, they react or decompose forming a solid phase which and are deposited onto the substrate. The substrate temperature is critical and can influence what reactions will take place.
Coating Characteristics
CVD coatings are typically:
• Fine grained
• Impervious
• High purity
• Harder than similar materials produced using conventional ceramic fabrication processes
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.
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.