MOCVD Metal-organic Chemical Vapor Deposition - LED Wiki

Metal-organic Chemical Vapor Deposition, short for MOCVD, is a chemical vapour deposition method used to produce single or polycrystalline thin films. The MOCVD machine is the most critical equipment in LED chip production processes. MOCVD is also known as organometallic vapour phase epitaxy (OMVPE) or Metalorganic vapour phase epitaxy (MOVPE). It is a highly complex process for growing crystalline layers to create complex semiconductor multilayer structures. – LED wiki

In contrast to molecular beam epitaxy (MBE) the growth of crystals is by chemical reaction and not physical deposition. This takes place not in a vacuum, but from the gas phase at moderate pressures (10 to 760 Torr). As such, this technique is preferred for the formation of devices incorporating thermodynamically metastable alloys, and it has become a major process in the manufacture of optoelectronics.

a-made-in-China-MOCVD-machine

Basic principles of the MOCVD process

In MOCVD ultra pure gases are injected into a reactor and finely dosed to deposit a very thin layer of atoms onto a semiconductor wafer. Surface reaction of organic compounds or metalorganics and hydrides containing the required chemical elements creates conditions for crystalline growth – epitaxy of materials and compound semiconductors. Unlike traditional silicon semiconductors, these semiconductors may contain combinations of Group III and Group V, Group II and Group VI, Group IV, or Group IV, V and VI elements.

For example, indium phosphide could be grown in a reactor on a heated substrate by introducing trimethylindium ((CH3)3In) and phosphine (PH3) in a first step. The heated organic precursor molecules decompose in the absence of oxygen – pyrolysis. Pyrolysis leaves the atoms on the substrate surface in the second step. The atoms bond to the substrate surface and a new crystalline layer is grown in the last step. Formation of this epitaxial layer occurs at the substrate surface.

Required pyrolysis temperature increases with increasing chemical bond strength of the precursor. The more carbon atoms are attached to the central metal atom the weaker the bond.The diffusion of atoms on the substrate surface is affected by atomic steps on the surface.

The vapor pressure of the metal organic source is an important consideration in MOCVD, since it determines the concentration of the source material in the reaction and the deposition rate.

mechanism-of-the-metal-organic-chemical-vapor-deposition-of-gallium-arsenide

MOCVD Metal-organic Chemical Vapor Deposition - LED Wiki