Basic Principles of The MOVPE Process
In MOVPE 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. Atoms move preferentially from high to low steps.
The vapor pressure of the metal organic source is an important consideration in MOVPE, since it determines the concentration of the source material in the reaction and the deposition rate.
Read more about this topic: Metalorganic Vapour Phase Epitaxy
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