It is a highly complex process for growing crystalline layers to create complex semiconductor multilayer structures. As such, this technique is preferred for the formation of devices incorporating thermodynamically metastable alloys, [ citation needed ] and it has become a major process in the manufacture of optoelectronics.
In MOCVD ultrapure precursor gases are injected into a reactor, usually with a non-reactive carrier gas. For example, indium phosphide can be grown with trimethylindium CH 3 3 In and phosphine PH 3 precursors. As the precursors approach the semiconductor wafer , they undergo pyrolysis and the subspecies absorb onto the semiconductor wafer surface.
Surface reaction of the precursor subspecies results in the incorporation of elements into a new epitaxial layer of the semiconductor crystal lattice.
In the mass-transport-limited growth regime in which MOCVD reactors typically operate, growth is driven by supersaturation of chemical species in the vapor phase. 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 vapor pressure of the group III metal organic source is an important control parameter for MOCVD growth, since it determines the growth rate in the mass-transport-limited regime. In the metal organic chemical vapor deposition MOCVD technique, reactant gases are combined at elevated temperatures in the reactor to cause a chemical interaction, resulting in the deposition of materials on the substrate. A reactor is a chamber made of a material that does not react with the chemicals being used.
It must also withstand high temperatures.
This chamber is composed by reactor walls, liner, a susceptor , gas injection units, and temperature control units. Usually, the reactor walls are made from stainless steel or quartz. Ceramic or special glasses , such as quartz, are often used as the liner in the reactor chamber between the reactor wall and the susceptor.
To prevent overheating, cooling water must be flowing through the channels within the reactor walls. A substrate sits on a susceptor which is at a controlled temperature. The susceptor is made from a material resistant to the metalorganic compounds used; graphite is sometimes used.
For growing nitrides and related materials, a special coating, typically of silicon nitride, on the graphite susceptor is necessary to prevent corrosion by ammonia NH 3 gas. In a cold-wall reactor, the substrate is supported by a pedestal, which also acts as a susceptor.
Only the susceptor is heated, so gases do not react before they reach the hot wafer surface. In contrast, the walls of the reaction chamber in a cold-wall reactor are typically made of quartz which is largely transparent to the electromagnetic radiation. In hot-wall CVD, the entire chamber is heated. This may be necessary for some gases to be pre-cracked before reaching the wafer surface to allow them to stick to the wafer. Gas is introduced via devices known as 'bubblers'.
The amount of metalorganic vapour transported depends on the rate of carrier gas flow and the bubbler temperature , and is usually controlled automatically and most accurately by using an ultrasonic concentration measuring feedback gas control system. Allowance must be made for saturated vapors.
Gas exhaust and cleaning system. Toxic waste products must be converted to liquid or solid wastes for recycling preferably or disposal.
Hydride vapour phase epitaxy
Ideally processes will be designed to minimize the production of waste products. As MOCVD has become well-established production technology, there are equally growing concerns associated with its bearing on personnel and community safety, environmental impact and maximum quantities of hazardous materials such as gases and metalorganics permissible in the device fabrication operations.
The safety as well as responsible environmental care have become major factors of paramount importance in the MOCVD-based crystal growth of compound semiconductors. As the application of this technique in industry has grown, a number of companies have also grown and evolved over the years to provide the ancillary equipment required to reduce risk.
Bulk and epitaxial growth of SiC
This equipment includes but is not limited to computer automated gas and chemical delivery systems, toxic and carrier gas sniffing sensors which can detect single digit ppb amounts of gas, and of course abatement equipment to fully capture toxic materials which can be present in the growth of arsenic containing alloys such as GaAs and InGaAsP.
From Wikipedia, the free encyclopedia. Method of producing thin fils polycrystalline and single crystal. Deposition Technology for Beginners, Aixtron, May Stringfellow 2 December Elsevier Science.
Categories : Chemical processes Semiconductor growth Thin film deposition Semiconductor device fabrication.
Vapor Phase Epitaxy
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