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Metalorganic vapour-phase epitaxy

March 08, 2023

Metalorganic vapour-phase epitaxy (MOVPE), also known as organometallic vapour-phase epitaxy (OMVPE) or metalorganic chemical vapour deposition (MOCVD),[1] is a chemical vapour deposition method used to produce single- or polycrystalline thin films. It is a process for growing crystalline layers to create complex semiconductor multilayer structures.[2] In contrast to molecular-beam epitaxy (MBE), the growth of crystals is by chemical reaction and not physical deposition. This takes place not in 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,[citation needed] and it has become a major process in the manufacture of optoelectronics, such as Light-emitting diodes. It was invented in 1968 at North American Aviation (later Rockwell International) Science Center by Harold M. Manasevit.

Illustration of the process

Basic principles

In MOCVD ultrapure precursor gases are injected into a reactor, usually with a non-reactive carrier gas. For a III-V semiconductor, a metalorganic could be used as the group III precursor and a hydride for the group V precursor. For example, indium phosphide can be grown with trimethylindium ((CH3)3In) and phosphine (PH3) 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.[3] MOCVD can grow films containing combinations of group III and group V, group II and group VI, group IV.

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.[4] The diffusion of atoms on the substrate surface is affected by atomic steps on the surface.

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. [5]

Reactor components

 
MOCVD apparatus

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 temperature and metalorganic compounds used, often it is machined from graphite. For growing nitrides and related materials, a special coating, typically of silicon nitride or tantalum carbide, on the graphite susceptor is necessary to prevent corrosion by ammonia (NH3) gas.

One type of reactor used to carry out MOCVD is a cold-wall reactor. In a cold-wall reactor, the substrate is supported by a pedestal, which also acts as a susceptor. The pedestal/susceptor is the primary origin of heat energy in the reaction chamber. Only the susceptor is heated, so gases do not react before they reach the hot wafer surface. The pedestal/susceptor is made of a radiation-absorbing material such as carbon. 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. The reaction chamber walls in a cold-wall reactor, however, may be indirectly heated by heat radiating from the hot pedestal/susceptor, but will remain cooler than the pedestal/susceptor and the substrate the pedestal/susceptor supports.

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 inlet and switching system

Gas is introduced via devices known as 'bubblers'. In a bubbler a carrier gas (usually hydrogen in arsenide & phosphide growth or nitrogen for nitride growth) is bubbled through the metalorganic liquid, which picks up some metalorganic vapour and transports it to the reactor. 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.

Pressure maintenance system

Gas exhaust and cleaning system. Toxic waste products must be converted to liquid or solid wastes for recycling (preferably) or disposal. Ideally processes will be designed to minimize the production of waste products.

Organometallic precursors

Semiconductors grown by MOCVD

III-V semiconductors

II-VI semiconductors

IV Semiconductors

IV-V-VI Semiconductors

Environment, health and safety

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. 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.[6]

See also

References

  1. ^ , Johnson Matthey, GPT.
  2. ^ How MOCVD works. Deposition Technology for Beginners, Aixtron, May 2011.
  3. ^ Gerald B. Stringfellow (2 December 2012). Organometallic Vapor-Phase Epitaxy: Theory and Practice. Elsevier Science. pp. 3–. ISBN 978-0-323-13917-5.
  4. ^ MOCVD Basics and Applications, Samsung Advanced Institute of Technology, 2004.
  5. ^ Metalorganic chemical vapor deposition (MOCVD). September 27, 2010, at the Wayback Machine
  6. ^ For examples see the websites of Matheson Tri Gas, Honeywell, Applied Energy, DOD Systems

March 08, 2023
metalorganic, vapour, phase, epitaxy, movpe, also, known, organometallic, vapour, phase, epitaxy, omvpe, metalorganic, chemical, vapour, deposition, mocvd, chemical, vapour, deposition, method, used, produce, single, polycrystalline, thin, films, process, grow. Metalorganic vapour phase epitaxy MOVPE also known as organometallic vapour phase epitaxy OMVPE or metalorganic chemical vapour deposition MOCVD 1 is a chemical vapour deposition method used to produce single or polycrystalline thin films It is a process for growing crystalline layers to create complex semiconductor multilayer structures 2 In contrast to molecular beam epitaxy MBE the growth of crystals is by chemical reaction and not physical deposition This takes place not in 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 citation needed and it has become a major process in the manufacture of optoelectronics such as Light emitting diodes It was invented in 1968 at North American Aviation later Rockwell International Science Center by Harold M Manasevit Illustration of the process Contents 1 Basic principles 2 Reactor components 2 1 Gas inlet and switching system 2 2 Pressure maintenance system 3 Organometallic precursors 4 Semiconductors grown by MOCVD 4 1 III V semiconductors 4 2 II VI semiconductors 4 3 IV Semiconductors 4 4 IV V VI Semiconductors 4 5 Environment health and safety 5 See also 6 ReferencesBasic principles EditIn MOCVD ultrapure precursor gases are injected into a reactor usually with a non reactive carrier gas For a III V semiconductor a metalorganic could be used as the group III precursor and a hydride for the group V precursor For example indium phosphide can be grown with trimethylindium CH3 3In and phosphine PH3 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 3 MOCVD can grow films containing combinations of group III and group V group II and group VI group IV 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 4 The diffusion of atoms on the substrate surface is affected by atomic steps on the surface 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 5 Reactor components Edit MOCVD apparatus 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 temperature and metalorganic compounds used often it is machined from graphite For growing nitrides and related materials a special coating typically of silicon nitride or tantalum carbide on the graphite susceptor is necessary to prevent corrosion by ammonia NH3 gas One type of reactor used to carry out MOCVD is a cold wall reactor In a cold wall reactor the substrate is supported by a pedestal which also acts as a susceptor The pedestal susceptor is the primary origin of heat energy in the reaction chamber Only the susceptor is heated so gases do not react before they reach the hot wafer surface The pedestal susceptor is made of a radiation absorbing material such as carbon 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 The reaction chamber walls in a cold wall reactor however may be indirectly heated by heat radiating from the hot pedestal susceptor but will remain cooler than the pedestal susceptor and the substrate the pedestal susceptor supports 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 inlet and switching system Edit Gas is introduced via devices known as bubblers In a bubbler a carrier gas usually hydrogen in arsenide amp phosphide growth or nitrogen for nitride growth is bubbled through the metalorganic liquid which picks up some metalorganic vapour and transports it to the reactor 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 Pressure maintenance system Edit Gas exhaust and cleaning system Toxic waste products must be converted to liquid or solid wastes for recycling preferably or disposal Ideally processes will be designed to minimize the production of waste products Organometallic precursors EditAluminium Trimethylaluminium TMA or TMAl Liquid Triethylaluminium TEA or TEAl Liquid Gallium Trimethylgallium TMG or TMGa Liquid Triethylgallium TEG or TEGa Liquid Indium Trimethylindium TMI or TMIn Solid Triethylindium TEI or TEIn Liquid Di isopropylmethylindium DIPMeIn Liquid Ethyldimethylindium EDMIn Liquid Germanium Isobutylgermane IBGe Liquid Dimethylamino germanium trichloride DiMAGeC Liquid Tetramethylgermane TMGe Liquid Tetraethylgermanium TEGe Liquid Germane GeH4 Gas Nitrogen Phenyl hydrazine Liquid Dimethylhydrazine DMHy Liquid Tertiarybutylamine TBAm Liquid Ammonia NH3 Gas Phosphorus Phosphine PH3 Gas Tertiarybutyl phosphine TBP Liquid Bisphosphinoethane BPE Liquid Arsenic Arsine AsH3 Gas Tertiarybutyl arsine TBAs Liquid Monoethyl arsine MEAs Liquid Trimethyl arsine TMAs Liquid Antimony Trimethyl antimony TMSb Liquid Triethyl antimony TESb Liquid Tri isopropyl antimony TIPSb Liquid Stibine SbH3 Gas Cadmium Dimethyl cadmium DMCd Liquid Diethyl cadmium DECd Liquid Methyl Allyl Cadmium MACd Liquid Tellurium Dimethyl telluride DMTe Liquid Diethyl telluride DETe Liquid Di isopropyl telluride DIPTe Liquid Titanium Alkoxides such as Titanium isopropoxide or Titanium ethoxide Selenium Dimethyl selenide DMSe Liquid Diethyl selenide DESe Liquid Di isopropyl selenide DIPSe Liquid Di tert butyl selenide DTBSe Liquid Zinc Dimethylzinc DMZ Liquid Diethylzinc DEZ LiquidSemiconductors grown by MOCVD EditIII V semiconductors Edit AlN AlP AlGaN AlGaP AlGaAs AlGaSb AlGaInP GaSb GaAsP GaAs GaN GaP InAlAs InAlP InSb InGaSb InGaN GaInAlAs GaInAlN GaInAsN GaInAsP GaInAs GaInP InN InP InAs InAsSb AlInNII VI semiconductors Edit ZnO ZnS ZnSe ZnTe CdO CdxHg1 xTeIV Semiconductors Edit Si Ge Strained siliconIV V VI Semiconductors Edit GeSbTeEnvironment health and safety Edit 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 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 6 See also EditAtomic layer deposition Hydrogen purifier List of semiconductor materials Metalorganics Molecular beam epitaxy Thin film depositionReferences Edit MOCVD Epitaxy Johnson Matthey GPT How MOCVD works Deposition Technology for Beginners Aixtron May 2011 Gerald B Stringfellow 2 December 2012 Organometallic Vapor Phase Epitaxy Theory and Practice Elsevier Science pp 3 ISBN 978 0 323 13917 5 MOCVD Basics and Applications Samsung Advanced Institute of Technology 2004 Metalorganic chemical vapor deposition MOCVD Archived September 27 2010 at the Wayback Machine For examples see the websites of Matheson Tri Gas Honeywell Applied Energy DOD Systems Retrieved from https en wikipedia org w index php title Metalorganic vapour phase epitaxy amp oldid 1133222560, wikipedia, wiki, book, books, library,

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