Bubbler cylinder
Encyclopedia
A Bubbler cylinder is a component of a unit for the metal organic chemical vapor deposition
(MOCVD). They are devices that are used for conveying electronic grade metalorganic compound
s from a liquid
or solid
precursor into a usable vapor
.
, moisture
). The bubbler has a supply pipe and a sampling tube. The inlet tube ends just before the bottom of the tube. In this tube, an inert gas is introduced, which bubbles through the liquid chemical; a solid chemical will sublime
. The mixture of the controlled inert gas
and the vaporized chemical leaves the cyclinder into a downstream reaction vessel. The temperature is controlled by a thermostat, so that a defined, constant steam pressure can be achieved. The supply of the often expensive and sensitive chemical is controlled by the regulated flow of inert gas and the temperature of the bubbler, resulting in a given vapor pressure
of the chemical.
The tube between the bubbler and the reactor has to have a higher temperature than the bubble, otherwise the precursor would condense
in the tube and therefore uncontrolled droplets would be passed into the reaction vessel. If this happens with a solid precursor, it could plug the line.
or other group III-V elements are epitaxially deposited onto a single crystal silicon
substrate. The gallium is introduced into the MOVPE reactor chamber via a vapor. This vapor is generated by bubbling an inert carrier gas (such as nitrogen
or argon
) through a cylinder with a dip tube through a metalorganic precursor such as trimethylgallium
. The inert carrier gas and the metalorganic vapor is then introduced into the MOVPE (or MOCVD) reactor chamber during the production of high brightness LEDs.
Chemical vapor deposition
Chemical vapor deposition is a chemical process used to produce high-purity, high-performance solid materials. The process is often used in the semiconductor industry to produce thin films. In a typical CVD process, the wafer is exposed to one or more volatile precursors, which react and/or...
(MOCVD). They are devices that are used for conveying electronic grade metalorganic compound
Organometallic chemistry
Organometallic chemistry is the study of chemical compounds containing bonds between carbon and a metal. Since many compounds without such bonds are chemically similar, an alternative may be compounds containing metal-element bonds of a largely covalent character...
s from a liquid
Liquid
Liquid is one of the three classical states of matter . Like a gas, a liquid is able to flow and take the shape of a container. Some liquids resist compression, while others can be compressed. Unlike a gas, a liquid does not disperse to fill every space of a container, and maintains a fairly...
or solid
Solid
Solid is one of the three classical states of matter . It is characterized by structural rigidity and resistance to changes of shape or volume. Unlike a liquid, a solid object does not flow to take on the shape of its container, nor does it expand to fill the entire volume available to it like a...
precursor into a usable vapor
Vapor
A vapor or vapour is a substance in the gas phase at a temperature lower than its critical point....
.
Apparatus
The container of the Bubblers is similar to the construction of a gas washing bottle and used for the protected storage of metalorganic compounds to exclude air (oxygenOxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
, moisture
Moisture
Humidity is the amount of moisture the air can hold before it rains. Moisture refers to the presence of a liquid, especially water, often in trace amounts...
). The bubbler has a supply pipe and a sampling tube. The inlet tube ends just before the bottom of the tube. In this tube, an inert gas is introduced, which bubbles through the liquid chemical; a solid chemical will sublime
Sublimation
Sublimation may refer to:* Sublimation , the change from solid to gas without entering liquid phase* Sublimation , the transformation of emotions* Sublimation , a music album by Canvas Solaris-See also:...
. The mixture of the controlled inert gas
Inert gas
An inert gas is a non-reactive gas used during chemical synthesis, chemical analysis, or preservation of reactive materials. Inert gases are selected for specific settings for which they are functionally inert since the cost of the gas and the cost of purifying the gas are usually a consideration...
and the vaporized chemical leaves the cyclinder into a downstream reaction vessel. The temperature is controlled by a thermostat, so that a defined, constant steam pressure can be achieved. The supply of the often expensive and sensitive chemical is controlled by the regulated flow of inert gas and the temperature of the bubbler, resulting in a given vapor pressure
Vapor pressure
Vapor pressure or equilibrium vapor pressure is the pressure of a vapor in thermodynamic equilibrium with its condensed phases in a closed system. All liquids have a tendency to evaporate, and some solids can sublimate into a gaseous form...
of the chemical.
The tube between the bubbler and the reactor has to have a higher temperature than the bubble, otherwise the precursor would condense
Condensation
Condensation is the change of the physical state of matter from gaseous phase into liquid phase, and is the reverse of vaporization. When the transition happens from the gaseous phase into the solid phase directly, the change is called deposition....
in the tube and therefore uncontrolled droplets would be passed into the reaction vessel. If this happens with a solid precursor, it could plug the line.
Application
For example, during the production of high brightness light emitting diodes, galliumGallium
Gallium is a chemical element that has the symbol Ga and atomic number 31. Elemental gallium does not occur in nature, but as the gallium salt in trace amounts in bauxite and zinc ores. A soft silvery metallic poor metal, elemental gallium is a brittle solid at low temperatures. As it liquefies...
or other group III-V elements are epitaxially deposited onto a single crystal silicon
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...
substrate. The gallium is introduced into the MOVPE reactor chamber via a vapor. This vapor is generated by bubbling an inert carrier gas (such as nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
or argon
Argon
Argon is a chemical element represented by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table . Argon is the third most common gas in the Earth's atmosphere, at 0.93%, making it more common than carbon dioxide...
) through a cylinder with a dip tube through a metalorganic precursor such as trimethylgallium
Trimethylgallium
Trimethylgallium, Ga3, often abbreviated to TMG or TMGa, is the preferred metalorganic source of gallium for metalorganic vapour phase epitaxy of gallium-containing compound semiconductors, such as GaAs, GaN, GaP, GaSb, InGaAs, InGaN, AlGaInP, InGaP and AlInGaNP.-Properties:TMG is a clear,...
. The inert carrier gas and the metalorganic vapor is then introduced into the MOVPE (or MOCVD) reactor chamber during the production of high brightness LEDs.