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HIGH & LOW TEMPERATURE GAS CRACKERS
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For certain applications it is preferable to use a gaseous source rather than a solid or liquid one. This may be the case in CBE (Chemical Beam Epitaxy), GSMBE (Gas Source MBE) and MOMBE (Metalorganic MBE). The gas source may be a cracker which thermally decomposes the gas molecules , or an injector which operates at a temperature high enough to avoid condensation and maintain a stable flux without, however, cracking the gas.
High performance gas crackers and cold injectors are available for most CBE or Gas MBE and C doping applications.
They provide safe and clean operation of group V gases (AsH3, PH3, metalorganic precursors) and group III metalorganic precursors (growth or doping). |
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| High pressure cracker for hybrides gas with two gas VCR inlet on a DN40CF flange. (70mn) |
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EXIT APPERTURES
Growth uniformity is very sensible to gas flux shape. ADDON can provide customized diaphragms
( number of holes, size, shape and orientation) calculated for a particular system geometry and substrate sizes.
GAS CONSUMPTION AND PUMP CAPACITY
Another very critical criteria is the uniformity versus efficiency of gas use ( ratio between the amount of injected gas and the part really intercepted by the substrate
( generally few % only). A bad design can rapidly lead to the need for huge expensive pumps.
CONSTRUCTION MATERIALS
Only high purity materials such as PBN and electronic grade Tantalum are used in the construction of the gas sources.
No Molybenum is used as in the source stucture. this metal does not meet the purity criteria due to relatively high contents of Fe, Si, S and C.
Pure Mo courbe used as catalyst.
CRACKING ZONE
The Low Temperature Injection of the metalorganic compounds can be set between room temperature and 100°C to avoid condensation and up to the degassing temperature 400°C.
The High Temperature version provides cracking temperatures up to 1250°C (1350°C for degassing).
For some gas like NH3 a cold ( system temperature) injector can be used.
GAS LINES
Up to 3 independent gas lines can be connected to separate gas entries. The tubing is designed to give a high gas conductance right up to to the cracking zone and to prevent cross-reactions between the different species. Dead volumes have been reduced to a minimum. ADDON sources may be equipped with both Mass Flow and Pressure Control regulated gas lines due to the flexible design.
Gas connections: In standard ADDON supply VCR types, VCO or others are available as a factory option.
Length and mounting flanges: The length (gas diffuser to sealing edge), the flux diffuser of the source and the flange size are compatible with the growth chamber geometry and thus give uniform depositions on wafers.
Custom designs are available.
Controls: Heating power and PID control are compatible with both the existing system or ADDON controls.
Although customized and special purpose gas sources are available on request Addon offers standards gas source for the following systems.
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| System Type |
OM |
Hybrides |
Nb of gas inlet |
| Riber 2300/32 |
LT2RB2 |
HT2RB2 |
2 |
| Epineat |
LT3RIE |
HT3RIE |
3 |
| Varian Gen II/III |
LT3VA3 |
HT3VA3 |
3 |
| VG80 |
LT3VG8 |
HT3VG8 |
3 |
| VG90 |
LT3VG9 |
HT3VG9 |
3 |
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INJECTORS
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Addon offers low temperature gas injectors with large conductance and system geometry matched diaphragms for many differents gas and in particular Amonia. NH3 is generally craked at the substrate surface and the injector is only keept at a mild temperature to prevent condensation in the source. Custom injectors are available upon request. See figure 2.
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The figure 2 represents the basic design of ADDON gas cracker.
The dimensions and the number of gas inlets vary according to the application and the CBE/GAS MBE geometry |
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GAS CONTROL SYSTEMS
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| Addon offers easy to integrate gas control systems conveniently integrated in rack. |
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H2/N2/O2/NH3 gas control rack (3U x 19’’). Here a MFC is used to control the amount of gas.
Pressure control lines are also available from Addon. |
