The two dominant methods of single-crystal ingot growth (HB and GF) use charged and sealed quartz ampoules in a high temperature furnace enclosure which is vented to a wet scrubber system.
The HB system consists of a two zone furnace in which the sealed quartz ampoule has separate temperature zones: the arsenic "cold" finger end at 610ºC, and the quartz gallium/dopant/seed-crystal boat containing the melt at 1240ºC. The basic principle in HB involves traversing two heated zones (one above the melting point of GaAs, and one below the melting point), over a boat of GaAs to provide the precisely controlled freezing of molten GaAs. The seed crystal, maintained at all times in the freeze zone, provides the initial crystal starting structure defining direction and orientation of the crystalline structure within the boat. Silicon-carbide liners called support tubes, which allow the resistance heater assembly to mechanically move the full distance of the ampoule, suspend the quartz boat and ampoule of gallium and arsenic within the heater chamber. Additionally, the ampoule rests on a table which must be raised and lowered during growth to provide the proper interface of the GaAs melt with the seed crystal.
GF is the second ingot growth method in use. A high-temperature furnace utilizing resistance heating is kept at 1200-1300ºC, with 1237ºC being the melt/freeze point of GaAs. The total ingot growth process duration is three days, comprised of the following steps:
- Furnace firing to temperature
- GaAs synthesis
- Seed melt
- Cool down
The quartz ampoule is also raised and lowered during the growth process by the use of a scissor-type manual jack.
The following are potential hazards for furnace growth.
- Possible explosion or implosion of ampoules during ingot growth, resulting in personnel injury and/or damage to equipment and facilities.
- Identify and eliminate possible causes of explosion/implosion. Use a Process Hazard Analysis (PHA) for identifying and controlling such hazards.
- Implement appropriate emergency procedures, including ventilation and PPE controls in the event of an explosion/implosion.
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