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MULTI-HEARTH ELECTRON BEAM SOURCE ～EGO-４０M
5)
Apply high voltage to the EB Gun.
An evaporant is metal, higher voltage of 7 kV to 10 kV is required. If an evaporant is compound, 8 kV
or lower voltage is suitable. On application of high voltage, abnormal local discharge may occur, but
it should decrease gradually.
An ULVAC EB power supply is so designed that it automatically lowers high voltage if over-current
is produced due to discharge, and high voltage is restored after discharge has ceased. If discharge
does not stop, possible cause is inside the vacuum chamber. So switch off the power and check
the EB Gun, filament cables and the high voltage feedthrough for insulation.
6)
When the abnormal discharge has stopped, increase emission current slowly.
The filament will light. Set emission current to 50 mA. The beam spot will be seen in the hearth.
Position the beam spot in the center of the crucible. Here, bluish white light might be seen around
the crucible. This is attributed to light emission caused by a small amount of scattered electrons
and secondary electrons hitting the contaminants or oxide film on the crucible surface.
7)
With the positioning of the beam spot being completed, increase the emission current until evaporant
is red heated.
Sometimes, abnormal discharge occurs due to the gas emitted from the evaporant. In that event, do
not try to apply power quickly, but take time. Generally, degassing can be done more quickly by
scanning with electron beam.
8)
Start deposition.
Increase the emission current up to a level at which evaporation is effected and open the shutter
when abnormal discharge has almost ceased and the emission has become stable.
9)
When the coating of a desired thickness is obtained, close the shutter, decrease the emission current,
and switch off the high voltage.
It takes 15 to 20 minutes before the evaporant and filament holder cool down. When the vacuum
chamber is vented to atmospheric pressure, introducing inert gas is recommended.
18
４．OPERATION
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