Filament Material Selection / Venting The Chamber - Instrutech Hornet User Manual

Instruction Manual IGM401 Hornet
5.5

Filament Material Selection / Venting the Chamber

The choice of which type of filament to use in the IGM401 is primarily dependent upon the process and process
gases the ion gauge will be used with. For general vacuum applications, dual yttria coated filaments are offered
for use with air and inert gases such as N , argon, etc. Optional dual tungsten filaments are available for use
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with gases not compatible with yttria filaments.
1) Yttria coated iridium filament
In most general vacuum applications, the yttria coated iridium filament is the best choice.
Yttria coated filaments typically operate at a lower temperature than tungsten filaments and thus have a lower
outgassing rate at UHV and lower chemical reactivity with active gases.
Yttria coated filaments typically have a longer operating life than tungsten filaments in clean applications.
The yttria coated filament can survive occasional accidental start attempts at atmosphere in air, but the overall
life of the filament may be shortened during each occurrence. Good vacuum practice is to use a separate
pressure gauge such as InstruTech's Stinger™ or Super Bee™ convection gauge to know when to turn on the ion
gauge filament. The relay outputs of convection gauges can be used to turn on the ion gauge filament.
2) Tungsten filament
Typically a bare tungsten filament is a better choice in those applications where an yttria coated filament is
quickly damaged due to the gas type in use. For example, processes such as ion implantation may only use
tungsten filaments. Be aware that corrosive applications are hard on any filament and filament life will be
shortened while operating in such environments. Tungsten filaments are easily damaged by exposure to
air/oxygen during accidental system vents or if considerable quantities of water vapor are outgassed during
pump-down and bake-out. It is very important to make sure the tungsten filament is turned off before bringing
the chamber up to atmosphere, especially if air is being used to vent the chamber. The use of pure N gas is
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highly recommended to vent or purge your vacuum chamber. Testing has shown that tungsten filaments can
withstand limited high pressure excursions when only N is present.
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Venting with air or other oxygen containing gases can damage the tungsten filaments. If you try to turn on an
ion gauge with tungsten filaments while it is sitting on your desk exposed to room air, you will immediately
damage or destroy the filament beyond repair.
NOTICE
Do not use another gauge to automatically turn off the ion gauge when the ion gauge filament
in use is constructed of tungsten (yttria coated filament is ok). The response time of other gauges may not
allow for timely turn off of the tungsten filament leading to filament damage. Always turn off the IG filament
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manually before pressure is to rise above 1.00 x 10 Torr.
Note - Both types of filaments will suffer eventual damage if operated at high pressures. The type and amount
of damage at high pressure is dependent upon the length of operating time, the pressure and the gas present.
InstruTech, Inc.
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