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Transpector MPH Operating Manual
3.3.1 Choosing the Proper Filament
Dual Yttria-coated Iridium and the optional Dual Tungsten filaments are available
for Transpector MPH. Determining which one should be used for a specific
application can be difficult. This section will detail the different scenarios wherein
one filament type is preferred over the other.
3.3.1.1 Yttria-Coated Iridium Filaments
Yttria-coated iridium filaments have a coating of yttrium oxide over an iridium core.
Yttria is a rare-earth element that, in its oxide form, is fully oxidized. This means
that the surface of the yttria-coated iridium filament is inert with respect to oxygen
damage. For applications which will include exposure to oxygen, choosing the
yttria-coated iridium filament is appropriate.
Yttria-coated iridium filaments do not withstand exposure to halogens. Upon
exposure to halogens, the yttria coating will form yttria-oxyhalides which will chip
off of the filament and cause direct exposure of the iridium core, shortening the
lifetime of the filament. Use tungsten filaments when an application includes
exposure to halogens (fluorine, chlorine, bromine or iodine).
3.3.1.2 Tungsten Filaments
Tungsten filaments are used for monitoring processes that utilize a large amount
of halogens (such as Etch). The tungsten filament is not easily attacked by
halogens and will have a much longer lifetime than the yttria-coated iridium
filaments.
Tungsten filaments are not able to withstand environments with a large level of
water or oxygen present (combined partial pressure of water or oxygen greater
than 1E-6 Torr). The heated tungsten filament forms tungsten oxides which can
either coat the ion source or contaminate a process. Use yttria-coated iridium
filaments for oxygen-heavy and/or water rich applications.
