2/4
C 00
Safety recommendations
for harsh processes
G 04128 - Edition 02 - July 12
Safety information related to SIH
4
/H
2
processes
Processes using high H2 or SiH4 flows require extended safety to prevent any problem. In order to avoid
any safety issue or risks relative to process and pumping conditions, it is necessary to set up the pump
with correct settings, following adixen recommendations.
Concerned processes : PECVD Si : (a/μc-Si using both SiH
4
and H
2
) ; PECVD SiN (using SiH
4
)
On these applications, and depending on working conditions (flows ratio and working pressure), these
risks can easily been identified.
Explosion of Si dust (only on PECVD Si)
Ignition of SiN powders (on PECVD SiN, when NH
3
/SiH
4
ratio < 1)
Ignition of SiH
4
/H
2
trapped into powders.
1 - Explosion of Si dust: (PECVD Si)
Some PECVD Si produces a lot of an orange/brown powder which is composed of very thin particles of Si.
Depending on exact process conditions, size of these particles may vary from 0,1 to 100
μ
m.
Available ignition sources sufficient to ignite:
Electronic charges loaded into particles naturally generated by plasma into process chamber
Friction between particles or air flow inrush
Local elevated temperature due to mechanical contact
Auto-ignition when Si dust produced in anaerobic conditions is violently put in contact with O
2
is also
possible
Overpressure generated by this kind of mix explosion/detonation is 10 to 11 times initial pressure.
2 - Explosion due to ignition of SiH
4
trapped in by-products: (PECVD Si & SiN)
Another well known phenomena is explosion due to trapped silane or poly-silane polymers. As PECVD Si
and SiN produce a lot of powder which deposits into vacuum line, pump, exhaust line… the different layers
of powder have the ability to retain/trap or desorbs flammable process gases (like Hydrogen & Silane).
In case of violent air inrush, a cloud may be generated. Trapped flammables gases can be released suddenly
and ignite.
3 - Explosion consequences:
An explosion, either in vacuum line or pump or exhaust line, is a complex chemical reaction. An explosion
can also generate a leak which which then could generate a second explosion due to the additionnal air
ingress.
Another important point is that vacuum pumps are also compressors. Depending on pressure in volume
to evacuate, pressure in different pump’s stages can be much greater than Atmosphere. Consequently,
explosion can generate high local overpressure (ie 25 · 10
3
hPa may be locally reached with an initial
pressure of 2.5 · 103 hPa obtained in the primary dry pump when the complete pumping system is exposed
to 1 Atm at inlet).
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adixen Vacuum Products – A3H Series Operating instructions
