Does anyone have experience they can share regarding gas effluent
treatment from a silicon nitride process in an LPCVD system?
Specifically, we are experiencing significant deposits of particulates
in our vacuum lines, fomblin recirc. pump/filters and process vacuum
pump after approx. 10 runs. The cold trap (58 F water) doesn't catch the
majority of the fine white residue, which makes its way into the pump
fluid, causing it to turn milky white and form "chunks". The oil recirc.
system has one activated alumina filter for acids and one Fuller's earth
filter for particulates. The particulate filter becomes loaded with the
chunks in 10 runs, also.
Does anyone use a particulate trap (mesh, screen, etc.) in the foreline
as opposed to a water cooled trap? If so, what type of trap media is
used? What temp. do you run your cold traps at?
How about a boatload of dummies near the pump end of the process tube to
act as a gettering surface?
Here are the numbers:
system - ASM LPCVD
pump - LH D60AC with LH Roots blower, with water cooled (60 F) foreline
trap
SiH2Cl2 flow - 60 sccm and 130sccm (silicon rich/low stress)
NH3 flow - 130 sccm
process pressure - 300 mT
center zone temp - 800 C
pump end temp - 810 C
tube diameter -
substrate size - 150mm
wafer load (typical) - 10 ea. (includes dummies both ends of boat)
Thanks for sharing your thoughts and ideas.
Scott
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