Hi,
  You should consider running an oxygen plasma clean on your samples in
the DRIE before you take them out. Check with the manufacturer as this
is hard on o-rings.

-Mike Martin

>>> mprao@engineering.ucsb.edu 03/25/03 06:06PM >>>
Hello All,

   Hoping someone might be able to provide advice regarding some Si
oxidation furnace contamination issues we're having.  We have a new
Tystar furnace that we've been using pretty heavily for the past year or
so.  Up until recently we hadn't been all that rigorous about
instituting a standard pre-furnace cleaning procedure so it wasn't
uncommon for wafers to be run that had come straight from the Si DRIE
(i.e. we didn't clean them in any way before putting them into the
furnace).  We assumed that the high temperature oxidizing environment
would take care of what little fluoropolymer remained on the etched
wafers so there wouldn't be any problems. However, we've recently
noticed a buildup of a thin, flaky, white, seemingly polymeric residue
on the cool parts of our furnace which is now making us reconsider that
assumption.

    The film is easily scraped off in small sheet-like sections of up
to a couple mm long, but it crumbles easily under further handling.  The
film looks a lot like teflon and FTIR seems to indicate that it does
bear at least some resemblance to teflon. Based on these observations,
we think that the contamination was caused by volatilization and
redeposition of the fluoropolymer put down in the Bosch process. In
light of this realization, we're now going to most likely institute some
sort of mandatory pre-furnace clean procedure (e.g. piranha and/or RCA 1
& 2), but we just want to make sure that our hypothesis regarding the
contamination source and it's mitigation are valid.  Any and all advise
and suggestions would be greatly appreciated.


Thanks for the help,

Masa

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