We have a STS DRIE for silicon and I understand that metal masking
layers are not an option due to metal contamination problems. How about
trying a nice thick resist? Or to minimize sputter etching, decrease the
substrate to plasma bias. I think a nitride mask would also get
etched.]

Good luck,
    Mike


>>> [email protected] 06/19/02 06:23AM >>>
> If your problem is related to erosion (mechanical) and less on
corrosion
> (electrochemical)

yes, during the RIE process the Aluminum mask is being sputtered away.

Primarily mechanical erosion due to ion bombardment.

> very good..... So the rule would be to consider your process and try
to do
> everything you can do to keep the temperature down

We can cool the target electrode to some extent (it is water cooled,
and
currently maintains room temp, but I think we could bring it close to
5-100C, I'd have to double check the system to see if there's a lower
limit.  I'd also rather not get to close to freezing the system.
Facilities manager wouldn't appreciate that too much :)

Anyway, would a 200C delta-T make that much of a difference in the
sputter threshold of the material?  I'm also concerned about how the
drop in temp will affect the etch rate of the SiO2.  I seem to recall
that polymer formation (etching with CHF3/O2) shows a strong temp
dependence when increasing temp, don't remember what happens if
cooling
increases polymer formation/strength, or if the effect tapers off
below
room temp.

> The second consideration for a strength increase is to alloy it...

We get the wafer from a foundry (through the MOSIS service) including
the aluminum.  I'm now looking into the exact aluminum composition,
but
it isn't something I have control over.

Anyway, I guess I'm still primaily focusing on finding a way to
controllably oxidize just a thin portion of the mask (i.e., more than
the native thickness (~2-3nm) but not more than 200-300nm).  Either
thermal or plasma oxidation seems to be the way to go, but I don't
have
any good numbers to start with (i.e., temp/time for oxidation), and
I'd
rather avoid just picking some parameters at random.

Someone else did mention that instead of oxide, possibly I could
nitride
the aluminum instead.  Starting to look into this now.  Seems like a
nitrogen plasma environment with the right parameters could do it, and
AlN is supposedly some pretty tough stuff.  With both oxidation and
?nitridation? I need to make sure that I don't convert the entire
mask,
as it needs to be present as Al after the etch process.

Hi ho hi ho....

Nick Jankowski
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