I think manufacturers of DRIE's recommend against using O2 plasmas since
it attacks O-rings. In particular, on STS systems with He back side
cooling the O-ring that seals the back of the wafer gets degraded.
Despite this I have used short O2 etches in the STS system and it works
great! I have used these short etches not so much to remove the teflon
like polymer but to change its surface from one that is very hydrophobic
to hydrophilic so that it can be wet etched in Nanostrip.

good luck,
   Mike Martin

>>> [email protected] 04/04/03 10:00AM >>>
>    7. C4F8 etchant ([email protected])

    If your problem is coming from the C4F8 gas what your dealing with
is
the removal of a fluorocarbon film, namely CFx where
x =1,2,3. Typical XPS data shows the F/C ratio of the fluorocarbon film
goes
down with decreasing F/C ratio of the parent molecule. To put it short
gases
like CF4 deposit very little in a HDP and C4F8 deposits a lot more
i.e.
CF4 Message: 7
> Date: Thu, 03 Apr 2003 10:13:55 -0800
> From: [email protected]
> Subject: [mems-talk] C4F8 etchant
> To: [email protected]
> Message-ID: <[email protected]>
>
> Hi MEMS Community,
>
> I would like to know if anyone knows of a chemical that
> would etch C4F8 (octofluorocyclobutane)
>
> During the DRIE process, C4F8 is deposited for sidewall
> passivation and mask protection in the alternate deposit and
> etch cycles. After the DRIE I remove the photoresist AZ4620
> by putting the wafers in a Barell Asher with O2 plasma
> (40mTorr, 300 Watts for 10mins) and subsequent treatment
> with resist strips EKC for 10 mins at 60C and AZ300T for 10
> mins at 75C.
> This I believe should remove the C4F8 deposits as well.
>
> However from our SEM pictures we find that, possibly the
> unremoved C4F8 acts as a mask for further Silicon etching
> (in RIE)and this mask is undercut resulting in the loss of
> our structures.
>
> I would appreciate very much if someone on the list could
> get back to be with an idea of how to strip the C4F8.
>
> Sincerely
> Anupama
>
> Anupama V. Govindarajan
> Graduate Student - EE MEMS laboratory
> Department of Electrical Engineering
> University of Washington
> Campus Box 352500, Seattle WA 98195
> Phone: (206)-221-5340
> email: [email protected]





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