Hello.
-----Ursprüngliche Nachricht-----
Von: anupama@ee.washington.edu 
An: mems-talk@memsnet.org 
Datum: Donnerstag, 3. April 2003 21:45
Betreff: [mems-talk] C4F8 etchant


>Hi MEMS Community,
>
>I would like to know if anyone knows of a chemical that
>would etch C4F8 (octofluorocyclobutane)


The polymers you are depositing are called "plasma polymerized fluorinated
monomer" (PPFM) films. The chemical formular depends on process conditions,
generally the films are more or less "teflon-like", consisting of
CF2-groups. Riccardo d'Agostino edited a book about the deposition and
etching of these films (Plasma deposition, treatment and etching of
polymers, Academic press, 1990, ISBN 0-12-200430-2), and also a number of
articles in "Journal of Vac. Sci. Technol.", "J. Applied Phys.", and "Plasma
Chem. and Plasma Process.". Find these articles on SPIN Web:
http://ojps.aip.org/spinweb/ -> search SPIN database. At least, you can
access the abstracts. Find articles with keywords "polymer" and "plasma" or
the like.

>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.

Some researchers report difficulties in removing the polymer films in the
absence of energetic ion bombardement. If your device can survive ion
bombardment, you could etch the polymer in a RIE etcher, with high DC bias
(100 to 200V) oxygen plasma. Some researchers suggest a mixture of CF4 and
O2 as etching gases. Maybe a small addition of SF6 to your O2 will help to
remove the polymer. If you want to use wet etching, a solution called
"piranha" might do the trick, but I would prefer plasma etching. Does the
manufacturer of your DRIE etching tool suggest a cleaning recipe for the
chamber?


I use a mixture of CHF3 and Methan (CH4) as process gases for sidewall
passivation, and we have not yet found difficulties in removing the sidewall
passivation layer, by oxygen resist stripper (asher). We don't have an etch
tunnel, maybe that's why.

Regards

Burkhard

>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: anupama@ee.washington.edu