>    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]