Hi Yuchin,

Unfortunately, your figure is not readable and you don't tell us what is
your cavity size (mm, um or sub-um),it may change the strategy.
I would like to suggest you the following scheme:
1. Remove Si3N4 using CF4 plasma;
2. Fill your cavities with photoresist (photolithography, resist
development);
3. Deposit hydrophobic FDTS self-assembled monolayer (MVD-100 system, vapor
phase deposition). It is a teflon-like layer, just very thin (1.3 nm) and
uniform. It adheres very well on Si (native oxide) surface, but does not
create dense coating on photoresist, so allows to lift it off.
4. Remove photoresist and any FDTS on it using acetone(lift-off).

There are few other methods of patterning hydrophobic layers, which might be
more appropriate (depends on your feature size). Please contact me for
further discussions.

Boris Kobrin
Director of Technology
Applied Microstructures, Inc.
(408) 907-2855 x2805 office
(408) 594-0654 mobile
[email protected]

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Message: 7
Date: Fri, 17 Mar 2006 15:32:42 +0800
From: Yuchin 
Subject: [mems-talk] teflon deposit problem
To: [email protected]
Message-ID: <[email protected]>
Content-Type: text/plain; charset=UTF-8; format=flowed


Hello all,

I have some questions about depositing teflon(or teflon-like)

1. If there are some cavites  on silicon substrate.  I want to deposit
teflon on Si surface but not on Si3N4
  (Si3N4 is in the cavity, as the figure).
   How do I remove the teflon on Si3N4 easily after the CVD teflon
process(or other teflon deposit process)??
   I know that the adhesion between teflon and Si3N4 is bad, may I immerse
the wafer in acetone(or something else)
   to remove the teflon on Si3N4??
   I can't use photolithography process, because the height of Si3N4
patterns are  much lower than Si. PR can't coater well on it.


2. After removing the teflon on Si3N4,  I will use RIE(CF4) to remove Si3N4.
   Will CF4 plasma attack teflon (I need the hydrophobic property of
teflon)???

Thanks for your advices.