Dear Suzanne,

Adding CF4 to the plasma (as suggested by other colleagues) is a good
way of increasing the etch rate. However, if your suspended layer is
Si3N4, you have to be careful about the percentage of CF4 that you add,
because CF4-added O2 plasma significantly attacks to the Si3N4. You
should not exceed 4-5% percent, which means that you can add ~2 sccm of
CF4 to 40 sccm of O2.

Some HD microsystems polyimides are etched in conventional photoresist
strippers, if not totally cured. We have been using PI2737 (which is out
of phase now, but they are producing HD4104 as a similar product) as the
sacrificial layer. But wet etching requires ciritical point drying at
the end of the process (as suggested by other colleagues).

Regards,

Kagan TOPALLI, Ph. D.
Senior Research Engineer
METU-MEMS Center
Middle East Technical University
TR-06531 Ankara Turkey
Phone: +90 312 210 45 46
Fax: +90 312 210 23 04
http://www.mems.eee.metu.edu.tr/~topalli/


Paradis, Suzanne wrote:
> Good afternoon,
>
> I want to use  polyimide as a sacrificial layer (4 microns gap) to do a
> suspended bridge.  My concern is that I do not have a asher, I have a
> Tegal 903E plasma etcher which is meant to run at high pressure (1.5 to
> 4 torr).  I ran a sample at 1 torr and 40 SCCM O2 for 2 hours. ( I
> understand that this is still too high as I read in the literature that
> much lower pressure is recommended for suspended material).  Anyway, the
> polyimide started to be etch in a wavy manner but the portion of the
> suspended layer that started to be free was..warping.  I stopped the
> process .  I tried with 275mt (even though I am out of range of the
> instrument) and it took forever to remove most polyimide but the freed
> layer was very warped.
>
> Is there any hope that I can remove the polyimide with this instrument
> or should I forget about it?
>
> Thank you very much
>
> Suzanne Paradis, ing. M.Sc.