Thank you very much,

Indeed, I am told by the Tegal company that I cannot go below 1.5Torr otherwise
I may damage the instrument.  With your comment, I will try to found out this
mean free path and see if I can use our instrument to etch the polyimide.

Thank you again :-)

Suzanne Paradis, eng. M.Sc.


-----Original Message-----
From: mems-talk-bounces@memsnet.org [mailto:mems-talk-bounces@memsnet.org] On
Behalf Of Samadhan B. Patil
Sent: July 6, 2009 4:43 PM
To: General MEMS discussion
Subject: Re: [mems-talk] Removal of polyimide sacrificial layer

Hi Suzanne,

To remove a sacrificial layer using asher, pressure in the chamber should be
such that the mean free path (of the species in a plasma) is less than the
thickness of the sacrificial layer.

I dont know much about the "Tegal 903E plasma etcher" but you will need to
find a compramise between too high pressure and the pressure just enough to
give less mean free path. Rough calculations should help you to decide this
pressure.

     Regarding warpage of the bridge, it can be because of the residual
stress in the structural layer and may arise because of  a difference in the
thermal expansion co-efficient of polyimide and the structural layer (or
deposition temperature of the structural layer).

regards,

Samadhan