Hi,

When I used a fixture to etch in KOH I learned the following. You need to
have 12 screws not 6 screws. You also need to place  the fixture on a hot
plate and heat it to the same temperature as the KOH bath. Then tighten the
screws using an alternate pattern, think the markers on a clock and go 12
then 6 then 1 then 7 ect. Using a fixture is still tricky because you create
a drum head effect because of the "O"-Ring seal.

After all the screws are snug then remove the fixture from the hot plate and
place it in the KOH HOT and slowly. When your etch is complete take the
fixture out and place it in warm water and then after it cools start the
rinse.

You can also try to use Apiezon black wax to protect the front side.

Rick Morrison
Radant Mems


-----Original Message-----
From: mems-talk-bounces+rmorrison=radantmems.com@memsnet.org
[mailto:mems-talk-bounces+rmorrison=radantmems.com@memsnet.org]On Behalf
Of Li Wang
Sent: Saturday, June 05, 2004 5:21 PM
To: General MEMS discussion
Subject: [mems-talk] KOH etching protection


Hello,

I want to protect my front side during KOH etching because there is
polysilicon on it. I designed a jig which seal the wafer with O-ring and
sandwiched the wafer in between two plastic pieces, fastened with six
screws. But my problem is that the forces on the screw is kind of difficult
to control and the wafers were broken several times in testing when the
wafers were etched thinner. Another way I tried is PDMS protection. I put
PDMS on the front side. The problem I met is that the PDMS will be detached
from the wafer after I put the wafer into hot KOH for 2 hours. Anyone has
any idea of KOH protection, please email me to help me out. Thanks a lot.

Li Wang





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