Hi Grace,

   I would also recommend trying the etch without the ammonium persulfate.
However, I am not sure what that will do to your oxide to aluminum
selectivity.  A typical recipe is listed below.

250ml TMAH (25% from Aldrich)
375 ml H2O
22g of silicic acid
90C with an etch rate ~1.0um

Phil Tabada

-----Original Message-----
From: gracekuo [mailto:super511_1028@yahoo.com.tw]
Sent: Sunday, August 18, 2002 10:13 PM
To: mems-talk@memsnet.org
Cc: gracekuo@gct.com.tw
Subject: [mems-talk] RE: Contamination issue of additive in THAH etching


Hi Philipe and Mike,
thank you for your reply,
let me describe the contamination more specific,
after we add the AP (2.5g dissolved in DI water, add
into the etchant per 15 min. )
into the heated etchant (2L ; include TMAH, AP, SA,
and DI water),
we can see white particulates float over the etchant
immediately,
the particulate size is quite big (~2x1x1 cm3),
and it can dissolve into the etchant after 10~15min.
And after the etching, we just clean the sample with
DI water,
but as we observe the etched sample,
there are plenty of particles over the sample surface,
and the particulates is especially big stored in
etched cavity,
as we analysis the particle with EDAX, it just have Si
and O composition,
i dont know if it is just the silicic acid that
precipitated out of solution,
and could anyone give us some suggestion to prevent
this particulates,

thank you for your help,
grace

Email:super511_1028@yahoo.com.tw

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