You should perform the etch at 5% wt. TMAH and add 7.5g/l ammonium persulphate
(AP).  In the past we have used silicic acid (SA) instead of silicon powder (it
is a little safer) at a concentration of 40g/l. The etch is performed at 80C
using a reflux condensor. I would wait until the solution reached temperature
before adding the ammonium persulphate.  It is common for some of the components
to not entirely dissolve.  This solution would remain stable for only about an
hour. After which you may need to refresh it with TMAH, AP, and SA. Note: be
careful if you continue adding silicon powder.  It can rapidly evolve hydrogen
and go boom! We have some first hand experience.


Good luck,
   Michael Martin
   U. of Louisville

>>> "abhaya joshi"  3/16/2007 7:19 AM >>>
Dear friends
i am working on Si etching using TMAH.
In my experiment, i am using 50 ml of 10wt% TMAH . In order to protect AL
metal, i am adding  Si powder  3.2 wt %  Si powder (1.6 gm)  and 1.3 wt %
ammonium persulphate (0.65 gm).
but at the time of etching at 90C, after 20-25 min ,  the TMAH is getting
vapourised and Added powder of Si and ammonium persulphate is remaining in
container
This is clearly sign of added material is not getting dissolved properly.
What i should do in order ti solve this problem?