Some help required regarding dual doped TMAHW solution

Ravi Shankar

2007-03-26

Hi all,
I am facing some problem regarding dual doped TMAHW solution. I am doing
silicon etching using dual doped TMAHW (5%) with silicic acid (SiA, 38
grams/lit) and Ammonim Peroxodisulphate (AP, 7.5 grams/lit) at 80 deg
celcius. (these data i got from some literature). After dissolving silicic
acid in TMAHW solution, I would like to know what is the exact way of adding
AP?
1) whether to add full amount of AP (i.e. 7.5 gms/lit) initially and then
dip the Si wafers into the { 5% TMAHW + 38 gms/lit SiA +
7.5gms/lit AP }
solution. (when i tried this method, i found after some time etching
stopped, but the etched Si surface was smooth. i could not get desired etch
depth of 250 microns) or
2) add 1.5 gms/lit AP, wait for some time, dip Si wafers inside the
solution {5% TMAHW + 38 gms/lit SiA + 1.5 gms/lit AP} and every one hour add
1.5 gms/lit AP (Total etching time was 5 hours, when i tried this method i
could get the etch depth of 250 microns. But, the etched Si surface was
rough and i could observe some hillocks formation on silicon surface by
optical microscope. Also, etching was not uniform. when tried this method to
fabricate array of cantilevers i found thickness of cantilevers were not
same for all. Also, within a single cantilever, thickness was not uniform
along the length of the cantilever).
How to get uniform cantilever structure (or any Si etched structure) with
smooth surface using dual doped TMAHW solution. Any help will be highly
appreciated. Thanks in advance.
Regards,
A. Ravi Shankar,
Research Scholar,
Microelectronic Centre,
Advanced Technology Centre / E&ECE Department,
IIT Kharagpur.