Dear MEMS researchers,

I'm now working on wet etching of silicon using KOH solution, I meet one
problem in my study, I wonder if anyone could help me.

I use KOH to etch 200um thick of (100) silicon, I propose to use 2000A
thick of Si3N4 as a mask, but before this etching step, a metal electrode
has been deposied on the wafer. The material of the electrode to be chosen
is TiW/Au, Al or Pt. By using TiW/Au I could use LPCVD to get good quality
Si3N4 which would satisfy my need of protecting the desired part on my
wafer through wet etching. But unfortunately, the process center don't
allow me to put a wafer whith Au into their LPCVD machine used mainly for
IC processing which would bring heavy pollition to the machine. Then other
alternatives of electrode material would be Al or Pt which can't withstand
the high temperature of LPCVD and other Si3N4 deposition process except for
PECVD. As you know, however, I can't get good quality Si3N4 mask that is
enough to protect sturcture on wafer by using KOH to etch 200um thick of
silicon in at least 3hrs.

Could anyone who have experiences in this field can give me any advice on
how to make my Si3N4 mask and how thick is the Si3N4 layer and the SiO2
layer under it, and how thick would be prefered if I have to use only SiO2
as a mask though my wet etching as a tradeoff.

Any help from you would be greatly appreciated!

Please return to Liujing@cenpok.net.

Sincerely yours,

Jing Liu