Zeng,

I have been using Piranha etch with H2O2 added to H2SO4 and its not
dangerous if used in the right ratio and concentration. I am citing some
links from the web which recommend adding H2O2 to H2SO4 and not the other
way round. As is widely known, adding water to concentrated H2SO4 is
dangerous but adding the right concentration of H2O2 (30% by vol.) though
exothermic, is a controlled reaction.


http://www.boldtech1.com/technical/piranha_etch.html

http://www.enma.umd.edu/LAMP/Sop/Piranha_SOP.htm

But I might be missing something and would like to hear from others who do
use Piranha as to what their procedure is.

Thanks
Sumant
Belford Research


-----Original Message-----
From: Hongjun-ECE
Subject: RE: [mems-talk] About the Piranha cleaning

Belford,

Please confirm that it is H2So4 added to H2O2, instead of H2O2 added to
H2So4, which might be dangerous.