Zhiwei,
For Piranha, I add 1 part of H2O2 (30%) to 3 parts concentrated H2SO4. The
reaction is exothermic and the solution heats up for the first few minutes.
Once the solution cools down, you can heat it upto 130 deg C for cleaning.

Sumant
Belford Research

-----Original Message-----
From: Zhiwei Zou
Subject: [mems-talk] About the Piranha cleaning

I am trying to get a very clean Au surface and then make the SAM layer on
it. I read some paper and find that many of them used hot Piranha
(H2O2_H2SO4) to clean the Au surface. But also I find that Piranha solution
is very dangerous.

So I want to know that whether there is another way to clean the Au surface
before deposit the SAM layer. e.g. Plasma ashing? RCA clean?
Or what's the right procedure for the Piranha cleaning (I find  someone add
the H2SO4 into the H2O2 but others do it reversely).