Any combination of sulfuric acid and hydrogen peroxide can be referred to as
Piranha.
For student labs, mixing in the 3:1 range and allowing self-heating seems
common.
The solution is only good while it's hot and there is still hydrogen
peroxide in it.
The peroxide eventually decomposes into water and oxygen and evaporates off.
The solution is then disposed of.
In many fab labs, such as the UC Berkeley Microlab, as well as production
labs, a dedicated sink sits ready all the time.
This sink starts with pure H2SO4 that is heated (to say 120 C) all the time.
Immediately before use, H2O2 is added. In the Berkeley Microlab, the ratio
is about 5 liters of H2SO4 to 100 ml of H2O2, or about 50:1.
The solution can be changed out semi-weekly.
Use of this technique in production labs shows that is works.
--Kirt Williams
----- Original Message -----
From: "Matteo Dainese"
To:
Sent: Thursday, March 01, 2007 9:20 AM
Subject: [mems-talk] Piranha etch
> Hello,
> I need to use piranha solution (H2SO4 + H2O2)
> to clean my wafers after etching, but it's not clear to
> me what is the best ratio in solution between these two
> chemicals to have optimal removal of resist and post etch
> fluoropolymers.
> In the literature I found H2SO4:H2O2 as 2:1 or 3:1 or even 6:1.
> Sometimes there is water dilution. On the other hand they
> never explain why they choose these ratios...
> Has anybody of you some knowledge about this?