Standard Operating Procedure
for Piranha Solutions
1- General notice
A piranha is used to remove organic residues from
substrates. Two different solutions are used. The most common is the
acid piranha: a 3:1 mixture of concentrated sulfuric acid (H2SO4) with
hydrogen peroxide (H2O2). Also used is the base piranha: a 3:1 mixture
of ammonium hydroxide ( NH4OH) with hydrogen peroxide (H2O2). Both are
equally dangerous when hot, although the reaction in the acid piranha is
self-starting whereas the base piranha must be heated to 60 degrees
before the reaction takes off. 
There are many things which will cause the reaction to accelerate out of
control. "Out of control" can mean anything from the piranha foaming out
of its bin and on the deck, to an explosion with a huge shock wave
including glove and acid-gown shredding glass sharps. Piranhas burn
organic compounds. If you provide sufficient fuel for them (i.e.
photoresist, IPA), they will generate enormous quantities of heat and
Any LAMP users who want to use Piranha
solutions in LAMP solution must be qualified and authorized by the
lab manager prior to do any work.
list of the authorized users is published on
this web site. If your name is not on this list, you are not allowed
to use Piranha solutions at any time.
Any accident regarding the use of Piranha
solutions must be
reported without delay to the lab manager.
The handling of Piranha solutions requires special protection equipment in
addition to the regular clean room protection outfit (see Lab Safety
The additional protective equipment include: a full face shield, heavy
duty rubber gloves (regular Nitrile gloves used in LAMP will not provide sufficient
protection), as well as an acid apron to wear on top of the lab coat.
Gloves are located in the acid cabinet, apron and mask are available
next to the wet bench.
a reminder, open-toed shoes are not allowed when working in
the lab and bare legs must be covered by wearing a full size bunny suit.
3 - Piranha solution handling
- Piranha solutions, as well as any corrosive or hazardous substances,
can only be used in LAMP during operational hours (9 am to 6 pm,
Monday to Friday) and requires at all time the presence of a second
knowledgeable user (buddy system).
- Whenever handling Piranha, only use glass containers (preferably
Pyrex). Containers used during the experiment
must be very clearly labeled and a warning sign, visible by any user
working under the flow hood, must be posted at all time to indicate
that the solutions contains Piranha mixture.
- Mix the solution in the flow
with the sash between you and the solution. Wear the full
- When preparing the piranha solution, always add the peroxide to
the acid. The H2O2 is added immediately before the etching process
because it immediately produces an exothermic reaction with gas
(pressure) release. If the H2O2 concentration is
at 50% or greater, an explosion could occur.
- Piranha solution is very energetic and potentially explosive. It
is very likely to become hot, more than 100 degrees C. Handle with
- Substrate should be rinsed and dried before placing them in a
piranha bath. Piranhas are used to remove photoresist and acetone
residue, not the compounds themselves
- Leave the hot piranha solution in an open container until cool.
- Never store hot piranha solutions. Piranha stored in a closed
container will likely explode.
- Adding any acids or bases to piranha or spraying it with water
will accelerate the reaction. This includes Photoresist, which is a
- Mixing hot piranha with organic compounds may cause an explosion.
This includes acetone, photoresist, isopropyl alcohol, and nylon.
- Do not store wash bottles containing organic compounds on the
4 - Piranha waste disposal
- The primary hazard from storage of piranha etch waste is the potential for
gas generation and over pressurization of the container when the solution is
still hot. If you store a hot solution in a air tight container, it will
- Therefore prior to store the piranha solution, it must be left in an open
container in order to cool down for several hours (overnight). It is your
responsibility to make sure that the open container is very clearly labeled
and left in a safe area for overnight cool down.
- Once cooled down, the solution can be transferred into a closed glass
container for waste storage. The container must be very clearly labeled with
the solution name and composition and must include VERY VISIBLE warning signs
not to add any other types of chemicals.
5 - Emergency procedure
- In case of
large exposure, the victim should be removed from the contaminated
area, placed under a safety shower while emergency personal is
- All contaminated
clothing should be removed immediately with appropriate gloves and
- In case of contact with
the skin, the affected area must be immediately rinsed with large
amounts of water for at least 15 min.
- In case of contact with
the eye, irrigate the eye for at least 30 minutes, keeping the eyelids
apart and away from eyeballs during irrigation. Place ice pack on eyes
until reaching emergency room.
- In case of inhalation,
it may irritate the respiratory tract. Conscious persons
should be assisted to an area with fresh, uncontaminated air. Seek
medical attention in the event of respiratory irritation, cough, or
tightness in the chest. Symptoms may be delayed.
Supply and storage
not store piranha. Mix fresh solution for each use. Excess
solutions should be disposed as explained in paragraph #4.
J. Park and L.
Henn-Lecordier; last update: January 2003 by L. Henn-Lecordier
 Lianne Lester, Safety and Training, Nano-Systems Fabrication Lab,
University of Manitoba