SOP for Piranha solutions


General Notice

These are not authorized official regulations for general use of piranha solutions. But, these are valuable rules to protect your safety and everyone should follow these rules whenever using Piranha in the LAMP cleanroom.

  1. A piranha solution 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. [1]

    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 gas. [1]

  2. 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.

  3. The 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.

  4. Any accident regarding the use of Piranha solutions must be reported without delay to the lab manager.

Protection equipment

  1. The handling of Piranha solutions requires special protection equipment in addition to the regular clean room protection outfit (see Lab Safety page) .

  2. 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.

  3. As 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.

Handling of Piranha solution

  1. 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).

  2. 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.

  3. Mix the solution in the flow hood with the sash between you and the solution. Wear the full protection.

  4. 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. 

  5. Piranha solution is very energetic and potentially explosive.  It is very likely to become hot, more than 100 degrees C.  Handle with care.

  6. 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 

  7. Leave the hot piranha solution in an open container until cool. 

  8. Never store hot piranha solutions.  Piranha stored in a closed container will likely explode. 

  9. Adding any acids or bases to piranha or spraying it with water will accelerate the reaction.  This includes Photoresist, which is a strong base. 

  10. Mixing hot piranha with organic compounds may cause an explosion.  This includes acetone, photoresist, isopropyl alcohol, and nylon.

  11. Do not store wash bottles containing organic compounds on the piranha deck. 

Piranha waste disposal

  1. 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 explode!

  2. 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.

  3. 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.

Emmergency procedure

  1. In case of large exposure, the victim should be removed from the contaminated area, placed under a safety shower while emergency personal is contacted (911)

  2. All contaminated clothing should be removed immediately with appropriate gloves and safely discarded.

  3. In case of contact with the skin, the affected area must be immediately rinsed with large amounts of water for at least 15 min.

  4. 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.

  5. 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

 Do not store piranha.  Mix fresh solution for each use. Excess solutions should be disposed as explained in paragraph #4.
Prepared by J. Park and L. Henn-Lecordier; last update: January 2003 by L. Henn-Lecordier
[1] Lianne Lester, Safety and Training, Nano-Systems Fabrication Lab,
University of Manitoba

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Laboratory for Advanced Materials Processing, University of Maryland - 2009