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General Chemical Safety

  1. Access to "wet labs":  General chemical safety training is required to access the following "wet lab" spaces: Cleanroom/L119, the MOCVD lab, L106 (ExFab Stinson), and rooms 155 (ExFab Mavericks) and 159 (ExFab Capitola).   Even if you do not intend to use any operations with hazardous gases and chemicals, anyone with access to these spaces must be trained to be aware of the hazards they present, the safety systems, and how to respond.  
  2. Room 155/ExFab Mavericks:  This space has fume hoods for chemical handling. Additional training is required to gain access to this space and is customized to accommodate each person's needs.  
  3. Station Specific training:  Safety training gains you access to lab spaces.  For training on specific equipment and modules, consult the equipment table or any staffer.


"Hazard Communications" describes the various resources for safety and use information about the chemicals, gases, and materials in the labs.  Here are resources available to labmembers.

  1. Chemical Labels. Each chemical container is required to have a label, provided by the manufacturer, which in addition to composition, contains the following information:

    - Precautionary Measures.
    - One or more Statements of Hazard, which describe in more detail the hazard presented.
    - A signal word, which is one of the following: “Caution”, “Warning” or “Danger”, indicating potential for hazard (in order of increasing potential hazard.)
    - First Aid or other information (this may not always be present on the label.)

    Remember, only chemicals in their original containers will have these labels. Chemicals that have been dispensed for use or into other containers may not have this information. Since gases are supplied remotely, their label information will not be handy. As a qualified user, it is your responsibility to know the chemicals being used at your station, and the hazards posed by each.
  2. SDS.  Chemicals manufacturers and distributors are required by federal law to provide safety information for each product. The Safety Data Sheet (SDS, once called “MSDS”) contains information on general composition, physical and chemical properties, toxicology, and storage and handling recommendations of each product. SDS documents for all the chemicals that SNF routinely stocks can be found on the SNF website. Labmembers wanting to bring in any new chemical or chemical mixture for use in the lab must provide an SDS as part of the New Process & Materials request.

    SDS information is written without specific regard to application or context for use in research. So, make sure to consult with the website and staff for any questions about safety and use of these materials. You should know the main hazards, handling requirements, and disposal methods for any chemical you use in the lab.
  3. Stanford EH&S. The Stanford University Environmental Health and Safety (EH&S) department maintains an extensive website library on chemical safety. Included in the library is educational material on safety basics, such as how to decipher the terminology in an SDS form.
  4. SNF Website has lots of info about hazardous materials and their specific use in the lab, including: links to SDS sheets; lists of approved materials in the lab; and procedures for safely bringing in new chemicals and new processes. The website contains links to Operating Procedures for each tool (in the Equipment section) which includes safety information for the chemicals and other hazards at each station. The Processes section of the website includes much information about the standard use of many of the common chemicals found in the lab.


The gases, chemicals and materials used at SNF are categorized into six general chemical hazard classes: corrosive, oxidizer, air/water reactive, flammable, toxic/poison, and non-toxic, as detailed below. Many chemicals fall into more than one class.   Safety policies on storage and use of chemicals begins with identifying the primary chemical hazard class.

  1. Corrosive or "caustic" damages or destroys living tissue, such as skin. Splashes in the eyes can cause blindness. Inhalation of vapors can destroy lung tissue. Corrosives include acids and bases. In case of localized external exposure, promptly flush the affected area with plenty of water, for at least 15 minutes. For more general external exposure, use a safety shower: remove clothing while showering and flush bare skin for at least 15 minutes. Exposure of corrosives to the eyes is extremely serious; flush immediately, either with a spray gun at your wet bench or the nearest eyewash station. Eyes should be rolled up and down, and side to side, continuously, to allow clean water to flush behind the eyeball. For any exposure to corrosives, get help. The victim should be taken to the emergency center for evaluation and treatment.
  2. Oxidizer compounds have a pair of electrons, often due to the presence of a reactive oxygen atom.  Examples of oxidizers at SNF include hydrogen peroxide, nitric acid, and sulfuric acid.  Mixing an oxidizer with an electron-accepting, reducing compound, may result in an often violent reaction, possibly an explosion. Oxidizers should not be stored or mixed with flammables or combustible chemicals and materials. 
  3. Water reactive compounds are generally concentrated acids or basis that rapidly generate heat and/or gas upon mixing with water. The primary hazard of water-reactive compounds is superheating of water.  Explosion may result, sometimes delayed well after the addition of water, due to incomplete mixing.  Never pour water-reactive mixtures directly into a sink drain.  Instead, aspirate water reactive mixtures at wet benches; the high dilution factor and rapid mixing dissipates heat and prevents superheating. Concentrated sulfuric acid and piranha clean are examples water reactive materials.
  4. Flammables include most solvents, such as acetone, isopropanol, and methanol. The “flash point” of a flammable is the lowest temperature at which its vapor concentration in air can ignite. The source of ignition may be heat (such as a hot plate) or a spark (such as from an electrical tool). Because the vapors travel, the ignition source can be far away from the flammables container. To minimize hazards, always work well within the exhausted area of the appropriate bench (behind the red line). The air pulled into the exhaust area will keep the concentration of vapors below the flash point. Where possible, minimize the quantities of flammables used. Before working with flammables, always note the location of the nearest safety shower and fire extinguisher. Flammables should be stored in the designated flammables cabinet; no flammables may be stored in the lab. Flammables must be kept away from oxidizers.
  5. Toxic/Poison: A toxic material is one that has poisonous or harmful effects. There are formal, quantifiable definitions as to what comprises a toxic material and to what degree it is toxic. These definitions are based on lethal dosages for lab animals when administered orally or through inhalation.
  6. Non-toxic: A non-toxic material is one that is not likely to result in harmful effects with normal use. 


Every chemical in the lab must be stored in the designated area appropriate for its hazard class. Each storage area is designed for safe storage of chemicals of a particular set of hazard classes (i.e., they are appropriately ventilated, chemically resistant, and built against the main physical hazards presented by the chemicals to be stored there.) Thus, it is a safety imperative that all chemicals in the lab be stored appropriately in one of these designated storage areas. No chemicals may be kept in personal storage bins. No chemicals may be stored on work surfaces of any wet benches.

  1. General use chemical storage: The SNF staff keeps general use chemicals stocked in these areas:
    • Chemicals Pass-through, for corrosives and oxidizers, such as etchants, cleaning agent
    • Flammables cabinets  solvents, bases, organics (Resists, developers, solvents
    • Flammables Refrigerator  for Solvents, organics, other temperature sensitive materials

      Ensure your safety and that of others when using these chemicals by following procedures for handling and transporting chemicals in the lab.
    • You must be trained and qualified in use of wet benches before working with chemicals.
    • When returning chemicals, the outside of the bottles must be clean and dry.
    • Use opened containers first.
    • Notify SNF staff when chemicals are running low (particularly important before a weekend!)
  2. Personal chemical storage: Labmembers may store chemicals for personal research use on request, provided it is registered in our Chemical Inventory and marked with a yellow label.  Submit your request to
    • Approval. The chemical must be approved for use in the lab and the process for which you plan to use it. 
    • Storage.  In must be stored in the designated personal storage area for the appropriate hazard class (adjacent to general use storage). 
    • Labeling. Containers for personal chemicals must be registered as indicated by the official yellow hazardous materials label, available from staff. The information required on the label includes:
      ⇒ Your contact info:  Full name and email.
      ⇒ The main hazard group (corrosive, flammable, oxidizer, reactive, toxic/poison, non-toxic)
      ⇒ Chemical Storage Group identifier (see the Stanford Chemical Safety Database and the SNF website) is denoted by a single letter.
      ⇒ Exact name(s) of the chemical.
      ⇒ Container volume (i.e., 500 ml)
      ⇒ End date:  not to exceed one year
    • Disposal. You are responsible for removing or disposing of the chemical when it is no longer needed.


  1. Before working with any chemical, you should always do the following:
    • Know the location of the nearest safety shower and eyewash station.
    • Work only in an appropriately exhausted hood area to prevent inhalation.
    • Use protective gear (safety goggles and face shield, tested and resistant gloves, chemical apron) to prevent direct contact with the chemical.
    • Know the main hazards and proper disposal method of the chemical you are using.
    • Make sure you have all the labware and materials you need before starting your work.
  2. For any suspected exposure to skin or eyes, immediately rinse the affected area:
    • For small areas of skin (i.e., your hand), you can use the hand sprayer or the dump rinse tank at a wet station. Remove the affected glove or clothing.
    • For larger areas, use the safety shower.  Remove the affected clothing.  At each safety shower, there is a bag with a towel and extra clothing.​
    • For exposure to eyes, use the eyewash.  Call for help to get to and use the eyewash.
    • Get medical attention, immediately if TMAH or HF are suspected. Bring the SDS to inform the medical professional of the chemical type and hazard.
    • Contact EH&S and/or SNF Duty Phone.

Training is required for any chemical handling in the labs.  Once trained, you are responsible for safe use and disposal of waste.  If you see chemicals improperly handled, you are responsible for following up with the individual or report to staff.  Safety is everyone's responsibility.  Improper disposal could result in explosion and injury. Policy violations may even result in lab shutdown. Therefore, take time to consider how to manage waste in your experimental plans. And remember that we all bear the economic and environmental costs; so please minimize the waste you generate. There are four ways of disposing of chemical waste; the safest method depends on the kind of chemical waste, as described below.  If you have any questions about the best method for handling chemical waste, please reach out to staff.

  1. The Acid Waste Neutralization (AWN) System is a network of piping that runs from the labs into a central system of holding tanks, where the chemical waste is successively neutralized and diluted, before draining into the sewer system.  Some wet stations are connected to the AWN system.  Only standard inorganic, non-heavy-metal containing, liquid waste, can be drained into the AWN system.  Mixtures containing solvents, metals, fluorine, and solvents must NEVER be dumped into the AWN system. [Link to list of Palo Alto/EH&S for specific] Unless you are trained at a station that allows it, you must never put any chemicals into an AWN drain.  If, by accident, such chemicals are poured into a processing module which normally drains into the AWN, do not drain. Instead, notify a staff member immediately, who will be able to arrange another method of disposal.  When the AWN system is not functioning, the AWN alarms located throughout the lab will flash. When the alarm is actuated, do not operate any of the wet stations, as this means the facilities are out of compliance.
  2. HF Drain System is a network of double-contained piping that runs from the labs to a central holding tank.  Because high concentrations of fluorine are a health and environmental hazards, the HF drain system is separate from the AWN system, in order to ensure fluorine waste is kept out of the sewer system.  Instead, waste collected in HF tank is routinely collected to be treated off-site.  Fluorine-containing chemicals that should be drained into the HF system include hydrofluoric acid, buffered oxide etchants (BOE's), ammonium fluoride, and any mixtures thereof.   Some wet stations are connected to the HF drain system.  Unless you are trained at a station that allows it, you must never put any chemicals into an HF drain. Do not dispose of fluorine-containing solutions into drains that are not labeled for HF waste.  And because aspirators drain into the AWN system, do not aspirate fluorine-containing solutions.
  3. Solvent Waste Collection.  Carboys containers and waste bins in the labs may be designated and labeled as Solvent Waste collection.  Standard, non-halogenated solvent waste is collected into 2.5 gallon carboy containers (liquid waste) or in labeled waste bins (solid waste only, secured in zip-locked bags) at the solvent wet benches. The standard solvents are: methanol, isopropanol, and acetone. Standard solvent waste includes these chemicals and photoresist waste. Do not put halogenated waste into the the solvent waste carboys or waste bins; instead, use Local Collection.  All labmembers qualified for access to wet labs can make use of the standard solvents for cleaning samples, and so must dispose of liquid and solid waste accordingly.
  4. Local Collection.  Many chemicals used at SNF cannot be disposed of using the AWN, the HF drain, or the general solvent waste collection tanks. Local collection is performed at the "flexible" wet stations which have sufficient exhaust and deck space to support this.  Only labmembers who are trained and qualified to use flexible wet stations and have privileges to the online hazardous waste tag system may use local collection. 

    - Waste containing toxics and heavy metals must be collected locally, as these chemicals cannot go into the AWN.  Examples include:  used gold or chromium etchants.  Prohibited heavy metals and other toxics include, but are not limited to, the following: Antimony, Arsenic, Barium, Beryllium, Boron, Cobalt, Gold, Manganese, Molybdenum, Selenium, Thallium, Vanadium, Cyanide, Formaldehyde, Phenols, any chemicals on the Federal List of Acutely Hazardous Chemicals or the California List of Extremely Hazardous Chemicals

    - Halogenated organics are discouraged from use in the lab and some are banned. Examples include chlorobenzene, TCA, borothene, and carbon tetrachloride. Halogenated organic waste must be treated by incineration at higher temperatures than for other wastes, to prevent the possible formation of highly toxic compounds such as PCB's and dioxin. So separate and properly label halogenated waste from other solvent waste.

    - Gallium Arsenide (GaAs) and its processing by-products are toxic. All persons working with GaAs should develop especially good "housekeeping" habits and be constantly aware of how arsenic might be generated during processing. Avoid direct physical contact with GaAs and anything that comes into direct contact with GaAs. When breaking and scribing GaAs wafers, work under the designated exhausted hood deck and wipe down all surfaces afterwards to prevent spreading of GaAs dust. Follow handling and decontamination procedures at each equipment where GaAs processing is done.  Any GaAs waste, no matter how small, must be considered hazardous, including GaAs-contaminated labwipes and old proximity-cap silicon wafers. Place GaAs waste in an airtight zip-lock plastic bag and place in a hazardous waste bag.  Label the waste bag as appropriate.

  1. Wet Bench Stations:  With the exception of using small amounts of alcohol for wiping down surfaces, chemicals must be used only at designated wet stations.  All wet bench stations have the following features:
    • Exhausted workspace.  Air is pulled in from the front, across the workspace (deck) of the bench, and drawn out of the lab.  This ensures that any vapors from chemicals on the workspace are pulled safely away from the user.  Each wet bench will have a dial exhaust meter; the exhaust system is functional when the needle remains between the red limit markers.   
    • Wet Bench shield.  A transparent shield in front of the workspace offers additional protection.  You must always keep this shield between you and the chemicals on the deck.  If your work requires full PPE, you must still keep this shield between you and the chemicals on the deck.  The wet bench shield is also designed to ensure the air flow directed across the work space; do not work with the shield out of place or place anything in from that could divert the air flow.
    • Red line.  On either side of each wet bench station, there will be a red tape line on the workspace deck, located 6 inches from where the wet bench shield is located.  Air turbulence at the very front of the wet bench means that vapors from chemical containers placed between there and the red line can escape into your breathing space.  Always work at least 6" from the front, towards the middle of the work deck, to ensure that all vapors are captured by the exhaust system.
    • Water spray and air gun are available at most wet bench stations.  
  2. “Standard" wet benches include all the WBClean, WBDecon, and WBResStrip stations which may be used only for processes and chemicals as described in the operating procedures for each station.   Standard wet benches are designed to handle whole cassettes of wafers and have a range of semi-automated modules (hot pots, wet tanks, dump rinsers) for processing cassettes.   Here are the main features of the Standard wet bench stations:​
    • Standard chemicals.  Each chemical tank is dedicated to specific chemicals or chemical mixtures which drain into the appropriate waste system (AWN or HF).  
    • Limited materials may be processed at the Standard wet benches, in order to ensure safety and avoid cross-contamination.  The materials allowed is described in the operating procedures for each of the wet stations.  
    • Dedicated labware.  Each Standard wet bench has dedicated labware, in order to avoid cross-contamination (do not use labware from one bench at another bench.)
    • No chemical containers.  The only chemical containers allowed are the chemical modules (hot pots and tanks) and the bottles used to fill them.  No beakers or any personal labware may be used for processing at these stations.  Except for what is contained in the chemical modules, no chemicals may be stored at the wet bench stations.
    • No local collection of waste.  Hot pots, tanks, and dump rinsers are directly connected to the appropriate waste system (AWN or HF.)  No non-standard chemicals or chemical waste, so no local collection is allowed at these stations. 
    • Training and qualification.  Labmembers must be trained and qualified in order to enable and use any of the Standard wet benches.
  3. "Non-standard" wet benches are the flexible wet stations, as indicated by "flex" in the station name (WBFlexCorr, WBFlexSolv).  These are mostly manual stations that can be used for a broader range of chemicals and processes. Here are the main features of the flexible wet stations:
    • Chemical containers: Beakers and other chemical containers may be used at these stations, but only for chemicals approved for use at the specific stations.
    • Hazardous In-Use material forms are absolutely required for each beaker or container with chemical, even for water.  These forms are available in the lab and require the date, your contact info, the full name of the chemical, and its hazard category.  An unlabeled or improperly labeled container of chemical is a violation of safety policy and grounds for loss of lab privileges.
  4. Squeeze or spray bottles: Isopropanol and ethanol in labeled squeeze or spray bottles are the only chemicals that may be used outside of wet benches, for wiping and disinfecting surfaces. The bottles must be put away and stored at the solvent benches when not in use. Because of their high vapor pressure and flammability, they should be used only very sparingly outside of solvent wet benches. They should never be used at non-solvent wet benches nor near any electrical equipment.
  5. Transporting chemicals TO the lab: You may bring in an approved chemical (see the PROM committee for approval) following these rules.
    • Shipping chemicals.  It is best to purchase chemicals and have them shipped directly to SNF Receiving.  Let staff know to expect these chemicals and to contact you when they arrive.
    • ​Do not transport chemicals through office spaces.  Chemical must be transported from the Receiving entry, through the main lab corridor.  For use in the Cleanroom, chemicals should be transported through the L119 Service door or the Chemicals Passthrough (staff can help).  Do not transport through the Gowning Room.
    • Use secondary containment for transport.  Chemicals may be hand carried in their original, unopened shipping box from the Receiving entry to the lab entry or wherever it is safe to transfer to a chemical carrier.  Contact staff if you need to borrow a chemical carrier.  Alternatively (and preferably) chemicals can be transported using chemical carts.
  6. Transporting Chemicals IN the Lab: Appropriate PPE is available near wet stations throughout the labs and must be worn when handling and transporting chemicals. Chemicals should be transported using the appropriate transfer carts (white polypropylene for corrosives/oxidizers; metal for solvents/resists/developers.) Chemicals must never be transported by hand, even hand-carrying a beaker of water.  For specific procedures on transporting chemicals in the lab, see wet bench operating procedures.
  7. Mixing and/or Heating Chemicals:  Chemicals can behave very differently when heated or mixed with other chemicals and present completely different risks. You are performing a non-standard process if you are heating a chemical which is not normally heated, or mixing chemicals that are not normally mixed -- even if the chemicals are normally stocked in the lab. The following hazard classes must never be mixed together:
    • Corrosives + Flammables = Explosion/fire
    • Corrosives + Poisons = Poison gas
    • Flammables + Oxidizers - Explosion/fire
    • Acids + Bases = Corrosive fumes/heat
  8. Chemically Resistant Labware: When using any wet bench, the labware (cassettes, cassette holders, etc.) must be chemically compatible with the chemicals you are using. Note that most wet benches have labware dedicated specifically for each bench in order to minimize cross-contamination risk.


Personal protective equipment (PPE) is required whenever handling or transporting chemicals in the lab. PPE required depends on the chemicals being used. Below lists the type of protective gear, in addition to your safety glasses and appropriate lab wear, that is generally used for various chemical types. This is only a guideline; the operating procedures for each wet bench should serve as the final word.  Remember, you are responsible for your own safety, and that of others around you. SNF provides you with information, recommendations, and necessary resources for you to be able to do your work safely. It is up to you to ensure that you take appropriate precautions for your safety and your fellow labmembers.

  1. Corrosives or oxidizers:  face shield, apron, tested chemically-resistant gloves
  2. Solvents: tested chemically-resistant gloves
  3. Photoresists or developers: vinyl gloves over regular clean gloves

  1. SNF Requirements: We are required to maintain an up-to-date list of the names and amounts of all hazardous chemicals and materials in the lab. With every chemical or material brought into the lab, we need to ensure there is:
    - a safe way and place to store it
    - a safe way to use it
    - a safe method of disposing of it and its byproducts
    - a way to prevent cross-contaminating other labmembers' work
  2. ProM Committee: All process chemicals and materials used in the lab must be approved by the Prom committee before use. New chemicals and materials are approved for a given process and may be on a case-by-case basis.  ProM requests are also required when using standard chemicals, but in a non-standard way, such as heating or new mixtures.  When in doubt, consult with a staffer. To register a new chemical, material, or process, submit a ProM request.
  3. Personal-use chemicals must be appropriately labeled (with identification of owner, contents, and other safety info, as per section 4.4). This is an ever-changing research environment with a lot of chemicals and materials -- we need your help to keep track of them all.
  4. Due diligence:  Because SNF is a community of researchers, we all need to be extremely considerate of potential problems posed by the hazards of new materials and how they will affect the research of others. The SNF website should answer the most common questions and concerns about which chemicals and materials and where their use is acceptable in the lab, but it is far from comprehensive. Please take time to carefully consider the process flow of your experiment and how it might affect other labmembers and other downstream processes. If you have any concerns, contact the Prom Committee (snf-, who would be glad to discuss.

  1. Flammables:
    • Standard Solvents. Acetone, isopropanol, and methanol may be found in the solvent wet benches. Acetone is often used to dissolve photoresist and other polymers. Isopropanol and methanol are often used for cleaning. These chemicals are all flammable solvents with low flash points, which means they can be easily ignited at room temperature and, therefore, pose significant fire hazard. Thus, solvents should not be used on or near hot plates or near any electrical system. Solvents may also ignite or explode when brought into contact with chemical oxidizers (such as many acids) and so should not be mixed with, nor collected in the same waste container as these compounds. Standard solvent waste should be disposed of in the solvent carboy or collected locally. These and other solvents must be stored in the designated flammables cabinet in the service area and may be transported in the lab only if carried in metal carts. Solvents may be used only in designated solvent hoods.
    • Chlorinated Solvents (such as chlorobenzene, trichloroethylene [TCE], and methylene chloride) may be present in some special resist processes, although these have been phased-out of general use. Long term, repeated exposure to some chlorinated solvents is correlated to cancer and liver and nerve damage. Because of environmental hazards, chlorinated solvent waste must be collected in a waste container, separate from other kinds of liquid solvent waste.
    • Glycol Ether Solvents: Methyl- and ethyl- glycol ethers may be present in some photoresists. These have been implicated in reproductive problems in semiconductor workers. SNF does not stock chemicals which contain these, but instead use ethyl lactate and propyl- glycol ethers which are the accepted replacements. However, some specialty chemicals, such as imported high performance resists, may contain methyl- or ethyl- glycol ethers. Glycol ethers may be referred to generically as "Cellosolve", but the following names also refer to glycol ether compounds: Methyl Cellosolve, 2-methoxyethanol, Ethyl Cellosolve, 2-ethoxyethanol (2EE), Ethylene glycol mono ethyl ether. Acetate salts of glycol ether compounds may also appear in some specialty photoresist formulations as: Cellosolve Acetate, Ethyl cellosolve acetate (ECA), Ethylene glycol mono ethyl ether acetate, 2-Ethyoxy ethyl acetate. Environmental monitoring studies done of the SNF indicate that there is no risk of significant exposure of these compounds, as long as handling of photoresists takes place only in designated exhausted work areas. As a labmember, your responsibility is to always observe proper chemical handling practices, and to make sure that the people working around you do so, as well.
  2.  Oxidizers:
    • ​​Peroxides: All peroxides are highly oxidizing materials; energy is released when they are reacted. Some peroxides are unstable, and can explode. 30% hydrogen peroxide in water is stocked the lab. Extreme care should be used in mixing solutions containing peroxides. Peroxides are incompatible with all forms of organic solvents and flammable materials.
    • Sulfuric acid and "Piranha" clean. The heated mixture of concentrated sulfuric acid and 30% hydrogen peroxide is commonly referred to in the semiconductor industry as "piranha clean." This mixture is an extremely aggressive oxidizer, used primarily for removing photoresist and, in sequence with other chemical mixtures, to remove contaminants (i.e., the "RCA" or pre-diffusion clean process). The proportions of sulfuric acid and hydrogen peroxide used will depend on the particular wet bench and application. The piranha solution self-heats when mixed and immediately destroys organic materials it contacts (photoresist, cleanroom wipes, vinyl or latex gloves, skin.) Piranha vapor is extremely caustic, so the piranha mix should be used only under an exhaust hood. Boiling piranha spatters, so always wear protective gear when working near a hot pot. Piranha is incompatible with all solvents and flammable materials. It reacts violently when mixed with base. Do not add water directly to piranha to try to cool it; sulfuric acid is water reactive, so adding water will cause heating (not cooling!) and can lead to an explosion.  General Information on Piranha Solutions is available on the EH&S reference site.
    • Nitric Acid is an oxidizer and is also water reactive (heats upon addition of water). Nitric and acetic acids are components of pre-mixed Aluminum etchants. All oxidizers should be kept away from solvents, bases, and flammable materials.
  3. Hydrofluoric Acid and Fluoride Containing Chemicals.  Hydrofluoric acid (HF) and related fluoride-containing mixtures (such as ammonium fluoride or BOE) are among the "high hazard" materials carefully monitored by Stanford EH&S. Concentrated HF produces extremely painful, deep tissue burns. Lower concentrations of HF are particularly insidious, as the initial contact may produce no pain at all, although tissue damage may continue over days following exposure.  It can be easily absorbed through skin and has a high vapor pressure, so can be easily inhaled.  HF can cause electrolyte imbalance that can lead to cardiac arrest and death.  If you will be working with HF and fluorine acids, make sure to read the EH&S Information on Hydrofluoric Acid reference.
    • BOE's ("buffered oxide etchants") and Pad Etchants are pre-mixed solutions of HF and buffer, or ammonium fluoride (NH4F). Although ammonium fluoride is a neutral salt of HF, it readily dissociates to yield fluorine ions, and so presents nearly the same hazard as HF. All BOE's contain nearly the same total fluorine as concentrated 49% HF.
    • Calcium gluconate is used treat exposure to HF by providing calcium ions to bind fluorine. In cases of exposure to skin, calcium gluconate gel must be applied immediately to the area of contact. For systemic exposure, calcium gluconate is delivered by injection, by a healthcare professional. Tubes of calcium gluconate gel, along with instructions for use in case of contact exposure, are mounted to the front panel of every wet bench where HF and fluorine-containing chemical mixtures are used. More about emergency treatment of HF exposure can be found in section 9.10.
  4. Alkali/Bases.  Alkaline compounds, or bases, are the chemical opposite of acids, and may react violently when mixed with them. They are most commonly used in the lab in lithography and etch. Alkalis are caustic, so protective gear should always be worn when working with them to prevent contact with skin and eyes.
    • Silicon Etchants.  Heated solutions of 25%-30% alkali solutions, such as potassium hydroxide (KOH) and tetramethyl ammonium hydroxide (TMAH) are as anisotropic etchants of silicon. These etchants may be used only at the wbflexcorr stations. TMAH is a "high hazard" material (see below) and so requires additional controls.
    • TMAH Solutions.  Tetramethyl ammonium is a nerve agent and its hydroxide form is easily absorbed through skin. Deaths have resulted in an industrial accident where 25% TMAH spilled onto workers even though they rinsed within a minute of exposure. TMAH is used at lower concentrations (2-3%) in most photoresist developer solutions. Health effects have been documented for large area exposure at these concentrations, so PPE should always be worn when handling developer solutions directly. All labmembers working with this chemical must review the TMAH Fact Sheet.  Use of 25% TMAH requires special training and advance arrangement with wet bench staff.
  5. Removers and strippers ( PRS 1000, PG Remover and related chemicals) These are organic base mixtures, which are used for removing photoresist from wafers containing metal films (which are corroded by conventional piranha clean.) Unlike other acids and bases used in the lab, these strippers are not water-based and are combustible; by some criteria, they may be considered solvents. These strippers must never be directly mixed with strong oxidizers.

  1. Storage: Most hazardous process gases are located in reinforced storage vaults away from the lab. Gases are stored by chemical class in individual gas cabinets and are monitored by an automated toxic gas detection system. Nitrogen, argon, hydrogen and oxygen, are kept in liquid form in large storage tanks outside the lab. Process gases are delivered to the lab through a series of valves, regulators and flow control systems. Few gas bottles are stored in the lab; those that are must be secured. 
  2. Handling and Usage: Because of the hazards present, only trained and qualified staff are permitted install, handle, and disconnect or change out gas cylinders. Hazards include the following.
    • Poison. Gases, such as phosphine and arsine, are extremely toxic. Small leaks may be fatal. 
    • High pressures. Cylinder gases may be at pressures as high as 3000 psi. When punctured or cracked open, these cylinders may become rockets.
    • Equipment. Gas regulators are designed to handle specific gases. If not properly chosen and installed, leaks or explosion may result.
    • Improper installation and purging can result in contamination of the gas cylinder.
  3. Toxic Gas Detection System consists of a network of remote sensors located throughout the lab and the gas pads and vaults. Depending on the sensor, when triggered, the system launches a preconfigured sequence which may include the following actions: 1. activation of gas shut-off valves; 2. activation of audible alarms; 3. notification of the appropriate response teams. This automated function ensure the appropriate response will be always taken in the event of a toxic gas emergency and, thus, enables the lab to run 24 hours/day, 7 days/week.

  1. Pyrophoric (flammable) Gases. These gases will spontaneously ignite in air within a critical concentration range.
    • Silane (SiH4) It is used for deposition of polysilicon, amorphous silicon, nitride, oxide, and oxynitride films. It is a high-pressure gas. When exposed to trace amounts of air or moisture, silica dust can form.
    • Dichlorosilane (SiH2Cl2) It is used for deposition of polysilicon and amorphous silicon. It is low vapor pressure liquid source. Like silane, it will form dust when exposed to trace amounts of air and moisture.
  2. Corrosive Gases
    • Hydrochloric acid (HCl) HCI gas is extremely corrosive to almost everything, including stainless steel. It is used for clean/etching deposition chambers.
    • Ammonia (NH3) NH3 gas is a severely corrosive alkaline vapor with a pungent odor. It is shipped in the cylinder as a liquid under its own vapor pressure of approximately 9 atm. NH3 gas is used in oxynitride and nitride film deposition (plasma and CVD.)
  3. Highly Toxic Gases. These gases described here are severe pulmonary irritants and acute systemic poisons. Overexposure can cause either sudden or delayed death due to lung destruction. Although each has a characteristic smell, the odor threshold is not much lower than the toxic exposure level. The gases described here are mixed at low concentrations in carrier gases (silane, hydrogen, or nitrogen) and used as film dopants in LPCVD and Epi2 systems.
    • Phosphine (PH3) PH3 is a colorless, highly toxic gas with an odor described as fishy.
    • Diborane (B2H6) Diborane is a colorless, poisonous, pyrophoric gas with an odor described as a repulsively sweet.
    • Arsine (AsH3) Arsine is a colorless, poisonous, flammable gas with an odor described as garlicky.
  4. Non-toxic Gases. These gases are considered non-toxic because they do not generally pose an immediate risk to health and safety. However, they can be asphyxiants and may pose other health risks at high concentrations or with long-term exposure.
    • Nitrogen (N2) and Clean Dry Air (CDA) House nitrogen and Clean Dry Air are plumbed throughout the lab for general use in equipment and other utilities. The supply can run up to 80 psi, which can pose a hazard: do not direct an N2 or air gun toward your own body (especially the face and eyes) or toward anyone else.
    • Etch Gases SF6, CF4, O2, N2, CHF3, C2ClF5, CBrF3, and C4F8 are commonly used in plasma etchers. Although the gases themselves generally pose low health risk, their by-products in etch systems are less benign. Make sure to follow proper operating procedures for pumping down or purging etch chamber systems following processing.
  5. Cryogens. Nitrogen, argon, helium, hydrogen, and oxygen are stored in liquid form outside the lab and are evaporated to be delivered to the lab in gas form. LN2 should not be used in an enclosed space because of the risk of asphyxiation. LN2 can also burn tissue on contact, so protective gear must be worn whenever handling.
Last modified: 5 May 2023