AMC Filtering

AMC (Airborne Molecular Contamination) is one of the major degradation sources of photolithography process equipment, which leads to important cost. AMC is a concern for any high technology manufacturing process, especially in the microelectronics industry. Organic contamination may cause adverse effects on production tools and consequently increase costs for high-tech companies. The level of AMC contamination in cleanroom environments is predominately created by internal sources of solvents and acetic acid, re-entrainment of exhaust air, aromatic compounds from ambient air and return air as well as material outgassing. Contamination-free manufacturing is a viable goal and is achieved by source control and source monitoring in combination with filtration solutions in the VIX concept. Real-Time monitoring of the AMC level helps identifying sources, stabilises production and prevents unexpected shortfalls of the service life of filtration units.

Typical examples of contaminating chemicals

  • Ammonia NH3
  • Dinonylphthalate C6H4
  • Ethylene oxide C2H4O
  • Cyclo hexylamine C6H11NH2
  • Formaldehyde HCHO
  • Heptane C7H16
  • Hexanal C6H12O
  • Isopropyl alcohol (CH3)2CHOH
  • Nitrogen dioxide NO2
  • Trimethylamine (C2H5)3N
  • Xylene (CH3)2C6H4

Sources of chemical contamination and concentration levels

1. Outdoor air

    Outdoor air contamination levels entering the incoming air to a cleanroom can include variable contamination levels from the same building exhaust, exhaust from neighbouring buildings, or other contamination sources including farms, sewer plants, dumps, highways, airports, train yards, local industry, and other sources. These levels can vary dramatically with wind direction, wind velocity, time of day, precipitation, temperature, sunlight or other factors. Thus it is important to use continuous monitoring where possible for the most important parameters, or to do periodic sampling on different dates and with sampling for many hours or days, so that atypical average or highest level can be assessed, rather than just a single data point.

    ABN use long-term average data for predicting chemical filter lifetimes, and real-time data is valuable to assess the highest levels encountered to assess if they will affect the most sensitive products.

    2. Construction materials

    Construction materials serving the facility can be sources of chemical contamination because of outgassing. The degree of material outgassing can be dependent upon the temperature, relative humidity and pressure of the cleanroom or controlled environment, and these effects should be established specific to the design of the facility. Outgassing from materials of construction can, in many cases, decay exponentially and asymptotically over a period of time. Thinner materials (e.g. coatings) and more volatile compounds (e.g. solvents) tend to decay more rapidly, but thicker materials (floor tiles, insulation) and higher boiling compounds (plasticisers, antioxidants, organophosphorus fire retardants, larger silicones) can decay much more slowly, and possibly outgas at significant levels for many years.

    3. Others
    • Sources from personnel, use of cosmetics, deodorants, hand lotions, soaps perfumes and hair products. Personal use of cleaning and disinfectant materials.
    • Heaters, insulation, computers, displays, printers, electronics
    • Reaction by-products, especially from etching or chemical vapour deposition

    Classification of air cleanliness by chemical concentration (ACC)

    The part of ISO 14644 currently considers only concentrations of air chemical contaminants between 100 and 10−12 g/m3 under cleanroom operational conditions. (expressed in terms of an ISO-ACC Class N, which represents the maximum allowable concentration of a given chemical species or a group of chemical species, expressed in grams per cubic metre)

    The maximum allowable concentrations are defined in Table conform 14644-8

    Air treatment processes for the abatement of air chemical contamination

    ABN Cleanroom Technology provide several processes in order to control or reduce the concentration of specific chemical contamination categories. These include

    • Sorption on suitable materials (activated carbon, treated activated carbon, ion exchange resin, zeolites)
    • Photoelectron ionization and electrostatic ion removal
    • Catalytic photo oxidation

    Questions about Airborne Molecular Contamination

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