Standard · Fab Ops, Yield & Metrology
ISO 14644
The international standard series that classifies cleanroom air cleanliness by particle concentration, from ISO Class 1 (cleanest) to ISO Class 9, and specifies how the classification must be tested and monitored.
- Also known as
- ISO 14644-1
- Type
- Standard
- Domain
- Fab Ops, Yield & Metrology, Cleanroom and facilities
Notes
ISO Class 5 roughly corresponds to the old Class 100, and is typical for open wafer handling zones.
Overview
ISO 14644 is the international standard series for cleanrooms and associated controlled environments, developed by ISO technical committee TC 209. Its best-known part, ISO 14644-1, classifies air cleanliness by the concentration of airborne particles, from ISO Class 1 (cleanest) to ISO Class 9. Other parts cover monitoring, test methods, design and construction, operations, separative devices and chemical cleanliness, and semiconductor fabs use the series to specify, certify and run their cleanrooms.
How it works
Under ISO 14644-1, the class number is the decimal logarithm of the number of particles of 0.1 micrometres or larger allowed per cubic metre of air, so an ISO Class 5 space permits at most 100,000 such particles per cubic metre, and ordinary room air is around ISO Class 9. Classification uses particles with threshold sizes from 0.1 to 5 micrometres, counted with light-scattering particle counters at defined sampling locations. A stated class should always say which particle sizes and which occupancy state (as-built, at-rest or operational) it refers to.
Other parts turn classification into practice. ISO 14644-2 sets minimum requirements for a monitoring plan showing that a cleanroom keeps performing; ISO 14644-3 gives test methods for classification and related conditions for rooms with unidirectional and non-unidirectional airflow; and further parts deal with design, construction and start-up, and with day-to-day operation. ISO 14644-8 grades air cleanliness by chemical concentration, the molecular contamination that particle classes cannot see.
Older US Federal Standard 209E classes such as 'Class 100', which count particles of 0.5 micrometres or larger per cubic foot, are still widely quoted, although that standard was cancelled in 2001. The parts of ISO 14644 are revised at different times, so the edition in force should be checked before a specification is written.
Examples
- A new fab bay certified as ISO Class 5 at rest before tools are moved in.
- A monitoring plan under ISO 14644-2 that places particle counters at critical locations and sets alert and action levels.
- Requalifying a cleanroom with ISO 14644-3 test methods after a major change to its air handling.
- Specifying chemical cleanliness grades under ISO 14644-8 for a lithography area sensitive to ammonia.
Why it matters
ISO 14644 gives fabs, cleanroom builders, equipment suppliers and auditors a shared language for how clean a space is and how to prove it. Cleanroom facilities engineers, contamination control engineers, commissioning teams and construction managers apply it, and certification against it is part of handing over a new fab or bay.
Related terms
Part of the Fab Ops, Yield & Metrology glossary, with every term in the topic and the lifecycles, tools and standards that use them.
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