Semiconductor cleanrooms: vibration criteria and airborne molecular contamination

By ZY Cleanroom · Updated 2026-11-01 · Sources at the end of the page

Vibration criteria

The criteria are RMS velocity limits in one-third octave bands from 8 to 100 Hz (Newport). The µm/s column is calculated at 1 µin = 0.0254 µm, so VC-D at 250 µin/s is 6.35 µm/s.

How to use the curves

Below VC-A, Newport lists the ISO building criteria: workshop 32,000 µin/s, office 16,000, residential day 8,000 and operating theatre 4,000. VC-A is half the operating theatre limit. VC-E is one thirty-second of it. The step from VC-A to VC-E is 2,000 ÷ 125, or 16 times tighter (calculated).

Newport says much fab design work sets goals of VC-D to VC-E, which it believes suits 0.3 µm line widths. It says lines of 0.18 µm and below will almost certainly need active isolation. The page is undated, so check these statements against your own tool maker.

Newport also says the curves are guidance and do not replace narrowband analysis for diagnostic studies. Ask each tool maker for its own floor limit and write the strictest one into the brief.

VC is a floor criterion, not a room class. Write it into the brief as its own line, next to the particle class.

AMC categories

An article by Robert Donovan, a process engineer assigned to Sandia National Laboratories, describes the four SEMI F21-95 categories. The class number is the cap in parts per trillion on a molar basis, so MA-10 allows 10 ppt of acids. That is the 1995 edition. SEMI has since issued F21-1016, so check the current edition before writing a spec.

Donovan lists the harm AMC can do: suppressed oxide growth, degraded oxide quality, corroded metal layers, chemical doping, altered electrical properties at interfaces and degraded photoresist. It also corrodes cleanroom tools and structures. For dopants he says the best control is to remove the source, and that any detectable level is probably too much.

Where the filters go

Donovan lists activated carbon, permanganate-treated carbon for sulphur oxides, ion-exchange fibres and fraipontite. Chemical filters often sit upstream of HEPA filters because they can shed particles.

The ISO page says the standard sets assessment processes to grade air chemical cleanliness by the airborne concentration of specific substances. It includes a protocol for test methods, analysis and time-weighted factors. It does not describe the nature of the contaminants.

Put four lines in the brief: the particle class, the VC limit, the AMC categories to control with a target level for each, and who will measure them. That list is a suggestion, not a standard.

ISO 14644-8:2022 is the third edition, titled Assessment of air cleanliness by chemical concentration (ACC). It does not classify surface chemical contamination.

If you have a room list for a semiconductor project, send it to ZY Cleanroom and we will review the panel, door and ceiling scope with you.

Related guides

• Writing a cleanroom URS: contents and testable wording
• Building a cleanroom inside an existing building
• Cleanroom cost per m²: published ranges by ISO class
• What a cleanroom costs to run: energy, filters and testing
• Turnkey cleanroom contractor
• Room list builder

Sources

• Newport, Environmental Vibration Criteria (undated web page; checked 1 November 2026)
• ISO 14644-8:2022, Cleanrooms and associated controlled environments, Part 8: Assessment of air cleanliness by chemical concentration (ACC) (edition 3, June 2022; checked 1 November 2026)
• Robert P. Donovan, AMCs: Properties and gaining control, Semiconductor Digest (undated web page; checked 1 November 2026)
• SEMI, F21: Classification of Airborne Molecular Contaminant Levels in Clean Environments (store listing, revision F21-1016; checked 1 November 2026)