AMC (Airborne Molecular Contamination)

Notes

Amine contamination causing resist T-topping is the classic AMC failure mode in litho areas.

Overview

AMC (airborne molecular contamination) is chemical contamination carried in cleanroom air as gases or vapours rather than as particles: acids, bases such as ammonia, condensable organics, dopants and trace metals. It can harm wafers and tools even when particle counts are excellent, because particle filters do not stop molecules. Fabs therefore control AMC separately, with chemical filtration, monitoring and their own classification standards.

How it works

AMC comes from outdoor air, process tools and chemical lines, off-gassing building materials and even people. Each family does different damage. Bases such as ammonia neutralise the acid generated in chemically amplified photoresists, which degrades line width and line shape; this became a recognised problem when those resists arrived in the 1990s. Acids such as HF, HCl and SO2 corrode exposed metal. Condensable organics such as siloxanes leave haze on photomasks and scanner optics, and boron or phosphorus compounds can alter the electrical properties of devices.

Control is layered. Make-up air units scrub outdoor air on the way in, recirculation units clean air already in the fab, and chemical filters in fan filter units above tools or in mini-environments protect sensitive steps such as lithography and metrology. Filters are often staged to remove organics, bases and acids in turn.

Measuring AMC is harder than counting particles. Some contaminants matter at parts per billion or lower, and manual sampling is slow and coarse, so fabs increasingly run continuous multi-point analysers to find sources quickly. SEMI F21 classifies clean environments by the levels of groups of molecular contaminants, and ISO 14644-8 sets out how to assess and grade air cleanliness by chemical concentration.

Examples

• Ammonia leaking near a lithography bay that neutralises acid in chemically amplified resist and distorts printed lines.
• Siloxane vapour condensing as haze on scanner optics or reticles.
• Acid vapours corroding exposed metal on wafers waiting between process steps.
• A multi-point ammonia monitoring system that samples several fab areas in turn and quickly pinpoints a source.

Why it matters

As features shrink, more process steps become sensitive to molecular contamination, so AMC control has spread from lithography to the whole fab. Contamination control engineers, cleanroom facilities engineers, lithography engineers and EHS teams share responsibility, and an undetected source can quietly cut yield or damage costly optics.

Related terms

• Cleanroom class
• ISO 14644
• Photoresist
• Defect density

Where it appears on the Hub

Used on 5 pages of the Hub. In each group, the pages that mention it most come first.