Airborne molecular contamination (AMC) is airborne non-particulate chemical contamination that has a detrimental effect on a product or a process. Specifically, AMC is chemical contamination in the form of vapors or aerosols that can be organic or inorganic in nature and includes acids, bases, polymer additives, organometallic compounds, and dopants.

These chemical vapors can come from many different sources including:

• Cleanroom construction materials (walls, floor tiles, filters, sealants)
• Make-up air (MUA)
• Recirculation air
• Process chemicals
• Misadjusted exhaust levels
• Operating personnel w Leaks of process fluids
• Chemical spills
• Cooling systems
• Outgassing of various materials as they age
• Cleaning solutions

Generally AMC sources fall into two general categories: internal and external. Internal sources of AMC are those sources that are internal to the operation and include process chemicals, accidental chemical spills, operating personnel, off-gassing of cleanroom construction materials (floor tiles, walls and sealants). External sources include factory emissions, automobile exhaust emissions, farm lands, and even exhaust emissions from the very same factory itself. External sources of AMC normally enter the fab through the make-up air handling system.

Realistically, every material in the cleanroom can be a source of AMC. When addressing AMC, the most important aspect to consider is what type of gases affect the process and at what level. Some processes or products may be extremely sensitive to one type of chemical and not another. When planning to monitor for AMC, it is important to understand that there is no “catch-all” AMC sensor. AMC monitoring is not like particle counting where you can assume that all of it can affect your product. Determining the types of chemicals that the products are most sensitive to and their possible sources can go a long way in determining the best control and monitoring plans.

Early detection of gas emissions means better environmental control, improved productivity, and cost savings. Consequently, the monitoring of trace gases has become a critical and extremely important function in maintaining process yields in the semiconductor manufacturing environment.

From: “AMC Measurement and Control: Essential For Process Yields”