Airborne molecular contamination (AMC) can be damaging to a product or process, making it essential to monitor and control. AMC is chemical contamination in the form of vapors or aerosols that can be organic or inorganic, and it includes everything from acids and bases to organometallic compounds and dopants.

These chemical vapors can result from a wide range of sources, including cleanroom materials, make-up air, process chemicals, operating personnel, cooling systems and even the outgassing of certain aging materials.

There are primarily two types of AMC: internal and external. Internal sources of AMC involve process chemicals, accidental chemical spills, operating personnel and off-gassing cleanroom construction materials like floor tiles, walls and sealants. External sources include factory emissions, automobile exhaust emissions and farm lands. The entry point of external sources of AMC, incidentally, is generally the fab through the make-up air handling system.

Evaluating Gases

When addressing AMC, it’s essential to consider what type of gasses affect the process and at what level. It’s also important to keep in mind that there is no “universal” AMC sensor for monitoring. AMC monitoring is not like particle counting where you can assume your product will be impacted by all AMC. Ideally, you should identify the types of chemicals that your products are most sensitive to, as well as their possible sources.

Ammonia contamination can be a serious threat. One of the most sensitive steps in the semiconductor manufacturing is photolithography. The technology has indicated increased sensitivity to basic contamination, with ammonia being identified as the dominant basic substance among AMC.

What compounds are monitored? Monitoring can be done for many types of compounds, including ammonia, NMP, and total amines acids and sulfur.

What are the minimum detection limits? The minimum limits will depend on the type of chemicals and technology involved. You must determine the appropriate minimum detection limits based on the requirements for your specific process.

Can I send data to our existing data management system? Yes. The manifold reads the data from multiple sensors, but provides all data via a single interface using industry-standard Modbus protocol.

Do the instruments contain radioactive materials? Some instruments do use a radioactive source to ionize the sample. Be sure to address this question with each instrument supplier.

How long can the tubing runs be from manifold to sample point? The runs can be as long as you wish. However, the chance of contaminating or diluting the sample increases with longer distances. We recommend not running sample tubing any longer than 80 meters or at least using a booster pump for longer distances.

What materials are used for tubing? Teflon is the most commonly used material. Stainless steel can also be used, but it is generally more costly and less compatible with a variety of chemicals.

How frequently should sensors be calibrated? The frequency should be based on zero drift of the sensor per day (the drift the sensor will experience from zero in a set time, normally a day or week); the span drift (drift experienced from a fixed concentration amount over a day or week); and the level of detection desired. (The lower the level, the more often you will need to calibrate to keep the zero and span drift from exceeding your minimum detection limit.)

What processes do you recommend monitoring? This will be determined by the type of manufacturing process you have. For example, the semiconductor industry generally involves photolithography, metals, etch, copper process areas and photomask manufacturing. Hard disk drive manufacturing typically includes wafer operations, HGA/HSA operations, final drive assembly and media.

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