Case Study and Control Practices for Gaseous Molecular Contaminants (AMC)

Airborne Molecular Contamination (AMC) is a hidden killer of yield rates in semiconductor and optoelectronics industries. According to SEMI F21 standard, AMC can be classified into four major categories: acidic (MA), basic (MB), condensable organic matter (MC), and dopants (MD). As process line widths advance to 7nm and below, AMC concentration control has escalated from ppb levels to ppt levels, imposing increasingly stringent requirements on air filtration systems.

In a real case at a 12-inch wafer fab, the lithography bay frequently experienced photoresist defects. Analysis revealed NH3 concentration in the environment reached 15 ppb, far exceeding the 1 ppb process limit. After Baisheng Technology's technical team conducted on-site assessment, we recommended installing activated carbon chemical filters impregnated with phosphoric acid at the MAU (Make-up Air Unit) end, and adding molecular sieve adsorption modules at the FFU return air end. After improvement, NH3 concentration dropped to below 0.3 ppb, and yield rate increased by approximately 2.5%.

The key to controlling AMC lies in a dual approach of "source reduction" and "pathway interception". On the source side, management should control building material volatilization, process exhaust backflow, and personnel introduction. On the pathway side, appropriate chemical filters must be installed in both external air treatment units (OAU/MAU) and indoor circulation systems (FFU/DCC). Filter selection must depend on pollutant type: acidic gases are suitable for activated carbon impregnated with KOH or Na2CO3, basic gases use activated carbon impregnated with H3PO4, while organic compounds are best served by unimpregnated high specific surface area activated carbon.

Baisheng Technology recommends customers establish a regular AMC monitoring program, coupled with filter life tracking system, replacing filters in time before penetration rate reaches the set threshold. In a six-generation TFT-LCD facility we serve, through quarterly monitoring and filter rotation strategy, chemical filter service life extended from the original 6 months to 9 months, reducing annual material costs by approximately 30%. Comprehensive AMC control not only protects yield rates, but also effectively reduces operating costs.