New billion dollar FABs go to great efforts to control particles at very low levels. Yet the mass arrival rates of molecular contaminants at the wafer surfaces are order of magnitude higher than the particle arrival rates. HEPA and ULPA filters remove particles, but have little or no effect on molecular compounds. Most cleanroom are dirtier than outside air for molecular contaminants, especially organics, acids, bases and dopants. Some of the molecular compounds can cause disastrous yield losses or degradation of electrical properties. These contaminants need to be better controlled. Read more