Ultrafine Aerosol Particles in Semiconductor Cleanrooms

The fabrication of VLSI chips with high yields on small device geometries requires control of particulate contamination during manufacture. One potential source of particulate contamination is the ambient air of the production facility. Monitoring and control of these ambient aerosol particles require increasingly sophisticated instrumentation capable of measuring smaller and smaller particles. This paper identifies three instrument types capable of sizing ultrafine (≤ 0.1 μm diam) aerosol particles in real time: the integral mobility analyzer, the differential mobility analyzer, and the diffusion battery. All three of these sizing instruments use an independent condensation nuclei counter to count particles in size‐separated channels. Two of these combinations, the differential mobility analyzer/condensation nuclei counter and the diffusion battery/condensation nuclei counter, have been used to measure the ultrafine aerosol particle size distribution of various quality semiconductor cleanrooms. The data reduction routines of the differential mobility analyzer/condensation nuclei counter combination break down when ultrafine aerosol particle concentration falls below about 1 particle/cm 3 . The diffusion battery/condensation nuclei counter combination functions to below 0.01 ultrafine aerosol particle/cm 3 . Data taken by this instrument combination in a state‐of‐the‐art cleanroom at rest show that the peak concentration of ultrafine aerosol particles occurs near 0.1 μm, the cumulative distribution curve being relatively flat below that size.