Witness Wafers for Measuring Sedimented Particles
Original Publication Date: 1986-Apr-01
Included in the Prior Art Database: 2005-Mar-08
Semiconductor wafers are manufactured in clean rooms with very low air pollution. The method described below allows dust particles of a size > 5 mm to be counted and measured by selectively collecting them on defined sedimentation or witness wafers. Known methods used for that purpose have a number of disadvantages. Larger dust particles or particles of material removed during manufacture, as well as fibers and generally polydisperse aerosols of > 5 mm, which, due to their size, are contained in clean air only for a limited time, cannot be reliably detected and analyzed by standard suction-type aerosol measuring devices. In clean rooms, the specific number of large particles is so low that, even when using an impactor, reliable samples can only be taken within several hours.