ABSTRACT
This chapter addresses the drawbacks of the particle per wafer per pass (PWP) method, that it is useful primarily in measuring particulate contamination from those tools and apparatus that process wafers directly, by reviewing methods of measuring absolute particle emission rates from clean-room apparatus that do not directly process wafers. The advantage of a continuous flowing duct measurement over the open area clean-room measurement is that the airflow is known and all the apparatus emissions can be assumed to be uniformly distributed in the downstream duct, or at least confined to well-defined streams in which particle concentration can be reproducibly measured. The continuous flowing duct method lends itself nicely to measurement of emission rate from this source. A duct geometry that minimizes dead space, such as a cylindrical tube with tapered entry and exit—no corners—would be preferable. Large particles, such as paper fibers or lint, will probably not be sampled and counted by this measurement configuration.
