Design and evaluation of a nitrogen purge system for the front opening unified pod (FOUP)

The technology roadmap toward smaller structures and thinner layers in semiconductor manufacturing directs attention more and more toward yield-affecting influences from the air quality of manufacturing environment. The so-called airborne molecular contaminants (AMCs) have become a key issue related to production yield. A useful method for reducing AMC is purging of wafer with nitrogen gas. In this study, parametric studies on purging a front opening unified pod (FOUP), a wafer box for handling 300-mm wafers, are studied by theoretical analysis, CFD simulation and experimental measurement. The results show that the inlet purge gas through plenum injector with 60° of diverging exhibits faster decrease in oxygen concentration than that with greater degree cases. The depletion on the 1st wafer is slow because of the uni-distance configuration of holes of the plenum injector, which created a non-uniform purge gas inlet profile. By adopting a ceramic plenum injector, a uniform inlet purge gas profile is created and the purge efficiency is therefore significantly improved.