Design Optimization Of Gas Pumping System For Ultra Clean Reduced-Gas-Pressure Processing Equipment

Impurity back diffusion through a UHV pump in reduced-gas-processing chambers has been experimentally studied. A large throughput of process gases severely degrades the main UHV pump capability in dragging impurities, resulting in the back diffusion of impurities to the processing chamber. Such degradation is greatly influenced by the pumping speed of the backing pump. However, we have found for the first time that the impurity level in the chamber can be made even lower than that for the best performance under UHV when the gas flow rate is optimized for the system. The scenario to the gas pumping system optimization is presented.