1. Field of the Invention
The invention relates to a vacuum system which comprises an evacuatable chamber, including a gas inlet and a gas outlet, for storage, measurement or treatment of objects sensitive to dust contamination.
2. Description of the Prior Art
Various means are known for realising a vacuum clean room for performing measurements on, the preprocessing or the processing, or the temporary storage of objects sensitive to dust contamination during a processing cycle.
U.S. Pat. No. 4,718,975 describes a processing chamber in which an object to be processed, that is to say a semiconductor wafer, is covered by a displaceable cover plate during the non-processing phases.
U.S. Pat. No. 4,687,542 describes a system for the intermediate storage of wafers where a number of wafers is arranged, accommodated in a sealed box, in a space to be evacuated, the box being opened only when the space has been sealed and evacuated.
JP-A 59-114814 describes a vacuum system in which a prevacuum pumping valve comprises a porous material which acts as a choke valve.
JP-A 61-58252 describes a specimen chamber in which the gas flow is always directed downwards during filling or evacuation of the space in order to achieve dust reduction. The aim is to prevent the stirring up of dust particles.
Even though all these means lead to a given improvement in view of dust contamination, it has been found that they are not adequate for many applications.