Patent Number: 046481060
Section: abstract

A controlled flow of X-ray attenuating gas such as helium is provided to an upper portion of a beam exposure chamber. A vent tube (21) extends from a lower portion of the chamber adjacent a mask to an exterior exit orifice (23) positioned at mask level to prevent ingress of air to the chamber and prevent mask membrane deflecton and change in the mask-to-silicon wafer substrate gap distance. The substrate (20) is positioned below the mask membrane and is surrounded by a mask-to-wafer zone into which is flowed a substrate fabrication process gas which is vented either by a gas flange (25) in spaced gapped relation to the mask holder and mask, or by a vent tube (46) extending from the zone to an orifice end (46a) approximate the level of the mask. There is then no pressure differential on the top and bottom surfaces of the mask membrane affecting the mask-to-wafer gap distance (8) during substrate fabrication operations.