Patent ID: 7300558

Claim:
An apparatus comprising: (a) a chamber defining an interior space adapted to be maintained at a reduced pressure; and (b) a gas supply means for supplying at least one burst of gas to said chamber for rapidly establishing at least one preselected gas pressure in said chamber, said gas supply means including: (i) a source of said gas; (ii) a supply ballast fluidly connected to said gas source for receiving said gas from said source; (iii) at least one burst ballast fluidly connected to said supply ballast via a metering valve for receiving said gas from said supply ballast; and (iv) an on/off valve fluidly connected to said at least one burst ballast and said chamber for supplying said process chamber with said gas from said at least one burst ballast and wherein: said gas supply means is adapted for sequentially supplying a plurality of different bursts of gas to said chamber for rapidly establishing a respective plurality of preselected gas pressures in said chamber, said gas supply means including a plurality of burst ballasts fluidly connected to said supply ballast via respective metering valves, and a corresponding plurality of on/off valves fluidly connected to respective ones of said plurality of burst ballasts and said chamber for supplying said process chamber with said gas from a selected one of said plurality of burst ballasts.