Patent ID: 6782907
Filing Date: 2004-08-31
Classification: C23C,Y10S,Y10T

Abstract:
A gas recirculation flow control method for use in an evacuation system having a vacuum chamber into which a gas is introduced, a first vacuum pump for exhausting said gas from said vacuum chamber and reducing a pressure in said vacuum chamber to a desired pressure, a second vacuum pump for performing evacuation to lower a back pressure of said first vacuum pump below an allowable back pressure, and a gas recirculation line for returning a part of gas exhausted from said first vacuum pump to said vacuum chamber,wherein a recirculation flow rate Q2 of the gas returning to said vacuum chamber through said gas recirculation line is controlled by adjusting a differential pressure Pdâˆ’Pc in said gas recirculation line by varying an effective pumping speed of said second vacuum pump using the following formula: Q2=CÃ—(Pdâˆ’Pc) where: Q2 denotes the recirculation flow rate of the gas returning to said vacuum chamber through said gas recirculation line; Pc denotes a pressure in said vacuum chamber; Pd denotes a pressure in an upstream side of said gas recirculation line; and C denotes a conductance of said gas recirculation line.