Patent ID: 8221638

Claim:
A gas supply method adopted in conjunction with a gas supply system that supplies gases into a processing chamber where a substrate is processed, wherein: said gas supply system comprises: a processing gas supply means for supplying a processing gas to be used to process the substrate; a processing gas supply passage through which the processing gas from said processing gas supply means flows; a first branch passage and a second branch passage branching from the processing gas supply passage and connected to said processing chamber at different positions; a divided flow rate adjustment means for adjusting the divided flow rates of the processing gas diverted into said branch passages from said processing gas supply passage based upon pressures in said branch passage; an additional gas supply means for supplying an additional gas; an additional gas supply passage through which the additional gas from said additional gas supply means is made to flow into said second branch passage at a position further downstream relative to said divided flow rate adjustment means; and a pressure controller for switching between a pressure ratio control which adjusts said divided flow rates to hold the pressure ratio in said branch passages at a target pressure ratio and a steady pressure control which adjusts said divided flow rates to hold the pressure value in said first branch passage, and executing each of said controls on said divided flow rate adjustment means; said gas supply method comprises: a step executed before processing the substrate in which the processing gas is supplied by said pressure controller via said processing gas supply means and said pressure ratio control is executed on said divided flow rate adjustment means to adjust the divided flow rates so as to achieve a target pressure ratio for the pressures in said branch passages; and a step executed once the pressures in said branch passages become stabilized through said pressure ratio control in which said steady pressure control is executed by said pressure controller on said divided flow rate adjustment means to adjust the divided flow rates to hold said pressure value in said first branch passage at a level achieved in stable pressure conditions; and a step in which the additional gas is supplied via said additional gas supply means after switching from the pressure ratio control to the steady pressure control.