Patent ID: 8236380

Claim:
A gas supply method for use with a gas supply system for supplying a gas into a processing chamber for processing a substrate to be processed, wherein the gas supply system includes a processing gas supply unit for supplying processing gas for processing the substrate to be processed; a processing gas supply line for allowing the processing gas from the processing gas supply unit to flow therein; a first and a second processing gas branch line branched from the processing gas supply line to be connected with different portions of the processing chamber; a branch flow control unit for controlling branch flows of the processing gas distributed from the processing gas supply line to the first and the second processing gas branch line based on inner pressures of the first and the second processing gas branch line, respectively; an additional gas supply unit for supplying additional gas; an additional gas supply line for allowing the additional gas from the additional gas supply unit to flow therein; a first additional gas branch line branched from the additional gas supply line to be connected with the first processing gas branch line at a downstream side of the branch flow control unit; a second additional gas branch line branched from the additional gas supply line to be connected with the second processing gas branch line at a downstream side of the branch flow control unit; and a flow path switching unit for switching a flow path of the additional gas from the additional gas supply line between the first and the second additional gas branch line, the method comprising the steps of: supplying, before processing the substrate to be processed, the processing gas from the processing gas supply unit while performing a pressure ratio control on the branch flow control unit such that a pressure ratio between the inner pressures of the first and the second processing gas branch line is kept at a target pressure ratio; and supplying the additional gas from the additional gas supply unit after the inner pressures of the first and the second processing gas branch line become stable to be at a first and a second stable inner pressure, wherein in case of supplying the additional gas to the second processing gas branch line via the second additional gas branch line, the additional gas is supplied from the additional gas supply unit after the control unit switches the pressure ratio control on the branch flow control unit to a first fixed pressure control that controls the branch flows such that the first stable inner pressure is maintained in the first processing gas branch line, whereas in case of supplying the additional gas to the first processing gas branch line via the first additional gas branch line, the additional gas is supplied from the additional gas supply unit after the control unit switches the pressure ratio control on the branch flow control unit to a second fixed pressure control that controls the branch flows such that the second stable inner pressure is maintained in the second processing gas branch line.