Plasma processing apparatus and plasma processing method

A plasma processing apparatus, comprising:

• a process chamber;
• a pedestal provided in the process chamber and configured to hold a substrate;
• a first gas supply part configured to be able to supply a first gas from a location facing the pedestal;
• a radio frequency power source configured to convert the first gas to plasma;
• a shield part to block the first gas converted to plasma and provided around the pedestal;
• an evacuation device configured to evacuate the process chamber through the shield part;
• a second gas supply part configured to be able to supply a second gas to a space between the shield part and the evacuation device;
• and
• a controller configured to control operation of the first gas supply part and the second gas supply part,
• wherein the first gas supply part is configured to be able to supply a first purge gas,
• wherein the controller configured to control the operation of the first gas supply part and the second gas supply part such that the first gas supply part supplies the first purge gas and that the second gas supply part, supplies the second gas, when supplying the second gas to the substrate,
• wherein the controller configured to control at least one of a flow rate of the first purge gas supplied from the first gas supply part and a distance between the pedestal and the first gas supply part such that gas diffusion rather than a gas flow dominates gas transportation from the first gas supply part to the second gas supply part, and
• wherein the controller, when L1 represents a distance from an edge of the substrate to the second gas supply part, S1 (x) represents a space cross-sectional area perpendicular to a flow of the first purge gas is made, Q1 represents a flow rate of the first purge gas, P1 represents a pressure in the process chamber, and D1 represents a diffusion coefficient of the second gas relative to the first purge gas, configured to control at least one of the flow rate of the first purge gas Q1 supplied from the first gas supply part and the space cross-sectional area S1(x) perpendicular to the flow of the first purge gas such that Peclet number Pe1 calculated from the following formula is smaller than one
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