Substrate processing apparatus and gas switching method for substrate processing apparatus

A substrate processing apparatus, comprising:

• a processing chamber configured to execute a processing on a substrate by an introduced gas;
• an exhaust chamber configured to exhaust a gas existing in the processing chamber;
• a vacuum pump configured to evacuate the exhaust chamber;
• a partition plate having a plurality of gas passing holes for bringing the processing chamber and the exhaust chamber into communication with each other therethrough;
• a measuring instrument configured to measure a state in the processing chamber;
• a first pipe configured to connect the processing chamber and the measuring instrument;
• a second pipe configured to bring the exhaust chamber of the vacuum pump and the measuring instrument into communication with each other therethrough via a first valve;
• and
• a controller,
• wherein the controller is configured to control the substrate processing apparatus to open the first valve to discharge a first gas into the exhaust chamber through the second pipe while allowing a second gas to reach the measuring instrument through the first pipe, when switching from a first processing condition to a second processing condition, and
• wherein the first gas is different from the second gas.