Device for processing a substrate, method of processing a substrate and method of manufacturing semiconductor device

A substrate processing apparatus comprising:

• a process chamber for oxidizing of a substrate;
• a water vapor gas-supplying module for supplying a water vapor gas into the process chamber;
• a water vapor gas-supplying line for supplying the water vapor gas from the water vapor gas-supplying module into the process chamber;
• an exhaust line for exhausting an inside of the process chamber;
• a pump provided in the exhaust line for vacuumizing the inside of the process chamber;
• a pressure-adjusting valve provided in the exhaust line for adjusting a pressure in the process chamber;
• a first pressure-measuring instrument for measuring an inside pressure of the process chamber;
• a second pressure-measuring instrument for measuring a differential pressure between the inside pressure of the process chamber and an outside pressure thereof;
• and
• a controller which controls the pressure-adjusting valve based on a value of the inside pressure of the process chamber measured by the first pressure-measuring instrument so as to keep the inside pressure of the process chamber constant, and controls the water vapor gas-supplying module based on a value of the differential pressure measured by the second pressure-measuring instrument so as to allow supply of the water vapor gas into the process chamber in a case of the inside pressure of the process chamber being smaller than the outside pressure thereof.