Precoat method for substrate processing apparatus and substrate processing apparatus

A precoat method for a substrate processing apparatus for depositing on a substrate using a raw material gas and a reducing gas, the method comprising:

• a) supplying a fluorine-containing gas into a processing chamber to clean an inside of the processing chamber;
• b) after a), supplying a reducing gas into the processing chamber to purge the inside of the processing chamber;
• c) after b), supplying a raw material gas and a reducing gas into the processing chamber to form a precoat film;
• and
• d) after c), supplying a reducing gas into the processing chamber to purge the inside of the processing chamber before depositing on a subsequent substrate, wherein
• the reducing gas supplied in b) is NH3 gas,
• the reducing gas supplied in d) is NH3 gas,
• in d), the NH3 gas is supplied from a buffer tank after being temporarily stored in the buffer tank to control a pressure in the processing chamber to approximately 400 Torr, such that a part of the precoat film containing Cl is physically removed by the NH3 gas based on the controlled pressure, and
• in b), the NH3 gas is not stored in a buffer tank before being supplied.