NOVELTY - The substrate processing method comprises supplying a film-forming gas into a processing chamber and exhausting the film-forming gas through an exhaust line to form a film on a substrate (200) in the chamber, and introducing an air from an outside of the chamber into an inside of the chamber by an air supply unit installed in the chamber, reacting an adherent adhered to the inside of the chamber and an inside of the exhaust line connected to the chamber with a moisture contained in the air to generate a hydrogen chloride gas and exhausting the hydrogen chloride gas through the exhaust line.    USE - The substrate processing method is useful for manufacturing a solar cell and a semiconductor device such as an integrated circuit, and for forming a semiconductor silicon film on a substrate such as semiconductor wafer.    ADVANTAGE - The substrate processing method prevents deposition of the reactive product to the inside of the processing chamber and the exhaust line, increases maintainability or safety of the processing chamber, and prevents the corrosion of the surroundings of the processing chamber.    DETAILED DESCRIPTION - The substrate processing method comprises supplying a film-forming gas into a processing chamber and exhausting the film-forming gas through an exhaust line to form a film on a substrate (200) in the chamber, and introducing an air from an outside of the chamber into an inside of the chamber by an air supply unit installed in the chamber, reacting an adherent adhered to the inside of the chamber and an inside of the exhaust line connected to the chamber with a moisture contained in the air to generate a hydrogen chloride gas and then exhausting the hydrogen chloride gas through the exhaust line. The air introduction step is performed: until a concentration level of the hydrogen chloride gas in the processing chamber is equal to or lower than a preset concentration level; in an unloading step in which the substrate having the film is unloaded from the processing chamber; or in a loading step in which a different substrate other than the substrate having the film is loaded into the processing chamber after the unloading step in a manner that a time for introducing the air from the outside of the processing chamber into the inside of the processing chamber in the unloading step is longer than a time for introducing the air from the outside of the processing chamber into the inside of the processing chamber in the loading step. The air supply unit includes an opening of the processing chamber, where the substrate is loaded and unloaded, an air supply line connected to the processing chamber, and a valve connected to the air supply line, and introduces the air into the processing chamber by opening the valve. In the step of introducing the air: the concentration level of the hydrogen chloride gas in the processing chamber is monitored; an amount of the air introduced into the inside of the processing chamber is increased when the concentration level of the hydrogen chloride gas exceeds the preset concentration level within a preset time; an inert gas is continuously supplied into the processing chamber from a processing gas supply unit supplying a processing gas; an amount of the inert gas supplied into the processing chamber is decreased when the concentration level of the hydrogen chloride gas exceeds the preset concentration level within the preset time; an opening degree of an opening of the processing chamber, where the substrate is loaded and unloaded, is increased when the concentration level of the hydrogen chloride gas exceeds the preset concentration level within the preset time; an exhaust velocity is varied, where the hydrogen chloride gas is exhausted through the exhaust line; and the exhaust velocity is higher at an end of the introduction step than at a start of the introduction step. An INDEPENDENT CLAIM is included for a substrate processing apparatus.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic view of a substrate processing apparatus.    Substrate processing apparatus (101)    Front maintenance port (103)    Front maintenance door (104)    Casing (111)    Front wall of the casing (111a)    Substrate. (200)