Automatic pressure control device, film forming apparatus and pressure control method

A method of controlling a pressure in a processing container which is included in a film forming apparatus to which a source gas is supplied, the method comprising:

• supplying the source gas into the processing container by a gas supplier of the film forming apparatus;
• controlling the pressure in the processing container, wherein, in a butterfly valve including an annular valve seat having an inner wall surface forming a portion of an exhaust path, and a valve body configured as a plate-shaped body that blocks at least a portion of a cross section that transverses the annular valve seat, the valve body being rotatably installed to the valve seat via a shaft and configured to change an opening area of the exhaust path by being arranged to be inclined and changing an inclination angle of the valve body with respect to the cross section by the shaft, and the butterfly valve being configured to control the pressure in the processing container by changing the inclination angle of the valve body based on a result of detecting the pressure in the processing container, when an upstream side surface of the valve body is called a front surface and a downstream side surface is called a rear surface as viewed from an upstream side in a flow direction of a gas in the exhaust path, the controlling of the pressure is performed by using a first tapered surface, which is formed on the front surface of the valve body in a first local region located in a downstream side end portion in the flow direction, and a second tapered surface, which is formed on the rear surface of the valve body in a second local region located in an upstream side end portion in the flow direction in the valve body arranged to be inclined at the inclination angle of 10 degrees to 30 degrees, and making a width between the valve body and an inner periphery of the valve seat uniform to exhaust the gas in the processing container;
• and
• growing, on the first tapered surface, a by-product generated due to the source gas remaining in the exhaust path,
• wherein each of an angle formed between the front surface and the first tapered surface and an angle formed between the rear surface and the second tapered surface is greater than 95 degrees and less than or equal to 150 degrees.