Gasification monitor, method for detecting mist, film forming method and film forming apparatus

A film forming method for forming a thin film on an object to be processed by thermally decomposing a processing gas obtained by vaporizing a liquid material or a solid material, the film forming method comprising the steps of:

• supplying the liquid material or the solid material from a source;
• vaporizing the liquid material or the solid material to provide a processing gas;
• conducting the processing gas to a processing chamber where the thin film is to be formed on the object to be processed;
• while conducting the processing gas to the processing chamber, monitoring a quantity of mist contained in the processing gas by
• detecting a first pressure Pq of the processing gas by a first method and producing a pressure measurement which is changeable by a quantity of mist contained in the gas,
• detecting a second pressure Pg of the processing gas by a second method and producing a second pressure measurement, which is unchangeable by the quantity of mist contained in the gas, by using a pressure detecting part that produces a pressure measurement which does not change when mist contained in the processing gas adheres to the pressure detecting part, the pressure detecting part being disposed such that the mist may adhere to it, and
• detecting the quantity of mist contained in the processing gas based on a difference ΔP between the first pressure Pq detected by the first method and the second pressure Pg detected by the second method;
• performing a film forming process in the processing chamber while the detected quantity of mist remains below a threshold value;
• and
• either outputting a warning or stopping the film forming process when the quantity of mist exceeds the predetermined threshold value.