Patent ID: 8597401

Claim:
An exhausting method of exhausting a flammable process gas from the chamber, which dilutes the process gas with a diluting gas and makes the process gas purify by using a purification system, the exhausting method comprising: introducing the process gas into the chamber to perform a process to a substrate at a predetermined process pressure; after the performing of the process is finished, determining an exhaust flow rate of the process gas from the chamber to be a predetermined value that is less than or equal to a gas flow rate corresponding to a maximum process capability of the purification system when the process gas is diluted to a lower explosive limit; calculating a pressure drop amount per unit time in the chamber to maintain the determined exhaust flow rate of the process gas, based on a relation between the exhaust flow rate and the pressure drop amount per unit time in the chamber; and evacuating the inside of the chamber to maintain the determined exhaust flow rate until the pressure inside the chamber is to be from the predetermined process pressure to a complete suction state in the chamber, while controlling the pressure inside the chamber through an automatic pressure control valve by setting a target pressure value in the chamber to be updated as a control value of the automatic pressure control valve at every predetermined time interval so as to achieve the calculated pressure drop amount per unit time in the chamber.