EFEM and method of controlling supply amount of inert gas

A method of controlling gas supplied to an EFEM including a housing having a substrate transfer space in the housing, a first supply part configured to supply gas into the housing via a first supply path, at least one second supply part configured to supply gas into the housing via a second supply path different from the first supply path, and a control part configured to control supplying the gas from the first gas supply, the method comprising:

• setting a total supply amount of gas to be supplied into the housing based on an oxygen concentration in the housing;
• determining whether the gas is supplied from the at least one second gas supply part into the housing;
• in response to determining that the gas is supplied from the at least one second gas supply part into the housing, calculating a target supply amount of the gas to be supplied from the first gas supply part into the housing, based on a value obtained by subtracting a supply amount of the gas supplied from the at least one second gas supply part from the total supply amount of the gas;
• and
• controlling the first gas supply part according to a calculation result for the target supply amount of the gas to be supplied from the first gas supply part into the housing.