In operation S402, with reference to FIG. 1, the wafer in the factory interface 110 is transferred by the robot in the factory interface 110 to the load lock chamber 120 through the valve V1. Before transferring the wafer, the wafer is loaded in the factory interface 110 under the first environment. In some embodiments, the first environment is under atmosphere and room temperature. Then the valve V1 between the load lock chamber 120 and the factory interface 110 is open. The environment in the factory interface 110 and the load lock chamber 120 are equalized. In some embodiments, before the valve V1 is open, a ventilation process is performed to the load lock chamber 120 to make the environment in the load lock chamber 120 similar to the first environment. Then, after the valve V1 is open, the environment in the factory interface 110 and the load lock chamber 120 are equalized, the wafer is transferred from the factory interface 110 to the load lock chamber 120. For illustration in FIG. 1, the wafer is transferred to position B in the load lock chamber 120. After the wafer is transferred to the load lock chamber 120, the valve V1 is closed in order to isolate the environment between the load lock chamber 120 and the factory interface 110.