In operation S408, with reference to FIG. 1, the wafer in the buffer chamber 130 is transferred to one of the process chambers 140 by the robot blade 132 of the robot 131 of the buffer chamber 130. For illustration in FIG. 1, the wafer is transferred from the position D or position E to the process chamber 140. In some embodiments, before the wafer is transferred, a vacuum process is performed on the buffer chamber 130 in order to compensate the pressure change during the valve V2 is open. In some other embodiments, the vacuum process on the buffer chamber 130 is constantly performed in order to avoid contamination and save process time.

In operation S410, with reference to FIG. 3A, the deposition process is performed to the wafer in the process chamber 140. In some embodiments, the deposition process is configured to deposit metal on the wafer. In some other embodiments, the deposition process is configured to deposit alloy on the wafer. In alternatively embodiments, the deposition process is configured to deposit insulator on the wafer. The materials the deposition process deposited are given for the explanation purposes. Various materials which are deposited by the deposition process are within the contemplated scope of the present disclosure.

In operation S412, with reference to FIG. 1, the wafer in the process chamber 140 is transferred to the buffer chamber 130 after the deposition process is done. For illustration in FIG. 1, the wafer is transferred from the process chamber 140 to the position D or position E by the robot blade 132 of the robot 131 of the buffer chamber 130.