Abstract: A method of vacuum treatment is performed using a vacuum treatment system (1) comprising a vacuum treatment unit (31) for treating a wafer (W) placed on a wafer stage (10) and a controller (51) for controlling the vacuum treatment unit (31). A sensor wafer (11) of substantially the same shape and size as a wafer (W), which includes a detector element (11d) for detecting data about the state of a vacuum treatment and a data processing element (11p) for processing the detected data, is placed on the wafer stage (10) and treated in a vacuum by the vacuum treatment unit (31). While the sensor wafer (11) is subjected to a vacuum treatment, data on the state of the vacuum treatment is detected and processed. Based on the processed data, the controller (51) controls the vacuum treatment unit (31) to treat the wafer (W).