An apparatus and a method for monitoring the relative relationship between the wafer and the chuck is provided, especially for monitoring whether the wafer is sticky on the chuck when the wafer is de-chucked. The lift pins may be extended outside the chuck to separate the wafer and the chuck when the wafer is de-chucked. By detecting the capacitance between the de-chucked wafer and the chuck, especially by comparing the detected capacitance with the capacitance that the wafer is held by the chuck, one may determine whether the wafer is sticky on the chuck, or even whether the wafer is properly supported by the lift pins. Accordingly, an early alarm may be issued if the wafer is sticky or improperly removed. Besides, by controlling a switch electrically connected to a lift pin that contacted the wafer, the charges at the wafer may be eliminated.