POSITIONING DEVICE

PURPOSE:To keep a detection position unchanged even when a treatment is executed at any threshold level by a method wherein an even-order harmonic wave of a pattern- detecting signal is removed and a measuring operation and a positioning operation are executed after signal waves have been made symmetrical with reference to a line. CONSTITUTION:A measuring operation and a positioning operation are executed in such a way that an even-order harmonic wave of a detection signal of a pattern 2 on a wafer, a mask, a reticle or the like is removed and that signal waves are made symmetrical with reference to a line. For example, a signal of the scattered light 1' caught by a detector 5 is amplified to a definite level by using a preamplifier equipped with an AGC; a fundamental wave(f) is extracted by a fundamental wave (f) extraction circuit and is digitized by a digitization circuit 9. From this signal a twofold frequency 2f is generated through a twofold frequency generation circuit 10 and is then converted into a DC voltage corresponding to the frequency by using an F/V converter 11. BEF 7 cuts only the twofold frequency; if an output detected by a synchronous detection circuit 12 is a voltage which is lower than a value set by a comparator 13, an analog SW 14 is turned on; a signal having no second harmonic wave is set to a signal processing circuit 15.