Abstract: An alignment device usable in the processes for manufacture of semiconductor integrated circuits, for bringing a mask and a semiconductor wafer into a predetermined positional relation by use of alignment marks, prior to effecting transfer of an integrated circuit pattern of the mask onto a photosensitive layer of the wafer. The alignment device is provided with a function of searching a mark signal included in a detection signal for the wafer, on the basis of the dimension of the alignment mark. By this, the alignment mark signal can be accurately detected irrespective of the fact that a noise component might be included in the detection signal for the wafer due to effects of the existence of the photosensitive layer or the like. In another aspect, the alignment device is operable in an operation mode including the mark signal searching step and in another operation mode not including the signal searching step.

Abstract: A system for photoelectrically detecting a light reflected from an object, such as a semiconductor wafer, irradiated by a light beam supplied from a light source, wherein the amount of irradiation is controlled so as to obtain an optimum photoelectrically-converted signal. According to another aspect of the invention, the amount of irradiation is controlled automatically on the basis of a reflectance of the object which has been detected preparatively. According to another preferred form of the invention, the amount of irradiation is controlled in a time-sharing fashion so as to obtain optimum photoelectrically-converted signals from different portions of the object.