PURPOSE: To improve the accuracy for determining the optimum exposure focusing position by performing second order approximation processing for detected signals, determining Z-position where the coefficient of the second order term of the approximation becomes a minimum, providing a detection processing system for automatically detecting focused position, and performing automatic correction as the optimum exposure focusing position.
CONSTITUTION: Detection of the quantity of light of a projected image 8 transmitting through a slit pattern 9 is performed by a light receiver 10 for receiving and detecting light. By the movement Zi in the optical axis direction of a projection optical system of a stage 5, the intensity distribution of the projected image 8 for the movement Xi in X/Y-direction of the stage 5 becomes a changing curve of quadratic function type, and the coefficient of the second order term of the quadratic function at the focused position becomes a minimum. Here, the coefficient of the second order term is determined for each movement in Z-direction of the stage 5. By doing this, a Z- position Zm, where the coefficient of the second order term becomes a minimum, can be determined by finding the relation between Z-stage position and the coefficient of the second order term. By doing this, focusing position of the projected optical system can be calculated.
IKEGAMI TORU
KOMURO OSAMU
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