| 摘要 |
PURPOSE:To enable the directional property to be accurately maintained when a cassette is housed in preventing dust from sticking on by detecting the quantity of dislocation of an area type positioning mark on a plate material from the reference position at the middle point between No.1 and No.2 positions by means of a projection method followed by the correction at both the middle point and No.2 point. CONSTITUTION:Light reflected from a mask positioning pattern is enlarged through a projection optical system 17, and reaches elements of a CCD camera tube. Elements 16a and 16b which correspond the edge 19a and 19b of the positioning pattern, are unconditionally determined by cutting the above mentioned output signal 21 with a given threshold value 22. Accordingly, the dislocation of the positioning pattern can be accurately detected by verifying the absolute position of the elements 16a, 16b, 16a', and 16b'. The accomplishment of position matching in the above said manner allows the middle point of the elements 16a, 16b, 16a', and 16b' to represent the '0' position permitting the absolute position of these elements 16a, 16b, 16a', and 16b' to arrive at the stated position. after the above said steps have been processed, no positioning can be accurately determined before the position of is determined, the quantity of dislocation of both directions X and Y is measured simultaneously, and both X and Y stages are driven. |
