| 摘要 |
<p>PROBLEM TO BE SOLVED: To detect the presence of a wafer without mounting wafer sensor, to improve accuracy without synchronizing a CCD liner sensor driving period, and to handle transparent and opaque wafers by simple operation. SOLUTION: A photodiode 27 is provided near the first pixel of the CCD liner sensor 5, and judgment is made according to whether the value of the quantity of light is the same as when light enters or shielded. Also, a timer 30 for measuring the time from a measurement command to an ROG signal, and a timer 31 for measuring the time between measurement commands are provided, and an angle error is corrected using each time when the ROG signal is received. When the edge of a transparent wafer 1 is to be detected, a scan- start end is directed in a direction that is opposite to the direction of the central axis of a wafer rotation means. When a signal-processing means receives the signal of the CCD linear sensor 5, inversion is made, and thresholding is made before reinversion, thus detecting the number of transmission clocks to a point where thresholding data that have been inverted again change from the scan- start end as the edge position of wafer.</p> |
