| 摘要 |
PURPOSE:To reduce the time for position sensing by a method wherein the resolving power of mark sensing is made variable with positions of a position- sensing mark in the field of view in the sensing of the position-sensing mark on a water. CONSTITUTION:When measurement starts, the resolving power of position sensing is set by determining the picture element sampling frequency. In this state picture elements are integrated independently in the X-Y directions, and binary search is carried out by setting the slice level by means of a microprocessor, thus detecting the peak position. Here, it is judged whether the mark center is on the screen of not: in case of the absence of the center, the wafer stage is moved. After wafer movement, integration, binary search, and mark detection are repeated again; thus, the mark center is judged again. The resolving power is discriminated when the mark center comes in the screen: in case of the low setting of the resolving power, the loop processing for the final detection of mark position is made after the resolving power is increased, resulting in the finish of position sensing. This process can reduce the time for sensing mark positions by making the resolving power of mark sensing variable with positions of position-sensing marks in the field of view. |
