| 摘要 |
The automatic wafer alignment technique may be used in a step-and-repeat photomicrolithographic exposure system accurately to prealign a wafer before exposure to the B-level and subsequent reticles and automatically to align the wafer at each die site prior to exposure. A search technique optimizes location of the global targets (36 min ) used for wafer prealignment. The search begins at the most likely target position and proceeds through a search area established by the maximum expected rough prealignment error. A wafer atignment target (36 min ) configuration consisting of a cross with one elongated arm (36Y min ) and a short crossbar (36X min ) is used to optimize target verification. Such verification is carried out by successively examining the middle, right and left arm parts and area of the wafer beyond the arm to determine whether the expected target features are present or absent. To locate targets, a video image is digitized and the average intensity at each video scan line and column is obtained and stored in a "data buffer" memory. The intensity differences between successive points is measured, and the signs of successive intensity differences are used to determine whether consecutive points belong to a run to points having the characteristics of a feature edge. |
