| 摘要 |
PROBLEM TO BE SOLVED: To provide apparatus and methods for measuring a characteristic, such as overlay, of a semiconductor target.SOLUTION: In general, order selected imaging and/or illumination is performed and an image is collected from a target by using a metrology system. In one implementation, tunable spatial modulation is provided only in an imaging path of the system. In other implementations, tunable spatial modulation is provided in both illumination and imaging paths of the system. In a specific implementation, the spatial modulation is used to image side-by-side gratings with diffraction orders of ±n. The side-by-side gratings may be in different layers or the same layer of a semiconductor wafer. The overlay between structures is generally found by measuring the distance between symmetry centers of the gratings. In this embodiment, only orders ±n for a given choice of (n) ((n) is an integer and not equal to zero) are selected and the gratings are only imaged with these diffraction orders. |
