Enhancing performance of overlay metrology

A method for metrology includes directing at least one illumination beam to illuminate a semiconductor wafer on which at least a first patterned layer and a second patterned layer have been successively deposited, a first target feature in the first patterned layer and a second target feature in the second patterned layer that overlaps the first target feature are included. Images of a sequence of the first target feature and the second target feature are captured while varying one or more imaging parameters that occur throughout the sequence. The images in the sequence are processed in order to identify respective centers of symmetry of the first target feature and the second target feature in the images and measure variations in the centers of symmetry with varying image parameters. A measured change is applied in measuring an overlap error between the first patterned layer and the second patterned layer. 一种用于计量的方法包含引导至少一个照明射束照明半导体晶片，在所述半导体晶片上已相继沉积了至少第一经图案化层及第二经图案化层，包含所述第一经图案化层中的第一目标特征及所述第二经图案化层中的重叠在所述第一目标特