Enhancing performance of overlay metrology

An optical apparatus comprising:

• an illumination assembly configured to direct one or more illumination beams to a semiconductor wafer, wherein the first and second target features at least partially overlap;
• an imaging assembly comprising:
• a first detector configured to image the semiconductor wafer with first imaging parameters;
• and
• a second detector configured to image the semiconductor wafer with second imaging parameters different than the first imaging parameters;
• and
• a controller including one or more processors configured to:
• receive a sequence of images from the first and second detectors, wherein at least one of the first imaging parameters or the second imaging parameters are varied across the sequence of images to provide varied image parameters at one or more sites on the semiconductor wafer;
• provide a metric indicative of center of symmetry (COS) variations of the first and second target features as a function of the varied imaging parameters based on the sequence of images;
• identify a landscape of values of the varied image parameters for which the metric are below one or more predefined limits;
• generate a recipe for metrology measurements in which the varied imaging parameters are set to values within the landscape;
• and
• generate one or more metrology measurements associated of one or more production wafers based on the recipe.

A method comprising:

• generating a sequence of images of a semiconductor wafer from first and second detectors of an imaging assembly, wherein the first detector is configured to image the semiconductor wafer with first imaging parameters, wherein the second detector is configured to image the semiconductor wafer with second imaging parameters different than the first imaging parameters, wherein at least one of the first imaging parameters or the second imaging parameters are varied across the sequence of images to provide varied image parameters at one or more sites on the semiconductor wafer;
• providing a metric indicative of center of symmetry (COS) variations of the first and second target features as a function of the varied imaging parameters based on the sequence of images;
• identifying a landscape of values of the varied image parameters for which the metric are below one or more predefined limits;
• generating a recipe for metrology measurements in which the varied imaging parameters are set to values within the landscape;
• and
• generating one or more metrology measurements associated of one or more production wafers based on the recipe.