Method of optimizing the position and/or size of a measurement illumination spot relative to a target on a substrate, and associated apparatus

Disclosed is a method of optimizing within an inspection apparatus, the position and/or size (and therefore focus) of a measurement illumination spot relative to a target on a substrate. The method comprises detecting scattered radiation from at least the target resultant from illuminating the target, for different sizes and/or positions of said illumination spot relative to the target; and optimizing said position and/or size of the measurement illumination spot relative to the target based on a characteristic of the detected scattered radiation for the different sizes and/or positions of said illumination spot relative to the target. 披露了一种在检查设备内优化测量照射光斑相对于衬底上的目标的位置和/或大小(以及因此聚焦)的方法。所述方法包括：针对所述照射光斑相对于所述目标的不同大小和/或位置，检测因照射所述目标而产生的来自至少所述目标的散射辐射；以及基于所检测到的散射辐射的特性，针对所述照射光斑相对于所述目标的不同大小和/或位置，优化所述测量照射光斑相对于所述目标的位置和/或大小。