Decreasing inaccuracy due to non-periodic effects on scatterometric signals

An apparatus comprising:

• a memory element configured to store a set of computer-readable instructions;
• one or more processors communicatively coupled to an optical system, the optical system including at least one of a detector, a coherent light source, a control unit, an optical scanning unit, or a mechanical scanning unit, wherein the detector is configured to measure light from a collected pupil of the optical system,
• wherein the one or more processors are configured to execute the set of computer-readable instructions to:
• receive a plurality of scans associated with a light distribution in the collected pupil of the optical system from the detector;
• derive an overlay linear response to at least one non-periodic effect based on at least one of an overlay value, a misalignment vector, or an overlay linear response vector;
• and
• estimate a corrected overlay value based on the derived overlay linear response to at least one non-periodic effect.

A metrology method, comprising:

• acquiring a plurality of scans associated with light distribution in a collected pupil of an optical system with a detector of the optical system;
• deriving an overlay linear response to at least one non-periodic effect based on at least one of an overlay value, a misalignment vector, or an overlay linear response vector;
• and
• estimating a corrected overlay value based on the derived overlay linear response to at least one non-periodic effect.