Patent attributes
An alignment sensor apparatus includes an illumination system, a first optical system, a second optical system, a detector system, and a processor. The illumination system is configured to transmit an illumination beam along an illumination path. The first optical system is configured to transmit the illumination beam toward a diffraction target on a substrate. The second optical system includes a first polarizing optic configured to separate and transmit an irradiance distribution. The detector system is configured to measure a center of gravity of the diffraction target based on the irradiance distribution outputted from a first polarization branch and a second polarization branch. The processor is configured to measure a shift in the center of gravity of the diffraction target caused by an asymmetry variation in the diffraction target and determine a sensor response function of the alignment sensor apparatus based on the center of gravity shift.
