Inspection apparatus, motorized apertures, and method background

A spatial filter comprising:

• an aperture comprising
• one or more obscurations having an angular dependent radius that azimuthally varies from a first radial distance to a second radial distance;
• and
• one or more ridges located at an inner edge of the one or more obscurations, and
• wherein the aperture is configured to rotate about its center.

A method, comprising:

• receiving a plurality of diffraction orders;
• blocking, using a spatial filter, one or more undesired diffraction orders of the plurality of diffraction orders and passing one or more desired diffraction orders of the plurality of diffraction orders;
• and
• measuring an intensity of the one or more desired diffraction orders, wherein the spatial filter comprises one or more obscurations having an angular dependent radius that varies azimuthally.