Abstract: A system includes an illumination system, an optical element, a switching element and a detector. The illumination system includes a broadband light source that generates a beam of radiation. The dispersive optical element receives the beam of radiation and generates a plurality of light beams having a narrower bandwidth than the broadband light source. The optical switch receives the plurality of light beams and transmits each one of the plurality of light beams to a respective one of a plurality of alignment sensor of a sensor array. The detector receives radiation returning from the sensor array and to generate a measurement signal based on the received radiation.

Abstract: A method of applying a measurement correction includes calculating a first correction value based on a first coefficient and the measurement; calculating a second correction value based on a second coefficient, greater than the first coefficient, and the measurement; and calculating a third correction value based on a third coefficient, greater than the second coefficient, and the measurement. The method also includes applying the third correction value to the measurement if a difference between the first correction value and the third correction value is above a first threshold value; applying the second correction value to the measurement if a difference between the first correction value and the second correction value is above a second threshold value; and applying the first correction value to the measurement if the difference between the first correction value and the second correction value is below or equal to the second threshold value.

Abstract: A method of applying a measurement correction includes calculating a first correction value based on a first coefficient and the measurement; calculating a second correction value based on a second coefficient, greater than the first coefficient, and the measurement; and calculating a third correction value based on a third coefficient, greater than the second coefficient, and the measurement. The method also includes applying the third correction value to the measurement if a difference between the first correction value and the third correction value is above a first threshold value; applying the second correction value to the measurement if a difference between the first correction value and the second correction value is above a second threshold value; and applying the first correction value to the measurement if the difference between the first correction value and the second correction value is below or equal to the second threshold value.