Method and Apparatus for Improving Measurement Accuracy

摘要

An optical system (10) includes an arrangement for splitting a source beam into a measurement beam and a reference beam. The reference beam is reflected off a reflective element (42) which mounted on a delay line (44). A target (35) scatters the radiation from the measurement beam. The scattered radiation and the reference beam are brought to interfere on a detector (40) by calibrating the delay line (44). The detected interference pattern is Fourier-transformed and filtered to select a region of interest around a side-band of the Fourier-transformed interference pattern in order to remove noise caused by stray radiation that hits the detector.

主权项

1. A method of inspecting a substrate, the method comprising:
splitting a source beam of radiation emitted by a radiation source into a measurement beam and a reference beam; illuminating a target area on a substrate with the measurement beam; collecting at least a portion of scattered radiation from the target area; delivering the collected scattered radiation to a detector; delivering the reference beam to the detector so as to interfere with the collected scattered radiation and form an interference pattern at the detector; modifying the interference pattern; and determining a parameter of the target based on the interference pattern.