Focus detection system for mutually-coherent illumination metrology

Abstract

A focus detection system may include an illumination system with one or more illumination lenses that may direct a first illumination beam and a second illumination beam to a sample at opposing azimuth angles. The system may include an imaging system with one or more collection lenses that may image the sample onto one or more detectors. A controller with one or more processors may be configured to execute program instructions that may cause the processors to determine a lateral shift between locations of features on the sample imaged by different combinations of the first and second illumination beams. The instructions may further cause the processors to generate a measurement of a focal position of the sample based on the lateral shift.

Images