Abstract: The system includes a dual interferometer sub-system including a first and second channel. The system includes an illumination source. The illumination source includes a first laser source disposed along a first input path and a second laser source disposed along a second input path. The illumination sources includes a combiner-splitter element optically coupled to an output of the first laser source and an output of the second laser source and is configured to combine light of a first wavelength from the first laser source and light of a second wavelength from the second laser source. The combiner-splitter element is further configured to split the combined light into a first channel and a second channel of the dual interferometer sub-system, where the first and second each receive a portion of the light of the first wavelength and the light of the second wavelength.

Abstract: The system includes a dual interferometer sub-system including a first and second channel. The system includes an illumination source. The illumination source includes a first laser source disposed along a first input path and a second laser source disposed along a second input path. The illumination sources includes a combiner-splitter element optically coupled to an output of the first laser source and an output of the second laser source and is configured to combine light of a first wavelength from the first laser source and light of a second wavelength from the second laser source. The combiner-splitter element is further configured to split the combined light into a first channel and a second channel of the dual interferometer sub-system, where the first and second each receive a portion of the light of the first wavelength and the light of the second wavelength.

Abstract: Methods and systems for reducing wafer shape and thickness measurement errors resulted from cavity shape changes are disclosed. Cavity calibration process is performed immediately before the wafer measurement. Calibrating the cavity characteristics every time the method is executed reduces wafer shape and thickness measurement errors resulted from cavity shape changes. Additionally or alternatively, a polynomial fitting process utilizing a polynomial of at least a second order is utilized for cavity tilt estimation. High order cavity shape information generated using high order polynomials takes into consideration cavity shape changes due to temperature variations, stress or the like, effectively increases accuracy of the wafer shape and thickness information computed.

Abstract: The disclosure is directed to focusing one or more detectors of an interferometry system. An initial focus position may be determined by focusing a detector on an edge of a sample by comparing image contrast of intensity frames collected by the detector. Data associated with an inner edge of a ring formed by the image of the sample reflected on a reference flat may be collected from one or more positions near the initial focus position. The detector can be focused to a selected position by comparing edge data collected at the various detector positions near the initial focus position.