| 摘要 |
The present invention is directed to a self referencing heterodyne reflectometer system and method for obtaining highly accurate phase shift information from heterodyned optical signals, without the availability of a reference wafer for calibrations. The self referencing heterodyne reflectometer rapidly alternates between a heterodyne reflectometry (HR) mode, in which an HR beam comprised of s-and p-polarized beam components at split angular frequencies of i and i + i is employed, and a self referencing (SR) mode, in which an SR beam comprised of p-polarized beam components at split angular frequencies of i and i + Ai is employed. When the two measurements are made in rapid succession, temperature induced noise in the detector is be assumed to be the same as for both measurements. A measured phase shift HRef/film is generated from the HR beam and a reference phase shift HRef/sub is generated from the SR beam. The measured phase shift HRef/film generated from the beat signals of the HR beam is used for film thickness measurements. The SR beam is p-polarized and no significant reflection will result from a film surface and will not carry any phase information pertaining to the film. The reference phase shift HRef/Sub generated from the beat signals of the SR beam is equivalent to that obtained using a reference sample. Film phase shift information is then derived from the measured phase shift HRef/film and the reference phase shift HRef/Sub which is independent of phase drift due to temperature. Film thickness is calculated from the film phase shift information.
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