Optics: measuring and testing – By light interference – Having light beams of different frequencies
Reexamination Certificate
2005-09-27
2009-06-09
Turner, Samuel A (Department: 2877)
Optics: measuring and testing
By light interference
Having light beams of different frequencies
C356S504000
Reexamination Certificate
active
07545503
ABSTRACT:
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 ω and ω+Δω is employed, and a self referencing (SR) mode, in which an SR beam comprised of p-polarized beam components at split angular frequencies of ω and ω+Δω 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 δRef/filmis generated from the HR beam and a reference phase shift δRef/Subis generated from the SR beam. The measured phase shift δRef/filmgenerated 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 δRef/Subgenerated 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 δRef/filmand the reference phase shift δRef/Subwhich is independent of phase drift due to temperature. Film thickness is calculated from the film phase shift information.
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Buchel, Jr. Rudolph J.
Turner Samuel A
Verity Instruments Inc.
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