Self referencing heterodyne reflectometer and method for implementing
First Claim
1. A method for measuring a thickness parameter comprising:
- measuring a heterodyne phase shift, comprising;
receiving a split frequency, dual polarized beam;
detecting a reference signal from the split frequency, dual polarized beam;
propagating the split frequency, dual polarized beam to a target;
receiving a reflected split frequency, dual polarized beam from the target;
detecting a measurement signal from the reflected split frequency, dual polarized beam; and
measuring a phase difference between the reference signal and the measurement signal for the reflected split frequency, dual polarized beam;
measuring a self referencing phase shift, comprising;
receiving a split frequency, p-polarized beam;
detecting a reference signal from the split frequency, p-polarized beam;
propagating the split frequency, p-polarized beam to a target;
receiving a reflected split frequency, p-polarized beam from the target;
detecting a second measurement signal from the reflected split frequency, p-polarized beam; and
measuring a self referencing phase difference between the reference signal and the measurement signal for the split frequency, p-polarized beam; and
calibrating the phase difference for the target with the self referencing phase difference.
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Accused Products
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/film is generated from the HR beam and a reference phase shift δRef/Sub is generated from the SR beam. The measured phase shift δRef/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 δRef/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 δRef/film and the reference phase shift δRef/Sub which is independent of phase drift due to temperature. Film thickness is calculated from the film phase shift information.
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Citations
1 Claim
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1. A method for measuring a thickness parameter comprising:
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measuring a heterodyne phase shift, comprising;
receiving a split frequency, dual polarized beam;
detecting a reference signal from the split frequency, dual polarized beam;
propagating the split frequency, dual polarized beam to a target;
receiving a reflected split frequency, dual polarized beam from the target;
detecting a measurement signal from the reflected split frequency, dual polarized beam; and
measuring a phase difference between the reference signal and the measurement signal for the reflected split frequency, dual polarized beam;
measuring a self referencing phase shift, comprising;
receiving a split frequency, p-polarized beam;
detecting a reference signal from the split frequency, p-polarized beam;
propagating the split frequency, p-polarized beam to a target;
receiving a reflected split frequency, p-polarized beam from the target;
detecting a second measurement signal from the reflected split frequency, p-polarized beam; and
measuring a self referencing phase difference between the reference signal and the measurement signal for the split frequency, p-polarized beam; and
calibrating the phase difference for the target with the self referencing phase difference.
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Specification