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;
calibrating the phase difference for the target with the self referencing phase difference; and
finding a thickness parameter from the phase difference for the target.
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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.
18 Citations
22 Claims
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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; calibrating the phase difference for the target with the self referencing phase difference; and finding a thickness parameter from the phase difference for the target.
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2. A method for measuring a thickness parameter comprising:
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operating in heterodyne ref lectometry mode, comprising; generating a ref lectometry beam; propagating the ref lectometry beam incident to a target material at a predetermined angle of incidence; measuring a ref lectometry beam heterodyne phase for the ref lectometry beam from the target; finding a ref lectometry beam heterodyne phase shift from the reflectometry beam heterodyne phase, wherein the ref lectometry beam heterodyne phase shift is induced by the ref lectometry beam interacting with the target material; operating in self referencing mode, comprising; generating a self referencing beam; propagating the self referencing beam incident to the target material at the predetermined angle of incidence; measuring a self referencing beam heterodyne phase for the self referencing beam from the target material; and finding a self referencing beam heterodyne phase shift from the self referencing beam heterodyne phase, wherein the self referencing beam heterodyne phase shift is induced by the self referencing beam interacting with the target material; and finding a thickness parameter from the reflectometry beam heterodyne phase shift and the self referencing beam heterodyne phase shift. - View Dependent Claims (3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A self referencing heterodyne reflectometer, comprising:
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a heterodyne ref lectometry beam source; a operating mode switcher for receiving the heterodyne reflectometry beam and converting the heterodyne ref lectometry beam to a self referencing beam; a reference detector for receiving the heterodyne reflectometry beam and generating a reference heterodyne reflectometry phase signal, and for receiving the self referencing beam and generating a reference self referencing phase signal; a target material; first optical elements for propagating the heterodyne reflectometry beam and the self referencing beam incident to the target material at a predetermined angle of incidence; a measurement detector for receiving the heterodyne reflectometry beam from the target material and generating a measurement heterodyne reflectometry phase signal, and for receiving the self referencing beam from the target material and generating a measurement self referencing phase signal; a heterodyne phase shift detector for detecting a heterodyne phase shift between the reference heterodyne reflectometry phase signal and the measurement heterodyne ref lectometry phase signal; and a self referencing phase shift detector for detecting a reference phase shift between the reference self referencing phase signal and the measurement self referencing phase signal. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20, 21)
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22. A method for measuring a thickness parameter comprising:
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iterating a beam between a heterodyne reflectometry operating mode and a self referencing operating mode, said heterodyne reflectometry operating mode including generating an s-polarized beam component at the first frequency and a p-polarized beam component at the second frequency and said self referencing operating mode including generating a p-polarized beam component at the first frequency and a p-polarized beam component at the second frequency; receiving the beam at a reference detector and generating a reference beam phase signal; propagating the reflectometry beam incident to a target material at a predetermined angle of incidence; receiving the beam at a measurement detector from the target material and generating a measurement beam phase signal; at each iteration, finding a reflectometry beam heterodyne phase shift from the measurement beam phase signal and the reference beam phase signal and finding a thickness parameter for the target material from the reflectometry beam heterodyne phase shift.
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Specification