Systems and methods for quantifying nonlinearities in interferometry systems
First Claim
Patent Images
1. An interferometry system comprising:
- an interferometer which during operation directs two beams along separate paths and then combines the beams to produce an overlapping pair of exit beams, the separate paths defining an optical path length difference;
a detector which responds to optical interference between the overlapping pair of exit beams and produces an interference signal s(t) indicative of the optical path length difference, the signal s(t) including a dominant term having a frequency equal to the sum of the frequency splitting ω
between the two beams, if any, and a Doppler shift {dot over (φ
)} defined by the rate of change of the optical path length difference, wherein properties of the interferometry system causes the signal s(t) to further include additional terms each having a frequency not equal to the sum of the frequency splitting ω and
the Doppler shift {dot over (φ
)}; and
an analyzer coupled to the detector which during operation;
i) applies a window function to a sequence of values of the signal s(t);
ii) Fourier transforms the windowed sequence of values, the Fourier transform defining a power spectrum equal to the square modulus of the Fourier transform; and
iii) identifies at least one of the additional terms based on at least one peak in the power spectrum at a frequency not equal to the sum of the frequency splitting ω and
the Doppler shift {dot over (φ
)}.
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Abstract
The invention features interferometry systems and methods that quantify nonlinearities, e.g., cyclic errors, in an interference signal produced by an interferometry system. The systems and methods analyze interference signals for each of multiple Doppler shifts to thereby resolve nonlinearities that may otherwise overlap spectrally with a dominant interference signal, and also, to interpolate the contributions of the nonlinearities to measurements at different Doppler shifts. The time-varying interference signal or the phase extracted from the time-varying interference signal is Fourier transformed and at least some of the nonlinearities are associated with peaks in the square modulus of the Fourier transformed signal (i.e., the power spectrum). The amplitude and phase of the Fourier transform at the frequency of each such peak are used to quantify the associated nonlinearity. The quantified nonlinearities are used to correct optical path length measurements by the system. Changes in the magnitude of one or more of the quantified nonlinearities can also be used to identify degradation of a component of the interferometry system.
96 Citations
27 Claims
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1. An interferometry system comprising:
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an interferometer which during operation directs two beams along separate paths and then combines the beams to produce an overlapping pair of exit beams, the separate paths defining an optical path length difference;
a detector which responds to optical interference between the overlapping pair of exit beams and produces an interference signal s(t) indicative of the optical path length difference, the signal s(t) including a dominant term having a frequency equal to the sum of the frequency splitting ω
between the two beams, if any, and a Doppler shift {dot over (φ
)} defined by the rate of change of the optical path length difference, wherein properties of the interferometry system causes the signal s(t) to further include additional terms each having a frequency not equal to the sum of the frequency splitting ω and
the Doppler shift {dot over (φ
)}; and
an analyzer coupled to the detector which during operation;
i) applies a window function to a sequence of values of the signal s(t);
ii) Fourier transforms the windowed sequence of values, the Fourier transform defining a power spectrum equal to the square modulus of the Fourier transform; and
iii) identifies at least one of the additional terms based on at least one peak in the power spectrum at a frequency not equal to the sum of the frequency splitting ω and
the Doppler shift {dot over (φ
)}.- View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 19, 20, 21)
a stage for supporting the wafer;
an illumination system for imaging spatially patterned radiation onto the wafer;
a positioning system for adjusting the position of the stage relative to the imaged radiation; and
the interferometry system of claim 1, 9, or 16 for measuring the position of the stage.
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20. A lithography system for use in fabricating integrated circuits on a wafer, the system comprising:
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a stage for supporting the wafer; and
an illumination system including a radiation source, a mask, a positioning system, a lens assembly, and the interferometry system of claim 1, 9, or 16 wherein during operation the source directs radiation through the mask to produce spatially patterned radiation, the positioning system adjusts the position of the mask relative to the radiation from the source, the lens assembly images the spatially patterned radiation onto the wafer, and the interferometry system measures the position of the mask relative to the radiation from the source.
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21. A beam writing system for use in fabricating a lithography mask, the system comprising:
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a source providing a write beam to pattern a substrate;
a stage supporting the substrate;
a beam directing assembly for delivering the write beam to the substrate;
a positioning system for positioning the stage and beam directing assembly relative one another; and
the interferometry system of claim 1, 9, or 16 for measuring the position of the stage relative to the beam directing assembly.
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9. An interferometry system comprising:
-
an interferometer which during operation directs two beams along separate paths and then combines the beams to produce an overlapping pair of exit beams, the separate paths defining an optical path length difference;
a detector which responds to optical interference between the overlapping pair of exit beams and produces an interference signal s(t) indicative of the optical path length difference, the signal s(t) including a dominant term having a frequency equal to the sum of the frequency splitting ω
between the two beams, if any, and a Doppler shift {dot over (φ
)} defined by the rate of change of the optical path length difference, wherein properties of the interferometry system causes the signal s(t) to further include additional terms each having a frequency not equal to the sum of the frequency splitting ω and
the Doppler shift {dot over (φ
)}; and
an analyzer coupled to the detector and comprising a low-pass filter, wherein during operation the analyzer;
i) tracks the value of the Doppler shift based on the signal s(t);
ii) calculates the frequency {tilde over (ω
)}′
ν
of one of the additional terms based on the tracked value of the Doppler shift;
iii) generates a first tuned-filter signal equal to s(t)cos({tilde over (ω
)}′
ν
t) and a second tuned-filter signal equal to s(t)sin({tilde over (ω
)}′
ν
t); and
iv) passes the tuned-filter signals through the low-pass filter to quantify the additional term corresponding to {tilde over (ω
)}′
ν
.- View Dependent Claims (10, 11, 12, 13, 14, 15)
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16. An interferometry system comprising:
-
an interferometer which during operation directs two beams along separate paths and then combines the beams to produce an overlapping pair of exit beams, the separate paths defining an optical path length difference;
a detector which responds to optical interference between the overlapping pair of exit beams and produces an interference signal s(t) indicative of the optical path length difference, the signal s(t) including a dominant term having a frequency equal to the sum of the frequency splitting ω
between the two beams, if any, and a Doppler shift {dot over (φ
)} defined by the rate of change of the optical path length difference, wherein properties of the interferometry system causes the signal s(t) to further include additional terms each having a frequency not equal to the sum of the frequency splitting ω and
the Doppler shift {dot over (φ
)}; and
an analyzer coupled to the detector which during operation;
i) provides a quantification for at least some of the additional terms;
ii) Fourier transforms at least one set of values of s(t); and
iii) estimates a value for the optical path length difference based on the amplitude and phase of the Fourier transform at the frequency ω
+{dot over (φ
)} and values of the quantification for the additional terms that contribute to the Fourier transform at the frequency ω
+{dot over (φ
)} based on the Doppler shift {dot over (φ
)} corresponding to the set of values of s(t).- View Dependent Claims (17, 18)
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22. An interferometry method for use with an interferometry system comprising:
-
directing two beams along separate paths;
combining the beams to produce an overlapping pair of exit beams, the separate paths defining an optical path length difference;
measuring optical interference between the overlapping pair of exit beams to produce an interference signal s(t) indicative of the optical path length difference, the signal s(t) including a dominant term having a frequency equal to the sum of the frequency splitting ω
between the two beams, if any, and a Doppler shift {dot over (φ
)} defined by the rate of change of the optical path length difference, wherein properties of the interferometry system causes the signal s(t) to further include additional terms each having a frequency not equal to the sum of the frequency splitting ω and
the Doppler shift {dot over (φ
)};
applying a window function to a sequence of values of the signal s(t);
Fourier transforming the windowed sequence of values, the Fourier transform defining a power spectrum equal to the square modulus of the Fourier transform; and
identifying at least one of the additional terms based on at least one peak in the power spectrum at a frequency not equal to the sum of the frequency splitting ω and
the Doppler shift {dot over (φ
)}.- View Dependent Claims (25, 26, 27)
supporting a wafer on a stage;
imaging spatially patterned radiation onto the wafer;
adjusting the position of the stage relative to the imaged radiation; and
using the interferometry method of claim 22, 23, or 24 to measure the relative position of the stage.
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26. A lithography method comprising:
-
supporting a wafer on a stage;
directing radiation from a source through a mask to produce spatially patterned radiation;
positioning the mask relative to the radiation;
using the interferometry method of claim 22, 23, or 24 to measures the position of the mask relative to the radiation; and
imaging the spatially patterned radiation onto the wafer.
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27. A beam writing method comprising:
-
providing a write beam to pattern a substrate;
supporting the substrate on a stage;
delivering the write beam to the substrate;
positioning the stage relative to the write beam; and
using the interferometry method of claim 22, 23, or 24 to measure the relative position of the stage.
-
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23. An interferometry method for use with an interferometry system comprising:
-
directing two beams along separate paths;
combining the beams to produce an overlapping pair of exit beams, the separate paths defining an optical path length difference;
measuring optical interference between the overlapping pair of exit beams to produce an interference signal s(t) indicative of the optical path length difference, the signal s(t) including a dominant term having a frequency equal to the sum of the frequency splitting ω
between the two beams, if any, and a Doppler shift {dot over (φ
)} defined by the rate of change of the optical path length difference, wherein properties of the interferometry system causes the signal s(t) to further include additional terms each having a frequency not equal to the sum of the frequency splitting ω and
the Doppler shift {dot over (φ
)};
tracking the value of the Doppler shift based on the signal s(t);
calculating the frequency {tilde over (ω
)}′
ν
of one of the additional terms based on the tracked value of the Doppler shift;
generating a first tuned-filter signal equal to s(t)cos({tilde over (ω
)}′
84 t) and a second tuned-filter signal equal to s(t)sin({tilde over (ω
)}′
84 t); and
passing the tuned-filter signals through a low-pass filter to quantify the additional term corresponding to {tilde over (ω
)}′
ν
.
-
-
24. An interferometry method for use with an interferometry system comprising:
-
directing two beams along separate paths;
combining the beams to produce an overlapping pair of exit beams, the separate paths defining an optical path length difference;
measuring optical interference between the overlapping pair of exit beams to produce an interference signal s(t) indicative of the optical path length difference, the signal s(t) including a dominant term having a frequency equal to the sum of the frequency splitting ω
between the two beams, if any, and a Doppler shift {dot over (φ
)} defined by the rate of change of the optical path length difference, wherein properties of the interferometry system causes the signal s(t) to further include additional terms each having a frequency not equal to the sum of the frequency splitting ω and
the Doppler shift {dot over (φ
)};
providing a quantification for at least some of the additional terms;
Fourier transforming at least one set of values of s(t); and
estimating a value for the optical path length difference based on the amplitude and phase of the Fourier transform at the frequency ω
+{dot over (φ
)} and values of the quantification for the additional terms that contribute to the Fourier transform at the frequency ω
+{dot over (φ
)} based on the Doppler shift {dot over (φ
)} corresponding to the set of values of s(t).
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Specification
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- Resources
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Current AssigneeZygo Corporation (Ametek Incorporated)
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Original AssigneeZygo Corporation (Ametek Incorporated)
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InventorsHill, Henry A.
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Primary Examiner(s)Kim, Robert H.
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Assistant Examiner(s)LEE, HWA S
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Application NumberUS09/583,368Time in Patent Office378 DaysField of Search356/484, 356/485, 356/486, 356/487, 356/496, 356/498US Class Current356/487CPC Class CodesG01B 2290/15 Cat eye, i.e. reflection al...G01B 2290/45 Multiple detectors for dete...G01B 2290/70 Using polarization in the i...G01B 9/02002 using two or more frequenciesG01B 9/02007 Two or more frequencies or ...G01B 9/02027 Two or more interferometric...G01B 9/02045 using the Doppler effectG01B 9/02059 Reducing effect of parasiti...G01B 9/02084 Processing in the Fourier o...G01N 21/45 using interferometric metho...G03F 7/70775 Position control, e.g. inte...
