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US 6,882,432 B2Granted
Frequency transform phase shifting interferometry
AssigneeZygo Corporation
InventorLeslie L. Deck
Life of this patent
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Abstract
The invention features methods and systems in which wavelength-tune PSI data is analyzed in the frequency domain to produce spectrally separated frequency peaks each corresponding to a particular pair of surfaces in an interferometric cavity defined by multiple pairs of surfaces. Each frequency peak provides optical path length information about a corresponding pair of surfaces in the cavity. As a result, the interferometric data from such cavities provides simultaneous information about multiple surfaces.
Claims34
An interferometry method for characterizing a test object, the method comprising:
- forming an optical interference image by combining different portions of an optical wave front reflected from multiple surfaces of the test object and at least one reference surface, the multiple surfaces of the test object and the at least one reference surface defining a set of cavity surfaces;
- recording an interference signal at different locations of the optical interference image in response to tuning the frequency of the optical wave front over a range of frequencies, wherein the interference signal includes a contribution from each pair of different surfaces in the set of cavity surfaces;
- for each location, calculating a frequency transform of the interference signal at a frequency corresponding to each of selected pairs of the different surfaces in the set of cavity surfaces and extracting the phase of the frequency transform at each of the frequencies corresponding to the selected pairs of surfaces;
- and
- determining at least one of i) a surface profile of at least one of the test object surfaces and ii) a relative optical thickness profile between two of the test object surfaces, based on at least some of the extracted phases.
2 more elements
An interferometry method for characterizing a test object, the method comprising:
- forming an optical interference image by combining different portions of an optical wave front reflected from multiple surfaces of the test object and at least one reference surface, the multiple surfaces of the test object and the at least one reference surface defining a set of cavity surfaces;
- recording an interference signal at different locations of the optical interference image in response to tuning the frequency of the optical wave front over a range of frequencies, wherein the interference signal includes a contribution from each pair of different surfaces in the set of cavity surfaces;
- and
- for each location, calculating a frequency transform of the interference signal at a frequency corresponding to each of selected pairs of the different surfaces in the set of cavity surfaces and extracting the phase of the frequency transform at each of the frequencies corresponding to the selected pairs of surfaces,
- wherein the at least one reference surface comprises two reference surfaces and the test object is positioned between the two reference surfaces.
2 more elements
An interferometry method for characterizing a test object, the method comprising:
- forming an optical interference image by combining different portions of an optical wave front reflected from multiple surfaces of the test object and at least one reference surface, the multiple surfaces of the test object and the at least one reference surface defining a set of cavity surfaces;
- recording an interference signal at different locations of the optical interference image in response to tuning the frequency of the optical wave front over a range of frequencies, wherein the interference signal includes a contribution from each pair of different surfaces in the set of cavity surfaces;
- for each location, calculating a frequency transform of the interference signal at a frequency corresponding to each of selected pairs of the different surfaces in the set of cavity surfaces and extracting the phase of the frequency transform at each of the frequencies corresponding to the selected pairs of surfaces, and
- positioning the test object relative to the at least one reference surface to cause the optical path length difference for each of the pairs of different surfaces in the set of cavity surfaces to differ and contributions to the interference signals from second order reflections in the set of cavity surfaces to occur at frequencies that differ from the frequencies corresponding to the selected pairs of surfaces, wherein the test object is positioned relative to the at least one reference surface such that the optical path lengths of successive, adjacent pairs of the cavity surfaces are substantially proportional to one another by a unique power of 3.
1 more element
An interferometry system for characterizing a test object, the system comprising:
- a frequency-tunable light source;
- an interferometer comprising at least one reference surface, wherein during operation the interferometer directs different portions of an optical wave front derived from the light source to multiple surfaces of the test object and the at least one reference surface and recombines the different portions to form an optical interference image, the multiple surfaces of the test object and the at least one reference surface defining a set of cavity surfaces;
- a multi-element photo-detector positioned to record an interference signal at different locations of the optical interference image in response to frequency tuning of the light source, wherein the interference signal includes a contribution from each pair of different surfaces in the set of cavity surfaces;
- and
- an electronic controller coupled to the light source and the photo-detector, wherein during operation the controller, for each location, calculates a frequency transform of the interference signal at a frequency corresponding to each of selected pairs of the different surfaces in the set of cavity surfaces, extracts the phase of the frequency transform at each of the frequencies corresponding to the selected pairs of surfaces, and determines at least one of i) a surface profile of at least one of the test object surfaces and ii) a relative optical thickness profile between two of the test object surfaces, based on at least some of the extracted phases.
2 more elements
An interferometry system for characterizing a test object, the system comprising:
- a frequency-tunable light source;
- an interferometer comprising at least one reference surface, wherein during operation the interferometer directs different portions of an optical wave front derived from the light source to multiple surfaces of the test object and the at least one reference surface and recombines the different portions to form an optical interference image, the multiple surfaces of the test object and the at least one reference surface defining a set of cavity surfaces;
- a multi-element photo-detector positioned to record an interference signal at different locations of the optical interference image in response to frequency tuning of the light source, wherein the interference signal includes a contribution from each pair of different surfaces in the set of cavity surfaces;
- and
- an electronic controller coupled to the light source and the photo-detector, wherein during operation the controller, for each location, calculates a frequency transform of the interference signal at a frequency corresponding to each of selected pairs of the different surfaces in the set of cavity surfaces and extracts the phase of the frequency transform at each of the frequencies corresponding to the selected pairs of surfaces,
- wherein the at least one reference surface comprises two reference surfaces and the interferometer is configured to position the test object between the two reference surfaces.
3 more elements
Dependencies are inferred from the claim text.