Catoptric and catadioptric imaging system with pellicle and aperture-array beam-splitters and non-adaptive and adaptive catoptric surfaces

Abstract

An interferometric system including: an interferometer that directs a measurement beam at an object point to produce a return measurement beam, focuses the return measurement beam to an image point in an image plane, and mixes the return measurement beam with a reference beam at the image point to form a mixed beam; a beam combining layer located at the image plane which is responsive to the mixed beam and produces an optical beam therefrom, wherein the layer comprises a thin film with an array of transmissive openings formed therein and further comprises a fluorescent material associated with each of the openings of the array of openings; a detector that is responsive to the optical beam from the beam combining layer; and an imaging system that directs the optical beam from the beam combining layer onto the detector.

Description

[0001] This application claims the benefit of U.S. Provisional Application No. 60 / 506,715, filed Sep. 26, 2003.BACKGROUND OF THE INVENTION [0002] A number of different applications of catadioptric imaging systems for far-field and near-field interferometric confocal and non-confocal microscopy have been described such as in commonly owned U.S. Pat. No. 6,552,852 (ZI-38) entitled “Catoptric And Catadioptric Imaging Systems” and No. 6,717,736 (ZI-43) entitled “Catoptric And Catadioptric Imaging Systems;” U.S. Provisional Patent Applications No. 60 / 447,254, filed Feb. 13, 2003, entitled “Transverse Differential Interferometric Confocal Microscopy,” (ZI-40); No. 60 / 448,360, filed Feb. 19, 2003, entitled “Longitudinal Differential Interferometric Confocal Microscopy for Surface Profiling,” (ZI-41); No. 60 / 448,250, filed Feb. 19, 2003, entitled “Method and Apparatus for Dark Field Interferometric Confocal Microscopy,” (ZI-42); No. 60 / 442,982, filed Jan. 28, 2003, entitled “Interferometric...

AI Technical Summary

Benefits of technology

[0013] When the shorter wavelength beam has a wavelength in the UV, VUV, or EUV and a thin fluorescent layer serves the beam combining function, there is a significant change in the required performance of the detector because it has to serve to only detect the longer wavelength optical beam instead of the shorter wavelength mixed beam. The advantage of the present invention with respect to the reduction on the required performance specifications of the optical elements and the detector is valid for measurement and reference beams comprising either UV, VUV, or EUV wavelengths.

[0014] The implementation of the N-dimensional bi- and quad-homodyne detection methods make it possible to extend the advantages of the bi- and quad-homodyne detection methods for measuring conjugated quadratures of fields jointly to homodyne methods for measuring conjugated quadratures of fields when measuring jointly N different properties of the fields.

[0015] In general, in one aspect, the invention features an interferometric system including: an interferometer that directs a measurement beam at an object point to produce a return measurement beam, focuses the return measurement beam to an image point in an image plane, and mixes the return measurement beam with a reference beam at the image point to form a mixed beam; a beam combining layer located at the image plane which is responsive to the mixed beam and produces an optical beam therefrom, wherein the layer includes a thin film with an array of transmissive openings formed therein and further includes a fluorescent material associated with each of the openings of the array of openings; a detector that is responsive to the optical beam from the beam combining layer; and an imaging system that directs the optical beam from the beam combining layer onto the detector.

[0016] Other embodiments include one or more of the following features. The beam combining layer includes a first layer in which the array of openings is formed and a second layer behind the first layer and includes the fluorescent material. The beam combining layer further includes a third layer including an array of microlenses, each of which is aligned with a different one of the openings in the array of openings. Alternatively, the fluorescent material is in each of the openings of the array of openings. Each of the openings in the array of openings is conically shaped. The fluorescent material is lumogen. The fluorescent material is sensitive to UV or VUV. The fluorescent material is responsive to radiation at a first wavelength and the detector is responsive to light at a second wavelength, wherein the first and second wavelengths are different. The fluorescent material is responsive to radiation in the UV or VUV region and the detector is responsive to light in the visible region. The fluorescent material absorbs radiation at a first wavelength and emits radiation at a second wavelength, wherein the second wavelength is longer than the first wavelength. The imaging system is a low power microscope. The interferometer includes a catadioptric imaging system. The interferometer includes: a beam splitter positioned to receive the return measurement beam from the object point and separate each of a plurality of rays into a transmitted portion and a reflected portion, the transmitted portions defining a first set of rays and the reflected portions defining a second set of rays; and a reflecting surface positioned to receive one of the sets of rays from the beam splitter and focus that set of rays towards the image point via the beam splitter. The beam splitter has an array of transmitting apertures formed therein and wherein the one set of rays travels along a path contacting on one end the beam splitter and on another end the concave reflecting surface and at least most of which passes through a gas or vacuum. The interferometer includes an array of independently positionable reflecting elements forming the reflecting surface. The reflecting surface is positioned to receive the first set of rays and reflect the first set of rays back to the beam splitter, and wherein the beam splitter is positioned to reflect at least a portion of each ray received from the reflecting surface to the image point.

[0017] In general, in another aspect, the invention features an imaging system for imaging an object point to an image point, the system including: a beam splitter positioned to receive light rays from the object point and separate each of a plurality of rays into a transmitted portion and a reflected portion, the transmitted portions defining a first set of rays and the reflected portions defining a second set of rays; and an optical structure forming a concave reflecting surface positioned to receive one of the sets of rays from the beam splitter and focus that set of rays towards the image point via the beam splitter, wherein the beam splitter has an array of transmitting apertures formed therein and wherein the one set of rays travels along a path contacting on one end the beam splitter and on another end the concave reflecting surface and at least most of which passes through a gas or vacuum.

[0018] Other embodiments include one or more of the following features. The beam splitter is a self-supporting structure. The beam splitter includes a thin reflective layer in which the array of transmitting apertures are formed. The thin reflective layer is highly reflective. The thin reflective layer is made of aluminum. The beam splitter includes a pellicle on which the thin reflective layer is formed. The beam splitter includes a first pellicle and a second pellicle with the thin reflective layer sandwiched between the first and second pellicles. The pellicle is made of a refractive material, e.g. UV grade fused silica, F—SiO2, CaF2, or LiF. The beam splitter is a vertically oriented, planar structure. The size of the apertures is larger than the wavelength of the light rays being imaged onto the image point. The beam splitter includes a grid of conducting wires which defines the array of transmitting apertures. The reflecting surface is positioned to receive the first set of rays and reflect the first set of rays back to the beam splitter, and wherein the beam splitter is positioned to reflect at least a portion of each ray received from the reflecting surface to the image point. The reflecting surface is substantially concentric with the object point. Alternatively, the reflecting surface is positioned to receive the second set of rays and reflect the second set of rays back to the beam splitter, wherein the beam splitter is positioned to transmit at least a portion of each ray received from the reflecting surface to the image point. In that case, the reflecting surface is substantially concentric with the image point. The optical structure includes an array of independently positionable reflecting elements forming the reflecting surface.

Problems solved by technology

In the case where a beam-splitter is used for the beam combining function, the measurement beam component and the reference beam component of the combined beam may have subsequent to the beam-splitter different paths in the optical elements which introduces the possibility of non-common path phase errors.

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