Zygo Corporation

Other

Kuchel, Michael

Carl A Zanoni

Leslie Ludwig Deck

Peter J De Groot

Christopher James Evans

Steven R Patterson

Michael Küchel

William A Shull

George C Hunter

Michael K&uuml;chel

Alan H Field

Peter De Groot

David Stephenson

Vivek G Badami

Alvin H Rosenfeld

Edward J Gratix

Edward J Gratrix

System for monitoring a position of one or more optical elements in a projection objective (PO) include a plurality of sensors each configured to receive input light and to form output light, each sensor including a first sensor optic and a second sensor optic, the first sensor optic of at least one of the sensors being affixed to a first PO optical element and the second sensor optic of the at least one sensor being affixed to a support element that positions the first PO optical element within the PO, the first and second sensor optics being configured introduce a first optical path length difference (OPD) between two components of the input light to form the output light, the first OPD being related to the position of the first PO optical element with respect to the support element. The systems also include a plurality of detectors configured to detect the output light from the sensors, a plurality of optical fibers configured to direct the input light to the sensors and to direct the output light from the sensors to the detectors, and an electronic controller in communication with the plurality of detectors, the electronic controller being configured to determine information about the position of the first PO optical element relative to the support element based on the detected output light from the at least one sensor.

Interferometer system for monitoring an object

In general, in one aspect, the invention features a system including a light source, a plurality of interferometers configured to receive light from the light source and to form output light, each interferometer including a first optic and a second optic, the first and second optics configured to be mounted on a first object and a second object, respectively, where first object is moveable with respect to the second object, the first and second optics being configured introduce an optical path length difference (OPD) between two components of the light to form the output light, the OPD being related to the position of the first optic with respect to the second optic. The system further includes a plurality of detectors configured to detect the output light from the interferometers, a modulation apparatus in the optical path between the light source and the detectors, the modulation apparatus being configured to vary an OPD between the two components of the light over a range including OPDs for which a net OPD of the output light from at least one of the interferometers at the detectors is zero, a plurality of waveguides configured to direct light between the interferometers, the modulation apparatus, and the detectors, and an electronic controller in communication with the detectors, the electronic controller being configured to determine information about a position of the first object based on the detected output light from at least one of the interferometers.

In general, in one aspect, the invention features a system that includes a first object mounted relative to a second object, the first object being moveable with respect to the second object. The system includes a plurality of interferometers each configured to derive a first wavefront and a second wavefront from input radiation and to combine the first and second wavefronts to provide output radiation including information about an optical path length difference between the paths of the first and second wavefronts, each interferometer including a reflective element positioned in the path of the first wavefront, and at least one of the interferometer's reflective element is mounted on the first object. The system also includes a plurality of fiber waveguides and an electronic controller. Each fiber waveguide is configured to deliver the input radiation to a corresponding interferometer or deliver the output radiation from the corresponding interferometer to a corresponding detector. The electronic controller is configured to monitor a degree of freedom of the first object relative to the second object based on the information from at least one of the interferometers, wherein the degree of freedom is an absolute displacement between the first and second objects.

Apparatus and methodology by which the position, angular orientation, and departure of a moving body, such as a scanning head, can be measured with high accuracy with respect to a nominally straight line as the body translates along that line. Monolithic metrology and scanning heads with integrally formed metrology surfaces are provided and fabricated of preferably identical materials having low thermal coefficients and high temporal stability. Measuring systems operate in conjunction with the integral metrology surfaces to provide interferometric information by which the position and angular attitude of the moving body is constantly monitored. Calibration arrangements are provided for determining the absolute position and attitude of the moving body with respect to the metrology frame as the two move relative to one another so that any errors can be compensated with appropriate correction functions.

Apparatus and methods for high accuracy metrology and positioning of a body

An optical sphere of nominal radius is positioned and supported within an assembly so that is can be activated with a predetermined motion with respect to an incoming converging spherical wavefront from an interferometer to calibrate the interferometer by determining the differences between the converging spherical wavefront and the reflected wavefront from portions of the area of the optical sphere as sampled thereover. The nominal optical sphere supported and sampled in this way mimics a &ldquo;perfect&rdquo; comparison sphere from which the systematic error of the interferometer wavefront may be determined. The optical sphere is preferably hollow and composed of Zerodur&reg;. Internal magnets in conjunction with external induction coils provide motion control while the optical sphere is mounted on an air bearing for freedom of rotation and safety in transportation.

Apparatus and method for calibrating an interferometer using a selectively rotatable sphere

Interferometric method(s) and apparatus for accurately measuring aspherical surfaces and transmitted wavefronts, particularly of the type having relatively large diameters and departure employed in lithographic applications used in the fabrication of integrated circuits and the like. An interferometer, preferably of the Fizeau type, is provided with at least one aspherical reference surface that is positioned adjacent the test optic. The test optic can be either rotationally or non-rotationally symmetric, a reflecting aspherical test surface, or a refracting system that is illuminated by an aspherical wavefront or produces a transmitted aspherical wavefront. In any case, the departure of the test optic from its intended performance is ultimately determined. The aspherical reference surface is illuminated by an aspherical wavefront provided by upstream optics structured so that the incident aspherical wavefront propagates normal to the aspherical reference surface across its entire surface. The illuminating aspherical wavefront is partially reflected and partially transmitted by the reference surface to provide an aspherical measurement wavefront that is incident to the test optic and has a shape nominally the same as that of the test surface in the reflective case or of the design transmitted wavefront in the refractive case. The aspherical test surface reflects the incident aspherical wavefront and it combines with the reference aspherical wavefront to provide an interferogram containing phase information indicative of the shape of the wavefront generated by the test optic. The interferogram is imaged onto a preferably two dimensional photodetection system that provides an output signal that is analyzed to extract the relevant phase information and convert it to numerical and display form. Phase shifting interferometric techniques are preferably used in the performance of the analysis along with alignment apparatus and procedures for assuring accurate measurement of the test optic.

Apparatus and method for measuring aspherical optical surfaces and wavefronts

The invention features a displacement and dispersion measuring interferometry system having a Helium-Neon laser light source. The light source can be a Helium-Neon laser that includes an intracavity doubling crystal and an intracavity etalon to generate two harmonically related, single-frequency wavelengths at sufficient powers for interferometric dispersion measurements. Alternatively, the light source can be a single-mode Helium-Neon laser that directs a single-frequency input beam into a resonant external cavity enclosing a doubling crystal to generate two harmonically related, single-frequency wavelengths at sufficient powers for interferometric dispersion measurements. In addition to dispersion measurements, the inherent wavelength stability of the Helium-Neon source permits high-accuracy displacement measurements. Thus, the Helium-Neon laser light source is sufficient for the interferometry system to simultaneously measure displacement and dispersion, and correct the displacement measurement for air-turbulence using the dispersion measurement.

Helium- Neon laser light source generating two harmonically related, single- frequency wavelengths for use in displacement and dispersion measuring interferometry

Interferometric apparatus and methods for reducing the effects of coherent artifacts in interferometers. Fringe contrast in interferograms is preserved while coherent artifacts that would otherwise be present in the interferogram because of coherent superposition of unwanted radiation generated in the interferometer are suppressed. Use is made of illumination and interferogrammetric imaging architectures that generate individual interferograms of the selected characteristics of a test surface from the perspective of different off-axis locations of illumination in an interferometer and then combine them to preserve fringe contrast while at the same time arranging for artifacts to exist at different field locations so that their contribution in the combined interferogram is diluted.

Apparatus and method(s) for reducing the effects of coherent artifacts in an interferometer

The invention features a phase measurement system for minimizing cyclic errors in a relative phase between exit reference and measurement beams emerging from an interferometer. The phase measurement system includes: a first optical processing channel including a first polarizer and a first detector, wherein during operation a first portion of the exit reference and measurement beams pass through the first polarizer to produce a first mixed beam and wherein the first detector measures an intensity of the first mixed beam; a second optical processing channel including a quarter wave retarder, a second polarizer, and a second detector, wherein during operation a second portion of the exit reference and measurement beams passes through the retarder and then the second polarizer to produce a second mixed beam and wherein the second detector measures an intensity of the second mixed beam; and a signal processor which during operation receives signals from the first and second detectors indicative of the intensities of the first and second mixed beams and processes the signals to determine, and minimize cyclic errors in, the relative phase between the exit reference and measurement beams. The invention also features interferometry, lithography, and beam writing systems that include the phase measurement system to improve the accuracy of interferometric distance measurements.

Interferometry system having reduced cyclic errors

An interferometric system for measuring motions of a stage 16 relative to fixed reflectors 24, 25 comprises a source 10 of a single frequency, linearly polarized, frequency stabilized light beam which is launched into an optical fiber 12 to deliver the beam to a module 14 on the moving stage 16. The module 14 contains an acousto-optical device 42 or single to two frequency generator, for generating a beam with a frequency difference between the two orthogonal polarization components states of the beam exiting the generator 42, as well as beam shaping and splitting optics 40, 46, a pair of interferometers 52, 54, optical mixers, and focusing optics 32, 34 for launching the output beams 55, 57 of the interferometers 52, 54 onto optical fibers 26, 28 which deliver the interference signals to photoelectric detectors 36, 38 and processing electronics which provide data for the stage 16 motion.

Interferometric apparatus for measuring motions of a stage relative to

A dual high stability interferometer system capable of measuring linear and angular displacement simultaneously of a movable plane mirror (90) comprises a frequency stabilized laser input beam (10) which is divided into two parallel spatially displaced beams by a beamsplitter (14). An optical system (20) is disposed to produce a first output beam having two orthogonally polarized components in which the phase difference between the two components of the third output beam is related to four times the linear displacement of the movable plane mirror (90) at a first position. A polarizer (93) mixes the orthogonal components of the third output beam with the interference between the two polarization components being detected by a photodetector (94) which produces an electrical signal (96) from which a phase meter/accumulator (99) extracts the phase change, with this phase change being related to four times the linear displacement of the movable mirror (90) at the first position. The optical system (20) also produce a second output beam whose orthogonally polarized components have a phase difference related to four times the linear displacement of the movable mirror (90) at a second position. Another polarizer (95) mixes these orthogonal components and a photoelectric detector (194) and another phase meter/accumulator (109) cooperate to provide a second measured phase which is related to four times the linear displacement of the movable mirror (90) at the second position.

Dual high stability interferometer

An interferometer system capable of measuring linear displacement and angular displacement simultaneously of a movable plane mirror (90) comprises a source (10) of a frequency stabilized input beam (12) and includes an optical system which reflects one polarization component of the input beam (12) twice from a first position on the movable plane mirror (90) to produce beams (30) and reflects the other polarization component of the input beam twice from a stationary plane mirror (89) to produce beam (28). A polarization beamsplitter (80) recombines these beams (30, 28) into a beam (66) in which the phase difference between the two components of the third output beam (66) is related to four times the linear displacement of the movable plane mirror (90) at the first position. Beam (66) is divided into beams (119) and (121), with the interference between the two polarization components detected by photodetector (94) to produce a signal (96) from which the phase change is extracted (99) to produce a measured phase which is related to four times the linear displacement of the movable plane mirror (90) at the first position. The polarization beamsplitter (80) and a retroreflector (81) reflect one polarization component of the other beam (121) twice from a second position on the movable plane mirror (90) and reflect the other polarization component of this beam (121) twice from the stationary plane mirror (89) with the beamsplitter (80) recombining the resultant beams into a beam (67) having two orthogonally polarized components in which the phase difference between the two components of the beam is related to four times the sum of the linear displacements of the movable plane mirror (90) at the first and second positions. The interference between the two components of beam (67) is detected by second photo detector (194) to produce a signal (97) for indicating a second measured phase, which is related to four times the sum of the linear displacement of the movable plane mirror (90) at the first and second positions. Electronic module (124) provides the difference between one-half of the second measured phase (101) and the first measured phase (100) to produce a signal (126) related to angular displacement (91) of the movable plane mirror (90).

Linear and angular displacement measuring interferometer

An electro-optical sensor is described which provides an output for precisely locating the centers of interference fringes in either a real-time interference pattern or an interferogram. By scanning the fringe pattern either by moving the fringe pattern, by effectively moving the photoelectric sensor, or both, the centers of the fringes can be rapidly and precisely determined from the first derive of the output of the photodetector.

Method and apparatus for interference fringe center sensing

An apparatus and method are herein disclosed for measuring interference patterns and interferograms using a standard monochrome closed-circuit television camera. The invention comprises, in one embodiment, means for processing the video output signal of the CCTV camera to obtain the two-dimensional coordinates for an array of points located on the centers of the interference fringes in one TV frame. The fringe centers are determined from the first and second derivatives of the video output signal of the CCTV camera. The coordinates are then ordered based on their average values in one direction, and the ordered coordinates are then processed in a computer to provide the desired least-squares reduction of the fringe pattern.

Apparatus and method for measuring interference patterns and

A lens system which has a built-in reference surface and which provides an emerging wavefront of variable radius of curvature useful in a Fizeau interferometer or a differential autocollimator is described. By interposing between the reference surface and the test surface a collimating lens whose distance from the reference surface can be varied, an emerging wavefront is produced whose radius of curvature can be varied from some positive value to infinity to some negative value depending on the distance of the lens from the reference surface. The improvement is particularly valuable in measuring long radius of curvature optical elements and systems.

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Middletown, CT, United States of America

Carl A Zanoni