Carl-Zeiss-Stiftung

Zygo Corporation

Michael Kuchel

Albrecht Hof

Klaus Freischlad

Peter J De Groot

Karl-Heinz Schuster

Xavier Colonna De Lega

Andreas Dorsel

Uwe Vry

An optical system includes a photolithography system, a low coherence interferometer, and a detector. The photolithography system is configured to illuminate a portion of an object with a light pattern and has a reference surface. The low coherence interferometer has a reference optical path and a measurement optical path. Light that passes along the reference optical path reflects at least once from the reference surface and light that passes along the measurement optical path reflects at least once from the object. The detector is configured to detect a low coherence interference signal including light that has passed along the reference optical path and light that has passed along the measurement optical path. The low coherence interference signal is indicative of a spatial relationship between the reference surface and the object.

Low coherence grazing incidence interferometry for profiling and tilt sensing

Interferometric apparatus and methodology for precisely measuring the shape of rotationally and non-rotationally symmetric optical surfaces comprising an illumination source with two wavelengths, a transmission flat with a reference surface, a basic optical system for producing a wavefront of predetermined shape, a compensation component having an aspheric wavefront shaping surface and an aspheric reference surface. The aspheric shaping surface modifies the predetermined wavefront so that it impinges on the aspheric reference surface with a shape substantially that same as that of aspheric reference surface. For a given aspheric reference surface, the radius or curvature and spacing of the aspheric shaping surface are optimized so that its aspheric departure is no larger than that of the aspheric reference surface. Precise alignment in six degrees of freedom is provided via feedback control.

Reconfigurable interferometer system

The invention relates to measuring a phase-modulated signal 5. The signal is measured along at least five different steps (P1-P5) corresponding to preselected phase angles of the carrier wave 4. From the associated sets of measured values, at least three sets of measured values are formulated in a manner that from each of the sets a phase value [.phi..sub.i =arctan (Z.sub.i /N.sub.i) where i is equal to or greater than 3] can be calculated. The same correct phase value is computed based upon these three sets for a signal with the frequency of the carrier wave. The essence of the invention is finding that linear combinations of a.sub.i Z.sub.i and a.sub.i N.sub.i can be used for the computation of an accurate phase measurement where the factors a.sub.i are selected so that the phase error, as a function of the preselected phase steps, has at least three zero positions among the measured phase steps (P1-P5). As a result, the systemic errors that normally accompany phase measuring are significantly reduced. The invention is particularly suitable for the evaluation of bar pattern images and multiple-bar pattern images.

Method and apparatus for phase evaluation of pattern images used in

The invention relates to an evaluation method for interferograms and an interferometer corresponding thereto with which tile influence of coherent noise is reduced with simultaneously high interference contrast. Several phase maps are computed from interferograms which are recorded with coherent light. The interferogram components of the test object and the interferogram components of the coherent noise are displaced relative to each other in the camera plane between recording the interferograms. The influence of the coherent noise is suppressed by subsequently averaging the phase maps.

Method for evaluating interferograms and interferometer therefor

The present invention relates to a method for evaluating fringe images, in particular, for topographic measurements. During a first step, several phase-displaced patterns are recorded sequentially in time, and the respective phase relations of these patterns are determined by evaluation in the spatial domain (14a, 14b, 15). During a second step, after the phase shifts have been determined accurately in this manner based on the video images themselves, a pixel-by-pixel evaluation of the phase-displaced pattern is performed in the time domain. The invention also includes computer hardware for performing the evaluation of the strip images in video real time.

Method for analyzing periodic brightness patterns

Two bar patterns are projected sequentially on the object (O) to be measured, e.g., by time-division multiplexing, at angles which are inclined toward each other. The bar patterns are produced by projectors having respective rectangular gratings. The periods of the gratings are the same, and the phase relationship of the gratings is fixed relative to each other. Each reflected bar pattern, as distorted by the surface of the object, is individually and sequentially recorded by a camera (K); and the bar phases (.psi..sub.1, .psi..sub.2) of each sequentially reflected bar pattern are calculated for each image point by a computer connected with the camera. The computer also computes the differences (.DELTA..psi.) between the bar phases of the two projections for each image point. These phase differences remain stationary even when the bar patterns are moved relative to the camera. A plurality of phase differences for each image point is stored, averaged, and then used to calculate the height measurement (z) for each image point for display on a television monitor (42).

Method and apparatus for non-contact measuring of object surfaces

Several bar patterns are projected in sequence on the object (O) to be measured by time-division multiplexing, and images of the bar patterns are recorded by a camera (K). The phases of each bar pattern, as distorted by the object, are calculated for preselected image points by a computer connected with the camera. For each image point, the calculated phases for one of said bar patterns are compared to the phases calculated for at least one other of said bar patterns, thereby producing a beat frequency which can be used to determine height measurements in the direction of the camera axis (z). In order to increase the range of the height measurements, at least two beat frequencies of quite different effective wavelengths are generated and evaluated. Different systems are disclosed for generating the different beat frequencies. In one embodiment, the bar patterns are projected by three different projectors (P.sub.1, P.sub.2, P.sub.3) which are inclined at different angles relative to each other (.alpha..sub.1, .alpha..sub.2). In a second embodiment, only two projectors are used, but each projector has two gratings, the respective periods of which differ from each other only slightly.

A relatively simple interferometric method for the absolute testing of plane surfaces is disclosed, along with special apparatus for carrying out the inventive method. Two plane surfaces to be tested (A.sub.6,B.sub.6) are inserted simultaneously into the interferometer's measuring-beam path so that the measuring beam is reflected from each plane surface at two respective and different incident angles (.alpha., .beta.). During successive steps, the plane surfaces (A.sub.6,B.sub.6) are angularly repositioned and shifted so that at least one of the incident angles (.alpha., .beta.) is changed. Interferograms are recorded during each step and analyzed mathematically.

Method and apparatus for absolute interferometric testing of plane

The invention relates to an optical rangefinding device which consists of two frequency-stabilized multi-mode lasers. Two modes of each laser are superimposed so that each laser generates its own respective amplitude-modulated beam; and each beam is used, alternately, as the measuring light beam. The amplitude-modulation frequencies are selected so that the electronic detection of the two amplitude-modulated light beams, followed by electronic mixing of the individually detected signals, generates an electronic pulse train having a difference frequency which is only a fraction of the two modulation frequencies. The emitted and reflected frequencies of each of these amplitude-modulated beams are phase-compared. Each of these phase comparisons and the difference between them are used to determine distance to the target. Since phase shifts are digitally measured at the relatively low difference frequency by a digital clock rate based upon the relatively high frequency-modulated signal of one of the lasers, phase shift is determined with high accuracy. Further, the device provides measurements having a relatively accuracy which corresponds to the difference in wavelengths of the two amplitude-modulated beams which, in turn, have an accuracy corresponding to the spectral sharpness of the frequency-stabilized lasers.

Optical distance-measuring device

The injection current for a laser diode is modulated so that a pregiven coherence function is obtained which drops off continuously at both ends outside of the coherence length. Several laser diodes are used for a very short coherence length for which the modulated wave numbers of the emitted radiation follow one another or overlap.

Radiation source for partially coherent radiation

For generating several interferograms which differ from each other in the relative phase position between the interfering partial beams, a light source is utilized having a coherence length less than the optical path difference between the two component beams in the measuring path of the interferometer. Furthermore, at least one optical delay device is provided which splits the beam into two component beams and which generates an optical path difference between these component beams which is approximately the same as the optical path difference of the partial beams in the measuring path of the interferometer. Thereafter, the delay device again unites the component beams congruently.

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Oberkochen, Germany

Michael Kuchel