WO2000058689A1 - Systeme d'emission de faisceau a poursuite automatique - Google Patents

Systeme d'emission de faisceau a poursuite automatique Download PDF

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Publication number
WO2000058689A1
WO2000058689A1 PCT/US1999/006460 US9906460W WO0058689A1 WO 2000058689 A1 WO2000058689 A1 WO 2000058689A1 US 9906460 W US9906460 W US 9906460W WO 0058689 A1 WO0058689 A1 WO 0058689A1
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WO
WIPO (PCT)
Prior art keywords
path
target
delivery system
along
input
Prior art date
Application number
PCT/US1999/006460
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English (en)
Inventor
Philip D. Henshaw
Robert F. Dillon
Original Assignee
Sparta, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Sparta, Inc. filed Critical Sparta, Inc.
Priority to AU33631/99A priority Critical patent/AU3363199A/en
Priority to PCT/US1999/006460 priority patent/WO2000058689A1/fr
Publication of WO2000058689A1 publication Critical patent/WO2000058689A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G01B11/26—Measuring arrangements characterised by the use of optical techniques for measuring angles or tapers; for testing the alignment of axes
    • G01B11/27—Measuring arrangements characterised by the use of optical techniques for measuring angles or tapers; for testing the alignment of axes for testing the alignment of axes

Definitions

  • This invention relates to a laser beam delivery system, and more particularly, to a broadband four-pass self-tracking beam delivery system which reflects a beam directed to a target back along its input path regardless of the distance and orientation of the target to reduce the effect of optical fabrication errors, to increase the "capture" range, to eliminate wave front shear and improve mixing efficiency of the reflected beam with a stationary reference beam.
  • Optical interferometry is a method of comparing two optical signals by combining the optical fields on a detector and evaluating the relative intensity to obtain the optical phase change. Changes in the length of the measurement path can be determined by evaluating the change in optical phase between the two beams. This method is commonly used to measure, for example, the position of a stage mirror attached to a positioning device. The exact position is crucial when making integrated circuits, during the integrated circuit mask-making processes and positioning substrates and tools in micro-machining applications.
  • Known methods include directing collinear beams along separate reference and measurement paths using cross-polarized beams and polarizing beam splitter optics, in combination with introducing a frequency or phase difference between two optical beams and measuring the phase of the beat frequency observed when the two beams interfere.
  • each optical surface is struck at a position different from the nominal beam path which encounters no stage tilt.
  • each beam interacts with as many as 25 surfaces.
  • the use of the corner cube between two bounces from the tilted stage mirror eliminates the tilt of the beam which is returned to the receiver.
  • the beam suffers a lateral displacement which may be as much as several millimeters for typical stage motions. This lateral displacement causes the measurement beam to interfere incorrectly with the reference beam, introducing errors into the measurement.
  • Additional measurement errors are caused by the combination of stage tilt and fabrication errors of the optical elements.
  • Solid beam splitter cubes typically have a small "wedge" between opposing faces, which is nearly impossible to eliminate using known fabrication techniques. The effect of this wedge is to change the length of the optical path as the beam translates.
  • a further source of error includes polishing errors which produce a random error in each surface of the beam splitter.
  • a laterally-translated beam will pass through different parts of the optical surface, causing path length errors.
  • all optical glass suffers from small index of refraction inhomogeneities. These index changes will cause errors as the translated beam passes through different parts of the beam splitter.
  • Second harmonic interferometers provide means for comparing the properties of a measurement path at two widely-separated wavelengths.
  • the interferometers make use of nonlinear optical elements to create phase-locked beams at two wavelengths, at both the input and output of a measurement path, and correct this measurement for air turbulence induced errors in real time.
  • Optical fabrication errors such as a "wedge" between opposing faces of a solid beam splitter cube, will cause errors in a second harmonic interferometer system.
  • an angular tilt of the beams will introduce a varying path length difference between the colors, due to Snell's law.
  • the invention results from the realization that a distance can be truly and accurately interferometrically measured using a four-pass, self-tracking beam delivery system in which a beam is directed along a first path to a first position on a target, and is reflected along a second path to a corner reflector which redirects it along yet a third path, parallel to the second path, back to the target which reflects it along a fourth path to a retroreflector which redirects the beam back along the fourth, third, second and first paths aligned with the input beam independent of the orientation and distance of the target, eliminating wavefront shear, maximizing mixing efficiency of the reflected measurement and reference beams, and increasing the capture range.
  • This invention features a four-pass self-tracking beam delivery system including means for directing an input beam along a first path to a first position on at least a locally flat surface of a target, a corner reflector for receiving the first reflection of the input beam along a second path from the first position and redirecting it along a third path parallel to the second path to a second position on the flat surface, and a return reflector for receiving the input beam along a fourth path from the second position and redirecting it as a reflected beam back along the first, second, third and fourth paths via the first and second positions aligned with the input beam independent of the orientation and distance of the target.
  • the corner reflector may include first, second and third petals, the first and second petals being reflective, and the third petal being transmissive to the input beam along the first path, reflective to the first reflection, transmissive to the beam along the fourth path and the reflected beam back along the fourth path, reflective to the reflected beam back along the second path and transmissive to the reflected beam back along the first path.
  • the third petal may include a polarizing beam splitter coating which reflects S polarization and transmits P polarization at a fixed oblique angle. There may be a polarizing beam splitter along the first path between the corner reflector and the quarter wave plate.
  • the polarizing beam splitter may include an embedded beam splitter coating which reflects S polarization and transmits P polarization.
  • the means for directing the input beam may include an aperture in the corner reflector.
  • the corner reflector may include three petals, each petal having a highly polished reflective surface for reflecting the beam.
  • the means for directing may include alignment means for guiding the input beam to strike the target at a known oblique angle.
  • the alignment means may include an alignment grating proximate the aperture for adjusting the angle at which the beam strikes the target.
  • the return reflector may be oriented to reflect the beam so that the reflected beam is aligned parallel with the input beam back along the first, second, third and fourth paths.
  • the return reflector may be oriented to reflect the beam so that the reflected beam is aligned coaxially with the input beam back along the first, second, third and fourth paths.
  • the first and second positions may lie in first and second parallel planes.
  • the first and second positions may be lie in the same plane.
  • the return reflector may be a flat mirror.
  • the flat mirror may include a glass substrate with an evaporated coating.
  • the return reflector may be a "cat's eye" reflector.
  • the return reflector may be a corner cube.
  • the input beam may include a laser beam source for determining the distance to the target.
  • the target may include a stage mirror.
  • the invention also features a system for measuring the distance to a moving target including first interferometer means for directing a distance measuring input beam to a target to determine the distance to the target, second interferometer means for directing a density measuring input beam to a target for determining the density of the air between the target and the first interferometer means, and a beam delivery system, responsive to the first and second interferometer means, for delivering the distance measuring and the density measuring beams along a first path to a first position on the target, receiving the first reflection of the input beam along a second path from the first position and redirecting it along a third path parallel to the second path to a second position on the target, receiving the input beam along a fourth path from the second position and reflecting the input beams back along the first, second, third and fourth paths via the first and second positions aligned with the input beams independent of the orientation and distance of the target.
  • the invention also features a system for measuring the distance to a moving target including interferometer means for directing a distance measuring input beam to a target to determine the distance to the target, and a four-pass beam delivery system responsive to the interferometer means for delivering the distance measuring beam along a first path to a first position on the target, receiving the first reflection of the input beam along a second path from the first position and redirecting it along a third path parallel to the second path to a second position on the target, receiving the input beam along a fourth path from the second position and reflecting the input beam back along the first, second, third and fourth paths via the first and second positions aligned with the input beam independent of the orientation and distance of the target.
  • the invention also features a system for measuring the density of air in the path of a distance measuring beam to a moving target including interferometer means for directing a density measuring input beam to a target to determine the density of air in the path of a distance measuring beam to the target, and a four-pass beam delivery system responsive to the interferometer means for delivering the density measuring input beam along a first path to a first position on the target, receiving the first reflection of the input beam along a second path from the first position and redirecting it along a third path parallel to the second path to a second position on the target, receiving the input beam along a fourth path from the second position and reflecting the input beam back along the first, second, third and fourth paths via the first and second positions aligned with the input beam independent of the orientation and distance of the target.
  • the input beam may be green and the second input beam may be ultraviolet.
  • FIG. 1 is a schematic diagram of a helium neon distance measuring interferometer system incorporating the self tracking beam delivery system according to the present invention
  • FIG. 2 is a schematic diagram of a second harmonic interferometer system incorporating the self tracking beam delivery system according to the present invention
  • FIG. 3 is a schematic diagram of a two interferometer system incorporating the self- tracking beam delivery system according to the present invention
  • FIG. 4 is a plan view of an all reflective four-pass self tracking beam delivery system according to the present invention.
  • FIG. 5 is a schematic diagram of a four-pass self-tracking beam delivery system in which the input beam enters a beam splitter having an embedded polarizing beam splitter coating;
  • FIG. 6 is a three dimensional view of a four-pass self-tracking beam delivery system in which a polarizing beam splitter coating is incorporated into one petal of a corner cube which selectively passes and reflects an input beam, and the other two petals are all reflective to the beam.
  • Interferometer transmitter and receiver system 10, Fig. 1 is used to determine the position of an object, such as a stage mirror, in two dimensions by determining the distance to the object in the x and y directions.
  • Helium Neon (HeNe) laser 12 delivers input beam 14 to 50/50 beam splitter 16. Because each path is the same, only one path will be described here.
  • Beam splitter 16 redirects a portion of input beam 14 to beam splitter 18b, for example a polarizing beam sphtter.
  • Beam sphtter 18b redirects a portion of beam 14 to receiver 20 to be used as a reference beam, and delivers a portion of beam 14 to four-pass beam delivery system 22.
  • Beam delivery system 22 redirects the beam as beam 14a to stage mirror 24a disposed on stage 24.
  • Stage mirror 24a redirects the beam as beam 14b back to beam delivery system 22 to a corner cube, not shown.
  • the beam is redirected as beam 14c back to stage mirror 24a which in turn redirects the beam as beam 14d back to beam delivery system 22 to a retroreflector, not shown, which redirects a reflected beam back along beams 14d, 14c, 14b and 14a via stage mirror 24a to be delivered from beam delivery system 22 to beam splitter 18b.
  • Beams 14a-d are shown in separate positions for clarity, and may overlap in some regions.
  • the reflected beam is collinear with the input beam such that no lateral translation occurs, independent of the orientation of stage 24, e.g. tilt.
  • Second harmonic interferometer 10a includes frequency-doubled neodymium yttrium aluminum garnet (Nd:YAG) laser 26 which produces laser beam 28 having a typical wavelength of 532 nm (green light), however, other wavelengths could also be used.
  • 50/50 beam splitter 17 redirects a portion of beam 28 to beam splitter 18, such as a dichroic beam splitter, which directs the 532 nm beam to frequency doubler 30.
  • Frequency doubler 30 produces a second beam 32 which consists of two components, the first having a wavelength of 532 nm, the same as input beam 28, and a second collinear beam that is in phase with the measurement component, but which has a wavelength of 266 nm (ultraviolet light), or a frequency twice that of input beam 28.
  • Frequency doubler 30 delivers collinear beam 32 to four-pass beam delivery system 22 which redirects collinear beam 32 as beam 32a to target 24a, such as a stage mirror.
  • Target 24a redirects the beam as beam 32b back to beam delivery system 22 which again directs the beam as beam 32c back to target 24a.
  • Target 24a redirects the beam as beam 32d to a retroreflecting mirror, not shown, within beam delivery system 22 which directs a reflected beam back along beams 32a-d, via target 24a, to beam delivery system 22 which delivers reflected beam 32' collinear with input beam 32 to beam sphtter 32 to beam splitter 18b via frequency doubler 30.
  • Beam sphtter 18b delivers the portion of reflected beam 32', consisting of the beam which traveled to stage mirror 24a as 266 nm light, and the beam which traveled to stage mirror 24a as 532 nm light, to receiver 20 which determines the air turbulence effects in the path to target 24a by comparing the phase of the two beams.
  • the reflected beam does not experience a lateral shift or increased path length.
  • the mixing efficiency between the reference beam and the measurement beam is maximized.
  • wavefront shear between interfering beams is eliminated thereby producing a more accurate air turbulence measurement to target 24a.
  • a laser such as a frequency doubled Nd:YAG laser 26
  • Laser 12 delivers input beam 14 to stage 24 in a similar manner as discussed with reference to Fig. 1, with the exception of an additional dichroic beam sphtter 16c.
  • Second laser 26 produces a second input beam 28.
  • Input beam 28 is delivered to non-polarizing beam splitter 16b which redirects a portion of beam 28 to beam splitter 18b which directs beam 28 to dichroic beam splitter 16c via frequency doubler 30.
  • Dichroic beam splitter 16c passes beam 14 and redirects beam 28, combining the beams so that the two beams are collinear when delivered to beam delivery system 22.
  • Beam delivery system 22 redirects the beam in a manner similar to that discussed with reference to Figs. 1 and 2.
  • All reflective beam delivery system 22, Fig. 4 includes corner cube 38 having an aperture 40 for directing input beam 14 to an object such as stage mirror 24a.
  • Input beam 14 may also be directed to stage mirror 24a using a scraper mirror 40', shown in phantom, well known in the art.
  • Aperture 40 may also initially include alignment grating 42 which is used to adjust the angle at which the beam, indicated as beam 14a, strikes stage mirror 24a and is removed prior to use of the system.
  • the input beam must strike stage mirror 24a at an obhque angle to ensure that the reflected beam strikes corner cube 38.
  • Beam 14a strikes stage mirror 24a at position 44a.
  • the beam is reflected along a second path indicated by beam 14b which strikes petal 38a of corner cube 38.
  • the petal has a highly polished reflective metal surface, or other highly reflective surface, which redirects the beam to a second petal, indicated by point 38b, which in turn redirects the beam to petal 38c.
  • Petal 38c redirects the beam, indicated by beam 14c, to second position 44b on stage mirror 24a.
  • Stage mirror 24a redirects the beam, beam 14d, to retroreflecting mirror 46.
  • Retroreflecting mirror 46 may include a glass substrate with an evaporated metal coating, an evaporated metal coating and protective overcoat, or dielectric coating, a highly polished planar mirror, a corner cube, or a "cat's eye", for example. Retroreflecting mirror 46 is positioned with its reflecting surface perpendicular to beam 14d.
  • An autocollimator may be used to orient retroreflector 46 as well as adjusting the input angle set by alignment grating 42. Such autocollimators are well known in the art.
  • Retroreflecting mirror 46 redirects a reflected beam back along the input path, beams 14d, 14c, 14b and 14a, via positions 44b and 44a, so that no lateral translation is induced between the reflected beam and the input beam.
  • second retroreflecting mirror 46a shown in phantom, may be included to accommodate a second input beam 14", also shown in phantom.
  • Beam 14" is reflected in the same manner as beam 14 so that the reflected beam is collinear with the input beam and no lateral displacement or translation is induced between the two beams.
  • Beams 14 and 14" each measure position to stage mirror 24a at different positions. By comparing the distance measurements made with 14 and 14", the tilt, or orientation, of the stage mirror can be determined.
  • four-pass beam delivery system 22a may include polarizing beam splitter 48 having embedded polarizing beam sphtter coating 49, known in the art, that passes the measurement component of beam 14 which has a P polarization and directs it to quarter wave plate 50 which circularly polarizes the beam which strikes stage mirror 24a at first position 44a.
  • Quarter wave plate 50 is designed for use at multiple, predetermined wavelengths over a broad range of frequencies by choosing the wave plate thickness according to the known indices of refraction of crystal quartz.
  • Stage mirror 24a reflects the beam, beam 14b, to quarter wave plate 50 which imparts S polarization on the beam so that polarizing beam sphtter 48 redirects beam 14b to petal 38a' of corner cube 38'.
  • Petal 38a' redirects the beam to a second petal indicated by point 38b' where it is then redirected to petal 38c, which redirects beam 14c back to beam sphtter 48.
  • Polarizing beam splitter 48 redirects beam 14c to quarter wave plate 50 which circularly polarizes the beam.
  • Circularly polarized beam 14c strikes stage mirror 24a at position 44b which redirects the beam back to quarter wave plate 50 which now imparts P polarization on the beam, allowing the beam to pass through polarizing beam sphtter 48 to retroreflecting mirror 46 as indicated by beam 14d.
  • Retroreflecting mirror 46 redirects a reflected beam, beam 14d' that maintains its P polarization back along beam 14d to beam sphtter 48 which passes reflected beam 14d' to quarter wave plate 50.
  • Quarter wave plate 50 circularly polarizes reflected beam 14d' as it passes back to position 44b on stage mirror 24a.
  • Stage mirror 24a redirects the reflected beam back along beam 14c to quarter wave plate 50 which imparts S polarization on beam 14c.
  • Beam sphtter 48 redirects S polarized reflected beam 14c to petal 38c of corner cube 38', which redirects the beam to petals 38b' and 38a'.
  • Petal 38a' redirects the reflected beam, which, because of its polarization is redirected by beam sphtter 48 to quarter wave plate 50 which circularly polarizes to the beam as it passes to position 44a on stage mirror 24a indicated by beam 14b'.
  • Stage mirror 24a redirects the reflected beam 14a' to quarter wave plate 50 which imparts P polarization on reflected beam 14a'.
  • Beam sphtter 48 passes reflected beam 14a' so that reflected beam 14' is collinear with input beam 14 and mixing efficiency between the reference beam component and the measurement beam component is maximized; wave front shear is ehminated by eh ' minating lateral translation of the reflected beam with respect to the reference beam.
  • corner cube 38" includes petals 38c and 38b" which have a highly polished, all reflective surface directed toward stage mirror 24a.
  • petal 38a" is selectively transmissive and reflective so that input beam 14 having P polarization strikes petal 38a" at a fixed obhque angle, typically greater than 45 degrees, and transmits through petal 38a".
  • Petal 38a" includes a polarizing beam sphtter coating which, when used at a fixed obhque angle of incidence, reflects S polarization and transmits P polarization at a discrete set of wavelengths.
  • Polarizing beam splitter coatings for a single wavelength are well known. Multiple wavelength coatings can be created by superimposing separate coatings for each wavelength.
  • Such coatings are available from VLOC, New Port Richey, FL.
  • a polarizing beam sphtter cube may also be used in place of petal 38a".
  • Beam 14a passes from petal 38a" to quarter wave plate 50 which circularly polarizes the beam as it passes to position 44a on stage mirror 24a.
  • Stage mirror 24a redirects the beam, beam 14b, to quarter wave plate 50 which imparts S polarization on beam 14b.
  • Quarter wave plate 50 transmits S polarized beam
  • Petal 38c" redirects the beam, beam 14c, to quarter wave plate 50 which again imparts circular polarization on the beam as it passes to position 44b on mirror 24a.
  • Stage mirror 24a redirects the beam, beam 14d to quarter wave plate 50 which imparts P polarization on the beam so that beam 14d is reflected by petals 38c and 38b" to petal 38a".
  • the beam is transmitted through petal 38a" to retroreflecting mirror
  • Retroreflecting mirror 46 is oriented to redirect a reflected beam 14d' back through petal
  • Reflected beam 14d' is redirected by petal 38c to quarter wave plate 50 which circularly polarizes reflected beam 14d' which strikes position 44b of stage mirror 24a.
  • Stage mirror 24a redirects the reflected beam as beam 14c along beam 14c to quarter wave plate 50 that imparts S polarization on reflected beam 14c which passes to petals
  • Stage mirror 24a redirects the reflected beam indicated as beam 14a' to quarter wave plate 50 which imparts P polarization on the reflected beam so that as the beam strikes petal
  • the beam is transmitted through petal 38a", collinear with input beam 14, thereby maximizing mixing efficiency between the reference beam component, not shown, and the measurement beam component, ehminating wave front shear typically induced by lateral translation of the reflected beam with respect to the input beam, independent of the orientation, or tilt, of stage mirror 24a.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Instruments For Measurement Of Length By Optical Means (AREA)

Abstract

Ce système d'émission de faisceau à poursuite automatique à quatre passages comporte des moyens permettant de diriger un faisceau en entrée (14) le long d'un premier trajet (14a') vers un premier emplacement sur au moins une surface (24a) plate localement d'une cible. Il comporte également un déflecteur de coin (38a, c) recevant la première réflexion du faisceau en entrée le long d'un deuxième trajet (14b') émanant du premier emplacement et le réorientant le long d'un troisième trajet (14c') parallèle au deuxième trajet en direction d'un second emplacement sur la surface plate. Il comporte, en outre, un réflecteur de retour recevant le faisceau en entrée le long d'un quatrième trajet (14d') émanant du deuxième emplacement et le réorientant en tant que faisceau réfléchissant.
PCT/US1999/006460 1999-03-26 1999-03-26 Systeme d'emission de faisceau a poursuite automatique WO2000058689A1 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
AU33631/99A AU3363199A (en) 1999-03-26 1999-03-26 Self tracking beam delivery system
PCT/US1999/006460 WO2000058689A1 (fr) 1999-03-26 1999-03-26 Systeme d'emission de faisceau a poursuite automatique

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/US1999/006460 WO2000058689A1 (fr) 1999-03-26 1999-03-26 Systeme d'emission de faisceau a poursuite automatique

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WO2000058689A1 true WO2000058689A1 (fr) 2000-10-05

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1424597A2 (fr) * 2002-11-27 2004-06-02 ASML Netherlands B.V. Appareil lithographique et méthode de fabrication d'un dispositif
CN106436510A (zh) * 2016-08-29 2017-02-22 重庆单轨交通工程有限责任公司 跨座式单轨交通线路线形测量方法和测量装置

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5764361A (en) * 1995-10-20 1998-06-09 Nikon Corporation Interferometer, adjusting method therefor, stage apparatus having the interferometer, and exposure apparatus having the stage apparatus

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5764361A (en) * 1995-10-20 1998-06-09 Nikon Corporation Interferometer, adjusting method therefor, stage apparatus having the interferometer, and exposure apparatus having the stage apparatus

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1424597A2 (fr) * 2002-11-27 2004-06-02 ASML Netherlands B.V. Appareil lithographique et méthode de fabrication d'un dispositif
EP1424597A3 (fr) * 2002-11-27 2006-05-17 ASML Netherlands B.V. Appareil lithographique et méthode de fabrication d'un dispositif
CN106436510A (zh) * 2016-08-29 2017-02-22 重庆单轨交通工程有限责任公司 跨座式单轨交通线路线形测量方法和测量装置
CN106436510B (zh) * 2016-08-29 2018-04-17 重庆单轨交通工程有限责任公司 跨座式单轨交通线路线形测量方法和测量装置

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