WO2020216325A1 - 位移测量装置、位移测量方法及光刻设备 - Google Patents

位移测量装置、位移测量方法及光刻设备 Download PDF

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WO2020216325A1
WO2020216325A1 PCT/CN2020/086684 CN2020086684W WO2020216325A1 WO 2020216325 A1 WO2020216325 A1 WO 2020216325A1 CN 2020086684 W CN2020086684 W CN 2020086684W WO 2020216325 A1 WO2020216325 A1 WO 2020216325A1
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input
light
output
displacement
diffraction
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PCT/CN2020/086684
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English (en)
French (fr)
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吴萍
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上海微电子装备（集团）股份有限公司
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Priority to KR1020217036616A priority Critical patent/KR20210149828A/ko
Priority to US17/606,321 priority patent/US20220214193A1/en
Priority to JP2021563595A priority patent/JP7383048B2/ja
Publication of WO2020216325A1 publication Critical patent/WO2020216325A1/zh

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
    • G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
    • G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
    • G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
    • G01D5/35306—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using an interferometer arrangement
    • 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
    • G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/70—Microphotolithographic exposure; Apparatus therefor
    • G03F7/70691—Handling of masks or workpieces
    • G03F7/70775—Position control, e.g. interferometers or encoders for determining the stage position
    • 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
    • G01B11/16—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge
    • G01B11/161—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge by interferometric means
    • 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
    • G01B11/16—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge
    • G01B11/165—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge by means of a grating deformed by the object
    • 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
    • G01B11/16—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge
    • G01B11/167—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge by projecting a pattern on the object
    • 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
    • G01B11/16—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge
    • G01B11/168—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge by means of polarisation
    • 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
    • G01B11/16—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge
    • G01B11/18—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge using photoelastic elements
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
    • G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
    • G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
    • G01D5/36—Forming the light into pulses
    • G01D5/38—Forming the light into pulses by diffraction gratings
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/12—Reflex reflectors
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/18—Diffraction gratings
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/70—Microphotolithographic exposure; Apparatus therefor
    • G03F7/708—Construction of apparatus, e.g. environment aspects, hygiene aspects or materials
    • G03F7/7085—Detection arrangement, e.g. detectors of apparatus alignment possibly mounted on wafers, exposure dose, photo-cleaning flux, stray light, thermal load
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
    • G01D5/268—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light using optical fibres

Definitions

  • the invention relates to the technical field of displacement measurement, in particular to a displacement measuring device, a displacement measuring method and a lithographic equipment.
  • Nanometer measurement technology including nanometer-scale displacement measurement, has been rapidly developed in recent years.
  • Nano measurement methods include optical methods and non-optical methods.
  • the optical method uses the interference fringe measurement of a laser or X-ray with a very short wavelength, which can achieve a measurement resolution of nanometer level.
  • the measurement accuracy of the traditional interferometer is greatly affected by the surrounding environment (such as measurement errors caused by changes in factors such as temperature and pressure), and the measurement repeat accuracy is not high, which is difficult to meet the requirements of the lithography machine to further improve the overlay accuracy.
  • the grating ruler (or grating ruler displacement sensor) is a measurement feedback device that uses the optical principle of the grating. It can be used to detect linear or angular displacement. In contrast, the optical path measured by the grating ruler has nothing to do with the measurement range. , It can be very small, the measurement optical path is usually a few millimeters, so its measurement accuracy is not sensitive to environmental influences, and it has the characteristics of high measurement stability, simple structure, and easy miniaturization, making it occupy an important role in the field of nanometer measurement A place.
  • the interferometer has been gradually replaced in the new generation of lithography systems to undertake high-precision, high-stability picometer precision measurement tasks.
  • the existing displacement measurement system based on grating ruler still has such problems as the independency of the displacement measurement in the horizontal and vertical directions (there is a coupling relationship and algorithm decoupling is required), the angle tolerance is small, and the common optical path structure in the reading head is more caused. Problems such as large nonlinear error.
  • the present invention provides a displacement measurement device.
  • a displacement measurement method and a lithography equipment including the displacement measurement device are provided.
  • a displacement measuring device including:
  • a light source module for generating a first input beam and a second input beam
  • the diffraction element includes a light contact surface and a plurality of repeating diffraction units arranged in a direction parallel to the light contact surface;
  • the read head assembly includes at least two retroreflective elements, the read head assembly is used to receive the first input light beam and the second input light beam, and guide the first input light beam and the second input light beam
  • the light beams contact the light contact surface of the diffractive element in parallel and are diffracted, and then the at least two retroreflective elements guide at least one of the diffracted first input light beam and the second input light beam so that it is
  • the other is combined to form at least one output beam, and each of the output beams includes the same spot position in the optical contact surface of the diffractive element and the same direction, respectively corresponding to the first input beam and the first input beam. 2.
  • a light detection module for detecting each of the output light beams
  • the signal analysis module is connected to the light detection module, and is used to obtain the displacement information of the diffraction element according to the phase change information of the interference signal generated by each output light beam.
  • the read head assembly guides the first input beam and the second input beam to contact the optical contact surface of the diffractive element in parallel
  • the first input beam is diffracted once at the first spot position
  • the second input beam is diffracted once at the second spot position
  • the first-order diffracted beam of the first input beam is reflected back and forth by the retroreflective element and the diffraction element, and then at the second spot position
  • the first-order diffracted beam of the second input beam at least partially overlaps and exits in the same direction to form a first output beam
  • the phase change information of the interference signal of the first output beam reflects the diffraction element along the optical contact surface
  • the read head assembly guides the first input beam and the second input beam to contact the optical contact surface of the diffractive element in parallel
  • the first input beam is diffracted once at the first spot position
  • the second input beam is diffracted once at the second spot position
  • the first-order diffracted beam of the second input beam is reflected back and forth by the retroreflective element and the diffractive element, and then at the first spot position
  • the first-order diffracted beam of the first input beam at least partially overlaps and exits in the same direction to form a second output beam
  • the phase change information of the interference signal of the second output beam reflects the diffractive element along the optical contact surface
  • both the first output light beam and the second output light beam include first-order diffracted light having the same diffraction order direction and being located at the same diffraction order and corresponding to the first input light beam and the second input light beam, respectively Signal; the interference phase of the first output beam and the second output beam are opposite.
  • the first output beam includes a +1 diffraction order first-order diffracted light signal of the first input beam and the second input beam
  • the second output beam includes the first input beam and the The -1 diffraction order first-order diffracted light signal of the second input beam.
  • the signal analysis module is further configured to obtain the rotation of the diffractive element along the axis deflection in the optical contact surface according to the phase change information of the interference signal of the first output beam and the second output beam Displacement information for degrees of freedom.
  • the read head assembly guides the first input beam and the second input beam to contact the optical contact surface of the diffractive element in parallel, the difference between the first input beam and the second input beam
  • the first-order diffracted light beams are retroreflected through the reverse retroreflective element and contact the diffractive element again, and both undergo second-order diffraction.
  • the third spot positions of the diffraction element are at least partially overlapped and emitted in the same direction to form a third output beam; the phase change information of the interference signal of the third output beam reflects the direction of the diffraction element parallel to the optical contact surface
  • the third displacement information of the horizontal degrees of freedom is the difference between the first input beam and the second input beam.
  • the diffractive element is a one-dimensional grating or a two-dimensional grating.
  • the retroreflective element is selected from one of a corner cube, a right-angle prism, a cat's eye reflector, and a dove prism.
  • the read head assembly includes a beam angle controller.
  • the beam angle controller is selected from one of a single wedge angle plate, a wedge angle plate pair, a diffraction grating, and a birefringent element.
  • the first input beam and the second input beam are laser beams with different frequencies.
  • the light source module includes a fiber-transmitted dual-frequency laser; before contacting the diffractive element in a parallel direction, the read head assembly is also used to compare the received first input beam and the second input beam. The beams are respectively split and combined to form a remote reference beam.
  • the light source module includes a free-space dual-frequency laser and a beam splitting element, wherein the free-space dual-frequency laser is used to generate a dual-frequency beam, and the beam splitting element is used to divide the dual-frequency beam into two polarizations. Orthogonal beams.
  • the light source module or the reading head assembly includes a polarization control element, and the polarization control element is configured to make each of the output light beams correspond to the first input light beam and the second input light beam respectively
  • the polarization directions of the multiple diffracted light signals when entering the light detection module are the same.
  • the first input beam and the second input beam are laser beams with the same frequency.
  • the light source module or the reading head assembly includes a polarization control element, and the polarization control element is configured to make each of the output light beams correspond to the first input light beam and the second input light beam respectively
  • the polarization directions of the plurality of diffracted light signals when entering the light detection module are orthogonal.
  • the read head assembly forms at least four output light beams, and after detecting the at least four output light beams, the light detection module is further configured to phase shift the interference signal of each output light beam, To output the four output beams with a 90 degree difference in sequence.
  • a displacement measurement method including the following steps:
  • a diffraction element including a light contact surface and a plurality of repeating diffraction units arranged in a direction parallel to the light contact surface;
  • each of the output light beams includes the same spot position in the optical contact surface of the diffractive element, respectively. Diffracted light signals corresponding to the first input light beam and the second input light beam;
  • the displacement information of the diffraction element is obtained according to the phase change information of the interference signal generated by each output beam.
  • the first input beam and the second input beam contact the optical contact surface of the diffractive element in parallel
  • the first input beam is diffracted once at the first spot position
  • the second input beam The light beam is diffracted once at the second spot position.
  • the first-order diffracted beams of the light beam at least partially overlap and exit in the same direction to form a first output beam;
  • the phase change information of the interference signal of the first output beam reflects the vertical direction of the diffraction element along the normal direction of the optical contact surface.
  • the first displacement information to the degree of freedom.
  • phase change of the interference signal of the first output light beam and the displacement of the diffraction element along the vertical degree of freedom satisfy the relationship:
  • ⁇ Z1 is the displacement of the diffraction element in the vertical degree of freedom
  • ⁇ is the average wavelength of the first input beam and the second input beam
  • ⁇ is the m-th order diffraction angle of the first diffraction that occurs after the first input beam and the second input beam contact the optical contact surface of the diffraction element in parallel
  • m is an integer other than 0.
  • the first input beam and the second input beam contact the optical contact surface of the diffractive element in parallel, the first input beam is diffracted once at the first spot position, and the second input beam The light beam is diffracted once at the second spot position.
  • the first spot position and the first input beam are at least partially overlapped and emitted along the same direction to form a second output light beam;
  • the phase change information of the interference signal of the second output light beam reflects the second displacement information of the diffraction element along the vertical degree of freedom;
  • the interference phases of the first output beam and the second output beam are opposite.
  • the displacement measurement method further includes:
  • the displacement of the diffractive element corresponding to the first output beam and the displacement corresponding to the second output beam satisfy a relationship:
  • ⁇ Z1 and ⁇ Z2 are the first displacement information of the diffraction element along the vertical degree of freedom reflected by the first output light beam and the second output light beam of the diffraction element along the vertical degree of freedom information.
  • Displacement information, D f1f2 is the distance between the first spot position and the second spot position.
  • the first-order diffracted beams of the first input beam and the second input beam are passed through respectively
  • the retroreflective element retroreflects and contacts the diffractive element again, and both undergo secondary diffraction.
  • the second-order diffracted beams of the first input beam and the second input beam are in the third diffracting element.
  • the spot positions are at least partially overlapped and emitted in the same direction to form a third output beam; the phase change information of the interference signal of the third output beam reflects the horizontal degree of freedom of the diffraction element along the direction parallel to the optical contact surface The third displacement information.
  • phase change of the interference signal of the third output beam and the displacement of the diffraction element in the corresponding horizontal degrees of freedom satisfy the relationship:
  • I the phase change of the interference signal of the third output beam
  • ⁇ X is the displacement of the diffraction element in the first direction
  • P is the displacement of the multiple repeating diffraction units of the diffraction element along the horizontal degree of freedom direction. Spacing, m is an integer other than 0.
  • the present invention also includes a lithographic apparatus, the lithographic apparatus includes a relatively movable wafer platform and a reticle platform, characterized in that the lithographic apparatus includes the above displacement measuring device, wherein, the diffractive element is attached to one of the wafer platform or the reticle platform, and the read head assembly is attached to the other one of the wafer platform or the reticle platform.
  • the displacement measuring device provided by the present invention has at least the following advantages: first, the displacement information of the diffractive element is obtained separately according to the phase change information of the interference signal of each output beam, without algorithmic decoupling; second, by separating the The first input beam and the second input beam contact the diffraction element in parallel to be diffracted, and the diffracted first input beam and the second input beam are guided and combined to form at least one output beam.
  • Each output beam includes The diffracted light signals corresponding to the first input beam and the second input beam are emitted from the same spot position in the light contact surface of the diffraction element and have the same direction, which is beneficial to eliminate the deflection of the diffraction element (for example, relative to the light contact).
  • the coherent light angle separation caused by the deflection of the axis in the plane, that is, the measurement process has wide-angle adaptability, which helps reduce the influence of the deflection of the diffraction element on the intensity of interference information, improves the measurement accuracy, and also helps to improve the device
  • the angle tolerance reduces the difficulty of installation and attitude control of the device; third, the two input beams of the input read head assembly are separated from each other (spatially).
  • the beams do not affect each other, only The light is combined before the final interference; compared to a measurement system that is likely to cause frequency aliasing through the same input beam, it can greatly reduce or even avoid the nonlinear error caused by the common optical path structure.
  • the displacement measuring method provided by the present invention belongs to a general concept with the above-mentioned displacement measuring device, and thus has the same or similar advantages.
  • the lithography equipment provided by the present invention includes the above-mentioned displacement measuring device, and thus also has the same or similar advantages as the above-mentioned displacement measuring device.
  • Fig. 1 is a schematic diagram of a first output beam obtained by a displacement measuring device according to an embodiment of the present invention.
  • Fig. 2(a) is a schematic diagram of a displacement measuring device according to an embodiment of the present invention using a corner cube as a retroreflective element.
  • Figure 2(b) is a schematic diagram of a displacement measuring device according to an embodiment of the present invention using a right-angle prism as a retroreflective element.
  • Fig. 2(c) is a schematic diagram of a displacement measuring device according to an embodiment of the present invention using a Dove prism as a retroreflective element.
  • Figure 2(d) is a schematic diagram of a displacement measuring device according to an embodiment of the present invention using a cat's eye reflector as a retroreflective element.
  • Fig. 3 is a schematic diagram of the first output beam and the third output beam obtained by the displacement measuring device according to an embodiment of the present invention.
  • FIG. 4 is a schematic diagram of obtaining a first output light beam, a second output light beam, and a third output light beam by a displacement measuring device according to an embodiment of the present invention.
  • FIG. 5 is a schematic diagram of obtaining a first output beam, a second output beam, and a third output beam by a displacement measuring device according to another embodiment of the present invention.
  • Fig. 6 is a schematic diagram when the input beams of the displacement measuring device according to an embodiment of the present invention are of the same frequency.
  • Fig. 7 is a schematic diagram of a displacement measuring device according to an embodiment of the present invention when the input beams have different frequencies.
  • Fig. 8 is a schematic diagram of a displacement measuring device according to another embodiment of the present invention when the input beams have different frequencies.
  • 320-Polarization state adjusting element 321-Second polarization beam splitter; 322-Isolator; 323-First acousto-optic frequency shifter; 324-Second acousto-optic frequency shifter; 325-First light barrier; 326-No. Second light barrier; 327-third light barrier;
  • the measurement signals in different directions are not independent and there is a coupling relationship. It is necessary to further decouple the grating ruler to obtain different freedoms.
  • the problem of displacement in degrees, as well as the problem of small angular tolerance and high system installation accuracy requirements due to the design of the optical path, such as when there are a large number of common optical path structures for different diffraction signals in the optical path of the optical encoder read head Will cause the problem of large non-linear error in the measurement signal.
  • the present invention intends to provide a specific displacement measurement solution to solve the above problem.
  • the present invention provides a displacement measuring device, a displacement measuring method, and a lithographic apparatus including the displacement measuring device.
  • the displacement measurement device includes at least the following parts: a light source module, a diffraction element, a reading head assembly, a light detection module, and a signal analysis module.
  • the light source module is used to generate a first input beam and a second input beam.
  • the diffraction element includes a light contact surface and a plurality of repeating diffraction units arranged in a direction parallel to the light contact surface.
  • the read head assembly includes at least one set of retroreflective elements, the read head assembly is used to receive the first input beam and the second input beam, and guide the first input beam and the second input beam.
  • the input light beams contact the diffractive element in parallel and are diffracted (here, "parallel” does not include overlap), and then guide and combine the diffracted first input light beam and the second input light beam to form at least one output light beam, each
  • the output light beam includes the same spot position within the light contact surface of the diffractive element (here, the same spot position refers to the position where the same spot is located, that is, within a certain range where the spot is located, for example, taking the center of a spot as the center of the circle , Within the range of 0.5 to 1.5 spot
  • the light detection module is used to detect the output light beam formed by the read head assembly.
  • the signal analysis module is connected with the light detection module, and the signal analysis module is configured to obtain the displacement information of the diffraction element according to the phase change information of the interference signal of each output light beam.
  • the above-mentioned parts can be part or all of components of an optical encoder system, where the diffractive element is, for example, a grating ruler of an optical encoder system, and the read head component is, for example, an optical encoder system.
  • the encoder head of the optical encoder system can be used to monitor the movement of a movable platform in a precision system such as a lithography machine.
  • Fig. 1 is a schematic diagram of a first output beam obtained by a displacement measuring device according to an embodiment of the present invention. 1, the displacement measurement device of this embodiment and the optical path (or method) for obtaining the first output beam 613 are described as follows.
  • the first input light beam 610 and the second input light beam 611 are generated by the light source module (not shown in FIG. 1). In this embodiment, the first input light beam 610 and the second input light beam 611 are outputted at a certain distance in space.
  • the first input beam 610 and the second input beam 611 are, for example, laser beams, and the wavelengths of both are approximately in the range of 150 nm to 2000 nm. More specifically, the wavelengths of both can be selected in the range of 400 nm to 1500 nm, or 1500 to 2000 nm. Within the range of selection, further, the first input beam 610 and the second input beam 611 may have a wavelength of, for example, 633 nm, 980 nm, or 1070 nm.
  • the frequencies of the first input beam 610 and the second input beam 611 may be the same or slightly different (the frequency difference is, for example, less than or equal to 10 Hz).
  • the separated first input light beam 610 and second input light beam 611 enter the read head assembly 100, and the read head assembly 100 guides the first input light beam 610 and the second input light beam 611 to contact the optical contact surface of the diffractive element 200 in parallel and diffract.
  • the first input beam 610 and the second input beam 611 contact (or are incident on the same arbitrary non-Littrow angle). ) Different positions of the light contact surface of the diffraction element 200 and diffraction occurs.
  • the diffraction element 200 includes a plurality of repeating diffraction units (not shown in FIG. 1) arranged in a direction parallel to the light contact surface.
  • FIG. 1 illustrates a cross-section of the displacement measuring device in a Cartesian coordinate system.
  • the X-axis direction in FIG. 1 is taken as one arrangement direction of multiple repeating diffraction units (ie multiple identical diffraction units) of the diffraction element 200.
  • the diffraction element 200 may be a one-dimensional or two-dimensional grating. When it is a two-dimensional grating, the Y-axis direction perpendicular to the XZ plane in FIG.
  • the diffractive element 200 can also be other diffractive structures such as holographic diffractive structures. . No matter which diffraction structure is used, the repeating diffraction unit should be included to realize the diffraction of the first input beam 610 and the second input beam 611 incident at a non-litre angle. In this embodiment, the diffraction element 200 also has a reflection effect on the first input beam 610 and the second input beam 611.
  • the above-mentioned read head assembly 100 includes at least two retroreflective elements, such as the first retroreflective element 110 and the second retroreflective element 111 in FIG. 1, and the light beam incident into the retroreflective element is reflected
  • the retroreflective effect can output the outgoing beam parallel to the incident beam but the propagation direction is opposite and offset by a certain distance, so that the first input beam 610 and/or the first input beam can be affected by changing the installation position and angle of the retroreflective element.
  • the optical path and propagation direction of the diffracted light beam after the second input light beam 611 contacts the diffraction element 200 are adjusted.
  • Figures 2(a) to 2(d) respectively illustrate the structures of four types of retroreflective elements.
  • one or both of the first retroreflective element 110 and the second retroreflective element 111 can be a corner cube as shown in Figure 2(a) ,
  • the right-angle prism shown in Figure 2(b) the Dove prism shown in Figure 2(c) and the cat’s eye reflector shown in Figure 2(d), wherein the incident light beam 621 of the retroreflective element is incident on the corresponding After the reverse retroreflective element is reversed, the outgoing beam 622 of the reverse retroreflective element is output.
  • the cat’s eye reflector includes a lens 1301 and a concave reflector 1302.
  • the spherical center of the concave reflector 1302 is placed on the principal point (thin lens center) of the lens 1301, and the focal point of the lens 1301 is on the concave reflector.
  • the incident light beam 621 is condensed by the lens 1301 onto the concave reflector 1302, reflected by the concave reflector 1302, and after passing through the lens 1301, the outgoing light beam 622 is still parallel to the original incident light beam but in the opposite direction.
  • the first retroreflective element 110 and the second retroreflective element 111 in the read head assembly 100 are, for example, a corner cube, where the incident light beam and the exit light beam incident on the corner cube are in the diffraction element
  • the incident point of 200 can be any non-overlapping position on the light contact surface.
  • the position of the corner cube can be designed and adjusted as required.
  • the first input beam 610 undergoes a first diffraction (or first diffraction) at the first spot position A, and the second input
  • the light beam 611 is diffracted once (or first diffracted) at the second spot position B.
  • the first spot position A and the second spot position B are both located at the center of the corresponding diffraction unit; or, the diffraction at both the first spot position A and the second spot position B
  • the patterns are the same, thereby further improving the measurement accuracy.
  • the first-order diffraction order directions of the first input beam 610 and the second input beam 611 are the same.
  • the direction of the diffraction orders is the same means that the first-order diffraction orders of the first input beam 610 and the second input beam 611 are both positive diffraction orders or both negative diffraction orders.
  • first-order diffraction orders of the first input beam 610 and the second input beam 611 are both positive diffraction orders or both negative diffraction orders.
  • the second input beam 611 generates a +n-order first-order diffracted beam at the second spot position B (n is an integer other than 0, such as ⁇ 1, ⁇ 2, ⁇ 3, ..., the same below , +n represents a positive integer, that is, +1, +2, +3...), and exits after being reflected by the first reflecting element 130; the first input beam 610 generates a +m-order first-order diffracted beam at the first spot position A ( m is an integer other than 0, such as ⁇ 1, ⁇ 2, ⁇ 3,..., the same below, +m represents a positive integer, that is, +1, +2, +3).
  • the first-order diffracted light beam corresponding to the first input light beam 610 is retroreflected to the diffraction element 200 through the second retroreflective element 111 and reflected on the optical contact surface of the diffraction element 200 Then, it enters the first retroreflective element 110 and again retroreflects to the diffractive element 200, and reflects again at the second spot position B of the optical contact surface of the diffractive element 200, so that the first input beam 610 is diffracted once
  • the reflected light beam and the first-order diffracted light beam of the second input light beam 611 at least partially overlap at the second spot position B and exit along the same direction to form a first output light beam 613.
  • the first output light beam 613 output by the read head assembly 100 is detected by the first light detection module 411.
  • the first light detection module 411 can collect the phase information of the interference signal of the first output light beam 613, and further, transmit the optical fiber through the first signal. 431.
  • the phase information collected by the first light detection module 411 can be transmitted to the signal analysis module 500.
  • the signal analysis module 500 analyzes the phase information of the interference signal of the first output light beam 613 to obtain the phase change information, and compare it with The relationship between the displacement of the diffractive element 200 along the vertical degree of freedom in the normal direction of the optical contact surface, and the displacement information of the diffractive element 200 in the vertical degree of freedom is obtained.
  • the read head assembly 100 directs the first input beam 610 and the second input beam 611 to contact the diffractive element 200 in parallel
  • the first input beam 610 occurs at the first spot position A- m-order first-order diffraction
  • the second input beam undergoes -n-order first-order diffraction at the second spot position B
  • the first-order diffracted beam corresponding to the second input beam 611 is retroreflected by the first retroreflective element 110
  • the diffractive element 200 After being reflected by the light contact surface of the diffractive element 200, it enters the second retroreflective element 111 and is back and retroreflects to the diffractive element 200 again, at the first spot position A on the light contact surface of the diffractive element 200 again The reflection occurs, so that the first-order diffracted reflected beam generated by the second input beam 611 and the first-order diffracted beam of the first input beam 610 at least partially overlap and exit in the same direction at the first spot position A, and exit
  • the second output light beam 614 output by the read head assembly 100 is detected by the second light detection module 412.
  • the second light detection module 412 can collect the phase information of the interference signal of the second output light beam 614, and further, transmit the optical fiber through the second signal. 432.
  • the phase information collected by the second light detection module 412 can be transmitted to the signal analysis module 500.
  • the signal analysis module 500 analyzes the phase information of the interference signal of the second output beam 614 to obtain the phase change information, and through it
  • the relationship between the displacement of the diffractive element 200 along the vertical degree of freedom located in the normal direction of the light contact surface can also obtain the displacement information of the diffractive element 200 in the vertical degree of freedom.
  • the “vertical direction” refers to the normal direction of the light contact surface of the diffraction element 200, such as the Z axis direction in FIGS. 1 and 4.
  • the first output light beam 613 and the second output light beam 614 both include first-order diffracted light signals with the same diffraction order direction and at the same diffraction order and corresponding to the first input beam 610 and the second input beam 611 respectively;
  • the interference phases of the first output beam 613 and the second output beam 614 are opposite, that is, the phase of the interference signal in the first output beam 613 and the phase of the interference signal in the second output beam 614 are opposite.
  • the first output beam 613 includes the +1 diffraction order first-order diffracted light signal of the first input beam 610 and the second input beam 611
  • the second output beam 614 includes the first input beam 610 and the second input beam 611. 1 diffraction order first diffraction light signal.
  • the first input beam 610 and the second input beam 611 generated by the light source module are preferably parallel beams, so that the phase interference signals of the first output beam 613 and the second output beam 614 can be directly collected through the above-mentioned optical path design, but the present invention is not limited to this
  • the direction of the beam can be controlled by setting a beam angle controller in the read head assembly 100.
  • the first input light beam 610 and the second input light beam 611 may be provided on the incident light path of one of the
  • the beam angle controller 700 which can control the beam direction, can be used to adjust the first input beam 610 and the second input beam 611 to keep parallel, similarly, for the first input beam 610 and the second input beam 611
  • the diffracted light signals at the same spot position on the optical contact surface at least partially overlap (that is, including complete or partial overlap, correspondingly, a completely or partially overlapping output beam is formed.
  • the same spot position refers to a certain range of the spot.
  • a second beam angle controller 701 is provided on the optical path of one of the diffracted beams.
  • the first beam angle controller 700 and the second beam angle controller 701 can be selected from one of a single wedge angle plate, a pair of wedge angle plates, a diffraction grating, and a birefringent element.
  • the first reflective element 130 and the second reflective element 131 in this embodiment are only optional components, which can be selectively adopted according to the installation size of the read head assembly 100 and the position of the light detection module.
  • the diffracted reflected beam of the first input beam 610 is always parallel to the first-order diffracted beam of the second input beam 611.
  • the displacement measurement device of this embodiment collects the first output beam 613 and the second output beam 614 through the above-mentioned beam transmission, which helps to eliminate the deflection of the diffraction element 200 (especially relative to the X axis and the coordinate system in FIG. 1
  • the coherent light angle separation caused by the deflection of the Y axis can significantly reduce the influence of the deflection of the diffraction element 200 on the interference signal intensity of the output beam, improve the measurement accuracy, and also help to improve the angular tolerance of the displacement measurement device.
  • the vertical measurement in this embodiment has wide-angle adaptability.
  • the first output light beam 613 includes the first-order diffracted light signals of the same diffraction order in the same direction and corresponding to the first input light beam 610 and the second input light beam 611, where the “first-order diffracted light signal” refers to The optical phase information in the first-order diffracted beam generated after the first input beam 610 and/or the second input beam 611 contacts the diffraction element 200 in parallel. It can be understood that the first-order diffracted beam is reflected by the retroreflective element and the diffraction element , Can change the optical path and propagation direction, but can retain the optical phase information of the first-order diffracted beam.
  • the relationship between the phase change of the interference signal of the first output light beam 613 and the displacement of the diffraction element 200 is explained as follows.
  • the first input light beam 610 and the second input light beam 611 contact the diffractive element 200 in parallel, the first input light beam 610 undergoes a +m-order first diffraction at the first spot position A, and the second input light beam 611 is at the second spot position B generates +n-order first-order diffraction, so that the first output beam 613 includes the +m-order first-order diffracted light signal of the first input beam 610 and the +n-order first-order diffracted light signal of the second input beam 611.
  • the phase change of the interference signal of the second output beam 614 can be obtained The relationship with the vertical displacement of the diffraction element 200 satisfies equation (2),
  • ⁇ is the wavelength of the first input beam 610 and the second input beam 611 (if the frequencies are different, the average wavelength), and ⁇ is the first input beam 610 and the second input beam 611.
  • ⁇ X is the displacement of the assumed diffraction element 200 in the X-axis direction
  • ⁇ Z1 is the first The displacement of the diffractive element 200 corresponding to the output light beam 613 in the Z-axis direction
  • ⁇ Z2 is the displacement of the diffractive element 200 corresponding to the second output light beam 614 in the Z-axis direction.
  • the displacement measuring device of this embodiment can not only form the first output beam 613 and the second output beam 614 corresponding to the displacement measurement of the vertical degree of freedom, but also form the horizontal freedom of the diffraction element 200 in the direction parallel to the optical contact surface. Degree of the output beam of displacement information.
  • FIG. 3 is a schematic diagram of a first output beam and a third output beam obtained by a displacement measuring device according to an embodiment of the present invention.
  • the read head assembly 100 can be used to output a first output beam 613 and a third output beam 612 separated from each other.
  • the first output beam 613 refer to the above description.
  • first-order diffracted beams with opposite directions of diffraction orders are generated, for example, incident diffracted beams at different incident points at any non-litre angle.
  • the first input beam 610 generates a +m-order first-order diffracted beam at the first spot position A
  • the second input beam 611 generates a -n-order first-order diffracted beam at the second spot position B.
  • the two first-order diffracted beams are respectively After reflecting and retroreflecting, the reverse retroreflective element again contacts the diffractive element 200, and respectively generates second-order diffraction in the same direction as the first-order diffraction order, and at the third spot position C, a corresponding first input beam is generated
  • the +m polar second-order diffracted beam of 610 and the -n-order second-order diffracted beam corresponding to the second input beam 611 that is, through the structural design of the read head assembly 100, the two The second-order diffracted beam and the second-order diffracted beam corresponding to the second input beam 611 at least partially overlap at the same spot position of the diffraction element and exit in the same direction, thereby forming a third output beam 612.
  • the third output light beam 612 output by the read head assembly 100 can be detected by the third light detection module 410, and the third light detection module 410 can collect the phase information of the interference signal of the third output light beam 612.
  • the third light detection module 410 can collect the phase information of the interference signal of the third output light beam 612.
  • Three-signal transmission optical fiber 430, the phase information collected by the third optical detection module 410 can be transmitted to the signal analysis module 500.
  • the signal analysis module 500 analyzes the received phase information and passes the phase of the interference signal of the third output beam 612
  • the change information obtains displacement information of the horizontal degree of freedom of the diffraction element 200 in a direction parallel to the light contact surface.
  • the displacement information of the diffraction element 200 in the X-axis direction can be obtained through the third output beam 612.
  • the diffractive element 200 is a two-dimensional diffractive structure along the X-axis direction and the Y-axis direction (that is, the direction perpendicular to the XZ plane)
  • the read head assembly 100 and the optical detection module in FIG. 3 are rotated 90 degrees with the Z axis as the center , Then the displacement information of the diffraction element 200 in the Y-axis direction can be obtained.
  • the first-order diffracted beam generated by the first input beam 610 parallel to the diffraction element 200 is reflected by the second retroreflective element 111 and the second input beam 611 is generated
  • the second-order diffracted beam of the first input beam 610 is parallel to the first input beam 610 before the first-order diffraction
  • the second-order diffracted beam of the second input beam 611 It is parallel to the second input beam 611 before the first-order diffraction, so that the two second-order diffracted beams are parallel.
  • the displacement measuring device of this embodiment also has wide-angle adaptability for horizontal measurement.
  • the third output light beam 612 includes the second-order diffracted light beams of the opposite diffraction order and at the same diffraction order and corresponding to the first input light beam 610 and the second input light beam 611 respectively.
  • phase of the diffracted light signal of the first input beam 610 included in the third output beam 612 is set as The phase of the diffracted light signal of the second input beam 611 included is After the two diffracted beams interfere, the phase of the interference signal changes
  • the calculation process of the relationship with the horizontal displacement of the corresponding diffraction element 200 is as follows:
  • P is the pitch between the repetitive diffraction units arranged in the X-axis direction of the diffraction element 200
  • m is the diffraction order.
  • it can be an integer other than 0, such as ⁇ 1, ⁇ 2, and ⁇ 3.
  • ⁇ X is the displacement of the diffraction element 200 to be measured in the X-axis direction.
  • the displacement in the horizontal direction can also be obtained by second-order diffracted beams of opposite diffraction orders.
  • the first input beam 610 generates a -m-order second-order diffracted beam
  • the second input beam 611 generates a +n-order second-order diffracted beam, so that the phase of the third output beam is (3) in The phase is opposite.
  • the diffraction element 200 may further include a plurality of repeating diffraction units arranged along the Y axis direction perpendicular to the XZ plane in FIG. 3, and the Y axis direction and the X axis direction are perpendicular to each other.
  • the read head assembly 100 can also form and obtain the optical path structure of the third output beam 612 by guiding and combining the first input beam 610 and the second input beam 611
  • the fourth output beam (not shown in the figure) is combined to form a fourth output beam (not shown in the figure) after the first diffraction, the reverse retroreflective element reflection and the second diffraction in the Y axis direction, and the fourth output beam includes the diffraction element 200
  • the second-order diffracted beam emitted from the same spot on the light contact surface in the same direction.
  • the phase change information of the interference signal of the fourth output light beam reflects the displacement information of the diffraction element 200 in the Y-axis direction.
  • the read head assembly 100 can be rotated 90 degrees along the Z axis in FIG. 3, so that the output beam corresponding to the displacement in the Y axis direction can be detected in a direction parallel to the third output beam 612, thereby The displacement information of the diffraction element 200 in the Y-axis direction is obtained.
  • the displacement measuring device described in this embodiment can simultaneously measure the displacement measurement of the diffractive element 200 along the horizontal direction parallel to the optical contact surface and the vertical direction along the normal direction of the optical contact surface.
  • Degree of freedom displacement measurement When the diffraction element 200 adopts a two-dimensional diffraction structure, at least three degrees of freedom displacement measurement can be realized. Further, by appropriately combining two or more input beams, read head assemblies, and optical detection modules with the above-mentioned optical path design, the displacement measurement of the diffractive element 200 in more than three degrees of freedom can be realized, for example, the X axis direction, Y axis direction, Z axis direction, R X direction (i.e. along the X axis deflection direction), R y direction (i.e. along the Y axis deflection direction), R Z direction (i.e. along the Z axis deflection direction) six free Degree of displacement measurement.
  • the displacement measuring device of this embodiment has the following advantages: First, it can realize the independent measurement of horizontal and vertical displacement without calculating decoupling, that is, it is necessary to measure the displacement in the X-axis direction separately or measure the Z-axis separately. When the axial displacement is required, the corresponding displacement can be calculated independently by collecting only one interference signal; secondly, it has a wide angle adaptation range for horizontal and vertical measurement, which helps to improve the angular tolerance of the device. Improve measurement accuracy, reduce the difficulty of installation and attitude control of the displacement measurement device; third, because the measurement signals are all self-parallel beams, no precise adjustment is required, and the integration is simple; fourth, the measurement system has a simple structure and large redundant space.
  • the displacement measurement device has fewer types of components and low cost; sixth, because the interference signal does not share the optical path before combining the light, it is not affected by the splitting and polarization performance of the device.
  • This solution can be seen from the measurement principle There is basically no nonlinear error; seventh, in this embodiment, after the input beam is diffracted on the optical contact surface of the diffractive element, the diffracted beam is collected by the light detection module for horizontal and vertical displacement signal detection, and there is no stray light overflow Displacement measuring device; eighth, because there is no stray light overflow, the optical power utilization rate of the displacement measuring device is very high.
  • FIG. 4 is a schematic diagram of obtaining a first output light beam, a second output light beam, and a third output light beam by a displacement measuring device according to an embodiment of the present invention.
  • the read head assembly 100 simultaneously forms the first output beam 613, the second output beam 614, and the third output beam 612.
  • displacement measurement in the horizontal direction in the X-axis direction in FIG. 4
  • biaxial vertical in the Z-axis direction in FIG. 4
  • two vertical displacement measurement results can be obtained.
  • the technical effect is that on the one hand, it can compensate for the influence of the environment on the measurement optical path (For example, when the two Z-axis output beams are measured in different environments), it helps to improve the accuracy of displacement measurement and improve the measurement accuracy; on the other hand, the two vertical displacement measurement results can further calculate the diffraction element 200.
  • Displacement information of the rotational freedom of rotation along an axis located in the light contact surface The details are as follows.
  • ⁇ Z1 and ⁇ Z2 are the vertical displacements measured by the first output beam 613 and the second output beam 614, respectively, and D f1f2 is the first output beam and the second output beam contacting the diffraction in parallel The distance between the components (the distance between the first spot position A and the second spot position B in Figure 4).
  • FIG. 5 is a schematic diagram of a first output beam, a second output beam, and a third output beam obtained by a displacement measuring device according to another embodiment of the present invention.
  • the read head assembly 100 after receiving the first input light beam 610 and the second input light beam 611, the read head assembly 100 directs them to be incident parallel to the optical contact surface of the diffraction element 200 and diffracted, and then utilizes the first reverse retroreflectivity
  • the element 110 and the second retroreflective element 111 realize the reflection of the diffracted light beam and the reflection of the incident light beam from the optical contact surface of the diffractive element 200, and collect the diffracted light beams that are opposite to the diffraction order in FIG.
  • the functions of the signal transmission fiber and the signal analysis module of this embodiment are the same as the structure of FIG. 4, so they are not shown in FIG. 5.
  • the -m-order first-order diffracted beam generated by the first input beam 610 on the optical contact surface of the diffraction element 200 is reflected back to the diffraction element 200 by the retroreflective element, and again produces -m First-order diffraction (second-order diffraction), the +n-order first-order diffracted light beam generated by the second input beam 611 on the optical contact surface of the diffraction element 200 is reflected back to the diffraction element 200 by the retroreflective element, and again produces +n-order diffraction (second Sub-diffraction), the second-order diffracted beam of the first input beam 610 and the second-order diffracted beam of the second input beam 611 are at least partially overlapped at the same spot position and emitted in the same direction.
  • the third output beam 612 includes a phase change corresponding to the displacement information in the X-axi
  • P is the grating pitch of the diffraction element 200 in the X-axis direction
  • m is the diffraction order.
  • it can be an integer other than 0 such as ⁇ 1, ⁇ 2, ⁇ 3, and ⁇ X is the diffraction element 200 to be measured along X Displacement in the axis direction.
  • the phase data collected by the two output beams related to the Z-axis displacement is also opposite to the phase data corresponding to FIG.
  • which diffraction order direction is used for optical path design can be considered according to the design requirements such as the shape of the read head assembly 100 and the installation space, and the phase change information of the interference signal corresponding to the output beams corresponding to different degrees of freedom ,
  • the displacement information of the diffraction element 200 in the corresponding degree of freedom can be obtained. Since the multiple output beams are not in the same path before the light is combined at the signal detection end, the quality of the interference signal is not affected by factors such as imperfect light splitting of the device and polarization aliasing, and the output signal quality of the displacement measurement device is better.
  • the light source module can be realized by a single-frequency laser, so that the frequencies of the first input beam 610 and the second input beam 611 generated by the light source module are the same.
  • a single-frequency laser is used, the size of the light source module is small, and it can be directly placed near the reading head assembly 100, or can be transmitted to the reading head assembly 100 via an optical fiber.
  • both the light source module and the light detection module can be integrated inside the read head assembly 100, that is, an integrated structure that can realize light source output, beam guiding combination, and light detection is formed.
  • the integrated structure is flexible in usage scenarios and can greatly reduce the integration and integration of field applications. It is difficult to maintain, improves efficiency, and is suitable for various high and low precision displacement measurement scenarios.
  • FIG. 6 is a schematic diagram of the displacement measuring device of an embodiment of the present invention when the input light beams are of the same frequency.
  • the first optical detection module 411 for receiving the first output beam 613 and the third optical detection module 410 for receiving the third output beam 612 both include a quarter wave plate, a non-polarizing beam splitter, and a polarization
  • the combination of the beam splitter uses the optical method to shift the phase of the interference signal to obtain four signal outputs with a phase difference of 90 degrees in sequence for subsequent displacement calculations.
  • the first light detection module 411 includes a quarter wave plate 481, a non-polarizing beam splitter 482, a first polarizing beam splitter 483, a second polarizing beam splitter 484, a first optical coupler 485, and a second light beam splitter.
  • the coupler 486, the third optical coupler 487, and the fourth optical coupler 488 perform the aforementioned four-channel phase shifting function.
  • the first input light beam 610 and the second input light beam 611 can be set to have polarization directions orthogonal to each other before they reach the read head assembly 100, or after they are received by the read head assembly 100, they can pass along the first
  • a polarization control element is provided on the optical path of one of the input light beam 610 and the second input light beam 611, so that before outputting to the corresponding light detection module, the output light beam includes those corresponding to the first input light beam 610 and the second input light beam 611, respectively.
  • the polarization directions of the two diffracted light beams (or diffracted light signals) are orthogonal, and the purpose is to make the polarization directions of the two diffracted light beams orthogonal when entering the optical detection module.
  • the polarization control element is, for example, a wave plate or a polarizing plate.
  • the light source module can also be implemented with a fiber-transmitted dual-frequency laser, so that the frequencies of the first input beam 610 and the second input beam 611 generated are different (usually the frequency difference between the two is limited to a small range).
  • Fig. 7 is a schematic diagram of a displacement measuring device according to an embodiment of the present invention when the input beams have different frequencies.
  • the light source module 300 is a fiber transmission dual-frequency laser.
  • the structure of the fiber transmission dual-frequency laser may include the following optical elements: a single-frequency laser 311, an isolator 322, and a first acousto-optic frequency shifter 323, second acousto-optic frequency shifter 324, first beam splitter 330, second beam splitter 331, third beam splitter 332, and fourth beam splitter 333, first mirror 334, second mirror 335, first stop The light plate 325, the second light blocking plate 326 and the third light blocking plate 327, the third beam angle controller 370, the first polarization maintaining fiber coupler 340, the second polarization maintaining fiber coupler 341 and the multimode fiber coupler 350.
  • the principle of the above-mentioned optical fiber transmission dual-frequency laser outputting a dual-frequency beam is as follows.
  • the single-frequency laser generated by the single-frequency laser 311 is divided into two beams, which are shifted by two acousto-optic frequency shifters with different driving frequencies to generate two laser beams with a first frequency and a second frequency.
  • Most of the energy in the laser beam is coupled through the polarization-maintaining fiber coupler and input into the read head assembly 100 through the polarization-maintaining fiber, while a small part of the energy is combined through the reflector and beam splitter to form the reference light signal of the laser.
  • the beam angle controller can be used to assist in adjusting the first frequency beam and the second frequency beam synthesis laser reference light signal.
  • a second polarization beam splitter or a grating diffraction method can also be used for beam combination.
  • the first frequency beam output by the light source module 300 is input to the first polarization-maintaining fiber collimator 450 through the first polarization-maintaining fiber 470, and enters the read head assembly 100 to form the aforementioned first input beam 610
  • the second frequency light beam output by the light source module 300 is input to the second polarization maintaining fiber collimator 451 via the second polarization maintaining fiber 471, and enters the read head assembly 100 to form the aforementioned second input light beam 611.
  • first input beam 611 and the second input beam 611 are guided by the read head assembly 100, they are diffracted once or twice on the optical contact surface of the diffractive element 200, so that the present embodiment can be obtained.
  • the first output beam 613, the second output beam 614, and the third output beam 612 described above are detected by the first light detection module 411, the second light detection module 412, and the third light detection module 410, respectively.
  • the detection module 411 transmits the collected interference signal of the first output light beam 613 to the signal analysis module 500 through the first signal transmission fiber 431, and the second optical detection module 412 transmits the collected interference signal of the second output light beam 614 through the second signal
  • the optical fiber 432 is transmitted to the signal analysis module 500, and the third optical detection module 410 transmits the collected interference signal of the third output beam 612 to the signal analysis module 500 through the third signal transmission optical fiber 430.
  • the above-mentioned fiber-transmitted dual-frequency laser also outputs a basic reference beam. After the basic reference beam comes out of the multimode fiber coupler 350, it is not received by the read head assembly 100, but is directly transmitted to the signal analysis module through the signal transmission fiber. 500.
  • a compensation method is to perform compensation inside the read head assembly 100. After the dual-frequency beam transmitted by the optical fiber is collimated into a free space beam, before the phase change occurs when it enters the optical contact surface of the diffraction element 200, A small part of the light energy is separated from the first input beam 610 and the second input beam 611 with different frequencies, and combined to form a remote reference light signal (the optical element used is the third reflective element in Fig. 7 132.
  • the first beam splitting element 133, the second beam splitting element 134, the third beam splitting element 135, the fourth beam angle controller 702, and the fourth light barrier 136), and the remote reference light signal is detected by the fourth light detection module 413 , And then output to the signal analysis module 500 through the fourth signal transmission fiber 433.
  • the signal analysis module 500 subtracts the displacement information corresponding to different degrees of freedom directly measured by the first output beam 613, the second output beam 614, and the third output beam 612 from the displacement information corresponding to the remote reference optical signal, respectively, Obtain the actual displacement information of different degrees of freedom that is not affected by optical fiber transmission.
  • the remote reference light signal may also be obtained in a beam splitter mode or a polarization beam splitter mode, and a grating diffraction mode may also be used to realize the combination of two beams.
  • one or more beam angle controllers can be provided in the read head assembly 100 as required. 7, the first beam angle controller 700 can be used to assist in adjusting the parallelism of the first input beam 610 and the second input beam 611 having different frequencies incident on the read head assembly 100, and the third beam angle controller 702 can be used to assist in adjusting the above The parallelism of the remote reference optical signal.
  • the input beams of the two frequencies are not in the same path before the signal detection end is combined.
  • the quality of the interference signal is not affected by factors such as imperfect beam splitting and polarization aliasing.
  • the measurement system basically does not exist. Non-linear error, so there is no need to compensate the non-linear error in the optical signal processing process;
  • the horizontal and vertical signals formed can be directly detected. There is no need to synthesize interference signals with polarizers in the light phase collection part to avoid the use of polarizers.
  • the signal intensity is the best this time, the optical power utilization rate can reach 100%, and the impact on the optical performance of the beam is small. The component manufacturing is less difficult.
  • the resulting Horizontal and vertical signals can also be detected directly, without the need to place a polarizer in the optical phase collection part.
  • the signal strength is slightly weaker and the optical power loss is slightly larger; when the polarization directions are orthogonal, the horizontal and vertical directions formed
  • the signal cannot be detected directly. It is necessary to place a polarizer in front of the optical detection module for detection. Due to the function of the polarizer, the optical power loss is about 50% at this time;
  • the read head assembly can be arbitrarily placed in the required measurement position, flexible use scenarios, can greatly reduce the difficulty of on-site application integration and maintenance, improve efficiency, for example, can be used to read head assembly Installed on the moving table to follow the moving table, and the diffraction element is installed in a fixed system.
  • the light source module may also include a free-space dual-frequency laser.
  • Fig. 8 is a schematic diagram of a displacement measuring device according to another embodiment of the present invention when the input beams have different frequencies.
  • the light source module 300 includes a free-space dual-frequency laser.
  • the light source module 300 may include: a free-space dual-frequency laser 310, a second polarization beam splitter 321, and a polarization state adjusting element 320.
  • the principle of the light source module 300 using the free-space dual-frequency laser 310 to output a dual-frequency beam is as follows.
  • a free-space dual-frequency laser contains two laser beams with slightly deviated frequencies: a laser beam with a first frequency and a laser beam with a second frequency, and the polarization directions of the two laser beams are orthogonal.
  • the polarization direction of the laser beam is S polarization
  • the polarization direction of the laser beam of the second frequency is P polarization.
  • the S-polarized beam of the first frequency is reflected on the polarization beam splitting surface to form the aforementioned first input beam 610; the P-polarized beam of the second frequency is transmitted on the polarization beam splitting surface After being reflected by the reflecting surface of the second polarization beam splitter 321, it is parallel to the first input beam 610 but shifted by a certain distance.
  • the polarization state adjustment element 320 acts on the beam, the polarization direction changes from P polarization to S polarization.
  • the aforementioned second input beam 611 is formed. Therefore, the light source module 300 can output two dual-frequency input beams with parallel propagation directions and the same polarization direction.
  • the light detection module is used for detection and the signal analysis module can obtain the displacement information of the diffractive element 200 in different degrees of freedom.
  • the second polarization beam splitter 321 is used for light splitting, there may be a small amount of non-linear errors.
  • the signal analysis module 500 can be designed and selected to have non-linear error compensation photoelectric detection and signal processing functions. To compensate for the small amount of non-linear error mentioned above.
  • the above-mentioned polarization state adjusting element 320 may adopt a half wave plate, two quarter wave plates or other polarization control and adjustment elements known in the art to realize the change of the polarization state of the light beam.
  • the above displacement measurement device using a free-space dual-frequency laser due to the large light source module, is preferably used in a measurement scene where the diffraction element 200 moves with the moving table and the read head assembly is fixed, so that the diffraction element 200 is in multiple degrees of freedom.
  • the displacement measurement compared to the above fiber transmission dual-frequency laser, when the light source module adopts a free-space dual-frequency laser, the read head assembly 100 does not need to form a remote reference optical signal, which has the advantages of simple optical transmission structure and fewer measurement axes, which can improve The optical power utilization rate of the device reduces the structural complexity.
  • This embodiment also includes a lithography apparatus, which includes a relatively movable wafer platform and a reticle platform.
  • the lithographic apparatus includes the above-mentioned displacement measuring device.
  • Lithography is a key process in semiconductor processing. Its work includes directing spatial pattern radiation onto photoresist-coated wafers (such as glass or silicon wafers), including determining which locations on the wafer receive radiation (called “alignment”) and The process of applying light radiation to the photoresist at which positions (called “exposure”).
  • the wafer platform supporting the photoresist-coated wafer is usually set as a movable platform (including translation And rotation) to move the wafer so that the light is radiated to the correct position of the wafer.
  • the reticle platform for positioning the reticle is usually stationary.
  • Lithography equipment In lithography equipment based on different designs, during the exposure period, the reticle The platform is set to drive the reticle and the wafer platform to move in coordination. Lithography equipment is also an important process equipment for the production of semiconductor devices and products including semiconductor devices, such as semiconductor chips, liquid crystal panels, OLED panels, and CCD sensors.
  • the above displacement measuring device can be used as an encoder system of a lithography equipment, and the encoder system is used to accurately measure the position of a wafer during the exposure work of the lithography equipment.
  • the diffractive element 200 for example, a grating
  • the read head assembly 100 can be attached to the wafer platform Or another one of the reticle platforms. Since the wafer platform and the reticle platform move relatively during the work of the lithography equipment, the attachment method of the specific grating and read head components can be considered according to the allowable weight and size of the specific installation.
  • the above displacement measuring device Since the above displacement measuring device has wide-angle adaptability, it can improve the angular tolerance of the displacement measuring device and the encoder system, reduce the influence of the deflection of the diffraction element on the intensity of interference information, and also help reduce the difficulty of installation and attitude control. It even avoids non-linear errors caused by the common optical path structure, and improves the measurement accuracy and the system accuracy of the lithography equipment.
  • This embodiment also includes a displacement measuring method, and the above-mentioned displacement measuring device can be used.
  • the displacement measurement method includes the following steps:
  • Step 1 Provide a diffraction element, including a light contact surface and a plurality of repeating diffraction units arranged in a direction parallel to the light contact surface;
  • Step 2 Obtain the first input beam and the second input beam
  • Step 3 Guide the first input beam and the second input beam to contact the diffractive element in parallel and diffract, and then guide and combine the diffracted first input beam and the diffracted first input beam through at least two retroreflective elements
  • the second input light beams form at least one output light beam, and each of the output light beams includes the same spot position in the optical contact surface of the diffractive element and corresponding to the first input light beam and the first light beam in the same direction. 2.
  • Step 4 Detect the output light beam
  • Step 5 Obtain the displacement information of the diffractive element according to the phase change information of the interference signal of each output beam.
  • the first input beam 610 and the second input beam 611 contact the diffractive element 200 in parallel, the first input beam 610 is diffracted once at the first spot position A, The second input beam 611 is first diffracted in the same diffraction order direction at the second spot position B, and the first-order diffracted beam of the first input beam 610 (the second input beam 611 in another embodiment) is guided to cause the first-order diffraction
  • the light beam is reflected back and forth between the retroreflective element and the diffractive element 200, for example, after being reflected and retroreflected by one retroreflective element, the diffractive element 200, and the other retroreflective element in turn, the light contact surface of the diffractive element 200 again Reflected and at least partially overlap with the second input beam 611 (the first input beam 610 in another embodiment) at the same spot position and exit in the same direction, thereby forming a first output beam 613 (the second output beam in another embodiment) Light beam 614),
  • Displacement information in the vertical degree of freedom of the line direction The phase change of the interference signal of the first output beam 613 and the vertical displacement of the corresponding diffraction element 200 satisfy the aforementioned formula (1) in this embodiment, and the phase change of the interference signal of the second output beam 614 corresponds to the corresponding diffraction element.
  • the vertical displacement of 200 satisfies the aforementioned formula (2) in this embodiment.
  • the aforementioned method is used to simultaneously form the aforementioned first output beam 613 and the aforementioned second output beam 613, that is, the vertical biaxial displacement measurement is realized.
  • the diffraction element 200 reflected by the interference signal of the first output beam 613 and the second output beam 614 is in the vertical direction
  • the displacement information in the degree of freedom can compensate for the influence of the environment on the measurement optical path and improve the measurement accuracy.
  • the degree of freedom of rotation of the diffraction element 200 along the axis located in the optical contact surface can be obtained by formula (4). Displacement information.
  • the displacement measurement method of this embodiment not only the displacement information of the vertical degree of freedom of the diffraction element 200 can be obtained, but also the displacement information of the horizontal degree of freedom of the diffraction element 200 can be obtained (in this embodiment, the XY plane in FIG. 1 is regarded as “horizontal”). described as follows.
  • the first-order diffracted light beams of the first input light beam 610 and the second input light beam 611 are retroreflected through the retroreflective element and contact the diffraction element again.
  • the second-order diffracted beams corresponding to the first input beam 610 and the second input beam 611 are at least partially overlapped at the third spot position C on the optical contact surface of the diffraction element 200 and are in the same direction.
  • the third output beam 612 is emitted to form the third output beam 612, and the phase change information of the interference signal of the third output beam 612 reflects the displacement information of the horizontal degree of freedom of the diffraction element 200 along the direction parallel to the optical contact surface.
  • the phase change of the interference signal of the third output beam 612 satisfies the aforementioned equation (3).
  • the first-order diffracted beams of the first input beam 610 and the second input beam 611 used to form the third output beam 612 have opposite directions, corresponding to the same input beam. The directions of diffraction orders of diffraction are the same.
  • the diffracted light signals of the third output beam 612 corresponding to the first input beam 610 and the second input beam 611 respectively correspond to the same diffraction order.
  • the third output beam 612 may include the +1-order second order diffraction corresponding to the first input beam 610 Light beam (or second-order diffracted light signal) and -1 order second-order diffracted light beam (or second-order diffracted light signal) corresponding to the second input light beam 611, or, in another embodiment, the third output light beam 612 may include a corresponding The -1 order second order diffracted light beam of the first input light beam 610 and the +1 order second order diffracted light beam corresponding to the second input light beam 611.
  • the displacement measurement of the diffractive element 200 in more than three degrees of freedom can be realized, for example, the X-axis direction, the Y-axis direction, and the Z-axis direction can be measured.
  • R X direction ie along the X axis deflection direction
  • R y direction ie along the Y axis deflection direction
  • R Z direction ie along the Z axis deflection direction
  • the optical detection (or phase detection) element can be used to The output beam is detected, and the detected optical signal can be further analyzed through a signal transmission fiber, and the displacement information of the diffraction element 200 in the corresponding degree of freedom can be obtained according to the phase change information of the interference signal of each output beam.
  • the first input beam 610 and the second input beam 611 contact the diffractive element 200 in parallel and are diffracted (first diffraction). After reflection, they correspond to the first input beam 610 and
  • the diffracted light signal of the second input light beam 611 is emitted from the same light spot in the optical contact surface of the diffraction element 200 and the directions are overlapped, thereby forming at least one output light beam independently associated with the displacement information of the diffraction element in one degree of freedom.
  • the displacement information of the diffractive element in different degrees of freedom can be obtained through multiple output beams, without algorithmic decoupling, which is beneficial to eliminate the coherent light angle separation caused by the deflection of the diffractive element (for example, the deflection relative to the inner axis of the optical contact surface).
  • the displacement measurement method of this embodiment can significantly reduce or even avoid the nonlinear error caused by the common optical path structure.
  • the displacement measuring method of this embodiment and the above-mentioned displacement measuring device are based on a general idea, and the related parts can refer to the description of the displacement measuring device.

Abstract

一种位移测量装置、位移测量方法及光刻设备，位移测量装置包括光源模块（300）、衍射元件（200）、读头组件（100）、光探测模块（410,411,412,413）以及信号分析模块（500），其中读头组件（100）用于接收光源模块（300）产生的两个输入光束（610,611），并引导它们平行地接触衍射元件（200）并均发生衍射，然后引导并组合经衍射的输入光束以形成至少一个输出光束（612,613,614），每个输出光束（612,613,614）包括从衍射元件（200）的同一光斑位置出射且方向一致的分别对应于两个输入光束（610,611）的衍射光信号，根据每个输出光束（612,613,614）的干涉信号的相位变化信息可以获得所述衍射元件（200）的位移信息。位移测量装置以及位移测量方法可实现不同方向的独立位移测量，并且有助于实现宽角度适应的位移测量，减小非线性误差。光刻设备包括该位移测量装置。

Description

位移测量装置、位移测量方法及光刻设备 技术领域
本发明涉及位移测量技术领域，特别涉及一种位移测量装置、一种位移测量方法以及一种光刻设备。
背景技术
在精密机械的制造、加工和应用过程中，均需要对位移敏感的测量装置或者传感装置的配合，例如目前在集成电路(IC)、精密机械、微机电系统等领域都需要设置高分辨率、高精度的位移测量装置(或者位移传感器)。以集成电路为例，随着集成电路朝大规模、高集成度的方向飞跃发展，光刻机的套刻精度要求也越来越高，与之相应地，获取工件台、掩模台位置信息的精度也随之提高。
纳米测量技术包括纳米尺度的位移测量，近年来得到迅速发展。纳米测量方法包括光学方法和非光学方法。其中，光学方法是利用波长很短的激光或X射线的干涉条纹测量，可以实现纳米量级的测量分辨率。然而，传统干涉仪的测量精度受周围环境影响(比如温度、压力等因素变化导致的测量误差)较大，测量重复精度不高，难以满足光刻机进一步提高套刻精度的要求。
光栅尺(或光栅尺位移传感器)是一种利用光栅的光学原理工作的测量反馈装置，可用作直线位移或者角位移的检测，相比之下，利用光栅尺测量的光程和测量范围无关，可以做到很小，测量光程通常为几毫米，因此它的测量精度对环境影响不敏感，具有测量稳定性高，结构简单，易于小型化的特点，使其在纳米测量领域占据重要的一席之地。在新一代光刻系统中已开始逐渐取代干涉仪，承担高精度、高稳定性皮米精度测量任务。
但是，现有基于光栅尺的位移测量系统仍然存在诸如水平方向和垂直方向的位移测量不独立(存在耦合关系，需要算法解耦)、角度容差小以及读头中较多的共光路结构导致非线性误差较大等问题。
发明内容
为了实现宽角度适应的位移测量，使不同方向的位移测量相互独立，减小非线性误差，本发明提供了一种位移测量装置。另外还提供了一种位移测量方法以及包括所述位移测量装置的一种光刻设备。
根据本发明的一个方面，提供了一种位移测量装置，包括：
光源模块，用于产生第一输入光束和第二输入光束；
衍射元件，包括光接触面以及沿平行于所述光接触面的方向排布的多个重复衍射单元；
读头组件，包括至少两个反向回射元件，所述读头组件用于接收所述第一输入光束和所述第二输入光束，并引导所述第一输入光束和所述第二输入光束平行地接触所述衍射元件的光接触面并均发生衍射，然后所述至少两个反向回射元件引导经衍射的第一输入光束和第二输入光束中的至少一者，使其与另一者组合形成至少一个输出光束，每个所述输出光束包括从所述衍射元件的光接触面内的同一光斑位置出射且方向一致的、分别对应于所述第一输入光束和所述第二输入光束的衍射光信号；
光探测模块，用于检测每个所述输出光束；以及
信号分析模块，与所述光探测模块连接，用于根据每个所述输出光束产生的干涉信号的相位变化信息获得所述衍射元件的位移信息。
可选的，所述读头组件引导所述第一输入光束和所述第二输入光束平行地接触所述衍射元件的光接触面时，所述第一输入光束在第一光斑位置发生一次衍射，所述第二输入光束在第二光斑位置发生一次衍射，所述第一输入光束的一次衍射光束经所述反向回射元件和所述衍射元件来回反射后，在所述第二光斑位置与所述第二输入光束的一次衍射光束至少部分重合并沿同一方向出射而形成第一输出光束；所述第一输出光束的干涉信号的相位变化信息反映了所述衍射元件沿光接触面的法线方向上的垂向自由度的第一位移信息。
可选的，所述读头组件引导所述第一输入光束和所述第二输入光束平行地接触所述衍射元件的光接触面时，所述第一输入光束在第一光斑位置发生一次衍射，所述第二输入光束在第二光斑位置发生一次衍射，所述第二输入 光束的一次衍射光束经所述反向回射元件和所述衍射元件来回反射后，在所述第一光斑位置与所述第一输入光束的一次衍射光束至少部分重合并沿同一方向出射而形成第二输出光束；所述第二输出光束的干涉信号的相位变化信息反映了所述衍射元件沿光接触面的法线方向上的垂向自由度的第二位移信息。
可选的，所述第一输出光束和所述第二输出光束均包括衍射级次方向相同且位于同一衍射阶且分别对应于所述第一输入光束和所述第二输入光束的一次衍射光信号；所述第一输出光束与所述第二输出光束的干涉相位相反。
可选的，所述第一输出光束包括所述第一输入光束和所述第二输入光束的+1衍射阶一次衍射光信号，所述第二输出光束包括所述第一输入光束和所述第二输入光束的-1衍射阶一次衍射光信号。
可选的，所述信号分析模块还用于根据所述第一输出光束和所述第二输出光束的干涉信号的相位变化信息，获得所述衍射元件沿以光接触面内的轴偏转的转动自由度的位移信息。
可选的，所述读头组件引导所述第一输入光束和所述第二输入光束平行地接触所述衍射元件的光接触面后，所述第一输入光束和所述第二输入光束的一次衍射光束分别通过所述反向回射元件回射并再次接触所述衍射元件，并均发生二次衍射，所述第一输入光束和所述第二输入光束的二次衍射光束在所述衍射元件的第三光斑位置至少部分重合并沿同一方向出射而形成第三输出光束；所述第三输出光束的干涉信号的相位变化信息反映了所述衍射元件沿平行于所述光接触面方向的水平自由度的第三位移信息。
可选的，所述衍射元件为一维光栅或二维光栅。
可选的，所述反向回射元件选自角锥棱镜、直角棱镜、猫眼反射器和道威棱镜中的一种。
可选的，所述读头组件包括光束角度控制器。
可选的，所述光束角度控制器选自单个的楔角片、楔角片对、衍射光栅以及双折射元件中的一种。
可选的，所述第一输入光束和所述第二输入光束为频率不同的激光束。
可选的，所述光源模块包括光纤传输双频激光器；在沿平行方向接触所述衍射元件前，所述读头组件还用于对接收到的所述第一输入光束和所述第二输入光束分别进行分光并合光以形成一远程参考光束。
可选的，所述光源模块包括自由空间双频激光器和分光元件，其中，所述自由空间双频激光器用于产生双频光束，所述分光元件用于将所述双频光束分成两个偏振方向正交的光束。
可选的，所述光源模块或所述读头组件包括偏振控制元件，所述偏振控制元件用于使每个所述输出光束中分别对应于所述第一输入光束和所述第二输入光束的所述多个衍射光信号在进入所述光探测模块时的偏振方向相同。
可选的，所述第一输入光束和所述第二输入光束为频率相同的激光束。
可选的，所述光源模块或所述读头组件包括偏振控制元件，所述偏振控制元件用于使每个所述输出光束中分别对应于所述第一输入光束和所述第二输入光束的所述多个衍射光信号在进入所述光探测模块时的偏振方向正交。
可选的，所述读头组件形成至少四个输出光束，所述光探测模块在检测到所述至少四个输出光束后，还用于对每个所述输出光束的干涉信号进行移相，以输出依次相差90度的四路所述输出光束。
根据本发明的另一方面，提供了一种位移测量方法，包括以下步骤：
提供一衍射元件，包括光接触面以及沿平行于所述光接触面的方向排布的多个重复衍射单元；
获得第一输入光束和第二输入光束；
引导所述第一输入光束和所述第二输入光束平行地接触所述衍射元件的光接触面并均发生衍射，然后通过至少两个反向回射元件引导经衍射的第一输入光束和第二输入光束中的至少一者，使其与另一者组合形成至少一个输出光束，每个所述输出光束包括从所述衍射元件的光接触面内的同一光斑位置出射且方向一致的、分别对应于所述第一输入光束和所述第二输入光束的衍射光信号；
检测所述输出光束；以及
根据每个所述输出光束产生的干涉信号的相位变化信息获得所述衍射元 件的位移信息。
可选的，所述第一输入光束和所述第二输入光束平行地接触所述衍射元件的光接触面时，所述第一输入光束在第一光斑位置发生一次衍射，所述第二输入光束在第二光斑位置发生一次衍射，所述第一输入光束的一次衍射光束经所述反向回射元件和所述衍射元件来回反射后，在所述第二光斑位置与所述第二输入光束的一次衍射光束至少部分重合并沿同一方向出射而形成第一输出光束；所述第一输出光束的干涉信号的相位变化信息反映了所述衍射元件沿光接触面的法线方向上的垂向自由度的第一位移信息。
可选的，所述第一输出光束的干涉信号的相位变化与所述衍射元件沿垂向自由度的位移满足关系式：
Figure PCTCN2020086684-appb-000001
其中，
Figure PCTCN2020086684-appb-000002
为所述第一输出光束的干涉信号的相位变化，ΔZ1为所述衍射元件在垂向自由度上的位移量，λ为所述第一输入光束和所述第二输入光束的波长平均值，θ为所述第一输入光束和所述第二输入光束平行地接触所述衍射元件的光接触面后发生的一次衍射的m级衍射角，m为0以外的整数。
可选的，所述第一输入光束和所述第二输入光束平行地接触所述衍射元件的光接触面时，所述第一输入光束在第一光斑位置发生一次衍射，所述第二输入光束在第二光斑位置发生一次衍射，所述第二输入光束的一次衍射光束经所述反向回射元件和所述衍射元件来回反射后，在所述第一光斑位置与所述第一输入光束的一次衍射光束至少部分重合并沿同一方向出射而形成第二输出光束；所述第二输出光束的干涉信号的相位变化信息反映了所述衍射元件沿垂向自由度的第二位移信息；所述第一输出光束与所述第二输出光束的干涉相位相反。
可选的，所述位移测量方法还包括：
在检测到所述第一输出光束和所述第二输出光束后，根据所述第一输出光束和所述第二输出光束的干涉信号所反映的所述衍射元件沿垂向自由度的位移信息，获得所述衍射元件沿以光接触面内的轴偏转的转动自由度的位移信息。
可选的，所述衍射元件与所述第一输出光束对应的位移和与所述第二输出光束对应的位移之间满足关系式：
Figure PCTCN2020086684-appb-000003
其中，ΔZ1和ΔZ2分别为所述第一输出光束反映的所述衍射元件沿垂向自由度的第一位移信息和所述第二输出光束反映的所述衍射元件沿垂向自由度的第二位移信息，D f1f2为所述第一光斑位置和所述第二光斑位置的间距。
可选的，所述第一输入光束和所述第二输入光束平行地接触所述衍射元件的光接触面后，使所述第一输入光束和所述第二输入光束的一次衍射光束分别通过所述反向回射元件回射并再次接触所述衍射元件，并均发生二次衍射，所述第一输入光束和所述第二输入光束的二次衍射光束在所述衍射元件的第三光斑位置至少部分重合并沿同一方向出射而形成第三输出光束；所述第三输出光束的干涉信号的相位变化信息反映了所述衍射元件沿平行于所述光接触面方向的水平自由度的第三位移信息。
可选的，所述第三输出光束的干涉信号的相位变化与所述衍射元件在对应的水平自由度的位移满足关系式：
Figure PCTCN2020086684-appb-000004
其中，
Figure PCTCN2020086684-appb-000005
为所述第三输出光束的干涉信号的相位变化，ΔX为所述衍射元件在所述第一方向上的位移，P为所述衍射元件的多个重复衍射单元沿所述水平自由度方向的间距，m为0以外的整数。
根据本发明的再一方面，本发明还包括一种光刻设备，所述光刻设备包括可相对移动的晶片平台和掩模版平台，其特征在于，所述光刻设备包括上述位移测量装置，其中，所述衍射元件贴附于所述晶片平台或所述掩模版平台中的一个，所述读头组件贴附于所述晶片平台或所述掩模版平台中的另外一个。
本发明提供的位移测量装置至少具有以下优点：第一，根据每个输出光束的干涉信号的相位变化信息分别获得衍射元件的位移信息，不需要进行算 法解耦；第二，通过使相互分离的第一输入光束和第二输入光束平行地接触衍射元件发生衍射，且对经衍射的第一输入光束和第二输入光束进行引导并组合形成至少一个输出光束，每个输出光束包括对应于从所述衍射元件的光接触面内的同一光斑位置出射且方向一致的分别对应于所述第一输入光束和所述第二输入光束的衍射光信号，有利于消除衍射元件偏转(例如相对于光接触面内的轴的偏转)造成的相干光角度分离，即测量过程具备了宽角度适应能力，有助于减小衍射元件偏转对干涉信息强度的影响，提高测量精度，此外还有助于提高装置的角度容差，减小装置的安装和姿态控制难度；第三，输入读头组件的两个输入光束之间相互分离(空间上)，在测量的过程中，光束不发生相互影响，只在最终干涉前才进行合光；相对于通过同一输入光束易造成频率混叠的测量系统来说，可以极大地减小甚至避免由于共光路结构导致的非线性误差。
本发明提供的位移测量方法，与上述位移测量装置属于一个总的构思，因而具有相同或类似的优点。
本发明提供的光刻设备，包括上述位移测量装置，因而也具有与上述位移测量装置相同或类似的优点。
附图说明
图1是本发明一实施例的位移测量装置获得第一输出光束的示意图。
图2(a)是本发明一实施例的位移测量装置采用角锥棱镜作为反向回射元件的示意图。
图2(b)是本发明一实施例的位移测量装置采用直角棱镜作为反向回射元件的示意图。
图2(c)是本发明一实施例的位移测量装置采用道威棱镜作为反向回射元件的示意图。
图2(d)是本发明一实施例的位移测量装置采用猫眼反射器作为反向回射元件的示意图。
图3是本发明一实施例的位移测量装置获得第一输出光束和第三输出光 束的示意图。
图4是本发明一实施例的位移测量装置获得第一输出光束、第二输出光束以及第三输出光束的示意图。
图5是本发明另一实施例的位移测量装置获得第一输出光束、第二输出光束以及第三输出光束的示意图。
图6是本发明一实施例的位移测量装置输入光束为相同频率时的示意图。
图7是本发明一实施例的位移测量装置输入光束为不同频率时的示意图。
图8是本发明另一实施例的位移测量装置输入光束为不同频率时的示意图。
附图标记说明：
100-读头组件；
110-第一反向回射元件；111-第二反向回射元件；
130-第一反射元件；131-第二反射元件；132-第三反射元件；133-第一分光元件；134-第二分光元件；135-第三分光元件；136-第四挡光板；
200-衍射元件；
300-光源模块；
310-自由空间双频激光器；311-单频激光器；
320-偏振态调节元件；321-第二偏振分光镜；322-隔离器；323-第一声光频移器；324-第二声光频移器；325-第一挡光板；326-第二挡光板；327-第三挡光板；
330-第一分光镜；331-第二分光镜；332-第三分光镜；333-第四分光镜；334-第一反射镜；335-第二反射镜；
340-第一保偏光纤耦合器；341-第二保偏光纤耦合器；
350-多模光纤耦合器；
370-第三光束角度控制器；
410-第三光探测模块；411-第一光探测模块；412-第二光探测模块；413-第四光探测模块；
430-第三信号传输光纤；431-第一信号传输光纤；432-第二信号传输光纤； 433-第四信号传输光纤；
450-第一保偏光纤准直器；451-第二保偏光纤准直器；
470-第一保偏光纤；471-第二保偏光纤；
481-四分之一波片；482-非偏振分光镜；483-第一偏振分光镜；484-第二偏振分光镜；485-第一光耦合器；486-第二光耦合器；487-第三光耦合器；488-第四光耦合器；
500-信号分析模块；
610-第一输入光束；611-第二输入光束；612-第三输出光束；613-第一输出光束；614-第二输出光束；
621-反向回射元件的入射光束；622-反向回射元件的出射光束；
700-第一光束角度控制器；701-第二光束角度控制器；702-第三光束角度控制器；
1301-透镜；1302-凹面反射镜。
具体实施方式
如背景技术所述，针对现有基于光栅尺的位移测量系统存在的问题，例如不同方向(自由度)的测量信号不独立、存在耦合关系，需要进一步通过算法解耦才能获得光栅尺在不同自由度上的位移的问题，以及由于光路设计的原因导致的角度容差小、系统安装精度要求高的问题，还比如在光学编码器读头中的光路中不同衍射信号存在大量的共光路结构时，会导致测量信号存在较大的非线性误差的问题，本发明意图提供具体的位移测量方案，以解决上述问题。
基于上述目的，本发明提供了一种位移测量装置、一种位移测量方法以及一种包括所述位移测量装置的光刻设备。其中，所述位移测量装置至少包括以下几个部分：光源模块、衍射元件、读头组件、光探测模块以及信号分析模块。
具体的，所述光源模块用于产生第一输入光束和第二输入光束。所述衍射元件包括光接触面以及沿平行于所述光接触面的方向排布的多个重复衍射 单元。所述读头组件包括至少一组反向回射元件，所述读头组件用于接收所述第一输入光束和所述第二输入光束，并引导所述第一输入光束和所述第二输入光束平行地接触所述衍射元件并均发生衍射(此处“平行”不包含重合情况)，然后引导并组合经衍射的第一输入光束和第二输入光束以形成至少一个输出光束，每个所述输出光束包括从所述衍射元件的光接触面内的同一光斑位置(在此，同一光斑位置指同一个光斑所在的位置，即光斑所在的一定范围内，例如以一个光斑的中心为圆心，0.5～1.5个光斑直径的范围内(即可以实现两个光斑相交或相切的位置)作为所述的同一光斑位置)出射且方向一致的分别对应于所述第一输入光束和所述第二输入光束的衍射光信号，每个所述输出光束产生的干涉信号的相位变化信息可以反映所述衍射元件沿二维或三维空间内的一个自由度的位移信息。所述光探测模块用于检测所述读头组件形成的输出光束。所述信号分析模块与所述光探测模块连接，所述信号分析模块用于根据每个所述输出光束的干涉信号的相位变化信息获得所述衍射元件的位移信息。需要说明的是，在应用中，上述几个部分可以部分或全部的属于一光学编码器系统的组件，其中衍射元件例如为光学编码器系统的光栅尺，而读头组件例如是光学编码器系统的编码器头(encoder head)，光学编码器系统可用于监控诸如光刻机等精密系统中可移动平台的移动。
以下结合附图和具体的实施例对本发明的位移测量装置、位移测量方法及光刻设备作进一步详细说明。应当理解，下述实施例仅是应用本发明的示例性的具体实施方式，并不构成对本发明保护范围的限制。
需说明的是，附图均采用非常简化的形式且均使用非精准的比例，仅用以方便、明晰地辅助说明本发明实施例的目的。除非另有其它说明，否则不同附图中的相应的数字和标号通常涉及相应的部件。并且，下文中的术语“第一”“第二”等用于在类似要素之间进行区分，且未必是用于描述特定次序或时间顺序。要理解，在适当情况下，如此使用的这些术语可替换，例如可使得本文所述的本发明实施例能够不同于本文所述的或所示的其它顺序来操作。类似的，如果本文所述的方法包括一系列步骤，且本文所呈现的这些步骤的顺序并非必须是可执行这些步骤的唯一顺序，且一些所述的步骤可被省 略和/或一些本文未描述的其他步骤可被添加到该方法。
图1是本发明一实施例的位移测量装置获得第一输出光束的示意图。参照图1，对本实施例的位移测量装置及获得第一输出光束613的光路(或方法)描述如下。
通过光源模块(图1未示出)产生了第一输入光束610和第二输入光束611，本实施例中，第一输入光束610和第二输入光束611在空间上保持一定间隔距离被输出。第一输入光束610和第二输入光束611例如均是激光光束，二者的波长约在150nm至2000nm的范围，更具体的，二者波长可在400nm至1500nm范围内选择，或者在1500至2000nm范围内选择，进一步的，第一输入光束610和第二输入光束611可以具有例如633nm、980nm或者1070nm的波长。第一输入光束610和第二输入光束611的频率可以相同或者略有差别(频率差例如小于等于10Hz)。该分离的第一输入光束610和第二输入光束611进入读头组件100，读头组件100引导第一输入光束610和第二输入光束611平行地接触衍射元件200的光接触面而发生衍射，在此，为了获得第一输入光束610和第二输入光束611的衍射信号，第一输入光束610和第二输入光束611以相同的任意非利特罗(non-Littrow)角度接触(或入射到)衍射元件200的光接触面的不同位置并发生衍射。
衍射元件200包括沿平行于光接触面的方向排布的多个重复衍射单元(图1未示出)，清楚起见，图1示意了位移测量装置在一笛卡尔坐标系中的剖面，本实施例中，以图1中的X轴方向作为衍射元件200的多个重复衍射单元(即多个相同的衍射单元)的一个排列方向。衍射元件200可以是一维或二维光栅，当是二维光栅时，垂直于图1中XZ平面的Y轴方向可以属于衍射元件200的多个重复衍射单元的另一个排列方向。对于光栅而言，可以采用正弦、矩形或锯齿光栅，还可以采用较复杂的线性调频脉冲光栅，但不限于此，在另一实施例中，衍射元件200还可以是全息衍射结构等其它衍射结构。无论采用哪种衍射结构，均应包括上述重复衍射单元，以实现对以非利特罗角入射的第一输入光束610和第二输入光束611的衍射。本实施例中，衍射元件200对于第一输入光束610和第二输入光束611也具有反射作用。
上述读头组件100包括至少两个反向回射元件，如图1中的第一反向回射元件110和第二反向回射元件111，入射至反向回射元件内的光束经反向回射作用可以输出与入射光束平行但传播方向相反、且偏移一定距离的出射光束，从而可以通过对反向回射元件的安装位置和角度的改变，对第一输入光束610和/或第二输入光束611接触衍射元件200后的衍射光束的光程和传播方向进行调节。
图2(a)至图2(d)分别示意了四种反向回射元件的结构。参照图2(a)至图2(d)，第一反向回射元件110和第二反向回射元件111中的一个或两个可以选用如图2(a)所示的角锥棱镜、图2(b)所示的直角棱镜、图2(c)所示的道威棱镜以及图2(d)所示的猫眼反射器，其中，反向回射元件的入射光束621入射至相应的反向回射元件后，经反向回射后，反向回射元件的出射光束622被输出。参照图2(d)，猫眼反射器包括一个透镜1301和一个凹面反射镜1302，凹面反射镜1302的球心置于透镜1301的主点(薄透镜中心)上，透镜1301的焦点在凹面反射镜1302的反射面上，入射光束621由透镜1301会聚到凹面反射镜1302上，被凹面反射镜1302反射，再经过透镜1301后出射光束622仍平行于原入射光束，但方向相反。本实施例中，读头组件100中的第一反向回射元件110和第二反向回射元件111例如是角锥棱镜，其中，入射至角锥棱镜的入射光束和出射光束在衍射元件200的入射点可以在光接触面上的任意不重合位置。角锥棱镜的位置可以根据需要设计和调节。
上述读头组件100引导第一输入光束610和第二输入光束611平行地接触衍射元件200时，第一输入光束610在第一光斑位置A发生一次衍射(或第一次衍射)，第二输入光束611在第二光斑位置B发生一次衍射(或第一次衍射)。优选的，所述第一光斑位置A和所述第二光斑位置B均位于相应的所述衍射单元的中心；或者，所述第一光斑位置A和所述第二光斑位置B两处的衍射图案是相同的，从而进一步提高测量精度。本实施例中，第一输入光束610和第二输入光束611的一次衍射级次方向相同。此处“衍射级次方向相同”指的是第一输入光束610和第二输入光束611的一次衍射的衍射级次 均为正向衍射级次或均为负向衍射级次。可选实施方式中，参照图1，第二输入光束611在第二光斑位置B产生+n级一次衍射光束(n为0以外的整数，例如±1、±2、±3、…，下同，+n表示正整数，即+1、+2、+3……)，并经第一反射元件130反射后出射；第一输入光束610在第一光斑位置A产生+m级一次衍射光束(m为0以外的整数，例如±1、±2、±3、…，下同，+m表示正整数，即+1、+2、+3……)。当角锥棱镜110的位置经特殊设计后，对应于第一输入光束610的一次衍射光束经第二反向回射元件111反向回射至衍射元件200，在衍射元件200的光接触面反射后，进入第一反向回射元件110并再次反向回射至衍射元件200，在衍射元件200光接触面的第二光斑位置B再次发生反射，使第一输入光束610产生的一次衍射后反射光束与第二输入光束611的一次衍射光束在第二光斑位置B至少部分重合并沿同一方向出射，形成第一输出光束613。由读头组件100输出的第一输出光束613通过第一光探测模块411检测，第一光探测模块411可以采集第一输出光束613的干涉信号的相位信息，进一步的，通过第一信号传输光纤431，第一光探测模块411采集的相位信息可被传输至信号分析模块500，信号分析模块500通过对第一输出光束613的干涉信号的相位信息进行分析，获得相位变化信息，并通过其与衍射元件200沿位于光接触面的法线方向上的垂向自由度的位移之间的关系，得到衍射元件200在垂向自由度的位移信息。
在另一可选实施方式中，参照图4，读头组件100引导第一输入光束610和第二输入光束611平行地接触衍射元件200时，第一输入光束610在第一光斑位置A发生-m级的一次衍射，所述第二输入光束在第二光斑位置B发生-n级的一次衍射，对应于第二输入光束611的一次衍射光束经第一反向回射元件110反向回射至衍射元件200，在衍射元件200的光接触面反射后，进入第二反向回射元件111并再次反向回射至衍射元件200，在衍射元件200光接触面的第一光斑位置A再次发生反射，使第二输入光束611产生的一次衍射后反射光束与第一输入光束610的一次衍射光束在第一光斑位置A至少部分重合并沿同一方向出射，经第二反射元件131反射后出射，形成第二输出光束614。由读头组件100输出的第二输出光束614通过第二光探测模块412检 测，第二光探测模块412可以采集第二输出光束614的干涉信号的相位信息，进一步的，通过第二信号传输光纤432，第二光探测模块412采集的相位信息可被传输至信号分析模块500，信号分析模块500通过对第二输出光束614的干涉信号的相位信息进行分析，获得相位变化信息，并通过其与衍射元件200沿位于光接触面的法线方向上的垂向自由度的位移之间的关系，也可以获得衍射元件200在垂向自由度的位移信息。此处“垂向”指的是衍射元件200光接触面的法线方向，如图1和图4中的Z轴方向。
本实施例中，上述第一输出光束613和第二输出光束614均包括衍射级次方向相同且位于同一衍射阶且分别对应于第一输入光束610和第二输入光束611的一次衍射光信号；第一输出光束613与第二输出光束614的干涉相位相反，即，第一输出光束613中的干涉信号的相位与第二输出光束614中的干涉信号的相位是相反的。优选方案中，第一输出光束613包括第一输入光束610和第二输入光束611的+1衍射阶一次衍射光信号，第二输出光束614包括第一输入光束610和第二输入光束611的-1衍射阶一次衍射光信号。
光源模块产生的第一输入光束610和第二输入光束611优选是平行光束，从而通过上述光路设计可直接采集第一输出光束613和第二输出光束614的相位干涉信号，但本发明不限于此，当第一输入光束610和第二输入光束611在入射衍射元件200前为非平行时，可以通过在读头组件100中设置光束角度控制器控制光束的方向。参照图1，为了使第一输入光束610和第二输入光束611较准确地平行入射至衍射元件200，可以在第一输入光束610和第二输入光束611中的一个的入射光路上设置第一光束角度控制器700，光束角度控制器可以控制光束方向，从而可用于调整第一输入光束610和第二输入光束611保持平行，类似的，为了第一输入光束610和第二输入光束611的一次衍射光信号在光接触面的同一光斑位置至少部分重合(即，包括完全重合或者部分重合，相应的，形成了完全或者部分重合的输出光束，在此，同一光斑位置是指光斑所在的一定范围内，例如以一个光斑的中心为圆心，0.5～1.5个光斑直径的范围内(即可以实现两个光斑相交或相切的位置)作为所述的同一光斑位置)并沿同一方向出射，可以在其中一个衍射光束的光路上设置第 二光束角度控制器701。第一光束角度控制器700和第二光束角度控制器701可选自单个的楔角片、楔角片对、衍射光栅以及双折射元件等光学结构中的一种。需要说明的是，本实施例中第一反射元件130和第二反射元件131仅为可选部件，可以根据读头组件100的安装尺寸以及光探测模块的位置选择性采用。
由于第一输入光束610和第二输入光束611平行入射至衍射元件200，且第一输入光束610的一次衍射光束，经过反向回射元件两次回射以及衍射元件200两次反射后，产生的反射光束与原始一次衍射光束平行。因此可知不论衍射元件200相对于读头组件100是否有角度变化，第一输入光束610的衍射后反射光束，与第二输入光束611的一次衍射光束，始终平行。也即，本实施例的位移测量装置通过上述光束传输采集第一输出光束613和第二输出光束614，有助于消除由于衍射元件200偏转(尤其是相对于图1中坐标系的X轴和Y轴的偏转)造成的相干光角度分离，从而可以显著减小衍射元件200偏转对输出光束的干涉信号强度的影响，提高了测量精度，并且也有助于提高位移测量装置的角度容差，因此本实施例中的垂向测量具有宽角度适应性。
上述第一输出光束613包括衍射级次的方向相同且位于同一衍射阶且分别对应于第一输入光束610和第二输入光束611的一次衍射光信号，此处“一次衍射光信号”指的是第一输入光束610和/或第二输入光束611平行地接触衍射元件200后产生的一次衍射光束中的光学相位信息，可以理解，所述一次衍射光束经反向回射元件和衍射元件反射后，可以改变光程及传播方向，但可以保留一次衍射光束的光学相位信息。
对第一输出光束613的干涉信号的相位变化与衍射元件200的位移之间的关系说明如下。第一输入光束610和第二输入光束611平行地接触衍射元件200时，第一输入光束610在第一光斑位置A发生+m级的一次衍射，所述第二输入光束611在第二光斑位置B发生+n级的一次衍射，从而第一输出光束613包括第一输入光束610的+m级一次衍射光信号与第二输入光束611的+n级一次衍射光信号，当m＝n时，沿第一输出光束613的方向形成对应垂 向位移的相位变化的干涉信号。为了获得第一输出光束613的干涉信号的相位变化
Figure PCTCN2020086684-appb-000006
与对应的衍射元件200的垂向位移之间的关系，在此，设定第一输出光束613中包含的第一输入光束610的衍射光信号相位为
Figure PCTCN2020086684-appb-000007
包含的第二输入光束611的衍射光信号相位为
Figure PCTCN2020086684-appb-000008
两束衍射光束干涉之后，干涉信号的相位变化
Figure PCTCN2020086684-appb-000009
与对应的衍射元件200的垂向位移之间关系的计算过程如下：
Figure PCTCN2020086684-appb-000010
Figure PCTCN2020086684-appb-000011
Figure PCTCN2020086684-appb-000012
从而得到式(1)，
Figure PCTCN2020086684-appb-000013
根据前述说明，第二输出光束614包括第一输入光束610的-m级一次衍射光信号和第二输入光束611的-n极一次衍射光信号(m＝n)。类似的，可以得到第二输出光束614的干涉信号的相位变化
Figure PCTCN2020086684-appb-000014
与衍射元件200的垂向位移之间的关系满足式(2)，
Figure PCTCN2020086684-appb-000015
式(1)和式(2)中，λ为第一输入光束610和第二输入光束611的波长(如果二者频率不同，则是平均波长)，θ为第一输入光束610和第二输入光束611平行入射衍射元件200后发生一次衍射形成的m级衍射角(m为±1、±2、±3、…)，ΔX为假设衍射元件200在X轴方向的位移，ΔZ1为与第一输出光束613对应的衍射元件200在Z轴方向的位移，ΔZ2为与第二输出光束614对应的衍射元件200在Z轴方向的位移。
本实施例的位移测量装置不仅可以形成对应于垂向自由度位移测量的第一输出光束613和第二输出光束614，还可以形成用于测量衍射元件200沿平 行于光接触面方向的水平自由度的位移信息的输出光束。
图3是本发明一实施例的位移测量装置获得第一输出光束和第三输出光束的示意图。参照图3，本实施例的位移测量装置中，读头组件100可用于输出相互分离的第一输出光束613和第三输出光束612。关于第一输出光束613的设计可参见上面的描述。以下主要对第三输出光束612进行说明。
本实施例中，第一输入光束610和第二输入光束611平行地接触衍射元件200后，产生衍射级次方向相反的一次衍射光束，例如以任意非利特罗角度在不同的入射点入射衍射元件200后，第一输入光束610在第一光斑位置A产生+m级一次衍射光束，第二输入光束611在第二光斑位置B产生-n级一次衍射光束，两个一次衍射光束分别经不同的反向回射元件反射回射后再次与衍射元件200接触，并分别发生与一次衍射的衍射级次方向相同的二次衍射，并且，在第三光斑位置C产生了对应于第一输入光束610的+m极二次衍射光束以及对应于第二输入光束611的-n级二次衍射光束，也即，通过对读头组件100的结构设计，可使得对应于第一输入光束610的二次衍射光束和对应于第二输入光束611的二次衍射光束在衍射元件的同一光斑位置至少部分重叠并以同一方向出射，从而形成第三输出光束612。
进一步的，由读头组件100输出的第三输出光束612可通过第三光探测模块410检测，第三光探测模块410可以采集第三输出光束612的干涉信号的相位信息，进一步的，通过第三信号传输光纤430，第三光探测模块410采集的相位信息可被传输至信号分析模块500，信号分析模块500通过对接收到的相位信息进行分析，通过第三输出光束612的干涉信号的相位变化信息获得衍射元件200沿平行于光接触面的方向上的水平自由度的位移信息。参照图3，当衍射元件200为沿X轴方向的一维衍射结构时，通过第三输出光束612可以获得衍射元件200在X轴方向上的位移信息。而当衍射元件200为沿X轴方向和Y轴方向(即垂直于XZ平面的方向)的二维衍射结构时，将图3中的读头组件100和光探测模块以Z轴为中心旋转90度，则可以获得衍射元件200在Y轴方向上的位移信息。
上述位移测量装置获得第三输出光束612的光路结构中，平行入射至衍 射元件200的第一输入光束610产生的一次衍射光束经第二反向回射元件111反射、第二输入光束611产生的一次衍射光束经第一反向回射元件110反射回射后，第一输入光束610的二次衍射光束与发生一次衍射前的第一输入光束610平行，第二输入光束611的二次衍射光束与发生一次衍射前的第二输入光束611平行，从而两个二次衍射光束平行，因此可知不论衍射元件200相对于读头组件100是否有角度变化(尤其是相对于X轴和Y轴的角度变化)，第一输入光束610的二次衍射光束与第二输入光束611的二次衍射光束始终平行，从而有助于消除衍射元件200例如光栅偏转造成的相干光角度分离，极大减小光栅偏转对干涉信号强度的影响，有助于提高装置的角度容差以及提高测量精度，因此利用本实施例的位移测量装置，针对水平方向的测量也具有宽角度适应性。
上述第三输出光束612包括衍射级次的方向相反且位于同一衍射阶且分别对应于第一输入光束610和第二输入光束611的二次衍射光束，对第三输出光束612的干涉信号的相位变化与衍射元件的位移之间的关系说明如下。经过两次衍射，读头组件100产生了对应于第一输入光束610的+m级二次衍射光束，以及对应于第二输入光束611的-n级二次衍射光束，当m＝n时，沿第三输出光束612方向形成了对应水平位移的相位变化的干涉信号。为了获得第三输出光束612的干涉信号的相位变化与对应的水平方向位移信息的相位变化
Figure PCTCN2020086684-appb-000016
之间的关系，在此，设定第三输出光束612中包含的第一输入光束610的衍射光信号相位为
Figure PCTCN2020086684-appb-000017
包含的第二输入光束611的衍射光信号相位为
Figure PCTCN2020086684-appb-000018
两束衍射光束干涉之后，干涉信号的相位变化
Figure PCTCN2020086684-appb-000019
与对应的衍射元件200的水平位移之间关系的计算过程如下：
Figure PCTCN2020086684-appb-000020
Figure PCTCN2020086684-appb-000021
Figure PCTCN2020086684-appb-000022
从而得到式(3)，
Figure PCTCN2020086684-appb-000023
式(3)中，P为衍射元件200在X轴方向上排布的重复衍射单元之间的间距，m为衍射级次，例如可以取±1、±2、±3等0以外的整数，ΔX为待测的衍射元件200在X轴方向的位移量。
水平方向的位移也可以通过相反衍射级次的二次衍射光束获得。例如，在另一实施例中，第一输入光束610产生了-m级二次衍射光束，第二输入光束611产生了+n级二次衍射光束，从而得到的第三输出光束的相位与式(3)中的
Figure PCTCN2020086684-appb-000024
相位相反。
本实施例中，衍射元件200还可以包括沿图3中垂直于XZ平面的Y轴方向排布的多个重复衍射单元，Y轴方向与X轴方向相互垂直。基于与上述第三输出光束612的测试目的类似的考量，上述读头组件100还可以通过对第一输入光束610和第二输入光束611的引导组合，形成与获得第三输出光束612的光路结构类似的设计，在Y轴方向经一次衍射、反向回射元件反射回射以及二次衍射之后组合形成第四输出光束(图中未示出)，所述第四输出光束包括从衍射元件200光接触面的同一光斑同一方向出射的二次衍射光束。所述第四输出光束的干涉信号的相位变化信息反映了衍射元件200在Y轴方向上的位移信息。在某一实施例中，可将读头组件100沿图3中Z轴转动90度，从而可在平行于第三输出光束612的方向上检测到对应于Y轴方向位移的输出光束，进而可以获得衍射元件200在Y轴方向上的位移信息。
根据上述描述可知，本实施例所述的位移测量装置可同时测量衍射元件200的沿平行于光接触面的水平方向上的自由度的位移测量和沿光接触面的法线方向上的垂向自由度的位移测量。当衍射元件200采用二维衍射结构时，至少可以实现三个自由度的位移测量。进一步的，通过适当组合两个或两个以上具有上述光路设计的输入光束、读头组件及光探测模块，可以实现对衍射元件200在三个以上的自由度上的位移测量，例如可以实现对X轴方向、Y轴方向、Z轴方向、R X方向(即沿X轴偏转方向)、R y方向(即沿Y轴偏转方向)、R Z方向(即沿Z轴偏转方向)六个自由度的位移测量。
本实施例的位移测量装置，具有以下几个方面优点：第一，可实现水平向和垂向位移的独立测量，不需要计算解耦，即对于只需要单独测X轴方向 位移或单独测Z轴方向位移的应用需求时，可以独立的只采集一路干涉信号即可计算出相应位移；第二，对水平向和垂向测量均有宽角度适应范围，有助于提高装置的角度容差，提高测量精度，减小位移测量装置的安装和姿态控制难度；第三，由于测量信号均为自平行光束，不需精确调整，集成简便；第四，测量系统结构简单，冗余空间大，可扩展性高；第五，位移测量装置的元件种类较少，成本低；第六，由于干涉信号在合光前不共光路，因此不受器件分光、偏振性能影响，本方案从测量原理上可知基本无非线性误差；第七，本实施例中，输入光束在衍射元件的光接触面发生衍射后，衍射光束均被光探测模块收集，用于水平向和垂向位移信号探测，没有杂散光溢出位移测量装置；第八，由于无杂散光溢出，因此位移测量装置的光功率利用率非常高。
图4是本发明一实施例的位移测量装置获得第一输出光束、第二输出光束以及第三输出光束的示意图。参照图4，本实施例中，读头组件100同时形成了上述第一输出光束613、第二输出光束614以及第三输出光束612。根据上述描述，通过这三个输出光束进行检测并分析后，可以实现水平方向(如图4中X轴方向)和双轴垂向(如图4中Z轴方向)的位移测量。关于第一输出光束613、第二输出光束614以及第三输出光束612的光路结构可参见上面的描述。
通过采集并分析两路由衍射元件200上不同光斑位置出射且均对应垂向自由度的输出光束，可得到两个垂向位移测量结果，其技术效果在于，一方面可以补偿环境对测量光路的影响(例如两路Z轴输出光束在不同的环境下测量时)，有助于提高位移测量的准确性，提升测量精度；另一方面，通过这两个垂向位移测量结果，可以进一步计算衍射元件200沿位于光接触面内的轴旋转的转动自由度的位移信息。具体说明如下。
以图4中均在XZ平面分布的第一输出光束613和第二输出光束614为例，当分别通过第一光探测模块411和第二光探测模块412对二者进行相位采集并传输至信号分析模块500后，得到分别根据第一输出光束613获得的衍射元件200在Z轴方向的位移量ΔZ1和根据第二输出光束614获得的衍射元件 200在Z轴方向的位移量ΔZ2。ΔZ1和ΔZ2满足式(4)的关系，
Figure PCTCN2020086684-appb-000025
式(4)中，ΔZ1和ΔZ2分别为通过第一输出光束613和第二输出光束614测得的垂向位移，D f1f2为第一输出光束和所述第二输出光束平行地接触所述衍射元件时的间距(如图4中第一光斑位置A与第二光斑位置B的距离)。
根据式(4)的关系，当第一输出光束和第二输出光束均在YZ平面分布时，通过采集两个包括垂向位移信息的输出光束并进行计算，可以获得衍射元件200沿图4中以X轴为轴线的偏转量，即可以获得Rx自由度的位移信息。
图5是本发明另一实施例的位移测量装置得到第一输出光束、第二输出光束以及第三输出光束的示意图。参照图4和图5，读头组件100在接收第一输入光束610和第二输入光束611后，引导二者平行入射至衍射元件200光接触面并发生衍射，进而利用第一反向回射元件110和第二反向回射元件111实现对衍射光束的反射和衍射元件200光接触面对入射光束的反射，采集与图4中衍射级次反向的衍射光束，得到与图4所示输出光束对应的衍射级次反向的第一输出光束613、第二输出光束614以及第三输出光束612。该实施例的信号传输光纤和信号分析模块的功能与图4结构相同，因此未在图5中示出。
以第三输出光束612为例，该实施例中，第一输入光束610在衍射元件200光接触面产生的-m级一次衍射光束经反向回射元件反射回衍射元件200，再次产生-m级衍射(第二次衍射)，第二输入光束611在衍射元件200光接触面产生的+n级一次衍射光束经反向回射元件反射回衍射元件200，再次产生+n级衍射(第二次衍射)，第一输入光束610的二次衍射光束与第二输入光束611的二次衍射光束在同一光斑位置至少部分重合并沿同一方向出射，当m＝n时，形成第三输出光束612，第三输出光束612包括对应于X轴方向位移信息的相位变化
Figure PCTCN2020086684-appb-000026
并满足式(5)所示关系：
Figure PCTCN2020086684-appb-000027
其中，P为衍射元件200例如光栅在X轴方向的栅距，m为衍射级次， 例如可以取±1、±2、±3等0以外的整数，ΔX为待测的衍射元件200沿X轴方向的位移。参照图5，该实施例中，利用与Z轴位移相关的两个输出光束采集的相位数据与图4对应的相位数据也相反。实际中具体采用哪种衍射级次方向进行光路设计，可以根据读头组件100的形状及安装空间等设计要求考量，并且，通过对应于不同自由度的输出光束所对应的干涉信号的相位变化信息，均可以获得衍射元件200在相应自由度的位移信息。由于多个输出光束在信号探测端合光之前均不共路，干涉信号质量不受器件分光不理想、偏振混叠等因素影响，位移测量装置的输出信号质量较好。
本实施例中，光源模块可以采用单频激光器实现，从而光源模块产生的上述第一输入光束610和第二输入光束611的频率相同。当采用单频激光器时，光源模块的尺寸较小，可以直接放在读头组件100附近，也可以通过光纤传输至读头组件100。或者，光源模块和光探测模块均可集成在读头组件100的内部，即形成可以实现光源输出、光束引导组合以及光探测的一体化结构，一体化结构使用场景灵活，可极大降低现场应用集成和维护难度，提高效率，适用于各种高、低精度位移测量场景中。
当读头组件100接收的两个输入光束为相同频率时，可以采用四通道移相检测方法实现相位探测，图6是本发明一实施例的位移测量装置输入光束为相同频率时的示意图。参照图6，用于接收第一输出光束613的第一光探测模块411和用于接收第三输出光束612的第三光探测模块410均包括四分之一波片、非偏振分光镜以及偏振分光镜的组合，以利用光学方法对干涉信号进行移相，得到依次相差90度的四路信号输出，用于后续位移计算。以第一光探测模块411为例，其包括四分之一波片481、非偏振分光镜482、第一偏振分光镜483、第二偏振分光镜484、第一光耦合器485、第二光耦合器486、第三光耦合器487以及第四光耦合器488，以执行上述四通道移相的功能。
采用四通道移相检测方法时，与衍射元件位移信息对应的输出光束中，两个分别对应于第一输入光束610和第二输入光束611的衍射光信号在输入光探测模块之前应满足偏振方向相互垂直(即正交)的要求。因而，可以设 置第一输入光束610和第二输入光束611到达读头组件100之前就具有彼此正交的偏振方向，也可以在被读头组件100接收之后，通过在读头组件100中沿第一输入光束610和第二输入光束611中的一个的光路上设置偏振控制元件，以便于输出至相应的光探测模块之前，输出光束包括的分别对应于第一输入光束610和第二输入光束611的两个衍射光束(或衍射光信号)的偏振方向正交，目的是使在进入光探测模块时两个衍射光束的偏振方向正交。所述偏振控制元件例如是波片或偏振片。
本实施例中，光源模块也可以采用光纤传输双频激光器实现，使产生的第一输入光束610和第二输入光束611的频率不同(通常二者频率差限定于较小范围内)。
图7是本发明一实施例的位移测量装置输入光束为不同频率时的示意图。参照图7，本实施例中，光源模块300为光纤传输双频激光器，所述光纤传输双频激光器的构造可包括以下光学元件：单频激光器311、隔离器322、第一声光频移器323、第二声光频移器324、第一分光镜330、第二分光镜331、第三分光镜332以及第四分光镜333、第一反射镜334、第二反射镜335、第一挡光板325、第二挡光板326以及第三挡光板327、第三光束角度控制器370、第一保偏光纤耦合器340、第二保偏光纤耦合器341以及多模光纤耦合器350。上述光纤传输双频激光器输出双频光束的原理如下。
单频激光器311产生的单频激光分为两束，分别通过两个驱动频率不同的声光频移器移频，产生频率分别为第一频率和第二频率的两束激光束，这两束激光束中大部分能量通过保偏光纤耦合器耦合，并通过保偏光纤输入读头组件100，而少部分能量通过反射镜，分光镜进行合束，形成激光器的参考光信号。其中光束角度控制器可用于辅助调整第一频率光束与第二频率光束合成激光器参考光信号，在另一实施例中，也可以使用第二偏振分光镜，或者光栅衍射方式进行合束。
经过上述光纤传输双频激光器，光源模块300输出的第一频率光束经第一保偏光纤470输入至第一保偏光纤准直器450，并进入读头组件100形成前述的第一输入光束610，光源模块300输出的第二频率光束经第二保偏光纤 471输入至第二保偏光纤准直器451，并进入读头组件100形成前述的第二输入光束611。为了得到不同自由度上的输出光束，第一输入光束611和第二输入光束611经读头组件100引导后，在衍射元件200的光接触面发生一次或两次衍射，从而可获得本实施例在前描述的第一输出光束613、第二输出光束614以及第三输出光束612，并分别通过第一光探测模块411、第二光探测模块412以及第三光探测模块410检测，第一光探测模块411将采集的第一输出光束613的干涉信号通过第一信号传输光纤431传输至信号分析模块500，第二光探测模块412将采集的第二输出光束614的干涉信号通过第二信号传输光纤432传输至信号分析模块500，第三光探测模块410将采集的第三输出光束612的干涉信号通过第三信号传输光纤430传输至信号分析模块500。此外，上述光纤传输双频激光器还输出一路基本参考光束，所述基本参考光束从多模光纤耦合器350出来后，不被读头组件100接收，而是直接通过信号传输光纤传输至信号分析模块500。
由于采用光纤传输双频激光束，光纤的相位随环境温度、压力、振动情况变化导致的相位变化需要补偿。参照图7，一种补偿的方法是在读头组件100的内部进行补偿，当光纤传输的双频光束重新准直为自由空间光束后，在入射至衍射元件200光接触面产生相位变化之前，可以通过分别由频率不同的第一输入光束610和第二输入光束611分出一小部分光能量，并进行合光而形成远程参考光信号(利用到的光学元件如图7中的第三反射元件132、第一分光元件133、第二分光元件134、第三分光元件135、第四光束角度控制器702、第四挡光板136)，并通过第四光探测模块413检测所述远程参考光信号，进而通过第四信号传输光纤433输出至信号分析模块500。信号分析模块500将通过第一输出光束613、第二输出光束614、第三输出光束612直接测得的对应不同自由度的位移信息分别与通过远程参考光信号对应的位移信息相减，即可获得不受光纤传输影响的实际不同自由度的位移信息。在另一实施例中，远程参考光信号也可以采用分光镜方式或者偏振分光镜方式获取，并且也可以采用光栅衍射方式实现两光束合光。本实施例中，可根据需要在读头组件100中设置一个或一个以上的光束角度控制器。参照图7，第一光束 角度控制器700可用于辅助调整入射读头组件100的具有不同频率的第一输入光束610和第二输入光束611平行，第三光束角度控制器702可用于辅助调整上述远程参考光信号的平行度。
位移测量装置的光源模块采用光纤传输双频激光器具有如下优点：
第一，在测量衍射元件位移时，两个频率的输入光束在信号探测端合光之前均不共路，干涉信号质量不受器件分光不理想、偏振混叠等因素影响，测量系统基本不存在非线性误差，因而不需要在光信号处理过程中补偿非线性误差；
第二，当光源模块输出的两入射频率光束的偏振方向相同时，所形成的水平向和垂向信号可直接探测，不需要在光相位采集部分用偏振片合成干涉信号，避免偏振片使用导致的能量损失，此次信号强度最佳，光功率利用率可达100％，并且对光束光学性能影响小，元件制造难度小，当两个输入光束的偏振方向不完全正交时，所形成的水平向和垂向信号也可直接探测，不需要在光相位采集部分放置偏振片，此时信号强度稍弱，光功率损耗稍大；当偏振方向正交时，所形成的水平向和垂向信号不能直接探测，需要在光探测模块前放置偏振片进行探测，由于偏振片的作用，此时光功率损耗约50％；
第三，利用光纤传输双频激光器作为光源模块，读头组件可以任意放置到所需测量位置，使用场景灵活，可极大降低现场应用集成和维护难度，提高效率，例如可用于将读头组件安装在运动台上跟随运动台移动，而衍射元件安装在固定不动的系统中。
为了提供不同频率的输入光束，本发明的位移测量装置中，光源模块也可包括自由空间双频激光器。图8是本发明另一实施例的位移测量装置输入光束为不同频率时的示意图。参照图8，该实施例中，光源模块300包括自由空间双频激光器，具体的，光源模块300可包括：自由空间双频激光器310、第二偏振分光镜321以及偏振态调节元件320。光源模块300利用自由空间双频激光器310输出双频光束的原理如下。
通常自由空间双频激光器含有两束频率稍有偏差的激光束：分别为第一频率的激光束和第二频率的激光束，且这两束激光束的偏振方向正交，设第 一频率的激光束偏振方向为S偏振，第二频率的激光束偏振方向为P偏振。当激光束经第二偏振分光镜321作用后，第一频率的S偏振光束在偏振分光面上发生反射，形成前述的第一输入光束610；第二频率的P偏振光束在偏振分光面上透射，并由第二偏振分光镜321的反射面反射后，与第一输入光束610平行但偏移了一定距离，该光束经偏振态调节元件320作用后，偏振方向由P偏振变为S偏振而形成前述的第二输入光束611。由此光源模块300可输出两束传播方向平行，且偏振方向相同的双频输入光束。
根据前面的描述，第一输入光束610和第二输入光束611被读头组件100接收后，经过其引导和组合，可形成第一输出光束613、第二输出光束614以及第三输出光束612，继而通过光探测模块进行检测以及通过信号分析模块可以获得衍射元件200在不同自由度的位移信息。由于使用第二偏振分光镜321进行分光，可能存在少量非线性误差，在此情况下，可通过对信号分析模块500的设计和选择，使其具有非线性误差补偿的光电探测及信号处理功能，以补偿上述少量的非线性误差。上述偏振态调节元件320可以采用一个二分之一波片、两个四分之一波片或者本领域公知的其它偏振控制和调节元件，以实现光束偏振态的改变。
上述采用了自由空间双频激光器的位移测量装置，由于光源模块较大，优选用于衍射元件200随运动台运动、读头组件固定不动的测量场景，从而实现衍射元件200在多个自由度的位移测量。此外，相对于上述光纤传输双频激光器的情形，光源模块采用自由空间双频激光器时，读头组件100不需要形成远程参考光信号，具有光路传输结构简单，测量轴数少的优点，可以提高装置的光功率利用率，降低结构复杂度。
本实施例还包括一种光刻设备，所述光刻设备包括可相对移动的晶片平台和掩模版平台。所述光刻设备包括上述位移测量装置。
光刻是半导体工艺的关键工艺，其工作包括引导空间图案辐射到涂覆光阻的晶片(例如玻璃或硅片)上，其中包括确定晶片的哪些位置接收辐射(称为“对准”)和哪些位置施加光辐射到光阻上(称为“曝光”)的过程，在引导晶片相对于空间图案辐射对准时，通常设置支撑涂覆有光阻的晶片的晶片 平台为可移动平台(包括平移和转动)，以移动晶片，从而光辐射至晶片的正确位置，在晶片平台移动时，定位掩模版的掩模版平台通常为静止，而基于不同设计的光刻设备中，在曝光期间，掩模版平台被设置为带动掩模版与晶片平台协同移动。光刻设备也是制作半导体器件及包括半导体器件的产品的重要工艺设备，例如可用于制造半导体芯片、液晶面板、OLED面板、CCD传感器等。
上述位移测量装置可以作为光刻设备的编码器系统，编码器系统用来在光刻设备的曝光工作中精确地测量晶片的位置。具体的，如图1至图8所示的衍射元件200(例如为光栅)可贴附于所述晶片平台或所述掩模版平台中的一个，读头组件100可贴附于所述晶片平台或所述掩模版平台中的另外一个。由于晶片平台和掩模版平台在光刻设备工作中相对移动，可以根据具体安装容许的重量及尺寸考虑具体光栅和读头组件的贴附方式。
由于上述位移测量装置具备宽角度适应性，可以提高位移测量装置以及编码器系统的角度容差，减小衍射元件偏转对干涉信息强度的影响，也有助于减小安装和姿态控制难度，减小甚至避免由于共光路结构导致的非线性误差，提高测量精度以及光刻设备的系统精度。
本实施例还包括一种位移测量方法，可采用上述位移测量装置。具体而言，所述位移测量方法包括以下步骤：
步骤一：提供一衍射元件，包括光接触面以及沿平行于所述光接触面的方向排布的多个重复衍射单元；
步骤二：获得第一输入光束和第二输入光束；
步骤三：引导所述第一输入光束和所述第二输入光束平行地接触所述衍射元件并均发生衍射，然后通过至少两个反向回射元件引导并组合经衍射的第一输入光束和第二输入光束以形成至少一个输出光束，每个所述输出光束包括从所述衍射元件的光接触面内的同一光斑位置出射且方向一致的分别对应于所述第一输入光束和所述第二输入光束的衍射光信号；
步骤四：检测所述输出光束；
步骤五：根据每个所述输出光束的干涉信号的相位变化信息获得所述衍 射元件的位移信息。
参照图1至图8，本实施例的位移测量方法中，第一输入光束610和第二输入光束611平行地接触衍射元件200时，第一输入光束610在第一光斑位置A发生一次衍射，第二输入光束611在第二光斑位置B发生衍射级次方向相同的一次衍射，对与第一输入光束610(另一实施方式为第二输入光束611)的一次衍射光束进行引导，使一次衍射光束在反向回射元件和衍射元件200被来回反射，例如依次被一个反向回射元件、衍射元件200、另一个反向回射元件反射回射后，在衍射元件200的光接触面再次反射，并在同一光斑位置与第二输入光束611(另一实施方式为第一输入光束610)至少部分重合并沿同一方向出射，从而形成第一输出光束613(另一实施方式为第二输出光束614)，第一输出光束613与第二输出光束614的干涉相位相反，第一输出光束613与第二输出光束614的干涉信号的相位变化信息反映了衍射元件200沿位于光接触面的法线方向的垂向自由度上的位移信息。第一输出光束613的干涉信号的相位变化与对应的衍射元件200的垂向位移之间满足本实施例前述的式(1)，第二输出光束614的干涉信号的相位变化与对应的衍射元件200的垂向位移之间满足本实施例前述的式(2)。
优选方案中，利用上述方法同时形成上述第一输出光束613和第二输出光束613，即实现了垂向双轴位移测量。在检测到第一输出光束613和第二输出光束614后，参照前述的式(4)，通过第一输出光束613和第二输出光束614的干涉信号所反映的所述衍射元件200在垂向自由度上的位移信息，一方面可以补偿环境对测量光路的影响，提升测量精度，另一方面还可以通过式(4)得到衍射元件200沿位于光接触面内的轴旋转的转动自由度的位移信息。
利用本实施例的位移测量方法不仅获得衍射元件200垂向自由度的位移信息，还可以获得衍射元件200水平自由度的位移信息(本实施例以图1中XY平面为“水平”)，具体说明如下。
在上述第一输入光束610和第二输入光束611平行地接触衍射元件200后，使第一输入光束610和第二输入光束611的一次衍射光束各自通过反向回射元件回射并再次接触衍射元件200，并均发生二次衍射，并且，对应于第 一输入光束610和第二输入光束611的二次衍射光束在衍射元件200光接触面的第三光斑位置C至少部分重合并沿同一方向出射而形成第三输出光束612，第三输出光束612的干涉信号的相位变化信息反映了衍射元件200沿平行于光接触面方向的水平自由度的位移信息。第三输出光束612的干涉信号的相位变化满足前述的式(3)。本实施例中，用于形成第三输出光束612的第一输入光束610和第二输入光束611的一次衍射光束的衍射级次方向相反，对应于同一输入光束，第二次衍射和第一次衍射的衍射级次方向相同。第三输出光束612中分别对应第一输入光束610和第二输入光束611的衍射光信号对应于同一衍射阶，例如第三输出光束612可包括对应第一输入光束610的+1阶二次衍射光束(或二次衍射光信号)和对应第二输入光束611的-1阶二次衍射光束(或二次衍射光信号)，或者，在另一实施例中，第三输出光束612可包括对应第一输入光束610的-1阶二次衍射光束和对应第二输入光束611的+1阶二次衍射光束。
通过适当组合两个或两个以上具有上述获得输出光束的过程，可以实现对衍射元件200在三个以上的自由度上的位移测量，例如可以实现对X轴方向、Y轴方向、Z轴方向、R X方向(即沿X轴偏转方向)、R y方向(即沿Y轴偏转方向)、R Z方向(即沿Z轴偏转方向)六个自由度的位移测量。
在获得诸如上述第一输出光束613、第二输出光束614、第三输出光束612等反映衍射元件200在不同自由度位移信息的输出光束后，可以利用光学探测(或相位探测)元件对所述输出光束进行检测，并进一步可以通过信号传输光纤将检测到的光信号进行分析，根据每个所述输出光束的干涉信号的相位变化信息获得衍射元件200在对应的自由度上的位移信息。
本实施例的位移测量方法，第一输入光束610和第二输入光束611平行地接触衍射元件200并均发生衍射(第一次衍射)后，经反射作用使分别对应于第一输入光束610和第二输入光束611的衍射光信号从衍射元件200的光接触面内的同一光斑出射且方向重合，从而形成独立的关联一个自由度上衍射元件位移信息的至少一个输出光束。通过多个输出光束可以获得衍射元件在不同自由度上的位移信息，不需要进行算法解耦，有利于消除衍射元件 偏转(例如相对于光接触面内轴的偏转)造成的相干光角度分离，减小衍射元件偏转对干涉信息强度的影响，提高测量精度，即具备了宽角度适应能力，同时也有助于提高应用该方法的位移测量装置的角度容差，减小装置的安装和姿态控制难度；并且，由于形成的多个输出光束之间相互独立，检测每个输出光束的干涉信号并分析可单独获得衍射元件在某一自由度(或方向)上的位移信息，有利于简化计算过程。此外，相对于通过同一输出光束进行算法解耦得到不同自由度上位移的测量方法来说，利用本实施例的位移测量方法可以显著减小甚至避免由于共光路结构导致的非线性误差。
本实施例的位移测量方法与上述位移测量装置基于一个总的构思，相关之处可参照关于位移测量装置的描述。
上述描述仅是对本发明较佳实施例的描述，并非对本发明权利范围的任何限定，任何本领域技术人员在不脱离本发明的精神和范围内，都可以利用上述揭示的方法和技术内容对本发明技术方案做出可能的变动和修改，因此，凡是未脱离本发明技术方案的内容，依据本发明的技术实质对以上实施例所作的任何简单修改、等同变化及修饰，均属于本发明技术方案的保护范围。

Claims (27)

  1. 一种位移测量装置，其特征在于，包括：
    光源模块，用于产生第一输入光束和第二输入光束；
    衍射元件，包括光接触面以及沿平行于所述光接触面的方向排布的多个重复衍射单元；
    读头组件，包括至少两个反向回射元件，所述读头组件用于接收所述第一输入光束和所述第二输入光束，并引导所述第一输入光束和所述第二输入光束平行地接触所述衍射元件的光接触面并均发生衍射，然后所述至少两个反向回射元件引导经衍射的第一输入光束和第二输入光束中的至少一者，使其与另一者组合形成至少一个输出光束，每个所述输出光束包括从所述衍射元件的光接触面内的同一光斑位置出射且方向一致的、分别对应于所述第一输入光束和所述第二输入光束的衍射光信号；
    光探测模块，用于检测每个所述输出光束；以及
    信号分析模块，与所述光探测模块连接，用于根据每个所述输出光束产生的干涉信号的相位变化信息获得所述衍射元件的位移信息。
  2. 如权利要求1所述的位移测量装置，其特征在于，所述读头组件引导所述第一输入光束和所述第二输入光束平行地接触所述衍射元件的光接触面时，所述第一输入光束在第一光斑位置发生一次衍射，所述第二输入光束在第二光斑位置发生一次衍射，所述第一输入光束的一次衍射光束经所述反向回射元件和所述衍射元件来回反射后，在所述第二光斑位置与所述第二输入光束的一次衍射光束至少部分重合并沿同一方向出射而形成第一输出光束；所述第一输出光束的干涉信号的相位变化信息反映了所述衍射元件沿光接触面的法线方向上的垂向自由度的第一位移信息。
  3. 如权利要求2所述的位移测量装置，其特征在于，所述读头组件引导所述第一输入光束和所述第二输入光束平行地接触所述衍射元件的光接触面时，所述第一输入光束在第一光斑位置发生一次衍射，所述第二输入光束在第二光斑位置发生一次衍射，所述第二输入光束的一次衍射光束经所述反向 回射元件和所述衍射元件来回反射后，在所述第一光斑位置与所述第一输入光束的一次衍射光束至少部分重合并沿同一方向出射而形成第二输出光束；所述第二输出光束的干涉信号的相位变化信息反映了所述衍射元件沿光接触面的法线方向上的垂向自由度的第二位移信息。
  4. 如权利要求3所述的位移测量装置，其特征在于，所述第一输出光束和所述第二输出光束均包括衍射级次方向相同且位于同一衍射阶且分别对应于所述第一输入光束和所述第二输入光束的一次衍射光信号；所述第一输出光束与所述第二输出光束的干涉相位相反。
  5. 如权利要求4所述的位移测量装置，其特征在于，所述第一输出光束包括所述第一输入光束和所述第二输入光束的+1衍射阶一次衍射光信号，所述第二输出光束包括所述第一输入光束和所述第二输入光束的-1衍射阶一次衍射光信号。
  6. 如权利要求3所述的位移测量装置，其特征在于，所述信号分析模块还用于根据所述第一输出光束和所述第二输出光束的干涉信号的相位变化信息，获得所述衍射元件沿以光接触面内的轴偏转的转动自由度的位移信息。
  7. 如权利要求1至5中任一项所述的位移测量装置，其特征在于，所述读头组件引导所述第一输入光束和所述第二输入光束平行地接触所述衍射元件的光接触面后，所述第一输入光束和所述第二输入光束的一次衍射光束分别通过所述反向回射元件回射并再次接触所述衍射元件，并均发生二次衍射，所述第一输入光束和所述第二输入光束的二次衍射光束在所述衍射元件的第三光斑位置至少部分重合并沿同一方向出射而形成第三输出光束；所述第三输出光束的干涉信号的相位变化信息反映了所述衍射元件沿平行于所述光接触面方向的水平自由度的第三位移信息。
  8. 如权利要求1所述的位移测量装置，其特征在于，所述衍射元件为一维光栅或二维光栅。
  9. 如权利要求1所述的位移测量装置，其特征在于，所述反向回射元件选自角锥棱镜、直角棱镜、猫眼反射器和道威棱镜中的一种。
  10. 如权利要求1所述的位移测量装置，其特征在于，所述读头组件包 括光束角度控制器。
  11. 如权利要求10所述的位移测量装置，其特征在于，所述光束角度控制器选自单个的楔角片、楔角片对、衍射光栅以及双折射元件中的一种。
  12. 如权利要求1所述的位移测量装置，其特征在于，所述第一输入光束和所述第二输入光束为频率不同的激光束。
  13. 如权利要求12所述的位移测量装置，其特征在于，所述光源模块包括光纤传输双频激光器；在沿平行方向接触所述衍射元件前，所述读头组件还用于对接收到的所述第一输入光束和所述第二输入光束分别进行分光并合光以形成一远程参考光束。
  14. 如权利要求12所述的位移测量装置，其特征在于，所述光源模块包括自由空间双频激光器和分光元件，其中，所述自由空间双频激光器用于产生双频光束，所述分光元件用于将所述双频光束分成两个偏振方向正交的光束。
  15. 如权利要求12至14中任一项所述的位移测量装置，其特征在于，所述光源模块或所述读头组件包括偏振控制元件，所述偏振控制元件用于使每个所述输出光束中分别对应于所述第一输入光束和所述第二输入光束的所述多个衍射光信号在进入所述光探测模块时的偏振方向相同。
  16. 如权利要求1所述的位移测量装置，其特征在于，所述第一输入光束和所述第二输入光束为频率相同的激光束。
  17. 如权利要求16所述的位移测量装置，其特征在于，所述光源模块或所述读头组件包括偏振控制元件，所述偏振控制元件用于使每个所述输出光束中分别对应于所述第一输入光束和所述第二输入光束的所述多个衍射光信号在进入所述光探测模块时的偏振方向正交。
  18. 如权利要求17所述的位移测量装置，其特征在于，所述读头组件形成至少四个输出光束，所述光探测模块在检测到所述至少四个输出光束后，还用于对每个所述输出光束的干涉信号进行移相，以输出依次相差90度的四路所述输出光束。
  19. 一种位移测量方法，其特征在于，包括：
    提供一衍射元件，包括光接触面以及沿平行于所述光接触面的方向排布的多个重复衍射单元；
    获得第一输入光束和第二输入光束；
    引导所述第一输入光束和所述第二输入光束平行地接触所述衍射元件的光接触面并均发生衍射，然后通过至少两个反向回射元件引导经衍射的第一输入光束和第二输入光束中的至少一者，使其与另一者组合形成至少一个输出光束，每个所述输出光束包括从所述衍射元件的光接触面内的同一光斑位置出射且方向一致的、分别对应于所述第一输入光束和所述第二输入光束的衍射光信号；
    检测所述输出光束；以及
    根据每个所述输出光束产生的干涉信号的相位变化信息获得所述衍射元件的位移信息。
  20. 如权利要求19所述的位移测量方法，其特征在于，所述第一输入光束和所述第二输入光束平行地接触所述衍射元件的光接触面时，所述第一输入光束在第一光斑位置发生一次衍射，所述第二输入光束在第二光斑位置发生一次衍射，所述第一输入光束的一次衍射光束经所述反向回射元件和所述衍射元件来回反射后，在所述第二光斑位置与所述第二输入光束的一次衍射光束至少部分重合并沿同一方向出射而形成第一输出光束；所述第一输出光束的干涉信号的相位变化信息反映了所述衍射元件沿光接触面的法线方向上的垂向自由度的第一位移信息。
  21. 如权利要求20所述的位移测量方法，其特征在于，所述第一输出光束的干涉信号的相位变化与所述衍射元件沿垂向自由度的位移满足关系式：
    Figure PCTCN2020086684-appb-100001
    其中，
    Figure PCTCN2020086684-appb-100002
    为所述第一输出光束的干涉信号的相位变化，ΔZ1为所述衍射元件在垂向自由度上的位移量，λ为所述第一输入光束和所述第二输入光束的波长平均值，θ为所述第一输入光束和所述第二输入光束平行地接触所述衍射元件的光接触面后发生的一次衍射的m级衍射角，m为0以外的整数。
  22. 如权利要求20所述的位移测量方法，其特征在于，所述第一输入光 束和所述第二输入光束平行地接触所述衍射元件的光接触面时，所述第一输入光束在第一光斑位置发生一次衍射，所述第二输入光束在第二光斑位置发生一次衍射，所述第二输入光束的一次衍射光束经所述反向回射元件和所述衍射元件来回反射后，在所述第一光斑位置与所述第一输入光束的一次衍射光束至少部分重合并沿同一方向出射而形成第二输出光束；所述第二输出光束的干涉信号的相位变化信息反映了所述衍射元件沿垂向自由度的第二位移信息；所述第一输出光束与所述第二输出光束的干涉相位相反。
  23. 如权利要求22所述的位移测量方法，其特征在于，还包括：
    在检测到所述第一输出光束和所述第二输出光束后，根据所述第一输出光束和所述第二输出光束的干涉信号所反映的所述衍射元件沿垂向自由度的位移信息，获得所述衍射元件沿以光接触面内的轴偏转的转动自由度的位移信息。
  24. 如权利要求23所述的位移测量方法，其特征在于，所述衍射元件与所述第一输出光束对应的位移和与所述第二输出光束对应的位移之间满足关系式：
    Figure PCTCN2020086684-appb-100003
    其中，ΔZ1和ΔZ2分别为所述第一输出光束反映的所述衍射元件沿垂向自由度的第一位移信息和所述第二输出光束反映的所述衍射元件沿垂向自由度的第二位移信息，D f1f2为所述第一光斑位置和所述第二光斑位置的间距。
  25. 如权利要求19至24中任一项所述的位移测量方法，其特征在于，所述第一输入光束和所述第二输入光束平行地接触所述衍射元件的光接触面后，使所述第一输入光束和所述第二输入光束的一次衍射光束分别通过所述反向回射元件回射并再次接触所述衍射元件，并均发生二次衍射，所述第一输入光束和所述第二输入光束的二次衍射光束在所述衍射元件的第三光斑位置至少部分重合并沿同一方向出射而形成第三输出光束；所述第三输出光束的干涉信号的相位变化信息反映了所述衍射元件沿平行于所述光接触面方向的水平自由度的第三位移信息。
  26. 如权利要求25所述的位移测量方法，其特征在于，所述第三输出光 束的干涉信号的相位变化与所述衍射元件在对应的水平自由度的位移满足关系式：
    Figure PCTCN2020086684-appb-100004
    其中，
    Figure PCTCN2020086684-appb-100005
    为所述第三输出光束的干涉信号的相位变化，ΔX为所述衍射元件在所述第一方向上的位移，P为所述衍射元件的多个重复衍射单元沿所述水平自由度方向的间距，m为0以外的整数。
  27. 一种光刻设备，所述光刻设备包括可相对移动的晶片平台和掩模版平台，其特征在于，所述光刻设备包括如权利要求1至18中任一项所述的位移测量装置，其中，所述衍射元件贴附于所述晶片平台或所述掩模版平台中的一个，所述读头组件贴附于所述晶片平台或所述掩模版平台中的另外一个。
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