WO2014059811A1 - 离轴对准系统及对准方法 - Google Patents

离轴对准系统及对准方法 Download PDF

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Publication number
WO2014059811A1
WO2014059811A1 PCT/CN2013/080800 CN2013080800W WO2014059811A1 WO 2014059811 A1 WO2014059811 A1 WO 2014059811A1 CN 2013080800 W CN2013080800 W CN 2013080800W WO 2014059811 A1 WO2014059811 A1 WO 2014059811A1
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WO
WIPO (PCT)
Prior art keywords
lens
beam splitter
splitter
incident
axis alignment
Prior art date
Application number
PCT/CN2013/080800
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English (en)
French (fr)
Inventor
张鹏黎
徐文
王帆
Original Assignee
上海微电子装备有限公司
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Application filed by 上海微电子装备有限公司 filed Critical 上海微电子装备有限公司
Priority to JP2015537121A priority Critical patent/JP6072267B2/ja
Priority to SG11201502974WA priority patent/SG11201502974WA/en
Priority to KR1020157010939A priority patent/KR101682171B1/ko
Priority to US14/434,079 priority patent/US9448488B2/en
Priority to EP13846613.1A priority patent/EP2911003B1/en
Publication of WO2014059811A1 publication Critical patent/WO2014059811A1/zh

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Classifications

    • 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
    • G03F7/70058—Mask illumination systems
    • G03F7/70141—Illumination system adjustment, e.g. adjustments during exposure or alignment during assembly of illumination system
    • 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
    • G03F9/00—Registration or positioning of originals, masks, frames, photographic sheets or textured or patterned surfaces, e.g. automatically
    • G03F9/70—Registration or positioning of originals, masks, frames, photographic sheets or textured or patterned surfaces, e.g. automatically for microlithography
    • G03F9/7088—Alignment mark detection, e.g. TTR, TTL, off-axis detection, array detector, video detection
    • 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
    • G03F9/00—Registration or positioning of originals, masks, frames, photographic sheets or textured or patterned surfaces, e.g. automatically
    • G03F9/70—Registration or positioning of originals, masks, frames, photographic sheets or textured or patterned surfaces, e.g. automatically for microlithography
    • G03F9/7003—Alignment type or strategy, e.g. leveling, global alignment
    • G03F9/7046—Strategy, e.g. mark, sensor or wavelength selection
    • 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
    • G03F9/00—Registration or positioning of originals, masks, frames, photographic sheets or textured or patterned surfaces, e.g. automatically
    • G03F9/70—Registration or positioning of originals, masks, frames, photographic sheets or textured or patterned surfaces, e.g. automatically for microlithography
    • G03F9/7069—Alignment mark illumination, e.g. darkfield, dual focus

Definitions

  • the present invention relates to a wafer alignment processing apparatus, and more particularly to an off-axis alignment system and alignment method therefor. Background technique
  • lithography equipment mostly uses an alignment system based on grating diffraction interference.
  • the basic features of this type of alignment system are: illumination of a single or multiple wavelength illumination beam is diffracted on a grating-type alignment mark, and the resulting diffracted light carries positional information about the alignment mark; beams of different orders Diffusion from the phase alignment grating at different diffraction angles, collecting the diffracted beams of each order by the alignment system, so that two symmetrical positive and negative diffraction orders (such as ⁇ 1, ⁇ 2, ⁇ 3, etc.) ) Intermittent coherence on the image plane or pupil plane of the alignment system to form interference signals at various levels.
  • the intensity variation of the interference signal is recorded by the photodetector, and the alignment center position is determined by signal processing.
  • an off-axis alignment system employed by ASML, the Netherlands, which uses a red, green, and dual light source in the source portion; and uses a wedge array or a wedge plate to Achieving overlapping and coherent imaging of the alignment mark multi-level diffracted light, and separating the imaging space on the image plane; the alignment signals of red and green light are separated by a polarizing beam splitting prism; The alignment light of the reference grating is obtained to obtain an alignment signal of the sinusoidal output.
  • the spectroscopic system can only separate the two wavelengths of color light, and the alignment signals of two wavelengths or more cannot be completed; secondly, the alignment system Multi-level diffracted light interferes on the image plane.
  • the alignment mark reflectance is uneven, the alignment error caused by the factors such as mark rotation and magnification error is large.
  • the alignment system uses the wedge array, the refraction is The shape and wedge angle consistency of the two wedges with positive and negative levels are very high, and the requirements for manufacturing, assembly and adjustment of the wedge plate group are also high. The specific implementation is difficult and costly.
  • the alignment system passes Two relative rotations 180 are produced by a rotating self-referencing interferometer.
  • the alignment mark image detects an interference signal of overlapping diffraction orders on the pupil plane, and obtains an alignment position signal according to the relative phase change of the detected interference signals of each level.
  • the alignment system adopts a rotating self-reference interferometer with multi-main section and spatial composite prism structure. The processing and mounting tolerance of the prism are very high, and the prism group is difficult to glue.
  • the beam is 180° overlapping interference, The spatial coherence of the illumination beam is relatively high and the implementation is difficult.
  • the object of the present invention is to provide an off-axis alignment system and an alignment method for solving the problem that the alignment mark tilt and defocus have a great influence on the detection result in the prior off-axis alignment system, and the illumination beam coherence requirement is relatively high. High or the need to use complex components such as wedge arrays to make the implementation difficult.
  • the present invention provides an off-axis alignment system, which in turn includes a lighting module, an interference module, and a detecting module according to a beam propagation path, the lighting module including a light source, a multi-wavelength incident fiber, and a beam splitting component;
  • the module includes a detecting lens group, a polarizing device, a detecting fiber, and a photodetector in sequence;
  • the interference module includes: a polarizing beam splitter having four sides, wherein the lighting module and the detecting module are both located in the polarizing beam splitter a first quarter wave plate and a first mirror, which are sequentially disposed on a second side of the polarization beam splitter opposite to the first side; a second quarter wave plate, a corner cube prism, a third side of the polarizing beam splitter; and a third quarter wave plate, a second mirror, and a lens, which are sequentially disposed on the fourth side of the polarizing beam splitter opposite to the third side On the side
  • the illumination module further comprises a shutter, an optical isolator and a phase modulator.
  • the light source is a laser.
  • the light source comprises at least four different wavelengths, two of which are in the infrared band.
  • the light source is a single frequency laser
  • the beam splitting element is a grating beam splitter or a fiber splitter or a planar optical waveguide power splitter.
  • the light source is a dual-frequency laser
  • the beam splitting element is a laser frequency splitter.
  • the laser frequency splitter is an electro-optic modulator or an acousto-optic modulator.
  • the polarizing means is one of a dichroic polarizer, a multi-layer coating based regular polarization beam splitter, and a birefringent beam splitter.
  • the present invention also provides an off-axis alignment method using the off-axis alignment system as described above, the off-axis alignment method comprising the steps of:
  • the light source emits a laser beam, and is divided into multi-wavelength multi-level illumination beams by the spectroscopic element, and the illumination beam is incident on the polarization beam splitter and is divided into a first beam and a second beam, the a light beam and a second light beam are respectively symmetrical with respect to an optical axis of the lens after being reflected by the mirror and the corner cube prism, and the first light beam and the second light beam are incident on the lens and are irradiated to the symmetrical incident angle to Aligning the mark, the first diffraction occurs;
  • Two diffracted beams pass through the lens, are reflected by a second mirror of the back focal plane of the lens, and the reflected beam is again incident on the alignment mark for a second diffraction;
  • the second diffracted beam After the second diffracted beam is collected by the lens, it passes through the polarization beam splitter, the corner cube and the first mirror again, and finally overlaps at the same position of the interface of the polarization beam splitter to form an interference signal;
  • the interference signal is incident on the photodetector via the detecting lens group and the polarizing device, respectively, and the photodetector determines information of the aligned position according to a phase change of the interference signal.
  • the incident beam passes through the alignment mark twice, and the second diffracted beam direction is completely opposite to the original incident direction to ensure that when the alignment mark is tilted and/or defocused , the detection results will not be affected;
  • the optical path structure is simple, no complicated optical components (wedge array, etc.) are used, and the volume is small, which facilitates assembly and integration.
  • FIG. 1 is a schematic structural view of an off-axis alignment system according to Embodiment 1 of the present invention.
  • Embodiment 2 is a schematic view of an optical path of Embodiment 1;
  • Figure 3 is a simplified optical path diagram of a corner cube
  • Figure 4 is a plan view of Figure 3;
  • Figure 5 is a schematic view showing the principle of the secondary mark 4 of the alignment mark
  • Figure 6 is a schematic view showing the optical path of the second diffraction in the case where the alignment mark is inclined;
  • FIG. 7 is a schematic diagram of an optical path of secondary diffraction in the case where the alignment mark is out of focus
  • Figure 8 is a schematic view showing the optical path of the second diffraction in the case where the alignment mark is inclined and out of focus;
  • Figure 9 is a schematic diagram of the splitting principle of the grating beam splitter
  • Figure 10 is a schematic diagram of the optical splitting principle of the fiber splitter
  • FIG. 11 is a schematic diagram of a splitting principle of a planar optical waveguide power splitter
  • Figure 12 is a front elevational view of the input/output end face of the polarization beam splitter in the case where the two directions are aligned;
  • Figure 13 is a schematic view showing the structure of the off-axis alignment system of the embodiment 2 of the present invention. detailed description
  • the off-axis alignment system provided by the present invention sequentially includes a lighting module 10, an interference module 20, and a detecting module 30 according to a beam propagation path, and the lighting module 10 and the detecting module 30 Located on the same side of the interference module 20, the illumination module 10 includes a light source (not shown), a multi-wavelength incident fiber 11 and a beam splitting element 12.
  • the light source is a laser because the brightness of the laser is high.
  • the light source is a single-frequency laser, and the emitted illumination beam is a linearly polarized light of a single frequency.
  • the illumination module 10 further includes a shutter (not shown), light.
  • the optical isolator being used to limit the direction of the beam so that the beam can only Passing in one direction
  • the phase adjuster is used for phase modulation of the illumination beam, effectively suppressing the coherence of the stray light and the signal light, reducing the contrast of the interference fringe, and improving the signal to noise ratio.
  • the spectroscopic element 12 is a grating.
  • the interference module 20 includes a polarization beam splitter 21, the polarization beam splitter 21 and the illumination module 10 and the detection module 30 a first quarter wave plate 22 and a first mirror 23 are disposed on the opposite side of the one side, and the second quarter wave plate 24 is sequentially disposed on the other two sides of the polarization beam splitter 21, respectively.
  • the detecting module 30 sequentially includes a detecting lens group 31, a polarizing device 32, a detecting fiber 33, and a photodetector 34.
  • the polarizing device 32 is one of a dichroic polarizer, a multi-layer coating based regular polarization beam splitter, and a birefringent beam splitter, such as a Savart plate, a ternary a light beam emitted by the illumination module 10 is diffracted twice by the interference module 20 to form an interference signal carrying the position information of the alignment mark 40, and finally incident on the detection module 30.
  • the detecting module 30 determines the alignment bit according to the phase change of the interference signal Information.
  • the present invention also provides an off-axis alignment method, with reference to Figures 1 and 2, employing an off-axis alignment system as described above, the off-axis alignment method comprising the steps of: the source emitting a laser beam through The multi-wavelength incident optical fiber 11 is transmitted, and is divided into multi-wavelength and multi-order illumination beams by the spectroscopic element 12, and the illumination beam 100 is a light beam of a certain wavelength thereof, and the polarization direction thereof and the light of the polarization beam splitter 21
  • the axial direction is at an angle of 45°, and the illumination beam 100 is incident on the polarization beam splitter 21 and is divided into a first beam 101a and a second beam 102a whose polarization directions are perpendicular to each other, and the first beam 101a is P-polarized.
  • the light is represented by a solid line and a solid arrow in FIG. 2, and the second light beam 102a is S-polarized light, which is indicated by a broken line and a hollow arrow in FIG. 2, and the first light beam 101a passes through the first quarter-wave plate.
  • 22 is incident on the first mirror 23, reflected by the first mirror 23, and passed through the polarization beam splitter 21 again, at which time the beam polarization direction is rotated by 90.
  • the alignment mark 40 When the alignment mark 40 is located on the front focal plane of the lens 28, and the alignment mark 40 is perpendicular to the optical axis of the lens 28, the light beams 101c and 102c become 101 d through the lens 28, respectively. 102d, and converge on the alignment mark 40, the incident angles of the beams 101d and 102d are symmetrically equal, and is equal to a diffraction angle of the order of the alignment marks 40, respectively generating the diffracted beam 101e of the order and 102e, the direction is perpendicular to the alignment mark 40, and the diffracted beams 101e and 102e are reflected by the mirror 27 located on the back focal plane 29 of the lens 28, incident on the alignment mark 40 again and diffracted again.
  • the secondary diffracted beams 101f and 102f are generated. Ideally, the second diffracted beams 101f and 102f are completely coincident with the optical paths of the original incident beams 101d and 102d, respectively, and are opposite in direction. In Fig. 2, the position is coincident for clearly indicating the transmission path. The opposite direction beams are shown separately.
  • the light beams 101c and 102c that are incident on the alignment mark 40 are both circularly polarized light.
  • the alignment mark 40 period is much larger than the illumination wavelength, the polarization selection is not important, but when the alignment mark 40 has a grating period
  • the wavelength of the illumination light is on the same order, the diffraction efficiency of the grating and the polarization of the illumination light sexually related, if linearly polarized light is incident, there is a risk that the diffraction efficiency of the grating will drop sharply in the polarization direction.
  • the risk can be effectively avoided by using circularly polarized light, which includes two lines perpendicular to each other. Polarized light ensures that there is always a polarization direction that produces highly efficient diffracted light.
  • illuminating the alignment marks with circularly polarized light can improve the adaptability of the alignment system to small period alignment targets.
  • the second-order diffracted beams 101f and 102f are collected by the lens 28 and then become P-polarized light 101g and S-polarized light 102g through the third quarter-wave plate 26, respectively, and the P-polarized light 101g passes through the polarization splitting beam.
  • the second quarter wave plate 24 is reflected by the corner cube prism 25 and passes through the second quarter wave plate 24 again to become S polarized light 101h.
  • the S polarized light 102g is reflected by the polarization beam splitter 21, passes through the first quarter-wave plate 22, is reflected by the first mirror 23, and passes through the first quarter-wave plate 22 to become P-polarized light.
  • the beams 101h and 102h are respectively reflected and transmitted at the same position of the polarization beam splitter 21, and simultaneously emitted from the left end surface of the polarization beam splitter 21 and become output beams 1101 and 1102.
  • the output beams 1101 and 1102 pass through the detecting lens group 31 to image the back focal plane 29 of the lens 28, and the polarization directions of the output beams 1101 and 1102 are perpendicular to each other without interference.
  • the The output beams 1101 and 1102 After passing through the polarizing device 32, the The output beams 1101 and 1102 have the same polarization direction, thereby Generate interference signal /,.
  • the interference signal is incident on the photodetector 34 via the probe fiber 33, and the photodetector 34 determines information on the alignment position based on a phase change of the interference signal /, .
  • the corner cube prism 25 has three mutually perpendicular reflecting surfaces, the bottom surface of which is an equilateral triangle, and the light incident from the bottom surface in any direction is sequentially reflected by the three reflecting surfaces. , is emitted from the bottom surface in the opposite direction to the incident ray (the internal optical path of the corner cube 25 is a simplified equivalent diagram).
  • the corner cube prism 25 has two functions in the alignment system: on the one hand, the beam is symmetrically reflected, and the beam 102a passes through the corner cube 25 to produce a reflected beam 102b.
  • the beams 102a and 102b are opposite in direction and positioned.
  • the corner cube 25 realizes the light beam 180. Rotating, first, the beam 102a is rotated 180. Then, the light beam 102b is turned; secondly, the second-diffracted light beam 101g passing through the alignment mark 40 is rotated by 180.
  • the beam 101h is changed, and the beam 102b is secondarily diffracted by the alignment mark 40 to generate the beam 102g, but no rotation occurs, and finally the two beams 101h and 102h output from the left end surface of the polarization beam splitter 21 have no relative rotation.
  • the originally input illumination beam 100 does not require strict spatial coherence.
  • the other beam of light 10 is the normalization parameter of the light field, which is the coordinate of the center point of the 102f light field on the pupil plane (spectral plane), and the coordinates are the same as the coordinates of the incident beam 102c at the back focal plane 29 of the lens, and the correlation analysis It will be given below. Similar to the beam 102f, the other beam of light 10 If the light field can be expressed as:
  • the intensity of the interference signal generated is:
  • said interference signal As can be seen from equation (5), said interference signal; the period of the alignment mark period 1 / 4 ⁇ , i.e. the optical magnification 4 ⁇ , double magnification optics are aligned prior art, using the same detection level In the second case, the resolution is also doubled.
  • the angle between the beam 102d and the normal of the alignment mark 40 becomes -, and the diffracted beam 102e is indicated by a broken line in the figure, and the alignment mark "The angle between the normals of the ⁇ " is: a - arcsin sin(6* - ⁇ ) ( 7 ) p )
  • the alignment mark 40 when the alignment mark 40 is out of focus ⁇ , that is, the alignment mark 40 is not on the front focal plane of the lens 28, the incident beam 102d produces Aztan on the alignment mark 40.
  • the secondary diffracted beam can be returned in the opposite direction to the original incident beam even in the case where the alignment mark is tilted and/or defocused.
  • the position of the spot on the back focal plane of the lens does not change after the secondary diffracted beam passes through the lens. Therefore, the final alignment result is not affected by the mark tilt and/or defocus.
  • the beam splitting element 12 is a grating beam splitter or a fiber splitter or a planar optical waveguide power splitter.
  • multi-beam illumination can be used on the incident end face, and separated by the spectroscopic element 12
  • Multiple incident beams enable multiple levels of detection.
  • the beam splitting element 12 is a grating beam splitter, including a transmissive phase grating 121 and a collimating lens 122, and adjusts the output beam " n , a i2 , a by the arrangement of parameters such as grating period and groove depth. Strength ratio.
  • the beam splitting element 12 is a fiber splitter, and the figure is a fused taper beam splitter 123, which bundles a plurality of fibers together, and then melts and stretches on a taper, and monitors during stretching.
  • Each fiber has a fiber-coupled splitting ratio, and the splitting ratio is completed, and the melt stretching is completed.
  • One end of the fiber is retained (the other is cut off) as an input end, and the other end is used as a multi-output.
  • the beam splitting element 12 is a planar optical waveguide power splitter, and the splitting function is performed in the chip 124.
  • each incident beam is at the back focal plane of the lens.
  • the distance between the position and the optical axis of the lens 28 must satisfy the following formula: arcta ( 9 )
  • the input/output end faces of the polarization beam splitter 21 are as shown in the figure, and the input beam, ⁇ ⁇ 1 in the X direction, realizes multi-wavelength multi-level detection. , with the output beam, ⁇ ⁇ 2. 180 ° rotational symmetry; ⁇ direction has an input beam, 2 , a xi , and the output beam ⁇ , I y2 , 180 ° rotational symmetry.
  • the light source is a dual-frequency laser
  • the beam splitting element 52 is a laser frequency splitter.
  • the laser frequency splitter is an electro-optic modulator or an acousto-optic modulator.
  • the off-axis alignment system provided by the present invention includes a lighting module 50, an interference module
  • the sounding module 50 and the detecting module 70 are located on the same side of the interference module 60.
  • the lighting module 50 includes a light source (not shown), a multi-wavelength incident fiber 51, and a beam splitting element 52.
  • the light source in the embodiment 2 is a dual-frequency laser, and the beam splitting element 52 is a laser frequency splitter.
  • the laser frequency splitter is an electro-optic modulator or an acousto-optic modulator; the interference module 60 includes a polarization component.
  • the polarizing beam splitter 61 is provided with a first quarter wave plate 62 and a first mirror 63 in a side opposite to a side where the illumination module 50 and the detecting module 70 are located, the polarization
  • the other two sides of the beam splitter 61 are respectively provided with a second quarter wave plate 64 and a corner cube prism 65.
  • the bottom surface of the corner cube 65 is located on the optical axis of the lens 68.
  • the detecting module 70 sequentially includes a detecting lens group 71, a polarizing device 72, a detecting fiber 73, and a photodetector 74.
  • the lighting module 50 The emitted light beam is twice diffracted by the interference module 60 to form position information of the interference signal carrying the alignment mark 50, and finally incident to the detecting module 70, and the detecting module 70 determines the phase change according to the interference signal. Align position information.
  • the laser frequency splitter splits the laser into two beams having a frequency difference of one another and a polarization perpendicular to each other.
  • EOM electro-optic modulator
  • the output beam of the light source is 45 with the fast axis direction of the EOM.
  • Angle of linearly polarized light E, ", EOM loading angle frequency is" half-wave voltage / 2
  • the output optical field Jones vectors having ⁇ ⁇ (Jones vectors) relationship namely: the column constituted by two orthogonal components
  • the matrix represents a plane vector.
  • Output light field E. Ut includes the light field E in both the horizontal and vertical polarization directions. x and E. y , the reflected beam and the transmitted beam are respectively generated after entering the polarization beam splitter 61, and then the transmission, diffraction, and interference processes of the reflected beam and the transmitted beam are the same as in Embodiment 1.
  • the final output of the detection signal is as follows
  • the present invention provides an off-axis alignment system and method.
  • the system includes a lighting module, an interference module, and a detection module.
  • the illumination module and the detection module are located on the same side of the interference module, and the illumination module includes a light source, a multi-wavelength incident fiber, and a beam splitting element;
  • the interference module includes a polarizing beam splitter, the polarizing beam splitter is provided with a first quarter-wave plate and a first mirror on a side opposite to a side where the illumination module and the detecting module are located, and the polarizing beam splitter is
  • the second side is respectively provided with a second quarter wave plate, a corner cube prism and a third quarter wave plate, a second mirror and a lens, and the second mirror is located on the back focal plane of the lens.
  • An alignment mark is located on the other side of the lens, and a center of a bottom surface of the corner cube is located on an optical axis of the lens;
  • the detection module includes a detection lens group, a polarization device, a detection fiber, and a photodetector in sequence.
  • the light beam emitted by the illumination module is diffracted twice by the interference module to form position information of the interference mark carrying the alignment mark, and finally incident to the detection module, and the detection module determines the pair according to the phase change of the interference signal. Quasi-position information.
  • the invention solves the problem that the alignment mark tilt and defocus have a great influence on the detection result in the existing off-axis alignment system, and the illumination beam coherence is required to be high or a complicated component such as a wedge array is needed. Implement difficult questions.
  • the spirit and scope of the invention Thus, it is intended that the present invention cover the modifications and the modifications of the invention

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Abstract

公开了一种离轴对准系统，按光束传播路径依次包括照明模块（10）、干涉模块（20）及探测模块（30），干涉模块（20）包括：具有四个侧面的偏振分束器（21），照明模块（10）和探测模块（30）均位于偏振分束器（21）的第一侧；第一1/4波片（22）和第一反射镜（23），依次位于与第一侧相对的第二侧；偏振分束器（21）的另外两侧分别设有第二1/4波片（24）、角锥棱镜（25）和第三1/4波片（26），第二反射镜（27）及透镜（28），第二反射镜（27）位于透镜（28）的后焦面上，角锥棱镜（25）的底面中心位于透镜（28）的光轴上。还公开了一种离轴对准方法。

Description

离轴对准系统及对准方法 技术领域
本发明涉及一种硅片对准的处理装置， 尤其涉及一种离轴对准系统及其 对准方法。 背景技术
目前， 光刻设备大多采用基于光栅衍射干涉的对准系统。 该类对准系统 基本特征为： 包含单波长或多波长的照明光束照射在光栅型对准标记上发生 衍射， 产生的各级衍射光携带有关于对准标记的位置信息； 不同级次的光束 以不同的衍射角从相位对准光栅上散开， 通过对准系统收集各级次的衍射光 束， 使两个对称的正负衍射级次（如 ±1级、 ±2级、 ±3级等）在对准系统的像 面或瞳面重叠相干， 形成各级干涉信号。 当对对准标记进行扫描时， 利用光 电探测器记录干涉信号的强度变化， 通过信号处理， 确定对准中心位置。
现有技术中具有代表性的是荷兰 ASML公司采用的一种离轴对准系统， 该对准系统在光源部分采用红光、 绿光双光源照射； 并采用楔块列阵或楔板 组来实现对准标记多级衍射光的重叠和相干成像， 并在像面上将成像空间分 开； 红光和绿光的对准信号通过一个偏振分束棱镜来分离； 通过探测对准标 记像透过参考光栅的透射光强， 得到正弦输出的对准信号。 该对准系统存在 的缺陷： 首先， 由于该系统采用偏振分束棱镜的分光系统只能分离两个波长 的色光， 对两个波长以上的对准信号则无法完成； 其次， 该对准系统的多级 衍射光在像面干涉， 在对准标记反射率不均勾时， 标记旋转、 倍率误差等因 素导致的对准误差较大； 最后， 该对准系统使用楔块列阵时， 对折射正、 负 相同级次的两楔块的面型和楔角一致性要求很高， 而楔板组的加工制造、 装 配和调整的要求也很高， 具体实施工程难度较大， 成本高。
另外一种现有技术也是荷兰 ASML公式采用的离轴对准系统。 该系统通 过一个旋转自参考干涉仪产生两个相对旋转 180。的对准标记像， 在光瞳面探 测重叠衍射级的干涉信号， 根据探测到的各级次干涉信号的相对相位变化得 到对准位置信号。 该对准系统采用了多主截面、 空间复合棱镜结构的旋转自 参考干涉仪， 棱镜的加工和装调公差要求很高， 棱镜组胶合难度较大， 同时， 由于光束是相对旋转 180°重叠干涉， 对照明光束的空间相干性要求较高， 实 施难度也较大。
因此， 如何提供一种既能够避免对照明光束空间相干性的要求、 消除对 准标记倾斜、 离焦对探测结果的影响， 且光路结构简单、 避免使用复杂光学 元件、 容易实现的离轴对准系统及对准方法是本领域技术人员亟待解决的一 个技术问题。 发明内容
本发明的目的在于提供一种离轴对准系统及对准方法， 以解决现有离轴 对准系统中对准标记倾斜、 离焦对探测结果的影响较大， 对照明光束相干性 要求较高或需要使用楔块列阵等复杂元件而使实施难度大的问题。
为解决上述技术问题， 本发明提供一种离轴对准系统， 按光束传播路径 依次包括照明模块、 干涉模块以及探测模块， 所述照明模块包括光源、 多波 长入射光纤以及分光元件； 所述探测模块依次包括探测透镜组、 偏振装置、 探测光纤以及光电探测器； 所述干涉模块包括： 偏振分束器， 具有四个侧面， 所述照明模块和探测模块均位于所述偏振分束器的第一侧；第一 1/4波片和第 一反射镜， 依次设在与所述第一侧相对的所述偏振分束器的第二侧； 第二 1/4 波片、 角锥棱镜， 依次设在所述偏振分束器的第三侧； 和第三 1/4波片、 第二 反射镜以及透镜， 依次设在与所述第三侧相对的所述偏振分束器的第四侧， 所述第二反射镜位于所述透镜的后焦面上， 所述角锥棱镜的底面中心位于所 述透镜的光轴上。
较佳地， 所述照明模块还包括快门、 光隔离器和相位调制器。 较佳地， 所述光源为激光器。
较佳地， 所述光源至少包含四个不同波长， 其中有两个波长在红外波段。 较佳地， 所述光源为单频激光器， 所述分光元件为光栅分束器或光纤分 束器或平面光波导功率分光器。
较佳地， 所述光源为双频激光器， 所述分光元件为激光频率分裂器。 较佳地 , 所述激光频率分裂器为电光调制器或声光调制器。
较佳地， 所述偏振装置为二向色偏振器、 基于多层涂层的正则偏振分光 器、 双折射分光器中的一种。
本发明还提供了一种离轴对准方法， 采用如上所述的离轴对准系统， 所 述离轴对准方法包括如下步骤：
所述光源发出激光束， 经所述分光元件分为多波长多级次的照明光束， 所述照明光束入射至所述偏振分束器并被分为第一光束和第二光束， 所述第 一光束和第二光束分别经所述反射镜和角锥棱镜的反射后关于所述透镜的光 轴对称， 所述第一光束和第二光束入射至所述透镜后以对称的入射角照射至 对准标记， 发生第一次衍射；
两束衍射光束通过所述透镜， 被所述透镜后焦面的第二反射镜反射， 反 射后的光束再次入射到所述对准标记发生第二次衍射；
二次衍射光束被所述透镜收集后， 再次经过所述偏振分束器、 角锥棱镜 以及第一反射镜， 最终在所述偏振分束器的分界面相同位置重叠， 形成干涉 信号；
所述干涉信号分别经所述探测透镜组及偏振装置入射至所述光电探测 器， 所述光电探测器根据所述干涉信号的相位变化确定对准位置的信息。
本发明具有如下有益效果：
1.采用光栅二次衍射技术， 入射光束先后两次经过所述对准标记， 且第二 次衍射光束方向与原入射方向完全相反， 以确保当所述对准标记倾斜和 /或离 焦时， 探测结果不会受到影响； 2.采用角锥棱镜实现入射光束的对称反射和 180。旋转，从而消除系统对照 明光束空间相干性的要求；
3.光路结构简单， 没有使用复杂的光学元件（楔块列阵等）， 体积小， 便 于装调和集成。 附图说明
图 1为本发明实施例 1离轴对准系统的结构示意图；
图 2为实施例 1的光路示意图；
图 3为角锥棱镜的简化光路示意图；
图 4为图 3的俯视图；
图 5为对准标记二次 4汙射的原理示意图；
图 6为对准标记倾斜的情况下二次衍射的光路示意图；
图 7为对准标记离焦的情况下二次衍射的光路示意图；
图 8为对准标记倾斜且离焦的情况下二次衍射的光路示意图；
图 9为光栅分束器分光原理示意图；
图 10为光纤分束器分光原理示意图；
图 11为平面光波导功率分光器分光原理示意图；
图 12为两个方向对准的情况下， 偏振分束器输入 /输出端面的正视图； 图 13为本发明实施例 2离轴对准系统的结构示意图。 具体实施方式
为使本发明的上述目的、 特征和优点能够更加明显易懂， 下面结合附图 对本发明的具体实施方式做详细的说明。
实施例 1
本发明提供的离轴对准系统， 如图 1 所示， 按光束传播路径依次包括照 明模块 10、 干涉模块 20以及探测模块 30, 所述照明模块 10和探测模块 30 位于所述干涉模块 20的同侧， 所述照明模块 10包括光源 （图中未示出）、 多 波长入射光纤 11以及分光元件 12, 较佳地， 所述光源为激光器， 因为激光的 亮度高、 方向性好， 实施例 1 中所述光源为单频激光器， 发出的照明光束为 单一频率的线偏振光， 较佳地， 所述照明模块 10还包括快门 （图中未示出）、 光隔离器（图中未示出）和相位调制器（图中未示出）， 所述快门用于在需要 时阻挡照明光束， 所述光隔离器用于对光束的方向进行限制， 使光束只能单 方向通过， 所述相位调节器用于照明光束的相位调制， 可有效抑制杂散光与 信号光的相干性， 降低干涉条纹的对比度， 提高信噪比， 较佳地， 所述分光 元件 12为光栅分束器或光纤分束器或平面光波导功率分光器； 所述干涉模块 20包括偏振分束器 21 ,所述偏振分束器 21与所述照明模块 10和探测模块 30 所在的一侧相对的一侧依次设有第一 1/4波片 22和第一反射镜 23 , 所述偏振 分束器 21的另外两侧分别依次设有第二 1/4波片 24、 角锥棱镜 25和第三 1/4 波片 26、 第二反射镜 27以及透镜 28, 所述第二反射镜 27位于所述透镜 28 的后焦面上， 对准标记 40位于所述透镜 28的另一侧， 所述角锥棱镜 25的底 面中心位于所述透镜 28的光轴上；所述探测模块 30依次包括探测透镜组 31、 偏振装置 32、 探测光纤 33以及光电探测器 34, 较佳地， 所述偏振装置 32为 二向色偏振器、 基于多层涂层的正则偏振分光器、 双折射分光器中的一种， 如萨伐尔板（ Savart plate )、 三元渥拉斯顿棱镜（ Wollaston prism )等， 所述照 明模块 10发出的光束经所述干涉模块 20两次衍射， 形成干涉信号携带所述 对准标记 40的位置信息， 最终入射至所述探测模块 30, 所述探测模块 30根 据所述干涉信号的相位变化确定对准位置信息。
较佳地， 所述光源至少包含四个不同波长， 其中有两个波长在红外波段， 例如： = 532nm、 Λ2 = 632 m、 Λ3 = 780nm、 Λ4 = 850腿 , 利用多波长光源照 明， 可以有效抑制干涉相消效应的影响， 提高工艺适应性； 使用近红外和远 红外波长的光源照明， 可以有效解决低 k值介质材料在可见光语范围的吸收 问题， 并可用于多晶硅工艺层的标记探测， 从而提高对准信号强度。 本发明还提供了一种离轴对准方法，请参考图 1和图 2, 采用如上所述的 离轴对准系统， 所述离轴对准方法包括如下步骤： 所述光源发出激光束通过 所述多波长入射光纤 11传输， 经所述分光元件 12分为多波长多级次的照明 光束， 照明光束 100为其中某个波长 的光束， 其偏振方向与所述偏振分束器 21的光轴方向成 45°夹角， 所述照明光束 100入射至所述偏振分束器 21并被 分为偏振方向相互垂直的第一光束 101a和第二光束 102a,所述第一光束 101a 为 P偏振光， 由图 2中的实线及实心箭头表示， 所述第二光束 102a为 S偏振 光， 由图 2中的虚线及空心箭头表示， 所述第一光束 101a经过第一 1/4波片 22进行消色差处理后入射至所述第一反射镜 23 , 被所述第一反射镜 23反射 后再次通过所述偏振分束器 21 , 此时光束偏振方向旋转了 90。， 变为 S偏振 光 101b, 光束 101b被所述偏振分束器 21反射经所述第三 1/4波片 26, 转变 为圓偏振光 101c; 所述第二光束 102a经所述第二 1/4波片 24转变为 P偏振 光 102b, 该 P偏振光 102b透过所述偏振分束器 21 , 经所述第三 1/4波片 26 转变为圓偏振光 102c, 所述光束 101c和 102c关于所述透镜 28的光轴对称。
当所述对准标记 40位于所述透镜 28的前焦面， 且所述对准标记 40垂直 于所述透镜 28的光轴时， 光束 101c和 102c通过所述透镜 28分别变为 101 d 和 102d,并汇聚于所述对准标记 40上，光束 101d和 102d的入射角对称相等， 且等于所述对准标记 40某个级次的衍射角^ 则分别产生该级次的衍射光束 101e和 102e, 其方向垂直于所述对准标记 40, 所述衍射光束 101e和 102e被 位于透镜 28后焦面 29上的反射镜 27反射后， 再次入射到所述对准标记 40 并再次发生衍射， 产生二次衍射光束 101f和 102f, 理想情况下， 所述二次衍 射光束 101f和 102f分别与原入射光束 101d和 102d光路完全重合且方向相反， 图 2中， 为清晰表明传输光路， 将位置重合、 方向相反的光束分开示出。
这样， 照射到所述对准标记 40的光束 101c和 102c均为圓偏振光， 当对 准标记 40周期远大于照明波长时， 偏振选择并不重要， 但当所述对准标记 40 的光栅周期与照明光波长在相同量级时， 光栅的衍射效率与照明光的偏振特 性有关， 如果采用线偏振光入射， 可能面临光栅的衍射效率在该偏振方向上 急剧下降的风险， 此处利用圓偏振光照明可有效避免该风险， 圓偏振光包含 两个方向相互垂直的线偏振光， 确保总有一偏振方向可以产生高效率的衍射 光。 因而， 采用圓偏振光照射对准标记可提高所述对准系统对小周期对准标 "^己的适应性。
二次衍射光束 101f和 102f被所述透镜 28收集后分别经过所述第三 1/4 波片 26变为 P偏振光 101g和 S偏振光 102g, 所述 P偏振光 101g通过所述 偏振分束器 21 , 经过所述第二 1/4波片 24被所述角锥棱镜 25反射后再次经 过所述第二 1/4波片 24, 变为 S偏振光 101h; 同时， 所述 S偏振光 102g被所 述偏振分束器 21反射， 经过所述第一 1/4波片 22后被所述第一反射镜 23反 射，再次经过所述第一 1/4波片 22变为 P偏振光 102h,所述光束 101h和 102h 分别在所述偏振分束器 21的相同位置发生反射和透射， 并同时从所述偏振分 束器 21的左端面射出并变为输出光束 1101和 1102,所述输出光束 1101和 1102 经过所述探测透镜组 31 , 对所述透镜 28后焦面 29成像， 所述输出光束 1101 和 1102偏振方向相互垂直， 不发生干涉， 经过所述偏振装置 32后， 所述输出 光束 1101和 1102具有相同的偏振方向， 从而产生干涉信号 /,.。
所述干涉信号 ,·经所述探测光纤 33入射至所述光电探测器 34, 所述光电 探测器 34根据所述干涉信号 /,·的相位变化确定对准位置的信息。
具体地， 请参考图 3和图 4, 所述角锥棱镜 25具有三个相互垂直的反射 面， 其底面呈等边三角形， 从底面以任意方向入射的光线， 经过三个反射面 依次反射后， 以与入射光线相反的方向从底面射出 （图中角锥棱镜 25内部光 路是简化的等效示意图）。 所述角锥棱镜 25在所述对准系统中具有两方面作 用： 一方面是实现光束对称反射， 光束 102a经过所述角锥棱镜 25后产生反 射光束 102b, 光束 102a和 102b方向相反、 且位置关于角锥棱镜 25底面中心 对称， 由于所述角锥棱镜 25底面中心位于所述透镜 28的光轴上， 光束 102a 和 102b是关于透镜 28的光轴对称的， 从而保证光束 101d和 102d在所述对 准标记 40上的入射角大小相等； 另一方面， 所述角锥棱镜 25实现光束 180。 旋转， 首先使光束 102a旋转 180。， 变为光束 102b; 其次使经过所述对准标记 40的二次衍射后的光束 101g旋转 180。， 变为光束 101h, 光束 102b经所述对 准标记 40二次衍射后产生光束 102g,但不会发生旋转， 最终从所述偏振分束 器 21左端面输出的两光束 101h和 102h没有相对旋转， 因此原始输入的照明 光束 100不需要严格的空间相干性。
请参考图 5 , 假设入射光束 102c在所述透镜后焦面 29的坐标为 ， 频率 带宽为 , 透镜 28焦距为 f , 光束 102c中心距离所述透镜 28光轴的距离 为 ί ， 则光束 102d的入射角度 6>的计算公式为：
Θ - arctan—
f ( 1 ) 由此可知， 通过调节参量 ί ， 使所述光束 102d的入射角等于所述对准标 记 40的某个级次的衍射角， 即满足光栅方程： sin ^ ± ^
P ( 2 ) 其中 P为对准标记周期， n为正整数， A为该照明光束 102c的波长。 此 时， 所述光束 102d经所述对准标记 40衍射后， 将产生近似平行于光轴的 n 级 (或 -n级 )衍射光 102e, 其经所述透镜 28汇聚到所述反射镜 27, 反射光 束经所述透镜 28后， 以与衍射光 102e相反的方向入射到所述对准标记 40 , 发生二次衍射， 产生光束 102f, 在理想情况下， 二次衍射光束 102f与入射光 束 102d完全重合。 二次 †射光束 102f携带对准标记 40的位置信息 X, 102f 光场 E2 ( 具有如下形式：
Figure imgf000010_0001
其中 4)为光场归一化参数， 是 102f光场的中心点在瞳面 （频谱面） 的 坐标， 且该坐标与入射光束 102c在透镜后焦面 29的坐标相同， 相关的分析 将在下文中给出。与光束 102f类似，另一束探测光 10 If光场 可表述为：
2n
Ε (-k0 ) = A0 ex (-7'2^— x) ( 4 )
P
当光束 101f、 102f通过偏振装置 32后， 产生的干涉信号强度 ,·为：
( 5 )
Figure imgf000011_0001
从（5 ) 式可以看出， 所述干涉信号 ;的周期为对准标记周期的 1/4η, 即 光学倍率为 4η, 比现有对准技术的光学倍率提高一倍， 在使用相同探测级次 情况下， 分辨率也增加一倍。
通过所述对准标记 40在 X方向的运动， 可获得探测信号 ,在 X方向的扫 描曲线， 利用计算机进行拟合处理， 可提取 /,·的相位
Figure imgf000011_0002
从而得到 对准标记的位置信息：
2π An ^ 当所述对准标记 40对称中心与所述透镜 28光轴重合， 即 x=0时， 所述 对准标记 40处于对准位置。
请参考图 6, 当对准标记倾斜角度为 时， 光束 102d相对于所述对准标 记 40的法线夹角变为 - ， 此时衍射光束 102e如图中虚线所示， 其与对准 标" ^己法线夹角为"： a - arcsin sin(6* - β) ( 7 ) p )
衍射光束 102e被所述反射镜 27反射， 经过所述透镜 28后与原入射方向 相反， 且位置重合， 产生二次衍射光束 102f与对准标记法线夹角 α'可由光栅 方程求得： a = arcsm
Figure imgf000011_0003
a θ— β ( 8 )
P 由 （8 ) 式可知， 二次衍射光束 102f与入射光束 102d完全重合， 经所述 透镜 28后， 在所述透镜后焦面 29处探测光斑也不会发生变化， 可见， 当所 述对准标记 40倾斜对探测结果没有影响。
请继续参考图 7, 当所述对准标记 40离焦 Δ 时， 即所述对准标记 40不 在所述透镜 28的前焦面上， 入射光束 102d在所述对准标记 40上产生 Aztan 的水平偏移，衍射光束 102e如图中虚线所示， 二次衍射光束 102f与原入射光 束 102d产生 A!, = 2Aztan 水平偏移， 但方向相反， 经所述透镜 28收集后， 在 所述透镜后焦面 29处探测光斑位置没有变化， 因而， 离焦也不会产生对准误 差。
请继续参考图 8, 当所述对准标记 40倾斜 角度， 同时偏移焦平面 Δζ时， 通过光栅方程和几何关系， 可以计算出二次衍射光束 102f 相对于入射光束 102d水平向偏移 ΔΙ2 = 2Az(tan 6>— tan ) ,其中 = arcsin[« I p - ύη(θ - β)] + β ^光束 102e与透镜 28光轴的夹角。 由于二次衍射光束 102f与 102d方向相反， 经所 述透镜 28收集后， 在所述透镜后焦面 29处探测光斑位置没有变化， 因而， 倾斜-离焦同样不会产生对准误差。
从前面分析可知， 利用探测光束的二次衍射， 即使在对准标记倾斜和 /或 离焦情况下， 也能使二次衍射光束沿与原入射光束相反的方向返回。 根据透 镜的特性可知， 只要二次衍射光束的方向与原入射光束相反， 即使存在水平 向偏移， 该二次衍射光束通过透镜后， 在透镜后焦面的光斑位置是不会发生 改变的， 因此， 最终的对准结果不受标记倾斜和 /或离焦的影响。
较佳地， 分光元件 12为光栅分束器或光纤分束器或平面光波导功率分光 器， 具体地， 为实现多级次探测， 可在入射端面采用多光束照射， 通过分光 元件 12分离出多个入射光束， 可实现多个级次探测。
如图 9所示， 所述分光元件 12为光栅分束器， 包括透射相位光栅 121和 准直透镜 122,通过光栅周期、槽深等参数的配置来调节输出光束《n、 ai2、 a 的强度比。
如图 10所示， 所述的分光元件 12为光纤分光器， 图中为熔融拉锥式分 光器 123 , 即将多根光纤捆在一起， 然后在拉锥机上熔融拉伸， 拉伸过程中监 控各路光纤耦合分光比， 分光比达到要求后结束熔融拉伸， 其中一端保留一 根光纤（其余剪掉）作为输入端， 另一端则作为多路输出端。
如图 11所示， 所述的分光元件 12为平面光波导功率分光器， 分光功能 在芯片 124 中完成， 根据公式（1 )和（2 )可知， 各入射光束在所述透镜后 焦面 29处位置与所述透镜 28光轴的距离需满足以下公式： arcta ( 9 )
Figure imgf000013_0001
请继续参考图 12, 当要实现 X、 Y两个方向对准时， 所述偏振分束器 21 输入 /输出端面如图所示， X方向有输入光束 、 αχ1、 实现多波长多级次探 测， 与输出光束 、 Ιχ2 . 180°旋转对称； Υ方向有输入光束 、 2、 axi , 与输出光束^、 Iy2、 180°旋转对称。
实施例 2
本实施例与实施例 1 的区别在于， 所述光源采用双频激光器， 所述分光 元件 52为激光频率分裂器， 较佳地， 所述激光频率分裂器为电光调制器或声 光调制器。
本发明提供的离轴对准系统， 如图 13所示， 包括照明模块 50、 干涉模块
60以及探测模块 70, 所述照明模块 50和探测模块 70位于所述干涉模块 60 的同侧， 所述照明模块 50包括光源 （图中未示出）、 多波长入射光纤 51以及 分光元件 52, 实施例 2中所述光源为双频激光器， 所述分光元件 52为激光频 率分裂器， 具体地， 所述激光频率分裂器为电光调制器或声光调制器； 所述 干涉模块 60包括偏振分束器 61 ,所述偏振分束器 61与所述照明模块 50和探 测模块 70所在的一侧相对的一侧依次设有第一 1/4波片 62和第一反射镜 63 , 所述偏振分束器 61 的另外两侧分别依次设有第二 1/4波片 64、 角锥棱镜 65 和第三 1/4波片 66、 第二反射镜 67以及透镜 68 , 所述第二反射镜 67位于所 述透镜 68的后焦面上， 对准标记 80位于所述透镜 68的另一侧， 所述角锥棱 镜 65的底面中心位于所述透镜 68的光轴上； 所述探测模块 70依次包括探测 透镜组 71、 偏振装置 72、 探测光纤 73以及光电探测器 74, 所述照明模块 50 发出的光束经所述干涉模块 60两次衍射，形成干涉信号携带所述对准标记 50 的位置信息， 最终入射至所述探测模块 70, 所述探测模块 70根据所述干涉信 号的相位变化确定对准位置信息。
所述激光频率分裂器， 可使激光分裂为频率相差为 、 且偏振相互垂直 的两个光束。 当所述激光频率分裂器为电光调制器（英文全称： electro-optic modulator, EOM ) 时， 其工作原理为： 光源的输出光束为与所述 EOM的快 轴方向成 45。角的线偏振光 E,„, EOM加载角频率为《的半波电压 /2 , 则输出 的光场^ ^具有琼斯矢量（Jones vectors )关系式， 即： 用两个正交分量构成的 列矩阵表示一个平面矢量。
Εοίΐί
Figure imgf000014_0001
Figure imgf000014_0003
输出光场 E。ut包括水平偏振和垂直偏振两个方向的光场 E。x和 E。y , 其进入 所述偏振分束器 61后分别产生反射光束和透射光束， 随后所述反射光束和透 射光束传输、 衍射、 干涉过程与实施例 1 相同。 最终输出的探测信号形式如 下
Figure imgf000014_0002
在角频率《已知的情况下， 对（11 )式中探测信号进行解调， 可获得其相 = 2π - ηχ Ι ρ , 从而计算出对准位置。
综上所述， 本发明提供的离轴对准系统及方法， 该系统包括照明模块、 干涉模块以及探测模块， 所述照明模块和探测模块位于所述干涉模块的同侧， 所述照明模块包括光源、 多波长入射光纤以及分光元件； 所述干涉模块包括 偏振分束器， 所述偏振分束器与所述照明模块和探测模块所在的一侧相对的 一侧依次设有第一 1/4波片和第一反射镜，所述偏振分束器的另外两侧分别依 次设有第二 1/4波片、 角锥棱镜和第三 1/4波片、 第二反射镜以及透镜， 所述 第二反射镜位于所述透镜的后焦面上， 对准标记位于所述透镜的另一侧， 所 述角锥棱镜的底面中心位于所述透镜的光轴上； 所述探测模块依次包括探测 透镜组、 偏振装置、 探测光纤以及光电探测器， 所述照明模块发出的光束经 所述干涉模块两次衍射， 形成干涉信号携带所述对准标记的位置信息， 最终 入射至所述探测模块， 所述探测模块根据所述干涉信号的相位变化确定对准 位置信息。 本发明很好的解决了现有离轴对准系统中对准标记倾斜、 离焦对 探测结果的影响较大， 对照明光束相干性要求较高或需要使用楔块列阵等复 杂元件而使实施难度大的问题。 发明的精神和范围。 这样， 倘若本发明的这些修改和变型属于本发明权利要 求及其等同技术的范围之内， 则本发明也意图包含这些改动和变型在内。

Claims

权利要求
1. 一种离轴对准系统， 其特征在于，按光束传播路径依次包括照明模块、 干涉模块以及探测模块， 其中：
所述照明模块包括光源、 多波长入射光纤以及分光元件；
所述探测模块依次包括探测透镜组、 偏振装置、 探测光纤以及光电探测 器；
所述干涉模块包括：
偏振分束器， 具有四个侧面， 所述照明模块和探测模块均位于所述 偏振分束器的第一侧；
第一 1/4波片和第一反射镜，依次设在与所述第一侧相对的所述偏振 分束器的第二侧；
第二 1/4波片、 角锥棱镜， 依次设在所述偏振分束器的第三侧； 和 第三 1/4波片、 第二反射镜以及透镜，依次设在与所述第三侧相对的 所述偏振分束器的第四侧， 所述第二反射镜位于所述透镜的后焦面上， 所述角锥棱镜的底面中心位于所述透镜的光轴上。
2. 如权利要求 1所述的离轴对准系统， 其特征在于， 所述照明模块还包 括快门、 光隔离器和相位调制器。
3. 如权利要求 1所述的离轴对准系统， 其特征在于， 所述光源为激光器。
4. 如权利要求 3所述的离轴对准系统， 其特征在于， 所述光源包含至少 四个不同波长， 其中有两个波长在红外波段。
5. 如权利要求 3所述的离轴对准系统， 其特征在于， 所述光源为单频激 光器， 所述分光元件为光栅分束器或光纤分束器或平面光波导功率分光器。
6. 如权利要求 3所述的离轴对准系统， 其特征在于， 所述光源为双频激 光器， 所述分光元件为激光频率分裂器。
7. 如权利要求 6所述的离轴对准系统， 其特征在于， 所述激光频率分裂 器为电光调制器或声光调制器。
8. 如权利要求 1所述的离轴对准系统， 其特征在于， 所述偏振装置为二 向色偏振器、 基于多层涂层的正则偏振分光器、 双折射分光器中的一种。
9. 一种离轴对准方法， 其特征在于， 采用如权利要求 1〜8中任意一项所 述的离轴对准系统， 所述离轴对准方法包括如下步骤：
所述光源发出激光束， 经所述分光元件分为多波长多级次的照明光束， 所述照明光束入射至所述偏振分束器并被分为第一光束和第二光束， 所述第 一光束和第二光束分别经所述反射镜和角锥棱镜的反射后关于所述透镜的光 轴对称， 所述第一光束和第二光束入射至所述透镜后以对称的入射角照射至 对准标记， 发生第一次衍射；
两束衍射光束通过所述透镜， 被所述透镜后焦面的第二反射镜反射， 反 射后的光束再次入射到所述对准标记发生第二次衍射；
二次衍射光束被所述透镜收集后， 再次经过所述偏振分束器、 角锥棱镜 以及第一反射镜， 最终在所述偏振分束器的分界面的一相同位置重叠， 形成 干涉信号；
所述干涉信号分别经所述探测透镜组及偏振装置入射至所述光电探测 器， 所述光电探测器根据所述干涉信号的相位变化确定对准标记的位置信息。
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