CN113448191B - Alignment system and photoetching machine - Google Patents
Alignment system and photoetching machine Download PDFInfo
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- CN113448191B CN113448191B CN202010224588.4A CN202010224588A CN113448191B CN 113448191 B CN113448191 B CN 113448191B CN 202010224588 A CN202010224588 A CN 202010224588A CN 113448191 B CN113448191 B CN 113448191B
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- 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
- G03F9/7049—Technique, e.g. interferometric
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- 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
- G03F9/7023—Aligning or positioning in direction perpendicular to substrate surface
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- 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
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- Length Measuring Devices By Optical Means (AREA)
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Abstract
The embodiment of the invention provides an alignment system and a photoetching machine, wherein the alignment system comprises: an alignment beam generating unit for generating an alignment beam; an objective lens; the alignment light beam passes through the objective lens and then is incident on the alignment mark to generate first-order diffraction light; the diffraction light retroreflection unit is positioned on one side of the objective lens, which is far away from the alignment mark, is arranged on at least one path of emergent light path of the primary diffraction light, and is used for reflecting the primary diffraction light incident to the diffraction light retroreflection unit to the alignment mark and generating secondary diffraction light; and interference information detection means provided on the light emission path of the primary diffracted light and the secondary diffracted light, for detecting the intensity of interference light of the primary diffracted light and the secondary diffracted light. The embodiment of the invention provides an alignment system and a photoetching machine, which aim to reduce the manufacturing and integration difficulty of an optical device in the alignment system and reduce the cost.
Description
Technical Field
The present invention relates to lithography, and more particularly, to an alignment system and a lithography machine.
Background
Lithographic projection apparatus can be used, for example, in the manufacture of Integrated Circuits (ICs). A critical step in the lithographic process is to align the substrate with the lithographic apparatus so that the projected image of the mask pattern is in the correct position on the substrate. Semiconductors and other devices due to photolithography require multiple exposures to form multiple layers in the device, and it is important that the layers be properly aligned. As smaller features are imaged, the requirements for overlap and, consequently, the accuracy of the alignment operation become more stringent.
In the existing alignment system, two images of the diffraction grating relative to each other by 180 degrees are generated by using a self-reference prism and are coherently superposed, and the alignment position is obtained by a signal after superposition. However, the self-reference prism has a high difficulty in processing and manufacturing, and the self-reference prism has a high requirement on the integration level, which increases the cost of the alignment system.
Disclosure of Invention
The embodiment of the invention provides an alignment system and a photoetching machine, which aim to reduce the manufacturing and integration difficulty of an optical device in the alignment system and reduce the cost.
In a first aspect, an embodiment of the present invention provides an alignment system, including:
an alignment beam generating unit for generating an alignment beam;
an objective lens; the alignment light beam is incident on the alignment mark after passing through the objective lens and generates first diffraction light;
the diffraction light retroreflection unit is positioned on one side of the objective lens, which is far away from the alignment mark, is arranged on at least one path of emergent light path of the primary diffraction light, and is used for reflecting the primary diffraction light incident to the diffraction light retroreflection unit to the alignment mark and generating secondary diffraction light;
and interference information detection means provided on the light emission path of the primary diffracted light and the secondary diffracted light, for detecting the intensity of interference light of the primary diffracted light and the secondary diffracted light.
Optionally, the diffraction light retroreflection unit includes a quarter wave plate and a mirror, the quarter wave plate being located between the mirror and the objective lens.
Optionally, the alignment system includes one of the diffractive light retroreflection units, and the diffractive light retroreflection unit is located on the optical axis side of the objective lens.
Optionally, the alignment system includes two interference information detection units, namely a first interference information detection unit and a second interference information detection unit; the incident end of the first interference information detection unit is positioned on the optical axis of the objective lens, and the second interference information detection unit and the diffraction light retroreflection unit are positioned on two opposite sides of the optical axis of the objective lens.
Optionally, the first interference information detection unit includes a first one-half wave plate, a first polarization splitting prism, a first detector and a second detector, the first one-half wave plate is located on the light incident surface of the first polarization splitting prism, and the first detector and the second detector are respectively located on two light emergent surfaces of the first polarization splitting prism.
Optionally, the second interference information detection unit includes a second half-wave plate, a second polarization splitting prism, a third detector, and a fourth detector, where the second half-wave plate is located on the light incident surface of the second polarization splitting prism, and the third detector and the fourth detector are respectively located on two light emergent surfaces of the second polarization splitting prism.
Optionally, the first interference information detecting unit is located on a propagation path of-1 st-order second-order diffracted light excited by the 0 st-order first-order diffracted light and the-1 st-order first-order diffracted light;
the second interference information detection unit is located on a propagation path of 0 th order second order diffracted light excited by the +1 st order first order diffracted light and the-1 st order first order diffracted light.
Optionally, the alignment beam generating unit includes a plurality of lasers and a light combiner, where the wavelengths of the laser beams emitted by any two of the lasers are different, and the light combiner is located on the emission light paths of the plurality of lasers and is configured to combine the laser beams emitted by the plurality of lasers into one beam;
the interference information detection unit further comprises an optical splitter and a detector, wherein the optical splitter is located on a receiving optical path of the detector and is used for splitting a beam of incident light into multiple paths of light according to wavelength and emitting the multiple paths of light to the detector respectively.
Optionally, the alignment mark further includes an alignment beam deflection unit, located on an exit light path of the alignment beam generation unit, for deflecting the alignment beam generated by the alignment beam generation unit, so that the alignment beam passes through the objective lens and then enters the alignment mark.
In a second aspect, an embodiment of the present invention provides a lithographic apparatus including the alignment system of the first aspect.
In the alignment system provided in the embodiment of the present invention, the diffraction light retroreflective unit is disposed on the emission light path of at least one path of the first-order diffracted light, and reflects the incident first-order diffracted light to the alignment mark to generate the second-order diffracted light, and the alignment position detection is realized by detecting the interference light intensity of the first-order diffracted light and the second-order diffracted light. The embodiment of the invention respectively operates the positive-order diffraction light, the 0-order diffraction light or the negative-order diffraction light generated by the alignment mark, and does not perform the relative deflection of 180 degrees on the diffraction image by the self-reference prism in the prior art, so that the self-reference prism is not needed, the manufacturing and integration difficulty of an optical device in an alignment system is reduced, and the cost is reduced.
Drawings
Fig. 1 is a schematic structural diagram of an alignment system according to an embodiment of the present invention;
FIG. 2 is a schematic structural diagram of another alignment system provided in an embodiment of the present invention;
fig. 3 is a schematic structural diagram of an alignment mark according to an embodiment of the present invention;
FIG. 4 is a graph of diffraction efficiency of the alignment mark shown in FIG. 3 as a function of depth of the alignment mark;
FIG. 5 is a graph showing the variation of light intensity with scan position of interference light formed by 0 < st > order first order diffracted light and-1 < st > order second order diffracted light excited by the-1 < st > order diffracted light in the alignment system shown in FIG. 1 at a mark depth of 10 nm;
FIG. 6 is a graph of the variation of light intensity with scan position for interference light formed by +1 st order first order diffracted light and 0 th order second order diffracted light excited by-1 st order first order diffracted light in the alignment system shown in FIG. 1 at a mark depth of 10 nm;
FIG. 7 is a graph of light intensity detected by a detector in an alignment system employing a self-referencing prism at a mark depth of 10nm as a function of scan position;
FIG. 8 is a graph of the normalized changes of FIGS. 5-7;
FIG. 9 is a graph of detector versus scan position for various alignment systems at a mark depth of 150 nm;
FIG. 10 is a graph showing the variation of FIG. 9 after normalization;
FIG. 11 is a graph of repeatability accuracy with modulation depth at a diffraction efficiency of 0.004;
fig. 12 is a graph of repeatability accuracy with modulation depth at a diffraction efficiency of 0.3548.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not to be construed as limiting the invention. It should be further noted that, for the convenience of description, only some structures related to the present invention are shown in the drawings, not all of them.
Fig. 1 is a schematic structural diagram of an alignment system according to an embodiment of the present invention, and referring to fig. 1, the alignment system includes an alignment beam generation unit 1, an objective lens 2, a diffracted light retroreflection unit 4, and an interference information detection unit 5. The alignment beam generating unit 1 is for generating an alignment beam. The alignment beam passes through the objective lens 2 and is incident on the alignment mark 3 to generate a first-order diffracted light. Illustratively, the alignment mark 3 includes a diffraction grating having a periodic structure. The alignment beam incident on the alignment mark 3 is first diffracted and first diffracted light is generated. The diffraction light retroreflection unit 4 is located on the side of the objective lens 2 far away from the alignment mark 3, is arranged on the exit light path of at least one path of the first-order diffraction light, and is used for reflecting the first-order diffraction light incident to the diffraction light retroreflection unit 4 to the alignment mark 3 and generating second-order diffraction light. That is, the diffracted light retroreflective unit 4 reflects the first-order diffracted light onto the alignment mark 3 to generate the second-order diffracted light, and generates the second-order diffracted light. The interference information detection means 5 is provided on the light path from the first-order diffracted light and the second-order diffracted light, and detects the intensity of interference light between the first-order diffracted light and the second-order diffracted light.
In the alignment system provided in the embodiment of the present invention, the diffraction light retroreflective unit is disposed on an emission light path of at least one path of the first-order diffracted light, and reflects the first-order diffracted light incident therein to the alignment mark to generate the second-order diffracted light, and the alignment position detection is realized by detecting interference light intensities of the first-order diffracted light and the second-order diffracted light. The embodiment of the invention respectively operates the positive-order diffraction light, the 0-order diffraction light or the negative-order diffraction light generated by the alignment mark, and does not perform the relative deflection of 180 degrees on the diffraction image by the self-reference prism in the prior art, so that the self-reference prism is not needed, the manufacturing and integration difficulty of an optical device in an alignment system is reduced, and the cost is reduced.
Optionally, referring to fig. 1, the alignment system may further include an alignment beam deflecting unit 6, where the alignment beam deflecting unit 6 is located on an emergent light path of the alignment beam generating unit 1, and is configured to deflect the alignment beam generated by the alignment beam generating unit 1, so that the alignment beam passes through the objective lens 2 and is incident on the alignment mark 3.
Alternatively, the alignment beam deflecting unit 6 may be located on the side of the objective lens 2 remote from the alignment mark 3, on the optical axis of the objective lens 2. The alignment beam deflection unit 6 may be, for example, a beam splitter prism or a polarization beam splitter prism.
Alternatively, referring to fig. 1, the diffraction light retroreflection unit 4 includes a quarter-wave plate 42 and a mirror 41, and the quarter-wave plate 42 is located between the mirror 41 and the objective lens 2.
Exemplarily, referring to fig. 1, the p-polarized linearly polarized light is incident to the quarter-wave plate 42 and the reflection mirror 41, reflected by the reflection mirror 41 and passes through the quarter-wave plate 42 again to be changed into S-polarized linearly polarized light. The P-polarized linearly polarized light refers to linearly polarized light with the polarization direction in the incident plane and the polarization direction perpendicular to the propagation direction of the light; s-polarized linearly polarized light refers to linearly polarized light having a polarization direction perpendicular to the plane of incidence. If the alignment beam generated by the alignment beam generating unit 1 in fig. 1 is S-polarized linearly polarized light, the S-polarized linearly polarized light is incident to the quarter-wave plate 42 and the reflecting mirror 41, reflected by the reflecting mirror 41 and passes through the quarter-wave plate 42 again to become P-polarized linearly polarized light.
Illustratively, the included angle between the fast axis of the quarter-wave plate 42 and the polarization direction of the P-polarized linearly polarized light is 45 °, and the included angle between the fast axis of the quarter-wave plate 42 and the polarization direction of the S-polarized linearly polarized light is 45 °.
Alternatively, referring to fig. 1, the alignment system includes one diffraction light retroreflection unit 4, and the diffraction light retroreflection unit 4 is located on the optical axis side of the objective lens 2. The interference information detection means 5 detects the intensity of interference light formed by the first order diffracted light and the second order diffracted light.
Exemplarily, referring to fig. 1, the diffraction light retroreflection unit 4 is located on the optical axis side of the objective lens 2, and the diffraction light retroreflection unit 4 is located on the exit optical path of the negative first order diffracted light. The minus-order first-order diffracted light refers to minus-order diffracted light among first-order diffracted light, for example, -1-order first-order diffracted light. In other embodiments, the diffracted light retroreflection unit 4 may be located on the exit optical path of the first-order diffracted light. The positive order first order diffracted light refers to positive order diffracted light among first order diffracted light, for example, the +1 st order diffracted light.
Alternatively, referring to fig. 1, the alignment system includes two interference information detection units 5, a first interference information detection unit 51 and a second interference information detection unit 52, respectively. The incident end of the first interference information detecting unit 51 is positioned on the optical axis of the objective lens 2, and the second interference information detecting unit 52 and the diffracted light retroreflection unit 4 are positioned on opposite sides of the optical axis of the objective lens 2.
Alternatively, referring to fig. 1, the diffraction light retroreflection unit 4 includes a quarter-wave plate 42 and a mirror 41, and the quarter-wave plate 42 is located between the mirror 41 and the objective lens 2. The first interference information detection unit 51 includes a first one-half wave plate 511, a first polarization splitting prism 512, a first detector 513 and a second detector 514, the first one-half wave plate 511 is located on the light incident surface of the first polarization splitting prism 512, and the first detector 513 and the second detector 514 are respectively located on two light emitting surfaces of the first polarization splitting prism 512. The second interference information detection unit 52 includes a second half-wave plate 521, a second polarization splitting prism 522, a third detector 523, and a fourth detector 524, where the second half-wave plate 521 is located on the light incident surface of the second polarization splitting prism 522, and the third detector 523 and the fourth detector 524 are respectively located on two light emergent surfaces of the second polarization splitting prism 522. In an embodiment of the present invention, 4 detectors 501 (including the first detector 513, the second detector 514, the third detector 523, and the fourth detector 524) are used, so that the optical signal detected by which detector 501 is used for alignment can be determined according to the diffraction efficiency of the specific process film layer and the alignment mark 3. In addition, the use of 4 detectors 501 is also beneficial to signal processing in the subsequent fitting process, for example, noise information can be obtained by performing a difference on the optical signals of two detectors 501, and further, the noise information can be reduced or even eliminated accordingly.
Illustratively, the fast axis of the first one-half wave plate 511 makes an angle of 22.5 ° with the polarization direction of P-polarized linearly polarized light, and the fast axis of the first one-half wave plate 511 makes an angle of 22.5 ° with the polarization direction of S-polarized linearly polarized light. The included angle between the fast axis of the second half-wave plate 521 and the polarization direction of the P-polarized linearly polarized light is 22.5 °, and the included angle between the fast axis of the second half-wave plate 521 and the polarization direction of the S-polarized linearly polarized light is 22.5 °.
For ease of understanding, the working principle of the alignment system shown in fig. 1 is briefly described in the embodiments of the present invention by taking ± 1 st order diffraction and 0 th order diffraction as examples, but not limited thereto, and higher order diffraction may be captured according to the numerical aperture of the objective lens.
Exemplarily, referring to fig. 1, the alignment beam generated by the alignment beam generating unit 1 is linearly polarized light of P polarization. The linearly polarized light with the P polarization is incident on the alignment mark 3 after passing through the objective lens 2 and generates a first diffraction light. The-1 st order first order diffracted light of the first order diffracted lights enters the diffracted light retroreflection unit 4 after passing through the objective lens 2, the light emitted from the diffracted light retroreflection unit 4 becomes S-polarized linearly polarized light, and the S-polarized linearly polarized light enters the alignment mark 3 to generate second order diffracted lights. At this time, the 0 th order first order diffracted light propagates along the same optical path as the-1 st order second order diffracted light excited by the-1 st order first order diffracted light, and is received by the first interference information detecting unit 51. Specifically, after the 0 st order first order diffracted light and the-1 st order second order diffracted light excited by the-1 st order first order diffracted light pass through the objective lens 2, the polarization directions of the two paths of light are deflected by 45 ° by the first one-half wave plate 511, and then after passing through the first polarization beam splitter prism 512, the light with the same polarization state will interfere and be received by the first detector 513 and the second detector 514, respectively. The +1 st order first order diffracted light propagates along the same optical path as the 0 th order second order diffracted light excited by the-1 st order first order diffracted light, and is received by the second interference information detecting unit 52. Specifically, after the +1 st order first order diffracted light and the-1 st order first order diffracted light excite the 0 th order second order diffracted light to pass through the objective lens 2, the polarization directions of the two paths of light are deflected by 45 ° by the second half wave plate 521, and then after passing through the second polarization beam splitter prism 522, the light with the same polarization state will interfere and be received by the third detector 523 and the fourth detector 524, respectively. It should be noted that the alignment beam generated by the alignment beam generating unit 1 may also be linearly polarized light with S polarization, which is not limited in the embodiment of the present invention.
The diffraction order light field of the alignment mark 3 can be expressed as:
where n is the diffraction order, p is the period of the diffraction grating, and x is the scanning position of the stage, we assume that the amplitude is 1. The following calculations we take as an example the coherence of +/-1 diffraction order and 0 diffraction order.
The 1 st order first order diffracted light passes through the objective lens 2, the quarter wave plate 42, the mirror 41 and the quarter wave plate 42, and the optical field after the objective lens 2 is:
wherein J is the Jones matrix of each optical device, E in To the incident light field, E -1 Is the light field of the-1 st order first order diffracted light, the incident light field is defined herein as (0. The optical path length between the +1 st order diffracted light and the 0 th order diffracted light excited by the-1 st order diffracted light is not taken into account in the above formula, and in the following formula, we add a phi phase.
The +1 st-order first-order diffracted light and the 0 th-order second-order diffracted light excited by the-1 st-order first-order diffracted light propagate along the same optical path, and a coherent light field after passing through the second half-wave plate 521 and the second polarization splitting prism 522 is:
therefore, the light intensity received by the fourth detector 524 is:
the intensity of light received by the third detector 523:
similarly, the 0 th order first order diffracted light and the-1 st order second order diffracted light excited by the-1 st order first order diffracted light propagate along the same optical path, and the coherent light field after passing through the first quarter wave plate 511 and the first polarization splitting prism 512 is:
wherein phi is the phase difference between the 0-order first-order diffraction light and the-1-order second-order diffraction light excited by the-1-order first-order diffraction light.
Therefore, the intensity of light received by the second detector 514 is:
the first detector 513 receives light of:
in summary, it can be seen that the light intensity varies with the scanning position of the stage and the signal is a cosine wave, but Φ in the above formula is a value varying with the incident wavelength, the grating period and the diffraction order of the alignment mark 3, which requires us to determine the difference between each incident wavelength, the grating period and the diffraction order of the alignment mark 3 by measurement in the initial setting of the detector 501 and to use as a writing machine constant as a correction value.
Fig. 2 is a schematic structural diagram of another alignment system according to an embodiment of the present invention, and referring to fig. 2, an alignment beam generating unit 1 includes a plurality of lasers 101 and a light combiner 15, where any two of the lasers 101 emit laser beams with different wavelengths, and the light combiner 15 is located on an outgoing light path of the plurality of lasers 101 and is configured to combine the laser beams emitted by the plurality of lasers 101 into one beam. The interference information detection unit 5 further includes an optical splitter 502 and a detector 501, where the optical splitter 502 is located on a receiving optical path of the detector 501, and is configured to split a beam of incident light into multiple paths of light according to wavelength and emit the multiple paths of light to multiple different detection channels of the detector 501 respectively.
Illustratively, the alignment beam generating unit 1 includes a first laser 11, a second laser 12, a third laser 13, and a fourth laser 14. The laser beam emitted by the first laser 11 is P-polarized linearly polarized light with a first wavelength, the laser beam emitted by the second laser 12 is S-polarized linearly polarized light with a second wavelength, the laser beam emitted by the third laser 13 is P-polarized linearly polarized light with a third wavelength, and the laser beam emitted by the fourth laser 14 is S-polarized linearly polarized light with a fourth wavelength. The first interference information detection unit 51 includes a first optical splitter 515 and a second optical splitter 516, and the first optical splitter 515 is located between the first polarization splitting prism 512 and the first detector 513. The second optical splitter 516 is located between the first polarization splitting prism 512 and the second detector 514. The second interference information detection unit 52 includes a third optical splitter 525 and a fourth optical splitter 526, and the third optical splitter 525 is located between the second polarization splitting prism 522 and the third detector 523. The fourth optical splitter 526 is located between the second polarization splitting prism 522 and the fourth detector 524. In this embodiment of the present invention, the first detector 513, the second detector 514, the third detector 523, and the fourth detector 524 may be four-channel detectors, and detect optical signals with four wavelengths respectively.
The embodiment of the invention also provides a photoetching machine which comprises the alignment system in the embodiment. The lithography machine may further include an exposure system, a mask stage system, an illumination system, etc., which are not described in detail herein. The photoetching machine provided by the embodiment of the invention comprises the alignment system in the embodiment, so that the manufacturing cost of the photoetching machine is reduced.
The embodiment of the invention also provides various performance evaluations of the alignment system in the embodiment. Fig. 3 is a schematic structural diagram of an alignment mark according to an embodiment of the present invention, fig. 4 is a graph illustrating a variation of diffraction efficiency of the alignment mark shown in fig. 3 with a depth of the alignment mark, and referring to fig. 3 and fig. 4, a simple silicon/air alignment mark is adopted, and a period P =16 μm of the alignment mark 3 is adopted, and a scan length of a workpiece stage is 40 μm. For the 0 th order diffracted light, the diffraction efficiency of alignment mark 3 with mark depth h =10nm is 0.3528; the diffraction efficiency of the alignment mark 3 with the mark depth h =150nm was 0.0123. For 1 st order diffracted light (+ 1 st order diffracted light or-1 st order diffracted light), the diffraction efficiency is 0.002 when the mark depth h =10nm of the alignment mark 3; the diffraction efficiency at a mark depth h =150nm of the alignment mark 3 is 0.1353.
Fig. 5 is a graph showing a change in light intensity with respect to a scanning position of interference light formed by the 0 < th > order first-order diffracted light and the-1 < st > order second-order diffracted light excited by the-1 < st > order first-order diffracted light in the alignment system shown in fig. 1 at a mark depth of 10nm in fig. 1, fig. 6 is a graph showing a change in light intensity with respect to a scanning position of interference light formed by the +1 < st > order first-order diffracted light and the 0 < st > order second-order diffracted light excited by the-1 < st > order first-order diffracted light in the alignment system shown in fig. 1 at a mark depth of 10nm in fig. 7, and fig. 5-7 show a change in light intensity with respect to a scanning position detected by a detector in the alignment system using a self-referencing prism at a mark depth of 10nm in fig. 5-7, and the diffraction efficiency of the alignment mark 3 at a mark depth of 10nm is low. The light intensity of interference light formed by the 0-order first-order diffraction light and-1-order second-order diffraction light excited by the-1-order first-order diffraction light is large. The light intensity of interference light formed by +1 order first-order diffraction light and 0 order second-order diffraction light excited by-1 order first-order diffraction light is weakened and is reduced by two orders of magnitude compared with the light intensity of interference light formed by 0 order first-order diffraction light and-1 order second-order diffraction light excited by-1 order first-order diffraction light. The light intensity detected by the detector in the alignment system of the self-reference prism is reduced by two orders of magnitude compared with the light intensity of interference light formed by 0-order first-order diffraction light and-1-order second-order diffraction light excited by-1-order first-order diffraction light.
FIG. 8 is a graph showing the variation after normalization process of FIGS. 5 to 7, and referring to FIG. 8, "0 th order 1 and-1X-1" represent that the 0 th order first order diffracted light and the-1 st order second order diffracted light excited by the-1 st order first order diffracted light form interference light in the alignment system shown in FIG. 1. "+1 st order 1 and-1X 0" represent interference light formed by +1 st order diffracted light and 0 th order diffracted light excited by-1 st order diffracted light in the alignment system shown in fig. 1, and "reference light" represents light detected by a detector in the alignment system using a self-reference prism. As can be seen from fig. 8, the contrast of light detected by the detector in the alignment system using the self-reference prism is 100%, the contrast of interference light formed by +1 st order diffracted light and 0 st order diffracted light excited by-1 st order diffracted light is 93%, and the contrast of interference light formed by 0 st order diffracted light and-1 st order diffracted light excited by-1 st order diffracted light is about 1%.
Fig. 9 is a graph showing the variation of the detector of various alignment systems with the scanning position at the mark depth of 150nm, and referring to fig. 9, the meaning of the same mark as that in fig. 8 is not repeated herein. The diffraction efficiency of the alignment mark 3 is high at a mark depth of 150 nm. The light intensity of interference light formed by the 0-order first-order diffraction light and-1-order second-order diffraction light excited by the-1-order first-order diffraction light is the highest. The +1 st order first order diffracted light and the 0 th order second order diffracted light excited by the-1 st order diffracted light form the light intensity of the interference light, and the light intensity is about one third of the light intensity detected by a detector in the alignment system of the reference prism. The 0-order first-order diffracted light and-1-order second-order diffracted light excited by the-1-order first-order diffracted light form the light intensity of interference light, which is about one tenth of the light intensity detected by a detector in an alignment system of the self-reference prism.
Fig. 10 is a graph of the change of the normalized graph of fig. 9, and referring to fig. 10, the same reference numerals as those in fig. 8 are not repeated herein. The contrast ratio of light detected by a detector in an alignment system using a self-reference prism is 100%, the contrast ratio of interference light formed by 0-order first-order diffracted light and-1-order second-order diffracted light excited by-1-order first-order diffracted light is 99%, and the contrast ratio of interference light formed by + 1-order first-order diffracted light and 0-order second-order diffracted light excited by-1-order first-order diffracted light is 33%.
Fig. 11 is a graph showing the variation of the repeatability accuracy with the modulation depth at a diffraction efficiency of 0.004, fig. 12 is a graph showing the variation of the repeatability accuracy with the modulation depth at a diffraction efficiency of 0.3548, and referring to fig. 11 and 12, the modulation depth and the light intensity (i.e., the diffraction efficiency of the alignment mark 3) directly affect the repeatability accuracy of the alignment. As can be seen from fig. 11 and 12, even in the case of the modulation depth of 0.01, as long as there is sufficient light intensity (diffraction efficiency is greater than 0.1), the repeatability accuracy effect can be controlled to be 0.4nm or less, which corresponds to the case where the 0 th order first order diffracted light forms interference light with the-1 st order second order diffracted light excited by the-1 st order diffracted light. The influence of repeatability precision of the interference light, namely the interference light formed by the +1 st-order first-order diffraction light and the 0 th-order second-order diffraction light excited by the-1 st-order first-order diffraction light, the higher modulation depth, the lower light intensity, the higher light intensity and the lower modulation depth is less than 0.2nm. When the modulation depth is 1, the repeatability precision is larger than 0.8nm along with the weakening of light intensity.
For the interference light formed by the 0-order first-order diffraction light and the-1-order second-order diffraction light excited by the-1-order first-order diffraction light, the repeatability precision is 2.5nm when the mark depth h =10nm of the alignment mark 3; the repeatability accuracy when the mark depth h =150nm of the alignment mark 3 was 0.019nm. For the interference light formed by the +1 st order first order diffraction light and the 0 th order second order diffraction light excited by the-1 st order diffraction light, the repeatability precision is 0.025nm when the mark depth h of the alignment mark 3 is =10 nm; the repeatability precision when the mark depth h =150nm of the alignment mark 3 is 0.083nm. For the light detected by the detector in the alignment system of the self-reference prism, the repeatability precision is 0.02nm when the mark depth h of the alignment mark 3 is =10 nm; the repeatability accuracy when the mark depth h =150nm of the alignment mark 3 was 0.018nm.
It is to be noted that the foregoing is only illustrative of the preferred embodiments of the present invention and the technical principles employed. It will be understood by those skilled in the art that the present invention is not limited to the particular embodiments described herein, but is capable of various obvious modifications, rearrangements, combinations and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, although the present invention has been described in some detail by the above embodiments, the invention is not limited to the above embodiments, and may include other equivalent embodiments without departing from the spirit of the invention, and the scope of the invention is determined by the scope of the appended claims.
Claims (9)
1. An alignment system, comprising:
an alignment beam generating unit for generating an alignment beam;
an objective lens; the alignment light beam is incident on the alignment mark after passing through the objective lens and generates first diffraction light;
the diffraction light retroreflection unit is positioned on one side of the objective lens, which is far away from the alignment mark, is arranged on at least one path of emergent light path of the primary diffraction light, and is used for reflecting the primary diffraction light incident to the diffraction light retroreflection unit to the alignment mark and generating secondary diffraction light;
interference information detection means provided on the light emission path of the primary diffracted light and the secondary diffracted light for detecting the intensity of interference light between the primary diffracted light and the secondary diffracted light;
the alignment system comprises two interference information detection units, namely a first interference information detection unit and a second interference information detection unit;
the first interference information detection unit is positioned on a propagation path of-1 st-order second-order diffracted light excited by 0 st-order first-order diffracted light and-1 st-order first-order diffracted light;
the second interference information detection unit is located on a propagation path of 0-order second-order diffracted light excited by + 1-order first-order diffracted light and-1-order first-order diffracted light.
2. The alignment system of claim 1, wherein the diffractive light retro-reflective unit comprises a quarter wave plate and a mirror, the quarter wave plate being located between the mirror and the objective lens.
3. The alignment system of claim 1, wherein the alignment system comprises one of the diffractive light retroreflecting units, and the diffractive light retroreflecting unit is located on an optical axis side of the objective lens.
4. The alignment system according to claim 3, wherein an incident end of the first interference information detecting unit is located on an optical axis of the objective lens, and the second interference information detecting unit and the diffracted light retroreflecting unit are located on opposite sides of the optical axis of the objective lens.
5. The alignment system of claim 4,
the first interference information detection unit comprises a first one-half wave plate, a first polarization beam splitter prism, a first detector and a second detector, wherein the first one-half wave plate is located on the light incoming surface of the first polarization beam splitter prism, and the first detector and the second detector are respectively located on two light outgoing surfaces of the first polarization beam splitter prism.
6. The alignment system according to claim 4, wherein the second interference information detection unit includes a second half-wave plate, a second polarization beam splitter prism, a third detector and a fourth detector, the second half-wave plate is located on a light incident surface of the second polarization beam splitter prism, and the third detector and the fourth detector are respectively located on two light emergent surfaces of the second polarization beam splitter prism.
7. The alignment system of claim 1, wherein the alignment beam generating unit comprises a plurality of lasers and a light combiner, the wavelengths of the laser beams emitted by any two of the lasers are different, and the light combiner is located in the emitting optical paths of the plurality of lasers and is used for combining the laser beams emitted by the plurality of lasers into one beam;
the interference information detection unit further comprises an optical splitter and a detector, wherein the optical splitter is positioned on a receiving optical path of the detector and is used for splitting a beam of incident light into multiple paths of light according to wavelength and respectively emitting the multiple paths of light to the detector.
8. The alignment system of claim 1, further comprising an alignment beam deflection unit, located on an exit optical path of the alignment beam generation unit, for deflecting the alignment beam generated by the alignment beam generation unit so that the alignment beam passes through the objective lens and is incident on the alignment mark.
9. A lithography machine comprising an alignment system according to any one of claims 1 to 8.
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