Displacement measuring device and photolithography equipment

Abstract

In the displacement measurement device provided by this invention, a readhead module receives and guides the propagation of an incident light beam. A first incident light beam, guided by the readhead module, is reflected back to a diffraction element and diffracts along the Y direction to generate at least two first and second diffracted beams. A second incident light beam, guided and split by the readhead module, is reflected back to the diffraction element and diffracts along the X direction to generate two second and second diffracted beams. The two second and second diffracted beams are emitted with at least partial overlap to at least one first and second diffracted beam, forming a first interference beam and a second interference beam. An optical signal processing module determines the two-dimensional displacement of the diffraction element based on the phase change of the first and second interference beams. The positions where the first and second incident light beams reflect back to the diffraction element at least partially overlap, which helps to reduce the spot layout for two-dimensional displacement measurement. This invention also provides a photolithography apparatus including the above-described displacement measurement device.

Description

Technical Field

[0001] This invention relates to displacement measuring devices, and more particularly to a displacement measuring device and a photolithography apparatus. Background Technology

[0002] Nanoscale measurement technology is fundamental to fields such as nanofabrication, nanomanipulation, and nanomaterials. The IC industry, precision machinery, and microelectromechanical systems (MEMS) all require high-resolution, high-precision displacement sensors to achieve nanoscale precision positioning. As integrated circuits rapidly advance towards large-scale and high-integration, the overlay accuracy requirements of lithography machines are also increasing, correspondingly demanding higher precision in acquiring the six-degree-of-freedom position information of the workpiece stage and mask stage.

[0003] Interferometers offer high measurement accuracy, reaching the nanometer scale, and are used in photolithography systems to measure the position of workpiece stages and mask stages. However, the measurement accuracy of current interferometers is nearing its limit, and it is significantly affected by the surrounding environment, resulting in low repeatability (even in ideal conditions, it can exceed 1 nm). Traditional interferometer measurement systems struggle to meet the requirements for further improvements in overlay accuracy. Therefore, high-precision and high-stability picometer measurement solutions are urgently needed. Grating ruler measurement systems can achieve very small optical path lengths, typically a few millimeters. Their optical path is independent of the measurement range, making their measurement accuracy insensitive to environmental influences. They also feature high measurement stability, simple structure, and ease of miniaturization, giving them a significant place in the field of nanometer measurement. In next-generation photolithography systems, they are gradually replacing interferometers, undertaking high-precision, high-stability picometer-level measurement tasks.

[0004] Patent application CN106931887A discloses a dual-frequency grating measurement device that can directly combine the positive and negative diffracted beams of the grating to achieve horizontal displacement measurement of the grating ruler. However, the two-dimensional measurement scheme adopted in this application uses a four-spot layout, which occupies a large space on the grating, and there is crosstalk between the measurement beams. Summary of the Invention

[0005] The purpose of this invention is to provide a displacement measuring device that can reduce the spot layout for two-dimensional displacement measurement, which is beneficial for reducing the size of the diffraction element.

[0006] To achieve the above objectives, the present invention provides a displacement measuring device. The displacement measuring device includes:

[0007] Diffraction elements include multiple repeating diffraction structures arranged in two dimensions periodically along the X and Y directions within the optical contact surface;

[0008] A readhead module is used to receive and guide the propagation of an incident light beam. A first incident light beam, guided by the readhead module, is projected onto the diffraction element and diffracts along the Y direction to generate two first primary diffraction beams. These two first primary diffraction beams, guided by the readhead module, are reflected back onto the diffraction element and diffract along the Y direction to generate at least two first secondary diffraction beams. A second incident light beam, guided by the readhead module, is projected onto the diffraction element and diffracts along the X direction to generate a second primary diffraction beam. The readhead module splits the second primary diffraction beam into two secondary diffraction beams. Two primary diffracted beams are reflected back to the diffraction element and diffracted along the X-direction to generate two secondary diffracted beams; wherein the positions where each primary diffracted beam and each secondary diffracted beam reflects back to the diffraction element at least partially overlap; at least one primary diffracted beam and one secondary diffracted beam exiting at least partially overlap form a first interference beam, and at least one primary diffracted beam and another secondary diffracted beam exiting at least partially overlap form a second interference beam; and

[0009] The optical signal processing module determines the displacement of the diffraction element in the X and Y directions based on the phase change of the first interference beam and the phase change of the second interference beam.

[0010] Optionally, the read head module includes a first polarization element and a first angle control element; the second primary diffraction beam is split by the first angle control element and the first polarization element to form the two second primary diffraction beams.

[0011] Optionally, the at least two first and second diffraction beams include a -m-order first and second diffraction beam and a +m-order first and second diffraction beam; the second diffraction beam includes a +n-order second diffraction beam; m and n are both diffraction orders; the -m-order first and second diffraction beam and one of the +n-order second diffraction beams are emitted with at least partial overlap to generate the first interference beam; the +m-order first and second diffraction beam and the other +n-order second diffraction beam are emitted with at least partial overlap to generate the second interference beam.

[0012] Optionally, the readhead module includes multiple retroreflection elements; after the first incident beam is projected onto the diffraction element, it diffracts along the Y direction to generate a -m-order first primary diffraction beam and a +m-order first primary diffraction beam; the -m-order first primary diffraction beam is guided back to the diffraction element by a first retroreflection element and diffracts along the Y direction to generate the -m-order first secondary diffraction beam; the +m-order first primary diffraction beam is guided back to the diffraction element by a second retroreflection element and diffracts along the Y direction to generate the +m-order first secondary diffraction beam; after the second incident beam is projected onto the diffraction element, it diffracts along the X direction to generate a +n-order second primary diffraction beam; the +n-order second primary diffraction beam is guided back towards the diffraction element by a third retroreflection element and splits into two +n-order second primary sub-diffraction beams during the back reflection process; the two +n-order second primary sub-diffraction beams are back to the diffraction element and diffract along the X direction to generate two +n-order second secondary diffraction beams.

[0013] Optionally, the readhead module includes a second angle control element and a third angle control element; the -m-order first primary diffraction beam is reflected back onto the diffraction element after passing through the second angle control element; the +m-order first primary diffraction beam is reflected back onto the diffraction element after passing through the third angle control element.

[0014] Optionally, the read head module includes a second polarization element and a third polarization element; the -m-order first primary diffraction beam is split into two -m-order first primary sub-diffraction beams after passing through the second angle control element and the second polarization element; the +m-order first primary diffraction beam is split into two +m-order first primary sub-diffraction beams after passing through the third angle control element and the third polarization element.

[0015] Optionally, both the second polarizing element and the third polarizing element include at least one of a waveplate, a Wollaston prism, a polarizer, a polarizing beam splitter, a beam splitter, and a transmission grating.

[0016] Optionally, the displacement of the diffraction element in the X direction is ΔX, and the displacement of the diffraction element in the Y direction is ΔY.

[0017]

[0018] Where P is the spacing between two adjacent repeating diffraction structures, m is the diffraction order of the first incident beam along the Y direction, and n is the diffraction order of the second incident beam along the X direction. This represents the phase change of the first interference beam. This represents the phase change of the second interference beam.

[0019] Optionally, the read head module includes a fourth angle control element and a fifth angle control element; the first incident beam and the second incident beam are projected onto the diffraction element after passing through the fourth angle control element and the fifth angle control element, respectively.

[0020] Optionally, the position measuring device includes a light detection module, which is used to receive the first interference beam and the second interference beam, and output the first interference signal and the second interference signal to the light signal processing module.

[0021] Optionally, the first interference beam and the second interference beam have different emission directions; the optical detection module includes a first detector and a second detector; the first detector receives the first interference beam, and the second detector receives the second interference beam.

[0022] In another aspect, the present invention provides a photolithography apparatus. The photolithography apparatus includes a substrate platform and a mask platform that are movable relative to each other, and also includes the aforementioned displacement measuring device, wherein the diffraction element is attached to one of the substrate platform or the mask platform.

[0023] In the displacement measuring device and photolithography equipment of the present invention, a first incident beam is projected onto a diffraction element under the guidance of a readhead module and diffracts along the Y direction to generate two first primary diffraction beams. The two first primary diffraction beams are then reflected back onto the diffraction element under the guidance of the readhead module and diffract along the Y direction to generate at least two first secondary diffraction beams. A second incident beam is projected onto the diffraction element under the guidance of the readhead module and diffracts along the X direction to generate a second primary diffraction beam. The readhead module splits the second primary diffraction beam into two second primary sub-diffraction beams. The two second primary sub-diffraction beams are reflected back onto the diffraction element and diffract along the X direction to generate two second secondary diffraction beams. Each first primary diffraction beam... The positions of each second primary diffracted beam reflected back to the diffracting element are at least partially overlapped, that is, when all the primary diffracted beams are reflected back to the diffracting element, a single spot is formed; at least one first secondary diffracted beam and one second secondary diffracted beam are emitted with at least partial overlap to form a first interference beam, and at least one first secondary diffracted beam and another second secondary diffracted beam are emitted with at least partial overlap to form a second interference beam. The optical signal processing module determines the displacement of the diffracting element in the X and Y directions based on the phase change of the first and second interference beams. This can reduce the spot layout of the two-dimensional displacement measurement while realizing two-dimensional displacement measurement, which is beneficial to reducing the size of the diffracting element. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the structure of a displacement measuring device according to an embodiment of the present invention.

[0025] Figure 2 a to Figure 2 f is a schematic diagram of different structures of the retroreflective element in one embodiment of the present invention.

[0026] Figure 3 This is a schematic diagram of the displacement measuring device according to another embodiment of the present invention. Detailed Implementation

[0027] The displacement measuring device and photolithography equipment proposed in this invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The advantages and features of this invention will become clearer from the following description. It should be noted that the drawings are all in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of this invention.

[0028] In order to reduce the spot layout and size of the diffraction element in two-dimensional displacement measurement, this application provides a displacement measurement device. Figure 1 This is a schematic diagram of the structure of a displacement measuring device according to an embodiment of the present invention. Figure 1 As shown, the displacement measuring device includes a diffraction element 200, a read head module 100, and an optical signal processing module 500.

[0029] The diffraction element 200 includes a plurality of repeating diffraction structures arranged in a two-dimensional periodic pattern along the X and Y directions within the optical contact surface. The diffraction element 200 includes, but is not limited to, a two-dimensional grating.

[0030] The readhead module 100 is used to receive and guide the propagation of the incident light beam. The readhead module 100 receives a first incident light beam 610 and a second incident light beam 611. The first incident light beam 610, guided by the readhead module 100, is projected onto the optical contact surface of the diffraction element 200 and diffracts along the Y direction to generate two first primary diffracted beams. These two first primary diffracted beams, guided by the readhead module 100, are reflected back to the diffraction element 200 and diffract along the Y direction to generate at least two first secondary diffracted beams. The second incident light beam 611, guided by the readhead module 100, is projected onto the diffraction element 200 and diffracts along the X direction to generate a second primary diffracted beam. The readhead module 100 splits the second primary diffracted beam into two second primary sub-diffracted beams. These two second primary sub-diffracted beams are reflected back to the diffraction element 200 to generate two second secondary diffracted beams.

[0031] In this configuration, the positions where each first primary diffracted beam and each second primary sub-diffracted beam are reflected back onto the diffraction element 200 at least partially overlap. That is, when all the first primary diffracted beams and all the second primary sub-diffracted beams are reflected back onto the diffraction element 200, only one light spot is formed. The emission of at least one first secondary diffracted beam and one second secondary diffracted beam, which at least partially overlap, forms a first interference beam 612, and the emission of at least one first secondary diffracted beam and another second secondary diffracted beam, which at least partially overlap, forms a second interference beam 613.

[0032] The optical signal processing module 500 determines the displacement of the diffraction element 200 in the X and Y directions based on the phase change of the first interference beam 612 and the phase change of the second interference beam 613.

[0033] The displacement measuring device may include a light source that provides a first incident beam 610 and a second incident beam 611. The first incident beam 610 and the second incident beam 611 may both be polarized light, for example, they may be polarized light with the same polarization state, or they may be polarized light with different polarization states, or they may be dynamically adjustable polarization beams.

[0034] The first incident beam 610 and the second incident beam 611 can both be frequency-stabilized beams. The frequencies of the first incident beam 610 and the second incident beam 611 can be the same. The first incident beam 610 and the second incident beam 611 can both be single-frequency beams or both be dual-frequency beams. The first incident beam 610 and the second incident beam 611 can be laser beams.

[0035] refer to Figure 1 The first incident beam 610 and the second incident beam 611 can be incident on the diffraction element 200 at any non-Litterow angle. The first incident beam 610 and the second incident beam 611 are incident on different positions on the diffraction element 200, that is, when the first incident beam 610 and the second incident beam 611 are incident on the diffraction element 200, two light spots are formed, and the two light spots are separated by a certain distance.

[0036] The readhead module 100 may include a fourth angle control element 700 and a fifth angle control element 702. The first incident beam 610 and the second incident beam 611, after passing through the fourth angle control element 700 and the fifth angle control element 702 respectively, are projected onto the diffraction element 200 at arbitrary filtroh angles. The fourth angle control element 700 and the fifth angle control element 702 can adjust the incident angles of the first incident beam 610 and the second incident beam 611, thereby adjusting the angle between their diffracted beams. This allows the secondary diffracted beams of the first incident beam 610 and the second incident beam 611 to achieve optimal interference, thus forming a first interference beam 612 and a second interference beam 613 with better interference effect, which is beneficial for improving the accuracy of displacement measurement by the displacement measuring device.

[0037] The at least two first and second diffracted beams generated by the first incident beam 610 through the diffraction element 200 may include a -m-order first and second diffracted beam and a +m-order first and second diffracted beam; the second diffracted beam generated by the second incident beam 611 through the diffraction element 200 may include two +n-order second and second diffracted beams; m and n are diffraction orders, for example, m and n are both 1, but not limited thereto, m and n can also be other natural numbers. The -m-order first and second diffracted beam and one of the +n-order second and second diffracted beams are emitted with at least partial overlap to generate a first interference beam 612; the +m-order first and second diffracted beam and the other +n-order second and second diffracted beam are emitted with at least partial overlap to generate a second interference beam 613.

[0038] Specifically, the read head module 100 may include multiple retroreflective elements, namely a first retroreflective element, a second retroreflective element, and a third retroreflective element.

[0039] In one embodiment, such as Figure 1 As shown, the first incident beam 610 is projected onto the diffraction element 200 and diffracts along the Y direction to generate a -m-order first primary diffraction beam and a +m-order first primary diffraction beam. The -m-order first primary diffraction beam is guided back to the diffraction element 200 by the first retroreflection element 110 and diffracts along the Y direction to generate a -m-order first secondary diffraction beam, which serves as part of the first interference beam 612. The +m-order first primary diffraction beam is guided back to the diffraction element 200 by the second retroreflection element 111 and diffracts along the Y direction to generate a +m-order first secondary diffraction beam, which serves as part of the second interference beam 613.

[0040] After the second incident beam 611 is projected onto the diffraction element 200, it diffracts along the X direction to generate a +n-order second primary diffraction beam. The +n-order second primary diffraction beam is guided by the third retroreflection element 112 and reflected back towards the diffraction element 200. During the reflection process, it is split to form two +n-order second primary sub-diffraction beams. The two +n-order second primary sub-diffraction beams are reflected back to the diffraction element 200 and diffract along the X direction to generate two +n-order second secondary diffraction beams. The two +n-order second secondary diffraction beams serve as another part of the first interference beam 612 and the second interference beam 613, respectively.

[0041] like Figure 1 As shown, the readhead module 100 may include a first polarization element 760 and a first angle control element 761; the second primary diffracted beam is split into two secondary primary diffracted beams after passing through the first angle control element 761 and the first polarization element 760. More specifically, the +n-order secondary primary diffracted beam can be guided by a third retroreflection element 112 and, after being split and controlled by the first angle control element 761 and the first polarization element 760, reflected back to the diffraction element 200. However, it is not limited to this; the secondary primary diffracted beam can also be split using other beam-splitting structures known in the art.

[0042] It should be noted that the positions where the -m-order first diffraction beam, the +m-order first diffraction beam, and the two +n-order second sub-diffraction beams are reflected back to the diffraction element at least partially overlap.

[0043] In this embodiment, the retroreflector element can change the direction of the incident beam and output an outgoing beam with a direction opposite to that of the incident beam, and the outgoing beam is offset by a certain distance relative to the incident beam. Figure 2 a to Figure 2 f is a schematic diagram of different structures of the retroreflective element in one embodiment of the present invention. The retroreflective element can be a corner cube prism (such as...). Figure 2 As shown in a), a right-angle prism (such as...) Figure 2 (as shown in b), cat's eye reflector (such as...) Figure 2 (as shown in c), Dove Prism (such as...) Figure 2 (as shown in d), hollow retroreflector (such as...) Figure 2 (as shown in e) or a grating reflector (such as...) Figure 2 (as shown in f).

[0044] like Figure 1As shown, the readhead module 100 may include a second angle control element 701 and a third angle control element 703. The -m-level first primary diffraction beam can be reflected back onto the diffraction element 200 after passing through the second angle control element 701. The +m-level first primary diffraction beam can be reflected back onto the diffraction element 200 after passing through the third angle control element 703. By adjusting the incident angle of the -m-level and +m-level first primary diffraction beams onto the diffraction element 200 through the second angle control element 701 and the third angle control element 703, the diffraction angle θ corresponding to the -m-level first primary diffraction beam is not equal to the diffraction angle β1 corresponding to the -m-level first secondary diffraction beam, and the diffraction angle (e.g., θ) corresponding to the +m-level first primary diffraction beam is not equal to the diffraction angle β2 corresponding to the +m-level first secondary diffraction beam. In this way, stray light and echo reflection interference can be eliminated, which is beneficial to improving the accuracy of displacement measurement.

[0045] Figure 3 This is a schematic diagram of the structure of a displacement measuring device according to another embodiment of the present invention. Figure 3 As shown, in one embodiment, the readhead module 200 may include a second polarization element 762 and a third polarization element 764. The -m-order first primary diffraction beam is split by the second angle control element 701 and the second polarization element 762 to form two -m-order first primary sub-diffraction beams. The +m-order first primary diffraction beam is split by the third angle control element 703 and the third polarization element 764 to form two +m-order first primary sub-diffraction beams. Due to the guidance of the first retroreflection element 110 and the second retroreflection element 111, both the -m-order first primary sub-diffraction beams and the two +m-order first primary sub-diffraction beams are reflected back onto the diffraction element 200, and the positions of all the first primary sub-diffraction beams (including -m-order and +m-order) and the two +n-order second primary sub-diffraction beams reflected back onto the diffraction element 200 at least partially overlap, that is, when all the first primary sub-diffraction beams and the two +n-order second primary sub-diffraction beams are reflected back onto the diffraction element 200, a single light spot is formed.

[0046] After diffraction by diffraction element 200, two -m-order first primary diffraction beams diffract along the Y direction to generate two -m-order first and second secondary diffraction beams. For example, the two -m-order first and second secondary diffraction beams can be emitted along the emission directions of the first interference beam 612 and the second interference beam 613, respectively. Two +m-order first primary diffraction beams diffract along the Y direction to generate two +m-order first and second secondary diffraction beams. For example, the two +m-order first and second secondary diffraction beams can be emitted along the emission directions of the first interference beam 612 and the second interference beam 613, respectively.

[0047] Depending on the application requirements, one -m-order first and second diffraction beam and one +n-order second and second diffraction beam can be selected to interfere to form a first interference beam 612, and one +m-order first and second diffraction beam and one +n-order second and second diffraction beam can be selected to interfere to form a second interference beam 613; or, both -m-order first and second diffraction beams and two +m-order first and second diffraction beams can participate in the final interference to form a redundant measurement axis for environmental compensation or measurement calibration.

[0048] In this application, the angle control elements (first, second, third, fourth, and fifth angle control elements) include, but are not limited to, a pair of wedge prisms, a wedge prism, or a polarization angle control element. The polarization elements (i.e., the first polarization element 760, the second polarization element 762, and the third polarization element 764) include, but are not limited to, at least one of a waveplate, a Wollaston prism, a polarizer, a polarizing beam splitter, a beam splitter, and a transmission grating.

[0049] Continue to refer to Figure 1 and Figure 3 The position measuring device includes an optical detection module, which receives a first interference beam 612 and a second interference beam 613, and outputs a first interference signal and a second interference signal to an optical signal processing module 500. The first interference signal contains information on the phase change of the first interference beam 612, and the second interference signal contains information on the phase change of the second interference beam 613.

[0050] More specifically, the first interference beam 612 and the second interference beam 613 have different emission directions; the optical detection module includes a first detector 410 and a second detector 411. The first detector 410 receives the first interference beam 612, converts it into a first interference signal, and transmits it to the optical signal processing module 500 through the first transmission optical fiber 430. The second detector 411 receives the second interference beam 613, converts it into a second interference signal, and transmits it to the optical signal processing module 500 through the second transmission optical fiber 431.

[0051] The optical signal processing module 500 determines the displacement of the diffraction element 200 in the X and Y directions based on the phase change of the first interference beam 612 and the phase change of the second interference beam 613.

[0052] Specifically, the spacing between the multiple repeating diffraction structures of the diffraction element 200 in the X direction and the Y direction can be equal, for example, both being P. The displacement of the diffraction element 200 in the X direction is ΔX, and the displacement of the diffraction element 200 in the Y direction is ΔY. ΔX and ΔY satisfy the following formulas (1) and (2).

[0053]

[0054]

[0055] Wherein, P is the spacing between two adjacent repeating diffraction structures, m is the diffraction order of the first incident beam 610 along the Y direction, and n is the diffraction order of the second incident beam 611 along the X direction. This represents the phase change of the first interference beam 612. This represents the phase change of the second interference beam 613.

[0056] In the displacement measuring device of this application, a first incident beam 610, guided by the read head module 100, is projected onto the diffraction element 200 and diffracts along the Y direction to generate two first primary diffracted beams. The two first primary diffracted beams, guided by the read head module 100, are reflected back onto the diffraction element 200 and diffract along the Y direction to generate at least two first secondary diffracted beams. A second incident beam 611, guided by the read head module 100, is projected onto the diffraction element 200 and diffracts along the X direction to generate a second primary diffracted beam. The read head module 100 splits the second primary diffracted beam into two second primary sub-diffracted beams. The two second primary sub-diffracted beams are reflected back onto the diffraction element 200 and diffract along the X direction to generate two second secondary diffracted beams. Each first primary diffracted beam and each second primary sub-diffracted beam is reflected back onto the diffraction element 200. The positions of the diffraction elements 200 at least partially overlap, that is, when all the primary diffracted beams are reflected back to the diffraction elements 200, a single light spot is formed; at least one primary diffracted beam and one secondary diffracted beam are emitted with at least partial overlap to form a first interference beam 612, and at least one primary diffracted beam and another secondary diffracted beam are emitted with at least partial overlap to form a second interference beam 613. The optical signal processing module 500 determines the displacement of the diffraction elements in the X and Y directions based on the phase change of the first interference beam 612 and the phase change of the second interference beam 613. In this way, while realizing two-dimensional displacement measurement, the light spot layout for two-dimensional displacement measurement is reduced (the prior art uses a four-spot layout, while this application uses a three-spot layout), which is beneficial to reducing the size of the diffraction elements 200.

[0057] This application also provides a photolithography apparatus, which includes a substrate platform and a mask platform that move relative to each other. The photolithography apparatus also includes the displacement measuring device described above, wherein the diffraction element 200 is attached to one of the substrate platform or the mask platform.

[0058] The above description is merely a description of preferred embodiments of the present invention and is not intended to limit the scope of the present invention. Any person skilled in the art can make possible changes and modifications to the technical solutions of the present invention by utilizing the methods and techniques disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the protection scope of the technical solutions of the present invention.

Claims

1. A displacement measuring device, characterized in that include: Diffraction elements include multiple repeating diffraction structures arranged in two dimensions periodically along the X and Y directions within the optical contact surface; A readhead module is used to receive and guide the propagation of an incident beam; the first incident beam is projected onto the diffraction element under the guidance of the readhead module and diffracts along the Y direction to generate two first primary diffraction beams; the two first primary diffraction beams are reflected back to the diffraction element under the guidance of the readhead module and diffract along the Y direction to generate at least two first secondary diffraction beams. The second incident beam, guided by the readhead module, is projected onto the diffraction element and diffracts along the X-direction to generate a second primary diffraction beam. The readhead module splits the second primary diffraction beam into two secondary sub-diffraction beams. The two secondary sub-diffraction beams are reflected back onto the diffraction element and diffract along the X-direction to generate two secondary diffraction beams. The positions where each primary diffraction beam and each secondary sub-diffraction beam reflects back onto the diffraction element at least partially overlap. At least one primary diffraction beam and one secondary diffraction beam exit at least partially overlap to form a first interference beam, and at least one other primary diffraction beam and another secondary diffraction beam exit at least partially overlap to form a second interference beam. The optical signal processing module determines the displacement of the diffraction element in the X and Y directions based on the phase change of the first interference beam and the phase change of the second interference beam.

2. The displacement measuring device of claim 1, wherein, The readhead module includes a first polarization element and a first angle control element; the second primary diffraction beam is split by the first angle control element and the first polarization element to form the two second primary diffraction beams.

3. The displacement measuring device of claim 1, wherein, The at least two first and second diffraction beams include a -m-order first and second diffraction beam and a +m-order first and second diffraction beam; the second diffraction beam includes a +n-order second diffraction beam; m and n are both diffraction orders; The -m-order first and second diffraction beams and one of the +n-order second and second diffraction beams are emitted with at least partial overlap to generate the first interference beam; the +m-order first and second diffraction beams and another of the +n-order second and second diffraction beams are emitted with at least partial overlap to generate the second interference beam.

4. The displacement measuring device as described in claim 3, characterized in that, The read head module includes multiple retroreflection elements; After the first incident beam is projected onto the diffraction element, it diffracts along the Y direction to produce a -m-order first primary diffraction beam and a +m-order first primary diffraction beam; The -m-order first primary diffraction beam is guided back to the diffraction element by the first retroreflection element, and diffracts along the Y direction to generate the -m-order first secondary diffraction beam; The +m-order first primary diffraction beam is guided back to the diffraction element by the second retroreflection element, and diffracts along the Y direction to generate the +m-order first secondary diffraction beam; After the second incident beam is projected onto the diffraction element, it diffracts along the X direction to generate a +n-order second primary diffraction beam. The +n-order second primary diffraction beam is guided by a third retroreflection element and reflected back toward the diffraction element. During the retroreflection process, it is split into two +n-order second primary sub-diffraction beams. The two +n-order second primary sub-diffraction beams are reflected back to the diffraction element and diffract along the X direction to generate two +n-order second secondary diffraction beams.

5. The displacement measuring device as described in claim 4, characterized in that, The readhead module includes a second angle control element and a third angle control element; the -m-order first primary diffraction beam is reflected back onto the diffraction element after passing through the second angle control element; the +m-order first primary diffraction beam is reflected back onto the diffraction element after passing through the third angle control element.

6. The displacement measuring device as described in claim 5, characterized in that, The readhead module includes a second polarization element and a third polarization element; the -m-order first primary diffraction beam is split into two -m-order first primary sub-diffraction beams after passing through the second angle control element and the second polarization element; the +m-order first primary diffraction beam is split into two +m-order first primary sub-diffraction beams after passing through the third angle control element and the third polarization element.

7. The displacement measuring device as described in claim 6, characterized in that, Both the second polarizing element and the third polarizing element include at least one of a waveplate, a Wollaston prism, a polarizer, and a polarizing beam splitter.

8. The displacement measuring device as described in claim 3, characterized in that, The displacement of the diffraction element in the X direction is ΔX, and the displacement of the diffraction element in the Y direction is ΔY. ， ； wherein P is a pitch between two adjacent repeating diffraction structures, m is a diffraction order of the first incident light beam along the Y direction, n is a diffraction order of the second incident light beam along the X direction, φ ch1 is a phase change amount of the first interference light beam, and φ ch2 is a phase change amount of the second interference light beam.

9. The displacement measuring device according to any one of claims 1 to 8, characterized in that, The read head module includes a fourth angle control element and a fifth angle control element; the first incident beam and the second incident beam are projected onto the diffraction element after passing through the fourth angle control element and the fifth angle control element, respectively.

10. The displacement measuring device according to any one of claims 1 to 8, characterized in that, The displacement measuring device includes an optical detection module, which is used to receive the first interference beam and the second interference beam, and output the first interference signal and the second interference signal to the optical signal processing module.

11. The displacement measuring device as described in claim 10, characterized in that, The first interference beam and the second interference beam have different emission directions; the optical detection module includes a first detector and a second detector; the first detector receives the first interference beam, and the second detector receives the second interference beam.

12. A photolithography apparatus, the photolithography apparatus comprising a substrate platform and a mask platform that are movable relative to each other, characterized in that, The photolithography apparatus further includes a displacement measuring device as described in any one of claims 1-11, wherein the diffraction element is attached to one of the substrate platform or the mask platform.

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