A two-degree-of-freedom alignment measurement method and system

Abstract

The application provides a two-degree-of-freedom alignment measurement method and system, which comprises the following steps: configuring a multi-directional oblique incidence illumination channel, and sequentially mapping and modulating illumination light to form two target spatial frequency components respectively carrying relative displacement information in an exit light field; imaging optics receives the exit light field, and uses an optical filtering structure to spatially screen the diffraction orders, so that the two target spatial frequency components propagate along the imaging light path and are imaged on the target surface of an image acquisition device; the image acquisition device acquires the light field intensity distribution at the target surface in a single exposure to obtain an intensity superposition image; and a processing unit performs frequency domain analysis on the intensity superposition image to solve the relative displacement between the planes to be measured. The application realizes single-region two-axis synchronous coding, greatly reduces the mark area, avoids the time displacement of polling exposure through single-frame acquisition, effectively suppresses the stray interference in combination with optical filtering, improves the solving stability, and can provide real-time high-precision position feedback for high-speed precision platforms.

Description

Technical Field

[0001] This application relates to the fields of micro-nano manufacturing, semiconductor photolithography alignment and precision motion measurement technology, and specifically to a two-degree-of-freedom alignment measurement method and system. Background Technology

[0002] In semiconductor photolithography, bonding, nanoimprinting and precision motion control processes, it is necessary to measure the in-plane relative displacement between the mask and the wafer or two relatively parallel moving planes, and provide position feedback with a high update rate to the motion platform.

[0003] Problems with existing technology: Area occupied by alignment marks: Some two-dimensional alignment schemes set one-dimensional grating marks in the x and y directions respectively. Multiple discrete marks will increase the area occupied on the mask or wafer. When the measurement positions in different directions are separated, the slight rotation of the motion stage may also introduce measurement errors related to the mark spacing.

[0004] Multi-directional measurements suffer from time misalignment: if different lighting directions or different displacement components are exposed and calculated sequentially, the effective update rate of each direction decreases, and the measurement results of different directions do not come from the same moment, which is not conducive to high-speed dual-axis closed-loop control.

[0005] Target frequencies are susceptible to the influence of non-target diffraction components: Two-dimensional binary checkerboard patterns contain zero-order and multiple higher-order spectral components, and finite field of view can also cause spectral leakage. If the illumination angle, target order, and receiving pupil are not designed in a coordinated manner, non-target components may reduce the stability of moiré phase extraction.

[0006] A search revealed a patent with application number 202310235782.6 that discloses a size measurement method that uses a checkerboard pattern of parallel isomorphic grids within the fields of view of two cameras to calculate the pose transformation matrix, and combines this with dual-view workpiece images to achieve workpiece size measurement. However, it relies on independent acquisition of data from two cameras with separate fields of view, resulting in data time misalignment and dynamic tracking errors. Furthermore, the discrete markers occupy a large area of ​​the display, which cannot meet the real-time synchronous alignment requirements of high-speed platforms. Summary of the Invention

[0007] In view of one of the deficiencies in the prior art, the purpose of this application is to provide a two-degree-of-freedom alignment measurement method and system.

[0008] A first aspect of this application provides a two-degree-of-freedom alignment measurement method, comprising: Configure a multi-directional oblique incidence illumination channel so that the illumination light is obliquely incident on the lower two-dimensional periodic mark on the plane to be measured; The illumination light is sequentially diffracted by the lower two-dimensional periodic marker and then by the upper two-dimensional periodic marker on the upper plane to be measured, or modulated, forming two target spatial frequency components in the outgoing light field that carry relative displacement information in the X and Y directions, respectively. The imaging optics receive the emitted light field and use an optical filtering structure to spatially filter the diffraction orders, so that the spatial frequency components of the two targets propagate along the imaging optical path and are imaged on the target surface of the image acquisition device. The image acquisition device acquires the light field intensity distribution at the target surface in a single exposure to obtain an intensity superimposed image; the processing unit performs frequency domain analysis on the intensity superimposed image to calculate the relative displacement between the upper and lower test planes.

[0009] Optionally, the incident azimuth and incident tilt angle of the multi-directional oblique incident illumination channel are determined based on the illumination light wavelength, the period of the upper two-dimensional periodic marker and the lower two-dimensional periodic marker in two directions, the selected diffraction order, and the target emission direction, so that the selected diffracted light enters the receiving range of the imaging optics.

[0010] Optionally, the multi-directional oblique incidence illumination channel includes a multi-path illumination beam formed by four independent light sources or by splitting the light of a single light source; The multiple illumination beams are lit synchronously during measurement, or sequentially during calibration and fault diagnosis; The multi-directional oblique incidence illumination channels employ mutually incoherent or low-coherence light sources to ensure that the intensity superimposed image is a linear superposition of the intensity patterns of each channel.

[0011] Optionally, the two-dimensional periodic marker is a two-dimensional checkerboard marker; The two-dimensional periodic markers are made using amplitude-type or phase-type gratings.

[0012] Optionally, when the target spatial frequency components in the intensity superimposed image have spectral overlap, at least one of polarization state, wavelength, modulation frequency, or spatial partitioning is used for auxiliary differentiation.

[0013] Optionally, the frequency domain analysis performed by the processing unit on the intensity superimposed image specifically includes: Using any one of the following methods—two-dimensional discrete Fourier transform, two-dimensional interpolated discrete Fourier transform, or fixed-frequency complex demodulation—the complex spectral coefficients of the two target spatial frequency components corresponding to the X and Y directions are calculated respectively. Extract the corresponding phase change based on the complex spectral coefficients. and .

[0014] Optionally, it also includes a calibration step for establishing the phase-displacement mapping relationship, specifically: Multiple sets of known standard relative displacements are applied to the upper and lower test planes along the X and Y directions, respectively, and the phase change values ​​of the spatial frequency components of the two targets are recorded simultaneously. Based on the known correspondence between standard relative displacement and phase change values, calibration parameters are determined by fitting, including the phase-displacement sensitivity matrix, direction cross-coupling coefficient, and zero-phase offset; The calibration parameters are used to perform zero-position compensation and cross-coupling correction on the phase change amount extracted in real time when calculating the relative displacement.

[0015] A second aspect of this application provides a two-degree-of-freedom alignment measurement system for implementing any of the two-degree-of-freedom alignment measurement methods described in the present application, the system comprising: The lighting module includes a multi-directional oblique incidence lighting channel configured to provide oblique incidence illumination light to a common measurement area; The marking module includes an upper two-dimensional periodic mark and a lower two-dimensional periodic mark arranged relatively parallel to each other. The upper two-dimensional periodic mark is fixed to the upper plane to be measured, and the lower two-dimensional periodic mark is fixed to the lower plane to be measured. Both the upper two-dimensional periodic mark and the lower two-dimensional periodic mark contain at least two non-collinear spatial frequency components. An imaging and filtering module is located on the light-emitting side of the upper two-dimensional periodic mark and includes an imaging optical device and an optical filtering structure. The imaging optical device is used to receive the emitted light field after diffraction by the lower two-dimensional periodic mark and modulation by the upper two-dimensional periodic mark. The optical filtering structure is used to spatially filter the diffraction order in the emitted light field so that the two target spatial frequency components carrying relative displacement information in the X and Y directions enter the imaging optical path. The acquisition and processing module includes an image acquisition device and a processing unit. The image acquisition device is located at the image plane of the imaging optical path and is used to acquire the light field intensity distribution transmitted by the imaging optical path in a single exposure to obtain an intensity superimposed image. The processing unit is electrically connected to the image acquisition device and is used to perform frequency domain analysis on the intensity superimposed image to extract the biaxial phase change and calculate the relative displacement between the upper and lower test planes.

[0016] A third aspect of this application provides an electronic device including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor, when executing the computer program, implements the two-degree-of-freedom alignment measurement method described in any one of the claims.

[0017] A fourth aspect of this application provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the two-degree-of-freedom alignment measurement method described in any one of the claims.

[0018] This application provides a dual-degree-of-freedom alignment measurement method. After a single exposure, the light signals from multiple obliquely incident illumination channels form an intensity superimposed image. The processing unit can directly perform frequency domain analysis on this single frame image to simultaneously extract dual-axis phase information and calculate relative displacement. This process eliminates the need for directional polling exposures, avoiding time misalignment between multi-channel measurements, significantly improving the effective update rate of position data, and meeting the real-time closed-loop feedback requirements of high-speed precision motion platforms.

[0019] This application utilizes two-dimensional periodic markers set on the upper and lower test planes. The illumination light is sequentially diffracted by the lower marker and modulated by the upper marker, directly forming two target spatial frequency components carrying relative displacement information in the X and Y directions respectively in the outgoing light field. This structure enables the bidirectional displacement information to be synchronously encoded in the same measurement area and the same image, avoiding the area occupation and measurement point separation errors caused by discrete markers, and effectively improving the space utilization of the marked area.

[0020] The imaging optics of this application utilize an optical filtering structure to spatially filter diffraction orders, ensuring that only light signals carrying the target's spatial frequency components propagate along the imaging optical path and are imaged onto the target surface. This optical pre-screening mechanism, in conjunction with subsequent frequency domain analysis, effectively suppresses interference from non-target stray light fields, reduces the impact of optical path adjustment deviations and directional crosstalk on the accuracy of biaxial calculations, and ensures the repeatability and reliability of relative displacement measurements.

[0021] Other technical effects resulting from the additional features will be further illustrated in the corresponding embodiments. Attached Figure Description

[0022] Other features, objects, and advantages of this application will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a flowchart illustrating a two-degree-of-freedom moiré measurement method according to an exemplary embodiment; Figure 2 A checkerboard pattern is shown according to an exemplary embodiment; Figure 3 This is a schematic diagram of a two-degree-of-freedom alignment system based on two-dimensional moiré fringe detection, according to an exemplary embodiment.

[0023] In the figure, 1-1 is the first light source; 1-2 is the second light source; 1-3 is the third light source; 1-4 is the fourth light source; 2 is the upper plane to be measured; 3 is the lower plane to be measured; 4 is the objective lens; and 5 is the acquisition and processing module. Detailed Implementation

[0024] The present application will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present application, but do not limit the present application in any way. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present application, and these all fall within the protection scope of the present application. Parts not described in detail in the following embodiments can be implemented using existing technology.

[0025] In the description of the embodiments of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0026] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature.

[0027] In the description of the embodiments in this application, "multiple" means two or more, unless otherwise explicitly specified. In this application, unless otherwise explicitly specified and limited, the terms "installed," "connected," "linked," "fixed," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0028] The terms "comprising" and "having," and any variations thereof, in the embodiments of this application are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not limited to the steps or units listed, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to such processes, methods, products, or devices.

[0029] Traditional time-division exposure results in time misalignment of X and Y axis data, leading to low effective update rates and susceptibility to dynamic tracking errors, making it difficult to meet the real-time closed-loop control requirements of high-speed platforms. To address these issues, this application provides a two-degree-of-freedom alignment measurement method.

[0030] Reference Figure 1 As shown, in one embodiment of this application, a two-degree-of-freedom alignment measurement method is provided, comprising the following steps: S100 is equipped with multi-directional oblique incidence illumination channels, so that the illumination light is obliquely incident on the lower two-dimensional periodic mark on the lower plane to be measured; S200, the illumination light is sequentially diffracted by the lower two-dimensional periodic mark on the lower test plane and by the upper two-dimensional periodic mark on the upper test plane, or modulated, forming two target spatial frequency components in the outgoing light field that carry relative displacement information in the X and Y directions respectively. S300: The imaging optics receive the outgoing light field and use an optical filter structure to spatially filter the diffraction orders, so that the spatial frequency components of the two targets propagate along the imaging optical path and are imaged on the target surface of the image acquisition device. S400: The image acquisition device acquires the light field intensity distribution at the target surface in a single exposure to obtain an intensity superimposed image; the processing unit performs frequency domain analysis on the intensity superimposed image to calculate the relative displacement between the upper and lower test planes.

[0031] The above embodiment employs four-directional synchronous oblique incident illumination and two-dimensional checkerboard bidirectional spatial frequency marking. Four intensity superimposed images are recorded in a single frame by the same camera, and two independent phase components, x and y, are extracted in the two-dimensional frequency domain, thereby realizing the synchronous calculation of two-degree-of-freedom relative displacement.

[0032] To address the issues of time misalignment in X and Y axis data caused by time-division exposure, and the large area occupied by discrete markers, in some specific embodiments of this application, in step S100, a multi-directional oblique incidence illumination channel is configured so that the illumination light is obliquely incident on the lower two-dimensional periodic markers on the lower plane to be measured. This can be achieved through the following steps: S101, set up multi-directional oblique incident lighting channels.

[0033] Specifically, multiple illumination channels are symmetrically arranged around the common measurement area (i.e., the area containing two-dimensional periodic marks on the upper and lower test surfaces).

[0034] For example, there can be four lighting channels, which are symmetrically arranged at equal height and radial distances around the common measurement area, and the optical axis of each lighting channel is precisely pointed to the common measurement area.

[0035] Specifically, the multi-channel lighting sources are preferably narrow-band light sources that are independent or have low coherence, and are configured to illuminate synchronously during measurement and sequentially during calibration or fault detection.

[0036] Low coherence here refers to the weak mutual interference between multiple light sources, making it difficult to form stable interference fringes.

[0037] It needs to be clearly defined that: "Incoherent" illumination channels do not interfere with each other; however, within the same illumination channel, incident light diffracted by the lower marker to produce different order beams, or outgoing beams with a common source after being cascaded by the upper and lower markers, will undergo self-coherent interference in the spatially overlapping region because their optical path difference is less than the coherence length of the source. For example, using a collimated LED array with a wide spectral bandwidth (e.g., Δλ≥15 nm); when the coherence length of the source is less than the maximum optical path difference of the system, only linear intensity superposition occurs between different channels on the target surface (Itotal≈I1+I2+I3+I4), thus completely eliminating the mutual interference noise between channels, while retaining the phase information formed by self-coherent interference within the channel, providing a high signal-to-noise ratio basis for the frequency domain phase solution of subsequent single-frame images.

[0038] It is understandable that, since the light sources are independent of each other, the total light intensity recorded by the image acquisition device is a linear superposition of the intensity patterns of each channel, thus avoiding phase noise introduced by multi-source interference. At the same time, the configuration of multi-channel synchronous lighting provides the optical path basis for synchronous acquisition of dual-axis information in a single frame image.

[0039] S102, two-dimensional periodic marks are set on the upper and lower planes to be measured respectively.

[0040] Specifically, the upper and lower planes to be measured are two functional surfaces that require precise alignment or relative displacement measurement.

[0041] For example, in semiconductor lithography or chip bonding applications, the upper test plane is typically a mask stage (or upper substrate fixing surface), and the lower test plane is typically a wafer stage (or lower substrate bearing surface); in precision motion measurement scenarios, the upper test plane can correspond to the upper moving stage of a stacked air-bearing guide platform or the moving platform mounting surface of a piezoelectric ceramic (PZT) displacement stage; the lower test plane can correspond to the lower fixed base of a stacked air-bearing guide platform or the static platform (fixed base) mounting surface of a piezoelectric ceramic (PZT) displacement stage.

[0042] Specifically, two-dimensional periodic markings are periodic optical modulation patterns etched or deposited on the plane under test.

[0043] For example, the two-dimensional periodic marker can be a two-dimensional checkerboard pattern, which contains at least two non-collinear spatial frequency components, and the period in each direction satisfies a preset beat frequency relationship.

[0044] Specifically, two-dimensional periodic markings can be achieved using amplitude-type gratings, which have lower manufacturing costs, or phase-type gratings, which have higher diffraction efficiency.

[0045] It is understood that in other embodiments, the two-dimensional periodic markers may also employ hole arrays, dot arrays, intersecting grids, or other patterns that are periodically repeated in two directions, as long as bidirectional displacement measurement can be achieved.

[0046] In the above embodiments, the multi-directional channel synchronous illumination and low coherence design of S101 enable the X and Y bidirectional light field information to be physically superimposed on a single frame image at the same time, completely avoiding the data delay and dynamic tracking error caused by time-division polling, and meeting the real-time requirements of high-frequency closed-loop control; S102 compresses the bidirectional frequency components into a single two-dimensional periodic mark, which greatly reduces the mask / wafer layout space occupied and avoids the area redundancy and position separation problems of traditional X and Y discrete gratings.

[0047] To address the problems of spectral aliasing between stray light and target signal generated by existing two-dimensional marker diffraction, poor phase extraction stability, and severe axial crosstalk due to the lack of optical pre-screening and decoupling mechanisms, this application achieves physical separation of the target signal through a cascaded diffraction-modulation mechanism of upper and lower markers. In some specific embodiments of this application, in S200, the illumination light is sequentially diffracted by the lower two-dimensional periodic marker on the lower test plane and modulated by the upper two-dimensional periodic marker on the upper test plane, forming two target spatial frequency components carrying relative displacement information in the X and Y directions respectively in the outgoing light field. This can be achieved through the following steps: S201, illumination light incident on the lower layer marker produces multi-level diffraction.

[0048] Specifically, obliquely incident light from multiple directions first illuminates the lower two-dimensional periodic marker. Influenced by the periodic structure of the marker, the light undergoes multi-level diffraction, forming a mixed light field in space containing zero-order direct light and multiple higher-order diffracted light.

[0049] S202, selects target diffraction orders and propagates them upwards in a directional manner.

[0050] Specifically, by coordinating the preset incident angle and the marking period, at least two target diffraction paths or target diffraction combinations are directionally selected from the mixed light field. The beam of this order propagates upward along the designed path, accurately covering the upper marking area, and completing the first loading of displacement information.

[0051] S203, the upper layer marker is secondarily modulated and the target frequency component is generated.

[0052] The upper marker modulates the target diffracted light a second time, forming multiple outgoing light field components carrying relative displacement information.

[0053] Specifically, at least two target diffracted light field components from the lower marker are incident on the upper two-dimensional periodic marker and are modulated by secondary diffraction from the upper marker. The upper and lower two-dimensional periodic markers each have at least two non-collinear reciprocal lattice vectors (spatial frequency vectors describing the size and direction of the checkerboard period).

[0054] By jointly designing the incident wave vector, the reciprocal lattice vectors marked on the upper and lower layers, the selected diffraction order, and the receiving range of the imaging objective, the components of the outgoing light field with different diffraction paths are made to overlap spatially within the imaging region.

[0055] Overlapping light fields with a fixed phase relationship within the same illumination channel undergo coherent interference, and their relative phase of interference changes linearly with the in-plane relative displacement of the upper and lower markings; the transverse wave vector difference between different diffraction path components is directly represented in the intensity image recorded by the camera as two target spatial frequency components carrying relative displacement information in the X and Y directions, respectively.

[0056] In the above embodiment, this step, through a cascaded optical path of lower-layer diffraction frequency selection and upper-layer secondary modulation, causes the obliquely incident light to beat and generate two independent moiré (target) spatial frequency components in the outgoing light field after continuously passing through the double-layer markings. This completely encodes the X and Y bidirectional relative displacement information into the phase of the optical field. It should be noted that the target spatial frequency components are represented in the frequency domain, while their corresponding spatial domain representation is moiré fringes (moiré signals). Both are descriptions of the same displacement physical information in different domains.

[0057] In some specific embodiments of this application, in S300, the imaging optics receives the emitted light field and uses an optical filtering structure to spatially filter the diffraction orders, so that the spatial frequency components of the two targets propagate along the imaging optical path and are imaged on the target surface of the image acquisition device. This can be achieved by the following steps: S301, Imaging device arrangement.

[0058] Specifically, imaging optics (such as imaging objectives) are positioned above the upper two-dimensional periodic markers, with the optical axis aligned with the common measurement area to construct a signal receiving optical path.

[0059] S302, Joint Design and Spatial Filtering.

[0060] Specifically, the optical filtering structure includes the inherent aperture stop of the imaging objective lens and / or a physical filtering element (such as a porous mask, a custom-shaped aperture stop, or a spatial light modulator) disposed at the Fourier conjugate surface of the imaging optical path. The aperture size and spatial position of the optical filtering structure are matched with the optical path parameters of the illumination incident angle, the marking period, and the target diffraction order, together forming a spatial angular spectrum screening unit, used to allow only the target diffracted light to pass through and physically block zero-order and non-target high-order stray light.

[0061] By jointly setting the illumination incident angle, marking period, target diffraction order, and objective lens numerical aperture (receiving pupil), the exit angle of the target diffracted light carrying displacement information is made to fall precisely within the objective lens receiving cone angle, and smoothly enter the imaging optical path; at the same time, the exit angle of the zero-order direct light and other non-target high-order diffracted light exceeds the receiving range and is naturally blocked by the objective lens frame or the edge of the pupil, thereby achieving spatial filtering of non-target light.

[0062] S303, target convergence imaging.

[0063] Specifically, the pure target light field, after spatial filtering, converges through the imaging objective lens, forming a clear light intensity distribution image on the photosensitive target surface of the image acquisition device (such as a CMOS / CCD camera), thus completing a single-frame physical recording.

[0064] The above embodiments, through the joint design of illumination direction, checkerboard spatial frequency, target diffraction order and objective lens receiving pupil, enable effective separation of target diffraction combination from zero-order light and some non-target orders in the spatial angular spectrum, thereby filtering out stray light interference and providing a clean signal basis with high signal-to-noise ratio for subsequent frequency domain phase extraction of single-frame images.

[0065] To facilitate a more intuitive understanding of this optical filtering mechanism, a specific example is provided in one particular implementation.

[0066] The illumination incident angle was set to 18°, the marking period was 10 μm, and the objective lens receiving half angle (numerical aperture) was 10°.

[0067] After joint design, the zero-order direct light, which is not subject to periodic modulation, is emitted at an 18° angle and is naturally blocked by the edge of the pupil because it exceeds the receiving cone angle of the objective lens by 10°.

[0068] After being modulated by the marker, the +1st order diffracted light from the target carrying displacement information is precisely deflected to 6° at the exit angle and successfully falls into the receiving range of the objective lens to enter the imaging optical path.

[0069] Other non-target high-order stray light (such as -1st order and ±2nd order) is also filtered out synchronously because its emission angle is -14° and 32° respectively, which are outside the receiving range.

[0070] Therefore, the objective lens collects only the pure target light field and focuses it onto the camera target surface, completely eliminating zero-order strong light saturation and high-order crosstalk.

[0071] It should be noted that the incident azimuth and tilt angle of each channel are determined jointly by the incident wave vector, the marked reciprocal vector, and the target exit direction, strictly following the vector diffraction matching relationship. Taking this example, to ensure that the exit angle of the +1st order diffracted light from the target falls precisely at 6° (≤10° objective lens receiving cone), the incident light is determined to be incident at an 18° tilt angle by inversely solving the spatial frequency (i.e., reciprocal vector) corresponding to the illumination wavelength and the 10 μm period. This parameter matching ensures that the target signal vector falls within the receiving pupil, while the zeroth order and other higher order components are naturally blocked because the deflection angle exceeds the cone angle range after vector superposition.

[0072] The formula for inverse solution is: The vector diffraction matching relationship is expressed as:

[0073] In the formula, and These are the wave vectors of the incident light and the final emitted light, respectively, both with a modulus of 2π / λ. and These are the integer diffraction orders corresponding to the action of light through the lower and upper markers, respectively; and These are the reciprocal vectors of the lower and upper layers, respectively, with their magnitudes periodically changing in the corresponding directions. and Decide.

[0074] Using this example as a reference, based on the target emission angle (e.g., 6°), illumination wavelength, and upper and lower layer period parameters, the incident wave vector direction (e.g., 18° tilt angle) is solved inversely using the above equations, so that the specific order combination of the final emission (e.g., ...) is obtained. The light precisely falls into the receiving pupil of the objective lens, while the zeroth-order and other higher-order components are naturally blocked because their angles exceed the cone angle range after vector superposition. This parameter matching mechanism ensures that the target signal vector passes through efficiently, while stray light is physically filtered out.

[0075] In some specific embodiments of this application, in S400, the image acquisition device acquires the light field intensity distribution at the target surface during a single exposure to obtain an intensity superimposed image; the processing unit performs frequency domain analysis on the intensity superimposed image to calculate the relative displacement between the upper and lower planes to be measured, which can be achieved by the following steps: S401, based on the non-coherent or low-coherence characteristics of the four light sources, the light fields of each channel are linearly superimposed on the target surface; the processing unit directly reads the single-frame intensity superimposed image as the original input data, without the need to perform time-sequential separation or independent extraction of the signals of each light source, ensuring that the dual-axis information comes from the same physical moment.

[0076] S402, the processing unit performs two-dimensional frequency domain analysis on the intensity superimposed image I(u, v).

[0077] Specifically, using two-dimensional discrete Fourier transform, two-dimensional interpolated discrete Fourier transform, fixed-frequency complex demodulation, or other equivalent algorithms, the complex spectral coefficients of the two target spatial frequency components corresponding to the X and Y direction displacements are located and calculated in the frequency domain, thereby extracting the corresponding phase change. , .

[0078] S403, extract the phase change amount , Substituting the preset phase-displacement mapping relationship or calibration sensitivity matrix, after directional cross-coupling compensation and zero-position offset subtraction, the relative displacement of the upper and lower test planes in the X and Y directions is jointly calculated and output.

[0079] The above embodiments completely avoid the time delay caused by multi-frame polling by directly analyzing the frequency domain of a single frame image. At the same time, the synergistic effect of frequency domain phase extraction and sensitivity matrix calibration effectively filters out residual stray light interference, reduces the impact of system assembly deviation and axial crosstalk on the solution results, and significantly improves the real-time performance, stability and repeatability of biaxial displacement measurement.

[0080] In another embodiment of this application, the method further includes a calibration and measurement process, specifically comprising the following steps: Calibration phase: Establish phase-displacement mapping model.

[0081] Specifically, the precision motion stage is controlled to apply multiple sets of known relative displacements along the X and Y directions, and the phase change data of the spatial frequency components of the two targets are recorded simultaneously. Based on the correspondence between the known displacement and phase change data, the phase-displacement sensitivity matrix, the directional cross-coupling coefficient and the zero-phase offset parameter are fitted and determined to complete the system calibration.

[0082] Measurement phase: Real-time displacement joint calculation.

[0083] Specifically, the current phase change is extracted from the real-time acquired single-frame intensity overlay image. , After deducting the zero-phase bias, the corrected phase change is substituted into the phase-displacement sensitivity matrix. After cross-coupling compensation, the real-time relative displacement of the upper and lower test planes in the X and Y directions is obtained through joint calculation.

[0084] Based on the same technical concept, some other embodiments of this application also provide a two-degree-of-freedom alignment measurement system for implementing the above-described measurement method, such as... Figure 3 As shown, the system includes: Illumination module: includes multi-directional oblique incidence illumination channels, configured to provide oblique incidence illumination light to the common measurement area of ​​two-dimensional periodic marks set on the upper and lower planes to be measured; The marking module includes an upper two-dimensional periodic marker and a lower two-dimensional periodic marker arranged in parallel, which are fixed to the upper and lower test planes respectively, and each contains at least two non-collinear spatial frequency components. Imaging and filtering module: Located above the upper two-dimensional periodic marker, it includes imaging optics and optical filtering structure. It is used to receive the outgoing light field and perform spatial filtering on the diffraction order, so that the light signal carrying the target spatial frequency component can enter the imaging optical path. Acquisition and Processing Module: Includes an image acquisition device and a processing unit. The image acquisition device is used to record the intensity superimposed image formed by multi-directional illumination channels. The processing unit is used to perform frequency domain analysis on the intensity superimposed image to extract the biaxial phase change and calculate the relative displacement.

[0085] In some specific embodiments, the illumination module is a symmetrical illumination assembly containing four obliquely incident illumination channels. Each channel can consist of four independent light sources, or be generated from a single light source via a beam splitter network, and are arranged symmetrically at equal heights and intervals around a common measurement area, with the optical axes all converging within this area (e.g., ...). Figure 3 The first light source (1-1), second light source (1-2), third light source (1-3), and fourth light source (1-4) are shown in the diagram. Each channel uses a non-coherent or low-coherence narrowband light source, configured to illuminate synchronously during routine measurements and sequentially during calibration or fault diagnosis.

[0086] In some specific embodiments, the marking module is a two-dimensional checkerboard measurement unit. It consists of an upper checkerboard and a lower checkerboard, which are relatively parallel. The upper checkerboard is fixed to the mask stage or the upper test plane 2, and the lower checkerboard is fixed to the wafer stage or the lower test plane 3. The two marks are preferably amplitude-type checkerboards, each containing spatial frequency components in the X and Y directions, and generating bidirectional moiré signals through corresponding periodic relationships; a phase-type checkerboard can also be used as an alternative.

[0087] In some specific embodiments, the imaging and filtering module is the imaging objective lens 4. Located above the upper checkerboard, its optical axis points towards the common measurement area. Its numerical aperture, receiving pupil, illumination angle, and checkerboard reciprocal vector are jointly designed to allow the target diffraction combination to enter the receiving optical path, and to keep the zeroth-order light and at least some non-target diffraction orders outside the receiving pupil, thus achieving spatial filtering.

[0088] In some specific implementations, the acquisition and processing module 5 comprises a camera and a calculation unit 5. A CMOS / CCD camera is mounted on the image plane of the imaging lens and is used to simultaneously record the intensity superposition image formed by four illumination sources in a single exposure. The processing unit (which can be an industrial computer, DSP, or FPGA) performs two-dimensional frequency domain analysis on the image (such as two-dimensional discrete Fourier transform, interpolation DFT, or fixed-frequency complex demodulation), extracts the complex coefficients and phase changes of the two target spatial frequency components, and calculates the biaxial relative displacement based on the calibrated sensitivity matrix.

[0089] The above embodiments, through the coordinated operation of various modules, fully realize the aforementioned measurement method. The combination of four-directional synchronous illumination and two-dimensional checkerboard marking allows for the acquisition of bidirectional displacement information within the same measurement area, effectively reducing the marking area occupancy and measurement point separation errors. The joint design of the imaging objective and receiving pupil suppresses zero-order light and non-target orders, improving the extractability and solution stability of target frequency components. Single-frame recording and superimposed image processing, combined with frequency domain calculation, avoids time misalignment caused by polling exposure, achieving single-frame dual-axis synchronous measurement. This system boasts a high effective update rate and strong anti-interference capability, making it suitable for providing real-time position feedback to high-speed precision motion platforms.

[0090] The preferred features in the above embodiments can be used individually in any embodiment, or in any combination thereof, provided they do not conflict with each other. Furthermore, parts not described in detail in the embodiments can be implemented using existing technologies.

[0091] Based on the same technical concept, in other embodiments of this application, a terminal is provided, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, it can be used to perform the above-described method.

[0092] Based on the same technical concept, in other embodiments of this application, a computer-readable storage medium is provided, on which a computer program is stored, which, when executed by a processor, can be used to perform the above-described method.

[0093] Optionally, the memory is used to store programs; the memory may include volatile memory, such as random-access memory (RAM), such as static random-access memory (SRAM), double data rate synchronous dynamic random-access memory (DDR SDRAM), etc.; the memory may also include non-volatile memory, such as flash memory. The memory is used to store computer programs (such as application programs and functional modules that implement the above methods), computer instructions, etc., and the aforementioned computer programs and computer instructions can be partitioned and stored in one or more memories. Furthermore, the aforementioned computer programs, computer instructions, data, etc., can be accessed by the processor.

[0094] The aforementioned computer programs, computer instructions, etc., can be stored in partitions within one or more memory locations. Furthermore, the aforementioned computer programs, computer instructions, data, etc., can be accessed by a processor.

[0095] A processor is used to execute a computer program stored in memory to implement the various steps of the methods involved in the above embodiments. For details, please refer to the relevant descriptions in the preceding method embodiments.

[0096] The processor and memory can be separate structures or integrated structures. When the processor and memory are separate structures, they can be coupled together via a bus.

[0097] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0098] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0099] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0100] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0101] The foregoing has described some specific embodiments of this application. It should be understood that this application is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the substantive content of this application. The above-described preferred features can be used in any combination without conflict.

Claims

1. A two-degree-of-freedom alignment measurement method, characterized in that, include: Configure a multi-directional oblique incidence illumination channel so that the illumination light is obliquely incident on the lower two-dimensional periodic mark on the plane to be measured; The illumination light is sequentially diffracted by the lower two-dimensional periodic marker and then by the upper two-dimensional periodic marker on the upper plane to be measured, or modulated, forming two target spatial frequency components in the outgoing light field that carry relative displacement information in the X and Y directions, respectively. The imaging optics receive the emitted light field and use an optical filtering structure to spatially filter the diffraction orders, so that the spatial frequency components of the two targets propagate along the imaging optical path and are imaged on the target surface of the image acquisition device. The image acquisition device acquires the light field intensity distribution at the target surface in a single exposure to obtain an intensity superimposed image; the processing unit performs frequency domain analysis on the intensity superimposed image to calculate the relative displacement between the upper and lower test planes.

2. The two-degree-of-freedom alignment measurement method according to claim 1, characterized in that, The incident azimuth and incident tilt angle of the multi-directional oblique incident illumination channel are determined based on the illumination light wavelength, the periods of the upper and lower two-dimensional periodic markers in two directions, the selected diffraction order, and the target emission direction, so that the selected diffracted light enters the receiving range of the imaging optics.

3. The two-degree-of-freedom alignment measurement method according to claim 1, characterized in that, The multi-directional oblique incidence illumination channel includes a multi-path illumination beam formed by four independent light sources or a single light source splitting the light. The multiple illumination beams are lit synchronously during measurement, or sequentially during calibration and fault diagnosis; The multi-directional oblique incidence illumination channels employ mutually incoherent or low-coherence light sources to ensure that the intensity superimposed image is a linear superposition of the intensity patterns of each channel.

4. The two-degree-of-freedom alignment measurement method according to claim 1, characterized in that, The two-dimensional periodic marker is a two-dimensional checkerboard marker; The two-dimensional periodic markers are made using amplitude-type or phase-type gratings.

5. The two-degree-of-freedom alignment measurement method according to claim 1, characterized in that, When the target spatial frequency components in the intensity superimposed image have spectral overlap, at least one of polarization state, wavelength, modulation frequency, or spatial partitioning is used for auxiliary differentiation.

6. The two-degree-of-freedom alignment measurement method according to claim 1, characterized in that, The frequency domain analysis performed by the processing unit on the intensity superimposed image specifically includes: Using any one of the following methods—two-dimensional discrete Fourier transform, two-dimensional interpolated discrete Fourier transform, or fixed-frequency complex demodulation—the complex spectral coefficients of the two target spatial frequency components corresponding to the X and Y directions are calculated respectively. Extract the corresponding phase change based on the complex spectral coefficients. and .

7. The two-degree-of-freedom alignment measurement method according to claim 1, characterized in that, It also includes calibration steps for establishing the phase-displacement mapping relationship, specifically: Multiple sets of known standard relative displacements are applied to the upper and lower test planes along the X and Y directions, respectively, and the phase change values ​​of the spatial frequency components of the two targets are recorded simultaneously. Based on the known correspondence between standard relative displacement and phase change values, calibration parameters are determined by fitting, including the phase-displacement sensitivity matrix, direction cross-coupling coefficient, and zero-phase offset; The calibration parameters are used to perform zero-position compensation and cross-coupling correction on the phase change amount extracted in real time when calculating the relative displacement.

8. A two-degree-of-freedom alignment measurement system, characterized in that, The system for implementing the method as described in any one of claims 1-7 includes: The lighting module includes a multi-directional oblique incidence lighting channel configured to provide oblique incidence illumination light to a common measurement area; The marking module includes an upper two-dimensional periodic mark and a lower two-dimensional periodic mark arranged relatively parallel to each other. The upper two-dimensional periodic mark is fixed to the upper plane to be measured, and the lower two-dimensional periodic mark is fixed to the lower plane to be measured. Both the upper two-dimensional periodic mark and the lower two-dimensional periodic mark contain at least two non-collinear spatial frequency components. An imaging and filtering module is located on the light-emitting side of the upper two-dimensional periodic mark and includes an imaging optical device and an optical filtering structure. The imaging optical device is used to receive the emitted light field after diffraction by the lower two-dimensional periodic mark and modulation by the upper two-dimensional periodic mark. The optical filtering structure is used to spatially filter the diffraction order in the emitted light field so that the two target spatial frequency components carrying relative displacement information in the X and Y directions enter the imaging optical path. The acquisition and processing module includes an image acquisition device and a processing unit. The image acquisition device is located at the image plane of the imaging optical path and is used to acquire the light field intensity distribution transmitted by the imaging optical path in a single exposure to obtain an intensity superimposed image. The processing unit is electrically connected to the image acquisition device and is used to perform frequency domain analysis on the intensity superimposed image to extract the biaxial phase change and calculate the relative displacement between the upper and lower test planes.

9. An electronic device, characterized in that, It includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor, when executing the computer program, implements the two-degree-of-freedom alignment measurement method as described in any one of claims 1-7.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the two-degree-of-freedom alignment measurement method as described in any one of claims 1-7.

Images