Autofocus system

Abstract

An autofocus system includes (a) an illumination path configured to illuminate a sample with an illumination beam, forming a plurality of point arrays on the sample, including an upstream point array formed on a first side of an imaging region and a downstream point array formed on the other side of the imaging region; (b) a mask located at an entrance pupil, the mask including a pair of off-axis slits for truncating each collection beam to provide a pair of rays for each collection beam; and (c) a splitter including (i) a first reflective surface configured to guide a first ray associated with a first collection beam to a first branch, and (ii) a second reflective surface facing the first reflective surface and configured to guide a ray associated with a second collection beam to a second branch; wherein the first and second reflective surfaces are located at reflective surface positions outside the image plane and at positions where there is separation between the first and second rays.

Description

Technical Field

[0001] This application claims the benefit and priority of U.S. Patent Application No. 18 / 762,574, filed July 2, 2024, entitled “Autofocus System with Divider,” the entire contents of which are incorporated herein by reference. Background Technology

[0002] In high-volume optical inspection systems, autofocus plays a crucial role in ensuring accurate and efficient inspection. These systems are designed to rapidly inspect samples, such as wafers or photomasks, to detect defects or anomalies.

[0003] A major challenge for these systems is maintaining consistent focus over large areas of the sample surface. Samples may vary in thickness, curvature, or surface topography, which can affect the focal plane. Without autofocus, the inspection system may struggle to maintain optimal focus, leading to inaccurate or incomplete inspection results.

[0004] The market increasingly demands effective and accurate autofocus systems and methods. Utility Model Content

[0005] An autofocus system and method thereof are provided, as shown in this application.

[0006] An autofocus system is provided, comprising (a) an illumination path configured to illuminate a sample with an illumination beam to form a plurality of point arrays on the sample, including an upstream point array formed on a first side of an imaging region and a downstream point array formed on the other side of the imaging region; (b) a mask located at an entrance pupil, the mask including a pair of off-axis slits for truncating each collection beam to provide a pair of rays for each collection beam; and (c) a splitter including (i) a first reflective surface configured to guide a first ray associated with the first collection beam to a first branch, and (ii) a second reflective surface facing the first reflective surface and configured to guide a second ray associated with the second collection beam to a second branch; wherein the first and second reflective surfaces are located at positions of the reflective surfaces outside an image plane and at positions where there is separation between the first and second rays.

[0007] A method for autofocusing by an autofocus system is provided, comprising: (a) illuminating a sample with an illumination beam to form a plurality of point arrays on the sample, including an upstream point array formed on one side of an imaging region and a downstream point array formed on the other side of the imaging region; (b) collecting a first collection beam and a second collection beam from the sample; (c) truncating each collection beam using a mask located at an entrance pupil, wherein the mask includes a pair of off-axis slits to provide a pair of rays for each collection beam; (d) guiding a first ray associated with the first collection beam to a first branch using a first reflective surface of an optical segmentation assembly located at a reflective surface location but outside an intermediate image plane; (e) guiding a second ray associated with the second collection beam to a second branch using a second reflective surface of the optical segmentation assembly, wherein the second reflective surface faces the first reflective surface; (f) ensuring separation between the first ray and the second ray at the reflective surface location; and (g) autofocusing the system according to the collection beams in the first branch and the second branch. Attached Figure Description

[0008] The subject matter considered as embodiments is specifically pointed out and explicitly claimed in the final part of the specification. However, the embodiments, in terms of their organization and operation, along with their samples, features, and advantages, can be best understood by referring to the following detailed description, which is read in conjunction with the accompanying illustrations:

[0009] Figure 1 It demonstrates an example of an autofocus system and its related evaluation system;

[0010] Figure 2 It demonstrates an example of a sample and the points formed on it;

[0011] Figure 3 An example of a mask with an off-axis slit is demonstrated, as well as the effect of the wavefront on the light rays exiting the mask;

[0012] Figure 4 An example of an optical process applied by a slit in a mask is demonstrated;

[0013] Figure 5 It demonstrates an example of distance-based focus sensing;

[0014] Figure 6 Examples of at least some components of an autofocus system are demonstrated;

[0015] Figure 7 Examples of at least some components of an autofocus system are demonstrated;

[0016] Figure 8 Examples of at least some components of an autofocus system are demonstrated;

[0017] Figure 9 Examples of at least some components of an autofocus system are demonstrated;

[0018] Figure 10 Examples of at least some components of an autofocus system are demonstrated;

[0019] Figure 11 Examples of at least some components of an autofocus system are demonstrated;

[0020] Figure 12 Examples of at least some components of an autofocus system are demonstrated;

[0021] Figure 13 An example of a divider was demonstrated;

[0022] Figure 14 Examples of at least some components of an autofocus system are demonstrated;

[0023] Figure 15 Examples of at least some components of an autofocus system are demonstrated;

[0024] Figure 16 Examples of at least some components of an autofocus system are demonstrated;

[0025] Figure 17 Examples of at least some components of an autofocus system are demonstrated;

[0026] Figure 18 It demonstrates an example of points formed on a sensor;

[0027] Figure 19 Examples of at least some components of an autofocus system are demonstrated;

[0028] Figure 20 An embodiment of the method is described;

[0029] Figure 21 An embodiment of a method is described; and

[0030] Figure 22 An embodiment of the method is described.

[0031] For simplification and clarity, components shown in the diagrams may not be drawn to scale. For example, the dimensions of some components may be exaggerated relative to others for better clarity. Furthermore, the same component symbols may be repeated across diagrams where appropriate to indicate corresponding or similar components. Detailed Implementation

[0032] Optical systems, particularly those used in large-field and high numerical aperture (NA) imaging applications such as inspection tools, face significant challenges in managing complexity while maintaining performance. These systems typically require sophisticated optical components to achieve the desired magnification and resolution across a wide field of view. However, the high NA required to achieve such performance often necessitates complex optical arrangements, which can introduce distortion and reduce transmitted intensity. This becomes particularly problematic when the sample or the specimen being inspected is sensitive to the intensity and quality of illumination.

[0033] Existing solutions to these challenges typically involve using multiple lenses and compensating optics to correct field curvature and other aberrations. While effective, these approaches tend to increase complexity and sensitivity to calibration and manufacturing tolerances. Furthermore, incorporating a large number of optics can lead to reduced transmission intensity due to light loss at each interface, which is particularly detrimental in applications where the sample cannot withstand high-intensity illumination, as the illumination intensity must be increased to compensate for the significant loss. In addition, the complexity of these systems often results in increased susceptibility to misalignment and manufacturing variations, which can impair optical performance and require more stringent and costly production controls.

[0034] This system addresses these and other problems by providing a simplified optical solution that enables field separation and the realization of near-diffraction-limited point arrays through field segmentation. The system includes a mask (in...) Figure 1 The standard designation is 110) and it has double slits (in Figure 1 The structure (denoted as 112) maintains the original optical axis and uses only an off-center slit to protect optical performance. In this way, the system introduces only field curvature, which can be effectively managed through simple window-based optical path compensation techniques—for example, a first field curvature compensator 144 and a second field curvature compensator 174, which are segmented optical components (see...). Figure 14 The elegance of this solution lies in its reduced system complexity, enabling high performance with minimal tolerance sensitivity. The system design integrates a smaller number of lenses, improving both transmission intensity and sensitivity without damaging the sample.

[0035] In addition, the system's divider (in) Figure 1 The 130 (labeled as 130) operates using a common optical axis, minimizing overlap between adjacent fields and enabling samples to be illuminated in a staggered dot array manner. This innovative approach to autofocus and field segmentation represents a significant advancement, providing a less complex, more robust, and efficient solution for imaging systems with high NA and large fields.

[0036] In the field of aerial imaging, practitioners often face challenges related to the limited field of view (FOV) captured by camera systems. Traditional methods for maximizing FOV typically involve placing multiple cameras side-by-side. This configuration aims to extract the maximum FOV from the scene while minimizing the number of optical relays required. However, this arrangement can lead to increased complexity, cost, and size of the imaging setup, as well as potential alignment issues between the individual camera units.

[0037] Existing solutions for enhancing the field of view (FOV) in aerial imaging tools typically require a large number of repetitive optical components, which can become cumbersome and economically inefficient. Furthermore, using multiple cameras to cover a wider area can introduce complexity in image processing and stitching, potentially impacting overall image quality. Additionally, the multiple optical repeaters required for focusing each camera can further complicate system design and reduce imaging efficiency.

[0038] This system addresses these challenges by introducing a strategic segmenter near the image plane downstream of the mask. The FLS effectively segments the field of view onto the wafer or mask without requiring additional optical relays to feed the image into the camera. By utilizing a relatively small numerical aperture (NA) in image space, the system minimizes the spacing between fields of view on the wafer or lithographic mask. The system also identifies optimal locations to segment the field of view from the middle image, ensuring that light is not truncated, which typically requires the use of a bladed mirror. This innovative approach allows for repeated capture of an extended FOV with minimal optical components, simplifying the design of imaging systems and reducing associated costs.

[0039] According to one embodiment, an autofocus system is provided, comprising: an illumination path configured to illuminate a sample with an illumination beam to form a plurality of point arrays on the sample, including a first set of point arrays formed on a first side of an imaging region and a second set of point arrays formed on the other side of the imaging region; a sensor; a controller; a collection path including an entrance pupil, the collection path configured to collect a collection beam emitted from the sample and to focus the collection beam on a first axis while imaging the entrance pupil along a second axis to provide a beam for optical processing; wherein the sensor is configured to generate a detection signal representing the optically processed beam; and wherein the controller is configured to determine a focus state of an evaluation beam incident on the imaging region.

[0040] The imaging area is provided by using aerial illumination.

[0041] According to one embodiment, the controller is configured to generate a preliminary autofocus estimate of the future focus state of the evaluation beam when the evaluation beam reaches a defined position of the first set of point arrays.

[0042] According to one embodiment, the controller is configured to update the initial autofocus estimate as the device approaches a defined location near the imaging region.

[0043] According to one embodiment, the first set of point arrays includes a first point array, a second point array, and a third point array.

[0044] According to one embodiment, the second set of point arrays includes a fourth point array, a fifth point array, and a sixth point array.

[0045] According to one embodiment, each plurality of point arrays and the first group of point arrays are staggered on the first axis and the second axis.

[0046] According to one embodiment, each point array is a linear point array.

[0047] According to one embodiment, the optically processed beam forms a pair of points in each plurality of point arrays, wherein the distance between each pair of points indicates the focus state associated with the corresponding point array.

[0048] According to one embodiment, the controller is configured to ignore detection signals based on sample components that are illuminated by at least a partial illumination beam.

[0049] According to one embodiment, the controller is configured to determine at least one of the pitch angle and roll angle of the illumination beam.

[0050] Figure 20 An example of an autofocus method 500 of an autofocus system (10) is shown, the method comprising:

[0051] a. Illuminate 510 samples with an illumination beam to form multiple dot arrays on the samples, wherein the dot arrays include a first set of dot arrays formed on a first side of the imaging region and a second set of dot arrays formed on the other side of the imaging region.

[0052] b. Collect the 520 beam emitted from the sample along the collection path including the entrance pupil.

[0053] c. Focus the collected beam along the first axis 530, while imaging the entrance pupil along the second axis to provide the beam for optical processing.

[0054] d. Generate a detection signal of 540 representing the optical processing beam.

[0055] e. Determine the focus state of the evaluation beam incident on the imaging region at 550°. The detection signal indicates the focus state at multiple locations on the sample—these multiple locations form a multidimensional array with two or more locations on each of multiple axes—and originate from different sides of the imaging region—therefore, deriving the focus state of the evaluation beam is straightforward.

[0056] f. Respond to the focus status 590. The response may include changing the focus status of the evaluation system.

[0057] According to one embodiment, the method includes generating a preliminary autofocus estimate of the future focus state of the evaluated beam when it reaches a defined position of a first set of point arrays.

[0058] According to one embodiment, the method includes updating the initial autofocus estimate when the imaging region approaches a defined position.

[0059] According to one embodiment, the first set of point arrays includes a first point array, a second point array, and a third point array.

[0060] According to one embodiment, the second set of point arrays includes a fourth point array, a fifth point array, and a sixth point array.

[0061] According to one embodiment, each plurality of point arrays and the first group of point arrays are staggered along a first axis and a second axis. This staggering along the two axes reduces the number of segmentation components required for separation between the plurality of point arrays.

[0062] According to one embodiment, each point array is a linear point array.

[0063] According to one embodiment, the optically processed beam forms a pair of points for each plurality of point arrays, wherein the distance between each pair of points represents the focus state associated with the corresponding point array.

[0064] According to one embodiment, method 500 includes ignoring detection signals based on a sample component, the sample component being illuminated by at least a portion of an illumination beam.

[0065] According to one embodiment, step 540 includes determining at least one of the pitch angle and roll angle of the illumination beam.

[0066] According to one embodiment, an autofocus system is provided, comprising:

[0067] a. An illumination path configured to illuminate a sample with an illumination beam, forming a plurality of point arrays on the sample, including a first set of point arrays formed on one side of the imaging region and a second set of point arrays formed on the other side of the imaging region.

[0068] b. Controller.

[0069] c. A collection path configured to receive a first collection beam and a second collection beam from the sample. The collection path includes:

[0070] i. A mask located at the entrance pupil, the mask comprising a pair of off-axis slits for truncating each collected beam to provide a pair of rays for each collected beam.

[0071] ii. A splitter configured to (i) guide a first ray associated with a first collected beam to a first branch, and (ii) guide a ray associated with a second collected beam to a second branch.

[0072] iii. A sensor following the first and second branches, configured to receive two points from each plurality of point arrays, wherein the distance between each pair of points indicates the focus state associated with the corresponding point array. The optical axis of the first branch faces the optical axis of the second branch.

[0073] According to one embodiment, the controller is configured to receive detection signals from at least one sensor, including a first sensor and a second sensor, and to determine the focus state of the evaluation beam. According to another embodiment, the controller is configured to change the focus of the evaluation system by controlling one or more engines that set the focus of the evaluation system, for example, by moving a lens or other optical component of the evaluation system, by changing the position of the evaluation system, by changing the position of the sample, etc.

[0074] According to one embodiment, the first branch includes a first spherical telescope, a first field curvature compensator, and a first collimation relay.

[0075] According to one embodiment, the second branch includes a second spherical telescope, a second field curvature compensator, and a second collimation relay.

[0076] According to one embodiment, the first field curvature compensator, unlike a lens, is essentially composed of a first segmented optical assembly comprising segments with different refractive indices. The first segmented optical assembly is located in a region where the field associated with light is very small (discrete).

[0077] According to one embodiment, the second field curvature compensator, unlike a lens, is essentially composed of a second segmented optical assembly comprising sections with different refractive indices.

[0078] According to one embodiment, each of the first segmented optical component and the second segmented optical component is located at a position where the field related to light is very small.

[0079] According to one embodiment, the first ray includes a pair of first central rays (in) Figure 12 The markings are 66-2, 67-2) and two pairs of first marginal rays (the first pair of marginal rays (in Figure 12 The middle label is 66-1, 67-1) and the second pair of edge rays (in Figure 12The first curvature compensator is the first segmented optical component, which is basically composed of (i) the first segment of the first refractive index (in Figure 14 (i) A pair of first central rays propagate through the first segment, and (ii) a second segment with a second refractive index (in...). Figure 14 (Illustrated as 144-2) Two first pair of edge rays propagate through the second segment, wherein the first refractive index is different from the second refractive index.

[0080] According to one embodiment, the second ray includes a pair of second central rays (in...) Figure 12 The middle label is 68-2, 69-2) and two pairs of marginal rays (including the first pair of marginal rays (in Figure 12 The middle label is 68-1, 69-1) and the second pair of edge rays (in Figure 12 The winning designation is indicated as 68-3, 69-3).

[0081] According to one embodiment, the second curvature compensator (in...) Figure 14 The section marked 174 is the second segmented optical component, essentially consisting of a first segment (174-1) with a first refractive index, through which a pair of second central rays (including a third pair of peripheral rays 68-2 and a fourth pair of peripheral rays 69-2) propagate, and a second segment with a second refractive index (in... Figure 14 (Illustrated as 174-2), two pairs of edge rays propagate through the second segment, wherein the first refractive index is different from the second refractive index.

[0082] According to one embodiment, the first spherical telescope is configured to provide a reduced image of the entrance pupil at the focal plane of the output lens of the first spherical telescope (the reduction factor may be between six and twelve or equal to ten, or any other value).

[0083] According to one embodiment, the second spherical telescope is configured to provide a reduced image of the entrance pupil at the focal plane of the output lens of the second spherical telescope.

[0084] According to one embodiment, the first collimation relay includes a first relay input spherical lens and a first relay output spherical lens.

[0085] According to one embodiment, the second collimation relay includes a second relay input spherical lens and a second relay output spherical lens.

[0086] According to one embodiment, the autofocus system includes a pair of first prisms located at the focal plane of the output lens of a first spherical telescope.

[0087] According to one embodiment, the autofocus system includes a pair of second prisms located at the focal plane of the output lens of a second spherical telescope. The pair of second prisms separates the rays of a first pair of light rays from each other.

[0088] According to one embodiment, the autofocus system includes a first collimation relay motion mechanism configured to change the distance between a first relay input spherical lens and a first relay output spherical lens.

[0089] According to one embodiment, a first collimation relay motion mechanism moves a first relay output spherical lens and simultaneously moves a first sensor to maintain the distance between the first relay output spherical lens and the first sensor. According to one embodiment, the first collimation relay motion mechanism includes a first motor.

[0090] According to one embodiment, the autofocus system includes a second collimation relay motion mechanism configured to change the distance between a second relay input spherical lens and a second relay output spherical lens.

[0091] According to one embodiment, the second collimating relay motion mechanism moves the second relay output spherical lens and the second sensor to maintain the distance between the second relay output spherical lens and the second sensor. According to one embodiment, the second collimating relay motion mechanism includes a second motor.

[0092] According to one embodiment, different distances between the relay input spherical lens and the relay output spherical lens result in different trade-offs with the dynamic range and sensitivity of the autofocus system. A larger dynamic range is associated with lower sensitivity. Different distances are related to different effective focal lengths of the collimating relay.

[0093] According to one embodiment, the different distances between the first relay input spherical lens and the first relay output spherical lens are associated with different effective focal lengths of the first collimating relay.

[0094] According to one embodiment, the first collimation relay is essentially composed of a first relay input spherical lens and a first relay output spherical lens.

[0095] The relay includes a relay input spherical lens and a relay output spherical lens with defects or aberrations, such that the optical power at different points on any relay spherical lens is different. These different optical powers will result in residual optical power even on the secondary axis of any relay spherical lens. According to one embodiment, the optical power value at a point on the relay spherical lens is related to the spatial relationship between that point and the center of the relay spherical lens. Optical power is related to magnification.

[0096] According to one embodiment, the first collimating repeater displays the main optical power along the main axis, and when a beam of oblique light (i.e. off-axis light) is received—the oblique light is directed toward the main axis and the collimating axis of the collimating repeater—the oblique light hits a point located outside the center of the repeater's spherical lens (off-center point) and displays the optical power on both axes.

[0097] The tilted light portion is deflected because the optical axis formed between the mask and the splitter has a non-zero angle with each optical axis of the first and second branches.

[0098] According to some embodiments, the autofocus system includes an optional depth-of-field unit configured to select a reference focal plane for the autofocus system.

[0099] According to some embodiments, the optional depth-of-field unit includes a first optional depth-of-field unit—the unit being optionally located within or outside the first branch. According to some embodiments, the first optional depth-of-field unit is a first window optionally located within the first spherical telescope. When located within the first spherical telescope, the depth of field of the first branch is at a first position; when located outside the first spherical telescope, the depth of field of the first branch is at a second position, which differs from the first position.

[0100] According to some embodiments, the optional depth-of-field unit includes a second optional depth-of-field unit—the unit being optionally located within or outside the second branch. According to some embodiments, the second optional depth-of-field unit is a second window optionally located within the second spherical telescope. When located within the second spherical telescope, the depth of field of the second branch is at a third position; when located outside the second spherical telescope, the depth of field of the second branch is at a fourth position, the second position being different from the first position.

[0101] Figure 21 An example of an autofocus method 501 in an autofocus system (10) is shown, the method comprising:

[0102] a. Illuminate the sample (510) with an illumination beam (30) to form a plurality of dot arrays (40) on the sample, wherein the dot arrays include a first set of dot arrays (42) formed on a first side of the imaging region (39) and a second set of dot arrays (44) formed on the other side of the imaging region (39).

[0103] b. Collection (520) A collection beam emitted from the sample along a collection path including the entrance pupil.

[0104] c. Focus (530) along the first axis (91) to collect the beam, while simultaneously imaging the entrance pupil along the second axis (92) to provide the beam for optical processing.

[0105] d. Generate (540) a detection signal (100) representing the optically processed beam.

[0106] e. Determine the focus state of the evaluation beam (38) incident on the imaging area (39) (550).

[0107] f. Respond to the focus status (590). The response may include changing the focus status of the evaluation system.

[0108] According to one embodiment, steps 510 to 550 are repeated multiple times at different time points.

[0109] According to one embodiment, step 560, following step 540, generates a preliminary autofocus estimate, which is the future focus state of the evaluation beam obtained when the evaluation beam reaches the defined position of the first set of point arrays. Step 560 may be included in step 590.

[0110] For example—assuming the sample is scanned such that the first dot array is used before the beam is evaluated—the initial autofocus estimate might be based on focus information embedded in the first dot array. The initial autofocus estimate might be equal to the focus state reflected by the first dot array—or it might be different from the focus state reflected by the first dot array.

[0111] For example—assuming the sample is scanned such that the second dot array is used before the beam is evaluated—the initial autofocus estimate might be based on focus information embedded in the second dot array. The initial autofocus estimate might be equal to the focus state reflected by the second dot array—or it might differ from the focus state reflected by the second dot array.

[0112] According to one embodiment, method 501 includes step 570, updating the preliminary autofocus estimate when a defined position is reached near the imaging region (39). Step 570 may be included in step 590.

[0113] The update may be based on the focus status of the imaging area (or the focus of any dot array group) obtained during one or more iterations of steps 510-550 performed after the iteration that provides the initial autofocus estimate.

[0114] For example, see Figure 2 . Figure 2 The right side displays sample 99 and the first and second sets of dot arrays. During this period, at a first time point, a preliminary autofocus estimate is made for the focus state of imaging region 39, based on focus information embedded in the first set of dot arrays. Step 570 may update the preliminary autofocus estimate before imaging region 39 reaches the position of the first set of dot arrays (at the first time point). Figure 2 The left side shows that the imaging area 39 reaches the position of the first set of point arrays (at the first time point).

[0115] According to one embodiment, each plurality of point arrays (40) and the first set of point arrays (42) are staggered on the first axis (91) and the second axis (92).

[0116] According to one embodiment, some or all of the point arrays are linear point arrays.

[0117] According to one embodiment, some or all of the point arrays are non-linear point arrays.

[0118] According to one embodiment, the optically processed beam forms a pair of points for each plurality of point arrays, wherein the distance between each pair of points (on the sensor plane) indicates the focus state associated with the corresponding point array.

[0119] According to one embodiment, step 550 includes ignoring detection signals (100) based on sample components illuminated by at least a partial illumination beam (30). Ignoring may be based on design information or other types of information indicating regions of the sample (e.g., high-density logic component regions) that would provide low signal-to-noise ratio signals and / or diffraction signals after illumination.

[0120] According to some embodiments, step 550 includes determining at least one of the pitch angle and roll angle of the illumination beam. Either of these angles can be detected by comparing focus information from different point arrays.

[0121] According to some embodiments, at least one of method 500 and method 501 includes adjusting the distance between optical components in the collection path of the evaluation system to optimize the focus state of the evaluation beam.

[0122] According to some embodiments, adjusting the distance between optical components includes moving lenses or mirrors in the collection path of the evaluation system.

[0123] According to some embodiments, the method includes adjusting the intensity of the illumination beam used by the evaluation system to optimize the focus state of the evaluation beam.

[0124] According to some embodiments, adjusting the intensity of the illumination beam of the evaluation system includes controlling the power of the light source or adjusting the aperture of the illumination path of the evaluation system.

[0125] According to some embodiments, at least one of method 500 and method 501 includes determining the depth of field of the autofocus system based on the focus state of the evaluation beam.

[0126] According to some embodiments, at least one of method 500 and method 501 includes adjusting the position of the imaging region according to a determined depth of field.

[0127] According to some embodiments, at least one of method 500 and method 501 includes compensating for aberrations in the collection path of the evaluation beam 38 to improve its focus.

[0128] According to some embodiments, aberration compensation includes adjusting the position or shape of one or more optical components in the collection path of the evaluation system.

[0129] According to some embodiments, at least one of methods 500 and 501 includes determining a focus pointer based on a detection signal to quantitatively evaluate the focus status of the light beam. The focus pointer may indicate information such as focus in any axis, relative focus error between light beams, etc.

[0130] According to one embodiment, step 590 includes adjusting the focus state of the evaluation beam based on a determined focus metric.

[0131] According to one embodiment, step 590 includes capturing an image of a sample by an evaluation system associated with the autofocus system, the image being based on the focus state of the evaluation beam.

[0132] According to one embodiment, step 590 includes analyzing the captured images to extract information about the sample.

[0133] According to one embodiment, step 590 includes adjusting the position or orientation of the sample based on the focus state of the evaluation beam.

[0134] According to one embodiment, step 590 includes determining a focus error signal based on the detection signal (100) to provide feedback for adjusting the focus state of the evaluation beam.

[0135] According to one embodiment, step 590 includes using a focus error signal to control the position or movement of one or more optical components of the evaluation system.

[0136] According to one embodiment, an autofocus system (10) is provided, comprising:

[0137] a. An illumination path configured to illuminate a sample with an illumination beam, forming a plurality of point arrays on the sample, including a first set of point arrays formed on a first side of the imaging region and a second set of point arrays formed on the other side of the imaging region.

[0138] b. Controller.

[0139] c. Collection path, including:

[0140] i. The first branch includes a first spherical telescope, a first field curvature compensator, a pair of first prisms, and a first collimating relay consisting essentially of a first relay input spherical lens and a first relay output spherical lens.

[0141] ii. The second branch includes a second spherical telescope, a second field curvature compensator, a pair of second prisms, and a second collimating relay consisting essentially of a second relay input spherical lens and a second relay output spherical lens;

[0142] iii. A shared module, the module being configured to (i) receive a first collected beam and a second collected beam, (ii) optically process the first collected beam to provide it to a first segment, each first collected beam having a pair of first rays, and (iii) optically process the second collected beam to provide it to a second segment, each second collected beam having a pair of second rays;

[0143] d. A sensor following the first branch and the second branch, the sensor being configured to generate a detection signal indicating the light output from the first branch and the light output from the second branch.

[0144] According to one embodiment, the shared module includes a mask located at the entrance pupil, the mask including a pair of off-axis slits for truncating each collected beam to provide a pair of rays for each collected beam.

[0145] According to one embodiment, the sharing module further includes a splitter configured to (i) guide a first ray associated with a first collected beam to a first branch, and (ii) guide a ray associated with a second collected beam to a second branch.

[0146] According to one embodiment, the first collimation relay displays the primary optical power along the main axis and the residual optical power along the secondary axis.

[0147] According to one embodiment, the autofocus system includes an optional depth-of-field unit configured to select a reference focal plane for the autofocus system.

[0148] According to one embodiment, the optional depth-of-field unit includes a first window that can be selectively placed within a first spherical telescope and a second window that can be selectively placed within a second spherical telescope.

[0149] According to one embodiment, a system is provided, comprising:

[0150] a. An illumination path configured to illuminate a sample with an illumination beam, forming a plurality of point arrays on the sample, including a first set of point arrays formed on a first side of the imaging region and a second set of point arrays formed on the other side of the imaging region.

[0151] b. Sensors.

[0152] c. Controller.

[0153] d. A collection path configured to receive a first collection beam and a second collection beam from a sample. The collection path includes:

[0154] i. A mask located at the entrance pupil, the mask comprising a pair of off-axis slits for truncating each collected beam to provide a pair of rays for each collected beam;

[0155] ii. A splitter, comprising an optical splitting assembly including (i) a first reflecting surface configured to guide a first ray associated with a first collected beam to a first branch, and (ii) a second reflecting surface facing the first reflecting surface and configured to guide a second ray associated with a second collected beam to a second branch. The first and second reflecting surfaces are located at a position (a) outside an image plane and (b) at which there is separation between the first and second rays.

[0156] According to one embodiment, the optical segmentation component is a prism.

[0157] According to one embodiment, the prism is a blade right-angle prism.

[0158] According to one embodiment, the shape and position of the optical segmentation component are designed to prevent vignetting of either the first or second ray.

[0159] According to one embodiment, the shape and position of the optical segmentation component are located at the farthest point of the intermediate image plane, at which point neither the first ray nor the second ray will be cut off by the prism.

[0160] According to one embodiment, the divider includes a housing and a mechanical interface connected to the housing and the optical dividing assembly.

[0161] According to one embodiment, the housing includes an input opening, a first light output opening, and a second light output opening.

[0162] Figure 22 This is an embodiment of a method for performing field operations (600), the method comprising:

[0163] a. Illuminate the (610) sample with an illumination beam to form multiple dot arrays on the sample, including a first set of dot arrays formed on a first side of the imaging region and a second set of dot arrays formed on the other side of the imaging region.

[0164] b. Collect (620) the first and second collection beams from the sample.

[0165] c. Each collected beam is truncated (630) using a mask (110) located in the entrance pupil, wherein the mask (110) includes a pair of off-axis slits (112) to provide a pair of rays for each collected beam.

[0166] d. Using the first reflective surface of an optical segmentation assembly located at the reflective surface position but outside the intermediate image plane, a first ray associated with the first collected beam is guided to a first part (640) of the system. The first part may be a first branch or any other part not used for autofocus.

[0167] e. Using the second reflective surface of the optical segmentation assembly, a second ray associated with the second collected beam is guided to a second part (650) of the system, wherein the second reflective surface faces the first reflective surface. The second part may be a second branch or any other part not used for autofocus.

[0168] According to one embodiment, steps 640 and 650 are based on the separation between the first ray and the second ray at the position of the reflecting surface.

[0169] According to one embodiment, steps 610-650 are used in an autofocus measurement system.

[0170] According to one embodiment, steps 610-650 are used for purposes other than autofocus.

[0171] According to one embodiment, the optical segmentation component is a prism.

[0172] According to one embodiment, the prism is a blade right-angle prism.

[0173] According to one embodiment, the method includes shaping and positioning optical segmentation components to prevent vignetting of any first and second rays.

[0174] According to one embodiment, the method includes shaping and positioning an optical segmentation component at its furthest point in an intermediate image plane to ensure that the first and second rays are not truncated by the prism.

[0175] According to one embodiment, the method includes connecting a mechanical interface to an optical segmentation assembly of a housing and a segmenter (130).

[0176] Figure 1 An example of an autofocus system 10 and an evaluation system 11 is illustrated, wherein the evaluation system 11 uses the autofocus system 10 to maintain an evaluation beam at a desired focus position on a sample 99. The evaluation system 11 includes an evaluation illumination 11, an evaluation system beam splitter 14, and an evaluation sensor 13. The evaluation system outputs an evaluation beam 38, which passes through a first beam splitter 24 and is focused by an objective lens 19 to illuminate the sample 99, forming a return beam that is collected by the objective lens 19 and then guided by the first beam splitter 24 to the evaluation system beam splitter 14, and then to the evaluation sensor 13.

[0177] The first beam splitter 24 and objective lens 19 are also used by the autofocus system 10.

[0178] The autofocus system 10 includes an autofocus (AF) illumination unit 19, an initial mirror 21, an illumination / collecting beam splitter 22, a third mirror 23, a mask 110 (with a slit 112), a splitter 130, a first mirror 125, a first branch 140, a first sensor 50-1, a second mirror 126, a second branch 170, and a second sensor 50-2.

[0179] The first branch 140 includes a first spherical telescope 142, a first field curvature compensator 144, and a first collimation relay 146.

[0180] The second branch 170 includes a second spherical telescope 172, a second field curvature compensator 174, and a second collimation relay 176.

[0181] Figure 1 The first conjugate surface 111 and the first conjugate surface 113 of the mask pupil are explained.

[0182] Figure 2 This illustrates sample 99 and multiple point arrays at two different time points.

[0183] The multiple point arrays include a first set of point arrays 42 and a second set of point arrays 44, which are staggered along the first axis 91 and the second axis 92.

[0184] The first set of point arrays 42 includes the first point array 42-1, the second point array 42-2, and the third point array 42-3.

[0185] The second set of dot arrays 44 includes the fourth dot array 44-1, the fifth dot array 44-2, and the sixth dot array 44-3.

[0186] Figure 3 The relationship between the focusing state of the collected beam with wavefront 31 reaching mask 110 and the light rays exiting from the slit, which is an off-axis slit, is explained. In the focusing state, wavefront 31 is parallel to the mask, and the light rays passing through the slit are parallel to each other and perpendicular to the mask. In the defocusing state, the wavefront is either convex (wavefront 32) or concave (wavefront 33), and the light rays passing through the slit are deflected to each other and not perpendicular to the mask.

[0187] Figure 4 The slit 112 of the mask 110 demonstrates how the first set of point arrays and the second set of point arrays are converted into a pair of spaced rays. For an exponent x ranging from 1 to 3, point array 42-x is converted into ray pairs 46-x and 47-x, while point array 44-x is converted into ray pairs 48-x and 49-x.

[0188] The distance between individual light pairs located behind mask 110 indicates the focus state associated with the light pairs. Figure 4 The following distances are shown: first distance D1 45-1 between first rays 46-1 and 47-1; second distance D2 45-2 between second rays 46-2 and 47-2; third distance D3 45-3 between third rays 46-3 and 47-3; fourth distance D4 45-4 between fourth rays 48-1 and 49-1; fifth distance D5 45-5 between fifth rays 48-2 and 49-2; and sixth distance D6 45-6 between sixth rays 48-3 and 49-3.

[0189] Figure 4 It also describes the reduced image 51 of the entrance pupil on the focal plane of the output lens of the first spherical telescope.

[0190] Figure 5 This explains the wavefront effect of light rays on the focal plane of the output lens of a spherical telescope, and how these rays are sensed by the sensor.

[0191] The focus state should be determined based on the distance between the light rays incident on the sensor. When the wavefront 1031 is parallel to the sensor, the distance clearly indicates the focus state. When the wavefront 1032 is concave or convex 1033, the distance may be ambiguous depending on the focus position associated with the light rays. To resolve this ambiguity, a prism or a pair of prisms is used, with the light rays spaced apart from each other.

[0192] Figure 6-8 Sections 9-18 describe an autofocus system or components of an autofocus system with a fixed collimation relay. Figure 9 An autofocus system is described, which includes a collimation relay motion mechanism configured to change the distance between the relay input spherical lens and the output spherical lens of the collimation relay. According to one embodiment, Figure 6-8 All of the autofocus systems in 9-18 include a collimation relay motion mechanism.

[0193] Figure 6 and Figure 7The autofocus system is described, including an entrance pupil 80, a mask 110, a splitter 130, a first lens 125, a second lens 126, a first spherical telescope input lens 142-1, a first selectable depth-of-field unit 203-1, a first field curvature compensator 144, a first spherical telescope output lens 142-2, a first prism 145, a first relay input spherical lens 146-1, a first relay output spherical lens 146-1, a first sensor 50-1, a second spherical telescope input lens 172-1, a second selectable depth-of-field unit 203-2, a second field curvature compensator 174, a second spherical telescope output lens 172-2, a second prism 175, a second relay input spherical lens 176-1, a second relay output spherical lens 176-1, and a second sensor 50-2.

[0194] Figure 8 The upper part shows an autofocus system, which has a first selectable depth-of-field unit 203-1 in the first branch 140 and a second selectable depth-of-field unit 203-2 in the second branch 170.

[0195] Figure 8 The lower part shows an autofocus system with a first selectable depth-of-field unit 203-1 outside the first branch 140 and a second selectable depth-of-field unit 203-2 outside the second branch 170.

[0196] The depth of focus is determined by moving the second selectable depth of field unit and the first selectable depth of field unit—while the other optical components of the first and second branches remain stationary—which improves the accuracy of the autofocus system.

[0197] Figure 9 The image shows the autofocus system at two points in time—and at two different distances between the collimating relay lenses.

[0198] The autofocus system includes:

[0199] a. A first lower folding mirror 222-5 and a first upper folding mirror 222-4 located between the first relay input spherical lens 146-1 and the first relay output spherical lens 146-2.

[0200] b. A second upper folding mirror 222-6 and a second lower folding mirror 222-7 located between the second relay input spherical lens 176-1 and the second relay output spherical lens 176-2.

[0201] c. A first collimation relay motion mechanism 202-1 configured to change the distance between the first relay input spherical lens 146-1 and the first relay output spherical lens 146-2.

[0202] d. A second collimation relay motion mechanism 202-2 configured to change the distance between the second relay input spherical lens 176-1 and the second relay output spherical lens 176-2.

[0203] Figure 8 The autofocus system in the system allows for continuous variation of the effective focal length during collimation.

[0204] Figure 10 and Figure 11 An example is shown with mask 110, first mirror 125, second mirror 126, first spherical telescope input lens 142-1 and second spherical telescope input lens 172-1. Splitter 130 separates two pairs of light rays, with the first mirror 125 deflecting light rays pairs 66-2 and 67-2, and the second mirror 126 deflecting light rays pairs 68-2 and 69-2.

[0205] Figure 12 The slit 112 of the display mask 110 converts each of the first and second set of point arrays into a pair of spaced rays and a split point formed on the splitter 130. For an exponent x between 1 and 3, point array 42-x is converted into a ray pair forming split points 66-x and 67-x, while point array 44-x is converted into a ray pair forming split points 68-x and 69-x.

[0206] Figure 13 A divider 130A is shown, comprising optical dividing components (e.g., prism 133), said components including a first reflective surface 131 and a second reflective surface 132. The divider 130A also includes a housing 134 and a mechanical interface. The housing includes a housing top 135, an input opening 136, a first light output opening 137, and a second light output opening 138.

[0207] Figure 14 and Figure 15 The optical processing of light pairs by various components of the first and second branches is demonstrated.

[0208] exist Figure 14 The various components include a first spherical telescope input lens 142-1, a first selectable depth-of-field unit 203-1, a first field curvature compensator, the first field curvature compensator including a first part 144-1 and a second part 144-2, a first spherical telescope output lens 142-2, a first prism 145 and a first relay input spherical lens 146-1, a second spherical telescope input lens 172-1, a second selectable depth-of-field unit 203-2, and a second field curvature compensator 174, the second field curvature compensator including a third part 174-1 and a fourth part 174-2, a second spherical telescope output lens 172-2, a second prism 175 and a second relay input spherical lens 176-1.

[0209] exist Figure 15 The components include a first field curvature compensator 144, a first spherical telescope output lens 142-2, a first prism 145, a first relay input spherical lens 146-1, a first relay output spherical lens 146-1, a first sensor 50-1, a second field curvature compensator 174, a second spherical telescope output lens 172-2, a second prism 175, a second relay input spherical lens 176-1, a second relay output spherical lens 176-1, and a second sensor 50-2.

[0210] Figure 14 and Figure 15 The first pair of rays 401 (including) were shown Figure 4 First pair of rays 46-1 and 47-1), second pair of rays 402 (including Figure 4 The second pair of rays 46-2 and 47-2), and the third pair of rays 403 (including Figure 4 The third pair of rays 46-3 and 47-3), and the fourth pair of rays 411 (including Figure 4 The fourth pair of rays 48-1 and 49-1), and the fifth pair of rays 412 (including Figure 4 The fifth pair of rays 48-2 and 49-2) and the sixth pair of rays 413 (including Figure 4 The sixth ray (48-3 and 49-3).

[0211] Figure 16 This shows the optical processing of light by various components in the first and second branches.

[0212] The components include a first selectable depth-of-field unit 203-1, a first field curvature compensator 144, a first spherical telescope output lens 142-2, a first prism 145, and a first relay input spherical lens 146-1.

[0213] Figure 16 Display the first rays 46-1 and 47-1, the first pair of rays 401, the second rays 46-2 and 47-2, the second pair of rays 402, the third rays 46-3 and 47-3, and the third pair of rays 403.

[0214] Figure 17 This shows the optical processing of the beam by various components in the first and second branches.

[0215] These components include a first spherical telescope output lens 142-2, a first prism 145, a first relay input spherical lens 146-1, and a first relay output spherical lens 146-2. Virtual lines 1463 illustrate the propagation of second rays 46-2 and 47-2.

[0216] Figure 17First rays 46-1 and 47-1 are shown. These first rays are located on a virtual line that is aligned with the principal axis 1462 of the collimation relay and oriented with the secondary axis 1461 of the collimation relay, and are subjected to the main optical power of the collimation relay.

[0217] Figure 18 The incident points of a pair of light rays on the first sensor 50-1 and the second sensor 50-2 are shown.

[0218] The first pair of light rays 66-1 and 67-1 form a first point 281-1 and a second point 281-2 on the first pair of pixels of the first sensor 50-1. The distance between these points is the first sensor distance DS1 271.

[0219] The second pair of light rays 66-2 and 67-2 form the third point 282-1 and the fourth point 282-2 on the second pair of pixels of the first sensor 50-1. The distance between these points is the second sensor distance DS2 272.

[0220] The third pair of light rays 66-3 and 67-3 form the fifth point 283-1 and the sixth point 283-2 on the third pair of pixels of the first sensor 50-1. The distance between these points is the third sensor distance DS3 273.

[0221] The fourth pair of light rays 68-1 and 69-1 form the seventh point 284-1 and the eighth point 284-2 on the fourth pair of pixels of the second sensor 50-2. The distance between these points is the fourth sensor distance DS4 274.

[0222] The fifth pair of rays 68-2 and 69-2 form the ninth point 285-1 and the tenth point 285-2 on the fifth pair of pixels of the second sensor 50-2. The distance between these points is the fifth sensor distance DS5 275.

[0223] The sixth pair of rays 68-3 and 69-3 form the eleventh point 286-1 and the twelfth point 286-2 on the sixth pair of pixels of the second sensor 50-2. The distance between these points is the sixth sensor distance DS6 276.

[0224] These sensor distances indicate the focus status.

[0225] Figure 19 Examples of autofocus systems are shown, including:

[0226] a. A first turntable equipped with a set of first spherical telescope output lenses (collectively referred to as 351), the difference between these lenses being their focal length, to provide different sensitivities for the autofocus system.

[0227] b. A second turntable equipped with a set of second spherical telescope output lenses (collectively referred to as 352), which differ in focal length to provide different sensitivities for the autofocus system.

[0228] Any reference to the sensor should apply to either the first sensor or the second sensor.

[0229] Any reference for light should be applied accordingly to the beam.

[0230] Any reference to a ray should be applied accordingly to the point formed by the ray.

[0231] Any reference for a beam should be applied accordingly to the light ray.

[0232] Any reference to a beam should be applied accordingly to the point where the beam forms.

[0233] In the foregoing detailed description, numerous specific details are set forth in order to provide a thorough understanding of the disclosed embodiments.

[0234] However, those skilled in the art will understand that the presently disclosed embodiments may be implemented without these specific details. In other instances, well-known methods, procedures, and components have not been described in detail so as not to obscure the presently disclosed embodiments.

[0235] The subject matter to be considered as disclosed embodiments is explicitly pointed out and clearly claimed at the end of this specification. However, the disclosed embodiments, whether in terms of organization or operation, together with their objectives, features, and advantages, can be best understood by referring to the following detailed description and accompanying drawings.

[0236] Please be aware that, for the sake of simplicity and clarity, the components shown in the diagrams may not be drawn to scale. For example, the size of some components may be exaggerated relative to others to enhance clarity. Furthermore, component symbols may be repeated in the diagrams, where appropriate, to indicate corresponding or similar components.

[0237] Because the embodiments shown in this disclosure can be implemented in most cases using optical components and circuits known to those skilled in the art, they will not be explained in excessive detail, but only to the extent necessary as described above, in order to understand and appreciate the basic concepts of the embodiments of this disclosure, and without obscuring or distracting the teachings of this disclosure.

[0238] Any references to methods in this specification should be adapted to systems capable of performing the methods.

[0239] Any references to the system in this specification shall apply to the methods that the system may perform, and shall be adapted accordingly.

[0240] The term "and / or" indicates additional or optional. For example, A and / or B means only A, only B, or A and B.

[0241] Numerous specific details are provided in the foregoing description in order to provide a full understanding of the embodiments of this disclosure.

[0242] However, those skilled in the art will understand that the present embodiments can be practiced without including these specific details. In other instances, known methods, procedures, and components have not been described in detail so as not to obscure the present embodiments.

[0243] The subject matter considered as embodiments of this disclosure is specifically pointed out and explicitly claimed at the end of this specification. However, embodiments of this disclosure, both in their organization and manner of operation, along with their objects, features, and advantages, can be best understood by referring to the following detailed description and accompanying drawings.

[0244] It will be understood that, for the sake of brevity and clarity, the components shown in the diagrams may not be drawn to scale. For example, the dimensions of some components may be exaggerated relative to others for clarity. Furthermore, where appropriate, component symbols may be repeated across diagrams to represent corresponding or similar components.

[0245] In the foregoing description, embodiments of the present disclosure have been described with reference to specific examples. However, it will be apparent that various modifications and alterations may be made without departing from the broader spirit and scope of the appended claims.

[0246] Furthermore, in the descriptions and requests, terms such as “front,” “back,” “top,” “bottom,” “above,” and “below” are used for descriptive purposes only and are not necessarily used to describe permanent relative positions. It should be understood that the terms used are interchangeable where appropriate to enable the embodiments of this disclosure described herein to operate, for example, in orientations different from those shown or otherwise described herein.

[0247] References involving terms such as “including”, “having”, or “comprising” should be understood as “consisting of” and / or “substantially consisting of”.

[0248] However, other modifications, changes, and alternatives are possible. Therefore, the instructions and illustrations should be considered illustrative rather than restrictive.

[0249] In the claims, any component symbols placed in parentheses should not be construed as limiting the claim. The word “comprising” does not exclude other components or steps listed in the claim. Furthermore, “a” or “an” as used herein is defined as one or more. Similarly, introductory phrases such as “at least one” and “one or more” used in the claim should not be construed as implying that any particular claim containing such an introductory claim component is limited to an embodiment containing only one such component, even if the same claim contains the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an.” The same applies to the use of definite articles. Unless otherwise stated, terms such as “first” and “second” are used to arbitrarily distinguish the described components. Therefore, these terms are not necessarily intended to indicate the time or other priority of these components. The fact that certain measures are listed in mutually different claim claims does not mean that combinations of these measures cannot be utilized.

[0250] While certain features of this embodiment have been demonstrated and described herein, many modifications, substitutions, alterations, and equivalents will appear to those skilled in the art. Therefore, it should be understood that the appended claims are intended to cover all such modifications and alterations that conform to the true spirit of the described embodiments.

Claims

1. An autofocus system, characterized by, The autofocus system comprises: an illumination path configured to illuminate a sample with an illumination beam to form a plurality of spot arrays on the sample, the sample comprising an upstream spot array formed on a first side of an imaging region and a downstream spot array formed on another side of the imaging region; a sensor; a controller; a collection path configured to receive first and second collection beams from the sample; wherein the collection path comprises: a mask located at an entrance pupil, the mask comprising a pair of off-axis slits for truncating each collection beam to provide a pair of rays for each collection beam; and a splitter comprising an optical splitting component comprising (i) a first reflective surface configured to direct a first ray associated with the first collection beam to a first branch of the autofocus system and (ii) a second reflective surface facing the first reflective surface and configured to direct a second ray associated with the second collection beam to a second branch of the autofocus system; wherein the first and second reflective surfaces are located at a reflective surface location that is (a) outside an image plane and (b) where there is separation between the first and second rays.

2. The autofocus system of claim 1, wherein the optical splitting component is a prism.

3. The autofocus system of claim 2, wherein the prism is a knife-edge right-angle prism.

4. The autofocus system of any one of the preceding claims, wherein the optical splitting component is shaped and positioned to prevent vignetting of any of the first and second rays.

5. The autofocus system of any one of claims 2 and 3, wherein the optical splitting component is shaped and positioned at a location furthest from an intermediate image plane at which neither the first nor the second rays are truncated by the prism.

6. The autofocus system of any one of claims 1-3, wherein the splitter comprises a housing and a mechanical interface connected to the housing and the optical splitting component.

7. The autofocus system of claim 6, wherein the housing comprises an input opening, a first ray output opening, and a second ray output opening.

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