Focus position measurement at the time of scanning

Abstract

A system and method for adjusting focus based on scanning are disclosed. The system can include an optical subsystem configured to detect light from a light modulation target of a sample as the sample is scanned along a scan direction. Two or more detection elements can be configured to detect the light modulation target at different points in time as the sample is scanned along the scan direction due to a spatial separation between the two or more detection elements. The system can determine a time difference between the different points in time at which the light modulation target is detected during the scan of the sample, determine a defocus value indicative of underfocus or overfocus based on the time difference, and direct an adjustment of a focus of the optical subsystem based on the defocus value.

Description

Technical Field

[0001] This invention generally relates to metrology and inspection systems, and more specifically, to defining the focus of a metrology and inspection system. Background Technology

[0002] Adjusting the focus of defocus measurement tools can present various challenges. For example, focus contrast methods measure focus by determining when an image is sharpest. Focus contrast methods typically require taking multiple images at several points of focus. In some instances, this can be used to find focus offset distances, but this can be time-consuming and require full image readout and processing.

[0003] In another example, in an interferometric setup, light can be separated into the secondary objective by a mirror at an ideal field location, and the focal point can be determined by monitoring the interference between the primary and secondary objectives. However, this method can be relatively expensive and may require separating and reducing the illumination power specifically sent for focal point measurement. For example, 50% of the illumination power could be dedicated to focal point measurement.

[0004] In another example, a dual-unit photodiode setup can be used with a choke positioned in the ideal field plane (relative to the objective). However, this method may also require an additional measuring arm that reduces beam power, and the choke may contribute to noise in metrology measurements due to vibration and heat generated during its movement.

[0005] Alignment metrology refers to the measurement of the relative alignment of layers on a sample (e.g., but not limited to a semiconductor device). Alignment measurement, or measurement of alignment error, typically refers to the measurement of misalignment of manufactured features on two or more sample layers. Alignment can include misalignment of features between different substrates, such as die alignment of dies stacked on another substrate. Proper alignment is essential for the proper functioning of the device.

[0006] The need to reduce feature size and increase feature density is leading to a corresponding increase in the demand for accurate and efficient overlay metrology. Metrology systems typically determine metrological data associated with a sample by measuring or otherwise verifying a dedicated metrological target distributed throughout the sample (i.e., an overlay target). Therefore, the sample is typically mounted on a translation stage, and translation is used to sequentially move the metrological target into the measurement field of view. Summary of the Invention

[0007] According to one or more illustrative embodiments of the present invention, a system is disclosed. In one illustrative embodiment, the system includes an optical subsystem. In another illustrative embodiment, the optical subsystem may include one or more detectors configured to detect light from an optically modulated target of the sample while scanning the sample along a scanning direction. In another illustrative embodiment, the one or more detectors may include two or more detection elements. In another illustrative embodiment, the two or more detection elements are configured to detect the optically modulated target at different time points while scanning the sample along the scanning direction due to spatial separation between the two or more detection elements. In another illustrative embodiment, the system may include a controller communicatively coupled to the one or more detectors. In another illustrative embodiment, the controller may include one or more processors configured to execute program instructions that cause the one or more processors to acquire a signal from the optically modulated target using the two or more detection elements of the one or more detectors while scanning the sample along the scanning direction. In another illustrative embodiment, the one or more processors may determine, based on the signal, the time difference between the different time points during the scanning of the sample when the optically modulated target was detected. In another illustrative embodiment, the one or more processors may determine, based on the time difference, a defocus value indicating that the one or more detectors are under-focused or over-focused. In another illustrative embodiment, the one or more processors may guide the focus adjustment of the optical subsystem based on the defocus value.

[0008] In another aspect, the defocus value may include a defocus distance based on the time difference. In another aspect, the defocus value may be further based on the scanning speed and directional angle of the illumination beam at the optical modulation target. In another aspect, the one or more detectors may be positioned in the pupil plane of the optical subsystem. In another aspect, the two or more detection elements may comprise four or more detection elements. In another aspect, a first group of the four or more detection elements may be configured for a first scanning direction, and a second group of the four or more detection elements may be configured for a second scanning direction orthogonal to the first scanning direction.

[0009] In another aspect, the optical modulation target may be configured to induce at least one of intensity modulation or phase modulation. In another aspect, the controller may be configured to continuously determine defocus values ​​of a plurality of optical modulation targets positioned along the scanning direction, and continuously guide the focus adjustment of the optical subsystem based on the defocus values. In another aspect, the scan along the scanning direction may include a pre-scan, and the controller may be further configured to guide a re-scan of the optical modulation targets, wherein the optical modulation targets include overlapping targets, and determine overlapping measurements based on the re-scan. In another aspect, the optical modulation targets may be spaced apart from the overlapping targets, wherein the focus adjustment of the optical subsystem is configured to be performed during the scan but before acquiring overlapping signals from the overlapping targets. In another aspect, the one or more detectors may include a multi-pixel detector comprising the two or more detection elements. In another aspect, each of the two or more detection elements may include a single photodiode detector. In another aspect, the scanning may include at least one of the following: actuation of a translation stage; or adjustment of components of the optical subsystem configured to scan the illumination spot along the scanning direction.

[0010] According to one or more illustrative embodiments of the present invention, a method for adjusting the focus of an optical subsystem is disclosed. In one illustrative embodiment, the method may include acquiring a signal from an optically modulated target using two or more detection elements of one or more detectors while scanning a sample along a scanning direction. In another illustrative embodiment, the method may include determining a time difference between different time points during the scanning of the sample when the optically modulated target is detected. In another illustrative embodiment, the method may include determining a defocus value based on the time difference, indicating that the one or more detectors are under-focused or over-focused. In another illustrative embodiment, the method may include guiding the adjustment of the focus of the optical subsystem based on the defocus value. In another illustrative embodiment, the one or more detectors are configured to detect light from the optically modulated target of the sample while scanning the sample along the scanning direction. In another illustrative embodiment, the one or more detectors may include two or more detection elements configured to detect the optically modulated target at different time points during the scanning of the sample along the scanning direction due to spatial separation between the two or more detection elements.

[0011] In another aspect, the defocus value may include a defocus distance based on the time difference. In another aspect, the defocus value may be further based on the scanning speed and directional angle of the illumination beam at the optical modulation target. In another aspect, the one or more detectors may be positioned in the pupil plane of the optical subsystem. In another aspect, the two or more detection elements may comprise four or more detection elements, wherein a first group of the four or more detection elements is configured for a first scanning direction, and a second group of the four or more detection elements is configured for a second scanning direction orthogonal to the first scanning direction. In another aspect, the optical modulation target may be configured to induce at least one of intensity modulation or phase modulation. In another aspect, the method may further comprise continuously determining defocus values ​​for a plurality of optical modulation targets positioned along the scanning direction, and continuously guiding the adjustment of the focus of the optical subsystem based on the defocus values. In another aspect, the scanning along the scanning direction may include a pre-scan, and the method may further comprise guiding a re-scan of the optical modulation targets, wherein the optical modulation targets include overlapping targets, and determining overlapping measurements based on the re-scan. In another aspect, the light modulation target may be spaced apart from the stacking target, wherein the adjustment of the focus of the optical subsystem is performed during the scan but before acquiring the stacking signal from the stacking target. In another aspect, the one or more detectors may comprise multi-pixel detectors, which include the two or more detection elements. In another aspect, each of the two or more detection elements may comprise a single photodiode detector. In another aspect, the scan may include at least one of the following: actuation of a translation stage; or adjustment of components of the optical subsystem configured to scan the illumination spot along the scan direction.

[0012] It should be understood that the foregoing general description and the following detailed description are merely exemplary and illustrative, and do not necessarily limit the invention as claimed. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the general description, serve to explain the principles of the invention. Attached Figure Description

[0013] Those skilled in the art will better understand the many advantages of this invention by referring to the accompanying drawings.

[0014] Figure 1A A conceptual diagram illustrating a system according to one or more embodiments of the present invention.

[0015] Figure 1B A schematic diagram illustrating an optical subsystem according to one or more embodiments of the present invention.

[0016] Figure 2AA schematic diagram illustrating the detection element of an optical subsystem that is in an over-focused state relative to a sample optical modulation target according to one or more embodiments of the present invention.

[0017] Figure 2B This describes the process of scanning samples according to one or more embodiments of the present invention. Figure 2A A graph showing the illumination intensity of the overfocusing detection element over time.

[0018] Figure 3A A schematic diagram illustrating a detection element in a focused state according to one or more embodiments of the present invention.

[0019] Figure 3B This describes the process of scanning samples according to one or more embodiments of the present invention. Figure 3A A graph showing the illumination intensity of the focusing detection element over time.

[0020] Figure 4A A schematic diagram illustrating a detection element in an underfocused state according to one or more embodiments of the present invention.

[0021] Figure 4B This describes the process of scanning samples according to one or more embodiments of the present invention. Figure 3A A graph showing the illumination intensity over time for the underfocus detection element.

[0022] Figure 5 A flowchart illustrating a method for adjusting focus according to one or more embodiments of the present invention is provided. Detailed Implementation

[0023] The invention has been specifically shown and described with respect to particular embodiments and their specific features. The embodiments set forth herein should be considered illustrative rather than restrictive. It will be readily apparent to those skilled in the art that various changes and modifications in form and detail may be made without departing from the spirit and scope of the invention. Reference will now be made in detail to the disclosed subject matter illustrated in the accompanying drawings.

[0024] refer to Figures 1A to 5 According to one or more embodiments of the present invention, a system and method for adjusting the focus based on the time difference of the signal during the scanning of a sample are disclosed.

[0025] Embodiments of the present invention relate to detecting focus loss in a scanning mode using spatially separated detection elements (e.g., individual / single photodiodes or multi-pixel cameras) based on the difference in time taken for the spatially separated detection elements to detect an optically modulated target (e.g., any feature / target of a sample that induces a change in phase and / or illumination). In embodiments, the operating mode may include the detection of changes in the angular distribution of light from the optically modulated target. To measure the angular distribution, the detection element may be located at or near the pupil plane, or otherwise capable of detecting the angular distribution. In embodiments, various types of features may be used as optically modulated targets, such as dedicated targets configured to modulate / change the illumination intensity and / or phase of light. In embodiments, the overlay target itself may be used as the optically modulated target, or a separate target may be used. The optically modulated target may be positioned in front of the overlay target such that, during scanning, the focus can be adjusted based on the optically modulated target before reaching the overlay target. By another example, the overlay target itself may act as the optically modulated target and can be rescanned after the focus has been adjusted.

[0026] The benefits of this invention may include, but are not limited to, extracting focus information in scanning mode without requiring a separate sensor to determine the focus information. In embodiments, the same setup with detectors in the pupil plane used for scan-based overlay metrology techniques can be used to sense and adjust the focus as described herein, without requiring any additional hardware. Scan-based scattering measurement techniques may include a fast detector for capturing time-varying interference signals generated during sample scanning. The detector can be positioned in the pupil plane at the overlap between selected diffraction orders to capture the time-varying interference signals during sample scanning. Various non-limiting scanning scattering measurement overlay metrology techniques are described in U.S. Patent Publication No. 2022 / 0034652, filed February 17, 2021; U.S. Patent Application No. 17 / 119,536, filed December 11, 2020; U.S. Patent Application No. 17 / 708,958, filed March 30, 2022; and U.S. Patent Application No. 17 / 709,104, filed March 30, 2022, all of which are incorporated herein by reference in their entirety. It should be noted that such scanning examples are non-limiting, and the embodiments described herein may include various types of detectors, such as one or more diode array sensors.

[0027] Furthermore, compared to using a cutoff in the system's optics to measure the focus, measuring the focus based on the sample itself, as described in this paper, provides more accurate results.

[0028] Figure 1AA conceptual diagram illustrating a system 100 for adjusting focus according to one or more embodiments of the present invention is provided. System 100 may include any system for any purpose. For example, system 100 may include a metrology system. For example, system 100 may include an inspection system. For example, the system may include a stacking metrology system configured to measure stacks of samples 104 (e.g., wafers).

[0029] In one embodiment, system 100 includes an optical subsystem 102 for performing measurements on sample 104. In another embodiment, sample 104 includes (or lacks) a feature / element configured to induce a change in the angular distribution of light as it passes through an unfocused portion of an illumination beam. For example, the portion / element / feature configured to induce a change in the angular distribution may be referred to as a light modulation target. For examples of light modulation targets 208 and detection elements 202, 204, see [link to relevant documentation]. Figure 2A The time difference in detecting changes in the angular distribution of light can be used to determine the focal point.

[0030] In embodiments, the light modulation target 208 may be configured to induce illumination intensity modulation. For example, the light modulation target 208 may include, but is not limited to, a coating (e.g., an anti-reflective coating) that causes the first detection element 202 to detect a decrease in the intensity of light emitted from the sample earlier than the second detection element 204 when the illumination beam 108 is scanned across the sample 104. By another example, the light modulation target 208 may include a layer. For example, the layer may be configured to be translucent, thereby reducing illumination passing through it. Other examples include a reflective layer (e.g., a layer that is more reflective than the surrounding area). These are non-limiting examples, and any feature, layer, coating, and / or the like that has different effective optical properties (e.g., thickness, density, reflectivity, transparency, luminescence, polarization sensitivity, refractive index, and / or any combination thereof) compared to the surrounding area may be used. The selection of the light modulation target may depend on the specific application, wavelength range, and desired intensity modulation characteristics.

[0031] In an embodiment, the light modulation target 208 may be configured to induce phase modulation. For example, the light modulation target 208 may comprise, but is not limited to, a transparent material having a refractive index different from that of the surrounding region, thereby causing a phase shift in light passing through it. When the illumination beam 108 is scanned across the sample 104, the first detection element 202 may detect this phase shift at a different time than the second detection element 204. The light modulation target 208 may comprise, for example, a material layer, a grating, or other features to introduce a phase shift in light based on the geometry, periodicity, material properties, or the like of said structure.

[0032] The light modulation target 208 can have any shape. For example, the light modulation target 208 can be a rectangular or square shape along the scanning path.

[0033] In one embodiment, the optical subsystem 102 includes an illumination subsystem 106 and a light-collecting subsystem 110. The light-collecting subsystem 110 may include a detector 112.

[0034] In one embodiment, system 100 includes a controller 122 communicatively coupled to optical subsystem 102. Controller 122 may include one or more processors 124 and a memory device 126 or memory. For example, one or more processors 124 may be configured to execute a set of program instructions maintained in memory device 126.

[0035] Figure 1B A schematic diagram of an optical subsystem 102 according to one or more embodiments of the present invention is illustrated. An illumination subsystem 106 is configured to generate illumination in the form of one or more illumination beams 108 to illuminate the sample 104. A light-collecting subsystem 110 is configured to collect light 138 from the illuminated sample 104. Furthermore, the one or more illumination beams 108 may be spatially restricted such that they illuminate selected portions of the sample 104. For example, each of the one or more illumination beams 108 may be spatially restricted to illuminate a specific stacked target.

[0036] Detector 112 may comprise any detector 112 known in the field of metrology. For example, detector 112 may comprise, but is not limited to, photodiodes (e.g., two or more photodiodes). For example, a photodiode may be referred to as a photodiode detector. For example, detector 112 may comprise two or more, or four or more photodiodes. In some embodiments, the photodiode comprises a photodiode having a bandwidth of at least 1 GHz. However, it should be understood that this value is not a requirement. In practice, the bandwidth of the photodiode and the scan speed along the scan direction can be selected together to provide the desired sampling rate of the signal. By another example, detector 112 may comprise, but is not limited to, a multi-pixel detector, such as a complementary metal-oxide-semiconductor (CMOS) detector, a charge-coupled device (CCD) detector, or the like. For example, each detection element 202, 204 may correspond to a specific pixel or group of pixels of the multi-pixel detector 112.

[0037] One or more detectors 112 may be positioned in the pupil plane 114 of the photon system 110.

[0038] In one embodiment, the optical subsystem 102 includes a translation stage 116 for moving the sample 104 through the measurement field of view of the optical subsystem 102 during scanning. By another example, components of the optical subsystem 102 configured to scan the illumination spot along the scanning direction (e.g., Figure 1B Any component, such as lens 136, is adjusted (e.g., angling) to scan the sample.

[0039] In one embodiment, the optical subsystem 102 includes an objective lens 136 for focusing an illumination beam 108 onto a sample 104. For example, the objective lens 136 may be configured to collect measurement light 138 emitted from the sample 104 in response to the illumination beam 108, according to a metrological formulation.

[0040] The optical subsystem 102 may include one or more beam splitters 146 for separating light (e.g., for separating illumination beam 108).

[0041] System 100 can be configured to use a "dosing recipe" for a specific type of sample or feature of sample 104. For example, system 100 can be programmed to calculate a superimposed measurement of a specific type of feature based on the dosing recipe.

[0042] Figure 2A , 3A Schematic diagrams of the optical subsystem 102 in underfocus, focused, and overfocus states are shown in Figures 4A and 4A, respectively. Figure 2B , 3B Figures 4B and 4B respectively illustrate the light intensity over time in underfocus, focused, and overfocused states. However, it should be understood that... Figures 2A to 4B The sample 104 and the optical modulation target 208, along with the associated description, are provided for illustrative purposes only and should not be construed as restrictive. In fact, the sample 104 and the optical modulation target 208 may include any suitable design and configuration.

[0043] Figure 2A A schematic diagram illustrating the detection elements 202, 204 of an optical subsystem 102 in which the optical modulation target 208 relative to the sample 104 is in an over-focused state according to one or more embodiments of the present invention. Figure 2B This describes the situation according to one or more embodiments of the present invention when scanning sample 104. Figure 2A Figure 220 shows the illumination intensity 210 and 212 of the over-focusing detection elements 202 and 204 over time.

[0044] like Figure 2B As shown, light intensities 210 and 212 decrease at different time points due to the movement of sample 104. The difference between these time points can be referred to as time difference 214. Time difference 214 can exist due to the spacing of detection elements 202 and 204 relative to each other and relative to the scanning direction. For example, a target can affect the angular distribution of light as it sweeps / scans through the unfocused portion of the illumination. When this occurs, the length span of this variation can indicate the degree of defocusing, and the direction can indicate underfocusing / overfocusing.

[0045] As the degree / amount of defocusing (e.g., underfocusing or overfocusing) increases, the time difference 214 also increases. The controller 122 can be configured to determine calibration and / or use calibration based on the time difference 214. For example, calibration can correlate the time difference 214 (e.g., picoseconds) with a correction distance 216 that might be needed to adjust / correct the amount of defocusing. For example, the correction distance 216 could be the amount by which the actuator is moved using a translation stage 116 or the like to bring the sample 104 closer to the desired position.

[0046] The defocus value can be based on the scanning speed of the illumination beam 108 at the light modulation target 208 and the turning angle 218.

[0047] The equation for focus deviation (e.g., defocus value, defocus distance 216) can be expressed as follows:

[0048] Focus deviation (Equation 1)

[0049] Where V is the scanning speed (e.g., the speed at which the illumination beam 108 scans across the sample 104), θ is the turning angle 218 of the illumination beam at the sample, Δt is the time difference 214, and NA is the numerical aperture of the illumination path 106 (e.g., the average numerical aperture value).

[0050] For scanning, the sample 104 can be moved in the sample movement direction 206 using the translation stage 116. Alternatively and / or additionally, the spot of the illumination beam 108 can be scanned along the sample 104. The sample movement direction 206 may be opposite to the scanning direction.

[0051] In embodiments, sample 104 includes any number of optical modulation targets 208. For example, sample 104 may be a wafer containing optical modulation targets 208 in scribe lines of the wafer. For example, optical subsystem 102 may be configured to continuously scan a series of optical modulation targets 208 to continuously adjust the focus of sample 104 to keep sample 104 in focus and determine measurements across sample 104. For example, the same detection elements 202, 204 (e.g., photodiodes) used to determine defocus values ​​and adjust focus may also be used for overlay measurements. The optical modulation targets 208 may be spaced apart from overlay targets such that focus can be adjusted before scanning reaches the overlay targets.

[0052] In static measurement mode, system 100 can be configured to perform a scan of optically modulated target 208 between static targets as it moves between static targets (e.g., stacked targets measured in static conditions) to adjust focus as it moves. This allows for increased throughput by eliminating the need to adjust focus upon reaching the static target. For example, in other methods, the static target can be imaged along the depth direction to determine focus by examining where the image is least blurred. In some embodiments of the invention, this depth direction scan can be eliminated. Static measurement mode can include various modes, such as Scatter Measurement Stacked (SCOL) and / or Image-Based Stacked (IBO). For example, IBO metrology methods can use grating patterns of dedicated stacked targets positioned in scribe lines on a wafer. For example, the size of the optically resolvable target can be about 10 micrometers or more (e.g., 30 micrometers).

[0053] Figure 3A A schematic diagram illustrating the detection elements 202, 204 in a focused state according to one or more embodiments of the present invention. Figure 3B This describes the scanning of sample 104 according to one or more embodiments of the present invention. Figure 3A Figure 230 shows the illumination intensities 210 and 212 of the focusing detection elements 202 and 204 over time.

[0054] When the illumination beam 108 is focused, the changes detected by the detection elements 202 and 204 can occur at the same (or nearly the same) time point, for example, at Figure 3B The intensity decreases of 210 and 212 occurred simultaneously.

[0055] Figure 4A A schematic diagram illustrating a detection element 202, 204 in an underfocused state according to one or more embodiments of the present invention. Figure 4B This describes the scanning of sample 104 according to one or more embodiments of the present invention. Figure 3A Figure 240 shows the in-focus detection elements 202 and 204 and the illumination intensity 210 and 212 over time.

[0056] An underfocus state can cause the relative detection element to be affected at an earlier point in time than an overfocus state. This difference in timing can be used to distinguish between overfocus and underfocus states. In this way, not only the amount of defocus can be determined, but also the type of defocus (e.g., overfocus or underfocus). For example, Figure 4B This indicates that the first intensity 210 corresponding to the first detection element 202 is now the last to be affected in time, which is consistent with... Figure 2B The opposite of an over-focused state.

[0057] Figure 5This description illustrates a process flow diagram of a method 500 for adjusting focus according to one or more embodiments of the present invention. It should be noted that the embodiments and implementation techniques previously described herein in the context of system 100 should be interpreted as extending to method 500. It should further be noted herein that the steps of method 500 may be implemented wholly or partially through system 100. However, it should be further recognized that method 500 is not limited to system 100, as additional or alternative system-level embodiments may implement all or part of the steps of method 500.

[0058] In step 502, while scanning sample 104 along the scanning direction, two or more detection elements 202, 204 are used to acquire signals from light-modulated target 208. For example, time-varying signals from photodiodes can be received and recorded in memory 126. By another example, optical subsystem 102 can use multi-pixel detector 112 to capture / acquire / receive images (e.g., a series of images over time), wherein two of the pixel sensors of multi-pixel detector 112 are corresponding detection elements 202, 204.

[0059] In step 504, the time difference 214 is determined based on different time points during the scanning of sample 104 when the light-modulated target 208 is detected using detection elements 202, 204. For example, a decrease or increase in intensity over time, or fluctuations, or the like, can be configured by software to be detected, corresponding to the time point at which this event occurs or begins to occur, or the like. For example, a phase change can be configured to be detected. For example, controller 122 can be configured to use a threshold to determine the time point. For example, the threshold can be any threshold, such as an intensity decrease from the average intensity greater than 1%, greater than 3%, and / or the like.

[0060] In step 506, a defocus value indicating underfocus or overfocus is determined based on time difference 214. For example, the defocus value may (but is not necessarily required to be) similar to... Figure 2A The defocus distance shown is proportional to 216. For example, a defocus value of -0.XX (negative) may indicate overfocus, and +0.XX (overfocus) may indicate underfocus, and vice versa.

[0061] In step 508, the focus adjustment of the optical subsystem 102 is guided based on the defocus value. For example, the controller 122 may guide (e.g., transmit signals to the actuator controller or actuator) the adjustment of the height of the sample 104 relative to the focus.

[0062] In another step (not shown), a superposition measurement corresponding to the superposition target is determined based on the acquired signal (e.g., a detection element signal). For example, controller 122 may compare the magnitude and / or phase of the detection signal to generate a superposition measurement. For example, U.S. Patent No. 10,824,079, issued November 3, 2020 and incorporated herein by reference in its entirety, substantially describes the diffraction order in a focusing pupil and further provides a specific relationship between superposition and measured intensity in the pupil plane.

[0063] In another step (not shown), one or more processes for manufacturing sample 104 are controlled based on overlay measurements. This may involve adjusting process parameters (e.g., optical frequency, intensity, or processing time) to minimize overlays. Adjustments can be made manually by an operator or automatically by a control system in response to overlay measurements. For example, if the overlay measurement is greater than a predetermined threshold, the process parameters can be adjusted to reduce the overlay. Conversely, if the overlay measurement is less than the threshold, the process parameters may remain unchanged or may be adjusted to slightly reduce the overlay to keep it within an optimal range. Such processes may include semiconductor manufacturing, photolithography, and many other processes.

[0064] In another step (not shown), scanning is performed in two different directions (e.g., the X direction orthogonal to the Y direction). To achieve this, two sets of detection elements can be used, such as a diamond arrangement of four detection elements. This arrangement may include two vertically aligned detection elements for the first direction and two horizontally aligned detection elements for the second direction. For example, the detection elements may comprise four or more detection elements. A first set of the four or more detection elements may be configured for the first scanning direction, and a second set of the four or more detection elements may be configured for a second scanning direction orthogonal to the first scanning direction.

[0065] In an embodiment, system 100 may be programmed to perform a pre-scan of the overlay target to adjust the focus, and then re-scan the overlay target. The overlay may then be determined based on a time-varying signal from detector 112, such as a signal obtained from overlapping diffraction orders in the pupil plane. For example, the signal in step 502 may include (or be) a pre-scan of the overlay target for measuring the focus. The same overlay target may then be re-scanned (i.e., scanned again, for example by reversing and re-scanning in the same direction, scanning in the opposite direction, and / or the like). In this respect, a single light-modulating target (e.g., the overlay target) may be used both to determine the focus and subsequently to determine the properties of sample 104 (e.g., the overlay).

[0066] Refer again Figures 1A to 1B Various components are described in more detail according to one or more embodiments of the present invention.

[0067] One or more processors 124 of controller 122 may comprise any processor or processing element known in the art. For the purposes of this invention, the terms "processor" or "processing element" may be broadly defined to encompass any device having one or more processing or logic elements (e.g., one or more microprocessor devices, one or more application-specific integrated circuit (ASIC) devices, one or more field-programmable gate arrays (FPGAs), or one or more digital signal processors (DSPs)). In this sense, one or more processors 124 may comprise any device configured to execute algorithms and / or instructions (e.g., program instructions stored in memory). In embodiments, one or more processors 124 may embody a desktop computer, host computer system, workstation, graphics computer, parallel processor, network computer, or any other computer system configured to execute programs configured to operate on or in conjunction with system 100 (as described throughout this invention). Furthermore, different subsystems of system 100 may comprise processors or logic elements suitable for carrying out at least a portion of the steps described herein. Therefore, the foregoing description should not be construed as limiting the embodiments of the invention but is merely illustrative. Furthermore, the steps described throughout this invention can be implemented by a single controller or, alternatively, multiple controllers. Additionally, controller 122 may comprise one or more controllers housed in a common housing or within multiple housings. In this manner, any controller or combination of controllers can be individually packaged as a module suitable for integration into system 100. Furthermore, controller 122 can analyze or otherwise process data received from one or more detectors 112 and feed the data to additional components, either within or outside system 100.

[0068] Furthermore, memory device 126 may comprise any storage medium known in the art suitable for storing program instructions executable by one or more associated processors 124. For example, memory device 126 may comprise a non-transitory memory medium. As additional examples, memory device 126 may comprise, but is not limited to, read-only memory, random access memory, magnetic or optical storage devices (e.g., magnetic disks), magnetic tape, solid-state drives, and the like. It should also be noted that memory device 126 may be housed in a common controller housing with one or more processors 124.

[0069] In this regard, controller 122 can perform any of a variety of processing steps. For example, controller 122 can be configured to generate control signals to guide or otherwise control optical subsystem 102 or any of its components. For example, controller 122 can be configured to receive signals corresponding to signals from one or more detectors 112. By another example, controller 122 can generate correctable terms for one or more additional manufacturing tools based on superimposed measurements from optical subsystem 102 as feedback and / or feedforward control for one or more additional manufacturing tools.

[0070] Furthermore, the controller 122 may calibrate or otherwise modify the stacked measurements based on known, assumed, or measured characteristics of the sample 104, which may also affect the signal, such as, but not limited to, sidewall angles or other sample asymmetries.

[0071] Refer again Figure 1B According to one or more embodiments of the present invention, various components of the optical subsystem 102 are described in more detail.

[0072] In one embodiment, the lighting subsystem 106 includes a lighting source 128 configured to generate at least one lighting beam 108. The lighting from the lighting source 128 may include one or more selected wavelengths of light, including, but not limited to, ultraviolet (UV) radiation, visible light radiation, or infrared (IR) radiation.

[0073] The illumination source 128 may comprise any type of illumination source suitable for providing at least one illumination beam 108. In an embodiment, the illumination source 128 is a laser source. For example, the illumination source 128 may comprise, but is not limited to, one or more narrowband laser sources, broadband laser sources, supercontinuum laser sources, white light laser sources, or the like. In this respect, the illumination source 128 may provide an illumination beam 108 with high coherence (e.g., high spatial coherence and / or temporal coherence). In an embodiment, the illumination source 128 comprises a laser sustained plasma (LSP) source. For example, the illumination source 128 may comprise, but is not limited to, an LSP lamp, LSP bulb, or LSP chamber suitable for housing one or more elements capable of emitting broadband illumination when excited into a plasma state by a laser source.

[0074] In an embodiment, the illumination subsystem 106 includes one or more optical components adapted to modify and / or adjust the illumination beam 108 and guide the illumination beam 108 to the sample 104. For example, the illumination subsystem 106 may include one or more illumination lenses 130 (e.g., for collimating the illumination beam 108, for relaying illumination pupil plane 120 and / or illumination field plane 132 or the like). In an embodiment, the illumination subsystem 106 includes one or more illumination control optics 134 for shaping or otherwise controlling the illumination beam 108. For example, the illumination control optics 134 may include, but are not limited to, one or more field stops, one or more pupil stops, one or more polarizers, one or more filters, one or more beam splitters, one or more diffusers, one or more homogenizers, one or more apodizers, one or more beam shapers, or one or more mirrors (e.g., static mirrors, translational mirrors, scanning mirrors or the like).

[0075] The light-collecting subsystem 110 may include one or more optical elements adapted to modify and / or adjust the collected light 138 from the sample 104. In one embodiment, the light-collecting subsystem 110 includes one or more light-collecting lenses 140. In another embodiment, the light-collecting subsystem 110 includes one or more light-collecting control optics 142 for shaping or otherwise controlling the collected light 138. For example, the light-collecting control optics 142 may include, but are not limited to, one or more field stops, one or more pupil stops, one or more polarizers, one or more filters, one or more beam splitters, one or more diffusers, one or more homogenizers, one or more apodizers, one or more beam shapers, or one or more mirrors (e.g., static mirrors, translational mirrors, scanning mirrors, or the like). In another example, the light-collecting subsystem 110 may include one or more light-collecting field planes 150.

[0076] Refer again Figure 1A It should be noted in this document that one or more components of system 100 may be communicatively coupled to various other components of system 100 in any manner known in the art. For example, one or more processors 124 may be communicatively coupled to each other and other components via wired (e.g., copper wire, fiber optic cable, and the like) or wireless connections (e.g., RF coupling, IR coupling, WiMax, Bluetooth, 3G, 4G, 4G LTE, 5G, and the like). By another example, controller 122 may be communicatively coupled to one or more components of optical subsystem 102 via any wired or wireless connection known in the art.

[0077] In embodiments, one or more processors 124 may comprise any one or more processing elements known in the art. In this sense, one or more processors 124 may comprise any microprocessor-type device configured to execute software algorithms and / or instructions. In embodiments, one or more processors 124 may comprise a desktop computer, host computer system, workstation, graphics computer, parallel processor, or other computer system (e.g., a network computer) configured to execute programs configured to operate system 100 (as described in various parts of the invention). It should be understood that the steps described in various parts of the invention can be implemented by a single computer system or alternatively by multiple computer systems. Furthermore, it should be understood that the steps described in various parts of the invention can be implemented on any one or more of the one or more processors 124. Generally, the term "processor" can be broadly defined to encompass any device having one or more processing elements that execute program instructions from memory 126. Furthermore, different subsystems of system 100 may include processors or logic elements suitable for implementing at least a portion of the steps described in various parts of the invention. Therefore, the foregoing description should not be construed as limiting the invention but is merely illustrative.

[0078] Those skilled in the art will recognize that the components (e.g., operations), apparatuses, objects, and accompanying discussions described herein are used as examples for conceptual clarity and with careful consideration of various configuration modifications. Therefore, as used herein, the specific paradigms and accompanying discussions are intended to represent their more general categories. In general, the use of any particular paradigm is intended to represent its category, and the omission of specific components (e.g., operations), apparatuses, and objects should not be considered limiting.

[0079] Those skilled in the art will understand that various vehicles (e.g., hardware, software, and / or firmware) exist to implement the processes and / or systems and / or other technologies described herein, and the preferred vehicle will vary depending on the context of the deployment of the process and / or system and / or other technology. For example, if the implementer determines that speed and accuracy are critical, the implementer may choose a primary hardware and / or firmware vehicle; alternatively, if flexibility is critical, the implementer may choose a primary software implementation; or alternatively, the implementer may choose a combination of hardware, software, and / or firmware. Thus, several feasible vehicles exist to implement the processes and / or apparatus and / or other technologies described herein, none of which is inherently superior to the others, as the choice of any vehicle to be utilized depends on the context in which the vehicle will be deployed and the implementer’s specific concerns (e.g., speed, flexibility, or predictability) (any of which may vary).

[0080] The foregoing description is presented to enable those skilled in the art to make and use the invention as provided in the context of a particular application and its requirements. Those skilled in the art will understand that various modifications to the described embodiments are possible, and that the general principles defined herein may be applied to other embodiments. Therefore, the invention is not intended to be limited to the specific embodiments shown and described, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

[0081] Regarding the use of any plural and / or singular terms in this document, those skilled in the art can convert them from plural to singular and / or from singular to plural depending on the context and / or application. For clarity, various singular / plural arrangements are not explicitly described herein.

[0082] All methods described herein may include storing the results of one or more steps of the method embodiments in memory. The results may include any of the results described herein and may be stored in any manner known in the art. The memory may include any memory described herein or any other suitable storage medium known in the art. After the results have been stored, they may be accessed in memory and used by any of the method or system embodiments described herein, formatted for display to a user, used by another software module, method, or system, and the like. Furthermore, the results may be stored “permanently,” “semi-permanently,” “temporarily,” or for a period of time. For example, the memory may be random access memory (RAM), and the results may not necessarily be stored in memory indefinitely.

[0083] Furthermore, it should be carefully considered that each of the embodiments of the methods described above may include any and any other steps of any and any other methods described herein. Additionally, each of the embodiments of the methods described above may be performed by any of the systems described herein.

[0084] The objects described herein sometimes refer to different components contained within or connected to other components. It should be understood that the architectures depicted are merely exemplary, and many other architectures can in fact be implemented to achieve the same functionality. Conceptually, any arrangement of components achieving the same functionality is effectively “associated” to achieve the desired functionality. Therefore, any two components combined herein to achieve a particular functionality can be considered “associated” with each other to achieve the desired functionality, regardless of the architecture or intermediate components. Similarly, any two such associated components can also be considered “connected” or “coupled” with each other to achieve the desired functionality, and any two components that can be suchly associated can also be considered “coupleable” with each other to achieve the desired functionality. Specific examples of coupleability include, but are not limited to, components that can be physically mated and / or physically interact, and / or components that can wirelessly interact and / or wirelessly interact, and / or components that can logically interact and / or logically interact.

[0085] Furthermore, it should be noted that the invention is defined by the appended claims. Those skilled in the art will understand that, generally, the terms used herein and especially in the appended claims (e.g., the body of the appended claims) are intended to be “open-ended” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “at least having,” the term “includes” should be interpreted as “including but not limited to,” and so on). Those skilled in the art will further understand that if a particular number is expected to be described by the introduced claim, then this intention will be explicitly stated in the claim, and if such a description is not present, then this intention will not exist. For example, to aid understanding, the appended claims may contain the introductory phrases “at least one” and “one or more” used in introducing the claim description. However, the use of such phrases should not be construed as implying that introducing a claim statement with the indefinite article "a" or "an" limits any particular claim containing this introduced claim statement to an invention containing only one of such statements, even if the same claim contains the introductory phrase "a or more" or "at least one" and the indefinite article (e.g., "a" or "an") (e.g., "a" and / or "an" should generally be interpreted as meaning "at least one" or "a or more"); the same applies to the use of definite articles used to introduce a claim statement. Furthermore, even if a specific number of statements is explicitly stated in the introduced claim statement, those skilled in the art should recognize that such a statement should generally be interpreted as meaning at least the number stated (e.g., a bare statement of "two statements" without other modifiers generally means at least two statements or two or more statements). Furthermore, in examples using conventional expressions such as "at least one of A, B, and C, and similar ones," a person skilled in the art will generally understand that this construction is expected in the sense of the conventional expression (e.g., "a system having at least one of A, B, and C" includes, but is not limited to, systems having only A, only B, only C, both A and B, both A and C, both B and C, and / or both A, B, and C, and similar ones). In examples using conventional expressions such as "at least one of A, B, or C, and similar ones," a person skilled in the art will generally understand that this construction is expected in the sense of the conventional expression (e.g., "a system having at least one of A, B, or C" includes, but is not limited to, systems having only A, only B, only C, both A and B, both A and C, both B and C, and / or both A, B, and C, and similar ones). Those skilled in the art should further understand that any conjunction and / or phrase presenting two or more alternative terms (whether in the description, claims or drawings) should be understood as a prudent consideration of the possibility of including one, any, or both of the terms.For example, the phrase “A or B” should be understood as including the possibility of “A” or “B” or “A and B”.

[0086] It will be understood from the foregoing description that the invention and its many accompanying advantages will be apparent, and it should be understood that various changes can be made to the form, construction, and arrangement of the components without departing from the disclosed subject matter or sacrificing all its material advantages. The forms described are merely illustrative, and the appended claims are intended to cover and encompass such changes. Furthermore, it should be understood that the invention is defined by the appended claims.

Claims

1. A system comprising: An optical subsystem, comprising: One or more detectors configured to detect light from a light-modulated target from the sample while scanning the sample along a scanning direction, wherein the one or more detectors include: Two or more detection elements, wherein the two or more detection elements are configured to detect the optically modulated target at different time points while scanning the sample along the scanning direction due to spatial separation between the two or more detection elements; and A controller communicatively coupled to the one or more detectors and comprising one or more processors configured to execute program instructions that cause the one or more processors to: While scanning the sample along the scanning direction, two or more detection elements of the one or more detectors acquire signals from the light-modulated target. The time difference between the different time points during the scanning of the sample when the optically modulated target was detected is determined based on the signal. Based on the time difference, a defocus value indicating under-focusing or over-focusing of the one or more detectors is determined; and The focus adjustment of the optical subsystem is guided based on the defocus value.

2. The system according to claim 1, The defocus value includes the defocus distance based on the time difference.

3. The system according to claim 1, The defocus value is further based on the scanning speed and directional angle of the illumination beam at the light modulation target.

4. The system of claim 1, wherein the one or more detectors are positioned in the pupil plane of the optical subsystem.

5. The system of claim 1, wherein the two or more detection elements comprise four or more detection elements, wherein a first group of the four or more detection elements is configured for a first scanning direction, and wherein a second group of the four or more detection elements is configured for a second scanning direction orthogonal to the first scanning direction.

6. The system of claim 1, wherein the optical modulation target is configured to induce at least one of the following: intensity modulation or phase modulation.

7. The system of claim 1, wherein the controller is configured to: The defocus values ​​of multiple optical modulation targets located along the scanning direction are continuously determined, and the focus adjustment of the optical subsystem is continuously guided based on the defocus values.

8. The system of claim 1, wherein the scan along the scanning direction includes a pre-scan, and wherein the controller is further configured to: Guide the rescanning of the optically modulated target, wherein the optically modulated target includes a pair of overlapping targets; and The overlay measurement is determined based on the rescan.

9. The system of claim 1, wherein the optical modulation target and the stacked target are spaced apart. The adjustment of the focus of the optical subsystem is configured to be performed during the scan but before acquiring the stacking signal from the stacking target.

10. The system of claim 1, wherein the one or more detectors include a multi-pixel detector, the multi-pixel detector including the two or more detection elements.

11. The system of claim 1, wherein each of the two or more detection elements comprises a single photodiode detector.

12. The system of claim 1, wherein the scanning includes at least one of: actuation of a translation stage, or adjustment of a component of the optical subsystem configured to scan an illumination spot along the scanning direction.

13. A method comprising: When scanning the sample along the scanning direction, two or more detection elements using one or more detectors acquire signals from the light-modulated target. The time difference between different time points during the scanning of the sample when the optically modulated target was detected is determined based on the signal. The defocus value indicating under-focusing or over-focusing of the one or more detectors is determined based on the time difference; and The focus adjustment of the optical subsystem is guided based on the aforementioned defocus value. The one or more detectors are configured to detect light from the light-modulating target of the sample while scanning the sample along the scanning direction, wherein the one or more detectors include: Two or more detection elements, wherein the two or more detection elements are configured to detect the optical modulation target at different time points when scanning the sample along the scanning direction due to spatial separation between the two or more detection elements.

14. The method according to claim 13, The defocus value includes the defocus distance based on the time difference.

15. The method according to claim 13, The defocus value is further based on the scanning speed and directional angle of the illumination beam at the light modulation target.

16. The method of claim 13, wherein the one or more detectors are positioned in the pupil plane of the optical subsystem.

17. The method of claim 13, wherein the two or more detection elements comprise four or more detection elements, wherein a first group of the four or more detection elements is configured for a first scanning direction, and wherein a second group of the four or more detection elements is configured for a second scanning direction orthogonal to the first scanning direction.

18. The method of claim 13, wherein the optical modulation target is configured to induce at least one of: intensity modulation or phase modulation.

19. The method of claim 13, further comprising: The defocus values ​​of multiple optical modulation targets located along the scanning direction are continuously determined, and the focus adjustment of the optical subsystem is continuously guided based on the defocus values.

20. The method of claim 13, wherein the scan along the scanning direction includes a pre-scan, and the method further comprises: Guide the rescanning of the optically modulated target, wherein the optically modulated target includes a pair of overlapping targets; and The overlay measurement is determined based on the rescan.

21. The method of claim 13, wherein the optical modulation target is spaced apart from the stacked target. The adjustment of the focus of the optical subsystem is performed during the scan but before acquiring the stacking signal from the stacking target.

22. The method of claim 13, wherein the one or more detectors include a multi-pixel detector, the multi-pixel detector including the two or more detection elements.

23. The method of claim 13, wherein each of the two or more detection elements comprises a single photodiode detector.

24. The method of claim 13, wherein the scanning includes at least one of: actuation of a translation stage, or adjustment of a component of the optical subsystem configured to scan an illumination spot along the scanning direction.

Images