Calibration of tilt angle of incident beam of inspection system

Abstract

Some systems and methods are provided that include acquiring a set of images of a target, where the set of images is acquired by an inspection system capable of emitting a light beam toward the target, where a first image of the set of images is capturing the target at a first height position, and a second image of the set of images is capturing the target at a second height position. A first image of the image set is captured at a first height position, and a second image of the image set is captured at a second height position different from the first height position, then data D [Delta] Z is determined, the data containing displacement information of the target in the image set, and the offset tilt angle of the inspection system beam is determined using the data D [Delta] Z and data relating to the first and second height positions.

Description

Technical Field

[0001] The presently disclosed subject matter generally relates to the field of inspection of specimens, and more particularly, to automated inspection of specimens. Background Art

[0002] The current demand for high density and performance associated with ultra-large-scale integration of fabricated devices requires sub-micron features, increased transistor and circuit speeds, and improved reliability. These demands necessitate forming device features with high precision and uniformity, which in turn necessitates careful monitoring of the fabrication process, including automated inspection of devices in the semiconductor wafer form.

[0003] Inspection processes are used at various steps in semiconductor manufacturing and may include metrology measurements (eg, critical dimension measurements, etc.). Summary of the Invention

[0004] According to certain aspects of the present disclosure, a system is provided, comprising one or more processing circuits configured to acquire a set of images of a target material, the set of images being acquired by an inspection system, wherein a first image in the set of images is acquired by capturing the target material at a first height position, and a second image is acquired by capturing the target material at a second height position different from the first height position, and determine data D ΔZ , to obtain the displacement information of the target in the set of images, and use the data D ΔZ and data regarding the first and second height positions to determine an offset tilt angle of the inspection system light beam.

[0005] According to some embodiments, the set of images is obtained after calibrating a light beam of the inspection system relative to an objective of the inspection system, wherein the calibration uses a target.

[0006] According to some embodiments, the calibration includes aligning the focus of the light beam to the symmetry axis of the objective lens according to a matching criterion.

[0007] According to certain embodiments, the accuracy of the calibration is equal to or less than 0.2 nm.

[0008] According to some embodiments, the set of images includes images I1 to I N , and N≥2, where each image I in the group of images i All are based on height position H i The target is captured and the height position H i With other images I j Get the height position H j Different, and i is different from j.

[0009] According to some embodiments, the system is configured to utilize the offset tilt angle, the data D ΔZThe above-mentioned offset tilt angle is determined by the geometric relationship between (the displacement information of the target in the set of images) and the data related to the first and second height positions.

[0010] According to some embodiments, the inspection system comprises an operating element for moving the target in a height direction, wherein the system is configured to use the model to at least partially compensate for errors in the offset tilt angle estimation caused by movement of the element in a direction different from the height direction.

[0011] According to certain embodiments, an inspection system includes a base having an area dedicated to receiving a sample to be inspected, wherein the target is located on the base or on a portion coupled to the base.

[0012] According to certain embodiments, the inspection system includes a base having an area dedicated to receiving a sample to be inspected, wherein the target is permanently fixed to the base or located on a portion coupled to the base.

[0013] According to certain embodiments, the system is configured to control the inspection system to switch between a first mode and a second mode, wherein in the first mode, the light beam is directed toward the target to determine the offset tilt angle, and in the second mode, the light beam is directed toward the sample for inspection, wherein the target and the sample are associated with the same base (that is, the target is located on the base, or on a portion coupled to the base, and the sample is located on the base, or on a portion coupled to the base).

[0014] According to certain embodiments, the inspection system is operable to switch between a first mode in which a light beam is directed toward a target to determine an offset tilt angle and a second mode in which a light beam is directed toward a sample for inspection, wherein the target and the sample are associated with the same pedestal (that is, the target is located on the pedestal, or on a portion coupled to the pedestal, and the sample is located on the pedestal, or on a portion coupled to the pedestal).

[0015] According to certain embodiments, the target has a flat pattern.

[0016] According to some embodiments, the system is configured to use data D ΔZ and data regarding the first and second height positions to determine a first estimate of an offset tilt angle of the inspection system beam, and generating an estimate of the offset tilt angle using the model and the first estimate.

[0017] According to certain embodiments, the model is used to simulate errors in offset tilt angle estimates when the estimates are obtained based on target height variations and target displacements in images associated with the height variations.

[0018] According to certain embodiments, the model simulates a relationship between estimated values ​​of a plurality of offset tilt angles and a plurality of true values ​​of the plurality of offset tilt angles.

[0019] According to certain embodiments, the system is configured to determine data regarding the height position of the target using a distance measuring device.

[0020] According to certain embodiments, the system is configured to acquire, for each given offset tilt angle of the inspection system beam, a given set of images of the target material from a plurality of offset tilt angles, wherein a given first image in the given set of images captures the target material at a given first height position, and a second image in the given set of images captures the target material at a given second height position different from the first height position, and then determine data D ΔZ,校准 , which contains information about the displacement of the target in a given image set, and uses data D ΔZ,校准 and data about given first and second height positions to determine a given estimated offset tilt angle of the inspection system light beam, thereby obtaining multiple estimated values ​​of the offset tilt angles, and using these offset tilt angles, or the true values ​​of the multiple offset tilt angles, plus these estimated offset tilt angles to generate a model.

[0021] According to some embodiments, the system is configured to use data D ΔZ and data regarding the first and second height positions to determine a first estimate of an offset tilt angle of the inspection system beam, and using the model and the first estimate to generate an estimate of the offset tilt angle.

[0022] According to certain embodiments, the true offset tilt angle value is obtained using a wafer having a height profile having a first slope and a second slope.

[0023] According to certain aspects of the present disclosure, a method is provided that includes one or more processing circuits performing one or more features related to the system (thus, these features are not repeated).

[0024] According to other aspects of the present disclosure, a non-transitory computer-readable medium is provided, containing instructions that, when executed by one or more processing circuits, cause the one or more processing circuits to perform operations or implement features of the related system (thus, these features are not repeated).

[0025] According to other aspects of the present disclosure, a system is provided, comprising one or more processing circuits configured to, for each given offset tilt angle of an inspection system beam, acquire a given set of images of a target material from a plurality of offset tilt angles, wherein a given first image in the given set of images captures the target material at a given first height position, and a second image in the given set of images captures the target material at a given second height position different from the first height position, and then determine data D ΔZ,校准, which contains the displacement information of the target in a given image group, and uses data D ΔZ,校准 and data about given first and second height positions to determine a given estimated offset tilt angle of the electron beam, thereby obtaining multiple estimated values ​​of the offset tilt angles, and using these offset tilt angles, or the true values ​​of the multiple offset tilt angles, plus these estimated offset tilt angles to generate a model.

[0026] According to certain embodiments, the system is configured to acquire a set of images of a target, wherein the set of images is acquired by an inspection system, wherein a first image in the set of images captures the target at a first height position, and a second image in the set of images captures the target at a second height position different from the first height position, and then determine data D ΔZ , which contains the displacement information of the target in the image group, and uses data D ΔZ and data regarding the first and second height positions to determine a first estimate of an offset tilt angle of the inspection system beam, and using the model and the first estimate to generate a second estimate of the offset tilt angle.

[0027] According to certain aspects of the present disclosure, a method is provided that includes one or more processing circuits performing one or more features related to the system (thus, these features are not repeated).

[0028] According to other aspects of the present disclosure, a non-transitory computer-readable medium is provided, containing instructions that, when executed by one or more processing circuits, cause the one or more processing circuits to perform operations or implement features of the related system (thus, these features are not repeated).

[0029] The proposed solution offers various technical advantages, at least some of which are listed below.

[0030] According to certain examples, the proposed solution enables determination of the offset tilt angle without using a tilted wafer (a wafer having one or more slopes).

[0031] According to certain embodiments, the proposed solution enables measurement without having to load a tilted wafer each time to measure the offset tilt angle. Therefore, the method is efficient in terms of both time and cost. The area dedicated to receiving the wafers to be inspected remains available in the inspection system, enabling real-time switching between measurement operations and determination of the offset tilt angle.

[0032] According to certain examples, the proposed solution can determine the offset tilt angle in a fast and efficient manner.

[0033] According to certain examples, the proposed solution is able to accurately determine the offset tilt angle.

[0034] According to certain examples, metrology measurements (eg, CD measurements, overlay matching) become more accurate due to the accurate determination of the offset tilt angle.

[0035] According to certain examples, the proposed solution is able to correct errors in offset tilt angle determination, which may be caused by height motion of the target. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to understand this disclosure and to see how it may be carried out in practice, embodiments will now be described by way of non-limiting examples with reference to the accompanying drawings.

[0037] Figure 1 A generalized block diagram of an inspection system according to certain examples of the present disclosure is illustrated.

[0038] Figure 2 A generalized flow chart is illustrated showing a method for determining an offset tilt angle of an inspection system light beam according to certain examples of the present disclosure.

[0039] Figure 3A A non-limiting example is described showing the acquisition of a target at a first height position.

[0040] Figure 3B A non-limiting example is described showing the acquisition of the target at a second height position.

[0041] Figure 4A A non-limiting example is shown in Figure 3A Configure the image of the target.

[0042] Figure 4B A non-limiting example is shown in Figure 3B Configure the image of the target.

[0043] Figure 5 An explanation of the target displacement in the set of images acquired for different height positions is provided.

[0044] Figure 6 A non-limiting example is described showing the target being located on the same susceptor as the wafer to be inspected.

[0045] Figure 7A Illustrate a generalized flow chart showing the use of Figure 6 The present invention provides an architecture and a method for determining the offset tilt angle of an inspection system light beam according to certain embodiments of the present invention.

[0046] Figure 7B Shows a list of commands that can be used to execute Figure 7A The architecture of the method.

[0047] Figure 8AA non-limiting example is described showing an electron beam inspection system including an objective lens.

[0048] Figure 8B A non-limiting example is described showing a misalignment of the electron beam relative to the objective lens.

[0049] Figure 8C A non-limiting example is described showing the alignment of the electron beam relative to the objective lens.

[0050] Figure 9 A schematic flow chart illustrating a method for calibrating the position of an electron beam relative to an objective lens of an electron beam inspection system, followed by determination of an offset tilt angle, according to certain examples of the present disclosure.

[0051] Figure 10 A non-limiting example is described showing the undesirable lateral displacement of a pedestal on which a target is mounted when the height thereof varies.

[0052] Figure 11 A general flow chart for generating a model that can be used to correct errors in offset tilt angle estimation, according to certain examples of the present disclosure, is described.

[0053] Figure 12 A non-limiting example is described showing a tilted wafer that can be used to determine the true value of the offset tilt angle and can be used to Figure 11 method.

[0054] Figure 13 A non-limiting example is shown, showing that Figure 11 The model generated by this method.

[0055] Figure 14 Illustrate a general flow chart showing how to use Figure 11 Methods for correcting errors in offset tilt angle estimation are disclosed according to certain examples.

[0056] Figure 15 Explained Figure 14 A non-limiting example of a method.

[0057] Figure 16 A schematic flow chart illustrating how to determine target height position data according to certain examples of the present disclosure is described. DETAILED DESCRIPTION

[0058] The offset tilt angle is the amount of unintended angular deviation of a light beam (e.g., an electron beam) from a desired direction. The desired direction can correspond to, for example, the normal to the sample (wafer) surface. A novel method and system for measuring the offset tilt angle are described below. According to certain currently disclosed embodiments, different images are acquired at different heights of a target. Due to variations in the height of the target, the position of the target in each image varies. An estimate of the offset tilt angle is determined using the geometric relationship between the target displacement in each image, the change in height, and the offset tilt angle.

[0059] See Figure 1 , which shows a functional block diagram of an inspection system 100 constructed according to certain examples disclosed herein. Figure 1 The inspection system 100 shown in FIG. 1 can be used to inspect samples (e.g., wafers and portions thereof) as part of a sample manufacturing process. The inspection system 100 shown includes a computer-based system 103. The system 103 can be operatively connected to one or more low-resolution inspection tools 101 and / or one or more high-resolution inspection tools 102 and / or other inspection tools. The inspection tools are configured to capture images and / or review the captured images and / or enable or provide measurements related to the captured images.

[0060] System 103 includes processing circuitry 104 comprising one or more processors and one or more memories. Processing circuitry 104 is configured to provide all processing required by operating system 103, as described in detail below (see methods that may be at least partially performed by system 103 and / or system 100, Figure 2 、 7A , 9, 11, 14 and 16).

[0061] The system 103 is configured to receive input data. The input data may include data generated by an inspection tool (and / or its derivatives and / or metadata associated therewith) and / or data generated and / or stored in one or more databases 109. It is noted that the input data may include images (e.g., captured images, images derived from captured images, simulated images, synthetic images, etc.) and associated digital data (e.g., metadata, custom attributes, etc.). It is further noted that the image data may include data associated with a layer of the sample and / or one or more other layers of the sample.

[0062] By way of non-limiting example, a sample can be inspected using one or more low-resolution inspection machines 101 (e.g., an optical inspection system, a low-resolution scanning electron microscope (SEM), etc.). The resulting data (low-resolution image data 121) provides information about a low-resolution image of the sample and can be transmitted directly or via one or more intermediary systems to system 103. Alternatively, the sample can be inspected using a high-resolution machine 102, such as a scanning electron microscope (SEM), an atomic force microscope (AFM), or an optical inspection tool (e.g., but not limited to, an optical inspection system proposed by the applicant). The resulting data (high-resolution image data 122) provides information about a high-resolution image of the sample and can be transmitted directly or via one or more intermediary systems to system 103.

[0063] It should be noted that the image data may be received and processed together with associated metadata (eg, pixel size, text description of defect type, parameters of the image capture process, etc.).

[0064] After processing the input data (e.g., low-resolution image data and / or high-resolution image data, along with other data such as design data, composite data, etc.), the system 103 can send instructions 123 and / or 124 to any inspection tool, store the results (e.g., data regarding offset tilt angles) in a storage system 107, present the results via a computer-based graphical user interface GUI 108, and / or send the results to an external system.

[0065] Those skilled in the art will readily appreciate that the teachings of the presently disclosed subject matter are not limited to Figure 1 The systems shown; equivalent and / or modified functionality may be combined or divided in other ways and implemented in any suitable combination of software and firmware and / or hardware.

[0066] Without limiting the scope of the present disclosure in any way, it should also be noted that the inspection tool can be implemented as various types of inspection machines, such as optical imaging machines, electron beam inspection machines, etc. In some cases, the same inspection tool can provide both low-resolution image data and high-resolution image data. In some cases, at least one inspection tool can have metrology capabilities.

[0067] Notice Figure 1 The inspection system shown can be implemented in a distributed computing environment where Figure 1The functional modules shown above can be distributed across several local and / or remote devices and connected via a communication network. It is further noted that in other embodiments, at least some of inspection tools 101 and / or 102, database 109, and storage system 107 can be located outside of inspection system 100 and communicate data with system 103. System 103 can be implemented as a standalone computer for use with the inspection tools. Alternatively, the respective functions of the system can be at least partially integrated with one or more inspection tools.

[0068] Now pay attention Figure 2 、 3A and 3B.

[0069] Figure 2 The method includes acquiring (operation 200) a set of images of a target 300. The set of images is acquired by an inspection system, such as inspection system 101 or 102, which is capable of emitting a light beam toward the target. The inspection system can be an electron beam inspection system (in which case the light beam is an electron beam) or an optical inspection system (in which case the light beam is an optical beam). The target 300 can correspond to, for example, a sample containing one or more patterns. Several non-limiting examples of target materials are provided herein.

[0070] The image set includes at least two images. In some instances, the image set may include more than two images. The first image of the target 300 captures the target 300 at a first height position 310. The height position can be measured along a vertical axis (Z axis) or along an axis orthogonal to the sample plane (which may coincide with the vertical Z axis).

[0071] The second image of the target 300 captures the target 300 at a second height position 320 , which is different from the first height position 310 .

[0072] The height difference ΔZ between the first height position 310 and the second height position 320 is Figure 3B It is marked as 330.

[0073] like Figure 3A and 3B As shown, due to the displacement of the target 300 along the vertical axis between the acquisition of the first image and the acquisition of the second image, the light beam 305 (which may correspond to an electron beam or an optical beam depending on the type of inspection system) hits the target 300 at different positions. Figure 3A In the embodiment, the light beam 305 hits the target 300 at the first region 311, and Figure 3B In FIG. 3 , the light beam 305 strikes the target 300 at a second region 312 that is different from the first region 311. Note that the same principle also applies to optical inspection systems.

[0074] Thus, a first position of target 300 in the first image is different from a second position of target 300 in the second image. The first position can be different from the second position by translation along the X-axis (horizontal axis in the sample plane) and / or along the Y-axis (vertical axis in the sample plane).

[0075] Non-limiting examples of the position displacement of the target 300 in the image are as follows: Figure 4A and 4B As shown. Figure 4A , the target 300 is located at the first position. Figure 4B , the targets 300 are located at the second position. The displacement between the targets 300 is represented by vector 310.

[0076] Figure 2 The method further includes (operation 210) determining data D ΔZ Specifically, operation 210 may include determining a first displacement of the target along the X-axis (horizontal axis of the image) and a second displacement along the Y-axis (vertical axis of the image) between the first image and the second image.

[0077] To determine the displacement of the target, various methods can be used. In some instances, the first image can be correlated with the second image. This correlation enables determination of the displacement of the target between the first and second images. In some instances, the first and / or second images can be correlated with a template image to determine the position of the target.

[0078] In some instances, an image processing algorithm (also known as a pattern recognition algorithm) can be used to identify the target in the first image and the second image. Once the location of the target in the first image and the location in the second image are determined, the displacement of the target can be determined. The image processing algorithm can include a machine learning model, such as a deep neural network (trained to detect the target). Examples of deep neural networks include convolutional neural networks, recurrent neural networks, etc. These examples are not limiting. Training can be performed using methods such as back propagation. Such training can be supervised (training using a training set of labeled training images with the target, the labels indicating the location of the target in the training images) or unsupervised.

[0079] Figure 2 The method further includes (operation 220) using the data D ΔZ The offset tilt angle of the inspection system beam is determined using the data on the first and second height positions. As described above, this can correspond to the offset tilt angle of the electron beam of an electron beam inspection system or the offset tilt angle of the beam of an optical inspection system.

[0080] Operation 220 may include utilizing the offset tilt angle, data D ΔZ(This data contains the displacement information of the target in the image group) and the geometric relationship between the height changes of the target in the image group. Figure 5 As shown, there is a geometric relationship between the offset tilt angle 510, the displacement (5201 or 5202) of the target 500 between the first image 530 and the second image (531 or 532), and the height change (540 or 541) of the target between the acquisition of the first image and the acquisition of the second image. In particular, the following relationship can be used:

[0081]

[0082] In Equation 1, θ represents the offset tilt angle, ΔR represents the displacement amplitude of the target between the first image and the second image, and ΔZ represents the height change of the target between the first image and the second image.

[0083] Assuming that the target is displaced by ΔX along the horizontal X-axis and ΔY along the vertical Y-axis between the first image and the second image, ΔR can be expressed as follows:

[0084] Assuming that the target moves between a first height position Z1 and a second height position Z2 along the height axis (Z axis) between the first image and the second image, ΔZ can be expressed as follows: ΔZ=|Z2−Z1|.

[0085] The offset tilt angle of the beam can be determined using the above equation. The offset tilt angle can be output to an operator and / or provided to other computerized systems.

[0086] According to some embodiments, the image set obtained in operation 200 includes images I1 to I N , N≥2, where each image in the image set I i At height H i Capture the target, the height position is consistent with other images in the image set I j Height position H j different, and i is different from j. The height can be modified by a fixed step size, but this is not mandatory. This allows a distribution to be obtained that relates the displacement of the target in the image (along the X or Y axis) to the height position of the target. Fitting the distribution to a model (e.g., a linear fit) can determine the relationship between the displacement of the target and the height position of the target. This model, combined with Equation 1, can be used to obtain a comprehensive estimate of the excess tilt angle based on the various measured displacements and heights. This is not limiting, and other methods can also be used.

[0087] The geometric relationship of Equation 1 can also be used multiple times with different pairs of images to obtain an estimate of the offset tilt angle for each pair of images. An aggregate estimate of the offset tilt angle can be generated (e.g., as an average of the different estimates). This is not limiting, and other methods can also be used.

[0088] In certain instances, once the offset tilt angle is determined according to the various methods described herein, metrological measurements can be performed. These metrological measurements can include, for example, CD measurements, overlay measurements, and the like. These metrological measurements are accurate due to the measurement of the offset tilt angle. In reality, the offset tilt angle can affect the accuracy of metrological measurements. A tilt of 0.1° due to a non-zero offset tilt angle can result in significant errors in metrological measurements. Accurately determining the offset tilt angle using the methods described herein helps improve the accuracy of metrological measurements.

[0089] In some instances, the measurement of the offset tilt angle can be used to calibrate the beam so that the offset tilt angle is equal to zero (or close to zero based on what can be stringent matching criteria). In some instances, an operator (and / or a computerized system for controlling the electronic beam inspection system, and / or the electronic beam inspection system itself) can modify parameters associated with the inspection system beam to obtain the desired offset tilt angle. In some instances, the inspection system can receive a current offset tilt angle value and can automatically modify one or more parameters to obtain the desired offset tilt angle. In particular, the current provided to the inspection system coils (such as the tilt coils and / or the displacement coils located below the objective lens) can be modified to obtain an offset tilt angle equal to or close to zero.

[0090] Figure 2 The proposed method enables the use of flat targets (since the method does not require the use of a target profile to determine the offset tilt angle). Furthermore, even when using non-flat targets, it is not necessary to know and / or determine the target height profile in advance. The method can operate without prior knowledge of the target height profile, or even with inaccurate knowledge of the target height profile.

[0091] Now pay attention Figure 6 , which describes an example target 600 that can be used to determine an offset tilt angle.

[0092] Inspection system 605 (e.g., a scanning electron microscope (SEM)—this is not limiting) generally includes a base 610 that includes an area 620 specifically configured to receive a sample (wafer) 630 to be inspected. During inspection of sample 630, sample 630 can be mechanically coupled to base 610 to maintain a fixed position of the sample relative to base 610. One or more mechanical connectors can be used to secure sample 630 to base 610.

[0093] The base 610 can move in one or more directions. The first stage 650 can control the translation of the base 610 along the Z axis, the second stage 651 can control the translation of the base 610 along the Y axis, and the third stage 652 can control the translation of the base 610 along the X axis. The first, second, and third stages 650, 651, and 652 can be coupled to the base 610 or can form the bottom portion of the base 610.

[0094] In some examples, the target 600 may be located on the base 610, or on a portion mechanically coupled to the base 610, at a location other than the area 610 specifically configured to receive the sample 630 to be inspected. Thus, displacement of the base 610 (along one or more of the X, Y, and Z axes) may result in displacement of the sample 630 to be inspected and the target 600.

[0095] In particular, the target 600 can be located on a side (corner) of the base 610, thereby freeing up an area specifically for receiving a sample 630 to be inspected. Thus, the sample 630 can be loaded into the inspection system 605 for inspection by the inspection system 605 while the target 600 is also present in the inspection system for determining the offset tilt angle.

[0096] In some embodiments, target 600 can be a target permanently present in the inspection system. This target 600 can be referred to as a "target island." As described above, target 600 can reside on base 610, leaving area 620 dedicated to receiving sample 630 to be inspected. Thus, compared to other solutions that require loading a tilted wafer to determine the offset tilt angle and then removing the tilted wafer from the inspection system for sample inspection, there is no need to load a target each time a new offset tilt angle measurement is required.

[0097] Typically, the target 600 is smaller than the sample 630 to be inspected. This is not a limiting condition. Note that the target 600 can also be used for other purposes if desired.

[0098] Now pay attention Figure 7A , which describes a method for determining the offset tilt angle, which can be used Figure 6 architecture.

[0099] Assume that a base 610 of an inspection system includes a sample 630 loaded in an area 620 on the base 610 specifically for receiving a sample 630 to be inspected.

[0100] Figure 7A The method includes acquiring images of one or more samples 630 using an inspection system (eg, a scanning electron microscope SEM) (operation 700). This corresponds to the runtime inspection phase of the samples.

[0101] During the inspection of the sample 610, or before the inspection of the sample 610 at the beginning of the run, a decision may be made whether to determine the offset tilt angle (operation 701). This decision may be made by an operator, who may provide instructions to the inspection system through an interface. Alternatively, the decision may be made automatically when one or more conditions are met. These conditions may include, for example, a time condition prior to the last offset tilt angle calibration. When the time since the last offset tilt angle calibration exceeds a threshold, calibration of the offset tilt angle may be triggered. In some instances, calibration of the offset tilt angle may be triggered when a new sample is detected to be loaded for inspection. This is not intended to be limiting.

[0102] After the decision to determine the offset tilt angle is made, Figure 7A The method further includes acquiring a set of images of the target 600 (operation 710). This may include moving the base 610 so that the beam is directed primarily toward the target 600 (rather than toward the sample 610). Alternatively, or in addition, the beam control rod 621 may be controlled to direct the beam toward the target 600. Figure 7B A non-limiting example is shown in .

[0103] As previously referenced Figure 2 As explained, a first image in the set of images captures the target 600 at a first height position, and a second image in the set of images captures the target 600 at a second height position different from the first height position.

[0104] Figure 7A The method further includes determining (operation 720) data D ΔZ , which contains the displacement information of the target in the image group.

[0105] Figure 7A The method further includes using (operation 730) the data D ΔZ and the data about the first and second height positions (particularly the difference between the first and second height positions) to determine the offset tilt angle of the inspection system beam. Operation 730 is similar to operation 220 described above.

[0106] Once the offset tilt angle is determined, inspection of sample 630 (or inspection of another sample that has been replaced with sample 630 on pedestal 610) can be resumed. This may involve moving pedestal 610 so that the beam is primarily directed toward sample 630 (rather than toward target 600). Alternatively, beam control rod 621 may be controlled to direct the beam toward sample 630.

[0107] Figure 7AThe method allows for a quick and efficient switch from a first mode, in which the target is used to determine the offset tilt angle, to a second mode in which the sample is inspected. Because the sample and target are located on the same pedestal, the switch from the first mode to the second mode, or vice versa, can be performed. The switch can be triggered by an operator and / or automatically by the inspection system, or by a computer-controlled system.

[0108] Now please note Figure 8A .

[0109] In an electron beam inspection tool (e.g., inspection tool 101 and / or 102), a radiation source 800 emits an electron beam, which passes through a first beam splitter 801 and is focused by an objective lens 802 onto a region of a sample 803. A tilt coil 807 (also referred to as an objective lens coil) can be used to control the deflection of the electron beam. Note that other coils (e.g., shift coil 811 and tilt coil 813) can be located below objective lens 802 to influence the deflection tilt angle of the electron beam.

[0110] Figure 8B An example of an uncalibrated state is shown, in which the electron beam 810 enters the objective lens 821 at an actual position that is offset from the center of the objective lens 821. As a result, the focus of the electron beam is translated in the XY plane relative to the target 825. When the height position of the target (along the Z axis) is modified, the position of the target in the XY plane moves from one image to the other.

[0111] Figure 8C A calibrated state is shown, where the electron beam 810 only strikes the objective lens 821 at its center. When the height position of the target 825 is modified (along the Z axis), the target does not shift due to the uncalibrated position of the electron beam 810 relative to the objective lens.

[0112] Applicants have discovered that it is beneficial to first calibrate the position of the electron beam relative to the objective lens before determining the offset tilt angle using the methods described herein, which rely on changes in the target height. Indeed, if the position of the electron beam relative to the objective lens is not calibrated, changes in the target height may produce an offset that is not caused by the offset tilt angle, but rather by the misalignment of the electron beam relative to the objective lens. This may therefore introduce errors in the estimation of the offset tilt angle. However, this is not limiting, and the various methods described herein can be performed without calibrating the position of the electron beam relative to the objective lens. Note that these principles can also be applied similarly to the beam of an optical inspection system.

[0113] Figure 9A method based on these principles is shown, including using a target (operation 900) to perform calibration of a beam (e.g., an electron beam or an optical beam) relative to an objective lens of an inspection system. This calibration may include aligning the focus of the electron beam with a symmetry axis of the objective lens according to a matching criterion. In some examples, this may include coinciding the focus of the electron beam with the target.

[0114] The calibration of the electron beam relative to the objective lens can rely on different methods. In some instances, the landing energy of the electron beam is modified. For each landing energy, an image of the wafer is acquired. Note that the wafer can correspond to the target material 600 mentioned above. A cross-correlation method, an image recognition algorithm or other adaptive method is used to determine the offset of the wafer between the images. This offset and a model that relates the offset to the current of the coil 807 that controls the position of the electron beam can be used to determine the adjustment of the coil 807 current so that the electron beam can hit the objective lens with its center. The model can be generated during a training phase. A non-limiting method for calibrating the position of the electron beam relative to the objective lens is described in U.S. Patent 7,335,893, which is cited in its entirety.

[0115] The position of the electron beam relative to the objective lens can be calibrated with close precision in order to minimize the error in the offset tilt angle. In some instances, the precision required by the matching standard can be selected so that the calibration error of the electron beam position is equal to or less than 0.2 nm. This value is not limiting, and other values ​​can also be used (in addition, as mentioned above, the offset tilt angle can be determined without performing this calibration). Please note that calibration of the electron beam relative to the objective lens does not necessarily mean that the offset tilt angle will be equal to zero. In fact, there are additional coils below the objective lens that affect the deflection of the electron beam and, therefore, the value of the offset tilt angle.

[0116] The method further includes (operation 910) determining an offset tilt angle using the target. Operation 910 may depend on Figure 2 The method in .

[0117] Once the offset tilt angle is determined, the method may include controlling the moving coil and / or the tilt coil to bring the offset tilt angle to zero or close to zero. Note that the calibration process of providing current to the moving coil and / or the tilt coil may be iterative in order to obtain an offset tilt angle close to zero.

[0118] from Figure 9 It can be understood from the method that the calibration of the electron beam to the objective lens and the determination of the offset tilt angle can both be performed using the same target material, which is efficient.

[0119] In some embodiments, the electron beam inspection system can be controlled to switch between a first mode and a second mode. In the first mode, the electron beam of the electron beam inspection system is directed toward the target to calibrate the position of the electron beam relative to the objective lens and then determine the offset tilt angle. In the second mode, the electron beam is directed toward the sample located in area 620 for inspection. During runtime inspection of the sample, switching between the first mode and the second mode, or vice versa, can be performed in real time in an efficient manner. These principles can also be similarly applied to the beam of the optical inspection system.

[0120] Now pay attention Figure 10 .

[0121] Applicants have discovered that the movement of stage 652 of base 610 (where the target is mounted) to modify the height of the target is not always perfectly vertical. Figure 10 As shown, when stage 652 modifies the height of the target 1011, it may occur that stage 652 also moves in directions other than the height direction (e.g., the X and / or Y directions corresponding to the horizontal and vertical directions within the target plane). This undesirable movement of stage 652 can cause the target to shift 1010 in the X and / or Y directions, which in turn causes the target to shift in the image, which is unrelated to the offset tilt angle. This can introduce errors in the offset tilt estimation, as most of the methods described herein rely on target height changes to determine the offset tilt angle.

[0122] Figure 11 The method of presents a solution for at least partially compensating for errors in the offset tilt angle determination. Figure 11 The method proposes to use a model to at least partially compensate for the error in the offset tilt angle estimation caused by the motion of the stage, which causes the base to move in the height direction. It should be noted that the model can also be used to correct other errors in the offset tilt angle estimation.

[0123] Figure 11 The method includes for each given offset tilt angle STA i Perform multiple operations, the offset tilt angle is a plurality of offset tilt angles STA1 to STA M The deflection tilt angle of the beam can be modified by modifying the current supplied to one or more coils (such as coils 811, 812), which will affect the deflection of the electron beam.

[0124] For each given electron beam offset tilt angle STA i , Figure 11The illustrated method includes acquiring a set of images of a target (operation 1110). The target may correspond to target 600 (located on a base of an inspection system capable of receiving a sample to be inspected). However, this is not limiting. The set of images is acquired by an electron beam inspection system, such as electron beam inspection system 101 or 102.

[0125] The set of images includes at least two images. The set of images may include more than two images. The first image of the target is obtained by capturing the target at a given first height position. The second image of the target is obtained by capturing the target at a given second height position different from the given first height position. It should be noted that the N images I1 to I N It is possible that N ≥ 2 and each image in the image group I i At height H i The target is captured and the height position H i With other images I j Get the height position H j different, and i is different from j.

[0126] Figure 11 The method shown further includes (operation 1120) determining data D ΔZ,校准 , which contains the displacement information of the target in a given image set. Operation 1120 is similar to operation 210.

[0127] Figure 11 The method further includes (operation 1130) using the data D ΔZ,校准 and data about the given first and second height positions (or data about N height positions) to determine an estimated value of a given offset tilt angle of the electron beam of the electronic inspection system. Operation 1130 is similar to operation 220. As mentioned above in connection with operation 220, determining the estimated value of the offset tilt angle may include using the offset tilt angle, data D ΔZ,校准 (provides information about the displacement of the target in a given set of images) and the geometric relationship between the height variation of the target in the set of images (in particular, equation 1 can be used). i to I N , and N ≥ 2, then the geometric relationship can be used to perform multiple calculations on different image pairs to obtain an estimate of the offset tilt angle for each image pair. An aggregate estimate of the offset tilt angle can be determined (the aggregate includes, for example, an average - this is not limiting).

[0128] Since operations 1110 , 1120 and 1130 are performed for a plurality of M different offset tilt angles, the method makes it possible to obtain a set of estimated values ​​of M offset tilt angles.

[0129] Figure 11 The method further includes obtaining (operation 1140) true values ​​of the M offset tilt angles. The true values ​​correspond to values ​​that are assumed to accurately reflect the true values ​​of the M offset tilt values.

[0130] In some instances, determining the true value of the offset tilt angle may include using a tilted wafer (see Figure 12 The height profile of the wafer comprises at least one slope. However, this is not restrictive. In this method, the height profile must be known in advance. Figure 12 In the example of FIG. 1 , the tilted wafer 1200 includes a first slope 1250, a top 1255, and a second slope 1260. Assuming that the tilted wafer 1200 is symmetrical, that is, assuming that the first slope and the second slope have the same angular tilt and opposite signs (see angular tilt 1270 and angular tilt 1275), and the projections of the first and second slopes (along the horizontal axis X) extend over the same horizontal distance 1280. The offset tilt angle 1210 can be estimated using the following formula:

[0131]

[0132] In formula 2, θ GT is the estimated value of the offset tilt angle (considered as the true value), E WL is the length of the first slope 1250 (see 1281), E WR is the length of the second slope 1260 (see 1282 ), and h is the height of the top 1255 of the tilted wafer 1200 (see 1290 ).

[0133] Figure 11 The method further includes generating (operation 1150) a model that models the relationship between the estimated excess tilt angle values ​​and the actual values ​​of the excess tilt angles. This model can be an affine function, but this is not limiting. Operation 1150 includes using a set of M estimated excess tilt angles and a set of M actual values ​​of the excess tilt angles. Specifically, operation 1150 can include fitting a function that models the relationship between the set of M estimated excess tilt angles and the actual values ​​of the set of M excess tilt angles. This fitting includes determining the coefficients of the function. For an affine function (whose expression is y=ax+b), the coefficients that need to be determined are "a" (slope) and "b" (intercept).

[0134] Non-limiting examples of models are given in Figure 13 Displayed in.

[0135] exist Figure 13In the example, the X-axis 1300 corresponds to the true value of the offset tilt angle (as obtained in operation 1140) and the Y-axis 1305 corresponds to the estimated value of the offset tilt angle (as obtained in operation 1130 or operation 220). To obtain the coefficients "a" and "b", an affine function is fitted (y = ax + b). It is desirable that "a" be close to 1. Applicants have found that close alignment of the beam with respect to the objective lens increases the likelihood that the coefficient "a" will be close to 1. Similarly, accurate knowledge of the actual height of the target also increases the likelihood that the coefficient "a" will be close to 1. The determination of the actual height of the target can rely on the following method described below. Figure 16 The coefficient "b" is not always equal to zero, because the movement caused by the stage 652 of the base 610 (on which the target is mounted) to change the height of the target is not always completely vertical, as shown in FIG. Figure 10 Note that other types of models (not necessarily affine functions) can also be used.

[0136] Once the model is generated (with Figure 11 relevant "training phase"), it can be used for prediction, such as Figure 14 and 15 shown.

[0137] Figure 14 The method includes executing Figure 2 Operations 200, 210, and 220 in the embodiment of the present invention are used to obtain a first estimate of the offset tilt angle of the inspection system's electron beam. This first estimate is obtained by vertically moving the target, measuring its displacement in the image, and using a relationship (e.g., Equation 1) to estimate the offset tilt angle. As described above, this first estimate may contain small errors, such as due to movement of stage 652 of the pedestal 610 (on which the target is mounted), which may change the height of the target, which is not necessarily perfectly vertical. Note that small errors in the first estimate may also be caused by other factors.

[0138] Figure 14 The method further includes using (operation 1450) the first estimate of the offset tilt angle and utilizing Figure 11 The second estimate of the offset tilt angle is determined using a model generated by the method of FIG. Note that the second estimate of the offset tilt angle is expected to be more accurate than the first estimate of the offset tilt angle.

[0139] As described above, the model relates each estimated value of the offset tilt angle to the corresponding true value of the offset tilt angle. For example, suppose the model F is expressed as follows: STA 估算值 =F(STA 真实值 ), where STA 估算值 is an estimate of the offset tilt angle, STA 真实值is the true value of the offset tilt angle. Therefore, the second estimated value STA of the offset tilt angle 第二估算值 The first estimated value STA of the offset tilt angle can be obtained by 第一估算值 Obtained as follows: STA 第二估算值 =F -1 (STA 第一估算值 ).

[0140] Figure 15 A non-limiting example is shown in FIG.

[0141] Assume that model 1500 has been generated and used Figure 2 The method obtains a first estimate of the offset tilt angle 1510. The model (using Figure 11 The second estimated value 1520 of the offset tilt angle can be determined by a method (generated by the method). This value can be selected to correspond to the same horizontal coordinate target point on the model curve. This horizontal coordinate is the first estimated value 1510 of the offset tilt angle.

[0142] In some examples, when the model is an affine function, operation 1450 may include subtracting an intercept coefficient of the affine function from the first estimate to generate a second estimate of the offset tilt angle.

[0143] Please note Figure 16 , which describes a method for determining the actual height position of the target.

[0144] Please note that Figure 16 The method described is merely an example; any other suitable method can be used to measure the target height. For example, an encoder can be used to measure the position of the target base. In other examples, any sensor suitable for measuring distance (laser, ultrasonic sensor, etc.) can be used to measure the target height. These methods can be combined, or other methods can be used.

[0145] As mentioned above Figure 6 In FIG. 6 , the target may be located on a base 610 of the inspection system, which is movable at least in the height direction. The inspection system may provide height information about an area 620 receiving a sample (wafer) 630. However, the height position of the wafer may differ from the height position of the area 620. In order to calibrate the height position of the target, Figure 16The method can include moving (operation 1600) a target in an XY plane so that the target is positioned in front of a distance measurement device of an inspection system along the Z axis, and measuring data regarding the height position of the target using (operation 1610) the distance measurement device. In some embodiments, the distance measurement device includes a laser, and the distance is measured based on the time required for the laser to make one round trip (displacement). This enables determination of a relationship between the height position of the pedestal 610 (possibly provided by an electron beam inspection system) and the actual height position of the target. Note that calibration of the target height is typically performed prior to evaluating the offset tilt angle, as explained in the various methods described herein.

[0146] In the detailed description, numerous specific details are set forth to provide a thorough understanding of the present disclosure. However, it will be apparent to those skilled in the art that the presently disclosed subject matter can be understood without these specific details. In other instances, well-known methods, procedures, components, and circuits have not been described in detail in order not to obscure the presently disclosed subject matter.

[0147] Unless otherwise expressly stated, in light of the foregoing discussion, it will be understood that terms such as "acquire," "determine," "execute," "use," "estimate," "train," or similar terms used throughout this specification refer to the actions and / or processes of at least one processing circuit that operates on and / or transforms data into other data, where the data is represented by physical (e.g., electronic) quantities or where the data represents physical objects.

[0148] The term "computer" or "computer-based system" should be interpreted broadly to include any hardware electronic device with data processing circuitry (e.g., digital signal processor (DSP), graphics processing unit (GPU), tensor processing unit (TPU), field programmable gate array (FPGA), application specific integrated circuit (ASIC), microcontroller, microprocessor, etc.), including as non-limiting examples Figure 1The computer-based system 103 and the corresponding parts disclosed in this application. The data processing circuit (also referred to as processing circuit) may include, for example, one or more processors operatively connected to a computer memory that is loaded with executable instructions to perform operations, as described in detail below. The data processing circuit encompasses a single processor or multiple processors that may be located in the same geographic area, or may be at least partially located in different areas and capable of communicating with each other. The one or more processors may represent one or more general-purpose processing devices, such as microprocessors, central processing units, etc. More particularly, a given processor may be: a complex instruction set computing (CISC) microprocessor, a reduced instruction set computing (RISC) microprocessor, a very long instruction word (VLIW) microprocessor, a processor that implements other instruction sets, or a processor that implements a combined instruction set. The one or more processors may also be special-purpose processing devices, such as an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), a digital signal processor (DSP), a network processor, etc. The one or more processors are configured to execute instructions to perform the operations and steps discussed herein.

[0149] The memory mentioned here may include one or more of the following: internal memory, such as processor registers and cache, main memory, such as read-only memory (ROM), flash memory, dynamic random access memory (DRAM) such as synchronous DRAM (SDRAM) or Rambus DRAM (RDRAM), etc.

[0150] As used herein, the terms "non-transitory memory" and "non-transitory storage medium" should be interpreted broadly to encompass any volatile or non-volatile computer memory suitable for use with the presently disclosed subject matter. These terms should include a single medium or multiple media (e.g., a centralized or distributed database, and / or associated caches and servers) that store one or more instruction sets. These terms should also include any medium capable of storing or encoding an instruction set for execution by a computer, and causing the computer to perform any one or more of the methodologies of the present disclosure. Thus, these terms should include, but are not limited to, read-only memory ("ROM"), random access memory ("RAM"), magnetic disk storage media, optical disk storage media, flash memory devices, and the like.

[0151] It should be noted that although the present disclosure refers to processing circuitry 104 being configured to perform various functions and / or operations, these functions / operations may be performed in a variety of ways by one or more processors of processing circuitry 104. For example, the operations described below may be performed by a specific processor or by a combination of multiple processors. Thus, these operations may be performed by a respective processor (or combination of processors) in processing circuitry 104, and optionally, at least some of these operations may be performed by the same processor. The present disclosure should not be construed as limiting the interpretation that a single processor always performs all operations.

[0152] The term "specimen" as used in this specification should be interpreted broadly to cover any kind of wafers, masks, and other structures, assemblies, and / or components thereof used in the manufacture of semiconductor integrated circuits, magnetic heads, flat panel displays, and other semiconductor manufacturing artifacts.

[0153] The term "inspection" as used in this specification should be interpreted broadly to cover any measurement-related operations and operations related to detecting and / or classifying defects during the sample manufacturing process. Inspection is performed using non-destructive inspection tools during or after the manufacturing process of the sample being inspected. By way of non-limiting example, the inspection process may include running scans (one or more scans), sampling, review, measurement, classification and / or other operations provided to the sample or part thereof, whether using the same or different inspection tools. Similarly, inspection may also be performed before the manufacture of the sample being inspected, and may include, for example, the generation of inspection recipes and / or other setup operations. It should be noted that, unless otherwise expressly stated, the term "inspection" or its derivatives as used in this specification is not limited by the resolution or size of the inspection area. Various non-destructive inspection tools include, by way of non-limiting example, scanning electron microscopes, atomic force microscopes, optical inspection tools, etc.

[0154] It should be understood that, unless otherwise expressly stated, certain features of the present disclosure, even if described in separate embodiments, may also be provided in combination in a single embodiment. Conversely, certain features of the present disclosure, even if described in a single embodiment, may also be provided separately or in any suitable subcombination. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the methods and apparatus.

[0155] In the presently disclosed embodiments, the execution phase may be less than, more than, or equal to the phases described in the preceding text. Figure 2 、 7A , 9, 11, 14 and 16. In the currently disclosed embodiment, Figure 2 、 7A One or more stages of the methods shown in , 9, 11, 14 and 16 may be performed in a different order, and / or one or more groups of stages may be performed simultaneously.

[0156] It should be understood that the invention is not limited to the details described herein or shown in the drawings.

[0157] Likewise, the system according to the present invention may be implemented at least in part on a suitably programmed computer. Furthermore, the present invention contemplates a computer program readable by a computer to perform the method of the present invention. The present invention further contemplates a non-transitory computer-readable memory embodying a program of instructions executable by a computer to perform the method of the present invention.

[0158] The present invention is capable of other embodiments and of being implemented in a variety of ways. Therefore, it should be understood that the terms and expressions used herein are for descriptive purposes only and should not be construed as limiting. Those skilled in the art will recognize that the concepts underlying this disclosure can be readily utilized as a basis for designing other structures, methods, and systems to achieve the various objectives of the presently disclosed subject matter.

[0159] Those skilled in the art will readily appreciate that various modifications and changes can be applied to the embodiments of the invention described herein without departing from the scope thereof, which is defined by the appended claims.

Claims

1. A system comprising one or more processing circuits, wherein the system is configured to: For each given offset tilt angle offset among a plurality of offset tilt angles of the light beam of the inspection system: Get a given set of images of the target material, wherein a given first image in the image group is obtained by capturing the target material at a given first height position, and a second image in the given image group is obtained by capturing the target material at a given second height position different from the first height position, Determine data D ΔZ,校准 , including the displacement information of the target in the given image group, and Using the data D ΔZ,校准 and data about said given first and second height positions to determine a given estimated offset tilt angle of said electron beam, Thus, a plurality of estimated offset tilt angles of the plurality of offset tilt angles are obtained, and A model is generated using the plurality of offset tilt angles or true values ​​of the plurality of offset tilt angle values ​​and the plurality of estimated offset tilt angles.

2. The system according to claim 1, wherein the system is configured as follows: Acquire an image group of the target material, wherein the image set is obtained by the inspection system, wherein the first image in the image group is obtained by capturing the target material at a first height position, and the second image in the image group is obtained by capturing the target material at a second height position different from the first height position, Determine data D ΔZ , the data includes displacement information of the target material in the image group, Using the data D ΔZ and data about the first and second height positions to determine a first estimate of a deflection tilt angle of a light beam of the inspection system, and A second estimate of the offset tilt angle is generated using the model and the first estimate.

3. A system comprising one or more processing circuits, wherein the system is configured to: Get the target image set, wherein the image set is obtained by an inspection system, wherein the first image in the image group is obtained by capturing the target material at a first height position, and the second image in the image group is obtained by capturing the target material at a second height position different from the first height position, Determine data D ΔZ , the data includes displacement information of the target in the image group, and Using the data D ΔZ and data about the first and second height positions to determine the offset tilt angle of the light beam of the inspection system.

4. The system of claim 3, wherein the set of images is obtained after calibrating the light beam of the inspection system relative to an objective lens of the inspection system, wherein the calibration uses the target.

5. The system of claim 4, wherein the calibration comprises aligning the focus of the light beam to the symmetry axis of the objective lens according to a matching criterion. The system of claim 4 , wherein the calibration accuracy is equal to or less than 0.2 nm.

7. The system of claim 3, wherein the image group comprises images I1 to I N , and N≥2, wherein each image I in the image group i At height H i The target is captured and the height position H is obtained. i With other images I j At height H j The capture target is different, and i is different from j.

8. The system of claim 3, wherein the system is configured to utilize the offset tilt angle, the data D containing the displacement information of the target material in the image group, ΔZ and a geometric relationship between the data regarding the first and second height positions to determine the offset tilt angle.

9. The system of claim 3 , wherein the inspection system comprises an operating element for moving the target along a height direction, wherein the system is configured to use a model to at least partially compensate for an error in the estimate of the offset tilt angle, the error being caused at least by movement of the element along a direction different from the height direction.

10. The system of claim 3, wherein (i) or (ii) is satisfied: (i) The inspection system includes a base, the base including an area specifically for receiving a sample to be inspected, wherein the target material is located on the base or on a portion coupled to the base; (ii) The inspection system includes a base, which contains an area specifically for receiving a sample to be inspected, wherein the target material is permanently fixed on the base or located on a part coupled to the base.

11. The system of claim 3, wherein (i) or (ii) is satisfied: (i) the system is configured to control the inspection system to switch between a first mode and a second mode, wherein in the first mode, the light beam is directed toward the target to determine the offset tilt angle, and in the second mode, the light beam is directed toward a sample for inspection, wherein the sample and the target are associated with the same pedestal; (ii) the inspection system is operable to switch between a first mode and a second mode, wherein in the first mode the light beam is directed toward the target to determine the offset tilt angle, and in the second mode the light beam is directed toward a sample for inspection, wherein the sample and the target are associated with the same pedestal.

12. The system of claim 3, wherein the target material has a flat pattern.

13. The system according to claim 3, wherein the system is configured as follows: Using the data D ΔZ and data regarding the first and second height positions to determine a first estimate of the offset tilt angle of the light beam of the inspection system, and The estimate of the offset tilt angle is generated using a model and the first estimate.

14. The system of claim 13, wherein the model is configured to simulate an error in the estimate of the offset tilt angle when the estimate is based on a height variation of the target and a displacement of the target in an image associated with the height variation.

15. The system of claim 13, wherein the model simulates a relationship between an estimated offset tilt angle of a plurality of offset tilt angles and a plurality of true values ​​of the plurality of offset tilt angles.

16. The system of claim 3, configured to use a distance measuring device to determine data regarding the height position of the target.

17. The system according to claim 3, wherein the system is configured as follows: For each given offset tilt angle among a plurality of offset tilt angles of the light beam of the inspection system: Obtaining a given set of images of the target material, wherein a given first image in the image group is obtained by capturing the target material at a given first height position, and a second image in the given image group is obtained by capturing the target material at a given second height position different from the first height position, Determine data D ΔZ,校准 , including the displacement information of the target in the given image group, and Using the data D ΔZ,校准 and data about said given first and second height positions to determine a given estimated offset tilt angle of said light beam of said inspection system, Thus, the estimated values ​​of the plurality of offset tilt angles are obtained, and A model is generated using the plurality of offset tilt angles or true values ​​of the plurality of offset tilt angle values ​​and the plurality of estimated offset tilt angles.

18. The system of claim 17, wherein the system is configured to use the data D ΔZ and data regarding the first and second height positions to determine a first estimate of the offset tilt angle of the light beam of the inspection system, and using the model and the first estimate to generate the estimate of the offset tilt angle.

19. The system of claim 17, wherein the true offset tilt angle value is obtained using a wafer having a height profile having a first slope and a second slope.

20. A non-transitory computer-readable medium comprising instructions that, when executed by at least one or more processing circuits, cause the at least one or more processing circuits to acquire a set of images of a target material, wherein the set of images is acquired by an inspection system, and a first image in the set of images is acquired when the target material is captured at a first height position, and a second image in the set of images is acquired when the target material is captured at a second height position different from the first height position, and then determine data D ΔZ , the data includes the displacement information of the target in the image group, and using the data D ΔZ and data about the first and second height positions to determine the offset tilt angle of the light beam of the inspection system.

Images