Charged particle evaluation system and method

Abstract

An evaluation method comprising: using an evaluation device to generate an evaluation signal representative of a property of a surface of a sample; processing the evaluation signal to identify a candidate defect and outputting a candidate defect signal; monitoring a state of the evaluation device for error conditions and generating a state signal indicative of any error conditions during operation of the evaluation device; and analyzing the candidate defect signal to determine whether the candidate defect is a real defect; wherein the analysis of the candidate defect is not completed if the status signal indicates that the evaluation signal and / or a candidate defect signal corresponding to the candidate defect has been affected by an error condition.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. application 63 / 391,194 filed on July 21, 2022, U.S. application 63 / 403,823 filed on September 5, 2022, and EP application 22193743.6 filed on September 2, 2022, which are incorporated herein by reference in their entirety. Technical Field

[0003] Embodiments provided herein generally relate to charged particle evaluation systems and methods of operating charged particle evaluation systems. Background Art

[0004] When manufacturing semiconductor integrated circuit (IC) chips, undesirable pattern defects will inevitably appear on the substrate (i.e., wafer) or mask during the manufacturing process due to, for example, optical effects and accidental particles, thereby reducing the yield. Therefore, monitoring the degree of undesirable pattern defects is an important process in IC chip manufacturing. More generally, inspecting and / or measuring the surface of a substrate or other object / material is an important process during and / or after its manufacture.

[0005] Pattern inspection devices with charged particle beams have been used to inspect objects (which may be referred to as samples), for example, to detect pattern defects. These devices typically use electron microscopy techniques, such as scanning electron microscopes (SEMs). In SEMs, a primary electron beam of relatively high-energy electrons is targeted and a final deceleration step is performed so that it lands on the sample with a relatively low landing energy. The electron beam is focused into a detection spot on the sample. The interaction between the material structure at the detection spot and the landing electrons from the electron beam results in the emission of signal electrons (such as secondary electrons, backscattered electrons, or Auger electrons) from the surface, which may be more generally referred to as signal particles. Signal electrons may be emitted from the material structure of the sample. By scanning the sample surface with the primary electron beam as a detection spot, signal electrons may be emitted to the sample surface. By collecting these emitted signal electrons from the sample surface, the pattern inspection device may obtain an image representing the characteristics of the material structure of the sample surface.

[0006] When a pattern inspection device is used to detect defects on a sample at a high throughput, a large amount of image data is generated and must be processed to detect defects. In particular, it is desirable to reduce the noise in the image data. US 8,712,184 B1 and US 9,436,985 B1 describe methods for reducing noise or improving the signal-to-noise ratio in images obtained from a scanning electron microscope. It is necessary to distinguish noise (such as nuisance signals) from real defects (or real defects), otherwise an excessive proportion of processed substrates may be rejected, thereby unnecessarily reducing the yield. Some noise can be eliminated by statistical methods and by applying thresholds, but this technique cannot distinguish all noise (such as some nuisance signals) from real defects. Therefore, there is still a need for improved technology to distinguish noise from real defects and reduce false alarms. Summary of the invention

[0007] An object of the present disclosure is to provide embodiments that avoid or improve bad data defects that affect the performance of a charged particle evaluation device for detecting defects.

[0008] According to one aspect of the present invention, an evaluation method is provided, comprising: using an evaluation device to generate an evaluation signal representing an attribute of a sample surface; processing the evaluation signal to identify a candidate defect and outputting a candidate defect signal; monitoring the status of the evaluation device for an error condition and generating a status signal indicating any error condition during operation of the evaluation device; and analyzing the candidate defect signal to determine whether the candidate defect is a real defect; wherein if the status signal indicates that (one or more) evaluation signals and / or a candidate defect signal corresponding to the candidate defect has been affected by the error condition, the analysis of the candidate defect is not completed.

[0009] According to one aspect of the present invention, an evaluation method is provided, comprising: using an evaluation device to generate an evaluation signal representing an attribute of a sample surface; processing the evaluation signal to identify candidate defects and outputting a candidate defect signal; monitoring the status of the evaluation device for error conditions and generating a status signal indicating any error conditions occurring during operation of the evaluation device; and analyzing the candidate defect signal to determine whether the candidate defect is a real defect; wherein the analysis of the candidate defect comprises using the status signal to verify whether the evaluation signal and / or the candidate defect signal corresponding to the candidate defect has been affected by the error condition, and stopping the analysis of the defect candidate after verification.

[0010] An evaluation system comprises: a detector unit configured to generate an evaluation signal representing a property of a sample surface; a data processor configured to process the evaluation signal to identify a candidate defect and output a candidate defect signal; a state monitor configured to monitor the state of the evaluation system for an error condition and generate a state signal indicating any error condition occurring during operation of the evaluation system; and an analysis unit configured to analyze the candidate defect signal to determine whether the candidate defect is a real defect; wherein if the state signal indicates that the evaluation signal and / or the candidate defect signal corresponding to the candidate defect has been affected by the error condition, the analysis unit is configured to stop analyzing the candidate defect before completion.

[0011] According to one aspect of the present invention, an evaluation system is provided, comprising: a detector unit configured to generate an evaluation signal representing a property of a sample surface; a data processor configured to process the evaluation signal to identify a candidate defect and output a candidate defect signal; a status monitor configured to monitor the status of the evaluation system for an error condition and generate a status signal indicating any error condition occurring during operation of the evaluation device; and an analysis unit configured to analyze the candidate defect signal to determine whether the candidate defect is a real defect; wherein if verification using the status signal indicates that (one or more) evaluation signals and / or the candidate defect signal corresponding to the candidate defect has been affected by the error condition, the analysis unit is configured to stop analysis of the candidate defect before completion.

[0012] According to one aspect of the present invention, there is provided a data processing device for analyzing candidate defects to identify real defects, the data processing device comprising: an interface configured to receive a candidate defect signal representing a candidate defect and a status signal indicating any error condition during the operation of the evaluation device from an evaluation device; an analysis unit configured to analyze the candidate defect signal to identify the real defect; wherein if the status signal indicates that the candidate defect signal corresponding to the candidate defect has been affected by the error condition, the analysis unit is configured to stop analyzing the candidate defect before completion.

[0013] According to one aspect of the present invention, there is provided a data processing method for analyzing candidate defects to identify real defects, the method comprising: receiving a candidate defect signal representing a candidate defect and a status signal indicating any error condition during operation of the evaluation device from an evaluation device; analyzing the candidate defect signal to identify the real defect; wherein if the status signal indicates that the candidate defect signal corresponding to the candidate defect has been affected by the error condition, stopping the analysis of the candidate defect before completion.

[0014] According to one aspect of the present invention, a charged particle evaluation system is provided for detecting defects in a sample by relatively scanning multiple charged particle beams (for example, in a beam grid) and the sample so that the grid passes over the surface; the device includes: a detector unit, which includes multiple detector elements and is configured to output a detection signal in response to a signal particle incident from the sample, the detection signal being generated by and associated with different beams of the beam grid; a signal processor, configured to process the detection signal to generate an evaluation signal, the evaluation signal including, for each detector element, attribute information related to an attribute of the sample and a detection time of the detection signal particle; and an analysis unit, configured to analyze the evaluation signal to identify defect candidates on the sample based on an analysis of the attribute information in the evaluation signal for each detector element; wherein the analysis unit is configured to analyze the attribute information from different detector elements to determine an error state associated with one or more beams of the beam grid.

[0015] According to one aspect of the present invention, a method for detecting defects in a sample in a charged particle evaluation device is provided, the charged particle evaluation device being used to project a charged particle beam toward the sample, the method comprising: relatively scanning the charged particle beam and the surface of the sample in the charged particle evaluation device so that the beam passes through the surface; outputting a detection signal from a detector of the charged particle evaluation device in response to signal particles from the sample, the detection signal having a time record relative to a timeline; emitting a status signal having a timestamp relative to the timeline, the status signal indicating a status of the charged particle evaluation device, the status including a transient error affecting the operation of the evaluation device; and processing the detection signal when the time record indicates a time different from the timestamp of the transient error.

[0016] According to one aspect of the present invention, a charged particle evaluation system is provided for detecting defects in a sample by relatively scanning a plurality of charged particle beams and a sample in a beam grid so that the beam grid passes over the surface; the device comprises: a detector unit comprising a plurality of detector elements and configured to output a detection signal in response to signal particles incident from the sample, the detection signal being generated by and associated with different beams of the beam grid; a controller configured to control the charged particle evaluation system to determine a failure of one or more beams of the beam grid and to identify a beam identity of a faulty beam; and based on the beam identity of the faulty beam, removing the detection signal of the faulty beam or information derived from the detection signal of the faulty beam from processing and / or analysis for use in determining candidate defects on the sample surface.

[0017] According to one aspect of the present invention, a method for detecting defects in a sample in a charged particle evaluation device is provided, the charged particle evaluation device being used to project a charged particle beam onto the sample, the method comprising: relatively scanning the charged particle beam and the surface of the sample in the charged particle evaluation device so that the beam passes through the surface; outputting a detection signal from a detector of the charged particle evaluation device in response to signal particles from the sample, the detection signal having a time record relative to a time line; emitting a status signal having a timestamp relative to the time line, the status signal indicating a status of the charged particle evaluation device, the status including a transient error affecting the operation of the evaluation device; and processing the detection signal when the time record indicates a time different from the timestamp of the transient error.

[0018] According to one aspect of the present invention, a charged particle evaluation system is provided for detecting defects in a sample by relatively scanning a plurality of charged particle beams in a beam grid and the sample so that the grid passes over the surface; the device comprises: a detector unit comprising a plurality of detector elements and configured to output a detection signal in response to signal particles incident from the sample, the detection signal being generated by and associated with different beams of the beam grid; a controller configured to control the charged particle evaluation system to determine a failure of one or more beams of the beam grid and to identify a beam identity of a faulty beam; and based on the beam identity of the faulty beam, removing the detection signal of the faulty beam or information derived from the detection signal of the faulty beam from processing and / or analysis for use in determining candidate defects on the sample surface.

[0019] According to one aspect of the present invention, an evaluation method is provided, comprising: using an evaluation device to generate an evaluation signal representing an attribute of a sample surface; processing the evaluation signal to identify a candidate defect and outputting a candidate defect signal; monitoring the state of the evaluation device for an error condition and generating a status signal indicating the occurrence of any error condition and otherwise indicating an operating state, which occurs during the operation of the evaluation device, and which will affect the evaluation signal generated during the occurrence and / or the candidate defect signal corresponding to the candidate defect and derived from the evaluation signal; and analyzing the candidate defect signal to determine whether the candidate defect is a real defect; wherein the analysis of the candidate defect is completed only when the status signal indicates an operating state.

[0020] According to one aspect of the present invention, an evaluation system is provided, comprising: a detector unit configured to generate an evaluation signal representing an attribute of a sample surface; a data processor configured to process the evaluation signal to identify a candidate defect and output a candidate defect signal; a state monitor configured to monitor the state of an evaluation device for an error condition and generate a state signal indicating the occurrence of any error condition and otherwise indicating an operating state, which occurs during the operation of the evaluation device and which will affect the evaluation signal generated during the occurrence and / or the candidate defect signal corresponding to the candidate defect and derived from the evaluation signal; wherein the analysis unit is configured to complete the analysis of the candidate defect only when the state signal indicates the operating state.

[0021] According to one aspect of the present invention, there is provided a computer program comprising instructions interpretable by a computer controlling an evaluation device, the computer program comprising instructions for executing a method according to another aspect of the present invention disclosed herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The above and other aspects of the present disclosure will become more apparent from the description of exemplary embodiments with reference to the attached drawings.

[0023] Figure 1 is a schematic diagram illustrating an exemplary charged particle beam evaluation system.

[0024] Figure 2 is a schematic diagram illustrating an exemplary multi-beam charged particle evaluation apparatus, which is Figure 1 A portion of an exemplary charged particle beam evaluation system.

[0025] Figure 3 is a schematic diagram of a data path according to an embodiment.

[0026] Figure 4 Schematic diagram of a state monitoring system according to an embodiment of the present invention.

[0027] Figure 5 is a flow chart of the method of the present invention.

[0028] The schematic diagrams and views illustrate the components described below. However, the components depicted in the figures are not drawn to scale. DETAILED DESCRIPTION

[0029] Reference will now be made in detail to exemplary embodiments, examples of which are illustrated in the accompanying drawings. The following description refers to the accompanying drawings, wherein, unless otherwise specified, the same numbers in different drawings represent the same or similar elements. The implementations set forth in the following description of exemplary embodiments do not represent all implementations consistent with the present invention. Instead, they are merely examples of devices and methods consistent with various aspects related to the present invention as described in the appended claims.

[0030] The increased computing power of electronic devices (which reduces the physical size of the devices) can be achieved by significantly increasing the packing density of circuit components such as transistors, capacitors, diodes, etc. on IC chips. This is achieved through improved resolution, which enables the manufacture of smaller structures. For example, an IC chip for a smartphone (which is the size of a thumbnail and available in 2019 or earlier) can include more than 2 billion transistors, each of which is less than one thousandth the size of a human hair. Therefore, it is not surprising that semiconductor IC manufacturing is a complex and time-consuming process with hundreds of individual steps. Even an error in one step has the potential to greatly affect the functionality of the final product. The goal of the manufacturing process is to increase the yield of the entire process. For example, in order to obtain a 75% yield for a 50-step process (where the step can indicate the number of layers formed on the wafer), each individual step must have a yield greater than 99.4%. If each individual step has a 95% yield, the overall process yield will be as low as 7%.

[0031] While high process yields are desirable in IC chip fabrication facilities, it is also essential to maintain high substrate (i.e., wafer) throughput, defined as the number of substrates processed per hour. High process yields and high substrate throughput can be impacted by the presence of defects. This is especially true if operator intervention is required to detect the defect. Therefore, high throughput detection and identification of micro- and nanoscale defects by inspection equipment, such as a scanning electron microscope ("SEM"), is critical to maintaining high yields and low costs.

[0032] An embodiment of the SEM includes a scanning device and a detection device. The scanning device includes an irradiation device, which includes an electron source for generating primary electrons (or charged particles), and a projection device for scanning a sample (e.g., a substrate) with one or more focused primary electron beams (or multiple beams). Multiple beams can be arranged as multiple beams. Multiple beams can have a multiple beam arrangement (which can have the form of a grid), which can be guided to the sample along a multiple beam path. At least the irradiation device or irradiation system and the projection device or projection system can be referred to as an electron optical system or device together. Primary electrons interact with the sample and generate secondary electrons. The detection device captures secondary electrons from the sample when scanning the sample so that the SEM can create an image of the scanning area of ​​the sample. For high-throughput inspection, some inspection devices use multiple focused beams of primary electrons, i.e., multiple beams. The component beams of multiple beams can be referred to as sub-beams or beam waves. Multiple beams can scan different parts of the sample at the same time. Therefore, a multi-beam inspection device can inspect the sample at a much higher speed than a single-beam inspection device.

[0033] A known implementation of a multi-beam inspection apparatus is described below.

[0034] Although the description and drawings are directed to electron optical systems, it should be understood that the embodiments are not intended to limit the disclosure to specific charged particles. Therefore, references to electrons throughout this document may be considered more generally as references to charged particles, where the charged particles are not necessarily electrons. The present invention may also be applied to optical inspection systems, such as optical microscopes and optical scatterometers.

[0035] Now to Figure 1 Reference is made to , which is a schematic diagram illustrating an exemplary charged particle beam evaluation system 100 (or simply evaluation system, which may also be referred to as a charged particle beam inspection system or simply inspection system or a charged particle metrology system or simply metrology system). Figure 1 The charged particle beam evaluation system 100 includes a main chamber 10, a load lock chamber 20, an electron beam device 40, an equipment front end module (EFEM) 30, and a controller 50. The electron beam device 40 is located in the main chamber 10.

[0036] The EFEM 30 includes a first loading port 30a and a second loading port 30b. The EFEM 30 may include additional loading ports. The first loading port 30a and the second loading port 30b may, for example, receive a substrate front opening pod (FOUP) containing a substrate to be inspected (e.g., a semiconductor substrate or a substrate made of (a plurality of) other materials) or a sample (substrate, wafer, and sample are collectively referred to as "sample" hereinafter). One or more robotic arms (not shown) in the EFEM 30 transfer the sample to the load lock chamber 20.

[0037] The load lock chamber 20 is used to remove the gas around the sample. This will produce a vacuum, which is a local gas pressure lower than the pressure in the surrounding environment. The load lock chamber 20 can be connected to a load lock vacuum pump system (not shown), which removes gas particles in the load lock chamber 20. The operation of the load lock vacuum pump system causes the load lock chamber to reach a first pressure lower than atmospheric pressure. After reaching the first pressure, one or more robotic arms (not shown) transfer the sample from the load lock chamber 20 to the main chamber 10. The main chamber 10 is connected to the main chamber vacuum pump system (not shown). The main chamber vacuum pump system removes gas particles in the main chamber 10 so that the pressure around the sample reaches a second pressure lower than the first pressure. After reaching the second pressure, the sample is transferred to the electron beam system, which can be inspected by the electron beam system. The electron beam device 40 may include a multi-beam electron optical device (which may be referred to as an electron optical column or device).

[0038] The controller 50 is electrically connected to the electron beam device 40. The controller 50 may be a processor (such as a computer) configured to control the charged particle beam evaluation system 100. The controller 50 may also include circuitry, which may be referred to as processing circuitry, configured to perform various signal and image processing functions. Figure 1 30, but it will be appreciated that the controller 50 may be part of the structure. The controller 50 may be located in one of the constituent elements of the charged particle beam inspection device, or it may be distributed over at least two constituent elements. Although the present disclosure provides an example of a main chamber 10 housing an electron beam device, it should be noted that the various aspects of the present disclosure are not limited to a chamber housing an electron beam device in its broadest sense. On the contrary, it will be appreciated that the aforementioned principles may also be applied to the arrangement of other devices and other apparatuses operating at a second pressure. For example, the controller may be a distributed controller having one or more portions at a second pressure, and optionally one or more portions at a first pressure.

[0039] Now to Figure 2 Reference is made to a schematic diagram illustrating an exemplary electron beam apparatus 40, which includes a multi-beam electron optical device 41 (or column), which is Figure 1 Part of an exemplary charged particle beam evaluation system 100 of the present invention. The electron beam device 40 includes an electron source 201 and a projection device 230. The electron beam device 40 also includes an actuation stage 209 and a sample holder 207. The actuation stage 209 and the sample holder 207 can be referred to as subsystems, respectively. The electron source 201 and the projection device 230 can be collectively referred to as an electron optical device 41 or an electron optical column. The sample holder 207 is supported by the actuation stage 209 so as to hold a sample 208 (e.g., a substrate or a mask) for inspection. The multi-beam electron optical device 41 also includes a detector 240 (e.g., an electronic detection device). Therefore, any one of the projection device 230, the source 201, the multi-beam electron optical device 41, the detector 240, and the signal processing system can be referred to as a subsystem. The electron beam device 40 may include other subsystems, such as a vacuum system for exhausting the main chamber 10.

[0040] The electron source 201 may include a cathode (not shown) and an extractor or anode (not shown). During operation, the electron source 201 is configured to emit electrons from the cathode as primary electrons. The primary electrons are extracted or accelerated by the extractor and / or the anode to form a primary electron beam 202.

[0041] The projection device 230 is configured to convert the primary electron beam 202 into a plurality of sub-beams 211, 212, 213 and direct each sub-beam onto the sample 208. Although three sub-beams are shown for simplicity, there may be tens, hundreds, thousands (e.g., about ten thousand, tens of thousands, or hundreds of thousands) of sub-beams. A sub-beam may be referred to as a beam wave or simply a beam.

[0042] The controller 50 may be connected to Figure 1 The controller 50 may include various parts of the charged particle beam evaluation system 100, such as the electron source 201, the detector 240, the projection device 230, and the actuation stage 209 (e.g., a motorized stage). The controller 50 may perform various image and signal processing functions. The controller 50 may also generate various control signals to control the operation of the charged particle beam inspection device (including the charged particle multi-beam device).

[0043] The electron optical device 230 can be configured to focus the sub-beams 211, 212 and 213 onto the sample 208 for inspection, and can form detection spots 221, 222 and 223 (for this example, three detection spots, one for each sub-beam) on the surface of the sample 208. The projection device 230 can be configured to deflect the primary sub-beams 211, 212 and 213 to scan the detection spots 221, 222 and 223 through the respective scanning areas in the surface portion of the sample 208. In response to the primary sub-beams 211, 212 and 213 being incident on the detection spots 221, 222 and 223 on the sample 208, electrons are generated from the sample 208, which include secondary electrons and backscattered electrons, which can be referred to as signal particles. The secondary electrons typically have an electron energy less than or equal to 50eV. Actual secondary electrons can have an energy less than 5eV, but any energy below 50eV is generally regarded as a secondary electron. The backscattered electrons typically have an electron energy between 0 eV and the landing energy of the primary beamlets 211, 212, and 213. Since detected electrons with energies less than 50 eV are typically considered secondary electrons, a portion of the actual backscattered electrons will be considered secondary electrons.

[0044] The detector 240 is configured to detect signal particles, such as secondary electrons and / or backscattered electrons, and generate a corresponding detection signal, which is sent to the signal processing system 280 for preprocessing, such as analog-to-digital conversion. The detector 240 can be part of a detector unit. The detector 240 can be incorporated into the projection device 230. The detector unit may include a detector array. Further details and alternative arrangements of detector modules, sensors, and detector arrays located upstream, downstream, or otherwise integrated into the objective lens can be found in EP application number 20216890.2 and PCT application number PCT / EP2021 / 068548, which are incorporated herein by reference at least in terms of the details of the detector modules, sensors, and detector arrays and similar elements. Such a detector array may include an array of detector elements.

[0045] The detector can be provided with a plurality of parts, more specifically, a plurality of detection parts. The detector comprising a plurality of parts can be associated with one of the sub-beams 211, 212, 213. Therefore, a plurality of parts of a detector 240 can be configured to detect signal particles (which can be additionally referred to as sub-beams 211, 212, 213) emitted from the sample 208 associated with a primary beam in the primary beam. In other words, the detector comprising a plurality of parts can be associated with a hole in at least one electrode of the objective lens assembly. A plurality of parts can be segments arranged radially and / or at an angle. More specifically, the detector comprising a plurality of parts can be arranged around a single hole, which provides an example of such a detector. As mentioned, the detection signal from the detector module is used to generate an image. For a plurality of detection parts, the detection signal includes components from different detection signals, which can be processed as a data set or in a detection image.

[0046] The objective lens can be an objective lens array and can include a plurality of planar electrodes or plates including holes for the corresponding paths of each of the multiple beams. Each plate can extend over the multiple beam arrangement. The objective lens can include at least two electrodes, which can be connected to corresponding potentials and controlled. Additional plates can be present, each of which controls additional degrees of freedom. The detector can be a plate associated with the objective lens, or even connected to the objective lens, having holes for each path of each of the multiple beams. The detector can be located above, below, or inside the objective lens.

[0047] The scanning deflector may be associated with the objective lens or even integrated into the objective lens, for example as a scanning deflector array. In one arrangement, the scanning deflector may be positioned upstream of the objective lens. In an arrangement where the path of the primary beam is collimated upstream of the objective lens, the scanning deflector may be positioned upstream of the objective lens. In the case where multiple beams are generated from a collimated primary beam from a source by a beam limiting aperture array of the objective lens or a beam limiting aperture array associated with the objective lens, the scanning deflector may be a macro scanning deflector positioned upstream of the objective lens so as to operate on the collimated primary beam. Other electron optical arrangements including one or more elements described herein may be envisioned. Such a scanning deflector may be controlled by a controller to deflect each of the multiple beams along an axis in the sample plane or, for example, two principal axes on a sample surface in the sample plane (which may be orthogonal to each other).

[0048] It should be noted that embodiments of scanning deflectors near the sample (e.g., integrated in or near the objective) may have a limited scanning deflection range. However, such scanning deflectors near the sample can be accurately controlled and have a fast response relative to other types of scanning actuators (such as an actuator stage).

[0049] The controller 50 may control the actuation stage 209 to move the sample 208 during the inspection of the sample 208. The controller 50 may cause the actuation stage 209 to move the sample 208 in a certain direction (e.g., continuously, e.g., at a constant speed) at least during the sample evaluation, which may be referred to as a type of scan. The controller 50 may control the movement of the actuation stage 209 so that it changes the movement speed of the sample 208 relative to the path of the multiple beams depending on various parameters. The controller 50 may control the deflection of the scanning deflector so that the path of the multiple beams moves relative to the stage, thereby moving over the sample surface. The controller 50 may change the beam deflection of the scanning deflector depending on various parameters, thereby changing the scanning of the beam over the sample surface. For example, the controller 50 may control the speed of the table (including its direction and duration) and / or the scanning deflector depending on the characteristics and stepping of the inspection scanning element (e.g., the stepping during the scanning process and / or the scanning during the scanning process) (e.g., as disclosed in EPA 21171877.0 filed on May 3, 2021). The contents of such applications are incorporated herein at least with respect to the combined stepping and scanning strategy of the stage and scanning deflector.

[0050] References in this document to relatively scanning one or more charged particle beams and a sample are intended to encompass any combination of moving the sample (e.g., by an actuation stage) and / or moving the beam (e.g., by scanning a deflector), unless the context requires otherwise. The actuation stage may be actuated to move the sample relative to the beam path of the charged particle beam.

[0051] Known multi-beam systems, such as the electron beam device 40 and charged particle beam evaluation system 100 described above, are disclosed in US2020 / 118784, US202002 / 03116, US2019 / 0259564 and WO2021078352, which are hereby incorporated by reference. The present invention is also applicable to single beam systems.

[0052] The electron beam device 40 may include a projection assembly to adjust the charge accumulated on the sample by irradiating the sample 208 .

[0053] There is a need to automatically process images output from a charged particle evaluation device, such as the electron beam device 40, to detect defects in the sample being evaluated. Figure 3 , a data processing device (or apparatus) 500 for detecting defects in an image generated by a charged particle evaluation device is depicted. The data processing device 500 or at least a portion of the data processing device 500 may be part of the controller 50, part of another computer in a factory or integrated elsewhere in the charged particle evaluation system 100, for example as part of the charged particle evaluation device 40, for example as part of the charged particle evaluation device 41 such as included in a detector unit. The controller may be a distributed controller or a plurality of controllers distributed in the charged particle evaluation device 40 or even the charged particle evaluation system 100.

[0054] Various methods can be adopted to detect defects in images generated by charged particle evaluation devices. A common method is to compare an image of a portion of a sample (referred to herein as a sample image) with a reference image. In practice, data points of a data stream representing a sample image are compared with data points of a reference image retrieved from a memory or delivered in a parallel data stream. For the sake of brevity, the process may be referred to as comparing images and data points as pixels hereinafter. Any pixel that differs from the corresponding pixel of the reference image by more than a threshold amount can be considered a defect. Such pixels that are different from the reference image and adjacent pixels that are also different from the reference image are considered a single defect. (In an embodiment, this may mean that pixels that are different from the reference image and have adjacent pixels that are the same as the reference image (i.e., no difference from the reference image) can be considered not to represent a defect). The reference image can be obtained in a variety of different ways, as discussed below.

[0055] The false alarm rate, where a sample is marked as defective when no significant defect actually exists, can be controlled. The false alarm rate can be controlled by setting a threshold for determining the presence of a defect. The threshold can be the difference of a pixel compared to a reference image, such as compared to an equivalent pixel of the reference image. The false alarm rate can be further controlled by applying noise reduction to either or both of the reference image and the sample image.

[0056] The reference image may be obtained by averaging the source images to obtain the reference image, and the averaging process may depend on the nature of the source images. When the source images are derived from a library of past scans, a large number (e.g., more than 20, more than 30, or about 35) of images may be averaged to obtain the reference image, as the averaging may be performed off-line. The source images may be aligned prior to averaging.

[0057] Alternatively, the sample image may be compared to a reference image derived from a "live" source image obtained from a different portion of the same sample. In this case, fewer (e.g., two) source images may be averaged to obtain the reference image. The two source images may be obtained from corresponding areas of different die of the sample. Alternatively, if the pattern being inspected has repeating elements, the source images may be obtained from the same die. In some cases, the source image may be a shifted portion of the sample image. In the case of comparing a sample image with a reference image derived from a live source image, the roles of the different images may be rotated. For example, if three images A, B, and C are output by a charged particle evaluation device: A and B may be averaged to provide a reference image for comparison with C; A and C may be averaged to provide a reference image for comparison with B; and B and C may be averaged to provide a reference image for comparison with A.

[0058] Another possibility is that the reference image is obtained from one or more "known good" patterns. Another possibility is that the reference image is obtained by simulation, for example based on pattern or design data (e.g., in GDSII format). Such a reference image that passes through at least the first processing module (e.g., in the first step of a two-step process) can be a simplification of one or more "known good" patterns or simulations.

[0059] The comparison result of the sample image and the reference image can be a simple binary value, which represents the difference or correspondence (i.e., match) between the sample image and the reference image. More desirably, the result of the comparison is a difference value representing the magnitude of the difference between the sample image and the reference image. Desirably, the result of the comparison is the difference value of each pixel (or each group of adjacent pixels which may be referred to as a "pixel region"), so that the defect location within the source image can be determined more accurately.

[0060] In order to determine whether the difference between a pixel or a pixel region between a source image and a reference image represents a defect in the inspected pattern, a threshold value may be applied to the difference corresponding to the pixel or pixel region. The threshold value may be fixed in advance, for example for a specific charged particle beam system or for a specific pattern to be inspected. The threshold value may be a parameter or other condition set by the user, for example, which is updated from time to time depending on the application or evaluation. The threshold value may be determined dynamically, updated during the processing, or both. Alternatively, a predetermined number of locations with the highest difference values ​​may be selected as candidate defects for further inspection. Adjacent pixels with a difference value above the threshold value may be considered as a single defect or candidate defect. All pixels of a single defect may be assigned the same difference value. Such adjacent pixels and all pixels of a single defect may be referred to as a pixel region.

[0061] like Figure 3 As depicted in the figure, the data processing device 500 includes: a filter module 501, which receives and filters the sample image from the charged particle evaluation device 41; a reference image generator 503, which generates a reference image based on the source image; a comparator 502, which compares the filtered sample image with the reference image; and an output module 504, which processes and outputs the comparison result.

[0062] Filter module 501 applies filter to input data, as discussed further below. Filter module 501 can be conveniently implemented by dedicated hardware (e.g., FPGA or ASIC). This dedicated hardware can be more efficient and economical than a general-purpose computing device (such as a standard or common type of CPU architecture) for programming. The processor may not be as powerful as a CPU, but may have an architecture suitable for processing software for processing detection signal data, i.e., images, and therefore can process images in the same or shorter time as a CPU. Although the processing power of this detection processing architecture is lower than that of most contemporary CPUs, the data architecture of the dedicated processing architecture is more efficient, so the speed of this detection processing architecture processing data may be just as fast. A general-purpose CPU may also be used, and may be conducive to providing greater flexibility to change the filter after manufacturing.

[0063] The reference image generator 503 can operate in one or more modes, each mode representing a different method of generating a reference image.

[0064] In library mode (also referred to as die-to-database mode), reference image generator 503 averages a large number of source images obtained from previous scans of patterns that are nominally the same as the pattern currently being evaluated. Such images may have been generated earlier in the same batch of samples, or from samples of a previous batch. The library images may be derived from test samples or production samples. Before averaging, the images are desirably aligned with each other. Averaging the source images to generate the reference images has the effect of reducing noise. Averaging the source images in this manner can also average out any defects that may be visible in the source images. The reference images in the library may include synthetic images, such as synthetic images generated by simulation of design data (e.g., GDSII data).

[0065] In the case where the pattern being examined is a repeating pattern, a reference image can be generated by averaging multiple offset versions of the source image. Each version of the source image is offset by an integer multiple of the cell size. If either or both dimensions of the cell are not equal to an integer pixel, the offset can be rounded to the nearest pixel, or fractional pixel offsets can be achieved by interpolation, such as linear or cubic interpolation, such as bicubic interpolation, or any other known interpolation technique. Another possibility is to offset a multiple of the spacing of the repeating pattern so that the multiple is an integer pixel. In practice, multiple instances of the cell are extracted from the source image and averaged. This approach can be referred to as exemplarization of an array pattern, and more specifically providing a reference image for an array pattern.

[0066] In die-to-die mode, the charged particle evaluation device is used to generate a sample image and two reference images with similar surface features, which may have a repeating pattern. In one arrangement, each of the two reference images and the sample image comes from a different die of the sample (e.g., so that similar portions of the surfaces of different dies can be compared), and the sample image can be compared with each reference image to identify the difference between each reference image. Such differences can be considered as candidate defects. Common differences in the comparison between the sample image and different reference images are considered defects. Differences that exist only in one of the comparisons between the sample image and different reference images are considered defects in the reference image, not in the sample image. Such defects in the reference image are removed from a set of candidate defects. An image aligner is provided to align the images before supplying them to the reference image generator 503 and the filter module 501. In one arrangement, three columns of a multi-column charged particle evaluation device are used to generate the sample image and two reference images. This arrangement is particularly effective when the column spacing is equal to the die size of the inspected sample, because the columns will automatically scan the corresponding pattern features simultaneously. Using this arrangement is also faster than using a single column because the sample image and the reference image can be acquired simultaneously, and in the event that there is a difference between the column spacing and the die size, such as due to variations in the surface position of features on the sample surface, a buffer can be employed to correct for the timing of image input to the data processing device.

[0067] In an alternative variant of the die-to-die mode, the same beam (the beam of the same column in the case of a multi-column system) is used to generate the sample image and the two reference images. This has the advantage that no column-to-column and beam-to-beam corrections are required, and the routing of the data can be simplified. For example, such a calibration is the relative position of the beam relative to the ideal beam position for that beam or even each beam. Using the same beam avoids calibrations between the beams of the different scans being compared, such as offset assessments. Using the same beam means that although the beams are offset relative to the ideal beam position, there is no position offset to correct for when comparing the data retrieved from the scans. However, the need for data buffering may increase, for example with an increase in frequency, if not an increase in the amount of data buffered before starting to compare data from different dies.

[0068] An alternative version of the array pattern using a single column 507 (eg of a single column system) provides a sample image that is compared to a reference image derived from two shifted versions of itself as source images. A buffer may be used to provide the shifted images.

[0069] Reference again Figure 3, comparator 502 can be any logic circuit that can compare two values, such as XOR gate or subtractor. Comparator 502 is also suitable for being realized by dedicated hardware (such as FPGA or ASIC). This dedicated hardware can be more efficient and more economical than the general computing device (such as CPU) of programming. Desirably, comparator 502 is implemented on identical dedicated hardware with filter module 501.

[0070] In some cases, the reference image generator 503 may also be implemented in dedicated hardware, particularly when the reference image generator operates only in a mode where the reference image is generated from a small number (e.g., two) of source images. In this case, it is desirable to implement the reference image generator in the same dedicated hardware as the comparator and / or filter module. Where appropriate, the mathematical operations of averaging the pixels of the source images and comparing them with the pixels of the sample image may be combined into a single logic circuit.

[0071] The output module 504 receives the results output by the comparator 502 and prepares them for output to the user, other factory systems or for further processing within the inspection system. The output can be any of several different forms. In the simplest option, the output can be just an indication that the sample has or does not have a defect. However, since almost all samples have at least one potential defect, more detailed information is needed, for example as a data set such as an image (e.g., a data set such as a data set that can be presented as an image). Therefore, the output can include, for example, a defect location map, a deviation image, a pixel data fragment (e.g., an image and a reference image or a pixel data fragment of a reference image) and / or information about the severity of possible defects represented by the magnitude of the difference between the sample image and the reference image, such as how the sample image deviates from the reference image. The output module 504 can also filter potential defects, such as by only outputting defect locations where the magnitude of the difference between the sample image and the reference image is greater than a threshold or the pixel density showing the difference is higher than a threshold. Another possibility is to output only a predetermined number of the most serious defect points indicated by the magnitude of the difference. This may be accomplished by storing the defect points in a buffer 510 and overwriting the lowest magnitude defect if a higher magnitude defect is detected when the buffer is full.

[0072] Any format suitable for outputting defect information may be used, such as a list, a data set, an image, or a map. Desirably, the output module 504 may output segments, which are images of sample areas where potential defects have been detected. This allows for further inspection of the potential defects to determine if the defects are real and severe enough to affect the operation of a device formed on or present in the sample. The remainder of the source image, i.e., those portions not saved as segments, may be discarded to save on data storage and transmission requirements. Thus, a data set may be a set of segments; an image may include a set of segments.

[0073] In order to obtain a two-dimensional image of the sample, the detection beam (or each detection beam) is scanned across the sample surface. Depending in part on the number of beams used, various different scanning strategies can be used, such as continuous scanning, jump scanning or hybrid scanning strategies. For example, a single beam or each beam in multiple beams can be scanned in a two-dimensional raster pattern. This involves the movement of the beam in two directions: the main scanning direction and the secondary scanning direction. The main scanning direction can be referred to as the fast scanning direction. For example, the scanning deflector can be controlled to drive the primary beam (e.g., multiple beams) in the fast direction. The secondary scanning direction can be referred to as the slow scanning direction. For example, the console can be controlled to actuate the sample relative to the path of the primary beam; the scanning deflector can be controlled to actuate the beam path on the sample surface in the slow direction; or the stage and the scanning deflector are both actuated to achieve scanning in the slow direction. The stage is preferably used only in the slow direction, because its inertia due to its large mass makes it more challenging to achieve scanning movement (e.g., acceleration) in the fast direction than alternatives such as scanning deflectors. The range of fast and slow scanning directions may be very different.

[0074] EPA 21171877.0, filed on May 3, 2021, discloses a scanning embodiment having slow and fast scanning directions within the field of view of a charged particle beam array (e.g., as a beam grid), which may be referred to as a hybrid jump scanning strategy. The document is incorporated herein by reference at least with respect to the disclosed scanning strategy. This scanning strategy steps the stage and therefore the sample after scanning the sample surface within the field of view of the beam array to scan different portions of the sample surface within the field of view of the beam array. This hybrid jump scanning strategy may be suitable for beam arrays with relatively large fields of view, such as 1 mm, 5 mm, 10 mm, or even 20 mm. This beam array may include many beams as described herein.

[0075] The charged particle evaluation system 100 can have high throughput and high resolution, which means that data can be output at a high rate. For example, a multi-beam charged particle evaluation device, particularly a multi-column charged particle evaluation device, can have up to one hundred, hundreds, thousands, or even tens of thousands or more beams, each with one or more detector sections, outputting data points at a rate of kilohertz or megahertz. High throughput is highly desirable, and efforts are constantly being made to increase the throughput of charged particle evaluation devices.

[0076] In normal situations of some sample inspection processes, such as in mass production, the defect rate in the samples subjected to evaluation is very low. In other words, a low proportion of areas of the sample contain defects. Desirably, there are no defects or only a small number of defects on each sample. However, due to the non-negligible false alarm rate, there may still be a large number of candidate defects that need to be analyzed in detail to determine whether they are actual defects. Such false alarms may at least initially or superficially appear to be indistinguishable from actual defects. Detailed analysis may require a lot of calculations, require specific complex algorithms, or require manual input (such as manual review, which is often time-consuming). Therefore, in order to improve efficiency and reduce the burden of analyzing candidate defects, it is hoped to reduce the false alarm rate.

[0077] The inventors have determined that a significant portion of false alarms originate from transient error conditions in the charged particle evaluation device or its environment. The event of such a transient error condition may be referred to as a transient error or transient error occurrence. Such a false alarm may be a nuisance signal having a signal magnitude similar to that of a true defect. Such a nuisance signal may be difficult to distinguish from a defect signal. When a transient error condition occurs, the charged particle evaluation device may be considered to be in an error state (or state) for a period of time, which is referred to herein as an error period. The error period or duration may be longer than the transient error condition that caused it. When an error event is detected, depending on the nature of the transient error condition, the error period may be considered to have started before the transient error condition was detected. Therefore, the start of the transient error may be considered to have started before the transient error condition (i.e., the transient error condition was detected). The error duration may be represented by a state signal (e.g., an error state signal).

[0078] The status signal can take the form of a log or event stream, which includes data indicating the nature of the transient error condition and at least one of the following: time information indicating the start time of the error condition, time information indicating the end time of the error condition, and duration information indicating the duration of the transient error condition (the duration of the transient error condition can be implicit in the nature of the transient error condition indicated in the data). As mentioned, the error duration may be different from the duration of the transient error condition that caused the error. Alternatively, the signal can be a signal that is output continuously or periodically, which indicates the state of the charged particle evaluation device when the signal is output. The signal that is output continuously or periodically can be a simple binary signal, such as 1 or 0 (for example, indicating "good" or "bad"), or a more complex signal indicating the state of multiple subsystems (such as beams or columns).

[0079] When the data detected by a detector (such as detector 240) is compared with the corresponding expected data of a sample without any defects, the difference between the detected data and the expected data can represent a combination of true defects and nuisance signals, such as nuisance signals caused by noise. Nuisance signals of noise are generally identified as those signals having a signal strength below a certain threshold. Signals with a signal strength equal to or greater than the threshold are considered possible defect signals, which can then be further analyzed to determine whether a defect exists and, if so, to classify the nature of the defect. A transient error condition may cause a signal to have an intensity greater than a threshold, which is selected to distinguish noise (such as nuisance signals in noise) from true defects. Nuisance signals generated by or when a transient error condition occurs may have a similar magnitude to a true defect and therefore cannot be filtered out using a threshold. Such nuisance signals may appear indistinguishable from actual defects.

[0080] Therefore, potential false positives in candidate defects can be identified by detecting transient error conditions and associating the detection of candidate defects with the state of the charged particle evaluation device when performing candidate defect detection. Alternatively, when the charged particle evaluation device may be in an error state, potential false positives in candidate defects can be identified in this way, rather than by detecting transient error conditions. Remedial actions can then be performed. Remedial actions can include ignoring any candidate defects detected during the error period. Remedial actions can be applied to all signals generated by the charged particle evaluation device during the error period. In some cases, such as when the transient error condition has only a local effect in the charged particle evaluation device, the remedial action may be applied only to signals derived from specific features (such as columns, beams, signal channels, signal processors, data processors, or detectors), or to subsets of these features (such as columns, beams, signal channels, signal processors, data processors, or detectors). Such remedial actions may be applied only to signals derived from specific features or feature groups affected by the error condition.

[0081] Figure 4 An embodiment of the present invention is depicted in as part of a charged particle evaluation apparatus (as an example of an evaluation apparatus) for detecting defects in a sample by scanning a charged particle beam through the sample. Figure 5A flow chart of a method performed by a charged particle evaluation system is shown in . An evaluation device is used to generate S1 an evaluation signal representing the properties of a sample surface. In an embodiment, the generation of the evaluation signal can be a two-step process, in which the detector unit 240 first detects charged particles incident from the sample and outputs a detection signal in response thereto. The signal processing system 280 then preprocesses the detection signal to generate an evaluation signal 290, which includes property information related to the properties of the sample. The preprocessing can be as simple as analog-to-digital conversion, so that the evaluation signal only measures the response of the sample to the charged particles directed thereto. The preprocessing can be more complex, such as distinguishing between backscatter and secondary electrons. Subsequently, the evaluation signal is processed S2 to identify candidate defects and output a candidate defect signal. The processing of identifying candidate defects can be performed by a data processor included in the evaluation device or elsewhere. The candidate defect signal can be a selection of a portion of the evaluation signal.

[0082] The evaluation signal and the candidate defect signal are linked to the detection time of the signal particle. Linking the evaluation signal and the candidate defect signal to time can include adding a timestamp to each data point or a predetermined proportion of the data points in the data stream. In some cases, the evaluation signal and the candidate defect signal can take the form of an image or other geometrically structured data file, in which case the individual data points can be linked to time by knowing the scanning pattern and scanning rate used to generate the image and data indicating the time of a reference point in the scan (e.g., its start or end). In the case of a charged particle evaluation device using multiple beams (or multiple beams, such as in an array of beams in a beam grid), the evaluation signal can also be linked to the beam from which the signal particle is derived. Some or all of the detection time, timestamp, and time of the reference point in the scan can be times in a timeline (e.g., a timeline of the evaluation signal). The timeline can be common to some or all subsystems of the charged particle evaluation device or even the charged particle evaluation system.

[0083] The charged particle evaluation device also includes a state monitor 300, which is configured to monitor the state of the S3 charged particle evaluation device for error conditions and generate a state signal 310 indicating any error conditions during the operation of the evaluation device. The state signal may also be referred to as an error state signal. The state signal may include time information indicating the time (e.g., on a timeline) when the charged particle evaluation device is in an error state. For example, the state monitor may be configured to output an error state signal when one or more events (e.g., on a timeline) occur in the charged particle evaluation device, the one or more events being selected from the following groups: abnormal vibration, abnormal discharge; power fluctuation; data processing error; data communication error; gas leakage; abnormal temperature fluctuation; and abnormal pressure fluctuation. Such events may have unusual characteristics compared to normal operation. Such faults may indicate a fault in a component (such as a subsystem), which may be temporary. For example, an abnormal vibration may be a vibration whose frequency exceeds the vibration frequency occurring during normal vibration and / or a vibration whose magnitude range exceeds the vibration during normal operation. Some events may indicate a certain type of event (as an error condition). For example, a pressure fluctuation may indicate a discharge in an electron optical component in a charged particle device. Such discharges may be considered abnormal discharges. In some cases, such as discharges, any occurrence of such an event may be considered an error condition. In other cases, such as power fluctuations, only events of a predetermined magnitude and / or duration may be considered an error condition. Other error conditions are of course possible, and these may not apply to certain types of evaluation devices. For example, in an optical evaluation device that does not operate in a vacuum, pressure fluctuations may not be considered an error state.

[0084] Thus, the state monitor may include one or more sensors selected from the group consisting of: a temperature sensor, such as a thermometer 321; a pressure sensor, such as a barometer or vacuum gauge 322; a microphone 323; a voltage detector 324; a current detector 325; and a photon sensor, such as a light sensor 326 and a radio wave detector 327. Other sensors may include accelerometers and position or displacement measurement systems, such as using an interferometer or encoder grid system. The present invention may also utilize existing sensors used to monitor various parts of the charged particle evaluation device, such as sensors for measuring beam resolution, beam current, and detector noise. Such sensors may typically be used to control parameters of the charged particle evaluation device, such as in a feedback loop or a feedforward loop, but may be configured to generate an error signal when a deviation from an expected value is detected that is too large to be compensated or controlled. If the moving average or moving standard deviation of the monitored parameter exceeds a predetermined limit, an error state is considered to have occurred.

[0085] A temperature sensor (such as a thermometer) can detect an abnormal change (e.g., a transient change) in the temperature of the charged particle evaluation device or a portion thereof. An abnormal change in temperature (or abnormal thermal change) can indicate an error condition, such as a malfunction or failure of a temperature control system of a clean room in which the charged particle evaluation device operates.

[0086] The barometer or vacuum gauge 322 can detect abnormal pressures in the charged particle evaluation device or portions thereof, such as transient pressure changes, which can indicate an error condition such as a malfunction or a leak or discharge that could release gas from the surface.

[0087] A microphone or accelerometer can detect vibrations in the charged particle evaluation device or part thereof, which can indicate an error state, such as a fault or external disturbance, such as a transient fault or transient external disturbance (e.g., an earthquake such as a tremor, etc.). In the event of such a transient fault or disturbance, the error is instantaneous, and the charged particle evaluation device continues to operate without intervention for the duration of the error. The charged particle evaluation device continues to operate after the error period. The microphone can detect abnormal vibration patterns caused by the moving parts of the device, such as the friction of a cable board with another component, or abnormal vibration patterns caused by an accidental collision of two components. Discharges in the device may also generate detectable sounds. A simple noise threshold (or sound amplitude or sound frequency, such as within a range of sound frequencies) can be applied to detect the error state, or a more complex signal analysis can be used to distinguish between normal operating sounds and abnormal noise (or sounds such as amplitude or frequency components) indicating an error state.

[0088] A voltage detector or a current detector can detect an abnormal voltage in the charged particle evaluation device or a portion thereof, such as a transient voltage, which can indicate an error condition such as a discharge. A photon detector (such as a light sensor or a radio wave detector) can also detect a discharge. It should be noted that the charged particle evaluation device has various components that operate at high voltages, so a discharge may occur, and the discharge itself may be a transient error condition or indicate another error condition.

[0089] The signal processing system 280 may include an error detector 281 configured to detect an error in the processing of the detection signal. Such an error in the processing of the detection signal may be a transient error. The signal processing system 280 (e.g., an error detector) may be configured to transmit a processing error signal to a state monitor.

[0090] The transmission channel 241 transmits the detection signal from the detector unit 240 to the signal processing system 280. The transmission error detector 242 (e.g., a checksum, a parity check, or a cyclic redundancy check) is configured to detect errors in the transmission of the detection signal. Such transmission errors may be transient errors. The transmission error detector 242 can be configured to transmit the transmission error signal to an optionally provided state monitor. Additional transmission error detectors can be provided to detect errors in the transmission of other signals.

[0091] The charged particle evaluation device has a controller 50 that generates a control signal for controlling a subsystem 340 of the charged particle evaluation device. Optionally, an anomaly detector 341 may be provided that is configured to detect an abnormal response of the subsystem to the control signal. The abnormal response may be a transient error. As a transient error, the subsystem may continue to operate because the transient error may be temporary. The operation of the subsystem may not be affected by the transient error. The anomaly detector may be configured to transmit an abnormal signal to a state monitor. The subsystem may include an actuation stage that is configured to support a sample that may not be able to move correctly in response to the control signal.

[0092] A communication interface 330 may be provided to transmit the evaluation signal and the error state signal to an external device, such as a data processing device. Any suitable communication system may be used. The signal data derived from the sample may be combined with the state information into a single data stream, or may be stored in a separate communication channel. The data may be transmitted continuously, in batches, or in groups. Desirably, a communication error detector 331 is provided to detect errors in the evaluation signal communication and to transmit the communication error signal to the state monitor 300.

[0093] In an embodiment, the evaluation signal includes a data record describing a defect candidate on the sample and detection time information, such as a timestamp indicating the detection time of the defect candidate. For example, the data record includes an image of a portion of the sample having a defect candidate. The data record may be an image of the defect candidate. Such an image may be referred to as a "segment". The image may be derived from a signal returned from the sample or from the difference between an image derived from the sample and a reference image. The error state signal includes information indicating the nature of the error state and the time of occurrence of the error state. In the case where the error condition only causes a local error in the device, such as a data processing or communication error may only affect signals from a specific beam or detector, the error state signal may also indicate the affected portion of the charged particle evaluation device (e.g., (multiple) beams, (multiple) columns, or (multiple) signal paths).

[0094] The data processing device 500 processes the evaluation signal, which includes attribute information related to the attribute of the sample and state information indicating the state of the charged particle evaluation device when the attribute information is generated. The data processing device includes an analysis unit, which is configured to determine S4 whether the candidate defect is a real defect on the sample based on the analysis of the attribute information of the candidate defect signal. A real defect represents some actual difference in the sample, which difference has sufficient importance, such as affecting the operation of the device formed on the sample. The analysis unit can use any suitable known technology to determine real defects and false alarms from among the candidate defects.

[0095] The analysis unit does not complete the analysis of the attribute information generated when the state information indicates that the charged particle evaluation device is in an error state. By not analyzing the attribute information obtained when the charged particle evaluation device is in an error state, the computational workload is reduced. Desirably, if the charged particle evaluation device is in an error state when the attribute information is generated, the analysis of the attribute information is not started. That is, if the state signal indicates that the (multiple) evaluation signals corresponding to the candidate defect have been affected by the occurrence of an error condition, the analysis of the candidate defect is not started. This saves the computational workload to the maximum extent. In an embodiment, the attribute information generated during the occurrence of the error condition is removed from the data stream to be analyzed. In an embodiment, the analysis of the attribute information generated during the occurrence of the error condition can be started but can be stopped in advance, that is, stopped before completion. This method may help to leave time to determine whether the state of the charged particle evaluation device is an error state when generating the detection signal from which the candidate defect is derived. During this error state, the operation of the charged particle evaluation device may be affected, so that the candidate defect may become a nuisance signal. This method of terminating the analysis early allows the candidate defect to be analyzed without delay whether it may be a real or true defect.

[0096] It is noteworthy that the analysis of candidate defects and the determination of whether to perform such analysis based on the status signal need not occur simultaneously with the evaluation of the sample. The evaluation of the sample can continue during and after the occurrence of the error condition. If the analysis of one or more candidate defects is not started or stopped due to the occurrence of the error condition, the analysis of other candidate defects can continue, such as candidate defects generated after the error condition ceases or candidate defects generated by parts of the evaluation system that are not affected by the error condition. A temporary or localized error condition does not cause the operation of the evaluation system to be interrupted. However, a prolonged and / or non-localized error condition may cause the operation of the evaluation system to be stopped.

[0097] In another aspect of the invention, error states may be inferred from attribute information, given the low probability of defects. Temporal or geometric coincidence of candidate defects may be more likely to occur due to error states in the charged particle evaluation device than due to multiple real defects or large defects. For example, in a multi-beam charged particle evaluation device, if attribute information obtained from several or even all beams simultaneously indicates a candidate defect, it may be that some common phenomenon affects several beams, rather than the sample having multiple defects that are arranged so that they are detected simultaneously by different beams. Defects in regular patterns may be more likely to be interference than real. Another example is that a high rate of candidate defects in attribute information from a particular subsystem (e.g., a single detector, beam, or column in a multi-column device) is likely to be due to an error or failure in that subsystem. For example, a high defect rate associated with a particular beam may be a temporary beam failure. For example, causes of beam failure may include one or more of the following: manufacturing errors in one of the lenses of a particular beam (e.g., a lens aperture has unexpected specifications, such as shape, size, or relative position with respect to other apertures, such as an unexpected (e.g., incorrect) diameter, or an unexpected shape, such as an elliptical shape); failure of a detector circuit device associated with the beam; particles, such as contamination particles, on one of the electron-optical elements; and the growth of contaminants, such as on the surface of a component such as the surface of an electron-optical element or a detector element.

[0098] Therefore, desirably, the analysis unit is configured to analyze the evaluation signals to detect correlations between the evaluation signals generated over time in response to different charged particle beams (desirably, two charged particle beams out of a plurality of beams) to determine whether the pattern of candidate defects is more likely to indicate an error state than an actual defect on the sample. If there are overlapping candidate defects, there may be a correlation between the evaluation signals. Various approaches may be taken to perform such analysis. For example, it may be sufficient to set a threshold for the number of candidate defects per unit time and / or per beam group. Such a threshold may be set based on an expected defect rate in the sample being evaluated and / or a historical error rate in the charged particle evaluation device. More sophisticated pattern recognition algorithms and well-known analysis techniques (e.g., machine learning) may also be used.

[0099] Once a fault condition has been identified by analysis of candidate defects, remedial actions as described above may be taken, such as not processing defects associated with a particular beam or group of beams, such as not processing detection signals from detector elements associated with a faulty beam. In the case of a beam failure, it may be desirable to deactivate the faulty beam or a detector associated with the faulty beam. The beams in the plurality of beams may each have a different beam identification. Each beam may have, for example, a unique identification of a beam array. Such a beam identification may be referred to as identification information. A faulty beam may be identified by its beam identification. Thus, detection signals and / or detector elements may be identified by beam information (e.g., the beam identification of the faulty beam). For example, in the case of a beam failure, the beam may be "blanked," for example, by a controller configured to set an electron optical component (such as a scanning deflector) to deflect the (multiple) faulty beams of the beam grid so that they do not reach the sample. Other remedial actions as described above may also be performed, such as removing candidate defects affected by the error condition from the data stream, such as to remove candidate defects associated with (e.g., originating from) a faulty beam.

[0100] A beam failure may be determined prior to generating the evaluation signal, desirably by generating a calibration evaluation signal and analyzing the calibration evaluation signal to identify a failure of at least one of the plurality of beams. The error state (e.g., beam failure) may be continuous, e.g., non-transient, such as during operation.

[0101] The present invention advantageously addresses transient error conditions, i.e., those that exist for a very short period of time, or are localized to a specific portion of a charged particle evaluation device, e.g., a few beams in a multi-beam device. A transient error condition or localized error condition can be considered to be an error condition that affects the evaluation of less than 1%, desirably less than 0.1%, and most desirably less than 0.01% of the sample area. A transient error condition can last for less than 10 seconds, desirably less than 1 second, and more desirably less than 0.1 seconds. Desirably, the evaluation system or its associated subsystems can continue to operate during or after a transient error because the transient error is temporary. The operation of the subsystem may not be affected by the transient error, or the degree of impact may not be sufficient to prevent continued operation.

[0102] References to upper and lower, up and down, above and below, etc. should be understood to refer to directions parallel to the (typically vertical but not always vertical) upstream and downstream directions of the electron beam or beams impinging on the sample 208. Thus, references to upstream and downstream are intended to refer to the direction of the beam path independent of any existing gravitational field.

[0103] The embodiments described herein may take the form of an array of holes or electron optical elements arranged in an array along a beam or multi-beam path. Such electron optical elements may be electrostatic. In an embodiment, all electron optical elements (e.g., the last electron optical element in the sub-beam path before the beam limiting hole array to the sample) may be electrostatic and / or may be in the form of a hole array or a plate array. In some arrangements, one or more of the electron optical elements are manufactured as a micro-electromechanical system (MEMS) (i.e., using MEMS manufacturing technology). The electron optical element may have magnetic elements and electrostatic elements. For example, a composite array lens may have a macro magnetic lens that surrounds a multi-beam path, wherein an upper pole plate and a lower pole plate are located within the magnetic lens and arranged along the multi-beam path. The pole plate may be an array of holes for the beam path of the multi-beam. Electrodes may be present above, below, or between the pole plates to control and optimize the electromagnetic field of the composite lens array.

[0104] The terms "beamlet" and "beamlet" are used interchangeably herein and are both understood to cover any radiation beam derived from a parent radiation beam by dividing or splitting the parent radiation beam. The term "manipulator" is used to cover any element that affects the path of a beamlet or beamlet, such as a lens or deflector. References to elements aligned along a beam path or beamlet path are to be understood as corresponding elements being positioned along the beam path or beamlet path. References to optics are to be understood to mean electron optics.

[0105] Evaluation tools or evaluation systems according to the present disclosure may include devices for qualitative evaluation of samples (e.g., pass / fail), devices for quantitative measurement of samples (e.g., size of features), or devices for generating images of graphs of samples. Examples of evaluation tools or systems are inspection tools (e.g., for identifying defects), review tools (e.g., for classifying defects), and metrology tools, or tools capable of performing any combination of evaluation functionality associated with inspection tools, review tools, or metrology tools (e.g., metrology inspection tools). Such tools and systems may operate optically or electro-optically.

[0106] Reference to the assembly or assembly or element system that can control to manipulate charged particle beam in some way comprises configuration controller or control system or control unit to control assembly to manipulate charged particle beam in described manner, and alternatively uses other controllers or equipment (such as voltage source) to control assembly to manipulate charged particle beam in this manner.For example, voltage source can be electrically connected to one or more assemblies to apply electric potential to assembly under the control of controller or control system or control unit, such as being applied to the electrode of control lens array and object lens array.Actuable assembly (such as stage) can be controllable to use one or more controllers, control system or control unit to actuate and therefore move relative to another assembly (such as beam path), to control the actuation of assembly.

[0107] The method of the present invention can be performed by a computer system including one or more computers. The computer used to implement the present invention may include one or more processors, including a general-purpose CPU, a graphics processing unit (GPU), a field programmable gate array (FPGA), an application-specific integrated circuit (ASIC) or other special-purpose processors. As discussed above, in some cases, a specific type of processor can provide advantages in reducing costs and / or increasing processing speed, and the method of the present invention can adapt to the use of a specific processor type. Some steps of the inventive method relate to parallel computing, which is easy to implement on a processor (such as a GPU) capable of parallel computing.

[0108] The computer used to implement the present invention may be physical or virtual. The computer used to implement the present invention may be a server, a client, or a workstation. Multiple computers used to implement the present invention may be distributed and interconnected via a local area network (LAN) or a wide area network (WAN). The results of the method of the present invention may be displayed to a user or stored in any suitable storage medium. The present invention may be embodied in a non-transient computer-readable storage medium that stores instructions for executing the method of the present invention. The present invention may be embodied in a computer system that includes one or more processors and a memory or storage device storing instructions for executing the method of the present invention.

[0109] Functionality provided by computer and processor (such as controller or control system or control unit) can be implemented by computer.Any suitable combination of elements can be used to provide required functionality, including, for example, CPU, RAM, SSD, mainboard, network connection, firmware, software and / or other elements known in the art that allow required computing operations to be performed.Required computing operations can be defined by one or more computer programs.Such computer programs can take the form of multiple computer programs, which can be distributed, such as implemented by different processors.One or more computer programs can be provided in the form of one or more media (optionally non-transient media) storing computer-readable instructions.When a computer reads a computer-readable instruction, the computer executes required method steps.A computer can be composed of an independent unit or a distributed computing system, which has a plurality of different computers connected to each other via a network.

[0110] The term "image" as used herein is intended to refer to a data structure of any value, wherein each value is associated with a sample of a position, and the arrangement of the values ​​in the array corresponds to the spatial arrangement of the sampled positions. The term "data map" can be used to describe such a data structure. An image can include a single layer or multiple layers. In the case of a multilayer image, each layer (which may also be referred to as a channel) represents a different sample of a position. The term "pixel" is intended to refer to a single value of an array, or in the case of a multilayer image, to a set of values ​​corresponding to a single position.

[0111] Various aspects of the invention are listed in the following numbered clauses.

[0112] Item 1. An evaluation method, comprising: using an evaluation device to generate an evaluation signal representing an attribute of a sample surface; processing the evaluation signal to identify a candidate defect and output a candidate defect signal; for an error condition, monitoring the state of the evaluation device and generating a status signal indicating any error condition during the operation of the evaluation device; and analyzing the candidate defect signal to determine whether the candidate defect is a real defect; wherein if the status signal indicates that the evaluation signal and / or the candidate defect signal corresponding to the candidate defect has been affected by the error condition, the analysis of the candidate defect is not completed.

[0113] Item 2. An evaluation method, comprising: using an evaluation device to generate an evaluation signal representing the properties of the sample surface; processing the evaluation signal to identify candidate defects and output a candidate defect signal; for error conditions, monitoring the state of the evaluation device and generating a status signal indicating any error condition occurring during the operation of the evaluation device; and analyzing the candidate defect signal to determine whether the candidate defect is a real defect; wherein the analysis of the candidate defect includes using the status signal to verify whether the evaluation signal and / or the candidate defect signal corresponding to the candidate defect has been affected by the error condition, and stopping the analysis of the defect candidate after verification.

[0114] Clause 3. A method according to clause 1 or 2, wherein the error condition includes one or more of the following: abnormal vibration, abnormal discharge; power fluctuation; data processing error; data communication error; gas leakage; abnormal temperature fluctuation; abnormal pressure fluctuation and abnormal response of a subsystem of the evaluation device, preferably, such abnormal response occurs temporarily and / or partially, and preferably, such occurrence is such error condition.

[0115] Clause 4. The method according to any of the preceding clauses further includes generating a control signal for controlling a subsystem of the evaluation device; and monitoring the state of the evaluation device for an error condition includes detecting an abnormal response of the subsystem to the control signal, and desirably, the detection includes detecting the occurrence of the abnormal response.

[0116] Clause 5. A method according to any of the preceding clauses, wherein the status signal comprises time information indicating a time of occurrence of the error condition.

[0117] Clause 6. A method according to any of the preceding clauses, wherein the status signal comprises duration information indicative of the duration of the occurrence.

[0118] Clause 7. A method according to any of the preceding clauses, wherein the evaluation device is a charged particle evaluation device configured to detect defects in a sample by relatively scanning a charged particle beam across a surface of the sample.

[0119] Item 8. A method according to Item 7, wherein the charged particle beam is a plurality of charged particle beams, the scanning comprises relatively scanning the surface of the sample and the plurality of charged particle beams, and the status signal comprises beam information indicating which of the plurality of charged particle beams is affected by the error condition.

[0120] Clause 9. A method according to clause 8, wherein the occurrence includes: expected failure of at least one beam among the multiple beams, expected determination of such error condition / occurrence before generating the evaluation signal, and expected identification of the failure of at least one beam among the multiple beams by generating a calibration evaluation signal and analyzing such calibration evaluation signal.

[0121] Clause 10. A method according to clause 8 or 9, wherein monitoring the state of the evaluation device for an error condition comprises detecting a correlation between evaluation signals generated in response to different charged particle beams to determine an occurrence, desirably, the different charged particle beams being two of the plurality of beams.

[0122] Clause 11. The method of any preceding clause, wherein the evaluation signal comprises a data record describing a candidate defect and detection time information indicating a detection time of the candidate defect.

[0123] Clause 12. The method of clause 11, wherein the data record comprises an image, such as a segment of an image for the defect candidate.

[0124] Item 13. An evaluation system comprising: a detector unit configured to generate an evaluation signal representing an attribute of a sample surface; a data processor configured to process the evaluation signal to identify a candidate defect and output a candidate defect signal; a state monitor configured to monitor the state of the evaluation system for an error condition and generate a state signal indicating any error condition occurring during operation of the evaluation system; and an analysis unit configured to analyze the candidate defect signal to determine whether the candidate defect is a real defect; wherein if the state signal indicates that the evaluation signal and / or the candidate defect signal corresponding to the candidate defect has been affected by the error condition, the analysis unit is configured to stop analysis of the candidate defect before completion.

[0125] Item 14. An evaluation system comprising: a detector unit configured to generate an evaluation signal representing an attribute of a sample surface; a data processor configured to process the evaluation signal to identify a candidate defect and output a candidate defect signal; a state monitor configured to monitor the state of the evaluation system for the error condition and generate a state signal indicating any error condition occurring during operation of the evaluation device; and an analysis unit configured to analyze the candidate defect signal to determine whether the candidate defect is a real defect; wherein if verification using the state signal indicates that the evaluation signal and / or the candidate defect signal corresponding to the candidate defect has been affected by the error condition, the analysis unit is configured to stop analysis of the candidate defect before completion.

[0126] Clause 15. An assessment according to clause 13 or 14, wherein the state monitor includes one or more sensors selected from the group consisting of: temperature sensors, such as thermometers; pressure sensors, such as barometers or vacuum gauges; microphones; accelerometers; position or displacement measurement systems; voltage detectors; current detectors; and photonic sensors, such as light sensors and radio wave detectors.

[0127] Clause 16. The evaluation system of clause 13, 14, or 15, wherein the state monitor comprises an error detector configured to detect errors in the operation of the data processor.

[0128] Clause 17. The evaluation device according to clause 13, 14, 15 or 16 further includes a transmission channel for transmitting the signal from the detector unit to the signal processor and / or between the signal processor and the analysis unit; and wherein the status monitor includes a transmission error detector, which is configured to detect errors in the transmission of the signal.

[0129] Clause 18. The evaluation device according to any one of clauses 13 to 17 further includes a controller configured to generate a control signal for controlling a subsystem of the evaluation system, and wherein the state monitor includes an anomaly detector configured to detect an abnormal response of the subsystem to the control signal.

[0130] Clause 19. The evaluation system of Clause 18, wherein the subsystem comprises a drive stage configured to support a sample.

[0131] Clause 20. An evaluation system according to any one of clauses 13 to 19, comprising a charged particle evaluation device, which is configured to detect defects in a sample by relatively scanning a charged particle beam across the surface of the sample, and desirably, the charged particle evaluation device includes a detector unit and a signal processor.

[0132] Clause 21. An evaluation system according to Clause 20, wherein the charged particle evaluation device is configured to detect defects in the sample by relatively scanning multiple charged particle beams across a surface of the sample.

[0133] Clause 22. A computer program comprising instructions interpretable by a computer controlling an evaluation device, the computer program comprising instructions for executing the method according to any one of clauses 1 to 12.

[0134] Item 23. A data processing device for analyzing candidate defects to identify real defects, the data processing device comprising: an interface configured to receive a candidate defect signal representing a candidate defect and a status signal indicating any error condition during the operation of the evaluation device from an evaluation device; an analysis unit configured to analyze the candidate defect signal to identify the real defect; wherein if the status signal indicates that the candidate defect signal corresponding to the candidate defect has been affected by the error condition, the analysis unit is configured to stop analyzing the candidate defect before completion.

[0135] Item 24. A data processing method for analyzing candidate defects to identify real defects, the method comprising: receiving a candidate defect signal representing a candidate defect and a status signal indicating any error condition during the operation of the evaluation device from an evaluation device; analyzing the candidate defect signal to identify the real defect; wherein if the status signal indicates that the candidate defect signal corresponding to the candidate defect has been affected by the error condition, stopping the analysis of the candidate defect before completion.

[0136] Clause 25. A method according to clause 24, wherein the status signal indicates that an error condition has occurred, such as: abnormal response of a subsystem of the evaluation device to a control signal, abnormal vibration, abnormal discharge; power fluctuation; data processing error; data communication error; gas leakage; abnormal temperature fluctuation; and abnormal pressure fluctuation.

[0137] Clause 26. The method of clause 24 or 25, wherein the status signal includes time information indicating a time of occurrence of the error condition and / or duration information indicating a duration of occurrence.

[0138] Clause 27. The method of clause 24, 25 or 26, wherein the evaluation device uses a plurality of charged particle beams and the status signal comprises beam information indicating which of the plurality of charged particle beams is affected by the error condition.

[0139] Clause 28. A method according to any one of clauses 24 to 27, wherein the evaluation signal comprises a data record describing a candidate defect and detection time information indicating a detection time of the candidate defect, preferably, the data record comprising an image, such as a fragment of an image for the defect candidate.

[0140] Clause 29. A computer program comprising instructions that can be interpreted by a computer, the computer program comprising instructions for executing the data processing method according to any one of clauses 24 to 28.

[0141] Item 30. A charged particle evaluation system for detecting defects in a sample by scanning multiple charged particle beams and the sample relative to each other, for example in a beam grid, so that the grid passes over a surface; the device comprising: a detector unit comprising multiple detector elements and configured to output a detection signal in response to a signal particle incident from the sample, the detection signal being generated by and associated with different beams of the beam grid; a signal processor configured to process the detection signal to generate an evaluation signal, the evaluation signal comprising, for each detector element, attribute information related to an attribute of the sample and a detection time of detection of the signal particle; and an analysis unit configured to analyze the evaluation signal to identify defect candidates on the sample based on an analysis of the attribute information in the evaluation signal for each detector element; wherein the analysis unit is configured to analyze the attribute information from different detector elements to determine an error state associated with one or more beams of the beam grid.

[0142] Clause 31. A charged particle evaluation system according to clause 30, wherein the signal processor is configured to assign beam identification information to the property information of the evaluation signal to identify the detector element from which the information was derived.

[0143] Clause 32. A charged particle evaluation system according to clause 30 or 31, wherein the analysis unit is configured to determine a failure of a particular beam of the beam grid as an error state based on consecutive candidate defects associated with the particular beam.

[0144] Clause 33. A charged particle evaluation system according to clause 30 or 31, wherein the analysis unit is configured to determine error states associated with the plurality of beams based on coincidence candidate defects associated with different ones of the plurality of charged particle beams.

[0145] Clause 34. A charged particle assessment system according to any one of clauses 30 to 33, wherein the analysis unit is configured to stop analysis of attribute information derived from a detector element among the plurality of detector elements for which the corresponding beam has been associated with an error state.

[0146] Clause 35. A charged particle assessment system according to any one of clauses 30 to 33, wherein the data processor is configured to stop processing detection signals derived from the detector element of the plurality of detector elements for which the corresponding beam has been associated with an error state.

[0147] Clause 36. A charged particle evaluation system according to any one of clauses 30 to 33, wherein the analysis unit or wherein the data processor is configured to remove from the evaluation signal attribute information derived from a detector element among the plurality of detector elements for which a corresponding beam has been associated with an error state.

[0148] Clause 37. A charged particle assessment system according to any one of clauses 30 to 33, further comprising a controller configured to control the detector unit to deactivate a detector element of a plurality of detector elements for which a corresponding beam has been associated with an error state.

[0149] Clause 38. A charged particle evaluation system according to any one of clauses 30 to 37, further comprising a charged particle device configured to direct the beam grid toward a sample, and a controller configured to control the charged particle device to blank each of the beams associated with an error state.

[0150] Item 39. A method for detecting defects in a sample in a charged particle evaluation device, wherein the charged particle evaluation device is used to project a charged particle beam onto the sample, the method comprising: relatively scanning the charged particle beam and the surface of the sample in the charged particle evaluation device so that the beam passes through the surface; outputting a detection signal from a detector of the charged particle evaluation device in response to a signal particle from the sample, the detection signal having a time record relative to a time line; emitting a status signal having a timestamp relative to the time line, the status signal indicating a status of the charged particle evaluation device, the status including a transient error affecting the operation of the evaluation device; and processing the detection signal when the time record indicates a time different from the timestamp of the transient error.

[0151] Item 40. A charged particle evaluation system for detecting defects in a sample by relatively scanning multiple charged particle beams and the sample in a beam grid so that the beam grid passes over the surface; the device comprising: a detector unit, including multiple detector elements and configured to output detection signals in response to signal particles incident from the sample, the detection signals being generated by different beams of the beam grid and associated with different beams of the beam grid; a controller, configured to control the charged particle evaluation system to determine a failure of one or more beams of the beam grid and identify a beam identity of the failed beam; and based on the beam identity of the failed beam, removing the detection signal of the failed beam or information derived from the detection signal of the failed beam from processing and / or analysis for determining candidate defects on the sample surface.

[0152] Item 41. A method for detecting defects in a sample in a charged particle evaluation device, wherein the charged particle evaluation device is used to project a charged particle beam onto the sample, the method comprising: relatively scanning the charged particle beam and the surface of the sample in the charged particle evaluation device so that the beam passes through the surface; outputting a detection signal from a detector of the charged particle evaluation device in response to a signal particle from the sample, the detection signal having a time record relative to a time line; emitting a status signal having a timestamp relative to the time line, the status signal indicating a status of the charged particle evaluation device, the status including a transient error affecting the operation of the evaluation device; and processing the detection signal when the time record indicates a time different from the timestamp of the transient error.

[0153] Clause 42. The method of clause 41, wherein the transient error is a temporary event.

[0154] Clause 43. The method of clause 41 or 42, wherein the scanning continues during the transient error.

[0155] Clause 44. The method of any one of clauses 41 to 43, wherein the processing continues after the transient event.

[0156] Clause 45. The method of any one of clauses 41 to 44, wherein the time record is the time of detection of the detection signal.

[0157] Item 46. A charged particle evaluation system for detecting defects in a sample by relatively scanning multiple charged particle beams and the sample in a beam grid so that the grid passes over the surface; the device comprising: a detector unit comprising multiple detector elements and configured to output detection signals in response to signal particles incident from the sample, the detection signals being generated by and associated with different beams of the beam grid; a controller configured to control the charged particle evaluation system to determine a failure of one or more beams of the beam grid and identify a beam identifier of a faulty beam; and based on the beam identifier of the faulty beam, removing the detection signal of the faulty beam or information derived from the detection signal of the faulty beam from processing and / or analysis for determining candidate defects on the surface of the sample.

[0158] Item 47. An evaluation method, comprising: using an evaluation device to generate an evaluation signal representing an attribute of a sample surface; processing the evaluation signal to identify a candidate defect and output a candidate defect signal; monitoring the state of the evaluation device for an error condition and generating a status signal indicating the occurrence of any error condition and otherwise indicating an operating state, wherein the occurrence occurs during the operation of the evaluation device, and the occurrence will affect the evaluation signal generated during the occurrence and / or the candidate defect signal corresponding to the candidate defect and derived from the evaluation signal; and analyzing the candidate defect signal to determine whether the candidate defect is a real defect; wherein the analysis of the candidate defect is completed only when the status signal indicates an operating state.

[0159] Item 48. An evaluation system comprising: a detector unit configured to generate an evaluation signal representing an attribute of a sample surface; a data processor configured to process the evaluation signal to identify a candidate defect and output a candidate defect signal; a state monitor configured to monitor the state of the evaluation system for an error condition and generate a state signal indicating any error condition occurring and otherwise indicating an operating state, wherein the occurrence occurs during the operation of the evaluation device, and the occurrence will affect the evaluation signal generated during the occurrence and / or the candidate defect signal corresponding to the candidate defect and derived from the evaluation signal; wherein the analysis unit is configured to complete the analysis of the candidate defect only when the state signal indicates an operating state.

[0160] Although the present invention has been described in conjunction with various embodiments, other embodiments of the present invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. The specification and examples are intended to be considered exemplary only, with the true scope and spirit of the present invention being indicated by the following claims and clauses herein.

Claims

1. An evaluation method comprising: using an evaluation device to generate an evaluation signal representative of a property of a surface of the sample; processing the evaluation signal to identify candidate defects and output a candidate defect signal; monitoring a status of the evaluation device for error conditions and generating a status signal indicative of any error condition occurring during operation of the evaluation device; as well as analyzing the candidate defect signal to determine whether the candidate defect is a real defect; The analysis of the candidate defect includes using the status signal to verify whether the evaluation signal and / or the candidate defect signal corresponding to the candidate defect has been affected by an error condition, and stopping the analysis of the defect candidate after verification.

2. The method according to claim 1, wherein the error condition includes one or more of the following: abnormal vibration, abnormal discharge; power fluctuation; data processing error; data communication error; gas leakage; abnormal temperature fluctuation; abnormal pressure fluctuation and abnormal response of a subsystem of the evaluation device, preferably, such abnormal response occurs temporarily and / or partially, and preferably, the occurrence is such an error condition.

3. The method according to claim 1 or 2, further comprising generating a control signal for controlling a subsystem of the evaluation device.

4. The method according to claim 3, further comprising: Monitoring the state of the evaluation device for an error condition comprises detecting an abnormal response of the subsystem to the control signal, desirably, the detecting comprises detecting the occurrence of an abnormal response.

5. A method according to any one of the preceding claims, wherein the status signal comprises time information indicating a time of occurrence of the error condition.

6. A method according to any one of the preceding claims, wherein the status signal comprises duration information indicative of the duration of the occurrence.

7. A method according to any one of the preceding claims, wherein the evaluation device is a charged particle evaluation device configured to detect defects in a sample by relatively scanning a charged particle beam across a surface of the sample.

8. The method of claim 7, wherein the charged particle beam is a plurality of charged particle beams, the scanning comprises relatively scanning the surface of the sample and the plurality of charged particle beams, and the status signal comprises beam information indicating which of the plurality of charged particle beams is affected by the error condition.

9. The method of claim 8, wherein the occurrence comprises: Desirably, at least one of the plurality of beams fails, desirably, such error condition / occurrence is determined prior to generating the evaluation signal, desirably, the failure of at least one of the plurality of beams is identified by generating a calibration evaluation signal and analyzing such calibration evaluation signal.

10. A method according to claim 8 or 9, wherein monitoring the state of the evaluation device for an error condition includes detecting a correlation between evaluation signals generated in response to different charged particle beams to determine the occurrence, desirably, the different charged particle beams are two charged particle beams of the plurality of beams.

11. The method according to any of the preceding claims, wherein the evaluation signal comprises a data record describing a candidate defect and detection time information indicating a detection time of the candidate defect.

12. The method according to claim 11, wherein the data record comprises an image, such as a segment of an image for the defect candidate.

13. An evaluation system comprising: a detector unit configured to generate an evaluation signal representative of a property of a sample surface; a data processor configured to process the evaluation signal to identify a candidate defect and output a candidate defect signal; a status monitor configured to monitor a status of the evaluation system for error conditions and to generate a status signal indicating any error condition occurring during operation of the evaluation device; as well as an analyzing unit configured to analyze the candidate defect signal to determine whether the candidate defect is a real defect; Wherein if the verification using the status signal indicates that the evaluation signal and / or the candidate defect signal corresponding to the candidate defect has been affected by an error condition, the analysis unit is configured to stop the analysis of the candidate defect before completion.

14. The evaluation device according to any one of claims 13, further comprising a controller configured to generate a control signal for controlling a subsystem of the evaluation system, wherein the state monitor comprises an anomaly detector configured to detect an abnormal response of the subsystem to the control signal.

15. An evaluation system according to claim 13 or 14, comprising a charged particle evaluation device, which is configured to detect defects in the sample by relatively scanning a charged particle beam across the surface of the sample, and desirably, the charged particle evaluation device includes a detector unit and a signal processor.

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