Data processing apparatus and method, charged particle evaluation system and method

Abstract

A charged particle evaluation apparatus for detecting a defect in a sample by scanning a charged particle beam on the sample; the apparatus includes a detector unit configured to output a digital detection signal of pixel values in response to signal particles incident from a sample, the pixel values representing elongated pixels.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to EP application 22175932.7 filed on May 27, 2022 and EP application 22197831.5 filed on September 26, 2022, which are incorporated herein by reference in their entirety. Technical Field

[0003] Embodiments provided herein relate generally to data processing apparatus and methods, and in particular for use with or in 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 as a result of, for example, optical effects and accidental particles, thereby reducing the yield. Therefore, monitoring the extent of undesirable pattern defects is an important process in IC chip manufacturing. More generally, inspection and / or measurement of 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 an SEM, a primary electron beam of relatively high energy electrons is targeted at a final deceleration step so as to land on a sample with a relatively low landing energy. The electron beam is focused onto the sample as a detection spot. The interaction between the material structure at the detection spot and the landing electrons from the electron beam causes signal electrons to be emitted from the surface, such as secondary electrons, backscattered electrons, or Auger electrons. Signal electrons can be emitted from the material structure of the sample. By scanning the primary electron beam as a detection spot on the sample surface, signal electrons can be emitted on the sample surface. By collecting these emitted signal electrons from the sample surface, the pattern inspection device can obtain an image representing the characteristics of the material structure of the sample surface.

[0006] When using a pattern inspection device to detect defects on a sample at high throughput, a large amount of image data is generated and must be processed to detect the defects. In particular, it is desirable to reduce the noise from 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. In some cases, the data generation rate may be an undesirable limit to the throughput of the pattern inspection device, for example because the transmission rate from the detector to the data processing equipment is limited. Summary of the invention

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

[0008] According to a first aspect of the present invention, there is provided a charged particle evaluation apparatus for detecting defects in a sample by scanning a charged particle beam across the sample; the apparatus comprises: a detector unit configured to output a digital detection signal of a pixel value in response to a signal particle incident from the sample, the pixel value representing an elongated pixel.

[0009] According to a second aspect of the present invention, an image analysis device is provided, comprising: an input module or an interface module configured to receive sample image data, the sample image data comprising pixel values ​​representing an image of a sample obtained by a charged particle evaluation device, wherein each pixel value represents an elongated pixel; and a denoising module or a downstream filter configured to apply a denoising filter to generate a filtered signal.

[0010] According to a third aspect of the present invention, a charged particle evaluation system is provided, comprising: a charged particle evaluation device according to the first aspect of the present invention; an image analysis device according to the second aspect of the present invention; and a communication channel configured to communicate a series of pixel values ​​from the charged particle evaluation device to the image analysis device.

[0011] According to a fourth aspect of the invention, there is provided a computer-readable storage medium storing sample image data, the sample image data comprising pixel values ​​representing an image of a sample obtained by a charged particle evaluation system, wherein each pixel value represents an elongated pixel, desirably each pixel value has a contrast value representing a contrast within a contrast range, wherein the relative contrast of adjacent elongated pixels exceeds a contrast difference indicating a defect, desirably the pixel values ​​are configured to be renderable as pixels, for example, in an image arranged in a two-dimensional array, desirably the two-dimensional array is a grid, the pixels desirably have unequal sizes, desirably are rectangular.

[0012] According to a fifth aspect of the invention, there is provided an image of a sample surface for detecting defects in the sample, the image comprising a plurality of elongated pixels each representing a portion of the sample surface and each having a different contrast, wherein the relative contrast of the elongated pixels indicates defects, the elongated pixels are desirably arranged in a two-dimensional array, desirably the two-dimensional array is a grid, the elongated pixels desirably have unequal sizes, desirably are rectangular.

[0013] According to a sixth aspect of the present invention, there is provided a method for data processing in an array pattern using at least an image of a sample surface having a repeating pattern, the method comprising: generating at least one image of a sample surface having a repeating pattern, the image having elongated pixels, the elongated pixels having an elongation direction and a reduction direction, for example using a detector unit / in a detector unit; and aligning at least a portion of at least one image relative to a repetition period of the pattern to be equal to an integer number of pixels in the elongation direction or an integer number of pixels in the reduction direction; wherein the alignment comprises changing the aspect ratio of the pixels.

[0014] According to a seventh aspect of the present invention, there is provided a data processing method in a die-to-database mode for comparing detection data with reference data, comprising: generating a detection data map of a sample surface, for example using a detector unit, the detection data having elongated detection pixels having a longitudinal direction and a reduction direction; shifting the reference data to form a reference data map corresponding to the detection data map; and processing the reference data map, comprising combining pixels of the reference data map in the longitudinal direction of the elongated detection pixels to derive a processed reference data map, the processed reference data map having the same pixel size as the elongated detection pixels, and the processed reference data map is configured to apply the same further processing as the detection data map.

[0015] According to an eighth aspect of the present invention, there is provided an image analysis method, comprising: receiving sample image data, the sample image data comprising pixel values ​​representing an image of a sample obtained by a charged particle evaluation method, wherein each pixel value represents an elongated pixel; and applying a denoising filter to generate a filtered signal.

[0016] According to a ninth aspect of the present invention, there is provided an image analysis method as described above, wherein the reference data includes reference pixel data having a higher resolution than the sample image data, and the comparison includes: aligning the reference pixel data with the sample image data and generating aligned reference pixel data; and downsampling the aligned reference pixel data to generate downsampled reference pixel data having the same resolution as the sample image data; and comparing the pixel data of the sample image data with the corresponding downsampled reference pixel data.

[0017] According to a tenth aspect of the present invention, a detector unit of a charged particle evaluation device is provided for detecting defects in a sample by scanning a charged particle beam across the sample, the detector unit being configured to output a digital detection signal of a pixel value representing an elongated pixel in response to a signal particle incident from the sample.

[0018] According to an eleventh aspect of the present invention, a detector unit of a charged particle evaluation device is provided, for detecting defects in a sample by scanning a charged particle beam across the sample and outputting a detection signal representing a pixel value of an elongated pixel, the detector unit comprising a detector element for generating a detector signal in response to incident charged particles; and an integrator configured to filter the detector signal to generate an integrated detection signal, wherein the integrator is configured to filter the detector signal in an elongated direction corresponding to the elongated dimension of the pixel.

[0019] According to a twelfth aspect of the present invention, there is provided a detector unit of a charged particle evaluation apparatus for detecting defects in a sample by scanning a charged particle beam over the sample, the detector unit being configured to output a digital detection signal of a pixel value in response to a signal particle incident from the sample, the detector unit comprising:

[0020] a detector element configured to generate a detector signal in response to incident charged particles; and

[0021] A transimpedance amplifier with capacitive feedback is configured to amplify the detector signal.

[0022] According to a thirteenth aspect of the present invention, there is provided a charged particle evaluation apparatus for detecting defects in a sample by scanning a charged particle beam across the sample; the apparatus comprising:

[0023] a charged particle device configured to direct a charged particle beam toward a sample;

[0024] a detector unit configured to output a digital detection signal of a pixel value in response to a signal particle incident from the sample, the pixel value representing an elongated pixel having a longitudinal direction and a transverse direction; and

[0025] A stage configured to support a sample; wherein:

[0026] The charged particle device and stage are configured to scan the surface of the sample with the charged particle beam;

[0027] The stage is configured to move in a sub-scanning direction when the sample surface is scanned with the charged particle beam, the sub-scanning direction corresponding to the lateral direction.

[0028] According to a fourteenth aspect of the present invention, there is provided a charged particle evaluation apparatus for detecting defects in a sample by scanning a charged particle beam across the sample; the apparatus comprising:

[0029] a charged particle device configured to direct a charged particle beam towards the sample, desirably the charged particle device comprises a deflector;

[0030] a detector unit configured to output a digital detection signal of a pixel value in response to a signal particle incident from the sample, the pixel value representing an elongated pixel having a longitudinal direction and a transverse direction; and

[0031] a stage configured to support a sample, the charged particle device and the stage configured to scan a surface of the sample using a charged particle beam; wherein:

[0032] The charged particle device (desirably a deflector) is configured to direct the beam in a main scanning direction corresponding to a longitudinal direction and / or in a secondary scanning direction corresponding to a transverse direction when a sample surface is scanned with a charged particle beam, the main scanning direction preferably having different orientations than the secondary scanning direction. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The above and other aspects of the present disclosure will become more apparent through the description of exemplary embodiments with reference to the attached drawings.

[0034] Figure 1 is a schematic diagram illustrating an exemplary charged particle beam inspection system.

[0035] Figure 2 It is illustrated as Figure 1 Schematic diagram of an exemplary multi-beam charged particle evaluation apparatus that is a portion of an exemplary charged particle beam inspection system.

[0036] Figure 3 is a schematic diagram illustrating an exemplary arrangement for sending data from a detector module to an external data processing device.

[0037] Figure 4 is a schematic diagram of a data path according to an embodiment.

[0038] Figure 5 is a graph of a uniform kernel of an embodiment.

[0039] Figure 6 is a diagram illustrating the relationship between defects, measurement spots, and image pixels in a conventional arrangement.

[0040] Figure 7 is a diagram illustrating the relationship between defects, measurement spots, and image pixels in the embodiment.

[0041] Figure 8 FIG. 4 is a schematic diagram of a circuit arrangement in an electron optical column, for example, in a detector module in an embodiment.

[0042] Fig. 9 is a schematic diagram of a filter in an embodiment.

[0043] Fig.10 is a schematic diagram of an image analysis system of an embodiment.

[0044] Fig.11 is a schematic diagram of a comparator of an embodiment.

[0045] The schematic diagrams and views illustrate the components described below. However, the components depicted in the drawings are not drawn to scale. DETAILED DESCRIPTION

[0046] 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 indicated, the same numbers in different drawings represent the same or similar elements. The implementations set forth in the following description of the 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 of the present invention as recited in the appended claims.

[0047] The enhanced computing power of electronic devices can be achieved by significantly increasing the packaging density of circuit components (such as transistors, capacitors, diodes, etc.) on IC chips, which reduces the physical size of the device. This is achieved by increasing the resolution, which enables the manufacture of smaller structures. For example, the IC chip of a smartphone (which is the size of a thumbnail and available in 2019 or earlier) may include more than 2 billion transistors, each of which is less than 1 / 1000 the size of a human hair. It is therefore 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 operation of the final product. The goal of the manufacturing process is to increase the overall yield of the process. For example, in order to obtain a 75% yield of a 50-step process (where one step can indicate the number of layers formed on the wafer), the yield of each individual step must be greater than 99.4%. If the yield of each individual step is 95%, the total process yield will be as low as 7%.

[0048] While high process yield is desired in IC chip manufacturing facilities, it is also essential to maintain high substrate (i.e., wafer) throughput (defined as the number of substrates processed per hour). The presence of defects may affect both high process yield and high substrate throughput. This is especially true if operator intervention is required to review the defects. Therefore, detecting and identifying micro- and nano-scale defects with high throughput by inspection equipment (such as a scanning electron microscope ('SEM')) is important to maintain high yield and low cost.

[0049] An embodiment of the SEM includes a scanning device and a detector device. The scanning device includes an irradiation device and a projection device, the irradiation device including an electron source for generating primary electrons (or charged particles), and the projection device is used to scan samples such as substrates using one or more focused primary electron beams (or multiple beams). Multiple beams can be arranged as multiple beams. Multiple beams can have a multi-beam device (which can have the form of a grid), which can be guided toward the sample along a multi-beam path. At least the irradiation device or irradiation system and the projection device or projection system can be collectively referred to as an electron optical system or device. Primary electrons interact with the sample and generate secondary electrons. The detection device captures secondary electrons from the sample when the sample is scanned, so that the SEM can create an image of the scanned area of ​​the sample. For high-throughput inspection, some inspection devices use multiple focused primary electron beams, that is, multiple beams. The component beams in the 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.

[0050] The following describes a known implementation of a multi-beam inspection device.

[0051] Although the description and drawings relate to electron optical systems, it is to 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, which are not necessarily electrons.

[0052] Now refer to Figure 1 , Figure 1 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 measurement system or simply measurement system. Figure 1 The charged particle beam evaluation system 100 includes a main chamber 10 (eg, a vacuum chamber), a load lock chamber 20, an electron beam system 40, an equipment front end module (EFEM) 30, and a controller 50. The electron beam system 40 is located in the main chamber 10.

[0053] 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, accommodate a front opening pod (FOUP) containing a substrate to be inspected (e.g., a semiconductor substrate or a substrate made of (multiple) 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 transport the sample to the load lock chamber 20.

[0054] The load lock chamber 20 is used to remove the gas around the sample. This will produce a vacuum with 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 the gas particles in the load lock chamber 20. The operation of the load lock vacuum pump system enables the load lock chamber to reach a first pressure lower than atmospheric pressure. After reaching the first pressure, one or more robot arms (not shown) transport 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 the 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 transported to the electron beam system, by which the sample can be inspected. The electron beam system 40 may include a multi-beam electron optical device (which may be referred to as an electron optical column or device).

[0055] The controller 50 is electronically connected to the electron beam system 40. The controller 50 may be a processor (such as a computer) configured to control the charged particle beam evaluation apparatus 100. The controller 50 may also include processing circuitry (which may be referred to as processing circuitry) configured to perform various signal and image processing functions. Figure 1 30, but it is understood that the controller 50 can be part of the structure. The controller 50 can be located in one of the components of the charged particle beam inspection device, or it can be distributed on at least two components. Although the present disclosure provides an example of a main chamber 10 that accommodates an electron beam system, it should be noted that the broadest aspects of the present disclosure are not limited to chambers that accommodate electron beam systems. On the contrary, it is understood that the foregoing principles can also be applied to other arrangements of other devices and apparatuses operating at a second pressure. For example, the controller can be a distributed controller having one or more portions at a second pressure and optionally one or more portions at a first pressure.

[0056] Now refer to Figure 2 , Figure 2 is a schematic diagram illustrating an exemplary electron beam system 40, including a multi-beam electron optical system 41, which is Figure 11 and 10. The electron beam system 40 includes an electron source 201 and a projection device 230. The electron beam system 40 also includes an actuation stage 209 and a sample holder 207. The electron source 201 and the projection device 230 can be collectively referred to as an electron optical system 41 or an electron optical train. 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 system 41 also includes a detector 240 (e.g., an electron detection device).

[0057] 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.

[0058] 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 illustrated for simplicity, there may be tens, hundreds, thousands (e.g., about ten thousand), tens of thousands, or hundreds of thousands of sub-beams. The sub-beams may be referred to as beamlets.

[0059] The controller 50 may be connected to Figure 1 The controller 50 may be used to control various parts of the charged particle beam evaluation device 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 manage the operation of the charged particle beam inspection device, including the charged particle multi-beam device.

[0060] 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 (three detection spots for this example, one detection spot 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 across separate scanning areas in a section of the surface 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 (which can be referred to as signal particles) including secondary electrons and backscattered electrons are generated from the sample 208. The electron energy of the secondary electrons is typically less than or equal to 50eV. Actual secondary electrons can have an energy less than 5eV, but anything below 50eV is typically processed at the secondary electrons. The electron energy of the backscattered electrons is generally between 0 eV and the landing energy of the primary beamlets 211, 212, and 213. Since the detected electrons with energy less than 50 eV are generally regarded as secondary electrons, a certain proportion of the actual backscattered electrons will be counted as secondary electrons.

[0061] The detector 240 is configured to detect signal particles, such as secondary electrons and / or backscattered electrons, and generate corresponding signals, which are sent to the signal processing system 280 for preprocessing, such as analog-to-digital conversion. The detector 240 can be incorporated into the projection device 230. Further details and alternative arrangements of detector modules, sensors and detector arrays positioned close to the objective, in the beam upstream direction of the objective, in the beam downstream direction of the objective or otherwise integrated into the objective can be found in EP application number 20216890.2 and PCT application number PCT / EP2021 / 068548, which are respectively incorporated herein by reference, at least as far as they disclose details of detector modules, sensors and detector arrays and similar elements.

[0062] Detector can be provided with multiple parts, more specifically multiple detection parts. Detector comprising multiple parts can be associated with a sub-beam in sub-beams 211, 212, 213. Therefore, multiple parts of a detector 240 can be configured to detect signal particles (otherwise can be referred to as sub-beams 211, 212, 213) emitted from sample 208 with respect to a primary beam in the primary beam. In other words, detector comprising multiple parts can be associated with an aperture in the aperture in at least one electrode of the objective lens assembly. Multiple parts can be radial and / or angularly arranged segments. More specifically, detector comprising multiple parts can be arranged around a single aperture, which provides an example of such a detector. As mentioned, the detection signal from the detector module is used to generate an image. Utilizing multiple detection parts, the detection signal includes components from different detection signals, which can be processed as a data set or in a detection image.

[0063] The objective lens can be an objective lens array and can include multiple planar electrodes or plates that include apertures for corresponding paths of the beams of the multiple beams. Each plate can extend across the multiple beam device. The objective lens can include at least two electrodes that can be connected to and controlled by corresponding potentials. Additional plates may be present to control additional degrees of freedom respectively. The detector can be a plate associated with or connected to the objective lens that has an aperture for each path of the beams of the multiple beams. The detector can be located above, below or inside the objective lens.

[0064] The scanning deflector can be associated with the objective lens, or even integrated into the objective lens, for example as a scanning deflector array. The scanning deflector array (e.g., an array of deflector elements) can be referred to as a deflector array. Each beamlet can be associated with a deflector element of the deflector array. In an arrangement, the scanning deflector can be positioned in the beam upstream direction of the objective lens. In an arrangement in which the path of the primary beam is collimated in the beam upstream direction of the objective lens, the scanning deflector can be positioned in the beam upstream direction of the objective lens. In an arrangement in which 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 can be a macro scanning deflector positioned in the beam upstream direction of the objective lens so as to operate on the collimated primary beam. Other electronic optical arrangements including one or more elements described herein can be envisioned. Such a scanning deflector can be controlled by a controller to deflect the beams of multiple beams along one axis in the plane of the sample or two primary axes on the surface of the sample (e.g., in the sample plane) (which can be orthogonal to each other).

[0065] It should be noted that embodiments of scanning deflectors close to the sample (e.g., integrated or close to the objective) may have a limited scanning deflection range. However, scanning deflectors close to the sample can be accurately controlled and have a fast response relative to other types of scanning actuators (such as an actuator stage).

[0066] 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 enable the actuation stage 209 to move the sample 208 in at least one direction during the inspection of the sample, preferably continuously, for example at a constant speed, which may be referred to as a scan. The controller 50 may control the movement of the actuation stage 209 so that it changes the speed of movement 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 on the sample surface. For example, the controller 50 may control the speed of the table (including its direction) and / or the scanning deflector depending on, for example, the characteristics of the scanning process and / or the inspection scanning elements and steps in the scanning of the scanning process, as disclosed in EPA 21171877.0 filed on May 3, 2021. The contents of such application are incorporated herein as long as a combined stepping and scanning strategy for at least the stage and scanning deflector is disclosed.

[0067] Known multi-beam systems (such as the above-mentioned electron beam system 40 and charged particle beam inspection device 100) are disclosed in US2020 / 118784, US202002 / 03116, US2019 / 0259564 and WO2021078352, which are incorporated herein by reference.

[0068] The electron beam system 40 may include a projection assembly to adjust the accumulated charge on the sample by irradiating the sample 208 .

[0069] The images output from a charged particle evaluation device (e.g., electron beam system 40) need to be automatically processed to detect defects in the sample being evaluated. Figure 4 1 and 2. A data processing device 500 for detecting defects in an image generated by a charged particle evaluation device is depicted in FIG. 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 manufacturing plant, or integrated elsewhere in the charged particle evaluation device.

[0070] In the charged particle detection system, the electron optical system 41 or each electron optical system 41 is located in the main (vacuum) chamber 10. Therefore, it is necessary to send data from the (multiple) electron optical systems to a device outside the vacuum chamber, such as a data processing device 500. The raw data generated by the (multiple) electron optical systems can be sent out of the vacuum chamber via a signal conduit. Considering the amount of data, the data can be sent optically, for example using a signal conduit with optical capabilities such as an optical fiber. An optical transceiver is used to convert an electrical signal representing the data into an optical signal. The optical transceiver is located near the detector module 240 of the electron optical system 41. The optical transceiver is configured to convert the electrical signal output by the detector module 240 into an optical signal for transmission along the optical fiber. The optical fiber may be able to send multiple channels simultaneously (for example using different wavelengths). Therefore, the detection signal from each individual electrode of the detector module is converted into an appropriate number of data streams. Multiple optical fibers can be used, whether single-channel optical fibers or multi-channel optical fibers.

[0071] The signal conduit or each signal conduit (e.g., an optical fiber) passes through the wall of the main chamber 10 (in use, the interior of the main chamber 10 is in a vacuum) via a vacuum lead 11. A suitable vacuum lead is described in US2018 / 0182514A1, which is incorporated herein by reference at least to the extent that it relates to the lead device. The signal conduit (e.g., an optical fiber) is connected to the data processing device 500, so that the data processing device 500 can be located outside the vacuum for easy access and avoids the need to increase the size of the vacuum chamber to accommodate the data processing device. In single-column and multi-column systems, multiple optical transceivers and multiple optical fibers per column can be used if convenient.

[0072] exist Figure 3 An arrangement involving multiple optical fibers (or other communication channels) is shown in FIG. Each optical fiber 242 is connected to a subunit (or detector unit) 241 of a detector module 240, and transmits the signal generated by the corresponding subunit 241 to a data processing device 500 outside the main chamber 10. Each subunit 241 may include one or more individual electrodes of the detector module 240. It will be seen that in a multi-column system capable of imaging a large portion of the sample 208 at a time, a large number of optical fibers 242 are required, and therefore the vacuum lead 11 must be large. In addition to taking up space, a large vacuum lead or multiple smaller leads may be difficult to seal.

[0073] It should be noted that a detector module or detector array for an arrangement including a plurality of planar electron optical elements (e.g., electrodes) placed along a plurality of beam paths may have internal circuitry. The internal circuitry may include some or all of a processing circuitry, such as a CMOS structure, for connecting individual detector elements or detector units in the detector array. In an alternative arrangement, two or more signal conduits for different detector units may have common or adjacent connections in the surface of the detector module. Co-locating the plurality of connections of the signal conduits to the detector module simplifies the connection of the signal conduits and the detector modules to each other. In an arrangement, a plurality of detector units have a common signal conduit, so that a plurality of detector units may be grouped. Each detector unit may be associated with a beam of a plurality of beams, so that the detector is arranged to detect signal particles from a sample generated by a specific beam of a plurality of beams. In a different arrangement, an array of detector units each associated with a different pixel may be associated with a beam of a plurality of beams. This arrangement may be suitable for an inspection system for finding defects. This arrangement may be suitable for a metrology system, in which each pixel (e.g., a detector unit) is used to count signal electrons.

[0074] Various methods can be adopted to detect defects in the images generated by the charged particle evaluation device. A common method is to compare an image of a portion of the sample (referred to herein as a sample image) with a reference image. In fact, the data points of the data stream representing the sample image are compared with the data points of the reference image retrieved from the memory or delivered in a parallel data stream. For the sake of simplicity, the process can be referred to as comparing the image and the data points as pixels. Any pixel that differs from the corresponding pixel of the reference image by more than a threshold amount can be regarded as a defect. Such pixels that are different from the reference image and adjacent pixels that are also different from the reference image are regarded as a single defect. (In an embodiment, this may mean that pixels that are different from the reference image and have the same adjacent pixels as the reference image (i.e., no difference from the reference image) can be considered not to represent defects). As discussed below, a reference image can be obtained in a variety of different ways. (Note: The data of the sample image can be referred to as sample image data; the data of the reference image (or reference data) can at least include or even be referred to as reference pixel data. The reference data can take the form of a reference data map).

[0075] The false alarm rate, i.e., samples marked as defective when in fact no obvious defect 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 the difference compared to an equivalent pixel of the reference image. The false alarm rate is further controlled by applying noise reduction to either or both of the reference image and the sample image. However, noise reduction increases the amount of processing required to detect defects.

[0076] An efficient and effective way to reduce noise in the sample image is to apply a simple filter by convolution, such as a uniform filter (convolution with a uniform kernel). To reduce noise in the reference image, multiple source images can be averaged. In some cases, such as when the reference image is obtained by simulation from design data (usually in GDSII format), noise reduction on the reference image can be omitted.

[0077] By appropriately selecting the size of the (uniform) filter, the efficiency and effectiveness of noise reduction in the sample image can be optimized. The optimal size of the filter may depend on a variety of factors, such as the size of the features on the sample, the size of the defects to be detected, the resolution of the charged particle evaluation equipment, the amount of noise in the image, and the desired trade-off between sensitivity and selectivity. The size of the kernel used to implement the filter can be equal to a non-integer number of pixels. The width of the kernel is in the range of 1.1 to 5 pixels (desirably in the range of 1.4 to 3.8 pixels) suitable for various use cases. The form of the uniform kernel will be discussed further below.

[0078] exist Figure 5 A square uniform kernel 505 with a non-integer size (width) is depicted in FIG. This uniform kernel includes a central region 505a of n x n values ​​(all values ​​are 1) and a peripheral region 505b consisting of a top row, a bottom row, a left column, and a right column. All values ​​in the peripheral region are f, where f<1, except for the corner values, which are f 2 The effective size of the uniform kernel is equal to n+2f pixels. Optionally, the uniform kernel can be normalized (i.e., all values ​​are divided by a constant so that the sum of all values ​​is 1). Alternatively or additionally, the filtered sample image can be normalized or rescaled.

[0079] In some cases, such as the uniform kernel described above, the 2D kernel can be decomposed into two 1D convolutions in orthogonal directions that are applied sequentially. This can be advantageous because the number of operations to perform nxn 2D convolutions scales with the square of n, while the number of operations to perform two n 1D convolutions scales linearly with n.

[0080] The kernel need not be square, and may, for example, be rectangular or any other convenient shape. The filter function implemented by the kernel need not be of the same shape and size as the kernel; a kernel larger than the filter function will include zero values. Desirably, the filter is symmetrical, but this is not required. Simulations have shown that kernels that implement uniform filters provide good results, but some deviations from mathematical uniform filters are allowed. For example, a corner filter may have a value f that may overweight these pixels slightly, but not significantly. Non-uniform filters (e.g., Gaussian filters) can be conveniently implemented by convolution with a suitable kernel.

[0081] The reference image may be obtained by averaging the source images, and the averaging process may depend on the nature of the source images. In the case where 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.

[0082] 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 image 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.

[0083] 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. GDSII format). Such a reference image (at least by the first processing module, for example in the first step of a two-step process) can be a simplification of one or more "known good" patterns or simulations.

[0084] The comparison result of the sample image with the reference image may be a simple binary value indicating the difference or correspondence (i.e., match) between the sample image and the reference image. More desirably, the comparison result is a difference value indicating the magnitude of the difference between the sample image and the reference image. Desirably, the comparison result is a difference value for each pixel (or each group of adjacent pixels, which may be referred to as a 'pixel region'), so that the location of the defect within the source image may be determined more accurately.

[0085] In order to determine whether the difference between a pixel or a pixel region between the source image and the reference image represents a defect in the pattern being inspected, a threshold value can be applied to the difference corresponding to the pixel or pixel region. The threshold value can be fixed in advance, for example for a specific charged particle beam system or a specific pattern to be inspected. The threshold value can be a parameter set by the user or updated from time to time by other conditions, for example, it will depend on the application or be updated from time to time by evaluation. The threshold value can be determined dynamically, updated during the processing process, or both. Alternatively, a predetermined number of positions with the highest difference values ​​can be selected as candidate defects for further inspection. Adjacent pixels with a difference value above the threshold value can be regarded as a single defect or candidate defect. All pixels of a single defect can be assigned the same difference value. Such adjacent pixels and all pixels of a single defect can be referred to as a pixel region.

[0086] An efficient method of identifying a predetermined number of locations with the highest difference values ​​is to process pixels in sequence and write pixel information and difference values ​​to a buffer. The pixel information may include a region of pixel data surrounding a pixel or group of pixels identified as a potential defect. Such a region of pixel data may be referred to as a clip. If the buffer is full and the difference value of the newly processed pixel is higher than the pixel with the lowest difference value in the buffer, the pixel information associated with the pixel with the smallest difference value will be overwritten. In one possible implementation, a threshold for pixel selection is set to a predetermined level until the buffer is full. When the buffer is full, the threshold is updated to the lowest difference value of the pixels stored in the buffer and is updated each time a pixel in the buffer is overwritten. In this way, only one comparison needs to be performed.

[0087] Alternatively, the threshold can be maintained constant and the initially selected pixels can be tested individually to see if they have a higher difference than the pixels in the buffer. This approach can select a predetermined proportion of pixels and a predetermined amount of data. Alternatively, the threshold can be set to select pixels that exceed the threshold so that the selected pixels tested have an amplitude corresponding to or exceeding the set threshold. In this approach, the proportion of pixels is not predetermined; therefore, the amount of data selected is not predetermined. The proportion of pixels selected may depend on the data set being processed. Because the number of selected pixels in this approach is much lower than the total number of pixels, further processing of the selected pixels can be performed asynchronously (e.g., by a different processor) from the initial processing without reducing throughput.

[0088] The charged particle evaluation apparatus 100 can have high throughput and high resolution, meaning that data can be output at a high rate. For example, a charged particle evaluation device may have thousands or even tens of thousands of beams or more, each with one or more detector sections that output data points at a rate of kilohertz or megahertz. Therefore, even when optical fiber is used, the rate at which data can be sent from the (multiple) detector modules to an image analysis device such as the data processing device 500 (whether incorporated with the charged particle evaluation device in the charged particle evaluation system or a standalone device) may limit the throughput of the charged particle evaluation device or system.

[0089] like Figure 4 As depicted, the data processing device 500 includes a filter module 501 that receives and filters a sample image from a charged particle evaluation device 40, a reference image generator 503 that generates a reference image based on a source image, a comparator 502 (e.g., a comparison module) that compares the filtered sample image with the reference image, and an output module 504 that processes and outputs the comparison results.

[0090] Filter module 501 applies filtering to input data, as discussed further below. Filter module 501 is conveniently implemented by dedicated hardware (e.g., FPGA or ASIC). Such dedicated hardware can be more efficient and economical than a programmed general-purpose computing device (such as a standard or common type of CPU architecture). The processor may not be as powerful as a CPU, but may have an architecture of processing software suitable for processing detection signal data (i.e., image), so that the image can be processed in the same or shorter time as the CPU. Although the processing power of this detected processing architecture is lower than that of most contemporary CPUs, it may be equally fast in processing data because the data architecture of the dedicated processing architecture is more efficient. A general-purpose CPU may be advantageous because it allows the filter to be easily changed.

[0091] The reference image generator 503 may be operable in one or more modes, each mode representing a different method of generating a reference image.

[0092] In library mode, the reference image generator 503 averages a large number of source images obtained from previous scans of a pattern that is 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 in a previous batch. The library images may be derived from test samples or production samples. It is desirable to align the images with each other before averaging. Averaging the source images to generate the reference image has the effect of reducing noise. Averaging the source images in this way may also average out any defects that may be visible in the source images.

[0093] In the case where the pattern being inspected is a repeating pattern, a reference image can be generated by averaging multiple shifted versions of the source image. Each version of the source image is shifted by an integer multiple of the unit cell size. If either or both of the sizes of the unit cell are not equal to an integer number of pixels, the shift amount can be rounded to the nearest pixel, or fractional pixel shifts can be achieved by interpolation, for example linear or cubic interpolation, such as bicubic interpolation or any other known interpolation technique. Another possibility is to shift a multiple of the pitch of the repeating pattern so that the multiple is an integer number of pixels. In practice, multiple instances of the unit cell are extracted from the source image and averaged. This approach can be referred to as an example of an array pattern, and more specifically an example of a reference image is provided for an array pattern.

[0094] In die-to-die mode, a sample image and two reference images of similar surface features that may have a repeating pattern are generated using a charged particle evaluation device. In the arrangement, each of the sample image and the two reference images is from a different die of the sample (e.g., so that similar portions of the surfaces of different die can be compared). The sample image can be compared with each of the reference images in the reference images to identify the differences between each of the reference images in the reference images. Such differences can be considered as candidate defects. Differences that are common 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 the 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 image before the image is appropriately supplied to the reference image generator 503 and the filter module 501. For example, such alignment can align at least a portion of the image or different portions of the sample with respect to the repetition period of the repeating pattern.

[0095] In an arrangement, three columns of a multi-column charged particle evaluation device are used to generate a sample image and two reference images. Where the spacing between the columns is equal to the die size of the sample being inspected, this arrangement is particularly efficient as the columns will then automatically scan the corresponding pattern features simultaneously. Using this arrangement is also faster than using a single column as the sample image and the reference image can be acquired simultaneously. Where 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 the timing of the input of the image to the data processing device.

[0096] In a variation of the die-to-die mode, the same 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 need to be performed and the routing of the data can be simplified. For example, such a calibration is of the relative position of the beam relative to the ideal beam position for that beam or even for each beam. Using the same beam avoids calibrations such as evaluating offsets between beams of different scans being compared. Using the same beam means that, although the beam has an offset relative to the ideal beam position, there is no position offset to correct for when comparing data retrieved from the scans. However, the need for data buffering may increase, for example in frequency, if not in the amount of data buffered before starting to compare data from different dies.

[0097] An alternative version of the array pattern using a single column, for example a single column system, provides a sample image as a source image which is compared to a reference image derived from two shifted versions of itself.A buffer may be used to provide the shifted image.

[0098] It should be noted that the uniformity filter may also be applied to the source image and / or the reference image, in particular when the reference image is derived from a small number of source images obtained concurrently with the source image.

[0099] Refer again Figure 4 , 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 may be more efficient and more economical than the general computing device (such as CPU) of programming. Desirably, comparator 502 is realized on the dedicated hardware identical with filter module 501.

[0100] 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 that the reference image generator be implemented in dedicated hardware identical to the comparator and / or filter module. Where appropriate, the mathematical operations of averaging the pixels of the source image and comparing them with the pixels of the sample image may be combined into a single logic circuit.

[0101] The output module 504 receives the results output by the comparator 502 and prepares them for output to a user, other fab systems, or for further processing within the inspection system. The output may be in any of a number of different forms. In the simplest option, the output may simply be an indication that the sample has or does not have a defect. However, since almost all samples will have at least one potential defect, more detailed information is required, for example as a data set, such as an image (e.g., such as a data set that can be rendered as an image). Thus, the output may include, for example, a defect location map (or inspection data map), a deviation image, a clip of pixel data (e.g., an image and a reference image, or a reference image), and / or information about the severity of a possible defect 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.

[0102] The output module 504 may also filter potential defects, for example by outputting only defect locations where the magnitude of the difference between the sample image and the reference is greater than a threshold or where the pixel density showing the difference is above a threshold. Another possibility is to output only a predetermined number of the worst defect sites indicated by the magnitude of the difference. This may be achieved by storing the defect sites in a buffer 510 and overwriting the lowest magnitude defect if a higher magnitude defect is detected when the buffer is full.

[0103] The defect information may be output using any suitable format, such as a list, a data set, an image, or a map. Desirably, the output module 504 may output a clip, which is an image of the sample area in which the potential defect has been detected. This allows for further review of the potential defect to determine if the defect is real and severe enough to affect the operation of a device formed or present on the sample. The remainder of the source image (i.e., the portion not saved as a clip) may be discarded to save on data storage and transmission requirements. Thus, a data set may be a collection of clips; an image may include a collection of clips.

[0104] As mentioned above, a problem with conventional charged particle assessment systems or devices may be that the rate at which data is sent from the detector to the image analysis module is the limiting factor in the throughput of the charged particle assessment system. Figure 3As discussed, the need to pass the signal through the vacuum chamber wall (e.g., using vacuum leads) can limit the available bandwidth for sending signals from the detector module 240 to the data processing device 500. In particular, in the case of a system with a large number of beams, the data rate generated by the system is very large. The present invention proposes to solve this problem by distribution (e.g., splitting). De-noising between circuit devices integrated in or near the detector (e.g., in CMOS features of the detector array) and circuit devices far from the detector (e.g., in the data processing device 500) reduces in this way the amount of data that must be transmitted from the detector or other circuit devices incorporated into the electron optical system 41 to remote circuit devices (e.g., outside the main chamber 10).

[0105] In order to obtain a two-dimensional image of the sample, the (or each) detection beam is scanned over the sample surface in a two-dimensional raster pattern. This involves movement of the beam in two directions: a main scanning direction and a secondary scanning direction, which have different orientations, such as orthogonal. The main scanning direction may be referred to as a fast scanning direction or a primary scanning direction. For example, a scanning deflector may be controlled to actuate a primary beam (e.g., multiple beams) in a fast direction. The secondary scanning direction may be referred to as a slow scanning direction or a secondary scanning direction. For example, the console may be controlled to actuate the sample relative to the path of the primary beam; the scanning deflector may be controlled to actuate the path of the beam on the sample surface in a slow direction; or both the stage and the scanning deflector may be actuated to achieve scanning in the slow direction. The stage is preferably used only in the slow direction because the inertia of its larger mass makes it more challenging to achieve scanning movement (e.g., acceleration) in the fast direction than alternatives such as scanning deflectors.

[0106] The signal from the detector is sampled at regular intervals so that the distance traveled between samples in the main scanning direction is equal to the distance between scan lines in the sub-scanning direction. Figure 6 , which depicts a square pixel grid overlaid on a sample having a defect d. The square pixel grid has axes represented by X and Y. The pixel size I is selected pix , so that the defect d def The expected size in either axis is two (2) pixels. spot The diameter of is four (4) pixels in either direction of the two axes. That is, the size of the square pixels is uniform or the same. Therefore, the signal collection area d affected by the defect sigCol The size of is six (6) pixels in the direction of either axis of the two axes. In the arrangement, the main scanning direction is the X direction, and the sub-scanning direction is the Y direction.

[0107] Signal collection area d sigColThe surface coverage size corresponding to the expected defect on the sample so that the detection spot can detect the defect. It is when the detection spot d spot Any part of the defect that is located at a size that is different from the expected size of the defect (i.e., the size of the pixel d def ;) is the area of ​​the sample surface corresponding to the sample surface area. The signal collection area also corresponds to the denoising filter. In order to add all the signals in the signal collection area, the pixel data is convolved with the denoising kernel. After applying the denoising filter, the sum of all the signals from the signal collection area will be present in the pixel close to the center of the defect. The filter can be of any suitable type, such as a Gaussian filter, or a rounded or square top hat (or rectangular function) (such as Figure 6 ). The filter can be uniform, such as a top hat filter. The filter can be a kernel as described herein for noise reduction and can therefore be referred to as a denoising filter. The filter can improve the signal-to-noise ratio. By convolving the signal with the kernel, both the noise and the detection signal are reduced, but differently. The larger the filter, the greater the reduction. When balancing the signal-to-noise ratio, the filter is selected so that the reduction in the signal is less than the noise. The optimal size of the filter strikes a balance between the reduction in signal-to-noise ratio when the size of the filter approaches (if not matches) the size of the desired feature. The size of such a filter can be nanometers, which may correspond to a size range of defects. The filter size can be considered to depend on the size range of the expected defects and therefore also on the application being evaluated.

[0108] In an embodiment, the denoising filter in the main scanning direction is performed by a circuit device integrated in or near the detector module 240. An embodiment of a circuit device that performs a denoising filter in the main scanning direction is a filter (or upstream filter or first filter) 402, as described later in this document. The effect of the denoising filter in the main scanning direction is to average the signal in the main scanning direction. Averaging the signal in the main scanning direction allows the sampling rate in the main scanning direction to be reduced, for example by a factor of two. This actually results in a rectangular pixel. Such a rectangular pixel has uneven, different or dissimilar sizes in different directions. The rectangular pixel is elongated, that is, longer in one direction (longitudinal direction) than in the vertical direction (lateral direction). In Figure 7 Such a grid of rectangular pixels is depicted in FIG. In an embodiment, the rectangular pixels have a size of I pix-x , for example, a first dimension in a first direction and having I pix-y , for example, a second dimension in a second direction. The first dimension and the second dimension of a rectangular pixel are not similar; despite the term 'rectangular', the first dimension and the second dimension (or the first side and the second side) of a rectangular pixel need not be orthogonal. Dimension I pix-x In the main scanning direction. Dimension I pix-yIn the sub-scanning direction. In this example, the size I pix-x (or main size) is the size in the sub-scanning direction. pix-y (or sub-scan size). However, the main size is in the range of one to four times the sub-scan size, for example, 1.5 to 4 times the sub-scan size. In a more desirable embodiment, the range is between 2 and 3, or even equal to or greater than 2. In the example, the main scan size I pix-x is the secondary scanning size I pix-y twice as much.

[0109] exist Figure 8 A circuit device implementing the above concepts is depicted in , which can be incorporated in an electron optical column, such as a detector module 240. The detector element 401 outputs an analog signal representing a signal particle, such as an electron received by the detector, such as a secondary electron emitted from a sample. When the detection spot is scanned on the sample in the main scanning direction, the detector receives such a signal particle. Therefore, the analog signal is a time-varying signal. In a time-varying signal, the time axis corresponds to the position of the sample in the main scanning direction, and the amplitude axis corresponds to the sample characteristics that affect its response to the detection beam. The denoising filter 402 applies a denoising filter to the analog signal in the analog domain to generate a filtered analog signal. The denoising filter 402 desirably has a time averaging characteristic, such as a uniform filter or a Gaussian filter with a predetermined time constant (e.g., a window size), or a low-pass filter with a predetermined cut-off frequency. Therefore, the denoising filter has the effect of reducing random noise and other high-frequency noise. The analog-to-digital converter 403 converts the filtered analog signal into a digital signal as a data set (e.g., an image), and outputs these data sets. Here, the digital signal output in the data set includes pixel values ​​at a predetermined sampling rate, for example as a series of pixel values.

[0110] Various parameters of the circuit arrangement are selected to achieve the desired data rate and other effects, such as the size of the rectangular pixel in the main scanning direction and the sub-scanning direction (i.e., the main scanning size and the sub-scanning size of the rectangular pixel) relative to the geometry of the rectangular pixel. Specifically, the time constant or cutoff frequency of the denoising filter 402 is set relative to the scanning speed of the detection beam in the main scanning direction to set an averaging length, which can be, for example, of the order of magnitude of the expected defect size. The sampling rate of the analog-to-digital converter 403 is selected relative to the scanning speed of the detection beam in the main scanning direction to set the main scanning size I in the main scanning direction. pix-x The effective pixel size.

[0111] Rectangular Pixel I pix-x The size in the main scanning direction (or the main size of a rectangular pixel) may, for example, be of the same order of magnitude as the defect size and / or be approximately the size of a pixel in the sub-scanning direction (or the sub-scanning size I pix-y) is twice the size of the secondary scanning size. pix-y It may be equal to the spacing between scan lines in the Y direction (sub-scan direction). (Here, a scan line is a line that the beam moves relative to the sample surface during scanning, for example on the sample surface).

[0112] In some cases, if the pixel size I in the main scanning direction is pix-x (or the main scanning size of rectangular pixels) is the sub-scanning size of pixels. pix-y (or pixel size I in the sub-scanning direction pix-y ), i.e., the aspect ratio of the pixel is an integer. Desirably, the pixel size in the main scanning direction is pix-x Greater than or equal to the pixel size I in the sub-scanning direction pix-y twice; that is, the aspect ratio of the pixel is greater than or equal to two (2). It has been found that, in various cases, an aspect ratio of no more than three (3) is an efficient compromise. All other things being equal, desirably, the data rate that must be sent from the electronic optical column is reduced by a factor equal to the pixel aspect ratio. Desirably, the length of the denoising filter in the main scan direction is approximately the same as the length of the pixel at the main scan angle. Therefore, the main scan size of the denoising filter in the main scan direction is similar to or approximately the same as the sub-scan size of the pixel. Therefore, data for rectangular pixels is output from the denoising filter 402, whose effective filter size is resulting from the operation of the denoising filter in the main scan direction, which is applied to the main scan size of the pixel, while the rectangular pixel has a filtering effect in the sub-scan direction.

[0113] Fig. 9 An embodiment of a filter 402 that can be used in embodiments of the present invention is depicted. The filter 402 comprises a transimpedance amplifier 4031 with a capacitive feedback 4032 as an example of an integrator. A switchable bypass 4033 allows the filtering effect to be turned off if not required. Fig. 9 As shown, the transimpedance amplifier with capacitive feedback acts as a uniform filter. A transimpedance amplifier with low-pass filter characteristics can also be used instead of capacitive feedback. This low-pass filter can be a transimpedance amplifier with resistive feedback or an electronic circuit with an RC low-pass filter. This will produce an effect similar to that of a Gaussian filter. The filter 402 outputs the filtered data to an analog-to-digital converter 403. This filter can be incorporated into a subunit or detector element of a detector array, or at any point in the data flow from a subunit to a processor away from the detector array. This filter can be implemented in a circuit device within a detector array, as disclosed in WO2022008462, which is incorporated herein by reference, as long as it includes, for example, a circuit device having a subunit or detector element of a detector array, such as a transimpedance amplifier.

[0114] exist Fig.10 An image analysis device of an embodiment is schematically depicted in . The image analysis device may form part of the data processing device 500. In an embodiment, the image analysis device is remote from the detector array, for example within a vacuum chamber. The image analysis device may be part of an electron optical assembly of an electron optical column; such an assembly may include a detector (such as a detector array) and an objective lens (such as an objective lens array). The detector may be located in the path of the beam grid, and the image analysis device may be remote from the path of the beam grid. The image analysis device may be separated from the detector, but electrically connected to the detector. In different embodiments, at least a portion (if not all) of the image analysis device is remote from the electron optical column, such as remote from the electron optical assembly, or even outside the vacuum chamber including the electron optical column. At least a portion of the image analysis device may be in signal communication with the detector via leads in the chamber wall.

[0115] The image analysis device is also used to process a digital signal from the analog-to-digital converter 403, which is based on the analog output from the denoising filter 402. The interface module 506 receives the pixel values ​​output by the analog-to-digital converter 403 via a communication channel 507, for example as a series of pixel values, buffers the pixel values ​​in, for example, a random access memory, and outputs them in a desired order for subsequent processing. The communication channel may include the above-mentioned optical fiber, or may be any other suitable high data rate channel or signal conduit. The communication channel may include a portion in the detector, in the vacuum electronic device, through the lead, an external vacuum electronic device near the lead, and an optical channel, for example to the image analysis device.

[0116] The downstream filter module (or second filter denoising module) 501 is a denoising filter, for example as a second denoising filter. The downstream filter module 501 applies a denoising filter in a sub-scanning direction (i.e., orthogonal to the main scanning direction). The denoising filter in the sub-scanning direction can be, for example, a uniform filter or a Gaussian filter. Desirably, the denoising filter in the sub-scanning direction is the same type of filter applied in the main scanning direction. However, in a different arrangement, at least a portion of the image analysis device is a separate detector array, for example away from the electron optical column (e.g. outside the vacuum chamber). Any communication channels passing through the wall in the chamber wall can take the form of a signal conduit, such as an optical fiber.

[0117] The combination of filtering in the main scanning direction performed in the circuit device incorporated into the electron optical column and filtering in the sub-scanning direction performed in the remote image analysis device is equivalent to the two-dimensional noise filter discussed above. By making the filter size (or dimension) of the denoising filter in the sub-scanning direction the same as the effective filter size in the main scanning direction, an effective square filter is obtained. That is, after filtering by the upstream filter and the downstream filter, the data values ​​are the same as the data values ​​filtered in one step using a square filter. That is, the resulting effective size of the filter size is approximately the same in both directions, for example on the defect scale being evaluated, such as nanometers.

[0118] The comparator 502 compares the filtered signal output by the denoising filter 501 with the reference image provided by the reference image generator 503 to detect the above-mentioned defect candidates.

[0119] Due to the use of non-square pixels (which may be rectangular), it may be desirable to store the reference image at a higher resolution than the sample image, such as for die-to-database mode. The sample image may be aligned with the higher resolution reference image. The higher resolution reference image may then be downsampled to the same resolution (and pixel shape) as the sample image. Downsampling may be performed by a variety of suitable techniques, including averaging, pixel skipping, interpolation, etc. Fig.11 An arrangement to achieve this is shown in .

[0120] like Fig.11As depicted, the comparator 502 includes an alignment unit 5021. The alignment unit 5021 determines the shift between the sample image and the high-resolution reference image, for example by determining a pixel shift value that minimizes the difference between the sample image and the reference image (e.g., between the sample reference data and the reference pixel data). The alignment can be considered as aligning the sample image (or sample reference data) and the high-resolution reference image (or reference pixel data). Since the sample image and the reference image are of the same or approximately the same size, only one sub-region or a few sub-regions of the corresponding image can be used to determine the pixel shift value. The sub-region can be predetermined or randomly selected. Based on the pixel shift value, the downsampling unit 5022 generates a low-resolution reference image for pixel-by-pixel comparison of at least the aligned portion with the sample image by the comparator 502, for example, by averaging the aligned reference pixel data. (The low-resolution reference can be the downsampled reference pixel data). In the case where the sub-pixel shift is different from (or not equal to) an integer number of pixels, the downsampling unit may include an interpolation function, for example, as an interpolation unit. Additionally and / or alternatively, the alignment unit has an interpolation function, for example, including an interpolation unit. Desirably, the down sampling unit applies the same denoising filter to the high resolution reference image as applied to the sample image. Sub-pixel shifting and filters can be combined into a single processing step, such as convolution, to reduce the number of computational steps. It should be noted that alignment can include changing the aspect ratio of the reference pixel data and / or the sample image data. This may help ensure that the sample image (or sample image data) and the reference image (reference pixel data) are the same size. Additionally and / or alternatively, the comparator may include a shift module. The shift module generates reference pixel data by shifting the sample image data by a multiple of its pixel size.

[0121] Note that, for example in die-to-die mode, alignment can align at least portions of the image or different portions of the sample image with each other relative to a repetition period of the repeating pattern. The repetition period can be equal to an integer number of pixels in the elongation direction or an integer number of pixels in the main scanning direction (or reduction direction or transverse direction).

[0122] It is particularly advantageous to use high resolution reference images, where the reference images are derived from design data (e.g., GDSII data) for inspection by simulation (e.g., in die to database mode). High resolution reference data (e.g., including reference pixel data) may also be obtained by scanning one or more (e.g., two or three) reference areas of a sample (e.g., a die) at a higher resolution (e.g., using square pixels) than the rest of the sample. Such a high resolution scan may be performed on some samples (e.g., one sample) in a batch of samples. Typically, at least two reference images are used in a comparator with sample images, e.g., in die to die mode, to reduce the risk that an apparent defect in a sample image is a defect in a reference image rather than in the sample image. However, reviewing a sample image using a single high resolution scan may provide results with an acceptable confidence level, provided, for example, that the high resolution scan is of a sample surface that is known to have a low or even zero probability of defects.

[0123] In array mode, where the sample image is compared to a shifted version of itself, the desired shift amount is equal to both an integer number of pixels of the inspected pattern and an integer multiple of the unit cell size, i.e., a common multiple of the pixel size and the unit cell size. Although it can be expected that increasing the pixel size will reduce the flexibility of selecting the shift amount, the present invention is able to compromise between the optimal pixel size for noise reduction and the shift amount for increased flexibility.

[0124] An advantage of the invention is that by varying the pixel size, a desired data rate for sample data sent from the detector to associated circuitry, a remote image analysis device and / or remote further processing of a sample data set or image can be provided. The pixel size in the main scanning direction is determined by the sampling rate of the analog-to-digital converter and the scanning speed of the sample. The pixel size in the secondary scanning direction is determined by the step size of the sample shift between scan lines. In the case of a limited bandwidth of the communication link between the detector and the remote image analysis device, the pixel size can be selected to optimally utilize this bandwidth.

[0125] It is noted that, unless otherwise specified, references to pixels may be considered as references to rectangular pixels. While the above description relates primarily to rectangular pixels, it is emphasized that pixels need not be rectangular and may have other shapes with aspect ratios greater than 1 (i.e., one dimension is greater than another). For example, if the scan directions are not orthogonal, it may be convenient to use pixels representing parallelogram-shaped areas whose sides are parallel to the respective scan directions. It will also be appreciated that the area in the output image represented by a pixel may not correspond exactly to the sample area where signal electrons were sampled to produce that pixel, for example if the beam spot size is different from the spacing between scan lines.

[0126] References to upper and lower, upward and downward, above and below, etc. should be understood to refer to directions parallel (typically but not always vertical) to the beam upstream and beam downstream directions of the electron beam or beams impinging on the sample 208. Thus, references to beam upstream and beam downstream are intended to refer to directions about the beam path that are independent of any present gravitational field.

[0127] The embodiments described herein may take the form of a series of aperture arrays or electron optical elements that are 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 beam path before the beam-limiting aperture array to the sample) may be electrostatic and / or may be in the form of an aperture array or a plate array. In some arrangements, one or more electron optical elements are manufactured as a micro-electromechanical system (MEMS) (i.e., using MEMS manufacturing technology). The electron optical element may have a magnetic element and an electrostatic element. For example, a composite array lens may have a macroscopic magnetic lens that covers a multi-beam path, wherein an upper pole plate and a lower pole plate are within the magnetic lens and arranged along the multi-beam path. In the pole plate may be an aperture array 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.

[0128] 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 understood to refer to the positioning of the corresponding element along the beam path or beamlet path. References to optics are understood to refer to electron optics.

[0129] An evaluation tool or evaluation system according to the present disclosure may include a device for qualitatively evaluating a sample (e.g., pass / fail), a device for quantitatively measuring a sample (e.g., the size of a feature), or a device for generating a mapped image of a sample. 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., subway inspection tools).

[0130] Reference to the system of parts or parts or elements that can be controlled to manipulate charged particle beam in some way includes that a controller or control system or control unit is configured to control parts to manipulate charged particle beam in the described manner, and optionally other controllers or devices (such as voltage supplies) are used to control parts to manipulate charged particle beam in this manner. For example, under the control of a controller or control system or control unit, a voltage supply can be electrically connected to one or more parts, so that electric potential is applied to parts, such as electrodes applied to control lens arrays and object lens arrays. Using one or more controllers, control systems or control units to control the actuation of parts, such as stages, actuable parts can be controllable to actuate and therefore move relative to another part such as beam path.

[0131] The method of the present invention can be performed by a computer system including one or more computers. The computer for implementing 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 be applicable to the use of a specific processor type. Some steps of the method of the present invention relate to parallel computing, which is easy to implement on a processor (such as a GPU) capable of parallel computing.

[0132] The computer for implementing the present invention may be physical or virtual. The computer for implementing the present invention may be a server, a client or a workstation. Multiple computers for implementing the present invention may be distributed and interconnected via a local area network (LAN) or a wide area network (WAN). The result 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 implemented in a non-transient computer-readable storage medium that stores instructions for performing the method of the present invention. The present invention may be implemented in a computer system that includes one or more processors and a memory or storage device storing instructions for performing the method of the present invention.

[0133] The functionality provided by a computer and a processor (such as a controller or a control system or a control unit) can be computer-implemented.Any suitable combination of elements can be used to provide the required functionality, including, for example, CPU, RAM, SSD, mainboard, network connection, firmware, software and / or other elements known in the art that allow the required computing operations to be performed.Required computing operations can be defined by one or more computer programs.This computer program can take the form of multiple computer programs, which can be distributed by different processors, such as implementations.One or more computer programs can be provided in the form of a medium (optionally non-transient medium) storing computer-readable instructions.When computer-readable instructions are read by a computer, the computer performs the required method steps.The computer can be composed of an independent unit or a distributed computing system, and the distributed computing system has a plurality of different computers connected to each other via a network.

[0134] The term "image" as used herein is intended to refer to any data structure of values, 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" may be used to describe such a data structure. An image may comprise 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. An image may be stored in a computer-readable storage medium in any convenient format.

[0135] 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 in view 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.

[0136] The following terms are provided:

[0137] Item 1. A charged particle evaluation device for detecting defects in a sample by scanning a charged particle beam across the sample; the device comprising: a detector unit configured to output a digital detection signal of a pixel value in response to a signal particle incident from the sample, the pixel value representing an elongated pixel.

[0138] Clause 2. The charged-particle evaluation apparatus of Clause 1, wherein the detector unit comprises: a detector configured to generate an analog signal in response to charged particles incident thereon from the sample.

[0139] Clause 3. The charged particle evaluation apparatus of clause 2, wherein the detector unit further comprises: a filter configured to filter the analog signal to generate a filtered analog signal.

[0140] Clause 4. A charged particle assessment apparatus according to clause 3, wherein the filter comprises an integrator, optionally an amplifier with capacitive feedback, such as a transimpedance amplifier.

[0141] Clause 5. A charged particle evaluation device according to clause 3 or 4, wherein the filter is a low pass filter.

[0142] Clause 6. A charged particle evaluation apparatus according to clause 3, 4 or 5, wherein the filter applies a uniform filter or a Gaussian filter.

[0143] Clause 7. A charged particle evaluation apparatus according to any one of clauses 3 to 6, wherein the detector unit comprises: an analog-to-digital converter configured to convert the filtered analog signal into a series of pixel values.

[0144] Clause 8. A charged particle evaluation apparatus according to any one of the preceding clauses, comprising: a charged particle device configured to direct a charged particle beam toward the sample; and a stage configured to support the sample, the charged particle device and the stage being configured to scan the surface of the sample using the charged particle beam.

[0145] Clause 9. The charged particle evaluation apparatus according to clause 8, wherein the charged particle device and the stage are configured to perform a scan having a main scanning direction and a sub-scanning direction, the sub-scanning direction having an orientation different from the main scanning direction.

[0146] Clause 10. The charged particle evaluation apparatus according to Clause 9, wherein the scanning in the main scanning direction is faster on the surface of the sample than in the sub-scanning direction.

[0147] Clause 11. A charged particle evaluation apparatus according to clause 9 or 10, wherein the charged particle device is configured to scan the charged particle beam over the sample at least in the main scanning direction, optionally in the main scanning direction and in a sub-scanning direction.

[0148] Clause 12. The charged particle evaluation apparatus according to clause 9, 10 or 11, wherein the stage is configured to move relative to the charged particle device to scan the charged particle beam over the sample in the sub-scanning direction.

[0149] Clause 13. The charged particle evaluation apparatus according to any one of clauses 9 to 12, wherein the elongated pixels are elongated in the main scanning direction.

[0150] Clause 14. A charged particle evaluation device according to any of the preceding clauses, wherein the detector is an array of detector elements, the charged particle beam is desirably a plurality of charged particle sub-beams, each sub-beam being associated with a detector element in the array of detector elements, and the deflector is desirably a deflector array, each sub-beam being associated with a deflector element of the deflector array.

[0151] Clause 15. A charged particle evaluation device according to any of the preceding clauses, wherein the aspect ratio of the pixels is between 1 and 4, desirably between 1.5 and 4, more desirably between 2 and 3, or even equal to or greater than 2.

[0152] Clause 16. A charged particle evaluation apparatus according to any of the preceding clauses, wherein the pixels have an integer aspect ratio.

[0153] Clause 17. A charged particle evaluation apparatus according to any of the preceding clauses, having a plurality of charged particle devices, for example arranged in an array, configured to direct respective charged particle beams towards a sample.

[0154] Clause 18. A charged particle evaluation apparatus according to any preceding clause, further comprising a controller configured to process the digital detection signal of pixel values.

[0155] Item 19. An image analysis device comprising: an interface module configured to receive sample image data, the sample image data comprising pixel values ​​representing an image of a sample obtained by a charged particle evaluation device, wherein each pixel value represents an elongated pixel; and a downstream filter module configured to apply a denoising filter to generate a filtered signal.

[0156] Clause 20. An image analysis device according to Clause 19, wherein the denoising filter is a uniform filter or a Gaussian filter.

[0157] Clause 21. An image analysis device according to clause 19 or 20, wherein the denoising filter comprises a kernel extending in an additional direction different from the longitudinal direction of the elongated pixels, desirably the additional direction being orthogonal to the longitudinal direction.

[0158] Clause 22. An image analysis device according to clause 19, 20 or 21, further comprising a comparator configured to compare the filtered signal with reference data.

[0159] Clause 23. An image analysis device according to Clause 22, wherein the reference data includes reference pixel data, the resolution of the reference pixel data is higher than the resolution of the sample image data, and the comparator includes: an alignment unit configured to align the reference pixel data with the sample image data and generate aligned reference pixel data; and a downsampling unit configured to average the aligned reference pixel data to generate a low-resolution reference image having the same resolution as the sample image data.

[0160] Clause 24. The image analysis device according to Clause 23 further includes: a comparator configured to compare the pixel data of the sample image data with the corresponding down-sampled reference pixel data.

[0161] Clause 25. An image analysis device according to clause 23 or 24, wherein the down-sampling unit comprises a second denoising filter, such as a uniform filter or a Gaussian filter, to generate the down-sampled reference pixel data.

[0162] Clause 26. An image analysis device according to clause 23, 24 or 25, wherein the alignment unit includes an interpolation unit configured to: shift the reference pixel data by an amount equal to or different from an integer multiple of the pixel size of the reference pixel data to generate aligned reference pixel data; and / or change the aspect ratio of the reference pixel data and / or the sample image data.

[0163] Clause 27. An image analysis device according to any one of Clauses 23 to 26, wherein a resolution of the reference pixel data is higher than a resolution of the sample image data in the longitudinal direction of the pixel.

[0164] Clause 28. The image analysis device of any one of clauses 22 to 27, wherein the reference pixel data is derived from design data.

[0165] Clause 29. The image analysis device according to any one of clauses 22 to 27 further includes a shift module configured to generate the reference pixel data by shifting the sample image data by a multiple of the pixel size of the sample image data.

[0166] Clause 30. An image analysis device according to any one of clauses 22 to 29, wherein the reference data represents a reference image that is at least a portion of the size of the sample image data, and it is desired that the reference image and the portion of the sample image data have a repeating pattern, preferably have the same repeating pattern.

[0167] Clause 31. A charged particle evaluation system comprising: a charged particle evaluation device according to any one of clauses 1 to 18; an image analysis device according to any one of clauses 19 to 30; and a communication channel configured to communicate the series of pixel values ​​from the charged particle evaluation device to the image analysis device.

[0168] Item 32. A computer-readable storage medium storing sample image data, the sample image data comprising pixel values ​​representing an image of a sample obtained by a charged particle evaluation system, wherein each pixel value represents an elongated pixel, desirably each pixel value has a contrast value representing a contrast within a contrast range, wherein the relative contrast of adjacent elongated pixels exceeds a contrast difference indicating a defect, desirably the pixel values ​​are configured to be capable of being rendered as pixels, for example, in an image arranged in a two-dimensional array, desirably the two-dimensional array is a grid, the pixels desirably having unequal sizes and desirably being rectangular.

[0169] Item 33. An image of a sample surface for detecting defects in the sample, the image comprising a plurality of elongated pixels each representing a portion of the sample surface and each having a different contrast, wherein the relative contrast of the elongated pixels indicates defects, the elongated pixels are desirably arranged in a two-dimensional array, desirably the two-dimensional array is a grid, the elongated pixels desirably have unequal sizes, desirably are rectangular.

[0170] Item 34. A method for performing array pattern data processing using at least an image of a sample surface having a repeating pattern, the method comprising: generating at least one image of a sample surface having a repeating pattern, for example using a detector unit, the image having elongated pixels, the elongated pixels having an elongated direction and a reduced or lateral direction; and aligning at least a portion of the at least one image relative to a repetition period of the repeating pattern to be equal to an integer number of pixels in the elongated direction or an integer number of pixels in the reduced or lateral direction; wherein the alignment comprises changing the aspect ratio of the pixels.

[0171] Clause 35. The data processing method according to Clause 35 further includes comparing the pixels of the aligned portion.

[0172] Clause 36. The data processing method according to Clause 34 further includes identifying pixels that indicate differences derived from comparing the pixels.

[0173] Clause 37. The data processing method according to Clause 36, further comprising identifying defects from the pixels identified as indicating differences.

[0174] Clause 38. A data processing method according to any one of clauses 34 to 37, wherein the elongated pixels are rectangular pixels.

[0175] Clause 39. The data processing method according to any one of clauses 34 to 38, wherein the elongated direction is a first direction and / or a fast scanning direction.

[0176] Clause 40. A data processing method according to any one of clauses 34 to 39, further comprising combining the aligned reference pixel data to generate downsampled reference pixel data having the same resolution as the at least one image.

[0177] Item 41. A data processing method in a die-to-database mode for comparing detection data with reference data, generating a detection data map of a sample surface, for example using a detector unit, wherein the detection data has elongated detection pixels, wherein the elongated detection pixels have a longitudinal direction and a lateral direction: shifting the reference data to form a reference data map corresponding to the detection data map; and processing the reference data map, including combining pixels of the reference data map in the longitudinal direction of the elongated detection pixels to derive a processed reference data map, wherein the processed reference data map has the same pixel size as the elongated detection pixels, and the processed reference data map is configured to apply the same further processing as the detection data map.

[0178] Clause 42. The data processing method according to Clause 41, wherein shifting comprises shifting the reference data by an amount equal to or different from an integer multiple of the size of the pixel of the reference data.

[0179] Clause 43. The data processing method according to clause 41 or 42 further comprises comparing the pixels of the detected data map with the pixels of the reference data map.

[0180] Clause 44. The data processing method according to Clause 43, further comprising identifying pixels indicating differences derived from comparing the pixels.

[0181] Clause 45. The data processing method according to Clause 44, further comprising identifying defects from the pixels identified as indicating differences.

[0182] Clause 46. A data processing method according to any one of clauses 41 to 45, wherein the elongated pixels are rectangular pixels.

[0183] Clause 47. The data processing method according to any one of clauses 41 to 46, wherein the elongated direction is a first direction and / or a fast scanning direction.

[0184] Clause 48. An image analysis method comprising: receiving sample image data, the sample image data comprising pixel values ​​representing an image of a sample obtained by a charged particle evaluation method, wherein each pixel value represents an elongated pixel; and applying a denoising filter to generate a filtered signal.

[0185] Clause 49. The image analysis method according to Clause 48, wherein the denoising filter is a uniform filter or a Gaussian filter.

[0186] Clause 50. An image analysis method according to clause 48 or 49, wherein the denoising filter comprises a kernel extending in an additional direction different from the longitudinal direction of the pixels, desirably the additional direction being orthogonal to the longitudinal direction.

[0187] Clause 51. The image analysis method of clause 48, 49 or 50, further comprising comparing the filtered signal with reference data.

[0188] Item 52. An image analysis method according to Item 51, wherein the reference data includes reference pixel data having a higher resolution than the sample image data, and the comparison includes: aligning the reference pixel data with the sample image data and generating aligned reference pixel data; and downsampling the aligned reference pixel data to generate downsampled reference pixel data having the same resolution as the sample image data; and comparing the pixel data of the sample image data with the corresponding downsampled reference pixel data.

[0189] Clause 53. An image analysis method according to clause 52, wherein the downsampling comprises applying a second denoising filter, such as a uniform filter or a Gaussian filter, to generate averaged reference pixel data.

[0190] Clause 54. An image analysis method according to clause 52 or 53, wherein the alignment comprises shifting the reference pixel data by an amount equal to or different from an integer multiple of the size of the pixel of the reference pixel data to generate aligned reference pixel data.

[0191] Clause 55. An image analysis method according to clauses 52, 53, and 54, wherein the alignment includes changing the aspect ratio of the reference pixel data and / or the sample image data.

[0192] Clause 56. An image analysis method according to any one of Clauses 52 to 55, wherein in the longitudinal direction of the pixel, the resolution of the reference pixel data is higher than that of the sample image data.

[0193] Clause 57. An image analysis method according to any one of clauses 48 to 56, wherein the reference pixel data is derived from design data.

[0194] Clause 58. The image analysis method according to any one of clauses 48 to 57 further comprises generating the reference pixel data by shifting the sample image data by a multiple of its pixel size.

[0195] Clause 59. An image analysis method according to any one of clauses 48 to 58, wherein the reference data represents a reference image that is at least a portion of the size of the sample image data, and it is desired that the reference image and the portion of the sample image data have a repeating pattern, preferably the same repeating pattern.

[0196] Item 60. A detector unit for a charged particle evaluation apparatus for detecting defects in a sample by scanning a charged particle beam across the sample, the detector unit being configured to output a digital detection signal of pixel values ​​representing elongated pixels in response to signal particles incident from the sample.

[0197] Clause 61. The detector unit of clause 60, further comprising: a detector element configured to generate an analog signal in response to incident charged particles; and a filter configured to filter the analog signal to generate a filtered analog signal.

[0198] Clause 62. The detector unit of clause 61, wherein the filter comprises an integrator, optionally an amplifier with capacitive feedback, such as a transimpedance amplifier.

[0199] Clause 63. The detector unit of clause 61 or 62, wherein the filter is a low pass filter.

[0200] Clause 64. A detector unit according to clause 61, 62 or 63, wherein the filter applies a uniform filter or a Gaussian filter.

[0201] Clause 65. The detector unit of any one of clauses 61 to 64, further comprising: an analog-to-digital converter configured to convert the filtered analog signal into a series of pixel values.

[0202] Item 66. A detector unit of a charged particle evaluation device for detecting defects in a sample by scanning a charged particle beam across the sample and outputting a detection signal representing a pixel value of an elongated pixel, the detector unit comprising a detector element for generating a detector signal in response to incident charged particles; and an integrator configured to filter the detector signal to generate an integrated detection signal, wherein the integrator is configured to filter the detector signal in an elongated direction corresponding to an elongated dimension of the pixel.

[0203] Clause 67. The detector unit of Clause 66, wherein the integrator comprises an amplifier with capacitive feedback, such as a transimpedance amplifier.

[0204] Clause 68. The detector unit of clause 66 or 67, further comprising: an analog-to-digital converter configured to convert the integrated detection signal into a series of pixel values.

[0205] Item 69. A detector unit of a charged particle evaluation device, for detecting defects in a sample by scanning a charged particle beam across the sample, the detector unit being configured to output a digital detection signal of a pixel value in response to a signal particle incident from the sample, the detector unit comprising: a detector element, configured to generate a detector signal in response to the incident charged particles; and a transimpedance amplifier with capacitive feedback, configured to amplify the detector signal.

[0206] Clause 70. The detector unit of clause 69, further comprising: an analog-to-digital converter configured to convert an analog signal output by the transimpedance amplifier into a series of pixel values.

[0207] Clause 71. A charged particle evaluation apparatus for detecting defects in a sample by scanning a charged particle beam across the sample; the apparatus comprising: a detector unit according to any one of clauses 60 to 70.

[0208] Item 72. A charged particle evaluation device for detecting defects in a sample by scanning a charged particle beam across the sample; the device comprising: a charged particle device configured to direct a charged particle beam toward the sample; a detector unit configured to output a digital detection signal of a pixel value in response to a signal particle incident from the sample, the pixel value representing an elongated pixel having a longitudinal direction and a lateral direction; and a stage configured to support the sample; wherein: the charged particle device and the stage are configured to scan the surface of the sample with the charged particle beam; the stage is configured to move in the sub-scanning direction corresponding to the lateral direction when the surface of the sample is scanned with the charged particle beam.

[0209] Item 73. A charged particle evaluation device for detecting defects in a sample by scanning a charged particle beam on the sample; the device comprising: a charged particle device configured to direct a charged particle beam toward the sample, preferably the charged particle device includes a deflector; a detector unit configured to output a digital detection signal of a pixel value in response to a signal particle incident from the sample, the pixel value representing an elongated pixel having a longitudinal direction and a transverse direction; and a stage configured to support the sample, the charged particle device and the stage being configured to scan the surface of the sample with the charged particle beam; wherein: the charged particle device (preferably the deflector) is configured to direct the beam in a main scanning direction corresponding to the longitudinal direction, and / or in a sub-scanning direction corresponding to the transverse direction when the surface of the sample is scanned with the charged particle beam, preferably the main scanning direction and the sub-scanning direction having a different orientation.

Claims

1. A charged particle evaluation apparatus for detecting defects in a sample by scanning a charged particle beam across the sample; the apparatus comprising: A detector unit is configured to output a digital detection signal of a pixel value in response to a signal particle incident from the sample, the pixel value representing the elongated pixel.

2. The charged particle evaluation device according to claim 1, wherein the detector unit comprises: A detector is configured to generate an analog signal in response to charged particles incident on the sample from the sample.

3. The charged particle evaluation device according to claim 2, wherein the detector unit further comprises: A filter is configured to filter the analog signal to generate a filtered analog signal.

4. A charged particle assessment apparatus according to claim 3, wherein the filter comprises an integrator, optionally an amplifier with capacitive feedback, such as a transimpedance amplifier. 5 . The charged particle evaluation device according to claim 3 , wherein the filter is a low-pass filter; and / or wherein the filter applies a uniform filter or a Gaussian filter.

6. The charged particle evaluation device according to any one of claims 3 to 5, wherein the detector unit comprises: An analog-to-digital converter is configured to convert the filtered analog signal into a series of pixel values.

7. A charged particle evaluation device according to any one of the preceding claims, comprising: a charged particle device configured to direct a charged particle beam toward the sample; as well as A stage is configured to support the sample, and the charged particle device and the stage are configured to scan the surface of the sample with the charged particle beam. 8 . The charged particle evaluation apparatus according to claim 7 , wherein the charged particle device and the stage are configured to perform scanning having a main scanning direction and a sub scanning direction having an orientation different from that of the main scanning direction. 9 . The charged particle evaluation apparatus according to claim 8 , wherein the scanning in the main scanning direction is faster on the surface of the sample than the sub-scanning direction.

10. A charged particle evaluation apparatus according to claim 8 or 9, wherein the charged particle device is configured to scan the charged particle beam across the sample at least in the main scanning direction, optionally in the main scanning direction and the sub-scanning direction; and / or wherein the stage is configured to move relative to the charged particle device to scan the charged particle beam on the sample in the sub-scanning direction. 11 . The charged particle evaluation apparatus according to claim 8 , wherein the elongated pixel is elongated in the main scanning direction.

12. A charged particle evaluation device according to any of the preceding claims, wherein the detector is an array of detector elements, the charged particle beam is desirably a plurality of charged particle sub-beams, each sub-beam being associated with a detector element in the array of detector elements, and the deflector is desirably a deflector array, each sub-beam being associated with a deflector element of the deflector array.

13. A charged particle evaluation device according to any one of the preceding claims, wherein the aspect ratio of the pixels is between 1 and 4, desirably between 1.5 and 4, more desirably between 2 and 3, or even equal to or greater than 2.

14. A charged particle evaluation apparatus according to any preceding claim, having a plurality of charged particle devices, for example arranged in an array, configured to direct respective charged particle beams towards a sample.

15. A charged particle evaluation apparatus according to any one of the preceding claims, further comprising a controller configured to process the digital detection signal of pixel values.

Images