Patent Application
20250087444
The embodiments provided herein generally relate to data processing devices and methods, especially for use with or in charged particle assessment systems and methods of operating charged particle assessment systems.
When manufacturing semiconductor integrated circuit (IC) chips, undesired pattern defects, as a consequence of, for example, optical effects and incidental particles, inevitably occur on a substrate (i.e. wafer) or a mask during the fabrication processes, thereby reducing the yield. Monitoring the extent of the undesired pattern defects is therefore an important process in the manufacture of IC chips. More generally, the inspection and/or measurement of a surface of a substrate, or other object/material, is an important process during and/or after its manufacture.
Pattern inspection apparatuses with a charged particle beam have been used to inspect objects, which may be referred to as samples, for example to detect pattern defects. These apparatuses typically use electron microscopy techniques, such as a scanning electron microscope (SEM). In a SEM, a primary electron beam of electrons at a relatively high energy is targeted with a final deceleration step in order to land on a sample at a relatively low landing energy. The beam of electrons is focused as a probing spot on the sample. The interactions between the material structure at the probing spot and the landing electrons from the beam of electrons cause signal electrons to be emitted from the surface, such as secondary electrons, backscattered electrons or Auger electrons. The signal electrons may be emitted from the material structure of the sample. By scanning the primary electron beam as the probing spot over the sample surface, signal electrons can be emitted across the surface of the sample. By collecting these emitted signal electrons from the sample surface, a pattern inspection apparatus may obtain an image representing characteristics of the material structure of the surface of the sample.
When a pattern inspection apparatus is used to detect defects on samples at a high throughput, a very large amount of image data is generated and must be processed to detect defects. In particular it is desirable to reduce noise from image data. U.S. Pat. No. 8,712,184 B1 and U.S. Pat. No. 9,436,985 B1 describe methods of reducing noise or improving signal-to-noise ratio in images obtained from scanning electron microscopes. In some cases, the rate of data generation can be an undesirable limit on the throughput of a pattern inspection apparatus, e.g. because the transmission rate from the detector to data processing equipment is limited.
It is an object of the present disclosure to provide embodiments that avoid or ameliorate data transmission limits on the throughput of charged particle assessment apparatus used to detect defects.
According to some embodiments of the present disclosure, there is provided a charged particle assessment apparatus for detecting defects in samples by scanning a charged particle beam across a sample; the apparatus comprising: a detector unit configured to output a digital detection signal of pixel values in response to signal particles incident from the sample, the pixel values representing elongate pixels.
According to some embodiments of the present disclosure, there is provided an image analysis device comprising: an input module or interface module configured to receive sample image data comprising pixel values representing an image of a sample obtained by a charged particle assessment device, wherein each pixel value represents a pixel that is elongate; and a de-noising module or downstream filter configured to apply a de-noising filter to generate a filtered signal.
According to some embodiments of the present disclosure, there is provided a charged particle assessment system comprising: a charged particle assessment apparatus as described above; an image analysis device as described above; and a communication channel configured to communicate the series of pixel values from the charged particle assessment device to the image analysis device.
According to some embodiments of the present disclosure, there is provided a computer readable storage medium storing sample image data comprising pixel values representing an image of a sample obtained by a charged particle assessment system, wherein each pixel value represents a pixel that is elongate, desirably each pixel value having a contrast value representing a contrast in a contrast range, wherein the relative contrasts of adjacent elongate pixels exceeding a contrast different being indicative of 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 having unequal dimensions, desirably being rectangular.
According to some embodiments of the present disclosure, there is provided an image of a surface of a sample for detecting defects in the sample, the image comprising a plurality of elongate pixels each representing a portion of the sample surface and each having a different contrast, wherein the relative contrast of the elongate pixels being indicative of a defect, desirably the elongate pixels arranged in a two dimensional array, desirably the two dimensional array is a grid, the elongate pixels desirably being having unequal dimensions, desirably being rectangular.
According to some embodiments of the present disclosure, there is provided a method of data processing for an array mode using at least an image of a surface of a sample having a repeating pattern, the method comprising: generating at least one image of a surface of a sample having a repeating pattern, e.g. using/in a detector unit, the image having elongate pixels having an elongate direction and a reduced direction; and aligning at least portions of the at least one image with respect to a repeating period of the pattern, to be equal to a whole number of pixels in the elongate direction or a whole number of pixels in the reduced direction; wherein the aligning comprises changing the aspect ratio of the pixels.
According to some embodiments of the present disclosure, there is provided a method of data processing for a die to database mode for comparing a detection data with reference data, comprising: generating detection data map of a sample surface, e.g. using a detector unit, the detection data having elongate detected pixels with an elongate direction and a reduced direction: shifting 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 elongate detected pixels to derive a processed reference data map, the processed reference data map having the same size of pixel as the elongate detected pixels and the processed reference data map configured to have the same further processing applied as the detection data map.
According to some embodiments of the present disclosure, there is provided an image analysis method comprising: receiving sample image data comprising pixel values representing an image of a sample obtained by a charged particle assessment method, wherein each pixel value represents a pixel that is elongate; applying a de-noising filter to generate a filtered signal.
According to some embodiments of the present disclosure, there is provided an image analysis method as described above wherein the reference data comprises reference pixel data that is higher resolution than the sample image data and the comparing comprises: aligning the reference pixel data to the sample image data and generate aligned reference pixel data; and down-sampling the aligned reference pixel data to generate down-sampling reference pixel data having the same resolution as the sample image data; and comparing pixel data of the sample image data to corresponding down-sampled reference pixel data.
According to some embodiments of the present disclosure, there is provided a detector unit for a charged particle assessment apparatus for detecting defects in samples by scanning a charged particle beam across a sample, the 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 elongate pixels.
According to some embodiments of the present disclosure, there is provided a detector unit for a charged particle assessment apparatus for detecting defects in samples by scanning a charged particle beam across a sample and outputting a detection signal of pixel values representing elongate pixels, the detector unit comprising a detector element to generate 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 elongate direction corresponding to an elongate dimension of the pixel.
According to some embodiments of the present disclosure, there is provided a detector unit for a charged particle assessment apparatus for detecting defects in samples by scanning a charged particle beam across a sample, the detector unit configured to output a digital detection signal of pixel values in response to signal particles incident from a sample, the detector unit, comprising: a detector element configured to generate a detector signal in response to incident charged particles; and a trans-impedance amplifier with a capacitive feedback configured to amplify the detector signal.
According to some embodiments of the present disclosure, there is provided a charged particle assessment apparatus for detecting defects in samples by scanning a charged particle beam across a sample; the apparatus comprising: a charged particle device configured to direct a charged particle beam toward a sample; a detector unit configured to output a digital detection signal of pixel values in response to signal particles incident from the sample, the pixel values representing elongate pixels having a longitudinal direction and a transverse direction; and a stage configured to support a sample; wherein: the charged particle device and the stage are configured to scan a surface of the sample with the charged particle beam; the stage is configured to move in a sub-scanning direction when the surface of the sample is scanned with the charged particle beam, the sub-scanning direction corresponding to the transverse direction.
According to some embodiments of the present disclosure, there is provided a charged particle assessment apparatus for detecting defects in samples by scanning a charged particle beam across a sample; the apparatus comprising: a charged particle device configured to direct a charged particle beam toward a sample, desirably the charged particle device comprising a deflector; a detector unit configured to output a digital detection signal of pixel values in response to signal particles incident from the sample, the pixel values representing elongate pixels having a longitudinal direction and a transverse direction; and a stage configured to support a sample, the charged particle device and the stage being configured to scan a surface of the sample with the charged particle beam; wherein: the charged particle device (desirably the deflector) is configured to direct the beam in a main scanning direction when the surface of the sample is scanned with the charged particle beam, the main scanning direction corresponding to the longitudinal direction, and/or in a sub-scanning direction corresponding to the transverse direction, desirably the main scanning direction has a different orientation from the sub-scanning direction.
The above and other aspects of the present disclosure will become more apparent from the description of exemplary embodiments, taken in conjunction with the accompanying drawings.
The schematic diagrams and views show the components described below. However, the components depicted in the figures are not to scale.
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 in which the same numbers in different drawings represent the same or similar elements unless otherwise represented. The implementations set forth in the following description of exemplary embodiments do not represent all implementations consistent with the invention. Instead, they are merely examples of apparatuses and methods consistent with aspects related to the invention as recited in the appended claims.
The enhanced computing power of electronic devices, which reduces the physical size of the devices, can be accomplished by significantly increasing the packing density of circuit components such as transistors, capacitors, diodes, etc. on an IC chip. This has been enabled by increased resolution enabling yet smaller structures to be made. For example, an IC chip of a smart phone. which is the size of a thumbnail and available in, or earlier than, 2019, may include over 2 billion transistors, the size of each transistor being less than 1/1000th of a human hair. Thus, it is not surprising that semiconductor IC manufacturing is a complex and time-consuming process, with hundreds of individual steps. Errors in even one step have the potential to dramatically affect the functioning of the final product. The goal of the manufacturing process is to improve the overall yield of the process. For example, to obtain a 75% yield for a 50-step process (where a step can indicate the number of layers formed on a wafer), each individual step must have a yield greater than 99.4%. If each individual step had a yield of 95%, the overall process yield would be as low as 7%.
While high process yield is desirable in an IC chip manufacturing facility, maintaining a high substrate (i.e. wafer) throughput, defined as the number of substrates processed per hour, is also essential. High process yield and high substrate throughput can be impacted by the presence of a defect. This is especially true if operator intervention is required for reviewing the defects. Thus, high throughput detection and identification of micro and nano-scale defects by inspection devices (such as a Scanning Electron Microscope (‘SEM’)) is essential for maintaining high yield and low cost.
An example of a SEM comprises a scanning device and a detector apparatus. The scanning device comprises an illumination apparatus that comprises an electron source, for generating primary electrons (or charged particles), and a projection apparatus for scanning a sample, such as a substrate, with one or more focused beams (or a plurality of beams) of primary electrons. The plurality of beams may be arranged as a multi-beam. The plurality of beams may have a multi-beam arrangement (which may have the form of a grid) which may be directed along a multi-beam path towards a sample. Together at least the illumination apparatus, or illumination system, and the projection apparatus, or projection system, may be referred to together as the electron-optical system or apparatus. The primary electrons interact with the sample and generate secondary electrons. The detection apparatus captures the secondary electrons from the sample as the sample is scanned so that the SEM can create an image of the scanned area of the sample. For high throughput inspection, some of the inspection apparatuses use multiple focused beams, i.e. a multi-beam, of primary electrons. The component beams of the multi-beam may be referred to as sub-beams or beamlets. A multi-beam can scan different parts of a sample simultaneously. A multi-beam inspection apparatus can therefore inspect a sample at a much higher speed than a single-beam inspection apparatus.
An implementation of a known multi-beam inspection apparatus is described below.
While the description and drawings are directed to an electron-optical system, it is appreciated that the embodiments are not used to limit the present disclosure to specific charged particles. References to electrons throughout the present document may therefore be more generally be considered to be references to charged particles, with the charged particles not necessarily being electrons.
Reference is now made to
The EFEM 30 includes a first loading port 30a and a second loading port 30b. The EFEM 30 may include additional loading port(s). The first loading port 30a and the second loading port 30b may, for example, receive substrate front opening unified pods (FOUPs) that contain substrates (e.g., semiconductor substrates or substrates made of other material(s)) or samples to be inspected (substrates, wafers and samples are collectively referred to as “samples” hereafter). One or more robot arms (not shown) in the EFEM 30 transport the samples to the load lock chamber 20.
The load lock chamber 20 is used to remove the gas around a sample. This creates a vacuum that is a local gas pressure lower than the pressure in the surrounding environment. The load lock chamber 20 may be connected to a load lock vacuum pump system (not shown), which removes gas particles in the load lock chamber 20. The operation of the load lock vacuum pump system enables the load lock chamber to reach a first pressure below the 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 a main chamber vacuum pump system (not shown). The main chamber vacuum pump system removes gas particles in the main chamber 10 so that the pressure in 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 it may be inspected. An electron beam system 40 may comprise a multi-beam electron-optical apparatus (which may be referred to as an electron-optical column or device).
The controller 50 is electronically connected to electron beam system 40. The controller 50 may be a processor (such as a computer) configured to control the charged particle beam assessment apparatus 100. The controller 50 may also include circuitry which may be referred to as processing circuitry configured to execute various signal and image processing functions. While the controller 50 is shown in
Reference is now made to
The electron source 201 may comprise a cathode (not shown) and an extractor or anode (not shown). During operation, the electron source 201 is configured to emit electrons as primary electrons from the cathode. The primary electrons are extracted or accelerated by the extractor and/or the anode to form a primary electron beam 202.
The projection apparatus 230 is configured to convert the primary electron beam 202 into a plurality of sub-beams 211, 212, 213 and to direct each sub-beam onto the sample 208. Although three sub-beams are illustrated for simplicity, there may be many tens, many hundreds, many thousands for example approximately ten thousand, many tens of thousands or many hundreds of thousands of sub-beams. The sub-beams may be referred to as beamlets.
The controller 50 may be connected to various parts of the charged particle beam assessment apparatus 100 of
The electron-optical apparatus 230 may be configured to focus sub-beams 211, 212, and 213 onto a sample 208 for inspection and may form probe spots 221, 222, and 223 (for this example three probe spots, one for each sub-beam) on the surface of sample 208. The projection apparatus 230 may be configured to deflect the primary sub-beams 211, 212, and 213 to scan the probe spots 221, 222, and 223 across individual scanning areas in a section of the surface of the sample 208. In response to incidence of the primary sub-beams 211, 212, and 213 on the probe spots 221, 222, and 223 on the sample 208, electrons are generated from the sample 208 which include secondary electrons and backscattered electrons which may be referred to as signal particles. The secondary electrons typically have electron energy less than or equal to 50 eV. Actual secondary electrons can have an energy of less than 5 eV, but anything beneath 50 eV is generally treated at a secondary electron. Backscattered electrons typically have electron energy between 0 eV and the landing energy of the primary sub-beams 211, 212, and 213. As electrons detected with an energy of less than 50 eV are generally treated as secondary electrons, a proportion of the actual backscatter electrons will be counted as secondary electrons.
The detector 240 is configured to detect signal particles such as secondary electrons and/or backscattered electrons and to generate corresponding signals which are sent to a signal processing system 280 for pre-processing, e.g. analog to digital conversion. The detector 240 may be incorporated into the projection apparatus 230. Further details and alternative arrangements of a detector module, sensor and detector array positioned proximate to, up beam, down beam or otherwise integrated into an objective lens can be found in EP application Ser. No. 20/216,890.2 and PCT Application number PCT/EP2021/068548, which documents are respectively hereby incorporated by reference at least so far as they disclose details of the detector module, sensor and detector array and similar elements.
The detector may be provided with multiple portions and more specifically, multiple detecting portions. The detector comprising multiple portions may be associated with one of the sub-beams 211, 212, 213. Thus, the multiple portions of one detector 240 may be configured to detect signal particles emitted from the sample 208 in relation to one of the primary beams (which may otherwise be referred to as sub-beams 211, 212, 213). In other words, the detector comprising multiple portions may be associated with one of the apertures in at least one of the electrodes of the objective lens assembly. The multiple portions may be segments arranged radially and/or angularly. More specifically, the detector comprising multiple portions may 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. With multiple detecting portions, the detection signal comprises components from the different detecting signals that may be processed as data sets or in a detection image.
The objective lens may be an objective lens array and may comprise a plurality of planar electrodes or plates comprising apertures for the respective paths of the beams of the multi-beam. Each plate may extend across the multibeam arrangement. The objective lens may comprise at least two electrodes that may be connected to and controlled respective potentials. There may be additional plates each to control an additional degree of freedom. The detector may be a plate associated with or connected to the objective lens with an aperture for each path of a beam of the multi-beam. The detector may be located above, below or within the objective lens.
A scan deflector may be associated or even integrated into the objective lens, for example as an array of scan deflectors. An array of scan deflectors (e.g. an array of deflector elements) may be referred to as a deflector array. Each sub-beam may be associated with a deflector element of the deflector array. In an arrangement the scan deflector may be positioned up beam of the object lens. In an arrangement in which the path of the primary beams are collimated up beam of the objective lens, the scan deflectors may be positioned up beam of the objective lens. In an arrangement in which the multibeam is generated from a collimated primary beam from a source by a beam limiting aperture array of or associated with the objective lens, the scan deflector may be a macro scan deflector positioned up beam of the objective lens and so as to operate on the collimated primary beam. Other electron-optical arrangements may be envisaged comprising one or more elements herein described. Such scan deflectors may be controlled by the controller to deflect the beams of the multi-beam along one axis in the plane of the sample or both primary axes over the surface of a sample e.g. in the plane of the sample (which may be orthogonal with respect to each other).
It should be noted that embodiments of scan deflectors that are proximate to the sample, for example integrated or proximate to the objective lens, may have a limited range of scan deflection. However scan deflectors proximate to the sample may be accurately controlled and have a fast response relative to other types of scanning actuators such as an actuated stage.
The controller 50 may control the actuated stage 209 to move sample 208 during inspection of the sample 208. The controller 50 may enable the actuated stage 209 to move the sample 208 in a direction, preferably continuously, for example at a constant speed, at least during sample inspection, which may be referred to as a type of scanning. The controller 50 may control movement of the actuated stage 209 so that it changes the speed of the movement of the sample 208 relative to the path of the multi-beam dependent on various parameters. The controller 50 may control deflection of the scan deflectors so that the path of the multibeam moves relative to the stage and thus over the sample surface. The controller 50 may change a beam deflection of the scan deflector and thus the scanning of the beams over the sample surface dependent on various parameters. For example, the controller 50 may control the stage speed (including its direction) and/or scan deflector depending on the characteristics of the inspection scanning elements and steps, for example in the scanning process and/or scans of the scanning process as disclosed in EPA 21171877.0 filed 3 May 2021. The content of such application is hereby incorporated in so far as it discloses a combined stepping and scanning strategy at least of the stage and scanning deflectors.
Known multi-beam systems, such as the electron beam system 40 and charged particle beam assessment apparatus 100 described above, are disclosed in US2020/118784, US202002/03116, US2019/0259564 and WO2021078352 which are hereby incorporated by reference.
The electron beam system 40 may comprise a projection assembly to regulate accumulated charges on the sample by illuminating the sample 208.
Images output from a charged particle assessment device, e.g. electron beam system 40 need to be processed automatically to detect defects in samples being assessed. A data processing device 500 for detecting defects in images generated by a charged particle assessment device is depicted in
In a charged particle inspection system, the or each electron-optical system 41 is located within main (vacuum) chamber 10. It is therefore necessary to transmit data from the electron-optical system(s) to devices outside the vacuum chamber such as data processing device 500. Raw data generated by the electron optical system(s) can be transmitted out of the vacuum chamber via signal conduits. Considering the quantity of data, the data may be optically transmitted, for example using optically capable signal conduits such as optic fibers. An optical transceiver is used to convert the electrical signals representative to the data to optical signals. 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 signals output by the detector module 240 to optical signals for transmission along an optical fiber. The optical fiber may be capable of transmitting multiple channels simultaneously (e.g. using different wavelengths). Thus the detection signals from each individual electrode of the detector module are converted into an appropriate number of data streams. Multiple optical fibers, either as single channel or multi-channel optic fibers, can be used.
The or each signal conduit, e.g. optical fiber, passes through the wall of main chamber 10 (inside of which is at vacuum in use) by a vacuum feedthrough 11. A suitable vacuum feedthrough is described in US2018/0182514 A1 which document is incorporated herein by reference at least insofar as it relates to a feedthrough device. The signal conduit, e.g. optical fiber, is connected to data processing device 500, which can therefore be located outside the vacuum for case of access and to avoid needing to increase the size of the vacuum chamber to accommodate the data processing device. In both single-column and multi-column systems, multiple optical transceivers and multiple optical fibers per column may be used if convenient.
An arrangement involving multiple optical fibers (or other communication channels) is shown in
It should be noted that a detector module, or detector array for an arrangement comprising a plurality of planar electron-optical elements, e.g. electrodes, placed along the multi-beam path, may have internal circuitry. The internal circuitry may comprise part or all of the processing circuitry, e.g. a CMOS structure, for connecting the individual detector elements, or detector units, in the detector array. In an alternative arrangement, two or more of the signal conduits for different detector units may have a common or adjacent connection in the surface of the detector module. Co-locating a plurality of connections for signal conduits to the detector module simplifies connection of the signal conduits and the detector module to each other. In an arrangement multiple detector units have a common signal conduit, so multiple detector units may be grouped. Each detector unit may be associated with a beam of a multi-beam, such that a detector is arranged to detect signal particles from the sample generated by a specific beam of the 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 the plurality of beams. Such an arrangement may be suited to an inspection system for finding defects. Such an arrangement may be suited to a metrology system where each pixel, e.g. a detector unit, is for counting signal electrons.
Various approaches may be taken to detect defects in images generated by a charged particle assessment device. A common approach is to compare an image of a part of the sample, referred to herein as a sample image, to a reference image. In practice, data points of a datastream representing the sample image are compared to data points of the reference image retrieved from a memory or delivered in a parallel datastream. For the sake of brevity, this process may be referred to below as comparing images and the data points as pixels. Any pixel that differs from the corresponding pixel of the reference image by more than a threshold amount may be considered a defect. Such a pixel that differs from the reference image, together with adjacent pixels that also differ from the reference image, is considered a single defect. (In some embodiments this may mean a pixel differing from the reference image and which has adjacent pixels which are the same as the reference image (i.e. do not differ from the reference image) can be considered to not represent a defect). The reference image may be obtained in various different ways, as discussed below. (Note: the data of the sample image may be referred to as sample image data; the data of the reference image (or reference data) may at least comprise, or even be referred to, as reference pixel data. The reference data may take the form of a reference data map).
The rate of false positives, i.e. samples labelled as having defects when in fact no significant defect is present, can be controlled. The rate of false positives can be controlled by setting a threshold for determining the presence of a defect. The threshold may be the difference of the pixel compared to the reference image, e.g. compared to the equivalent pixel of the reference image. The rate of false positives 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.
An efficient and effective approach to reduce noise in the sample image is by applying a simple filter by convolution, e.g. a uniform filter (convolution with a uniform kernel). To reduce noise in the reference image multiple source images may be averaged. In some cases, e.g. where the reference image is obtained by simulation from design data (often in GDSII format), noise reduction on the reference image may be omitted.
The efficiency and effectiveness of noise reduction in the sample image may be optimized by suitable selection of the size of the (uniform) filter. The optimum size of the filter may depend on factors such as the size of features on the sample, the size of defect to be detected, the resolution of the charged particle assessment device, the amount of noise in the images and the desired compromise between sensitivity and selectivity. The size of the kernel used to implement the filter may be equal to a non-integer number of pixels. A width in the range of 1.1 to 5 pixels, desirably in the range of 1.4 to 3.8 pixels, for the kernel is suitable in a variety of use cases. The form of the uniform kernel is discussed further below.
A square uniform kernel 505 with a non-integer size (width) is depicted in
In some cases, e.g. the uniform kernel described above, a two-dimensional kernel can be decomposed into two one-dimensional convolutions in orthogonal directions which are applied sequentially. This can be advantageous because the number of operations to perform an n×n two-dimensional convolution scales with the square of n whereas the number of operations to perform two n one-dimensional convolutions scales linearly with n.
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 the same shape and size as the kernel; a kernel that is larger than the filter function will include zero values. Desirably the filter is symmetrical but that is not essential. Simulations suggest that a kernel implementing a uniform filter provides good results but some deviation from a mathematically uniform filter is permissible. For example corner filters could have values f, which would slightly outweigh those pixels but not significantly. Non-uniform filters, e.g. a Gaussian filter, may be conveniently implemented by convolution with a suitable kernel.
The reference image may be obtained by averaging source images to obtain a reference image, and the averaging process may depend on the nature of the source images. Where the source images derive from a library of past scans, a large number of (e.g. more than 20, more than 30 or about 35) images may be averaged to obtain the reference image since the averaging can be performed off-line. The source images may be aligned before averaging.
Alternatively, the sample image may be compared to a reference image derived from “live” source images obtained from different parts 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 regions of different dies of the sample. Alternatively, if the pattern being inspected has a repeating element, the source images may be obtained from the same die. In some cases the source images may be shifted portions of the sample images. In cases where the sample image is compared to a reference image derived from live source images, the roles of the different images may rotate. For example if three images A, B and C are output by a charged particle assessment device: A and B may be averaged to provide a reference image to compare to C; A and C may be averaged to provide a reference image to compare to B; while B and C are averaged to provide a reference image to compare to A.
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, e.g. based on pattern or design data (e.g. in GDSII format). Such a reference image, at least by a first processing module e.g., in a first step of a two-step process, may be a simplification of the one or more “known-good” patterns or the simulation.
The result of the comparison of a sample image to a reference image may be a simple binary value representing a difference or a correspondence (i.e. matching) between the sample and references images. More desirably, the result of the comparison is a difference value representing the magnitude of the difference between the sample image and the reference image. Desirably, the result of the comparison is a difference value for each pixel (or each group of adjacent pixels which may be referred to a ‘region of pixels’) so that locations of defects within a source image can be determined greater precision.
To determine if a difference of a pixel or a region of pixels between source image and reference image represents a defect in the pattern being inspected, a threshold may be applied to the difference value corresponding to the pixel or region of pixels. The threshold may be fixed in advance, e.g. for a specific charged particle beam system or for a specific pattern to be inspected. The threshold may be a user-set parameter or by other conditions, for example it is updated from time to time dependent on application or from assessment. The threshold may be determined dynamically, updated during the course of processing, or both. Alternatively, a predetermined number of locations having the highest difference values may be selected as candidate defects for further inspection. Adjacent pixels having difference values higher than a threshold may be considered a single defect or candidate defect. All pixels of a single defect may be ascribed the same difference value. Such adjacent pixels and all pixels of a single defect may be referred to as a region of pixels.
An efficient approach to identifying a predetermined number of locations having the highest difference values is to process pixels in sequence and write pixel information and difference values to a buffer. 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 a newly processed pixel has a higher difference value than the pixel in the buffer with the lowest difference value, the pixel information relating to the pixel with the lowest difference value is overwritten. In one possible implementation, until the buffer is full, the threshold for selection of pixels is set at a predetermined level. When the buffer is full the threshold is updated to the lowest difference value of the pixels stored in the buffer and updated each time a pixel in the buffer is overwritten. In this way only one comparison need be performed.
Alternatively, the threshold can be maintained constant and initially selected pixels can be separately tested to see if they have a higher difference than a pixel in the buffer already. Such a method may select a predetermined proportion of pixels and a predetermined amount of data. Alternatively the threshold may be set to select pixels that exceed the threshold so that the selected pixels that are tested have a magnitude corresponding to or exceeding the set threshold. In such a method the proportion of pixels is not predetermined; so the quantity of data selected is not predetermined. The proportion of pixels selected may depend on the set of data being processed. Since the number of selected pixels in such methods 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 initial processing without reducing throughput.
The charged particle assessment apparatus 100 may have a high throughput and a high resolution, meaning that data may be output at a high rate. For example the charged particle assessment device may have thousands, even tens of thousands, of beams or more, with each beam having one or more detector portions outputting data points at a rate of kilo-or mega-Hertz. Therefore, the rate at which data can be transferred from the detector module(s) to an image analysis device such as data processing device 500 (whether incorporated with the charged particle assessment device in a charged particle assessment system or a stand-alone device) can limit the throughput of the charged particle assessment device or system even where optical fibers are used.
As depicted in
Filter module 501 applies a filter to the input data, as discussed further below. Filter module 501 is conveniently implemented by dedicated hardware, e.g. an FPGA or an ASIC. Such dedicated hardware can be more efficient and economic than programmed general purpose computing devices such as a standard or common type of CPU architecture. The processor may be less powerful than a CPU but may have architecture suited to processing software for processing the detection signal data, i.e. the images and so be capable of processing the images in the same or less time than the CPU. Such detected processing architecture, despite having a processing capability lower than most contemporaneous CPUs may be as fast at processing the data because the more efficient data architecture of the dedicated processing architecture. A general-purpose CPU may be advantageous in that it allows the filter to be changed easily.
The reference image generator 503 may be operable in one or more modes, each mode representing a different approach to generation of the reference image.
In a library mode, the reference image generator 503 averages a large number of source images obtained from previous scans of patterns nominally the same as the pattern currently being assessed. Such images may have been generated earlier in the same batch of samples, or from samples in previous batches. The library images may be derived from test samples or production samples. Before averaging the images are desirably aligned with one another. Averaging the source images to generate the reference image has the effect of reducing noise. Averaging the source images in this way also averages away any defects that might be visible in the source images.
In the case where the pattern being inspected is a repeating pattern it is possible to generate the reference image by averaging a plurality of shifted versions of a source image. Each version of the source image is shifted by integer multiples of the dimensions of the unit cell. If either or both dimensions of the unit cell are not equal to an integer number of pixels, the shift amount can be rounded to the nearest pixel or a fractional pixel shift can be effected by interpolation, for example linear or cubic interpolation, such as bicubic interpolation, or any other known interpolation technique. Another possibility is to shift by a multiple of the pitch of the repeating pattern such that the multiple is an integer number of pixels. In effect, multiple instances of the unit cell are extracted from the source image and averaged. This approach may be referred to as an example of array mode, more specifically of providing a reference image for an array mode.
In a die-to-die mode, a charged particle assessment device is used to generate a sample image and two reference images of similar surface features which may have a repeating pattern. In an arrangement the sample image and each of the two reference images are from different dies of the sample (for example so that similar portions of the surface of different dies may be compared). The sample image may be compared to each of the reference images to identify differences between each of the reference images. Such a difference may be considered as a candidate defect. Differences which are common to the comparison between the sample image and the different reference images are treated as a defect. Differences which are only present in one of the comparisons between the sample image and the different reference images are treated as being a defect in the reference image and not in the sample image. Such defects in the reference image are removed from a group of the candidate defects. An image aligner is provided to align the images before they are supplied to the reference image generator 503 and filter module 501 as appropriate. For example such aligning may align at least portions of the images, or different portions of the sample each other, with respect to a repeating period of the repeating pattern.
In an arrangement three columns of a multi-column charged particle assessment device are used to generate the sample image and the two reference images. This arrangement is particularly efficient where the spacing between columns is equal to the die size of the sample being inspected since the columns will then automatically scan corresponding pattern features simultaneously. Using such an arrangement is also faster than using a single column because the sample image and reference images may be acquired simultaneously. In case there is a difference between the column spacing and die size, such as due to variations in the surface position of features on the sample surface, a buffer may be employed to correct the timing of image input to the data processing device.
In a variant of die-to-die mode, the same beam (of the same column in the case of a multi-column system) is used to generate a sample image and two reference images. This has the advantage that column to column and beam to beam corrections are not required and the routing of data can be simplified. For example, such a calibration is the relative position of a beam relative to the ideal beam position for that beam or even for each beam. Using the same beam avoids the calibration, e.g. assessment of the offset, between beams for the different scans that are compared. Using the same beam means that although the beam has an offset with respect to the ideal beam position, there is no positional offset to correct for when comparing data retrieved from the scans. However, the need for data buffering might be increased, for example in frequency, if not in quantity of data buffered before the start of the comparison of the data from different dies.
An alternative version of array mode using single column, e.g. of a single-column system, provides a sample image which is compared against a reference image derived from two shifted versions of itself as source images. A buffer may be used to provide the shifted images.
It should be noted that it is also possible to apply the uniform filter to the source images and/or the reference images, in particular where the reference image is derived from a small number of source images that are obtained concurrently with the source image.
With reference again to
In some cases, the reference image generator 503 can also be implemented in dedicated hardware, especially where the reference image generator operates only in a mode where the reference image is generated from a small number of, e.g. two, source images. In that case it is desirable that the reference image generator is implemented in the same dedicated hardware as the comparator and/or filter module. The mathematical operations to average pixels of source images and compare to a pixel of a sample image can, in suitable cases, be combined into a single logic circuit.
Output module 504 receives the results output by comparator 502 and prepares output to the user, other fab systems or for further processing within the inspection system. The output may be in any of several 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 desirable for example as a data set, such as an image (e.g. such as a data set renderable as an image). Therefore the output may comprise, for example, a map of defect locations (or a detection data map), a deviation image, a clip of pixel data (for example of the image and the reference image, or of the reference image), and/or information as to the severity of a possible defect represented by the magnitude of the difference between the sample image and the reference image, for example how the sample image deviates from the reference image.
Output module 504 may also filter the potential defects, e.g. by only outputting defect locations where the magnitude of the difference between the sample image and the reference is greater than a threshold or the density of pixels showing a difference is higher than a threshold. Another possibility is to output only a predetermined number of most serious defect sites, indicated by the magnitude of the difference. This may be effected by storing defect sites in a buffer 510 and, when the buffer is full, overwriting the lowest magnitude defect if a higher magnitude defect is detected.
Any suitable format for the output of defect information may be used, e.g. a list, data set, image or a map. Desirably, output module 504 may output clips, that is images of regions of the sample where potential defects have been detected. This allows the potential defect to be further examined to determine if the defect is real and serious enough to affect operation of the device formed on or present in the sample. The rest of the source image, i.e. those parts not saved as clips, may be discarded to save on data storage and transfer requirements. The data set may thus be a set of clips; the image may comprise the set of clips,
As mentioned above, a problem with conventional charged particle assessment systems or devices may be that the rate at which data can be transferred from the detector to the image analysis module is a limiting factor in the throughput of the charged particle assessment system. As discussed with reference to
To obtain a two-dimensional image of the sample, the (or each) probe beam is scanned across the surface of the sample in a two-dimensional raster pattern. This involves movement of the beam in two directions: a main scanning direction and a sub-scanning direction which have different orientations, e.g. are orthogonal. The main scanning direction may be referred to as the fast scan direction or a major scanning direction. For example the scan deflector may be controlled to actuate the primary beam (e.g. multi-beam) in the fast direction. The sub-scanning direction may be referred to as the slow scan direction or a minor scanning direction. For example the stage maybe controlled to actuate the sample relative to the path of the primary beam; the scan deflector may be controlled to actuate the path of the beam over the sample surface in the slow direction; or both the stage and the scan deflector are actuated to achieve scanning in the slow direction. The stage is preferred to be used only in the slow direction because its inertia due to its large mass, makes achieving the movement of scanning in the fast direction, e.g. acceleration, more challenging than alternatives such as a scan deflector.
The signal from the detector is sampled at regular intervals such that the distance travelled in the main scanning direction between samples is equal to the distance between scan lines in the sub-scanning direction. The result is shown in
The signal collection region dsigCol corresponds to the size of a surface coverage of an expected defect on the sample for the defect to be detectable by the probe spot. It is the area of the sample surface when any part of the probe spot dspot is located on a region of the sample surface corresponding to the expected size of a defect, i.e. the size of a pixel, ddef;. The signal collection region also corresponds to a de-noising filter. In order to add up all the signals in the signal collection region, the pixel data is convoluted with a de-noising kernel. After applying the de-noising filter the sum of all the signals from the signal collection region will be present in the pixel proximate to the center of the defect. The filter may be of any suitable type such as Gaussian, or a top hat (or a rectangular function) which appears of a circular shape or square shape (as depicted in
In some embodiments, a de-noising filter in the main scanning direction is performed by circuitry integrated in or close to the detector module 240. An example of the circuitry that performs the de-noising filter in the main scanning direction is a filter (or upstream filter or first filter) 402 as will be described later herein. The effect of the de-noising filter in the main scanning direction is to average the signal in the main scanning direction. The averaging of the signal in the main scanning direction allows for the sampling rate in the main scanning direction can be reduced, e.g. by a factor of two. This results, in effect, in a rectangular pixel. Such a rectangular pixel has dimension in different directions that are not uniform, different or dissimilar. The rectangular pixels are elongated, i.e. longer in one direction (the longitudinal direction) than in the perpendicular direction (the transverse direction). A grid of such rectangular pixels is depicted in
Circuitry to effect the above concept and that may be incorporated in the electron optical column, e.g. in a detector module 240, is depicted in
Various parameters of the circuitry are selected to achieve a desired data rate and other effects, for example relative to the geometry of a rectangular pixel, including in terms of the dimensions of the rectangular pixel in the main scanning direction and the sub-scanning direction (i.e. the main scanning dimension and the sub-scanning dimension of a rectangular pixel). Specifically, the time constant or cut-off frequency of the de-noising filter 402 is set relative to the probe beam scanning speed in the main scanning direction to set an averaging length, which may be, for example, of the order of the expected defect size. The sampling rate of the analog-to-digital converter 403 is selected relative to the probe beam scanning speed in the main scanning direction to set an effective pixel dimension of the main scanning dimension Ipix-x in the main scanning direction.
The dimension of the rectangular pixel Ipix-x (or main dimension of the rectangular pixel) in the main scanning direction may for example have a size that is of the same order of magnitude of the defect size and/or about twice the pixel dimension in the sub-scanning direction (or sub-scanning dimension Ipix-y). The sub-scanning dimension Ipix-y may be equivalent to the spacing in the Y-direction (sub-scanning direction) between scanning lines. (Here a scanning line is the line along which the beam moves relative to the sample surface, for example over the sample surface, during scanning).
In some cases it is convenient if the pixel dimension Ipix-x in the main scanning direction (or main scanning dimension of a rectangular pixel) is an integer multiple of the sub-scanning dimension Ipix-y of the pixel (or the pixel dimension Ipix-y in the sub-scanning direction), i.e. the aspect ratio of the pixels is an integer. Desirably, the pixel dimension Ipix-x in the main scanning direction is greater than or equal to twice the pixel dimension Ipix-y in the sub-scanning direction; that is the aspect ratio of the pixels is greater than or equal to two (2). An aspect ratio of no more than three (3) has been found to be an effective compromise in various cases. All other things being equal, desirably the data rate that must be transmitted from the electron optical column is reduced by a factor equal to the aspect ratio of the pixels. Desirably, the length of the de-noising filter in the main scanning direction is about the same as the length of the pixel in the main scanning direction. So the de-noising filter has a main scanning dimension in the main scanning direction that is similar or approximately the same as the sub-scanning dimension of the pixel. Thus data of the rectangular pixel is output from the denoising filter 402 with an effective filter size resulting from operation of the de-noising filter in the main scanning direction applied to the main scanning dimension of the pixel together with the filtering effect of the rectangular pixel in the sub-scanning direction.
An example image analysis device is depicted schematically in
The image analysis device is for further processing the digital signal from the analog to digital converter 403 which digital signal is based on the analog output from the de-noising filter 402. An interface module 506 receives via a communication channel 507 the pixel values, e.g. as a series of pixel values, output by analog to digital converter 403, buffers the pixel values, e.g. in a random-access memory, and outputs them in a desired order for subsequent processing. The communication channel may comprise optical fibers as described above or be any other suitable high-data rate channel or signal conduit. The communication channel may include parts in the detector, in the vacuum electronics, through the feedthrough, in the outside vacuum electronics close to the feedthrough and optical channels for example to the image analysis device.
A downstream filter module (or a second filter de-noising module) 501 is a de-noising filter, for example as a second de-noising filter. The downstream filter module 501 applies a de-noising filter in the sub-scanning direction, i.e. orthogonal to the main scanning direction. The de-noising filter in the sub-scanning direction may be a uniform filter or a Gaussian filter, for example. Desirably, the de-noising filter in the sub-scanning direction is the same type of filter as has been applied in the main scanning direction. However, in different arrangements at least a part of the image analysis device is separate detector array, for example remote from the electron optical column (e.g. outside the vacuum chamber). Any communication channel passing through the wall of the chamber wall may take the form of a signal conduit such as an optical fiber.
The combination of the filtering in the main scanning direction performed in the circuity incorporated in the electron-optical column and the filtering in the sub-scanning direction performed in the remote image analysis device is equivalent to a two-dimensional noise filter as discussed above. By making the filter size (or dimension) of the de-noising 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 they would have been had they been filtered using a square filter in one step. That is, the resulting effective size of the filter size is approximately the same for both directions for example in the scale of defect being assessed, e.g. nanometers.
The comparator 502 compares the filtered signal output by de-noising filter 501 to a reference image provided by reference image generator 503 to detect defect candidates as described above.
Because of the use of non-square pixels (which may be rectangular), it may be desirable to store reference images at a higher resolution than the sample images, for example for a die to database mode. The sample image may be aligned to the higher-resolution reference image. The higher-resolution reference image may then be down-sampled to the same resolution (and pixel shape) as the sample image. Down-sampling may be performed by various suitable techniques including averaging, pixel skipping, interpolation, etc. An arrangement to achieve this is shown in
As depicted in
Note that aligning, for example in die-to-die mode, may align at least portions of the images or different portions of the sample image to each other with respect to a repeating period of the repeating pattern. The repeating period may be equal to a whole number of pixels in the elongate direction or a whole number of pixels in a main scanning direction (or the reduced direction or lateral direction).
The use of a high-resolution reference image is particularly advantageous where the reference image is derived from design data (e.g. GDSII data) by simulation for example in a die to database mode for inspection. High-resolution reference data can also be obtained (for example comprising reference pixel data) by scanning one or more (e.g. two or three) reference areas (e.g. dies) of the sample at a higher resolution (e.g. using square pixels) than the remainder of the sample. Such high-resolution scans can be performed on just some samples (e.g. one) of a batch of samples. Typically at least two reference images are used in the comparator with a sample image, for example in die-to-die mode, to reduce the risk of an apparent defect in the sample image being 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 acceptable confidence so long as for example, the high-resolution scan is of a sample surface known to have a low, even zero, likelihood of defects.
In an array mode, where the sample image is compared to a shifted version of itself, it is desirable that the shift amount is equal to both a whole number of pixels and an integer multiple of the unit cell size of the pattern being inspected, i.e. a common multiple of the pixel size and the unit cell size. Whilst it may be expected that increasing the pixel size reduces flexibility in the selection of the shift amount, the embodiments of the present disclosure enable a trade-off between optimum pixel size for noise reduction and shift amount that increases flexibility.
An advantage of the disclosed embodiments is that a desired data rate for sample data transmitted from the detector to associated circuitry, to a remote image analysis device and/or to remote further processing of sample data sets or images can be provided by varying the pixel dimensions. The pixel dimension 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 dimension in the sub-scanning direction is determined by the step size of the sample shift between scan lines. Where the communication link between detector and remote image analysis device has a limited bandwidth, the pixel dimensions can be chosen to make optimum use of that bandwidth.
It is noted that reference to a pixel can be considered to be reference to a rectangular pixel unless specified otherwise. Whilst the above description mostly refers to rectangular pixels, it is emphasized that the pixels need not be rectangular and can have other shapes with an aspect ratio greater than 1 (i.e. one dimension larger than another). For example, if the scan directions are not orthogonal, it may be convenient to use pixels that represent areas that are parallelograms, with sides parallel to respective scanning directions. It will also be appreciated that the area in an output image represented by a pixel may not exactly correspond to an area of the sample from which signal electrons were sampled to give rise to that pixel, e.g. if the beam spot size is not the same as the spacing between scan lines.
References to upper and lower, up and down, above and below, etc. should be understood as referring to directions parallel to the (typically but not always vertical) up-beam and down-beam directions of the electron beam or multi-beam impinging on the sample 208. Thus, references to up beam and down beam are intended to refer to directions in respect of the beam path independently of any present gravitational field.
The embodiments herein described may take the form of a series of aperture arrays or electron-optical elements arranged in arrays along a beam or a multi-beam path. Such electron-optical elements may be electrostatic. In some embodiments, all the electron-optical elements, for example from a beam limiting aperture array to a last electron-optical element in a sub-beam path before a 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 of the electron-optical elements are manufactured as a microelectromechanical system (MEMS) (i.e. using MEMS manufacturing techniques). Electron-optical elements may have magnetic elements and electrostatic elements. For example, a compound array lens may feature a macro magnetic lens encompassing the multi-beam path with an upper and lower pole plate within the magnetic lens and arranged along the multi-beam path. In the pole plates may be an array of apertures for the beam paths of the multi-beam. Electrodes may be present above, below or between the pole plates to control and optimize the electro-magnetic field of the compound lens array.
The terms “sub-beam” and “beamlet” are used interchangeably herein and are both understood to encompass any radiation beam derived from a parent radiation beam by dividing or splitting the parent radiation beam. The term “manipulator” is used to encompass any element which affects the path of a sub-beam or beamlet, such as a lens or deflector. References to elements being aligned along a beam path or sub-beam path are understood to mean that the respective elements are positioned along the beam path or sub-beam path. References to optics are understood to mean electron-optics.
An assessment tool or assessment system according to the disclosure may comprise apparatus which makes a qualitative assessment of a sample (e.g. pass/fail), one which makes a quantitative measurement (e.g. the size of a feature) of a sample or one which generates an image of map of a sample. Examples of assessment 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 assessment functionalities associated with inspection tools, review tools, or metrology tools (e.g. metro-inspection tools).
Reference to a component or system of components or elements being controllable to manipulate a charged particle beam in a certain manner includes configuring a controller or control system or control unit to control the component to manipulate the charged particle beam in the manner described, as well optionally using other controllers or devices (e.g. voltage supplies) to control the component to manipulate the charged particle beam in this manner. For example, a voltage supply may be electrically connected to one or more components to apply potentials to the components, such as to the electrodes of the control lens array and objective lens array, under the control of the controller or control system or control unit. An actuatable component, such as a stage, may be controllable to actuate and thus move relative to another components such as the beam path using one or more controllers, control systems, or control units to control the actuation of the component.
The methods of the present disclosure may be performed by computer systems comprising one or more computers. A computer used to implement these methods may comprise one or more processors, including general purpose CPUs, graphical processing units (GPUs), Field Programmable Gate Arrays (FPGAs), Application Specific Integrated Circuits (ASICs) or other specialized processors. As discussed above, in some cases specific types of processor may provide advantages in terms of reduced cost and/or increased processing speed and the method of the present disclosure may be adapted to the use of specific processor types. Certain steps of methods of the present disclosure involve parallel computations that are apt to be implemented on processers capable of parallel computation, for example GPUs.
A computer used to implement the embodiments of the present disclosure may be physical or virtual. A computer used to implement the embodiments of the present disclosure may be a server, a client or a workstation. Multiple computers used to implement the embodiments of the present disclosure may be distributed and interconnected via a local area network (LAN) or wide area network (WAN). Results of a method of embodiments of the present disclosure may be displayed to a user or stored in any suitable storage medium. The embodiments of the present disclosure may be embodied in a non-transitory computer-readable storage medium storing instructions to carry out the disclosed methods. The embodiments of the present disclosure may be embodied in a computer system comprising one or more processors and memory or storage storing instructions to carry out the disclosed methods.
Functionality provided by the computers and processors such as the controller or control system or control unit may be computer-implemented. Any suitable combination of elements may be used to provide the required functionality, including for example CPUs, RAM, SSDs, motherboards, network connections, firmware, software, and/or other elements known in the art that allow the required computing operations to be performed. The required computing operations may be defined by one or more computer programs. Such computer programs may take the form of multiple computer programs that may be distributed for example implemented by different processors. The one or more computer programs may be provided in the form of media, optionally non-transitory media, storing computer readable instructions. When the computer readable instructions are read by the computer, the computer performs the required method steps. The computer may consist of a self-contained unit or a distributed computing system having plural different computers connected to each other via a network.
The term “image” used herein is intended to refer to any data structure of values wherein each value relates to a sample of a location and the arrangement of values in the array corresponds to a spatial arrangement of the sampled locations. 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 multi-layer image, each layer, which may also be referred to as a channel, represents a different sample of the locations. The term “pixel” is intended to refer to a single value of the array or, in the case of a multi-layer image, a group of values corresponding to a single location. An image may be stored in any convenient format in a computer-readable storage medium.
While the present invention has been described in connection with various embodiments, other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the technology disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims and clauses.
There is provided the following clauses:
| Number | Date | Country | Kind |
|---|---|---|---|
| 22175932.7 | May 2022 | EP | regional |
| 22197831.5 | Sep 2022 | EP | regional |
This application claims priority of International application PCT/EP2023/063162, filed on 16 May 2023, which claims priority of EP application Ser. No. 22/175,932.7, filed on 27 May 2022 and of EP application Ser. No. 22/197,831.5, filed on 26 Sep. 2022. These applications are incorporated herein by reference in their entireties.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2023/063162 | May 2023 | WO |
| Child | 18959531 | US |
