Method and computer program for generating sample maps

Abstract

A method of generating a sample map and processing a sample is disclosed. In one configuration, the method includes measuring the positions of a first mark in each of a plurality of field regions on the sample. A first model is fitted to the measured positions of the first mark. The fitted first model represents the positions of the field regions. The method includes measuring the positions of a plurality of second marks in the field region or each of a plurality of field regions. A second model is fitted to the measured positions of the second marks. The fitted second model represents the shape of each field region. The sample map is output using the fitted first and second models.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. patent application Ser. No. 63 / 361,395, filed on December 15, 2021, and incorporated by reference in its entirety into this specification.

[0002] FIELD OF THE DISCLOSURE

[0002] Embodiments disclosed herein relate to generating sample maps for use in evaluation processes, for example, to identify defects in patterns. [Background technology]

[0003]

[0003] When manufacturing semiconductor integrated circuit (IC) chips, undesirable pattern defects inevitably occur on a substrate (i.e., wafer) or mask during the fabrication process, e.g., as a result of optical effects and accidental particles, thereby reducing yield. Therefore, monitoring the extent of undesirable pattern defects is an important process in the manufacture of IC chips. 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.

[0004]

[0004] Charged particle beam pattern inspection devices are 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 with a final deceleration step to land on the sample with a relatively low landing energy. The electron beam is focused as a probing spot on the sample. Interaction of the landing electrons from the electron beam with material structures at the probing spot causes signal electrons, such as secondary electrons, backscattered electrons or Auger electrons, to be emitted from the surface. The signal electrons may be emitted from the material structures of the sample. By scanning the primary electron beam as a probing spot across the sample surface, signal electrons may be emitted across the surface of the sample. By collecting these emitted signal electrons from the sample surface, the pattern inspection device may obtain an image that is representative of the material structure of the surface of the sample.

[0005]

[0005] The pattern may be arranged in a number of field regions. Furthermore, each field region may include a number of die regions. Typically, at least some of the field regions are nominally rectangular and arranged in a regular array of rows and columns. Imperfections in the patterning process result in deviations in the shape and position of the field regions. Alignment marks may be measured and used to predict the shape and position of the field regions (and the die regions therein). Inaccuracies in such maps may reduce the throughput of the sample evaluation method by making it more difficult to identify features of interest in the sample being evaluated.

[0006]

[0006] There is a general need to increase the throughput of sample evaluation methods. Summary of the Invention

[0007]

[0007] It is an object of the present disclosure to provide embodiments that assist in increasing the throughput of sample evaluation methods.

[0008]

[0008] According to one aspect of the disclosed embodiment, there is provided a method for generating a sample map comprising obtaining a sample having a field region, measuring a position of a first mark in each of a plurality of field regions, fitting a first model to the measured positions of the first mark, where the fitted first model represents the position of the field region, measuring positions of a plurality of second marks in the field region or each of a plurality of field regions, fitting a second model to the measured positions of the second marks, where the fitted second model represents a shape of each field region, and outputting the sample map using the fitted first and second models (a plurality of second models).

[0009]

[0009] According to one aspect of the disclosed embodiment, there is provided a method for generating a sample map, the sample map including information regarding positions and shapes of field areas on the sample, the method including providing a sample having field areas, receiving exposure correction data from a lithographic apparatus used to expose each of the field areas, and generating the sample map using the exposure correction data.

[0010]

[0010] According to one aspect of the disclosed embodiment, there is provided a computer program including instructions which, when executed by a computer, cause a computer to perform the following steps: receiving data representing measured positions of a first mark in each of a plurality of field regions on the sample and fitting a first model to the measured positions of the first mark, the fitted first model representing the position of the field region; receiving data representing measured positions of a plurality of second marks in a field region or each of a plurality of field regions and fitting a second model to the measured positions of the second marks, the fitted second model representing a shape of each field region; and outputting a sample map using the fitted first and second models (a plurality of second models).

[0011]

[0011] According to one aspect of the disclosed embodiment, there is provided a computer program including instructions which, when executed by a computer, cause the computer to perform the following steps: receive exposure correction data from a lithographic apparatus used to expose a field area on the sample, and use the exposure correction data to generate a sample map including information regarding the position and shape of the field area on the sample.

[0012]

[0012] According to one aspect of the disclosed embodiment, there is provided a charged particle beam inspection system including a sample holder configured to hold a sample having a field region; an electron beam system configured to project one or more electron beams onto the sample and detect signal electrons emitted from the sample; and a controller configured to: cause the electron beam system to measure a position of a first mark in each of a plurality of field regions and fit a first model to the measured position of the first mark, where the fitted first model represents the position of the field region; cause the electron beam system to measure positions of a plurality of second marks in the field region or each of a plurality of field regions and fit a second model to the measured positions of the second marks, where the fitted second model represents a shape of each field region; and outputting a sample map using the fitted first and second models (a plurality of second models).

[0013]

[0013] According to one aspect of the disclosed embodiment, there is provided a charged particle beam inspection system including a sample holder configured to hold a sample having a field region, an electron beam system configured to project one or more electron beams onto the sample and detect signal electrons emitted from the sample, and a controller configured to receive exposure correction data from a lithography apparatus used to expose the field region on the sample, and to use the exposure correction data to generate a sample map including information regarding the position and shape of the field region on the sample.

[0014]

[0014] The above and other aspects of the present disclosure will become more apparent from the following description of exemplary embodiments taken in conjunction with the accompanying drawings. [Brief description of the drawings]

[0015] [Figure 1]FIG. 1 is a schematic diagram illustrating an example charged particle beam inspection system. [Diagram 2]

[0016] FIG. 1 is a schematic diagram of an exemplary single-beam electron beam system. [Diagram 3]

[0017] FIG. 1 is a schematic diagram of an exemplary multi-beam electron beam system. [Figure 4]

[0018] FIG. 2 is a schematic diagram of a further exemplary multi-beam electron beam system. [Diagram 5]

[0019] FIG. 1 is a schematic diagram of an exemplary multi-beam electron beam system including a focusing lens array. [Figure 6]

[0020] FIG. 1 is a schematic diagram of an exemplary electron beam system including a beam separator. [Figure 7]

[0021] 1 is a schematic cross-sectional view of an objective lens array of a charged particle characterization system according to some embodiments. [Figure 8]

[0022] FIG. 8 is a bottom view of a modified version of the objective lens array of FIG. [Figure 9]

[0023] The samples are depicted with an actual sample map and a generated sample map, the generated sample map being based on rectangular field regions positioned on the grid points of a perfect rectangular grid. [Figure 10]

[0024] 10 depicts example actual and generated field regions for the arrangement of FIG. 9; [Figure 11]

[0025] The samples are depicted with an actual sample map and a generated sample map, where the generated sample map is based on a model capable of representing non-linear geometric shapes. [Figure 12]

[0026] 12 depicts example actual and generated field regions for the arrangement of FIG. 11 . [Figure 13]

[0027] 1 depicts measuring the position of a first mark on a sample (left) and fitting a first model to the measured position to represent the position of the field region (right). [Figure 14]

[0028] It depicts measuring the position of a second mark in the field region (left side) and fitting a second model to the measured position to represent the shape of the field region (right side). [Figure 15]

[0029] 1 depicts the generation of a sample map using exposure correction data from a lithography tool. [Figure 16]

[0030] FIG. 16 (left side) depicts fine-tuning of the sample map generated in FIG. 15, where FIG. 16 (left side) shows measurement of the positions of multiple reference marks and FIG. 16 (right side) shows application of a linear correction to the generated sample map of FIG. 15 based on the reference marks measured in FIG. 16 (left side). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016]

[0031] These schematic diagrams show the components described below, however, the components depicted in the figures are not drawn to scale.

[0017]

[0032] Reference will now be made in detail to the 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 indicated. The implementations set forth in the following description of the exemplary embodiments do not represent all implementations consistent with the present invention. Instead, the implementations are merely examples of apparatus and methods consistent with aspects related to the embodiments, as described in the appended claims.

[0018]

[0033] Increases in the computing power of electronic devices, which reduces the physical size of the device, can be achieved by greatly increasing the packing density of circuit components such as transistors, capacitors, and diodes on an IC chip. This has been made possible by improvements in resolution that allow for the creation of even smaller structures. For example, an IC chip in a smartphone the size of a thumbnail and available before 2019 can contain over 2 billion transistors, each 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. An error in even one step can dramatically affect the functionality of the final product. Only one "fatal defect" can cause the device to fail. The goal of a manufacturing process is to improve the overall yield of the process. For example, to obtain a 75% yield for a process with 50 steps (where a step can refer to the number of layers formed on a wafer), the individual steps must have a yield of greater than 99.4%. If each individual step had a yield of 95%, the overall process yield would be as low as 7%.

[0019]

[0034] In IC chip manufacturing facilities, while high process yields are desirable, it is also essential to maintain high substrate (i.e., wafer) throughput, defined as the number of substrates processed per hour. High process yields and high substrate throughput can be affected by the presence of defects. This is especially true when operator intervention is required to investigate the defects. Thus, high throughput detection and identification of micro- and nano-scale defects by inspection devices, such as scanning electron microscopes ("SEMs"), is essential to maintain high yields and low costs.

[0020]

[0035] The SEM includes a scanning device and a detector device. The scanning device includes an illumination device, which includes an electron source for generating primary electrons, and a projection device for scanning a sample, such as a substrate, with one or more focused beams of primary electrons. Together, at least the illumination device or illumination system and the projection device or projection system may be referred to as an electron optical system or device. The primary electrons interact with the sample and generate secondary electrons. The detector device captures the secondary electrons from the sample as it is scanned so that the SEM can generate an image of the scanned area of ​​the sample. For high throughput inspection, some inspection devices use multiple focused beams of primary electrons, i.e., multibeams. The component beams of a multibeam may be referred to as sub-beams or beamlets. The multibeams may scan different parts of the sample simultaneously. Thus, multibeam inspection devices can inspect samples much faster than single-beam inspection devices.

[0021]

[0036] Known implementations of multi-beam inspection devices are described below.

[0022]

[0037] Although the description and drawings are directed to electron-optical systems, it is understood that the embodiments are not used to limit the disclosure to specific charged particles, and thus, throughout this specification, references to electrons can be considered to be references to charged particles more generally, and charged particles are not necessarily electrons.

[0023]

[0038] Reference is now made to Figure 1, which is a schematic diagram illustrating an exemplary charged particle beam inspection system 100, which may also be referred to as a charged particle beam evaluation system or simply an evaluation system. The charged particle beam inspection system 100 of Figure 1 includes a main chamber 10, a load lock chamber 20, an electron beam system 40, a front end equipment module (EFEM) 30, and a controller 50. The electron beam system 40 is located within the main chamber 10.

[0024]

[0039] The EFEM 30 includes a first load port 30a and a second load port 30b. The EFEM 30 may include one or more additional load ports. The first load port 30a and the second load port 30b may receive, for example, a substrate front-opening integrated pod (FOUP) that contains a substrate (e.g., a semiconductor substrate or a substrate made of other material) or a sample to be inspected (hereinafter, substrates, wafers and samples are collectively referred to as "samples"). One or more robotic arms (not shown) in the EFEM 30 transport the sample to the load lock chamber 20.

[0025]

[0040] The load lock chamber 20 is used to remove gas from around the sample. This creates a vacuum, which is a local gas pressure lower than the pressure of the surrounding environment. The load lock chamber 20 may be connected to a load lock vacuum pumping system (not shown), which removes gas particles in the load lock chamber 20. Operation of the load lock vacuum pumping system allows the load lock chamber to reach a first pressure below atmospheric pressure. After the first pressure is reached, one or more robotic 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 pumping system (not shown). The main chamber vacuum pumping system removes gas particles in the main chamber 10 such that the pressure around the sample reaches a second pressure below the first pressure. After the second pressure is reached, the sample is transported to the electron beam system 40, where the sample can be inspected by the electron beam system 40. The electron beam system 40 may include a single beam electron optical device or a multi-beam electron optical device.

[0026]

[0041] 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 inspection apparatus 100. The controller 50 may also include processing circuitry configured to perform various signal and image processing functions. Although in FIG. 1 the controller 50 is shown as being external to the structure including the main chamber 10, the load lock chamber 20 and the EFEM 30, it is understood that the controller 50 may be part of the structure. The controller 50 may be located within one of the component elements of the charged particle beam inspection apparatus, or the controller 50 may be distributed among at least two of the component elements. It is noted that although the present disclosure provides an example of a main chamber 10 housing an electron beam system, aspects of the present disclosure are not limited in the broad sense to a chamber housing an electron beam system. Rather, it is understood that the principles described above may be applied to other devices and other arrangements of the apparatus operating under a second pressure.

[0027]

[0042] Reference is now made to FIG. 2, which is a schematic diagram of an exemplary single-beam electron beam system 40 that may be provided as part of the exemplary charged particle beam inspection system 100 of FIG. 1. The electron beam system 40 includes a sample holder 207 supported by a motorized stage 209 for holding a sample 208 to be inspected. The electron beam system 40 includes an electron source 201. The electron beam system 40 further includes a gun aperture 122, a beam limiting aperture 125, a condenser lens 126, a column aperture 135, objective lens assemblies 132a-132d, and an electron detector 144. The objective lens assemblies 132a-132d in some embodiments may be modified swinging objective deceleration immersion lenses (SORIL) that include a pole piece 132a, a control electrode 132b, a deflector 132c, and an excitation coil 132d. The control electrode 132b has an aperture formed therein for the passage of the electron beam. The control electrode 132 b forms the facing surface 72 .

[0028]

[0043] In the imaging process, the electron beam exiting the electron source 201 may pass through the gun aperture 122, the beam limiting aperture 125, the collection lens 126, and be focused by a modified SORIL lens into a probe spot, which may then impinge on the surface of the sample 208. The probe spot may be scanned across the surface of the sample 208 by the deflector 132c or other deflectors in the SORIL lens. Secondary electrons exiting the sample surface may be collected by the electron detector 144 to form an image of the area of ​​interest on the sample 208.

[0029]

[0044] The collection and illumination optical systems of the electron optical system 41 may include or be supplemented with electromagnetic quadrupole electron lenses. For example, as shown in FIG. 2, the electron beam system 40 may include a first quadrupole lens 148 and a second quadrupole lens 158. In some embodiments, the quadrupole lenses are used to control the electron beam. For example, the first quadrupole lens 148 may be controlled to adjust the beam current, and the second quadrupole lens 158 may be controlled to adjust the beam spot size and the beam shape.

[0030]

[0045] Reference is now made to FIG. 3, which is a schematic diagram illustrating an exemplary electron beam system 40 including a multi-beam electron optical system 41 that may be provided as part of the exemplary charged particle beam inspection system 100 of FIG. 1. The electron beam system 40 includes an electron source 201 and a projection device 230. The electron beam system 40 further includes a motorized stage 209 and a sample holder 207. The electron source 201 and the projection device 230 are collectively referred to as an electron optical system 41 or an electron optical column. The sample holder 207 is supported by the motorized stage 209 to hold a sample 208 (e.g., a substrate or a mask) for inspection. The multi-beam electron optical system 41 further includes a detector 240 (e.g., an electron detection device).

[0031]

[0046] The electron source 201 may include a cathode (not shown) and an extractor or anode (not shown). In 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 anode to form a primary electron beam 202.

[0032]

[0047] The projection device 230 is configured to convert the primary electron beam 202 into multiple sub-beams 211, 212, 213 and direct each sub-beam onto the sample 208. Although three sub-beams are shown for simplicity, there may be tens, hundreds, thousands or hundreds of thousands of sub-beams. The sub-beams may be referred to as beamlets.

[0033]

[0048] 1, such as the electron emitter 201, the detector 240, the projection device 230, and the motorized stage 209. The controller 50 may perform various image and signal processing functions. The controller 50 may also generate various control signals for controlling the operation of the charged particle beam inspection device, including the charged particle multi-beam device.

[0034]

[0049] The projection device 230 may be configured to focus the sub-beams 211, 212, and 213 onto the sample 208 for inspection, forming three probe spots 221, 222, and 223 on the surface of the sample 208. The projection device 230 may be configured to deflect the primary sub-beams 211, 212, and 213 to scan the probe spots 221, 222, and 223 over respective scan areas within a section of the surface of the sample 208. In response to the 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, including secondary electrons and backscattered electrons, which may be referred to as signal particles. Secondary electrons typically have electron energies of 50 eV or less. Actual secondary electrons may have energies less than 5 eV, but any energy less than 50 eV is typically treated as secondary electrons. Backscattered electrons typically have electron energies between 0 eV and the landing energy of the primary sub-beams 211, 212, 213. Detected electrons with energies less than 50 eV are typically treated as secondary electrons, so that a certain percentage of the actual backscattered electrons are counted as secondary electrons.

[0035]

[0050] 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 a signal processing system 280, for example, to construct an image of a corresponding scanned area of ​​the sample 208. The detector 240 may be integrated into the projection device 230.

[0036]

[0051] The signal processing system 280 may include circuitry (not shown) configured to process signals from the detector 240 to form an image. The signal processing system 280 may alternatively be referred to as an image processing system. The signal processing system may be incorporated within a component of the electron beam system 40, such as the detector 240 (as shown in FIG. 3). However, the signal processing system 280 may be incorporated within any number of components of the inspection apparatus 100 or the electron beam system 40, such as as part of the projection apparatus 230 or the controller 50. The signal processing system 280 may include an image acquirer (not shown) and a storage device (not shown). For example, the signal processing system may include a processor, a computer, a server, a mainframe host, a terminal, a personal computer, any type of mobile computing device, etc., or a combination thereof. The image acquirer may include at least a portion of the processing functionality of the controller. Thus, the image acquirer may include at least one or more processors. The image acquirer may be communicatively coupled to the detector 240 that allows for signal communication, such as electrical conductors, fiber optic cables, portable storage media, IR, Bluetooth, Internet, wireless networks, wireless radios, or combinations thereof, among others. The image acquirer may receive signals from the detector 240, process the data contained in the signals, and construct an image therefrom. Thus, the image acquirer may acquire an image of the sample 208. The image acquirer may also perform various post-processing functions, such as generating contours and superimposing indicators on the acquired image. The image acquirer may be configured to make adjustments, such as brightness and contrast, of the acquired image. The storage may be a storage medium, such as a hard disk, a flash drive, cloud storage, random access memory (RAM), or other types of computer readable memory. The storage may be coupled to the image acquirer and may be used to store the raw scanned image data as an original image or to store a post-processed image.

[0037]

[0052] The signal processing system 280 may include measurement circuitry (e.g., analog-to-digital converter) to obtain a distribution of detected secondary electrons. The electron distribution data collected during the detection time window, in combination with the corresponding scan path data of each of the primary sub-beams 211, 212 and 213 incident on the sample surface, may be used to reconstruct an image of the sample structure under inspection. The reconstructed image may be used to reveal various features of the internal or external structure of the sample 208. Thus, the reconstructed image may be used to reveal any defects that may be present in the sample. The above functions of the signal processing system 280 may be performed within the controller 50 or may be shared between the signal processing system 280 and the controller 50 as convenient.

[0038]

[0053] The controller 50 can control the motorized stage 209 to move the sample 208 during inspection of the sample 208. The controller 50 can enable the motorized stage 209 to move the sample 208 in a direction, e.g., at a constant speed, preferably continuously, at least during inspection of the sample, which can be referred to as a kind of scanning. The controller 50 can control the movement of the motorized stage 209 such that the motorized stage 209 varies the speed of the movement of the sample 208 depending on various parameters. For example, the controller 50 can control the stage speed (including its direction) depending on the characteristics of the inspection step of the scanning process and / or the scan of the scanning process, at least as far as the combined step / scan method of the stage is concerned, e.g., as disclosed in European Patent Application Publication No. A21171877.0, filed May 3, 2021, which is incorporated herein by reference.

[0039]

[0054] Known multi-beam systems, such as the electron beam system 40 and charged particle beam inspection apparatus 100 described above, are disclosed in U.S. Patent Application Publication No. 2020118784, U.S. Patent Application Publication No. 20200203116, U.S. Patent Application Publication No. 2019 / 0259570, and U.S. Patent Application Publication No. 2019 / 0259564, which are incorporated by reference herein.

[0040]

[0055] The electron beam system 40 may include a projection assembly for illuminating the sample 208 and thereby regulating charge build-up on the sample.

[0041]

[0056] Reference is now made to Figure 4, which is a schematic diagram illustrating an exemplary electron beam system 40 that may be provided as part of the exemplary charged particle beam inspection system 100 of Figure 1. As illustrated above in Figure 3, in some embodiments, the electron beam system 40 includes a detector 240 aligned to a primary electron optical axis of the electron beam system 40. Alternatively, the detector 240 may be aligned to a different axis, as shown in Figure 4.

[0042]

[0057] Features that are the same as those described above are given the same reference numerals. For the sake of brevity, such features will not be described in detail with reference to Figure 4. For example, the electron source 201, the primary electron beam 202, the sub-beams 211, 212 and 213, the projection device 230, the probe spots 221, 222, 223, the controller 50, the sample 208, the sample holder 207, the motorized stage 209 and the detector 240 may be as described above.

[0043]

[0058] The electron source 201, the Gun aperture plate 271, the condenser lens 210 and the source conversion unit 220 are components of an illumination device that forms part of the electron beam system 40. The Gun aperture plate 271 is configured to block the outermost electrons of the primary electron beam 202 in operation to reduce the Coulomb effect. The Gun aperture plate 271 may be referred to as a Coulomb aperture array. The Coulomb effect may enlarge the size of each of the probe spots 221, 222 and 223 of the primary sub-beams 211, 212, 213, resulting in a reduced inspection resolution. The Gun aperture plate 271 may also include multiple apertures for generating the primary sub-beams (not shown) before the source conversion unit 220, and may be referred to as a Coulomb aperture array.

[0044]

[0059] The collecting lens 210 is configured to focus (or collimate) the primary electron beam 202. In one example of the source conversion unit 220, the source conversion unit 220 may include an image forming element array, an aberration compensator array, a beam limiting aperture array, and a pre-bent micro-deflector array. The pre-bent micro-deflector array may, for example, be optional and may be present in embodiments where the collecting lens does not ensure that the sub-beams originating from the Coulomb aperture array are approximately perpendicularly incident on, for example, the beam limiting aperture array, the image forming element array, and / or the aberration compensator array.

[0045]

[0060] The electron beam system 40 may include a secondary projection arrangement 255 associated with the detector 240. The primary projection arrangement 230 may include an array of condenser lenses 231, which may be magnetic, that may function as an objective lens. The beam separator 233 and the deflection scanning unit 232 may be positioned within the primary projection arrangement 230. The beam separator 233 may include a Wien filter. The detector 240 may include a plurality of detector elements 405 (e.g., in the form of a detector array).

[0046]

[0061] The components used to generate the primary beam may be aligned to a primary electron optical axis 204 of the electron beam system 40. These components may include the electron source 201, the gun aperture plate 271, the collection lens 210, the source conversion unit 220, the beam separator 233, the deflection scanning unit 232, and the primary projection arrangement 230. The secondary projection arrangement 255 and its associated detector array 240 may be aligned to a secondary electron optical axis 251 of the electron beam system 40.

[0047]

[0062] In some embodiments, the secondary electrons propagate in three secondary electron beams 261, 262, and 263. The secondary projection device 255 then focuses the paths of the secondary electron beams 261, 262, and 263 onto multiple detector elements 405 of the detector 240.

[0048]

[0063] Detector element 405 can detect secondary electron beams 261, 262, and 263. When the secondary electron beams are incident on detector element 405, the element can generate a corresponding intensity signal output (not shown). In some embodiments, the detector element can be a capture electrode. The output can be directed to an image processing system.

[0049]

[0064] FIG. 5 diagrammatically depicts an electron beam system 40 including an electron optical column 41 according to some embodiments. The electron optical column 41 may form part of the electron beam system 40, which may be provided as part of the exemplary charged particle beam system 100 of FIG. 1. For ease of illustration, the lens array is diagrammatically depicted herein by an array of ellipses. Each elliptical shape represents one of the lenses in the lens array. An elliptical shape is conventionally used to represent a lens by analogy with the biconvex shape often adopted by optical lenses. However, it should be understood that in the context of charged particle arrangements as discussed herein, the lens array does not require any physical element to adopt a biconvex shape, since it typically operates electrostatically. As described below, the lens array may instead include multiple plates having apertures. Each plate having an aperture may be referred to as an electrode. The electrodes may be provided in series along the sub-beam paths of the sub-beams of the multi-beam.

[0050]

[0065] The electron source 201 directs electrons towards an array of collecting lenses 231 (otherwise referred to as a collecting lens array). The electron source 201 is preferably a high-brightness thermal field emitter with a good compromise between brightness and total emission current. There may be tens, hundreds or thousands of collecting lenses 231. The collecting lenses 231 may include multi-electrode lenses and may have a structure based on EP 1 602 121 A1, which is incorporated herein by reference, in particular for its disclosure of a lens array for splitting an electron beam into a number of sub-beams, the array providing one lens per sub-beam. The array of collecting lenses 231 may take the form of at least two, preferably three, plates acting as electrodes, the apertures of each plate being aligned with each other and corresponding to the position of a sub-beam. At least two of the plates are maintained at different potentials during operation to achieve the desired lens effect. Between the plates of the focusing lens array are electrically insulating plates, made of insulating material such as ceramic or glass, with one or more apertures for each sub-beam. One or more alternative arrangements of the plates may feature apertures, each with its own electrode, each with an array of electrodes around its periphery, or arranged as a group of apertures with a common electrode.

[0051]

[0066] In one arrangement, the array of collecting lenses 231 is formed from a three-plate array in which a charged particle has the same energy when it enters each lens as when it leaves each lens, and this arrangement may be called an Einzel lens. Dispersion therefore occurs only within the Einzel lens itself (between the entrance and exit electrodes of the lens), thereby limiting off-axis chromatic aberration. If the thickness of the collecting lens is small, for example a few mm, the effect of such aberrations is small or negligible.

[0052]

[0067] Each collecting lens in the array directs electrons into a respective sub-beam 211, 212, 213 that is focused at a respective intermediate focus 233. A collimator or an array of collimators may be positioned to operate on each intermediate focus 233. The collimator may take the form of a deflector 235 provided at the intermediate focus 233. The deflector 235 is configured to bend each beamlet 211, 212, 213 by an effective amount to ensure that the chief ray (which may also be referred to as the beam axis) is incident on the sample 208 approximately normal (i.e. at approximately 90° to the nominal surface of the sample).

[0053]

[0068] Below the deflector 235 (i.e. on the down-beam side of or further from the electron source 201) there is a control lens array 250 which includes a control lens 251 for each sub-beam 211, 212, 213. The control lens array 250 may for example include two or more, preferably at least three, plate electrode arrays in contact with respective potential sources between the electrodes, preferably with insulating plates in contact with the electrodes. Each of the plate electrode arrays may be referred to as a control electrode. The function of the control lens array 250 is to optimize the beam opening angle with respect to the beam reduction ratio and / or to control the beam energy delivered to the objective lenses 234, each of which directs the respective sub-beam 211, 212, 213 onto the sample 208.

[0054]

[0069] Optionally, an array of scan deflectors 260 is provided between the control lens array 250 and the array of objective lenses 234 (objective lens array). The array of scan deflectors 260 includes one scan deflector 261 for each sub-beam 211, 212, 213. Each scan deflector is configured to deflect a respective sub-beam 211, 212, 213 in one or two directions to scan the sub-beam in one or two directions across the sample 208.

[0055]

[0070] A detector module 240 of the detector is provided between the objective lens 234 and the sample 208 to detect signal electrons / particles emitted from the sample 208. An exemplary configuration of such a detector module 240 is described below. It should be noted that the detector may additionally or alternatively have detector elements on the up-beam side along the primary beam path of the objective lens array or even the control lens array.

[0056]

[0071] In a variation of the arrangement of FIG. 5, the array of condenser lenses 231 can be omitted. Sub-beams can be derived from the beam using, for example, a beam limiter defining an array of beam-limiting apertures. The beam can be separated into sub-beams when it strikes the control lens array 250. The sub-beams are approximately parallel upon incidence on the control lens array 250. The sub-beams of the multi-beam can be arranged in a pattern that can be referred to as a multi-beam arrangement. The pattern can form a grid. The grid can be hexagonal, linear, diamond or square. A collimator (not shown) can be provided on the up-beam side of the control lens array 250.

[0057]

[0072] In a variation (not shown) of the arrangement of Fig. 5, the collimator may include a macro-collimator, which acts on the beam from the electron source 201 before the beam is split into multiple beams. The macro-collimator bends each portion of the beam by an effective amount to ensure that the beam axis of each sub-beam derived from the beam is incident on the sample 208 approximately normal (i.e. at approximately 90° to the nominal surface of the sample 208). The macro-collimator may include a magnetic lens and / or an electrostatic lens. In another arrangement (not shown), the macro-collimator may be partially or wholly replaced by an array of collimator elements provided on the down-beam side of the upper beam restrictor.

[0058]

[0073] In a variation (not shown) of the arrangement of FIG. 5, a macro-scanning deflector may be provided to cause the sub-beams to scan across the sample 208. The macro-scanning deflector deflects the respective portions of the beam to cause the sub-beams to scan across the sample 208. In some embodiments, the macro-scanning deflector includes a macro-multipole deflector, for example with eight or more poles. The deflection is such that the sub-beams derived from the beam are caused to scan across the sample 208 in one direction (e.g. parallel to a single axis, such as the X-axis) or two directions (e.g. with respect to two non-parallel axes, such as the X-axis and the Y-axis). The macro-scanning deflector does not include an array of deflector elements each configured to act on a different individual portion of the beam, but acts macroscopically on all of the beam. The macro-scanning deflector may be provided between the macro-collimator and the control lens array 250. In another arrangement (not shown), the macro-scanning deflector may be partially or completely replaced by a scanning deflector array, for example as a scanning deflector for each sub-beam. In another arrangement (not shown), both a macro scan deflector and a scan deflector array may be provided and operated synchronously.

[0059]

[0074] In some embodiments, the electron optical column 41 further includes an upper beam limiter. The upper beam limiter defines an array of beam limiting apertures. The upper beam limiter may be referred to as an upper beam limiting aperture array or an up-beam side beam limiting aperture array. The upper beam limiter may include a plate having a plurality of apertures. The upper beam limiter forms sub-beams from the beam of charged particles emitted by the electron source 201. Portions of the beam other than those that contribute to the formation of the sub-beams may be blocked (e.g., absorbed) by the upper beam limiter so as not to interfere with the down-beam side sub-beams. The upper beam limiter may be referred to as a sub-beam defining aperture array.

[0060]

[0075] In some embodiments, the objective lens array assembly (which is the unit that includes the objective lens 234) further includes a beam-shaping limiter. The beam-shaping limiter defines an array of beam-limiting apertures. The beam-shaping limiter may be called a lower beam limiter, a lower beam-limiting aperture array, or a final beam-limiting aperture array. The beam-shaping limiter may include a plate (which may be a slab) with a plurality of apertures. The beam-shaping limiter may be down beam from at least one electrode (optionally all electrodes) of the control lens array 250. In some embodiments, the beam-shaping limiter is down beam from at least one electrode (optionally all electrodes) of the objective lens array. In one arrangement, the beam-shaping limiter may be structurally integrated with the electrodes of the objective lens array. Desirably, the beam-shaping limiter is positioned in an area of ​​low electrostatic field strength. The beam-limiting apertures are aligned with the objective lens array such that a portion of the sub-beam from the corresponding objective lens can pass through the beam-limiting aperture and impinge on the sample 208, so that only a selected portion of the sub-beam incident on the beam shaping restrictor passes through the beam-limiting aperture.

[0061]

[0076] Any of the objective lens array assemblies described herein may further include a detector 240. The detector detects electrons emitted from the sample 208. The detected electrons may include any of the electrons detected by the SEM, including signal particles such as secondary electrons and / or backscattered electrons emitted from the sample 208. An exemplary structure of the detector 240 is described in more detail below with reference to Figures 7 and 8.

[0062]

[0077] 6 illustrates a schematic representation of an electron beam system 40 including an electron optical column 41 according to some embodiments. Features that are the same as those described above are labeled with the same reference numerals. For the sake of brevity, such features will not be described in detail with reference to FIG. 6. For example, the electron source 201, the collection lens 231, the macro-collimator 270, the objective lens array 241, and the sample 208 may be as described above.

[0063]

[0078] As explained above, in some embodiments, the detector 240 is between the objective lens array 241 and the sample 208. The detector 240 may face the sample 208. Alternatively, as shown in FIG. 6, in some embodiments, an objective lens array 241 including multiple objective lenses is between the detector 240 and the sample 208.

[0064]

[0079] In some embodiments, the deflector array 95 is between the detector 240 and the objective lens array 241. In some embodiments, the deflector array 95 may be referred to as a beam separator because it includes a Wien filter array. The deflector array 95 is configured to provide a magnetic field to separate charged particles projected onto the sample 208 and secondary electrons traveling from the sample 208 towards the detector 240.

[0065]

[0080] In some embodiments, the detector 240 is configured to detect the signal particles by reference to the energy of the charged particles, i.e. depending on the band gap. Such a detector 240 may be called an indirect current detector. Secondary electrons emitted from the sample 208 gain energy from the electric field between the electrodes. When the secondary electrons reach the detector 240, they have sufficient energy. In a different arrangement, the detector 240 may be a scintillator array, e.g. a fluorescent strip between the beams, positioned on the up-beam side along the primary beam path relative to the Wien filter. The primary beam passing through the Wien filter array (of magnetic and electrostatic strips perpendicular to the primary beam path) has a path on the approximately parallel up-beam and down-beam sides of the Wien filter array, while the signal electrons from the sample are guided by the Wien filter array towards the scintillator array. The generated photons are guided via a photon transport unit (e.g. an array of optical fibers) to a remote photodetector that generates a detection signal in response to the detection of the photons.

[0066]

[0081] The objective lens array 241 may include at least two electrodes in which an aperture array is defined. In other words, the objective lens array includes at least two electrodes with a plurality of holes or apertures. FIG. 7 shows electrodes 242, 243 that are part of an exemplary objective lens array 241 with respective aperture arrays 245, 246. The position of each aperture in an electrode corresponds to the position of a corresponding aperture in another electrode. The corresponding apertures, in use, act on the same beam, sub-beam or group of beams in the multi-beam. In other words, the corresponding apertures in the at least two electrodes are aligned with and disposed along one of the sub-beam paths, i.e., the sub-beam paths 220. Thus, the electrodes each comprise an aperture through which the respective sub-beam 211, 212, 213 propagates.

[0067]

[0082] The objective lens array 241 may include two electrodes or three electrodes as shown in FIG. 7, or may have more electrodes (not shown). An objective lens array 241 with only two electrodes may have less aberration than an objective lens array 241 with more electrodes. A three-electrode objective lens allows for a stronger lens because the potential difference between the electrodes can be larger. Additional electrodes (i.e., more than two electrodes) provide additional degrees of freedom in controlling the electron trajectory, for example to focus secondary electrons in addition to the incident beam. The advantage of a two-electrode lens over an Einzel lens is that the energy of the incoming beam is not necessarily the same as the outgoing beam. The potential difference on such a two-electrode lens array advantageously allows it to function as either an acceleration or deceleration lens array.

[0068]

[0083] Adjacent electrodes of the objective lens array 241 are spaced apart from one another along the sub-beam paths such that the distance between adjacent electrodes is greater than the objective lenses of the objective lens array, and insulating structures may be arranged as described below.

[0069]

[0084] Preferably, each of the electrodes provided in the objective lens array 241 is a plate. The electrodes may alternatively be described as flat sheets. Preferably, each of the electrodes is flat. In other words, each of the electrodes is preferably provided as a thin flat plate in the form of a plate. Of course, the electrodes do not have to be flat. For example, the electrodes may bend due to forces resulting from high electrostatic fields. It is preferred to provide flat electrodes, as this makes the electrodes easier to manufacture, since known fabrication methods may be used. Flat electrodes may also be preferred, as they may provide a more accurate alignment of the apertures between the various electrodes.

[0070]

[0085] The objective lens array 241 may be configured to demagnify the charged particle beam by a factor of more than 10, preferably in the range of 50-100 or more.

[0071]

[0086] The detector 240 is provided for detecting signal particles, i.e. secondary charged particles and / or backscattered charged particles, emitted from the sample 208. The detector 240 is positioned between the objective lens 234 and the sample 208. Depending on the direction of the signal particles, the detector generates a detection signal. The detector 240 may alternatively be referred to as a detector array or a sensor array, and the terms "detector" and "sensor" are used interchangeably throughout this application.

[0072]

[0087] An electron optical device of the electron optical system 41 may be provided. The electron optical device is configured to project the electron beam towards the sample 208. The electron optical device may include an objective lens array 241. The electron optical device may include a detector 240. The array of objective lenses (i.e., objective lens array 241) may correspond to an array of detectors (i.e., detector 240) and / or may correspond to any of the beams (i.e., sub-beams).

[0073]

[0088] An exemplary detector 240 is described below. However, any reference to detector 240 may be a single detector (i.e., at least one detector) or multiple detectors, as appropriate. Detector 240 may include detector elements 405 (e.g., sensor elements such as capture electrodes). Detector 240 may include any suitable type of detector. For example, capture electrodes, scintillators, or PIN elements for, e.g., directly detecting electronic charges may be used. Detector 240 may be a direct current detector or an indirect current detector. Detector 240 may be a detector as described below with respect to FIG. 8.

[0074]

[0089] The detector 240 may be positioned between the objective lens array 241 and the sample 208. The detector 240 is configured to be close to the sample 208. The detector 240 may be very close to the sample 208. Alternatively, there may be a large gap from the detector 240 to the sample 208. The detector 240 may be positioned within the device such that it faces the sample 208. Alternatively, the detector 240 may be positioned elsewhere in the electron-optical system 41 such that a part of the electron-optical device that is not the detector faces the sample 208.

[0075]

[0090] FIG. 8 is a bottom view of a detector 240 including a substrate 404 on which are provided a number of detector elements 405 each surrounding a beam aperture 406. The beam apertures 406 may be formed by etching the substrate 404. In the arrangement shown in FIG. 8, the beam apertures 406 are arranged in a hexagonal close-packed array. The beam apertures 406 may also be arranged differently, for example in a rectangular or diamond array. The beam arrangement of the hexagonal arrangement of FIG. 8 may be more densely packed than a square beam arrangement. The detector elements 405 may be arranged in a rectangular array or a hexagonal array. The beam apertures may correspond to a multi-beam arrangement of sub-beams directed to the substrate 404.

[0076]

[0091] The capture electrode 405 forms the bottom, i.e., the surface closest to the sample, of the detector module 240. Between the capture electrode 405 and the body of the silicon substrate 404, a logic layer is provided. The logic layer may include amplifiers, e.g., transimpedance amplifiers, analog-to-digital converters, and readout logic. In some embodiments, there is one amplifier and one analog-to-digital converter per capture electrode 405. Circuits featuring these elements may be contained within unit areas called cells, each associated with an aperture. The detector module 240 may have several cells, each associated with an aperture. Within or on the substrate, there is a wiring layer that is connected to the logic layer and that connects the logic layer of each cell to the outside world, e.g., via power, control, and data lines. The integrated detector module 240 described above is particularly advantageous when used with systems with adjustable landing energies, since secondary electron capture can be optimized for a range of landing energies. The detector module in the form of an array may be integrated into other electrode arrays as well as the bottom electrode array. Such a detector module may, for example, feature a detector that is a scintillator or semiconductor detector, such as a PIN detector, above the most down-beam surface of the objective lens. Such a detector module may feature a circuit architecture similar to that of a detector module that includes a current detector. Further details and alternative arrangements of detector modules integrated into the objective lens, at least as far as the details of the detector module are concerned, may be found in European Patent Application Publication Nos. 20184160.8 and 20217152.6, which are incorporated herein by reference.

[0077]

[0092] The detector may comprise multiple parts, specifically multiple detection parts. A detector including multiple parts may be associated with one of the sub-beams 211, 212, 213. Thus, multiple parts of one detector 240 may be configured to detect signal particles emitted from the sample 208 in association with one of the primary beams (which may otherwise be referred to as sub-beams 211, 212, 213). In other words, a detector including multiple parts may be associated with one of the apertures in at least one electrode of the electrodes of the objective lens assembly. More specifically, a detector 405 including multiple parts may be arranged around a single aperture 406, 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 detection parts, the detection signal includes components from various detection signals that may be processed as a data set or in a detection image.

[0078]

[0093] In some embodiments, the objective lens array 241 is either a replaceable module by itself or in combination with other elements such as a control lens array and / or a detector array. The replaceable modules may be field replaceable, i.e., replaced with a new module by a field engineer. In some embodiments, multiple replaceable modules are included within the system and thus may be swapped between operative and inoperative positions without opening the electron beam system.

[0079]

[0094] In some embodiments, one or more aberration correctors are provided that reduce one or more aberrations in the sub-beams. The aberration correctors, positioned at or directly adjacent to the intermediate focus (or intermediate image plane), may include deflectors that correct the electron source 201 so that it appears to be in different positions for different beams. The correctors may be used to correct macro-aberrations due to the radiation source that prevent good alignment between each sub-beam and the corresponding objective lens. The aberration correctors may correct aberrations that prevent proper column alignment. The aberration correctors may be CMOS-based individual programmable deflectors as disclosed in EP 2702595 A1 or an array of multiple deflectors as disclosed in EP 2715768 A2, the description of the beamlet manipulator in both patent documents being incorporated herein by reference. The aberration correctors may reduce one or more of field curvature, focus error and astigmatism.

[0080]

[0095] A variety of different system architectures can be used to perform inspection methods consistent with embodiments of the present disclosure. For example, the electron beam system can be a single beam system or can include multiple single beam columns, or can include multiple multi-beam columns. The columns can include the electron optical column 41 described in any of the above embodiments or aspects. As a multiple column (or multi-column system), the devices can be arranged in an array that can reach a total of 2 to 100 or more columns. The electron beam system can take the form of the examples as described with respect to and depicted in any of Figures 2-8.

[0081]

[0096] As mentioned in the introduction of this specification, sample evaluation methods can be used to evaluate the degree of undesired pattern defects in a sample. Such methods can involve identifying features of interest on the sample and comparing those features to their respective reference versions elsewhere on the sample or in a database. Evaluation methods that involve comparison of measured images of features in different die areas can be referred to as die-to-die (D2D) processes. Evaluation methods that involve comparison of measured images of features in a die area to reference images in a database can be referred to as die-to-database (D2DB) processes.

[0082]

[0097] In some arrangements, alignment (e.g., for D2DB or D2D) may be performed using a sample map that provides information about the location of the field area and the die areas within the field area. The sample map may be imported from a metrology tool separate from the device performing the sample evaluation method (e.g., an optical metrology tool that does not use a charged particle beam). Alternatively, the sample map may be generated by measuring the positions of fiducial marks on the die and using the measured positions to generate the sample map. Such maps are typically generated assuming that the field area is rectangular and located on grid points of a regular rectangular grid. The die areas are also typically rectangular and located on grid points of a regular rectangular grid with a smaller pitch. The fiducial marks are measured to determine the position and pitch of the grid. For example, fiducial marks (which may be called die corner marks) may be provided that identify the position of each corner of the die area. Field areas may be defined that each include a group of connected die areas. Each field area may include, for example, a 2×3 array of die areas.

[0083]

[0098] Misalignment between the generated sample map and the actual sample map may result in features of interest not being present exactly at expected locations during the evaluation method. For this reason, the evaluation method generally requires a search procedure to identify the exact location of the features of interest. The search procedure may include searching for selected die marks, such as local alignment points (LAPs). The search region associated with each selected die mark needs to be large enough that the respective die mark is not located within the search region with other die marks. Increasing the size of the search region undesirably increases the amount of time required to search the search region. Increasing the size of the search region may also increase the risk that the search region includes more than one associated die mark (e.g., LAPs), which may present a risk of alignment being based on an incorrect die mark.

[0084]

[0099] In practice, the exposure of the dies on the sample is such that the die and field areas are not perfect rectangles and are not exactly centered on the grid points of a regular rectangular grid. These effects arise not only due to limitations of the lithographic apparatus used to make the exposure, but also because the lithographic apparatus itself applies corrections to minimize process-induced overlay drift. These corrections include both inter-field and intra-field corrections. Inter-field corrections may be referred to as wafer grid corrections. Intra-field corrections may be referred to as field grid corrections. Information about the corrections applied during exposure may be output as exposure correction data (see below).

[0085]

[0100] Inter-field correction is applied to correct the position of the field regions on the sample. The position correction may be required due to distortion of the sample. Various process steps may cause distortion of the sample. The distortion may be caused by chemical mechanical polishing and / or thermal annealing. The distortion may be caused by changes in the overall shape of the sample due to mechanical stress on the wafer and / or by movement of the wafer between different supports. To compensate for such distortion, inter-field correction is applied by the lithographic apparatus. Inter-field correction may involve higher order corrections, such as corrections based on third to fifth order fitting (e.g. based on third to fifth order polynomials). The lithographic apparatus exposes the field regions according to their corrected positions (after application of the inter-field correction).

[0086]

[0101] Intra-field corrections are applied to correct for each field shape. During exposure, the field shape may deform due to various factors such as image setup, lens heating, and reticle stage drift. Typically, a third to fifth order fitting is applied to represent the deformation of the field shape. The lithography apparatus may adjust the lens or reticle stage to ensure that each field region is exposed while taking the corrections into account. Due to scanning and / or exposure slit constraints of the lithography apparatus, some of the intra-field corrections are ignored during exposure.

[0087]

[0102] Complex nonlinear deviations in the position and / or shape of field areas that occur in practice can result in large mismatches between the positions of associated die marks (e.g., LAPs) and their expected positions in sample maps generated based on a simple model in which die and field areas are in a regular array of rectangular elements. Large position mismatches reduce throughput and reliability in the evaluation method. The mismatches are particularly problematic when it is desired to perform an offline setup procedure (which may be called waferless offline recipe setup) before a sample is available for measurement. The mismatches mean that a series of manual recipe adjustments must be made when the sample is available, which reduces the usefulness of the offline setup procedure.

[0088]

[0103] The embodiments described below aim to at least partially address one or more of the problems set forth above.

[0089]

[0104] 9 and 11 depict a sample 208 processed by a lithography apparatus to define a pattern on the sample 208. The sample 208 is processed in a number of die regions 502 (not shown) and a number of field regions 504. Each die region 502 may, for example, correspond to a respective die in a pattern defined by a lithography process. Each field region 504 may correspond to an area processed by a respective exposure of the sample 208 during a lithography process. Each field region 504 includes or is made up of a number of die regions 502. In the example described below with reference to FIG. 14, each field region 504 includes a 2×3 array of die regions 502.

[0090]

[0105] As discussed above, various factors result in the position and shape of the field regions 504 being distorted such that the actual sample map representing the position and shape of the field regions 504 differs significantly from the nominal sample map. A schematic example of an actual sample map of a field region 504 is depicted by the solid line grid labeled 510 in Figures 9 and 11. The solid lines of the grid represent the boundaries of the field regions 504. Each field region 504 includes multiple die regions 502, which are not shown.

[0091]

[0106] As discussed above, a sample map of the field area can be generated based on measurements of fiducial marks in the die area. An example of such a generated sample map is depicted by the dashed grid labeled 520 in Figures 9 and 11.

[0092]

[0107] FIG. 9 illustrates a case where the sample map is generated assuming that the field region 504 is rectangular and positioned on a regular rectangular array of grid points. FIG. 10 illustrates an exemplary one of the field regions 504 of FIG. 9, where the solid boundary labeled 510 represents the actual position and shape of the field region 504, and the dashed boundary labeled 520 represents the position and shape of the field region 504 according to the generated sample map. When the sample map is generated in this manner, it can be seen that there is a large mismatch between the actual position and shape of the field region 504 and the position and shape of the field region 504 predicted by the generated sample map. As shown in FIG. 10, in the subsequent alignment process, the search region 515 for searching the selected die mark (e.g., LAP) needs to be relatively large to reliably capture the die mark. This is because the predicted position 512 of the die mark according to the generated map is relatively far from the actual position 522 of the die mark.

[0093]

[0108] FIG. 11 illustrates the case where a sample map is generated using the methods of the present disclosure. These methods allow for more complex arrangements of field regions 504 on the sample 208, which allows for closer alignment between the generated sample map and reality. FIG. 12 illustrates an exemplary one of the field regions 504 of FIG. 11, where the solid boundary labeled 510 represents the actual position and shape of the field region 504, and the dashed boundary labeled 520 represents the position and shape of the field region 504 according to the generated sample map. It can be seen that compared to the situation shown in FIG. 9 and FIG. 10, the generated sample map provides a much closer alignment to reality with the arrangement of FIG. 11 and FIG. 12. As a result, the search region 515 can be made much smaller while still reliably capturing the die mark used for alignment.

[0094]

[0109] An example method for implementing the above functionality is described below with reference to Figures 13 and 14. The method generates a sample map. The sample map defines the location and shape of the field regions. The method may be performed by a charged particle inspection system as described above with reference to Figure 1. The charged particle inspection system may include an electron beam system 40. The electron beam system 40 projects one or more electron beams onto the sample 208 and detects signal electrons emitted from the sample 208 to obtain information about the surface of the sample 208, such as an image characteristic of the material structure of the surface. The electron beam system 40 may take any of the forms described above with reference to Figures 2-8 or other forms.

[0095]

[0110] A sample 208 is provided that has been processed by a lithography process as described above. The sample 208 includes a die region 502 (e.g., a die). The die region 502 is distributed among a number of field regions 504 (e.g., fields). Each field region 504 includes a number of die regions 502.

[0096]

[0111] 13 (left portion), the method further includes measuring a position of the first mark 532 in each of the plurality of field regions 504. The position of the first mark may be measured relative to a common reference position on the sample 208, such as the geometric center of the sample 208 (e.g., the center of the wafer). The first mark 532 is depicted generally as a cross and is shown relative to a nominal (undistorted) arrangement of the field regions 504 on the sample 208.

[0097]

[0112] The method further comprises fitting a first model to the measured position of the first mark 532. The fitted first model represents the position of the field region 504. The represented position is shown diagrammatically in Figure 13 (right part).

[0098]

[0113] 14 (left portion), the method further includes measuring positions of the second marks 534 in the field region 504 or in each of the field regions 504. The position of the second marks in each field region 504 may be measured relative to a reference point unique to that field region 504, such as relative to the geometric center of that field region 504.

[0099]

[0114] The method further includes fitting a second model to the measured positions of the second marks 534. The fitted second model represents the shape of each field region 504. An example of the represented shape of one of the field regions 504 is shown in FIG. 14 (right part). The second marks 534 may be measured in a number of field regions 504. The fitting of the second model may include determining the shape of a number of different field regions 504 individually using the second marks therein. Thus, the different field regions 504 may be determined to have different shapes. For example, in some embodiments, the second marks are measured in each of 3-10 field regions 504, optionally in each of 3-6 field regions 504, optionally in each of 3-4 field regions 504. The number of second marks measured in each of these field regions 504 may be in the range of 5-20, optionally in the range of 8-18, optionally in the range of 10-15. The measured second marks may be used to determine the shapes of these field regions 504 individually. An average of the determined shapes may be determined and applied to all field regions 504 in the map as an approximation. In this case, the second model may represent the shapes of the field regions 504 as all being the same as each other. In other embodiments, the fitted second model represents different shapes for the different field regions 504.

[0100]

[0115] The method further includes outputting a sample map using the fitted first and second models, such that a representation of the position of the field region 504 provided by the fitted first model is combined with a representation of the shape of the field region 504 provided by the fitted second model(s) to provide the sample map.

[0101]

[0116] Either or both of the first and second models are configured to represent non-linear geometric shapes, and thus, in contrast to the situation described above with reference to Figures 9 and 10, where the map was generated assuming that the die areas 502 and field areas 504 are rectangular and located on grid points of a regular rectangular grid, the first model and / or the second model are given more degrees of freedom, thereby allowing for a better match between the generated sample map and reality.

[0102]

[0117] In some embodiments, the first model is configured to represent the location of the field regions 504 in an array having rows of field regions 504 and columns of field regions 504. At least one of the rows is nonlinear and / or at least one of the columns is nonlinear. In a nonlinear row, the field regions 504 in the row are aligned along a row line that is nonlinear. The row line may be defined as a line that passes through the geometric center of the field regions 504 in the row. An example of a row line 533 is shown diagrammatically in FIG. 13 (right portion). Similarly, in a nonlinear column, the field regions 504 in the column are aligned along a column line (not shown) that is nonlinear. The intersection of the row line and the column line may define the location of the field region 504 in the array, such as the location of the geometric center of the field region 504. Providing the first model with sufficient degrees of freedom to allow for the row and / or column lines to be nonlinear increases the accuracy with which the first model can describe the location of the field regions 504.

[0103]

[0118] Various mathematical structures may be used to define the first model. In one example, the first model includes multiple equations that define row and column lines. Thus, the first model may represent each nonlinear row and / or nonlinear column with a respective nonlinear equation. In some embodiments, the equations are polynomials of degree 2 or higher. Optionally, the degree of the polynomial ranges from 3 to 5, inclusive. This has been found to provide a good balance between fitting accuracy and sampling throughput. The general formula for the polynomial f(x) is as follows, where the degree is the maximum value of k, with respect to which the corresponding coefficients a k There exists a non-zero value of

number

[0104]

[0119] The coefficients of each equation (e.g., a in the polynomial example above) k The values ​​of θ and θ) define the exact shape and position of the line that the equation represents. Each first mark has a known position relative to the field region 504 in which it is located. Thus, fitting of the first model to the measured positions of the first marks can be done by determining the coefficients of the equation that result in the field regions 504 in the generated sample map being positioned such that the first marks therein are, on average, as close as possible to their respective measured positions. Other curve representations are possible, such as spline representations.

[0105]

[0120] Similar considerations apply to the second model. The second model may be configured to represent the shape of each field region 504 such that at least a portion of the boundary of the shape is nonlinear, as illustrated in FIG. 14 (right portion). The second model may represent each nonlinear portion of the boundary with a respective nonlinear equation. The nonlinear equations may take any of the forms described above with respect to the first model, including polynomials of degree 2 or higher (optionally in the range of 3 to 5 inclusive).

[0106]

[0121] In some embodiments, the measurement of the position of the second mark is made using the position of the field region 504 represented by the fitted first model. The improved map of the position of the field region provided by the fitted first model can facilitate identification of the second mark, thereby increasing the speed and / or reliability of the measurement of the position of the second mark.

[0107]

[0122] Figures 15 and 16 depict generally a further method that may be used in combination with or instead of the methods described above with reference to Figures 11-14. The method again includes generating a sample map representing the positions and shapes of the field regions, as generally indicated by dashed grid 520. The samples 208 may include field regions 504 and die regions 502 in any of the configurations described above. The method further includes receiving exposure correction data 540 from a lithography apparatus used to expose each field region 504 in a lithography process. The method includes using the exposure correction data 540 to generate the sample map.

[0108]

[0123] As mentioned above, lithographic apparatus typically apply various complex (non-linear) corrections to the position and / or shape of the die areas on the sample. The exposure correction data 540 includes information about these corrections, thereby providing information about the expected position and shape of the field areas 504. The exposure correction data may include information about any of the inter-field and intra-field corrections mentioned above and / or any other corrections that affect the position and / or shape of the field areas 504. The exposure correction data 540 allows for the generation of a sample map (as illustrated in FIG. 15 (right part)) that is more realistic than the alternative method that assumes that the field areas 504 are rectangular and positioned on a regular rectangular array of grid points (as illustrated in FIG. 9 and FIG. 10 above). The position and / or shape of the field areas 504 may be defined in any of the ways described above with reference to FIG. 11-14. The position of the field areas 502 may be defined in an array having rows of field areas and columns of field areas, where at least one of the rows is non-linear and / or at least one of the columns is non-linear. The defined shape of the field region 505 may include a boundary having a non-linear portion.

[0109]

[0124] In some embodiments, as illustrated in FIG. 16, the method further comprises applying a correction to the generated sample map using the received exposure correction data (represented by grid 520 in the left part of FIG. 16) to obtain a corrected sample map (represented by grid 521 shown in the right part of FIG. 16). Such a correction may be required, for example, due to process drift or warping of the sample 208. Differences may also exist between a spatial measurement system used in a lithographic apparatus compared to a spatial measurement system used in an evaluation apparatus that uses the generated sample map to evaluate defects. In some embodiments, the method comprises measuring the positions of a number of fiducial marks 536 on the sample 208 and generating a corrected sample map using the measured positions. The corrected sample map may be such that it minimizes the average difference between the positions of the fiducial marks in the generated sample map and the actual positions of the fiducial marks on the sample 208. The radially inward directed arrows in the right part of FIG. 16 depict the corrections in a schematic manner, which in this example comprise a general radial shrinking of the grid to achieve an improved alignment to the measured positions of the fiducial marks.

[0110]

[0125] In some embodiments, the corrected map is generated by linearly adjusting the generated sample map using the exposure correction data to achieve an improved alignment to the measured positions of the fiducial marks. The linear adjustment may include, for example, increasing or decreasing the size of the generated sample map without changing the geometry (e.g., aspect ratio) of the generated sample map. The number of fiducial marks 536 can be chosen relatively freely. In some embodiments, a linear model using 6-10 fiducial marks 536 has been found to provide good performance. Alternatively, higher order corrections can be applied, but the inventors have found that a linear adjustment for this particular type of correction provides satisfactory performance in many situations. This is because information about the complex nonlinear distortion of the grid is already provided in the initial sample map generated based on the received exposure correction data.

[0111]

[0126] In some embodiments, information about the corrected map is provided as feedback to the lithography apparatus. This allows for adapting subsequent lithography processes to reduce errors in the lithography process. For example, if the corrected sample map indicates that the offset is drifting, this may provide information about instabilities in the lithography process. In some embodiments, the lithography apparatus adapts process parameters based on the corrected sample map to improve the performance of the lithography apparatus. The adaptation may reduce the need for corrections on future generated sample maps. Thus, a method of processing a sample may be provided that includes generating a corrected sample map using any of the above techniques and adapting a lithography process performed on a subsequent sample using the generated corrected map.

[0112]

[0127] In some embodiments, a method of evaluation is provided that includes generating a sample map according to any of the methods described above. The method of evaluation includes inspecting the sample 208 using the generated sample map to identify one or more features of interest. The method of evaluation may include evaluating the extent to which the one or more features of interest include defects. This may be accomplished by comparing the image of the feature of interest to reference images elsewhere on the sample, on other samples, or in a database.

[0113]

[0128] In some embodiments, inspection is performed by directing one or more charged particle (e.g., electron) beams onto the sample 208 and detecting one or more charged particles (e.g., electrons) emitted from the sample 208. Inspection may use any of the electron optical arrangements described above with reference to Figures 1-8 or any other suitable arrangement for inspecting a sample using a charged particle beam. Inspection may also be performed using other techniques, such as optical techniques based on electromagnetic radiation.

[0114]

[0129] References to top and bottom, up and down, above and below should be understood as referring to directions parallel to the (typically, but not always perpendicular) up-beam and down-beam directions of the electron beam or multi-beam impinging on the sample 208. Thus, up-beam and down-beam references are intended to refer to directions relative to the beam path, independent of any prevailing gravitational fields.

[0115]

[0130] The embodiments described herein may take the form of a series of aperture arrays or electron optical elements arranged in an array along the beam path or multi-beam path. Such electron optical elements may be electrostatic. In some embodiments, for example, all the electron optical elements from the beam limiting aperture array to the final electron optical element in the sub-beam path before the sample may be electrostatic and / or in the form of aperture arrays or plate arrays. In some arrangements, one or more of the electron optical elements are fabricated as a microelectromechanical system (MEMS) (i.e., by using MEMS fabrication techniques). The electron optical elements may have magnetic and electrostatic elements. For example, a compound array lens may feature a macro magnetic lens arranged along the multi-beam path, containing the multi-beam path by upper and lower pole plates within the magnetic lens. Within the pole plates there may be an array of apertures for the beam paths of the multi-beam. Electrodes may be above, below or between the pole plates to control and optimize the electromagnetic field of the compound lens array.

[0116]

[0131] Evaluation tools or systems according to the present disclosure may include devices that perform qualitative evaluations (e.g., pass / fail) of a sample, devices that perform quantitative (e.g., size of features) measurements of a sample, or devices that generate images of maps of a sample. Examples of evaluation tools or systems are inspection tools (e.g., to identify defects), review tools (e.g., to classify defects), and metrology tools or tools that can perform any combination of evaluation functions associated with an inspection tool, review tool, or metrology tool (e.g., macro inspection tool).

[0117]

[0132] Reference to a component or a system of components or elements that is controllable to manipulate a charged particle beam in a certain manner includes configuring a controller, or control system, or control unit to control the components to manipulate the charged particle beam in the manner described above, and optionally using other controllers or devices (e.g., voltage sources) to control the components to manipulate the charged particle beam in this manner. For example, a voltage source may be electrically connected to electrodes of one or more components, such as the control lens array 250 and the objective lens array 241, to apply a potential to the components under the control of the controller, or control system, or control unit. An activatable component, such as a stage, may be controllable to be activated and thus moved relative to other components, such as the beam path, by using one or more controllers, control systems, or control units to control the activation of the component.

[0118]

[0133] The functions provided by 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, CPU, RAM, SSD, motherboard, 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. The one or more computer programs may be provided in the form of a medium, optionally a non-transitory medium, that stores computer-readable instructions. The medium may be referred to as a computer program. When the computer-readable instructions are read by the computer, the computer performs the required method steps. The computer may be comprised in a distributed computing system having multiple different computers connected to each other in a self-contained unit or via a network.

[0119]

[0134] 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 splitting or separating the parent radiation beam. The term "manipulator" is used to encompass any element that affects the path of a sub-beam or beamlet, such as a lens or deflector. References to elements aligned along a beam path or sub-beam path are understood to mean that the respective element is positioned along the beam path or sub-beam path. References to an optical system are understood to mean an electron-optical system.

[0120]

[0135] The methods of the present disclosure may be performed by a computer system including one or more computers. A computer used to implement the embodiments of the present disclosure 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 dedicated processor. As discussed above, in some cases, a particular type of processor may provide advantages in terms of reduced cost and / or increased processing speed, and the methods of the embodiments of the present disclosure may be adapted to use a particular processor type. Some steps of the methods of the present disclosure involve parallel processing that is likely to be implemented on a processor capable of parallel processing, such as a GPU.

[0121]

[0136] The term "image" as used herein is intended to refer to any array of values, where each value relates to a sample at a location, and the arrangement of values ​​in the array corresponds to the spatial arrangement of the sampled locations. An image may include a single layer or multiple layers. In the case of a multiple layer image, each layer, which may also be called a channel, represents a different sample at some location. The term "pixel" is intended to refer to a single value of the array, or a group of values ​​corresponding to a single location in the case of a multiple layer image.

[0122]

[0137] The computer used to implement the embodiments of the present disclosure may be physical or virtual. The computer used to implement the embodiments of the present disclosure may be a server, a client, or a workstation. The computers used to implement the embodiments of the present disclosure may be distributed and interconnected via a local area network (LAN) or a wide area network (WAN). The results of the methods of the embodiments of the present disclosure may be displayed to a user or may be stored in any suitable storage medium. The present disclosure may be embodied in a non-transitory computer-readable storage medium that stores instructions for performing the methods of the present disclosure. The present disclosure may be embodied in a computer system including one or more processors and a memory or storage that stores instructions for performing the methods of the present disclosure.

[0123]

[0138] Various aspects of the disclosure are defined in the following numbered clauses. 1. A method for generating a sample map, comprising: obtaining a sample having a field area; Measuring a position of a first mark in each of a plurality of field regions; fitting a first model to the measured positions of the first marks, the fitted first model representing the positions of the field regions; Measuring positions of a plurality of second marks in the field region or in each of the plurality of field regions; fitting a second model to the measured positions of the second marks, the fitted second model representing the shape of each field region; outputting a sample map using the fitted first and second models; The method includes: 2. The method of claim 1, wherein either or both of the first and second models are configured to represent a non-linear geometric shape. 3. The method of claim 1 or 2, wherein measuring the position of the second mark is performed using the position of the field region represented by the fitted first model. 4. A method according to any one of the preceding clauses, wherein the first model is configured to represent the positions of the field areas in an array having rows of field areas and columns of field areas, at least one of the rows being non-linear and / or at least one of the columns being non-linear. 5. A method according to any one of the preceding clauses, wherein the second model is configured to represent the shape of each field region such that at least a portion of the boundary of the shape is non-linear. 6. The method of claim 4, wherein the first model represents each non-linear row and / or non-linear column by a respective non-linear equation. 7. The method of claim 5, wherein the second model represents each nonlinear portion of the boundary by a respective nonlinear equation. 8. The method of claim 6 or 7, wherein each nonlinear equation comprises a polynomial. 9. The method of claim 8, wherein the degree of the polynomial is in the range of 3 to 5, inclusive. 10. The method of any one of the preceding clauses, wherein the position of the first mark is measured relative to a common reference position on the sample. 11. A method according to any one of the preceding clauses, wherein the position of the second mark in each field region is measured relative to a reference point specific to that field region. 12. A method according to any one of the preceding clauses, wherein each field area corresponds to an area of ​​the sample that is processed by a respective exposure during a lithography process. 13. The method of any one of the preceding clauses, wherein the second marks are measured in each of 3 to 10 field regions. 14. The method of any one of the preceding clauses, wherein the positions of the 5 to 20 second marks are measured in one field region or in each of a plurality of field regions. 15. A method of generating a sample map, the sample map including information regarding the location and shape of field regions on a sample, the method comprising: Providing a sample having a field area; receiving exposure correction data from a lithographic apparatus used to expose each of the field regions; generating a sample map using the exposure corrected data; A method comprising: 16. The method of claim 15, wherein the sample map defines the locations of the field areas in an array having rows of field areas and columns of field areas, and at least one of the rows is non-linear and / or at least one of the columns is non-linear. 17. The method of claim 16, wherein the sample map defines a shape of a field region including a boundary having a nonlinear portion. 18. A method according to any one of clauses 15 to 17, further comprising measuring the positions of a plurality of reference marks on the sample and generating a corrected sample map using the measured positions. 19. The method of claim 18, wherein the corrected sample map is generated by linearly adjusting the generated sample map with the exposure corrected data. 20. The method of claim 18 or 19, further comprising providing information about the corrected sample map to a lithography apparatus to enable a subsequent lithography process to be adapted to reduce errors in the lithography process. 21. A computer program that, when executed by a computer, has the following steps: receiving data representative of a measured position of a first mark in each of a plurality of field regions on the sample; fitting a first model to the measured positions of the first marks, the fitted first model representing the positions of the field regions; receiving data representative of measured positions of a plurality of second marks in the field region or in each of the plurality of field regions; fitting a second model to the measured positions of the second marks, the fitted second model representing the shape of each field region; outputting a sample map using the fitted first and second models; A computer program containing instructions to cause a computer to execute the following: 22. The computer program of clause 21, wherein either or both of the first and second models are configured to represent a non-linear geometric shape. 23. A computer program according to clause 21 or 22, wherein measuring the position of the second mark is performed using the position of the field region represented by the fitted first model. 24. A computer program according to any one of clauses 21 to 23, wherein the first model is configured to represent the positions of the field areas in an array having rows of field areas and columns of field areas, wherein at least one of the rows is non-linear and / or at least one of the columns is non-linear. 25. A computer program according to any one of clauses 21 to 24, wherein the second model is configured to represent the shape of each field region such that at least a portion of the boundary of the shape is non-linear. 26. The computer program of clause 24, wherein the first model represents each non-linear row and / or non-linear column by a respective non-linear equation. 27. The computer program of clause 25, wherein the second model represents each nonlinear portion of the boundary by a respective nonlinear equation. 28. The computer program of clause 26 or 27, wherein each nonlinear equation comprises a polynomial. 29. The computer program of claim 28, wherein the degree of the polynomial is in the range of 3 to 5, inclusive. 30. A computer program according to any one of clauses 21 to 29, wherein the measured position of the first mark represents a position measured relative to a common reference position on the sample. 31. A computer program according to any one of clauses 21 to 30, wherein the measured position of the second mark in each field region represents a position measured relative to a reference point specific to that field region. 32. A computer program according to any one of clauses 21 to 31, wherein each field area corresponds to an area of ​​the sample that is processed by a respective exposure during a lithography process. 33. A computer program according to any one of clauses 21 to 32, wherein the received data representative of the measured positions of the second mark includes the measured positions of the second mark in each of the 3 to 10 field regions. 34. A computer program according to any one of clauses 21 to 33, wherein the received data representing the measured positions of the second marks includes positions of 5 to 20 second marks measured in one field area or in each of a plurality of field areas. 35. A computer program that, when executed by a computer, has the following steps: receiving exposure correction data from a lithographic apparatus used to expose a field region on the sample; generating a sample map using the exposure correction data, the sample map including information regarding the location and shape of the field regions on the sample; A computer program containing instructions to cause a computer to execute the following: 36. The computer program of clause 35, wherein the sample map defines the locations of the field areas in an array having rows of field areas and columns of field areas, at least one of the rows being non-linear and / or at least one of the columns being non-linear. 37. The computer program of clause 36, wherein the sample map defines a shape of the field region including a boundary having a nonlinear portion. 38. A computer program according to any one of clauses 35 to 37, further comprising instructions which, when executed by a computer, cause the computer to receive data representing measured positions of a plurality of reference marks on the sample, and generate a corrected sample map using the measured positions. 39. The computer program of clause 38, wherein the corrected sample map is generated by linearly adjusting the generated sample map with the exposure correction data. 40. A computer program according to clause 38 or 39, further comprising instructions which, when executed by a computer, cause the computer to provide information about the corrected sample map to a lithography apparatus to enable a subsequent lithography process to be adapted to reduce errors in the lithography process. 41. A sample holder configured to hold a sample having a field area; an electron beam system configured to project one or more electron beams onto the sample and detect signal electrons emitted from the sample; A controller, causing the electron beam system to measure a position of a first mark in each of a plurality of field regions; fitting a first model to the measured positions of the first marks, the fitted first model representing the positions of the field regions; causing the electron beam system to measure positions of a plurality of second marks in the field region or in each of a plurality of field regions; fitting a second model to the measured positions of the second marks, the fitted second model representing the shape of each field region; and outputting a sample map using the fitted first and second models; a controller configured to 23. A charged particle beam inspection system comprising: 42. The system of claim 41, wherein either or both of the first and second models are configured to represent a non-linear geometric shape. 43. A system as described in clause 41 or 42, wherein the controller is configured to cause the electron beam system to measure the position of the second mark using the position of the field region represented by the fitted first model. 44. A system described in any one of clauses 41 to 43, wherein the first model is configured to represent the positions of the field areas in an array having rows of field areas and columns of field areas, at least one of the rows being non-linear and / or at least one of the columns being non-linear. 45. A system according to any one of clauses 41 to 44, wherein the second model is configured to represent the shape of each field region such that at least a portion of the boundary of the shape is non-linear. 46. ​​The system of claim 44, wherein the first model represents each nonlinear row and / or nonlinear column by a respective nonlinear equation. 47. The system of clause 45, wherein the second model represents each nonlinear portion of the boundary with a respective nonlinear equation. 48. The system of clause 46 or 47, wherein each nonlinear equation includes a polynomial. 49. The system of claim 48, wherein the degree of the polynomial is in the range of 3 to 5, inclusive. 50. A system according to any one of clauses 41 to 49, wherein the controller is configured to cause the electron beam system to measure the position of the first mark relative to a common reference position on the sample. 51. A system described in any one of clauses 41 to 50, wherein the controller is configured to cause the electron beam system to measure the position of the second mark in each field region relative to a reference point specific to that field region. 52. A system according to any one of clauses 41 to 51, wherein each field area corresponds to an area of ​​the sample that is processed by a respective exposure during a lithography process. 53. A system according to any one of clauses 41 to 52, wherein the controller is configured to cause the electron beam system to measure the second mark in each of the 3 to 10 field regions. 54. A system described in any one of clauses 41 to 53, wherein the controller is configured to cause the electron beam system to measure the positions of 5 to 20 second marks in a field area or in each of a plurality of field areas. 55. A sample holder configured to hold a sample having a field area; an electron beam system configured to project one or more electron beams onto the sample and detect signal electrons emitted from the sample; A controller, receiving exposure correction data from a lithographic apparatus used to expose a field region on the sample; generating a sample map using the exposure correction data, the sample map including information regarding the location and shape of the field regions on the sample; a controller configured to 23. A charged particle beam inspection system comprising: 56. The system of clause 55, wherein the sample map defines the locations of the field areas in an array having rows of field areas and columns of field areas, at least one of the rows being non-linear and / or at least one of the columns being non-linear. 57. The system of claim 56, wherein the sample map defines a shape of the field region including a boundary having a nonlinear portion. 58. A system described in any one of clauses 55 to 57, wherein the controller is configured to cause the electron beam system to measure the positions of a plurality of reference marks on the sample and to generate a corrected sample map using the measured positions. 59. The system of clause 58, wherein the controller is configured to generate a corrected sample map by linearly adjusting the generated sample map using the exposure correction data. 60. A system as described in clause 58 or 59, wherein the controller is configured to provide information about the corrected sample map to the lithography apparatus to enable a subsequent lithography process to be adapted to reduce errors in the lithography process. 61. A method for processing a sample, comprising: Producing a corrected sample map using the method according to any one of clauses 18 to 20; Using the generated correction sample map to adapt a lithography process performed on a subsequent sample. The method includes: 62. An evaluation method comprising: Generating a sample map using the method according to any one of clauses 1 to 20; Inspecting the sample using the generated sample map to identify one or more features of interest. Evaluation methods including. 63. A method according to clause 62, wherein the inspection is performed by directing one or more charged particle beams onto the sample and detecting one or more charged particles emitted from the sample.

[0124]

[0139] While embodiments of the present disclosure have been described with reference to various examples, other embodiments consistent with the present disclosure will be apparent to those skilled in the art from consideration of the specification and practice disclosed herein. It is intended that the specification and examples be considered as exemplary only.

Claims

1. 1. A method for generating a sample map, comprising the steps of: obtaining a sample having a field area; measuring a position of a first mark in each of a plurality of said field regions; fitting a first model to the measured position of the first mark, the fitted first model representing a position of the field region; and Measuring positions of a plurality of second marks in the field region or in each of the plurality of field regions; fitting a second model to the measured positions of the second marks, the fitted second model representing the shape of each field region; and outputting a sample map using the fitted first and second models; and The method includes:

2. The method of claim 1 , wherein either or both of the first and second models represent non-linear geometric shapes.

3. The method of claim 1 , wherein the measurement of the position of the second mark is made using the position of the field region represented by the fitted first model.

4. 2. The method of claim 1, wherein the first model represents the positions of the field areas in an array having rows of field areas and columns of field areas, at least one of the rows being non-linear and / or at least one of the columns being non-linear.

5. The method of claim 1 , wherein the second model represents the shape of each field region such that at least a portion of the boundary of the shape is non-linear.

6. The method of claim 4 , wherein the first model represents each non-linear row and / or non-linear column by a respective non-linear equation.

7. The method of claim 5 , wherein the second model represents each nonlinear portion of the boundary with a respective nonlinear equation.

8. The method of claim 6 , wherein each nonlinear equation comprises a polynomial.

9. The method of claim 8, wherein the degree of the polynomial is in the range of 3 to 5, inclusive.

10. The method of claim 1 , wherein the positions of the first marks are measured relative to a common reference position on the sample.

11. The method of claim 1 , wherein the position of the second mark in each field region is measured relative to a reference point unique to the field region.

12. The method of claim 1 , wherein each field area corresponds to an area of ​​the sample that is processed by a respective exposure during a lithography process.

13. The method of claim 1 , wherein the second marks are measured in each of 3 to 10 field regions.

14. The method of claim 1 , wherein the positions of between 5 and 20 second marks are measured in the one field area or each of the plurality of field areas.

15. A computer program, which when executed by a computer, comprises the following steps: receiving data representative of a measured position of a first mark in each of a plurality of field regions on the sample; fitting a first model to the measured position of the first mark, the fitted first model representing a position of the field region; and receiving data representative of measured positions of a plurality of second marks in the field region or in each of the plurality of field regions; fitting a second model to the measured positions of the second marks, the fitted second model representing the shape of each field region; and outputting a sample map using the fitted first and second models; and A computer program comprising instructions for causing the computer to execute the above.

Images