This application claims priority of EP Application 20168278.8, which was filed on 06 Apr. 2020 and which is incorporated herein its entirety by reference.
The embodiments provided herein generally relate to a charged particle assessment tools and inspection methods, and particularly to charged particle assessment tools and inspection methods that use multiple sub-beams of charged particles, as well as to a corrector arrangement for use in such tools or methods.
When manufacturing semiconductor integrated circuit (IC) chips, undesired pattern defects, as a consequence of, for example, optical effects and incidental particles, inevitably occur on a substrate (i.e. wafer) or a mask during the fabrication processes, thereby reducing the yield. Monitoring the extent of the undesired pattern defects is therefore an important process in the manufacture of IC chips. More generally, the inspection and/or measurement of a surface of a substrate, or other object/material, is an important process during and/or after its manufacture.
Pattern inspection tools with a charged particle beam have been used to inspect objects, for example to detect pattern defects. These tools typically use electron microscopy techniques, such as a scanning electron microscope (SEM). In a SEM, a primary electron beam of electrons at a relatively high energy is targeted with a final deceleration step in order to land on a sample at a relatively low landing energy. The beam of electrons is focused as a probing spot on the sample. The interactions between the material structure at the probing spot and the landing electrons from the beam of electrons cause electrons to be emitted from the surface, such as secondary electrons, backscattered electrons or Auger electrons. The generated secondary electrons may be emitted from the material structure of the sample. By scanning the primary electron beam as the probing spot over the sample surface, secondary electrons can be emitted across the surface of the sample. By collecting these emitted secondary electrons from the sample surface, a pattern inspection tool may obtain an image representing characteristics of the material structure of the surface of the sample.
There is a general need to improve the throughput and other characteristics of a charged particle inspection apparatus.
The embodiments provided herein disclose a charged particle beam inspection apparatus.
According to a first aspect of the invention, there is provided a charged-particle tool comprising:
According to a second aspect of the invention, there is provided a charged-particle tool comprising:
According to a third aspect of the invention, there is provided a charged-particle tool comprising:
According to a fourth aspect of the invention, there is provided an inspection method comprising:
According to a fifth aspect of the invention, there is provided a multi-beam charged-particle-optical system comprising:
According to a sixth aspect of the invention, there is provided a charged-particle-optical element for a multi-beam projection system configured to project a plurality of charged particle beams onto a sample, the charged-particle-optical element comprising:
According to a seventh aspect of the invention, there is provided a charged-particle-optical element for a multi-beam projection system configured to project a plurality of charged particle beams onto a sample, the last charged-particle-optical element comprising:
The above and other aspects of the present disclosure will become more apparent from the description of exemplary embodiments, taken in conjunction with the accompanying drawings.
Reference will now be made in detail to exemplary embodiments, examples of which are illustrated in the accompanying drawings. The following description refers to the accompanying drawings in which the same numbers in different drawings represent the same or similar elements unless otherwise represented. The implementations set forth in the following description of exemplary embodiments do not represent all implementations consistent with the invention. Instead, they are merely examples of apparatuses and methods consistent with aspects related to the invention as recited in the appended claims.
The enhanced computing power of electronic devices, which reduces the physical size of the devices, can be accomplished by significantly increasing the packing density of circuit components such as transistors, capacitors, diodes, etc. on an IC chip. This has been enabled by increased resolution enabling yet smaller structures to be made. For example, an IC chip of a smart phone, which is the size of a thumbnail and available in, or earlier than, 2019, may include over 2 billion transistors, the size of each transistor being less than 1/1000th of a human hair. Thus, it is not surprising that semiconductor IC manufacturing is a complex and time-consuming process, with hundreds of individual steps. Errors in even one step have the potential to dramatically affect the functioning of the final product. Just one “killer defect” can cause device failure. The goal of the manufacturing process is to improve the overall yield of the process. For example, to obtain a 75% yield for a 50-step process (where a step can indicate the number of layers formed on a wafer), each individual step must have a yield greater than 99.4%,. If each individual step had a yield of 95%, the overall process yield would be as low as 7%.
While high process yield is desirable in an IC chip manufacturing facility, maintaining a high substrate (i.e. wafer) throughput, defined as the number of substrates processed per hour, is also essential. High process yield and high substrate throughput can be impacted by the presence of a defect. This is especially if operator intervention is required for reviewing the defects. Thus, high throughput detection and identification of micro and nano-scale defects by inspection tools (such as a Scanning Electron Microscope (‘SEM’)) is essential for maintaining high yield and low cost.
A SEM comprises an scanning device and a detector apparatus. The scanning device comprises an illumination apparatus that comprises an electron source, for generating primary electrons, and a projection apparatus for scanning a sample, such as a substrate, with one or more focused beams of primary electrons. Together at least the illumination apparatus, or illumination system, and the projection apparatus, or projection system, may be referred to together as the electron-optical system or apparatus. The primary electrons interact with the sample and generate secondary electrons. The detection apparatus captures the secondary electrons from the sample as the sample is scanned so that the SEM can create an image of the scanned area of the sample. For high throughput inspection, some of the inspection apparatuses use multiple focused beams, i.e. a multi-beam, of primary electrons. The component beams of the multi-beam may be referred to as sub-beams or beamlets. A multi-beam can scan different parts of a sample simultaneously. The sub-beams or beamlets may be arranged in the multi-beam, so the multi-beam may be referred to as having a multi-beam arrangement. The multi-beam arrangement may have a repeating pattern which may be rectilinear, for example rectangular or squire, or hexagonal, for example regular hexagonal. A multi-beam inspection apparatus can therefore inspect a sample at a much higher speed than a single-beam inspection apparatus.
An implementation of a known multi-beam inspection apparatus is described below.
The figures are schematic. Relative dimensions of components in drawings are therefore exaggerated for clarity. Within the following description of drawings the same or like reference numbers refer to the same or like components or entities, and only the differences with respect to the individual embodiments are described. While the description and drawings are directed to an electron-optical apparatus, it is appreciated that the embodiments are not used to limit the present disclosure to specific charged particles. References to electrons throughout the present document may therefore be more generally be considered to be references to charged particles, with the charged particles not necessarily being electrons.
Reference is now made to
EFEM 30 includes a first loading port 30a and a second loading port 30b. EFEM 30 may include additional loading port(s). First loading port 30a and second loading port 30b may, for example, receive substrate front opening unified pods (FOUPs) that contain substrates (e.g., semiconductor substrates or substrates made of other material(s)) or samples to be inspected (substrates, wafers and samples are collectively referred to as “samples” hereafter). One or more robot arms (not shown) in EFEM 30 transport the samples to load lock chamber 20.
Load lock chamber 20 is used to remove the gas around a sample. This creates a vacuum that is a local gas pressure lower than the pressure in the surrounding environment. The load lock chamber 20 may be connected to a load lock vacuum pump system (not shown), which removes gas particles in the load lock chamber 20. The operation of the load lock vacuum pump system enables the load lock chamber to reach a first pressure below the atmospheric pressure. After reaching the first pressure, one or more robot arms (not shown) transport the sample from load lock chamber 20 to main chamber 10. Main chamber 10 is connected to a main chamber vacuum pump system (not shown). The main chamber vacuum pump system removes gas particles in main chamber 10 so that the pressure in around the sample reaches a second pressure lower than the first pressure. After reaching the second pressure, the sample is transported to the electron beam tool by which it may be inspected. An electron beam tool 40 may comprise a multi-beam electron-optical apparatus.
Controller 50 is electronically connected to electron beam tool 40. Controller 50 may be a processor (such as a computer) configured to control the charged particle beam inspection apparatus 100. Controller 50 may also include a processing circuitry configured to execute various signal and image processing functions. While controller 50 is shown in
Reference is now made to
Electron source 201 may comprise a cathode (not shown) and an extractor or anode (not shown). During operation, electron source 201 is configured to emit electrons as primary electrons from the cathode. The primary electrons are extracted or accelerated by the extractor and/or the anode to form a primary electron beam 202.
Projection apparatus 230 is configured to convert primary electron beam 202 into a plurality of sub-beams 211, 212, 213 and to direct each sub-beam onto the sample 208. Although three sub-beams are illustrated for simplicity, there may be many tens, many hundreds or many thousands of sub-beams. The sub-beams may be referred to as beamlets.
Controller 50 may be connected to various parts of charged particle beam inspection apparatus 100 of
Projection apparatus 230 may be configured to focus sub-beams 211, 212, and 213 onto a sample 208 for inspection and may form three probe spots 221, 222, and 223 on the surface of sample 208. Projection apparatus 230 may be configured to deflect primary sub-beams 211, 212, and 213 to scan probe spots 221, 222, and 223 across individual scanning areas in a section of the surface of sample 208. In response to incidence of primary sub-beams 211, 212, and 213 on probe spots 221, 222, and 223 on sample 208, electrons are generated from the sample 208 which include secondary electrons and backscattered electrons. The secondary electrons typically have electron energy ≤ 50 eV and backscattered electrons typically have electron energy between 50 eV and the landing energy of primary sub-beams 211, 212, and 213.
Electron detection device 240 is configured to detect secondary electrons and/or backscattered electrons and to generate corresponding signals which are sent to controller 50 or a signal processing system (not shown), e.g. to construct images of the corresponding scanned areas of sample 208. Electron detection device may be incorporated into the projection apparatus or may be separate therefrom, with a secondary optical column being provided to direct secondary electrons and/or backscattered electrons to the electron detection device.
The controller 50 may comprise image processing system that includes an image acquirer (not shown) and a storage device (not shown). For example, the controller may comprise a processor, computer, server, mainframe host, terminals, personal computer, any kind of mobile computing devices, and the like, or a combination thereof. The image acquirer may comprise at least part of the processing function of the controller. Thus the image acquirer may comprise at least one or more processors. The image acquirer may be communicatively coupled to an electron detection device 240 of the apparatus 40 permitting signal communication, such as an electrical conductor, optical fiber cable, portable storage media, IR, Bluetooth, internet, wireless network, wireless radio, among others, or a combination thereof. The image acquirer may receive a signal from electron detection device 240, may process the data comprised in the signal and may construct an image therefrom. The image acquirer may thus acquire images of sample 208. The image acquirer may also perform various postprocessing functions, such as generating contours, superimposing indicators on an acquired image, and the like. The image acquirer may be configured to perform adjustments of brightness and contrast, etc. of acquired images. The storage may be a storage medium such as a hard disk, flash drive, cloud storage, random access memory (RAM), other types of computer readable memory, and the like. The storage may be coupled with the image acquirer and may be used for saving scanned raw image data as original images, and post-processed images.
The image acquirer may acquire one or more images of a sample based on an imaging signal received from the electron detection device 240. An imaging signal may correspond to a scanning operation for conducting charged particle imaging. An acquired image may be a single image comprising a plurality of imaging areas. The single image may be stored in the storage. The single image may be an original image that may be divided into a plurality of regions. Each of the regions may comprise one imaging area containing a feature of sample 208. The acquired images may comprise multiple images of a single imaging area of sample 208 sampled multiple times over a time period. The multiple images may be stored in the storage. The controller 50 may be configured to perform image processing steps with the multiple images of the same location of sample 208.
The controller 50 may include measurement circuitry (e.g., analog-to-digital converters) to obtain a distribution of the detected secondary electrons. The electron distribution data, collected during a detection time window, can be used in combination with corresponding scan path data of each of primary sub-beams 211, 212, and 213 incident on the sample surface, to reconstruct images of the sample structures under inspection. The reconstructed images can be used to reveal various features of the internal or external structures of sample 208. The reconstructed images can thereby be used to reveal any defects that may exist in the sample.
The controller 50 may control motorized stage 209 to move sample 208 during inspection of sample 208. The controller 50 may enable motorized stage 209 to move sample 208 in a direction, preferably continuously, for example at a constant speed, at least during sample inspection. The controller 50 may control movement of the motorized stage 209 so that it changes the speed of the movement of the sample 208 dependent on various parameters. For example, the controller may control the stage speed (including its direction) depending on the characteristics of the inspection steps of scanning process.
In an arrangement the condenser lens array is formed of three plate arrays in which charged particles have the same energy as they enter and leave each lens, which arrangement may be referred to as an Einzel lens. The beam energy is the same on entering as leaving the Einzel lens. Thus, dispersion only occurs within the Einzel lens itself (between entry and exit electrodes of the lens), thereby limiting off-axis chromatic aberrations. When the thickness of the condenser lenses is low, e.g. a few mm, such aberrations have a small or negligible effect.
Each condenser lens in the array directs electrons into a respective sub-beam 211, 212, 213 which is focused at a respective intermediate focus 233. At the intermediate focuses 233 are deflectors 235. Deflectors 235 are configured to bend a respective beamlet 211, 212, 213 by an amount effective to ensure that the principal ray (which may also be referred to as the beam axis) is incident on the sample 208 substantially normally (i.e. at substantially 90° to the nominal surface of the sample). Deflectors 235 may also be referred to as collimators. Down beam of the intermediate focuses 233 are a plurality of objective lenses 234, each of which directs a respective sub-beam 211, 212, 213 onto the sample 208. Objective lenses 234 can be configured to de-magnify the electron beam by a factor greater than 10, desirably in the range of 50 to 100 or more.
An electron detection device 240 is provided between the objective lenses 234 and the sample 208 to detect secondary and/or backscattered electrons emitted from the sample 208. An exemplary construction of the electron detection system is described below.
The system of
In some embodiments, the charged particle assessment tool further comprises one or more aberration correctors that reduce one or more aberrations in the sub-beams. In an embodiment, each of at least a subset of the aberration correctors is positioned in, or directly adjacent to, a respective one of the intermediate foci (e.g. in or adjacent to the intermediate image plane). The sub-beams have a smallest sectional area in or near a focal plane such as the intermediate plane. This provides more space for aberration correctors than is available elsewhere, i.e. upbeam or downbeam of the intermediate plane (or than would be available in alternative arrangements that do not have an intermediate image plane).
In an embodiment, aberration correctors positioned in, or directly adjacent to, the intermediate foci (or intermediate image plane) comprise deflectors to correct for the source 201 appearing to be at different positions for different beams. Correctors can be used to correct macroscopic aberrations resulting from the source that prevent a good alignment between each sub-beam and a corresponding objective lens.
The aberration correctors may correct aberrations that prevent a proper column alignment. Such aberrations may also lead to a misalignment between the sub-beams and the correctors. For this reason, it may be desirable to additionally or alternatively position aberration correctors at or near the condenser lenses 231 (e.g. with each such aberration corrector being integrated with, or directly adjacent to, one or more of the condenser lenses 231). This is desirable because at or near the condenser lenses 231 aberrations will not yet have led to a shift of corresponding sub-beams because the condenser lenses 231 are vertically close or coincident with the beam apertures. A challenge with positioning correctors at or near the condenser lenses 231, however, is that the sub-beams each have relatively large sectional areas and relatively small pitch at this location, relative to locations further downbeam.
In some embodiments, each of at least a subset of the aberration correctors is integrated with, or directly adjacent to, one or more of the objective lenses 234. In an embodiment, these aberration correctors reduce one or more of the following: field curvature; focus error; and astigmatism. Additionally or alternatively, one or more scanning deflectors (not shown) may be integrated with, or directly adjacent to, one or more of the objective lenses 234 for scanning the sub-beams 211, 212,214 over the sample 208. In an embodiment, the scanning deflectors described in US 2010/0276606, which document is hereby incorporated by reference in its entirety, may be used.
The aberration correctors may be CMOS based individual programmable deflectors as disclosed in EP2702595A1 or an array of multipole deflectors as disclosed EP2715768A2, of which the descriptions of the beamlet manipulators in both documents are hereby incorporated by reference.
In an embodiment the objective lens referred to in earlier embodiments is an array objective lens. Each element in the array is a micro-lens operating a different beam or group of beams in the multi-beam. An electrostatic array objective lens has at least two plates each with a plurality of holes or apertures. The position of each hole in a plate corresponds to the position of a corresponding hole in the other plate. The corresponding holes operate in use on the same beam or group of beams in the multi-beam. A suitable example of a type of lens for each element in the array is an two electrode decelerating lens. The bottom electrode of the objective lens is a CMOS chip detector integrated into a multi-beam manipulator array. Integration of a detector array into the objective lens replaces a secondary column. The CMOS chip is preferably orientated to face the sample (because of the small distance (e.g. 100 µm) between wafer and bottom of the electron-optical system). In an embodiment, electrodes to capture the secondary electron signals are formed in the top metal layer of the CMOS device. The electrodes can be formed in other layers. Power and control signals of the CMOS may be connected to the CMOS by through-silicon vias. For robustness, preferably the bottom electrode consist of two elements: the CMOS chip and a passive Si plate with holes. The plate shields the CMOS from high E-fields.
In order to maximize the detection efficiency it is desirable to make the electrode surface as large as possible, so that substantially all the area of the array objective lens (excepting the apertures) is occupied by electrodes and each electrode has a diameter substantially equal to the array pitch. In an embodiment the outer shape of the electrode is a circle, but this can be made a square to maximize the detection area. Also the diameter of the through-substrate hole can be minimized. Typical size of the electron beam is in the order of 5 to 15 micron.
In an embodiment, a single electrode surrounds each aperture. In another embodiment, a plurality of electrode elements are provided around each aperture. The electrons captured by the electrode elements surrounding one aperture may be combined into a single signal or used to generate independent signals. The electrode elements may be divided radially (i.e. to form a plurality of concentric annuluses), angularly (i.e. to form a plurality of sector-like pieces), both radially and angularly or in any other convenient manner.
However a larger electrode surface leads to a larger parasitic capacitance, so a lower bandwidth. For this reason it may be desirable to limit the outer diameter of the electrode. Especially in case a larger electrode gives only a slightly larger detection efficiency, but a significantly larger capacitance. A circular (annular) electrode may provide a good compromise between collection efficiency and parasitic capacitance.
A larger outer diameter of the electrode may also lead to a larger crosstalk (sensitivity to the signal of a neighboring hole). This can also be a reason to make the electrode outer diameter smaller. Especially in case a larger electrode gives only a slightly larger detection efficiency, but a significantly larger crosstalk.
The back-scattered and/or secondary electron current collected by electrode is amplified by a Trans Impedance Amplifier.
In an embodiment of the invention, the correctors at the intermediate focuses 233 are embodied by a slit deflector 300. Slit deflector 300 is an example of a manipulator and may also be referred to as a slit corrector. In arrangement the slit deflector may comprise part of a collimator array (for example as a deflector array 235 as described elsewhere herein) or adjoin a collimator array, or a part of such a collimator, as a corrector in the beam path, for example adjacently. As shown in
Slit deflectors 300 functioning as aberration correctors 235a may alternatively or in addition be positioned just below the condenser lenses 231. This can be advantageous in that any angular error to be corrected will not have been translated into a large positional shift. The aberration correctors 235a may correct aberrations that prevent a proper column alignment. Such aberrations may also lead to a misalignment between the sub-beams 211, 212, 213 and the correctors 235. For this reason, it may be desirable to additionally or alternatively position aberration correctors 235a at or near the condenser lenses 231 (e.g. with each such aberration corrector 235a being integrated with, or directly adjacent to, one or more of the condenser lenses 231). This is desirable because at or near the condenser lenses 231 aberrations will not yet have led to a shift of corresponding sub-beams 211, 212, 213 because the condenser lenses 231 are vertically close or coincident with the beam apertures 111a. A challenge with positioning correctors 235a at or near the condenser lenses 116, however, is that the sub-beams 212, 213, 214 each have relatively large cross-sectional areas and relatively small pitch at this location, relative to locations further downstream.
A line of sub-beam paths, for example for the sub-beams in operation of the tool, interposes a pair of elongate electrodes, that may take the form of an array of strips, so that a potential difference between the electrodes causes a deflection of the sub-beams. The direction of the deflection is determined by the relative polarity of the potential difference in a direction relative to the optical axis. The magnitude of the deflection is determined by the magnitude of the potential difference, the distance between the electrodes and the width of the electrodes in the direction parallel to the propagation of the sub-beams. These dimensions may be referred to as the width and depth of the slit, respectively. In an embodiment the width of the slits is in the range of from 10 to 100 µm, desirably 50 µm. In an embodiment the pitch of the slits is in the range of from 50 to 200 µm, desirably 100 µm. In an embodiment, the depth of the slit is in the range of from 50 to 200 µm.
In an embodiment, the electrodes are at the same potential along their lengths and the slit is of constant width or depth so that all sub-beams passing through a given slit experience substantially the same deflection as they all have substantially the same energy.
In an embodiment, the slit may have a non-constant cross-section, e.g. a variation in width or depth, to provide a predetermined variation in the deflection in the sub-beams according to their position along the length of the slit.
In an embodiment, the elongate electrodes define a set of parallel slits such that each of the sub-beams pass through a slit. The surface of each electrode that in part defines a slit may have a planar surface that may be parallel with a sub-beam path. Thus, facing elongate surfaces of the respective elongate electrodes define a corresponding slit. The facing surfaces of a slit may each be planar and mutually parallel. The slit may extend across the array of sub-beam paths, for example across the multi-beam arrangement, for example as depicted in
In an embodiment, each slit is defined by two dedicated electrodes. For example, as shown in
In an alternate embodiment, each electrode (except for the electrodes at the end of the array) serves to define one side of each of two slits. That is, in general, the opposite surfaces of the electrodes extending in the direction of the beam paths define in part adjoining slits. For example, as shown in
An advantage of the arrangement of
In an embodiment, a plurality of slit deflectors are provided adjacently in the beam propagation direction. Such an arrangement may be referred to as a stack of slit deflectors. The slit deflectors in a stack are differently oriented.
In an embodiment, the sub-beams are arranged in a rectangular array and two slit deflectors are provided with the slits of a first slit deflector being oriented perpendicularly to the slits of the second slit deflector. For example the first slit deflector has slits extending in the Y direction and provides a deflection in the X direction controllable as a function of sub-beam position in the X direction. The second slit deflector has slits extending in the X direction and provides a deflection in the Y direction controllable as a function of sub-beam position in the Y direction. The slit deflectors may be provided in any order in the stack. Further details of a slit deflector may be found in EPA20156253.5, in which the description of a multi-beam deflector apparatus is hereby incorporated by reference.
In an embodiment, the sub-beams are arranged in a hexagonal array and two slit deflectors are provided. The slits of the first slit deflector are orthogonal to the slits of the second slit detector. For example the first slit deflector has slits extending in the Y direction and provides a deflection in the X direction controllable as a function of sub-beam position in the X direction. The second slit deflector has slits extending in the X direction and provides a deflection in the Y direction controllable as a function of sub-beam position in the Y direction. The second slit detector has a smaller pitch than the first slit detector and fewer sub-beams per slit than the first slit detector. The slit deflectors may be provided in any order in the stack.
In an embodiment, the sub-beams are arranged in a hexagonal array and three slit deflectors in a stack are provided. The three slit deflectors are arranged such that there is a 60° angle between slits of the different slit detectors. For example as shown in
Using an arrangement such as shown in
In other words:
An additional advantage of using three slit deflector arrays (0, 60, 120 degree) over two slit deflector arrays (0, 90 degree) is that for 1st order effect (perfect lens) each array has to deflect only 2/3 of the angle compared to the case with two slit deflectors.
Other arrangements of multiple slit deflectors may be provided for other arrangements of sub-beams. For example the slits might be arranged as concentric hexagons.
In an embodiment of the invention, multiple beams pass through a slit defined by a pair of electrodes. This substantially reduces the number of connections required to provide the deflection potentials. In a multi-beam tool with many hundreds or thousands of beams, it is difficult, if not impossible, to provide independent deflection potentials for each sub-beam since there is limited space for wiring or circuit traces (routing). This problem is addressed by the present invention since the number of traces required is significantly reduced. In some cases, an embodiment of the invention may not be capable of completely correcting an aberration, for example a 3rd order rotationally symmetric aberration. However, an embodiment of the invention can effect a significant and useful reduction even in aberrations that cannot be completely corrected.
An error that can be corrected for by an embodiment of the invention occurs if the virtual source position of the electron source 201 is not constant for all emission angles. This effect is known as source grid errors.
A slit deflector as described above may introduce a slight focusing effect in the direction that the beam is deflected. If two or more differently oriented slit deflector arrays are used there will be a focusing affect in two or more directions. The magnitude of this focusing effect is proportional to the magnitude of the deflection. In some cases, this focusing effect may be undesirable.
To compensate for the focusing effect of a slit deflector, a slit lens may be added. As shown in
Another embodiment of a charged particle assessment tool 109 is illustrated schematically in
In an embodiment, aberration correctors 124 positioned in, or directly adjacent to, the intermediate foci 115 (or intermediate image plane 120) comprise deflectors to correct for the source 201 appearing to be at different positions for different sub-beams 114 derived from beam 112 emitted from source 201. Correctors 124 can be used to correct macroscopic aberrations resulting from the source 201 that prevent a good alignment between each sub-beam 114 and a corresponding objective lens 118.
The aberration correctors 124 may correct aberrations that prevent a proper column alignment. Such aberrations may also lead to a misalignment between the sub-beams 114 and the correctors 124. For this reason, it may be desirable to additionally or alternatively position aberration correctors 125 at or near the condenser lenses 116 (e.g. with each such aberration corrector 125 being integrated with, or directly adjacent to, one or more of the condenser lenses 116). This is desirable because at or near the condenser lenses 116 aberrations will not yet have led to a shift of corresponding sub-beams 114 because the condenser lenses 116 are vertically close or coincident with the beam apertures 110. A challenge with positioning correctors 125 at or near the condenser lenses 116, however, is that the sub-beams 114 each have relatively large cross-sectional areas and relatively small pitch at this location, relative to locations further downstream.
In some embodiments, as exemplified in
In the apparatus of
The electrodes may be electrically connected via their mounting to a recess. In another arrangement the electrodes are electrically conned to a finger although this may be less preferred. Since alternate electrodes are connected at a recess or a finger, similar potential differences may be applied to alternate electrodes. Electric potentials are provided to the electrodes through conductive traces 309 (for clarity only a few are shown in the figure) connected to the electrodes at the base portions, or recesses. The creep length cl, i.e. the length of the surface over which a creep discharge could occur, is the lateral distance along the recess and an end of the finger and the length of the finger. The creep length is the lateral distance over the surface of the frame, from the connection of an electrode at the recess to the surface of the finger extending from the frame, the length of the side surface of the finger extending from the frame, and the distance at the end of the finger from the side surface of the finger to the connection of the finger to the adjoining electrode The creep length, for example between adjoining electrodes, is therefore increased by the length of a finger 307. Isolation between electrodes is therefore improved. The risk of high voltage discharge between electrodes at the frame is reduced.
The frame 303 and fingers 307 are formed from an insulator, preferably ceramic, preferably silicon oxide, preferably glass. In an embodiment, the frame is formed by selective etching of a substrate, e.g. a silicon wafer. Preferably the frame, or at least each side, is monolithic.
An assessment tool according to an embodiment of the invention may be a tool which makes a qualitative assessment of a sample (e.g. pass/fail), one which makes a quantitative measurement (e.g. the size of a feature) of a sample or one which generates an image of map of a sample. Examples of assessment tools are inspection tools (e.g. for identifying defects), review tools (e.g. for classifying defects) and metrology tools or tools capable of performing any combination of assessment functionalities associated with inspection tools, review tools, or metrology tools (e.g. metro-inspection tools). The electron-optical column 40 may be a component of an assessment tool; such as an inspection tool or a metro-inspection tool, or part of an e-beam lithography tool. Any reference to a tool herein is intended to encompass a device, apparatus or system, the tool comprising various components which may or may not be collocated, and which may even be located in separate rooms, especially for example for data processing elements
A multi-beam electron beam tool may comprise a primary projection apparatus, a motorized stage and a sample holder. The primary projection apparatus is an illumination apparatus comprised by the multi-beam electron beam tool. The primary projection apparatus may comprise one or more of at least any of the following components: an electron source, a gun aperture plate, a condenser lens, an aperture array, beam manipulators (that may comprise MEMS structures), an objective lens and a beam separator (e.g. a Wien filter). The sample holder is supported by the motorized stage. The sample holder is arranged to hold a sample (e.g., a substrate or a mask) for inspection.
The multi-beam electron beam tool may further comprise a secondary projection apparatus and an associated electron detection device. The electron detection device may comprise a plurality of electron detection elements.
The primary projection apparatus is arranged to illuminate a sample. In response to the incidence of primary sub-beams or probe spots on a sample, electrons are generated from the sample which include secondary electrons and backscattered electrons. The secondary electrons propagate in a plurality of secondary electron beams. The secondary electron beams typically comprise secondary electrons (having electron energy ≤ 50 eV) and may also comprise at least some of the backscattered electrons (having electron energy between 50 eV and the landing energy of primary sub-beams). A beam separator in the primary projection apparatus may be arranged to deflect the path of the secondary electron beams towards the secondary projection apparatus. The secondary projection apparatus subsequently focuses the path of secondary electron beams onto the plurality of elements of the electron detection device. The detection elements generate corresponding signals which may be sent to a controller or a signal processing system, e.g. to construct images of the corresponding scanned areas of sample.
Reference to a component or system of components or elements being controllable to manipulate a charged particle beam in a certain manner includes configuring a controller or control system or control unit to control the component to manipulate the charged particle beam in the manner described, as well optionally using other controllers or devices (e.g. voltage supplies and or current supplies) to control the component to manipulate the charged particle beam in this manner. For example, a voltage supply may be electrically connected to one or more components to apply potentials to the components, such as in a non-limited list the, the objective lens array 234, the condenser lens 231, correctors 235a, and collimator array 235, under the control of the controller or control system or control unit. An actuatable component, such as a stage, may be controllable to actuate and thus move relative to another components such as the beam path using one or more controllers, control systems, or control units to control the actuation of the component.
The embodiments herein described may take the form of a series of aperture arrays or electron-optical elements arranged in arrays along a beam or a multi-beam path. Such electron-optical elements may be electrostatic. In an embodiment all the electron-optical elements, for example from a beam limiting aperture array to a last electron-optical element in a sub-beam path before a sample, may be electrostatic and/or may be in the form of an aperture array or a plate array. In some arrangements one or more of the electron-optical elements are manufactured as a microelectromechanical system (MEMS) (i.e. using MEMS manufacturing techniques).
The electron optical elements adjacent along the beam path may be structurally connected to each other for example with electrically isolating elements such as spacers. The Isolating elements may be made of an electrically insulating material such a ceramic such as glass.
References to upper and lower, up and down, above and below should be understood as referring to directions parallel to the (typically but not always vertical) up-beam and down-beam directions of the electron beam or multi-beam impinging on the sample 208. Thus, references to up beam and down beam are intended to refer to directions in respect of the beam path independently of any present gravitational field.
Exemplary embodiments of the invention are described below in the following numbered paragraphs
The terms “sub-beam” and “beamlet” are used interchangeably herein and are both understood to encompass any radiation beam derived from a parent radiation beam by dividing or splitting the parent radiation beam. The term “manipulator” is used to encompass any element which affects the path of a sub-beam or beamlet, such as a lens or deflector.
While the present invention has been described in connection with various embodiments, other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.
Number | Date | Country | Kind |
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20168278.8 | Apr 2020 | EP | regional |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2021/058824 | 4/4/2021 | WO |