Patent ID: 12196692

DETAILED DESCRIPTION

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. Instead, they are merely examples of apparatuses and methods consistent with aspects related to the disclosed embodiments as recited in the appended claims. For example, although some embodiments are described in the context of utilizing electron beams, the disclosure is not so limited. Other types of charged particle beams may be similarly applied. Furthermore, other imaging systems may be used, such as optical imaging, photo detection, x-ray detection, etc.

Electronic devices are constructed of circuits formed on a piece of silicon called a substrate. Many circuits may be formed together on the same piece of silicon and are called integrated circuits or ICs. The size of these circuits has decreased dramatically so that many more of them can fit on the substrate. For example, an IC chip in a smart phone can be as small as a thumbnail and yet may include over 2 billion transistors, the size of each transistor being less than 1/1000th the size of a human hair.

Making these extremely small ICs is a complex, time-consuming, and expensive process, often involving hundreds of individual steps. Errors in even one step have the potential to result in defects in the finished IC, thereby rendering it useless. Thus, one goal of the manufacturing process is to avoid such defects to maximize the number of functional ICs made in the process, that is, to improve the overall yield of the process.

One component of improving yield is monitoring the chip making process to ensure that it is producing a sufficient number of functional integrated circuits. One way to monitor the process is to inspect the chip circuit structures at various stages of their formation. Inspection can be carried out using a scanning electron microscope (SEM). An SEM can be used to image these extremely small structures, in effect, taking a “picture” of the structures. The image can be used to determine if the structure was formed properly and also if it was formed in the proper location. If the structure is defective, then the process can be adjusted so the defect is less likely to recur.

Detecting buried defects in vertical high-density structures such as 3D NAND flash memory devices, can be challenging. One of several ways to detect buried or on-surface electrical defects in such devices is by using a voltage contrast method in a SEM. In this method, electrical conductivity differences in materials, structures, or regions of a sample cause contrast differences in SEM images thereof. In the context of defect detection, an electrical defect under the sample surface may generate a charging variation on the sample surface, so the electrical defect can be detected by a contrast in the SEM image of the sample surface. To enhance the voltage contrast, a process called pre-charging or flooding may be employed in which the region of interest of the sample may be exposed to a large beam current before an inspection using a small beam current but high imaging resolution. For the inspection, some of the advantages of flooding may include reduction of charging of the wafer to minimize distortion of images due to the charging, and in some cases, increase of charging of the wafer to enhance difference of defective and surrounding non-defective features in images, among other things.

Some inspection systems, such as a SEM, equipped to detect defects of a wafer using the voltage contrast method may be operated in multiple modes such as a flooding mode to highlight the defect, followed by an inspection mode to detect the defect. In some inspection systems, to increase inspection resolution, a Coulomb aperture array (e.g., coulomb aperture array224ofFIGS.2A and2B) may be placed above a beam-limiting aperture array (e.g., beam-limiting aperture array235ofFIG.2A and2B) to reduce Coulomb interaction effects in the inspection mode. In addition, to increase throughput by eliminating moving the wafer to align with a flooding electron beam or an inspection beam, the primary beam with a large current may be used in the flooding mode (dash line inFIG.2B) and the primary beam with a small current may be used in the inspection mode (solid line inFIG.2B). To further increase the throughput, the same in-use aperture of Coulomb aperture array and the in-use aperture of the beam-limiting aperture array may be used in the flooding mode and the inspection mode. In the flooding mode, it may be preferable to allow maximum electrons to pass through an aperture and maximize the beam current of the primary electron beam irradiating the sample, to enhance the voltage contrast, and a large aperture of the Coulomb aperture array may therefore be desired. In the inspection mode, however, a small probe spot having a small beam current may be desirable for high resolution imaging. If the large aperture of the Coulomb aperture array is used in the inspection mode, the large beam current may negatively impact the imaging resolution due to increased Coulomb interaction effects. For voltage contrast defect detection in a SEM, switching between the flooding and inspection modes may include adjusting the beam current, for example, by selecting the aperture size of the Coulomb aperture array. Selecting and aligning apertures to produce the desired beam current may take several seconds and may reduce the overall inspection throughput, among other things. Therefore, for voltage contrast defect detection, it may be desirable to quickly adjust the beam current based on a selected mode of operation to maintain high inspection throughput.

In some embodiments of the present disclosure, a charged-particle beam apparatus may include an electron source configured to emit electrons along a primary optical axis to form the primary electron beam. The apparatus may also include a current-limiting aperture plate placed between the Coulomb aperture array and the beam-limiting aperture array. An aperture of the Coulomb aperture array may be configured to allow a first portion of the primary electron beam to pass through, a condenser lens configured to focus the first portion of the primary electron beam based on a selected mode of operation, and an aperture of the current-limiting aperture plate may be configured to allow all or a portion of the first portion of the primary electron beam to pass through based on the selected mode of operation. The portion passing through the aperture of the current-limiting aperture plate is a second portion of the primary electron beam. Subsequently, all or a portion of the second portion may pass through an aperture of a beam-limiting aperture array. The portion passing through the aperture of the beam-limiting aperture array is a third portion of the primary electron beam. Based on the mode of operation, the third portion of the primary electron beam may be used to flood or inspect a surface of the sample. Using the current-limiting aperture plate to block off peripheral electrons of the first portion of the primary charged-particle beam may allow a user to avoid switching the apertures of a Coulomb aperture array without sacrificing image resolution in the inspection mode, thus reducing system-related delays and maintaining high throughput.

When the charged-particle beam apparatus is operating in the flooding mode, the electrons in the primary electron beam may have substantially high energy. Therefore, during the flooding mode, when these primary electrons hit the sample, signal electrons with high energy can be generated from the sample. If these high-energy signal electrons hit an electron detector, the detector surface can be contaminated with the built-up electron charges, which may deteriorate the performance of the detector. Furthermore, the electronic circuitry (e.g., a low-noise amplifier) that are connected to the detector may be damaged due to a surge current or overcurrent caused by the high-energy signal electrons. To protect the electron detector during the flooding mode, in some embodiments, the charged-particle beam apparatus can have a detector protection mechanism that is configured to prevent the high-energy signal electrons from reaching the electron detector when the apparatus operates in the flooding mode.

Relative dimensions of components in drawings may be 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. As used herein, unless specifically stated otherwise, the term “or” encompasses all possible combinations, except where infeasible. For example, if it is stated that a component may include A or B, then, unless specifically stated otherwise or infeasible, the component may include A, or B, or A and B. As a second example, if it is stated that a component may include A, B, or C, then, unless specifically stated otherwise or infeasible, the component may include A, or B, or C, or A and B, or A and C, or B and C, or A and B and C.

Reference is now made toFIG.1, which illustrates an exemplary charge particle beam inspection system100, such as an electron beam inspection (EBI) system, consistent with embodiments of the present disclosure. As shown inFIG.1, charged particle beam inspection system100includes a main chamber10, a load-lock chamber20, an electron beam tool40, and an equipment front end module (EFEM)30. Electron beam tool40is located within main chamber10. While the description and drawings are directed to an electron beam, it is appreciated that the embodiments are not used to limit the present disclosure to specific charged particles.

EFEM30includes a first loading port30aand a second loading port30b. EFEM30may include additional loading port(s). First loading port30aand second loading port30breceive wafer front opening unified pods (FOUPs) that contain wafers (e.g., semiconductor wafers or wafers made of other material(s)) or samples to be inspected (wafers and samples are collectively referred to as “wafers” hereafter). One or more robot arms (not shown) in EFEM30transport the wafers to load-lock chamber20.

Load-lock chamber20is connected to a load/lock vacuum pump system (not shown), which removes gas molecules in load-lock chamber20to reach a first pressure below the atmospheric pressure. After reaching the first pressure, one or more robot arms (not shown) transport the wafer from load-lock chamber20to main chamber10. Main chamber10is connected to a main chamber vacuum pump system (not shown), which removes gas molecules in main chamber10to reach a second pressure below the first pressure. After reaching the second pressure, the wafer is subject to inspection by electron beam tool40. In some embodiments, electron beam tool40may comprise a single-beam inspection tool. In other embodiments, electron beam tool40may comprise a multi-beam inspection tool.

Controller50may be electronically connected to electron beam tool40and may be electronically connected to other components as well. Controller50may be a computer configured to execute various controls of charged particle beam inspection system100. Controller50may also include processing circuitry configured to execute various signal and image processing functions. While controller50is shown inFIG.1as being outside of the structure that includes main chamber10, load-lock chamber20, and EFEM30, it is appreciated that controller50can be part of the structure.

While the present disclosure provides examples of main chamber10housing an electron beam inspection system, it should be noted that aspects of the disclosure in their broadest sense, are not limited to a chamber housing an electron beam inspection system. Rather, it is appreciated that the foregoing principles may be applied to other chambers as well.

Reference is now made toFIG.2A, which is a schematic diagram illustrating an exemplary configuration of an electron beam tool40that can be a part of the charged particle beam inspection system100ofFIG.1, consistent with embodiments of the present disclosure. Electron beam tool40(also referred to herein as apparatus40) may comprise an electron emitter, which may comprise a cathode203, an anode220, and a gun aperture222. Electron beam tool40may further include a Coulomb aperture array224, a condenser lens226, a beam-limiting aperture array235, an objective lens assembly232, and an electron detector244. Electron beam tool40may further include a sample holder236supported by motorized stage234to hold a sample250to be inspected. It is to be appreciated that other relevant components may be added or omitted, as needed.

AlthoughFIG.2Ashows electron beam tool40as a single-beam inspection tool that uses only one primary electron beam to scan one location of sample250at a time, electron beam tool40may also be a multi-beam inspection tool that employs multiple primary electron beamlets to simultaneously scan multiple locations on sample250.

In some embodiments, electron emitter may include cathode203, an extractor anode220, wherein primary electrons can be emitted from the cathode and extracted or accelerated to form a primary electron beam204that forms a primary beam crossover202(virtual or real). Primary electron beam204can be visualized as being emitted from primary beam crossover202.

In some embodiments, the electron emitter, condenser lens226, objective lens assembly232, beam-limiting aperture array235, and electron detector244may be aligned with a primary optical axis201of apparatus40. In some embodiments, electron detector244may be placed off primary optical axis201, along a secondary optical axis (not shown).

Objective lens assembly232, in some embodiments, may comprise a modified swing objective retarding immersion lens (SORIL), which includes a magnetic lens body232a, a control electrode232b, a deflector232c(or more than one deflectors), an exciting coil232d, and a pole piece232e. In a general imaging process, primary electron beam204emanating from the tip of cathode203is accelerated by an accelerating voltage applied to anode220. A portion of primary electron beam204passes through gun aperture222, and an aperture of Coulomb aperture array224, and is focused by condenser lens226so as to fully or partially pass through an aperture of beam-limiting aperture array235. The electrons passing through the aperture of beam-limiting aperture array235may be focused to form a probe spot on the surface of sample250by the modified SORIL lens and deflected to scan the surface of sample250by deflector232c. Secondary electrons emanated from the sample surface may be collected by electron detector244to form an image of the scanned area of interest.

In objective lens assembly232, exciting coil232dand pole piece232emay generate a magnetic field that is leaked out through the gap between two ends of pole piece232eand distributed in the area surrounding optical axis201. A part of sample250being scanned by primary electron beam204can be immersed in the magnetic field and can be electrically charged, which, in turn, creates an electric field. The electric field may reduce the energy of impinging primary electron beam204near and on the surface of sample250. Control electrode232b, being electrically isolated from pole piece232e, controls the electric field above and on sample250to reduce aberrations of objective lens assembly232and control focusing situation of signal electron beams for high detection efficiency. Deflector232cmay deflect primary electron beam204to facilitate beam scanning on the wafer. For example, in a scanning process, deflector232ccan be controlled to deflect primary electron beam204, onto different locations of top surface of sample250at different time points, to provide data for image reconstruction for different parts of sample250.

Backscattered electrons (BSEs) and secondary electrons (SEs) can be emitted from the part of sample250upon receiving primary electron beam204. Electron detector244may capture the BSEs and SEs and generate one or more images of the sample based on the information collected from the captured signal electrons. If electron detector244is positioned off primary optical axis201, a beam separator (not shown) can direct the BSEs and SEs to a sensor surface of electron detector244. The detected signal electron beams can form corresponding secondary electron beam spots on the sensor surface of electron detector244. Electron detector244can generate signals (e.g., voltages, currents) that represent the intensities of the received signal electron beam spots, and provide the signals to a processing system, such as controller50. The intensity of secondary or backscattered electron beams, and the resultant beam spots, can vary according to the external or internal structure of sample250. Moreover, as discussed above, primary electron beam204can be deflected onto different locations of the top surface of sample250to generate secondary or backscattered signal electron beams (and the resultant beam spots) of different intensities. Therefore, by mapping the intensities of the signal electron beam spots with the locations of primary electron beam204on sample250, the processing system can reconstruct an image of sample250that reflects the internal or external structures of sample250.

In some embodiments, controller50may comprise an image processing system that includes an image acquirer (not shown) and a storage (not shown). The image acquirer may comprise one or more processors. For example, the image acquirer may comprise a computer, server, mainframe host, terminals, personal computer, any kind of mobile computing devices, and the like, or a combination thereof. The image acquirer may be communicatively coupled to electron detector244of apparatus40through a medium such as an electrical conductor, optical fiber cable, portable storage media, IR, Bluetooth, internet, wireless network, wireless radio, among others, or a combination thereof. In some embodiments, the image acquirer may receive a signal from electron detector244and may construct an image. The image acquirer may thus acquire images of regions of sample250. The image acquirer may also perform various post-processing 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. In some embodiments, 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.

In some embodiments, controller50may include measurement circuitries (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, in combination with corresponding scan path data of a primary beam204incident on the sample (e.g., a wafer) surface, can be used to reconstruct images of the wafer structures under inspection. The reconstructed images can be used to reveal various features of the internal or external structures of sample250, and thereby can be used to reveal any defects that may exist in the wafer.

In some embodiments, controller50may control operation and adjustment of excitation of condenser lens226. Controller50may adjust the electrical excitation of condenser lens226based on the mode of operation selected. As shown inFIG.2B, for example, in flooding mode, condenser lens226may be electrically excited by applying an electrical signal such that the incident primary electron beam204may be strongly focused to form a cross over at or near aperture235-2of beam-limiting aperture array235. In inspection mode, however, an electrical signal may be applied to condenser lens226such that the incident primary electron beam204may be weakly focused to allow a small portion of primary electron beam204pass through the aperture of beam-limiting aperture array235and is focused on sample250by objective lens232.

Reference is now made toFIG.3, which illustrates an exemplary configuration of electron beam tool300in a single-beam inspection apparatus, consistent with embodiments of the present disclosure. Electron beam tool300may comprise an electron source301, a Coulomb aperture array308, a condenser lens303, a current-limiting aperture plate309, a beam-limiting aperture array307, a secondary electron detector305, a scanning deflection unit306, and an objective lens assembly304. It is to be appreciated that relevant components may be added or omitted or reordered, as appropriate.

In some embodiments, electron source301may be configured to emit primary electrons from a cathode and extracted to form a primary electron beam310that emanates from a primary beam crossover (virtual or real)302. In some embodiments, primary electron beam310can be visualized as being emitted from primary beam crossover302along primary optical axis300_1. In some embodiments, one or more elements of electron beam tool300may be aligned with primary optical axis300_1.

With reference toFIG.3, Coulomb aperture array308may be positioned immediately downstream of electron source301. As used in the context of this disclosure, “downstream” refers to a position of an element along the path of primary electron beam310starting from electron source301, and “immediately downstream” refers to a position of a second element along the path of primary electron beam310such that there are no other elements between the first and the second element. For example, as illustrated inFIG.3, Coulomb aperture array308may be positioned immediately downstream of electron source301such that there are no other electrical, optical, or electro-optical elements placed between electron source301and Coulomb aperture array308. Such a configuration may be useful, among other things, in efficiently reducing the Coulomb effect. In some embodiments, an aperture plate (e.g., a gun aperture plate) (not shown) may be placed between electron source301and Coulomb aperture array308to block off peripheral electrons of primary electron beam310before being incident on Coulomb aperture array308, to reduce Coulomb interaction effects.

In some embodiments, Coulomb aperture array308may comprise a beam-forming mechanism. Coulomb aperture array308may be configured to block peripheral electrons from primary electron beam310that may ultimately not be used to form a probe spot, and to reduce Coulomb interaction effects, among other things. In some embodiments, where Coulomb aperture array308is positioned immediately downstream of electron source301, Coulomb aperture array308may be positioned as close as possible to electron source301to cut off electrons at an early stage, to further reduce Coulomb interaction effects.

Coulomb aperture array308may comprise a plurality of coulomb apertures308-1,308-2, and308-3. As shown inFIG.3, apertures308-1,308-2, and308-3may be dissimilar in size. In some embodiments, at least two apertures of Coulomb aperture array308are dissimilar in size. A larger aperture such as aperture308-1may allow more electrons to pass through, therefore forming an electron beam (e.g., primary electron beam310) having a large beam current. A smaller aperture such as308-2or308-3may block more peripheral electrons emanated from electron source301, therefore forming an electron beam with smaller beam current. Although, Coulomb aperture array308inFIG.3shows three apertures, it is to be appreciated that Coulomb aperture array308may comprise one or more apertures, as appropriate.

In some embodiments, Coulomb aperture array308may be disposed downstream or immediately downstream of electron source301and orthogonal to primary optical axis300_1and can be movable to align different apertures thereof with primary electron beam310. Coulomb aperture array308may be disposed on a plane perpendicular or substantially perpendicular to primary optical axis300_1. In some embodiments, the position of Coulomb aperture array308may be adjusted in the X- or Y-axis such that a desired aperture (e.g., aperture308-1,308-2, or308-3) may be aligned with and perpendicular to primary optical axis300_1. In some embodiments, the position of Coulomb aperture array308may be adjusted along primary optical axis300_1to be closer to or further away from electron source301.

In some embodiments, an aperture of Coulomb aperture array308through which at least a portion of the electrons of primary electron beam310may pass through, is determined based on the mode of operation. For example, in flooding mode, a larger aperture, such as aperture308-1, may be used to form the beam having large beam current by allowing more electrons to pass through, ultimately resulting in a larger beam spot. In some embodiments, in the inspection mode, any one of the apertures308-1,308-2, or308-3may be used to form the primary electron beam illuminating condenser lens303, based on the desired inspection resolution and the beam current. For high inspection resolution and sensitivity, it may be desirable to use smaller apertures, such as308-2or308-3, due to the limited number of electrons that may be allowed to pass through the aperture and resultantly reduce the Coulomb interaction effects. However, in some embodiments, switching from aperture308-1in flooding mode to aperture308-2or308-3in inspection mode may not be desirable due to the time consumed, among other things, thereby negatively affecting the inspection throughput.

In some embodiments, as shown inFIG.3, the geometric center of a desired aperture (e.g., aperture308-1,308-2, or308-3) may be aligned with primary optical axis300_1. In some embodiments, switching the aperture from, for example,308-1to308-2or308-1to308-3, may include aligning the geometric center of the aperture in use with primary optical axis300_1.

In some embodiments, condenser lens303may be substantially similar to condenser lens226ofFIG.2Aand may perform similar functions. In some embodiments, condenser lens303may be configured to receive the portion of primary electron beam310allowed to pass through the selected aperture of Coulomb aperture array308. In some embodiments, condenser lens303may be configured to focus the received portion of primary electron beam310based on the selected mode of operation. Condenser lens303may comprise an electrostatic, electromagnetic, or a compound electromagnetic lens, among others. In some embodiments, condenser lens303may be electrically or communicatively coupled with a controller, such as controller50illustrated inFIG.2A. Controller50may apply an electrical excitation signal to condenser lens303to adjust the focusing power of condenser lens303based on the selected mode of operation.

Reference is now made toFIG.4A, which illustrates an exemplary configuration of the electron beam tool300and electron beam path in the flooding mode. In the flooding mode shown inFIG.4A, controller50may apply an electrical signal to condenser lens303such that electrons of primary electron beam310fully or partially passing through a selected aperture of Coulomb aperture array308may be focused to pass through an in-use aperture (e.g., aperture307-2) of beam-limiting aperture array307. The in-use aperture may have a desired size for the inspection mode such that aperture307-2may be used for flooding and inspection modes to reduce the time needed to select and align apertures of beam-limiting aperture array307between different modes of operation. In some embodiments, the electrons may form a crossover in the in-use aperture along a crossover plane. The crossover plane may coincide with the plane in which beam-limiting aperture array307is disposed. In some embodiments, the position of the plane in which beam-limiting aperture array307is disposed may be adjustable along primary optical axis300_1to coincide with the crossover plane. The in-use aperture309-1of current-limiting aperture plate309may be configured to allow the electrons passing through the in-use apertures of Coulomb aperture array308and beam-limiting aperture array307. In some embodiments, controller50may apply an electrical signal to objective lens304, and the electrical signal may also be used in the inspection mode. Objective lens304may be configured to partially focus the electrons passing through the in-use apertures of Coulomb aperture array308and beam-limiting aperture array307onto sample350and form a large beam spot thereon and flood sample350with electrons.

In the inspection mode shown inFIG.4B, controller50may apply an electrical signal to condenser lens303such that a desired portion of primary electron beam310may pass through the in-use aperture307-2of beam-limiting aperture307. The desired portion then may be fully focused by objective lens304to form a small probe spot on the surface of sample350. In some embodiments, controller50may apply an electrical signal to objective lens304, and the electrical signal may also be used in the flooding mode. In the inspection mode, however, peripheral electrons passing through the in-use aperture308-1of Coulomb aperture array308may be mostly blocked off by the in-use aperture309-1of current-limiting aperture plate309. Cutting off the peripheral electrons may reduce the Coulomb effect between current-limiting aperture plate309and beam-limiting aperture array307, and therefore may improve image resolution without switching apertures of Coulomb aperture array308between the flooding mode and the inspection mode, while improving the inspection throughput.

Detection of voltage contrast defects may include, among other things, highlighting a defect by pre-charging or sample flooding in the flooding mode of operation, followed by detecting the defect by high resolution imaging in the inspection mode of operation. In some embodiments, the size of the probe spot in inspection mode may be smaller than the beam spot in flooding mode to provide higher resolution and inspection sensitivity. As mentioned earlier, though the probe size may be reduced by reducing the aperture size of Coulomb aperture array308, doing so may negatively impact the inspection throughput. Therefore, it may be desirable to reduce the probe size in the inspection mode while maintaining the inspection throughput.

In some embodiments, current-limiting aperture plate309may be disposed between condenser lens303and beam-limiting aperture array307. The position of current-limiting aperture plate309and the size of in-use aperture309-1may be selected to block peripheral electrons as much as possible in the inspection mode, while allowing substantially all electrons in the flooding mode, and consequently reducing Coulomb effect in the inspection mode and improving inspection throughput. In some embodiments, current-limiting aperture plate309may be disposed downstream or immediately downstream of condenser lens303and orthogonal to primary optical axis300_1, and may use an aperture having a larger opening. In some embodiments, current-limiting aperture plate309may be disposed along a plane orthogonal to primary optical axis300_1such that the distance between current-limiting aperture plate309and condenser lens303is substantially equal to the distance between current-limiting aperture plate309and beam-limiting aperture array307, and use an aperture with a smaller opening.

In some embodiments, the aperture size and the position of current-limiting aperture plate309may determine the efficiency of reducing Coulomb effect in the inspection mode. For example, if current-limiting aperture plate309is placed closer to condenser lens303, a larger aperture size may be used. In this case, though the aperture can block peripheral electrons of primary electron beam310earlier in the inspection mode, the number of peripheral electrons blocked may be lower. In some embodiments, the aperture size or the position of current-limiting aperture plate309may be changed to optimize the reduction of Coulomb effect in the inspection mode, while the number of electrons passing through current-limiting aperture plate309and beam-limiting aperture array307may be unaffected in the flooding mode. Accordingly, current-limiting aperture plate309may comprise more than one aperture (e.g.,409-1and409-2) as shown inFIG.5, or may be movable along primary optical axis500_1as shown inFIG.6, or may comprise more than one aperture (e.g.,509-1and509-2) and be movable along the primary optical axis600_1as shown inFIG.7.

In some embodiments, for example as shown inFIG.5, current-limiting aperture plate409may comprise two or more apertures409-1and409-2, and the apertures may be dissimilar in size, pitch, and shape. Current-limiting aperture plate409may be positioned along a plane orthogonal or substantially orthogonal to primary optical axis400_1such that the geometric center of a selected aperture of current-limiting aperture plate409is aligned with primary optical axis400_1.

In some embodiments, for example inFIG.6, the position of current-limiting aperture plate509may be adjustable along primary optical axis500_1based on, but is not limited to, the size of primary electron beam310, the focusing power of condenser lens303, the desired beam current in the flooding mode, etc. For example, in the flooding mode, current-limiting aperture plate509may be disposed at a first distance from condenser lens303along primary optical axis500_1such that it allows an electron beam having a desired beam current to pass through and to be incident on objective lens assembly304, and in the inspection mode, placing current-limiting aperture plate509at the same position as in the flooding mode may significantly reduce the Coulomb interaction effect.

In some embodiments, for example inFIG.7, current-limiting aperture array609may comprise two or more apertures and the position of limiting aperture plate609along primary optical axis600_1may be adjusted to minimize or reduce Coulomb interaction effects, thereby enhancing imaging resolution in the inspection mode of operation. One of the several problems that may be encountered while adjusting the size of a current-limiting aperture may be the time consumed to perform the operation of, including but not limiting, moving the current-limiting aperture plate (e.g., current-limiting aperture plate509), aligning the current-limiting aperture with primary optical axis600_1, thus negatively affecting the inspection throughput. In some embodiments, the size of current-limiting aperture509-1and the position of current-limiting aperture plate509along primary optical axis600_1may be fixed regardless of the mode of operation.

Referring back toFIG.3, beam-limiting aperture array307may be configured to allow substantially all electrons of the electron beam from condenser lens303in the flooding mode and to block off the peripheral electrons to achieve a desired probe current on sample350in the inspection mode. The size of the probe spot on sample350may be determined by the size of the selected aperture of beam-limiting aperture array307.

In some embodiments, beam-limiting aperture array307may comprise beam-limiting apertures307-1,307-2, and307-3. AlthoughFIG.3shows at least two beam-limiting apertures (e.g.,307-2and307-3) of dissimilar size, it is to be appreciated that all beam-limiting apertures may be of similar size. Beam-limiting aperture array307may be disposed downstream or immediately downstream of current-limiting aperture plate309and orthogonal to primary optical axis300_1. In some embodiments, beam-limiting aperture array307may be disposed between current-limiting aperture plate309and secondary electron detector305. The position of beam-limiting aperture array307may be adjustable along the X-, Y-, or Z-axis. In some embodiments, the position of beam-limiting aperture array307may be adjusted in the X-, or Y-axis so that a selected beam-limiting aperture may be aligned with primary optical axis300_1. In some embodiments, a beam-limiting aperture307-2, for example, may be aligned such that the geometric center of beam-limiting aperture307-2may be aligned with primary optical axis300_1. The position of beam-limiting aperture array307may be adjusted along the Z-axis, parallel to primary optical axis300_1to adjust the distance between beam-limiting aperture array307and current-limiting aperture plate309. In some embodiments, the distance between beam-limiting aperture array307and current-limiting aperture plate309may be adjusted to adjust the Coulomb interaction effects.

In existing voltage contrast defect detection and inspection tools, some of the challenges encountered include, among other things, limitations in the allowable size of beam-limiting aperture array307and a limited range of movement for beam-limiting aperture array307. In addition, beam-limiting apertures of beam-limiting aperture array307may be positioned farther apart from each other to block a desired portion of peripheral electrons of the electron beam from condenser lens303, thus limiting the number of beam-limiting apertures that may be employed. Therefore, it may be desirable to provide a current-limiting aperture such as in current-limiting aperture plate309between condenser lens303and beam-limiting aperture array307to block peripheral electrons and to reduce the size of the electron beam incident on beam-limiting aperture array307in the inspection mode, while allowing substantially all electrons of primary electron beam310to pass through in the flooding mode. Placing current-limiting aperture plate309between condenser lens303and beam-limiting aperture array307may further allow providing more beam-limiting apertures with a reduced pitch.

Electron beam tool300may further include deflection scanning unit306. In some embodiments, deflection scanning unit306may be positioned inside a primary projection optical system (not illustrated inFIG.3). In the inspection mode, deflection scanning unit306may be configured to deflect primary beam310to scan the surface of sample350. Objective lens assembly304and secondary electron detector305may be substantially similar to objective lens assembly232and electron detector244ofFIG.2A, respectively, and may perform substantially similar functions.

In some embodiments, Coulomb aperture array308may be adjusted to switch from using large aperture308-1to smaller apertures308-2or308-3to enhance inspection resolution and inspection sensitivity or defect detectability in the inspection mode.

Reference is now made toFIG.8, which illustrates an exemplary configuration of an electron beam tool800in a single-beam apparatus, consistent with embodiments of the present disclosure. Electron beam tool800may comprise an electron source301, a Coulomb aperture array308, a condenser lens303, a current-limiting aperture plate309, a beam-limiting aperture array307, an objective lens assembly822, and a signal electron deflector825. In some embodiments, electron beam tool800may further comprise multiple electron detectors, such as in-lens electron detectors803and805. In some embodiments, the in-lens electron detector803and805may be coupled to a first and second channels of electron beam tool800, respectively. In some embodiments, each channel may be optimized for different inspection characteristics. For example, in some embodiments, the first channel may be optimized for high-speed detection while the second channel may be optimized for high-resolution inspection.

As explained above with respect toFIG.4A, when the apparatus operates in the flooding mode, condenser lens303may focus a primary electron beam310such that electrons of the primary electron beam310may pass through a selected aperture308-1of Coulomb aperture array308and an in-use aperture (e.g., aperture307-2) of beam-limiting aperture array307. In some embodiments, the electrons may form a crossover near the in-use aperture307-2along a crossover plane. The crossover plane may coincide with the plane in which beam-limiting aperture array307is disposed. An in-use aperture309-1of current-limiting aperture plate309may be configured to allow the electrons passing through the in-use apertures of Coulomb aperture array308and beam-limiting aperture array307.

The electron beam tool800may comprise objective lens assembly822(e.g., the objective lens304ofFIG.4A). In some embodiments, objective lens assembly822may comprise a compound electromagnetic lens including a magnetic lens comprising an exciting coil822M, a magnetic lens body822A, and an inner pole piece822C, and an electrostatic lens formed by the inner pole piece822C (similar to pole piece232eofFIG.2) and a control electrode822B (similar to control electrode232bofFIG.2), which work in conjunction to focus primary electron beam310at sample850. When the apparatus operates in the flooding mode, objective lens assembly822may be configured to partially focus the primary electron beam310passing through the in-use apertures of Coulomb aperture array308and beam-limiting aperture array307onto a sample850, and form a large flooding beam spot872fon sample850to pre-charge a portion of the sample850.

As described earlier with respect toFIG.2A, interaction of electrons of primary electron beam310with sample850may generate signal electrons (e.g., signal electrons travel along paths881and891). In some embodiments, the signal electrons may include SEs and BSEs. When the apparatus is operating in the flooding mode, the current of the primary electron beam310may reach a substantially high level (e.g., >2000 nA) and the electrons of primary electron beam310may be accelerated to have substantially high kinetic energy. Accordingly, the signal electrons generated during the flooding mode may reach to a substantially high level (e.g., roughly up to the similar level of the primary beam current, if yield is 1), and depending on the landing energy, the signal electrons will also have a substantially high kinetic energy, for example, from few keV up to the electron source emission energy. If these large amount of high-energy signal electrons hit electron detectors803and805, the detector surface can be contaminated with the built-up carbonaceous materials that exist in vacuum and are bombarded by the high-energy and large amount of signal electrons, which may cause the detector aging over time. Furthermore, the electronic circuitry (e.g., a low-noise amplifier) that are connected to the detectors803and805may be damaged due to a surge current or overcurrent caused by the high-energy signal electrons.

To alleviate these potential issues during the flooding mode, in some embodiments, the electron beam tool800may comprise a detector protection mechanism that is configured to prevent the signal electrons from reaching the electron detector when the apparatus operates in the flooding mode.

In some embodiments, control electrode822B may be placed to form an active energy filter between sample850and in-lens electron detectors803and805. In some embodiments, control electrode822B may be disposed between sample850and magnetic lens822M of objective lens assembly822. When control electrode822B is biased to a voltage by power supply870with reference to sample850, an electric field is generated between control electrode822B and sample850, resulting in an electrostatic potential barrier for the signal electrons. The electrostatic potential barrier blocks off signal electrons that have emission energies lower than a threshold energy level of the barrier. It is appreciated that an “active filter” means an electron filter using active components, such as an electrode generating an “active” electric field—in contrast to a “passive filter” that uses only passive elements.

For example, as shown inFIG.8, control electrode822B is biased negatively with reference to sample850such that the negatively charged signal electrons (e.g., the SEs on path881) are reflected back to sample850because the SEs on path881do not have enough energy to pass through the energy barrier. Although signal electrons which have emission energies higher than the threshold energy level of the barrier (e.g., the BSEs on path891) may overcome the energy barrier and propagate towards in-lens electron detector805, these BSEs may not damage the detector805or the associated electronic circuitry because the yield of these BSEs is relatively low. For example, when the probe current of primary electron beam310in the flooding mode is within the range of 1000-2000 nA, resulting signal electrons may comprise mainly the SEs. Reflecting the SEs (e.g., electrons on path881) back to the sample850, therefore, may significantly reduce the number of total electrons reaching to the detector, thereby reducing the possibility of amplifier overcurrent or the detector contamination. Furthermore, the reflected SEs may assist the sample pre-charging process.

Reference is now made toFIGS.9A-9C, which illustrate an exemplary electron beam tool900including another embodiment of an electron detector protector906, consistent with embodiments of the present disclosure.

An active energy filter (such as the one shown inFIG.8) generates an electric field that may influence the electrons in the primary electron beam310. In some embodiments, it may be desired to protect the detectors while minimizing the influence on the primary electrons. Furthermore, in some embodiments, it may also be desired to maintain the primary beam condition (e.g., the strength of the magnetic field and the electric field applied to the primary electrons) unchanged between the flooding mode and the inspection mode to enable faster mode-switching. In comparison to the electron beam tool800ofFIG.8, the electron beam tool900comprises an active energy filter906disposed near in-lens electron detector805. Active energy filter906may be configured to filter out signal electrons991in the flooding mode. When the apparatus operates in the inspection mode, the active energy filter906may be inactivated so that the signal electrons991can pass through the active energy filter906and be detected by the detector805. As the energy filter906may be positioned away from the primary optical axis, the influence on the primary electron beams could be reduced compared to the electron beam tool800.

The active energy filter906, as shown inFIG.9B, may comprise a high-voltage electrode906hvand a ground electrode906g. The electrodes906hvand906gmay be mesh-type electrodes. During the flooding mode, the high-voltage electrode906hvmay be biased negatively with reference to the ground electrode906gto generate an electric field, such that the negatively charged signal electrons are reflected toward sample850. In some embodiments, the bias voltage supplied by a power supply905vmay be changed to adjust the energy barrier of the active energy filter906. For example, the bias voltage can be increased to block all signal electrons including the BSEs and SEs; and decreased to block only signal electrons with low emission energy (e.g., SEs) while allowing the signal electrons with high emission energy (e.g., BSEs) to pass through to the detector805.

In some embodiments, high-voltage electrode906hvand ground electrode906gmay comprise mesh-like structures fabricated from an electrically conducting material, such as a metal, an alloy, a semiconductor, or a composite, among other things. The high-voltage electrode906hvand ground electrode906gmay be disposed between objective lens assembly822and in-lens electron detector805. In some embodiments, high-voltage electrode906hvand ground electrode906gmay be disposed closer to in-lens electron detector805than objective lens assembly822.

As shown inFIG.9C, the active energy filter906may comprise a tube-electrode906einstead of a mesh-type structure. Similar to the mesh-type high-voltage electrode906hvinFIG.9B, the tube-electrode906emay be biased negatively with reference to the ground electrode906gto generate an electric field.

Reference is now made toFIGS.10A-10B, which are schematic diagrams illustrating an exemplary electron beam tool1000operating in a flooding mode (FIG.10A) and an inspection mode (FIG.10B), consistent with embodiments of the present disclosure. The electron beam tool1000may operate in a substantially similar way as the electron beam tool900ofFIG.9Ain that, when the tool is in the flooding mode, signal electrons1091are prevented from reaching an electron detector805.

In some embodiments, the tool1000may comprise an electron stopper1006movable between a first position for the flooding mode (FIG.10A) and a second position for the inspection mode (FIG.10B). As shown inFIG.10A, when the tool1000operates in the flooding mode, electron stopper1006may be positioned in the first position between a sample850and the electron detector805, so that signal electrons1091generated from sample850are blocked by the electron stopper1006. In some embodiments, electron stopper1006may be a plate made of materials capable of attenuating the energy of the incoming signal electrons. For example, electron stopper1006may comprise a semiconductor material (such as silicon nitride) or electric conduction material (such as aluminum film), which provide an attenuation capability while also providing a certain level of electric conductivity to discharge any charge that may build up within the electron stopper1006from the incidence of the signal electrons. In some embodiments, the electron stopper1006may be connected to a ground.

As shown inFIG.10B, when the tool1000operates in the inspection mode, electron stopper1006may be positioned in the second position away from the paths on which signals electrons1093travel, so that the signal electrons1093may reach the surface of electron detector805for detection.

In some embodiments, the tool1000may use a moving mechanism (not shown) that may be capable of moving the electron stopper1006quickly between the first and the second position, such that the throughput of the overall system will not be affected by the mode switching. For example, in some embodiments, a piezoelectric motor can be used to move the electron stopper1006.

Reference is now made toFIGS.11A-11B, which are schematic diagrams illustrating an exemplary electron beam tool1100operating in a flooding mode (FIG.11A) and an inspection mode (FIG.11B), consistent with embodiments of the present disclosure. In comparison to the electron beam tool1000ofFIGS.10A-10B, the electron beam tool1100may be configured to change the paths of signal electrons (e.g., between1191and1193) based on the mode of operation, rather than moving an energy filter (e.g., electron stopper1006ofFIGS.10A-10B).

In the flooding mode, as shown inFIG.11A, the signal electron deflector825may deflect signal electrons1191toward the electron detector803that is protected by an electron stopper1106. In the inspection mode, as shown inFIG.11B, the signal electron deflector825may deflect signal electrons1193toward the electron detector805for detection. In some embodiments, the signal electron deflector825may comprise Wien filter configured to generate an electric field and a magnetic field.

In some embodiments, the moving mechanism (not shown) for the electron stopper1106may be too slow that moving the filter in and out based on the operating mode may affect the overall system throughput negatively. In such cases, it may be desirable to place the electron stopper1106in front of the detector803(which is not in use), and reroute the signal electrons toward the detector805when the tool switches from the flooding mode to the inspection mode. Because the operating mode switching (between the flooding mode and the inspection mode) relies on rerouting of signal electrons (e.g., between1191and1193) rather than placement of the electron stopper1106, the tool1100can utilize a moving mechanism that is relatively slow, such as a stepper motor.

In some embodiments, the electron stopper1106may comprise an active filter, similar to the active energy filter906described with respect toFIGS.9A-9C. In some embodiments, electron stopper1106may comprise a passive energy filter, similar to the electron stopper1006shown inFIGS.10A-10B.

Reference is now made toFIGS.12A-12C, which are schematic diagrams illustrating an exemplary electron beam tool1200operating in a flooding mode (FIG.12A) and an inspection mode (FIG.12B), consistent with embodiments of the present disclosure. Similar to the electron beam tool1100shown inFIGS.11A-11B, the electron beam tool1200may use the signal electron deflector825to deflect signal electrons toward different targets based on the operating mode. For example, in the flooding mode, as shown inFIG.12A, the signal electron deflector825may deflect signal electrons1291toward an electron stopper1206positioned next to the electron detector805. In the inspection mode, as shown inFIG.12B, the signal electron deflector825may deflect signal electrons1293toward the electron detector805for detection. In some embodiments, the electron stopper1206may comprise a passive energy filter, similar to the electron stopper1006shown inFIGS.10A-10B.

As illustrated inFIGS.12A-12C, in some embodiments, the electron stopper1206may be positioned farther away from the primary optical axis800_1. Accordingly, during the flooding mode, the electron signal deflector825may need to produce stronger deflection power to bend to deflect the signal electrons with larger deflection polar angle (polar angle with respect to the primary optical axis800_1).

FIG.12Cshows a three-dimensional representation of the detectors803,805and the electron stopper1206of the electron beam tool1200shown inFIGS.12A-12B. In some embodiments, the detectors803,805and the electron stopper1206may be arranged on a XY-plane formed by X-axis and Y-axis, where the primary optical axis800_1is aligned with Z-axis. In some embodiments, the detectors803,805and the electron stopper1206may be positioned along with an axis800_2that is aligned with the X-axis.

When the electron beam tool1200operates in the inspection mode, signal electrons1293may be directed to the detector805. When the electron tool1200operates in the flooding mode, signal electrons1291may be bent further away from the primary optical axis800_1and directed to the electron stopper1206. Accordingly, in some embodiments, the distance1235between the primary optical axis800_1and the center of the detector805may be smaller than the distance1236between the primary optical axis800_1and the center of the stopper1206.

In a typical electron beam inspection system, an increased deflection polar angle can result in increased deflection aberration, such as dispersion-like chromatic aberration, which may deteriorate the primary beam resolution. However, because no image is generated during the flooding mode, the inspection system may not need to provide high resolution performance during the flooding mode, and therefore the signal electrons1291can be deflected with a larger deflection polar angle without affecting the overall system performance. Another way is to change the relative azimuth angle of the signal electrons with respect to the detectors. However, rotating the detector is less feasible than rotating the beam, which leads to the next embodiment.

FIG.13shows another exemplary arrangement of detectors803,805and an electron stopper1306of an electron beam tool1300, consistent with embodiments of the present disclosure. Similar to the electron beam tool1200ofFIG.12C, in some embodiments, the detectors803,805and the electron stopper1306may be arranged on the XY-plane. In some embodiments, the detectors803,805may be positioned along with an axis800_2that is aligned, for example, with the X-axis, and the electron stopper1306may be positioned along with an axis800_3that is aligned, for example, with the Y-axis.

When the electron beam tool1300operates in the inspection mode, signal electrons1393may be directed to the detector805. When the electron beam tool1300operates in the flooding mode, signal electrons1391may be bent around the primary optical axis800_1and directed to the electron stopper1306. For example, during the flooding mode, a signal electron deflector (such as the signal electron deflector825ofFIGS.12A-12B) may generate a rotational electro-magnetic field to rotate signal electrons1391around the primary optical axis800_1about 90 degrees (as shown by an azimuth angle1337) toward the electron stopper1306.

Accordingly, the distance1335(between the primary optical axis800_1and the center of the detector805) and the distance1336(between the primary optical axis800_1and the center of the stopper1306) may be the same. In other words, the deflection polar angle (polar angle with respect to the primary optical axis800_1) may not change substantially between the operating modes, while the signal electrons in the flooding mode is prevented from reaching the detector805as they are rotated azimuthally. In some embodiments, the polar angle may stay the same within 5 degrees. In such configurations, the bending power of the signal electron deflector does not need to be increased during the flooding mode, which may be desirable for certain embodiments because of reduced risk of an electric arc discharge and heat generation in the Wien Filter.

Reference is now made toFIG.14, which illustrates a process flowchart representing an exemplary method1400of forming a probe spot on a surface of a sample in a single-beam apparatus, consistent with embodiments of the present disclosure. Method1400may be performed by controller50of the charged particle beam inspection system100, as shown inFIG.1, for example. Controller50may be programmed to perform one or more blocks of method1400. For example, controller50may apply an electrical signal to condenser lens to adjust the focus of primary charged particle beam based on the selected mode of operation and carry out other functions.

In step1410, a charged particle source (e.g., electron source301ofFIG.3) may be activated to generate a charged particle beam (e.g., primary electron beam310ofFIG.3). The electron source may be activated by a controller (e.g., controller50ofFIG.1). For example, the electron source may be controlled to emit primary electrons to form an electron beam along a primary optical axis (e.g., primary optical axis300_1ofFIG.3). The electron source may be activated remotely, for example, by using a software, an application, or a set of instructions for a processor of a controller to power the electron source through a control circuitry.

The EBI system may provide a mechanism to support multiple modes of operation. For example, electron beam tool (e.g., electron beam tool300ofFIG.3) may be configured to operate in a flooding mode to highlight a voltage contrast defect by flooding a surface of a sample with charged particles (e.g., electrons), and an inspection mode to analyze any defects highlighted during the flooding mode, using high resolution imaging methods. Electron beam tool may be configured to switch between modes of operation. For example, a complete scan of voltage contrast defect detection and analysis may include flooding the surface of the sample for a predetermined time duration, followed by high resolution inspection of any defects identified by flooding.

In step1420, a mode of operation of the electron beam tool, such as a flooding mode or inspection mode, may be selected. In some embodiments, a user may select the mode of operation based on factors including, but are not limited to, the application, the requirements, and desired analysis. In some embodiments, electron beam tool may be programmed to run without user interaction, for example, performing selection of a mode of operation, operating the inspection tool in the selected mode of operation, or performing a series of steps including switching the mode of operation. For example, a controller (e.g., controller50ofFIG.2) may be programmed to initiate voltage contrast defect detection by activating the flooding mode, to adjust electrical excitation of a condenser lens (e.g., condenser lens303ofFIG.3) to adjust the focusing power, to switch to inspection mode after completing flooding, and the like.

In step1430, the electron beam tool may be configured to operate in the flooding mode in which, the controller may apply an electrical signal to the condenser lens such that substantially all electrons of the primary electron beam passing through a selected aperture of an aperture array (e.g., Coulomb aperture array308ofFIG.3) may be focused to form a crossover in a crossover plane. The crossover plane may coincide with the plane in which a beam-limiting aperture array (e.g., beam-limiting aperture array307ofFIG.3) is disposed. The beam-limiting aperture array may be configured to allow through substantially all electrons of the electron beam from the condenser lens and to direct the primary electron beam towards an objective lens (e.g., objective lens assembly304ofFIG.3). The objective lens may be configured to defocus the primary electron beam to form a probe spot on a surface of a sample (e.g., sample350ofFIG.3).

The electron beam tool may comprise a current-limiting aperture array (e.g., current-limiting aperture plate409ofFIG.5) configured to allow passage of electrons of the primary electron beam, based on the mode of operation. For example, in the flooding mode, the current-limiting aperture plate may allow substantially all electrons of the primary electron beam to pass through. The position of the current-limiting aperture plate along the Z-axis may be adjusted such that the maximum electrons may pass through to allow formation of a beam having a large beam current. The current-limiting aperture plate may be placed downstream of the condenser lens and at an optimum distance away from the condenser lens along the primary optical axis.

The electron beam exiting the objective lens and incident on the surface of the sample may comprise a defocused beam having large beam current. The probe spot formed by the defocused electron beam may comprise a defocused large probe spot configured to flood the surface of the sample with charged particles such as electrons. The sample may be flooded for a predetermined time duration, or the time may be adjusted based on factors including, but are not limited to, the sample, the application, the defect characteristics, and the like. The variability in conductivity of the features on sample surface causes a variability in contrast in the images produced from the secondary electrons emitted by the beam-sample interaction.

Furthermore, when the electron beam tool operates in the flooding mode, to protect the electron detector, a detector protector may be configured to prevent the plurality of signal electrons from reaching the electron detector. In some embodiments, the detector protector comprising an active energy filter (e.g., an energy filter formed by control electrode822B and the sample850inFIG.8; the active energy filter906ofFIG.9A) may be configured to filter out high-energy signal electrons generated from the sample during the flooding mode. When the apparatus operates in the inspection mode, the active energy filter may be inactivated so that the signal electrons can pass through the active energy filter and be detected by the electron detector. In some embodiments, the detector protector comprising an electron stopper (e.g., the electron stopper1006ofFIG.10A,1106ofFIG.11A, and1206ofFIG.12A) may be configured to block the high-energy signal electrons during the flooding mode.

In step1440, in the inspection mode of operation, the primary electron beam emanating from a primary beam crossover (virtual or real) (e.g., primary beam crossover302ofFIG.4B) may pass through a Coulomb aperture (e.g., aperture308-1ofFIG.4B) of the Coulomb aperture array. Though using a smaller aperture (e.g., aperture308-2or308-3ofFIG.4B) may enhance the inspection resolution and sensitivity by reducing the Coulomb interaction effects, adjusting the Coulomb aperture array to switch from a large aperture (e.g., aperture308-1) to smaller apertures (e.g., smaller apertures308-2or308-3) may negatively impact the inspection throughput. Therefore, it may be desirable to maintain the aperture size of the Coulomb aperture array during the flooding and inspection modes of operation. In some embodiments, the Coulomb aperture array may be adjusted to switch from using the larger aperture to smaller apertures to enhance inspection resolution and inspection sensitivity or defect detectability.

The controller may adjust the electrical excitation of the condenser lens to adjust the focusing power of the condenser lens. An electrical signal may be applied to the condenser lens such that the probing beamlet of the primary electron beam may be focused using the objective lens to form a focused probe spot on the surface of the sample. The electrical signal applied to the condenser lens may cause the primary electron beam to be incident on the aperture plate such that a portion of peripheral electrons of the primary electron beam may be blocked off from propagating towards the sample. In the inspection mode of operation, the aperture plate may function as a current-limiting aperture plate, configured to trim peripheral electrons of the primary electron beam and to reduce the Coulomb interaction effect. In some embodiments, the current-limiting aperture plate may comprise an array of apertures.

In the inspection mode of operation, the position of the current-limiting aperture plate may not be adjusted compared to its position in the flooding mode. This may help minimize inspection delays caused as a result of initiating mechanical components to enable movement of the current-limiting aperture plate, aligning the current-limiting aperture plate such that a geometric center of the current-limiting aperture aligns with the primary optical axis and other components of the system, while reducing Coulomb interaction effect by blocking off peripheral electrons.

In some embodiments, the position of the current-limiting aperture plate may be adjusted along the primary optical axis based on factors including, but are not limited to, the primary electron beam size, the focusing power of the condenser lens, the desired probing beam current, and the like. For example, the distance between the current-limiting aperture plate and beam-limiting aperture array may be increased by adjusting the position of the current-limiting aperture plate to minimize Coulomb interaction effects. In some embodiments, the size of aperture of the current-limiting aperture plate may be adjusted to minimize Coulomb interaction effects, for example, by reducing the size of the selected current-limiting aperture or selecting a smaller current-limiting aperture of the plurality of arrays in the current-limiting aperture plate. A smaller current-limiting aperture may allow fewer electrons to pass through, and therefore, minimize Coulomb interaction effects.

A portion of the electrons passing through the current-limiting aperture of the current-limiting aperture plate may pass through one beam-limiting aperture of the beam-limiting aperture array positioned downstream or immediately downstream of the current-limiting aperture plate. The portion may be directed towards and incident on the objective lens configured to focus the portion on the surface of sample to form a probe spot. The electrical excitation of objective lens may be the same in the flooding mode and in the inspection mode. The electrical excitation may comprise an electrical signal (e.g., voltage, current, and the like), for example, to adjust the electric or magnetic field influencing the energy, the path, the direction, and the like, of the electrons of that portion.

Furthermore, when the electron beam tool operates in the inspection mode, the detector protector may be configured to allow the plurality of signal electrons to reach the electron detector. In some embodiments, the detector protector comprising an active energy filter (e.g., an energy filter formed by control electrode822B and the sample850inFIG.8; the active energy filter906ofFIG.9A) may be inactivated so that the signal electrons can pass through the active energy filter and be detected by the electron detector. In some embodiments, the detector protector comprising an electron stopper (e.g., the electron stopper1006ofFIG.10A,1106ofFIG.11A, and1206ofFIG.12A) may be configured to move away from the path that signal electron travels, so that the signal electrons can be detected by the electron detector.

The embodiments may further be described using the following clauses:1. A charged-particle beam apparatus comprising:a charged-particle source configured to generate a primary charged-particle beam along a primary optical axis;a first aperture array comprising a first aperture configured to allow at least a first portion of the primary charged-particle beam to pass through;a condenser lens configured to focus the at least a first portion of the primary charged-particle beam based on a selected mode of operation of the apparatus, wherein the selected mode of operation includes a first mode and a second mode; andan aperture plate comprising a second aperture configured to form a second portion of the primary charged-particle beam, wherein:in the first mode of operation, substantially all of the second portion of the primary charged-particle beam is used to flood a surface of a sample, andin the second mode of operation, at least some of the second portion of the primary charged-particle beam is used to inspect the surface of the sample.2. The apparatus of clause 1, wherein the first aperture is configured to block peripheral charged particles of the primary charged-particle beam to form the first portion of the primary charged-particle beam.3. The apparatus of any one of clauses 1 and 2, wherein the first aperture array includes at least two apertures that are dissimilar in size.4. The apparatus of any one of clauses 1-3, wherein the first aperture array is disposed in and is movable in a first plane substantially perpendicular to the primary optical axis.5. The apparatus of any one of clauses 1-4, wherein the first aperture array is disposed between the charged-particle source and the condenser lens along the primary optical axis.6. The apparatus of any one of clauses 1-5, wherein the second aperture is a current-limiting aperture configured to:in the first mode of operation, allow substantially all charged particles of the first portion of the primary charged-particle beam to pass through to form the second portion of the primary charged-particle beam; andin the second mode of operation, block peripheral charged particles of the first portion of the primary charged-particle beam to form the second portion of the primary charged-particle beam.7. The apparatus of any one of clauses 1-6, wherein the aperture plate is movable along the primary optical axis.8. The apparatus of clause 7, wherein the aperture plate comprises a current-limiting aperture array movable along a second plane substantially perpendicular to the primary optical axis.9. The apparatus of any one of clauses 1-6, wherein the aperture plate comprises a current-limiting aperture array movable along a second plane substantially perpendicular to the primary optical axis.10. The apparatus of any one of clauses 1-9, further comprising a beam-limiting aperture array configured to limit a beam current of the second portion of the primary charged-particle beam in the second mode.11. The apparatus of clause 10, wherein the beam-limiting aperture array comprises a plurality of beam-limiting apertures, and at least two beam-limiting apertures of the plurality of beam-limiting apertures are dissimilar in size.12. The apparatus of any one of clauses 10 and 11, wherein the beam-limiting aperture array is disposed in and is movable in a third plane substantially perpendicular to the primary optical axis.13. The apparatus of any one of clauses 11 and 12, wherein in the first and the second modes of operation, the first aperture and a beam-limiting aperture of the plurality of beam-limiting apertures are the same.14. The apparatus of any one of clauses 12 and 13, wherein in the first mode of operation, the condenser lens is configured to cause the second portion of the primary charged-particle beam to form a crossover close to the third plane such that substantially all charged particles of the second portion of the primary charged-particle beam pass through an aperture of the beam-limiting aperture array.15. The apparatus of clause 14, wherein in the second mode of operation, the aperture of the beam-limiting aperture array is configured to limit a beam current of the second portion of the primary charged-particle beam.16. The apparatus of any one of clauses 8-15, further comprising an objective lens, wherein in the first mode of operation, the objective lens is configured to defocus the second portion of the primary charged-particle beam and to form a first spot on the surface of the sample, the first spot having a first current level.17. The apparatus of clause 16, wherein in the second mode of operation, the objective lens is configured to focus the at least some of the second portion of the primary charged-particle beam passing through the aperture of the beam-limiting aperture array to form a second spot on the surface of the sample, the second spot having a second current level.18. The apparatus of clause 17, wherein an electrical excitation of the objective lens in the first mode of operation is same or substantially similar to an electrical excitation of the objective lens in the second mode of operation.19. The apparatus of any one of clauses 17-18, wherein the first current level is greater than or equal to the second current level.20. The apparatus of any one of clauses 17-19, wherein the first spot is larger than or equal to the second spot.21. The apparatus of any one of clauses 1-20, further comprising a controller configured to:perform charged-particle flooding on the surface of the sample in the first mode; andperform charged-particle beam inspection of the surface of the sample in the second mode.22. The apparatus of clause 21, wherein the controller is further configured to adjust an electrical excitation of the condenser lens based on the selected mode of operation.23. The apparatus of any one of clauses 1-22, further comprising:an electron detector configured to detect a plurality of signal electrons generated from incidence of the primary charged-particle beam onto the sample when the apparatus is in the second mode of operation; anda detector protector configured to prevent the plurality of signal electrons from reaching the electron detector when the apparatus is in the first mode of the operation.24. The apparatus of clause 23, wherein the plurality of signal electrons comprises backscattered electrons (BSEs) or secondary electrons (SEs).25. The apparatus of any one of clauses 23 and 24, wherein the controller is further configured to control the detector protector based on the selected mode of operation.26. The apparatus of any one of clauses 23-25, wherein the detector protector comprises an active energy filter configured to generate an electric field that reflects all or a subset of the plurality of signal electrons.27. The apparatus of clause 26, wherein the active energy filter comprises an electrode positioned between the sample and the objective lens, wherein the electrode is configured to be negatively biased with respect to the sample to generate the electric field.28. The apparatus of clause 27, wherein the electrode is a part of the objective lens.29. The apparatus of clause 26, wherein the active energy filter comprises a first electrode and a second electrode positioned between the electron detector and the objective lens, wherein the first electrode is configured to be negatively biased with respect to the second electrode to generate the electric field.30. The apparatus of clause 29, wherein the first electrode comprises a mesh-electrode.31. The apparatus of clause 29, wherein the first electrode comprises a tube-electrode.32. The apparatus of any one of clauses 29-31, wherein the second electrode comprises a mesh-electrode.33. The apparatus of any one of clauses 29-32, wherein the second electrode is connected to a ground.34. The apparatus of any one of clauses 23-25, wherein the detector protector comprises an electron stopper movable between a first position and a second position, wherein:when the apparatus is in the first mode of operation, the electron stopper is positioned in the first position between the sample and the electron detector and is configured to block the plurality of signal electrons, andwhen the apparatus is in the second mode of operation, the electron stopper is positioned in the second position away from the electron detector and is configured to allow the plurality of signal electrons to pass through to the electron detector.35. The apparatus of clause 34, wherein the electron stopper comprises a metal plate.36. The apparatus of any one of clauses 34 and 35, wherein the electron stopper is connected to a ground.37. The apparatus of any one of clauses 34-36, wherein the detector protector further comprises a deflector configured to change directions of the plurality of signal electrons, wherein:when the apparatus is in the first mode of operation, the deflector is configured to deflect the plurality of signal electrons toward the electron stopper, andwhen the apparatus is in the second mode of operation, the deflector is configured to deflect the plurality of signal electrons toward the electron detector.38. The apparatus of clause 37, wherein the deflector comprises an electric field generator and a magnetic field generator.39. The apparatus of any one of clauses 37 and 38, wherein the deflector is a Wien filter.40. The apparatus of any one of clauses 23-25, wherein the detector protector comprises:an electron stopper positioned near the electron detector; anda deflector configured to change directions of the plurality of signal electrons, wherein:when the apparatus is in the first mode of operation, the deflector is configured to deflect the plurality of signal electrons toward the electron stopper at a first polar deflection angle and a first azimuthal deflection angle with respect to the primary optical axis, andwhen the apparatus is in the second mode of operation, the deflector is configured to deflect the plurality of signal electrons toward the electron detector at a second polar deflection angle and a second azimuthal deflection angle with respect to the primary optical axis.41. The apparatus of clause 40, wherein the electron stopper is positioned farther away from the primary optical axis than the electron detector.42. The apparatus of any one of clauses 40 and 41, wherein the first polar deflection angle is larger than the second polar deflection angle.43. The apparatus of any one of clauses 40-42, wherein the first azimuthal deflection angle and the second azimuthal deflection angle are the same or substantially similar.44. The apparatus of clause 40, wherein the electron detector and the electron stopper are positioned around the primary optical axis.45. The apparatus of any one of clauses 40 and 44, wherein the first polar deflection angle and the second polar deflection angle are the same or substantially similar.46. The apparatus of any one of clauses 40, 44-45, wherein the first azimuthal deflection angle and the second azimuthal deflection angle are different.47. The apparatus of any one of clauses 40, 44-46, wherein a difference between the first azimuthal deflection angle and the second azimuthal deflection angle is approximately 90 degrees.48. The apparatus of any one of clauses 40-47, wherein the electron stopper comprises a metal plate.49. The apparatus of any one of clauses 40-48, wherein the electron stopper is connected to a ground.50. The apparatus of any one of clauses 40-49, wherein the deflector comprises an electric field generator and a magnetic field generator.51. The apparatus of any one of clauses 40-50, wherein the deflector is a Wien filter.52. A method of forming a probe spot on a surface of a sample in a charged-particle beam apparatus comprising a first aperture array, a condenser lens, a second aperture array, and an aperture plate, the method comprising:activating a charged-particle source to generate a primary charged-particle beam along a primary optical axis; andselecting between a first mode and a second mode of operation of the charged-particle beam apparatus, wherein:in the first mode of operation, the condenser lens is configured to focus at least a first portion of the primary charged-particle beam such that the at least a first portion passes through an aperture of the aperture plate to form a second portion of the primary charged-particle beam, and substantially all of the second portion of the primary charged-particle beam is used to flood a surface of a sample, andin the second mode of operation, the condenser lens is configured to focus the at least a first portion of the primary charged-particle beam such that the aperture of the aperture plate blocks off peripheral charged-particles of the at least a first portion to form the second portion of the primary charged-particle beam, and at least some of the second portion of the primary charged-particle beam is used to inspect the surface of the sample.53. The method of clause 52, further comprising blocking peripheral charged particles of the primary charged-particle beam to form the at least the first portion of the primary charged-particle beam.54. The method of any one of clauses 52 and 53, wherein the first aperture array is disposed in and is movable in a first plane substantially perpendicular to the primary optical axis.55. The method of any one of clauses 52-54, wherein the first aperture array is disposed between the charged-particle source and the condenser lens.56. The method of any one of clauses 54-55, wherein forming the at least the first portion of the primary charged-particle beam comprises adjusting a position of the first aperture array in the first plane such that a center of an aperture of the first aperture array is aligned with the primary optical axis.57. The method of any one of clauses 52-56, wherein the aperture plate is movable along the primary optical axis.58. The method of clause 57, wherein the aperture plate comprises a current-limiting aperture array movable along a second plane substantially perpendicular to the primary optical axis.59. The method of clause 58, wherein the current-limiting aperture array is movable along the primary optical axis.60. The method of any one of clauses 52-59, further comprising, in the first mode, defocusing the second portion of the primary charged-particle beam and forming a first spot on the surface of the sample, the first spot having a first current level.61. The method of any one of clauses 57-60, further comprising, in the second mode:limiting a beam current of the second portion of the primary charged-particle beam using a beam-limiting aperture array, an aperture of the beam-limiting aperture array configured to form the at least some of the second portion of the primary charged-particle beam; andfocusing the at least some of the second portion of the primary charged-particle beam and forming a second spot on the surface of the sample, the second spot having a second current level.62. The method of clause 61, wherein in the first and the second modes of operation, the first aperture and the aperture of the beam-limiting aperture array are the same.63. The method of any one of clauses 61 and 62, wherein the first current level is greater than the second current level.64. The method of any one of clauses 61 and 63, wherein the first spot is larger than or equal to the second spot.65. The method of any one of clauses 52-64, further comprising switching, using a controller, between the first mode and the second mode of operation.66. The method of clause 65, further comprising adjusting, using the controller, an electrical excitation of the condenser lens based on the selected mode of operation.67. The method of any one of clauses 52-66, further comprising performing charged-particle flooding on the surface of the sample in the first mode of operation.68. The method of any one of clauses 52-67, further comprising performing charged-particle beam inspection of the surface of the sample in the second mode of operation.69. A non-transitory computer readable medium storing a set of instructions that is executable by one or more processors of a charged-particle beam apparatus to cause the charged particle beam apparatus to perform a method of inspecting a sample, the method comprising:activating a charged-particle source to generate a primary charged-particle beam along a primary optical axis; andselecting between a first mode and a second mode of operation of the charged-particle beam apparatus, wherein:in the first mode of operation, a condenser lens is configured to focus at least a first portion of the primary charged-particle beam such that the at least a first portion passes through an aperture of an aperture plate to form a second portion of the primary charged-particle beam, and substantially all of the second portion of the primary charged-particle beam is used to flood a surface of a sample, andin the second mode of operation, the condenser lens is configured to focus the at least a first portion of the primary charged-particle beam such that the aperture of the aperture plate blocks off peripheral charged-particles of the at least a first portion to form the second portion of the primary charged-particle beam, and at least some of the second portion of the primary charged-particle beam is used to inspect the surface of the sample.70. A charged-particle beam apparatus comprising:a charged-particle source configured to generate a primary charged-particle beam along a primary optical axis;a condenser lens configured to change a focus level of the primary charged-particle beam on a sample based on operation modes of the apparatus, wherein the operation modes include an inspection mode and a flooding mode,an electron detector configured to detect a plurality of signal electrons generated from incidence of the primary charged-particle beam onto the sample; anda detector protector configured to:prevent the plurality of signal electrons from reaching the electron detector when the apparatus operates in the flooding mode, andallow the plurality of signal electrons to reach the electron detector when the apparatus operates in the inspection mode.71. The apparatus of clause 70, wherein the plurality of signal electrons comprises backscattered electrons (BSEs) or secondary electrons (SEs).72. The apparatus of any one of clauses 70 and 71, wherein the detector protector comprises an active energy filter configured to generate an electric field that reflects all or a subset of the plurality of signal electrons.73. The apparatus of clause 72, wherein the active energy filter comprises an electrode positioned between the sample and the objective lens, wherein the electrode is configured to be negatively biased with respect to the sample to generate the electric field.74. The apparatus of clause 73, wherein the electrode is a part of the objective lens.75. The apparatus of clause 72, wherein the active energy filter comprises a first electrode and a second electrode positioned between the electron detector and the objective lens, wherein the first electrode is configured to be negatively biased with respect to the second electrode to generate the electric field.76. The apparatus of clause 75, wherein the first electrode comprises a mesh-electrode.77. The apparatus of clause 75, wherein the first electrode comprises a tube-electrode.78. The apparatus of any one of clauses 75-77, wherein the second electrode comprises a mesh-electrode.79. The apparatus of any one of clauses 75-78, wherein the second electrode is connected to a ground.80. The apparatus of any one of clauses 70 and 71, wherein the detector protector comprises an electron stopper movable between a first position and a second position, wherein:when the apparatus operates in the flooding mode, the electron stopper is positioned in the first position between the sample and the electron detector and is configured to block the plurality of signal electrons, andwhen the apparatus operates in the inspection mode, the electron stopper is positioned in the second position away from the electron detector and is configured to allow the plurality of signal electrons to pass through to the electron detector.81. The apparatus of clause 80, wherein the electron stopper comprises a metal plate.82. The apparatus of any one of clauses 80 and 81, wherein the electron stopper is connected to a ground.83. The apparatus of any one of clauses 80-82, wherein the detector protector further comprises a deflector configured to change directions of the plurality of signal electrons, wherein:when the apparatus operates in the flooding mode, the deflector is configured to deflect the plurality of signal electrons toward the electron stopper, andwhen the apparatus operates in the inspection mode, the deflector is configured to deflect the plurality of signal electrons toward the electron detector.84. The apparatus of clause 83, wherein the deflector comprises an electric field generator and a magnetic field generator.85. The apparatus of any one of clauses 83 and 84, wherein the deflector is a Wien filter.86. The apparatus of any one of clauses 70 and 71, wherein the detector protector comprises:an electron stopper positioned near the electron detector; anda deflector configured to change directions of the plurality of signal electrons, wherein:when the apparatus operates in the flooding mode, the deflector is configured to deflect the plurality of signal electrons toward the electron stopper at a first polar deflection angle and a first azimuthal deflection angle with respect to the primary optical axis, andwhen the apparatus operates in the inspection mode, the deflector is configured to deflect the plurality of signal electrons toward the electron detector at a second polar deflection angle and a second azimuthal deflection angle with respect to the primary optical axis.87. The apparatus of clause 86, wherein the electron stopper is positioned farther away from the primary optical axis than the electron detector.88. The apparatus of any one of clauses 86 and 87, wherein the first polar deflection angle is larger than the second polar deflection angle.89. The apparatus of any one of clauses 86-88, wherein the first azimuthal deflection angle and the second azimuthal deflection angle are the same or substantially similar.90. The apparatus of clause 86, wherein the electron detector and the electron stopper are positioned around the primary optical axis.91. The apparatus of any one of clauses 86 and 90, wherein the first polar deflection angle and the second polar deflection angle are the same or substantially similar.92. The apparatus of any one of clauses 86, 90-91, wherein the first azimuthal deflection angle and the second azimuthal deflection angle are different.93. The apparatus of any one of clauses 86, 90-92, wherein a difference between the first azimuthal deflection angle and the second azimuthal deflection angle is approximately 90 degrees.94. The apparatus of any one of clauses 86-93, wherein the electron stopper comprises a metal plate.95. The apparatus of any one of clauses 86-94, wherein the electron stopper is connected to a ground.96. The apparatus of any one of clauses 86-95, wherein the deflector comprises an electric field generator and a magnetic field generator.97. The apparatus of any one of clauses 86-96, wherein the deflector is a Wien filter.

A non-transitory computer readable medium may be provided that stores instructions for a processor of a controller (e.g., controller50ofFIG.1) for carrying out image inspection and image acquisition, selecting the modes of operation, activating charged-particle source, adjusting the electrical excitation of condenser lens, moving the sample stage to adjust the position of the sample, and the like. Common forms of non-transitory media include, for example, a floppy disk, a flexible disk, hard disk, solid state drive, magnetic tape, or any other magnetic data storage medium, a Compact Disc Read Only Memory (CD-ROM), any other optical data storage medium, any physical medium with patterns of holes, a Random Access Memory (RAM), a Programmable Read Only Memory (PROM), and Erasable Programmable Read Only Memory (EPROM), a FLASH-EPROM or any other flash memory, Non-Volatile Random Access Memory (NVRAM), a cache, a register, any other memory chip or cartridge, and networked versions of the same.

It will be appreciated that the embodiments of the present disclosure are not limited to the exact construction that has been described above and illustrated in the accompanying drawings, and that various modifications and changes may be made without departing from the scope thereof. The present disclosure 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.

The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made as described without departing from the scope of the claims set out below.