Band-pass charged particle energy filtering detector for charged particle tools

Abstract

Methods and systems for detecting charged particles from a sample are provided. One system includes a first repelling mesh configured to repel charged particles from the sample having an energy lower than a first predetermined energy, and a second repelling mesh configured to repel charged particles passing through the first repelling mesh and having an energy lower than a second predetermined energy. The system also includes a first attraction mesh configured to attract charged particles passing through the first repelling mesh and being repelled by the second repelling mesh and having an energy higher than the first predetermined energy and lower than the second predetermined energy. The system further includes a first detector configured to generate an output in response to the charged particles passing through the first attraction mesh.

Description

Technical Field

[0001] The present invention generally relates to methods and systems for detecting charged particles from a sample. Certain embodiments relate to a bandpass charged particle energy filtering detector for a charged particle tool.

Background Art

[0002] The following descriptions and examples are not admitted to be prior art by reason of their inclusion in this section.

[0003] Fabricating semiconductor devices such as logic and memory devices typically involves processing a substrate such as a semiconductor wafer using a number of semiconductor fabrication processes to form various features and multiple levels of the semiconductor device. For example, lithography is a semiconductor fabrication process that involves transferring a pattern from a reticle to a resist disposed on a semiconductor wafer. Further examples of semiconductor fabrication processes include, but are not limited to, chemical mechanical polishing (CMP), etching, deposition, and ion implantation. Multiple semiconductor devices can be fabricated within an arrangement on a single semiconductor wafer and then separated into individual semiconductor devices.

[0004] The inspection process is used at various steps during the semiconductor manufacturing process to detect defects on wafers and other substrates so as to promote higher yields and thus higher profits in the manufacturing process. Inspection has always been an important part of the fabrication of semiconductor devices such as ICs. However, inspection becomes even more important for the successful fabrication of acceptable semiconductor devices as the dimensions of semiconductor devices decrease, since smaller defects can cause the device to malfunction.

[0005] Defect review typically involves redetecting defects thus detected by the inspection process and generating additional information about the defects at a higher resolution using a high-magnification optical system or a scanning electron microscope (SEM). Defect review is thus performed at discrete locations on the sample where defects have been detected by inspection. The higher the resolution of the data generated for the defects by defect review, the more suitable it is for determining defect attributes such as contour, roughness, more accurate size information, etc.

[0006] The metrology process is also used at various steps during the semiconductor manufacturing process to monitor and manage the process. The metrology process differs from the inspection process in that, unlike the inspection process where defects are detected on the sample, the metrology process is used to measure one or more characteristics of the sample that cannot be determined using the currently available inspection tools. For example, the metrology process is used to measure one or more characteristics of the sample, such as the dimensions (e.g., line width, thickness, etc.) of features formed on the sample during the process, so that the performance of the process can be determined from one or more of the characteristics. Additionally, if one or more characteristics of the sample are unacceptable (e.g., outside a predetermined range for the characteristic), the measurement of one or more characteristics of the sample can be used to change one or more parameters of the process so that additional samples produced by the process have acceptable characteristics.

[0007] The measurement process also differs from the defect review process in that the defect detected by inspection is reconsidered in defect review. The measurement process can be performed at a location where no defect has been detected, which is different from the defect review process. In other words, unlike defect review, the location where the measurement process is performed on the sample can be independent of the result of the inspection process performed on the sample. In particular, the location where the measurement process is performed can be selected independently of the inspection result. In addition, since the location on the sample where measurement is performed can be selected independently of the inspection result, unlike defect review where the location on the sample where defect review will be performed cannot be determined until the inspection result for the sample is generated and available for use, the location where the measurement process is performed can be determined before the inspection process is performed on the sample.

[0008] In quality control processes such as inspection, defect review, and measurement using charged particles, for example, electrons or ions, it can often be important to detect only charged particles from the sample having a certain specific energy. In particular, different types of charged particles returned from the sample can have approximately the same sensitivity to a certain specific defect or measurement. Different types of charged particles can often be separated from each other because they have different energies. Several different methods have been created to separate charged particles having different energies, such as a threshold energy filter, an energy dispersive sector having a segmented detector, and a plurality of electrostatic suppressors.

[0009] Each of the charged particle separation methods described above has found some success in the art, but each of the currently used methods has one or more disadvantages. For example, a threshold energy filter can only separate electrons having energy greater than or less than a threshold energy applied to an energy filter mesh. In another example, due to the mixing of radiation energy and angle, it is quite difficult to clearly separate electrons having different energies using an energy dispersive sector with a segmented detector. In a further example, designing a plurality of detectors that float at a relatively high voltage for a plurality of electrostatic suppressors is quite challenging. Additionally, when a voltage close to or the same as these electrostatic suppressors is applied to the detector, the electrons hitting the detector have a relatively small collision energy, which can be difficult to generate a signal or can have a quite low signal-to-noise ratio.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0011] Therefore, it is advantageous to develop a system and / or method for detecting charged particles from a sample that does not have one or more of the above disadvantages.

Means for Solving the Problems

[0012] The following description of various embodiments should not be construed in any way as limiting the subject matter of the appended "claims".

[0013] One embodiment relates to a system configured to detect charged particles from a sample. The system includes a first repulsive mesh positioned within the path of charged particles from the sample and configured to repel charged particles having an energy lower than a first predetermined energy. The system also includes a second repulsive mesh that passes through the first repulsive mesh and is configured to repel charged particles having an energy lower than a second predetermined energy. Additionally, the system includes a first attractive mesh that passes through the first repulsive mesh, is repelled by the second repulsive mesh, and is configured to attract charged particles having an energy higher than the first predetermined energy and lower than the second predetermined energy. The system further includes a first detector configured to generate an output in response to charged particles that have passed through the first attractive mesh. The system may be further configured as described herein.

[0014] Another embodiment relates to a computer-implemented method for detecting charged particles from a sample. The method includes repelling, by a first repulsive mesh positioned within the path of charged particles from the sample, charged particles from the sample having an energy lower than a first predetermined energy. The method also includes repelling, by a second repulsive mesh, charged particles that have passed through the first repulsive mesh and have an energy lower than a second predetermined energy. Additionally, the method includes attracting, by a first attractive mesh, charged particles that have passed through the first repulsive mesh, are repelled by the second repulsive mesh, and have an energy higher than the first predetermined energy and lower than the second predetermined energy. The method further includes generating, by a first detector, an output in response to charged particles that have passed through the first attractive mesh.

[0015] Each of the steps of the method may be performed as further described herein. Additionally, the method may include any other steps of any other method described herein. The method may be performed by any of the systems described herein.

[0016] A further embodiment relates to a non-transitory computer-readable medium storing program instructions executable on a computer system for performing a computer-implemented method of detecting charged particles from a sample. The computer-implemented method includes the steps of the method described above. The computer-readable medium may be further configured as described herein. The steps of the computer-implemented method may be performed as further described herein. Additionally, the computer-implemented method for which the program instructions are executable may include any other steps of any other method described herein.

Brief Description of the Drawings

[0017] Other objects and advantages of the present invention will become apparent from the following detailed description when read in conjunction with the accompanying drawings.

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DETAILED DESCRIPTION OF THE INVENTION

[0018] Although the present invention is capable of various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and described in detail herein. However, the drawings and the detailed description thereof are not intended to limit the present invention to the specific forms, but rather are intended to cover all modifications, equivalent forms, and alternatives included within the spirit and scope of the present invention as defined by the appended "claims".

[0019] Next, referring to the drawings, it is noted that the figures are not drawn to scale. In particular, the scales of some of the elements of the figures are greatly exaggerated in order to emphasize the characteristics of the elements. It is also noted that the figures are not drawn to the same scale. Elements shown in two or more figures that may be similarly configured are indicated using the same reference numerals. Unless otherwise stated, any of the elements described and shown may include any suitable commercially available elements.

[0020] The embodiments described herein generally relate to bandpass charged particle (e.g., electron) energy filtering detectors for charged particle tools (e.g., electron microscopes). As further described herein, the embodiments are advantageous in that they have the ability to select any particular energy band for the returned charged particle signal, which is then used to generate a sample image (e.g., a scanning electron microscope (SEM) image) having enhanced contrast for any particular defect.

[0021] One embodiment relates to a system configured to detect charged particles from a sample. In one embodiment, the charged particles are electrons. In another embodiment, the charged particles are helium ions. Although some embodiments may be described herein with respect to electrons, all of the embodiments can be configured for use with charged particles such as electrons, helium ions, or any other suitable charged particles known in the art of semiconductor manufacturing. Charged particles from the sample can be caused by irradiation of the sample with charged particles (such as in an electron or ion beam imaging tool), or can be caused by some other non-charged particle means (e.g., x-rays). The charged particles can also include any of the charged particles described herein and can be “from the sample” in any manner, such as reflected, scattered, transmitted, from or by the sample.

[0022] In some embodiments, the sample is a wafer. The wafer can include any wafer known in semiconductor technology. Although some embodiments may be described herein with respect to one or more wafers, the embodiments are not limited to the samples for which they can be used. For example, the embodiments described herein can be used with samples such as reticles, flat panels, printed circuit (PC) boards, and other semiconductor samples.

[0023] The system includes a first repulsive mesh positioned within the path of charged particles from a sample and configured to repel charged particles having an energy lower than a first predetermined energy. In this specification, although some elements are described as "meshes", it should be understood that each such "mesh" can be replaced by a lattice or other suitable element that can function as described in this specification. As shown in FIG. 1, the system may include a first repulsive mesh 100 positioned within the path of charged particles 102 from a sample (not shown in FIG. 1). The first repulsive mesh repels charged particles 104 having an energy lower than a first predetermined energy by having a first voltage, V1, applied thereto. In other words, signal electrons from the sample having various energies within the energy band of [0, Em] can encounter the first repulsive mesh 100, and electrons having an energy of E1 or less, i.e., within the energy band of [0, E1], can be repelled by the first repulsive mesh, and electrons having an energy greater than E1 can be transmitted by the first repulsive mesh.

[0024] The system also includes a second repulsive mesh configured to pass charged particles having an energy lower than a second predetermined energy through a first repulsive mesh and repel them. The second repulsive mesh can also be configured such that any electrons having an energy higher than the second predetermined energy pass through the second repulsive mesh. As shown in FIG. 1, the system can include a second repulsive mesh 106 configured to pass charged particles 108 having an energy lower than a second predetermined energy and repel them by having a second voltage, V2, applied thereto as they pass through a first repulsive mesh 100. In other words, signal electrons having an energy greater than E1 can pass through the first repulsive mesh, and any electrons having an energy within the energy band [E1, E2] are repelled by the second repulsive mesh. Any other charged particles having an energy greater than E2, i.e., in the energy band [E2, Em], such as electron 110, cannot be repelled by the second repulsive mesh but can pass through that repulsive mesh and may or may not be separately detected as further described herein. Thus, the system can include one energy band (i.e., the energy between E1 and E2) bandpass filter and one high-pass energy band (i.e., energy greater than E2) filter, and the energy bands of both filters can be selectable by the user or as further described herein.

[0025] The system further includes a first attracting mesh configured to attract charged particles that pass through a first repulsive mesh, are repelled by a second repulsive mesh, and have an energy higher than a first predetermined energy and lower than a second predetermined energy. As shown in FIG. 1, the system may include a first attracting mesh 112 configured to attract charged particles that pass through a first repulsive mesh 100, are repelled by a second repulsive mesh 106, and have an energy higher than a first predetermined energy and lower than a second predetermined energy, i.e., [E1, E2]. The first attracting mesh can attract electrons having such energy by having a voltage of V1+ΔV applied thereto.

[0026] For both the first and second repulsive meshes, their applied voltages, V1 and V2 respectively, are negative with respect to electrons due to their repulsive nature. Thus, the value of V1 is typically greater than V2. V1+ΔV is also greater than V2, such that the first attracting mesh can attract electrons repelled from the second repulsive mesh. It is noted that ΔV can be made equal to zero, which means that the first repulsive mesh is at the same potential as the first attracting mesh, which can help simplify the external power supply and mechanical design.

[0027] The first and second repulsive meshes shown in FIG. 1, and the first attractive mesh, form one of a plurality of possible energy band cavities that can be included in the embodiments described herein. The term "cavity" as used herein is generally defined as a defined space formed by some combination of repulsive and attractive meshes (optionally having one or more additional elements such as electrode blocks) that control the flow of charged particles through the space defined in the combination. Each of the energy band cavities described herein is configured not only to store electrons having the corresponding desired energy band thereof, but also to deflect them automatically into the side detector without adding an additional deflector. The curves shown in the energy band cavity 114 of FIG. 1 formed by the first repulsive mesh 100, the second repulsive mesh 106, and the first attractive mesh 112 are simulated equipotential lines for one embodiment of the energy band cavity, and this can vary depending on the exact configuration of the elements forming the energy band cavity.

[0028] In this way, the energy band cavity is used to create a space in which only electrons having energy within the desired energy band remain, are deflected towards the side attraction mesh, and are then accelerated towards the detector (further described herein), for example because the detector has sufficient collision energy to generate a relatively strong signal and is more positively biased compared to the side attraction mesh. One improvement of the embodiments described herein over other methods and systems for detecting charged particles from a sample is to include an energy band cavity configured as described herein. One advantage of the embodiments described herein is that they can more precisely select any particular energy band of signal electrons to generate an image using the energy band cavities described herein. Another advantage of the embodiments described herein is that the transmittance of the selected energy band is substantially high (e.g., greater than 80%) using the energy band cavities described herein.

[0029] FIG. 2 shows an embodiment of a system including a deflector, a focusing lens, a differential potential electrode, an energy band cavity, and two detectors. In this embodiment, the energy band cavity 114 formed by the first repulsive mesh 100, the second repulsive mesh 106, and the first attractive mesh 112 can be configured as further described above. In one embodiment, the system includes a deflector configured to change the position of the path of charged particles from a sample before the charged particles reach the first repulsive mesh. As shown in FIG. 2, signal electrons 200 from a sample (not shown in FIG. 2) pass through the deflector 202. The deflector can be configured to center the signal electron cloud at the center of the focusing lens and to minimize the position offset of the electron cloud due to the scanning field of view of the sample and the deflection from the scanning deflector.

[0030] In one such embodiment, the system includes a focusing lens configured to focus charged particles from the deflector and to collimate charged particles having an energy higher than a first predetermined energy and lower than a second predetermined energy to pass through the first repulsive mesh. For example, after the signal electrons 200 pass through the deflector 202, they can pass through the focusing lens mesh 204 positioned between the ground electrodes 206. The focusing lens can be configured to focus the electron cloud and to collimate electrons having a desired energy to pass through the first repulsive mesh. In this way, the focusing lens can help to minimize the loss of electrons having an energy slightly higher than the lower end energy of the desired energy band.

[0031] In some such embodiments, the system includes a differential potential electrode surrounding the path of charged particles between a focusing lens and a first repulsive mesh. As shown in FIG. 2, the system may include a differential potential electrode 208 surrounding the path of signal electrons 200 between a focusing lens mesh 204 and a first repulsive mesh 100. As shown in FIG. 3, the differential potential electrode may include four electrodes arranged continuously along the path of charged particles between a focusing lens mesh 204 and a first repulsive mesh 100. The voltages below each of the elements shown in FIG. 3 are examples of the applied voltages for these respective elements. In particular, the applied voltage for the focusing lens mesh can be V0. The voltage applied to the ground electrode can be 0, and the voltage applied to the first repulsive mesh can be V1. The voltages applied to the first, second, third, and fourth differential potential electrodes can be

Number

[0032] In another such embodiment, the differential potential electrode is configured to reduce the formation of a lens field between the focusing lens and the first repelling mesh. Additionally, the differential potential electrode can be configured to prevent the formation of a lens field between the focusing lens mesh and the first repelling mesh. For example, the equipotential lines 400 shown in FIG. 4 indicate that there is little lens field between the focusing lens mesh and the first repelling mesh. The differential potential electrode is shown as including four differential potential electrodes in the various figures described herein, but in the embodiments described herein, any suitable number of differential potential electrodes can be included between the focusing lens mesh and the first repelling mesh.

[0033] The system also includes a first detector configured to generate an output in response to charged particles that have passed through the first attracting mesh. For example, as shown in FIG. 2, the system can include a first detector 210 configured to generate an output in response to electrons passing through the first attracting mesh 112. The first detector 112 (and other detectors described herein) can include any suitable detector known in the art. Each of the detectors described herein can be an imaging detector configured to detect charged particles as a function of position across the detector. However, the detector can be a non-imaging detector that does not output an image of the sample, but instead detects the number of electrons that collide and the collision energy. In some such embodiments, a computer subsystem such as those described herein can be configured to generate an image of the sample from the non-imaging output of the detector. In this way, the embodiments described herein can be configured to generate an image of the sample in different ways, and generating an image of the sample is not necessary for some of the system configurations further described herein.

[0034] In one embodiment, the first detector is grounded. In another embodiment, the first detector is biased at a positive voltage. In a further embodiment, the first detector is biased at an adjustable voltage. For example, the first detector (and any other detector described herein) can be grounded or, for any type of detector such as a semiconductor-based, microchannel plate, and scintillator photomultiplier tube (PMT) detector, can be biased at a relatively high positive voltage (e.g., several kV) to reach an optimal collision energy for electrons. One improvement provided by the embodiments described herein over other systems and methods for detecting charged particles from a sample is that the detector can have an adjustable voltage for optimization of the collision energy. Additionally, one advantage of the embodiments described herein is that the collision energy of the electrons hitting the detector is relatively high (e.g., greater than 5 keV) and adjustable without affecting the energy band filtering performance.

[0035] In one embodiment, the first detector is biased at a voltage and the first attracting mesh shields the space between the first repelling mesh, the second repelling mesh, and the first attracting mesh from the electric field from the detector. For example, the mesh immediately in front of the detector behaves like a shielding mesh such that the relatively high electric field from the detector cannot affect the performance of the energy band cavity.

[0036] In some embodiments, the system includes a second detector configured to detect charged particles passing through a second repelling mesh. For example, as shown in FIG. 2, the system may include a second detector 212 configured to detect electrons passing through a second repelling mesh 106. This detector may be further configured as described herein. If the system includes multiple detectors, each of the detectors may have the same or different configurations, e.g., depending on the energy and / or type of electrons they are to detect. In this way, embodiments can include two detectors, one that can be used to collect and detect electrons within a desired energy band (i.e., bandpass filtering), and the other that can be used to collect and detect electrons having energies higher than the upper energy of the desired energy band (i.e., highpass filtering).

[0037] In some embodiments, such as those shown in FIG. 2, the system may include an electrode block 214 configured to facilitate detection of many of the signal electrons passing through the second repelling mesh by at least partially surrounding the space between the second repelling mesh and the second detector. In this way, the second repelling mesh 106, the electrode block 214, and the second detector 212 (optionally having an attracting mesh positioned immediately before it, not shown in FIG. 2) may form a certain second energy band cavity within the system. The second energy band cavity may be further configured as described herein.

[0038] Figures 5 and 6 show simulation results of the paths of charged particles having different energies through the system embodiment of FIG. 2. FIG. 5 shows the paths of electrons having energies within the band of [0, Em]. In other words, FIG. 5 shows the simulated paths of all electrons entering the detector assembly of FIG. 2. In contrast, FIG. 6 shows only the electrons collected by the first detector. These electrons having energies within the band [E1, E2] are only a part of the electrons shown in FIG. 5. In other words, FIG. 6 shows the paths of only the electrons within a specific energy band entering the detector assembly. Therefore, FIG. 6 is included here to more clearly show the movement of the electrons within the bandpass filter energy band through the system, but is not intended to show all of the electrons that will actually move through the system.

[0039] As shown in FIG. 5, electrons 500 having energies lower than E1 are repelled and returned by the first repelling mesh. Electrons 502 having energies between E1 and E2 are collected on the first detector 210. Electrons 504 having energies higher than E2 are collected on the second detector 212. As more clearly shown in FIG. 6, electrons 600 having energies between E1 and E2 have a substantially high transmittance and are collected on the first detector 210 (i.e., almost all of the electrons having energies within the bandpass corresponding to the first energy band cavity are directed towards the first detector).

[0040] In one embodiment, the first repulsive mesh, the second repulsive mesh, and the first attractive mesh form a triangular energy band cavity (e.g., as shown in FIGS. 1 and 2). In another embodiment, the first repulsive mesh, the second repulsive mesh, and the first attractive mesh form at least a portion of a square energy band cavity. In this way, there are two types of energy band cavities, triangular and rectangular. Both types use three meshes having three potentials (V1, V2, and V1+ΔV) and an enclosing container having the same potential as V2. For example, in a further embodiment, the first repulsive mesh, the second repulsive mesh, the first attractive mesh, and the electrode block form a square energy band cavity, and the second repulsive mesh and the electrode block have the same potential.

[0041] FIG. 7 shows an embodiment of an energy band cavity having a square configuration. As shown in FIG. 7, the system may include a first repulsive mesh 700 positioned within the path of charged particles 702 from a sample (not shown in FIG. 7). The first repulsive mesh has a first voltage, V1, applied thereto and repels charged particles 704 having an energy lower than a first predetermined energy. In other words, signal electrons from the sample having a variety of energies [0, Em] can encounter the first repulsive mesh, electrons having energies within the energy band of [0, E1] can be repelled by the first repulsive mesh, and electrons having energies greater than E1 can be transmitted by the first repulsive mesh.

[0042] The system also includes a second repulsive mesh configured to pass charged particles having an energy lower than a second predetermined energy after passing through the first repulsive mesh. The second repulsive mesh may be configured such that any electrons having an energy higher than the second predetermined energy pass through the second repulsive mesh. As shown in FIG. 7, the system may include a second repulsive mesh 706 configured to repel charged particles 708 having an energy lower than a second predetermined energy by passing through the first repulsive mesh 700 and having a second voltage, V2, applied thereto. In other words, signal electrons having an energy greater than E1 can pass through the first repulsive mesh, and any electrons having an energy within the energy band of [E1, E2] are repelled by the second repulsive mesh. Electrons 710 having an energy greater than E2, i.e., having an energy in the range of [E2, Em], cannot be repelled by the second repulsive mesh but can pass through the repulsive mesh and may or may not be separately detected as further described herein. Thus, the system can include one energy band (i.e., the energy between E1 and E2) bandpass filter and one high-pass energy band (i.e., energy greater than E2) filter, and the energy bands of both filters can be made selectable by the user or as further described herein.

[0043] The system further includes a first attracting mesh configured to pass through the first repulsive mesh, be repelled by the second repulsive mesh, and attract charged particles having an energy higher than a first predetermined energy and lower than a second predetermined energy. As shown in FIG. 7, the system includes a first attracting mesh 712 configured to pass through the first repulsive mesh 700, be repelled by the second repulsive mesh 706, and attract charged particles having an energy higher than a first predetermined energy and lower than a second predetermined energy, i.e., having an energy in the range of [E1, E2]. The first attracting mesh can attract electrons having such an energy by having a voltage of V1 + ΔV applied thereto.

[0044] In some embodiments, such as those shown in FIG. 7, the system may include an electrode block 714 that forms a square energy band cavity 716 together with first and second repulsive meshes and a first attractive mesh shown in FIG. 7. The electrode block may have an applied voltage, V2, that is the same as the second repulsive mesh. V1, V2, and V1 + ΔV may be selected as described above. The curves shown within the energy band cavity 716 of FIG. 7 are simulated equipotential lines for one embodiment of the energy band cavity, which may vary depending on the exact configuration of the elements forming the energy band cavity. This energy band cavity can be further configured as described herein and have all of the improvements and advantages of the other energy band cavities described herein.

[0045] FIG. 8 shows one embodiment of a system that includes a deflector, a focusing lens, a differential potential electrode, a square energy band cavity, and two detectors. In this embodiment, the energy band cavity 716 formed by the first repulsive mesh 700, the second repulsive mesh 706, the first attractive mesh 712, and the electrode block 714 may be configured as further described above. As shown in FIG. 8, signal electrons 800 from a sample (not shown in FIG. 8) may pass through a deflector 802 that may be configured as further described herein. After passing through the deflector 802, the signal electrons 800 may pass through a focusing lens mesh 804 positioned between ground electrodes 806. The focusing lens mesh and the ground electrodes may be configured as further described herein.

[0046] The system also includes a differential potential electrode 808 that surrounds the path of signal electrons 800 between the focusing lens mesh 804 and the first repelling mesh 700. The differential potential electrode can be configured as further described herein. The system also includes a first detector configured to generate an output in response to charged particles that have passed through the first attracting mesh. For example, as shown in FIG. 8, the system can include a first detector 810 configured to generate an output in response to electrons passing through the first attracting mesh 712. The first detector 810 can be further configured as described herein.

[0047] In some embodiments, the system includes a second detector configured to detect charged particles passing through the second repelling mesh. For example, as shown in FIG. 8, the system can include a second detector 812 configured to detect electrons passing through the second repelling mesh 706. In this way, embodiments can include two detectors, one of which can be used to collect electrons within a desired energy band (i.e., band-pass filtering), and the other of which can be used to collect electrons having energies higher than the upper energy of the desired energy band (i.e., high-pass filtering). The second detector can be further configured as described herein.

[0048] Figures 9 and 10 show simulation results of the paths of charged particles with different energies through the system embodiment of FIG. 8. FIG. 9 shows the paths of electrons having energies within the band of [0, Em]. In other words, FIG. 9 shows the simulated paths of all electrons entering the detector assembly of FIG. 8. In contrast, FIG. 10 shows only the electrons collected by the first detector. These electrons having energies within the band [E1, E2] are only a part of the electrons shown in FIG. 9. In other words, FIG. 10 shows the paths of only the electrons within a specific energy band entering the detector assembly. Therefore, FIG. 10 is included here to more clearly show the movement of electrons within the bandpass filter energy band through the system, but is not intended to show all of the electrons that will actually move through the system.

[0049] As shown in FIG. 9, electrons 900 having energies lower than E1 are repelled and returned by the first repelling mesh. Electrons 902 having energies between E1 and E2 are collected on the first detector 810. Electrons 904 having energies higher than E2 are collected on the second detector 812. As more clearly shown in FIG. 10, electrons 1000 having energies between E1 and E2 have a substantially high transmittance and are collected on the first detector 810 (i.e., almost all of the electrons having energies within the bandpass corresponding to the first energy band cavity are directed towards the first detector).

[0050] FIG. 11 shows the overall collection spectrum for the detector assembly described above, including the first and second detectors. In other words, this graph shows an example of the overall collection spectrum for a system using both bandpass filtering and high-pass filtering. In FIG. 11 (and FIGS. 12, 13, and 19), the electron energy is plotted on the x-axis, the number of electrons N(E) is plotted on the y-axis, E1 = -eV1 and E2 = -eV2, where e is the charge of an electron, and Em is the maximum radiation energy of electrons from the sample, which is typically equal to the incident energy of the primary electrons. As shown in FIG. 11, some electrons having energies between 0 and E1 are "lost", which means that the detector assembly described herein filters out these electrons by the first repelling mesh and they are not detected. Electrons having energies between E1 and E2 are detected by detector 1 because these electrons are not repelled by the first repelling mesh, are repelled by the second repelling mesh, and are attracted by the first attracting mesh positioned immediately before the first detector. Electrons having energies between E2 and Em are detected by detector 2 because these electrons are not repelled by the first or second repelling mesh and can thus be detected by the second detector.

[0051] In one embodiment, the energy band between the first and second predetermined energies is equal to the energy band from 0 eV to 50 eV. In another embodiment, the energy band between the first and second predetermined energies is equal to the energy band of Em - 100 eV, where Em is the maximum radiation charged particle energy from the sample. In a further embodiment, the energy band between the first and second predetermined energies is equal to the energy band of 50 eV - Em, where Em is the maximum radiation charged particle energy from the sample.

[0052] In another embodiment, the first and second predetermined energies are selected based on the type of defect to be detected on the sample based on the output generated by the first detector. In particular, the embodiment has the ability to select any particular energy band for the returned charged particle signal, which is then advantageously used to generate a sample image with enhanced contrast for any particular defect. In one such example, the signal electrons emitted from the sample can include secondary electrons (SE) and backscattered electrons (BSE) having energies in the range of 0 eV to Em (Em = e×LE, where LE represents the incident energy of the primary electrons). Usually, these signal electrons are further accelerated by the potential difference (U) between the column and the sample after leaving the sample and before reaching the detector. Therefore, the energy of the electrons entering the detector assembly is [eU, eU+Em]. Next, for example, if it is desired to collect electrons having a radiation energy between 500 eV and 700 eV to enhance the contrast of a defect embedded near a depth of 100 nm, the voltage (V1) applied to the first retarding mesh should be equal to -(eU + 500) / e, and the voltage (V2) applied to the second retarding mesh should be equal to -(eU + 700) / e. The voltage (V1+ΔV) applied to the first attracting mesh should satisfy V1≦V1+ΔV, which means ΔV≧0V. Therefore, electrons having a residual energy within [0, 200] are trapped inside the energy band cavity and then deflected to the first detector by the dipole field between the second retarding mesh and the first attracting mesh. Assuming both detectors are grounded, the collision energy of the electrons hitting the first detector is [eU + 500, eU + 700], and the collision energy of the electrons hitting the second detector is [eU + 700, eU + Em].

[0053] In some embodiments, the first and second predetermined energies are selected based on the type of charged particles to be detected from the sample. For example, FIG. 12 shows an extreme case of the collection spectrum for the detector assembly described above, including the first and second detectors. This graph shows an example of an extreme case of the collection spectrum for a system that separates SEs from BSEs. As shown in FIG. 12, SEs having an energy between E1 and E2, for example, between 0 eV and 50 eV, are detected by detector 1 because these electrons are not repelled by the first repelling mesh, are repelled by the second repelling mesh, and are attracted by the first attracting mesh positioned immediately before the first detector. BSEs having an energy between E2 and Em are detected by detector 2 because these electrons are not repelled by the first or second repelling mesh and can thus be detected by the second detector.

[0054] FIG. 13 shows another extreme case of the collection spectrum for the detector assembly described above, including the first and second detectors. This graph shows an example of an extreme case of the collection spectrum for a system that separates low-loss BSEs from elastic BSEs. As shown in FIG. 13, some electrons having an energy between 0 and E1 are "lost", which means that the detector assembly described herein filters out these electrons by the first repelling mesh and they are not detected. Low-loss BSEs having an energy between E1 and E2 are detected by detector 1 because these electrons are not repelled by the first repelling mesh, are repelled by the second repelling mesh, and are attracted by the first attracting mesh positioned immediately before the first detector. Elastic BSEs having an energy between E2 and Em are detected by detector 2 because these electrons are not repelled by the first or second repelling mesh and can thus be detected by the second detector.

[0055] Figures 14 - 16 also show how BSEs having different energies entering the detector assembly are separated and separately detected according to the embodiments described herein. In Figures 14 - 16, the electron emission energy is plotted on the x - axis and the number of electrons N(E) is plotted on the y - axis. Figure 14 shows the number of BSEs having energy between 0 and LE entering the detector assembly. Figure 15 shows the number of BSEs having energy between 0 and LE collected on the second detector, i.e., detector 2, and Figure 16 shows the number of BSEs having energy between 0 and LE collected on the first detector, i.e., detector 1.

[0056] In a further embodiment, the energy band between the first and second predetermined energies corresponds to the energy of only secondary charged particles from the sample, and the system includes a computer subsystem configured to detect surface or voltage contrast defects on the sample based on the output generated by the first detector. For example, collecting only secondary electrons (e.g., within an energy band of 0 - 50 eV) can enhance surface contrast or voltage contrast defects. For an electron beam inspection (EBI) system, finding defects with relatively high contrast on an image has many advantages such as improving throughput and sensitivity, reducing the nuisance rate, and improving the accuracy of artificial - intelligence - based models for automatic defect capture. The computer subsystem of this embodiment can be further configured as described herein.

[0057] In another embodiment, the energy band between the first and second predetermined energies corresponds to the energy of only the elastic backscattered charged particles from the sample, and the system includes a computer subsystem configured to detect high aspect ratio or material contrast defects on the sample based on the output generated by the first detector. In another example, collecting only elastic backscattered electrons (e.g., within an energy band of Em - 100 eV, where Em is the maximum emitted electron energy from the sample, which is typically equal to the incident energy of the primary electrons) can enhance the contrast of high aspect ratio (HAR) or material contrast defects. In an electron beam wafer defect inspection system such as the eSL10(TM) commercially available from KLA Corp. in Milpitas, California, using the detector assembly embodiments described herein can help capture HAR defects (e.g., deep bottom holes and defects on trenches), which are specific defects that are difficult to capture. Additionally, the detector assembly embodiments described herein can capture many different types of buried defects (punch-through to an air spacer, deteriorating tungsten seams in a replacement metal gate (RMG), residues between nanosheets, punch-through vias, spacer nitride cracks beside bit lines, etc.). The computer subsystem of this embodiment can be further configured as described herein.

[0058] HAR defects can be defects within or on one or more 3D or HAR structures. In one embodiment, the 3D structure includes a 3D NAND structure formed on a wafer. 3D NAND (where NAND is a type of logic gate within a semiconductor device) is a type of non-volatile flash memory that includes a vertical stack of multiple layers of memory cells. For example, a 3D NAND structure is generally formed on a wafer and includes silicon bit cell gates formed from alternating conductive and insulating layers separated by one or more HAR structures formed from a material such as silicon nitride and a channel formed on silicon. This vertical stack of memory cells gives the 3D NAND structure its 3D quality.

[0059] The 3D structures described herein may also include any other HAR structure known in the art. As used herein, a "HAR structure" refers to any structure characterized by an aspect ratio that exceeds 10:1 and can be as high as 100:1 in next-generation devices. HAR structures often include a hard mask layer to facilitate the etching process for the HAR (see, e.g., U.S. Patent No. 8,237,213, issued to Liu on August 7, 2012, which is incorporated herein by reference as if fully set forth). In addition to vertical NAND or terabit cell array transistor (TCAT) structures, the embodiments described herein can be used for other HAR structures of interest in terms of their defects.

[0060] In an additional embodiment, the energy band between the first and second predetermined energies corresponds to the energy of only inelastically backscattered charged particles from the sample, and the system includes a computer subsystem configured to detect a buried defect on the sample based on the output generated by the first detector. Collecting only inelastically backscattered electrons (e.g., any energy band within 50 eV - Em) can enhance the contrast of buried defects (i.e., defects located entirely below the top surface of the sample). The computer subsystem of this embodiment can be further configured as described herein.

[0061] One newly advantageous feature of the embodiments described herein is that the energy band cavities can be cascaded (or arranged in series), which allows for the selection of multiple energy bands that can be separated and detected to generate different outputs or images at once. In some embodiments, the system comprises a third repulsive mesh configured to pass charged particles having an energy lower than a third predetermined energy and to repel the charged particles that have passed through a second repulsive mesh, a second attractive mesh configured to pass charged particles having an energy higher than a second predetermined energy and lower than the third predetermined energy and that have been repelled by the third repulsive mesh, and a second detector configured to generate an output in response to the charged particles passing through the second attractive mesh.

[0062] FIG. 17 shows one embodiment in which a plurality of square energy band cavities are arranged in series. As shown in FIG. 17, signal electrons 1700 from a sample (not shown in FIG. 17) can pass through a deflector 1702, a focusing lens mesh 1704 surrounded by a ground electrode 1706, and a differential potential electrode 1708, each of which is configured as further described herein. The first energy band cavity of this system is formed by a first repulsive mesh 1710, a second repulsive mesh 1712, an electrode block 1714, and a first attractive mesh 1716, all of which can be configured as further described herein. This system includes a first detector 1718, which can also be configured as described herein.

[0063] The system also includes a third repulsive mesh 1720 configured to repel charged particles that pass through the second repulsive mesh 1712 and have an energy lower than a third predetermined energy. The third repulsive mesh has an applied voltage, V3. A second attractive mesh 1722 is configured to attract charged particles that pass through the second repulsive mesh 1712, are repelled by the third repulsive mesh 1720, and have an energy higher than a second predetermined energy, E2 and lower than a third predetermined energy, E3. The second attractive mesh has an applied voltage of V2 + ΔV2. A second detector 1724 is configured to generate an output in response to charged particles passing through the second attractive mesh 1722. The system also includes a second electrode block 1726, which, in combination with the second repulsive mesh 1712, the third repulsive mesh 1720, and the second attractive mesh 1722, forms a second square energy band cavity. The second electrode block has an applied voltage, V3. The system may further include a third detector 1728 configured to generate an output in response to charged particles passing through the third repulsive mesh 1720. Each of these elements may also be further configured as described herein.

[0064] The system shown in FIG. 17 can thus include two energy bands (i.e., the energy between E1 and E2 and between E2 and E3) and one high-pass band (i.e., energy greater than E3), all of which can be selected by the user or as further described herein. In this way, the embodiments described herein can add more energy band cavities as permitted by the physical space within the tool.

[0065] Another such embodiment is shown in FIG. 18. In this embodiment, a series of triangular energy band cavities are cascaded so that two or more energy bands of electrons can be detected separately by the detector assembly. As shown in FIG. 18, signal electrons 1800 from a sample (not shown in FIG. 18) can pass through a deflector 1802, a focusing lens mesh 1804 surrounded by a ground electrode 1806, and a differential potential electrode 1808, each configured as further described herein. The first energy band cavity of this system is formed by a first repelling mesh 1810, a second repelling mesh 1812, and a first attracting mesh 1814, all of which can be configured as further described herein. This system includes a first detector 1816, which can also be configured as described herein.

[0066] The system also includes a third repelling mesh 1818 configured to repel charged particles that pass through the second repelling mesh 1812 and have an energy lower than a third predetermined energy. The third repelling mesh has an applied voltage, V3. A second attracting mesh 1820 is configured to attract charged particles that pass through the second repelling mesh 1812, are repelled by the third repelling mesh 1818, and have an energy higher than a second predetermined energy, E2 and lower than a third predetermined energy, E3. The second attracting mesh has an applied voltage of V2 + ΔV2. A second detector 1822 is configured to generate an output in response to charged particles passing through the second attracting mesh 1820. Each of these elements can also be further configured as described herein.

[0067] In a further embodiment, the system includes a fourth repulsive mesh configured to repel charged particles having an energy lower than a fourth predetermined energy that pass through the third repulsive mesh, a third attractive mesh configured to attract charged particles that pass through the third repulsive mesh and are repelled by the fourth repulsive mesh and have an energy higher than a third predetermined energy and lower than the fourth predetermined energy, and a third detector configured to generate an output in response to charged particles passing through the third attractive mesh. For example, as shown in FIG. 18, the system may include a fourth repulsive mesh 1824 configured to repel charged particles having an energy lower than a fourth predetermined energy, E4, that pass through the third repulsive mesh 1818. The fourth repulsive mesh has an applied voltage, V4. The third attractive mesh 1826 is configured to attract charged particles that pass through the third repulsive mesh 1818 and are repelled by the fourth repulsive mesh 1824 and have an energy higher than a third predetermined energy, E3, and lower than the fourth predetermined energy, E4. The third attractive mesh has an applied voltage of V3 + ΔV3. The third detector 1828 is configured to generate an output in response to charged particles passing through the third attractive mesh 1826. Each of these elements may also be further configured as described herein.

[0068] In an additional embodiment, the system includes a fifth repulsive mesh configured to pass charged particles having an energy lower than a fifth predetermined energy and repel them, a fourth attractive mesh configured to pass through the fourth repulsive mesh, be repelled by the fifth repulsive mesh, and attract charged particles having an energy higher than a fourth predetermined energy and lower than the fifth predetermined energy, and a fourth detector configured to generate an output in response to charged particles passing through the fourth attractive mesh. For example, as shown in FIG. 18, the system may include a fifth repulsive mesh 1830 configured to pass through the fourth repulsive mesh 1824 and repel charged particles having an energy lower than a fifth predetermined energy, E5. The fifth repulsive mesh has an applied voltage, V5. The fourth attractive mesh 1832 is configured to pass through the fourth repulsive mesh 1824, be repelled by the fifth repulsive mesh 1830, and attract charged particles having an energy higher than a fourth predetermined energy, E4 and lower than the fifth predetermined energy, E5. The fourth attractive mesh has an applied voltage of V4 + ΔV4. The fourth detector 1834 is configured to generate an output in response to charged particles passing through the fourth attractive mesh 1832. Each of these elements may also be further configured as described herein.

[0069] In some embodiments, the system includes a fifth detector configured to generate an output in response to charged particles passing through the fifth repulsive mesh. For example, as shown in FIG. 18, the fifth detector 1836 is configured to generate an output in response to charged particles passing through the fifth repulsive mesh 1830. This detector may also be further configured as described herein.

[0070] Accordingly, the system can include four energy bands (i.e., the energy between E1 and E2, between E2 and E3, between E3 and E4, and between E4 and E5) and one high-pass band (i.e., energy greater than E5), all of which can be selected by the user or as further described herein. In this way, the embodiments described herein can add more energy band cavities as long as the physical space within the tool permits.

[0071] FIG. 19 shows the overall collection spectrum for the detector assembly described above that includes five detectors. In other words, this graph shows an example of the overall collection spectrum for a system that uses both bandpass filtering and high-pass filtering. As shown in FIG. 19, some electrons having energy between 0 and E1 are “lost,” which means that the detector assembly described herein filters out these electrons by the first repelling mesh and they are not detected. Electrons having energy between E1 and E2 are detected by detector 1 because these electrons are not repelled by the first repelling mesh, are repelled by the second repelling mesh, and are attracted by the first attracting mesh positioned immediately before the first detector. Electrons having energy between E2 and E3 are detected by detector 2 because these electrons are not repelled by the first or second repelling mesh, are repelled by the third repelling mesh, and are attracted by the second attracting mesh positioned immediately before the second detector. Electrons having energy between E3 and E4 are detected by detector 3 because these electrons are not repelled by the first, second, and third repelling meshes, are repelled by the fourth repelling mesh, and are attracted by the third attracting mesh positioned immediately before the third detector. Electrons having energy between E4 and E5 are detected by detector 4 because these electrons are not repelled by the first, second, third, or fourth repelling mesh, are repelled by the fifth repelling mesh, and are attracted by the fourth attracting mesh positioned immediately before the fourth detector. Electrons having energy between E5 and Em are detected by detector 5 because these electrons are not repelled by the first, second, third, fourth, or fifth repelling mesh and can thus be detected by the fifth detector.

[0072] Figure 20 shows an alternative embodiment of the system of FIG. 2 that does not include a differential potential electrode. As shown in FIG. 20, signal electrons 2000 from a sample (not shown in FIG. 20) can pass through a deflector 2002 that can be configured as further described herein. After passing through the deflector 2002, the signal electrons 2000 can pass through a focusing lens mesh 2004 positioned between ground electrodes 2006. The focusing lens mesh and the ground electrodes can be configured as described herein. After passing through the focusing lens mesh, the signal electrons can be directed towards a first repelling mesh 100. The first repelling mesh 100, the second repelling mesh 106, and the first attracting mesh 112 can form a triangular energy band cavity, which can be further configured as described herein. This embodiment of the system can also include an electrode block 214, a first detector 210, and a second detector 212, which can be configured as further described herein.

[0073] Figure 21 shows the simulation results of the path of only the electrons collected by the first detector through the system embodiment of FIG. 20. In other words, FIG. 21 shows the path of only the electrons within a specific energy band entering the detector assembly. As shown in FIG. 21, electrons 2100 having an energy between E1 and E2 are collected on the first detector 210 with a substantially high transmittance. However, as further shown in FIG. 21, although this structure can have band-pass filtering performance, due to an undesirable lens field between the first repelling mesh and the focusing lens mesh, many "useful" electrons are repelled by the first repelling mesh, so the transmittance is much lower than that of other embodiments described herein.

[0074] In some embodiments, the system systematically changes the potentials applied to the first repulsive mesh, the second repulsive mesh, and the first attractive mesh, thereby systematically changing the first and second predetermined energies, and for at least two of the systematically changed potentials, compares the outputs generated by the first detector, and based on the result of the comparison of the outputs, selects the potentials applied to the first repulsive mesh, the second repulsive mesh, and the first attractive mesh for the process performed on the sample, and includes a computer subsystem configured to perform the above. FIG. 22 shows one embodiment of a method for dynamically exploring the optimal energy band to achieve the highest contrast of any particular defect. One advantage of the embodiments described herein is that they provide the ability to automatically explore the optimal energy band for the highest defect contrast.

[0075] As shown in step 2200 of FIG. 22, the computer subsystem can select an energy band width dE (e.g., dE = 200 eV). Then, as shown in step 2202 of FIG. 22, the computer subsystem can associate a potential difference among three meshes of the energy band cavity (e.g., V2 = V1 - dE / e, ΔV = 0). As shown in step 2204, the computer subsystem can set V1 = -U - n×dE and start n from 0. As shown in step 2206, the computer subsystem can generate and save an image from detector 1. As shown in step 2208, the computer subsystem can then check whether V1 < -(U + Em - dE) / e. As shown in step 2210, if V1 is not less than -(U + Em - dE) / e, the computer subsystem can set n = n + 1 and repeat steps 2204, 2206, and 2208. As shown in step 2212, if V1 is less than -(U + Em - dE) / e, the computer subsystem can generate and save an image from detector 2. As shown in step 2214, the computer subsystem can compare all the saved images, find the one with the highest defect contrast, and then determine the optimal energy band.

[0076] The detector assembly embodiments described herein can be implemented with a wide variety of tools, including electron beam systems commercially available from KLA. Such electron beam systems can also include, but are not limited to, single or multi-beam systems, imaging or non-imaging systems, analytical instruments such as spectrometers, and others. Additionally, the detector assembly embodiments described herein can be particularly beneficial for electron beam inspection and electron overlay tools since they can enhance the contrast of buried defects and features.

[0077] Figure 23 shows one embodiment of a tool in which the detector assembly embodiments described herein can be used. In this tool, the energy directed at the sample includes electrons, and the energy detected from the sample includes electrons. As shown in Figure 23, the tool includes an electron column 2300 and a computer subsystem 2302. The computer subsystem 2302 can be configured as further described herein.

[0078] Also as shown in Figure 23, the electron column includes an electron beam source 2304 configured to generate electrons focused on the sample 2306 by one or more elements 2308. The electron beam source can include, for example, a cathode source or an emitter chip, and the one or more elements 2308 can include, for example, a gun lens, an anode, a beam limiting aperture, a gate valve, a beam current selection aperture, an objective lens, and a scanning subsystem, all of which can include any such suitable elements known in the art.

[0079] Electrons returned from the sample (e.g., secondary electrons, etc.) can be focused on the detector assembly 2312 by one or more elements 2310. The one or more elements 2310 can include, for example, a scanning subsystem, which can be the same as the scanning subsystem included in the elements 2308. The detector assembly 2312 can include any of the detector assembly embodiments described herein.

[0080] The electron column may include any other suitable elements known in the art. Additionally, the electron column is further configured as described in U.S. Patent No. 7,141,791 issued to Masnaghetti et al. on November 28, 2006, U.S. Patent No. 7,276,694 issued to Bertsche on October 2, 2007, U.S. Patent No. 7,714,287 issued to James et al. on May 11, 2010, U.S. Patent No. 8,664,594 issued to Jiang et al. on April 4, 2014, U.S. Patent No. 8,692,204 issued to Kojima et al. on April 8, 2014, U.S. Patent No. 8,698,093 issued to Gubbens et al. on April 15, 2014, U.S. Patent No. 8,716,662 issued to MacDonald et al. on May 6, 2014, and U.S. Patent No. 9,000,395 issued to Ren et al. on April 7, 2015, which are incorporated herein by reference as if fully set forth.

[0081] The electron column shown in FIG. 23 is shown as being configured such that electrons are directed at the sample at an oblique angle of incidence and scattered from the sample at another oblique angle, but the electron beam can be directed at the sample and scattered from the sample at any suitable angle. Additionally, the electron beam tool can be configured to generate an output using a plurality of modes (e.g., different irradiation angles, collection angles, etc.) with respect to the sample. The plurality of modes of the electron beam tool can differ in any output generation parameter of the tool.

[0082] The detector of the detector assembly can detect electrons returned from the surface of the sample, thereby forming an electron beam image of the sample (or other output thereto). The electron beam image can include any suitable electron beam image. The computer subsystem 2302 can be coupled to a detector (not shown in FIG. 23) included in the detector assembly in any suitable manner so that the computer subsystem can receive the output generated by the detector (e.g., through one or more transmission media that can include "wired" and / or "wireless" transmission media). The computer subsystem 2302 can be configured to perform several functions using the output of the detector.

[0083] In another embodiment, the system includes a computer subsystem configured to detect defects on a sample based on the output generated by a first detector. For example, the computer subsystem can be configured to use the output of the detector to detect an event on the sample. Detecting an event on the sample is done by applying some defect detection algorithm and / or method to the output generated by the detector, which can include any suitable algorithm and / or method known in the art. For example, the computer subsystem can compare the output of the detector to a threshold value. Any output having a value exceeding the threshold can be identified as an event (e.g., a potential defect), and any output having a value less than the threshold cannot be identified as an event. The computer subsystem 2302 can be configured to perform any further steps described herein.

[0084] The computer subsystem of the tool (and other computer subsystems described herein) may also be referred to herein as a computer system. Each of the computer subsystems or systems described herein can take various forms, including a personal computer system, an image computer, a mainframe computer system, a workstation, a network device, an Internet device, or other devices. In general, the term "computer system" can be broadly defined to include any device having one or more processors that execute instructions from a memory medium. The computer subsystem or system can also include any suitable processor known in the art, such as a parallel processor. Additionally, the computer subsystem or system can include a computer platform having high-speed processing and software, either as a stand-alone or networked tool.

[0085] When the system includes two or more computer subsystems (not shown), the different computer subsystems can be coupled to each other so that images, data, information, instructions, etc. can be sent between the computer subsystems. The plurality of computer subsystems can be coupled to each other by any suitable transmission medium, including any suitable wired and / or wireless transmission media known in the art. Two or more such computer subsystems can also be effectively coupled by a shared computer-readable storage medium (not shown).

[0086] Note that FIG. 23 is provided to generally illustrate the configuration of an electron beam tool in which an embodiment of the detector assembly described herein can be used. The electron beam tool configuration described herein can be modified to optimize the performance of the tool, as is typically done when designing a commercial tool. In addition, the detector assembly described herein can be implemented in an existing tool, such as a tool commercially available from KLA (e.g., by adding the functionality described herein to an existing tool). For some such systems, the detector assembly described herein can be provided as an optional functionality of the system (e.g., in addition to other functionality of the system). Alternatively, the system described herein can be designed "from scratch" to provide an entirely new system. The system shown in FIG. 23 can be further configured as described herein.

[0087] Although the tool was described above as being an electron beam tool, the tool can be an ion beam tool. Such a tool can be configured as shown in FIG. 23, except that the electron beam source can be replaced with any suitable ion beam source known in the art. In addition, the tool can include any other suitable ion beam imaging tool, such as those included in commercially available focused ion beam (FIB) systems, helium ion microscopy (HIM) systems, and secondary ion mass spectrometry (SIMS) systems.

[0088] As described above, the computer subsystem can use the output generated by the detector to detect defects on the sample. In this way, the system described herein can be configured as an inspection system. In some embodiments, the system includes a computer subsystem configured to review defects detected on a sample by different systems based on the output generated by a first detector. In further embodiments, the system includes a computer subsystem configured to determine overlay information for a sample based on the output generated by a first detector. In yet another embodiment, the system includes a computer subsystem configured to determine one or more characteristics of a patterned feature formed on a sample based on the output generated by a first detector. For example, the system described herein can be configured as a metrology or defect review system. In particular, the embodiments of the system described herein and shown in FIG. 23 can be modified in one or more parameters to provide different imaging capabilities depending on the application for which it will be used. In one such example, the electron column shown in FIG. 23 can be configured to have a higher resolution when it is used for metrology rather than inspection. In other words, the embodiments of the system shown in FIG. 23 describe some general and various configurations for a system that can be adapted in several ways that will be apparent to those skilled in the art to create systems with different imaging capabilities that are generally appropriate for different applications.

[0089] The computer subsystem can be configured to review defects detected on a sample in any suitable manner. For example, the computer subsystem can cause an electron column to collect an image at the location of a defect detected by another system. The computer subsystem can apply some defect redetection algorithm or method to the image to relocate defects within the review image. The computer subsystem can then determine one or more characteristics of the redetected defects, such as size, shape, contrast, texture, roughness, and patterns near or surrounding the redetected defects. The computer subsystem can use that information about the one or more characteristics to determine further information about the redetected defects, such as classification, degree of severity, and the like.

[0090] The computer subsystem can be configured to determine one or more characteristics of a patterned feature formed on a sample and overlay information in any suitable manner known in the art. For example, the computer subsystem can cause an electron column to generate an image at a location where the patterned feature is to be measured and / or where overlay information is to be generated. The computer subsystem can then apply one or more image processing algorithms or methods to the image to determine one or more characteristics of the patterned feature, such as line width, texture, roughness, shape, and the like, and / or overlay information, such as the amount of displacement of one pattern on one layer of the sample with respect to another pattern on another layer of the sample.

[0091] In some embodiments, the system includes a second detector configured to generate an output in response to charged particles passing through a second repelling mesh, and a computer subsystem configured to determine information about a sample from the output generated by the first detector and the output generated by the second detector. For example, embodiments described herein may include multiple detectors that simultaneously generate an output for a sample. Thus, for any one position on the sample, multiple outputs can be generated simultaneously by multiple detectors and may be made available for use in accordance with the embodiments described herein. The computer subsystem may then determine any of the information described herein about the sample using the multiple outputs generated for the same position on the sample in a variety of ways including those described above.

[0092] The computer subsystem is not limited to using only the outputs from the first and second detectors to determine information, and may use the output for any of the detectors included in the system to determine information. The computer subsystem may select different sets of outputs to determine different information. For example, in some instances, the outputs generated by the first and second detectors are particularly useful for determining a first piece of information about the sample, and the outputs generated by the first and third detectors may be particularly useful for determining a second piece of information about the sample.

[0093] The embodiments described herein are flexible and can be readily configured based on the type and / or energy of the charged particles detected by each detector (e.g., by selecting an optimal energy band as described above), and based on information about which type of charged particle is sensitive to which sample information, the computer subsystem can select various parameters of the system to determine the sample information with the highest sensitivity and / or highest accuracy even when the sample information is determined using outputs generated by multiple detectors.

[0094] In one such embodiment, the computer subsystem is configured to determine information about a sample by generating an image of a defect on the sample from the output generated by a first detector and the output generated by a second detector. For example, the outputs from different detectors can be used not only separately to determine information about the sample, but also to generate a new output for the sample that is then used to determine information. In one such example, the comparison or algebraic operation (e.g., addition, subtraction, averaging, etc.) of two images from two detectors can enhance the contrast of the defects in the resulting image. Thus, two images can be used to generate a new third image having better contrast for the defects, and the computer subsystem can use the third image to detect the defects or determine information about the defects such as one or more defect characteristics. Such images can also be useful for determining other sample information described herein, such as patterned feature characteristics.

[0095] A computer subsystem can be configured to store the results of any step performed by the system on any suitable computer-readable storage medium. The results can be stored in any manner known in the art. The storage medium can include any storage medium described herein or any other suitable storage medium known in the art. After the results are stored, the results can be accessed within the storage medium and used by any of the methods or system embodiments described herein, formatted for display to a user, and used by another software module, method, or system, etc. For example, if the system is configured as an inspection tool, the system can perform an inspection process on a sample and produce results for any detected defects on the sample, such as information on the bounding box of the detected defect, e.g., position and others, information on defect classification such as detection score, class label or ID and others, or any such suitable information known in the art. The results for the defects can be generated by the computer subsystem in any suitable manner. The results for the defects can have any suitable form or format, such as a standard file type. The computer subsystem can generate and store the results so that the results can be used by the computer subsystem and / or another system or method to perform one or more functions on the sample or another sample of the same type.

[0096] The results and information generated by the system embodiments described herein can be used in a variety of ways by the embodiments described herein and / or by systems and methods. Such functionality includes, but is not limited to, changing a process, such as a fabrication process or step, that has been or is to be performed on a sample or another sample in a feedback or feedforward manner. For example, the computer subsystem described herein can be configured to determine one or more changes to a process performed on a sample being inspected and / or a process that is to be performed on the sample based on detected defects. A change to a process can include any suitable change to one or more parameters of the process. The computer subsystem described herein preferably determines changes such that defects on the sample can be corrected or removed in another process performed on the sample, such that defects can be reduced or prevented on other samples on which the modified process is performed, such that defects can be compensated for in another process performed on the sample, and the like. The computer subsystem described herein can determine these changes in any suitable manner known in the art. Such changes can also be determined using the results of other processes described herein.

[0097] These changes can then be sent to a semiconductor fabrication system (not shown) or a computer subsystem and a storage medium (not shown) accessible to the semiconductor fabrication system. The semiconductor fabrication system can be part of the system embodiments described herein or not. For example, the computer subsystem and / or tool described herein can be coupled to the semiconductor fabrication system through one or more common elements, such as a housing, a power supply, a sample handling device or mechanism, and the like. The semiconductor fabrication system can include any semiconductor fabrication system known in the art, such as a lithography tool, an etching tool, a chemical mechanical polishing (CMP) tool, a deposition tool, and the like.

[0098] Each of the embodiments of the system may be further configured in accordance with any other embodiment described herein.

[0099] Another embodiment relates to a computer-implemented method of detecting charged particles from a sample. The method includes repelling charged particles from the sample having an energy lower than a first predetermined energy by a first repelling mesh positioned within a path of charged particles from the sample, as shown in step 2400 of FIG. 24. The method also includes repelling charged particles that pass through the first repelling mesh and have an energy lower than a second predetermined energy by a second repelling mesh, as shown in step 2402 of FIG. 24. Additionally, the method includes attracting charged particles that pass through the first repelling mesh, are repelled by the second repelling mesh, and have an energy higher than the first predetermined energy and lower than the second predetermined energy by a first attracting mesh, as shown in step 2404 of FIG. 24. The method further includes generating an output in response to charged particles that have passed through the first attracting mesh by a first detector, as shown in step 2406 of FIG. 24. Each of the steps of the method may be performed as further described herein. The method may also include any other steps that may be performed by the systems described herein. The steps of the method can be performed by the systems described herein and they may be configured according to any of the embodiments described herein.

[0100] A further embodiment relates to a non-transitory computer-readable medium storing program instructions executable on a computer system for performing a computer-implemented method of detecting charged particles from a sample. One such embodiment is shown in FIG. 25. In particular, as shown in FIG. 25, the non-transitory computer-readable medium 2500 includes program instructions 2502 executable on a computer system 2504. The computer-implemented method may include any step of any method described herein.

[0101] Program instructions 2502 for implementing methods such as those described herein may be stored on a computer-readable medium 2500. The computer-readable medium can be a storage medium such as a magnetic or optical disk, magnetic tape, or any other suitable non-transitory computer-readable medium known in the art.

[0102] The program instructions can be implemented in any of various forms, including, among other things, procedure-based techniques, component-based techniques, and / or object-oriented techniques. For example, the program instructions can be implemented using ActiveX controls, C++ objects, JavaBeans, Microsoft Foundation Classes ("MFC"), SSE (Streaming SIMD Extension instructions), or other desired technologies or methodologies.

[0103] The computer system 2504 can be configured according to any of the embodiments described herein.

[0104] Further variations and alternative embodiments of the various aspects of the present invention will become apparent to those skilled in the art in view of this specification. For example, methods and systems for detecting charged particles from a sample are provided. Accordingly, this description should be construed as illustrative only and is for the purpose of teaching those skilled in the art a general way of carrying out the present invention. It should be understood that the forms of the present invention shown and described herein are to be construed as presently preferred embodiments. After receiving the benefit of this description of the present invention, it will be apparent to all those skilled in the art that elements and materials can be replaced, parts and processes can be reversed, and certain features of the present invention can be utilized independently, without departing from the spirit and scope of the present invention as set forth in the appended "claims". Changes can be made in the elements described herein without departing from the scope of the present invention.

Claims

1. A system configured to detect charged particles from a sample, a first repelling mesh positioned within a path of charged particles from the sample and configured to repel the charged particles having an energy lower than a first predetermined energy, a second repelling mesh passing through the first repelling mesh and configured to repel the charged particles having an energy lower than a second predetermined energy, a first attracting mesh passing through the first repelling mesh, repelled by the second repelling mesh, and configured to attract the charged particles having an energy higher than the first predetermined energy and lower than the second predetermined energy, a first detector configured to generate an output in response to the charged particles passing through the first attracting mesh, a computer subsystem configured to systematically change potentials applied to the first repelling mesh, the second repelling mesh, and the first attracting mesh, thereby systematically changing the first and second predetermined energies; compare the output generated by the first detector for at least two of the systematically changed potentials; and select the potentials applied to the first repelling mesh, the second repelling mesh, and the first attracting mesh for a process performed on the sample based on a result of the comparison of the outputs characterized by comprising the same.

2. The system according to claim 1, wherein the first repelling mesh, the second repelling mesh, and the first attracting mesh form a triangular energy band cavity.

3. The system according to claim 1, wherein the first repelling mesh, the second repelling mesh, and the first attracting mesh form at least a part of a square energy band cavity.

4. The system according to claim 1, wherein the first repelling mesh, the second repelling mesh, the first attracting mesh, and an electrode block form a square energy band cavity, and the second repelling mesh and the electrode block have the same potential.

5. The system according to claim 1, further comprising a second detector configured to detect the charged particles passing through the second repulsive mesh.

6. The system according to claim 1, wherein the first detector is grounded.

7. The system according to claim 1, wherein the first detector is biased at a positive voltage.

8. The system according to claim 1, wherein the first detector is biased at an adjustable voltage.

9. The system according to claim 1, wherein the first detector is biased at a certain voltage, and the first attracting mesh shields the space between the first repulsive mesh, the second repulsive mesh, and the first attracting mesh from the electric field from the detector.

10. The system according to claim 1, further comprising a deflector configured to change the position of the path of the charged particles from the sample before the charged particles reach the first repulsive mesh.

11. The system according to claim 10, further comprising a focusing lens configured to focus the charged particles from the deflector and collimate the charged particles having an energy higher than the first predetermined energy and lower than the second predetermined energy to pass through the first repulsive mesh.

12. The system according to claim 11, further comprising a differential potential electrode surrounding the path of the charged particles between the focusing lens and the first repulsive mesh.

13. The system according to claim 12, wherein the differential potential electrode is configured to reduce the formation of the lens field between the focusing lens and the first repulsive mesh.

14. The system according to claim 1, wherein the energy band between the first and second predetermined energies is equal to an energy band from 0 eV to 50 eV.

15. The system according to claim 1, wherein the energy band between the first and second predetermined energies is equal to an energy band of Em - 100 eV, and Em is the maximum radiated charged particle energy from the sample.

16. The system according to claim 1, wherein the energy band between the first and second predetermined energies is equal to an energy band of 50 eV - Em, and Em is the maximum radiated charged particle energy from the sample.

17. The system according to claim 1, wherein the first and second predetermined energies are selected based on the type of defect to be detected on the sample based on the output generated by the first detector.

18. The system according to claim 1, wherein the first and second predetermined energies are selected based on the type of charged particles to be detected from the sample.

19. The system according to claim 1, wherein the energy band between the first and second predetermined energies corresponds to the energy of only secondary charged particles from the sample, and the computer subsystem is further configured to detect surface or voltage contrast defects on the sample based on the output generated by the first detector.

20. The system according to claim 1, wherein the energy band between the first and second predetermined energies corresponds to the energy of only elastically backscattered charged particles from the sample, and the computer subsystem is further configured to detect high aspect ratio or material contrast defects on the sample based on the output generated by the first detector.

21. The system according to claim 1, wherein the energy band between the first and second predetermined energies corresponds to the energy of only inelastically backscattered charged particles from the sample, and the computer subsystem is further configured to detect buried defects on the sample based on the output generated by the first detector.

22. The system according to claim 21, further comprising: a third repulsive mesh configured to pass the charged particles having an energy lower than a third predetermined energy through the second repulsive mesh and repel the charged particles; a second attracting mesh configured to pass the charged particles through the second repulsive mesh, be repelled by the third repulsive mesh, and attract the charged particles having an energy higher than a second predetermined energy and lower than the third predetermined energy; and a second detector configured to generate an output in response to the charged particles passing through the second attracting mesh.

23. The system according to claim 22, further comprising: a fourth repulsive mesh configured to pass the charged particles having an energy lower than a fourth predetermined energy through the third repulsive mesh and repel the charged particles; a third attracting mesh configured to pass the charged particles through the third repulsive mesh, be repelled by the fourth repulsive mesh, and attract the charged particles having an energy higher than a third predetermined energy and lower than the fourth predetermined energy; and a third detector configured to generate an output in response to the charged particles passing through the third attracting mesh.

24. The system according to claim 23, further comprising: a fifth repulsive mesh configured to pass the charged particles having an energy lower than a fifth predetermined energy through the fourth repulsive mesh and repel the charged particles; a fourth attracting mesh configured to pass the charged particles through the fourth repulsive mesh, be repelled by the fifth repulsive mesh, and attract the charged particles having an energy higher than a fourth predetermined energy and lower than the fifth predetermined energy; and a fourth detector configured to generate an output in response to the charged particles passing through the fourth attracting mesh.

25. The system according to claim 24, further comprising: a fifth detector configured to generate an output in response to the charged particles passing through the fifth repulsive mesh.

26. The system according to claim 1, wherein the computer subsystem is further configured to detect a defect on the sample based on the output generated by the first detector.

27. The system according to claim 1, wherein the computer subsystem is further configured to review defects detected on the sample by a different system based on the output generated by the first detector.

28. The system according to claim 1, wherein the computer subsystem is further configured to determine overlay information for the sample based on the output generated by the first detector.

29. The system according to claim 1, wherein the computer subsystem is further configured to determine one or more characteristics of a patterned feature formed on the sample based on the output generated by the first detector.

30. The system according to claim 1, further comprising a second detector configured to generate an output in response to the charged particles passing through the second repulsive mesh, wherein the computer subsystem is further configured to determine information about the sample from the output generated by the first detector and the output generated by the second detector.

31. The system according to claim 30, wherein the computer subsystem is further configured to determine the information about the sample by generating an image of a defect on the sample from the output generated by the first detector and the output generated by the second detector.

32. The system according to claim 1, wherein the charged particles are electrons.

33. The system according to claim 1, wherein the charged particles are helium ions.

34. A system configured to detect charged particles from a sample, a first repulsive mesh positioned within a path of charged particles from the sample and configured to repel the charged particles having an energy lower than a first predetermined energy; a second repulsive mesh configured to pass through the first repulsive mesh and to repel the charged particles having an energy lower than a second predetermined energy; A first attracting mesh configured to attract charged particles that pass through the first repulsive mesh, are repelled by the second repulsive mesh, and have an energy higher than the first predetermined energy and lower than the second predetermined energy, wherein the energy band between the first and second predetermined energies corresponds to the energy of only the elastically backscattered charged particles from the sample, and the first attracting mesh; A first detector configured to generate an output in response to the charged particles that have passed through the first attracting mesh; A computer subsystem configured to detect high aspect ratio or material contrast defects on the sample based on the output generated by the first detector A system characterized by comprising the above.

35. A system configured to detect charged particles from a sample, A first repulsive mesh positioned within the path of charged particles from the sample and configured to repel charged particles having an energy lower than a first predetermined energy; A second repulsive mesh that passes through the first repulsive mesh and is configured to repel charged particles having an energy lower than a second predetermined energy; A first attracting mesh configured to attract charged particles that pass through the first repulsive mesh, are repelled by the second repulsive mesh, and have an energy higher than the first predetermined energy and lower than the second predetermined energy, wherein the energy band between the first and second predetermined energies corresponds to the energy of only the inelastically backscattered charged particles from the sample, and the first attracting mesh; A first detector configured to generate an output in response to the charged particles that have passed through the first attracting mesh; A computer subsystem configured to detect buried defects on the sample based on the output generated by the first detector A system characterized by comprising the above.

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