BANDPASS CHARGED PARTICLE ENERGY FILTERING DETECTOR FOR CHARGED PARTICLE TOOLS - Patent application

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 relates generally to methods and systems for detecting charged particles from a specimen. Certain embodiments relate to a bandpass charged particle energy filtering detector for a charged particle tool. [Background technology]

[0002] The following descriptions and examples are not admitted to be prior art by virtue 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 the various features and levels of the semiconductor device. For example, lithography is a semiconductor fabrication process that involves transferring a pattern from a reticle to a resist that is disposed on the 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 may be fabricated within a configuration on a single semiconductor wafer and then separated into individual semiconductor devices.

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

[0005] Defect review typically involves re-detecting the defects so detected by the inspection process and generating further information about the defects at higher resolution using high magnification optics or a scanning electron microscope (SEM). Defect review is thus performed at discrete locations on the specimen where defects were detected by inspection. The higher resolution data for the defects generated by defect review is more suitable for determining attributes of the defects, such as contour, roughness, more precise size information, etc.

[0006] Metrology processes are also used at various steps during semiconductor manufacturing processes to monitor and control the process. Metrology processes differ from inspection processes in that, unlike inspection processes in which defects are detected on a specimen, metrology processes are used to measure one or more properties of a specimen that cannot be determined using currently used inspection tools. For example, metrology processes are used to measure one or more properties of a specimen, such as dimensions (e.g., line width, thickness, etc.) of features formed on a specimen during a process, such that the performance of the process can be determined from the one or more properties. Additionally, if one or more properties of a specimen are unacceptable (e.g., outside a predetermined range for the property), the measurement of one or more properties of the specimen can be used to modify one or more parameters of the process so that additional specimens produced by the process have acceptable properties.

[0007] The metrology process also differs from the defect review process in that, unlike a defect review process in which defects detected by inspection are reviewed in the defect review, the metrology process may be performed at locations where no defects have been detected. In other words, unlike a defect review, the locations where the metrology process is performed on the specimen may be independent of the results of the inspection process performed on the specimen. In particular, the locations where the metrology process is performed may be selected independent of the inspection results. In addition, because the locations on the specimen where the measurements are performed may be selected independent of the inspection results, the locations where the metrology process is performed may be determined before the inspection process is performed on the specimen, unlike a defect review in which the locations on the specimen where the defect review will be performed may not be determined until the inspection results for the specimen have been generated and are available for use.

[0008] In quality control processes such as inspection, defect review, and metrology using charged particles, e.g., electrons or ions, it can often be important to detect only charged particles from a sample that have a certain energy. In particular, different types of charged particles returned from a sample can have near sensitivity to a certain 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 with different energies, such as threshold energy filters, energy dispersive sectors with segmented detectors, and multiple electrostatic suppressors.

[0009] Although each of the charged particle separation methods described above has found some success in the art, there are one or more disadvantages to each of the currently used methods. For example, a threshold energy filter can only separate electrons with energies greater than or less than a threshold energy applied to the energy filter mesh. In another example, due to the mixing of radiation energies and angles, it is quite difficult to clearly separate electrons with different energies using energy dispersion sectors with segmented detectors. In a further example, it is quite challenging to design multiple detectors that float at relatively high voltages for multiple electrostatic suppressors. In addition, if the detectors are applied with voltages close to or the same as those of the electrostatic suppressors, the electrons that hit the detectors have relatively small impact energies, which may be difficult to generate a signal or have a fairly low signal-to-noise ratio. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] U.S. Patent No. 7,276,694 [Patent Document 2] US Patent Application Publication No. 2014 / 0299767 [Patent Document 3] US Patent Application Publication No. 2016 / 0372304 Summary of the Invention [Problem to be solved by the invention]

[0011] It would therefore be advantageous to develop a system and / or method for detecting charged particles from a sample that does not have one or more of the disadvantages discussed above. [Means for solving the problem]

[0012] The following description of various embodiments is not to 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 repelling mesh positioned in a path of the 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 repelling mesh configured to repel charged particles passing through the first repelling mesh and having an energy lower than a second predetermined energy. In addition, the system 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. 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 charged particles from the sample having an energy lower than a first predetermined energy by a first repelling mesh positioned in a path of the charged particles from the sample. The method also includes repelling charged particles passing through the first repelling mesh and having an energy lower than the second predetermined energy by a second repelling mesh. In addition, the method includes attracting charged particles passing through the first repelling mesh and being repelled by the second repelling mesh by a first attracting mesh and having an energy higher than the first predetermined energy and lower than the second predetermined energy. The method further includes generating an output by a first detector in response to the charged particles passing through the first attracting mesh.

[0015] Each of the steps of the method may be performed as further described herein. In addition, 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 having stored thereon program instructions executable on a computer system to perform 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. In addition, 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 upon reading the following detailed description and upon reference to the accompanying drawings. [Figure 1] FIG. 1 is a schematic diagram illustrating a cross-sectional view of one embodiment of a triangular energy band cavity. [Diagram 2] FIG. 2 is a schematic diagram illustrating a cross-sectional view of an embodiment of a triangular energy band cavity included in an embodiment of a system configured to detect charged particles from a sample. [Diagram 3] FIG. 2 is a schematic diagram showing a cross-sectional view of one embodiment of a differential potential electrode that may be included in embodiments of the systems described herein. [Figure 4] FIG. 4 is a schematic diagram showing a cross-sectional view of the differential potential electrode of FIG. 3 with an example of simulated equipotential lines induced by and created therein. [Diagram 5] FIG. 3 is a schematic diagram showing a cross-sectional view of the embodiment of FIG. 2, according to an example of a simulation of the path of charged particles with various energies through the system. [Figure 6] FIG. 3 is a schematic diagram showing a cross-sectional view of the embodiment of FIG. 2, according to an example of a simulation of the path of charged particles with various energies through the system. [Figure 7] FIG. 2 is a schematic diagram illustrating a cross-sectional view of one embodiment of a square energy band cavity. [Figure 8]FIG. 2 is a schematic diagram illustrating a cross-sectional view of an embodiment of a square energy band cavity included in an embodiment of a system configured to detect charged particles from a sample. [Figure 9] FIG. 9 is a schematic diagram showing a cross-sectional view of the embodiment of FIG. 8, with an example of a simulation of the path of charged particles with various energies through the system. [Figure 10] FIG. 9 is a schematic diagram showing a cross-sectional view of the embodiment of FIG. 8, with an example of a simulation of the path of charged particles with various energies through the system. [Figure 11] 1 is a graph showing an example of how the energy band cavity embodiments described herein can be used in the system embodiments described herein to separately detect charged particles having different energies. [Figure 12] 1 is a graph showing an example of how the energy band cavity embodiments described herein can be used in one embodiment of the system described herein to separately detect secondary electrons and backscattered electrons. [Figure 13] 1 is a graph showing an example of how the energy band cavity embodiments described herein can be used in one embodiment of the system described herein to separately detect low-loss backscattered electrons and elastically backscattered electrons. [Figure 14] 1 is a graph showing an example of a simulation result of the energy of electrons entering a detector assembly of a system embodiment described herein. [Figure 15] 11 is a graph showing example simulation results of the energy of electrons being detected separately by different detectors of a detector assembly of a system embodiment described herein. [Figure 16] 11 is a graph showing example simulation results of the energy of electrons being detected separately by different detectors of a detector assembly of a system embodiment described herein. [Figure 17]FIG. 1 is a schematic diagram illustrating a cross-sectional view of one embodiment of a system configured to detect charged particles from a sample, including an embodiment of a multiple square energy band cavity. [Figure 18] FIG. 1 is a schematic diagram illustrating a cross-sectional view of an embodiment of a system configured to detect charged particles from a sample, including an embodiment of a multiple triangular energy band cavity. [Figure 19] 19 is a graph showing an example of how the energy band cavity embodiment shown in FIG. 18 can be used in system embodiments described herein to separately detect charged particles having different energies. [Figure 20] FIG. 3 is a schematic diagram showing a cross-sectional view of an embodiment of the system of FIG. 2 without a differential potential electrode. [Figure 21] 21 is a schematic diagram showing a cross-sectional view of the embodiment of FIG. 20 with an example of a simulation of the path of charged particles with various energies through the system. [Figure 22] 1 is a flow chart illustrating one embodiment of steps that may be taken to dynamically search for an optimal energy band for highest defect contrast. [Figure 23] FIG. 1 is a schematic diagram illustrating a side view of one embodiment of a system in which embodiments of a system configured to detect charged particles from a sample as described herein may be used. [Figure 24] 1 is a flow chart illustrating one embodiment of steps included in a method for detecting charged particles from a sample. [Diagram 25] FIG. 1 is a block diagram illustrating one embodiment of a non-transitory computer-readable medium having stored thereon program instructions executable on a computer system to perform one or more of the computer-implemented methods described herein. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular forms, but on the contrary are intended to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

[0019] Referring now to the drawings, it is noted that the figures are not drawn to scale. In particular, the scale of some of the elements in the figures has been greatly exaggerated to emphasize the characteristics of the elements. It is also noted that the figures are not drawn to scale. Elements shown in two or more figures that may be similarly configured are indicated using the same reference numerals. Unless otherwise noted, 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 described further herein, the embodiments are advantageous because 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) with enhanced contrast of 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 may 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 may be caused by irradiation of the sample with charged particles (such as in an electron or ion beam imaging tool) or may be caused by some other non-charged particle means (e.g., x-rays). Charged particles may also include any of the charged particles described herein and may be "from the sample" in any manner, such as reflected, scattered, transmitted, etc. from or by the sample.

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

[0023] The system includes a first repulsive mesh positioned in the path of the charged particles from the sample and configured to repel charged particles having an energy lower than a first predetermined energy. Although some elements are described herein as "meshes," it should be understood that each such "mesh" may be replaced with a grid or other suitable element capable of functioning as described herein. As shown in FIG. 1, the system may include a first repulsive mesh 100 positioned in the path of the charged particles 102 from the sample (not shown in FIG. 1). The first repulsive meshes repel 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 an energy band of [0,Em] may encounter the first repulsive mesh 100, electrons having an energy equal to or lower than E1, i.e., within the energy band of [0,E1], may be repelled by the first repulsive mesh, and electrons having an energy greater than E1 may be transmitted by the first repulsive mesh.

[0024] The system also includes a second repulsive mesh configured to repel charged particles passing through the first repulsive mesh and having an energy lower than a second predetermined energy. The second repulsive mesh may also be configured to repel any electrons having an energy higher than the second predetermined energy passing through the second repulsive mesh. As shown in FIG. 1, the system may include a second repulsive mesh 106 configured to repel charged particles 108 passing through the first repulsive mesh 100 and having an energy lower than a second predetermined energy by having a second voltage, V2, applied thereto. In other words, signal electrons having an energy higher than E1 may 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. Any other of the charged particles having an energy higher than E2, i.e., [E2, Em], e.g., electron 110, may not be repelled by the second repulsive mesh, but may pass through the repulsive mesh and may or may not be detected separately as further described herein. Thus, the system may include one energy band (i.e., 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 may be selectable by the user or as further described herein.

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

[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. Therefore, the value of V1 is usually larger than V2. V1+ΔV is also larger than V2, so that the first attractive mesh can attract the electrons repelled from the second repulsive mesh. It is noted that ΔV can also be equal to zero, which means that the first repulsive mesh is at the same potential as the first attractive mesh, which may help simplify the external power supply and mechanical design.

[0027] The first and second repulsive meshes and the first attractive mesh shown in FIG. 1 form one of several possible energy band cavities that may be included in the embodiments described herein. The term "cavity" as used herein is generally defined as a defined space formed by any combination of repulsive and attractive meshes (possibly with one or more additional elements such as electrode blocks) that in combination control the flow of charged particles through the defined space. Each of the energy band cavities described herein is configured not only to store electrons having its corresponding desired energy band, but also to automatically deflect them into a side detector without the addition of additional deflectors. 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, which may 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 where only electrons with energy within the desired energy band remain and are deflected to the side attraction mesh and then accelerated to the detector (as described further herein), for example, because the detector is biased more positively compared to the side attraction mesh with sufficient impact energy to generate a relatively strong signal. One improvement of the embodiments described herein over other methods and systems for detecting charged particles from a sample is the inclusion of 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 cavity 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 cavity 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 may be configured as further described above. In one embodiment, the system includes 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. As shown in FIG. 2, signal electrons 200 from the sample (not shown in FIG. 2) pass through a deflector 202. The deflector may 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 the charged particles from the deflector and collimate charged particles having energies higher than a first predetermined energy and lower than a second predetermined energy to pass through a first repelling mesh. For example, after the signal electrons 200 pass through the deflector 202, they may pass through a focusing lens mesh 204 positioned between ground electrodes 206. The focusing lens may be configured to focus the electron cloud and collimate electrons having a desired energy to pass through the first repelling mesh. In this manner, the focusing lens may help to minimize the loss of electrons having energies 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 the charged particle between the focusing lens and the first repelling mesh. As shown in FIG. 2, the system may include a differential potential electrode 208 surrounding the path of the signal electron 200 between the focusing lens mesh 204 and the first repelling mesh 100. As shown in FIG. 3, the differential potential electrode may include four electrodes arranged in series along the path of the charged particle between the focusing lens mesh 204 and the first repelling mesh 100. The voltages under each element shown in FIG. 3 are examples of applied voltages for these respective elements. In particular, the applied voltage for the focusing lens mesh may be V0. The voltage applied to the ground electrode may be 0, and the voltage applied to the first repelling mesh may be V1. The voltages applied to the first, second, third, and fourth differential potential electrodes may be V1, V2, V3, V4, V5, V6, V7, V8, V9, V10, V11, V12, V13, V14, V15, V16, V17, V18, V19, V20, V21, V22, V23, V24, V25, V26, V27, V28, V29, V30, V31, V32, V33, V34, V35, V36, V37, V38, V39, V40, V41, V42, V43, V44, V45, V46, V47, V48, V49, V50, V51, V52, V53, V54, V55, V56, V57, V58, V59, V60, V61, V62, V63, V64, V65, V66, V67, V68, V69, V70, V71, V72, V73, V74, V75, V76,

number

[0032] In another such embodiment, the differential potential electrodes are configured to reduce the formation of a lens field between the focusing lens and the first repelling mesh. In addition, the differential potential electrodes may 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 almost no lens field between the focusing lens mesh and the first repelling mesh. Although the differential potential electrodes are shown in various figures described herein as including four differential potential electrodes, any suitable number of differential potential electrodes may be included between the focusing lens mesh and the first repelling mesh in the embodiments described herein.

[0033] The system also includes a first detector configured to generate an output in response to the charged particles passing through the first attraction mesh. For example, as shown in FIG. 2, the system may include a first detector 210 configured to generate an output in response to electrons passing through the first attraction mesh 112. The first detector 112 (and other detectors described herein) may include any suitable detector known in the art. Each of the detectors described herein may be an imaging detector configured to detect charged particles as a function of position across the detector. However, the detectors may be non-imaging detectors that do not output an image of the sample, but rather detect the number of impinging electrons, and the impact energy. In some such embodiments, a computer subsystem such as those described herein may be configured to generate an image of the sample from the non-imaging output of the detector. In this manner, the embodiments described herein may 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 described further herein.

[0034] In one embodiment, the first detector is grounded. In another embodiment, the first detector is biased with a positive voltage. In a further embodiment, the first detector is biased with an adjustable voltage. For example, the first detector (and any other detector described herein) can be grounded or biased with a positive relatively high voltage (e.g., several kV) for any type of detector, such as semiconductor-based, microchannel plate, and scintillator photomultiplier tube (PMT) detectors, to reach the optimal impact energy of 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 impact energy. In addition, one advantage of the embodiments described herein is that the impact energy of electrons hitting the detector is relatively high (e.g., greater than 5 keV) and can be adjusted without affecting the energy band filtering performance.

[0035] In one embodiment, the first detector is biased at a voltage, and the first attractive mesh shields the space between the first repulsive mesh, the second repulsive mesh, and the first attractive mesh from the electric field from the detector. For example, the mesh immediately in front of the detector behaves like a shielding mesh, so 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 the second repelling mesh. For example, as shown in FIG. 2, the system may include a second detector 212 configured to detect electrons passing through the 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, depending, for example, on the energy and / or type of electrons they are to detect. In this manner, an embodiment may include two detectors, one of which may be used to collect and detect electrons within a desired energy band (i.e., band-pass filtering) and the other of which may be used to collect and detect electrons having energies higher than the top energy of the desired energy band (i.e., high-pass filtering).

[0037] In some embodiments, such as that shown in Figure 2, the system may include an electrode block 214 configured to at least partially enclose the space between the second repelling mesh and the second detector, thereby facilitating detection of many of the signal electrons passing through the second repelling mesh by the second detector. In this manner, the second repelling mesh 106, the electrode block 214, and the second detector 212 (possibly with an attractive mesh positioned immediately prior thereto, not shown in Figure 2) may form a sort of second energy band cavity within the system. That second energy band cavity may be further configured as described herein.

[0038] 5 and 6 show the results of a simulation of the paths of charged particles with different energies through the system embodiment of FIG. 2. FIG. 5 shows the paths of electrons with energies in the band [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 with energies in the band [E1,E2] are only a portion of the electrons shown in FIG. 5. In other words, FIG. 6 shows the paths of only electrons in a particular energy band entering the detector assembly. Thus, FIG. 6 is included here to more clearly show the movement of electrons in the bandpass filter energy band through the system, but is not intended to show all of the electrons that will actually travel through the system.

[0039] As shown in Figure 5, electrons 500 having energies lower than E1 are repelled back 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 shown more clearly in Figure 6, electrons 600 having energies between E1 and E2 are collected on the first detector 210 with substantially high transmission (i.e., almost all of the electrons having energies within the bandpass corresponding to the first energy band cavity are directed to the first detector).

[0040] In one embodiment, the first repelling mesh, the second repelling 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 repelling mesh, the second repelling mesh, and the first attractive mesh form at least a portion of a square energy band cavity. Thus, there are two types of energy band cavities: triangular and rectangular. Both types use three meshes with three potentials (V1, V2, and V1+ΔV) and a surrounding container with the same potential as V2. For example, in a further embodiment, the first repelling mesh, the second repelling mesh, the first attractive mesh, and the electrode block form a square energy band cavity, and the second repelling mesh and the electrode block have the same potential.

[0041] FIG. 7 illustrates 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 in the path of a charged particle 702 from a sample (not shown in FIG. 7). The first repulsive mesh repels charged particles 704 having an energy lower than a first predetermined energy by having a first voltage, V1, applied to them. In other words, signal electrons from the sample having various energies [0,Em] may encounter the first repulsive mesh, electrons having an energy within the energy band of [0,E1] may be repelled by the first repulsive mesh, and electrons having an energy greater than E1 may be transmitted by the first repulsive mesh.

[0042] The system also includes a second repulsive mesh configured to repel charged particles 708 that pass through the first repulsive mesh and have an energy lower than a second predetermined energy. The second repulsive mesh may be configured such that any electrons that have 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 that pass through the first repulsive mesh 700 and have an energy lower than a second predetermined energy by having a second voltage, V2, applied thereto. In other words, signal electrons with an energy greater than E1 may pass through the first repulsive mesh, and any electrons with an energy within the energy band of [E1, E2] are repelled by the second repulsive mesh. Electrons 710 with an energy greater than E2, i.e., [E2, Em], may not be repelled by the second repulsive mesh, but may pass through the repulsive mesh and may or may not be detected separately, as further described herein. Thus, the system may include one energy band (i.e., 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 may be selectable by the user or as further described herein.

[0043] The system further includes a first attraction mesh configured to attract charged particles that pass through the first repulsion mesh, are repelled by the second repulsion mesh, and have an energy higher than the first predetermined energy and lower than the second predetermined energy. As shown in Fig. 7, the system includes a first attraction mesh 712 configured to attract charged particles that pass through the first repulsion mesh 700, are repelled by the second repulsion mesh 706, and have an energy higher than the first predetermined energy and lower than the second predetermined energy, i.e., [E1, E2]. The first attraction mesh can attract electrons with such energy by having a voltage of V1+ΔV applied to it.

[0044] In some embodiments, such as that shown in FIG. 7, the system may include a first and second repulsive mesh shown in FIG. 7 and an electrode block 714 that, together with a first attractive mesh, forms a square energy band cavity 716. The electrode block may have the same applied voltage, V2, as the second repulsive mesh. V1, V2, and V1+ΔV may be selected as described above. The curves shown in the energy band cavity 716 in 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 may be further configured as described herein and has all of the improvements and advantages of the other energy band cavities described herein.

[0045] FIG. 8 illustrates one embodiment of a system including 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) pass through a deflector 802, which 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 surrounding a path of the signal electrons 800 between the focusing lens mesh 804 and the first repelling mesh 700. The differential potential electrode may be configured as further described herein. The system also includes a first detector configured to generate an output in response to the charged particles passing through the first attracting mesh. For example, as shown in FIG. 8, the system may include a first detector 810 configured to generate an output in response to the electrons passing through the first attracting mesh 712. The first detector 810 may 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 may include a second detector 812 configured to detect electrons passing through the second repelling mesh 706. In this manner, an embodiment may include two detectors, one of which may be used to collect electrons within a desired energy band (i.e., band-pass filtering) and the other of which may be used to collect electrons having energies higher than the top energy of the desired energy band (i.e., high-pass filtering). The second detector may be further configured as described herein.

[0048] 9 and 10 show the results of a simulation of the paths of charged particles with different energies through the system embodiment of FIG. 8. FIG. 9 shows the paths of electrons with energies in the band [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 with energies in the band [E1,E2] are only a portion of the electrons shown in FIG. 9. In other words, FIG. 10 shows the paths of only electrons in a particular energy band entering the detector assembly. Thus, FIG. 10 is included here to more clearly show the movement of electrons in the bandpass filter energy band through the system, but is not intended to show all of the electrons that will actually travel through the system.

[0049] As shown in Figure 9, electrons 900 having energies lower than E1 are repelled back 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 shown more clearly in Figure 10, electrons 1000 having energies between E1 and E2 are collected on the first detector 810 with substantially high transmission (i.e., almost all of the electrons having energies within the bandpass corresponding to the first energy band cavity are directed to the first detector).

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

[0051] In one embodiment, the energy band between the first and second predetermined energies is equal to an energy band from 0 eV to 50 eV. In another embodiment, the energy band between the first and second predetermined energies is equal to an energy band of Em-100 eV, where Em is the maximum emitted charged particle energy from the sample. In a further embodiment, the energy band between the first and second predetermined energies is equal to an energy band of 50 eV-Em, where Em is the maximum emitted 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 is advantageous because it has the ability to select any particular energy band for the returned charged particle signal, which is then used to generate a sample image with enhanced contrast of any particular defect. In one such example, the signal electrons emitted from the sample may include secondary electrons (SE) and backscattered electrons (BSE) with energies ranging from 0 eV to Em (Em=e×LE, where LE represents the incident energy of the primary electrons). Typically, these signal electrons become further accelerated by the potential difference (U) between the column and the sample after leaving the sample before reaching the detector. Thus, the energy of the electrons entering the detector assembly is [eU, eU+Em]. Next, if we want to collect electrons with radiation energy between 500eV and 700eV, for example, to enhance the contrast of defects buried near 100nm deep, the voltage (V1) applied to the first repulsive mesh should be equal to -(eU+500) / e, and the voltage (V2) applied to the second repulsive mesh should be equal to -(eU+700) / e. The voltage (V1+ΔV) applied to the first attractive mesh should be V1≦V1+ΔV, which means ΔV≧0V. Thus, electrons with residual energy within [0,200] will be trapped inside the energy band cavity and then deflected to the first detector by the dipole field between the second repulsive mesh and the first attractive mesh. Assuming both detectors are grounded, the impact energy of an electron hitting the first detector is [eU+500, eU+700] and the impact energy of an electron 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 the extreme cases of collected spectra for the above-mentioned detector assembly including the first and second detectors. This graph shows an example of the extreme cases of collected spectra for a system that separates SEs and BSEs. As shown in FIG. 12, SEs having energies between E1 and E2, e.g., 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 located just before the first detector. BSEs having energies between E2 and Em are detected by detector 2 because these electrons are not repelled by the first or second repelling meshes and therefore can be detected by the second detector.

[0054] FIG. 13 shows another extreme case of the collected spectrum for the above-mentioned detector assembly including the first and second detectors. This graph shows an example of an extreme case of the collected spectrum for a system that separates low-loss BSEs and elastic BSEs. As shown in FIG. 13, some electrons with energies between 0 and E1 are "lost", meaning that the detector assembly described herein filters out these electrons by the first repulsive mesh and they are not detected. Low-loss BSEs with energies between E1 and E2 are detected by detector 1 because these electrons are not repelled by the first repulsive mesh, are repelled by the second repulsive mesh, and are attracted by the first attractive mesh located just before the first detector. Elastic BSEs with energies between E2 and Em are detected by detector 2 because these electrons are not repelled by the first or second repulsive meshes and therefore can be detected by the second detector.

[0055] 14-16 also show how BSEs with different energies entering the detector assembly are separated and detected separately by the embodiments described herein. In FIGS. 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. FIG. 14 shows the number of BSEs with energies between 0 and LE entering the detector assembly. FIG. 15 shows the number of BSEs with energies between 0 and LE collected on the second detector, i.e., detector 2, and FIG. 16 shows the number of BSEs with energies 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 specimen, and the system includes a computer subsystem configured to detect surface or voltage contrast defects on the specimen based on the output generated by the first detector. For example, collecting only secondary electrons (e.g., in an energy band of 0-50 eV) may enhance surface contrast or voltage contrast defects. For electron beam inspection (EBI) systems, finding defects with relatively high contrast on the image has many advantages, such as increasing throughput and sensitivity, reducing nuisance rates, and improving the accuracy of artificial intelligence-based models for automatic defect capture. The computer subsystem of this embodiment may 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 elastically backscattered charged particles from the specimen, and the system includes a computer subsystem configured to detect high aspect ratio or material contrast defects on the specimen based on the output generated by the first detector. In another example, collecting only elastically backscattered electrons (e.g., within an energy band of Em-100 eV, where Em is the maximum emitted electron energy from the specimen, which is typically equal to the incident energy of the primary electrons) can enhance high aspect ratio (HAR) contrast or material contrast defects. Using the detector assembly embodiments described herein in an electron beam wafer defect inspection system, such as the eSL10™ available from KLA Corp., Milpitas, Calif., can help capture HAR defects (e.g., deep hole and trench defects), which are unique defects that are difficult to capture. In addition, the detector assembly embodiments described herein can capture many different types of buried defects (punch-through to air spacers, deteriorated tungsten seams in replacement metal gates (RMGs), residues between nanosheets, punch-through vias, spacer nitride cracks beside bitlines, etc.) The computer subsystem of this embodiment may be further configured as described herein.

[0058] The HAR defects can be defects in 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 in a semiconductor device) is a type of non-volatile flash memory that includes a vertical stacking of multiple layers of memory cells. For example, a 3D NAND structure generally includes a silicon bit cell gate formed on a wafer and 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 the silicon. This vertical stacking of memory cells gives 3D NAND structures their 3D quality.

[0059] The 3D structures described herein may also include any other HAR structures known in the art. As used herein, "HAR structure" refers to any structure characterized by an aspect ratio that exceeds 10:1 and may 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, for example, 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 may be used for other HAR structures whose defects are of concern.

[0060] In an additional embodiment, the energy band between the first and second predetermined energies corresponds to energies of only inelastically backscattered charged particles from the sample, and the system includes a computer subsystem configured to detect buried defects 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) may enhance the contrast of buried defects (i.e., defects located entirely below the top surface of the sample). The computer subsystem of this embodiment may be further configured as described herein.

[0061] One novel and advantageous feature of the embodiments described herein is that the energy band cavities may be cascaded (or arranged in series), which allows for the selection of multiple energy bands at one time that may be separated and detected to generate different outputs or images. In some embodiments, the system includes a third repelling mesh configured to repel charged particles passing through the second repelling mesh and having an energy lower than a third predetermined energy, a second attracting mesh configured to attract charged particles passing through the second repelling mesh and being repelled by the third repelling mesh and having an energy higher than the 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.

[0062] FIG. 17 illustrates an embodiment in which multiple square energy band cavities are arranged in series. As shown in FIG. 17, signal electrons 1700 from a sample (not shown in FIG. 17) may pass through a deflector 1702, a focusing lens mesh 1704 surrounded by a ground electrode 1706, and a differential potential electrode 1708, each configured as further described herein. A first energy band cavity of the 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 may be configured as further described herein. The system includes a first detector 1718, which may also be configured as further described herein.

[0063] The system also includes a third repelling mesh 1720 configured to repel charged particles passing through the second repelling mesh 1712 and having an energy lower than a third predetermined energy. The third repelling mesh has an applied voltage, V3. The second attracting mesh 1722 is configured to attract charged particles passing through the second repelling mesh 1712 and being repelled by the third repelling mesh 1720 and having an energy higher than the second predetermined energy, E2, and lower than a third predetermined energy, E3. The second attracting mesh has an applied voltage of V2+ΔV2. The second detector 1724 is configured to generate an output in response to the charged particles passing through the second attracting mesh 1722. The system also includes a second electrode block 1726, which in combination with the second repelling mesh 1712, the third repelling mesh 1720, and the second attracting 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 repelling mesh 1720. Each of these elements may also be further configured as described herein.

[0064] 17 can thus include two energy bands (i.e., energies between E1 and E2, and between E2 and E3), and one high pass band (i.e., energies greater than E3), all selectable by the user or as further described herein. In this manner, the embodiments described herein can add more energy band cavities as physical space within the tool allows.

[0065] Another such embodiment is shown in FIG. 18. In this embodiment, a series of triangular energy band cavities are cascaded such that two or more energy bands of electrons may be separately detected by a detector assembly. As shown in FIG. 18, signal electrons 1800 from a sample (not shown in FIG. 18) may 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. A first energy band cavity of the system is formed by a first repulsive mesh 1810, a second repulsive mesh 1812, and a first attractive mesh 1814, all of which may be configured as further described herein. The system includes a first detector 1816, which may also be configured as further described herein.

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

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

[0068] In an additional embodiment, the system includes a fifth repelling mesh configured to repel charged particles passing through the fourth repelling mesh and having an energy lower than a fifth predetermined energy, a fourth attraction mesh configured to attract charged particles passing through the fourth repelling mesh and being repelled by the fifth repelling mesh and having an energy higher than the 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 attraction mesh. For example, as shown in FIG. 18, the system may include a fifth repelling mesh 1830 configured to repel charged particles passing through the fourth repelling mesh 1824 and having an energy lower than a fifth predetermined energy, E5. The fifth repelling mesh has an applied voltage, V5. The fourth attraction mesh 1832 is configured to attract charged particles that pass through the fourth repulsion mesh 1824 and are repelled by the fifth repulsion mesh 1830 and have an energy greater than a fourth predetermined energy, E4, and less than a fifth predetermined energy, E5. The fourth attraction mesh has an applied voltage of V4+ΔV4. The fourth detector 1834 is configured to generate an output in response to the charged particles passing through the fourth attraction 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 the charged particles passing through the fifth repelling mesh. For example, as shown in FIG. 18, a fifth detector 1836 is configured to generate an output in response to the charged particles passing through the fifth repelling mesh 1830. This detector may also be further configured as described herein.

[0070] Thus, the system can include four energy bands (i.e., energies between E1 and E2, between E2 and E3, between E3 and E4, and between E4 and E5) and one high pass band (i.e., energies greater than E5), all selectable by the user or as further described herein. In this manner, the embodiments described herein can add more energy band cavities as physical space within the tool allows.

[0071] FIG. 19 shows the overall collected spectrum for the above-mentioned detector assembly including five detectors. In other words, this graph shows an example of the overall collected spectrum for a system using both band-pass filtering and high-pass filtering. As shown in FIG. 19, some electrons with energy between 0 and E1 are "lost", meaning that the detector assembly described herein filters out these electrons by the first repulsive mesh and they are not detected. Electrons with energy between E1 and E2 are detected by detector 1 because they are not repelled by the first repulsive mesh, are repelled by the second repulsive mesh, and are attracted by the first attractive mesh located just before the first detector. Electrons with energy between E2 and E3 are detected by detector 2 because they are not repelled by the first or second repulsive mesh, are repelled by the third repulsive mesh, and are attracted by the second attractive mesh located just before the second detector. Electrons with energies between E3 and E4 are detected by detector 3 because they are not repelled by the first, second, and third repulsive meshes, but are repelled by the fourth repulsive mesh, and are attracted by the third attractive mesh located just before the third detector. Electrons with energies between E4 and E5 are detected by detector 4 because they are not repelled by the first, second, third, or fourth repulsive meshes, but are repelled by the fifth repulsive mesh, and are attracted by the fourth attractive mesh located just before the fourth detector. Electrons with energies between E5 and Em are detected by detector 5 because they are not repelled by the first, second, third, fourth, or fifth repulsive meshes, and therefore can be detected by the fifth detector.

[0072] FIG. 20 illustrates 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) pass through a deflector 2002, which may be configured as further described herein. After passing through the deflector 2002, the signal electrons 2000 may pass through a focusing lens mesh 2004 positioned between ground electrodes 2006. The focusing lens mesh and the ground electrodes may be configured as described herein. After passing through the focusing lens mesh, the signal electrons may be directed to a first repelling mesh 100. The first repelling mesh 100, the second repelling mesh 106, and the first attracting mesh 112 may form a triangular energy band cavity, which may be further configured as described herein. This embodiment of the system may also include an electrode block 214, a first detector 210, and a second detector 212, which may be configured as further described herein.

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

[0074] In some embodiments, the system includes a computer subsystem configured to systematically vary the potentials applied to the first repulsive mesh, the second repulsive mesh, and the first attractive mesh, thereby systematically varying the first and second predetermined energies, compare the output generated by the first detector to at least two of the systematically varied potentials, and select the potentials applied to the first repulsive mesh, the second repulsive mesh, and the first attractive mesh for a process performed on the sample based on the results of the comparison of the outputs. Figure 22 illustrates one embodiment of a method for dynamically searching for an optimal energy band to achieve the highest contrast for any particular defect. One advantage of the embodiments described herein is that they provide the ability to automatically search for an optimal energy band for the highest defect contrast.

[0075] As shown in step 2200 of FIG. 22, the computer subsystem may choose an energy band width dE (e.g., dE=200 eV). The computer subsystem may then relate the potential difference between the three meshes of the energy band cavity (e.g., V2=V1-dE / e, ΔV=0) as shown in step 2202 of FIG. 22. As shown in step 2204, the computer subsystem may set V1=-Un×dE and start n from 0. As shown in step 2206, the computer subsystem may generate and store an image from detector 1. As shown in step 2208, the computer subsystem may 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 may set n=n+1 and repeat steps 2204, 2206, and 2208. If V1 is less than -(U+Em-dE) / e, then the computer subsystem may generate and store an image from detector 2, as shown in step 2212. As shown in step 2214, the computer subsystem may compare all stored images to find the one with the highest defect contrast and then determine the optimal energy band.

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

[0077] 23 illustrates one embodiment of a tool in which the detector assembly embodiments described herein may be used, where the energy directed to the sample includes electrons and the energy detected from the sample includes electrons. As shown in FIG. 23, the tool includes an electron column 2300 and a computer subsystem 2302. The computer subsystem 2302 may be configured as further described herein.

[0078] 23, the electron column includes an electron beam source 2304 configured to generate electrons that are focused by one or more elements 2308 onto the sample 2306. The electron beam source may include, for example, a cathode source or emitter tip, and the one or more elements 2308 may 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 may include any such suitable elements known in the art.

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

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

[0081] Although the electron column shown in Figure 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, the electron beam may be directed at and scattered from the sample at any suitable angle. In addition, the electron beam tool may be configured to generate output using multiple modes (e.g., different illumination angles, collection angles, etc.) relative to the sample. The multiple modes of the electron beam tool may differ in any output generation parameter of the tool.

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

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

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

[0085] Where a system includes two or more computer subsystems (not shown), the different computer subsystems may be coupled to each other such that images, data, information, instructions, etc. may be passed between the computer subsystems. The multiple computer subsystems may be coupled to each other by any suitable transmission medium, which may include any suitable wired and / or wireless transmission medium known in the art. Two or more such computer subsystems may also be effectively coupled by a shared computer-readable storage medium (not shown).

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

[0087] Although the tool is 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 mentioned above, the computer subsystem may use the output generated by the detector to detect defects on the specimen. In this manner, the system described herein may be configured as an inspection system. In some embodiments, the system includes a computer subsystem configured to review defects detected on the specimen by a different system based on the output generated by the first detector. In further embodiments, the system includes a computer subsystem configured to determine overlay information for the specimen based on the output generated by the 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 the specimen based on the output generated by the first detector. For example, the system described herein may be configured as a metrology or defect review system. In particular, the embodiment of the system described herein and shown in FIG. 23 may be modified in one or more parameters to provide different imaging capabilities depending on the application for which it is to be used. In one such example, the electron column shown in FIG. 23 may be configured to have a higher resolution when it is used for metrology rather than inspection. In other words, the system embodiments shown in FIG. 23 illustrate several general and various configurations for a system that can be adapted in several ways that will be apparent to one of ordinary skill in the art to create systems having different imaging capabilities more or less suitable for different applications.

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

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

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

[0092] The computer subsystem is also not limited to using output from only the first and second detectors to determine information, but may use 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 output generated by the first and second detectors may be particularly useful for determining a first piece of information for the sample, and the output generated by the first and third detectors may be particularly useful for determining a second piece of information for the sample.

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

[0094] In one such embodiment, the computer subsystem is configured to determine information for the sample by generating an image for defects on the sample from the output generated by the first detector and the output generated by the second detector. For example, the outputs from the different detectors can be used separately to determine information for the sample as well as to generate a new output for the sample that is then used to determine information. In one such example, a comparison or algebraic operation (e.g., addition, subtraction, averaging, etc.) of two images from the two detectors can enhance the contrast of the defects in the resulting image. Thus, the two images can be used to generate a new third image with better contrast for the defects, and the computer subsystem can use the third image to detect the defects or determine information for 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] The computer subsystem may be configured to store results of any steps performed by the system in any suitable computer readable storage medium. The results may be stored in any manner known in the art. The storage medium may include any storage medium described herein or any other suitable storage medium known in the art. After the results are stored, they may be accessed in the storage medium and used by any of the method or system embodiments described herein, formatted for display to a user, used by another software module, method, or system, etc. For example, if the system is configured as an inspection tool, the system may perform an inspection process on the specimen and produce results for any defects detected on the specimen, such as information of a bounding box of the detected defect, e.g., location or otherwise, information about the defect classification, such as a detection score, a class label or ID, or otherwise, or any such suitable information known in the art. The results for the defects may be generated by the computer subsystem in any suitable manner. The results for the defects may have any suitable form or format, such as a standard file type. The computer subsystem may generate results and store the results so that the results may 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 may be used in a variety of ways by the embodiments and / or systems and methods described herein. Such functions include, but are not limited to, modifying a process, such as a fabrication process or step, that has been or will be performed on a sample or another sample in a feedback or feedforward manner. For example, the computer subsystem described herein may be configured to determine one or more modifications to a process performed on an inspected sample and / or to a process to be performed on a sample based on a detected defect. The modifications to a process may include any suitable modifications to one or more parameters of the process. The computer subsystem described herein preferably determines modifications such that defects may be reduced or prevented on other samples to which the modified process is performed, such that defects on the sample may be corrected or removed in another process performed on the sample, such that defects may be compensated for in another process performed on the sample, etc. The computer subsystem described herein may determine these modifications in any suitable manner known in the art. Such modifications may also be determined using results of other processes described herein.

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

[0098] Each of the system embodiments may be further configured according to 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 in a path of the charged particles from the sample, as shown in step 2400 of Fig. 24. The method also includes repelling charged particles passing through the first repelling mesh and having an energy lower than a second predetermined energy by a second repelling mesh, as shown in step 2402 of Fig. 24. In addition, the method includes attracting charged particles passing through the first repelling mesh and being repelled by the second repelling mesh, having an energy higher than the first predetermined energy and lower than a second predetermined energy by a first attracting mesh, as shown in step 2404 of Fig. 24. The method further includes generating an output by a first detector in response to the charged particles passing through the first attracting mesh, 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 may 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 having stored thereon program instructions executable on a computer system to perform a computer implemented method of detecting charged particles from a sample. One such embodiment is shown in Figure 25. In particular, as shown in Figure 25, a 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 implementing methods such as those described herein may be stored on a computer-readable medium 2500. The computer-readable medium may 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 may be implemented in any of a variety of forms, including procedure-based techniques, component-based techniques, and / or object-oriented techniques, among others. For example, the program instructions may be implemented using ActiveX controls, C++ objects, JavaBeans, Microsoft Foundation Classes ("MFC"), SSE (Streaming SIMD Extensions), or any other desired technology or methodology.

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

[0104] Further modifications and alternative embodiments of various aspects of the invention will be apparent to those skilled in the art in view of this specification. For example, a method and system for detecting charged particles from a sample is provided. This description should therefore be interpreted as illustrative only and is intended to teach those skilled in the art the general manner of carrying out the invention. It should be understood that the forms of the invention shown and described herein should be interpreted as presently preferred embodiments. Elements and materials can be substituted, parts and processes can be reversed, and certain features of the invention can be utilized independently, as would all be apparent to those skilled in the art after having the benefit of this description of the invention. Changes can be made in the elements described herein without departing from the spirit and scope of the invention as set forth in the appended claims.

Claims

1. 1. A system configured to detect charged particles from a sample, comprising: a first repelling mesh positioned in a path of the charged particles from the sample and configured to repel the charged particles having energies below a first predetermined energy; a second repelling mesh configured to repel the charged particles that pass through the first repelling mesh and have an energy lower than a second predetermined energy; a first attraction mesh configured to attract the charged particles that pass through the first repulsion mesh and are repelled by the second repulsion mesh and have 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 attraction mesh; a computer subsystem configured to systematically vary potentials applied to the first repulsive mesh, the second repulsive mesh, and the first attractive mesh, thereby systematically varying the first and second predetermined energies, compare the output generated by the first detector to at least two of the systematically varied potentials, and select, based on a result of the comparison of the outputs, the potentials to be applied to the first repulsive mesh, the second repulsive mesh, and the first attractive mesh for a process to be performed on the sample; A system comprising:

2. 2. The system of claim 1, wherein the first repulsive mesh, the second repulsive mesh, and the first attractive mesh form a triangular energy band cavity.

3. 2. The system of claim 1, wherein the first repulsive mesh, the second repulsive mesh, and the first attractive mesh form at least a portion of a square energy band cavity.

4. 2. The system of claim 1, wherein 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 electrical potential.

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

6. 2. The system of claim 1, wherein the first detector is grounded.

7. 10. The system of claim 1, wherein the first detector is biased with a positive voltage.

8. 10. The system of claim 1, wherein the first detector is biased with an adjustable voltage.

9. 2. The system of claim 1, wherein the first detector is biased at a voltage and the first attractive mesh shields the spaces between the first repulsive mesh, the second repulsive mesh, and the first attractive mesh from an electric field from the detector.

10. 2. The system of claim 1, further comprising a deflector configured to change a position of the path of the charged particle from the sample before the charged particle reaches the first repelling mesh.

11. 11. The system of 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 repelling mesh.

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

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

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

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

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

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

18. 2. The system of 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. 2. The system of claim 1, wherein an energy band between the first and second predetermined energies corresponds to energies of only secondary charged particles from the specimen, and the computer subsystem is further configured to detect surface or voltage contrast defects on the specimen based on the output generated by the first detector.

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

21. 2. The system of claim 1, wherein an energy band between the first and second predetermined energies corresponds to energies 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. 22. The system of claim 21, further comprising: a third repulsive mesh configured to repel the charged particles that pass through the second repulsive mesh and have an energy lower than a third predetermined energy; a second attractive mesh configured to attract the charged particles that pass through the second repulsive mesh, are repelled by the third repulsive mesh, and have an energy higher than the 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 attractive mesh.

23. 23. The system of claim 22, further comprising: a fourth repulsive mesh configured to repel the charged particles that pass through the third repulsive mesh and have an energy lower than a fourth predetermined energy; a third attraction mesh configured to attract the charged particles that pass through the third repulsive mesh, are repelled by the fourth repulsive mesh, and have an energy higher than the 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 attraction mesh.

24. 24. The system of claim 23, further comprising: a fifth repulsive mesh configured to repel the charged particles that pass through the fourth repulsive mesh and have an energy lower than a fifth predetermined energy; a fourth attractive mesh configured to attract the charged particles that pass through the fourth repulsive mesh, are repelled by the fifth repulsive mesh, and have an energy higher than the 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 attractive mesh.

25. 25. The system of claim 24, further comprising a fifth detector configured to generate an output in response to the charged particle passing through the fifth repelling mesh.

26. 10. The system of claim 1, wherein the computer subsystem is further configured to detect defects on the specimen based on the output generated by the first detector.

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

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

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

30. 2. The system of claim 1, further comprising a second detector configured to generate an output in response to the charged particles passing through the second repelling mesh, and 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. 31. The system of claim 30, wherein the computer subsystem is further configured to determine the information for the specimen by generating an image for a defect on the specimen from the output generated by the first detector and the output generated by the second detector.

32. 2. The system of claim 1, wherein the charged particles are electrons.

33. 2. The system of claim 1, wherein the charged particles are helium ions.

34. 1. A system configured to detect charged particles from a sample, comprising: a first repelling mesh positioned in a path of the charged particles from the sample and configured to repel the charged particles having energies below a first predetermined energy; a second repelling mesh configured to repel the charged particles that pass through the first repelling mesh and have an energy lower than a second predetermined energy; a first attraction mesh configured to attract the charged particles passing through the first repulsion mesh and being repelled by the second repulsion mesh, the charged particles having an energy higher than the first predetermined energy and lower than the second predetermined energy, wherein an energy band between the first and second predetermined energies corresponds to the energy of only elastically backscattered charged particles from the sample; a first detector configured to generate an output in response to the charged particles passing through the first attraction mesh; a computer subsystem configured to detect high aspect ratio or material contrast defects on the specimen based on the output produced by the first detector; and A system comprising:

35. 1. A system configured to detect charged particles from a sample, comprising: a first repelling mesh positioned in a path of the charged particles from the sample and configured to repel the charged particles having energies below a first predetermined energy; a second repelling mesh configured to repel the charged particles that pass through the first repelling mesh and have an energy lower than a second predetermined energy; a first attraction mesh configured to attract the charged particles passing through the first repulsion mesh and being repelled by the second repulsion mesh, the charged particles having energies higher than the first predetermined energy and lower than the second predetermined energy, wherein an energy band between the first and second predetermined energies corresponds to the energies of only inelastically backscattered charged particles from the sample; a first detector configured to generate an output in response to the charged particles passing through the first attraction mesh; a computer subsystem configured to detect buried defects on the specimen based on the output generated by the first detector; and A system comprising:

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