Electron beam system and method for operating an electron beam system

Abstract

For an electron beam system, a Wien filter is located in the electron beam path between a transfer lens and a stage. The system includes a ground electrode between the Wien filter and the stage; a charge control plate between the ground electrode and the stage; and an accelerating electrode between the ground electrode and the charge control plate. The system can be magnetic or electrostatic.

Description

[Technical Field]

[0001] This invention relates to an electron beam system. [Previous Technology]

[0002] The development of the semiconductor manufacturing industry places higher demands on yield management, especially on metrology and inspection systems. As critical dimensions continue to shrink, the industry needs to reduce the time required to achieve high-yield, high-value production. Minimizing the total time from detecting a yield problem to resolving it determines a semiconductor manufacturer's return on investment.

[0003] Manufacturing semiconductor devices, such as logic and memory devices, typically involves processing a semiconductor wafer using numerous manufacturing processes to form various features and multiple levels of the semiconductor device. For example, lithography is a semiconductor manufacturing process involving transferring a pattern from a photomask to a photoresist disposed on a semiconductor wafer. Additional examples of semiconductor manufacturing processes include, but are not limited to, chemical mechanical polishing (CMP), etching, deposition, and ion implantation. One configuration of multiple semiconductor devices manufactured on a single semiconductor wafer can be divided into individual semiconductor devices.

[0004] Inspection procedures are used at various stages of semiconductor manufacturing to detect defects on wafers, thereby promoting higher yields and ultimately higher profits. Inspection has always been an important part of manufacturing semiconductor devices such as integrated circuits (ICs). However, as the size of semiconductor devices shrinks, inspection becomes even more critical for successfully manufacturing acceptable semiconductor devices, as even small defects can cause device malfunctions. For example, as the size of semiconductor devices decreases, the detection of defects in this smaller size becomes necessary, because even relatively small defects can cause unwanted aberrations in semiconductor devices.

[0005] However, as design rules shrink, semiconductor manufacturing processes can operate closer to the limits of process performance. Furthermore, as design rules shrink, even smaller defects can affect the electrical parameters of the device, driving more sensitive inspection. With shrinking design rules, the number of potentially yield-related defects detected by inspection increases dramatically, as does the number of harmful defects detected by inspection. Therefore, more defects may be detected on the wafer, and corrective processes to eliminate all defects can be difficult and expensive. Determining which defects actually affect the electrical parameters and yield of the device allows process control methods to focus on those defects while largely ignoring others. Moreover, under smaller design rules, process-induced failures are often systematic in some cases. That is, process-induced failures tend to occur repeatedly in predetermined design patterns throughout the design. Eliminating space-systematic, electrically related defects can impact yield.

[0006] Electron beam systems can be used for inspection. Previously, an electron source (e.g., a thermal or cold field emission source) emitted electrons from the tip of an emitter, and then the electrons were focused into a large-size electron beam by a gun lens (GL). The electron beam carrying a high beam current was collimated by the gun lens into a telecentric beam to illuminate a microaperture array (µAA). The number of apertures in the microaperture array determines the number of small beams. The apertures of the microaperture array can be distributed in a hexagonal shape.

[0007] The beam-limiting aperture (BLA) behind the gun lens is used to select the total beam current of the illumination aperture array, and the micro-aperture array is used to select the beam current of each individual small beam. A microlens array (MLA) is deployed to focus each small beam onto the intermediate image plane (IIP). A microlens (µL) can be a magnetic lens or an electrostatic lens. A magnetic microlens can be multiple magnetic pole pieces excited by coils or powered by permanent magnets. An electrostatic microlens can be an electrostatic single lens (Einzel lens) or an electrostatic accelerating / decelerating single-potential lens.

[0008] To inspect and examine a wafer, secondary electrons (SE) and / or backscattered electrons (BSE) emitted from the wafer, due to the bombardment of primary small beams of electrons, can be split from the optical axis and deflected toward a detection system by a Wien filter.

[0009] The total number of multiple bundles (MB) (MB tot) can be scaled using the following equation 1. (1)

[0010] Mx is the number of all bundles on the x-axis. For example, in five rings of hexagonal bundles, the number of all bundles on the x-axis is Mx = 11, given the total number of bundles MB tot = 91. In 10 rings, Mx = 21 and MB tot = 331.

[0011] The throughput of multi-beam equipment used for wafer inspection and viewing tends to be limited by the number of beams (MB tot). The resolution of each beam can be controlled by beam crossing (xo) in the projection optics, because the strong Coulomb interactions between high-density electrons around the crossing region inevitably produce optical blurring. The more beams there are (i.e., the higher the total beam current), the worse the resolution of each beam will be. This reflects the influence of Coulomb interactions between electrons on the resolution of a multi-beam system. Therefore, the resolution of a multi-beam system can be limited by the projection optics from the intermediate image plane to the wafer.

[0012] The throughput characteristic of a multi-electron beam device lies in the number of sub-beams or the total number of electron sub-beams. The greater the number of sub-beams, the higher the throughput. However, the increased number of sub-beams can be limited by the resolution of the sub-beams. Generally, the more sub-beams (or the higher the total beam current) in a multi-electron beam device, the worse the resolution of each sub-beam. All sub-beams (or all electrons of the total beam current) can optically meet to form a beam "cross", in which strong Coulomb interactions occur between electrons and degrade the resolution of the sub-beams. The cross (xo) is the point where the sub-beam currents meet, which leads to Coulomb interactions between electrons. Physically, there is a statistical deflection of electrons, given by the following Equation 2. (2)

[0013] Δαxo is the statistical deflection angle in the cross plane, BC is the total beam current, BExo is the beam energy around the cross, and θ is the cross angle. The statistical deflection at the wafer, attributed to the Coulomb interaction between electrons, optically produces a beam blur ΔSS, which can be provided by the following equation 3. (3)

[0014] The focal length (or image distance) in the image side (wafer side) of the f-series objective lens.

[0015] Improved systems and technologies are needed to address these shortcomings and limitations. [Summary of the Invention]

[0016] A system is provided in a first embodiment. A transfer lens is disposed in a path of an electron beam downstream of an intermediate image plane. A stage is disposed in the path of the electron beam. The stage is configured to hold a wafer. A Wien filter is disposed in the path of the electron beam between the transfer lens and the stage. A ground electrode is disposed in the path of the electron beam between the Wien filter and the stage. A charge control board is disposed in the path of the electron beam between the ground electrode and the stage. An accelerating electrode is disposed in the path of the electron beam between the ground electrode and the charge control board.

[0017] The system may further include an objective lens positioned downstream of the transfer lens in the path of the electron beam. The objective lens includes an upper electrode closer to the transfer lens and a lower electrode closer to the stage. The upper electrode defines a first aperture through which the electron beam is guided. The second electrode defines a second aperture through which the electron beam is guided. A charge control plate is disposed in the second aperture. A ground electrode is disposed in the first aperture. In this example, the objective lens may be a magnetic objective lens.

[0018] The objective lens can also be an electrostatic objective lens.

[0019] The accelerating electrode can be separated from the grounding electrode by a first distance and from the charge control board by a second distance. The first distance can be from 15 mm to 20 mm, and the second distance can be from about 20 mm to 25 mm.

[0020] The accelerating electrode may have a thickness of 12 mm to 16 mm in one direction of the electron beam path.

[0021] The accelerating electrode may define an opening through which the electron beam passes. The opening may have a diameter ranging from 15 mm to 25 mm.

[0022] The system may further include a hexagonal detector array.

[0023] A method is provided in a second embodiment. The method includes generating an electron beam. The electron beam is guided through a transfer lens positioned downstream of an intermediate image plane, a Wien filter positioned downstream of the transfer lens, a ground electrode positioned downstream of the Wien filter, an accelerating electrode positioned downstream of the ground electrode, and a charge control plate positioned downstream of the accelerating electrode. The electron beam is guided to a wafer on a stage positioned downstream of the charge control plate.

[0024] The method may further include guiding the electron beam through an objective lens positioned downstream of the transfer lens. The objective lens includes an upper electrode closer to the transfer lens and a lower electrode closer to the stage. The upper electrode defines a first aperture through which the electron beam is guided. A second electrode defines a second aperture through which the electron beam is guided. The charge control plate may be disposed in the second aperture, and the ground electrode may be disposed in the first aperture.

[0025] The objective lens can be configured to focus the electron beam onto the wafer.

[0026] The electron beam can be guided to cross one of a second electron beams. The crossing can be arranged at a distance from one of the image distances of the objective lens.

[0027] The method may further include selecting one of the principal planes of the objective lens at a position relative to the wafer to increase resolution.

[0028] An accelerating voltage applied to one of the accelerating electrodes can be configured to increase the energy of one beam around a cross.

[0029] The method may further include selecting a cross beam energy for the electron beam, the cross beam energy being configured to reduce Coulomb interaction effects.

Implementation Method

[0031] Although the claimed subject matter will be described with reference to specific embodiments, other embodiments, including those that do not provide all the benefits and features set forth herein, are also within the scope of the invention. Various structural, logical, procedural, and electronic changes may be made without departing from the scope of the invention. Therefore, the scope of the invention is defined only by reference to the appended claims.

[0032] Electron beams can be used for wafer inspection and examination, such as for inspecting completed or incomplete integrated circuit components at the nano-critical dimension (CD) level. The throughput of a single electron beam device is quite low, therefore multi-electron beam systems can be used to increase throughput. Since crossover reduces resolution, improved multi-beam resolution (e.g., reducing statistical ambiguity ΔSS) can be achieved by increasing the beam energy (BE xo) around the crossover and narrowing the objective-to-wafer image distance (f), while keeping the total beam current and crossover angle θ constant. The crossover angle θ reflects the distribution of small beams and the distance between them.

[0033] Figure 1 shows a first embodiment of a system 100. An electron source generates an electron beam 101. Although a single electron beam 101 is shown, more than one electron beam may pass through the system 100. In the case of multiple electron beams, there may be an intersection between the intermediate image plane 102 and the stage 111, for example, between the Wien filter 104 and the objective lens 112 or within the objective lens 112. The objective lens 112 is designed as an accelerating objective lens by means of an accelerating electrode 109 comprising an accelerating electrode 109 between a ground electrode 110 and a charge control plate 108. The accelerating electrode 109 can be used as a focusing electrode. An accelerating voltage (Va) is applied to the accelerating electrode 109 to increase the beam energy (BE) around the beam intersection and to position the objective lens 112 optically closer to the wafer 107 (i.e., narrowing the image distance f of the objective lens 112).

[0034] The system 100 includes a transfer lens 103 in one path of an electron beam 101 downstream of an intermediate image plane 102. An electron beam source is positioned upstream of the intermediate image plane 102. A stage 111 is configured to hold a wafer 107 in one path of the electron beam 101.

[0035] The transfer lens 103 may be an electrostatic lens or a magnetic lens. The transfer lens 103 is used to focus multiple beams to form a cross around the accelerating electrode in FIG1. ​​Compared with an electrostatic transfer lens 103, a magnetic transfer lens 103 can provide improved results in reducing off-axis optical blur in multi-beam projection optics, but any type of transfer lens may be used in system 100.

[0036] A Wien filter 104 is positioned in the path of the electron beam 101 between the transfer lens 103 and the stage 111. In one example, the Wien filter 104 is an EXB Wien filter (i.e., the electrostatic deflection field is perpendicular to the magnetic deflection field). To form a uniform deflection field for large-sized multiple beams over a large area, both the electrostatic and magnetic deflection fields can be generated using an octet deflector. The inner diameter and height of the octet can be approximately 48 mm to 80 mm. The Wien filter strength (voltage and current) can be selected to deflect the secondary electrons by approximately 10 to 20 degrees.

[0037] A detector (not shown) may be positioned upstream of the Wien filter 104 along the path of the electron beam 101. For example, the detector may be positioned between the Wien filter 104 and the transfer lens 103. The detector may also be positioned upstream of the transfer lens along the path of the electron beam 101.

[0038] A ground electrode 110 is positioned in the path of the electron beam 101 between the Wien filter 104 and the stage 111. The ground electrode 110 may serve as a holder for other components (e.g., electrodes or the Wien filter 104). The ground electrode 110 may also be used as a reference for aligning other components. Optically, the ground electrode 110 may serve as a boundary for the electrostatic field.

[0039] A charge control plate (CCP) 108 is disposed in the path of the electron beam 101 between the ground electrode 110 and the stage 111. The charge control plate 108 may be a thin conductive plate. In one example, the thickness of the charge control plate 108 is about 1 mm, wherein an aperture is about 1 mm to 5 mm. The charge control plate 108 may form an electro-extraction field at the surface of the wafer 107. For example, the field may range from 0 V / mm to 2000 V / mm.

[0040] An accelerating electrode 109 is placed in the path of the electron beam 101 between the ground electrode 110 and the charge control plate 108.

[0041] In the example of Figure 1, objective lens 112 is a magnetic objective lens. System 100 may also include objective lens 112, which is positioned in the path of electron beam 101 downstream of transfer lens 103. Objective lens 112 includes an upper electrode 105 closer to transfer lens 103 and a lower electrode 106 closer to stage 111. Upper electrode 105 defines a first aperture 113 through which electron beam 101 is guided. Second electrode 106 defines a second aperture 114 through which electron beam 101 is guided.

[0042] The objective lens 112 may include a magnetic section and an electrostatic section. The magnetic section includes an upper electrode 105 and a lower electrode 106. The upper electrode 105 and the lower electrode 106 may be sealed or may use, for example, a charge control plate 108 and a ground electrode 110 to provide reduced airflow.

[0043] As shown in Figure 1, the charge control plate 108 is disposed in the second hole 114. The ground electrode 110 is disposed in the first hole 113. In one example, the charge control plate 108 is in contact with the lower electrode 106 and the ground electrode 110 is in contact with the upper electrode 105.

[0044] Figure 2 shows the simulated beam size. Accelerating voltages Va of 0, 25, 50, and 100 kV were applied in the simulation. For each accelerating voltage Va, the magnetic excitation (coil current) of the objective lens was used to focus the beam onto the wafer. A cross (xo) was positioned around the accelerating electrode (Va) to increase the beam energy around the cross to (BE + Va), where BE is the beam energy in the column before electron acceleration.

[0045] Under the same total beam current in Figure 2, the spot size decreases with increasing accelerating voltage, reflecting the application of equations 2 and 3. According to Figure 2, the small beam resolution improves with increasing accelerating voltage Va.

[0046] Using the magnetic accelerator objective 112 in Figure 1, the larger the accelerating voltage Va, the smaller the magnetic excitation used, or the shorter the image distance f of the combined electrostatic / magnetic lens can be moved closer to the wafer 107. According to equations 2 and 3, a smaller Coulomb interaction blur ΔSS will appear, and an improved result can be achieved.

[0047] Figure 3 shows a second embodiment of system 150. Objective lens 151 is an electrostatic objective lens. In a particular example, system 150 can provide better small-beam resolution than system 100.

[0048] Referring to Figures 2 and 5, when Va < 50 kV, the magnetic system provides improved results for medium resolution, and when Va > 50 kV, the electrostatic system provides improved results for high resolution. In Figure 1, if Va is too high (e.g., Va > 50 kV), arcing can occur around the electrodes. Crossings typically occur around Va electrodes, and the resolution of each small beam is mainly degraded by Coulomb interactions around the crossings. Increasing Va can improve resolution. In Figures 2 and 5, the portion of the spot size that increases with beam current is mainly attributed to Coulomb interactions. Without Coulomb interactions, Figures 2 and 5 would be flat within the beam current range. Therefore, the position of one of the principal planes of the objective relative to one of the wafers can be selected to improve resolution. Va can be selected to increase the beam energy around a crossing.

[0049] Referring back to Figure 3, the accelerating electrode 109 is separated from the ground electrode 110 by a distance g1 in one direction of the electron beam 101 path. The accelerating electrode 109 is separated from the charge control plate 108 by a distance g2 in one direction of the electron beam 101 path. The accelerating electrode 109 has a thickness t in one direction of the electron beam 101 path. The accelerating electrode 109 also defines an opening 152 through which the electron beam 101 passes. The opening 152 has a diameter d. The distances g1 and g2, the diameter d, and the thickness t can be configured to avoid arcing.

[0050] Removing the magnetic accelerator objective 112 simplifies the design. The system 150 can be combined with an electron acceleration function for high BE xo and a focusing function for imaging the electron beam 101 on the wafer 107. Using an electrostatic objective, the wafer can be charged using a charge control plate, allowing electrons to land on the wafer 107 with the required energy, and the principal plane of the lens can be moved closer to the wafer 107, which provides a relatively short image distance (or focal length) f.

[0051] For the demonstration system 150, a computer simulation using electron ray tracing is used to display the projection optics from IIP 102 to wafer 107 in Figure 4. The simulated optical conditions are 30 keV beam energy, 1 keV landing energy, a 1.5 kV / mm extraction field charged by CCP voltage, and an acceleration voltage Va of approximately 100 kV used to accelerate and focus the small beam on wafer 107.

[0052] The optical reduction of the multi-beam image formed by electron beam tracing in Figure 4 is approximately 8X. In this case, the off-axis performance of the multi-beams (coherence aberration, field curvature, astigmatism, distortion, and shifted chromatic aberration) is minimized. If the field of view (FOV) of the microaperture array and the microlens array is Do = 2000 µm, then the multi-beam FOV at the wafer will be Di = 250 µm. The 2000 µm Do allows for the integration of hundreds of microlenses to split into hundreds of small beams. The 250 µm Di allows for the collection of secondary electron beams from the wafer to the detector, while controlling crosstalk between the secondary electron beams.

[0053] Figure 4 further illustrates the cross (xo) around the accelerating electrode, which provides high cross beam energy (BE xo = BE + Va). Pushing the cross closer to the wafer provides a fairly short image distance f. The cross beam energy can be selected to reduce Coulomb interaction effects.

[0054] Although it has been shown relative to FIG3, a similar cross as illustrated in FIG4 may appear in the embodiment of FIG1.

[0055] Figure 5 shows the primary electron beam resolution performance of system 150. Compared with the previous design, the multi-beam projection optics with a purely electrostatic objective lens in Figure 4 improves the resolution.

[0056] Figure 6 illustrates a simulation of secondary electron (SE) beam tracing from the wafer to the first image plane. Due to the primary electron beam bombarding the wafer, secondary electrons from the array of primary electron bombardments form an image via the electrostatic accelerating objective shown in Figure 3. The optical magnification from the wafer to the first image plane in Figure 6 can range from approximately 3X to 5X, depending on the landing energy.

[0057] Most or all of the secondary electron beams are deflected by a Wien filter and guided to the detector (e.g., about 70-80%). A primary electron projection optics may be present between the Wien filter and the detector to image objects in the first image plane onto the detector (i.e., the final secondary electron image plane). This primary electron projection optics may represent functions for adjusting the magnification, rotation, distortion correction, reverse scanning, or other variables of the secondary electron beam array to meet the collection requirements of the detector.

[0058] Some large-angle secondary electrons from a small beam may "crosstalk" with another small beam. One type of secondary electron optics, a spatial filter aperture, can be used to filter out large-angle secondary electrons and reduce or eliminate crosstalk.

[0059] Figure 7 shows one of the hexagonal detector arrays used to collect secondary electron beams. Each individual sub-detector is a hexagonal detector (e.g., a scintillation detector). One sub-detector can collect one secondary electron beam, as shown in Figure 7.

[0060] Using one of the accelerating magnetic objective lens schemes in Figure 1, the resolution of the multi-electron beam can be improved as the accelerating voltage Va increases. The accelerating voltage Va can be increased while avoiding electric arcs and assuming that the electron beam is stably focused on the wafer by magnetic excitation.

[0061] Using one of the accelerating electrostatic objective lens schemes in Figures 3 and 8, the resolution of the multi-electron beam is improved by the accelerating voltage Va that focuses the multi-electron beam onto the wafer. The magnetic section of the objective lens is removed in Figure 3.

[0062] In the absence of commonly used magnetic sections in the objectives of Figures 3 and 8, removing the rotation of the secondary electron beam array simplifies the secondary electron projection optics and may eliminate the need to correct the rotation of the secondary electron beam.

[0063] Figure 8 illustrates an embodiment of the actual construction of one of the accelerating electrostatic objectives in Figure 3. The embodiment of Figure 8 can accommodate and operate high beam energies (e.g., about 20 to 50 keV) and degrade the high beam energies to a specific landing energy (e.g., about 0.1 to 50 keV). The embodiment of Figure 8 can charge the wafer with various extraction fields on the wafer surface via a CCP voltage. The embodiment of Figure 8 can also accelerate all small beams with sufficiently high cross-beam energies via an accelerating voltage Va, and then focus these small beams onto the wafer with a relatively short focal length (or image distance) f. In one example, the accelerating voltage Va can be greater than 75 kV.

[0064] The design in Figure 8 can achieve arc-free operation by selecting and designing appropriate gaps between g1 and g2, thickness t, and diameter d of the accelerating electrodes. For example, g1 > 15 mm, g2 > 20 mm, t > 12 mm, and d > 15 mm.

[0065] In one embodiment, for typical use of beam energies from about 30 kV to 50 kV and landing energies from about 0.1 keV to 30 keV, g1 is from about 15 mm to 20 mm, g2 is from about 20 mm to 25 mm, t is from about 12 mm to 16 mm, and d is from about 15 mm to 25 mm. Depending on the requirements of the optical design (e.g., beam energy, landing energy, extraction field, etc.), the dimensions can be optimized and / or minimized to move the Va electrode as close to the wafer as possible to reduce the image distance f or spot size. This is illustrated using Equation 3.

[0066] The embodiment in Figure 8 can extract secondary electron beams from the wafer under immediate acceleration and focusing, and can make these secondary electron beams form an image on the primary electron image plane for secondary electron collection in the detector array through the primary electron projection optics.

[0067] The grounding electrode, accelerating electrode, and charge control plate can be designed as concave disks to increase the external gap distance in Figure 8. Two insulators between the grounding electrode, accelerating electrode, and charge control plate can connect and align these electrodes. The inner and outer surfaces of the insulators can be designed as curved, wavy, or other shapes to increase the surface distance or reduce the tangential electrical strength between the electrodes. The concave disks of the electrodes can be designed with a smooth curve and high polish to avoid arcing.

[0068] The gap between the charge control plate and the wafer is commonly referred to as the working distance (WD) of an objective lens. The working distance can be variably designed using a z-height stage to accommodate various landing energy applications. Depending on the landing energy used, the working distance can range from approximately 1 mm to 3 mm. Higher landing energy allows for a larger working distance to avoid excessively high focusing voltage Va. At an acceptable focusing voltage Va, the working distance should be as small as possible to reduce spherical aberration and image distance.

[0069] Figure 9 is an embodiment of method 200, which may correspond to the operation of Figure 1 or Figure 3. At 201, an electron beam is generated. At 202, the electron beam is guided through a transfer lens positioned downstream of an intermediate image plane. At 203, the electron beam is guided through a Wien filter positioned downstream of the transfer lens. At 204, the electron beam is guided through a ground electrode positioned downstream of the Wien filter. At 205, the electron beam is guided through an accelerating electrode disposed downstream of the ground electrode. At 206, the electron beam is guided through a charge control plate positioned downstream of the accelerating electrode. At 207, the electron beam is guided to a wafer on a stage positioned downstream of the charge control plate.

[0070] An accelerating voltage applied to one of the accelerating electrodes can be configured to increase the energy of a beam around a cross.

[0071] Method 200 may further include guiding an electron beam through an objective lens positioned downstream of a transfer lens, as shown in Figure 1. The objective lens may include an upper electrode closer to the transfer lens and a lower electrode closer to the stage. The upper electrode may define a first aperture through which the electron beam is guided. A second electrode may define a second aperture through which the electron beam is guided. A charge control plate may be disposed in the second aperture and a ground electrode may be disposed in the first aperture. The objective lens may be configured to focus the electron beam onto the wafer. The electron beam is guided through a crosshair arranged at an image distance from the objective lens.

[0072] Crossing blurring attributable to Coulomb interactions between electrons can affect a multi-electron beam apparatus where all electron beams are split from a single electron source. The blurring of Coulomb interactions may be related to the crossing properties. For example, these crossing properties may include the crossing angle, the crossing beam energy, the total beam current through the crossing, and the crossing position, as illustrated in Equations 2 and 3. The crossing position can be equivalent to the image distance of the objective lens.

[0073] In the accelerating magnetic objective of Figure 1, the blurring caused by Coulomb interactions between electrons can be reduced while increasing the accelerating voltage Va. The accelerating electrostatic objectives of Figures 3 and 8 may include lenses to improve optical performance (e.g., small beam resolution) and enable the formation of images from multiple electron beams. A purely electrostatic accelerating objective can extract secondary electrons and form an image in a first image plane (Figure 6) of a small beam of secondary electrons. Through secondary electron projection optics, the secondary electrons in the first image plane can be projected onto a detector array (Figure 7).

[0074] Although the invention has been described with respect to one or more specific embodiments, it should be understood that other embodiments of the invention may be made without departing from the scope of the invention. Therefore, the invention is considered to be limited only by the appended claims and their reasonable interpretation. [Simplified Explanation of the Diagram]

[0030] To more fully understand the nature and purpose of the present invention, reference should be made to the following detailed description in conjunction with the accompanying drawings, in which: Figure 1 is a first embodiment of a system using a magnetic accelerator objective; Figure 2 is a graph showing the improvement in resolution with accelerating voltage; Figure 3 is a second embodiment of a system using an electrostatic accelerator objective; Figure 4 shows a ray tracing simulation of a multi-beam projection from an IIP to a wafer using the embodiment of Figure 3; Figure 5 is a graph showing the performance using the embodiment of Figure 3; Figure 6 shows ray tracing of a secondary electron beam with image formation relationship from the wafer to a first image plane; Figure 7 is an exemplary hexagonal detector array for collecting secondary electron beams; Figure 8 is a cross-sectional view of an embodiment of an accelerating electrostatic objective in Figure 3; and Figure 9 is an embodiment of a method according to the present invention.

Claims

1. An electron beam system comprising: A transfer lens disposed in a path of an electron beam downstream of an intermediate image plane; a stage disposed in the path of the electron beam, wherein the stage is configured to hold a wafer; a Wien filter disposed in the path of the electron beam between the transfer lens and the stage; a ground electrode disposed in the path of the electron beam between the Wien filter and the stage; and a charge control board disposed in the path of the electron beam between the ground electrode and the stage. An accelerating electrode is disposed in the path of the electron beam between the ground electrode and the charge control plate; and an objective lens is disposed in the path of the electron beam downstream of the transfer lens, wherein the objective lens includes an upper electrode closer to the transfer lens and a lower electrode closer to the stage, wherein the upper electrode defines a first aperture through which the electron beam is guided, and wherein the lower electrode defines a second aperture through which the electron beam is guided; and wherein the electron beam is guided to intersect with a second electron beam, and wherein the intersection is arranged at an image distance from the objective lens.

2. The electron beam system of claim 1, wherein the objective lens is a magnetic objective lens.

3. The electron beam system of claim 1, wherein the objective lens is an electrostatic objective lens.

4. The electron beam system of claim 1, wherein the accelerating electrode is separated from the grounding electrode by a first distance and wherein the accelerating electrode is separated from the charge control board by a second distance, wherein the first distance is from 15 mm to 20 mm and the second distance is from about 20 mm to 25 mm.

5. The electron beam system of claim 1, wherein the accelerating electrode has a thickness of 12 mm to 16 mm in one direction of the path of the electron beam.

6. The electron beam system of claim 1, wherein the accelerating electrode defines an opening through which the electron beam passes, wherein the opening has a diameter of 15 mm to 25 mm.

7. The electron beam system of claim 1, further comprising a hexagonal detector array.

8. A method for operating an electron beam system, comprising: An electron beam is generated; the electron beam is guided through a transfer lens positioned downstream of an intermediate image plane; the electron beam is guided through a Wien filter positioned downstream of the transfer lens; the electron beam is guided through an objective lens positioned downstream of the transfer lens, wherein the objective lens includes an upper electrode closer to the transfer lens and a lower electrode closer to a stage, wherein the upper electrode defines a first aperture through which the electron beam is guided, and wherein the lower electrode defines a second aperture through which the electron beam is guided; the electron beam is guided through a ground electrode positioned downstream of the Wien filter; the electron beam is guided through an accelerating electrode positioned downstream of the ground electrode, wherein the electron beam is guided through an intersection with a second electron beam, and wherein the intersection is arranged at an image distance from the objective lens; the electron beam is guided through a charge control plate positioned downstream of the accelerating electrode; and the electron beam is guided to a wafer on the stage positioned downstream of the charge control plate.

9. The method of claim 8, wherein the charge control plate is disposed in the second hole and wherein the grounding electrode is disposed in the first hole.

10. The method of claim 8, wherein the objective lens is configured to focus the electron beam onto the wafer.

11. The method of claim 8, further comprising selecting one of the principal planes of the objective lens at a position relative to the wafer to increase resolution.

12. The method of claim 8, wherein an accelerating voltage applied to the accelerating electrode is configured to increase the energy of a beam around a cross.

13. The method of claim 8, further comprising selecting a cross beam energy for the electron beam, the cross beam energy being configured to reduce Coulomb interaction effects.

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