Device for performing optical measurements in charged particle devices

Abstract

Charged particle inspection systems can include a shield having an aperture or more than one aperture, for example, to allow additional inspection by additional instrumentation that requires line of sight to the region of interest. Field shaping elements such as window elements or raised edges are placed at the apertures to prevent or reduce components of the electric field.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Application No. 62 / 786,905, filed December 31, 2018, and is incorporated herein by reference in its entirety. Technical Field

[0003] Embodiments provided herein relate to charged particle devices utilizing one or more charged particle beams, such as electron microscopy devices utilizing one or more electron beams. Background Art

[0004] Integrated circuits are manufactured by creating patterns on a wafer (also referred to as a substrate). The wafer is supported on a wafer stage in an apparatus for creating the pattern. One part of the process of manufacturing integrated circuits involves viewing or "inspecting" portions of the wafer and / or wafer stage. This can be done using a scanning electron microscope. Even with a scanning electron microscope, in some cases it is desirable to be able to optically (i.e., based on light) inspect portions of the wafer and / or wafer stage, for example, using an optical microscope.

[0005] However, a scanning electron microscope may have a metal plate slightly above the wafer stage to smooth the electric field around the inspected area in conjunction with a conductive plate or surface mounted on the wafer stage that surrounds and / or covers the wafer below. This shield is also useful in preventing discharges caused by high electric fields around the edges of the above-mentioned conductive areas on the wafer stage. In order to visually inspect and align the wafer and stage using an optical microscope, the optical microscope is positioned above a large metal plate and looks down through a hole in the plate. The holes in the plate disrupt the smoothness of the electric field that the plate is intended to smooth, resulting in undesirable discharges. Summary of the invention

[0006] In order to provide a basic understanding of the embodiments, a simplified overview of one or more embodiments is presented below. This overview is not an extensive overview of all contemplated embodiments, and is not intended to identify key or important elements of all embodiments, nor is it intended to delineate the scope of any or all embodiments. Its sole purpose is to present some concepts of one or more embodiments in a simplified form as a prelude to a more detailed description that will be presented later.

[0007] According to one aspect of an embodiment, an article is disclosed, comprising: a substantially flat plate comprising a conductive material and a structure defining a through aperture; and a field shaping element. The field shaping element may include a window element positioned at the through aperture, the window element being conductive and light transmissive. The window element may include a conductive material that is transmissive to a portion of the spectrum in visible or near-visible light, for example, the wavelength of visible light is in the range of about 300 nm to about 1100 nm. The window element may include a transparent metal oxide, which may be indium tin oxide. The window element may include graphene. The window element may include carbon nanotubes. The window element may include an amorphous material. The window element may include a doped transparent semiconductor. The window element may include a conductive polymer.

[0008] The window element may include a body including a transparent material, and a coating of a conductive material. The coating of the conductive material may include gold. The coating of the conductive material may include aluminum. The coating of the conductive material may include titanium. The coating of the conductive material may include chromium. The coating may have a thickness in the range of about 10 nm to about 10 μm.

[0009] The window element may include a screen configured to be conductive and transmit visible light. The screen may include a mesh. The mesh may include wire. The mesh may be at least 30% open. The screen may be non-woven, such as a mesh, and may be at least 30% open.

[0010] The window element may be positioned in the aperture so as not to extend beyond the surface of the plate, for example so as to be recessed below the surface of the plate. The region of the plate adjacent the aperture may be raised, for example so that the height of the aperture is substantially equal to the width of the aperture. The aperture may be circular, in which case the width of the aperture is the diameter of the aperture.

[0011] The field shaping element may also or alternatively comprise a region of the plate adjacent the aperture which is raised to define a raised edge, for example such that the height of the edge is substantially equal to or greater than the width of the aperture. The aperture may be circular, in which case the width of the aperture is the diameter of the aperture.

[0012] According to another aspect of the embodiment, an inspection tool is disclosed, comprising: a platform, arranged to support an article to be inspected and to connect the article to a voltage source; a substantially flat plate, comprising a conductive material, and arranged parallel to the platform and separated from the platform by a gap, and used to adjust the electric field in the gap, the plate also comprising a structure defining a through aperture; and a field shaping element. The field shaping element may include a window element positioned in the through aperture, the window element being conductive and light-transmissive. The construction and placement of the window element and the characteristics of the aperture may be as described above. Here and elsewhere, "adjust" has its usual control meaning, including making the field more uniform and controlling the amplitude and / or gradient of the field, in particular making it zero.

[0013] According to another aspect of the embodiment, an inspection tool is disclosed, comprising: a platform, arranged to support an article to be inspected and connect the article to a voltage source; a substantially flat plate, comprising a conductive material, and arranged parallel to the platform and separated from the platform by a gap, and used to adjust the electric field in the gap, the plate also comprising a structure defining a through aperture; a window element, positioned in the through aperture, the window element being conductive and light-transmissive; and an optical measurement device, arranged to view the platform through the window element. The construction and placement of the window element and the characteristics of the aperture may be as described above.

[0014] The field shaping element may also or alternatively comprise a region of the plate adjacent the aperture which is raised to define a raised edge, for example such that the height of the edge is substantially equal to or greater than the width of the aperture. The aperture may be circular, in which case the width of the aperture is the diameter of the aperture.

[0015] The following describes in detail other features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention with reference to the accompanying drawings. Note that the present invention is not limited to the specific embodiments described herein. Such embodiments are presented herein for illustrative purposes only. Based on the teachings contained herein, additional embodiments will be apparent to those skilled in the relevant art. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the invention and enable one skilled in the relevant art to make and use the invention.

[0017] Figure 1 is a schematic diagram illustrating an exemplary electron beam inspection system consistent with embodiments of the present disclosure.

[0018] Figure 2 is a schematic diagram illustrating additional aspects of an exemplary electron beam inspection system consistent with embodiments of the present disclosure.

[0019] Figure 3 is a side view illustrating additional aspects of an exemplary electron beam inspection system consistent with embodiments of the present disclosure.

[0020] Figure 4 is a side view illustrating aspects of an exemplary electron beam inspection system according to an aspect of an embodiment.

[0021] Figure 5 is a side view illustrating aspects of an exemplary electron beam inspection system according to an aspect of an embodiment.

[0022] Figure 6is a side view illustrating aspects of an exemplary electron beam inspection system according to an aspect of an embodiment.

[0023] Figure 7 is a side view illustrating aspects of an exemplary electron beam inspection system according to an aspect of an embodiment.

[0024] Figure 8 is a side view illustrating aspects of an exemplary electron beam inspection system according to an aspect of an embodiment. DETAILED DESCRIPTION

[0025] Reference will now be made in detail to exemplary embodiments, examples of which are shown in the accompanying drawings. The following description refers to the accompanying drawings, wherein, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The implementations set forth in the following description of the exemplary embodiments do not represent all implementations consistent with the present invention. Instead, they are merely examples of systems, devices, and methods consistent with aspects related to the present invention as described in the appended claims. For clarity, the relative sizes of the components in the drawings may be exaggerated.

[0026] Electronic devices are made up of circuits formed on a silicon wafer called a substrate. Many circuits can be formed together on the same silicon wafer and are called an integrated circuit or IC. The size of these circuits has been greatly reduced so that more of them can be mounted on a substrate. For example, the IC chip in a smartphone can be as small as a thumbnail but can include more than 2 billion transistors, each less than 1 / 1000 the size of a human hair.

[0027] Manufacturing these extremely small ICs is a complex, time-consuming, and expensive process that typically involves hundreds of individual steps. An error in even one step can result in a defect in the finished IC, rendering it useless. Therefore, one goal of the manufacturing process is to avoid such defects in order to maximize the number of functional ICs manufactured in the process, i.e., to improve the overall yield of the process.

[0028] An integral part of improving yield is monitoring the chip manufacturing process to ensure that it is producing a sufficient number of functional integrated circuits. One way to monitor the process is to inspect the chip circuit structures at various stages of their formation. Inspection can be performed using a scanning electron microscope, SEM. These very small structures can be imaged using an SEM, in effect taking a "photograph" of the structure. The image can be used to determine if the structure was formed correctly and in the correct location. If the structure is defective, the process can be adjusted to make the defect less likely to occur again.

[0029] As the name implies, an SEM uses an electron beam because this beam can be used to observe structures that are too small to be observed by an optical microscope (i.e., a microscope that uses light). Here and elsewhere in this article, the term "light" is used to refer not only to visible light, but also to light with wavelengths outside the visible wavelengths. The path of electrons may be affected by the electric and magnetic fields encountered by the electrons as they travel to the substrate. This means that these fields need to be controlled. One way to control the fields is to use a metal shield. However, in some cases, it is desirable to be able to examine the substrate not only using an SEM, but also using an optical microscope. Providing this capability may involve placing one or more holes in the metal shield through which the optical microscope can see the substrate. However, the presence of the holes may interfere with the ability of the metal shield to control the fields.

[0030] An example of a technical challenge addressed by some embodiments is providing an optical microscope with a line of sight to a substrate without compromising the ability of the shield to control the electric field. Some of these embodiments address this challenge by using, for example, a field shaping element in or near the aperture. The field shaping element can be a window element placed in the aperture that is both transparent to the light used by the optical microscope and conductive. Because the window is conductive, the shield appears complete and uninterrupted to the electric field and thus the ability of the shield to control the electric field is not diminished. The field shaping element can be a raised portion of conductive material near the aperture. The raised portion shapes the field so that the ability of the shield to control the field is not diminished. These field shaping elements can be used alone or together.

[0031] Without limiting the scope of the present disclosure, the description and drawings of the embodiments may be illustratively referred to as using an electron beam. However, these embodiments are not intended to limit the present invention to specific charged particles. For example, the systems and methods for beam forming may be applied to photons, x-rays, and ions, etc. In addition, the term "beam" may refer to a primary electron beam, a primary electron beam wave, a secondary electron beam, or a secondary electron beam wave, etc.

[0032] As used herein, unless expressly stated otherwise, the term "or" encompasses all possible combinations unless not feasible. For example, if it is stated that a component may include A or B, then unless expressly stated otherwise or not feasible, the component may include A or B, or A and B. As a second example, if it is stated that a component may include A, B, or C, then unless expressly stated otherwise or not feasible, the component may include A or B or C, or A and B, or A and C, or B and C, or A and B and C.

[0033] In the specification and claims, the terms "upward", "downward", "top", "bottom", "vertical", "horizontal", etc. may be used. Unless otherwise indicated, these terms are intended to show only relative orientations and not any absolute orientation, such as orientation relative to gravity. Similarly, terms such as left, right, front, back, etc. are intended to give only relative orientations.

[0034] Reference now Figure 1 , Figure 1 An exemplary electron beam inspection (EBI) system 10 is illustrated in accordance with an embodiment of the present disclosure. Figure 1 As shown, the EBI system 10 includes a main chamber 11, a load / lock chamber 20, an electron beam tool 100, and an equipment front end module (EFEM) 30. The electron beam tool 100 is located in the main chamber 11.

[0035] The EFEM 30 includes a first loading port 30a and a second loading port 30b. The EFEM 30 may include additional loading ports. The first loading port 30a and the second loading port 30b may, for example, accommodate a wafer front opening pod (FOUP) containing wafers (e.g., semiconductor wafers or wafers made of other materials) or samples (wafers and samples may be collectively referred to as "wafers" hereinafter) to be inspected. One or more robotic arms (not shown) in the EFEM 30 may transport the wafers to the load / lock chamber 20.

[0036] The load / lock chamber 20 is connected to a load / lock vacuum pump system (not shown) that removes gas molecules in the load / lock chamber 20 to reach a first pressure below atmospheric pressure. After reaching the first pressure, one or more robotic arms (not shown) can transfer the wafer from the load / lock chamber 20 to the main chamber 11. The main chamber 11 is connected to a main chamber vacuum pump system (not shown) that removes gas molecules in the main chamber 11 to reach a second pressure below the first pressure. After reaching the second pressure, the wafer is inspected by the electron beam tool 100. The electron beam tool 100 can be a single beam system or a multi-beam system. The controller 19 is electrically connected to the electron beam tool 100. Although the controller 19 is Figure 1 1 is shown as being external to the structure including the main chamber 11, the load / lock chamber 20 and the EFEM 30, but it should be understood that the controller 19 may be part of the structure.

[0037] Although the present disclosure provides an example of a main chamber 11 housing an electron beam inspection system, it should be noted that the various aspects of the present disclosure in its broadest sense are not limited to a chamber housing an electron beam inspection system. Instead, it should be understood that the principles described herein can also be applied to other tools operating at a second pressure.

[0038] Figure 2 The diagram shows that it can be Figure 1 An exemplary electron beam tool 100A that is part of an EBI system. The electron beam tool 100A (also referred to herein as "device 100A") includes an electron source 101, a gun aperture plate 171, a condenser lens 110, a source conversion unit 120, a primary projection optical system 130, a secondary imaging system 150, and an electron detection device 140M. The primary projection optical system 130 may include an objective lens 131. A sample 1 having a sample surface 7 may be disposed on a movable stage (not shown). The electron detection device 140M may include a plurality of detection elements 140_1, 140_2, and 140_3. A beam splitter 160 and a deflection scanning unit 132 may be placed inside the primary projection optical system 130.

[0039] The electron source 101, the gun aperture plate 171, the condenser lens 110, the source conversion unit 120, the beam splitter 160, the deflection scanning unit 132 and the primary projection optical system 130 can be aligned with the main optical axis 100_1 of the apparatus 100A. The secondary imaging system 150 and the electron detection device 140M can be aligned with the auxiliary optical axis 150_1 of the apparatus 100A.

[0040] The electron source 101 may include a cathode (not shown) and an extractor or anode (not shown), wherein during operation, the electron source 101 is configured to emit primary electrons from the cathode, and the primary electrons are extracted or accelerated by the extractor or anode to form a primary electron beam 102, which forms a primary beam intersection (virtual or real) 101s. The primary electron beam 102 can be visualized as being emitted from the primary beam intersection 101s.

[0041] The source conversion unit 120 may include an image forming element array ( Figure 2 not shown) and the beam limiting aperture array ( Figure 2 1 , 102_2, 102_3). The image forming element array may include a plurality of micro-deflectors or micro-lenses which may affect a plurality of primary beam waves 102_1, 102_2, 102_3 of the primary electron beam 102 and form a plurality of parallel images (virtual or real) of the primary beam intersection 101s, one parallel image for each of the primary beam waves 102_1, 102_2, 102_3. The beam limiting aperture array may be configured to limit the diameter of the individual primary beam waves 102_1, 102_2 and 102_3. Figure 2As an example, three primary beams 102_1, 102_2, and 102_3 are shown, and it should be understood that the source conversion unit 120 can be configured to form any number of primary beams. For example, the source conversion unit 120 can be configured to form a 3×3 array of primary beams. The source conversion unit 120 may also include an aberration compensator array configured to compensate for the aberrations of the detection points 102_1S, 102_2S, and 102_3S. In some embodiments, the aberration compensator array may include a field curvature compensator array having microlenses, which are configured to compensate for the field curvature aberrations of the detection points 102_1S, 102_2S, and 102_3S, respectively. In some embodiments, the aberration compensator array may include an astigmatism compensator array having micro-diffusers, which are configured to compensate for the astigmatism aberrations of the detection points 102_1S, 102_2S, and 102_3S, respectively. In some embodiments, the image forming element array, the field curvature compensator array, and the astigmatism compensator array may include multiple layers of micro-deflectors, micro-lenses, and micro-astigmatism correctors, respectively.

[0042] The condenser lens 110 is configured to focus the primary electron beam 102. The condenser lens 110 can also be configured to adjust the current of the primary beam waves 102_1, 102_2 and 102_3 downstream of the source conversion unit 120 by changing the focusing ability of the condenser lens 110. Therefore, the beam waves 102_1, 102_2 and 102_3 can have a focusing state that can be changed by the condenser lens 110. Alternatively, the current can be changed by changing the radial size of the beam limiting apertures corresponding to the individual primary beam waves within the beam limiting aperture array. Therefore, the current of the beam wave can be different at different positions along the trajectory of the beam wave. The beam wave current can be adjusted so that the current of the beam wave on the sample surface (e.g., the detection point current) is set to a desired amount.

[0043] The focusing lens 110 can be a movable focusing lens, which can be configured so that the position of its first principal plane is movable. The movable focusing lens can be configured to be magnetic, or electrostatic or electromagnetic (e.g., composite). The movable focusing lens is further described in U.S. Patent No. 9,922,799 and U.S. Patent Application Publication No. 2017 / 0025243, the entire contents of which are incorporated herein by reference. In some embodiments, the focusing lens can be an anti-rotation lens that can keep the rotation angle of the off-axis beam wave unchanged while changing the current of the beam wave. In some embodiments, the focusing lens 110 can be a movable anti-rotation focusing lens, which includes an anti-rotation lens having a movable first principal plane. The anti-rotation or movable anti-rotation focusing lens is further described in International Application No. PCT / EP2017 / 084429, which is incorporated herein by reference in its entirety.

[0044] The objective lens 131 may be configured to focus the beams 102_1, 102_2, and 102_3 onto the sample 1 for inspection, and in the current embodiment, three detection points 102_1S, 102_2S, and 102_3S may be formed on the surface 7. In operation, the gun aperture plate 171 is configured to block peripheral electrons of the primary electron beam 102 to reduce the Coulomb effect. The Coulomb effect may increase the size of each detection point 102_1S, 102_2S, and 102_3S of the primary beams 102_1, 102_2, 102_3, thereby deteriorating the inspection resolution.

[0045] The beam splitter 160 can be, for example, a Wien filter including an electrostatic deflector that generates an electrostatic dipole field E1 and a magnetic dipole field B1. The beam splitter 160 can utilize the Lorentz force to affect the electrons passing therethrough. The beam splitter 160 can be activated to generate the electrostatic dipole field E1 and the magnetic dipole field B1. In operation, the beam splitter 160 can be configured to exert an electrostatic force on the individual electrons of the primary beam waves 102_1, 102_2, and 102_3 through the electrostatic dipole field E1. The magnitude of the electrostatic force can be equal to the magnitude of the magnetic force exerted by the magnetic dipole field B1 of the beam splitter 160 on the individual electrons, but in the opposite direction. The primary beam waves 102_1, 102_2, and 102_3 can pass through the beam splitter 160 substantially straight.

[0046] In operation, the deflection scanning unit 132 is configured to deflect the primary beam waves 102_1, 102_2 and 102_3 to scan the detection points 102_1S, 102_2S and 102_3S across the individual scanning areas in a portion of the surface 7. In response to the irradiation of the sample 1 by the primary beam waves 102_1, 102_2 and 102_3 at the detection points 102_1S, 102_2S and 102_3S, secondary electrons are emitted from the sample 1 and form three secondary electron beams 102_1se, 102_2se and 102_3se, which are emitted from the sample 1 in operation. Each of the secondary electron beams 102_1se, 102_2se, and 102_3se generally includes electrons with different energies, including secondary electrons (electron energy ≤ 50 eV) and backscattered electrons (having electron energies between 50 eV and the landing energies of the primary beams 102_1, 102_2, and 102_3). The beam splitter 160 is configured to deflect the secondary electron beams 102_1se, 102_2se, and 102_3se toward the secondary imaging system 150. The secondary imaging system 150 then focuses the secondary electron beams 102_1se, 102_2se, and 102_3se onto the detection elements 140_1, 140_2, and 140_3 of the electron detection device 140M. The detection elements 140_1 , 140_2 and 140_3 are arranged to detect the corresponding secondary electron beams 102_1se, 102_2se and 102_3se and to generate corresponding signals which may be sent to a signal processing unit (not shown) to, for example, construct an image of a corresponding scanned area of ​​the sample 1 .

[0047] like Figure 3 As shown in FIG, the EBI may include a flat metal plate 300 positioned slightly above a wafer stage 310. The wafer stage 310 supports an article such as a wafer 320 to be inspected and moves the wafer relative to the flat metal plate 300. Figure 3 In the example of FIG. 3 , wafer 320 is surrounded by conductive surface 330, which is part of wafer stage 310. Wafer stage 310 is connected to the same voltage as wafer 320 to generate a uniform electric field at all positions within the lateral range of motion of wafer stage 310, including around the inspection area. However, there is usually an edge of conductive surface 330 around the article. At this edge, the electric field should not have a tangential component, in other words, the equipotential surface should be as parallel to conductive surface 330 as possible.

[0048] In other words, the flat metal plate 300 can be arranged so that the electric field between the flat metal plate 300 and the wafer stage 310 has a minimum component parallel to the conductive surface at the stage. This is also to prevent discharges due to high electric fields around the edge of the wafer stage 310 where the conductive surface 330 on the wafer stage 310 terminates.

[0049] However, for visual inspection and alignment of the wafer 320 and the wafer stage 310, an optical measurement device 340, such as an optical microscope, is also included. The optical measurement device 340 can be any optical alignment or inspection device, including instruments that require line of sight using, for example, interference, moiré patterns, or phase change gratings. The optical measurement device 340 is arranged to look down (towards the wafer 320 and the wafer stage 310) through the aperture 350 in the flat metal plate 300, and the wafer stage 310 moves the wafer 320 so that a position on the wafer 320 located below the aperture 350 can be visually inspected. The aperture 350 can have any shape, for example, it can be circular. In addition, other optical devices and other general devices may also require an aperture in the flat metal plate 300.

[0050] As used herein, the term "light" is not limited to visible light, but is broad enough to cover portions of the electromagnetic spectrum that are not visible. According to one aspect of an embodiment, an optical measurement device that is sensitive to visible light (having a wavelength in the range of about 380 nm to about 700 nm) is used, but other optical measurement devices, such as those that are sensitive to infrared or near UV, may be used. Generally speaking, the wavelength of light will be in the range of about 300 nm to about 1100 nm.

[0051] The apertures 350 cause local deviations in the electric potential in the space between the flat metal plate 300 and the wafer stage 310 or the wafer 320. When the wafer stage 310 is translated laterally, the edge of the wafer stage 310 and other features of the wafer stage 310 may pass under these apertures 350. If no measures are taken to prevent it, the area under the apertures 350 may be affected by the tangential component of the electric field, as shown by line 360. This may damage the edge of the conductive surface 330 on the wafer stage 310 by causing discharges and / or arcs. The discharges may cause unwanted particles and contamination as well as local gas pressure increases, which in turn may cause electrical breakdown. The discharges may also occur near other parts of the wafer 320 and may damage them.

[0052] According to an aspect of the embodiment, a conductive window element is provided to prevent a component of the electric field tangential to the platform.The potential deviation at the location of the aperture in the flat metal plate 300 is reduced, and thus the discharge caused by field emission is also reduced.

[0053] The window element is a conductive but optically transparent element positioned in or at the aperture. For example, the element can be a bulk material that is conductive and transparent in itself. It can also be a transparent material with a conductive film. It can also be a screen.

[0054] Figure 4A window element 400 is shown that is made of a material that is both transparent and conductive. The material can be a conductive material such as ITO (indium tin oxide) that is transparent to at least the portion of the spectrum used by the optical measurement device. The material can be another transparent conductive oxide or graphene. Carbon nanotubes can be used. Doped transparent semiconductors will also meet the conductivity requirements. Crystalline materials can be used, or amorphous materials such as conductive polymers can be used. These are examples, and other materials can also be used.

[0055] Figure 5 An example of a window element 410 with a conductive film 430 is shown, the window element 410 being made of a first material that is transparent but not necessarily conductive. For example, the window element 410 can be a glass body 420 coated with a thin conductive film 430, the thin conductive film 430 being made of, for example, gold or aluminum. Other metals such as titanium and chromium can be used. The thin conductive film 430 can be applied by vapor deposition or any other suitable technique.

[0056] A conductive film 430 having a thickness above a threshold value (such as about 10 nm) will be thick enough to provide the desired conductivity. A conductive film 430 having a thickness less than a threshold value (such as about 1 μm) will provide sufficient light transmission. Typically, such a conductive film 430 may have a thickness in the range of about 10 nm to about 10 μm. Figure 5 In the specific embodiment shown in , the conductive film 430 is shown as being on the top surface of the first material, but it is obvious to those skilled in the art that the conductive film 430 can be on only the top surface, only the bottom surface, or both the top and bottom surfaces of the first material.

[0057] like Figure 6 As shown in , alternatively, the window element can be composed of a conductive screen 440, which is placed at a position on the optical axis outside the focusing range, for example, in the pupil plane of the optical device, so that it does not interfere with the imaging function. The screen 440 can be woven (e.g., a mesh of metal wires or nanowires) or non-woven (a mesh), and has a mesh structure that is open enough to allow light of the wavelength of interest to pass through. For example, the screen 440 can have a structure that opens at least one-third of its surface area to allow light to pass through.

[0058] The thickness and vertical (direction of the plate thickness) positioning of the window element can be selected so that the window element does not protrude beyond the upper or lower surface of the flat metal plate 300. Thus, the window element can have a thickness that is approximately equal to or less than the thickness of the flat metal plate 300. If the thickness of the window element is less than the thickness of the flat metal plate 300, the surface of the window element is recessed from one of the surfaces of the flat metal plate 300.

[0059] like Figure 7As shown in , according to another aspect of the embodiment, for some applications, the edge around the aperture 350 on the upper side of the flat metal plate 300 has a raised portion 500. The raised portion 500 can be formed integrally with the flat metal plate 300, or can be added to the flat metal plate 300 by a process such as welding. The raised portion 500 is made of a conductive material. The raised portion 500 can have a height so that the height of the aperture is about the same as or greater than its width, for example, if the aperture is circular, the width is the diameter, otherwise the width is its longest linear dimension. The raised portion 500 shapes the electric field to provide another measure to prevent the tangential component of the electric field at the surface of the wafer stage 310. In addition, the raised portion 500 allows the lateral size of the aperture 350 to be larger.

[0060] For some applications, the raised edge itself may sufficiently shape the electric field so that a separate window element is not required. Figure 8 310 . Similarly, the raised portion 500 can be integrally formed with the flat metal plate 300, or can be added to the flat metal plate 300 by a process such as welding. The raised portion 500 is made of a conductive material. The raised portion 500 can have a height such that the height of the aperture is approximately the same as or greater than its width, for example, if the aperture is circular, the width is the diameter, otherwise the width is its longest linear dimension. The raised portion 500 shapes the electric field to prevent the tangential component of the electric field at the surface of the wafer stage 310. In addition, the raised portion 500 allows the lateral size of the aperture 350 to be larger.

[0061] The embodiments may be further described using the following terms:

[0062] 1. A product comprising:

[0063] a substantially planar plate comprising a conductive material and a structure defining a through aperture; and

[0064] A field shaping element is positioned at the through-aperture, the field shaping element being configured to counteract an effect of the through-aperture on an electric field near the substantially planar plate.

[0065] 2. The article of claim 1, wherein the field shaping element comprises a window element positioned at the through aperture, the window element being electrically conductive and light transmissive.

[0066] 3. The article of claim 2, wherein the window element comprises a conductive material that transmits visible light having a wavelength in the range of about 300 nm to about 1100 nm.

[0067] 4. The article of any one of clauses 2 or 3, wherein the window element comprises a transparent metal oxide.

[0068] 5. The article of any one of clauses 2 to 4, wherein the window element comprises indium tin oxide.

[0069] 6. The article of any one of clauses 2 or 3, wherein the window element comprises graphene.

[0070] 7. The article of any of clauses 2 or 3, wherein the window element comprises carbon nanotubes.

[0071] 8. The article of any of clauses 2 or 3, wherein the window element comprises an amorphous material.

[0072] 9. The article of any of clauses 2 or 3, wherein the window element comprises a doped transparent semiconductor.

[0073] 10. The article of any of clauses 2 or 3, wherein the window element comprises a conductive polymer.

[0074] 11. The article of claim 2, wherein the window element comprises a body comprising a transparent material, and a coating of a conductive material.

[0075] 12. The article of clause 11, wherein the coating of conductive material comprises gold.

[0076] 13. The article of clause 11, wherein the coating of conductive material comprises aluminum.

[0077] 14. The article of clause 11, wherein the coating of conductive material comprises titanium.

[0078] 15. The article of clause 11, wherein the coating of conductive material comprises chromium.

[0079] 16. The article of any one of clauses 11 to 15, wherein the coating has a thickness in the range of about 10 nm to about 10 μm.

[0080] 17. The article of claim 2, wherein the window element comprises a screen configured to be electrically conductive and to transmit visible light.

[0081] 18. The article of clause 17, wherein the screen comprises a mesh.

[0082] 19. The article of clause 18, wherein the mesh comprises metal wires.

[0083] 20. The article of any of clauses 18 or 19, wherein the web is at least 30% open.

[0084] 21. The article of clause 17, wherein the screen is non-woven.

[0085] 22. The article of clause 21, wherein the screen is a mesh.

[0086] 23. The article of clause 22, wherein the mesh is at least 30% open.

[0087] 24. The article of claim 2, wherein the window element is positioned in the aperture so as not to extend beyond the surface of the plate.

[0088] 25. The article of claim 24, wherein the window element is positioned in the aperture so as to be recessed below the surface of the plate.

[0089] 26. The article of clause 2, wherein a region of the plate adjacent the aperture is raised to define a raised edge at least partially surrounding the aperture.

[0090] 27. The article of claim 26, wherein the raised edge is integral with the plate.

[0091] 28. An article according to clause 26 or 27, wherein the height of the raised edge is such that the height of the aperture together with the height of the raised edge is substantially equal to the width of the aperture.

[0092] 29. The article of any one of clauses 26 to 28, wherein the aperture is circular and the width of the aperture is the diameter of the aperture.

[0093] 30. The article of claim 1, wherein the field shaping element comprises a region of the plate adjacent the aperture, the region being raised to define a raised edge at least partially surrounding the aperture, the raised edge comprising a conductive material.

[0094] 31. The article of clause 30, wherein the raised edge is integral with the plate.

[0095] 32. An article according to clause 30 or 31, wherein the height of the raised edge is such that the height of the aperture together with the height of the raised edge is substantially equal to or greater than the width of the aperture.

[0096] 33. An article according to any of clauses 30 to 32, wherein the aperture is circular and the width of the aperture is the diameter of the aperture.

[0097] 34. An inspection tool comprising:

[0098] a platform arranged to support an article to be inspected and to connect said article to a voltage source;

[0099] a substantially planar plate comprising a conductive material and arranged parallel to the platform and separated from the platform by a gap and configured to modulate the electric field in the gap, the plate further comprising a structure defining a through aperture; and

[0100] A field shaping element is positioned at the through-aperture, the field shaping element being configured to counteract an effect of the through-aperture on an electric field near the substantially planar plate.

[0101] 35. The inspection tool of clause 34, wherein the field shaping element comprises a window element positioned at the through aperture, the window element being electrically conductive and light transmissive.

[0102] 36. The inspection tool of clause 35, wherein the window element comprises a conductive material that transmits visible light, the wavelength of the visible light being in the range of about 300 nm to about 1100 nm.

[0103] 37. An inspection tool according to clause 35 or 36, wherein the window element comprises a transparent metal oxide.

[0104] 38. An inspection tool according to any of clauses 35 to 37, wherein the window element comprises indium tin oxide.

[0105] 39. An inspection tool according to any of clauses 35 to 36, wherein the window element comprises graphene.

[0106] 40. An inspection tool according to any of clauses 35 to 36, wherein the window element comprises carbon nanotubes.

[0107] 41. An inspection tool according to any of clauses 35 to 36, wherein the window element comprises an amorphous material.

[0108] 42. An inspection tool according to any of clauses 35 to 36, wherein the window element comprises a doped transparent semiconductor.

[0109] 43. An inspection tool according to any of clauses 35 to 36, wherein the window element comprises a conductive polymer.

[0110] 44. An inspection tool according to any of clauses 35 to 36, wherein the window element comprises a body comprising a transparent material, and a coating of an electrically conductive material.

[0111] 45. The inspection tool of clause 44, wherein the coating of conductive material comprises gold.

[0112] 46. ​​The inspection tool of clause 44, wherein the coating of conductive material comprises aluminum.

[0113] 47. The inspection tool of clause 44, wherein the coating of conductive material comprises titanium.

[0114] 48. The inspection tool of clause 44, wherein the coating of conductive material comprises chromium.

[0115] 49. An inspection tool according to any of clauses 44 to 48, wherein the coating has a thickness in the range of about 10 nm to about 10 μm.

[0116] 50. The inspection tool of clause 35, wherein the window element comprises a screen configured to be electrically conductive and to transmit visible light.

[0117] 51. The inspection tool of clause 50, wherein the screen comprises a mesh.

[0118] 52. An inspection tool according to clause 51, wherein the mesh comprises metal wires.

[0119] 53. An inspection tool according to clause 51 or 52, wherein the web is at least 30% open.

[0120] 54. An inspection tool according to clause 50, wherein the screen is non-woven.

[0121] 55. An inspection tool according to clause 54, wherein the screen is a mesh.

[0122] 56. An inspection tool according to clause 55, wherein the grid is at least 30% open.

[0123] 57. The inspection tool of clause 35, wherein the window element is positioned in the aperture so as not to extend beyond a surface of the plate.

[0124] 58. An inspection tool according to clause 35 or 57, wherein the window element is positioned in the aperture so as to be recessed below the surface of the plate.

[0125] 59. An inspection tool according to any of clauses 35 to 58, wherein a region of the plate adjacent the aperture is raised to define a raised edge at least partially surrounding the aperture, wherein the raised edge comprises a conductive material.

[0126] 60. The inspection tool of clause 59, wherein the raised edge is integral with the plate.

[0127] 61. An inspection tool according to clause 59 or 60, wherein the height of the raised rim is such that the height of the aperture together with the height of the raised rim is substantially equal to the width of the aperture.

[0128] 62. An inspection tool according to any of clauses 59 to 61, wherein the aperture is circular and the width of the aperture is the diameter of the aperture.

[0129] 63. The inspection tool of clause 31, wherein the field shaping element comprises a region of the plate adjacent the aperture, the region being raised to define a raised edge at least partially surrounding the aperture, the raised edge comprising a conductive material.

[0130] 64. An inspection tool according to clause 63, wherein the raised edge is integral with the plate.

[0131] 65. An inspection tool according to clause 63 or 64, wherein the height of the raised edge is such that the height of the aperture together with the height of the raised edge is substantially equal to or greater than the width of the aperture.

[0132] 66. An inspection tool according to any of clauses 63 to 65, wherein the aperture is circular and the width of the aperture is the diameter of the aperture.

[0133] 67. An inspection tool comprising:

[0134] a platform arranged to support an article to be inspected and to connect said article to a voltage source;

[0135] a substantially planar plate comprising a conductive material and arranged parallel to the platform and separated from the platform by a gap and configured to modulate an electric field in the gap, the plate further comprising a structure defining a through aperture;

[0136] a field shaping element positioned at the through-aperture, the field shaping element being configured to counteract an effect of the through-aperture on an electric field near the substantially planar plate; and

[0137] An optical measurement device is arranged to view the platform through the window element.

[0138] 68. The inspection tool of clause 67, wherein the field shaping element comprises a window element positioned at the through aperture, the window element being electrically conductive and light transmissive.

[0139] 69. The inspection tool of clause 68, wherein the window element comprises a conductive material that transmits visible light, the wavelength of the visible light being in the range of about 300 nm to about 1100 nm.

[0140] 70. An inspection tool according to clause 68 or 69, wherein the window element comprises a transparent metal oxide.

[0141] 71. An inspection tool according to any of clauses 68 to 70, wherein the window element comprises indium tin oxide.

[0142] 72. An inspection tool according to clause 68 or 69, wherein the window element comprises graphene.

[0143] 73. An inspection tool according to clause 68 or 69, wherein the window element comprises carbon nanotubes.

[0144] 74. An inspection tool according to clause 68 or 69, wherein the window element comprises an amorphous material.

[0145] 75. An inspection tool according to clause 68 or 69, wherein the window element comprises a doped transparent semiconductor.

[0146] 76. An inspection tool according to clause 68 or 69, wherein the window element comprises a conductive polymer.

[0147] 77. The inspection tool of clause 68, wherein the window element comprises a body comprising a transparent material, and a coating of a conductive material.

[0148] 78. The inspection tool of clause 77, wherein the coating of conductive material comprises gold.

[0149] 79. An inspection tool according to clause 77, wherein the coating of conductive material comprises aluminum.

[0150] 80. The inspection tool of clause 77, wherein the coating of conductive material comprises titanium.

[0151] 81. The inspection tool of clause 77, wherein the coating of conductive material comprises chromium.

[0152] 82. An inspection tool according to any of clauses 77 to 81, wherein the coating has a thickness in the range of about 10 nm to about 10 μm.

[0153] 83. The inspection tool of clause 55, wherein the window element comprises a screen configured to be electrically conductive and to transmit visible light.

[0154] 84. The inspection tool of clause 70, wherein the screen comprises a mesh.

[0155] 85. The inspection tool of clause 71, wherein the mesh comprises metal wires.

[0156] 86. An inspection tool according to clause 71 or 72, wherein the web is at least 30% open.

[0157] 87. An inspection tool according to clause 55, wherein the screen is non-woven.

[0158] 88. An inspection tool according to clause 83, wherein the screen is a mesh.

[0159] 89. An inspection tool according to clause 88, wherein the grid is at least 30% open.

[0160] 90. The inspection tool of clause 68, wherein the window element is positioned in the aperture so as not to extend beyond a surface of the plate.

[0161] 91. The inspection tool of clause 90, wherein the window element is positioned in the aperture so as to be recessed below the surface of the plate.

[0162] 92. An inspection tool according to any of clauses 68 to 91, wherein a region of the plate adjacent the aperture is raised to define a raised edge at least partially surrounding the aperture, wherein the raised edge comprises a conductive material.

[0163] 93. An inspection tool according to clause 92, wherein the raised edge is integral with the plate.

[0164] 94. An inspection tool according to clause 92 or 93, wherein the height of the raised edge is such that the height of the aperture together with the height of the raised edge is substantially equal to the width of the aperture.

[0165] 95. An inspection tool according to any of clauses 92 to 94, wherein the aperture is circular and the width of the aperture is the diameter of the aperture.

[0166] 96. An inspection tool according to clause 67, wherein the field shaping element comprises a region of the plate adjacent to the aperture, the region being raised to define a raised edge at least partially surrounding the aperture, the raised edge comprising a conductive material.

[0167] 97. An inspection tool according to clause 96, wherein the raised edge is integral with the plate.

[0168] 98. An inspection tool according to clause 96 or 97, wherein the height of the raised edge is such that the height of the aperture together with the height of the raised edge is substantially equal to or greater than the width of the aperture.

[0169] The present invention has been described above with the help of functional building blocks, which illustrate the implementation of specific functions and their relationships. For ease of description, the boundaries of these functional building blocks are arbitrarily defined herein. Alternative boundaries may be defined as long as the specified functions and their relationships are properly performed.

[0170] The foregoing description of specific embodiments will so fully reveal the general nature of the invention that others, by applying knowledge in the art, can easily modify and / or adapt various applications of these specific embodiments without undue experimentation without departing from the general concept of the invention. Therefore, based on the teachings and guidance presented herein, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed embodiments. It should be understood that the terms or terminology herein are for descriptive purposes and not for limitation, so that the terms or terminology of this specification will be interpreted by those skilled in the art based on the teachings and guidance.

Claims

1. An electron beam inspection device, comprising: a planar plate comprising a conductive material and a structure defining a through aperture configured to be positioned over a conductive surface of a wafer stage; as well as a field shaping element positioned at the through-aperture, the field shaping element being configured to counteract the effect of the through-aperture on the electric field adjacent to the planar plate, the field shaping element being electrically conductive and optically transparent, Wherein the field shaping element comprises a region of the plate adjacent the through-aperture, the region being raised to define a raised edge at least partially surrounding the aperture, the raised edge comprising an electrically conductive material.

2. The electron beam inspection apparatus of claim 1, wherein the field shaping element comprises a window element positioned at the through aperture. 3 . The electron beam inspection apparatus according to claim 2 , wherein the window member comprises a conductive material that transmits visible light, the wavelength of the visible light being in the range of 300 nm to 1100 nm.

4. The electron beam inspection apparatus of claim 2, wherein the window element comprises a transparent metal oxide.

5. The electron beam inspection apparatus of claim 2, wherein the window element comprises indium tin oxide. The electron beam inspection apparatus according to claim 2 , wherein the window element comprises graphene.

7. The electron beam inspection apparatus of claim 2, wherein the window element comprises carbon nanotubes.

8. The electron beam inspection apparatus of claim 2, wherein the window element comprises a doped transparent semiconductor.

9. The electron beam inspection apparatus of claim 2, wherein the window element comprises a conductive polymer.

10. The electron beam inspection apparatus of claim 2, wherein the window member comprises a body including a coating of a transparent material and a conductive material.

11. The electron beam inspection apparatus of claim 10, wherein the coating of conductive material comprises gold.

12. The electron beam inspection apparatus of claim 10, wherein the coating of conductive material comprises aluminum.

13. The electron beam inspection apparatus of claim 10, wherein the coating of conductive material comprises titanium.

14. The electron beam inspection apparatus of claim 10, wherein the coating of conductive material comprises chromium. 15 . The electron beam inspection apparatus according to claim 10 , wherein a thickness of the coating layer is in a range of 10 nm to 10 μm.

16. The electron beam inspection apparatus of claim 1, wherein the wafer stage includes a non-conductive surface between the conductive surface and an edge of the wafer stage.

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