CN111261481B

CN111261481B - Method and system for charged particle microscopy

Info

Publication number: CN111261481B
Application number: CN202010097548.8A
Authority: CN
Inventors: D·马斯纳盖蒂; G·托特; D·特雷斯; R·博特罗; G·H·陈; R·克尼彭迈耶
Original assignee: KLA Tencor Corp
Current assignee: KLA Corp
Priority date: 2015-03-24
Filing date: 2016-03-24
Publication date: 2022-12-16
Anticipated expiration: 2036-03-24
Also published as: CN107408485A; CN111261481A; CN107408485B

Abstract

Embodiments of the present application relate to methods and systems for charged particle microscopy. An embodiment of the present application discloses a scanning electron microscope system with improved image beam stability. The system includes an electron beam source configured to generate an electron beam and a set of electro-optical elements that direct at least a portion of the electron beam onto a portion of a sample. The system includes an emittance analyzer assembly. The system includes a beamsplitter element configured to direct at least a portion of secondary and/or backscattered electrons emitted by a surface of the sample to the emittance analyzer assembly. The emittance analyzer assembly is configured to image at least one of the secondary electrons and/or the backscattered electrons.

Description

Method and system for charged particle microscope

The present application is a divisional application of the inventive patent application entitled "method and system for charged particle microscopy with improved image beam stability and interrogation" having application number "201680013667.2", 2016, 24/3/2016.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of and constitutes a formal (non-provisional) patent application of the following U.S. provisional application pursuant to 35U.S. c. § 119 (e): U.S. provisional application Ser. No. 62/137,229, filed 3/24/2015; U.S. provisional application Ser. No. 62/166,682 filed 5/27/2015; U.S. provisional application Ser. No. 62/214,737, filed on 9, 4, 2015; and 2016, 12, U.S. provisional application serial No. 62/277,670, each of which is incorporated herein by reference in its entirety.

Technical Field

The present invention relates generally to charged particle microscopes, and more particularly to scanning electron microscope systems with improved stability and interrogation of the image beam.

Background

The fabrication of semiconductor devices, such as logic and memory devices, typically includes the processing of a substrate, such as a semiconductor wafer, using a number of semiconductor fabrication processes to form the various features and multiple levels of the semiconductor device. As the size of semiconductor devices becomes smaller and smaller, the development of enhanced wafer inspection and review devices and procedures becomes particularly important. Accordingly, it would be advantageous to provide a system and method that provides improved electronic imaging of a sample (e.g., a semiconductor wafer).

Disclosure of Invention

A Scanning Electron Microscope (SEM) apparatus is disclosed in accordance with one or more embodiments of the present disclosure. In one illustrative embodiment, the SEM apparatus includes an electron beam source configured to generate an electron beam. In another illustrative embodiment, the SEM apparatus includes a set of electro-optical elements to direct at least a portion of an electron beam onto a portion of a sample. In another illustrative embodiment, the SEM apparatus includes an emittance analyzer assembly (emittance analyzer assembly). In another illustrative embodiment, the SEM apparatus includes a beamsplitter element configured to direct at least a portion of at least one of secondary electrons or backscattered electrons emitted by a surface of the sample to the emittance analyzer assembly. In another illustrative embodiment, the emittance analyzer assembly is configured to image at least one of secondary electrons or backscattered electrons. In another illustrative embodiment, the emittance analyzer assembly includes: a set of deflection optics; a first electro-optic lens; a first electron detector including a central aperture, wherein the first electron detector is configured to collect at least one of a portion of secondary electrons or a portion of backscattered electrons; a first mesh element disposed downstream of the first electron detector; a second mesh element disposed downstream of the first mesh element, wherein the first electron detector and the first mesh element form a deceleration region, wherein the first mesh element and the second mesh element form a drift region; an energy filter disposed downstream of the second grounded screen element; a second electro-optic lens; and a second electron detector configured to collect at least one of an additional portion of the secondary electrons or an additional portion of the backscattered electrons.

In another illustrative embodiment, the emittance analyzer is configured to operate in a secondary electron and backscattered electron imaging mode. In another illustrative embodiment, the emittance analyzer is configured to operate in a backscattered electron and high aspect ratio electron imaging mode. In another illustrative embodiment, the emittance analyzer is configured to operate in a backscatter electron only imaging mode. In another illustrative embodiment, the emittance analyzer is configured to switch between a secondary electron and backscattered electron imaging mode, a backscattered electron and high aspect ratio electron imaging mode, and a backscattered electron only imaging mode.

In another illustrative embodiment, the electron source and/or flood gun is configured to apply an in-situ flood pre-fill to the sample.

In another illustrative embodiment, the apparatus includes a gated integrator configured to lock one or more components in the emittance analyzer assembly to a surface potential of the sample.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not necessarily restrictive of the invention, as claimed. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the general description, serve to explain the principles of the invention.

Drawings

The several advantages of this invention may be better understood by those of ordinary skill in the art by reference to the accompanying drawings in which:

fig. 1A-6C illustrate one or more embodiments of a scanning electron microscope system with improved stability and interrogation of the image beam in accordance with the present disclosure.

Detailed Description

Reference will now be made in detail to the disclosed subject matter as illustrated in the accompanying drawings.

Referring generally to fig. 1A-6C, a system and method for performing a scanning electron microscope with improved stability and interrogation of the image beam is disclosed in accordance with the present invention.

Embodiments of the invention relate to an emittance analyzer assembly that extracts information from an electronic image beam from a sample surface. Further, the emittance analyzer assembly may be configured in various configurations. As discussed in this disclosure, the emittance analyzer assembly of the present disclosure may operate in a secondary electron/backscattered electron (SE-BSE) mode, a backscattered electron/high aspect ratio (BSE-HAR) mode, and/or a BSE-only mode, whereby the system is capable of switching between various analyzer modes. The emittance analyzer of the present invention also allows real-time wafer surface potential acquisition during any imaging mode. In addition, the emittance analyzer of the present invention allows for the generation of control signals to stabilize polar angle resolution drift and image beam position drift when imaging a wafer that generates surface voltages.

Additional embodiments of the present disclosure relate to gated integrators configured to lock image path optical elements to the surface potential of a given sample for the purpose of improving image quality. Additional embodiments of the present invention relate to implementing in-situ flood and emittance analyzer assemblies and/or gated integrators to stabilize image beams.

The present invention includes embodiments discussed at least in part in the following U.S. patents: 5210487, 6483120, 6570154, 6784425, 6844550, 6897458, 7041976, 7075078, 7683317, 7705301, 7141791, 7656171, 7714287, 8203119, 8263934, 8274048, 8288724, 8421027, 8884224, 8890068, 8946649, 8963083, 9000395, 9048062, 9048063, and 9165742, each of which is incorporated herein by reference in its entirety. The present invention includes embodiments discussed at least in part in the following U.S. patent publications: 2007/0090288, 2012/0273690, 2013/0032729, 2014/0299767, and 2014/029967, each of which is incorporated herein by reference in its entirety. The present invention includes embodiments discussed at least in part in U.S. patent application 14/6966122, which is incorporated by reference herein in its entirety.

Fig. 1A illustrates a charged particle imaging system 100 arranged to image a sample via collection of secondary and/or backscattered electrons, according to one embodiment of the invention.

In one embodiment, the system 100 includes an electron beam source 102, an electro-optic column 105, a beam splitter element 112, an emittance analyzer assembly 120, and a controller 121.

The emittance analyzer assembly 120 is used to extract information from the image beam regarding the emittance of the microscope system 100. The image beam includes backscattered electrons 114 and/or secondary electrons 116 emitted by the surface of the sample 110 in response to the incident primary light beam 104.

In one embodiment, the electron beam source 102 is configured to generate one or more primary electron beams 104. The electron beam source 102 may comprise any electron source known in the art. For example, the electron beam source 102 may include (but is not limited to) one or more electron guns. For example, the electron beam source 102 may include a single electron gun for generating a single primary electron beam 104. In another example, the electron beam source 102 may include a plurality of electron guns for generating a plurality of primary electron beams 104.

In another embodiment, the electro-optic column 105 may include a set of electro-optic elements. The set of electro-optical elements can direct at least a portion of the electron beam 104 onto a selected portion of a sample 110 (e.g., a semiconductor wafer). The set of electro-optical elements of the electro-optical column 105 may include any electro-optical element known in the art suitable for focusing and/or directing the electron beam 104 onto a selected portion of the sample 110. In one embodiment, the set of electro-optical elements includes one or more electro-optical lenses. For example, the electro-optic lens may include (but is not limited to) one or more condenser lenses 106 for collecting electrons from the electron beam source 102. By way of another example, the electro-optic lens may include (but is not limited to) one or more objective lenses 108 for focusing the electron beam 104 onto a selected area of the sample 110.

In another embodiment, the group of electro-optical elements of the electro-optical column 106 includes one or more electron beam scanning elements (not shown). For example, the one or more electron beam scanning elements may include, but are not limited to, one or more electromagnetic scanning coils or electrostatic deflectors suitable for controlling the position of the electron beam 104 relative to the surface of the sample 110. In this regard, one or more scanning elements may be used to scan the electron beam 104 in a selected pattern throughout the sample 110.

For purposes of brevity, a single photoelectric column 106 is depicted in FIG. 1A. It should be noted herein that this configuration should not be construed as limiting the invention. For example, the system 100 may include a plurality of optoelectronic columns 106.

In another embodiment, the splitter element 112 is arranged so as to deflect secondary and/or backscattered electrons emitted by the surface of the sample 110 to the inlet of the emittance analyzer assembly 120. For example, the splitter element 112 may include an electronic velocity selector, such as, but not limited to, a Wien filter. In another embodiment, the system 100 may include a Wehnelt cylinder (Wehnelt cylinder).

Fig. 1B illustrates secondary electron distribution 111 for conventional lens back dark field imaging and secondary electron distribution 113 imaged using the emittance analyzer of the present invention.

Graphs

111 and 113 represent the secondary electron distributions in the plane of the simulated detectors at 1eV, 2eV, 5eV, and 10 eV. As shown in graph 111, the polar angle alignment is poor throughout the secondary electron energy range. In contrast, as shown in graph 113, polar angle alignment throughout the secondary electron energy range is improved in the case of the emittance analyzer approach of the present invention.

FIG. 1C illustrates a block diagram of an emittance analyzer assembly 120 configured in a SE-BSE imaging mode, according to one embodiment of the invention.

The system 100 operates by rapidly moving secondary electrons 116 from the sample 110 to the entrance of an emittance analyzer 120. For example, this may be performed by: using a large electric field, the secondary electrons 116 are accelerated as they are emitted from the sample 110; then, a conjugate point is formed at the entrance of the analysis portion of the assembly 120 using a lens; decelerating the secondary electrons 116 back to their initial kinetic energy (drift entrance); and then the analysis optics are designed as if secondary electrons 116 were emitted from a conjugate point at the entrance to the drift region. It should be noted that a high "extraction field" is required not only for minimizing the transition time error in polarity resolution, but also for preventing large azimuth resolution errors introduced by the high magnetic field of the objective lens.

In one embodiment, the emittance analyzer assembly 120 includes a set of deflection optics 124. In one embodiment, the set of deflection optics is positioned before or upstream of one or more additional components of the emittance analyzer assembly 120. The set of deflection optics is configured to align the image beam including backscattered electrons 114 and/or secondary electrons 116 with one or more components of an emittance analyzer assembly 120. For example, the deflection optics 124 may be used to de-scan the (de-scan) image beam and align the image beams 114, 116 coaxially with respect to one or more of the additional components of the emittance analyzer assembly 120. It should be further noted that the set of deflection optics 124 can be utilized to counteract the lateral velocity component imparted to the backscattered electrons 114 and/or secondary electrons 116 from the primary beam scanning element.

The set of deflection optics may comprise one or more sets of deflection elements. For example, the set of deflection optics 124 may include, but is not limited to, one or more quadrupole elements, one or more octupole elements, or one or more higher-order electro-optic deflection elements. In one embodiment, the set of deflection optics 124 includes one or more electrostatic deflectors. In another embodiment, the set of deflection optics 124 includes one or more magnetic deflectors. For example, the one or more electrostatic or magnetic deflectors may be disposed within a high potential accelerating bushing and float at the bushing potential.

In another embodiment, the emittance analyzer assembly 120 includes one or several first electro-optic lenses 126. In one embodiment, a first electro-optic lens 126 is disposed downstream of the set of deflection optics 124. For example, the first electro-optic lens 126 may be disposed proximate to the set of deflection optics 124. In one example, a first electro-optic lens 126 may be used to terminate the output of the high potential bushing containing the set of deflection optics 124.

In one embodiment, the first electro-optic lens 126 comprises an electrostatic lens. For example, the first electro-optic lens 126 may include, but is not limited to, an electrostatic lens configured to accelerate the backscattered electrons 114 and/or secondary electrons 116 of the image beam. By way of another example, the first electro-optic lens 126 may include, but is not limited to, an electrostatic lens configured to decelerate the backscattered electrons 114 and/or secondary electrons 116 of the image beam. In another embodiment, the first electro-optic lens 126 comprises a magnetic lens.

In one embodiment, the emittance analyzer assembly 120 includes a first electron detector 128 that includes a central bore 130. It should be noted that in the present invention, the central bore 130 may be referred to as the entrance to the analysis portion of the emittance analyzer assembly 120. In the case of SE-BSE imaging, the first electron detector 128 is configured for measuring backscattered electrons 114.

For example, the first electro-optic lens 126 is used to form a demagnified secondary electron conjugate 130 in the plane of the first detector 128 having a demagnification of greater than 1. Most of the backscattered electrons 114 are collected by a detector 128 (e.g., a segmented detector) allowing both bright-field and dark-field backscatter imaging. The secondary electrons 116 and most of the axial backscattered electrons 114 pass through the first detector 128 aperture, minimizing BSE contamination of the SE beam.

The first electron detector 128 may comprise any electron detector known in the art. For example, the first electron detector 128 may include (but is not limited to) a solid state detector. By way of another example, the first electron detector 128 may include (but is not limited to) a multi-channel plate. By way of another example, the first electron detector 128 may include (but is not limited to) a scintillator type electron detector. In one embodiment, the first electron detector 128 is segmented into two or more segments (e.g., the segmented detector shown in fig. 1D). In one embodiment, the segments of the detector 128 are offset from the central aperture in the detector by a distance between the center of the backscattered electron 114 beam and the center of the secondary electron 116 beam in the plane of the detector 128. In another embodiment, the first electron detector 128 includes a magnetic shielding element (e.g., a layer of magnetic material) disposed behind the detection portion of the first electron detector 128.

In one embodiment, the emittance analyzer assembly 120 forms a deceleration region 134 and a drift region 136. In one embodiment, the emittance analyzer assembly 120 includes one or more mesh elements 133 disposed downstream of the first detector 128. In one embodiment, the first mesh component 133 comprises a flat mesh. The first electron detector 128 may be held at ground potential, with the first grounded mesh element 133 held at (or near) the same potential as the surface of the sample 110 (e.g., virtual ground). In this way, the electron decelerating region 133 is formed between the detector 128 and the first mesh element 133. After passing through the detector aperture, the secondary electrons 116 and the axially backscattered electrons 114 are rapidly decelerated to the sample potential. It should be noted that the distance between the detector 128 and the entrance of the drift region 136 (defined by the position of the first mesh element 133) may be selected so as to control (e.g., minimize) the deceleration time of the secondary electrons 116, which helps minimize errors introduced during this time while also preventing most backscattered electrons 114 from entering the drift region 136 of the emittance analyzer assembly 120.

In another embodiment, the emittance analyzer assembly 120 can include a separator tube 132, where the electrical surface resistance between the entrance and exit of the deceleration region 133 forms a linear deceleration voltage gradient. This configuration helps ensure that the equipotential between the entrance and exit of the deceleration zone 133 is flat and uniform.

In another embodiment, the emittance analyzer assembly 120 includes one or more second mesh elements 135. In one embodiment, the second mesh element 135 comprises a hemispherical wire mesh. The second mesh element 135 may also be held at (or near) the same potential as the surface of the sample 110. In this regard, the first mesh element 133 and the second mesh element 135 are held at the same potential, thereby forming an electron drift region 136. It should be noted that the secondary electrons 116 and backscattered electrons 114 enter the drift region 136 and follow the original momentum vector with which the sample emerges from the sample 110. During this drift time, the polar angles of the secondary electrons 116 and the backscattered electrons 114 are aligned. It should be noted that the longer drift times of the secondary electrons 116 and the backscattered electrons 114 result in smaller residual polar angle alignment errors.

In another embodiment, the emittance analyzer assembly 120 includes an energy filter 138. In one embodiment, the energy filter 138 includes a hemispherical mesh centered at a conjugate point in the secondary electron 116 beam path to ensure that the decelerating electric field equipotential from the energy filter is arranged perpendicular to the trajectory of the secondary electron 116 (regardless of the polar angle). It should be noted that the threshold of the energy filter 138 may be changed and the polar angle of the

electrons

114, 116 is hardly affected. The secondary electrons 116 and the axially backscattered electrons 114 may exit from a second mesh element 135 (e.g., a concave mesh) of the drift region 136 perpendicular to the mesh surface. After the secondary electrons 116 and axially backscattered electrons 114 exit the second mesh element 135 (which terminates the drift region 136), they begin to decelerate as the secondary electrons 116 and axially backscattered electrons 114 travel toward the energy filter 138 (e.g., energy filter mesh). The vertical interception of the secondary electrons 116 and the axial backscattered electrons 114 by the energy filter 138 helps ensure that the assembly 120 resolves the total energy of the

electrons

114, 116 and not just the components of the total energy of the

electrons

114, 116.

In some embodiments, the mesh openings of the first mesh element 133, the second mesh element 135, and/or the energy filter 138 may be formed of a magnetic material. It should be noted that the use of magnetic meshes for the first mesh element 133, the second mesh element 135 and/or the energy filter 138 can shield the deceleration region 134 and/or the drift region 136 from stray magnetic fields. In another embodiment, the emittance analyzer assembly 120 can include an axially symmetric magnetic shield surrounding the deceleration region 134 and/or the drift region 136 that also serves to shield the deceleration region 134 and/or the drift region 136 from stray magnetic fields.

In another embodiment, the emittance analyzer assembly 120 includes a deceleration tube 132, the deceleration tube 132 containing or connected to one or more first mesh elements 133 and/or one or more second mesh elements 135.

In another embodiment, the emittance analyzer assembly 120 includes one or several second electro-optic lenses 140. In one embodiment, a second electro-optic lens 140 is disposed downstream of the energy filter 138. In one embodiment, a second electro-optic lens 140 may be used to terminate the drift region 136 or the energy filter 138. In one embodiment, portions of the energy filter 138, the terminals of the drift region 136 (e.g., the second mesh element 135), or the second electron detector 142 (discussed below) may form part of the second electro-optic lens 140.

In one embodiment, the second electro-optic lens 140 comprises an electrostatic lens. For example, the second electro-optic lens 140 may include, but is not limited to, an electrostatic lens configured to accelerate the backscattered electrons 114 and/or secondary electrons 116 of the image beam. By way of another example, the second electro-optic lens 140 may include, but is not limited to, an electrostatic lens configured to decelerate the backscattered electrons 114 and/or secondary electrons 116 of the image beam. In another embodiment, the second electro-optic lens 140 includes a magnetic lens.

In another embodiment, the emittance analyzer assembly 120 includes a second electron detector. In this embodiment, the second electron detector 142 is configured to collect the secondary electrons 116 and/or the axial backscattered electrons 114. For example, as backscattered electrons 114 and/or secondary electrons 116 exit energy filter 138, they are accelerated through a second electro-optic lens 140, the second electro-optic lens 140 serving to demagnify the image beam in the plane of a second electron detector 142.

The second electron detector 142 may comprise any electron detector known in the art. For example, the second electron detector 142 may include (but is not limited to) a solid state detector. As another example, the second electron detector 142 may include (but is not limited to) a multi-channel plate. By way of another example, the second electron detector 142 may include (but is not limited to) a scintillator type electron detector. In one embodiment, the second electron detector 142 is segmented into two or more segments (e.g., the segmented detector shown in fig. 1D). In another embodiment, the second electron detector 142 includes a magnetic shielding element (e.g., a layer of magnetic material) disposed behind the detection portion of the second electron detector 142.

Fig. 1D illustrates a schematic diagram of a segmented electron detector suitable for use as the first electron detector 128, in accordance with one or more embodiments of the present disclosure. As shown in FIG. 1D, the segmented electron detector 128 (e.g., a segmented solid state detector) includes four quadrant detection portions Q1, Q2, Q3, and Q4. Further, the segmented electron detector 128 includes a central detecting portion C. Further, the hole 146 passes through the center of the central detecting portion C. The aperture 146 allows the secondary electrons 116 to pass through the detector 128 while the high angle backscattered electrons 114 are collected by the quadrant detection sections Q1, Q2, Q3, and Q4.

Fig. 1E illustrates a schematic diagram of a high density array electron detector suitable for use as the first electron detector 128, in accordance with one or more embodiments of the present disclosure. As shown in fig. 1E, the high density array electron detector includes a high density array 144 for collecting and resolving the location of electrons. The high density array detector 128 contains apertures 146, again apertures 146 allowing secondary electrons 116 to pass through the detector 128 while high angle backscattered electrons 114 are collected by the array 144.

It should be noted that the detector configurations depicted in fig. 1D-1E may also be implemented in the case of the detector 142, although the aperture 146 is not necessary for the detector 142. In the case where the detector 142 is a segmented detector (e.g., a segmented solid state detector) or a high density array detector, bright-field and/or dark-field images may be formed by the assembly 120.

FIG. 1F illustrates an emittance analyzer 150 according to an alternative embodiment of the present invention. In this embodiment, the emittance analyzer 150 eliminates the first detector thereby sacrificing synchronous detection of backscattered electrons. In another embodiment, the emittance analyzer 150 comprises an orifice plate 158. The aperture plate 158 serves to block backscattered electrons from reaching the detector 142. In this regard, the detector 142 will only detect secondary electrons or near-axis backscattered electrons.

FIG. 1G illustrates an emittance analyzer assembly 120 configured in a BSE-HAR imaging mode, according to one embodiment of the invention. As previously mentioned herein, the system 100 may switch from the SE-BSE configuration of FIG. 1C to the BSE-HAR configuration of FIG. 1G. In some embodiments, one or more controllers 121 may be used to adjust various components of the system 100 to transition from one configuration to a different configuration.

It should be noted that when a beam splitter 112, such as a wien filter, is used to deflect the secondary electron beam 116 and the backscattered electron beam 114 through different angles, the incident secondary electron beam 116 and the backscattered electron beam 114 are not concentric. In one embodiment, the set of deflecting elements 124 may center the backscattered electron cone 114 over the aperture of the first detector 128. In this regard, only a majority of the axially backscattered electrons pass through the apertures 146, as shown in fig. 1G.

In one embodiment, the energy filter 128 is configured to reject secondary electrons such that the second detector 142 simultaneously produces bright-field and dark-field images for high aspect ratio structure imaging using only near-axis backscattered electrons (through the aperture 146). In this regard, the controller 121 (or another controller) may adjust the energy filter 128 so as to reject secondary electrons, thereby converting the emittance analyzer assembly 120 from the SE-BSE mode to the BSE-HAR mode.

In another embodiment, the energy filter 128 is configured to pass only the highest energy backscattered electrons to the second electron detector 142, thereby enhancing the resolution of the images collected with the system 100. In another embodiment, the second electro-optic lens 140 is used to select the polar resolution ratio of the electrons.

In another embodiment, bright-field and/or dark-field images of larger polar angle backscattered electrons (i.e., electrons that are not transmitted through the aperture 146) may be obtained with the first electron detector 128. In this regard, an image of larger polar angle backscattered electrons may be obtained simultaneously with an image formed with paraxial backscattered electrons using second electron detector 142.

Fig. 1H illustrates an emittance analyzer assembly 120 configured for BSE-only mode according to one embodiment of the present invention. As previously mentioned herein, the system 100 may switch from the BSE-HAR configuration of fig. 1G to the BSE-only configuration of fig. 1H.

In one embodiment, the set of deflecting elements 124 may center the backscattered electron cone 114 on the aperture 146 of the first detector 128. In another embodiment, the first electro-optic lens 126 is used to focus the backscattered electrons 114 to form a conjugate point in the path of the backscattered electron beam in the plane of the first detector 128. In this regard, all or a substantial portion of backscattered electrons 114 pass through first detector 128.

In another embodiment, the energy filter 128 is configured (e.g., by the controller 121) to reject the secondary electrons 116. Thus, the second electron detector 142 can be used to simultaneously generate bright-field and dark-field backscattered electron images. In another embodiment, energy filter 128 is configured (e.g., by controller 121) to pass high-energy backscattered electrons (i.e., backscattered electrons above a selected threshold) to second electron detector 142 in order to enhance image resolution. In another embodiment, the second electro-optic lens 140 is used to select the polar angle resolution ratio of the electrons. The drift region 136 of the emittance analyzer assembly 120 can be aligned to the backscattered electron polar angle as effectively as it is aligned to the secondary electron polar angle. It should be noted, however, that backscattered electrons have a larger initial polar angle error than secondary electrons due to transfer from the sample 110 to the assembly 120.

In another embodiment, first electron detector 128 is used to generate a partially bright-field secondary electron image.

It should again be noted that the emittance analyzer assembly 120 can rapidly switch between SE-BSE, BSE-HAR, and BSE-only modes depicted in FIGS. 1C, 1G, and 1H. In some embodiments, one or more controllers 121 may be used to adjust various components of the system 100 to transition between SE-BSE, BSE-HAR, and BSE-only modes. In this regard, the set point for each of the modes may be pre-calibrated and stored in a memory (e.g., a memory of the controller 121). In addition, the set point may be recalled by the controller 121, which the controller 121 then uses to establish the preferred mode.

Fig. 2 illustrates a block diagram of a system 200 implementing two

emittance analyzer assemblies

120a, 120b to form a bandpass energy filter, in which high-pass and bandpass images are acquired simultaneously, in accordance with one or more embodiments of the present disclosure. In one embodiment, system 200 includes a first emittance analyzer 120a and a second emittance analyzer 120b. In another embodiment, the system 200 includes a beam splitter element 202 (e.g., a wien filter).

It is noted herein that the system 200 may be implemented to analyze secondary electrons and/or backscattered electrons. Although the following description focuses on the implementation of the system 200 in the context of secondary electrons, this is not a limitation of the present invention. It should be noted that system 200 and the embodiments and components described below may be extended to the context of backscattered electrons.

In one embodiment, deflection of emittance analyzer assembly 120a is used to remove the lateral momentum vector imposed on the image beam by the illumination scanning optics. In another embodiment, deflection optics 124a of first emittance analyzer assembly 120a are used to center the secondary electron cone onto the optical image path paraxial. In another embodiment, first electro-optic lens 126a of first emittance analyzer assembly 120a forms a point in the plane of detector 128a at the entrance of the deceleration region conjugate to a secondary electron emission point on a sample (not shown) in the secondary electron beam path to block backscattered electrons and coincide with an aperture opening in the plate large enough for secondary electrons to pass through.

In one embodiment, acceleration tube 204 submerges the image path from illumination/image splitter 202 to the entrance of the deceleration region in first emittance analyzer assembly 120a at positive high voltage. In another embodiment, the first electro-optic lens 126a of the first emittance assembly 120a demagnifies the secondary electron beam 114.

In another embodiment, the second electro-optic lens 140a of the first emittance analyzer assembly 120a selects the secondary electron polar angle resolution threshold for dark-field secondary electron imaging.

In another embodiment, energy filter 138a of first emittance analyzer assembly 120a passes only high energy secondary electrons and rejects low energy secondary electrons.

In another embodiment, beam splitter element 202 separates the incoming secondary electron image beam from secondary electrons rejected by first emittance analyzer assembly 120 a.

In another embodiment, the splitter element 202 includes one or more sets of magnetic deflection coils. In another embodiment, the beam splitter is a wien filter. In another embodiment, the accelerating liner 204 can extend along an image path between the first and second

emittance analyzer assemblies

120a and 120b.

In another embodiment, the second emittance analyzer assembly 120b can include an orifice plate at the entrance of the deceleration zone of the second emittance analyzer assembly 120b. For example, the well plate may be a magnetic plate.

In another embodiment, the deflection optics 124b of the second emittance analyzer assembly 120b centers the secondary electron beam cone on the aperture plate of the second emittance analyzer assembly 120b at the entrance of the deceleration zone.

In another embodiment, the second electro-optic lens 126b of the second emittance analyzer assembly 120b forms a conjugate point in the plane of the detector 128b that is centered on the aperture plate at the entrance of the deceleration zone.

In another embodiment, energy filter 138b of second emittance analyzer assembly 120b is used to pass only the highest energy secondary electrons rejected from first emittance analyzer assembly 120 a.

In another embodiment, the second electro-optic lens 126b of the second emittance analyzer assembly 120b sets the secondary electron polar angle resolution threshold.

In another embodiment, the system 200 simultaneously generates: using secondary electrons having greater energy than the energy filter arrangement of first emittance analyzer assembly 120a, while producing secondary high-pass, bright-field, and dark-field images; simultaneously generating bandpass, bright-field, and dark-field secondary electron images using energy between the energy filter settings of the first emittance analyzer assembly 120a and the energy filter settings of the second emittance analyzer assembly 120 b; and bright-field and dark-field backscattered electron images.

Fig. 3 illustrates a block diagram of a system 300 implementing three

emittance analyzer assemblies

120a, 120b, and 120c to capture a complete spectrum of electron energy in low, band pass, and high pass bands, in accordance with one or more embodiments of the present disclosure.

It is noted herein that the system 300 may be implemented to analyze secondary electrons and/or backscattered electrons. Although the following description focuses on the implementation of the system 300 in the context of secondary electrons, this is not a limitation of the present invention. It should be noted that the system 300 and the embodiments and components described below may be extended to the context of backscattered electrons.

In one embodiment, system 300 includes a first emittance analyzer assembly 120a, a second emittance analyzer assembly 120b, and a third emittance analyzer assembly 120c. In another embodiment, the system 300 includes a first beam splitter element 302a and a second beam splitter element 302b. In another embodiment, the system 300 includes three-

armed acceleration bushings

304, 306, 308.

In one embodiment, deflection of emittance analyzer assembly 120a is used to remove the lateral momentum vector imposed on the image beam by the illumination scanning optics. In another embodiment, deflection of first emittance analyzer assembly 120a is used to center the secondary electron cone onto the optical image path paraxial. In another embodiment, first electro-optic lens 126a of first emittance analyzer assembly 120a forms a point in the plane of detector 128 at the entrance of the deceleration region that is conjugate to the secondary electron emission point on the sample (not shown) in the secondary electron beam path to block backscattered electrons and coincide with an aperture opening in the plate that is large enough for the secondary electrons to pass through.

In one embodiment, acceleration tube 204 submerges the image path from illumination/image beam splitter 202 to the entrance of the deceleration region in first emittance analyzer assembly 120a at a positive high voltage. In another embodiment, first electro-optic lens 126a of first emittance analyzer assembly 120a demagnifies secondary electron beam 114.

In another embodiment, second electro-optic lens 140a of first emittance analyzer assembly 120a selects the secondary electron polar angle resolving threshold for dark-field secondary electron imaging.

In another embodiment, the beam splitter element 202 comprises one or more sets of magnetic deflection coils. In another embodiment, the beam splitter is a wien filter. In another embodiment, the accelerating liner 204 can extend along an image path between the first emittance analyzer assembly 120a and the second emittance analyzer assembly 120b.

In another embodiment, the second emittance analyzer assembly 120b may include an orifice plate at the entrance of the deceleration zone of the second emittance analyzer assembly 120b. For example, the well plate may be a magnetic plate.

In another embodiment, the second electro-optic lens 126b of the second emittance analyzer assembly 120b forms a conjugate point in a plane on the aperture plate at the entrance of the deceleration region, the conjugate point centered on the aperture plate at the entrance of the deceleration region.

In another embodiment, the energy filter of the second emittance analyzer 120b passes only the highest energy secondary electrons rejected from the first emittance analyzer 120a and simultaneously presents bright-and dark-field images using secondary electrons (whose energy is between the energy filter setting of the first emittance analyzer 120a and the energy filter setting of the second emittance analyzer 120 b).

In another embodiment, the second electro-optic lens of the second emittance analyzer 120b sets the secondary electron polar angle resolving threshold. In another embodiment, an accelerating

liner

304, 308 along the image path between the first emissivity analyzer 120a and the second emissivity analyzer 120b is used.

In another embodiment, the beam splitter element 302b separates secondary electrons entering the second emittance analyzer 120b from secondary electrons rejected by the second emittance analyzer 120b.

In another embodiment, the accelerating

liners

306, 308 follow an image path between the second emittance analyzer 120b and the third emittance analyzer 120c.

In another embodiment, the system 300 comprises an orifice plate (e.g., magnetic) at the entrance of the deceleration zone of the third emittance analyzer 120c.

In another embodiment, the deflection optics of the third emittance analyzer 120c are used to center the secondary electron beam cone on the aperture plate of the third emittance analyzer 120c at the entrance of the deceleration zone.

In another embodiment, the first electro-optic lens of the third emittance analyzer 120c forms a conjugate point in a plane on the aperture plate at the entrance of the deceleration zone, the conjugate point centered on the aperture plate at the entrance of the deceleration zone.

In another embodiment, the energy filter of the third emittance analyzer 120c passes all secondary electrons rejected from the second emittance analyzer 120b and simultaneously presents bright-field and dark-field images using secondary electrons (whose energy is between the energy filter settings of the first emittance analyzer 120a and the second emittance analyzer 120 b).

In another embodiment, the second electro-optic lens of the third emittance analyzer 120c sets the secondary electron polar angle resolving threshold.

In another embodiment, the system 300 concurrently generates: secondary electron high-pass, bright-field, and dark-field images of secondary electrons having greater energy than the energy filter settings of first emittance analyzer 120 a; band-pass, bright-field, and dark-field secondary electronic images using energy between the energy filter setting of the first emittance analyzer 120a and the filter setting of the second emittance analyzer 120 b; bright-field and dark-field images of secondary electrons having less energy than the energy filter setting of the second emittance analyzer 120 b; and bright-field and dark-field backscattered electron images.

Fig. 4A-4H illustrate the effects of wafer surface charging and beam drift during image acquisition in accordance with one or more embodiments of the present disclosure.

It should be noted that in order to operate the emittance analyzer assembly 120 of the present invention with full performance authority, the image beam position and image beam cone half angle must be unaffected by the local charge field and other external influences. The image beam focal plane from the first electron optics lens 124 should remain stable in the presence of the charged sample 110 and the image beam position in the plane spanned by the first electron optics lens 124 should be stable and coaxial with the emittance analyzer assembly 120. It should be noted that a combination of high extraction field, in-situ flood, and detector output feedback can be used to stabilize the image beam position and cone angle drift caused by sample charging.

Fig. 4A illustrates a conceptual diagram 400 of sample surface charging caused by a primary beam during image acquisition in a low extraction field environment, in accordance with one or more embodiments of the present disclosure. As charge accumulates on the sample 110 (e.g., wafer), the secondary electrons experience a strong transverse field of up to millions of volts per meter at the edge of the field of view (FOV), deflecting the secondary electron cone 116 from zero degrees (402) to non-zero degrees (404) alignment with respect to the optical axis. The deflection across the secondary electron energy spectrum is asymmetric, with slower secondary electrons undergoing greater deflection due to longer interaction times. In this example, the electric field is symmetric and the secondary electrons in the middle of the FOV are undeflected. Thus, the secondary electron image beam deflection angle varies with position in the FOV. In addition to secondary electron beam instability, the local charge presents a potential barrier (e.g., 5V in the example of fig. 4A) to secondary electrons (e.g., 5V in the example of fig. 4A). Thus, in this example, all secondary electrons having energies less than 5eV fail to reach the emittance analyzer assembly 120 (not shown in fig. 4A).

Fig. 4B illustrates a conceptual diagram 410 of local charge field equipotential and large extraction field equipotential in accordance with one or more embodiments of the present disclosure. Fig. 4C illustrates a conceptual diagram 420 of a superposition of a local charge field and a large extraction field, in accordance with one or more embodiments of the present disclosure. It should be noted that the extraction field reduces the potential barrier presented by the charge field to the secondary electrons and significantly reduces the lateral field strength at the edges of the FOV. Thus, the image beam 116 is not as strongly deflected at the edge of the FOV and more of the image signal reaches the detector of the emittance analyzer assembly 120. Fig. 4D depicts an image 430 obtained from the sample 110 in which secondary electron beam drift occurred during image acquisition. As shown, the image 430 shows a large amount of contrast variation that varies diagonally across the image due to image beam drift during imaging.

It should be noted that utilizing in-situ flood pre-fill can reduce charge barriers and lateral fields caused by surface charging.

Fig. 4E illustrates a conceptual diagram 440 of the effect of flood charge in accordance with one or more embodiments of the present disclosure. For example, as shown, an in-situ flood charge of 10 μm area is applied. The charge equipotential in the in-situ pre-fill surrounding the 1 μm image area and the equipotential lines in the large extraction field (1.5 kV/μm) are depicted. The flood field used should saturate the insulating material to be imaged. In this way, the charge added by the primary beam 104 during imaging should not significantly alter the surface potential of the sample 110.

Fig. 4F illustrates a conceptual diagram 450 of an overlay of an in-situ flood charge field and an extraction view, in accordance with one or more embodiments of the present disclosure. In the above example, the potential barrier presented to the secondary electrons is reduced to <0.5V and the transverse field is almost eliminated at the edges of the image FOV. Thus, the maximum image beam reaches the detector and the image beam position is more stable over the entire image FOV. Lensing of the image beam by local charging is significantly reduced by reducing the local field strength associated with local charging.

Fig. 4G illustrates a block diagram of a system 100 equipped with in-situ flood capability, in accordance with one or more embodiments of the present disclosure. The use of an in situ flood mode may be used in combination with the emittance analyzer assembly 120 of the present invention to help eliminate polarity error resolution errors caused by surface charging. Furthermore, the performance of the emittance analyzer assembly 120 is enhanced due to the stability of the image beam achieved using the in situ flood process.

In one embodiment, as shown in fig. 4G, system 100 may include a dedicated flood gun 455 configured to pre-fill the surface of sample 110 with a selected amount of charge. In another embodiment, not shown in fig. 4G, the system may pre-fill the surface of the sample 110 with the primary beam 104 from the electron source 102.

In one embodiment, the in situ flood time is determined by detecting with the emittance analyzer assembly 120 that the surface potential of the sample has been charged to a predetermined value. In another embodiment, system 100 may pre-fill the surface of the sample using primary beam 104 or dedicated flood gun 455 once it is determined that the surface potential of sample 110 has been charged to a predetermined value. For example, the controller 121 may receive surface potential measurements of the sample 110 from the emittance analyzer assembly 120. The controller 121 may then determine whether the surface of the sample 110 has been charged to a predetermined value or threshold. In the case where the surface of the sample 110 shows a charge above a predetermined value, the controller 121 may in turn direct the electron source 102 or the dedicated flood gun 455 to apply a pre-fill to the surface of the sample 110.

In another embodiment, immediately prior to image acquisition, system 100 may pre-fill sample 110 via in-situ flood gun 455 to a predetermined voltage, then hold emittance analyzer assembly 120 at that voltage for a predetermined time prior to asserting the control loop during the beginning of image acquisition.

In another embodiment, an accelerating liner is placed coaxially along the

image beam path

114, 116 to minimize the transition time of the secondary electrons 116 to the emittance analyzer assembly 120 and reduce the axial displacement of translation to polar angle errors.

Fig. 4H illustrates a landing pattern 462 of secondary electrons on the segmented electron detector 142, in accordance with one or more embodiments of the present disclosure.

In the event that residual image beam position drift exists, feedback from the emittance analyzer assembly 120 may be used to reduce (or eliminate altogether) this drift. For example, when the image beam is properly aligned and the current intercepted by the second electron detector 142 (see, e.g., fig. 1A) is stable, the difference between any two opposing outer quadrants of the five-segment detector (shown in fig. 4G) should be zero. If the image beam is offset, the difference between the opposing outer quadrants will become non-zero and can be used as an error signal to drive appropriate corrections via the deflection optics 124 (e.g., deflection plate) of the emittance analyzer assembly 120. In this regard, the following relationship may be used for deflection correction:

(Q1-Q3)/(C + Q1+ Q2+ Q3+ Q4)) equation 1

(Q2-Q4)/(C + Q1+ Q2+ Q3+ Q4)) equation 2

Wherein Q1, Q2, Q3, Q4 and C represent signals measured by the Q1, Q2, Q3, Q4 and C detection portions of the five-segment multi-segment detector. It should be noted that dividing the difference by the total signal helps enable these error signals to resist small changes in image beam current, which may result from changes in the primary beam 104 and sample-specific secondary emissions.

Fig. 4I illustrates a flow diagram 470 depicting a method for correcting beam misalignment in the emittance analyzer 120 (or similar configuration), in accordance with one or more embodiments of the present disclosure. In step 472, signals are acquired from the Q1, Q2, Q3, Q4, and C portions of the multi-segment detector 142. For example, the controller 121 may receive signals measured from the Q1, Q2, Q3, Q4, and C portions of the multi-segment detector 142. In step 474, one or more deflection corrections may be determined for the image beam. For example, the controller 121 may apply equation 1 and/or equation 2 described above to determine the deflection correction required for aligning the image beam incident on the detector 142. In step 476, the image beam alignment is adjusted based on the determined deflection correction. For example, the controller 121 may direct the set of deflection optics 124 to correct the position of the image beam based on the deflection corrections calculated using equations 1 and/or 2.

It should be noted that although the segmented detector 142 of FIG. 4H (or FIG. 1A) is described in the context of the emittance analyzer assembly 120, this is not a limitation on the use of the detector depicted in FIG. 4H. It should be recognized herein that the segmented detector of fig. 4H may be implemented in the context of any electronic analysis device, such as (but not limited to) an emissivity analyzer or a drift tube/energy filter system.

It should be further noted that one or more large detector arrays may be used as one or more detectors in the emittance analyzer assembly 120 to improve azimuthal and polar angle resolution. In one embodiment, a large detector array may be used to obtain the polarity and azimuthal distribution of each image pixel in one image capture. In another embodiment, subsequent to acquiring the polar and azimuthal distribution maps, a 3D image of the surface topology of the sample may be presented. In another embodiment, the polar and azimuthal distributions may be used to provide 3D metrology information about the sample 110.

In another embodiment, emittance analyzer assembly 120 may scan energy filter 128 while acquiring polar and azimuthal information to extract information about how the polar and azimuthal distributions vary according to secondary electron energy.

In another embodiment, utilizing polarity and azimuth information, emittance analyzer assembly 120 may render an image of the surface topology with only secondary electrons having energies above the programmable energy filter threshold.

In another embodiment, the emittance analyzer assembly 120 may acquire two images (each image acquired with different energy filter thresholds) and subtract the two images to render a dark-field image using only secondary electrons having energies between the two energy filter set points.

In another embodiment, the emittance analyzer assembly 120 may acquire the polarity and azimuthal information of secondary electrons above a threshold set by the energy filter 128, and also simultaneously acquire the average surface potential of the scanned area of the sample 110.

Fig. 5A illustrates a conceptual diagram 500 of the error introduced during energy resolution due to charging of the surface of the sample by the primary beam.

In some embodiments, the control voltage of the emittance analyzer 120 is referenced to the surface potential of the sample 110. In the case of isolation, charging of the wafer, tracking of the surface potential of the image beam emission point may be performed.

Curve 502 depicts the secondary electron energy spectrum obtained from a neutral surface (i.e., a surface potential of 0V). Curve 504 depicts the secondary electron energy spectrum obtained from the charged surface. It should be noted that the potential energy imposed on the secondary electrons from the surface voltage shifts the secondary electron energy distribution. Furthermore, charging during imaging of the insulating surface will cause the secondary electron energy spectrum to change over time. This effect introduces errors in the desired energy resolution threshold. For example, as shown in fig. 5A, the energy-resolving threshold is set to reject secondary electrons of 5eV and below. In the case where the secondary electron emitting surface is charged with a 2.5V positive voltage, the energy filter resolves the distribution threshold shift by that amount and introduces an error of 2.5eV in the desired 5eV threshold.

Controlling the voltage reference sample surface potential is generally described in U.S. patent publication 2013/0032729 and U.S. patent No. 7,141,791, which are incorporated herein by reference in their entirety.

Fig. 5B illustrates a block diagram of a system 500 equipped with a gated integrator 512, in accordance with one or more embodiments of the present disclosure. In one embodiment, the gated integrator 512 is used to close the control loop between the sample surface potential and the image path optics to eliminate charge-induced image artifacts. In this regard, the energy filter threshold offset may be locked to the sample surface potential.

It should be noted that the term "gating" is used to refer to that the input may be "disconnected" from the input of the integrator to ignore undesired surface voltage information. For example, it may be desirable to disconnect the input during one or more of the following operational settings: during an edge of an imaging scan frame; during retrace; when the light beam is blanked and the like.

The imaging optics may include, but are not limited to, a set of deflection optics 503, a first electro-optic lens 505, an energy filter 507, a second electro-optic lens 509, and a detector 511 (e.g., a segmented detector). In one embodiment, the image path optics that form the control loop with the gated integrator 512 includes an energy filter 507. The energy filter 507 may comprise, but is not limited to, a flat mesh, a hemispherical/concave mesh, or a plurality of meshes.

In one embodiment, the gated integrator 512 includes a front end and mixing module 528 and a D/a module 530. In one embodiment, the detector output is received by the front end and mixing module 528. For example, the output of each of the multi-channel segmented detectors (e.g., detectors 142) is transmitted to the front end and mixing module 528. The total detector current is in turn transmitted from the module front end and mixing module 528 to the difference module 532. Further, the front end and mixing module 528 may provide video output. The expected average value of the detector current is transmitted from the D/a module 530 to the difference module 532. The difference module 532 then compares the detector current (e.g., the sum of all channels of the segmented detector 142) to an expected average of the detector current for a particular energy threshold. It should be noted that the difference between the expected value of the detector current and the actual total value of the detector current indicates that more or less electrons are passing through the energy filter than expected. The output of the difference module 532 is then transmitted to the gating/integration module 534. The difference in the difference module 532 is then integrated by a gating/integration module 534 with a predetermined time constant. Thus, the output tracks the surface potential of the sample.

The output of the gating/integration module 534 is also transmitted to one or more signal processing elements 536 (e.g., processing circuits, converters, drivers, and the like). Processing element 536 then feeds the offset from gating/integration module 534 to energy filter 507 as the offset, thereby preserving the energy filter resolution threshold. In addition, processing element 536 provides a sample surface potential output.

In one embodiment, the integration time constant may be set to a range of values depending on the desired average quantity. In another embodiment, the integrator may be gated, wherein when gated, the output of the integrator remains at that value to ignore the detector during retrace or lock the control loop onto only a portion of the image area. In one embodiment, the gated integrator 512 locks with a signal from a pre-scan region outside the field of view and starts closed loop image acquisition using that pre-scan lock value. In another embodiment, the gated integrator 512 locks with a signal from a pre-scan region outside the image region and holds the lock value during image acquisition. In another embodiment, the gated integrator 512 uses signals from only part of the image area and gates or blocks signals from other areas of the image. In another embodiment, gated integrator 512 uses a gating signal generated during the retrace of the beam. In another embodiment, the system 510 stores one or more lock values of the gated integrator 512 corresponding to different image points in the recipe (recipe) and forces the gated integrator 512 to use those lock values when beginning each image acquisition during execution of the recipe.

In another embodiment, the gated integrator 512 may transmit one or more control signals to the

control circuits

514, 516, 518, 520, 522, 524, and 526 to control various components of the electro-optical system 500 in response to the output of the gated integrator 512.

It should be noted that one drawback to the approach depicted in fig. 5B is that small variations in secondary electron emission from wafer to wafer and variations in primary beam current or detector gain over time can introduce errors in the predetermined detector current that cause incorrect energy filter threshold set points. This disadvantage can be mitigated by an auto-calibration procedure, in part, at the start of the recipe or during movement of the stage between image points. In a first step, the calibration procedure may include setting the energy filter to 0V. In a second step, the calibration procedure may include measuring the detector current. In a third step, based on prior knowledge of the secondary electron distribution, the calibration procedure may include calculating an expected detector current value for a selected energy filter resolution threshold.

Fig. 5C illustrates a block diagram of a system 540 equipped with a gated integrator 512 for establishing a control loop for a multi-beam energy filter array, in accordance with one or more embodiments of the present disclosure.

In one embodiment, the system 540 includes a multi-beam electro-optical system 541. In one embodiment, the system 539 includes a cathode 542 and a multi-beam aperture 543 to form N primary beams 544. In response to the N primary light beams 544, the sample 110 emits N secondary electron beams 545. The electro-optical system 539 further comprises analyzer optics 541. In one embodiment, the analyzer optics 539 include one or more deflection optics 546, a first electro-optic lens 547, an energy filter array 549, a detector array 550, and a set of N detector preamplifiers 551.

In one embodiment, the beam energy filters 549 are generic and controlled as a group. It should be noted that in settings in which the beam energy filter 549 is controlled globally, the sum of all primary beam currents may be used to lock the control loop which provides a significantly reduced lock time. In another embodiment, each beam energy filter in the multiple energy filters 549 is controlled separately. In this regard, each beam energy filter 549 is controlled separately.

It should be noted that the control steps described in the context of gated integrator 512 of fig. 5B can be extended generally to the multiple beam context of 5C. In addition, the processing circuitry 536 may adjust the potential of the energy filter apertures 549 via the direct high voltage supply 538.

In one embodiment, the system 540 may obtain the multi-beam image set using a second energy filter setting and employing a difference between the first and second image sets to obtain the band-pass multi-beam image set. In another embodiment, system 540 may use a control loop to control-hold-control-hold sequence such that only a portion of the image frame is acquired using the control loop operation.

In another embodiment, the system 540 uses an energy filter to record the surface charge curve during recipe setup while an image is acquired and this wire is used to control the energy filter potential during image acquisition when the recipe is executed. Alternatively, the system 540 may bias the control loop during image acquisition when executing a recipe.

It should be noted that the drift tube/energy filter and emittance analyzer assembly benefits from having a control voltage that references the wafer surface potential. However, since they all employ a drift region, errors in controlling the reference voltage cause large variations in the radial distribution of the secondary electrons in the plane of the detector.

Fig. 5D illustrates the secondary electron distribution 560 in the plane of the detector without the loop controlled charged surface. Fig. 5E illustrates the secondary electron distribution 561 in the plane of the detector of the charged surface with a closed loop between the wafer surface potential and the emittance analyzer assembly 120. By generating the error signal of the gated integrator using the ratio of (center channel)/(outer channel) in the second detector 142, the polar angle resolved drift due to charging can be stabilized (see graph 561).

Fig. 5E illustrates a graph 550 depicting the relationship between drift region potential error and change in the ratio of the center channel divided by the sum of the four outer quadrants. The error signal derived from the ratio of the detector channels will be free from errors in primary beam current variations, secondary emission variations, and gain variations in the video chain.

For example, if we assume a current of 1nA in the secondary beam, the signal-to-noise ratio of the signal consisting of (center channel)/(outer channel) has the Taylor series approximation (Taylor series approximation) shown in the graph 560 of fig. 5F. Graph 560 also depicts the sum of all channels Q1-Q4 and C.

FIG. 5G illustrates a servo 580 for pinning the emittance analyzer 120 to the surface potential of the sample 110. It should be noted that the embodiments and components previously described herein with respect to the gated integrator 512 should be construed to extend to the embodiment illustrated in 5G. In one embodiment, the image path optics that form the control loop in conjunction with the gated integrator 512 includes an emittance analyzer assembly 120. For example, everything from the entrance of the deceleration region to the detector may act as image path optics, whereby the reference potentials for these components are determined by the gated integrator 512. In another embodiment, the gated integrator may use the control circuit components 581-589 to control the potentials of the various components.

In another embodiment, the system 580 includes an acceleration sleeve 590 positioned around the image path from the splitter element 112 to the entrance of the emittance analyzer deceleration zone to minimize the image beam transition time. It should be noted that the acceleration bushing can reduce transition time induced errors in polar angle resolution.

It is noted herein that the gated integrator scheme implemented in the context of the emittance analyzer 120 yields real-time (within the bandwidth of the control loop) surface potentials of the sample 110. In one embodiment, the emittance analyzer 120 of the system 580 can be used to construct a potential map of the sample surface.

Fig. 5H illustrates the elements of the emittance analyzer 120 controlled or "servoed" by the gated integrator 512. The scheme may present a static potential environment for the image beam. In one embodiment, all elements between first detector 128 and second detector 142, including first detector 128 and second detector 142, float at the surface potential of sample 110. It should be noted that the secondary electrons 116 in the sample 110 accelerate as they leave the sample 110 and their energy changes less due to surface charging. In one embodiment, one or more components of the emittance analyzer assembly 120 are servoed with a sample surface charge voltage such that the electric field environment presented to the secondary electrons is constant even in the presence of a charging surface voltage.

Fig. 5I illustrates a block diagram of a system 591 equipped with a gated integrator 512, in accordance with one or more embodiments of the present disclosure. In one embodiment, gated integrator 512 is used to close a control loop containing drift tube 579. It should be noted that the embodiments and components previously described herein with respect to the gated integrator 512 should be interpreted as extending to the embodiment illustrated in fig. 5I. The drift tube used in the embodiment of fig. 5I is generally described in U.S. patent No. 7,141,791, which is incorporated by reference above in its entirety.

In another embodiment, the gated integrator may control the potentials of the various components using control circuit components 592 through 599.

Fig. 6A illustrates a system 600 equipped with the in-situ flood, gated integrator, and emittance analyzer capabilities previously described herein, in accordance with one or more embodiments of the present disclosure. In one embodiment, the system 600 includes the emittance analyzer assembly 120 and the gated integrator 512. In another embodiment, system 600 includes an in-situ flood gun 602 and a flood gun controller 601. In an alternative embodiment, the electron source 102 may be used to provide in situ flood, as previously discussed herein.

The in-situ flood gun 602 and controller 601 (or electron source 102) can be configured to be combined with the emittance analyzer assembly 120 to reliably and repeatedly pre-fill the sample 110 to a predetermined voltage during a flood using feedback from the emittance analyzer assembly 120.

In one embodiment, during coarse stage travel, the emittance analyzer assembly 120 high voltage may be set to a value determined during recipe setup. In another embodiment, during coarse stage settling, the flood gun 602 and flood beam deflector 604 are powered on and the first electron detector 128 in the emittance analyzer assembly 120 is turned off. Furthermore, secondary electrons from the flood beam are routed to the deflector by the beam splitter element 112. As shown in fig. 6B, the first electron detector 128 eliminates most of the in-situ secondary electrons, thereby protecting the second electron detector 142 from saturation. As the surface of the sample 110 charges, the secondary electron energy approaches the cutoff energy of the energy filter 138. In this mode, the energy filter 128 need not be correct, but must be accurate and repeatable. As secondary electrons begin to be rejected by the energy filter 128, a drop in detector current is sensed by the gated integrator 512, which in turn sends a signal to the flood gun controller 601 and shuts down the flood gun.

During fine stage settling, the emittance analyzer assembly 120 has been set to near the surface potential of the sample 110 and only a small pre-scan outside the FOV is required to lock the gated integrator 512. Lock-gated integrator 512 image acquisition is then initiated.

It should be noted that in the case where the semiconductor is charged in order for the emittance analyzer assembly 120 to operate in a stable manner, a large area in-situ pre-fill may be required.

Fig. 6C illustrates a conceptual diagram 610 of the relationship between charge accumulation and layer thickness for sample 110. Sample 110 includes a sample of a semiconductor device including a silicon layer and a polysilicon layer and in SiO ₂ A metal layer coated in the layer. In addition, I _p Representing an initial current 612 associated with the primary beam. I is _c Representing the specific gravity of the current associated with the charge held in the surface. I is _L Representing the leakage current associated with charge leaking from the landing. I.C. A _SE,BSE Is the current associated with the secondary electrons and backscattered electrons emitted by the sample surface. It should be noted that the charging rate may be obtained by irradiating a known area with the primary beam 104 and allowing the emittance analyzer assembly 120 to track the wafer surface potential. Furthermore, it is possible to derive layer Critical Dimensions (CD) using prior knowledge of the processes and characteristics during recipe setup.

In one embodiment, one or more controllers (e.g., controller 121) or other similar control systems may include one or more processors communicatively coupled to an output device (e.g., detector 142) and a memory. In one embodiment, one or more processors are configured to execute a set of program instructions maintained in memory.

The one or more processors of the controller may include any one or more processing elements known in the art. In this regard, the one or more processors may include any microprocessor device configured to execute algorithms and/or instructions. In one embodiment, the one or more processors may be comprised of a desktop computer, mainframe computer system, workstation, graphics computer, parallel processor, or other computer system (e.g., network computer) configured to execute programs configured to operate one or more portions of the various system and subsystem embodiments, as described herein. It should be recognized that the steps described in this disclosure may be implemented by a single computer system or alternatively by multiple computer systems. In general, the term "processor" may be defined broadly to encompass any device having one or more processing elements that execute program instructions from a non-transitory memory medium. Further, different subsystems of the system may include processors or logic elements suitable for implementing at least a portion of the steps described herein. Accordingly, the foregoing description is not to be construed as limiting, but merely as illustrative of the present invention.

The memory may include any storage medium known in the art suitable for storing program instructions executable by the associated processor or processors. For example, the memory may include a non-transitory memory medium. For example, the memory may include, but is not limited to, read-only memory, random access memory, magnetic or optical memory devices (e.g., disks), magnetic tape, solid state drives, and the like. In another embodiment, it is noted herein that the memory is configured to store one or more results in the output of various systems/subsystems and/or various steps described herein. It should further be noted that the memory may be housed in a common controller that includes one or more processors. In alternative embodiments, the memory may be remotely located with respect to the physical location of the processor and controller. For example, one or more processors of the controller may access remote memory (e.g., a server) accessible over a network (e.g., the internet, an intranet, and the like). In another embodiment, the memory stores program instructions for causing one or more processors to implement the various steps described by this disclosure.

Those skilled in the art will recognize that advanced technology has advanced to the point where there is little distinction left between hardware and software implementations of aspects of the system; the use of hardware or software is often (but not always, because the choice between hardware and software can become significant in a particular context) a design choice representing a cost versus efficiency tradeoff. Those of skill in the art will appreciate that there are various vehicles by which processes and/or systems and/or other technologies described herein can be effected (e.g., hardware, software, and/or firmware), and that the preferred vehicle will vary with the context in which the processes and/or systems and/or other technologies are deployed. For example, if an implementer determines that speed and accuracy are highest, the implementer may select a primary hardware and/or firmware vehicle; alternatively, if flexibility is highest, the implementer may select a primary software implementation; or alternatively, the implementer may opt for some combination of hardware, software, and/or firmware. Thus, there are some possible vehicles to which the processes and/or devices and/or other techniques described herein may be affected, none of which is inherently superior to the other, as any vehicle to be used is a choice depending on the context of the vehicle in which it is to be deployed and the particular considerations (e.g., speed, flexibility, or predictability) of the implementer, any of which may be different. Those skilled in the art will recognize that optical aspects of implementations will typically employ optically-oriented hardware, software, and/or firmware.

Those skilled in the art will recognize that the devices and/or processes described in the art are typically described in the manner set forth herein, and that engineering practices are used hereinafter to integrate such devices and/or processes described into data processing systems. That is, at least a portion of the devices and/or processes described herein can be integrated into a data processing system with a reasonable amount of experimentation. Those skilled in the art will recognize that a typical data processing system typically includes one or more of system units including video display apparatus, memory (e.g., volatile and non-volatile memory), processors (e.g., microprocessors and digital signal processors), computational entities (e.g., operating systems, drivers, graphical user interfaces, and applications), one or more interactive devices (e.g., touch pads or screens), and/or a control system including feedback loops and control motors (e.g., feedback for sensing position and/or velocity; control motors for moving and/or adjusting components and/or quantities). A typical data processing system may be implemented using any suitable commercially available components, such as those commonly found in data computing/communication and/or network computing/communication systems.

It is believed that the present invention and many of its attendant advantages will be understood by the foregoing description, and it will be apparent that various changes may be made in the form, construction and arrangement of the components without departing from the disclosed subject matter or without sacrificing all of its material advantages. The form described is merely explanatory and the appended claims are intended to cover and encompass such changes.

Claims

1. A scanning electron microscope apparatus for suppressing errors caused by surface charging, comprising:

a primary electron beam source;

a set of electro-optical elements directing at least a portion of the primary electron beam onto a surface of a sample;

an emissivity analyzer assembly; and

a controller comprising one or more processors configured to execute a set of program instructions configured to cause the one or more processors to perform the steps of:

receiving one or more surface potential measurements of the surface of the sample from the emittance analyzer assembly;

determining whether the surface of the sample is charged to a selected potential threshold based on the one or more surface potential measurements; and

upon determining that the surface is charged above a selected threshold, directing at least one of the primary electron beam source or a flood source to provide an amount of charge to the surface of the sample.

2. The scanning electron microscope apparatus of claim 1, the emittance analyzer assembly including:

a set of deflection optics;

a first electro-optic lens;

a first electron detector including a central aperture, wherein the first electron detector is configured to collect at least one of a portion of secondary electrons or a portion of backscattered electrons;

a first mesh element disposed downstream of the first electron detector;

a second mesh element disposed downstream of the first mesh element, wherein the first electron detector and the first mesh element form a deceleration region, wherein the first mesh element and the second mesh element form a drift region;

an energy filter disposed downstream of the second grounded screen element;

a second electro-optic lens; and

a second electron detector configured to collect at least one of an additional portion of the secondary electrons or an additional portion of the backscattered electrons.

3. The scanning electron microscope apparatus of claim 2, wherein the set of deflection optics is configured to align an image beam comprising the at least one of the secondary electrons or the backscattered electrons with one or more components in the emittance analyzer assembly.

4. The scanning electron microscope apparatus of claim 2, wherein the set of deflection optics includes at least one of a set of electrostatic deflectors or magnetic deflectors.

5. The scanning electron microscope apparatus of claim 2, wherein the set of deflection optics is disposed within an acceleration sleeve.

6. The scanning electron microscope apparatus of claim 2, wherein the first electro-optic lens is disposed downstream of the set of deflection optics.

7. The scanning electron microscope apparatus of claim 2, wherein the first electro-optic lens comprises:

at least one of an electrostatic lens or a magnetic lens.

8. Scanning electron microscopy apparatus according to claim 2 wherein the first electron detector is held at ground.

9. The scanning electron microscope apparatus of claim 2, wherein the first mesh element is disposed downstream of the first electron detector and held at the same potential as a surface potential of the sample.

10. The scanning electron microscope apparatus of claim 2, wherein the second mesh element is disposed downstream of the first mesh element and held at the same potential as the surface potential of the sample.

11. The scanning electron microscope device according to claim 2, wherein the first mesh element comprises a flat wire mesh.

12. The scanning electron microscope device of claim 2, wherein the second mesh element comprises a hemispherical wire mesh.

13. The scanning electron microscope device of claim 2, wherein the energy filter comprises a hemispherical wire mesh.

14. The scanning electron microscope apparatus of claim 2, wherein at least one of the first electron detector or the second electron detector comprises:

at least one of a multi-channel plate detector, a solid state detector, or a scintillator detector.

15. The scanning electron microscope apparatus of claim 2, wherein at least one of the first electron detector or the second electron detector is segmented into two or more segments.

16. The scanning electron microscope apparatus of claim 1, wherein the emittance analyzer assembly is configured to operate in a secondary electron and backscattered electron imaging mode.

17. The scanning electron microscope apparatus of claim 1, wherein the emittance analyzer assembly is configured to operate in a backscattered electron and high aspect ratio electron imaging mode.

18. The scanning electron microscope apparatus of claim 1, wherein the emittance analyzer assembly is configured to operate in a backscatter electron only imaging mode.

19. The scanning electron microscope apparatus of claim 1, wherein the primary electron beam source is configured to apply an in-situ flood prefill to the sample by the flood source.