TW202338889A - Back-scatter electrons (bse) imaging with a sem in tilted mode using cap bias voltage - Google Patents

Abstract

A method of evaluating a region of a sample, the method comprising: positioning a sample within a vacuum chamber; generating an electron beam with a scanning electron microscope (SEM) column that includes an electron gun at one end of the column and a column cap at an opposite end of the column; focusing the electron beam on the sample and scanning the focused electron beam across the region of the sample, while the SEM column is operated in tilted mode, thereby generating secondary electrons and backscattered electrons from within the region; and during the scanning, collecting backscattered electrons with one or more detectors while applying a negative bias voltage to the column cap to alter a trajectory of the secondary electrons preventing the secondary electrons from reaching the one or more detectors.

Description

Scanning electron microscopy (SEM) in tilt mode using cap bias for backscattered electron (BSE) imaging

This application claims priority from U.S. Application No. 17/243,478 filed on April 28, 2021. The disclosures of this case are incorporated herein by reference in their entirety for all purposes.

In the study of electronic materials and processes used to fabricate such materials into electronic structures, samples of electronic structures may be used for microscopic examination for the purpose of failure analysis and device verification. For example, a sample such as the electronic structure of a silicon wafer can be analyzed in a scanning electron microscope (SEM) to study specific characteristics in the wafer. The characteristics may include the fabricated circuit and any defects formed during the manufacturing process. An electron microscope is one of the most useful pieces of equipment for analyzing the microstructure of semiconductor devices.

When a sample is examined using an electron beam from an SEM tool, secondary electrodes and backscattered electrons are created when the electron beam strikes the sample. Secondary electrons originate from the atoms of the sample itself and are the result of inelastic interactions between the electron beam and the sample. Secondary electrons have relatively low energy (e.g., 0-20 eV) and originate from or near the sample surface. After elastic interaction between the beam and the sample, backscattered electrons (BSE) are reflected back. The backscattered electrons may have an energy level close to that of the electron beam, and thus may originate from deeper regions of the sample.

Because of these and other differences, secondary electrons and backscattered electrons can provide different types of information. Secondary electrons can provide detailed surface information about the sample, while backscattered electrons show high sensitivity to differences in atomic number and are thus used to provide material contrast when imaging objects.

Typically, the secondary electron yield is much higher than the backscattered electron yield. Therefore, when backscattered electrons are collected, the secondary electron signal needs to be suppressed to accurately see the backscattered electron signal. In a typical SEM tool, suppression of secondary electron signals is accomplished by placing an energy filter between the sample and detector so that the energy filter prevents relatively low-energy secondary electrons from reaching the detector. Although this method has been used successfully in the past, new methods of detecting backscattered electrons are needed.

Some embodiments of the present invention relate to improved methods and techniques for collecting backscattered electrons when imaging a sample with a scanning electron microscope. The collected electrons can be used to evaluate properties of the sample, such as to provide material contrast.

In some embodiments, a method of evaluating an area of a sample includes: positioning the sample in a vacuum chamber; generating an electron beam with a scanning electron microscope (SEM) column including at one end of the column Electron guns and column caps at opposite ends of the column; focus the electron beam on the sample and scan the focused electron beam across the sample area while the SEM column is operated in tilt mode, thereby generating secondary electrons from within the area and Anti-scattered electrons; and during scanning, use one or more detectors to collect anti-scattered electrons, while applying a negative bias to the column cap to change the trajectory of secondary electrons, thereby preventing secondary electrons from reaching one or more detectors device.

Various implementations of the embodiments described herein may include one or more of the following features. An image of at least a portion of the area is generated from the detected backscattered electrons. Negative bias voltages of minus 50 volts and minus 1000 volts were applied to the column caps. Apply a negative bias voltage between minus 100 volts and minus 500 volts to the post cap. The column cap may have a tapered shape with an opening at its tip, and the electron beam may be directed through the opening. Backscattered electrons can be collected using in-lens detectors and top detectors. Backscattered electrons can be collected using external detectors.

Some embodiments relate to a non-transitory computer-readable medium storing instructions for performing X-ray spectroscopic surface material analysis of a region of a sample according to any method above or herein. For example, by positioning the sample in a vacuum chamber and generating an electron beam with a scanning electron microscope (SEM) column including an electron gun at one end of the column and an electron gun at an opposite end of the column. the column cap at , using one or more detectors to collect backscattered electrons, while applying a negative bias to the column cap to change the trajectory of secondary electrons, thereby preventing secondary electrons from reaching one or more detectors.

Some embodiments relate to systems for X-ray spectroscopic surface material analysis of a region of a sample according to any of the methods described above or herein. For example, the system may include: a vacuum chamber; a sample support configured to maintain the sample within the vacuum chamber during the sample evaluation process; and a scanning electron microscope (SEM) column configured to direct a charged particle beam toward the sample. In a vacuum chamber, the SEM column includes an electron gun at one end of the column and a column cap at an opposite end of the column; a detector configured to detect backscattered electrons; and a processor and memory coupled to the processor body. The memory may include a plurality of computer-readable instructions that, when executed by the processor, cause the system to: position a sample in a vacuum chamber; generate an electron beam using a scanning electron microscope (SEM) column; and the scanning An electron microscope column includes an electron gun at one end of the column and a column cap at an opposite end of the column; an electron beam is focused on a sample and the focused electron beam is scanned across the sample area while the SEM column is operated in a tilt mode , thereby generating secondary electrons and backscattered electrons from within the area; and using one or more detectors to collect backscattered electrons, while applying a negative bias to the column cap to change the trajectory of secondary electrons, thereby preventing secondary electrons Reach one or more detectors.

In order to better understand the nature and advantages of this case, reference should be made to the following description and accompanying drawings. It is to be understood, however, that each drawing is provided for the purpose of illustration only and is not intended as a definition of the limits of the scope of the invention. Furthermore, as a general rule, and unless the contrary is apparent from the description, where the same reference numerals are used for elements in different figures, such elements will generally be identical or at least similar in function or purpose.

Embodiments of the present application relate to improved methods and techniques for collecting backscattered electrons when imaging a sample with a scanning electron microscope. Exemplary Sample Evaluation Tool

In order to better understand and understand this case, first refer to Figure 1 , which is a simplified schematic diagram of a sample evaluation system 100 according to some embodiments of this case. Sample evaluation system 100 may be used, among other operations, for defect inspection and analysis of structures formed on samples, such as semiconductor wafers.

System 100 may include a vacuum chamber 110 and a scanning electron microscope (SEM) column 120 . Support element 150 may support sample 145 (eg, a semiconductor wafer) within chamber 110 during processing operations in which sample 145 (sometimes referred to herein as an "object" or "sample") is subjected to Effect of charged particle beam 126 on the SEM column.

SEM column 120 is connected to vacuum chamber 110 so that the charged particle beam generated by the column propagates through the vacuum environment created within vacuum chamber 110 before impacting sample 145 . SEM column 120 can produce an image of a portion of sample 145 by illuminating the sample with charged particle beam 126, detecting particles emitted due to the illumination, and generating a charged particle image based on the detected particles. To this end, SEM column 120 may include an electron beam source 122 (i.e., an "electron gun"), an anode tube 128 that defines the electron beam's drift space, a condenser lens assembly 124, one or more deflection lenses (such as lenses 130, 132), One or more focusing lenses 134 and column cap 136.

During the imaging process, electron beam source 122 generates electron beam 126 that passes through and is initially focused by condenser lens 124 and then by lens 134 before impacting sample 145 . The condenser lens 124 defines the numerical aperture and current of the electron beam (together with the final aperture) which are directly related to the resolution, while the focusing lens 134 focuses the electron beam onto the sample. Post cap 136 located between the lower end of anode tube 128 (first electrode) and sample 145 (second electrode) can be a third electrode in the system that regulates the electric field generated near the wafer.

Particle imaging processes typically involve scanning a charged particle beam back and forth (eg, in a raster or other scanning pattern) over a specific area of the imaged sample. Deflection lenses 130, 132, which may be magnetic lenses, electrostatic lenses, or a combination of electrolenses and magnetic lenses, may achieve scanning patterns known to those skilled in the art. The scanned area is typically a very small portion of the overall area of the sample. For example, the sample may be a 200 mm or 300 mm diameter semiconductor wafer, and each area scanned on the wafer may be a rectangular area having a width and/or length measured in microns or tens of microns.

SEM column 120 may also include one or more detectors to detect charged particles generated from the sample during the imaging process. For example, SEM column 120 may include an in-lens detector 162 and a top detector 144 that may be configured to detect secondary electrons and backscattered electrons emitted as a result of charged particle beam 126 illuminating a sample. The in-lens detector 142 may include a central aperture that allows the charged particle beam 126 to pass through the detector and allows secondary electrons and backscattered electrons entering the charged particle column 120 to pass through the detector 142 to the top detector. 144. In some embodiments, sample evaluation system 120 may also include an external detector (discussed below with respect to Figure 6), which may also be configured to detect secondary and backscattered electrons.

Additionally, system 100 may include a voltage supply 160 and one or more controllers 170, such as a processor or other hardware unit. The voltage supply can be operated to provide a desired effective voltage of the column to thereby enhance image resolution. This can be achieved by appropriately distributing the voltage supply between the first and second electrodes (ie, between the anode tube and the sample). Controller 170 may control the operation of the system, including voltage supply 160, by executing computer instructions stored in one or more computer-readable memories 180, as will be known to those of ordinary skill in the art. For example, computer-readable memory may include solid-state memory (such as random access memory (RAM) and/or read-only memory (ROM)), which may be programmable, flash-updatable and/or the like), disk drives, optical storage devices or similar non-transitory computer-readable storage media.

As shown in Figure 1, embodiments allow the SEM column 120 to be tilted at non-vertical angles relative to the sample 145. For example, as shown in Figure 1, post 120 may be tilted at a 45 degree angle relative to the upper generally flat surface of sample 145. To enable tilting of column 120, cap 136 may have a tapered shape that enables the column to be positioned very close to sample 145 without colliding column cap 136 with the sample. Additionally, and as described below, in some embodiments, SEM column 120 does not include an energy filter used by some SEM tools to prevent secondary electrons from reaching in-lens detector 142 . Alternatively, in some embodiments, the SEM column 120 may include an energy filter but may be used to evaluate samples without activating the energy filter. Challenges in collecting backscattered electrons

As discussed above, some embodiments collect backscattered electrons without using energy filters to suppress secondary ion signals. To better understand the advantages and benefits of some embodiments, reference is now made to Figure 2, which is a simplified schematic illustration of a portion of SEM column 200 spaced apart from sample 245. SEM column 200 may represent SEM column 120 shown in Figure 1 . For ease of illustration, only selected elements of the SEM column 200 are illustrated in Figure 2 . As shown, SEM column 200 includes a column cap 236 at the distal end of the column, an in-lens detector 242, and a top detector 244. A portion of anode tube 210 is also shown.

During imaging operations, SEM column 200 generates an electron beam (not shown) and directs the electron beam such that the electron beam strikes sample 245 . The interaction of the electron beam with the sample 245 produces various secondary electrons and backscattered electrons that travel away from the sample in all directions. The paths of some of the generated electrons are illustrated as path 250, path 252, and path 254. As shown, some of the generated electrons travel along path 250 away from the SEM column and therefore fail to reach either detector 242 or 244; some of the generated electrons travel along path 252 which causes the electrons to impact The trajectory on the in-lens detector 242 enters the SEM column; and some of the generated electrons travel along a path 254 that enables the electrons to pass through the central opening of the in-lens detector 242 to the top detector 244 Enter the SEM column on the track.

In some previously known SEM tools configured to collect backscattered electrons, the SEM column includes an energy filter 310 as shown in Figure 3. An energy filter 310 that can separate backscattered electrons from secondary electrons by preventing electrons below a predetermined energy level from passing through the filter. This filter is typically located just before the top detector 244. Therefore, an evaluation system including SEM column 300 will only see backscattered electrons that follow path 254 and reach top detector 244 . Electrons traveling along path 252 and reaching detector 242 will include secondary electrons and backscattered electrons. Since detector 242 cannot distinguish between different types of electrons, in-lens detector 242 cannot be used to isolate backscattered electron signals from secondary electron signals. Furthermore, backscattered electrons along path 250 will not reach either detector 242 or 244. Apply negative bias to column cap

According to some embodiments disclosed herein, a SEM column (eg, column 120 or 200) can be operated in a tilted mode (eg, at a 45 degree angle or other non-vertical angle to the sample) and a negative bias can be applied during imaging. to the column cap to inhibit secondary electrons from reaching any electronic detectors (including in-lens detectors 142, 242 and top detectors 144, 244 that are farther from the sample than the column cap).

Figure 4 is a simplified flowchart illustrating steps associated with a method 400 of imaging a sample, in accordance with some embodiments. Method 400 begins by positioning a sample within a processing chamber of a sample evaluation system (step 410). A processing chamber, such as chamber 110, may include a SEM column that can be operated with a tilt model and one or more electronic detectors, such as an in-lens detector 142 or a top detector 144. Step 410 may include positioning the sample, such as sample 145, on a sample support, such as support 150, within the vacuum chamber.

Next, a negative bias voltage is applied to the column cap (step 420), and the SEM column can be activated to generate an electron beam (step 430) that is focused and scanned across the region of interest of the sample (step 440). The electron beam may be focused via a focusing lens, such as lens 134, and the electron beam may be scanned across an area of the substrate using one or more deflection lenses, such as lenses 130 and 132.

As the electron beam scans across the area of interest, a negative bias voltage is applied to the column cap. The negative bias should be high enough to suppress secondary electrons, but it should not be high enough to affect the electron beam 126, which would adversely affect the resolution of the imaging process. When a negative bias is applied to the column cap, and as the electron beam scans across the region of interest, the backscattered electrons can be collected with an appropriate detector, such as an in-lens detector 142 or a top detector. 144 (step 450). In an actual implementation, steps 430, 440, and 450 may occur substantially simultaneously and may be very fast.

In some embodiments, the negative bias voltage may be the minimum voltage required to suppress secondary electrons. The appropriate value of negative bias will depend in part on the geometry of the pillar cap and can be determined through simulation or experimentation as can be readily determined by one skilled in the art. In some embodiments, the bias voltage may be between negative 50 and negative 1000 volts; and in other embodiments, the bias voltage may be between negative 100 and negative 500 volts.

Figures 5A and 5B are simplified diagrams illustrating the effects of applying a negative bias voltage to the cap of SEM column 500 in accordance with some embodiments. SEM column 500 may represent SEM column 120 or 200 discussed above. Specifically, Figure 5A illustrates the effect of applying a negative voltage of 200 volts to cap 236 of SEM column 500 on secondary electrons 510 produced during imaging operations, and Figure 5B illustrates applying the same negative voltage (200 volts ) applied to the effect of cap 236 on backscattered electrons 520 . In each of Figures 5A and 5B, SEM column 500 generates a 1 kV electron beam during the imaging process.

From a comparison of Figure 5A and Figure 5B based on simulation results, it can be seen that the negative voltage repels lower energy secondary electrons so that no secondary electrons 510 enter the SEM column 500. Therefore, applying a negative cap voltage ensures that no secondary electrons 510 can reach the in-lens or top detector within column 500 (not shown in Figure 5A or Figure 5B). In contrast, applying a negative voltage to cap 236 has minimal effect on higher energy backscattered electrons 520. Therefore, some of the backscattered electrons travel along the path into the SEM column, reaching either the in-lens detector or the top detector, and enable in-lens detectors within the column without the use of a separate filter. Provides backscattered signal.

Figures 6A and 6B are simplified diagrams of a portion of SEM column 500 illustrating exemplary paths of electrons generated during imaging when no bias (i.e., a bias of 0 volts) is applied to the electron cap. . Specifically, Figure 6A illustrates an exemplary trajectory of secondary electrons 610 when no bias is applied to cap 236, and Figure 6B illustrates an example trajectory of backscattered electrons 620 when no bias is applied to cap 236. Example trajectories. As can be seen in Figure 6B, when a negative bias of 200 volts is applied to the cap, the trajectory of backscattered electrons 620 is substantially the same as the trajectory of backscattered electrons 520 shown in Figure 5B. However, as shown in Figure 6A, without a negative bias on the cap, some secondary electrons 610 entering the SEM column 500 may thereby reach one of the in-lens or top detectors. Since the detector cannot distinguish between secondary electrons and backscattered electrons, secondary electrons can contaminate the signal at the detector, preventing an accurate backscattered signal from being obtained. Sample evaluation tool using external detector

Sample evaluation tools according to some embodiments may include an external detector that may be used to detect backscattered electrons. The external detector may be in addition to or in place of either or both of the in-lens detector and the top detector described above. Figure 7 is a simplified diagram of a sample evaluation system 700 according to some embodiments of the present invention. Sample evaluation system 700 may be similar to evaluation system 100 except that it includes an external detector 710 . For convenience, other elements of evaluation system 700 that are similar to evaluation system 100 have been labeled with the same element symbols and are not discussed below.

During the sample evaluation process, the SEM column 120 in the evaluation system 700 may be tilted relative to the sample 145 as discussed above with respect to FIG. 1 . As shown in FIG. 7 , external detector 710 may be spaced apart from cap 136 of the SEM column and positioned to collect electrons generated from sample 145 when the sample is bombarded by electron beam 126 . While in-lens detector 142 and top detector 144 are limited to detecting backscattered electrons entering the SEM column through the opening of cap 136, external detector 710 can detect backscattered electrons with trajectories that carry electrons away from the SEM column. Scattered electrons. Embodiments may apply a negative voltage to cap 136 during the imaging process to suppress secondary electron signals (i.e., prevent secondary electrons from reaching external detector 710) and ensure that external detector 710 collects primarily or only backscattered electrons. signal. Sample sample to be imaged

To provide context for some aspects of the embodiments described herein, reference is now made to FIG. 8, which is a simplified illustration of a region on a semiconductor wafer that may include various locations on the wafer in accordance with some embodiments. Multiple regions from which backscattered electrons can be collected to evaluate the sample. Specifically, FIG. 8 includes a top view of wafer 800 and two expanded views of specific portions of wafer 800 . Wafer 800 may be, for example, a 200 mm or 300 mm semiconductor wafer, and may include a plurality of integrated circuits 810 (52 in the example shown) formed thereon. The integrated circuit 810 may be in an intermediate stage of manufacturing, and the sample evaluation techniques described herein may be used to evaluate and analyze one or more areas 820 of the integrated circuit. For example, Expansion A of FIG. 8 illustrates multiple regions 820 of one of the integrated circuits 810 that may be evaluated and analyzed according to techniques described herein. Expansion B illustrates one of the regions 820 including different features formed therein.

Embodiments of the present invention may analyze and evaluate region 820 using, for example, method 400 discussed above with respect to FIG. 4 . Evaluation may be accomplished by scanning the SEM beam back and forth within area 820 according to a raster pattern, such as scan pattern 830 shown in simplified format in Expansion B of Figure 8. Additional Examples

The foregoing descriptions of the specific embodiments described herein have been presented for the purposes of illustration and description. This description is not intended to be exhaustive or to limit the embodiments to the precise forms disclosed. Furthermore, while different embodiments of the present invention are disclosed above, the specific details of the particular embodiments may be combined in any suitable manner without departing from the spirit and scope of the embodiments of the invention. Furthermore, it will be apparent to those of ordinary skill in the art that many modifications and variations are possible in light of the above teachings.

Any reference in the above specification to a method shall apply mutatis mutandis to a system capable of executing the method, and shall apply mutatis mutandis to a computer program product storing instructions that, when executed, cause the execution of the method. Similarly, any reference in the above specification to a system shall apply mutatis mutandis to a method executable by the system, which shall apply mutatis mutandis to a computer program product storing instructions executable by that system; and references in the specification to a computer program product shall apply mutatis mutandis to a method executable by the system. Any reference to shall apply mutatis mutandis to a method executable in the execution of instructions stored in a computer program product, and shall apply mutatis mutandis to a system configured to execute instructions stored in a computer program product.

To the extent that the illustrated embodiments of the present application can be implemented using electronic components and circuits known to those skilled in the art, in order to understand and understand the basic concepts of the present application and in order not to obscure or distract from the teachings of the present application, such Details will not be explained to a greater extent than is deemed necessary above.

100:Sample Evaluation System 110: Vacuum chamber 120: Scanning electron microscope (SEM) column 122: Electron beam source 124: Converging lens device 126:Electron beam 128:Anode tube 130:Deflection lens 132:Deflection lens 134:Focusing lens 136: Column cap 142:In-lens detector 144:Top detector 145:Sample 150:Support 160:Voltage supply source 170:Controller 180: Computer readable memory 200:SEM column 210:Anode tube 236: Column cap 242: In-lens detector 244:Top detector 245:Sample 250:Path 252:Path 254:Path 300:SEM column 310:Energy filter 400:Method 410: Steps 420: Steps 430: Steps 440: Steps 450: steps 500:SEM column 510: Secondary electrons 520: Anti-scattered electrons 610: Secondary electrons 620: Anti-scattered electrons 700:Sample Evaluation System 710:External detector 800:wafer 810:Integrated circuits 820:Area 830:Scan pattern

Figure 1 is a simplified diagram of a sample evaluation system according to some embodiments of the present invention.

Figure 2 is a simplified diagram illustrating an exemplary path of backscattered electrons generated by a sample when an electron beam generated by the SEM column strikes the sample.

Figure 3 is a simplified diagram illustrating placement of an energy filter in an example of a previously known SEM column;

Figure 4 is a simplified flowchart illustrating steps associated with some embodiments in accordance with the present invention.

Figure 5A is a simplified diagram illustrating an example of the impact on secondary electron trajectories when a negative bias is applied to a pillar cap, in accordance with some embodiments;

Figure 5B is a simplified diagram illustrating an example of the impact on backscattered electron trajectories when a negative bias is applied to a column cap, in accordance with some embodiments;

Figure 6A is a simplified diagram illustrating exemplary trajectories of secondary electrons when no bias voltage is applied to the pillar cap;

Figure 6B is a simplified diagram illustrating exemplary trajectories of backscattered electrons when no bias voltage is applied to the pillar cap;

Figure 7 is a simplified diagram of a sample evaluation system including an external detector according to some embodiments of the present case; and

Figure 8 is a simplified illustration of a region on a semiconductor wafer from which backscattered electrons may be collected in accordance with some embodiments.

Domestic storage information (please note in order of storage institution, date and number) without Overseas storage information (please note in order of storage country, institution, date, and number) without

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410: Steps

420: Steps

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Claims (20)

A method of evaluating an area of a sample that consists of the following steps: Position a sample within a vacuum chamber; Generating an electron beam using a scanning electron microscope (SEM) column including an electron gun at one end of the column and a column cap at an opposite end of the column; focusing the electron beam on the sample and scanning the focused electron beam across the sample area while the SEM column is operated in a tilt mode, thereby generating secondary electrons and backscattered electrons from within the area; and During the scan, one or more detectors are used to collect backscattered electrons, and a negative bias voltage is applied to the column cap to change a trajectory of the secondary electrons, thereby preventing the secondary electrons from reaching the one or more Detector. The method of evaluating a sample area as claimed in claim 1, further comprising the step of generating an image of at least a portion of the area from the collected backscattered electrons. The method of evaluating a sample area as claimed in claim 1, wherein the step of applying a negative bias voltage to the pillar cap includes the following steps: applying a bias voltage between negative 50 volts and negative 1000 volts. The method of evaluating a sample area as claimed in claim 1, wherein the column cap has a tapered shape with an opening at its tip, and the electron beam is directed through the opening. The method of evaluating a sample area as claimed in claim 1, wherein the one or more detectors include an in-lens detector and a top detector. The method of evaluating a sample area as described in claim 1, wherein the step of collecting backscattered electrons includes the following steps: using an external detector to collect the backscattered electrons. The method of evaluating a sample area as claimed in any one of claims 1 to 6, wherein the step of applying a negative bias voltage to the column cap includes the following steps: applying a bias voltage between negative 100 volts and negative 500 volts. pressure. A system for evaluating an area of a sample that includes: a vacuum chamber; a sample support configured to maintain a sample within the vacuum chamber during a sample evaluation process; A scanning electron microscope (SEM) column configured to direct a charged particle beam into the vacuum chamber toward the sample, the SEM column including an electron gun at one end of the column and an opposite end of the column a pillar cap; a detector configured to detect backscattered electrons; and A processor and a memory coupled to the processor. The memory includes a plurality of computer-readable instructions. When executed by the processor, the instructions cause the system to perform the following operations: Position a sample within a vacuum chamber; Using the scanning electron microscope (SEM) column to generate an electron beam; focusing the electron beam on the sample and scanning the focused electron beam across the sample area while the SEM column is operated in a tilt mode, thereby generating secondary electrons and backscattered electrons from within the area; and One or more detectors are used to collect backscattered electrons while the electron beam scans across the area, and a negative bias voltage is applied to the column cap to change a trajectory of the secondary electrons, thereby preventing the secondary electrons from Reach the one or more detectors. The system of claim 8, wherein the plurality of computer-readable instructions further causes the system, when executed by the processor, to generate an image of at least a portion of the area from the detected backscattered electrons. The system of claim 8, wherein applying a negative bias to the pillar cap includes applying a bias between negative 50 volts and negative 1000 volts. The system of claim 8, wherein applying a negative bias to the pillar cap includes applying a bias between negative 100 volts and negative 500 volts. The system of claim 8, wherein the column cap has a tapered shape with an opening at its tip, and the electron beam is directed through the opening. The system of claim 8, wherein the one or more detectors include an in-lens detector and a top detector. The system of any one of claims 8 to 13, wherein the system includes an external detector. A non-transitory computer-readable memory storing a plurality of computer-readable instructions for evaluating a region of a sample by: Position a sample within a vacuum chamber; Generating an electron beam using a scanning electron microscope (SEM) column including an electron gun at one end of the column and a column cap at an opposite end of the column; focusing the electron beam on the sample and scanning the focused electron beam across the sample area while the SEM column is operated in a tilt mode, thereby generating secondary electrons and backscattered electrons from within the area; and During the scan, one or more detectors are used to collect backscattered electrons, and a negative bias voltage is applied to the column cap to change a trajectory of the secondary electrons, thereby preventing the secondary electrons from reaching the one or more Detector. The non-transitory computer-readable memory of claim 15, wherein the plurality of computer-readable instructions for evaluating a sample area further includes generating an image of at least a portion of the area from the collected backscattered electrons. instructions. The non-transitory computer readable memory of claim 15, wherein applying a negative bias voltage to the pillar cap includes applying a bias voltage between negative 50 volts and negative 1000 volts. The non-transitory computer readable memory of claim 15, wherein applying a negative bias voltage to the pillar cap includes applying a bias voltage between negative 100 volts and negative 500 volts. The non-transitory computer readable memory of claim 15, wherein the pillar cap has a tapered shape with an opening at its tip, and the electron beam is guided through the opening. The non-transitory computer-readable memory of any one of claims 15 to 19, wherein the one or more detectors include an in-lens detector and a top detector.