Method, system, and non-transitory computer-readable memory for evaluating region of sample

Abstract

A method for evaluating a sample region includes: positioning the sample in a vacuum chamber; generating an electron beam using a scanning electron microscope (SEM) column, the SEM column including an electron gun at one end of the column and a column cap at the opposite end of the column; focusing the electron beam onto the sample and scanning the focused electron beam across the sample region while the SEM column operates in a tilt mode to generate secondary electrons and backscattered electrons from within the region; and during the scanning, collecting the backscattered electrons using one or more detectors while applying a negative bias to the column cap to alter the trajectory of the secondary electrons, thereby preventing the secondary electrons from reaching the one or more detectors.

Description

Backscattered electron (BSE) imaging was performed using a scanning electron microscope (SEM) in tilt mode with cap bias. This application claims priority to U.S. Application No. 17 / 243,478, filed April 28, 2021. The disclosure of that application is incorporated herein by reference in its entirety for all purposes. In the study of electronic materials and the processes used to manufacture such materials into electronic structures, samples of the electronic structures can be used for microscopic examination for purposes such as fault analysis and device verification. For example, samples of electronic structures, such as those from silicon wafers, can be analyzed using a scanning electron microscope (SEM) to study specific characteristics within the wafer. These characteristics may include fabricated circuitry and any defects formed during the manufacturing process. The 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 a SEM tool, secondary electrons and backscattered electrons are generated when the electron beam strikes the sample. Secondary electrons originate from the atoms within the sample itself and are a result of the inelastic interaction between the electron beam and the sample. These secondary electrons have relatively low energies (e.g., 0–20 eV) and originate from or near the sample surface. Following the elastic interaction between the beam and the sample, the backscattered electrons (BSE) are reflected back. Backscattered electrons can have energy levels close to the electron beam's energy level and thus can 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 exhibit 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 collecting backscattered electrons, the secondary electron signal needs to be suppressed to accurately detect it. In typical SEM tools, suppressing the secondary electron signal is accomplished by placing an energy filter between the sample and the detector, which prevents relatively low-energy secondary electrons from reaching the detector. While this method has been successfully used in the past, new methods for detecting backscattered electrons are still needed. Some embodiments of this application relate to improved methods and techniques for collecting backscattered electrons when imaging a sample using a scanning electron microscope. The collected electrons can be used to evaluate the properties of the sample, such as providing material contrast. In some embodiments, a method for evaluating a region of a sample includes: positioning the sample in a vacuum chamber; generating an electron beam using a scanning electron microscope (SEM) column, the SEM column including an electron gun at one end of the column and a column cap at the opposite end of the column; focusing the electron beam onto the sample and scanning the focused electron beam across the sample region while the SEM column operates in a tilt mode to generate secondary electrons and backscattered electrons from within the region; and during the scanning, collecting the backscattered electrons using one or more detectors while applying a negative bias to the column cap to alter the trajectory of the secondary electrons, thereby preventing the secondary electrons from reaching one or more detectors. 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 detected backscattered electron generating region; applying negative bias voltages of -50 volts and -1000 volts to the cap; applying a negative bias voltage between -100 volts and -500 volts to the cap; the cap may have a conical shape with an opening at its tip, through which the electron beam can be guided; backscattered electrons may be collected using an in-lens detector and a top detector; or backscattered electrons may be collected using an external detector. Some embodiments relate to a non-transitory computer-readable medium storing instructions for X-ray spectral surface material analysis of a region of a sample according to any of the methods described above or herein. For example, the method involves: positioning a sample in a vacuum chamber; generating an electron beam using a scanning electron microscope (SEM) column including an electron gun at one end and a column cap at the opposite end; focusing the electron beam onto the sample and scanning the focused electron beam across a region of the sample while the SEM column operates in a tilt mode to generate secondary electrons and backscattered electrons within the region; and during the scan, collecting the backscattered electrons using one or more detectors while applying a negative bias to the column cap to alter the trajectory of the secondary electrons, thereby preventing the secondary electrons from reaching one or more detectors. Some embodiments relate to systems for X-ray spectral surface material analysis of regions 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 hold the sample within the vacuum chamber during sample evaluation; a scanning electron microscope (SEM) column configured to direct a beam of charged particles toward the sample into the vacuum chamber, the SEM column including an electron gun at one end of the column and a column cap at the opposite end; a detector configured to detect backscattered electrons; and a processor and memory coupled to the processor. The memory may include a plurality of computer-readable instructions, which, when executed by a processor, cause the system to: position the sample in a vacuum chamber; generate an electron beam using a scanning electron microscope (SEM) column, the SEM column including an electron gun at one end of the column and a column cap at the opposite end of the column; focus the electron beam onto the sample and scan the focused electron beam across the sample region while the SEM column operates in a tilt mode to generate secondary electrons and backscattered electrons from within the region; and collect the backscattered electrons using one or more detectors while applying a negative bias to the column cap to alter the trajectory of the secondary electrons, thereby preventing the secondary electrons from reaching one or more detectors. To better understand the nature and advantages of this application, reference should be made to the following description and figures. However, it should be understood that each figure is provided for illustrative purposes only and is not intended to be a limitation on the scope of this application. Furthermore, as a general rule, and unless clearly contrary to the description, elements in different figures that use the same element symbol are generally identical or at least similar in function or purpose. The embodiments of this case relate to an improved method and technique for collecting backscattered electrons when imaging a sample with a scanning electron microscope. Exemplary Sample Evaluation Tool To better understand this case, refer first to Figure 1, which is a simplified schematic diagram of a sample evaluation system 100 according to some embodiments of this case. Among other operations, the sample evaluation system 100 can be used particularly 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 a sample 145 (e.g., a semiconductor wafer) within chamber 110 during a processing operation in which the sample 145 (sometimes referred to herein as "object" or "sample") is affected by a beam of charged particles 126 from the SEM column. SEM column 120 is connected to vacuum chamber 110 so that a 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 generate an image of a portion of sample 145 by irradiating the sample with charged particle beam 126, detecting particles emitted attribution to irradiation, and generating a charged particle image based on the detected particles. For this purpose, SEM column 120 may include electron beam source 122 (i.e., "electron gun"), anode tube 128 defining electron beam drift space, condenser lens assembly 124, one or more deflection lenses (such as lenses 130, 132), one or more focusing lenses 134, and column cap 136. In the imaging process, electron beam source 122 generates electron beam 126, which is passed through condenser lens 124 and initially converged by condenser lens 124, and then focused by lens 134 before impacting sample 145. Condenser lens 124 defines the numerical aperture and current (along with the final aperture) of the electron beam, which are directly related to resolution, while focusing lens 134 focuses the electron beam onto the sample. A cap 136 located between the lower end of anode tube 128 (first electrode) and sample 145 (second electrode) can serve as the third electrode in the system, modulating the electric field generated near the wafer. Particle imaging processes typically involve scanning a beam of charged particles back and forth over a specific area of ​​an imaged sample (e.g., with a grating or other scanning pattern). Deflecting lenses 130, 132, which may be magnetic lenses, electrostatic lenses, or combinations of electric and magnetic lenses, can achieve scanning patterns known to those skilled in the art. The scanned area is typically a very small fraction of the overall area of ​​the sample. For example, the sample may be a semiconductor wafer with a diameter of 200 mm or 300 mm, and each scanned area on the wafer may be a rectangular region with a width and / or length measured in micrometers or tens of micrometers. 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, which may be configured to detect secondary electrons and backscattered electrons emitted as a result of the charged particle beam 126 irradiating the sample. 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 detector 142 to reach top detector 144. In some embodiments, sample evaluation system 120 may also include external detectors (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 source 160 and one or more controllers 170, such as processors or other hardware units. The voltage supply source may be operated to provide the required effective voltage for the column, thereby improving image resolution. This may be achieved by appropriately distributing the voltage supply between the first and second electrodes (i.e., between the anode tube and the sample). Controller 170 may control the operation of the system (including voltage supply source 160) by executing computer instructions stored in one or more computer-readable memories 180, as will be known to those skilled in the art. For example, computer-readable memories may include solid-state memories (such as random access memory (RAM) and / or read-only memory (ROM), which may be programmable, flash memory updatable, and / or the like), disk drives, optical storage devices, or similar non-transitory computer-readable storage media. As shown in Figure 1, the embodiment allows the SEM column 120 to be tilted at a non-perpendicular angle relative to the sample 145. For example, as shown in Figure 1, the column 120 may be tilted at an angle of 45 degrees relative to the upper, generally flat surface of the sample 145. To enable the column 120 to tilt, the cap 136 may have a tapered shape that allows the column to be positioned very close to the sample 145 without the cap 136 colliding with the sample. Furthermore, and as described below, in some embodiments, the SEM column 120 does not include an energy filter used by some SEM tool to prevent secondary electrons from reaching the in-lens detector 142. Alternatively, in some embodiments, the SEM column 120 may include an energy filter, but may be used to evaluate the sample without activating the energy filter. Challenges in collecting backscattered electrons As described 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, a simplified schematic diagram of a portion of a SEM column 200 spaced apart from the sample 245. The SEM column 200 may represent the SEM column 120 shown in Figure 1. For ease of illustration, only selected elements of the SEM column 200 are shown in Figure 2. As shown, the 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 the anode tube 210 is also illustrated. During the imaging operation, the SEM column 200 generates and guides an electron beam (not shown) to impact the sample 245. The interaction between the electron beam and the sample 245 generates various secondary electrons and backscattered electrons that travel away from the sample in all directions. Some of the generated electron paths are illustrated as paths 250, 252, and 254. As shown, some generated electrons travel away from the SEM column along path 250 and therefore cannot reach either detector 242 or 244; some generated electrons travel along path 252, which enters the SEM column on a trajectory that causes the electrons to impact the in-lens detector 242; and some generated electrons travel along path 254, which enters the SEM column on a trajectory that allows the electrons to pass through the central opening of the in-lens detector 242 to reach the top detector 244. In some previously known SEM tools designed to collect backscattered electrons, the SEM column includes an energy filter 310, as shown in Figure 3. The energy filter 310, which separates backscattered electrons from secondary electrons by preventing electrons below a predetermined energy level from passing through the filter, is typically located just before the top detector 244. Therefore, an evaluation system including the SEM column 300 can only see backscattered electrons traveling along path 254 and reaching the top detector 244. Electrons traveling along path 252 and reaching detector 242 will include both secondary and backscattered electrons. Since detector 242 cannot distinguish between different types of electrons, the in-lens detector 242 cannot be used to isolate the backscattered electron signal from the secondary electron signal. Furthermore, backscattered electrons traveling along path 250 will not reach either detector 242 or 244. Apply negative bias to the column cap According to some embodiments disclosed herein, the SEM column (e.g., column 120 or 200) can be operated in tilt mode (e.g., at a 45-degree angle or other non-perpendicular angle to the sample) and a negative bias can be applied to the column cap during imaging to suppress secondary electrons from reaching any electron detectors (including in-lens detectors 142, 242 and top detectors 144, 244, which are farther from the sample than the column cap). Figure 4 is a simplified flowchart illustrating the steps associated with a method 400 for imaging a sample according to some embodiments. Method 400 begins by positioning the sample within a processing chamber of a sample evaluation system (step 410). The processing chamber, such as chamber 110, may include a tiltable SEM column for model operation and one or more electronic detectors, such as an in-lens detector 142 or a top detector 144. Step 410 may include positioning a sample (such as sample 145) on a sample support (such as support 150) within a vacuum chamber. Next, a negative bias is applied to the column cap (step 420), and the SEM column can be activated to generate an electron beam (step 430), which is focused and scans across the region of interest of the sample (step 440). The electron beam can be focused via a focusing lens such as lens 134, and the electron beam can be scanned across a region of the substrate using one or more deflecting lenses such as lenses 130 and 132. As the electron beam scans across the region of interest, a negative bias is applied to the pillar cap. The negative bias should be high enough to suppress secondary electrons, but not so high as to affect the electron beam 126, which would adversely affect the resolution of the imaging process. While the negative bias is applied to the pillar cap, and as the electron beam scans across the region of interest, backscattered electrons can be collected using a suitable detector, such as the in-lens detector 142 or the top detector 144 (step 450). In practice, steps 430, 440, and 450 can occur substantially simultaneously and very quickly. In some embodiments, the negative bias voltage may be the minimum voltage required to suppress secondary electrons. The appropriate value of the negative bias voltage will depend in part on the geometry of the cap and can be determined through simulation or experimentation, as can be readily determined by those skilled in the art. In some embodiments, the bias voltage may be between -50 and -1000 volts; and in other embodiments, the bias voltage may be between -100 and -500 volts. Figures 5A and 5B are simplified diagrams illustrating the effect of applying a negative bias voltage to the cap of the SEM column 500 according to some embodiments. The SEM column 500 may represent the SEM column 120 or 200 discussed above. Specifically, Figure 5A illustrates the effect of applying a negative voltage of 200 volts to the cap 236 of the SEM column 500 on secondary electrons 510 generated during imaging operation, and Figure 5B illustrates the effect of applying the same negative voltage (200 volts) to the cap 236 on backscattered electrons 520. In each of Figures 5A and 5B, the SEM column 500 generates a 1 kV electron beam during the imaging process. A comparison of Figures 5A and 5B based on simulation results shows that the negative voltage repels lower-energy secondary electrons, preventing any secondary electrons 510 from entering 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 the column 500 (not shown in Figures 5A or 5B). Conversely, applying a negative voltage to cap 236 has minimal effect on higher-energy backscattered electrons 520. Therefore, some backscattered electrons travel along the path into the SEM column, reaching either the in-lens or top detector, enabling the in-lens detector within the column to provide a backscattered signal without the need for a separate filter. Figures 6A and 6B are simplified diagrams of a portion of the SEM column 500, illustrating exemplary paths of electrons generated during imaging when no bias voltage (i.e., a 0-volt bias) is applied to the electron cap. Specifically, Figure 6A illustrates an exemplary trajectory of secondary electrons 610 when no bias voltage is applied to the cap 236, and Figure 6B illustrates an exemplary trajectory of backscattered electrons 620 when no bias voltage is applied to the cap 236. As can be seen in Figure 6B, when a negative bias voltage of 200 volts is applied to the cap, the trajectory of the backscattered electrons 620 is substantially the same as that of the backscattered electrons 520 shown in Figure 5B. However, as shown in Figure 6A, in the absence of a negative bias voltage on the cap, some secondary electrons 610 entering the SEM column 500 may thus reach either the lens or the top detector. Since the detector cannot distinguish between secondary electrons and backscattered electrons, the secondary electrons contaminate the signal at the detector, thereby preventing the acquisition of an accurate backscattered signal. Sample evaluation tools using external detectors According to some embodiments, the sample evaluation tool may include an external detector that can be used to detect backscattered electrons. The external detector may be a supplement to or replacement of one 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 this invention. The sample evaluation system 700 may be similar to evaluation system 100, except that it includes an external detector 710. For convenience, other elements of the evaluation system 700, similar to evaluation system 100, have been labeled with the same element symbols and will not be discussed further 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 Figure 1. As shown in Figure 7, an external detector 710 may be spaced apart from the cap 136 of the SEM column and positioned to collect electrons generated from the sample 145 when the sample is bombarded by the electron beam 126. While the in-lens detector 142 and the top detector 144 are limited to detecting backscattered electrons entering the SEM column through the opening in the cap 136, the external detector 710 may detect backscattered electrons with trajectories that carry electrons away from the SEM column. Embodiments may apply a negative voltage to the cap 136 during the imaging process to suppress secondary electron signals (i.e., prevent secondary electrons from reaching the external detector 710) and ensure that the external detector 710 collects signals that primarily or solely consist of backscattered electrons. To be imaged Sample examples To provide context for some aspects of the embodiments illustrated herein, reference is now made to Figure 8, a simplified illustration of regions on a semiconductor wafer according to some embodiments. These regions may include multiple regions at different locations on the wafer from which backscattered electrons can be collected for sample evaluation. Specifically, Figure 8 includes a top view of wafer 800 and two unfolded views of specific portions of wafer 800. Wafer 800 may be, for example, a 200 mm or 300 mm semiconductor wafer and may include multiple integrated circuits 810 (52 in the illustrated example) formed thereon. The integrated circuits 810 may be in an intermediate stage of fabrication, and the sample evaluation techniques described herein can be used to evaluate and analyze one or more regions 820 of the integrated circuits. For example, unfolded view A of Figure 8 illustrates multiple regions 820 of one of the integrated circuits 810 that can be evaluated and analyzed according to the techniques described herein. Unfolded view B illustrates one of those regions 820 including different features formed therein. The embodiments of this case may use, for example, the method 400 discussed above with respect to Figure 4 to analyze and evaluate region 820. Evaluation may be accomplished by scanning a SEM beam back and forth within region 820 according to a grating pattern, such as the scan pattern 830 shown in a simplified format in the unfolded view B of Figure 8. Additional Examples For purposes of illustration and description, the foregoing description of specific embodiments described herein is presented. 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 have been disclosed above, the specific details of particular embodiments may be combined in any suitable manner without departing from the spirit and scope of the embodiments of the present invention. Moreover, it will be apparent to those skilled in the art that many modifications and variations are possible in light of the foregoing teachings. Any references to methods in the foregoing specification shall be modified as necessary to apply to systems capable of executing the method, and shall be modified as necessary to apply to computer program products storing instructions that, upon execution, cause the method to be executed. Similarly, any references to systems in the foregoing specification shall be modified as necessary to apply to methods executable by a system, and the system shall be modified as necessary to apply to computer program products storing instructions executable by the system; and any references to computer program products in the specification shall be modified as necessary to apply to methods executable when instructions stored in the computer program product are executed, and shall be modified as necessary to apply to systems configured to execute instructions stored in the computer program product. Within the scope of electronic components and circuits known to those skilled in the art, as illustrated in this application, such details will not be interpreted to a greater extent than deemed necessary above in order to understand and comprehend the basic concepts of this application and to avoid confusing or distracting from the teachings of this application. 100: Sample evaluation system; 110: Vacuum chamber; 120: Scanning electron microscope (SEM) column; 122: Electron beam source; 124: Condenser lens assembly; 126: Electron beam; 128: Anode tube; 130: Deflecting lens; 132: Deflecting 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: Lens In-Lens Detector 244: Top Detector 245: Sample 250: Path 252: Path 254: Path 300: SEM Column 310: Energy Filter 400: Method 410: Step 420: Step 430: Step 440: Step 450: Step 500: SEM Column 510: Secondary Electrons 520: Backscattered Electrons 610: Secondary Electrons 620: Backscattered Electrons 700: Sample Evaluation System 710: External Detector 800: Wafer 810: Integrated Circuit 820: Region 830: Scan Pattern Figure 1 is a simplified diagram of a sample evaluation system according to some embodiments of this case. Figure 2 is a simplified diagram illustrating an exemplary path of backscattered electrons generated by the sample when an electron beam generated by an SEM column strikes the sample. Figure 3 is a simplified diagram illustrating the placement of the energy filter in a previously known example of a SEM column; Figure 4 is a simplified flowchart illustrating steps associated with some embodiments of this case. Figure 5A is a simplified diagram illustrating an example of the effect of a negative bias applied to the column cap on the secondary electron trajectory according to some embodiments; Figure 5B is a simplified diagram illustrating an example of the effect of a negative bias applied to the column cap on the trajectory of backscattered electrons according to some embodiments; Figure 6A is a simplified diagram illustrating an exemplary trajectory of secondary electrons when no bias voltage is applied to the column cap; Figure 6B is a simplified diagram illustrating an exemplary trajectory 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 this case; and Figure 8 is a simplified diagram of a region on a semiconductor wafer from which backscattered electrons can be collected, according to some embodiments. Domestic storage information (please note in order of storage institution, date, and number): None. International storage information (please note in order of storage country, institution, date, and number): None. 400: Method 410: Steps 420: Steps 430: Steps 440: Steps 450: Steps

Claims

1. A method for evaluating a region of a sample, the method comprising the steps of: positioning a sample within a vacuum chamber; generating an electron beam using a scanning electron microscope (SEM) column, the SEM column including an electron gun at one end of the column and a column cap at the opposite end of the column; focusing the electron beam onto the sample and scanning the focused electron beam across the sample region while the SEM column is operated in a tilt mode to generate secondary electrons and backscattered electrons from within the region; and during the scanning, collecting the backscattered electrons using an in-lens detector and a top detector in the SEM column while applying a negative bias to the column cap to alter a trajectory of the secondary electrons, thereby preventing the secondary electrons from reaching the in-lens detector and the top detector, wherein the backscattered electrons collide with the in-lens detector and pass through an opening in the in-lens detector to reach the top detector.

2. The method for evaluating a sample region as described in claim 1 further comprises the step of generating an image of at least a portion of the region from the collected backscattered electrons.

3. The method for evaluating a sample region as described in claim 1, wherein the step of applying a negative bias to the column cap comprises the following steps: applying a bias between -50 volts and -1000 volts.

4. The method for evaluating a sample region as described in claim 1, wherein the cap has a conical shape with an opening at its tip, and the electron beam is guided through the opening.

5. The method for evaluating a sample region as described in claim 1, wherein the step of collecting backscattered electrons includes the following steps: collecting the backscattered electrons using an external detector by applying a negative bias voltage to the cap to suppress secondary electrons.

6. The method for evaluating a sample region as described in any one of claims 1 to 5, wherein the step of applying a negative bias to the column cap comprises the following steps: applying a bias between -100 volts and -500 volts.

7. A system for evaluating a region of a sample, the system comprising: a vacuum chamber; a sample support configured to hold a sample within the vacuum chamber during a sample evaluation process; a scanning electron microscope (SEM) column configured to direct a beam of charged particles toward the sample into the vacuum chamber, the SEM column including 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 a memory coupled to the processor, the memory including a plurality of computer-readable instructions that, when executed by the processor, cause the system to: position a sample within the vacuum chamber; generate an electron beam using the scanning electron microscope (SEM) column; The electron beam is focused onto the sample and scanned across the sample region while the SEM column operates in tilt mode, thereby generating secondary electrons and backscattered electrons within the region. Backscattered electrons are collected using an in-lens detector and a top detector within the SEM column, while the electron beam scans across the region and a negative bias is applied to the column cap to alter the trajectory of the secondary electrons, thereby preventing them from reaching the in-lens detector and the top detector. The backscattered electrons collide with the in-lens detector and pass through an opening in the in-lens detector to reach the top detector.

8. The system as claimed in claim 7, wherein the plurality of computer-readable instructions further cause the system, when executed by the processor, to generate an image of at least a portion of the region from the detected backscattered electrons.

9. The system as described in claim 7, wherein applying a negative bias to the column cap comprises applying a bias between -50 volts and -1000 volts.

10. The system as described in claim 7, wherein applying a negative bias to the column cap comprises applying a bias between -100 volts and -500 volts.

11. The system as claimed in claim 7, wherein the cap has a conical shape with an opening at its tip, and the electron beam is guided through the opening.

12. The system as described in any one of claims 7 to 11, wherein the system includes an external detector.

13. A non-transitory computer-readable memory storing a plurality of computer-readable instructions for evaluating a sample region by: positioning a sample within a vacuum chamber; generating an electron beam using a scanning electron microscope (SEM) column, the SEM column including an electron gun at one end of the column and a column cap at the opposite end of the column; focusing the electron beam onto the sample and scanning the focused electron beam across the sample region while the SEM column operates in a tilt mode to generate secondary electrons and backscattered electrons from within the region; and during the scanning, collecting the backscattered electrons using an in-lens detector and a top detector in the SEM column while applying a negative bias to the column cap to alter a trajectory of the secondary electrons, thereby preventing the secondary electrons from reaching the in-lens detector and the top detector, wherein the backscattered electrons collide with the in-lens detector and pass through an opening in the in-lens detector to reach the top detector.

14. The non-transitory computer-readable memory as described in claim 13, wherein the plurality of computer-readable instructions for evaluating a sample region further include instructions for generating an image of at least a portion of the region from the collected backscattered electrons.

15. The nontransitory computer-readable memory as described in claim 13, wherein applying a negative bias to the cap comprises applying a bias between -50 volts and -1000 volts.

16. The nontransitory computer-readable memory as described in claim 13, wherein applying a negative bias to the cap comprises applying a bias between -100 volts and -500 volts.

17. The nontransitory computer-readable memory as claimed in claim 13, wherein the cap has a conical shape with an opening at its tip, and the electron beam is guided through the opening.

18. A nontransitory computer-readable memory as described in any one of claims 13 to 17, wherein the one or more detectors include an in-lens detector and a top detector.

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