Measurement of hole tilt angle using FIB oblique cutting

Abstract

1. A method for evaluating a region of a sample containing a plurality of holes, the method comprising: taking a first image of the region by scanning the region with a first charged particle beam; evaluating the first image to determine a first center-to-center distance between a first hole and a second hole of the plurality of holes; milling an angled cut in an area of ​​the region including the second hole at an angle such that a top surface of the sample in the milled area where the second hole is located is recessed with respect to a top surface of the sample where the first hole is located; thereafter taking a second image of the region by scanning the region with the first charged particle beam; evaluating the second image to determine a second center-to-center distance between the first hole and a second hole of the plurality of holes; and comparing the second center-to-center distance to the first center-to-center distance.

Description

[Technical Field]

[0001] cross reference This application claims priority to U.S. Patent Application No. 17 / 079,297, filed October 23, 2020, the disclosure of which is incorporated herein by reference in its entirety for all purposes. [Background technology]

[0002] In the study of electronic materials and the processes by which electronic materials are processed into electronic structures, specimens of electronic structures can be used for microscopic examination for failure analysis and device verification. For example, specimens such as silicon wafers, gallium nitride wafers, or other types of wafers having one or more integrated circuits (ICs) or other electronic structures formed thereon can be milled and analyzed using a focused ion beam (FIB) and / or a scanning electron microscope (SEM) to study specific characteristics of those circuits or other structures formed on the wafer.

[0003] One characteristic of structures formed on a wafer that can lead to defects is a hole that is etched at an angle rather than etched perpendicularly as intended. For example, in deep holes, such as vias for VNAND devices, even a slight unintended angle can result in a defective device. Refer to FIG. 1 for an illustration. FIG. 1 is a simplified cross-sectional view of a partially formed semiconductor device 100 formed on a substrate 110. As shown in FIG. 1, substrate 110 may have multiple alternating layers formed thereon, such as layers 120 and 130. A deep hole 140 can be etched through the layers to a feature 150. As an example, hole 140 can be a via filled with a metal or conductive material that provides an electrical connection to feature 150. If hole 140 is etched at a slightly oblique angle (e.g., angle α) such that hole 160 is formed instead of hole 140, hole 160 may not contact feature 150, and the circuit intended to have an electrical path between via 140 and feature 150 may become a defective circuit.

[0004] Furthermore, FIG. 1A is only a cross-sectional view of the substrate 110 and therefore only shows the sample (semiconductor device 100) along two axes (e.g., the X-axis and the Z-axis). The angle at which the hole 160 is etched may not be aligned with an ideal vertical hole in either or both of the X-axis and the Y-axis. FIG. 1B is a simplified diagram of the surface 170 of the substrate 110 on which the feature 150 is formed. As shown in FIG. 1B, the hole 160 may be misaligned with the structure 150 (relative to the intended via 140) in both the X- and Y-directions. In some applications, etching the hole 160 tilted by only 1 degree may result in the hole being misaligned to an undesirable distance from the feature 150 or other structures in the substrate 110, given the depth of the feature 150 from the top surface of the sample.

[0005] It can be difficult to accurately detect holes with tilt angles formed in structures such as semiconductor device 100. Therefore, it is desirable to improve the detection of tilted holes. Summary of the Invention

[0006] Embodiments of the present disclosure provide methods and systems for detecting angled holes formed in a specimen, such as a semiconductor wafer. The embodiments can evaluate a specimen having two or more holes etched therein and determine whether the holes were formed at an angled angle or whether the holes were formed perpendicular to the specimen's surface at a 90-degree angle. According to some embodiments, a region of the specimen containing two or more holes can be imaged at an angle perpendicular to the specimen's surface using a scanning electron microscope and then milled along a diagonal cut using a focused ion beam. After the angled milling, a second image of the region can be taken at the same angle perpendicular, and the two images can be compared to determine whether the center-to-center distance between adjacent holes changes with depth.

[0007] If the holes are etched perfectly perpendicular (i.e., at a 90 degree angle to the surface of the substrate), the center-to-center distance between adjacent holes will remain constant throughout the milled depth. On the other hand, if such a process detects a difference in the center-to-center distance of holes etched into the surface of the substrate compared to the center-to-center distance at the milled depth, then the holes are etched at an oblique, non-perpendicular angle (i.e., an angle other than 90 degrees), and some embodiments can determine the actual angle at which the angled holes were etched.

[0008] In some embodiments, a method of evaluating a region of a sample including a plurality of holes is provided, the method including: taking a first image of the region of the sample including the plurality of holes by scanning the region with a first charged particle beam; evaluating the first image to determine a first center-to-center distance between a first hole and a second hole of the plurality of holes; milling an angled cut in an area of ​​the region including the second hole at an angle such that a top surface of the sample in the milled area where the second hole is located is recessed with respect to a top surface of the sample where the first hole is located; thereafter taking a second image of the region of the sample including the first and second holes by scanning the region with the first charged particle beam; evaluating the second image to determine a second center-to-center distance between the first hole and the second hole of the plurality of holes; and comparing the second center-to-center distance to the first center-to-center distance.

[0009] In some embodiments, a system for evaluating a sample, such as the sample described above, is provided that includes a vacuum chamber, a sample support configured to hold the sample within the vacuum chamber during a sample evaluation process, a scanning electron microscope (SEM) column configured to direct a first charged particle beam into the vacuum chamber, a focused ion beam (FIB) column configured to direct a second charged particle beam into the vacuum chamber, a processor, and a memory coupled to the processor. The memory can include a plurality of computer-readable instructions that, when executed by the processor, cause the system to take a first image of a region of the sample including the plurality of holes by scanning the region with a first charged particle beam; evaluate the first image to determine a first center-to-center distance between a first hole and a second hole of the plurality of holes; mill an angled cut in an area of ​​the region including the second hole at an angle such that a top surface of the sample in the milled area where the second hole is located is recessed with respect to a top surface of the sample where the first hole is located; thereafter take a second image of the region of the sample including the first and second holes by scanning the region with the first charged particle beam; evaluate the second image to determine a second center-to-center distance between the first hole and a second hole of the plurality of holes; and compare the second center-to-center distance to the first center-to-center distance.

[0010] An additional embodiment also relates to a non-transitory computer-readable memory having stored thereon instructions for evaluating a region of a sample, such as the sample described above, where evaluating the region of the sample including a plurality of holes is carried out by taking a first image of the region of the sample including the plurality of holes by scanning the region with a first charged particle beam; evaluating the first image to determine a first center-center distance between a first hole and a second hole of the plurality of holes; milling an angled cut in an area of ​​the region including the second hole at an angle such that a top surface of the sample in the milled area where the second hole is located is recessed with respect to a top surface of the sample where the first hole is located; thereafter taking a second image of the region of the sample including the first and second holes by scanning the region with the first charged particle beam; evaluating the second image to determine a second center-center distance between the first hole and a second hole of the plurality of holes; and comparing the second center-center distance to the first center-center distance.

[0011] Various implementations of the embodiments described herein may include one or more of the following features. The method may further include determining an angle β at which the hole is inclined. The method may further include rejecting the sample from the production line if the angle β is greater than a predetermined value. The first hole may be outside an area of ​​a region milled at one angle. The sample may be placed in a vacuum chamber of an evaluation tool including a scanning electron microscope (SEM) column and a focused ion beam (FIB) column, and the first and second images may be captured in the SEM column, and the milling may be performed in the FIB column. The sample may be a semiconductor wafer.

[0012] In some embodiments, the angle β at which the hole is inclined can be determined according to the following formula:

number

[0013] In some embodiments, the holes can be etched at an angle inclined in a first horizontal plane, and the sample can be milled in the first horizontal plane, and the angle β at which the holes are inclined can be determined according to the following formula:

number

[0014] For a fuller understanding of the nature and advantages of the present disclosure, reference should be made to the following description and accompanying drawings. It should be understood, however, that each of the figures is provided for illustrative purposes only and is not intended to delimit the scope of the present disclosure. Furthermore, generally, unless clearly stated to the contrary in this description, when elements in different figures use the same reference numerals, those elements generally have the same, or at least similar, function or purpose. [Brief explanation of the drawings]

[0015] [Figure 1A] FIG. 1 is a simplified cross-sectional view of a sample having a hole formed at an oblique angle through a portion of the sample. [Figure 1B] 1B is a simplified diagram of the surface of the sample shown in FIG. 1A showing features formed on the surface of the sample and holes that are misaligned in both the X and Y directions. [Figure 2]FIG. 1 is a simplified diagram of a sample evaluation system according to some embodiments of the present disclosure. [Figure 3] 1 is a flow chart illustrating steps associated with a method for evaluating a sample, according to some embodiments of the present disclosure. [Figure 4A] 1 is a simplified cross-sectional view of a semiconductor wafer having multiple holes etched therein. [Figure 4B] FIG. 4B is a simplified cross-sectional view of the semiconductor wafer shown in FIG. 4A after performing an angled cut in an area that can be evaluated according to certain embodiments disclosed herein. [Figure 5] 4C illustrates a simplified cross-sectional view of the semiconductor wafer shown in FIG. 4B and a mathematical representation of the region being evaluated according to some embodiments. [Figure 6] FIG. 1 is a simplified diagram illustrating the evaluation of a sample according to some embodiments. [Figures 7A-7B] FIG. 1 is a simplified diagram illustrating the evaluation of a sample according to some embodiments. [Figure 8] 1 is a simplified diagram of an area on a semiconductor wafer that may contain holes that can be evaluated to determine whether the holes were etched at an oblique angle according to some embodiments. DETAILED DESCRIPTION OF THE INVENTION

[0016] Embodiments of the present disclosure relate to methods and systems for detecting angled holes formed in a sample, such as a semiconductor wafer. The embodiments can evaluate a sample having two or more holes etched therein (e.g., holes from an array of thousands or millions of equally spaced holes intended to have the same profile) and determine whether the holes were etched into the sample at a 90-degree angle relative to the sample's surface, or whether the holes were etched into the sample at a non-perpendicular, angled angle. According to some embodiments, a region of the sample containing two or more holes can be imaged at an angle perpendicular to the sample's surface using a scanning electron microscope and then milled along the angled cut using a focused ion beam. After this angled milling, a second image of the region can be taken at the same angle perpendicular, and the two images can be compared to determine whether the center-to-center distance of the holes changes with depth.

[0017] If the holes are etched perpendicularly (i.e., at a 90 degree angle relative to the surface of the substrate), the center-to-center distance between adjacent holes will remain constant throughout the milled depth. On the other hand, if such a process detects a difference in the center-to-center distance of holes etched into the surface of the substrate compared to the center-to-center distance at the milled depth, then the holes are etched at an oblique, non-perpendicular angle (i.e., an angle other than 90 degrees), and some embodiments can determine the actual angle at which the oblique holes were etched.

[0018] Exemplary Sample Evaluation System To more fully understand and appreciate the present disclosure, reference is first made to Figure 2, which is a simplified schematic diagram of an evaluation system suitable for detecting angled holes, according to an embodiment of the present disclosure. The specimen evaluation system 200 can be used to perform operations such as defect inspection and defect analysis of structures formed on semiconductor wafers.

[0019] The system 200 can include a vacuum chamber 210, as well as a scanning electron microscope (SEM) column 220 and a focused ion beam (FIB) column 230. A support element 250 (e.g., a sample support pedestal) can support a sample 255 (e.g., a semiconductor wafer) within the chamber 210 during processing operations in which the sample 255 (sometimes referred to herein as an "object" or "specimen") is exposed to a charged particle beam from one of the FIB column or the SEM column. The support element 250 can also move the sample within the vacuum chamber 210 between the fields of view of the two columns 220 and 230 as needed for processing.

[0020] For certain operations, one or more gases can be supplied to the sample being processed by the gas supply unit 260. For simplicity of illustration, the gas supply unit 260 is depicted in FIG. 2 as a nozzle; however, it should be noted that the gas supply unit 260 can include elements such as a gas reservoir, a gas source, a valve, one or more inlets, and one or more outlets. In some embodiments, the gas supply unit 260 can be configured to supply gas to the sample within an area of ​​the sample that is exposed to the scanning pattern of the charged particle beam, rather than to the entire top surface of the sample. For example, in some embodiments, the gas supply unit 260 has a nozzle diameter of several hundred microns (e.g., between 400 and 500 microns) configured to supply gas directly to a relatively small portion of the sample surface that encompasses the scanning pattern of the charged particle beam. In various embodiments, a first gas supply unit 260 can be configured to supply gas to a sample positioned below the SEM column 220, and a second gas supply unit 260 can be configured to supply gas to a sample positioned below the FIB column 230.

[0021] The SEM column 220 and the FIB column 230 are connected to the vacuum chamber 210 so that a charged particle beam generated by either of these charged particle columns propagates through an evacuated environment formed within the vacuum chamber 210 and then impinges on the sample 255. The SEM column 220 can generate an image of a portion of the sample 255 by irradiating the sample with the charged particle beam, detecting particles emitted by the irradiation, and generating a charged particle image based on the detected particles. The FIB column 230 can mill the sample 255 (e.g., drill holes in the sample 255) to form a cross-section by irradiating the sample with one or more charged particle beams, and can further smooth the cross-section. The cross-section can include one or more first portions of a first material and one or more second portions of a second material. The cross-section can also include additional portions of other materials. Advantageously, the smoothing operation typically involves using a lower acceleration voltage than that used to mill the sample.

[0022] Typically, the particle imaging and milling processes involve scanning a charged particle beam back and forth at a constant velocity (e.g., in a raster scan pattern) across a specific area of ​​the sample being imaged or milled, respectively. As known to those skilled in the art, one or more lenses (not shown) coupled to the charged particle column can implement this scanning pattern. The scanned area is typically a very small portion of the total area of ​​the sample. For example, the sample can be a semiconductor wafer with a diameter of 200 or 300 mm, and each scanned area on the wafer can be a rectangular area having a width and / or length of a few microns or tens of microns.

[0023] In some embodiments, to evaluate a sample 255 having two or more holes etched therein, the FIB column 230 can be used to mill the sample along the angled cut, and then the SEM column 220 can be used to image the sample in a top-down mode (i.e., at an angle normal to the surface of the sample 255). Such a process can detect differences in the center-to-center distance of holes etched at an angle that would not be present if the holes were etched vertically at a 90-degree angle. Additional details regarding the detection of angled holes using such techniques are described below with respect to Figures 3-8.

[0024] 2, system 200 may include one or more controllers, processors, or other hardware units that control operation of system 200 by executing computer instructions stored in one or more computer-readable memories, as known to those skilled in the art. By way of example, this 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-updateable, and / or the like), disk drives, optical storage devices, or similar non-transitory computer-readable storage media.

[0025] Milling the sample along an oblique cut As mentioned above, embodiments described in this disclosure can be used to evaluate samples, such as sample 255, that have two or more holes etched therein. A focused ion beam can be used to mill the sample along an oblique cut, and then a scanning electron microscope beam can be used to image the sample at an angle perpendicular to the surface of the sample. Such a process can detect whether there is a difference in the center-to-center distance of holes at the surface of the substrate compared to deeper portions of the substrate. If the holes are etched perfectly perpendicular (i.e., at a 90-degree angle with respect to the surface of the substrate), the center-to-center distance between adjacent holes will remain constant throughout the milled depth. On the other hand, if such a process detects a difference in the center-to-center distance of holes etched at the surface of the substrate compared to the center-to-center distance at the milled depth, embodiments can determine that the holes were etched at a non-perpendicular angle (i.e., an angle other than 90 degrees) and can determine the actual angle at which the holes were etched.

[0026] For illustrative purposes, reference is made to FIG. 3 , a flow chart illustrating steps associated with method 300 according to some embodiments of the present disclosure, and to FIGS. 4A and 4B , which are simplified cross-sectional views of a semiconductor wafer 400 subjected to steps of method 400. Semiconductor wafer 400 may include an array of numerous holes, e.g., thousands or millions of holes with small feature sizes and large aspect ratios, formed through one or more layers 420 formed on a semiconductor substrate 410 in an area 425 that can be evaluated according to embodiments of the present disclosure. For illustrative purposes only, semiconductor wafer 400 is shown as having two holes 440 etched vertically and two holes 460 etched at an angle β, resulting in non-perpendicular, “tilted” holes. The inclusion of both holes 440 and 460 shown in the overlapping area is for illustrative purposes only. Those skilled in the art will understand that semiconductor wafer 400 may actually include only one set of holes 440 or one set of holes 460 in the area 425 that can be evaluated by the methods disclosed herein. To further simplify the following discussion, the holes etched into semiconductor wafer 400 may hereinafter be collectively referred to as "holes 440, 460." Because semiconductor wafer 400 may only include one set of holes 440 or one set of holes 460, it is understood that such a description refers to a given sample wafer 400 actually including either one set of holes 440 or one set of holes 460. The embodiments described in this disclosure teach how to determine whether semiconductor wafer 400 includes vertically oriented holes, such as hole 440, or angled holes, such as hole 460.

[0027] 4A and 4B also show a structure 450 formed at a depth within semiconductor wafer 400, where holes 440, 460 are intended to be formed directly on top of the structure 450. As one non-limiting example, hole 440 can be a via formed through one or more layers of dielectric material 420, and structure 450 can be part of a memory cell or similar electronic device formed on substrate 410. Structure 450 need not be present in all samples, and embodiments described in this disclosure can detect whether holes 440, 460 are formed vertically or at an angle, regardless of whether structures such as structure 450 are formed below the hole.

[0028] The first step of method 300 may involve moving wafer 400 under the field of view of a scanning electron microscope, such as SEM column 220 shown in FIG. 2, and taking an initial image of a region of the wafer containing an array of holes 440, 460 using a top-down mode in which the SEM beam is perpendicular to surface 430 of wafer 400 (block 310). This initial image may be evaluated to determine the center-to-center distance between pairs of holes in the array (block 320), for example, using known image analysis techniques. In some embodiments, the pair of holes for which the center-to-center distance is determined may be adjacent holes, as shown in FIGS. 4A and 4B. However, in other embodiments, the holes need not be adjacent holes, and may be holes separated by many other holes. As a simple, non-limiting example, in an array of holes having five columns of 100 holes (i.e., 100 rows), the center-to-center distance between the first hole in row 10 of the first column and the second hole in row 40 of the first column may be determined in block 320. Alternatively, block 320 may determine the center-to-center distance between the first hole in column 1, row 10 and the second hole in column 5, row 10. Those skilled in the art will appreciate that when determining the center-to-center distance in block 320, any two holes in the array may be selected, provided that holes having the same expected spacing between them are selected for comparison in subsequent steps of method 300.

[0029] The semiconductor wafer 400 can then be moved under the field of view of a focused ion beam column, such as the FIB column 230 shown in Figure 3, and the area containing the imaged hole can be milled (block 330) with an angled cut 470. As shown in Figure 4B, the angled cut 470 can be performed at an angle α such that the cut 470 begins in a region 425a slightly removed from where the first of the holes 440, 460 was etched, and deepens as the cut extends into the region 425b where the second of the holes 440, 460 was etched.

[0030] After performing the angled cut 470, the semiconductor wafer 400 can again be moved under the field of view of the SEM column, and a second image 425 of the wafer containing the same holes imaged in block 310 can be taken (block 340) using the same top-down mode as used for the first image, with the SEM beam perpendicular to the surface 430 of the wafer 400. This second image can be evaluated to determine the center-to-center distance at the surface defined by the angled cut 470 between the same two holes whose center-to-center distance was determined in block 320 (block 350), for example, using the same known image analysis techniques used to determine the center-to-center distance of the holes in the first image.

[0031] The second center-to-center distance (determined in block 350) can then be compared to the first center-to-center distance (determined in block 320) to determine if there is a difference between the two measurements and to evaluate whether the holes are etched at an undesirable tilted angle (block 360). For example, as shown in FIG. 4B , if the holes formed in wafer 400 are tilted holes 460, the center-to-center distance between the holes increases along the diagonal cut. Thus, these two measurements differ from each other by a difference Δx. On the other hand, if the center-to-center distance does not change along the diagonal cut (i.e., Δx = 0), the holes formed in wafer 400 are vertical holes etched into the wafer at a 90-degree angle relative to surface 430. Understandably, a larger angle of the diagonal cut will result in a deeper cut in area 425b for a given tilt angle β of hole 460, and a larger Δx.

[0032] In addition to determining whether the holes etched in specimen 400 are vertical holes 440 or tilted holes 460, some embodiments may calculate the actual angle β of the holes. As previously discussed, if there is no difference between the center-to-center distance measured in block 320 and the center-to-center distance measured in block 350, then in some instances it may be assumed that the holes are vertical holes, such as hole 440. On the other hand, if there is a difference between the center-to-center distance measured in block 320 and the center-to-center distance measured in block 350, then it may be concluded that the holes are tilted holes, such as hole 460, and some embodiments may calculate (e.g., in block 360) the exact tilt angle β of the holes using one of the techniques described below.

[0033] Measurement of on-axis hole inclination angle For example, in some embodiments, block 330 may include the additional substep of determining whether holes 440, 460 were etched at an oblique angle and determining the direction of the obliqueness prior to milling oblique cut 470. For example, in some embodiments, block 330 may include performing a first oblique cut to determine whether the center-to-center distance between holes before cutting has changed after cutting, and, if the distance has changed, using imaging techniques to determine the direction in which holes 460 are oblique. After determining the direction, a second oblique cut (i.e., oblique cut 470) can be made in the area under evaluation in the direction of the obliqueness. Such embodiments may then calculate the angle β at which oblique hole 460 was etched using the following equation:

[0034]

number

[0035] Equation (1) can be simplified to obtain the following equation:

number

[0036] After the tilt angle is calculated, it can be used (e.g., by a manufacturer producing electronic devices on semiconductor wafer 400) to determine whether the tilt angle is within acceptable manufacturing tolerances or whether wafer 400 should be rejected.

[0037] Off-axis hole inclination angle measurement In other embodiments, angles α and β need not be in the same direction and therefore do not include additional substeps such as those described above in connection with block 330. For example, Figure 7A is a simplified diagram illustrating the change in position of the hole in region 425b when a first image of a pair of tilted holes 460 (as indicated by the distance x between the two hole centers 460a, e.g., measured in block 320) is compared to a second image of the tilted holes 460 (e.g., in which the hole center in region 425b has shifted to the hole center 460b in the second image taken during block 340) when the angled cut 470 is not in the same horizontal plane as the tilted holes 460. Instead, the direction of the angled cut 470 and the direction of the tilted holes can differ by an unknown angle.

[0038] Such an embodiment can still calculate the angle β at which the angled hole 460 is etched using the following formula:

number

[0039] Equation (3) can be simplified to obtain the following equation:

number

[0040] Then, equation (4) can be simplified to obtain:

number

[0041] After the tilt angle is calculated, it can be used (e.g., by a manufacturer producing electronic devices on semiconductor wafer 400) to determine whether the tilt angle is within acceptable manufacturing tolerances or whether wafer 400 should be rejected.

[0042] In some instances, the center-to-center distance between the holes in the first and second images may not change, even if the holes are etched at an undesirable tilted angle. That is, given a particular combination of angle θ and shift Δx, the center-to-center distance may not change. For illustration, refer to FIG. 7B, which is a simplified diagram showing the change in hole position between pre-milling and post-milling images of a pair of tilted holes 460 when the angled cut 470 is not in the same horizontal plane as the tilted holes 460 and when the center-to-center distance between the holes in each image is the same.

[0043] As shown in FIG. 7B , prior to angled milling as discussed herein, a pair of angled holes 460 are separated by a distance X (e.g., as indicated by the distance X between hole centers 460a of the respective holes). After the angled milling process, the centers of the angled holes in region 425b move from position 460a to position 460b. Although position 460b is separated from position 460a by a distance Δx, the holes in region 425b are actually separated from the holes adjacent to region 425a by the same distance X. Thus, some embodiments may determine (block 360) that holes are etched at an oblique angle if the center-to-center distance between the holes changes or if the direction (orientation) between the holes changes. In other words, embodiments may determine that holes are etched vertically if both the center-to-center distance between the holes and the direction (orientation) between the holes remain unchanged.

[0044] Example of a sample with multiple holes To provide background for some aspects of the embodiments described herein, reference is made to FIG. 8 . FIG. 8 is a simplified diagram of an area on a semiconductor wafer that may include adjacent holes that can be evaluated to determine whether the holes were etched at an oblique angle according to some embodiments. Specifically, FIG. 8 includes a top view of a wafer 800 and two close-up views of specific portions of the wafer 800. The wafer 800 may be, for example, a 200 mm or 300 mm semiconductor wafer and may include multiple integrated circuits 810 formed thereon (52 integrated circuits 810 are shown in this example). The integrated circuits 810 may be circuits in an intermediate manufacturing stage, and the de-layering techniques described herein may be used to evaluate and analyze one or more regions 820 of the integrated circuits. For example, close-up A of FIG. 8 shows multiple regions 820 of one of the integrated circuits 810 that can be evaluated and analyzed according to the techniques described herein. Close-up B shows one of those regions 820 with an array of holes 830 formed therein.

[0045] Embodiments of the present disclosure can analyze and evaluate the holes in region 820 by capturing a first SEM image of area 820, milling region 820 along the angled cut as discussed above, and then taking a second SEM image of area 820. The SEM image can be captured, for example, by scanning the SEM beam back and forth within the region according to a raster pattern, such as scan pattern 850 shown in simplified form in close-up B of FIG. 8 . In this milling process, region 820 can be milled by scanning the FIB beam back and forth within the region according to a similar raster pattern, scanning the beam line by line from a starting portion 850 a to an ending portion 850 b, with each scan line milling slightly longer than the previous scan line, such that the milled region 820 is angled such that the milled region at ending portion 850 b is deeper than at starting portion 850 a.

[0046] Any reference herein above to a method should, mutatis mutandis, apply to a system capable of carrying out that method, and should, mutatis mutandis, apply to a computer program product having stored thereon instructions that, when executed, perform the method. Similarly, any reference herein above to a system should, mutatis mutandis, apply to a method that can be carried out by that system, and should, mutatis mutandis, apply to a computer program product having stored thereon instructions that can be executed by that system. Any reference herein to a computer program product should, mutatis mutandis, apply to a method that can be carried out when executing instructions stored in the computer program product, and should, mutatis mutandis, apply to a system configured to carry out instructions stored in the computer program product.

[0047] In the foregoing description, for purposes of explanation, specific terminology was used to provide a thorough understanding of the described embodiments. However, it will be apparent to one skilled in the art that these specific details are not required to practice the described embodiments. For example, while some specific embodiments of the present disclosure described above use an exemplary semiconductor wafer as the sample, embodiments of the present disclosure can also be used to delayer other types of samples, including nanostructures formed on substrates other than semiconductor wafers. Accordingly, the foregoing descriptions of the specific embodiments described herein have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the embodiments to the precise forms disclosed. Moreover, while different embodiments of the present disclosure have been disclosed above, specific details of specific embodiments can be combined as appropriate without departing from the spirit and scope of the embodiments of the present disclosure.

[0048] Furthermore, many modifications and variations will be apparent to those skilled in the art in light of the above teachings. For example, while FIG. 3 illustrates a particular order of steps according to some embodiments, this order can be changed in other embodiments. As one specific example, in some embodiments, the center-to-center distance between adjacent holes in the first and second images can be determined at any suitable time after capturing the first and second images. As another example, in some embodiments, a single image can be used to determine the center-to-center distance of holes in both blocks 320 and 350. For example, holes formed in a sample are often part of a larger array of holes with the same spacing. The single image captured in block 340 can capture both holes in the milled region and holes outside the milled region that belong to the same array as the holes in the milled region. Because the spacing of holes within the array is consistent, in some embodiments, in block 360, the center-to-center distance of holes in the region milled in block 330 can be compared to the center-to-center distance of holes outside the milled region.

[0049] Because most of the illustrated embodiments of the present disclosure can be implemented using electronic components and circuits known to those skilled in the art, details of such electronic components and circuits will not be described beyond the extent deemed necessary for an understanding and appreciation of the ideas underlying the present disclosure, as explained above, so as not to obscure or detract from the teachings of the present disclosure.

Claims

1. 1. A method for evaluating a region of a sample comprising a plurality of pores, the method comprising: capturing a first image of the region of the sample including the plurality of holes by scanning the region with a first charged particle beam; evaluating the first image to determine a first center-to-center distance between a first hole and a second hole of the plurality of holes; milling an angled cut in an area including the second hole within the region at an angle such that a top surface of the sample in the milled area where the second hole is located is recessed relative to a top surface of the sample where the first hole is located; thereafter, taking a second image of the area of ​​the sample including the first and second holes by scanning the area with the first charged particle beam; evaluating the second image to determine a second center-to-center distance between the first hole and the second hole of the plurality of holes; and Comparing the second center-to-center distance to the first center-to-center distance. A method comprising:

2. The method of claim 1 further comprising determining an angle β at which the holes are inclined.

3. 3. The method of claim 2, further comprising rejecting the sample from a production line if the angle β is greater than a predetermined value.

4. and determining the angle β at which the holes are inclined according to the following formula: [Equation 1] where α is the angle of bevel cutting, x is the center-to-center distance between the first hole and the second hole measured in the first image, Δx is the difference in the exact position of the second hole before and after the bevel cutting, and θ is the angle between a first imaginary line passing through the centers of the first and second holes in the first image and a second imaginary line passing through the center of the second hole as initially imaged and the center of the second hole in the second image. The method of claim 1.

5. The method of claim 1 , wherein the first hole is outside the area of ​​the region milled at an angle.

6. 10. The method of claim 1, wherein the holes are etched at an angle in a first horizontal plane, and the sample is milled in the first horizontal plane.

7. determining an inclined angle β of the plurality of holes according to the following formula: [Equation 2] where α is the angle of the bevel cut, x is the center-to-center distance between the first hole and the second hole measured in the first image, and Δx is the difference between the center-to-center distance between the first hole and the second hole measured in the second image and the center-to-center distance between the first hole and the second hole measured in the first image. The method of claim 6.

8. 8. The method of claim 1, wherein the sample is placed in a vacuum chamber of an evaluation tool including a scanning electron microscope (SEM) column and a focused ion beam (FIB) column, the first and second images are taken with the SEM column, and the milling is performed with the FIB column.

9. The method of claim 8 , wherein the sample is a semiconductor wafer.

10. 1. A system for evaluating a region of a sample comprising a plurality of holes, 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 first charged particle beam into the vacuum chamber; a focused ion beam (FIB) column configured to direct a second charged particle beam into the vacuum chamber; a processor and a memory coupled to the processor; the memory includes a plurality of computer-readable instructions that, when executed by the processor, capturing a first image of the region of the sample including the plurality of holes by scanning the region with a first charged particle beam; evaluating the first image to determine a first center-to-center distance between a first hole and a second hole of the plurality of holes; milling an angled cut in an area including the second hole within the region at an angle such that a top surface of the sample in the milled area where the second hole is located is recessed relative to a top surface of the sample where the first hole is located; thereafter, taking a second image of the area of ​​the sample including the first and second holes by scanning the area with the first charged particle beam; evaluating the second image to determine a second center-to-center distance between the first hole and the second hole of the plurality of holes; and Comparing the second center-to-center distance to the first center-to-center distance. The system executes the above.

11. 11. The system for evaluating a specimen of claim 10, wherein the processor further causes the system to determine an angle β at which the hole is inclined.

12. the processor further causes the system to determine an inclined angle β of the hole according to the following formula: [Equation 3] where α is the angle of bevel cutting, x is the center-to-center distance between the first hole and the second hole measured in the first image, Δx is the difference in the exact position of the second hole before and after the bevel cutting, and θ is the angle between a first imaginary line passing through the centers of the first and second holes in the first image and a second imaginary line passing through the center of the second hole as initially imaged and the center of the second hole in the second image.

11. A system for evaluating a sample according to claim 10.

13. 11. The system for evaluating a specimen of claim 10, wherein the plurality of holes are etched at an angle in a first horizontal plane, and the processor further causes the system to mill the specimen in the first horizontal plane.

14. the processor further causes the system to determine an inclined angle β of the plurality of holes according to the following formula: [Equation 4] where α is the angle of the bevel cut, x is the center-to-center distance between the first hole and the second hole measured in the first image, and Δx is the difference between the center-to-center distance between the first hole and the second hole measured in the second image and the center-to-center distance between the first hole and the second hole measured in the first image.

14. A system for evaluating a sample according to claim 13.

15. 15. A system for evaluating a specimen according to any one of claims 10 to 14, wherein the first hole is outside the area of ​​the region milled at an angle.

16. 10. A non-transitory computer readable memory storing instructions for evaluating a region of a sample comprising a plurality of pores, wherein evaluating the region of the sample comprising the plurality of pores comprises: capturing a first image of the region of the sample including the plurality of holes by scanning the region with a first charged particle beam; evaluating the first image to determine a first center-to-center distance between a first hole and a second hole of the plurality of holes; milling an angled cut in an area including the second hole within the region at an angle such that a top surface of the sample in the milled area where the second hole is located is recessed relative to a top surface of the sample where the first hole is located; thereafter, taking a second image of the area of ​​the sample including the first and second holes by scanning the area with the first charged particle beam; evaluating the second image to determine a second center-to-center distance between the first hole and the second hole of the plurality of holes; and Comparing the second center-to-center distance to the first center-to-center distance. a non-transitory computer readable memory executed by the

17. 17. The non-transitory computer readable memory of claim 16, wherein the instructions for evaluating the region further comprise instructions for determining an angle β at which the hole is inclined.

18. the instructions for evaluating the region further include instructions for determining an angle β at which the hole is inclined according to the formula: [Equation 5] where α is the angle of bevel cutting, x is the center-to-center distance between the first hole and the second hole measured in the first image, Δx is the difference in the exact position of the second hole before and after the bevel cutting, and θ is the angle between a first imaginary line passing through the centers of the first and second holes in the first image and a second imaginary line passing through the center of the second hole as initially imaged and the center of the second hole in the second image.

17. The non-transitory computer readable memory of claim 16.

19. the plurality of holes are etched at an angle inclined within a first horizontal plane, and the instructions for evaluating the region further comprise instructions for determining an angle β at which the plurality of holes are inclined according to the following formula: [Equation 6] where α is the angle of the bevel cut, x is the center-to-center distance between the first hole and the second hole measured in the first image, and Δx is the difference between the center-to-center distance between the first hole and the second hole measured in the second image and the center-to-center distance between the first hole and the second hole measured in the first image.

17. The non-transitory computer readable memory of claim 16.

20. 20. The non-transitory computer readable memory of any of claims 16-19, wherein the first hole is outside the area of ​​the angle milled region.

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