Improving the accuracy of 3D measurements using pre-deposited layers

Abstract

A method for determining a depth of a hole drilled in a first region of a sample, the method including: positioning the sample in a processing chamber having a charged particle beam column; depositing material directly onto a top surface of the sample in a second region adjacent to the first region of the sample; drilling a hole in the first region of the sample using the charged particle beam generated by the charged particle beam column, the hole abutting the material deposited on the top surface and including a sidewall extending from a bottom surface of the hole to a junction between the deposited material and the top surface of the sample; and using stereometric techniques to calculate the depth of the hole based on distance measurements between a first point along the junction between the material and the top surface and a second point along the bottom surface of the hole.

Description

[Technical Field]

[0001] Cross-Reference to Related Application

[0001] This application claims the benefit and priority of U.S. Patent Application No. 17 / 983,225, entitled "PRECISION IN STEREOSCOPIC MEASUREMENTS USING A PRE-DEPOSITION LAYER", filed on November 8, 2022, the entire content of which is incorporated herein by reference. [Background Art]

[0002]

[0002] In research on electronic materials and processes for processing such materials into electronic structures, samples of electronic structures can be used for microscopic examination for the purposes of failure analysis and device verification. For example, to study specific properties of structures formed on a wafer, a sample such as a silicon wafer including one or more electronic structures formed thereon can be cut and analyzed using a focused ion beam (FIB).

[0003]

[0003] It is often desirable to determine the accurate depth of a hole cut into a sample. Scanning electron microscope (SEM) techniques can be advantageously used to determine the depth of a cut hole. However, in some cases, during the cutting process, the top surface of the sample may be partially cut at the immediate region around the cut hole. For example, in FIB equipment such as a plasma source FIB system, a focused ion beam may have a relatively large "tail" around the spot, which may damage the surface of the sample outside the region immediately adjacent to the beam focus. The damaged top surface may adversely affect the accuracy of thickness measurement.

[0004]

[0004] Therefore, an improved method for accurately determining the depth of a hole cut into a sample is desired. [Summary of the Invention]

[0005]

[0005] Embodiments described herein provide improved systems and methods for measuring the depth of holes cut into a sample. In some embodiments, a focused ion beam (FIB) is used to cut a hole (e.g., a box, trench, or other structure cut into the sample) into the sample as part of a sample evaluation process. As described above, in some cases, the cutting process may damage the top surface of the sample in the immediate vicinity of the hole. To maintain high accuracy in measuring the hole depth, it is important that the distance being measured is between the top surface, which was the surface that existed before the hole was cut, and the bottom surface of the hole. If there is any damage to the top surface near the hole, it may be difficult to correctly identify the exact location of the top surface.

[0006]

[0006] In some embodiments disclosed herein, it is possible to measure the depth of a cut hole with high accuracy even if the surface of the sample is damaged during the cutting process. To do this, in some embodiments, a small amount of material is deposited on the sample surface adjacent to the area to be cut before the cutting process. This small amount of deposit is partially cut during the cutting process, and a high-contrast boundary can be formed between the deposited material and the original surface. Images of the hole along the sidewall can be obtained from two different viewpoints, and the high-contrast boundary can be used in the images as the exact height of the original surface. Once the exact height of the original surface is known, the distance between the top surface of the sample along the sidewall of the hole and the bottom surface of the cut hole can be obtained, and the depth of the hole can be determined as described herein.

[0007]

[0007] Embodiments of the present disclosure can be used to perform measurements of holes cut into a wide variety of samples, but some embodiments are particularly useful for performing measurements of samples that are semiconductor wafers or similar specimens.

[0008]

[0008] In some embodiments, a method is provided for determining the depth of a hole cut in a first region of a sample. The method may include positioning the sample in a processing chamber having a charged particle beam column, depositing material directly onto the top surface of the sample in a second region adjacent to the first region of the sample, cutting a hole in the first region of the sample using a charged particle beam generated by the charged particle beam column, wherein the hole abuts the material deposited on the top surface and includes side walls extending from the bottom of the hole to the junction between the deposited material and the top surface of the sample, and using a stereometric technique to calculate the depth of the hole based on distance measurements between a first point along the junction between the material and the top surface and a second point along the bottom of the hole.

[0009]

[0009] In some embodiments, a system is provided for determining the depth of a hole cut into a first region of a sample. The system may include a vacuum chamber, a sample support configured to hold the sample within the vacuum chamber during the cutting process, a charged particle beam column configured to direct a charged particle beam into the vacuum chamber, a processor, and a memory coupled to the processor. The memory may include a number of computer-readable instructions, when executed by the processor, that cause the system to position the sample within the processing chamber having the charged particle beam column, to deposit material directly onto the top surface of the sample in a second region adjacent to the first region of the sample, to cut a hole in the first region of the sample using a charged particle beam generated by the charged particle beam column, and to use stereometric techniques to calculate the depth of the hole. The hole may abut the material deposited on the top surface and may include side walls extending from the bottom of the hole to the junction between the deposited material and the top surface of the sample. The depth of the hole may be calculated based on a distance measurement between a first point along the junction between the material and the top surface and a second point along the bottom of the hole.

[0010]

[0010] In some embodiments, a non-transient computer-readable memory is provided which stores instructions for determining the depth of a hole cut in a first region of a sample. When executed by a processor, the instructions can be used to position the sample in a processing chamber having a charged particle beam column, deposit material directly onto the top surface of the sample in a second region adjacent to the first region of the sample, cut a hole in the first region of the sample using a charged particle beam generated by the charged particle beam column, the hole being in contact with the material deposited on the top surface and including side walls extending from the bottom of the hole to the junction between the deposited material and the top surface of the sample, and to use a stereometric technique to calculate the depth of the hole based on distance measurements between a first point along the junction between the material and the top surface and a second point along the bottom of the hole.

[0011]

[0011] In some embodiments, the stereometric measurement technique used to calculate the depth of the hole may include (i) obtaining first and second images of the side wall from different viewpoints, (ii) measuring the distance between a first point along the joint between the material and the top surface and a second point along the bottom surface of the hole for each of the first and second images, and (iii) calculating the depth of the hole based on the first and second images and the measured distance.

[0012]

[0012] In some embodiments, the stereometric measurement technique used to calculate the depth of the hole includes: (i) obtaining a first image of the side wall of the spot, the first image being obtained from a first viewpoint associated with a first angle to the sample; (ii) using the first image to measure a first distance between a first point on the side wall at the junction between the deposited material and the top surface of the sample and a second point on the side wall corresponding to the bottom surface of the hole; and (iii) obtaining a second image of the side wall of the spot, the second image being obtained from a second viewpoint associated with a second angle to the sample, the first angle and the first viewpoint being different from the second angle and the second viewpoint. (iv) Using the second image, measure a second distance between a first point on the sidewall corresponding to the junction between the deposited material and the top surface of the sample and a second point on the sidewall corresponding to the bottom of the hole, wherein the first and second points are approximately on a line extending perpendicularly to the cut hole; (v) Using the first distance, a first angle associated with the first viewpoint, a second distance, and a second angle associated with the second viewpoint, the depth of the hole may be determined.

[0013]

[0013] In various implementations, embodiments may include one or more of the following features: The charged particle beam column may be a focused ion beam (FIB) column, and the charged particle beam may be a focused ion beam. Depositing the material may include (i) injecting a deposition precursor gas into a second region of the sample, (ii) generating a focused ion beam using a focused ion beam column and focusing the ion beam into the second region of the sample, and (iii) scanning the focused particle beam across the entire second region of the sample to activate the molecules of the deposition gas attached to the sample surface in the deposition region and deposit the material in the second region of the sample. The processing chamber may be a vacuum chamber containing both a focused ion beam (FIB) column and a scanning electron microscope (SEM) column. The sample may be a semiconductor wafer. The first and second images can each be acquired using scanning electron microscopy (SEM) techniques.

[0014]

[0014] To better understand the nature and merits of this disclosure, please refer to the following description and accompanying figures. However, please understand that each figure is provided for illustrative purposes only and is not intended to define the limits of the scope of this disclosure. Also, as a general rule, and unless otherwise clearly contradicted by the description, if elements in different figures use the same reference numeral, the elements are generally identical or at least similar in function or purpose. [Brief explanation of the drawing]

[0015] [Figure 1A] This is a simplified diagram of a sample evaluation system according to some embodiments of the present disclosure. [Figure 1B] Figure 1A is a simplified diagram of a sample evaluation system in which the SEM column is tilted, according to several embodiments. [Figure 2] This is a simplified cross-sectional view of a hole cut into a sample using a charged particle beam from a FIB system. [Figure 3]It is a simplified diagram showing undesirable damage occurring at a site immediately adjacent to a hole cut in a sample using a charged particle beam system. [Figure 4A-B] It is a simplified diagram showing various appearances and aspects of holes that can be measured using the three-dimensional measurement technique described in the present specification. [Figure 4C] It is a simplified diagram showing various appearances and aspects of holes that can be measured using the three-dimensional measurement technique described in the present specification. [Figure 5] It is a simplified diagram showing various appearances and aspects of holes that can be measured using the three-dimensional measurement technique described in the present specification. [Figure 6] A and B are simplified diagrams showing various appearances and aspects of holes that can be measured using the three-dimensional measurement technique described in the present specification. [Figure 7] It is a simplified diagram showing various appearances and aspects of holes that can be measured using the three-dimensional measurement technique described in the present specification. [Figure 8] It is a simplified diagram showing a method for calculating the vertical thickness of a buried layer using a three-dimensional measurement technique. [Figure 9] It is a flow diagram showing steps related to a method of determining the depth of a hole cut in a sample according to some embodiments. [Figure 10A-B] It is a simplified cross-sectional view of a sample according to some embodiments at different stages processed in accordance with the method described in Fig. 9. [Figure 10C-D] It is a simplified cross-sectional view of a sample according to some embodiments at different stages processed in accordance with the method described in Fig. 9. [Figure 11] A to C are simplified top views of samples having material deposited adjacent to a position where a hole is cut, according to some embodiments. [Figure 12] It is a simplified diagram of a sample that can have a structure or a buried layer formed and measured thereon according to an embodiment disclosed in the present specification. DETAILED DESCRIPTION OF EMBODIMENTS

[0016]

[0025] Embodiments described herein provide improved systems and methods for measuring the depth of a hole cut into a sample. In some embodiments, as part of a sample evaluation process, a focused ion beam (FIB) is used to cut a hole in the sample. During a typical cutting process, the top surface of the sample may be damaged at the immediate area around the hole, which can make it difficult to determine the exact position of the original top surface. In some embodiments disclosed herein, a small amount of material is deposited on the surface of the sample adjacent to the area to be cut before the cutting process. This small deposit can be partially cut during the cutting process, resulting in a high-contrast boundary between the deposited material and the original surface, so that the exact position of the original top surface of the sample can be retained. Then, images of the buried layer along the sidewall can be acquired from two different viewpoints, and the high-contrast boundary can be used as the exact height of the original surface in the images. Once the exact height of the original surface is known, the exact distance between the original top surface of the sample and the bottom of the cut hole along the sidewall can be obtained, as described herein, and the depth of the hole can be accurately determined.

[0017]

[0026] As used herein, the term "hole" can generally refer to a box, trench, or other structure cut into a sample, in which one or more surfaces of the hole are below the original surface of the sample prior to the cutting process.

[0018] Example of Focused Ion Beam (FIB) Tools

[0027] For a better understanding and appreciation of the present disclosure, reference is first made to FIG. 1A, which is a simplified schematic diagram of a sample evaluation system 100 in accordance with some embodiments of the present disclosure. The sample evaluation system 100 can be used, among other processes, for defect review and analysis of structures formed on samples such as semiconductor wafers.

[0019]

[0028] As shown in Figure 1A, the sample evaluation system 100 may include, among other elements, a vacuum chamber 110, a focused ion beam (FIB) column 120, a scanning electron microscope (SEM) column 130, a sample support element 140, a gas injection nozzle 160, and optionally, secondary electron detectors 162, 164 (or, in some embodiments, a secondary ion detector, or a combination of two detectors operating in parallel). The FIB column 120 and the SEM column 130 are connected to the vacuum chamber 110 so that a charged particle beam generated by either of the charged particle columns propagates through the vacuum environment formed within the vacuum chamber 110 before impacting the sample 150. For example, the FIB column 120 can generate a charged particle beam 122 and direct the charged particle beam 122 toward the sample 150 (which may be referred to herein as “object” or “sample”) to cut or otherwise process the sample. The SEM column 130 can generate an image of a portion of the sample 150 by irradiating the sample with a charged particle beam 132, detecting the particles emitted by the irradiation, and generating a charged particle image based on the detected particles.

[0020]

[0029] The sample 150, for example, a semiconductor wafer, may be supported on a sample support element 140 within a vacuum chamber 110. The sample support element 140 can also move the region of the sample within the vacuum chamber 110 between the fields of view of two charged particle columns 120 and 130, as needed for processing. For example, a region on the sample 150 can be cut using the FIB column 120, and then the support element 140 can move the sample so that the SEM column 130 can image the cut region of the sample 150.

[0021]

[0030] The FIB column 120 can cut (e.g., drill holes in) a sample 150 by irradiating the sample with one or more charged particle beams to form a cross-section or hole. The FIB cutting process typically operates by positioning the sample in a vacuum chamber 110 and emitting an ion beam toward the sample to etch or cut the material on the sample. In a typical cutting process, a cross-section of the sample 150 can be formed, and the cross-section can also be smoothed if necessary. In some cases, the vacuum environment can be purged with a background gas to control the etching rate and other parameters. Accelerated ions can be generated from xenon, gallium, or other suitable elements and accelerated toward the sample by voltages typically ranging from 500 volts to 100,000 volts, and more typically from 3,000 volts to 30,000 volts. The beam current is typically in the range of a few picoamperes to a few microamperes, depending on the configuration of the FIB instrument and the specific application, and the pressure is typically 10 in different parts of the system and different operating modes. -10 from 10 -5 It is controlled by mbar.

[0022]

[0031] During the cutting process, the charged particle beam 122 generated by the FIB column 120 propagates within the vacuum environment formed in the vacuum chamber 110 before colliding with the sample 150. The collision of ions with the sample generates secondary electrons and ions 124, which can be detected by the detector 162. The detected secondary electrons or ions 124 can be used to analyze the properties of the cut layers and structures, to determine the endpoint of the cutting process, and / or to form an image.

[0023]

[0032] During the particle imaging process, the charged particle beam 132 generated by the SEM column 130 propagates through the vacuum environment formed within the vacuum chamber 110 before colliding with the sample 150. Secondary electrons 134 are generated by the electron collision with the sample 150 and can be detected by the detector 164. The detected secondary electrons 134 can be used to form an image of the cut area and / or to analyze the characteristics of the cut layer and structure.

[0024]

[0033] The particle imaging and cutting processes each involve scanning a charged particle beam back and forth (e.g., in a raster scanning pattern) at a constant speed over a specific area of ​​the sample to be imaged or cut. One or more lenses (not shown) coupled to the charged particle column can perform the scanning pattern, as is well known to those skilled in the art. The area scanned is typically only a small portion of the total area of ​​the sample. For example, the sample may be a semiconductor wafer with a diameter of 200 mm or 300 mm, and each area scanned on the wafer may be a rectangular area with a width and / or length measured in microns or tens of microns.

[0025]

[0034] During several processing steps, one or more gases may be supplied into the chamber 110 by the gas injection system 160. For simplicity of explanation, the gas injection system 160 is shown as a nozzle in Figure 1, but it should be noted that the gas injection system 160 may also include, among other elements, a gas reservoir, a gas source, a valve, one or more inlets, and one or more outlets. In some embodiments, the gas injection system 160 may be configured to supply gas to a localized area of ​​the sample 150 exposed to the charged particle beam, as opposed to supplying gas to the entire upper surface of the sample. For example, in some embodiments, the gas injection system 160 has a nozzle diameter measured in the hundreds of microns (e.g., 400-500 microns) configured to supply gas directly to a relatively small portion of the sample surface encompassing the charged particle beam scanning pattern or impact zone. In various embodiments, a first gas injection system 160 may be configured to supply gas to a sample located below the FIB column 120, and a second gas injection system 160 (not shown) may be configured to supply gas to a sample located below the SEM column 130.

[0026]

[0035] As shown in Figure 1, the system 100 may include one or more controllers, processors, or other hardware units 170 that control the operation of the system 100 by executing computer instructions stored in one or more computer-readable memories 180, which are well known to those skilled in the art. For example, the computer-readable memory may include solid-state memory (e.g., random-access memory (RAM) and / or read-only memory (ROM) which may be programmable and / or flash-updatable), disk drives, optical storage devices, or similar non-transient computer-readable storage media.

[0027]

[0036] Figure 1B shows a substrate inspection system 100 with the SEM column 130 tilted. As will be described in more detail below, the SEM column 130 can be tilted relative to the surface of the sample 150 to acquire images at different angles (or from different viewpoints) relative to the surface of the sample 150. Alternatively, in some embodiments, the support element 140 can be configured to tilt the sample 150 to acquire images from different angles. The gas nozzle 160 and detectors 162, 164 are not shown in Figure 1B for ease of illustration.

[0028]

[0037] The inspection system 100 shown in Figures 1A and 1B is provided as an example of a system that can be used with some of the embodiments described herein. It should be understood that the embodiments are not limited to inspection system 100, and other inspection systems can be used with some of the embodiments. Furthermore, in some embodiments, a hole can be cut into the sample using a FIB tool, and an image of the hole can be obtained using another SEM tool.

[0029] Charged particle deposition process

[0038] Embodiments of this disclosure allow material to be deposited on a sample positioned on a support 140 by initiating the deposition process below the FIB column 120 using a sample evaluation system 100. As an example, in some embodiments, the FIB column 120 can be used in deposition mode to initiate a focused ion beam deposition process. For this purpose, a deposition gas can be supplied to the sample 150 by a gas injection system 160, and an ion beam 122 can be generated by the energy from the FIB column 120. The cascade of colliding ions activates the deposition gas, causing material to be deposited on the sample, localized to the region of the sample being scanned by the ion beam. Thus, the deposition resulting from such embodiments does not occur simultaneously across the entire surface of the sample or wafer being processed. Instead, deposition occurs only in approximate areas where the ion beam (in the case of xenon plasma, as a non-limiting example, may have a diameter ranging from 0.5 to 25 microns) collides with the wafer and the ion beam is scanned across those parts of the wafer. Thus, deposition according to some embodiments can be performed with micron-level resolution.

[0030] Examples of cut holes

[0039] Figure 2 is a simplified cross-sectional view of a sample 200 having a hole 210 cut therein using a charged particle beam of a FIB system, according to an embodiment. Sample 200 may represent sample 150 as shown in Figures 1A and 1B. Sample 200 may include the top surface 212 of sample 200 from which the hole 210 is cut. The hole 210 may then include a bottom surface 214 and a side wall 216 that may extend between the surface 212 of the sample and the bottom 214 of the hole, and may optionally be angled as shown in Figure 2.

[0031]

[0040] The hole 210 in Figure 2 is depicted as a theoretical or ideal shape. In the actual cutting process, the top surface 212 may be slightly damaged during the cutting of the hole 210. For illustrative purposes, refer to Figure 3, a simplified cross-sectional view of sample 300, similar to sample 200, in which the hole 310 is cut. As shown in Figure 3, the hole 310 is cut into the top surface 312 of sample 300, including the bottom surface 314. A side wall 316 may extend between the surface 312 of the sample and the bottom 314 of the hole, and may be inclined at a similar angle to the side wall 214 described above. As can be seen in the example illustrated in Figure 3, the side wall 316 may have portions with a relatively constant inclination angle. However, unlike the hole sample 200, sample 300 includes damaged portions 318 along one or more portions around the hole 310.

[0032]

[0041] The depths of holes 210 and 310 can be measured in a three-dimensional manner by measuring the length between two points from two different viewpoints. For example, if the first measurement is taken from a viewpoint looking from above and the second measurement is taken from an angled viewpoint (e.g., a 45-degree incline), the difference in length between the two measurements will be the vertical height of the measured slope (or, instead, the depth of the cut hole).

[0033]

[0042] To perform such three-dimensional measurements with high accuracy, it is necessary to accurately identify the positions of the two points to be measured. However, as shown in Figure 3, damaged areas 318 may exist on the surface 312 of the sample 300. Damaged areas 318 may be formed, for example, along the outer circumference of the hole 310 during the cutting process. As a non-limiting example, and as mentioned above, in some FIB instruments such as plasma source FIB systems, the focused ion beam may have a relatively large "tail" around spots on the sample surface that may form damaged areas 318. The surface of the damaged areas 318 may make it difficult to accurately identify the top surface 312 of the sample 300 during the SEM imaging process, which may negatively affect the accuracy of determining the depth of the hole 310.

[0034]

[0043] Before describing how the embodiments disclosed herein can accurately determine the depth of a cut hole even when there is damage to the sample surface near the periphery of the hole, such as the damaged area 318, some examples of how stereometric measurements can be performed according to several embodiments are shown below.

[0035] General Concept - 3D Measurement using SEM Equipment

[0044] Imaging devices such as scanning electron microscopes (SEMs) can use stereometric techniques to determine the thickness or depth of different structures formed on a sample. One such technique is described in U.S. Patent Application No. 17 / 408,876, filed July 19, 2021, entitled "Analyzing a Buried Layer of a Sample," by the same applicant. The contents of Application No. 17 / 408,876 are incorporated herein by reference in their entirety, but for convenience, a brief description of the stereometric technique described in Application No. 17 / 408,876 is provided below with reference to Figures 4A to 8.

[0036]

[0045] Figures 4A and 4B are simplified cross-sectional and top views, respectively, of an exemplary hole 400 cut into sample 410. The illustrated hole 400 includes an inclined side wall formed in sample 410. In this example, sample 410 includes a buried layer 420 having a different composition from sample 410. The buried layer 420 includes an upper surface 422 and a lower surface 424, and the height (thickness) of the buried layer 420, i.e., the distance between the upper surface 422 and the lower surface 424, can be determined using a technique described later.

[0037]

[0046] When the hole 400 is viewed from a different viewpoint, the apparent thickness of the buried layer 420 changes, as indicated by the distance between the top surface 422 of the buried layer 410 and the bottom surface 424 of the buried layer 410. More specifically, the distance between the top surface 422 and the bottom surface 424 of the buried layer 420 increases as the inclination angle increases, reaching a maximum at a certain inclination angle that depends on the inclination of the sidewall, and then decreasing as the inclination angle increases further. This is shown in a comparison of Figure 4B and Figure 4C, where Figure 4C is a simplified view of the hole 400 shown in Figures 4A and 4B from an inclined viewpoint. From this viewpoint, the buried layer 420 can be seen along the inclined sidewall of the hole 400. In some embodiments, the inclined viewpoint may be about 45° (e.g., within a few degrees) relative to the surface of the sample 410.

[0038]

[0047] The thickness (vertical thickness) of the buried layer 420 can be determined using the distance measured between the top and bottom surfaces of the buried layer from different viewpoints. Figure 5 is a simplified diagram (the same inclined viewpoint as Figure 4C) showing how images of the buried layer 420 in the sample 400 on the side wall of the hole 410 are acquired from different viewpoints according to an embodiment. In the illustrated example, a first image can be acquired from a first viewpoint 500a, and a second image can be acquired from a second viewpoint 500b. The images can be acquired using any type of imaging device or technique that enables the acquisition of distance measurements between points in the image. Examples include optical devices or SEM devices and techniques. The distances between points on the top and bottom surfaces of the buried layer 420 can then be measured using the images. It should be understood that the field of view of the imaging device may include not only the buried layer 420 but also a wider portion of the hole 410 (sometimes referred to as a spot herein) or the sample 400.

[0039]

[0048] Figures 6A and 6B are further simplified cross-sectional views of the hole 400 showing a first point 600a on the upper surface 422 of the buried layer 420 and a second point 600b on the lower surface 424 of the buried layer 420. Points 600a and 600b may be located in positions that have some single or multiple features that make points 600a and 600b identifiable in images acquired from different viewpoints.

[0040]

[0049] In Figure 6A, points 600a and 600b appear to be aligned vertically, as indicated by the dashed line 610. However, Figure 6B is rotated 90° relative to Figure 6A, showing that points 600a and 600b are offset vertically because they are located on the inclined sidewall of the cut hole 400. In practice, one of points 600a and 600b, for example point 600a, can be selected, and the distance between point 600a and another point on the underside 424 of the buried layer 420, which appears to be directly below point 600a, can be measured. The point associated with the shortest distance can be identified as point 600b. This technique should yield two points that are approximately located on a line 610 extending vertically through the buried layer 420, as shown in Figure 6A.

[0041]

[0050] Figure 7 is a simplified diagram showing some of the steps for determining the vertical thickness 710 of the buried layer 220 using the measured distance between points 600a and 600b. In this example, a first image of the buried layer 220 is acquired from a first viewpoint 700a, and a second image of the buried layer 220 is acquired from a second viewpoint 700b. The distance 710 between points 600a and 600b in each image can be determined using known measurement techniques that depend on a specific imaging device and measurement technique.

[0042]

[0051] Figure 8 is a simplified diagram showing how the vertical thickness of a structure 800 (such as a buried layer 420) or the vertical depth of a hole can be determined according to several embodiments. For ease of illustration, the top and bottom surfaces of the structure 800 are represented in this figure by horizontal lines 810 and 820, respectively. The horizontal lines are connected by lines 830 representing the side walls of the structure 800, which are inclined at an angle β from the perpendicular lines. In this example, a first image of the side wall at a first inclination angle α1 is acquired from a first viewpoint 850a, and a second image at a second inclination angle α2 is acquired from a second viewpoint 850b. The inclination angles α1 and α2 can be defined by the user and / or acquired from or determined by the imaging device. The vertical thickness (or height or depth) of the structure 800 is represented by H.

[0043]

[0052] When analyzing features from an inclined viewpoint, most conventional SEM imaging devices measure the distance projected onto a horizontal or vertical plane. For example, in Figure 8, the distance projected onto the horizontal plane from the first viewpoint 850a is L1, and the distance projected onto the vertical plane from the first viewpoint is h1. Similarly, the distance projected onto the horizontal plane from the second viewpoint 850b is L2, and the distance projected onto the vertical plane from the second viewpoint is h2. According to several embodiments, these measured distances can be used together with inclination angles α1 and α2 to determine the vertical thickness H of the buried layer 800 using one of the following equations. TIFF0007918352000001.tif27170

[0044]

[0053] In some embodiments, the first viewpoint 850a may be approximately top-down (perpendicular to the sample surface), and the second viewpoint 850b may be approximately 45° to the sample surface. In this configuration, the vertical thickness H of the embedded layer is simplified and can be determined using a formula. TIFF0007918352000002.tif11170

[0045] Determination of the depth of holes cut into the sample surface.

[0054] While the above description explains how to determine the thickness of the embedded layer using stereometric techniques, embodiments disclosed herein can also determine the depth (i.e., height) of a hole cut into a sample using the stereometric techniques described above. As described above with respect to Figure 3, in some cases, a portion of the upper surface of the sample surrounding the cut hole may be problematic in accurately determining the depth of the cut hole. For example, such damage may occur if the focused ion beam has a relatively large "tail" or other characteristics that cause some degree of damage to the upper surface. Embodiments disclosed herein can accurately determine the depth of the hole using the techniques described below, even if the upper surface is damaged.

[0046]

[0055] In some embodiments, the top surface of the sample can be accurately identified by depositing a small amount of material directly adjacent to the area to be cut. Even if a portion of the small deposit is partially cut during the cutting process, the remaining portion of the deposit forms a high-contrast boundary between the deposit and the original surface, allowing for accurate identification of the height of the original surface. Points along the high-contrast boundary can be used in conjunction with the stereometric techniques described herein to determine the precise depth of the cut hole.

[0047]

[0056] For illustrative purposes, see Figures 9, 10A–10D, and 11A–11C. Figure 9 is a flowchart showing steps related to Method 900 according to several embodiments disclosed herein. Figures 10A–10D are simplified cross-sectional views of Sample 1000 at different stages processed according to Method 900. And Figures 11A–11C are simplified top views showing different patterns on which material may be deposited on Sample 1000 during the implementation of Method 900 according to different embodiments.

[0048]

[0057] As shown in Figure 9, Method 900 begins by positioning the sample on a sample support in a chamber of a suitable evaluation system (step 910). For example, in some embodiments, step 910 includes positioning sample 1000 (Figure 10A) on a sample support 140 in a vacuum chamber 110 of a sample evaluation system 100. Sample 1000 may represent any of the samples 150, 200, 300, or 400 described above. Next, sample 1000 can be moved under the field of view of a focused ion beam column (step 920), and material 1020 can be locally deposited at one or more locations directly adjacent to the location where a hole 1010 (shown by a dashed line) is cut into the sample (step 930), as shown in Figure 10B.

[0049]

[0058] As those skilled in the art will understand well, material 1020 can be selected based on the composition of sample 1000 or the top layer of sample 1000 to be cut. Generally, material 1020 should have properties that exhibit a strong contrast with sample 1000 (or the top layer of sample 1000).

[0050]

[0059] The deposition of material onto sample 1000 in step 930 can be carried out using a charged particle deposition process such as a focused ion beam deposition process, as described above. For example, a suitable deposition gas can be supplied to sample 130 by a gas injection system 150, and an ion beam 122 can be generated by energy from the FIB column 120. The cascade of colliding ions activates the deposition gas, resulting in the deposition of material localized on the sample in the area of ​​the sample being scanned by the ion beam. Thus, system 1000 can control the location where material 1020 is deposited based on the position of the scanning pattern used in step 930. As various non-limiting examples, material 1020 can be deposited along the entire edge of the periphery of hole 1010 (Figure 11A), along only a portion of the edge (Figure 11B), or over most of or the entire periphery around the location where the hole is cut (Figure 11C).

[0051]

[0060] After material 1020 is deposited, a hole 1010 can be cut into the top surface 1012 of the sample 1000 (step 940). The cutting process can involve scanning a focused ion beam in a region of the sample directly adjacent to the location where material 1020 is deposited. As shown in Figure 10C, the hole 1010 may include a bottom surface 1014 and a side wall 1016 extending between the top surface 1012 and the bottom surface 1014.

[0052]

[0061] As described above, in some cases, the cutting step 940 may result in a damaged area 1018 surrounding part or all of the upper periphery of the hole 1010. Even if a portion of the material 1020 closest to the periphery of the hole 1010 is etched or cut by the damaged area, as long as some material 1020 remains, the joint (boundary) 1030 between the remaining material 1020 and the sample 1000 represents the original position of the upper surface 1012.

[0053]

[0062] Next, a first point 1032 along the joint 1030 and a second point 1034 at the bottom of the hole 1010 are identified, and the depth of the hole 1010 can be calculated using the stereometric measurement technique described above and illustrated in Figure 10D. Referring again to Figure 9, the depth of the hole 1010 can be determined by measuring a first distance between the first point 1032 and the second point 1034 from a first viewpoint (step 950), and then measuring a second distance between the same two points 1032 and 1034 from a second viewpoint (step 960). Once these two measurements are performed, the depth of the hole 1010 can be determined using the first distance, the first angle associated with the first viewpoint, the second distance, and the second angle associated with the second viewpoint, as described above with respect to Figure 8 (step 970).

[0054] Examples of samples that are cut and measured

[0063] As described above, the embodiments of this disclosure can be used to determine the depth of holes cut into a sample. The embodiments can be used to determine the depth of holes cut into many different types of samples, including electronic circuits formed on semiconductor structures, solar cells formed on polycrystalline substrates or other substrates, nanostructures formed on various substrates, and so on. As one non-limiting example, Figure 12 is a simplified diagram of a portion on a semiconductor wafer that may contain holes whose depth can be determined according to the embodiments described herein. Specifically, Figure 12 includes a top view of wafer 1200, along with two enlarged views of a particular portion of wafer 1200. Wafer 1200 may be, for example, a 150 mm, 200 mm, or 300 mm semiconductor wafer and may contain a plurality of integrated circuits 1210 (52 in the illustrated example) formed thereon. The integrated circuits 1210 may be in an intermediate stage of manufacturing, and one or more regions 1220 of the integrated circuits can be evaluated and analyzed using the techniques described herein.

[0055]

[0033] Embodiments of the present disclosure allow for the analysis and evaluation of region 1220 by sequentially cutting the material within the region that forms the cut hole. Then, as described above, the depth of the cut hole can be determined. When cutting a hole, the cutting process can cut region 1220 by back-scanning the FIB according to a raster pattern within the region until the hole is cut to a desired depth (with a desired gradient). Even if the cutting process unintentionally damages the upper surface of the sample 1200 in the immediate vicinity of region 1220, the depth of the cut hole can be accurately determined using the techniques described herein.

[0056] Additional Embodiments

[0064] In the foregoing description, a specific nomenclature was used for illustrative purposes to provide a complete understanding of the described embodiments. However, it will be apparent to those skilled in the art that specific details are not necessary to carry out the described embodiments. Therefore, the foregoing descriptions of the specific embodiments described herein are presented for illustrative and explanatory purposes only. They are not intended to be exhaustive or to limit embodiments to any specific form disclosed. For example, in the embodiments described above, a focused ion beam column was described as part of a tool having a single charged particle column, but in some embodiments, the focused ion beam column may be part of a SEM-FIB tool having both a scanning electron microscope column and a focused ion beam column. Furthermore, various simplified diagrams of holes whose depth can be measured have been described herein as examples, but it should be understood that the examples are generally highly simplified drawings for illustrative purposes only. Actual holes cut into a sample may have a different shape than those shown in the figures, and the embodiments described herein are not limited to any particular shape or shape of a cut hole. Furthermore, although the included figures show the profile of a smooth hole (e.g., hole 310), it should be understood that the profile can be coarse and jagged at the micro level without significantly affecting the depth measurement techniques described herein.

[0057]

[0065] Furthermore, although different embodiments of the present disclosure have been disclosed above, specific details of particular embodiments can be combined in any appropriate manner without departing from the spirit and scope of the embodiments of the present disclosure. Moreover, in light of the above teachings, it will be apparent to those skilled in the art that many modifications and variations are possible. Accordingly, it should be understood that the attached claims cover all of the above modifications and variations that constitute the true spirit of the embodiments of the present disclosure.

[0058]

[0066] Furthermore, references to methods in the above specification should apply mutatis mutandis to systems capable of executing such methods, and should apply mutatis mutandis to computer program products that store instructions for executing such methods once executed. Similarly, references to systems in the above specification should apply mutatis mutandis to methods that can be executed by a system, and should apply mutatis mutandis to computer program products that store instructions that can be executed by a system. In addition, references to computer program products in the above specification should apply mutatis mutandis to methods that can be executed when executing instructions stored in a computer program product, and should apply mutatis mutandis to systems configured to execute instructions stored in a computer program product.

[0059]

[0067] Furthermore, where the exemplary embodiments of this disclosure can be carried out in large part using electronic components and circuits known to those skilled in the art, such details are not described beyond what is considered necessary for understanding and appreciating the underlying concepts of this disclosure and so as not to obscure or deviate from the teachings of this disclosure, as illustrated above.

Claims

1. A method for determining the depth of a hole cut in a first region of a sample, Positioning the sample within a processing chamber having a charged particle beam column, The material is directly deposited on the upper surface of a second region of the sample adjacent to a first region of the sample, such that the material forms a joint with the upper surface of the sample. Cutting a hole in a first region of the sample using a charged particle beam generated by the charged particle beam column, wherein the cutting partially removes the deposited material so that the remaining portion of the material forms a high-contrast boundary with the upper surface, the hole abuts the material deposited on the upper surface, and includes side walls extending from the bottom of the hole to the high-contrast boundary formed at the junction between the deposited material and the upper surface of the sample, To obtain a first image and a second image of the side wall from different viewpoints, The depth of the hole is calculated based on the distance measured in the first and second images between a first point along the high-contrast boundary between the deposited material and the upper surface and a second point along the bottom surface of the hole. A method that includes this.

2. A method for determining the depth of a hole cut into a first region of a sample according to claim 1, wherein the first and second images are each obtained using a scanning electron microscope (SEM) technique.

3. A method for determining the depth of a hole cut into a first region of a sample according to any one of claims 1 to 2, wherein the charged particle beam column is a focused ion beam (FIB) column and the charged particle beam is a focused ion beam.

4. Depositing materials is Injecting a deposition precursor gas into the second region of the sample, A focused ion beam is generated using a focused ion beam column, and the ion beam is focused into a second region of the sample. To activate the molecules of the deposit gas attached to the sample surface in the deposition region and deposit material within the second region of the sample, a focused particle beam is scanned across the entire second region of the sample. A method for determining the depth of a hole cut into a first region of a sample according to claim 3, including the following:

5. The depth of the hole is calculated using a stereometric measurement technique, The aforementioned three-dimensional measurement technique is The first image of the side wall of the hole is obtained, wherein the first image is obtained from a first viewpoint associated with a first angle with respect to the sample. Using the first image, measure the first distance between a first point on the side wall at the joint between the deposited material and the upper surface of the sample, and a second point on the side wall corresponding to the bottom surface of the hole. The method involves obtaining a second image of the side wall of the hole, wherein the second image is obtained from a second viewpoint associated with a second angle to the sample, and the first angle and the first viewpoint are different from the second angle and the second viewpoint. Using the second image, measure a second distance between a first point on the side wall corresponding to the joint between the deposited material and the upper surface of the sample and a second point on the side wall corresponding to the bottom surface of the hole, wherein the first and second points are approximately on a line extending perpendicularly to the cut hole, using the second image, measure a second distance between a first point on the side wall corresponding to the joint between the deposited material and the upper surface of the sample and a second point on the side wall corresponding to the bottom surface of the hole, The depth of the hole is determined using the first distance, the first angle associated with the first viewpoint, the second distance, and the second angle associated with the second viewpoint. A method for determining the depth of a hole cut into a first region of a sample according to claim 1, including the following:

6. A method for determining the depth of a hole cut into a first region of a sample according to claim 5, wherein the first and second images are each obtained using a scanning electron microscope (SEM) technique.

7. A method for determining the depth of a hole cut in a first region of a sample according to claim 1, wherein the processing chamber is a vacuum chamber containing both a focused ion beam (FIB) column and a scanning electron microscope (SEM) column.

8. A method for determining the depth of a hole cut in a first region of a sample according to claim 1, wherein the sample is a semiconductor wafer.

9. A system for determining the depth of a hole cut in a first region of a sample, Vacuum chamber and A sample support configured to hold the sample within the vacuum chamber during the cutting process, A charged particle beam column configured to direct a charged particle beam into the vacuum chamber, A processor and a memory coupled to the processor, wherein when executed by the processor, the memory enables the system to Positioning the sample within a processing chamber having a charged particle beam column, The material is directly deposited on the upper surface of a second region of the sample adjacent to a first region of the sample, such that the material forms a joint with the upper surface of the sample. Cutting a hole in a first region of the sample using a charged particle beam generated by the charged particle beam column, wherein the cutting partially removes the deposited material so that the remaining portion of the material forms a high-contrast boundary with the upper surface, the hole abuts the material deposited on the upper surface, and includes side walls extending from the bottom of the hole to the high-contrast boundary formed at the junction between the deposited material and the upper surface of the sample, To obtain a first image and a second image of the side wall from different viewpoints, The depth of the hole is calculated based on the distance measured in the first and second images between a first point along the high-contrast boundary between the deposited material and the upper surface and a second point along the bottom surface of the hole. A processor and memory coupled to the processor, including a plurality of computer-readable instructions that cause the following to occur. A system equipped with these features.

10. The first and second images are each acquired using scanning electron microscopy (SEM) techniques. A system for determining the depth of a hole cut in a first region of a sample according to claim 9.

11. A system for determining the depth of a hole cut into a first region of a sample according to claim 9, wherein the charged particle beam column is a focused ion beam (FIB) column and the charged particle beam is a focused ion beam.

12. Depositing the aforementioned material is Injecting a deposition precursor gas into the second region of the sample, A focused ion beam is generated using a focused ion beam column, and the ion beam is focused into a second region of the sample. To activate the molecules of the deposit gas attached to the sample surface in the deposition region and deposit material within the second region of the sample, a focused particle beam is scanned across the entire second region of the sample. A system for determining the depth of a hole cut into a first region of a sample according to claim 11, including the following:

13. A system for determining the depth of a hole cut in a first region of a sample according to any one of claims 9 to 12, wherein the processing chamber is a vacuum chamber including both a focused ion beam (FIB) column and a scanning electron microscope (SEM) column.

14. Non-transient computer-readable memory, Positioning the sample within a processing chamber having a charged particle beam column, The material is directly deposited on the upper surface of a second region of the sample adjacent to a first region of the sample, such that the material forms a joint with the upper surface of the sample. Cutting a hole in a first region of the sample using a charged particle beam generated by the charged particle beam column, wherein the cutting partially removes the deposited material so that the remaining portion of the material forms a high-contrast boundary with the upper surface, the hole abuts the material deposited on the upper surface, and includes side walls extending from the bottom of the hole to the high-contrast boundary formed at the junction between the deposited material and the upper surface of the sample, To obtain a first image and a second image of the side wall from different viewpoints, The depth of the hole is calculated based on the distance measured in the first and second images between a first point along the high-contrast boundary between the deposited material and the upper surface and a second point along the bottom surface of the hole. A non-transient, computer-readable memory that stores instructions for determining the depth of a hole cut into a first region of the sample.

15. The first and second images are each acquired using scanning electron microscopy (SEM) techniques. A non-transient computer-readable memory storing instructions for determining the depth of a hole cut in a first region of the sample according to claim 14.

16. The charged particle beam column is a focused ion beam (FIB) column, and the charged particle beam is a focused ion beam, wherein a non-transient computer-readable memory storing instructions for determining the depth of a hole cut in a first region of a sample according to claim 14.

17. Depositing the aforementioned material is Injecting a deposition precursor gas into a position adjacent to the deposition region within the processing chamber, A focused ion beam is generated using a focused ion beam column, and the ion beam is focused into the deposition region of the sample. To activate the molecules of the deposition gas attached to the sample surface in the deposition region and deposit material within the deposition region of the sample, a focused particle beam is scanned over the entire deposition region of the sample. A non-transient computer-readable memory storing instructions for determining the depth of a hole cut into a first region of a sample according to any one of claims 14 to 16.

Images