Improving the accuracy of stereometry 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 APPLICATIONS

[0001] This application claims the benefit of and priority to U.S. patent application Ser. No. 17 / 983,225, filed Nov. 8, 2022, entitled "PRECISION IN STEREOSCOPIC MEASUREMENTS USING A PRE-DEPOSITION LAYER," the entire contents of which are incorporated herein by reference. [Background technology]

[0002]

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

[0003] It is often desirable to determine the exact depth of a hole drilled in a sample. Scanning electron microscopy (SEM) techniques can be beneficially used to determine the depth of the drilled hole. However, in some cases, the top surface of the sample may be partially ablated during the cutting process in the immediate vicinity of the drilled hole. For example, in FIB instruments such as plasma source FIB systems, the focused ion beam may have a relatively large "tail" around the spot, which can damage the surface of the sample outside the immediate vicinity of the beam focus. The damaged top surface may adversely affect the accuracy of thickness measurements.

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

[0005]

[0005] Embodiments described herein provide improved systems and methods for measuring the depth of a hole drilled in a sample. In some embodiments, a focused ion beam (FIB) is used to drill a hole (e.g., a box, trench, or other structure drilled into the sample) in the sample as part of the sample evaluation process. As noted above, in some cases, the drilling process may damage the top surface of the sample in the immediate vicinity of the hole. To ensure accurate measurement of the hole depth, it is important that the distance measured is between the top surface, which is the surface that existed before the hole was drilled, and the bottom surface of the hole. Any damage to the top surface near the hole may make it difficult to correctly identify the exact location of the top surface.

[0006] In some embodiments disclosed herein, it is possible to measure the depth of a drilled 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 prior to the cutting process. This small amount of deposit can be partially removed during the cutting process, forming a high-contrast boundary between the deposited material and the original surface. Images of the hole along the sidewall can be acquired from two different perspectives, 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 drilled hole can be obtained, and the depth of the hole can be determined as described herein.

[0007]

[0007] While embodiments of the present disclosure can be used to perform measurements of holes drilled in a wide variety of sample types, some embodiments are particularly useful for performing measurements on samples that are semiconductor wafers or similar specimens.

[0008] In some embodiments, a method for determining a depth of a hole drilled in a first region of a sample is provided, 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 produced 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.

[0009] In some embodiments, a system for determining the depth of a hole drilled in a first region of a sample is provided. The system can include a vacuum chamber, a sample support configured to hold the sample in the vacuum chamber during the drilling 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 can include a plurality of computer-readable instructions that, when executed by the processor, cause the system to position the sample in a processing chamber having the charged particle beam column, deposit material directly on a top surface of the sample in a second region adjacent to the first region of the sample, drill a hole in the first region of the sample using the charged particle beam generated by the charged particle beam column, and use stereometric techniques to calculate the depth of the hole. The hole can abut the material deposited on the top surface and include a sidewall extending from a bottom surface of the hole to a junction between the deposited material and the top surface of the sample. The depth of the hole can be calculated 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.

[0010] In some embodiments, a non-transitory computer-readable memory having stored thereon instructions for determining a depth of a hole drilled in a first region of a sample is provided, which, when executed by a processor, can cause the drilling to occur by 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 produced 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.

[0011]

[0011] In some embodiments, the stereo measurement technique used to calculate the depth of the hole may include (i) obtaining first and second images of the sidewall at different viewpoints, (ii) measuring the distance 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 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 distances.

[0012] In some embodiments, the stereometric technique used to calculate the depth of the hole includes: (i) acquiring a first image of a sidewall of the spot, the first image being acquired from a first perspective associated with a first angle relative to the sample; (ii) using the first image to measure a first distance between a first point on the sidewall at a junction between the deposited material and a top surface of the sample and a second point on the sidewall corresponding to a bottom surface of the hole; and (iii) acquiring a second image of the sidewall of the spot, the second image being acquired from a second perspective associated with a second angle relative to the sample, the first angle and the first perspective being different from the second angle and the second perspective. (iv) using the second image to measure a second distance between a first point on the sidewall corresponding to a junction between the deposited material and the top surface of the sample and a second point on the sidewall corresponding to a bottom of the hole, wherein the first and second points are approximately on a line extending perpendicularly through the cut hole; and (v) using the first distance, a first angle associated with the first perspective, the second distance, and a second angle associated with the second perspective to determine a depth of the hole.

[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 the focused ion beam column and focusing the ion beam within the second region of the sample; and (iii) scanning the focused particle beam across the second region of the sample to activate molecules of the deposition gas attached to the sample surface in the deposition region and deposit the material within the second region of the sample. The processing chamber may be a vacuum chamber including both a focused ion beam (FIB) column and a scanning electron microscope (SEM) column. The sample may be a semiconductor wafer. The first image and the second image may each be acquired using a scanning electron microscope (SEM) technique.

[0014]

[0014] For a better 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 figure is provided for illustrative purposes only and is not intended as a definition of the limits of the scope of the present disclosure. Also, as a general rule, and unless clearly inconsistent with the description, when elements in different figures use the same reference numerals, the elements are generally identical, or at least similar in function or purpose. [Brief explanation of the drawings]

[0015] [Figure 1A] 1 is a simplified diagram of a sample evaluation system according to some embodiments of the present disclosure. [Figure 1B] 1B is a simplified diagram of the sample evaluation system shown in FIG. 1A with the SEM column tilted, according to some embodiments. [Figure 2] FIG. 1 is a simplified cross-sectional view of a hole drilled in a sample using the charged particle beam of a FIB system. [Figure 3]1 is a simplified diagram illustrating unwanted damage occurring immediately adjacent to a hole drilled in a sample using a charged particle beam system. [Figure 4A-B] 1A-1C are simplified diagrams illustrating various views and aspects of holes that can be measured using the stereometric measurement techniques described herein. [Figure 4C] 1A-1C are simplified diagrams illustrating various views and aspects of holes that can be measured using the stereometric measurement techniques described herein. [Figure 5] 1A-1C are simplified diagrams illustrating various views and aspects of holes that can be measured using the stereometric measurement techniques described herein. [Figure 6] 1A and 1B are simplified diagrams showing various views and aspects of holes that can be measured using the stereometric measurement techniques described herein. [Figure 7] 1A-1C are simplified diagrams illustrating various views and aspects of holes that can be measured using the stereometric measurement techniques described herein. [Figure 8] 1 is a simplified diagram showing how the vertical thickness of a buried layer can be calculated using stereometric techniques. [Figure 9] FIG. 1 is a flow diagram illustrating steps associated with a method for determining the depth of a hole drilled in a sample, according to some embodiments. [Figure 10A-B] 10A-10C are simplified cross-sectional views of a sample according to some embodiments at different stages of processing according to the method described in FIG. 9. [Figure 10C-D] 10A-10C are simplified cross-sectional views of a sample according to some embodiments at different stages of processing according to the method described in FIG. 9. [Figure 11] 1A-C are simplified top views of a sample having material deposited adjacent to the location where a hole will be drilled, according to some embodiments. [Figure 12] 1 is a simplified diagram of a sample that may have a structure or buried layer formed thereon and measured according to embodiments disclosed herein. DETAILED DESCRIPTION OF THE INVENTION

[0016]

[0025] Embodiments described herein provide improved systems and methods for measuring the depth of a hole drilled in a sample. In some embodiments, a hole is drilled in a sample using a focused ion beam (FIB) as part of a sample evaluation process. During a typical drilling process, the top surface of the sample can be damaged in the immediate vicinity of the hole, making it difficult to determine the exact location of the original top surface. In some embodiments disclosed herein, prior to the drilling process, a small amount of material is deposited on the surface of the sample adjacent to the area to be drilled. This small amount of deposit is partially drilled during the drilling process, forming a high-contrast boundary between the deposited material and the original surface, thereby preserving the exact location of the sample's original top surface. Images of the buried layer along the sidewall can then be acquired from two different perspectives, 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 exact distance between the original top surface of the sample and the bottom of the drilled 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" may generally refer to a box, trench, or other structure cut into a sample where one or more surfaces of the hole are below the original surface of the sample before the cutting process.

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

[0027] To better understand and appreciate the present disclosure, reference is first made to Figure 1A, which is a simplified schematic diagram of a sample evaluation system 100 according to some embodiments of the present disclosure. The sample evaluation system 100 can be used for defect review and analysis of structures formed on a sample, such as a semiconductor wafer, among other processes.

[0019]

[0028] 1A, sample characterization system 100 can 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). FIB column 120 and SEM column 130 are connected to vacuum chamber 110 such that a charged particle beam generated by either of the charged particle columns propagates through a vacuum environment created within vacuum chamber 110 before impinging on sample 150. For example, FIB column 120 is operable to generate charged particle beam 122 and direct charged particle beam 122 toward sample 150 (which may be referred to herein as an “object” or “specimen”) 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 particles emitted by the irradiation, and generating a charged particle image based on the detected particles.

[0020]

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

[0021]

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

[0022]

[0031] During the cutting process, the charged particle beam 122 generated by the FIB column 120 propagates within the vacuum environment created within the vacuum chamber 110 before impacting the sample 150. Collisions of the ions with the sample generate secondary electrons and ions 124 that can be detected by a detector 162. The detected secondary electrons or ions 124 can be used to analyze the properties of the ablated layers and structures, to determine the endpoint of the cutting process, and / or to form an image.

[0023]

[0032] During the particle imaging process, a charged particle beam 132 generated by the SEM column 130 propagates within a vacuum environment formed within the vacuum chamber 110 before striking the sample 150. Collisions of the electrons with the sample 150 generate secondary electrons 134 that may be detected by a detector 164. The detected secondary electrons 134 may be used to form an image of the ablated site and / or to analyze the properties of the ablated layers and structures.

[0024]

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

[0025]

[0034] During some processing steps, one or more gases may be supplied into the chamber 110 by a gas injection system 160. For ease of explanation, the gas injection system 160 is illustrated in FIG. 1 as a nozzle; however, it should be noted that the gas injection system 160 may 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 portion of the sample 150 exposed to the charged particle beam, as opposed to supplying gas to the entire top surface of the sample. For example, in some embodiments, the gas injection system 160 has a nozzle diameter measured in 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 scan pattern or impact zone. In various embodiments, a first gas injection system 160 may be configured to supply gas to a sample disposed below the FIB column 120, and a second gas injection system 160 (not shown) may be configured to supply gas to a sample disposed below the SEM column 130.

[0026]

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

[0027]

[0036] 1B illustrates a substrate inspection system 100 in which the SEM column 130 is tilted. As 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 perspectives) 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 FIG. 1B for ease of illustration.

[0028]

[0037] 1A and 1B is provided as an example of a system that can be used with some embodiments described herein. It should be understood that embodiments are not limited to inspection system 100, and other inspection systems can be used with some embodiments. Also, in some embodiments, a FIB tool can be used to drill a hole in a sample, and a separate SEM tool can be used to acquire an image of the hole.

[0029] Charged Particle Deposition Process

[0038] Embodiments of the present disclosure can use the sample characterization system 100 to deposit material onto a sample positioned on a support 140 by initiating a deposition process below the FIB column 120. As an example, in some embodiments, the FIB column 120 can be used in a deposition mode to initiate a focused ion beam deposition process. To this end, a deposition gas can be supplied to the sample 150 by the gas injection system 160, and energy from the FIB column 120 can generate the ion beam 122. A cascade of impinging ions activates the deposition gas, depositing material on the sample localized to the region of the sample scanned by the ion beam. Thus, deposition produced by such embodiments does not occur simultaneously across the entire surface of the sample or wafer being processed. Instead, deposition occurs only approximately where the ion beam (which, by way of non-limiting example, for xenon plasma, can have a diameter ranging from 0.5 to 25 microns) strikes the wafer and the ion beam is scanned across those portions of the wafer. Thus, deposition by some embodiments can be performed with micron-level resolution.

[0030] Cutting hole example

[0039] 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. The sample 200 may represent the sample 150 described in FIGS. 1A and 1B. The sample 200 may include a top surface 212 of the sample 200 through which the hole 210 has been cut. The hole 210, in turn, may include a bottom surface 214 and sidewalls 216 that may extend between the sample surface 212 and the bottom of the hole 214 and, in some cases, may be sloped at an angle, as shown in FIG. 2.

[0031]

[0040] The hole 210 in FIG. 2 is depicted as a theoretical or idealized shape. In an actual cutting process, the top surface 212 may be somewhat damaged during the cutting of the hole 210. For illustrative purposes, refer to FIG. 3, which is a simplified cross-sectional view of a sample 300 similar to sample 200, with a hole 310 cut therein. As shown in FIG. 3, the hole 310 is cut into the top surface 312 of the sample 300 and includes a bottom surface 314. Sidewalls 316 may extend between the sample surface 312 and the bottom 314 of the hole and may be sloped at an angle similar to the sidewalls 214 described above. As can be seen in the example illustrated in FIG. 3, the sidewalls 316 may have portions with a relatively constant slope angle. However, unlike the hole sample 200, the sample 300 includes damaged regions 318 along one or more portions of the perimeter of the hole 310.

[0032]

[0041] The depth of holes 210 and 310 can be measured stereoscopically by measuring the length between two points from two different viewpoints. For example, if one measurement is taken from a top-down viewpoint and a second measurement is taken from an angled viewpoint (e.g., at a 45-degree angle), the difference in length between the two measurements is the vertical height of the measured bevel (or, alternatively, the depth of the drilled hole).

[0033]

[0042] To perform such stereoscopic measurements with high accuracy, the locations of the two points to be measured must be accurately identified. However, as shown in FIG. 3 , the surface 312 of the sample 300 may contain a damaged region 318. The damaged region 318 may be formed, for example, along the periphery of the hole 310 during the cutting process. As a non-limiting example and as described above, in some FIB instruments, such as plasma-source FIB systems, the focused ion beam may have a relatively large "tail" around the spot that can form the damaged region 318 on the surface of the sample. The damaged region 318 may make it difficult to accurately identify the top surface 312 of the sample 300 during the SEM imaging process, which may adversely 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 drilled hole even when there is damage to the sample surface near the hole periphery, such as damaged area 318, an example of how stereoscopic measurements according to some embodiments can be performed is first provided below.

[0035] General Concepts - 3D Measurement with SEM Equipment

[0044] Imaging devices such as scanning electron microscopes (SEMs) can use stereoscopic techniques to determine the thickness or depth of different structures formed on a sample. One technique for doing so is described in commonly assigned U.S. patent application Ser. No. 17 / 408,876, filed July 19, 2021, entitled "Analyzing a Buried Layer of a Sample." The entire contents of the 17 / 408,876 application are incorporated herein by reference, and for convenience, a brief description of the stereoscopic measurement technique described in the 17 / 408,876 application is provided below with reference to Figures 4A-8.

[0036]

[0045] 4A and 4B are simplified cross-sectional and top-down views, respectively, illustrating an exemplary hole 400 drilled in a sample 410. The illustrated hole 400 includes sloped sidewalls formed in the sample 410. In this example, the sample 410 includes a buried layer 420 having a different composition than the 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 techniques described below.

[0037]

[0046] When the hole 400 is viewed from different perspectives, the apparent thickness of the buried layer 420 varies, 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 tilt angle increases, reaches a maximum at a certain tilt angle that depends on the slope of the sidewalls, and then decreases as the tilt angle increases further. This is illustrated by a comparison of FIGS. 4B and 4C, which shows a simplified oblique view of the hole 400 depicted in FIGS. 4A and 4B. From this perspective, the buried layer 420 can be seen along the sloped sidewalls of the hole 400. In some embodiments, the oblique view can be approximately 45° (e.g., within a few degrees) relative to the surface of the sample 410.

[0038]

[0047] The distance measured between the top and bottom surfaces of the buried layer from different viewpoints can be used to determine the thickness (vertical thickness) of the buried layer 420. FIG. 5 is a simplified diagram (same oblique viewpoint as FIG. 4C ) showing how images of the buried layer 420 in the sample 400 on the sidewall 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 allows for obtaining distance measurements between points in the image. Examples include optical or SEM devices and techniques. The images can then be used to measure the distance between points on the top and bottom surfaces of the buried layer 420. It should be understood that the field of view of the imaging device can include not only the buried layer 420 but also the hole 410 (sometimes referred to herein as a spot) or a larger portion of the sample 400.

[0039]

[0048] 6A and 6B are further simplified cross-sectional views of hole 400 showing a first point 600a on top surface 422 of buried layer 420 and a second point 600b on bottom surface 424 of buried layer 420. Points 600a, 600b may be located with any single feature or multiple features that make points 600a, 600b distinguishable in images taken from different viewpoints.

[0040]

[0049] In FIG. 6A , points 600a, 600b appear to be vertically aligned, as indicated by dashed line 610. However, FIG. 6B is rotated 90 degrees relative to FIG. 6A , showing that points 600a, 600b are vertically offset because they are located on the sloping sidewalls of drilled hole 400. In practice, one of points 600a, 600b, for example point 600a, can be selected, and the distance between point 600a and another point on bottom surface 424 of buried layer 420 that 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 result in two points that lie approximately on line 610 extending vertically through buried layer 420, as shown in FIG. 6A .

[0041]

[0050] 7 is a simplified diagram illustrating some of the steps for determining the vertical thickness 710 of buried layer 220 using the measured distance between points 600a, 600b. In this example, a first image of buried layer 220 is acquired from a first viewpoint 700a, and a second image of 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 the particular imaging device and measurement technique.

[0042]

[0051] FIG. 8 is a simplified diagram illustrating how the vertical thickness of a structure 800 (such as buried layer 420) or the vertical depth of a hole can be determined, according to some embodiments. For ease of illustration, the top and bottom surfaces of the layers of structure 800 are represented by horizontal lines 810 and 820, respectively. The horizontal lines are connected by line 830, which represents a sidewall of structure 800 that is inclined at an angle β from normal. In this example, a first image of the sidewall is acquired from a first viewpoint 850a at a first tilt angle α1, and a second image is acquired from a second viewpoint 850b at a second tilt angle α2. The tilt angles α1 and α2 can be user-defined and / or obtained from or determined by an imaging device. The vertical thickness (or height or depth) of structure 800 is represented by H.

[0043]

[0052] When analyzing features from tilted viewpoints, many conventional SEM imaging devices measure distances projected onto a horizontal or vertical plane. As an example, in FIG. 8 , the distance projected onto the horizontal plane from a 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 a second viewpoint 850b is L2, and the distance projected onto the vertical plane from the second viewpoint is h2. According to some embodiments, these measured distances, along with tilt angles α1 and α2, can be used to determine the vertical thickness H of buried layer 800 using one of the following equations: TIFF2025537171000002.tif27170

[0044]

[0053] In some embodiments, the first viewpoint 850a may be approximately top-down (perpendicular to the surface of the sample) and the second viewpoint 850b may be approximately 45° to the surface of the sample. In this configuration, the vertical thickness H of the buried layer is simplified and can be determined using the formula: TIFF2025537171000003.tif11170

[0045] Determining the depth of holes drilled into the sample surface

[0054] While the discussion above describes using stereological techniques to determine the thickness of a buried layer, embodiments disclosed herein can also use the stereological techniques described above to determine the depth (i.e., height) of a hole drilled in a sample. As discussed above with respect to FIG. 3 , in some cases, a portion of the top surface of the sample surrounding the drilled hole is problematic for accurately determining the depth of the drilled hole. By way of example, such damage can occur when the focused ion beam has a relatively large “tail” or other characteristics that cause some degree of damage to the top surface. The embodiments disclosed herein can accurately determine the depth of the hole using the techniques described below, even when the top surface is damaged.

[0046]

[0055] In some embodiments, the top surface of a sample can be accurately identified by depositing a small amount of material on the surface directly next to the area to be cut. Even if some of the small amount of 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 the height of the original surface to be accurately identified. Points along the high-contrast boundary can be used in conjunction with the stereometric techniques described herein to determine the exact depth of the cut hole.

[0047]

[0056] For illustrative purposes, reference is made to Figures 9, 10A-10D, and 11A-11C. Figure 9 is a flow diagram illustrating steps associated with a method 900 according to some embodiments disclosed herein. Figures 10A-10D are simplified cross-sectional views of a sample 1000 at different stages of processing according to the method 900. And Figures 11A-11C are simplified top views illustrating different patterns in which material may be deposited on the sample 1000 during the performance of the method 900 according to different embodiments.

[0048]

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

[0049]

[0058] As will be appreciated by those skilled in the art, material 1020 may be selected based on the composition of sample 1000 or the top layer of sample 1000 being cut. Generally, material 1020 should have properties that provide a strong contrast with sample 1000 (or the top layer of sample 1000).

[0050]

[0059] Deposition of material onto sample 1000 in step 930 can be performed by 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 gas injection system 150, and ion beam 122 can be generated by energy from FIB column 120. A cascade of impinging ions activates the deposition gas, resulting in localized material deposition on the sample in the area of ​​the sample scanned by the ion beam. System 1000 can therefore control the location of material 1020 based on the position of the scan pattern used in step 930. As various non-limiting examples, material 1020 can be deposited along one entire edge of the periphery of hole 1010 ( FIG. 11A ), along only a portion of the edge ( FIG. 11B ), or along most or the entire periphery around the location where the hole will be drilled ( FIG. 11C ).

[0051]

[0060] After the material 1020 is deposited, a hole 1010 can be cut (step 940) in the top surface 1012 of the sample 1000. The cutting process can scan a focused ion beam over an area of ​​the sample directly adjacent to where the material 1020 was deposited. As shown in FIG. 10C , the hole 1010 can include a bottom surface 1014 and a sidewall 1016 extending between the top surface 1012 and the bottom surface 1014.

[0052]

[0061] As mentioned above, in some cases, the cutting step 940 may result in a damaged region 1018 that surrounds some or all of the upper periphery of the hole 1010. Even though the damaged region etches or cuts away a portion of the material 1020 closest to the periphery of the hole 1010, to the extent that some material 1020 remains, the junction (boundary) 1030 between the remaining material 1020 and the sample 1000 represents the original location of the top 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 can be identified and used to calculate the depth of the hole 1010 using the stereometric measurement techniques described above and illustrated in FIG. 10D. Referring again to FIG. 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 perspective (step 950), and then measuring a second distance between the same two points 1032, 1034 from a second perspective (step 960). Once these two measurements are taken, the depth of the hole 1010 can be determined (step 970) using the first distance, the first angle associated with the first perspective, the second distance, and the second angle associated with the second perspective, as described above with respect to FIG. 8.

[0054] Example of a sample to be cut and measured

[0063] As described above, embodiments of the present disclosure can be used to determine the depth of holes drilled in a sample. Embodiments can be used to determine the depth of holes drilled in many different types of samples, including electronic circuits formed on semiconductor structures, solar cells formed on polycrystalline or other substrates, nanostructures formed on various substrates, and the like. As one non-limiting example, FIG. 12 is a simplified diagram of a site on a semiconductor wafer that may contain drilled holes whose depths may be determined according to embodiments described herein. Specifically, FIG. 12 includes a top view of wafer 1200 along with two enlarged views of specific portions of wafer 1200. Wafer 1200 may be, for example, a 150 mm, 200 mm, or 300 mm semiconductor wafer and may include multiple integrated circuits 1210 (52 in the illustrated example) formed thereon. Integrated circuits 1210 may be at an intermediate stage of fabrication, and techniques described herein may be used to evaluate and analyze one or more regions 1220 of the integrated circuit.

[0055]

[0033] Embodiments of the present disclosure can analyze and evaluate region 1220 by sequentially removing material within the region to form the drilled hole. The depth of the drilled hole can then be determined, as described above. When drilling a hole, the drilling process can drill region 1220 by scanning the FIB back and forth in a raster pattern within the region until the hole is drilled to the desired depth (at the desired slope). Even if the drilling process unintentionally damages the top surface of sample 1200 in the immediate vicinity surrounding region 1220, the techniques described herein can still be used to accurately determine the depth of the drilled hole.

[0056] Additional Embodiments

[0064] In the foregoing description, for purposes of explanation, specific nomenclature was used to provide a thorough understanding of the described embodiments. However, it will be apparent to one skilled in the art that specific details are not required to practice the described embodiments. Accordingly, the foregoing descriptions of specific embodiments described herein are presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the embodiments to the precise forms disclosed. For example, while the embodiments described above describe the focused ion beam column as part of a tool having a single charged particle column, in some embodiments, the focused ion beam column may be part of an SEM-FIB tool having both a scanning electron microscope column and a focused ion beam column. Furthermore, while various simplified diagrams of holes whose depths may be measured have been described herein as examples, it should be understood that the examples are generally highly simplified drawings for illustrative purposes only. The actual holes drilled in the sample may have different geometries than those shown in the figures, and the embodiments described herein are not limited to any particular shape or geometry of the drilled holes. Additionally, while the included figures show the profile of a smooth hole (e.g., hole 310), it should be understood that the profile may be rough and jagged at the micro level without significantly affecting the depth measurement techniques described herein.

[0057]

[0065] Moreover, although different embodiments of the present disclosure have been disclosed above, the specific details of particular embodiments can be combined in any suitable manner without departing from the spirit and scope of the embodiments of the present disclosure. Moreover, many modifications and variations will be apparent to those skilled in the art in light of the above teachings. It is therefore to be understood that the appended claims are intended to cover all such modifications and variations that fall within the true spirit of the embodiments of the present disclosure.

[0058]

[0066] Furthermore, any reference in the specification to a method should be applied mutatis mutandis to a system capable of carrying out the method, and should be applied mutatis mutandis to a computer program product storing instructions that, once executed, cause the method to be carried out. Similarly, any reference in the specification to a system should be applied mutatis mutandis to a method that may be carried out by the system, and should be applied mutatis mutandis to a computer program product storing instructions that may be executed by the system. Furthermore, any reference in the specification to a computer program product should be applied mutatis mutandis to a method that may be carried out when executing instructions stored in the computer program product, and should be applied mutatis mutandis to a system configured to execute instructions stored in the computer program product.

[0059]

[0067] Furthermore, while the exemplary embodiments of the present disclosure may, for the most part, be implemented using electronic components and circuits known to those skilled in the art, such details have not been described beyond the extent deemed necessary for an understanding and appreciation of the concepts underlying the present disclosure and in order not to obscure or deviate from the teachings of the present disclosure, as exemplified above.

Claims

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

2. Using the stereometric technique to calculate the depth of the hole includes: acquiring a first image and a second image of the sidewall at different viewpoints; measuring a distance between a first point along a junction between the material and the top surface and a second point along a bottom surface of the hole for each of the first and second images; calculating a depth of the hole based on the first and second images and the measured distance; and 2. The method of claim 1 for determining the depth of a hole drilled in a first region of a sample, comprising:

3. 3. The method of claim 2, wherein the first image and the second image are each obtained using a scanning electron microscope (SEM) technique.

4. 4. The method of claim 1, wherein the charged particle beam column is a focused ion beam (FIB) column and the charged particle beam is a focused ion beam.

5. Depositing the material injecting a deposition precursor gas into a second region of the sample; generating a focused ion beam using a focused ion beam column and focusing the ion beam within a second region of the sample; scanning the focused particle beam across a second region of the sample to activate molecules of the deposition gas attached to the sample surface in the deposition region and deposit material within the second region of the sample; 5. The method of claim 4, comprising:

6. The stereometric technique comprises: acquiring a first image of the sidewall of the hole, the first image being acquired from a first perspective associated with a first angle relative to the sample; using the first image to measure a first distance between a first point on the sidewall at a junction between the deposited material and a top surface of the sample and a second point on the sidewall corresponding to a bottom surface of the hole; acquiring a second image of the sidewall of the hole, the second image being acquired from a second perspective associated with a second angle relative to the sample, the first angle and the first perspective being different from the second angle and the second perspective; using the second image to measure a second distance between a first point on the sidewall corresponding to a junction between the deposited material and the top surface of the sample and a second point on the sidewall corresponding to a bottom surface of the hole, wherein the first point and the second point are approximately on a line extending perpendicularly through the cut hole; using the second image to measure a second distance between a first point on the sidewall corresponding to a junction between the deposited material and the top surface of the sample and a second point on the sidewall corresponding to a bottom surface of the hole; determining a depth of the hole using the first distance, the first angle associated with the first viewpoint, the second distance, and the second angle associated with the second viewpoint; 2. The method of claim 1 for determining the depth of a hole drilled in a first region of a sample, comprising:

7. 7. The method of claim 6, wherein the first image and the second image are each obtained using a scanning electron microscope (SEM) technique.

8. 2. The method of claim 1, wherein the processing chamber is a vacuum chamber that includes both a focused ion beam (FIB) column and a scanning electron microscope (SEM) column.

9. 2. The method of claim 1, wherein the sample is a semiconductor wafer.

10. 1. A system for determining a depth of a hole drilled in a first region of a sample, comprising: a vacuum chamber; a sample support configured to hold a 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, when executed by the processor, providing the system with: positioning the sample in a processing chamber having a charged particle beam column; depositing a material directly onto the top surface of the sample in a second region adjacent to the first region of the sample; cutting the hole in a first region of the sample using the charged particle beam produced by the charged particle beam column, the hole abutting material deposited on a top surface and including a sidewall extending from a bottom of the hole to a junction between the deposited material and the top surface of the sample; using stereometric techniques to calculate a depth of the hole based on a distance measurement between a first point along a junction between the material and the top surface and a second point along a bottom surface of the hole; a processor and a memory coupled to the processor, the memory including a plurality of computer readable instructions for causing the processor to perform the steps of: A system comprising:

11. The stereometric technique used to calculate the depth of the hole is: acquiring a first image and a second image of the sidewall at different viewpoints; measuring a distance between a first point along a junction between the material and the top surface and a second point along a bottom surface of the hole for each of the first and second images; calculating a depth of the hole based on the first and second images and the measured distance; and 11. The system for determining the depth of a hole drilled in a first region of a sample of claim 10, comprising:

12. wherein the first image and the second image are each obtained using a scanning electron microscope (SEM) technique; 12. A system for determining the depth of a hole drilled in a first region of a sample according to claim 11.

13. 11. The system for determining a depth of a hole drilled in a first region of a sample of claim 10, wherein the charged particle beam column is a focused ion beam (FIB) column and the charged particle beam is a focused ion beam.

14. Depositing the material comprises: injecting a deposition precursor gas into a second region of the sample; generating a focused ion beam using a focused ion beam column and focusing the ion beam within a second region of the sample; scanning the focused particle beam across a second region of the sample to activate molecules of the deposition gas attached to the sample surface in the deposition region and deposit material within the second region of the sample; 14. The system for determining the depth of a hole drilled in a first region of a sample of claim 13, comprising:

15. 15. The system for determining the depth of a hole drilled in a first region of a sample according to any one of claims 10 to 14, wherein the processing chamber is a vacuum chamber containing both a focused ion beam (FIB) column and a scanning electron microscope (SEM) column.

16. 1. A non-transitory computer-readable memory, comprising: Positioning the sample in a processing chamber having a charged particle beam column; depositing a 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 a first region of the sample using the charged particle beam produced by the charged particle beam column, the hole abutting material deposited on a top surface and including a sidewall extending from a bottom of the hole to a junction between the deposited material and the top surface of the sample; using stereometric techniques to calculate a depth of the hole based on a distance measurement between a first point along a junction between the material and the top surface and a second point along a bottom surface of the hole; a non-transitory computer readable memory having stored thereon instructions for determining a depth of a hole drilled in a first region of the sample by:

17. The stereometric technique used to calculate the depth of the hole is: acquiring a first image and a second image of the sidewall at different viewpoints; measuring a distance between a first point along a junction between the material and the top surface and a second point along a bottom surface of the hole for each of the first and second images; calculating a depth of the hole based on the first and second images and the measured distance; and 20. A non-transitory computer readable memory having stored thereon instructions for determining a depth of a hole drilled in a first region of a sample according to claim 16, comprising:

18. wherein the first image and the second image are each obtained using a scanning electron microscope (SEM) technique; 20. A non-transitory computer readable memory having stored thereon instructions for determining a depth of a hole drilled in a first region of a sample according to claim 17.

19. 17. A non-transitory computer-readable memory having stored thereon instructions for determining a depth of a hole drilled in a first region of a sample as described in claim 16, wherein the charged particle beam column is a focused ion beam (FIB) column and the charged particle beam is a focused ion beam.

20. Depositing the material comprises: injecting a deposition precursor gas into the processing chamber adjacent to a deposition region; generating a focused ion beam using a focused ion beam column and focusing the ion beam within a deposition region of the sample; scanning the focused particle beam across a deposition region of the sample to activate molecules of a deposition gas attached to a surface of the sample in the deposition region and deposit material within the deposition region of the sample; 20. A non-transitory computer readable memory having stored thereon instructions for determining the depth of a hole drilled in a first region of a sample of any one of claims 16 to 19, comprising:

Images