Deposition under high-energy SEM to fill empty structures to achieve uniform layering

Abstract

A method of evaluating a region of a sample including an array of holes separated by solid portions. The method includes the steps of positioning the sample within a vacuum chamber of an evaluation tool including a scanning electron microscope (SEM) column and a focused ion beam (FIB); injecting a deposition gas onto the sample; scanning a portion of the sample including a plurality of holes in the array of holes with a first beam of charged particles to locally deposit material from the deposition gas within the plurality of holes in the scanned portion; and milling the portion of the sample including the plurality of holes in which material was locally deposited with the FIB column.

Description

[0001] This application claims priority to US 16 / 789,348, filed February 12, 2020. Its disclosure is incorporated herein by reference in its entirety for all purposes. Background Technology

[0002] In the study of electronic materials and the processes used to fabricate electronic structures from such materials, samples of electronic structures can be examined under a microscope for purposes of fault analysis and device verification. For example, samples of electronic structures (such as silicon wafers) can be analyzed using a scanning electron microscope (SEM) or a transmission electron microscope (TEM) to study specific characteristic features within the wafer. These characteristic features may include the fabricated circuitry and any defects formed during the manufacturing process. Electron microscopes are among the most useful tools for analyzing the microstructure of semiconductor devices.

[0003] In preparing samples of electronic structures for electron microscopy examination, various polishing and milling processes can be used to segment the structure until specific characteristic features are exposed. As device dimensions continue to shrink to the sub-half-micrometer level, techniques for preparing samples for study in electron microscopy become increasingly important. Due to the unacceptable resolution of optical microscopes, conventional methods for studying structures using optical microscopy cannot be used to study features in modern electronic structures.

[0004] While TEM techniques can provide high-resolution images and detailed descriptions of the internal structure of samples sufficient to analyze devices with sub-half-micrometer features, they are only effective for electron-transparent samples. Therefore, a fundamental requirement for TEM samples is that they must be thin enough to be penetrated by the electron beam and thin enough to avoid multiple scattering, which causes image blurring. Thin samples extracted from wafers for TEM processing can be brittle and prone to breakage or fragmentation. For these and other reasons, TEM imaging is not practical for certain defect inspection and analysis operations.

[0005] A dual-column system combining a scanning electron microscope (SEM) and a focused ion beam (FIB) unit can produce high-resolution SEM images of localized regions of electronic structures formed on a sample, such as a semiconductor wafer. A typical dual-column system includes an SEM column, an FIB column, a support element for supporting the sample, and a vacuum chamber, in which the sample is placed when it is milled (through the FIB column) and when it is imaged (through the SEM column).

[0006] Removing one or more selected layers (or portions of layers) to isolate structures on a sample is called delamination, and can be done in a two-column system, such as the one described above. Delamination can be performed, for example, by: (i) locating the area of ​​interest to be milled to remove a certain thickness of material from the sample (the area of ​​interest can be located via SEM navigation and sometimes by using an optical microscope); (ii) moving the sample (e.g., via a mechanical support element) so that the sample is positioned below the FIB cell; and (iii) milling the sample to remove the desired amount of material at the area of ​​interest. Delamination processes may include forming holes in the sample (typically sized to be several micrometers to tens of micrometers in both the lateral and vertical dimensions) to expose the material to be sampled at the bottom of the holes.

[0007] When attempting to mill certain structures formed on a sample, the geometry of the structure being milled can present challenges in uniformly layering the structure. For example, in devices comprising arrays of high aspect ratio channel holes or similar structures with solid portions (e.g., slits) between holes, the areas with channel holes may be milled faster than the areas with solid portions, making accurate metrology difficult or even impossible in those areas. Therefore, improved milling and layering techniques are desired. Summary of the Invention

[0008] Embodiments of this disclosure relate to an improved method and system for removing one or more selected layers (or portions of layers) of a sample comprising sub-half-micron features via a layering process. Embodiments of this disclosure can be used to uniformly layer portions of such samples, even if the layered portions comprise high aspect ratio channel hole arrays, holes having solid portions formed between the holes, or similar structures. While embodiments of this disclosure can be used to layer structures formed on a wide variety of sample types, some embodiments are particularly useful for layering samples that are semiconductor wafers or similar samples.

[0009] Some embodiments relate to a method for evaluating a region of a sample comprising an array of pores separated by solid portions. The method may include the steps of: positioning the sample within a vacuum chamber of an evaluation tool, the evaluation tool including a scanning electron microscope (SEM) column and a focused ion beam (FIB); injecting a deposition gas onto the sample; scanning a portion of the sample comprising a plurality of pores in the pore array with a first charged particle beam to locally deposit material from the deposition gas into the plurality of pores in the scanned portion; and milling the portion of the sample comprising the plurality of pores in which material is locally deposited with the FIB column.

[0010] The milling step may include the following steps: scanning an ion beam across both the material deposited in the pore array and the solid portions separating the pores, and the milling step may iteratively layer both the material in the pore array and the solid portions separating the pores. Furthermore, in some embodiments, after each iteration of the milling process removes a layer of the sample in the milled region, the sample can be imaged using an SEM column.

[0011] In some embodiments, material deposited during the scanning step may be deposited within the upper portion of a plurality of wells, and a milling step may mill the sample to the level exposing the lower unfilled portion of the plurality of wells. The method further includes the steps of: repeating the injection and scanning steps after the milling step to deposit additional material within the unfilled portion of the plurality of wells; and thereafter, milling the portion of the sample containing the plurality of wells in which additional material is locally deposited with an FIB column.

[0012] Some embodiments relate to a system for evaluating a region of a sample comprising an array of pores separated by solid portions. The system may include: a vacuum chamber; a sample support configured to hold a sample within the vacuum chamber during sample evaluation; a SEM column configured to guide a first charged particle beam into the vacuum chamber; a FIB column configured to guide a second charged particle beam into the vacuum chamber; a gas supply system configured to inject a deposition gas onto the sample; and a processor and a computer-readable memory coupled to the processor. The memory may include a plurality of computer-readable instructions that, when executed by the processor, cause the system to: inject the deposition gas onto the sample; scan a portion of the sample comprising a plurality of pores in the pore array with the charged particle beam to locally deposit material from the deposition gas into the plurality of pores in the scanned portion; and mill a portion of the sample comprising the plurality of pores in which material is locally deposited with the FIB column.

[0013] Some embodiments relate to a non-transitory computer-readable storage device that stores instructions for evaluating a region of a sample comprising an array of pores separated by solid portions by the following steps: positioning the sample within a vacuum chamber of an evaluation tool, the evaluation tool comprising an SEM column and a FIB column; injecting a deposition gas onto the sample; scanning a portion of the sample comprising a plurality of pores in the pore array with a first charged particle beam to locally deposit material from the deposition gas into the plurality of pores in the scanned portion; and milling the portion of the sample comprising the plurality of pores in which material is locally deposited with the FIB column.

[0014] Various implementations of the embodiments described herein may include one or more of the following features. The first charged particle beam may be a high-energy SEM beam generated by an SEM column, or the first charged particle beam may be generated by a FIB column operating in reverse bias mode. The implantation and scanning steps may occur simultaneously, or the implantation and scanning steps may occur sequentially, and the implantation and scanning steps may be repeated multiple times across different regions of the sample to be layered. The high-energy SEM beam has a power level of at least 15 keV. The sample may be a semiconductor wafer. Each of the plurality of holes may have a diameter of less than 100 nm and a depth of greater than 3 micrometers. In some implementations, the plurality of holes are contact holes for memory channels in a 3D-NAND structure, and in some implementations, the plurality of holes are holes in which capacitors in a DRAM device may be formed.

[0015] Other embodiments relate to a method for evaluating a region of a sample comprising an array of holes separated by solid portions. The method may include the steps of: positioning the sample on a support within a vacuum chamber of an evaluation tool, the evaluation tool including an SEM column and a FIB column; moving the sample within the chamber to a position below the field of view of the SEM column; injecting a deposition gas onto the sample; and scanning a portion of the sample comprising a plurality of holes in the array of holes using a high-energy SEM beam from the SEM column to locally deposit material within the plurality of holes in the scanned portion; moving the sample within the chamber to a position below the field of view of the FIB column; and milling the portion of the sample comprising the plurality of holes in which material is locally deposited using the FIB column.

[0016] To better understand the nature and advantages of this disclosure, reference should be made to the following description and accompanying drawings. However, it should be understood that each drawing is provided for illustrative purposes only and is not intended to be a limitation of the scope of this disclosure. Likewise, as a general rule, and unless it is clearly understood from the specification to the contrary, when elements in different drawings use the same reference numerals, said elements are generally the same or at least similar in function or purpose. Attached Figure Description

[0017] Figure 1A This is a simplified cross-sectional view of a semiconductor wafer, which includes an array of high aspect ratio channel holes separated by solid portions, and the semiconductor wafer is capable of undergoing milling operations as part of a layering process;

[0018] Figure 1B Figure 1 is a simplified cross-sectional view of a semiconductor wafer after a milling operation has been performed on the wafer according to existing technology.

[0019] Figure 2 It is a SEM image depicting the result of a FIB milling process through a high aspect ratio channel hole array according to the prior art;

[0020] Figure 3A This is a simplified diagram of a sample evaluation system according to some embodiments of the present disclosure;

[0021] Figure 3B This is a simplified diagram of a sample evaluation system according to an additional embodiment of the present disclosure;

[0022] Figure 4 This is a flowchart depicting the steps associated with a method for layered samples according to some embodiments of the present disclosure;

[0023] Figures 5A to 5C Based on some embodiments Figure 4 Simplified cross-sectional views of a semiconductor wafer at different stages of the layering process described in the text;

[0024] Figure 5D This is a simplified diagram of regions on a layerable semiconductor wafer according to some embodiments;

[0025] Figure 5E A simplified cross-sectional view of a semiconductor wafer is depicted according to some embodiments when different layers are sequentially milled away from the wafer;

[0026] Figures 6A to 6D It is a simplified cross-sectional view of another semiconductor wafer at different stages of a layering process according to some embodiments; and

[0027] Figure 7 This is a flowchart depicting the steps associated with a method for layered samples according to an additional embodiment of this disclosure. Detailed Implementation

[0028] Embodiments of this disclosure can be used to layer a portion of a sample comprising an array of holes having solid portions formed between the holes. While embodiments of this disclosure can be used to layer structures formed on a variety of different types of samples, some embodiments are particularly useful in layering samples comprising small feature sizes and / or high aspect ratio holes (e.g., holes with a diameter of 100 nm or less and / or aspect ratios of 30:1, 40:1, or 60:1 or higher) formed on a semiconductor wafer or similar sample. Non-limiting examples of layerable small feature size, high aspect ratio holes according to embodiments of this disclosure include contact holes for memory channels in 3D-NAND devices and holes in which capacitors in DRAM devices can be formed.

[0029] As described above, when using standard layering techniques to layer a portion of a sample comprising an array of holes with a high aspect ratio, the array of holes having solid portions therein (e.g., slits) typically mills the holes faster than the slits. The inventors believe that the uneven milling in such samples is caused by sputtering through the walls.

[0030] For illustrative purposes, see reference Figure 1A and Figure 1B , Figure 1A and Figure 1B This is a simplified cross-sectional view of a semiconductor wafer 100, which includes an array of high aspect ratio channel holes 110 separated by solid portions 120. Figure 1A In this process, milling operations are performed in two separate regions to deliver equal ion doses to all regions of the wafer (e.g., the FIB point takes the same amount of time at each location on the milled wafer). A first milling position (represented by beam 130) is performed in the channel hole array, and a second milling position (represented by beam 140) is performed in a region of the semiconductor wafer 100 excluding the channel holes 110. Ion penetration 150 in each region represents a real TRIM simulation.

[0031] Sputtered material from milling operations Figure 1A The diagram is indicated by arrows pointing 150 degrees away from each ion penetration region. Due to sputtering through the walls, the channel apertures are milled faster than slits. As a result, and as... Figure 1B As shown, the milling process may produce a non-uniform surface with a thin layer 160 of redeposited material, which is formed by material sputtered through the wall.

[0032] Figure 2 This phenomenon is illustrated by an SEM image of a FIB milling process through an array of vias. Specifically, in... Figure 2 In the image, the wafer 200 is imaged at a 45-degree angle, thus showing the milled areas 210 in the via array, as well as the unmilled wafer areas 215 of the via array. (See image from...) Figure 2 It is evident that the milled area 210 exhibits Figure 1B The depicted non-uniform groove profile that adversely affects the measurement results.

[0033] Embodiments of this disclosure overcome this challenge by filling the aperture array with a material that avoids the aforementioned phenomena while still providing contrast in SEM imaging used for aperture metrology.

[0034] In some embodiments, in a dual-column defect analysis system, the pore array is filled by a deposition process under high-energy SEM. Figure 3A This document describes an example of a system suitable for filled via arrays according to embodiments of the present disclosure, illustrating a simplified sample evaluation system 300 according to some embodiments of the present disclosure. Among other operations, the sample evaluation system 300 can be used for defect inspection and analysis of structures formed on semiconductor wafers.

[0035] System 300 may include a vacuum chamber 310 and a scanning electron microscope (SEM) column 320 and a focused ion beam (FIB) column 330. A support element 350 may support the sample 355 (e.g., a semiconductor wafer) within chamber 310 during processing operations in which the sample 355 (sometimes referred to herein as the “object” or “sample”) is subjected to a charged particle beam from one of the FIB or SEM columns, and may move the sample within vacuum chamber 310 between the fields of view of the two columns 320 and 330 as needed for processing.

[0036] One or more gases can be delivered to the sample to be processed via gas supply unit 360 for certain operations. For simplicity, gas supply unit 360 is described in... Figure 3A The nozzle is shown, but it should be noted that the gas supply unit 360 may include a gas reservoir, a gas source, valves, one or more inlets and one or more outlets, and other elements. In some embodiments, the gas supply unit 360 may be configured to deliver gas to the sample in a region that exposes the sample to the scanning pattern of the charged particle beam, rather than delivering gas to the entire upper surface of the sample. For example, in some embodiments, the gas supply unit 360 has a nozzle diameter measured in several hundred micrometers (e.g., between 400 and 500 micrometers) and is configured to deliver gas directly to a relatively small portion of the sample surface covering the charged particle beam scanning pattern. In various embodiments, a first gas supply unit 360 may be configured to deliver gas to a sample positioned below the SEM column 320, and a second gas supply unit 360 may be configured to deliver gas to a sample positioned below the FIB column 330.

[0037] SEM column 320 and FIB column 330 are connected to vacuum chamber 310 such that a beam of charged particles generated by either of the charged particle columns propagates through the vacuum environment formed within vacuum chamber 310 before impacting sample 355. SEM column 320 generates an image of a portion of sample 355 by irradiating the sample with the charged particle beam, detecting particles emitted due to the irradiation, and generating a charged particle image based on the detected particles. FIB column 330 mills (e.g., drills a hole in sample 355) sample 355 by irradiating it with one or more charged particle beams to form a cross-section, and may also smooth the cross-section. The cross-section may include one or more first portions of a first material and one or more second portions of a second material. The cross-section may also include additional portions of other materials. Conventionally, smoothing operations involve using a small accelerating voltage relative to the milling of the sample.

[0038] Particle imaging and milling processes typically involve scanning a beam of charged particles back and forth across a specific region of the sample being imaged or milled at a constant rate (e.g., using a raster scan pattern). One or more lenses (not shown) coupled to the charged particle beams enable the scan pattern, as is known to those skilled in the art. The scanned region typically occupies only a small fraction of the total area of ​​the sample. For example, the sample may be a semiconductor wafer with a diameter of either 200 mm or 300 mm, and each region scanned on the wafer may be a rectangular region with a width and / or length measured in micrometers or tens of micrometers.

[0039] In some embodiments, the defect analysis system 300 may include, for example, Figure 3B The illumination unit 370 and / or gas spraying unit 380 are shown. When the system 300 includes the illumination unit 370, the system can perform gas-assisted etching (discussed below) by exposing a photoactivated etchant gas to light generated by the illumination unit. For this purpose, the illumination unit 370 may include a light source 372 and a focusing optics 374. In some embodiments, each of the light source 372 and the focusing optics 374 may be located within the vacuum chamber 310, while in other embodiments, each of the light source 372 and the focusing optics 374 may be located outside the vacuum chamber 310. The light source 372 may be a monochromatic light source, a broadband light source, a pulsed light source, a continuous light source, a laser, a lamp (such as, but not limited to, a mercury lamp), and in some embodiments may generate light with a wavelength not exceeding 200 nanometers. The focusing optics 374 can focus the light from the light source 372 onto an area of ​​the sample 355 being processed, said area may include a cross-section, may include only a portion of the cross-section, or may be located near the cross-section. For example, said area may be located a few nanometers or a few micrometers away from the cross-section. It should be noted that even when the beam is focused onto the cross-section, the beam can still pass through photoactivated etchant gas not located near the cross-section. By focusing the beam onto the aforementioned area, selective etching can occur (primarily or only) near the cross-section, while other parts of the wafer are not substantially (or even non-substantially) etched.

[0040] In addition to or in place of the gas supply unit 360, a gas spraying unit 380 may be included, and the gas spraying unit 380 may include various gas sources, storage devices, valves, etc. as discussed above with respect to the gas supply unit 360, and may also include nozzles for spraying gas (e.g., deposition gas or etchant gas) onto the sample to deposit material or etch cross sections on the sample to provide fine morphology as described below.

[0041] Despite Figure 3A or Figure 3BNone of these are shown, but system 300 may include one or more controllers, processors, or other hardware units that control the operation of system 300 by executing computer instructions stored in one or more computer-readable storage devices, as known to those skilled in the art. For example, computer-readable storage devices may include solid-state storage (such as random access memory (RAM) and / or read-only memory (ROM), which may be programmable, flash-updatable, etc.), disk drives, optical storage devices, or similar non-transitory computer-readable storage media.

[0042] In addition to generating charged particle images using the SEM column 320, the system 300 can also deposit material on the sample and / or perform gas-assisted etching on the sample. The system 300 can perform gas-assisted etching of a cross-section to create, for example, morphological differences between at least one first portion and at least one second portion of the cross-section. For gas-assisted etching, the gas supply unit 360 (or gas spraying unit 380) can supply a suitable etchant source gas to a region that may include or be close to the cross-section. In some cases, while the sample is exposed to a beam of charged particles from the SEM column, the etchant source gas can be activated by secondary electrons appearing anywhere on the sample surface reached by the cascade of impact ions. In some cases, while the sample is exposed to a beam of charged particles from the FIB column, the etchant source gas can be activated by secondary electrons appearing anywhere on the sample surface reached by the impact ion jet. In the absence of a charged particle beam, the gas supplied during the gas-assisted etching step can be non-reactive or micro-reactive. Once activated, the etchant source gas can subsequently become reactive and can etch different materials at different rates to form fine morphologies.

[0043] In some embodiments of the gas-assisted etching process according to this disclosure, an electron beam with an energy level of several kiloelectron volts (a few keV) is used to generate secondary electrons that activate the etchant source gas. In other embodiments, it is convenient to use a low-energy (e.g., about several hundred electron volts) ion beam to initiate the aforementioned event of activating the etchant source gas.

[0044] Some embodiments of this disclosure can initiate a deposition process under high-energy SEM within a system, using a dual-column defect analysis system (such as system 300 discussed above) to fill an array (or similar structure) of high aspect ratio holes. For this purpose, deposition gas can be supplied to the sample 355 via a gas supply unit 360 (or a gas spraying unit 380), and energy from the SEM columns 320 can generate secondary electrons. The jet of impacting secondary electrons can further activate the deposition gas, resulting in material deposition on the sample and within the array of holes located in the region of the sample affected by the SEM particle beam. Therefore, deposition occurring according to such embodiments of this disclosure does not simultaneously occur on the entire surface of the sample or wafer being processed. Instead, deposition occurs only in general areas on the wafer where the SEM particle beam (by way of a non-limiting example, the diameter of the SEM particle beam may range from 0.5 nm to 10 nm) impacts and as the particle beam scans across those areas of the wafer. Therefore, deposition according to some embodiments can be performed at nanometer resolution.

[0045] Local deposition processes can fill pores with any material, the material of which will avoid relative to Figure 1A , Figure 1B and Figure 2 The non-uniform milling described above still provides contrast in SEM imaging for hole measurement. For example, in high-energy SEM processes (tens of kV), the penetration depth of electrons can exceed one micrometer. Therefore, when scanning over the aforementioned geometry, the yield of secondary electrons is higher closer to the bottom of the hole than at the surface. As a result, given the presence of deposited gas molecules inside the hole, deposition according to some embodiments of this disclosure occurs more rapidly inside the hole. The deposited material can then fill the hole, allowing the filled structure to be uniformly milled in subsequent milling operations.

[0046] For illustrative purposes, see reference Figure 4 And refer to Figures 5A to 5C , Figure 4 This is a flowchart illustrating the steps associated with method 400 according to some embodiments of the present disclosure. Figures 5A to 5C This is a simplified cross-sectional view of a semiconductor wafer 500 undergoing the steps of method 400. The semiconductor wafer 500 may include an array of small-feature-size, high aspect ratio holes 510 formed in the semiconductor wafer 500 and separated by solid portions or slits 520. The holes 510 and solid portions 520 may be related to the above-mentioned... Figure 1A and Figure 1B The hole 110 and slit 120 discussed are similar or identical.

[0047] The initial steps of method 400 may include moving wafer 500 within the field of view of the SEM column (box 410). Once the wafer is properly positioned, deposition gas can be injected onto the wafer (box 420). Figure 5A As shown, a deposition gas can adhere to both the upper surface 505 and the surface 515 within the hole, as indicated by gas layer 530. The deposition gas can be selected based on the material forming the hole 510. For example, the deposition gas can be selected to deposit (during box 430 discussed below) a material having a milling rate similar to the material forming the hole 510 (i.e., the material constituting the solid portion 520), but with a different contrast to the material of the portion 520 used for imaging purposes. As various examples, the solid portion 520 may comprise carbon, silicon oxide, or other suitable materials, and depending on the material of the portion 520, the deposition gas can be selected to deposit carbon, platinum, tungsten, cobalt, palladium, or any suitable material. In some specific examples, when the material to be deposited is a metal, the deposition gas may include a macromolecule carrying individual atoms of the metal to be deposited—for example, either tungsten hexafluoride (WF6) or tungsten hexacarbonyl (W(CO)6) may be a deposition gas for tungsten, while trimethyl(methylcyclopentadienyl)platinum ((C5H4CH3)(CH3)3Pt) may be a deposition gas for platinum.

[0048] Next, while gas is still being injected onto wafer 500, method 400 may include scanning a SEM charged particle beam 540 across wafer 500 in a portion of the wafer to form a hole 510 (box 430) at said portion of the wafer, which is subsequently milled in box 450. The charged particle beam may be focused at surface 505 of wafer 500 to ensure a high degree of lateral accuracy, and the scanning rate of the particle beam (i.e., as those skilled in the art will understand, the beam velocity is a combination of parameters including pixel size, dwell time, and overlap) and the i-probe (current) control the deposition rate and may be optimized to achieve the best effect in terms of deposition quality within the hole. The energy level of the SEM charged particle beam 540 pointing at the wafer in box 430 may be selected such that, based on the type of charged particles (e.g., electrons from SEM pillars) and the material penetrated, such as Figure 5B As shown, the beam penetrates several micrometers below the wafer surface 505 through the penetration of electrons 545. The penetration of electrons 545 triggers a reaction in reactive gas molecules, thereby depositing solid material 550 within a pore array located in the region where the SEM particle beam impacts the wafer. That is, deposition occurs only where the SEM beam impacts the wafer. The amount of deposition is controlled by the time it takes for the injected gas to be scanned with a charged particle beam from the SEM. Note that... Figure 5BThe wafer 500 is depicted at a point in time after the SEM beam 540 has scanned across region 552, thereby depositing material in the holes in region 552, and just as the SEM beam 540 begins scanning across region 554, thereby beginning to deposit material in the holes in region 554.

[0049] Once the SEM beam 540 has been fully scanned across the portion of the wafer to be deposited (e.g., across all the holes to be milled), material 550 will fill the holes in those areas. Next, the wafer can be moved to the field of view of the FIB pillars (box 440), and the filled area can be milled uniformly through the FIB pillars (box 450), as... Figure 5C As shown, once the milling process is completed, surface 505 has been milled to a lower, relatively flat surface 505b.

[0050] In some embodiments, the milling process of frame 450 may include multiple sub-steps. For example, in a first sub-step, the uppermost layer of the portion to be layered may be milled and removed. The sample may then be moved back to the field of view of the SEM pillar, and the milled area may be imaged. Next, the sample may be moved back to the FIB pillar, and subsequent layers may be milled in the same portion of the wafer. This process of removing layers from a specific region of the wafer and imaged that region may be repeated multiple times, essentially etching a hole in the sample, which becomes deeper with each iteration. Data captured during the imaging portion of the process can be used to evaluate the milling and imaging portions, including, for example, generating a 3D model of the sample in the milled region.

[0051] For further explanation, see reference Figure 5D and Figure 5E ,in Figure 5D yes Figures 5A to 5C A simplified diagram of the semiconductor wafer 500 depicted in the image, and Figure 5E It is a simplified cross-sectional view of wafer 500 when multiple layers within region 570 of wafer 500 are layered and analyzed. Figure 5D The diagram includes a top view of wafer 500 and two unfolded views of specific portions of wafer 500. Wafer 500 may be, for example, a 200mm or 300mm semiconductor wafer and may include multiple integrated circuits 560 (fifty-two in the depicted example) formed thereon. The integrated circuits 560 may be in an intermediate stage of fabrication, and the layering techniques described herein can be used to evaluate and analyze one or more regions 570 of the integrated circuit, including an array of high aspect ratio holes divided by solid portions. For example, Figure 5D Expanded diagram A depicts multiple regions 570 of an integrated circuit 560 that can be evaluated and analyzed according to the techniques described herein. Expanded diagram B depicts regions including those described above. Figures 5A to 5CThe array of holes 510 under discussion and one of those regions 570 of the solid portion 520.

[0052] Some embodiments can analyze and evaluate region 570 (box 450) by sequentially milling away the uppermost layer of the region during a milling step and imaging the milled region. The milling process can be performed according to a raster pattern (such as in a simplified format) Figure 5D The scanning pattern 580 depicted in the unfolded diagram B scans the FIB beam back and forth within the region to mill region 570, removing the upper portion of region 570. The removed portion may have a specific depth in the Z direction and may be removed entirely from region 570 in both the X and Y directions. For example, if region 570 is a square with a length and width of X micrometers, separate slices of X micrometers by X micrometers, each Z micrometer deep, can be sequentially removed from region 570 during the milling process, wherein in each layer, the removed square includes material deposited within the holes according to method 400 and solid portions between the holes. Thus, as Figure 5E As shown, the first milling sub-step removes a square layer 590(1) of approximately X μm by X μm from region 570, and an image of the region where layer 570(1) has been removed can be generated via SEM columnar mapping. Next, the second milling sub-step removes another square layer 590(2) of approximately X μm by X μm from region 570, and an image of the region where layers 590(1) and 590(2) have been removed can be generated via SEM columnar mapping. Although Figure 5E Four iterations of the layering process are described, and the implementation may repeat the layering process any number of times as appropriate or as needed for specific analysis and evaluation. Furthermore, instead of milling the same size region (i.e., a square of X micrometers by X micrometers in the example) in each iteration of the layering process, in some embodiments, one or more subsequent iterations may progressively remove smaller portions of the region than previous iterations.

[0053] Return to reference Figure 4 The embodiments of this disclosure can be used to fill holes with very small feature sizes and very deep depths, resulting in very high aspect ratios. As a non-limiting example, various embodiments can fill holes with diameters less than 100 nm and depths greater than 3 μm, diameters of 80 nm or less and depths of 3-5 μm, and diameters between 70-80 nm and depths between 4-5 μm in frames 420 and 430.

[0054] The energy level of the charged particle beam in a SEM should typically be high enough to achieve a high secondary electron yield at a location sufficiently far below the upper surface of the wafer, allowing the deposited material to reach the bottom of the vias to be filled. In some embodiments, the SEM will have energy levels in the tens of keV range (e.g., 15 keV or higher, 40 keV or higher, or 30 keV or higher). At such energy levels, the particle beam can penetrate more than one micrometer or 2-3 micrometers below the upper surface of the wafer.

[0055] Some currently known dual-column SEM / FIB systems have upper limits on the energy level of the SEM beam, such as 30 keV. Since the energy level of the SEM beam determines the depth to which the beam will penetrate within a given sample, some embodiments employ a multi-step approach when filling holes too deep to be filled by the tool in a single pass. For example, if a particular tool can produce a maximum 30 keV SEM beam penetrating 3 micrometers deep into a particular sample, some embodiments of this disclosure can use a multi-step, deposition-milling repeatable process to uniformly mill holes with small feature sizes and high aspect ratios deeper than 3 micrometers. As an example, see references... Figures 6A to 6D , Figures 6A to 6D This is a simplified cross-sectional view of wafer 600, which has an array of holes 610 that are approximately 610 micrometers deep and separated by solid portions 620.

[0056] For milling hole 610, embodiments of this disclosure may use the above-mentioned... Figure 4 The described technique involves depositing a first layer of material 650a within the hole to fill the upper 3 micrometers of the hole. Following this initial deposition step, the deposited material 650a can extend from the upper surface 605a to a depth of approximately 3 micrometers within the wafer 600. Figure 6A As shown, since the hole 610 is approximately 6 micrometers deep, a portion of the hole 610b (e.g., approximately 3 micrometers) will be unfilled.

[0057] like Figure 6B As shown, wafer 600 can be milled to remove a portion of the wafer including material 650a, thereby leaving a hole 610, which is now approximately 3 micrometers deep from the milled upper surface 605b. Then, according to... Figure 4 The method, through repetition Figure 6A and Figure 6B The steps are to further fill the hole 610 and mill it to the surface 610c, respectively by Figure 6C and Figure 6D As shown. As another example, a 9-micron deep hole can be filled by repeating the deposition milling steps three times instead of just twice. In this way, embodiments of this disclosure can mill the hole uniformly, which would otherwise be too deep to allow the deposited material to penetrate to the bottom portion of the hole.

[0058] In some embodiments, a method similar to that regarding Figure 4 The technique discussed, in addition to stopping the gas flow before applying a charged SEM beam to the wafer, allows gas molecules on the top surface to separate, while molecules traveling inside the holes remain, as the deep geometry within the holes results in a longer separation time. The energy level of the SEM beam can be selected so that electrons penetrate deep into the bulk material between the holes (i.e., the hole walls) to the desired deposition depth. Sufficiently high energy levels of the SEM beam can provide a higher yield of secondary electrons at the bottom of the hole rather than the top. Furthermore, the lack of depositing gas molecules on the top surface helps avoid rapid deposition at the top of the hole, which could otherwise lead to the hole being closed at the top before being filled at the bottom. Depending on the length of time the gas remains in the hole after the gas flow is stopped, some embodiments of this technique can repeatedly introduce gas into the chamber, stop the gas flow, and subsequently expose the wafer to the SEM beam to initiate multiple depositions deep within the holes, depositing material into the holes appearing at different locations on the wafer.

[0059] In an additional embodiment where the ion beam source of the FIB column is a plasma source, a dual-mode FIB can be used as part of a layering process to deposit material on a desired region of a sample, including pores, and subsequently mill both the desired region. For illustration, refer to Figure 7 , Figure 7 This is a flowchart illustrating the steps associated with method 700 according to some embodiments of the present disclosure. For example... Figure 7 The method 700 described herein begins by reversing the energy and extraction voltage of the plasma source of the FIB column (and other necessary voltages that those skilled in the art will understand to operate the FIB column in reverse bias mode) and moving the sample within the field of view of the FIB column (box 710). When the FIB column is operated in reverse bias mode, the FIB column can be used as a SEM column. Next, a deposition gas can be injected onto the sample (box 720), and a reverse biased FIB charged particle beam can be focused at the surface of the sample and partially scanned across the sample in the portion of the wafer to be milled (box 730). Depending on the type of charged particles and the material being penetrated, the energy level of the reverse biased FIB charged particle beam directed toward the wafer in box 730 can be selected such that the beam penetrates several micrometers below the surface of the wafer by penetration. As an example, in some embodiments, the energy level used to generate the reverse biased FIB beam is greater than 15 keV. The deposition process occurring in boxes 720 and 730 can be similar to that described above. Figure 4 Boxes 420 and 430 describe and relative to Figure 5B The process is shown.

[0060] Once the reverse-biased FIB charged particle beam has been fully scanned across the portion of the wafer where deposition is desired (e.g., across all the holes to be milled), the deposited material will fill the holes in those areas. Next, the FIB pillars can be switched back to normal mode (box 740), and the filled areas can be milled uniformly through the FIB pillars (box 750).

[0061] In other embodiments, dual-mode FIB can be used to deposit material on a desired region of a sample, including holes, using a repeated deposition milling process as part of a layering process, and subsequently milling both the desired region. That is, in some embodiments, dual-mode FIB can be used for structures where the layers are too deep to be filled with a single deposition step. For example, the above-described process can be used... Figure 7 The technique described in frames 720 and 730 involves depositing a first layer of material within a hole to fill the upper portion of the hole. Following this initial deposition step, the deposited material can extend from the upper surface of the sample to a very deep intermediate depth within the hole, without reaching the bottom portion. The sample can then be milled to remove the portion of the sample containing the deposited material, and the remaining portion of the hole in the milled area that was not filled with deposited material during the first deposition step can be... Figure 7 The method further fills and mills by repeating deposition and milling once or multiple times. This repeated deposition-milling process provides an alternative method to uniformly layer the holes, which would otherwise be too deep for the deposited material to reach the bottom portion of the hole in a single deposition step.

[0062] Any references to methods in the above specification shall be applied, with necessary modifications, to systems capable of performing the methods, and to computer program products storing instructions that, upon execution, cause the methods to be performed. Similarly, any references to systems in the above specification shall be applied, with necessary modifications, to methods executable by the system, and to computer program products storing instructions executable by the system; furthermore, any references to computer program products shall be applied, with necessary modifications, to methods executable when the instructions stored in the computer program product are executed, and to systems configured to execute the instructions stored in the computer program product.

[0063] For purposes of explanation, the foregoing description uses specific terminology to provide a thorough understanding of the described embodiments. However, it will be apparent to those skilled in the art that the specific details are not required to practice the described embodiments. For example, while several specific embodiments of the foregoing disclosure use example samples comprising an array of channel holes with small feature sizes and high aspect ratios separated by solid slits, this disclosure is not limited to samples having this geometry. Embodiments of this disclosure can be equally advantageously applied to samples layered with an array of filled holes having etched portions or slits between the filled holes. Embodiments can also be advantageously applied to any sample having very small feature sizes that are etched (e.g., trenches) or otherwise formed with a high aspect ratio between solid portions of the sample. Furthermore, embodiments of this disclosure are not limited to samples layered with holes (or other features) of a specific size or aspect ratio and can be advantageously applied to samples layered with holes or other features that are larger or shallower than those specifically discussed herein.

[0064] Therefore, for purposes of illustration and description, the foregoing description of specific embodiments described herein is presented. They are not intended to be exhaustive or to limit the embodiments to the precise forms disclosed. Moreover, although different embodiments of this disclosure have been disclosed above, specific details of particular embodiments may be combined in any suitable manner without departing from the spirit and scope of the embodiments of this disclosure. Furthermore, it will be apparent to those skilled in the art that many modifications and variations are possible in light of the foregoing teachings.

[0065] Because the embodiments shown in this disclosure can be implemented largely using electronic components and circuits known to those skilled in the art, these details are not interpreted to the extent deemed necessary, as shown above, in order to understand the basic concepts of this disclosure and to avoid confusing or distracting from its teachings.

Claims

1. A method for evaluating a region of a sample comprising an array of holes separated by solid portions, the method comprising the steps of: The sample is positioned within the vacuum chamber of an evaluation tool, which includes a scanning electron microscope (SEM) column and a focused ion beam (FIB) column. The deposition gas is injected onto the sample; The sample is scanned with a first charged particle beam to a portion comprising a plurality of pores in the pore array, so as to at least fill the upper portion of the plurality of pores by locally depositing material from the deposition gas into the scanned portion; and The portion of the sample comprising the plurality of pores in which the material is locally deposited is milled using the FIB column.

2. The method of claim 1, wherein the first charged particle beam is a high-energy SEM beam generated by the SEM column, wherein the high-energy SEM beam has a power level of at least 15 keV.

3. The method of claim 2, wherein the injection and scanning steps occur simultaneously.

4. The method of claim 2, wherein the electron penetration depth generates a high secondary electron yield at a location sufficiently far below the upper surface of the sample, such that the deposited material reaches the bottom of a plurality of the plurality of pores.

5. The method of claim 2, wherein the injection and scanning steps occur sequentially, and the injection and scanning steps are repeated multiple times across different regions of the sample to be stratified.

6. The method of claim 1, wherein the ion beam source of the FIB column is a plasma source, and the first charged particle beam is generated by the FIB column operating in reverse bias mode.

7. The method of claim 1, wherein the material deposited during the scanning step deposits material within the upper portion of the plurality of holes, and the milling step mills the sample to a level exposing the lower unfilled portion of the plurality of holes; and wherein the method further comprises the following steps: After the milling step, the injection and scanning steps are repeated to deposit additional material into the unfilled portions of the plurality of holes; as well as Subsequently, the portion of the sample comprising the plurality of holes in which the additional material is locally deposited is milled using the FIB column.

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

9. The method of claim 8, wherein each of the plurality of pores has a diameter of less than 100 nm and a depth of greater than 3 micrometers.

10. The method of claim 8, wherein the plurality of holes are contact holes for memory channels in a 3D-NAND structure.

11. The method of claim 8, wherein the plurality of holes are plurality of holes in which capacitors in a DRAM device can be formed.

12. The method of any one of claims 1 to 11, wherein the step of milling said portion of the sample comprises the following steps: An ion beam is scanned across both the material deposited in the pore array and the solid portions separating the pores to iteratively layer both the material in the pore array and the solid portions separating the pores.

13. The method of claim 12, wherein after each layer is removed by the milling process, the sample is imaged by the SEM column.

14. A system for evaluating a sample comprising a region of an array of holes separated by solid portions, the system comprising: Vacuum chamber; A sample support configured to hold the sample within the vacuum chamber during the sample evaluation process; A scanning electron microscope (SEM) column configured to guide a first beam of charged particles into the vacuum chamber; A focused ion beam (FIB) column, the FIB column being configured to guide a second charged particle beam into the vacuum chamber; A gas supply system configured to inject deposition gas onto the sample; A processor and memory coupled to the processor, the memory including a plurality of computer-readable instructions that, when executed by the processor, cause the system to: The deposition gas is injected onto the sample; A portion of the sample, including a plurality of pores in the pore array, is scanned with a charged particle beam to at least fill the upper portion of the plurality of pores by locally depositing material from the deposition gas into the scanned portion of the plurality of pores. as well as The portion of the sample comprising the plurality of pores in which the material is locally deposited is milled using the FIB column.

15. The system of claim 14, wherein the first charged particle beam is a high-energy SEM beam generated by the SEM column, wherein the high-energy SEM beam has a power level of at least 15 keV.

16. The system of claim 14 or 15, wherein the ion beam source of the FIB column is a plasma source, and the first charged particle beam is generated by the FIB column operating in reverse bias mode.

17. A non-transitory computer-readable storage memory that stores instructions for evaluating a region of a sample comprising an array of holes separated by solid portions by means of the following steps: The sample is positioned within the vacuum chamber of an evaluation tool, which includes a scanning electron microscope (SEM) column and a focused ion beam (FIB) column. The deposition gas is injected onto the sample; The sample is scanned with a first charged particle beam to a portion comprising a plurality of pores in the pore array, so as to at least fill the upper portion of the plurality of pores by locally depositing material from the deposition gas into the scanned portion; and The portion of the sample comprising the plurality of pores in which the material is locally deposited is milled using the FIB column.

18. The non-transitory computer-readable storage of claim 17, wherein the first charged particle beam is a high-energy SEM beam generated by the SEM column, wherein the high-energy SEM beam has a power level of at least 15 keV.

19. The non-transitory computer-readable storage device of claim 17 or 18, wherein the ion beam source of the FIB column is a plasma source, and the first charged particle beam is generated by the FIB column operating in reverse bias mode.

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