Determining focus settings for specimen scanning

Abstract

Methods and systems are provided for determining focus settings to use in scanning a specimen. One method includes generating a focus map defined by values ​​of best focus as a function of position on the specimen using output generated in one or more prefocus swaths scanned over the specimen by an output acquisition subsystem configured to direct energy at the specimen, detect energy from the specimen, and generate output responsive to the detected energy. The method further includes interpolating the focus map to generate focus settings for scans performed on the specimen during the process, and storing information about the generated focus settings for use in scans performed on the specimen during the process.

Description

[Technical field]

[0001] The present invention relates generally to a method and system for determining focus settings to use in scanning a specimen. [Background technology]

[0002] The following descriptions and examples are included in this section and therefore are not admitted to be prior art.

[0003] Fabricating semiconductor devices, such as logic and memory devices, typically involves processing a substrate, such as a semiconductor wafer, using a number of semiconductor manufacturing processes to form various features and levels of the semiconductor devices. For example, lithography is a semiconductor manufacturing process that involves transferring a pattern from a reticle to a resist that is placed on the semiconductor wafer. Additional examples of semiconductor manufacturing processes include, but are not limited to, chemical mechanical polishing (CMP), etching, deposition, and ion implantation. Multiple semiconductor devices may be fabricated in an array on a single semiconductor wafer and then separated into individual semiconductor devices.

[0004] Inspection processes are used at various steps during the semiconductor manufacturing process to detect defects on wafers, promoting higher yields and therefore higher profits in the manufacturing process. Inspection has always been an important part of manufacturing semiconductor devices such as ICs. However, as the dimensions of semiconductor devices decrease, inspection becomes even more important to the successful production of acceptable semiconductor devices because smaller defects can cause device failures.

[0005] Defect review typically involves re-detecting defects detected by the inspection process and generating additional information about the defects at higher resolution using either a high magnification optical system or a scanning electron microscope (SEM). Thus, defect review is performed at individual locations on the wafer where defects were detected by inspection. The higher resolution data of the defects generated by defect review is more suitable for determining attributes of the defects, such as profile, roughness, and more precise size information.

[0006] Metrology processes are also used at various steps during semiconductor manufacturing processes to monitor and control the process. Metrology processes differ from inspection processes in that, unlike inspection processes in which defects are detected on the wafer, metrology processes are used to measure one or more characteristics of the wafer that cannot be determined using currently used inspection tools. For example, a metrology process may be used to measure one or more characteristics of a wafer, such as dimensions (e.g., line width, thickness, etc.) of features formed on the wafer, during the process so that the performance of the process may be determined from the one or more characteristics. Furthermore, if one or more characteristics of a wafer are unacceptable (e.g., outside a predetermined range for the characteristic(s)), the measurement of one or more characteristics of the wafer may be used to modify one or more parameters of the process so that additional wafers produced by the process may have acceptable characteristic(s).

[0007] A metrology process also differs from a defect review process in that, unlike a defect review process in which defects detected by inspection are reviewed in the defect review, the metrology process may be performed at locations where defects are not detected. In other words, unlike a defect review, the locations on the wafer where the metrology process is performed may be independent of the results of the inspection process performed on the wafer. In particular, the locations on the wafer where the metrology process is performed may be selected independent of the inspection results. Further, because the locations on the wafer where the metrology is performed may be selected independent of the inspection results, unlike defect review in which the locations on the wafer where the defect review is performed may not be determined until inspection results for the wafer are generated and available, the locations where the metrology process is performed may be determined before the inspection process is performed on the wafer.

[0008] One parameter that can significantly affect the performance of quality control type processes such as those described above is the focus of the tool performing the scan or measurement of the specimen. In other words, if the system is not focused during a scan or measurement, then the properties of the specimen that are determined from the output generated during that scan or measurement will be less accurate than if the system was focused during the scan or measurement.

[0009] Even if the tool is focused prior to measurement or scanning, it may become out of focus as the tool scans over the specimen or performs measurements at other locations on the specimen. In particular, the specimens described herein may not be substantially flat, and / or the flatness of the specimen may vary across the specimen. For example, process variations on a specimen, such as a wafer, may cause relatively large focus tracking errors during scanning or measurement of the wafer. Additionally, some specimens described herein may include layers through which the light used by the tool can penetrate and / or may include layers that include patterned features that are located significantly below the top surface of the specimen. For example, some systems may have little or no control over the depth of focus within a significant Z3D inspection. Thus, the autofocus elements of such systems may track the desired top surface or may track features of the underlying structure causing the top surface to become out of focus. Thus, if it is not known where the focal plane of the tool is relative to the specimen during scanning or measurement, the output generated during scanning or measurement may be misinterpreted, may be useless, or may produce inaccuracies in the results generated from the output. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] US Patent Application Publication No. 2009 / 0212213 Summary of the Invention [Problem to be solved by the invention]

[0011] It would therefore be advantageous to develop a system and / or method for determining focus settings to use in scanning a specimen that does not have one or more of the disadvantages discussed above. [Means for solving the problem]

[0012] The following description of various embodiments is not to be construed in any way as limiting the subject matter of the appended claims.

[0013] One embodiment relates to a system configured to determine focus settings to use in scanning a specimen. The system includes an output acquisition subsystem configured to direct energy to the specimen, detect energy from the specimen, and generate an output responsive to the detected energy. The system further includes one or more computer subsystems configured to generate a focus map defined by optimal focus values ​​as a function of position on the specimen using the output generated in one or more prefocus swaths scanned on the specimen by the output acquisition subsystem. The one or more computer subsystems are also configured to interpolate the focus map to generate focus settings for scans performed on the specimen during the process. Additionally, the one or more computer subsystems are configured to store information regarding the generated focus settings to use in scans performed on the specimen during the process. The system may be further configured as described herein.

[0014] Another embodiment relates to a computer-implemented method for determining focus settings to use in scanning a specimen. The method includes generating a focus map defined by optimal focus values ​​as a function of position on the specimen using output generated in one or more prefocus swaths scanned on the specimen by an output acquisition subsystem configured to direct energy to the specimen, detect energy from the specimen, and generate output responsive to the detected energy. The method further includes interpolating the focus map to generate focus settings for scans performed on the specimen during the process. In addition, the method includes storing information of the generated focus settings for use in scans performed on the specimen during the process. The steps of generating, interpolating, and storing are performed by one or more computer subsystems coupled to the output acquisition subsystem.

[0015] Each step of the above-described method may be performed as further described herein. The above-described method may include another step(s) of another method(s) described herein. The above-described method may be performed by any of the systems described herein.

[0016] An additional embodiment relates to a non-transitory computer readable medium that stores program instructions executable on a computer system to perform a computer implemented method for determining focus settings to use in scanning a specimen. The computer implemented method includes the steps of the methods described above. The computer readable medium may be further configured as described herein. The steps of the computer implemented method may be performed as further described herein. In addition, the computer implemented method for which the program instructions are executable may include another step(s) of another method(s) described herein.

[0017] Other objects and advantages of the present invention will become apparent upon reading the following detailed description and upon reference to the accompanying drawings. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1 is a schematic diagram illustrating a side view of one embodiment of a system configured as described herein. [Diagram 2] FIG. 1 is a schematic diagram showing a plan view of an example swath in a scan performed on a specimen during a process. [Diagram 3] 1A-1C are schematic diagrams illustrating a plan view of example swaths in a scan performed on a specimen during a process, and an embodiment of a prefocused swath in one of the swaths. [Figure 4] 1A-1C are schematic diagrams illustrating a side view of an example of a patterned feature formed on a specimen and an embodiment of different z-positions of a prefocused swath relative to the specimen. [Diagram 5] 1 is a flow chart illustrating an embodiment of steps that may be performed to determine a focus setting to use for scanning a specimen. [Figure 6]1 is a flow chart illustrating an embodiment of steps that may be performed to determine a focus setting to use for scanning a specimen. [Figure 7] FIG. 1 is a block diagram illustrating one embodiment of a non-transitory computer-readable medium storing program instructions executable on a computer system to perform one or more of the computer-implemented methods described herein. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

[0020] As used herein, the terms "design," "design data," and "design information" generally refer to the physical design (layout) of an IC, and data derived from the physical design by complex simulations or simple geometric and Boolean operations. In addition, an image of a reticle acquired by a reticle inspection system and / or a derivative thereof may be used as a "proxy" or "proxies" for the design. Such a reticle image or a derivative thereof may serve as a substitute for the design layout in any embodiment described herein that uses the design. The design may include any other design data or design data proxies described in commonly owned U.S. Patent No. 7,570,796 issued to Zafer et al. on August 4, 2009, and U.S. Patent No. 7,676,077 issued to Kulkarni et al. on March 9, 2010, both of which are incorporated herein by reference as if fully set forth. In addition, the design data may be standard cell library data, integrated layout data, design data for one or more layers, derivatives of the design data, and full or partial chip design data.

[0021] However, in general, the design information or data cannot be generated by imaging a wafer with a wafer inspection system. For example, the design patterns formed on the wafer may not accurately represent the design of the wafer, and the wafer inspection system may not be able to generate images of the design patterns formed on the wafer with sufficient resolution, such that the images may not be used to determine information regarding the design for the wafer. Thus, the design information or design data typically cannot be generated using a physical wafer. In addition, "design" and "design data" as described herein refer to information and data generated by a semiconductor device designer in the design process and thus usable in the embodiments described herein well in advance of printing the design on any physical wafer.

[0022] Turning now to the drawings, it should be noted that the figures are not drawn to scale. In particular, the scale of some of the elements in the figures may be greatly exaggerated to emphasize the properties of the elements. It should also be noted that the figures are not drawn to scale. Elements shown in multiple figures that may be similarly configured are indicated using the same reference numerals. Unless otherwise stated herein, any of the elements described and illustrated may include any suitable commercially available elements.

[0023] One embodiment relates to a system configured to determine focus settings to use for scanning a specimen. In one embodiment, the specimen is a wafer. The wafer may include any wafer known in the semiconductor arts. Although some embodiments may be described herein with respect to one or more wafers, the embodiments are not limited to the specimens with which they may be used. For example, the embodiments described herein may be used with specimens such as reticles, flat panels, personal computer (PC) boards, and other semiconductor specimens.

[0024] In one embodiment, the specimen includes a wafer having a three-dimensional (3D) NAND structure formed thereon. 3D NAND (NAND stands for not-AND, a type of logic gate in a semiconductor device) is a type of non-volatile flash memory that includes a vertical stacking of multiple layers of memory cells. For example, a 3D NAND structure generally includes a silicon bit cell gate, which is formed of alternating conductive and insulating layers formed on a wafer, separated by one or more high aspect ratio (HAR) structures, such as charge traps formed of materials such as silicon nitride and channel(s) formed on the silicon. The vertical stacking of memory cells gives the 3D quality to the 3D NAND structure. Although some embodiments may be described herein as being used or configured with a 3D NAND structure or wafer, the embodiments described herein may be used to determine focus settings for scanning any specimen, including those in which the characteristics of the specimen make it difficult to maintain focus during scanning.

[0025] As used herein, the term "HAR structure" refers to any structure characterized by an aspect ratio greater than 10:1, and may be as high as 100:1 in next generation devices. HAR structures may include a hard mask layer (see, for example, U.S. Patent No. 8,237,213 to Liu, issued August 7, 2012, which is incorporated by reference as if fully set forth herein) to facilitate the HAR etching process. In addition to vertical NAND or terabit cell array transistor (TCAT) structures, the embodiments described herein may be used for other HAR structures where optical penetration into the structure is a limiting factor for inspection and / or metrology. For example, dynamic random access memory (DRAM) includes structures where the depth of deep trenches or holes etched into the substrate creates problems in maintaining focus during inspection or metrology.

[0026] The embodiments described herein provide an autofocus method and system that may be used to improve focus tracking of a pre-selected surface or plane of a specimen, e.g., a top surface of a specimen such as a wafer during 3D NAND inspection. The 3D nature of such semiconductor devices often causes existing autofocuses to mistrack due to a combination of process variations that bias the z-position of the autofocus and tracking deeper features within the 3D structure. The resulting out-of-focus images cause defects (DOIs) that one wishes to detect during wafer inspection to be missed. The only existing way to mitigate this is to scan the wafer at different focus offsets, resulting in reduced throughput and creating a new population of defects for each offset. In contrast, the embodiments described herein may use an image-based focus map acquired before each inspection (or other process) to correct the above autofocus tracking errors by explicitly estimating the best focus of the top surface from a series of images taken at different z-positions. The focus map is then applied during wafer inspection (or other quality control process) to ensure that the inspection image (or other output) is always in focus across the inspected (or scanned) area. Embodiments enable inspection and metrology, such as optical critical dimension (CD), film, and composition metrology, and other quality control processes, for semiconductor devices having HAR structures (e.g., 3D NAND, vertical NAND (or VNAND), TCAT, etc.), and more generally, for complex devices where inspection, optical metrology, etc. are difficult due to the difficulty of maintaining focus while scanning the specimen.

[0027] The system includes an output acquisition subsystem, which is configured to direct energy to the specimen, detect energy from the specimen, and generate an output responsive to the detected energy. One embodiment of such a system is shown in FIG. 1. In this embodiment, the energy directed to the specimen includes light, and the energy detected from the specimen includes light. As shown in FIG. 1, the output acquisition subsystem 10 includes an illumination subsystem configured to direct light to the specimen 14. In the embodiment shown in FIG. 1, the illumination subsystem includes two illumination channels, one configured to direct light to the specimen at a first angle of incidence (AOI) and another configured to direct light to the specimen at a second AOI. Further, as shown in FIG. 1, the first AOI is an orthogonal AOI and the second AOI is an oblique AOI. Although two illumination channels and two AOIs are shown in FIG. 1, the output acquisition subsystem may include any suitable number of illumination channels (i.e., one or more illumination channels) configured to direct energy to the specimen at any suitable number of AOIs (one or more AOIs).

[0028] Each of the illumination channels includes at least one light source. For example, as shown in FIG. 1, the first illumination channel includes a light source 16. Light from the light source 16 is directed through an optical element 18 and then through a lens 20 to a beam splitter 21, which directs the light to a lens 22, which directs the light to the specimen 14 at normal incidence. The second illumination channel includes a light source 24. Light from the light source 24 is directed through an optical element 26 and then through a lens 28, which directs the light to the specimen 14 in an oblique AOI. Thus, in one embodiment, the first AOI includes a normal AOI and the second AOI includes an oblique AOI. The oblique AOI may include any suitable oblique AOI and may vary depending on, for example, the characteristics of the specimen.

[0029] The first and second AOIs may also include different ranges of AOIs. For example, the first AOI may include a range of AOIs or be included in the first range of AOIs, and the second AOI may include a different range of AOIs or be included in the second range of AOIs. The first and second ranges of AOIs may be discrete and mutually exclusive. However, the various ranges of AOIs are not necessarily mutually exclusive.

[0030] The AOI through which light is directed to the specimen may be changeable from that shown in FIG. 1, for example, by changing the position of one or more elements of one or more of the illumination channels and / or changing one or more parameters of one or more elements of the illumination subsystem. For example, in another embodiment, the first and second AOIs include different oblique AOIs. In one such embodiment, parameters of the illumination channel that includes the light source 16 may be changed to direct light to the specimen in an oblique AOI rather than a perpendicular AOI as shown in FIG. 1. In another such embodiment, the illumination channel that includes the light source 24 may be configured to direct light to the specimen in one oblique AOI at some times and in a different oblique AOI at other times.

[0031] The illumination subsystem may be configured to direct light to the specimen at different AOIs at different times. For example, in one embodiment, the illumination subsystem is configured to direct light to the specimen at a first AOI in a first scan of the specimen and to direct light to the specimen at a second AOI in a second scan of the specimen. The first and second scans may be performed as described further herein. In one such embodiment, one of the illumination channels shown in FIG. 1 is used for the first scan and another of the illumination channels shown in FIG. 1 is used for the second scan. However, the same illumination channel may be used for the first and second scans and one or more parameters of the illumination channel may be changed between scans to change the AOI of the illumination channel.

[0032] In some cases, the illumination subsystem may be configured to simultaneously direct light to the specimen at a first and a second AOI. For example, when light is simultaneously directed to the specimen at different AOIs, one or more characteristics (e.g., wavelength, polarization, etc.) of the light directed to the specimen at the different AOIs may be different, and light resulting from illumination of the specimen at the different AOIs may be distinguished from one another at the detector(s). In one such example, one of the illumination channels shown in FIG. 1 may be configured for illumination using a first range of wavelengths, and another illumination channel may be configured for illumination using a second range of wavelengths different from the first. The different illumination channels may additionally or alternatively be configured for illumination using different polarizations.

[0033] In one embodiment, the first and second AOIs include different polar angles and one or more azimuthal angles. For example, light may be directed to the specimen at the same plane of incidence (and / or centered at the same plane of incidence) at different polar angles. In the embodiment shown in FIG. 1, the two illumination channels may be configured to direct light to the specimen at the same plane of incidence, which is the plane of the paper. The light directed to the specimen in the first and second AOIs may also be directed to the specimen at the same azimuthal angle and / or the same range of azimuthal angles. In either case, the different AOIs may only differ in polar angle (although the different AOIs do not necessarily have to have the same azimuthal angle(s)).

[0034] In another embodiment, the plane of incidence of the light directed at the specimen in the first and second AOIs is oriented at an angle between 0 and 180 degrees relative to the patterned features on the specimen. For example, the plane of incident light need not be oriented perpendicular to the patterned features, such as trench-like structures on the specimen, but can be oriented in any direction (0-180 degrees).

[0035] In another example, the illumination subsystem may include only one light source (e.g., light source 16 shown in FIG. 1 ), and light from the light source may be separated into different optical paths (e.g., by a beam splitter and / or based on wavelength, polarization, etc.) by one or more optical elements (not shown) of the illumination subsystem. The light in each of the different optical paths may then be directed to the specimen at different AOIs. Alternatively, the illumination subsystem may include only one illumination channel, and the illumination channel may be configured to direct light to the specimen at different AOIs at different times (e.g., by changing one or more parameters of the illumination channel between scans of the specimen). The illumination subsystem may have any other suitable configuration known in the art for directing light having different or the same characteristics to the specimen at different AOIs sequentially or simultaneously.

[0036] Light source 16 and / or light source 24 may include a broadband plasma (BBP) light source. Thus, the light generated by the light source and directed to the specimen may include broadband light. However, the light source may include any other suitable light source, such as a laser, which may include any suitable laser known in the art and may be configured to generate light at any suitable wavelength(s) known in the art. Furthermore, the laser may be configured to generate light that is monochromatic or nearly monochromatic. Thus, the laser may be a narrowband laser. The light source may also include a polychromatic light source that generates light at multiple discrete wavelengths or wavebands. Light sources 16 and 24 may also include different types of light sources and / or light sources having the same or different configurations.

[0037] The optical elements 18 and 26 may include optical elements such as polarizing components, spectral filters, spatial filters, reflective optical elements, apodizers, apertures, and the like, which may include any such suitable optical elements known in the art. The optical elements 18 and 26 may be different types of optical elements and / or have the same or different configurations. Although the lenses 20, 22, and 26 are shown in FIG. 1 as single refractive optical elements, in reality, each of the lenses 20, 22, and 26 may include several refractive and / or reflective optical elements that combine to focus the light from the optical element(s) to the specimen. The beam splitter 21 may include any suitable beam splitter known in the art. The illumination subsystem shown in FIG. 1 and described herein may include any other suitable optical elements (not shown).

[0038] The output acquisition subsystem may also include a scanning subsystem configured to scan the light over the specimen. For example, the output acquisition subsystem may include a stage 30, on which the specimen 14 is placed during scanning. The scanning subsystem may include any suitable mechanical and / or robotic assembly (including the stage 30) that may be configured to move the specimen so that the light may be scanned over the specimen. Additionally or alternatively, the output acquisition subsystem may be configured such that one or more optical elements of the output acquisition subsystem perform the scanning of the light over the specimen. The light may be scanned over the specimen in any suitable manner.

[0039] The detection subsystem includes one or more detection channels, each of which includes a detector configured to detect light from the sample due to illumination of the sample and generate an output responsive to the detected light. For example, the detection subsystem shown in FIG. 1 includes two detection channels, one formed by collector 32, element 34, and detector 36, and another formed by collector 38, element 40, and detector 42. As shown in FIG. 1, the two detection channels are configured to collect and detect light at different collection angles.

[0040] In one embodiment, the light detected by the detection subsystem due to light directed at the specimen in the first and / or second AOI includes specular reflected light. For example, in some cases, both detection channels are configured to detect specular reflected light. In particular, the detection channel including detector 36 may be configured to detect specular reflected light caused by illumination in a perpendicular AOI, and the detection channel including detector 42 may be configured to detect specular reflected light caused by illumination in an oblique AOI. Similarly, one of the detection channels may be configured to detect light caused by illumination in one oblique AOI, and another detection channel may be configured to detect light caused by illumination in a different oblique AOI. In this way, the different detection channels may be configured to detect light caused by illumination in different AOIs, respectively, regardless of what those AOIs are. In another embodiment, the different detection channels may be configured to detect light scattered from the specimen due to illumination of the specimen with different AOIs, respectively.

[0041] 1 illustrates one embodiment of an output acquisition subsystem that includes two detection channels, the output acquisition subsystem may include a different number of detection channels (e.g., only one detection channel or more than one detection channel). For example, one detection channel may be configured to detect light caused by illumination in one AOI in a first scan, and then detect light caused by illumination in another AOI in a second scan.

[0042] 1 as a single refractive optical element, each of the concentrators may include one or more refractive optical element(s) and / or one or more reflective optical element(s). Elements 34 and 40 may include any suitable optical elements, such as polarizing components, spectral filters, spatial filters, reflective optical elements, apertures, and the like, which may include any such suitable optical elements known in the art. Elements 34 and 40 may include different types of elements and / or may have the same or different configurations.

[0043] The detectors 36 and 42 may include different types of detectors and / or may have the same or different configurations. The detectors may include photomultiplier tubes (PMTs), charge-coupled devices (CCDs), time-delay integration (TDI) cameras, or any other suitable detectors known in the art. The detectors may also include non-imaging detectors or imaging detectors. When the detectors are non-imaging detectors, each of the detectors may be configured to detect a particular characteristic of the light, such as intensity, but may not be configured to detect such a characteristic as a function of position in the imaging plane. Thus, the output generated by each of the detectors included in each of the detection channels of the output acquisition subsystem may be a signal or data, but may not be an image signal or image data. In such a case, a computer subsystem, such as the computer subsystem 44 of the system, may be configured to generate an image of the specimen from the non-imaging output of the detectors. However, in another example, the detectors may be configured as imaging detectors configured to generate imaging signals or image data. Thus, the system may be configured to generate the outputs described herein in many ways.

[0044] It should be noted that FIG. 1 is provided herein to generally illustrate configurations of output acquisition subsystems that may be included in system embodiments described herein. Obviously, the output acquisition subsystem configurations described herein may be modified to optimize the performance of the system, as is typically performed when designing a commercially available system. In addition, the systems described herein may be implemented using existing systems (e.g., by adding the functionality described herein to the existing system), such as the 28xx and 29xx series of inspection tools commercially available from KLA, Milpitas, Calif. In some such systems, the methods described herein may be provided as selective features of the system (e.g., in addition to other functionality of the system). Alternatively, the systems described herein may be designed "from the ground up" to provide an entirely new system.

[0045] The computer subsystem 44 of the system may be coupled in any suitable manner (e.g., via one or more transmission media, which may include "wired" and / or "wireless" transmission media) to the detector of the output acquisition subsystem such that the computer subsystem can receive output generated by the detector during scanning of the specimen. The computer subsystem 44 may be configured to perform several functions that use the output of the detector as described herein, and any other functions as further described herein. This computer subsystem may be further configured as described herein.

[0046] This computer subsystem (as well as other computer subsystems described herein) may also be referred to herein as computer system(s). Each of the computer subsystem(s) or system(s) described herein may take a variety of forms, including a personal computer system, an image computer, a mainframe computer system, a workstation, a network appliance, an Internet appliance, or other devices. In general, the term "computer system" may be broadly defined to encompass any device having one or more processors that execute instructions from a memory medium. The computer subsystem(s) or system(s) may also include any suitable processor known in the art, such as a parallel processor. In addition, the computer subsystem(s) or system(s) may include a computer platform with high speed processing and software, either as a stand-alone or networked tool.

[0047] When a system includes two or more computer subsystems, the different computer subsystems may be coupled to one another and images, data, information, instructions, etc. may be transmitted between the computer subsystems as further described herein. For example, computer subsystem 44 may be coupled to computer subsystem(s) 46 (as indicated by the dashed lines in FIG. 1) by any suitable transmission medium, which may include any suitable wired and / or wireless transmission medium known in the art. Two or more of such computer subsystems may also be operatively coupled by a shared computer-readable storage medium (not shown).

[0048] The computer subsystem(s) 44 and / or 46 may include or be configured as one or more "virtual" systems (not shown) configured to perform one or more functions described further herein. Systems and methods configured as "virtual" inspection systems are described in commonly assigned U.S. Patent Nos. 8,126,255, issued to Bhaskar et al. on February 28, 2012, and 9,222,895, issued to Duffy et al. on December 29, 2015, both of which are incorporated by reference as if fully set forth herein. The embodiments described herein may be further configured as described in these patents. For example, one or more computer subsystems described herein may be further configured as described in these patents.

[0049] As further described above, the output acquisition subsystem may be configured to generate output for the specimen in multiple modes. In general, a "mode" may be defined by the value of a parameter of the output acquisition subsystem used to generate the output (e.g., an image) of the specimen. Thus, different modes may have different values ​​for at least one of the imaging parameters of the output acquisition subsystem. For example, different modes may use different wavelengths of light for illumination. The modes may differ in illumination wavelength (e.g., by using different light sources, different spectral filters, etc.) for different modes, as further described herein. In another embodiment, different modes use different illumination channels of the output acquisition subsystem. For example, as described above, the output acquisition subsystem may include multiple illumination channels. Thus, different illumination channels may be used for different modes.

[0050] The output acquisition subsystems described herein may be configured as inspection subsystems, in which case the computer subsystem(s) may be configured to receive output from the output acquisition subsystem (e.g., from the detector(s) of the output acquisition subsystem) as described above, and may be configured to detect defects on the specimen based on the output, as described further herein.

[0051] The output acquisition subsystem described herein may be configured as other types of semiconductor-related process / quality control type systems, such as defect review systems and metrology systems. For example, the embodiment of the output acquisition subsystem described herein and shown in FIG. 1 may be altered in one or more parameters to provide different output generation capabilities depending on the application in which it is used. In one embodiment, the output acquisition subsystem is configured as a defect review subsystem. In another embodiment, the output acquisition subsystem is configured as a metrology subsystem. For example, the output acquisition subsystem shown in FIG. 1 may be configured to have higher resolution when used for defect review or metrology rather than inspection. In other words, the embodiment of the output acquisition subsystem shown in FIG. 1 illustrates several common and various configurations of output acquisition subsystems, which may be adjusted in various ways that would be apparent to one of ordinary skill in the art to produce output acquisition subsystems having different capabilities that are more or less suitable for different applications.

[0052] The one or more computer subsystems are configured to generate a focus map, defined by values ​​of optimal focus as a function of position on the specimen, using output generated by the output acquisition subsystem in one or more prefocus swaths scanned on the specimen. For example, focus map generation may include scanning one or more prefocus swaths (e.g., 3-5 prefocus swaths) on the specimen according to an inspection sample plan. FIG. 2 illustrates an example of an inspection sample plan. In this example, a wafer 200 may be scanned in a direction indicated by arrow 204 in several swaths 202a-202h. Although an example of specimens, swaths, and scan directions is illustrated in FIG. 2, the embodiments described herein are not limited to such specimens, swaths, and scan directions. Instead, the embodiments described herein may be used with any scanning sample plan for any specimen and any process described herein.

[0053] As shown in FIG. 3, in swath 202a, one or more prefocus swaths 300 may be scanned in direction 302. As shown in FIG. 3, one or more prefocus swaths may be significantly smaller than the inspection swath in which they are located. The dimensions and placement of the prefocus swath(s) within the inspection swath may be determined as described herein. The direction 302 may be the same as the direction 204. In this manner, the prefocus swath(s) may be scanned in the same direction as the inspection swath even if the inspection swath is scanned in a different direction than that shown in FIG. 2 and FIG. 3. The prefocus swath(s) may be scanned in each of the inspection swaths 202a-202h, and then each of the swaths is scanned for inspection. The parameters of the prefocus swath(s) scanned for any one swath may be different or the same and may be determined as further described herein.

[0054] In one embodiment, the output includes an image of the specimen. As such, the embodiments described herein may be configured for image-based autofocus applications. Additionally, the embodiments described herein may be used with an output acquisition subsystem that uses broadband light, such as light generated by a BBP light source. As such, the embodiments described herein may be configured for BBP image-based autofocus applications. Additionally, the embodiments described herein may be configured to use image-based focus estimation to generate an accurate focus map of an area to be inspected (or scanned) prior to wafer inspection (or other specimen process).

[0055] In another embodiment, one or more prefocus swaths are predefined as completely overlapping regions on the specimen. For example, as shown in FIG. 3, one or more prefocus swaths 300 are positioned within the same region on the specimen. In other words, the same, completely overlapping region on the specimen may be scanned for each prefocus swath in the inspection swath. Defining the prefocus swaths as completely overlapping regions on the specimen is desirable because the prefocus swaths preferably generate data for the same x,y positions on the specimen that may be used together as described herein to determine the best focus at each of the x,y positions.

[0056] In additional embodiments, one or more prefocus swaths are scanned with a predefined care area that includes a predetermined patterned feature. For example, the predefined care area preferably includes a well-defined surface feature image for focus estimation. The predetermined patterned feature may vary depending on the specimen for which the focus setting is being determined. For example, in the case of a 3D NAND wafer, the care area may be located in an inspection area that includes a 3D NAND line-space structure that represents an area where a constant focus is preferably maintained during scanning.

[0057] A "care area," as commonly referred to in the art, is an area on a specimen that is of interest for inspection purposes. In some cases, care areas are used to distinguish areas of the specimen that are inspected from areas of the specimen that are not inspected in the inspection process. In addition, care areas are used to distinguish between areas on a specimen that are inspected using one or more different parameters. For example, if a first area of ​​the specimen is more important than a second area of ​​the specimen, the first area may be inspected with a higher sensitivity than the second area, such that defects are detected with a higher sensitivity in the first area. Another parameter of the inspection process may be changed from care area to care area in a similar manner.

[0058] In some embodiments, one or more prefocus swaths are scanned at different z positions relative to the specimen. For example, one or more prefocus swaths can be acquired at one or more z positions (e.g., 3-5 z positions) to capture variability in focus across the prefocus swath area (e.g., within a predefined care area described herein across one or more patterned feature areas (e.g., dies) on the specimen). One example of one or more prefocus swaths at different z positions relative to the specimen is shown in FIG. 4. As shown in FIG. 4, a patterned feature 402 is formed on a specimen 400. The patterned feature 402 is shown in FIG. 4 for illustrative purposes only and is not intended to depict patterned features having any particular dimensions, spatial relationship to one another, or number. In other words, the embodiments described herein are not limited to patterned features having any particular characteristics, although the embodiments described herein are particularly suited to the patterned feature types described herein. As further shown in FIG. 4, one or more prefocus swaths 404a-404e can be scanned at different z positions relative to the specimen. Although a particular number of prefocus swaths are shown in Figure 4, the embodiments described herein are not limited to the number of prefocus swaths shown in this figure. The z position may be determined in any suitable manner, for example, based on a best guess of where the optimal focus position is. The best guess may be determined based on a previous scan of another specimen of the same type, a scan of another similar specimen, a theoretical estimate, etc.

[0059] One or more prefocus swaths may be scanned on the specimen during the data collection phase 500 shown in FIG. 5. For example, as shown in FIG. 5, the data collection phase may include pre-training with dense z samples, as shown in step 506. Pre-training may include pre-training a through-focus curve (TFC) with dense z samples. The through-focus curve is a plot of focus metric value versus dense z (at the beginning) or coarse z (after successfully acquiring optimal focus during dense z). The data collection phase may also include determining a swath layout, as shown in step 508. Determining the swath layout may include determining characteristics of one or more parameters of the output acquisition subsystem used to scan the prefocus swath(s) on the specimen, such as pixel size (e.g., 200 nm), wavelength, gray level, type of imaging (e.g., BF), etc. As shown in step 510, the data collection stage may further include determining an x,y sampling plan (configurable) for one or more prefocused swaths from the swath layout information determined in step 508. The sampling plan for the prefocused swath(es) may be determined in any suitable manner. In some embodiments, the prefocused swath sampling plan may be the same as the inspection (or another process) sampling plan. However, the prefocused swath sampling plan may be less dense than the inspection (or another process) sampling plan and may be determined based on various information, such as patterned features on the specimen, the process being performed on the specimen, known or expected variations across the specimen, etc. The data collection stage may also include swathing at 3-5 focus offset values ​​to generate one or more prefocused swaths of output, as shown in step 512. Scanning the prefocused swaths in step 512 may be performed as further described herein. The swath scanning performed in step 512 may also include recording a readout of the z stage position as a function of x.

[0060] In a further embodiment, generating the focus map includes determining a focus metric as a function of x and y location within the one or more prefocus swaths, and determining the focus metric at one of the x and y locations includes determining the focus metric from all outputs generated within the one or more prefocus swaths at one of the x and y locations. For example, the focus metric may be calculated for each set of z images at intervals of about 0.3 μm in the x direction and at the center of each 1k sub-swath in the y direction. The number of sub-swaths per swath depends on the detector configuration and how the pixel height is divided into vertical jobs. In one example, there may be 4-8 sub-swaths for a total swath height of 4k-8k of pixels. These measurements may be a kind of coarse z measurements.

[0061] In another embodiment, generating the focus map includes determining a focus metric as a function of x and y positions within the one or more prefocus swaths, the focus metric including the coarse z focus measurements, and generating the focus map includes fitting the coarse z focus measurements to a polynomial, estimating an optimal focus at an x ​​and y position at a peak of the polynomial, and generating a focus map of x and y positions in a sample plan for a scan performed on the specimen during the process from the optimal focus at the x and y positions within the one or more prefocus swaths. For example, the computer subsystem(s) may be configured to fit a focus metric from a set of z values ​​to a polynomial to estimate optimal focus in semiconductor inspection and other applications described herein. In one such embodiment, each x, y position of the coarse z focus metric measurements may be determined as described above and then may be fitted to a polynomial, with optimal focus estimated at the peak of the polynomial. The polynomial to which the measurements are fitted may include any suitable polynomial, such as a quadratic parabola or a Gaussian.

[0062] The z-value at the best focus may then be used to generate a focus correction map for each x,y in the inspection sample plan. These steps may be performed during the error map generation stage 502 shown in FIG. 5. For example, as shown in step 514, the error map generation stage may include finding an optimal focus plane, which may be performed as described above. In one such example, step 514 may include fitting data from the data collection stage to a through-focus curve to find the optimal focus plane. Furthermore, as shown in step 516, the error map generation stage may include generating a discrete two-dimensional (2D) map, which may be performed as described above.

[0063] The one or more computer subsystems are also configured to interpolate the focus map to generate focus settings for scans performed on the specimen during the process. For example, as shown in FIG. 5, during the error map generation stage, the one or more computer subsystems may generate an interpolated 2D map 518 from the discrete 2D map generated in step 516. The error generation stage may also include converting the 2D map, as shown in step 520, which may include converting the interpolated 2D map into information, data, instructions, etc., that may be used by the system to control the focus of the output acquisition subsystem during scanning of the specimen. For example, the interpolated 2D map may be converted into an actual z-stage position readout.

[0064] In one embodiment, the interpolating includes interpolating the focus map to generate focus settings for a complete sample plan of scans performed on the specimen during the process. For example, the focus map generated as described above may be interpolated to provide estimates across the entire inspection sample plan. In other words, the focus map may be interpolated to generate focus settings for the entire inspection swath, even though the data collection stage may be performed using a prefocus swath that is smaller than the inspection swath. In particular, given the repetitive nature of the printed areas on the specimen as described herein and additional information that may be available to the computer subsystem(s), e.g., specimen profile(s), focus settings may be generated for scanning over a larger specimen area than that used in the data collection stage. The interpolation of the focus map may be performed in any suitable manner known in the art using any suitable function, algorithm, calculation, etc.

[0065] The one or more computer subsystems are further configured to store information of the generated focus settings for use in scans performed on the specimen during the process. The generated focus settings may then be applied as a swath trajectory during inspection, metrology, etc. A "swath trajectory" may generally be defined as a set of predefined z positions along the scan direction, e.g., x-movement. In standard autofocus, there is a servo loop that controls z. In contrast, in embodiments described herein, the best focus z values ​​of the prefocus map may be loaded to the stage height motor without feedback. For example, during the error correction stage 504 shown in FIG. 5, the computer subsystem(s) may store an output, as shown in step 522, which may include the converted 2D map and any of the other steps described herein. The output may be stored in step 522 by storing the output in a database or in another manner described herein. The error correction stage may also include scanning the specimen during the process, as shown in step 514. In one such example, an embodiment may use the stored information regarding the generated focus settings to control the autofocus subsystem 100 of the system shown in FIG. 1.

[0066] The autofocus subsystem 100 may include any suitable mechanical, robotic, computer hardware and / or software, etc. components that may be used to alter the z-position of the specimen relative to the output acquisition subsystem components, or vice versa. In this manner, the z-position of the specimen relative to the output acquisition subsystem may be controlled based on the output stored in step 522. For example, as shown in FIG. 1, computer subsystem(s) 44 and / or 46 may be coupled to the autofocus subsystem 100 as described above, such that the computer subsystem(s) cause the autofocus subsystem to move the stage 30 of the scanning subsystem based on the generated focus setting. Alternatively, the computer subsystem(s) may not control the autofocus subsystem, but may simply send the generated focus setting to the autofocus subsystem, which controls the position of the stage based on the generated focus setting. Alternatively or additionally, the autofocus subsystem may be similarly coupled to the output acquisition components of subsystem 10 and configured to alter the position of the output acquisition components relative to the specimen based on the generated focus setting. The autofocus subsystem may be an integral part of the scanning subsystem described above, or may be a separate component coupled thereto. The autofocus subsystem may also include any suitable commercially available autofocus subsystem, such as a servo-controlled light-based autofocus system.

[0067] The focus setting may be determined as described herein depending on where one desires the focal plane for scanning the specimen. For example, the optimal focus for most of the processes described herein may be at the top surface of the specimen, e.g., to ensure the highest sensitivity to defects on the top surface, or to ensure the highest sensitivity to measurements of patterned features on the top surface. However, a different focal plane may be more appropriate for some scans. For example, in some cases, the DOI may be located at the bottom of the patterned feature and / or below the top surface of the specimen. In such a case, the optimal focus may be below or near the bottom of the patterned feature on the top surface of the specimen. In one such example, defects may occur at any level, and defects typically become more difficult to detect with increasing depth. Different depths may be targeted by applying a fixed focus offset when the autofocus function focuses on a fixed plane of the sharpest pattern for a particular light mode. The fixed plane of optimal focus may be the top surface, or may be deeper where the wavelength penetrates to image the underlying pattern more clearly.

[0068] FIG. 6 illustrates another embodiment of steps that may be performed by the embodiments described herein for focus map generation. In phase 1 of this focus map generation, the steps are performed on the next Z ci where Z c is the z-value of the prefocus swath, i is 3 or more. In this focus map generation stage 2, the step ci is executed against.

[0069] As shown in step 600, the focus map generation is performed at z=Z ci The job input image may include scanning a first prefocus swath with a , which may be performed as described herein. Output generated from that scan may be sent to the IMC 602. The IMC 602 may create and submit a job to the Leaf fm 604. The job input image may be fThe job output may include one or more focus regions or images with fm for each focus region, where fm is any focus image region, I f The job parameters may include the x, y, and z of each focus area.

[0070] IMC is zi from each focus area in the swath back to the system control computer (SCC) 606. The SCC z1 … zi Keep track of the sequence, where C z1 … zi = Coarse focus measurements at 3-5 points (Z c , fm) and may include filling the array for each successive swath. In other words, the SCC may collect focus metric data from the image computer and perform fitting / interpolation and focus map generation as further described herein.

[0071] As shown in step 608, the focus fitting is performed on the input C z1 … zi Performed with focus Z f (optimal focus correction of focus map) or calculate the next swath Z c+1 The concept of predicting the next swath is that if the best focus cannot be calculated, the next coarser z value is likely out of focus range, and a different z value can be intelligently retried in the next swath. In implementation, predicting the next swath can be performed by extrapolating from the peakless focus curve (pointing the retry z in the direction of better focus). Z f Calculating Z may include fitting to a polynomial, as described further herein. f and Z c+1 may be output.

[0072] Next, the one or more computer subsystems may generate a fIt can be determined whether Z is good or bad. f If is determined to be good, then after the coarse map across the entire specimen is completed (after completion of the prefocus swath scan), one or more computer subsystems may perform focus map interpolation as shown in step 612. In this step, the one or more computer subsystems may calculate focus maps for fewer than all of the inspection swaths and then use them to interpolate focus maps for other inspection swaths without performing coarse focus measurements on the other inspection swaths. In one such example, all of the coarse data from every sub-swath may be averaged to obtain a swath value (only one value is allowed in y along the swath at any given x), which may then be interpolated in x to move from the care area coarsely located at x to a continuous map on x. Z f If is not judged to be good, then Z c+1 may be used to re-execute step 600.

[0073] Then, one or more computer subsystems generate a focus map, F map = focusMap(x,y,Z f ) may be stored and applied for inspection or another process for which a focus map is being generated. During the inspection or another process, the output acquisition subsystem may then vary the z positions along the entire x-swath.

[0074] In one embodiment, generating the focus map, interpolating the focus map, and storing the information are performed separately for a first and a second swath of a scan performed on the specimen during the process, the first swath being scanned before the second swath, and the one or more computer subsystems are configured to determine one or more parameters of one or more prefocus swaths scanned for the second swath based on the results of the optimal focus estimation performed for the first swath. For example, the embodiments described herein may be configured to feed forward the trajectory of the previous swath as a starting z value for the next swath, and then require fewer z swaths to estimate the optimal focus in the subsequent swath. The feed forward of the optimal z trajectory of the previous swath helps ensure that the optimal focus of the next swath is maintained within the coarse measurement range.

[0075] In some embodiments, a scan is performed on the specimen during the process based on a generated focus setting determined prior to the scan, and the generated focus setting is not changed during the scan. In other words, once the generated focus setting is determined as described herein, no dynamic or on-the-fly changing of the focus setting is required. In particular, the embodiments described herein can be used to reliably estimate the optimal focus setting throughout the entire sample plan of the scan, thereby effectively eliminating measuring and changing the focus setting during the scan, which reduces the time and resources required for the scan.

[0076] In another embodiment, the scan performed on the specimen during the process does not include autofocus of the output acquisition subsystem. For example, systems and methods performing specimen scans during the process may use a focus map generated as described herein during the process in place of conventional autofocus methods and systems. In this manner, an autofocus subsystem as described further herein may be used to adjust the focus settings of the output acquisition subsystem on the specimen during the scan based on the generated focus settings, but the autofocus subsystem does not need to perform autofocus in real time by making additional measurements and adjustments to the system. In this manner, an autofocus map may be established prior to the scan and then used without adjusting the focus settings of the autofocus map.

[0077] In additional embodiments, one or more prefocus swaths are placed in a first swath of a scan performed on the specimen during the process, and generating the focus map, interpolating the focus map, and storing the information are performed during the process performed on the specimen. For example, in some embodiments, the process may include performing a scan of one or more prefocus swaths in the first swath of the scan. Focus settings for the entire scan may then be determined based on the results of the scan of these prefocus swath(s). In this manner, one or more prefocus swaths may be placed only in the first swath scanned in the process. In addition, one or more prefocus swaths may be scanned in the first swath only for each specimen for which the process is performed. In other words, as part of a process performed on multiple specimens, one or more prefocus swaths may be scanned in the first swath of a first specimen, and then a scan of the first specimen may be performed using focus settings generated from those scans as described herein, and then the process may be repeated for each of the other specimens. In this way, focus settings can be generated separately for the entire scan of each specimen, independently from the prefocus swath within the first swath of each specimen.

[0078] In further embodiments, generating the focus map, interpolating the focus map, and storing the information are performed during the process and are performed separately for a first and a second swath of a scan performed on the specimen during the process, with the first swath being scanned before the second swath. In this manner, the steps described herein may be performed separately and independently for different swaths on the specimen. For example, one or more prefocus swaths in a first swath on the specimen may be used to generate focus settings for the entire first swath, one or more prefocus swaths in a second swath on the specimen may be used to generate focus settings for the entire second swath, etc. In this manner, a prefocus swath scan may be performed before each swath in the scan to generate an independent focus setting map for each swath. Generating focus settings for each swath may be performed in other manners as further described herein.

[0079] In such an embodiment, the number of one or more prefocus swaths used to generate a focus map for the first swath is greater than the number of one or more prefocus swaths used to generate a focus map for the second swath. For example, the embodiments described herein may be configured to use one or more additional sets of z-values ​​in the first swath to ensure accurate optimal focus. Using more prefocus swaths in the first swath in a scan may be advantageous because the variation between specimens in optimal focus settings may be greater than the variation within specimens. In other words, even if the focus settings of similar specimens or specimens of the same type that are scanned in a process are known, the focus settings may vary relatively dramatically between specimens, for example, due to variations in the process performed on the specimens. Thus, a greater number of prefocus swaths may be advantageous to ensure that an accurate optimal focus setting can be found for the first swath. However, once an optimal focus setting is found using a prefocus swath in a first swath, fewer prefocus swath(s) are required in the second (and subsequent) swaths, since focus settings may vary less dramatically between swaths on the same specimen. In addition, as described further herein, results generated using prefocus swath(s) in one swath may be fed forward to prefocus swath(s) in another swath of the same specimen. In this manner, parameters such as the number of prefocus swath(s) in another subsequent swath may be determined based on results generated using prefocus swath(s) in one swath.

[0080] In another such embodiment, the one or more computer subsystems are configured to determine one or more parameters of one or more prefocus swaths scanned on the specimen for the second swath based on the focus settings generated for the first swath. For example, the embodiments described herein may be configured to feed forward the trajectory of the previous swath as the starting z value for the next swath, after which fewer prefocus swaths of z are required to estimate optimal focus. In an additional example, the computer subsystem(s) may be configured for adaptive feed forward from a polynomial coarse z fitting algorithm for better estimation of the initial z trajectory, e.g., if the measurements deviate significantly from the nominal z, this bias may be removed from the subsequent swath(s).

[0081] In further embodiments, the output acquisition subsystem is configured to perform a scan on the specimen during the process using the generated focus settings, and the one or more computer subsystems are configured to apply the specimen surface profile to the generated focus settings during the scan, thereby determining the final focus settings used to scan the specimen during the process. For example, the embodiments described herein may be configured to apply a real-time wafer surface profile to the coarse z swath to correct for trends in the wafer chuck surface. The wafer surface profile may be a predefined function of the chuck surface. The system may be periodically calibrated to determine such a predefined function to help maintain the coarse z pre-map within optimal focus capture. Determining the predefined function may be performed during the coarse z focus scan of the pre-map. Applying the specimen surface profile to the generated focus settings may include adding the surface profile to the default z (at start) and feed forward the trajectory.

[0082] The computer subsystem(s) may be configured by storing information about the generated focus settings in a recipe or generating a recipe for the process in which the specimen scan is performed. The term "recipe" as used herein may be generally defined as a set of instructions that may be used by a tool to perform a process on a specimen. Thus, generating a recipe may include generating information about how a process is to be performed, which may be used to generate instructions for performing the process. The generated focus setting information stored by the computer subsystem(s) may include any information that may be used to cause the output acquisition subsystem and / or the scanning subsystem to apply the generated focus setting during scanning. The generated focus setting information stored may further include the actual generated focus setting itself, and / or any instructions for applying the generated focus setting during scanning.

[0083] The computer subsystem(s) may be configured to store information about the generated focus settings in any suitable computer-readable storage medium. The information may be stored with any results described herein or in any manner known in the art. The storage medium may include any storage medium described herein or any other suitable storage medium known in the art. After the information is stored, it may be accessed on the storage medium and used by any of the method or system embodiments described herein, formatted for display to a user, used by another software module, method, or system, etc. For example, the embodiments described herein may generate or modify an inspection recipe to include the generated focus settings. That generated or modified inspection recipe may then be stored and used by the system or method (or another system or method) to inspect a specimen or another specimen, thereby generating information about the specimen or another specimen (e.g., defect information).

[0084] In one embodiment, the one or more computer subsystems are configured to determine one or more characteristics of the specimen based on the generated focus settings. For example, the focus map itself (i.e., optimal image focus vs. autofocus servo position) may hold valuable information about the specimen. In one such example, the generated focus settings may be responsive to one or more characteristics of the specimen, such as changes in thickness of a film or patterned feature on the specimen as a function of position on the specimen. In particular, since the generated focus settings are responsive to the position of the specimen surface or feature(s) relative to the focal plane of the output acquisition subsystem, the generated focus settings also react to variations in z-position of feature(s) on the specimen surface or across the specimen. In one such example, the generated focus settings may be responsive to changes in z-position of a top surface of the specimen, or to changes in other characteristics of patterned features, films, etc. that form the top surface of the specimen as a function of position on the specimen. The generated focus settings may be similarly responsive to specimen characteristics when the desired focus position is below the top surface of the specimen. The generated focus settings may be used by computer subsystem(s) to determine various properties of the specimen, both globally (at an average or median property determined from all of the generated focus settings) and locally (at a map of the property of the specimen as a function of the specimen's position, the local average or median, etc.) The generated focus settings may thus be used as a measure of one or more properties of the specimen (which may allow one or more properties to be inferred or directly determined), which may be used by one or more computer subsystems for other step(s) further described herein.

[0085] The systems described herein, or another system or method, may then use the stored information to perform a scan of the specimen and determine information about the specimen from the scan output (e.g., an image, a signal, etc.). Depending on the process performed on the specimen, the determined information may include defect information (e.g., in the case of an inspection or defect review), measurements of patterned features (e.g., in the case of a metrology process), etc. The inspection, defect review, and metrology processes may include such suitable processes known in the art. The output generated by the system for such processes may include any suitable results, such as a standard inspection result file such as KLARF, which is a type of inspection result file output by some inspection tools commercially available from KLA, a standard metrology result file, a standard defect review result file, etc.

[0086] The system may also be configured to perform one or more functions based on the information determined regarding the specimen. Such functions include, but are not limited to, modifying a process, such as a manufacturing process or step that has been or is being performed in a feedback or feedforward manner on the specimen. For example, the virtualization system and other computer subsystems described herein may be configured to determine one or more modifications to a process performed on the specimen based on a process performed on the specimen and / or a detected defect(s) on the specimen inspected as described herein. The modifications to the process may include any suitable modifications to one or more parameters of the process. The virtualization system and / or other computer subsystems described herein preferably determine these modifications such that defects may be reduced or prevented on other specimens on which the modified process is performed, defects may be corrected or eliminated on the specimen in another process performed on the specimen, defects may be compensated for in another process performed on the specimen, etc. The virtualization system and other computer subsystems described herein may determine such modifications in any suitable manner known in the art.

[0087] These changes can then be transmitted to a semiconductor manufacturing system (not shown) or storage medium (not shown) that is accessible to the virtual system or other computer subsystems and semiconductor manufacturing systems described herein. The semiconductor manufacturing system may or may not be part of the system embodiments described herein. For example, the virtual system and other computer subsystems described herein may be coupled to the semiconductor manufacturing system through one or more common elements, such as, for example, a housing, a power supply, a specimen handling device or mechanism, etc. The semiconductor manufacturing system may include any semiconductor manufacturing system known in the art, such as, for example, a lithography tool, an etch tool, a chemical mechanical polishing (CMP) tool, a deposition tool, etc.

[0088] In one embodiment, the one or more computer subsystems are configured to determine one or more changes to one or more parameters of a manufacturing process performed on the specimen based on the determined one or more characteristics of the specimen. For example, as further described above, the generated focus settings may be used by the one or more computer subsystems to determine one or more characteristics of the specimen. These characteristic(s) may then be used by the computer subsystem(s) to determine change(s) to the parameter(s) of the manufacturing process as described above. In one such example, if the characteristic(s) indicate that there is a variation in the thickness of the patterned features across the specimen, the variation may be used to determine change(s) to the parameter(s) of the process used to form the patterned features on the specimen, e.g., a lithography process, an etch process, a CMP process, etc. The change(s) to the parameter(s) of the manufacturing process may otherwise be determined using any suitable algorithm, relationship, function, etc. known in the art.

[0089] The one or more computer subsystems may also determine which process or processes should be modified in response to the characteristic(s) of the specimen. In other words, the computer subsystem(s) may determine modification(s) to one or more processes performed on the specimen in response to the determined characteristic(s). In this manner, the focus map itself, which may hold valuable information about the specimen, may be used to control the process(es) used to create the specimen. Similarly, the focus map may be used to determine one or more modifications to processes not yet performed on the specimen for the purpose of modifying or compensating for the characteristic(s) of the specimen determined from the focus map. Such processes may include repair processes and subsequent manufacturing processes, whose normal and usual operation may modify the determined characteristic(s) of the specimen.

[0090] In one embodiment, the process is an inspection process. The inspection process may be performed in any suitable manner. For example, in general, the term "inspection process" is used herein to refer to a process in which defects are detected on a specimen. Detecting defects on the specimen may be performed in a variety of different ways, including, for example, comparing or applying a threshold to an output generated for the specimen by an inspection tool or system and determining that an output having a value above the threshold corresponds to a potential defect or defect candidate and that an output not having a value above the threshold does not correspond to a potential defect or defect candidate.

[0091] In some embodiments, the process is an inspection process that includes detecting defects on the specimen, and the one or more computer subsystems are configured to determine one or more modifications based on the determined one or more characteristics of the specimen in combination with information about the detected defects generated by the inspection process. For example, the focus map itself may be used to determine information about the specimen as described above, and that information about the specimen in conjunction with the defect inspection results may be used to control the process used to create the specimen. The one or more computer subsystems may use the characteristic(s) determined for the specimen from the generated focus settings in conjunction with information about the detected defects to determine modification(s) to a parameter(s) of the manufacturing process, as further described above. The information about the detected defects may include any of the information described herein or known in the art.

[0092] In one such example, there may be some relationship between the characteristic(s) of the specimen and one or more of the detected defects (e.g., some or all of the detected defects may be attributable, at least in part, to the characteristic(s) of the specimen determined from the generated focus settings, or vice versa), and / or one or more of the detected defects may be unrelated to the characteristic(s) determined from the generated focus settings. In this manner, the determined characteristic(s) of the specimen and the detected defects may have a common or related cause, or may have separate and unrelated causes. In this manner, change(s) to the parameter(s) of the manufacturing process may be advantageously determined in response to the determined characteristic(s) in combination with the detected defects, such that the cause(s) of the undesirable characteristic(s) and the detected defects may be precisely identified and corrected.

[0093] In another embodiment, the process is a metrology process. For example, the metrology process may be performed using one of the systems described further herein. The metrology process may be performed in any suitable manner known in the art. In another embodiment, the process is a defect review process and may be performed in any suitable manner known in the art.

[0094] The embodiments described herein have many advantages over alternative methods and systems for determining focus settings to use in scanning a specimen. For example, the embodiments described herein advantageously use outputs described herein, such as inspection images, to measure and estimate optimal focus. Additionally, the embodiments described herein advantageously use features within the image to provide a reliable and repeatable estimate of optimal focus.

[0095] Each of the system embodiments may be further calibrated according to any other embodiment or embodiments described herein.

[0096] Another embodiment relates to a computer-implemented method for determining focus settings to use in scanning a specimen. The method includes generating a focus map defined by optimal focus values ​​as a function of position on the specimen using output generated in one or more prefocus swaths scanned on the specimen by an output acquisition subsystem configured as described herein. The method further includes interpolating the focus map to generate focus settings for a scan performed on the specimen during the process. The method further includes storing information of the generated focus settings for use in a scan performed on the specimen during the process. The generating, interpolating, and storing are performed by one or more computer subsystems coupled to the output acquisition subsystem. The computer subsystem(s) may be further configured as described herein.

[0097] Each of the steps of the method may be performed as further described herein. The method may also include any other step(s) that may be performed by the output acquisition subsystem, computer subsystem(s), and / or system(s) described herein. The above-described methods may be performed by any of the system embodiments described herein.

[0098] An additional embodiment relates to a non-transitory computer readable medium having stored thereon program instructions executable on a computer system to perform a computer implemented method of determining focus settings to use for scanning a specimen. One such embodiment is shown in Figure 7. In particular, as shown in Figure 7, a non-transitory computer readable medium 700 includes program instructions 702 executable on a computer system 704. The computer implemented method may include any step(s) of any method(s) described herein.

[0099] Program instructions 702 implementing methods such as those described herein may be stored on a computer-readable medium 700. The computer-readable medium may be a storage medium such as a magnetic or optical disk, magnetic tape, or any other suitable non-transitory computer-readable medium known in the art.

[0100] The program instructions may be implemented in any of a variety of ways, including procedure-based, component-based, and / or object-oriented techniques, among others. For example, the program instructions may be implemented using ActiveX controls, C++ objects, JavaBeans, Microsoft Foundation Classes ("MFC"), SSE (Streaming SIMD Extensions), or other technologies or methodologies, as appropriate.

[0101] The computer system 704 may be configured according to any of the embodiments described herein.

[0102] Further modifications and alternative embodiments of various aspects of the invention will be apparent to those skilled in the art in view of this description. For example, a method and system for determining focus settings to use in scanning a specimen is provided. This description should therefore be interpreted as merely illustrative and is intended to teach those skilled in the art the general manner of carrying out the invention. It should be understood that the forms of the invention shown and described herein are to be taken as the presently preferred embodiments. Elements and materials may be substituted for those shown and described herein, parts and processes may be reversed, and certain features of the invention may be utilized independently, all as would be apparent to one skilled in the art given this description of the invention. Changes may be made in the elements described herein without departing from the spirit and scope of the invention as set forth in the following claims.

Claims

1. 1. A system configured for determining a focus setting for use in scanning a specimen, comprising: an output acquisition subsystem configured to direct energy to the specimen, detect energy from the specimen, and generate an output responsive to the detected energy; one or more computer subsystems, generating a focus map defined by best focus values ​​as a function of position on the specimen using output generated by one or more prefocused swaths scanned onto the specimen by the output acquisition subsystem; Interpolating the focus map to generate focus settings for scans performed on the specimen during the process; and one or more computer subsystems configured to store information regarding the generated focus settings for use in the scans performed on the specimen during the process; and Equipped with The one or more prefocused swaths are scanned at different z-positions relative to the specimen or are predefined as completely overlapping regions on the specimen. system.

2. The system of claim 1 , wherein the specimen comprises a wafer having a 3D NAND structure formed thereon.

3. The system of claim 1 , wherein the output includes an image of the specimen.

4. 2. The system of claim 1, wherein generating the focus map includes determining a focus metric as a function of x and y positions within the one or more prefocus swaths, and determining the focus metric at one of the x and y positions includes determining the focus metric from all the outputs generated within the one or more prefocus swaths at the one of the x and y positions.

5. 2. The system of claim 1, wherein generating the focus map includes determining a focus metric as a function of x and y positions within the one or more prefocus swaths, the focus metric including a coarse z-focus measurement, and generating the focus map further includes fitting the coarse z-focus measurement to a polynomial and estimating an optimal focus at the x and y positions at a peak of the polynomial, and generating the focus map of x and y positions in a sample plan for the scan performed on the specimen during the process from the optimal focus at the x and y positions within the one or more prefocus swaths.

6. 6. The system of claim 5, wherein generating the focus map, interpolating the focus map, and storing the information are performed separately during the process and for first and second swaths of the scan performed on the specimen during the process, the first swath being scanned before the second swath, and the one or more computer subsystems are further configured to determine one or more parameters of the one or more prefocus swaths scanned for the second swath based on results of the best focus estimate performed for the first swath.

7. 2. The system of claim 1, wherein the interpolating comprises interpolating the focus map to generate the focus settings for a complete sample plan of the scans performed on the specimen during the process.

8. 2. The system of claim 1, wherein the scan is performed on the specimen during the process based on the generated focus setting determined prior to the scan, and the generated focus setting is not changed during the scan.

9. The system of claim 1 , wherein the scan performed on the specimen during the process does not include autofocus of the output acquisition subsystem.

10. 2. The system of claim 1, wherein the one or more prefocus swaths are located within a first swath of the scan performed on the specimen during the process, and wherein generating the focus map, interpolating the focus map, and storing the information are performed during the process performed on the specimen.

11. 2. The system of claim 1, wherein generating the focus map, interpolating the focus map, and storing the information are performed during the process and separately for first and second swaths of the scan performed on the specimen during the process, the first swath being scanned before the second swath.

12. 12. The system of claim 11, wherein a number of the one or more prefocus swaths used to generate the focus map for the first swath is greater than a number of the one or more prefocus swaths used to generate the focus map for the second swath.

13. 12. The system of claim 11, wherein the one or more computer subsystems are configured to determine one or more parameters of the one or more prefocused swaths scanned on the specimen for the second swath based on the focus settings generated for the first swath.

14. 2. The system of claim 1, wherein the output acquisition subsystem is further configured to perform the scan on the specimen during the process using the generated focus settings, and the one or more computer subsystems are further configured to apply a specimen surface profile to the generated focus settings during the scan, thereby determining a final focus setting used for the scan of the specimen during the process.

15. 10. The system of claim 1, wherein the one or more computer subsystems are further configured to determine one or more characteristics of the specimen based on the generated focus setting.

16. 16. The system of claim 15, wherein the one or more computer subsystems are further configured to determine one or more changes to one or more parameters of a manufacturing process performed on the specimen based on the determined one or more characteristics of the specimen.

17. 17. The system of claim 16, wherein the process is an inspection process that includes detecting defects on the specimen, and the one or more computer subsystems are further configured to determine the one or more modifications based on the determined one or more characteristics of the specimen in combination with information generated by the inspection process about the detected defects.

18. The system of claim 1 , wherein the process is an inspection process.

19. The system of claim 1 , wherein the energy directed to the sample comprises light and the energy detected from the sample comprises light.

20. A non-transitory computer readable medium storing program instructions executable on a computer system to perform a method for determining focus settings to use in scanning a specimen, the method comprising: generating a focus map defined by values ​​of best focus as a function of position on the specimen using output generated in one or more prefocused swaths scanned over the specimen by an output acquisition subsystem configured to direct energy to the specimen, detect energy from the specimen, and generate output responsive to the detected energy; Interpolating the focus map to generate focus settings for scans performed on the specimen during the process; and storing information regarding the generated focus settings for use in the scan performed on the specimen during the process, wherein the generating, interpolating, and storing are performed by the computer system coupled to the output acquisition subsystem; The one or more prefocused swaths are scanned at different z-positions relative to the specimen or are predefined as completely overlapping regions on the specimen. Non-transitory computer-readable medium.

21. 1. A computer-implemented method for determining focus settings to use in scanning a specimen, comprising: generating a focus map defined by values ​​of best focus as a function of position on the specimen using output generated in one or more prefocused swaths scanned over the specimen by an output acquisition subsystem configured to direct energy to the specimen, detect energy from the specimen, and generate output responsive to the detected energy; Interpolating the focus map to generate focus settings for scans performed on the specimen during the process; and storing information regarding the generated focus settings for use in the scan performed on the specimen during the process, wherein the generating, interpolating, and storing are performed by one or more computer subsystems coupled to the output acquisition subsystem; A computer-implemented method, wherein the one or more prefocused swaths are scanned at different z positions relative to the specimen or are predefined as completely overlapping regions on the specimen.

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