Mask inspection for semiconductor specimen fabrication

Abstract

To provide a computerized system for inspecting a mask usable for fabricating a semiconductor specimen.SOLUTION: There is provided a system and method for mask inspection, comprising: obtaining a plurality of images, each representative of a respective part of the mask; generating a CD map of the mask comprising a plurality of composite values of a CD measurement of a POI respectively derived from the plurality of images, comprising, for each given image: dividing the given image into a plurality of sections; searching for the POI in the plurality of sections, giving rise to a set of sections, each with presence of at least one of the POI therein; for each section, obtaining a value of the CD measurement using a printing threshold, giving rise to a set of values of the CD measurement corresponding to the set of sections; and combining the set of values to a composite value of the CD measurement corresponding to the given image.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The subject matter of this disclosure relates generally to the field of mask inspection, and more particularly to critical dimension (CD) control for photomasks. [Background technology]

[0002] Current demands for high density and performance associated with ultra-large scale integration of fabricated microelectronic devices require submicron features, increased transistor and circuit speeds, and improved reliability. As semiconductor processes advance, pattern dimensions such as linewidths and other types of critical dimensions are continually reduced. These demands require highly accurate and uniform formation of device features, which requires careful monitoring of the fabrication process, including automated inspection of devices while they are still in the form of semiconductor wafers.

[0003] Semiconductor devices are often fabricated using photolithography masks (also called photomasks, masks, or reticles) in a photolithography process. The photolithography process is one of the key processes in the manufacturing of semiconductor devices and involves patterning the surface of a wafer according to the circuit design of the semiconductor device to be fabricated. Such circuit design is first patterned on a mask. Therefore, to obtain a working semiconductor device, the mask must be defect-free. Masks are manufactured through complex processes and can be subject to various defects and variations.

[0004] Additionally, masks are often used repeatedly to create many dies on a wafer. Therefore, a defect on the mask is replicated multiple times on the wafer, resulting in defects in multiple devices. To establish a manufacturing-worthy process, the entire lithography process must be tightly controlled, especially considering the increasing circuit integration and shrinking semiconductor device sizes. Within this process, CD control is a determining factor in device performance and yield. In particular, masks and fabricated devices are becoming increasingly sensitive to variations in CD uniformity. If uncorrected, these variations can cause the final device to not meet the desired performance and, in some cases, may even cause the final device to malfunction, thereby negatively impacting yield.

[0005] Various mask inspection methods have been developed and are commercially available. According to certain conventional techniques for designing and evaluating masks, a mask is created and used to expose a wafer through the mask, and then inspection is performed to determine whether the mask features / pattern were transferred to the wafer according to the design. Any variation in the final printed features from the intended design may require modifying the design, repairing the mask, creating a new mask, and / or exposing a new wafer. Alternatively, the mask can be inspected directly using various mask inspection tools.

[0006] Verifying the accuracy and quality of the printed features can be an indirect way to verify the mask. However, because the final printed pattern on the wafer or die is formed after the printing process, e.g., resist development, substrate processing (e.g., material etching or deposition), etc., it can be difficult to attribute, distinguish, or isolate errors in the final printed pattern to problems associated with the mask and / or resist deposition and / or development process. Furthermore, inspection of the final printed pattern on the wafer or die tends to limit the number of usable samples provided to detect, determine, and resolve any processing issues. This process can also be labor-intensive, requiring significant time for inspection and analysis. Summary of the Invention

[0007] According to certain aspects of the subject matter of the present disclosure, there is provided a computerized system for inspecting a mask usable in the manufacture of semiconductor samples, the system comprising: a processing and memory circuit (PMC) configured to acquire a plurality of images, each representing a respective portion of the mask, the images being acquired by emulating the optical configuration of a lithography tool usable in the manufacture of the semiconductor samples; and generate a critical dimension (CD) map of the mask including a plurality of composite values ​​of CD measurement values ​​of patterns of interest (POIs) respectively derived from the plurality of images, the PMC being configured to: divide the given image into a plurality of sections; search for POIs in the plurality of sections to produce a set of sections, with at least one of the POIs present in each section; for each section of the set of sections, obtain a value of the CD measurement for at least one POI using a printing threshold to produce a set of values ​​of the CD measurement corresponding to the set of sections; and combine the set of values ​​into a composite value of the CD measurement values ​​corresponding to the given image, wherein the CD map indicates a CD uniformity (CDU) of the mask with respect to the CD measurement values ​​of the POIs.

[0008] In addition to the features described above, systems according to this aspect of the disclosed subject matter can include one or more of the following listed features (i) through (xi) in any desired combination or permutation technically possible. (i) The mask is a memory mask or a logic mask. (ii) The images are acquired by an actinic inspection tool configured to emulate the optical configuration of a lithography tool. (iii) the plurality of images is obtained by acquiring a plurality of first images using a non-actinic inspection tool and performing a simulation on the plurality of first images to simulate an optical configuration of a lithography tool to produce the plurality of images. (iv) The CD measurement is selected depending on the particular inspection application. (v) A given image is divided into sections according to a grid, the grid being determined based on the dimensions and periodicity of the POIs. (vi) The POIs are searched for by using a pattern matching algorithm against a reference image of the POI. (vii) The PMC is configured to obtain a value of the CD measurement for each section by deriving a gray level (GL) profile of at least one POI from the section, the GL profile indicating a pixel intensity distribution of the at least one POI, applying a printing threshold to the GL profile to obtain two topo-points, and performing a CD measurement based on the two topo-points to obtain its value. (viii) The PMC is configured to obtain a value of the CD measurement for each section by applying a printing threshold to at least a portion of the section including at least one POI to produce a binary image portion, and performing a CD measurement on the binary image portion to obtain the value. (ix) The PMC is configured to generate one or more CD maps corresponding to one or more CD measurements of the POI depending on the particular inspection application, each CD map including a plurality of composite values ​​of a CD measurement of the one or more CD measurements respectively derived from the plurality of images. The PMC is configured to derive one or more composite values ​​from each given image of the plurality of images, including: for each section of the set of sections, obtaining one or more values ​​for the one or more CD measurements to yield a set of one or more values ​​for the one or more CD measurements corresponding to the set of sections; and combining each set of one or more values ​​respectively into one or more composite values ​​corresponding to the given image. (x) The PMC is further configured to determine a CD variance of the mask based on the CD map, and to report the presence of a defect with respect to the CDU when the CD variance passes a CDU threshold. (xi) The PMC is further configured to determine whether to accept the mask, correct the mask, or reject the mask in response to the presence of a defect related to the CDU.

[0009] According to another aspect of the subject matter of the present disclosure, there is provided a method for inspecting a mask usable in the manufacture of a semiconductor sample, the method being performed by a processing and memory circuit (PMC), the method comprising: acquiring a plurality of images each representing a respective portion of the mask, the images being acquired by emulating an optical configuration of a lithography tool usable in the manufacture of the semiconductor sample; and generating a critical dimension (CD) map of the mask including a plurality of composite values ​​of CD measurement values ​​of patterns of interest (POIs) respectively derived from the plurality of images, the CD map comprising: dividing the given image into a plurality of sections; searching for POIs in the plurality of sections to produce a set of sections, with at least one of the POIs present in each section; for each section of the set of sections, obtaining a value of the CD measurement for at least one POI using a printing threshold to produce a set of values ​​of the CD measurement corresponding to the set of sections; and combining the set of values ​​into a composite value of the CD measurement values ​​corresponding to the given image, wherein the CD map indicates a CD uniformity (CDU) of the mask with respect to the CD measurement values ​​of the POIs.

[0010] This aspect of the disclosed subject matter can include one or more of features (i) through (xi) listed above with respect to the system, in any desired combination or permutation technically possible, mutatis mutandis.

[0011] According to another aspect of the subject matter of the present disclosure, a non-transitory computer-readable medium is provided that, when executed by a computer, causes the computer to perform a method for inspecting a mask usable in the manufacture of semiconductor samples, the method including: acquiring a plurality of images each representing a respective portion of the mask, the images being acquired by emulating an optical configuration of a lithography tool usable in the manufacture of the semiconductor samples; and generating a critical dimension (CD) map of the mask including a plurality of composite values ​​of CD measurement values ​​of patterns of interest (POIs) respectively derived from the plurality of images, the CD map including: dividing the given image into a plurality of sections; searching for POIs in the plurality of sections to produce a set of sections, with at least one of the POIs present in each section; for each section of the set of sections, obtaining a value of the CD measurement for at least one POI using a printing threshold to produce a set of values ​​of the CD measurement corresponding to the set of sections; and combining the set of values ​​into a composite value of the CD measurement values ​​corresponding to the given image, wherein the CD map indicates a CD uniformity (CDU) of the mask with respect to the CD measurement values ​​of the POIs.

[0012] This aspect of the disclosed subject matter can include one or more of features (i) through (xi) listed above with respect to the system, in any desired combination or permutation technically possible, mutatis mutandis.

[0013] In order to understand the present disclosure and how it may be carried out in practice, reference will now be made to the accompanying drawings, in which embodiments will be described, by way of non-limiting example only, in which: [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a functional block diagram of a mask inspection system in accordance with certain embodiments of the presently disclosed subject matter. [Figure 2]1 is a generalized flow diagram of mask inspection for a mask that can be used in the fabrication of a semiconductor sample, in accordance with certain embodiments of the presently disclosed subject matter. [Figure 3] 1 is a generalized flow diagram of an example of obtaining values ​​for CD measurements for each section, according to certain embodiments of the presently disclosed subject matter. [Figure 4] 10 is a generalized flow diagram of another example of obtaining values ​​of CD measurements for each section, according to certain embodiments of the disclosed subject matter. [Figure 5] 1 is a schematic diagram of an actinic inspection tool and a lithography tool in accordance with certain embodiments of the presently disclosed subject matter. [Figure 6] 1A-1C are diagrams illustrating an example of a given image and multiple sections divided within the given image, in accordance with certain embodiments of the disclosed subject matter. [Figure 7] 1 is a schematic diagram of a process for applying a printing threshold, according to certain embodiments of the presently disclosed subject matter. [Figure 8] 1 is an exemplary image portion including at least one POI and a GL profile derived therefrom, according to certain embodiments of the disclosed subject matter. [Figure 9] FIG. 2 illustrates an example of a CD map of a mask in accordance with certain embodiments of the disclosed subject matter. DETAILED DESCRIPTION OF THE INVENTION

[0015] In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. However, it will be understood by those skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, components, and circuits have not been described in detail so as not to obscure the subject matter of the present disclosure.

[0016] Unless otherwise indicated, as will be apparent from the following description, throughout this specification, descriptions utilizing terms such as "inspect," "obtain," "emulate," "apply," "generate," "derive," "divide," "search," "combine," "obtain," "execute," "determine," "report," and the like, are understood to refer to computer operations and / or processes that manipulate and / or transform data into other data, said data being represented as physical quantities such as electron quantities, and / or said data representing physical objects. The term "computer" should be interpreted expansively to encompass any type of hardware-based electronic device having data processing capabilities, including, as non-limiting examples, the mask inspection system, mask CD uniformity (CDU) system, and respective portions thereof, disclosed herein.

[0017] The term "mask" as used herein may also be referred to as a "photolithography mask" or "photomask" or "reticle." Such terms should be interpreted equivalently and expansively to encompass a template bearing a circuit design (e.g., defining the layout of a particular layer of an integrated circuit) to be patterned on a semiconductor wafer in a photolithography process. By way of example, a mask may be implemented as a quartz glass plate covered with a pattern of opaque, transparent, and phase-shifting regions to be projected onto a wafer in a lithography process. By way of example, a mask may be an extreme ultraviolet (EUV) mask or an argon fluoride (ArF) mask. As another example, a mask may be a memory mask (usable to fabricate memory devices) or a logic mask (usable to fabricate logic devices).

[0018] The terms "inspection" or "mask inspection," as used herein, should be interpreted expansively to encompass any operation for evaluating the accuracy and completeness of a fabricated photomask with respect to a circuit design and its ability to produce an accurate representation of the circuit design on a wafer. Inspection can include any kind of operation related to defect detection, defect review, and / or various types of defect classification, and / or metrology operations during and / or after the mask fabrication process and / or during the use of the mask for semiconductor sample fabrication. Inspection can be performed by using a non-destructive inspection tool after the mask is fabricated. As a non-limiting example, the inspection process can include one or more of the following operations: scanning (single or multiple scans), imaging, sampling, detecting, measuring, classifying, and / or other operations performed on the mask or a portion thereof using an inspection tool. Similarly, mask inspection can also be interpreted to include generating an inspection strategy and / or other setup operations, for example, prior to the actual inspection of the mask. Note that unless otherwise specified, the term "inspection" or its derivatives as used herein is not limited with respect to the resolution or size of the inspection area. Various non-destructive inspection tools include, by way of non-limiting example, optical inspection tools, scanning electron microscopes, atomic force microscopes, and the like.

[0019] The term "metrology operation" as used herein should be expansively interpreted to encompass any metrology procedure used to extract metrology information about one or more structural elements on a mask. In some embodiments, a metrology operation can include, for example, a measurement operation such as a critical dimension (CD) measurement performed on a particular structural element on a sample, including, but not limited to, dimensions (e.g., line width, line spacing, contact diameter, element size, edge roughness, gray level statistics, etc.), element shape, distances within or between elements, associated angles, overlay information associated with elements corresponding to different design levels, etc. Measurement results, such as measurement images, are analyzed, for example, by using image processing techniques. It should be noted that unless otherwise specified, the term "metrology" or its derivatives as used herein is not limited with respect to measurement technique, measurement resolution, or size of inspection area.

[0020] The term "specimen" as used herein should be interpreted expansively to encompass any type of wafer, related structure, combination and / or portion thereof used to fabricate semiconductor integrated circuits, magnetic heads, flat panel displays, and other semiconductor manufacturing articles.

[0021] The term "defect" as used herein should be interpreted expansively to encompass any type of abnormality or undesirable feature / function formed on a mask. In some cases, a defect may refer to an actual defect or defect of interest (DOI) that, when printed on a wafer, has a specific impact on the functionality of the fabricated device, and therefore, detecting such defects is in the customer's interest. In some other cases, a defect may refer to a nuisance defect or a "false alarm" defect, which is a suspect defect that can be ignored because it does not affect the functionality of the finished device.

[0022] The terms "non-transitory memory" and "non-transitory storage medium" as used herein should be interpreted expansively to encompass any volatile or non-volatile computer memory suitable for the subject matter of the present disclosure. These terms should be interpreted to include a single medium or multiple media (e.g., a centralized or distributed database and / or associated caches and servers) that store one or more sets of instructions. These terms should also be interpreted to include any medium that can store or encode a set of instructions for execution by a computer, causing a computer to perform any one or more of the methodologies of the present disclosure. Thus, these terms should be interpreted to include, but are not limited to, read-only memory ("ROM"), random access memory ("RAM"), magnetic disk storage media, optical storage media, flash memory devices, and the like.

[0023] It will be understood that, unless otherwise stated, certain features of the presently disclosed subject matter, which are described in the context of separate embodiments, can also be provided in combination in a single embodiment. Conversely, various features of the presently disclosed subject matter, which are described in the context of a single embodiment, can also be provided separately or in any suitable subcombination. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the methods and apparatus.

[0024] With this in mind, attention is directed to FIG. 1, which illustrates a functional block diagram of a mask inspection system in accordance with certain embodiments of the disclosed subject matter.

[0025] The inspection system 100 shown in FIG. 1 can be used to inspect a mask during or after a mask manufacturing process and / or during a semiconductor sample manufacturing process using the mask. As mentioned above, inspection as referred to herein can be interpreted to encompass any type of operation related to defect inspection / detection, and / or various types of defect classification, and / or metrology operations, such as critical dimension (CD) measurements, on a mask or portion thereof. According to certain embodiments of the presently disclosed subject matter, the illustrated inspection system 100 includes a computer-based system 101 capable of automatically inspecting and detecting defects on a mask. Specifically, in some embodiments, the defects detected in this disclosure relate to mask CD uniformity (CDU). In such cases, the system 101 is configured to automatically monitor the mask CD uniformity and detect CDU-related defects when defects are present. The system 101 may also be referred to as a mask defect detection system, or more specifically, a mask CDU system, which is a subsystem of the inspection system 100.

[0026] System 101 may be operatively connected to a mask inspection tool 120 configured to scan the mask and capture one or more images of the mask for inspection of the mask. As used herein, the term "mask inspection tool" should be interpreted expansively to encompass any type of inspection tool that may be used in a mask inspection-related process, including, by way of non-limiting example, scanning (single or multiple scans), imaging, sampling, detecting, measuring, classifying, and / or other processes provided with respect to a mask or portion thereof.

[0027] It should also be noted that, without limiting the scope of the present disclosure in any way, mask inspection tool 120 may be implemented as various types of inspectors, such as an optical inspection tool, an electron beam tool, etc. In some cases, mask inspection tool 120 may be a relatively low-resolution inspection tool (e.g., an optical inspection tool, a low-resolution scanning electron microscope (SEM), etc.). In some cases, mask inspection tool 120 may be a relatively high-resolution inspection tool (e.g., a high-resolution SEM, an atomic force microscope (AFM), a transmission electron microscope (TEM), etc.). In some cases, the inspection tool may provide both low-resolution and high-resolution image data. In some embodiments, mask inspection tool 120 has metrology capabilities and may be configured to perform metrology operations on the captured images. The resulting image data (low-resolution image data and / or high-resolution image data) may be transmitted to system 101 directly or via one or more intermediate systems. The present disclosure is not limited to the resolution of the image data obtained from any particular type of mask inspection tool and / or inspection tool.

[0028] According to certain embodiments, the mask inspection tool may be implemented as an actinic inspection tool configured to emulate / mimic the optical configuration of a lithography tool (e.g., a scanner or stepper) that can be used in the manufacture of semiconductor samples, for example, by projecting a pattern formed on a mask onto a wafer, as described in further detail below with respect to FIG. 5.

[0029] Referring now to FIG. 5, there is shown a schematic diagram of an actinic inspection tool and a lithography tool in accordance with certain embodiments of the presently disclosed subject matter.

[0030] Similar to lithography tool 520, actinic inspection tool 500 may include an illumination source 502 configured to generate light at an exposure wavelength (e.g., a laser), illumination optics 504, a mask holder 506, and projection optics 508. Illumination optics 504 and projection optics 508 may include one or more optical elements (e.g., lenses, apertures, spatial filters, etc.).

[0031] In lithography tool 520, a mask is placed in a mask holder 506 and optically aligned to project an image of the circuit pattern to be replicated onto a wafer placed on a wafer holder 512 (e.g., by using various stepping, scanning, and / or imaging techniques to generate or replicate the pattern on the wafer). Unlike lithography tool 520, instead of positioning a wafer holder 512, actinic inspection tool 500 positions a detector 510 (e.g., a charge-coupled device (CCD), etc.) at the wafer holder location, and detector 510 is configured to detect light projected through the mask and generate an image of the mask.

[0032] As can be seen, actinic inspection tool 500 is configured to emulate the optical configuration of a lithography tool 520, including, but not limited to, illumination / exposure conditions such as wavelength, pupil shape, and numerical aperture (NA). Accordingly, a mask image 514 acquired by detector 510 is expected to resemble an image 516 of a wafer fabricated using the mask through a lithography tool. A mask image acquired using such an actinic inspection tool is also referred to as an aerial image. The aerial image is provided to system 101 for further processing, as described below.

[0033] According to certain embodiments, in some cases, mask inspection tool 120 may be implemented as a non-actinic inspection tool, such as, for example, a conventional optical inspection tool, an electron beam tool (e.g., SEM), etc. In such cases, a detector in the inspection tool may interface with the particular type of microscope used and digitize image information from the microscope, thereby obtaining an image of the mask.

[0034] A simulation may be performed on the acquired images to simulate the optical configuration of the lithography tool, thereby generating an aerial image. In some cases, the image simulation may be performed by system 101 (e.g., the simulation functionality may be integrated into PMC 102 by incorporating an image simulator therein), while in some other cases, the image simulation may be performed by a processing module of mask inspection tool 120 or by a separate simulation engine / unit operatively connected to mask inspection tool 120 and system 101.

[0035] System 101 includes a processor and memory circuit (PMC) 102 operatively connected to a hardware-based I / O interface 126. PMC 102 is configured to provide the processing necessary to operate the system, as described in further detail with reference to Figures 2, 3, and 4, and includes a processor (not separately shown) and memory (not separately shown). The processor of PMC 102 can be configured to execute several functional modules in accordance with computer-readable instructions embodied on non-transitory computer-readable memory included in the PMC. Such functional modules are hereinafter referred to as being included in the PMC.

[0036] A processor as referred to herein may represent one or more general-purpose processing devices, such as a microprocessor, a central processing unit, etc. More specifically, a processor may be a complex instruction set computing (CISC) microprocessor, a reduced instruction set computing (RISC) microprocessor, a very long instruction word (VLIW) microprocessor, a processor implementing other instruction sets, or a processor implementing a combination of instruction sets. A processor may also be one or more special-purpose processing devices, such as an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), a digital signal processor (DSP), a network processor, etc. A processor is configured to execute instructions to perform the operations and steps described herein.

[0037] The memory referred to in this specification may include main memory (e.g., read-only memory (ROM), flash memory, dynamic random access memory (DRAM) such as synchronous DRAM (SDRAM) or Rambus DRAM (RDRAM), etc.), and static memory (e.g., flash memory, static random access memory (SRAM), etc.).

[0038] As mentioned above, in some embodiments, the system 101 can be configured to detect defects related to CD uniformity on a mask. As used herein, the term “CD uniformity (CDU)” refers to the variance of CD measurements across an entire mask (or at least a portion thereof). Such CD variance can be caused by certain physical effects during the mask writing process, such as spatial writing errors in the mask manufacturing tool, which can be caused by factors such as laser energy variance, mask material, etc. If mask defects related to CDU are not detected before mass production of the wafers, they can be repeated multiple times on production wafers, thus causing defects in multiple semiconductor devices (e.g., affecting device functionality and failing to meet desired performance), thus negatively impacting yield. Therefore, it is desirable for CD variance to be tightly controlled.

[0039] To minimize the effects of CD variations on a mask, certain conventional techniques involve printing multiple wafers using the mask to determine the best lithography parameters to use for that mask. However, this iterative process is very time-consuming due to the large number of parameter variables that must be considered and their complex interactions. Furthermore, repeatedly using wafer fabrication tools solely to optimize parameters unnecessarily reduces the time the tools can be used for their intended function, i.e., to fabricate integrated circuits.

[0040] An alternative approach utilizes the linear correlation between CD measurements and pixel intensities in the mask image. CD variance is measured indirectly by calculating pixel intensities, e.g., by averaging gray-level intensities over a specific region of the image. However, the correlation coefficient (or conversion coefficient) k is typically unknown because it varies with many factors, such as the pattern of interest and the type of resist. Therefore, without knowing k, it is impossible to infer the actual CD measurement based on image intensities. While attempts have been made to learn the value of k, this has proven to be complex and time-consuming given the number of variables involved. Additionally, because the above-mentioned approach averages pixel intensities over a relatively large image region, it is only applicable to memory masks where features are widely repeated throughout the mask.

[0041] Therefore, current inspection methods are insufficient to provide the desired CD control of masks, especially for advanced processes and rapid development of complex photomask features. According to certain embodiments of the presently disclosed subject matter, an improved mask inspection system and method are proposed that are configured to automatically monitor mask CD uniformity (CDU) and detect defects related to the mask CDU. The proposed method has been proven to improve accuracy and sensitivity for advanced CD control of mask features without impacting inspection throughput.

[0042] According to certain embodiments, functional modules included in PMC 102 of system 101 may include image processing module 104, measurement module 106, and defect reporting module 108. PMC 102 may be configured to acquire, via I / O interface 126, multiple images, each representing a respective portion (e.g., part) of a mask. The images may be acquired by emulating the optical configuration of a lithography tool that may be used to fabricate semiconductor samples. By way of example, the images may be acquired by a mask inspection tool 120, such as, for example, an actinic inspection tool.

[0043] The PMC 102 may be further configured to generate a mask critical dimension (CD) map including a plurality of composite values ​​of CD measurements of the pattern of interest (POI), the composite values ​​being derived from the plurality of images, respectively. Specifically, the PMC 102 may be configured to derive the composite value from each given image of the plurality of images, as described below.

[0044] The image processing module 104 may be configured to divide a given image into multiple sections and search for POIs in the multiple sections to produce a set of sections in each of which at least one of the POIs is present.

[0045] The measurement module 106 may be configured to obtain, for each section of the set of sections, a value of the CD measurement for at least one POI using the printing threshold to produce a set of values ​​of the CD measurement corresponding to the set of sections, The measurement module 106 is further configured to combine the set of values ​​into a composite value of the CD measurements corresponding to the given image.

[0046] The CD map so generated indicates the CD uniformity of the mask relative to the CD measurements of the POI. Optionally, the defect reporting module 108 can be configured to report the presence of a defect for the CDU when the CD variance indicated by the CD map passes a CDU threshold (e.g., exceeds the threshold in some cases but falls below the threshold in some other cases). Optionally, the defect reporting module 108 can be further configured to determine how to respond to the detected defect, for example, whether to accept the mask, repair the mask, or reject the mask.

[0047] The operation of the systems 100, 101, PMC 102 and the functional modules therein are further detailed with reference to FIGS.

[0048] According to certain embodiments, system 100 may include a storage unit 122. Storage unit 122 may be configured to store any data required for operating systems 100 and 101, such as data related to the inputs and outputs of systems 100 and 101, as well as intermediate processing results generated by system 101. By way of example, storage unit 122 may be configured to store images and / or derivatives thereof (e.g., pre-processed images) generated by mask inspection tool 120. Thus, images may be retrieved from storage unit 122 and provided to PMC 102 for further processing.

[0049] In some embodiments, system 100 may optionally include a computer-based graphical user interface (GUI) 124 configured to enable user-specified input related to system 101. For example, a user may be presented with a visual representation of the mask (e.g., by a display forming part of GUI 124), including an image of the mask or a portion thereof. Through the GUI, the user may be provided with options to define certain operational parameters, such as, for example, POIs, print thresholds, CD variation thresholds, etc. In some cases, the user may also view operational results on the GUI, such as a CD map, detected defects related to the CDU, and / or further inspection results.

[0050] As described above, system 101 is configured to receive multiple images of a mask via I / O interface 126. The images may include image data (and / or derivatives thereof) generated by mask inspection tool 120 and / or image data stored in storage unit 122 or one or more data repositories. In some cases, image data may refer to images captured by the mask inspection tool and / or pre-processed images derived from captured images obtained by various pre-processing stages, etc. It is noted that in some cases, the images may include associated numerical data (e.g., metric data, handcraft attributes, etc.). It is further noted that the image data pertains to target layers of semiconductor devices to be printed on the wafer.

[0051] System 101 is further configured to process the received images and send the results (e.g., CD map, detected defects) via I / O interface 126 to storage unit 122 and / or GUI 124 for rendering and / or mask inspection tool 120.

[0052] In some embodiments, in addition to system 101, mask inspection system 100 may further include one or more inspection modules, such as additional defect detection modules and / or automatic defect review modules (ADR) and / or automatic defect classification modules (ADC) and / or metrology-related modules and / or other inspection modules that can be used to perform additional inspection of the mask. One or more inspection modules may be implemented as standalone computers, or the functionality of the inspection modules (or at least a portion thereof) may be integrated with mask inspection tool 120. In some embodiments, output obtained from system 101 may be used by mask inspection tool 120 and / or one or more inspection modules (or portions thereof) for further inspection of the mask.

[0053] Those skilled in the art will readily appreciate that the teachings of the presently disclosed subject matter are not bound by the system shown in FIG. 1 , and that equivalent and / or modified functionality may be integrated or divided in other ways and may be implemented in any suitable combination of software, firmware, and / or hardware.

[0054] 1 may be implemented in a distributed computing environment in which the aforementioned functional modules included in PMC 102 may be distributed across several local and / or remote devices and linked via a communications network. It is further noted that in other embodiments, one or more of mask inspection tool 120, storage unit 122, and / or GUI 124 may be external to system 100 and operate in data communication with system 101 via I / O interface 126. System 101 may be implemented as a standalone computer used in conjunction with a mask inspection tool. Alternatively, each of the functions of system 101 may be integrated, at least in part, with mask inspection tool 120, thereby facilitating and enhancing the functionality of mask inspection tool 120 in inspection-related processes.

[0055] Although not necessarily so, the processes of operation of systems 101 and 100 may correspond to some or all of the steps of the methods described with respect to Figures 2-4. Similarly, the methods described with respect to Figures 2-4 and their possible implementations may be implemented by systems 101 and 100. Accordingly, it should be noted that embodiments discussed in connection with the methods described with respect to Figures 2-4 may also be implemented as various embodiments of systems 101 and 100, and vice versa, mutatis mutandis.

[0056] Referring now to FIG. 2, there is shown a generalized flow diagram of mask inspection for a mask that can be used in the fabrication of a semiconductor specimen, in accordance with certain embodiments of the presently disclosed subject matter.

[0057] Multiple images, each representing a respective portion of the mask, may be acquired (202) (e.g., by PMC 102 via I / O interface 126, from mask inspection tool 120, or from storage unit 122). The images may be acquired by emulating the optical configuration of a lithography tool that may be used to fabricate the semiconductor specimen. In some embodiments, a region of interest (ROI) to be inspected on the mask may be predefined, and multiple images may be acquired of the ROI. For example, in some cases, the ROI may be defined as the entire mask, and in some other cases, the ROI may be defined as a portion of the mask.

[0058] In some embodiments, the image is acquired by an actinic mask inspection tool, such as, for example, an Aera Mask Inspection tool from Applied Materials Inc. As described above with reference to Figure 5, the actinic mask inspection tool is configured to emulate the optical configuration of a lithography tool (e.g., a scanner or stepper) used to manufacture semiconductor wafers according to the mask, among other things. The emulated optical configuration can include one or more of the illumination / exposure conditions, such as, for example, wavelength, pupil shape, numerical aperture (NA), etc.

[0059] The mask images acquired by such actinic inspection tools are expected to resemble images of wafers fabricated using the mask through a lithography tool, and are therefore also referred to as aerial images. In other words, actinic mask inspection tools are configured to capture mask images that can mimic how the design pattern in the mask will actually appear on a physical wafer after the manufacturing process.

[0060] In some cases, an actinic inspection tool may not be available to inspect the mask. In such cases, a non-actinic inspection tool, such as a conventional optical inspection tool, an electron beam tool, or the like, may be used to acquire a non-aerial image of the mask (referred to herein as a first image). A simulation may be performed on the acquired non-aerial image to simulate the optical configuration of the lithography tool, thereby generating an aerial image of the mask. Thus, in some embodiments, the mask inspection method described with reference to FIG. 2 may further include the preliminary steps of acquiring multiple first images acquired by a non-actinic inspection tool, and performing a simulation on the first images (e.g., by image processing module 104 of PMC 102 or by a processing module of mask inspection tool 120) to simulate the optical configuration of the lithography tool to generate multiple images (i.e., aerial images).

[0061] In some embodiments, during inspection, the mask can be moved in step sizes relative to a detector of the mask inspection tool during exposure (or the mask and tool can move in opposite directions), and the mask can be scanned step-by-step along a swath of the mask by the mask inspection tool, which images only a portion of the mask (within the swath) at a time. For example, at each step, light can be detected from a rectangular portion of the mask, and an image corresponding to the portion of the mask can be formed by converting such detected light into multiple intensity values ​​at multiple points on the portion. In one example, each image corresponding to a rectangular portion of the mask can be about 1000 pixels long and about 1000 pixels wide.

[0062] Thus, multiple images of the mask can be acquired sequentially while scanning sequentially along swaths of the mask, with each image representing a respective portion of the mask. For example, a first swath of the mask can be scanned from left to right to acquire a first set of images. Then, a second swath is scanned from right to left to acquire a second set of images, and so on until the entire mask has been scanned. The multiple sets of images constitute multiple images of the mask. In some cases, the multiple images can be acquired with a predefined step size such that the multiple fields of view (FOVs) of the multiple images do not overlap. In some other cases, the step size can be defined such that the FOVs of the multiple images partially overlap.

[0063] In some embodiments, the acquired images may be pre-processed before further processing, as described with reference to Figure 2. The pre-processing may include one or more of the following operations: interpolation (e.g., if the first image has a relatively low resolution), noise filtering, focus correction, aberration compensation, image format conversion, etc.

[0064] It should be noted that the present disclosure is not limited to a particular modality of mask inspection tool and / or the type of images acquired thereby and / or the pre-processing operations required to process the images.

[0065] A critical dimension (CD) map of the mask can be generated (204) (e.g., by PMC 102). The CD map includes multiple composite values ​​of CD measurements of the pattern of interest (POI), each derived from multiple images.

[0066] According to certain embodiments, the POI can be selected from a plurality of structural elements on the mask. As used herein, a structural element can refer to any original object / feature on the mask having a geometric shape or structure, possibly whose contours are combined / superimposed with other objects (thereby forming a pattern). Examples of structural elements can include, for example, general shape features such as contact points, lines, etc., and / or features having complex structures / shapes, and / or features combined with one or more other features. Thus, the POI can include one or more structural elements selected from a plurality of structural elements on the mask.

[0067] By way of example, the POIs may be selected based on one or more of the following factors: type and / or shape of one or more structural elements, user input regarding the importance of one or more structural elements with respect to the CDU, etc. In some cases, the POIs may be predetermined, and in some other cases, may be selected during inspection.

[0068] CD measurements can refer to any critical dimension measurement made on a POI, including, but not limited to, dimensions (e.g., line width, line spacing, contact diameter, feature size, edge roughness, gray level statistics, etc.), feature shapes, distances within or between elements, associated angles, overlay information associated with elements, corresponding to different design levels, etc. In some embodiments, the CD measurement can be selected depending on the particular inspection application.

[0069] Specifically, as described in more detail below, a composite value may be derived from each given image of the plurality of images according to the process described with reference to blocks 206-212.

[0070] A given image may be divided 206 into multiple sections (e.g., by the image processing module 104 of the PMC 102). In some embodiments, the given image may be divided into multiple sections according to a grid. The grid may be determined based on the dimensions and periodicity of the POIs. By way of example, the grid may be determined such that the size of each section can accommodate at least one POI. In some other embodiments, the given image may be divided unevenly, for example, according to different designs and functionality of the respective mask regions represented in the given image.

[0071] 6 illustrates an example of a given image and multiple sections divided within the given image, according to certain embodiments of the subject matter of this disclosure. As illustrated, image 600 refers to an image (aerial image) representing each portion of a mask (a logic mask in this example) acquired by a mask inspection tool. Image 610 illustrates multiple sections evenly divided according to a grid in image 600.

[0072] The POIs may be searched 208 in the multiple sections (e.g., by the image processing module 104 of the PMC 102) to produce a set of sections in each of which at least one of the POIs resides. In some embodiments, the POIs may be searched for by using a pattern matching algorithm against a reference image of the POI. In some cases, the reference image of the POI may be derived based on design data for the POI or may be provided / directed by a user.

[0073] As an example, for each section, a normalized cross-correlation against a reference image can be applied to each pixel of the section to identify the best matching pixel whose surrounding window best matches the reference image. The reference image and the identified surrounding window can be aligned and one subtracted from the other to produce a difference image. The difference image (or at least some of its pixel values) can be used to determine whether the window contains the same pattern as the POI.

[0074] Once a search has been performed on all of the sections in a given image, a set of sections identified by the presence of a POI (or at least one of the POIs) may be provided.

[0075] For each section of the set of sections, a value of the CD measurement for at least one POI may be obtained (210) using the printing threshold (e.g., by the measurement module 106 of the PMC 102) to produce a set of values ​​of the CD measurement corresponding to the set of sections.

[0076] Turning now to FIG. 3, an example generalized flow diagram for obtaining values ​​for CD measurements for each section is shown, in accordance with certain embodiments of the disclosed subject matter.

[0077] A printing threshold can be applied (302) to at least a portion of the section containing at least one POI to produce a binary image portion. The binary image portion provides information about structural elements / features of a corresponding portion of a mask that can be printed onto a semiconductor sample (e.g., a wafer). The printing threshold and its application will now be described with reference to FIG. 7.

[0078] Referring now to FIG. 7, a schematic diagram of a process for applying a printing threshold in accordance with certain embodiments of the presently disclosed subject matter is shown.

[0079] As shown, diagram 700 shows an exemplary (and simplified) mask that includes transparent regions 702 (e.g., made of quartz) that transmit light when illuminated, and opaque regions 704 (e.g., made of chrome) that block light. The resulting aerial images are images captured by a detector that collects transmitted light that passes through the mask.

[0080] In practice, the actual wafer fabrication process by a manufacturing tool (e.g., a scanner or stepper) involves a lithography process followed by a resist process and an etching process. The wafer is coated with photoresist, a light-sensitive material. Exposure hardens or softens portions of the resist, depending on the process. After exposure, the wafer is developed, dissolving the photoresist in certain areas depending on the amount of transmitted light (i.e., light intensity) that the area received during exposure.

[0081] As an example, waveform 705 is shown, representing the intensity of transmitted light. If the photoresist in a given area is exposed to less than a certain intensity of transmitted light, a pattern is printed on the wafer. These areas of photoresist, as well as areas without photoresist, reproduce the design pattern on the mask. The certain intensity is therefore known as the printing threshold 706, as illustrated in FIG. 7. The developed wafer is then exposed to a solvent that etches away silicon in portions of the wafer no longer protected by the photoresist coating, resulting in a printed wafer 708 (for a given layer).

[0082] Thus, in an actinic inspection tool that mimics the optical configuration of a wafer fabrication tool, waveform 705 represents the transmitted light captured by a detector of the actinic inspection tool to form a first image. In an actinic inspection tool, because the detector replaces the wafer and there are no actual resist and etch processes, to obtain an image that resembles a printed wafer, a print threshold 706 must be applied to the aerial image to mimic the effects of the resist and etch processes, resulting in a binary image that resembles the printed pattern on wafer 708. Specifically, the binary image provides information of multiple structural elements of a mask that can be printed on the wafer.

[0083] It should be noted that while in this example, patterns below the printing threshold are shown as printable on the wafer (i.e., positive resist), this is not necessarily the case. In some other cases, the reverse may be true, i.e., patterns above the printing threshold are printable on the wafer (i.e., negative resist). The present disclosure is not limited to a particular resist process for rendering printable features, nor to a particular application of the printing threshold.

[0084] Returning to FIG. 3, once the printing threshold is applied to at least a portion of the section, the derived binary image portion represents a printable structural element / feature of the corresponding portion of the mask (i.e., printable on the wafer). A CD measurement (304) can be performed on the binary image portion to obtain a value for the CD measurement. As an example, assume that the POI is a line structure and the CD measurement is to measure the width of the line. The line width can be obtained by measuring the distance between two edges of the line in the binary image portion.

[0085] According to certain embodiments, the CD measurements for at least one POI for each section can be obtained in alternative ways. Figure 4 shows a generalized flow diagram of another example of obtaining values ​​for CD measurements for each section according to certain embodiments of the subject matter of this disclosure.

[0086] As shown, a gray level (GL) profile of at least one POI can be derived from a section of the image (402). The GL profile indicates the pixel intensity distribution of the at least one POI. A printing threshold can be applied to the GL profile (404) to obtain two topo points. A topo point refers to a point on a signal profile or waveform (e.g., the GL profile) that is identified as corresponding to a specific location on a geometric structure of the mask. For example, the two resulting topo points can represent an estimated edge / boundary of the POI (e.g., the edge of a line structure). A CD measurement can be performed (406) based on the two topo points to obtain a CD value.

[0087] Referring now to FIG. 8, an exemplary image portion including at least one POI and a GL profile derived therefrom is shown, in accordance with certain embodiments of the subject matter of this disclosure.

[0088] In this example, assume that the POI is a line feature and the CD measurement of the POI is the line feature's width. Searching for POIs in multiple sections of a given image identifies a set of sections in which at least one POI is present. Image 802 shows an image portion within such a section that contains at least one POI (e.g., line feature 804). As shown, image 802 includes an image representation of multiple line features. For each line feature, the gray level intensity varies along a direction perpendicular to the line feature's longitudinal axis, representing the variation in the line's surface profile in that direction.

[0089] In some cases, an image patch in image 802 containing one POI can be optionally cropped and interpolated to obtain a relatively high-resolution interpolated patch 806. CD measurements can be made on the interpolated patch 806. By way of example, a GL profile 810 can be derived based on the interpolated patch, e.g., along a measurement vector 808 as illustrated.

[0090] As shown, a print threshold (e.g., 87.4 in this example) is applied to the GL profile 810, resulting in two topo points (marked by circles) on the GL profile. The two topo points represent the estimated edges / boundaries of the line features. By applying a print threshold (indicating a particular print intensity as described above with reference to FIG. 7) to the GL profile, topo points are obtained in the least sensitive regions of the GL profile (e.g., regions less sensitive to tool-energy drift), thereby enabling CD measurements to be obtained with greater accuracy.

[0091] A CD measurement can be made based on two topo points. For example, a line width can be obtained by measuring the distance 812 between the two topo points. In some cases, image 802 can include multiple POIs (e.g., multiple line features as shown in this example), and thus a CD measurement can be obtained for each (or at least some) of the multiple POIs. For example, the line width can be measured for all line features (or specific line features selected therefrom) as shown in image 802, and an averaged measurement can be obtained based on the multiple line widths.

[0092] It should be noted that the CD measurement implementations described with reference to Figures 3 and 4 are shown for illustrative purposes, and the present disclosure should not be limited to implementations utilizing printing thresholds and / or any other suitable alternative implementations.

[0093] 2, once the CD measurements have been performed and values ​​of the CD measurements have been obtained for each section of the set of sections, a set of values ​​of the CD measurements corresponding to the set of sections is obtained, as described with reference to block 210. The sets of values ​​may be combined (212) (e.g., by measurement module 106) into a composite value of CD measurements corresponding to the given image. By way of example, the sets of values ​​may be combined / aggregated by averaging (or weighted averaging) the sets of values, for example, based on a mean or median, or any other type of averaging calculation (with or without weighting).

[0094] Once a composite value of the CD measurements of the POI is derived for each given image of the plurality of images, a plurality of composite values ​​corresponding to the plurality of images is obtained. A critical dimension (CD) map of the mask can be generated that includes the plurality of composite values ​​of the CD measurements of the POI (204). Specifically, the plurality of composite values ​​are positioned in the CD map at locations that correspond to the locations of respective portions of the mask represented by the corresponding plurality of images of the mask.

[0095] The CD map generated as described above can indicate the CD uniformity of the mask relative to the CD measurements of the POI. Figure 9 shows an example of a CD map of a mask according to certain embodiments of the presently disclosed subject matter. As shown, there is a variance in gray levels between different regions of the CD map, indicating the variance in CD across the mask.

[0096] In some embodiments, the CD variance of the mask can be determined (214) based on the CD map (e.g., by the defect reporting module 108). The CD variance can be compared to a predetermined CDU threshold. If the CD variance passes the CDU threshold, the presence of a defect related to the CDU (also referred to as a CDU defect) can be reported. As an example, the CD variance can be calculated using a three-sigma method. For example, a CD histogram can be derived based on the CD map, and three sigma (e.g., three standard deviations from the population mean) indicating the CD variance can be extracted from the CD histogram. In some cases, the CDU threshold can be predetermined according to, for example, a particular inspection application, a type of CD measurement and / or POI, a technology node, and / or specifications used by a customer.

[0097] Optionally, in some embodiments, in response to the presence of a defect related to the CDU, a further determination can be made as to how to respond to the CDU defect, e.g., whether to accept the mask, repair the mask, or reject the mask. By way of example, this can be done by, for example, evaluating whether the CDU defect, when printed, will affect the functionality of a semiconductor sample manufactured using the mask. By way of example, the evaluation can include estimating a CD variation associated with the CDU defect when printed on a semiconductor sample. In some cases, possible processing actions in response to the presence of the CDU defect can include one or more of repairing the mask, defining the mask as a defective mask, defining the mask as functional, generating repair instructions for the mask, etc. For example, if these estimated CD variations are not acceptable, the mask can be sent to a mask factory for repair or rejected.

[0098] Additionally, in some embodiments, at least one of the following outputs / instructions, or any combination thereof, may be provided (e.g., by the defect reporting module 108 of the PMC 102): (i) providing qualification criteria for masks shipped from the mask factory, (ii) providing input to the mask generation process, (iii) providing input to the semiconductor sample fabrication process, (iv) providing input to simulation models used in the lithography process, (v) providing correction maps for the lithography tool, and (vi) identifying areas on the mask characterized by larger than expected CD variations.

[0099] In some embodiments, a user may be interested in estimating CDU for one or more CD measurements of a POI depending on the particular inspection application. For example, in the previous example where the POI is a line structure, CD measurements of interest based on the inspection application may include the line width and the distance between two adjacent lines. In such a case, the process described above with reference to FIG. 2 can be used to generate one or more CD maps corresponding to the one or more CD measurements of interest of the POI, each CD map including multiple composite values ​​of specific CD measurements from the one or more CD measurements derived from multiple images, respectively.

[0100] Specifically, one or more composite values ​​may be derived from each given image of the plurality of images by, for each section of the set of sections, obtaining one or more values ​​for one or more CD measurements to yield a set of one or more values ​​for the one or more CD measurements corresponding to the set of sections, and combining each set of one or more values ​​respectively into one or more composite values ​​corresponding to the given image.

[0101] Therefore, once one or more CD maps are generated, one or more CD variances for one or more CD measurements can be determined based on the one or more CD maps, respectively, and the presence of a CDU defect can be determined based on the respective CD variances for the respective CDU thresholds, respectively.

[0102] It should be noted that masks applicable to the inspection methods of the present disclosure can be any type of mask that may suffer from CDU defects of the type described herein, including, but not limited to, memory masks and / or logic masks, and / or ArF masks and / or EUV masks, etc. The present disclosure is not limited to any particular type or function of the mask inspected.

[0103] For purposes of illustration and explanation, certain embodiments and / or examples of the subject matter disclosed herein are described with respect to a particular POI as a line structure and its particular CD measurement value. This is not intended to limit the present disclosure in any way. It is understood that the proposed methods and systems may be applied to other types / shapes of POIs having particular CD measurements of interest. By way of example, if a POI is a contact point, the CD measurement value associated therewith may include one or more of the diameter of the contact point, the distance between different contact points, etc.

[0104] According to certain embodiments, the mask inspection processes described above with reference to Figures 2, 3, and 4 may be included as part of an inspection strategy usable by system 101 and / or inspection tool 120 for online mask inspection at runtime. Accordingly, the subject matter of this disclosure also includes systems and methods for generating an inspection strategy during a strategy-setting phase, where the strategy includes the steps described with reference to Figures 2, 3, and 4 (and various embodiments thereof). It should be noted that the term "inspection strategy" should be interpreted expansively to encompass any strategy that can be used by an inspection tool to perform operations related to any type of mask inspection, including the embodiments described above.

[0105] It should be noted that the examples provided in this disclosure, such as mask inspection tool architectures and configurations, mask types and / or layouts, illustrated POI and / or CD measurements, and particular manners of performing CD measurements as described above, are provided for illustrative purposes and should not be construed as limiting the disclosure in any way. Other suitable examples / implementations may be used in addition to or instead of the above.

[0106] Among the advantages of certain embodiments of the mask inspection process described herein are the ability to estimate the CD uniformity of a mask (or at least a portion thereof) and detect CDU-related defects (i.e., CDU defects) on the mask prior to mass production of wafers in a FAB.

[0107] Among the advantages of certain embodiments of the mask inspection process described herein is that the proposed inspection process does not rely on a known linear correlation between CD measurements and pixel intensities of the mask image, and therefore does not need to learn the correlation coefficient k, which is typically unknown and complex to learn because it varies with many factors, e.g., the pattern of interest, the type of resist, etc. The CD map derived using the proposed inspection process can directly represent the values ​​of the CD measurements.

[0108] Unlike conventional approaches that derive average pixel intensities over image sections and are therefore only applicable to memory masks where features are repeated within the averaging region and across the entire mask, the proposed inspection process searches for specific POIs within multiple sections of the image and derives actual CD measurements for the POIs within the detected sections, making it applicable to both logic and memory masks.

[0109] Among the advantages of certain embodiments of the mask inspection process described herein is that by applying a print threshold (indicating a particular print intensity) to an image portion that includes at least one POI (or applying the print threshold to the GL profile), measurements can be obtained in the least sensitive regions of the GL profile (e.g., regions that are less sensitive to tool energy drift), thereby obtaining CD measurements with improved sensitivity and accuracy.

[0110] It is to be understood that the present disclosure is not limited in its application to the details set forth in the description contained herein or shown in the drawings.

[0111] It will also be understood that a system according to the present disclosure may be implemented, at least in part, on a suitably programmed computer. Similarly, the present disclosure contemplates a computer program readable by a computer for performing the methods of the present disclosure. The present disclosure further contemplates a non-transitory computer-readable memory tangibly embodying a program of instructions executable by a computer for performing the methods of the present invention.

[0112] The present disclosure is capable of other embodiments and of being practiced and carried out in various ways. Accordingly, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. As such, those skilled in the art will appreciate that the conception underlying the present disclosure may readily be utilized as a basis for the designing of other structures, methods, and systems for carrying out some of the purposes of the subject matter of the present disclosure.

[0113] Those skilled in the art will readily appreciate that various modifications and changes can be made to the embodiments of the present disclosure, as described above, without departing from the scope of the present invention as defined in and by the appended claims. [Explanation of symbols]

[0114] 100 Mask Inspection System 101 System 102 PMC 104 Image Processing Module 106 Measurement Module 108 Defect Reporting Module 120 Mask Inspection Tools 122 Storage Unit 124 GUI 126 I / O interfaces 500 Actinic Inspection Tools 502 illumination source 504 Illumination optical system 506 Mask Holder 508 Projection optical system 510 detector 512 wafer holder 514 mask images 516 images 520 Lithography Tools 600 images 610 images 700 Figures 702 Transparent area 704 Opaque area 705 Waveform 706 Print Threshold 708 wafers 802 images 804 line structure 806 Interpolated Patches 808 measurement vectors 810 GL Profile 812 distance ADR Automated Defect Review Module CD Critical dimension CDU CD uniformity DOI Defect of Interest GL Gray Level PMC processing and memory circuits POI focus pattern ROI Region of Interest k correlation coefficient

Claims

1. 1. A computerized system for inspecting a mask usable in the manufacture of a semiconductor sample, the system comprising: acquiring a plurality of images, each representing a respective portion of the mask, the plurality of images being acquired with an actinic inspection tool that emulates an optical configuration of a lithography tool that can be used to manufacture the semiconductor sample, the plurality of images resembling an image of a semiconductor sample manufactured using the mask; a processing and memory circuit (PMC) configured to: generate a CD map of the mask representing direct critical dimension (CD) measurements from the plurality of images, the CD map including a plurality of composite values ​​of CD measurements of a pattern of interest (POI) respectively derived from the plurality of images; and Dividing a given image into multiple sections; searching for the POIs in the plurality of sections to generate a set of sections in each of which at least one of the POIs is present; obtaining, for each section of the set of sections, a value of the CD measurement for the at least one POI by applying a printing threshold usable to render a printable pattern on the semiconductor specimen to produce a set of values ​​of the CD measurement corresponding to the set of sections; and combining the set of values ​​into a composite value of the CD measurements corresponding to the given image; configured to derive a composite value from each said given image of said plurality of images by the CD map is used to determine the CD uniformity (CDU) of the mask with respect to the CD measurements of the POI; Computerized systems.

2. The computerized system of claim 1 , wherein the mask is a memory mask or a logic mask.

3. The computerized system of claim 1 , wherein the CD measurement is selected depending on the particular inspection application.

4. The computerized system of claim 1 , wherein the given image is divided into the plurality of sections according to a grid, the grid being determined based on a size and periodicity of the POI.

5. The computerized system of claim 1 , wherein the POI is searched for by using a pattern matching algorithm against a reference image of the POI.

6. 2. The computerized system of claim 1, wherein the PMC is configured to obtain the value of the CD measurement for each section by deriving a gray level (GL) profile of the at least one POI from the section, the GL profile indicating a pixel intensity distribution of the at least one POI, applying the printing threshold to the GL profile to obtain two topo points, and performing the CD measurement based on the two topo points to obtain the value thereof.

7. 2. The computerized system of claim 1, wherein the PMC is configured to obtain the value of the CD measurement for each section by applying the printing threshold to at least a portion of the section that includes the at least one POI to produce a binary image portion, and performing the CD measurement on the binary image portion to obtain the value thereof.

8. the PMC is configured to generate one or more CD maps corresponding to one or more CD measurements of the POI according to a particular inspection application, each CD map including a plurality of composite values ​​of a CD measurement of the one or more CD measurements respectively derived from the plurality of images; the PMC is configured to derive one or more composite values ​​from each given image of the plurality of images, including: for each section of the set of sections, obtaining one or more values ​​for the one or more CD measurements to yield a set of one or more values ​​for the one or more CD measurements corresponding to the set of sections; and combining each set of one or more values ​​into one or more composite values ​​corresponding to the given image, respectively; The computerized system of claim 1 .

9. 2. The computerized system of claim 1, wherein the PMC is further configured to determine a CD variance of the mask based on the CD map and report the presence of a CDU defect when the CD variance passes a CDU threshold.

10. 10. The computerized system of claim 9, wherein the PMC is further configured to determine whether to accept the mask, correct the mask, or reject the mask in response to the presence of the defect related to a CDU.

11. 1. A computerized method for inspecting a mask usable in the manufacture of a semiconductor sample, said method being performed by a processing and memory circuit (PMC), comprising: acquiring a plurality of images, each representing a respective portion of the mask, the plurality of images being acquired with an actinic inspection tool that emulates an optical configuration of a lithography tool that can be used to manufacture the semiconductor sample, and the plurality of images resemble images of a semiconductor sample manufactured using the mask; generating a critical dimension (CD) map of the mask representing direct CD measurements from the plurality of images, the CD map comprising a plurality of composite CD measurements of a pattern of interest (POI) respectively derived from the plurality of images; Dividing a given image into multiple sections; searching for the POIs in the plurality of sections to generate a set of sections in each of which at least one of the POIs is present; obtaining, for each section of the set of sections, a value of the CD measurement for the at least one POI by applying a printing threshold usable to render a printable pattern on the semiconductor specimen to produce a set of values ​​of the CD measurement corresponding to the set of sections; and deriving a composite value from each given image of the plurality of images by combining the set of values ​​with a composite value of the CD measurements corresponding to the given image; Including, the CD map is used to determine the CD uniformity (CDU) of the mask relative to the CD measurements of the POI; Computerized methods.

12. The computerized method of claim 11 , wherein the POI is located by using a pattern matching algorithm on a reference image of the POI.

13. 12. The computerized method of claim 11, wherein the obtaining the value of the CD measurement comprises: deriving a gray level (GL) profile of the at least one POI from the section, the GL profile indicating a pixel intensity distribution of the at least one POI; applying the printing threshold to the GL profile to obtain two topo points; and performing the CD measurement based on the two topo points to obtain the value thereof.

14. 14. The computerized method of claim 13, wherein the step of obtaining the value of the CD measurement comprises applying the print threshold to at least a portion of the section including the at least one POI to produce a binary image portion, and performing the CD measurement on the binary image portion to obtain the value thereof.

15. generating one or more CD maps corresponding to one or more CD measurements of the POI according to a particular inspection application, each CD map including a plurality of composite values ​​of a CD measurement of the one or more CD measurements respectively derived from the plurality of images; deriving one or more composite values ​​from each said given image of the plurality of images, comprising: for each section of the set of sections, obtaining one or more values ​​for the one or more CD measurements to yield a set of one or more values ​​for the one or more CD measurements corresponding to the set of sections; and combining each set of one or more values ​​respectively into one or more composite values ​​corresponding to the given image; 12. The computerized method of claim 11, comprising:

16. 1. A non-transitory computer-readable storage medium tangibly embodying a program of instructions that, when executed by a computer, causes the computer to perform a method of inspecting a mask usable in the manufacture of a semiconductor sample, the method comprising: acquiring a plurality of images, each representing a respective portion of the mask, the plurality of images being acquired with an actinic inspection tool that emulates an optical configuration of a lithography tool that can be used to manufacture the semiconductor sample, and the plurality of images resemble images of a semiconductor sample manufactured using the mask; generating a critical dimension (CD) map of the mask representing direct CD measurements from the plurality of images, the CD map comprising a plurality of composite CD measurements of a pattern of interest (POI) respectively derived from the plurality of images; Dividing a given image into multiple sections; searching for the POIs in the plurality of sections to generate a set of sections in each of which at least one of the POIs is present; obtaining, for each section of the set of sections, a value of the CD measurement for the at least one POI by applying a printing threshold usable to render a printable pattern on the semiconductor specimen to produce a set of values ​​of the CD measurement corresponding to the set of sections; and deriving a composite value from each given image of the plurality of images by combining the set of values ​​with a composite value of the CD measurements corresponding to the given image; Including, the CD map is used to determine the CD uniformity (CDU) of the mask relative to the CD measurements of the POI; A non-transitory computer-readable storage medium.

Images