Mask inspection for semiconductor sample manufacturing
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- APPL MATERIALS ISRAEL LTD
- Filing Date
- 2022-10-25
- Publication Date
- 2026-08-05
Smart Images
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Abstract
Description
Technical Field
[0001] The subject matter of the present disclosure generally relates to the field of mask inspection, and more particularly to critical dimension (CD) control related to photomasks.
Background Art
[0002] Current requirements for high density and high performance associated with the large-scale integration of manufactured microelectronic devices require submicron features, improved transistor and circuit speeds, and improved reliability. As semiconductor processes progress, pattern dimensions such as line widths, and other types of critical dimensions are constantly reduced. Such requirements necessitate the precise and uniform formation of device features, which requires careful monitoring of the manufacturing process, including automatically inspecting the device while it is still in the form of a semiconductor wafer.
[0003] Semiconductor devices are often manufactured using a photolithography mask (also referred to as a photomask or mask or reticle) in a photolithography process. The photolithography process is one of the main processes in the manufacture of semiconductor devices and involves patterning the surface of the wafer according to the circuit design of the semiconductor device to be manufactured. Such a circuit design is first patterned on a mask. Therefore, in order to obtain a functioning semiconductor device, the mask must be free of defects. Masks are manufactured by complex processes and can be subject to various defects and variations.
[0004] In addition, masks are often reused to create many dies on a wafer. Therefore, defects on the mask are repeated multiple times on the wafer, causing defects in multiple devices. To establish a process worth manufacturing, the entire lithography process must be strictly controlled, especially considering the increasing scale of circuit integration and the decreasing size of semiconductor devices. Within this process, CD control is a determinant of device performance and yield. In particular, masks and manufactured devices are becoming increasingly sensitive to variations in CD uniformity. If these variations are not corrected, the final device may not meet the desired performance, and in some cases, the final device may even malfunction, thus negatively impacting the yield.
[0005] Various mask inspection methods have been developed and are commercially available. According to certain prior art 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's features / patterns have been 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] Masks can be validated indirectly by verifying the accuracy and quality of printed features. However, because the final printed pattern on the wafer or die is formed after the printing process, such as resist development and substrate processing (material etching or deposition), 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 processes. Furthermore, inspection of the final printed pattern on the wafer or die tends to limit the number of usable samples provided to detect, judge, and resolve any processing issues. Also, this process can be labor-intensive, requiring considerable time for inspection and analysis. [Overview of the Initiative]
[0007] According to certain aspects of the subject matter of the present disclosure, a computerized system is provided for inspecting a mask usable for the manufacture of a semiconductor sample, the system comprising a processing and memory circuit (PMC) configured to acquire a plurality of images, each representing a respective part of the mask, the images being acquired by emulating the optical configuration of a lithography tool usable for the manufacture of a semiconductor sample, and to generate a limit dimension (CD) map of the mask containing a plurality of composite values of CD measurements of points of interest (POIs) derived from each of the plurality of images, wherein the PMC is configured to derive composite values from each given image of the plurality of images by dividing a given image into a plurality of sections, searching for POIs in the plurality of sections to produce a set of sections, each containing at least one POI, acquiring CD measurement values for at least one POI for each section of the set of sections using a print threshold to produce a set of CD measurement values corresponding to the set of sections, and combining the set of values with composite values of CD measurements corresponding to the given image, the CD map indicating the CD uniformity (CDU) of the mask with respect to the CD measurements of the POIs.
[0008] In addition to the features described above, the systems according to these embodiments of the subject matter of this disclosure may include one or more of the features (i) to (xi) listed below in any desired combination or permutation that is technically possible. (i) The mask is either a memory mask or a logic mask. (ii) Multiple images are acquired by a chemical beam inspection tool configured to emulate the optical configuration of the lithography tool. (iii) Multiple images are obtained by acquiring multiple first images using a non-chemical beam inspection tool, and then performing a simulation on the multiple first images to simulate the optical configuration of a lithography tool to produce multiple images. (iv) CD measurement is selected according to the specific testing application. (v) A given image is divided into multiple sections according to a grid, the grid being determined based on the dimensions and periodicity of the points of interest. (vi) POIs are found by using a pattern matching algorithm on a reference image of the POI. (vii) The PMC is configured to derive a gray level (GL) profile of at least one point of interest (POI) from a section, the GL profile showing the pixel intensity distribution of at least one POI, apply a printing threshold to the GL profile to obtain two topo-points, and obtain CD measurement values for each section by performing CD measurements based on the two topo-points and obtaining their values. (viii) The PMC is configured to obtain CD measurement values for each section by applying a print threshold to at least a portion of a section containing at least one POI to produce a binary image portion, and performing a CD measurement on the binary image portion to obtain its value. (ix) The PMC is configured to generate one or more CD maps corresponding to one or more CD measurements of a POI, depending on the specific inspection application, and each CD map contains a composite value of one or more CD measurements from one or more CD measurements derived from multiple images, respectively. The PMC is configured to derive one or more composite values from each given image of a plurality of images, including: obtaining one or more values for one or more CD measurements for each section of a set of sections to produce one or more sets of values for 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 a given image. (x) The PMC is further configured to determine the distribution of CDs in the mask based on the CD map, and to report the presence of defects with respect to CDUs if the distribution of CDs exceeds the CDU threshold. (xi) The PMC is further configured to decide whether to accept the mask, correct the mask, or reject the mask in response to the presence of defects in the CDU.
[0009] In other aspects of the subject matter of this disclosure, a method is provided for inspecting a mask usable for the manufacture of a semiconductor sample, the method comprising: an acquisition step, performed by a processing and memory circuit (PMC), which acquires a plurality of images, each representing a respective part of the mask, the images being acquired by emulating the optical configuration of a lithography tool usable for the manufacture of a semiconductor sample; and a generating step, which comprises dividing a given image into a plurality of sections, searching for POIs in the plurality of sections to produce a set of sections, each containing at least one POI, acquiring a CD measurement value for at least one POI for each section of the set of sections using a print threshold to produce a set of CD measurement values 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 into a composite value of CD measurements corresponding to the given image, the CD map indicating the CD uniformity (CDU) of the mask with respect to the CD measurements of the POIs.
[0010] This aspect of the disclosed subject matter may, with necessary modifications, include one or more of the features (i) to (xi) listed above with respect to the system in any desired combination or permutation that is technically possible.
[0011] In other aspects of the subject matter of this disclosure, a non-transient computer-readable medium is provided which, when executed by a computer, causes the computer to perform a method for inspecting a mask usable for the manufacture of a semiconductor sample, the method comprising: an acquisition step of acquiring a plurality of images, each representing a respective part of the mask, the images being acquired by emulating the optical configuration of a lithography tool usable for the manufacture of a semiconductor sample; and a generating step of generating a limit dimension (CD) map of the mask, which includes a plurality of composite values of CD measurements of points of interest (POIs) derived from each of the plurality of images, the CD map indicating the CD uniformity (CDU) of the mask with respect to the CD measurements of the POIs.
[0012] This aspect of the disclosed subject matter may, with necessary modifications, include one or more of the features (i) to (xi) listed above with respect to the system in any desired combination or permutation that is technically possible.
[0013] To understand this disclosure and how it may actually be put into practice, embodiments are described hereby with reference to the accompanying drawings, but only as non-limiting examples. [Brief explanation of the drawing]
[0014] [Figure 1] This is a functional block diagram of a mask inspection system according to a specific embodiment of the subject matter of this disclosure. [Figure 2]This is a generalized flowchart of mask inspection for masks usable in the manufacture of semiconductor samples, according to a particular embodiment of the subject matter of this disclosure. [Figure 3] This is a generalized flowchart of an example of obtaining CD measurement values for each section according to a particular embodiment of the subject matter of this disclosure. [Figure 4] This is a generalized flowchart of another example of obtaining CD measurement values for each section according to a particular embodiment of the subject matter of this disclosure. [Figure 5] This is a schematic diagram of a chemical beam inspection tool and a lithography tool according to a specific embodiment of the subject matter of this disclosure. [Figure 6] This figure schematically illustrates an example of a given image and multiple sections divided within a given image, according to a particular embodiment of the subject matter of this disclosure. [Figure 7] This is a schematic diagram of a process for applying a print threshold according to a particular embodiment of the subject matter of this disclosure. [Figure 8] This is an exemplary image portion, according to a particular embodiment of the subject matter of this disclosure, including at least one POI and a GL profile derived therefrom. [Figure 9] This figure shows an example of a CD map of a mask according to a specific embodiment of the subject matter of this disclosure. [Modes for carrying out the invention]
[0015] The following detailed description includes numerous specific details to provide a complete understanding of the disclosure. However, those skilled in the art will understand that the invention can be carried out without these specific details. In other instances, well-known methods, procedures, components, and circuits are not described in detail so as not to obscure the subject matter of the disclosure.
[0016] Unless otherwise specified, as will be apparent from the following description, throughout this specification, descriptions using terms such as "inspect", "acquire", "emulate", "apply", "generate", "derive", "split", "search", "combine", "acquire", "execute", "determine", "report", etc. refer to operations and / or processes of a computer that manipulate data and / or transform it into other data, where the data is represented as a physical quantity such as an electronic quantity and / or the data represents a physical object. The term "computer" should be construed expansively to include any type of hardware-based electronic device having data processing capabilities, including, by way of non-limiting example, the mask inspection system, mask CD uniformity (CDU) system, and their respective parts disclosed in this application.
[0017] The term "mask" as used in this specification is also referred to as "photolithography mask" or "photomask" or "reticle". Such terms should be construed equivalently and expansively to include a template that holds 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 can be implemented as a quartz glass plate covered with a pattern of opaque regions, transparent regions, and phase shift regions that are projected onto a wafer in a lithography process. By way of example, a mask can be an extreme ultraviolet (EUV) mask or an argon fluoride (ArF) mask. As another example, a mask can be a memory mask (usable for manufacturing a memory device) or a logic mask (usable for manufacturing a logic device).
[0018] As used herein, the terms “inspection” or “mask inspection” should be interpreted broadly to encompass any operations for evaluating the accuracy and integrity of a manufactured photomask, as well as its ability to produce an accurate representation of a circuit design on a wafer, with respect to circuit design. Inspection may include any type of operation relating to defect detection, defect review, and / or classification of various types of defects, as well as / or metrological operations during and / or after the mask manufacturing process, and / or while the mask is in use for semiconductor sample manufacturing. Inspection can be performed by using non-destructive testing tools after the mask has been manufactured. As a non-limiting example, the inspection process may include one or more of the following operations, namely, scanning (one or more scans), imaging, sampling, detection, measurement, classification, and / or other operations provided with respect to the mask or a portion thereof using inspection tools. Similarly, mask inspection may also be interpreted to include, for example, generating inspection strategies and / or other setting operations prior to the actual inspection of the mask. Unless otherwise noted, the term “inspection” or its derivatives as used herein is not limited in terms of the resolution or size of the inspection area. Various non-destructive testing tools include, but are not limited to, optical inspection tools, scanning electron microscopes, and atomic force microscopes.
[0019] The term "metrology operation" as used herein should be construed expansively to include any metrology operation procedure used to extract metrology information regarding one or more structural elements on a mask. In some embodiments, a metrology operation can include measurement operations such as critical dimension (CD) measurements performed on a particular structural element on a sample, which can include dimensions (e.g., line width, line pitch, contact diameter, element size, edge roughness, gray level statistics, etc.), element shape, distance within or between elements, associated angles, overlay information associated with elements corresponding to different design levels, etc., but is not limited thereto. Measurement results such as measurement images are analyzed, for example, by using image processing techniques. Note that unless otherwise specified, the term "metrology" or its derivatives used herein are not limited with respect to measurement technology, measurement resolution, or the size of the inspection area.
[0020] The term "sample" as used herein should be construed expansively to include any type of wafer, related structures, combinations thereof, and / or portions used to manufacture semiconductor integrated circuits, magnetic heads, flat panel displays, and other semiconductor manufactured articles.
[0021] The term "defect" as used herein should be construed expansively to include any type of abnormality or undesirable feature / function formed on a mask. A defect may, in some cases, refer to an actual defect or defect of interest (DOI) that has a specific impact on the function of the manufactured device when printed on a wafer, and thus detecting such a defect is to the customer's benefit. In some other cases, a defect may refer to a nuisance defect or "false alarm" defect that is a suspected defect that can be ignored because it does not affect the function of the completed device.
[0022] As used herein, the terms “non-transient memory” and “non-transient storage medium” should be interpreted more broadly to encompass any volatile or non-volatile computer memory suitable for the subject matter of this disclosure. These terms should be interpreted to include a single or multiple mediums that store one or more instruction sets (e.g., a centralized or distributed database, and / or associated caches and servers). These terms should also be interpreted to include any medium that stores or encodes a set of instructions for execution by a computer, causing a computer to execute one or more of the methodologies of this disclosure. Accordingly, these terms should be interpreted to include, but are not limited to, read-only memory ("ROM"), random-access memory ("RAM"), magnetic disk storage mediums, optical storage mediums, flash memory devices, and the like.
[0023] Unless otherwise specified, certain features of the subject matter of this disclosure described in the context of separate embodiments may also be provided in combination in a single embodiment. Conversely, various features of the subject matter of this disclosure described in the context of a single embodiment may also be provided separately or in any suitable subcombination. The following detailed description includes numerous specific details to provide a complete understanding of the methods and apparatus.
[0024] With this in mind, we will now focus on Figure 1, which shows a functional block diagram of a mask inspection system according to a particular embodiment of the subject matter of this disclosure.
[0025] The inspection system 100 shown in Figure 1 can be used to inspect a mask using a mask during or after the mask manufacturing process and / or during the semiconductor sample manufacturing process. As stated above, the inspections referred to herein can be interpreted as encompassing any type of operation related to defect inspection / detection, and / or various types of defect classification, and / or metrological operations relating to the mask or a part thereof, such as limit dimension (CD) measurement. According to certain embodiments of the subject matter of this disclosure, the illustrated inspection system 100 comprises a computer-based system 101 capable of automatically inspecting and detecting defects on the mask. Specifically, in some embodiments, the defects to be detected in this disclosure relate to the CD uniformity (CDU) of the mask. In such cases, the system 101 is configured to automatically monitor the CD uniformity of the mask and detect defects relating to the CDU when defects are present. The system 101 is also called the mask defect detection system, or more specifically, the mask CDU system, which is a subsystem of the inspection system 100.
[0026] System 101 can be operably connected to a mask inspection tool 120 configured to scan a mask and capture one or more images of the mask for inspection. The term “mask inspection tool” as used herein should be interpreted broadly to include, in non-limiting examples, any type of inspection tool that can be used in mask inspection-related processes, including scanning (one or more scans), imaging, sampling, detection, measurement, classification, and / or other processes provided with respect to a mask or part thereof.
[0027] Without limiting the scope of this disclosure, it should be noted that the mask inspection tool 120 may be implemented as various types of inspection machines, such as optical inspection tools and electron beam tools. In some cases, the 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, the 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, the mask inspection tool 120 may have metrological capabilities and be configured to perform metrological operations on the captured images. The obtained 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. This disclosure is not limited to the resolution of image data obtained from any particular type of mask inspection tool and / or inspection tool.
[0028] According to certain embodiments, the mask inspection tool can be implemented as a chemical beam inspection tool configured to emulate / mimic the optical configuration of a lithography tool (e.g., a scanner or stepper) usable for the manufacture of semiconductor samples, for example, by projecting a pattern formed on a mask onto a wafer, as will be described in more detail below with respect to Figure 5.
[0029] Referring now to Figure 5, schematic diagrams of chemical beam inspection tools and lithography tools according to specific embodiments of the subject matter of this disclosure are shown.
[0030] Similar to the lithography tool 520, the chemical beam inspection tool 500 may include an illumination source 502 configured to generate light of an exposure wavelength (e.g., a laser), an illumination optical system 504, a mask holder 506, and a projection optical system 508. The illumination optical system 504 and the projection optical system 508 may include one or more optical elements (e.g., lenses, apertures, spatial filters, etc.).
[0031] In the lithography tool 520, the mask is placed in the mask holder 506 and optically aligned to project an image of the circuit pattern to be replicated onto the wafer placed on the wafer holder 512 (for example, by using various stepping, scanning, and / or imaging techniques to generate or replicate the pattern on the wafer). Unlike the lithography tool 520, instead of placing the wafer holder 512, the chemical beam inspection tool 500 places a detector 510 (for example, a charge-coupled device (CCD)) in the position of the wafer holder, and the detector 510 is configured to detect the light projected through the mask and generate an image of the mask.
[0032] As can be seen from the figure, the chemical beam inspection tool 500 is configured to emulate the optical configuration of the lithography tool 520, including but not limited to illumination / exposure conditions such as wavelength, pupil shape, and numerical aperture (NA). Therefore, the mask image 514 acquired by the detector 510 is expected to be similar to the image 516 of the wafer manufactured using the mask via the lithography tool. The mask image acquired using such a chemical beam inspection tool is also called a spatial image. The spatial image is provided to the system 101 for further processing, as described below.
[0033] According to certain embodiments, the mask inspection tool 120 may be implemented as a non-chemical beam inspection tool, such as a conventional optical inspection tool or an electron beam tool (e.g., SEM). In such cases, the detector of the inspection tool interfaces with a specific type of microscope used, digitizes image information from the microscope, and thereby acquires an image of the mask.
[0034] The acquired images can be simulated to simulate the optical configuration of the lithography tool, thereby generating a spatial image. In some cases, the image simulation can be performed by system 101 (for example, the simulation function can be integrated into PMC102 by incorporating the image simulator into PMC102), and in some other cases, the image simulation can be performed by the processing module of the mask inspection tool 120, or by a separate simulation engine / unit operably connected to the mask inspection tool 120 and system 101.
[0035] System 101 includes a processor and memory circuit (PMC) 102 operably connected to a hardware-based I / O interface 126. The PMC 102 is configured to provide the processing necessary to operate the system, as further detailed with reference to Figures 2, 3, and 4, and comprises a processor (not shown separately) and memory (not shown separately). The processor of the PMC 102 can be configured to execute several functional modules according to computer-readable instructions implemented on non-transient computer-readable memory contained within the PMC. Such functional modules are hereafter referred to as being contained within the PMC.
[0036] The processors referred to herein may represent one or more general-purpose processing devices, such as microprocessors and central processing units. More specifically, a processor may be a composite instruction set computing (CISC) microprocessor, a reduced instruction set computing (RISC) microprocessor, a very long instruction word (VLIW) microprocessor, a processor implementing another instruction set, or a processor implementing a combination of instruction sets. A processor may also be one or more dedicated processing devices, such as an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), a digital signal processor (DSP), or a network processor. A processor is configured to execute instructions for performing the operations and steps described herein.
[0037] The memories referred to herein 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)), and static memory (e.g., flash memory, static random-access memory (SRAM)).
[0038] As described above, in some embodiments, the system 101 can be configured to detect defects related to CD uniformity on the mask. As used herein, the term “CD uniformity (CDU)” refers to the dispersion of CD measurements across the entire mask (or at least a portion thereof). Such CD dispersion can be caused by factors such as dispersion of laser energy, the material of the mask, or certain physical influences during the mask writing process, such as spatial writing errors of the mask manufacturing tool. Mask defects related to CDU, if not detected before mass production of wafers, can be repeated multiple times on production wafers, thus causing defects in multiple semiconductor devices (e.g., affecting the functionality of the devices and preventing them from meeting desired performance), and thus negatively impacting yield. Therefore, it is desirable that the CD dispersion 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 be used for that mask. However, this iterative process is extremely time-consuming due to the large number of parameter variables to consider and the complexity of their interactions. Furthermore, repeatedly using wafer manufacturing tools solely to optimize parameters unnecessarily reduces the time the tools could be used for their intended function, i.e., to manufacture integrated circuits.
[0040] An alternative method utilizes a linear correlation between CD measurements and the pixel intensity of the mask image. The variance of CD is measured indirectly by calculating the pixel intensity, for example, by averaging the gray-level intensity across a specific area of the image. However, the correlation coefficient (or transformation coefficient) k is typically unknown, as it varies with respect to many factors, such as the pattern of interest and the type of resist. Therefore, without knowing k, it is impossible to estimate the actual CD measurement based on the image intensity. Attempts have been made to learn the value of k, but this has proven to be complex and time-consuming given the number of variables involved. In addition, the above method averages pixel intensity over a relatively large image area, making it applicable only to memory masks where features are widely repeated across the entire mask.
[0041] Therefore, current inspection methods are insufficient to achieve desired CD control of masks, particularly with respect to the rapid development of advanced process and complex photomask features. According to certain embodiments of the subject matter of this disclosure, an improved mask inspection system and method are proposed, configured to automatically monitor the CD uniformity (CDU) of a mask and to detect defects relating to the CDU of the mask. The proposed method has been shown to improve accuracy and sensitivity for advanced CD control of mask features without affecting inspection throughput.
[0042] According to a particular embodiment, the functional modules included in the PMC102 of system 101 may include an image processing module 104, a measurement module 106, and a defect reporting module 108. The PMC102 can be configured to acquire multiple images via the I / O interface 126, each representing a different part (e.g., a portion) of the mask. The images can be acquired by emulating the optical configuration of a lithography tool usable for the fabrication of semiconductor samples. For example, the images can be acquired by a mask inspection tool 120, such as a chemical beam inspection tool.
[0043] The PMC102 can be further configured to generate a mask limit dimension (CD) map containing multiple composite values of CD measurements of a point of interest (POI). These composite values are derived from multiple images, respectively. Specifically, the PMC102 is configured to derive composite values from each given image of multiple images, as described below.
[0044] The image processing module 104 can be configured to divide a given image into multiple sections, search for points of interest (POIs) in the multiple sections, and generate a set of sections in which each section contains at least one POI.
[0045] The measurement module 106 can be configured to obtain a CD measurement value for at least one POI for each section of a set of sections using a print threshold, thereby producing a set of CD measurement values corresponding to the set of sections. The measurement module 106 is further configured to combine the set of values into a composite value of CD measurements corresponding to a given image.
[0046] The resulting CD map shows the CD uniformity of the mask with respect to the CD measurement of the POI. Optionally, the defect reporting module 108 can be configured to report the presence of a defect with respect to CDU if the CD variance shown by the CD map passes a CDU threshold (e.g., it exceeds the threshold in some cases but falls below it in some other cases). Optionally, the defect reporting module 108 can be further configured to determine how to respond to detected defects, for example, whether to accept the mask, repair the mask, or reject the mask.
[0047] The operation of systems 100, 101, PMC102, and their internal functional modules will be described in further detail with reference to Figures 2, 3, and 4.
[0048] According to a particular embodiment, system 100 may include a storage unit 122. The storage unit 122 may be configured to store any data required by the 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. For example, the storage unit 122 may be configured to store images and / or derivatives thereof generated by the mask inspection tool 120 (e.g., pre-processed images). Thus, the images can be retrieved from the storage unit 122 and provided to the PMC 102 for further processing.
[0049] In some embodiments, system 100 may optionally include a computer-based graphical user interface (GUI) 124 configured to allow user-specified input related to system 101. For example, the user may be presented with a visual representation of the mask, including an image of the mask or a part thereof (e.g., by a display forming part of the GUI 124). The user may be provided with the option to define certain operational parameters through the GUI, such as POI, print threshold, CD variation threshold, etc. In some cases, the user may also be able to 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 the mask via the I / O interface 126. The images may include image data (and / or derivatives thereof) generated by the mask inspection tool 120, as well as / or image data stored in the storage unit 122 or one or more data storage locations. In some cases, the 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 steps. Note that in some cases, the images may include associated numerical data (e.g., meter data, hand-crafted attributes, etc.). Further note that the image data is related to the target layer of the semiconductor device to be printed on the wafer.
[0051] The system 101 is further configured to process the received image and send the results (e.g., CD map, detected defects) via the I / O interface 126 to the storage unit 122 and / or the GUI 124 for rendering and / or the mask inspection tool 120.
[0052] In some embodiments, in addition to system 101, the mask inspection system 100 may further comprise one or more inspection modules, such as an additional defect detection module and / or an automated defect review module (ADR) and / or an automated defect classification module (ADC) and / or a metrology-related module and / or other inspection modules that can be used to perform additional inspections of the mask. One or more inspection modules may be implemented as standalone computers, or the functions (or at least part thereof) of the inspection modules may be integrated with the mask inspection tool 120. In some embodiments, the output obtained from system 101 may be used by the mask inspection tool 120 and / or one or more inspection modules (or part thereof) for further inspection of the mask.
[0053] Those skilled in the art will readily understand that the teachings of the subject matter of this disclosure are not constrained by the system shown in Figure 1, and that equivalent and / or modified functions can be integrated or separated in other ways and implemented in any suitable combination of software and firmware and / or hardware.
[0054] It should be noted that the mask inspection system shown in Figure 1 can be implemented in a distributed computing environment in which the aforementioned functional modules included in the PMC102 can be distributed across several local and / or remote devices and linked via a communication network. In other embodiments, it should be further noted that one or more of the mask inspection tool 120, storage unit 122, and / or GUI 124 may be outside the system 100 and may operate in data communication with the system 101 via the I / O interface 126. The system 101 may be implemented as a standalone computer used in conjunction with the mask inspection tool. Alternatively, each function of the system 101 can be integrated with the mask inspection tool 120, at least in part, thereby facilitating and enhancing the functionality of the mask inspection tool 120 in inspection-related processes.
[0055] While not always the case, the operational processes of systems 101 and 100 can correspond to some or all of the steps of the methods described with respect to Figures 2 to 4. Similarly, the methods described with respect to Figures 2 to 4 and their possible embodiments can be implemented by systems 101 and 100. Therefore, it should be noted that embodiments discussed in relation to the methods described with respect to Figures 2 to 4 can be implemented as various embodiments of systems 101 and 100 with necessary modifications, and vice versa.
[0056] Referring now to Figure 2, a generalized flowchart of mask inspection for use in the manufacture of semiconductor samples, according to a particular embodiment of the subject matter of this disclosure, is shown.
[0057] Multiple images representing different parts of the mask can be acquired (for example, by the PMC 102 via the I / O interface 126 from the mask inspection tool 120 or from the storage unit 122) (202). The images can be acquired by emulating the optical configuration of a lithography tool usable for the fabrication of semiconductor samples. In some embodiments, a region of interest (ROI) to be inspected on the mask can be predefined, and multiple images can be acquired for the ROI. For example, in some cases the ROI can be defined as the entire mask, and in some other cases the ROI can be defined as part of the mask.
[0058] In some embodiments, images are acquired by a chemical beam mask inspection tool, such as the Aera Mask Inspection tool from Applied Materials Inc. As described above with reference to Figure 5, the chemical beam mask inspection tool is configured, in particular, to emulate the optical configuration of a lithography tool (e.g., a scanner or stepper) used in the manufacture of semiconductor wafers according to the mask. The emulated optical configuration may include one or more of the illumination / exposure conditions, such as wavelength, pupil shape, and numerical aperture (NA).
[0059] The mask images acquired by such chemical beam inspection tools are expected to resemble the images of wafers manufactured using the masks via lithography tools, and are therefore also called spatial images. In other words, chemical beam mask inspection tools are configured to capture mask images that can mimic how the design patterns within the mask will actually appear on the physical wafer after the manufacturing process.
[0060] In some cases, a chemical beam inspection tool may not be available to inspect the mask. In such cases, a non-chemical beam inspection tool, such as a conventional optical inspection tool or an electron beam tool, can be used to obtain a non-spatial image of the mask (referred to herein as the first image). To simulate the optical configuration of the lithography tool, a simulation can be performed on the acquired non-spatial image, thereby generating a spatial image of the mask. Thus, in some embodiments, the mask inspection method described with reference to Figure 2 may further include a preliminary step of acquiring a plurality of first images acquired by a non-chemical beam inspection tool, and a preliminary step of performing a simulation on the first images (for example, by the image processing module 104 of the PMC 102, or by the processing module of the mask inspection tool 120, etc.) to simulate the optical configuration of the lithography tool and generate a plurality of images (i.e., spatial images).
[0061] In some embodiments, during inspection, the mask can be moved in step sizes relative to the 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 the swath of the mask by the mask inspection tool, and the mask inspection tool 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 a portion of the mask is formed by converting such detected light into multiple intensity values at multiple points in that portion. In one example, each image corresponding to a rectangular portion of the mask may have a length of approximately 1000 pixels and a width of approximately 1000 pixels.
[0062] Therefore, multiple images of the mask can be acquired sequentially while scanning along the swath of the mask, with each image representing a part / part of the mask. For example, the first swath of the mask can be scanned from left to right to acquire the first set of images. Then, the second swath is scanned from right to left to obtain the second set of images, and so on, until the entire mask has been scanned. Multiple sets of images constitute multiple images of the mask. In some cases, multiple images can be acquired in a predefined step size such that the multiple fields of view (FOV) of the multiple images do not overlap. In some other cases, the step size can be defined so that the FOVs of the multiple images partially overlap.
[0063] In some embodiments, the acquired images may be preprocessed before further processing, as described with reference to Figure 2. Preprocessing may include one or more operations such as interpolation (for example, if the first image has a relatively low resolution), noise filtering, focus correction, aberration compensation, and image format conversion.
[0064] Please note that this disclosure is not limited to the specific modality of the mask inspection tool, and / or the type of image obtained thereby, and / or the preprocessing operations required to process the image.
[0065] A limit dimension (CD) map of the mask can be generated (for example, by PMC102) (204). The CD map contains multiple composite values of CD measurements of the point of interest (POI), each of which is derived from multiple images.
[0066] According to certain embodiments, a POI can be selected from a plurality of structural elements on the mask. As used herein, structural elements may refer to any original object / feature on the mask having a geometric shape or geometric structure (therefore forming a pattern), where the contour is combined / overlaid with other objects, as may be in some cases. Examples of structural elements may include common shape features such as contact points and lines, and / or features having complex structures / shapes, and / or features that are combinations of one or more other features. Thus, a POI can include one or more structural elements selected from a plurality of structural elements on the mask.
[0067] For example, a Point of Interest (POI) can be selected based on one or more of the following factors: the 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 POI may be predetermined, and in some other cases, it may be selected during inspection.
[0068] CD measurement can refer to any limit dimensional measurement performed on a POI, including but not limited to dimensions (e.g., line width, line spacing, contact diameter, element size, edge roughness, gray level statistics, etc.), element shape, distance within or between elements, relevant angles, and overlay information associated with the element, corresponding to different design levels. In some embodiments, CD measurement can be selected depending on the specific inspection application.
[0069] Specifically, as detailed below, a composite value can be derived from each given image of multiple images by following the process described with reference to blocks 206-212.
[0070] A given image can be divided into multiple sections (for example, by the image processing module 104 of the PMC102) (206). In some embodiments, a given image can be divided into multiple sections according to a grid. The grid is determined based on the dimensions and periodicity of the points of interest (POIs). For example, the grid can be determined such that the size of each section can accommodate at least one POI. In some other embodiments, a given image can be divided unevenly, for example, according to the different designs and functionalities of each mask region represented in the given image.
[0071] Figure 6 shows an example of a given image and multiple sections divided within the given image, according to a particular embodiment of the subject matter of this disclosure. As shown, Image 600 refers to an image (spatial image) representing each part of a mask (a logic mask in this example) acquired by a mask inspection tool. Image 610 shows multiple sections evenly divided according to a grid in Image 600.
[0072] Points of Interest (POIs) can be searched in multiple sections (for example, by the image processing module 104 of the PMC102) (208), resulting in a set of sections, each containing at least one POI. In some embodiments, POIs can be searched by using a pattern matching algorithm on a reference image of the POI. In some cases, the reference image of the POI can be derived based on the design data of the POI or can be provided / instructed by the user.
[0073] For example, for each section, a normalized cross-correlation with respect to a reference image can be applied to each pixel in the section to identify the optimal matching pixel that has the surrounding window that best matches the reference image. The reference image and the identified surrounding window can be aligned, and one can be subtracted from the other to generate 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 Point of Interest (POI).
[0074] When a search is performed on all of the multiple sections within a given image, a set of sections may be provided that are identified by the presence of a Point of Interest (POI) (or at least one of a POI).
[0075] For each section in the set of sections, a print threshold can be used to obtain a CD measurement value for at least one POI (210) (e.g., by the measurement module 106 of the PMC102) to produce a set of CD measurement values corresponding to the set of sections.
[0076] Now, looking at Figure 3, we see a generalized flowchart of an example of obtaining CD measurement values for each section according to a particular embodiment of the subject matter of this disclosure.
[0077] A print threshold can be applied to at least a portion of a section containing at least one point of interest (POI) (302) to produce a binary image portion. The binary image portion provides information about the structural elements / features of the corresponding portion of the mask that can be printed on a semiconductor sample (e.g., a wafer). Next, with reference to Figure 7, the print threshold and its application will be described.
[0078] Referring now to Figure 7, a schematic diagram shows the process of applying a print threshold according to a particular embodiment of the subject matter of this disclosure.
[0079] As illustrated, Figure 700 shows an exemplary (and simplified) mask including a transparent region 702 (e.g., made of quartz) that transmits light when illuminated and an opaque region 704 (e.g., made of chromium) that blocks light. The multiple images (spatial images) obtained in this manner are images captured by a detector that focuses the transmitted light that has passed through the mask.
[0080] In practice, the actual wafer manufacturing process using manufacturing tools (e.g., scanners or steppers) includes a lithography process followed by a resist process and an etching process. The wafer is coated with a photoresist, which is a photosensitive material. Exposure hardens or softens parts of the resist, depending on the process. After exposure, the wafer is developed, dissolving the photoresist in specific areas depending on the amount of transmitted light (i.e., light intensity) received by the area during exposure.
[0081] As an example, a waveform 705 representing the intensity of transmitted light is shown. When a given region of photoresist is exposed to a transmitted light intensity below a certain level, a pattern is printed on the wafer. These regions of photoresist and regions without photoresist reproduce the design pattern on the mask. Thus, the specific intensity is known as the printing threshold 706, as illustrated in Figure 7. The developed wafer is then exposed to a solvent that etches away the silicon in the portions of the wafer that are no longer protected by the photoresist coating, resulting in a printed wafer 708 (for a given layer).
[0082] Therefore, in a chemical beam inspection tool that mimics the optical configuration of a wafer manufacturing tool, the waveform 705 represents transmitted light captured by the detector of the chemical beam inspection tool to form a first image. In the chemical beam inspection tool, the detector replaces the wafer, and there is no actual resist and etching process. Therefore, in order to obtain an image similar to that of a printed wafer, it is necessary to apply a printing threshold 706 to the spatial image to mimic the effects of the resist and etching process, thereby producing a binary image similar to the printed pattern on the wafer 708. Specifically, the binary image provides information about multiple structural elements of a mask that can be printed on the wafer.
[0083] In this example, patterns below the print threshold are shown as printable on the wafer (i.e., positive resist), but it should be noted that this is not necessarily the case. In some other cases, the opposite may be true, i.e., patterns above the print threshold are printable on the wafer (i.e., negative resist). This disclosure is not limited to any particular resist process for rendering printable features, nor to any particular application of the print threshold.
[0084] Returning to Figure 3, once the print threshold is applied to at least a portion of the section, the derived binary image portion represents the printable (i.e., printable on the wafer) structural elements / features of the corresponding portion of the mask. A CD measurement can be performed on the binary image portion (304) to obtain the CD measurement value. As an example, assume that the POI is a line structure and the CD measurement is measuring the width of the line. The line width can be obtained in the binary image portion by measuring the distance between two edges of the line.
[0085] According to a particular embodiment, CD measurements for at least one POI for each section can be obtained in an alternative manner. Figure 4 shows a generalized flowchart of another example of obtaining CD measurement values for each section according to a particular embodiment of the subject matter of this disclosure.
[0086] As shown in the figure, a gray-level (GL) profile of at least one point of interest (POI) can be derived from a section of the image (402). The GL profile shows the pixel intensity distribution of at least one POI. By applying a printing threshold to the GL profile (404), two topo points can be obtained. A topo point refers to a point on the signal profile or waveform (e.g., the GL profile) that is identified as corresponding to a specific location on the geometric structure of the mask. For example, the two obtained topo points may represent the estimated edges / boundaries of the POI (e.g., edges of the linear structure). A CD measurement can be performed based on the two topo points (406) and its value can be obtained.
[0087] Referring now to Figure 8, an exemplary image portion is shown that includes at least one POI and a GL profile derived therefrom, according to a particular embodiment of the subject matter of this disclosure.
[0088] In this example, we assume that the points of interest (POIs) are linear structures, and the CD measurement of the POI is the width of the linear structure. Searching for POIs in multiple sections of a given image identifies a set of sections in which at least one POI exists. Image 802 shows a portion of the image within such a section containing at least one POI (e.g., linear structure 804). As illustrated, Image 802 contains image representations of multiple linear structures. For each linear structure, the gray level intensity varies along a direction perpendicular to the longitudinal axis of the linear structure, representing the change in the surface profile of the line in that direction.
[0089] In some cases, an image patch within image 802 containing a single POI can be optionally cropped and interpolated to obtain an interpolated patch 806 with relatively high resolution. CD measurements can then be performed on the interpolated patch 806. For example, a GL profile 810 can be derived based on the interpolated patch, along a measurement vector 808, for example, as illustrated.
[0090] As illustrated, a print threshold (e.g., 87.4 in this example) is applied to the GL profile 810, creating two topo points (marked by circles) on the GL profile. The two topo points represent the estimated edges / boundaries of the linear structure. By applying a print threshold (showing the specific print intensity as described above, see Figure 7) to the GL profile, topo points are obtained in the least sensitive region of the GL profile (e.g., a region less sensitive to tool-energy drift), thereby enabling the acquisition of CD measurements with higher accuracy.
[0091] CD measurements can be performed based on two topo points. For example, line width can be obtained by measuring the distance 812 between two topo points. In some cases, image 802 may contain multiple points of interest (e.g., multiple line structures as shown in this example), so CD measurements can be obtained for each (or at least some of) of the multiple POIs. For example, line width can be measured for all line structures (or specific line structures selected from them) as shown in image 802, and an averaged measurement can be obtained based on multiple line widths.
[0092] It should be noted that the embodiments of CD measurement described with reference to Figures 3 and 4 are shown for illustrative purposes only. This disclosure should not be limited to embodiments utilizing a printed threshold and / or any other suitable alternative embodiments.
[0093] Referring back to the description of Figure 2, once the CD measurement is performed and the CD measurement values are obtained for each section of the set of sections, a set of CD measurement values corresponding to the set of sections is obtained, as described with reference to block 210. The set of values can be combined (212) by combining the CD measurement values corresponding to a given image (e.g., by the measurement module 106). For example, the set of values can be combined / aggregated by averaging (or weighted averaging) the set of values based on, for example, the mean or median, or any other type of averaging calculation (with or without weights).
[0094] When a composite value of the CD measurement of the POI is derived for each of the multiple images, multiple composite values corresponding to the multiple images are obtained. A limit dimension (CD) map of the mask can be generated that includes multiple composite values of the CD measurement of the POI (204). Specifically, in the CD map, the multiple composite values are placed at positions corresponding to the positions of each part of the mask represented by the corresponding multiple images of the mask.
[0095] As described above, the generated CD map can demonstrate the CD uniformity of the mask with respect to the CD measurement of the POI. Figure 9 shows an example of a CD map of a mask according to a particular embodiment of the subject matter of this disclosure. As shown, there is a gray level of dispersion between different regions of the CD map, indicating the dispersion of CD in the mask.
[0096] In some embodiments, the CD variance of a mask can be determined based on a CD map (e.g., by defect reporting module 108) (214). The CD variance can be compared to a predetermined CDU threshold. If the CD variance exceeds the CDU threshold, the presence of a defect with respect to CDU (also called a CDU defect) can be reported. As an example, the CD variance can be calculated using the 3-sigma method. For example, a CD histogram can be derived based on a CD map, and 3 sigma (e.g., 3 standard deviations of the population mean) representing the CD variance can be extracted from the CD histogram. In some cases, the CDU threshold can be predetermined according to, for example, a specific inspection application, type of CD measurement and / or POI, technology node, and / or specifications used by the customer.
[0097] Optionally, in some embodiments, in response to the presence of a defect relating to a CDU, it may be further determined how to respond to the CDU defect, for example, whether to accept the mask, repair the mask, or reject the mask. For example, this can be done by evaluating whether the CDU defect, once printed, would affect the functionality of a semiconductor sample manufactured using that mask. For example, the evaluation could include estimating the CD variation associated with the CDU defect when printed on a semiconductor sample. In some cases, possible processing operations in response to the presence of a CDU defect may include one or more of the following: repairing the mask, defining the mask as a defective mask, defining the mask as functional, or generating instructions to repair the mask. For example, if these estimated CD variations are unacceptable, the mask can be sent to a mask factory for repair or rejection.
[0098] Furthermore, in some embodiments, at least one of the following outputs / instructions, or any combination thereof, can be provided (e.g., by the defect reporting module 108 of the PMC102): namely, (i) providing qualification criteria for masks shipped from the mask factory; (ii) providing input to the mask production process; (iii) providing input to the semiconductor sample manufacturing process; (iv) providing input to a simulation model used in the lithography process; (v) providing a correction map for lithography tools; and (vi) identifying areas on the mask characterized by CD variability larger than expected.
[0099] In some embodiments, the user may be interested in estimating the CDD for one or more CD measurements of a POI, depending on a specific inspection application. For example, in the previous example where the POI is a linear structure, the CD measurements of interest based on the inspection application may include the line width and the distance between two adjacent lines. In such cases, one or more CD maps corresponding to the one or more CD measurements of interest of the POI can be generated using the process described above with reference to Figure 2, and each CD map contains a composite value of a particular CD measurement from one or more CD measurements derived from multiple images, respectively.
[0100] Specifically, one or more composite values can be derived from each given image of a plurality of images by taking one or more values for one or more CD measurements for each section of a set of sections to produce one or more sets of values for one or more CD measurements corresponding to the set of sections, and then combining each set of one or more values into one or more composite values corresponding to a given image.
[0101] Therefore, once one or more CD maps are generated, the variance of one or more CDs for one or more CD measurements can be determined based on the one or more CD maps, and the presence of CDU defects can be determined based on the variance of each CD for each CDU threshold.
[0102] It should be noted that the masks applicable to the inspection methods of this disclosure may be any type of mask that may be susceptible to 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. This disclosure is not limited to any particular type or function of the mask being inspected.
[0103] For illustrative and illustrative purposes, specific embodiments and / or examples of the subject matter disclosed herein are described with respect to specific points of interest (POIs) as linear structures and their specific CD measurements. This is not intended to limit the disclosure in any way. It is understood that the proposed methods and systems may be applicable to other types / shapes of POIs having specific CD measurements of interest. For example, if a POI is a contact point, the CD measurements associated with it 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 process described above with reference to Figures 2, 3, and 4 can be included as part of an inspection strategy available at runtime by System 101 and / or Inspection Tool 120 for online mask inspection. Thus, the subject matter of this disclosure also includes a system and method for generating an inspection strategy during the strategy setting stage, the strategy including the steps described with reference to Figures 2, 3, and 4 (and their various embodiments). It should be noted that the term “inspection strategy” should be interpreted broadly to include 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] For example, the examples shown in this disclosure, such as the mask inspection tool architecture and configuration, mask types and / or layouts, the illustrated POI and / or CD measurements, and the specific ways in which CD measurements are performed as described above, are provided for illustrative purposes only and should not be considered to limit this disclosure. In addition to or instead of the above, other suitable examples / embodiments may be used.
[0106] Among the advantages of certain embodiments of the mask inspection process described herein is the ability to estimate the CD uniformity of a mask (or at least a portion thereof) and to detect defects relating to CDU on the mask (i.e., CDU defects) before mass production of wafers in a FAB.
[0107] Among the advantages of the specific 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 the pixel intensity of the mask image, and therefore does not require learning the correlation coefficient k, which is typically unknown and complex to learn because the correlation coefficient k changes with respect to many factors, such as the pattern of interest and the type of resist. The CD map derived using the proposed inspection process can directly represent the CD measurement values.
[0108] Unlike conventional methods that derive average pixel intensity across 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 points of interest (POIs) within multiple sections of an 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 specific print intensity) to the image portion containing at least one POI (or applying a print threshold to its GL profile), measurements can be obtained in the least sensitive region of the GL profile (e.g., a region less sensitive to tool energy drift), thereby obtaining CD measurements with improved sensitivity and accuracy.
[0110] This disclosure should be understood to be limited in its application to the details contained herein or described in the drawings.
[0111] It will also be understood that the systems described herein may be implemented, at least in part, on a properly programmed computer. Similarly, this disclosure envisions a computer program readable by a computer to perform the methods described herein. This disclosure further envisions a non-transient computer-readable memory that explicitly embodies a program of computer-executable instructions for performing the methods of the present invention.
[0112] This disclosure is capable of other embodiments and can be implemented and carried out in various ways. Therefore, it should be understood that the terms and technical descriptions used herein are for illustrative purposes only and should not be considered limiting. Accordingly, those skilled in the art will recognize that the underlying concepts of this disclosure can be readily used as a basis for designing other structures, methods, and systems to accomplish some of the objectives of the subject matter of this disclosure.
[0113] Those skilled in the art will readily understand that, as described above, various modifications and changes can be applied to embodiments of this disclosure without departing from the scope of the invention as defined by the appended claims. [Explanation of Symbols]
[0114] 100 Mask Inspection System 101 System 102 PMC 104 Image Processing Module 106 Measurement Modules 108 Defect Reporting Module 120 Mask Inspection Tools 122 storage units 124 GUI 126 I / O interfaces 500 Chemical Ray Inspection Tools 502 illumination source 504 Illumination optical system 506 Mask Holder 508 Projection optical system 510 detector 512 Wafer Holder 514 Masked Images 516 images 520 Lithography Tools 600 images 610 images Figure 700 702 Transparent area 704 Opaque area 705 Waveform 706 Print threshold 708 wafer 802 images 804 line structure 806 Interpolated Patches 808 Measurement vector 810 GL Profile 812 distance ADR Automated Defect Review Module CD limit dimensions CDU CD uniformity DOI - Focus on defects GL Gray Level PMC processing and memory circuits Point of Interest (POI) - Patterns to Focus On ROI Focus Area k-correlation coefficient
Claims
1. A computerized system for inspecting masks usable in the manufacture of semiconductor samples, wherein the system Multiple images are obtained, each representing a different part of the mask; these multiple images are obtained by a chemical beam inspection tool; the optical configuration of a lithography tool usable for manufacturing the semiconductor sample is emulated; and the multiple images are similar to the image of the semiconductor sample manufactured using the mask. A processing and memory circuit (PMC) is configured to generate a CD map of the mask representing direct limit dimension (CD) measurements from the plurality of images, wherein the CD map includes a plurality of composite values of CD measurements of points of interest (POIs) derived from each of the plurality of images, and the PMC is configured to generate a CD map of the mask representing direct limit dimension (CD) measurements from CD map includes a plurality of composite values of CD measurements of points of interest (POIs) derived from each of the plurality of images, Dividing a given image into multiple sections, Search the POI in the aforementioned multiple sections to generate a set of sections in which at least one of the POI exists, For each section of the set of sections, a print threshold usable for rendering a printable pattern on the semiconductor sample is applied to obtain the CD measurement value for at least one POI, thereby generating a set of CD measurement values corresponding to the set of sections, and The set of values is combined with the composite value of the CD measurement values corresponding to the given image. It is configured to derive a composite value from each of the given images of the plurality of images, The CD map is used to determine the CD uniformity (CDU) of the mask with respect to the CD measurement value of the POI. A computerized system.
2. The computerized system according to claim 1, wherein the mask is a memory mask or a logic mask.
3. The computerized system according to claim 1, wherein the given image is divided into a plurality of sections according to a grid, and the grid is determined based on the dimensions and periodicity of the POI.
4. The computerized system according to claim 1, wherein the POI is searched by using a pattern matching algorithm on a reference image of the POI.
5. The computerized system according to claim 1, wherein the PMC is configured to derive a gray level (GL) profile of the at least one POI from the section, the GL profile showing the pixel intensity distribution of the at least one POI, apply the printing threshold to the GL profile to obtain two topo points, and perform the CD measurement based on the two topo points to obtain the value thereof, thereby obtaining the value of the CD measurement for each section.
6. The computerized system according to claim 1, wherein the PMC is configured to obtain the CD measurement values for each section by 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.
7. The PMC is configured to generate one or more CD maps corresponding to one or more CD measurements of the POI according to a specific inspection application, and each CD map includes a composite value of one or more CD measurements from the one or more CD measurements derived from the plurality of images. The PMC is configured to derive one or more composite values from each of the given images of the plurality of images, including: obtaining one or more values for one or more CD measurements for each section of the set of sections to produce a set of one or more values for one or more CD measurements corresponding to the set of sections; and combining each set of one or more values with one or more composite values corresponding to the given image. The computerized system according to claim 1.
8. The computerized system according to claim 1, wherein the PMC is further configured to determine the distribution of CDs in the mask based on the CD map, and to report the presence of defects relating to CDUs when the distribution of CDs exceeds a CDU threshold.
9. The computerized system according to claim 8, 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 relating to the CDU.
10. A computerized method for inspecting masks usable in the manufacture of semiconductor samples, wherein the method is performed by a processing and memory circuit (PMC), A step of acquiring a plurality of images, each representing a respective part of the mask, wherein the plurality of images are acquired by a chemical beam inspection tool, emulate the optical configuration of a lithography tool usable for the manufacture of the semiconductor sample, and the plurality of images are similar to images of a semiconductor sample manufactured using the mask. A step of generating a CD map of the mask representing direct limit dimension (CD) measurements from the plurality of images, wherein the CD map includes a plurality of composite values of CD measurements of the pattern of interest (POI) derived from each of the plurality of images, Dividing a given image into multiple sections, Search the POI in the aforementioned multiple sections to generate a set of sections in which at least one of the POI exists, For each section of the set of sections, a print threshold usable for rendering a printable pattern on the semiconductor sample is applied to obtain the CD measurement value for at least one POI, thereby generating a set of CD measurement values corresponding to the set of sections, and A generating step includes combining the set of values with a composite value of the CD measurement values corresponding to the given image, thereby deriving a composite value from each of the given images of the plurality of images, Includes, The CD map is used to determine the CD uniformity (CDU) of the mask with respect to the CD measurement value of the POI. A computerized method.
11. The computerized method according to claim 10, wherein the POI is retrieved by using a pattern matching algorithm on a reference image of the POI.
12. The computerized method according to claim 10, wherein the step of obtaining the value of the CD measurement includes the steps of deriving a gray level (GL) profile of the at least one POI from the section such that the GL profile shows the 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.
13. The computerized method according to claim 12, wherein the step of obtaining the value of the CD measurement includes the step of 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.
14. A step of generating one or more CD maps corresponding to one or more CD measurement values of the POI according to a specific inspection application, wherein each CD map includes a composite value of one of the CD measurement values among the one or more CD measurement values derived from the plurality of images, A generating step that includes deriving one or more composite values from each of the given images of the plurality of images, which includes, for each section of the set of sections, obtaining one or more values for one or more CD measurements to produce a set of one or more values for one or more CD measurements corresponding to the set of sections, and combining each set of one or more values to one or more composite values corresponding to a given image, The computerized method according to claim 10, including the method described in claim 10.
15. A non-transient computer-readable storage medium that, when executed by a computer, explicitly embodies a program of instructions causing the computer to perform a method for inspecting a mask usable for the manufacture of a semiconductor sample, wherein the method A step of acquiring a plurality of images, each representing a respective part of the mask, wherein the plurality of images are acquired by a chemical beam inspection tool, emulate the optical configuration of a lithography tool usable for the manufacture of the semiconductor sample, and the plurality of images are similar to images of a semiconductor sample manufactured using the mask. A step of generating a CD map of the mask representing direct limit dimension (CD) measurements from the plurality of images, wherein the CD map includes a plurality of composite values of CD measurements of the pattern of interest (POI) derived from each of the plurality of images, Dividing a given image into multiple sections, Search the POI in the aforementioned multiple sections to generate a set of sections in which at least one of the POI exists, For each section of the set of sections, a print threshold usable for rendering a printable pattern on the semiconductor sample is applied to obtain the CD measurement value for at least one POI, thereby generating a set of CD measurement values corresponding to the set of sections, and A generating step includes combining the set of values with a composite value of the CD measurement values corresponding to the given image, thereby deriving a composite value from each of the given images of the plurality of images, Includes, The CD map is used to determine the CD uniformity (CDU) of the mask with respect to the CD measurement value of the POI. Non-transient computer-readable storage medium.
Citation Information
Patent Citations
A system and method for providing printability analysis of mask defects.
JP2005500671A