Robust image-to-design alignment for DRAM

Abstract

This invention provides a method and system for alignment in semiconductor applications. The method includes determining multiple different design-to-alignment offsets by individually aligning images generated by an imaging subsystem to rendering images of alignment targets using different alignment methods for each instance of an alignment target formed on a sample. The method also includes identifying multiple instances where the difference between the different design-to-alignment offsets falls below a predetermined threshold. Furthermore, the method includes determining a runtime design-to-alignment offset of the alignment target from the design-to-alignment offsets determined only for the identified instances. This runtime design-to-alignment offset can then be used in processes performed on the sample using the imaging subsystem.

Description

[Technical Field]

[0001] The present invention generally relates to alignment for semiconductor applications. Particular embodiments relate to methods and systems for determining an offset for use in a process performed on a sample. [Background Art]

[0002] Integrated circuit (IC) designs may be developed using methods or systems such as electronic design automation (EDA), computer-aided design (CAD), and other IC design software. Such methods and systems may be used to generate a circuit pattern database from the IC design. The circuit pattern database includes data representing a plurality of layouts for various layers of the IC. Data in the circuit pattern database may be used to determine layouts for a plurality of reticles. A reticle layout generally includes a plurality of polygons that define characteristics of the pattern on the reticle. Each reticle is used to fabricate one of the various layers of an IC. The layers of an IC may include, for example, junction patterns in a semiconductor substrate, gate dielectric patterns, gate electrode patterns, contact patterns in interlayer dielectric films, and interconnection patterns on wiring layers.

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

[0004] Inspection processes are used at various steps in semiconductor manufacturing processes to detect defects on wafers, thereby increasing the yield of the manufacturing process and, consequently, profitability. Inspection has always been a crucial part of manufacturing semiconductor devices such as ICs. However, as design rules shrink, semiconductor manufacturing processes may operate near the limits of their performance capabilities. Furthermore, as design rules shrink, smaller defects can affect the electrical parameters of the device, which necessitates more sensitive inspection. Consequently, as design rules shrink, the population of potentially yield-related defects detected by inspection increases dramatically, as does the population of news (false information) defects detected by inspection.

[0005] Inspection systems and methods are increasingly designed to focus on the relationship between defects and designs, as it is the impact on the sample design that determines whether and how important a defect is. For example, several methods have been developed for aligning inspection coordinates with design coordinates. One such method relies on the accuracy of coordinate registration to the design in the inspection system. Another such method involves performing post-processing alignment on the inspection image patch and associated design clips.

[0006] Several methods currently in use perform patch-to-design alignment (PDA) to align sample images with a design. During setup, currently used methods may scan the sample to locate alignment targets and obtain the design for each target. Such methods may then render images from the design at each target and align the rendered images with the sample image at each target. For example, currently used methods may use an alignment method during PDA setup to calculate the PDA offset between the optical image of the PDA target and the design-rendered image. The currently used methods may then store the targets and offsets in a database for runtime inspection. The runtime PDA process can be performed in any suitable way. For example, during PDA runtime, the setup PDA target image and the runtime PDA target image may be aligned with each other.

[0007] While currently used PDA methods have proven useful in many applications, such methods and systems have several drawbacks. For example, some memory devices may have a limited number of suitable alignment targets for use with PDAs (or any alignment method). More specifically, a significant number of patterned features formed on such devices are not unique enough to be used for alignment. The relatively limited number of available alignment targets on such devices means that successful alignment can only be achieved if a significant majority of the alignment targets produce accurate results. For example, some alignment methods aggregate the alignment results of multiple alignment targets to produce a more robust alignment offset for at least a portion of the device. When the number of initially available alignment targets is relatively limited, the success of the alignment method may be more sensitive to the individual alignment results of each alignment target instance. In other words, if even a relatively limited number of alignment target instances produce inaccurate alignment results, the aggregated results may also be inaccurate. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] International Publication No. 2021 / 067203 [Overview of the project] [Problems that the invention aims to solve]

[0009] Therefore, it would be advantageous to develop a system and method for determining an offset for use in a process performed on a sample that does not have one or more of the aforementioned drawbacks. [Means for solving the problem]

[0010] The following descriptions relating to various embodiments should not be construed in any way as limiting the subject matter of the attached claims.

[0011] One embodiment relates to a system configured to determine offsets for use in a process performed on a sample. The system includes an imaging subsystem configured to generate an image of the sample. The system also includes a computer subsystem configured to determine first and second align-to-design offsets for multiple instances of an alignment target by individually aligning images of multiple instances of the alignment target, generated by the imaging subsystem and formed on the sample, to rendering images of the alignment target using first and second alignment methods, respectively. The computer subsystem is also configured to identify multiple instances in which the difference between the first and second align-to-design offsets falls below a predetermined threshold. In addition, the computer subsystem is configured to determine a runtime align-to-design offset of the alignment target from the first and second align-to-design offsets determined only for the identified multiple instances. The computer subsystem is further configured to store the runtime align-to-design offsets for use in a process performed on the sample using the imaging subsystem. The system may be further configured as described herein.

[0012] Another embodiment relates to a computer-implemented method for determining offsets for use in a process performed on a sample. This method includes determining first and second design-to-alignment offsets for multiple instances of an alignment target by individually aligning images of multiple instances of the alignment target formed on the sample by an imaging subsystem to rendering images of the alignment target using first and second alignment methods, respectively. This method also includes the steps of identifying, determining runtime design-to-alignment offsets, and saving. The steps of this method are performed by a computer system.

[0013] Each step of this method may be carried out as further described herein. This method may include any other step of any other method described herein. This method may be carried out by any system described herein.

[0014] An additional embodiment relates to a non-temporary computer-readable medium for storing program instructions for executing on a computer system a computer implementation method for determining an offset for use in a process performed on a sample. The computer implementation method includes the steps of the present method described above. The computer-readable medium may be further configured as described herein. The steps of the computer implementation method may be executed as described herein. In addition, a computer implementation method on which program instructions can be executed may include any other steps of any other method described herein. [Brief explanation of the drawing]

[0015] Further advantages of the present invention will become apparent to those skilled in the art by reading the following detailed description of preferred embodiments and referring to the accompanying drawings. [Figure 1]This is a schematic diagram showing a side view of an embodiment of the system configured as described herein. [Figure 2] This is a schematic diagram showing a side view of an embodiment of the system configured as described herein. [Figure 3] This flowchart shows the steps that can be performed by the systems and methods currently in use. [Figure 4] This flowchart shows the steps that may be performed by embodiments described herein. [Figure 5] This is a schematic plan view showing an example of a different block that may be included in the dynamic random access memory (DRAM) device portion of the sample. [Figure 6] Examples of images of different parts of a DRAM device containing a structure that can be used as an alignment target in embodiments described herein include examples of X and Y mean projection plots for said structure. [Figure 7] Examples of images of different parts of a DRAM device containing a structure that can be used as an alignment target in embodiments described herein include examples of X and Y mean projection plots for said structure. [Figure 8] Examples of images of different parts of a DRAM device containing a structure that can be used as an alignment target in embodiments described herein include examples of X and Y mean projection plots for said structure. [Figure 9]This block diagram shows one embodiment of a non-temporary computer-readable medium for storing program instructions for executing the computer implementation method described herein on a computer system. While various modifications and alternative forms of the present invention are possible, the drawings illustrate a specific embodiment, which is described in detail herein. The drawings may not necessarily be drawn to a consistent scale. However, it should be understood that the drawings and their detailed descriptions are not intended to limit the invention to any particular form disclosed, but rather to cover all modifications, equivalents, and alternatives that fall within the spirit and scope of the invention as defined by the appended claims. [Modes for carrying out the invention]

[0016] As used interchangeably herein, the terms "design", "design data", and "design information" generally refer to the physical design (layout) of an IC or other semiconductor device, and data derived from the physical design through complex simulation or simple geometric and Boolean operations. The design may include any other design data or design data proxies described in U.S. Patent No. 7,570,796 issued to Zafar et al. on August 4, 2009, and U.S. Patent No. 7,676,077 issued to Kulkarni et al. on March 9, 2010, both of which are incorporated by reference herein as if fully set forth herein. In addition, the design data can be standard cell library data, integrated layout data, design data for one or more layers, derivatives of design data, and full or partial chip design data. Furthermore, "design", "design data", and "design information" described herein refer to information and data generated by a semiconductor device designer in the design process, and are thus available for use in the embodiments described herein well before the design is printed on any physical sample such as a reticle or a wafer.

[0017] As used herein, the terms "first" and "second" are not intended to carry any implication other than indicating different items (e.g., different offsets, different alignment methods, etc.).

[0018] Turning to the drawings, it should be noted that the figures are not drawn to scale. In particular, the scale of some elements in the figures is greatly exaggerated to emphasize the features of the elements. It should also be noted that the figures are not drawn to the same scale. Elements that may be similarly configured and appear in multiple figures are indicated with the same reference numerals. Unless otherwise specified herein, any and all elements described and illustrated may include any suitable commercially available elements.

[0019] One embodiment relates to a system configured to determine an offset for use in a process performed on a specimen. The offset determined by the embodiments described herein can be used for applications such as alignment of an IC design to an optical (or other) image. The embodiments described herein are particularly suitable for patch-to-design (PDA) alignment for semiconductor applications such as dynamic random access memory (DRAM) inspection.

[0020] In some embodiments, the specimen is a wafer. The wafer may include any wafer known in the semiconductor art. Although some embodiments are described herein with reference to a wafer, the embodiments are not limited to the specimens on which they may be used. For example, the embodiments described herein can be used for specimens such as reticles, flat panels, personal computer (PC) boards, and other semiconductor specimens.

[0021] The system includes an imaging subsystem configured to generate an image of the specimen. Generally, the imaging subsystem includes at least an energy source and a detector. The energy source is configured to generate energy that is directed toward the specimen. The detector is configured to detect energy from the specimen and generate an output in response to the detected energy.

[0022] In one embodiment, the imaging subsystem is an optical imaging subsystem. For example, as shown in Figure 1, the imaging subsystem 10 includes an illumination subsystem configured to direct light onto a sample 14. The illumination subsystem includes at least one light source (e.g., light source 16). The illumination subsystem is configured to direct light onto the sample at one or more angles of incidence, which may include one or more oblique angles and / or one or more perpendicular angles. For example, as shown in Figure 1, light from the light source 16 is directed through an optical element 18, then a lens 20, to a beam splitter 21, which directs light onto the sample 14 at a perpendicular angle of incidence. The angles of incidence may include any appropriate angles of incidence that vary depending on, for example, the characteristics of the sample, defects to be detected on the sample, measurements to be performed on the sample, etc.

[0023] The illumination subsystem may be configured to direct light onto the sample at different angles of incidence at different times. For example, the imaging subsystem may be configured to direct light onto the sample at different angles of incidence than those shown in Figure 1 by modifying one or more properties of one or more elements of the illumination subsystem. In such an example, the imaging subsystem may be configured to direct light onto the sample at different angles of incidence by moving the light source 16, optical element 18, and lens 20.

[0024] In some cases, the imaging subsystem may be configured to direct light onto the sample at multiple incident angles simultaneously. For example, the imaging subsystem may include multiple illumination channels, one of which may include a light source 16, an optical element 18, and a lens 20 as shown in Figure 1, and another illumination channel (not shown) may include similar elements (which may be different or the same) or at least a light source and, optionally, one or more other components as further described herein. When such light is directed onto the sample simultaneously with other light, one or more properties (e.g., wavelength, polarization, etc.) of the light directed onto the sample at different incident angles may be different so that the light resulting from the illumination of the sample at different incident angles can be distinguished from one another in the detector.

[0025] In another example, the illumination subsystem may include only one light source (e.g., light source 16 shown in Figure 1), and the light from the light source may be separated into different optical paths (e.g., based on wavelength, polarization, etc.) by one or more optical elements (not shown) of the illumination subsystem. The light from each different optical path may then be directed onto the sample. Multiple illumination channels may be configured to direct light onto the sample simultaneously or at different times (e.g., if different illumination channels are used to sequentially illuminate the sample). In another example, the same illumination channel may be configured to direct light with different characteristics onto the sample at different times. For example, optical element 18 may be configured as a spectral filter, and the characteristics of the spectral filter may be changed in various ways (e.g., by changing the spectral filter) to direct light of different wavelengths onto the sample at different times. The illumination subsystem may have any other suitable configuration known in the art for directing light with different or the same characteristics onto the sample sequentially or simultaneously, at different or the same angle of incidence.

[0026] Light source 16 may include a broadband plasma (BBP) light source. Thus, the light produced by the light source and directed towards the sample may include broadband light. However, the light source may include any other suitable light source, such as any suitable laser configured to produce light of any suitable wavelength known in the art. The laser may be configured to produce monochromatic or quasi-monochromatic light. Thus, the laser may be a narrowband laser. The light source may also include a polychromatic light source that produces light at multiple discrete wavelengths or wavelength bands.

[0027] Light from the optical element 18 can be focused to the beam splitter 21 by the lens 20. Although the lens 20 is shown as a single refractive optical element in Figure 1, in practice the lens 20 may include multiple refractive and / or reflective optical elements that combine light from the optical elements and focus it onto the sample. The illumination subsystem shown in Figure 1 and described herein may include any other suitable optical elements (not shown). Examples of such optical elements include, but are not limited to, polarization components, spectral filters, spatial filters, reflective optical elements, apodizers, beam splitters, apertures, etc., and may include any such suitable optical elements known in the art. In addition, the system may be configured to modify one or more elements of the illumination subsystem based on the type of illumination used for inspection, measurement, etc.

[0028] The imaging subsystem may also include a scanning subsystem configured to scan light over a sample. For example, the imaging subsystem may include a stage 22 on which the sample 14 is placed during inspection or measurement. The scanning subsystem may include any suitable mechanical and / or robotic assembly (including the stage 22) that can be configured to move the sample so that light can scan over it. In addition, or alternatively, the imaging subsystem may be configured so that one or more optical elements of the imaging subsystem perform the scanning of light over the sample. The light can scan over the sample in any suitable manner.

[0029] The imaging subsystem includes one or more detection channels. At least one of the detection channels includes a detector configured to detect light from a sample resulting from illumination of the sample by the imaging subsystem and to generate an output in response to the detected light. For example, the imaging subsystem shown in Figure 1 includes two detection channels: one formed by collector 24, element 26, and detector 28, and another formed by collector 30, element 32, and detector 34. As shown in Figure 1, the two detection channels are configured to collect and detect light at different collection angles. In some cases, one detection channel is configured to detect specularly reflected light, and the other detection channel is configured to detect light that is not specularly reflected from the sample (e.g., scattered light, diffracted light, etc.). However, two or more detection channels may be configured to detect the same type of light from the sample (e.g., specularly reflected light). Although Figure 1 shows an imaging subsystem with two detection channels, the imaging subsystem may include a different number of detection channels (e.g., one or three or more). Although Figure 1 shows each collector as a single refractive optical element, each collector may contain one or more refractive optical elements and / or one or more reflective optical elements.

[0030] One or more detection channels may include any suitable detector known in the art, such as photomultiplier tubes (PMTs), charge-coupled devices (CCDs), and time-delay integral (TDI) cameras. Detectors may also include non-imaging detectors or imaging detectors. If the detectors are non-imaging detectors, each detector may be configured to detect certain properties of light, such as intensity, but not necessarily as a function of position in the imaging plane. Thus, the output produced by each detector included in each detection channel may be a signal or data, but not necessarily an image signal or image data. In such cases, a computer subsystem, such as the system's computer subsystem 36, may be configured to generate an image of the sample from the non-imaging output of the detectors. However, in other cases, the detectors may be configured as imaging detectors configured to generate an image signal or image data. Thus, the system may be configured to produce the outputs and / or images described herein in many ways.

[0031] Figure 1 is provided to generally illustrate the configuration of an imaging subsystem that may be included in the embodiments of the system described herein. Obviously, the configuration of the imaging subsystem described herein can be modified to optimize the system's performance, as is commonly done when designing commercially available inspection, measurement, and other systems. In addition, the systems described herein can be implemented using existing inspection or measurement systems, such as the 29xx and 39xx series tools, the SpectraShape family of tools, and the Archer series of tools, which are commercially available from KLA Corporation in Milpitas, California (for example, by adding the functions described herein to an existing inspection or measurement system). For some such systems, the embodiments described herein may be offered as optional features of the system (for example, in addition to other functions of the system). Alternatively, the imaging subsystem described herein can be designed "from scratch" to provide an entirely new system.

[0032] The system's computer subsystem 36 may be coupled to the detector of the imaging subsystem in any suitable manner (e.g., via one or more transmission media, which may include wired and / or wireless transmission media) so that the computer subsystem can receive the output generated by the detector during scanning. The computer subsystem 36 may be configured to perform a number of functions using the detector output described herein, and further to perform any other functions described herein. This computer subsystem may be further configured as described herein.

[0033] This computer subsystem (and other computer subsystems described herein) may also be referred to herein as a computer system. Each computer subsystem or system described herein may take various forms, including personal computer systems, image computers, mainframe computer systems, workstations, network appliances, internet appliances, or other devices. Generally, the term “computer system” may be broadly defined to encompass any device having one or more processors that execute instructions from a memory medium. A computer subsystem or system may also include any suitable processor known in the art, such as a parallel processor. In addition, a computer subsystem or system may include a computer platform with high-speed processing and software, either as a standalone or networked tool.

[0034] If the system includes multiple computer subsystems (not shown), different computer subsystems can be coupled to one another so that images, data, information, instructions, etc., can be transmitted between them. For example, computer subsystem 36 can be coupled to other computer subsystems by any suitable transmission medium, which may include any suitable wired and / or wireless transmission medium known in the art. Two or more such computer subsystems can also be effectively coupled by a shared computer-readable storage medium (not shown).

[0035] Although the imaging subsystem is described above as an optical or light-based subsystem, in another embodiment the imaging subsystem is an electron beam imaging subsystem. In one such embodiment shown in Figure 2, the imaging subsystem includes an electron column 122 coupled to a computer subsystem 124.

[0036] As shown in Figure 2, the electron column includes an electron beam source 126 configured to generate electrons focused onto a sample 128 by one or more elements 130. The electron beam source may include, for example, a cathode source or an emitter tip, and the one or more elements 130 may include, for example, a gun lens, an anode, a beam limiting aperture, a gate valve, a beam current selecting aperture, an objective lens, and a scanning subsystem, any of which may include any suitable elements known in the art.

[0037] Electrons returned from the sample (e.g., secondary electrons) can be focused onto the detector 134 by one or more elements 132. One or more elements 132 may include a scanning subsystem that is, for example, the same as the scanning subsystem included in element 130.

[0038] The electronic column may include any other suitable elements known in the art. In addition, the electronic column may be further configured as described in U.S. Patent No. 8,664,594 issued to Jiang et al. on April 4, 2014, No. 8,692,204 issued to Kojima et al. on April 8, 2014, No. 8,698,093 issued to Gubbens et al. on April 15, 2014, and No. 8,716,662 issued to MacDonald et al. on May 6, 2014 (these are incorporated by reference as if they were fully described herein).

[0039] In Figure 2, an electron column is shown configured such that electrons are directed at the sample at an oblique angle of incidence and collected from the sample at another oblique angle; however, the electron beam may be directed at the sample at any suitable angle and collected from the sample. In addition, the electron beam subsystem may be configured to generate images of the sample using multiple modes (e.g., different illumination angles, collection angles, etc.). The multiple modes of the electron beam subsystem may differ in any image generation parameters of the subsystem.

[0040] The computer subsystem 124 may be coupled to the detector 134 as described above. The detector may detect electrons returned from the surface of the sample, thereby forming an electron beam image of the sample. The computer subsystem 124 may be configured to use the electron beam image to perform any of the functions described herein. The computer subsystem 124 may be configured to perform any additional steps described herein. The system including the imaging subsystem shown in Figure 2 may be further configured as described herein.

[0041] Figure 2 is provided to illustrate in general terms the configuration of an electron beam-based imaging subsystem that may be included in the embodiments described herein. Similar to the optical subsystem described above, the configuration of the electron beam subsystem may be modified to optimize the subsystem's performance, as is typically done when designing commercially available inspection or measurement systems. In addition, the systems described herein may be implemented using existing inspection, measurement, or other systems, such as tools commercially available from KLA (e.g., by adding the functions described herein to an existing system). For some such systems, the embodiments described herein may be offered as optional features of the system (e.g., in addition to other functions of the system). Alternatively, the systems described herein may be designed "from scratch" to provide a completely new system.

[0042] Although the imaging subsystem has been described above as an optical or electron beam-based subsystem, the imaging subsystem may also be an ion beam-based subsystem. Such an imaging subsystem may be configured as shown in Figure 2, except that the electron beam source is replaced with any suitable ion beam source known in the art. Thus, in one embodiment, the energy directed to the sample includes ions. In addition, the imaging subsystem may be any other suitable ion beam-based imaging subsystem, such as those included in commercially available focused ion beam (FIB) systems, helium ion microscope (HIM) systems, and secondary ion mass spectrometry (SIMS) systems.

[0043] The imaging subsystem described herein may be configured to generate output from a sample in multiple modes. Generally, a “mode” is defined by the value of a parameter of the imaging subsystem used to generate an image of the sample. Thus, modes may differ in the value of at least one parameter of the imaging subsystem (other than the position on the sample where the output is generated). For example, in an optical subsystem, different modes may use light of different wavelengths for illumination. Modes may differ in illumination wavelength for different modes, as further described herein (e.g., by using different light sources, different spectral filters, etc.). In another embodiment, different modes may use different illumination channels of the imaging subsystem. For example, as described above, the imaging subsystem may include multiple illumination channels. Thus, different illumination channels may be used for different modes. Modes may differ in one or more modifiable parameters of the imaging subsystem (e.g., illumination polarization, angle, wavelength, etc.; detection polarization, angle, wavelength, etc.).

[0044] Similarly, the output generated by the electron beam subsystem may include the output generated by the electron beam subsystem using two or more different values ​​of the electron beam subsystem's parameters. Multiple modes of the electron beam subsystem may be defined by the values ​​of the electron beam subsystem's parameters used to generate the output of the sample. Thus, different modes may differ in at least one value of the electron beam parameters of the electron beam subsystem. For example, in one embodiment of the electron beam subsystem, different modes may use different incident angles for illumination.

[0045] Embodiments of imaging subsystems described herein may be configured for inspection, measurement, defect review, or other quality control-related processes performed on samples. For example, embodiments of imaging subsystems described herein and shown in Figures 1 and 2 may be modified in one or more parameters to provide different imaging capabilities depending on the application in which they are used. In such an example, the imaging subsystem shown in Figure 1 may be configured to have a higher resolution when used for defect review or measurement rather than inspection. In other words, embodiments of imaging subsystems shown in Figures 1 and 2 illustrate several common and diverse configurations of imaging subsystems that can be adjusted in many ways that will be apparent to those skilled in the art in order to produce imaging subsystems with different imaging capabilities that are more or less suitable for different applications.

[0046] As described above, the optical, electron, and ion beam subsystems are configured to scan energy (e.g., light, electrons, etc.) over a physical version of a sample, thereby generating an output from the physical version of the sample. In this way, the optical, electron, and ion beam subsystems can be configured as "actual" subsystems rather than "virtual" subsystems. However, the storage medium (not shown) and computer subsystem 36 shown in Figure 1 can be configured as a "virtual" system. In particular, the storage medium and computer subsystem can be configured as a "virtual" inspection system as described in the jointly owned U.S. Patent No. 8,126,255 (issued February 28, 2012, Bhaskar et al.) and No. 9,222,895 (issued December 29, 2015, Duffy et al.) (both of which are incorporated by reference as if they were fully described herein). Embodiments described herein can be further configured as described in those patents.

[0047] Figure 3 shows an example of how image-to-design alignment can currently be performed, and Figure 4 shows an embodiment of how image-to-design alignment can be performed by the system and method described herein. The steps shown in these figures are particularly suitable for DRAM PDAs. As shown in steps 300 and 400, the computer subsystem may find alignment targets and extract optical images of the alignment targets. For example, the computer subsystem may be configured to select alignment targets from a setup image of the sample generated by the imaging subsystem. The computer subsystem may select alignment targets for use in setup and runtime. The alignment targets selected for setup and runtime may be the same or different. For example, setup and runtime may be performed using the same alignment targets, but the number of instances of the alignment target in setup may be fewer than in runtime. The reverse is also possible. The alignment targets selected by the computer subsystem may also include different alignment targets having different properties as well as different locations on the sample or within the design. Alignment targets may be selected in any suitable way known in the art.

[0048] Steps 300 and 400 may include scanning a sample area to find a unique target. Scanning a suitable area on the sample may be performed as further described herein. A unique target may be unique in any way that makes the target suitable for alignment purposes. A unique target may be found in any suitable way (for example, by searching for a pattern that is different from other patterns in a given image window). For example, a unique target may be a pattern that has a unique shape compared to other patterns in a given search window, such as an image frame or a job, or a pattern that has a unique spatial relationship with one another in a given search window.

[0049] Alignment targets are preferably two-dimensional (2D) in that they can be used to perform alignment in both the X and Y directions, although this is not strictly necessary. For example, alignment targets may be selected such that one or more are useful for alignment in the X direction only, and one or more are useful for alignment in the Y direction only. The embodiments described herein may also be used with any suitable alignment targets known in the art, selected in any suitable manner known in the art. While it may be practical to select multiple unique targets for use in the embodiments described herein, generally, one or more unique targets may be selected. Each unique target may differ from one another in any unique way. In addition, a unique target may include multiple instances of the same unique target.

[0050] Examples of design-based alignment are described in U.S. Patent No. 9,830,421 (published November 28, 2017, Bhattacharyya et al.), No. 10,620,135 (published April 14, 2020, Brauer), and No. 10,698,325 (published June 30, 2020, Brauer) (these are incorporated by reference as if they were fully described herein). Embodiments described herein may be configured to select alignment targets as described in these patents and may be further configured as described in these patents.

[0051] As shown in steps 302 and 402, the computer subsystem may be configured to extract and render design clips of alignment targets. The computer subsystem may receive the design of each unique target found in the sample image. The computer subsystem may receive the design in any suitable way, such as by retrieving the sample design based on information of the unique target determined from the image generated by scanning, or by requesting a portion of the design (e.g., a design clip) at the location of the unique target from a storage medium or computer system containing the design. The design received by the computer subsystem may include any of the designs, design data, or design information described further herein.

[0052] Rendering images of alignment targets can be performed in any suitable method known in the Art. Rendering may be performed using deep learning (DL) or machine learning (ML) models. Rendering may also, or alternatively, be performed using forward simulation models, such as those that simulate the process of forming a design on a sample and generating an image of the sample in an imaging subsystem. Examples of methods and systems that may be used for rendering alignment target images are described in U.S. Patent Application Publication No. 2022 / 0375051 (published November 24, 2022, Brauer et al.), U.S. Patent Nos. 11,328,435 (issued May 10, 2022, Brauer et al.) and No. 11,580,650 (issued February 14, 2023, Brauer et al.), and U.S. Patent Application No. 18 / 178,528 (filed March 5, 2023, Chen et al.) (these are incorporated by reference as if they were fully described herein). The embodiments described herein may be further configured as described in these documents.

[0053] The system includes a computer subsystem configured to determine first and second design-to-alignment offsets for multiple instances of an alignment target by individually aligning images of multiple instances of the alignment target, generated by the imaging subsystem and formed on the sample, to the rendered image of the alignment target using first and second alignment methods, respectively. In this way, for each instance of the alignment target on the sample, two alignments are performed using two different alignment methods, and two different offsets are determined. Each alignment method can be performed individually for each instance of the alignment target. The offsets determined by each alignment method may be the same offset, i.e., the offset between the setup image of the alignment target on the sample and the rendered image of the alignment target, but may have different values ​​due to the different alignment methods. In addition, depending on the alignment target, the first and second design-to-alignment offsets may be offsets in the X direction only, offsets in the Y direction only, or offsets in both the X and Y directions. In this way, a first design-to-alignment offset for any alignment target instance may include one or more design-to-alignment offsets determined by the first alignment method, and a second design-to-alignment offset for any alignment target instance may include one or more design-to-alignment offsets determined by the second alignment method.

[0054] As shown in step 404 of Figure 4, the computer subsystem is configured to perform offset calculations between the optical (or other) image and the rendered image of the alignment target (using a first alignment method). In addition, as shown in step 406 of Figure 4, the computer subsystem is configured to perform offset calculations between the optical (or other) image and the rendered image of the alignment target (using a second alignment method). These steps are in contrast to how alignment is typically performed in setups using currently used methods. For example, as shown in step 304 of Figure 3, currently used methods typically perform offset calculations between the optical (or other) image and the rendered image of the alignment target using a single alignment method. In contrast, in the embodiments described herein, the computer subsystem is configured to determine different offsets between the sample image and the rendered alignment target image of the alignment target instance based on the results of aligning the images relative to each other using different alignment methods. These offsets may be determined by any suitable method and may be expressed in any suitable method (e.g., as a Cartesian offset, as a two-dimensional function, etc.).

[0055] In one embodiment, one of the first and second alignment methods includes normalized cross-correlation (NCC). NCC can be performed using any suitable method, algorithm, function, etc., known in the art. In another embodiment, one of the first and second alignment methods includes projection-based NCC. Thus, embodiments described herein may use projection NCC to calculate the PDA offset. Generally, projection NCC involves aligning the 1D projection profiles of the optical image and the rendered image during PDA setup. Other alignment methods may be used for the first and second alignment methods in the setup, but for the PDA targets described herein, using NCC and projection NCC for the first and second alignment methods may be the most robust approach.

[0056] The computer subsystem is also configured to identify multiple instances in which the difference between the first and second design-to-alignment offsets falls below a predetermined threshold. Thus, the identification step may include calculating the difference between the first and second design-to-alignment offsets for each instance of the alignment target, and then comparing that difference to the predetermined threshold. Any multiple instances identified as having a difference below the predetermined threshold may be retained for the additional steps described herein, while any multiple instances not identified may be rejected. For example, as shown in step 408 of Figure 4, the computer subsystem may be configured to reject any alignment target offsets determined by the first and second alignment methods that differ by more than a predetermined threshold. As can be seen from a comparison with Figure 3, the currently used method does not include such a step because it uses only one alignment method to calculate the design-to-alignment offsets during setup.

[0057] For 2D alignment targets, this step can be performed individually for each offset. For example, the difference between the design-to-alignment X offset determined for each instance of the alignment target using two alignment methods is compared to a predetermined threshold. Any design-to-alignment X offsets with a difference below the predetermined threshold are retained for further processing, while the others are rejected. The same step can be performed for the design-to-alignment Y offset determined for the alignment target instance using the first and second alignment methods. Thus, for any alignment target instance, (1) both the X and Y design-to-alignment offsets are retained, (2) one of the X or Y design-to-alignment offsets is retained and the other is rejected, or (3) both the X and Y design-to-alignment offsets are rejected. Thus, for any single instance of an alignment target, eight or nine times out of ten, both X and Y design-to-alignment offsets will be either retained or rejected. However, if there is an example where a 2D alignment target instance generates only one good design-to-alignment offset, that offset can be retained for further processing.

[0058] In one embodiment, a predetermined threshold is defined in pixels. The predetermined threshold used in the embodiments described herein may have different values ​​depending, for example, on the repeating pitch of the patterned features formed on the sample. The predetermined threshold may be selected by the user or determined by a computer subsystem based on, for example, information about the design formed on the sample. For example, using one of the PDA offsets calculated based on projection-based NCC, any offsets that are more than ±1 pixel away from the NCC-based PDA offset calculation can be rejected, and the remaining offsets can be used for PDA clustering. This can be used both at PDA setup and runtime to eliminate false-positive PDA offsets.

[0059] The computer subsystem is configured to determine the runtime design-to-alignment offset of an alignment target from first and second design-to-alignment offsets determined for only a specified number of instances. In one embodiment, determining the runtime design-to-alignment offset includes clustering the first and second design-to-alignment offsets. For example, as shown in step 410 of Figure 4, the computer subsystem may be configured to perform offset clustering to determine the design-to-alignment offset to be used at runtime. The PDA offsets from all targets within a subswath may vary by several pixels. Some of the offsets may be inaccurate due to either pattern repetition or misalignment. Clustering helps to identify the true offsets. Offset clustering can be performed using fuzzy K-Means with a multi-cluster arbitration algorithm, or any other suitable method or algorithm known in the art. For a one-dimensional (1D) alignment target, this step is performed only once for the X or Y offset. For a 2D alignment target, this step may be performed separately for the X and Y offsets.

[0060] The methods currently in use may also include offset clustering to determine the offset used at runtime between optical (or other) images and rendered images, such as the runtime design versus alignment offset (as shown in step 306 of Figure 3). The purpose of any offset clustering is to reject outliers and find the mean of groups with similar samples. However, the methods currently in use perform offset clustering of alignment targets using all offsets determined for all instances of the alignment target, without considering what the offset values ​​are. For some alignment targets, such as those further described herein, one alignment method may generate multiple, significantly different offsets for each target, which can lead to confusion in offset clustering. In other words, among the multiple offsets generated for each alignment target, there may be multiple inaccurate offsets or only one accurate offset. Therefore, by configuring the embodiments described herein to reject inaccurate offsets before clustering, the error in the clustering results can be reduced, and the clustering can even be made error-proof. In this way, the embodiments described herein modify the input to the runtime design versus alignment offset clustering step in an important and meaningful manner.

[0061] The computer subsystem is configured to store runtime design versus alignment offsets for use in processes performed on a sample using the imaging subsystem. The computer subsystem may store the runtime design versus alignment offsets on any suitable computer-readable storage medium. The runtime design versus alignment offsets may be stored together with any of the results described herein, or in any way known in the art. The storage medium may include any storage medium described herein, or any other suitable storage medium known in the art. After the runtime design versus alignment offsets are stored, they can be accessed within the storage medium and used by any embodiment of the method or system described herein, in a format for display to a user, or by another software module, method, or system.

[0062] Saving runtime design versus alignment offsets may include saving runtime design versus alignment offsets for use in processes performed on the sample and processes performed on at least one other sample of the same type as the sample. For example, embodiments described herein may set up the alignment of a sample for a process recipe, which may be performed as part of setting up, creating, calibrating, or updating the recipe. The recipe may then be saved and used by embodiments described herein (and / or other systems or methods) to perform processes on the sample and / or other samples, thereby generating information about the sample and / or other samples (e.g., defect information). In this way, runtime design versus alignment offsets may be generated and saved once for each layer of the sample, and the offsets may be used in processes performed on multiple samples of the same layer. Naturally, as with any process, if the process performed on a sample layer is updated, calibrated, modified, relearned, etc., the runtime design versus alignment offsets may also be updated, calibrated, modified, relearned, etc., as with any other arbitrary process parameters. The updating, calibration, modification, and retraining of the runtime design versus alignment offset can be performed in a manner similar to that described herein for determining the offset to be used in the process performed on the sample. Thus, the embodiments described herein may be configured to repeat the steps described herein at various points in time to modify a previously set up process.

[0063] Accordingly, as described herein, these embodiments may be used to set up a new process or recipe. These embodiments may also be used to modify an existing process or recipe, whether it is a process or recipe used for a particular sample or a process or recipe created for one sample and intended to be adapted for another sample. In addition, the embodiments described herein are not limited to creating or modifying inspection processes. For example, the embodiments described herein may be used in a similar manner to set up or modify processes for measurement, defect review, etc. In particular, the determination of offsets for use in a process and the performance of sample-to-design alignment, as described herein, may be performed regardless of the process being set up or modified. Accordingly, the embodiments described herein can be used not only to set up or modify inspection processes but also to set up or modify any type of quality control process performed on the sample described herein.

[0064] In one embodiment, the computer subsystem is configured to store one or more images of multiple instances of an alignment target for use as a setup alignment target image. For example, as further described herein, at runtime, the computer subsystem may align a runtime alignment target image with a setup alignment target image. The setup alignment target image may be any of the generated alignment target images as described herein. The setup alignment target image may be stored as further described herein so that it can be recalled and used during the process. If multiple alignment targets are used for a single sample, one or more setup alignment target images may be stored for each alignment target. However, the same setup alignment target image may be used for multiple instances of the same alignment target.

[0065] In one embodiment, the process includes generating runtime alignment target images for multiple instances of an alignment target using an imaging subsystem. The generation of runtime alignment target images for an alignment target may be carried out as further described herein.

[0066] During the process, the computer subsystem is configured to determine first and second runtime-to-setup offsets for multiple instances of an alignment target by individually aligning a runtime alignment target image to a setup alignment target image using first and second alignment methods, respectively. In this way, for each instance of the alignment target on the sample, two alignments are performed using two different alignment methods, and two different offsets are determined. Each alignment method may be performed individually for each instance of the alignment target.

[0067] The offsets determined by each alignment method may be the same offset, i.e., the offset between the runtime image of the alignment target on the sample and the setup image of the alignment target on the sample, but may have different values ​​due to different alignment methods. In addition, depending on the alignment target, the first and second runtime-to-setup offsets may be offsets in the X direction only, offsets in the Y direction only, or offsets in both the X and Y directions. Thus, the first runtime-to-setup offset for any alignment target instance may include one or more runtime-to-setup offsets determined by the first alignment method, and the second runtime-to-setup offset for any alignment target instance may include one or more runtime-to-setup offsets determined by the second alignment method.

[0068] As shown in step 412 of Figure 4, the computer subsystem is configured to calculate the offset between the setup alignment target image and the runtime alignment target image using a first alignment method. In addition, as shown in step 414, the computer subsystem is configured to calculate the offset between the setup alignment target image and the runtime alignment target image using a second alignment method. Both of these steps may be performed individually for each instance of the alignment target used in the process. These steps are in contrast to how alignment is typically performed at runtime in currently used methods. For example, as shown in step 308 of Figure 3, currently used methods typically perform the offset calculation between the setup alignment target image and the runtime alignment target image using a single alignment method. In contrast, in the embodiments described herein, the computer subsystem is configured to determine different offsets between the setup image and the runtime alignment target image of an alignment target instance based on the results of aligning the images to each other using different alignment methods. These offsets may be determined in any suitable way and may be expressed in any suitable way (e.g., as a Cartesian offset, as a two-dimensional function, etc.).

[0069] The first and second alignment methods used at runtime will almost certainly be the same as the first and second alignment methods used at setup. Generally, NCC and projected NCC can be performed at runtime as described herein, using different sets of images, such as setup alignment target images and runtime alignment target images, instead of the design. For example, runtime projected NCC involves aligning the 1D projected profiles of the setup image and the runtime PDA target image during runtime. Other alignment methods may be used for the first and second alignment methods at runtime, but for the PDA targets described herein, NCC and projected NCC may be the most robust approaches.

[0070] The computer subsystem is also configured to identify a subset of instances in which the difference between the first and second runtime-to-setup offsets falls below an additional predetermined threshold. Thus, the identification step may include calculating the difference between the first and second runtime-to-setup offsets for each instance of the alignment target, and then comparing that difference to an additional predetermined threshold. Any subset of instances identified as having a difference below the additional predetermined threshold may be retained for the additional steps described herein, while any instances not identified may be rejected. For example, as shown in step 416 of Figure 4, the computer subsystem is configured to reject any alignment target offsets determined by the first and second methods that differ by more than an additional predetermined threshold. As can be seen from a comparison with Figure 3, the currently used method does not include such a step because it uses only one alignment method to calculate the runtime-to-setup offsets during runtime. Step 416 may be performed for a 2D alignment target, as further described herein.

[0071] In one embodiment, an additional predetermined threshold is defined in pixels. The additional predetermined threshold may be greater than ±1 pixel. The additional predetermined threshold used in the embodiments described herein may have different values ​​and may be selected as further described herein. The predetermined threshold and the additional predetermined threshold used in the setup may be the same value or different values. For example, using one of the PDA offsets calculated based on projection-based NCC, any offsets that are more than ±1 pixel away from the NCC-based PDA offset calculation can be rejected, and the remaining offsets can be used for PDA clustering. This approach can be used at the PDA runtime to remove false-positive PDA offsets.

[0072] The computer subsystem is further configured to determine the final runtime-to-setup offset of the alignment target from first and second runtime-to-setup offsets determined for only a subset of identified instances. In one embodiment, determining the final runtime-to-setup offset includes clustering the first and second runtime-to-setup offsets. For example, as shown in step 418, the computer subsystem may be configured to perform offset clustering to determine the offset used at runtime. As with setup, during runtime, the PDA offset from all targets in a subswath may vary by several pixels for the same reasons further described herein. Clustering helps to identify the true offset. Offset clustering may be performed during runtime as further described herein.

[0073] Methods currently in use may also include offset clustering to determine the offsets used at runtime (e.g., runtime-versus-setup offsets) (as shown in step 310 of Figure 3). However, such methods perform offset clustering of alignment targets using all offsets determined for all instances of the alignment target, without considering what the offset values ​​are. As further described herein, the embodiments described herein can be configured to reject inaccurate offsets before clustering, thereby reducing errors in the clustering results and even making the clustering error-tolerant. In this way, the embodiments described herein modify the input to the final runtime-versus-setup offset clustering step in an important and meaningful manner.

[0074] The computer subsystem is further configured to determine the runtime-to-design offset based on the final runtime-to-setup offset and the runtime design-to-alignment offset. Determining the runtime-to-design offset based on the final runtime-to-setup offset and the runtime design-to-alignment offset may include correcting the runtime design-to-alignment offset by or using the final runtime-to-setup offset in any appropriate manner. This step may be performed to compensate for the runtime design-to-alignment offset for any other differences between the setup sample and the runtime sample, such as differences in the alignment of the setup sample and the runtime sample with respect to the imaging subsystem, and differences in the placement of alignment targets between different samples.

[0075] In one embodiment, during the process, a computer subsystem is configured to identify care areas (CAs) in the image of the sample generated by the imaging subsystem during the process, based on a runtime versus design offset. For example, as shown in step 420 of Figure 4, the computer subsystem may apply an offset to the CAs or position the care areas according to the offset correction. A “care area,” as commonly referred to in the art, is a region on the sample of interest for inspection purposes. Sometimes, care areas are used in an inspection process to distinguish between regions of the sample to be inspected and regions that are not. In addition, care areas may be used to distinguish regions of the sample to be inspected using one or more different parameters. For example, if a first region of the sample is more important than a second region, the first region may be inspected with higher sensitivity than the second region so that defects are detected with higher sensitivity in the first region. Other parameters of the inspection process may also be modified on a care area-by-care basis in a similar manner.

[0076] In these embodiments, the computer subsystem may use a CA border in the X and Y directions. For example, the embodiments described herein allow for substantially high-precision alignment of the sample image with respect to the design, and thus substantially high-precision identification of CAs within the sample image. For example, even if the offset in step 420 is applied to the CA in the same way as currently performed (e.g., step 312 in Figure 3), the offset is more accurate according to the embodiments described herein, allowing for more precise placement of the CA. Thus, the "border" commonly used to artificially enlarge the CA to account for errors in CA placement can be effectively eliminated by the embodiments described herein. Placing the CA with such high precision and eliminating the CA border is advantageous for many reasons, including a significant reduction in the detection of news on the sample and improved detection of defects of interest (DOIs) on the sample.

[0077] In some embodiments, multiple instances of the alignment target are formed on the DRAM device portion of the sample. For example, embodiments described herein provide a robust PDA for advanced DRAM devices. In the case of advanced design rule DRAM devices, due to repeating features within the bulk cell region, multiple PDA offsets may be generated for each PDA target from sense amplifier (SA) / subword line (SWD) / conjunction patterns, which can cause PDA clustering failures during PDA setup and runtime. Embodiments described herein address the current PDA deficiencies for advanced design rule DRAM devices, where a significant number of PDA setup and runtime failures have been observed.

[0078] More specifically, advanced design rule DRAM devices tend to have lower contrast in SA / SWD / conjunctions and smaller pitch repeating patterns in SA / SWDs in images generated by the imaging subsystems described herein. An NCC-based approach to calculating the offset between the optical image and the design-rendered image of the PDA target from the SA / SWD / conjunction may generate multiple offsets for each PDA target, which can lead to confusion in PDA clustering. For example, for targets without repeating patterns, only one set of X and Y offsets may be calculated. For targets with repeating patterns in either X or Y, multiple offsets may be calculated. Of the multiple offsets generated for each PDA target, only one may be accurate. Therefore, clustering can be made error-tolerant by rejecting inaccurate offsets beforehand.

[0079] Figure 5 shows one typical layout of a DRAM region that may be formed on a sample. Figure 5 is included here solely to illustrate the general spatial relationships between different DRAM regions. As shown, a DRAM region 500 contains multiple bulk cell regions 502. SA regions 506 are located between each bulk cell region in a row of DRAM regions. SWD regions 508 are formed between each bulk cell region in a column of DRAM regions. Conjunction regions 504 are formed between adjacent SA regions and adjacent SWD regions. The DRAM layout is unique compared to logic devices with static random access memory (SRAM) or other types of devices such as vertical NAND (VNAND). Embodiments described herein utilize the unique DRAM layout to identify PDA targets, calculate their offsets, and use them at runtime in a different way than currently used PDAs.

[0080] In one embodiment, multiple instances of the alignment target are formed within a conjunction block of the memory device region formed on the sample. For example, a PDA target selected from the conjunction of an advanced DRAM has relatively good separation between the bulk cell region and the SA / SWD / conjunction region. As shown in Figure 6, projections of the PDA target image and projections along the X and Y axes of their rendered images can provide multiple offsets without ambiguity. Image 600 is a DRAM image in the SA / SWD / conjunction region, the X-average projection 602 is the X projection generated for this image, and the Y-average projection 604 is the Y projection generated for this image. As can be seen from these projections, images of the SA / SWD / conjunction region can be used for both X and Y offsets.

[0081] In additional embodiments, multiple instances of the alignment target are formed in the boundary region between the SA block and the bulk cell block of the memory device region formed on the sample. In further embodiments, multiple instances of the alignment target are formed in the boundary region between the SWD block and the bulk cell block of the memory device region formed on the sample. For example, in the case of a PDA target from an SA / bulk cell boundary or an SWD / bulk cell boundary, the projection of the PDA target and the projections along the X and Y of their rendered images may give only one offset along either X or Y, with the other direction being repeated. In this case, for a PDA target where Y is repeated, only the X offset is used, and vice versa. In one such example, image 700 shown in Figure 7 is an example of a DRAMPDA target, the X-average projection 702 is the X projection generated for this image, and the Y-average projection 704 is the Y projection for this image. As can be seen from these projections, this PDA target has a valid X offset, but Y is repeated. In another example, image 800 shown in Figure 8 is an example of a DRAM PDA target, the X-mean projection 802 is the X projection generated for this image, and the Y-mean projection 804 is the Y projection generated for this image. As can be seen from these projections, this PDA target has a valid Y offset, but the X is repeated.

[0082] The images shown in Figures 6 to 8 are not intended to illustrate specific samples or their characteristics in which the embodiments described herein may be used. Instead, the images shown are simply for the purpose of aiding in the understanding of the embodiments described herein. The images actually used in the embodiments will vary depending on the characteristics of the sample and its design, as well as the configuration of the imaging subsystem that generates the actual image of the sample.

[0083] The embodiments described herein may also perform the process after the sample has been aligned at runtime as described above. In one embodiment, the process is an inspection process. However, the process may include any of the processes described herein, such as inspection, defect review, and measurement. The process may also include any appropriate processing of the image after the image has been aligned to the design. For example, in the case of inspection, the computer subsystem may determine the difference between the sample image and a reference image that can be aligned to the sample image using one of the offsets described herein. The computer subsystem may also compare the difference to a threshold and determine that an image difference exceeding the threshold corresponds to a defect or potential defect. Naturally, this may be the simplest method of defect detection, and the computer subsystem may be configured to detect defects in the image using any appropriate method or algorithm known in the art. Before performing defect detection, CAs may be placed in the runtime sample image as described further herein. The computer subsystem may also be configured to perform additional steps on detected defects, such as filtering or classifying defects based on their location in the design, which may be determined using the offsets described herein. The embodiments described herein may also be configured to perform any other steps that are normally performed during an inspection process.

[0084] The computer subsystem may be configured to store information about the sample generated by performing the process, such as information about detected defects, on any suitable computer-readable storage medium. The information may be stored together with any of the results described herein, or in any way known in the art. The storage medium may include any storage medium described herein, or any other suitable storage medium known in the art. After the information is stored, it may be accessed within the storage medium and made available for use by any method or system embodiment described herein, formatted for display to a user, or used by another software module, method, or system.

[0085] The results and information generated by performing the processes described herein on a sample or other samples of the same type may be used in various ways by the embodiments and / or other systems and methods described herein. Such functions include, but are not limited to, modifying processes, such as manufacturing processes or steps, that have been performed or are scheduled to be performed on the sample or another sample, in a feedback or feedforward manner. For example, a computer subsystem may be configured to determine one or more changes to processes that have been performed or are scheduled to be performed on a sample inspected as described herein, based on the detected defects. Changes to processes may include any appropriate changes to one or more parameters of the process. The computer subsystem preferably determines such changes so that the defects can be corrected or eliminated in another process performed on the sample, or compensated for in another process performed on the sample, so that the defects can be reduced or prevented in other samples on which the modified process is performed. The computer subsystem may determine such changes in any appropriate way known in the art.

[0086] These changes may then be transmitted to a semiconductor manufacturing system (not shown) or to a storage medium (not shown) accessible by the computer subsystem and the semiconductor manufacturing system. The semiconductor manufacturing system may be part of or not part of the embodiments of the system described herein. For example, the computer subsystem and / or imaging subsystem described herein may be coupled to the semiconductor manufacturing system via one or more common elements such as a housing, power supply, sample handling device or mechanism. The semiconductor manufacturing system may include any semiconductor manufacturing system known in the art, such as lithography tools, etching tools, chemical mechanical polishing (CMP) tools, and deposition tools.

[0087] The embodiments described herein offer many significant advantages over currently available methods and systems for PDAs for DRAM devices. For example, the embodiments described herein provide a solution for PDAs for advanced design rule DRAM devices, where currently used PDA methods struggle. Without the proposed embodiments, currently used systems and methods may not be able to inspect DRAM devices with the most advanced design rules, given the substantially high precision requirements of CA placement.

[0088] The advantages of the proposed embodiment are provided by several important new features. One such new feature is the use of projected NCC during PDA setup to align the PDA target image with the rendered image in order to eliminate NCC-based false positive offsets. Another such new feature is the use of projected NCC to align the PDA target image from setup with the runtime PDA target image in order to eliminate NCC-based false positive offsets.

[0089] Each embodiment of the above-described system can be combined into a single embodiment.

[0090] Another embodiment relates to a computer-implemented method for determining offsets for use in a process performed on a sample. This method includes determining first and second design-to-alignment offsets for multiple instances of an alignment target by individually aligning images of multiple instances of the alignment target formed on the sample by an imaging subsystem to rendering images of the alignment target using first and second alignment methods, respectively (as shown, for example, in steps 404 and 406 of Figure 4). The method also includes identifying multiple instances where the difference between the first and second design-to-alignment offsets falls below a predetermined threshold (as shown, for example, in step 408 of Figure 4). In addition, the method includes determining a runtime design-to-alignment offset for the alignment target from the first and second design-to-alignment offsets determined only for the identified multiple instances (as shown, for example, in step 410 of Figure 4). The method further includes saving the runtime design-to-alignment offset for use in a process performed on the sample using the imaging subsystem. These steps are performed by a computer system.

[0091] Each step of this method may be performed as further described herein. The method may also include any other steps that can be performed by the system, computer system, and / or imaging subsystem described herein. The computer system may be configured according to any of the embodiments described herein (e.g., computer subsystem 36), and the imaging subsystem may be configured according to any of the embodiments described herein (e.g., imaging subsystem 10). In addition, the above-described method may be performed by any of the embodiments of the system described herein.

[0092] Additional embodiments relate to a non-temporary computer-readable medium for storing program instructions for executing a computer implementation method on a computer system for use in a process performed on a sample. One such embodiment is shown in Figure 9. In particular, as shown in Figure 9, the non-temporary computer-readable medium 900 includes program instructions 902 that can be executed on a computer system 904. The computer implementation method may include any step of any method described herein.

[0093] Program instructions 902 implementing a method as described herein may be stored on a computer-readable medium 900. The computer-readable medium may be a storage medium such as a magnetic or optical disk, a magnetic tape, or any other suitable non-temporary computer-readable medium known in the art.

[0094] Program instructions can be implemented in a variety of ways, including procedure-based, component-based, and / or object-oriented approaches. For example, program instructions may be implemented using ActiveX controls, C++ objects, JavaBeans, Microsoft Foundation Classes ("MFC"), SSE (Streaming SIMD Extension), or other technologies or methodologies, as needed.

[0095] The computer system 904 may be configured according to any of the embodiments described herein.

[0096] Further modifications and alternative embodiments of various aspects of the present invention will be apparent to those skilled in the art in consideration of this description. For example, methods and systems for determining an offset for use in a process performed on a sample are provided. Thus, this description should be interpreted as illustrative only and is intended to teach those skilled in the art a general way of carrying out the present invention. It should be understood that the forms of the present invention shown and described herein should be interpreted as currently preferred embodiments. As will be apparent to those skilled in the art after benefiting from this description of the present invention, elements and materials may be substituted for those shown and described, parts and processes may be reversed, and certain functions of the present invention may be used independently. Modifications to the elements described herein can be made without departing from the spirit and scope of the present invention as set out in the following claims.

Claims

1. A system configured to determine an offset for use in a process performed on a sample, An imaging subsystem configured to generate an image of a sample, For multiple instances of the alignment target, the first and second design-to-alignment offsets are determined by individually aligning the images of the multiple instances of the alignment target generated by the imaging subsystem and formed on the sample with the rendered image of the alignment target using the first and second alignment methods, respectively. Identifying the plurality of instances in which the difference between the first and second design-to-alignment offsets falls below a predetermined threshold, Determining the runtime design-to-alignment offset of the alignment target from the first and second design-to-alignment offsets determined for only the specified plurality of instances, To save the runtime design versus alignment offset for use in a process performed on the sample using the imaging subsystem, A computer subsystem configured to perform the following: A system equipped with these features.

2. The system according to claim 1, wherein determining the runtime design-to-alignment offset includes clustering the first and second design-to-alignment offsets.

3. The system according to claim 1, wherein one of the first and second alignment methods includes normalized cross-correlation.

4. The system according to claim 1, wherein one of the first and second alignment methods includes projection-based normalized cross-correlation.

5. The system according to claim 1, wherein the predetermined threshold is defined in pixels.

6. The process includes generating runtime alignment target images for multiple instances of the alignment target using the imaging subsystem, During the process described above, the computer subsystem further: The first and second runtime-to-setup offsets are determined for multiple instances of the alignment target by individually aligning the runtime alignment target image with the setup alignment target image using the first and second alignment methods, respectively. Identifying a subset of the plurality of instances in which the difference between the first and second runtime versus setup offsets falls below an additional predetermined threshold, Determining the final runtime-to-setup offset of the alignment target from the first and second runtime-to-setup offsets determined for only a subset of the specified plurality of instances, Based on the final runtime versus setup offset and the runtime design versus alignment offset, the runtime versus design offset is determined. The system according to claim 1, configured to perform the following.

7. The system according to claim 6, wherein determining the final runtime-to-setup offset includes clustering the first and second runtime-to-setup offsets.

8. The system according to claim 6, wherein the additional predetermined threshold is defined in pixels.

9. The system according to claim 6, wherein during the process, the computer subsystem is further configured to identify care areas in the image of the sample generated by the imaging subsystem during the process, based on the runtime versus design offset.

10. The system according to claim 6, wherein the computer subsystem is further configured to store one or more images of multiple instances of the alignment target for use as the setup alignment target image.

11. The system according to claim 1, wherein multiple instances of the alignment target are formed on the dynamic random access memory device portion of the sample.

12. The system according to claim 1, wherein multiple instances of the alignment target are formed within a conjunction block of a memory device region formed on the sample.

13. The system according to claim 1, wherein multiple instances of the alignment target are formed in the boundary region between the sense amplifier block and the bulk cell block of the memory device region formed on the sample.

14. The system according to claim 1, wherein multiple instances of the alignment target are formed in the boundary region between the subword line driver block and the bulk cell block of the memory device region formed on the sample.

15. The system according to claim 1, wherein the computer subsystem is further configured to generate the rendering image of the alignment target from the design of the sample.

16. The system according to claim 1, wherein the process is an inspection process.

17. The system according to claim 1, wherein the imaging subsystem is an optical imaging subsystem.

18. The system according to claim 1, wherein the imaging subsystem is an electron beam imaging subsystem.

19. A non-temporary computer-readable medium for storing program instructions executable on a computer system for executing a computer-implemented method for determining an offset for use in a process performed on a sample, wherein the computer-implemented method is The image subsystem generates images of multiple instances of the alignment target formed on the sample, which are then individually aligned with the rendered image of the alignment target using the first and second alignment methods, thereby determining the first and second design-to-alignment offsets for each of the multiple instances of the alignment target. Identifying the plurality of instances in which the difference between the first and second design-to-alignment offsets falls below a predetermined threshold, Determining the runtime design-to-alignment offset of the alignment target from the first and second design-to-alignment offsets determined for only the specified plurality of instances, To save the runtime design versus alignment offset for use in a process performed on the sample using the imaging subsystem, Computer-readable media, including [specific media].

20. A computer-implemented method for determining an offset to be used in a process performed on a sample, The image subsystem generates images of multiple instances of the alignment target formed on the sample, which are then individually aligned with the rendered image of the alignment target using the first and second alignment methods, thereby determining the first and second design-to-alignment offsets for each of the multiple instances of the alignment target. Identifying the plurality of instances in which the difference between the first and second design-to-alignment offsets falls below a predetermined threshold, Determining the runtime design-to-alignment offset of the alignment target from the first and second design-to-alignment offsets determined for only the specified plurality of instances, To save the runtime design versus alignment offset for use in a process performed on the sample using the imaging subsystem, Includes, A method wherein determining the first and second design-to-alignment offsets, identifying the plurality of instances, determining the runtime design-to-alignment offsets, and saving the runtime design-to-alignment offsets are performed by a computer system.

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