Metrology sampling plan only for non-compliance detection

Abstract

Methods and systems are provided for determining information of a sample. A method includes generating a sampling plan only for non-compliance detection of characteristics of a sample during a metrology process. The method also includes generating an output of the sample by performing the metrology process on the sample using the generated sampling plan. In addition, the method includes determining the characteristics of the samples based on the generated output and detecting whether the characteristics of one or more of the samples are not compliant based on the determined characteristics of the samples. Embodiments described herein are particularly suited for overlay metrology with a substantially sparse sampling plan configured only for overlay non-compliance detection.

Description

Technical Field

[0001] The present invention generally relates to methods and systems configured for determining information about a sample. Certain embodiments relate to methods and systems for generating and using a sampling plan specifically designed to detect only non-compliant samples. Background Art

[0002] The following description and examples are not admitted to be prior art by inclusion in this section.

[0003] The manufacture of semiconductor devices such as logic and memory devices typically includes 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, photolithography is a semiconductor manufacturing process that involves transferring a pattern from a mask to a photoresist 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 manufactured on a single semiconductor wafer in a certain arrangement and then separated into individual semiconductor devices.

[0004] Inspection processes are used at various steps during the semiconductor manufacturing process to detect defects on the wafer to facilitate a higher yield of the manufacturing process and therefore a higher profit. Inspection has always been an important part of manufacturing semiconductor devices such as ICs. However, as the size of semiconductor devices decreases, inspection becomes more important to the successful manufacture of acceptable semiconductor devices because smaller defects can cause device failure.

[0005] Defect re-inspection typically involves re-inspecting a defect that was detected by an inspection process and generating additional information about the defect at a higher resolution using, for example, a high magnification optical system or a scanning electron microscope (SEM). Defect re-inspection is thus performed at discrete locations on the wafer where the defect was detected by inspection. The higher resolution data of the defect generated by defect re-inspection is more suitable for determining properties of the defect, such as profile, roughness, more accurate size information, etc.

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

[0007] The metrology process is also different from the defect recheck process in that, unlike the defect recheck process in which defects detected by inspection are revisited in the defect recheck, the metrology process can be performed at a location where no defects are detected. In other words, unlike defect recheck, the location where the metrology process is performed on the wafer can be independent of the result of the inspection process performed on the wafer. In particular, the location where the metrology process is performed can be selected independently of the inspection result. In addition, since the location on the wafer where the metrology is performed can be selected independently of the inspection result, unlike defect recheck in which the location on the wafer where the defect recheck is to be performed is not determined until the inspection result of the wafer is generated and available for use, the location where the metrology process is performed can be determined before the inspection process is performed on the wafer.

[0008] For all of the yield-related processes described above, it would be advantageous to inspect, re-inspect, and measure every possible point on every possible sample. Of course, this is not practical or desirable due to the time and cost that such sampling would require. Therefore, selecting which points, locations, areas, etc. on the sample to inspect, re-inspect, measure (i.e., sample) is a key aspect of creating a yield-related process recipe that produces results sufficient to monitor and / or control the manufacturing process while minimizing the time and cost required to produce the results. Some more time-consuming processes (such as metrology) can make such sampling more difficult. For example, it is extremely difficult to find the right balance between rapid metrology results and reasonably priced metrology results that also provide sufficient data for proper detection of non-compliant processes and / or feedback control of the process.

[0009] For metrology, sampling methods and systems in a wafer fab must make several decisions, such as which batches to measure, which wafers within a batch to measure, and which points on the wafer to measure. Sampling decisions involve a trade-off between the required throughput of a process and the criticality or impact of a process step on yield. In a wafer fab, overlay metrology is used for two main purposes: run-to-run (R2R) control and non-conformance detection, where a run can be a batch or multiple batches, depending on how critical a layer is. These goals often conflict with each other because the measurements performed for non-conformance detection may not be sufficient for R2R control and R2R control measurements may have a throughput that is too slow for the measurements to be adequately used for non-conformance detection. Therefore, designing an overlay metrology process typically involves a trade-off between the two goals.

[0010] Currently, the performance of these two tasks is not separated from each other. Depending on the layer and the device, the trend is to use enough measurement points to densely measure 2 to 4 wafers per batch to perform feedback control. In other words, in the currently used methods, only a subset of the batch and a substantially small subset of the wafers within the batch subset are measured using a full record process (POR) sampling plan to update the process tool (such as a scanner) calibration for advanced process control (APC) and detect non-compliant wafers. In this way, the currently used method is designed for APC, which also allows the results to be used for some non-compliant detection. If the measured wafer or batch does not meet the predefined compliance requirements, it is sent for rework. For more critical layers, every batch can be measured. For less critical layers, a random selection of batches is performed.

[0011] There are several important disadvantages of the currently used methods for stacking metrology and sampling. For example, due to random batch selection, the currently used methods may miss non-compliant batches, which can lead to reduced yield. In other words, if batches are randomly selected for metrology, some non-compliant batches may not be detected and may enter subsequent process steps to cause yield loss. In another example, due to the selection of "lucky" wafers for measurement within the batch, the currently used methods may miss non-compliant batches. If a relatively small number of wafers are measured per batch, they cannot represent the entire batch. In particular, these wafers may be compliant, while most other wafers may not be compliant. In additional examples, if "unlucky" wafers are selected within the batch, the currently used methods may cause false detection and rework. In the worst case, the "unlucky" wafers may cause a compliant batch to be non-compliant after rework. In particular, if a relatively small number of wafers are measured per batch, these wafers cannot represent the entire batch. These measured wafers may be non-compliant, while most of the unmeasured wafers may be compliant. In this case, non-representative wafers are used to calculate corrections for rework. When the batch is reworked, the measured wafers are repaired, but the remaining wafers within the batch may be degraded and may become non-compliant. In another example, currently used methods do not consider co-optimization of metrology tool settings and sampling to achieve higher throughput.

[0012]

[0006] It would therefore be advantageous to develop systems and methods for generating and using metrology sampling plans for non-compliance detection only that do not suffer from one or more of the above-mentioned disadvantages. Summary of the invention

[0013] The following description of various embodiments should in no way be construed as limiting the objectives of the appended claims.

[0014] One embodiment relates to a system configured for determining information of a sample. The system includes a computer system configured to generate a sampling plan for non-compliance detection of a characteristic of a sample only in a metrology process. The system also includes a metrology subsystem configured to generate an output of the sample by performing the metrology process on the sample using the generated sampling plan. The computer subsystem is further configured to determine the characteristic of the sample based on the generated output and detect whether the characteristic of one or more of the samples is non-compliant based on the determined characteristic of the sample. The system may be further configured as described herein.

[0015] Another embodiment relates to a computer-implemented method for determining information of a sample. The method includes generating a sampling plan for non-compliance detection of a characteristic of a sample only in a metrology process and generating an output of the sample by performing the metrology process on the sample using a metrology subsystem and the generated sampling plan. The method also includes determining the characteristic of the sample based on the generated output and detecting whether the characteristic of one or more of the samples is non-compliant based on the determined characteristic of the sample. The generating the sampling plan, determining the characteristic, and the detecting steps are performed by a computer system coupled to the metrology subsystem.

[0016] The steps of the method may be performed as described herein. In addition, the method may include any other steps of any other method described herein. In addition, the method may be performed by any of the systems described herein.

[0017] Another embodiment relates to a non-transitory computer-readable medium storing program instructions that can be executed on one or more computer systems to perform a computer-implemented method for determining information of a sample. The computer-implemented method includes the steps of the above method. The computer-readable medium can be further configured as described herein. The steps of the computer-implemented method can be executed as further described herein. In addition, the computer-implemented method executable by the program instructions can include any other steps of any other method described herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Further advantages of the present invention will become apparent to those skilled in the art having the benefit of the following detailed description of the preferred embodiments and with reference to the accompanying drawings, in which:

[0019] Figure 1 and 2 is a schematic diagram illustrating a side view of an embodiment of a system configured as described herein;

[0020] Figure 3is a flow chart illustrating one embodiment of a method for determining information of a sample; and

[0021] Figure 4 is a block diagram illustrating one embodiment of a non-transitory computer-readable medium storing program instructions for causing a computer system to perform the computer-implemented methods described herein.

[0022] Although the present invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and described in detail herein. The drawings may not be drawn to scale. However, it should be understood that the drawings and their detailed description are not intended to limit the present invention to the specific forms disclosed, but on the contrary, are intended to cover all modifications, equivalents and substitutions that fall within the spirit and scope of the present invention as defined by the appended claims. DETAILED DESCRIPTION

[0023] Turning now to the figures, it should be noted that the figures are not drawn to scale. In particular, the proportions of some elements of the figures are greatly exaggerated to highlight the characteristics of the elements. It should also be noted that the figures are not drawn to the same scale. Elements of similar configuration shown in more than one figure have been indicated using the same element numbers. Unless otherwise specified herein, any of the elements described and shown may include any suitable commercially available elements.

[0024] In general, embodiments described herein relate to methods and systems for determining information about a sample.Some embodiments described herein are configured for very sparse sampling methods for detecting non-compliant samples, such as wafers and lots.

[0025] In one embodiment, the sample is a wafer. The wafer may include any wafer known in semiconductor technology. Although some embodiments may be described herein with respect to a wafer, the embodiments are not limited to the samples to which they may be applied. For example, the embodiments described herein may be applied to samples such as photomasks, flat panels, personal computer (PC) boards, and other semiconductor samples.

[0026] Figure 1 One embodiment of a system configured for determining information of a sample is shown in FIG. The system includes a metrology subsystem 10, which includes at least an energy source and a detector. The energy source is configured to generate energy directed to a wafer. The detector is configured to detect energy from the wafer and generate an output in response to the detected energy.

[0027] In one embodiment, the metering subsystem is configured as a light-based metering subsystem. Figure 1, the metrology subsystem 10 includes an illumination subsystem configured to direct light to the wafer 14. The illumination subsystem includes at least one light source, such as light source 16. The illumination subsystem is configured to direct light to the wafer at one or more incident angles (which may include one or more oblique angles and / or one or more normal angles). For example, Figure 1 , light from light source 16 is directed through optical element 18 and then lens 20 to beam splitter 21, which directs the light at a normal angle of incidence to wafer 14. The angle of incidence may include any suitable angle of incidence, which may vary depending on, for example, the characteristics of the wafer.

[0028] The illumination subsystem may be configured to direct light to the wafer at different angles of incidence at different times. For example, the metrology subsystem may be configured to alter one or more characteristics of one or more elements of the illumination subsystem so that the light may be directed at different angles of incidence. Figure 1 In one such example, the metrology subsystem may be configured to move light source 16, optical element 18, and lens 20 so that light is directed to the wafer at different angles of incidence.

[0029] The metrology subsystem may be configured to direct light to the wafer at more than one incident angle simultaneously. For example, the illumination subsystem may include more than one illumination channel, one of which may include a light source 16, an optical element 18, and a lens 20 (e.g., Figure 1 One of the illumination channels (shown in FIG. 1 ) and the other of the illumination channels (not shown) may include similar elements, which may be differently or identically configured or may include at least a light source and possibly one or more other components, such as those described further herein. If this light is directed to the wafer simultaneously with other light, one or more characteristics (e.g., wavelength, polarization, etc.) of the light directed to the wafer at different angles of incidence may be different, such that light resulting from illumination of the wafer at different angles of incidence may be distinguished from one another at a detector.

[0030] The lighting subsystem may also include only one light source (e.g. 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 in each of the different optical paths may then be directed to the wafer. Multiple illumination channels may be configured to direct light to the wafer at the same time or at different times (e.g., when different illumination channels are used to illuminate the wafer sequentially). In another example, the same illumination channel may be configured to direct light with different characteristics to the wafer at different times. For example, in some examples, the optical element 18 may be configured as a spectral filter and the properties of the spectral filter may be changed in a variety of different ways (e.g., by swapping out the spectral filter) so that light of different wavelengths may be directed to the wafer at different times. The illumination subsystem may have any other suitable configuration known in the art.

[0031] Light source 16 may be a broadband plasma (BBP) light source. In this manner, the light generated by the light source and directed to the wafer may include broadband light. However, the light source may include any other suitable light source configured to generate light of any suitable wavelength known in the art, such as any suitable laser known in the art. The laser may be configured to generate monochromatic or near-monochromatic light. In this manner, the laser may be a narrow-band laser. The light source may also include a polychromatic light source that generates multiple discrete wavelengths or bands of light.

[0032] Light from optical element 18 can be focused by lens 20 onto beam splitter 21. Although lens 20 is Figure 1 2 is shown as a single refractive optical element, but in reality, lens 20 may include several refractive and / or reflective optical elements that, in combination, focus light from the optical element onto the wafer. The illumination subsystem 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, and the like, which may include any such suitable optical elements known in the art. Additionally, the system may be configured to alter one or more of the elements of the illumination subsystem based on the type of illumination used for the wafer.

[0033] The metrology subsystem may also include a scanning subsystem configured to move the wafer relative to the optical elements. For example, the metrology subsystem may include a stage 22 on which the wafer 14 is placed during metrology. The scanning subsystem may include any suitable mechanical and / or robotic assembly (including the stage 22) that may be configured to move the wafer so that one or more different measurement points on the wafer can be located in the field of view of the metrology subsystem. Additionally or alternatively, the metrology subsystem may be configured so that one or more optical elements of the metrology subsystem move relative to the wafer to thereby measure different points on the wafer. The wafer may be moved relative to the metrology subsystem (or vice versa) in any suitable manner.

[0034] The metrology subsystem further includes one or more detection channels. At least one of the detection channels includes a detector configured to detect light from the wafer due to the metrology subsystem illuminating the wafer and to generate an output in response to the detected light. For example, Figure 1 The metrology subsystem shown in FIG. 1 includes two detection channels, one formed by collector 24, element 26 and detector 28 and the other formed by collector 30, element 32 and detector 34. Figure 1, two detection channels are configured to collect and detect light at different collection angles. In some examples, one detection channel is configured to detect specularly reflected light, while the other detection channel is configured to detect light that is not specularly reflected from the wafer (e.g., scattered, diffracted, etc.). However, the detection channels can be configured to detect the same type of light from the wafer (e.g., specularly reflected light). The metrology subsystem can also include a different number of detection channels (e.g., only one detection channel or two or more detection channels). Although each of the collectors is Figure 1 is shown as a single refractive optical element, but each of the collectors may include a refractive optical element and / or a reflective optical element.

[0035] The detection channel may include any suitable detector known in the art, such as a photomultiplier tube (PMT), a charge coupled device (CCD), and a time-delay integration (TDI) camera. The detector and may include a non-imaging detector or an imaging detector. A non-imaging detector may be configured to detect certain characteristics of light (e.g., intensity) but may not be configured to detect such characteristics that vary depending on the position within the imaging plane. The output generated by such a detector may be a signal or data, but not an image signal or image data. In such an example, a computer subsystem of the system, such as computer subsystem 36, may be configured to generate an image of the wafer from the non-imaging output of the detector. However, the detector may be configured as an imaging detector configured to generate an imaging signal or image data. Thus, the system may be configured to generate the output described herein in many ways.

[0036] This article provides Figure 1 1 and 2 to generally illustrate configurations of metrology subsystems that may be included in embodiments of the systems described herein. Obviously, the metrology subsystem configurations described herein may be altered to optimize the performance of the system, as is typically performed when designing commercial systems. In addition, the systems described herein may be implemented using existing metrology systems (e.g., by adding the functionality described herein to an existing system), such as the Archer, ATL, SpectraShape, SpectraFilm, Aleris, and WaferSight families of tools available from KLA Corp. of Milpitas, Calif. For some such systems, the methods described herein may be provided as optional functionality of the system (e.g., in addition to other functionality of the system). Alternatively, the systems described herein may be designed "from the ground up" to provide an entirely new system.

[0037] The computer subsystem 36 of the system may be coupled to the detector of the metrology 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 may receive the output generated by the detector during metrology. The computer subsystem 36 may be configured to perform a number of functions using the output of the detector described herein and any other functions further described herein. For example, the computer subsystem may be configured to determine a characteristic of a sample based on the output generated.

[0038] The characteristics of the sample determined by the computer subsystem may vary depending on the configuration of the metrology subsystem and the sample being measured. In one embodiment, the characteristic is a superposition of one or more first patterned features formed on the sample and one or more second patterned features formed on the sample. The characteristics of the sample may be any other characteristic of interest, such as film thickness, patterned structure profile, critical dimension (CD), line edge roughness (LER), and line width roughness (LWR). These characteristics may be determined using the generated output in any manner known in the art. This computer subsystem may be further configured as described herein.

[0039] This computer subsystem (and other computer subsystems described herein) may also be referred to herein as a computer system. Each of the computer subsystems or systems described herein may take various forms, including personal computer systems, image computers, mainframe computer systems, workstations, network appliances, Internet appliances, or other devices. In general, the term "computer system" may be broadly defined to encompass any device having one or more processors that execute instructions from a memory medium. The computer subsystem or system may also include any suitable processor known in the art, such as a parallel processor. In addition, the computer subsystem or system may include a computer platform with high-speed processing and software as a stand-alone or networked tool.

[0040] If the system includes more than one computer subsystem, the different computer subsystems may be coupled to each other so that images, data, information, instructions, etc. may be sent between the computer subsystems, as further described herein. For example, computer subsystem 36 may be coupled to computer subsystem 102 (e.g., a wireless transmission medium) via any suitable transmission medium, which may include any suitable wired and / or wireless transmission medium known in the art. Figure 1 Two or more of such computer subsystems may also be operatively coupled by a shared computer-readable storage medium (not shown).

[0041] In another embodiment, the metrology subsystem is configured as an electron beam metrology subsystem. Figure 2In one such embodiment shown in FIG. 1 , the metering subsystem includes an electronic column 122 coupled to a computer subsystem 124. Figure 2 , the electron column includes an electron beam source 126 configured to generate electrons that are focused on a wafer 128 by one or more elements 130. The electron beam source may include, for example, a cathode source or 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 selection aperture, an objective lens, and a scanning subsystem, all of which may include any such suitable elements known in the art.

[0042] Electrons returning from the wafer (eg, secondary electrons) may be focused by one or more elements 132 onto a detector 134. One or more elements 132 may include, for example, a scanning subsystem, which may be the same scanning subsystem included in element 130.

[0043] The electron column may include any other suitable elements known in the art. In addition, the electron column may be further configured as described in U.S. Pat. No. 8,664,594 issued on April 4, 2014 to Jiang et al., U.S. Pat. No. 8,692,204 issued on April 8, 2014 to Kojima et al., U.S. Pat. No. 8,698,093 issued on April 15, 2014 to Gubbens et al., and U.S. Pat. No. 8,716,662 issued on May 6, 2014 to MacDonald et al., which are incorporated herein by reference as if fully set forth.

[0044] Although the electron column Figure 2 , is shown as being configured so that electrons are directed to the wafer at an oblique angle of incidence and collected from the wafer at another oblique angle, but the electron beam may be directed to and collected from the wafer at any suitable angle. Additionally, the metrology subsystem may be configured to generate output for the wafer using multiple modes (e.g., with different illumination angles, collection angles, etc.). The multiple modes of the metrology subsystem may differ in any image generation parameter of the subsystem.

[0045] The computer subsystem 124 may be coupled to a detector 134, as described above. The detector may detect electrons returning from the surface of the wafer, thereby forming an electron beam image of the wafer. The electron beam image may include any suitable electron beam image. The computer subsystem 124 may be configured to use the output of the detector and / or 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. Figure 2 The system of electron beam subsystems shown in may be further configured as described herein.

[0046] This article provides Figure 2 1 and 2 to generally illustrate the configuration of a metrology subsystem that may be included in the embodiments described herein. As with the optical subsystem described above, the electron beam subsystem described herein may be modified to optimize the performance of the metrology subsystem, as is typically performed when designing a commercial system. In addition, the systems described herein may be implemented using an existing electron beam system (e.g., by adding the functionality described herein to the existing electron beam system). For some such systems, the methods described herein may be provided as optional functionality of the system (e.g., in addition to other functionality of the system). Alternatively, the systems described herein may be designed "from the ground up" to provide an entirely new system.

[0047] Although the metrology subsystem is described above as an optical or electron beam subsystem, the metrology subsystem may be an ion beam subsystem. This metrology subsystem may be replaced by any suitable ion beam source known in the art, except that the electron beam source may be replaced by any suitable ion beam source known in the art. Figure 2 In addition, the metrology subsystem may also be any other suitable ion beam tool, such as ion beam tools included in commercially available focused ion beam (FIB) systems, helium ion microscope (HIM) systems, and secondary ion mass spectrometry (SIMS) systems.

[0048] As described above, the metrology subsystem is configured to direct energy (e.g., light, electrons, etc.) to a physical version of the sample, thereby producing an output of the physical version of the sample. In this way, the metrology subsystem can be configured as a "real" subsystem rather than a "virtual" subsystem. However, Figure 1 The storage media (not shown) and computer system 102 shown in the embodiment may be configured as a "virtual" system. In particular, the storage media and computer subsystem may be configured as a "virtual" system as described in commonly assigned U.S. Patent Nos. 8,126,255, issued on February 28, 2012 to Bhaskar et al. and 9,222,895, issued on December 29, 2015 to Duffy et al., both of which are incorporated herein by reference as if fully set forth. The embodiments described herein may be further configured as described in these patents.

[0049] The metrology subsystems described herein may be configured to generate outputs, such as images, of a wafer using multiple modes. In general, a "mode" is defined by the values ​​of the parameters of the metrology subsystem used to generate the outputs of the wafer. Thus, different modes may differ in the value of at least one of the parameters of the metrology subsystem (rather than in the location in which the output is generated). In this way, the output may be generated by the metrology subsystem using two or more different values ​​of the parameters of the metrology subsystem. For example, in the optical subsystem, different modes may use different wavelengths of light for illumination. The modes may differ in the illumination wavelength, as further described herein for different modes (e.g., by using different light sources, different spectral filters, etc.). In another embodiment, different modes may use different illumination channels. For example, as described above, the metrology subsystem may include more than one illumination channel. Thus, different illumination channels may be used for different modes.

[0050] In a similar manner, the output generated by the electron beam subsystem may include output, such as an image, generated by two or more different values ​​of parameters of the electron beam subsystem. Multiple modes of the electron beam subsystem may be defined by the values ​​of the parameters of the electron beam subsystem used to generate the output and / or image of the wafer. Thus, different modes may differ in the value of at least one of the electron beam parameters of the electron beam subsystem. For example, in the electron beam subsystem, different modes may use different incident angles for illumination.

[0051] The computer system is configured to generate a sampling plan for non-compliance detection of characteristics of samples only for use in the metrology process. Figure 3 As shown in step 304 of , the computer system may generate a sampling plan for non-compliance monitoring only. In one embodiment, the sampling plan is not configured for feedback control of the characteristic. Configuring the sampling plan for non-compliance detection only and not for feedback control can be done in many different ways as described herein. Therefore, these embodiments represent a major change from the old method in that the sampling plan is only for non-compliance detection, rather than superimposed feedback control.

[0052] The computer system determines the number and location of the metrology points on the wafer for non-conformity detection. For example, the sampling plan generated as described herein will generally include information about which wafers in which batches are measured and at which locations on each wafer to perform the measurements. This information can be included in the sampling plan in any suitable manner. For example, the location where the measurement is performed on the wafer can be represented by some coordinates, such as wafer coordinates, die coordinates, design coordinates, coordinates relative to alignment marks, and the like. The information of the batch of wafers measured can also be represented in different ways, such as batch ID, information about the number or frequency of batches to be measured (e.g., each batch, every other batch, etc.), percentages or portions of batches to be measured, and the like. The information of the wafers to be measured can also be represented in a similar manner, such as wafer ID, information about the number or frequency of wafers to be measured (e.g., each wafer, every other wafer, etc.), percentages or portions of wafers to be measured, and the like.

[0053] In one embodiment, the density of the sampling plan is less than that required to implement feedback control of the characteristic. For example, the embodiments described herein generate and use substantially sparse sampling dedicated only to non-conforming wafer detection. In particular, the sampling plan used only for non-conformance monitoring is substantially sparser than the metrology sampling required for superimposed feedback control. More specifically, the proposed substantially sparse sampling plan used only for non-conformance detection does not have enough metrology points to perform superimposed feedback control based on metrology results generated at the metrology points. For example, the sampling plan generated as described herein may be configured to have only one or two measurement points for each wafer (or subset of wafers) in each batch. In this way, the embodiments described herein may be configured to detect non-conforming wafers by performing metrology on a small number of points on each wafer.

[0054] In contrast, current methods for overlay metrology typically have tens or even hundreds of measurement points on each of fewer than a few wafers in all lots to prevent this metrology from negatively impacting the throughput of the overall process. Overlay non-conformance detection is typically performed using these same results. In this way, the embodiments described herein perform overlay metrology in a completely new way compared to currently used methods and systems. In particular, the embodiments described herein are configured for generating a sampling plan to measure many or all wafers within a lot (each lot) using a very sparse sampling plan to maximize non-conformance detection.

[0055] In additional embodiments, the sampling plan is configured to generate an output for each of the samples in the batch. For example, the embodiments described herein provide a sampling method that can use reduced metrology on each wafer to detect non-conforming wafers within a batch. In another embodiment, the sampling plan is configured to generate an output for a subset of the samples in the batch. For example, the computer system may generate a sampling plan so that a subset of the wafers in each batch are measured using substantially sparse sampling to detect non-conforming wafers. The embodiments described herein ideally use substantially sparse sampling to measure all wafers within the batch. If this is not practical or feasible, the computer system may determine the number of wafers in the subset based on throughput requirements. The computer system may select a subset of wafers from the batch uniformly, randomly, or based on some known distribution (for example, if a user or computer system observes that wafers from the batch that are processed first or last by a manufacturing tool are more likely to be non-conforming). In this way, the sampling method generated as described herein can use reduced metrology on each or a subset of the wafers within the batch to detect non-conforming batches.

[0056] In one embodiment, generating a sampling plan includes selecting the number and coordinates of locations where the metrology subsystem generates output during the metrology process to match the non-conformance criteria of the sample. For example, the number and locations of metrology points (i.e., the sampling plan) can be selected to match the non-conformance criteria for a given layer and device in the manufacturing process. In this way, the number of non-conforming wafers that can be detected and repaired is maximized with minimal processing hits.

[0057] The computer system may select the number and location of metrology points to match the non-compliance criteria, as described in the following example. A user (e.g., a device manufacturer) may use statistics such as the mean + 3*absolute value of the measurement overlay for wafer quality control. For each layer and device, a threshold is statistically defined above which a wafer or batch is considered non-compliant. If the computer system has access to historical data (e.g., overlay measurements performed on multiple wafers from a given layer and device using a relatively dense sampling plan), the computer system may use one of the existing sampling optimization methods to generate multiple relatively sparse sampling plans. On each wafer, the computer system may use all of the original measurement points to calculate the statistics and then use a subset of points defined by the optimization method to estimate the statistics. The sampling plan that tracks the original statistics may be best selected as the sampling plan for non-compliance detection.

[0058] In some embodiments, the computer system is configured to determine a metric based on the generated output and a predetermined statistical process control (SPC) metric that separates compliant samples from non-compliant samples. This computer system configuration is optional when historical metrology data is available. For example, the computer system can calculate a metric using a metrology collected by a sampling plan generated only for non-compliant detection, which tracks an existing SPC metric for separating compliant from non-compliant samples. More specifically, a user can measure multiple superimposed points per wafer and calculate the mean and standard deviation of these measurements. Statistics (such as the absolute value of the mean + 3* standard deviation) are examples of this metric. The computer system can use the resulting quality control chart to determine how this statistic changes with operation. The computer system can define a threshold on this metric to separate compliant wafers from non-compliant wafers. This threshold can be linked to a yield metric for a manufacturing process, such as the yield of an electrical test performed later in the process.

[0059] In one such embodiment, the computer system is configured to determine a threshold value for a certain metric for separating compliant samples from non-compliant samples. For example, the embodiments described herein may calculate a threshold value for non-compliant wafer detection on substantially sparse metrology data. This computer system configuration is also optional when historical metrology data is available. The computer system may calculate a new threshold value on a new metric to separate compliant from non-compliant wafers. In one such example, the computer system may track some reference metrics (e.g., wafer yield, electrical test, average value of a dense sampling plan + 3*absolute value of standard deviation) that have been used to separate non-compliant wafers from compliant wafers. The computer system may correlate the metric calculated using substantially a small number of measurements with the reference metric and define a threshold value so that the new metric captures all non-compliant wafers while minimizing the number of false detections. This threshold calculation may be a supplement to the currently used method, in which the same threshold value for non-compliant detection is typically used independent of the basic sampling plan.

[0060] In another embodiment, generating a sampling plan includes determining a frequency of lot sampling, a frequency of sampling within a lot, a sampling plan within a sample, and metrology subsystem settings based on constraints on a metrology budget and metrology subsystem throughput. For example, a computer system may determine a frequency of lot sampling, a frequency of sampling within a lot, and a sampling plan within a wafer and tool settings under constraints on an available metrology budget and a desired tool throughput. In this manner, the embodiments described herein may be configured to co-optimize sampling and metrology tool parameters to achieve a desired throughput. Generating a sampling plan in this manner is an improvement over currently used methods because it explicitly considers the metrology accuracy / precision tradeoff for tool throughput when allocating a metrology budget.

[0061] In a further embodiment, generating a sampling plan includes allocating a predetermined metrology budget between batch sampling, sample sampling, and intra-sample sampling to maximize the detection of non-compliant samples. For example, the embodiments described herein provide a sampling system that optimally allocates the available metrology budget between batches, wafers, and intra-wafer sampling to maximize the number of non-compliant wafers detected. The metrology budget can be expressed in many different ways, such as the time allowed for metrology or the number of measurements that can be performed without affecting the total throughput. The allowed time, number of measurements, or other metrology budget specifications can then be allocated between wafers, batches, and measurement points per wafer to maximize the detection of non-compliant samples. In one such example, the total number of measurements in the predetermined metrology budget can be allocated to measure each wafer in each batch, even if this means that a generally limited number of measurement points can be measured on each wafer.

[0062] In additional embodiments, generating a sampling plan includes co-optimizing sampling frequency and metrology subsystem settings to maximize detection of non-compliant samples at a predetermined metrology subsystem throughput. In other words, an important feature of the embodiments described herein is a sampling system that co-optimizes sampling frequency and metrology tool settings to achieve optimal non-compliant detection at a desired tool throughput. For example, a metrology subsystem (such as a metrology subsystem further described herein) has several settings that can be used to trade off measurement time and measurement quality. In one such example, several image frames can typically be collected during measurement to reduce noise in the measurement or dual image capture can typically be performed instead of single image capture. These measurement parameters can be checked to determine whether they can be modified to reduce the time involved in the measurement and the acceptable impact on the measurement results. In the above examples, the computer system can determine whether the number of image frames collected can be reduced without causing too much noise in the measurement or whether non-compliant detection can be performed using only single image capture instead of dual image capture. In this way, the computer system can determine the measurement settings that can be used to fully detect non-compliant wafers in the shortest time. Reducing the measurement time allows more points per wafer and / or more wafers within a batch to be measured to detect non-conforming wafers.

[0063] As shown in step 300, an embodiment described herein or another system or method may perform a manufacturing process step on one or more samples, one or more batches of samples, etc. This manufacturing process step may be a photolithography process performed by a photolithography tool including a scanner or other exposure tool. However, this manufacturing process step may vary depending on the characteristics monitored by the embodiments described herein. For example, this manufacturing process step may be an etching process step performed using an etching tool. Any of these manufacturing process steps may be performed in any suitable manner known in the art.

[0064] The manufacturing process steps 300 produce manufacturing samples 302. In general, these manufacturing samples can be wafers having patterned features formed thereon in one of the above-mentioned manufacturing process steps. However, the manufacturing samples can be any other samples described herein. As mentioned above, in one embodiment, the characteristic is the superposition of one or more first patterned features formed on the sample and one or more second patterned features formed on the sample. In general, the term "superposition" (sometimes also referred to as "superposition offset") used herein is defined as the position of the first patterned feature on the sample relative to the second patterned feature on the sample. The first patterned feature and the second patterned feature are formed in different process steps (i.e., different lithography process steps). Typically, the superposition is determined for patterned features formed on different layers of the sample (stacked on top of each other), although this is not required. For example, the embodiments described herein may be configured for non-compliant detection of other spatial relationships between patterned features formed on the sample, such as the spatial relationship between different patterned features formed on the same layer using different lithography exposure steps.

[0065] The metrology subsystem is configured to generate an output of the sample by performing a metrology process on the sample using the generated sampling plan. In this way, the system includes a metrology tool that performs measurements according to the sampling plan generated by the computer system. Figure 3 As shown in step 306 of , the metrology subsystem may perform a metrology process using the sparse sampling plan generated in step 304. For example, the computer system and / or the metrology subsystem may be configured to perform a metrology process on the sample using the results of one or more steps described herein.

[0066] In one embodiment, the sampling plan includes information of one or more selected lots, one or more selected samples within the one or more selected lots, one or more locations on the one or more selected samples, and one or more metrology subsystem settings for generating outputs at the one or more locations, the computer system is configured to send the information in the sampling plan to the metrology subsystem, and use the generated sampling plan to generate outputs based on the information from the computer system. For example, the computer system may communicate to the metrology tool decisions of which lots to measure, which wafers within a lot, which sampling points within a wafer, and which tool recipe parameters to use, all of which may be determined according to any of the embodiments described herein.

[0067] In some such embodiments, the computer system may be configured to store information for the generated sampling plan used in the metering process. The computer system may be configured to store information in a recipe or by generating a recipe for the process in which the sampling plan will be used. A "recipe" as used herein may generally be defined as a set of instructions that can be used by a tool to perform a process on a sample. In this way, generating a recipe may include generating information on how to perform a process, which can then be used to generate instructions for performing the process. Embodiments may be used to set up a new process or recipe. Embodiments may also be used to modify an existing process or recipe, whether it is a process or recipe for a sample or a process and recipe created for one sample and applicable to another sample.

[0068] The information of the sampling plan stored by the computer system may include any information that can be used to identify and / or use the sampling plan (e.g., such as a file name and its storage location, and the file may include information of the sampling plan, such as information about the wafer to be measured, the batch to be measured, the location on the wafer to be measured, etc.). The computer system may be configured to store the information used for sampling in any suitable computer-readable storage medium. The information may be stored with any of the results described herein and may be stored in any manner known in the art. The storage medium may include any storage medium described herein or any other suitable storage medium known in the art. After the information is stored, the information may be accessed in the storage medium and used by any of the method or system embodiments described herein, formatted for display to a user, used by another software module, method or system, etc. For example, the embodiments described herein may generate the above-mentioned metering recipe. Then, the metering recipe may be stored and used by the system or method (or another system or method) to perform a metering process on a sample to thereby generate information (e.g., measurement characteristics) of the sample.

[0069] The computer system is configured to determine the characteristics of the sample based on the generated output (as shown in step 308) and detect whether the characteristics of one or more samples are non-compliant based on the determined characteristics of the sample (as shown in step 310). For example, the computer system may receive metrology data from a metrology tool and determine the characteristics from the metrology data. The computer system may determine the characteristics of the sample using any suitable metrology method or algorithm known in the art. In general, for overlay measurements, this algorithm may be configured to identify different patterned features in one or more images generated by the metrology subsystem and determine the spatial relationship between the different patterned features based on, for example, the distance between the features in the image and the size of the pixels in the image. The computer system may detect whether the characteristics are non-compliant by applying a metric or threshold determined as described herein to the determined characteristics to decide which batches and / or wafers are non-compliant.

[0070] In one embodiment, the metrology subsystem is configured to generate additional outputs for at least one of the samples by performing additional metrology processes on at least one of the samples using a different sampling plan suitable for feedback control of the characteristic, and the computer system is configured to determine a corrective process for at least one of the samples based on the generated additional outputs. The different sampling plan suitable for feedback control of the characteristic can be any currently used sampling plan that can provide sufficient measurements for feedback control of the characteristic. The metrology performed using this sampling plan can be performed as further described herein or in any other suitable manner known in the art. The computer system can determine the corrective process as further described herein or in any suitable manner known in the art.

[0071] In one such example, in step 306, a metrology process is performed using a substantially sparse sampling plan to measure, for example, a subset (or all) of the wafers in each batch to detect non-conforming wafers. This metrology is performed independently of and possibly in conjunction with the metrology process using a process of record (POR) sampling plan designed to support stability of advanced process control (APC). In this way, the embodiments described herein provide a sampling method for non-conforming wafer monitoring and rework decisions. In addition, the embodiments described herein provide a sampling system that separates overlay control from non-conforming detection and rework decisions. This non-conforming target metrology may be performed in addition to metrology designed for APC.

[0072] In another embodiment, the computer system is configured to select at least one of the one or more samples detected as non-compliant for which the metrology process is performed using a more intensive sampling plan than the generated sampling plan. In another such embodiment, the more intensive sampling plan is configured for feedback control of the characteristic. For example, the computer system may receive metrology data from a metrology tool and may use a metric or threshold determined as described herein to determine which lots and / or wafers are non-compliant and whether they should be remeasured using more intensive (e.g., POR) sampling to determine rework corrections. Figure 3 As shown in step 312 of , when the computer system determines that one or more samples are non-compliant, the metrology subsystem may perform a metrology process on at least one of the samples using POR sampling. In this manner, because the sampling plan is generated herein for non-compliant detection rather than feedback control, the measurements generated using the sampling plan cannot be used to determine rework corrections or other suitable feedback control parameters. Therefore, performing metrology on any one or more samples detected as non-compliant using more intensive POR sampling can determine whether and how one or more parameters of the lithography process should be changed.

[0073] A more intensive sampling plan for feedback control of a characteristic may be a predetermined sampling plan (e.g., a POR sampling plan) that may be generated by a computer system or another system or method and accessed by the embodiments described herein. A "more intensive" sampling plan may be defined as being more intensive than a sampling plan generated only for non-compliance detection as described herein. For example, a "more intensive" sampling plan may be configured to measure dozens or even hundreds of measurement points on a few samples or batches.

[0074] Thus, the computer systems described herein may use a predetermined denser sampling plan for feedback control. However, in some embodiments, the computer system may be configured to generate a denser sampling plan, for example, based on any of the results described herein. For example, when a sample is determined to be noncompliant with a characteristic, a denser sampling plan may be generated by the computer system based on the degree of noncompliance of the characteristic. In one such example, if the characteristic of one or more samples is determined to be substantially very noncompliant, the denser sampling plan may include measuring more measurement points on more samples than when the characteristic of one or more samples is determined to be only slightly noncompliant. Any suitable relationship between the degree of noncompliance of the characteristic and the density of the sampling plan for feedback control may be used by the computer system to determine a denser sampling plan. The relationship may be based on information such as historical data, theoretical models, or processes.

[0075] In this way, the embodiments described herein may be configured to perform non-compliance detection using a sampling plan generated as described herein and to select samples for APC-type monitoring based on the results of the non-compliance detection. However, this metering process sequence may be modified in some cases. In one such example, a sampling plan generated as described herein may include information on which samples will be sent to POR metering for APC and which samples will be sent to non-compliance detection. In this way, a first subset of samples may be sent to APC metering, a second subset may be sent to non-compliance metering, and different subsets may be predetermined and not based on the results of any metering process. In some such examples, APC metering and non-compliance metering may be performed using the same metering subsystem and in the same metering process (e.g., when a batch is loaded into a metering tool), but other variations are feasible, such as performing different metering using different metering tools, in different processes, etc.

[0076] In one such embodiment, the computer system is configured to determine a corrective process for at least one of one or more of the samples based on output generated using a more intensive sampling plan. For example, the computer system may determine a characteristic of the sample based on output generated during a POR metrology process, such as Figure 3 The computer system may determine the characteristic based on the POR metering process output in any suitable manner known in the art. The computer system may also determine the characteristic based on the POR metering process output in any suitable manner known in the art. Figure 3In step 316 of determining whether a characteristic of the one or more samples is out of control. Determining whether a characteristic of the one or more samples is out of control may include applying a threshold to the determined characteristic and determining that the sample is out of control when the determined characteristic is above this threshold (or below the threshold, depending on the characteristic and the threshold). The threshold may be an SPC threshold determined as further described herein.

[0077] When the computer system determines that the characteristics of one or more samples are out of control, the computer system may determine rework parameters in step 318. Then, the determined rework parameters and the one or more samples with out-of-control characteristics may be sent back to the manufacturing process step 300. For example, if the characteristic is determined to be beyond the control limit, the computer system may determine whether the characteristics of the out-of-control sample can be remedied by changing one or more parameters of the manufacturing process steps or tools and then performing the process on the sample again using the changed parameters. In one such example, after performing lithography, the patterned features formed by lithography may be stripped from the sample, such as using an etching process, a polishing process, etc. Then, the sample may be re-performed with lithography using new process parameters. Determining the rework parameters may include determining any parameters involved in re-forming the patterned features on the sample, including any parameters of any stripping process, any new parameters of the lithography process, etc. The rework parameter determination may be performed using any suitable predetermined relationship between the process parameters and the sample characteristics.

[0078] Whether rework parameters are determined by the embodiments described herein may depend on the process performed on the sample. For example, not all manufacturing processes may be reworked or reworking some manufacturing processes may simply be impractical. One such example is an etching process. If the manufacturing process step is an etching process, it is still beneficial to detect non-compliant samples and / or out-of-control samples. For example, such wafers and / or batches may be scrapped rather than entering the next manufacturing process step, thereby avoiding spending time and money on wafers that must be scrapped anyway.

[0079] When the characteristic of the sample is not determined to be out of compliance in step 310 and / or the characteristic of the sample is not determined to be out of control in step 316, then the sample can be sent to the next manufacturing process step in step 320. In other words, when the sample is determined to be acceptable (e.g., not out of compliance and / or within control limits), the sample can be sent to the next manufacturing process step. In one such example, if the manufacturing process step 300 is a photolithography process, then the manufacturing process step 320 can be an etching process. In another such example, if the manufacturing process step 300 is an etching process, then the manufacturing process step 320 can be a deposition step.

[0080] The computer system can be configured to generate results for the sample, which can include any of the information described herein, such as the determined characteristics, whether any of the samples are noncompliant, which samples are noncompliant, rework parameters, etc. The results for the sample can be generated by the computer system in any suitable manner. In addition, the results for the sample can be stored as further described herein and used to perform one or more functions on the sample or other samples of the same type.

[0081] Such functions include, but are not limited to, changing a process, such as a manufacturing process or step that has been or will be performed on a sample in a feedback or feedforward manner, etc. For example, as further described herein, the computer system may be configured to determine one or more changes to a process that has been performed on a sample and / or a process that will be performed on a sample based on the determined characteristics. The change in process may include any suitable change in one or more parameters of the process. The computer system preferably determines the change so that any out-of-control characteristics can be prevented from occurring on other samples on which a correction process is performed, any out-of-control characteristics can be corrected or eliminated for the sample in another process performed on the sample, any out-of-control characteristics can be compensated for in another process performed on the sample, etc. The computer system may determine such changes in any suitable manner known in the art.

[0082] The changes may then be sent to a semiconductor manufacturing system (not shown) or a storage medium (not shown) accessible to both the computer system and the semiconductor manufacturing system. The semiconductor manufacturing system may or may not be part of the system embodiments described herein. For example, the metrology subsystem and / or computer system described herein may be coupled to the semiconductor manufacturing system, for example, via one or more common elements such as a housing, a power supply, a sample handling device or mechanism, etc. The semiconductor manufacturing system may include any semiconductor manufacturing system known in the art, such as a lithography tool, an etching tool, a chemical mechanical polishing (CMP) tool, a deposition tool, and the like.

[0083] The embodiments described herein have several important advantages over current methods for non-conforming metrology. For example, the embodiments described herein are configured to be able to capture and rework more non-conforming batches at a relatively low metrology cost and avoid yield loss. In another example, the embodiments described herein are able to capture and rework more non-conforming wafers within a batch at a relatively low metrology cost and avoid yield loss. In additional examples, the embodiments described herein are able to avoid unnecessary work by measuring more wafers within a batch at a relatively low metrology cost. The embodiments described herein can also avoid downgrading good batches due to unnecessary rework. In addition, the embodiments described herein are able to collaboratively optimize metrology tool settings and sampling to achieve desired throughput and non-conforming detection accuracy.

[0084] The advantages of the embodiments described herein over currently used metrology systems and methods are provided by several new features of the embodiments described herein, including but not limited to sampling methods and systems for non-conforming wafer monitoring and rework decisions only. Another new feature of the embodiments described herein is a sampling system that separates overlay control from non-conforming detection and rework decisions. An additional new feature of the embodiments described herein is a sampling method that can use reduced metrology on a subset of wafers within a batch to detect non-conforming batches. Another new feature includes a sampling method that can use reduced metrology on each wafer to detect non-conforming wafers within a batch. The new features also include a sampling system that can optimally allocate available metrology budgets between batches, wafers, and intra-wafer sampling to maximize the number of non-conforming wafers detected. Yet another new feature is a sampling system that collaboratively optimizes sampling frequency and metrology tool settings to achieve optimal non-conformity detection at the required tool throughput.

[0085] Each of the embodiments of each of the above-described systems may be combined together into a single embodiment.

[0086] Another embodiment relates to a computer-implemented method for determining information about a sample. The method includes generating a sampling plan for non-compliance detection of a characteristic of a sample only during a metrology process, such as Figure 3 The method also includes generating an output for the sample by performing a metrology process on the sample using the metrology subsystem and the generated sampling plan, as shown in step 306. In addition, the method includes determining a characteristic of the sample based on the generated output, as shown in step 308. The method further includes detecting whether a characteristic of one or more of the samples is non-compliant based on the determined characteristic of the sample, as shown in step 310. The generating sampling plan, determining the characteristic, and detecting steps are performed by a computer system (e.g., a computer system) coupled to a metrology subsystem (e.g., metrology subsystem 10). Figure 1 Executed by computer subsystem 36 and / or computer subsystem 102) shown in .

[0087] Each of the steps of the method may be performed as further described herein. The method may also include any other steps that may be performed by the system, computer system, and / or metering subsystem described herein. The computer system and metering subsystem may be configured according to any of the embodiments described herein, such as computer subsystem 36 and / or computer subsystem 102 and metering subsystem 10, respectively. In addition, the above method may be performed by any of the system embodiments described herein.

[0088] Additional embodiments relate to a non-transitory computer-readable medium storing program instructions executable on a computer system to perform a computer-implemented method for determining information of a sample. Figure 4 One such embodiment is shown in FIG. Figure 4 , non-transitory computer readable medium 400 includes program instructions 402 executable on a computer system 404. The computer-implemented method may include any of the steps of any of the methods described herein.

[0089] Program instructions 402 implementing methods such as those described herein may be stored on computer readable medium 400. The computer readable medium may be a storage medium such as a magnetic or optical disk, tape, or any other suitable non-transitory computer readable medium known in the art.

[0090] The program instructions may be implemented in any of a variety of ways, including process-based techniques, component-based techniques, and / or object-oriented techniques, etc. For example, the program instructions may optionally be implemented using ActiveX controls, C++ objects, JavaBeans, Microsoft Foundation Classes ("MFC"), SSE (Streaming SIMD Extensions), or other techniques or methods.

[0091] Computer system 404 may be configured according to any of the embodiments described herein.

[0092] Those skilled in the art will understand further modifications and alternative embodiments of various aspects of the present invention in view of the specific embodiments. For example, methods and systems for determining the information of a sample are provided. Therefore, the specific embodiments should be interpreted as being merely illustrative and used to teach the general manner in which a person skilled in the art implements the present invention. It should be understood that the forms of the present invention shown and described herein should be considered as currently preferred embodiments. Elements and materials may replace the elements and materials illustrated and described herein, parts and processes may be reversed, and certain features of the present invention may be utilized independently, as will be understood by those skilled in the art after benefiting from the specific embodiments of the present invention. Changes may be made to the elements described herein without departing from the spirit and scope of the present invention described in the following appended claims.

Claims

1. A system configured to determine information of a sample, comprising: a computer system configured to generate a sampling plan for non-compliance detection of a characteristic of a sample in a metrology process only; and a metrology subsystem configured to generate an output for the sample by performing the metrology process on the sample using the generated sampling plan; Wherein the computer subsystem is further configured for determining the characteristic of the samples based on the generated output and detecting whether the characteristic of one or more of the samples is non-compliant based on the determined characteristic of the samples.

2. The system of claim 1, wherein the feature is a superposition of one or more first patterned features formed on the sample and one or more second patterned features formed on the sample.

3. The system of claim 1, wherein the sampling plan is not configured for feedback control of the characteristic.

4. The system of claim 1, wherein the density of the sampling plan is less than a density required to implement feedback control of the characteristic.

5. The system of claim 1, wherein the sampling plan is configured to generate the output for each of the samples in a batch.

6. The system of claim 1, wherein the sampling plan is configured to generate the output of a subset of the samples in a batch.

7. The system of claim 1, wherein generating the sampling plan comprises selecting the number and coordinates of locations where the metrology subsystem generates the output during the metrology process to match non-compliance criteria for the sample.

8. The system of claim 1, wherein the computer system is further configured to determine a metric based on the generated output and a predetermined statistical process control metric that separates conforming samples from non-conforming samples.

9. The system of claim 8, wherein the computer system is further configured to determine a threshold value of the determined metric that separates the compliant samples from the non-compliant samples.

10. The system of claim 1, wherein generating the sampling plan comprises determining a frequency of batch sampling, a frequency of within-batch sampling, a within-sample sampling plan, and a metrology subsystem setting based on constraints on a metrology budget and metrology subsystem throughput.

11. The system of claim 1, wherein generating the sampling plan comprises allocating a predetermined metrology budget among batch sampling, sample sampling, and within-sample sampling to maximize detection of non-compliant samples.

12. The system of claim 1, wherein generating the sampling plan comprises co-optimizing sampling frequency and metering subsystem settings to maximize detection of non-compliant samples at a predetermined metering subsystem throughput.

13. The system of claim 1 , wherein the sampling plan comprises information of one or more selected batches, one or more selected samples within the one or more selected batches, one or more locations on the one or more selected samples, and one or more metrology subsystem settings for generating the output at the one or more locations, wherein the computer system is further configured to send the information in the sampling plan to the metrology subsystem, and wherein generating the output using the generated sampling plan is based on the information from the computer system.

14. The system of claim 1 , wherein the metrology subsystem is further configured to generate additional outputs for at least one of the samples by performing additional metrology processes on at least one of the samples using a different sampling plan suitable for feedback control of the characteristic, and wherein the computer system is further configured to determine a correction process for at least one of the samples based on the generated additional outputs.

15. The system of claim 1, wherein the computer system is further configured to select at least one of the one or more of the samples detected as non-compliant for which the metrology process is to be performed using a sampling plan that is more intensive than the generated sampling plan.

16. The system of claim 15, wherein the computer system is further configured for determining a correction process for the at least one of the one or more of the samples based on the output generated using the more intensive sampling plan.

17. The system of claim 15, wherein the more intensive sampling schedule is configured for feedback control of the characteristic.

18. The system of claim 1, wherein the metrology subsystem is further configured as a light-based metrology subsystem.

19. A non-transitory computer readable medium storing program instructions executable on a computer system to perform a computer-implemented method for determining information of a sample, wherein the computer-implemented method comprises: Sampling plans that produce non-conformance testing of characteristics of samples used only for metrological processes; generating an output for the sample by performing the metrology process on the sample using the generated sampling plan; determining the characteristic of the sample based on the generated output; and Whether the characteristic of one or more of the samples is non-compliant is detected based on the determined characteristic of the samples.

20. A computer-implemented method for determining information about a sample, comprising: Sampling plans that produce non-conformance testing of characteristics of samples used only for metrological processes; generating an output for the sample by performing the metrology process on the sample using a metrology subsystem and the generated sampling plan; determining the characteristic of the sample based on the generated output; and Based on the determined characteristic of the samples, detecting whether the characteristic of one or more of the samples is out of compliance, wherein generating the sampling plan, the determining, and the detecting are performed by a computer system coupled to the metrology subsystem.

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