Optical beam sensor with central transmissive cutout

Abstract

Methods and systems are provided for determining one or more properties of light in an optical system. One system includes a detector disposed in a path of light between a light source in the optical system and a sample on which the optical system performs a process. The detector includes a central cutout configured to allow only a first portion of the light from the light source to pass therethrough, and four or more detector segments disposed about the central cutout and in the path of only a second portion of the light from the light source. The four or more detector segments are configured to separately generate outputs in response to light incident thereon. The system also includes a control subsystem configured to determine one or more properties of the light from the light source based on the outputs separately generated by the four or more detector segments.

Description

[Technical Field]

[0001] The present invention generally relates to methods and systems for determining one or more properties of light in an optical system. [Background technology]

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

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

[0004] With the performance of 193 nm immersion lithography reaching its limits as well as the substantial high cost and yield issues associated with multi-patterning lithography processes, extreme ultraviolet (EUV) lithography is under extensive development and is being used for next generation lithography (NGL) technologies to extend Moore's Law and enable computer chips to become smaller, faster, and more efficient.

[0005] Defectivity control of EUV photomasks, which define the patterns printed on wafers, plays a critical role in process yield management. However, EUV photomask defectivity control has been considered one of the high-risk areas of EUV lithography development due to the lack of both actinic EUV photomask inspection tools and high-throughput charged particle beam inspection tools that can inspect photomasks with the required resolution. While there are currently some products on the market that perform relatively fast actinic EUV patterned mask inspection, these inspectors are relatively complex for several reasons that are not a factor at longer wavelengths in mask inspection.

[0006] The geometries on EUV masks require inspection systems with relatively high image fidelity and substantially low detection noise to resolve defect features that can cause performance degradation in integrated circuits fabricated from these masks during EUV lithography. However, the EUV spectral range poses many new challenges to the optical and system design of inspection tools due to the short wavelengths, high-energy photons, and low radiance (brightness) of laboratory (i.e., relatively compact) EUV radiation sources. Accurate knowledge of the spatial incident intensity distribution within the illumination field at the mask is essential for image analysis using an inspection tool.

[0007] Conventional beam stabilization systems utilize a beam splitter across the entire cross section of the beam to split off a portion of the light to an optical detector (e.g., a quad-cell detector, although position-sensitive detectors and cameras can also be used). Typically, a separate tooling camera or other imaging device is required to evaluate the beam shape.

[0008] The main drawback of conventional methods is that they require a beam splitter to redirect a portion of the beam to the detector, which would result in significant attenuation of the primary beam that is unacceptable for many applications, such as high-speed imaging inspection, for wavelengths such as EUV (e.g., 13.5 nm) for which efficient beam splitters do not yet exist.

[0009] Another drawback of conventional methods is that they require additional sensors, optical mechanisms, and tooling to evaluate the beam profile. Such additional hardware adds cost, complexity, and contamination risk to ultra-clean systems, and creates the same problems described above when a beam splitter is used to sample the primary beam. As an alternative to beam splitters, conventional applications have also involved moving a detector back and forth into and out of the primary beam for direct sampling. This approach has the drawbacks of requiring additional actuators and mechanisms, and of completely blocking the beam, so measurements cannot be made in situ while the system is fully operational. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] U.S. Patent No. 7,872,236 [Patent Document 2] U.S. Patent Application Publication No. 2021 / 0262944 Summary of the Invention [Problem to be solved by the invention]

[0011] It would therefore be advantageous to develop a system and / or method for determining one or more properties of light in an optical system that does not have one or more of the above-mentioned drawbacks. [Means for solving the problem]

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

[0013] One embodiment relates to a system configured to determine one or more properties of light in an optical system. The system includes a detector disposed in a path of light between a light source in the optical system and a sample on which the optical system performs a process. The detector includes a central cutout configured to allow only a first portion of light from the light source to pass therethrough. The first portion of light is directed by the optical system to the sample during the process. The detector also includes four or more detector segments disposed about the central cutout and in the path of only a second portion of light from the light source. The four or more detector segments are configured to separately generate outputs in response to light incident thereon. The system also includes a control subsystem configured to determine one or more properties of light from the light source based on the outputs separately generated by the four or more detector segments. The system may be further configured as described herein.

[0014] Another embodiment relates to a system configured to determine one or more properties of light in an optical system. The system includes a light source configured to generate light having one or more wavelengths shorter than 190 nm. The system also includes optical elements configured to direct the light generated by the light source to a sample and to direct the light from the sample to one or more first detectors configured to generate a first output in response to the light from the sample. The system further includes a computer subsystem configured to determine information about the sample based on the first output.

[0015] The system also includes a second detector disposed in the path of the light between the light source and the sample. The second detector further includes a central cutout configured to allow only a first portion of the light from the light source to pass therethrough. The first portion of the light is directed toward the sample by one or more of the optical elements. The second detector also includes four or more detector segments disposed about the central cutout and in the path of the second portion of the light from the light source. The four or more detector segments are configured to independently generate second outputs in response to light incident thereon. The system further includes a control subsystem configured to determine one or more characteristics of the light from the light source based on the second output, and to modify at least one of one or more parameters of the light source, one or more parameters of the optical element, one or more parameters of the one or more first detectors, and one or more parameters used by the computer subsystem to determine the information based on the determined one or more characteristics. The system may be further configured as described herein.

[0016] A further embodiment relates to a computer-implemented method for determining one or more properties of light in an optical system. The method includes detecting light in a path between a light source in the optical system and a sample on which the optical system is performing a process. The detecting includes passing only a first portion of the light from the light source through a central cutout of a detector. The first portion of the light is directed by the optical system to the sample during the process. The detecting also includes separately generating outputs in response to the light being incident on four or more detector segments of a detector positioned around the central cutout and in the path of only a second portion of the light from the light source. The method also includes determining one or more properties of the light from the light source based on the outputs separately generated by the four or more detector segments.

[0017] The steps of the method may be performed as further described herein. Additionally, the method may include any other step(s) of any other method(s) described herein. The method may be performed by any of the systems described herein.

[0018] A further embodiment relates to a non-transitory computer-readable medium storing program instructions executable on a computer system to perform a computer-implemented method for determining one or more properties of light in an optical system. The computer-implemented method includes the steps of the above-described method. The computer-readable medium may be further configured as described herein. The steps of the computer-implemented method may be further performed as described herein. Furthermore, the computer-implemented method for which the program instructions are executable may include any other step(s) of any other method(s) described herein.

[0019] Other objects and advantages of the present invention will become apparent upon reading the following detailed description and upon reference to the accompanying drawings. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a schematic diagram illustrating a side view of an embodiment of a system configured to determine one or more properties of light in an optical system. [Figure 2] FIG. 1 is a schematic diagram showing a plan view of an embodiment of a detector including a central cutout configured to allow only a first portion of light from a light source to pass therethrough, and four or more detector segments arranged around the central cutout and in the path of only a second portion of the light from the light source. [Figure 3] FIG. 1 is a schematic diagram illustrating a side view of an embodiment of a system configured to determine one or more properties of light in an optical system. [Figure 4]FIG. 1 is a block diagram illustrating one embodiment of a non-transitory computer-readable medium storing program instructions executable on a computer system to perform one or more of the computer-implemented methods described herein. DETAILED DESCRIPTION OF THE INVENTION

[0021] While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description set forth therein are not intended to limit the invention to the particular forms disclosed; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

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

[0023] The embodiments described herein generally relate to methods and systems for determining one or more characteristics of light in an optical system. The embodiments generally include a multicell (e.g., four-cell, eight-cell, etc.) beam position and / or aberration sensor with a central transmissive cutout. The described multicell detector with a central transmissive cutout is a segmented detector that can be conveniently placed along a light beam for in-situ measurement of beam position and / or shape. The detector's primary purpose may be to provide servo-controlled feedback for beam stabilization, in which actuator-mounted optical components are moved to maintain a desired beam pointing based on a measured position. While this beam position maintenance is traditionally performed using a four-cell detector, including five or more segments (e.g., eight segments instead of four) allows for simultaneous measurement of beam shape, which may be useful for several diagnostic purposes, such as guiding upstream optical alignment. Furthermore, the central cutout allows for unattenuated transmission of the primary beam, so that only the beam periphery is blocked. This design feature is essential for maximizing power transmission through systems operating at wavelengths such as extreme ultraviolet (EUV) (e.g., 13.5 nm), for which efficient beam splitters do not yet exist.

[0024] In one embodiment, the light is EUV light. In another embodiment, the light is vacuum ultraviolet (VUV) light. In a further embodiment, the light is soft x-ray. For example, the light can be EUV light having a wavelength of about 13.5 nm, one or more wavelengths in the range of about 10 nm to about 124 nm, or one or more wavelengths in the range of about 5 nm to about 30 nm, another VUV light having one or more wavelengths less than 190 nm (which would require the optical system to operate in a vacuum to prevent the light from being absorbed by the atmosphere), or soft x-ray having a wavelength of about 0.12 nm to about 5 nm. The light source can include any suitable light source known in the art capable of emitting light at one or more of these wavelengths. Such light sources include, but are not limited to, laser-induced plasma sources, discharge-induced plasma sources, cathode / anode-type sources, and the like. Furthermore, the embodiments described herein can be used with any light source that emits light that can be used for one or more of the applications described herein, such as inspection, metrology, and defect review.

[0025] One embodiment of a system configured to determine one or more properties of light in an optical system is shown in FIG. 1. The system includes a detector disposed in a path of light between a light source in the optical system and a sample on which the optical system performs a process. In other words, the detector may be inserted along a light beam requiring stabilization. For example, light source 100 may be configured to generate light 102. The light source may include any of the light sources further described herein, further configured to generate any of the light sources further described herein. For example, in one embodiment, the light from the light source has one or more wavelengths shorter than 190 nm.

[0026] Light from the light source may be directed to optical element 104, which may be, for example, a beam steering optical component coupled to an actuator (not shown). Although optical element 104 is shown in FIG. 1 as a single reflective optical element, in practice optical element 104 may include any suitable number and configuration of reflective and / or other optical elements. Detector 106 is positioned in the path of the light from optical element 104, and beam 108 transmitted by the detector may be incident on sample 110. As described further herein, the system may include several additional optical elements (not shown in FIG. 1), including an optical element configured to direct light transmitted by detector 106 to sample 110.

[0027] The detector includes a central cutout configured to allow only a first portion of the light from the light source to pass through. For example, as shown in FIG. 1 , the beam of light 102 directed at the detector has a larger cross-section than the light 108 transmitted by the detector, indicating that not all of the light incident on the detector is transmitted by the detector. Furthermore, as shown in cross-section in FIG. 2 , the detector 200 includes a central cutout 202 configured to allow only a first portion of the light from the light source to pass through. In particular, the central cutout can transmit substantially all of the light directed at it (perhaps all of the light directed at it except for a substantially negligible portion of the light that may be diffracted or scattered out of the path of the light beam by the edges of the central cutout), while, as described further herein, a portion of the detector surrounding the central cutout cannot transmit any of the light incident thereon. While the detector shown in FIG. 2 illustrates a square or rectangular sensor shape including a square or rectangular cutout, other shapes, such as a circle, an oval, or an octagon, could also be used in principle for either (or both) of these features.

[0028] A first portion of the light is directed to the sample by the optical system during processing. For example, as described further herein, the portion of the light transmitted by the central cutout may optionally be directed to the sample by one or more additional elements positioned downstream from the detector. An example of such an additional element is shown in FIG. 3. Thus, the first portion of the light transmitted through the central cutout is the light utilized by the optical system to determine one or more properties of the sample. Thus, the beam of light illuminating the sample passes through the detector as shown in FIGS. 1 and 3. Such a configuration of the detector and its central cutout is important because, as described further herein, this central cutout configuration allows the detector to be used for in situ determination of illumination beam properties, particularly at wavelengths for which partially transmissive optical elements currently do not exist.

[0029] In one embodiment, the first portion is greater than most of the light but less than all of the light. For example, the detector embodiments described herein differ from currently used four-cell beam position sensors by allowing a majority of the beam power to be transmitted through the center cutout. Because the first portion of the light transmitted by the detector's center cutout is used by the optical system as the illumination beam, the center cutout is preferably configured to transmit as much of the beam as possible while being small enough so that enough of the light beam is still incident on the detector segments as described herein. Therefore, the dimensions of the center cutout as well as other characteristics, such as its shape, may be determined based on known or expected parameters of the optical system, particularly parameters that affect the characteristics of the illumination beam.

[0030] In general, "greater than a majority of the light but less than all of the light," as this phrase is used herein, may be defined by a range of percentages of the cross-section of the beam that is transmitted by the central cutout; a suitable range for the detectors described herein may be, for example, greater than 50% but less than 95% of the light. Other numerical schemes, such as fractions, that quantify "greater than a majority of the light but less than all of the light" may also be used. Furthermore, although the first portion may be defined based on the dimensions of the cross-section of the light transmitted by the central cutout relative to the overall dimensions of the cross-section of the light directed at the detector, the first portion may also be defined based on other characteristics of the light, such as power.

[0031] In another embodiment, the central cutout is configured to allow a first portion of the light to pass through the central cutout without any attenuation of the power of the first portion of the light. For example, the central cutout is preferably configured to allow unattenuated transmission of the primary beam, such that only the peripheral portion of the beam is blocked. This is an essential design feature for maximizing power transmission through systems operating at wavelengths such as EUV (e.g., 13.5 nm), for which efficient beam splitters do not yet exist. In this manner, the central cutout may be an actual aperture in the detector, meaning that no optical elements that affect the light are located in the detector's central cutout. More specifically, because refractive optical elements for the wavelengths described herein do not currently exist, the central cutout is preferably simply an aperture in the detector with characteristics determined as further described herein. Thus, the embodiments described herein can be used to advantageously provide servo-controlled feedback to move mirrors (or other elements of the system) to stabilize beam pointing in EUV or soft X-ray beamlines without attenuating power within the central transmission region of the beam.

[0032] The embodiments described herein can also be used for wavelengths other than those described herein. However, for wavelengths of light for which refractive optical elements exist, e.g., wavelengths longer than 190 nm, a partially reflective beam splitter that directs a portion of the light to a conventional qual-cell detector (i.e., without a hole like the center cutout described herein) would be more suitable for such systems because such a detector can capture the entire shape and possibly other characteristics of the beam, rather than just the edges as described herein. Thus, the embodiments described herein are particularly suitable for wavelengths described herein (e.g., less than 190 nm) for which suitable beam splitters currently do not exist, and also for electron or ion beams, because these beams also cannot be split in the same way as light with wavelengths longer than 190 nm can be split.

[0033] The detector also includes four or more detector segments arranged around the central cutout and in the path of only the second portion of the light from the light source. The four or more detector segments are configured to separately generate outputs in response to light incident thereon. In this manner, the detector may be referred to as a segmented detector. Furthermore, while the detector is shown in FIG. 2 as an eight-segmented detector with a central cutout, the detector may include only four or five or more segments, depending on the one or more properties to be determined from the outputs separately generated by each of the segments. For example, if the detector is to be used only to determine spatial property(ies) of the light, the detector may include only four segments. However, if the detector is to be used to determine spatial property(ies), possibly in combination with geometric property(ies), five or more detector segments may be included in the detector.

[0034] Each of the detector segments may be configured as any suitable detector element, such as a two-dimensional (2D) detector, a charge-coupled device (CCD camera), a time-delay integration (TDI) camera, etc. In this manner, each of the detector segments may detect light as a function of position within the image plane of the detector. Other types of detectors may also be used. For example, position-sensitive detector(s) and photomultiplier tubes (PMTs) may be used as detector segments.

[0035] The detector segments can also include non-imaging detectors or imaging detectors. When the detector segments are non-imaging detectors, each of the detector segments may be configured to detect a particular characteristic of light, such as intensity, but may not be configured to detect such a characteristic as a function of position in the imaging plane. Thus, the output generated by each of the detector segments may be a signal or data, and not an image signal or image data. However, in other cases, the detector segments may be configured as imaging detectors configured to generate imaging signals or image data. Thus, the detector segments may be configured to generate the outputs and / or images described in several ways herein.

[0036] In one embodiment, the second portion of light is approximately equal to the minimum amount of light required to determine one or more properties. For example, as described above, the center cutout of the detector transmits the light used to illuminate the sample during the process. Therefore, the detector is preferably configured so that the center cutout transmits the maximum amount of light, while the detector segments block and detect only the amount of light necessary to accurately characterize the illumination light beam. In this way, the detector preferably maximizes the amount of light available for sample illumination while ensuring that sufficient light is available for detection of the light property(ies). The second portion of light may be "approximately equal" to the minimum amount of light required for light property determination because, once the minimum amount of light required for light property determination is determined, the minimum amount can be optionally adjusted, for example, by + / - 1%, depending on the actual implementation or other considerations. In other words, the second portion of light does not need to be exactly equal to the minimum amount of light required to determine one or more properties of the light, but preferably, the second portion of light is minimized as much as possible to maximize the light available for sample illumination while also ensuring that sufficient light can be detected for light beam characterization.

[0037] In another embodiment, the first and second portions of the light are mutually exclusive. In a further embodiment, four or more detector segments are configured to block the second portion of the light from reaching the sample. For example, a central cutout is sized to allow unattenuated transmission of the center of the beam, while peripheral portions of the beam are blocked and detected by the detector segments. In this manner, the detector is configured so that the central cutout transmits 100% of the light directed at it, while other portions of the detector, e.g., the detector segments and any materials on which the detector segments are formed, fabricated, or bonded, do not transmit any of the light incident thereon. In other words, no part or portion of the detector partially transmits the light for which the detector is configured. Thus, (substantially) all of the first portion of the light is transmitted by the detector central cutout, but all of the second portion is blocked by the detector segments. Thus, the detector prevents portions of the beam from illuminating the sample during use, but as further described herein, the detector can be configured to minimize reduction in beam power available for sample illumination.

[0038] In further embodiments, a detector is positioned in the optical path between the light source and the sample, while the optical system detects light from the sample during processing, thereby determining information about the sample. For example, the detector may be configured as a segmented detector, e.g., an 8-cell detector, with a central transmissive cutout that can be placed along the light beam for in-situ measurement of beam position and / or shape. The detector's primary purpose may be to provide servo-controlled feedback for beam stabilization, in which actuator-mounted optics are moved to maintain a desired beam pointing based on a measured position. Furthermore, by blocking and sampling only a substantially small portion of the beam power at the periphery of the beam (e.g., the minimum amount required for measurement purposes) while also transmitting the center of the unattenuated beam power, the detector can be used to monitor beam characteristics (e.g., position and / or shape) while a process is being performed on the sample. In other words, by utilizing only a minimal peripheral portion of the illumination beam, the detector can monitor illumination beam characteristics without interfering with primary system functions (e.g., sample inspection, metrology, defect review, etc.).

[0039] In further embodiments, the detector is configured to have a fixed position within the optical system during use. For example, a center cutout configuration allows the detector to be positioned in the path of light between the light source and the sample for the duration of the process being performed on the sample. In other words, because a partially transmissive beam splitter does not yet exist for the wavelengths of light described herein, any beam measurement device (detector or element directing light to the detector) without a 100% transmissive section, such as the detectors described herein, would have to be moved into the path of the light to measure beam properties and then out of the path of the light so that the sample can be interrogated with the light. However, the embodiments described herein can be used for beam measurements (e.g., position and / or shape) without having to move the device back and forth in and out of the beam path. This ability reduces system cost, complexity, and contamination risk compared to systems requiring device movement, which is particularly beneficial in ultra-clean and / or space-constrained environments.

[0040] Although the detector preferably has a fixed position during use, the system may be configured to change the position of the detector between uses. For example, the position of one or more elements of the system, possibly including the detector embodiments described herein, may be changed in response to an intentional change in beam position (e.g., for different process setups, calibrations, etc.). The system may be configured to change the position of any of the elements of the system, including the detector embodiments described herein, in any suitable manner known in the art.

[0041] In addition to having fixed positions during use, the detector segments may also have fixed positions relative to the detector, particularly when the detector is a single piece of fabricated semiconductor. Thus, each of the detector segments will also have a fixed position relative to the light beam and the system during use. In this way, the configuration of the center cutout and detector segments will generally not change during the use or life of the detector. However, for systems configured for different beam diameters, it may be desirable to configure the detector so that the detector segments can be moved toward and away from the center cutout to accommodate the different beam diameters (e.g., to ensure that a majority of the beam is transmitted by the center cutout and that peripheral portions of the beam are incident on the detector segments). In this way, if there is a change in beam diameter, the positions of the detector segments can be adjusted accordingly. Even if the detector segments can be moved relative to the detector, it will generally be advantageous for their positions to be fixed during use, for the same reasons described further herein. Configuring the detector so that individual segments can be moved relative to the detector would increase the complexity and cost of the detector, and therefore such a configuration may only be implemented when relatively significant changes in beam diameter are expected.

[0042] While a detector that is a single piece of fabricated semiconductor is a particularly advantageous way of implementing the detectors described herein, the detector may actually include physically separate detector segments. For example, each of the detector segments may be a different piece of fabricated semiconductor. In another example, two of the detector segments may be a first single piece of fabricated semiconductor, and two of the detector segments may be a second single piece of fabricated semiconductor. In this manner, each of the different detector segments may not have a central cutout within itself, but combined through their relative positions to each other, they may form a central cutout within the overall detector. In some such embodiments, the central cutout may then be formed by the relative positions of the detector segments to each other, rather than within a single piece of fabricated semiconductor. Thus, by positioning different detector segments at different locations relative to each other, various properties of the central transmissive portion of the overall detector (the combination of different detector segments) may be altered. These properties may include, but are not limited to, shape and size.

[0043] When different detector segments are formed from different pieces of material(s), they may be mounted in a system as further described herein, e.g., so that their positions are fixed during use, even if they may be moved between uses. Furthermore, when different detector segments are formed from different pieces of material(s), the different detector segments do not necessarily need to be positioned in the same plane along the optical path. Instead, the different detector segments may have different positions along the optical path (i.e., different planes along the optical path, or one detector segment may be downstream from another detector segment) while still being configured as further described herein. For example, one detector segment may be positioned to detect a portion of the light at one location in the optical path, and another detector segment may be positioned to detect a different portion of the light at another location in the optical path that is slightly downstream from the first detector segment, and the positions of the two detector segments relative to each other may define at least a portion of the boundary of a center cutout of the detector. The same configuration can be implemented when three or more detector segments are formed from a single piece of material, such as a two-cell detector element including two of the detector segments described herein. In some such instances, the different detector segments may not be located in the same plane along the optical path, to allow for appropriate clearance between the different pieces of material from which the different detector segments are formed, etc. Furthermore, in such situations, it may be most practical to have the different detector segments located as close as possible to each other along the optical path of the illumination beam, although any suitable location of the detector segments along the beam may be used.

[0044] The system also includes a control subsystem configured to determine one or more characteristics of the light from the light source based on the outputs separately generated by the four or more detector segments. Accordingly, the embodiments described herein can use the outputs separately generated by the different segments of the detector to determine one or more characteristics of the light, as further described herein. For example, as shown in FIG. 1 , the system may include a control subsystem 112 coupled to the detector 106. The control subsystem may include one or more computer subsystems and, possibly, other elements, such as firmware, servo loops, and any other suitable controller-type elements known in the art.

[0045] The control subsystem 112 may be coupled to the detector 106 in any suitable manner (e.g., via one or more transmission media, which may include “wired” and / or “wireless” transmission media) such that the control subsystem can receive output, images, etc. generated by the detector 106. The control subsystem 112 may be configured to perform several functions using the detector output as described herein, and any other functions further described herein. This control subsystem may be further configured as described herein.

[0046] The control subsystem may include one or more computer subsystems (not shown) configured to perform one or more functions, such as determining one or more characteristics of the light from the detector segment outputs. The computer subsystem(s) of the control subsystem (as well as other computer subsystems described herein) are also referred to herein as computer system(s). Each of the computer subsystem(s) or system(s) described herein can take various forms, including a personal computer system, an image computer, a mainframe computer system, a workstation, a network appliance, an internet appliance, or other device. In general, the term "computer system" may be broadly defined to encompass any device having one or more processors that execute instructions from a memory medium. The computer subsystem(s) or system(s) may also include any suitable processor known in the art, such as a parallel processor. Furthermore, the computer subsystem(s) or system(s) can include a computer platform with high-speed processing and software, either as a standalone or networked tool.

[0047] Where a system includes two or more computer subsystems, the different computer subsystems may be coupled to one another such that images, data, information, instructions, etc. may be transmitted between the computer subsystems as further described herein. For example, the computer subsystem of control subsystem 112 may be coupled to computer subsystem 320 shown in Figure 3 by any suitable transmission medium (not shown), which may include any suitable wired and / or wireless transmission medium known in the art. Two or more of such computer subsystems may also be effectively coupled by a shared computer-readable storage medium (not shown).

[0048] In one embodiment, the one or more characteristics include one or more spatial characteristics of the light. For example, measurements for control and positioning purposes may be obtained by comparing the ratio of incident power detected on each (or at least two or more) segment. Power imbalances for left vs. right and top vs. bottom segments provide position feedback, which can be used to control beam stabilization actuators. In one such embodiment shown in FIG. 2, detector 200 includes eight segments 204, labeled 0 through 7 and arranged around a central cutout 202. Then, in the following equations, S0 represents the output of segment 0, S1 represents the output of segment 1, and so on. Then, the beam position S in the x-direction is x can be determined using the following equation:

number

[0049] Beam position S in the y direction y can be determined using the following equation:

number

[0050] Similar equations can be used to determine position in the x and y directions for detectors having a different number of segments than shown in Figure 2. Furthermore, while the above equations provide a quick, simple, and accurate manner for determining beam position from detector segment outputs, any other method, algorithm, or function may be used to determine beam position from detector segment outputs. An appropriate method, algorithm, or function may be selected or determined based on the detector configuration and / or the beam position characteristics to be determined using the detector segment outputs.

[0051] In another embodiment, the four or more detector segments include six or more detector segments, the one or more properties include one or more spatial properties and one or more geometric properties of the light, and the control subsystem is configured to simultaneously determine the one or more spatial properties and one or more geometric properties based on the outputs separately generated by the six or more detector segments. For example, beam position detection may be performed using a four-cell detector; however, including five or more segments, e.g., six, eight, or even more, allows for simultaneous measurement of beam shape, which may be useful for several diagnostic purposes, such as guiding upstream optical alignment. In this manner, the embodiments described herein may include a detector configured as an eight-cell detector, and eight-cell detector metrics may be used for servo loop closure and beam quality assessment. Furthermore, utilizing five or more segments (e.g., eight) rather than just four segments allows for simultaneous in-situ measurement of beam position and beam aberrations within a single device.

[0052] In one such embodiment, the one or more shape characteristics include beam aberrations. In another embodiment, the one or more shape characteristics include anisotropy of the light. In a further embodiment, the one or more shape characteristics include one or more properties of multipole components of the light. For example, ratios other than those listed above may be used to measure the anisotropy of the beam profile (e.g., elliptical vs. circular) and the two hexapole and two octopole components. Referring back to the sensor shown in FIG. 2, the control subsystem may be configured to determine beam symmetry or astigmatism using the following two equations:

number

number

[0053] In addition to the position and shape characteristics described herein, the detector may additionally or alternatively be configured to monitor one or more other characteristics of the illumination beam. Such characteristics include, but are not limited to, wavelength, intensity, temporal characteristics, size, and rotational shape. For example, monitoring light characteristics as described herein may enable correction for variations in the illumination beam in the time and spatial domains. In such a configuration, the detector may generate output at different times (whether intermittently or continuously) and at different times relative to illumination of the sample (e.g., before, during, and / or after illumination of the sample). More specifically, the detector may generate output in response to light beam illumination without affecting the performance of the optical system, thereby enabling the detector to generate output that is responsive to both temporal and spatial characteristics of the light. The configuration enables the control subsystem to determine spatial and temporal characteristics of the light from the detector segment outputs, which may then be used to determine both spatial and temporal changes to one or more parameters of the optical system, as further described herein.

[0054] The configuration of the detector may vary depending on the light characteristic to be determined using the detector segment outputs. For example, if the detector is configured to detect wavelength characteristics of light, the detector segments are preferably configured to generate outputs in response to different wavelengths of light. Such a detector configuration would most likely increase the cost and complexity of the detector compared to wavelength-insensitive detectors. Therefore, the detector may be configured to detect only the light characteristic for which the detector will be used to avoid unnecessary complexity and increased cost of the detector.

[0055] In one embodiment, the control subsystem is configured to alter one or more parameters of the optical system based on the determined one or more characteristics. For example, the control subsystem 112 shown in FIG. 1 may include firmware (not shown) and a servo loop (not shown). The firmware and servo loop may have any suitable configuration known in the art suitable for comparing the determined one or more characteristics against a predetermined range of values ​​for the determined one or more characteristics, and then altering at least one parameter of the light source, one or more optical elements, and / or one or more other detectors accordingly. In one such example, the one or more determined characteristics may include beam position information, and the control subsystem may be configured to alter one or more parameters of the optical system by applying a correction to the optical element 104 based on unacceptable variations in any of the beam positions.

[0056] The parameter(s) of the optical system altered by the control subsystem may include any parameter that can cause a change in the property(ies) of light at one or more planes in the optical system, which parameter may vary depending on the configuration of the optical system. For example, although the control subsystem is shown altering a parameter, e.g., the position, of optical element 104 in FIG. 1 and optical element 302 in FIG. 3 , the control subsystem may be configured to alter one or more parameters of any other element in the system. In one such example, the position of optical element 312 shown in FIG. 3 may be altered in response to the position of the beam measured by detector 304. In another such example, rather than steering a mirror in response to the property(ies) of the illumination beam, the control subsystem may be configured to control one or more actuators to move the mirror or the entire platform or chamber on which the light source is mounted. Changes to the parameter(s) of the optical system may be determined in any suitable manner using any suitable type of control loop, algorithm, method, function, etc.

[0057] The parameter(s) of the optical system altered by the control subsystem may also include any parameter of any element that performs a function or step using the output of the detector(s) of the optical system. For example, the parameter(s) altered may include one or more parameters of a computer subsystem (e.g., computer subsystem 320 shown in FIG. 3 ) or one or more parameters of a method, step, algorithm, process, etc. performed by the computer subsystem on the output generated by the one or more first detectors 318. Such parameter(s) may include, for example, parameter(s) of image processing performed to correct the image generated by the first detector(s) for any variations in the light source. In one such example, the determined one or more characteristics of the light may be the spatial and temporal characteristics of the light intensity at the sample plane. If such characteristic(s) exhibit temporal variations, the control subsystem may determine one or more corrections to the sample image that may be made in the image processing performed by the computer subsystem to mitigate the effect that the temporal variations have on the sample image. Thus, the one or more parameters of the optical system that are controlled in response to the determined characteristic(s) may be optical parameters and / or image processing parameters.

[0058] In another embodiment, the control subsystem is configured to output the determined one or more characteristics to a computer subsystem of the optical system, and the computer subsystem is configured to alter one or more parameters of the optical system based on the determined one or more characteristics. For example, the control subsystem itself does not necessarily determine corrections and / or alterations to the optical system. Instead, the control subsystem can simply output the determined one or more characteristics in any suitable manner and in any suitable format to another system or method, such as computer subsystem 320 shown in FIG. 3, which determines alterations to one or more parameters of the optical system based on the determined one or more characteristics and alters the one or more parameters based on the determination. In other words, based on the determined one or more characteristics of the light, control of the optical system can be distributed across multiple subsystems, such as a control subsystem and a computer subsystem. However, the control subsystem can also be part of the computer subsystem, or vice versa, such that one subsystem both determines the characteristic(s) of the light and alters one or more parameters of the optical system based on the characteristic(s). The computer subsystem can alter one or more parameters of the optical system as further described herein.

[0059] In further embodiments, the control or computer subsystem is configured to alter one or more parameters of the optical system based on the determined one or more characteristics, including one or more parameters of a movable optical element in the optical system configured to control the position of the light on the sample. For example, regardless of which subsystem actually alters the one or more parameters of the optical system, the embodiments described herein can provide position feedback to servo-control elements such as the beam steering optics 104, which may be done via an actuator (not shown) coupled to the optics. Thus, the embodiments described herein can operate to close the beam stabilization servo loop using multi-cell (e.g., 8-cell) detector feedback with the beam center in unattenuated transmission.

[0060] Another embodiment of a system configured to determine one or more properties of light in an optical system is shown in Figure 3. The system includes a light source 300 configured to generate light having one or more wavelengths shorter than 190 nm. The light source may be configured as further described herein.

[0061] The system also includes optical elements configured to direct light generated by the light source to the sample and to direct light from the sample to one or more first detectors configured to generate a first output in response to the light from the sample. In this manner, the system can include elements configured to illuminate the sample and detect light from the sample. In the embodiment shown in FIG. 3 , the optical elements include optical elements 302, 312, and 316, and optionally, a homogenizer 308. Optical element 302 is configured to collect light from light source 300 and direct the light to detector 304 through optional homogenizer 308 disposed at intermediate field plane 310. Optical element 312 is configured to direct light transmitted by detector 304 and optional homogenizer 308 to sample 314. Light from sample 314 is collected by optical element 316, which directs the light from the sample to one or more first detectors 318.

[0062] As shown in FIG. 3 , detector 304 is positioned before (or upstream of) homogenizer 308. Generally, for any system that includes a homogenizer, the detector embodiments described herein would be positioned upstream of the homogenizer. Thus, the detector should generally be positioned between the optical element(s) responsible for beam positioning (and possibly other beam characteristics), e.g., optical element 302, and the homogenizer. However, for systems that do not include a homogenizer, the detector embodiments described herein may be positioned at other locations in the illumination beam path (e.g., between optical element 312 and sample 314). In systems that do not include a homogenizer, the detector embodiments described herein may also be positioned in the path of light from the sample. This detector positioning may require more complex calculations (to account for the effect of the sample on the illumination beam) than if the detector were positioned upstream of the sample, but this is another feasible consideration.

[0063] The embodiments described herein may also include two or more beam position and / or shape detectors configured as described herein. For example, one detector may be located in the illumination path and another detector may be located in the collection / detection path. The benefits of measuring beam position and / or shape at multiple points in the system should be weighed against the increased peripheral beam power loss with each additional detector.

[0064] 3 as a single concave reflective optical element, each of these optical elements may include any suitable number of optical elements having any suitable configuration. Optional homogenizer 308 may also have any suitable configuration known in the art.

[0065] The angle(s) at which the optical element 302 collects light from the light source can vary depending on the characteristics of the light source, the characteristics of the sample, and the purpose of the sample illumination. Additionally, the angle(s) at which the optical element 312 directs light to the sample 314 can vary based on similar variables. For example, the system may be configured to illuminate the sample 314 with light at different angles depending on whether the system is configured for inspection, metrology, or defect review.

[0066] Additionally, the angle(s) at which the optical elements 316 collect light from the sample 314 and direct or image the light onto the one or more first detectors 318 may vary depending on the characteristics of the sample and the characteristics of the light directed to the sample for illumination, which will affect the characteristics of the light from the sample and the configuration of the system, such as what type of light (e.g., scattered, specularly reflected, etc.) is directed to the one or more first detectors. The light from the sample that is collected by the optical elements may include scattered light, specularly reflected light, diffracted light, etc., or some combination thereof.

[0067] The system may also include a scanning subsystem (not shown) configured to scan the light over the sample. For example, the system may include a stage (not shown) on which the sample 314 is placed. The scanning subsystem may include any suitable mechanical and / or robotic assembly (including a stage) that may be configured to move the sample so that the light may be scanned over the sample. Additionally, or alternatively, the system may be configured such that one or more optical elements perform some light scanning over the sample. The light may be scanned over the sample in any suitable manner.

[0068] The one or more first detectors may include any suitable detector known in the art, including the detectors described herein. Generally, the one or more first detectors may be imaging detector(s), such as a CCD camera or TDI, although non-imaging detectors may also be used. Furthermore, while the first detector(s) 318 are shown in FIG. 3 as a single detector, the first detector(s) may include any suitable number of detector(s), e.g., one detector, two detectors, three detectors, etc., each of which may be configured the same or differently. When the first detector(s) include two or more detectors, each of the detectors may be positioned within the same image plane but at different positions within the image plane to separately detect different portions of the light directed at the image plane. Such a configuration of the two or more first detectors may be determined based, for example, on the dimensions of the illumination field within the image plane, the characteristics of the sample, and the configuration of the first detector(s).

[0069] It should be noted that Figures 1 and 3 are provided herein to generally illustrate some configurations of optical elements and detectors that may be included in the system embodiments described herein. Clearly, the optical element and detector configurations described herein may be modified to optimize the performance of the system, as is typically done when designing a commercial system. Furthermore, the systems described herein may be implemented with existing optical systems, such as the RAPID 7xxx systems commercially available from KLA Corp., Milpitas, California (e.g., by adding the segmented detectors and other features described herein to the existing optical system). For some such systems, the embodiments described herein may be offered as optional features of the existing system (in addition to other features of the system). Alternatively, the systems described herein may be designed "from scratch" to provide an entirely new system.

[0070] The system shown in FIG. 3 also includes a second detector 304 disposed in the path of the light between the light source 300 and the sample 314. The second detector may be further configured as described herein. For example, the second detector includes a central cutout 202 shown in FIG. 2 configured to allow only a first portion of the light from the light source to pass therethrough. The first portion of the light is directed to the sample by one or more optical elements (e.g., optical element 312 shown in FIG. 3). The central cutout and the first portion of the light may be further configured as described herein. The second detector also includes four or more detector segments 204 shown in FIG. 2 disposed around the central cutout and in the path of the second portion of the light from the light source. The four or more detector segments are configured to separately generate second outputs in response to light incident thereon. The four or more detector segments may be further configured as described herein.

[0071] 3 configured to determine one or more characteristics of the light from the light source based on the second output, and to alter, based on the determined one or more characteristics, at least one of one or more parameters of the light source 300, one or more parameters of the optical elements (e.g., one or more of optical elements 302, 312, and 316), one or more parameters of the one or more first detectors 318, and one or more parameters used by the computer subsystem 320 to determine the information. The control subsystem may be configured to determine the one or more light characteristics and alter at least one parameter of the optical system as further described herein.

[0072] In one embodiment, the specimen is a reticle. The reticle may include any reticle known in the semiconductor arts, including any reticle configured for use in a VUV lithography process, an EUV lithography process, or a soft x-ray lithography process. The reticle may also be a reticle for use in another lithography process (e.g., 193 nm lithography) when there is some advantage to performing one of the processes described herein (e.g., inspection, metrology, defect review) at wavelengths less than 190 nm. In another embodiment, the specimen is a wafer. The wafer may include any wafer known in the semiconductor arts. The embodiments are also not limited to specimens with which the embodiments may be used. For example, the embodiments described herein may be used with specimens such as flat panels, personal computer (PC) boards, and other semiconductor specimens.

[0073] The system further includes a computer subsystem 320 configured to determine information about the specimen based on the first output. The computer subsystem may be configured to determine the information in several different manners, depending, for example, on the specimen, the optical system configuration, and the information determined about the specimen. For example, in one embodiment, the optical system is configured as an inspection system. Such an optical system may be configured to generate an output suitable for detecting defects on the specimen. In such an embodiment, the computer subsystem 320 may be configured to detect defects on the specimen 314 by applying a defect detection method to the output generated by the first detector(s) 318. The computer subsystem 320 may be further coupled to the first detector(s) 318 as described herein such that it can receive the output generated by the first detector(s). Detection of defects on the specimen may be performed using any suitable defect detection method and / or algorithm in any suitable manner known in the art (e.g., applying a defect detection threshold to the output and determining that any output having a value above the threshold corresponds to a defect (or potential defect)).

[0074] If the specimen being inspected is a reticle, the wavelength(s) of light used to illuminate the reticle may be the same as the wavelength(s) of light under which the reticle will be used in the lithography process. In other words, the inspection system may be configured as an actinic reticle inspection system, but may additionally or alternatively be configured for non-actinic reticle inspection. In embodiments in which the optical system is configured for inspection, the embodiments may be further configured as described in U.S. Patent Application Publication No. 2010 / 0165310 to Sewell et al., published July 1, 2010; U.S. Patent Application Publication No. 2015 / 0192459 to Kvamme, published July 9, 2015; U.S. Patent Application Publication No. 2015 / 0253658 to Terasawa et al., published September 10, 2015; and U.S. Patent Application Publication No. 2019 / 0331611 to Ebstein, published October 31, 2019, which are incorporated by reference as if fully set forth herein. The embodiments described herein may be further configured as described in these publications.

[0075] In another embodiment, the optical system is configured as a metrology system. In a further embodiment, the optical system is configured as a defect review system. For example, the system embodiment shown in FIG. 3 may have one or more parameters modified to provide different imaging capabilities depending on the application for which it is to be used. In one such example, the optical system may be configured to have higher resolution if it is to be used for metrology rather than inspection. In other words, the optical system embodiment shown in FIG. 3 describes several general and various configurations for optical systems that can be adjusted in several ways that will be apparent to those skilled in the art to create systems with different imaging capabilities that are more or less suited to different applications.

[0076] In this manner, the optical system may be configured to generate output that is suitable for redetecting defects on the specimen, in the case of a defect review system, or suitable for measuring one or more properties of the specimen, in the case of a metrology system. In defect review system embodiments, the computer subsystem 320 may be configured to redetect defects on the specimen 314 by applying a defect redetection method to the output generated by the first detector(s) 318, and optionally to determine additional information about the redetected defects using the output generated by the first detector(s). In metrology system embodiments, the computer subsystem 320 may be configured to determine one or more properties of the specimen 314 using the output generated by the first detector(s). In both cases, the computer subsystem 320 may be coupled to the first detector(s) 318 as further described herein such that the computer subsystem 320 can receive the output generated by the first detector(s).

[0077] Defect review typically involves re-detecting defects detected as defects by the inspection process and generating additional information about the defects at higher resolution, e.g., using the optical system described herein in a high magnification mode. Thus, defect review is performed at distinct locations on the specimen where defects were detected by inspection. The higher resolution data for the defects generated by defect review is generally more suitable for determining attributes of the defects, such as profile, roughness, and more precise size information. The computer subsystem 320 may be configured to determine such information about defects on the specimen in any suitable manner known in the art.

[0078] Metrology processes are used at various steps during semiconductor production processes to monitor and control the process. Metrology processes differ from inspection processes in that, unlike inspection processes in which defects are detected on a specimen, metrology processes are used to measure one or more properties of a specimen that cannot be determined using currently used inspection tools. For example, metrology processes are used to measure one or more properties of a specimen, such as the dimensions (e.g., linewidth, thickness, etc.) of features formed on the specimen during the process, so that the performance of the process can be determined from the one or more properties. Furthermore, if one or more properties of the specimen are unacceptable (e.g., outside a predetermined range of the property(ies)), the results of the measurements of the one or more properties of the specimen may be used to alter one or more parameters of the process so that additional specimens produced by the process have acceptable property(ies).

[0079] A metrology process also differs from a defect review process in that the metrology process may be performed at a location where no defects have been detected, unlike a defect review process in which defects detected by inspection are reconfirmed in the defect review. In other words, unlike a defect review, the location where the metrology process is performed on the specimen may be independent of the results of the inspection process performed on the specimen. In particular, the location where the metrology process is performed may be selected independent of the inspection results. Further, because the location on the specimen where the metrology is performed may be selected independent of the inspection results, the location where the metrology process is performed may be determined before the inspection process is performed on the specimen, unlike a defect review in which the location on the specimen where the defect review will be performed cannot be determined until inspection results for the specimen have been generated and are available for use. The computer subsystem 320 may be configured to determine any suitable property of the specimen in any suitable manner known in the art.

[0080] In any of the system embodiments described herein, the computer subsystem 320 shown in FIG. 3 may be configured to generate results including at least determined information about the sample based on the output generated by the first detector(s), possibly including any other output generated by the computer subsystem. The results may have any suitable format (e.g., a KLARF file, which is a proprietary file format used by tools commercially available from KLA; a results file generated by Klarity, a tool commercially available from KLA; lot results; etc.). Additionally, all of the embodiments described herein may be configured to store the results of one or more steps of the embodiment on a computer-readable storage medium. The results may include any of the results described herein and may be stored in a manner known in the art. The storage medium may include any of the storage media described herein or any other suitable storage medium known in the art. After being stored, the results may be accessed on the storage medium, used by any of the method or system embodiments described herein, formatted for display to a user, used by another software module, method, system, or the like to perform one or more functions for the sample or another sample.

[0081] Such functionality includes, but is not limited to, altering a process, such as a manufacturing process or step, that has been performed or will be performed on the specimen in a feedback, feedforward, in-situ manner, etc. For example, the computer subsystem may be configured to determine one or more changes to a process that has been performed or will be performed on the specimen based on the detected defect(s) and / or other determined information. The changes to the process may include any suitable changes to one or more parameters of the process. For example, if the determined information is a defect detected on the specimen, the computer subsystem preferably determines those changes such that the defect may be reduced or prevented on other specimens on which the corrected process is performed, the defect may be corrected or eliminated on the specimen in another process performed on the specimen, the defect may be compensated for in another process performed on the specimen, etc. The computer subsystem may determine such changes in any suitable manner known in the art.

[0082] Those changes may then be transmitted to a semiconductor manufacturing system (not shown) or to a storage medium (not shown in FIG. 3 ) accessible to both the computer subsystem and the semiconductor manufacturing system. The semiconductor manufacturing system may or may not be part of the system embodiments described herein. For example, the systems described herein may be coupled to a semiconductor manufacturing system via one or more common elements, such as, for example, 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, and a deposition tool.

[0083] The embodiments described herein have several advantages over other methods and systems for monitoring and controlling light in the wavelength ranges described herein. For example, the embodiments avoid the shortcomings of currently used detectors by providing a central cutout so that the detector can be placed directly in line with the primary beam without the use of a beam splitter. The beam position can be measured by blocking / sampling a substantially small portion of the beam power at the periphery of the beam while transmitting unattenuated through the center of the beam. By using five or more detector segments (e.g., eight) instead of just four, beam shape measurements can be made in situ while the system is fully operational. Furthermore, this measurement can be made on the same device without the added cost, complexity, and contamination risk of traveling back and forth with another beam measurement device, such as a tooling camera. This capability is particularly beneficial in ultra-clean or space-constrained environments.

[0084] Each of the system embodiments described above may be further configured according to any other embodiment(s) described herein.

[0085] Another embodiment relates to a computer-implemented method for determining one or more properties of light in an optical system. The method includes detecting light in a path between a light source in the optical system (e.g., light source 300 shown in FIG. 3 ) and a sample (e.g., sample 314) on which the optical system performs a process. The detecting includes passing only a first portion of the light from the light source through a central cutout (e.g., central cutout 202 shown in FIG. 2 ) of a detector (e.g., detector 200). The detector may be further configured as described herein. The first portion of the light is directed by the optical system to the sample during the process. The detecting also includes separately generating outputs in response to the light being incident on four or more detector segments (segments 204) of the detector positioned around the central cutout and in the path of only a second portion of the light from the light source. The method also includes determining one or more properties of the light from the light source based on the outputs separately generated by the four or more detector segments.

[0086] Each of the method steps may be performed as further described herein. The method may also include any other step(s) that may be performed by the system(s) described herein. The method steps may be performed by the system(s) described herein, and the system may be configured according to any of the embodiments described herein.

[0087] A further embodiment relates to a non-transitory computer-readable medium storing program instructions executable on a computer system to perform a computer-implemented method for determining one or more properties of light in an optical system. One such embodiment is shown in Figure 4. In particular, as shown in Figure 4, a non-transitory computer-readable medium 400 includes program instructions 402 executable on a computer system 404. The computer-implemented method may include any step(s) of any method(s) described herein.

[0088] Program instructions 402 implementing methods such as those described herein may be stored on a computer-readable medium 400. The computer-readable medium may be a storage medium such as a magnetic or optical disk, magnetic tape, or any other suitable non-transitory computer-readable medium known in the art.

[0089] The program instructions may be implemented in any of a variety of ways, including procedure-based techniques, component-based techniques, and / or object-oriented techniques, among others. For example, the program instructions may be implemented using ActiveX controls, C++ objects, JavaBeans, Microsoft Foundation Classes ("MFC"), Streaming SIMD Extensions (SSE), or other technologies or approaches as desired.

[0090] The computer system 404 may be configured according to any of the embodiments described herein.

[0091] Further variations and alternative embodiments of various aspects of the invention will be apparent to those skilled in the art in view of this description. For example, methods and systems for determining one or more properties of light in an optical system are provided. Accordingly, this description is to be construed as merely illustrative and is intended to teach those skilled in the art the general manner of carrying out the invention. It is understood that the forms of the invention shown and described herein are to be taken as the presently preferred embodiments. Elements and materials may be substituted for those illustrated and described herein, parts and processes may be reversed, and certain features of the invention may be utilized alone, all as would be apparent to those skilled in the art after having the benefit of this description of the invention. Changes may be made in the elements described herein without departing from the spirit and scope of the invention, as set forth in the following claims.

Claims

1. 1. A system configured to determine one or more properties of light in an optical system, comprising: a detector disposed in a path of light between a light source in the optical system and a sample on which the optical system performs a process, the detector comprising: a central cutout configured to allow only a first portion of the light from the light source to pass therethrough, the first portion of the light being directed by the optical system to the sample during the process; four or more detector segments arranged about the central cutout and in a path of only a second portion of the light from the light source, the four or more detector segments configured to separately generate outputs in response to the light being incident on the four or more detector segments; a detector including: a control subsystem configured to determine one or more characteristics of the light from the light source based on the outputs separately produced by the four or more detector segments; and A system comprising:

2. 2. The system of claim 1, wherein the first portion is greater than most of the light and less than all of the light.

3. 10. The system of claim 1, wherein the second portion of the light is approximately equal to the minimum amount of light required to determine the one or more characteristics.

4. 10. The system of claim 1, wherein the first portion and the second portion of the light are mutually exclusive.

5. 10. The system of claim 1, wherein the light from the light source has one or more wavelengths less than 190 nm.

6. 2. The system of claim 1, wherein the detector is positioned in the path of the light between the light source and the sample, while the optical system detects the light from the sample during the process, thereby determining information about the sample.

7. 10. The system of claim 1, wherein the detector is configured to have a fixed position within the optical system during use.

8. 10. The system of claim 1, wherein the one or more characteristics comprises one or more spatial characteristics of the light.

9. 2. The system of claim 1, wherein the four or more detector segments comprise six or more detector segments, the one or more properties comprise one or more spatial properties and one or more geometric properties of the light, and the control subsystem is further configured to simultaneously determine the one or more spatial properties and the one or more geometric properties based on the outputs separately produced by the six or more detector segments.

10. 10. The system of claim 9, wherein the one or more geometric characteristics include beam aberrations.

11. 10. The system of claim 9, wherein the one or more geometric properties include anisotropy of the light.

12. 10. The system of claim 9, wherein the one or more geometric characteristics include one or more characteristics of multipole components of the light.

13. 10. The system of claim 1, wherein the central cutout is further configured to allow the first portion of the light to pass through the central cutout without any attenuation of the power of the first portion of the light.

14. 10. The system of claim 1, wherein the four or more detector segments are further configured to block the second portion of the light from reaching the sample.

15. 10. The system of claim 1, wherein the control subsystem is further configured to alter one or more parameters of the optical system based on the determined one or more characteristics.

16. 10. The system of claim 1, wherein the control subsystem is further configured to output the determined one or more characteristics to a computer subsystem of the optical system, and the computer subsystem is configured to modify one or more parameters of the optical system based on the determined one or more characteristics.

17. 2. The system of claim 1, wherein the control or computer subsystem is configured to alter one or more parameters of the optical system based on the determined one or more characteristics, the one or more parameters including one or more parameters of a movable optical element in the optical system configured to control the position of the light on the sample.

18. 2. The system of claim 1, wherein the light is extreme ultraviolet light.

19. 2. The system of claim 1, wherein the light is vacuum ultraviolet light.

20. 2. The system of claim 1, wherein the light is soft x-rays.

21. 10. The system of claim 1, wherein the optical system is configured as an inspection system.

22. 10. The system of claim 1, wherein the optical system is configured as a metrology system.

23. 10. The system of claim 1, wherein the optical system is configured as a defect review system.

24. 1. A system configured to determine one or more properties of light in an optical system, comprising: a light source configured to generate light having one or more wavelengths shorter than 190 nm; an optical element configured to direct the light generated by the light source to a sample and to direct the light from the sample to one or more first detectors configured to generate a first output in response to the light from the sample; a computer subsystem configured to determine information about the sample based on the first output; and a second detector disposed in the path of the light between the light source and the sample, the second detector comprising: a central cutout configured to allow only a first portion of the light from the light source to pass therethrough, the first portion of the light being directed to the sample by one or more of the optical elements; four or more detector segments arranged about the central cutout and in a path of a second portion of the light from the light source, the four or more detector segments configured to separately generate second outputs in response to the light being incident on the four or more detector segments; a second detector having a control subsystem configured to determine one or more characteristics of the light from the light source based on the second output, and to alter, based on the determined one or more characteristics, at least one of one or more parameters of the light source, one or more parameters of the optical element, one or more parameters of the one or more first detectors, and one or more parameters used by the computer subsystem to determine the information; A system comprising:

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