Sample testing with multiple measurement modes

Abstract

An inspection system can include an illumination source configured to generate an illumination beam having a plurality of wavelengths, an illumination subsystem including one or more illumination optics for directing the illumination beam to a sample at an off-axis angle, and an imaging subsystem. The system can include an objective lens for collecting sample light, where the objective lens exhibits chromatic aberration over the spectrum of the illumination beam. The system can include one or more detectors for imaging the sample. A size of a point spread function (PSF) of the imaging subsystem relative to a pixel size of at least one of the one or more detectors can be adjustable. The system can include a tunable spectral filter having an adjustable line width configured to selectively adjust a spectrum of at least one of the illumination beam or the sample light.

Description

Technical Field

[0001] This disclosure generally relates to particle inspection, and more specifically, to dark field particle inspection having multiple modes with different illumination linewidths. Background Technology

[0002] Particle detection systems are commonly used in semiconductor processing lines to identify defects or particles on samples (e.g., chips) that may or may not have films or other structures. Generally, detection sensitivity is affected by parameters of the inspection system (e.g., but not limited to the wavelength or power of the illumination). For example, sensitivity typically improves with increasing power and decreasing wavelength. In some cases, it may be desirable to perform defect inspection using relatively short wavelengths (e.g., but not limited to wavelengths in the deep ultraviolet (DUV) or vacuum ultraviolet (VUV) spectral regions).

[0003] Achieving high power at such short wavelengths presents several practical challenges. For example, continuous-wave (CW) laser sources providing DUV and / or VUV emission include a main laser cavity for generating laser light at a first wavelength and one or more additional resonant cavities for providing frequency conversion of the laser light to achieve the desired wavelength. However, this system can be relatively difficult to manufacture, costly, and sensitive to environmental factors such as temperature fluctuations or vibrations. As another example, pulsed laser sources providing DUV and / or VUV emission are relatively easier to manufacture and can also be more cost-effective. However, pulsed laser sources inherently have a larger spectral linewidth than CW laser sources, which can lead to dispersion in the inspection system, resulting in resolution degradation and / or the need for expensive aberration correction optics.

[0004] Therefore, it is necessary to develop systems and methods to mitigate the above-mentioned defects. Summary of the Invention

[0005] In embodiments, the technology described herein relates to an inspection system comprising: an illumination source configured to generate an illumination beam; an illumination subsystem comprising one or more illumination optics configured to direct the illumination beam to a sample; an imaging subsystem comprising: an objective lens configured to collect sample light from the sample in response to the illumination beam, wherein the objective lens exhibits chromatic aberration within the spectrum of the illumination beam; and one or more detectors for imaging the sample based on at least a portion of the sample light collected by the objective lens, wherein the image pixel size is adjustable, wherein the image pixel size is the pixel size of the one or more detectors projected onto a plane of the sample; and a tunable spectral filter having an adjustable linewidth configured to selectively adjust the spectrum of at least one of the illumination beam or the sample light, wherein the imaging subsystem and the tunable spectral filter are configured according to at least a first measurement mode and a second measurement mode, wherein the first measurement mode provides a relatively larger linewidth and a relatively larger image pixel size compared to the second measurement mode.

[0006] In an embodiment, the technology described herein relates to an inspection system in which the image pixel size can be adjusted by controlling the magnification of the imaging subsystem.

[0007] In an embodiment, the technology described herein relates to an inspection system in which the first measurement mode is provided with a relatively higher chromatic aberration by the objective lens compared to the second measurement mode.

[0008] In an embodiment, the technology described herein relates to an inspection system that further includes a controller communicatively coupled to at least one of the tunable spectral filter or the imaging subsystem, wherein the controller includes one or more processors configured to execute program instructions that cause the one or more processors to: receive one or more images of the sample from the one or more detectors; and identify or characterize at least one of one or more defects on the sample based on the one or more images.

[0009] In an embodiment, the technology described herein relates to an inspection system in which the illumination source comprises a pulsed laser.

[0010] In an embodiment, the technology described herein relates to an inspection system in which the illumination beam comprises pulses having a time pulse width greater than about 1 picometer.

[0011] In an embodiment, the technology described herein relates to an inspection system in which the illumination beam comprises pulses having a time pulse width greater than about 10 picometers.

[0012] In an embodiment, the technology described herein relates to an inspection system in which the tunable spectral filter adjusts the spectrum of the illumination beam.

[0013] In an embodiment, the technology described herein relates to an inspection system in which the tunable spectral filter is positioned within the illumination source.

[0014] In an embodiment, the technology described herein relates to an inspection system in which the tunable spectral filter is positioned between the illumination source and the sample.

[0015] In an embodiment, the technology described herein relates to an inspection system in which the tunable spectral filter adjusts the spectrum of the sample light.

[0016] In an embodiment, the technology described herein relates to an inspection system in which the spectrum of the illumination beam is contained in the ultraviolet spectrum (UV) or at wavelengths lower.

[0017] In an embodiment, the technology described herein relates to an inspection system in which the tunable spectral filter includes standard gauges.

[0018] In an embodiment, the technology described herein relates to an inspection system in which the tunable spectral filter comprises: one or more prisms; and a spatial filter.

[0019] In an embodiment, the technology described herein relates to an inspection system, wherein the tunable spectral filter comprises: one or more diffraction gratings; and a spatial filter.

[0020] In an embodiment, the technology described herein relates to an inspection system that further includes: a haze mask, wherein, when operating in at least a first measurement mode, the haze mask is configured to allow light scattered from one or more particles on the sample to pass through and suppress scattered light from the surface of the sample.

[0021] In an embodiment, the technology described herein relates to an inspection system in which the haze mask comprises: a wave plate; and a polarizer.

[0022] In an embodiment, the technology described herein relates to an inspection method comprising: generating an illumination beam; directing the illumination beam to a sample; selecting a measurement mode from at least a first measurement mode or a second measurement mode for imaging the sample using an inspection system, wherein the inspection system includes an imaging subsystem comprising: an objective lens configured to collect sample light from the sample in response to the illumination beam, wherein the objective lens exhibits chromatic aberration within the spectrum of the illumination beam; and one or more detectors for imaging the sample based on at least a portion of the sample light collected by the objective lens, wherein the image pixel size is adjustable, wherein... The image pixel size is the size of the pixels of the one or more detectors projected onto the plane of the sample, wherein the inspection system further includes a tunable spectral filter with an adjustable linewidth configured to selectively adjust the spectrum of at least one of the illumination beam or the sample light, wherein the first measurement mode provides a relatively larger linewidth and a relatively larger image pixel size compared to the second measurement mode; generating one or more images of the sample using the measurement mode selected from at least the first measurement mode or the second measurement mode; and identifying or characterizing at least one of one or more defects on the sample based on the one or more images.

[0023] In embodiments, the technology described herein relates to an inspection system comprising: a controller communicatively coupled to an illumination source configured to generate an illumination beam; an illumination subsystem comprising one or more lenses configured to guide the illumination beam to a sample; an imaging subsystem; or a tunable spectral filter, wherein the imaging subsystem comprises: an objective lens configured to collect sample light from the sample in response to the illumination beam, wherein the objective lens exhibits chromatic aberration within the spectrum of the illumination beam; and one or more detectors for imaging the sample based on at least a portion of the sample light collected by the objective lens, wherein the image pixel size is adjustable, wherein the image pixel size is the number of pixels of the one or more detectors projected onto a plane of the sample. Size; wherein the tunable spectral filter provides an adjustable linewidth configured to selectively adjust the spectrum of at least one of the illumination beam or the sample light, wherein the imaging subsystem and the tunable spectral filter are configurable according to at least a first measurement mode and a second measurement mode, wherein the first measurement mode provides a relatively larger linewidth and a relatively larger image pixel size compared to the second measurement mode; and wherein the controller includes one or more processors configured to execute program instructions that cause the one or more processors to: receive one or more images of the sample from at least one of the one or more detectors; and identify or characterize at least one of one or more defects on the sample based on the one or more images.

[0024] In an embodiment, the technology described herein relates to an inspection system, wherein the program instructions are further configured to cause the one or more processors to control at least one of the tunable spectral filter or the imaging subsystem to generate each of the one or more images in a selected measurement mode selected from one or more measurement modes including the first measurement mode and the second measurement mode.

[0025] In an embodiment, the technology described herein relates to an inspection system in which the image pixel size can be adjusted by controlling the magnification of the imaging subsystem.

[0026] In an embodiment, the technology described herein relates to an inspection system in which the first measurement mode is provided with a relatively higher chromatic aberration by the objective lens compared to the second measurement mode.

[0027] In an embodiment, the technology described herein relates to an inspection system in which the tunable spectral filter adjusts the spectrum of the illumination beam.

[0028] In an embodiment, the technology described herein relates to an inspection system in which the tunable spectral filter adjusts the spectrum of the sample light.

[0029] In an embodiment, the technology described herein relates to an inspection system in which the spectrum of the illumination beam is contained in the ultraviolet spectrum (UV) or at wavelengths lower.

[0030] It should be understood that the foregoing overview and the following detailed description are merely illustrative and not necessarily limiting of the invention. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the overview, serve to explain the principles of the invention. Attached Figure Description

[0031] Those skilled in the art will better understand the many advantages of this disclosure by referring to the accompanying drawings.

[0032] Figure 1A This is a block diagram depicting an inspection system according to one or more embodiments of the present disclosure.

[0033] Figure 1B This is a simplified schematic diagram depicting an inspection system according to one or more embodiments of the present disclosure.

[0034] Figure 1C This is a simplified schematic diagram depicting an inspection system having multiple detectors in different light-gathering paths according to one or more embodiments of the present disclosure.

[0035] Figure 1DThis is a simplified schematic diagram depicting a testing system having a tunable spectral filter within an illumination source according to one or more embodiments of the present disclosure.

[0036] Figure 1E This is a simplified schematic diagram depicting a testing system having a tunable spectral filter within an illumination subsystem according to one or more embodiments of the present disclosure.

[0037] Figure 1F This is a simplified schematic diagram depicting an inspection system having a tunable spectral filter within a portion of an imaging subsystem common to one or more detectors, according to one or more embodiments of the present disclosure.

[0038] Figure 1G This is a simplified schematic diagram depicting a testing system having multiple tunable spectral filters in different light-collecting paths of an imaging subsystem according to one or more embodiments of the present disclosure.

[0039] Figure 2A This is a simplified schematic diagram of a tunable spectral filter formed as a standard gauge according to one or more embodiments of the present disclosure.

[0040] Figure 2B This is a schematic diagram depicting the spectral patterns transmitted by a standard measuring instrument according to one or more embodiments of the present disclosure.

[0041] Figure 2C It is a plot of spectral transmission and reflection using a standard measuring tool with a length of 0.1 mm and a reflective surface with a reflectivity of 0.92, according to one or more embodiments of the present disclosure.

[0042] Figure 2D It is a plot of spectral transmission and reflection using a standard measuring tool with a length of 0.4 mm and a reflective surface with a reflectivity of 0.91, according to one or more embodiments of the present disclosure.

[0043] Figure 2E It is a plot of the linewidth (LW) of a standard gauge that varies according to the reflectivity of the reflective surface and the distance between the reflective surfaces, according to one or more embodiments of the present disclosure.

[0044] Figure 2F It is a plot of the transmittance of a standard gauge that varies according to the reflectivity of the reflective surface and the distance between the reflective surfaces, according to one or more embodiments of the present disclosure.

[0045] Figure 3A This is a simplified schematic diagram of a tunable spectral filter comprising a dispersive element formed as a prism, according to one or more embodiments of the present disclosure.

[0046] Figure 3BThis is a simplified schematic diagram of a tunable spectral filter comprising a dispersive element formed as a diffraction grating, according to one or more embodiments of the present disclosure.

[0047] Figure 3C It is a plot depicting the normalized wavelength distance of a prism and a grating in a Littrow configuration according to one or more embodiments of the present disclosure.

[0048] Figure 4 This is a flowchart illustrating the steps performed in a method for defect inspection according to one or more embodiments of the present disclosure. Detailed Implementation

[0049] The subject matter of the disclosure will now be described in detail with reference to the accompanying drawings. This disclosure has been particularly shown and described with respect to certain embodiments and their specific features. The embodiments set forth herein are to be regarded as illustrative rather than restrictive. It will be readily apparent to those skilled in the art that various changes and modifications in form and detail can be made without departing from the spirit and scope of this disclosure.

[0050] Embodiments of this disclosure relate to systems and methods for providing cost-effective image-based optical inspection using multiple selectable measurement configurations (referred to herein as measurement modes). In embodiments, the inspection system includes an illumination source providing a pulsed laser illumination beam with multiple longitudinal modes and a tunable spectral filter that selectively controls the linewidth (and therefore power) of the illumination beam. For example, the illumination source may comprise a high-power pulsed laser. The inspection system can be further configured with two or more configurations (e.g., measurement modes) based on different combinations of the linewidth and power of the illumination beam, image pixel size (e.g., the pixel size of the detector projected onto the sample plane), or imaging magnification. In this way, different optical modes can be tailored for different sample types and / or applications where different noise sources dominate.

[0051] Embodiments of this disclosure can provide robust operation using relatively cost-effective components. For example, embodiments of this disclosure may utilize high-power pulsed lasers, which can be a more cost-effective and / or robust approach to achieving high power compared to using CW lasers. Embodiments of this disclosure may further use any objective lens, including, but not limited to, weakly corrected or uncorrected objectives for chromatic aberration within the available linewidth of the illumination beam (e.g., uncorrected or weakly corrected objectives exhibiting fully formed or slightly residual chromatic aberration). It has been carefully considered herein that correcting chromatic aberration in high numerical aperture (NA) lenses in the deep ultraviolet (UV) wavelength range is significantly more expensive than for the visible light wavelength range. Clearly, image pixel sizes can be adjusted based on the relevant noise source in conjunction with the illumination linewidth to provide a high signal-to-noise ratio (SNR) across a wide range of applications or sample types. In embodiments, the inspection system may be configured to operate in at least two measurement configurations, wherein a first measurement configuration is tailored for a scenario where sensor noise is dominant, and a second configuration is tailored for a scenario where optical noise associated with surface scattering (e.g., surface haze) is dominant. The first configuration is applicable to samples with low surface haze (which is negligible (e.g., for well-polished samples, such as semiconductor chips) or suppressed by the inspection system) and is therefore referred to herein as the low-haze configuration. In this low-haze configuration, higher laser power and a larger image pixel size tend to provide a higher SNR. Furthermore, a relatively large image pixel size tolerates more chromatic aberration. Therefore, the tunable spectral filter can be wider or fully open to provide maximum illumination power. The second configuration is applicable to samples with relatively high surface haze (e.g., for samples with one or more deposited films). In this haze-limited configuration (e.g., high-haze configuration), a relatively small image pixel size improves the SNR. However, the relatively small image pixel size provides lower tolerances for the spectral linewidth, necessitating a narrower spectral linewidth (e.g., using a tunable spectral filter) to achieve a higher SNR. The loss of laser power due to the narrower spectral filter with a smaller image pixel size has a much smaller impact on the SNR. The spectral linewidth can be further optimized for cases between sensor noise-limited and haze-limited conditions.

[0052] For reference Figures 1A to 4 The present disclosure provides in more detail a system and method for sensitive optical inspection having a variety of selectable measurement configurations, according to one or more embodiments.

[0053] Figure 1AThis is a block diagram depicting an inspection system 100 according to one or more embodiments of the present disclosure. In an embodiment, the inspection system 100 includes an illumination source 102 for generating an illumination beam 104, and an illumination subsystem 106 including one or more illumination optics 108 to direct the illumination beam 104 to a sample 110. The inspection system 100 may also include an imaging subsystem 112 having at least one objective lens 114 to image the sample 110 based on light emitted from the sample 110 (referred to herein as sample light 116). For example, the imaging subsystem 112 may include one or more detectors 118 to generate an image of the sample 110 (e.g., its illuminated portion) based on the sample light 116. In an embodiment, the inspection system 100 further includes a tunable spectral filter 120 to control the spectral linewidth (e.g., imaging linewidth) associated with the spectrum of the light used to generate an image of the sample 110. For example, the tunable spectral filter 120 can control the linewidth (e.g., illumination linewidth) of the illumination beam 104 and / or the linewidth of the sample light 116 guided to the detector 118 for imaging. In this way, the tunable spectral filter 120 can be positioned in the illumination subsystem 106 and / or imaging subsystem 112 of the inspection system 100.

[0054] In an embodiment, such as Figure 1B The description states that the inspection system 100 is a dark-field imaging system configured to exclude specularly reflected light during imaging. In this respect, the inspection system 100 may image the sample 110 primarily based on scattered or diffracted light. Dark-field imaging can be implemented using any technique known in the art. For example, Figure 1B The configuration described herein includes an illumination subsystem 106 comprising illumination optics 108 arranged to guide an illumination beam 104 to a sample 110 at an angle of incidence excluded from the NA of an objective lens 114 for collecting sample light 116 for imaging. In this manner, specular reflections of the illumination beam 104 can also be excluded from the NA of the objective lens 114 and not collected. The angle of incidence can typically include any selected angle of incidence. For example, the angle of incidence relative to the surface normal can (but is not required to) be greater than 60 degrees. As another example, although not shown, the illumination subsystem 106 may guide the illumination beam 104 to the sample 110 via the objective lens 114 and may further include one or more beam blockers or apertures to prevent specular reflections of the illumination beam 104 from reaching the detector 118. It should be noted that the inspection system 100 is not limited to dark-field imaging and can implement bright-field imaging or any other suitable imaging technique. In this manner, the inspection system 100 can be configured as any type of imaging system known in the art. Furthermore, objective lens 114 may have (but is not required to have) an NA of about 0.9 or greater. In an embodiment, inspection system 100 may include one or more components to block specular reflections from reaching detector 118.

[0055] In an embodiment, the inspection system 100 further includes a controller 122, which includes one or more processors 124 configured to execute program instructions held on a memory 126 (e.g., memory media). The controller 122 may be communicatively coupled to any component of the inspection system 100 (e.g., but not limited to the tunable spectral filter 120 or detector 118). For example, the controller 122 may receive data from any component of the inspection system 100 and / or direct any component of the inspection system 100 to perform various actions via control signals. In this way, program instructions may cause the processor 124 to implement and / or direct any process steps within the present disclosure. For example, the controller 122 may control or otherwise (e.g., via control signals) a component (e.g., but not limited to the tunable spectral filter 120 or detector 118) to generate an image of the sample 110 using selected imaging parameters. As another example, the controller 122 may receive, analyze, and / or process the image of the sample 110 generated by the detector 118. As another example, the controller 122 may identify and / or characterize defects on the sample 110.

[0056] Inspection system 100 identifies and / or characterizes any type of defect on any type of sample 110, which is broadly referred to herein as inspection. In embodiments, inspection system 100 may identify and / or characterize defects on sample 110 associated with semiconductor manufacturing processes. For example, sample 110 may comprise, but is not limited to, untreated (e.g., bare) semiconductor chips, semiconductor chips having one or more films, or semiconductor chips having one or more patterned features (e.g., patterned films). In this configuration, defects of interest may comprise, but are not limited to, particles on sample 110 or structural damage to sample 110 in the form of scratches, dents, pits, or the like.

[0057] In many applications, the defects are smaller than the optical resolution of the imaging subsystem 112, such that an image of such a defect corresponds to the PSF of the imaging system, which is altered by the electric field distribution of light scattered by the defects and / or the sample 110. Specifically, the PSF of the imaging subsystem 112 describes the distribution of light associated with a point object (e.g., an infinitesimally small object) controlled by the optical diffraction of the entire imaging subsystem 112. Furthermore, the PSF can be defined on the plane of the sample 110 or otherwise characterized.

[0058] The inspection sensitivity may be based, at least in part, on the SNR associated with the defect signal measured by the pixels of detector 118 and various noise sources. For example, noise sources may include optical scattering noise associated with the scattering of the illumination beam 104 by air molecules near the sample (e.g., surface haze) and / or the imaging field. As another example, noise sources may include sensor noise, such as, but not limited to, dark current noise or readout noise.

[0059] With careful consideration, the noise sources described herein can vary widely for different types of samples 110 and / or applications. For example, a well-polished sample 110 (e.g., a bare semiconductor chip or the like) may have generally lower surface haze compared to a sample 110 with one or more deposited films or other features.

[0060] Further careful consideration has been given to this document, and different techniques can be used to improve SNR depending on which noise source is dominant for a particular application. In an embodiment, the testing system 100 can be configured to operate in two or more measurement configurations. In this way, the testing system 100 can be customized to provide high SNR in the presence of different dominant noise sources.

[0061] Each measurement configuration may correspond to a unique set of parameters for the inspection system 100, such as, but not limited to, spectral linewidth (e.g., the linewidth of the illumination beam 104 and / or the linewidth of the sample light 116 collected) or the image pixel size of the detector 118. The image pixel size refers to the size of the pixels of the detector 118 projected onto the plane of the sample 110 (e.g., the sensor pixel size), which may correspond to the sensor pixel size divided by the optical magnification of the imaging subsystem 112. In this way, the image pixel size can be determined by the sensor pixel size and the optical magnification of the imaging subsystem 112. With careful consideration, limiting the spectral linewidth can reduce signal intensity, but it can also limit chromatic aberration of the objective lens 114 or other components. In this way, a balance can be struck between the spectral linewidth and the image pixel size to provide different measurement modes suitable for different imaging and / or sample conditions (e.g., but not limited to the amount of surface haze).

[0062] Non-limiting examples of the measurement configuration of the inspection system 100 are now described in more detail according to one or more embodiments of the present disclosure.

[0063] In embodiments, the inspection system 100 may be configured to operate in a low-haze configuration (e.g., a first measurement configuration) tailored for applications where the noise associated with surface haze from sample 110 is sufficiently low to allow sensor noise to dominate during imaging. For example, for a well-polished sample 110, surface haze may be naturally low and / or effectively suppressed, allowing sensor noise to dominate. Suppression of surface haze in defect inspection is substantially described in the following patents: U.S. Patent No. 10,942,135, published March 9, 2021, and U.S. Patent No. 10,948,423, published March 16, 2021, the entire contents of which are incorporated herein by reference. For example, the inspection system 100 may include a haze mask that allows light scattered from one or more particles (e.g., defects) on sample 110 to pass through and suppresses scattered light (e.g., surface haze) from the surface of sample 110. The haze mask can use any technique to suppress surface haze, including but not limited to guiding or absorbing surface haze along an optical path different from the remaining sample light 116. For illustration, the haze mask may include, but is not limited to, one or more polarization-rotating optics (e.g., one or more waveplates) and / or one or more polarizers arranged to distinguish surface haze from defect signals.

[0064] When sensor noise dominates, the SNR associated with imaging defects can scale with increasing illumination power and / or image pixel size relative to the PSF to capture a larger percentage of signal per pixel. Furthermore, sensor noise can be fixed or known for a particular sensor and associated operating conditions (e.g., temperature or the like) and is generally independent (or only weakly dependent) of the sensor pixel size.

[0065] Advantageously, this configuration can tolerate chromatic aberration from objective 114 or other components associated with a broad spectral linewidth. For example, chromatic aberration can manifest as an increase in the size of imaging defects (e.g., PSF) and / or a decrease in peak power. However, even in the presence of chromatic aberration, the image pixel size can still be selected to capture a relatively large portion of the PSF, or in some cases, the entire PSF, to maintain a high SNR. Therefore, uncorrected or weakly corrected objective 114 can be used. Since uncorrected or weakly corrected objective 114 is generally less expensive than corrected objective 114, especially when corrected for UV wavelengths, this can substantially reduce the cost of inspection system 100.

[0066] In an embodiment, the inspection system 100 may be configured to operate in a high-haze configuration (e.g., a second measurement configuration) tailored for applications where the noise dominance associated with the surface haze from the sample 110 is higher than the sensor noise. This may be the case for samples containing deposited films or other features.

[0067] When noise associated with surface haze dominates, the SNR profile may not scale with increasing illumination power (or may scale only weakly), because both signal and noise depend on illumination power. Alternatively, the SNR can be improved by reducing the image pixel size (or reducing the magnification of the imaging subsystem 112), since optical noise associated with surface haze can be distributed across the image plane, and smaller image pixel sizes capture less of this noise per pixel. It should be understood that this scaling tends to plateau as the pixel size becomes much smaller than the PSF. It is also desirable to provide a diffraction-limited PSF (or more generally, a relatively small PSF with a peak value) to improve the signal strength captured by smaller pixels. For example, the PSF can be improved by limiting the spectral linewidth (e.g., using a tunable spectral filter 120) to reduce chromatic aberration in the objective lens 114 or other components. As an illustration, the tunable spectral filter 120 can limit the PSF to diffraction-limited (e.g., diffraction-limited in the imaging subsystem 112). As another illustration, the tunable spectral filter 120 can limit the PSF to be less than or equal to the image pixel size.

[0068] With careful consideration, the low-haze and high-haze configurations described herein do not require testing specific values ​​for various parameters of system 100, but rather provide relative changes to these parameters. For example, the high-haze configuration can provide a smaller image pixel size and / or higher magnification compared to the low-haze configuration. As another example, the high-haze configuration can provide a relatively lower spectral linewidth compared to the low-haze configuration.

[0069] Furthermore, the descriptions of the low-haze and high-haze configurations are for illustrative purposes only and should not be construed as limiting the scope of this disclosure. Rather, the testing system 100 can be configured to operate in any number of measurement configurations having any combination of parameters.

[0070] For reference Figures 1B to 1G The present disclosure describes in more detail, according to one or more embodiments, various measurement modes in optical inspection. Specifically, Figure 1B The inspection system 100 is described in general, while Figure 1C to 1G Various non-limiting configurations of the inspection system 100 that provides multiple measurement modes are described.

[0071] Figure 1B This is a simplified schematic diagram depicting an inspection system 100 according to one or more embodiments of the present disclosure.

[0072] Such as about Figure 1A As described, the inspection system 100 may include an illumination source 102 configured to generate an illumination beam 104, an illumination subsystem 106 having an illumination optics 108 configured to direct the illumination beam 104 to a sample 110, and an imaging subsystem 112 having at least one objective lens 114 for collecting sample light 116 and generating an image of the sample 110 on one or more detectors 118.

[0073] The illumination beam 104 may contain light of one or more selected wavelengths, including, but not limited to, ultraviolet (UV) radiation, visible light radiation, or infrared (IR) radiation. For example, the illumination source 102 may provide (but is not required to provide) an illumination beam 104 with a wavelength shorter than about 350 nm. By another example, the illumination beam 104 may provide a wavelength of about 266 nm. By another example, the illumination beam 104 may provide a wavelength of about 213 nm. By another example, the illumination beam 104 may provide a wavelength of about 193 nm. It should be appreciated herein that both imaging resolution and light scattering by small particles (e.g., relative to the wavelength of the illumination beam 104) are generally inversely proportional to wavelength, such that reducing the wavelength of the illumination beam 104 generally increases imaging resolution and the scattering signal from small particles. Therefore, the illumination beam 104 may contain short-wavelength light, including, but not limited to, extreme ultraviolet (EUV) light, deep ultraviolet (DUV) light, or vacuum ultraviolet (VUV) light.

[0074] The illumination beam 104 may further have any time profile. For example, the illumination beam 104 may have a continuous time profile, a modulated time profile, a pulsed time profile, or the like.

[0075] Illumination source 102 may comprise any type of light source known in the art. In an embodiment, illumination source 102 is a pulsed laser source (e.g., a high-power pulsed laser) providing an illumination beam 104 having multiple longitudinal modes. For example, illumination source 102 may comprise (but is not required to comprise) a high-power pulsed laser providing power in the range of 1 to 100 W. In the case of pulsed laser illumination source 102, the linewidth of illumination beam 104 (the sample light 116 associated with illumination beam 104) can be tuned using tunable spectral filter 120. For example, the linewidth of illumination beam 104 may be greater than about 1 picometer. As another example, the linewidth of illumination beam 104 may be greater than about 10 picometers. For example, the linewidth of illumination beam 104 may be greater than about 1 nanometer. As another example, the linewidth of illumination beam 104 may be large enough to induce dispersion in selected objective lens 114 used to collect sample light 116. As an illustration, it is desirable to use objective 114, which is either uncorrected or only weakly corrected for chromatic aberration at the wavelength associated with illumination beam 104. This objective 114 reduces cost compared to a better-corrected version. In this case, when the full linewidth of illumination beam 104 is used, chromatic aberration can manifest as a degradation of PSF at detector 118, such as, but not limited to, a decrease in the peak amplitude of PSF exceeding tolerance or an increase in the magnitude of PSF exceeding tolerance. As described throughout this disclosure, tunable spectral filter 120 can control the effective linewidth of the light used for imaging (e.g., control the linewidth of illumination beam 104 and / or sample light 116 reaching detector 118), and thus control the amount of PSF degradation attributable to chromatic aberration. In this way, different measurement modes can be imaged using light with different linewidths.

[0076] The illumination optics 108 in the illumination subsystem 106 may include any number of components for guiding or otherwise manipulating the illumination beam 104. For example, the illumination optics 108 may include one or more illumination lenses 128 to focus and / or relay the illumination beam 104. The illumination lenses 128 may further provide any number of relayed illumination pupil planes and / or illumination field planes. As another example, the illumination optics 108 may include one or more illumination beam control optics 130, such as, but not limited to, apodizers, polarizers, spectral filters, neutral density filters, or homogenizers. Furthermore, the illumination beam control optics 130 may be positioned at any suitable location (e.g., but not limited to, illumination pupil planes or illumination field planes).

[0077] It should be understood throughout this document that the intensity of surface haze can depend on several factors, including, but not limited to, the angle of incidence or polarization of the illumination beam 104. For example, the intensity of surface haze can be relatively high for near-normal angles of incidence and decrease for higher angles of incidence. In embodiments, the illumination subsystem 106 (e.g., via illumination lens 128 or other suitable element) directs the illumination beam 104 to the sample 110 at an angle of incidence to increase the defect signal (e.g., the intensity of sample light 116 associated with defects on the sample 110). The angle of incidence can typically include any selected angle of incidence. For example, the angle of incidence relative to the surface normal of the sample 110 can (but is not required to) be greater than 60 degrees. However, this is not limiting, and the illumination beam 104 can be directed to the sample 110 at any suitable angle of incidence.

[0078] The imaging subsystem 112 may include an objective lens 114 to collect sample light 116 from the sample 110 in response to illumination using an illumination beam 104 and may further include any number of detectors 118 that use at least a portion of the sample light 116 to generate one or more images of the sample 110.

[0079] The imaging subsystem 112 may include any number of imaging beam adjustment optics 132 for guiding and / or modifying the sample light 116, including but not limited to one or more lenses, one or more filters, one or more apertures, one or more polarizers, or one or more phase plates.

[0080] The imaging subsystem 112 may include any number of lenses 134 to manipulate the sample light 116 collected by the objective lens 114. For example, the lenses 134 may operate together with the objective lens 114 to generate an image of the sample 110 on the detector 118. As another example, the lenses 134 may relay one or more planes (e.g., relay one or more pupil planes 136 and / or field planes 138), which may allow further manipulation of the sample light 116 using the imaging beam adjustment optics 132.

[0081] In one embodiment, such as Figure 1B The description indicates that the imaging subsystem 112 includes one or more imaging beam adjustment optics 132 positioned at or near the pupil plane 136. For example, the imaging subsystem 112 may include imaging beam adjustment optics 132 configured to suppress surface haze reaching the detector 118, such as, but not limited to, haze suppression polarizers (e.g., radial polarizers or similar) or phase masks located at or near the pupil plane 136. In this regard, the inspection system 100 can control and adjust selected aspects of the sample light 116 used to generate an image on the detector 118, including, but not limited to, the intensity, phase, and polarization of the sample light 116 varying according to the scattering angle and / or position on the sample 110.

[0082] In an embodiment, such as Figure 1B As described, the imaging subsystem 112 includes one or more imaging beam adjustment optics 132 positioned at or near the pupil plane 136. For example, the imaging subsystem 112 may include imaging beam adjustment optics 132, such as, but not limited to, a haze mask configured to suppress surface haze from the sample 110. As an illustration, the haze mask may include, for example, but not limited to, components of polarization manipulation optics (e.g., polarization rotators, waveplates, polarizers, or the like) or phase masks. As another example, the imaging subsystem 112 may include one or more apertures or beam blockers to prevent specular reflections or other unwanted light from reaching the detector 118. In a general sense, the imaging beam adjustment optics 132 can be used to manipulate any combination of the intensity, phase, or polarization of the sample light 116.

[0083] However, it should be understood herein that a limited number of imaging beam adjustment optics 132 can be placed at or sufficiently close to a particular pupil plane 136 to provide the desired effect. Therefore, for the purposes of this disclosure, references to one or more elements at the pupil plane 136 generally describe one or more elements located at or sufficiently close to the pupil plane 136 to produce the desired effect. In some embodiments, although not shown, the imaging subsystem 112 may include additional lenses to generate one or more additional pupil planes 136, such that any number of imaging beam adjustment optics 132 can be placed at or near the pupil plane 136.

[0084] Detector 118 may comprise any type of sensor known in the art for measuring illumination received from sample 110. For example, detector 118 may comprise a multi-pixel detector suitable for capturing an image of sample 110, such as, but not limited to, a charge-coupled device (CCD) detector, a complementary metal-oxide-semiconductor (CMOS) detector, a time-delay integration (TDI) detector, a photomultiplier tube (PMT) array, an avalanche photodiode (APD) array, or the like. In an embodiment, detector 118 comprises a spectral detector suitable for identifying the wavelength of sample light 116.

[0085] The imaging subsystem 112 may typically contain any number of detectors 118.

[0086] Figure 1CThis is a simplified schematic diagram depicting an inspection system 100 having multiple detectors 118a, 118b in different light-collecting paths 140a, 140b according to one or more embodiments of the present disclosure. For example, the imaging subsystem 112 may include one or more beam splitters 142 to separate the sample light 116 collected by the objective lens 114 into any number of light-collecting paths 140 (e.g., light-collecting paths 140a, 140b here). The imaging subsystem 112 may then include one or more detectors 118 within each light-collecting path 140. Any or all of the light-collecting paths 140 may further include any combination of components suitable for imaging the sample 110, such as, but not limited to, imaging beam-adjusting optics 132 or lenses 134.

[0087] The imaging subsystem 112 may further include any component or combination of components suitable for selectively guiding the sample light 116 collected by the objective lens 114 to a selected light-collecting path 140, such as, but not limited to, one or more shutters or one or more polarization control optics (e.g., polarization rotators, polarization beam splitters, or the like). Figure 1C A non-limiting configuration is depicted in which a shutter 144 is included in the light-collecting path 140, the shutter 144 being coupled to the controller 122 for automatic control (e.g., via a control signal) or for manual operation (e.g., by a user).

[0088] This configuration can also be applied to polarization-based haze suppression techniques, where one sub-path provides an image of sample 110 with suppressed surface haze and another sub-path provides an image of the surface haze. For example, this configuration can be applied to, but is not limited to, polarization-based haze suppression techniques implemented in U.S. Patents Nos. 10,942,135 and 10,948,423, which are cited above and whose entire contents are incorporated herein by reference. For example, the surface haze may be directed at least substantially along one path to a first detector 118a, while the remaining sample light 116 (e.g., primarily comprising light associated with defects) may be directed to a second detector 118b.

[0089] As another example, although not shown, the light-collecting path 140 may include one or more additional beam splitters to separate the sample light 116 to multiple detectors 118 along additional sub-paths.

[0090] As another example, the inspection system 100 may include different detectors 118 with different sensor pixel sizes. For example, the first detector 118a and the second detector 118b may have different sensor pixel sizes that provide different usable image pixel sizes.

[0091] In an embodiment, the inspection system 100 includes at least one tunable spectral filter 120 to selectively control the linewidth of the light used to image the sample 110. The tunable spectral filter 120 may be located anywhere within the inspection system 100, including but not limited to within the illumination source 102, the illumination subsystem 106, or the imaging subsystem 112.

[0092] For reference Figures 1B to 1G Various non-limiting configurations of the inspection system 100 providing multiple measurement modes are shown according to one or more embodiments of the present disclosure.

[0093] As previously described herein, the measurement mode of the inspection system 100 may include a unique combination of the linewidth of the light used for imaging and the image pixel size. In other words, the measurement mode of the inspection system 100 may include a unique combination of the linewidth (e.g., spectral linewidth) of the light used for imaging and the image pixel size. In other words, the measurement mode may include a unique combination of the relationship between the linewidth of the light used for imaging and the image pixel size and the PSF size (e.g., the size of a diffraction-limited defect).

[0094] Spectral linewidth and / or image pixel size may be adjusted or otherwise controlled using any techniques known in the art.

[0095] For example, the image pixel size can be adjusted by controlling the optical magnification of the imaging subsystem 112. As an illustration, the imaging subsystem 112 may include one or more zoom lenses and / or lenses with adjustable positions suitable for adjusting the imaging magnification. For example, Figure 1B Any lens 134 in 1C may be implemented as a zoom lens and / or a lens with an adjustable position, such that the image pixel size can be adjusted or otherwise controlled. As another example, the imaging subsystem 112 may include a plurality of detectors 118 having different pixel sizes that can be selectively used for imaging. In this way, different measurement modes can selectively utilize different detectors 118 to achieve different pixel sizes. When imaging in a particular measurement mode, any suitable technique can be used to select among the multiple available detectors 118.

[0096] As another example, the spectral linewidth can be adjusted by a tunable spectral filter 120 placed at any location suitable for adjusting the linewidth of the illumination beam 104 and / or the sample light 116. Figure 1D to 1G A tunable spectral filter 120 is depicted in various non-restricted positions within the inspection system 100. Figure 1D to 1G Depicting Figure 1C The configuration of the testing system 100 shown is illustrated herein. However, this is for illustrative purposes only and should not be construed as limiting the scope of this disclosure. Rather, the tunable spectral filter 120 may be included in any configuration of the testing system 100 (including, but not limited to, [other configurations]). Figure 1B In any suitable location within the configuration described in the text.

[0097] Figure 1D This is a simplified schematic diagram depicting an inspection system 100 having a tunable spectral filter 120 within an illumination source 102, according to one or more embodiments of the present disclosure. In this configuration, the tunable spectral filter 120 can directly control the spectrum of the illumination beam 104.

[0098] Figure 1E This is a simplified schematic diagram depicting an inspection system 100 having a tunable spectral filter 120 within an illumination subsystem 106 according to one or more embodiments of the present disclosure. In this configuration, the tunable spectral filter 120 allows any selected portion of the spectrum of the illumination beam 104 to pass through.

[0099] Figure 1F This is a simplified schematic diagram depicting an inspection system 100 having a tunable spectral filter 120 within a portion of an imaging subsystem 112 shared by one or more detectors 118, according to one or more embodiments of the present disclosure. In this configuration, the tunable spectral filter 120 allows any selected portion of the spectrum of the sample light 116 collected by the objective lens 114 to pass through.

[0100] Figure 1G This is a simplified schematic diagram depicting an inspection system 100 having multiple tunable spectral filters 120 in different light-collecting paths 140 of an imaging subsystem 112 according to one or more embodiments of the present disclosure. In this configuration, any particular tunable spectral filter 120 allows a selected portion of the spectrum of sample light 116 within the associated light-collecting path 140 to pass through. In this way, the spectrum of sample light 116 used to generate an image of sample 110 can be customized for each detector 118. For example, the spectrum of sample light 116 used to generate an image of sample 110 can be customized to provide a selected size of PSF relative to the image pixel size.

[0101] For reference Figures 2A to 3C Various designs of the tunable spectral filter 120 are described according to one or more embodiments of this disclosure. The tunable spectral filter 120 may typically have any component or combination of components suitable for allowing a selected spectrum of light to pass through. In other words, the tunable spectral filter 120 may typically have any component or combination of components suitable for limiting the spectrum of light.

[0102] exist Figures 2A to 3CIn this system, the tunable spectral filter 120 receives input light 202 and allows filtered light 204 to pass through, wherein the linewidth of the filtered light 204 is equal to or less than the linewidth of the input light 202. As previously described herein, the tunable spectral filter 120 can operate on either the illumination beam 104 or the sample light 116. In this way, depending on the position of the tunable spectral filter 120 within the inspection system 100, the input light 202 can correspond to either the illumination beam 104 or the sample light 116.

[0103] The tunable spectral filter 120 can operate in either transmission or reflection mode to transmit or reflect the spectral components that pass through, respectively. For example, the filtered light 204 may correspond to light transmitted by one or more components of the tunable spectral filter 120 in transmission mode. As another example, the filtered light 204 may correspond to light reflected by one or more components of the tunable spectral filter 120 in reflection mode.

[0104] Figure 2A This is a simplified schematic diagram of a tunable spectral filter 120 formed as a standard gauge 206 according to one or more embodiments of the present disclosure. In an embodiment, the tunable spectral filter 120 includes a standard gauge 206 to provide spectral filtering via optical resonance. For example, the standard gauge 206 may include two parallel reflective surfaces 208 forming an optical cavity, wherein the spectral width and transmittance through the standard gauge 206 can be controlled by the reflectivity of the reflective surfaces 208. The standard gauge 206 can be formed using any suitable technique. For example, the reflective surfaces 208 may be formed as two mirrors. As another example, the reflective surfaces 208 may be formed as a surface of a solid material.

[0105] Figure 2B This is a schematic diagram depicting the spectral patterns transmitted by a standard gauge 206 according to one or more embodiments of the present disclosure. For example, optical resonances within the standard gauge 206 can limit transmission to separate, distinct frequencies.

[0106]

[0107] (e.g., free spectral range), where It is the speed of light and This is the distance between the reflecting surfaces 208. Furthermore, the linewidth (LW) of the transmitted light can be expressed as... Analytically, the standard gauge 206 can be characterized by precision.

[0108]

[0109] The precision is related to the resonator's quality factor. The spectral width can then be written as...

[0110]

[0111] Transmittance can be written as

[0112]

[0113] in It is the refractive index of the exterior of the reflective surface 208.

[0114] Numerically, the spectral properties of a pulse propagating through standard gauge 206 can be described as follows:

[0115]

[0116] in

[0117]

[0118] in and The amplitudes of the pulses corresponding to the input light 202 and the filtered light 204 (e.g., transmitted light), respectively.

[0119] Figures 2C to 2D The spectral filtering properties of a standard gauge 206 according to one or more embodiments of the present disclosure are described under various conditions. Figure 2C According to one or more embodiments of this disclosure, a length of 0.1 mm is used. The standard measuring instrument 206 has a reflectivity of 0.92. A plot of the spectral transmission and reflection of the reflective surface 208. Figure 2D According to one or more embodiments of this disclosure, a length of 0.4 mm is used. The standard measuring instrument 206 has a reflectivity of 0.91. A plot of the spectral transmission and reflection of the reflective surface 208. Figure 2C and 2D Of the two, the transmittance and reflectance values ​​of the filtered light 204 are provided based on equations (5) to (7) (e.g., based on pulsed input light 202), and the analyzed value of the transmittance of the filtered light 204 is provided based on equations (1) to (4) (e.g., based on CW input light 202). Figures 2C to 2D As depicted, the use of pulsed input light 202 (e.g., from mode-locked illumination source 102) can result in lower peak transmission and a larger spectral linewidth through standard gauge 206.

[0120] Figures 2E to 2F The structure of the standard gauge 206 according to one or more embodiments of the present disclosure further describes how the structure of the standard gauge 206 affects the linewidth and transmittance of the standard gauge 206. Figure 2E Based on one or more embodiments of this disclosure, the reflectivity of the reflective surface 208 is... and the distance between the reflective surfaces 208 The surface plot of the line width (LW) of the variable standard gauge 206. Figure 2F Based on one or more embodiments of this disclosure, the reflectivity of the reflective surface 208 is... and the distance between the reflective surfaces 208 The transmittance plot of the changing standard gauge 206. Figures 2E to 2F The data in this document is based on input light 202 with a pulse width of 20 ps, ​​a linewidth of 3 pm, and a center wavelength of 193 nm. It should be understood that this is for illustrative purposes only and should not be construed as limiting the scope of this disclosure.

[0121] Figures 3A to 3C Variations of the tunable spectral filter 120 formed by at least one dispersive element 302 and a spatial filter 304 are depicted. Any type of dispersive element 302 or spatial filter 304 is permitted within the spirit and scope of this disclosure. For example, the dispersive element 302 may comprise a diffraction grating, a prism, or the like. As another example, the spatial filter 304 may comprise an aperture, beam blocker, or the like suitable for allowing selected portions of the spectral spread (e.g., spatial dispersion) spectrum from the dispersive element 302 to pass through.

[0122] Figure 3A This is a simplified schematic diagram of a tunable spectral filter 120 comprising a dispersive element 302 formed as a prism, according to one or more embodiments of the present disclosure. Figure 3B This is a simplified schematic diagram of a tunable spectral filter 120 comprising a dispersive element 302 formed as a diffraction grating, according to one or more embodiments of the present disclosure. Figure 3A and 3B The lens 306 is further described as being suitable for focusing the spectrally expanded input light 202.

[0123] In this configuration, the dispersive element 302 spatially expands the spectrum of the input light 202, and the spatial filter 304 allows selected spectral components to pass through. The tunable spectral filter 120 can then reconstruct the passed spectral components either by propagating back through the dispersive element 302 (e.g., if the spatial filter 304 reflects a portion of the input light 202 as filtered light 204) or by using an additional dispersive element (e.g., if the spatial filter 304 transmits a portion of the input light 202 as filtered light 204).

[0124] In this document, it has been carefully considered that the type and configuration of the dispersive element 302 can affect various aspects of the tunable spectral filter 120, including but not limited to the sensitivity of spectral control, transmittance (e.g., efficiency), or linewidth of the filtered light 204. As an illustration, the sensitivity of the tunable spectral filter 120 used to provide spectral control can be measured by normalized wavelength distance. Characterization, in which It is the spatial distance of the light spot focused by lens 306 at the spatial filter 304, which is within the wavelength of the spectral linewidth. It is the size of the light spot focused by lens 306 onto the spatial filter 304 at the center wavelength. This ratio metric defines the performance of the spectral filter.

[0125] For example, the normalized wavelength distance of a prism based on this metric can be characterized as:

[0126]

[0127] in It is the diameter of the input light 202. It is the refractive index of the prism. It is the dispersion of the prism, It is the center wavelength of the input light 202. It is the linewidth of the input light 202 and It is the angle of incidence of the input light 202.

[0128] As another example, the normalized wavelength distance of a grating with a normal incident angle of input light 202 can be characterized by the following:

[0129]

[0130] in This is the exit angle of the diffracted light from the grating. In the case of the Littoral configuration, the normalized wavelength distance can be characterized by the following:

[0131]

[0132] Figure 3C This is a plot depicting the normalized wavelength range of a prism and a grating arranged in a Littlero configuration according to one or more embodiments of the present disclosure. Figure 3C The diagram shows that, for a given incident angle... The grating with a litero configuration can provide a greater normalized wavelength distance than a prism.

[0133] For reference Figures 2A to 3CIn this document, different embodiments of the tunable spectral filter 120, after careful consideration, may offer different trade-offs between parameters such as, but not limited to, size, transmittance (e.g., efficiency), linewidth control, alignment tolerance, or manufacturability. For example, a tunable spectral filter 120 incorporating a standard gauge 206 may offer a relatively compact solution but may offer relatively low transmittance, require sensitive alignment (and thus be sensitive to vibration or other mechanical movement), provide a relatively large linewidth, and / or require relatively large internal intensity between the reflective surfaces 208 (and thus may be power-limited). As another example, a tunable spectral filter 120 incorporating a prism as a dispersive element 302 and a spatial filter 304 may offer relatively high transmittance and good alignment tolerance but may be physically large, requiring a correspondingly large beam size and / or providing a relatively large linewidth. As another example, a tunable spectral filter 120, which includes a grating as a dispersive element 302 and a spatial filter 304, can provide relatively narrow linewidth and good alignment tolerance, but can provide relatively low efficiency and is challenging to manufacture for ultraviolet wavelengths.

[0134] It should be further understood that Figures 2A to 3C This is for illustrative purposes only and should not be construed as limiting the scope of this disclosure. Rather, the tunable spectral filter 120 may include any component or combination of components suitable for controlling the spectrum of the illumination beam 104 and / or the sample light 116.

[0135] Refer again Figure 1A Various additional aspects of the inspection system 100 are described in more detail according to one or more embodiments of the present disclosure.

[0136] One or more processors 124 of controller 122 may comprise any processing element known in the art. In this sense, one or more processors 124 may comprise any microprocessor-type device configured to execute algorithms and / or instructions. In embodiments, one or more processors 124 may comprise a desktop computer, host computer system, workstation, graphics computer, parallel processor, or any other computer system (e.g., a network-connected computer) configured to execute a program (which is configured to operate the inspection system 100), as described throughout this disclosure. It should be further appreciated that the term “processor” may be broadly defined to cover any device having one or more processing elements that execute program instructions from non-transitory memory 126. Furthermore, the steps described throughout this disclosure may be performed by a single controller 122 or alternatively by multiple controllers. Additionally, controller 122 may comprise one or more controllers housed in a common enclosure or multiple enclosures. In this way, any controller or combination of controllers may be individually packaged as a module suitable for integration into the inspection system 100.

[0137] Memory 126 may comprise any storage medium known in the art suitable for storing program instructions executable by one or more associated processors 124. For example, memory 126 may comprise a non-transitory memory medium. By another example, memory 126 may comprise, but is not limited to, read-only memory (ROM), random access memory (RAM), magnetic or optical memory devices (e.g., magnetic disks), magnetic tape, solid-state drives, and the like. It should be further noted that memory 126 may be housed together with one or more processors 124 in a common controller housing. In embodiments, memory 126 may be remotely located relative to the physical location of one or more processors 124 and controller 122. For example, one or more processors 124 of controller 122 may access remote memory (e.g., a server) accessible via a network (e.g., the Internet, an intranet, and the like). Therefore, the above description should not be construed as limiting the invention but is merely illustrative.

[0138] The controller 122 may be further communicatively coupled to any component of the inspection system 100. Therefore, the controller 122 may receive data from any such component and / or may be directed or otherwise controlled via one or more control signals. In this manner, the controller 122 (e.g., via one or more processors 124) may implement and / or direct any of the process steps described herein.

[0139] Figure 4 This is a flowchart illustrating the steps performed in a method 400 for defect inspection according to one or more embodiments of this disclosure. The applicant notes that the embodiments and implementation techniques previously described herein in the context of inspection system 100 should be interpreted as extending to method 400. However, it should be further noted that method 400 is not limited to the architecture of inspection system 100.

[0140] Figure 4 This is a flowchart of an instance verification method according to one or more embodiments of the present disclosure.

[0141] In an embodiment, method 400 includes step 402 of generating an illumination beam 104. The illumination beam 104 may have multiple longitudinal modes, allowing adjustment of the linewidth used for imaging. For example, the illumination beam 104 may be a pulsed beam (e.g., from a mode-locked laser source or any other suitable source) or a CW beam with multiple longitudinal modes.

[0142] In one embodiment, method 400 includes step 404 of directing illumination beam 104 to sample 110. Step 404 may include directing illumination beam 104 to sample 110 at any suitable angle.

[0143] In an embodiment, method 400 includes step 406 of selecting a measurement mode from at least a first measurement mode or a second measurement mode for imaging sample 110 using inspection system 100. For example, the first measurement mode may provide a relatively large linewidth of at least illumination beam 104 or sample light 116 collected from sample 110, which may result in a higher chromatic aberration in the first measurement mode relative to the second measurement mode objective. Furthermore, the image pixel size for the first measurement mode may be larger than the image pixel size for the second measurement mode. In this way, the first measurement mode may be suitable for, but not limited to, applications where surface haze from sample 110 is relatively low and / or suppressed by imaging subsystem 112. In some applications, the first measurement mode is used when sensor noise (e.g., noise from detector 118) is the dominant noise source. In this case, the SNR of defects on sample 110 can be increased by increasing the image pixel size. Furthermore, a larger image pixel size can tolerate more chromatic aberration associated with a relatively large linewidth. The second measurement mode may be suitable for, but not limited to, applications where surface haze from sample 110 is relatively high and, in some cases, is the dominant noise source. In this case, the SNR of the defect can be increased by reducing the image pixel size. Additionally, the linewidth can be reduced to provide a diffraction-limited PSF or at least a PSF smaller than the image pixel size.

[0144] However, it should be understood that the descriptions of the first and second measurement modes are illustrative only and should not be construed as limiting the scope of this disclosure. For example, step 406 may include selecting additional measurement modes in some applications. In a general sense, the inspection system 100 may be configurable to operate in any number of measurement modes. For illustration, the spectral linewidth (e.g., the linewidth associated with the illumination beam 104 and / or the sample light 116 delivered to the detector 118) and / or the image pixel size used to generate the image can be adjusted to any value in any number of measurement modes. For illustration, the spectral linewidth and / or image pixel size may be adjusted to maximize the SNR of defects within tolerances based on any imaging conditions.

[0145] The spectral linewidth (e.g., spectral linewidth) used to generate the image of the illumination beam 104 and / or sample light 116 can be adjusted using any technique known in the art. For example, the spectral linewidth can be adjusted using a tunable spectral filter 120. Furthermore, the spectral linewidth can be adjusted by controlling the linewidth of the illumination beam 104 prior to the sample 110 or by controlling the linewidth of the sample light 116 transmitted to the detector 118.

[0146] Image pixel size can be adjusted using any technique known in the art. For example, image pixel size can be adjusted by controlling the magnification (e.g., optical magnification) of the imaging subsystem 112 used to generate an image of sample 110. As another example, image pixel size can be adjusted by selecting a detector 118 from a plurality of available detectors 118 having different sensor pixel sizes.

[0147] In one embodiment, method 400 includes step 408 of generating one or more images of a sample using a selected measurement mode. In another embodiment, method 400 includes step 410 of identifying or characterizing at least one of one or more defects on the sample based on one or more images.

[0148] The objects described herein sometimes refer to different components contained within or connected to other components. It should be understood that such depicted architectures are merely exemplary, and many other architectures can in fact be implemented to achieve the same functionality. Conceptually, any arrangement of components used to achieve the same functionality is effectively “associated” to achieve the desired functionality. Therefore, any two components combined herein to achieve a particular functionality can be considered “associated” with each other to achieve the desired functionality, regardless of the architecture or intermediate components. Similarly, any two such associated components can also be considered “connected” or “coupled” to each other to achieve the desired functionality, and any two components that can be suchly associated can also be considered “coupleable” to each other to achieve the desired functionality. Specific examples of coupleability include, but are not limited to, physically interactive and / or physically interactive components and / or wirelessly interactive and / or logically interactive components.

[0149] It is believed that this disclosure and many of its accompanying advantages will be understood from the foregoing description, and it will be appreciated that various changes can be made to the form, construction, and arrangement of the components without departing from the subject matter of the disclosure or sacrificing all its significant advantages. The forms described are merely illustrative, and the appended claims are intended to cover and encompass such changes. Furthermore, it should be understood that the invention is defined by the appended claims.

Claims

1. An inspection system comprising: A light source configured to produce a beam of light; An illumination subsystem comprising one or more illumination optics configured to direct the illumination beam toward the sample; The imaging subsystem includes: An objective lens configured to collect sample light from the sample in response to the illumination beam, wherein the objective lens exhibits chromatic aberration within the spectrum of the illumination beam; and One or more detectors for imaging the sample based on at least a portion of the sample light collected by the objective lens, wherein the image pixel size is adjustable, and wherein the image pixel size is the pixel size of the one or more detectors projected onto the plane of the sample; and A tunable spectral filter having an adjustable linewidth configured to selectively adjust the spectrum of at least one of the illumination beam or the sample light, wherein the imaging subsystem and the tunable spectral filter can be configured according to at least a first measurement mode and a second measurement mode, wherein the first measurement mode provides a relatively larger linewidth and a relatively larger image pixel size compared to the second measurement mode.

2. The inspection system according to claim 1, wherein the image pixel size can be adjusted by controlling the magnification of the imaging subsystem.

3. The inspection system of claim 1, wherein the first measurement mode is provided with a relatively higher chromatic aberration by the objective lens compared to the second measurement mode.

4. The inspection system of claim 1, further comprising a controller communicatively coupled to at least one of the tunable spectral filter or the imaging subsystem, wherein the controller includes one or more processors configured to execute program instructions that cause the one or more processors to: Receive one or more images of the sample from the one or more detectors; and At least one of the following: identifying or characterizing one or more defects on the sample based on one or more images.

5. The inspection system according to claim 1, wherein the illumination source comprises a pulsed laser.

6. The inspection system of claim 5, wherein the illumination beam comprises a pulse having a time pulse width greater than about 1 picometer.

7. The inspection system of claim 5, wherein the illumination beam comprises a pulse having a time pulse width greater than about 10 picometers.

8. The inspection system of claim 1, wherein the tunable spectral filter adjusts the spectrum of the illumination beam.

9. The inspection system according to claim 8, wherein the tunable spectral filter is located within the illumination source.

10. The testing system of claim 8, wherein the tunable spectral filter is positioned between the illumination source and the sample.

11. The testing system of claim 1, wherein the tunable spectral filter adjusts the spectrum of the sample light.

12. The inspection system of claim 1, wherein the spectrum of the illumination beam is contained in the ultraviolet spectrum (UV) range or at a wavelength lower.

13. The testing system according to claim 1, wherein the tunable spectral filter comprises: Standard measuring tools.

14. The testing system according to claim 1, wherein the tunable spectral filter comprises: One or more prisms; and Spatial filter.

15. The testing system according to claim 1, wherein the tunable spectral filter comprises: One or more diffraction gratings; and Spatial filter.

16. The inspection system according to claim 1, further comprising: A haze mask when operating in at least the first measurement mode, wherein the haze mask is configured to allow light scattered from one or more particles on the sample to pass through and suppress scattered light from the surface of the sample.

17. The inspection system of claim 16, wherein the haze mask comprises: corrugated plate; and Polarizer.

18. A testing method, comprising: Generates a beam of illumination; Guide the illumination beam toward the sample; A measurement mode is selected from at least a first measurement mode or a second measurement mode for imaging the sample using the inspection system, wherein the inspection system includes an imaging subsystem comprising: An objective lens configured to collect sample light from the sample in response to the illumination beam, wherein the objective lens exhibits chromatic aberration within the spectrum of the illumination beam; and One or more detectors for imaging the sample based on at least a portion of the sample light collected by the objective lens, wherein the image pixel size is adjustable, wherein the image pixel size is the size of the pixels of the one or more detectors projected onto the plane of the sample, wherein the inspection system further includes a tunable spectral filter with an adjustable linewidth configured to selectively adjust the spectrum of at least one of the illumination beam or the sample light, wherein the first measurement mode provides a relatively larger linewidth and a relatively larger image pixel size compared to the second measurement mode; One or more images of the sample are generated using the measurement mode selected from at least the first measurement mode or the second measurement mode; and At least one of the following: identifying or characterizing one or more defects on the sample based on one or more images.

19. An inspection system comprising: A controller communicatively coupled to at least one of an illumination source configured to generate an illumination beam, an illumination subsystem comprising one or more lenses configured to guide the illumination beam to a sample, an imaging subsystem, or a tunable spectral filter, wherein the imaging subsystem includes: An objective lens configured to collect sample light from the sample in response to the illumination beam, wherein the objective lens exhibits chromatic aberration within the spectrum of the illumination beam; and One or more detectors for imaging the sample based on at least a portion of the sample light collected by the objective lens, wherein the image pixel size is adjustable, and wherein the image pixel size is the size of the pixels of the one or more detectors projected onto the plane of the sample; The tunable spectral filter provides an adjustable linewidth configured to selectively adjust the spectrum of at least one of the illumination beam or the sample light, wherein the imaging subsystem and the tunable spectral filter can be configured according to at least a first measurement mode and a second measurement mode, wherein the first measurement mode provides a relatively larger linewidth and a relatively larger image pixel size compared to the second measurement mode; and The controller includes one or more processors configured to execute program instructions, thereby causing the one or more processors to: Receive one or more images of the sample from at least one of the one or more detectors; and At least one of the following: identifying or characterizing one or more defects on the sample based on one or more images.

20. The inspection system of claim 19, wherein the program instructions are further configured to cause the one or more processors: Control at least one of the tunable spectral filter or the imaging subsystem to generate each of the one or more images in a selected measurement mode selected from one or more measurement modes including the first measurement mode and the second measurement mode.

21. The inspection system of claim 19, wherein the image pixel size can be adjusted by controlling the magnification of the imaging subsystem.

22. The inspection system of claim 19, wherein the first measurement mode is provided with a relatively higher chromatic aberration by the objective lens compared to the second measurement mode.

23. The inspection system of claim 19, wherein the tunable spectral filter adjusts the spectrum of the illumination beam.

24. The testing system of claim 19, wherein the tunable spectral filter adjusts the spectrum of the sample light.

25. The inspection system of claim 19, wherein the spectrum of the illumination beam is contained in the ultraviolet spectrum (UV) range or at a wavelength lower.

Images