Laser diffraction optical microscopy for ultra-thin pattern wafers

Abstract

An optical microscope is provided for inspecting a pattern or performing wafer alignment in an electron beam inspection system in an ultra-thin photoresist layer on a semiconductor substrate. The optical microscope may include a laser configured to generate diffracted light in a microscope objective. An optical microscope may be capable of generating an optical image of a latent image pattern in an ultra-thin photoresist.

Description

Cross-references to related applications

[0001] This application claims priority to U.S. Application 63 / 590,919, filed October 17, 2023, which is incorporated herein by reference in its entirety. Technical Field

[0002] The description herein relates to methods and apparatus for inspecting substrate surfaces, and more particularly to methods and apparatus for inspecting ultrathin resist layers on substrates using an optical microscope. Background Technology

[0003] Photolithography is a process of applying a desired pattern onto a substrate (typically onto a target portion of the substrate). Photolithography apparatus can be used, for example, in the fabrication of integrated circuits (ICs). In this case, a patterning apparatus (alternatively referred to as a mask or photomask) can be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g., a portion comprising one or more dies) on a substrate (e.g., a silicon wafer). The transfer of the pattern is typically via imaging onto a radiation-sensitive material (resist) layer provided on the substrate. Stepping or scanning movements can be involved to repeat the pattern at successive target portions across the substrate. Alternatively, the pattern can be transferred from the patterning apparatus to the substrate by imprinting the pattern onto the substrate.

[0004] To improve semiconductor process yield, defects must be identified as quickly as possible to mitigate their impact. Optical microscopy can be used in routine optical inspections, including bright-field and dark-field inspections. For example, an optical microscope can use a beam of light to scan each die on a wafer, and an image of each die can be generated and stored. Die-to-die (D2D), die-to-database (D2DB), or other comparisons can be used to identify any anomalies or defects in the images. Optical microscopy can also be used to image finished or intermediate structures on a wafer. For example, prior to the development step or other post-exposure operations, an optical microscope can scan the exposed resist layer to identify defects in the latent image.

[0005] Inspection systems using optical microscopes typically have resolutions as low as a few hundred nanometers, and this resolution is limited by the wavelength of light. As the physical dimensions of IC components continue to shrink to below 100 nanometers or even sub-10 nanometers, inspection systems with higher resolutions than those using optical microscopes are needed. For example, inspections can be performed using scanning electron microscopy (SEM) or other charged particle inspection devices. Nevertheless, optical microscopes can be useful in photolithography processes. For instance, an optical microscope can be used to quickly locate regions of interest on a substrate using its relatively large field of view. Higher resolution inspection devices such as SEMs can then examine the regions of interest. Furthermore, optical microscopes can be used in, for example, alignment operations. Summary of the Invention

[0006] Some embodiments of this disclosure provide an optical microscope. The optical microscope may include: an objective lens system including a first objective lens; an image sensor; and an off-axis illumination system including a first laser configured to irradiate a pattern on a substrate with a first laser beam to generate first diffracted light, wherein the objective lens is configured to collect the first diffracted light, and the optical microscope is configured to generate an image of the pattern on the image sensor using the first diffracted light.

[0007] Some embodiments of this disclosure provide methods. The methods may include: emitting a first laser beam toward a substrate from a first azimuth angle to generate first diffracted light; collecting the first diffracted light with a first objective lens of an optical microscope; emitting a second laser beam from a second azimuth angle to generate second diffracted light; collecting the second diffracted light with the first objective lens; and generating an optical microscope image based on one of the first and second diffracted lights.

[0008] Some embodiments of this disclosure provide a non-transitory computer-readable medium. The non-transitory computer-readable medium may store an instruction set that can be executed by at least one processor of the device to cause the device to perform operations including the methods described above. Attached Figure Description

[0009] The foregoing and other aspects of this disclosure will become more apparent from the description of the exemplary embodiments given in conjunction with the accompanying drawings.

[0010] Figure 1 An example lithography apparatus consistent with embodiments of the present disclosure is illustrated.

[0011] Figure 2 An example lithography unit consistent with an embodiment of this disclosure is illustrated.

[0012] Figures 3A to 3B An example optical microscope and an example optical microscope image are illustrated according to a comparative embodiment.

[0013] Figures 4A to 4B An example optical microscope consistent with embodiments of this disclosure is illustrated.

[0014] Figures 5A to 5C An example optical microscope image consistent with an embodiment of this disclosure is illustrated.

[0015] Figure 6A Figures 6 to 6C illustrate an example optical microscope consistent with embodiments of the present disclosure.

[0016] Figure 7 This is a flowchart illustrating an example method for generating optical microscope images that is consistent with embodiments of this disclosure. Detailed Implementation

[0017] Reference will now be made in detail to exemplary embodiments, examples of which are illustrated in the accompanying drawings. The following description refers to the accompanying drawings, in which, unless otherwise stated, the same reference numerals in different figures denote the same or similar elements. The implementations set forth in the following description of the exemplary embodiments do not represent all implementations consistent with the invention. Rather, they are merely examples of apparatuses, systems, and methods consistent with aspects that may relate to the subject matter recited in the appended claims. It is beneficial to present exemplary environments in which embodiments of the invention may be implemented before describing the embodiments of the invention in detail.

[0018] Figure 1 A lithography apparatus LA is schematically depicted. The apparatus includes: an irradiation system (irradiator) IL configured to modulate a radiation beam B (e.g., UV radiation, DUV radiation, or EUV radiation); a patterning apparatus support or support structure (e.g., a mask stage) MT configured to support a patterning apparatus (e.g., a mask) MA and connected to a first positioner PM configured to accurately position the patterning apparatus according to certain parameters; two substrate stages (e.g., wafer stages) WTa and WTb each configured to hold a substrate (e.g., a resist-coated wafer) W and each connected to a second positioner PW configured to accurately position the substrate according to certain parameters; and a projection system (e.g., a refractive projection lens system) PS configured to project a pattern imparted by the radiation beam B onto a target portion C (e.g., including one or more dies) of the substrate W via the patterning apparatus MA. The reference frame (RF) connects various components and acts as a reference for setting and measuring the position of the patterning equipment and the substrate and features thereon.

[0019] Irradiation systems may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic, or other types of optical components or any combination thereof, for guiding, shaping, or controlling radiation.

[0020] A patterning apparatus support holds the patterning apparatus in a manner dependent on the orientation of the patterning apparatus, the design of the lithography apparatus, and other conditions, such as whether the patterning apparatus is held in a vacuum environment. The patterning apparatus support can use mechanical, vacuum, electrostatic, or other clamping techniques to hold the patterning apparatus. The patterning apparatus support MT can be, for example, a frame or stage that can be fixed or moved as needed. The patterning apparatus support ensures that the patterning apparatus is, for example, in the desired position relative to the projection system.

[0021] As used herein, the term "patterning apparatus" should be interpreted broadly to refer to any apparatus that can be used to impart a pattern to a radiation beam in a cross-section, such as to create a pattern in a target portion of a substrate. It should be noted that, for example, if the pattern includes phase-shifting features or so-called auxiliary features, the pattern imparted to the radiation beam may not perfectly correspond to the desired pattern in the target portion of the substrate. Typically, the pattern imparted to the radiation beam will correspond to a specific functional layer in the apparatus (such as an integrated circuit) being created in the target portion.

[0022] As described herein, the apparatus is transmissive (e.g., employing a transmissive patterning apparatus). Alternatively, the apparatus may be reflective (e.g., employing a programmable mirror array of the type described above, or employing a reflective mask). Examples of patterning apparatus include masks, programmable mirror arrays, and programmable LCD panels. Any use of the terms "mask" or "mask" herein may be considered synonymous with the more general term "patterning apparatus." The term "patterning apparatus" may also be interpreted as referring to a device that stores pattern information in digital form for use in controlling such a programmable patterning apparatus.

[0023] The term "transmission system" as used herein should be broadly interpreted to encompass any type of projection system, including refractive, reflective, reflective-refractive, magnetic, electromagnetic, and electrostatic optical systems, or any combination thereof, as may be determined by the exposure radiation employed, or by other factors such as the use of immersion liquids or vacuum. Any use of the term "projection lens" herein may be considered synonymous with the more general term "projection system."

[0024] Photolithography apparatuses can also be of this type, in which at least a portion of the substrate can be covered by a liquid (e.g., water) with a relatively high refractive index to fill the space between the projection system and the substrate. Immersion liquids can also be applied to other spaces within the photolithography apparatus, for example, between the mask and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of a projection system.

[0025] In operation, the irradiator IL receives a radiation beam from the radiation source SO. For example, when the source is an excimer laser, the source and the lithography apparatus can be separate entities. In such cases, the source is not considered part of the lithography apparatus, and the radiation beam is delivered from the source SO to the irradiator IL via a beam delivery system BD, which includes, for example, suitable guide mirrors and / or beam expanders. In other cases, such as when the source is a mercury lamp, the source can be an integral part of the lithography apparatus. The source SO and the irradiator IL, together with the beam delivery system BD if necessary, can be referred to as the radiation system.

[0026] The irradiator IL may, for example, include an adjuster AD, an integrator IN, and a focuser CO for adjusting the angular intensity distribution of the radiation beam. The irradiator can be used to adjust the radiation beam to have a desired uniformity and intensity distribution in its cross-section.

[0027] A radiation beam B is incident on the patterning apparatus MA held on the patterning apparatus support MT and patterned by the patterning apparatus. After passing through the patterning apparatus (e.g., a mask) MA, the radiation beam B is passed through a projection system PS, which focuses the beam onto a target portion C of the substrate W. The substrate stage WTa or WTb can be accurately moved, for example, to position different target portions C within the path of the radiation beam B, using a second positioner PW and a position sensor IF (e.g., an interferometer, linear encoder, 2D encoder, or capacitive sensor). Similarly, for example, after mechanical acquisition from a mask library, or during scanning, a first positioner PM and another position sensor (whose...) Figure 1 (Not explicitly depicted in the text) can be used to accurately position the patterning device (e.g., a mask) MA relative to the path of the radiation beam B.

[0028] Patterning apparatus (e.g., mask) MA and substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks, as shown, occupy dedicated target portions, they can be positioned in the space between the target portions (these are referred to as scribing alignment marks). Similarly, when more than one die is provided on the patterning apparatus (e.g., mask) MA, mask alignment marks can be positioned between the dies. Small alignment marks can also be included within the die, within apparatus features, in which case it is desirable that the marks be as small as possible and do not require any imaging or process conditions different from adjacent features. Alignment systems for detecting alignment marks will be described further below.

[0029] The depicted apparatus can be used in various modes. In scanning mode, the patterning apparatus support (e.g., mask stage) MT and substrate stage WT are scanned synchronously while a pattern imparting a radiation beam is projected onto the target portion C (i.e., single dynamic exposure). The velocity and direction of the substrate stage WT relative to the patterning apparatus support (e.g., mask stage) MT can be determined by the (reduced) magnification and image inversion characteristics of the projection system PS. In scanning mode, the maximum size of the exposure field limits the width of the target portion in a single dynamic exposure (in the non-scanning direction), while the length of the scanning motion determines the height of the target portion (in the scanning direction). Other types of lithography apparatuses and operating modes are possible, as are well known in the art. For example, stepping mode is known. In so-called “maskless” lithography, the programmable patterning apparatus is kept stationary but has a changing pattern, and the substrate stage WT is moved or scanned.

[0030] Alternatively, combinations and / or variations of the usage patterns described above, or entirely different usage patterns, may be adopted.

[0031] The lithography apparatus LA is a so-called dual-stage type, featuring two substrate stages WTa and WTb and two stations (exposure station EXP and measurement station MEA), with the substrate stages interchangeable between the two stations. While one substrate on one stage is exposed at the exposure station, another substrate can be loaded onto the other substrate stage at the measurement station, and various preparation steps are performed. This allows for a significant increase in apparatus throughput. Preparation steps may include using a level sensor LS to map the surface height profile of the substrate and using an alignment sensor AS to measure the position of alignment marks on the substrate. If the position sensor IF cannot measure the position of the substrate stage while it is at both the measurement and exposure stations, a second position sensor may be provided so that the position of the substrate stage can be tracked relative to the reference frame RF at both stations. Other arrangements are known and may be used instead of the dual-stage arrangement shown. For example, other lithography apparatuses in which substrate stages and measurement stages are provided are known. The substrate stages and measurement stages are docked together during preparation measurements and disconnected during exposure of the substrate stage.

[0032] The apparatus also includes a Lithography Apparatus Control Unit (LACU), which controls all movements and measurements of the various actuators and sensors described. The LACU also includes signal and data processing capabilities to perform desired calculations related to the operation of the apparatus. In practice, the LACU will be implemented as a system of many sub-units, each handling real-time data acquisition, processing, and control of subsystems or components within the apparatus. For example, one processing subsystem could be dedicated to the servo control of the substrate positioner (PW). A single unit could even handle coarse and fine adjustment actuators, or different axes. Another unit could be dedicated to the readout of the position sensor (IF). Overall control of the apparatus can be achieved by a central processing unit (CPU) that communicates with these subsystems.

[0033] like Figure 2 As shown, the lithography apparatus LA forms part of the lithography unit LC (sometimes also called a lithography pool or cluster), which also includes devices for performing pre-exposure and post-exposure processes on the substrate. Typically, these devices include: a spin coater SC for depositing a resist layer; a developer DE for developing the exposed resist; a chiller CH; and a baking plate BK. A substrate processor or robot RO picks up the substrate from the input / output ports I / O1 and I / O2, moves the substrate between different process units, and then transfers the substrate to the feed stage LB of the lithography apparatus. These devices, generally referred to collectively as "tracks," are controlled by a track control unit TCU, which in turn is controlled by a supervisory control system SCS, which in turn controls the lithography apparatus via the lithography control unit LACU. Therefore, different units can be operated to maximize throughput and processing efficiency.

[0034] To ensure correct and consistent exposure of substrates by the photolithography apparatus, it is desirable to inspect the exposed substrates to measure properties such as overlay error between subsequent layers, line thickness, and critical dimension (CD). Therefore, the manufacturing facility containing the photolithography pool (LC) also includes a metrology system (MET), which receives some or all of the substrates (W) already processed in the photolithography pool. The measurement results are provided directly or indirectly to the supervisory control system (SCS). If an error is detected, especially if the inspection can be completed quickly enough that other substrates in the same batch are still awaiting exposure, the exposure of subsequent substrates can be adjusted. Furthermore, exposed substrates can be stripped and reprocessed to improve yield, or discarded, thereby avoiding further processing of substrates with known defects. In cases where only some target portions of the substrate are defective, additional exposure can be performed only on the intact target portions.

[0035] Within a metrology system (MET), an inspection apparatus is used to determine the properties of a substrate, specifically how the properties of different substrates or different layers of the same substrate vary with each layer. This inspection apparatus can be integrated into a photolithography (LA) apparatus or a photolithography (LC) bath, or it can be a standalone device. For the fastest possible measurement, it is desirable for the inspection apparatus to measure the properties in the exposed resist layer immediately after exposure. However, latent images in resist have very low contrast; that is, there is only a very small difference in refractive index between the irradiated and unirradiated portions of the resist, and not all inspection apparatuses have sufficient sensitivity to make useful measurements of latent images. Therefore, measurements can be performed after a post-exposure baking (PEB) step, which is typically the first step performed on the exposed substrate and increases the contrast between the exposed and unexposed portions of the resist. At this stage, the image in the resist can be referred to as a semi-latent image. However, both latent images and semi-latent images can be collectively referred to as latent images. Measurements can also be performed on developed resist images (where the exposed or unexposed portions of the resist have been removed), or after a pattern transfer step (such as etching). The latter possibility limits the reprocessing options for faulty substrates, but can still provide useful information.

[0036] As described above, an optical microscope can be provided as part of a lithography unit (LC). For example, an optical microscope (such as an alignment sensor (AS) or another microscope mounted on a reference frame (RF)) can be used by a lithography apparatus (LA). Alternatively or additionally, an optical microscope can be provided in a metrology system (MET) for, for example, performing inspection, alignment, or positioning of a region of interest on a substrate.

[0037] Figures 3A to 3BThe illustration shows the basic components of an optical microscope 300 according to a comparative embodiment and the resulting image. The optical microscope 300 can be configured for use with, for example, a photolithography unit LC as described above in a separate measurement or other measurement system. The optical microscope 300 may include: an illumination system 320; a beam splitter 314; an objective lens 318; a tube lens 312; an image sensor 310; and a microscope control unit 350.

[0038] The illumination system 320 may include a light source and an optical system configured to modulate the beam 316 of the illumination light. For example, the illumination system may include, for instance, a light source 321 and a lens 322. The light source 321 may include, for example, an LED light source, such as a white LED, a halogen lamp, a mercury lamp, a broadband source, a laser, or any suitable light source for imaging a photolithographic substrate. The light source 321 may emit the beam 316 of light onto a beam splitter 314 via the lens 322. The beam splitter 314 may guide the beam 316 through an objective lens 318. The objective lens 318 may focus the beam 316 onto a focal point at a region of interest on the surface of the substrate W. The surface may include, for example, a wafer surface containing a patterned structure or a latent image in a resist layer RL.

[0039] Scattered or reflected light from the substrate W can be captured by objective 318 and guided through beam splitter 314 to another optical element, such as tube mirror 312. Tube mirror 312 can focus the scattered or reflected light onto image sensor 310. Optical microscope 300 can be configured for multiple modes. For example, objective 318 may include an objective system with multiple selectable objectives having different optical powers or numerical apertures. Furthermore, optical microscope 300 can be configured to operate in bright-field imaging mode or dark-field imaging mode. For example, dark-field objective 318 or the selectable aperture can be configured to block the central portion of incident light reaching the substrate W, causing the light to be incident primarily at an oblique angle. The obliquely incident light can be scattered back to the objective, while the central mirror surface remains oblique. Dark-field imaging can be used to highlight features that are difficult to image under bright-field conditions due to, for example, poor contrast with their surroundings.

[0040] Image sensor 310 may include, for example, a camera, complementary metal-oxide-semiconductor (CMOS), charge-coupled device (CCD), or other suitable image sensor. Image sensor 310 can generate an image of the region of interest. The image can be received, stored, and processed by microscope control unit 350. For example, microscope control unit 350 may include an image processing unit. Microscope control unit 350 may include, for example, a control unit LACU or a dedicated control system. Microscope control unit 350 may include an image acquisition unit 351, a storage device 352, and a controller 353. Image acquisition unit 351 may include one or more processors. For example, image acquisition unit 351 may include a computer, server, mainframe, terminal, personal computer, any kind of mobile computing device, or a combination thereof. Image acquisition unit 351 can be communicatively coupled to image sensor 310 via a medium such as an electrical conductor, fiber optic cable, portable storage medium, IR, Bluetooth, Internet, wireless network, radio, or a combination thereof. Image acquisition unit 351 can receive signals from image sensor 310 and can construct an image. Image acquisition unit 351 can thus acquire an image of substrate W. Image acquisition unit 351 can also perform various post-processing functions, such as image averaging, contour generation, and overlaying indicators on the acquired image. Image acquisition unit 351 can be configured to perform adjustments to the brightness and contrast of the acquired image. Storage device 352 can be a storage medium such as a hard disk, random access memory (RAM), cloud storage device, or other types of computer-readable storage. Storage device 352 can be coupled to image acquisition unit 351 and can be used to store scanned raw image data as the original image, as well as the post-processed image. Image acquisition unit 351 and storage device 352 can be connected to controller 353. In some embodiments, image acquisition unit 351, storage device 352, and controller 353 can be integrated into a single electronic control unit.

[0041] The microscope control unit 350 can be configured to control an optical microscope 300, which includes an illumination system 320 and an image sensor 310. The microscope control unit 350 can also be configured to control a movable stage (not shown) for supporting and positioning a substrate W under an objective lens 318 in the x, y, or z directions. For example, the movable stage may include a six-degree-of-freedom (DOF) stage. By controlling image processing functions, the illumination system, the stage, or other components, the microscope control unit 350 can be configured to perform functions of the microscope 300, such as D2D or D2DB inspection, region of interest localization, alignment, etc.

[0042] As circuit pattern features continue to shrink, in areas such as Figure 3AProblems have arisen in optical microscopy inspection systems such as the Optical Microscope 300. The thickness of the photoresist layer RL is constantly shrinking, for example, to meet the increasingly narrow depth of focus in modern photolithography exposure systems, avoid pattern destruction, and ensure that resolution, line edge roughness, and other parameters are within design specifications. Extreme ultraviolet (EUV) systems (such as, for example, high-NA EUV) may require ultrathin photoresists with thicknesses of, for example, less than 40 nm, less than 20 nm, or less than 10 nm. For example, ultrathin photoresist layers can have thicknesses ranging from, for example, 5 nm to 40 nm. Future photoresist thicknesses are expected to be even smaller. When the photoresist layer becomes so thin, examining latent images using conventional optical microscopy techniques may become difficult or impossible. For example, most of the light from bright-field illumination can pass through the ultrathin photoresist layer RL to reach the patterned or unpatterned surface of the substrate W. In some cases, the reflectivity of the photoresist layer RL and the underlying substrate layer may be so similar that it is difficult to distinguish the two layers in an image. While dark-field illumination has been used to image fine features with poor contrast, typical dark-field objectives may include a frosted layer to achieve more uniform illumination. This can be detrimental to the total light irradiance or power density incident on the pattern or received by the image sensor. Reflections from the substrate may also cause stray light to re-enter the objective and incident on the image sensor 310, thereby reducing the signal-to-noise ratio and blurring the imaged pattern.

[0043] Figure 3B The illustrations depict these phenomena in two example measurements of latent images 341 and 342 in an ultrathin resist layer on a substrate. As illustrated, neither bright-field image 341 nor dark-field image 342 is suitable for imaging latent image features in the resist layer. Under these conditions, optical microscopy will be unable to perform any functions related to latent image inspection. For example, in a metrology system, the region of interest must be located using another device, such as a SEM or other charged particle inspection system. However, these devices have a much smaller field of view, and the time required to locate the region of interest will be greatly increased, thus impairing inspection throughput.

[0044] Embodiments of this disclosure provide optical microscopes capable of producing excellent images even in ultrathin resist layers. Figures 4A to 4B An example optical microscope 400 consistent with embodiments of this disclosure is illustrated. In some embodiments, unless otherwise described below, the optical microscope 400 may be, for example... Figure 3A It is similar to the optical microscope 300.

[0045] Optical microscope 400 may include an off-axis illumination system 430. The off-axis illumination system may include, for example, a laser 431. Laser 431 may be configured to emit non-photochemical light, such as in the visible spectrum between, for example, about 380 nm and 700 nm. In some embodiments, laser 431 may include, for example, a violet or blue laser having a center wavelength of substantially 405 nm, 445 nm, 447 nm, or 459 nm; a green laser having a center wavelength of substantially 520 nm or 532 nm; a red laser having a center wavelength between substantially 630 nm and 670 nm, etc. In some embodiments, laser 431 may output a center wavelength, for example, in the infrared or ultraviolet region. In some embodiments, laser 431 may include a tunable laser with an adjustable output wavelength to select the optimal wavelength for a given pattern being examined. Laser 431 may be configured to emit light at a wavelength higher than that of light source 421 (which may be used in conjunction with, for example...). Figure 3A (Similar to the light source 321) to irradiate the substrate W with a relatively higher power density. In some embodiments, the off-axis irradiation system 430 may include additional elements such as, for example, projection lenses, polarizers, filters, beam splitters, and other devices suitable for producing optimal diffraction and other beam characteristics.

[0046] Laser 431 can be configured to generate diffracted light 432 that can be incident on objective lens 418. Optical microscope 400 can be configured to receive diffracted light within a typical range for the periodic pattern being examined. For example, when the resist layer RL comprises a periodic latent image pattern, optical microscope 400 can be configured according to the following formula: (Equation 1) Where d includes the period of the latent image pattern, θ is the diffraction angle of the diffracted light 432, θ0 includes the incident angle of the light from the laser 431 on the substrate W, n includes the diffraction order of the diffracted light 432, and λ includes the laser wavelength. As an example calculation, the optical microscope 400 can be configured to generate an incident beam with an incident angle of 18° at a wavelength of 532 nm. If the objective lens 418 includes, for example, a numerical aperture (NA) of 0.23, first-order diffracted light can be collected for periodic latent image patterns with a period between about 1 µm and 6.3 µm. Taking into account multi-order diffraction, the optical microscope 400 under such conditions can observe any pattern with a period d greater than 1 µm, meaning that all patterns above an optical microscope resolution of about 1 µm can be observed using this technique. In some embodiments, the optical microscope 400 can be configured to collect diffracted light from periodic patterns with a periodicity between, for example, 800 nm and 10 µm, or 1 µm and 7 µm. The above description is given by way of example, and it should be understood that other values ​​are also considered within the embodiments of this disclosure. For example, the laser can be positioned at any angle of incidence, depending on the pattern being imaged and other parameters of the optical microscope 400. By using an off-axis laser, the optical microscope can achieve diffraction imaging with high power density illumination and lower stray light, thereby improving the signal-to-noise ratio.

[0047] As in Figure 4B As seen in some embodiments, the optical microscope can be based on Figure 3A The description at the location pertains to operation in coaxial mode. For example, if necessary, the microscope control unit 450 can irradiate the substrate W in a first mode via the laser 431 of the off-axis illumination system 430 to generate diffracted light as described above. The microscope control unit 450 can also operate in off-axis mode when, for example, the substrate being examined comprises a thin resist layer RL with a periodic latent image pattern, or in any other case where off-axis mode may be preferred. The microscope control unit 450 can also irradiate the substrate W in a second mode corresponding to the coaxial mode via the light source 421 of the illumination system 420.

[0048] In some embodiments, the same objective 418 can be used in both coaxial and off-axis modes. In some embodiments, the optical microscope 400 may include an objective system having a numerical aperture in the range of, for example, 0.01 to 0.5. In some embodiments, the optical microscope 400 may include an objective system having a plurality of optional objectives 418. For example, an off-axis laser configuration may be designed such that the objective can accept diffracted light at a numerical aperture smaller than that feasible in coaxial mode. This can advantageously increase the depth of focus of the optical microscope. Thus, the optical microscope may include a first objective for use with the laser 431 in off-axis mode and may include a second objective for use with the light source 421 in coaxial mode. The first objective may include a smaller numerical aperture compared to the second objective.

[0049] Figure 5A and Figure 5C Example optical microscope images 541-544, consistent with embodiments of this disclosure, are illustrated. Optical microscope images 541-544 can be used, for example, by an optical microscope 400, as described above. Figures 4A to 4B The off-axis laser irradiation technique discussed above is used to generate the images. Optical microscope images 541-544 can be generated using, for example, a laser irradiation technique. Figures 3A to 3B The comparative embodiments are generated using the same substrate used to generate optical microscope images 341-342. For example, optical microscope images 541-544 may correspond to latent images of periodic patterns in an ultrathin resist layer on a semiconductor substrate. Figure 5A As seen in optical microscope image 541, an off-axis laser configuration can generate more than Figure 3B The image shown is far superior. However, due to the diffraction properties of imaging, the quality of the image can be strongly dependent on the azimuth angle between the beam emitted from the laser and the periodic direction of the pattern in the latent image. For example, as... Figure 5B As illustrated, in addition to the predetermined incident angle θ, the laser 531 can also be positioned at a predetermined azimuth angle. It is positioned in the xy plane of substrate W. Figure 5C The effect of this positioning is illustrated using optical microscope images 542-544. Each image can be generated by radiating a periodic latent image pattern from different azimuth angles. For example, optical microscope images 542-544 can be generated at azimuth angles of 0, 45, and 90 degrees relative to the two-dimensional periodic pattern. When the azimuth angle... When the diffraction pattern is substantially perpendicular to the principal periodic direction, such as at 0 or 90 degrees as seen in optical microscope images 542 and 544, the diffraction pattern may be relatively strong. When the azimuth angle... At intermediate angles relative to the periodic direction, such as 45 degrees as seen in optical microscope image 543, the diffraction pattern may be relatively weak.

[0050] Therefore, in some embodiments, the optical microscope can be configured to generate multiple off-axis laser images from multiple azimuth angles. For example, the optical microscope can be configured to rotate the substrate to different azimuth angles, or it can be configured with multiple lasers to radiate the substrate from different azimuth angles. In some embodiments, a single laser can be configured to radiate the substrate from different azimuth angles by adjustment or actuation, for example, by a mirror, lens, or other optical element. By generating multiple images from multiple azimuth angles, it is possible, for example, to select preferred angles or to create composite images from a weighted combination of images. For example, a control unit (such as a lithography apparatus control unit LACU or a microscope control unit 450) can acquire multiple optical microscope images 542-544 from multiple azimuth angles (such as 0 degrees, 45 degrees, and 90 degrees). Based on these optical microscope images, it can be determined which azimuth angle produced a clear image of the pattern. The appropriate optical microscope image 542-544 showing a clear image of the pattern can then be selected for use in, for example, inspection or alignment processes. In some embodiments, the azimuth angle can be adjusted based on the optical microscope images 542-544 until an acceptable optical microscope image is generated. In some embodiments, the control unit can combine optical microscope images 542-544. In some embodiments, the control unit can add optical microscope images 542 and 544 while subtracting, for example, optical microscope image 543, to remove unwanted artifacts. In some embodiments, the control unit can perform other additions, subtractions, or transformations. For example, in some embodiments, the control unit can be configured to remove image information corresponding to the underlying layer to improve the image quality of latent images in the resist layer.

[0051] Figure 6A An example off-axis illumination system 630 consistent with embodiments of the present disclosure is illustrated. The off-axis illumination system 630 may include a laser 631 and a cylindrical mount 632. The cylindrical mount 632 may include, for example, an axial adjuster 633, a tilt adjuster 634, or an azimuth adjuster 635. The cylindrical mount 632 may be configured to mount the off-axis illumination system 630 to an optical microscope (such as...). Figure 3A Optical microscope 300 or Figures 4A to 4BThe cylindrical mount 632 is mounted on the microscope tube or other components of an optical microscope 400. The cylindrical mount 632 allows one or more lasers 631 to provide off-axis illumination for diffracting light from a periodic pattern on the substrate being examined. One or more lasers can be coupled to a microscope control unit via a wire 654 configured to, for example, supply power, receive control signals, or transmit imaging signals to the microscope control unit. In some embodiments, the cylindrical mount can be configured to position the lasers 631 according to Equation 1 above. In some embodiments, positioning can be achieved by an actuator controlled or powered by an additional wire 655, or positioning can be performed manually. For example, an axial adjuster 633 may include, for example, an adjusting screw, an actuator, or other devices configured to finely adjust the axial height of the lasers 631 (whether collectively or individually). Similarly, a tilt adjuster 634 may include an adjusting screw, an actuator, or other devices configured to finely adjust the angle of incidence of the lasers 631 (whether collectively or individually). In some embodiments, the off-axis illumination system 630 may further include an azimuth adjuster 635 having an adjusting screw, an actuator, or other device configured to finely adjust the azimuth angle of the laser 631 (whether collectively or individually). By providing fine adjustment in the axial, tilt, or azimuth directions, the laser 631 can be adapted to a variety of periodic patterns and optical microscopes. For example, the off-axis illumination system 630 can be retrofitted to existing optical microscopes to improve their performance when imaging difficult features, such as latent images in ultrathin resist layers. By providing multiple lasers 631 at multiple azimuth angles, multiple optical microscope images can be acquired rapidly and sequentially to achieve high-quality images with high throughput.

[0052] Figure 6B Further examples of an off-axis illumination system 630 consistent with embodiments of the present disclosure are illustrated. The off-axis illumination system 630 may include components of an optical microscope 600. On the left side, the off-axis illumination system 630 may include a cylindrical mount 632 for mounting a laser 631 to the body (such as a microscope tube 619) of the optical microscope 600. The laser 631 may be mounted at multiple azimuth angles around the optical axis of the optical microscope 600. In some embodiments, the laser 631 may be adjustable in at least one degree of freedom. For example, the off-axis illumination system 630 may include, for example... Figure 6A Various adjusters 633-635. Alternatively or additionally, such as in Figure 6BAs seen in the configuration on the right, the laser 631 can remain fixed in a degree of freedom, and the beam direction can be adjusted using an adjustable optical element 636. For example, as illustrated, the adjustable optical element 636 may include, for example, a tiltable mirror configured to adjust the incident angle of the off-axis beam. In some embodiments, the adjustable optical element may be configured as described above to adjust other degrees of freedom. The adjustable optical element can be adjusted manually or by an actuator. Furthermore, in some embodiments, the laser can be guided to the substrate via multiple paths by altering the optical element or by a beam-splitting optical element.

[0053] Figure 7 A flowchart of an example method 700 for off-axis laser imaging, consistent with embodiments of the present disclosure, is schematically illustrated. The method can be based on, for example... Figures 1 to 6B The embodiments disclosed herein shall be performed. For example, method 700 may use a controller (such as...) Figures 1 to 2 The LACU (Laser Lithography Unit Control Unit) in the photolithography apparatus or Figures 4A to 4B The microscope control unit 450 in the microscope is used to perform this operation.

[0054] At step 701, a first laser can be used to irradiate the substrate at a first azimuth angle. The laser can be emitted from a laser mounted off-axis to the end of an optical microscope. The optical microscope can be arranged in any module, such as a measurement system, a lithography apparatus, or a lithography pool. The laser can include, for example, a visible light laser, an infrared laser, or an ultraviolet laser. In some embodiments, the laser can emit non-photochemical radiation relative to a resist layer on the substrate. In some embodiments, the resist layer can include an ultrathin resist layer having a thickness of, for example, less than 40 nm. In some embodiments, the resist layer can include a latent image having a periodic pattern. The first laser can generate first diffracted light, such as from the periodic pattern in the latent image.

[0055] At step 702, the first diffracted light can be collected at the objective lens of the optical microscope. The collected first diffracted light may include, for example, first-order diffraction, second-order diffraction, or higher-order diffraction. The collected first diffracted light may include a single order or multiple orders. In some embodiments, the optical microscope may be configured such that the objective lens can be used according to formula d. (sinθ - sinθ0) = n A first diffracted light is collected using a parameter λ, where d comprises the period of the latent image pattern, θ comprises the diffraction angle of the diffracted light, θ0 comprises the incident angle of the light from the laser, n comprises the diffraction order of the diffracted light, and λ comprises the laser wavelength. In some embodiments, the numerical value of the objective lens can be adapted to the coaxial illumination system of the optical microscope. For example, the objective lens can include a numerical aperture, for example, between 0.01 and 0.5. In some embodiments, the optical microscope can include a first objective lens for use with a laser in off-axis mode and a second objective lens for use with a separate coaxial light source in coaxial mode. The first objective lens can include a smaller numerical aperture compared to the second objective lens. The collected first diffracted light can be focused onto the image sensor of the optical microscope and stored in, for example, the memory of a control unit.

[0056] Steps 703 and 704 can be performed similarly to steps 701 and 702. For example, at step 703, a second laser can be used to radiate the substrate at a second azimuth angle. In some embodiments, the second laser can be radiated by, for example, a second laser different from the first laser. Alternatively, the second laser can be radiated by the first laser at a different orientation relative to the periodic pattern. For example, the first laser can be moved by an actuator or other adjuster, the substrate can be rotated, or the laser can be redirected using an adjustable mirror, lens, beam splitter, or other optical element. The second azimuth angle can differ from the first azimuth angle by a predetermined amount, such as 45 degrees or 90 degrees. In some embodiments, the azimuth angle can differ by other amounts, such as 10 degrees, 15 degrees, 30 degrees, 60 degrees, etc. The second laser can generate second diffracted light. Then, at step 704, the second diffracted light can be collected at the objective lens in a manner similar to step 702 described above.

[0057] At step 705, the microscope image may be generated based on at least one of the collected first diffracted light or the collected second diffracted light. For example, in some embodiments, the controller may be configured to select an optimal microscope image from a plurality of microscope images, such as by selecting an image from the collected first diffracted light rather than an image from the collected second diffracted light. In some embodiments, the controller may be configured to create a combined optimal microscope image based on the collected first diffracted light and the collected second diffracted light.

[0058] In some embodiments, the generated microscope images can be used in other method steps (such as one of steps 706a to 706c). For example, the generated images can be used to examine, locate regions of interest on a substrate, or perform alignment operations.

[0059] A non-transitory computer-readable medium consistent with embodiments of this disclosure may be provided, the non-transitory computer-readable medium storing instructions for use by a controller (e.g., Figures 1 to 2 The LACU (Laser Lithography Unit Control Unit) in the photolithography apparatus, or Figures 4A to 4B The processor of the microscope control unit 450 is used to, for example, Figures 4A to 6B System 400-600 or Figure 7 Example method 700 is used to generate optical microscope images. For example, instructions stored in a non-transitory computer-readable medium can be executed by the circuitry of a controller to perform measurements, in part or in whole, according to system 400-600 or method 700. Common forms of non-transitory media include, for example, floppy disks, flexible disks, hard disks, solid-state drives, magnetic tape or any other magnetic data storage media, optical disc read-only memory (CD-ROM), any other optical data storage media, any physical media with a perforated pattern, random access memory (RAM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), FLASH-EPROM or any other flash memory, non-volatile random access memory (NVRAM), caches, registers, any other memory chips or tapes, and their networked versions.

[0060] The embodiments of this disclosure can also be described by the following terms: 1. An optical microscope, comprising: Objective lens system, the objective lens system including a first objective lens; Image sensors; and An off-axis illumination system, the off-axis illumination system including a first laser, the first laser being configured to irradiate a pattern on a substrate with a first laser beam to generate first diffracted light, wherein... The objective lens is configured to collect the first diffracted light, and The optical microscope is configured to generate an image of the pattern on the image sensor using the first diffracted light. 2. The optical microscope according to Clause 1 further includes: A coaxial illumination system, the coaxial illumination system including a light source configured to irradiate the substrate using a light beam from the objective lens system. 3. The optical microscope according to Clause 2, wherein: The objective lens system includes a second objective lens, the first objective lens having a first numerical aperture and the second objective lens having a second numerical aperture, and The first numerical aperture is smaller than the second numerical aperture. 4. The optical microscope according to clause 2 or 3, wherein the coaxial illumination system is configured to irradiate the substrate using the light beam from the first objective lens of the objective lens system. 5. The optical microscope according to any one of clauses 2 to 4 further comprises: Optical element, the optical element being configured as follows: Guide the light beam to the objective lens system; Receive the light beam from the objective lens system, and The first diffracted light is received from the objective lens system. 6. The optical microscope according to Clause 5, wherein the optical element includes a beam splitter. 7. The optical microscope according to any one of clauses 1 to 5, wherein the off-axis illumination system further comprises: A cylindrical mounting assembly configured to mount the first laser to the frame of the optical microscope, the cylindrical mounting assembly including an adjuster configured to adjust one of the axial height, tilt angle, or azimuth angle of the first laser. 8. The optical microscope according to Clause 7, wherein the off-axis illumination system further comprises: A second laser, wherein the cylindrical mount is configured to mount the second laser to the frame of the optical microscope. 9. The optical microscope according to clause 7 or 8, wherein the off-axis illumination system further comprises: A third laser, wherein the cylindrical mount is configured to mount the third laser to the frame of the optical microscope. 10. An optical microscope according to any one of clauses 1 to 9, wherein the first laser beam comprises wavelengths in the visible spectrum. 11. An optical microscope according to any one of clauses 1 to 10, wherein the first laser is configured to generate the first diffracted light by irradiating a pattern in a latent image in a resist layer. 12. The optical microscope according to Clause 11, wherein the resist layer has a thickness of 20 nm or less. 13. The optical microscope according to clause 11 or 12, wherein the resist layer has a thickness of 10 nm or less. 14. An optical microscope according to any one of clauses 11 to 13, wherein the pattern in the latent image comprises a periodic pattern having a periodicity of 800 nm or greater. 15. An optical microscope according to any one of clauses 11 to 14, wherein the pattern in the latent image comprises a periodic pattern having a periodicity between 800 nm and 10 μm. 16. The optical microscope according to any one of clauses 11 to 15, wherein the pattern in the latent image comprises a periodic pattern having a periodicity of 1 μm or greater. 17. The optical microscope according to any one of clauses 11 to 16, wherein the pattern in the latent image comprises a periodic pattern having a periodicity between 1 μm and 7 μm. 18. The optical microscope according to any one of clauses 11 to 17 further includes a controller configured to control the optical microscope to perform operations, said operations including: The first laser beam is emitted from the first azimuth angle to generate the first diffracted light; The first diffracted light is collected by the first objective lens; A second laser beam is emitted from a second azimuth angle to generate a second diffracted beam; The second diffracted light is collected by the first objective lens; and An optical microscope image is generated based on one of the first diffracted light and the second diffracted light. 19. The optical microscope according to Clause 18, wherein generating the optical microscope image based on one of the first diffracted light and the second diffracted light comprises: Determine the optimal diffracted beam between the first and second diffracted beams, and The optical microscope image is generated based on the optimal diffraction light. 20. An optical microscope according to clause 18 or 19, wherein generating the optical microscope image based on one of the first diffracted light and the second diffracted light comprises: The optical microscope image is generated based on the combination of the first diffracted light and the second diffracted light. 21. An optical microscope according to any one of clauses 18 to 20, wherein emitting the second laser beam at the second azimuth angle comprises: rotating the substrate and the first laser relative to each other. 22. The optical microscope according to any one of clauses 18 to 21 further comprises: The second laser, wherein emitting the second laser beam at the second azimuth angle comprises: emitting the second laser beam from the second laser. 23. The optical microscope according to any one of clauses 18 to 22 further comprises: An adjustable optical element, wherein emitting the second laser beam at the second azimuth angle comprises: emitting the second laser beam from the first laser and guiding the second laser beam to the substrate via the adjustable optical element. 24. A method comprising: A first laser beam is emitted from a first laser in an off-axis illumination system toward a substrate at a first azimuth angle to generate first diffracted light; The first diffracted light is collected by the first objective lens of the optical microscope; A second laser beam is emitted from a second azimuth angle to generate a second diffracted beam; The second diffracted light is collected by the first objective lens; and An optical microscope image is generated based on one of the first diffracted light and the second diffracted light. 25. The method described under Clause 24 further includes: Coaxial illumination is emitted from the light source to irradiate the substrate using a beam of light from the objective lens system. 26. The method described according to Clause 25, wherein: The objective lens system includes a second objective lens, the first objective lens having a first numerical aperture and the second objective lens having a second numerical aperture, and The first numerical aperture is smaller than the second numerical aperture. 27. The method according to clause 25 or 26, wherein the coaxial illumination system is configured to irradiate the substrate using the light beam from the first objective lens of the objective lens system. 28. The method according to any one of clauses 25 to 27, wherein the optical microscope further comprises: Optical element, the optical element being configured as follows: Guide the light beam to the objective lens system; Receive the light beam from the objective lens system, and The first diffracted light is received from the objective lens system. 29. The method according to Clause 28, wherein the optical element includes a beam splitter. 30. The method according to any one of clauses 24 to 29, wherein the off-axis irradiation system further comprises: A cylindrical mounting assembly configured to mount the first laser to the frame of the optical microscope, the cylindrical mounting assembly including an adjuster configured to adjust one of the axial height, tilt angle, or azimuth angle of the first laser. 31. The method according to clause 30, wherein the off-axis irradiation system further comprises: A second laser, wherein the cylindrical mount is configured to mount the second laser to the frame of the optical microscope. 32. The method according to clause 30 or 31, wherein the off-axis irradiation system further comprises: A third laser, wherein the cylindrical mount is configured to mount the third laser to the frame of the optical microscope. 33. The method according to any one of clauses 24 to 32, wherein the first laser beam comprises wavelengths in the visible spectrum. 34. The method according to any one of clauses 24 to 33 further comprises: The first diffracted light is generated by irradiating the pattern in the latent image in the resist layer with the first laser beam. 35. The method according to Clause 34, wherein the resist layer has a thickness of 20 nm or less. 36. The method according to clause 34 or 35, wherein the resist layer has a thickness of 10 nm or less. 37. The method according to any one of clauses 34 to 36, wherein the pattern in the latent image comprises a periodic pattern having a periodicity of 800 nm or greater. 38. The method according to any one of clauses 34 to 37, wherein the pattern in the latent image comprises a periodic pattern having a periodicity between 800 nm and 10 μm. 39. The method according to any one of clauses 34 to 38, wherein the pattern in the latent image comprises a periodic pattern having a periodicity of 1 μm or greater. 40. The method according to any one of clauses 34 to 39, wherein the pattern in the latent image comprises a periodic pattern having a periodicity between 1 μm and 7 μm. 41. The method according to any one of clauses 24 to 40, wherein generating the optical microscope image based on one of the first diffracted light and the second diffracted light comprises: Determine the optimal diffracted beam between the first and second diffracted beams, and The optical microscope image is generated based on the optimal diffraction light. 42. The method according to any one of clauses 24 to 41, wherein generating the optical microscope image based on one of the first diffracted light and the second diffracted light comprises: The optical microscope image is generated based on the combination of the first diffracted light and the second diffracted light. 43. The method according to any one of clauses 24 to 42, wherein emitting the second laser beam at the second azimuth angle comprises: rotating the substrate and the first laser relative to each other. 44. The method according to Clause 24, wherein emitting the second laser beam at the second azimuth angle comprises: emitting the second laser beam from a second laser of the off-axis irradiation system. 45. The method according to any one of clauses 24 to 44, wherein emitting the second laser beam at the second azimuth angle comprises: emitting the second laser beam from the first laser and guiding the second laser beam to the substrate via an adjustable optical element. 46. ​​A non-transitory computer-readable medium storing an instruction set executable by at least one processor of a device to cause the device to perform operations, the operations including: A first laser beam is emitted from a first laser in an off-axis illumination system toward a substrate at a first azimuth angle to generate first diffracted light; The first diffracted light is collected by the first objective lens of the optical microscope; A second laser beam is emitted from a second azimuth angle to generate a second diffracted beam; The second diffracted light is collected by the first objective lens; and An optical microscope image is generated based on one of the first diffracted light and the second diffracted light. 47. The non-transitory computer-readable medium as described in Clause 46 further includes: Coaxial illumination is emitted from the light source to irradiate the substrate using a beam of light from the objective lens system. 48. The non-transitory computer-readable medium as described in Clause 47, wherein: The objective lens system includes a second objective lens, the first objective lens having a first numerical aperture and the second objective lens having a second numerical aperture, and The first numerical aperture is smaller than the second numerical aperture. 49. The non-transitory computer-readable medium according to clause 47 or 48, wherein the coaxial illumination system is configured to irradiate the substrate using the light beam from the first objective lens of the objective lens system. 50. The non-transitory computer-readable medium according to any one of clauses 47 to 49, wherein the optical microscope further comprises: Optical element, the optical element being configured as follows: Guide the light beam to the objective lens system; Receive the light beam from the objective lens system, and The first diffracted light is received from the objective lens system. 51. The non-transitory computer-readable medium according to Clause 50, wherein the optical element includes a beam splitter. 52. The non-transitory computer-readable medium according to any one of clauses 46 to 51, wherein the off-axis irradiation system further comprises: A cylindrical mounting assembly configured to mount the first laser to the frame of the optical microscope, the cylindrical mounting assembly including an adjuster configured to adjust one of the axial height, tilt angle, or azimuth angle of the first laser. 53. The non-transitory computer-readable medium according to Clause 52, wherein the off-axis irradiation system further comprises: A second laser, wherein the cylindrical mount is configured to mount the second laser to the frame of the optical microscope. 54. The non-transitory computer-readable medium according to clause 52 or 53, wherein the off-axis irradiation system further comprises: A third laser, wherein the cylindrical mount is configured to mount the third laser to the frame of the optical microscope. 55. The non-transitory computer-readable medium according to any one of clauses 46 to 54, wherein the first laser beam comprises wavelengths in the visible spectrum. 56. The non-transitory computer-readable medium according to any one of clauses 46 to 55 further includes: The first diffracted light is generated by irradiating the pattern in the latent image in the resist layer with the first laser beam. 57. The non-transitory computer-readable medium according to Clause 56, wherein the resist layer has a thickness of 20 nm or less. 58. The non-transitory computer-readable medium according to clause 56 or 57, wherein the resist layer has a thickness of 10 nm or less. 59. A non-transitory computer-readable medium according to any one of clauses 56 to 58, wherein the pattern in the latent image comprises a periodic pattern having a periodicity of 800 nm or greater. 60. A non-transitory computer-readable medium according to any one of clauses 56 to 59, wherein the pattern in the latent image comprises a periodic pattern having a periodicity between 800 nm and 10 μm. 61. A non-transitory computer-readable medium according to any one of clauses 56 to 60, wherein the pattern in the latent image comprises a periodic pattern having a periodicity of 1 μm or greater. 62. The non-transitory computer-readable medium according to any one of clauses 56 to 61, wherein the pattern in the latent image comprises a periodic pattern having a periodicity between 1 μm and 7 μm. 63. A non-transitory computer-readable medium according to any one of clauses 46 to 62, wherein generating the optical microscope image based on one of the first diffracted light and the second diffracted light comprises: Determine the optimal diffracted beam between the first and second diffracted beams, and The optical microscope image is generated based on the optimal diffraction light. 64. A non-transitory computer-readable medium according to any one of clauses 46 to 63, wherein generating the optical microscope image based on one of the first diffracted light and the second diffracted light comprises: The optical microscope image is generated based on the combination of the first diffracted light and the second diffracted light. 65. The non-transitory computer-readable medium according to any one of clauses 46 to 64, wherein emitting the second laser beam at the second azimuth angle comprises: rotating the substrate and the first laser relative to each other. 66. The non-transitory computer-readable medium according to any one of clauses 46 to 65, wherein emitting the second laser beam at the second azimuth angle comprises: emitting the second laser beam from a second laser of the off-axis irradiation system. 67. The non-transitory computer-readable medium according to any one of clauses 46 to 66, wherein emitting the second laser beam at the second azimuth angle comprises: emitting the second laser beam from the first laser and guiding the second laser beam to the substrate via adjustable optical elements.

[0061] The block diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer hardware or software products according to various exemplary embodiments of the present disclosure. In this regard, each block in the diagram may represent a certain arithmetic or logical operation that can be implemented using hardware such as electronic circuits. A block may also represent a portion of a module, segment, or code that includes one or more executable instructions for implementing a specified logical function. It should be understood that in some alternative implementations, the functions indicated in the blocks may occur in a sequence other than that shown in the figures. For example, two blocks shown consecutively may be executed or implemented substantially simultaneously, or the two blocks may sometimes be executed in reverse order, depending on the functions involved. Some blocks may also be omitted. It should also be understood that each block in the block diagram, and combinations of blocks, may be implemented by a system based on dedicated hardware that performs the specified function or action, or by a combination of dedicated hardware and computer instructions.

[0062] It should be understood that the embodiments of this disclosure are not limited to the exact constructions already described above and illustrated in the accompanying drawings, and various modifications and variations can be made without departing from its scope.

Claims

1. An optical microscope, comprising: Objective lens system, the objective lens system including a first objective lens; Image sensor; as well as An off-axis illumination system, the off-axis illumination system including a first laser, the first laser being configured to irradiate a pattern on a substrate with a first laser beam to generate first diffracted light, wherein... The objective lens is configured to collect the first diffracted light, and The optical microscope is configured to generate an image of the pattern on the image sensor using the first diffracted light.

2. The optical microscope according to claim 1, further comprising: A coaxial illumination system, the coaxial illumination system including a light source configured to irradiate the substrate using a light beam from the objective lens system.

3. The optical microscope according to claim 2, wherein: The objective lens system includes a second objective lens, the first objective lens having a first numerical aperture and the second objective lens having a second numerical aperture, and The first numerical aperture is smaller than the second numerical aperture.

4. The optical microscope of claim 2, wherein the coaxial illumination system is configured to irradiate the substrate using the light beam from the first objective lens of the objective lens system.

5. The optical microscope according to claim 2, further comprising: Optical element, the optical element being configured as follows: Guide the light beam to the objective lens system; Receive the light beam from the objective lens system, and The first diffracted light is received from the objective lens system.

6. The optical microscope according to claim 1, wherein the off-axis illumination system further comprises: A cylindrical mounting assembly configured to mount the first laser to the frame of the optical microscope, the cylindrical mounting assembly including an adjuster configured to adjust one of the axial height, tilt angle, or azimuth angle of the first laser.

7. The optical microscope of claim 6, wherein the off-axis illumination system further comprises: A second laser, wherein the cylindrical mount is configured to mount the second laser to the frame of the optical microscope.

8. The optical microscope of claim 1, wherein the first laser beam comprises wavelengths in the visible spectrum.

9. The optical microscope of claim 1, wherein the first laser is configured to generate the first diffracted light by irradiating a pattern in a latent image in a resist layer.

10. The optical microscope of claim 9, wherein the resist layer has a thickness of 20 nm or less.

11. The optical microscope of claim 9, wherein the pattern in the latent image comprises a periodic pattern having a periodicity between 800 nm and 10 μm.

12. The optical microscope of claim 1, further comprising a controller configured to control the optical microscope to perform operations, the operations including: The first laser beam is emitted from the first azimuth angle to generate the first diffracted light; The first diffracted light is collected by the first objective lens; A second laser beam is emitted from a second azimuth angle to generate a second diffracted beam; The second diffracted light is collected by the first objective lens; as well as An optical microscope image is generated based on one of the first diffracted light and the second diffracted light.

13. The optical microscope according to claim 12, further comprising: The second laser, wherein emitting the second laser beam at the second azimuth angle comprises: emitting the second laser beam from the second laser.

14. The optical microscope according to claim 12, further comprising: An adjustable optical element, wherein emitting the second laser beam at the second azimuth angle comprises: emitting the second laser beam from the first laser and guiding the second laser beam to the substrate via the adjustable optical element.

15. A non-transitory computer-readable medium storing an instruction set executable by at least one processor of a device to cause the device to perform operations, the operations including: A first laser beam is emitted from a first laser in an off-axis illumination system toward a substrate from a first azimuth angle to generate first diffracted light; The first diffracted light is collected by the first objective lens of the optical microscope; A second laser beam is emitted from a second azimuth angle to generate a second diffracted beam; The second diffracted light is collected by the first objective lens; as well as An optical microscope image is generated based on one of the first diffracted light and the second diffracted light.

Images