Method and system for scatterometry-based metrology of structures fabricated on transparent substrates

Abstract

A method and system for performing spectroscopic ellipsometry (SE) measurements of surface structures of optical elements fabricated on transparent substrates is presented herein. The SE measurement system is configured to detect light from the measured structures without contamination from light reflected from the backside of the transparent substrate. The surface structures of the optical elements include film structures and grating structures fabricated on thin transparent substrates. The SE-based measurement system is configured with a relatively large illumination numerical aperture (NA) and a relatively high demagnification ratio from the illumination source to the measurement spot on the optically transparent substrate. This configuration results in a relatively small measurement spot size, a small depth of focus, and minimizes the amount of light reflected from the backside of the optically transparent substrate. In addition, the relatively small collection aperture size further minimizes the amount of light reflected from the backside that reaches the detector.

Description

[Technical Field]

[0001] [CROSS-REFERENCE TO RELATED APPLICATIONS] This patent application claims priority under 35 U.S.C. § 119 to U.S. Provisional Patent Application No. 63 / 432,386, filed December 14, 2022, entitled "Metalens metrology using Scatterometry CD (SCD)," the subject matter of which is incorporated herein by reference in its entirety.

[0002] The described embodiments relate to metrology systems and methods, and more particularly to methods and systems for improving measurements of advanced optical structures. [Background technology]

[0003] Semiconductor devices, such as logic and memory devices, are typically fabricated by a series of processing steps applied to a specimen. Various features and multiple structural levels of the semiconductor device are formed by these processing steps. For example, lithography is a semiconductor manufacturing process that involves creating patterns on a semiconductor optically transparent substrate. Further examples of semiconductor manufacturing processes include, but are not limited to, chemical-mechanical polishing, etching, deposition, and ion implantation. Multiple semiconductor devices can be fabricated on a single semiconductor optically transparent substrate and then separated into individual semiconductor devices.

[0004] Metrology processes are used at various steps during the semiconductor manufacturing process to detect defects on optically transparent substrates and improve yield. Optical metrology techniques offer the potential for high throughput without the risk of destroying the sample. Several optical metrology-based techniques, including implementations of scatterometry, ellipsometry, and reflectometry, as well as associated analysis algorithms, are frequently used to characterize critical dimensions of nanoscale structures, film thickness, composition, overlay, and other parameters.

[0005] Optical structures, commonly referred to as meta-optics or metalens structures, are rapidly becoming a popular lens technology enabling sensing and imaging applications in consumer electronic devices, autonomous vehicles, augmented reality displays, and more.

[0006] The focusing properties of conventional lenses, such as Fresnel lenses, are primarily based on the phase difference that accumulates as light propagates through separate optical paths within the lens. Although Fresnel lenses reduce the amount of material required to achieve a particular focusing performance compared to conventional lenses, Fresnel lenses are still bulky, expensive, require extremely precise polishing, etc.

[0007] Metalens optical elements contain micro- or nano-patterned surface relief structures that enable unique optical performance in a compact package. Metalens optical elements are extremely thin and planar in shape. The planar shape eliminates geometric aberrations, such as spherical aberration, that are induced by traditional non-planar optical structures with equivalent optical functions. The relatively small size of metalens optical elements allows for a high degree of mechanical integration. This results in extremely compact optical systems with complex and precise optical functions.

[0008] The flat and ultrathin properties of metalens optical elements have led to applications in a wide range of industrial equipment, including electron beam lithography and other imaging systems. In some examples, the surface structures of metalens elements have been incorporated into waveguide devices. In some examples, metalens structures have been used to integrate multiple color hologram generation and wavelength multiplexing on a single chip.

[0009] The surface structures of metalens optical elements control the amplitude, phase, polarization state, etc. of propagating light. In some examples, the surface structures of metalens optical elements include nanoantenna structures fabricated with subwavelength dimensions. In some examples, the nanoantenna structures are designed to match specific wavelengths of light. In some examples, the nanoantenna structures are designed with hybrid modes that reduce chromatic aberration.

[0010] Nanoantenna structures are designed to control the profile of light on the micrometer or nanometer dimension scale, and this ability to control light at this scale can be applied to a variety of industrial applications, including optical wireless communication systems, subwavelength imaging systems, and light trapping in solar cells.

[0011] In some examples, the radiation pattern of the nanoantenna structures is dynamically controlled. The ability to dynamically tune the optical properties of metalens-based optical devices integrated with programmable integrated circuits enables improved performance in many application areas, including dynamic hologram generation, LIDAR, imaging systems, and optical wireless communications.

[0012] Many surface structures of metalens optical elements are readily fabricated using manufacturing processes developed for the fabrication of semiconductor devices, such as lithography, etching, deposition, etc. In some instances, surface structures of metalens optical elements, such as nanoantennas, are fabricated at sub-wavelength dimensions using well-developed semiconductor processing techniques, such as CMOS processing techniques and equipment. The ability to leverage semiconductor manufacturing techniques for the fabrication of metalens-based optical structures enables the low-cost production of metalens-based optical elements on a large scale.

[0013] Metalens-based optical elements are typically fabricated on very thin, optically transparent substrates and typically contain structures with relatively large spatial periodicity compared to semiconductor memory or logic structures. These characteristics make film and CD metrology challenging. The ability to measure the critical dimensions that define the shape of metalens surface structures is crucial to achieving desired optical performance levels and device yields.

[0014] Existing metrology tools manufactured by KLA Corporation include the SpectraShape™ SS10k, SS11K, and S12k tools, which focus on critical dimension and shape metrology, and the SpectraFilm™ F1-F20 tools, which focus on film metrology. These tools contain relatively large collection NAs in the AOI direction, which causes light reflected from the bottom surface of the metalens substrate to contaminate the measurement signal. [Prior art documents] [Patent documents]

[0015] [Patent Document 1] U.S. Patent Application Publication No. 2013 / 0114085 Summary of the Invention [Problem to be solved by the invention]

[0016] In summary, the structural features of metalens optical elements fabricated on transparent substrates impose stringent requirements on optical metrology systems. Optical metrology systems must meet high precision and accuracy requirements for increasingly complex structures at high throughput to remain cost-effective. In this context, collection NA and spectrometer slit size have emerged as significant performance-limiting issues in the design of optical metrology systems suitable for advanced optical structures. Therefore, improved metrology systems and methods to overcome these limitations are desirable. [Means for solving the problem]

[0017] Presented herein are methods and systems for performing spectroscopic ellipsometry (SE) measurements of surface structures of optical elements fabricated on transparent substrates. The SE measurement system is configured to detect light from the measured structures without contamination from light reflected from the back surface of the transparent substrate. Surface structures of metalens-based optical elements include film structures and grating structures fabricated on transparent substrates for a variety of applications, including, but not limited to, optical waveguides, augmented and virtual reality display devices, imaging subsystems, and the like.

[0018] In one aspect, the surface structure of the metalens-based optical element is fabricated on an optically transparent substrate, such as a glass substrate, a sapphire substrate, or the like. In addition, the optically transparent substrate is very thin, e.g., less than 1 millimeter in thickness. In some embodiments, the optically transparent substrate has a thickness of less than 500 micrometers. In some embodiments, the optically transparent substrate has a thickness of less than 250 micrometers.

[0019] In another aspect, the SE-based measurement system is configured with a relatively large illumination numerical aperture (NA) and a relatively high demagnification ratio from the illumination source to the measurement spot on the optically transparent substrate. This configuration results in a relatively small measurement spot size, a small depth of focus, and minimizes the amount of light reflected from the backside of the optically transparent substrate into the optical path of the collection optics. In some embodiments, the illumination optics subsystem has an NA of at least 0.15, and the illumination optics subsystem has an image demagnification ratio of at least 10 from the illumination field stop to the measurement spot.

[0020] In a further aspect, to further minimize propagation of light reflected from the backside of the optically transparent substrate to the detector, the size of the aperture in the collection mask is relatively small, e.g., less than 1 millimeter. In some embodiments, the collection optical subsystem includes a collection mask positioned at or near the image plane of the collection optical subsystem. The collection mask includes an aperture having a dimension less than 1 millimeter in a direction corresponding to the direction in which the angle of incidence changes. In this way, reflection of the SE measurement beam from the backside of the optically transparent substrate is effectively blocked by the collection mask.

[0021] In a further aspect, a substrate handling chuck used to secure an optically transparent substrate is coated with a black pigmented material to minimize scattering from the chuck surface.

[0022] In some embodiments, the SE-based metrology system is configured to estimate the reflectivity of a metalens-based structure fabricated on an optically transparent substrate. In one example, the reflectivity of the metalens-based structure fabricated on the optically transparent substrate is estimated based on the average measured intensity measured by the detector of the SE-based metrology system.

[0023] In some embodiments, the metalens structure includes multiple lattice orientation vectors. In a further aspect, the metalens structure is measured sequentially at each lattice vector orientation at the same measurement site. In this manner, measuring multiple lattice clusters, each located at a different measurement site, minimizes measurement throughput. In some embodiments, SE measurements are performed sequentially at a variety of different azimuthal angles, each corresponding to a different lattice vector orientation associated with the metalens structure being measured. Estimates of parameters of interest characterizing the metalens structure along each lattice vector orientation are determined based on detection signals associated with measurements at the azimuthal angles corresponding to each lattice vector orientation.

[0024] The foregoing is a summary, and as such, necessarily contains simplifications, generalizations, and omissions of detail; thus, those skilled in the art will appreciate that the summary is merely illustrative and is not intended to be in any way limiting. Other aspects, unique features, and advantages of the devices and / or processes described herein will become apparent in the non-limiting detailed description set forth herein. [Brief explanation of the drawings]

[0025] [Figure 1] FIG. 1 illustrates an exemplary metrology system 100 for performing spectroscopic measurements of one or more structures disposed on an optically transparent substrate as described herein. [Figure 2] 1 illustrates a portion of the collection optical elements and collection optical path of metrology system 100 in more detail. [Figure 3] 1 is an image of a metalens-based structure including amorphous silicon pillars fabricated on a glass substrate. [Figure 4] FIG. 4 is a magnified image of the metalens-based structure shown in FIG. 3. [Figure 5] FIG. 4 is a further enlarged image of the metalens structure shown in FIG. 3. [Figure 6] FIG. 10 shows a top view of a geometric model of a metalens structure including amorphous silicon pillars fabricated in a three-dimensional pattern on a glass substrate. [Figure 7] FIG. 7 shows a side view of a geometric model of the metalens structure shown in FIG. [Figure 8] FIG. 1 illustrates a composite illumination source embodiment 180. [Figure 9A] FIG. 2 illustrates another embodiment 200 of a compound illumination source. [Figure 9B] FIG. 2 illustrates another embodiment 220 of a compound illumination source. [Figure 9C] FIG. 2 illustrates another embodiment 240 of a composite illumination source. [Figure 10] 1 is a graph showing the relative detectivity of various detector technologies operating at specified temperatures. [Figure 11] FIG. 2 is a diagram of a multi-zone infrared detector 270. [Figure 12] FIG. 1 shows typical photosensitivity curves for four available indium gallium arsenide (InGaAs) sensors. [Figure 13] FIG. 3 illustrates a method 300 for performing spectroscopic measurements of one or more structures disposed on an optically transparent substrate as described herein. DETAILED DESCRIPTION OF THE INVENTION

[0026] Reference will now be made in detail to certain background and exemplary embodiments of the present invention, examples of which are illustrated in the accompanying drawings.

[0027] Presented herein are methods and systems for performing spectroscopic ellipsometry (SE) measurements of surface structures of optical elements fabricated on transparent substrates. The SE measurement system is configured to detect light from the measured structures without contamination from light reflected from the back surface of the transparent substrate. Surface structures of metalens-based optical elements include film structures and grating structures fabricated on transparent substrates for a variety of applications, including, but not limited to, optical waveguides, augmented and virtual reality display devices, imaging subsystems, and the like.

[0028] The SE-based measurement system estimates the value of one or more parameters of interest that characterize the surface structure of the metalens-based optical element, including, but not limited to, pillar structures, support structures, etc. The parameters of interest include, but are not limited to, parameters that characterize the geometric or material properties of the metalens surface structure, such as critical dimensions, height, sidewall angle, film thickness, height, reflectivity, etc.

[0029] In one aspect, the surface structure of the metalens-based optical element is fabricated on an optically transparent substrate, such as a glass substrate, a sapphire substrate, or the like. In addition, the optically transparent substrate is very thin, e.g., less than 1 millimeter in thickness. In some embodiments, the optically transparent substrate has a thickness of less than 500 micrometers. In some embodiments, the optically transparent substrate has a thickness of less than 250 micrometers.

[0030] In another aspect, the SE-based measurement system is configured with a relatively large illumination numerical aperture (NA) and a relatively high demagnification ratio from the illumination source to the measurement spot on the optically transparent substrate. This configuration results in a relatively small measurement spot size, a small depth of focus, and minimizes the amount of light reflected from the backside of the optically transparent substrate into the optical path of the collection optics. In some embodiments, the illumination optics subsystem has an NA of at least 0.15, and the illumination optics subsystem has an image demagnification ratio of at least 10 from the illumination field stop to the measurement spot.

[0031] In a further aspect, to further minimize propagation of light reflected from the backside of the optically transparent substrate to the detector, the size of the aperture in the collection mask is relatively small, e.g., less than 1 millimeter. In some embodiments, the collection optical subsystem includes a collection mask positioned at or near the image plane of the collection optical subsystem. The collection mask includes an aperture having a dimension less than 1 millimeter in a direction corresponding to the direction in which the angle of incidence changes. In this way, reflection of the SE measurement beam from the backside of the optically transparent substrate is effectively blocked by the collection mask.

[0032] FIG. 1 illustrates an exemplary metrology system 100 for performing broadband spectroscopic measurements of structures fabricated on an optically transparent substrate. In some examples, the one or more structures include surface structures of a metalens optical element. In some of these examples, the surface structures are fabricated from an optically opaque material, such as an oxide material. As shown in FIG. 1, metrology system 100 is configured as a grazing incidence broadband spectroscopic ellipsometer. However, in general, metrology system 100 may also include additional spectroscopic ellipsometers, spectroscopic reflectometers, angle-resolved reflectometers, scatterometers, or any combination thereof.

[0033] The metrology system 100 includes an illumination source 110 that generates an illumination light beam 101 that is incident on an optically transparent substrate 120. The illumination source 110 includes one or more illumination sources that emit illumination light including wavelengths in the range of 120 nanometers to 2,500 nanometers. In some embodiments, the illumination source 110 is a composite illumination source that emits illumination light in the ultraviolet, visible, and infrared spectrums, including ultraviolet wavelengths up to 120 nanometers and infrared wavelengths greater than 2 micrometers, e.g., illumination wavelengths in the range of 120 nanometers to 2,500 nanometers. In other embodiments, the illumination source 110 is a composite illumination source that emits illumination light including wavelengths in the range of 120 nanometers to 7,000 nanometers.

[0034] In a preferred embodiment, the combined illumination source 110 includes a supercontinuum laser source and a laser-sustained plasma source. The supercontinuum laser source provides illumination at wavelengths greater than 2 micrometers, and in some embodiments, up to 5 micrometers or greater. The laser-sustained plasma (LSP) source (also known as a laser-driven plasma source) generates photons across the entire wavelength range from 120 nanometers to 2,500 nanometers or greater. The pump laser of an LSP source can be continuous wave or pulsed. In some embodiments, the combined illumination source 110 includes a supercontinuum laser source and an arc lamp, such as a xenon arc lamp. However, laser-driven plasma sources are preferred because they generate significantly more photons across the entire wavelength range from 120 nanometers to 2,500 nanometers than xenon lamps.

[0035] Generally, the composite illumination source 110 includes a combination of multiple broadband or discrete wavelength light sources. The light generated by the composite illumination source 110 includes a continuous spectrum or a portion of a continuous spectrum from ultraviolet to infrared (e.g., vacuum ultraviolet to long infrared). Generally, the composite illumination source 110 may include a supercontinuum laser source, an infrared helium-neon laser source, a silicon carbide glow bar source, a tungsten halogen light source, one or more infrared LEDs, one or more infrared lasers, or any other suitable infrared light source that generates wavelengths greater than 2 micrometers, as well as an arc lamp (e.g., a xenon arc lamp), a deuterium lamp, an LSP light source, or any other suitable light source that generates wavelengths less than 2 micrometers, including visible and ultraviolet wavelengths.

[0036] In general, the composite illumination source 110 includes multiple illumination sources optically coupled in any suitable manner. In some embodiments, light emitted by a supercontinuum laser source is coupled directly through a plasma generated by an ultraviolet / visible light source.

[0037] FIG. 8 illustrates an embodiment 180 of the composite illumination source 110. As shown in FIG. 8, an LSP pump laser source 181 generates pump light 182, which is focused by focusing optics 183 and maintains a plasma 184 confined by a bulb 185. The plasma 184 generates broadband light across a wavelength range from ultraviolet to short-infrared. The bulb 185 includes an exit port 186. LSP output light 187 is a portion of the light from the plasma 184 that passes through the exit port 186 and is directed toward the illumination optics subsystem, as described with reference to FIG. 1. In addition, a supercontinuum laser source 191 generates infrared light 192 that is focused by focusing optics 193 to a focal point 194 at or near the plasma 184. Supercontinuum output light 197 is a portion of the light from the focal point 194 that passes through the exit port 186 and is directed toward the illumination optics subsystem, as described with reference to FIG. 1. In one example, the LSP output light 187 and the super-continuum output light 197 are co-located. In this manner, the infrared light 197 from the super-continuum light source 191 is effectively combined with the ultraviolet / visible light 187 from the LSP laser light source 181. In one example, the LSP output light 187 and the super-continuum output light 197 have the same or similar numerical apertures. In another example, the LSP output light 187 and the super-continuum output light 197 have different numerical apertures. In some examples, the bulb 185 is made from calcium fluoride or magnesium fluoride to transmit wavelengths greater than 2.5 micrometers produced by the super-continuum laser light source 191. In other examples, the bulb 185 includes one or more exit ports 186 made from calcium fluoride or magnesium fluoride to transmit wavelengths greater than 2.5 micrometers produced by the super-continuum laser light source 191. Conventional light bulbs made from fused silica transmit little light above 2.5 micrometers and are therefore unsuitable for combining the light generated by the supercontinuum laser source 191 in the manner described herein.In some embodiments, LSP pump laser source 181 is a continuous wave laser. In other embodiments, LSP pump laser source 181 is a pulsed laser.

[0038] As shown in FIG. 1 , measurement system 100 includes an illumination optics subsystem configured to direct illumination light 101 to one or more structures formed on optically transparent substrate 120. The illumination subsystem may include any type and arrangement of optical filters, polarization components, field stops, pupil stops, etc. known in the field of spectroscopic metrology. As shown in FIG. 1 , the illumination subsystem includes light source 110, beam shaping optics 111, 112, 115, 121, polarization components 113, and pupil stop 114. As shown in FIG. 1 , as the beam propagates from illumination source 110 to optically transparent substrate 120, illumination light beam 101 reflects off beam shaping optics 111, 112, 115, 121 and passes through illumination pupil stop 114, polarization components 113, and illumination field stop 117. Beam 101 illuminates a portion of optically transparent substrate 120 across measurement spot 116. As shown in FIG. 1, the beam shaping optics 111, 112, 115, 121 include one or more optical elements with refractive focusing power.

[0039] In the embodiment shown in FIG. 1 , pupil stop 114 controls the numerical aperture (NA) of the illumination subsystem and may include any suitable commercially available aperture stop. In one aspect, the illumination subsystem is configured to direct illumination light 101 to optically transparent substrate 120 with an illumination numerical aperture (NA) of at least 0.15. Additionally, beam shaping optics 115, 121 control the demagnification of the image from illumination field stop 117 to measurement spot 116, i.e., project an image of illumination field stop 117 reduced by a demagnification factor onto measurement spot 116. In some embodiments, beam shaping optics 115, 121 demagnify the image of illumination field stop 117 by a demagnification factor of at least 10, i.e., 10 times smaller. Note that because substrate 120 is not oriented perpendicular to the illumination beam path at the point where illumination beam 101 enters substrate 120, the dimensions of measurement spot 116 are not reduced by a demagnification factor across the entire optically transparent substrate 120 compared to the dimensions of illumination field stop 117. In some embodiments, illumination light 101 is incident on optically transparent substrate 120 at an angle of incidence α of at or near 65 degrees from normal incidence. In some embodiments, the dimension of measurement spot 116 along the largest range of directions is less than 50 micrometers.

[0040] Additionally, the illumination optics subsystem may include filters, masks, apodizers, etc. For example, the illumination subsystem may include one or more optical filters (not shown). The optical filters are used to control the light level, the spectral output, or both from the illumination subsystem. In some examples, one or more multi-zone filters are used as the optical filters.

[0041] In some examples, the beam size of the quantity of illumination light 101 projected onto the surface of the optically transparent substrate 120 is smaller than the size of the measurement target to be measured on the surface of the sample. Exemplary beam shaping techniques are described in detail in U.S. Patent Application Publication No. 2013 / 0114085 to Wang et al., the contents of which are incorporated herein by reference in their entirety.

[0042] In some examples, noise and polarization optimization is performed to improve the performance of the illumination source 110. In some examples, depolarization is achieved using multimode fiber, Hanle depolarizers, or integrating spheres. In some examples, the etendue of the illumination source is optimized using light guides, fibers, and other optical elements (lenses, curved mirrors, apodizers, etc.). In some examples, the coherence or coherence effects of the light source are mitigated by coherence-breaking techniques or otherwise accounted for by modeling and simulation.

[0043] The polarization component 113 generates the desired polarization state exiting the illumination subsystem. In some embodiments, the polarization component may include a polarizer, a compensator, or both, and may include any suitable commercially available polarization component. The polarizer, the compensator, or both may be fixed, rotatable to different fixed positions, or continuously rotatable. While the illumination subsystem shown in FIG. 1 includes one polarization component, the illumination subsystem may include two or more polarization components. In some embodiments, the polarizer of the polarization component 113 is a magnesium fluoride Rochon polarizer. In some embodiments, the compensator of the polarization component 113 includes a quartz waveplate, a magnesium fluoride waveplate, a calcium fluoride K prism, a calcium fluoride double Fresnel rhomb, or any combination thereof. In some embodiments, the compensator of the polarization component 113 includes one or more waveplates. In some of these embodiments, a first waveplate includes a desired retardation over a first wavelength range, a second waveplate includes a desired retardation over a second wavelength range, and so on.

[0044] Measurement system 100 also includes a collection optics subsystem configured to collect light generated by the interaction between the one or more structures and incident illumination beam 101 and focus the collected light at or near a dispersive element of a spectrometer, e.g., a spectrometer slit. The collection optics subsystem may include any type and arrangement of optical filters, polarizing components, collection field stops, collection pupil stops, etc. known in the art of spectroscopic metrology. Generally, the collection optics subsystem includes a field stop, a pupil mask, and one or more optical elements having focusing power.

[0045] 1, collected light beam 102 is collected from measurement spot 116 by the collection optics subsystem. As collected light beam 102 propagates from optically transparent substrate 120 to dispersive element 127 of the spectrometer, collected light 102 reflects off elements of beam shaping optics 129, 122 and reflective collection relay optics 126, and passes through collection pupil stop 125, compensator 123, analyzer 124, and collection field stop 103 of the collection optics subsystem.

[0046] As shown in FIG. 1 , the collection optics subsystem includes a polarization component that analyzes the polarization state of the collected light. In some embodiments, the polarization component includes an analyzer, a compensator, or both, and may include any suitable commercially available polarization component. The analyzer, the compensator, or both may be fixed, rotatable to different fixed positions, or continuously rotatable. The collection subsystem shown in FIG. 1 includes a compensator 123 and an analyzer 124. In general, the collection optics subsystem may include any number of polarization elements.

[0047] In some embodiments, compensator 123 includes a quartz waveplate, a magnesium fluoride waveplate, a calcium fluoride K-prism, a calcium fluoride double Fresnel rhomb, or any combination thereof. In some embodiments, compensator 123 includes one or more waveplates. In some of these embodiments, a first waveplate includes a desired retardation over a first wavelength range, a second waveplate includes a desired retardation over a second wavelength range, etc. In some embodiments, analyzer 124 is a magnesium fluoride Rochon analyzer.

[0048] As shown in FIG. 1 , the collection optics subsystem includes a collection pupil diaphragm 125 positioned near the pupil of the collection optics subsystem. The collection pupil diaphragm 125 includes one or more apertures, or openings, configured to transmit collected light from the optically transparent substrate 120 at one or more angles of incidence (AOI) and block light from other AOIs. In some embodiments, the collection pupil diaphragm 125 includes three apertures that transmit collected light from three different AOI ranges from the optically transparent substrate 120. Furthermore, the collection pupil diaphragm 125 is configured to transmit collected light with a NA greater than 0.15 in the AOI direction at each of one or more ranges of angles of incidence. In some embodiments, the collection mask 125 transmits collected light with a NA in the AOI direction at each of one or more ranges of angles of incidence between 0.15 and 0.19. In some embodiments, the measurement system 100 is configured with a collection NA that is the same or approximately the same as the illumination NA.

[0049] 1 , the collection field stop 103 controls the field of view of the collection optics subsystem. In some other embodiments, a spectrometer slit is used to define the field of view of the collection optics subsystem. In a further aspect, the beam shaping optics 122, 129 control the image magnification from the measurement spot 116 to the detector 128, i.e., project an image of the measurement spot 116 onto the detector 128 that is increased by a magnification factor. In some embodiments, the beam shaping optics 122, 129 magnify the image of the measurement spot 116 by a magnification factor of at least 10, i.e., 10 times larger. In this manner, the beam shaping optics 122, 129 provide a field magnification of at least 10.

[0050] 1, the size of the opening of the collection field stop 103 in the direction coinciding with the changing angle of incidence is less than 1 millimeter. The relatively small size of the opening of the collection field stop 103 minimizes the propagation of light reflected from the backside of the optically transparent substrate to the detector.

[0051] As shown in FIG. 2 , illumination beam 101 is incident on top surface 120A of optically transparent substrate 120. A portion of illumination beam 101 interacts with structure 120C on top surface 120A of optically transparent substrate 120 and is effectively reflected off top surface 120A to form portion 102A of collected light 102. However, another portion of illumination beam 101 is refracted off top surface 120A, propagates to bottom surface 120B of optically transparent substrate 120, reflects off bottom surface 120B, returns to top surface 120A, and is refracted off top surface 120A. The light reflected off bottom surface 120B forms portion 102B of collected light 102. Both portions 102A and 102B of collected light 102 pass through beam shaping elements 129, 122 and are incident on collection field stop 103. As shown in FIG. 2 , collection field stop 103 is located at or near the image plane of the collection optical subsystem. Collection field stop 103 includes an opening having a dimension A of less than 1 millimeter in a direction corresponding to the direction in which the angle of incidence changes. In this manner, a portion 102B of collected light reflected from lower surface 120B of optically transparent substrate 120 is effectively blocked by collection field stop 103, while a portion 102C of collected light 102A reflected from upper surface 120A of optically transparent substrate 120 is transmitted toward detector 128. In one example, portion 102B of collected light reflected from lower surface 120B of optically transparent substrate 120 is offset from the opening of collection field stop 103 by approximately 5 millimeters. Thus, unwanted light is effectively blocked by collection field stop 103, which has an opening of approximately 1 millimeter.

[0052] In some embodiments, the spectrometer subsystem includes a collection field stop 103, a dispersive element 127, and one or more optics (not shown) having reflective focusing power. The collection field stop 103 receives light from the collection optics subsystem, which includes a relay optics 126, and transmits a portion of the collected light to the dispersive element 127. The dispersive element 127 disperses the light into discrete wavelengths on the active surface of the detector 128.

[0053] Dispersive element 127 is typically located at or near the pupil plane of the collection optics subsystem. Relay optics 126 receives light from collection pupil stop 125 and images the light from collection pupil stop 125 onto the pupil plane at or near dispersive element 127. In this way, collection relay optics 126 functions as a pupil relay, imaging collection pupil stop 125 onto dispersive element 127.

[0054] In some embodiments, the optical elements of the collection relay optics 126 are reflective optical elements. The reflective collection relay optics enable collection of light at shorter wavelengths, for example, wavelengths less than 190 nanometers. In some embodiments, the reflective collection relay optics enable collection of light having wavelengths in the range of 140 nanometers to 2,500 nanometers. As shown in FIG. 1 , the reflective collection relay optics 126 includes reflective optical elements 126A and 126B. However, in general, the reflective collection relay optics 126 may include any number of reflective optical elements. In some embodiments of the measurement system 100, the collection relay optics 126 is not included.

[0055] Dispersive element 127 is typically a diffraction grating or a dispersive prism. In some embodiments, dispersive element 127 includes one or more segments, each receiving light from one or more corresponding apertures in collection pupil stop 125. In this manner, the light dispersed by dispersive element 127 includes light corresponding to one or more discrete ranges of angles of incidence at the optically transparent substrate. In some embodiments, dispersive element 127 is a planar diffraction grating. In some of these embodiments, the planar diffraction grating is segmented to divide the pupil into segments, each corresponding to a different set of discrete ranges of angles of incidence at the optically transparent substrate. Details regarding pupil division are described in U.S. Pat. No. 10,690,602 to KLA-Tencor Corporation, the contents of which are incorporated herein by reference in their entirety.

[0056] As shown in FIG. 1, detector 128 receives collected light from optically transparent substrate 120 at one or more angles of incidence, at multiple wavelengths (e.g., wavelengths between 140 nanometers and 2,500 nanometers), and in one or more polarization states. In the embodiment shown in FIG. 1, a collection optics subsystem directs light to detector 128, which generates output signal 154 in response to the collected light from one or more structures illuminated by the illumination subsystem. Dispersive element 127 linearly disperses the diffracted light according to wavelength along one dimension of detector 128 (i.e., the wavelength dispersion direction shown in FIG. 1). Dispersive element 127 causes spatial separation between the different wavelengths of light projected onto the surface of detector 128. In this way, collected light from measurement spot 116 having a particular wavelength is projected onto detector 128 at a different spatial location than collected light from another, different wavelength of measurement spot 116.

[0057] The metrology system 100 also includes a computing system 130 configured to receive the detection signal 154 and to determine an estimate of a parameter of interest 155 of the measured structure based on the detection signal.

[0058] In some embodiments, the methods and systems for spectroscopic metrology described herein are applied to metrology of metalens-based structures, and in particular to metrology of critical dimensions of metalens-based structures, which are periodic in nature and therefore amenable to measurement using scatterometry techniques.

[0059] FIG. 3 is an image 160 showing a metalens-based structure including amorphous silicon pillars fabricated on a glass substrate.

[0060] FIG. 4 is a magnified image 161 showing the metalens-based structure shown in FIG.

[0061] FIG. 5 is a further enlarged image 162 showing the metalens structure shown in FIG.

[0062] Figure 6 is a diagram 170 illustrating a top view of a geometric model of a metalens structure including amorphous silicon pillars, e.g., pillar 172, fabricated in a three-dimensional pattern on a glass substrate. As shown in Figure 6, a repeating array of unit cells including pillar structures of different sizes is disposed on glass substrate 171. As shown in Figure 6, each unit cell, e.g., unit cell 173, includes five pillar structures, each having a different diameter.

[0063] FIG. 7 is a diagram 175 illustrating a side view of the geometric model of the metalens structure shown in FIG. 6. As shown in FIG. 7, each pillar of unit cell 173 is equidistantly spaced and has a different diameter. In one example, D1 is 170 nanometers, D2 is 190 nanometers, D3 is 210 nanometers, D4 is 230 nanometers, D5 is 250 nanometers, height H is 250 nanometers, sidewall angle SWA is 90 degrees, and the length of the unit cell is 2 micrometers. Simulations of measuring the parameters characterizing geometric model 170 using metrology system 100 have shown measurements with CD accuracy down to approximately 0.02 nanometers, with very low parameter correlation.

[0064] In yet another aspect, substrate handling chucks used to secure optically transparent substrates are coated with a black-pigmented material to minimize scattering from the chuck surface. In the embodiment shown in Figure 1, the substrate handling chuck 165 is coated, e.g., anodized, powder coated, etc., with a black material to avoid scattering from the chuck surface that may reach the detector 128.

[0065] In yet another embodiment, a spectroscopic ellipsometer, such as the SE-based metrology system 100 shown in FIG. 1 , is configured to estimate the reflectance of a metalens-based structure fabricated on an optically transparent substrate. In one example, the reflectance of the metalens-based structure fabricated on the optically transparent substrate is estimated based on the average measured intensity measured by detector 128 of the SE-based metrology system 100.

[0066] 5, the illustrated metalens structure includes two different lattice direction vectors, G1 and G2. Unit cell 164 includes eight different sized pillar structures aligned with direction vector G1, and unit cell 163 includes four different sized pillar structures aligned with direction vector G2. In general, metalens structures fabricated on optically transparent substrates are arranged with spatial periodicity along multiple lattice vector orientations.

[0067] In a further aspect, the metalens structure is measured sequentially at each lattice vector orientation at the same measurement site. In this manner, measurement throughput is minimized when measuring multiple lattice clusters, each located at a different measurement site.

[0068] In some embodiments, SE measurements are performed sequentially at a variety of different azimuthal angles, each corresponding to a different lattice vector orientation associated with the metalens structure being measured. Estimates of the parameters of interest characterizing the metalens structure along each lattice vector orientation are determined based on the detection signals associated with measurements at the azimuthal angles corresponding to each lattice vector orientation. In these embodiments, the azimuthal angles associated with each lattice vector orientation are known a priori based on design data associated with the metalens structure. Similarly, geometric models characterizing each lattice vector orientation are constructed based on the design data. In this manner, the measurement models used to estimate values ​​of the parameters of interest characterizing the metalens structure being measured are specific to the geometric features associated with each different lattice vector orientation.

[0069] 1, metrology system 100 includes a spectral ellipsometer measurement system. However, in general, metrology system 100 may include any number of additional measurement systems, such as an angle-resolved reflectometer system, a spectroscopic reflectometer system, etc. By way of non-limiting example, metrology system 100 may be configured to include a spectroscopic ellipsometer (including Mueller matrix ellipsometry), a spectroscopic reflectometer, a spectroscopic scatterometer, an overlay scatterometer, an angle-resolved beam profile reflectometer, a polarization-resolved beam profile reflectometer, a beam profile reflectometer, a beam profile ellipsometer, any single or multiple wavelength ellipsometer, or any combination thereof.

[0070] In general, the collection optics subsystem may direct light to two or more detectors, in these embodiments, each configured to simultaneously detect the collected light over a different wavelength range.

[0071] In one example, one detector is a charge-coupled device (CCD) sensitive to ultraviolet and visible light (e.g., light having wavelengths between 190 nanometers and 860 nanometers), and the other detector is a photodetector array (PDA) sensitive to infrared light (e.g., light having wavelengths between 950 nanometers and 5,000 nanometers). However, other two-dimensional detector technologies are generally contemplated (e.g., position-sensitive detectors (PSDs), infrared detectors, photovoltaic detectors, etc.). Each detector converts incident light into an electrical signal indicative of the spectral intensity of the incident light. In some embodiments, the detection subsystem is positioned so that collected light propagates to all detectors of the metrology system 100 simultaneously. Collecting the UV and IR spectra simultaneously reduces measurement time and ensures that all spectra are measured under the same alignment conditions. This allows for easier correction of wavelength errors, since a common correction can be applied to all spectral data sets.

[0072] In general, dispersive element 127 may be configured to subdivide the incident light into different wavelength bands, propagate the different wavelength bands in different directions, and disperse light from one of the wavelength bands onto one or more detectors in any suitable manner. In one example, dispersive element 127 is configured as a transmissive grating. In other examples, dispersive element 127 includes a beam splitting element to subdivide the beam into different wavelength bands and a reflective or transmissive grating structure to disperse light from one of the wavelength bands onto a detector.

[0073] In some embodiments, dispersive element 127 is a reflective grating configured to diffract a subset of the wavelengths of the incident light in + / -1 diffraction order towards one detector and diffract another subset of the wavelengths of the incident light in zero diffraction order towards another detector.

[0074] Measuring targets using infrared, visible, and ultraviolet light within a single system enables accurate characterization of complex three-dimensional structures. Generally, longer wavelengths penetrate deeper into structures, resulting in suppression of higher-order diffractions when measuring structures with relatively large pitches. Shorter wavelengths provide accurate dimensional information about structures, such as smaller CDs and roughness features. In some instances, longer wavelengths enable measurement of dimensional properties of targets with relatively rough surfaces or interfaces due to their reduced sensitivity to roughness. Generally, measuring targets using infrared, visible, and ultraviolet light within a single system increases sensitivity to some measurement parameters and reduces correlation between parameters.

[0075] In some embodiments, the spectroscopic measurement system includes a combined illumination source including a first illumination source that generates ultraviolet, visible, and near-infrared wavelengths (e.g., wavelengths less than 2 micrometers) and a second illumination source that generates mid-infrared and long-infrared wavelengths (e.g., wavelengths greater than or equal to 2 micrometers). In some examples, the combined illumination source generates illumination light having a wavelength up to 140 nanometers. In some examples, the combined illumination source generates illumination light having a wavelength less than or equal to 4.2 micrometers. In some examples, the combined illumination source generates illumination light having a wavelength less than or equal to 5 micrometers. In some examples, the combined illumination source generates illumination light having a wavelength greater than 5 micrometers. Furthermore, the spectroscopic measurement system includes one or more measurement channels that span a range of illumination wavelengths used to perform measurements on the semiconductor structure. The one or more measurement channels can operate in parallel (i.e., simultaneously measuring samples across the entire wavelength range) or sequentially (i.e., measuring samples sequentially across the wavelength range).

[0076] FIG. 9A illustrates an embodiment 200 of the composite illumination source 110. As shown in FIG. 9A , a voltage supplied between a cathode 208 and an anode 209 generates a plasma 204 confined in a bulb 205. Additionally, an LSP pump laser source 201 generates pump light 202, which is focused by focusing optics 203 to maintain the plasma 204 confined by the bulb 205. The plasma 204 generates broadband light spanning a wavelength range from ultraviolet to short-infrared. The ultraviolet / visible / short-infrared light 207 generated by the plasma 204 is provided to the illumination optics subsystem, as described with reference to FIG. 1 . Additionally, a supercontinuum laser source 211 generates infrared light 212. The infrared light 212 is focused by a focusing lens 213 to form a focal point 214 at or near the plasma 204. The infrared light 217 from the focal point 214 is provided to the illumination optics subsystem, as described with reference to FIG. 1 . In one example, UV / visible / short infrared light 207 and infrared light 217 are co-located and effectively combined. In some examples, light bulb 205 is made from calcium fluoride or magnesium fluoride to transmit wavelengths greater than 2.5 micrometers generated by super-continuum laser source 211. In other examples, light bulb 205 includes one or more exit ports 206 fabricated from calcium fluoride or magnesium fluoride to transmit wavelengths greater than 2.5 micrometers generated by super-continuum laser source 211. Conventional light bulbs made from fused silica transmit little light greater than 2.5 micrometers and are therefore unsuitable for combining light generated by super-continuum laser illumination source 211 in the manner described herein.

[0077] FIG. 9B illustrates an embodiment 220 of the composite illumination source 110. As shown in FIG. 9B, a voltage supplied between a cathode 228 and an anode 229 generates a plasma 224 confined in a bulb 225. Additionally, an LSP pump laser source 221 generates pump light 222, which is focused by focusing optics 223 to maintain the plasma 224 confined by the bulb 225. The plasma 224 generates broadband light spanning a wavelength range from ultraviolet to short-infrared. The ultraviolet / visible / short-infrared light 227 generated by the plasma 224 exits the bulb 225 through an exit port 226 and is provided to the illumination optics subsystem, as described with reference to FIG. 1. Additionally, a supercontinuum laser source 231 generates infrared light 232. The infrared light 232 is focused by a focusing lens 233. The infrared light 237 from the supercontinuum laser source 231 is provided to the illumination optics subsystem, as described with reference to FIG. 1.

[0078] As shown in FIG. 9B, UV / visible / short-infrared light 227 and infrared light 237 are combined by beam combiner 234. Thus, beam combiner 234 combines light generated by ultraviolet light source 221 (e.g., LSP light source 221) and light generated by infrared light source 231 (e.g., supercontinuum laser light source 231). In one example, beam combiner 234 has a separation wavelength of, for example, 900 nanometers. The beam combiner minimizes loss of light generated by the LSP light source (less than 10% LSP loss) and minimizes depolarization effects across all illumination wavelengths (e.g., less than 0.1%).

[0079] FIG. 9C illustrates an embodiment 240 of the composite illumination source 110. As shown in FIG. 9C, a voltage supplied between a cathode 248 and an anode 249 generates a plasma 244 confined in a bulb 245. Additionally, an LSP pump laser source 241 generates pump light 242, which is focused by focusing optics 243 to maintain the plasma 244 confined by the bulb 245. The plasma 244 generates broadband light spanning a wavelength range from ultraviolet to short-infrared. The ultraviolet / visible / short-infrared light 247 generated by the plasma 244 exits the bulb 245 through an exit port 246 and is provided to the illumination optics subsystem, as described with reference to FIG. 1. Additionally, a supercontinuum laser source 251 generates infrared light 252. The infrared light 252 is focused by a focusing lens 253. The infrared light 257 from the supercontinuum laser source 251 is provided to the illumination optics subsystem, as described with reference to FIG. 1.

[0080] As shown in FIG. 9C , combined illumination source 110 selectively provides ultraviolet and infrared illumination light to optically transparent substrate 120. In these examples, measurements are time-multiplexed. Mirror 254 is a movable mirror. In one example, movable mirror 254 is attached to a galvanometer that is used to selectively direct ultraviolet / visible light 247 and infrared light 257 to optically transparent substrate 120 based on whether movable mirror 254 is positioned in or out of the optical path of ultraviolet / visible light 247. In another example, a movable total internal reflection prism is used to selectively direct ultraviolet / visible light 247 and infrared light 257 to optically transparent substrate 120. In this manner, spectral measurements including the ultraviolet / visible spectrum are performed at a different time than spectral measurements including the infrared spectrum.

[0081] Figure 10 is a graph 260 illustrating the relative detectivity of various detector technologies operating at specified temperatures. As shown in Figure 10, both photovoltaic and photoconductive detector technologies are suitable for detecting radiation at infrared wavelengths beyond 1 micrometer up to 5 micrometers. In some examples, the metrology system 100 includes detectors such as sulfide (PbS), lead selenide (PbSe), indium antimonide (InSb), indium arsenide (InAs), mercury cadmium telluride (HgCdTe), indium gallium arsenide (InGaAs), x-InGaAs, pyroelectric, and bolometer detectors.

[0082] Pyroelectric and bolometric detectors are not quantum detectors, and therefore can accept high light levels without saturating, which can result in reduced noise sensitivity.

[0083] In some embodiments, the detector subsystem is shot noise limited rather than dark noise limited. In these instances, it is preferable to perform multiple measurements at high light levels to reduce the noise of the measurement system.

[0084] In some embodiments, a time-dependent measurement (eg, a pulsed light source, a chopper, etc.) is performed in conjunction with a lock-in amplifier or other phase-locked loop to increase the measurement signal-to-noise ratio.

[0085] In some embodiments, one or more detectors are cooled to -20°C, 210K°, 77K°, or other low temperatures to reduce measurement noise. In general, any suitable cooling element may be used to maintain the temperature of the detector at a constant temperature during operation. As non-limiting examples, any of a multi-stage Peltier cooler, a spinning disk cooler, a Stirling cycle cooler, a N2 cooler, a He cooler, etc. may be considered within the scope of this patent document.

[0086] In some embodiments, a wide range of wavelengths is detected by a detector that includes multiple photosensitive regions with different sensitivity characteristics. The collected light is linearly dispersed across the surface of the detector according to wavelength. Each different photosensitive region is positioned on the detector to sense a different range of incident wavelengths. In this way, a wide range of wavelengths is detected with a high signal-to-noise ratio by a single detector. These features, individually or in combination, enable high-throughput measurement of high-aspect-ratio structures (e.g., structures with depths of 1 micrometer or more) with high throughput, high precision, and high accuracy.

[0087] In some embodiments, the detector subsystem includes a multi-zone infrared detector that combines different sensitivity bands at different locations on a single detector package, where the detector is configured to deliver a continuous data spectrum with different sensitivities depending on the incident position.

[0088] Figure 12 shows typical optical sensitivity curves for available indium gallium arsenide (InGaAs) sensors. As shown in Figure 12, none of the available InGaAs sensors can provide sufficient optical sensitivity across the entire wavelength band from 1 micrometer to 2.5 micrometers. Therefore, the available sensors can only sense over a narrow wavelength band individually.

[0089] In some embodiments, multiple sensor chips, each sensitive to a different wavelength band, are combined into a single detector package, and this multi-zone detector is then implemented in the metrology systems described herein.

[0090] FIG. 11 shows four sensor chips 270A-270D with four different wavelength bands for fabricating a multi-zone infrared detector 180. Each of the four sensor chips includes a different material composition exhibiting different optical sensitivity characteristics. As shown in FIG. 11, sensor chip 270A exhibits high sensitivity across wavelength band A, sensor chip 270B exhibits high sensitivity across wavelength band B, sensor chip 270C exhibits high sensitivity across wavelength band C, and sensor chip 270D exhibits high sensitivity across wavelength band D. A measurement system incorporating detector 270 is configured to distribute wavelengths within wavelength band A onto sensor chip 270A, wavelengths within wavelength band B onto sensor chip 270B, wavelengths within wavelength band C onto sensor chip 270C, and wavelengths within wavelength band D onto sensor chip 270D. In this manner, high optical sensitivity (i.e., high SNR) across the collective wavelength bands including wavelength bands A-D is achieved from a single detector. As a result, measurement noise is reduced over the entire measurement range by restricting the use of a particular sensor to a narrow band with high measurement sensitivity and low measurement noise.

[0091] In some examples, multi-zone detectors include InGaAs sensors sensitive to different spectral regions assembled into a single sensor package to produce a single, unbroken spectrum covering wavelengths from 750 nanometers to 3,000 nanometers or more.

[0092] In general, any number of individual sensors can be assembled along the direction of wavelength dispersion of a multi-zone detector to provide a continuous spectrum from the detector. However, typically, two to four individual sensors are used in a multi-zone detector such as detector 270.

[0093] In one embodiment, three separate sensors are used, with a first segment spanning the range of 800 nanometers to 1,600 nanometers, a second segment spanning the range of 1,600 nanometers to 2,200 nanometers, and a third segment spanning the range of 2,200 nanometers to 2,600 nanometers.

[0094] Although the use of InGaAs-based infrared detectors is specifically described herein, in general, any suitable material that exhibits a narrow sensitivity range and a sharp sensitivity cutoff may be incorporated into the multi-zone detectors described herein.

[0095] As shown in Figure 1, the illustrated measurement channel includes a polarizer on the illumination side and an analyzer on the collection side. However, it is generally contemplated that the measurement channel may include any combination of illumination polarizers, collection analyzers, illumination compensators, and collection compensators to perform measurements of polarized reflectance of a sample, unpolarized reflectance of a sample, or both.

[0096] In some embodiments, one or more measurement channels of the metrology system are configured to measure the optically transparent substrate at different azimuthal angles in addition to different wavelength ranges and different angles of incidence. In some embodiments, a metrology system including an infrared spectrometer as described herein is configured to perform measurements of the optically transparent substrate at 0-degree and 90-degree azimuthal angles relative to the measurement target. In some embodiments, the metrology system is configured to measure the reflectivity of the optically transparent substrate simultaneously over one or more wavelength ranges, one or more AOI ranges, and one or more azimuthal angles. In some embodiments, the metrology system utilizes one or more combined LSP and supercontinuum light sources in one or more spectroscopic ellipsometers, spectroscopic reflectometers, discrete wavelength ellipsometers, rotating polarizer ellipsometers, rotating compensator ellipsometers, rotating polarizer rotating compensator ellipsometers, Mueller matrix ellipsometers, or any combination thereof.

[0097] In yet another aspect, the dimensions of the illumination field stop projected onto the optically transparent substrate plane are adjusted to optimize the accuracy and speed of the resulting measurement based on the properties of the target being measured.

[0098] In yet another aspect, the dimensions of the illumination field stop are adjusted to achieve the desired spectral resolution for each measurement application.

[0099] In some examples, for example, when the sample is a very thick film or grating structure, the illumination field stop projected onto the optically transparent substrate plane in a direction perpendicular to the plane of incidence is adjusted to reduce the field size to achieve improved spectral resolution. In some examples, for example, when the sample is a thin film, the illumination field stop projected onto the optically transparent substrate plane in a direction perpendicular to the plane of incidence is adjusted to increase the field size to achieve reduced measurement time without losing spectral resolution.

[0100] 1, computing system 130 is configured to receive signal 154 indicative of the spectral response detected by the detector subsystem. Computing system 130 is further configured to determine a control signal 119 that is communicated to programmable illumination field stop 117. Programmable illumination field stop 117 receives control signal 119 and adjusts the size of the illumination aperture to achieve a desired illumination field size.

[0101] In some examples, the illumination field stop is adjusted to optimize measurement accuracy and speed, as described previously herein. In another example, the illumination field stop is adjusted to prevent image clipping by the spectrometer slit and corresponding degradation of the measurement results. Thus, the illumination field size is adjusted so that the image of the measurement target does not underfill the spectrometer slit. In one example, the illumination field stop is adjusted so that the projection of the polarizer slit of the illumination optics does not fill the spectrometer slit of the measurement system. In another example, the illumination field stop is adjusted so that the projection of the polarizer slit of the illumination optics overfills the spectrometer slit of the measurement system.

[0102] 13 illustrates a method 300 for performing spectroscopic measurements in at least one novel aspect. Method 300 is suitable for implementation by a metrology system, such as metrology system 100 shown in FIG. 1 of the present invention. It is recognized that, in one aspect, the data processing blocks of method 300 may be performed via pre-programmed algorithms executed by one or more processors of computing system 130, or any other general-purpose computing system. It is recognized that the specific structural aspects of metrology system 100 herein should be construed as illustrative only, and not limiting.

[0103] In block 301, an amount of illumination light is generated, the illumination light including wavelengths in the range of 150 to 2,500 nanometers.

[0104] In block 302, an amount of illumination light from an illumination source is directed to a measurement spot including one or more structures disposed on an optically transparent substrate with a numerical aperture (NA) of at least 0.15. The image demagnification from the illumination field stop to the measurement spot is at least 10, and the amount of illumination light is directed to the one or more structures at one or more angles of incidence, at one or more azimuthal angles, or a combination thereof.

[0105] In block 303, a quantity of collected light is collected from the measurement spot. The collecting involves a collection mask positioned at or near the image plane of the collection optics subsystem. The collection mask includes an opening having a dimension of less than 1 millimeter in a direction coinciding with the direction in which the angle of incidence changes.

[0106] In block 304, an amount of the collected light is detected at a detector.

[0107] At block 305, an estimate of a first parameter of interest that characterizes one or more structures being measured is generated based on the detected amount of collected light.

[0108] In a further embodiment, the system 100 includes one or more computing systems 130 that are used to perform measurements of actual device structures based on the spectroscopic measurement data collected according to the methods described herein. The one or more computing systems 130 may be communicatively coupled to the spectrometer. In one aspect, the one or more computing systems 130 are configured to receive measurement data related to measurements of the structure of the sample being measured.

[0109] It should be appreciated that one or more steps described throughout this disclosure may be performed by a single computer system 130, or alternatively, by multiple computer systems 130. Furthermore, various different subsystems of system 100 may include computer systems suitable for performing at least some of the steps described herein. Accordingly, the foregoing description should not be construed as a limitation on the present invention, but rather as merely illustrative.

[0110] Additionally, computing system 130 may be communicatively coupled to the spectrometer in any manner known in the art. For example, one or more computing systems 130 may be coupled to a computing system associated with the spectrometer. In another example, the spectrometer may be directly controlled by a single computer system coupled to computer system 130.

[0111] The computer system 130 of the measurement system 100 may be configured to receive and / or acquire data or information from subsystems of the system (e.g., spectrometer, etc.) by way of a transmission medium, which may include wired and / or wireless portions. In this manner, the transmission medium may serve as a data link between the computer system 130 and other subsystems of the system 100.

[0112] The computer system 130 of the measurement system 100 may be configured to receive and / or acquire data or information (e.g., measurement results, modeling inputs, modeling results, reference measurement results, etc.) from other systems via a transmission medium, which may include wired and / or wireless portions. In this manner, the transmission medium may serve as a data link between the computer system 130 and other systems (e.g., the on-board memory of the measurement system 100, an external memory, or another external system). For example, the computing system 130 may be configured to receive measurement data from a storage medium (i.e., the memory 132 or an external memory) via the data link. For example, spectral results obtained using the spectrometers described herein may be stored in a permanent or semi-permanent memory device (e.g., the memory 132 or an external memory). In this regard, spectral results may be imported from the on-board memory or an external memory system. Additionally, the computer system 130 may transmit data to other systems via the transmission medium. For example, the measurement model or estimated parameter values ​​171 determined by the computer system 130 may be communicated and stored in an external memory. In this regard, the measurement results may be exported to another system.

[0113] Computing system 130 may include, but is not limited to, a personal computer system, a mainframe computer system, a workstation, an image computer, a parallel processor, or any other device known in the art. In general, the term "computing system" may be broadly defined to encompass any device having one or more processors and that executes instructions from a storage medium.

[0114] Program instructions 134 implementing methods such as those described herein may be transmitted over a transmission medium such as a wire, cable, or wireless transmission link. For example, as shown in Figure 1, program instructions 134 stored in memory 132 are transmitted to processor 131 over bus 133. Program instructions 134 are stored on a computer-readable medium (e.g., memory 132). Exemplary computer-readable media include read-only memory, random-access memory, a magnetic or optical disk, or a magnetic tape.

[0115] In some examples, the metrology model is implemented as an element of a SpectraShape® optical critical dimension metrology system available from KLA-Tencor Corporation of Milpitas, Calif., USA In this way, the model is created and available for use as soon as a spectrum is collected by the system.

[0116] In some other examples, the measurement model is implemented offline, for example, by a computing system implementing AcuShape® software available from KLA-Tencor Corporation of Milpitas, California, USA. The resulting trained model may be incorporated as an element of an AcuShape® library that can be accessed by the metrology system that performs the measurements.

[0117] In another aspect, the methods and systems for spectroscopic metrology of semiconductor devices described herein are applicable to measurements of high aspect ratio (HAR) structures, large lateral dimension structures, or both. The above-described embodiments enable optical critical dimension (CD), film, and composition metrology for semiconductor devices, including three-dimensional NAND structures such as vertical NAND (V-NAND) structures and dynamic random access memory (DRAM) structures, manufactured by various semiconductor manufacturers, such as Samsung Inc. (Korea), SK Hynix Inc. (Korea), Toshiba Corporation (Japan), and Micron Technology, Inc. (USA). These complex devices suffer from low light penetration into the structure under measurement. Figure 3 shows an exemplary high aspect ratio structure 160 that suffers from low light penetration into the structure under measurement. Spectroscopic ellipsometers with broadband capabilities, wide AOI, azimuthal angle, or both, and simultaneous spectral band detection capabilities as described herein are suitable for measuring these high aspect ratio structures. HAR structures often include a hard mask layer to facilitate the etching process for HAR. As described herein, the term "HAR structure" refers to a structure characterized by an aspect ratio greater than 2:1 or 10:1, and in some cases even greater than 100:1.

[0118] In yet another aspect, the measurements described herein can be used to provide active feedback to a process tool (e.g., a lithography tool, an etch tool, a deposition tool, etc.). For example, values ​​of measurement parameters determined based on the measurement methods described herein can be communicated to a lithography tool to adjust the lithography system to achieve a desired output. Similarly, etching parameters (e.g., etch time, diffusivity, etc.) or deposition parameters (e.g., time, concentration, etc.) may be included in a metrology model to provide active feedback to an etch tool or a deposition tool, respectively. In some examples, corrections to process parameters determined based on measured device parameter values ​​and a trained metrology model may be communicated to a lithography tool, an etch tool, or a deposition tool.

[0119] As described herein, the term "critical dimension" includes any critical dimension of a structure (e.g., bottom critical dimension, middle critical dimension, top critical dimension, sidewall angle, grating height, etc.), the critical dimension between any two or more structures (e.g., the distance between two structures), and the misregistration between two or more structures (e.g., the overlay misregistration between overlaying grating structures, etc.). The structures may include three-dimensional structures, patterned structures, overlay structures, etc.

[0120] As described herein, the terms "critical dimension application" or "critical dimension measurement application" include any critical dimension measurement.

[0121] As described herein, the term "metrology system" includes any system used at least in part to characterize a specimen in any manner, including measurement applications such as critical dimension metrology, overlay metrology, focus / dose metrology, and composition metrology. However, such terminology does not limit the scope of the term "metrology system" as described herein. Additionally, metrology system 100 may be configured for measurement of patterned and / or unpatterned optically transparent substrates. The metrology system may be configured as an LED inspection tool, an edge inspection tool, a backside inspection tool, a macro inspection tool, or a multi-mode inspection tool (with data from one or more platforms simultaneously), and any other metrology or inspection tool that would benefit from calibration of system parameters based on critical dimension data.

[0122] Described herein are various embodiments of semiconductor metrology systems that can be used to measure specimens in any semiconductor processing tool (e.g., an inspection system or a lithography system). The term "specimen" is used herein to refer to an optically transparent substrate, a reticle, or any other sample that can be processed (e.g., printed or inspected for defects) by means known in the art.

[0123] As used herein, the term "optically transparent substrate" generally refers to a substrate formed from a semiconductor or non-semiconductor material. Examples include, but are not limited to, monocrystalline silicon, gallium arsenide, and indium phosphide. Such substrates may be commonly found and / or processed in semiconductor manufacturing facilities. In some cases, an optically transparent substrate may include only the substrate (i.e., a bare optically transparent substrate). Alternatively, an optically transparent substrate may include one or more layers of different materials formed on the substrate. The one or more layers formed on the optically transparent substrate may be "patterned" or "unpatterned." For example, an optically transparent substrate may include multiple dies having repeatable pattern features.

[0124] A "reticle" may be a reticle at any stage in the reticle manufacturing process or a finished reticle that may or may not be released for use in a semiconductor manufacturing facility. A reticle, or "mask," is generally defined as a substantially transparent substrate having substantially opaque regions formed thereon, arranged in a pattern. The substrate may comprise, for example, a glass material such as amorphous SiO2. The reticle may be placed over a resist-coated wafer during the exposure step of the lithography process so that the pattern on the reticle can be transferred to the resist.

[0125] The layer or layers formed on the optically transparent substrate may be patterned or unpatterned. For example, the optically transparent substrate may include multiple dies, each having a repeatable pattern feature. Forming and processing such material layers may ultimately result in a completed device. Many different types of devices may be formed on the optically transparent substrate, and the term optically transparent substrate as used herein is intended to encompass an optically transparent substrate on which any type of device known in the art may be fabricated.

[0126] In one or more exemplary embodiments, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Computer-readable media includes both computer storage media and communication media, including any medium that facilitates transfer of a computer program from one place to another. Storage media may be any available medium that can be accessed by a general-purpose or special-purpose computer. By way of example, and not limitation, such computer-readable media may include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code means in the form of instructions or data structures and that can be accessed by a general-purpose or special-purpose computer or a general-purpose or special-purpose processor. Also, any connection may be properly termed a computer-readable medium. For example, if software is transmitted from a website, server, or other remote source using coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of media. As used herein, disk and disc include compact discs (CDs), laser discs, optical discs, digital versatile discs (DVDs), floppy disks, and Blu-ray discs, where disks typically reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.

[0127] Although certain specific embodiments are described above for illustrative purposes, the teachings of this patent document have general applicability and are not limited to the particular embodiments described above. Accordingly, various modifications, adaptations, and combinations of the various features of the described embodiments may be made without departing from the scope of the invention as set forth in the claims.

Claims

1. 1. A spectroscopic measurement system, comprising: an illumination source configured to generate an amount of illumination light comprising wavelengths in the range of 150 to 2,500 nanometers; an illumination optics subsystem configured to direct the amount of illumination light from the illumination source to one or more structures disposed on an optically transparent substrate at a measurement spot at one or more angles of incidence, at one or more azimuthal angles, or a combination thereof, wherein the illumination optics subsystem has a numerical aperture (NA) of at least 0.15 and an image demagnification ratio from an illumination field stop to the measurement spot of at least 10; a collection optics subsystem configured to collect a quantity of collected light from the measurement spot on the surface of the specimen, the collection optics subsystem including a collection mask positioned at or near an image plane of the collection optics, the collection mask including an aperture having a dimension of less than 1 millimeter in a direction coincident with a direction in which the angle of incidence changes; at least one detector having a planar, two-dimensional surface sensitive to incident light, the at least one detector configured to detect the amount of collected light and to generate an output signal indicative of the detected light; a computing system configured to generate an estimate of a first parameter of interest characterizing the one or more structures being measured based on an analysis of the output signal.

2. 2. The spectroscopic measurement system of claim 1, wherein the collection optics subsystem is configured to image the measurement spot onto the at least one detector with a field magnification of at least 10.

3. The spectroscopic measurement system of claim 1 , wherein the collection optical subsystem has a collection numerical aperture (NA) of at least 0.

15.

4. The spectroscopic measurement system of claim 1 , wherein a dimension of the measurement spot along a direction of maximum extent is less than 50 micrometers.

5. 2. The spectroscopic measurement system of claim 1, wherein the collection mask includes a plurality of apertures, each aperture configured to transmit an amount of the collected light associated with a different range of angles of incidence from the sample being measured.

6. The spectroscopic measurement system of claim 1 , wherein the illumination source is a hybrid illumination source including a laser-sustained plasma (LSP) illumination source and a supercontinuum laser illumination source.

7. the at least one detector includes two or more detectors; The spectroscopic measurement system of claim 1 , wherein each of the two or more detectors detects a portion of the quantity of collected light over a different spectral range.

8. The spectroscopic measurement system of claim 7 , wherein each of the two or more detectors simultaneously detects a respective portion of the quantity of collected light over a separate spectral range.

9. The spectroscopic measurement system of claim 1 , wherein the one or more structures under measurement include a grating structure.

10. The spectroscopic measurement system of claim 9 , wherein the grating structure includes a plurality of grating vector orientations at the measurement spot.

11. the computing system is further configured to generate an estimate of a second parameter of interest of the sample being measured based on analysis of the output signal; the amount of collected light includes light collected at a first azimuthal angle and a second azimuthal angle, and the output signal is indicative of the detected light at the first azimuthal angle and the second azimuthal angle; the estimate of the first parameter of interest is based on the output signal indicative of the detected light at the first azimuthal angle; the first parameter of interest characterizes the lattice structure along a first lattice vector orientation; the estimate of the second parameter of interest is based on the output signal indicative of the detected light at the second azimuthal angle; The spectroscopic measurement system of claim 10 , wherein the second parameter of interest characterizes the grating structure along a second grating vector orientation that is different from the first grating vector orientation.

12. 2. The spectroscopic measurement system of claim 1, wherein the amount of collected light collected from the measurement spot on the surface of the sample does not fill the aperture of the collection mask.

13. 10. The spectroscopic metrology system of claim 1 , wherein the one or more structures under measurement comprise a metalens optical element.

14. The spectroscopic metrology system of claim 9 , wherein the first parameter of interest is a critical dimension characterizing the grating structure disposed on the optically transparent substrate.

15. The spectroscopic measurement system of claim 1 , wherein the first parameter of interest is a film thickness.

16. The spectroscopic measurement system of claim 1 , wherein the one or more structures disposed on the optically transparent substrate comprise an augmented reality / virtual reality device.

17. generating an amount of illumination light comprising wavelengths in the range of 150 to 2,500 nanometers; directing the amount of illumination light to a measurement spot comprising one or more structures disposed on an optically transparent substrate with a numerical aperture (NA) of at least 0.15 and an image demagnification ratio from an illumination field stop to the measurement spot of at least 10, wherein the amount of illumination light is directed to the one or more structures at one or more angles of incidence, at one or more azimuthal angles, or a combination thereof; collecting a quantity of collected light from the measurement spot, said collecting involving a collection mask positioned at or near an image plane of a collection optics subsystem, said collection mask including an aperture having a dimension of less than 1 millimeter in a direction coincident with a direction in which the angle of incidence changes; detecting the amount of collected light; generating an estimate of a first parameter of interest characterizing the one or more structures being measured based on the detected amount of collected light.

18. 18. The method of claim 17, further comprising imaging the measurement spot onto the at least one detector with a field magnification of at least 10.

19. 18. The method of claim 17, wherein the collection optical subsystem has a collection numerical aperture (NA) of at least 0.

15.

20. 18. The method of claim 17, wherein the one or more structures being measured comprise a metalens optical element or an augmented reality / virtual reality device.

21. 20. The method of claim 17, wherein the first parameter of interest is a film thickness or a critical dimension, the critical dimension characterizing a grating structure disposed on the optically transparent substrate.

22. 1. A spectroscopic measurement system, comprising: an illumination source configured to generate an amount of illumination light comprising wavelengths in the range of 150 to 2,500 nanometers; an illumination optics subsystem configured to direct the amount of illumination light from the illumination source to one or more structures disposed on an optically transparent substrate at a measurement spot at one or more angles of incidence, at one or more azimuthal angles, or a combination thereof, wherein the illumination optics subsystem has a numerical aperture (NA) of at least 0.15 and an image demagnification ratio from an illumination field stop to the measurement spot of at least 10; a collection optics subsystem configured to collect a quantity of collected light from the measurement spot on the surface of the specimen, the collection optics subsystem including a collection mask positioned at or near an image plane of the collection optics, the collection mask including an aperture having a dimension of less than 1 millimeter in a direction coincident with a direction in which the angle of incidence changes; at least one detector having a planar, two-dimensional surface sensitive to incident light, the at least one detector configured to detect the amount of collected light and to generate an output signal indicative of the detected light; a non-transitory computer-readable medium having stored thereon instructions that, when executed by one or more processors, cause the one or more processors to generate an estimate of a first parameter of interest characterizing the one or more structures being measured based on an analysis of the output signal.

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