Soft x-ray optics with improved filtering

Abstract

Presented herein are optical elements that efficiently propagate x-ray radiation within a desired energy range and reject radiation outside the desired energy range. In one aspect, one or more optical elements of an x-ray based system include an integrated optical filter that includes one or more layers of material that absorb radiation having energies outside of a desired energy band. Generally, the integrated filter improves the optical performance of the x-ray based system by suppressing reflectivity in the infrared (IR), visible (vis), ultraviolet (UV), extreme ultraviolet (EUV) portions of the spectrum, or any other non-desired wavelength region. In another aspect, one or more diffusion barrier layers prevent degradation of the integrated optical filter, prevent diffusion between the integrated optical filter and other material layers, or both. In some embodiments, the thickness of one or more layers of material of the integrated optical filter varies within a spatial region of the filter.

Description

Technical Field

[0001] The described embodiments relate to x-ray optics and, more specifically, to thin-film optical layers for filtering out out-of-band radiation in optical systems. Background Technology

[0002] Semiconductor devices (such as logic and memory devices) are typically manufactured through a series of processing steps applied to a sample. The various features and multiple structural levels of a semiconductor device are formed by these processing steps. For example, photolithography is a semiconductor manufacturing process that specifically involves creating patterns on a semiconductor wafer. Additional 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 wafer and then separated into individual semiconductor devices.

[0003] Metrology processes are used at various steps during semiconductor manufacturing to detect defects on wafers and promote higher yields. Typically, several metrology and correlation analysis algorithms based on techniques incorporating scattering and reflection measurements are used to characterize critical dimensions, film thickness, composition, and other parameters of nanoscale structures.

[0004] Traditionally, critical dimension measurements in scattering measurements are performed on targets composed of thin films and / or repeating periodic structures. During device fabrication, these films and periodic structures typically represent the actual device geometry and material structure or intermediate design. As devices (e.g., logic and memory devices) move towards smaller nanoscale dimensions, characterization becomes more challenging. Devices incorporating complex three-dimensional geometries and materials with varying physical properties contribute to these characterization difficulties.

[0005] X-ray-based metrology systems, utilizing both scattering and reflection measurements, have become suitable tools for dimensional metrology of semiconductor structures. X-ray-based metrology systems have demonstrated measurement capabilities for both low and high aspect ratio structures. In some applications, X-ray-based metrology systems feature illumination beam spot sizes compatible with kerf targets. X-ray-based metrology systems have enabled the efficient development and validation of measurement formulations for challenging applications, and are feasible for operation in high-volume manufacturing (HVM) environments without extensive prior dimensional and material composition information.

[0006] High-reflectivity multilayer optics are key components of optical systems used in X-ray measurement and processing systems. High-reflectivity multilayer optics typically employ repeating pairs of layers made of different materials. Each pair of layers includes an absorber material layer and a spacer material layer. Common absorber materials include tungsten (W), tungsten disilicide (WSi2), ruthenium (Ru), vanadium (V), lanthanum (La), molybdenum (Mo), titanium dioxide (TiO2), and nickel (Ni). Common spacer materials include carbon (C), boron nitride (BN), boron carbide (B4C), and silicon (Si).

[0007] Figure 1 Illustration depicting a cross-sectional view of a multilayer optics device 10 for soft X-ray applications. A set of repeating pairs of multilayer coatings 12 are fabricated over a silicon substrate 11. The top four repeating pairs 13A to D of the multilayer coatings are illustrated. Each repeating pair of the multilayer coatings includes a spacer layer (e.g., layer 15 of repeating pair 13A) and an absorber layer (e.g., layer 14 of repeating pair 13A). Figure 1 In the embodiments depicted, the spacer layer is made of scandium (Sc), and the absorber layer is made of chromium (Cr). In one embodiment, a set of multilayer coatings 12 comprises four hundred repeating pairs of multilayer coatings. The spatial period P of a set of multilayer coatings (i.e., the thickness of each repeating material pair) is 1.56 nm to satisfy the Bragg condition. This is presented in Eriksson, Fredrik, et al., “14.5% near-normal incidence reflectance of Cr Sc x-ray multilayer mirrors of the water window,” Optics Letters 28-24 (2003): pp. 2494-2496. Figure 1 Additional descriptions of the multilayer optical devices depicted herein are incorporated herein by reference in their entirety.

[0008] The reflectivity of the multilayer optics 10 is typically extremely sensitive to the angle of incidence and the beam energy (i.e., wavelength). Figure 2This is a plot 20 illustrating a simulation of the reflectivity of a multilayer optics device 10, which varies with the beam energy based on an incident angle of five degrees. The simulation employs Fresnel equations assuming an ideal, flat interface. The optical constants associated with each material (i.e., Δ and β constants) are derived using a scattering factor table from the Center for X-ray Optics (CXRO) of the Materials Science Division at Lawrence Berkeley National Laboratory (accessible via the Internet at http: / / henke.lbl.gov / optical_constants / ). Figure 2 The study describes a maximum reflectivity of 53.1% at a beam energy of 399 electron volts (3.11 nanometers) (which is within the range of soft X-ray radiation, e.g., 80 eV to 3,000 eV).

[0009] Broadband, soft X-ray-based metrology requires high reflectivity at soft X-ray wavelengths. However, lower-energy radiation (e.g., EUV, UV, visible light, IR) contaminates soft X-ray-based measurements. Unfortunately, as... Figure 2 The text explains that conventional multilayer optics 10 used in soft X-ray systems exhibit high reflectivity in the extreme ultraviolet (EUV) spectrum (e.g., 10 eV to 80 eV). This is caused by the increased contrast between the refractive indices of air and the mirror material (e.g., Cr or Sc) as photon energy decreases. Therefore, soft X-ray-based systems employing conventional multilayer optics 10 are susceptible to EUV light pollution.

[0010] Traditionally, one or more transmissive, independent optical filters are used in the optical path of soft X-ray systems to filter out light contamination outside the desired soft X-ray band (e.g., EUV, UV, visible light, IR). These transmissive, independent optical filters are made of extremely thin films of material (e.g., 5 to 50 nanometers thick) spanning the cross-section of the X-ray beam (e.g., across hundreds of micrometers to millimeters). These extremely thin films, unsupported over relatively large distances, are expensive and extremely fragile. This negatively impacts the reliability and practicality of current soft X-ray-based systems.

[0011] In summary, there is a need for X-ray-based systems with improved optics. These improved optics should enable efficient propagation of X-ray radiation within the desired energy range and rejection of radiation outside that range. Specifically, it is desirable to have optics capable of propagating broadband, soft X-ray radiation and rejecting wavelengths in the EUV, UV, visible, and IR portions of the spectrum. Summary of the Invention

[0012] This document presents optical elements that effectively propagate X-ray radiation within a desired energy range and reject radiation outside that range. By way of non-limiting examples, the optical elements described herein are implemented in any of the following: X-ray metrology systems, projection lithography systems, microscope systems, astronomical systems, spectroscopic systems, laser illumination sources including laser cavities and optics, synchrotron illumination sources, etc.

[0013] In one aspect, one or more optical elements of an X-ray-based system include an integrated optical filter comprising one or more material layers that absorb radiation having energy outside the desired energy band. Generally, the integrated filter improves the optical performance of the X-ray-based system by suppressing reflectivity in the infrared (IR), visible (vis), ultraviolet (UV), extreme ultraviolet (EUV) portions of the spectrum, or any other non-desired wavelength regions.

[0014] In some embodiments, the multilayer X-ray reflecting optics includes an integrated optical filter comprising one or more material layers that absorb radiation having energies below the desired bandgap. Depending on the desired wavelength range or the wavelength range to be absorbed, the integrated optical filter may comprise a single material layer, two material layers, or more than two material layers.

[0015] In another embodiment, the integrated optical filter includes one or more diffusion barrier layers for preventing degradation of the integrated optical filter by the external environment, preventing diffusion between the integrated optical filter and other material layers, or both. In many embodiments, thin diffusion barrier layers effectively increase the lifetime of multilayer optics without affecting their optical performance.

[0016] In another aspect, the thickness of one or more layers of the integrated optical filter varies within the spatial region of the filter.

[0017] The foregoing is an overview and therefore necessarily contains simplifications, generalizations, and omissions of details; thus, those skilled in the art will understand that the overview is merely illustrative and not in any way limiting. Other aspects, inventive features, and advantages of the apparatus and / or processes described herein will become apparent from the non-limiting detailed description set forth herein. Attached Figure Description

[0018] Figure 1 Description of a cross-sectional view of a multilayer optics device 10 for use in soft X-ray applications.

[0019] Figure 2 This is a plot 20 illustrating the simulation of the reflectivity of a multilayer optical device 10, which varies with the beam energy based on an incident angle of five degrees.

[0020] Figure 3 A multilayer X-ray reflective optics device 100 comprising an integrated optical filter 101 is depicted in one embodiment.

[0021] Figure 4 Description Figure 3 A plot 110 showing the simulated reflectivity of the multilayer X-ray reflecting optical device 100 depicted in the figure.

[0022] Figure 5 Description of different thicknesses for integrated optical filters Figure 3 A plot 120 showing the simulated reflectivity of the multilayer X-ray reflecting optical device 100 depicted in the figure.

[0023] Figure 6 A multilayer X-ray reflective optics device 130 comprising an integrated optical filter 131 is depicted in one embodiment.

[0024] Figure 7 Description Figure 6 A plot 140 showing the simulated reflectivity of the multilayer X-ray reflecting optical device 130 depicted in the figure.

[0025] Figure 8 Describe the contamination zone ranging from 30 eV to 130 eV. Figure 7 A plot 150 showing the simulated reflectivity of the multilayer X-ray reflecting optical device 130 depicted in the figure.

[0026] Figure 9 The description illustrates the photonic bandgap from 30 eV to 70 eV for various thicknesses of the Te layer 133 and a constant thickness of 10.5 nm for the SiO2 layer 132. Figure 6 A plot 160 showing the simulated reflectivity of the multilayer X-ray reflecting optical device 130 depicted in the figure.

[0027] Figure 10 The description illustrates the photonic bandgap from 30 eV to 70 eV for various thicknesses of the SiO2 layer 132 and a constant thickness of 14.4 nm for the Te layer 133. Figure 6 A plot 170 showing the simulated reflectivity of the multilayer X-ray reflecting optical device 130 depicted in the figure.

[0028] Figure 11 Description of Table 180, Table 180 is for Figure 9 and 10 Overview of different combinations of Te and SiO2 layer thicknesses as described in the text Figure 6 The average reflectivity of the multilayer X-ray reflecting optical device 130 depicted in the figure is shown in three different contamination zones, and the reflectivity at the wavelength of the soft X-ray of interest (397.9 eV).

[0029] Figure 12 A multilayer X-ray reflective optical device 190 comprising an integrated optical filter 191 is depicted.

[0030] Figure 13 A curved optical element 260 is depicted, which includes an integrated optical filter 262 disposed on the surface of the curved optical element.

[0031] Figure 14 An embodiment of an RSAXS metrology tool 200 for measuring the properties of a sample is described in at least one novel aspect.

[0032] Figure 15 This is a simplified diagram illustrating an end view of a focusing optics device comprising four mirror elements arranged in a segmented ring around the beam axis A.

[0033] Figure 16 Describes an X-ray illumination beam incident on a wafer with a specific orientation, described by the incident angle θ and azimuth angle φ.

[0034] Figure 17 Another embodiment of the RSAXS metrology tool 300 for measuring the properties of a sample is described in at least one novel aspect. Detailed Implementation

[0035] Examples of the present invention will now be described in detail with reference to the background examples and some embodiments thereof, which are illustrated in the accompanying drawings.

[0036] This paper presents an optical element that effectively propagates X-ray radiation within a desired energy range and rejects radiation outside that range. Additionally, an X-ray-based metrology system incorporating this optical element is presented. Specifically, the broadband, soft X-ray-based metrology system employs an optical element that propagates broadband, soft X-ray radiation and rejects wavelengths in EUV, UV, visible light, IR, or any combination thereof.

[0037] In one aspect, one or more optical elements of an X-ray-based system include an integrated optical filter comprising one or more material layers that absorb radiation having energies below the desired bandgap. In some embodiments, the integrated optical filter absorbs radiation with wavelengths greater than 10 nanometers (i.e., less than 123.9 electron volts). In some embodiments, the integrated optical filter absorbs radiation with wavelengths greater than 13.7 nanometers (i.e., less than 90 electron volts). In some embodiments, the integrated optical filter absorbs radiation with wavelengths greater than 12.4 nanometers (i.e., less than 100 electron volts). In some embodiments, the integrated optical filter absorbs radiation with wavelengths greater than 10.3 nanometers (i.e., less than 120 electron volts). Generally, integrated filters improve the optical performance of X-ray-based systems by suppressing reflectivity in the infrared (IR), visible (vis), ultraviolet (UV), extreme ultraviolet (EUV) portions of the spectrum, or any other non-desired wavelength regions.

[0038] By way of non-limiting examples, one or more optical elements of an X-ray metrology system, a projection lithography system, a microscope system, an astronomical system, a spectroscopic system, a laser illumination source including a laser cavity and optics, a synchrotron illumination source, etc., include an integrated optical filter for absorbing non-desired radiation.

[0039] In some embodiments, multilayer X-ray reflective optics include an integrated optical filter comprising one or more material layers that absorb radiation having energies below the desired bandgap. Depending on the desired wavelength range or the wavelength range to be absorbed, the integrated optical filter may comprise a single material layer, two material layers, or more than two material layers. Typically, the thickness of each layer is chosen to maximize extinction within the range of photon energies to be suppressed for optimal π-phase matching (i.e., 180-degree phase matching). The thickness of each material layer is typically in the range of one to one hundred nanometers.

[0040] For an integrated optical filter comprising a single material layer on top of a set of repeating pairs of reflective multilayer coatings, the optical refractive index n of the single material layer can be approximately calculated using equations (1) and (2). filter and thickness t filter , where n top θ is the refractive index of the top layer of the reflective multilayer coating of the repeating pair of the lower subgroup, θ is the incident angle of the incident beam, and λ is the wavelength of the incident beam.

[0041]

[0042]

[0043] In practice, the selection of materials and deposition thickness for integrated optical filters is guided by performing a series of thickness optimizations for various materials, as directed by equations (1) and (2). For example, the complexity of multilayer structures can cause the optimal thickness to shift away from the optimal extinction valley estimated by equation (2). In addition, identifying materials that can be efficiently deposited in thin layers that perfectly match the requirements of equation (1) is challenging. Therefore, in practice, equation (1) helps to narrow the list of candidate materials, and equation (2) provides a good starting point for thickness optimization.

[0044] Furthermore, out-of-band contamination (e.g., EUV contamination) rarely occurs within sharp wavelength bands. Therefore, the selection and thickness optimization of individual material layers will typically involve trade-offs regarding out-of-band absorption. If these trade-offs render a single-layer filter ineffective, then one or more additional layers of different materials should be considered.

[0045] Figure 3 A multilayer X-ray reflective optical device 100 comprising an integrated optical filter 101 is described. Figure 3 The same number of elements and references depicted in the text Figure 1 The elements described are the same. For example... Figure 3 As depicted, the integrated optical filter 101 comprises a material layer specifically fabricated on top of the set of repeating pairs of multilayer coatings 12. In one example, the integrated optical filter 101 is a silicon dioxide (SiO2) layer deposited on top of a chromium absorber layer 14.

[0046] Figure 4 Description Figure 3 A plot 110 depicts a simulation of the reflectivity of a multilayer X-ray reflecting optical device 100. Plot line 111 depicts the reflectivity of the multilayer X-ray reflecting optical device 100 without an integrated optical filter 101, varying with beam energy. Plot line 112 depicts the reflectivity of the multilayer X-ray reflecting optical device 100 with an integrated optical filter 101 having a single layer of SiO2 (10 nanometers thick), varying with beam energy. Figure 4 The description states that the integrated optical filter 101 eliminates 99.3% of the 41.6 eV radiation and absorbs only 5.4% of the radiation at the wavelength of interest (397.9 eV). Within the contamination band from 30 eV to 130 eV, the integrated optical filter reduces the average reflectivity by 8 times compared to the unfiltered case.

[0047] Figure 5 Description of different thicknesses for integrated optical filters Figure 3Plot 120 depicts a simulation of the reflectivity of a multilayer X-ray reflecting optical device 100. Plot line 121 depicts the simulation of the reflectivity of the multilayer X-ray reflecting optical device 100 having an integrated optical filter 101 with a single layer of SiO2 (8 nm thick). Plot line 122 depicts the simulation of the reflectivity of the multilayer X-ray reflecting optical device 100 having an integrated optical filter 101 with a single layer of SiO2 (10 nm thick). Plot line 123 depicts the simulation of the reflectivity of the multilayer X-ray reflecting optical device 100 having an integrated optical filter 101 with a single layer of SiO2 (12 nm thick). As the thickness changes from 8 nm to 12 nm, the first extinction valley shifts from 47.0 eV (26.4 nm) to 39.1 eV (31.7 nm). In addition, the second extinction valley is shifted from 115.1 eV (10.8 nm) to 83.9 eV (14.8 nm). In this way, the stopband of the integrated optical filter 101 is tuned by adjusting the thickness.

[0048] In some embodiments, a single-layer integrated optical filter has too narrow a bandwidth to adequately suppress the range of contamination wavelengths of interest. In these embodiments, integrated optical filters with two or more layers are employed. In some embodiments, multilayer integrated optical filters can absorb less radiation at the desired wavelengths for operation of the X-ray system.

[0049] Generally, the order of the layers in a multilayer integrated optical filter can be arbitrary. However, in a preferred embodiment, the material layers of the multilayer integrated optical filter with the best matching refractive index of air (e.g., smaller Δ and β) are disposed on top of the multilayer stack to allow more radiation through the air / layer interface.

[0050] Figure 6 A multilayer X-ray reflective optical device 130 comprising an integrated optical filter 131 is depicted. Figure 6 The same number of elements and references depicted in the text Figure 1 The elements described are the same. For example... Figure 6 As depicted, the integrated optical filter 131 comprises two material layers 132 and 133 specifically fabricated on top of the set of repeating pairs of multilayer coatings 12. In one example, layer 132 is a silicon dioxide (SiO2) layer deposited on top of a chromium absorber layer 14, and layer 133 is a tellurium (Te) layer deposited on top of the SiO2 layer 132. The Te layer 133 is deposited on top because it has significantly smaller Δ and β values ​​compared to SiO2 below 60 eV. The integrated optical filter 131 is preferably used in X-ray systems where contamination is primarily concentrated in the photon energy range from 30 eV to 60 eV.

[0051] Figure 7 Description Figure 6 A plot 140 depicts a simulation of the reflectivity of a multilayer X-ray reflecting optical device 130. Plot line 141 depicts the reflectivity of the multilayer X-ray reflecting optical device 130 without an integrated optical filter 131, varying with photon energy. Plot line 142 depicts the reflectivity of a multilayer X-ray reflecting optical device 100 with an integrated optical filter 131 comprising a SiO2 layer 132 (10.5 nm thick) and a Te layer 133 (14.4 nm thick), varying with photon energy. (As shown...) Figure 7 The text explains that, compared to Figure 4 The integrated optical filter 101 described herein has a much wider stopband than the integrated optical filter 131. The integrated optical filter 131 contains three extinction valleys below 60 eV. Furthermore, compared to the unfiltered case, the integrated optical filter 131 absorbs only 13.8% of the radiation at the wavelength of interest (397.9 eV).

[0052] Figure 8 Describe the contamination zone ranging from 30 eV to 130 eV. Figure 7 A plot 150 showing the simulated reflectivity of the multilayer X-ray reflecting optical device 130 depicted in the figure. (See plot 150 for reference.) Figure 8 The peak extinction is depicted at 41.2 eV, where 98.9% of the photon energy is absorbed. Compared to the unfiltered case within the contamination band of interest from 30 eV to 60 eV, the integrated optical filter 130 reduces the average reflectivity by a factor of 17.

[0053] Figure 9 The description illustrates the photonic bandgap from 30 eV to 70 eV for various thicknesses of the Te layer 133 and a constant thickness of 10.5 nm for the SiO2 layer 132. Figure 6 A plot 160 depicts a simulation of the reflectivity of the multilayer X-ray reflecting optical device 130. Plot line 161 depicts the reflectivity of the multilayer X-ray reflecting optical device 130 having a Te layer 133 with a thickness of 13.4 nanometers. Plot line 162 depicts the reflectivity of the multilayer X-ray reflecting optical device 130 having a Te layer 133 with a thickness of 14.4 nanometers. Plot line 163 depicts the reflectivity of the multilayer X-ray reflecting optical device 130 having a Te layer 133 with a thickness of 15.4 nanometers.

[0054] Figure 10 The description illustrates the photonic bandgap from 30 eV to 70 eV for various thicknesses of the SiO2 layer 132 and a constant thickness of 14.4 nm for the Te layer 133. Figure 6A plot 170 depicts a simulated reflectivity of the multilayer X-ray reflecting optical device 130. Plot line 171 depicts the reflectivity of the multilayer X-ray reflecting optical device 130 having a SiO2 layer 132 with a thickness of 9.5 nanometers. Plot line 172 depicts the reflectivity of the multilayer X-ray reflecting optical device 130 having a SiO2 layer 132 with a thickness of 10.5 nanometers. Plot line 173 depicts the reflectivity of the multilayer X-ray reflecting optical device 130 having a SiO2 layer 132 with a thickness of 11.5 nanometers. (As shown...) Figure 9 and 10 The text explains that changing the thickness of the Te layer 133 affects the positions of the first extinction valley 164 and the third extinction valley 166, while changing the thickness of the SiO2 layer 132 causes the position of the second extinction valley 165 to shift.

[0055] Figure 11 Description of Table 180, Table 180 is for Figure 9 and 10 Overview of different combinations of Te and SiO2 layer thicknesses as described in the text Figure 6 The multilayer X-ray reflective optics 130 depicted in the figure show the average reflectance within three different contamination bands and the reflectance at the desired soft X-ray wavelength (397.9 eV). In one example, the output spectrum of the illumination source of the X-ray system specifies the contamination band in which maximum suppression is desired. Table 180 is used to select the optimal combination of film thicknesses for suppressing photon energy within the identified contamination bands.

[0056] In some embodiments, the X-ray optical element is designed to support multiple wavelengths of interest. In some of these embodiments, the integrated optical filter comprises a single-layer or multi-layer combination optimized across all wavelengths of interest. In other embodiments, the integrated optical filter comprises multiple single layers or multiple multi-layer combinations, each optimized in different portions of all wavelengths of interest and each optimized to suppress at least one contamination band.

[0057] In another embodiment, the integrated optical filter includes one or more diffusion barrier layers to prevent degradation of the integrated optical filter by the external environment, to prevent diffusion between the integrated optical filter and other material layers, or both. In many embodiments, thin diffusion barrier layers effectively increase the lifetime of multilayer optics without affecting their optical performance.

[0058] Figure 12 A multilayer X-ray reflective optical device 190 comprising an integrated optical filter 191 is depicted. Figure 12 The same number of elements and references depicted in the text Figure 1 and 6 The elements described are the same. For example... Figure 12As depicted, the integrated optical filter 191 includes a diffusion barrier layer 192 deposited on top of the chromium absorber layer 14 and below the SiO2 layer 132. In this embodiment, the diffusion barrier layer 192 prevents oxygen and water from degrading the set of repeating pairs of multilayer coatings 12 and also protects the set of repeating pairs of multilayer coatings 12 from diffusion into the SiO2 layer 132 and the Te layer 133. In another embodiment, the diffusion barrier layer 192 is deposited on top of the SiO2 layer 132 and below the Te layer 133. In yet another embodiment, the diffusion barrier layer 192 is deposited on top of the Te layer 133. In these embodiments, the diffusion barrier layer 192 prevents oxygen and water from degrading the set of repeating pairs of multilayer coatings 12. Generally, one or more diffusion barrier layers may be deposited anywhere in the stack of the integrated optical filter.

[0059] Generally, integrated optical filters can be positioned anywhere within a stack of multilayer optical elements. In some embodiments, the integrated optical filter is positioned as follows: Figure 3 , 6 And on top of the layer stack of the multilayer X-ray reflective optics described in 12. In some other embodiments, the integrated optical filter is positioned below a set of repeating pairs of multilayer coatings in the layer stack of the multilayer X-ray reflective optics (e.g., between the set of repeating pairs of multilayer coatings 12 and the substrate 11).

[0060] In some embodiments, one or more layers of the integrated optical filter are made of chemically inert materials to improve the stability and lifespan of the optical element. In these embodiments, the integrated optical filter is positioned on top of a multilayer stack of X-ray reflective optics, thereby isolating the set of repeating pairs of multilayer coatings from the external environment. In this way, the integrated optical filter also serves as a protective layer to prevent contamination of the repeating pairs of multilayer coatings by the surrounding environment.

[0061] By way of non-limiting examples, chemically inert materials suitable candidates for one or more layers of integrated optical filters include pure elements (e.g., tellurium, carbon, magnesium) and compounds (e.g., boron carbide (B4C), silicon nitride (Si3N4), silicon oxide (SiO2)). These materials can be deposited in thin layers on top of a multilayer reflective coating using various deposition techniques (e.g., sputtering). Alternatively, the deposition of these material layers can be performed directly by fabrication tools used to manufacture multilayer reflective coatings (e.g., magnetron sputtering tools).

[0062] In another embodiment, the thickness of one or more layers of the integrated optical filter varies within the spatial region of the filter. In some embodiments, the X-ray optical element is curved and one or more layers of the integrated optical filter have a gradient thickness that tracks the angle of incidence along the curved optics, such that the incident light has the same path length through the absorbing material regardless of the incident position along the curved optics. In this way, the suppression efficiency of the integrated optical element is uniform along the entire optical surface.

[0063] Figure 13 A curved optical element 260 is depicted, comprising an integrated optical filter 262 disposed on the surface of the curved optical element. Incident light 266 from source 264 is reflected from the curved optical element 260. The reflected light 267 is focused by the curved optical element 260 onto a focal region 265. The incident light 266 is incident on the surface of the curved optical element 260 over a relatively large area. In other words, different portions of the incident light beam are reflected from different locations on the surface of the curved optical element 260 having significantly different curvatures. For example, light incident at point 268 is incident on the surface of the curved optical element 260 at an angle α1, and light incident at point 269 is incident at a different angle α2. Figure 13 The path length L1 of light incident at point 268 across the integrated optical filter 262 is described in equation (3). The path length L1 is related to the incident angle α1 and thickness T1 of the integrated optical element 262 at point 268.

[0064]

[0065] Moreover, such as Figure 13 The path length L2 of light incident at point 269 across the integrated optical filter 262 is described in the figure. The path length L2 is related to the incident angle α2 and the thickness T2 of the integrated optical element 262 at point 269, as described by equation (4).

[0066]

[0067] In the depicted embodiment, the thickness T1 of the integrated filter element 262 at point 268 and the thickness of the integrated filter element 262 at point 269 are selected to maintain the same path length through the integrated optical filter 262 at both locations according to equation (5).

[0068]

[0069] X-ray-based metrology systems are used to measure the structural and material properties (e.g., material composition, dimensional properties, etc.) of semiconductor structures associated with different semiconductor manufacturing processes using X-ray illumination.

[0070] In some embodiments, the x-ray-based metrology system performs measurements of semiconductor structures based on high-brightness, multicolor reflectance small-angle x-ray scattering (RSAXS). Further description is provided in U.S. Patent Publication No. 2019 / 0017946 to Wack et al., the entire contents of which are incorporated herein by reference.

[0071] RSAXS measurements of semiconductor wafers are performed with a small beam spot size (e.g., less than 50 micrometers across the effective illumination point) over a range of wavelengths, incident angles, and azimuth angles. In one aspect, RSAXS measurements are performed using X-ray radiation in the soft X-ray (SXR) region (i.e., 80 eV to 3000 eV) at grazing incident angles in the range of 5 degrees to 20 degrees. The grazing incident angle for a particular measurement application is selected to achieve the desired penetration into the measured structure and to maximize the measurement information content with a small beam spot size (e.g., less than 50 micrometers).

[0072] Figure 14 This describes an embodiment of the RSAXS metrology tool 200 used for measuring the properties of a sample. For example... Figure 14 As shown, the system 100 can be used to perform RSAXS measurements on the measurement area 202 of a sample 201 illuminated by an incident illumination beam spot.

[0073] In the depicted embodiment, the metrology tool 200 includes an x-ray illumination source 210, focusing optics 211, a beam divergence control slit 212, and a slit 213. The x-ray illumination source 210 is configured to produce SXR radiation suitable for RSAXS measurements. The x-ray illumination source 210 is a multicolor, high-brightness, high-amplitude source. In some embodiments, the x-ray illumination source 210 is configured to produce x-ray radiation in the range of 80 electron volts to 3000 electron volts. Generally, any suitable high-brightness x-ray illumination source capable of producing high-brightness SXR at flux levels sufficient to achieve high throughput, in-line metrology can be carefully considered to supply x-ray illumination for RSAXS measurements.

[0074] By way of non-limiting examples, any of the following can be used as the x-ray illumination source 210: a particle accelerator source, a liquid anode source, a rotating anode source, a fixed solid anode source, a micro-focusing source, a micro-focusing rotating anode source, a plasma-based source, and an inverse Compton source.

[0075] Exemplary X-ray sources include electron beam sources configured to bombard solid or liquid targets to simulate X-ray radiation. A method and system for generating high-brightness, liquid metal X-ray illumination are described in U.S. Patent No. 7,929,667, issued to KLA-Tencor Corporation on April 19, 2011, the entire contents of which are incorporated herein by reference.

[0076] In some embodiments, the x-ray source includes a tunable monochromator that enables the x-ray source to deliver x-ray radiation at different, selectable wavelengths. In some embodiments, one or more x-ray sources are employed to ensure that the x-ray source supplies light at wavelengths that allow sufficient penetration into the sample being measured.

[0077] In some embodiments, illumination source 210 is a high harmonic generation (HHG) x-ray source. In some other embodiments, illumination source 210 is a oscillator / waver synchrotron radiation source (SRS). Exemplary oscillator / waver SRSs are described in U.S. Patents Nos. 8,941,336 and 8,749,179, the entire contents of which are incorporated herein by reference.

[0078] In some other embodiments, the illumination source 210 is a laser-generated plasma (LPP) source. In some of these embodiments, the LPP source comprises any of the emitting materials xenon, krypton, argon, neon, and nitrogen. Generally, the selection of a suitable LPP target material is optimized for brightness in the resonant SXR region. For example, plasma emitted by krypton provides high brightness at the silicon K edge. In another example, plasma emitted by xenon provides high brightness throughout the entire SXR region (80 eV to 3000 eV). Therefore, xenon is a preferred emitting material when broadband SXR illumination is desired.

[0079] The selection of LPP target materials can also be optimized for reliable and long-life light source operation. Inert gas target materials (such as xenon, krypton, and argon) are inert and can be reused in closed-loop operations with minimal or no decontamination. An exemplary SXR lighting source is described in U.S. Patent Publication No. 2019 / 0215940, the entire contents of which are incorporated herein by reference.

[0080] In another aspect, the wavelength emitted by the illumination source (e.g., illumination source 210) is selectable. In some embodiments, illumination source 210 is controlled by computing system 230 to maximize flux in one or more selected spectral regions of an LPP light source. The laser peak intensity at the target material controls the plasma temperature and thus the spectral region of emitted radiation. The laser peak intensity is varied by adjusting the pulse energy, pulse width, or both. In one example, a 100 picosecond pulse width is suitable for generating SXR radiation. Figure 14 As depicted, the computing system 230 transmits a command signal 236 to the illumination source 210, which causes the illumination source 210 to adjust the spectral range of wavelengths emitted from the illumination source 210. In one example, the illumination source 210 is an LPP light source, and the LPP light source adjusts any of the pulse duration, pulse frequency, and target material composition to achieve the desired spectral range of wavelengths emitted from the LPP light source.

[0081] X-ray illumination source 210 generates X-ray emission over a source region having a finite lateral dimension (i.e., a non-zero dimension orthogonal to the beam axis). In one aspect, the source region of illumination source 210 is characterized by a lateral dimension of less than 20 micrometers. In some embodiments, the source region is characterized by a lateral dimension of 10 micrometers or less. The small source size enables high-brightness illumination of small target areas on a sample, thus improving measurement accuracy, precision, and throughput.

[0082] Generally, X-ray optics shape and guide X-ray radiation onto sample 201. In some instances, X-ray optics use multilayer X-ray optics to collimate or focus the X-ray beam onto a measurement region 202 of sample 201 to a divergence of less than 1 milliradian. In some embodiments, X-ray optics include one or more X-ray collimators, X-ray apertures, X-ray beam stops, refractive X-ray optics, diffractive optics (e.g., zone plates, Schwarzschild optics, Kirkpatrick-Baez optics, Montel optics, Wolter optics), mirror X-ray optics (e.g., ellipsoidal mirrors), multicapillary optics (e.g., hollow capillary X-ray waveguides), multilayer optics or systems, or any combination thereof. Further details are described in U.S. Patent Publication No. 2015 / 0110249, the entire contents of which are incorporated herein by reference.

[0083] like Figure 14 As depicted herein, focusing optics 211 focuses source radiation onto a metrological target positioned on sample 201. The finite lateral source size results in a finite spot size 202 on the target defined by rays 216 from the edge of the source and any beam shaping provided by beam slits 212 and 213. In some embodiments, the multilayer X-ray optics of an X-ray-based metrology system (e.g., focusing optics 211 of RSAXS system 200) includes integrated optical filters as described herein.

[0084] In some embodiments, the focusing optics 211 includes an elliptical shaping focusing optics element. Figure 14 In the embodiment depicted, the magnification of the focusing optics 211 at the center of the ellipse is approximately 1. Therefore, due to the nominal grazing incidence angle (e.g., 5 to 20 degrees), the size of the illumination spot projected onto the surface of the sample 201 is approximately the same as the size of the illumination source adjusted for beam extension.

[0085] In another aspect, focusing optics 211 collects the light emitted from the source and selects one or more discrete wavelengths or spectral bands, and focuses the selected light onto the sample 201 at a grazing incidence angle in the range of 5 to 20 degrees.

[0086] The nominal grazing incidence angle is selected to achieve the desired penetration of the metrological target to maximize signal information content while remaining within the target boundary. Hard X-rays have a very small critical angle, while soft X-rays have a significantly larger critical angle. Due to this additional measurement flexibility, RSAXS measurements probe deeper into structures with lower sensitivity to precise values ​​of the grazing incidence angle.

[0087] In some embodiments, the focusing optics 211 includes a hierarchical multilayer structure that selects a desired wavelength or wavelength range for projection onto the sample 201. In some instances, the focusing optics 211 includes a hierarchical multilayer structure (e.g., layers or coatings) that includes an integrated optical filter that selects a wavelength and projects the selected wavelength onto the sample 201 within an incident angle range. In some instances, the focusing optics 211 includes a hierarchical multilayer structure that includes an integrated optical filter that selects a wavelength range and projects the selected wavelength onto the sample 201 within an incident angle range. In some instances, the focusing optics 211 includes a hierarchical multilayer structure that includes an integrated optical filter that selects a wavelength range and projects the selected wavelength onto the sample 201 within an incident angle range.

[0088] Hierarchical multilayer optics incorporating integrated optical filters are preferred for minimizing light loss when the single-layer grating structure is too deep. Generally, the multilayer optics selects the reflection wavelength. The spectral bandwidth of the selected wavelength is optimized to provide flux to sample 201, measure the information content in the diffraction order, and prevent signal degradation due to angular dispersion at the detector and overlap of diffraction peaks. Additionally, the hierarchical multilayer optics are used to control divergence. The angular divergence at each wavelength is optimized for flux at the detector and minimal spatial overlap.

[0089] In some instances, hierarchical multilayer optics incorporating integrated optical filters select wavelengths to enhance the contrast and information content of diffraction signals from specific material interfaces or structural dimensions, while suppressing contaminating wavelengths (e.g., wavelengths greater than 10 nanometers). For example, the selected wavelengths can be chosen to span specific resonant regions of elements (e.g., silicon K-edges, nitrogen K-edges, oxygen K-edges, etc.). Additionally, in these instances, the illumination source can be tuned to maximize flux in the selected spectral region (e.g., HHG spectral tuning, LPP laser tuning, etc.).

[0090] In some other instances, little to no prior structural information is available at the time of measurement. In these instances, multiple (e.g., 3 to 4) wavelengths are selected to achieve diffraction pattern measurements across absorption edges. Model-free measurements of structural properties are achieved using (e.g., multi-wavelength irregular diffraction techniques) with the measured signal, without prior information (other than the elemental composition of the measured structure). After estimating structural properties based on model-free measurements, model-based measurement techniques can be used to further refine the parameter estimates.

[0091] In some instances, the irregular scattering factor (i.e., scattering properties) of the measured target is not known a priori. In these instances, the reflectivity of a multilayer film is measured at multiple resonant wavelengths. The angular shift of the Bragg peak provides sufficient information for extracting the irregular scattering factor.

[0092] In some instances, non-resonant X-ray reflectivity measurements provide independent estimates of multilayer periodicity and interface roughness parameters, improving the fit of model-based measurements. In some embodiments, the combined metrology tool includes a multi-wavelength SXR diffraction subsystem and an X-ray reflectivity measurement subsystem as described herein to improve measurement throughput. In one embodiment, the multi-wavelength SXR diffraction subsystem and the X-ray reflectivity measurement subsystem employ orthogonal incident planes, enabling simultaneous or sequential measurements without moving the sample under test or any of the optical measurement subsystems. In some embodiments, if the AOI range provided by the SXR multilayer mirror is too small for X-ray reflectivity measurements, wafer rotation, detector rotation, or both can be used to extend the incident angle range.

[0093] In some embodiments, the focusing optics 211 includes a plurality of reflective optical elements, each having an elliptical surface shape. Each reflective optical element includes a substrate, a multilayer coating, and an integrated optical filter tuned to reflect different wavelengths or wavelength ranges and suppress different wavelengths or wavelength ranges.

[0094] In some embodiments, the focusing optics 211 focuses light of multiple wavelengths, azimuth angles, and AOI onto the same measurement target area. Figure 15The diagram depicts an end view (i.e., along the beam axis) of a focusing optics 250 comprising four mirror elements 250A to 250D arranged in a segmented annular configuration around a beam axis A. Each mirror element includes a multilayer coating tuned to reflect different wavelengths or wavelength ranges and an integrated optical filter tuned to suppress different wavelengths or wavelength ranges. In some embodiments, each mirror element 250A to 250D comprises a uniform multilayer design (i.e., the surface of a particular mirror element reflects the same wavelength or wavelength range over the entire mirror surface area of ​​the particular mirror element). In some other embodiments, each mirror element comprises a non-uniform multilayer design (i.e., the wavelength or wavelength range reflected by the mirror element depends on the incident position on the mirror surface). In some other embodiments, each mirror element is elliptical in shape and projects illumination light onto sample 201 within an incident angle range. Furthermore, because the mirror elements are arranged in an annular configuration, the mirror elements project illumination light onto sample 201 within an azimuth angle range. Although Figure 15 Four mirror elements are depicted, but in general, focusing optics can comprise any number of mirror elements arranged to focus light of multiple wavelengths, azimuth angles, and AOIs onto the same metrological target area. In some other embodiments, the focusing optics comprises several mirror elements nested in the incident plane (i.e., a nested Wörther configuration).

[0095] In another aspect, the range of wavelength, AOI, azimuth angle, or any combination thereof projected onto the same metrological area is adjusted by actively positioning one or more mirror elements of the focusing optics. For example... Figure 14 As depicted, the computing system 230 transmits a command signal to the actuator system 215, which causes the actuator system 215 to adjust the position, alignment, or both of one or more optical elements of the focusing optics 211 to achieve a desired range of wavelength, AOI, azimuth angle, or any combination thereof projected onto the sample 201.

[0096] Generally, the incident angle is selected for each wavelength to optimize the penetration of the illumination light and its absorption by the target being measured. In many instances, multilayer structures are measured, and the incident angle is selected to maximize the signal information associated with the layer of interest. In instances of superimposed metrology, the wavelength and incident angle are selected to maximize the signal information arising from interference between scattering from previous and current layers. Additionally, the azimuth angle is selected to optimize the signal information content. Furthermore, the azimuth angle is selected to ensure angular separation of diffraction peaks at the detector.

[0097] In another aspect, the RSAX metrology system (e.g., metrology tool 200) includes one or more beam slits or apertures for shaping the illumination beam 214 incident on the sample 201 and selectively blocking portions of the illumination light that would otherwise illuminate the measured metrology target. The beam slits define the beam size and shape such that the X-ray illumination spot is aligned with the region of the measured metrology target. Additionally, the beam slits define the illumination beam divergence to minimize overlap of diffraction orders on the detector.

[0098] In another aspect, an RSAX metrology system (e.g., metrology tool 200) includes one or more beam slits or apertures for selecting a set of illumination wavelengths to simultaneously illuminate the measured metrology target. In some embodiments, illumination comprising multiple wavelengths is simultaneously incident on the measured metrology target. In these embodiments, one or more slits are configured to deliver illumination comprising multiple illumination wavelengths. Generally, simultaneous illumination of the measured metrology target is preferred for increasing signal information and processing capacity. However, in practice, overlap of diffraction orders at the detector limits the range of illumination wavelengths. In some embodiments, one or more slits are configured to sequentially deliver different illumination wavelengths. In some instances, sequential illumination with a larger angular divergence provides higher processing capacity because the signal-to-noise ratio for sequential illumination can be higher than that for simultaneous illumination when the beam divergence is large. When measurements are performed sequentially, the problem of diffraction order overlap is not an issue. This increases measurement flexibility and improves the signal-to-noise ratio.

[0099] Figure 14 A beam divergence control slit 212 is depicted in the beam path between focusing optics 211 and beam shaping slit 213. The beam divergence control slit 212 limits the divergence of illumination provided to the sample under test. The beam shaping slit 213 is positioned in the beam path between the beam divergence control slit 212 and the sample 201. The beam shaping slit 213 further shapes the incident beam 214 and selects the illumination wavelength of the incident beam 214. The beam shaping slit 213 is positioned immediately preceding the sample 201 in the beam path. In one aspect, the slit of the beam shaping slit 213 is positioned immediately adjacent to the sample 201 to minimize the expansion of the incident beam spot size attributable to the beam divergence defined by the finite source size.

[0100] In some embodiments, the beam shaping slit 213 includes a plurality of independently actuated beam shaping slits. In one embodiment, the beam shaping slit 213 includes four independently actuated beam shaping slits. These four beam shaping slits effectively block portions of the incoming beam and produce an illumination beam 214 having a box-shaped illumination cross-section.

[0101] The slits of the beam-shaping slit 213 are constructed of a material that minimizes scattering and effectively blocks incident radiation. Exemplary materials include single-crystal materials such as germanium, gallium arsenide, and indium phosphide. Typically, the slit material is split rather than sawn along its crystal direction to minimize scattering across structural boundaries. Furthermore, the slits are oriented relative to the incoming beam so that the interaction between the incoming radiation and the internal structure of the slit material produces a minimal amount of scattering. Crystals are attached to each slit holder made of a high-density material (e.g., tungsten) to completely block the X-ray beam on one side of the slit.

[0102] X-ray detector 219 collects X-ray radiation 218 scattered from sample 201 and generates an output signal 235 indicating the properties of sample 201 that are sensitive to incident X-ray radiation, according to RSAXS measurement modes. In some embodiments, the scattered X-rays 218 are collected by X-ray detector 219 while sample positioning system 240 positions and orients sample 101 to produce angle-resolved scattered X-rays.

[0103] In some embodiments, the RSAXS system includes a high dynamic range (e.g., greater than 10). 5 One or more photon counting detectors. In some embodiments, a single photon counting detector detects the position and number of detected photons.

[0104] In some embodiments, the x-ray detector analyzes one or more x-ray photon energies and generates a signal indicating the properties of the sample for each x-ray energy component. In some embodiments, the x-ray detector 219 comprises any of a CCD array, a microchannel plate, a photodiode array, a microstrip proportional counter, a gas proportional counter, a scintillator, or a fluorescent material.

[0105] In this way, in addition to pixel location and count, X-ray photon interactions within the detector are also identified by energy. In some embodiments, X-ray photon interactions are identified by comparing the energy of the X-ray photon interactions with predetermined upper and lower thresholds. In one embodiment, this information is transmitted to a computing system 230 via an output signal 235 for further processing and storage.

[0106] The diffraction pattern originating from simultaneous illumination of a periodic target by multiple illumination wavelengths is separated at the detector due to angular dispersion in the diffraction. In these embodiments, an integral detector is employed. The diffraction pattern is measured using a region detector (e.g., a vacuum-compatible back-side CCD or a hybrid pixel array detector). Angular sampling is optimized for Bragg peak integration. If a pixel-level model fitting is used, then angular sampling is optimized for signal information content. The sampling rate is selected to prevent saturation of the zero-order signal.

[0107] In another approach, the RSAXS system is used to determine the properties of a sample (e.g., structural parameter values) based on one or more diffraction orders of the scattered light. Figure 14 As depicted, the metrology tool 100 includes a computational system 230 for acquiring a signal 235 generated by the detector 219 and determining the properties of the sample based at least in part on the acquired signal.

[0108] In some instances, RSAXS-based metrology involves determining sample size by inversely solving a predetermined measurement model from measured data. The measurement model contains several (approximately ten) adjustable parameters representing the geometry and optical properties of the sample, as well as the optical properties of the measurement system. Inverse solution methods include (but are not limited to) model-based regression, computed tomography, machine learning, or any combination thereof. In this way, target profile parameters are estimated by solving for the value of a parameterized measurement model that minimizes the error between the measured scattered X-ray intensity and the modeled result.

[0109] Measurements can be performed over a wide range of wavelengths, incident angles, and azimuth angles to increase the precision and accuracy of the measured parameter values. This method reduces the correlation between parameters by expanding the number and diversity of datasets available for analysis.

[0110] Measurements are taken of the intensity of diffracted radiation, which varies depending on the illumination wavelength and the X-ray incident angle relative to the wafer surface normal. The information contained in the multiple diffraction orders is generally unique among the parameters considered in each model. Therefore, X-ray scattering produces estimates of the values ​​of the parameters of interest with small errors and reduced parameter correlations.

[0111] Each orientation of the illuminating X-ray beam 214 relative to the surface normal of the semiconductor wafer 201 is described by rotating the wafer 201 relative to any two angles of the X-ray illuminating beam 214, or vice versa. In one example, the orientation may be described relative to a coordinate system fixed to the wafer. Figure 16 An X-ray illumination beam 214 is depicted, incident on wafer 201 with a specific orientation described by the incident angle θ and azimuth angle φ. A coordinate system XYZ is fixed to the metrology system (e.g., illumination beam 216), and a coordinate system X'Y'Z' is fixed to wafer 201. The Y-axis is aligned with the surface of wafer 201 in a plane. X and Z are not aligned with the surface of wafer 201. Z' is aligned with the axis normal to the surface of wafer 201, and X' and Y' are aligned with the surface of wafer 201 in a plane. Figure 16As depicted, the X-ray illumination beam 214 is aligned with the Z-axis and therefore lies within the XZ plane. The incident angle θ describes the orientation of the X-ray illumination beam 214 relative to the surface normal of the wafer in the XZ plane. Furthermore, the azimuth angle φ describes the orientation of the XZ plane relative to the X'Z' plane. Together, θ and φ uniquely define the orientation of the X-ray illumination beam 214 relative to the surface of the wafer 201.

[0112] In one aspect, the metrology tool 100 includes a wafer chuck 203 that permanently supports the wafer 201 and is coupled to a sample positioning system 240. The sample positioning system 240 is configured to actively position the sample 201 with six degrees of freedom relative to an illumination beam 214. In one example, a computing system 230 transmits a command signal (not shown) indicating the desired position of the sample 201 to the sample positioning system 240. In response, the sample positioning system 240 generates command signals to various actuators of the sample positioning system 240 to achieve the desired positioning of the sample 201.

[0113] In another aspect, the focusing optics of the RSAXS system project an image of the illumination source onto the sample under test with a reduction factor of at least 5 (i.e., a magnification factor of 0.2 or less). The RSAXS system described herein employs an SXR illumination source characterized by a source region of 20 micrometers or less (i.e., a source size of 20 micrometers or less). In some embodiments, focusing optics are used with a reduction factor of at least 5 (i.e., projecting an image of the source onto a wafer five times smaller than the source size) to project illumination onto a sample having an incident illumination spot size of four micrometers or less.

[0114] Figure 17 An embodiment of the RSAXS metering tool 300 is described in another embodiment. For example... Figure 17 The description states that system 300 can be used to perform RSAXS measurements on a measurement area 202 with a size of less than 1 to 2 micrometers. Figure 17 The same number of elements and references depicted in the text Figure 14 The elements described are the same. For example... Figure 17 As depicted, the focusing optics 211 is an elliptical optical element. However, the focusing optics 211 is arranged relative to the illumination source 210 and the sample 201 such that the distance A between the illumination source 210 and the focusing optics 211 is significantly greater than the distance B between the focusing optics 211 and the sample 201. In some embodiments, the A / B ratio is at least 5. In some embodiments, the A / B ratio is at least 10. This results in a reduction ratio of A / B times from the illumination source to the sample 201. In one embodiment, the size of the illumination source 210 is approximately 10 micrometers and the focusing optics 211 is arranged such that A / B is 10. In this embodiment, the size of the illumination spot projected onto the sample 201 is approximately 1 micrometer.

[0115] In some embodiments, the illumination source 210 is an LPP light source with a source size of 10 micrometers or less, and the focusing optics 211 has a reduction factor of approximately 10. This enables the RSAXS metrology tool 300 to focus the illumination light onto a metrology target with a size of 1 to 2 micrometers. By focusing the incident illumination light to an illumination spot size of 1 to 2 micrometers, the RSAXS metrology tool 300 achieves measurements of critical size targets and superimposed targets located within the die, rather than relying on larger metrology targets located in the wafer dicing area.

[0116] The ability to measure targets with dimensions of 1 to 2 micrometers reduces the wafer area dedicated to specific metrology targets. Furthermore, this capability enables direct measurement of the device structure rather than specific metrology targets. Measuring the device structure directly eliminates target-to-device deviation. This significantly improves measurement quality. Additionally, the measurement of targets within the die enables the characterization of parameter variations within the die. Exemplary parameters of concern include critical dimensions, stacking, and edge placement errors.

[0117] In some embodiments, the x-ray illumination source 210, focusing optics 211, slits 212 and 213, or any combination thereof, are maintained in the same atmospheric environment (e.g., a gas-flushed environment) as the sample 201. However, in some embodiments, the optical path lengths between and within any of these elements are long, and x-ray scattering in the air contributes noise to the image on the detector. Therefore, in some embodiments, the x-ray illumination source 210, focusing optics 211, and any of the slits 212 and 213 are maintained in a localized, vacuum environment. Figure 14 In the embodiment depicted, the illumination source 210, focusing optics 211, and slits 212 and 213 are maintained in a controlled environment (e.g., a vacuum) within a evacuated flight tube 217. The illumination beam 214 travels through window 220 at the end of the flight tube 217 before being incident on the sample 201.

[0118] Similarly, in some embodiments, the optical path length (i.e., the beam path) between sample 201 and detector 219 is long, and X-ray scattering in the air contributes noise to the image on the detector. Therefore, in a preferred embodiment, a large portion of the beam path length between sample 201 and detector 219 is maintained in a local vacuum environment separated from the sample (e.g., sample 201) by a vacuum window (e.g., vacuum window 224). In some embodiments, the X-ray detector 219 is maintained in a local vacuum environment with the same beam path length as between sample 201 and detector 219. For example, as... Figure 14The diagram depicts a vacuum chamber 223 maintaining a local vacuum environment around most of the beam path length between the detector 219 and the sample 201 and the detector 219.

[0119] In some other embodiments, the X-ray detector 219 is maintained in the same atmospheric environment (e.g., a gas-flushed environment) as the sample 201. This facilitates the removal of heat from the detector 219. However, in these embodiments, it is preferable to maintain the majority of the beam path length between the sample 201 and the detector 219 in a localized vacuum environment within a vacuum chamber.

[0120] In some embodiments, the entire optical system containing sample 201 is maintained in a vacuum. However, in general, the cost associated with maintaining sample 201 in a vacuum is high due to the complexity associated with the construction of sample positioning system 240.

[0121] In another aspect, the metrology tool 200 includes a computational system (e.g., computational system 230) configured to implement the beam control functionality as described herein. Figure 14 In the embodiments depicted, the computing system 230 is configured as a beam controller operable to control any illumination properties, such as the intensity, divergence, spot size, polarization, spectrum, and positioning of the incident illumination beam 214.

[0122] like Figure 14As described, computing system 230 is communicatively coupled to detector 219. Computing system 230 is configured to receive measurement data 235 from detector 219. In one example, measurement data 235 contains an indication of the measured response of the sample (i.e., the intensity of the diffraction order). Based on the distribution of the measured response on the surface of detector 219, computing system 230 determines the position and area of ​​illumination beam 214 incident on sample 201. In one example, computing system 230 applies pattern recognition technology to determine the position and area of ​​illumination beam 214 incident on sample 201 based on measurement data 235. In some examples, computing system 230 transmits command signal 236 to x-ray illumination source 210 to select the desired illumination wavelength. In some examples, computing system 230 transmits command signal 237 to actuator subsystem 215 to redirect x-ray emission to achieve the desired beam direction. In some instances, the computing system 230 transmits command signals 238 and 239 to beam shaping slits 212 and 213, respectively. This causes the beam shaping slits 212 and 213 to change the beam spot size and select the illumination wavelength, so that the incident illumination beam 214 reaches the sample 201 with the desired beam spot size, orientation, and wavelength. In one instance, command signals 238 and 239 cause actuators associated with slits 212 and 213 to change position to reshape the incident beam 214 to the desired shape and size and select the desired wavelength. In some other instances, the computing system 230 transmits command signals to the wafer positioning system 240 to position and orient the sample 201, so that the incident illumination beam 214 arrives with the desired position and angle relative to the sample 201.

[0123] In another aspect, RSAXS measurement data is used to generate an image of the measured structure based on the measured intensity of the detected diffraction order. In some embodiments, a generalized RSAXS response function model is used to describe scattering from a generalized electron density grid. This model is matched to the measured signal while constraining the modeled electron density in the grid to enforce continuity and sparse edges to provide a three-dimensional image of the sample.

[0124] While model-based geometric parameter inversion is preferred for critical dimension (CD) metrology based on RSAXS measurements, graphs of samples generated from the same RSAXS measurement data can be used to identify and correct model errors when the measured sample deviates from the assumptions of the geometric model.

[0125] In some instances, structural characteristics are compared between images and model-based geometric parameter inversion estimates derived from the same scattering measurement data. The differences are used to update the geometric model of the measured structure and improve measurement performance. The ability to converge on an accurate parameter measurement model is particularly important when measuring integrated circuits for controlling, monitoring, and debugging their manufacturing processes.

[0126] In some instances, the image is a two-dimensional (2-D) plot of electron density, absorption, complex refractive index, or a combination of these material properties. In some instances, the image is a three-dimensional (3-D) plot of electron density, absorption, complex refractive index, or a combination of these material properties. The plots are generated using relatively few physical constraints. In some instances, one or more parameters of interest, such as critical dimension (CD), sidewall angle (SWA), stacking, edge placement error, pitchwalk, etc., are estimated directly from the resulting plot. In some other instances, the plot can be used to debug wafer processes when the sample geometry or material deviates from the expected values ​​considered by the parametric structure model used for model-based CD measurements. In one instance, the difference between the plot and the representation of the structure predicted by the parametric structure model based on its measured parameters is used to update the parametric structure model and improve its measurement performance. Further details are described in U.S. Patent Publication No. 2015 / 0300965, the entire contents of which are incorporated herein by reference. Additional details are described in U.S. Patent Publication No. 2015 / 0117610, the entire contents of which are incorporated herein by reference.

[0127] It should be recognized that the various steps described throughout this disclosure may be performed by a single computer system 230 or alternatively by multiple computer systems 230. Furthermore, different subsystems of system 200 (e.g., sample positioning system 240) may include computer systems suitable for performing at least a portion of the steps described herein. Therefore, the foregoing description should not be construed as limiting the invention but is merely illustrative. Additionally, one or more computing systems 230 may be configured to perform any other steps of any method embodiment described herein.

[0128] Additionally, computer system 230 can be communicatively coupled to x-ray illumination source 210, beam shaping slits 212 and 213, focusing optics actuator system 215, sample positioning system 240, and detector 219 in any manner known in the art. For example, one or more computing systems 230 can be coupled to computing systems respectively associated with x-ray illumination source 210, beam shaping slits 212 and 213, focusing optics actuator system 215, sample positioning system 240, and detector 219. In another example, any of x-ray illumination source 210, beam shaping slits 212 and 213, focusing optics actuator system 215, sample positioning system 240, and detector 219 can be directly controlled by a single computer system coupled to computer system 230.

[0129] Computer system 230 can be configured to receive and / or acquire data or information from subsystems of the system (e.g., x-ray illumination source 210, beam shaping slits 212 and 213, focusing optics actuator system 215, sample positioning system 240, detector 219, and the like) via a transmission medium that may include wired and / or wireless components. In this manner, the transmission medium can be used as a data link between computer system 230 and other subsystems of system 200.

[0130] The computer system 230 of the metrology system 200 can be configured to receive and / or acquire data or information (e.g., measurement results, modeling inputs, modeling results, etc.) from other systems via a transmission medium that may include wired and / or wireless components. In this manner, the transmission medium can serve as a data link between the computer system 230 and other systems (e.g., on-board metrology system 200, external memory, or external systems). For example, the computer system 230 can be configured to receive measurement data (e.g., signal 235) from a storage medium (e.g., memory 232) via a data link. For example, spectral results obtained using detector 219 can be stored in a permanent or semi-permanent memory device (e.g., memory 232). In this respect, measurement results can be imported from on-board memory or from an external memory system. Furthermore, the computer system 230 can transmit data to other systems via the transmission medium. For example, sample parameter values ​​determined by the computer system 230 can be stored in a permanent or semi-permanent memory device (e.g., memory 232). In this respect, measurement results can be exported to another system.

[0131] The computing system 230 may include (but is not limited to) a personal computer system, a mainframe computer system, a workstation, a graphics computer, a parallel processor, or any other device known in the art. Generally, the term "computing system" can be broadly defined to encompass any device having one or more processors that execute instructions from memory media.

[0132] Program instructions 234 for implementing methods such as those described herein can be transmitted via a transmission medium such as a wire, cable, or wireless transmission link. For example, such as... Figure 14 As described, program instructions stored in memory 232 are transferred to processor 231 via bus 233. Program instructions 234 are stored in computer-readable media (e.g., memory 232). Exemplary computer-readable media include read-only memory, random access memory, magnetic disk or optical disk or magnetic tape.

[0133] In some embodiments, scattering measurements as described herein are implemented as part of a manufacturing process tool. Examples of manufacturing process tools include (but are not limited to) photolithography tools, film deposition tools, implantation tools, and etching tools. In this manner, the results of RSAXS analysis are used to control the manufacturing process. In one instance, RSAXS measurement data collected from one or more targets are sent to the manufacturing process tool. The RSAXS measurement data are analyzed as described herein, and the results are used to adjust the operation of the manufacturing process tool to reduce errors in the fabrication of semiconductor structures.

[0134] Scattering measurements, as described herein, can be used to determine the properties of various semiconductor structures. Exemplary structures include (but are not limited to) FinFETs, low-dimensional structures (e.g., nanowires or graphene), sub-10nm structures, photolithographic structures, through-substrate vias (TSVs), memory structures (e.g., DRAM, DRAM 4F2, FLASH, MRAM), and high aspect ratio memory structures. Exemplary structure properties include (but are not limited to) geometric parameters (e.g., line edge roughness, linewidth roughness, aperture diameter, aperture density, sidewall angles, profile, critical dimensions, spacing, thickness, stacking) and material parameters (e.g., electron density, composition, die structure, morphology, stress, strain, and element identification). In some embodiments, the metrological target is a periodic structure. In some other embodiments, the metrological target is a non-periodic structure.

[0135] Generally, an X-ray-based system employing a multilayer optical element with integrated optical filters, as described herein, may also include one or more independent transmittance-based optical filters to enhance the suppression of contamination wavelength bands.

[0136] Generally, integrated optical filters can be positioned on any optical element of an X-ray-based system. While the addition of integrated optical filters to reflective, multilayered X-ray optics is described in detail above, generally, integrated optical filters can be placed on any optical element in the optical path of an X-ray-based system. In some embodiments, the integrated optical filter is fabricated on a detector entrance window (e.g., a camera entrance window). In some embodiments, the integrated optical filter is fabricated on an exit window of an X-ray illumination source or on a focusing cavity of an X-ray illumination source. In this way, depending on the type of optics on which the integrated optical filter is fabricated, the integrated optical filter can operate in transmission mode (i.e., suppressing selected wavelengths from radiation from traveling through the integrated optical filter in a single pass) or in reflection mode (i.e., suppressing selected wavelengths from radiation from traveling through the integrated optical filter in two passes).

[0137] In one example, one or more integrated optical filters are incorporated into the optical path of a soft X-ray-based metrology system employing a laser-generated plasma (LPP) source. Typically, LPP sources generate harmonics in the IR and visible wavelength ranges. Additionally, it is desirable to suppress unwanted EUV wavelengths. In one example, the integrated optical filter is fabricated on an illumination source window, a detector window, or both to suppress IR and visible wavelengths. Alternatively, another integrated optical filter is fabricated as having multilayered, reflective X-ray focusing optics to suppress unwanted EUV wavelengths, as described above.

[0138] In some instances, the RSAXS measurement system, as described herein, is used to perform measurements of critical dimensions, thicknesses, stacking, and material properties of high aspect ratio semiconductor structures that include (but are not limited to) spin-transfer torque random access memory (STT-RAM), three-dimensional NAND memory (3D-NAND) or vertical NAND memory (V-NAND), dynamic random access memory (DRAM), three-dimensional FLASH memory (3D-FLASH), resistive random access memory (Re-RAM), and phase-change random access memory (PC-RAM).

[0139] 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 corner, grating height, etc.), any critical dimension between two or more structures (e.g., distance between two structures), and displacement between two or more structures (e.g., superposition displacement between superimposed grating structures, etc.). Structures may include three-dimensional structures, patterned structures, superimposed structures, etc.

[0140] As described in this document, the terms “critical dimension application” or “critical dimension measurement application” include any critical dimension measurement.

[0141] As described herein, the term "metrology system" includes any system used at least in part for characterizing samples in any respect, including critical dimension applications and overlay metrology applications. However, such terminology in the art does not limit the scope of the term "metrology system" as described herein. Furthermore, the metrology systems described herein can be configured to measure patterned wafers and / or unpatterned wafers. Metrology systems can be configured as LED inspection tools, edge inspection tools, back-side inspection tools, macroscopic inspection tools, or multi-mode inspection tools (involving data from one or more platforms simultaneously), and any other metrology or inspection tool that benefits from the measurement techniques described herein.

[0142] Various embodiments are described herein with respect to semiconductor processing systems (e.g., inspection systems or lithography systems) that can be used to process samples. The term "sample" is used herein to refer to a wafer, reticle, or any other sample that can be processed by means known in the art (e.g., printing or inspecting for defects).

[0143] As used herein, the term "wafer" generally refers to a substrate formed of semiconductor or non-semiconductor materials. Examples include (but are not limited to) single-crystal silicon, gallium arsenide, and indium phosphide. Such substrates are commonly found and / or processed in semiconductor manufacturing facilities. In some cases, a wafer may consist only of a substrate (i.e., a bare wafer). Alternatively, a wafer may contain one or more layers of different materials formed on the substrate. The one or more layers formed on the wafer may be "patterned" or "unpatterned." For example, a wafer may contain multiple bare wafers with repeatable pattern features.

[0144] A "reticle" can be a reticle at any stage of 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 areas formed thereon and arranged in a pattern. The substrate may comprise, for example, a glass material, such as amorphous SiO2. The reticle can be placed over a wafer coated with resist during the exposure step of a photolithography process, such that the pattern on the reticle can be transferred to the resist.

[0145] One or more layers formed on a wafer may be patterned or unpatterned. For example, a wafer may comprise multiple dies, each having repeatable patternable features. The formation and processing of such material layers can ultimately result in a finished device. Many different types of devices can be formed on a wafer, and the term wafer, as used herein, is intended to encompass wafers on which any type of device known in the art is manufactured.

[0146] In one or more exemplary embodiments, the functionality may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functionality may be stored as one or more instructions or program code on or transmitted via a computer-readable medium. Computer-readable media includes both computer storage media and communication media (including any media that facilitates the transfer of a computer program from one location to another). Storage media may be any available media accessible by a general-purpose computer or a specialized computer. By way of example and without limitation, such computer-readable media may include RAM, ROM, EEPROM, CD-ROM or other optical disc storage, disk storage or other magnetic storage devices, or any other media that can be used to carry or store desired program code elements in the form of instructions or data structures and is accessible by a general-purpose computer or a specialized computer or a general-purpose or specialized processor. Furthermore, any connection is appropriately referred to as computer-readable media. For example, if software is transmitted from a website, server, or other remote source using coaxial cable, optical fiber, twisted pair, digital subscriber line (DSL), or wireless technology (such as infrared, radio, and microwave), then coaxial cable, optical fiber, twisted pair, DSL, or wireless technology (such as infrared, radio, and microwave) is included in the definition of media. As used herein, disks and optical discs include optical discs (CDs), laser discs, XRF discs, digital versatile discs (DVDs), floppy disks, and Blu-ray discs, wherein disks typically magnetically reproduce data while optical discs optically reproduce data using lasers. The above combinations should also be included within the scope of computer-readable media.

[0147] While certain specific embodiments have been described above for illustrative purposes, the teachings of this patent file are of general applicability and are not limited to the specific embodiments described above. Therefore, various modifications, adaptations, and combinations of the features of the described embodiments can be practiced without departing from the scope of the invention as set forth in the claims.

Claims

1. A multilayer X-ray reflecting optical device, comprising: Substrate; A multilayer X-ray reflecting structure is disposed above the substrate; and An integrated optical filter is disposed above the substrate, the integrated optical filter comprising a silicon dioxide layer disposed on top of the multilayer X-ray reflective structure and a tellurium layer disposed on top of the silicon dioxide layer, the integrated optical filter being configured to absorb radiation having wavelengths higher than 10 nanometers.

2. The multilayer X-ray reflecting optical device according to claim 1, wherein the integrated optical filter comprises a single radiation-absorbing material layer.

3. The multilayer X-ray reflecting optical device according to claim 1, wherein the integrated optical filter comprises two or more layers of different radiation absorbing materials.

4. The multilayer X-ray reflecting optical device according to claim 1, wherein the integrated optical filter is disposed above the multilayer reflecting structure.

5. The multilayer X-ray reflecting optical device according to claim 1, wherein the integrated optical filter is disposed between the substrate and the multilayer X-ray reflecting structure.

6. The multilayer X-ray reflecting optical device according to claim 1, further comprising: A diffusion barrier layer is disposed between the integrated optical filter and the multilayer X-ray reflective structure, between the substrate and the multilayer X-ray reflective structure, or above the integrated optical filter.

7. The multilayer X-ray reflecting optical device according to claim 1, wherein the optical surface of the substrate is curved.

8. The multilayer X-ray reflecting optical device according to claim 1, wherein the thickness of the integrated optical filter varies depending on its position on the optical surface of the substrate.

9. The multilayer X-ray reflecting optical device according to claim 1, wherein the multilayer X-ray reflecting structure reflects incoming light within a wavelength range.

10. A measurement system comprising: An X-ray illumination source configured to produce soft X-ray radiation at multiple illumination wavelengths, including a desired photon energy range from 80 electron volts to 3,000 electron volts and a non-desired photon energy range below 80 electron volts. An X-ray detector configured to detect the amount of X-ray radiation scattered from a semiconductor wafer in response to the amount of soft X-ray radiation; A plurality of X-ray optical elements, each having at least one optical surface disposed in an optical path between the X-ray illumination source and the detector; An integrated optical filter is fabricated above the optical surface of at least one of the plurality of x-ray optical elements, the integrated optical filter comprising one or more material layers that absorb radiation outside the desired photon energy range and transmit radiation within the desired photon energy range. and A computing system configured to determine the values ​​of parameters of interest for a structure characterized on the semiconductor wafer based on the detected amount of X-ray radiation.

11. The metrology system according to claim 10, wherein the metrology system is a soft X-ray reflectance measurement system.

12. The metrology system of claim 11, wherein the soft X-ray reflectance measurement system operates in grazing incidence mode.

13. The metrology system of claim 11, wherein the metrology system operates in imaging mode.

14. The metrology system of claim 10, wherein the integrated optical filter is disposed above a multilayer x-ray reflective structure fabricated above the optical surface of at least one of the plurality of x-ray optical elements.

15. The metering system according to claim 14, further comprising: A diffusion barrier layer is disposed between one or more material layers of the integrated optical filter and the multilayer X-ray reflective structure, between the optical surface and the multilayer X-ray reflective structure, or above one or more material layers of the integrated optical filter.

16. The metrology system of claim 10, wherein the optical surface of at least one of the plurality of x-ray optical elements is curved.

17. The metrology system of claim 10, wherein the thickness of the integrated optical filter varies depending on its position on the optical surface of at least one of the plurality of x-ray optical elements.

18. The metering system according to claim 10, further comprising: An independent optical filter is disposed in the optical path between the x-ray illumination source and the detector.

19. An X-ray-based system comprising: An X-ray illumination source configured to produce X-ray radiation including a desired wavelength range and a non-desired wavelength range different from the desired wavelength range; One or more X-ray optical elements, each having at least one optical surface disposed in an optical path between the X-ray illumination source and the sample to be processed; and An integrated optical filter is fabricated on the optical surface of at least one of the one or more x-ray optical elements, the integrated optical filter comprising one or more material layers that absorb radiation in the off-desired wavelength range and transmit radiation in the desired wavelength range.

20. The x-ray-based system of claim 19, wherein the integrated optical filter is disposed above a multilayer x-ray reflective structure fabricated above the optical surface of at least one of the plurality of x-ray optical elements.

21. The X-ray-based system of claim 20, further comprising: A diffusion barrier layer is disposed between one or more material layers of the integrated optical filter and the multilayer X-ray reflective structure, between the optical surface and the multilayer X-ray reflective structure, or above one or more material layers of the integrated optical filter.

22. The x-ray-based system of claim 19, wherein the optical surface of at least one of the one or more x-ray optical elements is curved.

23. The x-ray-based system of claim 19, wherein the thickness of the integrated optical filter varies depending on its position on the optical surface of at least one of the one or more x-ray optical elements.

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