Transmission-type small-angle X-ray scattering metering system and method

Abstract

To provide techniques for characterizing dimensions and material properties of semiconductor devices by transmission small-angle x-ray scatterometry (TSAXS) systems.SOLUTION: An x-ray beam is focused closer to a wafer surface for relatively small targets and closer to a detector for relatively large targets. A high resolution detector with a small point spread function (PSF) is employed to mitigate detector PSF limits on achievable Q resolution. The detector locates an incident photon with sub-pixel accuracy by determining the centroid of a cloud of electrons stimulated by a photon conversion event. The detector resolves one or more x-ray photon energies in addition to location of incidence.SELECTED DRAWING: Figure 1

Description

[Technical Field] 【0001】 The embodiments described relate to weighing systems and methods, and more specifically to methods and systems with improved measurement accuracy. [Background technology] 【0002】 (Cross-reference to related applications) This patent application is based on U.S. Provisional Patent Application No. 62 / 485497 dated April 14, 2017, and claims priority under Section 119 of the U.S. Patent Act. Therefore, by reference to this application, the entire subject matter of that application is incorporated into this application. 【0003】 Semiconductor devices, such as logic devices and memory devices, are typically manufactured by applying a series of processing steps to a sample. These processing steps create various features (external characteristics) and structural hierarchies of these semiconductor devices. For example, lithography is one of the semiconductor manufacturing processes that involves the generation of patterns on a semiconductor wafer. Further examples of semiconductor manufacturing processes, though not limited to these, include chemical mechanical polishing, etching, deposition, and ion implantation. It is preferable to create multiple semiconductor devices on a single semiconductor wafer and then separate them into individual semiconductor devices. 【0004】 Metrology processes are used in various stages of semiconductor manufacturing, enabling the detection of defects on wafers and promoting yield improvement. Numerous metrology-based technologies, such as scatterometry and reflectometry equipment and related analytical algorithms, are widely used, leading to the elucidation of parameters of nanoscale structures, including critical dimensions, film thickness, and composition. 【0005】 Scatterometry limit dimension (SCD) measurements have long been performed on targets consisting of thin films and / or repeating periodic structures. During device manufacturing, these films and periodic structures typically embody the actual device geometry and material structure or intermediate design. Devices (e.g., logic devices and memory devices) are moving towards smaller nanometer-scale dimensions, making characterization increasingly difficult. The incorporation of complex three-dimensional geometry and materials with diverse physical properties into devices contributes to this difficulty. For example, modern memory structures often have high aspect ratio three-dimensional structures, making it difficult to penetrate optical radiation to the lower layers. While infrared to visible light used in optical metrology tools can penetrate numerous translucent material layers, longer wavelengths that achieve good penetration depth are not sufficiently sensitive to small anomalies. In addition, the number of parameters required to characterize complex structures (e.g., FinFETs) is increasing, leading to increased parameter correlations. As a result, it often becomes difficult to reliably isolate parameters describing the target's characteristics from available measurement results. 【0006】 For example, longer wavelengths (e.g., near-infrared) are used in an attempt to overcome the penetration problem associated with 3D-FLASH® devices, which utilize polysilicon as one of the materials arranged alternately within the stack. However, due to the mirror-like structure inherent in 3D-FLASH®, the light intensity inherently decreases as illumination propagates deeper within the film stack. This causes sensitivity loss and correlation problems in the deeper regions. Under this scenario, SCD can only successfully extract a small number of quantifiable dimensions with high sensitivity and low correlation. 【0007】 Furthermore, for example, the use of opaque, high-k materials is increasing in recent semiconductor structures. Optical radiation is often unable to penetrate layers made of these materials. As a result, measurements using thin-film scatterometry tools, such as ellipsometers and reflectometers, are becoming increasingly difficult. 【0008】 In light of these difficulties, more complex optical metrology tools have been developed. For example, tools have been developed that offer multiple illumination angles, shorter illumination wavelengths, wider illumination wavelength ranges, and more complete information acquisition from reflected signals (e.g., measuring multiple Müller matrix elements in addition to more conventional reflectance and ellipsometry signals). However, these methods have not reliably overcome the fundamental difficulties associated with the measurement of many advanced targets (e.g., complex 3D structures, small structures less than 10 nm, structures using opaque materials) and measurement applications (e.g., line edge roughness measurement and line width roughness measurement). 【0009】 Atomic force microscopes (AFM) and scanning tunneling microscopes (STM) can achieve atomic resolution, but they can only explore the surface of a sample. In addition, AFM and STM microscopes require long scanning times. Scanning electron microscopes (SEM) can achieve moderate resolution, but they cannot penetrate to a sufficient depth into the structure. Therefore, they cannot adequately characterize high aspect ratio pores. Furthermore, the unavoidable sample charging negatively affects imaging performance. X-ray reflectometers also suffer from penetration problems, which limits their effectiveness when measuring high aspect ratio structures. 【0010】 To overcome the problem of penetration depth, conventional imaging techniques such as TEM and SEM are often used in conjunction with destructive sample preparation techniques such as focused ion beam (FIB) machining, ion milling, blanket etching, and selective etching. For example, transmission electron microscopy (TEM) achieves high resolution levels and allows exploration to arbitrary depths, but it requires destructive fragmentation of the sample. By repeating material removal and measurement several times, information necessary to measure limiting metrological parameters across the entire three-dimensional structure is generally obtained. However, these techniques require sample destruction and long processing times. The cumbersome and time-consuming nature of these types of measurements introduces significant inaccuracies due to drift in the etching and metrological processes. In addition, these techniques require numerous iterations, which introduces registration errors. 【0011】 Transmission small-angle X-ray scatterometry (T-SAXS) systems, which employ hard X-ray energy levels (>15 keV) photons, have the potential to address challenging measurement applications. Various aspects of the application of SAXS technology to limit dimension measurement (CD-SAXS) and overlay measurement (OVL-SAXS) are described in: 1) Patent document 1 titled "High-brightness X-ray metrology" by Zhuang and Fielden; 2) Patent document 2 titled "Model Building And Analysis Engine For Combined X-Ray And Optical Metrology" by Bakeman, Shchegrov, Zhao and Tan; 3) Patent document 3 titled "Methods and Apparatus For Measuring Semiconductor Device Overlay Using X-Ray Metrology" by Veldman, Bakeman, Shchegrov and Mieher; and 4) "Measurement System Optimization For X-Ray Based Patent documents 4 and 5, titled "Metrology" under the names of Hench, Shchegrov, and Bakeman; Patent document 5, titled "X-ray Metrology For High Aspect Ratio Structures" under the names of Dziura, Gellineau, and Shchegrov; and 6), titled "Full Beam Metrology for X-Ray Scatterometry Systems" under the names of Gellineau, Dziura, Hench, Veldman, and Zalubovsky, are used to describe this, and the entire contents of each of these documents will be incorporated into this application by reference.The above-mentioned patents and applications have been assigned to KLA-Tencor Corporation, located in Milpitas, California, USA. In addition, Patent Document 6, titled "X-ray scatterometry apparatus" and attributed to Mazor et al., describes various aspects of the application of SAXS technology to semiconductor structures, and its entirety will be incorporated into this application by reference. 【0012】 SAXS is also applied to material characterization and other non-semiconductor related applications. Examples of its systems are commercialized by several companies, such as Xenocs SAS (www.xenocs.com), Bruker Corporation (www.bruker.com), and Rigaku Corporation (www.rigaku.com / en). Both Bruker and Rigaku offer small-angle and wide-angle X-ray scatterometry systems, named "Nanostar®" and "Nanopix®," respectively. In these systems, the sample-to-detector distance is adjustable. 【0013】 Research on CD-SAXS metricing of semiconductor structures is documented in scientific literature. Most research groups employ high-brightness synchrotron X-ray sources, but these are unsuitable for use in semiconductor manufacturing facilities due to their enormous size, high cost, etc. An example of such a system is described in Non-Patent Document 1, and the entire contents of that document will be incorporated into this application by reference. More recently, a group at the National Institute of Standards and Technology (NIST) has started research employing a compact and bright X-ray source similar to that described in Patent Document 1. This research is described in Non-Patent Document 2, and the entire contents of that document will be incorporated into this application by reference. 【0014】 In the SAXS system, several types of detectors are adopted, such as hybrid pixel photon counting detectors, charge integrating pixel array detectors, gas phase avalanche detectors, etc. The pixel sizes of available detectors range from about 50 μm to about 200 μm. A prototype with 25-μm pixels is currently under development. 【0015】 A major drawback in all conventional SAXS architectures is that the equipment required to measure typical semiconductor structures is quite large. To resolve the diffraction image with a detector, a fine angular resolution is required. Currently, that resolution is achieved by increasing the length of the equipment. 【0016】 As an example, by appropriately configuring the "Nanostar (trademark)" system manufactured by Bruker, the specimen-to-instrument distance can be made 1070 mm, the pixel size of the detector can be made 68 μm, and the q-space resolution can be made 5×10 -3 angstroms -1 . 【0017】 In semiconductor manufacturing equipment, throughput cannot be increased unless metrology tools and inspection tools are made to conform to a relatively small footprint size, thereby enhancing the utilization of the expensive clean room space and allowing more tools to be accommodated. Therefore, the tool length of the current SAXS system must be reduced from the current level to a level useful in actual semiconductor manufacturing equipment. 【Prior Art Documents】 【Patent Documents】 【0018】 【Patent Document 1】 U.S. Patent No. 7,929,667 【Patent Document 2】 U.S. Patent Application Publication No. 2014 / 0019097 【Patent Document 3】 U.S. Patent Application Publication No. 2015 / 0117610 【Patent Document 4】 U.S. Patent Application Publication No. 2016 / 0202193 [Patent Document 5] U.S. Patent Application Publication No. 2017 / 0167862 [Patent Document 6] U.S. Patent No. 9606073 [Patent Document 7] U.S. Patent Application Publication No. 2015 / 0110249 [Patent Document 8] U.S. Patent No. 7826071 [Patent Document 9] U.S. Patent No. 7478019 [Patent Document 10] U.S. Patent Application Publication No. 2015 / 0300965 [Patent Document 11] U.S. Patent Application Publication No. 2013 / 0304424 [Patent Document 12] U.S. Patent Application Publication No. 2016 / 0320319 [Non-Patent Document] 【0019】 [Non-Patent Document 1] "Intercomparison between optical and x-ray scatterometry measurements of FinFET structures" by Lemaillet, Germer, Kline et al., Proc. SPIE, v.8681, p. 86810Q (2013) [Non-Patent Document 2] "X-ray scattering critical dimensional metrology using a compact x-ray source for next generation semiconductor devices," J. Micro / Nanolith. MEMS MOEMS 16(1), 014001 (Jan-Mar 2017) [Summary of the Invention] [Problems that the invention aims to solve] 【0020】 In summary, current CD / OVL-SAXS systems are unsuitable for use in production semiconductor manufacturing facilities due to their large footprint (tool length), low resolution, and reliance on angular order isolation. To further improve device performance, the semiconductor industry continues to focus on vertical integration rather than lateral scaling. Therefore, accurate measurement of complex three-dimensional structures is crucial for ensuring feasibility and sustainable scaling improvements. Metrology-related challenges that will emerge in future metrology applications include further refinement of resolution requirements, multi-parameter correlations, increasing complexity of geometric structures such as high aspect ratio structures, and the increased use of opaque materials. Therefore, improved X-ray scatterometry measurement methods and systems, particularly those with improved resolution and smaller footprints (tool lengths), are desired. [Means for solving the problem] 【0021】 This application describes a method and system for determining the dimensions and material properties of semiconductor devices using a transmission small-angle X-ray scatterometry (TSAXS) system having a relatively small tool footprint (tool length). According to the method and system described herein, a Q-space resolution suitable for the measurement of semiconductor structures can be achieved with a shortened optical path length. 【0022】 In one embodiment, the TSAXS measurement system employs hard X-ray illumination over a relatively short optical path length (e.g., less than 3 m from the illumination source to the detector), thereby enabling measurement of targets ranging from relatively small dimensions (e.g., approximately 50 nm) to relatively large dimensions (e.g., up to 10 μm). 【0023】 In a further embodiment, when illuminating a sample with the TSAXS measurement system, the X-ray beam is focused to a point less than 200 mm in front of the wafer surface, either on the measurement target, the detector surface, or between the wafer surface and the detector surface, thereby reducing the optical focus limitations on the achievable Q resolution. Generally, in metrology applications involving relatively small targets that must be illuminated with the smallest possible illumination spot size, the X-ray beam is focused closer to the wafer surface. In metrology applications involving relatively large targets where high resolution and a strong photon flux are desirable, the X-ray beam is focused closer to the detector. 【0024】 In other further embodiments, the TSAXS measurement system is equipped with a high-resolution detector having a small PSF, thereby reducing the detector PSF limitation on the achievable Q resolution. A high-resolution detector is useful when the wafer-to-detector distance D is reduced to a relatively small value (e.g., less than 1 m), regardless of where the optical focus is located relative to the wafer and detector. 【0025】 In another embodiment, the position of the center of mass (center of gravity) of the electron cloud induced by the photon conversion event is calculated by the detector. The position of the incident photon can be determined with sub-pixel accuracy from the position of the center of mass. This effectively reduces the pixel size and achieves a Q resolution that exceeds the geometric limit. The sub-pixel spatial interpolation described in this application is desirable for TSAXS measurements of semiconductor structures at wafer-to-detector distances of less than 1 m. 【0026】 In some embodiments, a TSAXS system with a relatively short optical path length is configured so that a horizontal optical path is incident on a vertically positioned wafer (i.e., the normal to the wafer surface is approximately perpendicular to the gravity vector). On the other hand, in some other embodiments, a TSAXS system with a relatively short optical path length is configured so that a vertical optical path is incident on a horizontally positioned wafer (i.e., the normal to the wafer surface is approximately parallel to the gravity vector). Orienting the beamline vertically allows for a smaller tool footprint and simplifies wafer handling. 【0027】 In other further embodiments, the X-ray detector resolves one or more X-ray photon energies, generating signals for each X-ray energy component that characterize the sample. In this way, the X-ray photon interaction in the detector is discriminated by energy in addition to pixel position and count value. In some embodiments, the X-ray photon interaction is discriminated by comparing the energy of the X-ray photon interaction with a desired upper threshold and a desired lower threshold. 【0028】 In other embodiments, the TSAXS system is configured to measure a target based on orders that are spatially separated along a certain direction but overlap along a direction perpendicular to that direction. In some of these embodiments, the values ​​of one or more parameters of interest are determined along the direction in which their diffraction orders are spatially separated. Thereafter, these parameter values ​​are used to determine the values ​​of one or more parameters of interest based on the overlapping orders. 【0029】 In other embodiments, the slit of the beam shaping slit mechanism is positioned close to the sample under measurement, thereby minimizing the expansion of the incident beam spot size due to beam divergence, which is determined by the finite size of the light source. For example, when the X-ray source size is 10 μm and the distance between the beam shaping slit and the sample 101 is 25 mm, the beam spot size expansion due to shadows caused by the finite size of the light source is approximately 1 μm. In other examples, the beam shaping slit is positioned less than 100 mm from the sample, thereby controlling beam divergence. 【0030】 In other further embodiments, the characteristics of a sample (e.g., structural parameter values) are determined using a T-SAXS system based on one or more diffraction orders of scattered light. 【0031】 The above is a summary and therefore contains simplifications, generalizations, and omissions of details; and as will be apparent to those skilled in the art, this summary is purely illustrative and not limiting in any way. Other aspects, original features, and advantages of the apparatus and / or process described herein will be revealed in the non-limiting detailed description provided herein. [Brief explanation of the drawing] 【0032】 [Figure 1] This figure shows a weighing system 100 configured to perform X-ray scatterometry measurement as described in this application. [Figure 2] This diagram shows the slits in the beam shaping slit mechanism, which are positioned so as not to obstruct the incoming beam. [Figure 3] This diagram shows the slits in the beam shaping slit mechanism, which are positioned to block a portion of the incoming beam. [Figure 4] This diagram shows an X-ray illumination beam incident on a wafer in a specific orientation described by angles φ and θ. [Figure 5] This diagram shows a metering system 100 configured such that the focal point of the X-ray optical system is located on or near the detector surface. [Figure 6] This figure shows an image 171 of the scattering order measured by a weighing system, for example, weighing system 100. [Figure 7] This figure shows the image 172 of the scattering order measured by a weighing system, for example, weighing system 100. [Figure 8] This figure shows plot 173 of the intensity profile related to cross-section C of image 172 shown in Figure 7. [Figure 9] This diagram shows the components of the weighing system 100 housed in a vacuum environment separate from the sample being measured. [Figure 10] This figure shows a model building and analysis engine 150 configured to decompose sample parameter values ​​based on X-ray scatterometry data in accordance with the methods described in this application. [Figure 11A]This is an isometric view of a typical 3D-FLASH® memory device 190 used for measurement in accordance with the procedure described in this application. [Figure 11B] This is a top view of a typical 3D-FLASH® memory device 190 used for measurement in accordance with the procedure described in this application. [Figure 11C] This is a cross-sectional view of a typical 3D-FLASH® memory device 190 subjected to measurement in accordance with the procedure described in this application. [Figure 12] This flowchart illustrates 300 examples of a structural measurement method based on small-footprint X-ray scatterometry measurement as described in this application. [Modes for carrying out the invention] 【0033】 The following provides a detailed reference to the background examples and several embodiments of the invention, which are illustrated in the attached drawings. 【0034】 This application describes a method and system for determining the dimensions and material properties of semiconductor devices using a transmission small-angle X-ray scatterometry (TSAXS) system with a relatively small tool footprint. By employing this system and technology, structural and material properties related to different semiconductor manufacturing processes can be measured. To some extent, but not limited to these examples, the limit dimensions, thickness, overlay, and material properties of high aspect ratio semiconductor structures, including spin-transfer-reversal 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), can be measured using TSAXS. 【0035】 The use of high-brightness TSAXS enables high-flux X-ray radiation penetration into opaque areas of the target. Examples of geometric parameters measurable using X-ray scatterometry include pore size, pore density, line edge roughness, line width roughness, sidewall angle, profile, critical dimensions, overlay, edge placement error, and pitch. An example of a measurable material parameter is electron density. According to several examples, X-ray scatterometry can be used to measure small features less than 50 nm, and to measure advanced semiconductor structures such as STT-RAM, V-NAND®, DRAM, PC-RAM, and Re-RAM, when geometric and material parameter measurements are required. 【0036】 Figure 1 shows an embodiment of a T-SAXS weighing tool 100 for measuring the properties of a sample in at least one novel configuration. Using the system 100 shown in Figure 1, the inspection area 102 of the sample 101 can be illuminated by an illumination beam spot, and T-SAXS measurement can be performed on that area. 【0037】 The weighing tool 100 in the illustrated embodiment has an X-ray illumination source 110 configured to generate X-ray radiation suitable for T-SAXS measurement. In some embodiments, the X-ray illumination system 110 is configured to generate wavelengths of 0.01 nm to 1 nm. Generally, any suitable high-brightness X-ray illumination source capable of generating high-brightness X-rays at a luminous flux level sufficient to achieve high-throughput inline weighing can be considered for supplying X-ray illumination for T-SAXS measurement. In some embodiments, the X-ray source has a tunable monochromator, and the wavelength of the X-ray radiation supplied from the X-ray source can be selected from several options. 【0038】 In some embodiments, one or more X-ray sources emitting photon energies greater than 15 keV are employed so that light of wavelengths sufficient to penetrate the entire device and the wafer substrate is reliably supplied by the X-ray sources. In non-limiting examples, particle accelerator sources, liquid anode sources, rotating anode sources, stationary solid anode sources, microfocus sources, microfocus rotating anode sources, plasma sources, and inverse Compton sources can all be employed as X-ray sources 110. For example, an inverse Compton source available from Lyncan Technologies, Inc. in Palo Alto, California, USA, can be considered. Inverse Compton sources have the additional advantage of being able to generate X-rays over a certain photon energy range and allowing selection of several wavelengths for the X-ray radiation supplied from their own X-ray source. 【0039】 Examples of X-ray sources include electron beam sources configured to induce X-ray radiation by firing at a solid or liquid target. A method and system for generating high-brightness liquid metal X-ray illumination is described in Patent Document 1 dated April 19, 2011, under the name of KLA-Tencor Corp., and its entirety will be incorporated into this application by reference. 【0040】 The X-ray radiation emitted by the X-ray illumination source 110 extends over an illumination source area having a finite lateral dimension (i.e., a non-zero dimension perpendicular to the beam axis). The focusing optical system 111 focuses the illumination source radiation onto a metering target located on the sample 101. Because the lateral dimension of the illumination source is finite, a finite-sized spot 102 is produced on the target, and its spread is determined by the rays 117 coming from the edge of the illumination source. In some embodiments, the focusing optical system 111 has an elliptical focusing optical element. 【0041】 A beam divergence control slit 112 is located in the beam path between the focusing optical system 111 and the beam shaping slit mechanism 120. The beam divergence control slit 112 limits the divergence of the illumination supplied to the sample under measurement. An additional intermediate slit 113 is located in the beam path between the beam divergence control slit 112 and the beam shaping slit mechanism 120. The intermediate slit 113 performs further beam shaping. However, the intermediate slit 113 is generally optional. 【0042】 A beam shaping slit mechanism 120 is located in the beam path immediately before the sample 101. In one embodiment, the slit of the beam shaping slit mechanism 120 is positioned close to the sample 101, thereby minimizing the expansion of the incident beam spot size due to the beam divergence being determined by the finite size of the light source. For example, when the X-ray source size is 10 μm and the distance between the beam shaping slit and the sample 101 is 25 mm, the beam spot size expansion due to shadows caused by the finite size of the light source is approximately 1 μm. In other examples, the beam shaping slit is positioned less than 100 mm from the sample 101, thereby controlling the beam divergence. 【0043】 In some embodiments, the beam shaping slit mechanism 120 has a plurality of independently driven beam shaping slits. In one embodiment, the beam shaping slit mechanism 120 has four independently driven beam shaping slits. These four beam shaping slits effectively block a portion of the incoming beam 115 to generate an illumination beam 116 having a box-shaped illumination cross section. 【0044】 Figures 2 and 3 show two different end-face appearances of the beam shaping slit mechanism 120 shown in Figure 1. In the depictions in Figures 2 and 3, the beam axis is assumed to be perpendicular to the plane of the paper. The incoming beam 115 shown in Figure 2 has a large cross-section. In some embodiments, the diameter of the incoming beam 115 is approximately 1 mm. Furthermore, there is an uncertainty of approximately 3 mm in the position of the incoming beam 115 within the beam shaping slits 126-129 due to beam directionality errors. To accommodate the size of the incoming beam and its beam position uncertainty, the length L of each slit is set to approximately 6 mm. As shown in Figure 2, each slit can be moved in a direction perpendicular to the beam axis. In the depiction in Figure 2, the slits 126-129 are located at the maximum distance from the beam axis (i.e., the slits are fully open and do not restrict the passage of light within the beam shaping slit mechanism 120). 【0045】 The slits 126-129 of the beam shaping slit mechanism 120 shown in Figure 3 are positioned to block a portion of the incoming beam 115, so that the outgoing beam 116 supplied to the sample under measurement is small in size and has a clear shape. As shown in Figure 3, each of the slits 126-129 is moved inward toward the beam axis to achieve the desired outgoing beam shape. 【0046】 Slits 126-129 are constructed of materials that suppress scattering and effectively block incident radiation. Examples of materials include single-crystal materials such as germanium, gallium arsenide, and indium phosphide. Typically, to minimize scattering across structural boundaries, the slit material is not cut but cleaved along its crystallographic orientation. In addition, the orientation of the slits is determined relative to the incoming beam to minimize the amount of scattering due to the interaction between the incoming radiation and the internal structure of the slit material. These crystals are mounted on slit holders made of high-density material (e.g., tungsten) to ensure complete blocking of the X-ray beam along one side of the slit. In some embodiments, each slit has a rectangular cross-section with a width of approximately 0.5 mm and a height of approximately 1-2 mm. The length L of the slit shown in Figure 2 is approximately 6 mm. 【0047】 In general, the X-ray optical system shapes the X-ray radiation and directs it toward the sample 101. Some examples of X-ray optical systems include an X-ray monochromator that monochromatizes the X-ray beam incident on the sample 101. Some examples of X-ray optical systems parallelize or focus the X-ray beam to the measurement area 102 of the sample 101 and use a multilayer X-ray optical system to reduce the divergence to less than 1 mrad. In such examples, the multilayer X-ray optical system also functions as a beam monochromator. Some embodiments of the X-ray optical system include one or more X-ray parallelizing mirrors, X-ray apertures, X-ray beam diaphragms, refractive X-ray optical systems, diffractive optical systems such as zone plates, Montell optical systems, specular X-ray optical systems such as swirl-incident ellipsoidal mirrors, polycapillary optical systems such as hollow capillary X-ray waveguides, multilayer optical systems or systems, or any combination thereof. Further details are described in Patent Document 7, and its entirety will be incorporated into this application by reference. 【0048】 The X-ray detector 119 collects the X-ray radiation 114 scattered by the sample 101 and generates an output signal 135 that shows the characteristics of the sample 101 that are sensitive to the incident X-ray radiation, according to the T-SAXS measurement method. In some embodiments, when the scattered X-rays 114 are collected by the X-ray detector 119, the sample 101 is positioned and oriented by the sample positioning system 140 to generate angle-resolved X-rays. 【0049】 T-SAXS systems according to some embodiments have a wide dynamic range (e.g., 10 5 It has one or more photon counting detectors exhibiting ultra-high (H) values. In some embodiments, the position and number of detected photons are detected by a single photon counting detector. 【0050】 In a further embodiment, a T-SAXS system is used to determine the characteristics of a sample (e.g., structural parameter values) based on one or more diffraction orders of scattered light. By using the information processing system 130 provided in the weighing tool 100 shown in Figure 1, the signal 135 generated by the detector 119 can be obtained, and the characteristics of the sample can be determined at least partially based on the obtained signal. 【0051】 In some cases, during T-SAXS-based metrology, the dimensions of a sample are determined by inversely solving a predetermined measurement model using the measurement data. This measurement model includes a small number of tunable parameters (e.g., on the order of 10) and represents the geometric and optical properties of the sample, as well as the optical properties of the measurement system. Methods for inverse solving are not limited to this, but include model-based regression, tomography, machine learning, and any combination thereof. In this way, the target profile parameters are estimated by solving for the parameterized measurement model values ​​that minimize the error between the measured scattered X-ray intensity and the modeled result. 【0052】 Ideally, measurements should be performed over a wide range of incidence and azimuth angles to improve the accuracy and precision of parameter value measurements. This method reduces inter-parameter correlations by increasing the number and diversity of datasets available for analysis and including various large-angle off-plane orientations. For example, in a vertical orientation, T-SAXS can elucidate the critical dimensions of a feature, but it is largely insensitive to the sidewall angles and heights of the feature. However, by collecting measurement data over a wide range of off-plane angle orientations, the sidewall angles and heights of the feature can be elucidated. In other examples, performing measurements over a wide range of incidence and azimuth angles provides sufficient resolution and penetration depth to elucidate high aspect ratio structures across the entire depth. 【0053】 The intensity measurements of diffraction radiation are collected as a function of the X-ray incidence angle relative to the wafer surface normal. The information contained in these multiple diffraction orders is usually unique among the individual under-considered model parameters. Therefore, the estimation results obtained from X-ray scattering regarding the value of the parameter of interest have small errors and low parameter correlation. 【0054】 The individual orientations of the illumination X-ray beam 116 relative to the surface normal of the semiconductor wafer 101 are described by any two arbitrary angular rotations of the wafer 101 relative to the X-ray illumination beam, and vice versa. For example, the orientation can be described with reference to a coordinate system fixed to the wafer. Figure 4 shows an X-ray illumination beam 116 incident on the wafer 101 in a specific orientation described by the incident angle θ and the azimuth angle φ. The coordinate system XYZ is fixed to the metering system (e.g., illumination beam 116), and the coordinate system X'Y'Z' is fixed to the wafer 101. The Y-axis is aligned in-plane with respect to the surface of the wafer 101. X and Z are not aligned with respect to the surface of the wafer 101. Z' is aligned with an axis perpendicular to the surface of the wafer 101, and X' and Y' lie in a plane aligned with respect to the surface of the wafer 101. The X-ray illumination beam 116 shown in Figure 4 is aligned with the Z-axis and therefore in the XZ plane. The incident angle θ describes the direction of the X-ray illumination beam 116 in the XZ plane with respect to the surface normal of the wafer. Furthermore, the azimuth angle φ describes the direction of the XZ plane with respect to the X'Z' plane. Together, θ and φ uniquely specify the direction of the X-ray illumination beam 116 with respect to the surface of the wafer 101. In this example, the direction of the X-ray illumination beam with respect to the surface of the wafer 101 is described by rotation around an axis perpendicular to the surface of the wafer 101 (i.e., the Z' axis) and rotation around an axis aligned with the surface of the wafer 101 (i.e., the Y axis). In some other examples, the direction of the X-ray illumination beam with respect to the surface of the wafer 101 is described by rotation around a first axis aligned with the surface of the wafer 101 and rotation around another axis perpendicular to that first axis and aligned with the surface of the wafer 101. 【0055】 In one embodiment, hard X-ray illumination (e.g., 15 keV or higher) is used in the TSAXS measurement system over a relatively short optical path length (e.g., less than 3 m from the illumination source to the detector), thereby enabling measurement of targets ranging from relatively small dimensions (e.g., approximately 50 nm) to relatively large dimensions (e.g., up to 10 μm). Generally speaking, the method and system described herein can achieve a Q spatial resolution suitable for the measurement of semiconductor structures with a shortened optical path length. 【0056】 The geometric limit for the minimum achievable resolution of a TSAXS system is often the minimum Q value Q. min Characterized by Q min This is expressed by equation (1), where p is the pixel size in the detector, D is the distance between the sample under measurement and the detector, and λ is the wavelength of X-ray radiation. 【number】 【0057】 As illustrated by equation (1), the minimum achievable Q value for a given pixel size increases as the distance D between the measured sample and detector decreases. (i.e., Q) min To keep the value small, a proportional reduction in pixel size is necessary. For weighing the most advanced semiconductor metric targets, the Q value of the TSAXS system is 0.01 nm. -1 It needs to be less than [a certain value], but this has not yet been achieved in commercial TSAXS systems, which are limited by pixel size. 【0058】 The geometric limit of Q resolution is given in equation (1), but there are other limitations on Q resolution, and unless these are suppressed, the geometric limit cannot be reached. For example, the achievable Q resolution is limited by the spatial spread of the optical focus in the detector. Also, for example, the achievable Q resolution is limited by the point spread function (PSF) of the optical system in the detector. 【0059】 In a further embodiment, during the TSAXS measurement described herein, the sample is illuminated by an X-ray beam focused on either the measurement target, the detector surface, or the area between the wafer surface and the detector surface, less than 200 mm in front of the wafer surface, thereby reducing the optical focus limitation on the achievable Q resolution. Generally, focusing the X-ray beam closer to the wafer surface is suitable for metrology applications involving relatively small targets that must be illuminated with the smallest possible illumination spot size. Furthermore, focusing the X-ray beam closer to the detector is suitable for metrology applications involving relatively large targets where high image resolution and photon flux are desired. 【0060】 In some embodiments, as shown in Figure 1, the focus of the TSAXS measurement system is located on or near the wafer surface to measure relatively small targets (e.g., approximately 50-100 nm). By locating the illumination focus on the wafer, the measurement spot size is minimized within the structure under measurement. This minimizes signal contamination due to leakage of illumination light onto the structure around the target of interest. This configuration is desirable for small targets, i.e., when signal contamination due to a finite measurement spot size is a constraint. However, locating the illumination focus on the wafer instead of the detector increases the incident beam size on the detector. This increases the likelihood that the diffracted portions of the incident beam will overlap due to beam divergence. This becomes more pronounced when the wafer-detector distance is reduced to a relatively small size (e.g., less than 1 m), because the spatial separation between angular orders decreases as the wafer-detector distance decreases. However, for small targets (e.g., less than 100 nm), the angular separation between diffraction orders is relatively large, and the detector resolution enhancement technique described in this application overcomes the limitations imposed by detector focus limitations. 【0061】 In other embodiments, as shown in Figure 5, the focus of the TSAXS measurement system is located on or near the detector surface to measure relatively large targets (e.g., approximately 1-10 μm). By locating the illumination focus on the detector, the measurement spot size is minimized at the detector rather than the target under measurement. This configuration is desirable for relatively large targets, i.e., when the risk of signal contamination due to leakage of illumination light onto the structure around the target of interest is low, and signal contamination due to a finite measurement spot size on the wafer is not a constraint. However, with large targets, the angular separation between diffraction orders becomes relatively small. Consequently, the spatial separation of angular orders at the detector becomes relatively small. This becomes particularly pronounced when the wafer-detector distance is reduced to a relatively small dimension (e.g., less than 1 m). By locating the illumination focus on the detector, the probability of overlapping diffracted portions of the incident beam is minimized due to focal limitation. Furthermore, the limitation caused by the relatively small spatial separation of orders at the detector when the target size is relatively large is overcome by the detector resolution enhancement technology described in this application. 【0062】 Generally, the position of the optical focus can be adjusted to any position between the sample under measurement and the detector, with the associated trade-offs of advantages and disadvantages mentioned above. Generally, the smaller the target size, the more desirable it is to move the optical focus closer to the wafer, i.e., in front of the wafer surface, and the larger the target size, the more desirable it is to move the optical focus closer to the detector. 【0063】 In a further embodiment, in the TSAXS measurement described herein, a high-resolution detector with a small PSF reduces the detector PSF limitation on the achievable Q resolution. A high-resolution detector is useful when the wafer-to-detector distance D is relatively small (e.g., less than 1 m), regardless of where the optical focus is located relative to the wafer and detector. 【0064】 The Q resolution limitation imposed by the system's PSF depends on the metricing conditions and the source of the PSF. For example, in the case of weak scattering, reducing the PSF to 10% at a given Q may be necessary to resolve that Q. In other cases, reducing the PSF to 1% at a given Q may be necessary to resolve that Q. To achieve high Q resolution and the smallest possible wafer-to-detector distance D, this TSAXS system is designed to minimize Q-independent PSF. In some cases, by setting the detector pixel size to less than 100 μm and the detector PSF to be smaller than that pixel size, contamination of adjacent pixels by diffracted light incident on individual pixels is reduced to less than 0.1%. 【0065】 The detector material is selected to minimize transmission. Furthermore, depending on the detector configuration, PSF expansion in the detector is minimized. As a result, the system PSF becomes independent of the detector position. For example, conventional silicon detectors for detecting hard X-rays (e.g., 15 keV and above) have a significant problem of Q-independent PSF. Consequently, a large wafer-to-detector distance D (e.g., 2 m or more) is required to perform semiconductor structure quantization. By reducing transmission and backscattering, the PSF limitation is suppressed to below the geometric limit described by equation (1), enabling semiconductor structure quantization with a wafer-to-detector distance D of less than 1 m (e.g., D of 600 mm or less). 【0066】 TSAXS systems according to some embodiments offer high quantum efficiency and a wide dynamic range (e.g., 10 5 One or more photon counting detectors exhibiting ultra-high (U) characteristics are provided, each having a thick (e.g., more than 500 μm thick) high-absorption crystalline substrate that absorbs incident radiation without damage and with minimal parasitic backscattering. In some embodiments, the position and number of detected photons are detected by a single photon counting detector. 【0067】 In some embodiments, the zero-order beam is collected with higher diffraction orders. The zero-order beam has an amplitude several orders of magnitude stronger than the other orders. If the zero-order beam is not completely absorbed in the X-ray sensing section of the detector, it will scatter and generate parasitic signals. The dynamic range of the measurement is limited by the intensity of these parasitic signals. For example, if the parasitic signal is 10 -4 times that of the maximum beam signal (i.e., the zero-order signal), many signals related to higher orders will be contaminated. Therefore, it is important for the detector (e.g., detector 119) to exhibit a high conversion efficiency from X-rays to electron-hole pairs and a high X-ray absorption rate in order to broaden the effective dynamic range of X-ray metrology. 【0068】 Examples of detector materials suitable for small footprint X-ray scatterometry include crystals of cadmium telluride (CdTe), germanium (Ge), gallium arsenide (GaAs), and others. In some embodiments, the detector material is selected such that a high conversion efficiency is provided in a narrow energy band corresponding to the source energy. 【0069】 In some embodiments, the thickness of the detector material is selected such that the desired incoming X-ray absorption is achieved. In some embodiments, the detector is tilted with respect to the incoming X-ray beam (various diffraction orders) to increase the optical path length of the X-ray beam within the detector material, and thus increase the total absorption. 【0070】 In some embodiments, the SNR is improved by employing a dual threshold detector. 【0071】 In a further aspect, a TSAXS system is utilized, and the characteristics of the sample (e.g., structural parameter values) are determined based on multiple diffraction order measurement results. By using the information processing system 130 provided in the metrology tool 100 shown in FIG. 1, the signal 135 generated by the detector 119 can be acquired, and the characteristics of the sample can be determined at least partially based on the acquired signal. 【0072】 In TSAXS measurements, a parallelized X-ray beam is diffracted by a high-aspect-ratio fabricated structure, resulting in various diffraction orders. Each diffraction order propagates in a specific, predictable direction. The angular interval between these diffraction orders is inversely proportional to the sample's lattice constant divided by its wavelength. These diffraction orders are detected by a detector array positioned at a certain distance from the wafer. Each pixel of the detector outputs a signal indicating the number of photons that strike that pixel. 【0073】 The intensity of the diffraction order is given by the form I(m,n,θ,φ,λ), where {m,n} are integer exponents of the diffraction order, {θ,φ} are the elevation and azimuth angles of the incident beam (i.e., the polar coordinate values ​​of the incident principal ray relative to a coordinate system fixed to the wafer), and λ is the wavelength of the incident X-ray. 【0074】 As illumination light propagates from the light source to the sample, it is disturbed by several noise sources. Examples of disturbances include electron beam flow fluctuations and temperature-induced optical system drift. The disturbed incident light beam is represented as F0(1+n1). 【0075】 The target scatters the incident radiation in a manner that depends on the azimuth and elevation angles of the incident beam. The efficiency of light scattering up to order (m,n) is S mn It can be defined as (θ,φ). As the diffracted light propagates from the sample to the detector, all orders are similarly affected by other scattering media through which the beam passes, adding some variation (1+n2) and parasitic noise (n3). Thus, the total intensity I of each order measured at time t mn This can be expressed by equation (2). 【number】 【0076】 Figure 6 shows an image 171 of the scattering order measured by a metric system, for example, metric system 100. The bright spot at the center of the image drawn in Figure 6 is related to the 0th-order beam. 【0077】 The intensity of each diffraction order can be extracted in various ways. In some embodiments, these diffraction orders exhibit spatial separation in the detector. In such embodiments, these diffraction orders are detected individually by the detector array, and the outputs of pixels corresponding to the same diffraction order are combined (i.e., added together). In this configuration, the detected diffraction orders are discriminated by integrating the photon count values ​​of the pixels corresponding to each individual diffraction order. This scenario is likely to occur when measuring features with relatively small pitches or beams that exhibit relatively small divergence. 【0078】 In some other embodiments, diffraction orders overlap spatially. This is typical when performing TSAXS metricing on relatively large targets (e.g., targets with a pitch of 1 μm or more) at relatively small wafer-to-detector distances D (e.g., less than 2 m D) or when measuring with beams exhibiting relatively large divergence. In these embodiments, the diffraction orders are separated in Q space, thereby estimating the value of the structural parameter of interest. In some of these embodiments, the shape of the diffraction orders is estimated based on available beam shape information, and the Q resolution reduction due to overlap is accounted for using an accurate beam model. This is particularly important for meeting the requirements of on-device metricing. In some existing metricing systems, access to the beam shape information necessary to estimate the shape of these diffraction orders is hindered by the beam apposition employed in the system, making it impossible to separate overlapping orders. Such a system is described in Patent Document 6, titled "X-ray scatterometry apparatus," under the name of Mazor, et al., and we will incorporate its entirety into this application by referencing this document. 【0079】 When diffraction orders spatially overlap in a detector, simply combining the pixel outputs does not allow for the determination of the intensity for each individual diffraction order. In such embodiments, a measurement model that deconvolves these diffraction orders is used to discriminate the measured intensity of each detected diffraction order. 【0080】 In some embodiments, overlapping orders are deconvolved based on the zero-order beam shape measurement results. In some embodiments, this deconvolution is performed in real time. Beam profiles of higher diffraction orders (i.e., orders greater than zero) are modeled based on the profile of the zero-order beam. Figure 7 shows an image 172 of the scattering order measured by a metering system, for example, metering system 100. Figure 8 shows a plot 173 of the intensity profile related to cross-section C of the image 172 shown in Figure 7. A very accurate beam profile is provided by the relatively high-intensity zero-order beam, which can be used to model higher diffraction orders. 【0081】 In some embodiments, the intensity of each higher diffraction order is estimated based on the zero-order beam measurement result by simple division of the intensity or other methods. This significantly reduces the measurement uncertainty related to relatively weaker, higher-order signals. 【0082】 By estimating the intensity of higher diffraction orders based on simultaneously measured zero-order beams, scattered signals are separated from system disturbances during data acquisition. Disturbances caused by misalignment of optical components (e.g., slits, optics, spot shaping) and disturbances along the beam path (e.g., n1 and n2) are mitigated in real time. By using all scattering intensities, including the zero-order, the dependence of the scattered intensity on the measured sample thickness or material density is separated from beam disturbances before and after the wafer. 【0083】 The physical conversion of high-energy photons into electron clouds within the detector crystal also imposes detection limitations on high-q-resolution, short-path-length TSAXS systems. If the pixel size is small enough to perform short-path-length TSAXS metricing in a semiconductor structure, the electron cloud's action allows a single-photon event to be detected across several pixels. 【0084】 In another embodiment, the position of the centroid of the electron cloud induced by a photon conversion event is calculated by a detector (e.g., detector 119). The position of the centroid provides the position of the incident photon with sub-pixel accuracy. This substantially reduces the pixel size, enabling a Q resolution that exceeds the geometric limit described by equation (1). The sub-pixel spatial interpolation described herein is desirable for TSAXS measurements of semiconductor structures at wafer-to-detector distances of less than 1 m. 【0085】 In some embodiments, a TSAXS system with a relatively short optical path length is formed with a horizontal optical path incident on a vertically positioned wafer (i.e., the normal to the wafer surface is approximately perpendicular to the gravity vector). On the other hand, in some other embodiments, a TSAXS system with a relatively short optical path length is formed with a vertical optical path incident on a horizontally positioned wafer (i.e., the normal to the wafer surface is approximately parallel to the gravity vector). Orienting the beamline vertically allows for a smaller tool footprint and simplifies wafer handling. 【0086】 In a further embodiment, one or more X-ray photon energies are resolved by an X-ray detector, yielding signals for each X-ray energy component that characterize the sample. In some embodiments, the X-ray detector 119 is equipped with one of the following: a CCD array, a microchannel plate, a photodiode array, a microstrip proportional counter, a gas-filled proportional counter tube, a scintillator, and a fluorescent material. 【0087】 In this way, X-ray photon interactions in the detector are discriminated by energy in addition to pixel position and count value. In some embodiments, these X-ray photon interactions are discriminated by comparing the energy of the X-ray photon interaction with a predetermined upper threshold and a predetermined lower threshold. In one embodiment, this information is sent to an information processing system 130 by an output signal 135 for further processing and storage. 【0088】 In some embodiments, the target under measurement is periodic along one dimension (e.g., a FinFET structure). Therefore, it is sufficient to minimize the PSF of the TSAXS system in the detector along one direction. On the other hand, in some other embodiments, the target under measurement is periodic along two dimensions (e.g., a VNAND® contact). In such embodiments, it is beneficial to minimize the PSF of the TSAXS system in the detector along both directions. 【0089】 Other embodiments of the TSAXS system are configured to measure a target based on orders that are spatially separated in a certain direction, but overlap in a direction orthogonal to that direction. In some of these embodiments, the values ​​of one or more parameters of interest are determined along the direction in which their diffraction orders are spatially separated. Thereafter, these parameter values ​​are used, and the values ​​of one or more parameters of interest are determined based on the overlapping orders. 【0090】 In some embodiments, the X-ray illumination source 110, the focusing optical system 111, the slits 112 and 113, or any combination thereof, are held in the same atmospheric environment as that of the sample 101 (e.g., a gas-purged environment). However, in some embodiments, the optical paths between these components and within any of them become long, and air-borne X-ray scattering introduces noise into the image on the detector. Therefore, in some embodiments, the X-ray illumination source 110, the focusing optical system 111, and any of the slits 112 and 113 are held in a localized vacuum environment separated from the sample (e.g., sample 101) by a vacuum window. 【0091】 Similarly, in some embodiments, the X-ray detector 119 is held in the same atmospheric environment as that of the sample 101 (e.g., a gas-purged environment). However, in some embodiments, the distance between the sample 101 and the X-ray detector 119 becomes long, and airborne X-ray scattering introduces noise into the detected signal. Therefore, in some embodiments, one or more of the X-ray detectors (e.g., detector 119) are held in a localized vacuum environment separated from the sample (e.g., sample 101) by a vacuum window. 【0092】 Figure 9 shows a vacuum chamber 160 containing the X-ray illumination source 110, a vacuum chamber 162 containing the focusing optical system 111, and a vacuum chamber 163 containing the slits 112 and 113. The openings of each vacuum chamber are covered with vacuum windows. For example, the opening of vacuum chamber 160 is covered with vacuum window 161. Similarly, the opening of vacuum chamber 163 is covered with vacuum window 164. These vacuum windows may be made of some material that is substantially transparent to X-ray radiation and suitable (e.g., Kapton®, beryllium, etc.). By maintaining a suitable vacuum environment within each vacuum chamber, scattering of the illumination beam is minimized. A suitable vacuum environment may include any suitable level of vacuum, any suitable purging environment containing a low atomic number gas (e.g., helium), or any combination thereof. In this way, as much of the beam path as possible is in vacuum, so the luminous flux is maximized and scattering is minimized. 【0093】 In some embodiments, the entire optical system, including the sample 101, is held in a vacuum. However, the cost associated with holding the sample 101 in a vacuum is generally high due to the complexity of the sample positioning system 140. 【0094】 In other further embodiments, the beam shaping slit mechanism 120 is mechanically integrated with the vacuum chamber 163, thereby minimizing the beam path length exposed to the ambient environment. Generally, it is desirable to keep as much of the beam as possible in vacuum before it is incident on the sample 101. In some embodiments, the vacuum beamline extends into a hollow cylindrical cavity at the entrance of the beam shaping slit mechanism 120. By positioning a vacuum window 164 at the exit of the vacuum chamber 163 inside the beam shaping slit mechanism 120, the incoming beam 115 is kept in vacuum within a portion of the beam shaping slit mechanism 120 and then interacts with either the slits 126-129 or the sample 101 by passing through the vacuum window 164. 【0095】 In the embodiment shown in Figure 1, the focusing optical system 111, slits 112 and 113, and beam shaping slit mechanism 120 are held within a controlled environment (e.g., vacuum) inside the flight tube 118. 【0096】 In other further embodiments, the information processing system 130 is configured to generate a structural model (e.g., geometric model, material model, or geometric-material composite model) of the structure of the sample to be measured, generate a TSAXS response model that includes at least one geometric parameter derived from the structural model, and then perform a fitting analysis of TSAXS measurement data using the TSAXS response model to determine at least one sample parameter value. By using this analysis engine and comparing the simulated TSAXS signal with the measurement data, the geometric and material properties of the sample, such as electron density, can be determined. In the embodiment shown in Figure 1, the information processing system 130 is configured as a model building and analysis engine, and the engine is configured to realize model building and analysis functions as described in this application. 【0097】 Figure 10 shows an example 150 of a model building and analysis engine embodied by the information processing system 130. The model building and analysis engine 150 shown in Figure 10 has a structural model building module 151 that generates a structural model 152 of the structure to be measured in a sample. In some embodiments, the material properties of the sample are also incorporated into the structural model 152. The structural model 152 is received as input to the TSAXS response function building module 153. The TSAXS response function building module 153 generates a TSAXS response function model 155, at least partially relying on the structural model 152. In some examples, the TSAXS response function model 155 is X-ray form factor 【number】 This is based on the following equation, where F is the form factor, q is the scattering vector, and ρ(r) is the electron density of the sample in spherical coordinates. The X-ray scattering intensity is 【number】 The TSAXS response function model 155 is given by the TSAXS response function model 155, which is received as input to the fitting analysis module 157. The fitting analysis module 157 determines the geometric and material properties of the sample by comparing its modeled TSAXS response with the corresponding measurement data. 【0098】 In some cases, fitting model data to experimental data is achieved by minimizing the chi-squared value. For example, the chi-squared value related to TSAXS measurements. 【number】 It can be defined as follows. 【0099】 In the formula, S j SAXS experiment This is the TSAXS signal 135 measured in "channel" j, where the exponent j indicates a set of system parameters, such as diffraction order, energy, angular coordinate, etc. j SAXS model (v1,…,v L ) is a model of the TSAXS signal S related to the "channel" j. j A set of structure (target) parameters v1, ..., v L This evaluation concerns the following parameters, which refer to geometry (CD, sidewall angle, overlay, etc.) and material (electron density, etc.). σ SAXS,j This is an uncertainty related to the j-th channel. SAXS L is the total number of channels in the X-ray metering. L is the number of parameters that characterize the metering target. 【0100】 Equation (5) assumes that the uncertainty related to separate channels is not correlated. In cases where the uncertainty related to separate channels is correlated, the covariance between those uncertainty values ​​can be calculated. In such cases, the chi-squared value related to the X-ray scatterometry measurement can be used. 【number】 It can be expressed as follows. 【0101】 In the formula, V SAXS is the SAXS channel uncertainty covariance matrix, and T represents its transpose. 【0102】 In some cases, the fitting analysis module 157 performs a fitting analysis on the TSAXS measurement data 135 using the TSAXS response model 155, thereby determining at least one sample parameter value. In some cases, χ SAXS 2 This is optimized. 【0103】 As mentioned above, fitting the TSAXS data is achieved by minimizing the chi-squared value. However, in general, fitting the TSAXS data can also be achieved with other functions. 【0104】 Fitting TSAXS data is useful for any type of TSAXS technology that is sensitive to the geometry and / or material parameters of interest. Sample parameters can be deterministic (e.g., CD, SWA, etc.) or statistical (e.g., rms sidewall roughness, roughness correlation length, etc.), as long as a suitable model describing the TSAXS beam interaction with the sample is used. 【0105】 In general, the information processing system 130 is configured to access model parameters in real time using real-time limit dimension determination (RTCD), but it may also access a library of pre-calculated models to obtain at least one sample parameter value for sample 101. Generally, by using a certain form of CD engine, it is possible to evaluate the difference between the CD parameters assigned to a sample and the CD parameters related to the measured sample. An example of a sample parameter value calculation method and system is described in Patent Document 8 dated November 2, 2010, under the name of KLA-Tencor Corp., and its entirety will be incorporated into this application by reference. 【0106】 In some cases, the accuracy of parameter measurement results is improved in the model building and analysis engine 150 by some combination of feedside-way analysis, feedforward analysis, and parallel analysis. Feedside-way analysis involves taking multiple datasets from different areas of the same sample and passing common parameters obtained from the first dataset to the second dataset for analysis. Feedforward analysis involves taking datasets from separate samples and using a step-by-step copy exact parameter feedforward method to pass common parameters to subsequent analyses. Parallel analysis is the parallel or simultaneous application of a nonlinear fitting methodology to multiple datasets, in which at least one common parameter is combined during the fitting. 【0107】 Multiple-tool and structural analysis refers to feedforward, feedside-way, or parallel analysis that relies on regression, lookup tables (i.e., "library" matching), or other multiple-dataset fitting procedures. An example of a multiple-tool and structural analysis method and system is described in Patent Document 9 dated January 13, 2009, under the name of KLA-Tencor Corp., and its entirety will be incorporated into this application by reference. 【0108】 In a further embodiment, an information processing system (e.g., information processing system 130) provided in the weighing tool 100 is configured to realize the beam control function described in this application. In the embodiment shown in Figure 1, the information processing system 130 is configured as a beam controller capable of operating to control any of the illumination characteristics of the incident illumination beam 117, such as intensity, divergence, spot size, deflection, spectrum, and arrangement. 【0109】 As shown in Figure 1, the information processing system 130 is communicatively coupled to the detector 119. The information processing system 130 is configured to receive measurement data 135 from the detector 119. In one example, the measurement data 135 includes an indicator of the measurement result of the sample response (i.e., the intensity of the various diffraction components). Based on the distribution of the response measurement result on the surface of the detector 119, the incident position and area of ​​the illumination beam 116 on the sample 101 are determined by the information processing system 130. For example, by applying pattern recognition technology to the information processing system 130, the incident position and area of ​​the illumination beam 116 on the sample 101 are determined based on the measurement data 135. In some examples, the information processing system 130 sends a command signal 137 to the illumination source 110 to select a desired illumination wavelength, while a command signal 136 is sent to the beam selection subsystem 120 to redirect and reshape the illumination beam 116 so that it reaches a desired position on the sample 101 at a desired angular orientation. In some other examples, the information processing system 130 sends a command signal to the wafer positioning system 140, which then positions and orients the sample 101 so that the incident illumination beam 116 reaches the desired position on the sample 101 at a desired angle and orientation. 【0110】 In other embodiments, X-ray scatterometry measurement data is used to generate an image of the structure under measurement based on the intensity measurement results of the detected diffraction order. In some embodiments, a TSAXS response function model is generalized to describe scattering from a comprehensive electron density mesh. By fitting this model to the measured signal and imposing constraints on the modeled electron density in the mesh to emphasize continuity and sparse edges, a three-dimensional image of the sample is obtained. 【0111】 While a geometric, model-based parametric inverse transform is desirable for limit dimension (CD) measurement based on TSAXS measurements, when the sample under measurement deviates from the assumptions of its geometric model, a sample map generated from the same TSAXS data can help identify and correct model errors. 【0112】 In some cases, the image is compared to structural properties estimated by a geometric, model-based parametric inverse transform of the same scatterometry measurement data. The discrepancies can be used to update the geometric model of the structure under measurement and improve measurement performance. This ability to focus on an accurate parametric measurement model is particularly important when measuring integrated circuits to control, monitor, and troubleshoot their manufacturing processes. 【0113】 In some cases, the image becomes a two-dimensional (2D) map of electron density, absorbance, complex refractive index, or a combination of these material properties. In some cases, the image becomes a three-dimensional (3D) map of electron density, absorbance, complex refractive index, or a combination of these material properties. The map is generated using a relatively small number of physical constraints. In some cases, one or more parameters of interest, such as critical dimension (CD), sidewall angle (SWA), overlay, edge placement error, pitch walk, etc., are directly estimated from the obtained map. In some other cases, the map is used to debug the wafer process when the geometry or material of the sample falls outside the expected range estimated by the parametric structural model used for model-dependent CD measurement. For example, the parametric structural model predicts a representation of the structure according to the parameter being measured, and the difference between that representation and the map is used to update the parametric structural model and improve its measurement performance. Further details are described in Patent Document 10, and the full details will be incorporated into this application by reference. Since additional details are described in Patent Document 3, we will incorporate its entirety into this application by referencing it. 【0114】 In a further embodiment, an X-ray measurement optical measurement coupled analysis model is generated using the model building and analysis engine 150. In some examples, Maxwell's equations are solved by optical simulations, for example, based on exact coupled wave analysis (RWCA), and optical signals such as reflectance are calculated with respect to various deflections, ellipsometric parameters, phase changes, etc. 【0115】 The values ​​of one or more parameters of interest are determined by a combined fitting analysis of the intensity detection results and optical intensity detection results for X-ray diffraction orders at multiple different incident angles, based on a combined geometric parameterized response model. The optical intensity is measured by an optical metering tool, which may or may not be mechanically integrated with the X-ray metering system such as System 100 shown in Figure 1. Further details are described in Patent Documents 2 and 11, and the entire contents of those documents will be incorporated into this application by reference. 【0116】 In some embodiments, a metering target, whose characteristics are determined by X-ray scatterometry as described in this application, is placed within the scribe line of the wafer under measurement. In such embodiments, the metering target is sized to fit within the width of the scribe line. In some examples, the width of the scribe line is less than 80 μm. In some examples, the width of the scribe line is less than 50 μm. Generally, the width of scribe lines used in semiconductor manufacturing is trending downwards. 【0117】 In some embodiments, a metric target, whose characteristics are determined by X-ray scatterometry as described in this application, is placed within the active die area of ​​the wafer under measurement and becomes part of a functional integrated circuit (e.g., memory, image sensor, logic device, etc.). 【0118】 Generally, the aspect ratio characterizing a weighing target is defined as the ratio of the maximum height dimension of the weighing target (i.e., the dimension perpendicular to the wafer surface) to the maximum lateral dimension (i.e., the dimension aligned with the wafer surface). In some embodiments, the aspect ratio of the weighing target under measurement is at least 20. In some embodiments, the aspect ratio of the weighing target is at least 40. 【0119】 Figures 11A to 11C show, in order, the isometric, top, and cross-sectional views of a typical 3D-FLASH® memory device 190 subjected to measurement in accordance with the procedure described herein. The total height (equivalently, depth) of the memory device 190 is in the range of 1 to several μm. The memory device 190 is a vertically manufactured device. A vertically manufactured device, such as the memory device 190, is essentially a conventional planar memory device rotated 90° so that the bit lines and cell strings are oriented vertically (perpendicular to the wafer surface). To provide sufficient storage capacity, numerous alternating layers of different materials are deposited on the wafer. To do this with a structure having a maximum lateral spread of 100 nm or less, it is necessary to suitably execute the patterning process to a depth of several μm. As a result, aspect ratios of 25:1 or 50:1 are not uncommon. 【0120】 It should be recognized that the various steps described throughout this disclosure may be performed on a single computer system 130, or on multiple computer systems 130. Furthermore, subsystems of system 100, such as the sample positioning system 140, may have computer systems suitable for performing at least some of the steps described herein. Thus, the above statements should be taken as illustrative examples only, and not as limitations on the present invention. Furthermore, one or more information processing systems 130 may be configured to perform any other step(s) of any of the method embodiments described herein. 【0121】 In addition, the method for communicatingly coupling the computer system 130 to the detector 119 and the illumination optical element may be any method known in the present art. For example, one or more information processing systems 130 may be coupled to the information processing system related to the detector 119. Alternatively, for example, the detector 119 may be directly controlled by a single computer system coupled to the computer system 130. 【0122】 The computer system 130 may be configured to receive and / or acquire data or information from the subsystems of the system (e.g., detector 119, etc.) via a transmission medium, such as a wired and / or wireless section. In this configuration, the transmission medium can function as a data link between the computer system 130 and other subsystems of system 100. 【0123】 The computer system 130 of the weighing system 100 may 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, such as a wired and / or wireless section. In this configuration, the transmission medium can function as a data link between the computer system 130 and other systems (e.g., the weighing system 100's onboard memory, external memory, or external system). For example, the information processing system 130 may be configured to receive measurement data (e.g., signals 135) from a storage medium (i.e., memory 132 or 180) via the data link. As an example, the intensity measured by the detector 119 may be stored in a permanent or semi-permanent storage device (e.g., memory 132 or 180). In this case, the measurement results can be imported from onboard memory or from an external memory system. Furthermore, the computer system 130 may send data to other systems via the transmission medium. For example, the sample parameter values ​​170 obtained by the computer system 130 may be stored in a permanent or semi-permanent storage device (e.g., memory 180). In this case, the measurement results can be exported to other systems. 【0124】 Information processing system 130 may include, but is not limited to, personal computer systems, mainframe computer systems, workstations, image computers, parallel processors, and any other devices known in the art. Generally, the term "information processing system" can be broadly defined to include all devices having one or more processors that execute instructions obtained from a storage medium. 【0125】 For example, the program instructions 134 that implement the method 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, the program instructions stored in memory 132 are transmitted to the processor 131 via bus 133. The program instructions 134 are stored in a computer-readable medium (e.g., memory 132). Examples of computer-readable media include read-only memory, random-access memory, magnetic disks, optical disks, and magnetic tapes. 【0126】 In some embodiments, the scatterometry analysis described herein is implemented as part of a manufacturing process tool. Examples of manufacturing process tools include, but are not limited to, lithographic exposure tools, deposition tools, implantation tools, and etching tools. In this embodiment, the manufacturing process is controlled using the results of the TSAXS analysis. In one example, TSAXS measurement data collected from one or more targets is sent to a manufacturing process tool. The TSAXS measurement data is analyzed as described herein, and the operation of the manufacturing process tool is adjusted using the results. 【0127】 By using the scatterometry measurements described in this application, the properties of various semiconductor structures can be determined. Examples of structures, though not limited to these, include FinFETs, low-dimensional structures such as nanowires and graphene, sub-10nm structures, lithographic structures, through-substrate vias (TSVs), and memory structures such as DRAM, DRAM4F2, FLASH®, MRAM, and high aspect ratio memory structures. Examples of structural properties, though not limited to these, include geometric parameters such as line edge roughness, line width roughness, pore size, pore density, sidewall angle, profile, limit dimensions, and pitch, and material parameters such as electron density, composition, grain structure, morphology, stress, strain, and elemental type. 【0128】 Figure 12 illustrates a method 300 suitable for implementation by the weighing system 100 of the present invention. In one embodiment, as can be seen, the data processing blocks of method 300 can be executed by executing a pre-programmed algorithm using one or more processors provided in the information processing system 130. The following description is presented in the context of the weighing system 100, but as is understood in this application, the specific structural aspects of the weighing system 100 are not limiting, and should be understood solely as illustrative. 【0129】 In block 301, the measurement target formed on the wafer surface is illuminated with an X-ray radiation beam with an energy level of 15 keV or higher. 【0130】 In block 302, the intensities of multiple diffraction orders are detected from among the radiation chunks scattered by the measurement target according to the incident beam. The optical path length between the illumination source and the detector is less than 3m. In addition, two or more of these multiple diffraction orders spatially overlap on the detector surface. 【0131】 In block 303, the intensity of each of these overlapping diffraction orders is determined based on the beam shape of the zeroth order diffraction. 【0132】 In block 304, the value of the parameter of interest related to the measurement target is determined based on the intensity of these multiple diffraction orders. 【0133】 The term "limit dimension" as used in this application includes all limit dimensions of a structure (e.g., lower limit dimension, middle limit dimension, upper limit dimension, side wall angle, grid height, etc.), limit dimensions between any two or more structures (e.g., distance between two structures), and displacements between two or more structures (e.g., overlay positional displacement between overlapping grid structures, etc.). Structures may include three-dimensional structures, patterned structures, overlay structures, etc. 【0134】 The terms "limit dimension application" or "limit dimension measurement application" as used in this application encompass all limit dimension measurements. 【0135】 The term "weighing system" as used in this application encompasses all systems, in any form, that are at least partially employed in characterizing a sample, including limit dimension applications and overlay weighing applications. However, these technical terms do not limit the scope of the term "weighing system" as used in this application. In addition, the weighing system described in this application may be configured for the measurement of patterned wafers and / or unpatterned wafers. The weighing system may be configured as an LED inspection tool, edge inspection tool, back surface inspection tool, macro inspection tool, or multimode inspection tool (including those that obtain data simultaneously from one or more platforms), or any other weighing or inspection tool that benefits from the measurement techniques described in this application. 【0136】 This application describes various embodiments of semiconductor processing systems (e.g., inspection systems and lithography systems) that can be used for processing samples. The term "sample" in this application refers to any specimen, such as a wafer or reticle, that can be processed (e.g., printed or inspected for defects) by means known in the art. 【0137】 In this application, the term "wafer" generally refers to a substrate formed of semiconductor or non-semiconductor material. Examples include, but are not limited to, single-crystal silicon, gallium arsenide, and indium phosphide. Such substrates can be commonly found and / or processed in semiconductor manufacturing equipment. In some cases, a wafer may consist only of a substrate (a so-called bare wafer). Alternatively, a wafer may have one or more layers of different materials formed on the substrate. One or more layers formed on a wafer may be "patterned" or "unpatterned." For example, a wafer may contain multiple dies that have repeatable pattern features. 【0138】 A "reticle" can be a reticle at any stage of the reticle manufacturing process, a finished reticle, or a reticle that has been released for use in semiconductor manufacturing equipment. A reticle, or "mask," is generally defined as a nearly transparent substrate on which a nearly opaque region is formed, forming a pattern. The substrate may contain, for example, a glass material such as amorphous SiO2. By placing the reticle on a wafer covered with resist and performing the exposure step of the lithography process, the pattern on the reticle can be transferred to the resist. 【0139】 The one or more layers formed on the wafer may or may not form a pattern. For example, each of the multiple dies within the wafer may have repeatable pattern features. By forming and processing such material layers, a finished device can ultimately be obtained. While many types of devices can be formed on a wafer, the term "wafer" in this application is intended to encompass wafers on which all types of devices known in the art are fabricated. 【0140】 According to one or more exemplary embodiments, the functions described above can be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, these functions can be stored or transmitted on a computer-readable medium as one or more instructions or codes. Computer-readable medium includes both computer storage media and communication media, for example, all media that are useful for transferring computer programs from one place to another. The storage medium may be any available medium accessible by a general-purpose or dedicated computer. In non-limiting examples, such a computer-readable medium may consist of any medium that can be used to transport or store desired program code means in the form of instructions or data structures, and that is accessible by a general-purpose or dedicated computer or general-purpose or dedicated processor, such as RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices. Any connection may also be referred to as a computer-readable medium. For example, if coaxial cables, fiber optic cables, twisted pair cables, digital subscriber lines (DSL), or wireless technologies such as infrared, radio frequency, or microwave are used to transmit software from a website, server, or other remote source, then those coaxial cables, fiber optic cables, twisted pair cables, DSL, or wireless technologies such as infrared, radio frequency, or microwave fall within the definition of a medium. The term "disk" as used in this application includes compact discs (CDs), laserdiscs, XRF® discs, digital versatile discs (DVDs®), floppy disks, and Blu-ray® discs, as well as disks (disks) in which data is typically reproduced magnetically and disks (discs) in which data is reproduced optically by a laser. Combinations of the above should also be included within the scope of computer-readable media. 【0141】 Although certain embodiments have been described above for teaching purposes, the teachings of this patent application have general applicability and are not limited to the specific embodiments described above. Accordingly, various modifications, adaptations, and combinations can be made to the various features of the embodiments described above without deviating from the technical scope of the invention described in the claims.

Claims

[Claim 1] The steps include illuminating a measurement target formed on the wafer surface with an X-ray radiation beam, The step of detecting the intensity of diffracted beams of multiple diffraction orders from the radiation scattered by the measurement target in response to the incident beam using an X-ray detector, wherein the X-ray detector has multiple pixels, each of which has a size of less than 100 μm in the direction of its maximum length, The steps include determining the value of the parameter of interest related to the measurement target based on the intensity of the multiple diffraction orders, It has, The optical path length between the measurement target and the X-ray detector is less than 1 m. A method for determining the intensity of multiple diffraction orders using a measurement model that deconvolves the multiple diffraction orders based on the zero-order diffraction shape measurement results, wherein the multiple diffraction orders are spatially overlapping in the X-ray detector. [Claim 2] The method according to claim 1, The method wherein the X-ray detector is a photon counting type detector or an integrating type detector. [Claim 3] The method according to claim 1, A method wherein each of the plurality of pixels of the X-ray detector has a size of less than 50 μm in the direction of the maximum length. [Claim 4] The method according to claim 1, A method wherein the optical path length between the X-ray illumination source and the X-ray detector is less than 3 m. [Claim 5] The method according to claim 1, further, The steps include interpolating between multiple energy levels in each pixel of the X-ray detector, A method of having. [Claim 6] An X-ray illumination source configured to generate X-ray radiation, One or more X-ray illumination optical elements configured to illuminate a measurement target formed on the wafer surface with the incident focused beam of X-ray radiation, A sample positioning system for positioning the measurement target, which is the sample, in multiple orientations relative to the incident focused beam, An X-ray detector having multiple pixels, each pixel having a size of less than 50 μm in the direction of its maximum length, and configured to detect the intensity of each of multiple diffraction order diffracted beams from the radiation scattered by the measurement target in each direction according to the incident focused beam, Non-temporary computer-readable media and It is equipped with a non-temporary computer-readable medium, A code that causes an information processing system to determine the value of the parameter of interest related to the measurement target based on the intensity of the multiple diffraction orders, It has, The optical path length between the measurement target and the X-ray detector is less than 1 m. A metering system in which the multiple diffraction orders are spatially overlapping in the X-ray detector, and the intensity of the multiple diffraction orders is determined using a measurement model that deconvolves the multiple diffraction orders based on the zero-order diffraction shape measurement results. [Claim 7] A weighing system according to claim 6, A weighing system in which the X-ray detector is either a photon counting detector or an integrating detector. [Claim 8] A weighing system according to claim 6, A weighing system in which the optical path length between the X-ray illumination source and the X-ray detector is less than 3 m. [Claim 9] A weighing system according to claim 6, The aforementioned X-ray detector is a metric system that determines the position of the centroid of the interaction between a photon and the X-ray detector with a sub-pixel resolution smaller than the size of the pixel.

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