Method and system for characterization of an x-ray beam with high spatial resolution

Abstract

The present application relates to methods and systems for characterization of x-ray beams with high spatial resolution. Described herein are methods and systems for positioning a sample and characterizing an x-ray beam incident on the sample in a transmission small angle x-ray scattering measurement (T-SAXS) metrology system. A sample positioning system positions a wafer vertically and actively positions the wafer in six degrees of freedom relative to the x-ray illumination beam without attenuating the transmitted radiation. In some embodiments, a cylindrical obscuration element is scanned across the illumination beam to precisely position the beam center while measuring the detected intensity of the transmitted flux. In some other embodiments, a periodic calibration target is employed to precisely position the beam center.

Description

[0001] Information related to divisional application This case is a divisional application. The parent application of this divisional application is the invention patent application filed on May 10, 2018, with application number "201880029664.7" and invention title "Method and System for Characterizing X-ray Beams with High Spatial Resolution". Cross-reference of related applications

[0002] This patent application claims priority to U.S. Provisional Patent Application No. 62 / 505,014, filed May 11, 2017, pursuant to 35 USC §119, the subject matter of which is incorporated herein by reference in its entirety. Technical Field

[0003] The described embodiments relate to x-ray metrology systems and methods, and more specifically, to methods and systems for improving measurement accuracy. Background Technology

[0004] Semiconductor devices (such as logic and memory devices) are typically manufactured through a series of processing steps applied to a sample. These processing steps form various features and multiple structural levels of the semiconductor device. For example, photolithography is a semiconductor manufacturing process that 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.

[0005] Metrology processes are used at various stages of semiconductor manufacturing to detect defects on wafers in order to improve yield. Several metrology-based techniques, including scattering and reflection measurement implementations and associated analytical algorithms, are typically used to characterize the critical dimensions, film thickness, composition, and other parameters of nanoscale structures.

[0006] Traditionally, scattering measurements are performed on targets composed of thin films and / or repetitive periodic structures to determine critical size. During device fabrication, these films and periodic structures typically represent the actual device geometry and material structure or an 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 diverse physical properties create characterization difficulties. For example, modern memory structures are often high-aspect-ratio three-dimensional structures that make it difficult for optical radiation to penetrate to the underlying layers. Optical metrology tools using infrared to visible light can penetrate many translucent material layers, but longer wavelengths that provide good penetration depth do not offer sufficient sensitivity to small anomalies. Furthermore, the increasing number of parameters required to characterize complex structures (e.g., FinFETs) leads to increased parameter dependence. Therefore, the parameters of a characterized target are often not reliably decoupled from available measurements.

[0007] In one instance, an attempt was made to use longer wavelengths (e.g., near-infrared) to overcome the penetration problem in 3D flash devices that utilize polysilicon as one of the alternating materials in a stack. However, as illumination propagates deeper into the film stack, the mirror-like structure of the 3D flash inherently reduces light intensity. This leads to a loss of sensitivity and correlation issues at deeper depths. In this case, SCD was only able to successfully extract metrological dimensions from a reduced set with high sensitivity and low correlation.

[0008] In another example, opaque high-k materials are increasingly used in modern semiconductor structures. Optical radiation typically cannot penetrate layers constructed from these materials. Therefore, measurements using thin-film scattering measurement tools, such as ellipsometrists or reflectometers, are becoming increasingly challenging.

[0009] In response to these challenges, more sophisticated optical metrology tools have been developed. For example, tools with multiple illumination angles, shorter illumination wavelengths, wider illumination wavelength ranges, and more complete information from reflected signals have been developed (e.g., measuring multiple Mueller matrix elements in addition to conventional reflectivity or ellipsometric measurements). However, these approaches have not reliably overcome the fundamental challenges associated with the measurement of many advanced targets (e.g., complex 3D structures, structures smaller than 10 nm, structures using opaque materials) and their measurement applications (e.g., line edge roughness and linewidth roughness measurements).

[0010] Atomic force microscopy (AFM) and scanning tunneling microscopy (STM) can achieve atomic resolution, but they can only probe the surface of the sample. Furthermore, AFM and STM microscopy require long scan times. Scanning electron microscopy (SEM) achieves intermediate resolution levels, but cannot penetrate structures to sufficient depth. Therefore, it does not effectively characterize high aspect ratio holes. Additionally, the charging required for the sample negatively impacts imaging performance. X-ray reflectometers also suffer from penetration problems that limit their effectiveness when measuring high aspect ratio structures.

[0011] To overcome the penetration depth problem, traditional imaging techniques (such as TEM and SEM) are combined with destructive sample preparation techniques (e.g., focused ion beam (FIB) processing, ion milling, blanket etching, or selective etching). For example, transmission electron microscopy (TEM) achieves high resolution and can probe arbitrary depths, but TEM techniques require destructive segmentation of the sample. Several iterations of material removal and measurement often provide the information needed for key metrological parameters across three-dimensional structures. However, these techniques require sample destruction and lengthy process times. The complexity and time required to complete these types of measurements are attributed to the significant inaccuracies introduced by the drift of etching and metrological steps. In addition, these techniques require several iterations that introduce registration errors.

[0012] Transmission small-angle X-ray scattering (T-SAXS) systems using photons at hard X-ray energy levels (>15 keV) have shown promise for solving challenging measurement applications. The following cases describe various aspects of applying SAXS technology to the measurement of critical dimension (CD-SAXS) and overlay (OVL-SAXS): 1) U.S. Patent No. 7,929,667, entitled "High-brightness X-ray metrology," by Zhuang and Fielden; 2) U.S. Patent Publication No. 2014 / 0019097, entitled "Model Building And Analysis Engine For Combined X-ray And Optical Metrology," by Bakeman, Shchegrov, Zhao, and Tan; and 3) U.S. Patent No. 1, entitled "Methods and Apparatus for Measuring Semiconductor Device Overlay," by Veldman, Bakeman, Shchegrov, and Mieher. 4) U.S. Patent Publication No. 2015 / 0117610 entitled "Overlay Using X-Ray Metrology"; 5) U.S. Patent Publication No. 2016 / 0202193 entitled "Measurement System Optimization For X-Ray Based Metrology" by Hench, Shchegrov, and Bakeman; 6) U.S. Patent Publication No. 2017 / 0167862 entitled "X-ray Metrology For High Aspect Ratio Structures" by Dziura, Gellineau, and Shchegrov; and 7) U.S. Patent Publication No. 6) entitled "Full Beam Metrology for X-Ray" by Gellineau, Dziura, Hench, Veldman, and Zalubovsky. U.S. Patent Publication No. 2018 / 0106735, concerning “Scatterometry Systems”.The aforementioned patent documents were assigned to KLA-Tencor Corporation of Milpitas, California (United States).

[0013] SAXS has also been applied to material characterization and other non-semiconductor related applications. Demonstration systems have been commercialized by several companies, including Xenocs SAS (www.xenocs.com), Bruker Corporation (www.bruker.com), and Rigaku Corporation (www.rigaku.com / en).

[0014] Studies on CD-SAXS metrology of semiconductor structures are also described in the scientific literature. Most research teams have used high-brightness X-ray synchrotron sources, which are unsuitable for use in semiconductor manufacturing facilities due to their large size, cost, etc. An example of this system is described in the article entitled "Intercomparison between optical and x-ray scatterometry measurements of FinFET structures" by Lemaillet, Germer, Kline, et al., Proc. SPIE, Vol. 8681, p. 86810Q (2013). More recently, a team at the National Institute of Standards and Technology (NIST) has begun studies using a compact and bright X-ray source similar to that described in U.S. Patent No. 7,929,667. This study is described in the article entitled “X-ray scattering critical dimensional metrology using a compact x-ray source for next generation semiconductor devices” in the Journal of Micro / Nanolith. MEMS MOEMS 16(1), 014001 (January to March 2017).

[0015] A metrology system must be used to calibrate and align the interaction between the X-ray beam and the target to ensure effective measurements. Exemplary characterization includes: precisely positioning the peak intensity of the X-ray beam onto the target; measuring the X-ray beam intensity distribution; and identifying the boundaries of the X-ray beam such that a specific percentage of the beam flux lies outside the boundaries. Exemplary alignment includes aligning the X-ray beam with an optical vision system, aligning the X-ray beam with specific mechanical features of the tool (e.g., the wafer rotation axis), etc.

[0016] Generally, the wafer is navigated along the path of the X-ray beam based on optical measurements of alignment marks placed throughout the wafer using an optical microscope. To ensure accurate navigation of a specific target relative to the X-ray beam, the beam profile needs to be measured in the coordinates of the optical microscope used to measure the alignment marks.

[0017] In some instances, the optical microscope is aligned with the blade, and the blade is aligned with the X-ray beam. The characterization of the X-ray beam with a conventional blade is complex, attributable to the translucency of the blade material illuminated by X-ray radiation near the edge of the blade. For example, tungsten has a beam attenuation length of approximately 8.4 micrometers when illuminated by photons with an energy level of 20 keV. At this length, the transmittance drops to ~1 / e (e=2.718). For a blade shaped at a 30-degree angle, the length of the wedge corresponding to a height of 8.4 micrometers is approximately 14.5 micrometers. This simple estimate of the uncertainty in blade position during X-ray beam scanning illustrates that the translucency of the blade is limited when the required alignment accuracy is less than a few micrometers (e.g., less than 10 micrometers).

[0018] In some other instances, the X-ray beam profile is characterized by a high-resolution X-ray camera positioned relative to a point on the X-ray beam (e.g., the focal point of a focusing optics). In these instances, the beam profile is measured using the high-resolution X-ray camera, and the measured coordinates of the beam are transmitted to an optical microscope used to navigate the wafer in the path of the X-ray beam. Unfortunately, the error associated with transmitting the measured coordinates from the X-ray camera to the optical microscope is significant and exceeds the required navigation accuracy.

[0019] Furthermore, characterization of X-ray beams via X-ray cameras or blades is inherently indirect and does not provide quantitative data on the photon flux incident on the target or photon contamination in adjacent areas.

[0020] Future metrology applications face metrological challenges due to increasingly smaller resolution requirements, multi-parameter correlations, increasingly complex geometrologies (including high aspect ratio structures), and the growing use of opaque materials. Existing methods for X-ray tool alignment and target navigation are limited to accuracy of approximately 10 to 20 micrometers. These methods cannot achieve sufficient accuracy for locating and measuring metrological targets of small size (~50 micrometers) within an X-ray beam for semiconductor metrology applications. Therefore, improved methods and systems for X-ray beam alignment and calibration in SAXS systems are desired to meet the placement requirements of advanced manufacturing nodes. Summary of the Invention

[0021] This document describes methods and systems for locating samples and characterizing the X-ray beam incident on the sample in a transmission small-angle X-ray scattering (T-SAXS) metrology system. Practical T-SAXS measurements in semiconductor manufacturing environments require measurements over a wide range of incident and azimuth angles relative to the surface of a sample (e.g., a semiconductor wafer) with a small beam spot size (e.g., less than 50 micrometers across the effective illumination point). Accurate positioning of the wafer and characterization of the beam size and shape are required to achieve a small measurement cell size. Furthermore, this document presents calibration for accurately positioning the illumination beam on the desired target area on the surface of the semiconductor wafer across the entire range of incident and azimuth angles.

[0022] In one aspect, the metrology tool includes a sample positioning system configured to vertically position a wafer (i.e., the plane of the wafer surface is approximately aligned with the gravity vector) and to actively position the wafer relative to an illumination beam in six degrees of freedom. The sample positioning system supports the wafer at its edges, thereby allowing the illumination beam to penetrate the wafer at any location within the active region of the wafer without remounting. By vertically supporting the wafer at its edges, gravity-induced indentation of the wafer is effectively mitigated.

[0023] In another aspect, the balancer statically balances the rotating mass of the sample positioning system such that the center of gravity of the rotating mass is approximately aligned with its axis of rotation.

[0024] In some embodiments, three sensors are mounted on the sample positioning system to measure the distance of the back side of the wafer relative to the sample positioning system. In this way, wafer warpage is measured and compensated by moving the wafer using a tip-tilt Z-stage.

[0025] In another aspect, the SAXS metrology system employs at least one beam-blocking calibration target to position the X-ray illumination beam relative to a sample positioning system. The beam-blocking calibration target comprises at least one marker and a cylindrical blocking element. A alignment camera is used to position the marker in the coordinates of the sample positioning system. The position of the marker relative to the cylindrical blocking element is known in advance (e.g., with an accuracy of less than 200 nanometers). Therefore, the position of the cylindrical blocking element in the coordinates of the sample positioning system can be easily determined by a direct coordinate transformation. The cylindrical blocking element is scanned across the illumination beam while measuring the detected intensity of the transmission flux. The center of the illumination beam is precisely positioned relative to the cylindrical blocking element based on the measured intensity. Since the position of the cylindrical blocking element in the coordinates of the sample positioning system is known, the center of the illumination beam is precisely positioned in the coordinates of the sample positioning system by a simple coordinate transformation.

[0026] In some instances, a beam-blocking calibration target is used to calibrate the incident position of the illumination beam relative to the sample positioning system. In other instances, a beam-blocking calibration target is used to align the rotation axis of the stage reference frame relative to the illumination beam at the point of incidence of the illumination beam and the wafer.

[0027] In another aspect, the SAXS metrology system employs at least one periodic calibration target to position the X-ray illumination beam relative to the sample positioning system. Each periodic calibration target comprises one or more spatially defined regions having different periodic structures that diffract the X-ray illumination beam into dissimilar diffraction patterns measurable by the SAXS metrology system described herein. Additionally, each periodic calibration target includes one or more markers that can be read by an optical microscope to position the periodic calibration target relative to the sample positioning system with high alignment accuracy (e.g., 0.5 micrometers or less). Each spatially defined region has a spatially well-defined boundary line. The position of the boundary line relative to the marker is known to have high accuracy (e.g., 0.2 micrometers or less) in one or more dimensions.

[0028] In another aspect, the precise alignment of the illumination beam with the plane of the wafer surface is determined based on the interaction between the illumination beam and two or more beam-blocking calibration targets, such as those measured by an X-ray detector.

[0029] In another aspect, the precise alignment of the rotation axis with the calibration target mark in the plane of the surface of the wafer is determined based on images of the marks collected by an alignment camera mounted to a transverse alignment stage.

[0030] In another embodiment, the shape of the wafer's surface in the Z-direction is mapped using any of the alignment camera, optical proximity sensor, capacitive proximity sensor, interferometric sensor, or any other suitable proximity sensor. In some instances, the wafer surface is mapped onto the front side (i.e., the patterned side) of the wafer. In other instances, if the wafer thickness is sufficiently uniform, well-modeled, or measured in situ or pre-measured, the wafer surface is mapped onto the back side (i.e., the unpatterned side) of the wafer.

[0031] The foregoing is a summary of the invention and therefore must contain simplifications, generalizations, and omissions of details; thus, those skilled in the art will understand that the summary is merely illustrative and in no 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

[0032] Figure 1 This is a diagram illustrating a metrology system 100 configured to perform calibration of various system parameters according to the methods described herein.

[0033] Figure 2 An end view of a beam-shaping slit mechanism 120 in a configuration is depicted.

[0034] Figure 3 An end view of the beam-shaping slit mechanism 120 in another configuration is depicted.

[0035] Figure 4 A beam of X-ray illumination 116 is depicted incident on wafer 101 with a specific orientation described by angles φ and θ.

[0036] Figure 5 This is a diagram illustrating the sample positioning system 140, in which the wafer stage is moved to a position where the illumination beam 116 is incident on the wafer 101.

[0037] Figure 6 This is a diagram illustrating the sample positioning system 140 with additional details.

[0038] Figure 7 A beam blocking calibration target 190 is depicted in one embodiment.

[0039] Figure 8A Describing as Figure 5 The image depicts a top view of an illumination beam 116 incident on a wafer 101, wherein a rotation axis 153 intersects the illumination beam 116 at the point of incidence of the illumination beam 116 onto the wafer 101.

[0040] Figure 8B Describing as Figure 5The image depicts a top view of an illumination beam 116 incident on a wafer 101, wherein the rotation axis 153 is misaligned with the surface of the wafer 101 in the Z direction.

[0041] Figure 8C Describing as Figure 5 The image depicts a top view of an illumination beam 116 incident on a wafer 101, wherein a rotation axis 153 is offset from the illumination beam 116 in the X direction.

[0042] Figure 9 This is a diagram illustrating the sample positioning system 140, in which the wafer stage is moved to a position where the illumination beam 116 is blocked by the cylindrical pin element 151.

[0043] Figure 10 A graph 170 depicts the measured flux as a function of the cylindrical pin relative to the illumination beam 116.

[0044] Figure 11 Another illustration depicts a sample positioning system 140 including a periodic calibration target 171 positioned on a wafer 101.

[0045] Figure 12 An embodiment of the periodic calibration target 210 is depicted.

[0046] Figure 13 An embodiment of the periodic calibration target 220 is depicted.

[0047] Figure 14 An embodiment of the periodic calibration target 230 is depicted.

[0048] Figure 15 An embodiment of the periodic calibration target 240 is depicted.

[0049] Figure 16 An example of periodic calibration target 250 is described.

[0050] Figure 17 An embodiment of the periodic calibration target 260 is depicted.

[0051] Figure 18 An embodiment of the periodic calibration target 270 is depicted.

[0052] Figures 19A to 19B A set of periodic calibration targets 290 and 295 are depicted, each of which is adapted to position an illumination beam relative to the periodic calibration target in one direction.

[0053] Figure 20 Periodic calibration target 280 is depicted, which includes markers 288 and 289 and seven different periodic regions 281 to 287 arranged in a hexagonal pattern.

[0054] Figure 21 This is a diagram illustrating the components of the metering system 100 contained in a vacuum environment separated from the sample 101.

[0055] Figure 22 This is a diagram illustrating the model construction and analysis engine 180 configured to parse sample parameter values ​​based on T-SAXS data according to the methods described herein.

[0056] Figure 23 A flowchart illustrating an exemplary method 300 for calibrating incident angle offset values ​​based on T-SAXS measurements of multiple incident angles and azimuth angles as described herein is presented. Detailed Implementation

[0057] The background examples and some embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0058] This document describes methods and systems for locating samples and characterizing the X-ray beam incident on the sample in a transmission small-angle X-ray scattering (T-SAXS) metrology system. Practical T-SAXS measurements in semiconductor manufacturing environments require measurements over a wide range of incident and azimuth angles relative to the surface of a sample (e.g., a semiconductor wafer) with a small beam spot size (e.g., less than 50 micrometers across the effective illumination point). Accurate wafer positioning and beam size and shape characterization are required to achieve a small measurement cell size. Furthermore, this document presents calibration for accurately locating the illumination beam on the desired target area on the surface of the semiconductor wafer across the entire range of incident and azimuth angles.

[0059] This paper presents a six-DOF sample positioning system. Furthermore, a dedicated calibration target described herein enables highly accurate characterization of the X-ray beam profile and highly accurate alignment of the X-ray beam relative to the calibration target. This achieves precise navigation of wafers required for measuring small-sized metrology targets (e.g., metrology targets positioned in scribing channels with dimensions of 100 micrometers or less).

[0060] Figure 1 An embodiment of a T-SAXS metrological tool 100 for measuring the properties of a sample, in at least one novel aspect, is described. For example... Figure 1 As shown, the system 100 can be used to perform T-SAXS measurements over the inspection area 102 of a sample 101 illuminated by a point of illumination beam.

[0061] In the depicted embodiment, the metrology tool 100 includes an x-ray illumination subsystem 125, which includes an x-ray illumination source 110, focusing optics 111, a beam divergence control slit 112, an intermediate slit 113, and a beam shaping slit mechanism 120. The x-ray illumination source 110 is configured to generate x-ray radiation suitable for T-SAXS measurements. In some embodiments, the x-ray illumination source 110 is configured to generate wavelengths between 0.01 nanometers and 1 nanometer. Generally, any suitable high-brightness x-ray illumination source capable of generating high-brightness x-rays at flux levels sufficient to achieve high throughput, in-line metrology is conceivable for supplying x-ray illumination for T-SAXS measurements. 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.

[0062] In some embodiments, one or more X-ray sources emitting radiation with photon energies greater than 15 keV are employed to ensure that the X-ray source supplies light at wavelengths that allow sufficient transmission throughout the device and the wafer substrate. By way of non-limiting examples, any of particle accelerator sources, liquid anode sources, rotating anode sources, fixed solid anode sources, micro-focusing sources, micro-focusing rotating anode sources, plasma-based sources, and inverse Compton sources can be used as X-ray illumination source 110. In one example, an inverse Compton source available from Lyncean Technologies, Inc., Palo Alto, California (United States) is conceivable. Inverse Compton sources have the additional advantage of being able to generate X-rays in the range of photon energies, thereby enabling the X-ray source to deliver X-ray radiation at different selectable wavelengths.

[0063] Exemplary X-ray sources include electron beam sources configured to bombard solid or liquid targets to stimulate 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.

[0064] X-ray illumination source 110 generates X-ray emission over a source region having a finite lateral dimension (i.e., a non-zero dimension orthogonal to the beam axis). Focusing optics 111 focus the source radiation onto a metrological target positioned on sample 101. The finite lateral source dimension results in a finite point size 102 on the target defined by rays 117 originating from the edge of the source. In some embodiments, focusing optics 111 comprises elliptical focusing optics.

[0065] A beam divergence control slit 112 is positioned in the beam path between the focusing optics 111 and the beam shaping slit mechanism 120. The beam divergence control slit 112 limits the divergence of illumination provided to the sample to be measured. An additional intermediate slit 113 is positioned in the beam path between the beam divergence control slit 112 and the beam shaping slit mechanism 120. The intermediate slit 113 provides additional beam shaping. However, in general, the intermediate slit 113 is optional.

[0066] The beam-shaping slit mechanism 120 is positioned in the beam path immediately preceding the sample 101. In one aspect, the slit of the beam-shaping slit mechanism 120 is positioned close to the sample 101 to minimize the expansion of the incident beam size, defined by the finite source size, due to beam divergence. In one example, for a 10-micron X-ray source size and a distance of 25 millimeters between the beam-shaping slit and the sample 101, the expansion of the beam size due to shading caused by the finite source size is approximately 1 micron.

[0067] In some embodiments, the beam-shaping slit mechanism 120 includes a plurality of independently actuated beam-shaping slits. In one embodiment, the beam-shaping slit mechanism 120 includes four independently actuated beam-shaping slits. These four beam-shaping slits effectively block a portion of the incoming beam 115 and produce an illumination beam 116 having a box-shaped illumination cross-section.

[0068] Figure 2 and 3 Depicted in two different configurations Figure 1 An end view of the beam-shaping slit mechanism 120 depicted in the image. Figure 2 and 3 The diagram explains that the beam axis is perpendicular to the illustration page. (For example...) Figure 2 As depicted, the incoming beam 115 has a large cross-section. In some embodiments, the incoming beam 115 has a diameter of approximately 1 mm. Furthermore, the position of the incoming beam 115 within the beam-shaping slits 126 to 129 has an uncertainty of approximately 3 mm, attributable to beam pointing error. To accommodate the uncertainty in the size and position of the incoming beam, each slit has a length L of approximately 6 mm. Figure 2 As depicted, each slit can move in a direction perpendicular to the beam axis. Figure 2 In the description, slits 126 to 129 are positioned at the maximum distance from the beam axis (i.e., the slits are fully open and do not restrict light from passing through the beam-shaping slit mechanism 120).

[0069] Figure 3Slits 126 to 129 of a beam-shaping slit mechanism 120 are depicted in a position that blocks a portion of the incoming beam 115, thereby reducing the size and well-defined shape of the outgoing beam 116 delivered to the sample to be measured. (As shown) Figure 3 As depicted, each of the slits 126 to 129 has been moved inward toward the beam axis to achieve the desired output beam shape.

[0070] Slits 126 to 129 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 the crystal direction to minimize scattering across structural boundaries. Additionally, 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. In some embodiments, each slit has a rectangular cross-section with a width of approximately 0.5 mm and a height of approximately 1 to 2 mm. Figure 2 The slit length L is depicted as approximately 6 millimeters.

[0071] Generally, X-ray optics shape and direct X-ray radiation onto sample 101. In some instances, the X-ray optics include an X-ray monochromator to monochromate the X-ray beam incident on sample 101. In some instances, the X-ray optics use multilayer X-ray optics to collimate or focus the X-ray beam onto a measurement region 102 of sample 101 to a divergence of less than 1 milliradian. In these instances, multilayer X-ray optics also function as beam monochromators. In some embodiments, the 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), Montel optics, mirror X-ray optics (e.g., grazing-incidence 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 contents of which are incorporated herein by reference in their entirety.

[0072] X-ray detector 119 collects X-ray radiation 114 scattered from sample 101 and generates an output signal 135 indicating the properties of sample 101 that are sensitive to incident X-ray radiation, according to a T-SAXS measurement mode. In some embodiments, X-ray detector 119 collects scattered X-rays 114 while sample positioning system 140 positions and orients sample 101 to produce angle-resolved scattered X-rays.

[0073] In some embodiments, the T-SAXS system includes one or more photon counting detectors having a high dynamic range (e.g., greater than 10⁵). In some embodiments, the single-photon counting detector detects the position and number of detected photons.

[0074] In some embodiments, the x-ray detector resolves 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 119 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.

[0075] In this way, in addition to pixel position 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 a predetermined upper threshold and a predetermined lower threshold. In one embodiment, this information is transmitted to a computing system 130 via an output signal 135 for further processing and storage.

[0076] In another approach, the T-SAXS 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 1 As depicted, the metrology tool 100 includes a computational system 130 that employs a method to acquire a signal 135 generated by a detector 119 and to determine the properties of a sample based at least in part on the acquired signal.

[0077] In some instances, T-SAXS-based metrology involves determining sample size by inversely solving a pre-defined measurement model using measured data. The measurement model contains several (approximately ten) adjustable parameters and represents the geometry and optical properties of the sample, as well as the optical properties of the measurement system. Inverse methods include (but are not limited to) model-based regression, 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.

[0078] It is desirable to perform measurements over a wide range of incident and azimuth angles to increase the precision and accuracy of measured parameter values. This method reduces the correlation between parameters by expanding the number and diversity of datasets available for analysis to include a variety of large-angle, out-of-plane orientations. For example, in vertical orientation, T-SAXS can resolve the critical dimensions of a feature but is largely insensitive to the sidewall angles and height of the feature. However, by collecting measurements over a wide range of out-of-plane orientations, the sidewall angles and height of the feature can be resolved. In other instances, measurements performed over a wide range of incident and azimuth angles provide sufficient resolution and penetration depth to characterize high aspect ratio structures across their entire depth.

[0079] Measurements of the intensity of diffracted radiation, varying with the X-ray incident angle relative to the wafer surface normal, are collected. The information contained in the multiple diffraction orders is typically unique between each model parameter considered. Therefore, X-ray scattering produces estimates of the values ​​of the parameters of interest with small errors and reduced parameter correlations.

[0080] Each orientation of the illumination x-ray beam 116 relative to the surface normal of the wafer 101 can be described by rotating the semiconductor wafer 101 relative to any two angles of the x-ray illumination beam 115, or vice versa. In one example, the orientation can be described with respect to a coordinate system fixed to the wafer. Figure 4 An X-ray illumination beam 116 is depicted incident on wafer 101 with a specific orientation described by the incident angle θ and azimuth angle φ. The coordinate system XYZ is fixed to the metrology system (e.g., the illumination beam 116), and the coordinate system X'Y'Z' is fixed to wafer 101. The Y-axis is aligned with the surface of wafer 101 in a plane. The X and Z axes are not aligned with the surface of wafer 101. Z' is aligned with an axis perpendicular to the surface of wafer 101, and X' and Y' lie in a plane aligned with the surface of wafer 101. Figure 4 The image depicts an X-ray illumination beam 116 aligned with the Z-axis and therefore located within the XZ plane. The incident angle θ describes the orientation of the X-ray illumination beam 116 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 116 relative to the surface of the wafer 101. In this example, the orientation of the X-ray illumination beam relative to the surface of the wafer 101 is described by rotation about an axis perpendicular to the surface of the wafer 101 (i.e., the Z' axis) and rotation about an axis aligned with the surface of the wafer 101 (i.e., the Y-axis). In some other examples, the orientation of the X-ray illumination beam relative to the surface of the wafer 101 is described by rotation about a first axis aligned with the surface of the wafer 101 and another axis aligned with the surface of the wafer 101 and perpendicular to the first axis.

[0081] In one aspect, the metrology tool 100 includes a sample positioning system 140 configured to vertically position the wafer (i.e., the plane of the wafer surface is substantially aligned with the gravity vector) and to actively position the sample 101 relative to the illumination beam 116 in six degrees of freedom. Additionally, the sample positioning system 140 is configured to align the sample 101 and orient it within a large range of incident angles (e.g., at least 70 degrees) and azimuth angles (e.g., at least 190 degrees) relative to the illumination beam 116. In some embodiments, the sample positioning system 140 is configured to rotate the sample 101 within a large range of rotational angles (e.g., at least 70 degrees) aligned with the plane of the sample 101's surface. In this way, angularly resolved measurements of the sample 101 are collected by the metrology system 100 at any number of locations and orientations on the surface of the sample 101. In one example, a computational system 130 transmits a command signal (not shown) instructing the sample positioning system 140 to indicate the desired position of the sample 101. In response, the sample positioning system 140 generates command signals to various actuators of the sample positioning system 140 to achieve the desired positioning of the sample 101.

[0082] Figure 5 A sample positioning system 140 is depicted in one embodiment. In one aspect, the sample positioning system 140 provides active control over the position of wafer 101 relative to illumination beam 116 in all six degrees of freedom, while supporting wafer 101 perpendicularly relative to the gravity vector (i.e., the gravity vector is approximately in the same plane as the wafer surface). The sample positioning system 140 supports wafer 101 at its edges, thereby allowing illumination beam 116 to penetrate wafer 101 within any portion of the active region of wafer 101 without remounting wafer 101. By supporting wafer 101 perpendicularly at its edges, gravity-induced indentation of wafer 101 is effectively mitigated.

[0083] like Figure 5 The sample positioning system 140, as depicted, includes a base frame 141, a lateral alignment stage 142, a stage reference frame 143, and a wafer stage 144 mounted to the stage reference frame 143. For reference purposes, {X} BF Y BF Z BF The coordinate system is attached to the base frame 141, {X NF , Y NF Z NF The coordinate system is attached to the horizontally aligned stage 142, {X} RF ,Y RF Z RF The coordinate system is attached to the stage reference frame 143, and {X} SF Y SF ZSF A coordinate system is attached to the wafer stage 144. The wafer 101 is supported on the wafer stage 144 by a tilt-z stage 156 comprising actuators 150A to C. A rotary stage 158, mounted to the tilt-z stage 156, orients the wafer 101 relative to the illumination beam 116 within an azimuth angle φ. In the depicted embodiment, three linear actuators 150A to C are mounted to the wafer stage 144 and support the rotary stage 158, which in turn supports the wafer 101.

[0084] Actuator 145 causes the lateral alignment stage 142 to move along the X-axis. BF The axis translates relative to the base frame 141. The rotary actuator 146 causes the stage reference frame 143 to rotate around the Y-axis. NF The axially aligned rotation axis 153 rotates relative to the transversely aligned stage 142. The rotation actuator 146 orients the wafer 101 relative to the illumination beam 116 within the incident angle θ range. Wafer stage actuators 147 and 148 cause the wafer stage 144 to move along the X-axis... RF Axis and Y RF The axis translates relative to the stage reference frame 143.

[0085] In one aspect, the wafer stage 144 is an open-aperture, biaxial (XY) linearly stacked stage. The open aperture allows the measurement beam to penetrate any portion of the entire wafer (e.g., a 300 mm wafer). The wafer stage 144 is arranged such that the Y-axis stage extends in a direction generally parallel to the axis of rotation 153. Furthermore, the Y-axis stage extends in a direction generally aligned with the gravity vector.

[0086] Actuators 150A to C coordinate to rotate the stage 158 and the wafer 101 in Z... SF The stage 158 and the wafer 101 are translated relative to the wafer stage 144 in the X direction, and the rotating stage 158 and the wafer 101 are rotated around the X direction. SF -Y SFThe planar coplanar axis is flipped and tilted relative to the wafer stage 144. The rotating stage 158 rotates the wafer 101 about an axis perpendicular to the surface of the wafer 101. In another aspect, the frame of the rotating stage 158 is coupled to actuators 150A to C by a motion mounting system comprising motion mounting elements 157A to C, respectively. In one example, each motion mounting element 157A to C includes a ball attached to the corresponding actuator and a V-slot attached to the rotating stage 158. Each ball forms two-point contact with the corresponding V-slot. Each motion mounting element constrains the motion of the rotating stage 158 relative to the actuators 150A to C in two degrees of freedom, and the three motion mounting elements 157A to C collectively constrain the motion of the rotating stage 158 relative to the actuators 150A to C in six degrees of freedom. Each motion coupling element is preloaded to ensure that the ball always remains in contact with the corresponding V-slot. In some embodiments, the preload is provided by gravity, a mechanical spring mechanism, or a combination thereof.

[0087] In another aspect, the rotating stage 158 is an open-aperture rotating stage. The open aperture allows the measurement beam to penetrate any portion of the entire wafer (e.g., a 300 mm wafer). The rotating stage 158 is arranged such that its axis of rotation is substantially perpendicular to the axis of rotation 153. Furthermore, the axis of rotation of the rotating stage 158 is substantially perpendicular to the gravity vector. The wafer 101 is secured to the rotating stage 158 via an edge holder to provide complete wafer coverage with minimal edge exclusion.

[0088] In summary, the sample positioning system 140 can actively control the position of the wafer 101 relative to the illumination beam 116 in six degrees of freedom, such that the illumination beam 116 can be incident on any location on the surface of the wafer 101 (i.e., in the X-ray...). FR and Y RF The rotary actuator 146 is capable of rotating the stage reference frame 143 relative to the illumination beam 116, such that the illumination beam 116 can be incident on the surface of the wafer 101 at any of a large azimuth range (e.g., greater than two degrees). In one embodiment, the rotary actuator 146 is configured to rotate the stage reference frame 143 within a range of at least sixty degrees. A rotary actuator 158 mounted to the wafer stage 144 is capable of rotating the wafer 101 relative to the illumination beam 116, such that the illumination beam 116 can be incident on the surface of the wafer 101 at any of a large azimuth range (e.g., at least a ninety-degree rotation range). In some embodiments, the azimuth range is at least a one hundred and ninety-degree rotation range.

[0089] In some other embodiments, the laterally aligned stage 142 is removed and the stage reference frame 143 is rotated relative to the base frame 141 by a rotation actuator 146. In these embodiments, the x-ray illumination system includes one or more actuators that move one or more optical elements of the x-ray illumination system to cause the x-ray illumination beam 116, for example, in X-ray... BF The beam moves relative to the base frame 141 in the direction of rotation. In these embodiments, for example, movement of the stage reference frame 143 (replaced by movement of one or more optical elements of the x-ray illumination system for calibration purposes as described herein) moves the x-ray illumination beam relative to the rotation axis 153 to the desired position. Figure 1 and Figure 21 In the illustrated embodiment, the computing system 130 transmits a command signal 138 to the actuator subsystem 111' to redirect the x-ray emission relative to the substrate frame 141 by moving one or more elements of the x-ray illumination subsystem 125 to achieve the desired beam direction. In the illustrated embodiment, the actuator subsystem 111' moves the focusing optics 111 to redirect the x-ray emission relative to the substrate frame 141, and thus repositions the x-ray emission relative to the rotation axis 153.

[0090] Figure 6 Another description of the sample positioning system 140 in more detail. Figure 6 The same numbered elements depicted in the reference are similar. Figure 5 The described element. For example... Figure 5 As depicted, a rotary actuator 146 causes a bulk body comprising a stage reference frame 143, a wafer stage 144, a tilt-z stage 156, and a rotary stage 158 to rotate about a rotation axis 153. Figure 6 The wafer stage 144, the flip-tilt-Z stage 156, and the rotating stage 158 are depicted as being offset by a significant distance from the rotation axis 153.

[0091] In another aspect, a balancer 159 is mounted to the stage reference frame 143 to balance the wafer stage 144, the tilt-z stage 156, and the rotating stage 158, such that the center of gravity of the rotational mass of the stage reference frame 143 and all mounting elements is substantially aligned with the rotation axis 153. In this way, the force applied by the actuator 146 generates a torque about the rotation axis 153 with minimal parasitic linear force.

[0092] like Figure 6The diagram depicts an air bearing 172 guiding the movement of the lateral alignment stage 142 relative to the base frame 141. Similarly, an air bearing 171 guides the movement of the stage reference frame 143 relative to the lateral alignment stage 142. The air bearings, operating on a precision granite surface, minimize static friction and provide axial stability. This improves positioning performance (i.e., high repeatability and short settling time) while supporting heavy loads.

[0093] To ensure that the intersection position of the illumination beam 116 and the surface of the wafer 101 does not change over a large incident angle range, the rotation axis 153 must have very small synchronous and asynchronous errors. Additionally, any Abbe error must be minimized. To minimize Abbe error, air bearings 171 are radially equidistant around the rotation axis 153. The bearing races are large enough to prevent large angular errors. The bearings are constrained perpendicularly by the surface of the lateral alignment stage 142. In some embodiments, the surface of the lateral alignment stage 142 is perpendicular to the precision-ground granite surface of the rotation axis 153.

[0094] Generally, sample positioning systems provide automated positioning of semiconductor wafers in six degrees of freedom. Additionally, sample positioning systems include edge gripping features on a rotating stage and actuators to efficiently load and unload wafers in a vertical position in coordination with a wafer handling robot.

[0095] In some embodiments, three sensors are mounted on a sample positioning system to measure the distance between the back side of the wafer and the sample positioning system. In this way, wafer warpage is measured and compensated for by moving the wafer using a flip-tilt-Z stage.

[0096] In another aspect, the SAXS metrology system employs at least one beam-blocking calibration target to position the X-ray illumination beam relative to the sample positioning system. The beam-blocking calibration target comprises at least one marker and a cylindrical blocking element. A alignment camera is used to position the marker in the coordinates of the sample positioning system. The position of the marker relative to the cylindrical blocking element is known in advance (e.g., with an accuracy of less than 200 nanometers). Therefore, the position of the cylindrical blocking element in the coordinates of the sample positioning system can be easily determined by direct coordinate transformation. The cylindrical blocking element is scanned across the illumination beam while measuring the detected intensity of the transmission flux. The center of the illumination beam is precisely positioned relative to the cylindrical blocking element based on the measured intensity. Since the position of the cylindrical blocking element in the coordinates of the sample positioning system is known, the center of the illumination beam is precisely positioned in the coordinates of the sample positioning system by a simple coordinate transformation.

[0097] In some instances, a beam-blocking calibration target is used to calibrate the incident position of the illumination beam relative to the sample positioning system. In other instances, a beam-blocking calibration target is used to align the rotation axis of the stage reference frame relative to the illumination beam at the point of incidence of the illumination beam and the wafer.

[0098] Figure 7 A beam blocking calibration target 190 is depicted in one embodiment. Figure 7 In the embodiment depicted, the beam blocking calibration target 190 includes a precisely shaped cylindrical pin 192 and a frame 191 supporting the cylindrical pin 192. The cylindrical pin 192 is manufactured with high surface quality and precise dimensions on the order of target uncertainty (e.g., tolerance of less than 0.5 micrometers).

[0099] In some embodiments, frame 191 may be a structure mounted to a sample positioning system (e.g., sample positioning system 140). In these embodiments, the beam-blocking calibration target 190 is mounted to the sample positioning system 140 instead of a calibration wafer. In some other embodiments, frame 191 may be a dedicated calibration wafer comprising one or more cylindrical pins attached to the wafer itself. In these embodiments, the beam-blocking calibration target 190 is mounted to the calibration wafer. The beam-blocking calibration target 190 also includes openings 193 on one or both sides of the cylindrical pins 192. The openings 193 are sized such that an illumination beam (e.g., illumination beam 197) can pass through the beam-blocking calibration target 190 without obstruction (e.g., at least 2 mm by 2 mm). The beam-blocking calibration target 190 also includes one or more markings (e.g., markings 195 and 196) that can be read by an optical microscope mounted to the sample positioning system. The positions of markings 195 and 196 relative to the edges 198 and 199 of the cylindrical pins are precisely known. In this way, the position of the edge of the cylindrical pin 192 can be determined from the position of either mark 195 or 196, or both, through a simple coordinate transformation.

[0100] The cylindrical pin-shaped shielding element largely eliminates the limited transparency problem that arises when using a blade as the target. The beam path through the cylindrical pin is defined by the radius R of the cylinder and the irradiation depth S of the beam path relative to the edge of the cylindrical pin. When R is significantly greater than S, the length L of the beam path through the cylindrical pin is approximately calculated by equation (1).

[0101] (1)

[0102] When a tungsten carbide cylindrical pin with a diameter of approximately 2 mm is used, the edge position uncertainty attributable to the translucency of the hard X-rays is less than one micrometer. Generally, the cylindrical pin 192 can be made of any suitable dense, high atomic number material. By way of non-limiting examples, the cylindrical pin 192 can be constructed from tungsten carbide, tungsten, platinum, etc. The diameter of the cylindrical pin should be large enough that the induced uncertainty at the edge position attributable to the translucency of the material is entirely within the total alignment error budget. Typically, a diameter of 2 to 3 mm is sufficient to maintain the induced uncertainty at the edge position attributable to the translucency of the material below one to two micrometers.

[0103] like Figure 7 The image depicts a beam blocking calibration target 190 comprising one or more flat surfaces (e.g., flat surface 194) precisely aligned with the axis of a cylindrical pin 192. In some instances, surface 194 is a reference surface used to measure the target's position in a direction collinear with the X-ray beam by a distance sensor (e.g., a capacitive probe, an inductive probe, etc.). Additionally, in some embodiments, one or more markers are positioned on the flat surface. For example, as... Figure 7 In the depiction, mark 195 is positioned on flat surface 194.

[0104] exist Figure 5 In the embodiment depicted, beam blocking calibration targets 151 and 152 are mounted on a frame of a rotating stage 158 such that the central axis of the cylindrical pin is substantially coplanar with the surface of the wafer 101. Figure 5 As depicted, cylindrical pin 151 includes Y NF The axis is generally parallel to the central axis and the cylindrical pin 152 is included with X RF The axes are roughly parallel to the central axis. Each cylindrical pin blocks the beam by absorbing most of any X-rays that might be hitting the beam.

[0105] The sample positioning system 140 also includes an alignment camera 154 mounted to the stage reference frame 143. In the depicted embodiment, the alignment camera is mounted to the stage reference frame and thus rotates with the stage reference frame. The alignment camera 154 is configured to produce high-resolution images of objects (e.g., wafer 101) in its field of view. In some embodiments, the alignment camera 154 also includes an autofocus mechanism that maintains sharp image focus by precisely moving the camera's focus over a measured distance. In some of these embodiments, the alignment camera 154 can be used to measure the relative distance between the stage reference frame to which the camera body is mounted and the wafer 101 or markers 151A and 152A imaged by the camera by monitoring the z-displacement of the camera's focus.

[0106] In some other embodiments, the alignment camera is mounted to the lateral alignment stage 142. In some of these embodiments, the alignment camera is used to measure the position of the camera body mounted on {X} by monitoring the position of optical marks mounted on wafer 101 or marks 151A and 152A within the field of view of the alignment camera. NF Y NF Z NF The relative distance between the coordinate system and the chip 101 or markers 151A and 152A imaged by the camera.

[0107] In another aspect, the precise incident position of the illumination beam in two dimensions of the plane on the surface of the wafer is determined based on the interaction between the illumination beam and two or more beam-blocking calibration targets.

[0108] Figure 9 This is a diagram illustrating the sample positioning system 140, in which the wafer stage is moved to a position where the illumination beam 116 is blocked by the cylindrical pin element 151. The precise incident position of the illumination beam relative to the cylindrical pin 151 is determined based on the transmission flux, measured by the detector 119, which varies according to the x-position of the cylindrical pin 151 relative to the illumination beam 116 (e.g., the substrate frame 141). Figure 9 As depicted, as the cylindrical pin 151 moves in the positive X direction (in X... BF As the illumination beam 116 moves in the negative X direction (as opposed to X), more and more of it is blocked by the cylindrical pin 151. Therefore, fewer photons reach the detector 119. However, as the cylindrical pin 151 moves in the negative X direction (as opposed to X), more and more of the illumination beam 116 is blocked by the cylindrical pin 151. BF Conversely, as the illumination beam 116 moves upward, less and less of it is blocked by the cylindrical pin 151. The detector 119 generates a signal 155 indicating the measured flux that varies according to the X position, and the result is analyzed to identify the position of the cylindrical pin corresponding to the center of the illumination beam 116.

[0109] Figure 10 A graph 170 depicts the measured flux as it varies relative to the alignment of the cylindrical pin with respect to the illumination beam 116. The depicted relationship between the measured flux 155 and the alignment is an S-shaped function (e.g., a logic or other error function depending on the beam profile).

[0110] In some instances, the beam center is determined as the alignment of a cylindrical pin with respect to the illumination beam, where the measured flux is at a minimum flux value F. MIN With the maximum flux value F MAXOr the midpoint of the maximum value of the derivative dF / dx. However, in some other instances, the beam center can be determined at a different flux value than the median of the range of measured flux. In some instances, a more precise relationship is determined by modeling the interaction between the beam and the material and geometry of the cylindrical pin. In these instances, the modeled interaction is compared with the measured transmission flux, and a fitting algorithm is used to determine the relative position of the cylindrical pin with respect to the illumination beam (its alignment with the beam center) based on the fit between the measurements and the model.

[0111] In one example, the estimated distance ΔX between the current position of the cylindrical pin 151 relative to the center of the illumination beam 116 and the position of the cylindrical pin 151 coinciding with the beam center is based on a measured flux F that varies according to the position of the cylindrical pin. MEAS Flux midpoint F MID and the reciprocal of the derivative of the measured flux, as described by equation (2).

[0112] (2)

[0113] And F MID It is described by equation (3).

[0114] (3)

[0115] The maximum and minimum values ​​of the measured flux can be measured by scanning the wafer stage simultaneously with the measurement of the transmission flux. Furthermore, the slope at the midpoint can be estimated. Based on these quantities, the estimate of the change in the center position of the cylindrical pin can be determined solely by equation (2) by measuring the flux at a location. The change in center position can be iteratively determined as needed to converge to the center position.

[0116] Because the beam has centroid components in two directions (e.g., X and Y), the measurements are performed on two cylindrical pins oriented perpendicular to each centroid component. Figure 9 In the embodiment depicted, cylindrical pin 151 is used to position the beam center relative to the stage reference frame in the X direction, and cylindrical pin 152 is used to position the beam center relative to the stage reference frame in the Y direction. Generally, more than two cylindrical pins can be used to create redundancy and increase the accuracy of beam position calibration.

[0117] like Figure 9 As depicted, the center of the illumination beam 116 is aligned with the edges of the vertically and horizontally oriented cylindrical pins 151 and 152 as described above. Figure 9In the embodiment depicted, reference mark 151A is positioned coplanar with the central axis of cylindrical pin 151. Similarly, reference mark 152A is positioned coplanar with the central axis of cylindrical pin 152. At the position where the beam center is aligned with cylindrical pin 151, the position of illumination beam 116 relative to cylindrical pin 151 or reference mark 151A at or near cylindrical pin is recorded by alignment camera 154. This aligns the phase-matching position of the illumination beam with respect to a precise position in the field of view of the alignment camera (assuming the focus position remains unchanged). Figure 5 The image depicts a wafer 101 moving within the field of view of an alignment camera 154. This movement of the wafer 101 causes a desired location (e.g., a reference mark) on the wafer to be imaged within the field of view of the alignment camera 154. The alignment camera 154 determines the position of the illumination beam 116 relative to the desired location based on prior registration. In this way, the position of the illumination beam 116 on the wafer 101 in the X and Y directions is rapidly estimated based on the image collected by the alignment camera 154. In some embodiments, the Z-position of the wafer relative to the cylindrical pin 151 in the Z direction is measured by changing the focus position of the alignment camera 154 until the lithographic features on the surface of the wafer 101 are precisely focused. The change in focus position indicates the Z-position difference between the cylindrical pin and the imaged location on the wafer. In some other embodiments, the Z-position of the wafer relative to the cylindrical pin 151 in the Z direction is measured by one or more optical proximity sensors, capacitive proximity sensors, interferometric sensors, or other suitable proximity sensors. Actuators 150A to C can be used to reposition wafer 101 in the Z direction to reposition the imaging position in the same plane as the cylindrical pin (e.g., reference mark 151A).

[0118] In another approach, the incident position of the illumination beam is determined at any location on the wafer based on the wafer stage coordinates. Once the center of the illumination beam is aligned with the vertical and horizontal cylindrical pins, and the position of the illumination beam relative to the cylindrical pins is recorded by an alignment camera as described above, the incident position of the illumination beam can be transmitted to the stage coordinates. Figure 5 As depicted, wafer 101 moves within the field of view of alignment camera 154. The movement of wafer 101 is measured by a position measurement system (e.g., a linear encoder) on wafer stage 144. By moving wafer 101 to three or more desired positions (e.g., reference marks) on the wafer imaged within the field of view of alignment camera 154, the position of the illumination beam relative to the desired position and the position of the wafer in stage coordinates are determined at each desired position. Based on the known position of the illumination beam and the stage coordinates at the three or more positions, a mapping is generated that relates the stage coordinates to the incident position of the illumination beam.

[0119] After positioning the cylindrical pin 151 at the center of the illumination beam 116 (in the X direction), the alignment camera 154 images the position of the cylindrical pin itself or a reference mark positioned on or near the cylindrical pin to establish a relationship between the beam position and the image position within the field of view of the alignment camera 154. Since the alignment camera 154 is positioned in a fixed or repeatable position relative to the stage reference frame 143, the image registers the position of the illumination beam relative to the stage reference frame 143 and thus serves as a reference for the beam position in the X direction. Furthermore, the alignment camera 154 establishes a precise focus position for the reference mark to establish a precise Z position of the cylindrical pin relative to the stage reference frame 143. In embodiments where the alignment camera 154 rotates with the stage reference frame, the focus position of the alignment camera 154 serves as a reference for the Z position of the cylindrical pin relative to the stage reference frame.

[0120] Because the incident position of the beam is estimated using the blocked flux, there is a risk that changes in the flux within the illumination beam will be interpreted as a positional shift. In some embodiments, the flux of the illumination beam is measured immediately before, after, or simultaneously with the blocked measurement. Variations in the illumination flux are compensated for in the analysis of the measured flux 155 to eliminate their influence on the measurement.

[0121] In another aspect, the precise alignment of the illumination beam with the plane of the wafer surface is determined based on the interaction between the illumination beam and two or more beam-blocking calibration targets, such as those measured by the x-ray detector 119.

[0122] To ensure measurement integrity, the incident position of the illumination beam 116 on the surface of the wafer 101 should remain fixed within a wide range of incident and azimuth angles during the measurement. To achieve this, the rotation axis 153 of the stage reference frame 143 must be substantially coplanar with the surface of the wafer 101 at the measurement position. Furthermore, the rotation axis 153 must be within the X-axis range. BF The direction is aligned with the illumination beam 116, such that the rotation axis 153 intersects the illumination beam 116 at the point of incidence of the illumination beam 116 and the wafer 101 at the measurement position.

[0123] Figure 8A Describing as Figure 5 The image depicts a top view of an illumination beam 116 incident on a wafer 101. Figure 8A An end view of the rotation axis 153 in the aligned state is shown, wherein the rotation axis 153 is positioned 103 on the wafer 101 at the point of incidence of the illumination beam 116 onto the wafer 101. Figure 8AAs depicted, as the wafer 101 rotates about the rotation axis 153 within a large incident angle, the illumination beam 116 remains incident at position 103. Therefore, in this case, the incident position of the illumination beam 116 on the surface of the wafer 101 remains fixed within a large incident angle range during measurement.

[0124] Figure 8B Describing as Figure 5 The image depicts a top view of an illumination beam 116 incident on a wafer 101. Figure 8B An end view depicting the rotation axis 153 in an aligned state, wherein the rotation axis 153 is misaligned with the surface of the wafer 101 by a distance... z. For example Figure 8B As depicted, as wafer 101 rotates around rotation axis 153 over a large incident angle θ range, a portion of position 103 is no longer illuminated (i.e., some other portions of wafer 101 are illuminated instead). Therefore, in this case, the incident position of illumination beam 116 on the surface of wafer 101 drifts over a large incident angle range during measurement, which is highly undesirable.

[0125] Figure 8C Describing as Figure 5 The image depicts a top view of an illumination beam 116 incident on a wafer 101. Figure 8C An end view depicting the rotation axis 153 in an aligned state, wherein the rotation axis 153 is coplanar with the surface of the wafer 101 but offset from the illumination beam 116 by a distance. x. For example... Figure 8C As depicted, as wafer 101 rotates around rotation axis 153 over a large incident angle θ range, a portion of position 103 is no longer illuminated (i.e., instead, some other portion of wafer 101 is illuminated). Therefore, in this case, the incident position of illumination beam 116 on the surface of wafer 101 drifts over a large incident angle range during measurement, which is highly undesirable.

[0126] In some embodiments, the rotation axis of the stage reference frame is calibrated by aligning the center of the illumination beam with the cylindrical pin 151 in the X direction and measuring the flux at multiple different rotational positions θ of the stage reference frame. This is based on a selected occlusion model as described above (e.g., Figure 1 The S-shaped function or another model described in the figure determines the apparent motion of the cylindrical pin in the X direction. X). Furthermore, the apparent motion of the cylindrical pin in the X direction is a function of the following: 1) the distance of the cylindrical pin from the axis of rotation in the x direction. x and the distance from the axis of rotation in the z direction z; 2) Distance in the x-direction from the beam center and the rotation axis 153 n; and 3) the rotation angle θ about the rotation axis 153 of the stage reference frame. The relationship is described in equation (4).

[0127] (4)

[0128] In one instance, the transmitted flux is measured at three incident angles {-Θ, 0, +Θ}. The linear equations described by equation (5) are derived from equation (4).

[0129] (5)

[0130] Equation (6) is obtained by inverse calculation of equation (5). Equation (6) is solved from the apparent motion of the cylindrical pin in the X direction. n、 x and The value of z.

[0131] (6)

[0132] Equations (6) and (3) are combined to solve for the apparent motion of the cylindrical pin in the X direction, determined by the measured flux. n、 x and The value of z is obtained iteratively, as described by equation (7) in some instances. n、 x and Solution for z-value.

[0133] , of which (7)

[0134] Where k is the iteration exponent and w is the vector of displacement values ​​of the actuator of the sample positioning system 140 required to align the rotation axis 153 and the blade edge 151 in the X and Z directions. n、 x and Displacement is achieved by moving the entire stage reference frame 143 relative to the illumination beam 116 in the X direction via actuator 145. n. Displacement is achieved by moving the cylindrical pin 151 back to alignment with the beam via actuator 147. x. The cylindrical pin is moved in the Z direction by actuators 150A to C to align the rotating shaft 153 in the Z direction with the central axis plane of the cylindrical pin, thereby achieving displacement. z. Starting with the initial estimate w0, the recursion of equation (7) will converge to the point where the rotation axis 153 is aligned with the cylindrical pin 151.

[0135] Generally, it is not necessary to apply equation (7) precisely. A can be calculated using numerical approximations.Θ and X / The value of F. In other instances, other matrices can be used, as long as the iteration is stable and converges to the correct value.

[0136] Generally, the transmitted flux can be measured at any three or more different incident angles to determine the displacement values ​​required to align the rotating shaft 153 and the cylindrical pin 151 in the X and Z directions. The choice of any three different incident angles results in a system of linear equations that can be directly inversely calculated. The choice of four or more different incident angles results in an overdetermined system of linear equations that can be solved using a pseudo-inverse algorithm to determine the displacement values ​​required to align the rotating shaft 153 and the cylindrical pin 151 in the X and Z directions. The matrix terms described in equations (5) and (6) depend on the chosen incident angles. Therefore, in instances where different incident angles are chosen, the terms will differ from those in equations (5) and (6).

[0137] In another aspect, the precise alignment of the rotation axis 153 with the markings of the calibration target in the plane of the wafer surface (e.g., marking 151A of the beam-blocking calibration target 151, markings located on the wafer 101, etc.) is determined based on the images of the markings collected by the alignment camera mounted to the lateral alignment stage 142.

[0138] The apparent motion of the marker in the X direction within the field of view of the camera ( The distance of the X-axis from the axis of rotation in the x-direction. x and the distance from the axis of rotation in the z direction z is a function of the rotation angle θ around the rotation axis 153 of the stage reference frame. For the alignment camera mounted to the transverse alignment stage 142, the relationship is described in equation (8).

[0139] (8)

[0140] In some instances, the X position of a marker (e.g., marker 151A) is measured at any three different incident angles to determine the displacement values ​​required to align the rotation axis 153 with the cylindrical pin 151 in both the X and Z directions. The choice of any three different incident angles allows for direct inverse calculation to determine the distance of the marker from the rotation axis in the x direction. x and the distance from the axis of rotation in the z direction A system of linear equations for z.

[0141] For an idealized beam-blocking calibration target and rotation axis, a single beam-blocking calibration target would be sufficient for beam calibration. However, depending on system requirements, multiple beam-blocking calibration targets may be necessary. By aligning the edges of multiple blocking elements, the rotation axis and nominal Y-axis can be deduced. NFAny deviation of the axis. Moreover, multiple identical occlusion elements allow for edge calibration from the right and left or top and bottom sides, thereby helping to eliminate systematic errors in the imaging edges (i.e., those imaged by the aligned camera 154) and the apparent edges inferred from changes in the occluded flux.

[0142] In another aspect, the SAXS metrology system employs at least one periodic calibration target to position the X-ray illumination beam relative to a sample positioning system. Each periodic calibration target comprises one or more spatially defined regions having different periodic structures that diffract the X-ray illumination light into dissimilar diffraction patterns measurable by the SAXS metrology system described herein. Additionally, each periodic calibration target comprises one or more markers that can be read by an optical microscope to position the periodic calibration target relative to the sample positioning system with high alignment accuracy (e.g., 0.5 micrometers or less). Each spatially defined region has a spatially well-defined boundary line. The position of the boundary line relative to the markers is known to have high accuracy (e.g., 0.2 micrometers or less) in one or more dimensions.

[0143] In some embodiments, the size of each periodic region is designed to be larger than the projection of the illumination beam onto the periodic calibration target. In this way, the beam profile can be characterized by scanning the interface between each of two different periodic regions, each sized to be larger than the illumination beam. In some embodiments, the illumination beam 116 has a beam width of less than 200 micrometers. In some embodiments, the illumination beam 116 has a beam width of less than 100 micrometers. In some embodiments, the illumination beam 116 has a beam width of less than 50 micrometers. Additionally, in some instances, calibration measurements are performed at a large incident angle. In these instances, the projection of the illumination beam onto the periodic calibration target is elongated in one direction, and each periodic region is sized to be larger than the projected illumination area.

[0144] In some embodiments, the size of each periodic region varies depending on the direction relative to the illumination beam. For example, the periodic region may be larger in a direction perpendicular to the rotation axis 153 to accommodate a large incident angle. In another instance, the illumination beam may be larger in one direction than in another (e.g., a rectangular illumination beam shape) and the periodic region may be larger in the elongation direction.

[0145] In some embodiments, one or more of the periodic regions are sized to match the desired measurement box size. In one example, one of the periodic regions is sized to match the illumination beam size (e.g., 50 square micrometers or 100 square micrometers) or some other number used for calibrating the alignment of the rotation axis 153 relative to the illumination beam 116. In this example, perfect alignment is achieved when the illumination beam 116 does not move relative to the periodic calibration target over a large AOI range. In this example, if the illumination beam moves relative to the periodic calibration target as the AOI changes, the illumination beam will move from the periodic region sized to match the illumination beam size to an adjacent periodic region. This movement of the illumination beam across the boundary between regions is detected by detector 119.

[0146] Generally, a set of periodic calibration targets or a set of regions of periodic calibration targets contains regions of different sizes used to characterize the beam profile and size. Generally, one or more regions may be of a predetermined size that is larger than, smaller than, or the same as the size of the illumination beam.

[0147] Generally, the periodicity of the periodic calibration target is optimized to enhance X-ray scattering contrast. The spacing between each periodic structure is small enough to ensure adequate spatial separation of the detected order at the detector. The angle of each diffraction order should be significantly larger than the beam divergence to ensure adequate spatial separation, and the angle of each diffraction order increases as the spacing decreases. In some embodiments, the spacing between each periodic structure should be about 0.1 micrometers (e.g., less than 200 nanometers) to ensure adequate spatial separation and measurement accuracy.

[0148] Each periodic structure is made of a material with high contrast to hard X-rays and a large atomic number (e.g., tungsten, tungsten carbide, platinum, etc.).

[0149] In addition, each periodic structure is manufactured to a sufficient height to produce a measurable diffraction pattern within a reasonable exposure time. In some instances, periodic structures with a height of 0.5 mm or greater are advantageous.

[0150] In some embodiments, any of the periodic calibration targets described herein are mounted to a sample positioning system (e.g., sample positioning system 140). In some other embodiments, any of the periodic calibration targets described herein are mounted to a calibration wafer or a production wafer to be measured.

[0151] Figure 11 Another description of the sample positioning system 140 in more detail. Figure 11 The same numbered elements depicted in the reference are similar. Figure 5 The described element. Figure 11 In the embodiment depicted, the periodic calibration target 171 is positioned on the wafer 101.

[0152] The periodic calibration target 171 comprises at least one mark and multiple periodic structures (e.g., gratings). If the illumination beam 116 is incident on two or more different diffraction patterns, the ratio of the measured intensities of the orders associated with the different periodic structures provides information about the position of the illumination beam relative to the illuminated patterns. A alignment camera 154 is used to position the mark in the coordinates of the sample positioning system. The position of the mark relative to the periodic structures is known in advance. Therefore, the position of the periodic structures in the coordinates of the sample positioning system can be easily determined by direct coordinate transformation. The periodic calibration target 171 is scanned across the illumination beam 116 while the detected intensity of the diffraction orders is measured by detector 119. The center of the illumination beam 116 is precisely positioned relative to the periodic calibration target 171 based on the measured intensity. Since the position of the periodic calibration target 171 in the coordinates of the sample positioning system is known, the center of the illumination beam in the coordinates of the sample positioning system is precisely positioned by simple coordinate transformation.

[0153] In some instances, a periodic calibration target is used to calibrate the incident position of the illumination beam relative to the sample positioning system. In other instances, a periodic calibration target is used to align the rotation axis of the stage reference frame relative to the illumination beam at the incident point of the illumination beam and the wafer. In still other instances, the periodic calibration target is scanned across the illumination beam at numerous azimuth angles. In this way, in addition to calibrating the position of the illumination beam relative to the target, the beam profile is also characterized.

[0154] In some embodiments, the periodic calibration target includes a central periodic region and one or more periodic regions surrounding the central periodic region. Each periodic region includes different spacing, different spacing orientations, or combinations thereof.

[0155] Figure 12 An embodiment of the periodic calibration target 210 is depicted. For example... Figure 12 As depicted, the periodic calibration target 210 includes marks 211 and 212 readable by an optical microscope mounted to a sample positioning system, a small-pitch periodic structure 215 located in a central region 214, and a larger-pitch periodic structure 213 in a peripheral region surrounding the central region 214. Marks 211 and 212 are located in the same plane as the periodic structure of the periodic calibration target. Furthermore, the positions of marks 211 and 212 relative to the boundary of the central region 214 are precisely known. In this way, the position of the boundary is determined from the position of either mark 211 or 212, or both, through a simple coordinate transformation.

[0156] Illumination of the central region 214 (i.e., periodic structure 215) by illumination beam 116 results in multi-order diffraction across detector 119 with relatively large horizontal spacing (e.g., 100 micrometers). Illumination of the peripheral region (i.e., periodic structure 213) by illumination beam 116 results in multi-order diffraction across detector 119 with smaller horizontal spacing due to the larger spacing of grating 213. The intensity ratio between the measured orders of grating 215 and grating 213 indicates the position of illumination beam 116 relative to the boundary line between the central region 214 and the peripheral region.

[0157] Figure 13 An embodiment of the periodic calibration target 220 is depicted. For example... Figure 13 As depicted, the periodic calibration target 220 includes markers 221 and 222 readable by an optical microscope mounted to a sample positioning system, a vertically positioned periodic structure 225 located in a central region 224, and a horizontally positioned periodic structure 223 in a peripheral region surrounding the central region 224. Markers 221 and 222 are located in the same plane as the periodic structure of the periodic calibration target. Furthermore, the positions of markers 221 and 222 relative to the boundary of the central region 224 are precisely known. In this way, the position of the boundary is determined from the position of either marker 221 or 222, or both, through a simple coordinate transformation.

[0158] Illumination of the central region 224 (i.e., periodic structure 225) by illumination beam 116 results in multi-order diffraction across detector 119 in the horizontal direction. Illumination of the peripheral region (i.e., periodic structure 223) by illumination beam 116 results in multi-order diffraction across detector 119 in the vertical direction. The intensity ratio between the measured orders of gratings 225 and 223 indicates the position of illumination beam 116 relative to the boundary line between the central region 224 and the peripheral region.

[0159] Figure 14 An embodiment of the periodic calibration target 230 is depicted. For example... Figure 14 As depicted, the periodic calibration target 230 includes markers 231 and 232 readable by an optical microscope mounted to a sample positioning system, and a horizontally arranged periodic structure 233 in the peripheral region surrounding a central region 234 that is completely devoid of periodic structure. Markers 231 and 232 are positioned in the same plane as the periodic structure of the periodic calibration target. Furthermore, the positions of markers 231 and 232 relative to the boundary of the central region 234 are precisely known. In this way, the position of the boundary is determined from the position of either marker 231 or 232, or both, through a simple coordinate transformation.

[0160] Illumination of the central region 234 by illumination beam 116 does not cause diffraction; only the zeroth order is detected. Illumination of the peripheral region (i.e., the periodic structure 233) by illumination beam 116 causes multi-order diffraction across detector 119 in the vertical direction. The intensity ratio between the measured order and the zeroth order intensity of grating 233 indicates the position of illumination beam 116 relative to the boundary line between the central region 234 and the peripheral region.

[0161] In some embodiments, the periodic calibration target comprises any number of periodic zones intersecting at a common point. In this manner, the X-ray illumination beam is aligned with the common point shared by each of the periodic zones. Each periodic zone contains different spacing, different spacing orientations, or combinations thereof.

[0162] Figure 15 An embodiment of the periodic calibration target 240 is depicted. For example... Figure 15 As depicted, the periodic calibration target 240 includes markers 241 and 242 that can be read by an optical microscope mounted to the sample positioning system, and four periodic zones positioned in an orthogonal arrangement. Figure 15 As depicted, the vertically positioned periodic structure 243 is located in the first quadrant, the horizontally positioned periodic structure 244 is located in the second quadrant, the vertically positioned periodic structure 245 is located in the third quadrant, and the horizontally positioned periodic structure 266 is located in the fourth quadrant. Markers 241 and 242 are located in the same plane as the periodic structures of the periodic calibration target. Furthermore, the position of the common point of markers 241 and 242 relative to the center of the orthogonal arrangement is precisely known. In this way, the position of the common point is determined from the position of either marker 241 or 242, or both, through a simple coordinate transformation.

[0163] Illumination of structures 243 and 245 by illumination beam 116 results in multi-level diffraction across detector 119 in the horizontal direction. Illumination of structures 244 and 246 by illumination beam 116 results in multi-level diffraction across detector 119 in the vertical direction. The intensity ratio between the measured levels indicates the position of illumination beam 116 relative to a common point shared by structures 243 to 246.

[0164] Figure 16 An embodiment of the periodic calibration target 250 is depicted. For example... Figure 16 As depicted, the periodic calibration target 250 includes markers 251 and 252 that can be read by an optical microscope mounted to the sample positioning system, and four periodic zones positioned in an orthogonal arrangement. Figure 16The diagram depicts a periodic structure 253 oriented at -45 degrees to the vertical, positioned in the first quadrant; a periodic structure 254 oriented at 45 degrees to the vertical, positioned in the second quadrant; a horizontally positioned periodic structure 255, positioned in the third quadrant; and a vertically positioned periodic structure 256, positioned in the fourth quadrant. Markers 251 and 252 are located in the same plane as the periodic structures of the periodic calibration target. Furthermore, the position of the common point of markers 251 and 252 relative to the center of the orthogonal arrangement is precisely known. In this way, the position of the common point is determined from the position of either marker 251 or 252, or both, through a simple coordinate transformation.

[0165] Illumination of structures 253 and 254 by illumination beam 116 results in multi-order diffraction across detector 119 at +45 degrees and -45 degrees, respectively. Illumination of structures 255 and 256 by illumination beam 116 results in multi-order diffraction across detector 119 in the vertical and horizontal directions, respectively. The intensity ratio between the measured orders indicates the position of illumination beam 116 relative to a common point shared by structures 253 to 256.

[0166] Figure 17 An embodiment of the periodic calibration target 260 is depicted. (e.g.) Figure 17 As depicted, the periodic calibration target 260 includes markers 261 and 262 that can be read by an optical microscope mounted to the sample positioning system, and four periodic zones positioned in an orthogonal arrangement. Figure 17 The diagram depicts a vertically arranged periodic structure 263 with relatively small spacing positioned in the first quadrant, a horizontally arranged periodic structure 264 with relatively large spacing positioned in the second quadrant, a vertically arranged periodic structure 265 with relatively large spacing positioned in the third quadrant, and a horizontally arranged periodic structure 266 with relatively small spacing positioned in the fourth quadrant. Markers 261 and 262 are located in the same plane as the periodic structure of the periodic calibration target. Furthermore, the position of the common point of markers 261 and 262 relative to the center of the orthogonal arrangement is precisely known. In this way, the position of the common point is determined from the position of either marker 261 or 262, or both, through a simple coordinate transformation.

[0167] Illumination of structures 263 and 265 by illumination beam 116 results in multi-order diffraction across detector 119 in the horizontal direction. Illumination of structures 264 and 266 by illumination beam 116 results in multi-order diffraction across detector 119 in the vertical direction. The orders associated with structures 263 and 266 and the orders associated with structures 264 and 265 are distinctly separated. The intensity ratio between the orders is measured to indicate the position of illumination beam 116 relative to a common point shared by structures 263 to 266.

[0168] Figure 18An embodiment of the periodic calibration target 270 is depicted. (e.g.) Figure 18 As depicted, the periodic calibration target 270 includes markers 271 and 272 that can be read by an optical microscope mounted to the sample positioning system, and four periodic zones positioned in an orthogonal arrangement. Figure 18 The diagram depicts a vertically arranged periodic structure 273 with relatively small spacing positioned in the first quadrant, a horizontally arranged periodic structure 274 with relatively large spacing positioned in the second quadrant, a vertically arranged periodic structure 275 with relatively small spacing positioned in the third quadrant, and a horizontally arranged periodic structure 276 with relatively large spacing positioned in the fourth quadrant. Markers 271 and 272 are located in the same plane as the periodic structure of the periodic calibration target. Furthermore, the position of the common point of markers 271 and 272 relative to the center of the orthogonal arrangement is precisely known. In this way, the position of the common point is determined from the position of any one of markers 271 and 272, or both, through a simple coordinate transformation.

[0169] Illumination of structures 273 and 275 by illumination beam 116 results in multi-order diffraction across detector 119 in the horizontal direction. Illumination of structures 274 and 276 by illumination beam 116 results in multi-order diffraction across detector 119 in the vertical direction. The orders associated with structures 273 and 275 and the orders associated with structures 274 and 276 are distinctly separated. The intensity ratio between the diffraction orders is measured to indicate the position of illumination beam 116 relative to a common point shared by structures 273 to 276.

[0170] Figure 19A A set of periodic calibration targets 290 and 295 are depicted at point B, each suitable for positioning the illumination beam relative to the periodic calibration targets in one direction. When both targets 290 and 295 are used to calibrate the SAXS metrology system, the position of the illumination beam relative to the sample positioning system is determined in two orthogonal dimensions. For example... Figure 19A As depicted, the periodic calibration target 290 includes marks 291 and 292 that can be read by an optical microscope mounted to the sample positioning system, and two periodic regions positioned adjacent to each other along a boundary line. Figure 19A The diagram depicts a horizontally positioned periodic structure 293 positioned alongside a vertically positioned periodic structure 294. Markers 291 and 292 are positioned in the same plane as the periodic structure of the periodic calibration target. Furthermore, the positions of markers 291 and 292 relative to the boundary between structures 293 and 294 are precisely known. In this way, the position of the boundary line is determined from the position of either marker 291 or 292, or both, through a simple coordinate transformation.

[0171] Illumination of structures 293 and 294 by illumination beam 116 results in multi-level diffraction across detector 119 in the vertical and horizontal directions, respectively. The intensity ratio between the measured levels indicates the position of illumination beam 116 relative to the boundary line shared by structures 293 and 294.

[0172] Similarly, such as Figure 19B As depicted, the periodic calibration target 295 includes markers 296 and 297 that can be read by an optical microscope mounted to the sample positioning system, and two periodic regions positioned adjacent to each other along the boundary line. Figure 19B As depicted, the boundary line of target 295 intersects the boundary line of target 290. (As shown in the image) Figure 19B The diagram depicts a horizontally positioned periodic structure 298 positioned side-by-side with a vertically positioned periodic structure 299. Markers 296 and 297 are positioned in the same plane as the periodic structure of the periodic calibration target. Furthermore, the positions of markers 296 and 297 relative to the boundary between structures 298 and 299 are precisely known. In this way, the position of the boundary line is determined from the position of either marker 296 or 297, or both, through a simple coordinate transformation.

[0173] Illumination of structures 298 and 299 by illumination beam 116 results in multi-level diffraction across detector 119 in the vertical and horizontal directions, respectively. The intensity ratio between the measurement levels indicates the position of illumination beam 116 relative to the boundary line shared by structures 298 and 299.

[0174] Generally, a periodic calibration target may comprise multiple different periodic zones in any suitable configuration. In some embodiments, the periodic zones are arranged in a Cartesian pattern. However, other patterns of periodic zones are conceivable.

[0175] Figure 20 A periodic calibration target 280 is depicted, comprising markers 288 and 289 and seven different periodic zones 281 to 287 arranged in a hexagonal pattern. Each periodic zone contains different spacing, different spacing orientations, or combinations thereof.

[0176] In another embodiment, the shape of the wafer surface in the Z-direction is mapped using any of the following: a aligning camera, an optical proximity sensor, a capacitive proximity sensor, an interferometric sensor, or any other suitable proximity sensor. In some instances, the wafer surface is mapped onto the front side (i.e., the patterned side) of the wafer. In some other instances, if the wafer thickness is sufficiently uniform, well-modeled, or measured in situ or pre-measured, the wafer surface is mapped onto the back side (i.e., the unpatterned side) of the wafer. In some embodiments, a back-side sensor is used to measure wafer warpage because many sensor technologies are available for accurately measuring the location of the unpatterned surface. In some of these embodiments, only a back-side sensor is used to measure wafer warpage across the back side of the wafer and wafer warpage across the front side is estimated based on a thickness model or thickness mapping generated by a pre-performed thickness measurement. In some other embodiments, both a back-side sensor and a front-side sensor are used to measure wafer warpage. In some of these embodiments, a back-side sensor is used to measure wafer warpage across the back side of the wafer, and wafer warpage across the front side is estimated based on a thickness model or thickness map derived at least partially from wafer thickness estimates from front and back side measurements. In some instances, several standard interpolators (e.g., polynomial basis functions, rational functions, neural networks, etc.) are used to model the wafer pattern. Furthermore, analytical or numerical bending models of the wafer can be used to couple lateral and height displacements.

[0177] In another aspect, Z-actuators 150A to C are controlled to adjust the Z-position, Rx orientation, Ry orientation, or any combination thereof in response to the shape of the wafer surface at the incident position of the illumination beam 116. In one example, the Z-actuators 150A to C correct the wafer's tilt. Tilt correction may be based on a wafer tilt map or locally measured tilt values. This can also be achieved using an optically based tilt sensor that monitors the Rx and Ry orientations (i.e., flip and tilt) at the back surface of the wafer.

[0178] In another aspect, Z-actuators 150A to C are controlled to adjust the Z-position, Rx orientation, Ry orientation, or any combination thereof to align the rotation axis in the azimuth angle with the stage reference frame 143. In one example, Z-actuators 150A to C are adjusted such that a particular target remains in focus of the alignment camera 154 within the azimuth angle range. To perform this calibration, the wafer stage translates the wafer 101 in the X and Y directions to maintain the target within the field of view of the alignment camera 154 for all azimuth angles.

[0179] Generally, it is impossible to calibrate all offset effects. The calibration chosen to remove the largest deviation is usually ignored, and the remaining offset is handled by a stage pattern that addresses non-idealities in the wafer and stage.

[0180] Additionally, changes in temperature, air pressure, or any other ambient conditions can affect the positioning of the illumination beam. In some embodiments, beam motion is correlated with these variables and the beam position is adjusted based on measured temperature and pressure and related models.

[0181] Generally, the sample positioning system 140 may include any suitable combination of mechanical elements to achieve the desired linear and angular positioning performance, including (but not limited to) a goniometer stage, a hexapod stage, an angular stage, and a linear stage.

[0182] In some embodiments, the x-ray illumination source 110, focusing optics 111, slits 112 and 113, or any combination thereof, are maintained in the same atmospheric environment (e.g., a purged environment) as the sample 101. However, in some embodiments, the optical path lengths between and within any of these elements are long, and x-ray scattering in the air causes noise in the image on the detector. Therefore, in some embodiments, the x-ray illumination source 110, focusing optics 111, and any of slits 112 and 113 are maintained in a localized vacuum environment. Figure 1 In the embodiment depicted, focusing optics 111, slits 112 and 113, and beam-shaping slit mechanism 120 are maintained in a controlled environment (e.g., vacuum) within a evacuated flight tube 118. The illumination beam 116 passes through a window 121 at the end of the flight tube 118 before being incident on the sample 101.

[0183] In some embodiments, the x-ray illumination source 110, the focusing optics 111, and any one of the slits 112 and 113 are maintained in a localized vacuum environment that is separated from each other and from the sample (e.g., sample 101) by a vacuum window. Figure 21 This diagram illustrates a vacuum chamber 160 containing an X-ray illumination source 110, a vacuum chamber 162 containing a focusing optics device 111, and a vacuum chamber 163 containing slits 112 and 113. The opening of each vacuum chamber is covered by a vacuum window. For example, the opening of vacuum chamber 160 is covered by a vacuum window 161. Similarly, the opening of vacuum chamber 163 is covered by a vacuum window 164. The vacuum windows can be constructed of any suitable material that is substantially transparent to X-ray radiation (e.g., polyimide, beryllium, etc.). A suitable vacuum environment is maintained within each vacuum chamber to minimize scattering of the illumination beam. The suitable vacuum environment can include any suitable vacuum level, any suitable purging environment (containing a gas with a low atomic number (e.g., helium)), or any combination thereof. In this way, as many illumination beam paths as possible are positioned in the vacuum to maximize flux and minimize scattering.

[0184] Similarly, in some embodiments, the optical path (i.e., the beam-collecting path) between sample 101 and detector 119 is long, and X-ray scattering in the air causes noise in the image on the detector. Therefore, in a preferred embodiment, a significant portion of the beam-collecting path length between sample 101 and detector 119 is maintained in a localized vacuum environment separated from the sample (e.g., sample 101) by a vacuum window (e.g., vacuum window 124). In some embodiments, the X-ray detector 119 is maintained in a localized vacuum environment with the same beam path length as between sample 101 and detector 119. For example, as... Figure 1 and 21 As depicted, vacuum chamber 123 maintains a localized vacuum environment around detector 119 and a significant portion of the beam path length between the sample and detector 119.

[0185] In some other embodiments, the X-ray detector 119 is maintained in the same atmospheric environment (e.g., a gas-purged environment) as the sample 101. This can be advantageous for removing heat from the detector 119. However, in these embodiments, it is preferable to maintain a significant portion of the beam path length between the sample 101 and the detector 119 in a localized vacuum environment within a vacuum chamber.

[0186] In some embodiments, the entire optical system (including sample 101) is maintained in a vacuum. However, in general, the cost associated with maintaining sample 101 in a vacuum is high due to the complexity associated with the construction of sample positioning system 140.

[0187] In another aspect, the beam-shaping slit mechanism 120 is mechanically integrated with the vacuum chamber 163 to minimize the beam path length exposed to the atmospheric environment. Generally, it is desirable to encapsulate as much of the beam as possible in a vacuum before the beam is incident on the sample 101. In some embodiments, the vacuum beamline extends into a hollow, cylindrical cavity at the input of the beam-shaping slit mechanism 120. The vacuum window 164 is positioned at the output of the vacuum chamber 163 within the beam-shaping slit mechanism 120 such that the incoming beam 115 is held in a vacuum within a portion of the beam-shaping slit mechanism 120 and then passes through the vacuum window 164 before interacting with any of the slits 126 to 129 and the sample 101.

[0188] In another aspect, the computing system 130 is configured to: generate a structural model (e.g., a geometric model, a material model, or a combination of geometric and material models) of the measured structure of the sample; generate a T-SAXS response model from the structural model containing at least one geometric parameter; and resolve at least one sample parameter value by performing a fitting analysis of the T-SAXS measurement data using the T-SAXS response model. An analysis engine is used to compare the simulated T-SAXS signal with the measured data, thereby allowing the determination of the sample's geometry and material properties (e.g., electron density). Figure 1 In the embodiments depicted herein, computing system 130 is configured as a model building and analysis engine, which is configured to implement model building and analysis functionality as described herein.

[0189] Figure 22 This is a diagram illustrating the exemplary model construction and analysis engine 180 implemented through the computing system 130. For example... Figure 22 The model building and analysis engine 180 is described as including a structural model building module 181 that generates a structural model 182 of the measured structure of the sample. In some embodiments, the structural model 182 further includes the material properties of the sample. The structural model 182 is received as input to a T-SAXS response function building module 183. The T-SAXS response function building module 183 generates a T-SAXS response function model 184 based at least in part on the structural model 182. In some instances, the T-SAXS response function model 184 is based on the x-ray shape factor.

[0190] (9)

[0191] Where F is the shape 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 then given by the following equation.

[0192] (10)

[0193] The T-SAXS response function model 184 is received as input to the fitting analysis module 185. The fitting analysis module 185 compares the modeled T-SAXS response with the corresponding measured data to determine the geometry and material properties of the sample.

[0194] In some instances, the modeling data is fitted to the experimental data by minimizing the chi-square value. For example, for T-SAXS measurements, the chi-square value can be defined as:

[0195] (11)

[0196] in It is the measured T-SAXS signal 126 in "channel" j, where the exponent j describes a set of system parameters, such as diffraction order, energy, angular coordinates, etc. It is for a set of structural (target) parameters The evaluation of the T-SAXS signal S of the "channel" j j These parameters describe the geometry (CD, sidewall angles, stacking, etc.) and the material (electron density, etc.). This is the uncertainty associated with the j-th channel. N SAXS L is the total number of channels in X-ray metrology. L is the number of parameters of the characteristic metrology target.

[0197] Equation (11) assumes that the uncertainties associated with different channels are uncorrelated. In instances where the uncertainties associated with different channels are correlated, the covariance between the uncertainties can be calculated. In these instances, the chi-square value used for the T-SAXS measurement can be expressed as:

[0198]

[0199] Where V SAXS It is the covariance matrix of the SAXS channel uncertainty, and T represents the transpose.

[0200] In some instances, the fitting analysis module 185 resolves at least one sample parameter value by performing a fitting analysis on the T-SAXS measurement data 135 using the T-SAXS response model 184. In some instances, optimization... .

[0201] As described above, T-SAXS data fitting is achieved by minimizing the chi-square value. However, in general, T-SAXS data fitting can be achieved using other functions.

[0202] Fitting T-SAXS metrological data is advantageous for any type of T-SAXS technique that provides sensitivity to the geometric and / or material parameters of interest. Sample parameters can be deterministic (e.g., CD, SWA, etc.) or statistical (e.g., root mean square height of sidewall roughness, roughness correlation length, etc.) provided that an appropriate model describing the interaction of the T-SAXS beam with the sample is used.

[0203] Generally, the computing system 130 is configured to access model parameters in real time using Real-Time Critical Size (RTCD), or an accessible library of pre-computed models, to determine the value of at least one sample parameter associated with sample 101. Generally, some form of CD engine can be used to evaluate the difference between the assigned CD parameters of the sample and the CD parameters associated with the measured sample. An exemplary method and system for calculating sample parameter values ​​is described in U.S. Patent No. 7,826,071, issued to KLA-Tencor Corporation on November 2, 2010, the entire contents of which are incorporated herein by reference.

[0204] In some instances, the model building and analysis engine 180 improves the accuracy of measured parameters through any combination of feed sideways analysis, feedforward analysis, and parallel analysis. Feed sideways analysis involves acquiring multiple datasets from different regions of the same sample and transferring common parameters determined from the first dataset to a second dataset for analysis. Feedforward analysis involves acquiring datasets from different samples and using a progressive replication of accurate parameter feedforward methods to forward-propagate common parameters to subsequent analyses. Parallel analysis involves applying nonlinear fitting methods in parallel or simultaneously to multiple datasets, where at least one common parameter is coupled during fitting.

[0205] Multi-tool and structural analysis refers to feedforward, side-feedback, or parallel analysis based on another fitting procedure of regression, lookup table (i.e., "library" matching), or multiple datasets. Exemplary methods and systems for multi-tool and structural analysis are described in U.S. Patent No. 7,478,019, issued to KLA-Tencor Corp. on January 13, 2009, the entire contents of which are incorporated herein by reference.

[0206] In another aspect, initial estimates of one or more parameters of interest are determined based on T-SAXS measurements performed in a single orientation relative to the target of measurement. These initial estimates are then implemented as starting values ​​for the parameters of interest in regressions using measurement data collected from T-SAXS measurements in multiple orientations. In this way, a close estimate of the parameters of interest is determined with relatively little computational effort, and a refined estimate is obtained with even less overall computational effort by implementing this close estimate as the starting point for regressions within a much larger dataset.

[0207] In another aspect, the metrology tool 100 includes a computing system (e.g., computing system 130) configured to implement beam control functionality as described herein. Figure 1In the embodiment depicted, the computing system 130 is configured as a beam controller operable to control any of the illumination properties, such as the intensity, divergence, dot size, polarization, spectrum, and positioning of the incident illumination beam 116.

[0208] like Figure 1 As described, computing system 130 is communicatively coupled to detector 119. Computing system 130 is configured to receive measurement data 135 from detector 119. In one example, measurement data 135 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 119, computing system 130 determines the position and area of ​​illumination beam 116 incident on sample 101. In one example, computing system 130 applies pattern recognition techniques to determine the position and area of ​​illumination beam 116 incident on sample 101 based on measurement data 135. In some examples, computing system 130 transmits command signal 137 to x-ray illumination source 110 to select the desired illumination wavelength. In some examples, computing system 130 transmits command signal 138 to actuator subsystem 111' to redirect x-ray emission relative to substrate frame 141 to achieve the desired beam direction. In some instances, the computing system 130 transmits a command signal 136 to the beam-shaping slit mechanism 120 to change the beam spot size, causing the incident illumination beam 116 to reach the sample 101 with the desired beam spot size and orientation. In one instance, the command signal 136 causes... Figure 5 The rotary actuator 122 depicted rotates the beam shaping slit mechanism 120 to the desired orientation relative to the sample 101. In another example, a command signal 136 causes the actuators associated with each of the slits 126 to 129 to change position to reshape the incident beam 116 into the desired shape and size. In some other examples, the computing system 130 transmits a command signal to the wafer positioning system 140 to position and orient the sample 101 such that the incident illumination beam 116 reaches the desired position and angular orientation relative to the sample 101.

[0209] In another aspect, T-SAXS 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 T-SAXS 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 implement continuity and sparse edges to provide a three-dimensional image of the sample.

[0210] Although model-based geometric parameter inversion is preferred for critical size (CD) metrology based on T-SAXS measurements, the graph of the sample generated from T-SAXS measurement data can be used to identify and correct model errors when the measured sample deviates from the assumptions of the geometric model.

[0211] 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 to an accurate parametric measurement model is particularly important when measuring integrated circuits for controlling, monitoring, and fault-finding their manufacturing processes.

[0212] In some instances, the image is a two-dimensional (2-D) plot of electron density, absorbance, 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, absorbance, complex refractive index, or a combination of these material properties. The plot is 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, pitch walk, etc., are directly estimated from the resulting plot. In some other instances, the plot can be used for wafer fabrication debugging when the sample geometry or material deviates from the expected values ​​envisioned by a parametric structure model used for model-based CD measurements. In one instance, the difference between the plot and the evolution 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 contents of which are incorporated herein by reference in their entirety. Additional details are described in U.S. Patent Publication No. 2015 / 0117610, the contents of which are incorporated herein by reference in their entirety.

[0213] On the other hand, a model building and analysis engine 180 is used to generate a model that combines X-ray and optical measurement analyses. In some instances, the optical simulation is based on, for example, rigorous coupled-wave analysis (RCWA), in which Maxwell's equations are solved to calculate optical signals, such as reflectivity, ellipsometric parameters, phase changes, etc., for different polarizations.

[0214] The values ​​of one or more parameters of interest are determined by a combined fitting analysis of the detected intensities and detected optical intensities of X-ray diffraction orders at multiple incident angles using a combined geometrically parameterized response model. This is achieved through a system that may or may not be integrated with an X-ray metrology system (e.g., Figure 1 The system 100 depicted is a mechanically integrated optical metrology tool for measuring optical intensity. Further details are described in U.S. Patent Publication No. 2014 / 0019097 and U.S. Patent Publication No. 2013 / 0304424, the contents of each of which are incorporated herein by reference in their entirety.

[0215] Generally, a measurement target is characterized by its aspect ratio, defined as the maximum height dimension (i.e., the dimension perpendicular to the wafer surface) divided by its maximum lateral extent dimension (i.e., the dimension aligned with the wafer surface). In some embodiments, the measurement target has an aspect ratio of at least 20. In some embodiments, the measurement target has an aspect ratio of at least 40.

[0216] It should be understood that the various steps described throughout the invention can be performed by a single computer system 130 or alternatively by multiple computer systems 130. Furthermore, different subsystems of system 100 (e.g., sample positioning system 140) 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 rather as illustrative. Additionally, one or more computing systems 130 may be configured to perform any (or several) other steps of any method embodiment described herein.

[0217] Additionally, computer system 130 can be communicatively coupled to x-ray illumination source 110, beam shaping slit mechanism 120, sample positioning system 140, and detector 119 in any manner known in the art. For example, one or more computing computers 130 can be coupled to computing systems associated with x-ray illumination source 110, beam shaping slit mechanism 120, sample positioning system 140, and detector 119, respectively. In another example, any one of x-ray illumination source 110, beam shaping slit mechanism 120, sample positioning system 140, and detector 119 can be directly controlled by a single computer system coupled to computer system 130.

[0218] Computer system 130 may be configured to receive and / or acquire data or information from subsystems of the system (e.g., X-ray illumination source 110, beam shaping slit mechanism 120, sample positioning system 140, detector 119, and the like) via a transmission medium that may include wired and / or wireless components. In this manner, the transmission medium may serve as a data link between computer system 130 and other subsystems of system 100.

[0219] The computer system 130 of the metrology system 100 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 act as a data link between the computer system 130 and other systems (e.g., on-board metrology system 100, external memory, or external systems). For example, the computer system 130 can be configured to receive measurement data (e.g., signal 135) from a storage medium (i.e., memory 132 or 187) via a data link. For example, spectral results obtained using detector 119 can be stored in a permanent or semi-permanent memory device (e.g., memory 132 or 187). In this respect, measurement results can be imported from on-board memory or from an external memory system. Furthermore, the computer system 130 can transmit data to other systems via the transmission medium. For example, sample parameter values ​​186 determined by the computer system 130 can be stored in a permanent or semi-permanent memory device (e.g., memory 187). In this respect, measurement results can be exported to another system.

[0220] The computing system 130 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.

[0221] Program instructions 134 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 1 The diagram illustrates that program instructions stored in memory 132 are transferred to processor 131 via bus 133. Program instructions 134 are stored in a computer-readable medium (e.g., memory 132). Exemplary computer-readable media include read-only memory, random access memory, magnetic disk or optical disk, or magnetic tape.

[0222] Figure 23 A method 300 suitable for implementation by the metrology system 100 of the present invention is described. In one aspect, it should be understood that the data processing block of method 300 can be implemented via a pre-programmed algorithm executed by one or more processors of the computing system 130. Although the following description is presented in the context of metrology system 100, it should be understood herein that specific structural aspects of metrology system 100 are not intended to be limiting and should be interpreted as illustrative only.

[0223] In box 301, an x-ray illumination beam is generated by an x-ray illumination subsystem.

[0224] In box 302, the sample is positioned relative to the X-ray illumination beam such that the X-ray illumination beam is incident on the surface of the sample at any position on the sample surface.

[0225] In box 303, the sample is rotated about a rotation axis relative to the X-ray illumination beam, such that the X-ray illumination beam is incident on the surface of the sample at any position with multiple incident angles.

[0226] In frame 304, the sample is rotated about an azimuth rotation axis so that the X-ray illumination beam is incident on the surface of the sample at any position with multiple azimuth angles.

[0227] In box 305, the calibration target is illuminated using an X-ray illumination beam. The calibration target contains one or more markings.

[0228] In box 306, the amount of transmission flux is detected within the position range of the sample positioning system, wherein at least a portion of the X-ray illumination beam is incident on the calibration target within the position range.

[0229] In box 307, the incident position of the X-ray illumination beam is determined relative to the sample positioning system based on the detected amount of transmission flux.

[0230] In some embodiments, scattering measurements as described herein are performed 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 T-SAXS analysis are used to control the manufacturing process. In one instance, T-SAXS measurement data collected from one or more targets are sent to the manufacturing process tool. The T-SAXS measurement data are analyzed as described herein, and the results are used to adjust the operation of the manufacturing process tool.

[0231] Scattering measurements, as described herein, can be used to determine the properties of a variety of semiconductor structures. Exemplary structures include (but are not limited to) FinFETs, low-dimensional structures (e.g., nanowires or graphene), sub-10 nm structures, photolithographic structures, through-substrate vias (TSVs), and 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 size, aperture density, sidewall angles, profile, critical dimensions, spacing, thickness, and stacking) and material parameters (e.g., electron density, composition, grain 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.

[0232] In some instances, the T-SAXS measurement system, as described herein, is used to perform measurements of critical dimensions, thicknesses, stacking, and material properties of high aspect ratio semiconductor structures, including (but 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).

[0233] As described herein, the term "critical dimension" includes any critical dimension of a structure (e.g., bottom critical dimension, middle critical dimension, top critical dimension, sidewall angle, grating height, etc.), 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.

[0234] As described herein, the terms “critical size application” or “critical size measurement application” include any critical size measurement.

[0235] As described herein, the term "metrology system" includes at least a portion of any system used to characterize samples in any way, including critical-size applications and superimposed metrology applications. However, such technical terms do 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, macro 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.

[0236] 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, a photomask, or any other sample that can be processed (e.g., printing or inspecting defects) using components known in the art.

[0237] 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 typically found and / or processed in semiconductor manufacturing plants. 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 patterned features.

[0238] A "photomask" can be a photomask at any stage of the photomask assembly process, or a finished photomask that may or may not be released for use in a semiconductor manufacturing plant. A photomask or "mask" is generally defined as a substantially transmissive 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. A photomask can be placed over a wafer coated with resist during the exposure step of a photolithography process, such that the pattern on the photomask can be transferred to the resist.

[0239] One or more layers formed on a wafer may be patterned or unpatterned. For example, a wafer may comprise multiple dies, each having repeatable pattern features. The formation and processing of such material layers can ultimately result in a completed 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.

[0240] In one or more exemplary embodiments, the described 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 code on or transmitted via a computer-readable medium. A computer-readable medium includes both computer storage media and communication media, encompassing any medium that facilitates the transfer of a computer program from one location to another. Storage media may be any available medium accessible by a general-purpose computer or a special-purpose computer. For example (and without limitation), this computer-readable medium may include RAM, ROM, EEPROM, CD-ROM or other optical disc storage, disk storage or other magnetic storage devices, or any other medium 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 special-purpose computer or a general-purpose or special-purpose processor. Furthermore, any connection may be appropriately referred to as computer-readable media. For example, if software is transmitted from a website, server, or other remote source using coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technology (such as infrared, radio, and microwave), then coaxial cable, fiber optic cable, 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.

[0241] Although certain specific embodiments have been described above for illustrative purposes, the teachings of this patent document are generally applicable and 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 measurement system comprising: An X-ray illumination source configured to generate an X-ray illumination beam incident on a semiconductor wafer; A sample positioning system configured to actively control the position of the semiconductor wafer relative to the X-ray illumination beam in six degrees of freedom, wherein the vector perpendicular to the surface of the wafer is substantially perpendicular to the direction of gravity applied to the semiconductor wafer by gravity during measurement of the semiconductor wafer by the metrology system; An X-ray detector is configured to detect a first amount of X-ray radiation from the semiconductor wafer in response to the incident X-ray illumination beam; and A computing system configured to determine the values ​​of parameters of interest for a structure characterized on the semiconductor wafer.

2. The metrology system according to claim 1, wherein the sample positioning system comprises: Base frame; A stage reference frame configured to rotate relative to the substrate frame about a rotation axis that is perpendicular to the illumination beam and substantially parallel to the wafer surface; A wafer stage, mounted to a stage reference frame, is configured to position the wafer relative to the incident illumination beam at any desired location within the active region of the semiconductor wafer. A three-axis stage is mounted to the wafer stage, the stage being configured to move the semiconductor wafer in a direction substantially aligned with the illumination beam and to rotate the semiconductor wafer about two orthogonal rotation axes that are also substantially perpendicular to the illumination beam; and A rotating stage is mounted to the three-axis stage, the rotating stage being configured to allow the wafer to rotate about an axis substantially perpendicular to the wafer surface.

3. The metrology system of claim 2, wherein the wafer stage and the triaxial stage are mechanically coupled by six mechanical contact points arranged as motion couplers.

4. The metrology system according to claim 1, wherein the sample positioning system comprises: One or more sensors configured to measure the position of the back surface of the semiconductor wafer relative to the sample positioning system in a direction generally perpendicular to the wafer surface; one or more sensors configured to measure the position of the front surface of the semiconductor wafer relative to the sample positioning system in a direction generally perpendicular to the wafer surface; or a combination thereof.

5. The metrology system of claim 2, wherein the sample positioning system includes one or more edge gripper devices configured to mechanically couple the semiconductor wafer to the rotary stage at the edge of the semiconductor wafer.

6. The metrology system of claim 2, wherein the sample positioning system includes a rotational balancer mounted on the stage reference frame, wherein the center of mass of the stage reference frame, configured to rotate about the rotation axis relative to the base frame, is substantially aligned with the rotation axis.

7. The metering system according to claim 1, further comprising: A first vacuum chamber encloses a significant portion of the illumination beam path between the X-ray illumination source and the semiconductor wafer.

8. The metering system according to claim 1, further comprising: A first vacuum chamber encloses a significant portion of the beam-collecting path between the semiconductor wafer and the X-ray detector.

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