Transmission small-angle x-ray scattering metrology system and method

Abstract

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

Description

[Technical field]

[0001] The described embodiments relate to metrology systems and methods, and more particularly to methods and systems with improved measurement accuracy. [Background technology]

[0002] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims priority under 35 U.S.C. §119 from U.S. Provisional Patent Application No. 62 / 485,497, filed April 14, 2017, the subject matter of which is incorporated herein by reference in its entirety.

[0003] Semiconductor devices, such as logic and memory devices, are typically fabricated by applying a series of processing steps to a specimen that results in the formation of various features and structural levels of the semiconductor devices. For example, lithography, among others, is one of the semiconductor manufacturing processes that involves the creation of patterns on a semiconductor wafer. Further examples of semiconductor manufacturing processes include, but are not limited to, chemical mechanical polishing, etching, deposition, and ion implantation. Multiple semiconductor devices may be fabricated on a semiconductor wafer, which may then be separated into individual semiconductor devices.

[0004] Metrology processes are used at various steps during the semiconductor manufacturing process to detect defects on the wafer and help improve yield. A number of metrology-based techniques, such as scatterometry and reflectometry, tools and associated analysis algorithms are widely used to characterize the critical dimensions, film thickness, composition and other parameters of nanoscale structures.

[0005] Scatterometry critical dimension (SCD) metrology has been performed on targets consisting of thin films and / or repeating periodic structures. During device fabrication, these films and periodic structures typically embody the actual device geometry and material structure or intermediate design. Devices (e.g., logic and memory devices) are moving to smaller nanometer-scale dimensions and becoming more difficult to characterize. This is due to the incorporation of complex three-dimensional geometries and materials with diverse physical properties into the devices. For example, modern memory structures often have high aspect ratio three-dimensional structures, making it difficult to penetrate optical radiation to the underlying layers. Although the infrared-visible light used in optical metrology tools can penetrate many semi-transparent material layers, the longer wavelengths at which good penetration depths are achieved do not offer sufficient sensitivity to small anomalies. In addition, the number of parameters required to characterize complex structures (e.g., FinFETs) is increasing, leading to increased parameter correlation. As a result, the parameters describing the target's characteristics often cannot be reliably separated from the available measurements.

[0006] For example, longer wavelengths (e.g., near infrared) have been employed in an attempt to overcome the penetration problems associated with 3D-FLASH® devices that utilize polysilicon as one of the interleaved materials in the stack. However, due to the mirror-like structure of 3D-FLASH®, there is an inherent decrease in light intensity as the illumination propagates deeper into the film stack. This causes sensitivity loss and correlation problems at depth. In this scenario, SCDs can only successfully extract a small set of metric dimensions with high sensitivity and low correlation.

[0007] For example, modern semiconductor structures increasingly use opaque high-k materials. Optical radiation is often unable to penetrate layers made of these materials. As a result, measurements with thin film scatterometry tools, such as ellipsometers and reflectometers, become increasingly challenging.

[0008] In light of these challenges, more sophisticated optical metrology tools have been developed, including tools with multiple illumination angles, shorter illumination wavelengths, wider illumination wavelength ranges, and more robust information retrieval from the reflected signal (e.g., measuring multiple Mueller matrix elements in addition to more traditional reflectance and ellipsometry signals). However, these approaches do not reliably overcome the fundamental challenges associated with metrology of many advanced targets (e.g., complex 3D structures, small structures below 10 nm, and structures using opaque materials) and metrology applications (e.g., line edge roughness metrology and line width roughness metrology).

[0009] Atomic force microscopes (AFM) and scanning tunneling microscopes (STM) can achieve atomic resolution but can only probe the surface of a sample. In addition, AFM and STM microscopes require long scanning times. Scanning electron microscopes (SEM) can achieve moderate resolution but cannot penetrate structures to a sufficient depth, which means they cannot characterize high aspect ratio holes well. In addition, unavoidable sample charging adversely affects imaging performance. X-ray reflectometers also suffer from penetration issues, which limits their usefulness in measuring high aspect ratio structures.

[0010] To overcome the penetration depth problem, traditional imaging techniques such as TEM, SEM, etc., are used in conjunction with destructive specimen preparation techniques such as focused ion beam (FIB) machining, ion milling, blanket etching, selective etching, etc. Transmission electron microscopy (TEM), for example, can achieve high resolution levels and probe arbitrary depths, but requires destructive sectioning of the sample. Several iterations of material removal and measurement typically provide the information required to measure critical metrology parameters throughout the 3D structure. However, these techniques require specimen destruction and long processing times. The tedious and time-consuming nature of completing these types of measurements introduces significant inaccuracies due to drifts in the etching and metrology steps. In addition, these techniques require multiple iterations, which introduces registration errors.

[0011] Transmission small-angle X-ray scatterometry (T-SAXS) systems, which employ photons at hard X-ray energy levels (>15 keV), hold the promise of addressing challenging metrology applications. Various aspects of the application of SAXS technology to critical dimension metrology (CD-SAXS) and overlay metrology (OVL-SAXS) are described in US Pat. No. 6,393,313 to Zhuang and Fielden entitled "High-brightness X-ray metrology," US Pat. No. 6,393,313 to Bakeman, Shchegrov, Zhao and Tan entitled "Model Building And Analysis Engine For Combined X-Ray And Optical Metrology," US Pat. No. 6,393,313 to Veldman, Bakeman, Shchegrov and Mieher entitled "Methods and Apparatus For Measuring Semiconductor Device Overlay Using X-Ray Metrology," US Pat. No. 6,393,313 to Veldman, Bakeman, Shchegrov and Mieher entitled "Measurement System Optimization For X-Ray Based Metrology," US Pat. No. 6,393,313 to Mieher, ... No. 6) U.S. Pat. No. 5,393,433 to Hench, Shchegrov and Bakeman entitled “X-ray Metrology For High Aspect Ratio Structures,” 5) U.S. Pat. No. 5,393,433 to Dziura, Gellineau and Shchegrov entitled “X-ray Metrology For High Aspect Ratio Structures,” and U.S. patent application Ser. No. 15 / 419,130 ​​to Gellineau, Dziura, Hench, Veldman and Zalubovsky entitled “Full Beam Metrology for X-Ray Scatterometry Systems,” each of which is incorporated herein by reference in its entirety.The above-referenced patents and applications are assigned to KLA-Tencor Corporation, Milpitas, Calif. Additionally, U.S. Patent No. 6,363,433 to Mazor et al., entitled "X-ray scatterometry apparatus," describes various aspects of the application of SAXS technology to semiconductor structures, and is hereby incorporated by reference in its entirety.

[0012] SAXS has also been applied to materials characterization and other non-semiconductor related applications. Example systems are commercialized by several companies, such as Xenocs SAS (www.xenocs.com), Bruker Corporation (www.bruker.com) and Rigaku Corporation (www.rigaku.com / en). Both Bruker and Rigaku offer small angle and wide angle X-ray scatterometry systems, named "Nanostar™" and "Nanopix™", respectively. These systems allow for adjustable sample-to-detector distance.

[0013] Work on CD-SAXS metrology of semiconductor structures has also been described in the scientific literature. Most research groups employ high-brilliance synchrotron X-ray sources, which are not suitable for use in semiconductor manufacturing facilities due to their large size, high cost, etc. An example of such a system is described in "A New Approach to X-ray Measurements Using Synchrotron X-ray Sources," IEEE Transactions on Physics, Vol. 13, No. 1, 2003, which is incorporated herein by reference in its entirety. More recently, work initiated by a group at the National Institute of Standards and Technology (NIST) employs compact and bright X-ray sources similar to those described in US Patent No. 5,341, 2003, which is incorporated herein by reference in its entirety. This work is described in "A New Approach to X-ray Measurements Using Synchrotron X-ray Sources," IEEE Transactions on Physics, Vol. 13, No. 1, 2003, which is incorporated herein by reference in its entirety.

[0014] Several types of detectors are employed in SAXS systems, such as hybrid pixel photon counting detectors, charge integrating pixel array detectors, gas phase avalanche detectors, etc. Available detector pixel sizes range from about 50 μm to about 200 μm. A prototype with 25 μm pixels is currently under development.

[0015] A significant drawback of all conventional SAXS architectures is the rather large size of the instruments required to measure typical semiconductor structures: fine angular resolution is required to resolve the diffraction pattern at the detector, which is currently achieved by increasing the length of the instrument.

[0016] As an example, by appropriately configuring the Bruker Nanostar system, the sample-to-instrument distance can be set to 1070 mm, the detector pixel size to 68 μm, and the q spatial resolution to 5 × 10 -3 Angstrom -1 It can be.

[0017] In semiconductor manufacturing facilities, throughput cannot be increased without forcing metrology and inspection tools to conform to relatively small footprint sizes, thereby improving utilization of expensive clean room space to accommodate a larger number of tools. Therefore, the tool lengths of current SAXS systems must be reduced from current levels to be useful in practical semiconductor manufacturing equipment. [Prior art documents] [Patent documents]

[0018] [Patent Document 1] U.S. Patent No. 7,929,667 [Patent Document 2] US Patent Application Publication No. 2014 / 0019097 [Patent Document 3] US Patent Application Publication No. 2015 / 0117610 [Patent Document 4] US Patent Application Publication No. 2016 / 0202193 [Patent Document 5] US Patent Application Publication No. 2017 / 0167862 [Patent Document 6] U.S. Pat. No. 9,606,073 [Patent Document 7] US Patent Application Publication No. 2015 / 0110249 [Patent Document 8] U.S. Patent No. 7,826,071 [Patent Document 9] U.S. Patent No. 7,478,019 [Patent Document 10] US Patent Application Publication No. 2015 / 0300965 [Patent Document 11] US Patent Application Publication No. 2013 / 0304424 [Patent Document 12] US Patent Application Publication No. 2016 / 0320319 [Non-patent literature]

[0019] [Non-Patent Document 1] "Intercomparison between optical and x-ray scatterometry measurements of FinFET structures" by Lemaillet, Germer, Kline et al., Proc. SPIE, v.8681, p. 86810Q (2013) [Non-Patent Document 2] "X-ray scattering critical dimensional metrology using a compact x-ray source for next generation semiconductor devices," J. Micro / Nanolith. MEMS MOEMS 16(1), 014001 (Jan-Mar 2017) Summary of the Invention [Problem to be solved by the invention]

[0020] In summary, current CD / OVL-SAXS systems are not suitable for implementation in production semiconductor manufacturing facilities due to their large footprint (tool length), low resolution, and reliance on angular order separation. To further improve device performance, the semiconductor industry continues to focus on vertical integration instead of lateral scaling. Therefore, accurate metrology of complex all three-dimensional structures is essential to ensure the feasibility and continued scaling improvement. Metrology-related challenges that emerge in future metrology applications include ever-finer resolution requirements, multi-parameter correlation, more complex geometries, e.g., high aspect ratio structures, and the increasing use of opaque materials. Therefore, improved X-ray scatterometry metrology methods and systems, especially those with improved resolution and smaller footprint (tool length), are desired. [Means for solving the problem]

[0021] This application describes a method and system for characterizing semiconductor device dimensions and material properties using a transmission small angle X-ray scatterometry (TSAXS) system having a relatively small tool footprint (tool length), which provides Q spatial resolution suitable for metrology of semiconductor structures with reduced optical path length.

[0022] In one embodiment, the TSAXS metrology system employs hard x-ray illumination over a relatively short optical path length (e.g., less than 3 m from illumination source to detector) to measure targets ranging from relatively small dimensions (e.g., approximately 50 nm) to relatively large dimensions (e.g., up to 10 μm).

[0023] In a further aspect, to illuminate the sample in the TSAXS metrology system, the X-ray beam is focused less than 200 mm in front of the wafer surface, either on the metrology target, on the detector surface, or between the wafer surface and the detector surface, thereby reducing optical focusing limitations on achievable Q-resolution. In general, for metrology applications involving smaller targets that must be illuminated with as small an illumination spot size as possible, the X-ray beam is focused closer to the wafer surface. For metrology applications involving larger targets where high resolution and high photon flux are desired, the X-ray beam is focused closer to the detector.

[0024] In another further aspect, the TSAXS metrology system is provided with a high resolution detector with a small PSF, thereby alleviating the detector PSF limitations on the achievable Q-resolution. High resolution detectors are useful when the wafer-to-detector distance D shrinks to a relatively small value (e.g., less than 1 m) regardless of where the optical focus is relative to the wafer and detector.

[0025] In another embodiment, the position of the centroid (center of mass) of the electron cloud induced by the photon conversion event is calculated by the detector. The position of the centroid determines the position of the incident photon with sub-pixel accuracy. This effectively reduces the pixel size and provides Q-resolution beyond the geometric limit. The sub-pixel spatial interpolation described herein is desirable for TAXXS metrology of semiconductor structures with wafer-to-detector distances of less than 1 m.

[0026] In some embodiments, a TSAXS system with a relatively short optical path length is configured with a horizontal optical path incident on a vertically oriented wafer (i.e., the normal to the wafer surface is approximately perpendicular to the gravity vector), while in other embodiments, a TSAXS system with a relatively short optical path length is configured with a vertical optical path incident on a horizontally oriented wafer (i.e., the normal to the wafer surface is approximately parallel to the gravity vector). Orienting the beamline vertically allows for a smaller tool footprint and simplifies wafer handling.

[0027] In yet another aspect, the X-ray detector resolves one or more X-ray photon energies and generates a signal for each X-ray energy component that is indicative of a characteristic of the sample. In this manner, X-ray photon interactions at the detector are discriminated by energy in addition to pixel location and count value. In some embodiments, the X-ray photon interactions are discriminated by comparing the energy of the X-ray photon interaction to a desired upper threshold and a desired lower threshold.

[0028] In other aspects, the TSAXS system is configured to measure a target based on orders that are spatially separated along one direction, but overlap along an orthogonal direction. In some of these embodiments, values ​​of one or more parameters of interest are determined along the direction in which the diffraction orders are spatially separated. These parameter values ​​are then employed to determine values ​​of one or more parameters of interest based on the overlapping orders.

[0029] In another embodiment, the slit of the beam shaping slit mechanism is placed close to the sample under measurement, thereby minimizing the expansion of the incident beam spot size due to the beam divergence determined by the finite size of the light source. For example, when the size of the X-ray source is 10 μm and the distance between the beam shaping slit and the sample 101 is 25 mm, the expansion of the beam spot size due to the shadow caused by the finite size of the light source is about 1 μm. In other examples, the beam shaping slit is placed less than 100 mm from the sample, thereby controlling the beam divergence.

[0030] In yet another embodiment, a T-SAXS system is used to determine properties of a sample (eg, structural parameters) based on one or more diffraction orders of scattered light.

[0031] The foregoing is a summary, and as such contains various simplifications, generalizations, and omissions of detail; as such, those skilled in the art will appreciate that this summary is illustrative only and is not intended to be limiting in any way. Other aspects, unique features, and advantages of the devices and / or processes described herein will become apparent from the non-limiting detailed description set forth herein. [Brief description of the drawings]

[0032] [Figure 1] FIG. 1 illustrates a metrology system 100 configured to perform X-ray scatterometry measurements as described herein. [Diagram 2] FIG. 13 is a diagram showing the slits of the beam shaping slit mechanism in a position that does not block the incoming beam. [Diagram 3] FIG. 2 shows the slits of the beam shaping slit mechanism in a position to block a portion of the incoming beam. [Figure 4] FIG. 2 illustrates an X-ray illumination beam incident on a wafer at a particular orientation described by angles φ and θ. [Diagram 5] FIG. 1 illustrates a metrology system 100 configured such that the focal point of the X-ray optics is at or near the detector surface. [Figure 6] 1 illustrates an image 171 of a scattering order measured by a metrology system, such as metrology system 100. [Figure 7] 1 illustrates an image 172 of a scattering order measured by a metrology system, such as metrology system 100. [Figure 8] FIG. 8 shows a plot 173 of the intensity profile for cross section C of image 172 shown in FIG. 7. [Figure 9] The diagram illustrates that the components of the metrology system 100 are contained in a vacuum environment separate from the sample under measurement. [Figure 10] FIG. 1 illustrates a model building and analysis engine 150 configured to decompose sample parameter values ​​based on X-ray scatterometry data in accordance with the methods described herein. [Figure 11A]1 is an isometric view of an exemplary 3D-FLASH® memory device 190 subjected to measurements as described herein. [Figure 11B] FIG. 1 is a top view of an exemplary 3D-FLASH® memory device 190 subjected to measurements as described herein. [Figure 11C] FIG. 1 is a cross-sectional view of an exemplary 3D-FLASH® memory device 190 that has been subjected to measurements as described herein. [Figure 12] 3 is a flow chart illustrating an example method 300 for measuring structures based on small footprint X-ray scatterometry metrology as described herein. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] Reference will now be made in detail to certain background and embodiments of the invention, examples of which are illustrated in the accompanying drawings.

[0034] This application describes a method and system for characterizing the dimensions and material properties of semiconductor devices using a transmission small angle x-ray scatterometry (TSAXS) system with a relatively small tool footprint. The system and technique can be employed to measure structural and material properties associated with different semiconductor manufacturing processes. According to some examples, the critical dimensions, thickness, overlay and material properties of high aspect ratio semiconductor structures, including but not limited to spin transfer random access memory (STT-RAM), three-dimensional NAND memory (3D-NAND) or vertical NAND memory (V-NAND®), dynamic random access memory (DRAM), three-dimensional FLASH memory (3D-FLASH®), resistive random access memory (Re-RAM) and phase change random access memory (PC-RAM), can be measured using TSAXS.

[0035] The use of high brightness TSAXS allows for high flux X-ray radiation penetration into opaque areas of the target. Examples of geometric parameters that can be measured using X-ray scatterometry include pore size, hole density, line edge roughness, line width roughness, sidewall angle, profile, critical dimension, overlay, edge placement error, and pitch. Examples of material parameters that can be measured include electron density. According to some examples, X-ray scatterometry can be used to measure small features below 50 nm and advanced semiconductor structures such as STT-RAM, V-NAND, DRAM, PC-RAM, and Re-RAM when measurements of geometric and material parameters are required.

[0036] An embodiment of a T-SAXS metrology tool 100 for measuring properties of a sample in at least one novel manner is depicted in Figure 1. Using the system 100 shown in Figure 1, an examination area 102 of a sample 101 can be illuminated with an illumination beam spot and T-SAXS measurements can be performed on that area.

[0037] The metrology tool 100 in the illustrated embodiment includes an X-ray illumination source 110 configured to generate X-ray radiation suitable for T-SAXS metrology. In some embodiments, the X-ray illumination system 110 is configured to generate wavelengths between 0.01 nm and 1 nm. 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 can be envisioned for providing X-ray illumination for T-SAXS metrology. In some embodiments, the X-ray source includes a tunable monochromator, allowing the X-ray radiation to be delivered at one of several selectable wavelengths.

[0038] In some embodiments, one or more x-ray sources are employed that emit radiation with photon energies greater than 15 keV to ensure that the x-ray source provides light of a wavelength sufficient to penetrate the entire device and into the wafer substrate. By way of non-limiting example, any of particle accelerator sources, liquid anode sources, rotating anode sources, stationary solid anode sources, microfocus sources, microfocus rotating anode sources, plasma-based sources, and inverse Compton sources may be employed as the x-ray source 110. For example, an inverse Compton source available from Lyncean Technologies, Inc., Palo Alto, Calif., may be envisioned. An inverse Compton source has the added advantage of being capable of generating x-rays over a range of photon energies and providing a choice of wavelengths of x-ray radiation to be delivered from the source.

[0039] Examples of x-ray sources include electron beam sources configured to bombard a solid or liquid target to induce x-ray radiation. A method and system for producing high brightness liquid metal x-ray illumination is described in U.S. Pat. No. 6,393,323, issued Apr. 19, 2011, in the name of KLA-Tencor Corp., the entire contents of which are incorporated herein by reference.

[0040] X-ray radiation provided by the X-ray illumination source 110 spans an illumination source area having a finite lateral dimension (i.e., a non-zero dimension perpendicular to the beam axis). Focusing optics 111 focus the illumination source radiation onto a metrology target located on the sample 101. The finite lateral dimension of the illumination source results in a finite size spot 102 on the target, the extent of which is determined by rays 117 coming from the edge of the illumination source. In some embodiments, focusing optics 111 comprises an elliptical focusing optic.

[0041] A beam divergence control slit 112 is located in the beam path between the focusing optical system 111 and the beam shaping slit mechanism 120. The beam divergence control slit 112 limits the divergence of the illumination delivered to the sample under measurement. An additional intermediate slit 113 is located in the beam path between the beam divergence control slit 112 and the beam shaping slit mechanism 120. The intermediate slit 113 provides further beam shaping. However, the intermediate slit 113 is generally optional.

[0042] A beam shaping slit mechanism 120 is located in the beam path just before the sample 101. In one embodiment, the slit of the beam shaping slit mechanism 120 is placed very close to the sample 101, thereby minimizing the expansion of the incident beam spot size due to the expansion of the beam divergence determined by the finite light source size. For example, when the X-ray source size is 10 μm and the distance between the beam shaping slit and the sample 101 is 25 mm, the expansion of the beam spot size due to the shadow caused by the finite light source size is about 1 μm. In other examples, the beam shaping slit is placed less than 100 mm from the sample 101, thereby controlling the beam divergence.

[0043] In some embodiments, the beam-shaping slit mechanism 120 includes a plurality of independently actuable beam-shaping slits. In one embodiment, the beam-shaping slit mechanism 120 includes four independently actuable beam-shaping slits. The four beam-shaping slits effectively block a portion of the incoming beam 115 to produce an illumination beam 116 having a box-shaped illumination cross-section.

[0044] 2 and 3 show two different end views of the beam shaping slit mechanism 120 shown in FIG. 1. In the illustrations of FIG. 2 and FIG. 3, the beam axis is perpendicular to the paper. The incoming beam 115 shown in FIG. 2 has a large cross section. In some embodiments, the diameter of the incoming beam 115 is about 1 mm. Furthermore, the position of the incoming beam 115 in the beam shaping slits 126-129 has an uncertainty of about 3 mm due to beam pointing errors. To accommodate the size of the incoming beam and the uncertainty of its beam position, the length L of each slit is about 6 mm. As shown in FIG. 2, each slit can be moved in a direction perpendicular to the beam axis. In the illustration of FIG. 2, the slits 126-129 are located at a maximum distance from the beam axis (i.e., the slits are fully open and do not restrict the light passing through the beam shaping slit mechanism 120).

[0045] The slits 126-129 of the beam shaping slit mechanism 120 shown in Figure 3 are positioned to block a portion of the incoming beam 115, so that the exiting beam 116 delivered to the sample under measurement has a small size and well-defined shape. As shown in Figure 3, each slit 126-129 is moved inward toward the beam axis to achieve the desired exiting and entering beam shape.

[0046] The slits 126-129 are made of a material that effectively blocks the incoming radiation with minimal scattering. Examples of materials include single crystal materials such as germanium, gallium arsenide, indium phosphide, etc. Typically, the slit material is cleaved along a crystallographic orientation rather than sawed to minimize scattering across structure boundaries. In addition, the slits are oriented relative to the incoming beam to minimize the amount of scattering due to interactions between the incoming radiation and the internal structure of the slit material. The crystals are mounted in respective slit holders made of a high density material (e.g., tungsten) to ensure perfect blocking of the X-ray beam on one side of the slit. In some embodiments, each slit has a rectangular cross section with a width of about 0.5 mm and a height of about 1-2 mm. The length L of the slits shown in FIG. 2 is about 6 mm.

[0047] In general, the X-ray optics shapes and directs X-ray radiation to the sample 101. In some examples, the X-ray optics includes an X-ray monochromator that monochromatizes the X-ray beam incident on the sample 101. In some examples, the X-ray optics collimates or focuses the X-ray beam onto the measurement area 102 of the sample 101 to a divergence of less than 1 mrad using multi-layer X-ray optics. In these examples, the multi-layer X-ray optics also functions as a beam monochromator. In some embodiments, the X-ray optics includes one or more X-ray collimating mirrors, X-ray apertures, X-ray beam stops, refractive X-ray optics, diffractive optics such as zone plates, Montell optics, specular X-ray optics such as grazing incidence ellipsoidal mirrors, polycapillary optics such as hollow capillary X-ray waveguides, multi-layer optics or systems, or any combination thereof. Further details are described in U.S. Pat. No. 6,399,323, which is incorporated herein by reference in its entirety.

[0048] The X-ray detector 119 collects the X-ray radiation 114 scattered by the sample 101 and generates an output signal 135 indicative of a property of the sample 101 that is sensitive to the incident X-ray radiation in accordance with a T-SAXS metrology technique. In some embodiments, the sample 101 is positioned and oriented by a sample positioning system 140 as the scattered X-rays 114 are collected by the X-ray detector 119 to produce angle resolved X-rays.

[0049] The T-SAXS systems according to some embodiments have a wide dynamic range (e.g., 10 5 In some embodiments, a single photon-counting detector detects the location and number of detected photons.

[0050] In a further embodiment, a T-SAXS system is used to determine a property (e.g., a structural parameter value) of the sample based on one or more diffraction orders of the scattered light. An information processing system 130 included in the metrology tool 100 depicted in FIG. 1 can be used to acquire a signal 135 generated by the detector 119 and to determine a property of the sample based at least in part on the acquired signal.

[0051] In some examples, for T-SAXS-based metrology, the dimensions of the specimen are determined by inversely solving a given metrology model with the measurement data. The metrology model includes a small number of adjustable parameters (e.g., on the order of 10) that describe the geometric and optical properties of the sample and the optical properties of the metrology system. Inverse solution methods include, but are not limited to, model-based regression, tomography, machine learning, and any combination thereof. In this way, the target profile parameters are estimated by solving for the parameterized metrology model values ​​that minimize the error between the measured scattered X-ray intensity and the modeled results.

[0052] Desirably, measurements are performed over a wide range of incidence and azimuth angles to improve the precision and accuracy of parameter value measurements. This approach reduces inter-parameter correlation by increasing the number and diversity of data sets available for analysis to include a variety of large angle out-of-plane orientations. For example, in a vertical orientation, T-SAXS can resolve the critical dimensions of a feature, but is largely insensitive to the sidewall angle and height of the feature. However, by collecting metrology data over a wide range of out-of-plane angle orientations, the sidewall angle and height of the feature can be resolved. In other examples, measurements are performed over a wide range of incidence and azimuth angles to provide sufficient resolution and penetration depth to resolve high aspect ratio structures over their entire depth.

[0053] Intensity measurements of diffracted radiation are collected as a function of the angle of incidence of the X-rays relative to the wafer surface normal. The information contained in these multiple diffraction orders is typically unique for each model parameter under consideration. Therefore, X-ray scattering provides estimates of the values ​​of the parameters of interest with low error and low parameter correlation.

[0054] The individual orientation of the illuminating X-ray beam 116 with respect to the surface normal of the semiconductor wafer 101 can be described by any two angular rotations of the wafer 101 with respect to the X-ray illumination beam and vice versa. As an example, the orientation can be described with reference to a coordinate system fixed with respect to the wafer. FIG. 4 illustrates an X-ray illumination beam 116 incident on the wafer 101 at a particular orientation described by the incidence angle θ and the azimuth angle φ. The coordinate system XYZ is fixed with respect to the metrology system (e.g., the illumination beam 116), and the coordinate system X'Y'Z' is fixed with respect to the wafer 101. The Y axis is in-plane aligned with the surface of the wafer 101. X and Z are not aligned with the surface of the wafer 101. Z' is aligned with an axis perpendicular to the surface of the wafer 101, and X' and Y' lie in a plane aligned with the surface of the wafer 101. The X-ray illumination beam 116 illustrated in FIG. 4 is aligned with the Z axis and therefore lies within the XZ plane. The incidence angle θ describes the orientation of the X-ray illumination beam 116 in the XZ plane with respect to the surface normal of the wafer. Additionally, the azimuth angle φ describes the orientation of the XZ plane with respect to the X'Z' plane. Together, θ and φ uniquely identify the orientation of the X-ray illumination beam 116 with respect to the surface of the wafer 101. In this example, the orientation of the X-ray illumination beam with respect to the surface of the wafer 101 is described by a rotation about an axis perpendicular to the surface of the wafer 101 (i.e., the Z' axis) and a 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 with respect to the surface of the wafer 101 is described by a rotation about a first axis aligned with the surface of the wafer 101 and a rotation about another axis perpendicular to the first axis and aligned with the surface of the wafer 101.

[0055] In one embodiment, the TSAXS metrology system utilizes hard x-ray illumination (e.g., 15 keV or greater) over a relatively short optical path length (e.g., less than 3 m from illumination source to detector) to measure targets ranging from relatively small dimensions (e.g., about 50 nm) to relatively large dimensions (e.g., up to 10 μm). In general, the methods and systems described herein provide Q spatial resolution suitable for metrology of semiconductor structures with reduced optical path lengths.

[0056] The geometric limit for the minimum achievable resolution of a TSAXS system is often the minimum quality factor Q min It is characterized by Q min is expressed by equation (1), where p is the pixel size in the detector, D is the distance between the sample and the detector, and λ is the wavelength of the X-ray radiation.

number

[0057] As depicted by equation (1), the smaller the sample-to-detector distance D, the higher the minimum achievable Q value for a given pixel size. min To keep Q small, a proportional reduction in pixel size is required. For metrology of the most advanced semiconductor metrology targets, the TSAXS system has a Q value of 0.01 nm. -1 However, this has not been achieved so far in commercial TSAXS systems, which are limited by pixel size.

[0058] Although the geometric limit on the Q-resolution is given in equation (1), there are other limitations on the Q-resolution that must be suppressed before the geometric limit can be reached. For example, the spatial extent of the optical focus at the detector limits the achievable Q-resolution. Also, for example, the point spread function (PSF) of the optical system at the detector limits the achievable Q-resolution.

[0059] In a further aspect, in the TSAXS metrology described herein, the sample is illuminated with an X-ray beam focused less than 200 mm in front of the wafer surface, either on the metrology target, on the detector surface, or between the wafer surface and the detector surface, thereby reducing the optical focusing limitations on the achievable Q-resolution. In general, focusing the X-ray beam closer to the wafer surface is suitable for metrology applications involving relatively small targets that must be illuminated with as small an illumination spot size as possible. Additionally, focusing the X-ray beam closer to the detector is suitable for metrology applications involving relatively large targets where high image resolution and photon flux are desired.

[0060] In some embodiments, the focal point of the TSAXS metrology system is located at or near the wafer surface, as depicted in FIG. 1, to measure relatively small targets (e.g., about 50-100 nm). By placing the illumination focal point at the wafer, the measurement spot size is minimized at the structure under measurement. This minimizes signal contamination due to illumination light spilling onto structures around the target of interest. This configuration is desirable for small targets, where signal contamination due to finite measurement spot size is a constraint. However, by placing the illumination focal point at the wafer rather than the detector, an increase in the incident beam size on the detector occurs. This increases the probability that diffracted portions of the incident beam will overlap due to beam divergence. This becomes more severe as the wafer-to-detector distance shrinks to relatively small dimensions (e.g., less than 1 m) because the spatial separation between angular orders becomes smaller as the wafer-to-detector distance shrinks. However, for small targets (eg, less than 100 nm) where the angular separation between diffraction orders is relatively large, the detector resolution enhancement techniques described herein overcome limitations imposed by detector focal limitations.

[0061] In other embodiments, the TSAXS metrology system has its focal point located at or near the detector surface for measuring relatively large targets (e.g., about 1-10 μm), as depicted in FIG. 5. By having the illumination focal point located at the detector, the measurement spot size is smallest at the detector, not at the target under measurement. This configuration is desirable for relatively large targets, where signal contamination due to finite measurement spot size at the wafer is not a constraint, since there is little risk of signal contamination due to illumination light spilling onto structures around the target of interest. However, large targets result in relatively small angular separation between diffraction orders. Thus, the spatial separation of angular orders at the detector is relatively small. This becomes more acute as the wafer-to-detector distance shrinks to relatively small dimensions (e.g., less than 1 m). By having the illumination focal point located at the detector, the probability of diffracted portions of the incident beam overlapping due to focal limitations is minimized. Furthermore, the limitation due to the relatively small spatial separation of orders at the detector for relatively large target sizes is overcome by the detector resolution enhancement techniques described herein.

[0062] Generally, the position of the optical focus can be adjusted to any position between the sample under measurement and the detector, with the attendant trade-off of the advantages and disadvantages mentioned above. Generally, the smaller the target size, the more desirable it is to move the optical focus closer to the wafer or in front of the wafer surface, and the larger the target size, the more desirable it is to move the optical focus closer to the detector.

[0063] In a further aspect, a high resolution detector with a small PSF alleviates the detector PSF limitations on the achievable Q-resolution during TSAXS metrology as described herein. High resolution detectors are useful when the wafer-to-detector distance D shrinks to a relatively small value (e.g., less than 1 m) regardless of where the optical focus is relative to the wafer and detector.

[0064] The Q-resolution limit imposed by the system's PSF depends on the metrology conditions and the origin of the PSF. For example, in the case of weak scattering, a PSF down to 10% at a given Q may be required to resolve the Q. In other cases, a PSF down to 1% at a given Q may be required to resolve the Q. To achieve high Q-resolution and a smallest possible wafer-to-detector distance D, the TSAXS system is designed such that the Q-independent PSF is minimized. In some cases, the detector pixel size is less than 100 μm and the detector PSF is smaller than the pixel size, so that diffracted light incident on an individual pixel contaminates adjacent pixels by less than 0.1%.

[0065] The detector material is selected to minimize transmission. Furthermore, depending on the detector configuration, PSF expansion at the detector is minimized. As a result, the system PSF is independent of the detector position. For example, detection of hard x-rays (e.g., above 15 keV) with traditional silicon-based detectors suffers from a significant Q-independent PSF. As a result, large wafer-to-detector distances D (e.g., more than 2 m) are required to perform metrology of semiconductor structures. By reducing transmission and backscattering, the PSF performance limitations are suppressed below the geometric limit described by equation (1), and metrology of semiconductor structures with wafer-to-detector distances D less than 1 m (e.g., D less than 600 mm) is realized.

[0066] The TSAXS system of some embodiments has high quantum efficiency and a wide dynamic range (e.g., 10 5 One or more photon-counting detectors, each exhibiting a thickness greater than 500 μm, are provided, each having a thick (e.g., greater than 500 μm) highly absorbing crystalline substrate that absorbs the incident radiation without damage and with minimal parasitic backscatter. In some embodiments, a single photon-counting detector detects the location and number of detected photons.

[0067] In some embodiments, the zeroth order beam is collected along with the higher diffraction orders. The zeroth order beam has an amplitude several orders of magnitude stronger than the other orders. If the zeroth order beam is not completely absorbed in the X-ray sensitive section of the detector, it will scatter and generate parasitic signals. The strength of these parasitic signals limits the dynamic range of the measurement. For example, if the parasitic signals are less than 10 times the maximum flux signal (i.e., the zeroth order signal), -4 If the number of electrons was twice as large, many of the higher order signals would be contaminated. Therefore, it is essential that the detector (e.g., detector 119) exhibits high X-ray to electron-hole pair conversion efficiency as well as high X-ray absorption to extend the useful dynamic range of X-ray metrology.

[0068] Examples of detector materials suitable for small footprint x-ray scatterometry include cadmium telluride (CdTe), germanium (Ge), and gallium arsenide (GaAs) crystals, etc. In some embodiments, the detector material is selected to provide high conversion efficiency over a narrow energy band corresponding to the source energy.

[0069] In some embodiments, the thickness of the detector material is selected to achieve a desired absorption of the incoming x-rays. In some embodiments, tilting the detector with respect to the incoming x-ray beam (various diffraction orders) increases the optical path length of the x-ray beam within the detector material, thus increasing the total absorption.

[0070] In some embodiments, the SNR is improved by employing a dual threshold detector.

[0071] In a further embodiment, the TAXXS system is used to determine a property (e.g., a structural parameter value) of the sample based on the multiple diffraction order measurements. The information processing system 130 of the metrology tool 100 shown in FIG. 1 can be used to acquire a signal 135 generated by the detector 119 and to determine a property of the sample based at least in part on the acquired signal.

[0072] In a TSAXS measurement, a collimated X-ray beam is diffracted into diffraction orders by structures fabricated with high aspect ratios. Each diffraction order travels in a specific, predictable direction. The angular separation between the diffraction orders is inversely proportional to the lattice constant of the sample divided by the wavelength. The diffraction orders are detected by a detector array placed some distance from the wafer. Each pixel in the detector outputs a signal that indicates the number of photons that strike it.

[0073] The intensities of the diffraction orders are of the form I(m,n,θ,φ,λ), where {m,n} are integer indices of the diffraction orders, {θ,φ} are the elevation and azimuth angles of the incident beam (i.e., the polar coordinate values ​​of the incident chief ray with respect to a coordinate system fixed on the wafer), and λ is the wavelength of the incident X-ray.

[0074] The illumination light is perturbed by several noise sources as it leaves the illumination source and propagates to the sample, examples of perturbations include electron beam current wander, temperature induced optics drift, etc. The perturbed incident flux is denoted as F0(1+n1).

[0075] The target scatters the incident radiation in a manner that depends on the azimuth and elevation angles of the incident beam. The efficiency of light scattering up to order (m,n) is S mn (θ,φ). All orders are similarly affected by other scattering media through which the diffracted light travels from the sample to the detector, adding some variance (1+n2) and parasitic noise (n3). Thus, the total intensity I of each order measured at time t is mn can be expressed by equation (2).

number

[0076] In Fig. 6 there is depicted an image 171 of the scattered orders measured by a metrology system, for example metrology system 100. The bright spot in the center of the image depicted in Fig. 6 is associated with the zeroth order beam.

[0077] The intensity of each order can be extracted in a variety of ways. In some embodiments, the diffraction orders exhibit spatial separation at the detector. In such embodiments, the diffraction orders are detected separately by a detector array, and the outputs of pixels associated with the same diffraction order are combined (i.e., summed). In this configuration, the detected diffraction orders are discriminated by integrating the photon counts of the pixels associated with each individual diffraction order. This scenario is likely to occur when measuring features with relatively small pitches or when measuring beams that exhibit relatively small divergence.

[0078] In some other embodiments, the diffraction orders overlap spatially. This is typically the case when TSAXS metrology is performed on relatively large targets (e.g., targets with pitches of 1 μm or more) with relatively small wafer-to-detector distances D (e.g., D less than 2 m) or when measuring beams with relatively large divergence. In these embodiments, the diffraction orders are separated in Q-space to estimate the value of the structure of interest parameter. In some of these embodiments, the shape of the diffraction orders is estimated based on available beam shape information and an accurate beam model is used to account for the Q-resolution degradation due to the overlap. This is particularly important to meet the requirements of on-device metrology. Some existing metrology systems are unable to perform separation of overlapping orders because the beam stop employed in the system prevents access to the beam shape information required to estimate the shape of the diffraction orders. Such a system is described in US Pat. No. 6,399,323 to Mazor, et al., entitled "X-ray scatterometry apparatus," which is incorporated herein by reference in its entirety.

[0079] In cases where the diffraction orders are spatially overlapping at the detector, a simple combination of the pixel outputs cannot yield the intensities associated with the individual diffraction orders, and in such embodiments, a metrology model is utilized that deconvolves the diffraction orders to differentiate the measured intensities of each detected diffraction order.

[0080] In some embodiments, the overlapping orders are deconvoluted based on the zeroth order beam shape measurement. In some embodiments, this deconvolution is performed in real time. The beam profiles of the higher diffraction orders (i.e., orders above zero) are modeled based on the zeroth order beam profile. FIG. 7 shows an image 172 of the scattered orders measured by a metrology system, e.g., metrology system 100. FIG. 8 shows a plot 173 of the intensity profile for cross section C of image 172 shown in FIG. 7. The relatively high intensity zeroth order beam provides a very accurate beam profile that can be used to model the higher diffraction orders.

[0081] In some embodiments, the intensity of each of the higher diffraction orders is estimated relative to the zero beam measurement result, such as by simple division of the intensities, which significantly reduces the measurement uncertainty associated with the relatively weaker higher order signals.

[0082] By estimating the intensities of higher diffraction orders based on the simultaneously measured zeroth order beam, the scattered signal is separated from system disturbances during data collection. Disturbances due to misalignment of optical components (e.g. slits, optics, spot shaping) as well as disturbances along the beam path (e.g. n1 and n2) are mitigated in real time. By using all scattered intensities including the zeroth order, the dependence of the scattered intensity on the measured sample thickness or material density is separated from beam disturbances before and after the wafer.

[0083] The physical conversion of high-energy photons into electron clouds within the detector crystal also imposes detection limitations on high-q resolution short-pathlength TSAXS systems, where single photon events can be detected over several pixels if the pixel size is small enough to perform short-pathlength TSAXS metrology of semiconductor structures.

[0084] In another embodiment, the position of the center of gravity of the electron cloud induced by the photon conversion event is calculated by a detector (e.g., detector 119). The position of the center of gravity provides the position of the incident photon with sub-pixel accuracy. This effectively reduces the pixel size, thereby enabling a Q resolution that exceeds the geometric limit described by equation (1). The sub-pixel spatial interpolation described herein is desirable for TAXXS metrology of semiconductor structures at wafer-to-detector distances of less than 1 m.

[0085] In some embodiments, a TSAXS system having a relatively short optical path length is formed with a horizontal optical path incident on a vertically oriented wafer (i.e., the normal to the wafer surface is approximately perpendicular to the gravity vector), whereas in some other embodiments, a TSAXS system having a relatively short optical path length is formed with a vertical optical path incident on a horizontally oriented wafer (i.e., the normal to the wafer surface is approximately parallel to the gravity vector). The vertical beamline orientation allows for a smaller tool footprint to be achieved, simplifying wafer handling.

[0086] In a further aspect, the X-ray detector resolves one or more X-ray photon energies and provides a signal for each X-ray energy component characteristic of the sample, hi 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-filled proportional counter, a scintillator, and a phosphor material.

[0087] In this way, X-ray photon interactions at the detector are discriminated by energy in addition to pixel location and count value. In some embodiments, the X-ray photon interactions are discriminated by comparing the energy of the X-ray photon interaction with a predefined upper threshold and a predefined lower threshold. In some embodiments, this information is sent via output signal 135 to information processing system 130 for further processing and storage.

[0088] In some embodiments, the target being measured is periodic along one dimension (e.g., FinFET structures), so it is only necessary to minimize the PSF of the TSAXS system at the detector along one direction, whereas in some other embodiments, the target being measured is periodic along two dimensions (e.g., VNAND™ contacts), so in such embodiments it is useful to minimize the PSF of the TSAXS system at the detector along both directions.

[0089] In another aspect, the TSAXS system is configured to measure a target based on orders that are spatially separated in one direction, but overlap in an orthogonal direction. In some of these embodiments, values ​​of one or more parameters of interest are determined along the direction in which the diffraction orders are spatially separated. These parameter values ​​are then employed to determine values ​​of one or more parameters of interest based on the overlapping orders.

[0090] In some embodiments, X-ray illumination source 110, focusing optics 111, slits 112 and 113, or some combination thereof, are maintained in the same atmospheric environment (e.g., gas purged environment) as that of sample 101. However, in some embodiments, the optical paths between and within any of the components are long, and aerial X-ray scattering contributes noise to the image on the detector. Therefore, in some embodiments, X-ray illumination source 110, focusing optics 111, and any of slits 112 and 113 are maintained in a local vacuum environment that is mutually separated from the sample (e.g., sample 101) by a vacuum window.

[0091] Similarly, in some embodiments, the X-ray detectors 119 are maintained in the same ambient environment (e.g., gas purged environment) as that of the sample 101. However, in some embodiments, the distance between the sample 101 and the X-ray detectors 119 becomes so long that aerial X-ray scattering contributes noise to the detected signal. Therefore, in some embodiments, one or more of the X-ray detectors (e.g., detector 119) are maintained in a local vacuum environment separated from the sample (e.g., sample 101) by a vacuum window.

[0092] FIG. 9 illustrates vacuum chamber 160 housing x-ray illumination source 110, vacuum chamber 162 housing focusing optics 111, and vacuum chamber 163 housing slits 112 and 113. The openings of each vacuum chamber are covered with a vacuum window. For example, the opening of vacuum chamber 160 is covered with vacuum window 161. Similarly, the opening of vacuum chamber 163 is covered with vacuum window 164. The vacuum windows may be made of any suitable material that is substantially transparent to x-ray radiation (e.g., Kapton, beryllium, etc.). A suitable vacuum environment is maintained within each vacuum chamber to minimize scattering of the illumination beam. A suitable vacuum environment may include any suitable level of vacuum, any suitable purged environment containing a low atomic number gas (e.g., helium), or any combination thereof. In this manner, as much of the beam path as possible is in the vacuum, thereby maximizing the light flux and minimizing scattering.

[0093] In some embodiments, the entire optical system is kept in vacuum, including the sample 101. However, there are generally higher costs associated with keeping the sample 101 in vacuum due to the increased complexity of the sample positioning system 140.

[0094] In another further aspect, the beam shaping slit mechanism 120 is mechanically integrated with the vacuum chamber 163, thereby minimizing the beam path length exposed to the ambient environment. In general, it is desirable to keep as much of the beam in a vacuum as possible before it is incident on the sample 101. In some embodiments, the vacuum beam line is extended into a hollow cylindrical cavity at the entrance of the beam shaping slit mechanism 120. By locating a vacuum window 164 at the exit of the vacuum chamber 163 in the beam shaping slit mechanism 120, the incoming beam 115 is kept in a vacuum in a portion of the beam shaping slit mechanism 120 and then passes through the vacuum window 164 to interact with either the slits 126-129 or the sample 101.

[0095] In the embodiment depicted in FIG. 1, focusing optics 111, slits 112 and 113, and beam shaping slit mechanism 120 are maintained within a controlled environment (eg, vacuum) within flight tube 118.

[0096] In yet another embodiment, the information processing system 130 is configured to generate a structural model (e.g., a geometric model, a material model, or a combined geometric-material model) of the measured structure of the specimen, generate a TSAXS response model including at least one geometric parameter derived from the structural model, and perform a fitting analysis of the TSAXS measured data with the TSAXS response model to resolve at least one specimen parameter value. The analysis engine can be used to compare the simulated TSAXS signals with the measured data to determine geometric and material properties of the specimen, such as electron density. In the embodiment depicted in FIG. 1, the information processing system 130 is configured as a model building and analysis engine, and the engine is configured to perform the model building and analysis functions as described herein.

[0097] FIG. 10 illustrates an example model building and analysis engine 150 embodied by the information processing system 130. The model building and analysis engine 150 illustrated in FIG. 10 includes a structural model building module 151 that generates a structural model 152 of a measured structure of a sample. In some embodiments, the structural model 152 also incorporates material properties of the sample. The structural model 152 is received as an input to a TSAXS response function building module 153. The TSAXS response function building module 153 generates a TSAXS response function model 155 based at least in part on the structural model 152. In some examples, the TSAXS response function model 155 is an X-ray form factor.

number

number

[0098] In some instances, fitting the modeled data to the experimental data is accomplished by minimizing the chi-squared value. For example, the chi-squared value for the TSAXS measurements is

number

[0099] In the formula, S j SAXS experiment is the TAXXS signal 135 measured in "channel" j, where index j indicates a set of system parameters, such as diffraction order, energy, angular coordinate, etc. j SAXS model (v1,…,v L ) is the modeled TSAXS signal S associated with “channel” j. j Let v1,…,v be a set of structural (target) parameters. L The parameters are indicative of geometry (CD, sidewall angle, overlay, etc.) and material (electron density, etc.). σ SAXS,j is the uncertainty associated with the jth channel. N SAXS is the total number of channels in the X-ray metrology. L is the number of parameters characterizing the metrology target.

[0100] In equation (5), it is assumed that the uncertainties for the different channels are uncorrelated. In instances where the uncertainties for the different channels are correlated, the covariance between the uncertainties can be calculated. In such instances, the chi-squared value for the x-ray scatterometry measurements can be calculated as

number

[0101] In the formula, V SAXS is the covariance matrix of the SAXS channel uncertainties and T denotes its transpose.

[0102] In some examples, a fitting analysis module 157 performs a fitting analysis on the TSAXS measurement data 135 with the TSAXS response model 155 to resolve at least one sample parameter value. SAXS 2 is optimized.

[0103] As mentioned above, the fitting of the TSHAXS data is achieved by minimizing the chi-squared value, although in general the fitting of the TSHAXS data can be achieved with other functions.

[0104] Fitting of TSAXS data is useful for any kind of TSAXS technology that is sensitive to the geometric and / or material parameters of interest. The sample parameters can be either deterministic (e.g. CD, SWA, etc.) or statistical (e.g. rms sidewall roughness, roughness correlation length, etc.) as long as an appropriate model is used that describes the TSAXS beam interaction with the sample.

[0105] Generally, the information processing system 130 is configured to access model parameters in real time using real-time critical dimensioning (RTCD), or may access a library of pre-calculated models to determine at least one specimen parameter value for the specimen 101. Generally, some form of CD engine can be used to evaluate the difference between the CD parameters assigned to the specimen and the CD parameters for the measured specimen. An example of a specimen parameter value calculation method and system is described in U.S. Patent Application Publication No. 2010 / 0133994, filed Nov. 2, 2010 in the name of KLA-Tencor Corp., which is incorporated herein by reference in its entirety.

[0106] In some examples, the model building and analysis engine 150 improves the accuracy of the parameter measurements by some combination of feed-sideway analysis, feed-forward analysis, and parallel analysis. Feed-sideway analysis involves taking multiple data sets on different areas of the same sample and passing common parameters from the first data set to the second data set for analysis. Feed-forward analysis involves taking data sets on separate samples and using a stepwise copy exact parameter feed-forward technique to pass common parameters forward for subsequent analysis. Parallel analysis involves the parallel or simultaneous application of a nonlinear fitting methodology to multiple data sets, where at least one common parameter is combined during the fitting.

[0107] Multi-tool and structural analysis refers to feed-forward, feed-sideway, or parallel analysis that relies on regression, look-up tables (i.e., "library" matching), or other multiple data set fitting procedures. An example of a multi-tool and structural analysis method and system is described in U.S. Patent Application Publication No. 2009 / 0133634, issued Jan. 13, 2009 to KLA-Tencor Corp., which is incorporated herein by reference in its entirety.

[0108] In a further aspect, an information processing system (e.g., information processing system 130) included in metrology tool 100 is configured to implement the beam control functionality described herein. In the embodiment depicted in Figure 1, information processing system 130 is configured as a beam controller operable to control any illumination characteristic, including, for example, the intensity, divergence, spot size, deflection, spectrum, and geometry of incident illumination beam 117.

[0109] As depicted in FIG. 1 , the information processing system 130 is communicatively coupled to the detector 119. The information processing system 130 is configured to receive metrology data 135 from the detector 119. In one example, the metrology data 135 includes an indication of the measurement of the sample response (i.e., the intensities of the diffracted order components). Based on the distribution of the response measurements on the surface of the detector 119, the information processing system 130 determines the location and area of ​​incidence of the illumination beam 116 on the sample 101. For example, the information processing system 130 applies pattern recognition techniques to determine the location and area of ​​incidence of the illumination beam 116 on the sample 101 based on the metrology data 135. In some examples, the information processing system 130 sends a command signal 137 to the illumination source 110 to select a desired illumination wavelength, while sending a command signal 136 to the beam selection subsystem 120 to redirect and reshape the incident illumination beam 116 so that it reaches a desired location on the sample 101 at a desired angular orientation. In some other examples, command signals are sent by the information processing system 130 to the wafer positioning system 140 to position and orient the specimen 101 so that the incident illumination beam 116 reaches the desired location and angular orientation of the specimen 101 .

[0110] In another aspect, using X-ray scatterometry measurement data, an image of the measured structure is generated based on intensity measurements of the detected diffraction orders. In some embodiments, the TSAXS response function model is generalized to describe scattering from a global electron density mesh. Matching this model to the measured signal while constraining the modeled electron density in the mesh to emphasize continuity and sparse edges produces a three-dimensional image of the sample.

[0111] Although a geometric, model-based parametric inversion is desirable for critical dimension (CD) metrology based on TAXXS measurements, when the measured sample deviates from the geometric model assumptions, a sample map generated from the same TAXXS data can help identify and correct the model errors.

[0112] In some instances, the images are compared to structural properties estimated by a geometric, model-based, parametric inversion of the same scatterometry metrology data. The discrepancies can be used to update the geometric model of the measured structure to improve metrology performance. This ability to converge to accurate parametric metrology models is of particular importance in measuring integrated circuits to control, monitor, and troubleshoot their manufacturing processes.

[0113] In some examples, the image is a two-dimensional (2D) map of electron density, optical absorptivity, complex refractive index, or a combination of these material properties. In some examples, the image is a three-dimensional (3D) map of electron density, optical absorptivity, complex refractive index, or a combination of these material properties. The map is generated using relatively few physical constraints. In some examples, one or more parameters of interest, such as critical dimension (CD), sidewall angle (SWA), overlay, edge placement error, pitch walk, etc., are estimated directly from the resulting map. In some other examples, the map is used to debug the wafer process when the geometry or material of the specimen falls outside of the expected range estimated by the parametric structural model employed for model-based CD metrology. For example, a representation of the structure is predicted by the parametric structural model according to the measured parameters, and the difference between the representation and the map is used to update the parametric structural model to improve the metrology performance. Further details are described in U.S. Pat. No. 6,399,343, which is incorporated herein by reference in its entirety. Additional details are provided in US Pat. No. 6,399,323, which is incorporated herein by reference in its entirety.

[0114] In a further aspect, a combined X-ray metrology-optical metrology analysis model is generated using the model building and analysis engine 150. In some examples, Maxwell's equations are solved by optical simulations, e.g., based on Rigorous Coupled Wave Analysis (RWCA), and optical signals, e.g., reflectivity, are calculated for various polarizations, ellipsometry parameters, phase changes, etc.

[0115] Values ​​for one or more parameters of interest are determined in light of a joint fitting analysis of the intensity detection results of the X-ray diffraction orders at a plurality of different angles of incidence and the optical intensity detection results, according to a joint geometric parameterized response model. The optical intensity is measured by an optical metrology tool, which may or may not be mechanically integrated with the X-ray metrology system, such as system 100 depicted in FIG. 1. Further details are provided in U.S. Pat. Nos. 5,993,333 and 5,943,796, each of which is incorporated herein by reference in its entirety.

[0116] In some embodiments, a metrology target characterized by X-ray scatterometry metrology as described herein is placed in a scribe line of the wafer under measurement. In such embodiments, the metrology target is sized to fit within the width of the scribe line. In some examples, the scribe line width is less than 80 μm. In some examples, the scribe line width is less than 50 μm. In general, there is a trend toward smaller scribe line widths in semiconductor manufacturing.

[0117] In some embodiments, metrology targets characterized by X-ray scatterometry metrology as described herein are placed within the active die area of ​​the wafer under measurement and are part of a functional integrated circuit (e.g., memory, image sensor, logic device, etc.).

[0118] Generally, the aspect ratio characterizing a metrology target is defined as the maximum height dimension (i.e., the dimension perpendicular to the wafer surface) divided by the maximum lateral dimension (i.e., the dimension aligned to the wafer surface) of that metrology target. In some embodiments, the aspect ratio of the metrology target under measurement is at least 20. In some embodiments, the aspect ratio of the metrology target is at least 40.

[0119] 11A-11C show, respectively, isometric, top and cross-sectional views of a typical 3D-FLASH® memory device 190 that has been subjected to measurements as described herein. The total height (equivalently, the depth) of the memory device 190 is in the range of 1 to several μm. The memory device 190 is a vertically fabricated device. A vertically fabricated device, such as the memory device 190, is essentially a conventional planar memory device rotated 90° with the bit lines and cell strings oriented vertically (perpendicular to the wafer surface). To provide sufficient storage capacity, multiple alternating layers of different materials are deposited on the wafer. To do so for structures with maximum lateral extents of 100 nm or less, requires that the patterning process be carried out preferably to a depth of several μm. As a result, aspect ratios of 25:1 or 50:1 are not uncommon.

[0120] It should be appreciated that the various steps described throughout this disclosure may be performed by a single computer system 130 or, alternatively, by multiple computer systems 130. Additionally, subsystems of the system 100, such as the sample positioning system 140, may include computer systems suitable for performing at least a portion of the steps described herein. Thus, the above description should not be construed as a limitation on the present invention, but merely as an example. Additionally, the one or more information processing systems 130 may be configured to perform any other step(s) of any method embodiment described herein.

[0121] Additionally, computer system 130 may be communicatively coupled to detector 119 and illumination optics in any manner known in the art, such as by coupling one or more of information processing systems 130 to an information processing system associated with detector 119, or by directly controlling detector 119 via a single computer system coupled to computer system 130.

[0122] Computer system 130 may be configured to receive and / or acquire data or information from subsystems of the system (e.g., detector 119, etc.) through a transmission medium, such as a wired and / or wireless section, which may act as a data link between computer system 130 and other subsystems of system 100.

[0123] The computer system 130 of the metrology system 100 may be configured to receive and / or acquire data or information (e.g., measurement results, modeling inputs, modeling results, etc.) from other systems via a transmission medium, e.g., having a wired and / or wireless section. In this embodiment, the transmission medium may act as a data link between the computer system 130 and the other system (e.g., the on-board memory of the metrology system 100, an external memory, or an external system). For example, the information processing system 130 may be configured to receive measurement data (e.g., signal 135) from a storage medium (i.e., memory 132 or 180) via a data link. As an example, the intensity measured by the detector 119 may be stored in a permanent or semi-permanent storage device (e.g., memory 132 or 180). In this case, the measurement results may be imported from the on-board memory or from an external memory system. Additionally, the computer system 130 may send data to the other system via the transmission medium. As an example, the sample parameter values ​​170 determined by the computer system 130 may be stored in a permanent or semi-permanent storage device (e.g., memory 180) in order to allow the measurement results to be exported to other systems.

[0124] Information handling system 130 may include, but is not limited to, a personal computer system, a mainframe computer system, a workstation, an image computer, a parallel processor, or any other device known in the art. In general, the term "information handling system" may be broadly defined to encompass any device having one or more processors that executes instructions obtained from a storage medium.

[0125] Program instructions 134 implementing methods such as those described herein may be transmitted over a transmission medium such as a wire, cable or wireless transmission link. For example, as depicted in Figure 1, program instructions stored in memory 132 are transmitted to processor 131 via bus 133. Program instructions 134 are stored in a computer readable medium, such as memory 132. Examples of computer readable media include read-only memory, random access memory, magnetic disks, optical disks and magnetic tape.

[0126] In some embodiments, the scatterometry analysis described herein is implemented as part of a manufacturing process tool. Examples of manufacturing process tools include, but are not limited to, lithographic exposure tools, deposition tools, implant tools, and etch tools. In this configuration, the results of the TSAXS analysis are used to control the manufacturing process. In one example, TSAXS metrology data collected from one or more targets is sent to the manufacturing process tool. The TSAXS metrology data is analyzed as described herein, and the results are used to adjust the operation of the manufacturing process tool.

[0127] Using the scatterometry metrology described herein, a variety of semiconductor structures can be characterized, including but not limited to FinFETs, low dimensional structures such as nanowires and graphene, sub-10 nm structures, lithographic structures, through substrate vias (TSVs), memory structures such as DRAM, DRAM4F2, FLASH, MRAM, and high aspect ratio memory structures. Examples of structural properties include but are not limited to geometric parameters such as line edge roughness, line width roughness, pore size, pore density, sidewall angle, profile, critical dimension, pitch, and material parameters such as electron density, composition, grain structure, morphology, stress, strain, and elemental species.

[0128] 12 depicts a method 300 suitable for implementation by the metering system 100 of the present invention. According to certain embodiments, it will be appreciated that the data processing blocks of the method 300 may be implemented through execution of pre-programmed algorithms by one or more processors residing in the information processing system 130. Although the following description is presented in the context of the metering system 100, it is recognized herein that no limitations are intended to be expressed on the specific structural aspects of the metering system 100, which should be taken as illustrative only.

[0129] In block 301, a metrology target formed on the wafer surface is illuminated with a beam of X-ray radiation at an energy level of 15 keV or greater.

[0130] In block 302, the intensities of multiple diffraction orders of the radiation scattered by the measurement target in response to the incident beam are detected. The optical path length between the illumination source and the detector is less than 3 m. In addition, two or more of the multiple diffraction orders are spatially overlapped on the detector surface.

[0131] In block 303, the intensity of each of the overlapping diffraction orders is determined based on the beam shape of the zeroth diffraction order.

[0132] In block 304, a value of a parameter of interest associated with the measurement target is determined based on the intensities of the multiple diffraction orders.

[0133] The term "critical dimension" as used herein includes any critical dimension of a structure (e.g., bottom critical dimension, middle critical dimension, top critical dimension, sidewall angle, grating height, etc.), the critical dimension between any two or more structures (e.g., the distance between two structures), and the misalignment between two or more structures (e.g., the overlay misalignment between overlapping grating structures, etc.). Structures may include three-dimensional structures, patterned structures, overlay structures, etc.

[0134] As used herein, the terms "critical dimension application" or "critical dimension metrology application" include any critical dimension metrology.

[0135] The term "metrology system" as used herein includes any system that is at least partially employed to characterize a specimen in any manner, including critical dimension and overlay metrology applications. However, these technical terms are not intended to limit the scope of the term "metrology system" as used herein. Additionally, the metrology system as used herein may be configured for measuring patterned and / or unpatterned wafers. The metrology system may be configured as an LED inspection tool, an edge inspection tool, a backside inspection tool, a macro inspection tool, or a multi-mode inspection tool (including those that obtain data from one or more platforms simultaneously), or any other metrology or inspection tool that would benefit from the metrology techniques described herein.

[0136] Various embodiments are described herein in relation to semiconductor processing systems (e.g., inspection systems and lithography systems) that may be used to process specimens. As used herein, the term "specimen" refers to a wafer, reticle, or any other specimen that may be processed (e.g., printed or inspected for defects) by any means known in the art.

[0137] The term "wafer" as used herein generally refers to a substrate formed of a semiconductor or non-semiconductor material. Examples include, but are not limited to, monocrystalline silicon, gallium arsenide, and indium phosphide. Such substrates may be commonly found and / or processed in semiconductor manufacturing facilities. In some cases, a wafer may consist of only a substrate (a so-called bare wafer). Alternatively, a wafer may have one or more layers of dissimilar materials formed on a substrate. One or more layers formed on a wafer may be "patterned" or "unpatterned." For example, a wafer may have multiple dies with repeatable pattern features.

[0138] A "reticle" may be a reticle at any stage in the reticle manufacturing process or a finished reticle, which may or may not have been released for use in a semiconductor manufacturing facility. A reticle or "mask" is generally defined as a substantially transparent substrate having a pattern of substantially opaque areas formed thereon. The substrate may, for example, comprise a glass material such as amorphous SiO2. The reticle may be placed over a resist-covered wafer during the exposure step of the lithography process, allowing the pattern on the reticle to be transferred into the resist.

[0139] The layer or layers formed on the wafer may be patterned or unpatterned. For example, each of multiple dies in a wafer may have repeatable pattern features. The formation and processing of such layers of material may ultimately result in a completed device. Many types of devices may be formed on a wafer, and the term wafer as used herein is intended to encompass wafers upon which any type of device known in the art may be fabricated.

[0140] In accordance with one or more exemplary embodiments, the functions described above may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over a computer-readable medium as one or more instructions or code. Computer-readable media includes both computer storage media and communication media, such as any media that facilitates the transfer of a computer program from one place to another. A storage medium may be any available medium that can be accessed by a general purpose or special purpose computer. By way of non-limiting example, such computer-readable media may comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code means in the form of instructions or data structures and that can be accessed by a general purpose or special purpose computer or a general purpose or special purpose processor. Any connection may be referred to as a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio frequency, or microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio frequency, or microwave would fall within the definition of the medium. The term disk / disc in this application includes compact disks (CDs), laser disks, XRF™ disks, digital versatile disks (DVDs), floppy disks, and Blu-ray disks, as well as disks on which data is typically reproduced magnetically and disks on which data is reproduced optically with a laser. Combinations of the above should also be included within the scope of computer readable media.

[0141] While certain specific embodiments are described above for instructional purposes, the teachings of this patent application have general applicability and are not limited to the specific embodiments described above. Thus, various modifications, adaptations and combinations of the various features of the above-described embodiments can be made without departing from the scope of the invention as set forth in the claims.

Claims

1. illuminating a metrology target formed on the wafer surface with a beam of X-ray radiation; detecting intensities of diffracted beams of a plurality of diffraction orders of radiation scattered by the measurement target in response to the incident beam with an X-ray detector, the X-ray detector having a plurality of pixels, each pixel having a size of less than 100 μm in a direction of maximum length; determining a value of a parameter of interest associated with the measurement target based on the intensities of the plurality of diffraction orders; The method according to claim 1,

2. 2. The method of claim 1 , The method, wherein the X-ray detector is a photon counting detector or an integrating detector.

3. 2. The method of claim 1 , A method according to claim 1, wherein each of said plurality of pixels of said X-ray detector has a size in a direction of maximum length of less than 50 μm.

4. 2. The method of claim 1 , The method, wherein the optical path length between the X-ray illumination source and the X-ray detector is less than 3 m.

5. 10. The method of claim 1 further comprising: interpolating between a plurality of energy levels at each pixel of the x-ray detector; The method according to claim 1,

6. an x-ray illumination source configured to generate x-ray radiation; one or more x-ray illumination optics configured to illuminate a metrology target formed on a wafer surface with the incident focused beam of x-ray radiation; a sample positioning system for positioning the measurement target relative to the incident focused beam in a plurality of orientations; an x-ray detector having a plurality of pixels, each pixel having a size of less than 50 μm in a direction of maximum length, configured to detect intensities of respective diffracted beams of a plurality of diffraction orders of radiation scattered by the measurement target in response to the incident focused beam at each orientation; a non-transitory computer readable medium; the non-transitory computer readable medium comprising: code for causing an information processing system to determine a value of a parameter of interest associated with the measurement target based on the intensities of the plurality of diffraction orders; A weighing system having

7. 7. A weighing system according to claim 6, comprising: The metrology system, wherein the X-ray detector is a photon counting detector or an integrating detector.

8. 7. A weighing system according to claim 6, comprising: A metrology system, wherein the optical path length between the X-ray illumination source and the X-ray detector is less than 3 m.

9. 7. A weighing system according to claim 6, comprising: The X-ray detector determines a position of a center of gravity of photon interactions with the X-ray detector with a sub-pixel resolution, which is less than the size of a pixel.

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