Water-cooled, air-bearing-based rotating cathode X-ray illumination source

Abstract

A method and system for realizing a high-speed rotating cathode-based x-ray illumination source suitable for high-throughput x-ray metrology is disclosed. The high-speed rotating cathode includes a water-cooled rotating platen supported by radial and thrust air bearings using cascaded differential pumping. Extremely high bending stiffness of the rotating assembly is achieved by spaced-apart radial air bearings and locating the rotary motor and thrust bearing between the radial air bearings. The high bending stiffness increases the mechanical stability of the rotating assembly during high-speed operation, thereby reducing vibrations where the electron beam strikes the rotating cathode material. In some embodiments, a magnetic thrust bearing is used, and the air gap is controlled to maintain the desired air gap over an operating range of up to 3 millimeters.

Description

[Technical Field]

[0001] Embodiments of the present disclosure relate to x-ray based metrology systems and methods, and more particularly to methods and systems for improved x-ray illumination and measurement accuracy. [Background technology]

[0002] The various features and multiple structural levels of semiconductor devices, such as logic and memory devices, are typically fabricated by applying a series of processing steps to a specimen. For example, lithography, along with other processes, is one semiconductor fabrication process that involves creating patterns on a semiconductor wafer. Additional examples of semiconductor fabrication processes include, but are not limited to, chemical-mechanical polishing, etching, deposition, and ion implantation. Multiple semiconductor devices can be fabricated on a single semiconductor wafer and then separated into individual semiconductor devices.

[0003] Metrology processes are used at various steps during semiconductor fabrication processes to detect defects on wafers, thereby promoting higher yields. Optical metrology techniques offer the potential for high throughput without the risk of sample destruction. Optical metrology-based techniques, including scatterometry and reflectometry implementations and associated analysis algorithms, are commonly used to characterize critical dimensions, film thickness, composition, and other parameters of nanoscale structures.

[0004] As devices (e.g., logic and memory devices) move to smaller nanometer-scale dimensions, characterization becomes more challenging. Devices with complex three-dimensional geometries and materials with diverse physical properties contribute to this difficulty. For example, modern memory structures are often three-dimensional structures with high aspect ratios, making it difficult to penetrate them and allow optical radiation to reach the underlying layers. Additionally, the number of parameters required to characterize complex structures (e.g., FinFETs) is increasing, leading to increasing correlations between the parameters. As a result, the parameters used to characterize a target often cannot be reliably separated using available measurement techniques. As another example, modern semiconductor structures increasingly use opaque, high-dielectric-constant (high-k) materials. Optical radiation often cannot penetrate layers composed of these materials. As a result, measurements using thin-film scatterometry tools, such as ellipsometers and reflectometers, are becoming more challenging.

[0005] In response, more complex optical tools have been developed, including those with multiple illumination angles, short and wide illumination wavelength ranges, and more complete information acquisition from the reflected signal (e.g., measurement of multiple Mueller matrix elements in addition to traditional reflectance or ellipsometry signals). However, these solutions do not reliably address the inherent challenges associated with measuring many advanced targets (e.g., complex 3D structures, structures smaller than 10 nm, and structures using opaque materials) and measurement applications (e.g., line-edge roughness and line-width roughness measurements).

[0006] Atomic force microscopes (AFM) and scanning tunneling microscopes (STM) can achieve atomic-level resolution, but these instruments can only examine the surface of a sample. Furthermore, AFM and STM microscopes require long scanning times. Scanning electron microscopes (SEM) achieve intermediate resolution levels but cannot penetrate structures to sufficient depths. Thus, high-aspect-ratio holes cannot be well characterized. Furthermore, the required sample charging adversely affects imaging performance.

[0007] To address the issue of penetration depth, traditional imaging techniques such as TEM and SEM are often combined with destructive sample preparation techniques, such as focused ion beam (FIB) machining, ion milling, and blanket or selective etching. For example, transmission electron microscopy (TEM) can achieve high resolution levels and probe to any depth, but TEM requires destructive cutting of the sample. Several iterations of material removal and measurement typically provide the information needed to measure critical metrology parameters throughout a three-dimensional structure. However, these techniques require sample destruction and long processing times. The complexity and time required to complete these types of measurements result in significant inaccuracies due to misalignment of the etching and measurement steps. Additionally, these techniques require numerous iterations, which introduces alignment errors.

[0008] Another approach to modern metrology challenges is to adapt x-ray metrology to measurements including film thickness, critical dimensions, composition, strain, surface roughness, line edge roughness, and porosity.

[0009] Small-angle x-ray scattering (SAXS) systems have shown promise for addressing challenging measurement applications. Various aspects of applications of SAXS techniques, such as critical dimension measurement (CD-SAXS) and overlay measurement (OVL-SAXS), are discussed in 1) U.S. Pat. No. 7,929,667 to Zhuang and Fielden, entitled "High-brightness X-ray metrology," 2) U.S. Patent Application Publication No. 2014 / 0019097 to Bakeman, Shchegrov, Zhao, and Tan, entitled "Model Building And Analysis Engine For Combined X-ray And Optical Metrology," and 3) U.S. Patent Application Publication No. 2015 / 0117610 to Veldman, Bakeman, Shchegrov, and Mieher, entitled "Methods and Apparatus For Measuring Semiconductor Device Overlay Using X-ray Metrology." No. 2016 / 0202193, "Measurement System Optimization For X-Ray Based Metrology," by Hench, Shchegrov, and Bakeman; 5) U.S. Patent Application Publication No. 2017 / 0167862, "X-ray Metrology For High Aspect Ratio Structures," by Dziura, Gellineau, and Shchegrov; and 6) U.S. Patent Application Publication No. 2018 / 0106735, "Full Beam Metrology for X-ray Scatterometry Systems," by Gellineau, Dziura, Hench, Veldman, and Zalubovsky.The above patent documents are assigned to KLA-Tencor Corporation, Milpitas, California (USA), and are hereby incorporated by reference in their entirety.

[0010] Studies of CD-SAXS measurements of semiconductor structures have also been published in the scientific literature. Most research groups use high-brilliance X-ray synchrotron sources, but these sources are not suitable for use in semiconductor fabrication facilities due to their large size, cost, etc. An example of such a system is described in a paper by Lemaillet, Germer, Kline et al., entitled “Intercomparison between optical and x-ray scatterometry measurements of FinFET structures,” Proc. SPIE, v, 8681, p. 86810Q (2013).” More recently, a group at the National Institute of Standards and Technology (NIST) has begun work using a compact, high-brilliance X-ray source similar to that described in U.S. Patent No. 7,929,667. The research is disclosed in a paper titled “X-ray scattering critical dimensional metrology using a compact x-ray sources for next generation semiconductor devices,” J. Micro / Nanolith. MEMS MOEMS 16(1), 014001 (Jan-Mar 2017).

[0011] SAXS has also been applied to the characterization of materials and other non-semiconductor related applications. Exemplary systems are commercialized by several companies, including Xenocs SAS (www.xenocs.com), Bruker (www.bruker.com), and Rigaku (www.rigaku.com / en).

[0012] Many x-ray metrology techniques used in semiconductor manufacturing can benefit from high-brilliance x-ray sources. For example, critical dimension small-angle x-ray scattering (CD-SAXS) measurements often require long integration times due to the low scattering properties of certain materials. A high-brilliance source can improve the throughput of CD-SAXS measurements.

[0013] Research efforts in the field of extreme ultraviolet (EUV) lithography have focused on light sources that emit narrow-band radiation (e.g., ±0.1 nm) centered at 13 nanometers (i.e., 92.6 electron volts) at high power levels (e.g., 210 watts average power at the intermediate focus of the illuminator). Light sources for EUV lithography have been developed using laser droplet plasma designs. For example, xenon, tin, and lithium droplet targets operating at pulse repetition rates of approximately 100 kHz are pumped by a CO2 coherent light source. The resulting light is high power (210 watts average power at the intermediate focus of the illuminator is the target for lithography tools at 13 nanometers). However, the resulting radiation is relatively low energy (92.6 electron volts), significantly limiting the use of these illumination sources for metrology applications. An exemplary system is disclosed in US Pat. No. 7,518,134 to ASML Netherlands BV, which is incorporated herein by reference in its entirety.

[0014] In some examples, x-ray illumination is generated by high-energy electron beam bombardment of a solid target material, such as a rotating cathode target material. Rotating cathode x-ray sources are commonly used in medical imaging and analytical chemistry applications. Many versions of rotating cathode x-ray sources are manufactured by companies such as Philips, General Electric, Siemens, and others for medical imaging applications such as tomography, mammography, and angiography. Rigaku Corporation and Bruker Corporation manufacture continuously operating rotating cathode sources for analytical chemistry applications such as x-ray diffraction (XRD), x-ray reflectometry (XRR), small-angle x-ray scatterometry (SAXS), and wide-angle x-ray scatterometry (WAXS).

[0015] Rotating cathode targets allow for more efficient heat removal from the cathode material than stationary cathode targets. Continuously moving the electron beam impact location on the cathode surface results in convective heat dissipation, thereby reducing the focal spot impact temperature and improving the power loading capability of the x-ray tube. Typical rotating cathode sources rotate the cathode material at 5,000 to 10,000 revolutions per minute or more. The linear velocity of the cathode material at the focal spot location is 100 meters per second or more.

[0016] Improvements have been proposed for increased cathode heat dissipation and thermal conductivity. For example, the FR-X model X-ray source manufactured by Rigaku Corporation (Japan) and the MicroMax model X-ray source manufactured by Bruker AXS GmbH (Germany) use water cooling to dissipate heat generated at the cathode.

[0017] U.S. Patent No. 9,715,989 discloses a rotating cathode structure having a highly thermally conductive diamond layer. U.S. Patent No. 8,243,884 discloses improving heat dissipation by using a diamond-metal composite. U.S. Patent No. 7,440,549 discloses a rotating cathode device that dissipates heat through the heat pipe effect. U.S. Patent Application Publication No. 2015 / 0092924 discloses a microstructured cathode comprising a high atomic number material embedded in a highly thermally conductive matrix. U.S. Patent Nos. 9,159,524 and 9,715,989 disclose similar diamond-based thermal management solutions in the context of stationary cathode sources. The contents of the above U.S. patents and U.S. patent application publications are hereby incorporated by reference in their entireties.

[0018] Despite their improved power loading capabilities, rotating cathode sources have significant limitations. For example, operating rotating cathode structures at high speeds generates excessive amounts of heat that cannot be easily dissipated in a high-vacuum environment. The use of mechanical bearings also generates significant heat, which can lead to mechanical instability and bearing failure at high speeds. Furthermore, the use of magnetic fluid seals to isolate the rotary drive and bearing components from the high-vacuum environment results in significant friction losses and excessive heat generation, especially at high rotational speeds. Contamination of the high-vacuum environment by materials outgassed from the magnetic fluid seals is also a significant problem. [Prior art documents] [Patent documents]

[0019] [Patent Document 1] U.S. Patent Application Publication No. 2019 / 0115184 [Patent Document 2] U.S. Patent Application Publication No. 2021 / 0310717 Summary of the Invention [Problem to be solved by the invention]

[0020] Future metrology applications pose metrology challenges due to ever-increasing resolution requirements, correlations between multiple parameters, more complex geometries, and the increasing use of opaque materials. To adapt x-ray metrology to semiconductor applications, improved x-ray sources with the highest possible brightness are required. Rotating cathode-driven systems with higher speed capabilities, improved reliability, and reduced contamination are desired. [Means for solving the problem]

[0021] Disclosed herein are methods and systems for implementing a high-speed rotating cathode-based x-ray illumination source suitable for high-throughput x-ray metrology. A high-brightness x-ray source is produced by bombarding a rotating cathode material with an electron stream to generate x-ray radiation. The resulting x-ray emissions are collected and directed to a semiconductor sample, thereby performing x-ray-based metrology of the sample.

[0022] In one embodiment, the high-speed rotating cathode includes a water-cooled rotating platen supported by radial and thrust air bearings with cascaded differential pumping. Air bearings allow for extremely low friction and reliable rotation at very high speeds compared to mechanical bearings. The reduced friction allows a small rotary motor to provide sufficient torque to drive the rotating cathode at high speeds. The differential pumping creates a vacuum seal with significantly lower viscous drag than conventional magnetic fluid seals, without the risk of material contamination of the vacuum environment. The significantly lower friction minimizes heat generation in the rotating assembly and improves the stability of the rotating assembly during high-speed operation.

[0023] In another aspect, the rotary motor and thrust bearing are located between the radial air bearings. A very high bending stiffness of the rotary assembly is achieved by separating the radial air bearings and locating the rotary motor and thrust bearing between the radial air bearings. The high bending stiffness increases the mechanical stability of the rotary assembly during high speed operation, thereby reducing vibrations where the electron beam strikes the rotating cathode material.

[0024] In some embodiments, the distance D between the radial air bearings is greater than 80% of the overall length L of the rotating spindle shaft. The center of mass of the rotating assembly is located near the center of bending stiffness of the rotating assembly. In some embodiments, the center of mass of the rotating assembly is within 5 centimeters of the center of bending stiffness of the rotating assembly. Furthermore, in some embodiments, the rotation motor is located within 5 centimeters of the center of mass of the rotating assembly.

[0025] In another aspect, the radial air bearing facing the vacuum chamber includes an evacuated annular groove at its interface with the vacuum chamber, thereby minimizing molecular flow from the air bearing into the vacuum chamber.

[0026] In another aspect, a radial air bearing opposite the terminal end of the rotating spindle shaft includes a rotary coupling containing water cooling channels to deliver cooling fluid to the rotating platen.

[0027] In another aspect, the thrust bearing acts as a squeeze film damper, thereby minimizing vibrations in the axial direction.

[0028] In some embodiments, the thrust bearing is a magnetic bearing. Magnetic bearings generally have lower stiffness in the load direction than air bearings. However, the gap between the magnetic bearing and the opposing surface is actively controlled. In some embodiments, the magnetic bearing is controlled to maintain a fixed gap. In some other embodiments, the magnetic bearing is controlled to maintain a desired gap over an operating range of up to 3 millimeters. This may be desirable when operating a rotating platen at high speed while continuously moving the cathode material axially to continuously refresh the cathode material on the path of the electron beam.

[0029] The foregoing is a summary and necessarily contains simplifications, generalizations, and omissions of detail. Accordingly, those skilled in the art will appreciate that this summary is illustrative only and is not intended to be in any way limiting. Other aspects, inventive features, and advantages of the devices and / or methods disclosed herein will become apparent from the non-limiting detailed description included herein. [Brief explanation of the drawings]

[0030] [Figure 1] FIG. 1 is a simplified diagram illustrating an embodiment of a metrology system including a water-cooled, air-bearing-based rotating cathode X-ray illumination source for measuring features of a specimen, in accordance with at least one novel aspect. [Figure 2] FIG. 1 is a simplified diagram illustrating a cross-sectional view of an embodiment of a water-cooled, air-bearing-based rotating cathode subsystem in accordance with at least one novel aspect. [Figure 3] FIG. 3 is a simplified diagram illustrating a cross-sectional view of an embodiment of the water-cooled, air-bearing-based rotating cathode subsystem shown in FIG. 2. [Figure 4] FIG. 1 is a simplified diagram illustrating another embodiment of a metrology system including a water-cooled, air-bearing-based rotating cathode X-ray illumination source for measuring characteristics of a specimen, in accordance with at least one novel aspect. [Figure 5]1 is a flowchart of a method for performing measurements on a semiconductor wafer with a metrology system that uses a water-cooled, air-bearing-based rotating cathode X-ray illumination source in accordance with a method of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0031] Reference will now be made in detail to background examples and certain embodiments of the present invention, examples of which are illustrated in the accompanying drawings.

[0032] Systems are disclosed that can be used to measure structural and material characteristics (e.g., material composition, dimensional characteristics of structures and films, etc.) associated with different semiconductor fabrication processes based on x-ray illumination. More particularly, methods and systems are disclosed herein for implementing a high-speed, rotating cathode-based x-ray illumination source suitable for high-throughput x-ray metrology.

[0033] In one embodiment, a high brightness x-ray source is formed by bombarding a rotating cathode material with a stream of electrons to generate x-ray radiation, which is collected and directed to a semiconductor sample, and x-ray-based metrology is performed on the sample.

[0034] A water-cooled rotating platen supported by radial and thrust air bearings with cascaded differential pumping enables a high-speed rotating cathode that operates reliably in a high vacuum without generating excessive heat. The air bearings allow for very high-speed rotation with significantly lower friction and greater reliability than mechanical bearings. The reduced friction allows a small rotary motor to provide sufficient torque to drive the rotating cathode at high speeds. The differential pumping provides a vacuum seal with significantly lower viscous drag than conventional magnetic fluid seals, without the risk of material contamination of the vacuum environment. The significantly lower friction minimizes heat generated in the rotating assembly and improves the stability of the rotating assembly at high speeds.

[0035] The high energy nature of x-ray radiation allows x-rays to penetrate optically opaque thin films, buried structures, high aspect ratio structures, and devices containing many thin film layers. Many x-ray metrology techniques used in semiconductor manufacturing can benefit from high brightness, reliable x-ray sources, for example, critical dimension small angle x-ray scattering (CD-SAXS).

[0036] Measurements often require long integration times due to the low scattering efficiency of the materials that make up many modern semiconductor structures. High-brightness, high-power rotating cathode x-ray sources can improve the throughput of x-ray-based measurements, such as CD-SAXS.

[0037] Figure 1 illustrates an embodiment of an x-ray-based metrology system 100 that includes a high-speed rotating cathode subsystem 110 according to one embodiment. By way of non-limiting example, the x-ray metrology system 100 operates in a transmission mode. As shown in Figure 1, the x-ray illumination source includes an electron beam source 103 and a rotating cathode subsystem 110 that includes a cathode material 113 disposed on a rotating platen 111. The rotating cathode subsystem 110 includes a rotary actuator that rotates the platen 111 about a rotation axis A at an angular velocity ω.

[0038] In the embodiment shown in FIG. 1 , a computing system 130 is communicatively coupled to the rotating cathode subsystem 110. In one example, a command signal 136 indicating a desired angular velocity of the rotating platen 111 is communicated from the computing system 130 to the rotating cathode subsystem 110. In response, the rotating cathode subsystem 110 adjusts the angular velocity of the rotating platen 111 based on the command signal 136. The air-bearing-based rotating cathode subsystem 110 can achieve high rotational speeds without excessive friction losses or heat generation. In some embodiments, the rotating cathode subsystem 110 can operate at any desired rotational speed ranging from zero revolutions per minute to 40,000 revolutions per minute. For a platen 111 having a diameter of 100 millimeters, the tangential velocity of the cathode material 113 can be any desired linear velocity ranging from zero meters per second to 210 meters per second. In other embodiments, higher rotational speeds, for example, up to 100,000 revolutions per minute, are contemplated as being within the scope of the present disclosure.

[0039] 1, an x-ray illumination source provides high-intensity x-ray illumination delivered across an examination region 102 of a sample 101. The x-ray metrology system 100 is configured such that x-rays interacting with the sample 101 are collected by a detector 123, while a sample positioning system 140 positions the sample for angle-resolved interaction of the x-rays with the sample. In some embodiments, any other particles resulting from the interaction may be detected, such as photoelectrons, x-rays produced by fluorescence, or ions.

[0040] 1, the x-ray illumination source includes an electron beam source 103 (e.g., an electron gun) configured to generate electron emissions from an anode. In the illustrated embodiment, the electron beam source 103 generates a steady, free-flowing electron stream 105. The electron stream 105 is shaped by electron optics 104 and incident on a cathode material 113 supported on a rotating platen 111. In some embodiments, the electron beam source 103 is configured to generate a continuous electron beam. In some other embodiments, the electron beam source 103 is configured to generate a pulsed electron beam.

[0041] 1, the electron beam source 103 is communicatively coupled to a computing system 130, and the electron beam source 103 is actively controlled based on command signals 135 communicated from the computing system 130 to the electron beam source 103. In some examples, the command signals 135 include an indication of the desired electron beam energy to be provided by the electron beam source 103. In response, the electron beam source 103 adjusts the electron beam energy output to the desired value. In some embodiments, the electron beam source 103 accelerates the focused electron stream 105 by a voltage differential greater than 10 kV.

[0042] The electron optics 104 are configured to direct and / or focus the electron stream 105 onto the cathode material 113. The electron optics 104 include suitable electromagnets, permanent magnets, or any combination of electromagnets and permanent magnets to focus the electron beam and direct the electron stream 105. In some embodiments, the electron optics 104 may include electrostatic elements, such as solenoids, quadrupole lenses such as Halbach cylinders, or Einzel lenses, to focus and direct the electron beam. The electron optics 104 may also be configured as an electron monochromator. Additionally, the electron optics 104 may be used to focus the beam to further reduce electron beam noise.

[0043] The electron-optical component 104 may also be configured for active control by the computing system 130. In some embodiments (not shown), the computing system 130 is communicatively coupled to the electron-optical component 104. In some examples, the current or voltage supplied to the electromagnetic element may be actively controlled based on command signals communicated from the computing system 130 to the electron-optical component 104. In other examples, the position of a magnetic element (e.g., a permanent magnet) may be manipulated by a positioning system (not shown) based on command signals communicated from the computing system 130 to the electron-optical component 104. In this manner, focusing and directing of the electron stream 105 is achieved under the control of the computing system 130, thereby achieving a stable electron stream 105 incident on the cathode material 113.

[0044] As shown in FIG. 1, x-ray optics 106 are configured to collect the electron stream 105 and x-ray emissions from an incident spot on the cathode material 113 and direct an incident x-ray beam 108 towards the sample 101 .

[0045] In other aspects, the x-ray optics 106 are configured at a specific collection angle to capture x-ray emissions in a desired energy band at peak intensity. In some embodiments, the x-ray optics 106 are designed to focus x-ray radiation directly onto a measurement target. When a high-energy, focused electron beam strikes a cathode target, stimulated x-ray emissions include broadband bremsstrahlung and characteristic line emissions (i.e., Kα, Kβ, Lα, Lβ, etc.). In some embodiments, the x-ray collection optics are oriented to optimize x-ray brightness by collecting x-ray radiation over a range of collection angles.

[0046] In some embodiments, the x-ray optics 106 monochromatize the x-ray beam incident on the sample 101. In some examples, the x-ray optics 106 collimate or focus the x-ray beam 108 onto the inspection region 102 of the sample 101. In some embodiments, the x-ray optics 106 include one or more x-ray collimating mirrors, x-ray apertures, x-ray monochromators, x-ray beam stops, multilayer optics, refractive x-ray optics, diffractive optics such as zone plates, or any combination thereof.

[0047] In some embodiments, high-quality x-ray optics, such as polycapillary x-ray optics, specular optics, or optics arranged in a Loxlay-Tanner-Bowen configuration, are used to achieve high-brightness, small-spot-size illumination of the semiconductor sample. For example, a high-intensity x-ray beam can be shifted and focused to a spot size of less than 40 micrometers using specular x-ray optics such as grazing-incidence ellipsoidal mirrors, polycapillary optics such as hollow-capillary x-ray waveguides, multilayer optics, or crystalline optics such as a Loxlay-Tanner-Bowen system.

[0048] In preferred embodiments, the x-ray optic 106 is a multi-layer optic. In some of these embodiments, the multi-layer optic divides the x-ray beam 108 into 10 -1 This level of spectral purity is suitable for metrology techniques such as x-ray reflectivity (XRR), x-ray diffraction (XRD), and x-ray fluorescence (XRF). -6 A crystal monochromator is used to monochromatize the light to a spectral purity (δλ / λ) less than 1000 nm. This level of spectral purity is suitable for metrology techniques such as high resolution x-ray diffraction (HRXRD).

[0049] The x-ray optics 106 may be configured for active control by the computing system 130. In some embodiments, the computing system 130 is communicatively coupled to the x-ray optics 106 (not shown). In one example, command signals communicated from the computing system 130 to the x-ray optics 106 indicate desired positions of the optical elements. The positions of the optical elements may be adjusted by a positioning system (not shown) based on the command signals. In this manner, focusing and directing of the x-ray beam 108 is achieved under the control of the computing system 130, thereby achieving stable illumination incident on the sample 101. In some examples, the computing system 130 is configured to control the positioning and spot size of the x-ray beam 108 incident on the sample 101. In some examples, the computing system 130 is configured to control illumination characteristics (e.g., intensity, polarization, spectrum, etc.) of the x-ray beam 108.

[0050] 1, x-ray detector 123 collects x-ray radiation 122 scattered from sample 101 in response to incident x-ray illumination and generates output signal 124 indicative of a property of sample 101 that is sensitive to the incident x-ray radiation. Scattered x-rays 122 are collected by x-ray detector 123 while sample positioning system 140 positions and orients sample 101 to produce angularly resolved scattered x-rays.

[0051] 1, the x-ray illumination source is maintained in a vacuum environment maintained within vacuum chamber 120. In some embodiments, a vacuum of less than 1e-8 Torr is maintained within vacuum chamber 120. X-ray emission passes through vacuum window 121 as the x-rays propagate from cathode material 113 toward x-ray optic 106. Vacuum window 121 may be constructed from any suitable material that is substantially transparent to x-ray radiation (e.g., Kapton®, beryllium, etc.).

[0052] FIG. 2 is a cross-sectional view of one embodiment of the rotating cathode subassembly 110 shown in FIG. 2. As shown in FIG. 2, the rotating cathode subassembly 110 includes a rotating main shaft 151. One end of the rotating main shaft extends through an opening formed in the wall of a vacuum chamber 159. A rotating platen 154 is attached to the rotating main shaft 151 within the vacuum chamber 159. In this manner, the rotating platen 154 rotates within the vacuum chamber 159. A counterweight 158 ​​is attached to the opposite end of the rotating main shaft 151. In some embodiments, the rotating platen 154, the counterweight 158, or both are removably attached to the rotating main shaft 151. However, in some other embodiments, the rotating platen 154, the counterweight 158, or both are permanently fixed to the rotating main shaft 151. The rotating assembly, including the rotating spindle shaft 151, the platen 154, and the counterweight 158, rotates about an axis A at an angular velocity ω.

[0053] Cathode material 155 is disposed on the surface of rotating platen 154. In the embodiment shown in FIG. 2, cathode material 155 is disposed on the peripheral surface of rotating platen 154, which is oriented parallel to axis A. In some other embodiments, cathode material 155 is disposed on a surface of rotating platen 154 that is oriented perpendicular to axis A. In the embodiment shown in FIG. 2, rotating platen 154 has a disk-like shape. However, in other embodiments, different shapes, such as a conical or curved shape, may be contemplated. In this manner, cathode material 113 may be optimally positioned relative to the electron beam source. In some embodiments, the diameter of rotating platen 154 is approximately 100 millimeters. However, in general, the rotating platen may have any suitable diameter.

[0054] As shown in FIG. 2, the rotating assembly is supported by radial air bearings 152 and 153 and thrust bearings 156A and 156B. Bearings 152, 153, 156A, and 156B are secured to housing 164 and coupled to a pressurized gas source, such as a clean, dry, compressed air source. In the embodiment shown in FIG. 2, pressurized clean, dry air 163 is delivered to radial air bearings 152 and 153 and thrust bearings 156A and 156B via ports 169, 168A, 168B, and 167, respectively. In a preferred embodiment, radial air bearings 152 and 153 and thrust bearings 156A and 156B are porous air bearings. However, in some other embodiments, either radial air bearings 152 and 153 or thrust bearings 156A and 156B are groove-compensated air bearings.

[0055] Bearings 152, 153, 156A, and 156B allow the rotating assembly to rotate freely about axis A, but constrain all other degrees of freedom within very tight tolerances. Radial air bearings 152 and 153 exhibit high stiffness in a direction perpendicular to the axis A of the rotating spindle shaft. That is, radial air bearings 152 and 153 support very large loads in a direction perpendicular to the axis A of the rotating spindle shaft, while exhibiting very little deflection in that same direction. In one example, the maximum runout of the rotating assembly is less than 2 micrometers.

[0056] Thrust bearings 156A and 156B are located between radial air bearings 152 and 153. A flange 178 of rotating main shaft 151 is located between thrust bearings 156A and 156B. The surface of flange 178 facing counterweight 158 ​​is separated from the bearing surface of thrust bearing 156B by a small gap. The surface of flange 178 facing platen 154 is separated from the bearing surface of thrust bearing 156A by a small gap. In combination, thrust bearings 156A and 156B exhibit high stiffness in a direction parallel to the rotational axis A of the rotating main shaft. That is, thrust bearings 156A and 156B support very large loads in a direction parallel to the rotational axis A of the rotating main shaft while exhibiting very little deflection in this same direction.

[0057] As shown in FIG. 2 , the rotary cathode subassembly 110 includes a rotary motor 179 disposed between the radial air bearings 152 and 153. The rotary motor 179 includes a stator mechanically coupled to the housing 164 and a rotor 177 mechanically coupled to the main rotating shaft 151. In the embodiment shown in FIG. 2 , the rotor 177 is attached to the peripheral surface of the flange 178. However, in general, the rotor 177 may be attached to a different location on the main rotating shaft 151. The rotary motor 179 provides rotational torque to the main rotating shaft 151, driving the rotation of the platen 154. In some embodiments, the rotary motor 179 is a brushless servo motor. In some of these embodiments, the brushless servo motor does not contain iron. However, in some other embodiments, the brushless servo motor includes an iron core, which concentrates the magnetic flux and allows for higher torque with a smaller motor size.

[0058] In one embodiment, both rotary motor 179 and thrust bearings 156A and 156B are located between radial air bearings 152 and 153. By spacing radial air bearings 152 and 153 far apart and positioning rotary motor 179 and thrust bearings 156A and 156B between radial air bearings 152 and 153, a very high bending stiffness is achieved by the rotating assembly, for example, a bending stiffness greater than 500,000 Newton-meters per radian. This high bending stiffness increases the mechanical stability of the rotating assembly during high-speed operation, thereby reducing vibrations at the location where electron beam 105 impinges on cathode material 155.

[0059] 3, the distance D between radial air bearings 152 and 153 is approximately 250 millimeters. However, in general, the distance D between radial air bearings 152 and 153 may be any suitable distance. In some embodiments, the distance D between radial air bearings 152 and 153 is greater than 80% of the overall length L of the rotating main shaft.

[0060] As shown in Figure 3, the center of mass 180 of the rotating assembly is located near the center of bending stiffness of the rotating assembly. In some embodiments, the center of mass 180 of the rotating assembly is within 5 centimeters of the center of bending stiffness of the rotating assembly. In some embodiments, the center of mass 180 of the rotating assembly coincides with the center of bending stiffness of the rotating assembly. Additionally, in some embodiments, the rotation motor 179 is located within 5 centimeters of the center of mass 180 of the rotating assembly.

[0061] In another aspect, radial air bearing 153 includes a vacuum-evacuated annular groove at its interface with vacuum chamber 159, thereby minimizing molecular flow from air bearing 153 to vacuum chamber 159. As shown in FIG. 2, radial air bearing 153 includes annular groove 165 with a flow path to port 166. As such, annular groove 165 is coupled to a vacuum source. As shown in FIG. 2, annular groove 165 is positioned adjacent the rotating main shaft, between the load-bearing surface of rotary air bearing 153 and vacuum chamber 159. A vacuum 162 is drawn through port 166 to evacuate any air that leaks from the air film interface between radial air bearing 153's load-bearing surface and rotating main shaft 151 before the air reaches vacuum chamber 159. Vacuum chamber 159 also includes a molecular pump to remove any air that reaches vacuum chamber 159. 2 shows three annular grooves 165, generally any suitable number of vacuum-pumped annular grooves located between the load-bearing surface of radial air bearing 153 and vacuum chamber 159 are contemplated. Furthermore, each annular groove may be fluidly coupled to an individual port, or alternatively, multiple annular grooves may be fluidly coupled to a single port.

[0062] In another aspect, radial air bearing 152 includes at least four annular grooves between the load-bearing surface of radial air bearing 152 and the end of rotating main shaft 151 opposite platen 154. As shown in Figure 2, annular groove 176 closest to the load-bearing surface of radial air bearing 152 is coupled to a pressurized gas source, such as a clean, dry, compressed air source. In the embodiment shown in Figure 2, pressurized clean, dry air 163 is delivered to annular groove 176 through port 170.

[0063] Annular groove 173 is located nearest the terminal end of rotating spindle shaft 151 and is coupled to a vacuum source. Vacuum 161 is drawn from annular groove 173 through port 174.

[0064] Annular grooves 175 and 181 are also coupled to coolant source 160A and coolant return 160B, respectively. Coolant is provided to annular groove 175 via port 171, and coolant is returned from annular groove 181 via port 172. As shown in FIG. 2, coolant channels 182 and 183 are located within the spindle shaft. Coolant channels 182 and 183 extend from rotating platen 154 to annular grooves 175 and 181 in a direction parallel to the rotational axis of the spindle shaft. As shown in FIG. 2, annular groove 175 is coupled to coolant channel 182, which is coupled to a cooling channel within rotating platen 154. Similarly, annular groove 181 is coupled to coolant channel 183, which is coupled to a cooling channel within rotating platen 154. Coolant is channeled from annular groove 175 through cooling channels 182, through cooling channels in the rotating platen 154, and then returned through coolant channels 183 and annular groove 181. The flow of coolant through the rotating platen 154 extracts heat from the rotating platen 154, maintaining a constant temperature and minimizing temperature-change induced geometric distortion of the rotating platen 154. The heat extracted from the rotating platen 154 may come from several sources, including: 1) interaction of the electron beam 103 with the cathode material 155; 2) heat generated by the rotating motor 179 conducted to the rotating platen 154 through the rotating spindle shaft 151; and 3) heat generated by frictional losses at bearing surfaces conducted to the rotating platen 154 through the rotating spindle shaft 151. Although coolant channels 182 and 183 are shown as channels located side by side along rotating main shaft 151, in some other embodiments, coaxial channels may be located along rotating main shaft 151 concentric with rotation axis A.

[0065] As shown in FIG. 2 , annular grooves 175 and 181 are located between annular grooves 173 and 176. Vacuum 161 is drawn from annular groove 173 via port 174 to exhaust any refrigerant leaking from the refrigerant film interface near annular grooves 175 and 181 between radial air bearing 153 and main rotating shaft 151 before the refrigerant reaches environmental outer housing 164. Pressurized clean, dry air 163 is also applied to groove 176 to force any refrigerant leaking from the refrigerant film interface between radial air bearing 153 and main rotating shaft away from the load-bearing surface of radial air bearing 152 and toward annular groove 173. In this manner, annular grooves 173 and 176 work together to trap any refrigerant that leaks between annular grooves 173 and 176, allowing the trapped refrigerant to be removed from annular groove 173. Although annular groove 173 is shown as two annular grooves and annular groove 176 is shown as one annular groove, in general, any suitable number of grooves may be used.

[0066] In another embodiment, thrust bearings 156A and 156B are designed to act as squeeze film dampers, minimizing vibrations in the axial direction, ie, the direction parallel to axis A.

[0067] Although thrust bearings 156A and 156B are shown as air bearings, in some other embodiments, thrust bearings 156A and 156B are magnetic bearings. Magnetic bearings generally have lower stiffness in the load direction than air bearings. However, the gap between the magnetic bearing and the opposing surface, e.g., flange 178, is actively controlled. In some embodiments, the magnetic bearing is controlled to maintain a fixed gap. In other embodiments, the magnetic bearing is controlled to maintain a desired gap over an operating range of up to 3 millimeters. In these embodiments, the axial position of the rotating assembly containing cathode material 155 is precisely controlled to within at least 1 millimeter, e.g., up to 3 millimeters. This may be desirable if, during operation, the cathode material 155 is continuously moved axially while rotating rotating platen 154 at high speed to continuously refresh the cathode material on the path of electron beam 103.

[0068] The alignment of the cathode material 113 with the electron stream 105 generates x-ray emissions 108 that are incident on the inspection region 102 of the sample 101. In some embodiments, the x-ray illumination source collects K nuclear emissions, L nuclear emissions, or a combination thereof from the cathode material. In some embodiments, the x-ray source photon energy is preferably in the range of 10 keV to 25 keV, which allows penetration through silicon wafers with adequate transmission efficiency for transmission small-angle x-ray scattering (T-SAXS)-based semiconductor metrology applications, such as critical dimension and overlay metrology on patterned silicon wafers.

[0069] In some embodiments, the distance between the sample 101 and the cathode material 113 is long (e.g., greater than 1 meter). In these embodiments, the presence of air in the beam path causes unwanted beam scattering. Therefore, in some embodiments, it is preferred to propagate the x-ray beam 108 from the x-ray illumination source to the sample 101 through an evacuated flight tube.

[0070] In some embodiments, the x-ray detector 123 is maintained in the same atmospheric environment (e.g., a degassed environment) as the sample 101. However, in some embodiments, the distance between the sample 101 and the x-ray detector 123 is long (e.g., greater than 1 meter). In these embodiments, the presence of air in the beam path causes unwanted beam scattering, especially when the x-ray illumination source is configured to generate hard x-rays (e.g., photon energies greater than 5 keV). Thus, in some embodiments, the x-ray detector 123 is maintained in a localized vacuum environment separated from the sample (e.g., sample 101) by a vacuum window.

[0071] In some embodiments, it may be desirable to maintain the x-ray illumination beam 108, sample 101, collection beam 122, and detector 123 in an evacuated environment to minimize absorption of x-rays, especially when the x-ray illumination source is configured to produce soft x-rays (e.g., photon energies less than 5 keV).

[0072] FIG. 4 illustrates an x-ray metrology system 200 for performing semiconductor metrology measurements. As shown in FIG. 4, the x-ray metrology system 200 includes similar elements, labeled with similar numbers, to those described with reference to FIG. 1. By way of non-limiting example, the x-ray metrology system 200 operates in reflection mode rather than the transmission mode shown in FIG. 1. In some embodiments, the x-ray metrology system 200 is configured as a small-angle grazing incidence x-ray scattering (GISAXS) measurement system. Typical angles of incidence and collection are approximately 1 degree measured from the surface of the sample or approximately 89 degrees from an axis normal to the surface of the sample. The x-ray metrology system 200 includes the x-ray illumination source described with reference to FIG. 1. The x-ray metrology system 200 is configured such that x-rays scattered from the sample are collected by a detector while the sample positioning system 140 positions the sample. Any other particles generated during the interaction, such as photoelectrons, x-rays generated by fluorescence, or ions, may also be detected. Metrology systems configured to perform GISAXS measurements require a high-brightness x-ray source to maintain sufficient brightness over a relatively large sample area illuminated at a small angle. For this reason, rotating cathode-based x-ray illumination sources are particularly suitable for GISAXS measurements.

[0073] By way of non-limiting example, the x-ray metrology system 100 shown in FIG. 1 is configured as a transmission small-angle x-ray scatterometer (TSAXS), and the x-ray metrology system 200 shown in FIG. 4 is configured as a small-angle grazing incidence x-ray scatterometer (GISAXS). In general, however, x-ray metrology systems using rotating cathode-based x-ray illumination sources as described herein may use any one or more of the following metrology techniques: transmission small-angle x-ray scattering (TSAXS), small-angle grazing-incidence x-ray scattering (GISAXS), wide-angle x-ray scattering (WAXS), x-ray reflectometry (XRR), grazing-incidence x-ray reflectometry (GXR), x-ray diffraction (XRD), grazing-incidence x-ray diffraction (GIXRD), high-resolution x-ray diffraction (HRXRD), x-ray photoelectron spectroscopy (XPS), x-ray fluorescence (XRF), total reflection x-ray fluorescence (TXRF), grazing-incidence x-ray fluorescence (GIXRF), x-ray tomography, x-ray ellipsometry, and hard x-ray photoemission spectroscopy (HXPS).

[0074] X-ray metrology tool 100 also includes a computing system 130 that is used to acquire signals 124 generated by X-ray detector 123 and determine properties of the sample based at least in part on the acquired signals. As shown in FIG. 1 , computing system 130 is communicatively coupled to X-ray detector 123. In one example, X-ray detector 123 is an X-ray spectrometer, and measurement data 124 includes an indication of a measured spectral response of the sample based on one or more sampling processes performed by the X-ray spectrometer. Computing system 130 is configured to build a model of the sample, generate an X-ray simulation based on the model, and analyze the simulation and signals 124 received from X-ray detector 123 to determine one or more characteristics of the sample (e.g., the value of a parameter of interest 180 of the structure being measured).

[0075] In further embodiments, the computing system 130 may be configured to access model parameters in real time using real-time critical dimension (RTCD) techniques or may access a library of pre-calculated models to determine values ​​for at least one specimen parameter associated with the specimen 101. Generally, any form of CD engine may be used to evaluate the difference between the CD parameters assigned to the specimen and the CD parameters associated with the measured specimen. An exemplary method and system for calculating specimen parameter values ​​is described in U.S. Patent No. 7,826,071, issued November 2, 2010 to KLA Tencor Corporation, which is incorporated herein by reference in its entirety.

[0076] In one example, the measurement data 124 includes an indication of the measured x-ray response of the sample. Based on the distribution of the measured x-ray response on the surface of the detector 123, the location and region of incidence of the x-ray beam 108 on the sample 101 is determined by the computing system 130. In one example, pattern recognition techniques are applied by the computing system 130 to determine the location and region of incidence of the x-ray beam 108 on the sample 101 based on the measurement data 124. In response, the computing system 130 generates command signals to either the electron optics 104 or the x-ray optics 106 to redirect and reshape the incident x-ray illumination beam 108.

[0077] In other embodiments, x-ray measurements of a particular examination area are performed at several different out-of-plane orientations. This expands the number and variety of data sets available for analysis to include a variety of large angle out-of-plane orientations, increasing the precision and accuracy of the measured parameters and reducing correlation between parameters. Measuring sample parameters with deeper and more diverse data sets also reduces correlation between parameters and improves measurement accuracy.

[0078] As shown in FIG. 1 , the x-ray metrology tool 100 includes a sample positioning system 140 configured to align and orient the sample 101 over a large range of out-of-plane angular orientations relative to the x-ray illumination source. That is, the sample positioning system 140 is configured to rotate the sample 101 over a large angular range about one or more rotational axes aligned in the plane of the surface of the sample 101. In some embodiments, the sample positioning system 140 is configured to rotate the sample 101 over a range of at least 90 degrees about one or more rotational axes aligned in the plane of the surface of the sample 101. In some embodiments, the sample positioning system is configured to rotate the sample 101 over a range of at least 60 degrees about one or more rotational axes aligned in the plane of the surface of the sample 101. In some other embodiments, the sample positioning system is configured to rotate the sample 101 over a range of at least 1 degree about one or more rotational axes aligned in the plane of the surface of the sample 101. In this manner, angularly resolved measurements of the sample 101 may be collected by the x-ray metrology system 100 over any number of locations on the surface of the sample 101. In one example, the computing system 130 communicates command signals indicating a desired position of the sample 101 to a motion controller 145 of the sample positioning system 140. In response, the motion controller 145 generates command signals to various actuators of the sample positioning system 140 to achieve the desired positioning of the sample 101. By way of non-limiting example, the sample positioning system may include any combination of hexapod, linear, and angular stages.

[0079] As a non-limiting example, as shown in FIG. 1 , the sample positioning system 140 includes an edge-gripping chuck 141 that fixedly mounts the sample 101 to the sample positioning system 140. A rotary actuator 142 is configured to rotate the edge-gripping chuck 141 and the mounted sample 101 relative to a peripheral frame 143. In the illustrated embodiment, the rotary actuator 142 is configured to rotate the sample 101 about the x-axis of a coordinate system 146 shown in FIG. 1 . As shown in FIG. 1 , rotation of the sample 101 about the z-axis is an in-plane rotation of the sample 101. Rotation about the x-axis and rotation about the y-axis (not shown) are out-of-plane rotations of the sample 101, effectively tilting the surface of the sample relative to the measurement elements of the metrology system 100. A second rotary actuator, not shown, is configured to rotate the sample 101 about the y-axis. A linear actuator 144 is configured to translate the peripheral frame 143 in the x-direction. Another linear actuator (not shown) is configured to translate the peripheral frame 143 in the y-direction. In this way, all positions on the surface of the sample 101 are available for measurement over a range of out-of-plane angular positions. For example, in one embodiment, the position of the sample 101 is measured in several angular increments within a range of -45 degrees to +45 degrees relative to the normal orientation of the sample 101.

[0080] The large off-plane angular positioning capability of the sample positioning system 140 enhances measurement sensitivity and reduces correlation between parameters. For example, in normal orientation, SAXS can resolve feature critical dimensions but is largely insensitive to feature sidewall angle and height. However, collecting measurement data over a wide range of off-plane angular positions allows for the collection of measurement data associated with several different diffraction orders. This allows for the resolution of feature sidewall angle and height. It also allows for the resolution of other features, such as rounded or other shapes associated with advanced structures.

[0081] X-ray metrology tools using the rotating cathode-based x-ray illumination source described herein enable increased measurement sensitivity and throughput due to the high brightness and short wavelength radiation (e.g., photon energy greater than 500 eV) generated by the source. By way of non-limiting example, x-ray metrology tools enable measurement of geometric parameters (e.g., pitch, critical dimension (CD), sidewall angle (SWA), line width roughness (LWR), and line edge roughness (LER)) of structures smaller than 10 nanometers. Additionally, the high energy nature of x-ray radiation penetrates optically opaque thin films, buried structures, high aspect ratio structures, and devices containing many thin film layers.

[0082] X-ray metrology systems using high-brightness x-ray illumination sources described herein can be used to characterize semiconductor structures. Examples of structures include, but are not limited to, low-dimensional structures such as FinFETs, nanowires, and graphene, sub-10 nm structures, thin films, lithographic structures, through-silicon vias (TSVs), memory structures such as DRAM, DRAM 4F2, and FLASH, and high aspect ratio memory structures. Examples of structural characteristics include, but are not limited to, geometric parameters such as line-edge roughness, line-width roughness, pore size, pore density, sidewall angle, profile, film thickness, critical dimension, and pitch, and material parameters such as electron density, grain structure, morphology, orientation, stress, and strain.

[0083] 5 illustrates a method 300 suitable for implementation by x-ray metrology systems 100 and 200 of the present invention. It is recognized that, in one embodiment, any data processing elements of method 300 may be performed via pre-programmed algorithms executed by one or more processors of computing system 130. While the following description is presented in the context of x-ray metrology systems 100 and 200, it is recognized that the particular structural aspects of x-ray metrology systems 100 and 200 herein should be understood as merely exemplary, and not limiting.

[0084] A platen is rotated within a vacuum chamber in block 301. The platen has a surface coated with a quantity of cathode material, and the platen is coupled to a first end of a rotating mandrel shaft configured to extend through an opening formed in a wall of the vacuum chamber.

[0085] In block 302, the rotating main shaft is supported by a first radial air bearing disposed about the rotating main shaft adjacent a first end, the first radial air bearing configured to support a load in a direction perpendicular to the axis of rotation of the rotating main shaft.

[0086] In block 303, the spindle shaft is supported by a second radial air bearing disposed around the spindle shaft adjacent a second end of the spindle shaft opposite the first end, the second radial air bearing configured to support a load in a direction perpendicular to the axis of rotation of the spindle shaft.

[0087] A rotational torque is applied to the main rotating shaft by a rotational motor disposed between the first and second radial air bearings at block 304. The rotational motor includes a rotor coupled to the main rotating shaft.

[0088] In block 305, the rotating main shaft is supported by a thrust bearing disposed between first and second radial air bearings, the thrust bearing being configured to support a load in a direction parallel to the axis of rotation of the rotating main shaft.

[0089] It should be appreciated that the various steps described throughout this disclosure can be performed by a single computer system 130 or, alternatively, by multiple computer systems 130. Furthermore, different subsystems of the metrology systems 100 and 200, such as the sample positioning system 140, may include computer systems suitable for performing at least some of the steps described herein. Therefore, the above description should not be construed as a limitation on the present invention, but rather as merely exemplary. Furthermore, one or more computing systems 130 may be configured to perform any other steps in any of the method embodiments described herein.

[0090] Additionally, computing system 130 may be communicatively coupled to x-ray detector 123, electron optics 104, x-ray optics 106, electron beam source 103, rotating cathode subsystem 110, and specimen positioning system 140 in any manner known in the art. For example, one or more computing systems 130 may be coupled to computing systems associated with x-ray detector 123, electron optics 104, x-ray optics 106, electron beam source 103, rotating cathode subsystem 110, and specimen positioning system 140. In other examples, any of x-ray detector 123, electron optics 104, x-ray optics 106, electron beam source 103, rotating cathode subsystem 110, and specimen positioning system 140 may be directly controlled by a single computer system coupled to computer system 130.

[0091] The computer system 130 of the x-ray metrology systems 100 and 200 may be configured to receive and / or acquire data or information from the system's subsystems (e.g., x-ray detector 123, electron optics 104, x-ray optics 106, electron beam source 103, rotating cathode subsystem 110, and specimen positioning system 140) via a transmission medium that may include wired and / or wireless portions. In this manner, the transmission medium may serve as a data link between the computer system 130 and the other subsystems of the system 100.

[0092] The computer system 130 of the metrology systems 100 and 200 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, which may include wired and / or wireless portions. In this manner, the transmission medium may serve as a data link between the computer system 130 and other systems (e.g., memory onboard the metrology system 100, external memory, or an external system). For example, the computing system 130 may be configured to receive data (e.g., output signal 124) from a storage medium (e.g., memory 132) via a data link. For example, spectral results acquired using a spectrometer in the x-ray detector 123 may be stored in a fixed or semi-permanent memory device (e.g., memory 132). In this regard, the spectral results may be imported from onboard memory or an external memory system. Additionally, the computer system 130 may send data to other systems via the transmission medium. For example, sample parameter values ​​180 determined by the computer system 130 may be stored in a fixed or semi-permanent memory device. In this regard, the measurement results may be exported to other systems.

[0093] 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. In general, the term "computing system" can be broadly defined to include any device having one or more processors that execute instructions from a memory medium.

[0094] Program instructions 134 implementing the methods described herein can be transmitted over a transmission medium such as a wire, cable, or wireless transmission link. For example, as shown in Figure 1, program instructions stored in memory 132 are transmitted to processor 131 by bus 133. Program instructions 134 are stored in a computer-readable medium (e.g., memory 132). Examples of computer-readable media include read-only memory, random-access memory, a magnetic or optical disk, or magnetic tape.

[0095] In some embodiments, the x-ray metrology techniques described herein are implemented as part of a fabrication process tool. Examples of fabrication process tools include, but are not limited to, lithography exposure tools, film deposition tools, implant tools, and etch tools. In this manner, the results of the x-ray measurements are used to control the fabrication process. In one example, x-ray measurement data collected from one or more targets is sent to the fabrication process tool. The x-ray data is analyzed, and the results are used to adjust the operation of the fabrication process tool.

[0096] 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.), a critical dimension between two or more structures (e.g., distance between two structures), and a displacement between two or more structures (e.g., overlay displacement between overlay grating structures, etc.). The structures may include three-dimensional structures, patterned structures, overlay structures, etc.

[0097] As described herein, the terms "critical dimension application" or "critical dimension measurement application" include any critical dimension measurement.

[0098] As described herein, the term "metrology system" includes any system used at least in part to characterize a specimen in any manner, including critical dimension and overlay metrology applications. However, such terms in the art do not limit the scope of the term "metrology system" as described herein. Additionally, the metrology systems described herein may be configured for measurement of patterned wafers and / or measurement of unpatterned wafers. The metrology systems may be configured as LED inspection tools, edge inspection tools, backside inspection tools, macro inspection tools, or multi-mode inspection tools (tools that simultaneously involve data from one or more platforms), as well as any other metrology or inspection tool that can benefit from the measurement techniques described herein.

[0099] Described herein are various embodiments for semiconductor processing systems (e.g., inspection systems or lithography systems) that can be used to process specimens. The term "specimen" is used herein to mean a wafer, a reticle, or any other sample that can be processed (e.g., printed or inspected for defects) by means known in the art.

[0100] As used herein, the term "wafer" generally refers to a substrate formed from a semiconductor or non-semiconductor material. Examples include, but are not limited to, monocrystalline silicon, gallium arsenide, and indium phosphide. Such substrates are commonly found and / or processed in semiconductor fabrication facilities. In some cases, a wafer may include only a substrate (e.g., a bare wafer). Alternatively, a wafer may include one or more layers of different materials formed on a substrate. One or more layers formed on a wafer may be "patterned" or "unpatterned." For example, a wafer may include multiple dies having repeatable pattern features.

[0101] A "reticle" may be a reticle at any stage in the reticle fabrication process, or a fully fabricated reticle that may or may not be releasable for use in a semiconductor fabrication facility. A reticle or "mask" is generally defined as a substantially transparent substrate having substantially opaque regions formed thereon, configured as a pattern. The substrate may comprise, for example, a glass material such as amorphous SiO2. A reticle may be placed over a resist-coated wafer during the exposure step of a lithography process, allowing the pattern on the reticle to be transferred to the resist.

[0102] One or more layers formed on a wafer may be patterned or unpatterned. For example, a wafer may include multiple dies, each with repeatable pattern features. The formation and processing of these material layers ultimately results in a fully fabricated device. Many different types of devices may be formed on a wafer, and as used herein, the term wafer is intended to include a wafer having any type of device fabricated thereon as known in the art.

[0103] In one or more exemplary embodiments, the functions described may be implemented in hardware, software, firmware, or some combination thereof. If implemented in software, the functions may be stored on or transmitted as one or more instructions or code on a computer-readable medium. Computer-readable media includes both computer storage media and communication media, including any medium that facilitates transfer of a computer program from one place to another. Storage media may be any available medium that can be accessed by a general-purpose or special-purpose computer. By way of example, and not limitation, such computer-readable media may include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage, or any other medium that can be used to carry or store desired program code means in the form of instructions or data structures and that can be accessed by a general-purpose or special-purpose computer or a general-purpose or special-purpose processor. Also, any connection can be properly defined as a computer-readable medium. For example, if software is transmitted from a website, server, or other remote source using coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio waves, and microwaves, these coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio waves, and microwaves are included within the definition of media. As used herein, disk or disc includes compact disc (CD), laser disc, XRF disc, digital versatile disc (DVD), floppy disk, and Blu-ray disc, where a "disk" typically reproduces data magnetically, and a "disc" reproduces data optically using a laser. Combinations of the above media should also be included within the scope of computer-readable media.

[0104] While certain specific embodiments have been described above for instructional purposes, the disclosure of this patent document is of general applicability and is not limited to the specific embodiments described above. Accordingly, various modifications, adaptations, and combinations of various features of the described embodiments may be made without departing from the scope of the invention as set forth in the claims.

Claims

1. A high-speed rotating cathode system, A rotating spindle shaft, wherein the first end of the rotating spindle shaft extends through an opening formed in the wall of a vacuum chamber, A rotating platen coupled to the first end of the rotating main shaft, wherein a cathode material is placed on the surface of the rotating platen and the rotating platen is configured to rotate within the vacuum chamber, A counterweight configured to be attached to the second end of the rotating spindle shaft opposite to the first end, A first radial air bearing positioned adjacent to the first end around the rotating spindle shaft, the first radial air bearing configured to support a load in a direction perpendicular to the rotation axis of the rotating spindle shaft, A second radial air bearing, positioned around the rotating spindle shaft adjacent to the second end of the rotating spindle shaft, is configured to support a load in the direction perpendicular to the rotation axis of the rotating spindle shaft, A rotary motor is positioned between the first radial air bearing and the second radial air bearing, wherein the rotary motor is configured to apply rotational torque to the rotating main shaft, and includes a rotor coupled to the rotating main shaft. A thrust bearing disposed between the first radial air bearing and the second radial air bearing, the thrust bearing configured to support a load in a direction parallel to the rotation axis of the rotating main shaft, A high-speed rotating cathode system, including one.

2. A high-speed rotating cathode system according to claim 1, The rotary motor is a high-speed rotating cathode system located within 5 centimeters from the center of mass of a rotating assembly including the rotating main shaft, the rotating platen, the counterweight, and the rotor.

3. A high-speed rotating cathode system according to claim 1, A high-speed rotating cathode system in which the center of mass of a rotating assembly, including the rotating spindle shaft, the rotating platen, the counterweight, and the rotor, is within 5 centimeters of the center of bending rigidity of the rotating assembly.

4. A high-speed rotating cathode system according to claim 1, A high-speed rotating cathode system in which the first rotating air bearing includes one or more annular grooves coupled to a vacuum source, the one or more annular grooves are positioned adjacent to the rotating spindle shaft between the load-bearing surface of the first rotating air bearing and the vacuum chamber.

5. A high-speed rotating cathode system according to claim 1, A high-speed rotating cathode system wherein the second rotating air bearing includes a first annular groove connected to a refrigerant source, a second annular groove connected to a refrigerant return path, a third annular groove connected to a vacuum source, and a fourth annular groove connected to a pressurized gas source, wherein the third annular groove is located closest to the second end of the rotating spindle shaft, the fourth annular groove is located closest to the load-bearing surface of the second rotating air bearing, and the first and second annular grooves are located between the third and fourth annular grooves.

6. A high-speed rotating cathode system according to claim 5, Within the rotating spindle shaft are at least two refrigerant channels extending in a direction parallel to the axis of rotation of the rotating spindle shaft, the at least two refrigerant channels extending from the rotating platen to the first annular groove and the second annular groove, A high-speed rotating cathode system, further including the above.

7. A high-speed rotating cathode system according to claim 1, A high-speed rotating cathode system in which the distance between the first radial air bearing and the second radial air bearing is greater than 80% of the total length of the rotating spindle shaft.

8. A high-speed rotating cathode system according to claim 1, A high-speed rotating cathode system in which the first radial air bearing and the second radial air bearing are porous air bearings or groove-compensated air bearings.

9. A high-speed rotating cathode system according to claim 1, A high-speed rotating cathode system in which the rotating motor is a brushless servo motor.

10. A high-speed rotating cathode system according to claim 1, A high-speed rotating cathode system in which the rotating platen is detachable from the rotating spindle shaft.

11. A high-speed rotating cathode system according to claim 1, A high-speed rotating cathode system in which the thrust bearing is a porous air bearing or a groove-compensated air bearing.

12. A high-speed rotating cathode system according to claim 1, A high-speed rotating cathode system in which the thrust bearing is a magnetic bearing.

13. A high-speed rotating cathode system according to claim 12, A high-speed rotating cathode system in which the gap of the magnetic thrust bearing is controlled to a desired distance within a range of at least 1 millimeter.

14. It is a method, Rotating a platen within a vacuum chamber, wherein the platen has a surface covered with a certain amount of cathode material, and is coupled to the first end of a rotating spindle shaft configured to extend through an opening formed in the wall of the vacuum chamber. The rotating spindle shaft is supported by a first radial air bearing positioned adjacent to the first end of the rotating spindle shaft, wherein the first radial air bearing is configured to support a load in a direction perpendicular to the axis of rotation of the rotating spindle shaft. The rotating spindle is supported by a second radial air bearing positioned around the rotating spindle shaft adjacent to the second end of the rotating spindle shaft opposite to the first end, wherein the second radial air bearing is configured to support a load in the direction perpendicular to the rotation axis of the rotating spindle shaft. Applying rotational torque to the rotating spindle shaft by a rotary motor positioned between the first radial air bearing and the second radial air bearing, wherein the rotary motor includes a rotor coupled to the rotating spindle shaft. The rotating spindle shaft is supported by a thrust bearing positioned between the first radial air bearing and the second radial air bearing, wherein the thrust bearing is configured to support a load in a direction parallel to the rotation axis of the rotating spindle shaft. Methods that include...

15. The method according to claim 14, The process involves generating an electron beam directed at a certain amount of the cathode material at a certain position on the surface of the platen, wherein the interaction between the electron beam and the cathode material causes the cathode material to emit X-ray illumination light. The aforementioned X-ray illumination light is directed towards the sample being measured, To detect a certain amount of light from the sample in response to the X-ray illumination light, Based on the detected amount of light, the value of at least one parameter of interest of the sample being measured is determined, Methods that further include the above.

16. The method according to claim 14, A method further comprising translating the platen in a direction parallel to the rotation axis of the rotating spindle shaft within the vacuum chamber, wherein the thrust bearing is a magnetic bearing, and the translation involves controlling the gap between the magnetic bearing and the rotating spindle shaft to a desired distance within a range of at least 1 millimeter.

17. The method according to claim 14, A method wherein the distance between the first radial air bearing and the second radial air bearing is greater than 80% of the total length of the rotating spindle shaft.

18. The method according to claim 14, A method wherein the rotary motor is located within 5 centimeters of the center of mass of a rotary assembly including the rotary spindle shaft, the rotary platen, the counterweight, and the rotor.

19. The method according to claim 14, A method for removing heat from a platen by flowing a refrigerant through the rotating spindle shaft and the platen, wherein the flow of the fluid involves flowing the refrigerant through a first annular groove connected to a refrigerant source and a second annular groove connected to a refrigerant return path, the first annular groove and the second annular groove being located between a third annular groove and a fourth annular groove, the third annular groove being connected to a vacuum source and the fourth annular groove being connected to a pressurized gas source.

20. It is a measurement system, An electron beam source configured to generate an electron beam directed towards a cathode material located on the surface of a platen, wherein the interaction between the electron beam and the cathode material causes the cathode material to emit X-ray illumination light; A rotating spindle shaft, wherein the first end of the rotating spindle shaft extends through an opening formed in the wall of a vacuum chamber, and the platen is coupled to the first end of the rotating spindle shaft and rotates around the axis of rotation of the rotating spindle shaft, A first radial air bearing positioned adjacent to the first end of the rotating spindle shaft, the first radial air bearing configured to support a load in a direction perpendicular to the rotation axis of the rotating spindle shaft, A second radial air bearing is positioned around the rotating spindle shaft adjacent to the second end of the rotating spindle shaft opposite to the first end, and is configured to support a load in the direction perpendicular to the rotation axis of the rotating spindle shaft. A rotary motor is positioned between the first radial air bearing and the second radial air bearing, wherein the rotary rotor is configured to apply rotational torque to the rotating main shaft, and the rotary motor includes a rotor coupled to the rotating main shaft, A thrust bearing disposed between the first radial air bearing and the second radial air bearing, the thrust bearing configured to support a load in a direction parallel to the rotation axis of the rotating main shaft, One or more X-ray illumination optical components configured to direct the aforementioned X-ray illumination light onto the sample being measured, A detector configured to detect a certain amount of light from the sample in response to the X-ray irradiation light, A calculation system configured to determine the value of at least one parameter of interest of the sample being measured based on the detected amount of light, A measurement system including this.

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