Angle-resolved reflectivity measurements of thick films and high aspect ratio structures

Abstract

The system includes a light source configured to emit light at one or more wavelengths, one or more angles of incidence (AOI), and one or more azimuthal angles; a polarization assembly configured to generate one or more polarization states of light; a main objective configured to focus the light of the one or more polarization states onto a target that reflects the light; an analyzer assembly configured to analyze the one or more polarization states of light reflected from the target; a detector configured to detect the light reflected from the target and generate an output signal based on the detected light; and a processor configured to generate measurements of the target based on the output signals generated at the one or more polarization states, one or more wavelengths, one or more AOIs, and one or more azimuthal angles.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Patent Application No. 63 / 446,049, filed February 16, 2023, the disclosure of which is incorporated herein by reference.

[0002] The present disclosure relates to semiconductor metrology. [Background technology]

[0003] As the semiconductor manufacturing industry evolves, the demands on yield management, particularly metrology and inspection systems, increase. Although critical dimensions continue to shrink, the industry still faces the need to reduce the time to achieve high yields and high-volume production. Minimizing the total time from detection to resolution of a yield problem maximizes the return on investment for semiconductor manufacturers.

[0004] The fabrication of semiconductor devices, such as logic and memory devices, typically involves processing semiconductor wafers using a number of manufacturing processes to form multiple levels of semiconductor devices with various features. For example, lithography is a semiconductor manufacturing process that transfers a pattern from a reticle onto a photoresist disposed on a semiconductor wafer. Additional examples of semiconductor manufacturing processes include, but are not limited to, chemical mechanical polishing (CMP), etching, deposition, ion implantation, etc. Arrays of multiple semiconductor devices formed on a single semiconductor wafer may be separated into individual semiconductor devices. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] U.S. Patent No. 7,933,026 [Patent Document 2] U.S. Patent No. 7,478,015 Summary of the Invention [Problem to be solved by the invention]

[0006] Metrology processes are used at various steps in semiconductor manufacturing to monitor and control the process. Metrology processes differ from inspection processes in that, unlike inspection processes that detect defects on wafers, metrology processes are used to measure one or more characteristics of wafers that cannot be determined by existing inspection tools. Metrology processes can be used to measure one or more characteristics of wafers, so that the performance of the process can be determined from the one or more characteristics. For example, a metrology process can measure the dimensions (e.g., linewidth, thickness, etc.) of features formed on wafers during the process. Furthermore, if one or more characteristics of a wafer are unacceptable (e.g., fall outside a predetermined range of the characteristic(s)), the measurements of the one or more characteristics of the wafer can be used to modify one or more parameters of the process so that additional wafers produced by the process have acceptable characteristic(s).

[0007] In flash memory production, there is an increasing demand for metrology of thick films, high aspect ratio (HAR) structures, and large-pitch targets. Spectroscopic ellipsometry (SE), spectroscopic reflectometry (SR), and beam profile reflectometry (BPR) are techniques in film and critical dimension (CD) metrology that determine target characteristics by analyzing light reflected from the target at different wavelengths, angles of incidence (AOI), or polarization states. Measuring 3D structures is more complex because more wavelengths, polarization states, and angle information are required to characterize a wide range of 3D structures. Existing systems have limitations that affect measurement versatility, sensitivity, and / or throughput. For example, SE and SR systems typically can handle many wavelengths and polarization states, but their AOI range is limited, resulting in a loss of measurement versatility. For another example, some SE systems achieve relatively large AOI ranges by moving the stage or optics to sample one AOI at a time. These SE systems are typically too slow for mass production. For another example, some one-dimensional BPR systems sample X and Y slices of the pupil. These systems also lack the versatility to measure HAR structures. In another example, some 2D BPR systems capture the entire pupil but have a limited field of view of the target. Such systems cannot receive all the reflected light from the HAR structures and lack measurement sensitivity.

[0008] Therefore, there is a need for a 2D BPR system that is optimized for measuring thick films, HAR structures, and large pitch layers, and that can rapidly obtain results over a large wavelength and angle range. [Means for solving the problem]

[0009] One embodiment of the present disclosure provides a system. The system may include a light source. The light source may be configured to emit light at one or more wavelengths, at one or more angles of incidence (AOI), and at one or more azimuthal angles along an illumination path.

[0010] The system may further include a polarization assembly disposed in the illumination path, the polarization assembly being configured to generate one or more polarization states of light.

[0011] The system may further include a main objective lens disposed in the illumination path. The main objective lens may be configured to focus light of one or more polarization states onto a target. The target may be configured to reflect the light along the collection path. The main objective lens may further be configured to focus light reflected from the target.

[0012] The system may further include an analyzer assembly disposed in the light collection path, the analyzer assembly being configured to analyze one or more polarization states of the light reflected from the target.

[0013] The system may further include a detector disposed in the light collection path, the detector may be configured to detect light reflected from the target and generate an output signal based on the detected light.

[0014] The system may further include a processor in electronic communication with the detector, and may be configured to generate measurements of the target based on the output signals generated at one or more polarization states, one or more wavelengths, one or more AOIs, and one or more azimuth angles.

[0015] In some embodiments, the system may further include a collection pupil disposed in the collection path. The collection pupil may be configured to collect light reflected from the target. The xy position of the light collected in the collection pupil may correspond to a subset of one or more AOIs and one or more orientations.

[0016] In some embodiments, the detector may be conjugate to the collection pupil and configured to image each xy position of light collected at the collection pupil.

[0017] In some embodiments, the one or more wavelengths of light emitted by the light source may have a continuous spectrum or discrete wavelengths over a wavelength range of 150 to 2500 nm.

[0018] In some embodiments, the system may further include an illumination optical assembly disposed in the illumination path, the illumination optical assembly being configured to collimate the light emitted by the light source.

[0019] In some embodiments, the polarization assembly may include a polarizer and a compensator that generate Mueller matrix elements corresponding to one or more polarization states of light emitted by the light source. The polarizer and the compensator may be arranged as a rotating polarizer (RP), a rotating compensator (RC), a RPRC, or a RCRC.

[0020] In some embodiments, the numerical aperture at the target of the main objective may be between 0.6 and 0.99. The magnification of the main objective may be between 40x and 100x. The field of view of the main objective may be between 15 μm and 350 μm.

[0021] In some embodiments, the system may further include a second objective lens juxtaposed with the main objective lens, which may be configured to transmit a portion of light in the ultraviolet or deep ultraviolet wavelengths.

[0022] In some embodiments, the analyzer assembly may include an analyzer and a compensator that generates Mueller matrix elements that correspond to one or more polarization states of light reflected by the target.

[0023] In some embodiments, the detector may include a two-dimensional CCD, a two-dimensional photodiode array, or a combination of one-dimensional sensors.

[0024] In some embodiments, the target may be a high aspect ratio structure.

[0025] In some embodiments, the processor may be configured to generate target measurements based on a combination of beam shape reflectometry (BPR) data for multiple AOIs, multiple wavelengths, and multiple polarization states, and spectroscopic ellipsometry (SE) or spectroscopic reflectometry (SR) data.

[0026] Another embodiment of the present disclosure provides a method, which may include emitting light from a light source along an illumination path at one or more wavelengths, at one or more angles of incidence (AOI), and at one or more azimuthal angles.

[0027] The method may further include polarizing the light in one or more polarization states using a polarization assembly positioned in the illumination path.

[0028] The method may further include focusing the light of one or more polarization states using a main objective lens positioned in the illumination path.

[0029] The method may further include reflecting light focused by the main objective from the illumination path to the collection path by the target.

[0030] The method may further include collecting light reflected by the target with a main objective lens.

[0031] The method may further include analyzing one or more polarization states of the light reflected by the target with an analyzer assembly positioned in the light collection path.

[0032] The method may further include detecting the light reflected by the target with a detector positioned in the light collection path and generating an output signal based on the detected light.

[0033] The method may further include generating, by a processor in electronic communication with the detector, measurements of the target based on the output signals generated at one or more polarization states, one or more wavelengths, one or more AOIs, and one or more azimuth angles. [Brief explanation of the drawings]

[0034] For a better understanding of the nature and objects of the present disclosure, reference should be made to the following detailed description taken in conjunction with the accompanying drawings.

[0035] [Figure 1] FIG. 1 is a block diagram of a system according to one embodiment of the present disclosure. [Figure 2] FIG. 2 is a block diagram of a system according to another embodiment of the present disclosure. [Figure 3] FIG. 1 is a flow diagram of a method according to one embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0036] Although the claimed subject matter will be described in terms of certain embodiments, other embodiments, including embodiments that do not provide all of the advantages and features disclosed herein, are also within the scope of this disclosure. Various structural, logical, process, step, and electronic changes may be made without departing from the scope of this disclosure. Accordingly, the scope of this disclosure is defined solely by reference to the appended claims.

[0037] One embodiment of the present disclosure provides a system 100. The system 100 may be a metrology tool (e.g., a beam shape reflectometer (BPR)). By way of example, the system 100 of FIG. 1 may include an illumination system (e.g., a light source 110) that illuminates a sample (e.g., a target 150), a detector 180 that captures relevant information provided by the interaction of the illumination system with the target 150, an element, or a feature on the sample, and a processor 190 that analyzes the collected information using one or more algorithms. The light source 110 may direct light at the sample at a first angle, and the light may reflect from the sample to the detector 180 at a second angle. The first and second angles may be the same or different. The system 100 may capture measurements at thousands of different angles of incidence (AOI) and azimuthal angles.

[0038] The light source 110 may be configured to emit light along an illumination path 111. The wavelength of the light emitted by the light source 110 may be in the range of 150-2500 nm. In some embodiments, the wavelength of the light emitted by the light source 110 may be in the range of 350-900 nm. The light source 110 may emit light over a continuous spectrum across a wavelength range, or light at discrete wavelengths within the wavelength range. The light source 110 may be a laser, lamp, supercontinuum laser, glowbar, or laser-sustained plasma (LSP) light source. The light source 110 may be selected as the brightest light source across multiple wavelengths. For wavelengths in the 400-2500 nm range, a supercontinuum laser may be used. In some embodiments, the system 100 may be a broadband metrology tool, and the light source 110 may include a broadband LSP light source. The light source 110 may generate a beam of light using other light sources, or may measure the surface of a sample using other techniques. The light source 110 may include optics to condition and / or focus the light.

[0039] The system 100 may further include an illumination optical assembly 120. The illumination optical assembly 120 may be disposed in the illumination path 111. The illumination optical assembly may be configured to collimate the light emitted by the light source 110. The illumination optical assembly 120 may include one or more pupils 121, field stops 122, lenses, mirrors, filters, apodizers, or beam-conditioning optics to condition the light along the illumination path 111. In some embodiments, the illumination optical assembly 120 may include one or more optical elements having reflective optical power. Such optical elements may have one or more surfaces with reflective power and may have various shapes (e.g., spherical, aspherical, etc.). For example, the optical elements may be mirrors having flat, convex, or concave shapes. The optical elements may be selected to have reflective powers that support wavelengths emitted by the light source 110, such as ultraviolet (UV) or other wavelengths. In other embodiments, the illumination optical assembly 120 may include one or more optical elements that are refractive or catadioptric. Different optical element combinations may be selected based on magnification, numerical aperture, and geometry requirements.

[0040] The system 100 may further include a polarization assembly 130. The polarization assembly 130 may be disposed in the illumination path 111. The polarization assembly 130 may be configured to receive collimated light from the illumination optical assembly 120 and may be configured to generate one or more polarization states of the light. The polarization assembly 130 may include a polarizer and a compensator. The polarizer may be fixed or rotating. The compensator may be fixed or rotating. Thus, the polarization assembly 130 may support a rotating polarizer (RP) and / or a rotating compensator (RC) that generate Mueller matrix elements corresponding to one or more polarization states of the light emitted by the light source 110. The polarizing elements of the polarization assembly 130 may enable the system 100 to sample the target 150 with different polarization states, improving measurement sensitivity and versatility.

[0041] System 100 may further include beam splitter 140. Beam splitter 140 may be positioned downstream from polarization assembly 130 in illumination path 111. Beam splitter 140 may receive light of one or more polarization states from polarization assembly 130 and direct the light toward target 150. In an alternative embodiment shown in FIG. 2, beam splitter 140 may be a knife-edge mirror 141 that splits the light beam in illumination path 111 so that only 50% of the beam is directed toward the target.

[0042] System 100 may further include a main objective lens 145. The main objective lens 145 may be positioned downstream of beam splitter 140 in illumination path 111. The main objective lens 145 may be configured to focus light of one or more polarization states onto target 150. The main objective pupil 146 passes light of a numerical aperture at target 150. The main objective field stop 147 passes light of a field of view at target 150. The numerical aperture of the main objective lens 145 at target 150 may be between 0.6 and 0.99. For example, the numerical aperture may be 0.9. The magnification of the main objective lens 145 may be between 40x and 100x. For example, the magnification may be 80x or 100x. The field of view of the main objective lens 145 may be between 15 μm and 350 μm. For example, the field of view may be at least 15 μm, at least 30 μm, at least 50 μm, or at least 100 μm. Thus, the main objective lens 145 may provide a combination of a high numerical aperture and a high field of view for light focused on the target 150. The main objective lens 145 may be configured to transmit wavelengths in the range of 150-2500 nm. For example, the wavelength range may be 350-900 nm. The wavelength range may be a continuous spectrum, or may be one or more discrete wavelengths that are transmittable by the main objective lens 145. The main objective lens 145 may be reflective, refractive, or catadioptric.

[0043] The system may further include a second objective lens 148. The second objective lens 148 may be collocated with the main objective lens 145 in the illumination path 111. The second objective lens 148 may be used to expand the wavelength range otherwise limited by the high numerical aperture of the main objective lens 145. For example, the second objective lens 148 may be configured to transmit a portion of light in the ultraviolet or deep ultraviolet wavelengths. The second objective lens 148 may be reflective, refractive, or catadioptric.

[0044] The main objective lens 145 and the secondary objective lens 148 may be part of an objective lens selector 149 that allows selection of two or more objective lenses to be placed in the illumination path 111. The objective lens selector 149 may be a turret or slider configured to move the main objective lens 145 and / or the secondary objective lens 148 in and out of the illumination path 111. It should be understood that a single objective lens may support a first wavelength range, while a different single objective lens may support another wavelength range. The combination of the main objective lens 145 and the secondary objective lens 148 can achieve a large numerical aperture and a large wavelength range. The objective lens selector 149 may include an adjustable field stop, the size of which may be adjusted based on the thickness of the target 150, the wavelength of the light emitted by the light source 110, and stray light generated outside the field of view.

[0045] Target 150 may be disposed in illumination path 111. Target 150 may be configured to reflect light focused by illumination optics assembly 120 along collection path 112. Target 150 may include a high aspect ratio structure on a substrate. The high aspect ratio structure may be a structure having 500 or more layers. For example, target 150 may be a flash memory on a semiconductor wafer. Target 150 may be disposed on pedestal 155.

[0046] Light reflected along collection path 112 is collected by main objective lens 145. In some embodiments, the input and return beams of light may be focused to the same point on main objective lens 145. In other embodiments, the input and return beams may be spatially separated, with a first portion of main objective lens 145 receiving illumination path 111 and a second portion of main objective lens 145 receiving collection path. Light collected by main objective lens 145 may be returned to beam splitter 140. Alternatively, in the embodiment shown in FIG. 2, light in collection path 112 may be deflected from knife-edge mirror 141.

[0047] The system 100 may further include a collection assembly 160. The collection assembly 160 may be disposed in the collection path 112. The beam splitter 140 may direct light reflected from the target 150 to the collection assembly 160. The collection assembly 160 may include one or more pupils 161, field stops 162, lenses, mirrors, filters, apodizers, or beam-conditioning optics that condition the light along the collection path 112 to focus the light on the detector 180. For example, the collection assembly may include a collection pupil 161 configured to collect light reflected from the target 150. The position of the light collected at the collection pupil 161 may correspond to a subset of one or more AOIs and one or more orientations. In other words, by changing the AOI or orientation, the position of the light collected at the collection pupil 161 can be changed to generate a two-dimensional image. In the embodiment shown in FIG. 2 , the knife-edge mirror 141 directs only half of the light from the light source 110 through the main objective 145 to the target 150, so that the collection pupil 161 receives only half of the AOI and orientation from the target 150. In some embodiments, the collection assembly 160 may include one or more optical elements having reflective optical power. Such optical elements may have one or more surfaces with reflective power and may have various shapes (e.g., spherical, aspherical, etc.). For example, the optical elements may be mirrors having flat, convex, or concave shapes. The optical elements may be selected to have reflective powers that support wavelengths emitted by the light source 110, such as ultraviolet (UV) or other wavelengths. In other embodiments, the collection assembly 160 may include one or more optical elements that are refractive or catadioptric. Different combinations of optical elements may be selected based on magnification, numerical aperture, and geometry requirements.

[0048] The system may further include an analyzer assembly 170. The analyzer assembly 170 may be disposed in the light collection path 112. The analyzer assembly 170 may be disposed after the light collection assembly 160 in the light collection path 112 (as shown in FIG. 1) or before the light collection assembly 160. The beam splitter 140 may direct light reflected from the target 150 to the analyzer assembly 170. In the embodiment shown in FIG. 2, the knife-edge mirror 141 reflects only half of the light beam in the illumination path 111 toward the target 150, and the light collection path 112 passes by the knife-edge mirror 141, so that the analyzer assembly 170 receives only half of the light beam reflected by the target 150. The analyzer assembly 170 may be configured to analyze one or more polarization states of the light reflected from the target 150. The analyzer assembly 170 may generate polarization data 175 from the analyzed light. The analyzer assembly 170 may include an analyzer and a compensator. The analyzer may be fixed or rotating. The compensator may be fixed or rotating. Thus, analyzer assembly 170 can support a rotating polarizer (RP) and / or a rotating compensator (RC) that generate Mueller matrix elements corresponding to one or more polarization states of light reflected by target 150. The combination of polarization assembly 130 and analyzer assembly 170 can support RP, RC, RPRC, and / or RCRC based on the combination of the rotating or fixed polarizers and compensators of the two assemblies.

[0049] The detector 180 may be disposed in the light collection path 112. The detector 180 may be configured to detect light reflected by the target 150. For example, the detector 180 may detect light imaged onto the collection pupil 161. The detector 180 may resolve the light reflected from the target 150 into one or more segments, each segment corresponding to one or more AOIs and one or more azimuth subsets. The detector 180 may further be configured to generate an output signal 185 based on the detected light. The detector 180 may be a two-dimensional charge-coupled device (CCD), a two-dimensional sensor, or a photodiode array. The detector 180 may include one or more one-dimensional arrays. The detector 180 may include separate detectors for different wavelengths of light (e.g., UV and IR). The detector 180 may use any other type of high-speed one-dimensional and two-dimensional sensor.

[0050] Processor 190 may be in communication with analyzer assembly 170, detector 180, or other elements of system 100. Processor 190 may actually be implemented in any combination of hardware, software, and firmware. Also, the functionality described herein may be performed by a single unit or divided among different elements, each of which may alternatively be implemented in any combination of hardware, software, and firmware. Program code or instructions for processor 190 to perform the various methods and functions may be stored in a controller-readable storage medium, such as an electronic data storage device 195 in electronic communication with processor 190, within processor 190, in memory external to processor 190, or a combination thereof.

[0051] Processor 190 may be coupled to elements of system 100 in any suitable manner (e.g., via one or more transmission media, which may include wired and / or wireless transmission media) such that processor 190 can receive output generated by system 100, such as output from analyzer assembly 170 and detector 180. Processor 190 may be configured to perform a number of functions using the output. For example, processor 190 may be configured to generate measurements of target 150 based on polarization data 175 and output signal 185. The measurements may include one or more of critical dimension (CD), single line average (SWA), shape, stress, composition, film, bandgap, electrical properties, focus / dose, overlay, generation of process parameters (e.g., resist state, partial pressure, temperature, focus model), and / or any combination thereof. Processor 190 may be configured to transmit the output to electronic data storage device 195 or another storage medium without reviewing the output. Processor 190 may be further configured as described herein. The BPR data or a combination of BPR and SE / SR data collected by system 100 can be used to collect a data cube of measurements taken at many wavelengths, polarization states, and angles. A "data cube" refers to a multidimensional array of information, with cell values ​​corresponding to measurements that vary in each dimension. By fitting the data cube to a model, variability due to process errors can be identified and the process can be adjusted to reduce variability.

[0052] The processor 190, other system(s), or other subsystem(s) described herein can take a variety of forms, including a personal computer system, an image computer, a mainframe computer system, a workstation, a network appliance, an internet appliance, or other device. The subsystem(s) or system(s) may also include any suitable processor known in the art, such as a parallel processor. The subsystem(s) or system(s) may also include a platform with high-speed processing and software, either in the form of a stand-alone or network tool. For example, the processor 190 may include a microprocessor, a microcontroller, or other device.

[0053] Processor 190 may be in electronic communication with detector 180 or other elements of system 100. Processor 190 may be configured according to any embodiment described herein. Processor 190 may also be configured to perform other functions or additional steps using the output of detector 180 or using images, measurements, or data from other sources.

[0054] The system 100 can provide information about the target 150 or information used to form an image of the target 150. The system 100 can be configured to provide one or more of rotating polarizer data, rotating compensator spectroscopic ellipsometry data, Full Mueller matrix element data, rotating polarizer spectroscopic ellipsometry data, reflectance data, laser-driven spectroscopic reflectance data, or X-ray data. In one example, the system 100 performs spectroscopic ellipsometry using a broadband light source, a detector 180 that measures how the light source interacts with the target, and processing algorithms that extract relevant parameters of the target. In another example, the light source 110 can be an LSP light source, which, unlike a Xe lamp, can provide high intensity and improve the signal-to-noise ratio at the detector. To improve the target signature, the system 100 can extend the wavelength range to below 170 nm using an N or Ar gas purge.

[0055] System 100 may include one or more hardware configurations that may be used in conjunction with particular embodiments of the present invention to measure, for example, the various semiconductor structural and material properties described above. Examples of such hardware configurations include, but are not limited to, a spectroscopic ellipsometer (SE), an SE with multiple illumination angles, an SE that measures Mueller matrix elements (e.g., using a rotating compensator(s)), a single-wavelength ellipsometer, a beam-shaping ellipsometer (angle-resolved ellipsometer), a beam-shaping reflectometer (angle-resolved reflectometer), a broadband reflectance spectrometer (spectroscopic reflectometer), a single-wavelength reflectometer, an angle-resolved reflectometer, an imaging system, or a scatterometer (e.g., a speckle analyzer).

[0056] The hardware configuration may be divided into separate operational systems. One or more hardware configurations may be combined into a single tool. U.S. Patent No. 7,933,026, incorporated herein by reference in its entirety, provides an example. Such systems typically contain numerous optical elements, including specific lenses, collimators, mirrors, quarter-wave plates, polarizers, detectors, cameras, apertures, and / or light sources. The wavelength of the optical system may vary from approximately 120 nm to 3 microns. For non-ellipsometer systems, the collected signal may be polarization-resolved or unpolarized. Multiple metrology tools may be used to measure single or multiple metrology targets, as described in U.S. Patent No. 7,478,015.

[0057] An illumination system of a particular hardware configuration may include one or more light sources. The light source may generate light having only a single wavelength (i.e., monochromatic light), light having many discrete wavelengths (i.e., polychromatic light), light having multiple wavelengths (i.e., broadband light), and / or light swept continuously or discretely across multiple wavelengths (e.g., using a tunable or swept light source). Examples of suitable light sources include white light sources, ultraviolet (UV) lasers, arc lamps or electrodeless lamps, laser-sustained plasma (LSP) sources, ultra-continuous light sources (e.g., broadband laser sources), or short wavelength light sources such as x-ray sources, extreme UV light sources, or combinations thereof. The light source may also be configured to provide light with sufficient brightness, in some cases, to provide a power of approximately 1 W / (nmcm). 2 The light source output may be brighter than 1000 kJ / s (Sr). System 100 may also include high-speed feedback to the light source to stabilize the optical power and wavelength. The light source output may be transmitted via free-space propagation, or in some cases, via any type of optical fiber or light guide.

[0058] System 100 may be designed to perform many different types of measurements related to semiconductor manufacturing. For example, system 100 may measure characteristics of one or more targets, such as critical dimensions, overlay, sidewall angle, film thickness, and process-related parameters (e.g., focus and / or dose). A target may include a particular region of interest that is periodic in nature, such as a grating in a memory die. A target may include multiple layers (or films) whose thickness can be measured by a metrology tool. A target may include target designs located (or already present) on a semiconductor wafer, such as for use in alignment and / or overlay registration. A particular target may be located at various locations on a semiconductor wafer. For example, a target may be located within a scribe line (e.g., between dies) and / or on the die itself. In certain embodiments, multiple targets are measured (simultaneously or at different times) by the same or multiple metrology tools. Data from such measurements may be combined. Data from system 100 can be used in semiconductor manufacturing processes, for example, to feed forward, feedback, and / or feed sideway corrections to a process (eg, lithography or etching).

[0059] As semiconductor device feature sizes continue to shrink, smaller metrology targets are often required. Furthermore, measurement accuracy and alignment with actual device characteristics may increase the need for device-like targets, as well as in-die and even on-device measurements. For example, focused beam ellipsometry, primarily based on reflective optics, can be used. Apodizers can be used to mitigate the effects of optical diffraction, which causes the illumination spot to spread beyond the size defined by geometric optics. Small target capability can be achieved using high numerical aperture tools with simultaneous illumination at multiple angles of incidence.

[0060] Other example measurements may include measuring the composition of one or more layers of a semiconductor stack, measuring specific defects on (or within) a wafer, or measuring the amount of photolithographic radiation to which a wafer has been exposed. In some cases, the system 100 and algorithms may be configured to measure non-periodic targets.

[0061] Additionally, such systems typically include various optical elements, including specific lenses, collimators, mirrors, quarter-wave plates, polarizers, detectors, cameras, apertures, and / or light sources. The wavelength of the optical system can vary from approximately 120 nm to 3 microns. For non-ellipsometer systems, the collected signal can be polarization-resolved or unpolarized. Multiple metrology heads may be integrated into the same tool. However, in many cases, multiple metrology tools are used to measure a single or multiple metrology targets.

[0062] Measuring the parameters of interest typically involves multiple algorithms. For example, the optical interaction of the incident beam with the sample is modeled using an electromagnetic (EM) solver, using algorithms such as rigorous coupled wave analysis (RCWA), finite element modeling (FEM), the method of moments, surface integration, volume integration, finite difference time domain (FDTD), and others. The target of interest is typically modeled (parameterized) using a geometric engine, a process modeling engine, or a combination of both. Geometric engines are implemented, for example, in KLA's AcuShape software product.

[0063] The collected data can be analyzed by many data fitting and optimization techniques and technologies, including libraries, fast reduced order models, regression, machine learning algorithms, principal component analysis (PCA), independent component analysis (ICA), locally linear embedding (LLE), sparse representations such as Fourier or wavelet transforms, Kalman filters, algorithms that facilitate matching from the same or different tool types, etc. The collected data can also be analyzed by algorithms that do not involve modeling, optimization, and / or fitting.

[0064] Computational algorithms are typically optimized for metrology applications using one or more approaches such as computational hardware design and implementation, parallelization, computation distribution, load balancing, multi-service support, or dynamic load optimization. Different implementations of algorithms can be made in firmware, software, FPGAs, programmable optical elements, etc.

[0065] The data analysis and fitting steps may have one or more objectives. Critical dimensions, sidewall angles, shape, stress, composition, film, bandgap, electrical properties, focus / dose, overlay, generation of process parameters (e.g., resist state, partial pressure, temperature, focus model), and / or any combination thereof may be measured or otherwise determined. Metrology systems may be modeled or designed. Metrology objectives may also be modeled, designed, and / or optimized.

[0066] Embodiments of the present disclosure address the field of semiconductor metrology and are not limited to the hardware, algorithmic / software implementations and architectures and use cases outlined above.

[0067] The disclosed system 100 enables measurements of target 150 with greater versatility, accuracy, precision, sensitivity, signal fidelity, and rapid results for thick films and HAR structures. For example, system 100 can acquire measurements over a wide range of angles, complementary to SE and SR spectral data. Additional data is acquired by generating Mueller matrix elements in response to different polarization states. Furthermore, the wide field of view of the main objective lens 145 maintains signal fidelity while avoiding beam clipping of high AOI light in thick stacks. By providing a data cube of measurements acquired at many wavelengths, polarization states, and angles using BPR data or a combination of BPR and SE / SR data, system 100 enables increased measurement versatility and rapid results not previously possible with existing systems.

[0068] One embodiment of the present disclosure provides a method 200. The method 200 may be applied to metrology tools such as the above-described system 100. As shown in Figure 3, the method 200 may include the following steps.

[0069] In step 210, light is emitted from a light source along an illumination path at one or more wavelengths, one or more angles of incidence (AOI), and one or more azimuthal angles. The wavelength of the light emitted by the light source may be in the range of 150-2500 nm. In some embodiments, the wavelength of the light emitted by the light source may be in the range of 350-900 nm. The light source can emit a continuous spectrum of light across a wavelength range, or light at discrete wavelengths within the wavelength range. The light source can be a laser, a lamp, a glowbar, a supercontinuum laser, or an LSP light source. The light source can be selected as the brightest light source across multiple wavelengths. For wavelengths in the 400-2500 nm range, a supercontinuum laser can be used. In some embodiments, method 200 is applicable to broadband plasma tools, and the light source can include a broadband plasma source. The light source can generate the beam of light using other light sources, or can measure the surface of the sample using other techniques.

[0070] In some embodiments, the light may be collimated in the illumination path by an illumination optical assembly disposed in the illumination path. The illumination optical assembly may include one or more pupils, field stops, lenses, mirrors, filters, apodizers, or beam-conditioning optics to condition the light along the illumination path and / or focus the light on a target. In some embodiments, the illumination optical assembly may include one or more optical elements having reflective optical power. Such optical elements may have one or more surfaces with reflective power and may have various shapes (e.g., spherical, aspherical, etc.). For example, the optical elements may be mirrors having flat, convex, or concave shapes. The optical elements may be selected to have reflective powers that support wavelengths emitted by the light source, such as ultraviolet (UV) or other wavelengths. In other embodiments, the illumination optical assembly may include one or more optical elements that are refractive or catadioptric. Different combinations of optical elements may be selected based on magnification, numerical aperture, and geometry requirements.

[0071] In step 220, the light is polarized into one or more polarization states by a polarization assembly positioned in the illumination path. The polarization assembly may include a polarizer and a compensator. The polarizer may be fixed or rotating. The compensator may be fixed or rotating. Thus, the polarization assembly can support a rotating polarizer (RP) and / or a rotating compensator (RC) that generate Mueller matrix elements corresponding to one or more polarization states of the light emitted by the light source. The polarizing elements of the polarization assembly can improve the sensitivity and versatility of the measurement by allowing a target to be sampled in different polarization states.

[0072] In step 230, light of one or more polarization states is focused by a main objective lens positioned in the illumination path.

[0073] In step 240, the light focused by the main objective lens is reflected from the illumination path to the collection path by the target. The main objective lens may be positioned in the illumination path downstream of the polarization assembly. A beam splitter may be positioned in the illumination path between the polarization assembly and the main objective lens to receive light of one or more polarization states from the polarization assembly and combine the light into a common path toward the target. The numerical aperture of the main objective lens at the target may be between 0.6 and 0.99. For example, the numerical aperture may be 0.9. The magnification of the main objective lens may be between 40x and 100x. For example, the magnification may be 80x or 100x. The field of view of the main objective lens may be between 15 μm and 350 μm. For example, the field of view may be at least 15 μm, at least 30 μm, at least 50 μm, or at least 100 μm. Thus, the main objective lens can provide a combination of a high numerical aperture and a wide field of view for the light focused on the target. The main objective lens may be configured to transmit wavelengths in the range of 150-2500 nm. For example, the wavelength range may be 350-900 nm. The wavelength range may be a continuous spectrum or may be one or more discrete wavelengths transmittable by the main objective lens. The main objective lens may be reflective, refractive, or catadioptric. The target may include a high aspect ratio structure on a substrate. The high aspect ratio structure may be a structure having 500 or more layers. For example, the target may be a flash memory on a semiconductor wafer. The target may be disposed on a pedestal.

[0074] In some embodiments, a secondary objective lens juxtaposed with the primary objective lens in the illumination path may be configured to transmit a portion of light in the ultraviolet or deep ultraviolet wavelengths. The secondary objective lens 148 may be reflective, refractive, or catadioptric. The primary and secondary objective lenses may be part of an objective lens selector that allows selection of two or more objective lenses to be placed in the illumination path. The objective lens selector may be a turret or slider configured to move the primary and / or secondary objective lenses in and out of the illumination path. The combination of the primary and secondary objective lenses may achieve a large numerical aperture and a wide wavelength range. The objective lens selector may include an adjustable field stop, the size of which may be adjusted based on the target thickness, the wavelength of light emitted by the light source, and stray light generated outside the field of view.

[0075] In step 250, the light reflected by the target is collected by the main objective. In some embodiments, the input and return beams of light may be focused to the same point on the main objective and can coexist. In other embodiments, the input and return beams may be spatially separated, with a first portion of the main objective receiving the illumination path and a second portion of the main objective receiving the collection path. The light collected by the main objective may be returned to the beam splitter.

[0076] In some embodiments, a collection assembly configured to receive light reflected by the target may be disposed in the collection path. A beam splitter may direct light reflected from the target to the collection assembly. The collection assembly may include one or more pupils, field stops, lenses, mirrors, filters, apodizers, or beam-conditioning optics that condition the light along the collection path to focus the light on the detector. For example, the collection assembly may include a collection pupil configured to collect light reflected from the target. The position of the light collected at the collection pupil may correspond to a subset of one or more AOIs and one or more orientations. In other words, by changing the AOI or orientation, the position of the light collected at the collection pupil may change to generate a two-dimensional image. In some embodiments, the collection assembly may include one or more optical elements having reflective optical power. Such optical elements may have one or more surfaces with reflective power and may have various shapes (e.g., spherical, aspherical, etc.). For example, the optical elements may be mirrors having planar, convex, or concave shapes. The optical elements may be selected to have reflective powers that support wavelengths emitted by the light source 110, such as ultraviolet (UV) or other wavelengths. In other embodiments, the light collection assembly may include one or more optical elements that are refractive or catadioptric. Different combinations of optical elements may be selected based on magnification, numerical aperture, and geometry requirements.

[0077] In step 260, one or more polarization states of the light reflected by the target are analyzed by an analyzer assembly disposed in the light collection path. A beam splitter can direct the light reflected from the target to the analyzer assembly. The analyzer assembly can include an analyzer and a compensator. The analyzer can be fixed or rotating. The compensator can be fixed or rotating. Thus, the polarization assembly 130 can support a rotating polarizer (RP) and / or a rotating compensator (RC) that generate Mueller matrix elements corresponding to one or more polarization states of the light reflected by the target. The combination of the polarization assembly and the analyzer assembly can support RP, RC, RPRC, or RCRC based on the combination of the rotating polarizer or fixed polarizer and compensator of the two assemblies.

[0078] In step 270, the light reflected by the target is detected by a detector disposed in the collection path, and an output signal is generated based on the detected light. For example, the detector can detect light imaged onto the collection pupil. The detector can resolve the light reflected from the target into one or more segments, each segment corresponding to one or more AOIs and one or more azimuth subsets. The detector can be a two-dimensional charge-coupled device (CCD), a two-dimensional sensor, or a photodiode array. The detector can include one or more one-dimensional arrays. The detector can include separate detectors for different wavelengths of light (e.g., UV and IR). The detector can use any other type of high-speed one-dimensional and two-dimensional sensor.

[0079] In step 280, a processor in electronic communication with the detector generates target measurements based on the output signals generated at one or more polarization states, one or more wavelengths, one or more AOIs, and one or more azimuthal angles. The measurements may generate critical dimension (CD), single line area (SWA), shape, stress, composition, film, bandgap, electrical properties, focus / dose, overlay, process parameter generation (e.g., resist state, partial pressure, temperature, focus model), and / or any combination thereof. The processor may be configured to transmit the output to an electronic data storage device or another storage medium without verifying the output. Using BPR data, or a combination of BPR and SE / SR data, a data cube of measurements taken at many wavelengths, polarization states, and angles can be collected. A "data cube" refers to a multidimensional array of information, with cell values ​​corresponding to measurements that vary along each dimension. Fitting the data cube to a model allows for identification of variations due to process errors and adjustments to the process to reduce the variations.

[0080] The disclosed method 200 enables targeted measurements to be taken for thick films and HAR structures with greater versatility, accuracy, precision, sensitivity, and signal fidelity, while achieving faster results. For example, measurements can be taken over a wide range of angles, complementary to SE and SR spectral data. Additional data can be obtained by generating Mueller matrix elements corresponding to different polarization states. Furthermore, the wide field of view of the main objective lens maintains signal fidelity while avoiding beam clipping of high AOI light in thick stacks. Method 200 provides a data cube of measurements taken at many wavelengths, polarization states, and angles using BPR data or a combination of BPR and SE / SR data, enabling increased measurement versatility and faster results not previously possible with existing methods.

[0081] Although the present disclosure has been described with respect to one or more particular embodiments, it will be understood that other embodiments of the present disclosure may be made without departing from the scope of the present disclosure. Accordingly, the present disclosure is to be limited only by the appended claims and their reasonable interpretation.

Claims

1. a light source configured to emit light along an illumination path at one or more wavelengths, at one or more angles of incidence (AOI), and at one or more azimuthal angles; a polarization assembly disposed in the illumination path, the polarization assembly configured to generate one or more polarization states of the light; a main objective lens disposed in the illumination path and configured to focus light of the one or more polarization states onto a target, the target being configured to reflect light along a collection path, the main objective lens being further configured to collect light reflected from the target; and an analyzer assembly disposed in the light collection path, the analyzer assembly configured to analyze one or more polarization states of light reflected from the target; a detector disposed in the light collection path configured to detect light reflected from the target and to generate an output signal based on the detected light; a processor in electronic communication with the detector, the processor configured to generate measurements of the target based on the output signals generated at the one or more polarization states, the one or more wavelengths, the one or more AOIs, and the one or more azimuth angles.

2. 10. The system of claim 1, further comprising a collection pupil disposed in the collection path and configured to collect light reflected from the target, wherein an x-y position of light collected at the collection pupil corresponds to a subset of the one or more AOIs and the one or more azimuths.

3. 3. The system of claim 2, wherein the detector is conjugate with the collection pupil such that the detector is configured to image each xy position of light collected at the collection pupil.

4. 10. The system of claim 1, wherein the one or more wavelengths of light emitted by the light source are a continuous spectrum or discrete wavelengths over a wavelength range of 150 to 2500 nm.

5. The system of claim 1 , further comprising an illumination optical assembly disposed in the illumination path, the illumination optical assembly configured to collimate light emitted by the light source.

6. 10. The system of claim 1, wherein the polarization assembly includes a polarizer and a compensator that generate Mueller matrix elements corresponding to one or more polarization states of light emitted by the light source, the polarizer and the compensator configured as a rotating polarizer (RP), a rotating compensator (RC), a RPRC, or a RCRC.

7. The system of claim 1 , wherein the main objective lens has a numerical aperture of 0.6 to 0.

99.

8. The system of claim 1 , wherein the main objective lens has a magnification of 40x to 100x.

9. The system of claim 1 , wherein the field of view of the main objective is between 15 μm and 350 μm.

10. 10. The system of claim 1, further comprising a second objective lens juxtaposed with the main objective lens, the second objective lens configured to transmit a portion of light at ultraviolet or deep ultraviolet wavelengths.

11. The system of claim 1 , wherein the analyzer assembly includes an analyzer and a compensator that generates Mueller matrix elements corresponding to one or more polarization states of light reflected by the target.

12. The system of claim 1 , wherein the detector comprises a two-dimensional CCD, a two-dimensional photodiode array, or a combination of multiple one-dimensional sensors.

13. The system of claim 1 , wherein the target is a high aspect ratio structure.

14. 10. The system of claim 1, wherein the processor is configured to generate target measurements based on a combination of beam shape reflectometry (BPR) data for multiple AOIs, multiple wavelengths, and multiple polarization states and spectroscopic ellipsometry (SE) or spectroscopic reflectometry (SR) data.

15. emitting light from a light source along an illumination path at one or more wavelengths, at one or more angles of incidence (AOI), and at one or more azimuthal angles; polarizing the light of the one or more polarization states with a polarization assembly disposed in the illumination path; focusing the light of the one or more polarization states with a main objective lens disposed in the illumination path; reflecting the light focused by the main objective from the illumination path to the collection path by a target; collecting light reflected by the target with the main objective lens; analyzing one or more polarization states of light reflected by the target with an analyzer assembly disposed in the light collection path; detecting light reflected by the target with a detector disposed in the light collection path and generating an output signal based on the detected light; generating, by a processor in electronic communication with the detector, measurements of the target based on the output signals generated at the one or more polarization states, the one or more wavelengths, the one or more AOIs, and the one or more azimuth angles.

16. 16. The method of claim 15, wherein the one or more wavelengths of light emitted by the light source are a continuous spectrum or discrete wavelengths over a wavelength range of 150 to 2500 nm.

17. 16. The method of claim 15, wherein the main objective has a numerical aperture at the target of 0.6 to 0.

99.

18. The method of claim 15, wherein the magnification of the main objective is between 40x and 100x.

19. 16. The method of claim 15, wherein the field of view of the main objective is between 15 μm and 350 μm.

20. 16. The method of claim 15, wherein a collection pupil disposed in the collection path is configured to collect light reflected from the target, x-y positions of light collected at the collection pupil correspond to a subset of the one or more AOIs and the one or more orientations, and the detector is conjugate to the collection pupil to image each x-y position of light collected at the collection pupil and generate a corresponding output signal.

21. The method of claim 15 , wherein the target is a high aspect ratio structure.

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