Dimensional measurement by non-linear optics

Abstract

A system and method are disclosed for monitoring a manufacturing process and / or determining critical dimensions of a produced device with respect to changes that may affect the performance or yield of the produced device using second harmonic generation of light.

Description

Technical Field

[0001] This application claims the benefit of priority of U.S. Provisional Patent Application No. 63 / 352,602, filed on Jun. 15, 2022, and entitled "Dimensional Measurement by Nonlinear Optics", and U.S. Provisional Patent Application No. 63 / 353,003, filed on Jun. 16, 2022, and entitled "Dimensional Measurement by Nonlinear Optics". Each of the above applications is hereby incorporated by reference in its entirety. This application generally relates to systems and methods for dimensional measurement.

Background Art

[0002] The input of an optical beam in nonlinear optics is output as the sum, difference, or harmonic frequency of the input. Second harmonic generation is a nonlinear optical effect in which light having a certain frequency is converted into light having twice that frequency upon scattering from certain materials, structures, and shapes. Second harmonic generation appears particularly strongly at interfaces and defects that break the symmetry of the system. This process can be considered as two photons of energy E combining to generate one photon of energy 2E (i.e., generating light of twice the frequency (2ω) or half the wavelength of the incident radiation).

[0003] An investigation of scientific research employing SHG technology is published on page 452 of "Optical Second Harmonic Generation from Semiconductor Surfaces" by T. F. Heinz et al., edited by A. C. Tam, J. L. Cole, and W. C. Stwalley in "Advances in Laser Science III" (American Institute of Physics, New York, 1988). As examined, the SHG process does not occur within the bulk of materials that exhibit a center of symmetry (i.e., inversion or centrosymmetric materials). In these materials, the SHG process can only be evaluated at surfaces and / or interfaces where the inversion symmetry of the bulk material is broken. Thus, the SHG process provides a unique sensitivity to the characteristics of surfaces and interfaces.

[0004] Based on such understanding, the SHG effect is described in the specifications of U.S. Patent No. 5,294,289 by Heinz et al. and U.S. Patent No. 5,557,409 by Downer et al., and other approaches or tools that can be adopted are also described in the specifications of U.S. Patent Nos. 6,795,175, 6,781,686, 6,788,405, 6,819,844, 6,882,414, and 7,304,305 by Hunt et al., U.S. Patent No. 6,856,159 by Tolk et al., and U.S. Patent No. 7,158,284 by Alles et al. However, the teachings of these patents do not seem to overcome some of the main obstacles in adopting SHG as an established technique for semiconductor manufacturing and measurement. Dimensional measurement using non - linear optical effects

[0005] Some of the systems and methods described herein relate to the use of second - harmonic generation for monitoring semiconductor device fabrication. Changes in the second - harmonic generation of light can be used to monitor changes in the shape or material or material properties of a semiconductor device (e.g., when produced on a production line) and / or changes in the fabrication process. Second - harmonic generation can also be used to determine the critical dimensions of a semiconductor structure, device, part of a device, or any combination thereof. Other non - linear optical effects are also employed for measurement and in - line monitoring of semiconductor manufacturing processes.

[0006] In some embodiments, an optical measurement system can irradiate a sample with one or more primary light beams (e.g., light including pulsed light or pulsed laser light) to generate one or more light beams through second-order, third-order, fourth-order, or higher-order nonlinear optical interactions with the sample. Optionally, the interaction between the primary light beam and the sample may include inelastic light scattering of the primary light (e.g., Raman scattering). In some embodiments, the second-order, third-order, fourth-order, or higher-order nonlinear optical interactions may include third-harmonic generation, fourth-harmonic generation, or higher-harmonic generation. In various aspects, the nonlinear optical effect may include a degenerate or non-degenerate optical effect (e.g., a degenerate or non-degenerate multi-wave mixing process). The one or more light beams can include light generated by second-harmonic generation (SHG), difference-frequency generation (DFG), sum-frequency generation (SFG), multi-wave mixing (MWM), e.g., four-wave mixing (FWM), and / or Raman scattering. The optical measurement system can use one or more detectors to detect the one or more light beams and use the resulting detection signals to monitor the sample at a point in the semiconductor manufacturing process. Pulses of the incident light may generate SHG light, SFG light, DFG light, FWM light, or MWM light, Raman light (also referred to as SHG signal, SFG signal, DFG signal, FWM signal, MWM signal, or Raman signal, respectively). The detector can detect the SHG signal, SFG signal, DFG signal, FWM signal, MWM signal, or Raman signal and generate the detected SHG signal, the detected SFG signal, the detected DFG signal, the detected FWM signal, the detected MWM signal, or the detected Raman signal, respectively. The optical measurement system can use the detected DFG signal, the detected FWM signal, the detected MWM signal, or the detected Raman signal to determine a geometric feature (e.g., a critical dimension of the sample) or a change in a geometric feature, e.g., using a mapping between the detected signal and the corresponding geometric feature. The mapping can be generated using computer modeling, empirical data, or a combination thereof. Various methods and systems using SHG, e.g., measurement systems, in-line systems, etc., are described herein.However, such discussions are also applicable to SFG light, DFG light, FWM light, or MWM light, Raman light, and the use of such light for measurement (e.g., to determine critical dimensions and / or their changes) and / or the monitoring of semiconductor fabrication processes, such as in-line.

[0007] A non-linear optical (NLO) system (referred to herein as NLO-CD) for determining critical dimensions (CD) illuminates a sample and uses the second harmonic generation light emitted from the device to determine the physical structure (e.g., shape and / or dimensions) of the device and / or monitor changes in such features. The NLO-CD system can monitor the quality and stability of the production process and improve the production yield and performance of the manufactured devices by using the light emitted by the devices produced on the production line. The devices measured by the NLO-CD system may be completed or not yet completed, and the changes may be unplanned variations (e.g., changes associated with changes in process tools, changes associated with degradation, environmental changes, failures, changes in consumables used by the process tools, or any combination of these, or other possible factors).

[0008] In addition to, or instead of, monitoring changes in the physical characteristics (e.g., shape and / or dimensions) of a device or a part thereof, i.e., monitoring production, the NLO-CD system can provide a feedback signal, feedback data, or information that can be used to control the production steps of the device. In some cases, the feedback signal, feedback data, or information is used to control the production process that produces the monitored sample. The NLO-CD system can be included in a sample evaluation step and provide a feedback signal or feedback data to a step prior to the evaluation step (e.g., for another device(s) or wafer(s) to be fabricated thereafter). Such prior steps can include, for example, lithography, etching, deposition steps, or other possible fabrication steps. In some aspects, NLO-CD can provide a feedforward signal, feedforward data, or feedforward information that can be used to control a production step following a monitoring step or sample measurement. In some such aspects, subsequent or downstream steps can be adjusted based at least in part on the feedforward signal, feedforward data, and / or feedforward information provided by NLO-CD to adjust or correct changes in the fabrication process detected by the NLO-CD system.

[0009] The NLO-CD system irradiates a sample such as a silicon wafer having a semiconductor device or a semiconductor device partially constituted with light such as pulsed light (e.g., pulsed laser light). NLO-CD can be used to monitor a sample at a certain point in a semiconductor manufacturing process by irradiating light toward the sample and detecting light such as the generated SHG light (also referred to as SHG signal). In an example of SHG, for example, a pulse of incident light may generate light of the second harmonic (or half the wavelength) of the incident light, which may also be called the second harmonic generation (SHG) signal and / or SHG light. The SHG signal can be measured using one or more detectors. These detectors can be configured to measure one or more of the intensity, angular distribution, or polarization of the SHG signal, or any combination thereof, by generating the detected SHG signal (e.g., an electrical signal). In some cases, the detected SHG signal may be proportional to the intensity of the SHG light incident on the detector (e.g., the photoelectronic sensor of the detector). Further, the incident light pulse can be adjusted to improve (e.g., increase) the SHG signal from the sample, such as by selecting the polarization, wavelength, or intensity. Additionally or alternatively, the orientation of the sample can be adjusted, such as by rotating the sample with respect to the light scattering surface.

[0010] In some cases, the sample can be prepared for second harmonic generation measurement by exposing it to additional light (e.g., an auxiliary light beam or illumination) or charge. For example, the region of the sample where SHG light is emitted may be optically pumped by directing auxiliary illumination such as an auxiliary light beam toward that region. The auxiliary light beam may be referred to herein as a pump beam, and may have the same wavelength as the primary light beam (the pulse used to generate the SHG signal) incident on the sample, or a different wavelength. The charge is, for example, derived from a corona discharge.

[0011] It is possible to monitor the signal for the presence or absence of changes in the SHG signal (e.g., changes related to intensity, polarization, spatial distribution, etc.) that may indicate changes in the production of a semiconductor device (e.g., changes in one or more processes prior to measurement). In some cases, the SHG signal may be modified (e.g., by one or more optical components), and the modified SHG signal may indicate changes in the production of the sample or device. In some cases, the detected SHG signal may be modified (e.g., by an electronic processor), and the modified detected SHG signal may indicate changes in the production of the sample or device.

[0012] These changes in the production of a semiconductor device can result in changes in device dimensions (e.g., width, length, height, thickness), such as the width of transistor features (also referred to as feature portions), or changes in the alignment and / or spacing between features, such as changes in the geometric features of the device. Such changes in geometric features may also include changes in shape. In some cases, the SHG signal and / or the detected SHG signal may be processed (in the optical or electronic domain) to make changes in the SHG signal and / or the detected SHG signal more apparent. In some aspects, the SHG signal can be used to warn a manufacturer of potential production problems or to send a signal to one or more in-line fabrication tools. In some aspects, the SHG signal or the detected SHG signal may be used, for example, to provide feedback to a production apparatus early or upstream in the manufacturing process to improve the yield or performance of the device. In some aspects, the SHG signal or the detected SHG signal may be used to provide a feedforward to a subsequent or downstream process in the production process to adjust or correct for prior changes.

[0013] The SHG signal may be used to determine or provide information regarding the geometric or electronic structure of a feature of a fabricated device. The device may be a finished product or at an initial stage of production. In some aspects, for example, the SHG signal or the detected SHG signal may be compared to a database of (e.g., geometric) features to determine the structure of a device (e.g., geometric) feature. In some cases, the SHG signal or the detected SHG signal may be compared to a database of features (e.g., material properties) to determine the material properties (e.g., electronic structure) of the device. In some examples, the SHG signal and / or the detected SHG signal is modified, and the modified SHG signal, the modified detected SHG signal, and / or data based on any of these may be compared to other data (e.g., a previously measured / processed SHG signal or detected SHG signal, a modified SHG signal, a modified detected SHG signal, and / or other processed data). The SHG signal may also be used to calculate a structure (e.g., a geometric structure) based on prior knowledge of the structure (e.g., a geometric structure). For example, a database of (e.g., geometric and / or material property) features may include calculated and / or measured data of the device prior to measurement of the device to facilitate rapid identification of the device structure. These results (e.g., determined features) may also be used, as described above, to alert a manufacturer of process variations, communicate with in-line fabrication tools, and / or provide feedback or feedforward for adjustment of a semiconductor device fabrication process. In various designs, a primary pulsed laser beam impinges on a spot on the surface of a finished or partially formed integrated circuit (e.g., a silicon integrated circuit). The pulse may generate light at the second harmonic of the primary beam through interaction with the finished or partially formed integrated circuit (e.g., a finished or partially formed device within the integrated circuit). The SHG signal is measured using one or more detectors. The measurements include the intensity, angular distribution, polarization, or a combination thereof of the SHG light.Also, the sample may be rotated to perform multiple measurements (e.g., corresponding to SHG light emitted at different incident angles and / or in different directions), and / or the wavelength and / or polarization or other optical properties of the primary beam may be changed.

[0014] The detected SHG signal, whether processed or not, may be compared to a signal created by computer simulation using a model that simulates SHG (e.g., a simulated detected SHG signal or a simulated corrected detected SHG signal). The model can include geometric information such as one or more dimensions or shapes of the sample. In some examples, the geometric information (e.g., reference geometric information) can include at least two dimensions. For example, the geometric information can include any combination of the height, width, or length of a feature and can potentially include spacing. The geometric information may also include a shape that includes, for example, angles, directions, degree of smoothness, roughness, or other features or properties.

[0015] The model is generated empirically from measurements, calculated, or a combination of both. The model can be used to evaluate the SHG optical signal or the processed SHG optical signal to determine either the structure (e.g., geometric structure) of the device on the sample or a change in the structure (e.g., geometric structure).

[0016] The result of the comparison can be used to monitor the fabrication process. In some examples, if the comparison indicates a significant change to the device structure (e.g., an unexpected variation in geometric features), the process may be temporarily interrupted until the problem is corrected. The result of the comparison may additionally or alternatively be used to assist in the development of a new device structure or the fabrication process of a device. As described above, the features of such SHG systems and methods are alternatively applicable to other types of systems and methods such as SFG, DFG, FWM, or MWM, and Raman systems and methods, which may be used, for example, for in-line measurement and / or monitoring of semiconductor fabrication processes.

[0017] Thus, in some embodiments, an NLO-CD system can direct a primary optical beam (e.g., light including pulsed light or pulsed laser light) at a sample (e.g., a substrate such as a silicon wafer including a semiconductor device or a partially fabricated semiconductor device), and generate one or more optical beams via second-order, third-order, fourth-order, or higher-order nonlinear optical interactions, or other nonlinear optical interactions with the sample. The one or more optical beams can include light generated by second harmonic generation (SHG), difference frequency generation (DFG), sum frequency generation (SFG), four-wave mixing (FWM), multi-wave mixing (MWM), and / or the Raman effect. The NLO-CD can detect the one or more nonlinearly generated optical beams using one or more detectors, and monitor the sample at a point in the semiconductor fabrication process using the resulting detection signals. Pulses of the incident light can generate SHG signals, SFG signals, DFG signals, FWM signals, MWM signals, or Raman signals and can be used to detect changes in the critical dimensions of the sample or to determine the values of the geometric parameters of the sample.

[0018] In some embodiments, in addition to or instead of the detector, the NLO-CD system receives non-linearly generated signals such as SHG signals, MWM signals, or Raman signals received from the sample, and measures the intensity or relative intensity of the SHG signal to determine characteristics of the sample (e.g., geometric characteristics, material structure, critical dimensions). At least one spectrometer may be provided. Similarly, different detectors or sensors with different spectral responses, or filters with different wavelength spectra, can be used to sample different wavelengths and, in some cases, obtain different intensity values for different wavelengths. With information regarding the relative intensities of different wavelengths, it is easier to determine not only changes in the SHG output but also changes in the device and the sample.

[0019] In various embodiments described herein, a system for determining characteristics of a sample using second harmonic generation includes at least one light source configured to direct an optical beam onto the sample to create a second harmonic generation (SHG) signal, an optical detection system including at least one photodetector configured to receive the SHG signal emitted from the sample and generate a detected SHG signal, and one or more hardware processors (e.g., a hardware processor, processing electronics, a microprocessor, etc.) in communication with the optical detection system. The one or more hardware processors are configured to receive at least one detected SHG signal and determine geometric characteristics of the sample. The one or more hardware processors are configured to receive at least one detected SHG signal and determine geometric characteristics of the sample or variations in the geometric characteristics of the sample based on the at least one detected SHG signal.

[0020] In other aspects described herein, a method of determining the dimensions of a sample using second harmonic generation comprises receiving a first SHG signal, changing at least one parameter of the light beam of at least one light source or optical detection system, receiving a second SHG signal after changing the at least one parameter, and determining the shape of the feature of the sample based on the first SHG signal, the second SHG signal, and the mapping of the SHG signal to the shape of the feature of the sample.

[0021] In other aspects described herein, a system for determining features of a sample using second harmonic generation comprises at least one light source configured to direct a light beam onto the sample to create a second harmonic generation (SHG) signal, an optical detection system including at least one detector configured to receive the SHG signal emitted from the sample and generate a detected SHG signal, and one or more hardware processors in communication with the optical detection system, the one or more hardware processors being configured to receive at least a first detected SHG signal, determine a change in the first detected SHG signal or a feature of the sample, and output a display of the change.

[0022] In other aspects described herein, a system for evaluating the characteristics of a sample using second harmonic generation includes at least one light source configured to direct a light beam onto the sample to generate a second harmonic generation (SHG) signal, an optical detection system including at least one detector configured to receive the SHG signal emitted from the sample and generate a detected SHG signal, and one or more hardware processors in communication with the optical detection system. The one or more hardware processors receive the first detected SHG signal from the optical detection system, the first detected SHG signal being collected by the at least one detector at a first angle with respect to a feature of the sample, and the one or more hardware processors receive a second detected SHG signal from the optical detection system, the second detected SHG signal being collected by the at least one detector at a second angle with respect to the feature of the sample, the second angle being different from the first angle. The one or more hardware processors determine the dimensions of the features of the sample based on the first detected SHG signal, the second detected SHG signal, and a mapping of the detected SHG signal to the dimensions of the features of the sample.

[0023] In other aspects described herein, a system for evaluating the characteristics of a sample using second harmonic generation includes at least one light source configured to direct a light beam onto the sample to create a second harmonic generation (SHG) signal, an optical detection system including at least one detector configured to receive the SHG signal from the sample and generate a detected SHG signal, and one or more hardware processors in communication with the optical detection system. The one or more hardware processors receive the first detected SHG signal, determine a change in the detected first SHG signal, and are configured to output a display of the change.

[0024] In another embodiment described herein, a system for optically examining the surface of a sample, the system comprising: a first light source configured to emit a first incident light beam towards the surface of the sample; a second light source configured to emit a second incident light beam towards the surface of the sample; a light detection system configured to detect at least one four-wave mixing component from the sample to generate at least one detected four-wave mixing signal, or to detect at least one multi-wave mixing signal component from the sample to generate at least one detected multi-wave mixing signal; and one or more processors in communication with the light detection system to receive at least one detected four-wave mixing signal or at least one detected multi-wave mixing signal, and to determine a geometric feature of the sample or a variation in a geometric feature of the sample based on the at least one detected four-wave mixing signal or the at least one detected multi-wave mixing signal component.

[0025] In various aspects, the detected SHG signal is processed. For example, the detected SHG signal may be converted by one or more calculations or the like. This processed (or corrected) detected SHG signal may be used, for example, to determine geometric features (e.g., dimensions) of a partially or fully formed device or a part thereof, or data related to or based on geometric features, to monitor changes therein, and / or to monitor changes in a manufacturing process, among other things.

[0026] In various aspects, the detected SHG signal, processed or not, or a value derived therefrom, may be compared to a reference, such as a reference value or reference signal (simulated, empirically measured, or a combination thereof), to determine changes in the geometric shape or geometric features (e.g., dimensions) of a partially or fully formed device, changes in the device, changes in the manufacturing process, or any combination thereof.

[0027] In various aspects, the detected SHG signal or modified detected SHG signal, processed or other signal, or value obtained therefrom is comparable to a previously measured detected SHG signal or previously generated and modified detected SHG (e.g., stored in the system's memory). For example, for determining changes in the geometric shape or geometric features (e.g., dimensions) of a partially or fully formed device, such changes, changes in the fabrication process, or any combination thereof. In some cases, the change in geometric shape or geometric features may include variations in geometric shape or geometric features compared to a previously measured sample (e.g., a sample produced with the same process used to produce the sample from which the detected SHG signal was obtained).

[0028] As described above, the SHG signal may depend on the geometric shape or geometric features (e.g., dimensions) of a partially or fully formed device or a part thereof. Further, the SHG signal may depend on material properties such as, for example, the interface of the test sample or the electronic properties within the sample. Additional techniques that assist in obtaining such material (e.g., electronic) properties or features of the test sample from the measured SHG signal are described herein and can be used in combination with other techniques related to obtaining SHG signals that depend on the geometric shape of a partially or fully formed device. Similarly, in various aspects described herein, the SHG system can be configured to obtain an SHG signal that provides information regarding the shape or change in shape of a partially or fully formed device, as well as information regarding material properties such as the electronic properties of such a device or a part thereof. As described above, various systems and methods for using SHG, such as measurement systems, in-line systems, etc., are described herein. The features of such SHG systems and methods are alternatively applicable to other types of systems and methods such as SFG, DFG, FWM, or MWM, and Raman systems and methods, and these systems and methods may be used, for example, in-line to monitor measurement and / or semiconductor fabrication processes. Optical Measurement Based on SHG Part I

[0029] Regarding the SHG measurement tool, electrons in the layered semiconductor substrate are variously excited by each of a pump light source and a probe light source having different output characteristics for the purpose of second harmonic generation. For such an approach, an "additional" integrated light source (e.g., a UV flash lamp or a laser) that operates as a "pump" to induce a potential difference across the heterointerface of the layered semiconductor device template, and a short-time or ultrashort-time pulsed laser (e.g., a femtosecond solid-state laser) that operates as a "probe" light source are provided. Different from single-laser SHG or dual or multi-laser SFG systems, by using two different light sources in cooperation with each other (through various time offset and / or variable pump energy methods, as will be further explained) or in combination for different purposes, usefulness is obtained.

[0030] In one method, the pump is employed as a pre-excitation or pre-excitation light source to enable shortening the total characteristic evaluation time of some materials. In many such aspects, the time-dependent electric field is not mainly created by the probe / probe laser. In one variation of this method, the pump is used to UV flash the entire wafer, and then the probe laser is used to scan the entire wafer or a part thereof in a raster or other method. This option includes a row-by-row scan with steps along the (scan) columns due to wafer shifting. Additionally, there may be a method of rotating the wafer and scanning along the radius.

[0031] In another variation, the pump enables a rapid charge-up of the material interface at the sample site and then, in connection with the fast intercept method and / or the optical delay method, the decay of the charged interface is observed with a probe. Specifically, it is further described in Section II of "Charge Decay Measurement System and Method" which is part of U.S. Provisional Application No. 61 / 980,860, filed on April 17, 2014, entitled "Wafer Measurement Technology". Nevertheless, in various embodiments, the intention of using the pump for pre-excitation is to inject an amount of charge carriers sufficient to impact the interface, for example, into a dielectric.

[0032] In another method, the pump laser is employed as a post-excitation or post-excitation light source to affect the SHG signal already generated at the sample site by the probe laser. In yet another method, a comparison / contrast of the SHG signals generated by the probe before and after adding the energy of the pump laser is employed. By probing the sample to measure the SHG response before pumping, then adding radiation from the pump light source, and then re-probing, the difference in the SHG responses before and after pumping can be used to determine additional material properties such as the trap density in the material dielectric.

[0033] In the various methods discussed herein, a timing difference (i.e., the difference from the perspective of pre- and / or post-excitation by the pump source related to the use of the probe laser) is employed to provide an interrogation curve that reveals further information about the material interface.

[0034] In various methods, the pump light source and the probe light source are used simultaneously, and their combination is used to provide an SHG signal for determining the threshold injection carrier energy. Specifically, while probing with the probe laser, the frequency of the wavelength-variable pump laser is increased. At a specific frequency, the SHG signal exhibits an inflection point (or a discontinuous region). The value corresponding to the pump laser frequency at the inflection point (or discontinuous region) can be associated with the threshold injection carrier energy.

[0035] Various embodiments of the subject pump and probe systems also offer the potential for certain hardware-based advantages. In an example where the pump is a flash lamp, significant cost savings can be achieved compared to a two-laser system. Whether provided as a flash lamp or as a second laser, the pump and probe combinations as contemplated herein can also reduce the risk of optical damage to the substrate under examination, as above-threshold average output can cause overly intense illumination to degrade the dielectric and even the substrate. The threshold average output that causes optical damage to the substrate can be determined by experimental calibration studies.

[0036] To understand the latter possibility in the context of the subject hardware, some background is provided: in such hardware, the energy of both the pump and the probe alone can create an SHG signal. Although the pump and probe sources do not need to work in tandem to create an SHG signal, the pump generally does not have the peak power to adequately drive buried interface SHG, and so the relevant material properties are derived from the SHG intensity created primarily by the probe in the subject method. The time-dependent SHG intensity curve changes based on the distribution of charge carriers across, for example, the interface between the dielectric and the substrate. The time it takes for carriers to be injected across, for example, the interface between the dielectric and the semiconductor substrate, depends on the average power targeted at the sample. In some embodiments, the probe alone can enable the injection of carriers across the interface between the dielectric and the substrate. Because the average power cannot be decoupled from the peak power, the time to reach a target average power that can inject carriers into the dielectric-substrate interface without exceeding the optical damage threshold of the material in such embodiments may be longer than embodiments using a pump-probe combination. By using a high average power, but low peak power light source as a pump to inject carriers into the dielectric / substrate interface prior to the probe, the time savings of increased average power can be obtained without the associated potential damage issues that can be induced by high peak power in the average power.

[0037] Thus, compared to the pump, the target probe is typically a high peak power source with a low average power. In other words, the probe laser is typically relatively very weak. In one aspect, this allows one to obtain an initial time-independent signal with minimal disturbance to the inherent electric fields present at the substrate interface.

[0038] When the average output is high but the peak output is low, the pump induces an electric field (E) by jumping up the energy levels of charge carriers across or at the material interface. By using a source with a relatively high average output as the pump and giving all available electrons enough energy to at least jump into the dielectric, the interface is quickly "charged up", creating a situation where a probe laser with a high peak output (providing a high SHG conversion rate) but a low average output (due to a short pulse duration and a limited number of such pulses) can quickly examine the surface and provide time-independent SHG signal data.

[0039] Thus, in the various embodiments described herein, the probe laser can achieve a shortening of the time required to move electrons to a higher energy level or across an interface, thereby enabling faster evaluation of steady-state SHG signals and / or the time dynamics of charge carriers. Also, in this approach, the effect of the SHG probe and the influence on the electric field at the substrate interface can be separated. Further, over at least a portion of the signal obtained from the probe beam, SHG data that is independent of time can be acquired faster, and the time dependence of the SHG process can be accelerated or ignored. Similarly, in another aspect, the threshold energy for carrier injection into an interface (e.g., the interface between a semiconductor and a dielectric) can be determined more quickly or more accurately, and the throughput in a line tool environment can be increased. In any situation, the available time reduction can advantageously facilitate high-throughput testing in any type of in-line measurement tool in the semiconductor industry. As an example, applying SHG technology in an existing application to a device containing a 25 nm buried oxide layer under 10 nm SOI (10 nm device layer / 25 nm BOX SOI) to generate a time-dependent curve takes 6 to 12 seconds or more per point. With pre-excitation as described herein, considering the material and the output of the pump / probe, the time dependence can be generated in less than 1 second. This advancement enables covering more than 10 times the surface area on a wafer or obtaining equivalent reliability in 10% of the time if time / wafer is available on the line. Such numerical values vary depending on the material, layer thickness, and the output and wavelength of a particular pump / probe, but this is beneficial.

[0040] All of the recited embodiments of the invention of this specification, alone or in combination with elements, components, or features from different parts of this application, each include a methodology related to the approaches described herein, including the referenced co-pending patent applications, and any documents incorporated herein by reference, the hardware for implementing the methodology, the production systems incorporating the hardware, and their products (including product-by-process). Part II

[0041] Heretofore, the adoption of SHG-based measurement tools has been limited. This fact has been thought to be due to the inability to distinguish the interface characteristics detected in existing systems. In other words, existing SHG techniques provide a means to determine the electrically active and abnormal positions and presence at the interface, but the method relies on relative measurements and is not practical for distinguishing the type of electrically active anomaly (e.g., getter contaminants such as copper vs. bond voids) and / or quantifying the detected contaminants.

[0042] However, the systems and methods of the subject matter enable variously the capture of quantitative information for making the determinations necessary for such activities. In these systems and methods, after charging a wafer sample with optical electromagnetic radiation (using a pulsed laser, or a flash lamp or other electromagnetic energy source or light source or other means at a specific site), multiple measurements are made to monitor the transient electric field decay associated with the heterointerface that controls the decay period.

[0043] Using attenuation curve data generated and characterized at multiple points, spectroscopic parameters of abnormalities or problems in the sample site can be determined so that the type of defect and the distinction and / or quantification of contaminants are possible. Also, the lifetime of charge carriers, trap energy, and / or trapped charge density can be determined so that defects and contaminants can be distinguished or analyzed from each other for species distinction when contaminants are detected and / or for quantification when contaminants are detected, providing a system in which data dependent on attenuation is collected and used.

[0044] Such activities are determined for each site where the selected methodology is typically repeated to scan the entire wafer or other material sample or region thereof. Regarding the computer processing necessary to enable such determination, it can occur "in real time" (i.e., during a scan with no substantial delay in the output of results) or via post-processing. However, in various embodiments, control software can be executed without delay to provide accurate system timing for obtaining target data according to the methodology as described below.

[0045] Optionally, in relation to the generation of the SHG signal, the charge-up of the sample material is monitored. In this case, the information obtained via this signal can be used for material analysis and determination.

[0046] In any case, embodiments of the system can include an ultrashort pulse laser having a high-speed shutter operating in the range of 10 to the power of 2 seconds to picoseconds (10 to the power of minus 12 seconds). Such a system can be used to monitor SHG signal generation at the sample site from the surface and buried interfaces of thin film materials after introducing a plurality of short blocking intervals. These intervals can be timed to monitor the field attenuation of interest.

[0047] The system under consideration may also include an optical delay line. The delay line may be a fiber-based device, especially when combined with dispersion compensation and polarization control optics. Alternatively, the delay line may be mirror-based and similar to the embodiments of U.S. Patent No. 6,147,799 to MacDonald, U.S. Patent No. 6,356,377 to Bishop et al., or U.S. Patent No. 6,751,374 to Wu et al. In either case, delays are used in the system to enable laser interrogation of materials in the range from picoseconds (10^-12 seconds) to femtoseconds (10^-15 seconds), and in some cases attoseconds (10^-18 seconds). Such interrogation is useful when detecting data points that depend on multiple charge decays along a single decay curve.

[0048] The methods under consideration include those that measure the SHG signal for decay data points acquired after successive charge-up events. The conditions for obtaining the SHG signal may vary for each charge-up event. Additionally, the time intervals between successive charge-up events may also vary. In this method, it is possible to correlate multiple data points (at least two, usually three or more) and represent them as a single composite decay curve. In another method, after a single charge-up event, a minimally disruptive (i.e., the radiation used to create the SHG signal does not significantly re-charge the material) SHG signal interrogation event is used.

[0049] Yet another method for determining transient charge decay involves measuring the discharge current from the sample material (more precisely, its structure charged by optical radiation). The time dependence (dynamics) of this signal is treated in the same manner as when SHG sensing is employed. Additionally, as described above, such sensing is performed over the span of one decay interval and / or over multiple decay intervals after charging to a predetermined level. In any case, the electrode-specific hardware for such use is detailed below.

[0050] Regarding charge or charge level, this can be up to the point where the charge dynamics appear to saturate when observed on a standard linear or logarithmic time scale. As noted above, since the charge dynamics may provide important information, the methodology of interest optionally observes, records, and analyzes the charge dynamics.

[0051] For consecutive charge / interrogation events, the initial charge state of the sample is measured, and if the saturation level is not far from the initial charge state, the system can omit further or subsequent characterization. In this context, what can be considered "not far" can mean a charge increase of about 1% to about 10% relative to the initial charge state determined by learning when the tool of interest is used for a given time of sampling.

[0052] Put another way, so-called "saturation" is a relative term. Using a linear time scale, the material may appear to saturate very quickly. However, when observing the SHG signal intensity related to charging on a logarithmic time scale of 10 - 100 seconds, the latter part of saturation occurs with a different time constant and is observed to be relatively slow or time-consuming. Thus, in the examples of the methodology provided herein, while the charge up to saturation is discussed, delays and other timing are considered to occur with respect to the apparent saturation. Since it may take an unnecessarily long time to reach 100% saturation, rather than waiting the full time to reach 100% saturation, instead, the instrument may delay until the time to reach the apparent saturation or the time to extract important parameters, regardless of the time it takes to reach full saturation.

[0053] Furthermore, when monitoring the amount or degree of charge-up towards saturation (e.g., in relation to SHG monitoring), it should be understood that the subject methods and systems may operate at charge levels and / or recharge levels below saturation (as described above), while still providing meaningful attenuation curve information. However, in the absence of such measurements, when approximate saturation is a known parameter (e.g., from the experience of a target tool using a given material), the charge up to saturation is adopted as the target level.

[0054] It should be noted that, as further described in part in U.S. Provisional Application No. 61 / 980,860, filed Apr. 17, 2014, entitled “Wafer Measurement Techniques”, various interfacial material properties are determined using laser beam blocking or delay. This part refers to Section III entitled “Temperature Controlled Measurements” and is hereby incorporated by reference in its entirety. Introducing a DC bias to the sample being tested can also be useful for material analysis. The adoption of a DC bias actively changes the initial charge distribution at the interface before the photo-induced voltage has an effect. For this purpose, the sample to be tested may be mounted on a conductive chuck used as ground for applying a DC bias across the entire sample using an upper surface probe of the sample. As further described in the part referred to as Section IV entitled “Field Bias SHG Measurements” of U.S. Provisional Application No. 61 / 980,860, filed Apr. 17, 2014, entitled “Wafer Measurement Techniques”, other means of introducing an induced voltage bias are also possible without using a surface probe.

[0055] Also, the subject system can use a secondary light source in addition to the primary laser included in the blocking type analysis for charge decay determination. Such a set of light sources may be adopted as a radiation pump / probe combination, as further described in the part called Section I entitled “Pump and Probe Type SHG Measurements” of U.S. Provisional Application No. 61 / 980,860, filed Apr. 17, 2014, entitled “Wafer Measurement Techniques”.

[0056] Embodiments of the invention described herein include each of the methodologies associated with the approaches described herein, alone or in combination with elements, components, or features of different parts of this application, related pending patent applications, and any documents incorporated herein by reference. Hardware for implementing the methodologies, production systems incorporating the hardware, and their products (including product-by-process) are included herein. Part III

[0057] SHG-based systems subjected to various field biases (e.g., magnetic field bias, DC bias, and / or voltage bias induced only by capacitive coupling and / or AC fields with changing magnetic fields) and methods of using them will be described. These will be addressed in turn. These can be used independently and / or in combined systems. Various embodiments described herein include each of the methodologies associated with the approaches described above, hardware for implementing the methodologies, production systems incorporating the hardware, and their products (including product-by-process). Magnetic field bias

[0058] A static or changing magnetic field applied to a sample changes the material's second-order optical susceptibility tensor. Thus, the magnetic field can be used to increase the SHG signal from the sample to an optimum value. Further, as will be further described below, a changing magnetic field can be used to induce a bias. Inductive voltage bias for eliminating DC contact probes

[0059] In a system where the pulse of the probing laser and / or the gating of the detector can be synchronized with a given voltage amplitude of an alternating current, variable or pulsed bias that is applied to the sample to create an induced voltage field corresponding to or adjusted to the surface to be investigated, a system and method for characterizing the SHG response of a layered semiconductor material exposed to a discrete electric field across its interface without using a contact bias probe are described.

[0060] The hardware under consideration comprises, without making contact, means for inducing a voltage (e.g., components configured to induce) at or along the "device" surface of the sample, together with an SHG device (see, e.g., further described by reference to the section II of "Charge Decay Measurement System and Method" of US Provisional Application No. 61 / 980,860, filed April 17, 2014, entitled "Wafer Measurement Technology"). Such means or components include a capacitively coupled probe connected to a power supply that also communicates with a backside contact probe or such a chuck via a backside contact to the probe or conductive chuck, or applies a varying magnetic field to the sample for the purpose of inducing an external voltage field across its multilayer interface.

[0061] The transient electric field created by a variable waveform (optionally AC) power supply (via any of the above approaches) induces an electric field across the interface of the multilayer semiconductor material. The relationship between the voltage and the electric field at the material interface can be modeled by a transfer function or other means, including taking into account various (capacitive or other) external influences. The output of this function can be employed as a timing cue to simultaneously trigger the laser shutter and / or photon counter for SHG characterization of the test point, for a given amplitude and frequency of an alternating current (or other) current, corresponding to a substantially instantaneous value of the electric field amplitude at the interface. In this way, the system can simulate a constant (DC) voltage applied at the top side (i.e., the device layer of the substrate) via a contact electrical probe.

[0062] When applying AC directly to the back side of the sample, the system starts from a state where the chuck is in a "neutral" or grounded state and the bulk layer and the device layer are at the equilibrium potential. Next, an AC bias is applied to the chuck, and the chuck makes galvanic contact with the bulk layer or the substrate layer of the multilayer semiconductor material. Since the device layer is separated from the bulk by the buried oxide layer and is not directly connected to the conductor, an electric potential field, i.e., a voltage, is generated (i.e., induced) between the device layer and the bulk layer.

[0063] Alternatively, capacitive coupling probe(s) can be employed that are positioned near (within about 1 mm to about 2 mm) the sample without contacting the upper surface of the sample. A preferred approach in this regard is to suspend in air a plate sized to cover (without touching) the entire wafer, with small holes through which the incident laser passes on its way to the sample and through which the SHG beam passes on its way out of the sample.

[0064] In some embodiments, the non-contact electrodes can be implemented using MEMS technology. For example, in one aspect, a Si wafer can be oxidized on both sides. Thereafter, spiral or grid-shaped electrodes can be deposited and arranged at one or more locations on the wafer. The oxidized material can be removed from the back side of the wafer at those locations. The electromagnetic field applied to the electrodes can apply an induced bias to the wafer of such an aspect through near-field inductive coupling. The magnetic field generated by an external current can be used to generate a current in the wafer by inducing a current in the deposited electrodes. Other methods of implementing non-contact probes can also be used.

[0065] In any case, the SHG methodology is used to examine a sample, as further described, for example, in the section I entitled "Pump and Probe Type SHG Measurement" and / or the section III entitled "Temperature Controlled Measurement" of U.S. Provisional Application No. 61 / 980,860, filed on April 17, 2014, and entitled "Wafer Measurement Techniques", both of which are hereby incorporated by reference in their entirety. The same applies to other embodiments described below.

[0066] Nevertheless, in the embodiments of interest, since it is desirable to monitor SHG as a function of the voltage across the interface, the SHG signal is synchronized with the output source. This synchronization can be achieved by time controlling the laser(s) used for SHG signal generation and the SHG signal processing software, the laser(s) only, or the SHG signal processing software only, in accordance with the change in voltage. Also, the voltage of the chuck is controllable.

[0067] The advantage of this synchronization is that a voltage bias SHG measurement similar to a DC bias SHG measurement can be obtained without using a contact-type voltage bias probe on the front surface of the wafer. Instead of applying a DC bias, the system uses an AC bias synchronized with the SHG measurement and / or generation to collect SHG data at discrete points on the voltage cycle. The AC bias is applied via near-field inductive coupling or capacitive coupling of the sample. The SHG data collected with these bias techniques provides the same material property information as DC bias SHG.

[0068] To reduce or minimize noise and obtain a statistically relevant metric of SHG intensity as a function of the voltage across the interface, multiple photon counting windows may be desirable, as further described below. Inductive Voltage Bias for Characterizing Interface Leakage

[0069] As described above, a system and method for characterizing the interfacial leakage current and / or carrier injection energy between layers of a layered (e.g., semiconductor) material using SHG and a voltage change (alternating, variable, and / or pulsed voltage or current signal applied to the layered semiconductor material, or a device that varies a magnetic field to induce a voltage change in a device layer of the sample, etc.) of the layered semiconductor material are described.

[0070] The interfacial leakage current and / or carrier injection energy can be characterized by measuring the SHG response from an optical pulse generated by a pulsed laser directed at a layered semiconductor / dielectric structure while or immediately after an alternating, variable, or pulsed voltage is applied to the layered semiconductor material. In some embodiments, the time evolution of the SHG signal from the interface as a function of the decay time constant of the induced voltage can be measured. This provides information about the mobility of charge carriers across the interface.

[0071] Induced voltage bias for characterizing threshold carrier injection energy

[0072] Instead of using wavelength-variable laser excitation to determine the energy threshold for photoinduced charge carrier injection into a dielectric of a layered semiconductor material, a system and method for SHG measurement applied in relation to a varying electric field of a sample device layer are described. More specifically, to measure the threshold energy required for photoinduced charge carrier injection into a dielectric, a material is exposed to a substantially monochromatic incident photon beam for SHG generation, the voltage is incrementally varied across the interface of the exposed layered semiconductor material, and the SHG signal count is measured for each incremental voltage change until the SHG response has a significant inflection or discontinuity, or the slope suddenly changes from previous measurements. This change in slope can be a maximum or minimum (e.g., a local maximum or minimum), a cusp, or a step function, etc. The net charge change movement due to all these processes can be described as the integral of the contributions of the third harmonic injection current, the "forward" leakage current into the dielectric by a strong electric field, and the "backward" discharge leakage current. In equation form, it is as follows. [Number] The dynamic characteristics (time bending moment and saturation moment) of this curve shape provide information for determining the threshold carrier injection energy.

[0073] All embodiments of the invention herein include each of the methodologies related to the approaches described herein, alone or in combination with elements, components, or features from different parts of this application, related patent applications pending, and any documents incorporated herein by reference, for implementing the methodologies, including hardware, production systems incorporating the hardware, and their products (including product-by-process).

[0074] The drawings schematically illustrate aspects of various embodiments of variations of the present invention.

Brief Description of the Drawings

[0075]

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Best Mode for Carrying Out the Invention

[0076] Dimension Measurement Using Nonlinear Optics Monitoring the "critical dimension" (CD) of semiconductor devices produced by a production line is an important aspect of semiconductor manufacturing. Considering that even a slight change in the critical dimension due to fluctuations in the manufacturing process or the like can affect the performance of semiconductor devices, it is beneficial to capture the change at the initial stage of the manufacturing process in order to avoid the production of a large number of defective devices.

[0077] Conventional measurement tools used for monitoring semiconductor devices may not simultaneously satisfy many of the attributes desired for measurement tools, such as sensitivity, accuracy, reproducibility, reliability, and the cost of monitoring. The optical measurement tools, techniques, and systems described below can overcome some of the issues associated with monitoring semiconductor devices using second harmonic generation light (also referred to as second harmonic light) as a non-destructive probe for monitoring and evaluating samples. More specifically, a non-linear optics (Non-Linear Optics) system for determining the critical dimension (CD) of a sample (referred to herein as NLO-CD) is described. NLO-CD irradiates a sample with one or more light beams and, as a result, uses the second harmonic generation light emitted by one or more devices on the sample to determine the physical structure (e.g., shape and / or dimensions) of the device and / or monitor changes in such features. The sample may be composed of devices and structures (e.g., complete and / or incomplete devices and structures fabricated on a wafer). In some cases, NLO-CD can also determine the material properties (or changes in material properties) of the sample or the devices and structures included in the sample using second harmonic light.

[0078] In some examples, an optical measurement system can direct one or more primary light beams at a sample to generate one or more light beams through second-, third-, fourth-, higher-order non-linear, inelastic light scattering, and / or other non-linear optical interactions with the sample, which can include a completed semiconductor device or a partially fabricated semiconductor device. The one or more light beams can have light generated by second harmonic generation (SHG), difference frequency generation (DFG), sum frequency generation (SFG), four-wave mixing (FWM), multi-wave mixing (MWM), and / or the Raman effect. NLO-CD can use one or more detectors to detect the one or more light beams and use the resulting detection signals to monitor the sample at a point in the semiconductor manufacturing process. The incident light can generate SHG light, SFG light, DFG light, FWM light, MWM light, Raman light (also referred to as an SHG signal, SFG signal, DFG signal, FWM signal, MWM signal, or Raman signal, respectively). The detector can detect an SHG signal, SFG signal, DFG signal, FWM signal, MWM signal, or Raman signal to generate a detected SHG signal, a detected SFG signal, a detected DFG signal, a detected FWM signal, a detected MWM signal, or a detected Raman signal, respectively (collectively referred to as detection signals). The optical measurement system can use the detected signals to determine characteristics of the sample (e.g., geometric characteristics or critical dimension values, or material properties) or to detect changes in geometric characteristics or material properties. In some cases, the optical measurement system can use a mapping between the detected signals and corresponding geometric characteristics to detect changes or values of the geometric characteristics of the sample. The mapping is generated using computer modeling, empirical data, or a combination thereof. The detector is used to measure the intensity, polarization, wavelength, propagation direction, and other characteristics of the light beam emitted from the sample. In some cases, the detector can include a spectrometer that measures the spectrum of the light beam emitted from the sample. In some cases, the primary light beam is generated by one or more light sources including a laser light source, a wavelength-variable light source, a broadband light source, etc.In some embodiments, one or more characteristics of the primary light beam may be changed during measurement, and the system may determine geometric features of the sample based on corresponding changes in the light beam resulting from emission from the sample. In some embodiments, the pulses of the primary light beam may be delayed relative to the pulses of another primary light beam, and the system may determine characteristics of the sample by varying the delay and measuring the corresponding changes in the resulting light beam emitted from the sample.

[0079] In some examples, the results of SHG, DFG, SFG, FWM, MWM, Raman-based dimensional metrology can be used for process monitoring. For example, an NLO-CD system (or the monitoring method described above) can be used to estimate the characteristics of a sample produced by a process at the production stage. In some such examples, the NLO-CD system can be used for in-line and real-time process monitoring (e.g., an optical measurement system may be included in-line within a fabrication system as an in-line measurement tool), or for off-line monitoring of selected (e.g., randomly selected) samples.

[0080] The results of dimensional measurements based on SHG, SFG, DFG, FWM, MWM, or Raman signals emitted from a sample can be used to generate a feedback signal or a feedforward signal for modifying the process as needed. The feedback signal can be used to improve the process such that, compared to a sample produced before applying the feedback signal, after applying the feedback signal, the characteristics of the sample produced by the production step prior to the measurement step approach the reference characteristics. The feedforward signal can be used to adjust the production step after the measurement step to correct for a determined change in characteristics. As described above, various systems and methods for using SHG, such as measurement systems, in-line systems, etc., are described herein. The features of such SHG systems and methods are alternatively applicable to other types of systems and methods, such as SFG, DFG, FWM, MWM, or Raman systems and methods, and these systems and methods may be used, for example, in-line to monitor measurement and / or semiconductor manufacturing processes. SFG, DFG, FWM, MWM, or Raman systems can determine the geometric characteristics of a sample or detect changes in the geometric characteristics of a sample using SFG light, DFG light, FWM light, MWM light, or Raman light generated by the sample upon illumination with an incident beam. Optical Wafer Measurement Technology Based on SHG Part I

[0081] FIG. 1 is a diagram of a system 100 that can be employed in connection with a method for examining a sample, in some cases, to provide information regarding the material properties of the sample (e.g., properties of the electronic structure). Variations of other suitable systems are referred to, for example, with respect to the inclusion of intermediate optical systems, optical delay lines (singular and plural), and optional electrode features, to the portion presented as Section II, entitled "Charge Decay Measurement Systems and Methods," of U.S. Provisional Application No. 61 / 980,860, filed Apr. 17, 2014, entitled "Wafer Measurement Technology."

[0082] As shown, system 100 includes a primary or probe laser 10 for directing an interrogation beam 12 of electromagnetic radiation at a sample wafer 20 held by a vacuum chuck 30. As shown in FIG. 1B, chuck 30 includes an x-y stage and, optionally, a rotational stage for positioning a sample site 22 on the wafer relative to the location at which the laser is directed. The x-y stage enables scanning of multiple wafer surface sites or locations 22 without moving other hardware. The rotational stage can evaluate the effect of crystal structure on SHG, such as strain, and associated defects, or areas of concern of the material being characterized. Further optional features, aspects, and / or uses of chuck 30 are presented in Section IV, entitled “Field Bias SHG Measurements” and Section III, entitled “Temperature Controlled Measurements” of U.S. Provisional Application No. 61 / 980,860, filed Apr. 17, 2014, entitled “Wafer Measurement Techniques,” both of which are hereby incorporated by reference in their entirety. Sample site 22 can include one or more layers. Sample site 22 can include a composite substrate including at least two layers. Sample site 22 can include an interface between two dissimilar materials (e.g., between two different semiconductor materials, between two different doped semiconductor materials, between a semiconductor and an oxide, between a semiconductor and a dielectric material, between a semiconductor and a metal, or between an oxide and a metal).

[0083] When system 100 is in use, the beam 14 of reflected radiation directed towards detector 40 includes an SHG signal. The detector can be any of a photomultiplier tube, a CCD camera, an avalanche detector, a photodiode detector, a streak camera, or a silicon detector. System 100 can also include one or more shutter-type devices 50. The type of shutter hardware used depends on the time frame during which the laser radiation is blocked, discarded, or otherwise moved away from the sample site. Electro-optic shutoff devices such as Pockel cells or Kerr cells can be used to obtain very short shutoff times (i.e., operating times on the order of 10 to the minus 9th power seconds to 10 to the minus 12th power seconds).

[0084] When the shutoff time interval is long (e.g., about 10 to the minus 5th power seconds or more), mechanical shutters or flywheel chopper type devices can be employed. However, electro-optic shutoff devices make it possible to test a wider range of materials according to the following method. A photon counting system 44 can be employed that discretely gates very small time intervals, typically on the order of picoseconds to microseconds, to resolve time-dependent signal counts. For faster time frames, optical delay lines can be incorporated as described above.

[0085] System 100 can include an additional electromagnetic radiation source 60, also referred to as a pump source. In various embodiments, the radiation source 60 can be a laser shown to emit a directed beam 62, or a UV flashlamp that emits a diverging or optically collimated pulse 64. In the case of a laser source, its beam 62 can be parallel to beam 12 (e.g., directed by additional mirrors or prisms, etc.). Using wavelengths in this range that are shorter (e.g., less than about 450 nm) makes it possible to drive charge excitation with fewer photons and / or lower peak intensities than longer wavelengths.

[0086] In the case of a flash lamp, the energy per flash and the output level during the flash may depend on the material of the substrate. Flash lamps that generate a total energy of 1 J to 10 kJ per flash are suitable for fully depleted silicon-on-insulator (FD-SOI). However, pulsed or continuous UV light sources are also available. An important factor in the characteristics and use of the pump is that charge carriers are injected into the dielectric of the material being inspected. Suitable flash lamp manufacturers include Hellma USA, Inc. and Hamamatsu Photonics K.K.

[0087] When a laser is employed as the light source 60, it may be any of a nanosecond, picosecond, femtosecond, or longer pulse laser light source. It may also be a continuous solid-state laser. In various embodiments, the pump light source is wavelength-variable. Commercially available options for wavelength-variable lasers include the Velocity and Vortex tunable lasers from Spectra Physics. Other wavelength-variable solid-state technologies include the LT-22xx series of solid-state lasers from LOTIS Ltd.

[0088] Regardless of whether it is provided as a laser or as a flash lamp, the pump source 60 can select a relatively high average output. This can be from about 10 mW to about 10 W, depending on the material being examined, but more typically is from about 100 mW to about 4 W (again, taking into account ensuring that the charge carrier mobility is induced in such a way that charge carriers are injected into the interface of the material, e.g., the dielectric interface), and can be specific to the material. The average output of the pump source 60 is selected to be below the optical damage threshold of the material. For example, if the material being examined contains silicon, the pump source 60 can be selected to have an average optical output between 1 and 2 W so as not to exceed the optical damage threshold of silicon.

[0089] Probe laser 10 is a pulsed laser light source with pulses of nanoseconds, picoseconds, femtoseconds or longer. Among currently commercially available lasers, there are two options in terms of those having the required peak output, wavelength, and reliability: doped fiber and titanium sapphire units. Lasers such as Coherent's VITESSE and Spectra-Physics' MAI TAI are examples of suitable titanium sapphire devices. Femtolasers Gmbh and other manufacturers also produce related titanium sapphire devices. Suitable doped fiber lasers are manufactured by IMRA, One Five, and Toptica Photonics. Depending on the substrate material and the type of pump, picosecond lasers and nanosecond lasers from many manufacturers such as Hamamatsu Photonics are also options. Laser 10 operates in a wavelength range of approximately 100 nm to approximately 2000 nm, with a peak output of approximately 10 kW to 1 GW, and an average output of 150 mW or less.

[0090] System 100 may employ various other so-called "intermediate" optical components as options. For example, the system can include a dichroic reflection or refractive filter 70 for selectively passing an SHG signal coaxial with the radiation directly reflected from laser 10 and / or source 60. Alternatively, a prism can be employed to distinguish a weak SHG signal from a much stronger reflected primary beam. However, since the prism approach has proven to be very sensitive to misalignment, a dichroic system as described above may be preferred. Other options include the use of diffraction gratings and pellicle beam splitters. An optical bundle 80 for the focusing optical system and the collimating / column optical system may be provided. Alternatively, a filter wheel 90, a polarizing plate 92, and / or a zoom lens 94 may be incorporated into the system. Also, angular (or arc-shaped) rotational adjustment (accompanied by adjustment corresponding to the detector) and in-line optical components may be desirable in some cases.

[0091] In the embodiment shown in FIG. 1C, the beam 12 from the laser 10 can be split into two optical paths by the beam splitter 74. The beam splitter 74 can split the beam 12 unevenly between the two optical paths. For example, 70% of the energy of the beam 12 can be directed along the first optical path (e.g., as beam 16), and 30% of the energy of the beam 12 can be directed along the second optical path (e.g., as beam 18). As another example, 60% of the energy of the beam 12 can be directed along the first optical path, and 40% of the energy of the beam 12 can be directed along the second optical path. As yet another example, 80% of the energy of the beam 12 can be directed along the first optical path, and 20% of the energy of the beam 12 can be directed along the second optical path. Thus, the split can be uneven (e.g., 70 - 30%, 80 - 20%, 60 - 40%, or any range therebetween, e.g., between 60 - 90% in one path and between 40 - 10% in another path, and outside these ranges), with the majority of the output being sent to the pump beam and a portion being sent to the probe beam. For example, for the pump and probe respectively, it can be split into 60 - 70% and 40 - 30%, for the pump and probe respectively, 70 - 80% and 30 - 20%, for the pump and probe respectively, 80 - 90% and 20 - 10%, or for the pump and probe respectively, 90 - 99.999% and 10 - 0.001%. In different embodiments, the probe beam can be between 0.001% and 49.99%, and the pump beam can be, for example, between 50.001% and 99.999%. The sum of the two beams can be 100% or approximate thereto. The split may, in some cases, be determined by the particular material system being characterized. In the example shown in FIG. 1C, 5% of the beam energy of the beam 12 travels along the first optical path, and 95% of the energy of the beam 12 travels along the second optical path.

[0092] The beam splitter 74 can be composed of a dielectric mirror, a splitter cube, a metal-coated mirror, a pellicle mirror, or a waveguide splitter. In an embodiment where the beam 12 includes an optical pulse, the beam splitter 74 can include an optical component with negligible dispersion that splits the beam 12 between two optical paths so that the optical pulse is not broadened. As shown in FIG. 1C, each of the beams can be redirected or directed using various mirror elements 2072.

[0093] The output from the detector 40 and / or the photon counting system 44 can be input to the electronic device 48. The electronic device 48 can be a computing device, a computer, a tablet, a microcontroller, or an FPGA. The electronic device 48 can include a processor configured to execute one or more software modules. In addition to executing an operating system, the processor can be configured to execute one or more software applications, including a web browser, a phone application, an email program, or any other software application. The electronic device 48 can implement the methods discussed herein by executing instructions contained in a machine-readable non-transitory storage medium such as RAM, ROM, EEPROM, etc. The electronic device 48 can include a display device and / or a graphical user interface for interacting with a user. The electronic device 48 can communicate with one or more devices via a network interface. The network interface can include a transmitter, a receiver, and / or a transceiver capable of communication, such as wired Ethernet, Bluetooth®, or a wireless connection, for example.

[0094] For other options, since the SHG signal is weak compared to the reflected beam that generates it, it is desirable to improve the signal-to-noise ratio of the SHG count. As the photon count gate time of the photon counting system 44 decreases for the gating and / or delay processes described herein, the improvement becomes even more important. One way to reduce the noise that can be employed is to actively cool the photon counter. This can be done using cryogenic fluids such as liquid nitrogen or helium or solid cooling using a Peltier device. Other improvements include the use of a Marx bank circuit (MBC) related to the shutter speed. Further, the system 100 can be incorporated inline within a production line environment. The production line elements preceding or following the system 100 can include any of an epitaxial growth system, a lithography and / or film deposition (CVD, PVD, sputtering, etc.) system.

[0095] Next, referring to FIGS. 2A / 2B and FIGS. 3A / 3B, these are schematic diagrams showing examples of the types of SHG curves that can be generated in a method of using a target pump / probe system. In FIGS. 2A and 2B, the time scale for obtaining such signals is on the order of milliseconds (10 to the minus 3 seconds). Thus, these are "fast" processes. As will be described further below, these can provide an improvement of several orders of magnitude in terms of time compared to existing approaches. For example, if a flash lamp that can irradiate the entire surface of the test material with ultraviolet light before SHG probing is used, continuous measurements at each point are not required, so the overall scan time is significantly reduced.

[0096] Specifically, in FIG. 2A, the SHG signal 200 is measured at an initial intensity 202. This signal is generated by the probe light source emission applied to the surface position. When radiation from the pump light source (of the probe remaining in the on state) is added after a predetermined time offset (O1), the signal intensity decreases along the time-dependent curve 204 to a lower level 206. Conversely, in FIG. 2B, the SHG signal 200' at a low level 212 generated only by the probe radiation increases along the time-dependent curve 214 and reaches a high plateau region 216 when pump radiation is applied after a time offset (O2). The signals 200 and 200' also include time-independent components or portions at the beginning and end of the curves.

[0097] Both observations in FIGS. 2A and 2B can be performed on the target system depending on the substrate material and different laser outputs (e.g., in this case, the output of the pump). In various embodiments, charge separation includes electrons and holes that separate from each other after excitation from photons. Electrons injected from the valence band of silicon to the conduction band of SiO2 by photons from the laser are mainly trapped on the upper surface of the oxide. The holes mainly gather in the silicon valence band close to the Si / SiO2 interface. The separation of charge carriers by excitation by the incident radiation or internal light emission contributes to the electric field existing inside the target system, and as a result, the measured SHG changes. Which of FIGS. 2A and 2B is observed depends on various factors such as the presence of gaseous oxygen at the test site, the composition and structure of the target sample.

[0098] In fact, there have also been cases where combinations of signals 200 and 200′ were observed. In these cases, the signal intensity first decreased from the peak, reached the bottom, and then rose again to the asymptote. Generally, the SHG intensity curve is determined by the nonlinear susceptibility tensor, which is affected by molecular orientation, atomic structure, electronic structure, and external fields. Charge carriers moving across the interface change the charge state in the structure and the electric field in the lower layer of the interface where the SHG signal is generated. Different time-dependent curves are observed depending on the type of charge carrier (positive or negative) moving across the interface and the initial state of the field across the interface. The intensity of the detected SHG signal can depend on various factors including spot size, average laser output, and peak laser output. In various embodiments, system 100 can be configured to detect an SHG signal having an intensity in the range between about 400 counts / second and about 7 million counts / second. The pump / probe system described herein can shorten the time required for charge carriers moving across the interface to reach the saturation level. In various embodiments, in the pump / probe system described herein, the time required for charge carriers moving across the interface to reach the saturation level can be between 1 millisecond and 1000 seconds. Since it may be advantageous to obtain the time evolution of the SHG signal not only when the charge carrier density in the region containing the interface is below the saturation level but also when the charge carrier density in the region containing the interface reaches the saturation level, the system can be configured to obtain an SHG signal measurement within about 1 microsecond after turning the pump radiation on / off.For example, the system can be configured to obtain SHG signal measurements within 10 seconds after turning the pump emission (or probe emission) on / off, within about 6 seconds after turning the pump emission (or probe emission) on / off, within about 1 second after turning the pump emission (or probe emission) on / off, within about 100 milliseconds after turning the pump emission (or probe emission) on / off or within about 1 millisecond after turning the pump emission (or probe emission) on / off, within 1 microsecond after turning the pump emission (or probe emission) on / off, within 1 nanosecond after turning the pump emission (or probe emission) on / off or within any range formed by these values (e.g., time greater than nanoseconds, time greater than microseconds, time greater than milliseconds, etc.), and outside these ranges. These values and ranges are applied to obtain data from a single point, but with an appropriate imaging optical system, it can be increased to a significant area of the wafer, up to an area that includes the entire wafer at once. As indicated in the above parentheses, these values and ranges also apply to the probe emission. By shortening the charge time and the time required to obtain the SHG signal, the interface test can be performed more quickly, and as a result, the throughput during testing and / or during manufacturing on the production line can be improved.

[0099] For comparison, FIGS. 3A and 3B schematically show SHG signal curves 300 and 300' for corresponding materials using only one radiation source (in this case, a laser with high average output and high peak output) to examine the substrate in the same way as existing SHG techniques. The time scales for generating the signals 300 and 300 in FIGS. 3A and 3B are on the order of tens to hundreds (10 to the 2nd power of seconds) of seconds.

[0100] Over such a period of time, these signals (such as the signals of FIGS. 2A and 2B) can include lower and upper plateau regions 306, 316 that can be characterized after an initial 302 and / or time-dependent signal. Thus, similar (or identical) analysis can be performed using signals 200 / 200' and 300 / 300', with the main difference being that the system of interest (i.e., uses a lower high-peak output femtosecond probe laser in combination with a high average output pump for the pre-excitation material) results in a significant improvement in the temporal efficiency in obtaining the necessary signal information. Further, the approach of interest provides a way to more easily determine time-independent SHG measurements without using a filter wheel or other means.

[0101] In any case, FIG. 4 illustrates a method for determining the threshold injection carrier energy. In this case, the pump consists of a wavelength-variable laser. Thereby, the output frequency of the photons from the pump incident on the sample (and thus the energy according to E = hν) can be ramped up over time. The observed SHG activity effect is illustrated as signal 400. With the pump laser applied or engaged in that way, the initial SHG signal level 402 generated by the application of the probe laser is observed as the point where it suddenly changes (i.e., exhibits an inflection, discontinuity, maximum, minimum, step function, cusp, or some sudden change in slope at 404). The frequency at this point is taken to correspond to the threshold energy. In various embodiments, the threshold energy is the energy required to transport electrons from the valence band of one semiconductor material to the conduction band of another semiconductor material across an interface between two materials such as two semiconductor materials or a semiconductor material and a dielectric material (e.g., Si and SiO2, Si and Si2N4, Si and Ta2O5, Si and BaTiO3, Si and BaZrO3, Si and ZrO2, Si and HfO2, Si and La2O3, Si and Al2O3, Si and Y2O3, Si and ZrSiO4). The system 100 can be configured to measure a threshold energy in the range of about 1.0 eV to about 6.0 eV. The systems and methods described herein can be configured to determine the threshold energy of various interfaces, such as between two different semiconductors, between a semiconductor and a metal, between a semiconductor and a dielectric, etc.

[0102] FIG. 5 is a flowchart 500 showing one embodiment of a method for characterizing a semiconductor device using SHG. Various process flow paths are shown. Such a method can begin, at 502, by positioning a sample at a desired location (e.g., typically, by positioning chuck 30 after wafer 20 has been secured thereto). Progressive positioning (i.e., repositioning) may occur after any given SHG detection event 520, as further described to scan multiple surface positions, or all surface positions within a region of the sample, or all surface positions of the sample. Alternatively, such an operation may occur at 540, after a predetermined determination has been made regarding the detected SHG signal (either of the "return" options shown by the dotted lines). Further details regarding alternative determinations will be understood by reference to other parts of this application, referred to above. In any case, following positioning or repositioning of the sample, a predetermined flow path is selected (or, to generate different data, different flow paths may be run in sequence at the same surface position).

[0103] Following the flow path (partially solid line) of one process, probe light source radiation is applied to the sample surface at a predetermined position at 504. Next, pump light source radiation is applied at 506. In this example, the pump radiation is applied by varying the method to linearly increase the optical energy by (optionally) decreasing the radiation wavelength. The resulting SHG is detected at 520. The carrier injection threshold energy is determined by signal analysis at 542 (according to the example of FIG. 4). In various embodiments, the energy of the pump radiation can correspond to the threshold energy of the semiconductor interface. Thus, the energy of the pump radiation can be between about 1.0 eV and about 6.0 eV. For example, to determine the threshold energy across the interface of Si and SiO2, the threshold energy of the pump radiation can vary between about 4.1 eV and about 5.7 eV. The variation in the energy of the pump radiation can be achieved by changing the frequency (or wavelength) of the radiation. For example, to inspect a sample with a predicted threshold energy of around 3.2 eV, the wavelength of the pump radiation can be varied between about 443 nm and about 365 nm. In various embodiments, since photons from the pump radiation can generate electrons with twice the energy (for example, when one electron absorbs two photons), the energy of the pump radiation can be below the threshold energy of the semiconductor interface. In such embodiments, the charging time becomes longer, enabling observations with improved resolution and intensity. Also, increasing the charging time increases the time required to inspect the sample site, which may reduce throughput.

[0104] Following another flow path (partially dashed line), pump radiation is applied to the substrate at 508. Such application may be directed (e.g., by a laser) only to the surface to be immediately investigated, or may be directed (e.g., using a flash lamp) to the entire surface of the wafer. Next, at 510, a portion of the sample to be inspected is exposed to probe light source radiation. The resulting SHG is detected at 520. The pump-probe detection aspect of this method may potentially be repeated after repositioning of the sample at 502. However, such an action box 508 may be omitted, or pump re-injection may be avoided or omitted from a series of scanning processes, as in the above example where the entire substrate was first exposed to pump radiation. In any case, at 544, as discussed elsewhere in this patent application, any of a variety of SHG-based signal analyses may be performed to make determinations other than the threshold energy as in block 542.

[0105] Following another process flow path (partially, chain line / center line), probe interrogation is performed at 504 and 510 before and after pump irradiation at 508, along with SHG signal data collection at 520 immediately after probe irradiation at 504 and 510. Again, this method can be recursively executed by returning to flowchart element 502 and repeating the probe detection pump-probe detection method or sub-method to sample multiple positions such as all sections of the substrate or its regions.

[0106] Notably, either the SHG signal analysis method or sub-method (generally encompassed in boxes 540 and 542) can be executed in real time, such as with an instantaneous or near-instantaneous output. By doing so, any of the spectroscopic properties determined by the collected data can be calculated by either on-machine integration software or a remote software package. Alternatively, SHG signal analysis may be processed in post-processing after some or all of the SHG data has been detected or collected.

[0107] The systems and methods described herein can be used to evaluate the characteristics of a sample (e.g., a semiconductor wafer or a portion thereof). For example, the systems and methods described herein can be used to detect defects or contaminants in a sample, as described above. The systems and methods described herein can be configured to evaluate the characteristics of a sample during the fabrication or production of a semiconductor wafer. Thus, the present systems and methods can be used along a semiconductor manufacturing line within a semiconductor fabrication facility. The systems and methods described herein can be integrated into a semiconductor manufacturing / production line. The systems and methods described herein can be integrated into a semiconductor manufacturing line having an automated wafer handling function. For example, the system can be equipped in an attached equipment front end module (EFEM) that receives a wafer cassette such as a front opening unified pod (FOUP). Each of these cassettes is loaded into the machine by a human operator or by an automated cassette handling robot that moves the cassette from process to process along the fabrication / production line.

[0108] In various embodiments, the system can be configured such that when a cassette is loaded onto the EFEM, the FOUP is opened, a robotic arm selects an individual wafer from the FOUP, moves through an automatically opening and closing door included in the system, and into an optically sealed process box, and moves onto a bias-compatible vacuum chuck. The chuck may be designed to complementarily fit with the robotic arm such that the robotic arm can place the sample thereon. At some point in this process, the wafer can be held up to a scanner to identify a unique laser mark.

[0109] Accordingly, a system configured to be integrated into a semiconductor fabrication / assembly line can have an automatic wafer handling function from a FOUP or other type of cassette, integration with an EFEM as described above, a chuck designed to be compatible with robotic handling, an automatically light-sealed door that opens and closes to allow movement of a robotic wand / arm, and software signals to the EFEM for wafer loading / unloading and wafer identification.

[0110] Part II FIG. 6A is a diagram of a first system 2100 that can be employed in connection with the inspection of a sample using second harmonic generation. Alternative systems 2100' and 2100'' are shown in FIGS. 6B and 6C. Each system includes a primary laser 2010 for directing a primary beam 2012 of electromagnetic radiation at a sample wafer 2020, which is held by a vacuum chuck 2030. The chuck 2030 is set on an X-Y stage and optionally also has a rotational stage for positioning a sample site 2022 of the entire wafer relative to the position at which the laser is directed. The beam 2014 of radiation reflected by the detector 2040 includes an SHG signal. The detector can be any of a photomultiplier tube, a CCD camera, an avalanche detector, a photodiode detector, a streak camera, a silicon detector. The sample site 2022 can include one or more layers. The sample site 2022 can be composed of a composite substrate including at least two layers. The sample site 2022 can include an interface between two different materials (e.g., between two different semiconductor materials, between two different doped semiconductor materials, between a semiconductor and an oxide, between a semiconductor and a dielectric material, between a semiconductor and a metal, between an oxide and a metal, between a metal and a metal, or between a metal and a dielectric).

[0111] Also common to each embodiment is the inclusion of one or more shutter-type devices 2050. These are employed as will be described in connection with the following methodology. The type of shutter hardware used depends on the time frame during which the laser radiation is blocked, discarded, or otherwise kept away from the sample site.

[0112] To obtain a very short blocking time (i.e., switching times on the order of 10 to the minus 9th power seconds to 10 to the minus 12th power seconds), electro-optical blocking devices such as Pockel cells and Kerr cells are used. For longer blocking time intervals (e.g., about 10 to the minus 5th power seconds or more), mechanical shutters or flywheel chopper type devices are employed.

[0113] However, with electro-optical blocking devices, a wider range of materials can be tested according to the following method. To resolve time-dependent signal counting, a photon counting system 2044 that can be discretely gated at very small time intervals, typically on the order of picoseconds to microseconds, can be included.

[0114] Hardware for pushing the method into a faster time frame is conceivable. That is, as shown in FIG. 6C, the system(s) can include delay line hardware 2060. Beam splitting and switching (or shutter on / off) between a corresponding number of time-delayed interrogation events for multiple set time delay lines is possible. However, a variable delay line may be preferred as providing a single solution for multiple transient charge decay interrogation events on a time frame from immediately after the pump pulse (although in many methodologies only a delay of 10 to the minus 12th power seconds may be required) to tens of nanoseconds. Using a slower repetitive kilohertz laser, the desired delay time may reach the microsecond region. And such hardware is uniquely suitable for implementing the methodology in question (such methodology and hardware have both been considered unknown heretofore), but may also be used for other applications.

[0115] In the embodiment shown in FIG. 6C, the beam 2012 from the laser 2010 can be split into two optical paths by the beam splitter 2070. The beam splitter 2070 can split the beam 2012 unevenly between the two optical paths. For example, 70% of the energy of the beam 2012 can be directed along the first optical path (e.g., as beam 2016), and 30% of the energy of the beam 12 can be directed along the second optical path (e.g., as beam 2018). As another example, 60% of the energy of the beam 2012 can be directed along the first optical path, and 40% of the energy of the beam 2012 can be directed along the second optical path. As yet another example, 80% of the energy of the beam 2012 can be directed along the first optical path, and 20% of the energy of the beam 2012 can be directed along the second optical path. The beam splitter 2070 can be composed of a dielectric mirror, a splitter cube, a metal-coated mirror, a pellicle mirror, or a waveguide splitter. In an embodiment where the beam 2012 includes an optical pulse, the beam splitter 2070 can include an optical component having a negligible amount of spreading that splits the beam 2012 into two optical paths so that the optical pulse does not spread. As shown by the double arrow in FIG. 6C, the path of the "investigation" beam 2016 taken out from the beam splitter 2070 from the primary beam 2012 can be lengthened or shortened to change its arrival timing relative to the "pump" beam 2018, where each of the beams is shown to be directed or aimed by various mirror elements 2072. Another approach (described above) uses an optical delay component and / or an optical fiber in other optical paths (e.g., as presented in U.S. Patent No. 6,819,844, which is hereby incorporated by reference in its entirety for such description).

[0116] The output from detector 2040 and / or photon counting system 2044 can be input into electronic device 2048 (see, e.g., FIGS. 6A and 6B). Electronic device 2048 can be a computing device, computer, tablet, microcontroller, or FPGA. Electronic device 2048 includes a processor or processing electronics that can be configured to execute one or more software modules. In addition to executing an operating system, the processor can be configured to execute one or more software applications, including a web browser, phone application, email program, or any other software application. Electronic device 2048 can implement the methods discussed herein by executing instructions contained in a machine-readable non-transitory storage medium such as RAM, ROM, EEPROM, etc. Electronic device 2048 can include a display device and / or a graphical user interface for interacting with a user. Electronic device 2048 can communicate with one or more devices via a network interface. The network interface can include a transmitter, receiver, and / or transceiver that can communicate via a wired or wireless connection.

[0117] Another potential aspect of system 2100'' relates to how the initial beam splitter operates. That is, the split can be unequal (e.g., 70 - 30%, 80 - 20%, 60 - 40%, or any range in between, e.g., between 60 - 90% in one path and between 40 - 10% in another path, and outside these ranges), sending the majority of the output to the pump beam and a portion to the probe beam. For example, it can be split 60 - 70% and 40 - 30% for the pump and probe respectively, 70 - 80% and 30 - 20% for the pump and probe respectively, 80 - 90% and 20 - 10% for the pump and probe respectively, or 90 - 99.999% and 10 - 0.001% for the pump and probe respectively. In different embodiments, for example, the probe beam can be between 0.001% and 49.99% and the pump beam can be between 50.001% and 99.999%. The sum of the two beams is 100% or approximately so. The split may also be determined by a particular material system that is characterized in some cases. The (at least partial) value of doing so would be to facilitate, as will be described later, a method as shown in FIGS. 10 and 11 in which the output included in the SHG procedure following the material charge is desirably reduced or minimized. Yet another aspect is to incident the pump beam and the probe beam at different angles. Such an approach facilitates separately measuring the SHG responses of the pump and the probe. In such a case, two detectors can be advantageously employed, one for each reflected beam path.

[0118] Various other optional optical components distinguish the illustrated embodiments. For example, embodiments 2100 and 2100' are shown including a dichroic reflective or refractive filter 2080 for directly and selectively passing the SHG signal coaxial with the reflected radiation from laser 2010. Alternatively, a prism can be employed to distinguish the weak SHG signal from the much stronger reflected primary beam. However, when using a prism, it has been found to be very sensitive to misalignment, so it is desirable to use a dichroic system as described above. Other options include the use of diffraction gratings or pellicle beam splitters. As shown in system 2100, an optical bundle 2082 of focusing and collimating / collimation optics can be provided. As shown in system 2100', a filter wheel 2084, zoom lens 2086 and / or polarizer 2088 can be employed in the system(s). Also, an angular (or arcuate) rotational adjustment (accompanied by corresponding adjustments of detector 2040 and in-line optics) as shown in system 2100' may be desirable. An additional radiation source 2090 (either a laser as shown emitting a directed beam 2092, or a UV flash lamp emitting a divergent pulse or an optically collimated or focused pulse 2094) can also be incorporated into the system(s) to provide features as described above in connection with the section I entitled "Pump and Probe Type SHG Technology" of U.S. Provisional Application No. 61 / 980,860, filed Apr. 17, 2014, entitled "Wafer Measurement Techniques", and / or initial charging / saturation in the following methods.

[0119] In these systems, the laser 10 can operate at a peak output between about 10 kW and 1 GW in a wavelength range between about 700 nm and about 2000 nm, but is supplied with an average output of less than about 100 mW. In various embodiments, an average output between 10 mW and 10 W is sufficient. An additional light source 2090 (whether another laser or a flash lamp) can operate in a wavelength range between about 80 nm and about 800 nm that supplies an average power between about 10 mW and 10 W.

[0120] Regarding other system options, since the SHG signal is weak compared to the reflected beam that generates it, it may be desirable to improve the signal-to-noise ratio of the SHG count. The improvement becomes even more useful when the gate time of the photon count is shortened in the blocking and / or delaying processes described herein. One way to reduce the noise that can be employed is to actively cool the detector. Cooling can reduce the number of false positive photon detections that occur randomly due to thermal noise. This can be done using cryogenic fluids such as liquid nitrogen and helium, or solid cooling using Peltier elements. Other improvements include the use of an MBC (Marx Bank Circuit) related to the shutter speed.

[0121] These improvements are applicable to any of the systems of FIGS. 6A - 6C. Similarly, any or all of the features described above in relation to systems 2100 and 2100' may be incorporated into system 2100''. In fact, a mix and match of features and components is conceivable between all systems.

[0122] Such a system that performs the measurement of the object enables various determinations that were previously impossible by using techniques related to laser blocking and / or delay. FIG. 7 shows a process map or decision tree 2200 representing such possibilities. That is, the so-called detected problem 2210 can be analyzed between a defect 2220 (an extended defect such as a bond void or dislocation, crystal-originated particle (COP), etc.) and a contaminant 2230 (a point defect or a cluster-like copper-containing substance or other metal, etc.). Regarding the defect, a determination of the defect type 2222 and / or defect quantification 2224 (e.g., regarding density or degree) can also be made. Regarding the contaminant, a determination of the contaminant species or type 2232 and / or contaminant quantification 2234 can be made. Such analysis and species identification between the defect and the contaminant can be performed in relation to determining the charge carrier lifetime, trap energy, trap capture cross-section, and / or trap density, and then comparing these with the values in a lookup table or database. Essentially, these tables or databases contain a list of the properties of the material characterized by the target method, and then the properties described in the table or database entry corresponding to a specific defect or contaminant are collated.

[0123] The trap capture cross-section and trap density may optionally be observed in relation to the detected charge transfer rate. Regarding the determination of the charge carrier lifetime and trap energy, the following equations based on the research of I. Lundstrom serve as a guide.

Equation

[0124] Here, τ is the tunneling time constant of the tunneling mechanism of trap discharge, φr represents the trap energy, Eox represents the strength of the electric charge filed at the interface, and the remaining equation variables and context are described in I. Lundstrom, JAP, v.43, n.12, p.5045, 1972, and this subject is incorporated in its entirety by reference. Further modeling and calculation options can be understood by reference to the section III entitled "Temperature Controlled Measurements" of U.S. Provisional Application No. 61 / 980,860, filed on April 17, 2014, entitled "Wafer Measurement Techniques", which is incorporated herein in its entirety by reference.

[0125] In any case, the decay curve data obtained from the examination of the target sample can be used to determine the parameters of trap energy and charge carrier lifetime by using physical models and related mathematics. A representative set of curves 2300, 2300' as depicted in FIGS. 8A and 8B can be calculated from the above equations (where FIG. 8B emphasizes or enlarges a portion of the data from FIG. 8A).

[0126] These curves show the relationship between the time constant (vertical axis) for different traps or barrier energies and the dielectric thickness (horizontal axis). The vertical axis includes an ultra-fast time scale up to nanoseconds (1E-9 seconds). The horizontal axis is the tunneling distance (or dielectric thickness, both terms are generally equivalent in this example). Different curves are straight lines for a constant barrier energy. For example, in FIG. 8B, if the dielectric thickness is 40 angstroms, electrons trapped in a trap with a barrier energy of 0.7 eV energy depth exhibit a detrapping time constant of approximately 1E-5 seconds.

[0127] By further advancing the modeling with the Poisson / transport solver using the lifetime of charge carriers and known trap energies, the trap density in MOS-like structures and more special devices can be determined. Specifically, the optical injection current by femtosecond optical pulses induces a burst of charge carriers reaching the conduction band of the dielectric. The average value of this current is related to the carrier concentration and its lifetime in that region. The E-field across the interface is a surrogate when SHG measures these phenomena.

[0128] In the plot of FIG. 8A, it is observed that for traps with an energy of about 3 eV, an oxide of 20 angstroms has a discharge time constant of 1 msec (see dashed line). As shown in FIG. 8B (see highlighted box), an observable current flows between 1 μsec and about 1 msec, and then all the current disappears.

[0129] The decay curves discussed in this application can be the product of multiple processes (such as charge relaxation, charge recombination, etc.) from traps with different energies and different relaxation / recombination time constants. Nevertheless, in various embodiments, the decay curve can generally be represented by the exponential function f(t)=Aexp(-λt)+B. Here, A is the decay amplitude, B indicates the baseline offset constant, and λ indicates the decay constant. This general exponential function can be used to roughly characterize the "degree of decay" from the experimentally obtained decay data curve. In various embodiments, the half-life t1 / 2, the average lifetime τ, and the decay constant λ can be used to characterize the degree of decay of the decay curve (obtained experimentally or by simulation). For example, the parameters A, B, λ can be obtained from the experimentally obtained decay data points as described later. Next, the average lifetime τ can be calculated from the parameters A, B, and λ using the theory of radioactive decay as a method to set a benchmark for what is qualitatively called partial decay or complete decay. For example, in some embodiments, τ is given by the formula (t 1 / 2 ) / (ln(2)).

[0130] In various embodiments, the charge state can be considered to have completely decayed after a time span of three average lifetimes τ, which corresponds to a decay from full saturation to ~95%. A partial decay can be represented by a signal after a certain number of average lifetimes τ have elapsed.

[0131] In operation, the system determines parameters (e.g., carrier lifetime, trap energy, trap cross - sectional area, charge carrier density, trap charge density, carrier injection threshold energy, charge carrier lifetime, charge accumulation time, etc.) point - by - point for a part of the wafer (e.g., die - size portion) or the entire wafer, at least partially based on the methodology of interest. The entire wafer (depending on the desired material, surface area, and scan density) can often be scanned in less than about 10 minutes, and these parameters are determined for each scanned point. In various embodiments, a location on the wafer can be scanned at time intervals between about 100 milliseconds and about 3 seconds. For example, a location on the wafer can be scanned in about 950 milliseconds.

[0132] A matrix of data containing the spatial distribution of the determined parameters can be plotted as a heat map or contour map, individually color - coded for each parameter, as a means of quantitative inspection, feedback, and presentation. FIG. 9 shows one such map 2400. This shows how a defect 2402 is depicted. However, it is also possible to show any of the more refined themes of FIG. 7. Once quantitative data is obtained, providing such an output is simply a matter of changing the code of a plotting program / script.

[0133] Such information and / or other information dealt with below can be displayed on a computer monitor or a dedicated system display and / or recorded on a digital medium for later reference or use in analysis. Further, each wafer spatial distribution can be cross-correlated by referring to ellipsometry data to correct for variations in layer thickness and can also be cross-calibrated with independent contamination characteristic data obtained, for example, by total reflection fluorescence X-ray (TXRF), time-of-flight secondary ion mass spectrometry (TOF-SIMS), etc. By comparing these initial or corrected spatial distributions with the spatial distribution from a wafer known to be within specifications, it is possible to determine whether there are defects in the sample in question or whether there are problematic features that require further inspection. However, in general, it is desirable to calibrate low-cost SHG and other methods in combination with, in comparison with, or in combination with a slow and expensive direct method such as TXRF.

[0134] Until the tool is properly calibrated so that it can autonomously flag wafers, human judgment may initially be employed (e.g., when inspecting the generated heat map 2400) in determining what constitutes an acceptable or unacceptable wafer. In a well-characterized process within a factory, human judgment is required only to determine the root cause of systematic yield problems based on the characteristics of the flagged wafers.

[0135] However, FIG. 10 provides a plot 2500 showing an aspect of a first method of the present specification that can be used in making such a determination. This method, like other methods discussed and illustrated below, relies on characterizing the SHG response by a plurality of shutter blocking events in which the interrogation laser is gated for a fixed time.

[0136] In this first example, a portion of the sample to be investigated is charged (typically by a laser) until saturation. In this example, a single light source is used to generate the pump beam and the probe beam, although in other embodiments separate pump and probe light sources can be used. Meanwhile, the SHG signal can be monitored. The saturation level can be determined by observing the asymptotic behavior of the SHG signal intensity related to the material characterization and / or the charging (Ich). When saturation is reached (or after reaching it), the electromagnetic radiation from the laser (pump beam) is blocked from the sample section. The laser (probe beam) is gated for a selected time (tbl1). After the gating is stopped, SHG intensity measurement (Idch1) is performed with the laser (probe beam) illuminating the surface, and the decay of the charge at the first discharge point is observed. After charging the material portion (with the pump beam) to saturation again over a certain time (tch), a second blocking is performed at a time (tbl2) different from the first time in order to identify another point on the composite decay curve. When the blocking of the laser (probe beam) is lifted, the SHG signal intensity (Idchs2) is measured again. This decreased signal indicates the decay of the charge during the second gating event or the blocking interval. When charged again to saturation by the laser (pump beam), a third blocking is performed at a different timing (tbl3), and SHG interrogation and signal intensity measurement (Idch3) are performed for the third measurement of the charge decay with respect to the SHG intensity.

[0137] In the above example, the sample is charged to the saturation level, although in other examples the sample can be charged to a charge level below saturation. In the above example, the three blocking times tbl1, tbl2, and tbl3 are different, although in other examples the three blocking times tbl1, tbl2, and tbl3 can be the same. In various embodiments, the sample can first be charged to a charge level, and the SHG intensity measurements (Idch1), (Idch2), and (Idch3) can be obtained at different time intervals after the first charging event.

[0138] As described above, these three points (corresponding to Idch1, Idch2, and Idch3) can be used to construct a composite charge decay curve. In this specification, it is called a "composite" curve in the sense that its components are derived from multiple related events. Also, further repetitions can be employed, such as adopting four or more block-detection cycles (the possibility of using different gating times to generate more decay curve data points, or using the same correlation timing to confirm the certainty about the selected points and / or remove errors from the measured values), although it is also possible to adopt only two such cycles. Meaningful decay curve characteristics cannot be obtained from a single decay-related data point, but some usefulness can be obtained by defining a straight line that can model or extrapolate a curve from two data points, and fitting an exponential decay requires three or more points for a more accurate approximation. Put another way, a simple (e.g., not stretched by dispersive transport physics) decay dynamics has the general form Measurable(t) = M0*exp(-t / tau), and to determine the two unknown parameters M0 and tau, at least two points are required assuming this simple dynamics. For dispersive (i.e., non-linear) dynamics, when n points are measured, it is desirable to measure as many points as possible to extract (n - 1)th order correction parameters and apply a model suitable for that order of approximation. Also, that series of measurements must be made for different electric fields (E) to make the tau assigned to certain defects actually practical and accurate.

[0139] The above method can provide a dynamic curve of parameter versus time (such as interface leakage current or occupied trap density versus time) by obtaining measured values at several points in time. The time constant (τ) can be extracted from the dynamic curve of parameter versus time. This time constant can be attributed to a time constant characteristic of certain defects.

[0140] In any case, by obtaining SHG data while saturating the material with an interrogation (or probe) laser (as in the examples), data that depends on attenuation can be obtained. However, charging does not necessarily reach saturation (e.g., as described above). Also, it is not necessary to perform the measurement before the charging laser is blocked. Furthermore, charging is not necessarily performed with the interrogation / probe laser (see, for example, the optional pump / probe methodology cited above).

[0141] Nevertheless, after performing the targeted test on one sample site, the sample material is typically moved or indexed to position another part for the same (or similar) test. In this way, as described above, when scanning the entire wafer, multiple parts, or all parts of the sample material can be interrogated and quantified.

[0142] Plot 11 and Plot 2600 show an alternative (or complementary) approach in Plot 2600 for obtaining data related to charge decay by scanning. In this method, after charging to saturation, continuous (or at least semi - continuous) discharge over multiple blocking time intervals (tbl1, tbl2, tbl3) is investigated by laser pulses from an interrogation laser or probe laser that measure different SHG intensities (Idch1, Idch2, Idch3). The intensity and / or frequency of the laser pulses from the interrogation / probe laser are selected such that the average output of the interrogation / probe laser is reduced, while avoiding recharging of the material during the blocking intervals and obtaining a reasonable SHG signal. For this purpose, at least 1 - 3 laser pulses can be applied. When thus reduced (in number and / or output), material excitation due to the interrogation or probe laser pulse is either ignored or accounted for by calibration and / or modeling.

[0143] In various embodiments, another pump source can be used for charging. However, in some embodiments, a probe beam can be used to charge the sample.

[0144] In any case, the delay between pulses may be the same or adjusted, taking into account the expected transient charge decay profile or for other practical reasons. Similarly, although the delay has been described above in terms of the terms "gating" or "blocking", it should be understood that, as described above in connection with FIG. 6C, the delay may be generated using one or more optical delay lines. The same is true for the blocking / gating described in connection with FIG. 10.

[0145] Furthermore, as described above, the method of FIG. 11 can be implemented by varying the blocking or delay time or the number of events. Also, the SHG signal may or may not be measured during the charge up to saturation. In any case, the method of FIG. 11 can be implemented such that the last gating period brings the SHG signal to zero (as shown). Confirmation of this can be obtained by repeating the method at the same location in the mode of measuring the charging intensity (Ich), or by observing only the SHG signal in the (re)charging up to saturation.

[0146] Figures 12A-12E are useful with respect to the manner in which the target hardware is used to acquire data points related to attenuation. FIG. 12A provides a chart 2700 showing a series of laser pulses 2702 in which intermediate or alternating pulses are blocked by shutter hardware (e.g., as described above) in a so-called "pulse picking" approach. Over a given time interval, it is possible to pass individual pulses (shown as solid lines) and block other pulses (shown as dashed lines). FIG. 12B provides a chart 2710 showing the manner in which the resolution of the gating technique for SHG surveys can be limited by the repetition (rep) rate of the probe laser. Specifically, when an attenuation curve such as attenuation curve 2712 is shown, it is possible to resolve the time delay profile with the blocking of every other pulse using a pulsed laser illustrated to operate on the same time scale as in FIG. 12A. However, in such a situation, it is not possible to resolve or observe shorter curves 2714. Thus, the use of an optical delay stage can provide additional utility.

[0147] Therefore, chart 2720 in FIG. 12C shows (graphically and in text) how the introduction of blocking and delay can provide a useful overlapping region with respect to the reference time related to the charging of the sample, from the perspective of the decay time of the curve with respect to the repetition rate of the laser. It also shows how there exists a short time range in which the decay curve can be examined by the delay stage only, and a long time range that becomes practical by blocking the pumping and / or probing beam only. FIGS. 12D and 12E further show the usefulness of an apparatus combining block / delay. Chart 2730 shows an exemplary SHG signal generated by individual laser pulses 2702. With only the delay stage, by varying the optical delay, only the range (X) between such pulses can be examined. In contrast, in a system combining a delay stage with blocking or shutter means such as a chopper, shutter, modulator, etc., additional usefulness over the range (Y) may be achieved. As shown in chart 2740, such a system can measure the decay curves (and their associated time constants) in the range from one pulse time to several pulse times.

[0148] FIGS. 12D and 12E further show the usefulness of an apparatus combining block / delay. Chart 2730 shows an exemplary SHG signal generated by individual laser pulses 2702. With only the delay stage, by varying the optical delay, only the range (X) between such pulses can be examined. In contrast, in a system combining a delay stage with blocking or shutter means such as a chopper, shutter, modulator, etc., additional usefulness over the range (Y) may be achieved. As shown in chart 2740, such a system can measure the decay curves (and their associated time constants) in the range from one pulse time to several pulse times.

[0149] FIG. 13 is a plot 2800 showing an embodiment of a third method. This embodiment is similar to that of FIG. 11, except that the material is charged with a laser or other electromagnetic radiation source and then the application of laser radiation to the sample is blocked or otherwise stopped, thereby allowing the discharge, after which the discharge currents (Jdch1, Jdch2, Jdch3) are measured at time intervals. This approach provides an evaluation of the mobile carrier lifetime in the substrate by the instant at which the e-h-plasma in the substrate decays and the discharge current begins to be visible, and thus provides an important physical parameter of the wafer. Also, after the carrier lifetime is determined, the discharge current is interpreted for its time dependence (i.e., the dynamics regarding the decay of the charge) in the same way as obtained by SHG sensing of the discharge charge.

[0150] Using various embodiments, time constants (e.g., for decay) having a range of values can be measured. For example, the time constant can be between 0.1 femtosecond and 1 femtosecond, between 1 femtosecond and 10 femtoseconds, between 10 femtoseconds and 100 femtoseconds, between 100 femtoseconds and 1 picosecond, between 1 picosecond and 10 picoseconds, between 10 picoseconds and 100 picoseconds, between 100 picoseconds and 1 nanosecond, between 1 nanosecond and 10 nanoseconds, between 10 nanoseconds and 100 nanoseconds, between 100 nanoseconds and 1 microsecond, between 1 nanosecond and 100 microseconds, between 100 microseconds and 1 millisecond, between 1 microsecond and 100 microseconds, between 100 microseconds and 1 second, between 1 second and 10 seconds, or between 10 seconds and 100 seconds, or larger or smaller than that. Similarly, for example, the time delay (Δ) between the probe and the pump (or the pump and the probe) can be, for example, between 0.1 femtosecond and 1 femtosecond, between 1 femtosecond and 10 femtoseconds, between 10 femtoseconds and 100 femtoseconds, between 100 femtoseconds and 1 picosecond, between 1 picosecond and 10 picoseconds, between 10 picoseconds and 100 picoseconds, between 100 picoseconds and 1 nanosecond, between 1 nanosecond and 10 nanoseconds, between 10 nanoseconds and 100 nanoseconds, between 100 nanoseconds and 1 microsecond, between 1 nanosecond and 100 microseconds, between 100 microseconds and 1 millisecond, between 1 microsecond and 100 microseconds, between 100 microseconds and 1 second, between 1 second and 10 seconds, between 10 seconds and 100 seconds. Values outside these ranges are also possible.

[0151] When providing a system suitable for implementing the method of FIG. 13, various physical approaches can be taken, and this method can be modified in particular in the same way as those described above. Two such approaches are shown in FIGS. 14A and 14B.

[0152] Systems 2900 and 2900' each use gate electrodes 2910 and 2920 made of a conductive material that is transparent in the visible light region. Such electrodes may contact the wafer 2020 being inspected, but this is not necessary as long as they are separated by a minimal distance. In various embodiments, the electric field in the dielectric can be estimated by extracting electrode-dielectric-substrate structure parameters using an AC measurement of the capacitance-voltage curve (CV curve). The CV curve measurement is performed using a standard CV measurement setup available on the market and connecting it to a material sample of the target tool (for example, the applied voltage provides an electric field in the dielectric between about 0.1 MV / cm and about 5 MV / cm). The wafer is held on a conductive chuck 2030 that can provide electrical substrate contact. As another alternative structure for the gate electrode, it is conceivable to form an ultrathin Au film or Al film on glass with a thickness of 10 - 30 Å, but in this case, the sensitivity may decrease due to the absorption of some photons by the thin semi-transparent metal layer.

[0153] However, electrodes 2910 and 2920 do not exhibit significant absorption issues (although there may be calibration-based refractive considerations or other ways to explain in the system). These electrodes are composed of a transparent conductor gate layer 2930 made of materials such as ZnO, SnO, etc., which is connected to electrical contact 2932. This structure may include an anti-reflection top coat 2934. The gate layer 2930 may be provided on a transparent carrier 2936 made of a dielectric (SiO2) having a thickness (Dgc) as shown in the figure. In various embodiments, the transparent carrier is similar to that described in the section titled "Field Bias SHG Measurement" of US Provisional Application No. 61 / 980,860, filed on April 17, 2014, titled "Wafer Measurement Techniques", and is an insulator used as a gate for non-contact electrodes that can employ, for example, capacitive coupling to perform electrical measurements. When the wafer is charged by incident laser radiation, the electric field across one or more of its interfaces changes, and the layers of the wafer should capacitively couple to the plates of the electrodes, similar to a plate capacitor. The charging of the electrodes involves the movement of charge carriers measured as current.

[0154] Dgc is calibrated by measuring the CV curve on the semiconductor substrate with a non-invasive approach and is used in the electric field (E) calculation when the applied voltage is known. The negligible gap distance between the gate and the sample can be an air gap. Alternatively, instead of separating the electrodes by an air gap or a dielectric, the electrodes can be brought into direct contact with the sample. Thus, in various embodiments, normal CV or IV measurements can be performed.

[0155] Alternatively, considering that the refractive indices of water and SiO2 are close, filling the gap with deionized water may help reduce boundary layer reflection without adverse effects (or at least without being unaddressable). Deionized water (or cleanroom-grade water) can maintain the cleanliness around the electrically sensitive and chemically pure substrate wafer. Deionized water has lower conductivity than normal water.

[0156] In FIG. 14B, related structures are shown in which the structure of the carrier or gate holder 2938 is different. Here, it is configured as a ring optimally formed by etching away the central part and leaving material around the electrodes so as to be produced using MEMS technology. However, in any case, since there is a large non-occupied area through which the laser radiation and SHG radiation must pass, it is considered particularly desirable to fill this with deionized water as described above.

[0157] Nevertheless, in the overall structure of the electrodes 2910, 2920, each embodiment is typically stationary with respect to the radiation that excites the materials in use. Before and after use, the electrode structure(s) can be housed by a robotic arm or carriage assembly (not shown).

[0158] As described above, in various embodiments, the electrodes make direct contact with the wafer and perform electrical measurements such as measuring the flow of current. However, methods of measuring current non-contact can also be used, such as using electrodes capacitively coupled to the sample, for example.

[0159] The systems and methods described herein can be used to evaluate the characteristics of a sample (e.g., a semiconductor wafer or a portion thereof). For example, the systems and methods described herein can be used to detect defects or contaminants in a sample, as described above. The systems and methods described herein can be configured to characterize a sample during the fabrication or production of a semiconductor wafer. Thus, the present systems and methods can be used along a semiconductor manufacturing line within a semiconductor fabrication facility. The systems and methods described herein can be integrated into a semiconductor manufacturing / production line. The systems and methods described herein can be incorporated into a semiconductor manufacturing line having an automated wafer handling function. For example, the system can include an attached equipment front end module (EFEM) that accepts a wafer cassette such as a front opening unified pod (FOUP). Each of these cassettes is loaded into the machine by a human operator or by an automated cassette handling robot that moves the cassette from process to process along the fabrication / production line.

[0160] In various embodiments, when a cassette is loaded into the EFEM, the FOUP can be opened, a robotic arm can select an individual wafer from the FOUP, move through an automatically actuated door included in the system, and into an optically sealed process box, and be moved onto a bias-compatible vacuum chuck. The chuck may be designed to complementarily mate with the robotic arm such that the robotic arm can place the sample thereon. At some point in this process, the wafer can be held up to a scanner to identify unique laser marks.

[0161] Accordingly, a system configured to be integrated into a semiconductor fabrication / assembly line can have an automatic wafer handling function from a FOUP or other type of cassette, integration with an EFEM as described above, a chuck designed to be compatible with robotic handling, an optically sealed automatic door that opens and closes to allow movement of the robotic wand / arm, and software signals to the EFEM for wafer load / unload and wafer identification. Part III

[0162] Figures 15A and 15B show suitable hardware for use in SHG systems and methods as described in detail in Section I entitled "Pump and Probe Type SHG Measurements" of U.S. Provisional Application No. 61 / 980,860, filed Apr. 17, 2014, entitled "Wafer Measurement Techniques". Options for other systems and methods are presented in Section II entitled "Charge Decay Measurement Systems and Methods" of U.S. Provisional Application No. 61 / 980,860, filed Apr. 17, 2014, entitled "Wafer Measurement Techniques", and relate to, for example, an intermediate optical system, inclusion of optical delay line(s), and optional electrode functionality.

[0163] As shown, system 3000 includes a primary or probe laser 3010 for directing an electromagnetic radiation interrogation beam 3012 at a sample wafer 3020 held by a vacuum chuck 3030. As shown in FIG. 15B, chuck 3030 includes an x-y stage and, optionally, a rotary stage for positioning sample site 3022 across the wafer relative to the location at which the laser is directed. The x-y stage enables scanning of multiple wafer surface sites or locations 3022 without moving other hardware. The rotary stage optionally enables evaluation of the effect of crystal structure on SHG. Further optional features, aspects and / or uses of chuck 3030 are presented elsewhere in this application under separate headings. Sample site 3022 can include one or more layers. Sample site 3022 can comprise a composite substrate including at least two layers. Sample site 3022 can include an interface between two dissimilar materials (e.g., between two different semiconductor materials, between two different doped semiconductor materials, between a semiconductor and an oxide, between a semiconductor and a dielectric material, between a semiconductor and a metal, or between an oxide and a metal).

[0164] When system 3000 is in use, a beam 3014 of reflected radiation directed at detector 3040 includes an SHG signal. Detector 3040 can be any of a photomultiplier tube, a CCD camera, an avalanche detector, a photodiode detector, a streak camera, and a silicon detector. System 3000 can also include one or more shutter-type devices 3050. The type of shutter hardware used depends on the time frame during which the laser radiation is blocked, discarded, or otherwise moved away from sample site 3022. Electro-optic shutoff devices such as Pockel cells and Kerr cells can be used to obtain very short shutoff times (i.e., on the order of 10 to the minus 9th to 10 to the minus 12th seconds).

[0165] When the blocking time interval is long (e.g., 10 to the minus fifth power seconds or more), a mechanical shutter or a flywheel chopper type device can be employed. However, by using an electro-optical blocking device, it becomes possible to test a wider range of materials according to the following method. To resolve time-dependent signal counting, a photon counting system 3044 can be adopted that can discretely gate very small time intervals, typically on the order of picoseconds to microseconds. For a faster time frame, one or more optical delay lines can be incorporated as described above.

[0166] System 3000 can include an additional electromagnetic radiation source 3060, also referred to as a pump source. In various embodiments, the radiation source 3060 can be a laser depicted as emitting a directed beam 3062, or a UV flash lamp that emits a diverging or optically collimated pulse 3064. In the case of a laser light source, its beam 3062 can be parallel to beam 3012 (e.g., directed by additional mirrors or prisms, etc.). The output wavelength of the light source 3060 can be between about 80 nm and about 1000 nm. Using shorter wavelengths in this range (e.g., less than about 450 nm) can drive charge excitation with fewer photons and / or lower peak intensity than longer wavelengths.

[0167] In the case of a flash lamp, the energy per flash and the output level during the flash can depend on the material of the substrate. For a fully depleted silicon-on-insulator (FD-SOI), a flash lamp that generates a total energy of 1 J to 10 kJ per flash would be appropriate. However, a pulsed or constant UV light source would also be viable. An important factor in the characteristics and use of the pump is that charge carriers are injected into the dielectric of the material being investigated. Manufacturers of suitable flash lamps include Hellma USA, Inc. and Hamamatsu Photonics K.K.

[0168] When a laser is employed as the light source 3060, it may be any of the pulsed laser light sources with nanoseconds, picoseconds, femtoseconds or longer pulses. It may also be a continuous solid-state laser. In various embodiments, the pump light source is wavelength-variable. Commercially available options for wavelength-variable lasers include the Velocity and Vortex tunable lasers from Spectra Physics. Also, the solid-state lasers of the LT-22xx series from LOTIS Ltd. are also available as a solution for wavelength-variable solid-state lasers.

[0169] Regardless of whether it is provided as a laser or as a flash lamp, the pump light source 3060 can be selected to have a relatively high average output. This can be from about 10 mW to about 10 W depending on the material being investigated, but more typically is from about 100 mW to about 4 W (again, it is considered to ensure that the charge carrier mobility is induced in such a way that charge carriers are injected into the interface of the material (e.g., dielectric interface), which can be specific to the material). The average output of the pump light source 3060 is selected to be below the optical damage threshold of the material. For example, when the material being investigated has silicon, the pump light source 3060 can be selected to have an average optical output between 1 and 2 W so as not to exceed the optical damage threshold of silicon.

[0170] The probe laser 3010 is a pulsed laser light source with a speed of nanoseconds, picoseconds, femtoseconds or more. Currently, the two commercially available lasers with the required peak output, wavelength, and reliability are the doped fiber and titanium sapphire unit. The VITESSE from Coherent and the MAI TAI laser from Spectra-Physics are examples of suitable titanium sapphire devices. Femtolasers Gmbh and other manufacturers also produce related titanium sapphire devices. Suitable doped fiber lasers are produced by IMRA, OneFive, and Toptica Photonics. Picosecond and / or nanosecond lasers from many manufacturers such as Hamamatsu Photonics can also be optional depending on the substrate material and pump type. The laser 3010 operates in a wavelength range of approximately 100 nm to approximately 2000 nm, with a peak output of approximately 10 kW to 1 GW and an average output of approximately 150 mW or less.

[0171] The system 3000 may employ various other optional so-called "intermediate" optical components. For example, the system 3000 can include a dichroic reflection or refractive filter 3070 for selectively passing the SHG signal coaxial with the radiation directly reflected from the laser 3010 and / or the light source 3060. Alternatively, a prism may be employed to distinguish the weak SHG signal from the much stronger reflected primary beam. However, since the prism method has proven to be very sensitive to misalignment, a dichroic system as mentioned above may be preferred. Other options include the use of diffraction gratings and pellicle beam splitters. An optical bundle 3080 for the focusing optical system and the collimate / column optical system may be provided. Alternatively, a unit or assembly of a filter wheel 3090, a polarizer 3092, and / or a zoom lens 3094 may be employed in the system. Also, angular (or arc-shaped) rotation adjustment (accompanied by corresponding adjustment for the detector) and in-line optical components may be desirable in some cases.

[0172] The output from detector 3040 and / or photon counting system 3044 can be input into electronic device 3048. Electronic device 3048 can be a computing device, computer, tablet, microcontroller, or FPGA. Electronic device 3048 includes a processor that can be configured to execute one or more software modules. In addition to executing an operating system, the processor can be configured to execute one or more software applications, including a web browser, phone application, email program, or any other software application. Electronic device 3048 can implement the methods discussed herein by executing instructions contained in a machine-readable non-transitory storage medium such as RAM, ROM, EEPROM, etc. Electronic device 3048 can include a display device and / or a graphical user interface for interacting with a user. Electronic device 3048 can communicate with one or more devices via a network interface. The network interface can include a transmitter, receiver, and / or transceiver capable of communication, such as, for example, wired Ethernet, Bluetooth®, or a wireless connection.

[0173] For other options, since the SHG signal is weak compared to the reflected beam that creates it, it is desirable to improve the signal-to-noise ratio of the SHG count. As the photon count gate time of the photon counting system 3044 decreases with respect to the gating and / or delay processes described herein, the improvement becomes even more important. One way to reduce noise that can be employed is to actively cool the photon counter. This can be done using cryogenic fluids such as liquid nitrogen or helium or solid cooling using a Peltier device. Other improvements include the use of a Marx bank circuit (MBC) related to the shutter speed. Further, the system 3000 may be incorporated inline within a production line environment. Production line elements preceding or following the system 100 can include any of an epitaxial growth system, a lithography and / or film deposition (CVD, PVD, sputtering, etc.) system.

[0174] In any case, FIGS. 16A and 16B are diagrams of a first set of object-specific chuck hardware that can be employed in the SHG system of interest. The chuck 3030 holds the wafer 3020 by vacuum or other means. The chuck 3030 is conductive and is connected to an output source. Optionally, a capacitance coupling probe 3100 is also connected to the output source 3120. The output source may be computer controlled, or at least its output is adjusted by a computer for timing reasons as summarized above. The probe 3100 may be similarly controlled and / or monitored. It is controlled in the sense of being part of a capacitance circuit attached to the output source 3120. This probe is monitored with the chuck 3030 by a voltmeter to confirm that the voltage is being induced as intended.

[0175] Probe 3100 includes a hole 3102 or port (e.g., 0.2 mm in diameter) in ring 3104 such that light beams 3012, 3014 (investigation beam and reflected SHG beam) can pass through unblocked, and is fixed relative to the optical system so as to move or stay together with the optical elements and remain centered on the sample site 3022 that is (re)positioned when the device surface is scanned. The coupling part (shown as having a positive “+” charge) is disposed near the sample device surface (e.g., within about 1 mm to about 2 mm) but does not make contact. It is supported by a cantilever arm or the like. Probe 3100 may be provided as ring 3104 as shown in FIG. 16B, or may be composed of a larger disk or plate.

[0176] In the example shown in cross-section in FIG. 16B, the wafer 3020 or device surface (including silicon) is separated from the silicon bulk layer by a SiO2 insulator. Thus, as described above, an induced bias to the device surface is necessary, or (at least substantially) because it is electrically insulated or separated from the underlying silicon in contact with the conductive chuck 3030.

[0177] FIGS. 17A - 17C show in detail an electromagnetic chuck 3030 including an electric coil 3130 connected to an output source 3120. In use, the wafer 3020 is placed on and fixed to the chuck 3030. When an alternating current is applied to the coil(s) 3130, an alternating magnetic field is generated in the wafer 3020. This magnetic field induces a potential across the entire wafer 3020 including the device surface. This electric field enables the various modes of SHG investigation described above. Alternatively, a direct current can be passed through the coil 3130 oriented parallel to the chuck 3030 to form a constant magnetic field across the chuck and obtain other effects as described above.

[0178] FIG. 18A shows over time an example (sine wave) of an alternating voltage (V) profile applied to the bulk layer of a substrate. FIG. 18B shows a virtual response to the induced voltage between the device layer and the bulk layer (Vi) of the substrate of the fabricated device. In various embodiments, the substrate can be composed of a silicon wafer or a portion of a semiconductor material. FIG. 19A shows over time an example (square wave) of an alternating voltage (Vo) profile applied to the bulk layer of the substrate. FIG. 19B shows a virtual response to the induced voltage (Vi) between the device and the bulk layer. It should be noted that the voltage input (input) into either FIG. 18A or FIG. 19A can be different from that shown and can be applied in a stepped, sloped, sine wave, or other form.

[0179] More specifically with respect to FIGS. 18A and 18B, as described above, in order to minimize noise and obtain a statistically relevant indicator(s) of SHG intensity as a function of the voltage across the interface, multiple photon counting windows may be desirable. For such purposes, exemplary points A1 and A2 are timed such that the voltage A between the bulk layer and the device layer is the same at both points. This is also the case for exemplary points B1 and B2 at voltage B, and exemplary points C1 and C2 at voltage C. SHG is recorded for voltage A, the count at point A1 is summed with the count at point A2, and further with the counts at points A3, A4, An... within any length of column corresponding to the desired measurement time. The total number of counts measured during this period is divided by the time spanned by this "gate" to obtain the average number of counts per second, enabling the SHG intensity to be plotted as a function of the bulk device voltage A. Using the same method, the measured values of voltage B at points B1 and B2, and B3, B4, Bn... can be obtained in a column of arbitrarily length according to the desired measurement time. The total number of counts measured during this period is divided by the time spanned by this "gate" to obtain the average number of counts per second, allowing the SHG intensity to be plotted as a function of the bulk device voltage B. By dividing the total number of counts measured during this period by the time spanned by this "gate", the average number of counts per second can be obtained, thereby enabling the SHG intensity to be plotted as a function of the bulk device voltage C. Further details regarding the usefulness of SHG intensity as a function of the bias voltage are described in the literature on DC bias, examples of which include "Measurement of Charge Trapping in Irradiated SOI Wafers by Second Harmonic Generation", IEEE Transactions on Nuclear Science, Vol. 51, No. 6, Dec. 2004 and "Optical Probing of Silicon Integrated Circuits Using Electric-Field-Induced Second Harmonic Generation", Applied Physics Letters 88, 114107, (2006), each of which is hereby incorporated by reference in its entirety into this specification.

[0180] More specifically, with respect to FIGS. 19A and 19B, these figures illustrate an example of examining a Silicon-On-Insulator (SOI) device. In this example, the conductive chuck starts in a "neutral" ground state, and the bulk layer and the device layer are at equilibrium potential. At the instant of "A", the voltage applied to the chuck is rapidly changed and this voltage is applied to the conductive bulk layer of the sample. The device layer of the sample is separated from the bulk by a thin buried oxide layer and is not directly connected to the conductor, so an electric potential field, i.e., a voltage, is induced between the device layer and the bulk layer. Between time "A" and time "B", the voltage applied to the chuck does not change. Since the dielectric between the bulk layer and the device layer is not perfect, a leakage current flows between the layers due to the induced potential, and the potential between the bulk layer and the device layer returns to its natural state. By monitoring this electric field spike and decay with SHG, the leakage current can be known. At time "B", the voltage applied to the chuck is returned to ground and the voltage across the interface is reversed.

[0181] The systems and methods described herein can be used for characterizing a sample (e.g., a semiconductor wafer or a portion thereof). For example, the systems and methods described herein can be used to detect defects or contaminants in a sample, as described above. The systems and methods described herein can be configured to evaluate a sample during the fabrication or production of a semiconductor wafer. Thus, the present systems and methods can be used along a semiconductor manufacturing line within a semiconductor manufacturing facility. The systems and methods described herein can be integrated into a semiconductor manufacturing / production line. The systems and methods described herein can be incorporated into a semiconductor manufacturing line with an automated wafer handling function. For example, the system can include an attached front-end module equipment (EFEM) that accepts a wafer cassette such as a front opening unified pod (FOUP). Each of these cassettes is loaded into the machine by a human operator or by an automated cassette handling robot that moves the cassette from process to process along the fabrication / production line.

[0182] In various embodiments, the system can be configured such that when a cassette is attached to the EFEM, the FOUP is opened, a robotic arm selects individual wafers from the FOUP, moves through an automatically actuated door included in the system, and into a light-sealed process box, and moves onto a bias-compensated vacuum chuck. The chuck may be designed to complementarily fit with the robotic arm such that the robotic arm can place the sample thereon. At some point in this process, the wafer can be held up to a scanner to identify unique laser marks.

[0183] Accordingly, a system configured to be integrated into a semiconductor fabrication / assembly line can have an automated wafer handling function from a FOUP or other type of cassette, integration with an EFEM as described above, a chuck designed to be compatible with robotic handling, an automatically actuated light-sealed door that opens and closes to allow movement of the robotic wand / arm, and software signals to the EFEM for wafer loading / unloading and wafer identification.

[0184] Each of Sections I, II, III, and IV of U.S. Provisional Application No. 61 / 980,860, filed Apr. 17, 2014, entitled "Wafer Metrology Technologies," is hereby incorporated by reference in its entirety. Similarly, co-pending patent applications (i) U.S. Patent Application No. 14 / 690,179, filed Apr. 17, 2015, entitled "Pump and Probe Type Second Harmonic Generation Measurements," published as U.S. Publication No. 2015 / 0330908, (ii) U.S. Patent Application No. 14 / 690,256, filed Apr. 17, 2015, entitled "Charge Decay Measurement Systems and Methods," published as U.S. Publication No. 2015 / 0331029, and (iii) U.S. Patent Application No. 14 / 690,251, filed Apr. 17, 2015, entitled "Field Bias Second Harmonic Generation Measurements," published as U.S. Publication No. 2015 / 0331036 are hereby incorporated by reference in their entirety. The PCT Application No. PCT / US2015 / 026263, filed Apr. 16, 2015, entitled "WAFER METROLOGY TECHNOLOGIES" is also hereby incorporated by reference in its entirety. Accordingly, features from the disclosures of any of these documents incorporated by reference may be combined with features described elsewhere herein. Wafer Metrology Based on Four-Wave and Multi-Wave Mixing

[0185] In various aspects, an optical measurement system may use optical signals generated by non-linear optical processes other than SHG, such as four-wave mixing (FWM) and multi-wave mixing (MWM), to determine various properties (e.g., electrical properties, shape, critical dimensions, etc.) of a sample (e.g., a semiconductor device on a sample), as further described in part in U.S. Provisional Application No. 16 / 396,227, filed Apr. 26, 2019, entitled "Electric Field Biased Nonlinear Optical Measurements Using a Corona Discharge Source," the entirety of which is hereby incorporated by reference.

[0186] Four-wave mixing and multi-wave mixing are non-linear optical phenomena in which two or more incident optical beams having the same or different optical frequencies interact with each other as a result of the high-order non-linear susceptibility of the incident non-linear medium, generating an optical signal having one or more optical frequencies different from the optical frequencies of the two or more incident optical beams.

[0187] For example, four-wave mixing occurs when a first incident optical beam having an optical frequency f1 and a second incident optical beam having an optical frequency f2 (e.g., greater than f1) interact with each other as a result of the third-order non-linear susceptibility (χ (3) ) of the non-linear optical medium, generating a four-wave mixing signal component. The four-wave mixing (FWM) signal component may include a third beam having an optical frequency f3 = f1 - (f2 - f1) and a fourth beam having an optical frequency f4 = f2 + (f2 - f1). The optical frequency f3 of the third beam is the difference between twice the optical frequency f1 of the first beam and the optical frequency f2 of the second beam. The optical frequency f4 of the fourth beam is the difference between the optical frequency f1 of the first beam and twice the optical frequency f2 of the second beam. Various optical properties of the four-wave mixing signal component can be measured to determine the properties of the interface region of the semiconductor device. The optical properties of the four-wave mixing signal component may include spectral and / or temporal properties of intensity, frequency, and / or phase.

[0188] Without being bound by a particular theory, the third and fourth beams of the four-wave mixing signal component can be generated as a result of the third-order non-linear susceptibility (3) of the non-linear medium. Additional optical beams may be generated as a result of higher-order non-linear susceptibilities of the non-linear medium, such as (5), (7), etc. The optical properties of the generated additional optical beams can be measured to determine the properties of the interface region of the semiconductor device.

[0189] In some cases, an optical measurement system can detect and acquire the optical properties of one or more optical beams generated as a result of the third - order and / or higher - order nonlinear susceptibilities of a nonlinear medium contained in a sample, and use the optical properties to determine features or characteristics (e.g., material properties, geometric properties, critical dimensions, etc.). In such cases, the one or more optical beams may be composed of four - wave mixing signal components or multi - wave mixing signal components. In some cases, the optical measurement system may generate one or more optical beams by irradiating a sample with two or more incident optical beams. In some examples, the incident optical beams may include pulsed optical beams having different wavelengths. In some cases, the optical pulses of at least one incident optical beam may be delayed with respect to one or more optical pulses. In some cases, the delay between the pulses of two incident optical beams can be varied, and the resulting FWM and MWM signal components can be used to determine the features or characteristics of the sample. Alternatively, or in addition thereto, the system can vary the amount of charge on the sample, and the resulting FWM and MWM signal components can be used to determine the features or characteristics of the sample.

[0190] FIG. 20A shows an aspect of an optical measurement system 7000 configured to obtain the optical properties of an optical beam generated as a result of the third - order and / or higher - order nonlinear susceptibilities of the nonlinear medium of sample 3020. In some aspects, the optical measurement system 7000 can employ corona charging. The system 7000 includes two light sources 7001a and 7001b configured to output optical beams 7007a and 7007b incident on a sample 3020 supported by a chuck 3030, respectively. As described above, the chuck 3030 can hold the sample 3020 by vacuum or other mechanical means. The sample 3020 can be composed of a semiconductor wafer including an interface region. The interface region can include, for example, a semiconductor - oxide junction, a metal - oxide junction, a semiconductor - metal junction, or a junction between two semiconductors having different material compositions and / or doping profiles.

[0191] System 7000 further includes a detection system 7005 configured to receive various optical beams generated as a result of third and higher order nonlinear magnetic susceptibilities of a nonlinear medium. The optical properties of the various optical beams generated as a result of third and higher order nonlinear magnetic susceptibilities of the nonlinear medium can vary, for example, as the surface band bending of sample 3020 is altered as a result of charges deposited on sample 3020 by a corona discharge 3265 from a discharge source 3260 (e.g., a corona gun). In various aspects, the charges deposited by corona discharge 3265 from discharge source 3260 can alter the band bending or various electronic energy levels in the interfacial region of sample 3020.

[0192] In various aspects, one of light sources 7001a and 7001b can comprise a flash lamp or a continuous wave (CW) laser source. In various aspects, one or both of light sources 7001a and 7001b can comprise a pulsed light source (e.g., a pulsed laser light source). For example, one or both of light sources 7001a and 7001b can be configured to output pulses having a duration in the range of from about 1 microsecond to about 1 millisecond, from about 1 nanosecond to about 1 microsecond, from about 1 picosecond to about 1 nanosecond, from about 1 femtosecond to about 1 picosecond, and / or from about 1 femtosecond to about 1 attosecond, or any range between these values. In those aspects of system 7000 where both light sources 7001a and 7001b comprise pulsed light sources, a system can be provided that is configured to introduce a time delay (τ) between the pulses output from light sources 7001a and 7001b. The time delay (τ) between the pulses output from light sources 7001a and 7001b can be made smaller than the time period of the pulse train output from one or both of light sources 7001a and 7001b. In some aspects, the four-wave mixing signal can be measured with respect to the time delay to obtain information about the sample.

[0193] A delay system provided to introduce a time delay (τ) between the pulses output from light sources 7001a and 7001b can be composed of an electronic system integrated with one or both of the light sources 7001a and 7001b that introduces a time offset into the electrical signal driving one or both of the light sources 7001a and 7001b, and a mechanical system (e.g., a mechanical shutter, a flywheel chopper, etc.) that attenuates (e.g., blocks) one or more pulses output from one or both of the light sources 7001a and 7001b. Such a system can be, for example, a Pockels cell or a Kerr cell that attenuates (e.g., blocks) one or more pulses output from one or both of the light sources 7001a and 7001b, or an optical delay line (e.g., an optical fiber delay line, an integrated optical delay, or a free-space delay line including a reflective optical system) disposed in the optical path between one or both of the light sources 7001a and 7001b and the sample 3020, which introduces a time delay (τ) between the pulses output from the light sources 7001a and 7001b. In various aspects, the delay system can be configured to provide a variable time delay (τ) between the pulses output from the light sources 7001a and 7001b.

[0194] In some aspects, the light sources 7001a and 7001b can be configured to output light having the same wavelength (λ) or optical frequency (ω). A four-wave / multi-wave mixing signal generated by incident light having the same wavelength (λ) or optical frequency (ω) is called a degenerate four-wave / multi-wave mixing signal. In some other aspects, the light sources 7001a and 7001b can be configured to output light having different wavelengths (λa and λb) or optical frequencies (ωa and ωb). A four-wave / multi-wave mixing signal generated by incident light having different wavelengths or optical frequencies is called a non-degenerate four-wave / multi-wave mixing signal. In some aspects, the light sources 7001a and 7001b can be configured to change or adjust the wavelength or optical frequency of the output light.

[0195] Light sources 7001a and 7001b can be directed so that light beams 7007a and 7007b are incident obliquely on the region of sample 3020 where the light beams are investigated, as shown in the schematic top perspective view shown in FIG. 20B. In some embodiments, light beams 7007a and 7007b can be incident at different angles of incidence with respect to the normal of the surface of sample 3020. In some embodiments, light beams 7007a and 7007b can be incident at the same angle of incidence with respect to the normal of the surface of sample 3020 as shown in FIG. 20B, but at different azimuth angles. In some embodiments, light beams 7007a and 7007b can be incident not only at different angles of incidence with respect to the normal of the surface of sample 3020, but also at different azimuth angles. The spot sizes of light beams 7007a and 7007b can be configured so that light beams 7007a and 7007b at least partially overlap in the region of sample 3020 being investigated.

[0196] The incident light beams 7007a and 7007b can be specularly reflected from the surface of sample 3020 as reflected light beams 7007ar and 7007br. The four-wave mixing signal components 7007ax3 and 7007bx3 can be detected on either side of the specularly reflected light beams 7007ar and 7007br. The direction of the four-wave mixing signal component is the wave vector of the reflected beams 7007ar and 7007br It can be along the direction of JPEG2025523437000004.jpg65144. The four-wave mixing signal components can be received and detected by one or more detectors (such as photodetectors, photodiodes, photomultiplier tubes, etc.) arranged in the direction along the directions of the four-wave mixing signal components 7007ax3 and 7007bx3. The one or more detectors can use the received four-wave mixing signal components to generate a detected four-wave mixing (FWM) signal (such as an electrical signal). In some cases, additional optical signals 7007ax5 and 7007bx5 generated by the high-order nonlinear susceptibility can also be detected respectively on either side of the reflected beams 7007ar and 7007br. The cross-sections of the reflected beams 7007ar and 7007br, the four-wave mixing signal components 7007ax3 and 7007bx3, and the high-order four-wave or multi-wave mixing signal components 7007ax5, 7007bx5, 7007ax7, and 7007bx7 at the detection surface of the detection system 7005 are shown in Figure 20C. In some cases, the one or more detectors can use the received multi-wave mixing signal components to generate a detected multi-wave mixing (MWM) signal (such as an electrical signal).

[0197] As described above, the surface band bending of sample 3020 is altered as a result of the charge deposited on sample 3020 by corona discharge 3265. In various embodiments, the amount of charge deposited on sample 3020 can be determined by measuring the current induced by the charge deposited on the surface of sample 3020 using an electrometer 3225 (e.g., an electrometer or ammeter) disposed between sample 3020 and electrical ground, as shown in FIG. 20A (e.g., via conductive vacuum chuck 3030). An electronic processor 3295 (e.g., an electronic processor within a control system) can be configured to execute programmable instructions for determining the amount of charge deposited on the surface of sample 3020 by corona discharge 3265 from corona discharge source 3260 based on the output provided by electrometer 3225 that depends on the current between sample 3020 and electrical ground. In various embodiments, electronic processor 3295 can be further configured to control the voltage output from voltage supply device 3220. For example, electronic processor 3295 can be configured to turn off or modify (e.g., decrease or increase) the voltage output from voltage supply source 3220 to corona discharge source 3260. By changing the voltage output from voltage supply source 3220 to corona discharge source 3260, the amount of charge deposited on the surface of sample 3020 by corona discharge 3265 from corona discharge source 3260 can be changed. In some embodiments, electronic processor 3295 can be configured to repeatedly turn on / turn off the voltage supply to corona discharge source 3260. A four-wave mixing signal or a multi-wave mixing signal can be detected and / or measured for different amounts of charge deposited on the surface of sample 3020. The amount of charge deposited on the surface of sample 3020 can be associated with different band bending states. Thus, a four-wave mixing signal or a multi-wave mixing signal can be detected and / or measured for different band bending states. Time-resolved four-wave mixing signals and multi-wave mixing signals are also obtained with respect to different amounts of time delay (τ) between the pulses output from light sources 7001a and 7001b, and different amounts of charge deposited on the surface indicating different band bending states.The obtained time-resolved four-wave mixing and multi-wave mixing signals can be analyzed to obtain information related to the charge dynamics in the region of sample 3020. Alternatively or additionally, the obtained time-resolved four-wave mixing signals and multi-wave mixing signals can be analyzed to obtain information related to the geometric characteristics of the sample (e.g., the critical dimensions of the devices on the sample). In various embodiments, sample 3020 can be repositioned to detect four-wave mixing signals and / or multi-wave mixing signals from another region of sample 3020. The non-contact nature of corona charging and four-wave mixing / multi-wave mixing is particularly beneficial for interface property evaluation as an in-line monitor in semiconductor manufacturing / production lines. Dimension Measurement by Nonlinear Optics

[0198] Semiconductor measurements can include measuring the "critical dimensions" of devices. These critical dimensions include, for example, measuring the width, length, depth of transistors and memory cells, the thickness of the gate oxide, the diameter of contact holes (vias) through the interlayer insulating film, and the like. Due to variations in the production process, even a slight change in any of these dimensions can cause the device's function to degrade or stop working. Therefore, it may be useful to monitor these dimensions during manufacturing to prevent yield and performance problems. Monitoring the production process at the initial stage of device fabrication is particularly beneficial. For example, it may take several weeks to manufacture a complete semiconductor product. If there are defects in the initial part of the production process but they are not detected until the final test, there is a risk that all the products produced during that time will be defective. Therefore, it is beneficial to monitor the initial stage of the production process. Missing a mistake at the initial stage could result in the loss of millions of parts.

[0199] Techniques for measuring device dimensions at the initial stage of the production process include optical approaches and electron beam-based approaches. Two methods for monitoring production of critical device dimensions are critical dimension scanning electron microscopy (CD-SEM) and optical critical dimension (OCD) tools. CD-SEM is a scanning electron microscope specially designed to measure the critical dimension (CD) of semiconductor electronic devices, and optical CD tools (OCD) use the scattering of light from the surface of a semiconductor wafer containing the device to monitor changes in the dimensions of the device during manufacturing. Also, although less frequently used, there are tools such as transmission electron microscopes (TEM) and atomic force microscopes (AFM). Each tool has advantages and disadvantages.

[0200] As device dimensions are shrinking, it is useful to improve the accuracy of measurement tools used to monitor the production process. Furthermore, three-dimensional (3D) shapes are being used that make measurement and monitoring of the production process more difficult. These 3D shapes include FinFET, gate all-around, and nanowire as transistor shapes. NAND memory devices are currently produced by vertically stacking multiple layers of devices. These devices benefit from measurements of the entire stack, including functions buried beneath the surface. Shrinking dimensions and the introduction of 3D complex shapes can pose challenges to current measurement tools.

[0201] The measuring tool ideally should have high sensitivity, accuracy, reproducibility, and reliability, and be fast. Sensitivity refers to how small a change can be detected, such as whether the measuring tool can detect a 5 percent change in dimensions. In the case of a feature of 10 nanometers, the measuring tool would benefit from detecting sub-nanometer dimensional changes. Accuracy can be different from sensitivity. Can the measuring tool distinguish different changes? Problems can occur if the measuring tool cannot distinguish different changes, for example, the width at the top and the width at the bottom of a feature. When many different shape changes result in the same outcome, it becomes ambiguous what is causing the measurement change, making it difficult to monitor the process using that tool. A highly sensitive tool lacking in accuracy may raise alarms for process variations, but many of them may not be important. Instead, a measuring tool that can independently measure different important parameters of a device such that there is a one-to-one correlation between the measurement and the shape change may be advantageous.

[0202] Reproducibility is different from sensitivity and accuracy. When monitoring a production process, it is advantageous if the variations introduced by the measuring tool are much smaller than the process variations being detected. Having a tool that produces different results over time comparable to or larger than the variations of the device being monitored can be disadvantageous. Measuring tools can drift over time due to changes in environmental conditions (such as temperature) or internal components (such as lens fouling). In contrast, a measuring tool is advantageous because it has high reproducibility and the same result can be obtained for the dimensions of the same feature.

[0203] In measurement tools, reproducibility, sensitivity, and accuracy can potentially conflict with each other. For example, in a tool that always produces the same result regardless of the shape of the device, the reproducibility is perfect but the sensitivity is lacking. A tool that can detect any change may be too sensitive to unimportant changes, i.e., changes lacking in accuracy and reproducibility. A useful tool can detect and identify important process changes and exclude unimportant changes with a filter. These requirements may change over time as the manufacturing process matures or new processes are introduced. Therefore, it is convenient for a measurement tool to have a certain degree of flexibility.

[0204] For measurement tools used in production, the ownership cost is also an important consideration. In addition to the initial cost and capital cost of the tool, there are maintenance costs for the tool, including preventive maintenance and repairs. The lifespan of the tool is important. Can the tool only be used for one generation of products, or can it be used for several generations of production? Another cost factor is the throughput of the tool, i.e., how fast it takes to perform the measurement. If the tool is too slow, many tools may be required, doubling the cost. A convenient tool can favorably keep pace with the production line. For example, if the production line can process 60 silicon wafers per hour, the measurement tool can measure 60 wafers per hour. Low throughput may slow down the production process or prevent complete measurement results from being obtained. Even if the throughput is fast, since the speed of the production line will not increase, it may not generally be necessary.

[0205] All costs have two further elements, damage to parts and time to result. If the measurement tool has to damage and discard inspected parts, this is added to the cost of the tool. Each time a part is discarded, the cost of the tool increases and, especially in mass production, the overall cost of ownership can increase significantly. Time to result is an indirect cost and depends on how quickly production changes can be detected. If one measurement tool can detect a change in minutes, while another takes hours, the former tool is likely to be far more valuable. There is a possibility that defective parts are produced between the occurrence and correction of a process change. Since these defective parts are likely to be discarded, the cost of the measurement tool increases. Therefore, to reduce or minimize production losses (i.e., maintain or improve yield), it can be advantageous to obtain results quickly.

[0206] Current measurement tools used for monitoring semiconductor devices can vary quite significantly in terms of attributes such as sensitivity, accuracy, reproducibility, reliability, speed, non-destructive evaluation, cost, etc. For example, TEM (transmission electron microscope) is very sensitive and accurate, capable of measurements below one tenth of a nanometer for a single transistor. However, it is necessary to remove a part of the device and there is a possibility of destroying the sample. Also, TEM analysis requires expensive tools and experienced operators, and it takes a relatively long time, from several hours to sometimes several days, to obtain results. Therefore, although TEM is very precise and sensitive, it cannot be used as an "in-line" monitor or be a direct part of the production line.

[0207] There are two common tools used in the production of advanced semiconductor integrated circuits, CD-SEM and optical CD. CD-SEM can take a downward image directly above the device. The obtained image can be used to measure the dimensions of the device. When there are multiple devices in the image, the measurement sensitivity can be improved by averaging, and many measurements can be made. CD-SEM provides simple and direct measurements, but there are measurement errors that are problematic. In particular, the charging of the device by electron beam irradiation can cause image distortion that is the cause of measurement errors. Also, the device may be contaminated by electron beam irradiation, resulting in a change in dimensions and a decrease in accuracy. For example, a device that initially appears to be 10 nanometers wide may appear to be 12 nanometers wide due to contamination. Also, CD-SEM is generally not as fast as optical tools and is a more complex tool, so the ownership cost is high.

[0208] Optical critical dimension measurement tools (OCD) can provide a way to measure the critical dimensions of a device quickly and non-destructively. However, it can be difficult for smaller shapes and 3D structures. The wavelength of light used is either in the visible, ultraviolet (UV), or infrared (IR) spectrum of light. These light wavelengths range from about 200 nanometers to over 1,000 nanometers, which can be much longer than the dimensions of the device being measured currently (in the range of 1 - 100 nanometers). Therefore, sensitivity can be an issue with these tools. Also, since the image is not directly measured, it can be difficult to distinguish between changes in the measurement values and the root causes of those changes, and problems with accuracy can occur. Also, OCD tools average over many devices and combine hundreds to thousands of devices into one measurement. This improves measurement accuracy and sensitivity but also brings limitations in use. OCD tools cannot measure individual devices like CD-SEM or TEM. OCD tools typically have a large sample area measured in units of tens to hundreds of microns and are therefore typically used in large fields of the same device, such as test structures or memory arrays. In this regard, it is also disadvantaged compared to CD-SEM tools that can measure individual devices or small areas. On the other hand, OCD tools are fast and relatively reliable and do not damage the sample. Therefore, OCD tools are used for monitoring the production of many types of semiconductor devices.

[0209] Unfortunately, as device dimensions get smaller, shapes become 3D, and more complex, it is becoming difficult for OCD tools to maintain the required accuracy and sensitivity. One way to compensate for the shrinking size of the feature is to lower the wavelength of light used in OCD from visible light to ultraviolet light, but ultraviolet light may have reduced penetrability into 3D structures, especially as used in NAND memory devices. Silicon is transparent at infrared wavelengths but not at visible or ultraviolet wavelengths, so measuring buried structures is difficult or impossible. Infrared light can be used to measure buried structures, but due to the long wavelength of the light, it has low sensitivity to small dimensional changes.

[0210] Small Angle X-ray Scattering (SAXS) has been proposed and tools using this technique have been developed. X-rays have the advantage of having a very short wavelength, typically less than 1 nanometer, so very precise measurements are possible. First, compared to OCD, X-rays may require complex and expensive equipment for generation, focusing, and detection. Second, X-rays can damage electronic devices, which is a problem for use in production sites. Third, measurements may take longer compared to OCD or CD-SEM. Due to these factors, it is not clear whether SAXS can be used as an alternative to OCD or CD-SEM. Therefore, there is currently an increasing need for new technologies to expand or replace current in-line production measurement tools.

[0211] To address some of the difficulties associated with making measurements on semiconductor devices (e.g., semiconductor devices at various stages of production) that are becoming more complex and shrinking in size, new dimensional measurement systems and methods based on non-linear generated light (also referred to herein as Nonlinear Optical - Critical Dimension or NLO-CD) are disclosed herein.

[0212] Second harmonic generation (SHG) is a non-linear optical phenomenon in which light of a certain frequency (e.g., a light pulse) impinges on a sample and generates light of twice the frequency, herein referred to as SHG light, SHG signal, SHG light, or second harmonic generation light. Additional information regarding second harmonic generation has been described above and is, for example, described in U.S. Patent No. 10,591,525, issued March 17, 2020, to Koldiaev et al. entitled "Wafer Metrology Technologies", which is hereby incorporated by reference in its entirety. Second harmonic generation generally involves non-centrosymmetric materials, interfaces or defects, or some property of the sample that breaks the inversion symmetry of the sample (e.g., a point or region where an interaction with the incident light occurs). In materials with centrosymmetry such as silicon, second harmonic generation occurs at interfaces or defects where the inversion symmetry is broken. Second harmonic generation can be enhanced by an electrostatic field (DC) at the interface or defect. Such electrostatic fields are caused by interfaces between different materials, space charge regions (SCRs), doping, defects, etc. The resulting "electric field-induced second harmonic generation" (EFISHG) of light can be used to probe the electronic properties of the sample, such as the electronic states (including band bending, density of states, charging, adatoms adsorption) at buried interfaces or defects. Infrared light can be used to measure buried structures, but due to the long wavelength of the light, it is less sensitive to small dimensional changes.

[0213] Furthermore, small changes in the physical characteristics of a semiconductor device can sometimes cause large changes in the electric field within the device. Changes in the electric field within the sample caused by changes in the dimensions of the device, in turn, change the second harmonic generation of light within the sample. Similarly, this effect is also referred to as electric field-induced second harmonic generation (EFISHG).

[0214] A second harmonic generation system (also referred to as an NLO-CD system) for determining critical dimensions illuminates a sample, structure, and / or device (e.g., an electronic device), and uses the SHG light emitted by the device to determine the corresponding physical structure (e.g., shape and / or dimensions) of the device and / or monitor changes in such features. In some cases, the NLO-CD system can use the SHG light emitted by a device produced on a production line to monitor the quality and stability of the production process and, in some cases, improve production yield and / or the performance of the produced device. The devices measured by the NLO-CD system can be completed or not yet completed, and the changes can be unplanned variations (e.g., variations associated with process tool changes due to degradation, environmental changes, malfunction, variations in consumables used by the process tool, etc.). In some cases, the NLO-CD system can use the SHG light emitted by a sample, device, and / or structure to determine one or more material properties of the sample, device, and / or structure. In some cases, the NLO-CD system can use the SHG light emitted by a sample, device, and / or structure to determine both the geometric features and material properties of the sample, device, and / or structure. The NLO-CD system is more sensitive to small local changes in three-dimensional shape than other non-destructive techniques such as OCD and CD-SEM, and can reduce or eliminate the need for destructive production monitoring such as cross-sectional TEM, SEM, and X-ray analysis. The NLO-CD system is faster than electron beam and X-ray technologies and can reduce the cost of sample monitoring (e.g., on a production line).

[0215] Monitoring changes in the physical characteristics (e.g., shape and / or dimensions) of a device or a part thereof, as a result, in addition to or instead of monitoring production, the NLO-CD system can provide a feedback signal, feedback data, or information that can be used to control the production steps of the device. In some cases, the feedback signal, feedback data, or information can be used to control the production steps for producing the monitored sample. In some cases, the NLO-CD system is included in the sample evaluation step and can provide a feedback signal or feedback data to a step preceding or upstream of the evaluation step. This preceding step in the fabrication process can include, for example, a lithography, etching, or deposition step. In some aspects, NLO-CD can provide a feedforward signal, feedforward data, or feedforward information that can be used to control production steps following the monitoring step or sample measurement. In some aspects, based at least in part on the feedforward signal, feedforward data, and / or feedforward information provided by NLO-CD, subsequent or downstream steps can be adjusted to adjust or correct changes in the production process detected by the NLO-CD system.

[0216] In some examples, an NLO-CD system irradiates a sample, such as a silicon wafer including a semiconductor device or a semiconductor device partially configured, with light such as pulsed light (e.g., pulsed laser light). NLO-CD can be used to monitor a sample at a certain point in the semiconductor manufacturing process by irradiating the sample with light and detecting the resulting SHG light (also referred to as the SHG signal). The pulse of the incident light may generate light of the second harmonic (or half the wavelength) of the incident light, which may also be referred to as the second harmonic generation (SHG) signal and / or SHG light. The SHG signal can be measured using one or more detectors. These detectors can be configured to measure one or more of the intensity, angular distribution, or polarization of the detected SHG signal (e.g., an electrical signal), or any combination thereof. In some cases, the detected SHG signal may be proportional to the intensity of the SHG light incident on the detector (e.g., the photoelectronic sensor of the detector). Further, the incident light pulse can be adjusted to improve (e.g., increase) the SHG signal from the sample, such as by selecting polarization, wavelength, or intensity. Further, the orientation of the sample can be adjusted, such as by rotating the sample with respect to the plane of light scattering (e.g., the plane formed by the axis perpendicular to the incident beam and the sample surface).

[0217] In some cases, the sample can be prepared for second harmonic generation measurement by exposing the sample to a second optical beam or charge. For example, the region of the sample where SHG light is emitted can be optically pumped by directing a second optical beam or an auxiliary optical beam at that region. The second or auxiliary optical beam may be the same wavelength as the first optical beam (the pulse used to generate the SHG signal) incident on the sample, or a different wavelength. The charge is, for example, derived from a corona discharge. Some examples of optical pumping using an auxiliary light source and example configurations for supplying charge have been described above. However, optical pumping and / or the accumulation or deposition of electrical charge need not be provided, and thus, NLO-CD need not include a light source for optical pumping in addition to the probe light source.

[0218] In various systems and methods, the SHG signal can be monitored for changes in the SHG signal (e.g., changes related to intensity, polarization, spatial distribution, etc.) that may indicate changes in the production of a semiconductor device (e.g., changes in one or more processes prior to measurement). Such changes in the production of a semiconductor device can cause changes in the geometric features of the device (e.g., dimensions such as width, length, height, thickness), such as the width of a transistor feature, or the arrangement or spacing between features. Changes in these geometric features may sometimes include changes in shape. In some cases, the SHG signal and / or the detected SHG signal may be processed (in the optical or electronic domain) to make changes in the SHG signal and / or the detected SHG signal more apparent. In some aspects, the SHG signal may be used to warn a manufacturer or facility of potential production problems. In some aspects, the SHG signal or the detected SHG signal may be used to provide feedback to a production apparatus in a pre - production or upstream process of a production process to improve the yield or performance of a device. In some aspects, the SHG signal or the detected SHG signal may be used to provide a feed - forward signal to a subsequent or downstream process of a production process to correct a prior change.

[0219] In some cases, a change or variation in the geometric features of a sample or device may include the difference between the geometric features of the sample or device and stored geometric features stored in the memory of the system. In some examples, the stored geometric features may consist of reference geometric features (e.g., provided by a user), or geometric features previously determined by the NLO - CD system.

[0220] In some examples, the SHG signal can be used to determine the geometric or electronic structure of the features of a fabricated device. The device may be a finished product or in an initial stage of production. The SHG signal may be compared to a database of (e.g., geometric) features to determine the structure of the device (e.g., geometric) features. In some cases, the SHG signal can be compared to a database of (e.g., material property) features to determine the electronic structure (e.g., material property) of the device. Also, the SHG signal may be used to calculate a structure (e.g., geometric structure) based on known knowledge about the structure. For example, a database of (e.g., geometric and / or material property) features can include calculated and / or measured data of the device prior to measurement of the device to facilitate rapid identification of the device structure. Also, these results (e.g., determined features) can be used, as described above, to alert a manufacturing person of process variations, feedback or feedforward.

[0221] In various designs, the primary pulsed laser beam strikes a spot on the surface of an integrated circuit (e.g., a silicon integrated circuit). The pulse can generate light at the second harmonic of the primary beam through interaction with the integrated circuit (e.g., a device within the integrated circuit). The SHG signal is measured using one or more detectors. The measurements include the intensity, angular distribution, polarization, or a combination thereof of the SHG light. Also, the sample may be rotated to make multiple measurements (e.g., corresponding to SHG light emitted at different angles of incidence and / or in different directions), or the wavelength of the primary beam may be varied.

[0222] The detected SHG signal may be processed and compared to a detected SHG signal created by computer simulation using a model. The model can include geometric information from a sample such as one or more dimensions or shapes. In some examples, the geometric information (e.g., reference geometric information) may include at least two dimensions. For example, the geometric information may include the height, width, or length of a feature and potentially thickness and / or spacing. The geometric information may also include a shape that includes, for example, angles, orientations, degrees of smoothness, roughness, or other features or properties.

[0223] The model is generated empirically from measurements, generated computationally, or a combination of both. This model can be used to evaluate the processed SHG optical signal and determine either the structure (e.g., geometric structure) of a device on the sample or a change in the structure (e.g., geometric structure).

[0224] The result of the comparison can be used to monitor the fabrication process. In some examples, if the comparison indicates a significant change to the device structure such as an unexpected variation in the device geometry (e.g., in geometric features), the process can be temporarily interrupted until the problem is corrected. The result of the comparison can be used, additionally or alternatively, to assist in the development of a new device structure or process for device fabrication.

[0225] FIG. 21 shows an example of an NLO-CD system 4000 for measuring and monitoring characteristics (e.g., critical dimensions) of a sample or a device included in the sample. In the example shown in FIG. 21, a laser light source 4100 (e.g., a pulsed laser source such as a titanium sapphire laser) is used to generate a laser beam 4110. In some cases, the laser beam 4110 may be composed of pulses having a duration of 10 to 50 femtoseconds, 50 to 100 femtoseconds, 100 to 150 femtoseconds, 150 femtoseconds to 200 femtoseconds, or any value between these ranges, or greater or less than these. In some cases, the laser beam 4110 can have a wavelength of 500 nm to 700 nm, 700 nm to 900 nm, 900 nm to 1200 nm, 1200 nm to 1500 nm, 1500 nm to 2000 nm, or any value between these, or greater or less than these (e.g., a central wavelength). In some cases, the laser beam 4110 can be composed of pulses having a duration of 100 femtoseconds and a wavelength (e.g., central wavelength) of 800 nm. In such a case, the laser light source 4100 can be a coherent mira titanium sapphire laser. The laser beam 4110 can be directed towards the sample 4302 to be inspected. In some examples, a polarizer 4120 selects the polarization of the laser beam 4110, and a focusing optical system 4130 focuses the laser beam 4110 onto the sample 4302, thereby illuminating a spot or region 4300 on the sample 4302. In some cases, the illuminated spot or region can include one or more devices (e.g., semiconductor devices) or structures. In some cases, a portion of one or more devices may overlap the illuminated region. In some cases, the sample 4302 can be placed on a stage 4301 that can position (e.g., laterally in a plane parallel to the upper surface of the sample 4302 along the x direction and / or the y direction) and / or rotate (e.g., azimuthally or polar direction with respect to a Cartesian coordinate system having an axis perpendicular to the surface of the sample (e.g., the z axis of the xyz system shown in FIG. 21)) the sample 4302.The device on the sample 4302 may be at various stages of completion or production (e.g., initial stages), such as after the fabrication of the gate layer, after lithographic exposure and development of the photoresist or hard mask. In some cases, the stage 4301 may be movable or adjustable such that it can move (e.g., laterally) a portion of the sample 4302 that is irradiated by the laser beam 4110. In some examples, the height and / or rotational state of the stage 4301 may be adjustable (e.g., manually or electronically). For example, the angle of incidence of the laser beam 4110 with respect to the sample 4302 can be controlled by controlling the azimuth angle of the stage 4301.

[0226] In some embodiments, the stage 4301 may not be part of the NLO-CD system 4000. In some cases, the stage 4301 may be included in a tool of the corresponding production line. In such cases, the NLO-CD system 4000 can communicate with the tool to send control signals for controlling the position / orientation of the stage 4301 or to receive readout signals indicative of the position / orientation of the stage 4301.

[0227] In some embodiments, one or more detectors 4201, 4210 may be positioned relative to an illuminated spot or region 4300 to collect at least one light beam 4400 emitted or reflected from the illuminated region 4300. Optionally, the light beam 4400 may include the second harmonic of the laser beam 4110 emitted by the sample 4302 (e.g., via second harmonic generation interaction of the laser beam 4110 with the sample 4302). In some cases, the detectors 4201, 4210 can detect second harmonic generation light 4400 (also referred to as SHG signal and / or SHG light) having a wavelength of 400 nm generated in connection with the interaction of the laser beam 4110 having a wavelength of 800 nm. Optionally, the detectors 4201, 4210 may be arranged or moved to different positions to sample light beams (e.g., SHG light) propagating at different angles (e.g., different tilt angles and / or different azimuth angles). In some cases, the detectors 4201, 4210 can include one or more filters (e.g., filter 4230). In some such examples, the spectral filter 4230 can be used to block, filter, or remove light having a wavelength different from the second harmonic of the beam 4400. Optionally, the detectors 4201, 4210 can include one or more polarizers (e.g., polarizer 4220). In some such cases, the polarizer 4220 may be used to select the polarization of the detected light, for example, by allowing the transmission of light having a first polarization state and absorbing or redirecting light having a second polarization state. In some cases, the detectors 4201, 4210 may be composed of photomultiplier tubes (e.g., for measuring the intensity of SHG light). In some cases, the detectors 4201, 4210 may be composed of one or more optical elements configured to direct and / or focus the SHG light 4400 onto the detector 4210. In some embodiments, at least one detector may be used to detect light having the wavelength of the laser light 4110 (also referred to as the fundamental wavelength).

[0228] In some embodiments, the system can compare the measured SHG signal (e.g., the detected SHG signal) with a predicted SHG signal or a predicted and detected SHG signal. The predicted SHG signal or the predicted and detected SHG signal is generated by simulating second harmonic generation by a measured device (e.g., an electronic device such as a semiconductor device) using a digital model of the measured device. The result of such a comparison can be used, for example, to determine the dimensions (or shape) of the physical characteristics of the measured device or to determine whether a change has occurred in the dimensions (or shape) by comparing with previously measured dimensions (e.g., stored in the system's memory), the dimensions used in the simulation of the SHG signal, or reference dimensions (e.g., stored in the system's memory).

[0229] In some embodiments, the NLO-CD system can compare, for example, a first SHG signal or a first group of SHG signals received from a first sample with a second SHG signal or a second group of SHG signals received from a second sample to detect changes in the manufacturing process. For example, the NLO-CD system can measure a first detected SHG signal or a first group of detected SHG signals and compare it with a second detected SHG signal or a second group of detected SHG signals stored in the system's memory. The second detected SHG signal or the second group of detected SHG signals can be received and stored from the second sample after receiving the first SHG signal or the first group of SHG signals from the first sample. In some cases, the first sample and the second sample may be manufactured by the same manufacturing system. In some cases, the difference between the first detected SHG signal and the second detected SHG signal may indicate a change in a manufacturing step in the manufacturing process. In some cases, if the difference exceeds a specified value (e.g., a specified value stored in the memory of the NLO-CD system), the NLO-CD system can output a signal indicating a change in the manufacturing step. In some cases, the manufacturing step can be a manufacturing step performed on the first sample and the second sample before the SHG measurement.

[0230] To generate a digital model of the SHG signal, the shape and material for the device structure and optical configuration (used to illuminate the device) can be input into a modeling program (e.g., a program for modeling non-linear light-matter interactions), which calculates the predicted SHG emission for the provided device structure and optical configuration. For example, FIG. 22 shows a simplified configuration of a FinFET transistor 4500 on a silicon wafer 4540. This FinFET transistor includes a silicon fin 4510 with a width of 5 nm, a hafnium oxide gate oxide layer 4520, and a tungsten gate contact layer 4530. As shown in FIG. 22, this transistor has geometric features such as dimensions (e.g., height, width, etc.), and / or shape including inclination (or lack thereof) and sidewall inclination (or lack thereof). FIG. 23 shows a one-dimensional array 4560 formed by a plurality of FinFET transistors. In some cases, for simulation purposes, the one-dimensional array 4560 may be assumed to be infinitely wide and infinitely repeating. As shown in FIG. 23, the one-dimensional array has geometric features such as the spacing between FinFET transistors, the dimensions of each FinFET transistor (e.g., height, width, etc.), and / or shape (e.g., inclination (or lack thereof), sidewall inclination (or lack thereof), etc.).

[0231] FIG. 24 shows an example of a process that can be used to generate a predicted SHG signal and a predicted detected SHG signal. The device model 4610 (e.g., a digital model) of the FinFET array 4560 of FIG. 23, and the beam model 4620 of the incident pulse beam 4110 are used as inputs to software 4630 that can model the SHG light emitted by a structure (e.g., a structure on a test sample) when illuminated by the incident light beam. Examples of such software include, but are not limited to, Lumerical's FDTD (Finite Difference Time Domain) software available from Ansys Canada Ltd in Vancouver, British Columbia. In some cases, the device model can include the geometric and material properties of the test structure (e.g., the FinFET array), and the beam model can include the beam parameters of the light beam incident on the structure. The modeling software 4630 can calculate the emission pattern of the SHG light expected from illuminating the structure with the incident light beam. In some examples, the resulting emission pattern may be input into a detector model 4640 (e.g., a detector model related to the detector or detector type used to measure the emitted SHG light), which may filter the emission pattern and create a predicted detected SHG signal 4650 for the sample shape and material 4610. In some cases, the detector model can filter the emission pattern, for example, based on the entrance aperture of the detector.

[0232] FIG. 25 plots the detected SHG signal simulated with respect to the width of a FinFET transistor (such as a silicon FinFET), showing an example of the relationship between the simulated detected SHG signal and the Fin width. In some cases, the detected SHG signal may be proportional to the intensity of the SHG light generated by the FinFET during illumination. In the illustrated example, the data points of the SHG signal are calculated for a series of fin widths in the range from 1 nm to 10 nm in 1 nm steps. As a result, as shown in FIG. 25, a graph 4670 of the values of the relative SHG intensity (e.g., normalized intensity) for different fin widths is obtained (solid circles). In some cases, the graph 4670 can be used to predict the width of the test FinFET (e.g., having the same shape as the FinFET used in the simulation) based on the measured value of the SHG signal from the test FinFET. For example, using the measured SHG signal intensity 4680, the width of the silicon fin on the device (5.5 nm in this case) can be determined by interpolating between the calculated data points at 5 nm and 6 nm. Interpolation, extrapolation, or other methods may be employed.

[0233] In some examples, multiple possible changes in the shape of the device may cause similar changes in the SHG signal generated by the device, making it difficult to identify the changes that have occurred (e.g., with respect to a previously measured device or a reference device). For example, a change in the height or width of the device may cause the same change in the SHG signal. Therefore, it may be desirable to use additional detectors that measure the SHG emitted light at different angles (e.g., tilt angles) and / or with different polarizations to more accurately capture the changes using the additional data obtained from the signals provided by the additional detectors. In some examples, an additional detector can be introduced into the detector model 4640 of FIG. 24. This provides additional signals that can be used to compare the predicted detected SHG signal (or SHG signal) with the measured detected SHG signal (or SHG signal). These additional signals can, in some cases, be used to distinguish different geometric changes in the device.

[0234] There are various ways to introduce an additional detector into the system. As an example, there is a way to add a detector as shown in FIG. 26. In FIG. 26, the detector 4201 is complemented by additional detectors 4202 and 4203 that can be used to measure SHG at additional angles (e.g., different tilt angles) and / or with different polarizations of the SHG signal. The detectors may also be arranged at different azimuthal angles with respect to the sample and the sample holder / sample stage. In some cases, the additional detector may include a polarizer 4220 having different polarization selection characteristics compared to one or more detectors within the SHG-OC system. In some cases, the additional detector may include a filter 4230 having different polarization selection characteristics compared to one or more detectors of the SHG-OC system.

[0235] In some examples, the SHG signal can be detected with a detector array, such as a linear detector or an area detector, that can capture light at multiple angles simultaneously. FIG. 27 shows an NLO-CD system that includes at least one linear or area detector array 4795 for detecting SHG light emitted from sample 4770 along different directions. In the example shown in FIG. 27, detection through a lens is used. In this configuration, the pulsed beam 4700 passes through the optical system 4701 and the polarizer 4702, and then is directed by the dichroic beam splitter 4710 through the objective lens 4720 disposed above the sample 730 to irradiate the spot 4760 on the sample 4770 placed on the stage 4780. The emitted SHG light 4790 is collected by the objective lens 4720, passes through the dichroic beam splitter, the optical filter (e.g., a spectral filter) 4740, and the collimating optics 4750, and is incident on the linear or area detector array 4795 (e.g., a one-dimensional or two-dimensional detector array). In some cases, light incident on the objective lens at different angles is mapped to different pixels of the detector array 4795. In some cases, SHG light collected from different tilt angles can be measured simultaneously.

[0236] In some embodiments, the SHG light may additionally or alternatively be used in a production monitor, for example, by monitoring the dimensions (e.g., height, width, etc.) or geometric variations (e.g., shape) of a device produced during manufacturing. FIG. 27 shows an exemplary process for using an NLO-CD system (e.g., the NLO-CD system described above) in a manufacturing scenario. In various embodiments, the NLO-CD system can be used for real-time monitoring of samples produced on a production line. In such cases, the NLO-CD system can illuminate the sample after a selected production stage and measure the corresponding SHG signal to determine one or more characteristics of the sample (e.g., geometric and / or material characteristics). In the illustrated example, the SHG signal can be monitored for changes indicating changes in the dimensions of the features of the device being fabricated (e.g., compared to reference dimensions). In FIG. 28, a process window 4802 can be created using a model 4801 and compared to the SHG signal 4803 collected from the sample. In some examples, the signal can be monitored by software 4805 for changes beyond the process window. In some cases, the process window may include upper and / or lower limits on geometric features or critical dimensions. In some cases, the upper and lower limits may be stored in the system's memory. When the signal exceeds the process window, a warning may be sent to the factory computer or production line operator 4806 or otherwise indicated. As described above, these SHG signals may correspond to separate SHG signals measured at different tilt angles, azimuth angles, polarizations, or any combination thereof.

[0237] In some embodiments, the NLO-CD system can include a non-transitory memory configured to store data and machine-executable instructions, and a processor (e.g., a hardware processor, processing electronics, microprocessor, etc.) configured to execute the machine-readable instructions to perform one or more processes related to monitoring a sample that includes one or more devices using the second harmonic generation method described above. In some examples, a reference SHG model and modeling software (e.g., electromagnetic simulation software capable of modeling second harmonic generation) for the devices included in the sample may be stored in the non-transitory memory as reference information and instructions, respectively. The processor can execute instructions with at least the reference information as an input to calculate one or more expected second harmonic emission patterns related to the device. Optionally, the processor may use one or more parameters of the incident beam of light used by the NLO-CD system for the generation of SHG light to calculate the expected emission pattern. In some examples, the parameters of the incident beam of light may be stored in the memory of the NLO-CD system (e.g., as part of the reference information). In some embodiments, the processor can receive the parameters of the incident beam of light from a control system of the NLO-CD system that controls the incident beam irradiating the sample. In various embodiments, the reference information may include the values of one or more parameters used for determination of the reference model, generation of a look-up table, reference values related to a process window, values of parameters related to a detector, etc.

[0238] In addition to, or instead of, calculating the reference SHG model using non-linear electromagnetic modeling software 4630 or other theoretical modeling approaches, the characteristics of the second harmonic light (SHG signal) generated and emitted from the device may be determined experimentally and used to construct the reference SHG model.

[0239] In some examples, the reference SHG model is empirically generated by measuring the SHG signal from a reference sample having known dimensions and / or material properties, or creating a plot similar to graph 4670 or another reference database (e.g., a look-up table or LUT), where the reference database is then used with the measured second harmonic generation light generated by a new sample (e.g., a device within the new sample) to determine the properties (e.g., dimensions and / or material properties) of the new sample (e.g., a device within the sample) having unknown properties.

[0240] In some cases, the geometric features of the sample can be determined at least in part based on a mapping of the SHG signal generated by the sample (e.g., an integrated circuit) to geometric features of the sample or one or more portions of the sample (e.g., a look-up table of SHG signal values to geometric features). In various aspects, the sample can be either complete or not yet complete. In some cases, the mapping can be generated using empirical data, simulated data, or a combination thereof. In some cases, the mapping can be generated using a machine learning algorithm. In some cases, the mapping of the SHG signal to the geometric features of the sample can include a mapping of the detected SHG signal to geometric features of the sample or one or more portions of the sample (e.g., a look-up table of detected SHG signal values to geometric features). In some cases, the mapping can be composed of a mapping of the detected SHG signal to geometric features of one or more structures on the sample at a stage of the fabrication process (e.g., whether one or more structures are complete or not yet complete).

[0241] In some cases, the geometric features of a sample (e.g., an integrated circuit) can be determined using changes in the SHG signal generated by the sample as a result of changes in the parameters of the incident light beam that generates the SHG signal (e.g., polarization, angle of incidence, intensity, and / or wavelength). In these cases, the geometric features can be determined based on a mapping of the changes in the SHG signal to the geometric features of the sample or one or more parts of the sample (e.g., a look-up table of changes in SHG signal values to geometric features). In various aspects, the sample can be either complete or not yet complete. In some cases, the mapping may be generated using empirical data, simulated data, or a combination thereof. In some cases, the mapping may be generated using a machine learning algorithm. In some cases, the mapping of the changes in the SHG signal to the geometric features of the sample may include a mapping of the detected changes in the SHG signal to the geometric features of the sample or one or more parts of the sample (e.g., a look-up table of detected changes in SHG signal values to geometric features).

[0242] In some examples, the reference SHG model can be generated using a machine learning algorithm including supervised learning algorithms, unsupervised learning algorithms, semi-supervised learning algorithms, or reinforcement learning. In these examples, machine learning techniques can use physical measurements and / or computer modeling, or a combination thereof, to generate the reference SHG model. In some cases, the reference SHG model may include a mapping of the SHG signal and / or the detected SHG signal to the characteristics of the sample (e.g., geometric features, material structure, critical dimensions, etc.). In various aspects, machine learning algorithms used to generate the mapping include linear regression, logistic regression, decision trees, SVM (support vector machine) algorithms, naive Bayes algorithms, KNN (K-Nearest Neighbors) algorithms, K-means algorithms, random forest algorithms, dimensionality reduction algorithms, gradient boosting algorithms, or AdaBoost algorithms.

[0243] In some examples, the processor of the NLO-CD system or a separate computing system may be used to generate a reference SHG model using a series of specified measurements performed on a plurality of reference devices having machine learning techniques and known characteristics. In some cases, the processor of the NLO-CD system or a separate computing system may also be used to generate a reference SHG model using unsupervised machine learning techniques such that the system is used for in-line monitoring of samples produced on a production line.

[0244] In some examples, the angular distribution of SHG emission from a sample can be used to improve dimensional measurements. For example, separate SHG signals collected from at least two angles (tilt angle and / or azimuth angle) can be used.

[0245] In some examples, the polarization of the light source or the polarizer used in the detector or the polarization of the polarizer used in the optical path between the sample and the detector can be varied to generate an incident beam having different polarizations or to selectively detect SHG light having a specific polarization. In some cases, separate SHG signals collected for at least two polarizations can also be used to improve dimensional measurements.

[0246] In some examples, separate SHG signals can be collected for at least two different incident light beams having different wavelengths. For example, at least two separate light sources, such as lasers, having separate center wavelengths are used to irradiate a sample, and as a result, different SHG signals having different wavelengths are collected by different detectors (e.g., detectors having different filters, or detectors having different filters in the optical path from the sample to the detector). In some cases, the separate SHG signals can also be used for the analysis of the device under test (e.g., to improve dimensional measurements). Other configurations are also possible. For example, a broadband light source can be used to generate broadband incident light, and a plurality of detectors, a detector array, or a spectrometer can be used to detect and analyze the resulting SHG light. In some cases, the light source may include a wavelength-variable laser source. In some cases, a single light source can be used to simultaneously generate two light beams having two different wavelengths, or light beams having different wavelengths can be generated at different times.

[0247] In some examples, the NLO-CD system can use at least two detected SHG signals with at least one parameter being different to determine the geometric features of the sample or the variations in the geometric features of the sample. The at least one parameter can be associated with the generation and / or detection of the corresponding SHG signals that respectively generate one of the detected SHG signals at the time of detection. In some cases, the at least one parameter can include parameters associated with the incident light beam that generates the SHG signal. For example, the incident light beam can have different wavelengths, azimuth angles, polarizations (e.g., linear polarization or circular polarization), intensities, angles of incidence (e.g., with respect to the sample), etc. In some cases, the incident light beam may have different polarization parameters. In some cases, the at least one parameter can include parameters associated with the detected SHG signal. For example, the SHG signal may propagate along different directions (e.g., with respect to the sample), have different polarizations, or have different wavelengths, etc. Thus, in some cases, the at least one parameter can constitute parameters associated with the light beam from the sample to the detector. In various embodiments, a polarizer, a filter, or other optical components may be included in the optical path between the sample and the detector(s) to select, for example, polarization, wavelength, angle, etc. In some cases, the at least one parameter can include parameters associated with the detector used to detect the SHG signal and generate the detected SHG signal. For example, the detector can have different tilt angles (e.g., with respect to the sample), different polarizers, different filters, different azimuth angles, different out-of-plane angles with respect to the sample, different in-plane angles, etc. In some cases, the in-plane angle may include an angle in the plane formed by the incident light beam and the axis perpendicular to the sample. In some cases, the out-of-plane angle may include an angle in a plane different (e.g., not parallel) to the plane formed by the incident light beam and the axis perpendicular to the sample.In some embodiments, the NLO-CD system can vary the parameters (e.g., polarization, wavelength, angle, etc.) of the incident beam and / or the SHG signal and / or the detector beam over time to obtain different SHG signals and / or detected SHG signals for different parameters.

[0248] In some embodiments, the NLO-CD system generates at least two detected SHG signals that differ in at least one parameter and uses at least one light source and one detector to determine the geometric features of the sample or variations in the geometric features of the sample. The at least one parameter is associated with the generation and / or detection of the corresponding SHG signal that gives rise to one of the detected SHG signals upon detection. In some cases, the at least two detected SHG signals can be created at different times. In such cases, the at least one parameter has a first value at a first time and a second value at a second time after the first time, such that two different detected SHG signals may be generated. In some cases, the at least one parameter may include a parameter associated with one incident light beam that generates the SHG signal. For example, the parameter may be composed of wavelength, azimuth angle, polarization (e.g., linear polarization or circular polarization), intensity, angle of incidence (e.g., with respect to the sample), etc. In some cases, the parameter may include a polarization parameter of the polarization (e.g., linear polarization or circular polarization). In some cases, the at least one parameter can constitute a parameter associated with the detected SHG signal. For example, the parameter may include the propagation direction of the SHG signal direction (e.g., with respect to the sample), polarization, wavelength, etc. In some cases, the at least one parameter may include a parameter associated with the detector used to detect the SHG signal and generate the detected SHG signal. For example, the parameter may include the position of the detector, tilt angle (e.g., with respect to the sample), detection wavelength of the detector, passband of the filter, azimuth angle, out-of-plane angle with respect to the sample, different in-plane angles with respect to the sample, etc. In some cases, the in-plane angle with respect to the sample may include the in-plane angle formed by the incident light beam and the axis perpendicular to the sample. In some cases, the out-of-plane angle with the sample may constitute an in-plane angle that is different (e.g., not parallel) from the plane formed by the incident light beam and the axis perpendicular to the sample.

[0249] In some examples, the results of SHG dimension measurements are used for process monitoring. For example, an NLO-CD system (or the monitoring method described above) can be used to estimate the characteristics of samples produced by a process at the production stage. In some such examples, the NLO-CD system may be used for in-line and real-time process monitoring (e.g., the NLO-CD system may be included in-line in a fabrication system, such as a semiconductor fabrication system, as an in-line measurement tool). In some examples, the NLO-CD system (or the monitoring method described above) may be used for off-line monitoring of selected (e.g., randomly selected) samples. Thus, in various aspects, the NLO-CD dimension measurement system comprises a production or process monitor for dimensional or geometric changes in a device being manufactured.

[0250] In another example, the results of SHG dimension measurements may be used as process feedback or feedforward to modify a process as needed, as shown in FIGS. 29 and 30, respectively. In some exemplary processes such as those shown in FIG. 29, an NLO-CD system (or the sample monitoring method described herein) is used to determine changes in the characteristics (e.g., dimensional features) of a sample after a process has been executed at a selected stage of a production line, and to generate one or more feedback signals based at least in part on the determined characteristics to adjust one or more parameters of the process. In some cases, one or more feedback signals can be used to improve the process such that the characteristics of the sample produced by the selected stage after application of the feedback signal approach a reference characteristic (e.g., the characteristics of a reference device), as compared to the sample generated before application of the feedback signal.

[0251] In some exemplary processes as shown in FIG. 30, the NLO-CD system or the monitoring method described herein determines changes in the characteristics of a sample prior to a process (hereinafter sometimes also referred to as a process) that is executed at a selected stage of a production line, and generates one or more feedforward signals based at least in part on the determined characteristics, which may be used to adjust one or more parameters of the process. In some cases, one or more feedforward signals are used to improve the process such that the determined characteristics of the sample produced after applying the feedforward signal approach a reference characteristic (e.g., the characteristics of a reference device) compared to the sample produced before applying the feedforward signal at a selected stage. In some cases, the feedforward signal can be used to adjust the process to correct for changes in the determined characteristics.

[0252] In some examples, the NLO-CD system can generate a feedback signal (or a feedforward signal) configured to determine unexpected variations in the geometric features of a sample by measuring the sample (using the SHG signal) and then adjusting the process tools of the production line to reduce or eliminate (or correct the detected unexpected variations in the measured sample) the unexpected variations in the samples to be produced thereafter. In some cases, the NLO-CD system can generate a signal or data indicating the unexpected variation when it is identified and transmit the signal or data to an NLO-CD user interface where the user can observe and evaluate the detected unexpected variation or to a computing system that communicates with the NLO-CD.

[0253] In some exemplary embodiments, the results of SHG dimension measurement(s) may be used in combination with results obtained from one or more other systems, such as one or more other test and / or measurement systems (e.g., an optical critical dimension system, also referred to as an OCD system), to determine geometric features or changes in geometric features. The results from the NLO - CD system and the results of the OCD system may be received, for example, by one or more processors, which determine geometric features or changes thereto based on inputs from the SHG system and the OCD system. Instead of, or in addition to, the OCD system, one or more other systems may also be used.

[0254] In some embodiments, based on one or more SHG signals, one or more processors and / or process electronics as described herein are used to determine geometric features or changes in geometric features of one or more completed or partially completed devices or portions of one or more devices.

[0255] In various aspects, an optical measurement system, such as an NLO-CD system (e.g., NLO-CD systems 4000, 6000, 7000, 8000), may be controlled by a control system. In some cases, the control system is configured to control parameters of the light beam incident on the sample (angle of incidence, polarization, wavelength, intensity, divergence, etc.). In some cases, the control system may be configured to control parameters of the detector module of the NLO-CD system (e.g., gain of the photodetector, polarization and / or wavelength of the light received by the photodetector, etc.). In some cases, the control may be part of the NLO-CD system. In such cases, the control system may include a non-transitory memory and at least a processor or process electronics. In some cases, the NLO-CD system may include a computing system configured to perform calculations and simulations to generate characteristics of a device monitored by the NLO-CD system using at least one SHG signal generated by a detector. In some cases, the computing system can communicate with the control system, the detector, and / or the light source. In some cases, the computing system can include a non-transitory memory configured to store data and machine-executable instructions, and a processor configured to execute machine-readable instructions to perform one or more processes related to sample monitoring using at least one SHG signal.

[0256] In some cases, the control system may be composed of a programmable controller (e.g., a field programmable gate array). In some cases, the computing system and / or the control system are separate from the NLO-CD system but can communicate with the interface of the NLO-CD system via a wired or wireless link. In some cases, the computing system may include the control system. For example, the instructions stored in the memory of the computing system can include instructions for controlling the NLO-CD system and instructions related to electromagnetic simulation software.

[0257] In some cases, the control system can control one or more parameters related to the detected SHG signal. For example, the control system can change the parameters of a light source that generates an incident light beam, the parameters of the light beam after being emitted by the light source and before entering the sample, the parameters of the SHG signal generated by the sample, or the parameters of a detector that detects the SHG signal to generate the detected SHG signal.

[0258] In some embodiments, NLO-CD may be used to monitor a fabrication process without determining the characteristics (e.g., geometric characteristics, material properties, or critical dimensions) of a sample (or a partially or fully formed device included in the sample) fabricated by the fabrication process. For example, an NLO-CD system may compare one or more detected SHG signals received from a first sample produced by a fabrication step in the fabrication process with one or more detected SHG signals received from a second sample produced by the same fabrication step after processing the first sample to detect changes in the fabrication step. In this example, the difference between the SHG signals (and thus the detected SHG signals) received from the first sample and the second sample may indicate a change in the fabrication step after the fabrication step has been previously performed on the first sample. In some cases, the difference between the corrected or processed detected SHG signals received from the first sample and the second sample, respectively, may indicate a change in the fabrication step after the fabrication step performed on the first sample. Similarly, the SHG signal of a sample may be compared with one or more references, such as a reference database, one or more reference values, or one or more reference signals, without determining the characteristics (e.g., geometric characteristics, material properties, or critical dimensions) of the sample (or a partially or fully formed device included in the sample) fabricated by the fabrication process. Thus, in some cases, a corrected or processed detected SHG signal can be generated by an NLO-CD processing system from the detected SHG signal without determining, for example, quantifying from the detected SHG signal, the geometric properties (e.g., size, shape, etc.) of the (plural) characteristics of the sample that control the intensity of the SHG signal. In some cases, the first and second samples may be measured using a plurality of incident beams based on a plurality of SHG signals generated by the incident beams. In such cases, changes in different detected SHG signals, or relative changes between two detected SHG signals, may indicate a change in the fabrication step.In some embodiments, a comparison with the detected SHG signal (whether modified or not) from the first sample can be made with the detected SHG signal (whether modified or not) from the second signal. In some embodiments, the detected SHG signal (modified or unmodified) from one or more samples can be compared with one or more references, such as a reference database, one or more reference values, or one or more reference signals.

[0259] Thus, in some cases, the NLO-CD system can use the change in one or more detected SHG signals (or modified SHG signals) received from the fabricated sample to detect a change in the corresponding fabrication process without determining the characteristics of the sample (e.g., geometric features, material properties, or critical dimensions). In such cases, NLO-CD can generate a feedback signal to correct a previous fabrication step of the fabrication process performed on the sample before detecting the change, or a feedforward signal to correct the next fabrication step to be performed on the sample after detecting the change.

[0260] Similarly, in some embodiments, the NLO-CD system can compare one or more detected SHG signals received from a sample produced by a fabrication process with a reference (e.g., a value or range of values from a look-up table) to detect a change in a fabrication step of the fabrication process without determining the characteristics of the sample (e.g., geometric features, material properties, or critical dimensions). Additional embodiments

[0261] This specification discloses additional embodiments and aspects of the systems and methods disclosed herein.

[0262] In some cases, NLO-CD (or the sample monitoring method described herein) can be used to monitor the dimensional characteristics of the type of an integrated circuit, a part of an integrated circuit, or a device fabricated on an integrated circuit.

[0263] In various aspects, the dimensional or geometric features can include dimensional or geometric features of finFETs, GAA, tri-gates, and other electronic or photonic devices.

[0264] In some cases, the dimensional or geometric features can include dimensional or geometric features for building blocks of devices in digital circuits (e.g., NAND gates).

[0265] In some aspects, NLO-CD can constitute a lens transmission imaging system, an optical system based on the use of a solid immersion lens (SIL), or an angular resolution imaging system. In some cases, the NLO-CD system can use a solid immersion lens (SIL) to fill the object space between the sample and the objective lens, thereby providing a higher magnification, higher spatial resolution, and / or higher numerical aperture than a conventional lens. In some cases, the SIL is placed under the front lens of a microscope objective. In some cases, the SIL can comprise a hemisphere with a flat bottom, a super-sphere (Weierstrass) with a flat bottom, a hemisphere with a conical tip, a super-sphere with a conical tip, a hemisphere SIL with a conical dielectric probe, or a diffraction-based SIL. In some examples, the NLO-CD system can use a lens transmission imaging system to measure the intensity (e.g., SHG signal) of an optical beam received from a sample through the same lens used to image the sample. In some examples, the NLO-CD system can use an angular resolution imaging system to capture an image of the sample, where an array of photodetectors having a plurality of pixels (e.g., 1D or 2D) is used, and each of the above-described pixels of such a captured image corresponds to a unique emission direction from the sample. In some cases, the image can be converted to a polar coordinate system to display the angular distribution of light emitted or reflected by the sample.

[0266] In various aspects, the NLO-CD system can be configured to collect SHG light emitted by a sample at different scattering angles, in-plane (e.g., the plane formed by the incident beam and the reflection of the incident beam from the sample surface), and out-of-plane detection angles.

[0267] In some cases, the NLO-CD system can measure the dimensions / geometric features of a device by varying the incident angle of the incident beam. In some cases, the sample under monitoring in the SHG-CD system can be rotated to measure the dimensional or geometric features of one or more devices on the sample.

[0268] In some cases, the light beam incident on the sample may be varied. For example, multiple wavelengths may be supplied in series, e.g., different wavelengths at different times. Also, in some aspects, multiple wavelengths may be supplied together, e.g., simultaneously. In some designs, the light source includes a broadband light source. In these various configurations, the wavelength of the light is varied to create different SHG signals for different wavelengths incident on the sample.

[0269] In some cases, the sample may be charged (pre-charged) before measuring the SHG signal. Such charging can be done, for example, by a corona gun. Also, charging can be induced using light. In some configurations as described above, a pump and a probe are arranged, and the pump light source and the probe light source are used together with the SHG beam for examining the sample for charging.

[0270] In various aspects, the SHG system analyzes the SHG signal, e.g., data obtained from the SHG signal, and provides feedback (or feedforward) based on this analysis. As described herein, the SHG signal or data obtained therefrom can be compared to a look-up table. The SHG systems and methods described herein may include model-based measurements. For example, the SHG signal (modified or unmodified) may be compared to reference data provided by a model, e.g., the model may be used with simulation software to generate the reference data to which the detected SHG signal (modified or unmodified) is compared. Also, as described herein, artificial intelligence can be used in connection with the analysis of data obtained from the SHG signal.

[0271] In some cases, the NLO-CD system detects electrical defects in a sample using SHG light. In some cases, the NLO-CD system detects changes in strain of a sample using SHG light. In some aspects, the SHG system can evaluate, e.g., the process used in the production of a sample, by combining the detected dimensional changes with the detected strain changes or electrical defects.

[0272] In certain embodiments, the NLO-CD system is used in combination with other measurement devices, such as other optical measurement devices like a light scatterometer, also known as OCD. In some exemplary embodiments, the results of the SHG dimension measurement(s) are used in combination with the results of one or more other systems, such as other inspection and / or measurement systems like OCD, to determine geometric features or variations in geometric features. The results from the SHG system and the results of the OCD system may, for example, be received by one or more processors, which determine the geometric features or changes thereof based on the inputs from the SHG system and the OCD system. Instead of, or in addition to, the OCD system, one or more other systems may also be used. In some configurations, the light scatterometer system can be included in the NLO-CD system within a single tool that can perform both measurements. In some embodiments, a reference model incorporating both OCD measurements and NLO-CD measurements can be used. For example, as described above, signals from these devices (e.g., OCD and NLO-CD) can be compared to a reference from the reference model to determine geometric features such as dimensions and shapes, or variations in geometric features.

[0273] In some cases, an NLO-CD system or a separate system may control the charge amount on the surface of the sample being monitored (e.g., using a corona gun or capacitive coupling). In some cases, the charge amount on the surface of the sample being monitored can be controlled to enhance or vary the SHG signal. In such cases, the NLO-CD system (e.g., a controller or processor of the NLO-CD system) can use an electrical sensor to control the corona discharge applied to the sample (e.g., using a corona gun) to vary the amount of charge disposed on the sample and determine the characteristics of one or more SHG signals for different amounts of charge. Four-wave mixing signals, multi-wave mixing signals, and / or Raman signals for different charge amounts. In various aspects, an ammeter (e.g., an electrometer or a galvanometer) disposed between the sample and an electrical entity can be used to measure the current induced by the charge deposited on the surface of the sample to determine the amount of charge deposited on the sample. In various aspects, an electrical meter (e.g., an electrometer or a galvanometer) disposed between the sample and an electrical entity can be used to measure the current induced by the charge deposited on the surface of the sample to determine the amount of charge deposited on the sample.

[0274] In some cases, the sample (e.g., the monitored surface of the sample) may be charged (pre-charged) before measuring the SHG signal.

[0275] In some cases, the NLO-CD system can illuminate a region of the sample illuminated by the first and second (e.g., beam-like) light or light sources. In some cases, the first (e.g., beam-like) light is used for SHG light generation, and the second (e.g., beam-like) light controls or probes the SHG light generation.

[0276] As described above, various methods and configurations can be used to evaluate the properties of a sample by controlling the charge density on the sample or by using additional light (pump-probe techniques). In these configurations, NLO-CD can include at least one light source for generating probing radiation and at least one light source for generating pumping radiation.

[0277] In some cases, the NLO-CD system can use SHG light to detect electrical defects in the sample. In some cases, the NLO-CD system uses SHG light to detect changes in strain of the sample. In some embodiments, the SHG system combines the detected dimensional changes with the detected strain changes or electrical defects to evaluate the process used to produce the sample and generate a feedback signal for adjusting one or more parameters of the process and / or a feedforward signal for adjusting the parameters of a subsequent process.

[0278] In various embodiments, an NLO-CD system (e.g., NLO-CD systems 4000, 6000, 7000, 8000) can include the use of one or more of the methods, configurations, or tools described above with respect to FIGS. 1-19.

[0279] In some cases, an NLO-CD system (e.g., NLO-CD systems 4000, 6000, 7000, or 8000) may include one or more of the features described above with respect to the optical measurement system 7000.

[0280] In some embodiments, the NLO-CD system (e.g., SHG-CD systems 4000, 6000, 7000, 8000) may include a plurality of light sources that each generate a respective light beam having a different wavelength. The system may illuminate a device with the plurality of light beams, and the device may be capable of generating one or more SHG signals. The generated light beams may be received by one or more detectors that generate detection signals that can be used to determine the critical dimensions of the device. Optionally, different filters may be used along the optical paths to different detectors such that each detector generates a detection signal associated with the respective wavelength that has passed through the corresponding filter. Alternatively, one or more of the generated light beams may be directed to a spectrometer that measures the intensity of the generated SHG signals (SHG light) having different frequencies. Optionally, the critical dimensions of the device may be determined using the measurement results of the SHG spectrum or the signals generated by the optical spectrometer. As described above, various systems and methods for using SHG, such as measurement systems, in-line systems, etc., are described herein. The features of such SHG systems and methods are alternatively applicable to other types of systems and methods, such as SFG, DFG, FWM, or MWM, and Raman systems and methods, and these systems and methods may be used for metrology and / or monitoring of semiconductor manufacturing processes, e.g., in-line.

[0281] In some cases, an NLO-CD system (e.g., NLO-CD systems 4000, 6000, 7000, or 8000) can include two or more light sources (e.g., two or more laser light sources) having different wavelengths that are used to irradiate a spot on a sample and generate light having a frequency that is substantially equal to the sum of the frequencies of a first light source and a second light source. For example, the first light source and the second light source can generate a first beam and a second beam having a first frequency and a second frequency, respectively. The device on the sample can be irradiated by both the first and second beams, and the first and second beams can be directed onto the sample such that a third beam having a third frequency that is substantially equal to the sum or the difference of the first and second frequencies is generated. In some cases, a third beam having a third frequency that is substantially equal to the sum of the first and second frequencies can be referred to as sum frequency generation (SFG) light or an SFG signal. In some cases, a third beam having a third frequency that is substantially equal to the difference between the first and second frequencies can be referred to as difference frequency generation (DFG) light or a DFG signal. In some cases, a detector of the system can receive the SFG signal and / or the DFG signal and generate a detected SFG signal and / or a detected DFG signal (e.g., an electrical signal). In some cases, one or more of the features described above regarding using the SHG signal and the detected SHG signal to determine sample characteristics (e.g., geometric features, material structure, critical dimensions) can be used to determine sample characteristics using the SFG / detected SFG signal and / or the DFG / detected DFG signal.

[0282] In some embodiments, in addition to, or instead of, a detector, the NLO-CD system (e.g., NLO-CD system 4000, 6000, 7000, or 8000) can include at least one spectrometer configured to receive SHG, SFG, DFG, FWM, MWM, or Raman signals having different frequencies from a sample and measure the intensity or ratio between the intensities of different SHG signals. Optionally, spectral characteristics of the SHG, SFG, DFG, FWM, MWM, or Raman signals can be used to determine characteristics of the sample (e.g., geometric features, material structure, critical dimensions).

[0283] In some embodiments, the NLO-CD system (e.g., NLO-CD system 4000, 6000, 7000, or 8000) can have a plurality of light sources each generating an optical beam having a different wavelength. The system can illuminate a device with the plurality of optical beams, and the device can generate one or more optical beams via one or more non-linear processes. The generated optical beams can be received by one or more detectors that generate a detection signal that can be used to determine the critical dimensions of the device. Optionally, different filters can be used along the optical paths to different detectors such that each detector generates a detection signal related to the wavelength that has passed through the corresponding filter. Alternatively, one or more of the generated optical beams can be directed to a spectrometer that measures the intensities of the generated optical beams having different frequencies. Optionally, spectral measurements or signals generated by the optical spectrometer can be used to determine the critical dimensions of the device.

[0284] In some embodiments, an NLO-CD system (e.g., NLO-CD system 4000, 6000, 7000, or 8000) may include one or more features described above with respect to FIGS. 20A-20C. Optionally, an NLO-CD system (e.g., NLO-CD system 4000, 6000, 7000, or 8000) can include two or more light sources (e.g., two or more laser light sources) having the same or different wavelengths that are used to irradiate spots on a sample. The two or more light sources can generate two or more light beams that at least partially overlap in the region of the sample being measured and / or investigated. In such cases, as a result of the interaction of the two or more light beams with the sample, one or more four-wave mixing (FWM), multi-wave mixing (MWM), or Raman signal components may be generated. In some examples, the resulting FWM mixing, MWM, and Raman signal components may be detected by one or more detectors that generate a detected FWM or MWM mixing signal associated with the FWM, MWM, or Raman signal component. Optionally, the resulting FWM mixing, MWM, or Raman signal components may be received by a spectrometer that generates a spectrum including the spectral irradiance of the received FWM, MWM, and Raman signal components. Optionally, the detected FWM, MWM, or Raman signal or spectrum resulting therefrom may be used to determine sample characteristics (e.g., critical dimensions or material properties) using the methods described above with respect to FIGS. 20A-20C.

[0285] In some cases, an NLO-CD system (e.g., NLO-CD systems 4000, 6000, 7000, or 8000) can use a single light source (e.g., a laser light source) to irradiate a spot on a sample with an incident light beam and generate light through second-, third-, fourth-, or higher-order nonlinear optical processes or effects (e.g., degenerate nonlinear optical processes). In some cases, the nonlinear optical process may include a multi-wave mixing process. In some cases, the detector of the system receives the light emitted by the sample and generates a detection signal (e.g., an electronic signal). In some cases, one or more of the features described above regarding determining the characteristics of a sample (e.g., geometric features, material structure, critical dimensions) using the detected SHG signal may be used to determine the characteristics of the sample using the detection signal corresponding to the SHG light.

[0286] In some embodiments, the NLO-CD may communicate (e.g., wired or wireless communication) with an optical scattering measurement system (e.g., an OCD system). In some cases, a processor of a computing system (e.g., the computing system of the NLO-CD or the OCD system, or a separate computing system) may receive measurement data or evaluation data (e.g., detected dimensions, materials, defects, process evaluation data, etc.) from the NLO-CD and the OCD system. In such cases, the computing system may combine the measurement data or evaluation data received from the NLO-CD and the OCD system to generate an evaluation report, or generate a feedback signal and / or a feedforward signal for controlling the process of the corresponding production line. In some cases, the NLO-CD system and the OCD system may be combined as a single tool. In such cases, the NLO-CD system and the OCD system may be integrated into the same housing and may share one or more optical or electronic components used for monitoring the sample. In some cases, a single control system may control both the NLO-CD system and the OCD system. In some cases, the reference SHG model (e.g., an empirical reference model) used in the NLO-CD system may be created using measurement results obtained from both the OCD system and the SHG-CD system, or may incorporate both OCD measurements and NLO-CD measurements.

[0287] FIG. 31A is a block diagram showing an example of an NLO-CD system 4950 that includes an optical system 4952, a control system 4954, and a computing system 4956. In some examples, the optical system 4952 can include one or more light sources configured to generate one or more primary light beams incident on a sample, one or more detectors configured to receive one or more secondary light beams reflected, scattered, or generated by the sample, and one or more optical, mechanical, and opto-mechanical components configured to manipulate (e.g., control polarization, filter, redirect, control divergence, etc.) the primary and secondary light beams. In some examples, the optical system 4952 can include at least one mechanical stage configured to control the position and orientation of the sample relative to the light source and the detector. In some cases, the control system 4954 can be configured to control the optical system 4952 according to instructions and / or data stored in the memory of the control system 4952, instructions and / or data received from the computing system 4956, and / or the user interface 4957. In some cases, the computing system 4956 can be configured to simulate second harmonic generation by the sample using one or more models (e.g., a reference model, a device model, etc.) and data received from the control system 4954 (e.g., data related to the incident light beam). In some examples, the computing system 4956 can be configured to determine changes in the SHG signal (NLO signal), characteristics of the sample (e.g., geometric parameters and / or material properties), or changes in the characteristics of the sample using the simulated data (e.g., data related to the simulated SHG emission) and data received from the optical system 4952 (e.g., measurement data related to the SHG light received from the sample). In some examples, the model can be stored in the memory of the computing system 4956 or received from the user interface 4957.In some cases, the user interface may include an input interface (e.g., keyboard, mouse, touch screen, touch pad, etc.) for receiving data and instructions from the user, and an output interface (e.g., display) for presenting measurement data, evaluation results, images, graphs, data / instructions stored in the computing system 4956 and / or the control system 4954 to the user.

[0288] FIG. 31B is a block diagram showing another example of an NLO-CD system 4960 that includes an optical system 4952 and an interface 4962 that communicates with the optical system 4952. In some cases, the interface 4962 may be configured to receive commands and data from a control and computing system 4964 separate from the NLO-CD system 4960 and generate one or more control signals based on the received data and commands. The interface 4962 may further be configured to transmit data received from the optical system 4952 (e.g., measurement data and / or data related to the configuration of the optical system 4952) to the control and computing system 4964. The control and computing system 4964 may include a user interface 4966. In some cases, the user interface 4966 may include an input interface (e.g., keyboard, mouse, touch screen, touch pad, etc.) for receiving data and instructions from the user, and an output interface (e.g., display) for presenting measurement data, evaluation results, images, graphs, data / instructions stored in or received by the control and computing system 4964 to the user. In some cases, the control and computing system 4964 may be composed of a desktop computer, a laptop, or other electronic devices.

[0289] In some cases, computing system 4954 and control / computing system 4964 can include at least one hardware processor and at least one non-transitory memory that communicates with the hardware processor. In some aspects, the hardware processor can execute computer-executable instructions stored in the non-transitory memory to perform the following. Calculating an expected SHG signal (NLO signal), an expected SHG (NLO) emission pattern, or an expected signal generated by a detector of optical system 4952, Generating a control signal (e.g., for controlling a light source, detector, and / or light beam of optical system 4952), Comparing the expected SHG / NLO emission with the measured SHG / NLO emission, Determining geometric and material properties of a sample (or a device within the sample), generating graphical data related to the measured SHG / NLO emission or the expected SHG / NLO emission, or any combination thereof, Or performing other tasks.

[0290] In some cases, an optical measurement system can monitor a sample using first and second light sources configured to emit first and second incident light beams toward the surface of the sample in order to generate one or more light beams containing four-wave mixing signal components or multi-wave mixing signal components in the sample. The optical measurement system can include an optical detection system configured to detect four-wave mixing signals in order to generate detected four-wave mixing (FWM) signal components from the sample, to generate detected multi-wave mixing (MWM) signal components, or to detect multi-wave mixing signal components. In some aspects, the optical measurement system can use the detected four-wave mixing signal or the detected multi-wave mixing signal to determine geometric features of the sample or variations in geometric features. In some cases, the first and second light sources may be composed of pulsed light sources. In some cases, the system may introduce a time delay between the pulse output from the first light source and the pulse output from the second light source. In some cases, the first light source and / or the second light source may include a nanosecond, picosecond, or femtosecond laser. In some cases, the system may determine the characteristics of the detected four-wave mixing signal or multi-wave mixing signal. In some cases, the system may determine the geometric features of the sample or variations in the geometric features of the sample based on the determined characteristics of the detected four-wave mixing signal or the detected multi-wave mixing signal. In some cases, the system may introduce a variable time delay between the pulse output from the first light source and the pulse output from the second light source and, for different amounts of the time delay, determine the geometric features of the sample or variations in the geometric features of the sample based on the determined characteristics of the detected four-wave mixing signal or the detected multi-wave mixing signal. In some cases, the optical measurement system can include a corona discharge source (e.g., a corona gun) capable of supplying different amounts of charge to the sample and an electrical sensor configured to measure the amount of charge supplied to the sample.An optical measurement system can measure, and in some cases control, the amount of charge placed on a sample using an electrical sensor and a discharge source (e.g., using a hardware processor or a control system). In such cases, the system uses the electrical sensor and the discharge source to supply a variable amount of charge to the sample and, based on the determined characteristics of the detected signal for different amounts of charge, can determine the variation of the detected signal (e.g., SHG signal, MWM signal, Raman signal), or the geometric features of the sample, or the variation of the geometric features of the sample.

[0291] It should be understood that an optical measurement system (e.g., a system for measuring, monitoring, and characterizing the critical dimensions of a sample) that monitors a sample based on the SHG effect or NLO effect (e.g., in a production line) is not limited to those described above (e.g., it may include fewer components, different configurations, additional features and / or components, alternative features and / or components). As described above, the features of the SHG systems and methods described herein are alternatively applicable to other types of NLO systems and methods, such as SFG, DFG, FWM, or MWM Raman systems and methods, and these systems may be used, for example, inline, to measure and / or monitor semiconductor manufacturing processes.

[0292] Figs. 32A - 32C schematically show examples of stacks of gate - all - around (GAA) field - effect (FET) transistors having spacer layers at different etching levels (e.g., a lateral direction parallel to the top surface of the substrate). In some cases, each GAA FET may include a stack of semiconductor layers alternately including a silicon - germanium (Si - Ge) layer 5004 and a silicon (Si) layer 5002 disposed on a silicon substrate 5000. The GAA FET can include a top layer including silicon nitride (SiN) disposed on the topmost silicon layer. The spacing between the Si layer 5002 and the Si - Ge layer 5004 (e.g., a vertical spacing perpendicular to the top surface of the substrate) may be filled with a dielectric spacer 5006 (e.g., a nitride - based dielectric such as SiN). To form the spacer layer, after fabricating the Si - Ge layer 5004 and the Si layer 5002 and disposing the topmost SiN layer, the resulting structure may be covered with a thick dielectric layer 5006. Next, the thick dielectric layer 5006 is etched to form dielectric spacers 5008 between the Si layers 5002. The performance of the GAA FET can be significantly affected by the lateral thickness of the spacer layer. Fig. 32A shows a transistor with insufficient etching of the dielectric layer 5006 (no separate dielectric spacers are formed). Fig. 32B shows a sufficiently etched dielectric layer with individual spacers 5008 having an appropriate lateral thickness. Fig. 32C shows an over - etched dielectric layer with individual spacers 5010 formed, but their lateral thickness is too small. Thus, it is desirable to monitor the thickness of the dielectric spacers during manufacturing, detect deviations from a desired etching level (e.g., the etching level shown in Fig. 32B), and adjust the etching rate or etching time to maintain a predetermined lateral thickness of the dielectric spacers of the transistors fabricated on the sample or on different samples.

[0293] In some cases, the above-described SHG-based optical measurement system and technology can be used for monitoring the spacer layer of a GAA FET. FIGS. 33A and 33B show simulations of the intensity distributions of linear scattered light (Part A) and second harmonic generation (SHG) light (Part B) in the vicinity of a stack of GAA FETs (e.g., a stack similar to the stack shown in FIG. 33C) illuminated by an incident light beam. Here, the wavelength of the incident light beam is 785 nm, and the wavelength of the resulting SHG light is 392.5 nm. As shown in FIGS. 33A and 33B, the distribution of the linear scattered light (having the same wavelength as the incident light) is relatively uniform throughout the transistor, whereas the distribution of the SHG light is highly non-uniform and stronger near the edge of the Si layer 5002. Therefore, the intensity of the linear scattered light is less sensitive to the geometric features of the transistor, while the intensity of the SHG light is highly sensitive to the geometric features of the transistor. Considering that the lateral thickness of the spacer layer may affect the intensity of SHG near the end of the Si layer 5002, monitoring the intensity of the SHG light emitted by the transistor can be used to monitor changes in the lateral thickness of the spacer and control the etching process accordingly.

[0294] In some embodiments, by changing the polarization of the incident light and measuring the intensity of the resulting non-linearly generated light (e.g., SHG light, SFG light, DFG light, MWM light, or Raman light) having different polarizations for each polarization of the incident light, the geometric features of the sample can be determined or changes in the geometric features of the sample can be detected. In some examples, a preliminary measurement can be used to identify a specific input (input) polarization of the incident light and a corresponding specific output polarization of the non-linearly generated (NLG) light that provides a greater gradient with respect to changes in the intensity of the NLG light with respect to changes in the geometric features. The specific input polarization and the specific output polarization can be used for in-line monitoring of the geometric features of samples produced on a production line based on the NLG light.

[0295] FIG. 34A is an electron microscope image of a part of a GAA FET having the same structure as the transistors shown in FIGS. 32A to 32C. FIG. 34B is a plot of the measured intensity of the SHG light emitted by the GAA FET shown in the figure against the spacer etching. FIG. 34A is a plot against the spacer etching for three different combinations of the polarization of the incident light beam and the polarization of the measured SHG light. The spacer etching can be quantified as the thickness of the removed spacer (e.g., the lateral direction parallel to the upper surface of the substrate). The experimental arrangement used to generate these measurements is the same as that of FIG. 21, the polarization of the incident light 4110 is controlled by the first polarizer 4120, and the second polarizer 4220 in front of the detector 4201 is used to selectively measure the intensity of a part of the SHG light having the specified polarization. In FIG. 34B, curve 5012 corresponds to the intensity of the SHG light having P polarization when the incident light is S polarized. Curve 5016 corresponds to the intensity of the SHG light having P polarization when the incident light is P polarized. Curve 5018 corresponds to the intensity of the SHG light having S polarization when the polarization of the incident light is rotated 45 degrees with respect to P polarization (or S polarization). The large slope of curve 5012 indicates that by using S polarization to illuminate the sample shown in FIG. 34A and measuring the intensity of the P-polarized SHG light emitted by the sample, the sensitivity in measuring or monitoring the thickness of the dielectric spacer (e.g., the lateral thickness) may be increased and the accuracy may be improved.

[0296] In some embodiments, the polarization of the incident light and the polarization at which the intensity of the NLG light is measured to measure or detect changes in the geometric features of the sample can be determined by a preliminary measurement. Such a preliminary measurement varies (e.g., continuously scans) the polarization direction (polarization angle) of the incident light within a range and separately measures the intensities of the resulting S-polarized and / or P-polarized NLG light (e.g., SHG light, SFG light, DFG light, MWM light, or Raman light). The results of the preliminary measurement can be used to determine the preferred polarization direction of the incident light and the preferred polarization of the NLG light related to the geometric features of the sample.

[0297] In some cases, changes in the geometric features of a sample can be detected or the geometric features can be measured by using the change in P-polarized NLG light or S-polarized NLG light with respect to the polarization (e.g., polarization angle) of incident light over a specific range of the polarization direction of the incident light.

[0298] FIG. 35A is an electron micrograph of a test sample having a periodically patterned layer structure. This test sample includes, similar to the GAA FET shown in FIGS. 32A - 32C, an alternating stack of Si layer 5002 and Si-Ge layer. FIG. 35B is a schematic diagram of a cell of the test sample shown in FIG. 35A.

[0299] The polarization dependence of the SHG light generated from the samples shown in FIGS. 35A to 35B was characterized using an experimental setup similar to that described in FIG. 21 (for FIG. 34B). FIG. 36A plots the measured intensities of S-polarized and P-polarized SHG light emitted by three test samples etched differently against the polarization angle of the light beam incident on the sample measured with respect to a reference angle (e.g., related to S polarization). In some cases, the first polarizer 4120 (FIG. 21) may be used to scan the polarization angle of the incident light stepwise or continuously. FIG. 36B shows the measured intensity of S-polarized SHG light plotted against the polarization angle of the light beam incident on the sample in the vicinity of region A 6002 (where the polarization angle of the incident light is near zero). FIG. 36C shows the measured intensity of P-polarized SHG light plotted against the polarization angle of the light beam incident on the sample in the vicinity of region B 6004 (where the polarization angle of the incident light is near 140 degrees). The green curves (the upper curve in FIG. 36B and the lower curve in FIG. 36C) are the measured intensities of the SHG light emitted by the nominally etched samples, the yellow curves (the middle curve in FIG. 36B and the upper curve in FIG. 36C) are the intensities of the SHG light emitted by the underetched samples, and the red curves (the lower curve in FIG. 36B and the middle curve in FIG. 36C) are the intensities of the SHG light emitted by the overetched samples. FIGS. 36B and 36C show that, in order to evaluate the etching depth (e.g., along the lateral direction or the direction perpendicular to the surface of the dielectric spacer) in the sample shown in FIG. 35A, when monitoring S-polarized SHG light, an input (input) polarization angle of 0 degrees (the polarization angle of the incident light) (e.g., S-polarized input) can be used, and when monitoring P-polarized SHG light, an input polarization angle of 137 degrees can be used. Alternatively or additionally, in some cases, during the measurement of the sample or during real-time and / or in-line sample monitoring, the polarization angle of the incident light can be scanned within a range centered around 0 degrees when measuring S-polarized SHG light and 137 degrees when measuring P-polarized SHG light to monitor the change of SHG light as a function of the input polarization, and the characteristics of the obtained SHG-input polarization curve can be used to measure the geometric features of the sample or detect changes in the geometric features of the sample.Similar methods can also be used when MWM light, high-order harmonic generation light (higher than the second harmonic), SFG light, DFG light, or Raman light is used for measuring or monitoring the geometric features of a sample. Examples Group 1

[0300] Some additional non-limiting examples of the above-described embodiments are provided below. These should not be read as in any way limiting the scope of the present disclosure.

[0301] Example 1: A system for characterizing a sample using second harmonic generation, comprising a sample holder configured to support a sample, at least one light source configured to direct a light beam at the sample to create a second harmonic generation (SHG) signal, an optical detection system including at least one photodetector configured to receive the SHG signal emitted from the sample and generate a detected SHG signal, one or more hardware processors in communication with the optical detection system, wherein the one or more hardware processors receive at least one detected SHG signal, and are configured to determine the geometric features of the sample or variations in the geometric features of the sample based on the at least one detected SHG signal.

[0302] Example 2: The system of Example 1, wherein the geometric features of the sample are at least partially determined based on a mapping of the detected SHG signal to the geometric features of one or more structures on a completed or incomplete sample.

[0303] Example 3: The system of Example 1, wherein the one or more hardware processors receive at least one detected SHG signal after a first fabrication step is performed on the sample.

[0304] Example 4: The system is the system described in Example 3, included inline in the manufacturing system.

[0305] Example 5: The system is the system described in Example 4, where the first manufacturing step is a step in the manufacturing process executed by the manufacturing system.

[0306] Example 6: One or more hardware processors are configured to identify unexpected variations in the geometric characteristics of a sample and output a display of the unexpected variations, for the system described in any of the above examples.

[0307] Example 7: The system is the system described in Example 6, where one or more hardware processors are configured to output a display of unexpected variations to a sample process tool within the manufacturing system to adjust for unexpected variations in the sample.

[0308] Example 8: The system is the system described in Example 7, where one or more hardware processors are configured to output a display of unexpected variations to a sample process tool used to perform a second manufacturing step on the sample after the first manufacturing step to adjust for unexpected variations in the sample.

[0309] Example 9: The system is the system described in Example 6, where one or more hardware processors are configured to output a display of unexpected variations to a user via the system's user interface.

[0310] Example 10: The system is the system described in any of the above examples, where the geometric characteristics include the dimensions of one or more devices or one or more parts of a device, whether completed or not.

[0311] Example 11: The system is the system described in any of the above examples, where the geometric characteristics include the critical dimensions of one or more devices or one or more parts of a device, whether completed or not.

[0312] Example 12: The geometric feature is a system according to any of the above examples, including the shape of one or more devices, whether completed or not, or a part of one or more devices.

[0313] Example 13: The geometric feature is a system according to any of the above examples, including a lateral dimension including the width or length of one or more devices, whether completed or not, or a part of one or more devices.

[0314] Example 14: The geometric feature is a system according to any of the above examples, including the height of one or more devices, whether completed or not, or a part of one or more devices.

[0315] Example 15: The geometric feature is a system according to any of the above examples, including the lateral spacing between a plurality of devices, whether completed or not, or a plurality of parts of a device.

[0316] Example 16: The geometric feature is a system according to any of the above examples, including the inclination or slope of one or more devices, whether completed or not, or a part of one or more devices.

[0317] Example 17: The geometric feature is a system according to any of the above examples, including the sidewall inclination or slope of one or more devices, whether completed or not, or a part of one or more devices.

[0318] Example 18: At least one detected SHG signal includes first and second detected SHG signals, and the first and second detected SHG signals are such that at least one measurement parameter is measured in different states for the first and second detected SHG signals, one or more hardware processors, receive the first and second detected SHG signals, and The system according to any of the above embodiments, which determines the geometric features of the sample or the variation of the geometric features of the sample based on the first detected SHG signal and the second detected SHG signal.

[0319] Example 19: The system according to Example 18, wherein at least one measurement parameter includes at least one of a measurement position, a measurement angle, polarization, or a wavelength.

[0320] Example 20: The system according to any of Examples 18 or 19, wherein at least one measurement parameter includes the tilt angle of the SHG signal measured with respect to the sample.

[0321] Example 21: The system according to any of Examples 18 to 20, wherein at least one measurement parameter includes the tilt angle of at least one detector with respect to the sample.

[0322] Example 22: The system according to any of Examples 18 to 21, wherein at least one measurement parameter includes the azimuth angle of the SHG signal measured with respect to an axis perpendicular to the surface of the sample.

[0323] Example 23: The system according to any of Examples 18 to 22, wherein at least one measurement parameter includes the azimuth angle of at least one detector with respect to an axis perpendicular to the surface of the sample.

[0324] Example 24: The system according to any of Examples 18 to 23, wherein at least one measurement parameter includes the polarization of the SHG signal received by at least one photodetector.

[0325] Example 25: The system according to any of Examples 18 to 24, wherein at least one measurement parameter includes the polarization of the polarizer of at least one detector.

[0326] Example 26: The system according to any of Examples 18 to 25, wherein at least one measurement parameter includes the polarization of the light beam incident on the sample.

[0327] Example 27: The system according to any one of Examples 18 to 26, wherein at least one measurement parameter includes the tilt angle of at least one light beam directed at the sample with respect to the sample.

[0328] Example 28: The system according to any one of Examples 18 to 27, wherein at least one measurement parameter includes the azimuth angle of at least one light beam directed at the sample with respect to the axis perpendicular to the surface of the sample.

[0329] Example 29: The system according to any one of Examples 18 to 28, wherein at least one measurement parameter includes the wavelength of at least one light beam directed at the sample.

[0330] Example 30: The system according to any one of Examples 18 to 29, wherein at least one measurement parameter includes the output wavelength of at least one light source.

[0331] Example 31: The system according to any one of Examples 18 to 30, wherein at least one measurement parameter includes the detection wavelength of at least one detector.

[0332] Example 32: The system according to any one of Examples 18 to 31, wherein at least one measurement parameter includes the wavelength of the SHG signal received by at least one photodetector.

[0333] Example 33: The system according to any one of Examples 18 to 32, wherein the sample is configured to rotate with respect to the light beam and / or at least one detector.

[0334] Example 34: The system according to any one of Examples 18 to 33, wherein at least one measurement parameter includes the angle of at least one detector that receives the SHG signal propagating in the plane formed by the light beam and the axis perpendicular to the sample.

[0335] Example 35: The system according to any one of Examples 18 to 34, wherein at least one parameter includes the angle of at least one detector that receives an SHG signal propagating out of a plane formed by the optical beam and an axis perpendicular to the sample.

[0336] Example 36: The system according to any one of Examples 18 to 35, wherein at least one parameter includes the polarization parameter of linear polarization or circular polarization of at least one light source.

[0337] Example 37: The system according to any one of Examples 18 to 36, wherein at least one light source includes a broadband light source.

[0338] Example 38: The system according to any one of Examples 18 to 37, wherein at least one light source includes light sources of at least two different wavelengths.

[0339] Example 39: The system according to any one of Examples 18 to 38, wherein the system is configured to change at least one measurement parameter.

[0340] Example 40: The system according to Example 39, wherein, in order to change at least one measurement parameter, one or more hardware processors are configured to cause at least one light source to emit a plurality of wavelengths simultaneously.

[0341] Example 41: The system according to Example 39, wherein, in order to change at least one measurement parameter, one or more hardware processors are configured to cause at least one light source to emit different wavelengths at different times.

[0342] Example 42: The system according to any one of Examples 18 to 41, wherein at least one parameter includes the angle of at least one detected SHG signal and the polarization of the detected SHG signal.

[0343] Example 43: The geometric feature is the system according to any of the above examples, including the geometric features of an integrated circuit device or one or more parts of an integrated circuit device that is completed or not yet completed.

[0344] Example 44: The system is the system according to any of the above examples, included inline in a semiconductor device manufacturing system.

[0345] Example 45: The geometric feature is the system according to any of the above examples, including the geometric features of one or more integrated circuit devices, or one or more partially completed integrated circuit devices, or one or more parts thereof.

[0346] Example 46: The geometric feature is the system according to any of the above examples, including the geometric features of one or more finFETs, GAAs, trigates or NAND structures.

[0347] Example 47: The geometric feature is the system according to any of the above examples, including the geometric features of one or more three-dimensional structures of the sample.

[0348] Example 48: The at least one light source includes a first light source configured to emit probing radiation and a second light source configured to emit pumping radiation, in the system according to any of the above examples.

[0349] Example 49: The system according to any of the above examples further includes a corona gun configured to deposit different amounts of charge on the upper side of the sample.

[0350] Example 50: The one or more hardware processors are configured to determine the characteristics of at least one detected SHG signal, a first detected SHG signal, or a second detected SHG signal for different amounts of charge, in the system according to Example 49.

[0351] Example 51: The sample is the system according to any of the above examples, including a semiconductor.

[0352] Example 52: The system according to any of the above examples, wherein at least one light source includes a first light source configured to emit a first light beam at a first wavelength and a second light source configured to emit a second light beam at a second wavelength.

[0353] Example 53: The system according to any of the above examples, wherein at least one detector includes a first detector configured to receive an SHG signal at a first angle and a second detector configured to receive an SHG signal at a second angle.

[0354] Example 54: The system according to any of the above examples, wherein at least one detector includes a first detector configured to receive an SHG signal with a first polarization and a second detector configured to receive an SHG signal with a second polarization.

[0355] Example 55: The system according to any of the above examples, wherein at least one detector includes a detector array including a plurality of pixels.

[0356] Example 56: The system according to any of the above examples, wherein at least one detector includes a 1D detector array.

[0357] Example 57: The system according to any of the above examples, wherein at least one detector includes a 2D detector array.

[0358] Example 58: The system according to any of Examples 55 to 57, further comprising at least one lens configured to direct SHG signals emitted from the sample at different angles to different positions on the detector array.

[0359] Example 59: The system according to any of the above examples, wherein the mapping is generated based on empirical data.

[0360] Example 60: The mapping is a system according to any of the above examples, generated via a machine learning algorithm.

[0361] Example 61: The mapping is a system according to any of the above examples, including a look-up table of SHG signal values and geometric features.

[0362] Example 62: The variation in geometric features is a system according to any of the above examples, including the difference between the geometric features of the sample and the stored geometric features stored in the memory of the system.

[0363] Example 63: The stored geometric features are a system according to Example 62, including reference geometric features provided by the user.

[0364] Example 64: The stored geometric features are a system acc...

Claims

1. A system for optically examining the surface of a sample, comprising: a first light source configured to emit a first incident light beam toward the surface of the sample; a second light source configured to emit a second incident light beam toward the surface of the sample; an optical detection system configured to generate at least one detected four-wave mixing signal, at least one detected multi-wave mixing signal component, or at least one Raman signal component to generate at least one detected multi-wave mixing signal and detect at least one four-wave mixing component from the sample; a processor in communication with the optical detection system, receiving the at least one detected four-wave mixing signal, the at least one detected multi-wave mixing signal, or the at least one Raman signal; and one or more processors configured to determine a geometric feature of the sample or a variation in the geometric feature of the sample based on the at least one detected four-wave mixing signal, the at least one detected multi-wave mixing signal, or the at least one detected Raman signal.

2. The system of claim 1, wherein the first light source includes a pulsed light source configured to output pulses.

3. The system of claim 1, wherein the second light source includes a pulsed light source configured to output pulses.

4. The system of claim 3, further comprising a system configured to introduce a time delay between the pulse output from the first light source and the pulse output from the second light source.

5. The system of claim 1, wherein at least one of the first and second light sources includes a pulsed laser configured to output pulses.

6. The system of claim 5, wherein the pulsed laser is selected from a nanosecond laser, a picosecond laser, and a femtosecond laser.

7. The system of claim 1, further comprising an optical delay system configured to introduce a variable time delay between the optical pulses of the first incident beam and the second incident beam.

8. The system of claim 1, further comprising a corona discharge source disposed with respect to the sample and configured to supply different amounts of charge to the sample.

9. The system of claim 1, wherein the one or more processors are configured to determine different amounts of charge provided by the corona discharge source.

10. The system of claim 1, further comprising an electrical sensor configured to measure a current between the sample and electrical ground.

11. The system of claim 10, wherein the one or more processors communicate electrically with the electrical sensor.

12. The system of claim 11, wherein the one or more processors are configured to determine different amounts of charge supplied by the corona discharge source based on a measured current between the sample and electrical ground.

13. The system of claim 1, wherein the one or more processors are configured to determine characteristics of the at least one detected four-wave mixing signal or the at least one detected multi-wave mixing signal detected for the different amounts of charge.

14. The system of claim 13, wherein the one or more processors are configured to determine geometric features of the sample or variations in geometric features of the sample based on the determined characteristics of the at least one detected four-wave mixing signal or the at least one detected multi-wave mixing signal for the different amounts of charge.

15. The system of claim 13, wherein the one or more processors are configured to obtain information related to the charge dynamics of the sample based on the determined characteristics of the at least one detected four-wave mixing signal or the multi-wave mixing signal for the different amounts of charge.

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